Phase I/II Study of [225Ac]Ac-PSMA-R2 in PSMA-positive Prostate Cancer, With/Without Prior 177Lu-PSMA RLT

First in human (FIH) phase I/II study of 225Ac-PSMA-R2 in PSMA-positive metastatic prostate cancer across three groups: post-177Lu mCRPC, pre-177Lu mCRPC, and 177Lu-naïve mHSPC, evaluating Q6W/Q4W dosing. Dose escalation will enroll \~18-22 participants per group/schedule to define MTD/RDE, guided by safety, tolerability, PK/dosimetry, and preliminary anti-tumor activity, with possible expansion based on benefit-risk. Enrollment and dosing for all participants in Group 1, Group 2, and Group 3 have been completed. Further enrollment has been halted, and no additional dose escalation cohorts or Phase 2 dose expansion cohorts will be opened; enrollment in this study is now considered complete. The decision to halt enrolment was not driven by any safety concerns identified in the study to date, but rather by a lowered expectation of benefit. Accordingly, the study will not proceed to Phase 2, and a recommended Phase 2 dose was not established