0001564590-19-028999 | 10-Q | XBRL Viewer | Aeglea Biotherapeutics INC

Document and Entity Information - shares	6 Months Ended
Document and Entity Information - shares	Jun. 30, 2019	Aug. 01, 2019
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Jun. 30, 2019
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q2
Trading Symbol	AGLE
Entity Registrant Name	AEGLEA BIOTHERAPEUTICS, INC.
Entity Central Index Key	0001636282
Current Fiscal Year End Date	--12-31
Entity Filer Category	Accelerated Filer
Entity File Number	001-37722
Entity Tax Identification Number	464312787
Entity Address, Address Line One	901 S. MoPac Expressway
Entity Address, Address Line Two	Barton Oaks Plaza One
Entity Address, Address Line Three	Suite 250
Entity Address, City or Town	Austin
Entity Address, Postal Zip Code	78746
City Area Code	512
Local Phone Number	942-2935
Entity Address, State or Province	TX
Entity Shell Company	false
Entity Small Business	false
Entity Emerging Growth Company	true
Entity Current Reporting Status	Yes
Entity Ex Transition Period	true
Entity Common Stock, Shares Outstanding		28,885,469

Condensed Consolidated Balance Sheets (unaudited) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
CURRENT ASSETS
Cash and cash equivalents	$ 25,430	$ 22,461
Marketable securities	80,111	52,052
Prepaid expenses and other current assets	4,394	2,158
Total current assets	109,935	76,671
Restricted cash	1,500
Property and equipment, net	921	1,018
Operating lease right-of-use assets	5,018
Other non-current assets	120	50
TOTAL ASSETS	117,494	77,739
CURRENT LIABILITIES
Accounts payable	2,724	663
Operating lease liabilities	328
Accrued and other current liabilities	9,967	9,576
Total current liabilities	13,019	10,239
Non-current operating lease liabilities	4,815
Other non-current liabilities	45	72
TOTAL LIABILITIES	17,879	10,311
Commitments and Contingencies (Note 6 and 10)
STOCKHOLDERS’ EQUITY
Preferred stock, $0.0001 par value; 10,000,000 shares authorized as of June 30, 2019 and December 31, 2018; no shares issued and outstanding as of June 30, 2019 and December 31, 2018
Common stock, $0.0001 par value; 500,000,000 shares authorized as of June 30, 2019 and December 31, 2018; 28,848,303 shares and 24,140,097 shares issued and outstanding as of June 30, 2019 and December 31, 2018, respectively	3	2
Additional paid-in capital	251,592	184,314
Accumulated other comprehensive income (loss)	67	(27)
Accumulated deficit	(152,047)	(116,861)
TOTAL STOCKHOLDERS’ EQUITY	99,615	67,428
TOTAL LIABILITIES AND STOCKHOLDERS’ EQUITY	$ 117,494	$ 77,739

Condensed Consolidated Balance Sheets (unaudited) (Parenthetical) - $ / shares	Jun. 30, 2019	Dec. 31, 2018
Statement Of Financial Position [Abstract]
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	500,000,000	500,000,000
Common stock, shares issued	28,848,303	24,140,097
Common stock, shares outstanding	28,848,303	24,140,097

Condensed Consolidated Statements of Operations (Unaudited) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Revenues:
Grant		$ 2,378,000	$ 0	$ 3,888,000
Type of revenue [extensible list]	us-gaap:GrantMember	us-gaap:GrantMember	us-gaap:GrantMember	us-gaap:GrantMember
Operating expenses:
Research and development	$ 14,806,000	$ 9,122,000	$ 29,195,000	$ 15,992,000
General and administrative	3,816,000	2,926,000	7,084,000	5,811,000
Total operating expenses	18,622,000	12,048,000	36,279,000	21,803,000
Loss from operations	(18,622,000)	(9,670,000)	(36,279,000)	(17,915,000)
Other income (expense):
Interest income	619,000	263,000	1,126,000	406,000
Other expense, net	(16,000)	(7,000)	(33,000)	(24,000)
Total other income	603,000	256,000	1,093,000	382,000
Net loss	$ (18,019,000)	$ (9,414,000)	$ (35,186,000)	$ (17,533,000)
Net loss per share, basic and diluted	$ (0.55)	$ (0.46)	$ (1.14)	$ (0.94)
Weighted-average common shares outstanding, basic and diluted	32,840,357	20,598,711	30,936,623	18,646,265

Condensed Consolidated Statements of Comprehensive Loss (Unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Statement Of Income And Comprehensive Income [Abstract]
Net loss	$ (18,019)	$ (9,414)	$ (35,186)	$ (17,533)
Other comprehensive income:
Unrealized gain on marketable securities	54	42	94	46
Total comprehensive loss	$ (17,965)	$ (9,372)	$ (35,092)	$ (17,487)

- Definition

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

+ References + Details

Condensed Consolidated Statements of Changes in Stockholders' Equity (Unaudited) - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Income (Loss)	Accumulated Deficit
Balances at Dec. 31, 2017	$ 50,337	$ 2	$ 122,950	$ (102)	$ (72,513)
Balances (in shares) at Dec. 31, 2017		16,670,000
Issuance of common stock in connection with employee stock purchase plan	78		78
Issuance of common stock in connection with employee stock purchase plan (in shares)		31,000
Issuance of common stock in connection with exercise of stock options	785		785
Issuance of common stock in connection with exercise of stock options (in shares)		109,000
Stock-based compensation expense	835		835
Unrealized gain on marketable securities	4			4
Net loss	(8,119)				(8,119)
Balances at Mar. 31, 2018	43,920	$ 2	124,648	(98)	(80,632)
Balances (in shares) at Mar. 31, 2018		16,810,000
Balances at Dec. 31, 2017	50,337	$ 2	122,950	(102)	(72,513)
Balances (in shares) at Dec. 31, 2017		16,670,000
Unrealized gain on marketable securities	46
Net loss	(17,533)
Balances at Jun. 30, 2018	73,447	$ 2	163,547	(56)	(90,046)
Balances (in shares) at Jun. 30, 2018		21,908,000
Balances at Mar. 31, 2018	43,920	$ 2	124,648	(98)	(80,632)
Balances (in shares) at Mar. 31, 2018		16,810,000
Issuance of common stock in connection with exercise of stock options	248		248
Issuance of common stock in connection with exercise of stock options (in shares)		51,000
Issuance of common stock in connection with public offering, net of offering costs	37,655		37,655
Issuance of common stock in connection with public offering,net of offering costs (in shares)		5,047,000
Stock-based compensation expense	996		996
Unrealized gain on marketable securities	42			42
Net loss	(9,414)				(9,414)
Balances at Jun. 30, 2018	73,447	$ 2	163,547	(56)	(90,046)
Balances (in shares) at Jun. 30, 2018		21,908,000
Balances at Dec. 31, 2018	67,428	$ 2	184,314	(27)	(116,861)
Balances (in shares) at Dec. 31, 2018		24,140,000
Issuance of common stock in connection with employee stock purchase plan	143		143
Issuance of common stock in connection with employee stock purchase plan (in shares)		20,000
Issuance of common stock in connection with exercise of stock options	261		261
Issuance of common stock in connection with exercise of stock options (in shares)		52,000
Issuance of common stock and pre-funded warrants in connection with public offering, net of offering costs	64,503	$ 1	64,502
Issuance of common stock and pre-funded warrants in connection with public offering, net of offering costs (in shares)		4,625,000
Stock-based compensation expense	1,081		1,081
Unrealized gain on marketable securities	40			40
Net loss	(17,167)				(17,167)
Balances at Mar. 31, 2019	116,289	$ 3	250,301	13	(134,028)
Balances (in shares) at Mar. 31, 2019		28,837,000
Balances at Dec. 31, 2018	67,428	$ 2	184,314	(27)	(116,861)
Balances (in shares) at Dec. 31, 2018		24,140,000
Unrealized gain on marketable securities	94
Net loss	(35,186)
Balances at Jun. 30, 2019	99,615	$ 3	251,592	67	(152,047)
Balances (in shares) at Jun. 30, 2019		28,848,000
Balances at Mar. 31, 2019	116,289	$ 3	250,301	13	(134,028)
Balances (in shares) at Mar. 31, 2019		28,837,000
Issuance of common stock in connection with exercise of stock options	46		46
Issuance of common stock in connection with exercise of stock options (in shares)		11,000
Stock-based compensation expense	1,245		1,245
Unrealized gain on marketable securities	54			54
Net loss	(18,019)				(18,019)
Balances at Jun. 30, 2019	$ 99,615	$ 3	$ 251,592	$ 67	$ (152,047)
Balances (in shares) at Jun. 30, 2019		28,848,000

Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
CASH FLOWS FROM OPERATING ACTIVITIES
Net loss	$ (35,186)	$ (17,533)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	207	145
Purchase net discount on marketable securities	480	401
Net accretion of discount on marketable securities	(543)	(107)
Stock-based compensation	2,326	1,831
Research and development services settled with stock		41
Non-cash operating lease expense	191
Other, net		(20)
Changes in operating assets and liabilities:
Accounts receivable - grant		(1,203)
Prepaid expenses and other assets	(2,223)	(573)
Accounts payable	2,141	579
Deferred revenue		(20)
Operating lease liabilities	(178)
Accrued and other liabilities	595	(32)
Net cash used in operating activities	(32,190)	(16,491)
CASH FLOWS FROM INVESTING ACTIVITIES
Purchases of property and equipment	(175)	(118)
Purchases of marketable securities	(77,956)	(26,250)
Proceeds from maturities of marketable securities	50,054	11,870
Net cash used in investing activities	(28,077)	(14,498)
CASH FLOWS FROM FINANCING ACTIVITIES
Proceeds from issuance of common stock and pre-funded warrants in public offering, net of offering costs	64,298	37,690
Proceeds from employee stock plan purchases and stock option exercises	450	1,061
Principal payments on finance lease obligation	(12)
Net cash provided by financing activities	64,736	38,751
NET INCREASE IN CASH, CASH EQUIVALENTS, AND RESTRICTED CASH	4,469	7,762
CASH, CASH EQUIVALENTS, AND RESTRICTED CASH
Beginning of period	22,461	12,817
End of period	26,930	$ 20,579
Supplemental Disclosure of Non-Cash Investing and Financing Information:
Leased assets obtained in exchange for lease obligations	$ 5,294

The Company and Basis of Presentation

6 Months Ended

Jun. 30, 2019

Organization Consolidation And Presentation Of Financial Statements [Abstract]

The Company and Basis of Presentation

1. The Company and Basis of Presentation

Aeglea BioTherapeutics, Inc. (“Aeglea” or the “Company”) is clinical-stage biotechnology company that engineers next generation human enzymes to provide solutions for diseases with unmet medical need. The Company was formed as a Limited Liability Company (LLC) in Delaware on December 16, 2013 under the name Aeglea BioTherapeutics Holdings, LLC and was converted from a Delaware LLC to a Delaware corporation on March 10, 2015. The Company operates in one segment and has its principal offices in Austin, Texas.

Liquidity

As of June 30, 2019, the Company had working capital of $96.9 million, an accumulated deficit of $152.0 million, and cash, cash equivalents, marketable securities, and restricted cash of $107.0 million. The Company has not generated any product revenues and has not achieved profitable operations. There is no assurance that profitable operations will ever be achieved, and, if achieved, could be sustained on a continuing basis. In addition, development activities, clinical and nonclinical testing, and commercialization of the Company’s products will require significant additional financing.

The Company is subject to a number of risks similar to other life science companies, including, but not limited to, risks related to the successful discovery and development of product candidates, raising additional capital, development of competing drugs and therapies, protection of proprietary technology and market acceptance of the Company’s products. As a result of these and other factors and the related uncertainties, there can be no assurance of the Company’s future success.

Based upon the Company’s current operating plans, the Company believes that it has sufficient resources to fund operations through the first quarter of 2021 with its existing cash, cash equivalents, and marketable securities. The Company will need to secure additional funding in the future, in order to carry out all of its planned research and development activities. If the Company is unable to obtain additional financing or generate license or product revenue, the lack of liquidity could have a material adverse effect on the Company’s future prospects.

Unaudited Interim Financial Information

The interim condensed consolidated financial statements included in this document are unaudited. The unaudited interim financial statements have been prepared on the same basis as the annual financial statements and reflect, in the opinion of management, all adjustments of a normal and recurring nature that are necessary for a fair statement of the Company’s financial position as of June 30, 2019, and its results of operations for the three and six months ended June 30, 2019 and 2018, changes in stockholders’ equity for the three and six months ended June 30, 2019 and 2018, and cash flows for the six months ended June 30, 2019 and 2018. The results of operations for the six months ended June 30, 2019 are not necessarily indicative of the results to be expected for the year ending December 31, 2019 or for any other future annual or interim period. The December 31, 2018 balance sheet was derived from audited financial statements, but does not include all disclosures required by accounting principles generally accepted in the United States (“U.S. GAAP”). These financial statements should be read in conjunction with the audited financial statements included in the Company’s Form 10-K for the year ended December 31, 2018 as filed with the SEC.

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

Use of Estimates

The preparation of financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the amounts reported in the consolidated financial statements and accompanying notes. Such management estimates include those related to accruals of research and development related costs, stock-based compensation, and certain company income tax related items. Management bases its estimates on historical experience and on various other market-specific and relevant assumptions that management believes to be reasonable under the circumstances. Actual results could differ significantly from those estimates.

Cash and Cash Equivalents

The Company considers all highly liquid investments with original maturities of three months or less from the date of purchase to be cash equivalents. Cash equivalents consist of money market funds and debt securities and are stated at fair value.

Marketable Securities

All investments have been classified as available-for-sale and are carried at estimated fair value as determined based upon quoted market prices or pricing models for similar securities. Management determines the appropriate classification of its investments in debt securities at the time of purchase. The Company may or may not hold securities with stated maturities greater than one year until maturity. All available-for-sale securities are considered available to support current operations and are classified as current assets.

Unrealized gains and losses are excluded from earnings and are reported as a component of accumulated comprehensive loss. Realized gains and losses and declines in fair value judged to be other than temporary, if any, on available-for-sale securities are included in other income (expense). The cost of securities sold is based on the specific-identification method. There were no realized gains or losses on marketable securities for the six months ended June 30, 2019 and 2018. Interest on marketable securities is included in interest income.

Restricted Cash

Restricted cash consists of a money market account held by a financial institution as collateral for the Company’s obligations under its facility lease for the Company’s corporate headquarters in Austin, TX.

Concentration of Credit Risk

Financial instruments that potentially subject the Company to a concentration of credit risk consist of cash, cash equivalents, marketable securities, and restricted cash. The Company’s investment policy limits investments to high credit quality securities issued by the U.S. government, U.S. government-sponsored agencies, highly rated banks, and corporate issuers, subject to certain concentration limits and restrictions on maturities. The Company’s cash, cash equivalents, marketable securities, and restricted cash are held by financial institutions in the United States that management believes are of high credit quality. Amounts on deposit may at times exceed federally insured limits. The Company has not experienced any losses on its deposits of cash, cash equivalents, and restricted cash and its accounts are monitored by management to mitigate risk. The Company is exposed to credit risk in the event of default by the financial institutions holding its cash, cash equivalents, restricted cash, and bond issuers.

Property and Equipment

Property and equipment are stated at cost, net of accumulated depreciation and amortization. Depreciation and amortization are computed using the straight-line method over the estimated useful lives of the assets. Repairs and maintenance that do not extend the life or improve an asset are expensed as incurred. Upon retirement or sale, the cost of disposed assets and their related accumulated depreciation and amortization are removed from the balance sheet. Any gain or loss is credited or charged to operations.

The useful lives of the property and equipment are as follows:

Laboratory equipment		5 years
Furniture and office equipment		5 years
Computer equipment		3 years
Software		3 years
Leasehold improvements		Shorter of remaining lease term or estimated useful life

Impairment of Long-Lived Assets

Long-lived assets are reviewed for indications of possible impairment whenever events or changes in circumstances indicate that the carrying amount of an asset may not be recoverable. Recoverability is measured by comparison of the carrying amounts to the future undiscounted cash flows attributable to these assets. An impairment loss is recognized to the extent an asset group is not recoverable, and the carrying amount exceeds the projected discounted future cash flows arising from these assets. There were no impairments of long-lived assets for the six months ended June 30, 2019 and 2018.

Accrued Research and Development Costs

The Company records the costs associated with research nonclinical studies, clinical trials, and manufacturing development as incurred. These costs are a significant component of the Company’s research and development expenses, with a substantial portion of the Company’s on-going research and development activities conducted by third-party service providers, including contract research and manufacturing organizations.

The Company accrues for expenses resulting from obligations under agreements with contract research organizations (“CROs”), contract manufacturing organizations (“CMOs”), and other outside service providers for which payment flows do not match the periods over which materials or services are provided to the Company. Accruals are recorded based on estimates of services received and efforts expended pursuant to agreements established with CROs, CMOs, and other outside service providers. These estimates are typically based on contracted amounts applied to the proportion of work performed and determined through analysis with internal personnel and external service providers as to the progress or stage of completion of the services. The Company makes significant judgments and estimates in determining the accrual balance in each reporting period. In the event advance payments are made to a CRO, CMO, or outside service provider, the payments will be recorded as a prepaid asset which will be amortized as the contracted services are performed. As actual costs become known, the Company adjusts its accruals. Inputs, such as the services performed, the number of patients enrolled, or the study duration, may vary from the Company’s estimates, resulting in adjustments to research and development expense in future periods. Changes in these estimates that result in material changes to the Company’s accruals could materially affect the Company’s results of operations. The Company has not experienced any material deviations between accrued and actual research and development expenses.

Leases

The Company determines if an arrangement is a lease at inception. Right-of-use ("ROU") assets represent the Company's right to use an underlying asset for the lease term and lease liabilities represent the Company's obligation to make lease payments arising from the lease. The classification of the Company's leases as operating or finance leases along with the initial measurement and recognition of the associated ROU assets and lease liabilities is performed at the lease commencement date. The measurement of lease liabilities is based on the present value of future lease payments over the lease term. As the Company's leases do not provide an implicit rate, the Company uses its incremental borrowing rate based on the information available at the lease commencement date in determining the present value of future lease payments. The ROU asset is based on the measurement of the lease liability and also includes any lease payments made prior to or on lease commencement and excludes lease incentives and initial direct costs incurred, as applicable. The lease terms may include options to extend or terminate the lease when it is reasonably certain the Company will exercise any such options. Rent expense for the Company's operating leases is recognized on a straight-line basis over the lease term. Amortization expense for the ROU asset associated with its finance leases is recognized on a straight-line basis over the term of the lease and interest expense associated with its finance leases is recognized on the balance of the lease liability using the effective interest method based on the estimated incremental borrowing rate.

The Company has lease agreements with lease and non-lease components. As allowed under Topic 842, the Company has elected to not separate lease and non-lease components for any leases involving real estate and office equipment classes of assets and, as a result, accounts for the lease and non-lease components as a single lease component. The Company has also elected to not apply the recognition requirement of Topic 842 to leases with a term of 12 months or less for all classes of assets.

Fair Value of Financial Instruments

The Company uses fair value measurements to record fair value adjustments to certain financial and non-financial assets and liabilities and to determine fair value disclosures. The accounting standards define fair value, establish a framework for measuring fair value, and require disclosures about fair value measurements. Fair value is defined as the price that would be received from selling an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. When determining the fair value measurements for assets and liabilities required to be recorded at fair value, the principal or most advantageous market in which the Company would transact are considered along with assumptions that market participants would use when pricing the asset or liability, such as inherent risk, transfer restrictions, and risk of nonperformance.

The accounting standard for fair value establishes a fair value hierarchy based on three levels of inputs, the first two of which are considered observable and the last unobservable, that requires an entity to maximize the use of observable inputs and minimize the use of unobservable inputs when measuring fair value. A financial instrument’s categorization within the fair value hierarchy is based upon the lowest level of input that is significant to the fair value measurement.

The three levels of inputs that may be used to measure fair value are as follows:

Level 1:

Observable inputs, such as quoted prices in active markets for identical assets or liabilities.

Level 2:

Observable inputs other than Level 1 prices, such as quoted prices for similar assets or liabilities, or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities.

Level 3:

Valuations based on unobservable inputs to the valuation methodology and including data about assumptions that market participants would use in pricing the asset or liability based on the best information available under the circumstances.

Financial instruments carried at fair value include cash, cash equivalents, marketable securities, and restricted cash. The carrying amount of accounts receivable, accounts payable and accrued liabilities approximate fair value due to their relatively short maturities.

Revenue Recognition

The Company’s sole source of revenue was grant revenue related to a $19.8 million research grant received from the Cancer Prevention and Research Institute of Texas (“CPRIT”), covering a four-year period from June 1, 2014 through May 31, 2018. Grant revenue was recognized when qualifying costs were incurred and there was reasonable assurance that the conditions of the award had been met for collection. Proceeds received prior to the costs being incurred or the conditions of the award being met were recognized as deferred revenue until the services were performed and the conditions of the award were met (see Note 7).

Research and Development Costs

Research and development costs are expensed as incurred. Research and development costs include, but are not limited to, salaries, benefits, travel, stock-based compensation, consulting costs, contract research service costs, laboratory supplies and facilities, contract manufacturing costs, and costs paid to other third parties that conduct research and development activities on the Company’s behalf. Amounts incurred in connection with license agreements are also included in research and development expense.

Advance payments for goods or services to be rendered in the future for use in research and development activities are recorded as a prepaid asset and expensed as the related goods are delivered or the services are performed.

Stock-Based Compensation

The Company recognizes the cost of stock-based awards granted to employees and non-employees based on the estimated grant-date fair values of the awards. The value of the award is recognized as compensation expense on a straight-line basis over the requisite service period. Forfeitures are recognized when they occur, which may result in the reversal of compensation costs in subsequent periods as the forfeitures arise. Compensation expense for employee and non-employee share-based payment awards with performance conditions is recognized when the performance condition is deemed probable.

Income Taxes

The Company and its seven wholly-owned subsidiary corporations use the asset and liability method of accounting for income taxes. Under this method, deferred tax assets and liabilities are recognized for the expected future tax consequences of temporary differences between the financial statements and the tax bases of assets and liabilities. Additionally, any changes in income tax laws are immediately recognized in the year of enactment.

A valuation allowance is established against the deferred tax assets to reduce their carrying value to an amount that is more likely than not to be realized. The deferred tax assets and liabilities are classified as noncurrent along with the related valuation allowance. Due to a lack of earnings history, the net deferred tax assets have been fully offset by a valuation allowance.

The Company recognizes benefits of uncertain tax positions if it is more likely than not that such positions will be sustained upon examination based solely on the technical merits, as the largest amount of benefits that is more likely than not to be realized upon the ultimate settlement. The Company’s policy is to recognize interest and penalties related to the unrecognized tax benefits as a component of income tax expense.

Comprehensive Loss

Comprehensive loss is the change in stockholders’ equity from transactions and other events and circumstances other than those resulting from investments by stockholders and distributions to stockholders. The Company’s other comprehensive income is currently comprised of changes in unrealized gains on available-for-sale securities.

Recent Accounting Pronouncements

In February 2016, the FASB issued ASU No. 2016-02, Leases (Topic 842), which establishes a comprehensive new lease accounting model. The new standard: (a) clarifies the definition of a lease; (b) requires a dual approach to lease classification similar to current lease classifications; and, (c) causes lessees to recognize leases on the balance sheet as a lease liability with a corresponding right-of-use (ROU) asset. On January 1, 2019, the Company adopted Topic 842 using the modified retrospective approach as of the adoption date in accordance with ASU No. 2018-11, Leases (Topic 842): Targeted Improvements. Results for the three and six months ended June 30, 2019 are presented under Topic 842. No prior period amounts were adjusted and continue to be reported in accordance with previous lease guidance, ASC Topic 840, Leases. The Company elected all of the available practical expedients permitted under the transition guidance within the new standard, which among other things, allowed the Company to carry forward the historical lease classification of those leases in place as of January 1, 2019.

The following table summarizes the impact of the adoption of Topic 842 on the accompanying balance sheet as of January 1, 2019 (in thousands):

	December 31,		Effect of the Adoption of			January 1,
	2018		Topic 842			2019
Other non-current assets⁽¹⁾	$	50	$	691		$	741

Lease Liabilities:
Current operating lease liabilities	$	—	$	339		$	339
Non-current operating lease liabilities	$	—	$	465		$	465
Accrued and other current liabilities⁽²⁾	$	9,576	$	(41	)	$	9,535
Other non-current liabilities⁽³⁾	$	72	$	(72	)	$	—

(1)

Operating lease right-of-use assets are classified within other non-current assets.

(2)

Current deferred rent was classified within accrued and other current liabilities as of December 31, 2018.

(3)

Non-current deferred rent was classified within other non-current liabilities as of December 31, 2018.

The adjustments due to the adoption of Topic 842 related to the recognition of operating lease right-of-use assets and lease liabilities for the existing operating leases. A cumulative-effect adjustment to the beginning accumulated deficit balance was not required.

In June 2016, the FASB issued ASU No. 2016-13, Financial Instruments-Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments, which changes the impairment model for most financial assets and certain other instruments. For available-for-sale debt securities with unrealized losses, the losses will be recognized as allowances rather than as reductions in the amortized cost of the securities. The guidance is effective for interim and annual periods beginning after December 15, 2019. The guidance will be applied using a modified retrospective approach with the cumulative effect recognized as an adjustment to retained earnings. The Company is currently evaluating the impact that the adoption of ASU 2016-13 will have on its consolidated financial statements.

In August 2018, the FASB issued ASU No. 2018-15, Intangibles – Goodwill and Other – Internal Use Software (Subtopic 350-40), to align the requirements for capitalizing implementation costs incurred in a hosting arrangement that is a service contract with the requirements for capitalizing implementation costs incurred to develop or obtain internal-use software (and hosting arrangements that include an internal-use software license). The amendments in the update require an entity in a hosting arrangement that is a service contract to follow the guidance in Subtopic 350-40 to determine which implementation costs to capitalize as an asset related to the service contract and which costs to expense. The new standard is effective for fiscal years and interim periods beginning after December 15, 2019 and can be applied either retrospectively or prospectively to all implementation costs incurred after the date of adoption. Early adoption is permitted. The Company is currently evaluating the impact that the adoption of ASU 2018-15 will have on its consolidated financial statements.

Fair Value Measurements

6 Months Ended

Jun. 30, 2019

Fair Value Disclosures [Abstract]

Fair Value Measurements

3. Fair Value Measurements

The Company measures and reports certain financial instruments as assets and liabilities at fair value on a recurring basis. The following tables sets forth the fair value of the Company’s financial assets and liabilities at fair value on a recurring basis based on the three-tier fair value hierarchy (in thousands):

	June 30, 2019
	Level 1		Level 2		Level 3		Total
Financial Assets
Money market funds	$	5,947	$	—	$	—	$	5,947
Reverse repurchase agreements		—		6,250		—		6,250
Commercial paper		—		49,435		—		49,435
U.S. government securities		—		38,666		—		38,666
Total financial assets	$	5,947	$	94,351	$	—	$	100,298

	December 31, 2018
	Level 1		Level 2		Level 3		Total
Financial Assets
Money market funds	$	7,180	$	—	$	—	$	7,180
Reverse repurchase agreements		—		6,250		—		6,250
Commercial paper		—		53,916		—		53,916
U.S. government securities		—		4,112		—		4,112
Total financial assets	$	7,180	$	64,278	$	—	$	71,458

The Company measures the fair value of money market funds on quoted prices in active markets for identical asset or liabilities. The Level 2 assets include reverse repurchase agreements, commercial paper, and U.S. government securities and are valued based on quoted prices for similar assets in active markets and inputs other than quoted prices that are derived from observable market data.

The Company evaluates transfers between levels at the end of each reporting period. There were no transfers between Level 1 and Level 2 during the periods presented.

- Definition

The entire disclosure for the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments as well as disclosures related to the fair value of non-financial assets and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the entity is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risks are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information.

+ References + Details

Cash Equivalents and Marketable Securities

6 Months Ended

Jun. 30, 2019

Investments Debt And Equity Securities [Abstract]

Cash Equivalents and Marketable Securities

4. Cash Equivalents and Marketable Securities

The following tables summarize the estimated fair value of the Company’s cash equivalents and marketable securities and the gross unrealized gains and losses (in thousands):

	June 30, 2019
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
Cash equivalents
Money market funds	$	5,947	$	—	$	—		$	5,947
Reverse repurchase agreements		6,250		—		—			6,250
Commercial paper		7,991		—		(1	)		7,990
Total cash equivalents		20,188		—		(1	)		20,187

Marketable securities
Commercial paper		41,407		39		(1	)		41,445
U.S. government securities		38,636		43		(13	)		38,666
Total marketable securities	$	80,043	$	82	$	(14	)	$	80,111

	December 31, 2018
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
Cash equivalents
Money market funds	$	7,180	$	—	$	—		$	7,180
Reverse repurchase agreements		6,250		—		—			6,250
Commercial paper		5,977		—		(1	)		5,976
Total cash equivalents		19,407		—		(1	)		19,406

Marketable securities
Commercial paper		47,964		—		(24	)		47,940
U.S. government securities		4,114		—		(2	)		4,112
Total marketable securities	$	52,078	$	—	$	(26	)	$	52,052

The reverse repurchase agreements are settled in cash nightly, and as such are classified as cash equivalents.

As of June 30, 2019 and December 31, 2018, all debt securities with an unrealized loss position have been in a loss position for less than one year. The aggregate fair value of debt securities in an unrealized loss position as of June 30, 2019 and December 31, 2018 were $22.0 million and $45.6 million, respectively, with no individual securities in a significant unrealized loss position. The Company evaluated its securities for other-than-temporary impairment and considered the decline in market value for the securities to be primarily attributable to current economic and market conditions and would not be required to sell the securities before recovery of the amortized cost basis. Based on this analysis, these marketable securities were not considered to be other-than-temporarily impaired as of June 30, 2019 and December 31, 2018.

The following table summarizes the contractual maturities of the Company’s marketable securities at estimated fair value (in thousands):

	June 30,		December 31,
	2019		2018
Due in one year or less	$	67,330	$	52,052
Due in 1 - 2 years		12,781		—
Total marketable securities	$	80,111	$	52,052

The Company may sell investments at any time for use in current operations even if they have not yet reached maturity. As a result, the Company classifies marketable securities, including securities with maturities beyond twelve months as current assets.

Accrued and Other Current Liabilities

6 Months Ended

Jun. 30, 2019

Accrued Liabilities And Other Liabilities [Abstract]

Accrued and Other Current Liabilities

5. Accrued and Other Current Liabilities

Accrued and other current liabilities consist of the following (in thousands):

	June 30,		December 31,
	2019		2018
Accrued compensation	$	1,850	$	2,643
Accrued contracted research and development costs		7,307		5,993
Accrued professional and consulting fees		716		807
Other		94		133
Total accrued and other current liabilities	$	9,967	$	9,576

Leases

6 Months Ended

Jun. 30, 2019

Leases [Abstract]

Leases

6. Leases

The Company leases certain office space, laboratory facilities, and equipment. These leases require monthly lease payments that may be subject to annual increases throughout the lease term. Certain of these leases also include renewal options at the election of the Company to renew or extend the lease for an additional three to five years. These optional periods have not been considered in the determination of the right-of-use-assets or lease liabilities associated with these leases as the Company did not consider it reasonably certain it would exercise the options. The Company performed evaluations of its contracts and determined it has both operating and finance leases.

In April 2019, the Company entered into a lease agreement (the “Las Cimas Lease”) for its corporate headquarters and laboratory space located in Austin, TX. The Las Cimas Lease includes approximately 30,000 square feet and commenced on April 30, 2019, with an expiration on April 30, 2028. The Company posted a customary letter of credit in the amount of $1.5 million as security, which is subject to automatic reductions per the terms of the Las Cimas Lease. A tenant allowance of up to $1.0 million is provided by the lessor.

The following table summarizes the Company’s recognition of its operating and finance leases (in thousands):

	Classification	June 30, 2019
Assets
Operating	Operating lease right-of-use assets	$	5,018
Finance	Other non-current assets		70
Total leased assets			5,088

Liabilities
Current
Operating	Operating lease liabilities		328
Finance	Accrued and other current liabilities		27
Non-current
Operating	Non-current operating lease liabilities		4,815
Finance	Other non-current liabilities		45
Total lease liabilities		$	5,215

The following table summarizes the weighted-average remaining lease term and discount rates for the Company’s operating and finance leases:

	June 30, 2019
Lease term (years)
Operating leases		8.0
Finance leases		2.5

Discount rate
Operating leases	10.6%
Finance leases	9.5%

The Company incurred rent expense for its operating leases of $0.3 million and $0.2 million during the three months ended June 30, 2019 and 2018, respectively, and $0.4 million and $0.3 million during the six months ended June 30, 2019 and 2018, respectively, included within operating expenses in the results of operations. Cash paid for amounts included in the measurement of operating lease liabilities during the six months ended June 30, 2019 was $0.3 million and was included within net cash used in operating activities in the cash flows.

The maturities of the Company’s operating and finance lease liabilities as of June 30, 2019 were as follows (in thousands):

	Operating Leases			Finance Leases
2019 (excluding the six months ended June 30, 2019)	$	319		$	17
2020		1,252			32
2021		1,061			32
2022		1,007			—
2023		1,037			—
Thereafter		4,865			—
Total lease payments		9,541			81
Less:
Imputed interest		(3,394	)		(9	)
Tenant allowance		(1,004	)		—
Total	$	5,143		$	72

As of December 31, 2018, future annual minimum lease payments, as defined under the previous lease accounting guidance of ASC Topic 840, due under non-cancelable operating leases at December 31 of each year are as follows (in thousands):

2019	$	397
2020		409
2021		83
Thereafter		—
Total minimum lease payments	$	889

Grant Revenues

6 Months Ended

Jun. 30, 2019

Grant Revenues [Abstract]

Grant Revenues

7. Grant Revenues

In June 2015, the Company entered into a Cancer Research Grant Contract (“Grant Contract”) with CPRIT, under which CPRIT awarded a grant not to exceed $19.8 million for use in developing cancer treatments by exploiting the metabolism of cancer cells. The Grant Contract covered a four-year period from June 1, 2014 through May 31, 2018.

Upon commercialization of the product, the terms of the Grant Contract require the Company to pay tiered royalties in the low to mid-single digit percentages. Such royalties reduce to less than one percent after a mid-single-digit multiple of the grant funds have been paid to CPRIT as royalties.

The contract ended in May 2018 with the full $19.8 million grant recognized as revenue over the life of the award. The Company did not recognize any grant revenue in the six months ended June 30, 2019. For the three and six months ended June 30, 2018, the Company recognized $2.4 million and $3.9 million, respectively, for qualified expenditures under the grant. As of December 31, 2018, all grant proceeds had been collected.

Stockholders' Equity

6 Months Ended

Jun. 30, 2019

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Stockholders' Equity

8. Stockholders’ Equity

Public Offering

In February 2019, the Company issued and sold 4,625,000 shares of common stock at a public offering price of $8.00 per share and pre-funded warrants to purchase up to 4,000,000 shares of common stock at a public offering price of $7.9999 per warrant in an underwritten public offering pursuant to a shelf registration statement on Form S-3. This includes the full exercise by the underwriters of their option to purchase up to 1,125,000 additional shares of common stock. The net proceeds to the Company from this offering were $64.5 million, after deducting underwriting discounts and commissions of $4.1 million and offering costs of $0.4 million.

The public offering price for the pre-funded warrants was equal to the public offering price of the common stock, less the $0.0001 per share exercise price of each warrant. These warrants were recorded as a component of stockholders’ equity within additional paid-in capital and have no expiration date. Per the terms of the warrant agreement, the outstanding warrants to purchase shares of common stock may not be exercised if the holder’s ownership of the Company’s common stock would exceed 4.99% (“Maximum Ownership Percentage”). By written notice to the Company, the holders may increase or decrease the Maximum Ownership Percentage. The revised Maximum Ownership Percentage would be effective 60 days after the notice is received by the Company. As of June 30, 2019, none of the pre-funded warrants have been exercised.

Stock-Based Compensation

The 2016 Equity Incentive Plan (“2016 Plan”) provides for an automatic increase in the number of shares reserved for issuance thereunder on January 1 of each year for the remaining term of the plan (through 2028) equal to (a) 4.0% of the number of issued and outstanding shares of common stock on December 31 of the immediately preceding year, or (b) a lesser amount as approved by the Company’s board of directors each year. As a result of this provision, on January 1, 2019 and January 1, 2018, an additional 965,603 and 666,807 shares, respectively, became available for issuance under the 2016 Plan.

As of June 30, 2019, the 2016 Plan had 1,459,072 shares available for future issuance.

During the three months ended June 30, 2019 and 2018, the Company issued an aggregate of 159,600 and 203,600 options to purchase common stock, respectively, under the Company’s equity incentive plans for an aggregate fair value of $0.7 million and $1.5 million, respectively.

During the six months ended June 30, 2019 and 2018, the Company issued an aggregate of 1,201,900 and 1,033,100 options to purchase common stock, respectively, under the Company’s equity incentive plans for an aggregate fair value of $6.9 million and $5.4 million, respectively.

There were no shares issued and sold under the Company’s 2016 Employee Stock Purchase Plan (“2016 ESPP”) during the three months ended June 30, 2019 and 2018. The Company issued and sold 20,132 shares for aggregate cash proceeds of $0.1 million during the six months ended June 30, 2019 and 30,937 shares for aggregate cash proceeds of $0.1 million during the six months ended June 30, 2018.

Total stock-based compensation expense related to the Company’s equity incentive plans and 2016 ESPP was as follows (in thousands):

	Three Months Ended				Six Months Ended
	June 30,				June 30,
	2019		2018		2019		2018
Research and development	$	464	$	390	$	866	$	713
General and administrative		781		606		1,460		1,118
Total stock-based compensation expense	$	1,245	$	996	$	2,326	$	1,831

The following table summarizes the weighted-average Black-Scholes option pricing model assumptions used to estimate the fair value of stock options granted under the Company’s equity incentive plans, and the shares purchasable under the 2016 ESPP during the periods presented:

	Three Months Ended						Six Months Ended
	June 30,						June 30,
	2019			2018			2019			2018
Equity Incentive Plans
Expected term (in years)		5.70			5.70			5.99			5.95
Expected volatility		78	%		84	%		81	%		85	%
Risk-free interest		2.05	%		2.79	%		2.50	%		2.73	%
Dividend yield		0	%		0	%		0	%		0	%

2016 ESPP
Expected term (in years)		—			—			0.49			0.49
Expected volatility		—			—			66	%		69	%
Risk-free interest		—			—			2.55	%		2.00	%
Dividend yield		—			—			0	%		0	%

Net Loss Per Share

6 Months Ended

Jun. 30, 2019

Earnings Per Share [Abstract]

Net Loss Per Share

9. Net Loss Per Share

Basic and diluted net loss per share is computed by dividing net loss by the weighted-average number of common stock and pre-funded warrants outstanding during the period. The pre-funded warrants are included in the computation of basic net loss per share as the exercise price is negligible and they are fully vested and exercisable. For periods in which the Company generated a net loss, the Company does not include the potential impact of dilutive securities in diluted net loss per share, as the impact of these items is anti-dilutive.

The following weighted-average equity instruments were excluded from the calculation of diluted net loss per share because their effect would have been anti-dilutive for the periods presented:

	Three Months Ended				Six Months Ended
	June 30,				June 30,
	2019		2018		2019		2018
Unvested restricted common stock		6,861		30,408		6,861		31,233
Options to purchase common stock		4,081,102		3,015,991		3,781,559		2,856,763

License Agreements

6 Months Ended

Jun. 30, 2019

Licensing Agreements [Abstract]

License Agreements

10. License Agreements

License Agreements

In December 2013, two of the Company’s wholly owned subsidiaries, AECase, Inc. (“AECase”) and AEMase, Inc. (“AEMase”), entered into license agreements with the University of Texas at Austin (the “University”) under which the University granted to AECase and AEMase exclusive, worldwide, sublicenseable licenses. The University granted the AECase license under a patent application relating to the right to use technology related to the Company’s AEB3103 product candidate. The University granted the AEMase license under a patent relating to the right to use technology related to the Company’s AEB2109 product candidate.

In January 2017, the Company entered into an Amended and Restated Patent License Agreement (the “Restated License”) with the University which consolidated the two license agreements, revised certain obligations, and licensed additional patent applications and invention disclosures to the Company. The Restated License was amended in August 2017, December 2017, and December 2018 to license additional patent applications, including the Company’s product candidates under the AEB4104 and AEB5100 programs. Pursuant to the terms of the Restated License, the Company may be required to pay the University up to $6.4 million in milestone payments based on the achievement of certain development milestones, including clinical trials and regulatory approvals, the majority of which are due upon the achievement of later development milestones, including a $5.0 million payment due on regulatory approval of a product and a $0.5 million payment payable on final regulatory approval of a product for a second indication. In addition, the Company is required to pay the University a low single-digit royalty on worldwide-net sales of products covered under the Restated License, together with a revenue share on non-royalty consideration received from sublicensees. The rate of the revenue share ranges from 6.5% to 25% depending on the date the sublicense agreement is signed.

Summary of Significant Accounting Policies (Policies)

6 Months Ended

Jun. 30, 2019

Accounting Policies [Abstract]

Use of Estimates

Cash and Cash Equivalents

Marketable Securities

Restricted Cash

Concentration of Credit Risk

Property and Equipment

The useful lives of the property and equipment are as follows:

Laboratory equipment		5 years
Furniture and office equipment		5 years
Computer equipment		3 years
Software		3 years
Leasehold improvements		Shorter of remaining lease term or estimated useful life

Impairment of Long-Lived Assets

Accrued Research And Development Costs

Accrued Research and Development Costs

Leases

Fair Value of Financial Instruments

The three levels of inputs that may be used to measure fair value are as follows:

Level 1:

Observable inputs, such as quoted prices in active markets for identical assets or liabilities.

Level 2:

Level 3:

Revenue Recognition

Research and Development Costs

Stock-Based Compensation

Income Taxes

Comprehensive Loss

Recent Accounting Pronouncements

The following table summarizes the impact of the adoption of Topic 842 on the accompanying balance sheet as of January 1, 2019 (in thousands):

	December 31,		Effect of the Adoption of			January 1,
	2018		Topic 842			2019
Other non-current assets⁽¹⁾	$	50	$	691		$	741

Lease Liabilities:
Current operating lease liabilities	$	—	$	339		$	339
Non-current operating lease liabilities	$	—	$	465		$	465
Accrued and other current liabilities⁽²⁾	$	9,576	$	(41	)	$	9,535
Other non-current liabilities⁽³⁾	$	72	$	(72	)	$	—

(1)

Operating lease right-of-use assets are classified within other non-current assets.

(2)

Current deferred rent was classified within accrued and other current liabilities as of December 31, 2018.

(3)

Non-current deferred rent was classified within other non-current liabilities as of December 31, 2018.

Summary of Significant Accounting Policies (Tables)

6 Months Ended

Jun. 30, 2019

Accounting Policies [Abstract]

Schedule Of Estimated Useful Lives Of Property Plant And Equipment

The useful lives of the property and equipment are as follows:

Laboratory equipment		5 years
Furniture and office equipment		5 years
Computer equipment		3 years
Software		3 years
Leasehold improvements		Shorter of remaining lease term or estimated useful life

Summary of Impact of the Adoption of Topic 842

The following table summarizes the impact of the adoption of Topic 842 on the accompanying balance sheet as of January 1, 2019 (in thousands):

	December 31,		Effect of the Adoption of			January 1,
	2018		Topic 842			2019
Other non-current assets⁽¹⁾	$	50	$	691		$	741

Lease Liabilities:
Current operating lease liabilities	$	—	$	339		$	339
Non-current operating lease liabilities	$	—	$	465		$	465
Accrued and other current liabilities⁽²⁾	$	9,576	$	(41	)	$	9,535
Other non-current liabilities⁽³⁾	$	72	$	(72	)	$	—

(1)

Operating lease right-of-use assets are classified within other non-current assets.

(2)

Current deferred rent was classified within accrued and other current liabilities as of December 31, 2018.

(3)

Non-current deferred rent was classified within other non-current liabilities as of December 31, 2018.

Fair Value Measurement (Tables)

6 Months Ended

Jun. 30, 2019

Fair Value Disclosures [Abstract]

Financial Assets and Liabilities Measured at Fair Value on Recurring Basis

The following tables sets forth the fair value of the Company’s financial assets and liabilities at fair value on a recurring basis based on the three-tier fair value hierarchy (in thousands):

	June 30, 2019
	Level 1		Level 2		Level 3		Total
Financial Assets
Money market funds	$	5,947	$	—	$	—	$	5,947
Reverse repurchase agreements		—		6,250		—		6,250
Commercial paper		—		49,435		—		49,435
U.S. government securities		—		38,666		—		38,666
Total financial assets	$	5,947	$	94,351	$	—	$	100,298

	December 31, 2018
	Level 1		Level 2		Level 3		Total
Financial Assets
Money market funds	$	7,180	$	—	$	—	$	7,180
Reverse repurchase agreements		—		6,250		—		6,250
Commercial paper		—		53,916		—		53,916
U.S. government securities		—		4,112		—		4,112
Total financial assets	$	7,180	$	64,278	$	—	$	71,458

Cash Equivalents and Marketable Securities (Tables)

6 Months Ended

Jun. 30, 2019

Investments Debt And Equity Securities [Abstract]

Schedule of Estimated Fair Value of Cash Equivalents and Marketable Securities

The following tables summarize the estimated fair value of the Company’s cash equivalents and marketable securities and the gross unrealized gains and losses (in thousands):

	June 30, 2019
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
Cash equivalents
Money market funds	$	5,947	$	—	$	—		$	5,947
Reverse repurchase agreements		6,250		—		—			6,250
Commercial paper		7,991		—		(1	)		7,990
Total cash equivalents		20,188		—		(1	)		20,187

Marketable securities
Commercial paper		41,407		39		(1	)		41,445
U.S. government securities		38,636		43		(13	)		38,666
Total marketable securities	$	80,043	$	82	$	(14	)	$	80,111

	December 31, 2018
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
Cash equivalents
Money market funds	$	7,180	$	—	$	—		$	7,180
Reverse repurchase agreements		6,250		—		—			6,250
Commercial paper		5,977		—		(1	)		5,976
Total cash equivalents		19,407		—		(1	)		19,406

Marketable securities
Commercial paper		47,964		—		(24	)		47,940
U.S. government securities		4,114		—		(2	)		4,112
Total marketable securities	$	52,078	$	—	$	(26	)	$	52,052

Summary of Contractual Maturities of Marketable Securities at Estimated Fair Value

The following table summarizes the contractual maturities of the Company’s marketable securities at estimated fair value (in thousands):

	June 30,		December 31,
	2019		2018
Due in one year or less	$	67,330	$	52,052
Due in 1 - 2 years		12,781		—
Total marketable securities	$	80,111	$	52,052

Accrued and Other Current Liabilities (Tables)

6 Months Ended

Jun. 30, 2019

Accrued Liabilities And Other Liabilities [Abstract]

Accrued and Other Current Liabilities

Accrued and other current liabilities consist of the following (in thousands):

	June 30,		December 31,
	2019		2018
Accrued compensation	$	1,850	$	2,643
Accrued contracted research and development costs		7,307		5,993
Accrued professional and consulting fees		716		807
Other		94		133
Total accrued and other current liabilities	$	9,967	$	9,576

Leases (Tables)

6 Months Ended

Jun. 30, 2019

Leases [Abstract]

Summary of Operating and Finance Leases Presented in Balance Sheet

The following table summarizes the Company’s recognition of its operating and finance leases (in thousands):

	Classification	June 30, 2019
Assets
Operating	Operating lease right-of-use assets	$	5,018
Finance	Other non-current assets		70
Total leased assets			5,088

Liabilities
Current
Operating	Operating lease liabilities		328
Finance	Accrued and other current liabilities		27
Non-current
Operating	Non-current operating lease liabilities		4,815
Finance	Other non-current liabilities		45
Total lease liabilities		$	5,215

Summary of Weighted Average Remaining Lease Term and Discount Rates For Company's Operating and Finance Leases

The following table summarizes the weighted-average remaining lease term and discount rates for the Company’s operating and finance leases:

	June 30, 2019
Lease term (years)
Operating leases		8.0
Finance leases		2.5

Discount rate
Operating leases	10.6%
Finance leases	9.5%

Schedule of Maturities of Operating and Finance Lease Liabilities

The maturities of the Company’s operating and finance lease liabilities as of June 30, 2019 were as follows (in thousands):

	Operating Leases			Finance Leases
2019 (excluding the six months ended June 30, 2019)	$	319		$	17
2020		1,252			32
2021		1,061			32
2022		1,007			—
2023		1,037			—
Thereafter		4,865			—
Total lease payments		9,541			81
Less:
Imputed interest		(3,394	)		(9	)
Tenant allowance		(1,004	)		—
Total	$	5,143		$	72

Summary of Future Annual Minimum Lease Payments Due Under Non-cancellable Operating Leases

2019	$	397
2020		409
2021		83
Thereafter		—
Total minimum lease payments	$	889

Stockholders' Equity (Tables)

6 Months Ended

Jun. 30, 2019

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Summary of Stock-Based Compensation Expense

Total stock-based compensation expense related to the Company’s equity incentive plans and 2016 ESPP was as follows (in thousands):

	Three Months Ended				Six Months Ended
	June 30,				June 30,
	2019		2018		2019		2018
Research and development	$	464	$	390	$	866	$	713
General and administrative		781		606		1,460		1,118
Total stock-based compensation expense	$	1,245	$	996	$	2,326	$	1,831

Schedule of Estimated Fair Value of Stock Options Granted

	Three Months Ended						Six Months Ended
	June 30,						June 30,
	2019			2018			2019			2018
Equity Incentive Plans
Expected term (in years)		5.70			5.70			5.99			5.95
Expected volatility		78	%		84	%		81	%		85	%
Risk-free interest		2.05	%		2.79	%		2.50	%		2.73	%
Dividend yield		0	%		0	%		0	%		0	%

2016 ESPP
Expected term (in years)		—			—			0.49			0.49
Expected volatility		—			—			66	%		69	%
Risk-free interest		—			—			2.55	%		2.00	%
Dividend yield		—			—			0	%		0	%

Net Loss Per Share (Tables)

6 Months Ended

Jun. 30, 2019

Earnings Per Share [Abstract]

Weighted-Average Equity Instruments Excluded from Calculation of Diluted Net Loss Per Share

The following weighted-average equity instruments were excluded from the calculation of diluted net loss per share because their effect would have been anti-dilutive for the periods presented:

	Three Months Ended				Six Months Ended
	June 30,				June 30,
	2019		2018		2019		2018
Unvested restricted common stock		6,861		30,408		6,861		31,233
Options to purchase common stock		4,081,102		3,015,991		3,781,559		2,856,763

The Company and Basis of Presentation - Additional Information (Details) $ in Thousands	6 Months Ended
	Jun. 30, 2019 USD ($) Segment	Dec. 31, 2018 USD ($)
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Number of operating segments \| Segment	1
Working capital	$ 96,900
Accumulated deficit	(152,047)	$ (116,861)
Cash, cash equivalents, marketable securities, and restricted cash	$ 107,000

Summary of Significant Accounting Policies - Additional Information (Details)		6 Months Ended
	Jun. 01, 2014 USD ($)	Jun. 30, 2019 USD ($) Subsidary	Jun. 30, 2018 USD ($)
Summary Of Significant Accounting Policies [Line Items]
Marketable Securities, Realized Gain (Loss)		$ 0	$ 0
Impairments of long-lived assets		$ 0	$ 0
Number of subsidiary corporations owned \| Subsidary		7
Maximum
Summary Of Significant Accounting Policies [Line Items]
Marketable securities stated maturity period		1 year
Maximum \| CPRIT
Summary Of Significant Accounting Policies [Line Items]
Research grant contract amount	$ 19,800,000

Summary of Significant Accounting Policies - Summary of Useful Lives of Property and Equipment (Details)	6 Months Ended
	Jun. 30, 2019
Laboratory Equipment
Property Plant And Equipment [Line Items]
Useful lives of the property and equipment	5 years
Furniture and Office Equipment
Property Plant And Equipment [Line Items]
Useful lives of the property and equipment	5 years
Computer Equipment
Property Plant And Equipment [Line Items]
Useful lives of the property and equipment	3 years
Software
Property Plant And Equipment [Line Items]
Useful lives of the property and equipment	3 years
Leasehold Improvements
Property Plant And Equipment [Line Items]
Useful lives of the property and equipment	Shorter of remaining lease term or estimated useful life

Summary of Significant Accounting Policies - Summary of Impact of the Adoption of Topic 842 (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Jan. 01, 2019	Dec. 31, 2018
Summary Of Significant Accounting Policies [Line Items]
Other non-current assets	$ 120		$ 50
Lease Liabilities:
Current operating lease liabilities	328
Non-current operating lease liabilities	4,815
Accrued and other current liabilities	9,967		9,576
Other non-current liabilities	$ 45		$ 72
ASU 2016-02
Summary Of Significant Accounting Policies [Line Items]
Other non-current assets		$ 741
Lease Liabilities:
Current operating lease liabilities		339
Non-current operating lease liabilities		465
Accrued and other current liabilities		9,535
ASU 2016-02 \| Effect of the Adoption of Topic 842
Summary Of Significant Accounting Policies [Line Items]
Other non-current assets		691
Lease Liabilities:
Current operating lease liabilities		339
Non-current operating lease liabilities		465
Accrued and other current liabilities		(41)
Other non-current liabilities		$ (72)

Fair Value Measurements - Financial Assets and Liabilities Measured at Fair Value on Recurring Basis (Details) - Fair Value, Measurements, Recurring - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Financial Assets
Financial assets, fair value	$ 100,298	$ 71,458
Money market funds
Financial Assets
Financial assets, fair value	5,947	7,180
Reverse repurchase agreements
Financial Assets
Financial assets, fair value	6,250	6,250
Commercial paper
Financial Assets
Financial assets, fair value	49,435	53,916
Level 1
Financial Assets
Financial assets, fair value	5,947	7,180
Level 1 \| Money market funds
Financial Assets
Financial assets, fair value	5,947	7,180
Level 2
Financial Assets
Financial assets, fair value	94,351	64,278
Level 2 \| Reverse repurchase agreements
Financial Assets
Financial assets, fair value	6,250	6,250
Level 2 \| Commercial paper
Financial Assets
Financial assets, fair value	49,435	53,916
U.S. government securities
Financial Assets
Financial assets, fair value	38,666	4,112
U.S. government securities \| Level 2
Financial Assets
Financial assets, fair value	$ 38,666	$ 4,112

Fair Value Measurements - Additional Information (Details)	Jun. 30, 2019 USD ($)
Fair Value Disclosures [Abstract]
Fair value assets transferred from level 1 to level 2	$ 0

Cash Equivalents and Marketable Securities - Schedule of Estimated Fair Value of Cash Equivalents and Marketable Securities (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Schedule Of Available For Sale Securities [Line Items]
Cash equivalents, amortized cost	$ 20,188	$ 19,407
Cash equivalents, gross unrealized losses	(1)	(1)
Cash equivalents, estimated fair value	20,187	19,406
Marketable securities, amortized cost	80,043	52,078
Marketable securities, gross unrealized gains	82
Marketable securities, gross unrealized losses	(14)	(26)
Marketable securities, estimated fair value	80,111	52,052
Money market funds
Schedule Of Available For Sale Securities [Line Items]
Cash equivalents, amortized cost	5,947	7,180
Cash equivalents, estimated fair value	5,947	7,180
Reverse repurchase agreements
Schedule Of Available For Sale Securities [Line Items]
Cash equivalents, amortized cost	6,250	6,250
Cash equivalents, estimated fair value	6,250	6,250
Commercial paper
Schedule Of Available For Sale Securities [Line Items]
Cash equivalents, amortized cost	7,991	5,977
Cash equivalents, gross unrealized losses	(1)	(1)
Cash equivalents, estimated fair value	7,990	5,976
Marketable securities, amortized cost	41,407	47,964
Marketable securities, gross unrealized gains	39
Marketable securities, gross unrealized losses	(1)	(24)
Marketable securities, estimated fair value	41,445	47,940
U.S. government securities
Schedule Of Available For Sale Securities [Line Items]
Marketable securities, amortized cost	38,636	4,114
Marketable securities, gross unrealized gains	43
Marketable securities, gross unrealized losses	(13)	(2)
Marketable securities, estimated fair value	$ 38,666	$ 4,112

Cash Equivalents and Marketable Securities - Additional Information (Details) - U.S. government and agency securities $ in Millions	Jun. 30, 2019 USD ($) Security	Dec. 31, 2018 USD ($) Security
Cash Equivalents And Marketable Securities [Line Items]
Fair value of debt securities in an unrealized loss position \| $	$ 22.0	$ 45.6
Number of securities in a significant unrealized loss position \| Security	0	0

Cash Equivalents and Marketable Securities - Summary of Contractual Maturities of Marketable Securities at Estimated Fair Value (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Investments Debt And Equity Securities [Abstract]
Due in one year or less	$ 67,330	$ 52,052
Due in 1 - 2 years	12,781
Total marketable securities	$ 80,111	$ 52,052

Accrued and Other Current Liabilities (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Accrued Liabilities And Other Liabilities [Abstract]
Accrued compensation	$ 1,850	$ 2,643
Accrued contracted research and development costs	7,307	5,993
Accrued professional and consulting fees	716	807
Other	94	133
Total accrued and other current liabilities	$ 9,967	$ 9,576

Leases - Additional Information (Details)	1 Months Ended	3 Months Ended		6 Months Ended
Leases - Additional Information (Details)	Apr. 30, 2019 USD ($) ft²	Jun. 30, 2019 USD ($)	Jun. 30, 2018 USD ($)	Jun. 30, 2019 USD ($)	Jun. 30, 2018 USD ($)
Schedule Of Operating And Finance Leased Assets [Line Items]
Area of land \| ft²	30,000
Lease expiration date	Apr. 30, 2028
Operating lease, expense		$ 300,000	$ 200,000	$ 400,000	$ 300,000
Operating lease, payments				$ 300,000
Minimum
Schedule Of Operating And Finance Leased Assets [Line Items]
Lessee, operating lease, renewal term		3 years		3 years
Lessee, finance lease, renewal term		3 years		3 years
Maximum
Schedule Of Operating And Finance Leased Assets [Line Items]
Lessee, operating lease, renewal term		5 years		5 years
Lessee, finance lease, renewal term		5 years		5 years
Tenant improvement allowance	$ 1,000,000.0
Letter of Credit
Schedule Of Operating And Finance Leased Assets [Line Items]
Letter of credit	$ 1,500,000

Leases - Schedule of Operating and Financing Leases Presented in Balance Sheet (Details) $ in Thousands	Jun. 30, 2019 USD ($)
Leases [Abstract]
Operating	$ 5,018
Operating Lease, Right-of-Use Asset, Statement of Financial Position [Extensible List]	us-gaap:OperatingLeaseRightOfUseAsset
Finance	$ 70
Finance Lease, Right-of-Use Asset, Statement of Financial Position [Extensible List]	us-gaap:OtherAssetsNoncurrent
Total leased assets	$ 5,088
Operating lease liabilities, current	$ 328
Operating Lease, Liability, Current, Statement of Financial Position [Extensible List]	us-gaap:OperatingLeaseLiabilityCurrent
Finance lease liabilities, current	$ 27
Finance Lease, Liabilities, Current, Statement of Financial Position [Extensible List]	us-gaap:AccruedLiabilitiesAndOtherLiabilities
Operating lease liabilities, noncurrent	$ 4,815
Operating Lease, Liability, Noncurrent, Statement of Financial Position [Extensible List]	us-gaap:OperatingLeaseLiabilityNoncurrent
Finance lease liabilities, noncurrent	$ 45
Finance Lease, Liability, Noncurrent, Statement of Financial Position [Extensible List]	us-gaap:OtherLiabilitiesNoncurrent
Total lease liabilities	$ 5,215

Leases - Summary of Weighted-Average Remaining Lease Term and Discount Rates for Operating and Finance Leases (Details)	Jun. 30, 2019
Leases [Abstract]
Operating leases, Weighted-average remaining lease term	8 years
Finance leases, Weighted-average remaining lease term	2 years 6 months
Operating leases, Weighted-average discount rate	10.60%
Finance leases, Weighted-average discount rate	9.50%

Leases - Schedule of Maturities of Operating and Finance Lease Liabilities (Details) $ in Thousands	Jun. 30, 2019 USD ($)
Operating Leases
2019 (excluding the six months ended June 30, 2019)	$ 319
2020	1,252
2021	1,061
2022	1,007
2023	1,037
Thereafter	4,865
Total lease payments	9,541
Imputed interest	(3,394)
Tenant allowance	(1,004)
Total	5,143
Finance Lease Liabilities, Payments, Due [Abstract]
2019 (excluding the six months ended June 30, 2019)	17
2020	32
2021	32
Total lease payments	81
Imputed interest	(9)
Total	$ 72

Leases - Summary of Future Annual Minimum Lease Payments Due Under Non-cancellable Operating Leases (Details) $ in Thousands	Dec. 31, 2018 USD ($)
Leases [Abstract]
2019	$ 397
2020	409
2021	83
Total minimum lease payments	$ 889

Grant Revenues - Additional Information (Details) - USD ($)		3 Months Ended		6 Months Ended		48 Months Ended
	Jun. 01, 2014	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	May 31, 2018
Research And Development Arrangement Contract To Perform For Others [Line Items]
Grant revenues			$ 2,378,000	$ 0	$ 3,888,000
Type of revenue [extensible list]		us-gaap:GrantMember	us-gaap:GrantMember	us-gaap:GrantMember	us-gaap:GrantMember
CPRIT
Research And Development Arrangement Contract To Perform For Others [Line Items]
Grant contract term	4 years
Grant contract beginning date	Jun. 01, 2014
Grant contract expiration date	May 31, 2018
Grant revenues						$ 19,800,000
Type of revenue [extensible list]						us-gaap:GrantMember
CPRIT \| Maximum
Research And Development Arrangement Contract To Perform For Others [Line Items]
Research grant contract amount	$ 19,800,000

Stockholders' Equity - Additional Information (Details) - USD ($)	1 Months Ended	3 Months Ended		6 Months Ended
	Feb. 28, 2019	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Jan. 01, 2019	Jan. 01, 2018
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Net proceeds from sale of common stock	$ 64,500,000
Underwriting discounts and commissions	4,100,000
Offering costs	$ 400,000
Reduction in exercise price of each warrant from public offering price for pre-funded warrants per share	$ 0.0001
Maximum ownership percentage for outstanding warrants to purchase shares of common stock to be exercised	4.99%
Period after notice received by company maximum ownership percentage to be effective description				The revised Maximum Ownership Percentage would be effective 60 days after the notice is received by the Company.
Proceeds from Warrant Exercises				$ 0
2016 Equity Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Percentage of outstanding share of common stock				4.00%
Additional number of shares available for issuance						965,603	666,807
Common stock available for future issuance		1,459,072		1,459,072
2016 Equity Incentive Plan \| Stock Options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock option to purchase an aggregate of common stock shares		159,600	203,600	1,201,900	1,033,100
Stock options to purchase common stock aggregate fair value		$ 700,000	$ 1,500,000	$ 6,900,000	$ 5,400,000
2016 Employee Stock Purchase Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock option to purchase an aggregate of common stock shares		0	0	20,132	30,937
Aggregate cash proceeds from sale of shares				$ 100,000	$ 100,000
Common Stock
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares issued			5,047,000
Follow-on Public Offering \| Common Stock
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares issued	4,625,000
Public offering price	$ 8.00
Public offering price of warrant	$ 7.9999
Follow-on Public Offering \| Common Stock \| Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Warrants to purchase shares	4,000,000
Underwriters' Over-allotment Option
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares issued	1,125,000

Stockholders' Equity - Summary of Stock-Based Compensation Expense (Details) - 2016 Equity Incentive Plans and Employee Stock Purchase Plan - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Employee Service Share Based Compensation Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expense	$ 1,245	$ 996	$ 2,326	$ 1,831
Research and Development
Employee Service Share Based Compensation Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expense	464	390	866	713
General and Administrative
Employee Service Share Based Compensation Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expense	$ 781	$ 606	$ 1,460	$ 1,118

Stockholders' Equity - Schedule of Estimate Fair Value of Stock Options Granted (Details)	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Equity Incentive Plans
Employee Service Share Based Compensation Allocation of Recognized Period Costs [Line Items]
Expected term (in years)	5 years 8 months 12 days	5 years 8 months 12 days	5 years 11 months 26 days	5 years 11 months 12 days
Expected volatility	78.00%	84.00%	81.00%	85.00%
Risk-free interest	2.05%	2.79%	2.50%	2.73%
Dividend yield	0.00%	0.00%	0.00%	0.00%
2016 Employee Stock Purchase Plan
Employee Service Share Based Compensation Allocation of Recognized Period Costs [Line Items]
Expected term (in years)	0 years	0 years	5 months 26 days	5 months 26 days
Expected volatility			66.00%	69.00%
Risk-free interest			2.55%	2.00%
Dividend yield			0.00%	0.00%

Net Loss Per Share - Weighted-Average Equity Instruments Excluded from Calculation of Diluted Net Loss Per Share (Details) - shares	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Unvested Restricted Common Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share	6,861	30,408	6,861	31,233
Options to Purchase Common Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share	4,081,102	3,015,991	3,781,559	2,856,763

License Agreements - Additional Information (Details) - License Agreements $ in Millions	1 Months Ended	6 Months Ended
	Jan. 31, 2017 USD ($) LicenseAgreement	Jun. 30, 2019
Research And Development Arrangement Contract To Perform For Others [Line Items]
Research agreement date		2013-12
Number of license agreements \| LicenseAgreement	2
Maximum future contingent license payment	$ 6.4
Aggregate potential milestone payments for receipt of regulatory approval	5.0
Aggregate potential milestone payments for final regulatory approval of second indication	$ 0.5
Minimum
Research And Development Arrangement Contract To Perform For Others [Line Items]
Rate of revenue share	6.50%
Maximum
Research And Development Arrangement Contract To Perform For Others [Line Items]
Rate of revenue share	25.00%