Identification of Tamoxifen−DNA Adducts Induced by α-Acetoxy-N-desmethyltamoxifen

Treatment with tamoxifen increased the risk of endometrial cancers in breast cancer patients and women participating in the chemoprevention study. In our laboratory, tamoxifen-DNA adducts, including alpha-(N-2-deoxyguanosinyl)tamoxifen (dG-N-2-TAM), were detected in the endometrium of women taking tamoxifen [Shibutani, S., et al. (1999) Chem. Res. Toxicol. 12, 646-653]. On the basis of recent animal studies, deoxyguanosinyl-N-desmethyltamoxifen (dG-N-desmethylTAM) adducts are also suspected to be formed in the liver. In the study presented here, we synthesized alpha-acetoxy-N-desmethyltamoxifen as a model activated metabolite of N-desmethyltamoxifen. The overall yield of alpha-acetoxy-N-desmethyltamoxifen from alpha-hydroxytamoxifen was approximately 42%. alpha-Acetoxy-N-desmethyltamoxifen was highly reactive to 2'-deoxyguanosine, as was similarly observed for tamoxifen alpha-sulfate. The two reaction products were identified as a mixture of epimers of the trans form or cis form of alpha-(N-2-deoxyguanosinyl)N-desmethyltamoxifen (dG-N-2-N-desmethylTAM) by mass and proton magnetic resonance spectres copy. In addition, the trans and cis forms of dG 3'-monophosphate-N-2-N-desmethylTAM were prepared as standard markers for P-32-postlabeling/HPLC analysis. Using this technique, dG-N-2-N-desmethylTAM adducts were detected in calf thymus DNA reacted with alpha-acetoxy-N-desmethyltamoxifen.