Identification of hepatic tamoxifen–DNA adducts in mice: α-(N2-deoxyguanosinyl)tamoxifen and α-(N2-deoxyguanosinyl)tamoxifen N-oxide

Tamoxifen‐DNA adducts detected in the liver of mice Among such anti-cancer drugs, the treatment period of treated with tamoxifen have not yet been identified. In the tamoxifen is exceptionally long (3–5 years). Therefore, careful present study a new type of tamoxifen‐DNA adduct, four evaluation of safety for chronic use of tamoxifen is required. stereoisomers of α-(N 2 -deoxyguanosinyl)tamoxifen N-oxide Tamoxifen is a potent carcinogen targeting the liver in rats 3-monophosphate (dG3P-N 2 -TAM N-oxide) were prepared (9,10). Carcinogenic actions of tamoxifen toward rat liver as standard DNA adducts by reacting 2-deoxyguanosine are not related to its estrogen antagonist activity but occur 3-monophosphate with trans-α-acetoxytamoxifen N-oxide through DNA adduct formation (11). When liver DNA from in addition to four stereoisomers of α-(N 2 -deoxyguano- tamoxifen-treated mice and rats were analyzed by 32 P-postsinyl)tamoxifen 3-monophosphate (dG3P-N 2 -TAM) that labeling HPLC analysis, many tamoxifen–DNA adduct peaks was reported previously. Liquid chromatography-electro- were observed (12). Osborne et al. (13) indicated that trans-αspray ionization‐mass spectrometry of the reaction (N 2 -deoxyguanosinyl)tamoxifen (trans-dG-N 2 -TAM) is a major products gave the most abundant ion at m/z 731 ([M ‐ H] ‐ ), tamoxifen–DNA adduct in rat liver. Using the in vitro reaction which corresponded to dG3P-N 2 -TAM N-oxide. The modi- of DNA with tamoxifen α-sulfate or α-acetoxytamoxifen, cisfied products digested by alkaline phosphatase corre- dG-N 2 -TAM was also identified as a minor adduct by mass sponded to the isomers of dG-N 2 -TAM N-oxide whose spectrometry and nuclear magnetic resonance (14,15). Howstructures were identified previously by mass spectrometry ever, no information was available on whether such minor and nuclear magnetic resonance. Using these standard adducts are formed in tissues of tamoxifen-treated animals. In markers, we analyzed the hepatic DNA adducts of female theory, reaction of α-acetoxytamoxifen or tamoxifen α-sulfate DBA/2 mice treated with tamoxifen at a dosage of 120 mg/ with DNA or 2-deoxyguanosine (dG) yielded four stereokg/day for 7 days by 32 P-post-labeling coupled with an isomers of dG-N 2 -TAM (two epimers at α-position of the trans HPLC/radioactive detector. Mixtures of eight isomers of form and two epimers of the cis form) (14). Therefore, to dG3P-N 2 -TAM and dG3P-N 2 -TAM N-oxide were separated identify the epimers of dG-N 2 -TAM adducts in tamoxifeninto six peaks, since each of the cis epimers were not treated animals, authentic isomers and high-resolution HPLC separated under the present HPLC conditions. Nine conditions are required.