Characterization of the novel OXA-213-like ß-lactamase OXA-822 from Acinetobacter calcoaceticus.

OBJECTIVES: This study analysed the novel carbapenem-hydrolysing class D ß-lactamase OXA-822 identified in the clinical Acinetobacter calcoaceticus isolate AC_2117. METHODS: WGS was employed for identification of ß-lactamases. Micro-broth dilution was used for evaluation of antibiotic susceptibility of AC_2117 and transformants containing blaOXA-822. After heterologous purification of OXA-822, OXA-359 and OXA-213, enzyme kinetics were determined using spectrometry. The effect of OXA-822 upon meropenem treatment was analysed in the Galleria mellonella in vivo infection model. RESULTS: OXA-822 is a member of the intrinsic OXA-213-like family found in A. calcoaceticus and Acinetobacter pittii. Amino acid sequence similarity to the nearest related OXA-359 was 97%. Production of OXA-822, OXA-359 and OXA-213 in Acinetobacter baumannii ATCC® 19606T resulted in elevated MICs for carbapenems (up to 16-fold). Penicillinase activity of the purified OXA-822 revealed high KM values, in the millimolar range, combined with high turnover numbers. OXA-822 showed the highest affinity to carbapenems, but affinity to imipenem was ∼10-fold lower compared with other carbapenems. Molecular modelling revealed that imipenem does not interact with a negatively charged side chain of OXA-822, as doripenem does, leading to the lower affinity. Presence of OXA-822 decreased survival of infected Galleria mellonella larvae after treatment with meropenem. Only 52.7% ±â€Š7.7% of the larvae survived after 24 h compared with 90.9% ±â€Š3.7% survival in the control group. CONCLUSIONS: The novel OXA-822 from a clinical A. calcoaceticus isolate displayed penicillinase and carbapenemase activity in vitro, elevated MICs in different species and decreased carbapenem susceptibility in A. baumannii in vivo.

Identification of the novel class D ß-lactamase OXA-679 involved in carbapenem resistance in Acinetobacter calcoaceticus.

OBJECTIVES: The aim of this study was to characterize the Acinetobacter calcoaceticus clinical isolate AC_2117 with the novel carbapenem-hydrolysing class D ß-lactamase (CHDL) OXA-679. METHODS: Identification of the species and ß-lactamases was verified by genome sequencing (PacBio) and phylogenetic analyses. Antibiotic susceptibility of AC_2117 and transformants harbouring cloned blaOXA-679 was evaluated using antibiotic gradient strips and microbroth dilution. OXA-679 was purified heterologously and kinetic parameters were determined using spectrometry or isothermal titration calorimetry. The impact of OXA-679 production during imipenem therapy was evaluated in the Galleria mellonella infection model. RESULTS: Sequencing of the complete genome of the clinical A. calcoaceticus isolate AC_2117 identified a novel CHDL, termed OXA-679. This enzyme shared sequence similarity of 71% to each of the families OXA-143 and OXA-24/40. Phylogenetic analyses revealed that OXA-679 represents a member of a new OXA family. Cloning and expression of blaOXA-679 as well as measurement of kinetic parameters revealed the effective hydrolysis of carbapenems which resulted in reduced susceptibility to carbapenems in Escherichia coli and A. calcoaceticus, and high-level carbapenem resistance in Acinetobacter baumannii. Infection of larvae of G. mellonella with a sublethal dose of blaOXA-679-expressing A. baumannii could not be cured by high-dose imipenem therapy, indicating carbapenem resistance in vivo. CONCLUSIONS: We identified blaOXA-679 in a clinical A. calcoaceticus isolate that represents a member of the new OXA-679 family and that conferred high-level carbapenem resistance in vitro and in vivo.

Capillary electrophoresis-based enzyme assays for ß-lactamase enzymes.

Generic in-capillary as well as offline CE-based enzyme assays were developed for serine-ß-lactamases and metallo-ß-lactamases. The hydrolysis of benzylpenicillin to benzylpenicilloic acid was analyzed using 100 mM sodium phosphate solution, pH 6.0, as a background electrolyte. In-capillary assays employed an uncoated as well as a polyethylene oxide-coated capillary, while the offline assays employing long end and short end injection were performed in an uncoated capillary. Using procaine hydrochloride or 4-hydroxybenzoic acid as internal standard, the respective assays were validated with regard to linearity, LOD and LOQ, repeatability, precision, and accuracy. The assays were applied to the determination of the Michaelis-Menten parameters Km and Vmax of Bacillus cereus penicillinase as well as New Delhi metallo-ß-lactamase 1 and Verona integrin-encoded metallo-ß-lactamase 2. Furthermore, the inhibition of the enzymes by irreversible and competitive inhibitors was evaluated. Comparable data were obtained with all assays. The use of a simple substrate ensured broad applicability to the various types of ß-lactamases.

Thermodynamic properties of leukotriene A4 hydrolase inhibitors.

The leukotriene A4 hydrolase (LTA4H) is a bifunctional enzyme, containing a peptidase and a hydrolase activity both activities having opposing functions regulating inflammatory response. The hydrolase activity is responsible for the conversion of leukotriene A4 to pro-inflammatory leukotriene B4, and hence, selective inhibitors of the hydrolase activity are of high pharmacological interest. Here we present the thermodynamic characterization of structurally distinct inhibitors of the LTA4H that occupy different regions of the binding site using different biophysical methods. An in silico method for the determination of stabilized water molecules in the binding site of the apo structure of LTA4H is used to interpret the measured thermodynamic data and provided insights for design of novel LTA4H inhibitors.

Compilation and evaluation of a fatty acid mimetics screening library.

Focused compound libraries are well-established tools for hit identification in drug discovery and chemical probe development. We present the compilation and application of a focused screening library of fatty acid mimetics (FAMs), which are compounds designed to bind the orthosteric site of proteins that endogenously accommodate natural fatty acids and lipid metabolites. This set complies with chemical properties of FAM and was found suitable for use also in cellular setting. Several hits were retrieved in screening the focused library against diverse fatty acid binding targets including the enzymes soluble epoxide hydrolase (sEH) and leukotriene A4 hydrolase (LTA4H), the nuclear receptors peroxisome proliferator-activated receptor γ (PPARγ) and retinoid X receptor α (RXRα), the carrier proteins fatty acid binding protein 4 and 5 (FABP4 and FABP5), as well as the G-protein coupled receptors leukotriene B4 receptor 1 (BLT1) and free-fatty acid receptor 1 (FFAR1). Thus, the focused FAM library is suitable to obtain chemical starting matter for fatty acid binding proteins and provides a valuable extension to available screening collections.

N-Aryl Mercaptopropionamides as Broad-Spectrum Inhibitors of Metallo-ß-Lactamases.

Drug-resistant pathogens pose a global challenge to public health as they cause diseases that are extremely difficult to cure. Metallo-ß-lactamases (MBLs) are a diverse set of zinc-containing enzymes that catalyze the hydrolysis of ß-lactam drugs, including carbapenems, which are considered as the last resort to fight severe infections. To restore the activity of current ß-lactam antibiotics and to offer an orthogonal strategy to the discovery of new antibiotics, we have identified a series of polar N-aryl mercaptopropionamide derivatives as potent inhibitors of several class B1 MBLs. We have identified a hit structure with high selectivity restoring the effect of imipenem and reducing minimum inhibitory concentration (MIC) values up to 256-fold in resistant isolates from Escherichia coli. Furthermore, the combination of imipenem with our inhibitor showed in vivo efficacy in a Galleria mellonella model, increasing the survival rate of infected larvae by up to 31%.

Development and in†vitro Profiling of Dual FXR/LTA4H Modulators.

Designed polypharmacology presents as an attractive strategy to increase therapeutic efficacy in multi-factorial diseases by a directed modulation of multiple involved targets with a single molecule. Such an approach appears particularly suitable in non-alcoholic steatohepatitis (NASH) which involves hepatic steatosis, inflammation and fibrosis as pathological hallmarks. Among various potential pharmacodynamic mechanisms, activation of the farnesoid X receptor (FXRa) and inhibition of leukotriene A4 hydrolase (LTA4Hi) hold promise to counteract NASH according to preclinical and clinical observations. We have developed dual FXR/LTA4H modulators as pharmacological tools, enabling evaluation of this polypharmacology concept to treat NASH and related pathologies. The optimized FXRa/LTA4Hi exhibits well-balanced dual activity on the intended targets with sub-micromolar potency and is highly selective over related nuclear receptors and enzymes rendering it suitable as tool to probe synergies of dual FXR/LTA4H targeting.

Systematic Assessment of Fragment Identification for Multitarget Drug Design.

Designed multitarget ligands are a popular approach to generating efficient and safe drugs, and fragment-based strategies have been postulated as a versatile avenue to discover multitarget ligand leads. To systematically probe the potential of fragment-based multiple ligand discovery, we have employed a large fragment library for comprehensive screening on five targets chosen from proteins for which multitarget ligands have been successfully developed previously (soluble epoxide hydrolase, leukotriene A4 hydrolase, 5-lipoxygenase, retinoid X receptor, farnesoid X receptor). Differential scanning fluorimetry served as primary screening method before fragments hitting at least two targets were validated in orthogonal assays. Thereby, we obtained valuable fragment leads with dual-target engagement for six out of ten target combinations. Our results demonstrate the applicability of fragment-based approaches to identify starting points for polypharmacological compound development with certain limitations.

N-Aryl mercaptoacetamides as potential multi-target inhibitors of metallo-ß-lactamases (MBLs) and the virulence factor LasB from Pseudomonas aeruginosa.

Increasing antimicrobial resistance is evolving to be one of the major threats to public health. To reduce the selection pressure and thus to avoid a fast development of resistance, novel approaches aim to target bacterial virulence instead of growth. Another strategy is to restore the activity of antibiotics already in clinical use. This can be achieved by the inhibition of resistance factors such as metallo-ß-lactamases (MBLs). Since MBLs can cleave almost all ß-lactam antibiotics, including the "last resort" carbapenems, their inhibition is of utmost importance. Here, we report on the synthesis and in vitro evaluation of N-aryl mercaptoacetamides as inhibitors of both clinically relevant MBLs and the virulence factor LasB from Pseudomonas aeruginosa. All tested N-aryl mercaptoacetamides showed low micromolar to submicromolar activities on the tested enzymes IMP-7, NDM-1 and VIM-1. The two most promising compounds were further examined in NDM-1 expressing Klebsiella pneumoniae isolates, where they restored the full activity of imipenem. Together with their LasB-inhibitory activity in the micromolar range, this class of compounds can now serve as a starting point for a multi-target inhibitor approach against both bacterial resistance and virulence, which is unprecedented in antibacterial drug discovery.

RhII -Catalyzed De-symmetrization of Ethane-1,2-dithiol and Propane-1,3-dithiol Yields Metallo-ß-lactamase Inhibitors.

Diversity-oriented synthesis (DOS) is a rich source for novel lead structures in Medicinal Chemistry. In this study, we present a DOS-compatible method for synthesis of compounds bearing a free thiol moiety. The procedure relies on Rh(II)-catalyzed coupling of dithiols to diazo building blocks. The synthetized library was probed against metallo-ß-lactamases (MBLs) NDM-1 and VIM-1. Biochemical and biological evaluation led to identification of novel potent MBL inhibitors with antibiotic adjuvant activity.

Demonstrating Ligandability of the LC3A and LC3B Adapter Interface.

Autophagy is the common name for a number of lysosome-based degradation pathways of cytosolic cargos. The key components of autophagy are members of Atg8 family proteins involved in almost all steps of the process, from autophagosome formation to their selective fusion with lysosomes. In this study, we show that the homologous members of the human Atg8 family proteins, LC3A and LC3B, are druggable by a small molecule inhibitor novobiocin. Structure-activity relationship (SAR) studies of the 4-hydroxy coumarin core scaffold were performed, supported by a crystal structure of the LC3A dihydronovobiocin complex. The study reports the first nonpeptide inhibitors for these protein interaction targets and will lay the foundation for the development of more potent chemical probes for the Atg8 protein family which may also find applications for the development of autophagy-mediated degraders (AUTACs).

Combined Cardioprotective and Adipocyte Browning Effects Promoted by the Eutomer of Dual sEH/PPARγ Modulator.

The metabolic syndrome (MetS) is a constellation of cardiovascular and metabolic symptoms involving insulin resistance, steatohepatitis, obesity, hypertension, and heart disease, and patients suffering from MetS often require polypharmaceutical treatment. PPARγ agonists are highly effective oral antidiabetics with great potential in MetS, which promote adipocyte browning and insulin sensitization. However, the application of PPARγ agonists in clinics is restricted by potential cardiovascular adverse events. We have previously demonstrated that the racemic dual sEH/PPARγ modulator RB394 (3) simultaneously improves all risk factors of MetS in vivo. In this study, we identify and characterize the eutomer of 3. We provide structural rationale for molecular recognition of the eutomer. Furthermore, we could show that the dual sEH/PPARγ modulator is able to promote adipocyte browning and simultaneously exhibits cardioprotective activity which underlines its exciting potential in treatment of MetS.

Structure-Based Design of Dual Partial Peroxisome Proliferator-Activated Receptor γ Agonists/Soluble Epoxide Hydrolase Inhibitors.

Polypharmaceutical regimens often impair treatment of patients with metabolic syndrome (MetS), a complex disease cluster, including obesity, hypertension, heart disease, and type II diabetes. Simultaneous targeting of soluble epoxide hydrolase (sEH) and peroxisome proliferator-activated receptor γ (PPARγ) synergistically counteracted MetS in various in vivo models, and dual sEH inhibitors/PPARγ agonists hold great potential to reduce the problems associated with polypharmacy in the context of MetS. However, full activation of PPARγ leads to fluid retention associated with edema and weight gain, while partial PPARγ agonists do not have these drawbacks. In this study, we designed a dual partial PPARγ agonist/sEH inhibitor using a structure-guided approach. Exhaustive structure-activity relationship studies lead to the successful optimization of the designed lead. Crystal structures of one representative compound with both targets revealed potential points for optimization. The optimized compounds exhibited favorable metabolic stability, toxicity, selectivity, and desirable activity in adipocytes and macrophages.

Computer-Aided Fragment Growing Strategies to Design Dual Inhibitors of Soluble Epoxide Hydrolase and LTA4 Hydrolase.

Multitarget ligands are interesting candidates for drug discovery and development due to improved safety and efficacy. However, rational design and optimization of multitarget ligands is tedious because affinity optimization for two or more targets has to be performed simultaneously. In this study, we demonstrate that, given a molecular fragment, which binds to two targets of interest, computer-aided fragment growing can be applied to optimize compound potency, relying on either ligand- or structure-derived information. This methodology is applied to the design of dual inhibitors of soluble epoxide hydrolase and leukotriene A4 hydrolase.

Design of Dual Inhibitors of Soluble Epoxide Hydrolase and LTA4 Hydrolase.

Multitarget anti-inflammatory drugs interfering with the arachidonic acid cascade exhibit superior efficacy. In this study, a prototype dual inhibitor of soluble epoxide hydrolase (sEH) and LTA4 hydrolase (LTA4H) with submicromolar activity toward both targets has been designed and synthesized. Preliminary structure-activity relationship studies were performed to identify optimal substitution patterns. X-ray structure analysis of a promising dual inhibitor in complex with sEH, as well as molecular docking with LTA4H provided a rationale for further optimization. Hereby, scaffold extension was successfully applied to yield potent dual sEH/LTA4H inhibitors. The spectrum of pro- and anti-inflammatory lipid mediators was evaluated in M1 and M2 macrophages, stimulated with LPS, and incubated with the most promising compound 14. The effect of 14 on the inflammatory lipid mediator profile characterizes dual sEH/LTA4H inhibitors as an interesting option for future anti-inflammatory agent investigations.

Design, Synthesis, and Structure-Activity Relationship Studies of Dual Inhibitors of Soluble Epoxide Hydrolase and 5-Lipoxygenase.

Inhibition of multiple enzymes of the arachidonic acid cascade leads to synergistic anti-inflammatory effects. Merging of 5-lipoxygenase (5-LOX) and soluble epoxide hydrolase (sEH) pharmacophores led to the discovery of a dual 5-LOX/sEH inhibitor, which was subsequently optimized in terms of potency toward both targets and metabolic stability. The optimized lead structure displayed cellular activity in human polymorphonuclear leukocytes, oral bioavailability, and target engagement in vivo and demonstrated profound anti-inflammatory and anti-fibrotic efficiency in a kidney injury model caused by unilateral ureteral obstruction in mice. These results pave the way for investigating the therapeutic potential of dual 5-LOX/sEH inhibitors in other inflammation- and fibrosis-related disease models.

Computer-Aided Selective Optimization of Side Activities of Talinolol.

Selective optimization of side activities is a valuable source of novel lead structures in drug discovery. In this study, a computer-aided approach was used to deorphanize the pleiotropic cholesterol-lowering effects of the beta-blocker talinolol, which result from the inhibition of the enzyme soluble epoxide hydrolase (sEH). X-ray structure analysis of the sEH in complex with talinolol enables a straightforward optimization of inhibitory potency. The resulting lead structure exhibited in vivo activity in a rat model of diabetic neuropatic pain.

Discovery of the First in Vivo Active Inhibitors of the Soluble Epoxide Hydrolase Phosphatase Domain.

The emerging pharmacological target soluble epoxide hydrolase (sEH) is a bifunctional enzyme exhibiting two different catalytic activities that are located in two distinct domains. Although the physiological role of the C-terminal hydrolase domain is well-investigated, little is known about its phosphatase activity, located in the N-terminal phosphatase domain of sEH (sEH-P). Herein we report the discovery and optimization of the first inhibitor of human and rat sEH-P that is applicable in vivo. X-ray structure analysis of the sEH phosphatase domain complexed with an inhibitor provides insights in the molecular basis of small-molecule sEH-P inhibition and helps to rationalize the structure-activity relationships. 4-(4-(3,4-Dichlorophenyl)-5-phenyloxazol-2-yl)butanoic acid (22b, SWE101) has an excellent pharmacokinetic and pharmacodynamic profile in rats and enables the investigation of the physiological and pathophysiological role of sEH-P in vivo.

Challenges in the Development of a Thiol-Based Broad-Spectrum Inhibitor for Metallo-ß-Lactamases.

Pathogens, expressing metallo-ß-lactamases (MBLs), become resistant against most ß-lactam antibiotics. Besides the dragging search for new antibiotics, development of MBL inhibitors would be an alternative weapon against resistant bacterial pathogens. Inhibition of resistance enzymes could restore the antibacterial activity of ß-lactams. Various approaches to MBL inhibitors are described; among others, the promising motif of a zinc coordinating thiol moiety is very popular. Nevertheless, since the first report of a thiol-based MBL inhibitor (thiomandelic acid) in 2001, no steps in development of thiol based MBL inhibitors were reported that go beyond clinical isolate testing. In this study, we report on the synthesis and biochemical characterization of thiol-based MBL inhibitors and highlight the challenges behind the development of thiol-based compounds, which exhibit good in vitro activity toward a broad spectrum of MBLs, selectivity against human off-targets, and reasonable activity against clinical isolates.