Comparative DNA binding of 7, 12-dimethylbenz[a]anthracene and some of its metabolites in mouse epidermis in vivo as revealed by the 32P-postlabeling technique

The binding of some mouse skin metabolites and related derivativesof the tumor initiator 7,12-dimethylbenz[a]-anthracene (DMBA)was investigated by ³²P-postlabeling analysis after its topicaladministration. DMBA and trans-3,4-dihydro3,4-dihydroxy-DMBA(DMBA-3,4-dihydro-diol) both led to the formation of four DNAadducts, which showed a very similar pattern of spots on thin-layer chromato-grams. With trans-8,9-Ktihdbro-8,9-dihydroxy-7,12-dimethyl-benz[a]anthracene(DMBA-8,9-dihydrodiol) one major adduct was obtained which waschromatographically indistinguishable from one of the DMBA adducts.In contrast, 7-hydroxymethyl-12-methylbenz[a]anthracene (7-OHM-12-MBA)gave rise to two major adducts which were separable from DMBAadducts. 3-hydroxy-7, 12-dimethyIbenz[a]anthra-cene (3-OH-DMBA)and 7,12-dimethylbenz[a]anthracene-7, 12-epoxide (DMBA-O2) didnot lead to detectable amounts of adducts. Quantitative determinationof DNA binding showed that an initiating dose (i = 100 nmol)of DMBA yielded {small tilde}12 adducts/10⁷ normal nucleotides.Adduct formation with the same dose of DMBA-3,4-dihydrodiolwas 7-8 times higher. At a 4-fold higher dose level, DMBA-8,9-dihydrodiolexhibited a 3- to 6-times weaker binding and 7-OHM-12-MBA aslightly stronger binding than DMBA. Chromatography of the DMBAand DMBA-3,4-dihydrodiol adducts with a solvent containing borateshowed a decreased mobility of two out of four adducts in eachcase. These adducts were also sensitive to oxidation by periodate.The results suggest that two DMBA adducts carried vicinal cis-hydroxylgroups and thus were probably derived from the anti3,4-dihydrodiol1,2-oxide(s)of DMBA. The other two adducts were probably derived from thesyn-stereoisomer(s). When the DNA-modifying capabilities andinitiating activities of the more prominent mouse-skin metabolitesare considered in relation to DMBA, DMBA-3,4-dihydrodiol ispostulated to be a proximate and DMBA-3,4-dihydrodiol-1,2-oxide(s)to be ultimate initiators.