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DNA damage by drugs and radiation: what is important and how is it measured?
1Radiotherapy Research Unit, Institute of Cancer Research, Sutton, Surrey, U.K.
Abstract:
DNA is the most important target for drug and radiation induced cell killing. The mode of cell killing by cytotoxic drugs and radiation has been derived by correlating the type and quantity of DNA damage induced with lethality. Cytotoxic drugs can be classified by their main mode of action, while ionising radiation causes a range of lesions with the DNA double-strand break (dsb) being the most significant. Strand-breaks are measured from the reduction in the size of DNA molecules following treatment. Molecule size can be derived from the rate that DNA fragments sediment when centrifuged, elute through filters or migrate under electrophoresis. The effect of strand-breaks on DNA loop supercoiling allow a sensitive assay of DNA damage. Specific assays for base damage and drug adducts include changes in chromatographic mobility or binding by specific antibodies. By comparing the levels of damage in the genome overall with damage in specific gene targets, regions susceptible to damage induction, and varying in repair efficiency, have been revealed.
Insights
Understanding DNA damage is key to cell killing by drugs and radiation. This study correlates DNA damage types and levels with cell death, revealing specific genomic regions vulnerable to damage and repair.
Area of Science:
- Molecular Biology
- Genetics
- Biochemistry
Background:
- DNA is the primary target for cytotoxic drugs and radiation, leading to cell death.
- Cell killing mechanisms are understood by linking DNA damage to lethality.
- DNA double-strand breaks (DSBs) are the most critical DNA lesions induced by ionizing radiation.
Purpose of the Study:
- To classify cytotoxic drugs by their DNA damage mechanisms.
- To investigate the significance of DNA double-strand breaks (DSBs) in radiation-induced cell killing.
- To develop and apply sensitive assays for quantifying various types of DNA damage.
Main Methods:
- Measuring DNA strand breaks via sedimentation, filtration, or electrophoresis.
- Utilizing DNA loop supercoiling assays for sensitive DNA damage detection.
- Employing chromatographic mobility shifts and antibody binding for base damage and drug adduct analysis.
Main Results:
- Correlating specific DNA damage types and quantities with cell lethality.
- Identifying genomic regions with higher susceptibility to DNA damage induction.
- Revealing variations in DNA repair efficiency across different genomic regions.
Conclusions:
- The type and extent of DNA damage are critical determinants of cell killing by cytotoxic agents and radiation.
- Sensitive assays enable precise quantification of DNA damage, including strand breaks and base modifications.
- Comparative analysis of genome-wide versus gene-specific damage highlights regional differences in susceptibility and repair.