Plus Therapeutics Completes Dosing in Cohort 4 of ReSPECT-LM Phase 1 Clinical Trial of Rhenium (¹⁸⁶Re) Obisbemeda in Leptomeningeal Metastases

Plus Therapeutics, a clinical-stage pharmaceutical company, has announced a significant milestone in its ReSPECT-LM Phase 1/2a dose escalation clinical trial. The company has successfully completed dosing in Cohort 4 of the trial, which is evaluating the efficacy of rhenium (186Re) obisbemeda in treating leptomeningeal metastases (LM) from solid tumors. This achievement marks the completion of the first of four planned cohorts in Part B of the trial.

The rapid enrollment in the ReSPECT-LM trial can be attributed to several factors, including the increasing number of patients diagnosed with LM, the lack of effective treatment options, and growing enthusiasm for the trial. Plus Therapeutics’ President and CEO, Marc H. Hedrick, MD, expressed confidence in the trial’s progress and highlighted the company’s commitment to addressing the urgent need for better therapeutic options for LM patients.

The ReSPECT-LM trial has shown promising results in its Phase 1, Part A, with an average 53% reduction in CNSide tumor cell counts observed at Day 28 post-treatment in ten patients who received a single administration of rhenium (186Re) obisbemeda. Encouraged by these findings, the FDA has approved continued dose escalation and expansion into Part B of the trial.

Importantly, there have been no observed dose-limiting toxicities with radiation doses of up to 44.10 millicuries, further supporting the safety profile of rhenium (186Re) obisbemeda. The company plans to initiate dosing in Cohort 5 in the current quarter, pending approval from the Data Safety Monitoring Board (DSMB).

Plus Therapeutics is also set to provide significant updates on both the ReSPECT-LM and ReSPECT-GBM trials at the upcoming Society for Neuro-Oncology (SNO) Annual Meeting, scheduled for November 15-19, 2023. These updates will shed light on the latest advancements in the company’s efforts to develop targeted radiotherapeutics for central nervous system (CNS) cancers.

In addition to the progress made in the ReSPECT-LM trial, Plus Therapeutics has completed the transfer of proprietary materials, protocols, and equipment from Biocept. This transfer is part of an expanded agreement for CNSide, a cerebrospinal fluid (CSF)-based tumor cell capture and enumeration assay used in the ReSPECT-LM clinical trial. The acquired materials and protocols will ensure Plus Therapeutics’ continued access to the CNSide assay, which has the potential to serve as an LM diagnostic assay, a surrogate endpoint in clinical trials for CNS cancers, and a disease monitoring biomarker assay for patients undergoing radiotherapy for LM.

The positive momentum of Plus Therapeutics’ clinical trials is supported by the FDA’s Fast Track designation for rhenium (186Re) obisbemeda in the treatment of LM. Furthermore, the ReSPECT-LM Phase 1 program is partially funded by a $17.6 million grant from the Cancer Prevention & Research Institute of Texas (CPRIT).

With the completion of Cohort 4 in the ReSPECT-LM trial, Plus Therapeutics is making significant strides in its mission to develop targeted radiotherapeutics for CNS cancers. The company’s dedication to advancing innovative therapies and its strategic partnerships position it well to make a meaningful impact on the lives of LM patients. Further updates on the trials and the potential of rhenium (186Re) obisbemeda are eagerly anticipated, with additional data releases expected in 2024.