Determination of Tamoxifen−DNA Adducts in Leukocytes from Breast Cancer Patients Treated with Tamoxifen

Tamoxifen (TAM), a widely used antiestrogen for breast cancer therapy and chemoprevention, increases the incidence of endometrial cancer in women. The formation of DNA adducts induced by tamoxifen may initiate endometrial cancer. To evaluate the genotoxic risk of TAM, the formation of DNA adducts in leukocytes was examined. Blood samples were collected from 47 breast cancer patients (61.7 ± 12.5 years) taking TAM (20 mg/day; average duration until sampling, ∼37 months) and 20 untreated patients (58.2 ± 12.3 years), and their leukocyte DNA was analyzed by 32P-postlabeling/HPLC analysis. This assay resolves synthetic standards, trans- and cis-diastereoisomers of α-(N 2-deoxyguanosinyl)tamoxifen 3‘-monophosphate (dG3 ‘ P-N 2-TAM), α-(N 2-deoxyguanosinyl)-N-desmethyltamoxifen 3‘-monophosphate (dG3 ‘ P-N 2-N-dMeTAM), and α-(N 2-deoxyguanosinyl)tamoxifen N-oxide 3‘-monophosphate‘, and is capable of determining TAM adducts quantitatively. The detection limit of this assay is 0.6 adducts/109 nucleotides. trans-dG3 ‘ P-N 2-TAM (fr-2; one of the two trans-isomers) was detected in six of 47 breast cancer patients treated with TAM. Among them, trans-dG3 ‘ P-N 2-N-dMeTAM (fr-2) was also detected in two patients. The total amounts of TAM−DNA adducts in the positive patients were 2.6 ± 3.0 adducts/109 nucleotides. No adducts were detected in the controls. The presence of TAM−DNA adducts in the leukocyte DNA samples was confirmed using several 32P-postlabeling/HPLC systems.