Identification of tamoxifen-DNA adducts formed by alpha-sulfate tamoxifen and alpha-acetoxytamoxifen.

alpha-Sulfate trans-tamoxifen and alpha-sulfate cis-tamoxifen were synthesized as proposed active metabolites of tamoxifen that react with DNA. alpha-Acetoxytamoxifen was prepared as a model-activated form to produce a reactive carbocation. Calf thymus DNA was reacted with alpha-hydroxytamoxifen or the activated forms of tamoxifen, and tamoxifen-DNA adducts were analyzed by a 32P-postlabeling method. The reactivity of alpha-sulfate trans-tamoxifen to DNA was much higher than that of alpha-hydroxytamoxifen. The formation of tamoxifen-DNA adducts induced by alpha-acetoxytamoxifen and alpha-sulfate cis-tamoxifen was 1100- and 1600-fold, respectively, higher than that of alpha-hydroxytamoxifen. Both alpha-sulfate tamoxifens and alpha-acetoxytamoxifen were highly reactive to 2'-deoxyguanosine. Four reaction products of dG-tamoxifen were isolated by HPLC and characterized by mass- and proton magnetic resonance spectroscopy. Fractions 1 and 2 that eluted first were identified as the epimers of trans form of dG-N2-tamoxifen. Fractions 3 and 4 were identified as the epimers of cis form of dG-N2-tamoxifen. When DNA was reacted with alpha-acetoxytamoxifen in vitro, three isomers of dG-N2-tamoxifen were detected: fraction 2 was the major adduct while fractions 1 and 3 were minor adducts.