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Document and Entity Information	3 Months Ended
Document and Entity Information	Mar. 31, 2017
Document And Entity Information [Abstract]
Document Type	S-1/A
Amendment Flag	true
Amendment Description	Amendment No. 1 to FORM S-1
Document Period End Date	Mar. 31, 2017
Entity Registrant Name	Aerpio Pharmaceuticals, Inc.
Entity Central Index Key	0001422142
Entity Filer Category	Smaller Reporting Company

Condensed Consolidated Balance Sheets - USD ($)	Mar. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Current assets:
Cash and cash equivalents	$ 35,139,109	$ 1,609,694	$ 5,144,211
Short-term investments	50,000	50,000	50,000
Accounts receivable	32,453	4,157	118,516
Prepaid research and development contracts	297,158	353,434	266,327
Other current assets	602,488	209,038	386,549
Total current assets	36,121,208	2,226,323	5,965,603
Furniture and equipment, net	138,147	149,595	105,971
Deposits	20,960	20,960	20,960
Total assets	36,280,315	2,396,878	6,092,534
Current liabilities:
Accounts payable and accrued expenses	2,970,048	2,470,970	2,159,874
Convertible notes		12,386,647
Total current liabilities	2,970,048	14,857,617	2,159,874
Commitments and contingencies
Redeemable convertible preferred stock		73,757,890	70,487,415
Stockholders' equity (deficit):
Common stock, value	2,705	124	115
Additional paid-in capital	125,465,315
Accumulated deficit	(92,157,753)	(86,218,753)	(66,554,870)
Total stockholders' equity (deficit)	33,310,267	(86,218,629)	(66,554,755)
Total liabilities, redeemable convertible preferred stock, and stockholders' equity (deficit)	$ 36,280,315	2,396,878	6,092,534
Series A Redeemable Convertible Preferred Stock [Member]
Current liabilities:
Redeemable convertible preferred stock		7,016,515	7,119,204
Series A1 Redeemable Convertible Preferred Stock [Member]
Current liabilities:
Redeemable convertible preferred stock		40,897,311	39,016,008
Series A2 Redeemable Convertible Preferred Stock [Member]
Current liabilities:
Redeemable convertible preferred stock		$ 25,844,064	$ 24,352,203

Condensed Consolidated Balance Sheets (Parenthetical) - $ / shares	Mar. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Common stock, par value	$ 0.0001	$ 0.0001	$ 0.0001
Common stock, shares authorized	300,000,000	17,440,436	17,140,478
Common stock, shares issued	27,049,555	1,240,925	1,157,251
Common stock, shares outstanding	27,049,555	1,240,925	1,157,251
Series A Redeemable Convertible Preferred Stock [Member]
Redeemable convertible preferred stock, shares authorized		1,326,147	1,326,147
Redeemable convertible preferred stock, shares issued		1,239,338	1,326,145
Redeemable convertible preferred stock, shares outstanding		1,239,338	1,326,145
Series A1 Redeemable Convertible Preferred Stock [Member]
Redeemable convertible preferred stock, shares authorized		8,368,247	8,368,247
Redeemable convertible preferred stock, shares issued		8,289,663	8,368,230
Redeemable convertible preferred stock, shares outstanding		8,289,663	8,368,230
Series A2 Redeemable Convertible Preferred Stock [Member]
Redeemable convertible preferred stock, shares authorized		4,660,573	4,489,169
Redeemable convertible preferred stock, shares issued		4,486,015	4,489,160
Redeemable convertible preferred stock, shares outstanding		4,486,015	4,489,160

Condensed Consolidated Statements of Operations and Comprehensive Loss - USD ($)	3 Months Ended		12 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016	Dec. 31, 2015
Operating expenses:
Research and development	$ 2,255,584	$ 2,989,558	$ 11,367,590	$ 11,625,404
General and administrative	2,504,001	1,215,885	5,265,995	5,861,151
Total operating expenses	4,759,585	4,205,443	16,633,585	17,486,555
Loss from operations	(4,759,585)	(4,205,443)	(16,633,585)	(17,486,555)
Grant income	35,657	8,670	131,281	369,688
Interest (expense) income, net	(271,775)	1,078	(482,204)	19,622
Other income, net		997	997	27,022
Total other (expense) income	(236,118)	10,745	(349,926)	416,332
Net loss and comprehensive loss	(4,995,703)	(4,194,698)	(16,983,511)	(17,070,223)
Reconciliation to net loss attributable to common stockholders:
Net loss and comprehensive loss	(4,995,703)	(4,194,698)	(16,983,511)	(17,070,223)
Extinguishment of preferred stock			224,224
Accretion of preferred stock to redemption value	(943,297)	(1,015,371)	(4,152,801)	(348,436)
Net Loss attributable to common stockholders	$ (5,939,000)	$ (5,210,069)	$ (20,912,088)	$ (17,418,659)
Net loss per share attributable to common stockholders, basic and diluted	$ (1.06)	$ (7.07)	$ (24.52)	$ (31.14)
Weighted average number of common shares used in computing net loss per share attributable to common stockholders, basic and diluted	5,605,151	737,016	852,665	559,419

Condensed Consolidated Statements of Stockholders Equity (Deficit) - USD ($)	Total	Common Stock [Member]	Additional Paid-In Capital [Member]	Accumulated Deficit [Member]	Series A Redeemable Convertible Preferred Stock [Member]	Series A1 Redeemable Convertible Preferred Stock [Member]	Series A2 Redeemable Convertible Preferred Stock [Member]	Redeemable Convertible Preferred Stock
Redeemable convertible preferred stock, Balance at Dec. 31, 2014	$ 70,138,979				$ 6,754,096	$ 40,180,140	$ 23,204,743
Redeemable convertible preferred stock, Balance, Shares at Dec. 31, 2014					1,326,145	8,368,230	4,489,160
Redeemable convertible preferred stock, Adjustment of redeemable convertible preferred stock to redemption value	348,436				$ 365,108	$ (1,164,132)	$ 1,147,460
Redeemable convertible preferred stock, Balance at Dec. 31, 2015	70,487,415				$ 7,119,204	$ 39,016,008	$ 24,352,203
Redeemable convertible preferred stock, Balance, Shares at Dec. 31, 2015					1,326,145	8,368,230	4,489,160
Balance at Dec. 31, 2014	(49,608,942)	$ 115		$ 49,609,057
Balance, Shares at Dec. 31, 2014		1,153,235
Adjustment of redeemable convertible preferred stock to redemption value	(348,436)		$ (472,846)	124,410
Exercise of stock options	3,000		3,000
Exercise of stock options, shares		4,016
Share-based compensation expense	469,846		469,846
Net loss	(17,070,223)			(17,070,223)
Balance at Dec. 31, 2015	(66,554,755)	$ 115		(66,554,870)
Balance, Shares at Dec. 31, 2015		1,157,251
Redeemable convertible preferred stock, Adjustment of redeemable convertible preferred stock to redemption value	4,152,801				$ 379,777	$ 2,263,804	$ 1,509,220
Redeemable convertible preferred stock, Conversion of preferred stock	(658,102)				$ (324,774)	$ (333,328)
Redeemable convertible preferred stock, Conversion of preferred stock, Shares					(57,877)	(68,191)
Redeemable convertible preferred stock, Extinguishment of preferred stock	(224,224)				$ (157,692)	$ (49,173)	$ (17,359)
Redeemable convertible preferred stock, Extinguishment of preferred stock, shares					(28,930)	(10,376)	(3,145)
Redeemable convertible preferred stock, Balance at Dec. 31, 2016	73,757,890				$ 7,016,515	$ 40,897,311	$ 25,844,064	$ 73,757,890
Redeemable convertible preferred stock, Balance, Shares at Dec. 31, 2016					1,239,338	8,289,663	4,486,015	14,015,016
Adjustment of redeemable convertible preferred stock to redemption value	(4,152,801)		(1,273,631)	(2,879,170)
Conversion of preferred stock	658,102	$ 6	658,096
Conversion of preferred stock, shares		61,803
Extinguishment of preferred stock	224,224		25,426	198,798
Conversion of convertible notes and accrued interest	82,818		82,818
Exercise of stock options	$ 18,968	$ 3	18,965
Exercise of stock options, shares	21,870	21,871
Share-based compensation expense	$ 488,326		488,326
Net loss	(16,983,511)			(16,983,511)
Balance at Dec. 31, 2016	(86,218,629)	$ 124		(86,218,753)
Balance, Shares at Dec. 31, 2016		1,240,925
Redeemable convertible preferred stock, Adjustment of redeemable convertible preferred stock to redemption value								$ 943,297
Redeemable convertible preferred stock, Conversion of preferred stock								$ (74,701,187)
Redeemable convertible preferred stock, Conversion of preferred stock, Shares								(14,015,016)
Adjustment of redeemable convertible preferred stock to redemption value	(943,297)			(943,297)
Conversion of preferred stock	74,701,187	$ 1,402	74,699,785
Conversion of preferred stock, shares		14,015,016
Conversion of convertible notes and accrued interest	13,447,934	$ 274	13,447,660
Conversion of convertible notes and accrued interest, Shares		2,744,059
Share exchange in connection with Merger		$ 100	(100)
Share exchange in connection with Merger, Shares		1,000,000
Issuance of common stock, net of issuance costs	37,163,390	$ 805	37,162,585
Issuance of common stock, net of issuance costs, Shares		8,049,555
Share-based compensation expense	155,385		155,385
Net loss	(4,995,703)			(4,995,703)
Balance at Mar. 31, 2017	$ 33,310,267	$ 2,705	$ 125,465,315	$ (92,157,753)
Balance, Shares at Mar. 31, 2017		27,049,555

Condensed Consolidated Statements of Cash Flows - USD ($)	3 Months Ended		12 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016	Dec. 31, 2015
Operating activities:
Net loss	$ (4,995,703)	$ (4,194,698)	$ (16,983,511)	$ (17,070,223)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation	13,656	16,485	69,673	57,977
Stock-based compensation	155,385	125,215	488,326	469,846
Amortization of debt issuance costs	75,561		188,686
Interest expense related to convertible note conversion	204,929		2,823
Changes in operating assets and liabilities:
Accounts receivable	(28,296)	63,457	114,359	(60,566)
Prepaid expenses and current other assets	(337,174)	214,040	90,404	(210,106)
Accounts payable and other current liabilities	982,521	(97,626)
Accounts payable and accrued expenses			311,096	(1,071,610)
Net cash used in operating activities	(3,929,121)	(3,873,127)	(15,718,144)	(17,884,682)
Investing activities:
Purchase of furniture and equipment	(2,208)	(110,449)	(113,297)	(41,037)
Net cash used in investing activities	(2,208)	(110,449)	(113,297)	(41,037)
Financing activities:
Proceeds from exercise of stock options			18,968	3,000
Proceeds from issuances of convertible notes	297,354		12,542,203
Proceeds from sale of common stock	40,247,775
Cash paid for debt issuance costs			(264,247)
Cash paid in connection with the sale of common stock	(3,084,385)
Net cash provided by financing activities	37,460,744		12,296,924	3,000
Net increase (decrease) in cash and cash equivalents	33,529,415	(3,983,576)	(3,534,517)	(17,922,719)
Cash and cash equivalents at beginning of year	1,609,694	5,144,211	5,144,211	23,066,930
Cash and cash equivalents, end of year	35,139,109	1,160,635	1,609,694	5,144,211
Non-cash financing activities
Conversion of preferred stock into common stock	74,701,187
Conversion of notes and accrued interest into common stock	13,447,934
Accretion of preferred stock to redemption value	$ 943,297	$ 1,015,371	4,152,801	$ 348,436
Extinguishment of preferred stock			$ (224,224)

Nature of Organization and Operations

3 Months Ended

12 Months Ended

Mar. 31, 2017

Dec. 31, 2016

Organization, Consolidation and Presentation of Financial Statements [Abstract]

Nature of Organization and Operations

1.	Nature of Organization and Operations

Aerpio Pharmaceuticals, Inc. (the “Company”) was incorporated as Zeta Acquisition Corp. II (“Zeta”) in the State of Delaware on November 16, 2007. Prior to the Merger, (as defined below), Zeta was a “shell company” (as defined in Rule 12b-2 of the Securities Exchange Act of 1934, as amended).

On March 3, 2017, the Company’s Board of Directors, and on March 10, 2017, the Company’s pre-Merger (as defined below) stockholders, approved an amended and restated certificate of incorporation, which, among other things, increased authorized capital stock from 100,000,000 shares of common stock, par value $0.0001 per share, and 10,000,000 shares of preferred stock, par value $0.0001 per share, to 300,000,000 shares of common stock, par value $0.0001 per share, and 10,000,000 shares of preferred stock, par value $0.0001 per share.

On March 15, 2017, Zeta changed its name to Aerpio Pharmaceuticals, Inc. and its wholly-owned subsidiary, Aerpio Acquisition Corp., a corporation formed in the State of Delaware on March 3, 2017, merged with and into Aerpio Therapeutics, Inc., (“Aerpio”), (the “Merger”), a corporation incorporated on November 17, 2011 in the State of Delaware. Pursuant to the Merger, Aerpio remained as the surviving corporation and became the Company’s wholly-owned subsidiary.

At the effective time of the Merger, the shares of the Aerpio’s (i) common stock issued and outstanding immediately prior to the closing of the Merger (including restricted common stock, whether vested or unvested, issued under the Aerpio’s 2011 Equity Incentive Plan), and (ii) redeemable convertible preferred stock issued and outstanding immediately prior to the closing of the Merger, were converted into shares of the Company’s common stock. In addition, immediately prior to the Merger, the outstanding amounts under certain Senior Secured Convertible Promissory Notes issued by Aerpio to its pre-Merger noteholders were converted into shares of Aerpio’s preferred stock, which were then converted to shares of Aerpio’s common stock and subsequently were converted into shares of the Company’s common stock, together with the other shares of the Aerpio’s common stock described above. In addition, pursuant to the Merger Agreement options to purchase shares of the Aerpio’s common stock issued and outstanding immediately prior to the closing of the Merger were assumed and converted into options to purchase shares of the Company’s common stock. All the outstanding capital stock of Aerpio was converted into shares of the Company’s common stock on a 2.3336572:1 basis.

As a result of the Merger, the Company acquired the business of Aerpio and will continue the existing business operations of Aerpio as a public reporting company under the name Aerpio Pharmaceuticals, Inc. Immediately after the Merger, on March 15, 2017, Aerpio converted into a Delaware limited liability company (the “Conversion”).

Immediately following the Conversion, the pre-Merger stockholders of Zeta surrendered for cancellation 4,000,000 of the 5,000,000 shares of the outstanding common stock of Zeta, (the “Share Cancellation”). Following the Share Cancellation, on March 15, 2017, the Company closed a private placement offering (the “Offering”) of 8,049,555 shares of the Company’s common stock, at a purchase price of $5.00 per share, for net proceeds of approximately $37.2 million and the issuance of warrants with a term of three years, to purchase 317,562 shares of the Company’s common stock at an exercise price of $5.00 per share.

The Merger was treated as a recapitalization and reverse acquisition for financial reporting purposes. The Company is the legal acquirer of Aerpio in the transaction. However, Aerpio is considered the acquiring company for accounting purposes since (i) former Aerpio stockholders own in excess of 50% of the combined enterprise on a fully diluted basis immediately following the Merger and Offering, and (ii) all members of the Company’s executive management and Board of Directors are from Aerpio. In accordance with “reverse merger” or “reverse acquisition” accounting treatment, the unaudited condensed consolidated interim financial statements for the period ended March 31, 2017 include the accounts of the Company and its wholly owned subsidiary, Aerpio Therapeutics, LLC. The comparative historical financial statements for periods ended prior to the date of the Merger are the historical financial statements of Aerpio. Consequently, the assets and liabilities and the historical operations that are reflected in these condensed consolidated financial statements of the company are those of Aerpio, which were recorded at their historical cost basis. Unless otherwise indicated, all share and per share figures reflect the exchange of each 2.3336572 shares of Aerpio capital stock, convertible notes and share based awards, then outstanding, for 1 share of the Company’s common stock at the effective time of the Merger.

The Company is a biopharmaceutical company focused on advancing first-in-class treatments for ocular disease. The Company’s lead product candidate, AKB-9778, a small molecule activator of the tie-2 pathway, is being developed for the treatment of diabetic retinopathy (“DR”). Tie-2 signaling is essential for regulating blood vessel development and the stability of mature vessels. The Company has completed a Phase 2a clinical trial in diabetic macular edema (“DME”), a swelling of the retina that is a common cause of vision loss in patients with DR and intends to initiate a twelve month, double blind Phase 2b clinical trial in patients with DR who have not developed more serious complications such as DME or proliferative diabetic retinopathy. The DR clinical trial will be initiated in the second quarter of 2017.

In addition, the Company has two pipeline programs. AKB-4924 is a drug candidate for the treatment of inflammatory bowel disease and ARP-1536, humanized monoclonal antibody is a drug candidate for ocular disease. Humanized antibodies are antibodies from non-human species whose protein sequences have been modified to increase their similarity to antibodies produced naturally in humans. The Company completed a Phase 1a clinical trial in healthy volunteers for AKB-4924 and APR-1536 is currently in preclinical development. Further development on the pipeline programs is subject to receiving additional funding, which the Company may seek through collaborations with potential strategic and commercial partners.

The Company’s operations to date have been limited to organizing and staffing the Company, business planning, raising capital, acquiring and developing its technology, identifying potential product candidates, and undertaking preclinical and clinical studies. The Company has not generated any revenues to date, nor is there any assurance of any future revenues. The Company’s product candidates are subject to long development cycles, and there is no assurance the Company will be able to successfully develop, obtain regulatory approval for, or market its product candidates.

The Company is subject to a number of risks similar to other life science companies in the current stage of its life cycle, including, but not limited to, the need to obtain adequate additional funding, possible failure of preclinical testing or clinical trials, the need to obtain marketing approval for its product candidates, competitors developing new technological innovations, the need to successfully commercialize and gain market acceptance of any of the Company’s products that are approved, and protection of proprietary technology. If the Company does not successfully commercialize any of its products or mitigate any of these other risks, it will be unable to generate revenue or achieve profitability.

1.	Nature of Organization and Operations

Merger and Offering

On March 15, 2017, Zeta changed its name to Aerpio Pharmaceuticals, Inc. and its wholly-owned subsidiary, Aerpio Acquisition Corp., a corporation formed in the State of Delaware on March 3, 2017, merged with and into Aerpio Therapeutics, Inc., (“Aerpio”), (the “Merger”), a corporation incorporated on November 17, 2011 in the State of Delaware. Aerpio was initially capitalized in December 2011 in a spinout transaction from Akebia Therapeutics, Inc. (Akebia) to enable more rapid development of its compounds. Pursuant to the Merger, Aerpio remained as the surviving corporation and became the Company’s wholly-owned subsidiary.

The Merger was treated as a recapitalization and reverse acquisition for financial reporting purposes. The Company is the legal acquirer of Aerpio in the transaction. However, Aerpio is considered the acquiring company for accounting purposes since (i) former Aerpio stockholders own in excess of 50% of the combined enterprise on a fully diluted basis immediately following the Merger and Offering, and (ii) all members of the Company’s executive management and Board of Directors are from Aerpio. In accordance with “reverse merger” or “reverse acquisition” accounting treatment, the consolidated financial statements as of and for each of the years ended December 31, 2016 and 2015 are the historical financial statements of Aerpio. Consequently, the assets and liabilities and the historical operations that are reflected in these consolidated financial statements are those of Aerpio, which were recorded at their historical cost basis. Unless otherwise indicated, all share and per share figures reflect the exchange of each 2.3336572 shares of Aerpio capital stock, convertible notes and share based awards, then outstanding, for 1 share of the Company’s common stock at the effective time of the Merger.

Operations Background

Summary of Significant Accounting Policies

3 Months Ended

12 Months Ended

Mar. 31, 2017

Dec. 31, 2016

Accounting Policies [Abstract]

Summary of Significant Accounting Policies

2.	Summary of Significant Accounting Policies

Basis of Presentation

The unaudited condensed consolidated financial statements have been prepared in accordance with U.S. Securities and Exchange Commission (SEC) regulations and include all of the information and disclosures required by generally accepted accounting principles in the United States (“U.S. GAAP” or “GAAP”) for interim financial reporting, and, in the opinion of management include all adjustments necessary for a fair presentation of the results of operations, financial position and cash flows for each period presented. All adjustments are of a normal and recurring nature. These unaudited condensed consolidated financial statements should be read in conjunction with the consolidated financial statements of Aerpio Pharmaceuticals, Inc. and related footnotes for the year ended December 31, 2016, included in the Company’s Registration Statement on Form S-1. The results of operations for the interim periods are not necessarily indicative of results of operations for a full year. The Company’s condensed consolidated financial statements are stated in U.S. Dollars.

Segment Information

Operating segments are defined as components of an enterprise about which separate discrete information is available for evaluation by the chief operating decision maker, or decision-making group, in deciding how to allocate resources and in assessing performance. The Company views its operations and manages its business in one operating segment, which is the business of developing and commercializing proprietary therapeutics. All the assets and operations of the Company’s sole operating segment are located in the United States of America.

Use of Estimates

The preparation of financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. Actual results may differ from those estimates. Management considers many factors in selecting appropriate financial accounting policies and controls and in developing the estimates and assumptions that are used in the preparation of these consolidated financial statements. Management must apply significant judgment in this process. In addition, other factors may affect estimates, including expected business and operational changes, sensitivity and volatility associated with the assumptions used in developing estimates, and whether historical trends are expected to be representative of future trends. The estimation process often may yield a range of potentially reasonable estimates of the ultimate future outcomes, and management must select an amount that falls within that range of reasonable estimates. Estimates are used in the following areas, among others: fair value of the Company’s common stock and other equity instruments, accrued expenses, and income taxes.

The Company utilizes significant estimates and assumptions in determining the fair value of its common stock and other equity instruments. The Company granted stock options at exercise prices not less than the fair value of its common stock, as determined by the Board of Directors contemporaneously at the date such grants were made. The Board of Directors has determined the estimated fair value of the Company’s common stock based on a number of objective and subjective factors, including external market conditions affecting the biotechnology industry sector and the prices at which the Company sold shares of preferred stock, the superior rights and preferences of securities senior to the Company’s common stock at the time, and the likelihood of achieving a liquidity event, such as a public offering or sale of the Company.

Historically, the Company utilized various valuation methodologies in accordance with the framework of the American Institute of Certified Public Accountants Technical Practice Aid, Valuation of Privately-Held Company Equity Securities Issued as Compensation, to estimate the fair value of its common stock. Each valuation methodology includes estimates and assumptions that require the Company’s judgment. These estimates and assumptions include a number of objective and subjective factors, including external market conditions, the prices at which the Company sold shares of redeemable convertible preferred stock, the superior rights and preferences of securities senior to the Company’s common stock at the time, and, at December 31, 2016, a probability analysis of various liquidity events under differing scenarios, including both a potential public trading scenario and potential sale scenario. Significant changes to the key assumptions used in the valuations could result in different fair values of common stock and other equity instruments at each valuation date.

The Company’s results can also be affected by economic, political, legislative, regulatory, and legal actions. Economic conditions, such as recessionary trends, inflation, interest and monetary exchange rates, government fiscal policies, and changes in the prices of research studies, can have a significant effect on operations. While the Company maintains reserves for anticipated liabilities and carries various levels of insurance, the Company could be affected by civil, criminal, regulatory or administrative actions, claims, or proceedings.

Cash and Cash Equivalents

Cash and cash equivalents consist of all cash on hand, deposits, and funds invested in short-term investments with remaining maturities of three months or less at the time of purchase. The Company may maintain balances with its banks in excess of federally insured limits.

Short-Term Investments

Time deposits with remaining maturities of greater than three months but less than one year at the time of purchase are classified as short-term investments in the accompanying balance sheets.

Grant Income

Grant income is recognized as earned based on contract work performed.

Research and Development

Costs incurred in connection with research and development activities are expensed as incurred. Research and development expense consists of (i) employee-related expenses, including salaries, benefits, travel, and stock-based compensation expense; (ii) external research and development expenses incurred under arrangements with third parties, such as contract research organizations and consultants; (iii) the cost of acquiring, developing, and manufacturing clinical study materials; (iv) facilities and other expenses, which include direct and allocated expenses for rent and maintenance of facilities and laboratory and other supplies; and (v) costs associated with preclinical activities and regulatory operations.

The Company enters into consulting, research, and other agreements with commercial firms, researchers, universities, and others for the provision of goods and services.

Under such agreements, the Company may pay for services on a monthly, quarterly, project, or other basis. Such arrangements are generally cancellable upon reasonable notice and payment of costs incurred. Costs are considered incurred based on an evaluation of the progress to completion of specific tasks under each contract using information and data provided to the Company by its clinical sites and vendors. These costs consist of direct and indirect costs associated with specific projects, as well as fees paid to various entities that perform certain research on behalf of the Company.

Patents

Costs incurred in connection with the application for and issuances of patents are expensed as incurred.

Income Taxes

Income taxes are recorded in accordance with Financial Accounting Standards Board (“FASB”) Accounting Standards Codification (ASC) Topic 740, Income Taxes, which provides for deferred taxes using an asset and liability approach. The Company recognizes deferred tax assets and liabilities for the expected future tax consequences of events that have been included in the financial statements or tax returns. Deferred tax assets and liabilities are determined based on the difference between the financial statement and tax bases of assets and liabilities and for loss and credit carryforwards using enacted tax rates anticipated to be in effect for the year in which the differences are expected to reverse. Valuation allowances are provided, if, based upon the weight of available evidence, it is more likely than not that some or all of the deferred tax assets will not be realized.

The Company accounts for uncertain tax positions in accordance with the provisions of ASC 740. When uncertain tax positions exist, the Company recognizes the tax benefit of tax positions to the extent that some or all of the benefit will more likely than not be realized. The determination as to whether the tax benefit will more likely than not be realized is based upon the technical merits of the tax position, as well as consideration of the available facts and circumstances. As of March 31, 2017, and December 31, 2016, the Company does not have any significant uncertain tax positions. If incurred, the Company would classify interest and penalties on uncertain tax positions as income tax expense.

Net Loss per Share

The Company’s basic net loss per share attributable to common stockholders is calculated by dividing the net loss attributable to common stockholders by the weighted average number of shares of common stock outstanding for the period. The diluted net loss per share attributable to common stockholders is computed by adjusting the weighted average shares outstanding for the dilutive effect of common stock equivalents outstanding for the period, determined using the treasury stock method. For purposes of this calculation, convertible preferred stock, convertible notes payable, stock options to purchase common stock, warrants, and unvested restricted stock awards are considered to be common stock equivalents but have been excluded from the calculation of diluted net loss per share attributable to common stockholders as their effect is anti-dilutive for all periods presented. Therefore, basic and diluted net loss per share were the same for all periods presented.

For all periods presented, all share and per share amounts have been retrospectively adjusted to reflect the exchange of each 2.3336572 shares of Aerpio capital stock and share based awards then outstanding, for 1 share of the Company’s common stock at the effective time of the Merger.

Stock-Based Compensation

The Company accounts for its stock-based compensation awards in accordance with FASB ASC Topic 718, Compensation—Stock Compensation. ASC 718 requires all stock-based payments to employees, including grants of employee stock options and restricted stock, to be recognized in the statements of operations and comprehensive loss based on their fair values. All the Company’s stock-based awards are subject only to service-based vesting conditions. The Company estimates the fair value of its stock-based awards using the Black-Scholes option pricing model, which requires the input of subjective assumptions, including (a) the expected stock price volatility, (b) the calculation of expected term of the award, (c) the risk-free interest rate, and (d) expected dividends. The fair value of restricted stock awards is determined based on the Company’s estimated common stock value.

Due to the lack of a public market for the trading of the Company’s common stock and a lack of company-specific historical and implied volatility data, the Company has based its estimate of expected volatility on the historical volatility of a group of similar companies that are publicly traded. The computation of expected volatility is based on the historical volatility of a representative group of companies with similar characteristics to the Company, including stage of product development and life science industry focus. The Company believes the group selected has sufficient similar economic and industry characteristics and includes companies that are most representative of the Company.

The Company uses the simplified method as prescribed by the Securities and Exchange Commission Staff Accounting Bulletin No. 107, Share-Based Payment, to calculate the expected term, as it does not have sufficient historical exercise data to provide a reasonable basis upon which to estimate the expected term for options granted to employees, and utilizes the contractual term for options granted to non-employees. The expected term is applied to the stock option grant group as a whole, as the Company does not expect substantially different exercise or post-vesting termination behavior among its employee population. The risk-free interest rate is based on a treasury instrument whose term is consistent with the expected life of the stock options.

Compensation expense related to awards to employees is calculated on a straight-line basis by recognizing the grant date fair value over the associated service period of the award, which is generally the vesting term. Awards to non-employees are adjusted through share-based compensation expense as the award vests to reflect the current fair value of such awards and are expensed using an accelerated attribution model.

Fair Value of Financial Instruments

The Company’s financial instruments consist of cash equivalents, short-term investments, accounts receivable, and accounts payable. The Company values cash equivalents using quoted market prices. The valuation technique used to measure the fair value of short-term investments was based on net asset values corroborated with observable market data. The fair value of accounts receivable and accounts payable approximate the carrying value because of their short-term nature.

The Company is required to disclose information on all assets and liabilities reported at fair value that enables an assessment of the inputs used in determining the reported fair values. FASB ASC Topic 820, Fair Value Measurements and Disclosures, establishes a hierarchy of inputs used in measuring fair value that maximizes the use of observable inputs and minimizes the use of unobservable inputs by requiring that the observable inputs be used when available.

Observable inputs are inputs that market participants would use in pricing the asset or liability based on market data obtained from sources independent of the Company. Unobservable inputs are inputs that reflect the Company’s assumptions about the inputs that market participants would use in pricing the asset or liability and are developed based on the best information available in the circumstances. The fair value hierarchy applies only to the valuation inputs used in determining the reported fair value of the investments and is not a measure of the investment credit quality. The three levels of the fair value hierarchy are described below:

•

Level 1—Valuations based on unadjusted quoted prices in active markets for identical assets or liabilities that the Company has the ability to access at the measurement date

•

Level 2—Valuations based on quoted prices for similar assets or liabilities in markets that are not active or for which all significant inputs are observable, either directly or indirectly

•

Level 3—Valuations that require inputs that reflect the Company’s own assumptions that are both significant to the fair value measurement and unobservable

To the extent that a valuation is based on models or inputs that are less observable or unobservable in the market, the determination of fair value requires more judgment. Accordingly, the degree of judgment exercised by the Company in determining fair value is greatest for instruments categorized in Level 3. A financial instrument’s level within the fair value hierarchy is based on the lowest level of any input that is significant to the fair value measurement. There were no transfers within the fair value hierarchy in the three months ended March 31, 2017 or March 31, 2016. The assets of the Company measured on a recurring basis as of March 31, 2017 and December 31, 2016 basis are summarized below:


	Fair Value Measurements Using
	Level 1		Level 2		Level 3		Total
March 31, 2017
Assets:
Cash and cash equivalents	$	35,139,109	$	—	$	—	$	35,139,109
Short-term investments		—		50,000		—		50,000

Total assets	$	35,139,109	$	50,000	$	—	$	35,189,109

December 31, 2016
Assets:
Cash and cash equivalents	$	1,609,694	$	—	$	—	$	1,609,694
Short-term investments		—		50,000		—		50,000

	$	1,609,694	$	50,000	$	—	$	1,659,694

Concentrations of Credit Risk and Off-Balance Sheet Risk

Cash and cash equivalents and short-term investments are the only financial instruments that potentially subject the Company to concentrations of credit risk. At March 31, 2017 and December 31, 2016, all the Company’s cash was deposited in accounts at two principal financial institutions. The Company maintains its cash and cash equivalents and short-term investments with a high-quality, accredited financial institution and, accordingly, such funds are subject to minimal credit risk. The Company has no significant off-balance sheet concentrations of credit risk, such as foreign currency exchange contracts, option contracts, or other hedging arrangements.

Comprehensive Loss

Comprehensive loss is defined as the change in equity of a business enterprise during a period from transactions and other events and circumstances from non-owner sources, if any. Comprehensive loss equaled net loss for all periods presented.

Furniture and Equipment

Furniture and equipment is stated at cost, less accumulated depreciation. Furniture and equipment is depreciated using the straight-line method over the estimated useful lives of the assets, generally three to seven years. Such costs are periodically reviewed for recoverability when impairment indicators are present. Such indicators include, among other factors, operating losses, unused capacity, market value declines, and technological obsolescence. Recorded values of asset groups of property, plant, and equipment that are not expected to be recovered through undiscounted future net cash flows are written down to current fair value, which generally is determined from estimated discounted future net cash flows (assets held for use) or net realizable value (assets held for sale).

Research and Development Costs

Research and development costs are expensed as incurred.

Recent Accounting Pronouncements

From time to time, new accounting pronouncements are issued by the FASB or other standard setting bodies and adopted by the Company as of the specified effective date. Unless otherwise discussed, the Company believes the impact of recently issued standards that are not yet effective will not have a material impact on its financial position or results of operations upon adoption.

In March 2016, the FASB issued ASU 2016-09, “Improvements to Employee Share-Based Payment Accounting.” This ASU is intended to simplify accounting for share-based payments and requires that excess tax benefits for share-based payments be recorded as a reduction of income tax expense and reflected within operating cash flows rather than being recorded within equity and reflected within financing cash flows. The ASU also provides an option for companies to recognize forfeitures as they occur rather than estimating the number of awards expected to be forfeited. The Company adopted this ASU on January 1, 2017 and is applying the new guidance related to excess tax benefits on a prospective basis. The Company has also elected to account for forfeitures of share-based payments as they occur. The effect of adoption was not material to the condensed consolidated financial statements.

In February 2016, the FASB issued ASU 2016-02, Leases. This ASU will require lessees to recognize almost all leases on the balance sheet as a right-of-use asset and a lease liability. For income statement purposes, the FASB retained a dual model, requiring leases to be classified as finance leases or operating leases. This update is effective for interim and annual periods beginning after December 15, 2018, with early adoption permitted. The Company is currently assessing the effect that adoption of the new standard will have on its condensed consolidated financial statements.

2.	Summary of Significant Accounting Policies

Basis of Presentation

The Company’s financial statements are prepared in accordance with U.S. generally accepted accounting principles (“U.S. GAAP”) and stated in U.S. dollars.

Segment Information

Operating segments are defined as components of an enterprise about which separate discrete information is available for evaluation by the chief operating decision maker, or decision-making group, in deciding how to allocate resources and in assessing performance. The Company views its operations and manages its business in one operating segment, which is the business of developing and commercializing proprietary therapeutics in vascular disorders of the eye. All of the assets and operations of the Company’s sole operating segment are located in the United States of America.

Use of Estimates

The preparation of financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. Actual results may differ from those estimates. Management considers many factors in selecting appropriate financial accounting policies and controls and in developing the estimates and assumptions that are used in the preparation of these financial statements. Management must apply significant judgment in this process. In addition, other factors may affect estimates, including expected business and operational changes, sensitivity and volatility associated with the assumptions used in developing estimates, and whether historical trends are expected to be representative of future trends. The estimation process often may yield a range of potentially reasonable estimates of the ultimate future outcomes, and management must select an amount that falls within that range of reasonable estimates. Estimates are used in the following areas, among others: fair value of the Company’s common stock and other equity instruments, accrued expenses, and income taxes.

The Company utilized various valuation methodologies in accordance with the framework of the American Institute of Certified Public Accountants Technical Practice Aid, Valuation of Privately-Held Company Equity Securities Issued as Compensation, to estimate the fair value of its common stock. Each valuation methodology includes estimates and assumptions that require the Company’s judgment. These estimates and assumptions include a number of objective and subjective factors, including external market conditions, the prices at which the Company sold shares of redeemable convertible preferred stock, the superior rights and preferences of securities senior to the Company’s common stock at the time, and, at December 31, 2016, a probability analysis of various liquidity events under differing scenarios, including both a potential public trading scenario and potential sale scenario. Significant changes to the key assumptions used in the valuations could result in different fair values of common stock and other equity instruments at each valuation date.

Cash and Cash Equivalents

Short-Term Investments

Time deposits with remaining maturities of greater than three months but less than one year at the time of purchase are classified as short-term investments in the accompanying balance sheets.

Grant Income

Grant income is recognized as earned based on contract work performed. Grant income also includes qualifying therapeutic credits from the U.S. Treasury related to discovery projects.

Research and Development

The Company enters into consulting, research, and other agreements with commercial firms, researchers, universities, and others for the provision of goods and services.

Patents

Costs incurred in connection with the application for and issuances of patents are expensed as incurred.

Income Taxes

Income taxes are recorded in accordance with Financial Accounting Standards Board (“FASB”) Accounting Standards Codification (“ASC”) Topic 740, Income Taxes, which provides for deferred taxes using an asset and liability approach. The Company recognizes deferred tax assets and liabilities for the expected future tax consequences of events that have been included in the financial statements or tax returns. Deferred tax assets and liabilities are determined based on the difference between the financial statement and tax bases of assets and liabilities and for loss and credit carryforwards using enacted tax rates anticipated to be in effect for the year in which the differences are expected to reverse. Valuation allowances are provided, if, based upon the weight of available evidence, it is more likely than not that some or all of the deferred tax assets will not be realized.

The Company accounts for uncertain tax positions in accordance with the provisions of ASC 740. When uncertain tax positions exist, the Company recognizes the tax benefit of tax positions to the extent that some or all of the benefit will more likely than not be realized. The determination as to whether the tax benefit will more likely than not be realized is based upon the technical merits of the tax position, as well as consideration of the available facts and circumstances. As of December 31, 2016 and 2015, the Company does not have any significant uncertain tax positions. If incurred, the Company would classify interest and penalties on uncertain tax positions as income tax expense.

Net Loss per Share

The Company’s basic net loss per share attributable to common stockholders is calculated by dividing the net loss attributable to common stockholders by the weighted average number of shares of common stock outstanding for the period. The diluted net loss per share attributable to common stockholders is computed by adjusting weighted average shares outstanding for the dilutive effect of common stock equivalents outstanding for the period, determined using the treasury stock method. For purposes of this calculation, convertible preferred stock, stock options to purchase common stock, and restricted stock awards are considered to be common stock equivalents but have been excluded from the calculation of diluted net loss per share attributable to common stockholders as their effect is anti-dilutive for all periods presented. Therefore, basic and diluted net loss per share were the same for all periods presented.

Stock-Based Compensation

The Company accounts for its stock-based compensation awards in accordance with FASB ASC Topic 718, Compensation—Stock Compensation. ASC 718 requires all stock-based payments to employees, including grants of employee stock options and restricted stock, to be recognized in the statements of operations and comprehensive loss based on their fair values. All of the Company’s stock-based awards are subject only to service-based vesting conditions. The Company estimates the fair value of its stock-based awards using the Black-Scholes option pricing model, which requires the input of subjective assumptions, including (a) the expected stock price volatility, (b) the calculation of expected term of the award, (c) the risk-free interest rate, and (d) expected dividends. The fair value of restricted stock award are determined based on the Company’s estimated common stock value.

Due to the lack of a public market for the trading of the Company’s Common Stock and a lack of company-specific historical and implied volatility data, the Company has based its estimate of expected volatility on the historical volatility of a group of similar companies that are publicly traded. The computation of expected volatility is based on the historical volatility of a representative group of companies with similar characteristics to the Company, including stage of product development and life science industry focus. The Company believes the group selected has sufficient similar economic and industry characteristics and includes companies that are most representative of the Company.

Fair Value of Financial Instruments

•

Level 1—Valuations based on unadjusted quoted prices in active markets for identical assets or liabilities that the Company has the ability to access at the measurement date

•

Level 2—Valuations based on quoted prices for similar assets or liabilities in markets that are not active or for which all significant inputs are observable, either directly or indirectly

•

Level 3—Valuations that require inputs that reflect the Company’s own assumptions that are both significant to the fair value measurement and unobservable

Based on the fair value hierarchy, assets measured or disclosed at fair value on a recurring basis are summarized below:


	Fair Value Measurements Using
	Level 1		Level 2		Level 3		Total
December 31, 2016
Assets:
Cash and cash equivalents	$	1,609,694	$	—	$	—	$	1,609,694
Short-term investments		—		50,000		—		50,000

Total assets	$	1,609,694	$	50,000	$	—	$	1,659,694

December 31, 2015
Assets:
Cash and cash equivalents	$	5,144,211	$	—	$	—	$	5,144,211
Short-term investments		—		50,000		—		50,000

	$	5,144,211	$	50,000	$	—	$	5,194,211

Concentrations of Credit Risk and Off-Balance Sheet Risk

Cash and cash equivalents and short-term investments are the only financial instruments that potentially subject the Company to concentrations of credit risk. At December 31, 2016 and 2015, all of the Company’s cash was deposited in accounts at two principal financial institutions. The Company maintains its cash and cash equivalents and short-term investments with a high-quality, accredited financial institution and, accordingly, such funds are subject to minimal credit risk. The Company has no significant off-balance sheet concentrations of credit risk, such as foreign currency exchange contracts, option contracts, or other hedging arrangements.

Comprehensive Loss

Furniture and Equipment

Research and Development Costs

Research and development costs are expensed as incurred.

Reclassifications

Certain prior year balances in the balance sheet have been reclassified to conform to the current year presentation. The reclassifications were not material to the financial statements.

Recent Accounting Pronouncements

In March 2016, the FASB issued Accounting Standards Update (“ASU”) 2016-09, Improvements to Employee Share-Based Payment Accounting. This ASU is intended to simplify accounting for share-based payments. Upon adoption, this ASU will require that excess tax benefits for share-based payments be recorded as a reduction of income tax expense and reflected within operating cash flows rather than being recorded within equity and reflected within financing cash flows. This update is effective for the Company on January 1, 2017. The adoption of this new standard will not have a material impact on the Company’s financial position or results of operations.

In April 2015, the FASB issued ASU 2015-03, Simplifying the Presentation of Debt Issuance Costs. This ASU requires debt issuance costs to be presented in the balance sheet as a direct deduction from the carrying value of the associated debt liability, consistent with the presentation of a debt discount. This ASU was effective for interim and annual periods beginning after December 15, 2015 and was required to be applied retrospectively. The Company adopted this ASU as of December 31, 2016, and as a result debt issuance costs of $75,561 are reducing the carrying amounts of the Company’s Convertible Notes as of December 31, 2016. There was no outstanding debt at December 31, 2015 to apply retrospective application.

In November 2015, the FASB issued ASU 2015-17, Balance Sheet Classification of Deferred Taxes. This ASU requires all deferred tax assets and liabilities to be classified as non-current on the balance sheet instead of separating into current and non-current amounts. This update is effective for annual periods beginning after December 15, 2016, and may be applied on a prospective or retrospective basis. The Company elected to early adopt this standard on a retrospective basis as of December 31, 2015. As described in Note 9, there was no impact on the current or prior period balance sheets as a result of the adoption of ASU 2015-17.

Related-Party Arrangements

3 Months Ended

12 Months Ended

Mar. 31, 2017

Dec. 31, 2016

Related-Party Arrangements

3.	Related-Party Arrangements

Aerpio was initially capitalized in December 2011 in a spinout transaction from Akebia Therapeutics, Inc. (Akebia) to enable more rapid development of its compounds. In connection with the spinout of Aerpio from Akebia, the companies entered into shared services agreements. Under the terms of the shared services agreements, Akebia and Aerpio obtained from and provided to each other certain services, as outlined below. These agreements were expired at December 31, 2016.

Below is a summary of the activities included in the statements of operations and comprehensive loss:


		Three Months Ended March 31,
Activity	Financial Statement Caption	2017		2016
Akebia related employee costs	Research and development operating expenses	$	—	$	12,923
Facility-related reimbursement	Other income, net		—		997

3.	Related-Party Arrangements

On December 22, 2011, in connection with the spinout of the Company from Akebia, the Company’s former parent company, Akebia assigned certain assets and liabilities to the Company.

In connection with the spinout of Aerpio from Akebia, the companies entered into shared services agreements. Under the terms of the shared services agreements, Akebia and Aerpio obtain from and provide to each other certain services, as outlined below. These agreements are cancelable upon mutual agreement or a sale of either company.

Below is a summary of the activities included in the statements of operations and comprehensive loss:


		Year Ended December 31
Activity	Financial Statement Caption	2016		2015
Payments to Akebia for employee costs	Research and development operating expenses	$	31,246	$	263,501
Payments from Akebia for facility-related charges and employee costs	Other income, net		997		27,022

A summary of Akebia receivables and payables included in the accompanying balance sheets are as follow:


		December 31
Activity	Financial Statement Caption	2016		2015
Amounts receivable from Akebia	Accounts receivable	$	—	$	997
Amounts payable to Akebia	Accounts payable		—		15,173

Accounts Payable and Accrued Expenses

3 Months Ended

12 Months Ended

Mar. 31, 2017

Dec. 31, 2016

Payables and Accruals [Abstract]

Accounts Payable and Accrued Expenses

4.	Accounts Payable and Accrued Expenses

Accounts payable and accrued expenses are as follows:


	March 31, 2017		December 31, 2016
Accounts payable	$	1,871,662	$	1,135,608
Professional fees		300,356		200,468
Accrued bonus		125,576		—
Accrued interest		—		483,442
Accrued vacation		106,199		52,835
Accrued project costs		510,828		541,158
Other		55,427		57,459

Total accounts payable and accrued expenses	$	2,970,048	$	2,470,970

5.	Accounts Payable and Accrued Expenses

Accounts payable and accrued expenses are as follows:


	December 31
	2016		2015
Accounts payable	$	1,135,608	$	890,610
Professional fees		200,468		126,722
Accrued bonus		—		380,020
Accrued interest		483,442		—
Accrued vacation		52,835		56,796
Accrued project costs		541,158		696,158
Other		57,459		9,568

Total accounts payable and accrued expenses	$	2,470,970	$	2,159,874

Notes Payable to Investors

3 Months Ended

12 Months Ended

Mar. 31, 2017

Dec. 31, 2016

Debt Disclosure [Abstract]

Notes Payable to Investors

5.	Notes Payable to Investors

In March 2016, Aerpio entered into a senior secured convertible note financing (the “Convertible Notes” or the “Convertible Note Financing”) totaling approximately $9,000,000, with certain preferred investors of Aerpio. All preferred investors were invited to participate in the Convertible Notes Financing. At March 31, 2017 and December 31, 2016 the unamortized debt issuance costs related to Convertible Note financings was $0 and $75,561. In connection with the Convertible Note Financing, Aerpio’s Articles of Incorporation were amended such that any Aerpio preferred that did not participate in the Aerpio Convertible Note Financing would have their respective shares of Aerpio preferred stock automatically converted into Aerpio common stock using a 3-to-1 conversion ratio and such preferred stockholders would lose the right to representation on the Aerpio Board of Directors and other preferred rights.

The Convertible Note Financing had two separate closings of approximately $4,500,000 each on April 14, 2016 and July 15, 2016. Certain Aerpio preferred stockholders chose not to participate in the Aerpio Convertible Note Financing and their respective Aerpio preferred stock was converted into shares of Aerpio common stock in April 2016 in accordance with the terms of the Articles of Incorporation. Aerpio treated this as an extinguishment of its preferred stock. The Convertible Notes accrued interest at 8% per annum, compounded annually. The Company incurred $138,312 of costs in association with the issuance of the Convertible Notes that was amortized over the seven-month expected life of the Convertible Notes, from the date of execution (March 31, 2016). The Convertible Notes were also subject to mandatory prepayment upon the occurrence of certain events, such as a liquidation, dissolution, or the sale of Aerpio. In addition, and prior to maturity, the Convertible Notes were automatically convertible into shares of Aerpio capital stock upon the occurrence of a sale of Aerpio’s capital stock in a single transaction resulting in gross proceeds to Aerpio of $30,000,000 (hereinafter referred to as an “Investor Sale”). The type and class of Aerpio capital stock of to be issued to the holder of each Convertible Note upon conversion would have been identical to the type and class of Aerpio capital stock issued in the Investor Sale. The holder of each Convertible Note was entitled to a number of shares of Aerpio capital determined by dividing (i) the outstanding principal amount of the Convertible Note plus any unpaid accrued interest by (ii) an amount equal to the price per share of Aerpio capital stock paid by the purchasers of such shares in connection with the Investor Sale. The Convertible Notes were secured by a first priority perfected security interest in all of the Aerpio’s assets.

In October 2016 and February 2017, Aerpio executed an additional senior secured Convertible Note financings (the “Additional Convertible Notes” or the “Additional Convertible Note Financings”) totaling approximately $3,500,000 and $300,000 respectively, with certain preferred investors of Aerpio. The terms of the Additional Convertible Notes are identical to the Convertible Notes and are treated as extensions of the original Convertible Note Financing. The Company incurred $125,935 of costs associated with these transactions, which were amortized to the maturity date of March 31, 2017. In connection with the Additional Convertible Note Financings, the Convertible Notes were amended and their respective maturity dates were extended from October 31, 2016 to March 31, 2017. The amendments are accounted for as a modification for accounting purposes.

In connection with the Merger (Note 1) the Convertible Notes and accrued interest were converted into the Company’s common stock.

6.	Notes Payable to Investors

In March 2016, Aerpio entered into a senior secured convertible note financing (the Convertible Notes or Convertible Note Financing) totaling $9,000,000, with certain preferred investors of Aerpio. All preferred investors were invited to participate in the Convertible Notes Financing. In connection with the Convertible Note Financing, Aerpio’s Articles of Incorporation were amended such that any Aerpio preferred stockholder that did not participate in the Convertible Note Financing would have their respective shares of Aerpio preferred stock automatically converted into Aerpio’s common stock using a 3-to-1 conversion ratio and such Aerpio preferred stockholders would lose the right to representation on Aerpio’s Board of Directors and other preferred rights.

The Convertible Note Financing had two separate closings of $4,500,000 each on April 14, 2016 and July 15, 2016. Certain Aerpio Preferred Stockholders chose not to participate in the Convertible Note Financing and their respective Aerpio preferred stock was converted into shares of Aerpio’s common stock in April 2016 in accordance with the terms of Aerpio’s Articles of Incorporation. Aerpio treated this as an extinguishment of its preferred stock. The Convertible Notes accrue interest at 8% per annum, compounded annually. Aerpio incurred $138,312 of costs in association with the issuance of the Convertible Notes that was amortized over the seven month expected life of the Convertible Notes from the date of issuance (October 31, 2016). The Convertible Notes are also subject to mandatory prepayment upon the occurrence of certain events, such as a liquidation, dissolution, or sale of Aerpio. In addition and prior to maturity, the Convertible Notes are automatically convertible into shares of capital stock of Aerpio upon the occurrence of a sale of Aerpio’s capital stock in a single transaction resulting in gross proceeds to Aerpio of $30,000,000 (hereinafter referred to as an “Investor Sale”). The type and class of capital stock of Aerpio to be issued to the holder of each Convertible Note upon conversion shall be identical to the type and class of the Aerpio capital stock issued in the Investor Sale. The holder of each Convertible Note will be entitled to a number of shares of capital determined by dividing (i) the outstanding principal amount of the Convertible Note plus any unpaid accrued interest by (ii) an amount equal to the price per share of Aerpio capital stock paid by the purchasers of such shares in connection with the Investor Sale. The Convertible Notes are secured by a first priority perfected security interest in all of Aerpio’s assets.

In October 2016, Aerpio executed an additional senior secured Convertible Note financing (the October Convertible Notes or October Convertible Note Financing) totaling $3,500,000 with a certain preferred investors of Aerpio. The terms of the October Convertible Notes are identical to the Convertible Notes and are treated as an extension of the original Convertible Note Financing. Aerpio incurred $125,935 of costs associated with this transaction which will be amortized to the maturity date of March 31, 2017. In connection with the October Convertible Note Financing, the Convertible Notes were amended and their respective maturity dates were extended from October 31, 2016 to March 31, 2017. The amendments are accounted for as a modification for accounting purposes.

Common Stock

3 Months Ended

12 Months Ended

Mar. 31, 2017

Dec. 31, 2016

Equity [Abstract]

Common Stock

6.	Common Stock

As of March 31, 2017, and December 31, 2016, the Company had 300,000,000 and 17,440,436 shares, respectively, of authorized common stock with par value of $0.0001 per share. On March 15, 2017, in connection with the Merger, (Note 1) all the outstanding redeemable convertible preferred stock, was converted into 14,015,016 shares of the Company’s common stock and the Convertible Notes, both principal and accrued interest, were converted into 2,744,059 shares of the Company’s common stock.

The common stock has the following characteristics.

Voting

The holders of common stock are entitled to one vote for each share of common stock held at all meetings of stockholders and written actions in lieu of meetings.

Dividends

The holders of common stock are entitled to receive dividends, if and when declared by the Board of Directors. Since the Company’s inception, no dividends have been declared or paid to the holders of common stock.

Liquidation

In the event of any voluntary or involuntary liquidation, dissolution, or winding-up of the Company, the holders of common stock are entitled to share ratably in the Company’s assets.

Lock-up Agreements and Other Restrictions

In connection with the Merger, each of the Company’s executive officers, directors, stockholders holding substantially all of the shares of common stock issued in exchange for shares held in Aerpio immediately prior to the Merger, certain other stockholders, and certain key employees, (the “Restricted Holders”), holding at the closing date of the Merger (the “Closing Date”) an aggregate of approximately 18.9 million shares of common stock, entered into lock-up agreements,(the “Lock-Up Agreements”), whereby they are restricted for a period of nine months after the Merger, or the Restricted Period, from certain sales or dispositions (including pledge) of all (or 80% in the case of the holders of 915,000 shares) of the Company’s common stock held by (or issuable to) them, (such restrictions together referred to as the “Lock-Up”). The foregoing restrictions will not apply to the resale of shares of common stock by any Restricted Holder in any registered secondary offering of equity securities by the Company (and, if such offering is underwritten, with the written consent of the lead or managing underwriter), or to certain other transfers customarily excepted.

In addition, each Restricted Holder and any stockholders holding or beneficially owning 1% or more of our common stock after giving effect to the Merger, agreed, for a period of 12 months following the Closing Date, that it will not, directly or indirectly, effect or agree to effect any short sale (as defined in Rule 200 under Regulation SHO of the Exchange Act), whether or not against the box, establish any “put equivalent position” (as defined in Rule 16a-1(h) under the Exchange Act) with respect to the common stock, borrow or pre-borrow any shares of common stock, or grant any other right (including, without limitation, any put or call option) with respect to the common stock or with respect to any security that includes, relates to or derives any significant part of its value from the common stock or otherwise seek to hedge its position in the common stock.

Anti-dilution protection

Investors in the Offering have anti-dilution protection with respect to the shares of the Company’s common stock sold in the Offering such that if within six (6) months after the initial closing of the Offering the Company issues additional shares of common stock or common stock equivalents (subject to certain exceptions), for consideration per share less than the Offering Price, or the Lower Price, each such investor will be entitled to receive from the Company additional shares of common stock in an amount such that, when added to the number of shares of common stock initially purchased by such investor and still held of record and beneficially owned by such investor at the time of the dilutive issuance, or the Held Shares, will equal the number of shares of common stock that such investor’s Offering subscription amount for the Held Shares would have purchased at the Lower Price. Either (i) holders of a majority of the then-held Held Shares or (ii) a representative of the holders of the then-held Held Shares, which representative shall be appointed by three (3) investors who then hold the largest number of Held Shares, may waive the anti-dilution rights of all Offering investors with respect to a particular issuance by the Company. These anti-dilution rights were determined not to be a freestanding financial instrument and do not meet the definition of a derivative. Accordingly, the anti-dilution rights are embedded into the shares of the Company’s common stock and do not require separate accounting at March 31, 2017.

Warrants to Purchase Common Stock

At March 31, 2017, the Company had warrants outstanding for the purchase of 317,562 shares of the Company’s common stock at an exercise price of $5.00 per share. The warrants have a three-year term and expire on March 15, 2020. The Warrants were issued in connection with the Offering. At the expiration date of the warrant, if the fair value of the Company’s common stock exceeds the exercise price, the warrant will be automatically exercised and the exercise price will be fulfilled through the net share settlement provisions. The number of shares and the exercise price shall be adjusted for standard ant-dilution events such as stock splits, combinations, reorganizations, or issue shares as part of a stock dividend. Upon a change of control, the warrant holder will have the right to receive securities, cash or other properties it would have been entitled to receive had the warrant been exercised. The Warrants are equity classified instruments and do not contain contingent exercise provisions, or other features, that would preclude the Company from concluding that the Warrants are indexed solely to the Company’s stock.

8.	Common Stock

As of December 31, 2016, Aerpio had 17,440,436 shares of authorized Aerpio common stock with par value of $0.0001 per share. All share and per share amounts are on an as converted basis to reflect the effect of the Merger. The voting, dividend, and liquidation rights of the holders of Aerpio common stock are subject to and qualified by the rights, powers, and preferences of the holders of Preferred Stock. The Aerpio common stock has the following characteristics prior to the Merger.

Voting

The holders of Aerpio common stock are entitled to one vote for each share of Aerpio common stock held at all meetings of stockholders and written actions in lieu of meetings. Notwithstanding the foregoing, except as otherwise required by law, holders of Aerpio common stock shall not be entitled to vote on any amendment to the certificate of incorporation that relates solely to the terms of one or more outstanding series of Preferred Stock or pursuant to General Corporation Law.

Dividends

The holders of Aerpio common stock are entitled to receive dividends, if and when declared by the Aerpio Board of Directors. Aerpio may not declare or pay any cash dividends to the holders of Aerpio common stock unless, in addition to obtaining any necessary consents, dividends are paid on each series of Preferred Stock in accordance with their respective terms. Since Aerpio’s inception, no dividends have been declared or paid to the holders of Aerpio common stock.

Liquidation

In the event of any voluntary or involuntary liquidation, dissolution, or winding-up of Aerpio, the holders of Aerpio common stock are entitled to share ratably in Aerpio’s assets available for distribution to stockholders after payment to the holders of Preferred Stock of their liquidation preferences have been satisfied.

Common Stock Reserved for Future Issuance

As of December 31, 2016, Aerpio has reserved the following shares of Aerpio common stock for future issuance:


Conversion of Series A Preferred Stock			1,239,338
Conversion of Series A1 Preferred Stock			8,289,663
Conversion of Series A2 Preferred Stock			4,486,015
Conversion of unvested restricted stock awards			241,096
Exercise of options to purchase Aerpio common stock			927,593

Total			15,183,705

Preferred Stock

3 Months Ended

12 Months Ended

Mar. 31, 2017

Dec. 31, 2016

Equity [Abstract]

Preferred Stock

7.	Preferred Stock

At March 31, 2017, the Company had 10,000,000 shares of preferred stock, par value $0.0001 per share, in authorized capital. No preferred stock was issued and outstanding at March 31, 2017. In connection with the Merger (Note 1), all the Aerpio redeemable convertible preferred stock issued and outstanding prior to the Merger was converted into shares of the Company’s common stock.

At December 31, 2016, Aerpio’s redeemable convertible preferred stock consisted of the following:

•

Series A redeemable convertible preferred stock: 1,326,147 shares authorized and 1,239,338 shares issued and outstanding;

•

Series A1 redeemable convertible preferred stock: 8,368,247 shares authorized and 8,289,663 shares issued and outstanding; and

•

Series A2 redeemable convertible preferred stock: 4,660,573 shares authorized and 4,486,015 shares issued and outstanding.

All share and per share amounts are on an as converted basis to reflect the effect of the Merger. The rights, preferences, and privileges of the redeemable convertible preferred stock issued and outstanding prior to the Merger were as follows:

Voting

The holders of redeemable convertible preferred stock were entitled to the number of votes equal to the number of whole shares of Aerpio common stock into which the shares of redeemable convertible preferred stock were convertible. Except as provided by law or otherwise, the holders of redeemable convertible preferred stock voted together with the holders of Aerpio common stock as a single class. Certain significant actions required approval by at least 50% of the holders of redeemable convertible preferred stock voting as a single class on an as converted basis. Such significant actions include significant asset transfers, acquisitions, liquidation, amendments to the certificate of incorporation, new indebtedness, repurchase of common stock, changes in the authorized numbers of directors constituting the Board of Directors, and the declaration of dividends.

The holders of shares of redeemable convertible preferred stock were entitled to elect six members of Aerpio’s Board of Directors, which was subject to reduction to not less than four directors under certain circumstances. The holders of Aerpio common stock (including any holders of all shares of redeemable convertible preferred stock on an as converted basis) were entitled to elect two members of Aerpio’s Board of Directors, which was subject to reduction to one director under certain circumstances.

Dividends

Dividends were payable, if permitted by law, in accordance with redeemable convertible preferred stock terms or when and if declared by Aerpio Board of Directors. Prior to the issuance of Series A2 Preferred Stock, dividends on Series A Preferred Stock and Series A1 Preferred Stock were cumulative and accrued daily at a rate of 6% per annum whether or not declared. As part of the Series A2 Preferred Stock issuance, the dividend provisions for Series A Preferred Stock and Series A1 Preferred Stock were retrospectively amended to be noncumulative with the cumulative provision to begin after the Series A2 Preferred Stock issuance date at a rate of 6% per annum. This amendment did not significantly affect the nature of the Series A Preferred Stock and Series A1 Preferred Stock or their fair value. Accordingly, the amendment was treated as a modification for accounting purposes.

Liquidation

In the event of any voluntary or involuntary liquidation, dissolution, or winding-up of Aerpio, or upon the occurrence of a Deemed Liquidation Event, as defined, at the election of more than 50% of the holders of Series A2 Preferred Stock and Series A1 Preferred Stock, those holders were entitled to be paid, in preference to the holders of Series A Preferred Stock and Aerpio common stock, out of the assets of Aerpio available for distribution at $4.90 per share for Series A2 Preferred Stock and $3.97 per share for Series A1 Preferred Stock, plus any accrued but unpaid dividends. After the holders of Series A1 Preferred Stock and Series A2 Preferred Stock are satisfied, the holders of Series A Preferred Stock were paid at $4.27 per share, plus any accrued but unpaid dividends before any payment was made to the holders of Aerpio’s common stock.

In the event the assets of Aerpio available for distribution to stockholders were insufficient to pay the full amount to which the holder was entitled, the holders of Series A2 Preferred Stock and Series A1 Preferred Stock would share ratably any assets available for distribution in proportion to their relative original investment amounts. Any remaining assets of Aerpio would be distributed ratably among the holders of Series A Preferred Stock based upon aggregate applicable dividends accrued on Series A Preferred Stock not previously paid.

After the payment of all preferential amounts required to be paid to the holders of redeemable convertible preferred stock, the remaining assets available for distribution would be distributed among the holders of redeemable convertible preferred stock and Aerpio common stock based on the pro rata number of shares held by each holder, treating such securities as if they had been converted to Aerpio common stock immediately prior to such dissolution, liquidation, or winding-up of Aerpio.

Conversion

Each share of redeemable convertible preferred stock was convertible at the option of the holder, at any time and from time to time, into fully paid and non-assessable shares of Aerpio common stock. The initial conversion ratio was one share of redeemable convertible preferred stock for one share of Aerpio’s common stock. The applicable conversion rate was subject to adjustments upon the occurrence of certain events.

Each share of redeemable convertible preferred stock was automatically convertible into fully paid and non-assessable shares of Aerpio common stock at the then-applicable conversion ratio, as defined, upon either: (i) the closing of the sale of shares of Aerpio’s common stock to the public in an underwritten public offering at a price of $14.70 resulting in at least $40,000,000 of gross proceeds, or (ii) the date and time, or the occurrence of an event, specified by vote or written consent of the holders of more than 50% of the then outstanding shares of redeemable convertible preferred stock on an as-converted basis.

Aerpio evaluated each series of its redeemable convertible preferred stock and determined that each individual series is considered an equity host under ASC Topic 815, Derivatives and Hedging. In making this determination, Aerpio’s analysis followed the whole instrument approach, which compares an individual feature against the entire redeemable convertible preferred stock instrument that includes that feature. Aerpio’s analysis was based on a consideration of the economic characteristics and risks of each series of redeemable convertible preferred stock. More specifically, Aerpio evaluated all the stated and implied substantive terms and features, including: (i) whether the redeemable convertible preferred stock included redemption features, (ii) how and when any redemption features could be exercised, (iii) whether the holders of redeemable convertible preferred stock were entitled to dividends, (iv) the voting rights of the redeemable convertible preferred stock, and (v) the existence and nature of any conversion rights. Aerpio concluded that as the redeemable convertible preferred stock represents an equity host, the conversion feature included in all series of redeemable convertible preferred stock is clearly and closely related to the associated host instrument. Accordingly, the conversion feature of all series of redeemable convertible preferred stock was not considered an embedded derivative that required bifurcation.

Aerpio accounted for potentially beneficial conversion features under ASC Topic 470-20, Debt with Conversion and Other Options. At the time of each of the issuances of redeemable convertible preferred stock, Aerpio’s common stock into which each series of the redeemable convertible preferred stock was convertible had an estimated fair value less than the effective conversion prices of the redeemable convertible preferred stock. Therefore, there was no beneficial conversion element on the respective commitment dates.

In March 2016, in connection with the Convertible Note Financing described more fully in Note 5, Aerpio’s Articles of Incorporation were amended such that any preferred stockholder that did not participate in the Convertible Note Financing would have their respective shares of redeemable convertible preferred stock automatically converted into Aerpio common stock using a 3-to-1 conversion ratio and such preferred stockholders would lose the right to representation on Aerpio’s Board of Directors and other preferred rights. The amendment did not represent an increase in value to the preferred stockholders and was treated as a modification to the redeemable convertible preferred stock for accounting purposes. Certain shares of redeemable convertible preferred stock held by preferred stockholders that elected to not participate in the Convertible Note Financing were converted to shares in Aerpio’s common stock.

Redemption

The redeemable convertible preferred stock was redeemable on or after July 31, 2017, upon a request by more than 50% of the holders of redeemable convertible preferred stock then outstanding, payable in three annual installments commencing not more than 60 days following receipt by notice at a price equal to the greater of (i) the applicable original purchase price and dividends accrued but unpaid (Applicable Accrued Value), which is equal to its liquidation preference, or (ii) the redeemable convertible preferred stock fair value per share. Due to this redemption option, the redeemable convertible preferred stock was recorded in the mezzanine equity and subject to subsequent measurement under the guidance provided under ASC 480-10-S99. In accordance with that guidance, Aerpio elected to recognize changes in redemption value immediately as they occur through adjustments to the carrying amounts of the instruments at the end of each reporting period. As of December 31, 2016, the redemption values of all series of redeemable convertible preferred stock were equal to their respective Applicable Accrued Value. The fair values of redeemable convertible preferred stock were based upon a hybrid of the probability-weighted expected returns method and an option pricing model (OPM), which is a nonrecurring Level 3 fair value measurement within the fair value hierarchy. Under this hybrid model, share value is based on the probability weighted value of Aerpio in a potential public trading scenario, in which the redeemable convertible preferred stock converted to Aerpio common stock, and a second scenario in which equity value is allocated using the OPM. For the public trading scenario, Aerpio used the guideline public company method under the market approach.

7.	Redeemable Convertible Preferred Stock

On December 23, 2011, Aerpio issued 1,326,147 shares of $.00001 par value of Series A Redeemable Convertible Preferred Stock (Series A Preferred Stock) to Akebia’s stockholders in exchange for the assignment of certain development programs and related intellectual property, assets, and liabilities as part of the spinout from Akebia (see Note 3). The Company’s Series A Preferred Stock and common stock were distributed to Akebia’s stockholders as a distribution on the basis of 0.4285120 share of Aerpio’s Series A Preferred Stock for every 35 shares of Akebia’s Series A Preferred Stock, 0.4285120 share of Aerpio’s Series A Preferred Stock for every 100 shares of Akebia’s Series B Preferred Stock, and 0.4285120 share of Aerpio’s Common Stock for every 175 shares of Akebia’s Common Stock.

On August 28, 2012, Aerpio issued 2,520,658 shares of $.00001 par value of Series A1 Redeemable Convertible Preferred Stock (Series A1 Preferred Stock) at $3.97 per share for gross proceeds of $10,000,000, less issuance costs of $210,638, for net proceeds to Aerpio of $9,789,362. In connection with the financing, Aerpio exchanged its then outstanding convertible promissory notes and accrued interest into 1,562,469 shares of Series A1 Preferred Stock. The exchange was pursuant to the contractual provisions of the promissory notes and was accounted for as an extinguishment and share-settled redemption. In August and November 2013, Aerpio issued 2,016,526 and 2,268,594 shares, respectively, of Series A1 Preferred Stock at $3.97 for gross proceeds of $8,000,000 and $9,000,000, respectively, and incurred total issuance costs of $94,326.

On April 22, 2014, Aerpio issued 4,489,169 shares of $.00001 par value Series A2 Redeemable Convertible Preferred Stock (Series A2 Preferred Stock) at $4.90 per share for total gross proceeds of $22,000,000. Aerpio incurred issuance costs of $168,648 for net proceeds to Aerpio of $21,831,352.

In March 2016, in connection with the Convertible Note Financing described more fully in Note 6, Aerpio’s Articles of Incorporation were amended such that any Aerpio Preferred Stockholder that did not participate in the Convertible Note Financing would have their respective shares of Aerpio Preferred Stock automatically converted into Aerpio common stock using a 3-to-1 conversion ratio and such Aerpio Preferred Stockholders would lose the right to representation on Aerpio’s Board of Directors and other preferred rights. The amendment did not represent an increase in value to the Aerpio preferred stockholders and was treated as a modification to the Aerpio Preferred Stock for accounting purposes. Certain shares of redeemable convertible preferred stock held by Aerpio’s Preferred Stockholders that elected to not participate in the Convertible Note Financing were converted to shares in Aerpio’s common stock.

The rights, preferences, and privileges of Aerpio’s Preferred Stock are as follows:

Voting

The holders of Aerpio’s Preferred Stock are entitled to the number of votes equal to the number of whole shares of Aerpio common stock into which the shares of Aerpio Preferred Stock are convertible. Except as provided by law or otherwise, the holders of Aerpio’s Preferred Stock vote together with the holders of Aerpio’s common stock as a single class. Certain significant actions must be approved by at least 50% of the holders of Aerpio’s Preferred Stock voting as a single class on an as converted basis. Such significant actions include significant asset transfers, acquisitions, liquidation, amendments to the certificate of incorporation, new indebtedness, repurchase of Aerpio common stock, changes in the authorized numbers of directors constituting the Aerpio Board of Directors, and the declaration of dividends.

The holders of shares of Aerpio’s Preferred Stock are entitled to elect six members of Aerpio’s Board of Directors, which is subject to reduction to not less than four directors under certain circumstances. The holders of shares of Aerpio common stock (including any holders of all shares of Aerpio Preferred Stock on an as converted basis) are entitled to elect two members of Aerpio’s Board of Directors, which is subject to reduction to one director under certain circumstances.

Dividends

Dividends are payable, if permitted by law, in accordance with Preferred Stock terms or when and if declared by Aerpio’s Board of Directors. Prior to the issuance of Series A2 Preferred Stock, dividends on Series A Preferred Stock and Series A1 Preferred Stock were cumulative and accrued daily at a rate of 6% per annum whether or not declared. As part of the Series A2 Preferred Stock issuance, the dividend provisions for Series A Preferred Stock and Series A1 Preferred Stock were retrospectively amended to be noncumulative with the cumulative provision to begin after the Series A2 Preferred Stock issuance date at a rate of 6% per annum. This amendment did not significantly affect the nature of the Series A Preferred Stock and Series A1 Preferred Stock or their fair value. Accordingly, the amendment was treated as a modification for accounting purposes.

Liquidation

In the event of any voluntary or involuntary liquidation, dissolution, or winding-up of Aerpio, or upon the occurrence of a Deemed Liquidation Event, as defined, at the election of more than 50% of the holders of Series A2 Preferred Stock and Series A1 Preferred Stock, those holders are entitled to be paid, in preference to the holders of Series A Preferred Stock and Aerpio common stock, out of the assets of Aerpio available for distribution at $4.90 per share for Series A2 Preferred Stock and $3.97 per share for Series A1 Preferred Stock, plus any accrued but unpaid dividends. After the holders of Series A1 Preferred Stock and Series A2 Preferred Stock are satisfied, the holders of Series A Preferred Stock are paid at $4.27 per share, plus any accrued but unpaid dividends before any payment is made to the holders of Aerpio common stock.

In the event the assets of Aerpio available for distribution to stockholders are insufficient to pay the full amount to which the holder are entitled, the holders of Series A2 Preferred Stock and Series A1 Preferred Stock will share ratably any assets available for distribution in proportion to their relative original investment amounts. Any remaining assets of Aerpio will be distributed ratably among the holders of Series A Preferred Stock based upon aggregate applicable dividends accrued on Series A Preferred Stock not previously paid.

After the payment of all preferential amounts required to be paid to the holders of Preferred Stock, the remaining assets available for distribution will be distributed among the holders of Preferred Stock and Aerpio common stock based on the pro rata number of shares held by each holder, treating such securities as if they had been converted to Aerpio common stock immediately prior to such dissolution, liquidation, or winding-up of Aerpio .

Conversion

Each share of Preferred Stock is convertible at the option of the holder, at any time and from time to time, into fully paid and non-assessable shares of Aerpio common stock. The initial conversion ratio is one share of Preferred Stock for one share of the Aerpio’s common stock. The applicable conversion rate is subject to future adjustments upon the occurrence of certain events.

Each share of Preferred Stock is automatically convertible into fully paid and non-assessable shares of Aerpio common stock at the then-applicable conversion ratio, as defined, upon either: (i) the closing of the sale of shares of the Aerpio’s common stock to the public in an underwritten public offering at a price of $14.70 resulting in at least $40,000,000 of gross proceeds to Aerpio, or (ii) the date and time, or the occurrence of an event, specified by vote or written consent of the holders of more than 50% of the then outstanding shares of Preferred Stock on an as-converted basis.

Aerpio evaluated each series of its Preferred Stock and determined that each individual series is considered an equity host under ASC Topic 815, Derivatives and Hedging. In making this determination, Aerpio’s analysis followed the whole instrument approach, which compares an individual feature against the entire Preferred Stock instrument that includes that feature. Aerpio’s analysis was based on a consideration of the economic characteristics and risks of each series of Preferred Stock. More specifically, Aerpio evaluated all of the stated and implied substantive terms and features, including: (i) whether the Preferred Stock included redemption features, (ii) how and when any redemption features could be exercised, (iii) whether the holders of Preferred Stock were entitled to dividends, (iv) the voting rights of the Preferred Stock, and (v) the existence and nature of any conversion rights. Aerpio concluded that as the Preferred Stock represents an equity host, the conversion feature included in all series of Preferred Stock is clearly and closely related to the associated host instrument. Accordingly, the conversion feature of all series of Preferred Stock is not considered an embedded derivative that requires bifurcation.

Aerpio accounts for potentially beneficial conversion features under ASC Topic 470-20, Debt with Conversion and Other Options. At the time of each of the issuances of Preferred Stock, Aerpio’s common stock into which each series of Aerpio’s Preferred Stock is convertible had an estimated fair value less than the effective conversion prices of the convertible Preferred Stock. Therefore, there was no beneficial conversion element on the respective commitment dates.

Redemption

Preferred Stock are redeemable on or after July 31, 2017, upon a request by more than 50% of the holders of Preferred Stock then outstanding, payable in three annual installments commencing not more than 60 days following receipt by notice at a price equal to the greater of (i) the applicable original purchase price and dividends accrued but unpaid (Applicable Accrued Value), which is equal to its liquidation preference, or (ii) the Preferred Stock fair value per share. Due to this redemption option, the Preferred Stock is are recorded in mezzanine equity and subject to subsequent measurement under the guidance provided under ASC 480-10-S99. In accordance with that guidance, Aerpio has elected to recognize changes in redemption value immediately as they occur through adjustments to the carrying amounts of the instruments at the end of each reporting period. As of December 31, 2016 and 2015, the redemption values of all series of Preferred Stock were equal to their respective Applicable Accrued Value. The fair values of Preferred Stock are based upon a hybrid of the probability-weighted expected returns method and an option pricing model (OPM), which is a nonrecurring Level 3 fair value measurement within the fair value hierarchy. Under this hybrid model, share value is based on the probability weighted value of Aerpio in an a potential public trading scenario, in which the Preferred Stock converts to Aerpio common stock, and a second scenario in which equity value is allocated using the OPM. For the public trading scenario, Aerpio used the guideline public company method under the market approach.

Stock-Based Compensation

3 Months Ended

12 Months Ended

Mar. 31, 2017

Dec. 31, 2016

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

Stock-Based Compensation

8.	Stock-Based Compensation

Pursuant to the Merger (Note 1), the Company assumed each option to purchase Aerpio common stock that remained outstanding under the Aerpio Therapeutics, Inc. 2011 Equity Incentive Plan (the “Plan”), whether vested or unvested, and converted it into an option to purchase such number of shares of the Company’s common stock equal to the number of shares of Aerpio common stock subject to the option immediately prior to the Merger, divided by the applicable Merger exchange rate of 2.3336572, with any fraction rounded down to the nearest whole number. The exercise price per share of each assumed option is equal to the exercise price of the Aerpio option prior to the assumption, multiplied by the applicable Merger exchange rate of 2.3336572, rounded up to the nearest whole cent. The terms of the 2011 Plan continue to govern the options covering an aggregate of 924,706 shares of the Company’s common stock at March 31, 2017 and December 31, 2016, subject to awards assumed by the Company, except that all references in the 2011 Plan to Aerpio, will now be the Company. In addition, each unvested share of Aerpio restricted common stock issued under the 2011 Plan that was outstanding immediately prior to the effective time of the Merger, was converted by virtue of the Merger into restricted common stock of the Company, equal to the number of shares of Aerpio common stock subject to the unvested shares of Aerpio restricted common stock immediately prior to the Merger divided by the applicable Merger exchange rate of 2.3336572, with any fraction rounded down to the nearest whole number.

In March 2017, the Company’s Board of Directors adopted, and the stockholders approved, the 2017 Stock Option and Incentive Plan (the “2017 Plan”), that became effective in April 2017. The 2017 Plan provides for the issuance of incentive awards up to 4,600,000 shares of common stock to officers, employees, consultants and directors, less the number of shares subject to issued and outstanding awards under the 2011 Plan that were assumed in the Merger. The 2017 Plan also provides that the number of shares reserved for issuance thereunder will be increased annually on the first day of each year beginning in 2018 by four percent (4%) of the shares of our common stock outstanding on the last day of the immediately preceding year or such smaller increase as determined by our board of directors. No awards were granted under the 2017 Plan as of March 31, 2017.

Stock Options

The options granted generally vest over 48 months. For employees with less than one year’s service, options vest in installments of 25% at the one-year anniversary and thereafter in 36 equal monthly installments beginning in the 13 month after the initial Vesting Commencement Date (as defined), subject to the employee’s continuous service with the Company. Options granted to other employees vest in 48 equal monthly installments after the initial Vesting Commencement Date, subject to the employee’s continuous service with the Company. The options generally expire ten years after the date of grant. The fair value of the options at the date of grant is recognized as an expense over the requisite service period. No option awards were granted in the three months ended March 31, 2017 and 2016.

The following table summarizes the stock option activity during the three-months ended March 31, 2017:


	Shares			Weighted Average Exercise Price		Weighted Average Remaining Contractual Term (in Years)		Aggregate Intrinsic Value
Outstanding, January 1, 2017		927,592		$	1.70		7.48	$	1,030,217
Granted		—		$	—
Exercised		—		$	—
Expired/cancelled		(2,886	)	$	2.11

Outstanding, March 31, 2017		924,706		$	1.70		7.24	$	3,056,035

Expected to vest, March 31, 2017		265,647		$	1.81		8.45	$	848,613
Options exercisable, March 31, 2017		659,059		$	1.65		6.75	$	2,207,422

Aggregate intrinsic value represents the estimated fair value of the Company’s common stock at the end of the period in excess of the weighted average exercise price multiplied by the number of options outstanding or exercisable.

Compensation expense for stock options was $81,120 and $42,816 for the three months ended March 31, 2017 and 2016, respectively. As of March 31, 2017, there was $264,823 of unrecognized compensation cost related to stock options, which is expected to be recognized over a weighted average period of 2.1 years.

Restricted Stock

Shares of restricted stock generally have similar vesting terms as stock options. A summary of the Company’s restricted stock activity and related information during the three months ended March 31, 2017 is as follows:


	Shares			Weighted Average Grant Date Fair Value
Nonvested, January 1, 2017		241,096		$	1.91
Granted		—			—
Vested		(39,455	)	$	1.79
Forfeited		(5,222	)	$	2.20

Nonvested, March 31, 2017		196,419		$	1.93

The Company recognized compensation expense for restricted stock of $74,265 and $82,399 for the three months ended March 31, 2017 and 2016, respectively. As of March 31, 2017, there was $366,970 of unrecognized compensation cost related to these restricted stock grants, which is expected to be recognized over a weighted average period of 1.4 years.

Compensation Expense Summary

The Company has recognized the following compensation cost related to employee and non-employee stock-based compensation activity:


	Three Months Ended March 31,
	2017		2016
Research and development	$	115,302	$	81,733
General and administrative		40,083		43,482

Total	$	155,385	$	125,215

9.	Stock-Based Compensation

On November 17, 2011, Aerpio established the Aerpio Therapeutics, Inc. 2011 Equity Incentive Plan (the Plan). The Plan allows for the grant of either incentive stock options or non-qualified stock options to purchase Common Stock, stock bonuses, or restricted stock awards for management and certain persons performing services for the Company. As of December 31, 2016, a total of 5,860,874 shares of Aerpio common stock were authorized for issuance in accordance with the provisions of the Plan.

Stock Options

The options granted generally vest over 48 months. For employees with less than one year’s service, options vest in installments of 25% at the one-year anniversary and thereafter in 36 equal monthly installments beginning in the 13 month after the initial Vesting Commencement Date (as defined), subject to the employee’s continuous service with the Company. Options granted to other employees vest in 48 equal monthly installments after the initial Vesting Commencement Date, subject to the employee’s continuous service with the Company. The options generally expire ten years after the date of grant. The fair value of these options granted is recognized as an expense over the requisite service period.

The fair value of each stock option award granted during the year ended December 31, 2016 and 2015 respectively, was estimated on the grant date using the Black-Scholes option pricing model using the following weighted average assumptions:


	Year Ended December 31
	2016			2015
Expected term (years)		6.00			6.00
Risk-free interest rate		1.39	%		1.97	%
Expected volatility		61.00	%		78.00	%
Expected dividend yield		—			—

The determination of the fair value of stock option awards on the date of grant using the Black-Scholes option pricing model is affected by the estimated fair value of Aerpio’s common stock price, as well as a number of subjective variables. The Company engaged an independent valuation firm to assist management in estimating the fair value of Aerpio’s common stock to be used for purposes of estimating the fair value of options to purchase shares of Aerpio’s common stock. The Company estimates the expected term of options granted utilizing the simplified method. As there has been no public market for Aerpio’s common stock, Aerpio has determined the volatility assumption for options granted based on data from a peer group of companies that issued options with substantially similar terms. The expected volatility of options granted has been determined using the average of the historical volatility measures of this peer group of companies for a period equal to the expected life of the option. The risk-free interest rate is based on the rate applicable to U.S. Treasury zero-coupon issues, with remaining maturities commensurate with the expected term of the options granted in effect on the date of grant. The Company has not paid, and does not anticipate paying, cash dividends on shares of Aerpio common stock; therefore, the expected dividend yield is assumed to be zero in the option valuation model.

The following table summarizes the stock option activity during 2016:


	Shares			Weighted Average Exercise Price		Weighted Average Remaining Contractual Term (in Years)		Aggregate Intrinsic Value
Outstanding, January 1, 2016		907,485		$	1.66			$	135,711
Granted		50,228			1.80
Exercised		(21,870	)		0.87
Expired/cancelled		(8,251	)		1.24

Outstanding, December 31, 2016		927,592		$	1.70		7.48	$	1,030,217

Expected to vest, December 31, 2016		312,547		$	1.82		8.60	$	308,767
Options exercisable, December 31, 2016		615,045		$	1.63		6.92	$	721,451

Aggregate intrinsic value represents the estimated fair value of Aerpio’s common stock at the end of the period in excess of the weighted average exercise price multiplied by the number of options outstanding or exercisable. The aggregate intrinsic value of options exercisable at December 31, 2015 was $116,924.

The weighted average grant date fair value of stock options granted during the years ended December 31, 2016 was $1.22. Stock options exercised during 2016 and 2015 had an intrinsic value of $20,335 and $5,813 respectively. Compensation expense for stock options was $180,399 and $125,926 for the years ended December 31, 2016 and 2015, respectively. As of December 31, 2016, there was $293,796 of unrecognized compensation cost related to stock options, which is expected to be recognized over a weighted average period of 2.4 years.

Restricted Stock

Shares of restricted stock generally have similar vesting terms as stock options. A summary of the Company’s restricted stock activity and related information during 2016 is as follows:


	Shares			Weighted Average Grant Date Fair Value
Nonvested, January 1, 2016		444,199		$	1.69
Granted		—			—
Vested		(203,103	)		1.54
Forfeited		—			—

Nonvested, December 31, 2016		241,096		$	1.91

The Company recognized compensation expense for restricted stock of $307,927 and $343,919 for the years ended December 31, 2016 and 2015, respectively. As of December 31, 2016, there was $447,617 of unrecognized compensation cost related to these restricted stock grants, which is expected to be recognized over a weighted average period of 1.7 years.

Compensation Expense Summary

The Company has recognized the following compensation cost related to employee and non-employee stock-based compensation activity:


	Year Ended December 31
	2016		2015
Research and development	$	317,644	$	295,304
General and administrative		170,682		174,542

Total	$	488,326	$	469,846

- Definition

The entire disclosure for compensation-related costs for equity-based compensation, which may include disclosure of policies, compensation plan details, allocation of equity compensation, incentive distributions, equity-based arrangements to obtain goods and services, deferred compensation arrangements, employee stock ownership plan details and employee stock purchase plan details.

+ References + Details

Income Taxes

3 Months Ended

12 Months Ended

Mar. 31, 2017

Dec. 31, 2016

Income Tax Disclosure [Abstract]

Income Taxes

9.	Income Taxes

The Company did not record a current or deferred income tax expense of benefit for the three months ended March 31, 2017 and 2016, due to the Company’s net losses and increases in its deferred tax asset valuation allowance.

10.

Income Taxes

There was no current or deferred income tax expense or benefit for the years ended December 31, 2016 and 2015, due to the Company’s net losses and increases in its deferred tax asset valuation allowance. The components of loss before income taxes and a reconciliation of the statutory federal income tax with the provision for income taxes are as follows:


	Year Ended December 31
	2016			2015
Federal tax at statutory rate		34.00	%		34.00	%
State and local tax at statutory rates		0.83			0.83
Research and development credits		3.77			4.06
Change in valuation allowance		(37.28	)		(38.26	)
Other		(1.32	)		(0.63	)

Effective tax rate		0.00	%		0.00	%

The Company’s income tax provision was computed based on the federal statutory rate and the average state statutory rates, net of the related federal benefit.

Deferred income taxes reflect the net tax effects of temporary differences between the carrying amounts of assets and liabilities for financial reporting purposes and the amounts used for income and for tax carryforwards. Significant components of the Company’s deferred tax assets and liabilities are as follows:


	December 31
	2016			2015
Deferred tax assets:
Net operating loss carryforwards	$	23,146,178		$	17,427,880
Accrued expenses		18,400			143,295
Stock-based compensation		96,570			—
Research and development credits		2,670,688			2,031,211
Other		20,784			19,565

Total deferred tax assets		25,952,620			19,621,951
Deferred tax liabilities:
Stock-based compensation		—			2,803
Fixed assets		8,434			9,220

Total deferred tax liabilities		8,434			12,023

Net deferred tax assets before valuation allowance		25,944,186			19,609,928
Less valuation allowance		(25,944,186	)		(19,609,928	)

Net deferred tax asset	$	—		$	—

When realization of the deferred tax asset is more likely than not to occur, the benefit related to the deductible temporary differences attributable to operations is recognized as a reduction of income tax expense. Valuation allowances are provided against deferred tax assets when, based on all available evidence, it is considered more likely than not that some portion or all of the recorded deferred tax assets will not be realized in future periods. The Company cannot be certain that future taxable income will be sufficient to realize its deferred tax assets, and accordingly, a full valuation allowance has been provided on its net deferred tax assets. The valuation allowance increased $6,334,258 in 2016 and $6,530,455 in 2015 primarily as a result of an increase in the net operating loss (NOL) and research and development credits carryforwards. The Company continues to monitor the need for a valuation allowance based on the profitability of its future operations.

At December 31, 2016, the Company has approximately $66,464,259 of federal NOL carryforwards and approximately $66,464,259 of state NOL carryforwards that expire at various dates through 2034 and 2019, respectively. At December 31, 2016, the Company had approximately $2,670,688 of federal research and development credit carryforwards that expire at various dates through 2034.

Under the provisions of the Internal Revenue Code, NOL and tax credit carryforwards are subject to review and possible adjustment by the Internal Revenue Service and state tax authorities. NOL and tax credit carryforwards may be subject to an annual limitation in the event of certain cumulative changes in the ownership interest of significant stockholders by more than 50% over a three-year period, as defined in Sections 382 and 383 of the Internal Revenue Code and similar state provisions. The amount of the annual limitation is determined based on the value of the Company immediately before the ownership change. Subsequent ownership changes may further affect the limitation in future years. The Company has not completed a study to assess whether a change of control has occurred or whether there have been multiple changes of control since the date of the Company’s formation due to the significant complexity and cost associated with such study and that there could be additional changes in control in the future. As a result, the Company is unable to estimate the effect of these limitations, if any, on the Company’s ability to utilize NOL and tax credit carryforwards in the future.

The Company has not yet conducted a study to document whether its research activities may qualify for the research and development tax credit. Such a study may result in an adjustment to the Company’s research and development credit carryforwards; however, until a study is completed and any adjustment is known, no amounts are being presented as an uncertain tax position. A full valuation allowance has been provided against the Company’s research and development credit and, if an adjustment is required, this adjustment would be offset by an adjustment to the deferred tax asset established for the research and development credit carryforwards and the valuation allowance.

As of December 31, 2016 and 2015, the Company had no accrued uncertain tax positions or associated interest or penalties and no amounts have been recognized in the Company’s statements of operations and comprehensive loss.

The Company files income tax returns in the U.S. federal jurisdiction and various state jurisdictions. The tax years since inception remain open and subject to examination by federal and state taxing authorities.

Net Loss per Share

3 Months Ended

12 Months Ended

Mar. 31, 2017

Dec. 31, 2016

Earnings Per Share [Abstract]

Net Loss per Share

10.

Net Loss per Share

The following table sets forth the computation of the Company’s basic and diluted net loss per share for the periods presented:


	Three Months Ended March 31,
	2017			2016
Net loss and comprehensive loss	$	(4,995,703	)	$	(4,194,698	)
Accretion of preferred stock to redemption value		(943,297	)		(1,015,371	)

Net loss attributable to common stockholders	$	(5,939,000	)	$	(5,210,069	)

Net loss per share attributable to common stockholders, basic and diluted	$	(1.06	)	$	(7.07	)

Weighted average common shares used in computing net loss per share attributable to common stockholders, basic and diluted		5,605,151			737,016

The following weighted average common stock equivalents were excluded from the calculation of diluted net loss per share for the periods presented because including them would have had an anti-dilutive effect:


	March 31,
	2017		2016
Convertible preferred stock (if converted)		—		14,183,564
Options to purchase common stock		924,706		907,485
Unvested restricted stock		196,419		241,096
Warrants to purchase common stock		317,562		—

11.

Net Loss per Share

The following table sets forth the computation of the Company’s basic and diluted net loss per share for the periods presented:


	Year Ended December 31
	2016			2015
Net loss and comprehensive loss	$	(16,983,511	)	$	(17,070,223	)
Extinguishment of preferred stock		224,224			—
Accretion of preferred stock to redemption value		(4,152,801	)		(348,436	)

Net loss attributable to common stockholders	$	(20,912,088	)	$	(17,418,659	)

Net loss per share attributable to common stockholders, basic and diluted	$	(24.52	)	$	(31.14	)

Weighted average common shares used in computing net loss per share attributable to common stockholders, basic and diluted		852,665			559,419


	December 31
	2016		2015
Convertible preferred stock (if converted)		14,015,016		14,183,535
Options to purchase Aerpio common stock		615,045		424,160
Convertible notes (if converted)		2,641,602		—

Commitments and Contingencies

3 Months Ended

12 Months Ended

Mar. 31, 2017

Dec. 31, 2016

Commitments and Contingencies Disclosure [Abstract]

Commitments and Contingencies

11.

Commitments and Contingencies

The Company contracts with various organizations to conduct research and development activities. In addition, the Company is a party to a lease covering 7,580 square feet of space in Cincinnati, Ohio that expires in June 2018. Total rent expense for all operating leases was $51,289 and $45,180 for the three months ended March 31, 2017 and 2016, respectively. The lease agreement contains free rent, escalating rent payments and reimbursement for tenant improvements that amounted to $46,390 in the three months ended March 31, 2016. Rent expense is recorded on the straight-line basis over the initial term with the differences between rent expense and rent payments recorded as deferred rent. As of March 31, 2017, the Company had deferred rent of $47,948, which is included in accrued expenses in the accompanying condensed consolidated balance sheet. As of March 31, 2017, non-cancelable future minimum lease payments under the existing operating lease were $131,684. In addition, as of December 31, 2016, future payments related to operating leases and other operating commitments arising from contracts related to research and development activities are presented in the table below.


	2017		2018		2019 and Thereafter		Total
Operating leases	$	104,440	$	52,978	$	—	$	157,418
All other operating commitments		2,761,501		—		—		2,761,501

Total commitments	$	2,865,941	$	52,978	$	—	$	2,918,919

12.

Commitments and Contingencies

The Company contracts with various organizations to conduct research and development activities. In addition, the Company is a party to a lease covering 7,580 square feet of space in Cincinnati, Ohio that expires in June 2018. Total rent expense for all operating leases in 2016 and 2015 was $214,595 and $160,221 respectively. The lease agreement contains free rent, escalating rent payments and reimbursement for tenant improvements that amounted to $46,390 in fiscal 2016. Rent expense is recorded on the straight-line basis over the initial terms with the differences between rent expense and rent payments recorded as deferred rent. As of December 31, 2016 and 2015, the Company had deferred rent of $49,209 and $8,486, respectively, which is included in accrued expenses in the accompanying balance sheets. As of December 31, 2016, non-cancelable future minimum lease payments under the existing operating lease were $157,418. In addition, as of December 31, 2016, future payments related to other operating commitments arising from contracts related to research and development activities were $2,761,501 due in 2017.


	2017		2018		2019 and Thereafter		Total
Operating leases	$	104,440	$	52,978	$	—	$	157,418
All other operating commitments		2,761,501		—		—		2,761,501

Total commitments	$	2,865,941	$	52,978	$	—	$	2,918,919

Employee Stock Purchase Plan

3 Months Ended

Mar. 31, 2017

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

Employee Stock Purchase Plan

12.

Employee Stock Purchase Plan

In March 2017, the Board of Directors adopted and the stockholders approved, the Employee Stock Purchase Plan (the “ESPP”), that became effective in April 2017. The ESPP provides for the issuance of up to 300,000 shares of the Company’s common stock for the purchases made under the ESPP. The ESPP also provides that the number of shares reserved for issuance thereunder will be increased annually on the first day of each year beginning in 2018 by one percent (1%) of the shares of the Company’s common stock outstanding on the last day of the immediately preceding year or such smaller increase as determined by the Company’s Board of Directors. The Board of Directors has not yet determined the timing for the offering periods under the ESPP.

Furniture and Equipment

12 Months Ended

Dec. 31, 2016

Property, Plant and Equipment [Abstract]

Furniture and Equipment

4.	Furniture and Equipment

Furniture and equipment and accumulated depreciation balances are as follows:


	December 31
	2016			2015
Furniture	$	156,928		$	143,435
Computers		111,446			107,160
Equipment		141,067			81,418
Leasehold improvements		35,869			—

Total furniture and equipment		445,310			332,013
Accumulated depreciation		(295,715	)		(226,042	)

Furniture and equipment, net	$	149,595		$	105,971

Employee Retirement Plan

12 Months Ended

Dec. 31, 2016

Compensation and Retirement Disclosure [Abstract]

Employee Retirement Plan

13.

Employee Retirement Plan

The Company created Aerpio’s 401(k) plan in 2015. Before then, the Company’s employees participated in Akebia’s 401(k) plan (Akebia Plan). In accordance with both Plans, all employees who have attained the age of 21 are eligible to participate in the Plan as of the first Entry Date, as defined, following the employment date. Each employee can contribute a percentage of compensation up to a maximum of the statutory limits per year. Company contributions are discretionary, and no contributions were made during 2016 and 2015.

Employee Bonus Plan

12 Months Ended

Dec. 31, 2016

Employee Bonus Plan

14.

Employee Bonus Plan

During 2012, the Company established a non-calendar year bonus plan for certain employees of the Company based on the achievement of certain milestones. The amount of bonus accrued at December 31, 2015, was $380,020, which was paid in 2016. No bonus was accrued at December 31, 2016.

- Definition

The entire disclosure for compensation costs, including compensated absences accruals, compensated absences liability, deferred compensation arrangements and income statement compensation items. Deferred compensation arrangements may include a description of an arrangement with an individual employee, which is generally an employment contract between the entity and a selected officer or key employee containing a promise by the employer to pay certain amounts at designated future dates, usually including a period after retirement, upon compliance with stipulated requirements. This type of arrangement is distinguished from broader based employee benefit plans as it is usually tailored to the employee. Disclosure also typically includes the amount of related compensation expense recognized during the reporting period, the number of shares (units) issued during the period under such arrangements, and the carrying amount as of the balance sheet date of the related liability.

+ References + Details

Subsequent Events

12 Months Ended

Dec. 31, 2016

Subsequent Events [Abstract]

Subsequent Events

15.

Subsequent Events

In February 2017, Aerpio executed a term sheet for a senior secured convertible note financing (the February Convertible Notes or February Convertible Note Financing) totaling $297,355, with certain preferred investor of Aerpio. The terms of the February Convertible Notes are identical to the Convertible Notes.

Merger and Offering

On March 15, 2017, the Company completed the Merger and Offering as further described in Note 1 to the consolidated financial statements. As a result of the Offering, the conditions that raised substantial doubt about whether the Company will continue as a going concern have been alleviated.

Summary of Significant Accounting Policies (Policies)

3 Months Ended

12 Months Ended

Mar. 31, 2017

Dec. 31, 2016

Accounting Policies [Abstract]

Basis of Presentation

Basis of Presentation

The Company’s financial statements are prepared in accordance with U.S. generally accepted accounting principles (“U.S. GAAP”) and stated in U.S. dollars.

Segment Information

Segment Information

Operating segments are defined as components of an enterprise about which separate discrete information is available for evaluation by the chief operating decision maker, or decision-making group, in deciding how to allocate resources and in assessing performance. The Company views its operations and manages its business in one operating segment, which is the business of developing and commercializing proprietary therapeutics in vascular disorders of the eye. All of the assets and operations of the Company’s sole operating segment are located in the United States of America.

Use of Estimates

Use of Estimates

The preparation of financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. Actual results may differ from those estimates. Management considers many factors in selecting appropriate financial accounting policies and controls and in developing the estimates and assumptions that are used in the preparation of these financial statements. Management must apply significant judgment in this process. In addition, other factors may affect estimates, including expected business and operational changes, sensitivity and volatility associated with the assumptions used in developing estimates, and whether historical trends are expected to be representative of future trends. The estimation process often may yield a range of potentially reasonable estimates of the ultimate future outcomes, and management must select an amount that falls within that range of reasonable estimates. Estimates are used in the following areas, among others: fair value of the Company’s common stock and other equity instruments, accrued expenses, and income taxes.

Cash and Cash Equivalents

Cash and Cash Equivalents

Short-Term Investments

Short-Term Investments

Time deposits with remaining maturities of greater than three months but less than one year at the time of purchase are classified as short-term investments in the accompanying balance sheets.

Short-Term Investments

Time deposits with remaining maturities of greater than three months but less than one year at the time of purchase are classified as short-term investments in the accompanying balance sheets.

Grant Income

Grant Income

Grant income is recognized as earned based on contract work performed.

Grant Income

Grant income is recognized as earned based on contract work performed. Grant income also includes qualifying therapeutic credits from the U.S. Treasury related to discovery projects.

Research and Development Costs

Research and Development

The Company enters into consulting, research, and other agreements with commercial firms, researchers, universities, and others for the provision of goods and services.

Research and Development Costs

Research and development costs are expensed as incurred.

Research and Development Costs

Research and development costs are expensed as incurred.

Patents

Patents

Costs incurred in connection with the application for and issuances of patents are expensed as incurred.

Patents

Costs incurred in connection with the application for and issuances of patents are expensed as incurred.

Income Taxes

Income Taxes

The Company accounts for uncertain tax positions in accordance with the provisions of ASC 740. When uncertain tax positions exist, the Company recognizes the tax benefit of tax positions to the extent that some or all of the benefit will more likely than not be realized. The determination as to whether the tax benefit will more likely than not be realized is based upon the technical merits of the tax position, as well as consideration of the available facts and circumstances. As of December 31, 2016 and 2015, the Company does not have any significant uncertain tax positions. If incurred, the Company would classify interest and penalties on uncertain tax positions as income tax expense.

Net Loss per Share

Net Loss per Share

The Company’s basic net loss per share attributable to common stockholders is calculated by dividing the net loss attributable to common stockholders by the weighted average number of shares of common stock outstanding for the period. The diluted net loss per share attributable to common stockholders is computed by adjusting weighted average shares outstanding for the dilutive effect of common stock equivalents outstanding for the period, determined using the treasury stock method. For purposes of this calculation, convertible preferred stock, stock options to purchase common stock, and restricted stock awards are considered to be common stock equivalents but have been excluded from the calculation of diluted net loss per share attributable to common stockholders as their effect is anti-dilutive for all periods presented. Therefore, basic and diluted net loss per share were the same for all periods presented.

Stock-Based Compensation

Stock-Based Compensation

The Company accounts for its stock-based compensation awards in accordance with FASB ASC Topic 718, Compensation—Stock Compensation. ASC 718 requires all stock-based payments to employees, including grants of employee stock options and restricted stock, to be recognized in the statements of operations and comprehensive loss based on their fair values. All of the Company’s stock-based awards are subject only to service-based vesting conditions. The Company estimates the fair value of its stock-based awards using the Black-Scholes option pricing model, which requires the input of subjective assumptions, including (a) the expected stock price volatility, (b) the calculation of expected term of the award, (c) the risk-free interest rate, and (d) expected dividends. The fair value of restricted stock award are determined based on the Company’s estimated common stock value.

Fair Value of Financial Instruments

Fair Value of Financial Instruments

•

Level 1—Valuations based on unadjusted quoted prices in active markets for identical assets or liabilities that the Company has the ability to access at the measurement date

•

Level 2—Valuations based on quoted prices for similar assets or liabilities in markets that are not active or for which all significant inputs are observable, either directly or indirectly

•

Level 3—Valuations that require inputs that reflect the Company’s own assumptions that are both significant to the fair value measurement and unobservable


	Fair Value Measurements Using
	Level 1		Level 2		Level 3		Total
March 31, 2017
Assets:
Cash and cash equivalents	$	35,139,109	$	—	$	—	$	35,139,109
Short-term investments		—		50,000		—		50,000

Total assets	$	35,139,109	$	50,000	$	—	$	35,189,109

December 31, 2016
Assets:
Cash and cash equivalents	$	1,609,694	$	—	$	—	$	1,609,694
Short-term investments		—		50,000		—		50,000

	$	1,609,694	$	50,000	$	—	$	1,659,694

Fair Value of Financial Instruments

•

Level 1—Valuations based on unadjusted quoted prices in active markets for identical assets or liabilities that the Company has the ability to access at the measurement date

•

Level 2—Valuations based on quoted prices for similar assets or liabilities in markets that are not active or for which all significant inputs are observable, either directly or indirectly

•

Level 3—Valuations that require inputs that reflect the Company’s own assumptions that are both significant to the fair value measurement and unobservable

Based on the fair value hierarchy, assets measured or disclosed at fair value on a recurring basis are summarized below:


	Fair Value Measurements Using
	Level 1		Level 2		Level 3		Total
December 31, 2016
Assets:
Cash and cash equivalents	$	1,609,694	$	—	$	—	$	1,609,694
Short-term investments		—		50,000		—		50,000

Total assets	$	1,609,694	$	50,000	$	—	$	1,659,694

December 31, 2015
Assets:
Cash and cash equivalents	$	5,144,211	$	—	$	—	$	5,144,211
Short-term investments		—		50,000		—		50,000

	$	5,144,211	$	50,000	$	—	$	5,194,211

Concentrations of Credit Risk and Off-Balance Sheet Risk

Concentrations of Credit Risk and Off-Balance Sheet Risk

Comprehensive Loss

Comprehensive Loss

Furniture and Equipment

Furniture and Equipment

Recent Accounting Pronouncements

Recent Accounting Pronouncements

Research and Development

Research and Development

The Company enters into consulting, research, and other agreements with commercial firms, researchers, universities, and others for the provision of goods and services.

Reclassifications

Reclassifications

Certain prior year balances in the balance sheet have been reclassified to conform to the current year presentation. The reclassifications were not material to the financial statements.

Summary of Significant Accounting Policies (Tables)

3 Months Ended

12 Months Ended

Mar. 31, 2017

Dec. 31, 2016

Accounting Policies [Abstract]

Schedule of Assets Measured on Recurring Basis

The assets of the Company measured on a recurring basis as of March 31, 2017 and December 31, 2016 basis are summarized below:


	Fair Value Measurements Using
	Level 1		Level 2		Level 3		Total
March 31, 2017
Assets:
Cash and cash equivalents	$	35,139,109	$	—	$	—	$	35,139,109
Short-term investments		—		50,000		—		50,000

Total assets	$	35,139,109	$	50,000	$	—	$	35,189,109

December 31, 2016
Assets:
Cash and cash equivalents	$	1,609,694	$	—	$	—	$	1,609,694
Short-term investments		—		50,000		—		50,000

	$	1,609,694	$	50,000	$	—	$	1,659,694

Based on the fair value hierarchy, assets measured or disclosed at fair value on a recurring basis are summarized below:


	Fair Value Measurements Using
	Level 1		Level 2		Level 3		Total
December 31, 2016
Assets:
Cash and cash equivalents	$	1,609,694	$	—	$	—	$	1,609,694
Short-term investments		—		50,000		—		50,000

Total assets	$	1,609,694	$	50,000	$	—	$	1,659,694

December 31, 2015
Assets:
Cash and cash equivalents	$	5,144,211	$	—	$	—	$	5,144,211
Short-term investments		—		50,000		—		50,000

	$	5,144,211	$	50,000	$	—	$	5,194,211

Related-Party Arrangements (Tables)

3 Months Ended

12 Months Ended

Mar. 31, 2017

Dec. 31, 2016

Akebia [Member]

Summary of activities included in statements of operations and comprehensive loss

Below is a summary of the activities included in the statements of operations and comprehensive loss:


		Three Months Ended March 31,
Activity	Financial Statement Caption	2017		2016
Akebia related employee costs	Research and development operating expenses	$	—	$	12,923
Facility-related reimbursement	Other income, net		—		997

Below is a summary of the activities included in the statements of operations and comprehensive loss:


		Year Ended December 31
Activity	Financial Statement Caption	2016		2015
Payments to Akebia for employee costs	Research and development operating expenses	$	31,246	$	263,501
Payments from Akebia for facility-related charges and employee costs	Other income, net		997		27,022

A summary of Akebia receivables and payables included in the accompanying balance sheets are as follow:


		December 31
Activity	Financial Statement Caption	2016		2015
Amounts receivable from Akebia	Accounts receivable	$	—	$	997
Amounts payable to Akebia	Accounts payable		—		15,173

Accounts Payable and Accrued Expenses (Tables)

3 Months Ended

12 Months Ended

Mar. 31, 2017

Dec. 31, 2016

Payables and Accruals [Abstract]

Schedule of Accounts Payable and Accrued Expenses

Accounts payable and accrued expenses are as follows:


	March 31, 2017		December 31, 2016
Accounts payable	$	1,871,662	$	1,135,608
Professional fees		300,356		200,468
Accrued bonus		125,576		—
Accrued interest		—		483,442
Accrued vacation		106,199		52,835
Accrued project costs		510,828		541,158
Other		55,427		57,459

Total accounts payable and accrued expenses	$	2,970,048	$	2,470,970

Accounts payable and accrued expenses are as follows:


	December 31
	2016		2015
Accounts payable	$	1,135,608	$	890,610
Professional fees		200,468		126,722
Accrued bonus		—		380,020
Accrued interest		483,442		—
Accrued vacation		52,835		56,796
Accrued project costs		541,158		696,158
Other		57,459		9,568

Total accounts payable and accrued expenses	$	2,470,970	$	2,159,874

Stock-Based Compensation (Tables)

3 Months Ended

12 Months Ended

Mar. 31, 2017

Dec. 31, 2016

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

Summary of stock option activity

The following table summarizes the stock option activity during the three-months ended March 31, 2017:


	Shares			Weighted Average Exercise Price		Weighted Average Remaining Contractual Term (in Years)		Aggregate Intrinsic Value
Outstanding, January 1, 2017		927,592		$	1.70		7.48	$	1,030,217
Granted		—		$	—
Exercised		—		$	—
Expired/cancelled		(2,886	)	$	2.11

Outstanding, March 31, 2017		924,706		$	1.70		7.24	$	3,056,035

Expected to vest, March 31, 2017		265,647		$	1.81		8.45	$	848,613
Options exercisable, March 31, 2017		659,059		$	1.65		6.75	$	2,207,422

The following table summarizes the stock option activity during 2016:


	Shares			Weighted Average Exercise Price		Weighted Average Remaining Contractual Term (in Years)		Aggregate Intrinsic Value
Outstanding, January 1, 2016		907,485		$	1.66			$	135,711
Granted		50,228			1.80
Exercised		(21,870	)		0.87
Expired/cancelled		(8,251	)		1.24

Outstanding, December 31, 2016		927,592		$	1.70		7.48	$	1,030,217

Expected to vest, December 31, 2016		312,547		$	1.82		8.60	$	308,767
Options exercisable, December 31, 2016		615,045		$	1.63		6.92	$	721,451

Summary of restricted stock activity

A summary of the Company’s restricted stock activity and related information during the three months ended March 31, 2017 is as follows:


	Shares			Weighted Average Grant Date Fair Value
Nonvested, January 1, 2017		241,096		$	1.91
Granted		—			—
Vested		(39,455	)	$	1.79
Forfeited		(5,222	)	$	2.20

Nonvested, March 31, 2017		196,419		$	1.93

A summary of the Company’s restricted stock activity and related information during 2016 is as follows:


	Shares			Weighted Average Grant Date Fair Value
Nonvested, January 1, 2016		444,199		$	1.69
Granted		—			—
Vested		(203,103	)		1.54
Forfeited		—			—

Nonvested, December 31, 2016		241,096		$	1.91

Summary of recognized compensation cost related to employee and non-employee stock-based compensation activity

The Company has recognized the following compensation cost related to employee and non-employee stock-based compensation activity:


	Three Months Ended March 31,
	2017		2016
Research and development	$	115,302	$	81,733
General and administrative		40,083		43,482

Total	$	155,385	$	125,215

The Company has recognized the following compensation cost related to employee and non-employee stock-based compensation activity:


	Year Ended December 31
	2016		2015
Research and development	$	317,644	$	295,304
General and administrative		170,682		174,542

Total	$	488,326	$	469,846

Summary of Grant date Using the Black-Scholes Option Pricing Model Using at Weighted Average Assumptions


	Year Ended December 31
	2016			2015
Expected term (years)		6.00			6.00
Risk-free interest rate		1.39	%		1.97	%
Expected volatility		61.00	%		78.00	%
Expected dividend yield		—			—

Net Loss per Share (Tables)

3 Months Ended

12 Months Ended

Mar. 31, 2017

Dec. 31, 2016

Earnings Per Share [Abstract]

Schedule of Company's Basic and Diluted Net Loss Per Share

The following table sets forth the computation of the Company’s basic and diluted net loss per share for the periods presented:


	Three Months Ended March 31,
	2017			2016
Net loss and comprehensive loss	$	(4,995,703	)	$	(4,194,698	)
Accretion of preferred stock to redemption value		(943,297	)		(1,015,371	)

Net loss attributable to common stockholders	$	(5,939,000	)	$	(5,210,069	)

Net loss per share attributable to common stockholders, basic and diluted	$	(1.06	)	$	(7.07	)

Weighted average common shares used in computing net loss per share attributable to common stockholders, basic and diluted		5,605,151			737,016

The following table sets forth the computation of the Company’s basic and diluted net loss per share for the periods presented:


	Year Ended December 31
	2016			2015
Net loss and comprehensive loss	$	(16,983,511	)	$	(17,070,223	)
Extinguishment of preferred stock		224,224			—
Accretion of preferred stock to redemption value		(4,152,801	)		(348,436	)

Net loss attributable to common stockholders	$	(20,912,088	)	$	(17,418,659	)

Net loss per share attributable to common stockholders, basic and diluted	$	(24.52	)	$	(31.14	)

Weighted average common shares used in computing net loss per share attributable to common stockholders, basic and diluted		852,665			559,419

Schedule of weighted average common stock equivalents excluded from calculation of diluted net loss per share


	March 31,
	2017		2016
Convertible preferred stock (if converted)		—		14,183,564
Options to purchase common stock		924,706		907,485
Unvested restricted stock		196,419		241,096
Warrants to purchase common stock		317,562		—


	December 31
	2016		2015
Convertible preferred stock (if converted)		14,015,016		14,183,535
Options to purchase Aerpio common stock		615,045		424,160
Convertible notes (if converted)		2,641,602		—

Commitments and Contingencies (Tables)

3 Months Ended

12 Months Ended

Mar. 31, 2017

Dec. 31, 2016

Commitments and Contingencies Disclosure [Abstract]

Schedule of operating leases and commitments


	2017		2018		2019 and Thereafter		Total
Operating leases	$	104,440	$	52,978	$	—	$	157,418
All other operating commitments		2,761,501		—		—		2,761,501

Total commitments	$	2,865,941	$	52,978	$	—	$	2,918,919


	2017		2018		2019 and Thereafter		Total
Operating leases	$	104,440	$	52,978	$	—	$	157,418
All other operating commitments		2,761,501		—		—		2,761,501

Total commitments	$	2,865,941	$	52,978	$	—	$	2,918,919

Furniture and Equipment (Tables)

12 Months Ended

Dec. 31, 2016

Property, Plant and Equipment [Abstract]

Schedule of Furniture and Equipment

Furniture and equipment and accumulated depreciation balances are as follows:


	December 31
	2016			2015
Furniture	$	156,928		$	143,435
Computers		111,446			107,160
Equipment		141,067			81,418
Leasehold improvements		35,869			—

Total furniture and equipment		445,310			332,013
Accumulated depreciation		(295,715	)		(226,042	)

Furniture and equipment, net	$	149,595		$	105,971

Common Stock (Tables)

12 Months Ended

Dec. 31, 2016

Equity [Abstract]

Summary of Shares Common Stock for Future Issuance

As of December 31, 2016, Aerpio has reserved the following shares of Aerpio common stock for future issuance:


Conversion of Series A Preferred Stock			1,239,338
Conversion of Series A1 Preferred Stock			8,289,663
Conversion of Series A2 Preferred Stock			4,486,015
Conversion of unvested restricted stock awards			241,096
Exercise of options to purchase Aerpio common stock			927,593

Total			15,183,705

- Definition

Tabular disclosure of an entity's stock, including par or stated value per share, number and dollar amount of share subscriptions, shares authorized, shares issued, shares outstanding, number and dollar amount of shares held in an employee trust, dividend per share, total dividends, share conversion features, par value plus additional paid in capital, the value of treasury stock and other information necessary to a fair presentation, and EPS information. Stock by class includes common, convertible, and preferred stocks which are not redeemable or redeemable solely at the option of the issuer. Includes preferred stock with redemption features that are solely within the control of the issuer and mandatorily redeemable stock if redemption is required to occur only upon liquidation or termination of the reporting entity. If more than one issue is outstanding, state the title of each issue and the corresponding dollar amount; dollar amount of any shares subscribed but unissued and the deduction of subscriptions receivable there from; number of shares authorized, issued, and outstanding.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
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Reference 3: http://www.xbrl.org/2003/role/presentationRef
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+ Details

Income Taxes (Tables)

12 Months Ended

Dec. 31, 2016

Income Tax Disclosure [Abstract]

Reconciliation of Federal Statutory Income Tax Rate

The components of loss before income taxes and a reconciliation of the statutory federal income tax with the provision for income taxes are as follows:


	Year Ended December 31
	2016			2015
Federal tax at statutory rate		34.00	%		34.00	%
State and local tax at statutory rates		0.83			0.83
Research and development credits		3.77			4.06
Change in valuation allowance		(37.28	)		(38.26	)
Other		(1.32	)		(0.63	)

Effective tax rate		0.00	%		0.00	%

Significant Components of Deferred Tax Assets and Liabilities

Significant components of the Company’s deferred tax assets and liabilities are as follows:


	December 31
	2016			2015
Deferred tax assets:
Net operating loss carryforwards	$	23,146,178		$	17,427,880
Accrued expenses		18,400			143,295
Stock-based compensation		96,570			—
Research and development credits		2,670,688			2,031,211
Other		20,784			19,565

Total deferred tax assets		25,952,620			19,621,951
Deferred tax liabilities:
Stock-based compensation		—			2,803
Fixed assets		8,434			9,220

Total deferred tax liabilities		8,434			12,023

Net deferred tax assets before valuation allowance		25,944,186			19,609,928
Less valuation allowance		(25,944,186	)		(19,609,928	)

Net deferred tax asset	$	—		$	—

Nature of Organization and Operations - Additional Information (Detail)		3 Months Ended
	Mar. 15, 2017 USD ($) $ / shares shares	Mar. 31, 2017 USD ($) $ / shares shares	Mar. 14, 2017 shares	Mar. 10, 2017 $ / shares shares	Mar. 03, 2017 $ / shares shares	Dec. 31, 2016 $ / shares shares	Dec. 31, 2015 $ / shares shares
Class Of Stock [Line Items]
Common stock, shares authorized		300,000,000		300,000,000	100,000,000	17,440,436	17,140,478
Common stock, par value \| $ / shares		$ 0.0001		$ 0.0001	$ 0.0001	$ 0.0001	$ 0.0001
Preferred stock, shares authorized		10,000,000		10,000,000	10,000,000
Preferred stock, par value \| $ / shares		$ 0.0001		$ 0.0001	$ 0.0001
Capital stock conversion basis ratio	2.3336572
Common stock, shares outstanding		27,049,555				1,240,925	1,157,251
Common stock issued to private placement, price per share \| $ / shares						$ 14.70
Net proceeds of common stock issued to private placement \| $		$ 37,163,390
Warrants issued to purchase common stock, exercise price \| $ / shares		$ 5.00
Minimum [Member]
Class Of Stock [Line Items]
Percentage of Interest owned in the combined enterprise	50.00%
Common Stock [Member]
Class Of Stock [Line Items]
Common stock issued to private placement		8,049,555
Net proceeds of common stock issued to private placement \| $		$ 805
ZETA ACQUISITION CORP. II [Member]
Class Of Stock [Line Items]
Number of shares surrendered for cancellation	4,000,000
Common stock, shares outstanding			5,000,000
Issuance of warrants term	3 years
Number of warrants issued to purchase common stock	317,562
Warrants issued to purchase common stock, exercise price \| $ / shares	$ 5.00
ZETA ACQUISITION CORP. II [Member] \| Common Stock [Member]
Class Of Stock [Line Items]
Common stock issued to private placement	8,049,555
Common stock issued to private placement, price per share \| $ / shares	$ 5.00
Net proceeds of common stock issued to private placement \| $	$ 37,200,000

Summary of Significant Accounting Policies - Additional Information (Detail)		3 Months Ended	12 Months Ended
	Mar. 15, 2017	Mar. 31, 2017 USD ($) Institution Segment	Dec. 31, 2016 USD ($) Institution Segment
Summary Of Significant Accounting Policies [Line Items]
Number of operating segment \| Segment		1	1
Significant uncertain tax positions		$ 0	$ 0
Capital stock conversion basis ratio	2.3336572
Number of principal financial institutions in cash deposit \| Institution		2	2
Minimum [Member]
Summary Of Significant Accounting Policies [Line Items]
Furniture and equipment estimated useful lives		3 years
Maximum [Member]
Summary Of Significant Accounting Policies [Line Items]
Furniture and equipment estimated useful lives		7 years
Accounting Standards Update 2015-03 [Member] \| Convertible Notes [Member]
Summary Of Significant Accounting Policies [Line Items]
Effect of adoption of new ASU			$ (75,561)
Furniture and Equipment [Member] \| Minimum [Member]
Summary Of Significant Accounting Policies [Line Items]
Furniture and equipment estimated useful lives			3 years
Furniture and Equipment [Member] \| Maximum [Member]
Summary Of Significant Accounting Policies [Line Items]
Furniture and equipment estimated useful lives			7 years

Summary of Significant Accounting Policies (Detail) - Fair Value, Measurements, Recurring [Member] - USD ($)	Mar. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Assets:
Cash and cash equivalents	$ 35,139,109	$ 1,609,694	$ 5,144,211
Short-term investments	50,000	50,000	50,000
Total assets	35,189,109	1,659,694	5,194,211
Level 1 [Member]
Assets:
Cash and cash equivalents	35,139,109	1,609,694	5,144,211
Total assets	35,139,109	1,609,694	5,144,211
Level 2 [Member]
Assets:
Short-term investments	50,000	50,000	50,000
Total assets	$ 50,000	$ 50,000	$ 50,000

- Definition

Fair value portion of investment securities, including, but not limited to, marketable securities, derivative financial instruments, and investments accounted for under the equity method.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
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-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(12))
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Reference 2: http://www.xbrl.org/2003/role/presentationRef
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-Name Accounting Standards Codification
-Glossary Trading Securities
-URI http://asc.fasb.org/extlink&oid=6526789

Reference 3: http://www.xbrl.org/2003/role/presentationRef
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Reference 9: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Available-for-Sale Securities
-URI http://asc.fasb.org/extlink&oid=6505594

+ Details

Related-Party Arrangements (Detail) - USD ($)	3 Months Ended		12 Months Ended
Related-Party Arrangements (Detail) - USD ($)	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016	Dec. 31, 2015
Related Party Transaction [Line Items]
Research and development	$ 2,255,584	$ 2,989,558	$ 11,367,590	$ 11,625,404
Other income, net		997	997	27,022
Akebia [Member] \| Employee Costs [Member]
Related Party Transaction [Line Items]
Research and development		12,923	31,246	263,501
Akebia [Member] \| Facility Related Reimbursement [Member]
Related Party Transaction [Line Items]
Other income, net		$ 997	$ 997	$ 27,022

Accounts Payable and Accrued Expenses (Detail) - USD ($)	Mar. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Payables and Accruals [Abstract]
Accounts payable	$ 1,871,662	$ 1,135,608	$ 890,610
Professional fees	300,356	200,468	126,722
Accrued bonus	125,576	0	380,020
Accrued interest		483,442
Accrued vacation	106,199	52,835	56,796
Accrued project costs	510,828	541,158	696,158
Other	55,427	57,459	9,568
Total accounts payable and accrued expenses	$ 2,970,048	$ 2,470,970	$ 2,159,874

Notes Payable to Investors - Additional Information (Detail)	1 Months Ended			3 Months Ended	12 Months Ended
	Feb. 28, 2017 USD ($)	Oct. 31, 2016 USD ($)	Mar. 31, 2016 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Jul. 15, 2016 USD ($)	Apr. 14, 2016 USD ($)
Debt Instrument [Line Items]
Proceeds from sale of capital stock				$ 40,247,775
Convertible Note Financing [Member]
Debt Instrument [Line Items]
Convertible notes payable			$ 9,000,000			$ 4,500,000	$ 4,500,000
Conversion description				In connection with the Convertible Note Financing, Aerpio’s Articles of Incorporation were amended such that any Aerpio preferred that did not participate in the Aerpio Convertible Note Financing would have their respective shares of Aerpio preferred stock automatically converted into Aerpio common stock using a 3-to-1 conversion ratio and such preferred stockholders would lose the right to representation on the Aerpio Board of Directors and other preferred rights	In connection with the Convertible Note Financing, Aerpio’s Articles of Incorporation were amended such that any Aerpio preferred stockholder that did not participate in the Convertible Note Financing would have their respective shares of Aerpio preferred stock automatically converted into Aerpio’s common stock using a 3-to-1 conversion ratio and such Aerpio preferred stockholders would lose the right to representation on Aerpio’s Board of Directors and other preferred rights.
Unamortized debt issuance costs				$ 0	$ 75,561
Conversion ratio			0.33		0.33
Convertible Notes accrue interest rate per annum				8.00%	8.00%
Debt issuance cost				$ 138,312	$ 138,312
Amortization period				7 months	7 months
Maturity date				Mar. 31, 2016	Oct. 31, 2016
Gross proceeds from sale of capital stock				$ 30,000,000
Convertible Note Financing [Member] \| Investor Sale [Member]
Debt Instrument [Line Items]
Proceeds from sale of capital stock					$ 30,000,000
Additional Convertible Note Financings [Member]
Debt Instrument [Line Items]
Convertible notes payable	$ 300,000	$ 3,500,000
Debt issuance cost	$ 125,935	$ 125,935
Maturity date	Mar. 31, 2017	Mar. 31, 2017

Common Stock - Additional Information (Detail) - USD ($)			3 Months Ended
	Mar. 31, 2017	Mar. 15, 2017	Mar. 31, 2017	Mar. 10, 2017	Mar. 03, 2017	Dec. 31, 2016	Dec. 31, 2015
Class Of Stock [Line Items]
Common stock, shares authorized	300,000,000		300,000,000	300,000,000	100,000,000	17,440,436	17,140,478
Common stock, par value	$ 0.0001		$ 0.0001	$ 0.0001	$ 0.0001	$ 0.0001	$ 0.0001
Dividends common stock declared or paid			$ 0
Number of shares of common stock in lock-up agreements	18,900,000		18,900,000
Restricted period for shares of common stock in lock-up agreements			9 months
Restricted percentage of common stock for holders of 915,000 shares			80.00%
Number of shares of common stockholders with 80% restriction	915,000		915,000
Period agreed by common stockholder not to effect short sale after merger			12 months
Warrants outstanding	317,562		317,562
Warrants exercise price per share	$ 5.00		$ 5.00
Warrants term	3 years
Warrants expiration date			Mar. 15, 2020
Minimum [Member]
Class Of Stock [Line Items]
Percentage of common stockholder agreed not to effect short sale after merger			1.00%
Convertible Note Financing [Member]
Class Of Stock [Line Items]
Conversion of convertible notes and accrued interest, Shares		2,744,059
Redeemable Convertible Preferred Stock
Class Of Stock [Line Items]
Conversion of preferred stock, shares		14,015,016

Preferred Stock - Additional Information (Detail)	1 Months Ended	3 Months Ended
Preferred Stock - Additional Information (Detail)	Mar. 31, 2016	Mar. 31, 2017 USD ($) Director Installment $ / shares shares	Mar. 10, 2017 $ / shares shares	Mar. 03, 2017 $ / shares shares	Dec. 31, 2016 shares
Temporary Equity [Line Items]
Preferred stock, shares authorized		10,000,000	10,000,000	10,000,000
Preferred stock, par value \| $ / shares		$ 0.0001	$ 0.0001	$ 0.0001
Preferred stock, shares issued		0
Preferred stock, shares outstanding		0
Redeemable convertible preferred stock, voting rights		The holders of redeemable convertible preferred stock were entitled to the number of votes equal to the number of whole shares of Aerpio common stock into which the shares of redeemable convertible preferred stock were convertible. Except as provided by law or otherwise, the holders of redeemable convertible preferred stock voted together with the holders of Aerpio common stock as a single class. Certain significant actions required approval by at least 50% of the holders of redeemable convertible preferred stock voting as a single class on an as converted basis.
Redeemable convertible preferred stock conversion percentage	300.00%	100.00%
Redeemable convertible preferred stock redemption date		Jul. 31, 2017
Minimum [Member]
Temporary Equity [Line Items]
Percentage of redeemable convertible preferred stock voting rights		50.00%
Proceeds from Issuance Initial Public Offering \| $		$ 40,000,000
Series A Redeemable Convertible Preferred Stock [Member]
Temporary Equity [Line Items]
Redeemable convertible preferred stock, shares authorized					1,326,147
Redeemable convertible preferred stock, shares issued					1,239,338
Redeemable convertible preferred, shares outstanding					1,239,338
Redeemable convertible preferred stock distribution to be paid \| $ / shares		$ 4.27
Series A1 Redeemable Convertible Preferred Stock [Member]
Temporary Equity [Line Items]
Redeemable convertible preferred stock, shares authorized					8,368,247
Redeemable convertible preferred stock, shares issued					8,289,663
Redeemable convertible preferred, shares outstanding					8,289,663
Redeemable convertible preferred stock distribution to be paid \| $ / shares		$ 3.97
Series A2 Redeemable Convertible Preferred Stock [Member]
Temporary Equity [Line Items]
Redeemable convertible preferred stock, shares authorized					4,660,573
Redeemable convertible preferred stock, shares issued					4,486,015
Redeemable convertible preferred, shares outstanding					4,486,015
Redeemable convertible preferred stock, dividend rate, percentage		6.00%
Redeemable convertible preferred stock distribution to be paid \| $ / shares		$ 4.90
Redeemable Convertible Preferred Stock
Temporary Equity [Line Items]
Redeemable convertible preferred, shares outstanding					14,015,016
Number of board of directors appointed by redeemable convertible preferred shares holders \| Director		6
Number of board of directors appointed by common shares holders \| Director		2
Number of board of directors appointed by common shares holders under certain circumstances \| Director		1
Share Price \| $ / shares		$ 14.70
Number of installments payable \| Installment		3
Annual installment payable commencing period		60 days
Redeemable Convertible Preferred Stock \| Minimum [Member]
Temporary Equity [Line Items]
Redeemable convertible preferred stock conversion basis percentage		50.00%
Redeemable Convertible Preferred Stock \| Maximum [Member]
Temporary Equity [Line Items]
Number of board of directors appointed by redeemable convertible preferred shares holders under certain circumstances \| Director		4
Series A Redeemable Convertible Preferred Stock and Series A1 Redeemable Convertible Preferred Stock [Member]
Temporary Equity [Line Items]
Redeemable convertible preferred stock, dividend rate, percentage		6.00%

Stock Based Compensation - Additional Information (Detail)		3 Months Ended		12 Months Ended
	Mar. 15, 2017	Mar. 31, 2017 USD ($) shares	Mar. 31, 2016 USD ($) shares	Dec. 31, 2016 USD ($) $ / shares shares	Dec. 31, 2015 USD ($) shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Merger exchange rate	2.3336572
Aggregate number of common stock		924,706		927,592	907,485
Common stock shares available for issuance				15,183,705
Number of awards granted				50,228
Unrecognized compensation cost related to stock options \| $		$ 264,823		$ 293,796
Aggregate intrinsic value of options exercisable \| $					$ 116,924
Weighted average grant date fair value of stock options granted \| $ / shares				$ 1.22
Stock options exercised intrinsic value \| $				$ 20,335	$ 5,813
2011 Equity Incentive Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Merger exchange rate	2.3336572
Aggregate number of common stock		924,706		924,706
2017 Stock Option and Incentive Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock shares available for issuance		4,600,000
Percentage applied to the outstanding shares as annual increase in number of shares authorized for issuance		4.00%
Number of awards granted		0
Equity Incentive Plan [Member] \| Common Stock [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based compensation, number of shares authorized				5,860,874
Stock Option [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of awards granted		0	0
Vesting period		48 months		48 months
Term of options to be granted		10 years		10 years
Compensation expense for stock options \| $		$ 81,120	$ 42,816
Weighted average period expected to be recognized		2 years 1 month 6 days		2 years 4 months 24 days
Expected dividend yield				0.00%	0.00%
Compensation expense for stock options \| $				$ 180,399	$ 125,926
Stock Option [Member] \| One-year Anniversary [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting percentage		25.00%		25.00%
Restricted Stock [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Compensation expense for stock options \| $		$ 74,265	$ 82,399	$ 307,927	$ 343,919
Weighted average period expected to be recognized		1 year 4 months 24 days		1 year 8 months 12 days
Unrecognized compensation cost related to restricted stock grants \| $		$ 366,970		$ 447,617

Summary of Stock Option Activity (Detail) - USD ($)	3 Months Ended	12 Months Ended
Summary of Stock Option Activity (Detail) - USD ($)	Mar. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award, Options Outstanding, Weighted Average Exercise Price, and Additional Disclosures [Abstract]
Shares, Outstanding at beginning balance	927,592	907,485
Shares, Granted		50,228
Shares, Exercised		(21,870)
Shares, Expired/cancelled	(2,886)	(8,251)
Shares, Outstanding at ending balance	924,706	927,592
Shares, Expected to vest	265,647	312,547
Shares, Options exercisable	659,059	615,045
Weighted Average Exercise Price, Outstanding at beginning balance	$ 1.70	$ 1.66
Weighted average exercise price, Granted		1.80
Weighted average exercise price, Exercised		0.87
Weighted Average Exercise Price, Expired/cancelled	2.11	1.24
Weighted Average Exercise Price, Outstanding at ending balance	1.70	1.70
Weighted Average Exercise Price, Expected to vest	1.81	1.82
Weighted Average Exercise Price, Options exercisable	$ 1.65	$ 1.63
Weighted average remaining contractual term, outstanding	7 years 2 months 27 days	7 years 5 months 23 days
Weighted average remaining contractual term, expected to vest	8 years 5 months 12 days	8 years 7 months 6 days
Weighted average remaining contractual term, options exercisable	6 years 9 months	6 years 11 months 1 day
Aggregate intrinsic value, outstanding beginning balance	$ 1,030,217	$ 135,711
Aggregate intrinsic value, outstanding ending balance	3,056,035	1,030,217
Aggregate intrinsic value, expected to vest	848,613	308,767
Aggregate Intrinsic Value, Options exercisable	$ 2,207,422	$ 721,451

Stock-based compensation - Restricted Stock (Detail) - Restricted Stock [Member] - $ / shares	3 Months Ended	12 Months Ended
	Mar. 31, 2017	Dec. 31, 2016
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares, Nonvested beginning balance	241,096	444,199
Shares, Granted		0
Shares, Vested	(39,455)	(203,103)
Shares, Forfeited	(5,222)
Shares, Nonvested ending balance	196,419	241,096
Nonvested Weighted Average Grant Date Fair Value balance at beginning of period	$ 1.91	$ 1.69
Weighted Average Grant Date Fair Value, Granted		0
Weighted Average Grant Date Fair Value, Vested	1.79	1.54
Weighted Average Grant Date Fair Value, Forfeited	2.20
Nonvested Weighted Average Grant Date Fair Value balance at end of period	$ 1.93	$ 1.91

Compensation Cost Related to Employee and Non-employee Stock-based Compensation Activity (Detail) - USD ($)	3 Months Ended		12 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	$ 155,385	$ 125,215	$ 488,326	$ 469,846
Research and development [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	115,302	81,733	317,644	295,304
General and administrative [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	$ 40,083	$ 43,482	$ 170,682	$ 174,542

Income Taxes - Additional Information (Detail) - USD ($)	3 Months Ended		12 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Current income tax expense or benefit	$ 0	$ 0	$ 0	$ 0
Deferred income tax expense or benefit	$ 0	$ 0	0	0
Increase (decrease) Valuation allowance			6,334,258	6,530,455
Accrued uncertain tax positions			0	$ 0
Federal [Member]
Income Tax Disclosure [Abstract]
Operating loss carryforwards			$ 66,464,259
Operating loss carryforwards, expiration date			Expire at various dates through 2034
State [Member]
Income Tax Disclosure [Abstract]
Operating loss carryforwards			$ 66,464,259
Operating loss carryforwards, expiration date			Expire at various dates through 2019
Research and Development [Member] \| Federal [Member]
Income Tax Disclosure [Abstract]
Tax credit carryforwards			$ 2,670,688
Tax credit carryforwards, expiration date			Expire at various dates through 2034

Net Loss Per Share (Detail) - USD ($)	3 Months Ended		12 Months Ended
Net Loss Per Share (Detail) - USD ($)	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016	Dec. 31, 2015
Earnings Per Share [Abstract]
Net loss and comprehensive loss	$ (4,995,703)	$ (4,194,698)	$ (16,983,511)	$ (17,070,223)
Extinguishment of preferred stock			224,224
Accretion of preferred stock to redemption value	(943,297)	(1,015,371)	(4,152,801)	(348,436)
Net loss attributable to common stockholders	$ (5,939,000)	$ (5,210,069)	$ (20,912,088)	$ (17,418,659)
Net loss per share attributable to common stockholders, basic and diluted	$ (1.06)	$ (7.07)	$ (24.52)	$ (31.14)
Weighted average number of common shares used in computing net loss per share attributable to common stockholders, basic and diluted	5,605,151	737,016	852,665	559,419

Schedule of Weighted Average Common Stock Equivalents were Excluded from Calculation of Diluted Net Loss per Share (Detail) - Weighted Average [Member] - shares	3 Months Ended		12 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016	Dec. 31, 2015
Stock Option [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Total amount of anti-dilutive securities excluded from computation of earnings per share	924,706	907,485	615,045	424,160
Restricted Stock [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Total amount of anti-dilutive securities excluded from computation of earnings per share	196,419	241,096
Warrants to Purchase Common Stock [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Total amount of anti-dilutive securities excluded from computation of earnings per share	317,562
Convertible Notes [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Total amount of anti-dilutive securities excluded from computation of earnings per share			2,641,602
Convertible Preferred Stock (If Converted) [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Total amount of anti-dilutive securities excluded from computation of earnings per share		14,183,564	14,015,016	14,183,535

Commitments and Contingencies - Additional Information (Detail)	3 Months Ended		12 Months Ended
	Mar. 31, 2017 USD ($) ft²	Mar. 31, 2016 USD ($)	Dec. 31, 2016 USD ($) ft²	Dec. 31, 2015 USD ($)
Commitments and Contingencies Disclosure [Abstract]
Area of lease property \| ft²	7,580		7,580
Lease expiration date	Jun. 30, 2018		Jun. 30, 2018
Total operating leases rent expense	$ 51,289	$ 45,180	$ 214,595	$ 160,221
Lease agreement allowances for tenant improvements		$ 46,390	46,390
Deferred rent included in accrued expenses	47,948		49,209	$ 8,486
Non-cancelable future minimum lease payments	$ 131,684		157,418
Future payments related to other operating commitments			$ 2,761,501

Commitments and Contingencies (Detail) - USD ($)	Mar. 31, 2017	Dec. 31, 2016
Commitments and Contingencies Disclosure [Abstract]
Operating leases, 2017		$ 104,440
Operating leases, 2018		52,978
Operating leases, Total	$ 131,684	157,418
All other operating commitments, 2017		2,761,501
All other operating commitments, Total		2,761,501
Total commitments, 2017		2,865,941
Total commitments, 2018		52,978
Total commitments, Total		$ 2,918,919

Employee Stock Purchase Plan - Additional Information (Detail) - Common Stock [Member] - Employee Stock Purchase Plan [Member]	1 Months Ended
	Mar. 31, 2017 shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Maximum number of shares provided for issuance	300,000
Percentage of annual increase in number of shares reserved for issuance	1.00%

Summary of Related Party Transaction Activities Included in the Balance Sheets (Detail) - Akebia [Member]	Dec. 31, 2015 USD ($)
Related Party Transaction [Line Items]
Amounts receivable from Akebia	$ 997
Amounts payable to Akebia	$ 15,173

Furniture and Equipment - Summary of Components of Furniture and Equipment (Detail) - USD ($)	Mar. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment [Line Items]
Furniture and equipment		$ 445,310	$ 332,013
Accumulated depreciation		(295,715)	(226,042)
Furniture and equipment, net	$ 138,147	149,595	105,971
Furniture [Member]
Property, Plant and Equipment [Line Items]
Furniture and equipment		156,928	143,435
Computers [Member]
Property, Plant and Equipment [Line Items]
Furniture and equipment		111,446	107,160
Equipment [Member]
Property, Plant and Equipment [Line Items]
Furniture and equipment		141,067	$ 81,418
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Furniture and equipment		$ 35,869

Redeemable Convertible Preferred Stock - Additional Information (Detail) - USD ($)			1 Months Ended				3 Months Ended	12 Months Ended
	Apr. 22, 2014	Aug. 28, 2012	Mar. 31, 2016	Nov. 30, 2013	Aug. 31, 2013	Aug. 28, 2012	Mar. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 23, 2011
Temporary Equity [Line Items]
Conversion of Preferred Stock			3-to-1					The initial conversion ratio is one share of Preferred Stock for one share of the Aerpio’s common stock.
Stock issued, issuance price								$ 14.70
Preferred Stock, Voting Rights								Preferred Stock are entitled to the number of votes equal to the number of whole shares of Aerpio common stock into which the shares of Aerpio Preferred Stock are convertible. Except as provided by law or otherwise, the holders of Aerpio’s Preferred Stock vote together with the holders of Aerpio’s common stock as a single class. Certain significant actions must be approved by at least 50% of the holders of Aerpio’s Preferred Stock voting as a single class on an as converted basis.
Preferred stock terms of conversion								(i) the closing of the sale of shares of the Aerpio’s common stock to the public in an underwritten public offering at a price of $14.70 resulting in at least $40,000,000 of gross proceeds to Aerpio, or (ii) the date and time, or the occurrence of an event, specified by vote or written consent of the holders of more than 50% of the then outstanding shares of Preferred Stock on an as-converted basis.
Proceeds from issuance of common stock							$ 40,247,775
Akebia [Member]
Temporary Equity [Line Items]
Conversion of Preferred Stock								0.4285120 share of Aerpio’s Series A Preferred Stock for every 35 shares of Akebia’s Series A Preferred Stock, 0.4285120 share of Aerpio’s Series A Preferred Stock for every 100 shares of Akebia’s Series B Preferred Stock
Conversion of Preferred Stock								0.4285120 share of Aerpio’s Common Stock for every 175 shares of Akebia’s Common Stock
Minimum [Member]
Temporary Equity [Line Items]
Proceeds from issuance of common stock								$ 40,000,000
Series A2 Redeemable Convertible Preferred Stock [Member]
Temporary Equity [Line Items]
Redeemable convertible preferred stock, shares issued								4,486,015	4,489,160
Redeemable convertible preferred stock, par value	$ 0.00001
Stock issued, issuance price	$ 4.90
Gross proceeds from issuance of redeemable convertible Preferred Stock	$ 22,000,000
Issuance cost of redeemable convertible Preferred Stock	168,648
Net proceeds from issuance of redeemable Convertible Preferred Stock	$ 21,831,352
Redeemable convertible preferred stock, shares issued	4,489,169							4,660,573	4,489,169
Preferred stock, dividend rate, percentage								6.00%
Preferred stock, liquidation preference per share								$ 4.90
Series A Redeemable Convertible Preferred Stock [Member]
Temporary Equity [Line Items]
Redeemable convertible preferred stock, shares issued								1,239,338	1,326,145	1,326,147
Redeemable convertible preferred stock, par value										$ 0.00001
Redeemable convertible preferred stock, shares issued								1,326,147	1,326,147
Preferred stock, liquidation preference per share								$ 4.27
Series A1 Redeemable Convertible Preferred Stock [Member]
Temporary Equity [Line Items]
Redeemable convertible preferred stock, shares issued		2,520,658		2,268,594	2,016,526	2,520,658		8,289,663	8,368,230
Redeemable convertible preferred stock, par value		$ 0.00001				$ 0.00001
Stock issued, issuance price		$ 3.97		$ 3.97	$ 3.97	$ 3.97
Gross proceeds from issuance of redeemable convertible Preferred Stock		$ 10,000,000		$ 9,000,000	$ 8,000,000
Issuance cost of redeemable convertible Preferred Stock		210,638			$ 94,326
Net proceeds from issuance of redeemable Convertible Preferred Stock		$ 9,789,362
Debt conversion, preferred stock issued						1,562,469
Redeemable convertible preferred stock, shares issued								8,368,247	8,368,247
Preferred stock, dividend rate, percentage								6.00%
Preferred stock, liquidation preference per share								$ 3.97

Common Stock Reserved for Future issuance (Detail)	Dec. 31, 2016 shares
Class Of Stock [Line Items]
Common stock reserved for future issuance	15,183,705
Series A Convertible Preferred Units [Member]
Class Of Stock [Line Items]
Common stock reserved for future issuance	1,239,338
Series A1 Redeemable Convertible Preferred Stock [Member]
Class Of Stock [Line Items]
Common stock reserved for future issuance	8,289,663
Series A2 Redeemable Convertible Preferred Stock [Member]
Class Of Stock [Line Items]
Common stock reserved for future issuance	4,486,015
Unvested Restricted Stock Awards [Member]
Class Of Stock [Line Items]
Common stock reserved for future issuance	241,096
Options To Purchase Common Stock [Member]
Class Of Stock [Line Items]
Common stock reserved for future issuance	927,593

Stock Option Award Granted Using Black Scholes Option Pricing Model (Detail) - Stock Option [Member]	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (years)	6 years	6 years
Risk-free interest rate	1.39%	1.97%
Expected volatility	61.00%	78.00%
Expected dividend yield	0.00%	0.00%

Loss Before Income Tax and Reconciliation of Statutory Federal Income Tax (Detail)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Federal tax at statutory rate	34.00%	34.00%
State and local tax at statutory rates	0.83%	0.83%
Research and development credits	3.77%	4.06%
Change in valuation allowance	(37.28%)	(38.26%)
Other	(1.32%)	(0.63%)
Effective tax rate	0.00%	0.00%

Income Taxes - Deferred Tax Assets and Liabilities (Detail) - USD ($)	Dec. 31, 2016	Dec. 31, 2015
Deferred tax assets:
Net operating loss carryforwards	$ 23,146,178	$ 17,427,880
Accrued expenses	18,400	143,295
Stock-based compensation	96,570
Research and development credits	2,670,688	2,031,211
Other	20,784	19,565
Total deferred tax assets	25,952,620	19,621,951
Deferred tax liabilities:
Stock-based compensation		2,803
Fixed assets	8,434	9,220
Total deferred tax liabilities	8,434	12,023
Net deferred tax assets before valuation allowance	25,944,186	19,609,928
Less valuation allowance	(25,944,186)	(19,609,928)
Net deferred tax asset	$ 0	$ 0

Employee Retirement Plan - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Compensation and Retirement Disclosure [Abstract]
Contributions made under Plan	$ 0	$ 0

Employee Bonus Plan - Additional Information (Detail) - USD ($)	Mar. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Deferred Compensation Arrangements [Abstract]
Amount of bonus accrued	$ 125,576	$ 0	$ 380,020

Subsequent Events - Additional Information (Detail)	Feb. 28, 2017 USD ($)
Senior secured convertible note [Member] \| February Convertible Notes [Member]
Subsequent Event [Line Items]
Debt instrument amount	$ 297,355