Study Comparing AAA817+ARPI Versus Standard of Care in Adult Participants With PSMA-positive mCRPC

The purpose of this study is to determine whether \[225Ac\]Ac-PSMA-617 (AAA817), given for up to 6 cycles at a dose of 10 Megabecquerel (MBq) +/- 10%, plus androgen receptor pathway inhibitor (ARPI), improves the radiographic progression free survival (rPFS) compared to investigator's choice of standard of care (SOC) (ARPI change or taxane-based chemotherapy) in adult participants with PSMA-positive metastatic castration resistant prostate cancer (mCRPC) treated with another ARPI as last treatment and who have not been exposed to a taxane-containing chemotherapy in the mCRPC setting nor have received any prior PSMA-targeting radioligand therapy. This is a phase III, open label, multicenter randomized study. The study aims at evaluating the superiority of 225Ac-PSMA-617 combined with androgen receptor pathway inhibitor (ARPI) over a change of ARPI or chemotherapy in prolonging progression free survival (rPFS).

Screening period: At screening, the participants will be assessed for eligibility and will undergo a positron emission tomography (PET)/computed tomography (CT) scan to evaluate PSMA positivity. Only participants with PSMA positive cancer and confirmed eligibility criteria will be randomized.

Participants randomized to the investigational arms will receive up to 6 doses of AAA817 10 Mbq +/- 10% given intravenously with or without an ARPI (oral enzalutamide or oral abiraterone) per investigator's choice. Treatment with ARPI should continue as per protocol end of treatment criteria.

Participants randomized to SoC will be treated with an ARPI change (oral enzalutamide or oral abiraterone) or taxane-based chemotherapy (docetaxel or cabazitaxel) per investigator's choice. Treatment with ARPI should continue as per protocol end of treatment criteria. Treatment duration with taxane-based chemotherapy will depend on the chosen regimen per the investigator's discretion following local guidelines as per standard of care and product labels and adhere to the protocol end of treatment criteria.

Supportive care will be allowed in both arms at the discretion of the investigator and includes available care for the eligible participant according to best institutional practice for mCRPC treatment, including androgen deprivation therapy (ADT).

Safety will be assessed routinely during the study. Crossover is not allowed among study arms.

The study will be conducted in the USA among other countries globally.