title: Identification of Tazarotenic Acid as the First Xenobiotic Substrate of Human Retinoic Acid Hydroxylase CYP26A1 and CYP26B1.
abstract: Cytochrome P450 (CYP) 26A1 and 26B1 are heme-containing enzymes responsible for metabolizing all-trans retinoic acid (at-RA). No crystal structures have been solved, and therefore homology models that provide structural information are extremely valuable for the development of inhibitors of cytochrome P450 family 26 (CYP26). The objectives of this study were to use homology models of CYP26A1 and CYP26B1 to characterize substrate binding characteristics, to compare structural aspects of their active sites, and to support the role of CYP26 in the metabolism of xenobiotics. Each model was verified by dockingat-RA in the active site and comparing the results to known metabolic profiles ofat-RA. The models were then used to predict the metabolic sites of tazarotenic acid with results verified by in vitro metabolite identification experiments. The CYP26A1 and CYP26B1 homology models predicted that the benzothiopyranyl moiety of tazarotenic acid would be oriented toward the heme of each enzyme and suggested that tazarotenic acid would be a substrate of CYP26A1 and CYP26B1. Metabolite identification experiments indicated that CYP26A1 and CYP26B1 oxidatively metabolized tazarotenic acid on the predicted moiety, with in vitro rates of metabolite formation by CYP26A1 and CYP26B1 being the highest across a panel of enzymes. Molecular analysis of the active sites estimated the active-site volumes of CYP26A1 and CYP26B1 to be 918 Å(3)and 977 Å(3), respectively. Overall, the homology models presented herein describe the enzyme characteristics leading to the metabolism of tazarotenic acid by CYP26A1 and CYP26B1 and support a potential role for the CYP26 enzymes in the metabolism of xenobiotics.
authors.affiliation: Amgen Pharmacokinetics and Drug Metabolism, Seattle, Washington (R.S.F.); Department of Pharmaceutics, University of Washington, Seattle, Washington (N.I., A.Z., L.J.D., B.R.B.); Core Laboratory for Neuromolecular Production, Department of Biomedical and Pharmaceutical Sciences, University of Montana, Missoula, Montana (P.D.); CNRS, Université Nice Sophia Antipolis, Institut de Pharmacologie Moléculaire et Cellulaire, UMR 7275, Valbonne, France (D.D.) rfoti@amgen.com.
authors.forename: Robert S
authors.initials: RS
authors.lastname: Foti
authors.affiliation: Amgen Pharmacokinetics and Drug Metabolism, Seattle, Washington (R.S.F.); Department of Pharmaceutics, University of Washington, Seattle, Washington (N.I., A.Z., L.J.D., B.R.B.); Core Laboratory for Neuromolecular Production, Department of Biomedical and Pharmaceutical Sciences, University of Montana, Missoula, Montana (P.D.); CNRS, Université Nice Sophia Antipolis, Institut de Pharmacologie Moléculaire et Cellulaire, UMR 7275, Valbonne, France (D.D.).
authors.forename: Nina
authors.initials: N
authors.lastname: Isoherranen
authors.affiliation: Amgen Pharmacokinetics and Drug Metabolism, Seattle, Washington (R.S.F.); Department of Pharmaceutics, University of Washington, Seattle, Washington (N.I., A.Z., L.J.D., B.R.B.); Core Laboratory for Neuromolecular Production, Department of Biomedical and Pharmaceutical Sciences, University of Montana, Missoula, Montana (P.D.); CNRS, Université Nice Sophia Antipolis, Institut de Pharmacologie Moléculaire et Cellulaire, UMR 7275, Valbonne, France (D.D.).
authors.forename: Alex
authors.initials: A
authors.lastname: Zelter
authors.affiliation: Amgen Pharmacokinetics and Drug Metabolism, Seattle, Washington (R.S.F.); Department of Pharmaceutics, University of Washington, Seattle, Washington (N.I., A.Z., L.J.D., B.R.B.); Core Laboratory for Neuromolecular Production, Department of Biomedical and Pharmaceutical Sciences, University of Montana, Missoula, Montana (P.D.); CNRS, Université Nice Sophia Antipolis, Institut de Pharmacologie Moléculaire et Cellulaire, UMR 7275, Valbonne, France (D.D.).
authors.forename: Leslie J
authors.initials: LJ
authors.lastname: Dickmann
authors.affiliation: Amgen Pharmacokinetics and Drug Metabolism, Seattle, Washington (R.S.F.); Department of Pharmaceutics, University of Washington, Seattle, Washington (N.I., A.Z., L.J.D., B.R.B.); Core Laboratory for Neuromolecular Production, Department of Biomedical and Pharmaceutical Sciences, University of Montana, Missoula, Montana (P.D.); CNRS, Université Nice Sophia Antipolis, Institut de Pharmacologie Moléculaire et Cellulaire, UMR 7275, Valbonne, France (D.D.).
authors.forename: Brian R
authors.initials: BR
authors.lastname: Buttrick
authors.affiliation: Amgen Pharmacokinetics and Drug Metabolism, Seattle, Washington (R.S.F.); Department of Pharmaceutics, University of Washington, Seattle, Washington (N.I., A.Z., L.J.D., B.R.B.); Core Laboratory for Neuromolecular Production, Department of Biomedical and Pharmaceutical Sciences, University of Montana, Missoula, Montana (P.D.); CNRS, Université Nice Sophia Antipolis, Institut de Pharmacologie Moléculaire et Cellulaire, UMR 7275, Valbonne, France (D.D.).
authors.forename: Philippe
authors.initials: P
authors.lastname: Diaz
authors.affiliation: Amgen Pharmacokinetics and Drug Metabolism, Seattle, Washington (R.S.F.); Department of Pharmaceutics, University of Washington, Seattle, Washington (N.I., A.Z., L.J.D., B.R.B.); Core Laboratory for Neuromolecular Production, Department of Biomedical and Pharmaceutical Sciences, University of Montana, Missoula, Montana (P.D.); CNRS, Université Nice Sophia Antipolis, Institut de Pharmacologie Moléculaire et Cellulaire, UMR 7275, Valbonne, France (D.D.).
authors.forename: Dominique
authors.initials: D
authors.lastname: Douguet
mesh_terms: D000595:Amino Acid Sequence; D020134:Catalytic Domain; D003577:Cytochrome P-450 Enzyme System / Q000737:chemistry / Q000378:metabolism*; D006801:Humans; D007700:Kinetics; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009539:Nicotinic Acids / Q000378:metabolism*; D004364:Pharmaceutical Preparations / Q000378:metabolism; D018168:Receptors, Retinoic Acid / Q000819:agonists; D000072516:Retinoic Acid 4-Hydroxylase; D013379:Substrate Specificity; D014212:Tretinoin / Q000378:metabolism; D015262:Xenobiotics / Q000378:metabolism*
chemical_list: D009539:Nicotinic Acids; D004364:Pharmaceutical Preparations; D018168:Receptors, Retinoic Acid; D015262:Xenobiotics; C000609782:tazarotenic acid; D014212:Tretinoin; D003577:Cytochrome P-450 Enzyme System; C000607079:CYP26B1 protein, human; D000072516:Retinoic Acid 4-Hydroxylase