Identification of prostaglandin D2 receptor antagonists based on a tetrahydropyridoindole scaffold

A new series of indole-based antagonists of the PGD(2) receptor subtype 1 (DP1 receptor) was identified and the progress of the structure-activity relationship study to the identification of potent and selective antagonists is presented. Selective DP1 antagonists with high potency and selectivity were prepared. Of particular interest is the DP1 antagonist 26 with a K(i) value of 1 nM for the DP1 receptor and an IC(50) value of 4.6 nM in a DP1 functional assay for the inhibition of the PGD(2) induced cAMP production in platelet rich plasma (PRP).     

Identification of an indole series of prostaglandin D2 receptor antagonists

A novel indole series of PGD2 receptor (DP receptor) antagonists is presented. Optimization of this series led to the identification of potent and selective DP receptor antagonists. In particular, antagonists 35 and 36 were identified with Ki values of 2.6 and 1.8 nM, respectively. These two antagonists are also potent in a DP functional assay where they inhibit the PGD2 induced cAMP production in platelet rich plasma with IC50 values of 7.9 and 8.6 nM, respectively. The structure-activity relationships of this indole series of DP receptor antagonists will also be discussed.     

Optimization of phenylacetic acid derivatives for balanced CRTH2 and DP dual antagonists

Our first generation CRTH2 and DP dual antagonists, represented by AMG 009, are more potent toward the CRTH2 receptor than to the DP receptor. Here we report our efforts in the discovery of CRTH2 and DP dual antagonists with more balanced potencies to both receptors, such as compound 15.     

Potent and highly selective DP1 antagonists with 2,3,4,9-tetrahydro-1H-carbazole as pharmacophore

We discovered that the introduction of a methyl group to the benzylic position of the N-benzyl group in lead compound 1a has a dramatic effect on improving the binding selectivity of this ligand for the prostanoid receptors DP1 (receptor for prostaglandin D(2)) as compared to TP (receptor for thromboxane A(2)). Based on this discovery, we have synthesized a series of potent and highly selective DP1 antagonists. Among them, compound 1h was identified as a highly selective DP1 antagonist with excellent overall properties. It has a K(i) of 0.43 nM to DP1 in binding assay and an IC(50) of 2.5 nM in the DP1 functional assay. Its selectivity for DP1 over TP (the most potent receptor after DP1) exceeds 750-fold based on both binding and functional assays. These properties make 1h a very potent and highly selective DP1 receptor antagonist suitable for investigating the biological functions of DP1 in normal physiology and models of disease.     

Benzimidazoles as new potent and selective DP antagonists for the treatment of allergic rhinitis

A series of 2-substituted N-benzyl benzimidazole containing molecules has been synthesized and its structure-activity relationship for the human DP receptor has been evaluated. Selective DP antagonists with nanomolar potency for the DP receptor were identified in this novel series of benzimidazoles.     

Stromal cell-derived factors 1alpha and 1beta, inflammatory protein-10 and interferon-inducible T cell chemo-attractant are novel substrates of dipeptidyl peptidase 8

N-terminal truncation of chemokines by proteases including dipeptidyl peptidase (DP) IV significantly alters their biological activity; generally ablating cognate G-protein coupled receptor engagement and often generating potent receptor antagonists. DP8 is a recently recognised member of the prolyl oligopeptidase gene family that includes DPIV. Since DPIV is known to process chemokines we surveyed 27 chemokines for cleavage by DP8. We report DP8 cleavage of the N-terminal two residues of IP10 (CXCL10), ITAC (CXCL11) and SDF-1 (CXCL12). This has implications for DP8 substrate specificity. Chemokine cleavage and inactivation may occur in vivo upon cell lysis and release of DP8 or in the inactivation of internalized chemokine/receptor complexes.     

Inverse Agonist and Pharmacochaperone Properties of MK-0524 on the Prostanoid DP1 Receptor

Prostaglandin D₂ (PGD₂) acts through two G protein-coupled receptors (GPCRs), the prostanoid DP receptor and CRTH2 also known as DP1 and DP2, respectively. Several previously characterized GPCR antagonists are now classified as inverse agonists and a number of GPCR ligands are known to display pharmacochaperone activity towards a given receptor. Here, we demonstrate that a DP1 specific antagonist, MK-0524 (also known as laropiprant), decreased basal levels of intracellular cAMP produced by DP1, a Gα_s-coupled receptor, in HEK293 cells. This reduction in cAMP levels was not altered by pertussis toxin treatment, indicating that MK-0524 did not induce coupling of DP1 to Gα_i/o proteins and that this ligand is a DP1 inverse agonist. Basal ERK1/2 activation by DP1 was not modulated by MK-0524. Interestingly, treatment of HEK293 cells expressing Flag-tagged DP1 with MK-0524 promoted DP1 cell surface expression time-dependently to reach a maximum increase of 50% compared to control after 24 h. In contrast, PGD₂ induced the internalization of 75% of cell surface DP1 after the same time of stimulation. The increase in DP1 cell surface targeting by MK-0524 was inhibited by Brefeldin A, an inhibitor of transport from the endoplasmic reticulum-Golgi to the plasma membrane. Confocal microscopy confirmed that a large population of DP1 remained trapped intracellularly and co-localized with calnexin, an endoplasmic reticulum marker. Redistribution of DP1 from intracellular compartments to the plasma membrane was observed following treatment with MK-0524 for 24 h. Furthermore, MK-0524 promoted the interaction between DP1 and the ANKRD13C protein, which we showed previously to display chaperone-like effects towards the receptor. We thus report that MK-0524 is an inverse agonist and a pharmacochaperone of DP1. Our findings may have important implications during therapeutic treatments with MK-0524 and for the development of new molecules targeting DP1.     

The anti-inflammatory effect of neuropeptide Y (NPY) in rats is dependent on dipeptidyl peptidase 4 (DP4) activity and age

Neuropeptide Y (NPY)-induced modulation of the immune and inflammatory responses is regulated by tissue-specific expression of different receptor subtypes (Y1–Y6) and the activity of the enzyme dipeptidyl peptidase 4 (DP4, CD26) which terminates the action of NPY on Y1 receptor subtype. The present study investigated the age-dependent effect of NPY on inflammatory paw edema and macrophage nitric oxide production in Dark Agouti rats exhibiting a high-plasma DP4 activity, as acknowledged earlier. The results showed that NPY suppressed paw edema in adult and aged, but not in young rats. Furthermore, plasma DP4 activity decreased, while macrophage DP4 activity, as well as macrophage CD26 expression increased with aging. The use of NPY-related peptides and Y receptor-specific antagonists revealed that anti-inflammatory effect of NPY is mediated via Y1 and Y5 receptors. NPY-induced suppression of paw edema in young rats following inhibition of DP4 additionally emphasized the role for Y1 receptor in the anti-inflammatory action of NPY. In contrast to the in vivo situation, NPY stimulated macrophage nitric oxide production in vitro only in young rats, and this effect was mediated via Y1 and Y2 receptors. It can be concluded that age-dependant modulation of inflammatory reactions by NPY is determined by plasma, but not macrophage DP4 activity at different ages.     

Activation of the prostaglandin D2 receptor DP2/CRTH2 increases allergic inflammation in mouse

Allergic pathologies are often associated with IgE production, mast cell activation, and eosinophilia. PGD2 is the major eicosanoid, among several inflammatory mediators, released by mast cells. PGD2 binds to two membrane receptors, D prostanoid receptor (DP)1 and DP2, endowed with antagonistic properties. In humans, DP2 is preferentially expressed on type 2 lymphocytes, eosinophils, and basophils and mediates chemotaxis in vitro. Although not yet supported by in vivo studies, DP2 is thought to be important in the promotion of Th2-related inflammation. Herein, we demonstrate that mouse eosinophils express both DP1 and DP2 and that PGD2 exerts in vitro chemotactic effects on eosinophils through DP2 activation. Furthermore, 13,14-dihydro-15-keto-PGD2, a specific DP2 agonist not only increases eosinophil recruitment at inflammatory sites but also the pathology in two in vivo models of allergic inflammation: atopic dermatitis and allergic asthma. By contrast, DP1 activation tends to ameliorate the pathology in asthma. Taken together, these results support the hypothesis that DP2 might play a critical role in allergic diseases and underline the interest of DP2 antagonists in human therapy.     

The DP receptor,allergic inflammation and asthma

Prostaglandin (PG) D(2) is the major cyclooxygenase metabolite of arachidonic acid produced by mast cells in response to allergen in diseases, such as asthma, atopic dermatitis, allergic rhinitis and allergic conjunctivitis. However, whether PGD(2) regulates allergic process per se, and, if so, whether it facilitates or down-regulates the disease process has remained unknown. PGD(2) exerts its actions by binding to two types of specific cell surface receptor. One is DP (the PGD receptor) and the other is chemoattractant receptor-homologous molecule expressed on Th2. Between the two, the DP receptor has been better characterized since its cDNA cloning in 1994, and novel class of DP antagonists have been and are being developed. Furthermore, mice deficient in DP were generated and have been subjected to several models of allergic diseases to reveal the role of PGD(2) in allergy. In this article, we summarize these findings and provide an overview of the current status of the DP receptor research to discuss the therapeutic potential of modulating the PGD(2)-DP pathway in allergic diseases.     

2,3-Diarylthiophenes as selective EP1 receptor antagonists

The synthesis and the EP(1) receptor binding affinity of 2,3-diarylthiophene derivatives are described. The evaluation of the structure-activity relationship (SAR) in this series led to the identification of compounds 4, 7, and 12a, which exhibit high affinity for the human EP(1) receptor and a selectivity greater than 100-fold against the EP(2), EP(3), EP(4), DP, FP, and IP receptors and greater than 25-fold versus the TP receptor. These three antagonists present good pharmacokinetics in rats and significant differences in the way they are distributed in the brain.     

Metabolic activation of indole-containing prostaglandin D2 receptor 1 antagonists: impacts of glutathione trapping and glucuronide conjugation on covalent binding

Some DP1 receptor antagonists from an indole-containing series were shown to cause in vitro covalent binding to protein in rat and human liver microsomes. Glutathione trapping experiments along with in vitro labeling assays confirmed that the presence of a strong electron withdrawing group was necessary to abrogate in vitro covalent binding, leading to the discovery of MK-0524. Hepatocyte incubations and in vivo studies showed that acyl-glucuronide formation did not translate into covalent binding.     

Novel tricyclic antagonists of the prostaglandin D2 receptor DP2 with efficacy in a murine model of allergic rhinitis

The synthesis of a series of tricyclic antagonists for the prostaglandin D₂ receptor DP2 (CRTH2) is disclosed. The activities of the compounds were evaluated in a human DP2 binding assay and a human whole blood eosinophil shape change assay. Potential metabolic liabilities of the compounds were addressed through in vitro CYP studies. The lead compound was demonstrated to have efficacy in a mouse model of allergic rhinitis following oral dosing.     

Discovery and optimization of a biphenylacetic acid series of prostaglandin D2 receptor DP2 antagonists with efficacy in a murine model of allergic rhinitis

Biphenylacetic acid (5) was identified through a library screen as an inhibitor of the prostaglandin D(2) receptor DP2 (CRTH2). Optimization for potency and pharmacokinetic properties led to a series of selective CRTH2 antagonists. Compounds demonstrated potency in a human DP2 binding assay and a human whole blood eosinophil shape change assay, as well as good oral bioavailability in rat and dog, and efficacy in a mouse model of allergic rhinitis following oral dosing.     

Optimization of phenylacetic acid derivatives for CRTH2 and DP selective antagonism

We have previously reported that optimization of a series of phenylacetic acid derivatives led to the discovery of CRTH2 and DP dual antagonists, such as AMG 009 and AMG 853. During the optimization process, we discovered that minor structural modifications also afforded potent and selective CRTH2 or DP antagonists. Here we report the structure-activity relationship that led to the discovery of selective CRTH2 antagonists such as 2 and 17, and selective DP antagonists, such as 4 and 5.     

Switching between agonists and antagonists at CRTh2 in a series of highly potent and selective biaryl phenoxyacetic acids

A novel series of biaryl phenoxyacetic acids was discovered as potent, selective antagonists of the chemoattractant receptor-homologous expressed on Th2 lymphocytes receptor (CRTh2 or DP2). A hit compound 4 was discovered from high throughput screening. Modulation of multiple aryl substituents afforded both agonists and antagonists, with small changes often reversing the mode of action. Understanding the complex SAR allowed design of potent antagonists such as potential candidate 34.     

The role of the prostaglandin D2 receptor, DP, in eosinophil trafficking

Prostaglandin (PG) D2 is a major mast cell product that acts via two receptors, the D-type prostanoid (DP) and the chemoattractant receptor-homologous molecule expressed on Th2 cells (CRTH2) receptors. Whereas CRTH2 mediates the chemotaxis of eosinophils, basophils, and Th2 lymphocytes, the role of DP has remained unclear. We report in this study that, in addition to CRTH2, the DP receptor plays an important role in eosinophil trafficking. First, we investigated the release of eosinophils from bone marrow using the in situ perfused guinea pig hind limb preparation. PGD2 induced the rapid release of eosinophils from bone marrow and this effect was inhibited by either the DP receptor antagonist BWA868c or the CRTH2 receptor antagonist ramatroban. In contrast, BWA868c did not inhibit the release of bone marrow eosinophils when this was induced by the CRTH2-selective agonist 13,14-dihydro-15-keto-PGD2. In additional experiments, we isolated bone marrow eosinophils from the femoral cavity and found that these cells migrated toward PGD2. We also observed that BWA868c inhibited this response to a similar extent as ramatroban. Finally, using immunohistochemistry we could demonstrate that eosinophils in human bone marrow specimens expressed DP and CRTH2 receptors at similar levels. Eosinophils isolated from human peripheral blood likewise expressed DP receptor protein but at lower levels than CRTH2. In agreement with this, the chemotaxis of human peripheral blood eosinophils was inhibited both by BWA868c and ramatroban. These findings suggest that DP receptors comediate with CRTH2 the mobilization of eosinophils from bone marrow and their chemotaxis, which might provide the rationale for DP antagonists in the treatment of allergic disease.     

Substituted indole-1-acetic acids as potent and selective CRTh2 antagonists-discovery of AZD1981

Novel indole-3-thio-, 3-sulfonyl- and 3-oxy-aryl-1-acetic acids are reported which are potent, selective antagonists of the chemoattractant receptor-homologous expressed on Th2 lymphocytes receptor (CRTh2 or DP2). Optimization required maintenance of high CRTh2 potency whilst achieving a concomitant reduction in rates of metabolism, removal of cyp p450 inhibition and minimization of aldose reductase and aldehyde reductase activity. High quality compounds suitable for in vivo studies are highlighted, culminating in the discovery of AZD1981 (22).     

Discovery of orally active prostaglandin D2 receptor antagonists

A series of N-(p-alkoxy)benzoyl-2-methylindole-4-acetic acids were synthesized and evaluated for prostaglandin D(2) (DP) receptor affinity and antagonist activity. Some of them exhibited strong receptor binding and were potent in the cAMP formation assays. These antagonists also suppressed allergic inflammatory responses such as the PGD(2)-induced increase of microvascular permeability. Structure-activity relationship (SAR) data are presented.     

Design and synthesis of new prostaglandin D₂ receptor antagonists

To identify new cost-effective prostaglandin D? (DP) receptor antagonists, a series of novel 3-benzoylaminophenylacetic acids were synthesized and biologically evaluated. Among those tested, some representative compounds were found to be orally available. Receptor selectivity and rat PK profiles were also evaluated. The structure-activity relationship (SAR) study is presented.