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A series of 2,6,9-trisubstituted purine derivatives were designed and synthesized with diverse chemical moieties. Through a comprehensive biological evaluation, we identified 4-(6-(methylamino)-2-(phenylethynyl)-9H-purin-9-yl)phenol (6a) as a promising A 2A AR antagonist with potent antifibrotic properties. Compound 6a demonstrated significant efficacy in inhibiting CRE promoter activity and in reducing the expression of fibrogenic marker proteins and downstream effectors of A 2A AR activation, surpassing the A 2A AR antagonist ZM241385 and initial screening hits, 9-benzyl-N-methyl-2-(phenylethynyl)-9H-purin-6-amine (5a) and 9-((benzyloxy)methyl)-N-methyl-2-(phenylethynyl)-9H-purin-6-amine (5j). Further validation revealed that compound 6a effectively inhibited fibrogenic marker proteins induced by A 2A AR overexpression or TGF-β1 treatment in hepatic stellate cells, alongside reducing PKA and CREB phosphorylation. These findings suggest that compound 6a exerts its antifibrotic action by modulating the cAMP/PKA/CREB pathway through A 2A AR inhibition. Overall, our study provides valuable insights for the development of novel therapeutics that target hepatic fibrosis through A 2A AR antagonism., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024. Published by Elsevier Ltd.)

The adenosine A 2A receptor (A 2A R) has been identified as a therapeutic target for treating neurodegenerative diseases and cancer. In recent years, we have highlighted the 2-aminoquinazoline heterocycle as an promising scaffold for designing new A 2A R antagonists, exemplified by 6-bromo-4-(furan-2-yl)quinazolin-2-amine 1 ( K i ( h A 2A R) = 20 nM). Here, we report the synthesis of new 2-aminoquinazoline derivatives with substitutions at the C6- and C7-positions, and the introduction of aminoalkyl chains containing tertiary amines at the C2-position to enhance antagonist activity and solubility properties. Compound 5m showed a high affinity for h A 2A R with a K i value of 5 nM and demonstrated antagonist activity with an IC 50 of 6 µM in a cyclic AMP assay. Introducing aminopentylpiperidine and 4-[(piperidin-1-yl)methyl]aniline substituents maintained the binding affinities ( 9x , K i = 21 nM; 10d , K i = 15 nM) and functional antagonist activities ( 9x , IC 50 = 9 µM; 10d , IC 50 = 5 µM) of the synthesized compounds while improving solubility. This study provides insights into the future development of A 2A R antagonists for therapeutic applications.

The COVID-19 pandemic reminded us of the urgent need for new antivirals to control emerging infectious diseases and potential future pandemics. Immunotherapy has revolutionized oncology and could complement the use of antivirals, but its application to infectious diseases remains largely unexplored. Nucleoside analogs are a class of agents widely used as antiviral and anti-neoplastic drugs. Their antiviral activity is generally based on interference with viral nucleic acid replication or transcription. Based on our previous work and computer modeling, we hypothesize that antiviral adenosine analogs, like remdesivir, have previously unrecognized immunomodulatory properties which contribute to their therapeutic activity. In the case of remdesivir, we here show that these properties are due to its metabolite, GS-441524, acting as an Adenosine A2A Receptor antagonist. Our findings support a new rationale for the design of next-generation antiviral agents with dual - immunomodulatory and intrinsic - antiviral properties. These compounds could represent game-changing therapies to control emerging viral diseases and future pandemics., (© 2024. The Author(s).)

Building on the preceding structural analysis and a structure-activity relationship (SAR) of 8-aryl-2-hexynyl nucleoside hA 2A AR antagonist 2a , we strategically inverted C2/C8 substituents and eliminated the ribose moiety. These modifications aimed to mitigate potential steric interactions between ribose and adenosine receptors. The SAR findings indicated that such inversions significantly modulated hA 3 AR binding affinities depending on the type of ribose, whereas removal of ribose altered the functional efficacy via hA 2A AR. Among the synthesized derivatives, 2-aryl-8-hexynyl adenine 4a demonstrated the highest selectivity for hA 2A AR ( K i ,hA2A = 5.0 ± 0.5 nM, K i ,hA3 / K i ,hA2A = 86) and effectively blocked cAMP production and restored IL-2 secretion in PBMCs. Favorable pharmacokinetic properties and a notable enhancement of anticancer effects in combination with an mAb immune checkpoint blockade were observed upon oral administration of 4a . These findings establish 4a as a viable immune-oncology therapeutic candidate.

The adenosine subfamily G protein-coupled receptors A 2A R and A 2B R have been identified as promising cancer immunotherapy candidates. One of the A 2A R/A 2B R dual antagonists, AB928, has progressed to a phase II clinical trial to treat rectal cancer. However, the precise mechanism underlying its dual-antagonistic properties remains elusive. Herein, we report crystal structures of the A 2A R complexed with AB928 and a selective A 2A R antagonist 2-118. The structures revealed a common binding mode on A 2A R, wherein the ligands established extensive interactions with residues from the orthosteric and secondary pockets. In contrast, the cAMP assay and A 2A R and A 2B R molecular dynamics simulations indicated that the ligands adopted distinct binding modes on A 2B R. Detailed analysis of their chemical structures suggested that AB928 readily adapted to the A 2B R pocket, while 2-118 did not due to intrinsic differences. This disparity potentially accounted for the difference in inhibitory efficacy between A 2B R and A 2A R. This study serves as a valuable structural template for the future development of selective or dual inhibitors targeting A 2A R/A 2B R for cancer therapy., (© 2024. Science China Press.)

Development of subtype-selective leads is essential in drug discovery campaigns targeting G protein-coupled receptors (GPCRs). Herein, a structure-based virtual screening approach to rationally design subtype-selective ligands was applied to the A 1 and A 2A adenosine receptors (A 1 R and A 2A R). Crystal structures of these closely related subtypes revealed a non-conserved subpocket in the binding sites that could be exploited to identify A 1 R selective ligands. A library of 4.6 million compounds was screened computationally against both receptors using molecular docking and 20 A 1 R selective ligands were predicted. Of these, seven antagonized the A 1 R with micromolar activities and several compounds displayed slight selectivity for this subtype. Twenty-seven analogs of two discovered scaffolds were designed, resulting in antagonists with nanomolar potency and up to 76-fold A 1 R-selectivity. Our results show the potential of structure-based virtual screening to guide discovery and optimization of subtype-selective ligands, which could facilitate the development of safer drugs., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 The Authors. Published by Elsevier Masson SAS.. All rights reserved.)

Numerous basic studies have reported on the neuroprotective properties of several purine derivatives such as caffeine and uric acid (UA). Epidemiological studies have also shown the inverse association of appropriate caffeine intake or serum urate levels with neurodegenerative diseases such as Alzheimer disease (AD) and Parkinson's disease (PD). The well-established neuroprotective mechanisms of caffeine and UA involve adenosine A 2A receptor antagonism and antioxidant activity, respectively. Our recent study found that another purine derivative, paraxanthine, has neuroprotective effects similar to those of caffeine and UA. These purine derivatives can promote neuronal cysteine uptake through excitatory amino acid carrier protein 1 (EAAC1) to increase neuronal glutathione (GSH) levels in the brain. This review summarizes the GSH-mediated neuroprotective effects of purine derivatives. Considering the fact that GSH depletion is a manifestation in the brains of AD and PD patients, administration of purine derivatives may be a new therapeutic approach to prevent or delay the onset of these neurodegenerative diseases.

Multitarget drugs based on a hybrid dopamine-xanthine core were designed as potential drug candidates for the treatment of neurodegenerative diseases. Monoamine oxidase B (MAO-B) inhibitors with significant ancillary A 2A adenosine receptor (A 2A AR) antagonistic properties were further developed to exhibit additional phosphodiesterase-4 and -10 (PDE4/10) inhibition and/or dopamine D 2 receptor (D 2 R) agonistic activity. While all of the designed compounds showed MAO-B inhibition in the nanomolar range mostly combined with submicromolar A 2A AR affinity, significant enhancement of PDE-inhibitory and D 2 R-agonistic activity was additionally reached for some compounds through various structural modifications. The final multitarget drugs also showed promising antioxidant properties in vitro. In order to evaluate their potential neuroprotective effect, representative ligands were tested in a cellular model of toxin-induced neurotoxicity. As a result, protective effects against oxidative stress in neuroblastoma cells were observed, confirming the utility of the applied strategy. Further evaluation of the newly developed multitarget ligands in preclinical models of Alzheimer's and Parkinson's diseases is warranted.

We used a range of computational techniques to assess the effect of selective C-H deuteration on the antagonist istradefylline affinity for the adenosine A 2A receptor, which was discussed relative to its structural analogue caffeine, a well-known and likely the most widely used stimulant. The obtained results revealed that smaller caffeine shows high receptor flexibility and exchanges between two distinct poses, which agrees with crystallographic data. In contrast, the additional C8- trans -styryl fragment in istradefylline locks the ligand within a uniform binding pose, while contributing to the affinity through the C-H···π and π···π contacts with surface residues, which, together with its much lower hydration prior to binding, enhances the affinity over caffeine. In addition, the aromatic C8-unit shows a higher deuteration sensitivity over the xanthine part, so when both of its methoxy groups are d 6 -deuterated, the affinity improvement is -0.4 kcal mol -1 , which surpasses the overall affinity gain of -0.3 kcal mol -1 in the perdeuterated d 9 -caffeine. Yet, the latter predicts around 1.7-fold potency increase, being relevant for its pharmaceutical implementations, and also those within the coffee and energy drink production industries. Still, the full potential of our strategy is achieved in polydeuterated d 19 -istradefylline, whose A 2A affinity improves by -0.6 kcal mol -1 , signifying a 2.8-fold potency increase that strongly promotes it as a potential synthetic target. This knowledge supports deuterium application in drug design, and while the literature already reports about over 20 deuterated drugs currently in the clinical development, it is easily foreseen that more examples will hit the market in the years to come. With this in mind, we propose that the devised computational methodology, involving the ONIOM division of the QM region for the ligand and the MM region for its environment, with an implicit quantization of nuclear motions relevant for the H/D exchange, allows fast and efficient estimates of the binding isotope effects in any biological system.

Background/aim: Recent research suggests that adenosine receptors (ARs) influence many of the metabolic abnormalities associated with diabetes. A non-xanthine benzylidene indanone derivative 2-(3,4-dihydroxybenzylidene)-4-methoxy-2,3-dihydro-1 H-inden-1-one (2-BI), has shown to exhibit higher affinity at A 1 /A 2A ARs compared to caffeine. Due to its structural similarity to caffeine, and the established antidiabetic effects of caffeine, the current study was initiated to explore the possible antidiabetic effect of 2-BI., Methods: The study was designed to assess the antidiabetic effects of several A 1 and/or A 2A AR antagonists, via intestinal glucose absorption and glucose-lowering effects in fructose-streptozotocin (STZ) induced diabetic rats. Six-week-old male Sprague-Dawley rats were induced with diabetes via fructose and streptozotocin. Rats were treated for 4 weeks with AR antagonists, metformin and pioglitazone, respectively. Non-fasting blood glucose (NFBG) was determined weekly and the oral glucose tolerance test (OGTT) was conducted at the end of the intervention period., Results: Dual A 1 /A 2A AR antagonists (caffeine and 2-BI) decreased glucose absorption in the intestinal membrane significantly (p < 0.01), while the selective A 2A AR antagonist (Istradefylline), showed the highest significant (p < 0.001) reduction in intestinal glucose absorption. The selective A 1 antagonist (DPCPX) had the least significant (p < 0.05) reduction in glucose absorption. Similarly, dual A 1 /A 2A AR antagonists and selective A 2A AR antagonists significantly reduced non-fast blood glucose and improved glucose tolerance in diabetic rats from the first week of the treatment. Conversely, the selective A 1 AR antagonist did not reduce non-fast blood glucose significantly until the 4th week of treatment. 2-BI, caffeine and istradefylline compared well with standard antidiabetic treatments, metformin and pioglitazone, and in some cases performed even better., Conclusion: 2-BI exhibited good antidiabetic activity by reducing intestinal postprandial glucose absorption and improving glucose tolerance in a diabetic animal model. The dual antagonism of A 1 /A 2A ARs presents a positive synergism that could provide a new possibility for the treatment of diabetes., (© 2023. The Author(s).)

The past fifty years have been marked by the surge of neurodegenerative diseases. Unfortunately, current treatments are only symptomatic. Hence, the search for new and innovative therapeutic targets for curative treatments becomes a major challenge. Among these targets, the adenosine A 2A receptor (A 2A AR) has been the subject of much research in recent years. In this paper, we report the design, synthesis and pharmacological analysis of quinazoline derivatives as A 2A AR antagonists with high ligand efficiency. This class of molecules has been discovered by a virtual screening and bears no structural semblance with reference antagonist ZM-241385. More precisely, we identified a series of 2-aminoquinazoline as promising A 2A AR antagonists. Among them, one compound showed a high affinity towards A 2A AR (21a, K i  = 20 nM). We crystallized this ligand in complex with A 2A AR, confirming one of our predicted docking poses and opening up possibilities for further optimization to derive selective ligands for specific adenosine receptor subtypes., (Copyright © 2022 Elsevier Masson SAS. All rights reserved.)

Parkinson's disease is considered the second most frequent neurodegenerative disease. It is described by the loss of dopaminergic neurons in the mid-brain. For many decades, L-DOPA has been considered as the gold standard for treating Parkinson's disease motor symptoms, however, due to the decrease of efficacy, in the long run, there is an urgent need for novel antiparkinsonian drugs. Caffeine derivatives have been reported several times for their neuroprotective properties and dual blockade of monoamine oxidase (MAO) and adenosine A 2A receptors (AA 2A R). Natural products are currently attracting more focus due to structural diversity and safety in contrast to synthetic drugs. In the present work, computational studies were conducted on natural product-like caffeine derivatives to search for novel potent candidates acting as dual MAO-B inhibitors/AA 2A R antagonists for Parkinson's disease. Our findings revealed two natural products among the top hits: CNP0202316 and CNP0365210 fulfill the requirements of drugs acting on the brain. The selected lead compounds were further studied using molecular dynamics simulation to assess their stability with MAO-B. Current findings might shift the interest towards natural-based compounds and could be exploited to further optimize caffeine derivatives into a successful dual-target-directed drug for managing and halting the neuronal damage in Parkinson's disease patients., (© 2022 the author(s), published by De Gruyter, Berlin/Boston.)

Modulators of the G protein-coupled A 2A adenosine receptor (A 2A AR) have been considered promising agents to treat Parkinson's disease, inflammation, cancer, and central nervous system disorders. Herein, we demonstrate that a thiophene modification at the C8 position in the common adenine scaffold converted an A 2A AR agonist into an antagonist. We synthesized and characterized a novel A 2A AR antagonist, 2 (LJ-4517), with K i = 18.3 nM. X-ray crystallographic structures of 2 in complex with two thermostabilized A 2A AR constructs were solved at 2.05 and 2.80 Å resolutions. In contrast to A 2A AR agonists, which simultaneously interact with both Ser277 7.42 and His278 7.43 , 2 only transiently contacts His278 7.43 , which can be direct or water-mediated. The n -hexynyl group of 2 extends into an A 2A AR exosite. Structural analysis revealed that the introduced thiophene modification restricted receptor conformational rearrangements required for subsequent activation. This approach can expand the repertoire of adenosine receptor antagonists that can be designed based on available agonist scaffolds.

The A 2A adenosine receptor (A 2A AR) is one of the four subtypes activated by nucleoside adenosine, and the molecules able to selectively counteract its action are attractive tools for neurodegenerative disorders. In order to find novel A 2A AR ligands, two series of compounds based on purine and triazolotriazine scaffolds were synthesized and tested at ARs. Compound 13 was also tested in an in vitro model of neuroinflammation. Some compounds were found to possess high affinity for A 2A AR, and it was observed that compound 13 exerted anti-inflammatory properties in microglial cells. Molecular modeling studies results were in good agreement with the binding affinity data and underlined that triazolotriazine and purine scaffolds are interchangeable only when 5- and 2-positions of the triazolotriazine moiety (corresponding to the purine 2- and 8-positions) are substituted.

Sickle cell disease (SCD) is a disease resulting from mutation in the globin portion of hemoglobin caused by the replacement of adenine for thymine in the codon of the β globin gene. In Brazil, SCD affects about 0.3% of the black and Caucasian population. Until now, there is no specific treatment and the available drugs have several serious adverse effects which makes the search for new drugs an emergently need. The use of computational techniques can accelerate the drug development process by prioritization of molecules with affinity against essential targets. Adenosine A2b receptor (rA2b) has been studied in SCD due to its relationship with red blood cells concentration of 2,3-diphosphoglycerate which reduces the hemoglobin affinity for oxygen (O 2 ), facilitating its availability for the tissues. Then, development of rA2b antagonists could be helpful for the treatment of SCD. However, there is still no 3D structure of rA2b and to overcome this limitation, homology modeling should be applied. In this scenario, this study aims to build a suitable 3D model of rA2b by SWISS MODEL and to evaluate the structural aspects of rA2b with known antagonists that may be useful for the identification of new potential antagonists by molecular dynamics on a lipid bilayer environment using GROMACS 5.1.4. The complexes with antagonists ZINC223070016 and ZINC17974526 interacted with key residues by hydrophobic contacts and hydrogen bonds which stabilized them at the rA2b binding site. This intermolecular profile can contribute to the development of more potent rA2b antagonists. Communicated by Ramaswamy H. Sarma.

Transmembranal G Protein-Coupled Receptors (GPCRs) transduce extracellular chemical signals to the cell, via conformational change from a resting (inactive) to an active (canonically bound to a G-protein) conformation. Receptor activation is normally modulated by extracellular ligand binding, but mutations in the receptor can also shift this equilibrium by stabilizing different conformational states. In this work, we built structure-energetic relationships of receptor activation based on original thermodynamic cycles that represent the conformational equilibrium of the prototypical A2A adenosine receptor (AR). These cycles were solved with efficient free energy perturbation (FEP) protocols, allowing to distinguish the pharmacological profile of different series of A2AAR agonists with different efficacies. The modulatory effects of point mutations on the basal activity of the receptor or on ligand efficacies could also be detected. This methodology can guide GPCR ligand design with tailored pharmacological properties, or allow the identification of mutations that modulate receptor activation with potential clinical implications., Competing Interests: The authors have declared that no competing interests exist.

Allosteric ligands provide new opportunities to modulate G protein-coupled receptor (GPCR) function and present therapeutic benefits over orthosteric molecules. Negative allosteric modulators (NAMs) can inhibit the activation of a receptor and downstream signal transduction. Screening NAMs for a GPCR target is particularly challenging because of the difficulty in distinguishing NAMs from antagonists bound to the orthosteric site as they both show inhibitory effects in receptor signaling assays. Here we report an affinity mass spectrometry (MS)-based approach tailored to screening potential NAMs of a GPCR target especially from fragment libraries. Compared to regular surface plasmon resonance or NMR-based methods for fragment screening, our approach features a reduction of the protein and compound consumption by 2-4 orders of magnitude and an increase in the data acquisition speed by 2-3 orders of magnitude. Our affinity MS-based fragment screening led to the identification of a new NAM of the adenosine A 2A receptor (A 2A AR) bearing an unprecedented azetidine moiety predicted to occupy the allosteric sodium binding site. Molecular dynamics simulations, ligand structure-activity relationship (SAR) studies, and in-solution NMR analyses further revealed the unique binding mode and antagonistic property of this compound that differs considerably from HMA (5-( N , N -hexamethylene)amiloride), a well-characterized NAM of A 2A AR. Taken together, our work would facilitate fragment-based screening of allosteric modulators, as well as guide the design of novel NAMs acting at the sodium ion pocket of class A GPCRs.

Two novel alkaloids compounds together with fifteen know metabolites were identified from Aspergillus ochraceus. The stereochemistry features of the new molecules were determined via HRESIMS, NMR, ECD, and XRD analyses. Amongst these, compounds two compounds exhibited potential efficacy as anti-Parkinson's disease with the EC 50 values of 2.30 and 2.45 μM, respectively. ADMET prediction showed that these compounds owned favorable drug-like characteristics and safe toxicity scores towards CNS drugs. Virtual screening analyses manifested that the compounds exhibited not only robust and reliable interactions to adenosine receptors A 2A , but also higher binding selectivity to A 2A receptors than to A 1 and A 3 receptors. Molecular dynamics simulation demonstrated the reliability of molecular docking results and the stability of the complexes obtained with the novel compounds and A 2A receptors in natural environments. It is the first time that anti-PD lead compounds have been identified from Aspergillus ochraceus and targeting adenosine A 2A receptors., (© 2021 The Authors. Published by Wiley-VCH GmbH.)

With the aim to obtain potent adenosine A 2A receptor (A 2A R) ligands, a series of eighteen derivatives of 4-hydroxy-N-(4-methoxy-7-morpholin-4-yl-1,3-benzo[d]thiazol-2-yl)-4-methylpiperidine-1-carboxamide (SYN-115, Tozadenant) were designed and synthesized. The target compounds were obtained by a chemical building block principle that involved reaction of the appropriate aminobenzothiazole phenyl carbamates with either commercially available or readily synthesized functionalized piperidines. Their affinity and subtype selectivity with regard to human adenosine A 1 -and A 2A receptors were determined using radioligand binding assays. K i values for human A 2A R ranged from 2.4 to 38 nM, with more than 120-fold selectivity over A 1 receptors for all evaluated compounds except 13k which had a K i of 361 nM and 18-fold selectivity. The most potent fluorine-containing derivatives 13e, 13g and 13l exhibited K i values of 4.9 nM, 3.6 nM and 2.8 nM for the human A 2A R. Interestingly, the corresponding values for rat A 2A R were found to be four to five times higher. Their binding to A 2A R was further confirmed by radiolabeling with 18 F and in vitro autoradiography in rat brain slices, which showed almost exclusive striatal binding and complete displacement by the A 2A R antagonist ZM 241385. We conclude that these compounds represent potential candidates for the visualization of the A 2A receptor and open pathways to novel therapeutic treatments of neurodegenerative disorders or cancer., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2021 Elsevier Masson SAS. All rights reserved.)

Parkinson's disease (PD) is a chronic neuro-degenerative ailment characterized by impairment in various motor and nonmotor functions of the body. In the past few years, adenosine A 2 A receptor (A 2 AR) antagonists have attracted much attention due to significant relief in PD. Therefore, in the current study, we intend to disclose the development of novel 1,3,5-triazines as A 2 AR antagonist. The radioligand binding and selectivity of analogs were tested in HEK293 (human embryonic kidney) and the cells were transfected with pcDNA 3.1(+) containing full-length human A 2 AR cDNA and pcDNA 3.1(+) containing full-length human A 1 R cDNA, where they exhibit selective affinity for A 2 AR. Molecular docking analysis was also conducted to rationalize the probable mode of action, binding affinity, and orientation of the most potent molecule (7c) at the active site of A 2 AR. It has been shown that compound 7c form numerous nonbonded interactions in the active site of A 2 AR by interacting with Ala59, Ala63, Ile80, Val84 Glu169, Phe168, Met270, and Ile274. The study revealed 1,3,5-triazines as a novel class of A 2 AR antagonists., (© 2020 Wiley Periodicals LLC.)

The adenosine A 2A receptor (A 2A R) represents a potential therapeutic target for neurodegenerative diseases. Aiming at the development of a positron emission tomography (PET) radiotracer to monitor changes of receptor density and/or occupancy during the A 2A R-tailored therapy, we designed a library of fluorinated analogs based on a recently published lead compound ( PPY ). Among those, the highly affine 4-fluorobenzyl derivate ( PPY1 ; K i ( h A 2A R) = 5.3 nM) and the 2-fluorobenzyl derivate ( PPY2 ; K i ( h A 2A R) = 2.1 nM) were chosen for 18 F-labeling via an alcohol-enhanced copper-mediated procedure starting from the corresponding boronic acid pinacol ester precursors. Investigations of the metabolic stability of [ 18 F] PPY 1 and [18F] PPY2 in CD-1 mice by radio-HPLC analysis revealed parent fractions of more than 76% of total activity in the brain. Specific binding of [ 18 F] PPY 2 on mice brain slices was demonstrated by in vitro autoradiography. In vivo PET/magnetic resonance imaging (MRI) studies in CD-1 mice revealed a reasonable high initial brain uptake for both radiotracers, followed by a fast clearance.

Antagonists of adenosine receptor are under exploration as potential drug candidates for treatment of neurological disorders, depression, certain cancers and potentially used as a cancer immunotherapy. Herein, we describe design and synthesis of novel scaffold benzo[4,5]imidazo [1,2-a]pyrazin-1-amine (6) derivatives. All the compounds were evaluated for A 2A AR antagonist activity and displayed encouraging results (IC 50 9-300 nM) of A 2A AR antagonist binding affinity in biochemical assay. Compound 27 exhibits good activity in A 2A AR antagonist cAMP functional assay (IC 50 31 nM) and further this compound shows T-cell activation at the IL-2 production assay (EC 50 165 nM). Molecular docking studies were carried out to rationalize the observed binding affinity of compound 27., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020. Published by Elsevier Masson SAS.)

Currently, the most promising therapeutic modality for cancer treatment is the blockade of immune checkpoint pathways, which has revolutionized cancer therapy in the past 15 years. Strategies targeting and modulating adenosine A 2A receptor (A 2A R), an emerging alternative immune checkpoint, have shown the potential to produce significant therapeutic effects. In this review, we describe the immunosuppressive activities of A 2A R and A 2B R in the tumor microenvironment (TME), followed by a summary and discussion of the structure-activity relationship (SAR) of the A 2A R (and dual A 2A R/A 2B R) antagonists that have been experimentally confirmed to exert oncoimmunological effects. This review also provides an update on the compounds under clinical evaluation and insights into the ligand binding modes of the receptor.

We report a selective LC-MS/MS method for the simultaneous quantitative determinations of the adenosine A2a receptor antagonist NIR178 (NIR178) and its major metabolite NJI765 in human plasma. Sample preparation steps involved protein precipitation, sample evaporation and reconstitution using a plasma sample volume of 0.1 ml plasma. Separation was achieved in 10 min on an Acquity UPLC BEH C 18 1.7 μm, 2.1 × 50 mm column heated at 60°C with a gradient elution at 0.6 ml/min mobile phase made of water and acetonitrile both acidified with 0.1% formic acid. The detection was performed in positive ion mode and quantification based on multiple reaction monitoring. The linear response range was 1.00-1,000 ng/ml using a 1/x 2 weighting factor. The intra- and inter-day accuracies (bias %) and intra- and inter-day precisions (CV, %) obtained for NIR178 and NJI765 were within the acceptance criteria. The normalized NIR178 and NJI765 matrix factor calculated from six lots of normal, lipemic and hemolyzed plasmas ranged from 0.97 to 1.05. The normalized recoveries of both NIR178 and NJI765 compared with their internal standards were consistent and reproducible with a CV ≤8.0. This method was successfully applied to support pharmacokinetic studies in adult patients with cancer., (© 2020 John Wiley & Sons, Ltd.)

Overexpression of adenosine in the tumor region leads to suppression of various immune cells, particularly T cells through ligation with adenosine 2a receptor (A2aR). In this study, we intended to increase the efficacy of tumor lysate-loaded DC vaccine by silencing the expression of A2aR on T cells through the application of A2aR-specific siRNA-loaded PEG-chitosan-lactate (PCL) nanoparticles (NPs) in the 4T1 breast tumor-bearing mice. Combination therapy by DC vaccine and siRNA-loaded NPs markedly induced tumor regression and increased survival time of mice. These ameliorative effects were partly via downregulation of immunosuppressive cells, increased function of cytotoxic T lymphocytes, and induction of immune-stimulatory cytokines. Moreover, combination therapy could markedly suppress angiogenesis and metastasis processes. These results imply the efficacy of novel combination therapy for the treatment of breast cancer by using A2aR siRNA-loaded NPs and DC vaccine which can be translated into the initial phase of clinical trials in the near future., Competing Interests: Conflict of interest There is no conflict of interest., (Copyright © 2020 Elsevier Inc. All rights reserved.)

Various studies showed adenosine A 2 A receptors (A 2 ARs) antagonists have profound therapeutic efficacy in Parkinsons Disease (PD) by improving dopamine transmission, thus being active in reversing motor deficits and extrapyramidal symptoms related to the disease. Therefore, in the presents study, we have showed the development of novel 1,3,5-triazine-thiadiazole derivative as potent A 2 ARs antagonist. In the radioligand binding assay, these molecules showed excellent binding affinity with A 2 AR compared to A 1 R, with significant selectivity. Results suggest, compound 7e as most potent antagonist of A 2 AR among the tested series. In docking analysis with A 2 AR protein model, compound 7e found to be deeply buried into the cavity of receptor lined via making numerous interatomic contacts with His264, Tyr271, His278, Glu169, Ala63, Val84, Ile274, Met270, Phe169. Collectively, our study demonstrated 1,3,5-triazine-thiadiazole hybrid as a highly effective scaffold for the design of new A 2 A antagonists., (Copyright © 2020 Elsevier B.V. All rights reserved.)

This paper describes identification of the first-in-class multi-target adenosine A 2A receptor antagonists-carbonic anhydrase (CA) IX and XII inhibitors, as new potential antitumor agents. To obtain the multi-acting ligands, the 8-amino-2,6-diphenyltriazolo[4,3-a]pyrazin-3-one, a potent adenosine hA 2A receptor (AR) antagonist, was taken as lead compound. To address activity against the tumor-associated CA isoforms, it was modified by introduction of different substituents (OH, COOH, CONHOH, SO 2 NH 2 ) on the 6-phenyl ring or on a phenyl pendant connected to the former through different spacers. Among the new triazolopyrazines 1-23, the most active were those featuring the sulfonamide residue. Derivative 20, featuring a 4-sulfonamidophenyl residue attached through a CONH(CH 2 ) 2 CONH spacer at the para-position of the 6-phenyl ring, showed the best combination of activity at the three targets. In fact, it inhibited both the tumor-associated hCA IX and XII isozymes at nanomolar concentration (K i  = 5.0 and 27.0 nM), and also displayed a quite good affinity for the hA 2A AR (K i  = 108 nM). Compound 14, bearing the 4-sulfonamidophenyl residue linked at the para-position of the 6-phenyl ring by a CONH spacer, was remarkable because both its hA 2A AR affinity and hCA XII inhibitory potency were in the low nanomolar range (K i  = 6.4 and 6.2 nM, respectively). Molecular docking studies highlighted the interaction mode of selected triazolopyrazines in the hA 2A AR recognition pocket and in the active site of hCA II, IX and XII isoforms., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier Masson SAS. All rights reserved.)

Antagonists of the adenosine receptors (A 1 and A 2A subtypes) are widely researched as potential drug candidates for their role in Parkinson's disease-related cognitive deficits (A 1 subtype), motor dysfunction (A 2A subtype) and to exhibit neuroprotective properties (A 2A subtype). Previously the benzo-α-pyrone based derivative, 3-phenyl-1H-2-benzopyran-1-one, was found to display both A 1 and A 2A adenosine receptor affinity in the low micromolar range. Prompted by this, the α-pyrone core was structurally modified to explore related benzoxazinone and quinazolinone homologues previously unknown as adenosine receptor antagonists. Overall, the C2-substituted quinazolinone analogues displayed superior A 1 and A 2A adenosine receptor affinity over their C2-substituted benzoxazinone homologues. The benzoxazinones were devoid of A 2A adenosine receptor binding, with only two compounds displaying A 1 adenosine receptor affinity. In turn, the quinazolinones displayed varying degrees of affinity (low micromolar range) towards the A 1 and A 2A adenosine receptor subtypes. The highest A 1 adenosine receptor affinity and selectivity were favoured by methyl para-substitution of phenyl ring B (A 1 K i  = 2.50 μM). On the other hand, 3,4-dimethoxy substitution of phenyl ring B afforded the best A 2A adenosine receptor binding (A 2A K i  = 2.81 μM) among the quinazolinones investigated. In conclusion, the quinazolinones are ideal lead compounds for further structural optimization to gain improved adenosine receptor affinity, which may find therapeutic relevance in Parkinson's disease-associated cognitive deficits and motor dysfunctions as well as exerting neuroprotective properties., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

This paper introduces BRADSHAW (Biological Response Analysis and Design System using an Heterogenous, Automated Workflow), a system for automated molecular design which integrates methods for chemical structure generation, experimental design, active learning and cheminformatics tools. The simple user interface is designed to facilitate access to large scale automated design whilst minimising software development required to introduce new algorithms, a critical requirement in what is a very fast moving field. The system embodies a philosophy of automation, best practice, experimental design and the use of both traditional cheminformatics and modern machine learning algorithms.

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 A 2A 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 hA 2A AR (K i  = 3.6-11.8 nM). Also derivatives 1-9, featuring an ether linker, preferentially targeted the hA 2A AR but with lower affinity, compared to those of the relative amide compounds. Docking studies, carried out at the hA 2A AR binding site, highlighted some crucial ligand-receptor interactions, particularly those provided by the appended substituent whose nature deeply affected hA 2A AR affinity., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

The adenosine A 2B receptor has been proposed as a novel therapeutic target in cancer, as its expression is drastically elevated in several tumors and cancer cells. Noninvasive molecular imaging via positron emission tomography (PET) would allow the in vivo quantification of this receptor in pathological processes and most likely enable the identification and clinical monitoring of respective cancer therapies. On the basis of a bicyclic pyridopyrimidine-2,4-dione core structure, the new adenosine A 2B receptor ligand 9 was synthesized, containing a 2-fluoropyridine moiety suitable for labeling with the short-lived PET radionuclide fluorine-18. Compound 9 showed a high binding affinity for the human A 2B receptor (K i (A 2B ) = 2.51 nM), along with high selectivities versus the A 1 , A 2A , and A 3 receptor subtypes. Therefore, it was radiofluorinated via nucleophilic aromatic substitution of the corresponding nitro precursor using [ 18 F]F - /K 2.2.2. /K 2 CO 3 in DMSO at 120 °C. Metabolic studies of [ 18 F]9 in mice revealed about 60% of radiotracer intact in plasma at 30 minutes p.i. A preliminary PET study in healthy mice showed an overall biodistribution of [ 18 F]9 , corresponding to the known ubiquitous but low expression of the A 2B receptor. Consequently, [ 18 F]9 represents a novel PET radiotracer with high affinity and selectivity toward the adenosine A 2B receptor and a suitable in vivo profile. Subsequent studies are envisaged to investigate the applicability of [ 18 F]9 to detect alterations in the receptor density in certain cancer-related disease models., Competing Interests: The authors declare no conflict of interest. The founding sponsors had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, and in the decision to publish the results.

The adenosine A 2A receptor (A 2A R) is regarded as a particularly appropriate target for non-dopaminergic treatment of Parkinson's disease (PD). An increased A 2A R availability has been found in the human striatum at early stages of PD and in patients with PD and dyskinesias. The aim of this small animal positron emission tomography/magnetic resonance (PET/MR) imaging study was to investigate whether rotenone-treated mice reflect the aspect of striatal A 2A R upregulation in PD. For that purpose, we selected the known A 2A R-specific radiotracer [ 18 F] FESCH and developed a simplified two-step one-pot radiosynthesis. PET images showed a high uptake of [ 18 F] FESCH in the mouse striatum. Concomitantly, metabolism studies with [ 18 F] FESCH revealed the presence of a brain-penetrant radiometabolite. In rotenone-treated mice, a slightly higher striatal A 2A R binding of [ 18 F] FESCH was found. Nonetheless, the correlation between the increased A 2A R levels within the proposed PD animal model remains to be further investigated.

Among class A G protein-coupled receptors (GPCR), the human adenosine A 2A receptor (hA 2A AR) remains an attractive drug target. However, translation of A 2A AR ligands into the clinic has proved challenging and an improved understanding of A 2A AR pharmacology could promote development of more efficacious therapies. Subtype-selective fluorescent probes would allow detailed real-time pharmacological investigations both in vitro and in vivo. In the present study, two families of fluorescent probes were designed around the known hA 2A AR selective antagonist preladenant (SCH 420814). Both families of fluorescent antagonists retained affinity at the hA 2A AR, selectivity over all other adenosine receptor subtypes and allowed clear visualization of specific receptor localization through confocal imaging. Furthermore, the Alexa Fluor 647-labeled conjugate allowed measurement of ligand binding affinities of unlabeled hA 2A AR antagonists using a bioluminescence resonance energy transfer (NanoBRET) assay. The fluorescent ligands developed here can therefore be applied to a range of fluorescence-based techniques to further interrogate hA 2A AR pharmacology and signaling.

The adenosine A 2B receptor is a critical protein in intestinal water secretion. In the present study, we screened compound libraries to identify inhibitors of the A 2B receptor and evaluated their effect on adenosine-induced intestinal fluid secretion. The screening identified the dihydropyridine calcium antagonists nifedipine and nisoldipine. Their respective affinities for the A 2B receptor (K i value) were 886 and 1,399 nM. Nifedipine and nisoldipine, but not amlodipine or nitrendipine, inhibited both calcium mobilization and adenosine-induced cAMP accumulation in cell lines. Moreover, adenosine injection into the lumen significantly increased fluid volume in the colonic loop of wild-type mice but not A 2B receptor-deficient mice. PSB-1115, a selective A 2B receptor antagonist, and nifedipine prevented elevated adenosine-stimulated fluid secretion in mice. Our results may provide useful insights into the structure-activity relationship of dihydropyridines for A 2B receptor. As colonic fluid secretion by adenosine seems to rely predominantly on the A 2B receptor, nifedipine could be a therapeutic candidate for diarrhoea-related diseases.

A series of fourteen methoxy substituted 2-benzoyl-1-benzofuran derivatives were synthesised and their affinities determined for adenosine A 1 and A 2A receptors via radioligand binding assays to establish the structure activity relationships pertinent for A 1 and A 2A affinity. Compound 3j (6,7-dimethoxybenzofuran-2-yl)(3-methoxyphenyl)methanone exhibited A 1 affinity (A 1 K i (rat) = 6.880 µM) as well as A 2A affinity (A 2A K i (rat) = 0.5161 µM). Compounds 3a-b &3i-k exhibited selective affinity towards A 1 with K i values below 10 µM. The results indicate that C6,7-diOCH 3 substitution on ring A in combination with meta (C3')-OCH 3 substitution on ring B is beneficial for A 1 and A 2A affinity and activity. Compounds 3a-b &3j-k showed low cytotoxicity. Upon in vitro and in silico evaluation, compound 3j may be considered lead-like (i.e. a molecular entity suitable for optimization) and, thus, of value in the design of novel, potent and selective adenosine A 1 and A 2A receptor antagonists., (Copyright © 2019 Elsevier Inc. All rights reserved.)

We report the identification of two subsets of fluorinated nonxanthine A 2B adenosine receptor antagonists. The novel derivatives explore the effect of fluorination at different positions of two pyrimidine-based scaffolds. The most interesting ligands combine excellent hA 2B affinity ( K i < 15 nM) and remarkable subtype selectivity. The results of functional cAMP experiments confirmed the antagonistic behavior of representative ligands. The compounds were designed on the basis of previous molecular models of the stereoselective binding of the parent scaffolds to the hA 2B receptor, and we herein provide refinement of such models with the fluorinated compounds, which allows the explanation of the spurious effects of the fluorination at the different positions explored. These models are importantly confirmed by a synergistic study combining chiral HPLC, circular dichroism, diastereoselective synthesis, molecular modeling, and X-ray crystallography, providing experimental evidence toward the stereospecific interaction between optimized trifluorinated stereoisomers and the hA 2B receptor.

There are four subtypes of adenosine receptors (ARs), named A 1 , A 2A , A 2B and A 3 , all of which are G protein-coupled receptors (GPCRs). Locally produced adenosine is a suppressant in anti-tumor immune surveillance. The A 2B AR, coupled to both Gαs and Gαi G proteins, is one of the several GPCRs that are expressed in a significantly higher level in certain cancer tissues, in comparison to adjacent normal tissues. There is growing evidence that the A 2B AR plays an important role in tumor cell proliferation, angiogenesis, metastasis, and immune suppression. Thus, A 2B AR antagonists are novel, potentially attractive anticancer agents. Several antagonists targeting A 2B AR are currently in clinical trials for various types of cancers. In this review, we first describe the signaling, agonists, and antagonists of the A 2B AR. We further discuss the role of the A 2B AR in the progression of various cancers, and the rationale of using A 2B AR antagonists in cancer therapy.

Human A 3 adenosine receptor hA 3 AR has been implicated in gastrointestinal cancer, where its cellular expression has been found increased, thus suggesting its potential as a molecular target for novel anticancer compounds. Observation made in our previous work indicated the importance of the carbonyl group of amide in the indolylpyrimidylpiperazine (IPP) for its human A 2A adenosine receptor (hA 2A AR) subtype binding selectivity over the other AR subtypes. Taking this observation into account, we structurally modified an indolylpyrimidylpiperazine (IPP) scaffold, 1 (a non-selective adenosine receptors' ligand) into a modified IPP (mIPP) scaffold by switching the position of the carbonyl group, resulting in the formation of both ketone and tertiary amine groups in the new scaffold. Results showed that such modification diminished the A 2A activity and instead conferred hA 3 AR agonistic activity. Among the new mIPP derivatives ( 3 - 6 ), compound 4 showed potential as a hA 3 AR partial agonist, with an E max of 30% and EC 50 of 2.89 ± 0.55 μM. In the cytotoxicity assays, compound 4 also exhibited higher cytotoxicity against both colorectal and liver cancer cells as compared to normal cells. Overall, this new series of compounds provide a promising starting point for further development of potent and selective hA 3 AR partial agonists for the treatment of gastrointestinal cancers.

Adenosine receptors (ARs) are classified as A 1 , A 2A , A 2B , and A 3 subtypes belonging to the superfamily of G-protein-coupled receptors (GPCRs). Several molecular modeling approaches have been developed for A 2B AR and its antagonists, from the construction of a homology model, molecular docking, molecular dynamics (MD) simulations, and 3D quantitative structure-activity relationship (QSAR) modeling to pharmacophore modeling, each of which has different objectives and outcomes. In this review, we provide a systematic outline of advances in molecular modeling approaches towards A 2B AR for deducing its structure and interactions with various types of antagonist. The information, methods and perspectives presented here provides impetus for medicinal chemists to discover potential ligands that can bind selectively with higher affinity to A 2B AR., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

Adenosine is a ubiquitous endogenous nucleoside that controls numerous physiological functions via interacting with its specific G-coupled receptors. Activation of adenosine receptors (AdoRs), particularly A 2B AdoRs promotes the release of inflammatory cytokines; reduces vascular permeabilization and induces angiogenesis, thereby making A 2B AdoR becomes a potentially pharmacological target for drug development. Presently, for investigating the structural determinants of 164 xanthine derivatives as A 2B AdoR antagonists, we performed an in silico study integrating with 3D-QSAR, docking and molecular dynamics (MD) simulation. The obtained optimal model shows strong predictability ( Q 2  = 0.647, R 2 ncv  = 0.955, and R 2 pred  = 0.848). Additionally, to explore the binding mode of the ligand with A 2B AdoR and to understand their binding mechanism, docking analysis, MD simulations (20 ns), and the calculation of binding free energy were also carried out. Finally, the structural determinants of these xanthine derivatives were identified and a total of 20 novel A 2B AdoR antagonists with improved potency were computationally designed, and their synthetic feasibility and selectivity were also evaluated. The information derived from the present study offers a better appreciation for exploring the interaction mechanism of the ligand with A 2B AdoR, which could be helpful for designing novel potent A 2B AdoR antagonists. Communicated by Ramaswamy H. Sarma.

Previous studies explored 2-benzylidine-1-tetralone derivatives as innovative adenosine A 1 and A 2A receptor antagonists for alternative non-dopaminergic treatment of Parkinson's disease. This study's aim is to investigate structurally related 2-benzylidene-1-indanones with substitutions on ring A and B as novel, potent and selective adenosine A 1 and A 2A receptor blockers. 2-Benzylidene-1-indanone derivatives were synthesised via acid catalysed aldol condensation reactions and evaluated via radioligand binding assays to ascertain structure activity relationships to govern A 1 and A 2A AR affinity. The results indicated that hydroxy substitution at C4 of ring A and meta (3'), or para (4') substitution on ring B of the 2-benzylidene-1-indanone scaffold (2C: ) is preferred over substitution at C5 (2D: ) or C6 (2E: ) of ring A for adenosine A 1 receptor activity and selectivity in the micromolar range. Furthermore, substitution at the meta (3') position of ring B with chlorine lead to the highly potent and selective adenosine A 2A receptor antagonist, compound 2 H: . Compound 2C: and the 2Q: behaved as adenosine A 1 receptor antagonists in the performed GTP shift assays. In view of these findings, compounds 2C: , 2 H: , 2Q: and 2P: are potent and selective adenosine A 1 and A 2A receptor antagonists for the potential treatment of neurological conditions., Competing Interests: The authors have no conflict of interest to declare., (© Georg Thieme Verlag KG Stuttgart · New York.)

8-Arylethynylxanthine derivatives are potent, selective adenosine A 2A receptor antagonists, which represent (potential) therapeutics for Parkinson's disease, Alzheimer's dementia, and the immunotherapy of cancer. 6-Amino-5-amidouracil derivatives are important precursors for the synthesis of such xanthines. We noticed an unexpected duplication of NMR signals in many of these uracil derivatives. Here, we present a detailed analytical study of structurally diverse 6-amino-5-carboxamidouracils employing dynamic and two-dimensional NMR spectroscopy, density functional theory calculations, and X-ray analysis to explain the unexpected properties of these valuable drug intermediates.

In the present study, an attempt has been made to develop a new series of 1,3,7,8-tetrasubstituted xanthine based potent and selective AR ligands for the treatment of Parkinson's disease. Antagonistic interactions between dopamine and A 2A adenosine receptors serve as the basis for the development of AR antagonists as potential drug candidates for PD. All the synthesized compounds have been evaluated for their affinity toward AR subtypes using in vitro radioligand binding assays. 1,3-Dipropylxanthine 7a with a methyl substituent at N-7 position represents the most potent compound of the series and displayed highest affinity (A 2A , K i  = 0.108 µM), however incorporation of a propargyl group at 7-positon of the xanthine nucleus seems to be the most appropriate substitution to improve selectivity towards the A 2A subtype along with reasonable potency. Antiparkinsonian activity has been evaluated using perphenazine induced catatonia in rats. Most of the synthesized xanthines significantly lowered the catatonic score as compared to control and displayed antiparkinsonian effects comparable to standard drug. All the synthesized compounds were subjected to grid-based molecular docking studies to understand the key structural requirements for the development of new molecules well-endowed with intrinsic efficacy and selectivity as adenosine receptor ligands. In silico studies carried out on newly synthesized xanthines provided further support to the pharmacological results., (Copyright © 2019 Elsevier Inc. All rights reserved.)

The A 2B adenosine receptor (A 2B AR) was proposed as a novel target for the (immuno)therapy of cancer since A 2B AR blockade results in antiproliferative, antiangiogenic, antimetastatic, and immunostimulatory effects. In this study, we explored the structure-activity relationships of xanthin-8-yl-benzenesulfonamides mainly by introducing a variety of linkers and substituents attached to the sulfonamide residue. A new, convergent strategy was established, which facilitated the synthesis of the target compounds. Many of the new compounds exhibited subnanomolar affinity for the A 2B AR combined with high selectivity. Functional groups were introduced, which will allow the attachment of dyes and other reporter groups. 8-(4-((4-(4-Bromophenyl)piperazin-1-yl)sulfonyl)phenyl)-1-propylxanthine (34, PSB-1901) was the most potent A 2B -antagonist ( K i 0.0835 nM, K B 0.0598 nM, human A 2B AR) with >10 000-fold selectivity versus all other AR subtypes. It was similarly potent and selective at the mouse A 2B AR, making it a promising tool for preclinical studies. Computational studies predicted halogen bonding to contribute to the outstanding potency of 34.

Through their coupling to G proteins, G Protein-Coupled Receptors (GPCRs) trigger cellular responses to various signals. Some recent experiments have interestingly demonstrated that the G protein can also act on the receptor by favoring a closed conformation of its orthosteric site, even in the absence of a bound agonist. In this work, we explored such an allosteric modulation by performing extensive molecular dynamics simulations on the adenosine A2 receptor (A2AR) coupled to the Mini-Gs protein. In the presence of the Mini-Gs, we confirmed a restriction of the receptor's agonist binding site that can be explained by a modulation of the intrinsic network of contacts of the receptor. Of interest, we observed similar effects with the C-terminal helix of the Mini-Gs, showing that the observed effect on the binding pocket results from direct local contacts with the bound protein partner that cause a rewiring of the whole receptor's interaction network.

N9-Benzyl-substituted imidazo-, pyrimido- and 1,3-diazepino[2,1-f]purinediones were designed as dual-target-directed ligands combining A 2A adenosine receptor (AR) antagonistic activity with blockade of monoamine oxidase B (MAO-B). A library of 37 novel compounds was synthesized and biologically evaluated in radioligand binding studies at AR subtypes and for their ability to inhibit MAO-B. A systematic modification of the tricyclic structures based on a xanthine core by enlargement of the third heterocyclic ring or attachment of various substituted benzyl moieties resulted in the development of 9-(2-chloro-6-fluorobenzyl)-1,3-dimethyl-6,7,8,9-tetrahydropyrimido[2,1-f]purine-2,4(1H,3H)-dione (9u; K i human A 2A AR: 189 nM and IC 50 human MAO-B: 570 nM) as the most potent dual acting ligand of the series displaying high selectivity versus related targets. Moreover, some potent, selective MAO-B inhibitors were identified in the group of pyrimido- and 1,3-diazepino[2,1-f]purinediones. Compound 10d (10-(3,4-dichlorobenzyl)-1,3-dimethyl-7,8,9,10-tetrahydro-1H-[1,3]diazepino[2,1-f]purine-2,4(3H,6H)-dione) displayed an IC 50 value at human MAO-B of 83 nM. Analysis of structure-activity relationships was complemented by molecular docking studies based on previously published X-ray structures of the protein targets. An extended biological profile was determined for selected compounds including in vitro evaluation of potential hepatotoxicity calculated in silico and antioxidant properties as an additional desirable activity. The new molecules acting as dual target drugs may provide symptomatic relief as well as disease-modifying effects for neurodegenerative diseases, in particular Parkinson's disease., (Copyright © 2019. Published by Elsevier Ltd.)

Parkinson's disease (PD) is a neurodegenerative disease with significant unmet medical needs. The current dopamine-centered treatments aim to restore motor functions of patients without slowing the disease progression. Long-term usage of these drugs is associated with diminished efficacy, motor fluctuation, and dyskinesia. Furthermore, the nonmotor features associated with PD such as sleep disorder, pain, and psychiatric symptoms are poorly addressed by the dopaminergic treatments. Adenosine receptor A 2A antagonists have emerged as potential treatment for PD in the past decade. Here we summarize the recent work (2015-2018) on adenosine receptor A 2A antagonists and discuss the challenge and opportunity for the treatment of PD.

The A 2B adenosine receptor is a G protein-coupled receptor that belongs to the four member family of adenosine receptors: A 1 , A 2A , A 2B , A 3 . While adenosine-mediated A 2B receptor signaling attenuates acute inflammation, facilitates tissue adaptation to hypoxia, and induces increased ischemia tolerance under conditions of an acute insult, persistently elevated adenosine levels and A 2B receptor signaling are characteristics of a number of chronic disease states. In this report we describe the discovery of certain thienouracils (thieno[2,3-d]pyrimidine-2,4(1H,3H)-diones) as antagonists of the A 2B adenosine receptor by high-throughput screening from our corporate substance collection. The structure optimization of the initial screening hits led to BAY-545, an A 2B receptor antagonist that was suitable for in vivo testing. The structure optimization work, SAR that was derived from there, as well as the properties of BAY-545 are also described. In vivo efficacy of BAY-545 was demonstrated in two models of lung fibrosis and data is presented., (Copyright © 2018 Elsevier Masson SAS. All rights reserved.)

Safety pharmacology screening against a wide range of unintended vital targets using in vitro assays is crucial to understand off-target interactions with drug candidates. With the increasing demand for in vitro assays, ligand- and structure-based virtual screening approaches have been evaluated for potential utilization in safety profiling. Although ligand based approaches have been actively applied in retrospective analysis or prospectively within well-defined chemical space during the early discovery stage (i.e., HTS screening and lead optimization), virtual screening is rarely implemented in later stage of drug discovery (i.e., safety). Here we present a case study to evaluate ligand-based 3D QSAR models built based on in vitro antagonistic activity data against adenosine receptor 2A (A2A). The resulting models, obtained from 268 chemically diverse compounds, were used to test a set of 1,897 chemically distinct drugs, simulating the real-world challenge of safety screening when presented with novel chemistry and a limited training set. Due to the unique requirements of safety screening versus discovery screening, the limitations of 3D QSAR methods (i.e., chemotypes, dependence on large training set, and prone to false positives) are less critical than early discovery screen. We demonstrated that 3D QSAR modeling can be effectively applied in safety assessment prior to in vitro assays, even with chemotypes that are drastically different from training compounds. It is also worth noting that our model is able to adequately make the mechanistic distinction between agonists and antagonists, which is important to inform subsequent in vivo studies. Overall, we present an in-depth analysis of the appropriate utilization and interpretation of pharmacophore-based 3D QSAR models for safety screening., Competing Interests: The authors declare the following competing interests: Amgen Inc. provided support in the form of salaries for authors FF, DTW, HDH, RTD; and at the initial planning stage of the presented study, DTW was an employee for Schrodinger Inc. This does not alter our adherence to PLOS ONE policies on sharing data and materials. There are no patents, products in development or marketed products associated with this research to declare.

A2A receptor belongs to the family of GPCRs, which are the most abundant membrane protein family. Studies in the last few decades have shown the therapeutic applications of A2A receptor in various diseases. In the present mini-review, we have discussed the recent progress in the in-silico studies of the A2A receptor. Herein, we described the different structures of A2A receptor, the discovery of new agonists and antagonists using virtualscreening/ docking, pharmacophore modeling, and QSAR based pharmacophore modeling. We have also discussed various molecular dynamics (MD) simulations studies of A2A receptor in complex with ligands., (Copyright© Bentham Science Publishers; For any queries, please email at epub@benthamscience.net.)