 This study is being conducted to characterize the safety and recommended phase 2 dose RP2D of combining afuresertib, independently with 2 approved drugs: enzalutamide Xtandi, Xtandi is a trademark of Astellas Pharma, Inc. and abiraterone Zygita, Zytiga is a trademark of Janssen Biotech, Inc.. The study will be conducted in two parts. Part 1, a dose escalation phase, will establish RP2D of afuresertib when administered with enzalutamide or abiraterone. Part 2, a dose expansion phase, will further evaluate long-term safety of the combinations at the RP2Ds in additional subjects. Dose-finding cohorts will be studied in parallel and will evaluate safety and pharmacokinetic to guide selection of the dose regimens for further evaluation. Part 2 will begin once the RP2Ds have been established in Part 1. Additional doses andor schedules may be explored if warranted, based upon the pharmacokinetic PK and pharmacodynamic PD assessments or emerging preclinical evidence. Overall, approximately 60 chemotherapy-naïve subjects with mCRPC and who are receiving either enzalutamide or abiraterone will be enrolled into the study. 