This phase I trial is evaluating the safety and dose of an investigational immunotherapy drug (AMG 160) in patients with metastatic castration resistant prostate cancerA Phase 1 Study Evaluating the Safety, Tolerability, Pharmacokinetics, and Efficacy of Prostate Specific Membrane Antigen Half-life Extended Bispecific T-cell Engager AMG 160 in Subjects With Metastatic Castration-resistant Prostate Cancer

Exclusion

• 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