Inclusion Criteria:

          -  Pathologically confirmed prostatic adenocarcinoma.

          -  History of metastatic disease.

          -  Chemically or surgically castrate.

          -  Subject has received at least 2 lines of systemic therapy approved for mCRPC, with
             disease progression on the most recent systemic therapy as defined in Prostate Cancer
             Working Group 3 (PCWG3) recommendations.

          -  HIV, HBV, and/or HCV-infected subjects that have been cured or who are on effective
             anti-retroviral therapy with undetectable viral load within 6 months are eligible for
             this trial.

          -  An Eastern Cooperative Oncology Group (ECOG) Performance Status of ≤ 2.

          -  Subject must have adequate heart, liver, bone marrow and kidney function (e.g. eGFR ≥
             30 mL/min, AST/ALT ≤ 3 x ULN, Hgb ≥ 9 g/dL, Plt ≥ 100,000 / mm3, ANC ≥ 1500 / mm3).

        Exclusion Criteria:

          -  Subject has been diagnosed with or treated for another malignancy whose natural
             history or treatment may interfere with the safety or efficacy assessment of the
             investigational regimen.

          -  History of neuroendocrine differentiation in the subject's disease.

          -  Subject has a history of central nervous system (CNS) involvement by their mCRPC.
             Metastases stemming from bone are allowed.

          -  Subject has clinically significant CNS pathology.

          -  Subject requires chronic immunosuppressive therapy.

          -  Subject has a history of major cardiac abnormalities.