title: Roles of cytochromes P450 1A2, 2A6, and 2C8 in 5-fluorouracil formation from tegafur, an anticancer prodrug, in human liver microsomes.
abstract: Tegafur, an anticancer prodrug, is bioactivated to 5-fluorouracil (5-FU) mainly by cytochrome P450 (P450) enzymes. The conversion from tegafur into 5-FU catalyzed by human liver microsomal P450 enzymes was investigated. In fourteen cDNA-expressed human P450 enzymes having measurable activities, CYP1A2, CYP2A6, CYP2E1, and CYP3A5 were highly active in catalyzing 5-FU formation at a tegafur concentration of 100 microM. Kinetic analysis revealed that CYP1A2 had the highest V(max)/K(m) value and that the V(max) value of CYP2A6 was high in 5-FU formation. In human liver microsomes, the activities of 5-FU formation from 10 microM, 100 microM, and 1 mM tegafur were significantly correlated with both coumarin 7-hydroxylation (r = 0.83, 0.86, and 0.74) and paclitaxel 6 alpha-hydroxylation (r = 0.77, 0.62, and 0.85) activities, respectively. Coumarin efficiently inhibited the 5-FU formation activities from 100 microM and 1 mM tegafur catalyzed by human liver microsomes that had high coumarin 7-hydroxylation activity. On the other hand, furafylline, fluvoxamine, and quercetin, as well as coumarin, showed inhibitory effects in liver microsomes that had high catalytic activities of 5-FU formation. The other P450 inhibitors examined showed weak or no inhibition in human liver microsomes. Polyclonal anti-CYP1A2 antibody, monoclonal anti-CYP2A6, and anti-CYP2C8 antibodies inhibited 5-FU formation activities to different extents in those two microsomal samples. These results suggest that CYP1A2, CYP2A6, and CYP2C8 have important roles in human liver microsomal 5-FU formation and that the involvement of these three P450 forms differs among individual humans.
authors.affiliation: Faculty of Pharmaceutical Sciences, Kanazawa University, Kanazawa, Japan.
authors.forename: T
authors.initials: T
authors.lastname: Komatsu
authors.forename: H
authors.initials: H
authors.lastname: Yamazaki
authors.forename: N
authors.initials: N
authors.lastname: Shimada
authors.forename: M
authors.initials: M
authors.lastname: Nakajima
authors.forename: T
authors.initials: T
authors.lastname: Yokoi
mesh_terms: D000964:Antimetabolites, Antineoplastic / Q000378:metabolism*; D001189:Aryl Hydrocarbon Hydroxylases; D016367:Baculoviridae / Q000378:metabolism; D019388:Cytochrome P-450 CYP1A2 / Q000378:metabolism*; D065637:Cytochrome P-450 CYP2A6; D065727:Cytochrome P-450 CYP2C8; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism*; D005472:Fluorouracil / Q000378:metabolism*; D006801:Humans; D066298:In Vitro Techniques; D007700:Kinetics; D008862:Microsomes, Liver / Q000201:enzymology*; D006899:Mixed Function Oxygenases / Q000378:metabolism*; D011355:Prodrugs / Q000378:metabolism*; D011994:Recombinant Proteins / Q000378:metabolism; D039181:Steroid 16-alpha-Hydroxylase; D013250:Steroid Hydroxylases / Q000378:metabolism*; D005641:Tegafur / Q000378:metabolism*
chemical_list: D000964:Antimetabolites, Antineoplastic; D011355:Prodrugs; D011994:Recombinant Proteins; D005641:Tegafur; D003577:Cytochrome P-450 Enzyme System; D006899:Mixed Function Oxygenases; D013250:Steroid Hydroxylases; D001189:Aryl Hydrocarbon Hydroxylases; C504573:CYP1A2 protein, human; C585710:CYP2A6 protein, human; C450259:CYP2C8 protein, human; D019388:Cytochrome P-450 CYP1A2; D065637:Cytochrome P-450 CYP2A6; D065727:Cytochrome P-450 CYP2C8; D039181:Steroid 16-alpha-Hydroxylase; D005472:Fluorouracil