Figure 6. Differential efficacy of metformin on GBM TIC and differentiated cell survival and glucose uptake; lack of effects on human MSC. (A) Effect of metformin (1–50 mM, 72 h) on survival of GBM TIC (white circles) and differentiated cells (black diamonds) derived from GBM1, GBM3 and GBM4, by MTT assay. While metformin reduced TIC viability (p < 0.01), differentiated cells were only slightly affected (statistically significant effect observed only at 50 mM, p < 0.01). Dotted lines represent the values of untreated control cells, taken as 100%. Data are the average of four replica experiments. (B) Effect of metformin (20 mM, 72 h) on the survival of GBM TICs and differentiated cells derived from GBM1, GBM3 and GBM4, grown in monolayer on matrigel and evaluated by percentage of expression of Ki-67 in IF experiments. Data are reported as percentage of Ki-67⁺ cells over total cells stained with DAPI. (n = 3; ** = p < 0.01.) (C) (¹⁸F)-fluoro-deoxyglucose (FDG) uptake in GBM1 TIC and differentiated cells in basal and metformin-treated (20 mM, 24 h) conditions. While basal FDG uptake was significantly higher in TICs, metformin was able to increase this value only in differentiated GBM cells. Data are means of two independent experiments ± SD. Statistical significances are reported; ns, non-significant. (D) Effect of metformin (72 h) on survival of GBM TICs (black circles) and MSC (white squares), by MTT assay. Lines represent the average of independent experiments performed on GBM1, GBM3 and GBM4 and three individual MSC cultures, repeated three times and pooled together. Dotted lines represent the values of respective untreated control cells, taken as 100%. (** = p < 0.01 vs. respective control values.)