DNA adduct-formation by tamoxifen and structurally-related compounds in rat liver

Binding of diethylstilbestrol and four different triphenylethylene derivatives: tamoxifen, toremifene, clomiphene and triparanol to DNA in rat liver, was studied using the P-32-postlabelling method with HPLC-radioactivity detection. Three different modifications of the P-32-postlabelling technique (a) a bisphosphate method with adduct enrichment by nuclease P1 (NP1)-treatment or (b) by butanol extraction and (c) a monophosphate method, were applied in order to provide an unbiased analysis of adduct formation. When tamoxifen was administered by daily gavage for 4 weeks (80 mu mol/kg for 2 weeks and 40 mu mol/kg for a further 2 weeks) two major adducts and about six minor adducts were produced in the liver of female Sprague-Dawley rats. Equimolar doses of toremifene produced one apparent adduct. The adduct levels in the tamoxifen and toremifene treated rats were 600 and 2/10(8) nucleotides, respectively. Under conditions used, clomiphene, triparanol and diethylstilbestrol did not produce DNA adducts. The present and previous data suggest that modification (a) is the P-32-postlabelling method of choice for risk assessment in human subjects. Modification (c) with butanol extraction after labelling has the advantage of low background radioactivity and may be preferable if large amounts of DNA are available. The main tamoxifen adducts were suggested to be alpha-(N-2-deoxyguanosinyl)tamoxifen and alpha-(N-2-deoxyguanosinyl)-N-desmethyltamoxifen. (C) 1998 Elsevier Science Ireland Ltd. All rights reserved.