Mutagenic selectivity of carcinogenic nitroso compounds: III. N,alpha-acetoxymethyl-N-methylnitrosamine

A comparative genetic study was undertaken on the testicular tissue of Drosophila with N-alpha-acetoxymethol-N-METHYLNITROSAMINE (AcODMN) and its unsubstituted parent N,N-dimethylnitrosamine (DMN), to assess the role of intracellular metabolism on their mutagenicities. The relative genetic potencies of the two compounds were deduced from regression studies of the dose effect on the metabolically inert sperm and the metabolizing early germ cells (spermatocytes and spermatogonia) with respect to the induction of the non-specific X-chromosome recessives (lethals and visibles) and the specific effects on representatives of the RNA genes, especially rDNA. Genetic activity per unit molar dose was invariably higher for the acetoxy derivative as compared to the parent amine, but the differential in this respect varied significantly for various mutational classes and as a function of the metabolic level in the target cells. The induction of point-mutations (X-recessives) increased with the level of intracellular metabolism with bothe compounds and this was more pronounced with the parent amine, which was in accordance with the DNA methylation mechanism. In contrast, the yield of the specific rDNA deletions was not markedly enhanced with the increased metabolic activity in the early germ cells, especially with the acetoxy derivative. The induction of these deletions could not, therefore, be explained on the basis of DNA methylation, but was reconcilable with the posible generation of a nitroso-aldehydic metabolite, which could effect DNA-protein cross-linkage within the genic nucleoproteins. The two test compounds gave comparable frequencies of mosaicism among corresponding mutations and the same rDNA selectivity index, which indicated identical molecular mechanisms of mutagenesis. The higher genetic potency of the acetoxy derivative as compared to the parent amine would thus be indicative of its greater yield of the same mutagenic metabolites. Carcinogenicity studies with the two compounds paralleled the mutagenicity results, which whould suggest that the same molecular mechanisms could well be responsible for the initiation of both phenomena.