Identification of human CYP forms involved in the activation of tamoxifen and irreversible binding to DNA

被引:80
作者
Boocock, DJ
Brown, K
Gibbs, AH
Sanchez, E
Turteltaub, KW
White, INH
机构
[1] Univ Leicester, Dept Obstet & Gynaecol, MRC, Mol Endocrinol Grp, Leicester LE2 7LX, Leics, England
[2] Univ Leicester, Canc Biomarkers & Prevent Grp, Leicester LE1 7RH, Leics, England
[3] Lawrence Livermore Natl Lab, Biol & Biotechnol Res Program, Livermore, CA 94550 USA
关键词
D O I
10.1093/carcin/23.11.1897
中图分类号
R73 [肿瘤学];
学科分类号
100214 ;
摘要
This study investigates which CYP forms are responsible for the conversion of tamoxifen to its putative active metabolite a-hydroxytamoxifen and irreversible binding to DNA. We have used eight different baculovirus expressed recombinant human CYP forms and liquid chromatography-mass spectrometry to show that only CYP3A4 is responsible for the NADPH-dependent alpha-hydroxylation of tamoxifen. Surprisingly, this CYP did not catalyse the formation of 4-hydroxytamoxifen. We demonstrate for the first time, by means of accelerator mass spectrometry, that CYP3A4 also catalysed the activation of [C-14]tamoxifen to intermediates that irreversibly bind to exogenous DNA. Incubation of [C-14]tamoxifen (20.6 kBq, 100 muM) with CYP3A4, in the presence of NADPH for 60 min led to levels of DNA binding of 39.0+/-9.0 adducts/10(8) nucleotides (mean +/- SE, n = 6). While CYP3A4 converted tamoxifen to N-desmethyltamoxifen (38.3 +/- 7.20 pmol/20 min/pmol CYP, n = 4), the polymorphic CYP2D6 showed the highest activity for producing this metabolite (48.6 +/- 1.52 pmol/20 min/pmol CYP). CYP2D6 was also the most active in catalysing 4-hydroxylation of tamoxifen, although an order of magnitude lower level was also detected with CYP2C19. With tamoxifen as substrate, no 3,4-dihydroxytamoxifen could be detected with any CYP form. CYP2B6 did not catalyse the metabolism or the binding of tamoxifen to DNA. It is concluded that CYP3A4 is the only P450 of those tested that converts tamoxifen to a-hydroxytamoxifen and the only one that results in appreciable levels of irreversible binding of tamoxifen to DNA.
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页码:1897 / 1901
页数:5
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