Isolation and Degradation of DNA from Cells Treated with Tritium-labeled 7,12-Dimethylbenz(a)anthracene: Studies on the Nature of the Binding of This Carcinogen to DNA¹

In an attempt to obtain a source of material for chemical studies, the binding of 7,12-dimethylbenz(a)anthracene (DMBA) was studied in E. coli, B. subtilis, and ascites tumor cells. For the bacteria a dose-dependent binding was found, but the level of binding was low. In the case of the ascites tumor cells in the mouse, binding of DMBA to DNA, RNA, and protein showed a dependence on time after injection of the hydrocarbon, but again the level of binding was much less than that found earlier for mouse skin. Mouse L-cells and chicken fibroblasts in tissue culture again gave a low level of DMBA binding, but rodent embryo cells in culture, as reported earlier, were a good source of DNA having bound DMBA. Enzymic degradation of this material and subsequent fractionation suggested that the DMBA was bound to the bases of DNA, resulting in partial inhibition of the enzymic degradation of the DNA. A similar partial inhibition was observed for DNA alkylated with half-sulphur mustard but not for methylated DNA. The low level of in vivo, binding obtained suggests that alternative methods will be needed to establish both the nature of the bound hydrocarbon moiety and the base at which it is attached.