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


METHODS
EMT6 cells were treated with DCQ for 4h prior to ionizing radiation (IR). Flow cytometry, clonogenic assay, TUNEL, and Western blotting were performed to assess the effect of treatment on cells.


RESULTS
Propidium 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% 24h 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-X(L). DCQ also caused the phosphorylation of mitogen-activated protein kinases Erk and Jnk.


CONCLUSIONS
The radiosensitization effect of DCQ occurs through enhancement of radiation-induced apoptosis, which correlates to the inhibition of p-Akt kinase and Bcl-X(L) 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.
Haykal
Joelle
J
Department of Biology, American University of Beirut, Beirut, Lebanon.
Fernainy
Pamela
P
Itani
Wafica
W
Haddadin
Makhluf
M
Geara
Fady
F
Smith
Colin
C
Gali-Muhtasib
Hala
H
D017209:Apoptosis / Q000187:drug effects* / Q000528:radiation effects; D001943:Breast Neoplasms; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000187:drug effects; D005260:Female; D005434:Flow Cytometry; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D006801:Humans; D011810:Quinoxalines / Q000494:pharmacology*; D011836:Radiation Tolerance / Q000187:drug effects*; D011839:Radiation, Ionizing; D011838:Radiation-Sensitizing Agents / Q000494:pharmacology*
C490569:2-benzoyl-3-phenyl-6,7-dichloroquinoxaline-1,4-dioxide; D011810:Quinoxalines; D011838:Radiation-Sensitizing Agents