A pathway-directed positive growth restoration assay to facilitate the discovery of lipid A and fatty acid biosynthesis inhibitors in Acinetobacter baumannii

PLoS One. 2018 Mar 5;13(3):e0193851. doi: 10.1371/journal.pone.0193851. eCollection 2018.

Abstract

Acinetobacter baumannii ATCC 19606 can grow without lipooligosaccharide (LOS). Lack of LOS can result from disruption of the early lipid A biosynthetic pathway genes lpxA, lpxC or lpxD. Although LOS itself is not essential for growth of A. baumannii ATCC 19606, it was previously shown that depletion of the lipid A biosynthetic enzyme LpxK in cells inhibited growth due to the toxic accumulation of lipid A pathway intermediates. Growth of LpxK-depleted cells was restored by chemical inhibition of LOS biosynthesis using CHIR-090 (LpxC) and fatty acid biosynthesis using cerulenin (FabB/F) and pyridopyrimidine (acetyl-CoA-carboxylase). Here, we expand on this by showing that inhibition of enoyl-acyl carrier protein reductase (FabI), responsible for converting trans-2-enoyl-ACP into acyl-ACP during the fatty acid elongation cycle also restored growth during LpxK depletion. Inhibition of fatty acid biosynthesis during LpxK depletion rescued growth at 37°C, but not at 30°C, whereas rescue by LpxC inhibition was temperature independent. We exploited these observations to demonstrate proof of concept for a targeted medium-throughput growth restoration screening assay to identify small molecule inhibitors of LOS and fatty acid biosynthesis. The differential temperature dependence of fatty acid and LpxC inhibition provides a simple means by which to separate growth stimulating compounds by pathway. Targeted cell-based screening platforms such as this are important for faster identification of compounds inhibiting pathways of interest in antibacterial discovery for clinically relevant Gram-negative pathogens.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Acinetobacter baumannii / metabolism*
  • Biological Assay / methods
  • Cerulenin / pharmacology
  • Enoyl-(Acyl-Carrier-Protein) Reductase (NADH) / metabolism
  • Fatty Acid Synthases / metabolism
  • Fatty Acid Synthesis Inhibitors / metabolism*
  • Fatty Acids / biosynthesis*
  • Hydroxamic Acids / pharmacology
  • Lipid A / metabolism*
  • Threonine / analogs & derivatives
  • Threonine / pharmacology

Substances

  • CHIR 090
  • Fatty Acid Synthesis Inhibitors
  • Fatty Acids
  • Hydroxamic Acids
  • Lipid A
  • Cerulenin
  • Threonine
  • Enoyl-(Acyl-Carrier-Protein) Reductase (NADH)
  • Fatty Acid Synthases

Grants and funding

Funding of this research was provided solely within the Novartis organization as per standard research activities. The funder provided support in the form of salaries for authors [DLR, LW, HC, GP, DAS, J-RW, CRD], but did not have any additional role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript. The specific roles of these authors are articulated in the ‘author contributions’ section.