Mechanism of Action of Abiraterone Acetate
Abiraterone acetate is an irreversible inhibitor of CYP17A (17α-hydroxylase/C17,20-lyase), a critical enzyme that blocks androgen biosynthesis in the testes, adrenal glands, and prostate tumor tissue itself. 1, 2
Primary Enzymatic Blockade
Abiraterone inhibits CYP17A through two sequential enzymatic reactions 2:
- Blocks 17α-hydroxylase activity: Prevents conversion of pregnenolone and progesterone to their 17α-hydroxy derivatives 2
- Blocks C17,20-lyase activity: Prevents subsequent formation of DHEA (dehydroepiandrosterone) and androstenedione, which are direct androgen precursors to testosterone 1, 2
Comprehensive Androgen Suppression
The mechanism addresses a critical limitation of traditional androgen deprivation therapy 2:
- Traditional ADT (GnRH agonists/orchiectomy): Only decreases testicular androgen production 2
- Abiraterone advantage: Blocks androgen production in all three sources—testes, adrenal glands, and within prostate tumor tissue itself 2, 3
This comprehensive blockade explains why castration-resistant prostate cancer responds to abiraterone despite castrate testosterone levels, as tumors continue producing androgens locally even after surgical or medical castration 3.
Mineralocorticoid Excess Mechanism
Mandatory prednisone co-administration (5 mg twice daily) is required because CYP17A inhibition causes upstream accumulation of mineralocorticoid precursors. 1, 2
The biochemical cascade 1:
- CYP17A blockade prevents conversion of C21 progesterone precursors
- Upstream mineralocorticoid precursors accumulate
- Increased ACTH production occurs
- Results in hypertension (22% incidence), hypokalemia (17% incidence), and peripheral edema (28% incidence) 1, 4
Low-dose glucocorticoids (prednisone) suppress ACTH and prevent these mineralocorticoid-related adverse effects 1.
Clinical Pharmacology
Abiraterone acetate is a prodrug that converts in vivo to the active form, abiraterone. 2
Key pharmacokinetic features 2:
- Oral administration with peak plasma concentrations at 2 hours
- Abiraterone acetate plasma levels are undetectable (<0.2 ng/mL) in >99% of samples, confirming rapid conversion to active abiraterone 2
- Steady-state achieved with 2-fold accumulation compared to single dose 2
Important Clinical Caveat
Abiraterone must be taken on an empty stomach (at least 1 hour before or 2 hours after food) at standard dosing, as food significantly increases systemic exposure and unpredictable absorption. 2 An alternative low-fat breakfast dosing strategy (250 mg with food) exists but requires specific protocol adherence 5, 4.