Multivalent Rhamnose‐Modified EGFR‐Targeting Nanobody Gains Enhanced Innate Fc Effector Immunity and Overcomes Cetuximab Resistance via Recruitment of Endogenous Antibodies

Abstract Cetuximab resistance is a significant challenge in cancer treatment, requiring the development of novel therapeutic strategies. In this study, a series of multivalent rhamnose (Rha)‐modified nanobody conjugates are synthesized and their antitumor activities and their potential to overcome cetuximab resistance are investigated. Structure‐activity relationship studies reveal that the multivalent conjugate D5 , bearing sixteen Rha haptens, elicits the most potent innate fragment crystallizable (Fc) effector immunity in vitro and exhibits an excellent in vivo pharmacokinetics by recruiting endogenous antibodies. Notably, it is found that the optimal conjugate D5 represents a novel entity capable of reversing cetuximab‐resistance induced by serine protease (PRSS). Moreover, in a xenograft mouse model, conjugate D5 exhibits significantly improved antitumor efficacy compared to unmodified nanobodies and cetuximab. The findings suggest that Rha‐Nanobody (Nb) conjugates hold promise as a novel therapeutic strategy for the treatment of cetuximab‐resistant tumors by enhancing the innate Fc effector immunity and enhancing the recruitment of endogenous antibodies to promote cancer cell clearance by innate immune cells.