Synthesis and structure-activity relationship of piperidine-derived non-urea soluble epoxide hydrolase inhibitors

Characterizing the Metabolism of Tire Rubber-Derived p-Phenylenediamine Quinones to Identify Potential Exposure Biomarkers in Humans

There is growing evidence of the frequent detection of tire rubber-derived contaminants p-phenylenediamine-derived quinones (PPD-Qs) (e.g., highly toxic N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine quinone (6PPD-Q)) in the environment and biota and the adverse impact on organisms. Hence, a better understanding of their biotransformation/metabolism in humans is essential. However, relevant data are lacking owing to recent discoveries. Herein, the biotransformation patterns of 6PPD-Q and other five commonly detected PPD-Qs were characterized via combined in vitro assay and maternal cord blood screening monitoring. Rapid metabolism was found for each PPD-Q incubated with human liver S9 fraction and microsomes, resulting in the formation of abundant phase I and phase II metabolites. The subsequent screening for potential PPD-Q metabolites in blood samples showed the presence of suspect metabolites. Three detected metabolites were confirmed by matching the mass spectra and retention times of in vitro metabolites. N-Dealkylated, carboxy, carbonyl, and reductive metabolites and glucose, cysteine, and methionine conjugates were observed for the first time. The semiquantitative concentrations of metabolites were higher than those of the parent PPD-Qs, and several metabolites such as carboxy products were proposed as candidate biomarkers of PPD-Q exposure to humans. 6PPD-Q and N,N'-diphenyl-p-phenylenediamine quinone were detected in maternal and/or cord whole blood samples for the first time. This study holds great importance in elucidating the potential risks and health effects of PPD-Qs.

Quinolinyl-based multitarget-directed ligands with soluble epoxide hydrolase and fatty acid amide hydrolase inhibitory activities: Synthetic studies and pharmacological evaluations

Simultaneous inhibition of soluble epoxide hydrolase (sEH) and fatty acid amide hydrolase (FAAH) with a single small molecule represents a novel therapeutic approach in treating inflammatory pain, since both targets are involved in pain and inflammation processes. In this study using multi-target directed ligands methodology we designed and synthesized 7 quinolinyl-based dual sEH/FAAH inhibitors, using an optimized microwave-assisted Suzuki-Miyaura coupling reaction and tested their potency in human FAAH and human, rat, and mouse sEH inhibition assays. The structure-activity relationship study showed that quinolinyl moiety is well tolerated in the active sites of both enzymes, yielding several very potent dual sEH/FAAH inhibitors with the IC50 values in the low nanomolar range. The most potent dual inhibitor 4d was further evaluated in stability assay in human and rat plasma where it performed better than the standard Warfarin while in vivo study revealed that 1 mg/kg 4d can inhibit acute inflammatory pain in male rats to a similar degree as the traditional nonsteroidal anti-inflammatory drug ketoprofen (30 mg/kg) after intraperitoneal injection. ADMET prediction studies for this dual inhibitor show favorable pharmacokinetic properties which will guide the future in vivo evaluations.

Evaluation of nanoplastics toxicity to the human placenta in systems

Following the discovery of plastics in the human placenta, this study evaluated the toxicity of ten different nanoplastics (NPs) in the human placenta. Since the placenta performs metabolic and excretion functions by the enzymatic system, the NPs were docked on these human enzymes including soluble epoxide hydrolase, uracil phosphoribosyltransferase, beta 1,3-glucuronyltransferase I, sulfotransferase, N-acetyltransferase 2, and cytochrome P450 1A1at their active sites with toxicity (binding affinity) determined and compared to control compounds. Density functional theory analysis were conducted on the NPs to identify their global reactivity descriptors and Artificial Neural Networks to predict toxicity based on reactivity descriptors. Polycarbonate (PC), polyethylene terephthalate (PET) and polystyrene (PS) showed the highest toxicity to all enzymes and thus the most toxic polymers due to the presence of an electron-withdrawing group in their aromatic rings, which demonstrated an improved recognition of the enzyme active site by pi- and alkyl interactions. A 2^10-6 fractional factorial design approach was used in conjunction with a fixed effects model to assess the primary and secondary effects of NPs in a composite system on binding affinity to the placental enzymes. The simulation results suggest that NPs mixture may pose significant risks to the placenta through inhibition of its key enzymes.

Structure-activity relationship studies of benzothiazole-phenyl analogs as multi-target ligands to alleviate pain without affecting normal behavior

Soluble epoxide hydrolase (sEH) and fatty acid amide hydrolase (FAAH) are potential targets for several diseases. Previous studies have reported that concomitant selective inhibition of sEH and FAAH produced antinociception effects in an animal model of pain. However, the co-administration of a selective sEH inhibitor and a selective FAAH inhibitor might produce serious side effects due to drug-drug interactions that could complicate drug development in the long term. Thus, discovering dual sEH/FAAH inhibitors, single small molecules that can simultaneously inhibit both sEH and FAAH, would be a significant accomplishment in the medicinal chemistry field. Herein, we report the synthesis and biological evaluation of benzothiazole-phenyl-based analogs as potential dual sEH/FAAH inhibitors. This work represents a follow-up structure-activity relationship (SAR) and metabolic-stability studies of our best dual sEH/FAAH inhibitor identified previously, as well as in vivo evaluation of its effects on voluntary locomotor behavior in rats. Our SAR study indicates that trifluoromethyl groups on the aromatic rings are well tolerated by the targeted enzymes when placed at the ortho and para positions; however, they, surprisingly, did not improve metabolic stability in liver microsomes. Our behavioral studies indicate that doses of dual sEH/FAAH inhibitors that alleviate pain do not depress voluntary behavior in naïve rats, which is a common side effect of currently available analgesic drugs (e.g., opioids). Thus, dual sEH/FAAH inhibitors may be a safe and effective approach to treat pain.

Repositioning of Quinazolinedione-Based Compounds on Soluble Epoxide Hydrolase (sEH) through 3D Structure-Based Pharmacophore Model-Driven Investigation

The development of new bioactive compounds represents one of the main purposes of the drug discovery process. Various tools can be employed to identify new drug candidates against pharmacologically relevant biological targets, and the search for new approaches and methodologies often represents a critical issue. In this context, in silico drug repositioning procedures are required even more in order to re-evaluate compounds that already showed poor biological results against a specific biological target. 3D structure-based pharmacophoric models, usually built for specific targets to accelerate the identification of new promising compounds, can be employed for drug repositioning campaigns as well. In this work, an in-house library of 190 synthesized compounds was re-evaluated using a 3D structure-based pharmacophoric model developed on soluble epoxide hydrolase (sEH). Among the analyzed compounds, a small set of quinazolinedione-based molecules, originally selected from a virtual combinatorial library and showing poor results when preliminarily investigated against heat shock protein 90 (Hsp90), was successfully repositioned against sEH, accounting the related built 3D structure-based pharmacophoric model. The promising results here obtained highlight the reliability of this computational workflow for accelerating the drug discovery/repositioning processes.

Further exploration of the structure-activity relationship of dual soluble epoxide hydrolase/fatty acid amide hydrolase inhibitors

Fatty acid amide hydrolase (FAAH) is a membrane protein that hydrolyzes endocannabinoids, and its inhibition produces analgesic and anti-inflammatory effects. The soluble epoxide hydrolase (sEH) hydrolyzes epoxyeicosatrienoic acids (EETs) to dihydroxyeicosatetraenoic acids. EETs have anti-inflammatory and inflammation resolving properties, thus inhibition of sEH consequently reduces inflammation. Concurrent inhibition of both enzymes may represent a novel approach in the treatment of chronic pain. Drugs with multiple targets can provide a superior therapeutic effect and a decrease in side effects compared to ligands with single targets. Previously, microwave-assisted methodologies were employed to synthesize libraries of benzothiazole analogs from which high affinity dual inhibitors (e.g. 3, sEH IC₅₀ = 9.6 nM; FAAH IC₅₀ = 7 nM) were identified. Here, our structure-activity relationship studies revealed that the 4-phenylthiazole moiety is well tolerated by both enzymes, producing excellent inhibition potencies in the low nanomolar range (e.g. 6o, sEH IC₅₀ = 2.5 nM; FAAH IC₅₀ = 9.8 nM). Docking experiments show that the new class of dual inhibitors bind within the catalytic sites of both enzymes. Prediction of several pharmacokinetic/pharmacodynamic properties suggest that these new dual inhibitors are good candidates for further in vivo evaluation. Finally, dual inhibitor 3 was tested in the Formalin Test, a rat model of acute inflammatory pain. The data indicate that 3 produces antinociception against the inflammatory phase of the Formalin Test in vivo and is metabolically stable following intraperitoneal administration in male rats. Further, antinociception produced by 3 is comparable to that of ketoprofen, a traditional nonsteroidal anti-inflammatory drug. The results presented here will help toward the long-term goal of developing novel non-opioid therapeutics for pain management.

Design, synthesis and mechanistic study of novel diarylpyrazole derivatives as anti-inflammatory agents with reduced cardiovascular side effects

Novel diarylpyrazole (5a-d, 6a-e, 12, 13, 14, 15a-c and 11a-g) derivatives were designed, synthesized and evaluated for their dual COX-2/sEH inhibitory activities via recombinant enzyme assays to explore their anti-inflammatory activities and cardiovascular safety profiles. Comprehensively, the structures of the synthesized compounds were established via spectral and elemental analyses, followed by the assessment of both their in vitro COX inhibitory and in vivo anti-inflammatory activities. The most active compounds as COX inhibitors were further evaluated for their in vitro 5-LOX and sEH inhibitory activities, alongside with their in vivo analgesic and ulcerogenic effects. Compounds 6d and 11f showed excellent inhibitory activities against both COX-2 and sEH (COX-2 IC₅₀ = 0.043 and 0.048 µM; sEH IC₅₀ = 83.58 and 83.52 μM, respectively). Moreover, the compounds demonstrated promising results as anti-inflammatory and analgesic agents with considerable ED₅₀ values and gastric safety profiles. Remarkably, the most active COX inhibitors 6d and 11f possessed improved cardiovascular safety profiles, if compared to celecoxib, as shown by the laboratory evaluation of both essential cardiac biochemical parameters (troponin-1, prostacyclin, tumor necrosis factor-α, lactate dehydrogenase, reduced glutathione and creatine kinase-M) and histopathological studies. On the other hand, docking simulations confirmed that the newly synthesized compounds displayed sufficient structural features required for binding to the target COX-2 and sEH enzymes. Also, in silico ADME studies prediction and drug-like properties of the compounds revealed favorable oral bioavailability results. Collectively, the present work could be featured as a promising future approach towards novel selective COX-2 inhibitors with declined cardiovascular risks.

A thiol redox sensor in soluble epoxide hydrolase enables oxidative activation by intra-protein disulfide bond formation

Soluble epoxide hydrolase (sEH), an enzyme that broadly regulates the cardiovascular system, hydrolyses epoxyeicosatrienoic acids (EETs) to their corresponding dihydroxyeicosatrienoic acids (DHETs). We previously showed that endogenous lipid electrophiles adduct within the catalytic domain, inhibiting sEH to lower blood pressure in angiotensin II-induced hypertensive mice. As angiotensin II increases vascular H2O2, we explored sEH redox regulation by this oxidant and how this integrates with inhibition by lipid electrophiles to regulate vasotone. Kinetics analyses revealed that H2O2 not only increased the specific activity of sEH but increased its affinity for substrate and increased its catalytic efficiency. This oxidative activation was mediated by formation of an intra-disulfide bond between C262 and C264, as determined by mass spectrometry and substantiated by biotin-phenylarsinate and thioredoxin-trapping mutant assays. C262S/264S sEH mutants were resistant to peroxide-induced activation, corroborating the disulfide-activation mechanism. The physiological impact of sEH redox state was determined in isolated arteries and the effect of the pro-oxidant vasopressor angiotensin II on arterial sEH redox state and vasodilatory EETs indexed in mice. Angiotensin II induced the activating intra-disulfide in sEH, causing a decrease in plasma EET/DHET ratios that is consistent with the pressor response to this hormone. Although sEH C262-C264 disulfide formation enhances hydrolysis of vasodilatory EETs, this modification also sensitized sEH to inhibition by lipid electrophiles. This explains why angiotensin II decreases EETs and increases blood pressure, but when lipid electrophiles are also present, that EETs are increased and blood pressure lowered.

Computational insights into the known inhibitors of human soluble epoxide hydrolase

Human soluble epoxide hydrolase (hsEH) is involved in the hydrolysis of epoxyeicosatrienoic acids (EETs), which have potent anti-inflammatory properties. Given that EET conversion generates nonbioactive molecules, inhibition of this enzyme would be beneficial. Past decades of work on hsEH inhibitors resulted in numerous potential compounds, of which a hundred hsEH-ligand complexes were crystallized and deposited in the Protein Data Bank (PDB). We analyzed all deposited hsEH-ligand complexes to gain insight into the binding of inhibitors and to provide feedback on the future drug design processes. We also reviewed computationally driven strategies that were used to propose novel hsEH inhibitors.

Mutation of an atypical oxirane oxyanion hole improves regioselectivity of the α/β-fold epoxide hydrolase Alp1U

Epoxide hydrolases (EHs) have been characterized and engineered as biocatalysts that convert epoxides to valuable chiral vicinal diol precursors of drugs and bioactive compounds. Nonetheless, the regioselectivity control of the epoxide ring opening by EHs remains challenging. Alp1U is an α/β-fold EH that exhibits poor regioselectivity in the epoxide hydrolysis of fluostatin C (compound 1) and produces a pair of stereoisomers. Herein, we established the absolute configuration of the two stereoisomeric products and determined the crystal structure of Alp1U. A Trp-186/Trp-187/Tyr-247 oxirane oxygen hole was identified in Alp1U that replaced the canonical Tyr/Tyr pair in α/β-EHs. Mutation of residues in the atypical oxirane oxygen hole of Alp1U improved the regioselectivity for epoxide hydrolysis on 1. The single site Y247F mutation led to highly regioselective (98%) attack at C-3 of 1, whereas the double mutation W187F/Y247F resulted in regioselective (94%) nucleophilic attack at C-2. Furthermore, single-crystal X-ray structures of the two regioselective Alp1U variants in complex with 1 were determined. These findings allowed insights into the reaction details of Alp1U and provided a new approach for engineering regioselective epoxide hydrolases.

Small Molecule Soluble Epoxide Hydrolase Inhibitors in Multitarget and Combination Therapies for Inflammation and Cancer

The enzyme soluble epoxide hydrolase (sEH) plays a central role in metabolism of bioactive lipid signaling molecules. The substrate-specific hydrolase activity of sEH converts epoxyeicosatrienoic acids (EETs) to less bioactive dihydroxyeicosatrienoic acids. EETs exhibit anti-inflammatory, analgesic, antihypertensive, cardio-protective and organ-protective properties. Accordingly, sEH inhibition is a promising therapeutic strategy for addressing a variety of diseases. In this review, we describe small molecule architectures that have been commonly deployed as sEH inhibitors with respect to angiogenesis, inflammation and cancer. We juxtapose commonly used synthetic scaffolds and natural products within the paradigm of a multitarget approach for addressing inflammation and inflammation induced carcinogenesis. Structural insights from the inhibitor complexes and novel strategies for development of sEH-based multitarget inhibitors are also presented. While sEH inhibition is likely to suppress inflammation-induced carcinogenesis, it can also lead to enhanced angiogenesis via increased EET concentrations. In this regard, sEH inhibitors in combination chemotherapy are described. Urea and amide-based architectures feature prominently across multitarget inhibition and combination chemotherapy applications of sEH inhibitors.

Development of multitarget inhibitors for the treatment of pain: Design, synthesis, biological evaluation and molecular modeling studies

Multitarget-directed ligands are a promising class of drugs for discovering innovative new therapies for difficult to treat diseases. In this study, we designed dual inhibitors targeting the human fatty acid amide hydrolase (FAAH) enzyme and human soluble epoxide hydrolase (sEH) enzyme. Targeting both of these enzymes concurrently with single target inhibitors synergistically reduces inflammatory and neuropathic pain; thus, dual FAAH/sEH inhibitors are likely to be powerful analgesics. Here, we identified the piperidinyl-sulfonamide moiety as a common pharmacophore and optimized several inhibitors to have excellent inhibition profiles on both targeted enzymes simultaneously. In addition, several inhibitors show good predicted pharmacokinetic properties. These results suggest that this series of inhibitors has the potential to be further developed as new lead candidates and therapeutics in pain management.

Dual Farnesoid X Receptor/Soluble Epoxide Hydrolase Modulators Derived from Zafirlukast

The nuclear farnesoid X receptor (FXR) and the enzyme soluble epoxide hydrolase (sEH) are validated molecular targets to treat metabolic disorders such as non-alcoholic steatohepatitis (NASH). Their simultaneous modulation in vivo has demonstrated a triad of anti-NASH effects and thus may generate synergistic efficacy. Here we report dual FXR activators/sEH inhibitors derived from the anti-asthma drug Zafirlukast. Systematic structural optimization of the scaffold has produced favorable dual potency on FXR and sEH while depleting the original cysteinyl leukotriene receptor antagonism of the lead drug. The resulting polypharmacological activity profile holds promise in the treatment of liver-related metabolic diseases.

Discovery of Novel Soluble Epoxide Hydrolase Inhibitors as Potent Vasodilators

In view of the role of sEH (soluble epoxide hydrolase) in hypertension, we have developed a rigorously validated pharmacophore model containing one HBA (Hydrogen Bond Acceptor), two HY (Hydrophobic) and one RA (Ring Aromatic) features. The model was used as a query to search the NCI (National Cancer Institute) and Maybridge database leading to retrieval of many compounds which were sorted on the basis of predicted activity, fit value and Lipinski’s violation. The selected compounds were docked into the active site of enzyme soluble epoxide hydrolase. Potential interactions were observed between the features of the identified hits and the amino acids present in the docking site. The three selected compounds were subjected to in vitro evaluation using enzyme- based assay and the isolated rat aortic model followed by cytotoxicity studies. The results demonstrate that the identified compounds are potent, safe and novel soluble epoxide hydrolase inhibitors.

Novel piperidine-derived amide sEH inhibitors as mediators of lipid metabolism with improved stability

We have previously identified and reported several potent piperidine-derived amide inhibitors of the human soluble epoxide hydrolase (sEH) enzyme. The inhibition of this enzyme leads to elevated levels of epoxyeicosatrienoic acids (EETs), which are known to possess anti-inflammatory, vasodilatory, and anti-fibrotic effects. Herein, we report the synthesis of 9 analogs of the lead sEH inhibitor and the follow-up structure-activity relationship and liver microsome stability studies. Our findings show that isosteric modifications that lead to significant alterations in the steric and electronic properties at a specific position in the molecule can reduce the efficacy by up to 75-fold. On the other hand, substituting hydrogen with deuterium produces a notable increase (∼30%) in the molecules' half-lives in both rat and human microsomes, while maintaining sEH inhibition potency. These data highlight the utility of isosteric replacement for improving bioavailability, and the newly-synthesized inhibitor structures may thus, serve as a starting point for preclinical development. Our docking study reveals that in the catalytic pocket of sEH, these analogs are in proximity of the key amino acids involved in hydrolysis of EETs.

Investigation of the binding mode of 1, 3, 4-oxadiazole derivatives as amide-based inhibitors for soluble epoxide hydrolase (sEH) by molecular docking and MM-GBSA

The soluble epoxide hydrolase (sEH) enzyme plays an important role in the metabolism of endogenous chemical mediators involved in the regulation of blood pressure and inflammation. Inhibition of sEH provides a new approach to the treatment of inflammation, hypertension and atherosclerosis. In this study, the binding modes and inhibition mechanisms of the new oxadiazole-based amide inhibitors of the human soluble epoxide hydrolase were investigated by molecular docking and molecular dynamics (MD) simulation followed by the MM-GBSA method to calculate the binding free energy of each inhibitor to sEH. The results obtained from the binding free energy (ΔG _binding) calculation and normal mode analysis indicate that the major favorable contributors are the van der Waals and electrostatic terms, whereas the polar solvation term opposes binding. In addition, a good agreement between the calculated ΔG _binding and the experimental IC₅₀ was obtained [correlation coefficient, r ² = 0.89 (with) and 0.87 (without) entropy]. Besides, comparison of the enthalpy changes (ΔG _MM-GBSA) with entropy changes (-TΔS) indicates that binding process of all inhibitors to sEH is enthalpy-driven. Based on the ΔG _binding on per residue decomposition, Asp335 and Tyr383 residues from the active site and Trp336, Leu499 and His524 residues from hydrophobic pockets contribute the most to ΔG _binding. Moreover, hydrogen bond analysis reveals that Tyr383, Tyr466 and Asp335 residues have an important role in the binding to inhibitors by forming hydrogen bonds with high occupancies. Our obtained results are useful for the understanding of the sEH-inhibitor interactions and may have great importance in the design of future sEH inhibitors.

Stacking with No Planarity?

This viewpoint describes the results obtained from matched molecular pair analyses and quantum mechanics calculations that show unsaturated rings found in drug-like molecules may be replaced with their saturated counterparts without losing potency even if they are engaged in stacking interactions with the side chains of aromatic residues.

Fragment Screening of Soluble Epoxide Hydrolase for Lead Generation-Structure-Based Hit Evaluation and Chemistry Exploration

Soluble epoxide hydrolase (sEH) is involved in the regulation of many biological processes by metabolizing the key bioactive lipid mediator, epoxyeicosatrienoic acids. For the development of sEH inhibitors with improved physicochemical properties, we performed both a fragment screening and a high-throughput screening aiming at an integrated hit evaluation and lead generation. Followed by a joint dose-response analysis to confirm the hits, the identified actives were then effectively triaged by a structure-based hit-classification approach to three prioritized series. Two distinct scaffolds were identified as tractable starting points for potential lead chemistry work. The oxoindoline series bind at the right-hand side of the active-site pocket with hydrogen bonds to the protein. The 2-phenylbenzimidazole-4-sulfonamide series bind at the central channel with significant induced fit, which has not been previously reported. On the basis of the encouraging initial results, we envision that a new lead series with improved properties could be generated if a vector is found that could merge the cyclohexyl functionality of the oxoindoline series with the trifluoromethyl moiety of the 2-phenylbenzimidazole-4-sulfonamide series.

Novel soluble epoxide hydrolase inhibitors with a dihydropyrimidinone scaffold: design, synthesis and biological evaluation

Amide non-urea derivatives with a dihydropyrimidinone ring as a novel secondary pharmacophore against the sEH enzyme were designed, synthesized and biologically evaluated.

Symmetric adamantyl-diureas as soluble epoxide hydrolase inhibitors

A series of inhibitors of the soluble epoxide hydrolase (sEH) containing two urea groups has been developed. Inhibition potency of the described compounds ranges from 2.0 μM to 0.4 nM. 1,6-(Hexamethylene)bis[(adamant-1-yl)urea] (3b) was found to be a potent slow tight binding inhibitor (IC50=0.5 nM) with a strong binding to sEH (Ki=3.1 nM) and a moderately long residence time on the enzyme (koff=1.05 × 10(-3) s(-1); t1/2=11 min).

Design, synthesis and biological evaluation of 4-benzamidobenzoic Acid hydrazide derivatives as novel soluble epoxide hydrolase inhibitors

Inhibitors of soluble epoxide hydrolase (sEH) represent one of the novel pharmaceutical approaches for treating hypertension, vascular inflammation, pain and other cardiovascular related diseases. Most of the potent sEH inhibitors reported in literature often suffer from poor solubility and bioavailability. Toward improving pharmacokinetic profile beside favorable potency, two series of 4-benzamidobenzoic acid hydrazide derivatives with hydrazide group as a novel secondary pharmacophore against sEH enzyme were developed. The designed compounds were synthesized in acceptable yield and their in vitro assay was determined. Most of the synthesized compounds have appropriate physical properties and exhibited considerable in-vitro sEH inhibitory activity in comparison with 12-(3-Adamantan-1-yl-ureido)- dodecanoicacid (AUDA), a potent urea-based sEH inhibitor. 4-(2-(4-(4-chlorobenzamido) benzoyl)hydrazinyl)-4-oxobutanoic acid 6c was found to be the most potent inhibitor with inhibitory activity of 72% targeting sEH enzyme.