An <i>ex vivo</i> model to evaluate DNA damage by comet assay in breast-cancer tissue

Single cell gel electrophoresis (comet assay) is a research tool known for its use in the assessment of DNA damage in which peripheral blood lymphocytes are used as a cellular model. The objective of this study was to adapt the comet assay to fresh normal and tumor breast tissue explants to assess DNA damage. Representative samples were obtained from nine patients with infiltrating ductal adenocarcinoma during the time of surgical intervention for the resection of the tumor. One hundred micrometer thick explants were prepared from normal and tumor breast tissue using a tissue slicer. Explants were harvested into six-well microplates with 4 mL of sterile serum-free Dulbecco's modified Eagle's medium/Ham's F12 medium at 4 °C for immediate processing of the comet assay. The results indicated that the comet assay can be used to analyze DNA damage in tumors and healthy breast tissue in an <i>ex vivo</i> model that allows visualization of the level of DNA damage. Compared to non-tumor cells, DNA damage in breast cancer was significantly increased (<i>p</i> < 0.05); furthermore, DNA damage was higher in samples treated with H₂O₂ (positive control) and confirmed that cells in the explants can interact with the chemicals tested, as well as the functionality of the technique. The comet assay using fresh tissue explants represents an alternative tool with potential to identify DNA damage in tumor tissue and to study new drugs to personalize the use of DNA-damaging therapies.