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

Area of Science:

• Microbiology
• Biochemistry
• Drug Discovery

Background:

• Multidrug-resistant (MDR) gram-negative bacteria pose a significant global health threat.
• Current antimicrobial strategies face challenges due to bacterial resistance and limited efficacy.
• Outer membrane (OM)-perturbing peptides offer a potential alternative but suffer from poor stability and specificity.

Purpose of the Study:

• To develop novel OM-perturbing peptides with enhanced stability and specificity.
• To investigate the mechanism of action and therapeutic efficacy of histidine-modified peptides.
• To evaluate the potential of histidine substitution as a strategy for improving peptide-based antimicrobials.

Main Methods:

• Histidine residues were substituted for lysine in a parent peptide (KL-L9P) to create KLH3 and KLH4.
• Peptide binding, membrane permeabilization, and antibiotic influx were assessed under varying pH conditions.
• In vivo stability was evaluated by assessing recognition by the mononuclear phagocyte system (MPS).
• Therapeutic efficacy was tested in mouse models of multidrug-resistant *Acinetobacter baumannii* skin infection and *Escherichia coli* NDM-1 bacteremia.

Main Results:

• KLH3 and KLH4 exhibited pH-dependent selective binding to bacterial membranes and permeabilized the OM without complete disruption.
• Under acidic pH, these peptides significantly increased the influx of non-permeable antibiotics.
• KLH3 and KLH4 demonstrated enhanced stability compared to KL-L9P, attributed to reduced MPS recognition.
• Improved therapeutic efficacy against MDR *A. baumannii* and *E. coli* infections was observed with KLH3 and KLH4, alongside reduced host toxicity.

Conclusions:

• Substituting cationic residues with histidine is an effective strategy to improve the in vivo stability of OM-perturbing peptides.
• Histidine-modified peptides offer enhanced specificity and therapeutic efficacy for treating gram-negative bacterial infections.
• These findings pave the way for developing more stable and effective peptide-based antimicrobial agents against challenging pathogens.