RNAi-Mediated ß-Catenin Inhibition Promotes T Cell Infiltration and Antitumor Activity in Combination with Immune Checkpoint Blockade.

Wnt/ß-catenin signaling mediates cancer immune evasion and resistance to immune checkpoint therapy, in part by blocking cytokines that trigger immune cell recruitment. Inhibition of ß-catenin may be an effective strategy for increasing the low response rate to these effective medicines in numerous cancer populations. DCR-BCAT is a nanoparticle drug product containing a chemically optimized RNAi trigger targeting CTNNB1, the gene that encodes ß-catenin. In syngeneic mouse tumor models, ß-catenin inhibition with DCR-BCAT significantly increased T cell infiltration and potentiated the sensitivity of the tumors to checkpoint inhibition. The combination of DCR-BCAT and immunotherapy yielded significantly greater tumor growth inhibition (TGI) compared to monotherapy in B16F10 melanoma, 4T1 mammary carcinoma, Neuro2A neuroblastoma, and Renca renal adenocarcinoma. Response to the RNAi-containing combination therapy was not dependent on Wnt activation status of the tumor. Importantly, this drug combination was associated with elevated levels of biomarkers of T cell-mediated cytotoxicity. Finally, when CTLA-4 and PD-1 antibodies were combined with DCR-BCAT in MMTV-Wnt1 transgenic mice, a genetic model of spontaneous Wnt-driven tumors, complete regressions were achieved in the majority of treated subjects. These data support RNAi-mediated ß-catenin inhibition as an effective strategy to increase response rates to cancer immunotherapy.

ß-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/ß-catenin and MAPK pathways, often simultaneously. Although the MAPK pathway can be targeted using potent small-molecule drugs, including BRAF and MEK inhibitors, ß-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 ß-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 ß-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 ß-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/ß-catenin and MAPK pathway mutations. Mol Cancer Ther; 17(2); 544-53. ©2017 AACR.