ABSTRACT
Bacterial enoyl-ACP reductase (FabI) catalyzes the final step in each cycle of bacterial fatty acid biosynthesis and is an attractive target for the development of new antibacterial agents. Our efforts to identify potent, selective FabI inhibitors began with screening of the GlaxoSmithKline proprietary compound collection, which identified several small-molecule inhibitors of Staphylococcus aureus FabI. Through a combination of iterative medicinal chemistry and X-ray crystal structure based design, one of these leads was developed into the novel aminopyridine derivative 9, a low micromolar inhibitor of FabI from S. aureus (IC(50) = 2.4 microM) and Haemophilus influenzae (IC(50) = 4.2 microM). Compound 9 has good in vitro antibacterial activity against several organisms, including S. aureus (MIC = 0.5 microg/mL), and is effective in vivo in a S. aureus groin abscess infection model in rats. Through FabI overexpressor and macromolecular synthesis studies, the mode of action of 9 has been confirmed to be inhibition of fatty acid biosynthesis via inhibition of FabI. Taken together, these results support FabI as a valid antibacterial target and demonstrate the potential of small-molecule FabI inhibitors for the treatment of bacterial infections.
Subject(s)
Acrylamides/chemical synthesis , Aminopyridines/chemical synthesis , Anti-Bacterial Agents/chemical synthesis , Enzyme Inhibitors/chemical synthesis , Fatty Acid Synthases/antagonists & inhibitors , Oxidoreductases/antagonists & inhibitors , Acrylamides/chemistry , Acrylamides/pharmacology , Aminopyridines/chemistry , Aminopyridines/pharmacology , Animals , Anti-Bacterial Agents/chemistry , Anti-Bacterial Agents/pharmacology , Crystallography, X-Ray , Databases, Factual , Enoyl-(Acyl-Carrier-Protein) Reductase (NADH) , Enzyme Inhibitors/chemistry , Enzyme Inhibitors/pharmacology , Fatty Acid Synthases/chemistry , Haemophilus influenzae/drug effects , Inhibitory Concentration 50 , Microbial Sensitivity Tests , Models, Molecular , Oxidoreductases/chemistry , Rats , Staphylococcal Infections/drug therapy , Staphylococcus aureus/drug effects , Structure-Activity RelationshipABSTRACT
Homologues of Escherichia coli bacA, encoding extremely hydrophobic proteins, were identified in the genomes of Staphylococcus aureus and Streptococcus pneumoniae. Allelic replacement mutagenesis demonstrated that the gene is not essential for in vitro growth in either organism, and the mutants showed no significant changes in growth rate or morphology. The Staph. aureus bacA mutant showed slightly reduced virulence in a mouse model of infection and an eightfold increase in bacitracin susceptibility. However, a Strep. pneumoniae bacA mutant was highly attenuated in a mouse model of infection, and demonstrated an increase in susceptibility to bacitracin of up to 160000-fold. These observations are consistent with the previously proposed role of BacA protein as undecaprenol kinase.
