Metformin Enhanced in Vitro Radiosensitivity Associates with G2/M Cell Cycle Arrest and Elevated pAMPK Levels in Glioblastoma

Abstract

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. Altough 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 O⁶-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 72h. 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.

Conclusion

Together with our previous clinical findings, radiosensitzing effects of metformin on ionizing irradiation and temozolomide in glioblastoma cell lines merit further investigation.