Safety, Tolerability, Pharmacokinetics, and Efficacy of acapatamab in Subjects with mCRPC

All Parts Inclusion Criteria: - Subject has provided informed consent prior to initiation of any study specific activities/procedures - Subjects with histologically or cytologically confirmed mCRPC who are refractory to a novel antiandrogen therapy (abiraterone, enzalutamide, and/or apalutamide) and have failed at least 1 (but not more than 2) taxane regimens (or who are deemed medically unsuitable to be treated with a taxane regimen or have actively refused treatment with a taxane regimen). Progression on novel antiandrogen therapy may have occurred in the non-metastatic CRPC setting - Subjects must have undergone bilateral orchiectomy or must be on continuous ADT with a gonadotropin releasing hormone (GnRH) agonist or antagonist - Total serum testosterone /= 1 ng/mL that has increased on at least 2 successive occasions at least 1 week apart - nodal or visceral progression as defined by RECIST 1.1 with PCGW3 modifications - appearance of 2 or more new lesions in bone scan - Eastern Cooperative Oncology Group (ECOG) performance status of 0 – 1 - Life expectancy >/= 6months Exclusion Criteria: - Any anticancer therapy or immunotherapy within 4 weeks of start of first dose, not including luteinizing hormone-releasing hormone agonist (LHRH)/GnRH analogue (agonist/antagonist). Subjects on a stable bisophosphonate or denosumab regimen for >/= 30 days prior to randomization are eligible - Prior PSMA-targeted therapy (subjects on prior therapy may be eligible if discussed with Amgen medical monitor prior to enrollment) - Central nervous system (CNS) metastases, leptomeningeal disease, or spinal cord compression - Active autoimmune disease or any other diseases requiring immunosuppressive therapy while on study - Needing chronic systemic corticosteroid therapy (prednisone > 10 mg per day or equivalent) or any other immunosuppressive therapies (including anti-tumor necrosis factor alpha [TNF alpha] therapies) unless stopped 7 days prior to start of first dose - Myocardial infarction, unstable angina, cardiac arrhythmia requiring medication, and/or symptomatic congestive heart failure (New York Heart Association > class II) within 12 months of first dose of acapatamab Part 2 only: - Subjects on a prior PD-1 or PD-L1 inhibitor who experienced a Grade 3 or higher immune-related adverse event prior to first day of dosing - History or evidence of interstitial lung disease or active, non-infectious pneumonitis Part 3 only: - Evidence of active tuberculosis on chest radiograph within 3 months prior to the first dose of investigational product Part 6 only: Subjects are excluded from this cohort if any of the following additional criteria apply: - Subjects taking strong OAT3 inhibitors (eg, probenecid) or adjust the dosing to 1 mg PO QD. - Subjects with latent or active tuberculosis at screening