Ajiroghene Thomas

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. Results of these experiments prove that guanosine, 6‐thioguanosine, and their derivatives activate a G protein‐coupled receptor that is different from the well‐characterized adenosine receptors.

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. Differently from agonists, P2X receptor antagonists belong to different chemical classes such as high molecular weight aryl polysulfonate molecules like suramin and its simplified derivatives and anthraquinone compounds. All these molecules proved to be non selective at P2X receptors, and they are endowed with micromolar activity and not favourable pharmacokinetic properties due to the presence of several charged groups. Also modification of the natural ligand ATP led to the discovery of P2X receptor antagonists like TNP-ATP (29), which, although not selective, showed high potency at P2X1, P2X3 (IC50 of 0.006 µM and 0.001 µM, respectively), and heteromeric P2X2/3 receptors. Also the dinucleotide inosine polyphosphate Ip5I (33) was found to be a potent and selective antagonist at P2X1 vs P2X3 receptors with IC50 = 0.003 µM. A significant improvement has been gained from the interest of pharmaceutical companies that in the last years discovered, through the use of high-throughput screening, potent and selective antagonists endowed with novel structures, some of which are currently in clinical trials for several therapeutic applications.

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 EC50 or IC50 values for agonists and antagonists, respectively, showed a strong correlation with those obtained with [35S]GTPγS binding assay, thus confirming the validity of this approach in the study of new ligands for GPR17. Moreover, this method allowed confirming that GPR17 is coupled with a Gαi.

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. The development of ligands that selectively activate or block specific P2X receptor subtypes hence represents a promising strategy to obtain novel pharmacological tools for the treatment of pain, cancer, inflammation, and neurological, cardiovascular, and endocrine diseases. The publication of the crystal structures of zebrafish P2X4 receptor in inactive and ATP-bound active forms provided structural data for the analysis of the receptor structure, the interpretation of mutagenesis data, and the depiction of ligand binding and receptor activation mechanism. In addition, the availability of ATP-competitive ligands presenting selectivity for P2X receptor subtypes supports the design of new potent and selective ligands with possibly improved pharmacokinetic profiles, with the final aim to obtain new drugs. This study describes molecular modelling studies performed to develop structural models of the human and rat P2X receptors in inactive and active states. These models allowed to analyse the role of some non-conserved residues at ATP binding site and to study the receptor interaction with some non-specific or subtype selective agonists and antagonists.

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

PurposeA2B 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. The aim of this work is to analyse the binding mode of these molecules at 3D models of the human A2B receptor to identify possible common interaction features and the key receptor residues involved in ligand interaction.MethodsThe A2B receptor models are built by using two recently published crystal structures of the human A2A receptor in complex with two different agonists. The developed models are used as targets for molecular docking studies of nucleoside and non-nucleoside agonists. The generated docking conformations are subjected to energy minimization and rescoring by using three different scoring functions. Further analysis of top-score conformations are performed with a tool evaluating the interaction energy between the ligand and the binding site residues.ResultsResults suggest a set of common interaction points between the two structural families of agonists and the receptor binding site, as evidenced by the superimposition of docking conformations and by analysis of interaction energy with the receptor residues.ConclusionsThe obtained results show that there is a conserved pattern of interaction between the A2B receptor and its agonists. These information and can provide useful data to support the design and the development of A2B receptor agonists belonging to nucleoside or non-nucleoside structural families.

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. Compound 2-(4-chlorophenyl)-5-methyl-thiazolo[5,4-d]pyrimidine-7-one 4 was found to be the most potent and selective ligand of the series (K(I) hA3 = 18 nM). Molecular docking studies of the reported derivatives were carried out to depict their hypothetical binding mode in our hA3 receptor model.

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. Hoechst 33258 assay was performed in order to study the growth inhibition mechanism in prostate cancer cell line; the results indicate that isofuranodiene induces apoptosis. Overall, the understudy compound has a good anticancer activity especially towards the PC 3. On the contrary, it is less active on Chinese hamster ovary cells (CHO) and human embryonic kidney (HEK 293) appearing as a good candidate as a potential natural anticancer drug with low side effects.

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. Further modification of this compound with introduction of arylacetyl or arylcarbamoyl groups in N(6)-position takes to different effects on the A₂A affinity and in particular on the selectivity versus the other three adenosine receptor subtypes. A molecular modelling analysis at three different A₂A receptor crystal structures provides an interpretation of the obtained biological results.

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 (LTD4, LTC4, and LTE4), 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. GPR17 is also highly expressed in organs typically undergoing ischemic damage and has various roles in specific phases of adaptations that follow a stroke. Under such conditions, GPR17 plays a crucial role; in fact, its inhibition decreases the progression of ischemic damage. This review summarizes some important features of this receptor that could be a novel therapeutic target for the treatment of demyelinating diseases and for repairing traumatic injury.

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. In the last year, several studies have been reported in literature which present various series of small molecules as antagonists of this receptor. The results allow a comparison of the structures and activities of these molecules, leading to the design of new ligands with increased potency and improved pharmacological and pharmacokinetic profiles. This work presents a brief overview of the available information regarding structural features and pharmacological characterization of published nonpeptide NPSR antagonists.