Productsof Bindingof 7,12-Dimethylbenz(a)anthraceneto DMAin Mouse Skin1

Dimethylbenz(a)anthracene (DMBA):deoxyribonucleo- side-adducts, from enzymatic hydrolysis of DNA from mouse skin exposed to (3H)DMBA in vivo, were analyzed by reverse- phase high-pressure liquid chromatography. Double-labeling studies showed that the adducts were qualitatively identical to those formed in mouse embryo cell cultures. These have been tentatively identified as bay-region anf/'-dihydrodiol epoxide: deoxyguanosine- and :deoxyadenosine adducts and a bay-re gion syn-dihydrodiol epoxide:deoxyadenosine-adduct (where the terms syn and anti define dihydrodiol-epoxides wherein the ben- zylic hydroxyl group and epoxide oxygen are cis or frans to one another, respectively). The relative amounts of individual adducts did not vary substantially with time or with the sex of the mice. However, the syn-dihydrodiol-epoxide:deoxyadenosine-adduct did increase with dose and constituted as much as 40% of the total DNA binding at high doses of DMBA. This is in contrast to the much lower (2 to 3%) levels of binding to deoxyadenosine residues in mouse skin reported for the less potent tumor initiator benzo(a)pyrene. The greater reactivity of DMBA with deoxy adenosine residues in mouse skin may play a role in determining its greater tumor initiating potential.