title: A-ring modified steroidal azoles retaining similar potent and slowly reversible CYP17A1 inhibition as abiraterone.
abstract: Abiraterone acetate is a potent inhibitor of human cytochrome P450c17 (CYP17A1, 17α-hydroxylase/17,20-lyase) and is clinically used in combination with prednisone for the treatment of castration-resistant prostate cancer. Although many studies have documented the potency of abiraterone (Abi) in a variety of in vitro and in vivo systems for several species, the exact potency of Abi for human CYP17A1 enzyme has not yet been determined, and the structural requirements for high-potency steroidal azole inhibitors are not established. We synthesized 4 Abi analogs differing in the A-B ring substitution patterns: 3α-hydroxy-Δ(4)-Abi (13), 3-keto-Δ(4)-Abi (11), 3-keto-5α-Abi (6), and 3α-hydroxy-5α-Abi (5). We measured the spectral binding constants (Ks) using purified and modified human CYP17A1 along with the determination constants (Ki) applying a native human CYP17A1 enzyme in yeast microsomes for these compounds as well as for ketoconazole. For Abi, 3-keto-Δ(4)-Abi, 3-keto-5α-Abi, and 3α-hydroxy-5α-Abi, the type 2 spectral changes gave the best fit for a quadratic equation, since in these experiments Ks values were 0.1-2.6nM, much lower than that for ketoconazole and 3α-hydroxy-Δ(4)-Abi (Ks values were 140 and 1660nM, respectively). Inhibition experiments showed mixed inhibition patterns with Ki values of 7-80nM. Abi dissociation from the CYP17A1-Abi complex was incomplete and slow; the t1/2 for dissociation was 1.8h, with 55% of complex remaining after 5h. We conclude that Abi and the 3 related steroidal azoles (3-keto-Δ(4)-Abi, 3-keto-5α-Abi, and 3α-hydroxy-5α-Abi), which also mimic natural substrates, are extraordinarily potent inhibitors of human CYP17A1, whereas the 3α-hydroxy-Δ(4)-Abi is moderately potent and comparable to ketoconazole.
authors: Department of Pharmacy, Faculty of Chemistry, National University of Mexico, Mexico, D.F., Mexico.
authors: Mariana
authors: M
authors: Garrido
authors: Division of Metabolism, Diabetes, and Endocrinology, Department of Internal Medicine, University of Michigan, Ann Arbor, MI 48019.
authors: Hwei-Ming
authors: HM
authors: Peng
authors: Division of Metabolism, Diabetes, and Endocrinology, Department of Internal Medicine, University of Michigan, Ann Arbor, MI 48019.
authors: Francis K
authors: FK
authors: Yoshimoto
authors: Division of Metabolism, Diabetes, and Endocrinology, Department of Internal Medicine, University of Michigan, Ann Arbor, MI 48019.
authors: Sunil K
authors: SK
authors: Upadhyay
authors: Department of Pharmacy, Faculty of Chemistry, National University of Mexico, Mexico, D.F., Mexico.
authors: Eugene
authors: E
authors: Bratoeff
authors: Division of Metabolism, Diabetes, and Endocrinology, Department of Internal Medicine, University of Michigan, Ann Arbor, MI 48019.
authors: Richard J
authors: RJ
authors: Auchus
mesh_terms: D000736:Androstenes; D000737:Androstenols / Q000494:pharmacology*; D001393:Azoles / Q000737:chemistry*; D004791:Enzyme Inhibitors / Q000737:chemistry / Q000494:pharmacology*; D006801:Humans; D015394:Molecular Structure; D013254:Steroid 17-alpha-Hydroxylase / Q000037:antagonists & inhibitors* / Q000378:metabolism; D013256:Steroids / Q000737:chemistry*; D013329:Structure-Activity Relationship
chemical_list: D000736:Androstenes; D000737:Androstenols; D001393:Azoles; D004791:Enzyme Inhibitors; D013256:Steroids; C501892:CYP17A1 protein, human; D013254:Steroid 17-alpha-Hydroxylase; C089740:abiraterone
keywords: Abiraterone; Androgen; CYP17A1; Cytochrome P450; Enzymology; Prostate cancer; Steroidogenesis