The G Protein-Coupled Receptor GPR17: Overview and Update.

The GPR17 receptor is a G protein-coupled receptor (GPCR) that seems to respond to two unrelated families of endogenous ligands: nucleotide sugars (UDP, UDP-galactose, and UDP-glucose) and cysteinyl leukotrienes (LTD , LTC , and LTE ), with significant affinity at micromolar and nanomolar concentrations, respectively. This receptor has a broad distribution at the level of the central nervous system (CNS) and is found in neurons and in a subset of oligodendrocyte precursor cells (OPCs). Unfortunately, disparate results emerging from different laboratories have resulted in a lack of clarity with regard to the role of GPR17-targeting ligands in OPC differentiation and in myelination.

2',3'-O-Substituted ATP derivatives as potent antagonists of purinergic P2X3 receptors and potential analgesic agents.

Blocking membrane currents evoked by the activation of purinergic P2X3 receptors localized on nociceptive neurons represents a promising strategy for the development of agents useful for the treatment of chronic pain conditions. Among compounds endowed with such antagonistic action, 2',3'-O-(2,4,6-trinitrophenyl)-ATP (TNP-ATP) is an ATP analogue, whose inhibitory activity on P2X receptors has been previously reported. Based on the results of molecular modelling studies performed with homology models of the P2X3 receptor, novel adenosine nucleotide analogues bearing cycloalkyl or arylalkyl substituents replacing the trinitrophenyl moiety of TNP-ATP were designed and synthesized.

Imidazo[1,2-a]pyrazin-8-amine core for the design of new adenosine receptor antagonists: Structural exploration to target the A and A subtypes.

The imidazo[1,2-a]pyrazine ring system has been chosen as a new decorable core skeleton for the design of novel adenosine receptor (AR) antagonists targeting either the human (h) A or the hA receptor subtype. The N-(hetero)arylcarboxyamido substituted compounds 4-14 and 21-30, bearing a 6-phenyl moiety or not, respectively, show good hA receptor affinity and selectivity versus the other ARs. In contrast, the 8-amino-6-(hetero)aryl substituted derivatives designed for targeting the hA receptor subtype (compounds 31-38) and also the 6-phenyl analogues 18-20 do not bind the hA AR, or show hA or balanced hA/hA AR affinity in the micromolar range.

Simulation and Comparative Analysis of Different Binding Modes of Non-nucleoside Agonists at the A2A Adenosine Receptor.

Non-nucleoside agonists of adenosine receptors were analysed at the A2A adenosine receptor to simulate and compare their possible binding modes. The docking studies were performed by using different arrangements of the binding cavity and various docking tools. Mutagenesis results reported in literature were used as reference data for the assessment of the different ligand arrangements observed in this study.

Overview on Radiolabel-Free in vitro Assays for GPCRs.

G-protein coupled receptors (GPCRs) represent important targets for drug discovery because they participate in a wide range of cellular signalling pathways that play a role in a variety of pathological conditions. The characterization of the patho-physiological profile and functional roles of new receptors is highly dependent on the availability of potent and selective ligands and new screening assays. The study of the pharmacological profile of new chemical entities is very important in order to predict the activity of drugs and their clinical adverse effect in humans.

The Length and Flexibility of the 2-Substituent of 9-Ethyladenine Derivatives Modulate Affinity and Selectivity for the Human A2A Adenosine Receptor.

The A2A adenosine receptor (A2A AR) is a key target for the development of pharmacological tools for the treatment of central nervous system disorders. Previous works have demonstrated that the insertion of substituents at various positions on adenine leads to A2A AR antagonists with affinity in the micromolar to nanomolar range. In this work, a series of 9-ethyladenine derivatives bearing phenylalkylamino, phenylakyloxy or phenylakylthio groups of different lengths at the 2-position were synthesised and tested against the human adenosine receptors.

A Novel Class of Dopamine D4 Receptor Ligands Bearing an Imidazoline Nucleus.

Over the years, the 2-substituted imidazoline nucleus has been demonstrated to be a bioversatile structural motif. In this study, novel imidazoline derivatives bearing a 3- and/or 4-hydroxy- or methoxy-substituted phenyl ring, linked by an ethylene bridge to position 2 of an N-benzyl- or N-phenethyl-substituted imidazoline nucleus, were prepared and studied against D2 -like receptor subtypes. Binding studies highlighted that a set of N-phenethylimidazoline compounds are selective for D4 over D2 and D3 receptors.

Exploring the 7-oxo-thiazolo[5,4-d]pyrimidine core for the design of new human adenosine A3 receptor antagonists. Synthesis, molecular modeling studies and pharmacological evaluation.

A new series of 5-methyl-thiazolo[5,4-d]pyrimidine-7-ones bearing different substituents at position 2 (aryl, heteroaryl and arylamino groups) was synthesized and evaluated in radioligand binding assays to determine their affinities at the human (h) A1, A2A, and A3 adenosine receptors (ARs). Efficacy at the hA(2B) and antagonism of selected ligands at the hA3 were also assessed through cAMP experiments. Some of the new derivatives exhibited good to high hA3AR affinity and selectivity versus all the other AR subtypes.

Medicinal chemistry of P2X receptors: agonists and orthosteric antagonists.

In this work, we have highlighted data reported in the literature trying to draw a complete picture of the structures and biological activity of agonists and orthosteric antagonists of P2X receptors. Actually, only few P2X receptor agonists have been found and most of them are derived from modification of the natural ligand ATP and they are P2X receptor subtype unselective. In particular, BzATP (9) is one of the most potent P2X receptor agonists with EC50 value in the nanomolar range at some subtypes.

1,2,4-triazolo[1,5-a]quinoxaline derivatives and their simplified analogues as adenosine A₃ receptor antagonists. Synthesis, structure-affinity relationships and molecular modeling studies.

The 1,2,4-triazolo[1,5-a]quinoxaline (TQX) scaffold was extensively investigated in our previously reported studies and recently, our attention was focused at position 5 of the tricyclic nucleus where different acyl and carboxylate moieties were introduced (compounds 2-15). This study produced some interesting compounds endowed with good hA3 receptor affinity and selectivity. In addition, to find new insights about the structural requirements for hA3 receptor-ligand interaction, the tricyclic TQX ring was destroyed yielding some 1,2,4-triazole derivatives (compounds 16-23).

Purinergic P2X receptors: structural models and analysis of ligand-target interaction.

The purinergic P2X receptors are ligand-gated cation channels activated by the endogenous ligand ATP. They assemble as homo- or heterotrimers from seven cloned subtypes (P2X1-7) and all trimer subunits present a common topology consisting in intracellular N- and C- termini, two transmembrane domains and a large extracellular domain. These membrane proteins are present in virtually all mammalian tissues and regulate a large variety of responses in physio- and pathological conditions.

Antiproliferative evaluation of isofuranodiene on breast and prostate cancer cell lines.

The anticancer activity of isofuranodiene, extracted from Smyrnium olusatrum, was evaluated in human breast adenocarcinomas MDA-MB 231 and BT 474, and Caucasian prostate adenocarcinoma PC 3 cell lines by MTS assay. MTS assay showed a dose-dependent growth inhibition in the tumor cell lines after isofuranodiene treatment. The best antiproliferative activity of the isofuranodiene was found on PC 3 cells with an IC50 value of 29 μM, which was slightly less than the inhibition against the two breast adenocarcinoma cell lines with IC50 values of 59 and 55 μM on MDA-MB 231 and BT 474, respectively.

8-(2-Furyl)adenine derivatives as A₂A adenosine receptor ligands.

Selective adenosine receptor modulators are potential tools for numerous therapeutic applications, including cardiovascular, inflammatory, and neurodegenerative diseases. In this work, the synthesis and biological evaluation at the four human adenosine receptor subtypes of a series of 9-substituted 8-(2-furyl)adenine derivatives are reported. Results show that 8-(2-furyl)-9-methyladenine is endowed with high affinity at the A₂A subtype.

Different efficacy of adenosine and NECA derivatives at the human A3 adenosine receptor: insight into the receptor activation switch.

A3 Adenosine receptors are promising drug targets for a number of diseases and intense efforts are dedicated to develop selective agonists and antagonists of these receptors. A series of adenosine derivatives with 2-(ar)-alkynyl chains, with high affinity and different degrees of selectivity for human A3 adenosine receptors was tested for the ability to inhibit forskolin-stimulated adenylyl cyclase. All these derivatives are partial agonists at A3 adenosine receptors; their efficacy is not significantly modified by the introduction of small alkyl substituents in the N(6)-position.

Evaluation of adenine as scaffold for the development of novel P2X3 receptor antagonists.

Ligands that selectively block P2X3 receptors localized on nociceptive sensory fibres may be useful for the treatment of chronic pain conditions including neuropathic pain, migraine, and inflammatory pain. With the aim at exploring the suitability of adenine moiety as a scaffold for the development of antagonists of this receptor, a series of 9-benzyl-2-aminoadenine derivatives were designed and synthesized. These new compounds were functionally evaluated at rat or human P2X3 receptors expressed in human embryonic kidney (HEK) cells and on native P2X3 receptors from mouse trigeminal ganglion sensory neurons using patch clamp recording under voltage clamp configuration.

Simulation and comparative analysis of binding modes of nucleoside and non-nucleoside agonists at the A2B adenosine receptor.

Purpose: A2B receptor agonists are studied as possible therapeutic tools for a variety of pathological conditions. Unfortunately, medicinal chemistry efforts have led to the development of a limited number of potent agonists of this receptor, in most cases with a low or no selectivity versus the other adenosine receptor subtypes. Among the developed molecules, two structural families of compounds have been identified based on nucleoside and non-nucleoside (pyridine) scaffolds.

Innovative functional cAMP assay for studying G protein-coupled receptors: application to the pharmacological characterization of GPR17.

In this work, an innovative and non-radioactive functional cAMP assay was validated at the GPR17 receptor. This assay provides a simple and powerful new system to monitor G protein-coupled receptor activity through change in the intracellular cAMP concentration by using a mutant form of Photinus pyralis luciferase into which a cAMP-binding protein moiety has been inserted. Results, expressed as EC(50) or IC(50) values for agonists and antagonists, respectively, showed a strong correlation with those obtained with [(35)S]GTPγS binding assay, thus confirming the validity of this approach in the study of new ligands for GPR17.

Evidence for the existence of a specific g protein-coupled receptor activated by guanosine.

Guanosine, released extracellularly from neurons and glial cells, plays important roles in the central nervous system, including neuroprotection. The innovative DELFIA Eu-GTP binding assay was optimized for characterization of the putative guanosine receptor binding site at rat brain membranes by using a series of novel and known guanosine derivatives. These nucleosides were prepared by modifying the purine and sugar moieties of guanosine at the 6- and 5'-positions, respectively.

Neuropeptide S receptor: recent updates on nonpeptide antagonist discovery.

Neuropeptide S (NPS) is a 20-amino acid peptide of great interest due to its possible involvement in several biological processes, including food intake, locomotion, wakefulness, arousal, and anxiety. Structure-activity relationship studies of NPS have identified key points for structural modifications with the goal of modulating NPS receptor (NPSR) agonist activity or achieving antagonism at the same receptor. Only limited information is available for nonpeptide NPSR antagonists.

Molecular modeling study on potent and selective adenosine A(3) receptor agonists.

Adenosine A(3) receptor (A(3)AR) is involved in a variety of key physio-pathological processes and its agonists are potential therapeutic agents for the treatment of rheumatoid arthritis, dry eye disorders, asthma, as anti-inflammatory agents, and in cancer therapy. Recently reported MECA (5'-N-methylcarboxamidoadenosine) derivatives bearing a methyl group in N(6)-position and an arylethynyl substituent in 2-position demonstrated to possess sub-nanomolar affinity and remarkable selectivity for the human A(3)AR, behaving as full agonists of this receptor. In this study, we made an attempt to get a rationalization of the high affinities and selectivities of these molecules for the human A(3)AR, by using adenosine receptor (AR) structural models based on the A(2A)AR crystal structure and molecular docking analysis.