title: Relative contributions of the five major human cytochromes P450, 1A2, 2C9, 2C19, 2D6, and 3A4, to the hepatic metabolism of the proteasome inhibitor bortezomib.
abstract: VELCADE (bortezomib, PS-341), reversibly inhibits the 20S proteasome and exhibits cytotoxic and antitumor activities. Pretreatment of cancer cells with bortezomib increases the chemosensitivity of these cells, suggesting that bortezomib may be used in combination chemotherapy. The relative contributions of the five major human cytochromes P450 (P450s), 1A2, 2C9, 2C19, 2D6, and 3A4 (the focus of the present study), to the metabolism of bortezomib are an important aspect of potential drug interactions. Relative activity factor (RAF), chemical inhibition, and immunoinhibition using monoclonal antibodies were three approaches employed to determine the relative contributions of the major human P450s to the net hepatic metabolism of bortezomib. RAFs for the P450 isoform-selective substrates were determined; the ratio of the rate of metabolism of bortezomib with cDNA-expressed P450s versus rate of metabolism with human liver microsomes was normalized with respect to the RAF for each P450 isoform to determine the percentage contributions of the P450s to the net hepatic metabolism of bortezomib. CYP3A4 followed by CYP2C19 were determined to be the major contributors to the metabolism of bortezomib. Chemical inhibition and immunoinhibition confirmed that CYP3A4 and CYP2C19 were the major P450s responsible for the hepatic metabolism of bortezomib. The studies were conducted with 2 muM bortezomib, and the disappearance of bortezomib, rather than appearance of a specific metabolite, was quantified to determine the contributions of the P450s to the overall hepatic metabolism of bortezomib in humans.
authors.affiliation: Department of Drug Metabolism and Pharmacokinetics, Drug Safety and Disposition, Millennium Pharmaceuticals, Cambridge, MA 02139, USA. vinita.uttamsingh@mpi.com
authors.forename: Vinita
authors.initials: V
authors.lastname: Uttamsingh
authors.forename: Chuang
authors.initials: C
authors.lastname: Lu
authors.forename: Gerald
authors.initials: G
authors.lastname: Miwa
authors.forename: Liang-Shang
authors.initials: LS
authors.lastname: Gan
mesh_terms: D000911:Antibodies, Monoclonal / Q000494:pharmacology; D001189:Aryl Hydrocarbon Hydroxylases / Q000037:antagonists & inhibitors / Q000276:immunology / Q000378:metabolism*; D001897:Boronic Acids / Q000378:metabolism*; D000069286:Bortezomib; D019388:Cytochrome P-450 CYP1A2 / Q000276:immunology / Q000378:metabolism; D065609:Cytochrome P-450 CYP1A2 Inhibitors; D065731:Cytochrome P-450 CYP2C19; D065729:Cytochrome P-450 CYP2C9; D019389:Cytochrome P-450 CYP2D6 / Q000276:immunology / Q000378:metabolism; D065690:Cytochrome P-450 CYP2D6 Inhibitors; D051544:Cytochrome P-450 CYP3A; D065607:Cytochrome P-450 Enzyme Inhibitors; D003577:Cytochrome P-450 Enzyme System / Q000276:immunology / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006801:Humans; D007700:Kinetics; D008862:Microsomes, Liver / Q000378:metabolism*; D006899:Mixed Function Oxygenases / Q000037:antagonists & inhibitors / Q000276:immunology / Q000378:metabolism*; D011480:Protease Inhibitors / Q000378:metabolism*; D011719:Pyrazines / Q000378:metabolism*; D011994:Recombinant Proteins / Q000378:metabolism
chemical_list: D000911:Antibodies, Monoclonal; D001897:Boronic Acids; D065609:Cytochrome P-450 CYP1A2 Inhibitors; D065690:Cytochrome P-450 CYP2D6 Inhibitors; D065607:Cytochrome P-450 Enzyme Inhibitors; D004791:Enzyme Inhibitors; D011480:Protease Inhibitors; D011719:Pyrazines; D011994:Recombinant Proteins; D000069286:Bortezomib; D003577:Cytochrome P-450 Enzyme System; D006899:Mixed Function Oxygenases; C450260:CYP2C9 protein, human; D065729:Cytochrome P-450 CYP2C9; D001189:Aryl Hydrocarbon Hydroxylases; C504573:CYP1A2 protein, human; C045793:CYP2C19 protein, human; D019388:Cytochrome P-450 CYP1A2; D065731:Cytochrome P-450 CYP2C19; D019389:Cytochrome P-450 CYP2D6; D051544:Cytochrome P-450 CYP3A; C510163:CYP3A4 protein, human