Untersuchung der Mechanismen, die für die antineoplastische Wirkung von Metformin bei malignen Gliomen verantwortlich sind

Metformin has an antineoplastic effect on various types of cancer, including gliomas. To date, the mechanisms or targets underlying this effect have not been identified. The aim of our study is to investigate the glycerol-3-phosphate shuttle (G3PS) as a potential target of metformin in different glioblastoma (GBM) cell lines.

To investigate the effect of metformin on cell viability, cells were exposed to different concentrations of metformin (0–20 mM). After 24 hours, viability was determined by measuring ATP in cell lysates using the CellTiter-Glo assay. Cells were then exposed to metformin at the IC50 (half maximal inhibitory concentration) for several days while confluence was measured at 4-hour intervals by live-cell imaging. RT-qPCR and Western blotting were performed to quantify the expression of GPD1, GPD1L and GPD2 enzymes responsible for G3PS.

Most GBM cell lines showed a sigmoidal response to 24-hour incubation with metformin, but with differences in IC50 (1.1–3.9 mM) and total viable cell count. G55T2, U251 and LN229 showed the strongest response with a final value of less than 70 % compared to the control (0 mM metformin). LN405, MZ18 and MZ54 showed a deviating behavior with a cell viability of more than 100 % at lower metformin concentrations. During long-term incubation, all cell lines showed significant differences in cell growth when incubated with metformin. The greatest effect was observed in 1321N1, U343 and LN229 with a percentage increase in doubling time during treatment of over 65 %. U87 showed little to no response with a percentage increase of 2.89±0.75 %, and U251 even showed a shorter doubling time than the control (control: 30.93±1.09 hours; with treatment: 27.84±0.19 hours). The GBM cell lines showed significantly higher mRNA expression of GPD1L and GPD2 than normal tissue. Expression at the RNA and protein level in GBM cell lines correlated significantly for both GPD1L and GPD2. The GPD1 protein was expressed at such low levels that it was not detectable by Western blot.

Since the antineoplastic effect of metformin is different in different cell lines, we hypothesize that a more comprehensive knowledge of the mechanisms and cellular targets may increase the utility of metformin for stratified tumor treatment.