A Phase I/II, Open-label, Multi-center Study of [225Ac]Ac-PSMA-R2 in Men With PSMA-positive Prostate Cancer With or Without Prior 177Lu-PSMA Radioligand Therapy.

The purpose of the study is to characterize the safety, tolerability, pharmacokinetics (PK), and anti-tumor activity of 225Ac-PSMA-R2 in male adult participants with metastatic castration-resistant prostate cancer (mCRPC) previously treated with androgen receptor pathway inhibitors in post-177Lu and pre-177Lu settings.

This is an open label, phase I/II, multi-center study which contains two treatment groups (Group 1 and Group 2). Each group has a dose escalation part, once the Maximum Tolerated Dose/Recommended Dose for Expansion (MTD/RDE) is determined in each of the dose escalation parts, the study will continue with an expansion part in the respective group.

The dose escalation parts will establish the MTD/RDE of the 225Ac-PSMA-R2 guided by the well-established Bayesian Logistic Regression Model (BLRM) method. The adaptive BLRM will be guided by the Escalation with Overdose Control (EWOC) principle to control the risk of DLT in future participants on study. Dose escalation decisions will be performed by the Investigators and Novartis during dose escalation meetings (DEMs) based on safety and tolerability information (BLRM summaries of DLT risk) along with PK and preliminary efficacy information.

The dose expansion parts will assess the anti-tumor activity (Overall Response Rate (ORR) by Prostate Cancer Working Group 3 (PCWG3) modified RECIST 1.1 and Prostate Specific Antigen 50 (PSA50) response rate) as well as further assess the safety, tolerability, and PK of 225Ac-PSMA-R2.