Activity of Debio1452, a FabI inhibitor with potent activity against Staphylococcus aureus and coagulase-negative Staphylococcus spp., including multidrug-resistant strains.

Staphylococcus aureus and coagulase-negative staphylococci (CoNS) are responsible for a wide variety of human infections. The investigational antibacterial Debio1450 (previously AFN-1720), a prodrug of Debio1452 (previously AFN-1252), specifically targets staphylococci without significant activity against other Gram-positive or Gram-negative species. Debio1452 inhibits FabI, an enzyme critical to fatty acid biosynthesis in staphylococci. The activity of Debio1452 against CoNS, methicillin-susceptible S. aureus (MSSA), and methicillin-resistant S. aureus (MRSA), including significant clones, was determined. A globally diverse collection of 574 patient isolates from 35 countries was tested that included CoNS (6 species, 103 strains), MSSA (154 strains), MRSA (163 strains), and molecularly characterized strains (including spa-typed MRSA clones; 154 strains). The isolates were tested for susceptibility by CLSI broth microdilution methods against Debio1452 and 10 comparators. The susceptibility rates for the comparators were determined using CLSI and EUCAST breakpoint criteria. All S. aureus and CoNS strains were inhibited by Debio1452 concentrations of ≤ 0.12 and ≤ 0.5 µg/ml, respectively. The MIC50s for MSSA, MRSA, and molecularly characterized MRSA strains were 0.004 µg/ml, and the MIC90s ranged from 0.008 to 0.03 µg/ml. The MICs were higher for the CoNS isolates (MIC50/90, 0.015/0.12 µg/ml). Among S. aureus strains, resistance was common for erythromycin (61.6%), levofloxacin (49.0%), clindamycin (27.6%), tetracycline (15.7%), and trimethoprim-sulfamethoxazole (7.0%). Debio1452 demonstrated potent activity against MSSA, MRSA, and CoNS. Debio1452 showed significantly greater activity overall (MIC50, 0.004 µg/ml) than the other agents tested against these staphylococcal species, which included dominant MRSA clones and strains resistant to currently utilized antimicrobial agents.

Perturbation of Staphylococcus aureus gene expression by the enoyl-acyl carrier protein reductase inhibitor AFN-1252.

This study examines the alteration in Staphylococcus aureus gene expression following treatment with the type 2 fatty acid synthesis inhibitor AFN-1252. An Affymetrix array study showed that AFN-1252 rapidly increased the expression of fatty acid synthetic genes and repressed the expression of virulence genes controlled by the SaeRS 2-component regulator in exponentially growing cells. AFN-1252 did not alter virulence mRNA levels in a saeR deletion strain or in strain Newman expressing a constitutively active SaeS kinase. AFN-1252 caused a more pronounced increase in fabH mRNA levels in cells entering stationary phase, whereas the depression of virulence factor transcription was attenuated. The effect of AFN-1252 on gene expression in vivo was determined using a mouse subcutaneous granuloma infection model. AFN-1252 was therapeutically effective, and the exposure (area under the concentration-time curve from 0 to 48 h [AUC(0-48)]) of AFN-1252 in the pouch fluid was comparable to the plasma levels in orally dosed animals. The inhibition of fatty acid biosynthesis by AFN-1252 in the infected pouches was signified by the substantial and sustained increase in fabH mRNA levels in pouch-associated bacteria, whereas depression of virulence factor mRNA levels in the AFN-1252-treated pouch bacteria was not as evident as it was in exponentially growing cells in vitro. The trends in fabH and virulence factor gene expression in the animal were similar to those in slower-growing bacteria in vitro. These data indicate that the effects of AFN-1252 on virulence factor gene expression depend on the physiological state of the bacteria.

Mode of action, in vitro activity, and in vivo efficacy of AFN-1252, a selective antistaphylococcal FabI inhibitor.

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 µg/ml) and coagulase-negative staphylococci (MIC(90), 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 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.

AFN-1252, a FabI inhibitor, demonstrates a Staphylococcus-specific spectrum of activity.

AFN-1252, a potent inhibitor of enoyl-acyl carrier protein reductase (FabI), inhibited all clinical isolates of Staphylococcus aureus (n = 502) and Staphylococcus epidermidis (n = 51) tested, including methicillin (meticillin)-resistant isolates, at concentrations of 4 microg/ml) against clinical isolates of Streptococcus pneumoniae, beta-hemolytic streptococci, Enterococcus spp., Enterobacteriaceae, nonfermentative gram-negative bacilli, and Moraxella catarrhalis. These data support the continued development of AFN-1252 for the treatment of patients with resistant staphylococcal infections.

Spiro-naphthyridinone piperidines as inhibitors of S. aureus and E. coli enoyl-ACP reductase (FabI).

Spiropiperidine naphthyridinone inhibitors of Staphylococcus aureus and Escherichia coli FabI have been prepared. Compounds 14a and 14c were identified as having sub-nanomolar E. coli FabI activity and are among the most potent FabI inhibitors yet described. The structural model of 14a bound to E. coli FabI is shown.

2,3,4,5-Tetrahydro-1H-pyrido[2,3-b and e][1,4]diazepines as inhibitors of the bacterial enoyl ACP reductase, FabI.

In the search for new antibacterial agents, the enzyme FabI has been identified as an attractive target. Employing a structure guided approach, the previously reported ene-amide series of FabI inhibitors were expanded to include 2,3,4,5-tetrahydro-1H-pyrido[2,3-b and e][1,4]diazepines. These novel series incorporate additional H-bonding functions and can be more water soluble than their naphthyridinone progenitors; diazepine 16c is shown to be efficacious in a mouse infection model.

Safety, tolerability and pharmacokinetics of multiple oral doses of AFN-1252 administered as immediate release (IR) tablets in healthy subjects.

BACKGROUND: AFN-1252 is a novel inhibitor of FabI, which is essential in Staphylococcus spp. This study evaluated the safety, tolerability and pharmacokinetics of multiple oral doses of AFN-1252 immediate-release tablets. METHODS: Part I evaluated AFN-1252 as a single 200 mg dose in fed versus fasted subjects. Part II evaluated 200, 300 and 400 mg doses of AFN-1252 administered once-daily for 10 days. RESULTS: Pharmacokinetics indicated good absorption with a median Tmax of 2-3 hours, and a mean t1/2 of 7-10 hours, for all doses. Cmax and AUC responses were non-linear. A high-fat meal reduced AUC0-t and Cmax values by 62% and 48%, respectively, and delayed Tmax by 2.5 hours. All adverse events, including possibly drug-related headache and nausea, were mild or moderate. CONCLUSIONS: Multiple ascending doses of AFN-1252 were safe and well tolerated. AFN-1252 has potential for once- or twice-daily dosing in the treatment of staphylococcal infections.

Safety, tolerability and pharmacokinetics of AFN-1252 administered as immediate release tablets in healthy subjects.

AIMS: AFN-1252 is a novel inhibitor of FabI, an essential enzyme in Staphylococcus spp. This study was undertaken to assess the safety, tolerability and pharmacokinetic properties of AFN-1252, following oral administration in an ascending dose trial. MATERIALS & METHODS: This was a double-blind, randomized, placebo-controlled, two-part study. In Part I, single doses (QD) of 100, 200, 300, or 400 mg AFN-1252 were administered. In Part II, subjects received 200, 400, 600, or 800 mg (total daily dose) where 100, 200 and 400-mg doses were given twice in one day. RESULTS: AFN-1252 was well-absorbed with Cmax at 3-4 h when given once per day and 2.5-9 h when dosed twice in a single dosing day. T½ ranged from 8 to 11 h. Total and peak exposures of AFN-1252 increased nonlinearly. Adverse events were primarily mild and resolved promptly. CONCLUSIONS: Oral doses of AFN-1252 were safe and well tolerated. AFN-1252 has the potential for once or twice-a-day dosing for treatment of staphylococcal infections.

AFN-1252 in vitro absorption studies and pharmacokinetics following microdosing in healthy subjects.

OBJECTIVES: To investigate the absorption, distribution, metabolism and excretion of AFN-1252, a novel inhibitor of the essential FabI enzyme in Staphylococcus spp., in vitro and following microdosing in healthy adult male subjects following intravenous and oral administration. METHODS: Three ADME studies, comprising a Caco-2 assay, a rat intestinal perfusion model and a microdosing study in healthy human volunteers, were conducted. RESULTS: The Caco-2 assay indicated that AFN-1252 in solution is well-absorbed and undergoes insignificant efflux, and its transport across the intestinal wall is probably passive. In the rat intestinal perfusion model, AFN-1252 exhibited high permeability potential across three segments, in the rank order of jejunum=ileum>colon. Taken together with the low aqueous solubility, the data from these studies indicate that AFN-1252 is a BCS Class II molecule with solubility-limited absorption. Analysis of the [(14)C]-AFN-1252 radioactivity concentration-time data indicated similar pharmacokinetics following intravenous and oral administration in the microdosing study in healthy volunteers. These included long terminal half-lives of ∼7 h and 83% bioavailability, indicating that there was little first-pass metabolism following oral dosing. AFN-1252 exhibited good distribution to skin and skin structures where its anti-staphylococcal activity may be required. Urinary and faecal excretion are major elimination routes for [(14)C]-AFN-1252 following intravenous or oral administration. CONCLUSIONS: AFN-1252 has the potential for both intravenous and oral administration, once- or twice-daily dosing and good tissue distribution in humans. Further safety, efficacy and pharmacokinetic studies in man are required to investigate therapeutically-relevant doses for this novel agent and its targeted selectivity and high potency against Staphylococcus spp.

Pharmacokinetics, pharmacodynamics and efficacy of novel FabI inhibitor AFN-1252 against MSSA and MRSA in the murine thigh infection model.

AFN-1252, a new antimicrobial agent, specifically and potently inhibits fatty acid synthesis in Staphylococcus aureus. We characterized in vivo pharmacokinetic and pharmacodynamic profiles of AFN-1252 administered orally to neutropenic mice inoculated in thighs (∼10(6) CFU) with methicillin-susceptible S. aureus (MSSA) ATCC 29213. Efficacy was also assessed in mice inoculated with MSSA, hospital-acquired Methicillin-resistant Staphylococcus aureus (HA-MRSA) or community-acquired (CA)-MRSA, and administered AFN-1252 or linezolid orally. Bacterial density was determined after 24 hours and efficacy defined as the change in CFU/thigh versus untreated controls at time 0. With MSSA, antibacterial reductions of ≥1 log were observed at ≥20 mg/kg doses, with ƒAUC/minimum inhibitory concentration (MIC) best describing the pharmacodynamic profile of AFN-1252. The 80, 50 and 5% maximum effects were observed with ƒAUC/MIC values of 22·3, 17·0, and 9·6, respectively. Similar values were obtained for CA-MRSA and HA-MRSA. AFN-1252 was 4-40 fold more effective than linezolid against CA-MRSA and HA-MRSA. These data demonstrate the excellent in vivo potency of AFN-1252 against phenotypically diverse S. aureus.