Disruption of Hif-1α enhances cytotoxic effects of metformin in murine squamous cell carcinoma

Purpose: In the present study, we investigated whether the disruption of the Hif-1 alpha gene affects the sensitivity of SCC VII cells to metformin and also if metformin functions as a radiosensitizer using murine squamous cell carcinoma (SCC VII) cells. Materials and methods: Cultured SCC VII and SCC VII Hif-1 alpha-deficient cells were incubated with metformin under glucose-free and/or hypoxia-mimetic conditions and cell viabilities were measured. Tumor-bearing mice were continuously given 5-bromo-2'-deoxyuridine (BrdU) to label all proliferating cells. Tumor-bearing mice were then subjected to c-ray irradiation after the metformin treatment. Immediately after irradiation, cells were isolated from some tumors and incubated with a cytokinesis blocker. The responses of quiescent and total (= proliferating + quiescent) cell populations were assessed based on the frequency of micronuclei using immunofluorescence staining for BrdU. Results: The disruption of Hif-1 alpha increased the sensitivity of SCC VII cells to metformin in glucose-free medium. Metformin-induced decreases in the percentage of dead cells in the presence of CoCl2 were partially reduced when Hif-1 alpha was disrupted. In vivo, metformin increased the radiosensitivity of SCC VII Hif-1 alpha-deficient cells. Conclusion: The combination of disruption of Hif-1a and metformin effectively enhanced the radiosensitivity of SCC VII cells.