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Correlations between intercalator-induced DNA strand breaks and sister chromatid exchanges, mutations, and
Abstract:
Intercalator-induced DNA strand breaks in mammalian cells represent topoisomerase II:DNA complexes trapped by intercalators. These complexes are detected as protein-associated DNA single-strand breaks (SSB) and DNA double-strand breaks (DSB) by filter elution. Using Chinese hamster lung fibroblasts (V79 cells) that were treated for 30 min with various concentrations of 4'-(9-acridinylamino)methanesulfon-m-anisidide or 5-iminodaunorubicin, we measured DNA strand breaks (SSB and DSB), sister chromatid exchanges (SCE), mutations at the hypoxanthine:guanine phosphoribosyltransferase locus, and cell killing. Further, we correlated DNA strand breakage with the three other parameters. Both drugs induced SCE, mutations, and cell killing at concentrations which also produced reversible DNA strand breaks. While the quantity of DSB correlated with SCE, mutations, and cytotoxicity for both drugs, we found more SCE, mutations, and cytotoxicity per SSB in cells treated with 5-iminodaunorubicin than in those treated with 4'-(9-acridinylamino)methanesulfon-m-anisidide. These data show that the DSB (but not the SSB) induced by 4'-(9-acridinylamino)methanesulfon-m-anisidide and 5-iminodaunorubicin at DNA topoisomerase II binding sites correlated closely with SCE, mutations, and cell killing and could therefore be responsible for their production.
Insights
DNA topoisomerase II inhibitors cause DNA double-strand breaks (DSB), which correlate with sister chromatid exchanges, mutations, and cell death in mammalian cells. These findings highlight DSB as key to drug-induced genotoxicity.
Area of Science:
- Molecular Biology
- Genetics
- Toxicology
Background:
- Intercalator drugs trap topoisomerase II:DNA complexes, leading to DNA strand breaks.
- Protein-associated DNA single-strand breaks (SSB) and double-strand breaks (DSB) are key indicators of genotoxicity.
Purpose of the Study:
- To investigate the correlation between intercalator-induced DNA strand breaks and genotoxic effects.
- To determine if DNA double-strand breaks (DSB) are responsible for sister chromatid exchanges (SCE), mutations, and cell killing.
Main Methods:
- Chinese hamster lung fibroblasts (V79 cells) were treated with 4'-(9-acridinylamino)methanesulfon-m-anisidide or 5-iminodaunorubicin.
- Assessed DNA strand breaks (SSB and DSB), SCE, mutations at the hypoxanthine:guanine phosphoribosyltransferase locus, and cell killing.
- Correlated DNA strand breakage levels with observed genotoxic endpoints.
Main Results:
- Both drugs induced reversible DNA strand breaks, SCE, mutations, and cell killing.
- DNA double-strand breaks (DSB) strongly correlated with SCE, mutations, and cytotoxicity for both agents.
- 5-iminodaunorubicin induced more SCE, mutations, and cytotoxicity per SSB compared to 4'-(9-acridinylamino)methanesulfon-m-anisidide.
Conclusions:
- DNA double-strand breaks (DSB) induced by intercalators at topoisomerase II binding sites are closely linked to their genotoxic effects.
- DSB, not SSB, are likely responsible for the observed sister chromatid exchanges, mutations, and cell killing.
- This study elucidates the mechanism of topoisomerase II inhibitor-induced genotoxicity.