Quantitative comparison of carcinogenicity, mutagenicity and electrophilicity of 10 direct-acting alkylating agents and of the initial O6:7-alkylguanine ratio in DNA with carcinogenic potency in rodents.

The quantitative relationship between carcinogenicity in rodents and mutagenicity in Salmonella typhimurium was examined, by using 10 monofunctional alkylating agents, including N-nitrosamides, alkyl methanesulfonates, epoxides, beta-propiolactone and 1,3-propane sultone. The compounds were assayed for mutagenicity in two S. typhimurium strains (TA1535 and TA100) and in plate and liquid assays. The mutagenic activity of the agents was compared with their alkylating activity towards 4-(4'-nitrobenzyl)pyridine and with their half-lives (solvolysis constants) in an aqueous medium. No correlations between these variables were found, nor was mutagenic activity correlated with estimates of carcinogenicity in rodents. There was a positive relationship between carcinogenicity and the initial ratios of 7-:O6-alkylguanine formed or expected after their reaction with double-stranded DNA in vitro. The results suggest that alkylation of guanine at position O6 (or at other O atoms of DNA bases) may be a critical DNA-base modification that determines the overall carcinogenicity of these alkylating agents in rodents.