Fig. 2

GBM cell lines show high intrinsic tolerance to alkylating cytostatics cisplatin and TMZ. a Cisplatin resistance status of U87, U251, and U373 cell lines was assessed by MTT assays (n = 4). b Intrinsic resistance of GBM cell lines is demonstrated in comparison to cell pairs of non-resistant and cells with acquired resistance. GBM cell line IC₅₀ concentrations of cisplatin parallel the ones of resistant MCF-7 breast-, and A2780 ovarian cancer cell lines (determined by MTT assays; n = 3). c GBM cell lines were treated by weekly cycles of cisplatin and IC₅₀ values were assayed after each treatment cycle in MTT assays. IC₅₀ values were obtained from sigmoidal concentration–response curves and dotted in a time-dependent manner. d Western blots showing MRP-2 and P-gp expression in GBM cell lines untreated and after 24 cycles of weekly intermittent cisplatin exposure. β-actin Western blot was performed to control for loading. e TMZ resistance status in U87, U251 and U373 cells was assessed by MTT assays (upper graph; n ≥ 6). The respective IC₅₀ values for each cell line are shown in the table below the graph