Inclusion Criteria:

   - ≥ 18 years of age.

   - Metastatic CRPC with castrate levels of testosterone (≤ 50 ng/dL or ≤ 1.7 nmol/L).

   - Eastern Cooperative Oncology Group (ECOG) performance status of 0 to 1.

   - Progressed (by PSA or radiologic criteria) during or following treatment with a novel
   androgen receptor signaling inhibitor (ARSI, eg, abiraterone, enzalutamide,
   apalutamide, darolutamide), which may have been given for either hormone-sensitive
   prostate cancer or CRPC.

   - Received 1 to 2 prior lines of taxane chemotherapy, unless the physician and patient
   believe the patient is medically ineligible or the patient refuses (ineligibility or
   refusal must be documented in the source documents).

   - Progressed by PSA or radiologic criteria on or during last therapy for prostate
   cancer.

   - Measurable or non-measurable disease as per radiographic evaluation. Lesions situated
   in a previously irradiated area are considered evaluable if progression has been
   demonstrated in such lesions since radiation.

   • Note: If disease is considered non-measurable, a minimum PSA of 1 ng/dL is required
   with at least 1 confirmed rise at a minimum of a 1-week interval.

   - Adequate hematologic function, defined as absolute neutrophil count ≥ 1.5 × 109/L,
   hemoglobin ≥ 9.0 g/dL, and platelet count ≥ 100 × 109/L. Transfusions are permitted to
   meet hemoglobin and platelet criteria. However, the patient must have a stable
   hemoglobin level and platelet count for ≥ 2 weeks prior to dosing without transfusion.

   - Adequate renal function, defined as serum creatinine clearance ≥ 30 mL/min per
   Cockcroft-Gault formula.

   - Total bilirubin ≤ 1.5 × upper limit of normal (ULN) (≤ 3 × ULN if elevated because of
   Gilbert's syndrome, and ≤ 2 × ULN for patients with known liver metastases).

   - Aspartate aminotransferase and alanine aminotransferase < 2.5 × ULN (< 5 × ULN if
   liver metastases present).

   - Prothrombin time (PT) or international normalized ratio (INR) and activated partial
   thromboplastin time (aPTT) ≤ 1.5 × ULN unless the patient is receiving anticoagulant
   therapy, in which case PT/INR or aPTT must be within therapeutic range of intended use
   of anticoagulants.

Exclusion Criteria:

   - Currently participating in or has participated in a trial of an investigational device
   or has used an investigational device within 21 days before the first dose of study
   drug.

   - Any component of small cell or neuroendocrine histology.

   - Previously received an anti-CD39 antibody, anti-CD39 targeted therapy, or other agent
   targeting the adenosine pathway.

   - Prior treatment with programmed death-ligand 1 (PD-L1)/programmed death receptor-1
   (PD-1) inhibitors.

   - Prior treatment with ≥ 3 lines of taxane chemotherapy administered as a single agent
   or as part of a combination regimen.

   - Symptomatic or untreated brain metastases (including leptomeningeal metastases).
   Patients previously treated for brain metastases must be at least 4 weeks from
   completion of radiation treatment with follow-up imaging showing no progression.

   - Current pneumonitis with or without steroid requirement or history of pneumonitis
   requiring steroids.

   - Another malignancy other than prostate within 2 years of trial entry, except for those
   with a low risk of spreading or negligible risk of death such as non-melanoma skin
   cancer or Ta superficial bladder cancer.

   - Active autoimmune disease that has required systemic treatment in past 2 years (ie,
   with use of disease modifying agents, corticosteroids, or immunosuppressive drugs).

   - Medical conditions requiring chronic steroid (ie, > 10 mg/day of prednisone or its
   equivalent).

   • Note: Replacement therapy (eg, levothyroxine, insulin, or physiologic corticosteroid
   replacement therapy for thyroid, adrenal, or pituitary insufficiency) is allowed.

   - Administration of a live attenuated vaccine within 6 weeks before the first dose of
   study drug.

   • Exception: Health Authority approved COVID-19 vaccines are permitted.

   - Any gastrointestinal condition that would preclude the use of oral medications (eg,
   difficulty swallowing, nausea, vomiting, or malabsorption).