The LanthaScreen™ TR-FRET Androgen Receptor Coactivator Assay Kit provides a sensitive and robust method for high-throughput screening of potential androgen receptor (AR) ligands as agonists of coactivator recruitment or antagonists of agonist-dependent coactivator recruitment. In both the agonist and antagonist modes, the homogeneous mix-and-read assay uses a rat AR ligand-binding domain (AR-LBD) tagged with hexahistidine and glutathione-S-transferase (GST) (also available separately), a terbium (Tb)-labeled anti-GST antibody, and a fluorescein-labeled coactivator peptide. Agonist Mode When the LanthaScreen TR-FRET Androgen Receptor Coactivator Assay is run in agonist mode (to identify agonist compounds), AR-LBD is added to ligand test compounds, followed by the addition of a mixture of fluorescein-coactivator peptide and Tb-anti-GST antibody. After room temperature incubation, the TR-FRET 520:495 nm emission ratio is calculated and used to determine the EC50 from a dose response curve of the compound. This ligand EC50 is a composite value representing the amount of ligand required to bind to receptor, effect a conformational change, and recruit coactivator peptide (see figure). Antagonist Mode When the LanthaScreen TR-FRET Androgen Receptor Coactivator Assay is run in antagonist mode (to identify antagonist compounds), AR-LBD is added to ligand test compounds, followed by addition of a mixture of DHT agonist, fluorescein-coactivator peptide, and Tb-anti-GST antibody. The concentration of DHT agonist used in this mode is the EC80 concentration as determined by first running the assay in agonist mode. An example of data produced in the antagonist mode is shown in the figure below.