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Oncogenic transformation and mutation of C3H/10T 1/2 clone 8 mouse embryo fibroblasts by alkylating agents
Abstract:
Two-hr treatments with N-methyl- and N-ethyl-N'-nitro-N-nitrosoguanidines and ethyl methanesulfonate induced ouabain-resistant mutants in C3H/10T 1/2 cells. The alkylnitronitroso-guanidines gave linear dose-response curves and were more potent mutagens than were ethyl methanesulfonate and methyl methanesulfonate. These differences in potency were largely due to differences in the half-lives of the alkylating agents in culture medium. Differences in mutation frequencies at equitoxic concentrations of the alkylating agents are considered to reflect differences in the chemical mechanisms of alkylation and mutagenesis by the compounds. However, the frequencies of mutations produced at equitoxic concentrations were not uniformly associated with the nucleophilic selectivities of the compounds as expressed by their published Swain-Scott substrate constants. Whether or not followed by repeated replating, the yield of oncogenically transformed foci of asynchronous cells after treatment with the alkylating agents was so low that we could not obtain dose-response curves, and the yield may not be significant. By contrast, in previous experiments with N-methyl-N'-nitro-N-nitrosoguanidines and polycyclic hydrocarbons in Syrian hamster embryo fibroblasts and with ultraviolet light and polycyclic hydrocarbons in C3H/10T 1/2 cells, transformation occurred to an equal or greater extent than mutation measured in the same cells.
Insights
N-methyl- and N-ethyl-N-nitrosoguanidines are potent mutagens, inducing mutations in C3H/10T 1/2 cells. Their potency relates to chemical stability, though oncogenic transformation yields were too low to measure.
Area of Science:
- Chemical Mutagenesis
- Cellular Toxicology
- Carcinogenesis Research
Background:
- Alkylating agents are used to study mutagenesis and carcinogenesis.
- Understanding the dose-response and mechanisms of these agents is crucial.
- Previous studies showed varying mutation and transformation frequencies.
Purpose of the Study:
- To compare the mutagenic potency of N-methyl-N'-nitro-N-nitrosoguanidine (MNNG), N-ethyl-N'-nitro-N-nitrosoguanidine (ENNG), and ethyl methanesulfonate (EMS).
- To investigate the relationship between chemical stability, mutagenicity, and oncogenic transformation.
- To assess the role of nucleophilic selectivity in mutagenesis.
Main Methods:
- Treatment of C3H/10T 1/2 cells with MNNG, ENNG, and EMS for two hours.
- Induction of ouabain-resistant mutants to measure mutation frequency.
- Assessment of oncogenic transformation foci yield.
Main Results:
- MNNG and ENNG were more potent mutagens than EMS, showing linear dose-response curves.
- Mutagenic potency differences were primarily attributed to the varying half-lives of the agents in culture medium.
- Mutation frequencies at equitoxic concentrations did not consistently correlate with nucleophilic selectivity (Swain-Scott constants).
- The yield of oncogenic transformation was too low to establish dose-response curves.
Conclusions:
- Alkylnitrosoguanidines are potent mutagens, with potency influenced by chemical stability.
- The mechanism of mutagenesis is complex and not solely predicted by nucleophilic selectivity.
- Oncogenic transformation yields were significantly lower than mutation induction, unlike in previous studies with other agents or cell types.