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Correlation between Formation of a Specific Hydrocarbon-Deoxyribonucleoside Adduct and Tumor-initiating Activity of 7,12-Dimethylbenz(a)anthracene and Its 9- and 10-Monofluoroderivatives in Mice¹

The University of Texas System Cancer Center, Science Park-Research Division, Smithville, Texas 78957

The formation of epidermal DNA adducts from 9-fluoro-7,12-dimethylbenz(a)anthracene (9-F-DMBA) was compared with 7,12-dimethylbenz(a)anthracene (DMBA) and 10-fluoro-7,12-dimethylbenz(a)anthracene (10-F-DMBA) in SENCAR mice. 9-F-DMBA is equipotent, whereas 10-F-DMBA is more potent than DMBA for skin tumor initiation in this mouse stock. The quantity of covalently bound DNA adducts was essentially identical between 9-F-DMBA and DMBA at all doses tested in the range of 10 to 100 nmol/mouse. These results correlated closely with the dose-response relationships for tumor initiation by the two hydrocarbons. A quantitative comparison of the hydrocarbon-DNA adducts formed after topical application of 100 nmol of DMBA, 9-F-DMBA, and 10-F-DMBA yielded interesting results. The total binding for the three hydrocarbons at this dose was 16.2 ± 2.6, 18.4 ± 2.4, and 52.3 ± 6.8 pmol/mg of epidermal DNA, respectively. Analysis of these DNA adduct samples by dihydroboronate chromatography demonstrated marked reductions in the percentage of syn-diol-epoxide-DNA adducts with both 9-F-DMBA (24%) and 10-F-DMBA (18%) compared with DMBA (57%).

Analysis of DNA adduct samples from DMBA-, 9-F-DMBA-, and 10-F-DMBA-treated mice (100 nmol/mouse) by high-pressure liquid chromatography revealed qualitatively similar profiles. However, a quantitative comparison of the three major DNA adducts, tentatively identified as anti-diol-epoxide-deoxyguanosine (Peak I), syn-diol-epoxide-deoxyadenosine (Peak II), and anti-diol-epoxide-deoxyadenosine (Peak III), revealed significant differences. With both 9-F-DMBA and 10-F-DMBA there were marked increases (236% and 644%, respectively) in the quantity of Peak I compared to DMBA. On the other hand, Peak II was formed in approximately equal amounts with DMBA and 10-F-DMBA but only 50% of the DMBA value with 9-F-DMBA. Interestingly, Peak III was formed in approximately equal amounts with both DMBA and 9-F-DMBA but was increased to 337% of the DMBA value with 10-F-DMBA. Thus, the actual level of Peak III (tentatively identified as anti-diol-epoxide-deoxyadenosine) correlated closely with the tumor-initiating activity of these three hydrocarbons, whereas the levels of the other two adducts did not. These data suggest that formation of a specific DNA adduct may be important for DMBA skin tumor initiation. These data are discussed in relation to skin tumor initiation by other hydrocarbons.

¹ Research was supported by NIH Grant CA-36979 from the Department of Health and Human Services.

² To whom requests for reprints should be addressed.

Received 1/13/86. Revised 4/25/86. Accepted 5/19/86.

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