ALPHA-HYDROXYTAMOXIFEN IS A SUBSTRATE OF HYDROXYSTEROID (ALCOHOL) SULFOTRANSFERASE, RESULTING IN TAMOXIFEN DNA-ADDUCTS

When alpha-hydroxytamoxifen (alpha-OHTAM) was incubated with rat liver hydroxysteroid (alcohol) sulfotransferase a (STa) and 3'-phosphoadeno sine 5'-phosphosulfate, (E)-alpha-OHTAM was found to be a better subst rate for STa than (Z)-alpha-OHTAM. To explore the formation of tamoxif en (TAM)-derived DNA adducts, DNA was incubated with STa and either (E )-alpha-OHTAM or (Z)-alpha-OHTAM in the presence of 3'-phosphoadenosin e 5'-phosphosulfate, Using P-32-postlabeling analysis, the amount of T AM-DNA adducts resulting from (E)-alpha-OHTAM was 29 times higher than that observed with (E)-alpha-OHTAM alone. Using (Z)-alpha-OHTAM and S Ta, some TAM-DNA adducts were also detected but at levels 6.5 times lo wer than that observed with (E)-alpha-OHTAM and STa. When compared wit h standards of stereoisomers of 2'-deoxyguanosine 3'-monophosphate-N-2 -tamoxifen, the major tamoxifen adduct was identified chromatographica lly as an epimer of the trans form of alpha-(N-2-deoxyguanosinyl)tamox ifen, and the minor adduct was identified as an epimer of the cis form , In the reaction mixture, a conversion from (E)-alpha-OHTAM to (Z)-al pha-OHTAM through the carbocation intermediate was also detected, Thes e results show that sulfation of alpha-OHTAM catalyzed by STa results in the formation of TAM-DNA adducts.