Cetuximab increases LGR5 expression and augments LGR5-targeting antibody-drug conjugate efficacy in patient-derived colorectal cancer models

Colorectal cancer (CRC) remains the second-leading cause of cancer-associated deaths, indicating an urgent need for improved therapeutic options. We previously generated antibody-drug conjugates (ADCs) targeting the cancer stem-like cell marker leucine-rich repeat-containing G protein-coupled receptor 5 (LGR5). However, tumor relapse due to LGR5 downregulation and suboptimal payload selection warranted strategies to improve ADC efficacy. Here we report cetuximab, an EGFR-targeting monoclonal antibody indicated for RAS ^WT metastatic CRC, augments LGR5 expression independent of RAS/PIK3CA mutation status and promotes EGFR-LGR5 interactions. Furthermore, we describe the development of LGR5 ADCs incorporating a camptothecin-derived payload that is well-tolerated and significantly inhibits tumor growth. Importantly, cetuximab in combination with LGR5 ADCs results in enhanced tumor inhibition or regression versus single-agent treatment and extends survival in RAS ^MUT patient-derived xenografts. These findings support growing evidence that ADC combination therapies may be more effective than monotherapies and suggests a broader clinical use for cetuximab in treating RAS ^MUT CRC.