Cutting edge: agonistic effect of indomethacin on a prostaglandin D2 receptor, CRTH2

DP2 receptor activity sensor suited for antagonist screening and measurement of receptor dynamics in real-time

The DP2 receptor is a G-protein coupled receptor involved in allergic inflammation and is the target of recently developed antagonists already being tested in clinics. To get insights into DP2 receptor dynamics and to study its pharmacology on the level of the receptor, we constructed a fluorescence resonance energy transfer-based conformation sensor. The sensor reflects the selectivity profile of the DP2 receptor-wt and is suited for screening of agonists and antagonists due to its robust response. Furthermore, the sensor enables the direct measurement of DP2 receptor dynamics in real-time and revealed markedly distinct on- and off-rates of prostaglandin D2 between DP2 and DP1 receptors, suggesting a different mechanism of ligand receptor interaction.

Biochemical aspects of the inflammatory process: A narrative review

Inflammation is a protective response of the body potentially caused by microbial, viral, or fungal infections, tissue damage, or even autoimmune reactions. The cardinal signs of inflammation are consequences of immunological, biochemical, and physiological changes that trigger the release of pro-inflammatory chemical mediators at the local of the injured site thus, increasing blood flow, vascular permeability, and leukocyte recruitment. The aim of this study is to give an overview of the inflammatory process, focusing on chemical mediators. The literature review was based on a search of journals published between the years 2009 and 2023, regarding the role of major chemical mediators in the inflammatory process and current studies in pathogenesis, diagnosis, and therapy. Some of the recent contributions in the study of inflammatory pathologies and their mediators, including cytokines and chemokines, the kinin system, free radicals, nitric oxide, histamine, cell adhesion molecules, leukotrienes, prostaglandins and the complement system and their role in human health and chronic diseases.

Indole-Based and Cyclopentenylindole-Based Analogues Containing Fluorine Group as Potential 18F-Labeled Positron Emission Tomography (PET) G-Protein Coupled Receptor 44 (GPR44) Tracers

Recently, growing evidence of the relationship between G-protein coupled receptor 44 (GPR44) and the inflammation-cancer system has garnered tremendous interest, while the exact role of GPR44 has not been fully elucidated. Currently, there is a strong and urgent need for the development of non-invasive in vivo GPR44 positron emission tomography (PET) radiotracers that can be used to aid the exploration of the relationship between inflammation and tumor biologic behavior. Accordingly, the choosing and radiolabeling of existing GPR44 antagonists containing a fluorine group could serve as a viable method to accelerate PET tracers development for in vivo imaging to this purpose. The present study aims to evaluate published (2000-present) indole-based and cyclopentenyl-indole-based analogues of the GPR44 antagonist to guide the development of fluorine-18 labeled PET tracers that can accurately detect inflammatory processes. The selected analogues contained a crucial fluorine nuclide and were characterized for various properties including binding affinity, selectivity, and pharmacokinetic and metabolic profile. Overall, 26 compounds with favorable to strong binding properties were identified. This review highlights the potential of GPR44 analogues for the development of PET tracers to study inflammation and cancer development and ultimately guide the development of targeted clinical therapies.

Sebaceous immunobiology - skin homeostasis, pathophysiology, coordination of innate immunity and inflammatory response and disease associations

This review presents several aspects of the innovative concept of sebaceous immunobiology, which summarizes the numerous activities of the sebaceous gland including its classical physiological and pathophysiological tasks, namely sebum production and the development of seborrhea and acne. Sebaceous lipids, which represent 90% of the skin surface lipids in adolescents and adults, are markedly involved in the skin barrier function and perifollicular and dermal innate immune processes, leading to inflammatory skin diseases. Innovative experimental techniques using stem cell and sebocyte models have clarified the roles of distinct stem cells in sebaceous gland physiology and sebocyte function control mechanisms. The sebaceous gland represents an integral part of the pilosebaceous unit and its status is connected to hair follicle morphogenesis. Interestingly, professional inflammatory cells contribute to sebocyte differentiation and homeostasis, whereas the regulation of sebaceous gland function by immune cells is antigen-independent. Inflammation is involved in the very earliest differentiation changes of the pilosebaceous unit in acne. Sebocytes behave as potent immune regulators, integrating into the innate immune responses of the skin. Expressing inflammatory mediators, sebocytes also contribute to the polarization of cutaneous T cells towards the Th17 phenotype. In addition, the immune response of the perifollicular infiltrate depends on factors produced by the sebaceous glands, mostly sebaceous lipids. Human sebocytes in vitro express functional pattern recognition receptors, which are likely to interact with bacteria in acne pathogenesis. Sex steroids, peroxisome proliferator-activated receptor ligands, neuropeptides, endocannabinoids and a selective apoptotic process contribute to a complex regulation of sebocyte-induced immunological reaction in numerous acquired and congenital skin diseases, including hair diseases and atopic dermatitis.

AMG853, A Bispecific Prostaglandin D2 Receptor 1 and 2 Antagonist, Dampens Basophil Activation and Related Lupus-Like Nephritis Activity in Lyn-Deficient Mice

Systemic lupus erythematosus is a complex autoimmune disease during which patients develop autoantibodies raised against nuclear antigens. During the course of the disease, by accumulating in secondary lymphoid organs (SLOs), basophils support autoreactive plasma cells to amplify autoantibody production. We have recently shown that murine lupus-like disease could be controlled by 10 days of oral treatment with a combination of prostaglandin D₂ (PGD₂) receptor (PTGDR) antagonists through the inhibition of basophil activation and recruitment to SLOs. Importantly, inhibiting solely PTGDR-1 or PTGDR-2 was ineffective, and the development of lupus-like disease could only be dampened by using antagonists for both PTGDR-1 and PTGDR-2. Here, we aimed at establishing a proof of concept that a clinically relevant bispecific antagonist of PTGDR-1 and PTGDR-2 could be efficient to treat murine lupus-like nephritis. Diseased Lyn-deficient female mice received treatment with AMG853 (vidupiprant, a bispecific PTGDR-1/PTGDR-2 antagonist) for 10 days. This led to the dampening of basophil activation and recruitment in SLOs and was associated with a decrease in plasmablast expansion and immunoglobulin E (IgE) production. Ten days of treatment with AMG853 was consequently sufficient in reducing the dsDNA-specific IgG titers, circulating immune complex glomerular deposition, and renal inflammation, which are hallmarks of lupus-like disease. Thus, bispecific PTGDR-1 and PTGDR-2 antagonists, such as AMG853, are a promising class of drugs for the treatment or prevention of organ damage in systemic lupus erythematosus.

Maternal Inflammation Exaggerates Offspring Susceptibility to Cerebral Ischemia–Reperfusion Injury via the COX-2/PGD2/DP2 Pathway Activation

The pathogenesis of cerebral ischemia–reperfusion (I/R) injury is complex and does not exhibit an effective strategy. Maternal inflammation represents one of the most important factors involved in the etiology of brain injury in newborns. We aimed to investigate the effect of maternal inflammation on offspring susceptibility to cerebral I/R injury and the mechanisms by which it exerts its effects. Pregnant SD rats were intraperitoneally injected with LPS (300 μg/kg/day) at gestational days 11, 14, and 18. Pups were subjected to MCAO/R on postnatal day 60. Primary neurons were obtained from postnatal day 0 SD rats and subjected to OGD/R. Neurological deficits, brain injury, neuronal viability, neuronal damage, and neuronal apoptosis were assessed. Oxidative stress and inflammation were evaluated, and the expression levels of COX-2/PGD2/DP pathway-related proteins and apoptotic proteins were detected. Maternal LPS exposure significantly increased the levels of oxidative stress and inflammation, significantly activated the COX-2/PGD2/DP₂ pathway, and increased proapoptotic protein expression. However, maternal LPS exposure significantly decreased the antiapoptotic protein expression, which subsequently increased neurological deficits and cerebral I/R injury in offspring rats. The corresponding results were observed in primary neurons. Moreover, these effects of maternal LPS exposure were reversed by a COX-2 inhibitor and DP₁ agonist but exacerbated by a DP₂ agonist. In conclusion, maternal inflammatory exposure may increase offspring susceptibility to cerebral I/R injury. Moreover, the underlying mechanism might be related to the activation of the COX-2/PGD2/DP₂ pathway. These findings provide a theoretical foundation for the development of therapeutic drugs for cerebral I/R injury.

The imbalance of PGD2-DPs pathway is involved in the type 2 diabetes brain injury by regulating autophagy

Prostaglandin D2 (PGD2) is the most abundant prostaglandin in the brain, but its involvement in brain damage caused by type 2 diabetes (T2D) has not been reported. In the present study, we found that increased PGD2 content is related to the inhibition of autophagy, which aggravates brain damage in T2D, and may be involved in the imbalanced expression of the corresponding PGD2 receptors DP1 and DP2. We demonstrated that DP2 inhibited autophagy and promotedT2D-induced brain damage by activating the PI3K/AKT/mTOR pathway, whereas DP1enhanced autophagy and amelioratedT2D brain damage by activating the cAMP/PKA pathway. In a T2D rat model, DP1 expression was decreased, and DP2 expression was increased; therefore, the imbalance in PGD2-DPs may be involved in T2D brain damage through the regulation of autophagy. However, there have been no reports on whether PKA can directly inhibit mTOR. The PKA catalytic subunit (PKA-C) has three subtypes (α, β and γ), and γ is not expressed in the brain. Subsequently, we suggested that PKA could directly interact with mTOR through PKA-C(α) and PKA-C(β). Our results suggest that the imbalance in PGD2-DPs is related to changes in autophagy levels in T2D brain damage, and PGD2 is involved in T2D brain damage by promoting autophagy via DP1-PKA/mTOR and inhibiting autophagy via DP2-PI3K/AKT/mTOR.

A Review of Prostanoid Receptors: Expression, Characterization, Regulation, and Mechanism of Action

Prostaglandin signaling controls a wide range of biological processes from blood pressure homeostasis to inflammation and resolution thereof to the perception of pain to cell survival. Disruption of normal prostanoid signaling is implicated in numerous disease states. Prostaglandin signaling is facilitated by G-protein-coupled, prostanoid-specific receptors and the array of associated G-proteins. This review focuses on the expression, characterization, regulation, and mechanism of action of prostanoid receptors with particular emphasis on human isoforms.

Same Target, Different Therapeutic Outcomes: The Case of CAY10471 and Fevipiprant on CRTh2 Receptor in Treatment of Allergic Rhinitis and Asthma

OBJECTIVE

Prostaglandin 2 (PGD2) mediated signalling of Chemoattractant Receptorhomologous molecule expressed on Th2 cells (CRTh2) receptor has been implicated in the recruitment of inflammatory cells. This explains the design of highly selective compounds with innate abilities to antagonize PGD2-CRTh2 interactions and prevent pro-inflammatory allergies such as rhinitis and uncontrolled asthma. The development of PGD2-competitive CRTh2 binders; CAY10471 and Fevipiprant represent remarkable therapeutic progress even though they elicit disparate pharmacological propensities despite utilizing the same binding pocket.

METHODS & RESULTS

In this study, we seek to pinpoint the underlying phenomenon associated with differential CRTh2 therapeutic inhibition by CAY10471 and Fevipiprant using membraneembedded molecular dynamics simulation. Findings revealed that the common carboxylate group of both compounds elicited strong attractive charges with active site Arg170 and Lys210. Interestingly, a distinctive feature was the steady occurrence of high-affinity salt-bridges and an Arg170-mediated pi-cation interaction with the tetrahydrocarbozole ring of CAY10471. Further investigations into the active site motions of both ligands revealed that CAY10471 was relatively more stable. Comparative binding analyses also revealed that CAY10471 exhibited higher ΔG, indicating the cruciality of the ring stabilization role mediated by Arg170. Moreover, conformational analyses revealed that the inhibitory activity of CAY10471 was more prominent on CRTh2 compared to Fevipiprant.

CONCLUSIONS

These findings could further advance the strategic design of novel CRTh2 binders in the treatment of diseases related to pro-inflammatory allergies.

Evidence for the induction of Th2 inflammation by group 2 innate lymphoid cells in response to prostaglandin D2 and cysteinyl leukotrienes in allergic rhinitis

BACKGROUND

Group 2 innate lymphoid cells (ILC2s) play important roles in allergic inflammation. However, their roles in the pathophysiology of allergic rhinitis (AR) are poorly understood.

OBJECTIVE

Prevalence of ILC2s in the inferior nasal turbinate (INT) tissues and the activating mechanisms of ILC2s were examined in patients with house dust mite (HDM)-induced AR.

METHODS

Eighteen patients with HDM-induced AR and 13 control subjects were recruited. Fresh INT tissues and peripheral blood mononuclear cells (PBMCs) were analysed using flow cytometry. Nasal lavage fluids (NLF) were collected at 10 minutes after the nasal provocation test (NPT) with HDM disc, and released mediators were measured by ELISA. Sorted ILC2s were cultured and stimulated with mediators associated with AR.

RESULTS

The prevalence of ILC2s was significantly increased in nasal mucosa of patients with HDM-induced AR, and it was positively correlated with the number of infiltrating eosinophils. ILC2s in the INT tissues expressed a prostaglandin D₂ (PGD₂ ) receptor, chemoattractant receptor-homologous molecule-expressed TH2 cells (CRTH2) and a cysteinyl leukotriene (cysLTs) receptor, CysLT1. After NPT, the number of eosinophils and concentrations of PGD₂ and cysLTs were significantly increased in the NLF from AR patients. PGD₂ and cysLTs significantly induced IL-5 production from cultured PBMC-derived ILC2s dose-dependently. PGD₂ -induced and cysLTs-induced productions of IL-5 and IL-13 from ILC2s were completely inhibited by ramatroban, a dual CRTH2 and thromboxane receptor antagonist, and montelukast, a CysLT1 antagonist, respectively.

CONCLUSIONS

PGD₂ -CRTH2 and cysLTs-CysLT1 axes may activate tissue-resident ILC2s to produce Th2 cytokines, IL-5 and IL-13, leading to the development of allergic inflammation in AR.

Mast Cells and Their Progenitors in Allergic Asthma

Mast cells and their mediators have been implicated in the pathogenesis of asthma and allergy for decades. Allergic asthma is a complex chronic lung disease in which several different immune cells, genetic factors and environmental exposures influence the pathology. Mast cells are key players in the asthmatic response through secretion of a multitude of mediators with pro-inflammatory and airway-constrictive effects. Well-known mast cell mediators, such as histamine and bioactive lipids are responsible for many of the physiological effects observed in the acute phase of allergic reactions. The accumulation of mast cells at particular sites of the allergic lung is likely relevant to the asthma phenotype, severity and progression. Mast cells located in different compartments in the lung and airways have different characteristics and express different mediators. According to in vivo experiments in mice, lung mast cells develop from mast cell progenitors induced by inflammatory stimuli to migrate to the airways. Human mast cell progenitors have been identified in the blood circulation. A high frequency of circulating human mast cell progenitors may reflect ongoing pathological changes in the allergic lung. In allergic asthma, mast cells become activated mainly via IgE-mediated crosslinking of the high affinity receptor for IgE (FcεRI) with allergens. However, mast cells can also be activated by numerous other stimuli e.g. toll-like receptors and MAS-related G protein-coupled receptor X2. In this review, we summarize research with implications on the role and development of mast cells and their progenitors in allergic asthma and cover selected activation pathways and mast cell mediators that have been implicated in the pathogenesis. The review places an emphasis on describing mechanisms identified using in vivo mouse models and data obtained by analysis of clinical samples.

Synthesis and preclinical evaluation of the CRTH2 antagonist [11C]MK-7246 as a novel PET tracer and potential surrogate marker for pancreatic beta-cell mass

INTRODUCTION

MK-7246 is a potent and selective antagonist for chemoattractant receptor-homologous molecule expressed on T_h2 cells (CRTH2). Within the pancreas CRTH2 is selectively expressed in pancreatic β-cells where it is believed to play a role in insulin release. Reduction in β-cell mass and insufficient insulin secretion in response to elevated blood glucose levels is a hallmark for type 1 and type 2 diabetes. Reported here is the synthesis of [¹¹C]MK-7246 and initial preclinical evaluation towards CRTH2 imaging. The aim is to develop a method to quantify β-cell mass with PET and facilitate non-invasive studies of disease progression in individuals with type 2 diabetes.

METHODS

The precursor N-desmethyl-O-methyl MK-7246 was synthesized in seven steps and subjected to methylation with [¹¹C]methyl iodide followed by hydrolysis to obtain [¹¹C]MK-7246 labelled in the N-methyl position. Preclinical evaluation included in vitro radiography and immune-staining performed in human pancreatic biopsies. Biodistribution studies were performed in rat by PET-MRI and in pig by PET-CT imaging. Saturable tracer binding was examined in pig by scanning before and after administration of MK-7246 (1 mg/kg). Predicted dosimetry of [¹¹C]MK-7246 in human males was estimated based on the biodistribution in rat.

RESULTS

[¹¹C]MK-7246 was obtained with activities sufficient for the current investigations (270 ± 120 MBq) and a radiochemical purity of 93 ± 2%. The tracer displayed focal binding in areas with insulin positive islet of Langerhans in human pancreas sections. Baseline uptake in pig was reduced in tissues with known expression of CRTH2 after administration of MK-7246; pancreas (66% reduction) and spleen (88% reduction). [¹¹C]MK-7246 exhibited a safe human predicted dosimetry profile as extrapolated from the rat biodistribution data.

CONCLUSIONS

Initial preclinical in vitro and in vivo evaluations of [¹¹C]MK-7246 show binding and biodistribution properties suitable for PET imaging of CRTH2. Further studies are warranted to assess its potential in β-cell mass imaging and CRTH2 drug development.

Comparison of the Effects of Two Different Analgesics on Bone Regeneration During Mandibular Distraction Osteogenesis

INTRODUCTION

Mandibular distraction osteogenesis (DO) is frequently used in the management of bone defects and craniofacial deformities, with analgesics commonly administered to relieve acute postoperative pain. This experimental animal study investigated the effects of 2 analgesics, acetaminophen and acemetacin, on bone regeneration after DO.

MATERIALS AND METHODS

This study was conducted with 14 mature male New Zealand rabbits (2.8-3.2 kg) randomized into 2 groups of 7. Mandibular osteotomies were performed under optimal operating conditions, and a custom-made distractor was applied to the mandible of each subject, with distraction initiated after a 5-day latency period at a rate of 1.0 mm/d (2 × 0.5 mm/d) for 10 days. Analgesics were administered via oral gavage during the latency period and for the first 5 days of the distraction period for 10 days in total, with group I receiving acetaminophen (200 mg/kg/d) and group II receiving acemetacin (5 mg/kg/d). Subjects were sacrificed and their mandibles dissected at the end of 4 weeks postoperatively. Bone mineral density (BMD) and bone mineral content (BMC) were measured using dual-energy X-ray absorptiometry (DEXA), and histomorphometric analysis was performed to evaluate the quality of newly formed bone. Paired group comparisons of non-normally distributed numerical variables were made using the Mann-Whitney U test, with a P value of <0.05 considered statistically significant.

RESULTS

No significant differences in BMC and BMD values of intact bone, newly formed bone, or bone around the pin site were observed between the 2 groups. Histometric analysis also indicated acetaminophen and acemetacin to have similar effects on bone regeneration during distraction.

CONCLUSION

Acemetacin may be an alternative to acetaminophen for treating pain associated with DO, given the similarities in the effects of the 2 analgesics on bone regeneration. However, this finding should be supported by further experimental and human studies.

Structures of the Human PGD2 Receptor CRTH2 Reveal Novel Mechanisms for Ligand Recognition

The signaling of prostaglandin D₂ (PGD₂) through G-protein-coupled receptor (GPCR) CRTH2 is a major pathway in type 2 inflammation. Compelling evidence suggests the therapeutic benefits of blocking CRTH2 signaling in many inflammatory disorders. Currently, a number of CRTH2 antagonists are under clinical investigation, and one compound, fevipiprant, has advanced to phase 3 clinical trials for asthma. Here, we present the crystal structures of human CRTH2 with two antagonists, fevipiprant and CAY10471. The structures, together with docking and ligand-binding data, reveal a semi-occluded pocket covered by a well-structured amino terminus and different binding modes of chemically diverse CRTH2 antagonists. Structural analysis suggests a ligand entry port and a binding process that is facilitated by opposite charge attraction for PGD₂, which differs significantly from the binding pose and binding environment of lysophospholipids and endocannabinoids, revealing a new mechanism for lipid recognition by GPCRs.

Discovery of MK-8318, a Potent and Selective CRTh2 Receptor Antagonist for the Treatment of Asthma

A novel series of tricyclic tetrahydroquinolines were identified as potent and selective CRTh2 receptor antagonists. The agonism and antagonism switch was achieved through structure-based drug design (SBDD) using a CRTh2 receptor homologue model. The challenge of very low exposures in pharmacokinetic studies was overcome by exhaustive medicinal chemistry lead optimization through focused SAR studies on the tricyclic core. Further optimization resulted in the identification of the preclinical candidate 4-(cyclopropyl((3aS,9R,9aR)-7-fluoro-4-(4-(trifluoromethoxy)benzoyl)-2,3,3a,4,9,9a-hexahydro-1H-cyclopenta[b]quinolin-9-yl)amino)-4-oxobutanoic acid (15c, MK-8318) with potent and selective CRTh2 antagonist activity and a favorable PK profile suitable for once daily oral dosing for potential treatment of asthma.

Targeting the PGD2/CRTH2/DP1 Signaling Pathway in Asthma and Allergic Disease: Current Status and Future Perspectives

Prostaglandin D₂ (PGD₂) released by degranulating mast cells is believed to play a key role in orchestrating mechanisms of inflammation in allergies and asthma. The biological effects of PGD₂ are mediated by D-prostanoid (DP1), CRTH2 (DP2), and thromboxane prostanoid (TP) receptors. The CRTH2 receptor is involved in induction of migration and activation of T helper type 2 (Th₂) lymphocytes, eosinophils, and basophils; up-regulation of adhesion molecules; and promotion of pro-inflammatory Th₂-type cytokines (interleukin [IL]-4, 5, 13), whereas the DP receptor is associated with relaxation of smooth muscles, vasodilation, inhibition of cell migration, and apoptosis of eosinophils. A number of CRTH2/PGD₂ receptor antagonists have been investigated in asthma and allergic diseases. The CRTH2 antagonist (OC000459) or dual CRTH2 and TP receptor antagonist (ramatroban) were effective in reducing eosinophilia, nasal mucosal swelling, and clinical symptoms of allergic rhinitis, with the latter drug registered for clinical use in this indication. OC000459 and setipiprant reduced the late but not early phase of response in an allergen challenge in atopic asthmatics. In persistent asthma, some molecules induced limited improvement in lung function, quality of life, and asthma symptoms (OC000459, BI671800), but in other trials with AMG 853 and AZ1981 these findings were not confirmed. The clear discrepancy between animal studies and clinical efficacy of CRTH2 antagonism in allergic rhinitis, and lack of efficacy in a general cohort of asthmatics, highlight the issue of patient phenotyping. There is no doubt that the PGD₂/CATH2/DP1 pathway plays a key role in allergic inflammation and further studies with selective or combined antagonisms in well defined cohorts of patients are needed.

Human intrahepatic ILC2 are IL-13positive amphiregulinpositive and their frequency correlates with model of end stage liver disease score

Introduction

Innate lymphoid cells (ILC) have been implicated in the initiation of inflammation and fibrosis in mice. However, ILC have not been characterized in inflamed human liver tissue.

Methods

Human intrahepatic lymphocytes were isolated by mechanical digestion and phenotyped by flow cytometry. Conditioned medium from cultures of primary human biliary epithelial cells, stellate cells, fibroblasts and inflamed human liver tissue was used to model the effects of the inflammatory liver environment of ILC phenotype and function.

Results

All three ILC subsets were present in the human liver, with the ILC1 (CRTH2^negCD117^neg) subset constituting around 70% of intrahepatic ILCs. Both NCR^pos (NKp44⁺) and NCR^neg ILC3 (CRTH2^negCD117^pos) subsets were also detected. ILC2 (CRTH2^pos) frequency correlated with disease severity measured by model of end stage liver disease (MELD) scoring leading us to study this subset in more detail. ILC2 displayed a tissue resident CD69⁺ CD161⁺⁺ phenotype and expressed chemokine receptor CCR6 allowing them to respond to CCL20 secreted by cholangiocytes and stellate cells. ILC2 expressed integrins VLA-5 and VLA-6 and the IL-2 and IL-7 cytokine receptors CD25 and CD127 although IL-2 and IL-7 were barely detectable in inflamed liver tissue. Although biliary epithelial cells secrete IL-33, intrahepatic ILC2 had low expression of the ST2 receptor. Intrahepatic ILC2 secreted the immunoregulatory and repair cytokines IL-13 and amphiregulin.

Conclusions

Intrahepatic ILC2 express receptors allowing them to be recruited to bile ducts in inflamed portal tracts. Their frequencies increased with worsening liver function. Their secretion of IL-13 and amphiregulin suggests they may be recruited to promote resolution and repair and thereby they may contribute to ongoing fibrogenesis in liver disease.

CRTH2 antagonists in asthma: current perspectives

Chemoattractant receptor-homologous molecule expressed on T_H2 cells (CRTH2) binds to prostaglandin D₂. CRTH2 is expressed on various cell types including eosinophils, mast cells, and basophils. CRTH2 and prostaglandin D₂ are involved in allergic inflammation and eosinophil activation. Orally administered CRTH2 antagonists are in clinical development for the treatment of asthma. The biology and clinical trial data indicate that CRTH2 antagonists should be targeted toward eosinophilic asthma. This article reviews the clinical evidence for CRTH2 involvement in asthma pathophysiology and clinical trials of CRTH2 antagonists in asthma. CRTH2 antagonists could provide a practical alternative to biological treatments for patients with severe asthma. Future perspectives for this class of drug are considered, including the selection of the subgroup of patients most likely to show a meaningful treatment response.

Group 2 innate lymphoid cells are recruited to the nasal mucosa in patients with aspirin-exacerbated respiratory disease

BACKGROUND

Aspirin-exacerbated respiratory disease (AERD) is characterized by tissue eosinophilia and mast cell activation, including abundant production of prostaglandin D₂ (PGD₂). Group 2 innate lymphoid cells (ILC2s), which promote tissue eosinophilia and mast cell responses, undergo chemotaxis and cytokine production in response to PGD₂, but it is unknown whether ILC2s are active in patients with AERD.

OBJECTIVE

We sought to determine whether ILC2 numbers change in peripheral blood and the nasal mucosa during COX-1 inhibitor-induced reactions in patients with AERD.

METHODS

Blood and nasal scrapings were collected at baseline, during reactions, and after completion of ketorolac/aspirin challenge/desensitization in 12 patients with AERD. ILC2s and eosinophils were quantitated by means of flow cytometry. Urine was also collected, and quantification of PGD₂ metabolite and leukotriene E₄ levels was done by using ELISA. Baseline and nonsteroidal anti-inflammatory drug reaction clinical data were correlated with cell changes.

RESULTS

ILC2 numbers significantly increased in nasal mucosal samples and decreased in blood at the time of COX-1 inhibitor reactions in 12 patients with AERD. These changes were not observed in 2 patients without AERD. Furthermore, eosinophil numbers decreased in blood concurrently with significant increases in urinary PGD₂ metabolite and leukotriene E₄ levels. The magnitude of increases in nasal mucosal ILC2 numbers positively correlated with maximum symptom scores during challenges. Furthermore, blood ILC2 numbers during the reaction correlated with time for the reaction to resolve, possibly reflecting reaction severity.

CONCLUSIONS

ILC2s are recruited to the nasal mucosa during COX-1 inhibitor-induced reactions in patients with AERD, correlating with enhanced production of prostaglandins and leukotrienes.

Two Phase II randomized trials on the CRTh2 antagonist AZD1981 in adults with asthma

Background

Chemoattractant receptor-homologous molecule expressed on T helper type 2 (Th2) cell (CRTh2) receptor antagonists is being investigated for asthma.

Objectives

The aim of this study was to assess the effects of the CRTh2 receptor antagonist, AZD1981 (with/without inhaled corticosteroids [ICSs]), on lung function and asthma control.

Patients and methods

Adults aged 18–60 years were enrolled in two randomized, placebo-controlled, parallel-group trials (protocol number: D9830C00003 [study 1, n=209] and protocol number: D9830C00004 [study 2, n=510]). In study 1, patients with stable asthma (forced expiratory volume in 1 second [FEV₁]: 65%−110%) were withdrawn from ICS (<400 µg/d) and randomized to AZD1981 1,000 mg twice daily (bid) or placebo. In study 2, patients with uncontrolled asthma (FEV₁: 40%−85%) despite ICS therapy (≥500 µg/d) were randomized to 50 mg, 400 mg, or 1,000 mg bid AZD1981 or placebo. The primary efficacy variable for both trials was the change in morning peak expiratory flow after 4 weeks of treatment. Secondary variables included Asthma Control Questionnaire (ACQ-5) scores, FEV₁ assessments, safety, and tolerability. In study 2, efficacy was also assessed according to atopic status.

Results

Following 4 weeks of treatment, there was a nonsignificant increase in morning peak expiratory flow on AZD1981 1,000 mg bid (9.5 L/min vs placebo, P=0.086 [study 1] and 12 L/min vs placebo, P=0.16 [study 2]). In study 2, all doses of AZD1981 provided significant improvements in ACQ-5 scores (0.26–0.3 units vs placebo, P=0.010–0.022); however, there was no dose–response relationship. Improved ACQ-5 scores and FEV₁ were observed in the majority of atopic patients treated with AZD1981. AZD1981 was well tolerated across treatment groups.

Conclusion

Further research may be warranted in atopic patients to fully evaluate the clinical efficacy of AZD1981.

Effect of the PGD2-DP signaling pathway on primary cultured rat hippocampal neuron injury caused by aluminum overload

In the present study, the agonists and antagonists of DP receptor were used to examine whether the PGD₂-DP signaling pathway affects neuronal function. Primary cultured hippocampal neuron was prepared and treated with aluminum maltolate (100 μM) to establish the neuronal damage model. PGD₂ and cAMP content was detected by ELISA. L-PGDS and DPs mRNA and protein expression were measured by RT-PCR and Western blotting, respectively. The aluminium-load neuron was treated with the DP₁ agonist BW245C, the DP₁ antagonist BWA868C, the DP₂ agonist DK-PGD_2, and the DP₂ antagonist CAY10471, respectively. Neuronal pathomorphology was observed using H-E staining. The cell viability and the lactate dehydrogenase leakage rates of neurons were measured with MTT and LDH kit, respectively. Ca²⁺ level was detected by Fluo-3/AM. In the model group, the MTT values obviously decreased; LDH leakage rates and PGD₂ content increased significantly; L-PGDS, DP₁ mRNA and protein expressions increased, and DP₂ level decreased. BW245C reduced the Ca²⁺ fluorescence intensity and protected the neurons. DK-PGD₂ increased the intensity of Ca²⁺ fluorescence, while CAY10471 had the opposite effect. In conclusion, contrary to the effect of DP₂, the PGD₂-DP₁ signaling pathway protects against the primary cultured rat hippocampal neuronal injury caused by aluminum overload.

Type-2 innate lymphoid cells in human allergic disease

PURPOSE OF REVIEW

Recent decades have seen allergic diseases become endemic in a number of developed countries. Understanding the inflammatory processes that dictate these allergic responses is therefore important.

RECENT FINDINGS

Critical to many allergic responses is the inappropriate release of the type-2 immune-regulatory cytokines: interleukin-4, interleukin-5, interleukin-9, and interleukin-13. The study of these inflammatory mediators has led directly to the development of two new asthma treatments: anti-interleukin-5 and anti-interleukin-13. Until recently, T helper 2 cells were considered to be the major cellular source of type-2 cytokines; however, a paradigm shift occurred with the discovery of a novel population, type-2 innate lymphoid cells (ILC2s), that can produce huge levels of type-2 cytokines and are sufficient to induce allergy in mice. This discovery raises interesting questions about how innate and adaptive type-2 immunity might interact to induce relapsing and remitting episodes of allergy in patients.

SUMMARY

It is essential that alongside the mechanistic investigation using model organisms, the roles of ILC2s in human disease be explored. Here, we discuss how ILC2 traits, discovered in mouse models, have informed research in humans and how newly identified human ILC2 pathways might provide potential therapeutic benefits in the future.

Recent advance in investigation of gene polymorphisms in Japanese patients with aspirin-exacerbated respiratory disease

Aspirin-exacerbated respiratory disease (AERD) is a complex clinical syndrome characterised by severe asthmatic attack upon treatment with aspirin and/or non-steroidal anti-inflammatory drugs (NSAIDs). Genetic predisposition has been considered as a crucial determinant and candidate genes have concentrated especially on cysteinyl leukotrienes (LTs)-related genes as the inhibitory action of aspirin and NSAIDs on cyclooxygenase activity may cause overproduction of cysteinyl LTs. However, conflicting results have been reported, in parallel with replication studies in different ethnic groups. Thus, future areas of investigations need to focus on comprehensive approaches towards the discovery of other genetic biomarkers. Unfortunately, few papers have been reported about gene polymorphisms in Japanese patients with AERD. Here, we described on our recent genetic investigations on B2ADR, IL-13, IL-17A, CYP2C19, TBXA2R, CRTH2 and HSP70. This review indicates potential genetic biomarkers contributing to the early diagnosis of AERD, which may include CYP2C19 and HSP70 gene polymorphisms, and future validation studies in independent population are required to provide reassurance about our findings.

Expression of DP2 (CRTh2), a prostaglandin D₂ receptor, in human mast cells

PGD₂ has long been implicated in allergic diseases. Recent cloning of a second PGD₂ receptor, DP2 (also known as CRTh2), led to a greater understanding of the physiological and pathophysiological implications of PGD₂. PGD₂ signaling through DP1 and DP2 mediates different and often opposite effects in many cell types of the immune system. Although mast cells (MC) are the largest source of PGD₂ in the body, there is little information about their potential expression of DP2 and its functional significance. In this study, we show that tissue MC in human nasal polyps express DP2 protein, and that human MC lines and primary cultured human MC express mRNA as well as protein of DP2. By immunohistochemistry, we detected that 34% of MC in human nasal polyps expressed DP2. In addition, flow cytometry showed that 87% of the LAD2 human MC line and 98% of primary cultured human MC contained intracellular DP2. However, we could not detect surface expression of DP2 on human MC by single cell analysis using imaging flow cytometry. Blocking of endogenous PGD2 production with aspirin did not induce surface expression of DP2 in human MC. Two DP2 selective agonists, DK-PGD₂ and 15R-15-methyl PGD₂ induced dose-dependent intracellular calcium mobilization that was abrogated by pertussis toxin, but not by three DP2 selective antagonists. MC mediator release including degranulation was not affected by DP2 selective agonists. Thus, human MC express DP2 intracellularly rather than on their surface, and the function of DP2 in human MC is different than in other immune cells such as Th2 cells, eosinophils and basophils where it is expressed on the cell surface and induces Th2 cytokine and/or granule associated mediator release. Further studies to elucidate the role of intracellular DP2 in human MC may expand our understanding of this molecule and provide novel therapeutic opportunities.

Quality by design (QbD) of amide isosteres: 5,5-Disubstituted isoxazolines as potent CRTh2 antagonists with favorable pharmacokinetic and drug-like properties

Isoxazoles are frequently used amide isosteres, as shown in the context of discovery of CRTh2 antagonists from amide 1 to isoxazole 2. However, persistent agonism and poor solubility in isoxazole series presented challenges to its further development. Based on the concept of quality by design (QbD), 5,5-disubstituted isoxazolines 3 were introduced. The chirality at 5 position of isoxazolines controlled the switch between two modes of actions, which led to a novel series of pure antagonists. This non-planar motif also conferred a change of shape of these molecules, which avoided flat structures and improved their physical properties.

Prostaglandin D2 activates group 2 innate lymphoid cells through chemoattractant receptor-homologous molecule expressed on TH2 cells

Background

Activation of the group 2 innate lymphoid cell (ILC2) population leads to production of the classical type 2 cytokines, thus promoting type 2 immunity. Chemoattractant receptor-homologous molecule expressed on T_H2 cells (CRTH2), a receptor for prostaglandin D₂ (PGD₂), is expressed by human ILC2s. However, the function of CRTH2 in these cells is unclear.

Objectives

We sought to determine the role of PGD₂ and CRTH2 in human ILC2s and compare it with that of the established ILC2 activators IL-25 and IL-33.

Methods

The effects of PGD₂, IL-25, and IL-33 on the cell migration, cytokine production, gene regulation, and receptor expression of ILC2s were measured with chemotaxis, ELISA, Luminex, flow cytometry, quantitative RT-PCR, and QuantiGene assays. The effects of PGD₂ under physiologic conditions were evaluated by using the supernatant from activated mast cells.

Results

PGD₂ binding to CRTH2 induced ILC2 migration and production of type 2 cytokines and many other cytokines. ILC2 activation through CRTH2 also upregulated the expression of IL-33 and IL-25 receptor subunits (ST2 and IL-17RA). The effects of PGD₂ on ILC2s could be mimicked by the supernatant from activated human mast cells and inhibited by a CRTH2 antagonist.

Conclusions

PGD₂ is an important and potent activator of ILC2s through CRTH2 mediating strong proallergic inflammatory responses. Through IgE-mediated mast cell degranulation, these innate cells can also contribute to adaptive type 2 immunity; thus CRTH2 bridges the innate and adaptive pathways in human ILC2s.

Cyclooxygenase metabolites in the kidney

In the mammalian kidney, prostaglandins (PGs) are important mediators of physiologic processes, including modulation of vascular tone and salt and water. PGs arise from enzymatic metabolism of free arachidonic acid (AA), which is cleaved from membrane phospholipids by phospholipase A2 activity. The cyclooxygenase (COX) enzyme system is a major pathway for metabolism of AA in the kidney. COX are the enzymes responsible for the initial conversion of AA to PGG2 and subsequently to PGH2, which serves as the precursor for subsequent metabolism by PG and thromboxane synthases. In addition to high levels of expression of the "constitutive" rate-limiting enzyme responsible for prostanoid production, COX-1, the "inducible" isoform of cyclooxygenase, COX-2, is also constitutively expressed in the kidney and is highly regulated in response to alterations in intravascular volume. PGs and thromboxane A2 exert their biological functions predominantly through activation of specific 7-transmembrane G-protein-coupled receptors. COX metabolites have been shown to exert important physiologic functions in maintenance of renal blood flow, mediation of renin release and regulation of sodium excretion. In addition to physiologic regulation of prostanoid production in the kidney, increases in prostanoid production are also seen in a variety of inflammatory renal injuries, and COX metabolites may serve as mediators of inflammatory injury in renal disease.

Biochemical and pharmacological characterization of AZD1981, an orally available selective DP2 antagonist in clinical development for asthma

BACKGROUND AND PURPOSE

The discovery of DP2 as a second receptor for PGD2 has prompted the search for antagonists as potential novel therapies based on the associations between PGD2 and disease. Here we describe the biochemical and pharmacological properties of 4-(acetylamino)-3-[(4-chlorophenyl)thio]-2-methyl-1H-indole-1-acetic acid (AZD1981), a novel DP2 receptor antagonist.

EXPERIMENTAL APPROACH

Binding to DP2 , functional receptor pharmacology and selectivity were studied in both human and animal systems.

KEY RESULTS

AZD1981 displaced radio-labelled PGD2 from human recombinant DP2 with high potency (pIC50 = 8.4). Binding was reversible, non-competitive and highly selective against a panel of more than 340 other enzymes and receptors, including DP1 (>1000-fold selective). AZD1981 inhibited DP2 -mediated shape change and CD11b up-regulation in human eosinophils, shape change in basophils and chemotaxis of human eosinophils and Th2 cells with similar potency. AZD1981 exhibited good cross-species binding activity against mouse, rat, guinea pig, rabbit and dog DP2 . Evaluation in mouse, rat or rabbit cell systems was not possible as they did not respond to DP2 agonists. Agonist responses were seen in guinea pig and dog, and AZD1981 blocked DP2 -mediated eosinophil shape change. Such responses were more robust in the guinea pig, where AZD1981 also blocked DP2 -dependent eosinophil emigration from bone marrow.

CONCLUSIONS AND IMPLICATIONS

AZD1981 is a DP2 antagonist that blocks functional responses in eosinophils, Th2 cells and basophils. It exhibited similar potency irrespective of the cell type, DP2 agonist or species used. This selective orally active agent is currently under clinical evaluation as a potential therapeutic agent in respiratory diseases including asthma.

Indomethacin inhibits eosinophil migration to prostaglandin D2 : therapeutic potential of CRTH2 desensitization for eosinophilic pustular folliculitis

Indomethacin is a cyclo-oxygenase inhibitor, and shows therapeutic potential for various eosinophilic skin diseases, particularly eosinophilic pustular folliculitis. One of the unique characteristics of indomethacin is that, unlike other non-steroidal anti-inflammatory drugs, it is a potent agonist of chemoattractant receptor-homologous molecule expressed on T helper type 2 cells (CRTH2), a receptor for prostaglandin D2 (PGD2 ). This study investigated the pharmacological actions of indomethacin on eosinophil migration to clarify the actual mechanisms underlying the therapeutic effects of indomethacin on eosinophilic pustular folliculitis. Eosinophils exhibited chemokinetic and chemotactic responses to both PGD2 and indomethacin through CRTH2 receptors. Pre-treatment of eosinophils with indomethacin greatly inhibited eosinophil migration to PGD2 and, to a much lesser extent, to eotaxin (CCL11); these effects could be mediated by homologous and heterologous desensitization of eosinophil CRTH2 and CCR3, respectively, by agonistic effects of indomethacin on CRTH2. Indomethacin also cancelled a priming effect of Δ(12) -PGJ2 , a plasma metabolite of PGD2 , on eosinophil chemotaxis to eotaxin. Indomethacin down-modulated cell surface expression of both CRTH2 and CCR3. Hair follicle epithelium and epidermal keratinocytes around eosinophilic pustules together with the eccrine apparatus of palmoplantar lesions of eosinophilic pustular folliculitis were immunohistochemically positive for lipocalin-type PGD synthase. Indomethacin may exert therapeutic effects against eosinophilic skin diseases in which PGD2 -CRTH2 signals play major roles by reducing eosinophil responses to PGD2 .

A novel indole compound, AWT-489, inhibits prostaglandin D2-induced CD55 expression by acting on DP prostanoid receptors as an antagonist in LS174T human colon cancer cells

Indoles are composed of a common core structure, the indole ring, and are widely used as pharmaceuticals and their precursors. In this study, a newly composed relatively small indole compound, AWT-489 was examined to find a novel specific antagonist for DP receptors; the cognate receptors for prostaglandin D2 (PGD2), to prevent colon cancer malignancy. Here we showed that AWT-489 antagonized DP receptor-mediated cyclic AMP formation, and expression of CD55, an inhibitor of the complement system that correlates with poor survival in patients with colorectal cancer, in LS174T human colon cancer cells. Interestingly, unlike a popular indole compound, indomethacin, AWT-489 did not act on the cyclooxygenases as a non-steroidal anti-inflammatory drug. Moreover, AWT-489 exhibited a better inhibitory effect than that of the well-used DP receptor antagonist, BWA868C when a dose close to the physiological concentration of PGD2 was used. These results suggest that AWT-489 can act as a novel human DP receptor antagonist to reduce the expression of CD55 in LS174T human colon cancer cells. We believe that AWT-489 has potential as a lead compound for designing a new DP receptor antagonist that may help improve PGD2-related diseases, especially colon cancer in the near future.

Identification of 2-(2-(1-naphthoyl)-8-fluoro-3,4-dihydro-1H-pyrido[4,3-b]indol-5(2H)-yl)acetic acid (setipiprant/ACT-129968), a potent, selective, and orally bioavailable chemoattractant receptor-homologous molecule expressed on Th2 cells (CRTH2) antagonist

Herein we describe the discovery of the novel CRTh2 antagonist 2-(2-(1-naphthoyl)-8-fluoro-3,4-dihydro-1H-pyrido[4,3-b]indol-5(2H)-yl)acetic acid 28 (setipiprant/ACT-129968), a clinical development candidate for the treatment of asthma and seasonal allergic rhinitis. A lead optimization program was started based on the discovery of the recently disclosed CRTh2 antagonist 2-(2-benzoyl-3,4-dihydro-1H-pyrido[4,3-b]indol-5(2H)-yl)acetic acid 5. An already favorable and druglike profile could be assessed for lead compound 5. Therefore, the lead optimization program mainly focused on the improvement in potency and oral bioavailability. Data of newly synthesized analogs were collected from in vitro pharmacological, physicochemical, in vitro ADME, and in vivo pharmacokinetic studies in the rat and the dog. The data were then analyzed using a traffic light selection tool as a visualization device in order to evaluate and prioritize candidates displaying a balanced overall profile. This data-driven process and the excellent results of the PK study in the rat (F = 44%) and the dog (F = 55%) facilitated the identification of 28 as a potent (IC50 = 6 nM), selective, and orally available CRTh2 antagonist.

Yin-Yang regulation of prostaglandins and nitric oxide by PGD2 in human arthritis: reversal by celecoxib

The role of PGD2 has been recognized in allergy, innate immunity and inflammation. Western blot analysis identified 21 kDa lipocalin (L)-prostaglandin D2 (PGD2) synthase (S) in human osteoarthritis (OA)-affected cartilage, whose expression was increased by IL-1β and TNFα. Similarly, PGD2 was spontaneously released by human OA-affected cartilage (and upregulated by IL-β) in ex vivo conditions and could be inhibited by indomethacin. Addition of PGD2 to human OA-affected cartilage significantly increased accumulation of PGE2, PGF1α, PGF2α, TXB2, but inhibited LTB4 and nitric oxide (NO) accumulation. Similarly, PGD2 (but not 13,14-dihydro-15-keto PGD2) augmented IL-1β induced PGE2 but inhibited IL-β induced nitric oxide (NO) in human chondrocytes. Celecoxib (10 μM) inhibits COX-1 mediated PGD2, and nitric oxide synthase (NOS) mediated NO in human OA-affected cartilage. Furthermore, celecoxib (1 μM) counter balances (IL-1β induced+PGD2 modulated) levels of NO and PGE2 in human OA-affected cartilage and chondrocytes to basal levels. These results show concentration-dependent, pro- and anti-inflammatory activity of PGD2 in human chondrocytes and cartilage, which can be neutralized by celecoxib. In view of the broad prostaglandin dependent and independent mechanism of action of celecoxib, these observations further reaffirm the broader role of celecoxib as a "Disease Modifying Drug" for human Osteoarthritis.

A leukotriene C4 synthase inhibitor with the backbone of 5-(5-methylene-4-oxo-4,5-dihydrothiazol-2-ylamino) isophthalic acid

The cysteinyl leukotrienes (cys-LTs), leukotriene C4 (LTC4) and its metabolites, LTD4 and LTE4, are proinflammatory lipid mediators in asthma and other inflammatory diseases. They are generated through the 5-lipoxygenase/LTC4 synthase (LTC4S) pathway and act via at least two distinct G protein-coupled receptors. The inhibition of human LTC4S will make a simple way to treat the cys-LT relevant inflammatory diseases. Here, we show that compounds having 5-(5-methylene-4-oxo-4,5-dihydrothiazol-2-ylamino) isophthalic acid moiety suppress LTC4 synthesis, glutathione conjugation to the precursor LTA4, in both an enzyme assay and a whole-cell assay. Hierarchical in silico screenings of 6 million compounds provided 300,000 dataset for docking, and after energy minimization based on the crystal structure of LTC4S, 111 compounds were selected as candidates for a competitive inhibitor to glutathione. One of those compounds showed significant inhibitory activity, and subsequently, its derivative 5-((Z)-5-((E)-2-methyl-3-phenylallylidene)-4-oxo-4,5-dihydrothiazol-2-ylamino) isophthalic acid (compound 1) was found to be the most potent inhibitor. The enzyme assay showed the IC50 was 1.9 µM and the corresponding 95% confidence interval was from 1.7 to 2.2 µM. The whole-cell assay showed that compound 1 was cell permeable and inhibited LTC4 synthesis in a concentration dependent manner.

Chemoattractant receptor homologous to the T helper 2 cell (CRTH2) is not expressed in human amniocytes and myocytes

BACKGROUND

15-deoxy-Δ 12,14- Prostaglandin J2 (15dPGJ2) inhibits Nuclear factor kappa B (NF-κB) in human myocytes and amniocytes and delays inflammation induced preterm labour in the mouse. 15dPGJ2 is a ligand for the Chemoattractant Receptor Homologous to the T helper 2 cell (CRTH2), a G protein-coupled receptor, present on a subset of T helper 2 (Th2) cells, eosinophils and basophils. It is the second receptor for Prostaglandin D2, whose activation leads to chemotaxis and the production of Th2-type interleukins. The cellular distribution of CRTH2 in non-immune cells has not been extensively researched, and its identification at the protein level has been limited by the lack of specific antibodies. In this study we explored the possibility that CRTH2 plays a role in 15dPGJ2-mediated inhibition of NF-κB and would therefore represent a novel small molecule therapeutic target for the prevention of inflammation induced preterm labour.

METHODS

The effect of a small molecule CRTH2 agonist on NF-κB activity in human cultured amniocytes and myocytes was assessed by detection of p65 and phospho-p65 by immunoblot. Endogenous CRTH2 expression in amniocytes, myocytes and peripheral blood mononuclear cells (PBMCs) was examined by PCR, western analysis and flow cytometry, with amniocytes and myocytes transfected with CRTH2 acting as a positive control in flow cytometry studies.

RESULTS

The CRTH2 agonist had no effect on NF-κB activity in amniocytes and myocytes. Although CRTH2 mRNA was detected in amniocytes and myocytes, CRTH2 was not detectable at the protein level, as demonstrated by western analysis and flow cytometry. 15dPGJ2 inhibited phospho-65 in PBMC'S, however the CRTH2 antagonist was not able to attenuate this effect. In conclusion, CRTH2 is not expressed on human amniocytes or myocytes and plays no role in the mechanism of 15dPGJ2-mediated inhibition of NF-κB.

CRTH2 Antagonists

Prostaglandin D2 (PGD2) plays a key role in many of the physiological markings of allergic inflammation including vasodilation, bronchoconstriction, vascular permeability and lymphocyte recruitment. The action of this molecule is elicited through its two primary receptors, DP and CRTH2. Activation of CRTH2 leads to lymphocyte chemotaxis, potentiation of histamine release from basophils, production of inflammatory cytokines (IL-4, IL-5 and IL-13) by Th2 cells, eosinophil degranulation and prevention of Th2 cell apoptosis. As such, antagonism of CRTH2 has been reported to ameliorate the symptoms associated with various allergen challenge animal models including murine antigen induced lung inflammation, murine cigarette smoke induced lung inflammation, murine allergic rhinitis, guinea pig PGD2-induced airflow obstruction, guinea pig airway hyper-responsiveness, sheep airway hyper-responsiveness and murine contact hypersensitivity. CRTH2 antagonists fall into four broad categories: tricyclic ramatroban analogues, indole acetic acids, phenyl/phenoxy acetic acids and non-acid-containing tetrahydroquinolines. Numerous CRTH2 antagonists have been advanced into the clinic and early reports from two Phase II trials suggest promising activity in the alleviation of atopic symptoms.

PGH1, the precursor for the anti-inflammatory prostaglandins of the 1-series, is a potent activator of the pro-inflammatory receptor CRTH2/DP2

Prostaglandin H₁ (PGH₁) is the cyclo-oxygenase metabolite of dihomo-γ-linolenic acid (DGLA) and the precursor for the 1-series of prostaglandins which are often viewed as “anti-inflammatory”. Herein we present evidence that PGH₁ is a potent activator of the pro-inflammatory PGD₂ receptor CRTH2, an attractive therapeutic target to treat allergic diseases such as asthma and atopic dermatitis. Non-invasive, real time dynamic mass redistribution analysis of living human CRTH2 transfectants and Ca²⁺ flux studies reveal that PGH₁ activates CRTH2 as PGH₂, PGD₂ or PGD₁ do. The PGH₁ precursor DGLA and the other PGH₁ metabolites did not display such effect. PGH₁ specifically internalizes CRTH2 in stable CRTH2 transfectants as assessed by antibody feeding assays. Physiological relevance of CRTH2 ligation by PGH₁ is demonstrated in several primary human hematopoietic lineages, which endogenously express CRTH2: PGH₁ mediates migration of and Ca²⁺ flux in Th2 lymphocytes, shape change of eosinophils, and their adhesion to human pulmonary microvascular endothelial cells under physiological flow conditions. All these effects are abrogated in the presence of the CRTH2 specific antagonist TM30089. Together, our results identify PGH₁ as an important lipid intermediate and novel CRTH2 agonist which may trigger CRTH2 activation in vivo in the absence of functional prostaglandin D synthase.

Indomethacin antagonizes EP(2) prostanoid receptor activation in LS174T human colon cancer cells

Increases in the level of cyclooxygenase (COX)-2 and prostanoids such as prostaglandin E(2) (PGE(2)) are considered biomarkers of colorectal cancer. Therefore, non-steroidal anti-inflammatory drugs (NSAID) have been used to reduce the risk of cancer development by reducing prostanoid biosynthesis as COX inhibitors. Along with their activity as COX inhibitors, NSAID have been reported to have other effects. One major NSAID, indomethacin, has been shown to have several effects independent of COX inhibition. To further examine the COX-inhibition-independent effects of indomethacin on colorectal cancer, we used human colon cancer LS174T cells, known to have express little COX-2 and have no detectable PGE(2) production. Here we show that indomethacin has a potential antagonizing effect on human EP(2) receptors. We believe this study raises the reasons to use indomethacin as a lead-compound for setting up another EP(2) receptor-specific antagonist as a relatively cost-efficient strategy for anti-cancer medication in the future.

Leukotriene E4 activates human Th2 cells for exaggerated proinflammatory cytokine production in response to prostaglandin D2

PGD(2) exerts a number of proinflammatory responses through a high-affinity interaction with chemoattractant receptor-homologous molecule expressed on Th2 cells (CRTH2) and has been detected at high concentrations at sites of allergic inflammation. Because cysteinyl leukotrienes (cysLTs) are also produced during the allergic response, we investigated the possibility that cysLTs may modulate the response of human Th2 cells to PGD(2). PGD(2) induced concentration-dependent Th2 cytokine production in the absence of TCR stimulation. Leukotrienes D(4) and E(4) (LTE(4)) also stimulated the cytokine production but were much less active than PGD(2). However, when combined with PGD(2), cysLTs caused a greater than additive enhancement of the response, with LTE(4) being most effective in activating Th2 cells. LTE(4) enhanced calcium mobilization in response to PGD(2) in Th2 cells without affecting endogenous PGD(2) production or CRTH2 receptor expression. The effect of LTE(4) was inhibited by montelukast but not by the P2Y(12) antagonist methylthioadenosine 5'-monophosphate. The enhancing effect was also evident with endogenous cysLTs produced from immunologically activated mast cells because inhibition of cysLT action by montelukast or cysLT synthesis by MK886, an inhibitor of 5-lipoxygenase-activating protein, reduced the response of Th2 cells to the levels produced by PGD(2) alone. These findings reveal that cysLTs, in particular LTE(4), have a significant proinflammatory impact on T cells and demonstrate their effects on Th2 cells are mediated by a montelukast-sensitive receptor.

Pharmacologic profile of OC000459, a potent, selective, and orally active D prostanoid receptor 2 antagonist that inhibits mast cell-dependent activation of T helper 2 lymphocytes and eosinophils

D prostanoid receptor 2 (DP₂) [also known as chemoattractant receptor-homologous molecule expressed on T helper 2 (Th2) cells (CRTH2)] is selectively expressed by Th2 lymphocytes, eosinophils, and basophils and mediates recruitment and activation of these cell types in response to prostaglandin D₂ (PGD₂). (5-Fluoro-2-methyl-3-quinolin-2-ylmethylindo-1-yl)-acetic acid (OC000459) is an indole-acetic acid derivative that potently displaces [³H]PGD₂ from human recombinant DP₂ (K(i) = 0.013 μM), rat recombinant DP₂ (K(i) = 0.003 μM), and human native DP₂ (Th2 cell membranes; K(i) = 0.004 μM) but does not interfere with the ligand binding properties or functional activities of other prostanoid receptors (prostaglandin E₁₋₄ receptors, D prostanoid receptor 1, thromboxane receptor, prostacyclin receptor, and prostaglandin F receptor). OC000459 inhibited chemotaxis (IC₅₀ = 0.028 μM) of human Th2 lymphocytes and cytokine production (IC₅₀ = 0.019 μM) by human Th2 lymphocytes. OC000459 competitively antagonized eosinophil shape change responses induced by PGD₂ in both isolated human leukocytes (pK(B) = 7.9) and human whole blood (pK(B) = 7.5) but did not inhibit responses to eotaxin, 5-oxo-eicosatetraenoic acid, or complement component C5a. OC000459 also inhibited the activation of Th2 cells and eosinophils in response to supernatants from IgE/anti-IgE-activated human mast cells. OC000459 had no significant inhibitory activity on a battery of 69 receptors and 19 enzymes including cyclooxygenase 1 (COX1) and COX2. OC000459 was found to be orally bioavailable in rats and effective in inhibiting blood eosinophilia induced by 13,14-dihydro-15-keto-PGD₂ (DK-PGD₂) in this species (ED₅₀ = 0.04 mg/kg p.o.) and airway eosinophilia in response to an aerosol of DK-PGD₂ in guinea pigs (ED₅₀ = 0.01 mg/kg p.o.). These data indicate that OC000459 is a potent, selective, and orally active DP₂ antagonist that retains activity in human whole blood and inhibits mast cell-dependent activation of both human Th2 lymphocytes and eosinophils.