Pharmacological characterization of P2Y receptor subtypes – an update

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). The widely expressed P2Y receptors play important roles in physiology and pathophysiology. This review summarizes the use of pharmacological tools to characterize the P2Y receptor subtypes involved in these responses. MRS2500 is a potent and selective antagonist acting at the P2Y1 receptor. AR-C118925 is useful for the selective antagonism of the P2Y2 receptor. PSB16133 blocks the P2Y4 receptor, MRS2578 is an antagonist at the P2Y6 receptor and NF157 as well as NF340 block the P2Y11 receptor. ADP-induced platelet aggregation is mediated by P2Y1 and P2Y12 receptors. A number of compounds or their active metabolites reduce ADP-induced platelet aggregation by blocking the P2Y12 receptor. These include the active metabolites of the thienopyridine compounds clopidogrel and prasugrel, the nucleoside analogue ticagrelor and the nucleotide analogue cangrelor. PSB0739 is also a potent antagonist at the P2Y12 receptor useful for both in vitro and in vivo studies. MRS2211 and MRS2603 inhibit P2Y13 mediated responses. PPTN is a very potent antagonist at the P2Y14 receptor.

This article is dedicated to late Professor María Teresa Miras-Portugal.She was a leading scientist in the field of purinergic signaling and P2 receptors for extracellular nucleotides [111][112][113][114].She contributed to many important studies, advisory and editorial boards, the Purine club and the IUPHAR sub-committee for the nomenclature of P2Y receptors.She was the expert in the field of biochemistry, physiology and pharmacology of dinucleoside polyphosphates.
There are eight human subtypes of G-protein-coupled receptors (GPCRs) for extracellular nucleotides, P2Y receptors [23,89].They belong to the delta-subgroup of class A GPCRs [49].The P2Y receptor family can be divided into two subfamilies [2,156].The first subfamily consists of the P2Y 1 , P2Y 2 , P2Y 4 , P2Y 6 and P2Y 11 receptors.The receptors couple via G q -proteins to stimulation of phospholipase C (references in Tables 1, 2, 3, 4, and 5).P2Y 11 -receptors couple in addition through G s and increases in adenylate cyclase activity (references in Table 5).In contrast, the P2Y 12 receptor subfamily (P2Y 12 , P2Y 13 , and P2Y 14 receptors) signals through activation of G i -proteins (references in Tables 6, 7, and 8; see also [83,158,160].P2Y receptors play important roles in physiology and pathophysiology [2,22,24,120,138,139,156,158,159].Genetic knockout models can be used to identify the subtypes involved in responses to nucelotides.A fast alternative is the use of subtype specific ligands modifying cellular or tissue responses.Due to the efforts of medicinal chemistry novel compounds have been developed [10, 80-82, 118, 119, 121, 135, 143].This article discusses pharmacological tools used to characterize P2Y receptor subtypes.
When using nucleotides such as ATP as agonists an interaction with ecto-nucleotidases [172] may be important.Hence, ATP may be degraded to ADP and further to adenosine which may activate adenosine receptors [74].
Suramin and the suramin analogues NF157 and NF340 act as antagonists at the human P2Y 11 receptor Table 5; [109,154].NF340 is selective and slightly more potent Table 5, [109].
Thienopyridine compounds are used for decades to reduce platelet aggregation in patients with cardiovascular diseases [15,26].The active metabolites of clopidogrel Table 6, [144], and prasugrel [149,150] interact in an irreversible manner with Cys97 3.25 of the receptor protein (see red arrow in Fig. 1, [4,41,144].Treatment with prasugrel is more potent when compared to ticlopidine or clopidogrel [15].
The crystallography of P2Y 12 receptor proteins bound to agonists and antagonists will further facilitate the development of novel P2Y 12 receptor ligands [169,170].

Authors' contributions
Ivar von Kügelgen wrote the manuscript and prepared the figure.Funding Open Access funding enabled and organized by Projekt DEAL.Medical faculty of the University of Bonn.

Fig. 1
Fig.1Predicted two-dimensional structure of the human P2Y 12 receptor.TM transmembrane region, EL extracellular loop.Modified from[156].The red arrow indicates Cys97 that is important for the interaction with the active metabolites of clopidogrel and prasugrel[4,41,144] and plays a role in receptor activation[169,170].The roles of the amino acid residues marked in red have been analyzed by Hoffmann et al.[69].Arg256 and Lys280 are important for ligand recognition.

Table 8
Selected ligands acting at the human P2Y 14 -receptor