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Rapid detection of DNA-damaging agents using repair-deficient CHO cells
Abstract:
A screening method is introduced to detect and classify DNA-damaging agents using DNA repair-deficient strains of Chinese hamster ovary cells. Differential cytotoxicity (relative growth) of the mutant cells compared to the wild-type cells was interpreted as a measure of lethal, potentially repairable damage to DNA. The assay consists of exposing the wild-type cells and three mutant strains to the test compound in a 24-well tray and using staining intensity to estimate growth after 72 h. The battery of mutants consists of two UV-sensitive strains (UV4 and UV5) that are deficient in different aspects of nucleotide excision repair, and strain EM9, which is defective in DNA-strand-break rejoining. The assay was highly reproducible, and the magnitude of the differential cytotoxicity response compared favorably with the amount of differential killing measured by colony-formation survival curves for several chemicals. 15 direct-acting and 7 metabolism-dependent agents that were expected to produce bulky, covalent DNA adducts were tested in the assay, and all produced a differential cytotoxicity response in at least two of the mutants. UV4 and UV5 showed a response to all of the test compounds whereas EM9 showed a response to 7 of the test compounds. Thus, the pattern of mutant responses presumably reflects the types of DNA damage produced by a compound. Although this aspect is still under development, these results indicate the potential of a larger battery of mutants to classify a wide spectrum of chemicals according to the lesions they produce. 13 non-DNA damaging agents were also tested and none produced a differential cytotoxicity response, suggesting that this endpoint is specific for DNA damage. We conclude that this assay may be a cost-effective alternative or adjunct to the existing short-term tests.
Insights
A new screening method uses DNA repair-deficient Chinese hamster ovary cells to detect and classify DNA-damaging agents. This cost-effective assay shows high reproducibility and specificity for identifying genotoxic chemicals.
Area of Science:
- Toxicology
- Genetics
- Cell Biology
Background:
- Detecting DNA-damaging agents is crucial for assessing chemical safety.
- Existing methods can be time-consuming and costly.
- A need exists for efficient and specific screening assays for genotoxicity.
Purpose of the Study:
- To introduce and validate a novel screening assay for detecting and classifying DNA-damaging agents.
- To utilize DNA repair-deficient Chinese hamster ovary cell lines for genotoxicity assessment.
- To establish a cost-effective and reproducible method for chemical safety evaluation.
Main Methods:
- Employing a battery of DNA repair-deficient Chinese hamster ovary cell strains (UV4, UV5, EM9) alongside wild-type cells.
- Exposing cells to test compounds in a 24-well tray format.
- Quantifying differential cytotoxicity via staining intensity to estimate cell growth after 72 hours.
Main Results:
- The assay demonstrated high reproducibility and correlated well with colony-formation survival curves.
- All 22 tested DNA-damaging agents (direct-acting and metabolism-dependent) elicited a differential cytotoxicity response in at least two mutant strains.
- 13 non-DNA damaging agents did not produce a response, indicating assay specificity for DNA damage.
Conclusions:
- The developed assay effectively detects and classifies DNA-damaging agents based on differential cytotoxicity patterns in repair-deficient cells.
- The assay shows promise as a cost-effective alternative or adjunct to existing genotoxicity testing methods.
- Further development with a larger mutant battery could enable classification of a wider spectrum of chemical-induced DNA lesions.