As shown by flow cytometry, the ratios of cells in the G2/M phase were markedly increased in cultures treated with 4 μM RB compared to the DMSO control, but RB-mediated G2/M phase arrest was significantly rescued by U0126 in P3#GBM and U251 cells (Figure 3E and Supplementary Figure S1C). Here, RB1 is linked to glioblastoma.