INCLUSION

1. Written informed consent obtained.
2. Male aged greater or equal than 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 gonadotropin-releasing hormone (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 androgen receptor (AR) targeted therapy (e.g., abiraterone, enzalutamide). Patients who have refused or were intolerant to taxane-based chemotherapy may be enrolled.
8. Eastern Cooperative Oncology Group (ECOG) performance status 0-1.
9. Adequate marrow, liver, and renal function:

a. Adequate bone marrow function:

• absolute neutrophil count (ANC) ≥ 1.5×109/L
• platelets ≥ 75×109/L
• hemoglobin ≥9 g/dL without transfusion or demonstrate stability with no significant decline in hemoglobin for 2 weeks after transfusion.

b. Adequate liver function:

• Total bilirubin ≤1.5 x upper limit of normal range (ULN) or ≤3.0 x ULN for patients with Gilbert’s disease.
• AST/ALT ≤2.5 x ULN

c. Adequate renal function:

• Calculated creatinine clearance >60mL/min (calculated using the Cockcroft-Gault formula).

1. International normalized ratio (INR) ≤1.5
2. Able to swallow study treatment.
3. Has a life expectancy of >3 months
4. 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 9.4.2).

EXCLUSION

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 (e.g., 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 of enrollment; or has not recovered from AEs due to mAbs administered more than 4 weeks before the date of enrollment.
18. Diagnosis of immunodeficiency or is receiving chronic sy