Synthorx 10-Q 30 Apr 19 2019 Q1 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	3 Months Ended
	Mar. 31, 2019	Apr. 22, 2019
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Mar. 31, 2019
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q1
Trading Symbol	THOR
Entity Registrant Name	Synthorx, Inc.
Entity Central Index Key	0001609727
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	true
Entity Ex Transition Period	true
Entity Common Stock, Shares Outstanding		32,142,214

CONDENSED BALANCE SHEETS (Unaud

CONDENSED BALANCE SHEETS (Unaudited) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Current Assets:
Cash and cash equivalents	$ 41,716	$ 188,356
Investment securities, available-for-sale	137,621
Prepaid expenses and other current assets (including related party amounts of $0 and $28, respectively)	1,315	1,688
Total current assets	180,652	190,044
Operating lease right-of-use asset (including related party amounts of $2,060 and $0, respectively)	3,106
Property and equipment, net	1,428	1,382
Other assets	80	80
Total assets	185,266	191,506
Current Liabilities:
Accounts payable	2,963	2,228
Accrued liabilities (including related party amounts of $98 and $123, respectively)	4,802	4,814
Lease liability, current (including related party amounts of $145 and $0, respectively)	390
Total current liabilities	8,155	7,042
Lease liability, noncurrent (including related party amounts of $2,022 and $0, respectively)	2,931
Deferred rent (including related party amounts of $0 and $72, respectively)		104
Total liabilities	11,086	7,146
Commitments and contingencies (Note 8)
Stockholders’ equity:
Common stock, $0.001 par value; authorized shares 200,000,000 at March 31, 2019 and December 31, 2018, respectively; issued shares — 32,142,214 and 32,103,953 at March 31, 2019 and December 31, 2018, respectively; outstanding shares— 31,442,454 and 31,394,830 at March 31, 2019 and December 31, 2018, respectively	31	31
Additional paid-in capital	254,442	253,807
Accumulated deficit	(80,329)	(69,478)
Accumulated other comprehensive income	36
Total stockholders’ equity	174,180	184,360
Total liabilities and stockholders’ equity	$ 185,266	$ 191,506

CONDENSED BALANCE SHEETS (Una_2

CONDENSED BALANCE SHEETS (Unaudited) (Parenthetical) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Statement Of Financial Position [Abstract]
Other prepaids and current assets, related parties, current	$ 0	$ 28
Operating sublease right-of-use asset, related party	2,060	0
Accrued liabilities, related parties, current	98	123
Lease liabilities, related parties, current	145	0
Lease liabilities, related parties, noncurrent	2,022	0
Deferred rent, related parties, noncurrent	$ 0	$ 72
Common stock, par or stated value per share	$ 0.001	$ 0.001
Common stock, shares authorized	200,000,000	200,000,000
Common stock, shares, issued	32,142,214	32,103,953
Common stock, shares, outstanding	31,442,454	31,394,830

CONDENSED STATEMENTS OF OPERATI

CONDENSED STATEMENTS OF OPERATIONS (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Operating expenses:
Research and development (includes related party amounts of $241 and $251, respectively)	$ 9,564	$ 1,765
General and administrative (includes related party amounts of $82 and $65, respectively)	2,355	425
Total operating expenses	11,919	2,190
Loss from operations	(11,919)	(2,190)
Other income:
Interest income, net	1,068
Net loss	$ (10,851)	$ (2,190)
Net loss per common share, basic and diluted	$ (0.35)	$ (2.32)
Weighted average common shares outstanding, basic and diluted	31,430,071	942,605

CONDENSED STATEMENTS OF OPERA_2

CONDENSED STATEMENTS OF OPERATIONS (Unaudited) (Parenthetical) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Income Statement [Abstract]
Research and development (includes related party)	$ 241	$ 251
General and administrative (includes related party)	$ 82	$ 65

CONDENSED STATEMENTS OF COMPREH

CONDENSED STATEMENTS OF COMPREHENSIVE LOSS (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Statement Of Income And Comprehensive Income [Abstract]
Net loss	$ (10,851)	$ (2,190)
Other comprehensive gain:
Unrealized gain on investment securities	36
Comprehensive loss	$ (10,815)	$ (2,190)

CONDENSED STATEMENTS OF CONVERT

CONDENSED STATEMENTS OF CONVERTIBLE PREFERRED STOCK AND STOCKHOLDERS' EQUITY (DEFICIT) (Unaudited) - USD ($) $ in Thousands	Total	Convertible Preferred Stock	Common Stock	Additional Paid-in Capital	Accumulated Deficit	Other Comprehensive Income
Balance, Equity, Shares at Dec. 31, 2017			935,723
Balance, Equity at Dec. 31, 2017	$ (12,528)		$ 1	$ 340	$ (12,869)
Balance, Temporary Equity, Shares at Dec. 31, 2017		7,253,898
Balance, Temporary Equity at Dec. 31, 2017		$ 16,103
Exercise of common stock options and vesting of founder shares	1			1
Exercise of common stock options and vesting of founder shares, Shares			15,346
Stock-based compensation	26			26
Net loss	(2,190)				(2,190)
Balance, Equity, Shares at Mar. 31, 2018			951,069
Balance, Equity at Mar. 31, 2018	(14,691)		$ 1	367	(15,059)
Balance, Temporary Equity, Shares at Mar. 31, 2018		7,253,898
Balance, Temporary Equity at Mar. 31, 2018		$ 16,103
Balance, Equity, Shares at Dec. 31, 2018			31,394,830
Balance, Equity at Dec. 31, 2018	184,360		$ 31	253,807	(69,478)
Exercise of common stock options and vesting of early exercised common stock options	51			51
Exercise of common stock options and vesting of early exercised common stock options, Shares			47,624
Stock-based compensation	584			584
Other comprehensive income	36					$ 36
Net loss	(10,851)				(10,851)
Balance, Equity, Shares at Mar. 31, 2019			31,442,454
Balance, Equity at Mar. 31, 2019	$ 174,180		$ 31	$ 254,442	$ (80,329)	$ 36

CONDENSED STATEMENTS OF CASH FL

CONDENSED STATEMENTS OF CASH FLOWS (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Cash flows from operating activities
Net loss	$ (10,851)	$ (2,190)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation	584	26
(Amortization of premiums) and accretion of discounts on investment securities, net	(426)
Depreciation	93	42
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	345	(249)
Prepaid expenses and other current assets—related parties	28	(115)
Accounts payable and accrued liabilities	775	590
Accounts payable and accrued liabilities—related parties	(25)	(254)
Deferred rent - related parties		37
Operating lease right-of-use assets and liabilities, net	75
Operating lease right-of-use assets and liabilities, net—related parties	36
Net cash used in operating activities	(9,366)	(2,113)
Cash flows from investing activities
Purchases of investment securities	(137,159)
Purchases of property and equipment	(139)	(46)
Net cash used in investing activities	(137,298)	(46)
Cash flows from financing activities
Proceeds from exercise of common stock options	24	1
Net cash used in financing activities	24	1
Net decrease in cash and cash equivalents	(146,640)	(2,158)
Cash and cash equivalents
Beginning of period	188,356	3,661
End of period	$ 41,716	$ 1,503

Organization and Business

Organization and Business	3 Months Ended
	Mar. 31, 2019
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Organization and Business	1. Organization and Business Synthorx, Inc. (the “Company”) was incorporated in the state of Delaware in January 2014 and is based in San Diego, California. The Company is a biopharmaceutical company focused on prolonging and improving the lives of people with cancer and autoimmune disorders. The Company’s platform technology expands the genetic code by adding a new DNA base pair and is designed to create optimized biologics, which the Company refers to as Synthorins. The Company has incurred significant operating losses since inception and expects to incur operating losses for the foreseeable future as it pursues the preclinical and clinical development of its programs and product candidates. As the Company continues to incur losses, its transition to profitability will depend on the successful development, approval and commercialization of its product candidates and on the achievement of sufficient revenues to support its cost structure. The Company may never achieve profitability, and unless and until it does, will need to continue to raise additional capital to fund its operations.

Basis of Presentation and Summa

Basis of Presentation and Summary of Significant Accounting Policies	3 Months Ended
	Mar. 31, 2019
Accounting Policies [Abstract]
Basis of Presentation and Summary of Significant Accounting Policies	2. Basis of Presentation and Summary of Significant Accounting Policies Basis of Presentation The accompanying unaudited condensed financial statements of the Company should be read in conjunction with the audited financial statements and notes thereto as of and for the year ended December 31, 2018 included in the Company’s Annual Report on Form 10-K (“Annual Report”) filed with the Securities and Exchange Commission (the “SEC”) on March 12, 2019. The accompanying financial statements have been prepared in accordance with accounting principles generally accepted in the United States (“GAAP”) for interim financial information and in accordance with the instructions to Form 10-Q and Article 10 of Regulation S-X. Accordingly, since they are interim statements, the accompanying financial statements do not include all of the information and notes required by GAAP for complete financial statements. In the opinion of management, the accompanying financial statements reflect all adjustments (consisting of normal recurring adjustments) that are necessary for a fair statement of the financial position, results of operations, comprehensive loss, convertible preferred stock and stockholders’ equity (deficit) and cash flows for the interim periods presented. Interim results are not necessarily indicative of results for a full year. The preparation of the Company’s financial statements requires it to make estimates and assumptions that impact the reported amounts of assets, liabilities and expenses and the disclosure of contingent assets and liabilities in the Company’s financial statements and accompanying notes. The most significant estimates in the Company’s financial statements relate to accruals for research and development expenses and the valuation of equity awards. These estimates and assumptions are based on current facts, historical experience and various other factors believed to be reasonable under the circumstances, the results of which form the basis for making judgments about the carrying values of assets and liabilities and the recording of expenses that are not readily apparent from other sources. Actual results may differ materially and adversely from these estimates. Reverse Stock Split On November 26, 2018, the Company effected a 1-for-1.60224 reverse stock split of its common stock. The par value and the authorized shares of the common stock were not adjusted as a result of the reverse stock split. The accompanying financial statements and notes to the financial statements give retroactive effect to the reverse stock split for all periods presented. Cash and Cash Equivalents The Company considers all highly liquid investments with maturities at the date of acquisition of three months or less to be cash equivalents. These investments may include money market funds, U.S. Government agencies, corporate debt securities and commercial paper. Marketable Securities Investments with maturities at the date of acquisition of more than three months are considered marketable securities. The Company determines the appropriate classification of its investments at the time of acquisition and reevaluates such determination at each balance sheet date. The Company has classified its investment holdings as available-for-sale, as the sale of such securities may be required prior to maturity to implement management strategies. The Company’s investment policy sets minimum credit quality criteria and maximum maturity limits on its investments to provide for safety of principle, liquidity and a reasonable rate of return. Available-for-sale securities are recorded at fair value, based on current market valuations. Unrealized holding gains and losses on available-for-sale securities are excluded from earnings and are reported as a separate component of other comprehensive income (loss) until realized. Realized gains and losses are included in non-operating other income (expense) on the statement of operations and are derived using the specific identification method for determining the cost of the securities sold. During the periods presented, no realized gains or losses were recorded on the sale or maturity of the Company’s marketable securities and no impairments to reduce the value of an available-for-sale equity security were taken. See Note 5 for further discussion. Research and Development Expenses All research and development costs are expensed in the period incurred. Research and development expenses primarily consist of services provided by contract organizations for preclinical development, salaries and related expenses for personnel, including stock-based compensation expense, outside service providers, facilities costs, fees paid to consultants and other professional services, license fees, depreciation and supplies used in research and development. Payments made prior to the receipt of goods or services to be used in research and development are capitalized until the related goods or services are received. Stock-Based Compensation Stock options issued pursuant to the Company’s 2018 Equity Incentive Plan (the “2018 Plan”) and 2014 Equity Incentive Plan (the “2014 Plan”) and option features associated with the rights to purchase shares pursuant to the Company’s 2018 Employee Stock Purchase Plan (the “ESPP”) are valued using the Black-Scholes option pricing model on the date of grant or subscription period. This option pricing model involves a number of estimates, including the expected term of an award or subscription period, the anticipated stock volatility and risk-free interest rates. Stock-based compensation expense is recognized using the straight-line method and is based on the value of the portion of stock awards that are ultimately expected to vest or the number of shares estimated to be issued pursuant to the ESPP. The table below summarizes the total stock-based compensation expense included in the Company’s condensed statements of operations for stock options and shares subject to purchase under the ESPP for the periods presented (in thousands): Three Months Ended March 31, 2019 2018 Research and development $ 400 $ 16 General and administrative 184 10 $ 584 $ 26 Recent Accounting Pronouncements In February 2016, the Financial Accounting Standards Board (“FASB”) established Topic 842, Leases Land Easement Practical Expedient for Transition to Topic 842 Codification Improvements to Topic 842, Leases Targeted Improvements A modified In August 2018, the FASB issued ASU No. 2018-13, Fair Value Measurement: Disclosure Framework – Changes to the Disclosure Requirements for Fair Value Measurement, In June 2016, the FASB issued ASU 2016-13, Financial Instruments-Credit Losses: Measurement of Credit Losses on Financial Instruments

Net Loss Per Share

Net Loss Per Share	3 Months Ended
	Mar. 31, 2019
Earnings Per Share [Abstract]
Net Loss Per Share	3. Net Loss Per Share Basic net loss per share is computed by dividing the net loss by the weighted average number of common shares outstanding for the period, without consideration for potentially dilutive securities. Diluted net loss per share is computed by dividing the net loss by the weighted average number of common shares and dilutive common share equivalents outstanding for the period determined using the treasury-stock and if-converted methods. For purposes of this calculation, convertible preferred stock, stock options, employee stock purchase rights, and unvested common stock subject to repurchase are considered to be common stock equivalents but are not included in the calculations of diluted net loss per share for the periods presented as their effect would be antidilutive. The Company incurred net losses for all periods presented and there were no reconciling items for potentially dilutive securities. More specifically, at March 31, 2019 and 2018, convertible preferred stock, stock options, employee stock purchase rights, and unvested common stock subject to repurchase totaling approximately 4,880,000 shares and 9,517,000 shares, respectively, were excluded from the calculation of diluted net loss per share because to do so would be anti-dilutive.

Fair Value Measurements

Fair Value Measurements	3 Months Ended
	Mar. 31, 2019
Fair Value Disclosures [Abstract]
Fair Value Measurements	4. Fair Value Measurements The Company follows authoritative accounting guidance, which among other things, defines fair value, establishes a consistent framework for measuring fair value and expands disclosure for each major asset and liability category measured at fair value on either a recurring or non-recurring basis. Fair value is defined as an exit price, representing the amount that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants. As such, fair value is a market-based measurement that should be determined based on assumptions that market participants would use in pricing an asset or liability. As a basis for considering such assumptions, the accounting guidance establishes a three-tier fair value hierarchy, which prioritizes the inputs used in measuring fair value as follows: Level 1: Observable inputs such as quoted prices in active markets. Level 2: Inputs, other than the quoted prices in active markets, that are observable either directly or indirectly. Level 3: Unobservable inputs in which there is little or no market data, which require the reporting entity to develop its own assumptions. The carrying amounts of the Company’s prepaid expenses and other current assets, accounts payable and accrued liabilities are generally considered to be representative of their Assets measured at fair value on a recurring basis at March 31, 2019 and December 31, 2018, consisted of the following (in thousands): Fair Value Measurements at Reporting Date Using: Balance at March 31, 2019 Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Money market funds (1) $ 25,922 $ 25,922 $ — $ — Commercial paper (2) 116,032 — 116,032 — Corporate debt securities 37,282 — 37,282 — Total $ 179,236 $ 25,922 $ 153,314 $ — (1) Included within cash and cash equivalents on the Company’s condensed balance sheet. (2) Commercial paper purchased within three months of maturity valued at $7.0 million is included within cash and cash equivalents on the Company’s condensed balance sheet. Fair Value Measurements at Reporting Date Using: Balance at December 31, 2018 Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Money market funds (1) $ 185,203 $ 185,203 $ — $ — Total $ 185,203 $ 185,203 $ — $ — (1) Included within cash and cash equivalents on the Company’s condensed balance sheet. The Company determines the fair value of commercial paper and corporate bonds with the aid of valuations provided by third parties using proprietary valuation models and analytical tools. o transfers between levels occurred during the periods presented.

Investments In Marketable Secur

Investments In Marketable Securities	3 Months Ended
	Mar. 31, 2019
Investments Debt And Equity Securities [Abstract]
Investments In Marketable Securities	5. Investments in Marketable Securities The Company’s investment policy defines allowable investment securities and establishes guidelines relating to credit quality, diversification, and maturities of its investments to preserve principal and maintain liquidity. In accordance with the Company’s investment policy, it has invested funds in marketable securities at March 31, 2019. The Company had no investments in marketable securities at December 31, 2018. The cost, gross unrealized holding gains, gross unrealized holding losses and fair value of available-for-sale investments by types and classes of security at March 31, 2019 consisted of the following (in thousands): March 31, 2019 Maturity (in years) Amortized Cost Basis Other-than- temporary Impairments Gross Unrealized Holding Gains Gross Unrealized Holding Losses Fair Value Commercial paper 1 year or less $ 109,011 $ — $ 30 $ (2 ) $ 109,039 Corporate debt securities 1 year or less 28,574 — 10 (2 ) 28,582 Total available-for-sale securities $ 137,585 $ — $ 40 $ (4 ) $ 137,621 At March 31, 2019, there were nine securities in unrealized loss positions. These securities have not been in a continuous unrealized loss position for more than 12 months. Further, the Company does not intend to sell these investments and it is not more likely than not that the Company will be required to sell these investments before recovery of their amortized cost basis which may be at maturity. As such, the Company has classified these losses as temporary in nature. The Company reviews its investments to identify and evaluate investments that have an indication of possible other-than-temporary impairment. Factors considered in determining whether a loss is other-than-temporary include the length of time and extent to which fair value has been less than the cost basis, the financial condition and near-term prospects of the investee, and the Company’s intent and ability to hold the investment for a period of time sufficient to allow for any anticipated recovery in market value.

Balance Sheet Details

Balance Sheet Details	3 Months Ended
	Mar. 31, 2019
Balance Sheet Related Disclosures [Abstract]
Balance Sheet Details	6. Balance Sheet Details Prepaid expenses and other current assets consisted of the following (in thousands): March 31, 2019 December 31, 2018 Prepaid insurance $ 836 $ 1,171 Interest receivable 243 265 Prepaid clinical trial costs 99 — Prepaid manufacturing and process development costs 21 175 Other prepaids and current assets (including related party amounts of $0 and $28, respectively) 116 77 $ 1,315 $ 1,688 Property and equipment for the consisted of the following (in thousands): March 31, 2019 December 31, 2018 Laboratory equipment $ 1,691 $ 1,635 Leasehold improvements 118 72 Software/Hardware 55 — Furniture and fixtures 55 36 Construction in progress 4 41 $ 1,923 $ 1,784 Less accumulated depreciation and amortization (495 ) (402 ) $ 1,428 $ 1,382 Accrued liabilities consisted of the following (in thousands): March 31, 2019 December 31, 2018 Accrued research and development (including related party amounts of $0 and $59, respectively) $ 2,414 $ 1,579 Stock repurchase liability 1,117 1,143 Accrued compensation 723 895 Other accrued liabilities (including related party amounts of $98 and $64, respectively) 548 1,197 $ 4,802 $ 4,814

Related Party Transactions

Related Party Transactions	3 Months Ended
	Mar. 31, 2019
Related Party Transactions [Abstract]
Related Party Transactions	In February 2015, as amended in October 2017, the Company entered into a Support Services Agreement with COI Pharmaceuticals, Inc. (“COI”) that outlines the terms of services provided by COI to the Company, as well as the fees charged for such services. Jay Lichter, Ph.D., a member of the Company’s board of directors, and Tighe Reardon, the Company’s Acting Chief Financial Officer, are each an executive officer and director of Expense recognized by the Company under the support services agreement with COI and costs incurred pursuant to a sublease with COI, as further described in Note 8, for the periods presented were as follows (in thousands): Three Months Ended March 31, 2019 2018 Research and development $ 152 $ 158 General and administrative 79 62 $ 231 $ 220 At March 31, 2019 and December 31, 2018, the Company had accounts payable and accrued expenses due to COI of $0.1 million and $0.1 million, respectively. As of December 31, 2018 the Company had prepaid expenses to COI of less than $0.1 million. No amounts were due from COI and the Company had no prepaid expenses to COI at March 31, 2019. Research Funding and Option Agreement In July 2014, the Company entered into a Research Funding and Option Agreement (the “Research Agreement”) for certain technologies from The Scripps Research Institute (“TSRI”), and in August 2018, amended the Research Agreement. Pursuant to the agreement (as amended), the Company provides funding to TSRI to conduct certain research activities under a research program. The agreement continues in effect until the earlier of (a) July 2019, and (b) the completion of the research program, unless extended or terminated by mutual agreement and subject to customary termination provisions related to failure to make payments, breach or insolvency. Under the research funding and option agreement, TSRI granted the Company an option to enter into a license agreement for certain patent rights and technology related to the research program. As described below, the license agreement was entered into in July 2014, and any intellectual property to which the Company exercises the foregoing option will be included in such license agreement. The Company is obligated to provide research funding to TSRI in the amount of $0.2 million both during 2018 and 2019, of which $0.1 million was paid in 2018 and $0.1 million had been paid in 2019 as of March 31, 2019. License Agreement In July 2014, the Company entered into a License Agreement (the “TSRI License”) with TSRI. Under the TSRI License (as amended), TSRI granted the Company an exclusive, worldwide, royalty-bearing, sublicensable, license to certain TSRI patent rights, know-how and biological materials (the “Licensed Technology”), to make, use, sell, offer for sale, and import products covered by the claims of the licensed patent rights or developed by the Company through the use of the Licensed Technology (the “Licensed Products”) and to otherwise exploit the Licensed Technology. The Licensed Technology forms the basis for the Company’s proprietary Expanded Genetic Alphabet platform technology. The license granted to the Company by TSRI under the Licensed Technology is subject to certain U.S. Government rights and certain other limited rights retained by TSRI. In consideration for the license, the Company issued TSRI 30,663 shares of the Company’s common stock. In July 2015, the Company issued an additional 8,711 shares of its common stock to TSRI. Beginning in July 2017, and annually thereafter, the Company is required to pay TSRI an immaterial annual minimum royalty. The Company is also obligated to pay running royalties in the low single digit percentages on its or its sublicensees’ net sales of the Licensed Products on a country-by-country and product-by-product basis. Certain of these payment obligations may be increased during the pendency of any challenge of the licensed patent rights by the Company, its affiliates, or sublicensees. In the event that the Company is required to obtain a license under patent rights held by a third party to prevent infringement of the Licensed Products, the Company may offset its royalty obligations to TSRI by up to a maximum mid-double digit percentage of any royalties the Company pays to such third party. However, in no event, can the Company reduce the royalties payable to TSRI by more than a mid-double digit percentage in any calendar quarter. The Company’s royalty obligations as to each product terminate on a country-by-country basis upon the expiration of the last-to-expire of the licensed patent claims that cover the Licensed Products. In addition, the Company is also required to pay TSRI (i) an amount in the low-double digit percent range of sublicensing revenues, (ii) an amount in the high-single digit percent range of non-sublicensing transaction revenues, such as amounts received for grants of licenses to third parties and grants of other distribution or marketing rights, payable in shares of the Company’s capital stock and (iii) milestone payments of up to $2.4 million for each Licensed Product. The Company is responsible for reimbursing TSRI for its patent costs incurred in connection with prosecuting and maintaining the TSRI License patent rights. The parties may terminate the TSRI License at any time by mutual agreement. In addition, the Company may terminate the TSRI License by giving 90 days’ notice to TSRI and TSRI may terminate the TSRI License immediately in the event of certain breaches of the agreement by the Company or upon the Company’s failure to undertake certain activities in furtherance of commercial development goals. Unless terminated earlier by either or both parties, the term of the TSRI License will continue until the final expiration of all royalty obligations under the agreement. Academic Development Program Awards The Company has incurred research and development expense in connection with academic development program awards to TSRI to fund direct research. A member of the Company’s board of directors is a faculty member at TSRI and such payments fund a portion of his research activities conducted at TSRI. Expense recognized by the Company related to the above agreements with TSRI for the periods presented was as follows (in thousands): Three Months Ended March 31, 2019 2018 Research and development $ 89 $ 93 General and administrative 3 3 $ 92 $ 96 As of December 31, 2018, the Company had accounts payable and accrued expenses due to TSRI of $0.1 million. The Company had no

Commitments and Contingencies

Commitments and Contingencies	3 Months Ended
	Mar. 31, 2019
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingencies	8. Commitments and Contingencies Operating Lease In August 2017, the Company entered into a sublease with COI, a related party, for its corporate office and laboratory space in La Jolla, California (the “2017 Sublease”). In November 2018, the Company amended the 2017 Sublease to provide the Company with a one-time right to terminate as of March 1, 2024, subject to certain conditions and fees. The 2017 Sublease, as amended, which expires in February 2027, contains rent escalations and the Company is required to pay for common area maintenance and other costs during the term of the lease. In connection with the 2017 Sublease, the Company recognized an operating lease right-of-use asset of $2.1 million as of March 31, 2019 and an aggregate lease liability of $2.2 million in its balance sheet. The remaining lease term is 7 years and 11 months, and the estimated incremental borrowing rate used by the Company to recognize the lease liability was 8.5%. The right to early terminate the lease was not recognized as part of the Company’s lease liability and right-of-use lease asset. In addition, in September 2018, the Company entered into a noncancelable operating lease for additional corporate office and laboratory space (the “Lease”). The Lease commenced in November 2018 and will expire in February 2023, however, the Company has the option to extend the Lease for a 12-month period. The Lease provided for abatement of rent during the first four months of the lease, contains rent escalations and the Company is required to pay for common area maintenance and other costs during the term of the lease. In connection with the Lease, the Company recognized an operating lease right-of-use asset of $1.0 million as of March 31, 2019 and an aggregate lease liability of $1.2 million in its balance sheet. The remaining lease term is 4 years, and the estimated incremental borrowing rate used by the Company to recognize the lease liability was 7%. The option to extend the lease was not recognized as part of the Company’s lease liability and right-of-use lease asset. Future minimum lease payments under the 2017 Sublease and the Lease as of March 31, 2019 are as follows (in thousands): 2019 $ 501 2020 655 2021 675 2022 727 2023 483 Thereafter 1,327 Total future minimum lease payments 4,368 Less interest (1,047 ) Total lease liability $ 3,321 Weighted average lease term 6.7 years Weighted average discount rate 8.0 % Operating lease costs were $0.3 million and $0.1 million for the three months ended March 31, 2019 and 2018, respectively. Contingencies From time to time, the Company becomes subject to claims or suits arising in the ordinary course of business. The Company accrues a liability for such matters when it is probable that future expenditures will be made and such expenditures can be reasonably estimated. The Company had no such contingent liabilities as of March 31, 2019 or December 31, 2018, respectively.

Convertible Preferred Stock and

Convertible Preferred Stock and Stockholders’ Equity (Deficit)	3 Months Ended
	Mar. 31, 2019
Stockholders Equity Note [Abstract]
Convertible Preferred Stock and Stockholders’ Equity (Deficit)	9. Convertible Preferred Stock and Stockholders’ Equity (Deficit) Authorized Shares In connection with the completion of the Company’s initial public offering (“IPO”) in December 2018, the Company amended its Certificate of Incorporation to authorize 200,000,000 shares of common stock, par value $0.001 per share, and 10,000,000 shares of preferred stock, par value $0.001 per share, respectively. Public Offering and Related Transaction In December 2018, the Company completed its IPO selling 13,699,636 shares its common stock at $11.00 per share. Proceeds from the Company’s IPO, net of underwriting discounts and commissions and other offering costs, were $137.5 million. In connection with the IPO, Convertible Preferred Stock Prior to its conversion to common stock, the Company’s convertible preferred stock was classified as temporary equity on the Company’s balance sheets in accordance with authoritative guidance for the classification and measurement of potentially redeemable securities whose redemption is based upon certain change in control events outside of the Company’s control, including liquidation, sale or transfer of control of the Company. The Company had determined not to adjust the carrying values of the convertible preferred stock to the liquidation preferences of such shares because of the uncertainty of whether or when such events would occur. During the year ended December 31, 2018, the Company issued convertible preferred stock as follows: ▪ in April 2018, the Company issued 8,118,108 shares of Series C convertible preferred stock, raising proceeds, net of offering costs, of $26.3 million; and ▪ in November 2018, the Company issued 11,365,348 shares of Series C convertible preferred stock, raising proceeds, net of offering costs, of $37.1 million. Equity Incentive Plans In November 2018, the Company’s board of directors and stockholders approved the 2018 Plan that became effective upon the date of the underwriting agreement related to the IPO. Upon adoption of the 2018 Plan, the Company restricted future grants from its 2014 Plan. A total of 3,428,492 new shares of common stock were initially reserved for issuance under the 2018 Plan. The number of shares reserved under the 2018 Plan also include 87,111 shares of common stock that remained available for issuance under the 2014 Plan at the time the 2018 Plan became effective, and will be increased by the number of shares under the 2014 Plan that are repurchased, forfeited, expired or cancelled on or after the effective date of the 2018 Plan. In addition, the number of shares of common stock available for issuance under the 2018 Plan will automatically increase on January 1 of each calendar year, starting on January 1, 2019 through January 1, 2028, in an amount equal to 4% of the total number of shares of the Company’s common stock on the last day of the calendar month before the date of each automatic increase, or a lesser number of shares determined by the Company’s board of directors. On January 1, 2019, 1,284,158 shares were automatically added to the 2018 Plan pursuant to the provision. Early Exercise of Stock Options Certain stock options granted under the Company’s 2014 Plan provide option holders the right to elect to exercise unvested options in exchange for restricted common stock. A summary of the early exercised shares is as follows: Shares Balance as of December 31, 2018 709,123 Shares vested (9,363 ) Balance as of March 31, 2019 699,760 The shares are subject to repurchase by the Company at the original exercise price in the event the optionee’s service is terminated either voluntarily or involuntarily prior to vesting. As of March 31, 2019 and December 31, 2018, the Company recorded accrued liabilities of $1.1 million and $1.1 million, respectively, associated with the repurchase rights for early exercised stock options. 2018 Employee Stock Purchase Plan In November 2018, the Company’s board of directors and stockholders approved and adopted the ESPP that became effective immediately prior to the date of the underwriting agreement related to the IPO. The ESPP permits eligible employees who elect to participate in an offering under the ESPP to have up to 15% of their eligible earnings withheld, subject to certain limitations, to purchase shares of common stock pursuant to the ESPP. The price of common stock purchased under the ESPP is equal to 85 percent of the lower of the fair market value of the common stock at the commencement date of each offering period or the relevant date of purchase. A total of 645,000 shares of common stock were initially reserved for issuance under the ESPP. In addition, the number of shares of common stock available for issuance under the ESPP will automatically increase on January 1 of each calendar year, starting on January 1, 2019 through January 1, 2028, in an amount equal to the lesser of (i) 1% of the total number of shares of the Company’s common stock on the last day of the calendar month before the date of each automatic increase and (ii) 750,000 shares; provided that before the date of any such increase, the Company’s board of directors may determine that such increase will be less than the amount set forth in clauses (i) and (ii). On January 1, 2019, 321,039 shares were automatically added to the ESPP pursuant to the provision. As of March 31, 2019, no shares were issued under the ESPP.

Basis of Presentation and Sum_2

Basis of Presentation and Summary of Significant Accounting Policies (Policies)	3 Months Ended
	Mar. 31, 2019
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The accompanying unaudited condensed financial statements of the Company should be read in conjunction with the audited financial statements and notes thereto as of and for the year ended December 31, 2018 included in the Company’s Annual Report on Form 10-K (“Annual Report”) filed with the Securities and Exchange Commission (the “SEC”) on March 12, 2019. The accompanying financial statements have been prepared in accordance with accounting principles generally accepted in the United States (“GAAP”) for interim financial information and in accordance with the instructions to Form 10-Q and Article 10 of Regulation S-X. Accordingly, since they are interim statements, the accompanying financial statements do not include all of the information and notes required by GAAP for complete financial statements. In the opinion of management, the accompanying financial statements reflect all adjustments (consisting of normal recurring adjustments) that are necessary for a fair statement of the financial position, results of operations, comprehensive loss, convertible preferred stock and stockholders’ equity (deficit) and cash flows for the interim periods presented. Interim results are not necessarily indicative of results for a full year. The preparation of the Company’s financial statements requires it to make estimates and assumptions that impact the reported amounts of assets, liabilities and expenses and the disclosure of contingent assets and liabilities in the Company’s financial statements and accompanying notes. The most significant estimates in the Company’s financial statements relate to accruals for research and development expenses and the valuation of equity awards. These estimates and assumptions are based on current facts, historical experience and various other factors believed to be reasonable under the circumstances, the results of which form the basis for making judgments about the carrying values of assets and liabilities and the recording of expenses that are not readily apparent from other sources. Actual results may differ materially and adversely from these estimates.
Reserve Stock Split	Reverse Stock Split On November 26, 2018, the Company effected a 1-for-1.60224 reverse stock split of its common stock. The par value and the authorized shares of the common stock were not adjusted as a result of the reverse stock split. The accompanying financial statements and notes to the financial statements give retroactive effect to the reverse stock split for all periods presented.
Cash and Cash Equivalents	Cash and Cash Equivalents The Company considers all highly liquid investments with maturities at the date of acquisition of three months or less to be cash equivalents. These investments may include money market funds, U.S. Government agencies, corporate debt securities and commercial paper.
Marketable Securities	Marketable Securities Investments with maturities at the date of acquisition of more than three months are considered marketable securities. The Company determines the appropriate classification of its investments at the time of acquisition and reevaluates such determination at each balance sheet date. The Company has classified its investment holdings as available-for-sale, as the sale of such securities may be required prior to maturity to implement management strategies. The Company’s investment policy sets minimum credit quality criteria and maximum maturity limits on its investments to provide for safety of principle, liquidity and a reasonable rate of return. Available-for-sale securities are recorded at fair value, based on current market valuations. Unrealized holding gains and losses on available-for-sale securities are excluded from earnings and are reported as a separate component of other comprehensive income (loss) until realized. Realized gains and losses are included in non-operating other income (expense) on the statement of operations and are derived using the specific identification method for determining the cost of the securities sold. During the periods presented, no realized gains or losses were recorded on the sale or maturity of the Company’s marketable securities and no impairments to reduce the value of an available-for-sale equity security were taken. See Note 5 for further discussion.
Research and Development Expenses	Research and Development Expenses All research and development costs are expensed in the period incurred. Research and development expenses primarily consist of services provided by contract organizations for preclinical development, salaries and related expenses for personnel, including stock-based compensation expense, outside service providers, facilities costs, fees paid to consultants and other professional services, license fees, depreciation and supplies used in research and development. Payments made prior to the receipt of goods or services to be used in research and development are capitalized until the related goods or services are received.
Stock-Based Compensation	Stock-Based Compensation Stock options issued pursuant to the Company’s 2018 Equity Incentive Plan (the “2018 Plan”) and 2014 Equity Incentive Plan (the “2014 Plan”) and option features associated with the rights to purchase shares pursuant to the Company’s 2018 Employee Stock Purchase Plan (the “ESPP”) are valued using the Black-Scholes option pricing model on the date of grant or subscription period. This option pricing model involves a number of estimates, including the expected term of an award or subscription period, the anticipated stock volatility and risk-free interest rates. Stock-based compensation expense is recognized using the straight-line method and is based on the value of the portion of stock awards that are ultimately expected to vest or the number of shares estimated to be issued pursuant to the ESPP. The table below summarizes the total stock-based compensation expense included in the Company’s condensed statements of operations for stock options and shares subject to purchase under the ESPP for the periods presented (in thousands): Three Months Ended March 31, 2019 2018 Research and development $ 400 $ 16 General and administrative 184 10 $ 584 $ 26
Recent Accounting Pronouncements	Recent Accounting Pronouncements In February 2016, the Financial Accounting Standards Board (“FASB”) established Topic 842, Leases Land Easement Practical Expedient for Transition to Topic 842 Codification Improvements to Topic 842, Leases Targeted Improvements A modified In August 2018, the FASB issued ASU No. 2018-13, Fair Value Measurement: Disclosure Framework – Changes to the Disclosure Requirements for Fair Value Measurement, In June 2016, the FASB issued ASU 2016-13, Financial Instruments-Credit Losses: Measurement of Credit Losses on Financial Instruments

Basis of Presentation and Sum_3

Basis of Presentation and Summary of Significant Accounting Policies (Tables)	3 Months Ended
	Mar. 31, 2019
Accounting Policies [Abstract]
Summary of Total Stock-Based Compensation Expense	The table below summarizes the total stock-based compensation expense included in the Company’s condensed statements of operations for stock options and shares subject to purchase under the ESPP for the periods presented (in thousands): Three Months Ended March 31, 2019 2018 Research and development $ 400 $ 16 General and administrative 184 10 $ 584 $ 26

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	3 Months Ended
	Mar. 31, 2019
Fair Value Disclosures [Abstract]
Summary of Assets Measured at Fair Value on a Recurring Basis	Assets measured at fair value on a recurring basis at March 31, 2019 and December 31, 2018, consisted of the following (in thousands): Fair Value Measurements at Reporting Date Using: Balance at March 31, 2019 Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Money market funds (1) $ 25,922 $ 25,922 $ — $ — Commercial paper (2) 116,032 — 116,032 — Corporate debt securities 37,282 — 37,282 — Total $ 179,236 $ 25,922 $ 153,314 $ — (1) Included within cash and cash equivalents on the Company’s condensed balance sheet. (2) Commercial paper purchased within three months of maturity valued at $7.0 million is included within cash and cash equivalents on the Company’s condensed balance sheet. Fair Value Measurements at Reporting Date Using: Balance at December 31, 2018 Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Money market funds (1) $ 185,203 $ 185,203 $ — $ — Total $ 185,203 $ 185,203 $ — $ — (1) Included within cash and cash equivalents on the Company’s condensed balance sheet.

Investments In Marketable Sec_2

Investments In Marketable Securities (Tables)	3 Months Ended
	Mar. 31, 2019
Investments Debt And Equity Securities [Abstract]
Summary of Cost, Gross Unrealized Holding Gains and Losses and Fair Value of Available-for-sale Investments by Types and Classes of Security	The cost, gross unrealized holding gains, gross unrealized holding losses and fair value of available-for-sale investments by types and classes of security at March 31, 2019 consisted of the following (in thousands): March 31, 2019 Maturity (in years) Amortized Cost Basis Other-than- temporary Impairments Gross Unrealized Holding Gains Gross Unrealized Holding Losses Fair Value Commercial paper 1 year or less $ 109,011 $ — $ 30 $ (2 ) $ 109,039 Corporate debt securities 1 year or less 28,574 — 10 (2 ) 28,582 Total available-for-sale securities $ 137,585 $ — $ 40 $ (4 ) $ 137,621

Balance Sheet Details (Tables)

Balance Sheet Details (Tables)	3 Months Ended
	Mar. 31, 2019
Balance Sheet Related Disclosures [Abstract]
Summary of Prepaid Expenses and Other Current Assets	Prepaid expenses and other current assets consisted of the following (in thousands): March 31, 2019 December 31, 2018 Prepaid insurance $ 836 $ 1,171 Interest receivable 243 265 Prepaid clinical trial costs 99 — Prepaid manufacturing and process development costs 21 175 Other prepaids and current assets (including related party amounts of $0 and $28, respectively) 116 77 $ 1,315 $ 1,688
Summary of Property and Equipment	Property and equipment for the consisted of the following (in thousands): March 31, 2019 December 31, 2018 Laboratory equipment $ 1,691 $ 1,635 Leasehold improvements 118 72 Software/Hardware 55 — Furniture and fixtures 55 36 Construction in progress 4 41 $ 1,923 $ 1,784 Less accumulated depreciation and amortization (495 ) (402 ) $ 1,428 $ 1,382
Summary of Accrued Liabilities	Accrued liabilities consisted of the following (in thousands): March 31, 2019 December 31, 2018 Accrued research and development (including related party amounts of $0 and $59, respectively) $ 2,414 $ 1,579 Stock repurchase liability 1,117 1,143 Accrued compensation 723 895 Other accrued liabilities (including related party amounts of $98 and $64, respectively) 548 1,197 $ 4,802 $ 4,814

Related Party Transactions (Tab

Related Party Transactions (Tables)	3 Months Ended
	Mar. 31, 2019
COI Pharmaceuticals, Inc
Schedule of Expense Recognized Under Agreement	Expense recognized by the Company under the support services agreement with COI and costs incurred pursuant to a sublease with COI, as further described in Note 8, for the periods presented were as follows (in thousands): Three Months Ended March 31, 2019 2018 Research and development $ 152 $ 158 General and administrative 79 62 $ 231 $ 220
TSRI
Schedule of Expense Recognized Under Agreement	Expense recognized by the Company related to the above agreements with TSRI for the periods presented was as follows (in thousands): Three Months Ended March 31, 2019 2018 Research and development $ 89 $ 93 General and administrative 3 3 $ 92 $ 96

Commitments and Contingencies (

Commitments and Contingencies (Tables)	3 Months Ended
	Mar. 31, 2019
Commitments And Contingencies Disclosure [Abstract]
Schedule of Future Minimum Lease Payments under 2017 Sublease and Lease	Future minimum lease payments under the 2017 Sublease and the Lease as of March 31, 2019 are as follows (in thousands): 2019 $ 501 2020 655 2021 675 2022 727 2023 483 Thereafter 1,327 Total future minimum lease payments 4,368 Less interest (1,047 ) Total lease liability $ 3,321 Weighted average lease term 6.7 years Weighted average discount rate 8.0 %

Convertible Preferred Stock a_2

Convertible Preferred Stock and Stockholders’ Equity (Deficit) (Tables)	3 Months Ended
	Mar. 31, 2019
Stockholders Equity Note [Abstract]
Summary of Early Exercise of Stock Options	A summary of the early exercised shares is as follows: Shares Balance as of December 31, 2018 709,123 Shares vested (9,363 ) Balance as of March 31, 2019 699,760

Basis of Presentation and Sum_4

Basis of Presentation and Summary of Significant Accounting Policies - Additional Information (Details)	Nov. 26, 2018	Mar. 31, 2019USD ($)	Jan. 01, 2019USD ($)
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Reverse stock split description		1-for-1.60224 reverse stock split of its common stock
Reverse stock split ratio	0.62
Realized gains (losses) on sale or maturity of marketable securities		$ 0
Impairment on available- for- sale of equity securities		0
Operating lease right-of-use asset		$ 3,106,000
ASU 2016-02
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Operating lease, liabilities			$ 3,300,000
Operating lease right-of-use asset			$ 3,200,000

Basis of Presentation and Sum_5

Basis of Presentation and Summary of Significant Accounting Policies - Summary of Total Stock-Based Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	$ 584	$ 26
Research and development
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	400	16
General and administrative
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	$ 184	$ 10

Net Loss Per Share - Additional

Net Loss Per Share - Additional Information (Details) - shares	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Earnings Per Share [Abstract]
Anti-dilutive securities excluded from calculation of diluted net loss per share	4,880,000	9,517,000

Fair Value Measurements - Summa

Fair Value Measurements - Summary of Assets Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets	$ 179,236	$ 185,203
Corporate Debt Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets	37,282
Fair Value Measurements Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets	25,922	185,203
Fair Value Measurements Recurring | Significant Other Observable Inputs (Level 2)
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets	153,314	0
Fair Value Measurements Recurring | Significant Unobservable Inputs (Level 3)
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets	0	0
Fair Value Measurements Recurring | Corporate Debt Securities | Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets	0
Fair Value Measurements Recurring | Corporate Debt Securities | Significant Other Observable Inputs (Level 2)
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets	37,282
Fair Value Measurements Recurring | Corporate Debt Securities | Significant Unobservable Inputs (Level 3)
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets	0
Money Market Funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets	25,922	185,203
Money Market Funds | Fair Value Measurements Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets	25,922	185,203
Money Market Funds | Fair Value Measurements Recurring | Significant Other Observable Inputs (Level 2)
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets	0	0
Money Market Funds | Fair Value Measurements Recurring | Significant Unobservable Inputs (Level 3)
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets	0	$ 0
Commercial Paper
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets	116,032
Commercial Paper | Fair Value Measurements Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets	0
Commercial Paper | Fair Value Measurements Recurring | Significant Other Observable Inputs (Level 2)
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets	116,032
Commercial Paper | Fair Value Measurements Recurring | Significant Unobservable Inputs (Level 3)
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets	$ 0

Fair Value Measurements - Sum_2

Fair Value Measurements - Summary of Assets Measured at Fair Value on a Recurring Basis (Parenthetical) (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash and cash equivalents	$ 41,716	$ 188,356
Money Market Funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash and cash equivalents	$ 7,000

Investments In Marketable Sec_3

Investments In Marketable Securities - Additional Information (Details)	3 Months Ended
	Mar. 31, 2019Security	Dec. 31, 2018USD ($)
Investments Debt And Equity Securities [Abstract]
Marketable securities | $		$ 0
Number of securities in unrealized loss position | Security	9

Investments In Marketable Sec_4

Investments In Marketable Securities - Summary of Cost, Gross Unrealized Holding Gains and Losses and Fair Value of Available-for-sale Investments by Types and Classes of Security (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2019USD ($)
Schedule Of Available For Sale Securities [Line Items]
Available-for-sale investment securities, Amortized Cost	$ 137,585
Available-for-sale investment securities, Gross Unrealized Gains	40
Available-for-sale investment securities, Gross Unrealized Losses	(4)
Available-for-sale investment securities, Fair Market Value	137,621
Commercial Paper
Schedule Of Available For Sale Securities [Line Items]
Available-for-sale investment securities, Amortized Cost	109,011
Available-for-sale investment securities, Gross Unrealized Gains	30
Available-for-sale investment securities, Gross Unrealized Losses	(2)
Available-for-sale investment securities, Fair Market Value	$ 109,039
Commercial Paper | Maximum
Schedule Of Available For Sale Securities [Line Items]
Available-for-sale investment securities, Maturity (in years)	1 year
Corporate Debt Securities
Schedule Of Available For Sale Securities [Line Items]
Available-for-sale investment securities, Amortized Cost	$ 28,574
Available-for-sale investment securities, Gross Unrealized Gains	10
Available-for-sale investment securities, Gross Unrealized Losses	(2)
Available-for-sale investment securities, Fair Market Value	$ 28,582
Corporate Debt Securities | Maximum
Schedule Of Available For Sale Securities [Line Items]
Available-for-sale investment securities, Maturity (in years)	1 year

Balance Sheet Details - Summary

Balance Sheet Details - Summary of Prepaid Expenses and Other Assets (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Balance Sheet Related Disclosures [Abstract]
Prepaid insurance	$ 836	$ 1,171
Interest receivable	243	265
Prepaid clinical trial costs	99
Prepaid manufacturing and process development costs	21	175
Other prepaids and current assets (including related party amounts of $0 and $28, respectively)	116	77
Prepaid expenses and other current assets	$ 1,315	$ 1,688

Balance Sheet Details - Summa_2

Balance Sheet Details - Summary of Prepaid Expenses and Other Assets (Parenthetical) (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018
Balance Sheet Related Disclosures [Abstract]
Other prepaids and current assets, related parties, current	$ 0	$ 28	$ 0

Balance Sheet Details -Summary

Balance Sheet Details -Summary of Property and Equipment (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 1,923	$ 1,784
Less accumulated depreciation and amortization	(495)	(402)
Property and equipment, net	1,428	1,382
Laboratory Equipment
Property Plant And Equipment [Line Items]
Property and equipment, gross	1,691	1,635
Furniture and Fixtures
Property Plant And Equipment [Line Items]
Property and equipment, gross	55	36
Leasehold Improvements
Property Plant And Equipment [Line Items]
Property and equipment, gross	118	72
Software/Hardware
Property Plant And Equipment [Line Items]
Property and equipment, gross	55
Construction in Progress
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 4	$ 41

Balance Sheet Details - Summa_3

Balance Sheet Details - Summary of Accrued Liabilities (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Balance Sheet Related Disclosures [Abstract]
Accrued research and development (including related party amounts of $0 and $59, respectively)	$ 2,414	$ 1,579
Stock repurchase liability	1,117	1,143
Accrued compensation	723	895
Other accrued liabilities (including related party amounts of $98 and $64, respectively)	548	1,197
Total	$ 4,802	$ 4,814

Balance Sheet Details - Summa_4

Balance Sheet Details - Summary of Accrued Liabilities (Parenthetical) (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Mar. 31, 2018
Balance Sheet Related Disclosures [Abstract]
Accrued research and development, related parties, current	$ 59	$ 0
Other accrued liabilities, related parties, current	$ 64	$ 98

Related Party Transactions - Ad

Related Party Transactions - Additional Information (Details) - USD ($)	1 Months Ended		3 Months Ended	12 Months Ended
	Jul. 31, 2015	Jul. 31, 2014	Mar. 31, 2019	Dec. 31, 2018
Related Party Transaction [Line Items]
Accounts payable and accrued expenses due to related party			$ 98,000	$ 123,000
COI Pharmaceuticals, Inc
Related Party Transaction [Line Items]
Agreement termination period			30 days
Accounts payable and accrued expenses due to related party			$ 100,000	100,000
Prepaid expenses to related party			0
Due from related party			$ 0
COI Pharmaceuticals, Inc | Maximum
Related Party Transaction [Line Items]
Prepaid expenses to related party				100,000
TSRI
Related Party Transaction [Line Items]
Agreement termination period			90 days
Accounts payable and accrued expenses due to related party			$ 0	100,000
Prepaid expenses to related party			$ 0	0
Related party transaction description			As described below, the license agreement was entered into in July 2014, and any intellectual property to which the Company exercises the foregoing option will be included in such license agreement.
Research funding amount			$ 200,000	200,000
Payments of research funding amount			100,000	$ 100,000
Milestone payments			$ 2,400,000
TSRI | Common Stock
Related Party Transaction [Line Items]
Common stock shares issued in consideration for license	8,711	30,663

Related Party Transactions - Sc

Related Party Transactions - Schedule of Expense Recognized Under Agreement (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
COI Pharmaceuticals, Inc
Related Party Transaction [Line Items]
Related party transaction,expenses from transactions with related party	$ 231	$ 220
COI Pharmaceuticals, Inc | Research and development
Related Party Transaction [Line Items]
Related party transaction,expenses from transactions with related party	152	158
COI Pharmaceuticals, Inc | General and administrative
Related Party Transaction [Line Items]
Related party transaction,expenses from transactions with related party	79	62
TSRI
Related Party Transaction [Line Items]
Related party transaction,expenses from transactions with related party	92	96
TSRI | Research and development
Related Party Transaction [Line Items]
Related party transaction,expenses from transactions with related party	89	93
TSRI | General and administrative
Related Party Transaction [Line Items]
Related party transaction,expenses from transactions with related party	$ 3	$ 3

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Details) - USD ($)	1 Months Ended		3 Months Ended
	Nov. 30, 2018	Aug. 31, 2017	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Commitments And Contingencies [Line Items]
Operating sublease, right-of-use asset			$ 2,060,000		$ 0
Operating lease right-of-use asset			3,106,000
Operating lease costs			300,000	$ 100,000
Contingent liabilities			$ 0		$ 0
Office and Laboratory Space
Commitments And Contingencies [Line Items]
Operating lease commencement year			2018-11
Operating lease expiration year			2023-02
Operating lease, option to extend, description			The Lease commenced in November 2018 and will expire in February 2023, however, the Company has the option to extend the Lease for a 12-month period.
Operating lease, renewal term			12 months
Operating lease right-of-use asset			$ 1,000,000
Operating lease, liabilities			$ 1,200,000
Operating lease, remaining term			4 years
Estimated incremental borrowing rate to recognize lease liability, percentage			7.00%
Office and Laboratory Space | COI Pharmaceuticals, Inc
Commitments And Contingencies [Line Items]
Lessee, operating sublease, option to terminate, description			In November 2018, the Company amended the 2017 Sublease to provide the Company with a one-time right to terminate as of March 1, 2024, subject to certain conditions and fees.
Lessee, operating sublease, termination date	Mar. 1, 2024
Lessee, operating sublease, expiration year	2027-02
Operating sublease, right-of-use asset			$ 2,100,000
Operating sublease, aggregate lease liability			$ 2,200,000
Operating sublease, remaining term			7 years 11 months
Estimated incremental borrowing rate to recognize lease liability, percentage			8.50%
California | Office and Laboratory Space | COI Pharmaceuticals, Inc
Commitments And Contingencies [Line Items]
Sublease entered date		2017-08

Commitments and Contingencies_2

Commitments and Contingencies - Schedule of Future Minimum Lease Payments under 2017 Sublease and Lease (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2019USD ($)
Commitments And Contingencies Disclosure [Abstract]
2019	$ 501
2020	655
2021	675
2022	727
2023	483
Thereafter	1,327
Total future minimum lease payments	4,368
Less interest	(1,047)
Total lease liability	$ 3,321
Weighted average lease term	6 years 8 months 12 days
Weighted average discount rate	8.00%

Convertible Preferred Stock a_3

Convertible Preferred Stock and Stockholders'Equity (Deficit) - Additional Information (Details) - USD ($) $ / shares in Units, $ in Millions	Jan. 02, 2019	Nov. 30, 2018	Apr. 30, 2018	Mar. 31, 2019	Dec. 31, 2018
Class Of Stock [Line Items]
Common stock, shares authorized				200,000,000	200,000,000
Common stock, par or stated value per share				$ 0.001	$ 0.001
Preferred stock, shares authorized					10,000,000
Preferred stock, par value					$ 0.001
2018 Equity Incentive Plan
Class Of Stock [Line Items]
Common stock reserved for issuance	1,284,158	3,428,492
Shares of common stock available for issuance		87,111
Percentage of additional common shares reserved for issuance automatically increase on January 1 of each calendar year		4.00%
Share-based compensation, description				In addition, the number of shares of common stock available for issuance under the 2018 Plan will automatically increase on January 1 of each calendar year, starting on January 1, 2019 through January 1, 2028, in an amount equal to 4% of the total number of shares of the Company’s common stock on the last day of the calendar month before the date of each automatic increase, or a lesser number of shares determined by the Company’s board of directors.
Accrued liabilities, repurchase rights for early exercise of stock option				$ 1.1	$ 1.1
2018 Employee Stock Purchase Plan
Class Of Stock [Line Items]
Common stock reserved for issuance	321,039	645,000
Shares of common stock available for issuance	750,000
Percentage of additional common shares reserved for issuance automatically increase on January 1 of each calendar year	1.00%
Share-based compensation, description				In addition, the number of shares of common stock available for issuance under the ESPP will automatically increase on January 1 of each calendar year, starting on January 1, 2019 through January 1, 2028, in an amount equal to the lesser of (i) 1% of the total number of shares of the Company’s common stock on the last day of the calendar month before the date of each automatic increase and (ii) 750,000 shares; provided that before the date of any such increase, the Company’s board of directors may determine that such increase will be less than the amount set forth in clauses (i) and (ii). On January 1, 2019, 321,039 shares were automatically added to the ESPP pursuant to the provision
Maximum percentage of eligible earnings withheld to purchase shares of common stock pursuant to ESPP		15.00%
Price of common stock purchased under ESPP as a percentage of fair value		85.00%
Number of shares issued under ESPP				0
Series C Convertible Preferred Stock
Class Of Stock [Line Items]
Preferred stock, shares issued		11,365,348	8,118,108
Proceeds from issuance of convertible preferred stock		$ 37.1	$ 26.3
IPO | Convertible Preferred Stock
Class Of Stock [Line Items]
Convertible preferred stock outstanding					26,737,354
IPO | Common Stock
Class Of Stock [Line Items]
Common stock issued, shares					13,699,636
Shares price, per share					$ 11
Proceeds from IPO, net of underwriting discounts and commissions and other offering costs					$ 137.5
Outstanding shares of convertible preferred stock converted into common stock, shares					16,687,477

Convertible Preferred Stock a_4

Convertible Preferred Stock and Stockholders'Equity (Deficit) - Summary of Early Exercise of Stock Options (Details) - 2014 Plan	3 Months Ended
	Mar. 31, 2019shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Balance as of December 31, 2018	709,123
Shares vested	(9,363)
Balance as of March 31, 2019	699,760