1. A B Supplementary Figure 1. (A) Western blots were performed on the three cell lines to analyze the levels of p-ERK, which is a key protein involved in cellular proliferation and growth. The treatment of the three cell lines with GSK112012 led to a reduction in p-ERK with both increasing concentrations (0-100nM) and increasing time after the administration of 10nM (0-24hrs); Dose enhancing ratios corresponding to figure 5A.

2. A Supplementary Figure 2. (A) MTS assays on additional cell lines (e.g. H23, SK-LU-1, and Calu-1) were performed with increasing concentrations of both MEKi and CDKi; (B)Kras mutant NSCLC cell lines treated with the GSK1120212, PD-0332991, or the combination for 72h. Green squares represent significant effect, yellow squares indicate over less than 50% of the effect range, and red squares show lack of significant effect. Mutational status of cell lines obtained from the Sanger Cancer Cell Line Project (http://cancer.sanger.ac.uk) and The TP53 Mutation Database (http://p53.fr/). Abbreviations: NSCLC, non–small cell lung cancer not otherwise specified; wt, wild- type; Del, deletion. B

3. Supplementary Figure 3.. Cells were treated with various concentrations of GSK1120212 in combination with PD0332991 for 72 hours, and cell viability was measured by MTS assay (left). The combination index value was determined from the fraction-affected value of each combination according to the Chou-Talalay method by using CompuSyn software (ComboSyn, Inc.), and a combination index value below 1 represents synergism. H358 demonstrated no synergism when MEKi and CDKi were coadministered (right).

4. Supplementary Figure 4. Isobologram for the combination of GSK1120212 with PD0332991 in A549 and H460 cell lines. X-axis means concentration of GSK1120212 (nM), y-axis means concentration of PD0332991(nM).

5. A549 H460 - + - + - - + + p-RB 807 RB p-ERK ERK PARP - + - + - - + + H358 GSK112 RT 6Gy β-Actin c-PARP - + - + - - + + Supplemantry FIgure 5. MEK inhibitor enhances radiosensitivity of KRAS mutant NSCLC cell lines. Western blots were performed demonstrating that MEK inhibitor enhanced radiosensitizing effect via activated RB in the sensitive cell line H358, with little effect on the more resistant cell lines (A549 and H460).