To dissect the potential mechanism by which DNA-PKcs inhibition mediated antiproliferative effect and synergized with TMZ, we treated U87 and M059K cells with AKT inhibitor MK-2206 or MEK inhibitor PD98059 either alone or in combination with TMZ. After 3-day administration, both single and combination strategies of MK-2206 treatment resulted in a substantial decrease in cell viability. However, PD98059 did not induce additional growth inhibition in glioma cells, suggesting that AKT signaling contributed to the biological effect of KU0060648 (Figure 5A). We further observed that KU0060648 caused a strong and dose-dependent decrease in AKT phosphorylation (p-AKT Ser 473) of U87 and M059K cells using immunoblotting (Figure 5B), which indicated that inhibition of DNA-PKcs could suppress the activation of AKT in glioma cells.