In vitro activity: Apalutamide (brand name Erleada), previously known as ARN-509 and JNJ-56021927, is a potent, selective and competitive, orally bioavailable androgen receptor inhibitor with IC50 of 16 nM in a cell-free assay. ARN-509 (< 10 μM) inhibits androgen-mediated induction or repression of mRNA expression levels for 13 endogenous genes including PSA and TMPRSS2 in the LNCaP/AR prostate cancer cell line. ARN-509 (< 10 μM) inhibits the proliferative effect of R1881 (30 pM) in the LNCaP/AR prostate cancer cell line. ARN-509 (10 μM) impairs AR nuclear localization and thus reduces the concentration of AR available to bind androgen response elements (ARE) in LNCaP cells expressing AR-EYFP. ARN-509 (10 μM) is able to effectively compete with R1881 (1 nM) and prevent AR from binding to promoter regions. ARN-509 inhibits R1881-induced VP16-AR–mediated transcription with IC50 of 0.2 μM in Hep-G2 cells expressing a VP16-AR fusion protein and an ARE-driven luciferase reporter.

Kinase Assay: Competitor assay kits (green) are used to determine relative in vitro binding affinities of ARN-509 for the rat AR ligand binding domain (LBD), human progesterone receptor (PR) LBD, and full-length human estrogen receptor-alpha (ERα) and human glucocorticoid receptor (GR). Each hormone dose is performed in triplicate, relative error is calculated from the standard error of the mean (SEM), and binding curves are fit using a single binding site competition model (Prism statistical analysis software package) with R2>0.8. Experiments are conducted multiple times with SEM<0.3 log units from the average logIC50 value. Ki values are calculated as averages across experiments with SEM, and binding affinities are reported as a percentage relative to the tight-binding ligand control for that receptor.

Cell Assay: Cells are incubated for 48 hours, after which ARN-509 is added in a 16 μL volume to the RPMI culture medium. For the antagonist mode assay, the ARN-509 is diluted in culture medium also containing 30 pM R1881. After 7 days' incubation, 16 μL of CellTiter-Glo Luminescent Cell Viability Assay is added and Relative Luminescence Units (RLUs) measured.