A Study to Evaluate the Safety, Pharmacokinetics, Pharmacodynamics, and Antitumor Activity of INV-9956 in Adult Patients With Advanced Metastatic Castration Resistant Prostate Cancer

Inclusion Criteria: 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. 10. INR ≤1.5. 11. Able to swallow study treatment. 12. Has a life expectancy of \> 3 months. Exclusion Criteria: 1. 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. 2. History of pituitary or adrenal dysfunction. 3. Poorly controlled diabetes mellitus. 4. Clinically significant abnormality in serum potassium and sodium. 5. 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. 6. Active or unstable cardio-/cerebro-vascular disease, including thromboembolic events. 7. History of congestive heart failure; cardiac disease, myocardial infarction within 6 months prior to enrollment. 8. Prolonged QTcF interval. 9. Active infection or other medical condition that would make corticosteroid contraindicated.