Metformin Enhanced in Vitro Radiosensitivity Associates with G2/M Cell Cycle Arrest and Elevated Adenosine-5’-monophosphate-activated Protein Kinase Levels in Glioblastoma

BACKGROUND: It is hypothesized that metabolism plays a strong role in cancer cell regulation. We have recently demonstrated improved progression-free survival in patients with glioblastoma who received metformin as an antidiabetic substance during chemoradiation. Although metformin is well-established in clinical use the influence of metformin in glioblastoma is far from being understood especially in combination with other treatment modalities such as radiation and temozolomide. MATERIALS AND METHODS: In this study, we examined the influence of metformin in combinations with radiation and temozolomide on cell survival (clonogenic survival), cell cycle (routine flow cytometric analysis, FACScan), and phosphorylated Adenosine-5’-monophosphate-activated protein kinase (AMPK) (Phopho-AMPKalpha1 - ELISA) levels in glioblastoma cell lines LN18 and LN229. RESULTS: Metformin and temozolomide enhanced the effectiveness of photon irradiation in glioblastoma cells. Cell toxicity was more pronounced in O(6)-methylguanine DNA methyltransferase (MGMT) promoter non-methylated LN18 cells. Induction of a G2/M phase cell cycle block through metformin and combined treatments was observed up to 72 h. These findings were associated with elevated levels of activated AMPK levels in LN229 cells but not in LN18 cells after irradiation, metformin, and temozolomide treatment. CONCLUSIONS: Radiosensitizing effects of metformin on glioblastoma cells treated with irradiation and temozolomide in vitro coincided with G2/M arrest and changes in pAMPK levels.