This multicenter study will evaluate safety and efficacy of niraparib in combination with other anti-cancer agents. Combination 1 will combine niraparib with the anti-programmed cell death protein (PD)-1 monoclonal antibody cetrelimab, in participants with mCRPC. Combination 1 has 2 parts: in Part 1 (dose selection), participants will be enrolled to establish RP2D doses of niraparib and cetrelimab; and Part 2 (dose expansion) will evaluate the combination therapy in an expanded number of participants into 2 cohorts (biomarker positive or biomarker negative). Combination 2 will combine niraparib with abiraterone acetate plus prednisone (AA-P) in mCRPC participants with DNA-repair gene defects (DRD). Combination 3 will evaluate the relative bioavailability (BA) of niraparib and AA in combination. In a pharmacokinetics (PK) assessment phase, niraparib and AA will be administered, and in an extension phase, niraparib and AA-P will be administered. Combinations 1 and 2 will have 5 phases: A Pre-screening Phase, a Screening Phase, a Treatment Phase, a Follow-up Phase, and a Long-term Extension (LTE) Phase; Combination 3 has 3 phases: A Screening Phase, A PK Assessment Phase, an Extension Phase (including LTE phase). Study evaluations will include efficacy, PK, PK/pharmacodynamics, biomarkers, safety and tolerability.
The purpose of this study is to: a) establish the recommended phase 2 dose (RP2D) and to evaluate the antitumor activity and safety of niraparib combination therapies (Combinations 1 and 2) and b) to determine the relative bioavailability of niraparib and abiraterone acetate (AA) in combination (Combination 3) in participants with metastatic castration-resistant prostate cancer (mCRPC).