Concentration-dependent mutation by alkylating agents in human lymphoblasts and Salmonella typhimurium: N-methyl-N-nitrosourethane and beta-propiolactone.

ABSTRACT

The toxic and mutagenic effects of the alkylating agents N-methyl-N-nitrosourethane (MNUT) and beta-propiolactone (BPL) were quantitatively measured in human lymphoblasts and Salmonella typhimurium. Forward mutation to 6-thioguanine resistance was measured in the human lymphoblasts, and forward mutation to 8-azaguanine resistance was measured in the bacterial cells after equigenerational (1.5 doubling times) exposures. In both systems, the induced mutant fraction rose linearly as a function of concentration for BPL and was biphasic for MNUT. The responses of the two assay systems to eight alkylating agents were compared. The exposure of the cells to each alkylating agent was calculated as exposure concentration multiplied by the time of exposure, and allowance was made for the decomposition of the alkylating agents during exposure (integral exposure). Human cells were 2.5--13 times more sensitive than was S. typhimurium to the alkylating agents methyl methanesulfonate, ethyl methanesulfonate, propyl methanesulfonate, N-methyl-N'-nitro-N-nitrosoguanidine, methylnitrosourea, and MNUT. S. typhimurium cells were three times more sensitive to butyl methanesulfonate and 25 times more sensitive to BPL than were human cells.