A Study of ZEN003694 in Combination With Enzalutamide in Patients With Metastatic Castration-Resistant Prostate Cancer

Inclusion Criteria:

1. Males age ≥ 18 years
2. Metastatic, castrate resistant, histologically confirmed prostate cancer; surgically castrated or continuous medical castration for ≥ 8 weeks prior to screening
3. Serum testosterone \< 50 ng/dL determined within 4 weeks of first administration of study drug
4. Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1
5. Adequate laboratory parameters \[absolute neutrophil (ANC), platelets, asparate aminotransferase (AST), alanine aminotransferase (ALT), total bilirubin, creatinine and coagulation parameters\] at screening
6. Dose Escalation Cohort DE-A: Prior progression on enzalutamide or apalutamide at any time by PCWG2 criteria and receiving a stable dose of enzalutamide at the start of study treatment.
7. Dose Escalation Cohort DE-B: Enzalutamide-naïve and apalutamide-naïve patients following prior progression on abiraterone by PCWG2 criteria and receiving a stable dose of enzalutamide at the start of study treatment.
8. Dose Confirmation Cohort A (DC-A) only: Currently receiving enzalutamide as most recent systemic therapy for mCRPC and have experienced PSA progression by PCWG2 criteria in the absence of radiographic and/or clinical progression. Patients may or may not have experienced prior progression on abiraterone.
9. Dose Confirmation Cohort B (DC-B) only: Enzalutamide-naïve patients following prior progression on abiraterone by PCWG2 criteria and within 12 weeks of discontinuing abiraterone.

Exclusion Criteria:

1. Any history of brain metastases or prior seizure or conditions predisposing to seizure activity
2. Have previously received an investigational BET inhibitor (including previous participation in this study or Study ZEN003694-001)
3. Have received prior systemic anti-cancer therapy (including abiraterone) or investigational therapy within 2 weeks or five half-lives, whichever is shorter, prior to the first administration of study drug
4. Failure to recover to Grade 1 or lower toxicity related to prior systemic therapy (excluding alopecia and neuropathy) prior to study entry
5. Radiation therapy within 2 weeks of the first administration of study drug
6. Have received prior chemotherapy in the metastatic castration-resistant setting (prior chemotherapy in the hormone-sensitive setting is allowed provided last dose was at least 6 months prior to study entry)
7. Have received prior investigational anti-androgen therapy, including ARN-509
8. Currently receiving medications known to be strong inhibitors of CYP2C8, strong inducers (except enzalutamide) or inhibitors of CYP3A4 and substrates of CYP3A4, CYP2C9 and CYP2C19 with a narrow therapeutic window. Strong inducers, inhibitors and substrates must be discontinued at least 7 days prior to the first administration of study drug.
9. Not a candidate for enzalutamide treatment, in the opinion of the Investigator