Structural Insights into the Intrinsically Disordered GPCR C-Terminal Region, Major Actor in Arrestin-GPCR Interaction.

Arrestin-dependent pathways are a central component of G protein-coupled receptor (GPCRs) signaling. However, the molecular processes regulating arrestin binding are to be further illuminated, in particular with regard to the structural impact of GPCR C-terminal disordered regions. Here, we used an integrated biophysical strategy to describe the basal conformations of the C-terminal domains of three class A GPCRs, the vasopressin V2 receptor (V2R), the growth hormone secretagogue or ghrelin receptor type 1a (GHSR) and the ß2-adernergic receptor (ß2AR). By doing so, we revealed the presence of transient secondary structures in these regions that are potentially involved in the interaction with arrestin. These secondary structure elements differ from those described in the literature in interaction with arrestin. This suggests a mechanism where the secondary structure conformational preferences in the C-terminal regions of GPCRs could be a central feature for optimizing arrestins recognition.

Adenosine Receptors as Neuroinflammation Modulators: Role of A1 Agonists and A2A Antagonists.

The pathological condition of neuroinflammation is caused by the activation of the neuroimmune cells astrocytes and microglia. The autacoid adenosine seems to be an important neuromodulator in this condition. Its main receptors involved in the neuroinflammation modulation are A1AR and A2AAR. Evidence suggests that A1AR activation produces a neuroprotective effect and A2AARs block prevents neuroinflammation. The aim of this work is to elucidate the effects of these receptors in neuroinflammation using the partial agonist 2'-dCCPA (2-chloro-N6-cyclopentyl-2'-deoxyadenosine) (C1 KiA1AR = 550 nM, KiA2AAR = 24,800 nM, and KiA3AR = 5560 nM, α = 0.70, EC50A1AR = 832 nM) and the newly synthesized in house compound 8-chloro-9-ethyl-2-phenethoxyadenine (C2 KiA2AAR = 0.75 nM; KiA1AR = 17 nM and KiA3AR = 227 nM, IC50A2AAR = 251 nM unpublished results). The experiments were performed in in vitro and in in vivo models of neuroinflammation. Results showed that C1 was able to prevent the inflammatory effect induced by cytokine cocktail (TNF-α, IL-1ß, and IFN-γ) while C2 possess both anti-inflammatory and antioxidant properties, counteracting both neuroinflammation in mixed glial cells and in an animal model of neuroinflammation. In conclusion, C2 is a potential candidate for neuroinflammation therapy.

New 8-amino-1,2,4-triazolo[4,3-a]pyrazin-3-one derivatives. Evaluation of different moieties on the 6-aryl ring to obtain potent and selective human A2A adenosine receptor antagonists.

In this work, further structural investigations on the 8-amino-2-phenyl-6-aryl-1,2,4-triazolo[4,3-a]pyrazin-3-one series were carried out to achieve potent and selective human A2A adenosine receptor (AR) antagonists. Different ether and amide moieties were attached at the para-position of the 6-phenyl ring, thus leading to compounds 1-9 and 10-18, respectively. Most of these moieties contained terminal basic rings (pyrrolidine, morpholine, piperidine and substituted piperazines) which were thought to confer good physicochemical and drug-like properties. Compounds 11-16, bearing the amide linker, possessed high affinity and selectivity for the hA2A AR (Ki = 3.6-11.8 nM). Also derivatives 1-9, featuring an ether linker, preferentially targeted the hA2A AR but with lower affinity, compared to those of the relative amide compounds. Docking studies, carried out at the hA2A AR binding site, highlighted some crucial ligand-receptor interactions, particularly those provided by the appended substituent whose nature deeply affected hA2A AR affinity.

Update on novel purinergic P2X3 and P2X2/3 receptor antagonists and their potential therapeutic applications.

Introduction: Purinergic P2X3-P2X2/3 receptors are placed in nociceptive neurons' strategic location and show unique desensitization properties; hence, they represent an attractive target for many pain-related diseases. Therefore, a broad interest from academic and pharmaceutical scientists has focused on the search for P2X3 and P2X2/3 receptor ligands and has led to the discovery of numerous new selective antagonists. Some of them have been studied in clinical trials for the treatment of pathological conditions such as bladder disorders, gastrointestinal and chronic obstructive pulmonary diseases.Areas covered: This review provides a summary of the patents concerning the discovery of P2X3 and/or P2X2/3 receptor antagonists published between 2015 and 2019 and their potential clinical use. Thus, the structures and biological data of the most representative molecules are reported.Expert opinion: The 2016 publication of the crystallographic structure of the human P2X3 receptor subtype gave an improvement of published patents in 2017. Hence, a great number of small molecules with dual antagonist activity on P2X3-P2X2/3 receptors, a favorable pharmacokinetic profile, and reasonable oral bioavailability was discovered. The most promising compounds are the phenoxy-diaminopyrimidines including gefapixant (AF-219), and the imidazo-pyridines like BLU-5937, which are in phase III and phase II clinical trials, respectively, for refractory chronic cough.

Non-Nucleoside Agonists of the Adenosine Receptors: An Overview.

Potent and selective adenosine receptor (AR) agonists are of pharmacological interest for the treatment of a wide range of diseases and conditions. Among these derivatives, nucleoside-based agonists represent the great majority of molecules developed and reported to date. However, the limited availability of compounds selective for a specific AR subtype (i.e., A2BAR) and a generally long and complex synthetic route for largely substituted nucleosides are the main drawbacks of this category of molecules. Non-nucleoside agonists represent an alternative set of compounds able to stimulate the AR function and based on simplified structures. This review provides an updated overview on the structural classes of non-nucleoside AR agonists and their biological activities, with emphasis on the main derivatives reported in the literature. A focus is also given to the synthetic routes employed to develop these derivatives and on molecular modeling studies simulating their interaction with ARs.

New sensible method to quantize the intestinal absorption of receptor ligands.

In recent years, special attention has been paid to the A3 adenosine receptor (A3AR) as a possible pharmacological target to treat intestinal inflammation. In this work, it was set up a novel method to quantify the concentration of a promising anti-inflammatory agent inside and outside of intestinal barrier using the everted gut sac technique. The compound chosen for the present study is one of the most potent and selective A3AR agonist reported so far, named AR 170 (N6-methyl-2-phenylethynyl-5'-N-methylcarboxamidoadenosine). In order to evaluate the intestinal absorption of AR 170 the radioligand binding assay in comparison with HPLC-DAD was used. Results showed that the compound is absorbed via passive diffusion by paracellular pathway. The concentrations determined in the serosal (inside the sac) fluid by radioligand binding assay are in good agreement with those obtained through the widely used HPLC/MS protocol, demonstrating the reliability of the method. It is worthwhile to note that the radioligand binding assay allows detecting very low concentrations of analyte, thus offering an excellent tool to measure the intestinal absorption of receptor ligands. Moreover, the AR 170 quantity outside the gut sac and the interaction with A3AR could presuppose good topical anti-inflammatory effects of this compound.

GPR17 receptor modulators and their therapeutic implications: review of recent patents.

INTRODUCTION: The GPR17 receptor, phylogenetically related to both purinergic P2Y and CysLT receptors, is mainly expressed in the CNS and, in general, in organs that can typically undergo ischemic damage. This receptor is involved in various pathologies including stroke, brain and spinal cord trauma, multiple sclerosis and in all diseases characterized by neuronal and myelin dysfunction. Therefore, there is a strong needed to identify molecules capable of binding specifically to GPR17 receptors. AREAS COVERED: The review provides a summary of patents, published between 2009 and 2018, on chemicals and biologics and their clinical use. In this work, information is reported about the representative structures and biological activity of recently developed GPR17 receptor ligands. EXPERT OPINION: The GPR17 receptor is an enigmatic receptor and an interesting therapeutic target in a variety of brain disorders and demyelinating diseases such as multiple sclerosis, stroke, schizophrenia, and depression. The modulation of this receptor could also be potentially useful in obesity treatment. Unfortunately, so far, there are no compounds under investigation in clinical trials but many researchers and companies are investing in the discovery of future potential GPR17 receptor drugs.