ANALYSIS OF 7-METHYLBENZ[A]ANTHRACENE-DNA ADDUCTS FORMED IN SENCAR MOUSE EPIDERMIS BY P-32 POSTLABELING

The present study has analysed the DNA adducts formed in SENCAR mouse epidermis following topical application of 7-methylbenz[a]anthracene ( 7-MBA). Mice were treated with 400 mmol of 7-MBA, which represents an initiating dose of this hydrocarbon for SENCAR mice, DNA adducts were analysed 24 h after topical application of the hydrocarbon by P-32-pos tlabeling coupled with either HPLC analysis or an improved TLC procedu re giving better resolution of DNA adducts through the use of a D6 sol vent [isopropanol:4N NH4OH (1:1)] following D5, Twenty-four hours afte r topical application of 400 nmol 7-MBA, the level of total covalent b inding was 0.37 +/- 0.07 pmol/mg DNA as determined by P-32-postlabelin g. This level of binding correlated web with the relative tumor initia ting activity of this hydrocarbon compared to 7,12-dimethylbenz[a]anth racene (6.4 +/- 0.01 pmol/mg DNA) and dibenz[a,j]anthracene (0.03 +/- 0.01 pmol/mg DNA), Analysis of the P-32-labeled 3',5'-diphosphodeoxyri bonucleosides by HPLC and TLC revealed the presence of deoxyguanosine (dGuo) and deoxyadenosine (dAdo) adducts formed from both the anti- an d syn-bay-region diol-epoxides of 7-MBA (anti- and syn-7-MBADEs). The major DNA adduct derived from 7-MBA in mouse epidermis was tentatively identified as (+) anti-7-MBADE-trans-N-2-dGuo. In addition, a minor d Guo adduct derived from the bay-region syn-diol-epoxide of 7-MBA was d etected as well as a minor dAdo adduct from this diol-epoxide. Another minor dAdo adduct was also detectably present which arose from either the anti- or syn-diol epoxide, Furthermore, several unidentified DNA adducts were present in both HPLC and TLC chromatograms of DNA samples from 7-MBA-treated mice. These results are discussed in terms of the role of specific 7-MBA-DNA adducts in tumor initiation by this hydroca rbon.