Spyre Therapeutics (SYRE) 10-Q 9 May 17 2017 Q1 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	3 Months Ended
	Mar. 31, 2017	May 08, 2017
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Mar. 31, 2017
Document Fiscal Year Focus	2,017
Document Fiscal Period Focus	Q1
Trading Symbol	AGLE
Entity Registrant Name	Aeglea BioTherapeutics, Inc.
Entity Central Index Key	1,636,282
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Entity Common Stock, Shares Outstanding		13,452,260

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets (unaudited) - USD ($)	Mar. 31, 2017	Dec. 31, 2016
CURRENT ASSETS
Cash and cash equivalents	$ 16,801,000	$ 47,748,000
Marketable securities	41,067,000	15,754,000
Accounts receivable - grant	981,000	1,215,000
Prepaid expenses and other current assets	1,456,000	1,707,000
Total current assets	60,305,000	66,424,000
Property and equipment, net	822,000	599,000
Other non-current assets	140,000	40,000
TOTAL ASSETS	61,267,000	67,063,000
CURRENT LIABILITIES
Accounts payable	267,000	168,000
Deferred revenue	51,000	71,000
Accrued and other current liabilities	3,639,000	3,726,000
Total current liabilities	3,957,000	3,965,000
Other non-current liabilities	127,000	132,000
TOTAL LIABILITIES	4,084,000	4,097,000
Commitments and Contingencies (Notes 9 and 11)
STOCKHOLDERS’ EQUITY
Preferred stock, $0.0001 par value; 10,000,000 shares authorized as of March 31, 2017 and December 31, 2016; no shares issued and outstanding as of March 31, 2017 and December 31, 2016
Common stock, $0.0001 par value; 500,000,000 shares authorized as of March 31, 2017 and December 31, 2016; 13,452,260 shares and 13,430,833 shares issued and outstanding as of March 31, 2017 and December 31, 2016, respectively	1,000	1,000
Additional paid-in capital	108,743,000	108,246,000
Accumulated other comprehensive loss	(37,000)	(4,000)
Accumulated deficit	(51,524,000)	(45,277,000)
TOTAL STOCKHOLDERS’ EQUITY	57,183,000	62,966,000
TOTAL LIABILITIES AND STOCKHOLDERS’ EQUITY	$ 61,267,000	$ 67,063,000

Condensed Consolidated Balance3

Condensed Consolidated Balance Sheets (unaudited) (Parenthetical) - $ / shares	Mar. 31, 2017	Dec. 31, 2016
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	13,452,260	13,430,833
Common stock, shares outstanding	13,452,260	13,430,833

Condensed Consolidated Statemen

Condensed Consolidated Statements of Operations (Unaudited) - USD ($)	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Revenues:
Grant	$ 982,000	$ 859,000
Operating expenses:
Research and development	4,949,000	3,596,000
General and administrative	2,364,000	1,830,000
Total operating expenses	7,313,000	5,426,000
Loss from operations	(6,331,000)	(4,567,000)
Other income (expense):
Interest income	95,000	26,000
Other expense, net	(11,000)	(6,000)
Total other income	84,000	20,000
Net loss	$ (6,247,000)	$ (4,547,000)
Net loss per share, basic and diluted	$ (0.47)	$ (7.10)
Weighted-average common shares outstanding, basic and diluted	13,365,823	640,699

Condensed Consolidated Stateme5

Condensed Consolidated Statements of Comprehensive Loss (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Statement Of Income And Comprehensive Income [Abstract]
Net loss	$ (6,247)	$ (4,547)
Other comprehensive income (loss):
Unrealized gain (loss) on marketable securities	(33)	4
Total comprehensive loss	$ (6,280)	$ (4,543)

Condensed Consolidated Stateme6

Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
CASH FLOWS FROM OPERATING ACTIVITIES
Net loss	$ (6,247)	$ (4,547)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	52	29
Purchase premium on marketable securities	(55)	(16)
Amortization of premium on marketable securities	49	8
Deferred rent	5
Amortization of lease allowance liability	(10)	(6)
Stock-based compensation	401	140
Research and development services settled with convertible preferred stock		20
Changes in operating assets and liabilities:
Accounts receivable - grant	234	79
Prepaid expenses and other assets	151	(431)
Accounts payable	95	261
Deferred revenue	(20)
Accrued and other liabilities	(87)	475
Net cash used in operating activities	(5,432)	(3,988)
CASH FLOWS FROM INVESTING ACTIVITIES
Purchases of property and equipment	(271)	(2)
Purchases of marketable securities	(32,780)	(2,940)
Proceeds from maturities of marketable securities	7,440	1,750
Net cash used in investing activities	(25,611)	(1,192)
CASH FLOWS FROM FINANCING ACTIVITIES
Payment of deferred offering costs		(98)
Proceeds from employee stock plan purchases and issuance of common stock	96
Net cash provided (used) by financing activities	96	(98)
NET DECREASE IN CASH AND CASH EQUIVALENTS	(30,947)	(5,278)
CASH AND CASH EQUIVALENTS
Beginning of period	47,748	29,294
End of period	16,801	$ 24,016
Supplemental Disclosure of Non-Cash Investing and Financing Information:
Unpaid amounts related to purchase of property and equipment	$ 4

The Company and Basis of Presen

The Company and Basis of Presentation	3 Months Ended
	Mar. 31, 2017
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 a clinical-stage biotechnology company committed to developing enzyme-based therapeutics in the field of amino acid metabolism to treat rare genetic diseases and cancer. 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 (the “LLC Conversion”) on March 10, 2015. The Company operates in one segment and has its principal offices in Austin, Texas. Initial Public Offering On April 6, 2016, the Company’s Registration Statement on Form S-1 (File No. 333-205001) relating to the initial public offering (“IPO”) of its common stock was declared effective by the Securities and Exchange Commission (“SEC”). The IPO closed on April 12, 2016, and 5,481,940 shares of common stock were sold at a public offering price of $10.00 per share, including 481,940 shares of common stock issued upon the partial exercise by the underwriters of their option to purchase additional shares. The Company received $47.3 million in aggregate cash proceeds, net of underwriting discounts and commissions of $3.8 million and offering costs of $3.7 million incurred by the Company. Immediately prior to the closing of the IPO, all shares of outstanding convertible preferred stock were automatically converted, at a ratio of one share of common stock for each share of convertible preferred stock, into 7,172,496 shares of common stock with the related carrying value of $58.3 million reclassified to common stock and additional paid-in capital. In connection with the IPO, the Company amended its Restated Certificate of Incorporation to change the authorized capital stock to 510,000,000 shares of which 500,000,000 shares are designated as common stock and 10,000,000 shares are designated as preferred stock, all with a par value of $0.0001 per share. There are no shares of preferred stock outstanding as of March 31, 2017. Liquidity As of March 31, 2017, the Company had working capital of $56.3 million, an accumulated deficit of $51.5 million, and cash, cash equivalents, and marketable securities of $57.9 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 plan, the Company believes that it has sufficient resources to fund operations through March 31, 2019 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 March 31, 2017, and its results of operations for the three months ended March 31, 2017 and 2016, and cash flows for the three months ended March 31, 2017 and 2016. The results of operations for the three months ended March 31, 2017 are not necessarily indicative of the results to be expected for the year ending December 31, 2017 or for any other future annual or interim period. The December 31, 2016 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, 2016 as filed with the SEC.

Summary of Significant Accounti

Summary of Significant Accounting Policies	3 Months Ended
	Mar. 31, 2017
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, fair values of preferred and common stock, 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 three months ended March 31, 2017 and 2016. Interest on marketable securities is included in interest Concentration of Credit Risk Financial instruments that potentially subject the Company to a concentration of credit risk consist of cash, cash equivalents, and marketable securities. The Company’s investment policy limits investments to high credit quality securities issued by the U.S. government, U.S. government-sponsored agencies and highly rated banks, subject to certain concentration limits and restrictions on maturities. The Company’s cash, cash equivalents, and marketable securities 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 and cash equivalents 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 and cash equivalents 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 three months ended March 31, 2017 and 2016. 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 entered into lease agreements for its office and laboratory facilities. The leases are classified as operating leases. The Company records rent expense on a straight-line basis over the term of the leases and, accordingly records the difference between cash rent payments and the recognition of rent expense as a deferred rent liability. Incentives granted under the Company’s facilities leases, including allowances to fund leasehold improvements, are deferred and are recognized as adjustments to rental expense on a straight-line basis over the term of the lease. 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 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, and marketable securities. 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 is 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 is recognized when qualifying costs are incurred and there is reasonable assurance that the conditions of the award have been met for collection. Proceeds received prior to the costs being incurred or the conditions of the award being met are recognized as deferred revenue until the services are performed and the conditions of the award are met (see Note 5). 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, share-based compensation, consulting costs, contract research service costs, laboratory supplies, 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. Certain research and development costs incurred were settled contractually by the Company issuing a variable number of the Company’s shares determined by dividing the fixed monetary amount of costs incurred by the issuance-date fair value of the issuable shares. The Company recorded research and development expense for these costs and accrued for the fixed monetary amount as an accrued liability as the services were rendered until the amount was settled. In June 2015, the remaining Company obligation to settle these costs with Company shares was converted to a cash-based payment through a contract amendment with the service provider. 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 based on the estimated grant-date fair values of the awards. The value of the award is recognized as expense ratably over the requisite service period. The Company recognizes the compensation costs for awards that vest over several years on a straight-line basis over the vesting period. Forfeitures are recognized when they occur, which may result in the reversal of compensation costs in subsequent periods as the forfeitures arise. The Company recognizes the cost of stock-based awards granted to nonemployees at their then-current fair values as services are performed, and are remeasured through the counterparty performance date. Income Taxes Effective January 1, 2015, the Company, for tax purposes, converted from a partnership to a corporation and continues to serve as a holding company for seven wholly-owned subsidiary corporations. Beginning with the year ended December 31, 2015, the Company filed a consolidated corporate federal income tax return. The Company and its subsidiaries 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. 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 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 (loss) is currently comprised of changes in unrealized gains and losses on available-for-sale securities. Reclassification Certain reclassifications have been made to prior period amounts to conform to current period presentation. These reclassifications did not have an impact on the Company’s results of operations or financial position as of March 31, 2017 and December 31, 2016. Recent Accounting Pronouncements In February 2016, the FASB issued ASU No. 2016-02, Leases (Topic 842)

Cash Equivalents and Marketable

Cash Equivalents and Marketable Securities	3 Months Ended
	Mar. 31, 2017
Investments Debt And Equity Securities [Abstract]
Cash Equivalents and Marketable Securities	3. 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): March 31, 2017 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Estimated Fair Value Cash equivalents: Money market funds $ 3,781 $ — $ — $ 3,781 Reverse repurchase agreements 10,250 — — 10,250 Total cash equivalents 14,031 — — 14,031 Marketable securities: US government and agency securities 41,104 — (37 ) 41,067 Total marketable securities $ 41,104 $ — $ (37 ) $ 41,067 December 31, 2016 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Estimated Fair Value Cash equivalents: Money market funds $ 4,584 $ — $ — $ 4,584 Reverse repurchase agreements 39,250 — — 39,250 Total cash equivalents 43,834 — — 43,834 Marketable securities: US government and agency securities 15,758 — (4 ) 15,754 Total marketable securities $ 15,758 $ — $ (4 ) $ 15,754 The reverse repurchase agreements are settled in cash nightly, and as such are classified as cash equivalents. As of March 31, 2017 and December 31, 2016, the Company held 22 and nine debt securities, respectively, that were in an unrealized loss position for less than one year. The aggregate fair value of debt securities in an unrealized loss position as of March 31, 2017 and December 31, 2016 were $41.1 million and $15.8 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 March 31, 2017 and December 31, 2016. The following tables summarizes the contractual maturities of the Company’s marketable securities at estimated fair value (in thousands): March 31, December 31, 2017 2016 Due in one year or less $ 39,075 $ 15,754 Due in 1 - 2 years 1,992 — Total marketable securities $ 41,067 $ 15,754 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 Liabi

Accrued and Other Current Liabilities	3 Months Ended
	Mar. 31, 2017
Accrued Liabilities And Other Liabilities [Abstract]
Accrued and Other Current Liabilities	4. Accrued and Other Current Liabilities Accrued and other current liabilities consist of the following (in thousands): March 31, December 31, 2017 2016 Accrued compensation $ 759 $ 1,270 Accrued contracted research and development costs 2,022 1,749 Accrued professional and consulting fees 743 480 Accrued other and other current liabilities 115 227 Total accrued and other current liabilities $ 3,639 $ 3,726

Grant Revenues

Grant Revenues	3 Months Ended
	Mar. 31, 2017
Grant Revenues [Abstract]
Grant Revenues	5. 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 covers 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 in royalties. The Company recognized grant revenue of $982,000 and $859,000 in the three months ended March 31, 2017 and 2016, respectively, for qualified expenditures under the grant. As of March 31, 2017 and December 31, 2016, the Company had an outstanding grant receivable of $981,000 and $1.2 million, respectively, for the grant expenditures that were paid but had not been reimbursed and deferred revenue of $51,000 and $71,000, respectively, for proceeds received but for which the costs had not been incurred or the conditions of the award had not been met.

Stock-Based Compensation

Stock-Based Compensation	3 Months Ended
	Mar. 31, 2017
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Stock-Based Compensation	6. Stock-Based Compensation The 2016 Equity Incentive Plan (“2016 Plan”) provides for an automatic annual increase in the number of shares available for issuance thereunder, to be added on the first day of each fiscal year, beginning on January 1, 2017 and continuing through 2023, up to 4% of the outstanding number of shares of the Company’s common stock on the December 31 immediately prior to the date of increase, provided that an increase is only effective if the Company’s board of directors either confirmed the automatic increase or approved the increase of a lesser number of shares prior to January 1 of each relevant year The Company granted equity awards under its 2015 Equity Incentive Plan (“2015 Plan”) until April 2016 when it was terminated as to future awards, although it continues to govern the terms of awards that remain outstanding under the 2015 Plan. In connection with the Company’s adoption of the 2016 Plan, all remaining shares available for future issuance under the 2015 Plan were transferred to the 2016 Plan. During the three months ended March 31, 2017 and 2016, the Company issued an aggregate of 772,800 and 84,417 options, respectively, to purchase common stock under its equity incentive plans for an aggregate fair value of $4,161,205 and $332,000, respectively. Additionally, the Company issued and sold 18,184 shares under the 2016 Employee Stock Purchase Plan (“2016 ESPP”) for aggregate cash proceeds of $78,000 during the three months ended March 31, 2017. There were no shares issued and sold under the 2016 ESPP during the three months ended March 31, 2016. Total stock-based compensation expense related to the Company’s equity incentive plans and 2016 ESPP was as follows (in thousands): Three Months Ended March 31, 2017 2016 Research and development $ 110 $ 54 General and administrative 291 86 Total stock-based compensation expense $ 401 $ 140 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 equity incentive plans and the shares purchasable under the 2016 ESPP during the periods presented: Three Months Ended March 31, 2017 2016 Equity Incentive Plans Expected term 5.99 5.94 Expected volatility 86 % 87 % Risk-free interest 2.13 % 1.26 % Dividend yield 0 % 0 % 2016 ESPP Expected term 0.50 — Expected volatility 79 % — Risk-free interest 0.68 % — Dividend yield 0 % —

Fair Value Measurements

Fair Value Measurements	3 Months Ended
	Mar. 31, 2017
Fair Value Disclosures [Abstract]
Fair Value Measurements	7. 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): March 31, 2017 Level 1 Level 2 Level 3 Total Financial Assets Money market funds $ 3,781 $ — $ — $ 3,781 Reverse repurchase agreements — 10,250 — 10,250 US government and agency securities — 41,067 — 41,067 Total financial assets $ 3,781 $ 51,317 $ — $ 55,098 December 31, 2016 Level 1 Level 2 Level 3 Total Financial Assets Money market funds $ 4,584 $ — $ — $ 4,584 Reverse repurchase agreements — 39,250 — 39,250 US government and agency securities — 15,754 — 15,754 Total financial assets $ 4,584 $ 55,004 $ — $ 59,588 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 and U.S. government and agency 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.

Net Loss Per Share Attributable

Net Loss Per Share Attributable to Common Stockholders	3 Months Ended
	Mar. 31, 2017
Earnings Per Share [Abstract]
Net Loss Per Share Attributable to Common Stockholders	8. Net Loss Per Share Attributable to Common Stockholders The Company computed net loss attributable per common stockholder using the two-class method required for participating securities through the date of the IPO. Immediately prior to the IPO, all outstanding convertible preferred stock was converted into common stock (see Note 1). The Company considered convertible preferred stock to be participating securities. In the event that the Company had paid out distributions, holders of convertible preferred stock would have participated in the distribution. The two-class method is an earnings (loss) allocation method under which earnings (loss) per share is calculated for common stock and participating security considering a participating security’s rights to undistributed earnings (loss) as if all such earnings (loss) had been distributed during the period. The convertible preferred stock did not have an obligation to fund losses and are therefore excluded from the calculation of basic net loss per share. The Company’s Series A and B convertible preferred stock were entitled to receive noncumulative dividends and in preference to any dividends on shares of the Company’s common stock. Basic and diluted net loss per share attributable to common stockholders is computed by dividing net loss attributable to common stock by the weighted-average number of common stock outstanding during the period. 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 March 31, 2017 2016 Series A convertible preferred stock — 2,172,520 Series B convertible preferred stock — 4,999,976 Unvested restricted common stock 74,013 116,635 Options to purchase common stock 1,330,481 588,832

Research and License Agreements

Research and License Agreements	3 Months Ended
	Mar. 31, 2017
Licensing Agreements [Abstract]
Research and License Agreements	9. Research and License Agreements University Research Agreement In December 2013, the Company entered into a research agreement with the University of Texas at Austin (the “University”). Under the terms of this research agreement, the Company engaged the University to perform certain nonclinical research activities related to the systemic depletion of amino acids for cancer therapy and rare disease therapy. Under the research agreement, the Company was required to pay the University an annual amount not to exceed $386,000 during the one year term of the agreement from the effective date. Pursuant to subsequent amendments to the research agreement, the term and maximum expenditure limitation were extended and increased through August 31, 2017 for a combined $1.8 million. For the three months ended March 31, 2017 and 2016, the Company paid $188,000 and $457,000, respectively, the University under the research agreement. 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 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. Pursuant to the terms of the Restated License, the Company may be required to pay the University up to $6.4 million 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 $500,000 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.

Related Party Transactions

Related Party Transactions	3 Months Ended
	Mar. 31, 2017
Related Party Transactions [Abstract]
Related Party Transactions	10. Related Party Transactions The spouse of the Company’s Chief Executive Officer previously provided consulting services to the Company. For the three months ended March 31, 2017, there were no payments made to the spouse in consulting fees. For the three months ended March 31, 2016, the Company paid $129,000 to the spouse in consulting fees, which were recorded in Research and Development expenses. As of March 31, 2017 and December 31, 2016, the Company had no outstanding liability to the related party. One of the founders, a non-employee member of the Company’s Board of Directors, entered into a consulting agreement with the Company in 2014 under which the founder would receive $50,000 per year for a fixed number of hours of consulting and advisory services and receive equity incentive shares, which converted into 43,290 restricted stock awards and 13,852 stock options upon the LLC Conversion, with the vesting contingent on time and performance milestones being achieved. For the three months ended March 31, 2017, there were no payments made to the Founder under the consulting agreement. For the three months ended March 31, 2016, the Company paid $13,000 to the Founder under the consulting agreement. As of March 31, 2017 and December 31, 2016, the Company had no outstanding liability to the related party.

Commitments and Contingencies

Commitments and Contingencies	3 Months Ended
	Mar. 31, 2017
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingencies	11. Commitments and Contingencies The Company leases office space in Austin, Texas under an operating lease that commenced in January 2015. The lease was amended in September 2016 to increase office space and extend the term to December 31, 2020. Under the terms of the amended office lease agreement, the security deposit requirement was set at $39,000 until the expiration of the lease. The lessor is entitled to retain all or any part of the security deposit for payment in the event of any uncured default by the Company under the terms of the lease. In February 2017, the Company entered into a lease agreement for laboratory facilities in Austin, Texas under an operating lease, which will expire in December 2017. The following table summarizes the Company’s future minimum lease commitments as of March 31, 2017 (in thousands): Year ending December 31: 2017 $ 314 2018 283 2019 291 2020 300 2021 — Total minimum lease payments $ 1,188 For the three months ended March 31, 2017 and 2016, the Company incurred $76,000 and $35,000, respectively, in rent expense under noncancellable operating leases.

Subsequent Events

Subsequent Events	3 Months Ended
	Mar. 31, 2017
Subsequent Events [Abstract]
Subsequent Events	12. Subsequent Events On April 21, 2017, the Company appointed a member of its board of directors as interim chief medical officer (“interim CMO”). Under the employment agreement, the interim CMO will receive a salary of $27,000 per month and an option to purchase 24,000 shares of common stock, subject to a service condition. On May 1, 2017, the Company filed a shelf registration statement on Form S-3 for the potential offering, issuance and sale by the Company of up to $150 million of common stock, preferred stock, debt securities, warrants to purchase common stock, preferred stock and debt securities, subscription rights to purchase common stock, preferred stock and debt securities, and units consisting of all or some of these securities. The shelf registration statement has not been declared effective by the SEC. Up to $20 million of the maximum aggregate offering price of $150 million under the registration statement, if declared effective by the SEC, may be issued and sold pursuant to an “at-the-market” offering for sales of the Company’s common stock pursuant to a sales agreement between the Company and JonesTrading Institutional Services LLC.

Summary of Significant Accoun19

Summary of Significant Accounting Policies (Policies)	3 Months Ended
	Mar. 31, 2017
Accounting Policies [Abstract]
Use of Estimates	Use of Estimates The preparation of financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the amounts reported in the consolidated financial statements and accompanying notes. Such management estimates include those related to accruals of research and development related costs, fair values of preferred and common stock, 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	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	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 three months ended March 31, 2017 and 2016. Interest on marketable securities is included in interest
Concentration of Credit Risk	Concentration of Credit Risk Financial instruments that potentially subject the Company to a concentration of credit risk consist of cash, cash equivalents, and marketable securities. The Company’s investment policy limits investments to high credit quality securities issued by the U.S. government, U.S. government-sponsored agencies and highly rated banks, subject to certain concentration limits and restrictions on maturities. The Company’s cash, cash equivalents, and marketable securities 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 and cash equivalents 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 and cash equivalents and bond issuers.
Property and Equipment	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	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 three months ended March 31, 2017 and 2016.
Accrued Research And Development Costs	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	Leases The Company entered into lease agreements for its office and laboratory facilities. The leases are classified as operating leases. The Company records rent expense on a straight-line basis over the term of the leases and, accordingly records the difference between cash rent payments and the recognition of rent expense as a deferred rent liability. Incentives granted under the Company’s facilities leases, including allowances to fund leasehold improvements, are deferred and are recognized as adjustments to rental expense on a straight-line basis over the term of the lease.
Fair Value of Financial Instruments	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 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, and marketable securities. The carrying amount of accounts receivable, accounts payable and accrued liabilities approximate fair value due to their relatively short maturities.
Revenue Recognition	Revenue Recognition The Company’s sole source of revenue is 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 is recognized when qualifying costs are incurred and there is reasonable assurance that the conditions of the award have been met for collection. Proceeds received prior to the costs being incurred or the conditions of the award being met are recognized as deferred revenue until the services are performed and the conditions of the award are met (see Note 5).
Research and Development Costs	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, share-based compensation, consulting costs, contract research service costs, laboratory supplies, 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. Certain research and development costs incurred were settled contractually by the Company issuing a variable number of the Company’s shares determined by dividing the fixed monetary amount of costs incurred by the issuance-date fair value of the issuable shares. The Company recorded research and development expense for these costs and accrued for the fixed monetary amount as an accrued liability as the services were rendered until the amount was settled. In June 2015, the remaining Company obligation to settle these costs with Company shares was converted to a cash-based payment through a contract amendment with the service provider. 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	Stock-Based Compensation The Company recognizes the cost of stock-based awards granted to employees based on the estimated grant-date fair values of the awards. The value of the award is recognized as expense ratably over the requisite service period. The Company recognizes the compensation costs for awards that vest over several years on a straight-line basis over the vesting period. Forfeitures are recognized when they occur, which may result in the reversal of compensation costs in subsequent periods as the forfeitures arise. The Company recognizes the cost of stock-based awards granted to nonemployees at their then-current fair values as services are performed, and are remeasured through the counterparty performance date.
Income Taxes	Income Taxes Effective January 1, 2015, the Company, for tax purposes, converted from a partnership to a corporation and continues to serve as a holding company for seven wholly-owned subsidiary corporations. Beginning with the year ended December 31, 2015, the Company filed a consolidated corporate federal income tax return. The Company and its subsidiaries 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. 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 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 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 (loss) is currently comprised of changes in unrealized gains and losses on available-for-sale securities.
Reclassification	Reclassification Certain reclassifications have been made to prior period amounts to conform to current period presentation. These reclassifications did not have an impact on the Company’s results of operations or financial position as of March 31, 2017 and December 31, 2016.
Recent Accounting Pronouncements	Recent Accounting Pronouncements In February 2016, the FASB issued ASU No. 2016-02, Leases (Topic 842)

Summary of Significant Accoun20

Summary of Significant Accounting Policies (Tables)	3 Months Ended
	Mar. 31, 2017
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

Cash Equivalents and Marketab21

Cash Equivalents and Marketable Securities (Tables)	3 Months Ended
	Mar. 31, 2017
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): March 31, 2017 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Estimated Fair Value Cash equivalents: Money market funds $ 3,781 $ — $ — $ 3,781 Reverse repurchase agreements 10,250 — — 10,250 Total cash equivalents 14,031 — — 14,031 Marketable securities: US government and agency securities 41,104 — (37 ) 41,067 Total marketable securities $ 41,104 $ — $ (37 ) $ 41,067 December 31, 2016 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Estimated Fair Value Cash equivalents: Money market funds $ 4,584 $ — $ — $ 4,584 Reverse repurchase agreements 39,250 — — 39,250 Total cash equivalents 43,834 — — 43,834 Marketable securities: US government and agency securities 15,758 — (4 ) 15,754 Total marketable securities $ 15,758 $ — $ (4 ) $ 15,754
Summary of Contractual Maturities of Marketable Securities at Estimated Fair Value	The following tables summarizes the contractual maturities of the Company’s marketable securities at estimated fair value (in thousands): March 31, December 31, 2017 2016 Due in one year or less $ 39,075 $ 15,754 Due in 1 - 2 years 1,992 — Total marketable securities $ 41,067 $ 15,754

Accrued and Other Current Lia22

Accrued and Other Current Liabilities (Tables)	3 Months Ended
	Mar. 31, 2017
Accrued Liabilities And Other Liabilities [Abstract]
Accrued and Other Current Liabilities	Accrued and other current liabilities consist of the following (in thousands): March 31, December 31, 2017 2016 Accrued compensation $ 759 $ 1,270 Accrued contracted research and development costs 2,022 1,749 Accrued professional and consulting fees 743 480 Accrued other and other current liabilities 115 227 Total accrued and other current liabilities $ 3,639 $ 3,726

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	3 Months Ended
	Mar. 31, 2017
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 March 31, 2017 2016 Research and development $ 110 $ 54 General and administrative 291 86 Total stock-based compensation expense $ 401 $ 140
Schedule of Estimated Fair Value of Stock Options Granted	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 equity incentive plans and the shares purchasable under the 2016 ESPP during the periods presented: Three Months Ended March 31, 2017 2016 Equity Incentive Plans Expected term 5.99 5.94 Expected volatility 86 % 87 % Risk-free interest 2.13 % 1.26 % Dividend yield 0 % 0 % 2016 ESPP Expected term 0.50 — Expected volatility 79 % — Risk-free interest 0.68 % — Dividend yield 0 % —

Fair Value Measurement (Tables)

Fair Value Measurement (Tables)	3 Months Ended
	Mar. 31, 2017
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): March 31, 2017 Level 1 Level 2 Level 3 Total Financial Assets Money market funds $ 3,781 $ — $ — $ 3,781 Reverse repurchase agreements — 10,250 — 10,250 US government and agency securities — 41,067 — 41,067 Total financial assets $ 3,781 $ 51,317 $ — $ 55,098 December 31, 2016 Level 1 Level 2 Level 3 Total Financial Assets Money market funds $ 4,584 $ — $ — $ 4,584 Reverse repurchase agreements — 39,250 — 39,250 US government and agency securities — 15,754 — 15,754 Total financial assets $ 4,584 $ 55,004 $ — $ 59,588

Net Loss Per Share Attributab25

Net Loss Per Share Attributable to Common Stockholders (Tables)	3 Months Ended
	Mar. 31, 2017
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 March 31, 2017 2016 Series A convertible preferred stock — 2,172,520 Series B convertible preferred stock — 4,999,976 Unvested restricted common stock 74,013 116,635 Options to purchase common stock 1,330,481 588,832

Commitments and Contingencies (

Commitments and Contingencies (Tables)	3 Months Ended
	Mar. 31, 2017
Commitments And Contingencies Disclosure [Abstract]
Summary of Future Minimum Commitments for Operating Leases	The following table summarizes the Company’s future minimum lease commitments as of March 31, 2017 (in thousands): Year ending December 31: 2017 $ 314 2018 283 2019 291 2020 300 2021 — Total minimum lease payments $ 1,188

The Company and Basis of Pres27

The Company and Basis of Presentation - Additional Information (Details) $ / shares in Units, $ in Thousands	Apr. 12, 2016USD ($)$ / sharesshares	Mar. 31, 2017USD ($)Segment$ / sharesshares	Mar. 31, 2016USD ($)	Dec. 31, 2016USD ($)$ / sharesshares
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Number of operating segments | Segment		1
Offering costs			$ 98
Capital stock, shares authorized | shares	510,000,000
Common stock, shares authorized | shares	500,000,000	500,000,000		500,000,000
Preferred stock, shares authorized | shares	10,000,000	10,000,000		10,000,000
Common stock, par value | $ / shares	$ 0.0001	$ 0.0001		$ 0.0001
Preferred stock, par value | $ / shares	$ 0.0001	$ 0.0001		$ 0.0001
Preferred stock, shares outstanding | shares		0		0
Working capital		$ 56,300
Accumulated deficit		(51,524)		$ (45,277)
Cash, cash equivalents and marketable securities		$ 57,900
Common Stock
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Proceeds from issuance of common stock upon initial public offering, net	$ 47,300
IPO
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Convertible preferred stock, terms of conversion		Ratio of one share of common stock for each share of convertible preferred stock
Convertible preferred stock converted into common stock | shares	7,172,496
Convertible preferred stock reclassified into common stock and additional paid-in-capital	$ 58,311
IPO | Common Stock
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Number of shares issued | shares	5,481,940
Public offering price | $ / shares	$ 10
Underwriting discounts and commissions	$ 3,800
Offering costs	$ 3,700
Underwriters' Over-allotment Option | Common Stock
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Number of shares issued | shares	481,940

Summary of Significant Accoun28

Summary of Significant Accounting Policies - Additional Information (Details)	Jun. 30, 2015USD ($)	Mar. 31, 2017USD ($)	Mar. 31, 2016USD ($)	Jan. 01, 2015Subsidary
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	$ 19,800,000

Summary of Significant Accoun29

Summary of Significant Accounting Policies - Summary of Useful Lives of Property and Equipment (Details)	3 Months Ended
	Mar. 31, 2017
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

Cash Equivalents and Marketab30

Cash Equivalents and Marketable Securities - Schedule of Estimated Fair Value of Cash Equivalents and Marketable Securities (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Schedule Of Available For Sale Securities [Line Items]
Cash equivalents, amortized cost	$ 14,031	$ 43,834
Cash equivalents, estimated fair value	14,031	43,834
Marketable securities, amortized cost	41,104	15,758
Marketable securities, gross unrealized losses	(37)	(4)
Marketable securities, estimated fair value	41,067	15,754
Money market funds
Schedule Of Available For Sale Securities [Line Items]
Cash equivalents, amortized cost	3,781	4,584
Cash equivalents, estimated fair value	3,781	4,584
Reverse repurchase agreements
Schedule Of Available For Sale Securities [Line Items]
Cash equivalents, amortized cost	10,250	39,250
Cash equivalents, estimated fair value	10,250	39,250
US government and agency securities
Schedule Of Available For Sale Securities [Line Items]
Marketable securities, amortized cost	41,104	15,758
Marketable securities, gross unrealized losses	(37)	(4)
Marketable securities, estimated fair value	$ 41,067	$ 15,754

Cash Equivalents and Marketab31

Cash Equivalents and Marketable Securities - Additional Information (Details) - US government and agency securities $ in Millions	Mar. 31, 2017USD ($)Security	Dec. 31, 2016USD ($)Security
Cash Equivalents And Marketable Securities [Line Items]
Number of securities in an unrealized loss position for less than one year	22	9
Fair value of debt securities in an unrealized loss position | $	$ 41.1	$ 15.8
Number of securities in a significant unrealized loss position	0	0

Cash Equivalents and Marketab32

Cash Equivalents and Marketable Securities - Summary of Contractual Maturities of Marketable Securities at Estimated Fair Value (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Investments Debt And Equity Securities [Abstract]
Due in one year or less	$ 39,075	$ 15,754
Due in 1 - 2 years	1,992
Total marketable securities	$ 41,067	$ 15,754

Accrued and Other Current Lia33

Accrued and Other Current Liabilities (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Accrued Liabilities And Other Liabilities [Abstract]
Accrued compensation	$ 759	$ 1,270
Accrued contracted research and development costs	2,022	1,749
Accrued professional and consulting fees	743	480
Accrued other and other current liabilities	115	227
Total accrued and other current liabilities	$ 3,639	$ 3,726

Grant Revenues - Additional Inf

Grant Revenues - Additional Information (Details) - USD ($)	Jun. 30, 2015	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016
Research And Development Arrangement Contract To Perform For Others [Line Items]
Grant revenues		$ 982,000	$ 859,000
Outstanding grant receivable		981,000		$ 1,215,000
Deferred revenue		51,000		$ 71,000
CPRIT
Research And Development Arrangement Contract To Perform For Others [Line Items]
Grant contract term	4 years
Grant contract beginning date	Jun. 1, 2014
Grant contract expiration date	May 31, 2018
CPRIT | Maximum
Research And Development Arrangement Contract To Perform For Others [Line Items]
Research grant contract amount	$ 19,800,000	$ 19,800,000

Stock-Based Compensation - Addi

Stock-Based Compensation - Additional Information (Details) - USD ($)	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Jan. 01, 2017
Stock Options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock option to purchase an aggregate of common stock shares	772,800	84,417
Stock options to purchase common stock aggregate fair value	$ 4,161,205	$ 332,000
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			537,233
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	18,184	0
Aggregate cash proceeds from sale of shares	$ 78,000

Stock-Based Compensation - Summ

Stock-Based Compensation - Summary of Stock-Based Compensation Expense (Details) - 2016 Employee Stock Purchase Plan - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Employee Service Share Based Compensation Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expense	$ 401	$ 140
Research and Development
Employee Service Share Based Compensation Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expense	110	54
General and Administrative
Employee Service Share Based Compensation Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expense	$ 291	$ 86

Stock-Based Compensation - Sche

Stock-Based Compensation - Schedule of Estimate Fair Value of Stock Options Granted (Details)	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Equity Incentive Plans
Employee Service Share Based Compensation Allocation of Recognized Period Costs [Line Items]
Expected term	5 years 11 months 27 days	5 years 11 months 9 days
Expected volatility	86.00%	87.00%
Risk-free interest	2.13%	1.26%
Dividend yield	0.00%	0.00%
2016 Employee Stock Purchase Plan
Employee Service Share Based Compensation Allocation of Recognized Period Costs [Line Items]
Expected term	6 months
Expected volatility	79.00%
Risk-free interest	0.68%
Dividend yield	0.00%

Fair Value Measurements - Finan

Fair Value Measurements - Financial Assets and Liabilities Measured at Fair Value on Recurring Basis (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Financial Assets
Financial assets, fair value	$ 55,098	$ 59,588
Money market funds
Financial Assets
Financial assets, fair value	3,781	4,584
Reverse repurchase agreements
Financial Assets
Financial assets, fair value	10,250	39,250
US government and agency securities
Financial Assets
Financial assets, fair value	41,067	15,754
Level 1
Financial Assets
Financial assets, fair value	3,781	4,584
Level 1 | Money market funds
Financial Assets
Financial assets, fair value	3,781	4,584
Level 2
Financial Assets
Financial assets, fair value	51,317	55,004
Level 2 | Reverse repurchase agreements
Financial Assets
Financial assets, fair value	10,250	39,250
Level 2 | US government and agency securities
Financial Assets
Financial assets, fair value	$ 41,067	$ 15,754

Fair Value Measurements - Addit

Fair Value Measurements - Additional Information (Details)	Mar. 31, 2017USD ($)
Fair Value Disclosures [Abstract]
Fair value assets transferred from level 1 to level 2	$ 0

Net Loss Per Share Attributab40

Net Loss Per Share Attributable to Common Stockholders - Weighted-Average Equity Instruments Excluded from Calculation of Diluted Net Loss Per Share (Details) - shares	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Series A Convertible Preferred Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share		2,172,520
Series B Convertible Preferred Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share		4,999,976
Unvested Restricted Common Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share	74,013	116,635
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	1,330,481	588,832

Research and License Agreemen41

Research and License Agreements - Additional Information (Detail)	1 Months Ended	3 Months Ended
	Jan. 31, 2017USD ($)LicenseAgreement	Mar. 31, 2017USD ($)	Mar. 31, 2016USD ($)	Dec. 31, 2013USD ($)
University Research Agreement
Research And Development Arrangement Contract To Perform For Others [Line Items]
Research agreement date		2013-12
Maximum allowable research and development expenses per year		$ 1,800,000		$ 386,000
Research agreement expiration date		Aug. 31, 2017
Payments pursuant to research agreements		$ 188,000	$ 457,000
License Agreements
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	$ 6,400,000
Aggregate potential milestone payments for receipt of regulatory approval	5,000,000
Aggregate potential milestone payments for final regulatory approval of second indication	$ 500,000
License Agreements | Minimum
Research And Development Arrangement Contract To Perform For Others [Line Items]
Rate of revenue share	6.50%
License Agreements | Maximum
Research And Development Arrangement Contract To Perform For Others [Line Items]
Rate of revenue share	25.00%

Related Party Transactions - Ad

Related Party Transactions - Additional Information (Details) - USD ($)	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016
Spouse Of Chief Executive Officer
Related Party Transaction [Line Items]
Outstanding liability to related party	$ 0		$ 0
Spouse Of Chief Executive Officer | Research and Development
Related Party Transaction [Line Items]
Consulting fees	0	$ 129,000
One Of The Founders
Related Party Transaction [Line Items]
Consulting fees	0	$ 13,000
Outstanding liability to related party	0		$ 0
Annual consulting fees to company founder	$ 50,000
One Of The Founders | Stock Option
Related Party Transaction [Line Items]
Shares issued to related party converted into stock options	13,852
One Of The Founders | Unvested Restricted Common Stock
Related Party Transaction [Line Items]
Shares issued to related party converted into restricted stock awards	43,290

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Details) - USD ($)	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Commitments and Contingencies [Line Items]
Security deposit of lease agreement	$ 39,000
Rent expense	$ 76,000	$ 35,000
Austin, Texas
Commitments and Contingencies [Line Items]
Operating lease agreement, commencement date	2015-01
Operating lease agreement, amended date	2016-09
Operating lease agreement, expiration date	Dec. 31, 2020
Austin, Texas | Laboratory Facility
Commitments and Contingencies [Line Items]
Operating lease agreement, commencement date	2017-02
Operating lease agreement, expiration date	2017-12

Commitments and Contingencies44

Commitments and Contingencies - Summary of Future Minimum Commitments for Operating Leases (Details) $ in Thousands	Mar. 31, 2017USD ($)
Commitments And Contingencies Disclosure [Abstract]
2,017	$ 314
2,018	283
2,019	291
2,020	300
Total minimum lease payments	$ 1,188

Subsequent Events - Additional

Subsequent Events - Additional Information (Details) - Subsequent Event - USD ($)	May 01, 2017	Apr. 21, 2017
Subsequent Event [Line Items]
Maximum aggregate offering price	$ 150,000,000
At The Market Sales Agreement | JonesTrading Institutional Services LLC
Subsequent Event [Line Items]
Maximum aggregate offering price of common stock	$ 20,000,000
interim CMO
Subsequent Event [Line Items]
Salary per month		$ 27,000
Option to purchase common stock, subject to service condition		24,000