Loss of LGR5 through therapy-induced downregulation or gene ablation is associated with resistance and enhanced MET-STAT3 signaling in colorectal cancer cells.

LGR5 is highly expressed in colorectal cancer (CRC) and cancer stem cells that play important roles in tumor initiation, progression, and metastasis. Loss of LGR5 has been shown to enhance therapy resistance. However, the molecular mechanisms that mediate this resistance remain elusive. In this study, we demonstrate conversion of LGR5+ CRC cells to an LGR5- state in response to chemotherapy, LGR5-targeted antibody-drug conjugates (ADCs), or LGR5 gene ablation, led to activation of STAT3. Further investigation revealed increased STAT3 activation occurred a result of increased MET activity. LGR5 overexpression decreased MET-STAT3 activity and sensitized CRC cells to therapy. STAT3 inhibition suppressed MET phosphorylation, while constitutively active STAT3 reduced LGR5 levels and increased MET activity, suggesting a potential feedback mechanism. Combination treatment of MET-STAT3 inhibitors with irinotecan or ADCs substantiated synergistic effects in CRC cells and tumor organoids. In CRC xenografts, STAT3 inhibition combined with irinotecan enhanced tumor growth suppression and prolonged survival. These findings suggest a mechanism by which drug-resistant LGR5- CRC cells acquire a survival advantage through activation of MET-STAT3 and provide rationale for new treatment strategies to target CRC.