title: Cytochrome P450-mediated metabolism of the HIV-1 protease inhibitor ritonavir (ABT-538) in human liver microsomes.
abstract: The HIV-1 protease inhibitor ritonavir (ABT-538) undergoes cytochrome P450-mediated biotransformation in human liver microsomes to three major metabolites, Ml, M2 and M11, with wide interindividual variation in the rates of metabolite formation. The structures of these metabolites were determined with the use of electrospray ionization mass spectrometry. Chemical inhibition, metabolic correlation, immunoinhibition and metabolism by microsomes derived from specific CYP cDNA-transfected B-lymphoblastoid cell lines indicated that the CYP3A subfamily of enzymes was the major contributor to the formation of M1 and M11, whereas both CYP3A and CYP2D6 contributed to the formation of M2. None of the typical CYP3A substrates/inhibitors (e.g., ketoconazole, troleandomycin) were able to completely inhibit ritonavir metabolism, even at high concentrations. Ritonavir was found to be a potent inhibitor of CYP3A-mediated biotransformations (nifedipine oxidation, IC50) = 0.07 microM; 17alpha-ethynylestradiol 2-hydroxylation, IC50 = 2 microM; terfenadine hydroxylation, IC50 = 0.14 microM). Ritonavir was also found to be an inhibitor of the reactions mediated by CYP2D6 (IC50 = 2.5 microM) and CYP2C9/10 (IC50 = 8.0 microM). The results of this study indicate the potential for in vivo inhibition of the metabolism by ritonavir of drugs that are CYP3A, CYP2D6 and, to a lesser extent, CYP2C9/10 substrates.
authors.affiliation: Department of Biotransformation, Pharmaceutical Products Division, Abbott Laboratories, Abbott Park, Illinois, USA.
authors.forename: G N
authors.initials: GN
authors.lastname: Kumar
authors.forename: A D
authors.initials: AD
authors.lastname: Rodrigues
authors.forename: A M
authors.initials: AM
authors.lastname: Buko
authors.forename: J F
authors.initials: JF
authors.lastname: Denissen
mesh_terms: D000818:Animals; D000998:Antiviral Agents / Q000378:metabolism*; D065607:Cytochrome P-450 Enzyme Inhibitors; D003577:Cytochrome P-450 Enzyme System / Q000502:physiology*; D017320:HIV Protease Inhibitors / Q000378:metabolism*; D006801:Humans; D008862:Microsomes, Liver / Q000378:metabolism*; D011817:Rabbits; D019438:Ritonavir; D013844:Thiazoles / Q000378:metabolism*; D014633:Valine / Q000031:analogs & derivatives* / Q000378:metabolism
chemical_list: D000998:Antiviral Agents; D065607:Cytochrome P-450 Enzyme Inhibitors; D017320:HIV Protease Inhibitors; D013844:Thiazoles; D003577:Cytochrome P-450 Enzyme System; D014633:Valine; D019438:Ritonavir