Coibamide Analogue as a Novel-Class Payload for Antibody-Drug Conjugate

Although antibody-drug conjugates (ADCs) have made substantial progress as targeted therapies, the range of suitable ADC payloads remains limited. In this study, the highly N-methylated cyclodepsipeptide [MeAla3-MeAla6]-coibamide (CA) was selected as a novel toxin for ADC construction due to its potent toxicity and unique mechanism of action. Using a quaternary ammonium salt approach, two linker-payload variants, MC-VA-PAB-CA and MC-GGFG-PAB-CA, with distinct cathepsin B (CTB)-cleavable linkers, were synthesized and assessed. Among them, MC-GGFG-PAB-CA demonstrated higher enzyme-responsive cleavage efficiency and superior plasma stability and was selected for conjugation with the epidermal growth factor receptor (EGFR) antibody cetuximab (Ctx), resulting in the formation of Ctx-CA. This conjugate exhibited EGFR-dependent antitumor activity, a pronounced “bystander killing effect”, and a significant tumor suppression effect in mouse models. Furthermore, the applicability of this conjugation strategy was confirmed through validation with the HER2 antibody. These findings suggest that CA is a promising weapon for next-generation ADCs.