Fractionated and Multiple Dose 225Ac-J591 for Progressive mCRPC

This clinical trial is for men with progressive metastatic castration resistant prostate cancer. The purpose of this study is to find the highest dose level of the study drug, 225Ac-J591, that can be given without severe side effects. The research study is being done because the standard treatments for prostate cancer that has spread beyond the prostate gland are intended to minimize the adverse effects of the disease. These treatments, however, are not curative. Patients who choose to participate in this study will have a screening visit to determine whether or not they are eligible to participate in the study. There are two different regimens for men with progressive mCRPC with and without prior 177Lu-PSMA-RL treatment. The fractionated dose regimen is a single cycle of study drug administered on Day 1 and Day 15. The dose-limiting toxicity assessment period is 8 weeks for the fractionated dose regimen (starting from Cycle 1 Day 1). The multiple dose regimen is a single dose of 225Ac-J591 per cycle, with each cycle administered every 6 weeks up to 4 cycles. The dose-limiting toxicity assessment period is up to 9 weeks past the 2nd dose of 225Ac-J591. Following treatment, short-term follow up is planned until radiographic progression, expected to be 6 months. The study medication is called 225Ac-J591, and is administered as a single fractionated cycle day 1 and day 15 in the fractionated dose regimen and as a single dose per cycle repeated every 6 weeks in the multiple dose regimen. Upon completion of investigational treatment with 225Ac-J591, participants will undergo 68Ga-PSMA-HBED-CC injection and same day PET/CT to document treatment response. 68Ga-PSMA-HBED-CC is comprised of gallium-68, which is a positron-emitting radionuclide linked to PSMA-HBED-CC (aka PSMA11), which is a small molecule targeting PSMA. 68Ga-PSMA-HBED-CC will be administered intravenously prior to PET/CT at screening and at follow up imaging x2. Subsequent survival data and additional treatment(s) information will be captured from their routine standard of care (SOC) visits. During the other study visits, participants will undergo routine tests and procedures, such as physical examinations, and blood tests. Some blood tests will be done for research purposes only. After completion of therapy, participants may be contacted on a periodic basis to see how they are doing.