title: The role of CYP2C in the in vitro bioactivation of the contraceptive steroid desogestrel.
abstract: Desogestrel is a 3-deoxo progestogenic steroid that requires bioactivation to 3-ketodesogestrel. In these studies we have attempted to define the pathway of 3-ketodesogestrel formation and characterise the enzymes responsible for this biotransformation in vitro. Initial studies using deuterated desogestrel confirmed that desogestrel is metabolised by human liver microsomes via 3alpha-hydroxy and 3beta-hydroxydesogestrel to 3-ketodesogestrel. Metabolites were analysed by radiometric high-performance liquid chromatography and were identified by liquid chromatography-mass spectrometry and by cochromatography with authentic standards. Desogestrel was metabolised by microsomes from lymphoblasts containing cDNA-expressed CYP2C9 and CYP2C19 to 3alpha-hydroxydesogestrel with small amounts of 3beta-hydroxydesogestrel also being observed. The Km value for 3alpha-hydroxylation by CYP2C9 cell line microsomes was 6.5 microM and the corresponding Vmax value was 1269 pmole. mg-1. min-1. Sulfaphenazole potently inhibited 3alpha-hydroxydesogestrel formation by CYP2C9 microsomes with a Ki value of 0.91 microM. There was a significant negative correlation between 3-ketodesogestrel and CYP3A4 content/activity in a panel of human livers suggesting that the further metabolism of 3-ketodesogestrel is mediated by CYP3A4. Sulfaphenazole partially inhibited 3alpha-hydroxydesogestrel and 3-ketodesogestrel formation in human liver microsomes indicating a possible in vivo role for CYP2C9. In addition, when sulfaphenazole was combined with S-mephenytoin, further inhibition of 3alpha-hydroxydesogestrel formation was observed suggesting a possible role for CYP2C19. This was confirmed in incubations with inhibitory antibodies. Whereas an anti-CYP2C9/2C19 antibody completely abolished desogestrel metabolism, anti-CYP3A4 and anti-CYP2E1 were not inhibitory. We conclude that CYP2C9 and possibly CYP2C19 and important isoforms catalysing the initial hydroxylation of desogestrel.
authors.affiliation: Department of Pharmacology and Therapeutics, New Medical Building, Liverpool, L69 3GE, United Kingdom.
authors.forename: D M
authors.initials: DM
authors.lastname: Gentile
authors.forename: C H
authors.initials: CH
authors.lastname: Verhoeven
authors.forename: T
authors.initials: T
authors.lastname: Shimada
authors.forename: D J
authors.initials: DJ
authors.lastname: Back
mesh_terms: D001189:Aryl Hydrocarbon Hydroxylases; D001711:Biotransformation; D002460:Cell Line; D003280:Contraceptives, Oral, Synthetic / Q000494:pharmacology*; D065731:Cytochrome P-450 CYP2C19; D065729:Cytochrome P-450 CYP2C9; D051544:Cytochrome P-450 CYP3A; D065607:Cytochrome P-450 Enzyme Inhibitors; D003577:Cytochrome P-450 Enzyme System / Q000235:genetics / Q000378:metabolism*; D017135:Desogestrel / Q000378:metabolism / Q000493:pharmacokinetics / Q000494:pharmacology*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006801:Humans; D006900:Hydroxylation; D008862:Microsomes, Liver / Q000201:enzymology; D006899:Mixed Function Oxygenases / Q000378:metabolism; D045167:Progesterone Congeners / Q000494:pharmacology*; D039181:Steroid 16-alpha-Hydroxylase; D013250:Steroid Hydroxylases / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*
chemical_list: D003280:Contraceptives, Oral, Synthetic; D065607:Cytochrome P-450 Enzyme Inhibitors; D004791:Enzyme Inhibitors; D045167:Progesterone Congeners; C044815:etonogestrel; D017135:Desogestrel; D003577:Cytochrome P-450 Enzyme System; D006899:Mixed Function Oxygenases; D013250:Steroid Hydroxylases; C450260:CYP2C9 protein, human; D065729:Cytochrome P-450 CYP2C9; D001189:Aryl Hydrocarbon Hydroxylases; C045793:CYP2C19 protein, human; C104464:CYP3A protein, human; D065731:Cytochrome P-450 CYP2C19; D051544:Cytochrome P-450 CYP3A; D039181:Steroid 16-alpha-Hydroxylase; C510163:CYP3A4 protein, human