Wednesday, April 2, 2025
4/2/2025
Modifications of Lipid A with Phospho-Ethanolamine Impacting Polymyxin Resistance - Modifications of Lipid A with Phospho-Ethanolamine Impacting Polymyxin Resistance Marcelo Sousa University of Colorado Boulder Project Summary Human Cationic AntiMicrobial Peptides (CAMPs) represent a conserved branch of the innate immune system. CAMPs constitute a first line of defense against bacterial colonization that is particularly important in exposed tissues and surfaces such as the skin, eyes, airways and lungs. Furthermore, CAMP antibiotics such as colistin and related polymyxins are a class of essential drugs in clinical use to treat recalcitrant infection with multidrug resistant Gram-negative bacteria. These include the “urgent threat” pathogens carbapenem resistant Acinetobacter baumannii, Carbapenem Resistant Enterobacteriaceae (CRE) as well as “serious threat” pathogens such as Multidrug Resistant (MDR) Pseudomonas aeruginosa. However, these and other Gram- negative pathogens have acquired mechanisms to attach cationic modifiers such as phosphoethanolamine (pEtN) to lipid A in the outer membrane of bacteria (the CAMP/colistin target) which result in resistance to the bactericidal activity of CAMPs and colistin. This is a significant clinical problem with pathogens that produce persistent infections with high mortality rates. Therefore, development of inhibitors of the enzyme that catalyzes the Lipid A modification with phosphoethanolamine (pEtN) is a desirable therapeutic strategy that would result in potentiators of colistin against deadly multidrug resistant pathogens. A pEtN transferase is required for pEtN- lipid A biosynthesis and colistin resistance. Therefore, this protein is validated target for drug development to combat colistin resistance. However, the biochemical characterization of pEtN transferase is incomplete. Furthermore, in vitro activity assays are either currently unavailable or inadequate for quantitative evaluation of putative inhibitors. This knowledge gap impairs development of colistin adjuvants that could improve the efficacy of this life-saving antibiotic. We will close this gap with an integrated, collaborative research program to structurally and functionally characterize pEtN transferases directly responsible for CAMP/colistin resistance, screen for probes to define inhibitory strategies, and develop a platform to quantitative test impact of target activity in vitro. Successful completion of this exploratory multidisciplinary program will result in new insights into the mechanisms of lipid A modification leading to CAMP/colistin resistance and provide a fully characterized target with validated assays and active site binding probes. This represents a superb platform for future development of adjuvant drugs that augment the efficacy of colistin in treatment of infections with multidrug resistant bacteria.
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