Plus Therapeutics has announced promising results from a Phase 1 clinical trial of Rhenium (186Re) Obisbemeda for recurrent glioblastoma (GBM), with findings published in the prestigious journal Nature Communications.
The study demonstrated that patients receiving higher radiation doses of the targeted radiotherapeutic achieved survival rates more than double the current standard of care, potentially representing a significant advancement for a devastating disease with few effective treatment options.
Trial Results Show Dose-Dependent Survival Benefits
The Phase 1 trial enrolled 21 patients who received doses up to 22.3 mCi of Rhenium (186Re) Obisbemeda delivered directly to brain tumors using convection-enhanced delivery (CED). This minimally invasive approach allows for precise placement of the therapeutic agent directly into the tumor site.
Key findings revealed a strong correlation between radiation absorbed dose and patient outcomes:
- Patients receiving >100 Gy (n=12) achieved a median overall survival of 17 months
- Patients receiving <100 Gy (n=9) had a median overall survival of 6 months (p=0.001)
- The overall median survival across all patients was 11 months, compared to approximately 8 months with standard care for recurrent GBM
"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."
Exceptional Safety Profile Despite High Radiation Doses
Perhaps most remarkable was the safety profile observed in the trial. No dose-limiting toxicities were reported, and most adverse events were unrelated to the study treatment. This safety profile was maintained even as absorbed radiation doses to tumors reached as high as 739.5 Gy—far exceeding levels achievable with conventional external beam radiation therapy.
The ability to deliver such high radiation doses directly to the tumor while sparing surrounding healthy tissue represents a potential paradigm shift in GBM treatment, where radiation toxicity typically limits therapeutic efficacy.
Addressing an Urgent Unmet Need
GBM affects approximately 15,000 patients annually in the United States and remains the most common and lethal form of brain cancer. Current treatment options provide limited benefit, with average life expectancy less than 24 months and a five-year survival rate of only about 5%.
The challenge is particularly acute for recurrent GBM, where approximately 90% of patients experience tumor recurrence at or near the original tumor location. Currently, there are no FDA-approved treatments in the recurrent setting that significantly extend patient survival.
Innovative Approach to CNS Cancer Treatment
Rhenium (186Re) Obisbemeda represents a novel approach to treating central nervous system (CNS) cancers. The therapy combines several advantageous properties:
- Rhenium-186's short half-life minimizes prolonged radiation exposure
- Beta energy effectively destroys cancerous tissue
- Gamma energy allows for real-time imaging during treatment
- Convection-enhanced delivery enables precise targeting
The therapy is currently being evaluated in two clinical programs: the ReSPECT-GBM trial for recurrent glioblastoma and the ReSPECT-LM trial for leptomeningeal metastases. The GBM program is supported by the National Cancer Institute, while the leptomeningeal metastases program is funded by a $17.6 million grant from the Cancer Prevention & Research Institute of Texas.
Path Forward
Based on these encouraging Phase 1 results, Plus Therapeutics is actively enrolling patients in its Phase 2 ReSPECT-GBM trial at multiple leading medical centers. The company has established strategic partnerships to build a supply chain that enables development, manufacturing, and potential future commercialization.
For patients with recurrent GBM who currently face extremely limited options, these results represent a potential new avenue of treatment that could significantly extend survival while maintaining quality of life—a critical consideration in this devastating disease.
