# Structural determinants of activity and mechanism of cationic peptide antibiotic activity against colistin-resistant bacteria

> **NIH NIH R01** · UNIVERSITY OF PITTSBURGH AT PITTSBURGH · 2024 · $626,415

## Abstract

Abstract. The emergence of antibiotic resistance (AR) underscores the urgent need to develop novel
antimicrobial agents that are able to overcome current AR mechanisms. Antimicrobial peptides (AMPs) tend to
disrupt bacterial membranes regardless of resistance to traditional antibiotics. However, bacteria have also
evolved to resist the effects of AMPs by reducing (e.g., incorporation of phosphoethanolamine), not eliminating,
the net electronegative charge of lipid A, an important component of LPS targeted by AMPs. Because a
minimum electronegative charge is essential to bacterial membrane integrity, AMPs can be optimized to
overcome limited changes in LPS, the most common resistance mechanism against endogenous AMPs and
colistin. We have developed an iterative framework for rational design of engineered cationic peptide antibiotics
(PAX) optimized for broad activity against multidrug-resistant (MDR) bacteria. We used libraries of rationally
designed series of novel Trp-rich peptides differing by 2 residues at a time, 1 Val and 1 Arg to establish the
distinction between structural determinants of antimicrobial potency and those of host toxicity. As predicted,
lowest minimum inhibitory concentrations (MIC) are achieved against MDR clinical isolates without substantial
increase in red blood cell lysis or toxicity to white blood cells at maximum test concentrations. Remarkably, one
of the selected PAX (E35) demonstrates efficacy when systemically administered at 4-5mg/kg either a single
dose (MDR P. aeruginosa infection) or multiple doses (MDR Klebsiella pneumonia infection) in mice. PAX
E35 also displayed a maximum tolerated dose of 30 mg/kg compared to 12-15 mg/kg of our initial lead peptide
WLBU2 now in phase 2 clinical trial. Our iterative framework minimizes trial and error for designing PAX with
enhanced systemic efficacy against MDR bacteria. Given the success against colistin-resistant (Col-R) bacteria,
the tendency is to claim that our work is done without thinking of potential shortcomings of the current PAX.
However, there are still too many unknowns. (1) MDR bacteria have not been exposed clinically to the peptides
as they have been to colistin. Once they do, it is almost certain that resistance frequency will steadily increase.
(2) The current structural optimization is only minimal because we have not yet determined how each of the
cationic (C) and hydrophobic (H) motifs contributes to bacterial recognition and killing. Thus, it is critical to
continue this important work while some of the PAX may progress to advanced pre-clinical and clinical studies.
We propose to define the contribution of the 2 motifs to target recognition and elimination using Col-R strains
that can be passaged to evolve resistance to the current PAX. The overarching goal of this proposal is to elucidate
the molecular determinants for bacterial resistance to PAX by uncoupling the C and H motifs of PAX to allow
C/H correlation with changes in LPS structures and corr...

## Key facts

- **NIH application ID:** 10852973
- **Project number:** 5R01AI172861-02
- **Recipient organization:** UNIVERSITY OF PITTSBURGH AT PITTSBURGH
- **Principal Investigator:** Berthony Deslouches
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2024
- **Award amount:** $626,415
- **Award type:** 5
- **Project period:** 2023-06-01 → 2028-05-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10852973

## Citation

> US National Institutes of Health, RePORTER application 10852973, Structural determinants of activity and mechanism of cationic peptide antibiotic activity against colistin-resistant bacteria (5R01AI172861-02). Retrieved via AI Analytics 2026-06-24 from https://api.ai-analytics.org/grant/nih/10852973. Licensed CC0.

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