Plus Therapeutics Shares Positive Interim ReSPECT-LM Phase 1 Data for Leptomeningeal Metastases at 2024 SNO/ASCO CNS Metastases Conference

Plus Therapeutics, Inc., a clinical-stage pharmaceutical company listed on Nasdaq under the ticker PSTV, recently presented promising data from its ReSPECT-LM clinical trial involving Rhenium (186Re) Obisbemeda during the 2024 Society for Neuro-Oncology (SNO) and American Society for Clinical Oncology (ASCO) CNS Metastases Conference held in Denver, Colorado. The trial focuses on treating leptomeningeal disease (LM) with intrathecal doses of the radiotherapeutic agent.

The presentation, led by Dr. Andrew Brenner, detailed the safety and efficacy outcomes of the Phase 1 dose-escalation study. Involving 16 patients across four cohorts, the trial is now recruiting for its fifth cohort. The primary cancers among participants included breast cancer (8 patients), lung cancer (4 patients), and a mixed group of other cancers (4 patients).

Key findings from Cohorts 1 through 4 demonstrate that:
- No dose-limiting toxicities were identified, indicating that the maximum tolerated dose or maximum feasible dose has not yet been reached.
- A linear increase in absorbed radiation dose was observed in the spinal fluid and ventricles, as well as the cranial subarachnoid space as the dosage escalated.
- For Cohort 4, the mean average absorbed radiation dose to the ventricles and cranial subarachnoid space was significantly higher (156 Gy) compared to the spleen (1 Gy).
- Most adverse events reported were mild or moderate, and not related or unlikely linked to the study drug.
- There was an average reduction of circulating tumor cells (CTCs) in the cerebrospinal fluid by 53% after 28 days post-treatment in Cohorts 1-3.
- Median overall survival for patients in the first four cohorts was 12 months, with half of the participants still alive at the time of analysis.

Dr. Brenner highlighted the encouraging results, noting the feasibility, safety, and apparent efficacy in reducing circulating tumor cells, alongside delivering high absorbed radiation doses contributing to the median overall survival of 12 months. This is considered a significant outcome given the challenging nature of treating LM.

The U.S. Food and Drug Administration (FDA) has recognized the potential of Rhenium (186Re) Obisbemeda by granting it Fast Track designation for LM treatment. Additionally, the FDA has awarded Orphan Drug designation for the treatment of LM in breast cancer patients.

Leptomeningeal metastases involve the spread of cancer to the cerebrospinal fluid and the membranes surrounding the brain and spinal cord. This condition is rare but severe, often linked with breast cancer, lung cancer, gastrointestinal cancers, and melanoma. With a growing incidence, LM typically results in low survival rates, making the development of effective treatments critical.

Rhenium (186Re) Obisbemeda is an innovative injectable radiotherapy designed to deliver high doses of radiation directly to CNS tumors, while minimizing off-target effects. This targeted approach is under evaluation for recurrent glioblastoma and leptomeningeal metastases in the ReSPECT-GBM and ReSPECT-LM clinical trials. The trials are funded through significant grants, including a $17.6 million award from the Cancer Prevention & Research Institute of Texas (CPRIT).

Plus Therapeutics, headquartered in Texas, is focused on developing advanced radiotherapeutics for treating challenging CNS cancers. The company leverages image-guided local beta radiation and strategic partnerships to advance its promising pipeline, with a goal of improving clinical outcomes for patients.