Interaction of new, very potent non-nucleotide antagonists with Arg256 of the human platelet P2Y12 receptor

Microglial TNFα controls daily changes in synaptic GABAARs and sleep slow waves

Microglia sense the changes in their environment. How microglia actively translate these changes into suitable cues to adapt brain physiology is unknown. We reveal an activity-dependent regulation of cortical inhibitory synapses by microglia, driven by purinergic signaling acting on P2RX7 and mediated by microglia-derived TNFα. We demonstrate that sleep induces microglia-dependent synaptic enrichment of GABAARs in a manner dependent on microglial TNFα and P2RX7. We further show that microglia-specific depletion of TNFα alters slow waves during NREM sleep and blunt memory consolidation in sleep-dependent learning tasks. Together, our results reveal that microglia orchestrate sleep-intrinsic plasticity of synaptic GABAARs, sculpt sleep slow waves, and support memory consolidation.

Pharmacological Profile of the Purinergic P2Y Receptors That Modulate, in Response to ADPβS, the Vasodepressor Sensory CGRPergic Outflow in Pithed Rats

Calcitonin gene-related peptide (CGRP), an endogenous neuropeptide released from perivascular sensory nerves, exerts a powerful vasodilatation. Interestingly, adenosine triphosphate (ATP) stimulates the release of CGRP by activation of prejunctional P2X_2/3 receptors, and adenosine 5'-O-2-thiodiphosphate (ADPβS), a stable adenosine diphosphate (ADP) analogue, produces vasodilator/vasodepressor responses by endothelial P2Y₁ receptors. Since the role of ADP in the prejunctional modulation of the vasodepressor sensory CGRPergic drive and the receptors involved remain unknown, this study investigated whether ADPβS inhibits this CGRPergic drive. Accordingly, 132 male Wistar rats were pithed and subsequently divided into two sets. In set 1, ADPβS (5.6 and 10 µg/kg·min) inhibited the vasodepressor CGRPergic responses by electrical stimulation of the spinal T₉-T₁₂ segment. This inhibition by ADPβS (5.6 µg/kg·min) was reverted after i.v. administration of the purinergic antagonists MRS2500 (300 µg/kg; P2Y₁) or MRS2211 (3000 µg/kg; P2Y₁₃), but not by PSB0739 (300 µg/kg; P2Y₁₂), MRS2211 (1000 µg/kg; P2Y₁₃) or the K_ATP blocker glibenclamide (20 mg/kg). In set 2, ADPβS (5.6 µg/kg·min) failed to modify the vasodepressor responses to exogenous α-CGRP. These results suggest that ADPβS inhibits CGRP release in perivascular sensory nerves. This inhibition, apparently unrelated to activation of ATP-sensitive K⁺ channels, involves P2Y₁ and probably P2Y₁₃, but not P2Y₁₂ receptors.

Strategies for targeting the P2Y12 receptor in the central nervous system

The purinergic 2Y type 12 receptor (P2Y₁₂R) is a well-known biological target for anti-thrombotic drugs due to its role in platelet aggregation and blood clotting. While the importance of the P2Y₁₂R in the periphery has been known for decades, much less is known about its expression and roles in the central nervous system (CNS), where it is expressed exclusively on microglia - the first responders to brain insults and neurodegeneration. Several seminal studies have shown that P2Y₁₂ is a robust, translatable biomarker for anti-inflammatory and neuroprotective microglial phenotypes in models of degenerative diseases such as multiple sclerosis and Alzheimer's disease. An enduring problem for studying this receptor in vivo, however, is the lack of selective, high-affinity small molecule ligands that can bypass the blood-brain barrier and accumulate in the CNS. In this Digest, we discuss previous attempts by researchers to target the P2Y₁₂R in the CNS and opine on strategies that may be employed to design and assess the suitability of novel P2Y₁₂ ligands for this purpose going forward.

The dualistic role of the purinergic P2Y12-receptor in an in vivo model of Parkinson's disease: Signalling pathway and novel therapeutic targets

Parkinson's disease (PD) is a chronic, progressive neurodegenerative condition; characterized with the degeneration of the nigrostriatal dopaminergic pathway and neuroinflammation. During PD progression, microglia, the resident immune cells in the central nervous system (CNS) display altered activity, but their role in maintaining PD development has remained unclear to date. The purinergic P2Y12-receptor (P2Y12R), which is expressed on the microglia in the CNS has been shown to regulate microglial activity and responses; however, the function of the P2Y12R in PD is unknown. Here we show that MPTP-induced PD symptoms in mice are associated with marked neuroinflammatory changes and P2Y12R contribute to the activation of microglia and progression of the disease. Surprisingly, while pharmacological or genetic targeting of the P2Y12R augments acute mortality in MPTP-treated mice, these interventions protect against the neurodegenerative cell loss and the development of neuroinflammation in vivo. Pharmacological inhibition of receptors during disease development reverses the symptoms of PD and halts disease progression. We found that P2Y12R regulates ROCK and p38 MAPK activity and control cytokine production. Our principal finding is that the receptor has a dualistic role in PD: functional P2Y12Rs are essential to initiate a protective inflammatory response, since the lack of the receptor leads to reduced survival; however, at later stages of neurodegeneration, P2Y12Rs are apparently responsible for maintaining the activated state of microglia and stimulating pro-inflammatory cytokine response. Understanding protective and detrimental P2Y12R-mediated actions in the CNS may reveal novel approaches to control neuroinflammation and modify disease progression in PD.

Recommended tool compounds and drugs for blocking P2X and P2Y receptors

This review article presents a collection of tool compounds that selectively block and are recommended for studying P2Y and P2X receptor subtypes, investigating their roles in physiology and validating them as future drug targets. Moreover, drug candidates and approved drugs for P2 receptors will be discussed.

Medicinal chemistry of P2 and adenosine receptors: Common scaffolds adapted for multiple targets

Prof. Geoffrey Burnstock originated the concept of purinergic signaling. He demonstrated the interactions and biological roles of ionotropic P2X and metabotropic P2Y receptors. This review paper traces the historical origins of many currently used antagonists and agonists for P2 receptors, as well as adenosine receptors, in early attempts to identify ligands for these receptors - prior to the use of chemical libraries for screening. Rather than presenting a general review of current purinergic ligands, we focus on common chemical scaffolds (privileged scaffolds) that can be adapted for multiple receptor targets. By carefully analyzing the structure activity relationships, one can direct the selectivity of these scaffolds toward different receptor subtypes. For example, the weak and non-selective P2 antagonist reactive blue 2 (RB-2) was derivatized using combinatorial synthetic approaches, leading to the identification of selective P2Y2, P2Y4, P2Y12 or P2X2 receptor antagonists. A P2X4 antagonist NC-2600 is in a clinical trial, and A3 adenosine agonists show promise, for chronic pain. P2X7 antagonists have been in clinical trials for depression (JNJ-54175446), inflammatory bowel disease (IBD), Crohn's disease, rheumatoid arthritis, inflammatory pain and chronic obstructive pulmonary disease (COPD). P2X3 antagonists are in clinical trials for chronic cough, and an antagonist named after Burnstock, gefapixant, is expected to be the first P2X3 antagonist filed for approval. We are seeing that the vision of Prof. Burnstock to use purinergic signaling modulators, most recently at P2XRs, for treating disease is coming to fruition.

Molecular pharmacology of P2Y receptor subtypes

Professor Geoffrey Burnstock proposed the concept of purinergic signaling via P1 and P2 receptors. P2Y receptors are G-protein-coupled receptors (GPCRs) for extracellular adenine and uracil nucleotides. Eight mammalian P2Y receptor subtypes have been identified. They are divided into two subgroups (P2Y₁, P2Y₂, P2Y₄, P2Y₆, and P2Y₁₁) and (P2Y₁₂, P2Y₁₃, and P2Y₁₄). P2Y receptors are found in almost all cells and mediate responses in physiology and pathophysiology including pain and inflammation. The antagonism of platelet P2Y₁₂ receptors by cangrelor, ticagrelor or active metabolites of the thienopyridine compounds ticlopidine, clopidogrel and prasugrel reduces the ADP-induced platelet aggregation in patients with thrombotic complications of vascular diseases. The nucleotide agonist diquafosol acting at P2Y₂ receptors is used for the treatment of the dry eye syndrome. Structural information obtained by crystallography of the human P2Y₁ and P2Y₁₂ receptor proteins, site-directed mutagenesis and molecular modeling will facilitate the rational design of novel selective drugs.

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.

The role of purinergic P2Y12 and P2Y13 receptors in ADPβS-induced inhibition of the cardioaccelerator sympathetic drive in pithed rats

ATP is a cotransmitter released with other neurotransmitters from sympathetic nerves, where it stimulates purinergic receptors. Purinergic adenosine P₁ receptors (coupled to G_i/o proteins) produce sympatho-inhibition in several autonomic effectors by prejunctional inhibition of neurotransmitter release. Similarly, signalling through P2Y₁₂ and P2Y₁₃ receptors coupled to G_i/o proteins is initiated by the ATP breakdown product ADP. Hence, this study has pharmacologically investigated a possible role of ADP-induced inhibition of the cardioaccelerator sympathetic drive in pithed rats, using a stable ADP analogue (ADPβS) and selective antagonists for the purinergic P2Y₁, P2Y₁₂ and P2Y₁₃ receptors. Accordingly, male Wistar rats were pithed and: (i) pretreated i.v. with gallamine (25 mg/kg) and desipramine (50 μg/kg) for preganglionic spinal (C₇-T₁) stimulation of the cardioaccelerator sympathetic drive (n = 78); or (ii) prepared for receiving i.v. injections of exogenous noradrenaline (n = 12). The i.v. continuous infusions of ADPβS (10 and 30 μg/kg/min) dose-dependently inhibited the tachycardic responses to electrical sympathetic stimulation, but not those to exogenous noradrenaline. The cardiac sympatho-inhibition produced by 30 μg/kg/min ADPβS was (after i.v. administration of compounds) (i) unchanged by 1-ml/kg bidistilled water or 300-μg/kg MRS 2500 (P2Y₁ receptor antagonist), (ii) abolished by 300-μg/kg PSB 0739 (P2Y₁₂ receptor antagonist) and (iii) partially blocked by 3000-μg/kg MRS 2211 (P2Y₁₃ receptor antagonist). Our results suggest that ADPβS induces a cardiac sympatho-inhibition that mainly involves the P2Y₁₂ receptor subtype and, probably to a lesser extent, the P2Y₁₃ receptor subtype. These receptors may represent therapeutic targets for treating cardiovascular pathologies, including stroke and myocardial infarctions.

Platelet-Derived Extracellular Vesicles as Target of Antiplatelet Agents. What Is the Evidence?

Platelet-derived large extracellular vesicles (often referred to as microparticles in the field of cardiovascular disease) have been identified as effector in the atherothrombotic process, therefore representing a target of pharmacological intervention of potential interest. Despite that, limited evidence is so far available concerning the effects of antiplatelet agents on the release of platelet-derived extracellular vesicles. In the present narrative review, the mechanisms leading to vesiculation in platelets and the pathophysiological processes implicated will be discussed. This will be followed by a summary of the present evidence concerning the effects of antiplatelet agents under experimental conditions and in clinical settings.

Pharmacology of P2Y receptors

P2Y receptors are G-protein-coupled receptors (GPCRs) for extracellular nucleotides. There are eight mammalian P2Y receptor subtypes divided into two subgroups (P2Y₁, P2Y₂, P2Y₄, P2Y₆, and P2Y₁₁) and (P2Y₁₂, P2Y₁₃, and P2Y₁₄). The P2Y receptors are expressed in various cell types and play important roles in physiology and pathophysiology including inflammatory responses and neuropathic pain. The antagonism of P2Y₁₂ receptors is used in pharmacotherapy for the prevention and therapy of cardiovascular events. The nucleoside analogue ticagrelor and active metabolites of the thienopyridine compounds ticlopidine, clopidogrel and prasugrel inhibit platelet P2Y₁₂ receptors and reduce thereby platelet aggregation. The P2Y₂ receptor agonist diquafosol is used for the treatment of the dry eye syndrome. The P2Y receptor subtypes differ in their amino acid sequences, their pharmacological profiles and their signaling transduction pathways. Recently, selective receptor ligands have been developed for all subtypes. The published crystal structures of the human P2Y₁ and P2Y₁₂ receptors as well as receptor models will facilitate the development of novel drugs for pharmacotherapy.

[PSB0739 inhibits formation of semen-derived amyloid fibril]

OBJECTIVE

To explore the inhibitory effect of PSB0739 on the formation of semen-derived amyloid fibrils.

METHODS

PAP248-286 (440 μmol/L) was incubated with PSB0739 at different concentrations, and at different time points of incubation, aliquots were taken from each sample for Congo red staining to detect the formation of amyloid fibers. The morphology of amyloid fibrils incubated in the presence or absence of PSB0739 was visualized using transmission electron microscope. The effect of PSB0739 on amyloid fibril formation was determined using virus infection assays at different time points, and the surface charges of amyloid fibril incubated with PSB0739 were calculated using a Zeta potentiometer. The cytotoxicity of PSB0739 in Hela cells was determined using MTT assay. The antiviral effect of PSB0738 against HIV- 1 was evaluated by infection assay.

RESULTS

PSB0739 inhibited SEVI fibril formation in a dose-dependent manner in vitro. At 48 h of incubation, 220 μmol/L of PSB0739 obviously inhibited the formation of amyloid fibrils in 440 μmol/L of SEVI. Transmission electron microscopy revealed that 220 μmol/L PSB0739 prevented PAP248- 286 (440 μmol/L) from forming amyloid fibrils. PSB0739 antagonized SEVI-mediated enhancement of HIV-1 infection, and 1760 μmol/L of PSB0739 completely reversed the positive charge of SEVI (P < 0.05). PSB0739 below the concentration of 62.5 μmol/L showed no obvious cytotoxicity in Hela cells in vitro (P>0.05). PSB0739 showed a direct anti-HIV activity with an IC₅₀ of 21.77±5.15 μmol/L.

CONCLUSIONS

PSB0739 can inhibit the formation of semen-derived amyloid fibrils in vitro.

Constitutive P2Y2 receptor activity regulates basal lipolysis in human adipocytes

White adipocytes are key regulators of metabolic homeostasis, which release stored energy as free fatty acids via lipolysis. Adipocytes possess both basal and stimulated lipolytic capacity, but limited information exists regarding the molecular mechanisms that regulate basal lipolysis. Here, we describe a mechanism whereby autocrine purinergic signalling and constitutive P2Y₂ receptor activation suppresses basal lipolysis in primary human in vitro-differentiated adipocytes. We found that human adipocytes possess cytoplasmic Ca²⁺ tone due to ATP secretion and constitutive P2Y₂ receptor activation. Pharmacological antagonism or knockdown of P2Y₂ receptors increases intracellular cAMP levels and enhances basal lipolysis. P2Y₂ receptor antagonism works synergistically with phosphodiesterase inhibitors in elevating basal lipolysis, but is dependent upon adenylate cyclase activity. Mechanistically, we suggest that the increased Ca²⁺ tone exerts an anti-lipolytic effect by suppression of Ca²⁺-sensitive adenylate cyclase isoforms. We also observed that acute enhancement of basal lipolysis following P2Y₂ receptor antagonism alters the profile of secreted adipokines leading to longer-term adaptive decreases in basal lipolysis. Our findings demonstrate that basal lipolysis and adipokine secretion are controlled by autocrine purinergic signalling in human adipocytes.

Antithrombotic P2Y12 receptor antagonists: recent developments in drug discovery

The P2Y₁₂ receptor is one of eight known P2Y receptor subtypes, and belongs to the G-protein-coupled receptor (GPCR) family. The P2Y₁₂ receptor is highly expressed on blood platelets and in the brain. Potent, selective, peripherally acting antagonists for the P2Y₁₂ receptor are used clinically as antithrombotic drugs. Several different scaffolds have been identified as P2Y₁₂ receptor antagonists, including irreversibly acting thienotetrahydropyridines (prodrugs), and reversible competitive antagonists, including adenine nucleotide analogs, piperazinyl-glutamate-quinolines, -pyridines, and -pyrimidines, and anthraquinone derivatives. Here, we provide an overview of the different scaffolds that have been developed as P2Y₁₂ receptor antagonists, some of which have become important therapeutics.

P2Y2 and P2Y6 receptor activation elicits intracellular calcium responses in human adipose-derived mesenchymal stromal cells

Adipose tissue contains self-renewing multipotent cells termed mesenchymal stromal cells. In situ, these cells serve to expand adipose tissue by adipogenesis, but their multipotency has gained interest for use in tissue regeneration. Little is known regarding the repertoire of receptors expressed by adipose-derived mesenchymal stromal cells (AD-MSCs). The purpose of this study was to undertake a comprehensive analysis of purinergic receptor expression. Mesenchymal stromal cells were isolated from human subcutaneous adipose tissue and confirmed by flow cytometry. The expression profile of purinergic receptors was determined by quantitative real-time PCR and immunocytochemistry. The molecular basis for adenine and uracil nucleotide-evoked intracellular calcium responses was determined using Fura-2 measurements. All the known subtypes of P2X and P2Y receptors, excluding P2X2, P2X3 and P2Y₁₂ receptors, were detected at the mRNA and protein level. ATP, ADP and UTP elicited concentration-dependent calcium responses in mesenchymal cells (N = 7–9 donors), with a potency ranking ADP (EC₅₀ 1.3 ± 1.0 μM) > ATP (EC₅₀ 2.2 ± 1.1 μM) = UTP (3.2 ± 2.8 μM). Cells were unresponsive to UDP (< 30 μM) and UDP-glucose (< 30 μM). ATP responses were attenuated by selective P2Y₂ receptor antagonism (AR-C118925XX; IC₅₀ 1.1 ± 0.8 μM, 73.0 ± 8.5% max inhibition; N = 7 donors), and UTP responses were abolished. ADP responses were attenuated by the selective P2Y₆ receptor antagonist, MRS2587 (IC₅₀ 437 ± 133nM, 81.0 ± 8.4% max inhibition; N = 6 donors). These data demonstrate that adenine and uracil nucleotides elicit intracellular calcium responses in human AD-MSCs with a predominant role for P2Y₂ and P2Y₆ receptor activation. This study furthers understanding about how human adipose-derived mesenchymal stromal cells can respond to external signalling cues.

Structure, Pharmacology and Roles in Physiology of the P2Y12 Receptor

P2Y receptors are G-protein-coupled receptors (GPCRs) for extracellular nucleotides. The platelet ADP-receptor which has been denominated P2Y₁₂ receptor is an important target in pharmacotherapy. The receptor couples to G_αi2 mediating an inhibition of cyclic AMP accumulation and additional downstream events including the activation of phosphatidylinositol-3-kinase and Rap1b proteins. The nucleoside analogue ticagrelor and active metabolites of the thienopyridine compounds ticlopidine, clopidogrel and prasugrel block P2Y₁₂ receptors and, thereby, inhibit ADP-induced platelet aggregation. These drugs are used for the prevention and therapy of cardiovascular events such as acute coronary syndromes or stroke. The recently published three-dimensional crystal structures of the human P2Y₁₂ receptor in complex with agonists and antagonists will facilitate the development of novel therapeutic agents with reduced adverse effects. P2Y₁₂ receptors are also expressed on vascular smooth muscle cells and may be involved in the pathophysiology of atherogenesis. P2Y₁₂ receptors on microglial cells operate as sensors for adenine nucleotides released during brain injury. A recent study indicated the involvement of microglial P2Y₁₂ receptors in the activity-dependent neuronal plasticity. Interestingly, there is evidence for changes in P2Y₁₂ receptor expression in CNS pathologies including Alzheimer's diseases and multiple sclerosis. P2Y₁₂ receptors may also be involved in systemic immune modulating responses and the susceptibility to develop bronchial asthma.

Tools and drugs for uracil nucleotide-activated P2Y receptors

P2Y receptors (P2YRs) are a family of G protein-coupled receptors activated by extracellular nucleotides. Physiological P2YR agonists include purine and pyrimidine nucleoside di- and triphosphates, such as ATP, ADP, UTP, UDP, nucleotide sugars, and dinucleotides. Eight subtypes exist, P2Y₁, P2Y₂, P2Y₄, P2Y₆, P2Y₁₁, P2Y₁₂, P2Y₁₃, and P2Y₁₄, which represent current or potential future drug targets. Here we provide a comprehensive overview of ligands for the subgroup of the P2YR family that is activated by uracil nucleotides: P2Y₂ (UTP, also ATP and dinucleotides), P2Y₄ (UTP), P2Y₆ (UDP), and P2Y₁₄ (UDP, UDP-glucose, UDP-galactose). The physiological agonists are metabolically unstable due to their fast hydrolysis by ectonucleotidases. A number of agonists with increased potency, subtype-selectivity and/or enzymatic stability have been developed in recent years. Useful P2Y₂R agonists include MRS2698 (6-01, highly selective) and PSB-1114 (6-05, increased metabolic stability). A potent and selective P2Y₂R antagonist is AR-C118925 (10-01). For studies of the P2Y₄R, MRS4062 (3-15) may be used as a selective agonist, while PSB-16133 (10-06) is a selective antagonist. Several potent P2Y₆R agonists have been developed including 5-methoxyuridine 5'-O-((R_p)α-boranodiphosphate) (6-12), PSB-0474 (3-11), and MRS2693 (3-26). The isocyanate MRS2578 (10-08) is used as a selective P2Y₆R antagonist, although its reactivity and low water-solubility are limiting. With MRS2905 (6-08), a potent and metabolically stable P2Y₁₄R agonist is available, while PPTN (10-14) represents a potent and selective P2Y₁₄R antagonist. The radioligand [³H]UDP can be used to label P2Y₁₄Rs. In addition, several fluorescent probes have been developed. Uracil nucleotide-activated P2YRs show great potential as drug targets, especially in inflammation, cancer, cardiovascular and neurodegenerative diseases.

Microglial Ramification, Surveillance, and Interleukin-1β Release Are Regulated by the Two-Pore Domain K+ Channel THIK-1

Microglia exhibit two modes of motility: they constantly extend and retract their processes to survey the brain, but they also send out targeted processes to envelop sites of tissue damage. We now show that these motility modes differ mechanistically. We identify the two-pore domain channel THIK-1 as the main K⁺ channel expressed in microglia in situ. THIK-1 is tonically active, and its activity is potentiated by P2Y₁₂ receptors. Inhibiting THIK-1 function pharmacologically or by gene knockout depolarizes microglia, which decreases microglial ramification and thus reduces surveillance, whereas blocking P2Y₁₂ receptors does not affect membrane potential, ramification, or surveillance. In contrast, process outgrowth to damaged tissue requires P2Y₁₂ receptor activation but is unaffected by blocking THIK-1. Block of THIK-1 function also inhibits release of the pro-inflammatory cytokine interleukin-1β from activated microglia, consistent with K⁺ loss being needed for inflammasome assembly. Thus, microglial immune surveillance and cytokine release require THIK-1 channel activity.

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The two-pore domain channel THIK-1 is the main K⁺ channel in “resting” microglia

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Tonic activity of THIK-1 maintains the microglial resting potential

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Blocking THIK-1 reduces microglial ramification, surveillance, and IL-1β release

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Surveillance depends on THIK-1, not P2Y₁₂; chemotaxis depends on P2Y₁₂, not THIK-1

Rapid and accurate assessment of GPCR-ligand interactions Using the fragment molecular orbital-based density-functional tight-binding method

The reliable and precise evaluation of receptor–ligand interactions and pair‐interaction energy is an essential element of rational drug design. While quantum mechanical (QM) methods have been a promising means by which to achieve this, traditional QM is not applicable for large biological systems due to its high computational cost. Here, the fragment molecular orbital (FMO) method has been used to accelerate QM calculations, and by combining FMO with the density‐functional tight‐binding (DFTB) method we are able to decrease computational cost 1000 times, achieving results in seconds, instead of hours. We have applied FMO‐DFTB to three different GPCR–ligand systems. Our results correlate well with site directed mutagenesis data and findings presented in the published literature, demonstrating that FMO‐DFTB is a rapid and accurate means of GPCR–ligand interactions. © 2017 Authors. Journal of Computational Chemistry Published by Wiley Periodicals, Inc.

Contribution of platelet P2Y12 receptors to chronic Complete Freund's adjuvant-induced inflammatory pain

Essentials The role of platelet P2Y12 receptors in the regulation of chronic inflammatory pain is unknown. Complete Freund's Adjuvant (CFA)-induced chronic inflammatory pain model was used in mice. Gene deficiency and antagonists of P2Y12 receptors attenuate hyperalgesia and local inflammation. Platelet P2Y12 receptors contribute to these effects in the chronic phase of inflammation.

SUMMARY

Background P2Y12 receptor antagonists are widely used in clinical practice to inhibit platelet aggregation. P2Y12 receptors are also known to regulate different forms of pain as well as local and systemic inflammation. However, it is not known whether platelet P2Y12 receptors contribute to these effects. Objectives To explore the contribution of platelet P2Y12 receptors to chronic inflammatory pain in mice. Methods Complete Freund's adjuvant (CFA)-induced chronic inflammatory pain was induced in wild-type and P2ry12 gene-deficient (P2ry12-/- ) mice, and the potent, direct-acting and reversible P2Y12 receptor antagonists PSB-0739 and cangrelor were used. Results CFA-induced mechanical hyperalgesia was significantly decreased in P2ry12-/- mice for up to 14 days, and increased neutrophil myeloperoxidase activity and tumor necrosis factor (TNF)-α and CXCL1 (KC) levels in the hind paws were also attenuated in the acute inflammation phase. At day 14, increased interleukin (IL)-1β, IL-6, TNF-α and KC levels were attenuated in P2ry12-/- mice. PSB-0739 and cangrelor reversed hyperalgesia in wild-type mice but had no effect in P2ry12-/- mice, and PSB-0739 was also effective when applied locally. The effects of both local and systemic PSB-0739 were prevented by A-803467, a selective NaV1.8 channel antagonist, suggesting the involvement of NaV1.8 channels in the antihyperalgesic effect. Platelet depletion by anti-mouse CD41 antibody decreased hyperalgesia and attenuated the proinflammatory cytokine response in wild-type but not in P2ry12-/- mice on day 14. Conclusions In conclusion, P2Y12 receptors regulate CFA-induced hyperalgesia and the local inflammatory response, and platelet P2Y12 receptors contribute to these effects in the chronic inflammation phase.

Development of Potent and Selective Antagonists for the UTP-Activated P2Y4 Receptor

P2Y₄ is a G_q protein-coupled receptor activated by uridine-5'-triphosphate (UTP), which is widely expressed in the body, e.g., in intestine, heart, and brain. No selective P2Y₄ receptor antagonist has been described so far. Therefore, we developed and optimized P2Y₄ receptor antagonists based on an anthraquinone scaffold. Potency was assessed by a fluorescence-based assay measuring inhibition of UTP-induced intracellular calcium release in 1321N1 astrocytoma cells stably transfected with the human P2Y₄ receptor. The most potent compound of the present series, sodium 1-amino-4-[4-(2,4-dimethylphenylthio)phenylamino]-9,10-dioxo-9,10-dihydroanthracene-2-sulfonate (PSB-16133, 61) exhibited an IC₅₀ value of 233 nM, selectivity versus other P2Y receptor subtypes, and is thought to act as an allosteric antagonist. A receptor homology model was built and docking studies were performed to analyze ligand-receptor interactions. Compound 64 (PSB-1699, sodium 1-amino-4-[4-(3-pyridin-3-ylmethylthio)phenylamino]-9,10-dioxo-9,10-dihydroanthracene-2-sulfonate) represents the most selective P2Y₄ receptor antagonist known to date. Compounds 61 and 64 are therefore anticipated to become useful tools for studying this scarcely investigated receptor.

Inverse agonism at the P2Y12 receptor and ENT1 transporter blockade contribute to platelet inhibition by ticagrelor

Ticagrelor is a potent antagonist of the P2Y₁₂ receptor (P2Y₁₂R) and consequently an inhibitor of platelet activity effective in the treatment of atherothrombosis. Here, we sought to further characterize its molecular mechanism of action. Initial studies showed that ticagrelor promoted a greater inhibition of adenosine 5'-diphosphate (ADP)-induced Ca²⁺ release in washed platelets vs other P2Y₁₂R antagonists. This additional effect of ticagrelor beyond P2Y₁₂R antagonism was in part as a consequence of ticagrelor inhibiting the equilibrative nucleoside transporter 1 (ENT1) on platelets, leading to accumulation of extracellular adenosine and activation of G_s-coupled adenosine A_2A receptors. This contributed to an increase in basal cyclic adenosine monophosphate (cAMP) and vasodilator-stimulated phosphoprotein phosphorylation (VASP-P). In addition, ticagrelor increased platelet cAMP and VASP-P in the absence of ADP in an adenosine receptor-independent manner. We hypothesized that this increase originated from a direct effect on basal agonist-independent P2Y₁₂R signaling, and this was validated in 1321N1 cells stably transfected with human P2Y₁₂R. In these cells, ticagrelor blocked the constitutive agonist-independent activity of the P2Y₁₂R, limiting basal G_i-coupled signaling and thereby increasing cAMP levels. These data suggest that ticagrelor has the pharmacological profile of an inverse agonist. Based on our results showing insurmountable inhibition of ADP-induced Ca²⁺ release and forskolin-induced cAMP, the mode of antagonism of ticagrelor also appears noncompetitive, at least functionally. In summary, our studies describe 2 novel modes of action of ticagrelor, inhibition of platelet ENT1 and inverse agonism at the P2Y₁₂R that contribute to its effective inhibition of platelet activation.

Antiplatelet Agents Inhibit the Generation of Platelet-Derived Microparticles

Platelet microparticles (PMPs) contribute to thrombogenesis but the effects of antiplatelet drugs on PMPs generation is undefined. The present study investigated the cellular events regulating PMPs shedding, testing in vitro platelet agonists and inhibitors. Platelet-rich plasma from healthy subjects was stimulated with arachidonic acid (AA), U46619, collagen type-I (10 and 1.5 μg/mL), epinephrine, ADP or TRAP-6 and pre-incubated with acetylsalicylic acid (ASA, 100 and 10 μmol/L), SQ-29,548, apyrase, PSB-0739, or eptifibatide. PMPs were detected by flow-cytometry using CD61 and annexin-V as fluorescent markers. Platelet agonists induced annexin V-positive PMPs shedding. The strongest response was to high concentration collagen. ADP-triggered PMPs shedding was dose-independent. ASA reduced PMPs induced by AA- (645, 347–2946 vs. 3061, 446–4901 PMPs/μL; median ad range, n = 9, P < 0.001), collagen 10 μg/mL (5317, 2027–15935 vs. 10252, 4187–46316 PMPs/μL; n = 13, P < 0.001), collagen 1.5 μg/mL (1078, 528–2820 vs. 1465, 582–5948 PMPs/μL; n = 21, P < 0.001) and TRAP-6 (2008, 1621–2495 vs. 2840, 2404–3031 PMPs/μL; n = 3, P < 0.01) but did not affect the response to epinephrine or ADP. The ADP scavenger apyrase reduced PMPs induced by U46619 (1256, 395–2908 vs. 3045, 1119–5494 PMPs/μL, n = 6, P < 0.05), collagen 1.5 μg/mL (1006, 780–1309 vs. 2422, 1839–3494 PMPs/μL, n = 3, P < 0.01) and TRAP-6 (904, 761–1224 vs. 2840, 2404–3031 PMPs/μL, n = 3, P < 0.01). The TP receptor antagonist SQ-29,548 and the P2Y₁₂ receptor antagonist PSB-0739 markedly inhibited PMPs induced by low doses of collagen. Except for high-dose collagen, eptifibatide abolished agonist-induced PMPs release. Both TXA₂ generation and ADP secretion are required as amplifiers of PMP shedding. The crucial role of the fibrinogen receptor and the collagen receptor in PMPs generation, independently of platelet aggregation, was identified.

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.

Blood cells: an historical account of the roles of purinergic signalling

The involvement of purinergic signalling in the physiology of erythrocytes, platelets and leukocytes was recognised early. The release of ATP and the expression of purinoceptors and ectonucleotidases on erythrocytes in health and disease are reviewed. The release of ATP and ADP from platelets and the expression and roles of P1, P2Y(1), P2Y(12) and P2X1 receptors on platelets are described. P2Y(1) and P2X(1) receptors mediate changes in platelet shape, while P2Y(12) receptors mediate platelet aggregation. The changes in the role of purinergic signalling in a variety of disease conditions are considered. The successful use of P2Y(12) receptor antagonists, such as clopidogrel and ticagrelor, for the treatment of thrombosis, myocardial infarction and stroke is discussed.

Pharmacology and structure of P2Y receptors

P2Y receptors are G-protein-coupled receptors (GPCRs) for extracellular nucleotides. There are eight mammalian P2Y receptor subtypes (P2Y1, P2Y2, P2Y4, P2Y6, P2Y11, P2Y12, P2Y13, and P2Y14). P2Y receptors are widely expressed and play important roles in physiology and pathophysiology. One important example is the ADP-induced platelet aggregation mediated by P2Y1 and P2Y12 receptors. Active metabolites of the thienopyridine compounds ticlopidine, clopidogrel and prasugrel as well as the nucleoside analogue ticagrelor block P2Y12 receptors and thereby platelet aggregation. These drugs are used for the prevention and therapy of cardiovascular events. Moreover, P2Y receptors play important roles in the nervous system. Adenine nucleotides modulate neuronal activity and neuronal fibre outgrowth by activation of P2Y1 receptors and control migration of microglia by P2Y12 receptors. UDP stimulates microglial phagocytosis through activation of P2Y6 receptors. There is evidence for a role for P2Y2 receptors in Alzheimer's disease pathology. The P2Y receptor subtypes are highly diverse in both their amino acid sequences and their pharmacological profiles. Selective receptor ligands have been developed for the pharmacological characterization of the receptor subtypes. The recently published three-dimensional crystal structures of the human P2Y1 and P2Y12 receptors will facilitate the development of therapeutic agents that selectively target P2Y receptors. This article is part of the Special Issue entitled 'Purines in Neurodegeneration and Neuroregeneration'.

Modeling ligand recognition at the P2Y12 receptor in light of X-ray structural information

The G protein-coupled P2Y12 receptor (P2Y12R) is an important antithrombotic target and of great interest for pharmaceutical discovery. Its recently solved, highly divergent crystallographic structures in complex either with nucleotides (full or partial agonist) or with a nonnucleotide antagonist raise the question of which structure is more useful to understand ligand recognition. Therefore, we performed extensive molecular modeling studies based on these structures and mutagenesis, to predict the binding modes of major classes of P2Y12R ligands previously reported. Various nucleotide derivatives docked readily to the agonist-bound P2Y12R, but uncharged nucleotide-like antagonist ticagrelor required a hybrid receptor resembling the agonist-bound P2Y12R except for the top portion of TM6. Supervised molecular dynamics (SuMD) of ticagrelor binding indicated interactions with the extracellular regions of P2Y12R, defining possible meta-binding sites. Ureas, sulfonylureas, sulfonamides, anthraquinones and glutamic acid piperazines docked readily to the antagonist-bound P2Y12R. Docking dinucleotides at both agonist- and antagonist-bound structures suggested interactions with two P2Y12R pockets. Thus, our structure-based approach consistently rationalized the main structure-activity relationships within each ligand class, giving useful information for designing improved ligands.

Targeting renal purinergic signalling for the treatment of lithium-induced nephrogenic diabetes insipidus

Lithium still retains its critical position in the treatment of bipolar disorder by virtue of its ability to prevent suicidal tendencies. However, chronic use of lithium is often limited by the development of nephrogenic diabetes insipidus (NDI), a debilitating condition. Lithium-induced NDI is due to resistance of the kidney to arginine vasopressin (AVP), leading to polyuria, natriuresis and kaliuresis. Purinergic signalling mediated by extracellular nucleotides (ATP/UTP), acting via P2Y receptors, opposes the action of AVP on renal collecting duct (CD) by decreasing the cellular cAMP and thus AQP2 protein levels. Taking a cue from this phenomenon, we discovered the potential involvement of ATP/UTP-activated P2Y2 receptor in lithium-induced NDI in rats and showed that P2Y2 receptor knockout mice are significantly resistant to Li-induced polyuria, natriuresis and kaliuresis. Extension of these studies revealed that ADP-activated P2Y12 receptor is expressed in the kidney, and its irreversible blockade by the administration of clopidogrel bisulphate (Plavix(®)) ameliorates Li-induced NDI in rodents. Parallel in vitro studies showed that P2Y12 receptor blockade by the reversible antagonist PSB-0739 sensitizes CD to the action of AVP. Thus, our studies unravelled the potential beneficial effects of targeting P2Y2 or P2Y12 receptors to counter AVP resistance in lithium-induced NDI. If established in further studies, our findings may pave the way for the development of better and safer methods for the treatment of NDI by bringing a paradigm shift in the approach from the current therapies that predominantly counter the anti-AVP effects to those that enhance the sensitivity of the kidney to AVP action.

Purinergic signalling in the enteric nervous system (An overview of current perspectives)

Purinergic Signalling in the Enteric Nervous System involves the regulated release of ATP (or a structurally-related nucleotide) which activates an extensive suite of membrane-inserted receptors (P2X and P2Y subtypes) on a variety of cell types in the gastrointestinal tract. P2X receptors are gated ion-channels permeable to sodium, potassium and calcium. They depolarise cells, act as a pathway for calcium influx to activate calcium-dependent processes and initiate gene transcription, interact at a molecular level as a form of self-regulation with lipids within the cell wall (e.g. PIP2) and cross-react with other membrane-inserted receptors to regulate their activity (e.g. nAChRs). P2Y receptors are metabotropic receptors that couple to G-proteins. They may release calcium ions from intracellular stores to activate calcium-dependent processes, but also may activate calcium-independent signalling pathways and influence gene transcription. Originally ATP was a candidate only for NANC neurotransmission, for inhibitory motoneurons supplying the muscularis externa of the gastrointestinal tract and bringing about the fast IJP. Purinergic signalling later included neuron-neuron signalling in the ENS, via the production of either fast or slow EPSPs. Later still, purinergic signalling included the neuro-epithelial synapse-for efferent signalling to epithelia cells participating in secretion and absorption, and afferent signalling for chemoreception and mechanoreception at the surface of the mucosa. Many aspects of purinergic signalling have since been addressed in a series of highly-focussed and authoritative reviews. In this overview however, the current focus is on key aspects of purinergic signalling where there remains uncertainty and ambiguity, with the view to stimulating further research in these areas.

P2Y12 Receptor Localizes in the Renal Collecting Duct and Its Blockade Augments Arginine Vasopressin Action and Alleviates Nephrogenic Diabetes Insipidus

P2Y12 receptor (P2Y12-R) signaling is mediated through Gi, ultimately reducing cellular cAMP levels. Because cAMP is a central modulator of arginine vasopressin (AVP)-induced water transport in the renal collecting duct (CD), we hypothesized that if expressed in the CD, P2Y12-R may play a role in renal handling of water in health and in nephrogenic diabetes insipidus. We found P2Y12-R mRNA expression in rat kidney, and immunolocalized its protein and aquaporin-2 (AQP2) in CD principal cells. Administration of clopidogrel bisulfate, an irreversible inhibitor of P2Y12-R, significantly increased urine concentration and AQP2 protein in the kidneys of Sprague-Dawley rats. Notably, clopidogrel did not alter urine concentration in Brattleboro rats that lack AVP. Clopidogrel administration also significantly ameliorated lithium-induced polyuria, improved urine concentrating ability and AQP2 protein abundance, and reversed the lithium-induced increase in free-water excretion, without decreasing blood or kidney tissue lithium levels. Clopidogrel administration also augmented the lithium-induced increase in urinary AVP excretion and suppressed the lithium-induced increase in urinary nitrates/nitrites (nitric oxide production) and 8-isoprostane (oxidative stress). Furthermore, selective blockade of P2Y12-R by the reversible antagonist PSB-0739 in primary cultures of rat inner medullary CD cells potentiated the expression of AQP2 and AQP3 mRNA, and cAMP production induced by dDAVP (desmopressin). In conclusion, pharmacologic blockade of renal P2Y12-R increases urinary concentrating ability by augmenting the effect of AVP on the kidney and ameliorates lithium-induced NDI by potentiating the action of AVP on the CD. This strategy may offer a novel and effective therapy for lithium-induced NDI.

Rare platelet GPCR variants: what can we learn?

Platelet-expressed GPCRs are critical regulators of platelet function. Pharmacological blockade of these receptors forms a powerful therapeutic tool in the treatment and prevention of arterial thrombosis associated with coronary atherosclerosis and ischaemic stroke. However, anti-thrombotic drug therapy is associated with high inter-patient variability in therapeutic response and adverse bleeding side effects. In order to optimize the use of existing anti-platelet drugs and to develop new therapies, more detailed knowledge is required relating to the molecular mechanisms that regulate GPCR and therefore platelet function. One approach has been to identify rare, function-disrupting mutations within key platelet proteins in patients with bleeding disorders. In this review, we describe how an integrated functional genomics strategy has contributed important structure-function information about platelet GPCRs with specific emphasis upon purinergic and thromboxane A2 receptors. We also discuss the potential implications these findings have for pharmacotherapy and for understanding the molecular basis of mild bleeding disorders.

Competitive mode and site of interaction of ticagrelor at the human platelet P2Y12 -receptor

BACKGROUND

The G-protein-coupled P2Y12 -receptor plays a crucial role in platelet aggregation. Recently, ticagrelor was licensed as the first perorally active and reversible P2Y12 -receptor antagonist.

OBJECTIVE

The present study investigated the site and the antagonistic mode of action of ticagrelor at wild-type or mutant human P2Y12 -receptors.

METHODS

Recombinant wild-type or mutant human P2Y12 -receptors were stably expressed in Chinese hamster ovary Flp-In cells. Receptor function was assessed by quantification of ADP- and 2-methylthio-ADP-mediated inhibition of forskolin-induced cellular cAMP production either using a [(3) H]cAMP-radioaffinity assay or a cAMP response element-driven luciferase reporter gene assay.

RESULTS

The natural agonist ADP inhibited forskolin-induced cAMP formation at the wild-type P2Y12 -receptor with a lower potency (EC50 209 nm) than the synthetic agonist 2-methylthio-ADP (EC50 1.0 nm). Ticagrelor shifted the concentration-response curves of both agonists in a parallel and surmountable manner to the right. Increasing concentrations of ticagrelor caused increasing shifts. Schild-plot analysis revealed pA2 values of 8.85 for ticagrelor against ADP, and 8.69 against 2-methylthio-ADP, and slopes of the regression lines not different from unity. In cells expressing a recombinant C194A(5.43) -mutant P2Y12 -receptor construct, ticagrelor lost antagonistic potency when tested against ADP or 2-methylthio-ADP.

CONCLUSIONS

The experiments reveal a surmountable and competitive mode of antagonism of ticagrelor at P2Y12 -receptors activated by either the natural agonist ADP or the synthetic agonist 2-methylthio-ADP. Cys194(5.43) is likely to be involved in the interaction of ticagrelor with ADP and 2-methylthio-ADP. The data give new insights into the site and mode of action of ticagrelor at the human P2Y12 -receptor.

Central P2Y12 receptor blockade alleviates inflammatory and neuropathic pain and cytokine production in rodents

In this study the role of P2Y₁₂ receptors (P2Y₁₂R) was explored in rodent models of inflammatory and neuropathic pain and in acute thermal nociception. In correlation with their activity to block the recombinant human P2Y₁₂R, the majority of P2Y₁₂R antagonists alleviated mechanical hyperalgesia dose-dependently, following intraplantar CFA injection, and after partial ligation of the sciatic nerve in rats. They also caused an increase in thermal nociceptive threshold in the hot plate test. Among the six P2Y₁₂R antagonists evaluated in the pain studies, the selective P2Y₁₂ receptor antagonist PSB-0739 was most potent upon intrathecal application.

P2Y₁₂R mRNA and IL-1β protein were time-dependently overexpressed in the rat hind paw and lumbar spinal cord following intraplantar CFA injection. This was accompanied by the upregulation of TNF-α, IL-6 and IL-10 in the hind paw. PSB-0739 (0.3 mg/kg i.t.) attenuated CFA-induced expression of cytokines in the hind paw and of IL-1β in the spinal cord. Subdiaphragmatic vagotomy and the α7 nicotinic acetylcholine receptor antagonist MLA occluded the effect of PSB-0739 (i.t.) on pain behavior and peripheral cytokine induction. Denervation of sympathetic nerves by 6-OHDA pretreatment did not affect the action of PSB-0739. PSB-0739, in an analgesic dose, did not influence motor coordination and platelet aggregation. Genetic deletion of the P2Y₁₂R in mice reproduced the effect of P2Y₁₂R antagonists on mechanical hyperalgesia in inflammatory and neuropathic pain models, on acute thermal nociception and on the induction of spinal IL-1β.

Here we report the robust involvement of the P2Y₁₂R in inflammatory pain. The anti-hyperalgesic effect of P2Y₁₂R antagonism could be mediated by the inhibition of both central and peripheral cytokine production and involves α7-receptor mediated efferent pathways.

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Pharmacological blockade of P2Y₁₂ receptors alleviates inflammatory and neuropathic pain.

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Central inhibition of P2Y₁₂ receptors attenuates cytokine production in the spinal cord.

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Central P2Y₁₂ receptor inhibition attenuates cytokine production in the inflamed hind paw.

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α7-Receptors mediate the effect of P2Y₁₂ receptor blockade on hyperalgesia and cytokine level.

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Genetic deletion of P2Y₁₂ receptors alleviates inflammatory, neuropathic and acute pain.

Therapeutic potentials of ecto-nucleoside triphosphate diphosphohydrolase, ecto-nucleotide pyrophosphatase/phosphodiesterase, ecto-5'-nucleotidase, and alkaline phosphatase inhibitors

The modulatory role of extracellular nucleotides and adenosine in relevance to purinergic cell signaling mechanisms has long been known and is an object of much research worldwide. These extracellular nucleotides are released by a variety of cell types either innately or as a response to patho-physiological stress or injury. A variety of surface-located ecto-nucleotidases (of four major types; nucleoside triphosphate diphosphohydrolases or NTPDases, nucleotide pyrophosphatase/phosphodiesterases or NPPs, alkaline phosphatases APs or ALPs, and ecto-5'-nucleotidase or e5NT) are responsible for meticulously controlling the availability of these important signaling molecules (at their respective receptors) in extracellular environment and are therefore crucial for maintaining the integrity of normal cell functioning. Overexpression of many of these ubiquitous ecto-enzymes has been implicated in a variety of disorders including cell adhesion, activation, proliferation, apoptosis, and degenerative neurological and immunological responses. Selective inhibition of these ecto-enzymes is an area that is currently being explored with great interest and hopes remain high that development of selective ecto-nucleotidase inhibitors will prove to have many beneficial therapeutic implications. The aim of this review is to emphasize and focus on recent developments made in the field of inhibitors of ecto-nucleotidases and to highlight their structure activity relationships wherever possible. Most recent and significant advances in field of NTPDase, NPP, AP, and e5NT inhibitors is being discussed in detail in anticipation of providing prolific leads and relevant background for research groups interested in synthesis of selective ecto-nucleotidase inhibitors.

P2X and P2Y nucleotide receptors as targets in cardiovascular disease

Endogenous nucleotides have widespread actions in the cardiovascular system, but it is only recently that the P2X and P2Y receptor subtypes, at which they act, have been identified and subtype-selective agonists and antagonists developed. These advances have greatly increased our understanding of the physiological and pathophysiological functions of P2X and P2Y receptors, but investigation of the clinical usefulness of selective ligands is at an early stage. Nonetheless, the evidence considered in this review demonstrates clearly that various cardiovascular disorders, including vasospasm, hypertension, congestive heart failure and cardiac damage during ischemic episodes, may be viable targets. With further development of novel, selective agonists and antagonists, our understanding will continue to improve and further therapeutic applications are likely to be discovered.

P2Y receptors in the mammalian nervous system: pharmacology, ligands and therapeutic potential

P2Y receptors for extracellular nucleotides are coupled to activation of a variety of G proteins and stimulate diverse intracellular signaling pathways that regulate functions of cell types that comprise the central nervous system (CNS). There are 8 different subtypes of P2Y receptor expressed in cells of the CNS that are activated by a select group of nucleotide agonists. Here, the agonist selectivity of these 8 P2Y receptor subtypes is reviewed with an emphasis on synthetic agonists with high potency and resistance to degradation by extracellular nucleotidases that have potential applications as therapeutic agents. In addition, the recent identification of a wide variety of subtype-selective antagonists is discussed, since these compounds are critical for discerning cellular responses mediated by activation of individual P2Y receptor subtypes. The functional expression of P2Y receptor subtypes in cells that comprise the CNS is also reviewed and the role of each subtype in the regulation of physiological and pathophysiological responses is considered. Other topics include the role of P2Y receptors in the regulation of blood-brain barrier integrity and potential interactions between different P2Y receptor subtypes that likely impact tissue responses to extracellular nucleotides in the CNS. Overall, current research suggests that P2Y receptors in the CNS regulate repair mechanisms that are triggered by tissue damage, inflammation and disease and thus P2Y receptors represent promising targets for the treatment of neurodegenerative diseases.

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).

G protein-coupled adenosine (P1) and P2Y receptors: ligand design and receptor interactions

The medicinal chemistry and pharmacology of the four subtypes of adenosine receptors (ARs) and the eight subtypes of P2Y receptors (P2YRs, activated by a range of purine and pyrimidine mono- and dinucleotides) has recently advanced significantly leading to selective ligands. X-ray crystallographic structures of both agonist- and antagonist-bound forms of the A(2A)AR have provided unprecedented three-dimensional detail concerning molecular recognition in the binding site and the conformational changes in receptor activation. It is apparent that this ubiquitous cell signaling system has implications for understanding and treating many diseases. ATP and other nucleotides are readily released from intracellular sources under conditions of injury and organ stress, such as hypoxia, ischemia, or mechanical stress, and through channels and vesicular release. Adenosine may be generated extracellularly or by cellular release. Therefore, depending on pathophysiological factors, in a given tissue, there is often a tonic activation of one or more of the ARs or P2YRs that can be modulated by exogenous agents for a beneficial effect. Thus, this field has provided fertile ground for pharmaceutical development, leading to clinical trials of selective receptor ligands as imaging agents or for conditions including cardiac arrhythmias, ischemia/reperfusion injury, diabetes, pain, thrombosis, Parkinson's disease, rheumatoid arthritis, psoriasis, dry eye disease, pulmonary diseases such as cystic fibrosis, glaucoma, cancer, chronic hepatitis C, and other diseases.

Convergent synthesis of the potent P2Y receptor antagonist MG 50-3-1 based on a regioselective Ullmann coupling reaction

MG 50-3-1 (3, trisodium 1-amino-4-{4-[4-chloro-6-(2-sulfophenylamino)-1,3,5-triazin-2-ylamino]-2-sulfophenylamino}-9,10-dioxo-9,10-dihydroanthracene 2-sulfonate) is the most potent and selective antagonist (IC₅₀ 4.6 nM) for "P2Y₁-like" nucleotide-activated membrane receptors in guinea-pig taenia coli responsible for smooth muscle relaxation. Full characterization of the compound, however, e.g., at the human P2Y₁ receptor, which is a novel potential target for antithrombotic drugs, as well as other P2 receptor subtypes, has been hampered due to difficulties in synthesizing the compound in sufficient quantity. MG 50-3-1 would be highly useful as a biological tool for detailed investigation of signal transduction in the gut. We have now developed a convenient, fast, mild, and efficient convergent synthesis of 3 based on retrosynthetic analysis. A new, regioselective Ullmann coupling reaction under microwave irradiation was successfully developed to obtain 1-amino-4-(4-amino-2-sulfophenylamino)-9,10-dioxo-9,10-dihydro-anthracene 2-sulfonate (8). Four different copper catalysts (Cu, CuCl, CuCl₂, and CuSO₄) were investigated at different pH values of sodium phosphate buffer, and in water in the absence or presence of base. Results showed that CuSO₄ in water in the presence of triethylamine provided the best conditions for the regioselective Ullmann coupling reaction yielding the key intermediate compound 8. A new synthon (sodium 2-(4,6-dichloro-1,3,5-triazin-2-ylamino)benzenesulfonate, 13) which can easily be obtained on a gram scale was prepared, and 13 was successfully coupled with 8 yielding the target compound 3.

Development of a comprehensive set of P2 receptor pharmacological research compounds

Pharmacological manipulation of P2X and P2Y receptors has been critical to the elucidation of the biological roles of these receptors within a multitude of physiological and pathological processes. Initial purinergic signalling research made use of compounds based on pyridoxal phosphate, suramin and nucleotide analogues; recently developed compounds are often derivatives of these early tools. Tocris Bioscience first entered the field of purinergic signalling reagents with the commercial release of the pyridoxal phosphate derivative, iso-PPADS. During the past two decades, Tocris has assembled a collection of over 50 compounds for P2 receptor modulation, including research tools commercialised from both academic and industrial laboratories. Recently, a number of P2X subtype-selective compounds have been generated by pharmaceutical company medicinal chemistry programmes, supplementing our range of P2Y-selective compounds. Here, we detail the current, commercially available agonists and antagonists of P2X(1,2/3,3,4,7) and P2Y(1,6,11,12) receptors; considered together, they form the foundations of a comprehensive P2 receptor pharmacological 'toolkit'.

Comparison of three GPCR structural templates for modeling of the P2Y12 nucleotide receptor

The P2Y(12) receptor (P2Y(12)R) is an ADP-activated G protein-coupled receptor (GPCR) that is an important target for antithrombotic drugs. Three homology models of P2Y(12)R were compared, based on different GPCR structural templates: bovine rhodopsin (bRHO), human A(2A) adenosine receptor (A(2A)AR), and human C-X-C chemokine receptor type 4 (CXCR4). By criteria of sequence analysis (25.6% identity in transmembrane region), deviation from helicity in the second transmembrane helix (TM2), docked poses of ligands highlighting the role of key residues, accessibility of a conserved disulfide bridge that is reactive toward irreversibly-binding antagonists, and the presence of a shared disulfide bridge between the third extracellular loop (EL3) and the N-terminus, the CXCR4-based model appeared to be the most consistent with known characteristics of P2Y(12)R. The docked poses of agonist 2MeSADP and charged anthraquinone antagonist PSB-0739 in the binding pocket of P2Y(12)R-CXC agree with previously published site-directed mutagenesis studies of Arg256 and Lys280. A sulfonate at position 2 of the anthraquinone core created a strong interaction with the Lys174(EL2) side chain. The docking poses of the irreversibly-binding, active metabolite (existing as two diastereoisomers in vivo) of the clinically utilized antagonist Clopidogrel were compared. The free thiol group of the 4S diastereoisomer, but not the 4R isomer, was found in close proximity (~4.7 Å) to the sulfur atom of a disulfide bridge involving Cys175, suggesting greater activity in covalent binding. Therefore, ligand docking to the CXCR4-based model of the P2Y(12)R predicted poses of both reversibly and irreversibly-binding small molecules, consistent with observed pharmacology and mutagenesis studies.

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.

Discovery of potent competitive antagonists and positive modulators of the P2X2 receptor

Evaluation and optimization of anthraquinone derivatives related to Reactive Blue 2 at P2X2 receptors yielded the first potent and selective P2X2 receptor antagonists. The compounds were tested for inhibition of ATP (10 μM) mediated currents in Xenopus oocytes expressing the rat P2X2 receptor. The most potent antagonists were sodium 1-amino-4-[3-(4,6-dichloro[1,3,5]triazine-2-ylamino)phenylamino]-9,10-dioxo-9,10-dihydroanthracene-2-sulfonate (63, PSB-10211, IC(50) 86 nM) and disodium 1-amino-4-[3-(4,6-dichloro[1,3,5]triazine-2-ylamino)-4-sulfophenylamino]-9,10-dioxo-9,10-dihydroanthracene-2-sulfonate (57, PSB-1011, IC(50) 79 nM). Compound 57 exhibited a competitive mechanism of action (pA(2) 7.49). It was >100-fold selective versus P2X4, P2X7, and several investigated P2Y receptor subtypes (P2Y(2,4,6,12)); selectivity versus P2X1 and P2X3 receptors was moderate (>5-fold). Compound 57 was >13-fold more potent at the homomeric P2X2 than at the heteromeric P2X2/3 receptor. Several anthraquinone derivatives were found to act as positive modulators of ATP effects at P2X2 receptors, for example, sodium 1-amino-4-(3-phenoxyphenylamino)-9,10-dioxo-9,10-dihydroanthracene-2-sulfonate (51, PSB-10129, EC(50) 489 nM), which led to about a 3-fold increase in the ATP-elicited current.

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.