Plus Therapeutics reports interim updates from two ReSPECT trials

Plus Therapeutics reported positive interim updates from the ReSPECT-GBM and ReSPECT-LM clinical studies evaluating the Company’s lead radiotherapeutic, rhenium obisbemeda, for the treatment of recurrent glioblastoma and leptomeningeal metastases at the Society of Nuclear Medicine & Molecular Imaging, SNMMI, Annual Meeting, which took place June 24-27, 2023 in Chicago, Illinois. An oral presentation titled, Safety and Feasibility Results from a Phase 1/2 Clinical Trial of 186RNL Obisbemeda in Recurrent Glioma: The ReSPECT-GBM Trial (P988), brief highlights include: Data from 21 patients in the Phase 1 trial used to support the recommended Phase 2 trial dose for patients with tumor volumes less than or equal to20 mL was presented. A single dose of rhenium obisbemeda was generally safe and well-tolerated, with no dose-limiting toxicities and minimal systemic radiation exposure. The data demonstrates efficacy signals in a prognostically unfavorable patient population. The median overall survival in all 21 patients was 11 months or a 38% increase in OS versus a median OS of approximately 8 months for standard of care in rGBM. Median OS in patients receiving greater than100 Gy of absorbed radiation dose was 76 weeks versus 22 weeks for those receiving less than100 Gy. Increased absorbed radiation dose and percent tumor volume treated correlates with improvement in overall survival, specifically: For each 100 Gy increase of Total Dose in Distribution Volume, the risk of death decreases by 45.6%. For each 10% increase in the Ratio of Treated to Total Tumor Volume, the risk of death decreases by 66.9%. A poster presentation titled, Preliminary Clinical Data in The Phase 1/2a Dose Escalation Trial of 186RNL Obisbemeda in Leptomeningeal Metastases: The ReSPECT-LM Trial, includes data that showed: Interim results from 10 patients in the Phase 1 trial show a single treatment with rhenium obisbemeda decreased cerebrospinal fluid tumor cell count and was well-tolerated in patients with LM. Rhenium obisbemeda doses administered through an intraventricular catheter showed prompt, complete and durable distribution throughout the CSF through Day 7. A single rhenium obisbemeda administered dose between 6.6 mCi and 26.4 mCi achieved absorbed doses of up to 88.98 Gy to the ventricles and cranial subarachnoid space. No dose limiting toxicities were observed and safety observations were generally minor and resolved. Phase 1/Part B, for continued dose escalation, will open following review by the U.S. Food and Drug Administration, and repeated dosing will be explored. An expansion in Cohort 3 is currently enrolling eligible patients.