Abiraterone acetate is metabolized in vivo to abiraterone, which is an inhibitor of androgen biosynthesis. In particular, abiraterone selectively inhibits the enzyme 17α-hydroxylase/C17,20-lyase (CYP17). This enzyme is required for androgen biosynthesis in testicular tissues, adrenal cortex, and prostate tumors. CYP17 catalyzes the conversion of pregnenolone and progesterone to the precursors of testosterone, DHEA, and androstenedione, respectively, via 17α-hydroxylation and cleavage of the C17,20 bond. Inhibition of CYP17 also leads to increased production of mineralocorticoids by the adrenal glands (see section "Special warnings and precautions for use").