Inclusion Criteria:  Histological, pathological, or cytological confirmed diagnosis of adenocarcinoma of the prostate. Progression on at least 2 prior approved systemic therapies for metastatic prostate cancer (at least one must be a second-generation androgen inhibitor, e.g., abiraterone, enzalutamide, darolutamide, apalutamide). Progressive mCRPC Ongoing androgen deprivation therapy (ADT) with a gonadotropin releasing hormone analog or inhibitor, or orchiectomy (surgical or medical castration). Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1  Exclusion Criteria:  Known symptomatic brain metastases requiring steroids (above physiologic replacement doses). Active inflammatory gastrointestinal disease, chronic diarrhea, known diverticular disease, or previous gastric resection or lap band surgery. Radiation therapy within 4 weeks of first dose of study drug or prior irradiation to >25% of the bone marrow. Receipt of an investigational drug(s) within 4 weeks prior to anticipated first dose