FabI/enoyl-acyl carrier protein reductase

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[1].

Melioidosis is a tropical bacterial infection caused by Burkholderia pseudomallei (B. pseudomallei; Bpm), a Gram-negative bacterium. Current therapeutic options are largely limited to trimethoprim-sulfamethoxazole and β-lactam drugs, and the treatment duration is about 4 months. Moreover, resistance has been reported to these drugs. Hence, there is a pressing need to develop new antibiotics for Melioidosis. Inhibition of enoyl-ACP reducatase (FabI), a key enzyme in the fatty acid biosynthesis pathway has shown significant promise for antibacterial drug development. FabI has been identified as the major enoyl-ACP reductase present in B. pseudomallei. In this study, we evaluated AFN-1252, a Staphylococcus aureus FabI inhibitor currently in clinical development, for its potential to bind to BpmFabI enzyme and inhibit B. pseudomallei bacterial growth. AFN-1252 stabilized BpmFabI and inhibited the enzyme activity with an IC50 of 9.6 nM. It showed good antibacterial activity against B. pseudomallei R15 strain, isolated from a melioidosis patient (MIC of 2.35 mg/L). X-ray structure of BpmFabI with AFN-1252 was determined at a resolution of 2.3 Å. Complex of BpmFabI with AFN-1252 formed a symmetrical tetrameric structure with one molecule of AFN-1252 bound to each monomeric subunit. The kinetic and thermal melting studies supported the finding that AFN-1252 can bind to BpmFabI independent of cofactor. The structural and mechanistic insights from these studies might help the rational design and development of new FabI inhibitors[2].

BpmFabI enzyme inhibition assay for AFN-1252[2]
AFN-1252 was synthesized in-house using a published synthetic scheme.38 The potency of AFN-1252 to inhibit BpmFabI was evaluated in a spectrophotometric assay by monitoring the oxidation of the cofactor NADH.33 Buffer used for the assay was 30 mM PIPES, pH 6.8, containing 150 mM NaCl, and 1 mM EDTA. 175 nM BpmFabI enzyme was used in the assay. Michaelis–Menton constant (Km) and Kcat were determined from the enzyme activity at increasing concentrations of crotonyl-CoA. The values of Km (257 µM) and Kcat (307 min−1) were slightly higher than the reported values (188 µM and 215 min−1, respectively). To determine the IC50, AFN-1252 was preincubated with BpmFabI for 30 min and the reaction was started by adding substrate mix containing crotonyl-CoA (300 µM) and NADH (375 µM). The oxidation of NADH was monitored by following the decrease of absorbance at 340 nm. IC50 value was determined by fitting the dose-response data to sigmoidal dose response (variable slope) curve using Graphpad Prism software V4. To determine the mechanism of binding, kinetic studies were carried out at different concentrations of inhibitor and varying the concentration of NADH at a fixed concentration of crotonoyl-CoA (300 µM) and also by varying the concentrations of crotonoyl-CoA keeping NADH concentration fixed at 375 µM. Lineweaver–Burk plots were subsequently generated to determine the mechanism of binding of AFN-1252 to BpmFabI.

---

Thermofluor assay[2]
Melting temperature of BpmFabI protein in presence and absence of inhibitors were determined with ABI Prism 7500 instrument (Applied Biosystems, Carlsbad) in the presence of 5× SYPRO Orange dye. 2 µM BpmFabI in 20 mM Tris pH 8.0, 500 mM NaCl, 5 mM imidazole with/without 50 µM NADH was incubated with 20 µM AFN-1252/Triclosan for 1 h followed by the addition of SYPRO Orange dye. Melting temperatures were determined with Boltzmann equation using Protein thermal shift™ software version 1.1.

Minimum inhibitory concentration (MIC) determination was carried out using the microdilution technique described by Wiegand et al. with some modifications.39 A twofold serial dilution of the compound was prepared in Brain Heart infusion broth (BHIB) and dispensed into 96-well plate. An inoculum of 1 × 108 cfu/mL of BpR15 was added into each well and incubated at 37°C for 24 h. Growth control (bacterial inoculum only), sterility control (broth only) and positive control (bacterial inoculum with Triclosan) wells were prepared and incubated simultaneously. The MIC, defined as the lowest concentration of AFN-1252 that inhibited visible growth of BpR15, was recorded. The MIC results are average of n = 2[2].

Burkholderia pseudomallei strain R15 (herein referred to as BpR15) was isolated from an individual who succumbed to melioidosis at the Kuala Lumpur Hospital in Malaysia.40 BpR15 was routinely cultured on Ashdown agar at 37°C and overnight bacterial cultures were prepared in BHIB. AFN-1252 was dissolved in dimethyl sulfoxide (DMSO) and stored at −20°C until use[2].

[1]. AFN-1252, a FabI inhibitor, demonstrates a Staphylococcus-specific spectrum of activity. Antimicrob Agents Chemother. 2009 Aug;53(8):3544-8.

[2]. AFN-1252 is a potent inhibitor of enoyl-ACP reductase from Burkholderia pseudomallei-Crystal structure, mode of action, and biological activity. Protein Sci. 2015 May;24(5):832-40.

[3]. Resistance to AFN-1252 arises from missense mutations in Staphylococcus aureus enoyl-acyl carrier protein reductase (FabI). J Biol Chem. 2013 Dec 20;288(51):36261-71.

[4].Perturbation of Staphylococcus aureus gene expression by the enoyl-acyl carrier protein reductase inhibitor AFN-1252. Antimicrob Agents Chemother. 2013 May;57(5):2182-90.

[5]. Yao J, Ericson ME, Frank MW, Rock CO. Enoyl-Acyl Carrier Protein Reductase I (FabI) is Essential for the Intracellular Growth of Listeria monocytogenes. Infect Immun. 2016 Oct 10. pii: IAI.00647-16. PubMed PMID: 27736774.

AFN-1252 has been used in trials studying the treatment of Cellulitis, Burn Infection, Wound Infection, Cutaneous Abscess, and Skin and Subcutaneous Tissue Bacterial Infections.

---

AFN-1252 is a potent antibiotic against Staphylococcus aureus that targets the enoyl-acyl carrier protein reductase (FabI). A thorough screen for AFN-1252-resistant strains was undertaken to identify the spectrum of mechanisms for acquired resistance. A missense mutation in fabI predicted to encode FabI(M99T) was isolated 49 times, and a single isolate was predicted to encode FabI(Y147H). AFN-1252 only bound to the NADPH form of FabI, and the close interactions between the drug and Met-99 and Tyr-147 explained how the mutations would result in resistant enzymes. The clone expressing FabI(Y147H) had a pronounced growth defect that was rescued by exogenous fatty acid supplementation, and the purified protein had less than 5% of the enzymatic activity of FabI. FabI(Y147F) was also catalytically defective but retained its sensitivity to AFN-1252, illustrating the importance of the conserved Tyr-147 hydroxyl group in FabI function. The strains expressing FabI(M99T) exhibited normal growth, and the biochemical properties of the purified protein were indistinguishable from those of FabI. The AFN-1252 Ki(app) increased from 4 nm in FabI to 69 nm in FabI(M99T), accounting for the increased resistance of the corresponding mutant strain. The low activity of FabI(Y147H) precluded an accurate Ki measurement. The strain expressing FabI(Y147H) was also resistant to triclosan; however, the strain expressing FabI(M99T) was more susceptible. Strains with higher levels of AFN-1252 resistance were not obtained. The AFN-1252-resistant strains remained sensitive to submicromolar concentrations of AFN-1252, which blocked growth through inhibition of fatty acid biosynthesis at the FabI step.[3]

---

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. [4]

---

Enoyl-acyl carrier protein reductase catalyzes the last step in each elongation cycle of type II bacterial fatty acid synthesis and is a key regulatory protein in bacterial fatty acid synthesis. Genes of the facultative intracellular pathogen Listeria monocytogenes encode two functional enoyl-acyl carrier protein isoforms based on their ability to complement the temperature-sensitive growth phenotype of Escherichia coli strain JP1111 [fabI(Ts)]. The FabI isoform was inactivated by the FabI selective inhibitor AFN-1252, but the FabK isoform was not affected by the drug, as expected. Inhibition of FabI by AFN-1252 decreased endogenous fatty acid synthesis by 80% and lowered the growth rate of L. monocytogenes in laboratory medium. Robust exogenous fatty acid incorporation was not detected in L. monocytogenes unless the pathway was partially inactivated by AFN-1252 treatment. However, supplementation with exogenous fatty acids did not restore normal growth in the presence of AFN-1252. FabI inactivation prevented the intracellular growth of L. monocytogenes, showing that neither FabK nor the incorporation of host cellular fatty acids was sufficient to support the intracellular growth of L. monocytogenes Our results show that FabI is the primary enoyl-acyl carrier protein reductase of type II bacterial fatty acid synthesis and is essential for the intracellular growth of L. monocytogenes. [5]

---

C22H21N3O3

375.4204

375.16

C, 70.38; H, 5.64; N, 11.19; O, 12.78

620175-39-5

1047981-31-6;620175-39-5;1047981-30-5 (tosylate hydrate);

10407120

White to off-white solid powder.

3.78

78.930

O=C(N(C)CC1=C(C)C2=CC=CC=C2O1)/C=C/C3=CC(CC4)=C(N=C3)NC4=O

QXTWSUQCXCWEHF-JXMROGBWSA-N

InChI=1S/C22H21N3O3/c1-14-17-5-3-4-6-18(17)28-19(14)13-25(2)21(27)10-7-15-11-16-8-9-20(26)24-22(16)23-12-15/h3-7,10-12H,8-9,13H2,1-2H3,(H,23,24,26)/b10-7+

(E)-N-methyl-N-((3-methylbenzofuran-2-yl)methyl)-3-(7-oxo-5,6,7,8-tetrahydro-1,8-naphthyridin-3-yl)acrylamide

AFN-1252; AFN 1252; AFN1252; API-1252; API1252; API 1252; AFN12520000; AFN 12520000; AFN12520000; Debio1452; Debio 1452; Debio1452; afabicin desphosphono; API 1252; DEBIO1452; DEBIO-1452; Debio 1452;

2934.99.9001

Powder      -20°C    3 years

                     4°C     2 years

In solvent   -80°C    6 months

                  -20°C    1 month

Room temperature (This product is stable at ambient temperature for a few days during ordinary shipping and time spent in Customs)

DMSO :5.8~9 mg/mL ( 15.45~23.97 mM）

Note: Listed below are some common formulations that may be used to formulate products with low water solubility (e.g. < 1 mg/mL), you may test these formulations using a minute amount of products to avoid loss of samples.

---

Injection Formulation 1: DMSO : Tween 80： Saline = 10 : 5 : 85 (i.e. 100 μL DMSO stock solution → 50 μL Tween 80 → 850 μL Saline)
*Preparation of saline: Dissolve 0.9 g of sodium chloride in 100 mL ddH ₂ O to obtain a clear solution.
Injection Formulation 2: DMSO : PEG300 ：Tween 80 : Saline = 10 : 40 : 5 : 45 (i.e. 100 μL DMSO → 400 μLPEG300 → 50 μL Tween 80 → 450 μL Saline)
Injection Formulation 3: DMSO : Corn oil = 10 : 90 (i.e. 100 μL DMSO → 900 μL Corn oil)
Example: Take the Injection Formulation 3 (DMSO : Corn oil = 10 : 90) as an example, if 1 mL of 2.5 mg/mL working solution is to be prepared, you can take 100 μL 25 mg/mL DMSO stock solution and add to 900 μL corn oil, mix well to obtain a clear or suspension solution (2.5 mg/mL, ready for use in animals).

View More

Injection Formulation 4: DMSO : 20% SBE-β-CD in saline = 10 : 90 [i.e. 100 μL DMSO → 900 μL (20% SBE-β-CD in saline)]
*Preparation of 20% SBE-β-CD in Saline (4°C，1 week): Dissolve 2 g SBE-β-CD in 10 mL saline to obtain a clear solution.
Injection Formulation 5: 2-Hydroxypropyl-β-cyclodextrin : Saline = 50 : 50 (i.e. 500 μL 2-Hydroxypropyl-β-cyclodextrin → 500 μL Saline)
Injection Formulation 6: DMSO : PEG300 : castor oil : Saline = 5 : 10 : 20 : 65 (i.e. 50 μL DMSO → 100 μLPEG300 → 200 μL castor oil → 650 μL Saline)
Injection Formulation 7: Ethanol : Cremophor : Saline = 10： 10 : 80 (i.e. 100 μL Ethanol → 100 μL Cremophor → 800 μL Saline)
Injection Formulation 8: Dissolve in Cremophor/Ethanol (50 : 50), then diluted by Saline
Injection Formulation 9: EtOH : Corn oil = 10 : 90 (i.e. 100 μL EtOH → 900 μL Corn oil)
Injection Formulation 10: EtOH : PEG300：Tween 80 : Saline = 10 : 40 : 5 : 45 (i.e. 100 μL EtOH → 400 μLPEG300 → 50 μL Tween 80 → 450 μL Saline)

---

Oral Formulation 1: Suspend in 0.5% CMC Na (carboxymethylcellulose sodium)
Oral Formulation 2: Suspend in 0.5% Carboxymethyl cellulose
Example: Take the Oral Formulation 1 (Suspend in 0.5% CMC Na) as an example, if 100 mL of 2.5 mg/mL working solution is to be prepared, you can first prepare 0.5% CMC Na solution by measuring 0.5 g CMC Na and dissolve it in 100 mL ddH2O to obtain a clear solution; then add 250 mg of the product to 100 mL 0.5% CMC Na solution, to make the suspension solution (2.5 mg/mL, ready for use in animals).

View More

Oral Formulation 3: Dissolved in PEG400
Oral Formulation 4: Suspend in 0.2% Carboxymethyl cellulose
Oral Formulation 5: Dissolve in 0.25% Tween 80 and 0.5% Carboxymethyl cellulose
Oral Formulation 6: Mixing with food powders

---

Note: Please be aware that the above formulations are for reference only. InvivoChem strongly recommends customers to read literature methods/protocols carefully before determining which formulation you should use for in vivo studies, as different compounds have different solubility properties and have to be formulated differently.

---

 (Please use freshly prepared in vivo formulations for optimal results.)