Plus Therapeutics (PSTV) 10-Q 20 Apr 23 2023 Q1 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	3 Months Ended
	Mar. 31, 2023	Apr. 18, 2023
Cover [Abstract]
Entity Registrant Name	PLUS THERAPEUTICS, INC.
Entity Central Index Key	0001095981
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Entity Emerging Growth Company	false
Entity Small Business	true
Entity Common Stock, Shares Outstanding		36,690,934
Document Fiscal Year Focus	2023
Document Fiscal Period Focus	Q1
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Mar. 31, 2023
Document Quarterly Report	true
Document Transition Report	false
Entity Interactive Data Current	Yes
Entity Current Reporting Status	Yes
Entity Shell Company	false
Trading Symbol	PSTV
Title of 12(b) Security	Common Stock, par value $0.001
Security Exchange Name	NASDAQ
Entity File Number	001-34375
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	33-0827593
Entity Address, Address Line One	4200 MARATHON BLVD
Entity Address, Address Line Two	SUITE 200
Entity Address, City or Town	AUSTIN
Entity Address, State or Province	TX
Entity Address, Postal Zip Code	78756
City Area Code	737
Local Phone Number	255-7194

CONDENSED BALANCE SHEETS (UNAUD

CONDENSED BALANCE SHEETS (UNAUDITED) - USD ($) $ in Thousands	Mar. 31, 2023	Dec. 31, 2022
Current assets:
Cash and cash equivalents	$ 12,723	$ 18,120
Other current assets	906	3,697
Total current assets	13,629	21,817
Property and equipment, net	1,276	1,324
Operating lease right-use-of assets	270	248
Goodwill	372	372
Intangible assets, net	79	94
Other assets	12	12
Total assets	15,638	23,867
Current liabilities:
Accounts payable and accrued expenses	6,495	10,134
Operating lease liability	107	110
Term loan obligation, current	5,057	1,608
Deferred grant liability, current	1,137
Total current liabilities	12,796	11,852
Term loan obligation		3,786
Noncurrent operating lease liability	166	141
Deferred grant liability		1,643
Total liabilities	12,962	17,422
Commitments and contingencies (Note 8)
Stockholders’ equity:
Preferred stock, $0.001 par value; 5,000,000 shares authorized; 1,953 and 1,952 shares issued and outstanding at March 31, 2023 and December 31, 2022, respectively
Common stock, $0.001 par value; 100,000,000 shares authorized; 36,123,833 and 33,601,373 issued and outstanding at March 31, 2023 and December 31, 2022, respectively	36	34
Additional paid-in capital	474,630	473,596
Accumulated deficit	(471,990)	(467,185)
Total stockholders’ equity	2,676	6,445
Total liabilities and stockholders’ equity	$ 15,638	$ 23,867

CONDENSED BALANCE SHEETS (UNA_2

CONDENSED BALANCE SHEETS (UNAUDITED) (Parenthetical) - $ / shares	Mar. 31, 2023	Dec. 31, 2022
Stockholders’ equity:
Preferred stock, par value (in dollars per share)	$ 0.001	$ 0.001
Preferred stock, shares authorized (in shares)	5,000,000	5,000,000
Preferred stock, shares issued (in shares)	1,953	1,952
Preferred stock, shares outstanding (in shares)	1,953	1,952
Common stock, par value (in dollars per share)	$ 0.001	$ 0.001
Common stock, shares authorized (in shares)	100,000,000	100,000,000
Common stock, shares issued (in shares)	36,123,833	33,601,373
Common stock, shares outstanding (in shares)	36,123,833	33,601,373

CONDENSED STATEMENTS OF OPERATI

CONDENSED STATEMENTS OF OPERATIONS (UNAUDITED) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Operating expenses:
Research and development	$ 2,983	$ 1,785
General and administrative	2,243	2,141
Total operating expenses	5,226	3,926
Operating loss	(4,720)	(3,926)
Other income (expense):
Interest income	51	7
Interest expense	(134)	(198)
Change in fair value of liability instruments		1
Loss on disposal of property and equipment	(2)	0
Total other expense	(85)	(190)
Net loss	$ (4,805)	$ (4,116)
Net loss per share, basic	$ (0.14)	$ (0.19)
Net loss per share, diluted	$ (0.14)	$ (0.19)
Basic weighted average shares used in calculating net loss per share attributable to common stockholders	34,800,260	21,507,061
Diluted weighted average shares used in calculating net loss per share attributable to common stockholders	34,800,260	21,507,061
Grant [Member]
Revenue	$ 506

CONDENSED STATEMENTS OF STOCKHO

CONDENSED STATEMENTS OF STOCKHOLDERS' EQUITY (UNAUDITED) - USD ($) $ in Thousands	Total	Convertible Preferred Stock [Member]	Series F Preferred Stock [Member]	Preferred Stock [Member]	Preferred Stock [Member] Series F Preferred Stock [Member]	Common Stock [Member]	Additional Paid-in Capital [Member]	Additional Paid-in Capital [Member] Series F Preferred Stock [Member]	Accumulated Deficit [Member]
Balance at Dec. 31, 2021	$ 10,836					$ 16	$ 457,730		$ (446,910)
Balance (in shares) at Dec. 31, 2021		1,952				15,510,025
Stock-based compensation	180						180
Issue and sale of stock, net	7,742					$ 6	7,736
Issue and sale of share						6,687,610
Net loss	(4,116)								(4,116)
Balance at Mar. 31, 2022	14,642					$ 22	465,646		(451,026)
Balance (in shares) at Mar. 31, 2022		1,952				22,197,635
Balance at Dec. 31, 2021	10,836					$ 16	457,730		(446,910)
Balance (in shares) at Dec. 31, 2021		1,952				15,510,025
Balance at Dec. 31, 2022	6,445					$ 34	473,596		(467,185)
Balance (in shares) at Dec. 31, 2022		1,952				33,601,373
Stock-based compensation	140						140
Issue and sale of stock, net	895		$ 1			$ 2	893	$ 1
Issue and sale of share					1	2,522,460
Net loss	(4,805)								(4,805)
Balance at Mar. 31, 2023	$ 2,676					$ 36	$ 474,630		$ (471,990)
Balance (in shares) at Mar. 31, 2023		1,952		1		36,123,833

CONDENSED STATEMENTS OF CASH FL

CONDENSED STATEMENTS OF CASH FLOWS (UNAUDITED) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2023	Mar. 31, 2022	Dec. 31, 2022
Cash flows used in operating activities:
Net loss	$ (4,805)	$ (4,116)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	158	147
Amortization of deferred financing costs and debt discount	66	115
Change in fair value of liability instruments	0	(1)
Stock-based compensation expense	140	180
Amortization of operating lease right-of-use assets	29	25
Loss on disposal of property and equipment	2	0
Increases (decreases) in cash caused by changes in operating assets and liabilities:
Other current assets	2,791	459
Accounts payable and accrued expenses	(3,639)	(650)
Change in operating lease liabilities	(29)	(35)
Deferred revenue	(506)	0
Net cash used in operating activities	(5,793)	(3,876)
Cash flows used in investing activities:
Purchases of property and equipment	(97)	(210)
Purchase of intangible assets	0	(117)
In process research and development acquired	0	(250)
Net cash used in investing activities	(97)	(577)
Cash flows from financing activities:
Principal payments of term loan obligation	(402)	(402)
Proceeds from sale of common stock, net	895	7,694
Net cash provided by financing activities	493	7,292
Net (decrease) increase in cash and cash equivalents	(5,397)	2,839
Cash and cash equivalents at beginning of period	18,120	18,400	$ 18,400
Cash and cash equivalents at end of period	12,723	21,239	$ 18,120
Cash paid during period for:
Interest	73	87
Supplemental schedule of non-cash investing and financing activities:
Unpaid offering cost	25	171
Right-of-use assets obtained in exchange for operating lease liability	$ 51	$ 0

Basis of Presentation and New A

Basis of Presentation and New Accounting Standards	3 Months Ended
	Mar. 31, 2023
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Basis of Presentation and New Accounting Standards	1. Basis of Presentation and New Accounting Standards The accompanying unaudited condensed financial statements for the three months ended March 31, 2023 and 2022 have been prepared in accordance with accounting principles generally accepted in the United States of America for interim financial information. Accordingly, they do not include all of the information and footnotes required by accounting principles generally accepted in the United States of America for annual financial statements. The condensed balance sheet at December 31, 2022 has been derived from the audited financial statements at December 31, 2022, but does not include all of the information and footnotes required by accounting principles generally accepted in the United States of America for complete financial statements. In the opinion of management, all adjustments (consisting of normal recurring adjustments) considered necessary for a fair presentation of the financial position and results of operations of Plus Therapeutics, Inc., and its subsidiaries (collectively, the “Company”) have been included. Operating results for the three months ended March 31, 2023 are not necessarily indicative of the results that may be expected for the year ending December 31, 2023. These financial statements should be read in conjunction with the financial statements and notes therein included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2022, filed with the Securities and Exchange Commission on February 23, 2023. Grant Receivable and Revenue Recognition In applying the provisions of Accounting Standards Codification (“ASC”) Topic 606, Revenue from Contracts with Customers (“ASC 606”), the Company has determined that government grants are out of the scope of ASC 606 because the funding entities do not meet the definition of a “customer”, as defined by ASC 606, as there is not considered to be a transfer of control of goods or services. With respect to the grant, the Company determines if it has a collaboration in accordance with ASC Topic 808, Collaborative Arrangements (“ASC 808”). For grants outside the scope of ASC 808, the Company applies ASC 606 or International Accounting Standards No. 20, Accounting for Government Grants and Disclosure of Government Assistance, by analogy, and revenue is recognized when the Company incurs expenses related to the grant for the amount the Company is entitled to under the provisions of the contract. The Company also considers the guidance in ASC Topic 730, Research and Development, which requires an assessment, at the inception of the grant, of whether the agreement is a liability. If the Company is obligated to repay funds received regardless of the outcome of the related research and development activities, then the Company is required to estimate and recognize that liability. Alternatively, if the Company is not required to repay the funds, then payments received are recorded as revenue or contra-expense as the expenses are incurred. Deferred grant liability represents grant funds received or receivable for which the allowable expenses have not yet been incurred as of the balance sheet date. Recently Issued Accounting Pronouncements In June 2016, the FASB issued ASU 2016-13, Financial Instruments - Credit Losses (Topic 326), Measurement of Credit Losses on Financial Instruments. The standard amends the impairment model by requiring entities to use a forward-looking approach based on expected losses to estimate credit losses for most financial assets and certain other instruments that aren’t measured at fair value through net income. For available-for-sale debt securities, entities will be required to recognize an allowance for credit losses rather than a reduction in carrying value of the asset. Entities will no longer be permitted to consider the length of time that fair value has been less than amortized cost when evaluating when credit losses should be recognized. This new guidance is effective in the first quarter of 2023 for calendar-year SEC filers that are smaller reporting companies as of the one-time determination date. Early adoption is permitted beginning in 2019. The Company has adopted the new guidance as of January 1, 2023 , and it did no t have a material impact on its financial statements and related disclosures.

Use of Estimates

Use of Estimates	3 Months Ended
	Mar. 31, 2023
Use Of Estimates [Abstract]
Use of Estimates	2. Use of Estimates The preparation of financial statements in conformity with U.S. generally accepted accounting principles requires management to make estimates and assumptions affecting the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements, and the reported amounts of revenue and expenses during the reporting period. The Company’s most significant estimates and critical accounting policies involve grant revenue recognition, reviewing assets for impairment, and determining the assumptions used in measuring stock-based compensation expense. As discussed in more detail in Note 7, on September 19, 2022, the Company entered into a Cancer Research Grant Contract (the “CPRIT Contract”), effective as of August 31, 2022 , with the Cancer Prevention and Research Institute of Texas (“CPRIT”), pursuant to which the Company will receive up to $ 17.6 million to fund a portion of the clinical trials. The Company estimates the amount of clinical trial costs that should be borne by CPRIT in accordance with the CPRIT Contract, based on the actual costs incurred and progress of the trial. Actual results could differ from these estimates. Management’s estimates and assumptions are reviewed regularly, and the effects of revisions are reflected in the financial statements in the periods they are determined to be necessary.

Liquidity and Going Concern

Liquidity and Going Concern	3 Months Ended
	Mar. 31, 2023
Liquidity [Abstract]
Liquidity and Going Concern	3. Liquidity and Going Concern The Company incurred a net loss of $ 4.8 million for the three months ended March 31, 2023. The Company had an accumulated deficit of $ 472.0 million as of March 31, 2023. Additionally, the Company used net cash of $ 5.8 million to fund its operating activities for the three months ended March 31, 2023. These factors raise substantial doubt about the Company’s ability to continue as a going concern. To date, the Company's operating losses have been funded primarily from outside sources of invested capital from issuance of its common and preferred stocks, proceeds from its term loan and grant funding. However, the Company has had, and will continue to have, an ongoing need to raise additional cash from outside sources to fund its future clinical development programs and other operations. There can be no assurance that the Company will be able to continue to raise additional capital in the future. The Company's inability to raise additional cash would have a material and adverse impact on its operations and would cause the Company to default on it term loan. On May 24, 2022, the Company received notice from The Nasdaq Stock Market LLC (“Nasdaq”) that, because the closing bid price for the Company’s common stock had fallen below $ 1.00 per share for 30 consecutive business days, the Company no longer complied with the minimum bid price requirement pursuant to Nasdaq Listing Rule 5550(a)(2) (the “Minimum Bid Requirement”). Nasdaq’s notice had no immediate effect on the listing or trading of the Company’s common stock. On November 22, 2022, the Company received a second letter from Nasdaq advising that the Company had been granted an additional 180 calendar days, or to May 22, 2023 , to regain compliance with the Minimum Bid Requirement, in accordance with Nasdaq Listing Rule 5810(c)(3)(A). The Company intends to continue to actively monitor the closing bid price of its common stock and will evaluate available options to regain compliance with the Minimum Bid Requirement. Specifically, the Company has confirmed to Nasdaq that, if necessary, it will implement a reverse stock split of its outstanding common stock (if approved by the Company’s stockholders) to attempt to regain compliance. The Company is scheduled to hold its annual meeting of stockholders on April 20, 2023 and one of the proposals for approval is an amendment to the Company’s Amended and Restated Certificate of Incorporation, as amended (the “Charter”), to effect a reverse stock split of its issued and outstanding shares of common stock, at a specific ratio, ranging from one-for-three ( 1:3 ) to one-for-fifteen ( 1:15 ). If the stockholders do not approve the amendment to the Charter to effect a reverse stock split, or if the Company does not otherwise regain compliance within the additional compliance period, Nasdaq will provide notice that the Company’s common stock will be subject to delisting. The Company would then be entitled to appeal that determination to a Nasdaq hearings panel. There can be no assurance that the Company will regain compliance with the Minimum Bid Requirement during the 180-day additional compliance period or maintain compliance with the other Nasdaq listing requirements. The Company continues to seek additional capital from other financing alternatives and other sources. Without additional capital, current working capital will not provide adequate funding for research and product development activities at their current levels. If sufficient capital is not raised, the Company will at a minimum need to significantly reduce or curtail its research and development and other operations, and this would negatively affect its ability to achieve corporate growth goals. Should the Company fail to raise additional cash from outside sources, this would have a material adverse impact on its operations. The accompanying condensed financial statements have been prepared assuming the Company will continue to operate as a going concern, which contemplates the realization of assets and settlement of liabilities in the normal course of business, and do not include any adjustments to reflect the possible future effects on the recoverability and classification of assets or the amounts and classifications of liabilities that may result from uncertainty related to its ability to continue as a going concern.

Fair Value Measurements

Fair Value Measurements	3 Months Ended
	Mar. 31, 2023
Fair Value Disclosures [Abstract]
Fair Value Measurements	4. Fair Value Measurements Fair value measurements are market-based measurements, not entity-specific measurements. Therefore, fair value measurements are determined based on the assumptions that market participants would use in pricing the asset or liability. The Company follows a three-level hierarchy to prioritize the inputs used in the valuation techniques to derive fair values. The basis for fair value measurements for each level within the hierarchy is described below: • Level 1: Quoted prices in active markets for identical assets or liabilities. • Level 2: Quoted prices for similar assets or liabilities in active markets; quoted prices for identical or similar instruments in markets that are not active; and model-derived valuations in which all significant inputs are observable in active markets. • Level 3: Valuations derived from valuation techniques in which one or more significant inputs are unobservable in active markets. Certain warrants issued in an underwritten public offering in September 2019 (the “Series U Warrants”) are classified as liability instruments. The Company estimated the fair value of the Series U Warrants with the Black Scholes model. Because some of the inputs to the Company’s valuation model are either not observable or are not derived principally from or corroborated by observable market data by correlation or other means, the warrant liability is classified as Level 3 in the fair value hierarchy. Liability-classified Series U Warrants are marked to market as of each balance sheet date until they are exercised or upon expiration, with the changes in fair value recorded as non-operating income or loss in the statements of operations. As of March 31, 2023, the fair value of the Series U Warrants was immaterial, and the change in the fair value of liability classified Series U Warrants during the three months ended March 31, 2023 and 2022 was immaterial.

Term Loan Obligations

Term Loan Obligations	3 Months Ended
	Mar. 31, 2023
Debt Disclosure [Abstract]
Term Loan Obligations	5. Term Loan Obligations On May 29, 2015 , the Company entered into the Loan and Security Agreement (the “Loan and Security Agreement”), pursuant to which Oxford Finance, LLC (“Oxford”) funded an aggregate principal amount of $ 17.7 million (the “Term Loan”), subject to the terms and conditions set forth in the Loan and Security Agreement. The Term Loan accrues interest at a floating rate of at least 8.95 % per annum, comprised of a three-month LIBOR rate with a floor of 1.00 % plus 7.95 %. Pursuant to the Loan and Security Agreement, as amended, the Company made interest only payments through May 1, 2021 , and thereafter is required to make payments of principal and accrued interest in equal monthly installments sufficient to amortize the Term Loan through June 1, 2024, the maturity date. At maturity of the Term Loan, or earlier repayment in full following voluntary prepayment or upon acceleration, the Company is required to make a final payment in an aggregate amount equal to approximately $ 3.2 million. In connection with the Term Loan, on May 29, 2015, the Company issued to Oxford warrants to purchase an aggregate of 188 shares of the Company’s common stock at an exercise price of $ 5,175 per share. These warrants became exercisable as of November 30, 2015 , and will expire on May 29, 2025 and, following authoritative accounting guidance, are equity classified and their respective fair value was recorded as a discount to the debt. From September 2017 to July 2019, the Company entered into a total of eight amendments to the Term Loan that, among other things, extended the interest only period, required repayment of $ 3.1 million using the proceeds received from sale of the Company’s former UK and Japan subsidiaries in April 2019, increased the final payment, increased the final payment fee upon maturity or early repayment of the Term Loan, and increased the minimum liquidity covenant level to $ 2.0 million. On March 29, 2020, the Company entered into the Ninth Amendment of the Loan and Security Agreement (the “Ninth Amendment”), pursuant to which Oxford agreed to defer the start date of principal repayment from May 1, 2020 to May 1, 2021 and extended the term of the Term Loan from September 1, 2021 to June 1, 2024 . Under authoritative guidance, the Ninth Amendment did not meet the criteria to be accounted for as a troubled debt restructuring. In addition, the Company performed a quantitative analysis and determined that the terms of the new debt and original debt instrument are not substantially different. Accordingly, the Ninth Amendment is accounted for as a debt modification. A new effective interest rate that equates the revised cash flows to the carrying amount of the original debt is computed and applied prospectively. The Term Loan, as amended, is collateralized by a security interest in substantially all of the Company’s existing and subsequently acquired assets, including its intellectual property assets, subject to certain exceptions set forth in the Loan and Security Agreement, as amended. The intellectual property asset collateral will be released upon the Company achieving a certain liquidity level when the total principal outstanding under the Loan and Security Agreement is less than $ 3.0 million. As of March 31, 2023 , there was $ 2.0 million principal amount outstanding under the Term Loan, excluding the $ 3.2 million final payment fee, and the Company was in compliance with all of the debt covenants under the Loan and Security Agreement. The Company’s interest expense for the three months ended March 31, 2023 and 2022 was $ 0.1 million and $ 0.2 million, respectively. Interest expense is calculated using the effective interest method; therefore it is inclusive of non-cash amortization in the amount of $ 0.1 million for each of the three months ended March 31, 2023 and 2022, related to the amortization of the debt discount, capitalized loan costs, and accretion of final payment. The Loan and Security Agreement, as amended, contains customary indemnification obligations and customary events of default, including, among other things, the Company’s failure to fulfill certain obligations under the Term Loan, as amended, and the occurrence of a material adverse change, which is defined as a material adverse change in the Company’s business, operations, or condition (financial or otherwise), a material impairment of the prospect of repayment of any portion of the loan. In the event of default by the Company or a declaration of material adverse change by its lender, under the Term Loan, the lender would be entitled to exercise its remedies thereunder, including the right to accelerate the debt, upon which the Company may be required to repay all amounts then outstanding under the Term Loan, which could materially harm the Company’s financial condition. As of March 31, 2023, the Company has not received any notification or indication from Oxford that it intends to invoke the material adverse change clause. However, due to the Company’s current cash flow position and the substantial doubt about its ability to continue as a going concern, the entire principal amount of the Term Loan is presented as short-term. The Company will continue to evaluate the debt classification on a quarterly basis and evaluate for reclassification in the future should its financial condition improve.

Loss per Share

Loss per Share	3 Months Ended
	Mar. 31, 2023
Earnings Per Share [Abstract]
Loss per Share	6 . Loss per Share Basic per share data is computed by dividing net income or loss applicable to common stockholders by the weighted average number of common shares outstanding during the period. Diluted per share data is computed by dividing net income or loss applicable to common stockholders by the weighted average number of common shares outstanding during the period increased to include, if dilutive, the number of additional common shares that would have been outstanding as calculated using the treasury stock method. Potential common shares were related to outstanding but unexercised options, multiple series of convertible preferred stock, and warrants for all periods presented. The following were excluded from the diluted loss per share calculation for the periods presented because their effect would be anti-dilutive: As of March 31, 2023 2022 Outstanding stock options 2,014,245 1,170,873 Preferred stock 422,867 422,867 Outstanding warrants 2,141,189 2,141,378 Total 4,578,301 3,735,118

Grant Revenue

Grant Revenue	3 Months Ended
	Mar. 31, 2023
Revenue from Contract with Customer [Abstract]
Grant Revenue	7. Grant Revenue On September 19, 2022, the Company entered into the CPRIT Contract, effective as of August 31, 2022 , with CPRIT, pursuant to which CPRIT will provide the Company a grant of up to $ 17.6 million (the “CPRIT Grant”) over a three-year period to fund the continued development of rhenium ( 186 Re) obisbemeda (previously known as 186 RNL) for the treatment of patients with leptomeningeal metastases (“LM”). The CPRIT Grant is subject to customary CPRIT funding conditions, including, but not limited to, a matching fund requirement (one dollar for every two dollars awarded by CPRIT), revenue sharing obligations upon commercialization of rhenium ( 186 Re) obisbemeda based on specific dollar thresholds and tiered low single digit royalty rates until CPRIT receives the aggregate amount of 400 % of the proceeds awarded under the CPRIT Grant, and certain reporting requirements. The CPRIT Contract will terminate on August 30, 2025 , unless terminated earlier by (a) the mutual written consent of all parties to the CPRIT Contract, (b) CPRIT for an event of default by the Company, (c) CPRIT, if the funds allocated to the CPRIT Grant become legally unavailable during the term of the CPRIT Contract and CPRIT is unable to obtain additional funds for such purposes, and (d) the Company for convenience. CPRIT may require the Company to repay some or all of the disbursed CPRIT Grant proceeds (with interest not to exceed 5 % annually) in the event of the early termination of the CPRIT Contract by CPRIT for an event of default by the Company or by the Company for convenience. The Company retains ownership over any intellectual property developed under the contract (each, a “Project Result”). With respect to non-commercial use of any Project Result, the Company granted to CPRIT a nonexclusive, irrevocable, royalty-free, perpetual, worldwide license with right to sublicense any necessary additional intellectual property rights to exploit all Project Results by CPRIT, other governmental entities and agencies of the State of Texas, and private or independent institutions of higher education located in Texas, for education, research and other non-commercial purposes. The Company determined that the CPRIT Contract is not in the scope of ASC 808 or ASC 606. Applying ASC 606 by analogy, the Company recognizes proceeds received under the CPRIT Contract as grant revenue on the statement of operations when related costs are incurred. The Company recognized $ 0.5 million and $ 0 in grant revenue from the CPRIT Contract during the three months ended March 31, 2023 and 2022, respectively.

Commitments and Contingencies

Commitments and Contingencies	3 Months Ended
	Mar. 31, 2023
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingencies	8. Commitments and Contingencies Leases At the inception of a contractual arrangement, the Company determines whether the contract contains a lease by assessing whether there is an identified asset and whether the contract conveys the right to control the use of the identified asset in exchange for consideration over a period of time. If both criteria are met, the Company calculates the associated lease liability and corresponding right-of-use asset upon lease commencement using a discount rate based on the rate implicit in the lease or an incremental borrowing rate commensurate with the term of the lease. Lease renewable options are included in the estimation of lease term when it is reasonably certain that the Company will exercise such options. The Company records lease liabilities within current liabilities or long-term liabilities based upon the length of time associated with the lease payments. The Company records its operating lease right-of-use assets as long-term assets. Right-of-use assets for finance leases are recorded within property and equipment, net in the condensed balance sheets. Leases with an initial term of 12 months or less are not recorded on the condensed balance sheets. Instead, the Company recognizes lease expense for these leases on a straight-line basis over the lease term in the condensed statements of operations. The Company leases laboratory, office and storage facilities in San Antonio, Texas, under operating lease agreements that expire in 2025 . The Company also leases certain office space in Austin, Texas under a month-to-month operating lease agreement and certain office space in Charlottesville, Virginia (the “Charlottesville Lease”). The Charlottesville Lease has a term of 12 months and the Company has the ability to renew for three additional one-year periods. The Charlottesville Lease is currently set to expire on March 31, 2024 , and is renewable twice for twelve months each time. As of March 31, 2023, the Company believed that it was reasonably certain that the Charlottesville Lease will be renewed through March 31, 2026, and as a result, it remeasured the related lease liability as of March 31, 2023 to be $ 80,000 using the then-in-effect discount rate of 12.76 %. The Company’s existing operating lease agreements generally provide for periodic rent increases, and renewal and termination options. The Company’s lease agreements do not contain any material variable lease payments, residual value guarantees or material restrictive covenants. Certain leases require the Company to pay taxes, insurance, and maintenance. Payments for the transfer of goods or services such as common area maintenance and utilities represent non-lease components. The Company elected the package of practical expedients and therefore does not separate non-lease components from lease components. The Company’s operating lease liabilities and corresponding right-of-use assets are included in the condensed balance sheets. As of March 31, 2023 , the weighted average discount rate used to measure operating lease liabilities and the operating leases remaining term were 9.0 % and 2.27 years, respectively. The table below summarizes the Company’s lease costs from its unaudited condensed statements of operations, and cash payments from its unaudited condensed statements of cash flows during the three months ended March 31, 2023 and 2022 (in thousands): Three Months Ended March 31, 2023 2022 Lease expense: Total lease expense $ 34 $ 45 Cash payment information: Operating cash used for operating leases $ 34 $ 45 Total rent expenses for the three months ended March 31, 2023 and 2022 were $ 47,000 and $ 60,000 , respectively, which includes leases in the table above, month-to-month operating leases, and common area maintenance charges. The Company’s future minimum annual lease payments under operating leases at March 31, 2023 are as follows (in thousands): Remainder of 2023 $ 103 2024 138 2025 51 2026 8 Thereafter - Total minimum lease payments 300 Less: amount representing interest ( 27 ) Present value of obligations under leases 273 Less: current portion ( 107 ) Noncurrent lease obligations $ 166 Services Agreement and Sales Order with Medidata On March 31, 2022, the Company and Medidata Solutions, Inc. (“Medidata”) entered into a Sales Order (the “Sales Order”), pursuant to which Medidata will build a Synthetic Control Arm ® (“SCA”) platform that facilitates the use of historical clinical data to incorporate into the Company’s Phase 2 clinical trial of rhenium ( 186 Re) obisbemeda in recurrent glioblastoma (“GBM”). The Sales Order is governed under the terms of a services agreement (the “Services Agreement”), dated November 5, 2021. The Sales Order had a term of six months , and work under the Sales Order has been completed. Piramal Master Services Agreement On January 8, 2021 , the Company entered into a Master Services Agreement (the “MSA”) with Piramal Pharma Solutions, Inc. (“Piramal”), for Piramal to perform certain services related to the development, manufacture, and supply of the Company’s rhenium ( 186 Re) obisbemeda Intermediate Drug Product. The MSA includes the transfer of analytical methods, development of microbiological methods, process transfer and optimization, intermediate drug product manufacturing, and stability studies for the Company, which has been initiated at Piramal’s facility located in Lexington, Kentucky. The MSA has a term of five years and will automatically renew for successive one-year terms unless either party notifies the other no later than six months prior to the original term or any additional terms of its intention to not renew the MSA. The Company has the right to terminate the MSA for convenience upon thirty days’ prior written notice. Either party may terminate the MSA upon an uncured material breach by the other party or upon the bankruptcy or insolvency of the other party. Other commitments and contingencies The Company has entered into agreements with various research organizations for pre-clinical and clinical development studies, which have provisions for cancellation. Under the terms of these agreements, the vendors provide a variety of services including conducting research, recruiting and enrolling patients, monitoring studies and data analysis. Payments under these agreements typically include fees for services and reimbursement of expenses. The timing of payments due under these agreements is estimated based on current study progress. As of March 31, 2023 , the Company did no t have any clinical research study obligations. Legal proceedings On June 22, 2021, the Company was named as a defendant in an action brought by Lorem Vascular, Pte. Ltd. (“Lorem”) in the District Court for the District of Delaware. The complaint alleged false representations were made to Lorem regarding the manufacturing facility in the United Kingdom (the “UK Facility”) that Lorem purchased from the Company under the Asset and Equity Purchase Agreement, dated March 29, 2019, between the Company and Lorem (the “Lorem Agreement”). Lorem also claimed that false representations were made regarding the UK Facility’s certification to sell and distribute devices in the European Union and export such devices to China. In connection with these allegations, Lorem claimed entitlement to at least $ 6,000,000 in compensatory damages and operational costs and expenses (collectively, the “Lorem Claim”). On December 9, 2022, the Company entered into a settlement agreement (the “Settlement Agreement”) with Lorem to settle the Lorem Claim. Under the terms of the Settlement Agreement, the Company made a payment to Lorem, and Lorem moved to dismiss the lawsuit with prejudice. The Settlement Agreement released the Company from all claims made by Lorem. The parties to the Settlement Agreement recognized that it did not constitute an admission of liability, wrongdoing, or any matter of fact or law. The Settlement was conditioned on the customary terms contained in the Settlement Agreement and was approved by the Court and the case was dismissed on January 17, 2023. As of December 31, 2022, the Company accrued the settlement amount, as well as the accounts that the Company has confirmed to be recoverable under its insurance claims on the matter. The net amount of $ 1.4 million that was not recoverable under the Company's insurance has been reflected as an expense in the condensed statement of operations for the year ended December 31, 2022. The full settlement amount was paid in January 2023. All legal costs related to the Lorem Claim were expensed as incurred. The Company is subject to various claims and contingencies related to legal proceedings. Due to their nature, such legal proceedings involve inherent uncertainties including, but not limited to, court rulings, negotiations between affected parties and governmental actions. Management assesses the probability of loss for such contingencies and accrues a liability and/or discloses the relevant circumstances, as appropriate.

License Agreements

License Agreements	3 Months Ended
	Mar. 31, 2023
License Agreement [Abstract]
License Agreements	9. License Agreements UT Health Science Center at San Antonio (“UTHSCSA”) License Agreement On December 31, 2021, the Company entered into a Patent and Know-How License Agreement (the “UTHSCSA License Agreement”) with The University of Texas Health Science Center at San Antonio (“UTHSCSA”), pursuant to which UTHSCSA granted the Company an irrevocable, perpetual, exclusive, fully paid-up license, with the right to sublicense and to make, develop, commercialize and otherwise exploit certain patents, know-how and technology related to the development of biodegradable alginate microspheres (“BAM”) containing nanoliposomes loaded with imaging and/or therapeutic payloads. Pursuant to the UTHSCSA License Agreement, the Company was required to make an upfront payment, which was recorded as in-process research and development acquired in the condensed statement of operations for the year ended December 31, 2021. The upfront payment of $ 0.3 million was paid in cash in January 2022. NanoTx License Agreement On March 29, 2020, the Company and NanoTx, Corp. (“NanoTx”) entered into a Patent and Know-How License Agreement (the “NanoTx License Agreement”), pursuant to which NanoTx granted the Company an irrevocable, perpetual, exclusive, fully paid-up license, with the right to sublicense and to make, develop, commercialize and otherwise exploit certain patents, know-how and technology related to the development of radiolabeled nanoliposomes. The transaction terms included an upfront payment of $ 0.4 million in cash and $ 0.3 million in the Company's voting stock. The transaction terms also included success-based milestone and royalty payments contingent on key clinical, regulatory and sales milestones, as well as the requirement to pay 15 % of any non-dilutive monetary awards or grants received from external agencies to support product development of the nanoliposome encapsulated BMEDA-chelated radioisotope, which includes grants from CPRIT. As of March 31, 2023 , the Company accrued $ 1.0 million of payments due to NanoTx as a result of the CPRIT grant received (Note 7).

Stockholders' Equity

Stockholders' Equity	3 Months Ended
	Mar. 31, 2023
Stockholders Equity Note [Abstract]
Stockholders' Equity	10. Stockholders’ Equity Preferred Stock The Company has authorized 5,000,000 shares of preferred stock, par value $ 0.001 per share. The Company’s Board of Directors is authorized to designate the terms and conditions of any preferred stock the Company issues without further action by the common stockholders. Series F Preferred Stock On March 3, 2023, the Company filed a certificate of designation (the “Certificate of Designation”) with the Secretary of State of the State of Delaware, effective as of the time of filing, designating the rights, preferences, privileges and restrictions of the Series F Preferred Stock, with the total authorization of 1 share of Series F Preferred Stock. The Certificate of Designation provides that the share of Series F Preferred Stock will have 50,000,000 votes per share of Series F Preferred Stock and will vote together with the Company’s common stock, $ 0.001 par value (the “Common Stock”) as a single class exclusively with respect to any proposal to amend the Company’s Charter to effect a reverse stock split of the Common Stock (the “Reverse Stock Split”). The Series F Preferred Stock will be voted, without action by the holder, on any such proposal in the same proportion as shares of Common Stock are voted on such proposal. The Series F Preferred Stock otherwise has no voting rights except as otherwise required by the General Corporation Law of the State of Delaware. The Series F Preferred Stock is not convertible into, or exchangeable for, shares of any other class or series of stock or other securities of the Company. The Series F Preferred Stock has no rights with respect to any distribution of assets of the Company, including upon a liquidation, bankruptcy, reorganization, merger, acquisition, sale, dissolution or winding up of the Company, whether voluntarily or involuntarily. The holder of the Series F Preferred Stock will not be entitled to receive dividends of any kind. The outstanding share of Series F Preferred Stock shall be redeemed in whole, but not in part, at any time: (i) if such redemption is approved by the board of directors in its sole discretion or (ii) automatically and effective upon the approval by the Company’s stockholders of a Reverse Stock Split. Upon such redemption, the holder of the Series F Preferred Stock will receive consideration of $ 1,000 in cash. On March 3, 2023, the Company entered into a Subscription and Investment Representation Agreement (the “Subscription Agreement”) with Richard J. Hawkins, Chairman of the board of directors of the Company, who is an accredited investor (the “Purchaser”), pursuant to which the Company agreed to issue and sell one ( 1 ) share of the Company’s Series F Preferred Stock, par value $ 0.001 per share (the “Preferred Stock”), to the Purchaser for $ 1,000 in cash. The sale closed on March 3, 2023 . Series B and C Preferred Stock There were 1,014 shares of Series B Convertible Preferred Stock outstanding as of March 31, 2023 and December 31, 2022 . There were 938 shares of Series C Preferred Stock outstanding as of March 31, 2023 and December 31, 2022. As of March 31, 2023 , there were 938 outstanding shares of Series C Preferred Stock that can be converted into an aggregate of 416,889 shares of common stock, and 1,014 shares of Series B Convertible Preferred Stock that can be converted into an aggregate of 5,978 shares of common stock. Warrants On September 25, 2019, the Company completed an underwritten public offering. The Company issued 289,000 shares of its common stock, along with pre-funded warrants to purchase 2,711,000 shares of its common stock and Series U Warrants to purchase 3,450,000 shares of its common stock at $ 5.00 per share. The Series U Warrants have a term of five years from the issuance date. In addition, the Company issued warrants to H.C. Wainwright & Co., LLC, as representatives of the underwriters, to purchase 75,000 shares of its common stock at $ 6.25 per share with a term of 5 years from the issuance date, in the form of Series U Warrants (the “Representative Warrants”). In accordance with authoritative guidance, the pre-funded warrants are classified as equity. The Series U Warrants and the Representative Warrants were initially classified at issuance as liabilities due to a contingent obligation for the Company to settle the Series U Warrants with cash upon certain change in control events. In 2020, all but 2,500 Series U Warrants were amended and met the requirements to be classified within stockholder’s equity. As of March 31, 2023 , there were 2,141,000 outstanding Series U Warrants which can be exercised into an aggregate of 2,141,000 shares of common stock. Common Stock Lincoln Park Purchase Agreements On August 2, 2022, the Company entered into a purchase agreement (the “2022 Purchase Agreement”) and registration rights agreement pursuant to which Lincoln Park committed to purchase up to $ 50.0 million of the Company’s common stock. Under the terms and subject to the conditions of the 2022 Purchase Agreement, the Company has the right, but not the obligation, to sell to Lincoln Park, and Lincoln Park is obligated to purchase up to $ 50.0 million of the Company’s common stock. Such sales of common stock by the Company are subject to certain limitations, and can occur from time to time, at the Company’s sole discretion, over the 36-month period commencing on August 17, 2022, subject to the satisfaction of certain conditions. Lincoln Park has no right to require the Company to sell any shares of common stock to Lincoln Park, but Lincoln Park is obligated to make purchases as the Company directs, subject to certain conditions. On May 16, 2022, the Company received stockholder approval for purposes of the Nasdaq listing rules to permit issuances of up to 57.5 million shares of the Company’s common stock (including the issuance of more than 19.99 % of the Company’s common stock) to Lincoln Park, and it was pursuant to that approval that the Company entered into the 2022 Purchase Agreement. Upon execution of the 2022 Purchase Agreement, the Company paid $ 125,000 in cash as the initial commitment fee, and issued 492,698 shares as the initial commitment shares, to Lincoln Park as consideration for its irrevocable commitment to purchase shares of the Company's common stock at its direction under the Purchase Agreement. The Company has agreed to pay an additional commitment fee, which it may elect to pay in cash and/or shares of its common stock, upon receipt of $ 25.0 million aggregate gross proceeds from sales of common stock to Lincoln Park under the 2022 Purchase Agreement. On August 17, 2022, a registration statement was declared effective to cover the resale of up to 9,500,000 shares of the Company's common stock comprised of (i) the 492,698 initial commitment shares, and (ii) up to 9,007,302 that the Company has reserved for issuance and sale to Lincoln Park under the Purchase Agreement from time to time from and after the date of this prospectus. The Company cannot sell more shares under the 2022 Purchase Agreement without registering additional shares. Actual sales of shares of common stock to Lincoln Park under the 2022 Purchase Agreement depend on a variety of factors to be determined by the Company from time to time, including, among others, market conditions, the trading price of the common stock and determinations by the Company as to the appropriate sources of funding for the Company and its operations. The net proceeds under the 2022 Purchase Agreement to the Company depend on the frequency and prices at which the Company sells shares of its stock to Lincoln Park. During the period from August 17, 2022 to December 31, 2022, the Company issued 4,000,000 shares under the 2022 Purchase Agreement for net proceeds of approximately $ 3.2 million. No shares were issued under the 2022 Purchase Agreement subsequent to December 31, 2022. On September 30, 2020, the Company entered into a purchase agreement (the “2020 Purchase Agreement”) and registration rights agreement pursuant to which Lincoln Park committed to purchase up to $ 25.0 million of the Company’s common stock. Under the terms and subject to the conditions of the 2020 Purchase Agreement, the Company had the right, but not the obligation, to sell to Lincoln Park, and Lincoln Park was obligated to purchase up to $ 25.0 million of the Company’s common stock. Such sales of common stock by the Company were subject to certain limitations, and could occur from time to time, at the Company’s sole discretion, over the 36 -month period commencing on November 6, 2020, subject to the satisfaction of certain conditions. During the year ended December 31, 2021, the Company issued 5,685,186 shares of its common stock under the 2020 Purchase Agreement for net proceeds of approximately $ 12.5 million. During the year issued December 31, 2022, the Company issued 5,665,000 shares of its common stock under the 2020 Purchase Agreement for net proceeds of approximately $ 7.0 million. The Company no longer has any additional shares of common stock registered to sell under the 2020 Purchase Agreement and has terminated the 2020 Purchase Agreement. At-the-market Issuances On September 9, 2022, the Company entered into an Equity Distribution Agreement (the “September 2022 Distribution Agreement”) with Canaccord Genuity LLC (“Canaccord”), pursuant to which the Company may issue and sell, from time to time, shares of its common stock having an aggregate offering price of up to $ 5,000,000 , depending on market demand, with Canaccord acting as an agent for sales. Sales of the Company's common stock may be made by any method permitted by law deemed to be an “at-the-market offering” as defined in Rule 415(a)(4) of the Securities Act of 1933, as amended (the “Securities Act”), including, without limitation, sales made directly on or through the NASDAQ Capital Market. Canaccord will use its commercially reasonable efforts to sell common stock requested by the Company to be sold on its behalf, consistent with Canaccord's normal trading and sales practices, under the terms and subject to the conditions set forth in the September 2022 Distribution Agreement. The Company has no obligation to sell any of its common stock. The Company may instruct Canaccord not to sell any common stock if the sales cannot be effected at or above the price designated by the Company from time to time and the Company may at any time suspend sales pursuant to the September 2022 Distribution Agreement. During the period from September 9, 2022 to December 31, 2022, the Company issued 1,031,371 shares of its common stock under the September 2022 Distribution Agreement for net proceeds of approximately $ 0.6 million. From January 1, 2023 through April 18, 2023, the Co mpany issued 3,136,058 shares under the September 2022 Distribution Agreement for net proceeds of approximately $ 1.1 million. The Company is obligated to pay Canaccord a commission of up to 3.0 % of the gross proceeds from the sale of its common stock under the September 2022 Distribution Agreement. The Company has also agreed to reimburse Canaccord for its reasonable documented out-of-pocket expenses, including fees and disbursements of its counsel, in the amount of $ 50,000 . In addition, the Company has agreed to provide customary indemnification rights to Canaccord. The Offering will terminate upon the earlier of (1) the issuance and sale of all shares of the Company’s common stock subject to the September 2022 Distribution Agreement, or (2) the termination of the Distribution Agreement as permitted therein, including by either party at any time without liability of any party. On January 14, 2022, the Company entered into an Equity Distribution Agreement (the “January 2022 Distribution Agreement”) with Canaccord, pursuant to which the Company could issue and sell, from time to time, shares of its common stock having an aggregate offering price of up to $ 5,000,000 shares, with Canaccord acting as an agent for sales. The Company had no obligation to sell any of the Company’s shares and it could instruct Canaccord not to sell any shares if the sales could not be effected at or above the price designated by the Company from time to time and the Company could at any time suspend sales pursuant to the January 2022 Distribution Agreement. During the year ended December 31, 2022, the Company issued 6,902,279 shares under the January 2022 Distribution Agreement for net proceeds of approximately $ 4.8 million. The January 2022 Distribution Agreement has been terminated after all available registered shares were fully utilized. Stock Repurchase Program On August 15, 2022, the Company announced that its Board of Directors has approved a share repurchase program pursuant to which the Company is authorized to repurchase up to $ 2.0 million of the Company’s outstanding common stock. The timing and amount of any shares repurchased will be determined based on the Company’s evaluation of market conditions and other factors, including consent of Oxford. Repurchases may be made from time to time on the open market over the course of 12 months. The Company is not obligated to acquire any shares and the program may be discontinued or suspended at any time. Through the date of filing of this Form 10-Q, the Company has no t repurchased any of its common stock under this share repurchase program.

Stock-based Compensation

Stock-based Compensation	3 Months Ended
	Mar. 31, 2023
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Stock-based Compensation	11. Stock-based Compensation Under the Company’s 2015 New Employee Incentive Plan (the “2015 Plan”), awards may only be granted to employees who were not previously an employee or director of the Company, or following a bona fide period of non-employment, as a material inducement to entering into employment with the Company. As of March 31, 2023 , there were 90,389 shares of common stock remaining and available for future issuances under the 2015 Plan. The Company’s 2020 Stock Incentive Plan (the “2020 Plan”), which replaced the Company’s 2014 Equity Incentive Plan, provides for the award or sale of shares of common stock (including restricted stock), the award of stock units and stock appreciation rights, and the grant of both incentive stock options to purchase common stock to directors, officers, employees and consultants of the Company. The 2020 Plan, as amended, provides for the issuance of up to 3,550,000 shares of common stock, plus the number of shares available for issuance is increased to the extent that awards granted under the 2020 Plan and the Company’s 2014 Equity Incentive Plan are forfeited or expire (except as otherwise provided in the 2020 Plan). As of March 31, 2023 , there were 1,796,451 shares remaining and available for future issuances under the 2020 Plan. Generally, options issued under the 2020 Plan are subject to a two-year or four-year vesting schedule with 25 % of the options vesting on the one year anniversary of the grant date followed by equal monthly installment vesting, and have a contractual term of 10 years. A summary of activity for the three months ended March 31, 2023 is as follows: Options Weighted Weighted Aggregate Balance as of December 31, 2022 1,175,016 $ 4.54 8.00 Granted 839,266 $ 0.39 Cancelled/forfeited ( 37 ) $ 26,059.46 Balance as of March 31, 2023 2,014,245 $ 2.33 8.65 $ - Vested and expected to vest at March 31, 2023 1,886,155 $ 2.41 8.59 $ - Exercisable at March 31, 2023 756,581 $ 4.35 7.69 $ - As of March 31, 2023 , the total compensation cost related to non-vested stock options not yet recognized for all the Company’s plans is approximately $ 1.1 million, which is expected to be recognized as a result of vesting under service conditions over a weighted average period of 2.3 years.

Basis of Presentation and New_2

Basis of Presentation and New Accounting Standards (Policies)	3 Months Ended
	Mar. 31, 2023
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Basis of Presentation and New Accounting Standards	The accompanying unaudited condensed financial statements for the three months ended March 31, 2023 and 2022 have been prepared in accordance with accounting principles generally accepted in the United States of America for interim financial information. Accordingly, they do not include all of the information and footnotes required by accounting principles generally accepted in the United States of America for annual financial statements. The condensed balance sheet at December 31, 2022 has been derived from the audited financial statements at December 31, 2022, but does not include all of the information and footnotes required by accounting principles generally accepted in the United States of America for complete financial statements. In the opinion of management, all adjustments (consisting of normal recurring adjustments) considered necessary for a fair presentation of the financial position and results of operations of Plus Therapeutics, Inc., and its subsidiaries (collectively, the “Company”) have been included. Operating results for the three months ended March 31, 2023 are not necessarily indicative of the results that may be expected for the year ending December 31, 2023. These financial statements should be read in conjunction with the financial statements and notes therein included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2022, filed with the Securities and Exchange Commission on February 23, 2023.
Grant Receivable and Revenue Recognition	Grant Receivable and Revenue Recognition In applying the provisions of Accounting Standards Codification (“ASC”) Topic 606, Revenue from Contracts with Customers (“ASC 606”), the Company has determined that government grants are out of the scope of ASC 606 because the funding entities do not meet the definition of a “customer”, as defined by ASC 606, as there is not considered to be a transfer of control of goods or services. With respect to the grant, the Company determines if it has a collaboration in accordance with ASC Topic 808, Collaborative Arrangements (“ASC 808”). For grants outside the scope of ASC 808, the Company applies ASC 606 or International Accounting Standards No. 20, Accounting for Government Grants and Disclosure of Government Assistance, by analogy, and revenue is recognized when the Company incurs expenses related to the grant for the amount the Company is entitled to under the provisions of the contract. The Company also considers the guidance in ASC Topic 730, Research and Development, which requires an assessment, at the inception of the grant, of whether the agreement is a liability. If the Company is obligated to repay funds received regardless of the outcome of the related research and development activities, then the Company is required to estimate and recognize that liability. Alternatively, if the Company is not required to repay the funds, then payments received are recorded as revenue or contra-expense as the expenses are incurred. Deferred grant liability represents grant funds received or receivable for which the allowable expenses have not yet been incurred as of the balance sheet date.
Recently Issued Accounting Pronouncements	Recently Issued Accounting Pronouncements In June 2016, the FASB issued ASU 2016-13, Financial Instruments - Credit Losses (Topic 326), Measurement of Credit Losses on Financial Instruments. The standard amends the impairment model by requiring entities to use a forward-looking approach based on expected losses to estimate credit losses for most financial assets and certain other instruments that aren’t measured at fair value through net income. For available-for-sale debt securities, entities will be required to recognize an allowance for credit losses rather than a reduction in carrying value of the asset. Entities will no longer be permitted to consider the length of time that fair value has been less than amortized cost when evaluating when credit losses should be recognized. This new guidance is effective in the first quarter of 2023 for calendar-year SEC filers that are smaller reporting companies as of the one-time determination date. Early adoption is permitted beginning in 2019. The Company has adopted the new guidance as of January 1, 2023 , and it did no t have a material impact on its financial statements and related disclosures.
Use of Estimates	The preparation of financial statements in conformity with U.S. generally accepted accounting principles requires management to make estimates and assumptions affecting the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements, and the reported amounts of revenue and expenses during the reporting period. The Company’s most significant estimates and critical accounting policies involve grant revenue recognition, reviewing assets for impairment, and determining the assumptions used in measuring stock-based compensation expense. As discussed in more detail in Note 7, on September 19, 2022, the Company entered into a Cancer Research Grant Contract (the “CPRIT Contract”), effective as of August 31, 2022 , with the Cancer Prevention and Research Institute of Texas (“CPRIT”), pursuant to which the Company will receive up to $ 17.6 million to fund a portion of the clinical trials. The Company estimates the amount of clinical trial costs that should be borne by CPRIT in accordance with the CPRIT Contract, based on the actual costs incurred and progress of the trial. Actual results could differ from these estimates. Management’s estimates and assumptions are reviewed regularly, and the effects of revisions are reflected in the financial statements in the periods they are determined to be necessary.

Loss per Share (Tables)

Loss per Share (Tables)	3 Months Ended
	Mar. 31, 2023
Earnings Per Share [Abstract]
Schedule of Antidilutive Securities Excluded from Diluted Income (Loss) per Share	The following were excluded from the diluted loss per share calculation for the periods presented because their effect would be anti-dilutive: As of March 31, 2023 2022 Outstanding stock options 2,014,245 1,170,873 Preferred stock 422,867 422,867 Outstanding warrants 2,141,189 2,141,378 Total 4,578,301 3,735,118

Commitments and Contingencies (

Commitments and Contingencies (Tables)	3 Months Ended
	Mar. 31, 2023
Commitments And Contingencies Disclosure [Abstract]
Summary of Lease Costs	The table below summarizes the Company’s lease costs from its unaudited condensed statements of operations, and cash payments from its unaudited condensed statements of cash flows during the three months ended March 31, 2023 and 2022 (in thousands): Three Months Ended March 31, 2023 2022 Lease expense: Total lease expense $ 34 $ 45 Cash payment information: Operating cash used for operating leases $ 34 $ 45
Summary of Future Minimum Annual Lease Payments under Operating Leases	The Company’s future minimum annual lease payments under operating leases at March 31, 2023 are as follows (in thousands): Remainder of 2023 $ 103 2024 138 2025 51 2026 8 Thereafter - Total minimum lease payments 300 Less: amount representing interest ( 27 ) Present value of obligations under leases 273 Less: current portion ( 107 ) Noncurrent lease obligations $ 166

Stock-based Compensation (Table

Stock-based Compensation (Tables)	3 Months Ended
	Mar. 31, 2023
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Stock Option Activity	A summary of activity for the three months ended March 31, 2023 is as follows: Options Weighted Weighted Aggregate Balance as of December 31, 2022 1,175,016 $ 4.54 8.00 Granted 839,266 $ 0.39 Cancelled/forfeited ( 37 ) $ 26,059.46 Balance as of March 31, 2023 2,014,245 $ 2.33 8.65 $ - Vested and expected to vest at March 31, 2023 1,886,155 $ 2.41 8.59 $ - Exercisable at March 31, 2023 756,581 $ 4.35 7.69 $ -

Basis of Presentation and New_3

Basis of Presentation and New Accounting Standards (Additional Information) (Details) - ASU 2016-13	Mar. 31, 2023
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Change in accounting principle, accounting standards update, adopted	true
Change in accounting principle, accounting standards update, adoption date	Jan. 01, 2023
Change in accounting principle, accounting standards update, immaterial effect	true

Use of Estimates - Additional I

Use of Estimates - Additional Information (Details) - CPRIT Contract [Member]	Sep. 19, 2022 USD ($)
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Maximum grant amount to be received as per grant contract	$ 17,600,000
Contract effective date	Aug. 31, 2022

Liquidity and Going Concern - A

Liquidity and Going Concern - Additional Information (Details) $ / shares in Units, $ in Thousands			3 Months Ended
	Nov. 22, 2022	May 24, 2022 $ / shares	Mar. 31, 2023 USD ($)	Mar. 31, 2022 USD ($)	Dec. 31, 2022 USD ($)
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net loss			$ (4,805)	$ (4,116)
Accumulated deficit			(471,990)		$ (467,185)
Net cash used in operating activities			$ (5,793)	$ (3,876)
Closing bid price for common stock had fallen below | $ / shares		$ 1
Consecutive business days		30 days
Period for regain compliance	180 days
Regain compliance expiry date	May 22, 2023
Maximum [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Stock split conversion ratio			0.06
Reverse stock split			one-for-fifteen
Minimum [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Stock split conversion ratio			0.33
Reverse stock split			one-for-three

Fair Value Measurements - Addit

Fair Value Measurements - Additional Information (Details)	3 Months Ended
	Mar. 31, 2023
Series U Warrants [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Warrants issued, underwritten public offering, period	2019-09

Term Loan Obligations - Additio

Term Loan Obligations - Additional Information (Details) - USD ($)				3 Months Ended
	Mar. 29, 2020	Mar. 28, 2020	May 29, 2015	Mar. 31, 2023	Mar. 31, 2022
Debt Instrument [Line Items]
Interest expense				$ 134,000	$ 198,000
Non-cash amortization				$ 100,000	$ 100,000
LIBOR [Member] | Interest Rate Floor [Member]
Debt Instrument [Line Items]
Basis variable rate			1%
Term Loan [Member]
Debt Instrument [Line Items]
Origination date				May 29, 2015
Original loan amount			$ 17,700,000
Basis variable rate			7.95%
Maturity date	Jun. 01, 2024	Sep. 01, 2021	May 01, 2021
Fees amount associated with loan			$ 3,200,000	$ 3,200,000
Number of shares callable by warrants (in shares)			188
Warrant exercise price (in dollars per share)			$ 5,175
Date from which warrants are exercisable				Nov. 30, 2015
Warrant expiration date				May 29, 2025
Minimum liquidity covenant				$ 2,000,000
Debt principal repayment start date	May 01, 2021	May 01, 2020
Debt instrument, covenant compliance				the Company was in compliance with all of the debt covenants under the Loan and Security Agreement.
Term Loan [Member] | Loan and Security Agreement [Member] | Sale of the Japanese Subsidiary and Certain Assets [Member]
Debt Instrument [Line Items]
Payments for principal, interest and fees			$ 3,100,000
Term Loan [Member] | Minimum [Member]
Debt Instrument [Line Items]
Interest rate			8.95%
Term Loan [Member] | Maximum [Member]
Debt Instrument [Line Items]
Original loan amount				$ 3,000,000
Long term debt outstanding threshold amount				$ 2,000,000

Loss per Share - Schedule of An

Loss per Share - Schedule of Antidilutive Securities Excluded from Diluted Income (Loss) per Share (Details) - shares	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Dilutive common shares excluded from the calculations of diluted loss per share (in shares)	4,578,301	3,735,118
Outstanding Stock Options [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Dilutive common shares excluded from the calculations of diluted loss per share (in shares)	2,014,245	1,170,873
Convertible Preferred Stock [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Dilutive common shares excluded from the calculations of diluted loss per share (in shares)	422,867	422,867
Outstanding Warrants [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Dilutive common shares excluded from the calculations of diluted loss per share (in shares)	2,141,189	2,141,378

Grant Revenue - Additional Info

Grant Revenue - Additional Information (Details) - USD ($)		3 Months Ended
	Sep. 19, 2022	Mar. 31, 2023	Mar. 31, 2022
Grant [Member]
Disaggregation of Revenue [Line Items]
Revenue recognized		$ 506,000
CPRIT Contract [Member]
Disaggregation of Revenue [Line Items]
Maximum grant amount to be received as per grant contract	$ 17,600,000
Grant funding term	3 years
CPRIT grant funding term, description		The CPRIT Grant is subject to customary CPRIT funding conditions, including, but not limited to, a matching fund requirement (one dollar for every two dollars awarded by CPRIT), revenue sharing obligations upon commercialization of rhenium (186Re) obisbemeda based on specific dollar thresholds and tiered low single digit royalty rates until CPRIT receives the aggregate amount of 400% of the proceeds awarded under the CPRIT Grant, and certain reporting requirements.
Contract effective date	Aug. 31, 2022
Contract termination date	Aug. 30, 2025
Percentage of aggregate amount of proceeds awarded under CPRIT grant	400%
Percentage of grant proceeds with interest not exceed annually	5%
CPRIT Contract [Member] | Grant [Member]
Disaggregation of Revenue [Line Items]
Revenue recognized		$ 500,000	$ 0

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Details) - USD ($)				3 Months Ended
	Mar. 31, 2022	Jun. 22, 2021	Jan. 08, 2021	Mar. 31, 2023	Mar. 31, 2022
Recorded Unconditional Purchase Obligation [Line Items]
Operating leases expiry year				2025
Lease liability				$ 273,000
Operating lease, weighted average discount rate				9%
Operating lease, weighted average remaining term				2 years 3 months 7 days
Rent expense				$ 47,000	$ 60,000
Lorem Vascular Pte Ltd [Member]
Recorded Unconditional Purchase Obligation [Line Items]
Compensatory damages and operational		$ 6,000,000
Litigation settlement, expense				1,400,000
Pre-clinical Research Study Obligations [Member]
Recorded Unconditional Purchase Obligation [Line Items]
Contractual obligation				$ 0
Charlottesville [Member]
Recorded Unconditional Purchase Obligation [Line Items]
Lessee, operating lease, term of contract				12 months
Lessee, operating lease, existence of option to extend [true false]				true
Lessee, operating lease, option to extend				The Charlottesville Lease has a term of 12 months and the Company has the ability to renew for three additional one-year periods.
Lessee, operating lease, renewal term				1 year
Operating leases, expiration date				Mar. 31, 2024
Lease liability				$ 80,000
Operating lease discount rate				12.76%
Medidata Solutions, Inc. [Member] | Services Agreement [Member]
Recorded Unconditional Purchase Obligation [Line Items]
Sales order term	6 months
Piramal Pharma Solutions, Inc. [Member]
Recorded Unconditional Purchase Obligation [Line Items]
Master service agreement date			Jan. 08, 2021
Master services agreement initial term			5 years
Master services agreement terms, Description				The MSA has a term of five years and will automatically renew for successive one-year terms unless either party notifies the other no later than six months prior to the original term or any additional terms of its intention to not renew the MSA. The Company has the right to terminate the MSA for convenience upon thirty days’ prior written notice.

Commitments and Contingencies_2

Commitments and Contingencies - Summary of Lease Costs (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Lease expense:
Total lease expense	$ 34	$ 45
Cash payment information:
Operating cash used for operating leases	$ 34	$ 45

Commitments and Contingencies_3

Commitments and Contingencies - Summary of Future Minimum Annual Lease Payments under Operating Leases (Details) - USD ($) $ in Thousands	Mar. 31, 2023	Dec. 31, 2022
Operating Leases
Remainder of 2023	$ 103
2024	138
2025	51
2026	8
Total minimum lease payments	300
Less: amount representing interest	(27)
Present value of obligations under leases	273
Less: current portion	(107)	$ (110)
Noncurrent operating lease liability	$ 166	$ 141

License Agreements - Additional

License Agreements - Additional Information (Details) - USD ($) $ in Thousands		1 Months Ended
	Mar. 29, 2020	Jan. 31, 2022	Mar. 31, 2023	Dec. 31, 2022
Voting stock, value			$ 36	$ 34
UTHSCSA License Agreement [Member]
License fee payment in cash		$ 300
Nano Tx Licenses Agreement [Member]
License fee payment in cash	$ 400
Voting stock, value	$ 300
Percentage of non-dilutive monetary awards required to pay	15%
Accrued payments due to NanoTx			$ 1,000

Stockholders' Equity - Preferre

Stockholders' Equity - Preferred Stock (Details)		3 Months Ended
	Mar. 03, 2023 USD ($) Votes $ / shares shares	Mar. 31, 2023 $ / shares shares	Dec. 31, 2022 $ / shares shares
Class of Stock [Line Items]
Preferred stock, shares authorized (in shares)		5,000,000	5,000,000
Preferred stock, par value (in dollars per share) | $ / shares		$ 0.001	$ 0.001
Preferred stock, shares outstanding (in shares)		1,953	1,952
Common stock, par value (in dollars per share) | $ / shares		$ 0.001	$ 0.001
Series B Convertible Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock, shares outstanding (in shares)		1,014	1,014
Series B Convertible Preferred Stock [Member] | 2018 Rights Offering [Member]
Class of Stock [Line Items]
Preferred stock, shares outstanding (in shares)		1,014
Number of preferred stock, shares converted		5,978
Series C Convertible Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock, shares outstanding (in shares)		938	938
Series C Convertible Preferred Stock [Member] | 2018 Rights Offering [Member]
Class of Stock [Line Items]
Preferred stock, shares outstanding (in shares)		938
Number of preferred stock, shares converted		416,889
Series F Convertible Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock, shares authorized (in shares)	1
Number Of Votes Per Share | Votes	50,000,000
Common stock, par value (in dollars per share) | $ / shares	$ 0.001
Preferred stock, voting rights	no
Rights related to distribution of assets	no
Consideration paid to preferred stock holders | $	$ 1,000
Series F Convertible Preferred Stock [Member] | Subscription Agreement [Member]
Class of Stock [Line Items]
Preferred stock, par value (in dollars per share) | $ / shares	$ 0.001
Consideration to purchaser in cash | $	$ 1,000
Issue and sale of share	1
Sale closed date	Mar. 03, 2023

Stockholders' Equity - Warrants

Stockholders' Equity - Warrants (Details) - $ / shares	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022	Dec. 31, 2020
Series U Warrants [Member]
Class of Stock [Line Items]
Common stock issued (in shares)	3,450,000
Sale of Stock, Price Per Share	$ 5
Warrants expected term	5 years
Representative Warrants [Member]
Class of Stock [Line Items]
Number of securities called by warrant or right	75,000
Warrant exercise price (in dollars per share)	$ 6.25
Common Stock [Member]
Class of Stock [Line Items]
Common stock issued (in shares)	2,522,460	6,687,610
Warrants expected term	5 years
Outstanding Warrants [Member] | Series U Warrants [Member]
Class of Stock [Line Items]
Number of securities called by warrant or right			2,500
Class of warrant outstanding	2,141,000
Number of warrants exercised	2,141,000
Common Class A [Member]
Class of Stock [Line Items]
Common stock issued (in shares)	289,000
Common Class B [Member]
Class of Stock [Line Items]
Number of securities called by warrant or right	2,711,000

Stockholders' Equity - Common s

Stockholders' Equity - Common stock (Details) - USD ($)

3 Months Ended

4 Months Ended

9 Months Ended

12 Months Ended

Sep. 09, 2022

Aug. 02, 2022

May 16, 2022

Jan. 14, 2022

Mar. 31, 2023

Mar. 31, 2022

Apr. 18, 2023

Dec. 31, 2022

Dec. 31, 2022

Sep. 30, 2020

Dec. 31, 2022

Dec. 31, 2021

Aug. 17, 2022

Aug. 15, 2022

Jul. 14, 2022

Class of Stock [Line Items]

Sale of common stock, net

$ 895,000

$ 7,742,000

Common stock, shares authorized (in shares)

100,000,000

100,000,000

100,000,000

100,000,000

Proceeds from sale of common stock, net

$ 895,000

7,694,000

Common Stock [Member]

Class of Stock [Line Items]

Sale of common stock, net

$ 2,000

$ 6,000

Common stock issued (in shares)

2,522,460

6,687,610

Number of stock repurchased

0

Common Stock [Member] | Minimum [Member]

Class of Stock [Line Items]

Authorized amount of repurchase of stock

$ 2,000,000

2022 Purchase Agreement [Member] | Lincoln Park Capital Fund, LLC [Member] | Maximum [Member]

Class of Stock [Line Items]

Common stock, shares authorized (in shares)

57,500,000

2022 Purchase Agreement [Member] | Lincoln Park Capital Fund, LLC [Member] | Common Stock [Member]

Class of Stock [Line Items]

Maximum value of shares to be issued under agreement

$ 50,000,000

Common stock issued (in shares)

0

4,000,000

Period exercisable from the date of issuance

36 months

Number of maximum common shares can be resale

9,500,000

Initial commitment shares

492,698

492,698

Initial commitment fee paid in cash

$ 125,000

Aggregate gross proceeds from sales of common stock

$ 25,000,000

Proceeds from sale of common stock, net

$ 3,200,000

2022 Purchase Agreement [Member] | Lincoln Park Capital Fund, LLC [Member] | Common Stock [Member] | Minimum [Member]

Class of Stock [Line Items]

Percentage issuance of common stock

19.99%

2022 Purchase Agreement [Member] | Lincoln Park Capital Fund, LLC [Member] | Common Stock [Member] | Maximum [Member]

Class of Stock [Line Items]

Number of shares reserved for issuance and sale

9,007,302

2020 Purchase Agreement [Member] | Lincoln Park Capital Fund, LLC [Member] | Common Stock [Member]

Class of Stock [Line Items]

Sale of common stock, net

$ 5,685,186

Maximum value of shares to be issued under agreement

$ 25,000,000

Common stock issued (in shares)

5,665,000

Period exercisable from the date of issuance

36 months

Proceeds from sale of common stock, net

$ 7,000,000

$ 12,500,000

Remaining common stock issued and sold (in shares)

0

0

0

September 2022 Distribution Agreement [Member] | Canaccord Genuity LLC [Member] | At The Market Offering Program [Member]

Class of Stock [Line Items]

Reimburse of fee and disbursements expenses

$ 50,000

September 2022 Distribution Agreement [Member] | Canaccord Genuity LLC [Member] | Common Stock [Member] | At The Market Offering Program [Member]

Class of Stock [Line Items]

Common stock issued (in shares)

1,031,371

Proceeds from sale of common stock, net

$ 600,000

September 2022 Distribution Agreement [Member] | Canaccord Genuity LLC [Member] | Common Stock [Member] | At The Market Offering Program [Member] | Subsequent Event [Member]

Class of Stock [Line Items]

Common stock issued (in shares)

3,136,058

Proceeds from sale of common stock, net

$ 1,100,000

September 2022 Distribution Agreement [Member] | Canaccord Genuity LLC [Member] | Common Stock [Member] | Maximum [Member] | At The Market Offering Program [Member]

Class of Stock [Line Items]

Proceeds from sale of common stock, net

$ 5,000,000

Percentage of commission on gross proceeds from sale of common stock

3%

January 2022 Distribution Agreement [Member] | Canaccord Genuity LLC [Member] | Common Stock [Member]

Class of Stock [Line Items]

Common stock issued (in shares)

6,902,279

Proceeds from sale of common stock, net

$ 4,800,000

January 2022 Distribution Agreement [Member] | Canaccord Genuity LLC [Member] | Common Stock [Member] | At The Market Offering Program [Member]

Class of Stock [Line Items]

Remaining availability under financing facility

$ 0

January 2022 Distribution Agreement [Member] | Canaccord Genuity LLC [Member] | Common Stock [Member] | Maximum [Member] | At The Market Offering Program [Member]

Class of Stock [Line Items]

Proceeds from sale of common stock, net

$ 5,000,000

Stock-based Compensation - Addi

Stock-based Compensation - Additional Information (Details) $ in Millions	3 Months Ended
	Mar. 31, 2023 USD ($) shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock shares to be issued (in shares)	839,266
Stock option contractual term	10 years
Stock option vesting percentage	25%
Total unamortized compensation cost related to outstanding unvested stock options and restricted stock awards | $	$ 1.1
Weighted average period for recognition of cost	2 years 3 months 18 days
Minimum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock option vesting period	2 years
Maximum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock option vesting period	4 years
2015 Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Securities remaining and available for future issuances (in shares)	90,389
2020 Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Securities remaining and available for future issuances (in shares)	1,796,451
Common stock shares to be issued (in shares)	3,550,000

Stock-based Compensation - Stoc

Stock-based Compensation - Stock Option Activity (Details) - $ / shares	3 Months Ended	12 Months Ended
	Mar. 31, 2023	Dec. 31, 2022
Options [Roll Forward]
Balance as of December 31, 2022 (in shares)	1,175,016
Granted (in shares)	839,266
Cancelled/forfeited (in shares)	(37)
Balance as of March 31, 2023 (in shares)	2,014,245	1,175,016
Vested and expected to vest at March 31, 2023 (in shares)	1,886,155
Exercisable at March 31, 2023 (in shares)	756,581
Weighted Average Exercise Price [Roll Forward]
Balance as of December 31, 2022 (in dollars per share)	$ 4.54
Granted (in dollars per share)	0.39
Cancelled/forfeited (in dollars per share)	26,059.46
Balance as of March 31, 2023 (in dollars per share)	2.33	$ 4.54
Vested and expected to vest at March 31, 2023 (in dollars per share)	2.41
Exercisable at March 31, 2023 (in dollars per share)	$ 4.35
Weighted Average Remaining Contractual Life (years) [Roll Forward]
Balance as of March 31, 2023	8 years 7 months 24 days	8 years
Vested and expected to vest at March 31, 2023	8 years 7 months 2 days
Exercisable at March 31, 2023	7 years 8 months 8 days