CHR-6494 and MEK inhibitor synergistically reduced cell viability of MeWo and MDA-MB-435 melanoma cell lines. MeWo and MDA-MB-435 melanoma cells or human dermal fibroblasts (HDFs) were treated with CHR-6494, MEK inhibitor GSK1120212 (MEKi), or the combination of two compounds at various concentrations for 5 d. Cell viabilities were measured by crystal violet staining assay in: (A) Cells treated with CHR-6494 as single agent; (B) MeWo melanoma cells. (C) MDA-MB-435 melanoma cells; (D) HDFs. Respective values are presented as mean-percentage of control ± S.E.M. *, p < 0.05, **, p < 0.01 ***, p < 0.001, N=3. (E) The degree of synergy between CHR-6494 and MEKi was assessed numerically employing Combination Index (CI) and Dose Reduction Index (DRI), which were calculated based on the Chou-Talalay method using the CalcuSyn Software. CI < 1, synergy; CI = 1, additive; CI > 1, antagonism. DRI = 1, no dose-reduction; DRI > 1, favorable dose-reduction; DRI < 1, unfavorable dose-reduction.