Radiosensitization of EMT6 mammary carcinoma cells by 2-benzoyl-3-phenyl-6,7-dichloroquinoxaline 1,4-dioxide

Background and purposePreviously, we have reported that 2-benzoyl-3-phenyl-6,7-dichloroquinoxaline 1,4-dioxide (DCQ) is a radiosensitizer. Here, we investigate the mechanism of radiosensitization.Materials and methodsEMT6 cells were treated with DCQ for 4 h prior to ionizing radiation (IR). Flow cytometry, clonogenic assay, TUNEL, and Western blotting were performed to assess the effect of treatment on cells.ResultsPropidium iodide staining of EMT6 cells treated with IR ± DCQ revealed high numbers of cells with decreased DNA, consistent with an apoptotic response. TUNEL assay revealed apoptosis was 4%, 38%, and 49% 24 h after treatment with IR alone, DCQ alone, and DCQ + IR, respectively. Clonogenic assays revealed that the survival of irradiated EMT6 cells was significantly reduced by DCQ treatment. DCQ treatment abrogated the radiation-induced expression of p21 and p53. The increased apoptosis observed in DCQ + IR-treated cells was correlated to suppression of radiation-induced phosphorylation of Akt and the expression of Bcl-XL. DCQ also caused the phosphorylation of mitogen-activated protein kinases Erk and Jnk.ConclusionsThe radiosensitization effect of DCQ occurs through enhancement of radiation-induced apoptosis, which correlates to the inhibition of p-Akt kinase and Bcl-XL and the activation of Erk and Jnk kinases, but appears independent of p53 induction or modulation of Bax/Bcl-2 gene expression. These data suggest DCQ should be tested as a radiosensitizer in vivo and has potential in the treatment of human solid tumors.