Patients must meet all of the following criteria in order to be enrolled in study:

1. Written informed consent obtained.

2. Male aged ≥ 18 years.

3. Histologically confirmed adenocarcinoma of the prostate.

4. Castration resistant prostate cancer with serum testosterone < 50 ng/dL.

5. Metastatic disease.

6. Ongoing androgen deprivation therapy with GnRH analogue or antagonist, or have had bilateral orchiectomy.

7. Received at least one prior line of taxane-based chemotherapy and at least one line of hormonal AR targeted therapy (eg, abiraterone, enzalutamide). Patients who have refused or were intolerant to taxane-based chemotherapy may be enrolled.

8. ECOG performance status 0-1.

9. Adequate marrow, liver and kidney function: a. Adequate bone marrow function:  o ANC ≥1,500/mL o platelets ≥75,000/mL o hemoglobin ≥9 g/dL without transfusion or demonstrate stability with no significant decline in hemoglobin for 2 weeks after transfusion. b. Adequate liver function:  o Total bilirubin ≤1.5 x ULN or ≤3.0 x ULN for patients with Gilbert’s disease. o AST/ALT ≤2.5 x ULN c. Adequate renal function: o Calculated creatinine clearance >60mL/min (calculated using the Cockcroft-Gault formula).

10. INR ≤1.5.

11. Able to swallow study treatment.

12. Has a life expectancy of >3 months.

​​​​​​​13. Patients with partners of childbearing potential must agree to use an acceptable method of birth control for the duration of study treatment and for 6 months following the last dose of study treatment (see Section 9.5.2). 

Patients with any of the following conditions will be excluded from study enrollment:

1. History of a second malignancy, unless potentially curative treatment has been completed with no evidence of malignancy for 3 years. 

2. Have a medical condition such as Crohn’s disease or have undergone significant surgery to the gastrointestinal tract that could impair absorption or that could result in short bowel syndrome with diarrhea due to malabsorption.

3. History of pituitary or adrenal dysfunction.

4. Poorly controlled diabetes mellitus.

5. Clinically significant abnormality in serum potassium and sodium.

6. Have a serious nonmalignant disease (eg, hydronephrosis, liver failure, or other conditions) that could compromise protocol objectives in the opinion of the Investigator and/or the Sponsor.

7. Previous treatment with CYP11A1 inhibitors.

8. Have exhibited allergic reactions to a similar structural compound, biological agent, or formulation.

9. Are currently receiving any other investigational agent.

10. Have received treatment with radiation therapy, surgery, chemotherapy, or investigational therapy within 28 days or 5 half-lives, whichever occurs first, prior to study entry (6 weeks for nitrosoureas or mitomycin C).

11. Presence of symptomatic central nervous system metastatic disease or disease that requires local therapy such as radiotherapy, surgery, or increasing dose of steroids within 28 days prior to study entry.

12. Active or unstable cardio-/cerebro-vascular disease, including thromboembolic events.

13. History of congestive heart failure; cardiac disease, myocardial infarction within 6 months prior to enrollment.

14. QTc interval ≥470 msec using Fridericia formula (determined as the mean of 3 QTc values from triplicate ECG at Screening) or history of Long QT Syndrome.

15. Severe chronic obstructive pulmonary disease with hypoxemia (defined as resting O2 saturation of ≤90% breathing room air).

16. Major surgery, including local prostate intervention (except prostate biopsy), within 2 weeks prior to the start of study treatment.

17. Has received an anticancer monoclonal antibody (mAb) within 4 weeks prior to enrollment; or has not recovered from AEs due to mAbs administered more than 4 weeks prior to enrollment.

18. Diagnosis of immunodeficiency or is receiving chronic systemic steroid therapy (in dosing exceeding 10 mg daily of prednisone equivalent) or any form of immunosuppressive therapy within 7 days prior to the start of study intervention.

19. Known active CNS metastases and/or carcinomatous meningitis.

20. Active autoimmune disease that has required systemic treatment in the past 2 years. 

21. Active, uncontrolled bacterial, viral, or fungal infections requiring systemic therapy. Patients with HIV, hepatitis B or hepatitis C virus infection that is well-controlled with antiviral therapies may be enrolled.

​​​​​​​22. History of allogenic tissue or solid organ transplant. 23. Are unwilling or unable to comply with procedures required in this protocol.