Fig. 1

A selection of clonogenic GSC clones able to survive high-dose TMZ treatment from MGMT-expressing GSC culture lines. a. Growth activity of GSC lines treated with indicated TMZ doses was determined via MTS-based cell proliferation assay. The dose response curve of GSCs derived from each patient tumor, is presented both individually and combined together. The concentration of TMZ required for 50 % inhibition of GSC viability in vitro (IC50) was estimated using the mean of growth activity of 3 GSC lines. Values of TMZ-treated cells represent the percentage of growth relative to that of untreated cells, which was converted to 100 %. Data represent mean values ± SD of triplicate measurements of three independent experiments. *p < 0.05 and **p < 0.001 in relation to untreated control. b. Cell cycle distribution of GSC treated with and without 500 μM TMZ was determined on day 2 or day 7 after treatment. Numbers in the respective cell cycle distributions indicate the percentage of cells in each phase of the cell cycle. c. In vitro selection of clonogenic survival of GSC in the presence of 200 or 500 μM TMZ or left untreated. Photos were taken at indicated time periods after treatment. d. sqRT-PCR analysis of MGMT mRNA expression levels in untreated parental GSC (GSC-parental) and clonogenic clones surviving 500 μM TMZ treatment (GSC-500 μM TMZ). The graph shows the mean values of fold change for MGMT mRNA expression levels in indicated GSC-500 μM TMZ lines relative to those of untreated GSC-parental. All values are relative to those of the internal control gene β-actin, with values of GSC-500 μM TMZ representing the fold change relative to that of GSC-parental, which was converted to 1. Data represent mean values ± SD of triplicate measurements in three independent experiments. *p < 0.05 and **p < 0.001 in relation to GSC-parental