Tetrahydro-4-quinolinamines identified as novel P2Y(1) receptor antagonists

Exploring bias in platelet P2Y1 signalling: Host defence versus haemostasis

Platelets are necessary for maintaining haemostasis. Separately, platelets are important for the propagation of inflammation during the host immune response against infection. The activation of platelets also causes inappropriate inflammation in various disease pathologies, often in the absence of changes to haemostasis. The separate functions of platelets during inflammation compared with haemostasis are therefore varied and this will be reflected in distinct pathways of activation. The activation of platelets by the nucleotide adenosine diphosphate (ADP) acting on P2Y1 and P2Y12 receptors is important for the development of platelet thrombi during haemostasis. However, P2Y1 stimulation of platelets is also important during the inflammatory response and paradoxically in scenarios where no changes to haemostasis and platelet aggregation occur. In these events, Rho-GTPase signalling, rather than the canonical phospholipase Cβ (PLCβ) signalling pathway, is necessary. We describe our current understanding of these differences, reflecting on recent advances in knowledge of P2Y1 structure, and the possibility of biased agonism occurring from activation via other endogenous nucleotides compared with ADP. Knowledge arising from these different pathways of P2Y1 stimulation of platelets during inflammation compared with haemostasis may help therapeutic control of platelet function during inflammation or infection, while preserving essential haemostasis. LINKED ARTICLES: This article is part of a themed issue on Platelet purinergic receptor and non-thrombotic disease. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v181.4/issuetoc.

Update of P2Y receptor pharmacology: IUPHAR Review 27

Eight G protein-coupled P2Y receptor subtypes respond to extracellular adenine and uracil mononucleotides and dinucleotides. P2Y receptors belong to the δ group of rhodopsin-like GPCRs and contain two structurally distinct subfamilies: P2Y₁ , P2Y₂ , P2Y₄ , P2Y₆ , and P2Y₁₁ (principally G_q protein-coupled P2Y₁ -like) and P2Y_12-14 (principally G_i protein-coupled P2Y₁₂ -like) receptors. Brain P2Y receptors occur in neurons, glial cells, and vasculature. Endothelial P2Y₁ , P2Y₂ , P2Y₄ , and P2Y₆ receptors induce vasodilation, while smooth muscle P2Y₂ , P2Y₄ , and P2Y₆ receptor activation leads to vasoconstriction. Pancreatic P2Y₁ and P2Y₆ receptors stimulate while P2Y₁₃ receptors inhibits insulin secretion. Antagonists of P2Y₁₂ receptors, and potentially P2Y₁ receptors, are anti-thrombotic agents, and a P2Y₂ /P2Y₄ receptor agonist treats dry eye syndrome in Asia. P2Y receptor agonists are generally pro-inflammatory, and antagonists may eventually treat inflammatory conditions. This article reviews recent developments in P2Y receptor pharmacology (using synthetic agonists and antagonists), structure and biophysical properties (using X-ray crystallography, mutagenesis and modelling), physiological and pathophysiological roles, and present and potentially future therapeutic targeting.

Demystifying P2Y1 Receptor Ligand Recognition through Docking and Molecular Dynamics Analyses

We performed a molecular modeling analysis of 100 nucleotide-like bisphosphates and 46 non-nucleotide arylurea derivatives previously reported as P2Y₁R binders using the recently solved hP2Y₁R structures. We initially docked the compounds at the X-ray structures and identified the binding modes of representative compounds highlighting key patterns in the structure-activity relationship (SAR). We subsequently subjected receptor complexes with selected key agonists (2MeSADP and MRS2268) and antagonists (MRS2500 and BPTU) to membrane molecular dynamics (MD) simulations (at least 200 ns run in triplicate, simulation time 0.6-1.6 μs per ligand system) while considering alternative protonation states of nucleotides. Comparing the temporal evolution of the ligand-protein interaction patterns with available site-directed mutagenesis (SDM) data and P2Y₁R apo state simulation provided further SAR insights and suggested reasonable explanations for loss/gain of binding affinity as well as the most relevant charged species for nucleotide ligands. The MD analysis also predicted local conformational changes required for the receptor inactive state to accommodate nucleotide agonists.

Drug-like Antagonists of P2Y Receptors-From Lead Identification to Drug Development

P2Y receptors are expressed in virtually all cells and tissue types and mediate an astonishing array of biological functions, including platelet aggregation, smooth muscle cell proliferation, and immune regulation. The P2Y receptors belong to the G protein-coupled receptor superfamily and are composed of eight members encoded by distinct genes that can be subdivided into two groups on the basis of their coupling to specific G-proteins. Extensive research has been undertaken to find modulators of P2Y receptors, although to date only a limited number of small-molecule P2Y receptor antagonists have been approved by drug/medicines agencies. This Perspective reviews the known P2Y receptor antagonists, highlighting oral drug-like receptor antagonists, and considers future opportunities for the development of small molecules for clinical evaluation.

Discovery of 4-aryl-7-hydroxyindoline-based P2Y1 antagonists as novel antiplatelet agents

Adenosine diphosphate (ADP)-mediated platelet aggregation is signaled through two distinct G protein-coupled receptors (GPCR) on the platelet surface: P2Y12 and P2Y1. Blocking P2Y12 receptor is a clinically well-validated strategy for antithrombotic therapy. P2Y1 antagonists have been shown to have the potential to provide equivalent antithrombotic efficacy as P2Y12 inhibitors with reduced bleeding in preclinical animal models. We have previously reported the discovery of a potent and orally bioavailable P2Y1 antagonist, 1. This paper describes further optimization of 1 by introducing 4-aryl groups at the hydroxylindoline in two series. In the neutral series, 10q was identified with excellent potency and desirable pharmacokinetic (PK) profile. It also demonstrated similar antithrombotic efficacy with less bleeding compared with the known P2Y12 antagonist prasugrel in rabbit efficacy/bleeding models. In the basic series, 20c (BMS-884775) was discovered with an improved PK and liability profile over 1. These results support P2Y1 antagonism as a promising new antiplatelet target.

4-Benzothiazole-7-hydroxyindolinyl diaryl ureas are potent P2Y1 antagonists with favorable pharmacokinetics: low clearance and small volume of distribution

Current antithrombotic discovery efforts target compounds that are highly efficacious in thrombus reduction with less bleeding liability than the standard of care. Preclinical data suggest that P2Y1 antagonists may have lower bleeding liabilities than P2Y12 antagonists while providing similar antithrombotic efficacy. This article describes our continuous SAR efforts in a series of 7-hydroxyindolinyl diaryl ureas. When dosed orally, 4-trifluoromethyl-7-hydroxy-3,3-dimethylindolinyl analogue 4 was highly efficacious in a model of arterial thrombosis in rats with limited bleeding. The chemically labile CF3 group in 4 was then transformed to various groups via a novel one-step synthesis, yielding a series of potent P2Y1 antagonists. Among them, the 4-benzothiazole-substituted indolines had desirable PK properties in rats, specifically, low clearance and small volume of distribution. In addition, compound 40 had high i.v. exposure and modest bioavailability, giving it the best overall profile.

2-Amino-1,3,4-thiadiazoles in the 7-hydroxy-N-neopentyl spiropiperidine indolinyl series as potent P2Y1 receptor antagonists

Blockade of the P2Y1 receptor is important to the treatment of thrombosis with potentially improved safety margins compared with P2Y12 receptor antagonists. Investigation of a series of urea surrogates of the diaryl urea lead 3 led to the discovery of 2-amino-1,3,4-thiadiazoles in the 7-hydroxy-N-neopentyl spiropiperidine indolinyl series as potent P2Y1 receptor antagonists, among which compound 5a was the most potent and the first non-urea analog with platelet aggregation (PA) IC50 less than 0.5 μM with 10 μM ADP. Several 2-amino-1,3,4-thiadiazole analogs such as 5b and 5f had a more favorable pharmacokinetic profile, such as higher Ctrough, lower Cl, smaller Vdss, and similar bioavailability compared with 3.

Identification of 1-{2-[4-chloro-1'-(2,2-dimethylpropyl)-7-hydroxy-1,2-dihydrospiro[indole-3,4'-piperidine]-1-yl]phenyl}-3-{5-chloro-[1,3]thiazolo[5,4-b]pyridin-2-yl}urea, a potent, efficacious and orally bioavailable P2Y(1) antagonist as an antiplatelet agent

Spiropiperidine indoline-substituted diaryl ureas had been identified as antagonists of the P2Y1 receptor. Enhancements in potency were realized through the introduction of a 7-hydroxyl substitution on the spiropiperidinylindoline chemotype. SAR studies were conducted to improve PK and potency, resulting in the identification of compound 3e, a potent, orally bioavailable P2Y1 antagonist with a suitable PK profile in preclinical species. Compound 3e demonstrated a robust antithrombotic effect in vivo and improved bleeding risk profile compared to the P2Y12 antagonist clopidogrel in rat efficacy/bleeding models.

Conformationally constrained ortho-anilino diaryl ureas: discovery of 1-(2-(1'-neopentylspiro[indoline-3,4'-piperidine]-1-yl)phenyl)-3-(4-(trifluoromethoxy)phenyl)urea, a potent, selective, and bioavailable P2Y1 antagonist

Preclinical antithrombotic efficacy and bleeding models have demonstrated that P2Y1 antagonists are efficacious as antiplatelet agents and may offer a safety advantage over P2Y12 antagonists in terms of reduced bleeding liabilities. In this article, we describe the structural modification of the tert-butyl phenoxy portion of lead compound 1 and the subsequent discovery of a novel series of conformationally constrained ortho-anilino diaryl ureas. In particular, spiropiperidine indoline-substituted diaryl ureas are described as potent, orally bioavailable small-molecule P2Y1 antagonists with improved activity in functional assays and improved oral bioavailability in rats. Homology modeling and rat PK/PD studies on benchmark compound 3l will also be presented. Compound 3l was our first P2Y1 antagonist to demonstrate a robust oral antithrombotic effect with mild bleeding liability in the rat thrombosis and hemostasis models.

Potent P2Y1 urea antagonists bearing various cyclic amine scaffolds

A number of new amine scaffolds with good inhibitory activity in the ADP-induced platelet aggregation assay have been found to be potent antagonists of the P2Y1 receptor. SAR optimization led to the identification of isoindoline 3c and piperidine 4a which showed good in vitro binding and functional activities, as well as improved aqueous solubility. Among them, the piperidine 4a showed the best overall profile with favorable PK parameters.

New azole antagonists with high affinity for the P2Y(1) receptor

Five-membered-ring heterocyclic urea mimics have been found to be potent and selective antagonists of the P2Y1 receptor. SAR of the various heterocyclic replacements is presented, as well as side-chain SAR of the more potent thiadiazole ring system which leads to thiadiazole 4c as a new antiplatelet agent.

Discovery of diarylurea P2Y(1) antagonists with improved aqueous solubility

Preclinical data suggests that P2Y1 antagonists, such as diarylurea compound 1, may provide antithrombotic efficacy similar to P2Y12 antagonists and may have the potential of providing reduced bleeding liabilities. This manuscript describes a series of diarylureas bearing solublizing amine side chains as potent P2Y1 antagonists. Among them, compounds 2l and 3h had improved aqueous solubility and maintained antiplatelet activity compared with compound 1. Compound 2l was moderately efficacious in both rat and rabbit thrombosis models and had a moderate prolongation of bleeding time in rats similar to that of compound 1.

Discovery of 2-(phenoxypyridine)-3-phenylureas as small molecule P2Y1 antagonists

Two distinct G protein-coupled purinergic receptors, P2Y1 and P2Y12, mediate ADP-driven platelet activation. The clinical effectiveness of P2Y12 blockade is well established. Recent preclinical data suggest that P2Y1 and P2Y12 inhibition provide equivalent antithrombotic efficacy, while targeting P2Y1 has the potential for reduced bleeding liability. In this account, the discovery of a 2-(phenoxypyridine)-3-phenylurea chemotype that inhibited ADP-mediated platelet aggregation in human blood samples is described. Optimization of this series led to the identification of compound 16, 1-(2-(2-tert-butylphenoxy)pyridin-3-yl)-3-4-(trifluoromethoxy)phenylurea, which demonstrated a 68 ± 7% thrombus weight reduction in an established rat arterial thrombosis model (10 mg/kg plus 10 mg/kg/h) while only prolonging cuticle and mesenteric bleeding times by 3.3- and 3.1-fold, respectively, in provoked rat bleeding time models. These results suggest that a P2Y1 antagonist could potentially provide a safe and efficacious antithrombotic profile.

Quinoline: A versatile heterocyclic

Quinoline or 1-aza-naphthalene is a weak tertiary base. Quinoline ring has been found to possess antimalarial, anti-bacterial, antifungal, anthelmintic, cardiotonic, anticonvulsant, anti-inflammatory, and analgesic activity. Quinoline not only has a wide range of biological and pharmacological activities but there are several established protocols for the synthesis of this ring. The article aims at highlighting these very diversities of the ring.

Molecular Structure of P2Y Receptors: Mutagenesis, Modeling, and Chemical Probes

There are eight subtypes of P2Y receptors (P2YRs) that are activated, and in some cases inhibited, by a range of extracellular nucleotides. These nucleotides are ubiquitous, but their extracellular concentration can rise dramatically in response to hypoxia, ischemia, or mechanical stress, injury, and release through channels and from vesicles. Two subclasses of P2YRs were defined based on clustering of sequences, second messengers, and receptor sequence analysis. The numbering system for P2YR subtypes is discontinuous; i.e., P2Y(1-14)Rs have been defined, but six of the intermediate-numbered cloned receptor sequences (e.g., P2y(3), P2y(5), P2y(7-10)) are not functional mammalian nucleotide receptors. Of these two clusters, the P2Y(12-14) subtypes couple via Gα(i) to inhibit adenylate cyclase, while the remaining subtypes couple through Gα(q) to activate phospholipase C. Collectively, the P2YRs respond to both purine and pyrimidine nucleotides, in the form of 5'-mono- and dinucleotides and nucleoside-5'-diphosphosugars. In recent years, the medicinal chemistry of P2Y receptors has advanced significantly, to provide selective agonists and antagonists for many but not all of the subtypes. Ligand design has been aided by insights from structural probing using molecular modelling and mutagenesis. Currently, the molecular modelling of the receptors is effectively based on the X-ray structure of the CXCR4 receptor, which is the closest to the P2Y receptors among all the currently crystallized receptors in terms of sequence similarity. It is now a challenge to develop novel and selective P2YR ligands for disease treatment (although antagonists of the P2Y(12)R are already widely used as antithrombotics).

Virtual screening leads to the discovery of novel non-nucleotide P2Y₁ receptor antagonists

The P2Y(1) receptor (P2Y(1)R) is a G protein-coupled receptor naturally activated by extracellular ADP. Its stimulation is an essential requirement of ADP-induced platelet aggregation, thus making antagonists highly sought compounds for the development of antithrombotic agents. Here, through a virtual screening campaign based on a pharmacophoric representation of the common characteristics of known P2Y(1)R ligands and the putative shape and size of the receptor binding pocket, we have identified novel antagonist hits of μM affinity derived from a N,N'-bis-arylurea chemotype. Unlike the vast majority of known P2Y(1)R antagonists, these drug-like compounds do not have a nucleotidic scaffold or highly negatively charged phosphate groups. Hence, our compounds may provide a direction for the development of receptor probes with altered physicochemical properties.

P2 receptors and platelet function

Following vessel wall injury, platelets adhere to the exposed subendothelium, become activated and release mediators such as TXA(2) and nucleotides stored at very high concentration in the so-called dense granules. Released nucleotides and other soluble agents act in a positive feedback mechanism to cause further platelet activation and amplify platelet responses induced by agents such as thrombin or collagen. Adenine nucleotides act on platelets through three distinct P2 receptors: two are G protein-coupled ADP receptors, namely the P2Y(1) and P2Y(12) receptor subtypes, while the P2X(1) receptor ligand-gated cation channel is activated by ATP. The P2Y(1) receptor initiates platelet aggregation but is not sufficient for a full platelet aggregation in response to ADP, while the P2Y(12) receptor is responsible for completion of the aggregation to ADP. The latter receptor, the molecular target of the antithrombotic drugs clopidogrel, prasugrel and ticagrelor, is responsible for most of the potentiating effects of ADP when platelets are stimulated by agents such as thrombin, collagen or immune complexes. The P2X(1) receptor is involved in platelet shape change and in activation by collagen under shear conditions. Each of these receptors is coupled to specific signal transduction pathways in response to ADP or ATP and is differentially involved in all the sequential events involved in platelet function and haemostasis. As such, they represent potential targets for antithrombotic drugs.

Pharmacochemistry of the platelet purinergic receptors

Platelets contain at least five purinergic G protein-coupled receptors, e.g., the pro-aggregatory P2Y(1) and P2Y(12) receptors, a P2Y(14) receptor (GPR105) of unknown function, and anti-aggregatory A(2A) and A(2B) adenosine receptor (ARs), in addition to the ligand-gated P2X1 ion channel. Probing the structure-activity relationships (SARs) of the P2X and P2Y receptors for extracellular nucleotides has resulted in numerous new agonist and antagonist ligands. Selective agents derived from known ligands and novel chemotypes can be used to help define the subtypes pharmacologically. Some of these agents have entered into clinical trials in spite of the challenges of drug development for these classes of receptors. The functional architecture of P2 receptors was extensively explored using mutagenesis and molecular modeling, which are useful tools in drug discovery. In general, novel drug delivery methods, prodrug approaches, allosteric modulation, and biased agonism would be desirable to overcome side effects that tend to occur even with receptor subtype-selective ligands. Detailed SAR analyses have been constructed for nucleotide and non-nucleotide ligands at the P2Y(1), P2Y(12), and P2Y(14) receptors. The thienopyridine antithrombotic drugs Clopidogrel and Prasugrel require enzymatic pre-activation in vivo and react irreversibly with the P2Y(12) receptor. There is much pharmaceutical development activity aimed at identifying reversible P2Y(12) receptor antagonists. The screening of chemically diverse compound libraries has identified novel chemotypes that act as competitive, non-nucleotide antagonists of the P2Y(1) receptor or the P2Y(12) receptor, and antithrombotic properties of the structurally optimized analogues were demonstrated. In silico screening at the A(2A) AR has identified antagonist molecules having novel chemotypes. Fluorescent and other reporter groups incorporated into ligands can enable new technology for receptor assays and imaging. The A(2A) agonist CGS21680 and the P2Y(1) receptor antagonist MRS2500 were derivatized for covalent attachment to polyamidoamine dendrimeric carriers of MW 20,000, and the resulting multivalent conjugates inhibited ADP-promoted platelet aggregation. In conclusion, a wide range of new pharmacological tools is available to control platelet function by interacting with cell surface purine receptors.

Molecular pharmacology, physiology, and structure of the P2Y receptors

The P2Y receptors are a widely expressed group of eight nucleotide-activated G protein-coupled receptors (GPCRs). The P2Y(1)(ADP), P2Y(2)(ATP/UTP), P2Y(4)(UTP), P2Y(6)(UDP), and P2Y(11)(ATP) receptors activate G(q) and therefore robustly promote inositol lipid signaling responses. The P2Y(12)(ADP), P2Y(13)(ADP), and P2Y(14)(UDP/UDP-glucose) receptors activate G(i) leading to inhibition of adenylyl cyclase and to Gβγ-mediated activation of a range of effector proteins including phosphoinositide 3-kinase-γ, inward rectifying K(+) (GIRK) channels, phospholipase C-β2 and -β3, and G protein-receptor kinases 2 and 3. A broad range of physiological responses occur downstream of activation of these receptors ranging from Cl(-) secretion by epithelia to aggregation of platelets to neurotransmission. Useful structural models of the P2Y receptors have evolved from extensive genetic analyses coupled with molecular modeling based on three-dimensional structures obtained for rhodopsin and several other GPCRs. Selective ligands have been synthesized for most of the P2Y receptors with the most prominent successes attained with highly selective agonist and antagonist molecules for the ADP-activated P2Y(1) and P2Y(12) receptors. The widely prescribed drug, clopidogrel, which results in irreversible blockade of the platelet P2Y(12) receptor, is the most important therapeutic agent that targets a P2Y receptor.

P2Y nucleotide receptors: promise of therapeutic applications

Extracellular nucleotides, such as ATP and UTP, have distinct signaling roles through a class of G-protein-coupled receptors, termed P2Y. The receptor ligands are typically charged molecules of low bioavailability and stability in vivo. Recent progress in the development of selective agonists and antagonists for P2Y receptors and study of knockout mice have led to new drug concepts based on these receptors. The rapidly accelerating progress in this field has already resulted in drug candidates for cystic fibrosis, dry eye disease and thrombosis. On the horizon are novel treatments for cardiovascular diseases, inflammatory diseases and neurodegeneration.