Metformin Sensitizes Prostate Cancer Cells to Radiation Through EGFR/p-DNA-PKCS In Vitro and In Vivo

Although neo-adjuvant radiotherapy is generally successful in treatment of advanced prostate cancer, radioresistance is still a major therapeutic problem in many patients. In the current study, we investigated the effects of metformin (1,1-dimethylbiguanide hydrochloride), a widely used antidiabetic drug, on tumor cell radiosensitivity in prostate cancer. Through clonogenic survival assays, we found that metformin treatment enhanced radiosensitivity of prostate cancer cells with a dose enhancement factor. Moreover, irradiation of subcutaneous C4-2 tumors in mice treated with metformin resulted in an increase in radiation-induced tumor growth delay (17.3 days to 29.5 days, P < 0.01), which indicates that the tumor radiosensitivity increased by metformin in vivo. We also measured the sublethal damage repair and analyzed double-strand breaks (DSBs) in X-irradiated cells. γ-H2AX, as an indicator of DSBs, had significantly more foci per cell in the group treated with metformin and radiation compared to groups ...