Table of Contents As filed with the Securities and Exchange Commission on August 12, 2025. Registration No. 333- UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 Form S-1 REGISTRATION STATEMENT Under The Securities Act of 1933 PLUS THERAPEUTICS, INC. (Exact name of Registrant as specified in its charter) (State or other jurisdiction of incorporation or organization) Delaware 2834 33-0827593 (Primary Standard Industrial Classification Code Number) (I.R.S. Employer Identification Number ...

Core Insights - Plus Therapeutics, Inc. has received an advance payment of $1.6 million from the Cancer Prevention and Research Institute of Texas (CPRIT) as part of a $17.6 million grant for the development of targeted radiotherapeutics for leptomeningeal cancer [1][2] - The company expects to receive an additional $6 million in funding over the next 12 months, which will provide significant non-dilutive financing to support its clinical programs [2] - Plus Therapeutics is developing REYOBIQ™, a novel injectable radiotherapy aimed at treating CNS tumors, and is conducting clinical trials for recurrent glioblastoma, leptomeningeal metastases, and pediatric brain cancer [4][7] Funding and Financial Support - The funding from CPRIT, along with active grants from the NIH and DoD, reflects strong institutional support for Plus Therapeutics' clinical programs and enhances its capital position for long-term growth [2] - CPRIT is recognized as the second-largest public cancer research funder globally, with a mission to invest in cancer research and prevention initiatives in Texas [5] Clinical Development and Research - Leptomeningeal metastases (LM) occur in approximately 5% of patients with metastatic cancer, with limited effective treatment options available, highlighting the need for innovative therapies [3] - REYOBIQ is designed to deliver targeted high-dose radiation specifically to CNS tumors, potentially improving patient outcomes compared to existing therapies [4] - The CNSide diagnostic test is being developed to identify tumor cells that have metastasized to the central nervous system, which is crucial for managing patients with leptomeningeal metastases [6]

Core Insights - Plus Therapeutics is set to present the final results of its ReSPECT-LM clinical trial at the SNO/ASCO CNS Metastases Conference, highlighting the safety and efficacy of its treatment for leptomeningeal metastases [1][2] - The company will also host an educational symposium focusing on advancements in managing leptomeningeal metastases, featuring presentations from leading neuro-oncologists [3] Company Overview - Plus Therapeutics, Inc. is a clinical-stage pharmaceutical company based in Houston, Texas, specializing in targeted radiotherapeutics for central nervous system cancers [8] - The company is advancing a pipeline of product candidates, particularly in the areas of leptomeningeal metastases and recurrent glioblastoma, utilizing image-guided local beta radiation and targeted drug delivery [8] Product Information - REYOBIQ (rhenium Re186 obisbemeda) is a novel injectable radiotherapy developed by Plus Therapeutics, designed to deliver targeted high-dose radiation to CNS tumors [6] - REYOBIQ is currently being evaluated in clinical trials for recurrent glioblastoma, leptomeningeal metastases, and pediatric brain cancer, with significant funding support from various institutions [6] Industry Context - Leptomeningeal metastases are a severe complication of advanced cancer, occurring in approximately 5% of metastatic cancer patients, with limited effective treatment options available [5] - The median survival for patients with leptomeningeal metastases is typically between 2 to 6 months, underscoring the urgent need for novel therapies [5]

Core Insights - Plus Therapeutics, Inc. is advancing its ReSPECT-LM dose optimization trial for REYOBIQ, targeting leptomeningeal metastases (LM) with initial patient treatments underway [1][2] - The trial aims to identify optimal dosing regimens to maximize efficacy and safety, building on positive results from a previous Phase 1 study [3][4] - The company anticipates rapid enrollment due to the lack of FDA-approved therapies for LM and expects to complete Cohort 1 by the end of the year [2][4] Company Overview - Plus Therapeutics is a clinical-stage pharmaceutical company focused on developing targeted radiotherapeutics for central nervous system cancers [11] - The company’s lead product, REYOBIQ, is designed to deliver high-dose radiation directly to CNS tumors, potentially improving patient outcomes compared to existing therapies [8][11] - The ReSPECT-LM trial is supported by a $17.6 million grant from the Cancer Prevention & Research Institute of Texas (CPRIT), a significant funding source for cancer research [6][9] Clinical Trial Details - The ReSPECT-LM trial's primary objectives include determining the safety and tolerability of multiple REYOBIQ doses and identifying the maximum tolerated dose and minimum effective dose [3] - The previous Phase 1 trial demonstrated that a single dose of REYOBIQ could deliver an average absorbed dose of over 250 Gy, with significant tumor reduction observed in patients [4] - Data from the completed Phase 1 study will be presented at the upcoming SNO/ASCO CNS Metastases Conference in August 2025 [5] Industry Context - Leptomeningeal metastases occur in approximately 5% of patients with metastatic cancer, with limited treatment options available, highlighting the need for innovative therapies [7] - REYOBIQ is being evaluated for multiple indications, including recurrent glioblastoma and pediatric brain cancer, indicating a broad potential application in CNS oncology [8][9]

Core Viewpoint - Plus Therapeutics has initiated the ReSPECT-LM dose optimization trial for REYOBIQ™ to determine the optimal dosing schedule for treating leptomeningeal metastases, building on previous trial results and supported by a $17.6 million grant from CPRIT [1][7]. Trial Design and Objectives - The trial aims to optimize treatment dosing for maximum efficacy and safety, focusing on the safety and tolerability of multiple REYOBIQ doses administered via intraventricular catheter [2]. - Primary objectives include identifying the maximum tolerated dose and minimum effective dose for patients with LM from any primary solid tumor cancer [2]. Enrollment and Study Details - The trial will enroll up to 24 patients, evaluating REYOBIQ at a recommended Phase 2 dose of 44.1 mCi across three dosing intervals [4]. - Key cohorts include dosing intervals of 56 days, 28 days, and 14 days, with up to six patients per cohort [4]. Efficacy and Safety Data - Previous trials showed a clinical benefit rate of 76%, with 29% of patients achieving partial responses and 47% maintaining stable disease [5]. - No dose-limiting toxicities were observed in the first four cohorts, although one Grade 4 DLT occurred in each of Cohorts 5 and 6 [5]. Future Plans - The company plans to present data from the completed single-dose escalation trial at the SNO/ASCO CNS Metastases Conference in August 2025 and will request an End of Phase 1 Type B meeting with the FDA [6]. About Leptomeningeal Metastases - Leptomeningeal metastases occur in approximately 5% of patients with metastatic cancer, with median survival typically ranging from 2 to 6 months, highlighting the urgent need for effective treatment options [8]. About REYOBIQ™ - REYOBIQ™ is a novel injectable radiotherapy designed for targeted high-dose radiation in CNS tumors, with potential advantages over currently approved therapies [9]. Company Overview - Plus Therapeutics is a clinical-stage pharmaceutical company focused on developing targeted radiotherapeutics for challenging CNS cancers, with a pipeline that includes treatments for leptomeningeal metastases, recurrent glioblastoma, and pediatric brain cancer [10].

Core Insights - Plus Therapeutics has received FDA clearance for its Investigational New Drug application for REYOBIQ, aimed at treating pediatric patients with high-grade glioma and ependymoma [2][5] - The Phase 1/2a trial, named ReSPECT-PBC, is supported by a $3 million grant from the U.S. Department of Defense and will focus on determining the maximum tolerated dose and safety of REYOBIQ in children aged 6 to 21 [1][4][7] Company Overview - Plus Therapeutics is a clinical-stage pharmaceutical company based in Houston, Texas, specializing in targeted radiotherapeutics for central nervous system cancers [9] - The company is advancing a pipeline that includes treatments for recurrent glioblastoma, leptomeningeal metastases, and pediatric brain cancer [9] Trial Design and Objectives - The ReSPECT-PBC trial is a two-part, single-arm study designed to assess the safety and tolerability of REYOBIQ, with a focus on pediatric patients with rare and aggressive brain tumors [4][7] - The trial will enroll approximately 56 patients, with 24 in Phase 1a for dose escalation and 32 in Phase 2a to assess efficacy [7] Treatment Potential - REYOBIQ is designed to deliver high doses of beta radiation directly to brain tumors while minimizing damage to surrounding healthy tissue, potentially improving outcomes for patients with limited treatment options [5][8] - The targeted delivery method via convection enhanced delivery (CED) aims to bypass the blood-brain barrier, which is a significant challenge in treating CNS tumors [4][5]

Core Insights - ASP Isotopes Inc. and Isotopia Molecular Imaging Ltd. have formed a strategic agreement to secure the supply of Gadolinium-160 (Gd-160), essential for producing Terbium-161 (Tb-161), a promising medical isotope for targeted radiotherapeutics [1][2] Group 1: Partnership Details - The partnership aims to resolve supply challenges for Gd-160, facilitating the advancement of Tb-161-based therapies for various cancers, including prostate cancer and neuroendocrine tumors [2] - ASP Isotopes will utilize its proprietary Quantum Enrichment technology to provide enriched Gd-160, which is crucial for Tb-161 manufacturing [3] - The collaboration combines ASP Isotopes' large-scale isotope enrichment expertise with Isotopia's capabilities in commercial-scale medical isotope production [3] Group 2: Strategic Importance - The agreement is significant as it eliminates a major bottleneck in the development of Tb-161 therapies, supporting the growing demand for stable isotopes in the radiopharmaceutical industry [4] - Tb-161's dual mechanism of action allows for precise targeting of cancer cells while minimizing damage to healthy tissues, aligning with the oncology field's shift towards targeted radiotherapeutics [4] Group 3: Company Profiles - ASP Isotopes specializes in advanced isotope separation technologies, focusing on producing and commercializing highly enriched isotopes for healthcare and technology [5] - Isotopia is a global leader in medical isotope production, with facilities in Israel, Europe, and the U.S., and collaborates with researchers to develop novel radiopharmaceuticals [6] Group 4: Industry Outlook - This partnership positions both companies at the forefront of the radiopharmaceutical revolution, potentially expanding treatment options for cancer patients globally [7]

Core Viewpoint - Plus Therapeutics, Inc. has received a delinquency notification from Nasdaq due to the delayed filing of its Quarterly Report for the period ended March 31, 2025, but this does not immediately affect its listing status on Nasdaq [1][2]. Group 1: Compliance and Filing Status - The Company must submit a plan to regain compliance with Nasdaq Listing Rule 5250(c)(1) by July 21, 2025 [2]. - If the compliance plan is accepted, Nasdaq may grant an extension of up to 180 calendar days, allowing the Company until November 17, 2025, to regain compliance [2]. - The Company is actively working to file the Quarterly Report as soon as possible and aims to return to a normal filing schedule for the remainder of 2025 [2]. Group 2: Company Overview - Plus Therapeutics, Inc. is a clinical-stage pharmaceutical company based in Houston, Texas, focused on developing targeted radiotherapeutics for challenging cancers of the central nervous system [3]. - The Company employs a combination of image-guided local beta radiation and targeted drug delivery methods, with key programs targeting leptomeningeal metastases and recurrent glioblastoma [3]. - Plus Therapeutics has established a supply chain through strategic partnerships to support the development, manufacturing, and potential commercialization of its products [3].

Core Insights - Plus Therapeutics presented new data on its lead drug REYOBIQ™ at the Nuclear Medicine and Neurooncology Conference, highlighting its potential in treating Leptomeningeal Metastases (LM) [1][2] Group 1: REYOBIQ™ Data Presentation - The data indicates safety and clinical benefits of REYOBIQ in patients with LM, with multiple doses administered under compassionate use contributing to long-term survival [2] - The study titled "Rhenium Obisbemeda (REYOBIQ) in Leptomeningeal Metastases" provides additional insights from the completed Phase 1 ReSPECT-LM dose escalation trial [2] Group 2: Leptomeningeal Metastases Overview - LM is a rare but severe complication of cancer, affecting approximately 5% of cancer patients, with a notably low 1-year survival rate of 7% and a 2-year survival rate of 3% [4] - The incidence of LM is increasing, partly due to longer cancer patient lifespans and the ineffectiveness of standard chemotherapies in reaching sufficient concentrations in the cerebrospinal fluid [4] Group 3: REYOBIQ™ Mechanism and Efficacy - REYOBIQ™ is designed to deliver targeted high-dose radiation to CNS tumors, potentially improving outcomes compared to existing therapies [5] - The study reported a dose-dependent increase in the average absorbed dose to the cranial and spinal subarachnoid space, reaching 253 Gy in Cohort 5 [6] - Clinical benefit rates were high, with 76% of patients showing complete response, partial response, or stable disease, and 87% demonstrating clinical response based on physician evaluation [6] Group 4: Clinical Trials and Funding - REYOBIQ™ is being evaluated in clinical trials for recurrent glioblastoma and leptomeningeal metastases, with funding support from the National Cancer Institute and a $17.6 million grant from the Cancer Prevention & Research Institute of Texas [7]

HOUSTON, March 10, 2025 (GLOBE NEWSWIRE) -- Plus Therapeutics, Inc. (Nasdaq: PSTV) (the “Company” or “Plus Therapeutics”), a clinical-stage pharmaceutical company developing targeted radiotherapeutics with advanced platform technologies for central nervous system cancers, today announced that on March 7, 2025 the Company received confirmation from Nasdaq that the Company has regained compliance with Nasdaq’s minimum stockholders’ equity requirement. The Company’s common stock will continue to be listed and ...