Fig. 9
The combination affects the self-renewal capacity of TMZ-resistant glioblastoma stem-like cells (GSCs). Stem cell frequency was determined by extreme limiting dilution assay (ELDA) in DMSO-selected 1080 GSCs and TMZ-selected 1080 GSCs. Cells were treated with the DMSO control (red line), 48 µM TMZ (blue line), 2.66 µM SKI-II (green line) and the combination (TMZ + SKI-II) (black line) for 4 weeks under normoxia (21% O2; n = 3). A, B Log-fraction plots, where the y axis “log fraction nonresponding” indicates frequency of cells incapable of forming clonal spheres and the x axis “dose (number of cells)” indicates number of cells per ml. The slope of the line is the log-active cell fraction, and dotted lines give the 95% confidence interval. Note that the panels in A and B have slightly different Y-axis scales. C Estimated stem cell frequency, 1/(stem cell frequency). D Pairwise test for differences in stem cell frequencies between groups. Data analysis was performed via the ELDA webtool (see Additional file 11 for complete ELDA results)