Sandra K. Wittmann

PADI4 acts as a coactivator of Tal1 by counteracting repressive histone arginine methylation

The transcription factor Tal1 is a critical activator or repressor of gene expression in hematopoiesis and leukaemia. The mechanism by which Tal1 differentially influences transcription of distinct genes is not fully understood. Here we show that Tal1 interacts with the peptidylarginine deiminase IV (PADI4). We demonstrate that PADI4 can act as an epigenetic coactivator through influencing H3R2me2a. At the Tal1/PADI4 target gene IL6ST the repressive H3R2me2a mark triggered by PRMT6 is counteracted by PADI4, which augments the active H3K4me3 mark and thus increases IL6ST expression. In contrast, at the CTCF promoter PADI4 acts as a repressor. We propose that the influence of PADI4 on IL6ST transcription plays a role in the control of IL6ST expression during lineage differentiation of hematopoietic stem/progenitor cells. These results open the possibility to pharmacologically influence Tal1 in leukaemia.

Synthesis and structure-activity relationship studies of novel dual inhibitors of soluble epoxide hydrolase and 5-lipoxygenase.

Current research leads to the assumption that drugs affecting more than one target could result in a more efficient treatment of diseases and fewer safety concerns. Administration of drugs inhibiting only one branch of the arachidonic acid cascade is usually accompanied by side effects. We therefore designed and synthesized a library of hybrid molecules incorporating an imidazo[1,2-a]pyridine and an urea moiety as novel soluble epoxide hydrolase (sEH)/5-lipoxygenase (5-LO) dual inhibitors. Evaluation of the compounds was accomplished by in vitro testing using recombinant enzyme assays.

A Dual Modulator of Farnesoid X Receptor and Soluble Epoxide Hydrolase To Counter Nonalcoholic Steatohepatitis

Nonalcoholic steatohepatitis arising from Western diet and lifestyle is characterized by accumulation of fat in liver causing inflammation and fibrosis. It evolves as serious health burden with alarming incidence, but there is no satisfying pharmacological therapy to date. Considering the diseases multifactorial nature, modulation of multiple targets might provide superior therapeutic efficacy. In particular, farnesoid X receptor (FXR) activation that revealed antisteatotic and antifibrotic effects in clinical trials combined with inhibition of soluble epoxide hydrolase (sEH) as anti-inflammatory strategy promises synergies. To exploit this dual concept, we developed agents exerting partial FXR agonism and sEH inhibitory activity. Merging known pharmacophores and systematic exploration of the structure-activity relationship on both targets produced dual modulators with low nanomolar potency. Extensive in vitro characterization confirmed high dual efficacy in cellular context combined with low toxicity, and pilot in vivo data revealed favorable pharmacokinetics as well as engagement on both targets in vivo.

N-Benzylbenzamides: A Novel Merged Scaffold for Orally Available Dual Soluble Epoxide Hydrolase/Peroxisome Proliferator-Activated Receptor γ Modulators

Metabolic syndrome (MetS) is a multifactorial disease cluster that consists of dyslipidemia, cardiovascular disease, type 2 diabetes mellitus, and obesity. MetS patients are strongly exposed to polypharmacy; however, the number of pharmacological compounds required for MetS treatment can be reduced by the application of multitarget compounds. This study describes the design of dual-target ligands that target soluble epoxide hydrolase (sEH) and the peroxisome proliferator-activated receptor type γ (PPARγ). Simultaneous modulation of sEH and PPARγ can improve diabetic conditions and hypertension at once. N-Benzylbenzamide derivatives were determined to fit a merged sEH/PPARγ pharmacophore, and structure-activity relationship studies were performed on both targets, resulting in a submicromolar (sEH IC50 = 0.3 μM/PPARγ EC50 = 0.3 μM) modulator 14c. In vitro and in vivo evaluations revealed good ADME properties qualifying 14c as a pharmacological tool compound for long-term animal models of MetS.

PENG: A Neural Gas-Based Approach for Pharmacophore Elucidation. Method Design, Validation, and Virtual Screening for Novel Ligands of LTA4H

The pharmacophore concept is commonly employed in virtual screening for hit identification. A pharmacophore is generally defined as the three-dimensional arrangement of the structural and physicochemical features of a compound responsible for its affinity to a pharmacological target. Given a number of active ligands binding to a particular target in the same manner, it can reasonably be assumed that they have some shared features, a common pharmacophore. We present a growing neural gas (GNG)-based approach for the extraction of the relevant features which we called PENG (pharmacophore elucidation by neural gas). Results of retrospective validation indicate an acceptable quality of the generated models. Additionally a prospective virtual screening for leukotriene A4 hydrolase (LTA4H) inhibitors was performed. LTA4H is a bifunctional zinc metalloprotease which displays both epoxide hydrolase and aminopeptidase activity. We could show that the PENG approach is able to predict the binding mode of the ligand by X-ray crystallography. Furthermore, we identified a novel chemotype of LTA4H inhibitors.

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

Pathogens, expressing metallo-β-lactamases (MBLs), become resistant against most β-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 β-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.

Design, Synthesis and Cellular Characterization of a Dual Inhibitor of 5-Lipoxygenase and Soluble Epoxide Hydrolase.

The arachidonic acid cascade is a key player in inflammation, and numerous well-established drugs interfere with this pathway. Previous studies have suggested that simultaneous inhibition of 5-lipoxygenase (5-LO) and soluble epoxide hydrolase (sEH) results in synergistic anti-inflammatory effects. In this study, a novel prototype of a dual 5-LO/sEH inhibitor KM55 was rationally designed and synthesized. KM55 was evaluated in enzyme activity assays with recombinant enzymes. Furthermore, activity of KM55 in human whole blood and endothelial cells was investigated. KM55 potently inhibited both enzymes in vitro and attenuated the formation of leukotrienes in human whole blood. KM55 was also tested in a cell function-based assay. The compound significantly inhibited the LPS-induced adhesion of leukocytes to endothelial cells by blocking leukocyte activation.

Bacterial Expression and HTS Assessment of Soluble Epoxide Hydrolase Phosphatase

Soluble epoxide hydrolase (sEH) is a bifunctional enzyme that possesses an epoxide hydrolase and lipid phosphatase activity (sEH-P) at two distinct catalytic domains. While the physiological role of the epoxide hydrolase domain is well understood, the consequences of the phosphatase activity remain unclear. Herein we describe the bacterial expression of the recombinant N-terminal domain of sEH-P and the development of a high-throughput screening protocol using a sensitive and commercially available substrate fluorescein diphosphate. The usability of the assay system was demonstrated and novel inhibitors of sEH-P were identified.

Pharmacological profile and efficiency in vivo of diflapolin, the first dual inhibitor of 5-lipoxygenase-activating protein and soluble epoxide hydrolase

Arachidonic acid (AA) is metabolized to diverse bioactive lipid mediators. Whereas the 5-lipoxygenase-activating protein (FLAP) facilitates AA conversion by 5-lipoxygenase (5-LOX) to pro-inflammatory leukotrienes (LTs), the soluble epoxide hydrolase (sEH) degrades anti-inflammatory epoxyeicosatrienoic acids (EETs). Accordingly, dual FLAP/sEH inhibition might be advantageous drugs for intervention of inflammation. We present the in vivo pharmacological profile and efficiency of N-[4-(benzothiazol-2-ylmethoxy)-2-methylphenyl]-N′-(3,4-dichlorophenyl)urea (diflapolin) that dually targets FLAP and sEH. Diflapolin inhibited 5-LOX product formation in intact human monocytes and neutrophils with IC50 = 30 and 170 nM, respectively, and suppressed the activity of isolated sEH (IC50 = 20 nM). Characteristic for FLAP inhibitors, diflapolin (I) failed to inhibit isolated 5-LOX, (II) blocked 5-LOX product formation in HEK cells only when 5-LOX/FLAP was co-expressed, (III) lost potency in intact cells when exogenous AA was supplied, and (IV) prevented 5-LOX/FLAP complex assembly in leukocytes. Diflapolin showed target specificity, as other enzymes related to AA metabolism (i.e., COX1/2, 12/15-LOX, LTA4H, LTC4S, mPGES1, and cPLA2) were not inhibited. In the zymosan-induced mouse peritonitis model, diflapolin impaired vascular permeability, inhibited cysteinyl-LTs and LTB4 formation, and suppressed neutrophil infiltration. Diflapolin is a highly active dual FLAP/sEH inhibitor in vitro and in vivo with target specificity to treat inflammation-related diseases.

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.