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Effect of excision repair on the mutagenesis of misonidazole
Abstract:
The mutagenic and toxic effects of the nitroimidazole hypoxic cell sensitizer misonidazole (Ro-07-0582) have been studied in two strains of E. coli that differ in their abilities to repair DNA. It was found that even though the strain defective in excision repair was only slightly more sensitive than the original wild-type strain to killing by misonidazole, a large difference in the mutagenesis of the two strains was observed. While the wild-type strain was not mutated by misonidazole at any of the concentrations tested, the uvr strain was strongly mutated by the drug. This demonstrates the presence of a mutagenic lesion in DNA that is removed by excision repair.
Insights
Misonidazole, a cancer drug, caused mutations in bacteria with faulty DNA repair but not in normal bacteria. This indicates DNA damage from the drug is repaired by excision repair mechanisms.
Area of Science:
- Molecular Biology
- Genetics
- Pharmacology
Background:
- Nitroimidazoles like misonidazole are used as hypoxic cell sensitizers in cancer therapy.
- Understanding their mutagenic and toxic effects is crucial for therapeutic safety and efficacy.
Purpose of the Study:
- To investigate the mutagenic and toxic effects of misonidazole in Escherichia coli (E. coli).
- To compare these effects in bacterial strains with differing DNA repair capabilities, specifically focusing on excision repair.
Main Methods:
- Utilized two strains of E. coli: a wild-type strain and a strain deficient in excision repair (uvr strain).
- Exposed both strains to varying concentrations of misonidazole.
- Assessed bacterial survival (toxicity) and mutation frequency (mutagenesis).
Main Results:
- The excision repair-deficient strain showed only a slight increase in sensitivity to misonidazole-induced killing compared to the wild-type strain.
- A significant difference in mutagenesis was observed: misonidazole did not induce mutations in the wild-type strain but strongly mutated the uvr strain.
- This highlights that the mutagenic potential of misonidazole is linked to unrepaired DNA lesions.
Conclusions:
- Misonidazole induces DNA lesions that are mutagenic in bacteria lacking functional excision repair.
- Excision repair is a critical pathway for preventing misonidazole-induced mutagenesis.
- The study demonstrates the presence of a specific mutagenic lesion in DNA that is effectively removed by excision repair.