Formation of tamoxifen-DNA adducts in human endometrial explants exposed to α-hydroxytamoxifen

An increased risk of developing endometrial cancer has been observed in women receiving tamoxifen (TAM) endocrine therapy and chemoprevention. The genotoxic damage induced by TAM metabolites may be involved in the development of endometrial cancer. To investigate the capability of endometrial tissues to form TAM-DNA adducts, primary cultured human endometrial explants were exposed to α-hydroxytamoxifen (α-OHTAM) and used for quantitative analysis of TAM-DNA adducts, using ³²P-postlabeling/HPLC analysis. A trans isoform of α-(N²-deoxyguanosinyl)tamoxifen (dG-N ²-TAM) was detected as the major adduct in eight of nine endometrial explants exposed to 100 μM α-OHTAM at levels of 7.7 ± 5.3 (mean ± SD) adducts/10⁷ nucleotides. Approximately 25- and 37-fold lower amounts of the cis form of dG-N²-TAM and another trans isoform were also detected. The dG-N₂-TAM adduct (3.3 adducts/ 10⁷ nucleotides) was detected in one of three endometrial explants exposed to 25 μM α-OHTAM No TAM-DNA adducts were detected in any unexposed tissues. These results indicate that TAM-DNA adducts are capable of forming through O-sulfonation and/or O-acetylation of α-OHTAM in the endometrium. The endometrial explant culture can be used as a model system to explore the genotoxic mechanism of antiestrogens for humans.