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Document and Entity Information - shares	6 Months Ended
Document and Entity Information - shares	Jun. 30, 2019	Aug. 06, 2019
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Document Period End Date	Jun. 30, 2019
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q2
Trading Symbol	ARPO
Entity Filer Category	Accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	true
Entity Ex Transition Period	true
Entity Registrant Name	Aerpio Pharmaceuticals, Inc.
Entity Central Index Key	0001422142
Entity Common Stock, Shares Outstanding		40,588,004
Entity Shell Company	false
Entity Current Reporting Status	Yes
Entity File Number	001-38560
Entity Tax Identification Number	611547850
Entity Address, Address Line One	9987 Carver Road
Entity Address, City or Town	Cincinnati
Entity Address, State or Province	OH
Entity Address, Postal Zip Code	45242
City Area Code	513
Local Phone Number	985-1920

Condensed Consolidated Balance Sheets (Unaudited) - USD ($)	Jun. 30, 2019	Dec. 31, 2018
Current assets:
Cash and cash equivalents	$ 48,157,010	$ 62,614,010
Prepaid research and development contracts	368,048	754,392
Other current assets	264,305	615,681
Total current assets	48,789,363	63,984,083
Furniture and equipment, net	297,618	98,449
Operating lease right-of-use assets, net	472,135
Deposits	40,960	40,960
Total assets	49,600,076	64,123,492
Current liabilities:
Accounts payable and accrued expenses	3,402,257	5,456,917
Current portion of operating lease liability	193,284
Total current liabilities	3,595,541	5,456,917
Operating lease liability, net of current portion	288,055
Total liabilities	3,883,596	5,456,917
Commitments and contingencies (Note 9)
Stockholders’ equity:
Common stock, $0.0001 par value per share; 300,000,000 shares authorized and 40,588,004 shares issued and outstanding at June 30, 2019 and December 31, 2018.	4,059	4,059
Additional paid-in capital	178,853,870	177,621,807
Accumulated deficit	(133,141,449)	(118,959,291)
Total stockholders’ equity	45,716,480	58,666,575
Total liabilities and stockholders’ equity	$ 49,600,076	$ 64,123,492

Condensed Consolidated Balance Sheets (Parenthetical) (Unaudited) - $ / shares	Jun. 30, 2019	Dec. 31, 2018
Statement Of Financial Position [Abstract]
Common stock, par value	$ 0.0001	$ 0.0001
Common stock, shares authorized	300,000,000	300,000,000
Common stock, shares issued	40,588,004	40,588,004
Common stock, shares outstanding	40,588,004	40,588,004

Condensed Consolidated Statements of Operations and Comprehensive Loss (unaudited) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Income Statement [Abstract]
License revenue, and other		$ 1,333,333		$ 1,333,333
Type of Revenue [Extensible List]		arpo:LicenseRevenueAndOtherMember		arpo:LicenseRevenueAndOtherMember
Operating expenses
Research and development	$ 2,264,255	$ 4,228,934	$ 7,850,506	$ 8,257,746
General and administrative	2,799,570	3,140,854	6,054,612	6,588,690
Restructuring expense	915,094		915,094
Total operating expenses	5,978,919	7,369,788	14,820,212	14,846,436
Loss from operations	(5,978,919)	(6,036,455)	(14,820,212)	(13,513,103)
Grant income	4,924		20,272
Interest income	290,379	46,464	623,499	97,580
Total other income	295,303	46,464	643,771	97,580
Net and comprehensive loss	$ (5,683,616)	$ (5,989,991)	$ (14,176,441)	$ (13,415,523)
Net and comprehensive loss per share
Basic and diluted	$ (0.14)	$ (0.22)	$ (0.35)	$ (0.49)
Weighted average number of common shares used in computing net and comprehensive loss per share, basic and diluted	40,588,004	27,340,914	40,588,004	27,194,028

Condensed Consolidated Statements of Stockholders' Equity (Unaudited) - USD ($)	Total	Common Stock [Member]	Additional Paid-In Capital [Member]	Accumulated Deficit [Member]
Balance at Dec. 31, 2017	$ 17,435,489	$ 2,707	$ 125,995,438	$ (108,562,656)
Balance, Shares at Dec. 31, 2017		27,070,038
Issuance of restricted stock		$ 6	(6)
Issuance of restricted stock, Shares		60,000
Issuance of common stock upon exercise of stock options	21,992	$ 2	21,990
Issuance of common stock upon exercise of stock options, Shares		16,802
Forfeiture of restricted stock, Shares		(741)
Stock-based compensation expense	1,079,721		1,079,721
Net and comprehensive loss	(7,425,532)			(7,425,532)
Balance at Mar. 31, 2018	11,111,670	$ 2,715	127,097,143	(115,988,188)
Balance, Shares at Mar. 31, 2018		27,146,099
Balance at Dec. 31, 2017	17,435,489	$ 2,707	125,995,438	(108,562,656)
Balance, Shares at Dec. 31, 2017		27,070,038
Net and comprehensive loss	(13,415,523)
Balance at Jun. 30, 2018	47,906,408	$ 3,884	169,880,703	(121,978,179)
Balance, Shares at Jun. 30, 2018		38,833,507
Balance at Mar. 31, 2018	11,111,670	$ 2,715	127,097,143	(115,988,188)
Balance, Shares at Mar. 31, 2018		27,146,099
Issuance of common stock upon exercise of stock options	1,660		1,660
Issuance of common stock upon exercise of stock options, Shares		1,000
Issuance of common stock,net of issuance costs	41,905,312	$ 1,169	41,904,143
Issuance of common stock, net of issuance costs, Shares		11,688,000
Forfeiture of restricted stock, Shares		(1,592)
Stock-based compensation expense	877,757		877,757
Net and comprehensive loss	(5,989,991)			(5,989,991)
Balance at Jun. 30, 2018	47,906,408	$ 3,884	169,880,703	(121,978,179)
Balance, Shares at Jun. 30, 2018		38,833,507
Balance at Dec. 31, 2018	58,666,575	$ 4,059	177,621,807	(118,959,291)
Balance, Shares at Dec. 31, 2018		40,588,004
Cumulative effect of change in accounting principle			5,717	(5,717)
Stock-based compensation expense	621,685		621,685
Net and comprehensive loss	(8,492,825)			(8,492,825)
Balance at Mar. 31, 2019	50,795,435	$ 4,059	178,249,209	(127,457,833)
Balance, Shares at Mar. 31, 2019		40,588,004
Balance at Dec. 31, 2018	58,666,575	$ 4,059	177,621,807	(118,959,291)
Balance, Shares at Dec. 31, 2018		40,588,004
Net and comprehensive loss	(14,176,441)
Balance at Jun. 30, 2019	45,716,480	$ 4,059	178,853,870	(133,141,449)
Balance, Shares at Jun. 30, 2019		40,588,004
Balance at Mar. 31, 2019	50,795,435	$ 4,059	178,249,209	(127,457,833)
Balance, Shares at Mar. 31, 2019		40,588,004
Stock-based compensation expense	604,661		604,661
Net and comprehensive loss	(5,683,616)			(5,683,616)
Balance at Jun. 30, 2019	$ 45,716,480	$ 4,059	$ 178,853,870	$ (133,141,449)
Balance, Shares at Jun. 30, 2019		40,588,004

Condensed Consolidated Statements of Stockholders' Equity (Parenthetical) (Unaudited) - USD ($)	3 Months Ended	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2018
Statement Of Stockholders Equity [Abstract]
Payments of stock issuance cost	$ 3,093,489	$ 3,093,489

Condensed Consolidated Statements of Cash Flows (unaudited) - USD ($)	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
Operating activities:
Net and comprehensive loss	$ (14,176,441)	$ (13,415,523)
Adjustments to reconcile net and comprehensive loss to net cash used in (provided by) operating activities:
Depreciation	33,503	23,665
Stock-based compensation	1,226,346	1,957,478
Changes in operating assets and liabilities:
Prepaid research and development contracts	386,344	(115,705)
Other current assets	351,376	108,760
Accounts payable and other current liabilities	(2,045,456)	(626,707)
Deferred revenue		18,666,667
Net cash (used in) provided by operating activities	(14,224,328)	6,598,635
Investing activities:
Purchase of furniture and equipment	(232,672)	(8,498)
Net cash used in investing activities	(232,672)	(8,498)
Financing activities:
Proceeds from exercise of stock options		23,652
Proceeds from issuance of common stock		44,998,801
Cash paid in connection with the sale of common stock		(3,093,489)
Net cash provided by financing activities		41,928,964
Net (decrease) increase in cash and cash equivalents	(14,457,000)	48,519,101
Cash and cash equivalents at beginning of year	62,614,010	20,264,109
Cash and cash equivalents, six months ended	$ 48,157,010	$ 68,783,210

Nature of Organization and Operations

6 Months Ended

Jun. 30, 2019

Organization Consolidation And Presentation Of Financial Statements [Abstract]

Nature of Organization and Operations

1. Nature of Organization and Operations

Aerpio Pharmaceuticals, Inc. (the “Company”) is a biopharmaceutical company focused on developing compounds that activate Tie2 to treat ocular diseases and complications of diabetes. In March 2019, the Company announced the top line results of its AKB-9778 Phase 2b (TIME-2b) clinical trial initiated in June 2017 for the treatment of non-proliferative diabetic retinopathy, or NPDR, a disease characterized by progressive compromise of blood vessels in the back of the eye. While the Company believed AKB-9778 had the potential to slow down or possibly reverse retinal vascular changes caused by diabetes, the subcutaneous administration of AKB-9778 twice daily did not meet the study’s primary endpoint of increasing the percentage of patients with an improvement of two or more steps in diabetic retinopathy severity score in the study eye, compared to placebo. However, the Company did see encouraging data in a number of prespecified, key secondary endpoints related to the changes in the Urine Albumin-Creatinine Ratio, a measure of kidney function, and in reducing intraocular pressure. As a result, the Company plans to advance a topical drop formulation of AKB-9778 into clinical development as a potential treatment for open-angle glaucoma and initiated a Phase 1b clinical trial in the second quarter of 2019 with results anticipated by the end of 2019.

In addition, the Company’s pipeline program, ARP-1536, a humanized monoclonal antibody directed at the same target as AKB-9778 is in preclinical development. The Company is evaluating development options for ARP-1536, including subcutaneous injection for the treatment of diabetic vascular complications.

The Company was incorporated as Zeta Acquisition Corp. II (“Zeta”) in the State of Delaware on November 16, 2007. Zeta was a “shell company” (as defined in Rule 12b-2 of the Securities Exchange Act of 1934, as amended). On March 3, 2017, the Company’s Board of Directors, and on March 10, 2017, the Company’s pre-Merger (as defined below) stockholders, approved an amended and restated certificate of incorporation, which, among other things, increased authorized capital stock from 100,000,000 shares of common stock, par value $0.0001 per share, and 10,000,000 shares of preferred stock, par value $0.0001 per share, to 300,000,000 shares of common stock, par value $0.0001 per share, and 10,000,000 shares of preferred stock, par value $0.0001 per share.

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

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

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

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

The Merger was treated as a recapitalization and reverse acquisition for financial reporting purposes. The Company is the legal acquirer of Aerpio in the transaction. However, Aerpio is considered the acquiring company for accounting purposes since (i) former Aerpio stockholders own in excess of 50% of the combined enterprise on a fully diluted basis immediately following the Merger and 2017 Offering, and (ii) all members of the Company’s executive management and Board of Directors are from Aerpio. In accordance with “reverse merger” or “reverse acquisition” accounting treatment, the unaudited condensed consolidated financial statements for the periods ended June 30, 2019 and 2018, include the accounts of the Company and its wholly owned subsidiary, Aerpio Therapeutics, LLC.

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’s revenue to date has been primarily limited to license revenue from Gossamer Bio., Inc, during 2018. Future revenue is dependent on the terms of the license agreement with Gossamer Bio., Inc as further described in Note 11. 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.

The Company’s inability to obtain required funding in the near future could have a material adverse effect on its operations and strategic development plan for future growth. If the Company cannot successfully raise additional capital and implement its strategic development plan, its liquidity, financial condition and business prospects will be materially and adversely affected, and the Company may have to cease operations. Based on the Company’s current cash reserves of $48.2 million at June 30, 2019 and financial condition as of this Quarterly Report on Form 10-Q, we believe our existing cash and cash equivalent will be sufficient to fund currently planned operations at least through the second quarter of 2021.

Summary of Significant Accounting Policies

6 Months Ended

Jun. 30, 2019

Accounting Policies [Abstract]

Summary of Significant Accounting Policies

2. Summary of Significant Accounting Policies

Basis of Presentation

The unaudited condensed consolidated financial statements have been prepared in accordance with U.S. Securities and Exchange Commission (“SEC”) regulations and include all of the information and disclosures required by U.S. generally accepted accounting principles ("U.S. GAAP" or "GAAP") for interim financial reporting, and, in the opinion of management include all adjustments necessary for a fair presentation of the results of operations, financial position, changes in stockholders’ equity and cash flows for each period presented. All adjustments are of a normal and recurring in nature. These unaudited condensed consolidated financial statements should be read in conjunction with the consolidated financial statements of the Company for the year ended December 31, 2018, included in the Annual Report on Form 10-K filed with the SEC on March 7, 2019. The results of operations for the interim periods are not necessarily indicative of results of operations for a full year. The Company’s condensed consolidated financial statements are stated in U.S. Dollars.

Segment Information

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

Use of Estimates

The preparation of condensed consolidated 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 condensed consolidated financial statements and the reported amounts of revenue 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 used in the preparation of these condensed consolidated financial statements. Management must apply significant judgment in this process. In addition, other factors may affect estimates, including expected business and operational changes, sensitivity and volatility associated with the assumptions used in developing estimates, and whether historical trends are expected to be representative of future trends. The estimation process often may yield a range of potentially reasonable estimates of the ultimate future outcomes, and management must select an amount that falls within that range of reasonable estimates. Estimates are used in the following areas, among others: grant date fair value of the Company’s stock-based awards, accrued expenses, revenue recognition and income taxes.

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 original maturities of three months or less at the time of purchase. The Company does maintain balances with its banks in excess of federally insured limits.

Revenue Recognition

At the inception of an arrangement, the Company evaluates if a counterparty to a contract is a customer, if the arrangement is within the scope of revenue from contracts with customers guidance and the term of the contract. The Company recognizes revenue when its customer obtains control of promised goods or services in a contract for an amount that reflects the consideration the Company expects to receive in exchange for those goods or services. For contracts with customers, the Company applies the following five-step model in order to determine this amount: (i) identification of the promised goods or services in the contract; (ii) determination of whether the promised goods or services are performance obligations, including whether they are distinct in the context of the contract; (iii) measurement of the transaction price, including the constraint on variable consideration; (iv) allocation of the transaction price to the performance obligations; and (v) recognition of revenue when (or as) the Company satisfies each performance obligation. The Company only applies the five-step model to contracts when it is probable that the entity will collect the consideration it is entitled to in exchange for the goods or services it transfers to the customer. As part of the accounting for contracts with customers, the Company must develop assumptions that require judgment to determine the standalone selling price of each performance obligation identified in the contract. The Company then allocates the total transaction price to each performance obligation based on the estimated standalone selling prices of each performance obligation. The Company recognizes the amount of the transaction price as revenue that is allocated to the respective performance obligation when the performance obligation is satisfied or as it is satisfied.

The Company enters into collaboration arrangements, under which it licenses certain rights to its intellectual property to third parties. The terms of these agreements may include payment to the Company of one or more of the following: nonrefundable upfront license fees; development, sale and commercial milestone payments and royalties on net sales of licensed products. Each of these types of payments are classified as license revenue except for revenue from royalties on net sales of licensed products, which are classified as royalty revenue.

For each collaboration agreement that results in revenues, the Company identifies all material promised goods and services, which may include a license to intellectual property, research and development activities and/or transition activities. Promised goods or services are considered to be separate performance obligations if they are distinct. In order to determine the transaction price to be allocated to each performance obligation, in addition to any upfront payment, the Company estimates the amount of variable consideration at the outset of the contract either utilizing the expected value or most likely amount method, depending on the facts and circumstances relative to the contract. The Company constrains (reduces) the estimates of variable consideration such that it is probable that a significant reversal of previously recognized revenue will not occur throughout the life of the contract. When determining if variable consideration should be constrained, management considers whether there are factors outside the Company’s control that could result in a significant reversal of revenue. In making these assessments, the Company considers the likelihood and magnitude of a potential reversal of revenue. These estimates are re-assessed each reporting period as required.

Once the estimated transaction price is established, amounts are allocated to the performance obligations that have been identified. The transaction price is generally allocated to each separate performance obligation on a relative standalone selling price basis. The Company must develop assumptions that require judgment to determine the standalone selling price (SSP) in order to account for these agreements. To determine the standalone selling price the Company’s assumptions may include (i) assumptions regarding the probability of obtaining marketing approval for the drug candidate; (ii) estimates regarding the timing of and the expected costs to develop and commercialize the drug candidate; (iii) estimates of future cash flows from potential product sales with respect to the drug candidate; and (iv) appropriate discount and tax rates. Standalone selling prices used to perform the initial allocation are not updated after contract inception. The Company does not include a financing component to its estimated transaction price at contract inception unless it estimates that certain performance obligations will not be satisfied within one year.

Upfront License Fees: If a license to the Company’s intellectual property is determined to be distinct from the other performance obligations identified in the arrangement, the Company recognizes revenues from nonrefundable, upfront license fees based on the relative value prescribed to the license compared to the total value of the arrangement. The revenue is recognized when the license is transferred to the collaborator and the collaborator is able to use and benefit from the license. For licenses that are not distinct from other obligations identified in the arrangement, the Company utilizes judgment to assess the nature of the combined performance obligation to determine whether the combined performance obligation is satisfied over time or at a point in time. If the combined performance obligation is satisfied over time, the Company applies an appropriate method of measuring progress for purposes of recognizing revenue from nonrefundable, upfront license fees. The Company evaluates the measure of progress each reporting period and, if necessary, adjusts the measure of performance and related revenue recognition.

Development Milestone Payments: Depending on facts and circumstances, the Company may conclude it is appropriate to include the milestone in the estimated transaction price using the most likely amount method or it is appropriate to fully constrain the milestone. A milestone payment is included in the transaction price in the reporting period the Company concludes that it is probable that recording revenue in the period will not result in a significant reversal in amounts recognized in future periods. The Company may record revenues from certain milestones in a reporting period before the milestone is achieved if the Company concludes that achievement of the milestone is probable and that recognition of revenue related to the milestone will not result in a significant reversal in amounts recognized in future periods. The Company records a corresponding contract asset when this conclusion is reached. Milestone payments that have not been included in the transaction price to date are fully constrained. These milestones remain fully constrained until the Company concludes that achievement of the milestone is probable and recognition of revenue related to the milestone will not result in a significant reversal in amounts recognized in future periods. The Company re-evaluates the probability of achievement of such development milestones and any related constraint each reporting period. The Company adjusts its estimate of the overall transaction price, including the amount of collaborative revenue that it has recorded, if necessary.

Sales-based Milestone and Royalty Payments: The Company’s collaborators may be required to pay the Company sales-based milestone payments or royalties on future sales of commercial products. The Company recognizes revenues related to sales-based milestone and royalty payments upon the later to occur of (i) achievement of the collaborator’s underlying sales or (ii) satisfaction of any performance obligation(s) related to these sales, in each case assuming the license to the Company’s intellectual property is deemed to be the predominant item to which the sales-based milestones and/or royalties relate.

Grant Income

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

Research and Development

Costs incurred in connection with research and development activities are expensed as incurred. Research and development expense consists of (i) employee-related expenses, including salaries, benefits, travel and stock-based compensation expense, (ii) external research and development expenses incurred under arrangements with third parties, such as contract research organizations and consultants, (iii) the cost of acquiring, developing and manufacturing clinical study materials, and (iv) 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 Accounting Standards Codification (ASC) Topic 740, Income Taxes, or ASC 740, 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 condensed consolidated financial statements or tax returns. Deferred tax assets and liabilities are determined based on the difference between the condensed consolidated 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 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 June 30, 2019 and December 31, 2018, the Company does not have any uncertain tax positions. The Company recognizes interest and penalties related to uncertain tax positions, if any exist, in income tax expense.

Net and Comprehensive Loss per Share

The Company’s basic net and comprehensive loss per share is calculated by dividing the net and comprehensive loss by the weighted average number of shares of common stock outstanding for the period. The diluted net and comprehensive loss per share attributable to common stockholders is computed by adjusting the weighted average shares outstanding for the dilutive effect of common stock equivalents outstanding for the period, determined using the treasury stock method.

Stock-Based Compensation

The Company accounts for its stock-based compensation awards in accordance with ASC Topic 718, Compensation – Stock Compensation, or ASC 718. ASC 718 requires all stock-based payments to employees, including grants of employee stock options, to be recognized in the condensed consolidated statements of operations and comprehensive net loss based on their fair values. All the Company’s stock-based awards are subject only to service-based vesting conditions. The Company estimates the fair value of its stock-based awards using the Black-Scholes option pricing model, which requires the input of 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.

Due to the historical lack of significant trading on a public market 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 SEC 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.

Fair Value of Financial Instruments

The Company’s financial instruments consist of cash and cash equivalents, accounts payable and accrued expenses. The Company values cash equivalents using quoted market prices. The fair value of accounts payable and accrued expenses approximates its carrying value because of its 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. ASC Topic 820, Fair Value Measurements and Disclosures, or ASC 820, 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 during the six months ended June 30, 2019 or 2018. The assets of the Company measured at fair value on a recurring basis as of June 30, 2019 and December 31, 2018, are summarized below:

	Fair Value Measurements Using
	Level 1		Level 2		Level 3		Total
June 30, 2019
Assets:
Cash and cash equivalents	$	48,157,010	$	—	$	—	$	48,157,010
Total assets	$	48,157,010	$	—	$	—	$	48,157,010
December 31, 2018
Assets:
Cash and cash equivalents	$	62,614,010	$	—	$	—	$	62,614,010
Total assets	$	62,614,010	$	—	$	—	$	62,614,010

Concentrations of Credit Risk and Off-Balance Sheet Risk

Cash and cash equivalents are the only financial instruments that potentially subject the Company to concentrations of credit risk. At June 30, 2019 and December 31, 2018, the Company maintains its cash and cash equivalents with high-quality, accredited financial institutions 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 furniture 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).

Leases

At the inception of an arrangement the Company determines whether the arrangement is or contains a lease based on the circumstances present. All leases with a term greater than one year are recognized on the condensed consolidated balance sheet as right-of-use assets, lease liabilities and, if applicable, long-term lease liabilities. The Company has elected not to recognize on the condensed consolidated balance sheet leases with terms of one-year or less if entered into. Lease liabilities and their corresponding right-of-use assets are recorded based on the present value of lease payments over the expected lease term. The interest rate implicit in lease contracts is typically not readily determinable. As such, the Company utilizes the appropriate incremental borrowing rate, which is the rate incurred to borrow on a collateralized basis over a similar term an amount equal to the lease payments in a similar economic environment. Certain adjustments to the right-of-use asset may be required for items such as initial direct costs paid or incentives received.

Recent Accounting Pronouncements

From time to time, new accounting pronouncements are issued by the Financial Accounting Standards Board (“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 condensed consolidated financial position or results of operations upon adoption.

In May 2014, the FASB issued amended guidance for revenue recognition, Accounting Standards Update (“ASU”) 2014-09, “Revenue from Contracts with Customers (Topic 606).” This ASU outlines a single comprehensive model for entities to use in accounting for revenue arising from contracts with customers. The core principle of the guidance is that an entity should recognize revenue for the transfer of promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods and services. Additionally, the ASU requires improved disclosure to help users of financial statements better understand the nature, amount, timing and uncertainty of revenue that is recognized. The Company adopted the new guidance on January 1, 2018, as it relates to the Agreement discussed in Note 11.

In February 2016, the FASB issued ASU No. 2016-02, Leases, to enhance the transparency and comparability of financial reporting related to leasing arrangements. Under this new lease standard, leases are required to be recognized on the balance sheet as right-of-use assets and operating lease liabilities. Disclosure requirements have been enhanced with the objective of enabling financial statement users to assess the amount, timing, and uncertainty of cash flows arising from leases. The Company adopted the new guidance on January 1, 2019. See additional discussion in Note 9.

In July 2018, the FASB issued ASU 2018-11, Leases, Targeted Improvements, (“ASU 2018-11”), which contains certain amendments to ASU 2016-02 intended to provide relief in implementing the new standard. ASU 2018-11 provides registrants with an option to not restate comparative periods presented in the financial statements. The Company adopted this new standard on January 1, 2019 (the “adoption date”) using a cumulative-effect adjustment on the effective date of the standard, for which comparative periods are presented in accordance with the previous guidance in ASC 840, Leases. In adopting the new standard, the Company elected to utilize the available package of practical expedients permitted under the transition guidance within the new standard The expedients used by the Company are as follows: (1) allowing an entity to not reassess the lease classification for any expired or existing leases, (2) allowing an entity to not reassess the treatment of initial direct costs as they related to existing leases, and (3) allowing an entity to not reassess whether expired or existing contracts are or contain leases. Additionally, the Company made an accounting policy election to keep leases with a term of 12 months or less off of its condensed consolidated balance sheet. The Company adopted the new guidance on January 1, 2019. See additional discussion in Note 9

In June 2018, the FASB issued ASU 2018-07, “Improvements to Nonemployee Share-Based Payment Accounting.” This ASU improves financial reporting for share-based payments issued to nonemployees under ASC 718 by expanding the scope of the employee share-based payments guidance to include share-based payments issued to nonemployees. The amendments in this ASU are effective for public companies for fiscal years beginning after December 31, 2018, including interim periods within that fiscal year. The Company adopted this ASU as of January 1, 2019 and recorded a one-time cumulative adjustment of $5,717 upon adoption.

No other new accounting pronouncement recently issued or newly effective had or is expected to have a material impact on the Company’s condensed consolidated financial statements.

Accounts Payable and Accrued Expenses

6 Months Ended

Jun. 30, 2019

Payables And Accruals [Abstract]

Accounts Payable and Accrued Expenses

3. Accounts Payable and Accrued Expenses

Accounts payable and accrued expenses are as follows:

	June 30,		December 31,
	2019		2018
Accounts payable	$	511,190	$	595,680
Restructuring accrual (see Note 12)		591,827		—
Professional fees		264,571		487,923
Accrued bonus		451,644		1,877,455
Accrued retention bonus		157,716		—
Accrued vacation		88,945		90,663
Accrued project costs		1,306,752		2,232,014
Other		29,612		173,182
Total accounts payable and accrued expenses	$	3,402,257	$	5,456,917

Common Stock

6 Months Ended

Jun. 30, 2019

Equity [Abstract]

Common Stock

4. Common Stock

As of June 30, 2019 and December 31, 2018, the Company had 300,000,000 shares of authorized common stock with par value of $0.0001 per share.

The common stock has the following characteristics:

Voting

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

Dividends

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

Liquidation

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

Warrants to Purchase Common Stock

At June 30, 2019 and December 31, 2018, the Company had warrants outstanding for the purchase of 317,562 shares of the Company’s common stock at an exercise price of $5.00 per share. The warrants have a three-year term and expire on March 15, 2020. At the expiration date of the warrant, if the fair value of the Company’s common stock exceeds the exercise price, the warrant will be automatically exercised and the exercise price will be fulfilled through the net share settlement provisions. The number of shares and the exercise price shall be adjusted for standard anti-dilution events such as stock splits, combinations, reorganizations, or issue shares as part of a stock dividend. Upon a change of control, the warrant holder will have the right to receive securities, cash or other properties it would have been entitled to receive had the warrant been exercised. The warrants are equity classified instruments and do not contain contingent exercise provisions, or other features, that would preclude the Company from concluding that the warrants are indexed solely to the Company’s common stock.

Preferred Stock

6 Months Ended

Jun. 30, 2019

Equity [Abstract]

Preferred Stock

5. Preferred Stock

As of June 30, 2019 and December 31, 2018, the Company had 10,000,000 shares of preferred stock, par value $0.0001 per share, in authorized capital. No preferred stock was issued and outstanding at June 30, 2019 and December 31, 2018.

Stock-Based Compensation

6 Months Ended

Jun. 30, 2019

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Stock-Based Compensation

6. Stock-Based Compensation

In March 2017, the Company’s Board of Directors adopted, and the stockholders approved, the 2017 Stock Option and Incentive Plan (the “2017 Plan”), that became effective in April 2017. The 2017 Plan provides for the issuance of incentive awards up to 4,600,000 shares of common stock to officers, employees, consultants and directors, less the number of shares subject to issued and outstanding awards under the 2011 Plan that were assumed in the Merger. The 2017 Plan also provides that the number of shares reserved for issuance thereunder will be increased annually on the first day of each year beginning in 2018 by four percent (4%) of the shares of our common stock outstanding on the last day of the immediately preceding year or such smaller increase as determined by our Board of Directors. In March 2019, the Company’s Board of Directors approved a 4% increase, adding 1,623,520 shares to the 2017 Plan, which was effective as of January 1, 2019.

Stock Options

The options granted generally vest over 48 months. Under the 2017 Plan, options vest in installments of 25% at the one-year anniversary and thereafter in 36 equal monthly installments beginning on the 1^st of the month after the one-year anniversary date, subject to the employee’s continuous service with the Company. In May 2019, the Company issued a special retention grant of options to purchase an aggregate of 2,419,050 shares of common stock which vest in installments of 50% at June 30, 2020 and 50% at June 30, 2021, subject to the employee’s continuous service with the Company. The options generally expire ten years after the date of grant. The fair value of the options at the date of grant is recognized as an expense over the requisite service period. During the three months ended June 30, 2019 and 2018, option awards to purchase an aggregate of 2,801,600 and 1,515,200 shares of common stock were granted, respectively, and option awards to purchase an aggregate of 4,622,428 and 1,515,200 shares of common stock were granted in the six months ended June 30, 2019 and 2018, respectively.

As of June 30, 2019 and December 31, 2018, 969,529 and 2,959,562 shares are reserved for issuance under the 2017 Plan, respectively.

The following table summarizes the stock option activity during the six months ended June 30, 2019:

	Stock Option Shares			Weighted Average Exercise Price		Weighted Average Remaining Contractual Term (in Years)		Aggregate Intrinsic Value
Outstanding, January 1, 2019		3,351,132		$	3.73		8.24	$	142,788
Granted		4,622,428			1.86
Exercised		—			—
Expired/cancelled		(1,201,753	)		2.80
Outstanding, June 30, 2019		6,771,807		$	2.62		8.65	$	17,133
Expected to vest, June 30, 2019		5,183,231		$	2.37	9.35		$	—
Options exercisable, June 30, 2019		1,588,576		$	3.43		6.37	$	17,133

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

Compensation expense for stock options was $604,661 and $822,850 for the three months ended June 30, 2019 and 2018, respectively, and $1,226,346 and $1,554,223 for the six months ended June 30, 2019 and 2018, respectively. As of June 30, 2019, there was $5,956,838 of unrecognized compensation cost related to stock options, which is expected to be recognized over a weighted average period of 2.60.

Restricted Stock

The Company recognized compensation expense for restricted stock of $0 and $54,907 for the three months ended June 30, 2019 and 2018, respectively, and $0 and $403,255 for the six months ended June 30, 2019 and 2018. All restricted stock vested in October 2018.

Compensation Expense Summary

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

	Three Months Ended June 30,				Six Months Ended June 30,
	2019		2018		2019		2018
Research and development	$	73,463	$	114,949	$	232,794	$	174,013
General and administrative		531,198		762,808		993,552		1,783,465
Total	$	604,661	$	877,757	$	1,226,346	$	1,957,478

The Company uses the Black-Scholes option pricing model to determine the estimated fair value for stock-based awards. Option pricing and models require the input of various assumptions, including the option’s expected life, expected dividend yield, price volatility and risk-free interest rate of the underlying stock. Accordingly, the weighted-average fair value of the options granted during the three months ended June 30, 2019 was $0.62 per share, and $1.11 per share for the six months ended June 30, 2019. The calculation was based on the following assumptions.

	Three Months Ended	Six Months Ended
	June 30, 2019	June 30, 2019
Expected term (years)	5.82	5.77
Risk-free interest rate	2.21%	2.32%
Expected volatility	65.97%	65.83%
Expected dividend yield	0.00%	0.00%

Income Taxes

6 Months Ended

Jun. 30, 2019

Income Tax Disclosure [Abstract]

Income Taxes

7. Income Taxes

The Company did not record a current or deferred income tax expense or benefit for the three and six months ended June 30, 2019 and 2018, due to the Company’s net losses and increases in its deferred tax asset valuation allowance.

Net and Comprehensive Loss Per Share

6 Months Ended

Jun. 30, 2019

Earnings Per Share [Abstract]

Net and Comprehensive Loss Per Share

8. Net and Comprehensive Loss per Share

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

	Three Months Ended June 30,						Six Months Ended June 30,
	2019			2018			2019			2018
Net and comprehensive loss attributable to common stockholders	$	(5,683,616	)	$	(5,989,991	)	$	(14,176,441	)	$	(13,415,523	)
Weighted average common shares used in computing net and comprehensive loss per share attributable to common stockholders, basic and diluted		40,588,004			27,340,914			40,588,004			27,194,028
Net and comprehensive loss per share attributable to common stockholders, basic and diluted	$	(0.14	)	$	(0.22	)	$	(0.35	)	$	(0.49	)

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

	Six Months Ended June 30,
	2019		2018
Options to purchase common stock		6,771,807		3,285,429
Unvested restricted stock		—		53,223
Warrants to purchase common stock		317,562		317,562

Leases

6 Months Ended

Jun. 30, 2019

Leases [Abstract]

Leases

9. Leases

The Company leases certain properties and buildings under various arrangements which provide the right to use the underlying asset and require lease payments for the lease term. Many of the property and building lease agreements obligate the Company to pay real estate taxes, insurance and certain maintenance costs (hereinafter referred to as non-lease components). Certain of the Company’s lease arrangements contain renewal provisions from 1 to 3 years, exercisable at the Company's option. The Company’s lease agreements do not contain any material residual value guarantees or material restrictive covenants.

The Company determines if an arrangement is an operating lease at inception. Leases with an initial term of 12 months or less are not recorded on the balance sheet. All other leases are recorded on the balance sheet with a corresponding operating lease asset, net, representing the right to use the underlying asset for the lease term and the operating lease liabilities representing the obligation to make lease payments arising from the lease.

Operating lease assets and operating lease liabilities are recognized at commencement date based on the present value of lease payments over the lease term and include options to extend or terminate the lease when they are reasonably certain to be exercised. The present value of lease payments is determined primarily using the incremental borrowing rate based on the information available at lease commencement date. Lease agreements with lease and non-lease components are generally accounted for as a single lease component. The Company’s operating lease expense is recognized on a straight-line basis over the lease term and are recorded in general and administrative expenses on the condensed consolidated statements of operations and comprehensive loss.

The following table presents the lease cost and information related to the right-of-use assets and operating lease liabilities:

	Three Months Ended June 30,		Six Months Ended June 30,
	2019		2019
Lease cost
Average rent expense	$	62,085	$	124,140
Other information
Cash paid for amounts included in the measurement of operating lease liabilities
Operating cash flows from operating leases	$	62,154	$	124,308

The weighted average remaining lease term and discount rate at June 30, 2019
Weighted-average remaining lease term - operating leases				2.29
Weighted-average discount rate - operating leases				13.22	%

As of June 30, 2019, future payments related to operating leases activities are presented in the table below:

	2019		2020		2021 and Thereafter		Total Lease Payments
Operating leases	$	123,354	$	239,781	$	191,685	$	554,820
Less interest								73,481
Present value of lease liabilities							$	481,339

Employee Stock Purchase Plan

6 Months Ended

Jun. 30, 2019

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Employee Stock Purchase Plan

10. Employee Stock Purchase Plan

In March 2017, the Board of Directors adopted and the stockholders approved the Employee Stock Purchase Plan that became effective in April 2017. On June 20, 2018, the Company’s shareholders approved the Amended and Restated 2017 Employee Stock Purchase Plan ("ESPP") at the Annual Meeting of Shareholders. Pursuant to the terms of the ESPP, the Company will reserve for issuance 300,000 shares of the Company's common stock in the aggregate, plus, on January 1, 2019 and each January 1 thereafter through January 1, 2028, the number of shares of the Company's common stock reserved and available for issuance under the ESPP will be cumulatively increased by the least of (i) one percent of the number of shares of the Company’s common stock issued and outstanding on the immediately preceding December 31; (ii) 350,000 shares; or (iii) such lesser number of shares of the Company’s common stock as determined by the Board of Directors, in each case subject to adjustment in accordance with the terms of the ESPP. In March 2019, the Company’s Board of Directors approved an increase of 350,000 shares to the ESPP, which was effective as of January 1, 2019. No shares under the ESPP are outstanding at June 30, 2019 and December 31, 2018.

License Agreement

6 Months Ended

Jun. 30, 2019

Revenue From Contract With Customer [Abstract]

License Agreement

11. License Agreement

On June 24, 2018, the Company entered into a License Agreement (the “Agreement”) with a wholly-owned subsidiary of Gossamer Bio, Inc., GB004, Inc. (collectively “Gossamer”), under which the Company granted Gossamer an exclusive, sublicensable license to develop and commercialize AKB-4924 and other structurally related products worldwide, with initial development expected in the indications of induction and maintenance in ulcerative colitis and Crohn’s Disease (collectively “initial indications”).

Gossamer is responsible for the development and commercialization of the licensed products, and a joint development committee has been formed to oversee the development and manufacturing activities related to the licensed products. Under the terms of the Agreement, Gossamer is obligated to use its commercially reasonable efforts to develop and commercialize licensed products in the United States, two major European countries and Japan for at least one of the initial indications. The Agreement includes an exclusivity provision that prohibits the Company from developing, manufacturing or commercializing, and prohibits Gossamer from clinically developing or commercializing certain HIF stabilizing compounds other than as permitted in the Agreement. Pursuant to the terms of the Agreement, Gossamer made an upfront payment to the Company of $20.0 million on June 28, 2018, which was fully recognized in 2018 (in accordance with ASC 606).

The Company is also eligible to receive development, commercial and sales milestone payments, with such payments contingent on the achievement of specified milestones with respect to the first licensed product for each of the first two initial indications. The Company is also eligible to receive tiered royalties on sales of licensed products at percentages ranging from a high-single-digit to mid-teens, subject to certain customary reductions. In addition, under certain circumstances, in lieu of receiving the foregoing milestone payments and royalties, the Company may elect to receive a specified percentage of payments received by Gossamer and its stockholders (with some exclusions) in connection with Gossamer’s grant of a sublicense or other rights to the licensed products or if Gossamer undergoes a change of control and the value of the transaction exceeds a certain value (provided that Gossamer can prevent the Company from exercising this option if the parent company of Gossamer is the entity undergoing the change of control). Conversely, the Company could be required to accept such a specified percentage of those payments if Gossamer agrees to pay the Company a certain minimum upon Gossamer and its stockholders being paid. Such amount may be reduced if the subject transaction includes pharmaceutical candidates or products or other named asset categories in addition to the licensed products.

The Agreement expires on a licensed-product-by-licensed-product and country-by-country basis on the later of fifteen years from the date of first commercial sale or when there is no longer a valid patent claim covering such licensed product in such country. Either party may terminate the Agreement for an uncured material breach by the other party or upon the bankruptcy or insolvency of the other party. Gossamer may terminate the Agreement in the event Gossamer determines there is a potential safety or efficacy issue with the licensed products. The Company may terminate the Agreement if Gossamer institutes certain actions related to the licensed patents. Under certain termination circumstances, the Company would have worldwide rights to the terminated program.

As of June 30, 2019 all development milestones, sales-based milestones and royalty payments within the Agreement are constrained to the point where no transaction price has been allocated to the future milestones or royalty payments.

Restructuring

6 Months Ended

Jun. 30, 2019

Restructuring And Related Activities [Abstract]

Restructuring

12. Restructuring

In April 2019, the Company adopted a realignment plan to reduce operating costs and better align its workforce with the needs of its ongoing business. The realignment plan reduced the Company’s workforce by 11 employees, representing approximately 41% of its workforce. As a result of this realignment plan, the Company recorded employee severance expense of $0.9 million during the three months ended June 30, 2019 . These amounts are included within Restructuring expense in the condensed consolidated statements of operations and comprehensive loss and are expected to be substantially paid in cash by December 31, 2019. The total remaining liability under these severance related actions was $0.6 million as of June 30, 2019 and is included in Accounts payable and accrued expenses in the condensed consolidated balance sheets.

Summary of Significant Accounting Policies (Policies)

6 Months Ended

Jun. 30, 2019

Accounting Policies [Abstract]

Basis of Presentation

Segment Information

Use of Estimates

Cash and Cash Equivalents

Revenue Recognition

Grant Income

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

Research and Development

Patents

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

Income Taxes

Net and Comprehensive Loss per Share

Stock-Based Compensation

Fair Value of Financial Instruments

•

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

•

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

•

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

	Fair Value Measurements Using
	Level 1		Level 2		Level 3		Total
June 30, 2019
Assets:
Cash and cash equivalents	$	48,157,010	$	—	$	—	$	48,157,010
Total assets	$	48,157,010	$	—	$	—	$	48,157,010
December 31, 2018
Assets:
Cash and cash equivalents	$	62,614,010	$	—	$	—	$	62,614,010
Total assets	$	62,614,010	$	—	$	—	$	62,614,010

Concentrations of Credit Risk and Off-Balance Sheet Risk

Comprehensive Loss

Furniture and Equipment

Leases

Recent Accounting Pronouncements

No other new accounting pronouncement recently issued or newly effective had or is expected to have a material impact on the Company’s condensed consolidated financial statements.

Summary of Significant Accounting Policies (Tables)

6 Months Ended

Jun. 30, 2019

Accounting Policies [Abstract]

Schedule of Assets Measured on Recurring Basis

The assets of the Company measured at fair value on a recurring basis as of June 30, 2019 and December 31, 2018, are summarized below:

	Fair Value Measurements Using
	Level 1		Level 2		Level 3		Total
June 30, 2019
Assets:
Cash and cash equivalents	$	48,157,010	$	—	$	—	$	48,157,010
Total assets	$	48,157,010	$	—	$	—	$	48,157,010
December 31, 2018
Assets:
Cash and cash equivalents	$	62,614,010	$	—	$	—	$	62,614,010
Total assets	$	62,614,010	$	—	$	—	$	62,614,010

Accounts Payable and Accrued Expenses (Tables)

6 Months Ended

Jun. 30, 2019

Payables And Accruals [Abstract]

Schedule of Accounts Payable and Accrued Expenses

Accounts payable and accrued expenses are as follows:

	June 30,		December 31,
	2019		2018
Accounts payable	$	511,190	$	595,680
Restructuring accrual (see Note 12)		591,827		—
Professional fees		264,571		487,923
Accrued bonus		451,644		1,877,455
Accrued retention bonus		157,716		—
Accrued vacation		88,945		90,663
Accrued project costs		1,306,752		2,232,014
Other		29,612		173,182
Total accounts payable and accrued expenses	$	3,402,257	$	5,456,917

Stock-Based Compensation (Tables)

6 Months Ended

Jun. 30, 2019

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Summary of Stock Option Activity

The following table summarizes the stock option activity during the six months ended June 30, 2019:

	Stock Option Shares			Weighted Average Exercise Price		Weighted Average Remaining Contractual Term (in Years)		Aggregate Intrinsic Value
Outstanding, January 1, 2019		3,351,132		$	3.73		8.24	$	142,788
Granted		4,622,428			1.86
Exercised		—			—
Expired/cancelled		(1,201,753	)		2.80
Outstanding, June 30, 2019		6,771,807		$	2.62		8.65	$	17,133
Expected to vest, June 30, 2019		5,183,231		$	2.37	9.35		$	—
Options exercisable, June 30, 2019		1,588,576		$	3.43		6.37	$	17,133

Summary of Recognized Compensation Cost Related to Employee and Non-employee Stock-Based Compensation Activity

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

	Three Months Ended June 30,				Six Months Ended June 30,
	2019		2018		2019		2018
Research and development	$	73,463	$	114,949	$	232,794	$	174,013
General and administrative		531,198		762,808		993,552		1,783,465
Total	$	604,661	$	877,757	$	1,226,346	$	1,957,478

Stock Options Valuation Assumptions

The calculation was based on the following assumptions.

	Three Months Ended	Six Months Ended
	June 30, 2019	June 30, 2019
Expected term (years)	5.82	5.77
Risk-free interest rate	2.21%	2.32%
Expected volatility	65.97%	65.83%
Expected dividend yield	0.00%	0.00%

Net and Comprehensive Loss Per Share (Tables)

6 Months Ended

Jun. 30, 2019

Earnings Per Share [Abstract]

Schedule of Computation of 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 attributable to common stockholders for the periods presented:

	Three Months Ended June 30,						Six Months Ended June 30,
	2019			2018			2019			2018
Net and comprehensive loss attributable to common stockholders	$	(5,683,616	)	$	(5,989,991	)	$	(14,176,441	)	$	(13,415,523	)
Weighted average common shares used in computing net and comprehensive loss per share attributable to common stockholders, basic and diluted		40,588,004			27,340,914			40,588,004			27,194,028
Net and comprehensive loss per share attributable to common stockholders, basic and diluted	$	(0.14	)	$	(0.22	)	$	(0.35	)	$	(0.49	)

Schedule of Weighted Average Common Stock Equivalents Excluded from Calculation of Basic and Diluted Net and Comprehensive Loss per Share

	Six Months Ended June 30,
	2019		2018
Options to purchase common stock		6,771,807		3,285,429
Unvested restricted stock		—		53,223
Warrants to purchase common stock		317,562		317,562

Leases (Tables)

6 Months Ended

Jun. 30, 2019

Leases [Abstract]

Summary of Lease Cost and Information Related to the Right-of-Use Assets and Operating Lease Liabilities

The following table presents the lease cost and information related to the right-of-use assets and operating lease liabilities:

	Three Months Ended June 30,		Six Months Ended June 30,
	2019		2019
Lease cost
Average rent expense	$	62,085	$	124,140
Other information
Cash paid for amounts included in the measurement of operating lease liabilities
Operating cash flows from operating leases	$	62,154	$	124,308

The weighted average remaining lease term and discount rate at June 30, 2019
Weighted-average remaining lease term - operating leases				2.29
Weighted-average discount rate - operating leases				13.22	%

Schedule of Future Payments Related to Operating Leases Activities

As of June 30, 2019, future payments related to operating leases activities are presented in the table below:

	2019		2020		2021 and Thereafter		Total Lease Payments
Operating leases	$	123,354	$	239,781	$	191,685	$	554,820
Less interest								73,481
Present value of lease liabilities							$	481,339

Nature of Organization and Operations - Additional Information (Detail)		3 Months Ended
	Mar. 15, 2017 USD ($) $ / shares shares	Jun. 30, 2018 USD ($) shares	Jun. 30, 2019 USD ($) $ / shares shares	Dec. 31, 2018 USD ($) $ / shares shares	Dec. 31, 2017 USD ($)	Mar. 14, 2017 shares	Mar. 09, 2017 $ / shares shares
Class Of Stock [Line Items]
Common stock, shares authorized			300,000,000	300,000,000			100,000,000
Common stock, par value \| $ / shares			$ 0.0001	$ 0.0001			$ 0.0001
Preferred stock, shares authorized			10,000,000	10,000,000			10,000,000
Preferred stock, par value \| $ / shares			$ 0.0001	$ 0.0001			$ 0.0001
Capital stock conversion basis ratio	2.3336572
Common stock, shares outstanding			40,588,004	40,588,004
Warrants issued to purchase common stock, exercise price \| $ / shares			$ 5.00	$ 5.00
Cash and cash equivalents \| $		$ 68,783,210	$ 48,157,010	$ 62,614,010	$ 20,264,109
Minimum [Member]
Class Of Stock [Line Items]
Percentage of Interest owned in the combined enterprise	50.00%
Common Stock [Member]
Class Of Stock [Line Items]
Common stock sold in offering		11,688,000
Zeta Acquisition Corp. II [Member]
Class Of Stock [Line Items]
Number of shares surrendered for cancellation	4,000,000
Common stock, shares outstanding						5,000,000
Issuance of warrants term	3 years
Number of warrants issued to purchase common stock	317,562
Warrants issued to purchase common stock, exercise price \| $ / shares	$ 5.00
Zeta Acquisition Corp. II [Member] \| Common Stock [Member]
Class Of Stock [Line Items]
Net proceeds from issuance of common stock in private placement \| $	$ 37,200,000
Zeta Acquisition Corp. II [Member] \| Common Stock [Member] \| Private Placement [Member]
Class Of Stock [Line Items]
Common stock sold in offering	8,049,555
Common stock issued to private placement, price per share \| $ / shares	$ 5.00

Summary of Significant Accounting Policies - Additional Information (Detail)	6 Months Ended
	Jun. 30, 2019 USD ($) Segment	Jan. 01, 2019 USD ($)	Dec. 31, 2018 USD ($)
Summary Of Significant Accounting Policies [Line Items]
Number of operating segment \| Segment	1
Uncertain tax positions	$ 0		$ 0
ASU 2018-07 [Member]
Summary Of Significant Accounting Policies [Line Items]
One-time cumulative adjustment upon adoption		$ 5,717
Minimum [Member]
Summary Of Significant Accounting Policies [Line Items]
Furniture and equipment estimated useful lives	3 years
Maximum [Member]
Summary Of Significant Accounting Policies [Line Items]
Furniture and equipment estimated useful lives	7 years

Summary of Significant Accounting Policies - Schedule of Assets Measured on Recurring Basis (Detail) - Fair Value, Measurements, Recurring [Member] - USD ($)	Jun. 30, 2019	Dec. 31, 2018
Assets:
Cash and cash equivalents	$ 48,157,010	$ 62,614,010
Total assets	48,157,010	62,614,010
Level 1 [Member]
Assets:
Cash and cash equivalents	48,157,010	62,614,010
Total assets	$ 48,157,010	$ 62,614,010

Accounts Payable and Accrued Expenses - Schedule of Accounts Payable and Accrued Expenses (Details) - USD ($)	Jun. 30, 2019	Dec. 31, 2018
Payables And Accruals [Abstract]
Accounts payable	$ 511,190	$ 595,680
Restructuring accrual (see Note 12)	591,827
Professional fees	264,571	487,923
Accrued bonus	451,644	1,877,455
Accrued retention bonus	157,716
Accrued vacation	88,945	90,663
Accrued project costs	1,306,752	2,232,014
Other	29,612	173,182
Total accounts payable and accrued expenses	$ 3,402,257	$ 5,456,917

Common Stock - Additional Information (Detail) - USD ($)	6 Months Ended	12 Months Ended
	Jun. 30, 2019	Dec. 31, 2018	Mar. 09, 2017
Equity [Abstract]
Common stock, shares authorized	300,000,000	300,000,000	100,000,000
Common stock, par value	$ 0.0001	$ 0.0001	$ 0.0001
Dividends common stock declared or paid	$ 0
Warrants outstanding	317,562	317,562
Warrants exercise price per share	$ 5.00	$ 5.00
Warrants term	3 years	3 years
Warrants expiration date	Mar. 15, 2020	Mar. 15, 2020

Preferred Stock - Additional Information (Detail) - $ / shares	Jun. 30, 2019	Dec. 31, 2018	Mar. 09, 2017
Temporary Equity Disclosure [Abstract]
Preferred stock, shares authorized	10,000,000	10,000,000	10,000,000
Preferred stock, par value	$ 0.0001	$ 0.0001	$ 0.0001
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0

Stock-Based Compensation - Additional Information (Detail) - USD ($)	1 Months Ended			3 Months Ended		6 Months Ended
	May 31, 2019	Mar. 31, 2019	Mar. 31, 2017	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Options to purchase common stock, granted						4,622,428
Unrecognized compensation cost related to stock options				$ 5,956,838		$ 5,956,838
Weighted-average fair value of options granted				$ 0.62		$ 1.11
Stock Option [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting period						48 months
Compensation expense				$ 604,661	$ 822,850	$ 1,226,346	$ 1,554,223
Weighted average period expected to be recognized						2 years 7 months 6 days
Restricted Stock [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Compensation expense				$ 0	$ 54,907	$ 0	$ 403,255
2017 Stock Option and Incentive Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock shares available for issuance		1,623,520	4,600,000
Percentage applied to the outstanding shares as annual increase in number of shares authorized for issuance		4.00%	4.00%
2017 Stock Option and Incentive Plan [Member] \| Stock Option [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock shares available for issuance				969,529		969,529		2,959,562
Term of options to be granted						10 years
Shares issued for special retention grant	2,419,050
Options to purchase common stock, granted				2,801,600	1,515,200	4,622,428	1,515,200
2017 Stock Option and Incentive Plan [Member] \| Stock Option [Member] \| One-year Anniversary [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting percentage						25.00%
2017 Stock Option and Incentive Plan [Member] \| Stock Option [Member] \| First Installment [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting percentage	50.00%
Option, vesting date	Jun. 30, 2020
2017 Stock Option and Incentive Plan [Member] \| Stock Option [Member] \| Second Installment [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting percentage	50.00%
Option, vesting date	Jun. 30, 2021

Stock-Based Compensation - Summary of Stock Option Activity (Detail)	6 Months Ended	12 Months Ended
	Jun. 30, 2019 USD ($) $ / shares shares	Dec. 31, 2018 USD ($) $ / shares shares
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Shares, Outstanding at beginning balance \| shares	3,351,132
Shares, Granted \| shares	4,622,428
Shares, Expired/cancelled \| shares	(1,201,753)
Shares, Outstanding at ending balance \| shares	6,771,807	3,351,132
Shares, Expected to vest \| shares	5,183,231
Shares, Options exercisable \| shares	1,588,576
Weighted Average Exercise Price, Outstanding at beginning balance \| $ / shares	$ 3.73
Weighted Average Exercise Price, Granted \| $ / shares	1.86
Weighted Average Exercise Price, Expired/cancelled \| $ / shares	2.80
Weighted Average Exercise Price, Outstanding at ending balance \| $ / shares	2.62	$ 3.73
Weighted Average Exercise Price, Expected to vest \| $ / shares	2.37
Weighted Average Exercise Price, Options exercisable \| $ / shares	$ 3.43
Weighted Average Remaining Contractual Term, Outstanding	8 years 7 months 24 days	8 years 2 months 26 days
Weighted Average Remaining Contractual Term, Expected to vest	9 years 4 months 6 days
Weighted Average Remaining Contractual Term, Options exercisable	6 years 4 months 13 days
Aggregate Intrinsic Value, Outstanding \| $	$ 17,133	$ 142,788
Aggregate Intrinsic Value, Options exercisable \| $	$ 17,133

Stock-Based Compensation - Summary of Recognized Compensation Cost Related to Employee and Non-employee Stock-Based Compensation Activity (Detail) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	$ 604,661	$ 877,757	$ 1,226,346	$ 1,957,478
Research and development [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	73,463	114,949	232,794	174,013
General and administrative [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	$ 531,198	$ 762,808	$ 993,552	$ 1,783,465

Stock-Based Compensation - Stock Options Valuation Assumptions (Detail)	3 Months Ended	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2019
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Expected term (years)	5 years 9 months 25 days	5 years 9 months 7 days
Risk-free interest rate	2.21%	2.32%
Expected volatility	65.97%	65.83%
Expected dividend yield	0.00%	0.00%

Income Taxes - Additional Information (Detail) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Income Tax Disclosure [Abstract]
Current income tax expense or benefit	$ 0	$ 0	$ 0	$ 0
Deferred income tax expense or benefit	$ 0	$ 0	$ 0	$ 0

Net and Comprehensive Loss Per Share - Schedule of Computation of Basic and Diluted Net Loss per Share (Detail) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Earnings Per Share [Abstract]
Net and comprehensive loss attributable to common stockholders	$ (5,683,616)	$ (5,989,991)	$ (14,176,441)	$ (13,415,523)
Weighted average common shares used in computing net and comprehensive loss per share attributable to common stockholders, basic and diluted	40,588,004	27,340,914	40,588,004	27,194,028
Net and comprehensive loss per share attributable to common stockholders, basic and diluted	$ (0.14)	$ (0.22)	$ (0.35)	$ (0.49)

Net and Comprehensive Loss Per Share - Schedule of Weighted Average Common Stock Equivalents Excluded from Calculation of Basic and Diluted Net and Comprehensive Loss per Share (Detail) - Weighted Average [Member] - shares	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
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	6,771,807	3,285,429
Unvested Restricted Stock [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Total amount of anti-dilutive securities excluded from computation of earnings per share		53,223
Warrants to Purchase Common Stock [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Total amount of anti-dilutive securities excluded from computation of earnings per share	317,562	317,562

Leases - Additional Information (Detail)	Jun. 30, 2019
Minimum [Member]
Lessee Lease Description [Line Items]
Lease arrangements renewal provisions	1 year
Leases initial term	12 months
Maximum [Member]
Lessee Lease Description [Line Items]
Lease arrangements renewal provisions	3 years

Leases - Summary of Lease Cost and Information Related to the Right-of-Use Assets and Operating Lease Liabilities (Detail)	3 Months Ended	6 Months Ended
	Jun. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)
Lease cost
Average rent expense	$ 62,085	$ 124,140
Cash paid for amounts included in the measurement of operating lease liabilities
Operating cash flows from operating leases	$ 62,154	$ 124,308
The weighted average remaining lease term and discount rate
Weighted-average remaining lease term - operating leases	2 years 3 months 14 days	2 years 3 months 14 days
Weighted-average discount rate - operating leases	13.22%	13.22%

Leases - Schedule of Future Payments Related to Operating Leases Activities (Detail)	Jun. 30, 2019 USD ($)
Leases [Abstract]
Operating leases, 2019	$ 123,354
Operating leases, 2020	239,781
Operating leases, 2021 and thereafter	191,685
Total Lease Payments	554,820
Less interest	73,481
Present value of lease liabilities	$ 481,339

Employee Stock Purchase Plan - Additional Information (Detail) - shares	Jun. 20, 2018	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares outstanding		6,771,807		3,351,132
Employee Stock Purchase Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares outstanding		0		0
Common Stock [Member] \| Employee Stock Purchase Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock shares available for issuance	300,000
Maximum number of shares provided for issuance	350,000		350,000
Percentage of annual increase in number of shares reserved for issuance	1.00%

License Agreement - Additional Information (Detail) $ in Millions	Jun. 28, 2018 USD ($)
Revenue From Contract With Customer [Abstract]
Cash received from license agreement	$ 20.0

Restructuring - Additional Information (Detail)	1 Months Ended	3 Months Ended
Restructuring - Additional Information (Detail)	Apr. 30, 2019 Employee	Jun. 30, 2019 USD ($)
Restructuring Cost And Reserve [Line Items]
Remaining liability related to severance		$ 591,827
Accounts Payable and Accrued Liabilities [Member]
Restructuring Cost And Reserve [Line Items]
Remaining liability related to severance		600,000
Workforce Reduction [Member]
Restructuring Cost And Reserve [Line Items]
Realignment plan, number of current workforce reduced \| Employee	11
Realignment plan, number of workforce reduced, period percent	41.00%
Realignment plan, employee severance expense		$ 900,000