The study consists of a screening period, a randomization period, a treatment period, a post-treatment safety follow-up followed by a long-term follow-up period.
JSB462 administration starts at day 1 of randomization, whereas AAA617 administration starts at day 1 of treatment period. Participants in arm 1 and arm 2 will therefore receive JSB462 during the 14-day randomization period before first administration of AAA617.
* JSB462 is administered orally, daily and continuously (100 mg or 300 mg once a day (QD)) until disease progression per Prostate Cancer Working Group (PCWG) 3-modified Response Evaluation Criteria In Solid Tumors (RECIST) v1.1 as assessed by the investigator, the occurrence of unacceptable toxicities, death, participant decision or investigator decision.
* AAA617 will be administered at 7.4 gigabecquerel (GBq) intravenously every 6 weeks for up to 6 doses, unless there is disease progression per PCWG3-modified RECIST v1.1 as assessed by the investigator, the occurrence of unacceptable toxicities, death, participant decision or investigator decision.
During the post-treatment follow up period:
* Safety follow-Up: After discontinuation of study treatment, all participants will be followed for at least 1 safety follow-up visit (30 days \[+/- 7 days\] after end of treatment visit). Subsequent lines of therapy may be administered according to investigator's discretion after treatment discontinuation.
* Long-term follow-up: Starts after the Safety follow-up period and lasts until the end of study. Safety, efficacy and survival information may be collected from the participants during this period.
Key Inclusion Criteria:
* Adult male participants with histologically and/or cytologically confirmed adenocarcinoma of the prostate. Participants with mixed histology (neuroendocrine) are not eligible.
* An Eastern Cooperative Oncology Group (ECOG) Performance Status (PS) grade ≤2.
* At least 1 bone or visceral metastatic lesion present on baseline CT, MRI, or bone scan imaging obtained ≤28 days prior to initiation of study treatment.
* Participants must be \[68Ga\]Ga-PSMA-11 PET/CT scan positive and eligible as determined by the sponsor's central reader.
* Participant must have prior exposure to at least one second generation ARPI in the metastatic/advanced setting.
* Previous treatment with a maximum of 2 taxane regimens is allowed.
* Participants eligible for PARPi and/or immune checkpoint inhibitor (per local testing and according to investigator's judgement) are eligible to participate if they have previous exposure to this(these) therapy(ies).
Key Exclusion Criteria:
* Prior treatment with any RLT (approved or investigational) is not allowed
* Prior treatment with a protein degrader compound that targets AR is not allowed
Other protocol-defined inclusion/exclusion criteria may apply.
