A Serum‐Stable Antimicrobial Peptide‐Based Delivery Platform for Selective Treatment of Nontargetable and Chemoresistant Tumors

Abstract Antibody–drug conjugates (ADCs) have transformed cancer therapy but remain limited by their dependence on internalizing antigens, poor applicability to untargetable tumors, and susceptibility to drug resistance. Therefore, a modular antimicrobial‐peptide (AMP)‐based therapeutic system centered on a rationally designed conjugate, 270, is presented, which integrates three optimized components: a selectivity‐enhanced AMP core via a membrane affinity reconstruction strategy, a conformation‐driven polyethylene glycolylated blocker to minimize off‐target effects, and an N‐terminal cap to improve stability in human serum. By targeting nonendocytic membrane surface receptors via small‐molecule ligands, conjugate 270 exhibits potent and selective cytotoxicity against target tumor cells, effectively eliminating the majority of tumor cells within a few hours. Meanwhile, it exhibits high serum stability, minimal hemolysis, and negligible cytotoxicity toward normal cells at therapeutic concentrations. Mechanistic studies confirm ligand‐dependent membrane localization, rapid depolarization, and disruption, along with mitochondrial dysfunction. Moreover, it demonstrates significant therapeutic efficacy against four cell lines resistant to conventional chemotherapeutic agents. While additional in vivo validation is warranted, this work lays the foundation for a flexible AMP‐based approach to address untargetable and drug‐resistant cancers.