Additional file 4: of G-quadruplex ligand RHPS4 radiosensitizes glioblastoma xenograft in vivo through a differential targeting of bulky differentiated- and stem-cancer cells

Figure S4. Silencing of CHK1 increases GSC response to low concentrations of RHPS4. Protein levels of GSC #163 stably expressing either a non-targeting control shRNA (NTC) or three different shRNAs targeting human CHK1 (named shCHK1 B5, E1 and F11) are shown (A). Densitometric analysis confirmed the significant reduction of CHK1 protein levels in shCHK1 cell lines (B) and a similar reduction was also observed by means of qRT-PCR (C). Growth curves showing the effect of RHPS4 treatment (1, 2, and 4 μM) in both NTC and shCHK1 cells evaluated up to 7 days (D). Cell viability at day 7 from treatment suggests a significant impairment of cell growth in all shCHK1 cells only after 1 μM RHPS4 (E). Conversely, higher concentrations (2 and 4 μM) do not affect cell viability (E). Indeed, RHPS4 treatment in the GSC #163 is able per se to downregulate the levels of CHK1 in a dose-dependent manner (F and G) masking the difference in cell viability between NTC and shCHK1 cells after higher RHPS4 concentrations (2 and 4 μM). Data represent mean values ± s.d. (n = 2). * P