F, H358 cells transfected with E2F1-specific or control siRNAs for 24h were subsequently treated with vehicle (DMSO), AZD4547 (5 µM) and BI2536 (5 nM), alone or combination for 48h before apoptotic assay. Data were shown as mean ± SD (n=3). *P<0.05, **P<0.01 and P＞0.05 (ns) by two-way ANOVA with Tukey's multiple comparisons test. 