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.
