Purity >98%. The cytochrome P450 (CYP) isoform CYP17 is also known as steroid 17Alpha-hydroxylase/17,20 lyase because it catalyzes both 17Alpha-hydroxylase and 17,20 lyase reactions in the synthesis of steroids, including androgens, estrogens, glucocorticoids, and mineralocorticoids. Galeterone is a CYP17 inhibitor (IC50 = 300 nM) that has been shown to competitively block synthetic androgen binding (EC50 = 845 nM) and to antagonize the androgen receptor in transcriptional activation assays. Galeterone can inhibit the growth of castration-resistant prostate cancer cells with an IC50 value of 2.9 μM and demonstrates synergy with everolimus or gefitinib for growth inhibition.