Potent sub-MIC effect of GSK1322322 and other peptide deformylase inhibitors on in vitro growth of Staphylococcus aureus.

Peptide deformylase (PDF), a clinically unexploited antibacterial target, plays an essential role in protein maturation. PDF inhibitors, therefore, represent a new antibiotic class with a unique mode of action that provides an alternative therapy for the treatment of infections caused by drug-resistant pathogens, including methicillin-resistant Staphylococcus aureus (MRSA). GSK1322322 is a novel PDF inhibitor that is in phase II clinical development for the treatment of lower respiratory tract and skin infections. We have discovered that PDF inhibitors can prevent S. aureus in vitro growth for up to 6 h at concentrations 8- to 32-fold below their MICs. This phenomenon seems specific to PDF inhibitors, as none of the antimicrobial agents with alternative mechanisms of action tested show such a potent and widespread effect. It also appears limited to S. aureus, as PDF inhibitors do not show such an inhibition of growth at sub-MIC levels in Streptococcus pneumoniae or Haemophilus influenzae. Analysis of the effect of GSK1322322 on the early growth of 100 randomly selected S. aureus strains showed that concentrations equal to or below 1/8× MIC inhibited growth of 91% of the strains tested for 6 h, while the corresponding amount of moxifloxacin or linezolid only affected the growth of 1% and 6% of strains, respectively. Furthermore, the sub-MIC effect demonstrated by GSK1322322 appears more substantial on those strains at the higher end of the MIC spectrum. These effects may impact the clinical efficacy of GSK1322322 in serious infections caused by multidrug-resistant S. aureus.