Blocking endothelin-1-receptor/β-catenin circuit sensitizes to chemotherapy in colorectal cancer

The limited clinical response to conventional chemotherapeutics observed in colorectal cancer (CRC) may be related to the connections between the hyperactivated beta-catenin signaling and other pathways in CRC stem-like cells (CRC-SC). Here, we show the mechanistic link between the endothelin-1 (ET-1)/ET-1 receptor (ET-1R) signaling and beta-catenin pathway through the specific interaction with the signal transducer beta-arrestin1 (beta-arr1), which initiates signaling cascades as part of the signaling complex. Using a panel of patient-derived CRC-SC, we show that these cells secrete ET-1 and express ETAR and beta-arr1, and that the activation of ETAR/beta-arr1 axis promotes the cross-talk with beta-catenin signaling to sustain stemness, epithelial-to-mesenchymal transition (EMT) phenotype and response to chemotherapy. Upon ETAR activation, beta-arr1 acts as a transcription co-activator that binds beta-catenin, thereby promoting nuclear complex with beta-catenin/TFC4 and p300 and histone acetylation, inducing chromatin reorganization on target genes, such as ET-1. The enhanced transcription of ET-1 increases the self-sustained ET-1/beta-catenin network. All these findings provide a strong rationale for targeting ET-1R to hamper downstream beta-catenin/ET-1 autocrine circuit. Interestingly, treatment with macitentan, a dual ETAR and ETBR antagonist, able to interfere with tumor and microenvironment, disrupts the ET-1R/beta-arr1-beta-catenin interaction impairing pathways involved in cell survival, EMT, invasion, and enhancing sensitivity to oxaliplatin (OX) and 5-fluorouracil (5-FU). In CRC-SC xenografts, the combination of macitentan and OX or 5-FU enhances the therapeutic effects of cytotoxic drugs. Together, these results provide mechanistic insight into how ET-1R coopts beta-catenin signaling and offer a novel therapeutic strategy to manage CRC based on the combination of macitentan and chemotherapy that might benefit patients whose tumors show high ETAR and beta-catenin expression.