This is a three-part study evaluating the safety and efficacy of a PSMA-directed radioantibody (rosopatamab tetraxetan, conjugated to either In-111 or Ac-225). Part 1 will consist of one administration of In-111-rosopatamab tetraxetan to characterize the biodistribution of the radioantibody to target organs and prostate cancer lesions. Participants then will be enrolled into either Part 2 (Dose Optimization) or Part 3 (Dose Escalation and Expansion) depending on their prior treatment history. Participants qualifying for Part 2 will be randomized to receive Ac-225 rosopatamab tetraxetan in a single fractionated cycle (dose administration on Day 1 and Day 15) at either 45 or 60 kBq/Kg. Participants qualifying for Part 3 must have received prior Lu-177-PSMA-radioligand therapy and will receive Ac-225 rosopatamab tetraxetan in a single fractionated cycle at 45, 55, or 60 kBq/Kg. Dose limiting toxicities (DLTs) will be monitored in Part 3 to determine the recommended phase 2 dose (RP2D), and the study may enroll additional participants to be treated with the RP2D dose level. Participants enrolled into any part will attend study visits which will include blood samples, electrocardiogram (ECG), radiographic imaging, and physical examinations along with other assessments.
Serum PSA progression consisting of two consecutive increases in PSA measured at least 1 week apart. The minimal study baseline value is 2.0 ng/mL
Soft tissue progression defined as a ≥20% increase in the sum of the diameter (short axis for nodal lesions and long axis for non-nodal lesions) of all target lesions based on the smallest sum of the diameter since the previous treatment was started or the appearance of one or more new lesions by CT/magnetic resonance imaging (MRI)
Progression of bone disease defined by PCWG3 as evaluable disease or new bone lesions by bone scan
Identification of new soft tissue or bone lesions on PSMA PET imaging
Superscans by nuclear medicine/99mTc bone scan
A known malignancy that is progressing or has required active treatment within the past 3 years other than CRPC, which is expected to alter life expectancy or may interfere with CRPC disease assessment
Prior platinum-based chemotherapy
Prior PARP inhibitors (e.g., olaparib or rucaparib)