Phase I/II Trial of Pembrolizumab and Androgen-receptor Inhibitor With or Without 225Ac-J591 for Progressive Metastatic Castration Resistant Prostate Cancer

Alpha-emitter Actinium-225 conjugated to the anti-PSMA antibody J591.

Pembrolizumab will be administered intravenously, 400mg every 6 weeks. Patients may receive maximum 18 cycles of therapy, approximately 2 years.

Patients will receive an oral androgen receptor inhibitor (ARI). Examples include enzalutamide, apalutamide, darolutamide. Dosing will be the standard dosing, as described by the package insert.

\[185 ±74 MBq or 5 ±2 mCi\] intravenous during screening and 12 weeks. Imaging agent for PSMA PET/CT.