P17.39TURN OLD INTO NEW: METFORMIN AS ANTINEOPLASTIC AGENT IN GLIOBLASTOMA.

Metformin is one of the most widely prescribed oral antidiabetic drugs. In addition to its known hypoglycemic effects there is current evidence, that metformin may also reduce the risk and mortality of cancer in diabetic patients. The antineoplastic role of metformin has been extensively studied in breast-, prostate-, pancreatic-, lung- and colon cancer, however, the effect of metformin on glioblastomas, one of the most devastating forms of human tumors, has not been thoroughly investigated. We examined the effects of metformin on a variety of brain tumor initiating cells (BTIC) from fresh tumor resections of primary glioblastomas using proliferation assays (cell count, BRDU-assay) and migration assays (scratch and spheroid migration assay), and investigated differentiation of cells by means of immunocytochemistry. Tumor cell metabolism was investigated by measuring extracellular lactate levels, mitochondrial respiration by high resolution respirometry and determination of cellular oxygen consumption under cell culture conditions using the PreSens-assay. Important signalling molecules, such as AMPK, Akt and mTOR were investigated by means of Western Blot analysis. Functional assays were compared in BTIC and differentiated tumor cells from the same patients. In BTIC, we observed a markedly impaired proliferation and migration of cells after treatment with metformin and inhibition of complex I of the respiratory chain. In addition, we observed increased extracellular lactate levels and activation of the AMPK/mTOR signalling cascade. Metformin-treated BTIC showed reduced expression of stem cell markers. Differentiated tumor cells were distinctly less responsive to treatment with metformin. We hypothesize that differential sensitivity of brain tumor initiating cells and differentiated tumor cells to metformin is due to different use of and dependence on oxidative energy production and impaired glycolytic and glutaminolytic rescue pathways in BTIC. Further investigation of metformin as a possible antineoplastic agent in glioblastoma is warranted, especially in the light of a multitude of promising ongoing clinical studies on metformin and other tumor types.