CYCLONE 2: This phase II trial is trying to determine how safe and effective the oral drug Abemaciclib is when given together with Abiraterone Acetate plus Prednisone (two other oral drugs) in patients with metastatic castrate resistant prostate cancerA Phase 2, Randomized, Double-Blind, Placebo-Controlled Study of Abiraterone Acetate Plus Prednisone With or Without Abemaciclib in Patients With Metastatic Castration-Resistant Prostate Cancer

Exclusion

• Prior therapy with cytochrome P450 (CYP)17 inhibitors.
• Prior treatment with abemaciclib or any cyclin-dependent kinase (CDK) 4 & 6 inhibitors.
• Prior cytotoxic chemotherapy for metastatic castration resistant prostate cancer (participants treated with docetaxel in the metastatic hormone-sensitive prostate cancer [mHSPC] are eligible). Prior radiopharmaceuticals for prostate cancer, or prior enzalutamide, apalutamide, darolutamide or sipuleucel-T. Participants who had prior radiation or surgery to all target lesions.
• Currently enrolled in a clinical study involving an investigational product.
• Gastrointestinal disorder affecting the absorption or ability to swallow large pills.
• Clinically significant heart disease, active or chronic liver disease, moderate/severe hepatic impairment (Child-Pugh Class B and C).