Fig. 3

Temozolomide (TMZ) sensitivity of primary and established GBM cell lines. Error bars indicate the standard deviation. a Cell viability (MTT reduction assay; ANOVA and Tukey’s test) of primary, patient-derived GBM cells after 5-day exposure to TMZ ± calpain inhibition by PD150606 (PD, f.c. 50 µM). b Western blot analysis of five selected GBM cell lines for their CAPN1, CAPN2, and calpastatin (CAST) expression. GAPDH was used as loading control. c Cell viability (CellTiter Glo assay; ANOVA and Tukey’s test) of established GBM cell lines (n = 3) after 5-day TMZ ± 50 µM PD administration. d Cell death rate in U251N cells after 5-day TMZ (f.c. 70 µM) and PD (f.c. 50 µM) treatment. Cell death rate was counted as the number of propidium iodide (PI) positive cells relative to the total number of cell nuclei stained with Hoechst (n = 3, ANOVA and Tukey’s test). e Exemplary fluorescent images showing Hoechst stained nuclei (blue) and PI stained dead cells (red) after the indicated treatment. The numbers below the images indicate the percentage of PI positive nuclei in these images. f Calpain activity is increased in U251N cells upon 5-day TMZ administration (n = 3). Calpain activity (fluorometric intensity (Ex/EM 400/505 nm)) is calculated relative to the DMSO treated control cells