LpxC Inhibitors as New Antibacterial Agents and Tools for Studying Regulation of Lipid A Biosynthesis in Gram-Negative Pathogens

Abstract

The problem of multidrug resistance in serious Gram-negative bacterial pathogens has escalated so severely that new cellular targets and pathways need to be exploited to avoid many of the preexisting antibiotic resistance mechanisms that are rapidly disseminating to new strains. The discovery of small-molecule inhibitors of LpxC, the enzyme responsible for the first committed step in the biosynthesis of lipid A, represents a clinically unprecedented strategy to specifically act against Gram-negative organisms such as Pseudomonas aeruginosa and members of the Enterobacteriaceae. In this report, we describe the microbiological characterization of LpxC-4, a recently disclosed inhibitor of this bacterial target, and demonstrate that its spectrum of activity extends to several of the pathogenic species that are most threatening to human health today. We also show that spontaneous generation of LpxC-4 resistance occurs at frequencies comparable to those seen with marketed antibiotics, and we provide an in-depth analysis of the mechanisms of resistance utilized by target pathogens. Interestingly, these isolates also served as tools to further our understanding of the regulation of lipid A biosynthesis and enabled the discovery that this process occurs very distinctly between P. aeruginosa and members of the Enterobacteriaceae. Finally, we demonstrate that LpxC-4 is efficacious in vivo against multiple strains in different models of bacterial infection and that the major first-step resistance mechanisms employed by the intended target organisms can still be effectively treated with this new inhibitor.

Mutant Alleles of lptD Increase the Permeability of Pseudomonas aeruginosa and Define Determinants of Intrinsic Resistance to Antibiotics

“…When there is success in attaining cellular bioactivity, close attention must be paid to overcoming intrinsic resistance mechanisms such as efflux and permeability. Such efforts have shown promise in recent years with the development of hydroxamate LpxC inhibitors (84)(85)(86), novel bacterial type II topoisomerase inhibitors (NBTIs) (87,88), tricyclic GyrB/ParE (TriBE) inhibitors (89), and pyrrolocytosine ribosome inhibitors (90). Although these classes of compounds have not yet reached clinical utility, they demonstrate progress and inspire confidence that novel Gram-negative antibiotics can be discovered.…”

Inhibition of LpxC Increases Antibiotic Susceptibility in Acinetobacter baumannii

“…Inhibitors of LpxC, a zinc-dependent deacetylase that catalyzes the first committed step in the biosynthesis of lipid A, have been identified and are currently being developed for use as antimicrobial agents (2,3). LpxC inhibitors have demonstrated potent antibacterial activity against a number of Gram-negative species, including Pseudomonas aeruginosa, Escherichia coli, and Klebsiella pneumoniae (3)(4)(5)(6).…”

“…LpxC inhibitors have demonstrated potent antibacterial activity against a number of Gram-negative species, including Pseudomonas aeruginosa, Escherichia coli, and Klebsiella pneumoniae (3)(4)(5)(6). However, these inhibitors have been reported to have poor antimicrobial activity against A. baumannii strains in vitro (3,6,7), which may be explained by the finding that lipopolysaccharide (LPS) biosynthesis is not essential for viability in A. baumannii (8,9). In spite of a lack of in vitro antibacterial activity, a recent study has reported that LpxC inhibition can contribute to A. baumannii clearance in vivo by enhancing bacterial opsonophagocytosis and reducing inflammation (7).…”

“…Inhibitors of LpxC, a zinc-dependent deacetylase that catalyzes the first committed step in the biosynthesis of lipid A, have been identified and are currently being developed for use as antimicrobial agents (2,3). LpxC inhibitors have demonstrated potent antibacterial activity against a number of Gram-negative species, including Pseudomonas aeruginosa, Escherichia coli, and Klebsiella pneumoniae (3)(4)(5)(6). However, these inhibitors have been reported to have poor antimicrobial activity against A. baumannii strains in vitro (3,6,7), which may be explained by the finding that lipopolysaccharide (LPS) biosynthesis is not essential for viability in A. baumannii (8,9).…”

In Vitro and In Vivo Efficacy of an LpxC Inhibitor, CHIR-090, Alone or Combined with Colistin against Pseudomonas aeruginosa Biofilm

“…In-depth studies are therefore required to (i) elucidate the mechanisms of synergy and (ii) investigate the therapeutic potential of CHIR-090 in combination with colistin. Nevertheless, our results suggest the strong potential of CHIR-090 and maybe other LpxC inhibitors to be adjunct treatments to prevent the emergence of colistin resistance during therapy (23,24).…”