Plus Therapeutics’ REYOBIQ Delivers 76% Response in Early Brain-Metastasis Trial

Plus Therapeutics said its experimental radiotherapeutic REYOBIQ produced strong early signals of efficacy in patients with leptomeningeal metastases, a rare and often fatal complication of advanced cancer. In a Phase 1 single-dose escalation study involving 29 subjects, the injectable rhenium-186 formulation achieved a 76% radiographic response rate and an 87% clinical response rate through day 112. Median overall survival among the first four dose cohorts reached nine months—more than double the two-to-six-month range typically reported in medical literature. Cerebrospinal-fluid assays showed a 100% reduction in circulating tumor cells at day 28, and five of seven patients with an >80% reduction survived at least one year. Safety was manageable, with no dose-limiting toxicities observed in the lower four cohorts and single cases of grade-4 cytopenia at higher doses. Investigators selected 44.1 mCi as the recommended Phase 2 single dose, citing a favourable balance between efficacy and tolerability. The findings were presented on 18 August at the SNO/ASCO CNS Metastases Conference in Baltimore. Plus Therapeutics said the data support ongoing dosing-optimization work and lay the groundwork for a potential registrational trial of REYOBIQ in leptomeningeal metastases.