Received for publication April 26, 2005.
Revised June 24, 2005.
Accepted for publication August 11, 2005.

Formation of Tamoxifen-DNA Adducts via O-Sulfonation, not O-Acetylation, of -Hydroxytamoxifen in Rat and Human Livers

Abstract

Tamoxifen (TAM) is used as the standard endocrine therapy for breast cancer patients and as a chemopreventive agent for women at high risk for this disease. Unfortunately, treatment of TAM increases the incidence of endometrial cancer; this may be due to the genotoxic damage induced by TAM metabolites. Formation of TAM-DNA adducts in rat liver correlates with the development of hepatocarcinoma. TAM-DNA adducts are proposed to be formed through O-sulfonation and/or O-acetylation of -hydroxylated TAM and its metabolites. However, the role of O-sulfonation and O-acetylation in the formation of TAM-DNA adducts has not extensively investigated. Rat or human hydroxysteroid sulfotransferaes (HST), acetyltransferases and liver cytosol was incubated with calf thymus DNA, -OHTAM, and either 3'-phosphoadenosine 5'-phosphosulfate (PAPS) or acetyl coenzyme A (acetyl-CoA) as a cofactor and analyzed for TAM-DNA adduct formation, using ³²P-postlableling/polyacrylamide gel electrophoresis analysis. TAM-DNA adduct was formed when PAPS, not acetyl-CoA, was used. No TAM-DNA adducts were produced using human N-acetyltransferase I and II. HST antibody inhibited approximately 90 % of TAM-DNA adduct formation generated by the cytosol or HST, suggesting that HST is primarily involved in the formation of TAM-DNA adducts. The formation of TAM-DNA adducts with rat liver cytosol and HST was much higher than that of human liver cytosol and HST. Our results indicate that TAM-DNA adducts are formed via O-sulfonation, not O-acetylation, of -hydroxylated TAM and its metabolites.

Key words: acetyltransferases, chemical carcinogenesis, DNA adducts, drug toxicity, phase II drug metabolism, sulfotransferases

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