β-catenin mRNA silencing and MEK inhibition display synergistic efficacy in preclinical tumor models

Colorectal carcinomas harbor well-defined genetic abnormalities, including aberrant activation of Wnt/β-catenin and MAPK pathways, often simultaneously. Although the MAPK pathway can be targeted using potent small-molecule drugs, including BRAF and MEK inhibitors, β-catenin inhibition has been historically challenging. RNAi approaches have advanced to the stage of clinical viability and are especially well suited for transcriptional modulators, such as β-catenin. In this study, we report therapeutic effects of combined targeting of these pathways with pharmacologic agents. Using a recently described tumor-selective nanoparticle containing a β-catenin–targeting RNAi trigger, in combination with the FDA-approved MEK inhibitor (MEKi) trametinib, we demonstrate synergistic tumor growth inhibition in in vivo models of colorectal cancer, melanoma, and hepatocellular carcinoma. At dose levels that were insufficient to significantly impact tumor growth as monotherapies, combination regimens resulted in synergistic efficacy and complete tumor growth inhibition. Importantly, dual MEKi/RNAi therapy dramatically improved survival of mice bearing colorectal cancer liver metastases. In addition, pharmacologic silencing of β-catenin mRNA was effective against tumors that are inherently resistant or that acquire drug-induced resistance to trametinib. These results provide a strong rationale for clinical evaluation of this dual-targeting approach for cancers harboring Wnt/β-catenin and MAPK pathway mutations. Mol Cancer Ther; 17(2); 544–53. ©2017 AACR.