The radiosensitizer 2-benzoyl-3-phenyl-6,7-dichloroquinoxaline 1,4-dioxide induces DNA damage in EMT-6 mammary carcinoma cells.
BACKGROUND
DCQ (2-benzoyl-3-phenyl-6,7-dichloroquinoxaline 1,4-dioxide), a synthetic quinoxaline 1,4-dioxide, enhances the cytotoxic effect of ionizing radiation (IR) in vivo and in vitro. We sought to clarify whether increased radiation-induced DNA damage, decreased rate of damage repair, and the generation of reactive oxygen species (ROS) contribute to DCQ enhancement of IR.


METHODS
Murine mammary adenocarcinoma EMT-6 cells were treated with DCQ for 4 h before exposure to 10 Gy IR. Treated cells were monitored for modulations in cell cycle, induction of DNA damage, and generation of ROS.


RESULTS
Combined DCQ and IR treatments (DCQ+IR) induced rapid cell-cycle arrests in EMT-6 cells, particularly in S and G2/M phases. Alkaline comet assays revealed high levels of DNA damage in cells after exposure to DCQ+IR, consistent with damage-induced arrest. Unlike IR-only and DCQ-only treated cells, the damage induced by combined DCQ+IR was repaired at a slower rate. Combined treatment, compared to separate DCQ and IR treatments, activated DNA-protein kinase and induced more p-ATM, supporting a role for double strand breaks (DSBs), which are more toxic and difficult to repair than single strand breaks (SSBs). Contributing factors to DCQ radiosensitization appear to be the induction of ROS and DSBs.


CONCLUSIONS
Collectively, our findings indicate that radiosensitization by DCQ is mediated by DNA damage and decreased repair and that ROS are at least partially responsible.
Haykal
Joelle
J
Department of Biology, American University of Beirut, Beirut, Lebanon. jmh05@aub.edu.lb
Geara
Fady
F
Haddadin
Makhluf J
MJ
Smith
Colin A
CA
Gali-Muhtasib
Hala
H
D000230:Adenocarcinoma / Q000378:metabolism / Q000628:therapy*; D017209:Apoptosis / Q000187:drug effects / Q000528:radiation effects; D064007:Ataxia Telangiectasia Mutated Proteins; D015153:Blotting, Western; D002453:Cell Cycle / Q000187:drug effects / Q000528:radiation effects; D018797:Cell Cycle Proteins / Q000378:metabolism; D049109:Cell Proliferation / Q000187:drug effects / Q000528:radiation effects; D047369:Chromatin Immunoprecipitation; D003131:Combined Modality Therapy; D020552:Comet Assay; D004249:DNA Damage; D004273:DNA, Neoplasm / Q000528:radiation effects*; D051747:DNA-Activated Protein Kinase / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism; D005260:Female; D005434:Flow Cytometry; D006801:Humans; D007124:Immunoenzyme Techniques; D008325:Mammary Neoplasms, Experimental / Q000378:metabolism / Q000628:therapy*; D009687:Nuclear Proteins / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D011810:Quinoxalines / Q000627:therapeutic use*; D011839:Radiation, Ionizing; D011838:Radiation-Sensitizing Agents / Q000627:therapeutic use*; D017382:Reactive Oxygen Species / Q000378:metabolism; D014407:Tumor Cells, Cultured; D025521:Tumor Suppressor Proteins / Q000378:metabolism
C490569:2-benzoyl-3-phenyl-6,7-dichloroquinoxaline-1,4-dioxide; D018797:Cell Cycle Proteins; D004273:DNA, Neoplasm; D004268:DNA-Binding Proteins; D009687:Nuclear Proteins; D011810:Quinoxalines; D011838:Radiation-Sensitizing Agents; D017382:Reactive Oxygen Species; D025521:Tumor Suppressor Proteins; C576324:ATM protein, human; D064007:Ataxia Telangiectasia Mutated Proteins; C576325:Atm protein, mouse; D051747:DNA-Activated Protein Kinase; C497264:Prkdc protein, mouse; D017346:Protein Serine-Threonine Kinases