ALPHA-HYDROXYTAMOXIFEN, A METABOLITE OF TAMOXIFEN WITH EXCEPTIONALLY HIGH DNA-BINDING ACTIVITY IN RAT HEPATOCYTES

It has been proposed that the antiestrogen tamoxifen induces liver tum ors in rats and genotoxic effects in vitro through metabolic activatio n involving, initially, alpha-hydroxylation of the ethyl group. To tes t this hypothesis, the extent of DNA adduct formation in primary rat h epatocytes treated with tamoxifen and alpha-hydroxytamoxifen was inves tigated. Hepatocytes from female Fischer F-344 rats were treated with 1 or 10 mu M concentrations of either alpha-hydroxytamoxifen or tamoxi fen. DNA was isolated and analyzed for the presence of DNA adducts by P-32 postlabeling. Chromatography on polyethyleneimine cellulose thin layer chromatography and reverse-phase high performance liquid chromat ography revealed that the same pattern of adducts was formed by both c ompounds. However, the level of adduct formation was 25 and 49 times g reater with alpha-hydroxytamoxifen than with tamoxifen at 1 and 10 mu M, respectively. The formation of alpha-hydroxytamoxifen as a metaboli te of tamoxifen was demonstrated by mass spectrometric analysis of the extracted culture medium. alpha-Hydroxytamoxifen was found to react w ith DNA in the absence of metabolizing enzymes. These results demonstr ate the involvement of alpha-hydroxylation in the metabolic activation of tamoxifen.