LpxC inhibitors as new antibacterial agents and tools for studying regulation of lipid A biosynthesis in Gram-negative pathogens.
Bottom Line: The limited number of validated cellular targets and approaches, along with the increasing amount of antibiotic resistance that is spreading throughout the clinical environment, has prompted us to explore the utility of inhibitors of novel targets and pathways in these resistant organisms, since preexisting target-based resistance should be negligible.Lipid A biosynthesis is an essential process for the formation of lipopolysaccharide, which is a critical component of the Gram-negative outer membrane.In this report, we describe the in vitro and in vivo characterization of novel inhibitors of LpxC, an enzyme whose activity is required for proper lipid A biosynthesis, and demonstrate that our lead compound has the requisite attributes to warrant further consideration as a novel antibiotic.
Affiliation: Discovery Biology, Antibacterials Research Unit, Pfizer Worldwide Research and Development, Groton, Connecticut, USA firstname.lastname@example.org.Show MeSH
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Mentions: Our efforts to identify a potent, broad-spectrum inhibitor of LpxC have focused on a Zn2+ binding class of hydroxamic acids. The structures of the lead molecules from two different series of compounds are shown in Fig. 1. LpxC-2, one of our leads from the biphenyl methylsulfone-containing series, has been described previously (11), as have the pyridone-substituted compounds LpxC-3 and LpxC-4 (12). While the 50% inhibitory concentrations (IC50s) for each of these compounds against the Pseudomonas aeruginosa LpxC enzyme are not substantially different, the pyridone analog LpxC-4 demonstrates a clear MIC90 advantage over the biphenyl analog LpxC-2 when tested against a panel of 106 recent clinical isolates (Table 1). By comparison, despite it having enzyme inhibitory activity roughly equivalent to that of LpxC-4, the MIC90 of CHIR-090, a highly potent LpxC inhibitor that is active against a wide variety of MDR Gram-negative bacteria (13, 14), was found to be 4-fold higher against P. aeruginosa. In the case of Klebsiella pneumoniae, an ~10-fold decrease in the enzyme IC50 between LpxC-3 and LpxC-4 resulted in a 16-fold decrease in MIC90 to 1 µg/ml (Table 1). In Acinetobacter baumannii, however, all LpxC inhibitors tested had considerably higher enzyme IC50s and MIC90 values that were 32 µg/ml or greater. It should be noted, however, that a structurally related LpxC inhibitor from the pyridone class was recently demonstrated to have significant in vivo efficacy against an MDR clinical isolate of A. baumannii despite having no whole-cell activity in vitro (15), a disconnect which is likely due to the unusual ability of A. baumannii to survive in vitro without LPS (16). Many of our compounds, most notably LpxC-4, also have strong activity against other important Gram-negative species, including Escherichia coli, Enterobacter spp., Burkholderia cepacia, and Stenotrophomonas maltophilia (Table 1). Since it proved to be a potent compound with broad-spectrum activity, we chose to further characterize LpxC-4 both in vitro and in vivo.
Affiliation: Discovery Biology, Antibacterials Research Unit, Pfizer Worldwide Research and Development, Groton, Connecticut, USA email@example.com.