Soluble Epoxide Hydrolase Regulation of Lipid Mediators Limits Pain

4-Phenyl-thiazole-based dual inhibitors of fatty acid amide hydrolase and soluble epoxide hydrolase do not alleviate orofacial inflammatory pain in female rats

Pain arising from trigeminal systems such as headache is common, debilitating, and current treatments (e.g., sumatriptan) are limited. New treatments that target novel mechanisms of action may be required to innovate both short- and long-term pain therapy. Fatty acid amide hydrolase and soluble epoxide hydrolase are two pain-related enzymes that regulate pain and inflammation via independent pathways. We have previously demonstrated that simultaneous inhibition of these enzymes using a novel dual inhibitor alleviates acute inflammatory pain in the hindpaw and does not depress wheel running in rats. Here, we expanded on these findings and performed structure-activity relationships of our lead compound, the 4-phenyl-thiazole-based dual inhibitor SW-17, to generate 18 analogs and tested them for their inhibition at both enzymes. Conversion of the sulfonamide group to a tertiary amine led to a general decrease in the potency for the sEH enzyme, while this change was well-tolerated at the FAAH enzyme yielding several strong inhibitors. Six selected inhibitors were evaluated in mouse and rat sEH inhibition assays and results showed a species difference, i.e. 4-phenyl-thiazole-based analogs are significantly less or not active in mouse sEH compared to human and rat enzymes. The most potent inhibitor, SW-17, was evaluated in a plasma stability assay in human and rat plasma and showed moderate stability. However, SW-17 did not alleviate orofacial inflammatory pain in female rats compared to the traditional anti-migraine agent sumatriptan. Although modification of 4-phenyl-thiazole-based dual inhibitor SW-17 changes potencies at both FAAH and sEH, these approaches may not produce antinociception against trigeminal pain. Key Words: polypharmacology, formalin, inflammation, enzyme inhibition, structure-activity relationship studies.

Identification and characterization of the in-vivo metabolites of the novel soluble epoxide hydrolase inhibitor EC5026 using liquid chromatography quadrupole time of flight mass spectrometry

EC5026 is a novel soluble epoxide hydrolase inhibitor being developed clinically to treat neuropathic pain and inflammation. In the current study, we employed the LC-ESI-Q-TOF-MS/MS technique to identify four in-vivo phase-I metabolites of EC5026 in rat model, out of which three were found to be novel. The identified metabolites include aliphatic hydroxylation, di-hydroxylation, terminal desaturation, and carboxylation. No phase-II metabolites were found. The pharmacokinetic profile of identified metabolites was established after a single oral dose of EC5026 to Wistar rats. The Tmax of the drug and metabolites were found to be in the range of 1-2 hours and 4-12 hours, respectively. The major metabolites M1 and M2 were found to have more than 2-fold (263.87% AUC) and equivalent exposure (96.33% AUC) compared to the parent drug, respectively. Further, the docking study revealed that the mono-hydroxylated and terminally desaturated metabolites possess better binding affinity than the parent drug. Therefore, these metabolites may hold sEH inhibition potential and can be followed through future research.

Role of soluble epoxide hydrolase in pain and depression comorbidity

The coexistence of chronic pain and depression in clinical practice places a substantial social burden and profoundly impacts in patients. Although a clear correlation exists, the underlying mechanism of comorbidity between chronic pain and depression remains elusive. Research conducted in recent decades has uncovered that soluble epoxide hydrolase, a pivotal enzyme in the metabolism of polyunsaturated fatty acids, plays a crucial role in inflammation. Interestingly, this enzyme is intricately linked to the development of both pain and depression. With this understanding, this review aims to summarize the roles of soluble epoxide hydrolase in pain, depression, and their comorbidity. Simultaneously, we will also explore the underlying mechanisms, providing guidance for future research and drug development.

Development and validation of LC-MS/MS method for estimating the pharmacokinetics, protein binding, and metabolic stability of soluble epoxide hydrolase inhibitor EC5026

EC5026 is a soluble epoxide hydrolase (SEH) inhibitor which is being developed clinically (Phase-1) as a first-in-class analgesic for the treatment of pain. In the present study, we report the development and validation of the LC-MS/MS method for the estimation of EC5026 from rat plasma. The developed method is simple, specific, and sensitive for the quantification of EC5026 from rat plasma. The method was applied to investigate in-vivo pharmacokinetics after single oral administration (P.O.) of EC5026 (5.0 mg/kg) in Wistar rats. Further, the in-vitro metabolic stability and rat plasma protein binding of EC5026 were evaluated using the developed method. The in-vitro results demonstrated a moderate clearance with a value of 10.8 mL/min/kg and half-life (t1/2) of 57.75 min. The results show moderate clearance by the liver manifesting in satisfactory oral bioavailability. The rat plasma protein binding was estimated to be 96.24% ± 0.97% and 96.38% ± 0.56% at 1 µM and 10 µM concentrations, respectively. The developed analytical method is expected to facilitate future pre-clinical, clinical investigations of EC5026.

Synthesis and biological profile of benzoxazolone derivatives

The benzoxazolone nucleus is an ideal scaffold for drug design, owing to its discrete physicochemical profile, bioisosteric preference over pharmacokinetically weaker moieties, weakly acidic behavior, presence of both lipophilic and hydrophilic fragments on a single framework, and a wider choice of chemical modification on the benzene and oxazolone rings. These properties apparently influence the interactions of benzoxazolone-based derivatives with their respective biological targets. Hence, the benzoxazolone ring is implicated in the synthesis and development of pharmaceuticals with a diverse biological profile ranging from anticancer, analgesics, insecticides, anti-inflammatory, and neuroprotective agents. This has further led to the commercialization of several benzoxazolone-based molecules and a few others under clinical trials. Nevertheless, the SAR exploration of benzoxazolone derivatives for the identification of potential "hits" followed by the screening of "leads" provides a plethora of opportunities for further exploration of the pharmacological profile of the benzoxazolone nucleus. In this review, we aim to present the biological profile of different derivatives based on the benzoxazolone framework.

Soluble epoxide hydrolase inhibition alleviates chemotherapy induced neuropathic pain

Chemotherapy induced peripheral neuropathy (CIPN) is a particularly pernicious form of neuropathy and the associated pain is the primary dose-limiting factor of life-prolonging chemotherapy treatment. The prevalence of CIPN is high and can last long after treatment has been stopped. Currently, late in the COVID-19 pandemic, there are still increased psychological pressures on cancer patients as well as additional challenges in providing analgesia for them. These include the risks of nonsteroidal anti-inflammatory drug (NSAID) analgesics potentially masking early infection symptoms and the immunosuppression of steroidal and opiate based approaches. Even without these concerns, CIPN is often inadequately treated with few therapies that offer significant pain relief. The experiments we report use soluble epoxide hydrolase inhibitors (sEHI) which relieved this intractable pain in preclinical models. Doses of EC5026, an IND candidate intended to treat neuropathic pain, elicited dose dependent analgesic responses in multiple models including platinum-based, taxane, and vinca alkaloid-based CIPN pain in Sprague Dawley rats. At the same time as a class, the sEHI are known to result in fewer debilitating side effects of other analgesics, likely due to their novel mechanism of action. Overall, the observed dose-dependent analgesia in both male and female rats across multiple models of chemotherapy induced neuropathic pain holds promise as a useful tool when translated to the clinic.

Synthesis, In Vitro Profiling, and In Vivo Evaluation of Benzohomoadamantane-Based Ureas for Visceral Pain: A New Indication for Soluble Epoxide Hydrolase Inhibitors

The soluble epoxide hydrolase (sEH) has been suggested as a pharmacological target for the treatment of several diseases, including pain-related disorders. Herein, we report further medicinal chemistry around new benzohomoadamantane-based sEH inhibitors (sEHI) in order to improve the drug metabolism and pharmacokinetics properties of a previous hit. After an extensive in vitro screening cascade, molecular modeling, and in vivo pharmacokinetics studies, two candidates were evaluated in vivo in a murine model of capsaicin-induced allodynia. The two compounds showed an anti-allodynic effect in a dose-dependent manner. Moreover, the most potent compound presented robust analgesic efficacy in the cyclophosphamide-induced murine model of cystitis, a well-established model of visceral pain. Overall, these results suggest painful bladder syndrome as a new possible indication for sEHI, opening a new range of applications for them in the visceral pain field.

Molecular and cellular mechanisms of itch and pain in atopic dermatitis and implications for novel therapeutics

Atopic dermatitis is a chronic inflammatory skin disease. Patients with atopic dermatitis experience inflammatory lesions associated with intense itch and pain, which lead to sleep disturbance and poor mental health and quality of life. We review the molecular mechanisms underlying itch and pain symptoms in atopic dermatitis and discuss the current clinical development of treatments for moderate-to-severe atopic dermatitis. The molecular pathology of atopic dermatitis includes aberrant immune activation involving significant cross-talk among the skin and immune and neuronal cells. Exogenous and endogenous triggers modulate stimulation of mediators including cytokine/chemokine expression/release by the skin and immune cells, which causes inflammation, skin barrier disruption, activation and growth of sensory neurons, itch and pain. These complex interactions among cell types are mediated primarily by cytokines, but also involve chemokines, neurotransmitters, lipids, proteases, antimicrobial peptides, agonists of ion channels or various G protein-coupled receptors. Patients with atopic dermatitis have a cytokine profile characterised by abnormal levels of interleukins 4, 12, 13, 18, 22, 31 and 33; thymic stromal lymphopoietin; and interferon gamma. Cytokine receptors mainly signal through the Janus kinase/signal transducer and activator of transcription pathway. Among emerging novel therapeutics, several Janus kinase inhibitors are being developed for topical or systemic treatment of moderate-to-severe atopic dermatitis because of their potential to modulate cytokine expression and release. Janus kinase inhibitors lead to changes in gene expression that have favourable effects on local and systemic cytokine release, and probably other mediators, thus successfully modulating molecular mechanisms responsible for itch and pain in atopic dermatitis.

Structure-guided discovery of potent and oral soluble epoxide hydrolase inhibitors for the treatment of neuropathic pain

Soluble epoxide hydrolase (sEH) is related to arachidonic acid cascade and is over-expressed in a variety of diseases, making sEH an attractive target for the treatment of pain as well as inflammatory-related diseases. A new series of memantyl urea derivatives as potent sEH inhibitors was obtained using our previous reported compound 4 as lead compound. A preferential modification of piperidinyl to 3-carbamoyl piperidinyl was identified for this series via structure-based rational drug design. Compound A20 exhibited moderate percentage plasma protein binding (88.6%) and better metabolic stability in vitro. After oral administration, the bioavailability of A20 was 28.6%. Acute toxicity test showed that A20 was well tolerated and there was no adverse event encountered at dose of 6.0 g/kg. Inhibitor A20 also displayed robust analgesic effect in vivo and dose-dependently attenuated neuropathic pain in rat model induced by spared nerve injury, which was better than gabapentin and sEH inhibitor (±)-EC-5026. In one word, the oral administration of A20 significantly alleviated pain and improved the health status of the rats, demonstrating that A20 was a promising candidate to be further evaluated for the treatment of neuropathic pain.

Discovery of memantyl urea derivatives as potent soluble epoxide hydrolase inhibitors against lipopolysaccharide-induced sepsis

Sepsis, a systemic inflammatory response, caused by pathogenic factors including microorganisms, has high mortality and limited therapeutic approaches. Herein, a new soluble epoxide hydrolase (sEH) inhibitor series comprising a phenyl ring connected to a memantyl moiety via a urea or amide linkage has been designed. A preferential urea pharmacophore that improved the binding properties of the compounds was identified for those series via biochemical assay in vitro and in vivo studies. Molecular docking displayed that 3,5-dimethyl on the adamantyl group in B401 could make van der Waals interactions with residues at a hydrophobic pocket of sEH active site, which might indirectly explain the subnanomolar level activities of memantyl urea derivatives in vitro better than AR-9281. Among them, compound B401 significantly improved the inhibition potency with human and murine sEH IC50 values as 0.4 nM and 0.5 nM, respectively. Although the median survival time of C57BL/6 mice in LPS-induced sepsis model was slightly increased, the survival rate did not reach significant efficacy. Based on safety profile, metabolic stability, pharmacokinetic and in vivo efficacy, B401 demonstrated the proof of potential for this class of memantyl urea-based sEH inhibitors as therapeutic agents in sepsis.

Proteasome Inhibitors and Their Pharmacokinetics, Pharmacodynamics, and Metabolism

The proteasome is responsible for mediating intracellular protein degradation and regulating cellular function with impact on tumor and immune effector cell biology. The proteasome is found predominantly in two forms, the constitutive proteasome and the immunoproteasome. It has been validated as a therapeutic drug target through regulatory approval with 2 distinct chemical classes of small molecular inhibitors (boronic acid derivatives and peptide epoxyketones), including 3 compounds, bortezomib (VELCADE), carfilzomib (KYPROLIS), and ixazomib (NINLARO), for use in the treatment of the plasma cell neoplasm, multiple myeloma. Additionally, a selective inhibitor of immunoproteasome (KZR-616) is being developed for the treatment of autoimmune diseases. Here, we compare and contrast the pharmacokinetics (PK), pharmacodynamics (PD), and metabolism of these 2 classes of compounds in preclinical models and clinical studies. The distinct metabolism of peptide epoxyketones, which is primarily mediated by microsomal epoxide hydrolase, is highlighted and postulated as a favorable property for the development of this class of compound in chronic conditions.

Pain Treatment in the Companion Canine Model to Validate Rodent Results and Incentivize the Transition to Human Clinical Trials

One of the biggest challenges for analgesic drug development is how to decide if a potential analgesic candidate will work in humans. What preclinical data are the most convincing, incentivizing and most predictive of success? Such a predicament is not unique to analgesics, and the pain field has certain advantages over drug development efforts in areas like neuropsychiatry where the etiological origins are either unknown or difficult to ascertain. For pain, the origin of the problem frequently is known, and the causative peripheral tissue insult might be observable. The main conundrum centers around evaluation of translational cell- and rodent-based results. While cell and rodent models are undeniably important first steps for screening, probing mechanism of action, and understanding factors of adsorption, distribution metabolism and excretion, two questions arise from such studies. First, are they reliable indicators of analgesic performance of a candidate drug in human acute and chronic pain? Second, what additional model systems might be capable of increasing translational confidence? We address this second question by assessing, primarily, the companion canine model, which can provide particularly strong predictive information for candidate analgesic agents in humans. This statement is mainly derived from our studies with resiniferatoxin (RTX) a potent TRPV1 agonist but also from protein therapeutics using a conjugate of Substance P and saporin. Our experience, to date, is that rodent models might be very well suited for acute pain translation, but companion canine models, and other large animal studies, can augment initial discovery research using rodent models for neuropathic or chronic pain. The larger animal models also provide strong translational predictive capacity for analgesic performance in humans, better predict dosing parameters for human trials and provide insight into behavior changes (bladder, bowel, mood, etc.) that are not readily assessed in laboratory animals. They are, however, not without problems that can be encountered with any experimental drug treatment or clinical trial. It also is important to recognize that pain treatment is a major veterinary concern and is an intrinsically worthwhile endeavor for animals as well as humans.

A Soluble Epoxide Hydrolase Inhibitor, 1-TrifluoromethoxyPhenyl-3-(1-Propionylpiperidin-4-yl) Urea, Ameliorates Experimental Autoimmune Encephalomyelitis

Polyunsaturated fatty acids (PUFAs) are essential FAs for human health. Cytochrome P450 oxygenates PUFAs to produce anti-inflammatory and pain-resolving epoxy fatty acids (EpFAs) and other oxylipins whose epoxide ring is opened by the soluble epoxide hydrolase (sEH/Ephx2), resulting in the formation of toxic and pro-inflammatory vicinal diols (dihydroxy-FAs). Pharmacological inhibition of sEH is a promising strategy for the treatment of pain, inflammation, cardiovascular diseases, and other conditions. We tested the efficacy of a potent, selective sEH inhibitor, 1-trifluoromethoxyphenyl-3-(1-propionylpiperidin-4-yl) urea (TPPU), in an animal model of multiple sclerosis (MS), experimental autoimmune encephalomyelitis (EAE). Prophylactic TPPU treatment significantly ameliorated EAE without affecting circulating white blood cell counts. TPPU accumulated in the spinal cords (SCs), which was correlated with plasma TPPU concentration. Targeted lipidomics in EAE SCs and plasma identified that TPPU blocked production of dihydroxy-FAs efficiently and increased some EpFA species including 12(13)-epoxy-octadecenoic acid (12(13)-EpOME) and 17(18)-epoxy-eicosatrienoic acid (17(18)-EpETE). TPPU did not alter levels of cyclooxygenase (COX-1/2) metabolites, while it increased 12-hydroxyeicosatetraenoic acid (12-HETE) and other 12/15-lipoxygenase metabolites. These analytical results are consistent with sEH inhibitors that reduce neuroinflammation and accelerate anti-inflammatory responses, providing the possibility that sEH inhibitors could be used as a disease modifying therapy, as well as for MS-associated pain relief.

Movement to the Clinic of Soluble Epoxide Hydrolase Inhibitor EC5026 as an Analgesic for Neuropathic Pain and for Use as a Nonaddictive Opioid Alternative

This report describes the development of an orally active analgesic that resolves inflammation and neuropathic pain without the addictive potential of opioids. EC5026 acts on the cytochrome P450 branch of the arachidonate cascade to stabilize epoxides of polyunsaturated fatty acids (EpFA), which are natural mediators that reduce pain, resolve inflammation, and maintain normal blood pressure. EC5026 is a slow-tight binding transition-state mimic that inhibits the soluble epoxide hydrolase (sEH) at picomolar concentrations. The sEH rapidly degrades EpFA; thus, inhibiting sEH increases EpFA in vivo and confers beneficial effects. This mechanism addresses disease states by shifting endoplasmic reticulum stress from promoting cellular senescence and inflammation toward cell survival and homeostasis. We describe the synthesis and optimization of EC5026 and its development through human Phase 1a trials with no drug-related adverse events. Additionally, we outline fundamental work leading to discovery of the analgesic and inflammation-resolving CYP450 branch of the arachidonate cascade.

Sigma-1 receptor: A drug target for the modulation of neuroimmune and neuroglial interactions during chronic pain

Immune and glial cells play a pivotal role in chronic pain. Therefore, it is possible that the pharmacological modulation of neurotransmission from an exclusively neuronal perspective may not be enough for adequate pain management, and the modulation of complex interactions between neurons and other cell types might be needed for successful pain relief. In this article, we review the current scientific evidence for the modulatory effects of sigma-1 receptors on communication between the immune and nervous systems during inflammation, as well as the influence of this receptor on peripheral and central neuroinflammation. Several experimental models of pathological pain are considered, including peripheral and central neuropathic pain, osteoarthritic, and cancer pain. Sigma-1 receptor inhibition prevents peripheral (macrophage infiltration into the dorsal root ganglion) and central (activation of microglia and astrocytes) neuroinflammation in several pain models, and enhances immune-driven peripheral opioid analgesia during painful inflammation, maximizing the analgesic potential of peripheral immune cells. Therefore, sigma-1 antagonists may constitute a new class of analgesics with an unprecedented mechanism of action and potential utility in several painful disorders.