CTNI-67. PHASE 1 MULTICENTER STUDY OF MULTIPLE DOSES OF RHENIUM (186RE) OBISBEMEDA (REYOBIQ) FOR LEPTOMENINGEAL METASTASES: RATIONALE, DESIGN, AND PRELIMINARY COHORT 1 DATA

Abstract Leptomeningeal metastases (LM) are a devastating complication of solid tumors with limited treatment options and poor survival outcomes. Reyobiq, a nanoliposome-encapsulated beta-emitting radionuclide, offers focused radiation delivery to the cerebrospinal fluid (CSF) with a 2 mm beta particle path length and gamma emissions for imaging. The recently completed ReSPECT-LM phase 1 trial (NCT05034497) showed a single dose of Reyobiq was well-tolerated up to a MTD of 66mCi, a recommended phase 2 dose of 44.1 mCi, and delivering absorbed doses >300 Gy. Doses ranged from 6.6mCi in cohort 1 through 75mCi in cohort 6. No dose limiting toxicity (DLT) was observed in cohorts 1-4, with 1 DLT in each cohort 5 and 6 of grade 4 thrombocytopenia. Neuroimaging, CSF circulating tumor cell counts, and clinical assessment data demonstrated clinical benefit rates (CR+PR+SD) of 76%, 93%, and 87% up to 112 days, respectively. Given the success of the single dose study, we have initiated a multicenter, open-label Phase 1 study to evaluate the safety and efficacy of multiple Reyobiq doses (13.2 mCi) administered via intraventricular catheter in patients with LM from any primary solid tumor. The study aims to identify the maximum tolerated/feasible dose (MTD/MFD) across varying dosing intervals: Cohort 1 (56 days, 3 doses), Cohort 2 (28 days, 3 doses), and Cohort 3 (14 days, 3 or 6 doses). Primary endpoints include safety and DLT incidence; secondary endpoints include objective response rate, progression-free survival, overall survival, and pharmacokinetics. Cohort 1 data, including safety and preliminary efficacy, will be presented. This study builds on single-dose findings, aiming to optimize dosing regimens to improve outcomes for LM patients, addressing an unmet clinical need with a novel radiotherapeutic approach.