Purity >98%. The cytochrome P450 (CYP) isoform CYP17A1 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. Abiraterone acetate blocks CYP17A1 by potently inhibiting both the 17Alpha-hydroxylase and the 17,20 lyase activities (IC50 = 18 and 17 nM, respectively). In mice as well as men, it essentially eliminates plasma testosterone while producing a 3- to 4-fold increase in plasma luteinizing hormone. It improves radiographic progression-free survival and significantly delays decline in human metastatic castration-resistant prostate cancer.