DNA ADDUCT-FORMATION BY TAMOXIFEN AND STRUCTURALLY-RELATED COMPOUNDS IN RAT-LIVER

Binding of diethylstilbestrol and four different triphenylethylene der ivatives: tamoxifen, toremifene, clomiphene and triparanol to DNA in r at liver, was studied using the P-32-postlabelling method with HPLC-ra dioactivity detection. Three different modifications of the P-32-postl abelling technique (a) a bisphosphate method with adduct enrichment by nuclease P1 (NP1)-treatment or (b) by butanol extraction and (c) a mo nophosphate method, were applied in order to provide an unbiased analy sis of adduct formation. When tamoxifen was administered by daily gava ge for 4 weeks (80 mu mol/kg for 2 weeks and 40 mu mol/kg for a furthe r 2 weeks) two major adducts and about six minor adducts were produced in the liver of female Sprague-Dawley rats. Equimolar doses of toremi fene produced one apparent adduct. The adduct levels in the tamoxifen and toremifene treated rats were 600 and 2/10(8) nucleotides, respecti vely. Under conditions used, clomiphene, triparanol and diethylstilbes trol did not produce DNA adducts. The present and previous data sugges t that modification (a) is the P-32-postlabelling method of choice for risk assessment in human subjects. Modification (c) with butanol extr action after labelling has the advantage of low background radioactivi ty and may be preferable if large amounts of DNA are available. The ma in tamoxifen adducts were suggested to be alpha-(N-2-deoxyguanosinyl)t amoxifen and alpha-(N-2-deoxyguanosinyl)-N-desmethyltamoxifen. (C) 199 8 Elsevier Science Ireland Ltd. All rights reserved.