Plus Therapeutics Announces Peer-Reviewed Publication in Nature Communications Highlighting Promising Phase 1 Results for Rhenium (186Re) Obisbemeda in Glioblastoma

Rhea-AI Summary

Plus Therapeutics (PSTV) has published promising Phase 1 clinical trial results for Rhenium (186Re) Obisbemeda in treating glioblastoma (GBM) in Nature Communications. The study demonstrated significant survival benefits:

Key findings from the trial of 21 patients include:

• Median overall survival of 11 months, exceeding the standard care's 8-month survival rate
• Patients receiving >100 Gy achieved 17-month median survival, compared to 6 months for those receiving <100 Gy
• Treatment doses up to 22.3 mCi showed no dose-limiting toxicity
• Achieved tumor radiation doses up to 739.5 Gy without significant toxicity

The company is currently enrolling patients in its ReSPECT-GBM Phase 2 trial at leading medical centers.

Positive

• Phase 1 trial showed 17-month median survival for high-dose patients vs 8-month standard care
• No dose-limiting toxicity observed in Phase 1
• Successfully achieved high radiation doses (739.5 Gy) without significant toxicity
• Results published in prestigious Nature Communications journal
• Phase 2 trial actively enrolling patients

Negative

• Low-dose patients (<100 Gy) showed only 6-month median survival

Insights

Oncology Research Specialist

Plus Therapeutics' published Phase 1 results for Rhenium (186Re) Obisbemeda represent a significant clinical milestone in glioblastoma treatment. The peer-reviewed Nature Communications publication validates their approach and strengthens credibility with the scientific community.

The most compelling data point is the median overall survival of 17 months for patients receiving >100 Gy dosage—more than double the 8-month survival with standard of care. This substantial survival advantage in recurrent glioblastoma, a notoriously treatment-resistant cancer with poor outcomes, cannot be overstated.

The demonstrated safety profile is particularly noteworthy. The ability to deliver extremely high radiation doses (up to 739.5 Gy) directly to tumors without dose-limiting toxicities represents a potential breakthrough in targeted radiotherapy. Conventional external beam radiation therapy cannot achieve these radiation levels without significant collateral damage.

The dose-response relationship observed—where survival strongly correlated with radiation dose and tumor coverage—provides a clear path for optimizing treatment parameters in the ongoing Phase 2 trial. This creates a rational framework for trial design and potential regulatory discussions.

With the ReSPECT-GBM Phase 2 trial actively enrolling at major medical centers, Plus Therapeutics has momentum toward potential regulatory consideration if these impressive early results are replicated in a larger patient population.

Biotechnology Investment Analyst

This Nature Communications publication represents a important validation milestone for Plus Therapeutics' lead program. For a company with a micro-cap valuation of ~$2 million, securing high-profile peer validation significantly strengthens their scientific positioning and potential partnership opportunities.

The demonstrated 17-month median survival in the >100 Gy cohort provides a clear efficacy signal that justifies the ongoing Phase 2 investment. This positions the ReSPECT-GBM program as potentially paradigm-shifting in a therapeutic area with minimal innovation over the past decade.

From a mechanism perspective, the ability to deliver targeted radiation at doses up to 739.5 Gy without significant toxicity represents a technological differentiation with possible applications beyond glioblastoma. This suggests potential platform value exceeding single-indication expectations.

The established dose-response relationship provides valuable de-risking for the Phase 2 program by establishing clear dosing parameters. This correlation between radiation dose, tumor coverage, and survival outcomes creates a rational framework for efficacy expectations.

While impressive, these results require context—the 21-patient sample size is typical for Phase 1 but will need confirmation in the larger Phase 2 cohort. The company's execution of the Phase 2 program across multiple medical centers demonstrates operational capability necessary to advance toward potential regulatory discussions if positive results continue.

Rhenium (¹⁸⁶Re) Obisbemeda demonstrates safety, response, and potential efficacy for glioblastoma (GBM) patients

Patients receiving >100 Gy of Rhenium (¹⁸⁶Re) Obisbemeda achieved a median overall survival of 17 months, more than double the 8-month median overall survival with standard of care

HOUSTON, March 07, 2025 (GLOBE NEWSWIRE) -- Plus Therapeutics, Inc. (Nasdaq: PSTV) (“Plus” or the “Company”), a clinical-stage pharmaceutical company developing targeted radiotherapeutics with advanced platform technologies for central nervous system (CNS) cancers, today announces the publication of results in a peer-reviewed manuscript titled, "Treatment of Recurrent Glioma by Rhenium (¹⁸⁶Re) Obisbemeda (¹⁸⁶RNL): a Phase 1 clinical trial" in the peer-reviewed medical journal Nature Communications.

“Peer-reviewed publication of our Phase 1 glioma data in a prestigious, high-impact factor journal is substantial validation for this important clinical program,” said Marc H. Hedrick, M.D., Plus Therapeutics President and Chief Executive Officer. “Based largely on this data, our ReSPECT-GBM Phase 2 trial is currently enrolling patients at leading medical centers, bringing us closer to delivering a much-needed treatment option for this devastating disease.”

Key highlights from the publication:

• Twenty-one patients were treated with doses up to 22.3 mCi of Rhenium (¹⁸⁶Re) Obisbemeda
• No dose-limiting toxicity was observed, and most adverse events were unrelated to the study treatment
• Median overall survival (OS) was 11 months, surpassing the standard of care for recurrent glioblastoma, which is approximately 8 months
• Median OS was strongly correlated with radiation absorbed dose to the tumor and the percentage of tumor treated
• Patients receiving >100 Gy (n=12) had a median OS of 17 months, compared to 6 months for those receiving <100 Gy (n=9) (p=0.001)
• Absorbed radiation doses to the tumor were as high as 739.5 Gy and were delivered without significant toxicity, exceeding levels achievable with external beam radiation therapy

The full manuscript can be accessed here.

The ReSPECT-GBM trial is actively enrolling patients; additional information about the ReSPECT-GBM trial can be found here.

About Recurrent Glioblastoma (GBM)

GBM affects approximately 15,000 patients annually in the U.S. and is the most common and lethal form of brain cancer. The average life expectancy with GBM is less than 24 months, with a one-year survival rate of 40% and a five-year survival rate of around 5%. There is no clear standard of care for recurrent GBM and the few currently approved treatments provide only marginal survival benefit and are associated with significant side effects, which limit dosing and prolonged use. Approximately 90% of patients experience GBM tumor recurrence at or near the original tumor location, yet there are no FDA-approved treatments in the recurrent or progressive setting that can significantly extend a patient’s life.

About Rhenium (¹⁸⁶Re) Obisbemeda

Rhenium (¹⁸⁶Re) Obisbemeda is a novel injectable radiotherapy specifically formulated to deliver direct targeted high dose radiation in CNS tumors in a safe, effective, and convenient manner to optimize patient outcomes. Rhenium (¹⁸⁶Re) Obisbemeda has the potential to reduce off target risks and improve outcomes for CNS cancer patients, versus currently approved therapies, with a more targeted and potent radiation dose. Rhenium-186 is an ideal radioisotope for CNS therapeutic applications due to its short half-life, beta energy for destroying cancerous tissue, and gamma energy for real-time imaging. Rhenium (¹⁸⁶Re) Obisbemeda is being evaluated for the treatment of recurrent glioblastoma and leptomeningeal metastases in the ReSPECT-GBM and ReSPECT-LM clinical trials. ReSPECT-GBM is supported by an award from the National Cancer Institute (NCI), part of the U.S. National Institutes of Health (NIH), and ReSPECT-LM is funded by a three-year $17.6M grant by the Cancer Prevention & Research Institute of Texas (CPRIT).

About Convection-Enhanced Delivery

Convection Enhanced Delivery (CED) is a therapeutic strategy that was developed to facilitate targeted delivery of pharmaceuticals to the brain. The CED procedure involves a minimally invasive surgical exposure of the brain, followed by placement of small diameter catheters directly into the brain tumor.

About Plus Therapeutics
Plus Therapeutics, Inc. is a clinical-stage pharmaceutical company developing targeted radiotherapeutics for difficult-to-treat cancers of the central nervous system with the potential to enhance clinical outcomes for patients. Combining image-guided local beta radiation and targeted drug delivery approaches, the Company is advancing a pipeline of product candidates with lead programs in recurrent glioblastoma (GBM) and leptomeningeal metastases (LM). The Company has built a supply chain through strategic partnerships that enable the development, manufacturing, and future potential commercialization of its products. Plus Therapeutics is led by an experienced and dedicated leadership team and has operations in key cancer clinical development hubs including Austin and San Antonio, Texas. For more information, visit https://plustherapeutics.com/.

Cautionary Statement Regarding Forward-Looking Statements
This presentation contains statements that may be deemed “forward-looking statements” within the meaning of U.S. securities laws, including statements regarding clinical trials, expected operations and upcoming developments. All statements in this press release other than statements of historical fact are forward-looking statements. These forward-looking statements may be identified by future verbs, as well as terms such as “potential,” “anticipating,” “planning” and similar expressions or the negatives thereof. Such statements are based upon certain assumptions and assessments made by management in light of their experience and their perception of historical trends, current conditions, expected future developments and other factors they believe to be appropriate. These statements include, without limitation, statements regarding the following: the potential promise of Rhenium (¹⁸⁶Re) Obisbemeda including the ability of Rhenium (¹⁸⁶Re) Obisbemeda to safely and effectively deliver radiation directly to the tumor at high doses; expectations as to the Company’s future performance including the next steps in developing the Company’s current assets; the Company’s clinical trials including statements regarding the timing and characteristics of the ReSPECT-GBM, ReSPECT-LM and ReSPECT-PBC, clinical trials; possible negative effects of Rhenium (¹⁸⁶Re) Obisbemeda; the continued evaluation of Rhenium (¹⁸⁶Re) Obisbemeda including through evaluations in additional patient cohorts; the intended functions of the Company’s platform and expected benefits from such functions; and the development, utility and potential of the CNSide leptomeningeal metastases diagnostic test.

The forward-looking statements included in this press release could differ materially from those expressed or implied by these forward-looking statements because of risks, uncertainties, and other factors that include, but are not limited to, the following: the early stage of the Company’s product candidates and therapies, the results of the Company’s research and development activities, including uncertainties relating to the clinical trials of its product candidates and therapies; the Company’s liquidity and capital resources and its ability to raise additional cash, the outcome of the Company’s partnering/licensing efforts, risks associated with laws or regulatory requirements applicable to it, market conditions, product performance, litigation or potential litigation, and competition within the cancer diagnostics and therapeutics field, ability to develop and protect proprietary intellectual property or obtain licenses to intellectual property developed by others on commercially reasonable and competitive terms, and material security breach or cybersecurity attack affecting the Company’s operations or property. This list of risks, uncertainties, and other factors is not complete. Plus Therapeutics discusses some of these matters more fully, as well as certain risk factors that could affect Plus Therapeutics’ business, financial condition, results of operations, and prospects, in its reports filed with the SEC, including Plus Therapeutics’ annual report on Form 10-K for the fiscal year ended December 31, 2023, quarterly reports on Form 10-Q, and current reports on Form 8-K. These filings are available for review through the SEC’s website at www.sec.gov. Any or all forward-looking statements Plus Therapeutics makes may turn out to be wrong and can be affected by inaccurate assumptions Plus Therapeutics might make or by known or unknown risks, uncertainties, and other factors, including those identified in this press release. Accordingly, you should not place undue reliance on the forward-looking statements made in this press release, which speak only as of its date. The Company assumes no responsibility to update or revise any forward-looking statements to reflect events, trends or circumstances after the date they are made unless the Company has an obligation under U.S. federal securities laws to do so.

Investor Contact
Charles Y. Huang, MBA
Director of Capital Markets and Investor Relations
Office: (202)-209-5751 | Direct (301)-728-7222
chuang@plustherapeutics.com

FAQ

What were the survival rates in PSTV's Phase 1 trial for Rhenium Obisbemeda in glioblastoma?

Patients receiving >100 Gy achieved 17-month median survival, while those receiving <100 Gy had 6-month survival. Overall median survival was 11 months, surpassing the standard care's 8-month rate.

How safe was Rhenium Obisbemeda in PSTV's Phase 1 glioblastoma trial?

The treatment showed no dose-limiting toxicity up to 22.3 mCi, with most adverse events unrelated to treatment. It achieved high radiation doses (up to 739.5 Gy) without significant toxicity.

What is the current status of PSTV's ReSPECT-GBM clinical trial?

Following successful Phase 1 results, the ReSPECT-GBM Phase 2 trial is actively enrolling patients at leading medical centers.

How does PSTV's Rhenium Obisbemeda compare to standard treatment for recurrent glioblastoma?

The treatment achieved 11-month median overall survival, exceeding the standard of care's approximately 8-month survival rate for recurrent glioblastoma.