Identification and in vivo formation of ³²P-postlabeled rat mammary DMBA—DNA adducts

The in vivo formation of ³²P-postlabeled mammary 7,12-dimethylbenz[a]anthracene (DMBA)-DNA adducts was evaluated for female Sprague-Dawley rats following administration of DMBA (i.g.) at 1, 3, 5, 10 and 20 mg/ rat. Adduct formation was also measured as a function of time following DMBA intubation. At least eight adducts were formed in vivo in mammary epithelial cells. The identities of four of these nucleoside bisphosphate adduct spots were determined by cross-referencing with previously characterized ³H-labeled nucleoside DMBA adducts. These identified adducts constitute four of the five major adducts formed in vivo. Two adducts were identified as the anti-dihydrodiolepoxide of DMBA reacted with deoxyguanosine (dGuo). Two other major adducts were derived from the syn-dihydrodiolepoxide and bound to dGuo and to deoxyadenosine (dAdo). Total DMBA-DNA binding increased at all DMBA doses investigated (r = 0.94). Total binding values were ($X¯$ ± SEM) 39.3 ± 6.1, 158.0 ± 16.9, 194.7 ± 9.9, 326.9 ± 21.5 and 443.2 ± 20.8 nmol DMBA/mol DNA for rats administered DMBA at 1, 3, 5, 10 and 20 mg/ rat respectively. The anti-dGuo adduct predominated at all doses and times evaluated, contributing to ˜52% of total binding. The occurrence of anti-derived adducts was greater than that of syn-derived adducts. Binding of DMBA to dGuo substantially exceeded binding to dAdo. The ³²P-postlabeling procedure represents a sensitive technique for detecting specific DMBA-DNA adducts formed in vivo in the rat mammary gland.