A Study of JNJ-69086420, an Actinium-225-Labeled Antibody Targeting Human Kallikrein-2 (hK2) for Advanced Prostate Cancer

The purpose of this study is to determine the recommended Phase 2 dose(s) (RP2D\[s\]) of JNJ-69086420 in Part 1 (Dose Escalation), to determine safety and preliminary signs of clinical activity at the RP2D(s) in Part 2 (Dose Expansion), to determine safety of JNJ-69086420 at the RP2D(s) as a combination therapy in Part 3 (combination therapy) and to determine safety of JNJ-69086420 at the RP2D(s) in participants with metastatic hormone-sensitive prostate cancer (mHSPC) in Part 4.

Inclusion Criteria: * For Part 1, Part 2, Part 3: Metastatic castration resistant prostate cancer (mCRPC) with histologic confirmation of adenocarcinoma (adenocarcinoma with small-cell or neuroendocrine features is allowed) with prior exposure to at least one androgen receptor (AR) targeted therapy (for example \[e.g.\], abiraterone acetate, enzalutamide, apalutamide, darolutamide). In addition: Part 1: prior taxane or other chemotherapy is acceptable but not required. Part 2a: prior taxane or other chemotherapy required, Part 2b: no prior taxane or other chemotherapy, Part 2c: mCRPC that has progressed after prior treatment with lutetium Lu-177 vipivotide tetraxetan, with or without prior chemotherapy, Part 3: prior taxane or other chemotherapy is acceptable but not required \& For Part 4a: metastatic HSPC, For Part 4b: disease that can be treated with less than or equal to (\) 2 weeks prior to start of study drug except for palliative radiotherapy for pain (e.g., bone pain), which may be used any time prior to first dose * Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1 * Adequate organ functions as reflected in laboratory parameters Exclusion Criteria: * Prior treatment with radium Xofigo (Ra 223 dichloride), strontium, samarium, or other radioconjugate therapy, other systemic anti-neoplastic therapy \