Rain Oncology 10-Q 9 Nov 23 2023 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2023	Nov. 03, 2023
Document and Entity Information
Document Type	10-Q
Document Quarterly Report	true
Document Transition Report	false
Document Period End Date	Sep. 30, 2023
Entity File Number	001-40356
Entity Registrant Name	Rain Oncology Inc.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	82-1130967
Entity Address, Address Line One	8000 Jarvis Avenue
Entity Address, Address Line Two	Suite 204
Entity Address, City or Town	Newark
Entity Address, State or Province	CA
Entity Address, Postal Zip Code	94560
City Area Code	510
Local Phone Number	953-5559
Title of 12(b) Security	Common Stock, par value $0.001 per share
Trading Symbol	RAIN
Security Exchange Name	NASDAQ
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	true
Entity Ex Transition Period	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		36,375,671
Entity Central Index Key	0001724979
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2023
Document Fiscal Period Focus	Q3
Amendment Flag	false

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets (unaudited) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Current assets:
Cash and cash equivalents	$ 37,312	$ 61,955
Short-term investments	40,008	68,499
Prepaid and other current assets	3,496	3,174
Total current assets	80,816	133,628
Property and equipment, net	628	93
Operating lease right-of-use asset	436	258
Other assets	180	1,201
Total assets	82,060	135,180
Current liabilities:
Accounts payable	8,973	7,146
Accrued research and development	2,858	8,232
Other accrued liabilities	2,190	6,424
Operating lease liability, current portion	456	164
Total current liabilities	14,477	21,966
Operating lease liability, net of current portion		113
Other long-term liabilities	64	65
Total liabilities	14,541	22,144
Commitments and contingencies
Stockholders' equity:
Preferred stock, $0.001 par value; 10,000,000 shares authorized; no shares issued and outstanding
Common stock, $0.001 par value; 250,000,000 shares authorized as of September 30, 2023 and December 31, 2022; 36,375,671 shares (comprised of 27,579,947 shares of common stock and 8,795,724 shares of non-voting common stock) and 36,290,292 shares (comprised of 25,947,572 shares of common stock and 10,342,720 shares of non-voting common stock) issued and outstanding as of September 30, 2023 and December 31, 2022, respectively	37	37
Additional paid-in capital	282,816	278,853
Accumulated other comprehensive loss	(64)	(166)
Accumulated deficit	(215,270)	(165,688)
Total stockholders' equity	67,519	113,036
Total liabilities and stockholders' equity	$ 82,060	$ 135,180

Condensed Consolidated Balanc_2

Condensed Consolidated Balance Sheets (Parenthetical) (unaudited) - $ / shares	Sep. 30, 2023	Dec. 31, 2022
Preferred stock, par value	$ 0.001	$ 0.001
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	$ 0.001	$ 0.001
Common stock, shares authorized	250,000,000	250,000,000
Common stock, shares issued	36,375,671	36,290,292
Common stock, shares outstanding	36,375,671	36,290,292
Common Stock
Common stock, shares issued	27,579,947	25,947,572
Common stock, shares outstanding	27,579,947	25,947,572
Non-voting Common Stock
Common stock, shares issued	8,795,724	10,342,720
Common stock, shares outstanding	8,795,724	10,342,720

Condensed Consolidated Statemen

Condensed Consolidated Statements of Operations and Comprehensive Loss (unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Operating expenses:
Research and development	$ 3,965	$ 14,510	$ 35,622	$ 42,322
General and administrative	4,113	3,901	14,593	11,257
Restructuring charges			2,837
Total operating expenses	8,078	18,411	53,052	53,579
Loss from operations	(8,078)	(18,411)	(53,052)	(53,579)
Other income:
Interest income	1,044	370	3,470	533
Total other income	1,044	370	3,470	533
Net loss	$ (7,034)	$ (18,041)	$ (49,582)	$ (53,046)
Net loss per share, basic	$ (0.19)	$ (0.68)	$ (1.36)	$ (2)
Net loss per share, diluted	$ (0.19)	$ (0.68)	$ (1.36)	$ (2)
Weighted-average shares used to compute net loss per share, basic	36,375,671	26,564,615	36,359,744	26,535,474
Weighted-average shares used to compute net loss per share, diluted	36,375,671	26,564,615	36,359,744	26,535,474
Other comprehensive loss:
Unrealized gain (loss) on short-term investments	$ 36	$ 71	$ 102	$ (213)
Comprehensive loss	$ (6,998)	$ (17,970)	$ (49,480)	$ (53,259)

Condensed Consolidated Statem_2

Condensed Consolidated Statements of Stockholders' Equity (unaudited) - USD ($) $ in Thousands	Common Stock	Additional Paid-in Capital	Accumulated Deficit	Accumulated Other Comprehensive Loss	Total
Balance at Dec. 31, 2021	$ 27	$ 220,530	$ (89,964)	$ (89)	$ 130,504
Balance, Shares at Dec. 31, 2021	26,475,812
Exercise of stock options		106			106
Exercise of stock options, shares	24,262
Issuance of common stock from employee stock purchase plan		293			293
Issuance of common stock from employee stock purchase plan, shares	26,804
Stock-based compensation expense		1,242			1,242
Unrealized gain (loss) on investments				(300)	(300)
Net loss			(17,394)		(17,394)
Balance at Mar. 31, 2022	$ 27	222,171	(107,358)	(389)	114,451
Balance, Shares at Mar. 31, 2022	26,526,878
Balance at Dec. 31, 2021	$ 27	220,530	(89,964)	(89)	130,504
Balance, Shares at Dec. 31, 2021	26,475,812
Unrealized gain (loss) on investments					(213)
Net loss					(53,046)
Balance at Sep. 30, 2022	$ 27	224,694	(143,010)	(302)	81,409
Balance, Shares at Sep. 30, 2022	26,564,826
Balance at Mar. 31, 2022	$ 27	222,171	(107,358)	(389)	114,451
Balance, Shares at Mar. 31, 2022	26,526,878
Exercise of stock options		12			12
Exercise of stock options, shares	3,000
Stock-based compensation expense		1,417			1,417
Unrealized gain (loss) on investments				16	16
Net loss			(17,611)		(17,611)
Balance at Jun. 30, 2022	$ 27	223,600	(124,969)	(373)	98,285
Balance, Shares at Jun. 30, 2022	26,529,878
Exercise of stock options		15			15
Exercise of stock options, shares	3,890
Issuance of common stock from employee stock purchase plan		147			147
Issuance of common stock from employee stock purchase plan, shares	31,058
Stock-based compensation expense		932			932
Unrealized gain (loss) on investments				71	71
Net loss			(18,041)		(18,041)
Balance at Sep. 30, 2022	$ 27	224,694	(143,010)	(302)	81,409
Balance, Shares at Sep. 30, 2022	26,564,826
Balance at Dec. 31, 2022	$ 37	278,853	(165,688)	(166)	113,036
Balance, Shares at Dec. 31, 2022	36,290,292
Exercise of stock options		75			75
Exercise of stock options, shares	20,757
Issuance of common stock from employee stock purchase plan		137			137
Issuance of common stock from employee stock purchase plan, shares	20,129
Issuance of common stock in connection with equity financings, net of issuance costs		106			106
Issuance of common stock in connection with equity financings, net of issuance costs, shares	32,000
Stock-based compensation expense		1,568			1,568
Unrealized gain (loss) on investments				119	119
Net loss			(20,484)		(20,484)
Balance at Mar. 31, 2023	$ 37	280,739	(186,172)	(47)	94,557
Balance, Shares at Mar. 31, 2023	36,363,178
Balance at Dec. 31, 2022	$ 37	278,853	(165,688)	(166)	113,036
Balance, Shares at Dec. 31, 2022	36,290,292
Unrealized gain (loss) on investments					102
Net loss					(49,582)
Balance at Sep. 30, 2023	$ 37	282,816	(215,270)	(64)	67,519
Balance, Shares at Sep. 30, 2023	36,375,671
Balance at Mar. 31, 2023	$ 37	280,739	(186,172)	(47)	94,557
Balance, Shares at Mar. 31, 2023	36,363,178
Issuance of common stock from employee stock purchase plan		12			12
Issuance of common stock from employee stock purchase plan, shares	12,493
Stock-based compensation expense		837			837
Unrealized gain (loss) on investments				(53)	(53)
Net loss			(22,064)		(22,064)
Balance at Jun. 30, 2023	$ 37	281,588	(208,236)	(100)	73,289
Balance, Shares at Jun. 30, 2023	36,375,671
Stock-based compensation expense		1,228			1,228
Unrealized gain (loss) on investments				36	36
Net loss			(7,034)		(7,034)
Balance at Sep. 30, 2023	$ 37	$ 282,816	$ (215,270)	$ (64)	$ 67,519
Balance, Shares at Sep. 30, 2023	36,375,671

Condensed Consolidated Statem_3

Condensed Consolidated Statements of Cash Flows (unaudited) - USD ($)	9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022
Operating activities
Net loss	$ (49,582,000)	$ (53,046,000)
Adjustments to reconcile net loss to cash used in operating activities:
Stock-based compensation expense	3,633,000	3,591,000
Amortization of premium and accretion of discounts on short-term investments, net	(1,441,000)	(35,000)
Depreciation and amortization expense	189,000	62,000
Fair value gain on investments	8,000
In-process research and development expense		(1,000,000)
Changes in operating assets and liabilities:
Prepaid and other current assets	(322,000)	2,891,000
Operating lease right-of-use asset and liability, net	1,000	(5,000)
Other assets	724,000	(53,000)
Accounts payable	1,786,000	(2,028,000)
Accrued research and development	(5,374,000)	4,000
Other accrued liabilities	(2,084,000)	(286,000)
Net cash used in operating activities	(52,462,000)	(49,905,000)
Investing activities
Maturities of short-term investments	69,650,000	99,150,000
Purchases of short-term investments	(39,625,000)	(34,764,000)
Purchases of property and equipment, net	(684,000)
Payment of in-process research and development expense	(2,000,000)
Net cash provided by investing activities	27,341,000	64,386,000
Financing Activities
Proceeds from issuance of common stock in connection with the Company's at-the-market facility	343,000
Proceeds from the issuance of common stock under the Company's equity incentive plans and employee stock purchase plan	224,000	573,000
Payments of issuance costs related to equity financings	(89,000)
Net cash provided by financing activities	478,000	573,000
Net (decrease) increase in cash and cash equivalents	(24,643,000)	15,054,000
Cash and cash equivalents at beginning of period	61,955,000	24,780,000
Cash and cash equivalents at end of period	37,312,000	39,834,000
Supplemental schedule of non-cash investing and financing activities:
Operating lease right-of-use asset obtained in exchange for lease liabilities	349,000
Non-cash additions to property and equipment	$ 40,000
Non-cash in-process research and development accrual		$ 1,000,000

Organization and Nature of Oper

Organization and Nature of Operations	9 Months Ended
	Sep. 30, 2023
Organization and Nature of Operations
Organization and Nature of Operations	Note 1 – Organization and Nature of Operations Description of Business Rain Oncology Inc. (“Rain” or the “Company”), formerly known as Rain Therapeutics Inc., was incorporated in the state of Delaware in April 2017. Rain is a precision oncology company developing therapies that target oncogenic drivers for which the Company is able to genetically select patients the Company believes will most likely benefit. Rain’s product candidate, milademetan, is a small molecule, oral inhibitor of the MDM2-p53 complex that reactivates p53. The Company operates in one business segment and its principal operations are in the United States, with its headquarters in Newark, California. On June 22, 2022, the Company formed Rain Oncology Australia Pty Ltd (“Rain Oncology Australia”), a wholly owned subsidiary incorporated under the laws of Australia. On December 22, 2022, the Company filed a Certificate of Amendment to its Amended and Restated Certificate of Incorporation with the Secretary of State of the State of Delaware to effect a change of the Company’s name from “Rain Therapeutics Inc.” to “Rain Oncology Inc.” effective as of December 30, 2022. Basis of Presentation The accompanying interim unaudited condensed consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the United States (“U.S. GAAP”) related to a Quarterly Report on Form 10-Q. These condensed consolidated financial statements include the accounts of the Company and Rain Oncology Australia. All significant inter-company transactions, balances and expenses have been eliminated upon consolidation. Any reference in these notes to applicable guidance is meant to refer to U.S. GAAP as found in the Accounting Standards Codification (“ASC”) and Accounting Standards Updates (“ASU”) promulgated by the Financial Accounting Standards Board (“FASB”). The year-end balance sheet data was derived from the Company’s audited financial statements but does not include all disclosures required by U.S. GAAP. These condensed consolidated financial statements should be read in conjunction with the Company’s audited financial statements for the year ended December 31, 2022, included in the Company’s Annual Report on Form 10-K, filed pursuant to Section 13(a) or 15(d) of the Securities Exchange Act of 1934, as amended (the “Exchange Act”). The unaudited financial information for the interim periods presented herein reflects all adjustments which, in the opinion of management, are necessary for a fair presentation of the financial condition and results of operation for the periods presented, with such adjustments consisting only of normal recurring adjustments. Liquidity and Capital Resources The Company has devoted substantially all of its efforts to drug discovery and development, raising capital and building operations. The Company has a limited operating history and has not generated any revenue since its inception, and the sales and income potential of the Company’s business is unproven. The Company has incurred net losses and negative cash flows from operating activities since its inception and expects to continue to incur net losses into the foreseeable future as it continues the development of its product candidates. From inception through September 30, 2023, the Company has funded its operations through net proceeds from its initial public offering in April 2021, the offering, issuance and sale of its common stock in November 2022, as well as the issuance of convertible promissory notes and convertible preferred stock. The accompanying condensed consolidated financial statements have been prepared assuming the Company will continue as a going concern. Management believes that the Company’s current cash, cash equivalents and short-term investments will provide sufficient funds to enable the Company to meet its obligations for at least twelve months from the filing date of this report.

Summary of Significant Accounti

Summary of Significant Accounting Policies	9 Months Ended
	Sep. 30, 2023
Summary of Significant Accounting Policies
Summary of Significant Accounting Policies	Note 2 – Summary of Significant Accounting Policies Use of Estimates The preparation of the Company’s condensed consolidated financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that impact the reported amounts of assets, liabilities and expenses and the disclosure of contingent liabilities in the Company’s condensed consolidated financial statements and accompanying notes. The most significant estimate in the Company’s condensed consolidated financial statements relates to the clinical trial expense accruals. Management evaluates its estimates on an ongoing basis. Although these estimates are based on the Company’s historical experience, knowledge of current events and actions it may undertake in the future, actual results may ultimately materially differ from these estimates and assumptions. Cash and Cash Equivalents The Company considers all highly liquid investments with an original maturity of three months or less at the date of purchase to be cash equivalents. Cash equivalents include money market funds, commercial paper, U.S. government securities and U.S. agency bonds. Available-for-Sale Investments The Company holds investment grade securities consisting of commercial paper, corporate debt securities, U.S. government securities and U.S. agency bonds, classified as available-for-sale (AFS) securities at the time of purchase, since it is the Company’s intent that these investments be available for current operations. The Company has classified all of its AFS securities as current assets in the condensed consolidated balance sheets even though the stated maturity date may be one year or more beyond the current condensed consolidated balance sheet date, which reflects management’s intention to use the proceeds from sales of these securities to fund its operations, as necessary. The Company carries these securities at fair value and reports unrealized gains and losses, if any, as a separate component of accumulated other comprehensive loss. The cost of debt securities is adjusted for amortization of purchase premiums and accretion of discounts to maturity. Such amortization and accretion are included in interest income in the condensed consolidated statements of operations and comprehensive loss. Realized gains and losses on sales of securities are determined using the specific identification method and recorded in interest income in the condensed consolidated statement of operations and comprehensive loss. Allowance for Credit Losses For AFS securities in an unrealized loss position, the Company first assesses whether it intends to sell, or if it is more likely than not that the Company will be required to sell, the security before recovery of its amortized cost basis. If either of the criteria regarding intent or requirement to sell is met, the security’s amortized cost basis is written down to fair value through earnings. For AFS securities that do not meet the aforementioned criteria, the Company evaluates whether the decline in fair value has resulted from credit losses or other factors. In making this assessment, the Company considers the severity of the impairment, any changes in interest rates, market conditions, changes to the underlying credit ratings and forecasted recovery, among other factors. The credit-related portion of unrealized losses, and any subsequent improvements, are recorded in interest income through an allowance account. Any impairment that has not been recorded through an allowance for credit losses is included in other comprehensive loss in the condensed consolidated statement of operations and comprehensive loss. The Company elected the practical expedient to exclude the applicable accrued interest from both the fair value and amortized costs basis of its AFS securities for purposes of identifying and measuring an impairment. Accrued interest receivable on AFS securities is recorded in prepaid and other current assets in the condensed consolidated balance sheets. The Company’s accounting policy is to not measure an allowance for credit loss for accrued interest receivable and to write-off any uncollectible accrued interest receivable as a reversal of interest income in a timely manner, which the Company considers to be in the period in which it determines the accrued interest will not be collected by the Company. Research and Development Costs Research and development costs primarily consist of costs associated with the Company’s research and development activities, including its drug discovery efforts, and the preclinical and clinical development of its product candidates. Research and development costs are expensed as incurred. Preclinical Studies and Clinical Trial Accruals The Company is required to estimate its expenses resulting from its obligations under contracts with vendors, consultants, clinical research organizations and clinical site agreements in connection with conducting preclinical activities and clinical trials. The financial terms of these contracts are subject to negotiations which vary from contract to contract and may result in payment flows that do not match the periods over which materials or services are provided under such contracts. The Company reflects preclinical study and clinical trial expenses in its condensed consolidated financial statements by matching those expenses with the period in which services and efforts are expended. The Company accounts for these expenses according to the progress of the preclinical study or clinical trial as measured by the timing of various aspects of the preclinical study, clinical trial or related activities. The Company determines accrual and prepaid estimates through review of the underlying contracts along with preparation of financial models taking into account correspondence with clinical and other key personnel and third-party service providers as to the progress of preclinical studies, clinical trials or other services being conducted. During the course of a preclinical study or clinical trial, the Company adjusts its expense recognition if actual results differ from its estimates. To date, the Company has not experienced any material differences between accrued costs and actual costs incurred. Stock-Based Compensation Stock-based compensation expense represents the grant date fair value of equity awards recognized over the requisite service period of the awards (generally the vesting period) on a straight-line basis. The Company recognizes forfeitures as they occur. The Company estimates the fair value of stock option grants using the Black-Scholes option pricing model. The fair value of restricted stock units (“RSUs”) granted is based on the Company’s closing stock price on the date of grant. Income Taxes The Company accounts for income taxes under the asset and liability method, which requires the recognition of deferred tax assets and liabilities for the expected future tax consequences of events that have been included in the condensed consolidated financial statements. Under this method, deferred tax assets and liabilities are determined on the basis of the differences between the financial statements and tax basis of assets and liabilities using enacted tax rates in effect for the year in which the differences are expected to reverse. The effect of a change in tax rates on deferred tax assets and liabilities is recognized in income in the period that includes the enactment date. The Company recognizes deferred tax assets to the extent that the Company believes these assets are more likely than not to be realized. In making such a determination, management considers all available positive and negative evidence, including future reversals of existing taxable temporary differences, projected future taxable income, tax-planning strategies and results of recent operations. If management determines that the Company would be able to realize its deferred tax assets in the future in excess of their recorded amount, management would make an adjustment to the deferred tax asset valuation allowance, which would reduce the provision for income taxes. The Company records uncertain tax positions on the basis of a two-step process whereby (1) management determines whether it is more likely than not that the tax positions will be sustained on the basis of the technical merits of the position and (2) for those tax positions that meet the more likely than not recognition threshold, management recognizes the largest amount of tax benefit that is more than 50 percent likely to be realized upon ultimate settlement with the related tax authority. The Company recognizes interest and penalties related to unrecognized tax benefits within income tax expense. Any accrued interest and penalties are included within the related tax liability. Restructuring Restructuring costs comprised of severance, other termination benefit costs and stock-based compensation expense for stock option modifications related to workforce reductions. The Company recognizes restructuring charges when the liability is probable, and the amount is estimable. Employee termination benefits are accrued at the date management has committed to a plan of termination and affected employees have been notified of their termination date and expected severance benefits. Comprehensive Loss Comprehensive loss is defined as a change in equity during a period from transactions and other events and circumstances from non-owner sources. The Company’s comprehensive loss includes unrealized gains and losses from short-term investments. Net Loss Per Share Basic net loss per share is calculated by dividing the net loss attributable to common stockholders by the weighted-average number of shares of common stock outstanding for the period, without consideration of potential dilutive securities. Diluted net loss per share is computed by dividing the net loss attributable to common stockholders by the sum of the weighted-average number of shares of common stock plus the potential dilutive effects of potential dilutive securities outstanding during the period. Potential dilutive securities are excluded from diluted earnings or loss per share if the effect of such inclusion is antidilutive. The Company’s potentially dilutive securities, which include shares from the 2021 Employee Stock Purchase Plan (the “ESPP”) and outstanding stock options and RSUs under the Company’s equity incentive plan, have been excluded from the computation of diluted net loss per share as they would be anti-dilutive to the net loss per share. For the periods presented, there is no difference in the number of shares used to calculate basic and diluted shares outstanding due to the Company’s net loss position. Recent Accounting Pronouncements Financial Instruments . In June 2016, the FASB issued ASU 2016-13, Financial Instruments—Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments. The objective of the standard is to improve financial reporting of expected credit losses on financial instruments and other commitments to extend credit. ASU 2016-13 requires that an entity measure and recognize expected credit losses for financial assets held at amortized cost and replaces the incurred loss impairment methodology in prior U.S. GAAP with a methodology that requires consideration of a broader range of information to estimate credit losses, and establishes additional disclosures related to credit risks. The Company adopted Topic 326 on January 1, 2023. The adoption did not have a significant impact on the Company’s condensed consolidated financial statements or the related disclosures. There were no other significant updates to the recently issued accounting standards other than as disclosed herein for the three and nine months ended September 30, 2023. Although there are several other new accounting pronouncements issued or proposed by the FASB, based on the Company’s preliminary assessment, the Company does not believe any of those accounting pronouncements have had or will have a material impact on its financial position or operating results .

Fair Value Measurements

Fair Value Measurements	9 Months Ended
	Sep. 30, 2023
Fair Value Measurements
Fair Value Measurements	Note 3 – Fair Value Measurements The accounting guidance 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 Level 2 Level 3 Financial assets measured at fair value on a recurring basis consist of the Company’s cash equivalents and AFS securities. The Company obtains pricing information from its investment manager and generally determines the fair value of investment securities using standard observable inputs, including reported trades, broker/dealer quotes, and bids and/or offers. Investments are classified as Level 1 within the fair value hierarchy if their quoted prices are available in active markets for identical securities. Investments in money market funds and U.S. government securities were classified as Level 1 instruments. Investments in commercial paper, corporate debt securities and U.S. agency bonds are valued using Level 2 inputs. The Company classifies investments within Level 2 if the investments are valued using model driven valuations using observable inputs such as quoted market prices, benchmark yields, reported trades, broker/dealer quotes or alternative pricing sources with reasonable levels of price transparency. Investments are held by custodians who obtain investment prices from a third-party pricing provider that incorporates standard inputs in various asset pricing models. The carrying amounts of cash, prepaid expenses and other current assets, other assets, accounts payable, accrued research and development and other current liabilities are reasonable estimates of their fair value due to the short-term nature of these accounts. The Company’s money market funds under cash and cash equivalents are classified using Level 1 inputs within the fair value hierarchy because they are valued using quoted market prices, broker or dealer quotations, or alternative pricing sources with reasonable levels of price transparency. There were no transfers between levels of the fair value hierarchy during The following tables summarize financial assets that the Company measured at fair value on a recurring basis, classified in accordance with the fair value hierarchy (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Fair Value Measurements at Reporting Date Using: ​ ​ Level 1 ​ Level 2 ​ Level 3 ​ Total As of September 30, 2023: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Money market funds ​ $ 8,669 ​ $ — ​ $ — ​ $ 8,669 Commercial paper ​ ​ — ​ ​ 22,968 ​ ​ — ​ ​ 22,968 U.S. government securities ​ ​ 18,578 ​ ​ — ​ ​ — ​ ​ 18,578 U.S. agency bonds ​ ​ — ​ ​ 26,568 ​ ​ — ​ ​ 26,568 Total cash equivalents and short-term investments ​ $ 27,247 ​ $ 49,536 ​ $ — ​ $ 76,783 Reported as: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Cash and cash equivalents (includes cash of $537) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ $ 37,312 Short-term investments ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 40,008 Total cash, cash equivalents and short-term investments ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ $ 77,320 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Fair Value Measurements at Reporting Date Using: ​ ​ Level 1 ​ Level 2 ​ Level 3 ​ Total As of December 31, 2022: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Money market funds ​ $ 8,528 ​ $ — ​ $ — ​ $ 8,528 Commercial paper ​ ​ — ​ ​ 83,423 ​ ​ — ​ ​ 83,423 U.S. government securities ​ ​ 10,837 ​ ​ — ​ ​ — ​ ​ 10,837 U.S. agency bonds ​ ​ — ​ ​ 22,143 ​ ​ — ​ ​ 22,143 Corporate debt securities ​ ​ — ​ ​ 997 ​ ​ — ​ ​ 997 Total cash equivalents and short-term investments ​ $ 19,365 ​ $ 106,563 ​ $ — ​ $ 125,928 Reported as: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Cash and cash equivalents (includes cash of $4,526) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ $ 61,955 Short-term investments ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 68,499 Total cash, cash equivalents and short-term investments ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ $ 130,454 ​ ​ There were no liabilities measured at fair value on a recurring basis as of September 30­­­, 2023 and December 31, 2022.

Investments

Investments	9 Months Ended
	Sep. 30, 2023
Investments
Investments	Note 4 – Investments The Company invests in available-for-sale securities consisting of money market funds, commercial paper, U.S. government securities, U.S. agency bonds and corporate debt securities. Available-for-sale securities are classified as either cash and cash equivalents or short-term investments in the condensed consolidated balance sheets. The following tables summarize, by major types of cash equivalents, and investments that are measured at fair value on a recurring basis (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ As of September 30, 2023 ​ ​ Amortized ​ Unrealized ​ Unrealized ​ Estimated ​ ​ Cost ​ Gains ​ Losses ​ Fair Value Money market funds ​ $ 8,669 ​ $ — ​ $ — ​ $ 8,669 Commercial paper ​ ​ 22,979 ​ ​ — ​ ​ (11) ​ ​ 22,968 U.S. government securities ​ ​ 18,588 ​ ​ 1 ​ ​ (11) ​ ​ 18,578 U.S. agency bonds ​ ​ 26,611 ​ ​ 1 ​ ​ (44) ​ ​ 26,568 Cash equivalents and short-term investments ​ $ 76,847 ​ $ 2 ​ $ (66) ​ $ 76,783 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ As of December 31, 2022 ​ ​ Amortized ​ Unrealized ​ Unrealized ​ Estimated ​ ​ Cost ​ Gains ​ Losses ​ Fair Value Money market funds ​ $ 8,528 ​ $ — ​ $ — ​ $ 8,528 Commercial paper ​ ​ 83,479 ​ ​ 11 ​ ​ (67) ​ ​ 83,423 U.S. government securities ​ ​ 10,910 ​ ​ — ​ ​ (73) ​ ​ 10,837 U.S. agency bonds ​ ​ 22,175 ​ ​ 4 ​ ​ (36) ​ ​ 22,143 Corporate debt securities ​ ​ 1,002 ​ ​ — ​ ​ (5) ​ ​ 997 Cash equivalents and short-term investments ​ $ 126,094 ​ $ 15 ​ $ (181) ​ $ 125,928 ​ The contractual maturities of the Company’s AFS securities were as follows (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ As of September 30, 2023 ​ As of December 31, 2022 Due within one year ​ $ 37,354 ​ $ 63,595 Due within one to two years ​ ​ 2,654 ​ ​ 4,904 Total ​ $ 40,008 ​ $ 68,499 ​ The AFS investments are classified as current assets, even though the stated maturity date may be one year or more beyond the current condensed consolidated balance sheet date, which reflects management’s intention to use the proceeds from sales of these securities to fund the Company’s operations, as necessary. There were no realized gains or losses due to investment sales for the three and nine months ended September 30, 2023 and 2022. As of September 30, 2023, $44.9 million of the Company’s marketable securities were in gross unrealized loss positions, of which none had been in such position for greater than 12 months and $22.5 million will mature within three months of September 30, 2023. The Company does not intend to sell its AFS investments before maturity, and it is unlikely that the Company will be required to sell such investments before recovery of their amortized cost basis. Based on the Company’s review of these AFS securities, the unrealized losses as of September 30, 2023 were primarily due to changes in interest rates and not due to increased credit risks associated with specific securities. The Company has no allowance for credit losses as of September 30, 2023 and December 31, 2022. Unrealized gains and losses that are not credit-related are included in accumulated other comprehensive loss. Accrued interest receivables on AFS securities were $0.2 million and $0.1 million as of September 30, 2023 and December 31, 2022, respectively. The Company has not written off any accrued interest receivables for the three and nine months ended September 30, 2023 and 2022 .

Condensed Consolidated Balanc_3

Condensed Consolidated Balance Sheet Details	9 Months Ended
	Sep. 30, 2023
Condensed Consolidated Balance Sheet Details
Condensed Consolidated Balance Sheet Details	Note 5 - Condensed Consolidated Balance Sheet Details Prepaid and Other Current Assets Prepaid and other current assets consist of the following (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ As of September 30, 2023 ​ As of December 31, 2022 Prepaid insurance ​ $ 1,226 ​ $ 913 Prepaid research and development ​ ​ 991 ​ ​ 1,103 FICA tax credit receivable ​ ​ 531 ​ ​ 571 Prepaid other ​ ​ 448 ​ ​ 416 Other current assets ​ ​ 281 ​ ​ 152 Deposits ​ ​ 19 ​ ​ 19 Prepaid and other current assets ​ $ 3,496 ​ $ 3,174 ​ Property and Equipment, Net Property and equipment, net, consist of the following (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ As of September 30, 2023 ​ As of December 31, 2022 Leasehold improvements ​ $ 794 ​ $ 67 Furniture and equipment ​ ​ 209 ​ ​ 204 Computer equipment ​ ​ 50 ​ ​ 50 Construction in progress ​ ​ — ​ ​ 8 ​ ​ ​ 1,053 ​ ​ 329 Less: accumulated depreciation and amortization expense ​ ​ (425) ​ ​ (236) Property and equipment, net ​ $ 628 ​ $ 93 ​ Depreciation and amortization expense for the three months ended September 30, 2023 and 2022 was $154,000 and $18,000, respectively. Depreciation and amortization expense for the nine months ended September 30, 2023 and 2022 was $189,000 and $62,000, respectively. Other Non-Current Assets Other non-current assets consist of the following (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ As of September 30, 2023 ​ As of December 31, 2022 Deposits ​ $ 110 ​ $ 781 FICA tax credit receivable ​ ​ — ​ ​ 52 Other ​ ​ 70 ​ ​ 368 Other non-current assets ​ $ 180 ​ $ 1,201 ​ Other Accrued Liabilities Other accrued liabilities consist of the following (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ As of September 30, 2023 ​ As of December 31, 2022 Accrued bonus ​ $ 1,481 ​ $ 3,379 Accrued payroll and related ​ ​ 36 ​ ​ 229 ESPP liability ​ ​ 35 ​ ​ 155 Other ​ ​ 638 ​ ​ 2,661 Other accrued liabilities ​ $ 2,190 ​ $ 6,424 ​

Stockholders' Equity

Stockholders' Equity	9 Months Ended
	Sep. 30, 2023
Stockholders' Equity
Stockholders' Equity	Note 6 – Stockholders’ Equity In April 2021, the Company filed a certificate of amendment to its certificate of incorporation, which authorized 260,000,000 shares of capital stock, consisting of 250,000,000 shares of common stock, par value $0.001 per share, and 10,000,000 shares of undesignated preferred stock, par value $0.001 per share that may be issued from time to time by the Company’s board of directors (the “Board of Directors”) in one or more series. Of the 250,000,000 shares of common stock, 200,000,000 shares were designated as “Common Stock” and 50,000,000 shares were designated as “Non-Voting Common Stock.” Equity Incentive Plan In August 2020, the Board of Directors amended the Amended and Restated 2018 Stock Option—Stock Issuance Plan (the “2018 Plan”) to increase the maximum number of shares of common stock that may be issued over the term of the plan. The 2018 Plan provided for the grant of stock options, non-statutory stock options, incentive stock options and stock issuances to employees, nonemployees and consultants of the Company. In April 2021, the Company’s 2021 Equity Incentive Plan (the “2021 Plan”) was approved by the Board of Directors and became effective on April 15, 2021. Upon the effectiveness of the 2021 Plan, no further grants may be made under the 2018 Plan. The 2021 Plan allows the Company to grant equity-based awards to its officers, employees, directors and other key persons (including consultants). The Company initially reserved up to 3,246,120 shares of common stock for issuance under the 2021 Plan, plus (i) 1,722 shares that remained available for the issuance of awards under the 2018 Plan at the time the 2021 Plan became effective, and (ii) any shares subject to outstanding options or other share awards that were granted under the 2018 Plan that terminate or expire prior to exercise or settlement; are forfeited because of the failure to vest; or are reacquired or withheld (or not issued) to satisfy a tax withholding obligation or the purchase or exercise price. The 2021 Plan provides that the number of shares reserved and available for issuance under the plan will automatically increase each January 1, beginning on January 1, 2022 and each January 1 thereafter through January 31, 2032, by 4.0% of the outstanding number of shares of common stock on the immediately preceding December 31, or such lesser number of shares as determined by the Board of Directors. As a result, the number of shares of common stock reserved for issuance under the 2021 Plan increased by 1,451,611 shares on January 1, 2023. Stock Options A summary of the Company’s stock option activities during the nine months ended September 30, 2023 is as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted- ​ Weighted- ​ ​ ​ ​ ​ ​ Average ​ Average ​ Aggregate ​ ​ ​ ​ Exercise ​ Remaining ​ Intrinsic ​ ​ ​ ​ Price Per ​ Contract Term ​ Value ​ ​ Total Options ​ Share ​ (in years) ​ (in millions) Outstanding as of December 31, 2022 ​ 2,593,761 ​ $ 8.08 ​ 8.2 ​ $ — Granted ​ 2,517,700 ​ $ 5.49 ​ ​ ​ ​ ​ Exercised ​ (20,757) ​ $ 3.59 ​ ​ ​ ​ ​ Forfeited or cancelled ​ (1,130,674) ​ $ (9.25) ​ ​ ​ ​ ​ Outstanding as of September 30, 2023 ​ 3,960,030 ​ $ 6.12 ​ 7.8 ​ $ — Vested and expected to vest as of September 30, 2023 ​ 3,960,030 ​ $ 6.12 ​ 7.8 ​ $ — Vested and exercisable as of September 30, 2023 ​ 1,514,801 ​ $ 7.20 ​ 5.4 ​ $ — ​ The weighted-average grant date fair values of option grants during the nine months ended September 30, 2023 and 2022 were $4.54 and $7.33 per share, respectively. The weighted-average grant date fair values of options forfeited during the nine months ended September 30, 2023 and 2022 were $9.31 and $12.05 per share, respectively. Restricted Stock Units A summary of the Company’s RSU activities during the nine months ended September 30, 2023 is as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted- ​ Aggregate ​ ​ Total ​ Average ​ Intrinsic ​ ​ Restricted ​ Grant Date ​ Value ​ ​ Stock Units ​ Fair Values ​ (in millions) Outstanding as of December 31, 2022 ​ 8,945 ​ $ 6.25 ​ $ — Granted ​ 95,333 ​ $ 9.59 ​ ​ ​ Vested ​ (9,038) ​ $ 8.71 ​ ​ ​ Forfeited or cancelled ​ (53,755) ​ $ 9.31 ​ ​ ​ Outstanding as of September 30, 2023 ​ 41,485 ​ $ 9.42 ​ $ — ​ Employee Stock Purchase Plan The ESPP was approved by the Board of Directors and became effective on April 15, 2021. The ESPP initially reserved and authorized the issuance of up to 259,689 shares of common stock to participating employees. Under the ESPP, eligible employees can contribute up to 15% of their eligible compensation, as defined in the ESPP, towards the purchase of the Company’s common stock at a price of 85% of the lower of the fair market value of the Company’s common stock on the first trading day of the offering period or on the last trading day of the offering period. The ESPP provides for twenty-four-month offering periods with four six-month purchase periods in each offering period. The ESPP provides that the number of shares reserved and available for issuance will automatically increase each January 1, beginning on January 1, 2022 and each January 1 thereafter through January 31, 2032, by 1.0% of the total number of shares of common stock outstanding on December 31 of the preceding calendar year. As a result, the number of shares of common stock reserved for issuance under the ESPP increased by 362,902 shares on January 1, 2023. Under the ESPP, the Company issued 32,622 shares of common stock for aggregate cash proceeds of $0.1 million during the nine months ended September 30, 2023. Stock-Based Compensation Expense The Company recognized stock-based compensation expense as follows (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended September 30, ​ Nine Months Ended September 30, ​ ​ 2023 ​ 2022 ​ 2023 ​ 2022 Research and development ​ $ 656 ​ $ 728 ​ $ 2,316 ​ $ 2,821 General and administrative ​ ​ 572 ​ ​ 204 ​ ​ 1,280 ​ ​ 770 Restructuring charges ​ ​ — ​ ​ - ​ ​ 37 ​ ​ - Total stock-based compensation expense ​ $ 1,228 ​ $ 932 ​ $ 3,633 ​ $ 3,591 ​ As of September 30, 2023, the total unrecognized compensation cost was $10.5 million and is expected to be recognized as expense over approximately 1.9 years. The weighted-average assumptions used in the Black-Scholes option pricing model to determine the fair value of the stock option grants were as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended September 30, ​ ​ Nine Months Ended September 30, ​ ​ ​ 2023 ​ ​ 2022 ​ ​ 2023 ​ ​ 2022 Risk-free interest rate ​ ​ 5.1% ​ ​ 3.2% ​ ​ 1.6% - 5.1% ​ ​ 1.6% - 3.2% Expected volatility ​ ​ 118.5% ​ ​ 103.3% ​ ​ 88.1% - 118.5% ​ ​ 88.1% - 112.1% Expected term (in years) ​ ​ 5.6 ​ ​ 6.1 ​ ​ 5.3 - 6.1 ​ ​ 5.3 - 6.1 Expected dividend yield ​ ​ 0% ​ ​ 0% ​ ​ 0% ​ ​ 0% ​ The determination of the fair value of share-based payment awards utilizing the Black-Scholes option-pricing model is affected by the Company’s stock price and the following assumptions: Risk-free interest rate. Expected volatility. Expected term. Expected dividend yield. Forfeitures Common Stock Reserved for Future Issuance Common stock reserved for future issuance consist of the following: ​ ​ ​ ​ ​ ​ ​ ​ As of September 30, 2023 ​ As of December 31, 2022 Stock options ​ 3,960,030 ​ 2,593,761 Restricted stock units ​ 41,485 ​ 8,945 Reserved for future equity award grants ​ 3,107,739 ​ 3,084,732 Reserved for future ESPP issuances ​ 824,065 ​ 466,585 Common stock reserved for future issuance ​ 7,933,319 ​ 6,154,023 ​

License Agreements

License Agreements	9 Months Ended
	Sep. 30, 2023
License Agreements
License Agreements	Note 7 – License Agreements The Company has entered into license agreements, accounted for as asset acquisitions, under which the Company is required to use commercially reasonable efforts to meet certain specified development and regulatory milestones related to the licensed technologies within specified time periods. In consideration of the rights granted to the Company under the agreements, the Company is required to make cash milestone payments to the licensors upon the completion of certain development, regulatory and commercial milestones. For the arrangements that the Company accounted for as asset acquisitions, contingent consideration liabilities are recorded as an additional cost of the acquired assets when the contingency is resolved, and the consideration is paid or becomes payable. Additionally, the Company has agreed to pay royalties on net sales of products applicable to the license agreements. The Company may terminate the agreements upon written notice to the licensors. Daiichi Sankyo License Agreement On September 2, 2020, the Company licensed the rights to milademetan (DS-3032b) for all human prophylactic or therapeutic uses in all countries and territories of the world from Daiichi Sankyo Company, Limited (“Daiichi Sankyo”), a Japanese corporation (the “Daiichi Sankyo License Agreement”). Daiichi Sankyo conducted clinical studies of milademetan prior to the Company’s licensing the rights to this product. The Company refers to this product candidate as milademetan. In accordance with the terms of the Daiichi Sankyo License Agreement, the Company paid Daiichi Sankyo an initial upfront payment of $5.0 million in September 2020. Under the Daiichi Sankyo License Agreement, the Company obtained worldwide, sublicensable exclusive rights to seven families of patents with respect to milademetan (the “Licensed Compound”). The Company is solely responsible under the Daiichi Sankyo License Agreement for the research, development and registration of milademetan. Pursuant to the Daiichi Sankyo License Agreement, Daiichi Sankyo had the right to continue to conduct three clinical trials and prepare final reports with respect to these clinical trials, and such right expires upon all subjects completing the study treatment. The Company has agreed to reimburse Daiichi Sankyo certain third-party expenses incurred while conducting such trials. On March 3, 2022, the Company and Daiichi Sankyo entered into a Memorandum of Understanding, which provides that Daiichi Sankyo will terminate its U105 study, and the Company will reimburse a total of $2.0 million to Daiichi Sankyo for expenses related to such study in four installments of $0.5 million each until December 31, 2022. As of September 30, 2023, the Company paid all four installments under the Memorandum of Understanding. Under the Daiichi Sankyo License Agreement, the Company made other clinical trials payments in the aggregate of $30,000 for the three and nine months ended September 30, 2023. The Company made other clinical trials payments of $57,000 and $87,000 under the Daiichi Sankyo License Agreement for the three and nine months ended September 30, 2022, respectively. The Company is required to make aggregate future milestone payments of up to $223.5 million, contingent on the attainment of certain development, regulatory and sales milestones. The $223.5 million aggregate future milestone payments include a $2.0 million increase that was agreed upon in the Memorandum of Understanding with Daiichi Sankyo. On July 20, 2021, the Company announced that the first patient has been randomized in the multicenter, open-label, Phase 3 registrational trial (MANTRA) evaluating milademetan for the treatment of de-differentiated liposarcoma. Accordingly, pursuant to the Daiichi Sankyo License Agreement, the Company recorded $5.5 million in milestone fees as research and development expense in the consolidated statement of operations and comprehensive loss during the year ended December 31, 2021. Of the $5.5 million milestone fees, $2.5 million was paid in the third quarter of 2021 and $3.0 million was accrued as part of accrued research and development in the consolidated balance sheet as of December 31, 2021. On June 29, 2022, the Company and Daiichi Sankyo entered into an amendment to the Daiichi Sankyo License Agreement. The amendment reduced the $3.0 million milestone fee liability associated with the previously achieved milestone to $2.0 million. The amendment also extended the due date of the previously achieved milestone fee payment to June 30, 2023 and the previously achieved milestone was paid in full as of September 30, 2023. During the three and nine months ended September 30, 2023 and 2022, the Company incurred Additionally, the Company is required to pay Daiichi Sankyo a high single digit royalty based on the annual net sales of products containing milademetan as an active pharmaceutical ingredient (the “Products”), subject to reduction at an agreed rate upon expiration of the licensed patent in the particular country where the Products are sold. To date, no royalty payments have been made to Daiichi Sankyo under the Daiichi Sankyo License Agreement. The royalty obligation terminates on a country-by-country and on a product-by-product basis on the later of: (i) loss of all market exclusivity for such Product in such country, (ii) the last-to-expire patent that covers the Licensed Compound or the Product in such country and (iii) twelve years from launch of the first Product sold by the Company in such country. Unless sooner terminated or extended, the Daiichi Sankyo License Agreement will remain in full force and effect until the Company, its affiliates and its sublicensees cease all development and commercial activity related to milademetan. Either party may terminate the Daiichi Sankyo License Agreement for cause in the event of an uncured material breach (subject to a 90-day six months Drexel License Agreement and Sponsored Research Agreement In February 2023, the Company decided to discontinue further development of its preclinical program focused on targeting RAD52 in the DNA damage repair pathway, and the Company notified Drexel University (“Drexel”) of the termination of the intellectual property license agreement, dated July 30, 2020, between Drexel and the Company to focus use of the Company’s financial and personnel resources on the milademetan clinical program. Roche Clinical Supply Agreement In December 2021, the Company entered into a clinical supply agreement with Roche for the supply of the anti-Programmed Death Ligand-1 (PD-L1) monoclonal antibody, atezolizumab. Clinical trials are planned to evaluate milademetan, in combination with atezolizumab for the treatment of patients in genetically selected populations. Under this agreement, Rain is the sponsor of the anticipated clinical trials, and Roche will supply atezolizumab. The Company does not have any financial commitments to Roche under this agreement. In May 2023, the Company notified Roche of the termination of the clinical supply agreement.

Commitments and Contingencies

Commitments and Contingencies	9 Months Ended
	Sep. 30, 2023
Commitments and Contingencies.
Commitments and Contingencies	Note 8 – Commitments and Contingencies Leases In September 2018, the Company entered into a noncancelable operating lease agreement for office space for its corporate headquarters in Newark, California with an initial term of 5.25 years. The lease commenced in January 2019 and ends March 2024. Under the terms of the lease, the Company pays annual base rent, subject to an annual fixed percentage increase of 2% on March 1st of each year. The Company is obligated to pay for its share of direct expenses including operating expense and taxes, which are considered variable lease costs and are expensed as incurred. In March 2020, Governor Newsom issued State of California Executive Order No. N-33-20 instructing all individuals in California to stay at home due to the COVID-19 pandemic. In connection with such order, the Company entered into an amendment to the noncancelable operating lease agreement in June 2020. The amendment provided the Company rent relief for three months in 2020. In consideration of the rent relief, the Company agreed to adjust the base rent annual fixed percentage increase of 3% on February 1st of each year and extend the lease until September 2024. The amendment was determined to be a lease modification that qualified as a change of accounting on the existing lease and not a separate contract. Remeasurement of the right-of-use asset and operating lease liabilities at the date of modification did not result in a material increase of the right-of-use asset and operating lease liabilities. In October 2022, the Company entered into a second amendment to its corporate headquarters lease agreement to expand the leased premises by approximately 3,880 square feet. The lease commencement date for the expansion premises was in July 2023 and will expire in September 2024. In March 2023, the Company entered into a third amendment to its corporate headquarters lease agreement to expand the leased premises by approximately 5,600 square feet on a temporary basis. The lease commencement date for the expansion into the temporary space was March 2023 and will expire on the date the expanded premises under the second amendment are ready for occupancy. The expanded premises were occupied in July 2023. Pursuant to this third amendment, the Company will not pay any rent on the temporary space, but the Company will be responsible for its share of operating costs, taxes, and utilities. The future minimum lease payments required under the operating lease are summarized as follows (in thousands): ​ ​ ​ ​ ​ ​ As of September 30, 2023 2023 - remainder ​ $ 119 2024 ​ ​ 358 Total minimum lease payments ​ $ 477 Less: amount representing interest ​ ​ (21) Present value of operating lease liabilities ​ $ 456 Operating lease liabilities, current ​ ​ 456 Operating lease liabilities, non-current ​ ​ — Total operating lease liabilities ​ $ 456 ​ ​ ​ ​ Weighted-average remaining lease term (in years) ​ ​ 1.0 Weighted-average incremental borrowing rate ​ ​ 10.0% ​ ​ The table below summarizes the Company’s lease costs and cash payments in connection with operating lease obligations (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended September 30, ​ Nine Months Ended September 30, ​ ​ 2023 ​ 2022 ​ 2023 ​ 2022 Total operating lease expense ​ $ 114 ​ $ 40 ​ $ 194 ​ $ 120 Operating cash flows used for operating lease ​ $ 108 ​ $ 42 ​ $ 194 ​ $ 124 ​ Contingencies From time to time, the Company may become involved in various legal actions arising in the ordinary course of business. On July 17, 2023, a purported securities class action lawsuit was commenced in the United States District Court for the Northern District of California, naming the Company and certain of the Company’s officers as defendants (the “Shareholders Class Action Lawsuit”), captioned Thant v. Rain Oncology, et al., Case No. 5:23-cv-3518-EJD . The Shareholder Class Action Lawsuit alleges violations of Sections 10(b) and 20(a) of the Exchange Act in connection with allegedly false and misleading information about the Phase 3 MANTRA trial design quality and risks related to its clinical development strategy and regulatory approval. On September 27, 2023, a purported shareholder of the Company filed a shareholder derivative lawsuit purportedly on behalf of the Company in the United States District Court for the Northern District of California, naming the Company’s directors and certain of its officers as defendants (the “Shareholder Derivative Lawsuit”), captioned Livingston v. Vellanki, et al. The Shareholder Class Action Lawsuit, the Shareholder Derivative Lawsuit and any other related lawsuits are subject to inherent uncertainties and the actual costs to be incurred relating to the Shareholder Class Action Lawsuit and Shareholder Derivative Lawsuit will depend upon many unknown factors. The outcome of the litigation is uncertain and the Company may not prevail. The Company could be forced to expend significant resources in the defense of the Shareholder Class Action Lawsuit and Shareholder Derivative Lawsuit. The Company is not currently able to estimate the possible cost to the Company from these matters, as the Shareholder Class Action Lawsuit and Shareholder Derivative Lawsuit are currently at an early stage and the Company cannot ascertain how long they may take to resolve. The Company has not established any reserve for any potential liability relating to the Shareholder Class Action Lawsuit or Shareholder Derivative Lawsuit. The Company and its officers and directors named as defendants in these matters believes that it has meritorious defenses and intends to defend the Shareholder Class Action Lawsuit and Shareholder Derivative Lawsuit vigorously. ​ Given the uncertainty of litigation, the preliminary stages of the litigation and other matters described above, and the legal standards that must be met for, among other things, success on the merits, the Company is unable to predict the ultimate outcome of these actions, and therefore cannot estimate the reasonably possible loss or range of loss, if any, that may result from these actions. The Company would accrue a liability for such matters when it is probable that future expenditures will be made, and such expenditures can be reasonably estimated.

Employee Benefits

Employee Benefits	9 Months Ended
	Sep. 30, 2023
Employee Benefits
Employee Benefits	Note 9 – Employee Benefits The Company has a defined contribution 401(k) plan available to eligible employees. Under the terms of the plan, employees may make voluntary contributions as a percent of compensation, limited to the maximum amount allowable under federal tax regulations. The Company, at its discretion, may make certain contributions to the 401(k) plan. The Company made matching contributions of $54,000 and $164,000 for the three months ended September 30, 2023 and 2022, respectively. The Company made matching contributions of $630,000 and $320,000 for the nine months ended September 30, 2023 and 2022, respectively.

Restructuring Charges

Restructuring Charges	9 Months Ended
	Sep. 30, 2023
Restructuring Charges.
Restructuring Charges	Note 10 – Restructuring Charges In May 2023, the Company announced a reduction in its workforce in connection with the reprioritization of the Company’s clinical strategy designed to optimize Company resources. The Company recorded restructuring charges of $2.8 million in the statements of operations and comprehensive loss in the second quarter of 2023, comprised of $2.8 million cash severance, employee transition and related employee benefits and taxes of affected employees, as well as $37,000 of stock-based compensation expense related to option modifications. 1 As of September 30, 2023, the Company has paid in full the cash severance, employee transition and related employee benefits and taxes.

Net Loss Per Share

Net Loss Per Share	9 Months Ended
	Sep. 30, 2023
Net Loss Per Share
Net Loss Per Share	Note 11 – Net Loss Per Share The following table summarizes the computation of the basic and diluted net loss per share (in thousands, except share and per share data): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended September 30, ​ Nine Months Ended September 30, ​ ​ 2023 ​ 2022 ​ 2023 ​ 2022 Numerator: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Net loss ​ $ (7,034) ​ $ (18,041) ​ $ (49,582) ​ $ (53,046) Denominator: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted-average shares of common stock outstanding, basic and diluted ​ ​ 36,375,671 ​ ​ 26,564,615 ​ ​ 36,359,744 ​ ​ 26,535,474 Weighted-average shares used to compute net loss per share, basic and diluted ​ ​ 36,375,671 ​ ​ 26,564,615 ​ ​ 36,359,744 ​ ​ 26,535,474 Net loss per share, basic and diluted ​ $ (0.19) ​ $ (0.68) ​ $ (1.36) ​ $ (2.00) ​ The following table sets forth the outstanding potentially dilutive securities that have been excluded in the calculation of diluted net loss per share because their inclusion would be anti-dilutive: ​ ​ ​ ​ ​ ​ ​ ​ As of September 30, ​ ​ 2023 ​ 2022 Stock options ​ 3,960,030 ​ 2,630,258 Restricted stock units ​ 41,485 ​ 9,289 ESPP shares ​ 41,097 ​ 27,379 Total ​ 4,042,612 ​ 2,666,926 ​

Subsequent Event

Subsequent Event	9 Months Ended
	Sep. 30, 2023
Subsequent Event
Subsequent Event	Note 12 – Subsequent Event In October 2023, the Company received an unsolicited proposal from Tang Capital, LP on behalf of Concentra Biosciences LLC (“Concentra Biosciences”) to acquire all outstanding shares of common stock of the Company for $1.25 per share in cash, plus a contingent value right representing the right to receive 80% of the net proceeds payable from any license or disposition of the Company’s programs. The Board of Directors and the Company’s management team regularly review opportunities to generate stockholder value and are committed to acting in the best interests of all stockholders. Consistent with its fiduciary duties, the Board of Directors, in consultation with the Company’s independent financial and legal advisors, is currently reviewing and evaluating the proposal from Concentra Biosciences.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	9 Months Ended
	Sep. 30, 2023
Summary of Significant Accounting Policies
Use of Estimates	Use of Estimates The preparation of the Company’s condensed consolidated financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that impact the reported amounts of assets, liabilities and expenses and the disclosure of contingent liabilities in the Company’s condensed consolidated financial statements and accompanying notes. The most significant estimate in the Company’s condensed consolidated financial statements relates to the clinical trial expense accruals. Management evaluates its estimates on an ongoing basis. Although these estimates are based on the Company’s historical experience, knowledge of current events and actions it may undertake in the future, actual results may ultimately materially differ from these estimates and assumptions.
Cash and Cash Equivalents	Cash and Cash Equivalents The Company considers all highly liquid investments with an original maturity of three months or less at the date of purchase to be cash equivalents. Cash equivalents include money market funds, commercial paper, U.S. government securities and U.S. agency bonds.
Available-for-Sale Investments	Available-for-Sale Investments The Company holds investment grade securities consisting of commercial paper, corporate debt securities, U.S. government securities and U.S. agency bonds, classified as available-for-sale (AFS) securities at the time of purchase, since it is the Company’s intent that these investments be available for current operations. The Company has classified all of its AFS securities as current assets in the condensed consolidated balance sheets even though the stated maturity date may be one year or more beyond the current condensed consolidated balance sheet date, which reflects management’s intention to use the proceeds from sales of these securities to fund its operations, as necessary. The Company carries these securities at fair value and reports unrealized gains and losses, if any, as a separate component of accumulated other comprehensive loss. The cost of debt securities is adjusted for amortization of purchase premiums and accretion of discounts to maturity. Such amortization and accretion are included in interest income in the condensed consolidated statements of operations and comprehensive loss. Realized gains and losses on sales of securities are determined using the specific identification method and recorded in interest income in the condensed consolidated statement of operations and comprehensive loss.
Allowance for Credit Losses	Allowance for Credit Losses For AFS securities in an unrealized loss position, the Company first assesses whether it intends to sell, or if it is more likely than not that the Company will be required to sell, the security before recovery of its amortized cost basis. If either of the criteria regarding intent or requirement to sell is met, the security’s amortized cost basis is written down to fair value through earnings. For AFS securities that do not meet the aforementioned criteria, the Company evaluates whether the decline in fair value has resulted from credit losses or other factors. In making this assessment, the Company considers the severity of the impairment, any changes in interest rates, market conditions, changes to the underlying credit ratings and forecasted recovery, among other factors. The credit-related portion of unrealized losses, and any subsequent improvements, are recorded in interest income through an allowance account. Any impairment that has not been recorded through an allowance for credit losses is included in other comprehensive loss in the condensed consolidated statement of operations and comprehensive loss. The Company elected the practical expedient to exclude the applicable accrued interest from both the fair value and amortized costs basis of its AFS securities for purposes of identifying and measuring an impairment. Accrued interest receivable on AFS securities is recorded in prepaid and other current assets in the condensed consolidated balance sheets. The Company’s accounting policy is to not measure an allowance for credit loss for accrued interest receivable and to write-off any uncollectible accrued interest receivable as a reversal of interest income in a timely manner, which the Company considers to be in the period in which it determines the accrued interest will not be collected by the Company.
Research and Development Costs	Research and Development Costs Research and development costs primarily consist of costs associated with the Company’s research and development activities, including its drug discovery efforts, and the preclinical and clinical development of its product candidates. Research and development costs are expensed as incurred.
Preclinical Studies and Clinical Trial Accruals	Preclinical Studies and Clinical Trial Accruals The Company is required to estimate its expenses resulting from its obligations under contracts with vendors, consultants, clinical research organizations and clinical site agreements in connection with conducting preclinical activities and clinical trials. The financial terms of these contracts are subject to negotiations which vary from contract to contract and may result in payment flows that do not match the periods over which materials or services are provided under such contracts. The Company reflects preclinical study and clinical trial expenses in its condensed consolidated financial statements by matching those expenses with the period in which services and efforts are expended. The Company accounts for these expenses according to the progress of the preclinical study or clinical trial as measured by the timing of various aspects of the preclinical study, clinical trial or related activities. The Company determines accrual and prepaid estimates through review of the underlying contracts along with preparation of financial models taking into account correspondence with clinical and other key personnel and third-party service providers as to the progress of preclinical studies, clinical trials or other services being conducted. During the course of a preclinical study or clinical trial, the Company adjusts its expense recognition if actual results differ from its estimates. To date, the Company has not experienced any material differences between accrued costs and actual costs incurred.
Stock-Based Compensation	Stock-Based Compensation Stock-based compensation expense represents the grant date fair value of equity awards recognized over the requisite service period of the awards (generally the vesting period) on a straight-line basis. The Company recognizes forfeitures as they occur. The Company estimates the fair value of stock option grants using the Black-Scholes option pricing model. The fair value of restricted stock units (“RSUs”) granted is based on the Company’s closing stock price on the date of grant.
Income Taxes	Income Taxes The Company accounts for income taxes under the asset and liability method, which requires the recognition of deferred tax assets and liabilities for the expected future tax consequences of events that have been included in the condensed consolidated financial statements. Under this method, deferred tax assets and liabilities are determined on the basis of the differences between the financial statements and tax basis of assets and liabilities using enacted tax rates in effect for the year in which the differences are expected to reverse. The effect of a change in tax rates on deferred tax assets and liabilities is recognized in income in the period that includes the enactment date. The Company recognizes deferred tax assets to the extent that the Company believes these assets are more likely than not to be realized. In making such a determination, management considers all available positive and negative evidence, including future reversals of existing taxable temporary differences, projected future taxable income, tax-planning strategies and results of recent operations. If management determines that the Company would be able to realize its deferred tax assets in the future in excess of their recorded amount, management would make an adjustment to the deferred tax asset valuation allowance, which would reduce the provision for income taxes. The Company records uncertain tax positions on the basis of a two-step process whereby (1) management determines whether it is more likely than not that the tax positions will be sustained on the basis of the technical merits of the position and (2) for those tax positions that meet the more likely than not recognition threshold, management recognizes the largest amount of tax benefit that is more than 50 percent likely to be realized upon ultimate settlement with the related tax authority. The Company recognizes interest and penalties related to unrecognized tax benefits within income tax expense. Any accrued interest and penalties are included within the related tax liability.
Restructuring	Restructuring Restructuring costs comprised of severance, other termination benefit costs and stock-based compensation expense for stock option modifications related to workforce reductions. The Company recognizes restructuring charges when the liability is probable, and the amount is estimable. Employee termination benefits are accrued at the date management has committed to a plan of termination and affected employees have been notified of their termination date and expected severance benefits.
Comprehensive Loss	Comprehensive Loss Comprehensive loss is defined as a change in equity during a period from transactions and other events and circumstances from non-owner sources. The Company’s comprehensive loss includes unrealized gains and losses from short-term investments.
Net Loss Per Share	Net Loss Per Share Basic net loss per share is calculated by dividing the net loss attributable to common stockholders by the weighted-average number of shares of common stock outstanding for the period, without consideration of potential dilutive securities. Diluted net loss per share is computed by dividing the net loss attributable to common stockholders by the sum of the weighted-average number of shares of common stock plus the potential dilutive effects of potential dilutive securities outstanding during the period. Potential dilutive securities are excluded from diluted earnings or loss per share if the effect of such inclusion is antidilutive. The Company’s potentially dilutive securities, which include shares from the 2021 Employee Stock Purchase Plan (the “ESPP”) and outstanding stock options and RSUs under the Company’s equity incentive plan, have been excluded from the computation of diluted net loss per share as they would be anti-dilutive to the net loss per share. For the periods presented, there is no difference in the number of shares used to calculate basic and diluted shares outstanding due to the Company’s net loss position.
Recent Accounting Pronouncements	Recent Accounting Pronouncements Financial Instruments . In June 2016, the FASB issued ASU 2016-13, Financial Instruments—Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments. The objective of the standard is to improve financial reporting of expected credit losses on financial instruments and other commitments to extend credit. ASU 2016-13 requires that an entity measure and recognize expected credit losses for financial assets held at amortized cost and replaces the incurred loss impairment methodology in prior U.S. GAAP with a methodology that requires consideration of a broader range of information to estimate credit losses, and establishes additional disclosures related to credit risks. The Company adopted Topic 326 on January 1, 2023. The adoption did not have a significant impact on the Company’s condensed consolidated financial statements or the related disclosures. There were no other significant updates to the recently issued accounting standards other than as disclosed herein for the three and nine months ended September 30, 2023. Although there are several other new accounting pronouncements issued or proposed by the FASB, based on the Company’s preliminary assessment, the Company does not believe any of those accounting pronouncements have had or will have a material impact on its financial position or operating results .

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	9 Months Ended
	Sep. 30, 2023
Fair Value Measurements
Summary of Financial Assets Measured at Fair Value on Recurring Basis	The following tables summarize financial assets that the Company measured at fair value on a recurring basis, classified in accordance with the fair value hierarchy (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Fair Value Measurements at Reporting Date Using: ​ ​ Level 1 ​ Level 2 ​ Level 3 ​ Total As of September 30, 2023: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Money market funds ​ $ 8,669 ​ $ — ​ $ — ​ $ 8,669 Commercial paper ​ ​ — ​ ​ 22,968 ​ ​ — ​ ​ 22,968 U.S. government securities ​ ​ 18,578 ​ ​ — ​ ​ — ​ ​ 18,578 U.S. agency bonds ​ ​ — ​ ​ 26,568 ​ ​ — ​ ​ 26,568 Total cash equivalents and short-term investments ​ $ 27,247 ​ $ 49,536 ​ $ — ​ $ 76,783 Reported as: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Cash and cash equivalents (includes cash of $537) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ $ 37,312 Short-term investments ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 40,008 Total cash, cash equivalents and short-term investments ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ $ 77,320 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Fair Value Measurements at Reporting Date Using: ​ ​ Level 1 ​ Level 2 ​ Level 3 ​ Total As of December 31, 2022: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Money market funds ​ $ 8,528 ​ $ — ​ $ — ​ $ 8,528 Commercial paper ​ ​ — ​ ​ 83,423 ​ ​ — ​ ​ 83,423 U.S. government securities ​ ​ 10,837 ​ ​ — ​ ​ — ​ ​ 10,837 U.S. agency bonds ​ ​ — ​ ​ 22,143 ​ ​ — ​ ​ 22,143 Corporate debt securities ​ ​ — ​ ​ 997 ​ ​ — ​ ​ 997 Total cash equivalents and short-term investments ​ $ 19,365 ​ $ 106,563 ​ $ — ​ $ 125,928 Reported as: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Cash and cash equivalents (includes cash of $4,526) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ $ 61,955 Short-term investments ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 68,499 Total cash, cash equivalents and short-term investments ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ $ 130,454

Investments (Tables)

Investments (Tables)	9 Months Ended
	Sep. 30, 2023
Investments
Summary of Cash Equivalents and Investments Measured at Fair Value on Recurring Basis	The following tables summarize, by major types of cash equivalents, and investments that are measured at fair value on a recurring basis (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ As of September 30, 2023 ​ ​ Amortized ​ Unrealized ​ Unrealized ​ Estimated ​ ​ Cost ​ Gains ​ Losses ​ Fair Value Money market funds ​ $ 8,669 ​ $ — ​ $ — ​ $ 8,669 Commercial paper ​ ​ 22,979 ​ ​ — ​ ​ (11) ​ ​ 22,968 U.S. government securities ​ ​ 18,588 ​ ​ 1 ​ ​ (11) ​ ​ 18,578 U.S. agency bonds ​ ​ 26,611 ​ ​ 1 ​ ​ (44) ​ ​ 26,568 Cash equivalents and short-term investments ​ $ 76,847 ​ $ 2 ​ $ (66) ​ $ 76,783 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ As of December 31, 2022 ​ ​ Amortized ​ Unrealized ​ Unrealized ​ Estimated ​ ​ Cost ​ Gains ​ Losses ​ Fair Value Money market funds ​ $ 8,528 ​ $ — ​ $ — ​ $ 8,528 Commercial paper ​ ​ 83,479 ​ ​ 11 ​ ​ (67) ​ ​ 83,423 U.S. government securities ​ ​ 10,910 ​ ​ — ​ ​ (73) ​ ​ 10,837 U.S. agency bonds ​ ​ 22,175 ​ ​ 4 ​ ​ (36) ​ ​ 22,143 Corporate debt securities ​ ​ 1,002 ​ ​ — ​ ​ (5) ​ ​ 997 Cash equivalents and short-term investments ​ $ 126,094 ​ $ 15 ​ $ (181) ​ $ 125,928
Schedule of Contractual Maturities of AFS Securities	The contractual maturities of the Company’s AFS securities were as follows (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ As of September 30, 2023 ​ As of December 31, 2022 Due within one year ​ $ 37,354 ​ $ 63,595 Due within one to two years ​ ​ 2,654 ​ ​ 4,904 Total ​ $ 40,008 ​ $ 68,499

Condensed Consolidated Balanc_4

Condensed Consolidated Balance Sheet Details (Tables)	9 Months Ended
	Sep. 30, 2023
Condensed Consolidated Balance Sheet Details
Schedule of Prepaid and Other Current Assets	Prepaid and other current assets consist of the following (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ As of September 30, 2023 ​ As of December 31, 2022 Prepaid insurance ​ $ 1,226 ​ $ 913 Prepaid research and development ​ ​ 991 ​ ​ 1,103 FICA tax credit receivable ​ ​ 531 ​ ​ 571 Prepaid other ​ ​ 448 ​ ​ 416 Other current assets ​ ​ 281 ​ ​ 152 Deposits ​ ​ 19 ​ ​ 19 Prepaid and other current assets ​ $ 3,496 ​ $ 3,174
Schedule of Property and Equipment, Net	Property and equipment, net, consist of the following (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ As of September 30, 2023 ​ As of December 31, 2022 Leasehold improvements ​ $ 794 ​ $ 67 Furniture and equipment ​ ​ 209 ​ ​ 204 Computer equipment ​ ​ 50 ​ ​ 50 Construction in progress ​ ​ — ​ ​ 8 ​ ​ ​ 1,053 ​ ​ 329 Less: accumulated depreciation and amortization expense ​ ​ (425) ​ ​ (236) Property and equipment, net ​ $ 628 ​ $ 93
Schedule of Other Non-Current Assets	Other non-current assets consist of the following (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ As of September 30, 2023 ​ As of December 31, 2022 Deposits ​ $ 110 ​ $ 781 FICA tax credit receivable ​ ​ — ​ ​ 52 Other ​ ​ 70 ​ ​ 368 Other non-current assets ​ $ 180 ​ $ 1,201
Schedule of Other Accrued Liabilities	Other accrued liabilities consist of the following (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ As of September 30, 2023 ​ As of December 31, 2022 Accrued bonus ​ $ 1,481 ​ $ 3,379 Accrued payroll and related ​ ​ 36 ​ ​ 229 ESPP liability ​ ​ 35 ​ ​ 155 Other ​ ​ 638 ​ ​ 2,661 Other accrued liabilities ​ $ 2,190 ​ $ 6,424 ​

Stockholders' Equity (Tables)

Stockholders' Equity (Tables)	9 Months Ended
	Sep. 30, 2023
Summary of Stock Option Activities	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted- ​ Weighted- ​ ​ ​ ​ ​ ​ Average ​ Average ​ Aggregate ​ ​ ​ ​ Exercise ​ Remaining ​ Intrinsic ​ ​ ​ ​ Price Per ​ Contract Term ​ Value ​ ​ Total Options ​ Share ​ (in years) ​ (in millions) Outstanding as of December 31, 2022 ​ 2,593,761 ​ $ 8.08 ​ 8.2 ​ $ — Granted ​ 2,517,700 ​ $ 5.49 ​ ​ ​ ​ ​ Exercised ​ (20,757) ​ $ 3.59 ​ ​ ​ ​ ​ Forfeited or cancelled ​ (1,130,674) ​ $ (9.25) ​ ​ ​ ​ ​ Outstanding as of September 30, 2023 ​ 3,960,030 ​ $ 6.12 ​ 7.8 ​ $ — Vested and expected to vest as of September 30, 2023 ​ 3,960,030 ​ $ 6.12 ​ 7.8 ​ $ — Vested and exercisable as of September 30, 2023 ​ 1,514,801 ​ $ 7.20 ​ 5.4 ​ $ —
Summary of Stock-Based Compensation Expense Recognized	The Company recognized stock-based compensation expense as follows (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended September 30, ​ Nine Months Ended September 30, ​ ​ 2023 ​ 2022 ​ 2023 ​ 2022 Research and development ​ $ 656 ​ $ 728 ​ $ 2,316 ​ $ 2,821 General and administrative ​ ​ 572 ​ ​ 204 ​ ​ 1,280 ​ ​ 770 Restructuring charges ​ ​ — ​ ​ - ​ ​ 37 ​ ​ - Total stock-based compensation expense ​ $ 1,228 ​ $ 932 ​ $ 3,633 ​ $ 3,591
Weighted-Average Assumptions Used in Black-Scholes Option Pricing Model to Determine Fair Value of Stock Option Grants	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended September 30, ​ ​ Nine Months Ended September 30, ​ ​ ​ 2023 ​ ​ 2022 ​ ​ 2023 ​ ​ 2022 Risk-free interest rate ​ ​ 5.1% ​ ​ 3.2% ​ ​ 1.6% - 5.1% ​ ​ 1.6% - 3.2% Expected volatility ​ ​ 118.5% ​ ​ 103.3% ​ ​ 88.1% - 118.5% ​ ​ 88.1% - 112.1% Expected term (in years) ​ ​ 5.6 ​ ​ 6.1 ​ ​ 5.3 - 6.1 ​ ​ 5.3 - 6.1 Expected dividend yield ​ ​ 0% ​ ​ 0% ​ ​ 0% ​ ​ 0%
Schedule of Common Stock Reserved for Future Issuance	​ ​ ​ ​ ​ ​ ​ ​ As of September 30, 2023 ​ As of December 31, 2022 Stock options ​ 3,960,030 ​ 2,593,761 Restricted stock units ​ 41,485 ​ 8,945 Reserved for future equity award grants ​ 3,107,739 ​ 3,084,732 Reserved for future ESPP issuances ​ 824,065 ​ 466,585 Common stock reserved for future issuance ​ 7,933,319 ​ 6,154,023 ​
RSU
Summary of Restricted Stock Units Activities	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted- ​ Aggregate ​ ​ Total ​ Average ​ Intrinsic ​ ​ Restricted ​ Grant Date ​ Value ​ ​ Stock Units ​ Fair Values ​ (in millions) Outstanding as of December 31, 2022 ​ 8,945 ​ $ 6.25 ​ $ — Granted ​ 95,333 ​ $ 9.59 ​ ​ ​ Vested ​ (9,038) ​ $ 8.71 ​ ​ ​ Forfeited or cancelled ​ (53,755) ​ $ 9.31 ​ ​ ​ Outstanding as of September 30, 2023 ​ 41,485 ​ $ 9.42 ​ $ —

Commitments and Contingencies (

Commitments and Contingencies (Tables)	9 Months Ended
	Sep. 30, 2023
Commitments and Contingencies.
Schedule of Future Minimum Lease Payments Required under Operating Lease	The future minimum lease payments required under the operating lease are summarized as follows (in thousands): ​ ​ ​ ​ ​ ​ As of September 30, 2023 2023 - remainder ​ $ 119 2024 ​ ​ 358 Total minimum lease payments ​ $ 477 Less: amount representing interest ​ ​ (21) Present value of operating lease liabilities ​ $ 456 Operating lease liabilities, current ​ ​ 456 Operating lease liabilities, non-current ​ ​ — Total operating lease liabilities ​ $ 456 ​ ​ ​ ​ Weighted-average remaining lease term (in years) ​ ​ 1.0 Weighted-average incremental borrowing rate ​ ​ 10.0%
Summary of Lease Costs and Cash Payments	The table below summarizes the Company’s lease costs and cash payments in connection with operating lease obligations (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended September 30, ​ Nine Months Ended September 30, ​ ​ 2023 ​ 2022 ​ 2023 ​ 2022 Total operating lease expense ​ $ 114 ​ $ 40 ​ $ 194 ​ $ 120 Operating cash flows used for operating lease ​ $ 108 ​ $ 42 ​ $ 194 ​ $ 124 ​

Net Loss Per Share (Tables)

Net Loss Per Share (Tables)	9 Months Ended
	Sep. 30, 2023
Net Loss Per Share
Schedule of Computation of Basic and Diluted Net Loss per Share	The following table summarizes the computation of the basic and diluted net loss per share (in thousands, except share and per share data): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended September 30, ​ Nine Months Ended September 30, ​ ​ 2023 ​ 2022 ​ 2023 ​ 2022 Numerator: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Net loss ​ $ (7,034) ​ $ (18,041) ​ $ (49,582) ​ $ (53,046) Denominator: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted-average shares of common stock outstanding, basic and diluted ​ ​ 36,375,671 ​ ​ 26,564,615 ​ ​ 36,359,744 ​ ​ 26,535,474 Weighted-average shares used to compute net loss per share, basic and diluted ​ ​ 36,375,671 ​ ​ 26,564,615 ​ ​ 36,359,744 ​ ​ 26,535,474 Net loss per share, basic and diluted ​ $ (0.19) ​ $ (0.68) ​ $ (1.36) ​ $ (2.00)
Schedule of Potentially Dilutive Securities Excluded from Calculation of Diluted Net Loss per Share	​ ​ ​ ​ ​ ​ ​ ​ As of September 30, ​ ​ 2023 ​ 2022 Stock options ​ 3,960,030 ​ 2,630,258 Restricted stock units ​ 41,485 ​ 9,289 ESPP shares ​ 41,097 ​ 27,379 Total ​ 4,042,612 ​ 2,666,926 ​

Organization and Nature of Op_2

Organization and Nature of Operations (Details)	9 Months Ended
	Sep. 30, 2023 segment
Organization and Nature of Operations
Number of operating segments	1

Fair Value Measurements (Detail

Fair Value Measurements (Details) - USD ($)	3 Months Ended	9 Months Ended
	Sep. 30, 2023	Sep. 30, 2023	Dec. 31, 2022
Fair Value Measurements
Assets transfer, Level 1 to 2	$ 0	$ 0
Assets transfer, Level 2 to 1	0	0
Assets transfer, out of Level 3	0	0
Assets transfer, into Level 3	0	0
Liabilities transfer, Level 1 to 2	0	0
Liabilities transfer, Level 2 to 1	0	0
Liabilities transfer, into of Level 3	0	0
Liabilities transfer, out of Level 3		0
Financial liabilities	$ 0	$ 0	$ 0

Fair Value Measurements - Summa

Fair Value Measurements - Summary of Financial Assets Measured at Fair Value on Recurring Basis (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments	$ 40,008	$ 68,499
Fair Value on Recurring Basis
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total cash equivalents and short-term investments	76,783	125,928
Cash and cash equivalents (includes cash)	37,312	61,955
Short-term investments	40,008	68,499
Total cash, cash equivalents and short-term investments	77,320	130,454
Fair Value on Recurring Basis | Money Market Funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total cash equivalents and short-term investments	8,669	8,528
Fair Value on Recurring Basis | Commercial Paper
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total cash equivalents and short-term investments	22,968	83,423
Fair Value on Recurring Basis | U.S. Government Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total cash equivalents and short-term investments	18,578	10,837
Fair Value on Recurring Basis | U.S. Agency Bonds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total cash equivalents and short-term investments	26,568	22,143
Fair Value on Recurring Basis | Corporate Debt Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total cash equivalents and short-term investments		997
Fair Value on Recurring Basis | Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total cash equivalents and short-term investments	27,247	19,365
Fair Value on Recurring Basis | Level 1 | Money Market Funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total cash equivalents and short-term investments	8,669	8,528
Fair Value on Recurring Basis | Level 1 | U.S. Government Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total cash equivalents and short-term investments	18,578	10,837
Fair Value on Recurring Basis | Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total cash equivalents and short-term investments	49,536	106,563
Fair Value on Recurring Basis | Level 2 | Commercial Paper
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total cash equivalents and short-term investments	22,968	83,423
Fair Value on Recurring Basis | Level 2 | U.S. Agency Bonds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total cash equivalents and short-term investments	$ 26,568	22,143
Fair Value on Recurring Basis | Level 2 | Corporate Debt Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total cash equivalents and short-term investments		$ 997

Fair Value Measurements - Sum_2

Fair Value Measurements - Summary of Financial Assets Measured at Fair Value on Recurring Basis - Additional Information (Details) - Fair Value on Recurring Basis - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash and cash equivalents (includes cash)	$ 37,312	$ 61,955
Cash
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash and cash equivalents (includes cash)	$ 537	$ 4,526

Investments - Summary of Cash E

Investments - Summary of Cash Equivalents and Investments Measured at Fair Value on Recurring Basis (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Cash Cash Equivalents And Investments [Line Items]
Investments, estimated fair value	$ 40,008	$ 68,499
Fair Value on Recurring Basis
Cash Cash Equivalents And Investments [Line Items]
Cash equivalents and short-term investments, amortized cost	76,847	126,094
Cash equivalents and short-term investments, unrealized gains	2	15
Cash equivalents and short-term investments, unrealized losses	(66)	(181)
Cash equivalents and short-term investments, estimated fair value	76,783	125,928
Fair Value on Recurring Basis | Money Market Funds [Member]
Cash Cash Equivalents And Investments [Line Items]
Cash equivalents, amortized cost	8,669	8,528
Cash equivalents, estimated fair value	8,669	8,528
Commercial Paper [Member] | Fair Value on Recurring Basis
Cash Cash Equivalents And Investments [Line Items]
Investments, amortized cost	22,979	83,479
Investments, unrealized gains		11
Investments, unrealized losses	(11)	(67)
Investments, estimated fair value	22,968	83,423
U.S. Government Securities | Fair Value on Recurring Basis
Cash Cash Equivalents And Investments [Line Items]
Investments, amortized cost	18,588	10,910
Investments, unrealized gains	1
Investments, unrealized losses	(11)	(73)
Investments, estimated fair value	18,578	10,837
U.S. Agency Bonds | Fair Value on Recurring Basis
Cash Cash Equivalents And Investments [Line Items]
Investments, amortized cost	26,611	22,175
Investments, unrealized gains	1	4
Investments, unrealized losses	(44)	(36)
Investments, estimated fair value	$ 26,568	22,143
Corporate Debt Securities | Fair Value on Recurring Basis
Cash Cash Equivalents And Investments [Line Items]
Investments, amortized cost		1,002
Investments, unrealized losses		(5)
Investments, estimated fair value		$ 997

Investments - Schedule of Contr

Investments - Schedule of Contractual Maturities of AFS Securities (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Investments
Due within one year	$ 37,354	$ 63,595
Due within one to two years	2,654	4,904
Total	$ 40,008	$ 68,499

Investments - Narrative (Detail

Investments - Narrative (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022
Investments
Investments, realized gains or losses	$ 0	$ 0	$ 0	$ 0
Marketable securities, gross unrealized loss position	44,900,000		44,900,000
Marketable securities, continuous unrealized loss position, greater than 12 months	0		0
Marketable securities, continuous unrealized loss position, less than 12 months	22,500,000		22,500,000
Allowance for credit losses	0		0		$ 0
Accrued interest receivable on AFS securities	200,000		200,000		$ 100,000
Accrued interest receivable written off	$ 0	$ 0	$ 0	$ 0

Condensed Consolidated Balanc_5

Condensed Consolidated Balance Sheet Details - Schedule of Prepaid and Other Current Assets (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Condensed Consolidated Balance Sheet Details
Prepaid insurance	$ 1,226	$ 913
Prepaid research and development	991	1,103
FICA tax credit receivable	531	571
Prepaid other	448	416
Other current assets	281	152
Deposits	19	19
Prepaid and other current assets	$ 3,496	$ 3,174

Condensed Consolidated Balanc_6

Condensed Consolidated Balance Sheet Details - Schedule of Property and Equipment, Net (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 1,053	$ 329
Less: accumulated depreciation and amortization expense	(425)	(236)
Property and equipment, net	628	93
Leasehold Improvements
Property Plant And Equipment [Line Items]
Property and equipment, gross	794	67
Furniture and Equipment
Property Plant And Equipment [Line Items]
Property and equipment, gross	209	204
Computer Equipment
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 50	50
Construction in Progress
Property Plant And Equipment [Line Items]
Property and equipment, gross		$ 8

Condensed Consolidated Balanc_7

Condensed Consolidated Balance Sheet Details - Narrative (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Condensed Consolidated Balance Sheet Details
Depreciation and amortization expense	$ 154,000	$ 18,000	$ 189,000	$ 62,000

Condensed Consolidated Balanc_8

Condensed Consolidated Balance Sheet Details - Schedule of Other Non-Current Assets (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Condensed Consolidated Balance Sheet Details
Deposits	$ 110	$ 781
FICA tax credit receivable		52
Other	70	368
Other non-current assets	$ 180	$ 1,201

Condensed Consolidated Balanc_9

Condensed Consolidated Balance Sheet Details - Schedule of Other Accrued Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Condensed Consolidated Balance Sheet Details
Accrued bonus	$ 1,481	$ 3,379
Accrued payroll and related	36	229
ESPP liability	35	155
Other	638	2,661
Other accrued liabilities	$ 2,190	$ 6,424

Stockholders' Equity - Narrativ

Stockholders' Equity - Narrative (Details) - USD ($) $ / shares in Units, $ in Thousands		9 Months Ended
	Apr. 15, 2021	Sep. 30, 2023	Sep. 30, 2022	Jan. 01, 2023	Dec. 31, 2022	Apr. 16, 2021
Class Of Stock [Line Items]
Common stock, shares authorized		250,000,000			250,000,000	250,000,000
Preferred Stock, shares authorized		10,000,000			10,000,000
Common stock, Par value		$ 0.001			$ 0.001	$ 0.001
Preferred stock, par value		$ 0.001			$ 0.001
Common stock, reserved for future issuance		7,933,319			6,154,023
Weighted-average grant date fair values of option grants		$ 4.54	$ 7.33
Weighted-average grant date fair values of options forfeited		$ 9.31	$ 12.05
Aggregate cash proceeds from issued shares of common stock		$ 343
Common Stock Options
Class Of Stock [Line Items]
Common stock, reserved for future issuance		3,960,030			2,593,761
Stock options and restricted stock units
Class Of Stock [Line Items]
Unrecognized compensation cost related to outstanding options		$ 10,500
Cost not yet recognized, period for Recognition		1 year 10 months 24 days
2018 Stock Issuance Plan
Class Of Stock [Line Items]
Stock options granted	0
2018 Stock Issuance Plan | Common Stock Options
Class Of Stock [Line Items]
Stock options, grant equity-based awards issued		1,722
2021 Equity Incentive Plan
Class Of Stock [Line Items]
Stock options granted		2,517,700
Percentage of outstanding number of shares of common stock	4%
2021 Equity Incentive Plan | Common Stock Options
Class Of Stock [Line Items]
Common stock, reserved for future issuance				1,451,611
Employee Stock Purchase Plan
Class Of Stock [Line Items]
Common stock, reserved for future issuance				362,902
Percentage of outstanding number of shares of common stock	1%
Maximum contribution made by employees compensation	15%
Purchase of common stock at discount from market price, offering date	85%
Stock plan offering period	24 months
Shares issued in period		32,622
Aggregate cash proceeds from issued shares of common stock		$ 100
Maximum | 2021 Equity Incentive Plan | Common Stock Options
Class Of Stock [Line Items]
Common stock, reserved for future issuance	3,246,120
Maximum | Employee Stock Purchase Plan
Class Of Stock [Line Items]
Shares authorized for issuance	259,689
IPO
Class Of Stock [Line Items]
Common stock, shares authorized						260,000,000
Undesignated Preferred Stock
Class Of Stock [Line Items]
Preferred Stock, shares authorized						10,000,000
Preferred stock, par value						$ 0.001
Common Stock
Class Of Stock [Line Items]
Common stock, shares authorized						200,000,000
Non-voting Common Stock
Class Of Stock [Line Items]
Common stock, shares authorized						50,000,000

Stockholders' Equity - Summary

Stockholders' Equity - Summary of Stock Option Activities (Details) - 2021 Equity Incentive Plan - $ / shares	9 Months Ended	12 Months Ended
	Sep. 30, 2023	Dec. 31, 2022
Total Options
Total Options Outstanding, Beginning balance	2,593,761
Total Options, Granted	2,517,700
Total Options, Exercised	(20,757)
Total Options Forfeited or cancelled	(1,130,674)
Total Options Outstanding, Ending balance	3,960,030	2,593,761
Vested and expected to vest as of September 30, 2023	3,960,030
Vested and exercisable as of September 30, 2023	1,514,801
Weighted-Average Exercise Price Per Share
Weighted-Average Exercise Price Per Share	$ 8.08
Weighted-Average Exercise Price Per Share, Granted	5.49
Weighted-Average Exercise Price Per Share, Exercised	3.59
Weighted-Average Exercise Price Per Share, Forfeited or cancelled	(9.25)
Weighted-Average Exercise Price Per Share	6.12	$ 8.08
Weighted-Average Exercise Price Per Share, Vested and expected to vest	6.12
Weighted-Average Exercise Price Per Share, Vested and exercisable	$ 7.20
Weighted-Average Remaining Contract Term
Weighted-Average Remaining Contract Term	7 years 9 months 18 days	8 years 2 months 12 days
Weighted-Average Remaining Contract Term, Vested and expected to vest	7 years 9 months 18 days
Weighted-Average Remaining Contract Term, Vested and exercisable	5 years 4 months 24 days

Stockholders' Equity - RSU Acti

Stockholders' Equity - RSU Activities (Details) - RSU	9 Months Ended
	Sep. 30, 2023 $ / shares shares
Total Restricted Stock Units
Total Restricted Stock Units Outstanding, Beginning balance | shares	8,945
Total Restricted Stock Units, Granted | shares	95,333
Total Restricted Stock Units, Vested | shares	(9,038)
Total Restricted Stock Units, Forfeited or cancelled | shares	(53,755)
Total Restricted Stock Units Outstanding, Ending balance | shares	41,485
Weighted-Average Grant Date Fair Values
Weighted-Average Grant Date Fair Values Outstanding, Beginning balance | $ / shares	$ 6.25
Weighted-Average Grant Date Fair Values, Granted | $ / shares	9.59
Weighted-Average Grant Date Fair Values, Vested | $ / shares	8.71
Weighted-Average Grant Date Fair Values, Forfeited or cancelled | $ / shares	9.31
Weighted-Average Grant Date Fair Values Outstanding, Ending balance | $ / shares	$ 9.42

Stockholders' Equity - Summar_2

Stockholders' Equity - Summary of Stock-Based Compensation Expense Recognized (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	$ 1,228	$ 932	$ 3,633	$ 3,591
Research and Development
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	656	728	2,316	2,821
General and Administrative
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	$ 572	$ 204	1,280	$ 770
Restructuring charges
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense			$ 37

Stockholders' Equity - Weighted

Stockholders' Equity - Weighted-Average Assumptions Used in Black-Scholes Option Pricing Model to Determine Fair Value of Stock Option Grants (Details)	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Risk-free interest rate	5.10%	3.20%
Risk-free interest rate, minimum			1.60%	1.60%
Risk-free interest rate, maximum			5.10%	3.20%
Expected volatility	118.50%	103.30%
Expected volatility, minimum			88.10%	88.10%
Expected volatility, maximum			118.50%	112.10%
Expected term (in years)	5 years 7 months 6 days	6 years 1 month 6 days	5 years 7 months 6 days
Expected dividend yield	0%	0%	0%	0%
Minimum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (in years)			5 years 3 months 18 days	5 years 3 months 18 days
Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (in years)			6 years 1 month 6 days	6 years 1 month 6 days

Stockholders' Equity - Schedule

Stockholders' Equity - Schedule of Common Stock Reserved for Future Issuance (Details) - shares	Sep. 30, 2023	Dec. 31, 2022
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock reserved for future issuance	7,933,319	6,154,023
Stock options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock reserved for future issuance	3,960,030	2,593,761
RSU
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock reserved for future issuance	41,485	8,945
Reserved for future equity award grants
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock reserved for future issuance	3,107,739	3,084,732
Reserved for future ESPP issuances
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock reserved for future issuance	824,065	466,585

License Agreements (Details)

License Agreements (Details)		1 Months Ended	3 Months Ended		9 Months Ended
	Mar. 03, 2022 USD ($) installment	Sep. 30, 2020 USD ($)	Sep. 30, 2023 USD ($)	Sep. 30, 2022 USD ($)	Sep. 30, 2023 USD ($) item	Sep. 30, 2022 USD ($)	Jun. 29, 2022 USD ($)	Jun. 28, 2022 USD ($)	Dec. 31, 2021 USD ($)	Sep. 30, 2021 USD ($)
License Agreements [Line Items]
Accrued milestone payment							$ 2,000,000	$ 3,000,000
Daiichi Sankyo License Agreement
License Agreements [Line Items]
License agreement, effective date					Sep. 02, 2020
Upfront payment		$ 5,000,000
Sublicensable rights, number of families of patents | item					7
Number of clinical trials | item					3
Reimbursement total	$ 2,000,000
Number of reimbursement installments | installment	4
Reimbursement paid in each installment	$ 500,000
Period of installment maturity date					Dec. 31, 2022
Other clinical trials payments			$ 30,000	$ 57,000	$ 30,000	$ 87,000
Maximum future milestone payments			223,500,000		223,500,000
Clinical trials reimbursement expense					2,000,000
Milestone fees			$ 0	$ 0	0	$ 0			$ 5,500,000
Milestone payments										$ 2,500,000
Accrued milestone payment									$ 3,000,000
Royalty payments					$ 0
Royalty obligation termination description					The royalty obligation terminates on a country-by-country and on a product-by-product basis on the later of: (i) loss of all market exclusivity for such Product in such country, (ii) the last-to-expire patent that covers the Licensed Compound or the Product in such country and (iii) twelve years from launch of the first Product sold by the Company in such country.
Cure period					90 days
Agreement termination written notice period					6 months

Commitments and Contingencies -

Commitments and Contingencies - Narrative (Details) - ft²	1 Months Ended
	Jun. 30, 2020	Sep. 30, 2018	Mar. 31, 2023	Oct. 31, 2022
Commitments and Contingencies.
Initial term of operating lease		5 years 3 months
Operating lease commencement month and year		2019-01
Operating lease expiration month and year		2024-03
Increase in annual base rent percentage	3%	2%
Increase in annual base rent month and day of each year	--02-01	--03-01
Rent relief period	3 months
Operating lease extended expiration month and year	2024-09
Lease agreement to expand the leased premises			5,600	3,880

Commitments and Contingencies_2

Commitments and Contingencies - Schedule of Future Minimum Lease Payments Required under Operating Lease (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Commitments and Contingencies.
2023 - remainder	$ 119
2024	358
Total minimum lease payments	477
Less: amount representing interest	(21)
Present value of operating lease liabilities	456
Operating lease liabilities, current	$ 456	$ 164
Operating lease liabilities, non-current		$ 113
Weighted-average remaining lease term (in years)	1 year
Weighted-average incremental borrowing rate	10%

Commitments and Contingencies_3

Commitments and Contingencies - Summary of Lease Costs and Cash Payments (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Commitments and Contingencies.
Total operating lease expense	$ 114	$ 40	$ 194	$ 120
Operating cash flows used for operating lease	$ 108	$ 42	$ 194	$ 124

Employee Benefits (Details)

Employee Benefits (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Employee Benefits
Defined contribution plan, employer matching contribution amount	$ 54,000	$ 164,000	$ 630,000	$ 320,000

Restructuring Charges (Details)

Restructuring Charges (Details) - USD ($)	3 Months Ended	9 Months Ended
	Jun. 30, 2023	Sep. 30, 2023
Restructuring Charges.
Restructuring charges	$ 2,800,000	$ 2,837,000
Severance costs	2,800,000
Stock based compensation	$ 37,000

Net Loss Per Share - Schedule o

Net Loss Per Share - Schedule of Computation of Basic and Diluted Net Loss per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2023	Jun. 30, 2023	Mar. 31, 2023	Sep. 30, 2022	Jun. 30, 2022	Mar. 31, 2022	Sep. 30, 2023	Sep. 30, 2022
Numerator:
Net loss	$ (7,034)	$ (22,064)	$ (20,484)	$ (18,041)	$ (17,611)	$ (17,394)	$ (49,582)	$ (53,046)
Denominator:
Weighted-average shares of common stock outstanding, basic	36,375,671			26,564,615			36,359,744	26,535,474
Weighted-average shares of common stock outstanding, diluted	36,375,671			26,564,615			36,359,744	26,535,474
Weighted-average shares used to compute net loss per share, basic	36,375,671			26,564,615			36,359,744	26,535,474
Weighted-average shares used to compute net loss per share, diluted	36,375,671			26,564,615			36,359,744	26,535,474
Net loss per share, basic	$ (0.19)			$ (0.68)			$ (1.36)	$ (2)
Net loss per share, diluted	$ (0.19)			$ (0.68)			$ (1.36)	$ (2)

Net Loss Per Share - Schedule_2

Net Loss Per Share - Schedule of Potentially Dilutive Securities Excluded from Calculation of Diluted Net Loss per Share (Details) - shares	9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities	4,042,612	2,666,926
Stock options
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities	3,960,030	2,630,258
Restricted stock units
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities	41,485	9,289
ESPP shares
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities	41,097	27,379

Subsequent Events (Details)

Subsequent Events (Details) - Subsequent Event - Tang Capital, LP - Rain Oncology Inc.	1 Months Ended
	Oct. 31, 2023 $ / shares
Subsequent Event [Line Items]
Per share value for shares proposed to be acquired	$ 1.25
Contingent value right	80%