Mode of Action,In VitroActivity, andIn VivoEfficacy of AFN-1252, a Selective Antistaphylococcal FabI Inhibitor

Abstract

ABSTRACTThe mechanism of action of AFN-1252, a selective inhibitor ofStaphylococcus aureusenoyl-acyl carrier protein reductase (FabI), which is involved in fatty acid biosynthesis, was confirmed by using biochemistry, macromolecular synthesis, genetics, and cocrystallization of an AFN-1252–FabI complex. AFN-1252 demonstrated a low propensity for spontaneous resistance development and a time-dependent reduction of the viability of both methicillin-susceptible and methicillin-resistantS. aureus, achieving a ≥2-log10reduction inS. aureuscounts over 24 h, and was extremely potent against clinical isolates ofS. aureus(MIC90, 0.015 μg/ml) and coagulase-negative staphylococci (MIC90, 0.12 μg/ml), regardless of their drug resistance, hospital- or community-associated origin, or other clinical subgroup. AFN-1252 was orally available in mouse pharmacokinetic studies, and a single oral dose of 1 mg/kg AFN-1252 was efficacious in a mouse model of septicemia, providing 100% protection from an otherwise lethal peritoneal infection ofS. aureusSmith. A median effective dose of 0.15 mg/kg indicated that AFN-1252 was 12 to 24 times more potent than linezolid in the model. These studies, demonstrating a selective mode of action, potentin vitroactivity, andin vivoefficacy, support the continued investigation of AFN-1252 as a targeted therapeutic for staphylococcal infections.