In vitro activity: Enzalutamide has greater affinity to AR than Bicalutamide does in a competition assay with 16β-[18F]fluoro-5α-DHT (18-FDHT) in castration-resistant LNCaP/AR cells (AR-overexpressing). While Enzalutamide shows no agonism in LNCaP/AR prostate cells. Enzalutamide antagonizes induction of prostate-specific antigen (PSA) and transmembrane serine protease 2 (TMPRSS2), combination with the synthetic androgen R1881 in parental LNCaP cells. Enzalutamide could inhibit the transcriptional activity of a mutant AR protein (W741C, mutation of Trp741 to Cys). Enzalutamide also prevents nuclear translocation and co-activator recruitment of the ligand-receptor complex.

Kinase Assay: Enzalutamide is evaluated by an artificial AR response reporter system in a hormone refractory prostate cancer cell line. In this system, the prostate cancer LNCaP cells are engineered to stably express about 5-fold higher level of AR than endogenous level. The exogenous AR has similar properties to endogenous AR in that both are stabilized by a synthetic androgen R1881. The AR-over expressed cells are also engineered to stably incorporate an AR response reporter and the reporter activity of these cells shows features of hormone refractory prostate cancer. The antagonistic activity of Enzalutamide is tested in the presence of 100 pM of R1881. Engineered LNCaP cells are maintained in Iscove's medium containing 10% fetal bovine serum (FBS). Two days prior to Enzalutamide treatment, the cells are grown in Iscove's medium containing 10% charcoal-stripped FBS (CS-FBS) to deprive of androgens. The cells are split and grown in Iscove's medium containing 10% CS-FBS with 100 pM of R1881 and increasing concentrations of Enzalutamide. After two days of incubation, reporter activities are assayed.

Cell Assay: Enzalutamide is diluted in DMSO. LNCaP or LNCaP/AR cells (104 cells/well) are androgen-starved by growth in media containing 5-10% charcoal-stripped serum for 3-5 days. Then the cells are challenged with various concentrations of Enzalutamide in media containing 5-10% charcoal-stripped serum.