Mechanism of action of oxazolidinones: Effects of linezolid and eperezolid on translation reactions

The oxazolidinones are a new class of synthetic antibiotics with good activity against gram-positive pathogenic bacteria, Experiments with a susceptible Escherichia coli strain, UC6782, demonstrated that in vivo protein synthesis was inhibited by both eperezolid (formerly U-100592) and linezolid (formerly U-100766), Both linezolid and eperezolid were potent inhibitors of cell-free transcription-translation in E. coli, exhibiting 50% inhibitory concentrations (IC(50)s) of 1.8 and 2.5 mu M, respectively. The ability to demonstrate inhibition of in vitro translation directed by phage MS2 RNA was greatly dependent upon the amount of RNA added to the assay, For eperezolid, 128 mu g of RNA per mi produced an IC50 of 50 mu M whereas a concentration of 32 mu g/ml yielded an IC50 of 20 mu M. Investigating lower RNA template concentrations in linezolid inhibition experiments revealed that 32 and 8 mu g of MS2 phage RNA per mi produced IC(50)s of 24 and 15 mu M, respectively, This phenomenon was shared by the translation initiation inhibitor kasugamycin but not by streptomycin, Neither oxazolidinone inhibited the formation of N-formylmethionyl-tRNA, elongation, or termination reactions of bacterial translation. The oxazolidinones appear to inhibit bacterial translation at the initiation phase of protein synthesis.