Abiraterone Acetate (Molecule of the Month for May 2017)
Zytiga, Abiratas, Abretone, Abirapro
Abiraterone acetate is indicated for use in combination with prednisone as a treatment for metastatic castration-resistant prostate cancer. Abiraterone acetate is a steroidal CYP17A1 inhibitor and by extension androgen synthesis inhibitor which is used in combination with prednisone in metastatic castration-resistant prostate cancer (previously called hormone-resistant or hormone-refractory prostate cancer) – i.e., prostate cancer not responding to androgen deprivation or treatment with androgen receptor antagonists.
Abiraterone, the active metabolite of abiraterone acetate, inhibits CYP17A1, which manifests as two enzymes, 17α-hydroxylase (IC50 = 2.5 nM) and 17,20-lyase (IC50 = 15 nM) (six-fold more selective for inhibition of 17α-hydroxylase over 17,20-lyase) that are expressed in testicular, adrenal, and prostatic tumor tissues. CYP17 catalyzes two sequential reactions: (a) the conversion of pregnenolone and progesterone to their 17α-hydroxy derivatives by its 17α-hydroxylase activity, and (b) the subsequent formation of dehydroepiandrosterone (DHEA) and androstenedione, respectively, by its 17,20-lyase activity. DHEA and androstenedione are androgens and precursors of testosterone. Inhibition of CYP17 activity by abiraterone thus decreases circulating levels of androgens such as DHEA, testosterone, and dihydrotestosterone (DHT).
A phase III study in subjects previously treated with docetaxel started in 2008. In September 2010, an independent panel found that the interim results in patients previously treated with docetaxel were so much better compared to those treated with placebo that it was unethical to keep half the study participants on placebo, and all patients began receiving the drug.
Formal Chemical Name (IUPAC)
Update by Karl Harrison
(Molecule of the Month for May 2017 )
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