Mode of Action, In Vitro Activity, and In Vivo Efficacy of AFN-1252, a Selective Antistaphylococcal FabI Inhibitor

Abstract

The mechanism of action of AFN-1252, a selective inhibitor of Staphylococcus aureus enoyl-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-resistant S. aureus, achieving a >2-log 10 reduction in S. aureus counts over 24 h, and was extremely potent against clinical isolates of S. aureus (MIC 90 , 0.015 g/ml) and coagulase-negative staphylococci (MIC 90 , 0.12 g/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 of S. aureus Smith. 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, potent in vitro activity, and in vivo efficacy, support the continued investigation of AFN-1252 as a targeted therapeutic for staphylococcal infections.

Type II Fatty Acid Synthesis Is Essential for the Replication of Chlamydia trachomatis

“…However, its potency may have to be improved in order for it to be effectively deployed to treat C. trachomatis. Our CtFabI⅐NADH⅐AFN-1252 crystal structure shows that AFN-1252 inhibits CtFabI by making similar contacts to the backbone amides and nucleotide cofactor as SaFabI (12). Our structure characterization also clearly points to the absence of the Met-99 side chain interaction with the oxotetrahydronaphthyridine ring of AFN-1252 as the primary reason for the lower affinity of AFN-1252 binding to CtFabI compared with SaFabI.…”

“…The IC 50 against the prototypical FabI inhibitor, triclosan, was also determined (0.32 Ϯ 0.08 M). AFN-1252 inhibited SaFabI by forming a FabI⅐ NADPH⅐AFN-1252 complex (12,17). The formation of this ternary complex on CtFabI was demonstrated by examining the effects of AFN-1252 on the CtFabI melting temperature using a protein thermal denaturation assay ( …”

“…FabI is characterized by a flexible substrate-binding loop, called the "flipping loop," that "closes" to orient the substrate with respect to the cofactor nicotinamide ring for reduction (37)(38)(39). This loop (residues 228 -240) adopts the "closed" conformation that has been observed with other FabI⅐inhibitor complexes (12,40,41), and the cisamide stacks onto the nicotinamide ring to apparently mimic the targeted double bond of the bound substrate (33).…”

“…Thus, one function of FASII would be to provide these 3-hydroxy fatty acids for LOS synthesis in C. trachomatis, but it is unknown whether FASII is needed for phospholipid synthesis. We used AFN-1252 as a chemical biology tool to specifically inhibit the enoyl-acyl carrier protein (ACP) reductase (FabI) (11)(12)(13) and assess the role of FASII in C. trachomatis replication. C. trachomatis is predicted to encode a FASII system that depends on FabI (Fig.…”

Molecular Evaluation of Antistaphylococcal Secondary Metabolites of Bacterial Isolates From Hospital Wastewater Environment

“…Antibiotics, also called antibacterials, are a type of antimicrobial drugs used in the treatment and prevention of bacterial infection [1]. They may either kill or inhibit the growth of bacteria.…”