enzalutamide-sensitive human prostate cancer cell line model C4–2b cells were maintained as described previously (12 (link)). NCI-H660 cells were purchased from ATCC and maintained in suggested culture medium. C4–2b was validated by short tandem repeat DNA fingerprint with the AmpFLSTR Identifier PCR Amplification Kit (Thermo Fisher Scientific) in MD Anderson’s Characterized Cell Line Core Facility. Genomic mutation/deletion analysis for all cell lines was performed previously by targeted DNA sequencing. Palbociclib (S1116), abemaciclib (S5716), olaparib (KU-0059436), and enzalutamide (S1250) were purchased from Selleck Chemicals.