Hinged amphipathic peptides with pH-inducible positive charges: A selective battering ram against bacterial outer membrane in infection sites.

With the growing concerns about multidrug-resistant (MDR) gram-negative bacteria, many efforts have been made to develop alternative antimicrobial agents. Exploiting outer membrane (OM)-perturbing peptides is one strategy, but their low stability and specificity have hindered clinical application. Here, two histidine-modified peptides (KLH3 and KLH4) were developed by substituting lysine residues in a novel membrane-perturbing peptide, KL-L9P, with histidine. These peptides show pH-dependent selective binding to the bacterial membrane and permeabilize the OM of gram-negative bacteria without completely disrupting it. Notably, they specifically increase the influx of non-permeable antibiotics under acidic pH. Moreover, stability studies show that KLH3 and KLH4 peptides were more stable than KL-L9P peptides, primarily due to reduced recognition by the mononuclear phagocyte system (MPS). Consequently, KLH3 and KLH4 demonstrate improved therapeutic efficacy compared to KL-L9P in mouse model of both MDR A. baumannii skin infection and E. coli NDM-1 bacteremia, while showing reduced host toxicity. These results suggest that substituting cationic residues, such as lysine or arginine, with histidine residues is a simple yet effective strategy to enhance in vivo stability and infection site specificity of OM-perturbing peptides.