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Document and Entity Information	12 Months Ended
Document and Entity Information	Dec. 31, 2016
Document And Entity Information [Abstract]
Document Type	S-1
Amendment Flag	false
Document Period End Date	Dec. 31, 2016
Entity Registrant Name	Aerpio Pharmaceuticals, Inc.
Entity Central Index Key	0001422142
Entity Filer Category	Smaller Reporting Company

Balance Sheets - USD ($)	Dec. 31, 2016	Dec. 31, 2015
Current assets:
Cash and cash equivalents	$ 1,609,694	$ 5,144,211
Short-term investments	50,000	50,000
Accounts receivable	4,157	118,516
Prepaid research and development contracts	353,434	266,327
Other current assets	209,038	386,549
Total current assets	2,226,323	5,965,603
Furniture and equipment, net	149,595	105,971
Deposits	20,960	20,960
Total assets	2,396,878	6,092,534
Current liabilities:
Accounts payable	1,135,608	890,610
Accounts payable and accrued expenses	2,470,970	2,159,874
Accrued interest	483,442
Convertible notes	12,386,647
Total current liabilities	14,857,617	2,159,874
Commitments and contingencies
Stockholders' deficit
Common stock, value	29	27
Accumulated deficit	(86,218,658)	(66,554,782)
Total stockholders' deficit	(86,218,629)	(66,554,755)
Total liabilities and stockholders' deficit	2,396,878	6,092,534
Redeemable convertible preferred stock	73,757,890	70,487,415
Series A Redeemable Convertible Preferred Stock [Member]
Stockholders' deficit
Redeemable convertible preferred stock	7,016,515	7,119,204
Series A1 Redeemable Convertible Preferred Stock [Member]
Stockholders' deficit
Redeemable convertible preferred stock	40,897,311	39,016,008
Series A2 Redeemable Convertible Preferred Stock [Member]
Stockholders' deficit
Redeemable convertible preferred stock	25,844,064	24,352,203
ZETA ACQUISITION CORP. II [Member]
Current assets:
Cash and cash equivalents	4,012	18,529
Total assets	4,012	18,529
Current liabilities:
Accounts payable	4,274	3,674
Accrued interest	42,378	32,436
Accrued expenses	13,275	8,900
Notes payable, stockholders	170,000	160,000
Total current liabilities	229,927	205,010
Stockholders' deficit
Preferred stock, value
Common stock, value	500	500
Additional paid-incapital	49,500	49,500
Accumulated deficit	(275,915)	(236,481)
Total stockholders' deficit	(225,915)	(186,481)
Total liabilities and stockholders' deficit	$ 4,012	$ 18,529

Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2016	Dec. 31, 2015
Common stock, par value	$ 0.00001	$ 0.00001
Common stock, shares authorized	40,700,000	40,000,000
Common stock, shares issued	2,895,994	2,895,994
Common stock, shares outstanding	2,700,719	2,700,719
Series A Redeemable Convertible Preferred Stock [Member]
Redeemable convertible preferred stock, shares authorized	3,094,774	3,094,774
Redeemable convertible preferred stock, shares issued	2,892,193	3,094,774
Redeemable convertible preferred stock, shares outstanding	2,892,193	3,094,774
Series A1 Redeemable Convertible Preferred Stock [Member]
Redeemable convertible preferred stock, shares authorized	19,528,622	19,528,622
Redeemable convertible preferred stock, shares issued	19,345,272	19,528,622
Redeemable convertible preferred stock, shares outstanding	19,345,272	19,528,622
Series A2 Redeemable Convertible Preferred Stock [Member]
Redeemable convertible preferred stock, shares authorized	10,876,182	10,476,182
Redeemable convertible preferred stock, shares issued	10,468,842	10,476,182
Redeemable convertible preferred stock, shares outstanding	10,468,842	10,476,182
ZETA ACQUISITION CORP. II [Member]
Preferred stock, par value	$ 0.0001	$ 0.0001
Preferred stock, shares authorized	10,000,000	10,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.0001	$ 0.0001
Common stock, shares authorized	100,000,000	100,000,000
Common stock, shares issued	5,000,000	5,000,000
Common stock, shares outstanding	5,000,000	5,000,000

Statements of Operations and Comprehensive Loss - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Operating expenses:
Research and development	$ 11,367,590	$ 11,625,404
General and administrative	5,265,995	5,861,151
Total operating expenses	16,633,585	17,486,555
Operating loss	(16,633,585)	(17,486,555)
Other:
Grant income	131,281	369,688
Interest (expense) income, net	(482,204)	19,622
Reimbursements from Akebia	997	27,022
Total other	(349,926)	416,332
Net loss and comprehensive loss	(16,983,511)	(17,070,223)
Reconciliation to net loss attributable to common stockholders:
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 basic and diluted common share	$ (10.51)	$ (13.52)
Weighted average common shares used in computing net loss per share attributable to common stockholders, basic and diluted	1,989,863	1,288,631
ZETA ACQUISITION CORP. II [Member]
Operating expenses:
General and administrative	$ 29,492	$ 23,006
Operating loss	(29,492)	(23,006)
Other:
Interest expense	9,942	8,434
Net loss and comprehensive loss	(39,434)	(31,440)
Reconciliation to net loss attributable to common stockholders:
Net loss and comprehensive loss	$ (39,434)	$ (31,440)
Net loss per basic and diluted common share	$ (0.01)	$ (0.01)
Weighted average common shares used in computing net loss per share attributable to common stockholders, basic and diluted	5,000,000	5,000,000

Statements of Redeemable Convertible Preferred Stock and Stockholders' 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]
Balance (ZETA ACQUISITION CORP. II [Member]) at Dec. 31, 2014	$ (155,041)	$ 500	$ 49,500	$ (205,041)
Balance at Dec. 31, 2014	(49,608,942)	$ 26		(49,608,968)
Temporary equity, balance at Dec. 31, 2014	70,138,979				$ 6,754,096	$ 40,180,140	$ 23,204,743
Balance, shares (ZETA ACQUISITION CORP. II [Member]) at Dec. 31, 2014		5,000,000
Balance, shares at Dec. 31, 2014		2,691,344
Temporary equity, balance shares at Dec. 31, 2014					3,094,774	19,528,622	10,476,182
Adjustment of redeemable convertible preferred stock to redemption value	(348,436)		(472,845)	124,409
Temporary equity, Adjustment of redeemable convertible preferred stock to redemption value	348,436				$ 365,108	$ (1,164,132)	$ 1,147,460
Exercise of stock options	3,000	$ 1	2,999
Temporary equity, balance at Dec. 31, 2015	70,487,415				$ 7,119,204	$ 39,016,008	$ 24,352,203
Exercise of stock options, shares		9,375
Temporary equity, balance shares at Dec. 31, 2015					3,094,774	19,528,622	10,476,182
Share-based compensation expense	469,846		469,846
Net loss \| ZETA ACQUISITION CORP. II [Member]	(31,440)			(31,440)
Net loss	(17,070,223)			(17,070,223)
Balance (ZETA ACQUISITION CORP. II [Member]) at Dec. 31, 2015	(186,481)	$ 500	49,500	(236,481)
Balance at Dec. 31, 2015	(66,554,755)	$ 27		(66,554,782)
Balance, shares (ZETA ACQUISITION CORP. II [Member]) at Dec. 31, 2015		5,000,000
Balance, shares at Dec. 31, 2015		2,700,719
Adjustment of redeemable convertible preferred stock to redemption value	(4,152,801)		(1,273,638)	(2,879,163)
Temporary equity, Adjustment of redeemable convertible preferred stock to redemption value	4,152,801				$ 379,777	$ 2,263,804	$ 1,509,220
Conversion of preferred stock	658,102	$ 1	658,101
Temporary equity, Conversion of preferred stock	(658,102)				$ (324,774)	$ (333,328)
Conversion of preferred stock, shares		144,233			(135,066)	(159,135)
Extinguishment of preferred stock	224,224		25,426	198,798
Temporary equity, Extinguishment of preferred stock	(224,224)				$ (157,692)	$ (49,173)	$ (17,359)
Conversion of Convertible Notes	82,818		82,818
Temporary equity, Extinguishment of preferred stock, shares					(67,515)	(24,215)	(7,340)
Exercise of stock options	18,968	$ 1	18,967
Temporary equity, balance at Dec. 31, 2016	$ 73,757,890				$ 7,016,515	$ 40,897,311	$ 25,844,064
Exercise of stock options, shares	51,043	51,042
Temporary equity, balance shares at Dec. 31, 2016					2,892,193	19,345,272	10,468,842
Share-based compensation expense	$ 488,326		488,326
Net loss \| ZETA ACQUISITION CORP. II [Member]	(39,434)			(39,434)
Net loss	(16,983,511)			(16,983,511)
Balance (ZETA ACQUISITION CORP. II [Member]) at Dec. 31, 2016	(225,915)	$ 500	$ 49,500	(275,915)
Balance at Dec. 31, 2016	$ (86,218,629)	$ 29		$ (86,218,658)
Balance, shares (ZETA ACQUISITION CORP. II [Member]) at Dec. 31, 2016		5,000,000
Balance, shares at Dec. 31, 2016		2,895,994

Statements of Cash Flows - USD ($)	12 Months Ended
Statements of Cash Flows - USD ($)	Dec. 31, 2016	Dec. 31, 2015
Operating activities
Net loss	$ (16,983,511)	$ (17,070,223)
Adjustments to reconcile net loss to net cash
Depreciation	69,673	57,977
Compensation recognized under equity incentive plan	488,326	469,846
Amortization of debt issuance costs	188,686
Interest expense related to convertible note conversion	2,823
Accounts receivable	114,359	(60,566)
Prepaid expenses and other current assets	90,404	(210,106)
Accounts payable and accrued expenses	311,096	(1,071,610)
Net cash used in operating activities	(15,718,144)	(17,884,682)
Investing activities
Purchase of furniture and equipment	(113,297)	(41,037)
Net cash used in investing activities	(113,297)	(41,037)
Financing activities
Proceeds from exercise of stock options	18,968	3,000
Proceeds from issuances of convertible notes	12,542,203
Cash paid for debt issuance costs	(264,247)
Net cash provided by financing activities	12,296,924	3,000
Net increase (decrease) in cash and cash equivalents	(3,534,517)	(17,922,719)
Cash and cash equivalents at beginning of period	5,144,211	23,066,930
Cash and cash equivalents at end of period	1,609,694	5,144,211
Non-cash financing activities
Accretion of preferred stock to redemption value	4,152,801	348,436
Extinguishment of preferred stock	(224,224)
ZETA ACQUISITION CORP. II [Member]
Operating activities
Net loss	(39,434)	(31,440)
Adjustments to reconcile net loss to net cash
Used in operating activities:	0	0
Increase in accounts payable	600	1,272
Increase in accrued interest	9,942	8,434
Increase in accrued expenses	4,375
Net cash used in operating activities	(24,517)	(21,734)
Financing activities
Proceeds from notes payable, stockholders	10,000	35,000
Net cash provided by financing activities	10,000	35,000
Net increase (decrease) in cash and cash equivalents	(14,517)	13,266
Cash and cash equivalents at beginning of period	18,529	5,263
Cash and cash equivalents at end of period	$ 4,012	$ 18,529

Nature of Organization and Operations

12 Months Ended

Dec. 31, 2016

Organization, Consolidation and Presentation of Financial Statements [Abstract]

Nature of Organization and Operations

1.	Nature of Organization and Operations

Aerpio Therapeutics, Inc. (Aerpio or the Company) is a biopharmaceutical company focused on advanced treatment for ocular disease. The Company’s lead product, AKB-9778, a small molecule activator of the Tie-2 pathway, is being developed for diabetic retinopathy. In addition to AKB-9778, the Company is advancing a humanized monoclonal antibody directed at the same target as AKB-9778, ARP-1536 in vascular disorders of the eye. ARP-1536, currently at the preclinical development stage, is designed to address the same pathway as AKB-9778. Aerpio is also completing clinical studies with AKB-4924, a selective stabilizer of hypoxia-inducible factor-1 alpha, or HIF-1 alpha, that is being developed for the treatment of inflammatory bowel disease. The Company was incorporated on November 17, 2011, under the laws of the State of Delaware and was capitalized in December 2011 in a spinout transaction from Akebia Therapeutics, Inc. (Akebia) to enable more rapid development of its compounds.

On March 7, 2017, the Company entered into an Agreement and Plan of Merger and Reorganization, or the Merger Agreement, with Zeta Acquisition Corp. II and Aerpio Acquisition Corp., a wholly owned subsidiary of Zeta Acquisition Corp. II. Pursuant to the Merger Agreement, the Company became a wholly-owned subsidiary of Zeta Acquisition Corp. II. All of the outstanding stock of the Company was converted into shares of Zeta Acquisition Corp. II. On March 15, 2017, Zeta Acquisition Corp. II closed a private placement offering, or the Offering, of 8,049,555 shares of its common stock, at a purchase price of $5.00 per share. Aerpio is considered the accounting acquirer in the Merger and will account for the transaction as a recapitalization because Aerpio’s former stockholders received substantially all of the voting rights in the combined entity and Aerpio’s senior management represents all of the senior management of the combined entity. See Note 15 for additional information.

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.

Summary of Significant Accounting Policies

12 Months Ended

Dec. 31, 2016

Accounting Policies [Abstract]

Summary of Significant Accounting Policies

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 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.

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. Grant income also includes qualifying therapeutic credits from the U.S. Treasury related to discovery projects.

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 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.

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 2016 or 2015.

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

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.

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

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 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 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 financial statements.

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.

Subsequent Events

The Company evaluates events and transactions occurring subsequent to the date of the financial statements for matters requiring recognition or disclosure in the financial statements. The accompanying financial statements considered events through March 9, 2017, the date on which the financial statements were available to be issued.

Notes Payable, Stockholders

12 Months Ended

Dec. 31, 2016

Notes Payable, Stockholders

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	Reimbursements from Akebia		1,994		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

ZETA ACQUISITION CORP. II [Member]

Notes Payable, Stockholders

2. Notes Payable, Stockholders

During 2016, various stockholders loaned the Company $10,000 and were issued unsecured promissory notes which bear interest at 6% and are due on demand. Similar stockholder loans amounted to $35,000 during 2015, $15,000 during 2014, $25,000 during 2013, $25,000 during 2012, $35,000 during 2010, and $25,000 during 2009. Interest of $42,378 and $32,436 was accrued and unpaid at December 31, 2016 and 2015, respectively.

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

Accounts Payable and Accrued Expenses

12 Months Ended

Dec. 31, 2016

Payables and Accruals [Abstract]

Accounts Payable and Accrued Expenses

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

12 Months Ended

Dec. 31, 2016

Debt Disclosure [Abstract]

Notes Payable to Investors

6.	Notes Payable to Investors

In March 2016, the Company entered into a senior secured convertible note financing (the Convertible Notes or Convertible Note Financing) totaling $9,000,000, with certain preferred investors of the Company. All preferred investors were invited to participate in the Convertible Notes Financing. In connection with the Convertible Note Financing, the Company’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 Preferred Stock automatically converted into Common Stock using a 3-to-1 conversion ratio and such Preferred Stockholders would lose the right to representation on the Company’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 Preferred Stockholders chose not to participate in the Convertible Note Financing and their respective Preferred Stock was converted into shares of Common Stock in April 2016 in accordance with the terms of the Articles of Incorporation. The Company treated this as an extinguishment of Preferred Stock. The Convertible Notes accrue 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 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 the Company. In addition and prior to maturity, the Convertible Notes are automatically convertible into shares of capital stock of the Company upon the occurrence of a sale of the Company’s capital stock in a single transaction resulting in gross proceeds to the Company of $30,000,000 (hereinafter referred to as an “Investor Sale”). The type and class of capital stock of the Company to be issued to the holder of each Convertible Note upon conversion shall be identical to the type and class of the 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 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 the Company’s assets.

In October 2016 the Company 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 the Company. 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. The Company 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.

Preferred Stock

12 Months Ended

Dec. 31, 2016

Preferred Stock

7.	Redeemable Convertible Preferred Stock

On December 23, 2011, the Company issued 3,094,774 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 1 share of Aerpio’s Series A Preferred Stock for every 35 shares of Akebia’s Series A Preferred Stock, 1 share of Aerpio’s Series A Preferred Stock for every 100 shares of Akebia’s Series B Preferred Stock, and 1 share of Aerpio’s Common Stock for every 175 shares of Akebia’s Common Stock.

On August 28, 2012, the Company issued 5,882,353 shares of $.00001 par value of Series A1 Redeemable Convertible Preferred Stock (Series A1 Preferred Stock) at $1.70 per share for gross proceeds of $10,000,000, less issuance costs of $210,638, for net proceeds to the Company of $9,789,362. In connection with the financing, the Company exchange its then outstanding convertible promissory notes and accrued interest into 3,646,269 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, the Company issued 4,705,882 and 5,294,118 shares, respectively, of Series A1 Preferred Stock at $1.70 for gross proceeds of $8,000,000 and $9,000,000, respectively, and incurred total issuance costs of $94,326.

On April 22, 2014, the Company issued 10,476,182 shares of $.00001 par value Series A2 Redeemable Convertible Preferred Stock (Series A2 Preferred Stock) at $2.10 per share for total gross proceeds of $22,000,000. The Company incurred issuance costs of $168,648 for net proceeds to the Company of $21,831,352.

In March 2016, in connection with the Convertible Note Financing described more fully in Note 6, the Company’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 Preferred Stock automatically converted into Common Stock using a 3-to-1 conversion ratio and such Preferred Stockholders would lose the right to representation on the Company’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 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 the Company’s Common stock.

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

Voting

The holders of Preferred Stock are entitled to the number of votes equal to the number of whole shares of Common Stock into which the shares of Preferred Stock are convertible. Except as provided by law or otherwise, the holders of Preferred Stock vote together with the holders of Common Stock as a single class. Certain significant actions must be approved by at least 50% of the holders of 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 Preferred Stock are entitled to elect six members of the Company’s Board of Directors, which is subject to reduction to not less than four directors under certain circumstances. The holders of shares of Common Stock (including any holders of all shares of Preferred Stock on an as converted basis) are entitled to elect two members of the Company’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 the 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 the Company, 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 Common Stock, out of the assets of the Company available for distribution at $2.10 per share for Series A2 Preferred Stock and $1.70 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 $1.83 per share, plus any accrued but unpaid dividends before any payment is made to the holders of Common Stock.

In the event the assets of the Company 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 the Company 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 Common Stock based on the pro rata number of shares held by each holder, treating such securities as if they had been converted to Common Stock immediately prior to such dissolution, liquidation, or winding-up of the Company.

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 Common Stock. The initial conversion ratio is one share of Preferred Stock for one share of the Company’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 Common Stock at the then-applicable conversion ratio, as defined, upon either: (i) the closing of the sale of shares of the Company’s Common Stock to the public in an underwritten public offering at a price of $6.30 resulting in at least $40,000,000 of gross proceeds to the Company, 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.

The Company 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, the Company’s analysis followed the whole instrument approach, which compares an individual feature against the entire Preferred Stock instrument that includes that feature. The Company’s analysis was based on a consideration of the economic characteristics and risks of each series of Preferred Stock. More specifically, the Company 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. The Company 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.

The Company 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, the Company’s Common Stock into which each series of the Company’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 Shares are recorded in the mezzanine equity and subject to subsequent measurement under the guidance provided under ASC 480-10-S99. In accordance with that guidance, the Company 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 the Company in an a potential public trading scenario, in which the Preferred Stock converts to Common Stock, and a second scenario in which equity value is allocated using the OPM. For the public trading scenario, the Company used the guideline public company method under the market approach.

ZETA ACQUISITION CORP. II [Member]

Preferred Stock

3. Preferred Stock

The Company is authorized to issue 10,000,000 shares of preferred stock with such designations, voting and other rights and preferences as may be determined from time to time by the Board of Directors.

Common Stock

12 Months Ended

Dec. 31, 2016

Common Stock

8.	Common Stock

As of December 31, 2016, the Company had 40,700,000 shares of authorized Common Stock with par value of $0.00001 per share. The voting, dividend, and liquidation rights of the holders of Common Stock are subject to and qualified by the rights, powers, and preferences of the holders of Preferred 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. Notwithstanding the foregoing, except as otherwise required by law, holders of 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 Common Stock are entitled to receive dividends, if and when declared by the Board of Directors. The Company may not declare or pay any cash dividends to the holders of 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 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 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, the Company has reserved the following shares of Common Stock for future issuance:


Conversion of Series A Preferred Stock			2,892,193
Conversion of Series A1 Preferred Stock			19,345,272
Conversion of Series A2 Preferred Stock			10,468,842
Conversion of unvested restricted stock awards			562,649
Exercise of options to purchase Common Stock			2,164,776

Total			35,433,732

ZETA ACQUISITION CORP. II [Member]

Common Stock

4. Common Stock

The Company is authorized to issue 100,000,000 shares of common stock with such designations, voting and other rights and preferences as may be determined from time to time by the Board of Directors. During December 2007, the Company issued 5,000,000 shares of its common stock pursuant to a private placement for $50,000.

Stock-Based Compensation

12 Months Ended

Dec. 31, 2016

Text Block [Abstract]

Stock-Based Compensation

9.	Stock-Based Compensation

On November 17, 2011, the Company 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 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 the Company’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 the Company’s Common Stock to be used for purposes of estimating the fair value of options to purchase shares of Common Stock. The Company estimates the expected term of options granted utilizing the simplified method. As there has been no public market for the Company’s Common Stock, the Company 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 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		2,117,852		$	0.71			$	135,711
Granted		117,217			0.77
Exercised		(51,043	)		0.37
Expired/cancelled		(19,250	)		0.53

Outstanding, December 31, 2016		2,164,776		$	0.72		7.48	$	1,030,217

Expected to vest, December 31, 2016		729,391		$	0.78		8.60	$	308,767
Options exercisable, December 31, 2016		1,435,385		$	0.70		6.92	$	721,451

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. 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 $0.52. 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		1,036,629		$	0.72
Granted		—			—
Vested		(473,980	)		0.66
Forfeited		—			—

Nonvested, December 31, 2016		562,649		$	0.78

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

Income Taxes

12 Months Ended

Dec. 31, 2016

Income Taxes

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.

ZETA ACQUISITION CORP. II [Member]

Income Taxes

5. Income Taxes

The Company has reviewed its tax positions as of December 31, 2016 and 2015, and has not identified any positions that are uncertain. Income tax returns filed and to be filed for the years ended December 31, 2014, 2015, and 2016 are open to review by the Internal Revenue Service.

The tax effects of temporary differences that give rise to significant portions of the Company’s net deferred tax asset at December 31, 2016 and 2015 are as follows:


	December 31, 2016			December 31, 2015
Deferred tax asset:
Capitalized formation costs	$	79,400		$	69,400
Net operating loss carryforward		14,400			11,000
Valuation allowance		(93,800	)		(80,400	)

Net deferred tax asset recognized	$	—		$	—

A full valuation allowance has been recorded against the Company’s deferred tax asset because, based on the weight of available evidence, it is more likely than not that such benefits will not be realized. As of December 31, 2016, the Company has a net operating loss carryforward for federal and state income tax purposes of approximately $42,400. The net operating loss carryforward will begin to expire in 2029.

The benefit from income taxes differs from the amount computed by applying the United States (US) federal income tax rate of thirty-four percent (34%) in 2016 and 2015 to loss before income taxes for the years ended December 31, 2016 and 2015 as follows:


	Year Ended December 31, 2016			Year Ended December 31, 2015
US federal income tax benefit at statutory rate	$	(13,400	)	$	(10,700	)
Other		—			100
Change in valuation allowance		13,400			10,600

Benefit from income taxes	$	—		$	—

Net Loss per Share

12 Months Ended

Dec. 31, 2016

Earnings Per Share [Abstract]

Net Loss per Share

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	$	(10.51	)	$	(13.52	)

Weighted average common shares used in computing net loss per share attributable to common stockholders, basic and diluted		1,989,863			1,288,631

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:


	December 31
	2016		2015
Convertible preferred stock (if converted)		32,706,307		33,099,578
Options to purchase common stock		1,435,385		989,845
Convertible notes (if converted)		6,164,595		—

Commitments and Contingencies

12 Months Ended

Dec. 31, 2016

Commitments and Contingencies Disclosure [Abstract]

Commitments and Contingencies

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 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, the Company 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 the Company. The terms of the February Convertible Notes are identical to the Convertible Notes.

On March 7, 2017, the Company entered into the Merger Agreement with Zeta Acquisition Corp. II and Aerpio Acquisition Corp., a wholly owned subsidiary of Zeta Acquisition Corp. II. Zeta Acquisition Corp. II is a “shell company” as defined in Rule 12b-2 of the Securities Exchange Act of 1934, as amended. Pursuant to the terms of the Merger Agreement, on March 15, 2017, or the Closing Date, Aerpio Acquisition Corp. merged with and into the Company. Pursuant to this transaction, or the Merger, the Company was the surviving corporation and became a wholly-owned subsidiary of Zeta Acquisition Corp. II (which also effective March 15, 2017 changed its name to Aerpio Pharmaceuticals, Inc.).

At the effective time of the Merger, the shares of the Company’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 Company’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 Zeta Acquisition Corp. II common stock. In addition, immediately prior to the Merger, the outstanding amounts under certain Senior Secured Convertible Promissory Notes issued by the Company to its pre-Merger noteholders were converted into shares of the Company’s equity, which were then converted to shares of the Company’s common stock and subsequently were converted into shares of Zeta Acquisition Corp. II common stock, together with the other shares of the Company’s common stock described above. In addition, pursuant to the Merger Agreement options to purchase shares of the Company’s common stock issued and outstanding immediately prior to the closing of the Merger were assumed and converted into options to purchase shares of Zeta Acquisition Corp. II common stock. All of the outstanding capital stock of the Company was converted into shares of Zeta Acquisition Corp. II common stock on a 2.3336572:1 basis.

Immediately after the Effective Time, on March 15, 2017, the Company converted into a Delaware limited liability company.

Following the Merger, on March 15, 2017, Zeta Acquisition Corp. II closed the Offering and sold to accredited investors approximately $40,250,000 of its shares of common stock, or 8,049,555 shares, at a price of $5.00 per share (proceeds net of placement agent and offering costs were approximately $37,200,000). Also, it granted the investors in the Offering registration rights requiring the registration of those shares of common stock for public resale. The then existing stockholders of the Company who agreed to become parties to the registration rights agreement also became entitled to such registration rights. The Offering closed on March 15, 2017. As a result of the Offering, the conditions that previously raised substantial doubt about whether the Company will continue as a going concern have been alleviated.

In accordance with ASC 805, “Business Combinations,” the Company is considered the accounting acquirer in the Merger and will account for the transaction as a recapitalization and reverse acquisition for financial reporting purposes. Consequently, the assets and liabilities and the historical operations that will be reflected in the consolidated financial statements of Aerpio Pharmaceuticals, Inc. will be those of the Company and will be recorded at their historical cost bases.

Nature of Operations and Significant Accounting Policies	12 Months Ended
	Dec. 31, 2016
ZETA ACQUISITION CORP. II [Member]
Nature of Operations and Significant Accounting Policies	1. Nature of Operations and Significant Accounting Policies Nature of Operations Zeta Acquisition Corp. II (the “Company”) was incorporated under the laws of the State of Delaware on November 16, 2007. The Company was organized as a vehicle to investigate and, if such investigation warrants, acquire a target company or business seeking the perceived advantages of being a publicly held corporation. The Company’s principal business objective for the next twelve (12) months and beyond will be to achieve long-term growth potential through a combination with a business. The Company will not restrict its potential candidate target companies to any specific business, industry or geographical location and, thus, may acquire any type of business. Liquidity Since its inception, the Company has generated no revenues and has incurred a net loss of $275,915. Since inception, the Company has been dependent upon the receipt of capital investment or other financing to fund its continuing activities. In addition, the Company is dependent upon certain related parties to provide continued funding and capital resources but it is uncertain whether this funding will continue. The accompanying financial statements have been presented on the basis of the continuation of the Company as a going concern and do not include any adjustments relating to the recoverability and classification of recorded asset amounts or the amounts and classification of liabilities that might be necessary should the Company be unable to continue as a going concern. Use of Estimates The preparation of financial statements in conformity with accounting principles generally accepted in the United States of America requires management to make certain 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 revenue and expenses during the reporting periods. Actual results could differ from those estimates. Cash and Cash Equivalents For purposes of the statement of cash flows, the Company considers all highly liquid investments with a maturity of three (3) months or less to be cash equivalents. Income Taxes The Company accounts for income taxes in accordance with ASC Topic 740, Income Taxes, which requires the recognition of deferred tax liabilities and assets at currently enacted tax rates for the expected future tax consequences of events that have been included in the financial statements or tax returns. A valuation allowance is recognized to reduce the net deferred tax asset to an amount that is more likely than not to be realized. Fair Value of Financial Instruments Pursuant to ASC Topic 820-10, Fair Value Measurements and Disclosures, the Company is required to estimate the fair value of all financial instruments included on its balance sheet as of December 31, 2016 and 2015. The Company considers the carrying value of cash and cash equivalents, accounts payable, accrued expenses, accrued interest, and notes payable to stockholders to approximate fair value due to their short maturities. Net Loss Per Share Basic loss per share is computed by dividing net loss by the weighted-average number of common shares outstanding for the period. The Company currently has no dilutive securities and as such, basic and diluted loss per share are the same for all periods presented. Recently Issued Accounting Pronouncements On January 1, 2015, the Company adopted Financial Accounting Standards Board, (“FASB”), Accounting Standards Update, (“ASU”), No. 2014-10, which eliminates the concept of a development stage entity, (“DSE”), in its entirety from United States Generally Accepted Accounting Principles, (“U.S. GAAP”). In accordance with ASU No. 2014-10, the Company has removed labeling the financial statements as a DSE and has eliminated inception-to-date information in the financial statements. In August 2014, the FASB issued ASU 2014-15, Presentation of Financial Statements – Going Concern (Subtopic 205-40) “Disclosure of Uncertainties about an Entity’s Ability to Continue as a Going Concern.” The objective of the guidance is to require management to explicitly assess an entity’s ability to continue as a going concern, and to provide related footnote disclosures in certain circumstances. In connection with each annual and interim period, management will assess if there is substantial doubt about an entity’s ability to continue as a going concern within one year after the issuance date of an entity’s financial statements. The new standard defines substantial doubt and provides examples of indicators thereof. The definition of substantial doubt incorporates a likelihood threshold of “probable” similar to the current use of that term in U.S. GAAP for loss contingencies. The new standard will be effective for all entities in the first annual period ending after December 15, 2015. Earlier application is permitted. The Company has adopted this standard.

Summary of Significant Accounting Policies (Policies)

12 Months Ended

Dec. 31, 2016

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

Use of Estimates

Use of Estimates

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.

Grant Income

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

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

Patents

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

Income Taxes

Income Taxes

Net Loss per Share

Net Loss per Share

Stock-Based Compensation

Stock-Based Compensation

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

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

Research and Development Costs

Research and Development Costs

Research and development costs are expensed as incurred.

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.

Recent Accounting Pronouncements

Recent Accounting Pronouncements

Subsequent Events

Subsequent Events

ZETA ACQUISITION CORP. II [Member]

Use of Estimates

Use of Estimates

The preparation of financial statements in conformity with accounting principles generally accepted in the United States of America requires management to make certain 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 revenue and expenses during the reporting periods. Actual results could differ from those estimates.

Cash and Cash Equivalents

Cash and Cash Equivalents

For purposes of the statement of cash flows, the Company considers all highly liquid investments with a maturity of three (3) months or less to be cash equivalents.

Income Taxes

Income Taxes

The Company accounts for income taxes in accordance with ASC Topic 740, Income Taxes, which requires the recognition of deferred tax liabilities and assets at currently enacted tax rates for the expected future tax consequences of events that have been included in the financial statements or tax returns. A valuation allowance is recognized to reduce the net deferred tax asset to an amount that is more likely than not to be realized.

Net Loss per Share

Net Loss Per Share

Basic loss per share is computed by dividing net loss by the weighted-average number of common shares outstanding for the period. The Company currently has no dilutive securities and as such, basic and diluted loss per share are the same for all periods presented.

Recent Accounting Pronouncements

Recently Issued Accounting Pronouncements

On January 1, 2015, the Company adopted Financial Accounting Standards Board, (“FASB”), Accounting Standards Update, (“ASU”), No. 2014-10, which eliminates the concept of a development stage entity, (“DSE”), in its entirety from United States Generally Accepted Accounting Principles, (“U.S. GAAP”). In accordance with ASU No. 2014-10, the Company has removed labeling the financial statements as a DSE and has eliminated inception-to-date information in the financial statements.

In August 2014, the FASB issued ASU 2014-15, Presentation of Financial Statements – Going Concern (Subtopic 205-40) “Disclosure of Uncertainties about an Entity’s Ability to Continue as a Going Concern.” The objective of the guidance is to require management to explicitly assess an entity’s ability to continue as a going concern, and to provide related footnote disclosures in certain circumstances. In connection with each annual and interim period, management will assess if there is substantial doubt about an entity’s ability to continue as a going concern within one year after the issuance date of an entity’s financial statements. The new standard defines substantial doubt and provides examples of indicators thereof. The definition of substantial doubt incorporates a likelihood threshold of “probable” similar to the current use of that term in U.S. GAAP for loss contingencies. The new standard will be effective for all entities in the first annual period ending after December 15, 2015. Earlier application is permitted. The Company has adopted this standard.

Liquidity

Liquidity

Since its inception, the Company has generated no revenues and has incurred a net loss of $275,915. Since inception, the Company has been dependent upon the receipt of capital investment or other financing to fund its continuing activities. In addition, the Company is dependent upon certain related parties to provide continued funding and capital resources but it is uncertain whether this funding will continue. The accompanying financial statements have been presented on the basis of the continuation of the Company as a going concern and do not include any adjustments relating to the recoverability and classification of recorded asset amounts or the amounts and classification of liabilities that might be necessary should the Company be unable to continue as a going concern.

Fair Value of Financial Instruments

Fair Value of Financial Instruments

Pursuant to ASC Topic 820-10, Fair Value Measurements and Disclosures, the Company is required to estimate the fair value of all financial instruments included on its balance sheet as of December 31, 2016 and 2015. The Company considers the carrying value of cash and cash equivalents, accounts payable, accrued expenses, accrued interest, and notes payable to stockholders to approximate fair value due to their short maturities.

Summary of Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2016

Accounting Policies [Abstract]

Assets Measured or Disclosed at Fair Value on a Recurring Basis

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

Notes Payable, Stockholders (Tables)

12 Months Ended

Dec. 31, 2016

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	Reimbursements from Akebia		1,994		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

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

Accounts Payable and Accrued Expenses (Tables)

12 Months Ended

Dec. 31, 2016

Payables and Accruals [Abstract]

Schedule of 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

Common Stock (Tables)

12 Months Ended

Dec. 31, 2016

Text Block [Abstract]

Summary of Shares Common Stock for Future Issuance

As of December 31, 2016, the Company has reserved the following shares of Common Stock for future issuance:


Conversion of Series A Preferred Stock			2,892,193
Conversion of Series A1 Preferred Stock			19,345,272
Conversion of Series A2 Preferred Stock			10,468,842
Conversion of unvested restricted stock awards			562,649
Exercise of options to purchase Common Stock			2,164,776

Total			35,433,732

- 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

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+ Details

Stock-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2016

Text Block [Abstract]

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		—			—

Summary of Stock Activity

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		2,117,852		$	0.71			$	135,711
Granted		117,217			0.77
Exercised		(51,043	)		0.37
Expired/cancelled		(19,250	)		0.53

Outstanding, December 31, 2016		2,164,776		$	0.72		7.48	$	1,030,217

Expected to vest, December 31, 2016		729,391		$	0.78		8.60	$	308,767
Options exercisable, December 31, 2016		1,435,385		$	0.70		6.92	$	721,451

Summary of Non-Vested 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		1,036,629		$	0.72
Granted		—			—
Vested		(473,980	)		0.66
Forfeited		—			—

Nonvested, December 31, 2016		562,649		$	0.78

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:


	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

Income Taxes (Tables)

12 Months Ended

Dec. 31, 2016

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	%

Schedule of tax effects on significant portions of deferred tax asset

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	$	—		$	—

ZETA ACQUISITION CORP. II [Member]

Reconciliation of Federal Statutory Income Tax Rate


	Year Ended December 31, 2016			Year Ended December 31, 2015
US federal income tax benefit at statutory rate	$	(13,400	)	$	(10,700	)
Other		—			100
Change in valuation allowance		13,400			10,600

Benefit from income taxes	$	—		$	—

Schedule of tax effects on significant portions of deferred tax asset

The tax effects of temporary differences that give rise to significant portions of the Company’s net deferred tax asset at December 31, 2016 and 2015 are as follows:


	December 31, 2016			December 31, 2015
Deferred tax asset:
Capitalized formation costs	$	79,400		$	69,400
Net operating loss carryforward		14,400			11,000
Valuation allowance		(93,800	)		(80,400	)

Net deferred tax asset recognized	$	—		$	—

Net Loss per Share (Tables)

12 Months Ended

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:


	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	$	(10.51	)	$	(13.52	)

Weighted average common shares used in computing net loss per share attributable to common stockholders, basic and diluted		1,989,863			1,288,631

Schedule of Anti Diluted Securites Excluded from Computation of Net Loss Per Share


	December 31
	2016		2015
Convertible preferred stock (if converted)		32,706,307		33,099,578
Options to purchase common stock		1,435,385		989,845
Convertible notes (if converted)		6,164,595		—

Commitments and Contingencies (Tables)

12 Months Ended

Dec. 31, 2016

Commitments and Contingencies Disclosure [Abstract]

Components of Future Commitments and Contingencies

	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

Nature of Operations and Significant Accounting Policies (Detail) - USD ($)		1 Months Ended
	Mar. 15, 2017	Dec. 31, 2007	Dec. 31, 2016	Dec. 31, 2015
Nature of Operations and Significant Accounting Policies (Textual)
Stock issued, issuance price			$ 6.30
Deficit accumulated since inception			$ (86,218,658)	$ (66,554,782)
ZETA ACQUISITION CORP. II [Member]
Nature of Operations and Significant Accounting Policies (Textual)
Deficit accumulated since inception			$ (275,915)	$ (236,481)
ZETA ACQUISITION CORP. II [Member] \| Common Stock [Member] \| Private Placement [Member]
Nature of Operations and Significant Accounting Policies (Textual)
Share issued, private placement		5,000,000
ZETA ACQUISITION CORP. II [Member] \| Subsequent Event [Member] \| Common Stock [Member] \| Private Placement [Member]
Nature of Operations and Significant Accounting Policies (Textual)
Share issued, private placement	8,049,555
Stock issued, issuance price	$ 5

Summary of Significant Accounting Policies - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2016 USD ($) Segment
Summary Of Significant Accounting Policy [Line Items]
Number of operating segment \| Segment	1
Accounting Standards Update 2015-03 [Member] \| Convertible Notes [Member]
Summary Of Significant Accounting Policy [Line Items]
Effect of adoption of new ASU \| $	$ (75,561)
Furniture and Equipment [Member] \| Minimum [Member]
Summary Of Significant Accounting Policy [Line Items]
Property, plant and equipment, estimated useful life	3 years
Furniture and Equipment [Member] \| Maximum [Member]
Summary Of Significant Accounting Policy [Line Items]
Property, plant and equipment, estimated useful life	7 years

Summary of Fair Value assets Measured On Recurring Basis (Detail) - Fair Value, Measurements, Recurring [Member] - USD ($)	Dec. 31, 2016	Dec. 31, 2015
Assets:
Cash and cash equivalents	$ 1,609,694	$ 5,144,211
Short-term investments	50,000	50,000
Total assets	1,659,694	5,194,211
Level 1 [Member]
Assets:
Cash and cash equivalents	1,609,694	5,144,211
Total assets	1,609,694	5,144,211
Level 2 [Member]
Assets:
Short-term investments	50,000	50,000
Total assets	$ 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
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(12))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Trading Securities
-URI http://asc.fasb.org/extlink&oid=6526789

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(5))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(6))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Reference 5: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 35
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=27723805&loc=d3e24584-111560

Reference 6: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(2))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 7: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 25
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=65884222&loc=d3e22054-111558

Reference 8: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(a)(1))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

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

Summary of Related Party Transaction Activities Included in the Statements of Operations and Comprehensive Loss (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Related Party Transaction [Line Items]
Payments from Akebia for facility-related charges and employee costs	$ 997	$ 27,022
Akebia [Member] \| Research and development [Member]
Related Party Transaction [Line Items]
Payments to Akebia for employee costs	31,246	263,501
Akebia [Member] \| Reimbursements from Akebia [Member]
Related Party Transaction [Line Items]
Payments from Akebia for facility-related charges and employee costs	$ 1,994	$ 27,022

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 ($)	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	149,595	105,971
Furniture [Member]
Property, Plant and Equipment [Line Items]
Furniture and equipment	156,928	143,435
Computer [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

Accounts Payable and Accrued Expense (Detail) - USD ($)	Dec. 31, 2016	Dec. 31, 2015
Payables and Accruals [Abstract]
Accounts payable	$ 1,135,608	$ 890,610
Professional fees	200,468	126,722
Accrued bonus	0	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 - Additional Information (Detail) - USD ($)	1 Months Ended		12 Months Ended
	Oct. 31, 2016	Mar. 31, 2016	Dec. 31, 2016
Debt Instrument [Line Items]
Preferred stock conversion ratio		3-to-1	The initial conversion ratio is one share of Preferred Stock for one share of the Company's Common Stock.
October Convertible Note [Member]
Debt Instrument [Line Items]
Debt instrument amount	$ 3,500,000
Debt issuance costs	$ 125,935
Debt maturity date	Mar. 31, 2017
Convertible Notes Payable [Member]
Debt Instrument [Line Items]
Debt instrument amount		$ 9,000,000
Preferred stock conversion ratio			3-to-1
Convertible Notes accrue interest rate per annum			8.00%
Debt issuance costs			$ 138,312
Amortization period of Convertible Notes			7 months
Convertible Notes Payable [Member] \| Investor Sale [Member]
Debt Instrument [Line Items]
Proceeds from sale of capital stock			$ 30,000,000
Convertible Notes Payable [Member] \| April 14, 2016 Closing Date [Member]
Debt Instrument [Line Items]
Debt instrument amount		4,500,000
Convertible Notes Payable [Member] \| July 15, 2016 Closing Date [Member]
Debt Instrument [Line Items]
Debt instrument amount		$ 4,500,000

Redeemable Convertible Preferred Stock - Additional Information (Detail) - USD ($)			1 Months Ended				12 Months Ended
	Apr. 22, 2014	Aug. 28, 2012	Mar. 31, 2016	Nov. 30, 2013	Aug. 31, 2013	Aug. 28, 2012	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 Company's Common Stock.
Stock issued, issuance price							$ 6.30
Preferred Stock, Voting Rights							Preferred Stock are entitled to the number of votes equal to the number of whole shares of Common Stock into which the shares of Preferred Stock are convertible. Except as provided by law or otherwise, the holders of Preferred Stock vote together with the holders of Common Stock as a single class. Certain significant actions must be approved by at least 50% of the holders of 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 Company's Common Stock to the public in an underwritten public offering at a price of $6.30 resulting in at least $40,000,000 of gross proceeds to the Company, 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
Akebia [Member]
Temporary Equity [Line Items]
Conversion of Preferred Stock							1 share of Aerpio's Series A Preferred Stock for every 35 shares of Akebia's Series A Preferred Stock, 1 share of Aerpio's Series A Preferred Stock for every 100 shares of Akebia's Series B Preferred Stock
Conversion of Preferred Stock							1 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							10,468,842	10,476,182
Redeemable convertible preferred stock, par value	$ 0.00001
Stock issued, issuance price	$ 2.10
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	10,476,182						10,876,182	10,476,182
Preferred stock, dividend rate, percentage							6.00%
Preferred stock, liquidation preference per share							$ 2.10
Series A Redeemable Convertible Preferred Stock [Member]
Temporary Equity [Line Items]
Redeemable convertible preferred stock, shares issued							2,892,193	3,094,774	3,094,774
Redeemable convertible preferred stock, par value									$ 0.00001
Redeemable convertible preferred stock, shares issued							3,094,774	3,094,774
Preferred stock, liquidation preference per share							$ 1.83
Series A1 Redeemable Convertible Preferred Stock [Member]
Temporary Equity [Line Items]
Redeemable convertible preferred stock, shares issued		5,882,353		5,294,118	4,705,882	5,882,353	19,345,272	19,528,622
Redeemable convertible preferred stock, par value		$ 0.00001				$ 0.00001
Stock issued, issuance price		$ 1.70		$ 1.70	$ 1.70	$ 1.70
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						3,646,269
Redeemable convertible preferred stock, shares issued							19,528,622	19,528,622
Preferred stock, dividend rate, percentage							6.00%
Preferred stock, liquidation preference per share							$ 1.70

Common Stock (Detail) - USD ($)	1 Months Ended
Common Stock (Detail) - USD ($)	Dec. 31, 2007	Dec. 31, 2016	Dec. 31, 2015
Common Stock (Textual)
Common stock, shares authorized		40,700,000	40,000,000
Common stock, par value		$ 0.00001	$ 0.00001
ZETA ACQUISITION CORP. II [Member]
Common Stock (Textual)
Common stock, shares authorized		100,000,000	100,000,000
Common stock, par value		$ 0.0001	$ 0.0001
ZETA ACQUISITION CORP. II [Member] \| Common Stock [Member]
Common Stock (Textual)
Proceeds from private placement	$ 50,000
ZETA ACQUISITION CORP. II [Member] \| Common Stock [Member] \| Private Placement [Member]
Common Stock (Textual)
Share issued, private placement	5,000,000

Common Stock Reserved for Future issuance (Detail)	Dec. 31, 2016 shares
Class of Stock [Line Items]
Common stock reserved for future issuance	35,433,732
Series A Convertible Preferred Units [Member]
Class of Stock [Line Items]
Common stock reserved for future issuance	2,892,193
Series A1 Redeemable Convertible Preferred Stock [Member]
Class of Stock [Line Items]
Common stock reserved for future issuance	19,345,272
Series A2 Redeemable Convertible Preferred Stock [Member]
Class of Stock [Line Items]
Common stock reserved for future issuance	10,468,842
Unvested Restricted Stock Awards [Member]
Class of Stock [Line Items]
Common stock reserved for future issuance	562,649
Options To Purchase Common Stock [Member]
Class of Stock [Line Items]
Common stock reserved for future issuance	2,164,776

Stock Based Compensation - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation, number of shares authorized	5,860,874
Aggregate intrinsic value of options exercisable		$ 116,924
Weighted average grant date fair value of stock options granted	$ 0.52
Stock options exercised intrinsic value	$ 20,335	5,813
Compensation expense for stock options	180,399	125,926
Unrecognized compensation cost related to stock options	293,796
Company recognized compensation expense for restricted stock	$ 307,927	$ 343,919
Employee Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Option granted vesting period	48 months
Share-based compensation, award vesting description	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.
Option expiry period	10 years
Expected dividend yield	0.00%	0.00%
Weighted average period expected to be recognized	2 years 4 months 24 days
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average period expected to be recognized	1 year 8 months 12 days
Unrecognized compensation cost related to these restricted stock grants	$ 447,617

Stock Option Award Granted Using Black Scholes Option Pricing Model (Detail) - Employee 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%

Stock Option Activities (Detail)	12 Months Ended
Stock Option Activities (Detail)	Dec. 31, 2016 USD ($) $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award, Options Outstanding, Weighted Average Exercise Price, and Additional Disclosures [Abstract]
Number of options, Outstanding at beginning of year \| shares	2,117,852
Number of options, Granted \| shares	117,217
Number of options, Exercised \| shares	(51,043)
Number of option Expired/cancelled \| shares	(19,250)
Number of options, Outstanding at end of year \| shares	2,164,776
Number of options, Expected to vest, end of year \| shares	729,391
Number of options, Exercisable at end of year \| shares	1,435,385
Weighted average exercise price, Outstanding at beginning of year \| $ / shares	$ 0.71
Weighted average exercise price, Granted \| $ / shares	0.77
Weighted average exercise price, Exercised \| $ / shares	0.37
Weighted average exercise price, Expired/cancelled \| $ / shares	0.53
Weighted average exercise price, Outstanding at end of year of year \| $ / shares	0.72
Weighted average exercise price, Expected to vest at end of year \| $ / shares	0.78
Weighted average exercise price, Exercisable at end of year \| $ / shares	$ 0.70
Weighted average remaining contractual term, outstanding	7 years 5 months 23 days
Weighted average remaining contractual term, expected to vest	8 years 7 months 6 days
Weighted average remaining contractual term, options exercisable	6 years 11 months 1 day
Aggregate intrinsic value, outstanding beginning balance \| $	$ 135,711
Aggregate intrinsic value, outstanding ending balance \| $	1,030,217
Aggregate intrinsic value, expected to vest \| $	308,767
Aggregate intrinsic value, options exercisable \| $	$ 721,451

Stock-based compensation - Restricted Stock (Detail) - Restricted Stock [Member]	12 Months Ended
	Dec. 31, 2016 $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Nonvested at beginning of period \| shares	1,036,629
Granted \| shares	0
Vested \| shares	(473,980)
Forfeited \| shares	0
Nonvested at end of period \| shares	562,649
Nonvested Weighted Average Grant Date Fair Value balance at beginning of year \| $ / shares	$ 0.72
Weighted Average Grant Date Fair Value, Granted \| $ / shares	0
Weighted Average Grant Date Fair Value, Vested \| $ / shares	0.66
Weighted Average Grant Date Fair Value, Forfeited \| $ / shares	0
Nonvested Weighted Average Grant Date Fair Value balance at end of year \| $ / shares	$ 0.78

Compensation Cost Related to Employee and Non-employee Stock-based Compensation Activity (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	$ 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	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	$ 170,682	$ 174,542

Income Taxes (Details Textual) (Detail) - USD ($)	12 Months Ended
Income Taxes (Details Textual) (Detail) - USD ($)	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Line Items]
Current income tax expense or benefit	$ 0	$ 0
Deferred income tax expense or benefit	0	0
Income Taxes (Textual)
Increase (decrease) Valuation allowance	6,334,258	6,530,455
Accrued uncertain tax positions	$ 0	$ 0
Effective federal statutory income tax rate, percent	34.00%	34.00%
Federal [Member]
Income Taxes (Textual)
Operating loss carryforwards	$ 66,464,259
Operating loss carryforwards, expiration date	Expire at various dates through 2034
State [Member]
Income Taxes (Textual)
Operating loss carryforwards	$ 66,464,259
Operating loss carryforwards, expiration date	Expire at various dates through 2019
Research and Development [Member] \| Federal [Member]
Income Taxes (Textual)
Tax credit carryforwards	$ 2,670,688
Tax credit carryforwards, expiration date	Expire at various dates through 2034
ZETA ACQUISITION CORP. II [Member]
Income Taxes (Textual)
Operating loss carryforwards	$ 42,400
Operating loss carryforwards, expiration date	Begin to expire in 2029
Effective federal statutory income tax rate, percent	34.00%	34.00%

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]
Statutory Federal income tax 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 asset:
Net operating loss carryforward	$ 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
ZETA ACQUISITION CORP. II [Member]
Deferred tax asset:
Capitalized formation costs	79,400	69,400
Net operating loss carryforward	14,400	11,000
Deferred tax liabilities:
Less valuation allowance	(93,800)	(80,400)
Net deferred tax asset	$ 0	$ 0

Schedule of Computation of Basic and Diluted Net Loss per Share (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Earnings Per Share [Abstract]
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	$ (10.51)	$ (13.52)
Weighted average common shares used in computing net loss per share attributable to common stockholders, basic and diluted	1,989,863	1,288,631

Schedule of Weighted Average Common Stock Equivalents were Excluded from Calculation of Diluted Net Loss per Share (Detail) - shares	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Convertible Preferred 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	32,706,307	33,099,578
Options 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	1,435,385	989,845
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	6,164,595

Commitments and Contingencies - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2016 USD ($) ft²	Dec. 31, 2015 USD ($)
Commitments and Contingencies Disclosure [Abstract]
Area of lease space \| ft²	7,580
Rent expense for operating leases	$ 214,595	$ 160,221
Reimbursement for tenant improvements	46,390
Deferred rent	49,209	$ 8,486
Non-cancelable future minimum lease payments	157,418
Future payments related to other operating commitments	$ 2,761,501

Future Payments Related to Operating Commitments (Detail)	Dec. 31, 2016 USD ($)
Contractual Obligation, Fiscal Year Maturity [Abstract]
2017	$ 104,440
2018	52,978
Total	157,418
2017	2,761,501
Total	2,761,501
2017	2,865,941
2018	52,978
Total	$ 2,918,919

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 ($)	Dec. 31, 2016	Dec. 31, 2015
Deferred Compensation Arrangements [Abstract]
Amount of bonus accrued	$ 0	$ 380,020

Subsequent Events - Additional Information (Detail) - USD ($)		1 Months Ended
	Mar. 15, 2017	Dec. 31, 2007	Feb. 28, 2017	Dec. 31, 2016
Subsequent Event [Line Items]
Stock issued, issuance price				$ 6.30
ZETA ACQUISITION CORP. II [Member] \| Common Stock [Member]
Subsequent Event [Line Items]
Proceeds from private placement		$ 50,000
ZETA ACQUISITION CORP. II [Member] \| Common Stock [Member] \| Private Placement [Member]
Subsequent Event [Line Items]
Share issued, private placement		5,000,000
Subsequent Event [Member] \| ZETA ACQUISITION CORP. II [Member]
Subsequent Event [Line Items]
Common stock conversion basis	2.3336572:1 basis
Subsequent Event [Member] \| ZETA ACQUISITION CORP. II [Member] \| Common Stock [Member]
Subsequent Event [Line Items]
Proceeds from private placement	$ 37,200,000
Subsequent Event [Member] \| ZETA ACQUISITION CORP. II [Member] \| Common Stock [Member] \| Private Placement [Member]
Subsequent Event [Line Items]
Share issued, value private placement	$ 40,250,000
Share issued, private placement	8,049,555
Stock issued, issuance price	$ 5
Subsequent Event [Member] \| Senior secured convertible note [Member] \| February Convertible Notes [Member]
Subsequent Event [Line Items]
Debt instrument amount			$ 297,355

Notes Payable, Stockholders (Detail) - USD ($)	12 Months Ended
Notes Payable, Stockholders (Detail) - USD ($)	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2010	Dec. 31, 2009
Notes Payable, Stockholders (Textual)
Accrued interest on unsecured promissory note	$ 483,442
ZETA ACQUISITION CORP. II [Member]
Notes Payable, Stockholders (Textual)
Proceeds from issuance of unsecured promissory note	$ 10,000	$ 35,000	$ 15,000	$ 25,000	$ 25,000	$ 35,000	$ 25,000
Interest rate on unsecured promissory note	6.00%
Accrued interest on unsecured promissory note	$ 42,378	$ 32,436

Preferred Stock (Detail) - shares	Dec. 31, 2016	Dec. 31, 2015
ZETA ACQUISITION CORP. II [Member]
Preferred Stock (Textual)
Preferred stock, shares authorized	10,000,000	10,000,000

Income Taxes (Details 1) (Detail) - ZETA ACQUISITION CORP. II [Member] - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Income Tax Reconciliation [Line Items]
US federal income tax benefit at statutory rate	$ (13,400)	$ (10,700)
Other		100
Change in valuation allowance	13,400	10,600
Benefit from income taxes	$ 0	$ 0