D, E, Immunoblots (D) and viability assay (E) of H358 and A549 cells transfected with E2F1-specific or control siRNAs followed by treatment (48 h post transfection) with vehicle (DMSO) or combined AZD 4547 (5 µM)/BI2536(5 nM) for additional 24 hours. Data were shown as mean ± SD (n=3). **P<0.01, ****P<0.0001 and P＞0.05 (ns) by two-way ANOVA with Tukey's multiple comparisons test. 