Article

Large interindividual variability in the in vitro formation of tamoxifen metabolites related to the development of genotoxicity.

Dr Margarete Fischer-Bosch Institut für Klinische Pharmakologie, Auerbachstr. 112, D-70376 Stuttgart, Germany.
British Journal of Clinical Pharmacology (Impact Factor: 3.69). 01/2002; 57(1):105-11. DOI: 10.1046/j.1365-2125.2003.01970.x
Source: PubMed

ABSTRACT To characterize the interindividual variability and the individual CYP involved in the formation of alpha-hydroxy-, N-desmethyl- and N-didesmethyl-tamoxifen from tamoxifen.
Microsomes from 50 human livers were used to characterize the interindividual variability in the alpha-hydroxylation, N-desmethylation and N-didesmethylation of tamoxifen. Selective inhibitors and recombinant enzymes were used to identify the forms of CYP catalysing these reactions.
The rates of formation of alpha-hydroxy-, N-desmethyl- and N-didesmethyl-tamoxifen were highly variable, and correlated with each other (P < 0.0001). The respective ranges were 0.7-11.4, 25.7-411, and below the limit of quantification--4.4 pmol mg(-1) protein min(-1). Formation of all metabolites was observed with expressed recombinant CYP3A4, inhibited by troleandomycin (65, 77 and 35%, respectively, P < 0.05) and associated with CYP3A4 expression (rs = 0.612, rs = 0.585 and rs = 0.430, P < 0.01, respectively).
Formation of alpha-hydroxy-, N-desmethyl- and N-didesmethyl-tamoxifen in vitro is highly variable and mediated predominantly by CYP3A4.

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