Design, Synthesis, and Biological Evaluation of Novel MCR-1 Inhibitors against Colistin-Resistant Bacteria

Abstract The plasmid-encoded phosphoethanolamine transferase (MCR-1) impairs the efficacy of colistin, a last-line antibiotic for multidrug-resistant Gram-negative bacteria. To address this antibiotic resistance challenge, we designed and synthesized a series of benzopyran derivatives as MCR-1 inhibitors. Among these, compound 65 potently restored colistin susceptibility in clinical mobilized colistin resistance-1 (mcr-1)-positive Escherichia coli (E. coli) strains, showing a 14-fold enhancement compared to the initial hit. Mechanism of action studies confirmed that compound 65 bound directly to MCR-1 and inhibited its enzymatic activity. Molecular docking and mutagenesis assays suggested that compound 65 engages multiple residues within the catalytic pocket of the MCR-1 protein. In a murine peritonitis infection model, the combination of compound 65 and colistin significantly improved the survival rates and reduced bacterial loads. These results highlight the promising potential of benzopyran derivatives, especially compound 65, as adjuvants for counteracting colistin resistance mediated by MCR-1.