Human Adenosine Research Articles

Effect of a toggle switch mutation in TM6 of the human adenosine A₃ receptor on Gi protein-dependent signalling and Gi-independent receptor internalization.

BACKGROUND AND PURPOSEThe highly conserved tryptophan (W6.48) in transmembrane domain 6 of GPCRs has been shown to play a central role in forming an active conformation in response to agonist binding. We set out to characterize the effect of this mutation on the efficacy of two agonists at multiple signalling pathways downstream of the adenosine A3 receptor.EXPERIMENTAL APPROACHResidue W6.48 in the human adenosine A3 receptor fused to yellow fluorescent protein was mutated to phenylalanine and expressed in CHO-K1 cells containing a cAMP response element reporter gene. The effects on agonist-mediated receptor internalization were monitored by automated confocal microscopy and image analysis. Further experiments were carried out to investigate agonist-mediated ERK1/2 phosphorylation, inhibition of [3H]-cAMP accumulation and β-arrestin2 binding.KEY RESULTSNECA was able to stimulate agonist-mediated internalization of the W6.48F mutant receptor, while the agonist HEMADO was inactive. Investigation of other downstream signalling pathways indicated that G-protein coupling was impaired for both agonists tested. Mutation of W6.48F therefore resulted in differential effects on agonist efficacy, and introduced signalling pathway bias for HEMADO at the adenosine A3 receptor.CONCLUSIONS AND IMPLICATIONSInvestigation of the pharmacology of the W6.48F mutant of the adenosine A3 receptor confirms that this region is important in forming the active conformation of the receptor for stimulating a number of different signalling pathways and that mutations in this residue can lead to changes in agonist efficacy and signalling bias.

7-Amino-2-phenylpyrazolo[4,3-d]pyrimidine derivatives: Structural investigations at the 5-position to target human A1 and A2A adenosine receptors. Molecular modeling and pharmacological studies

In previous research, several 7-amino-2-arylpyrazolo[4,3-d]pyrimidine derivatives were identified as highly potent and selective antagonists at the human A3 adenosine receptor. Structure–activity relationship studies highlighted that affinity and selectivity depended on the nature of the substituents at the 5- and 7-positions of the pyrazolo[4,3-d]pyrimidine scaffold. In particular, small lipophilic residues at the 5-position and a free amino group at position 7 afforded compounds able to bind all four human (h) adenosine receptors. Hence, to shift affinity toward the hA1 and/or hA2A subtypes, alkyl and arylalkyl chains of different length were appended at position 5 of the 2-phenylpyrazolo[4,3-d]pyrimidin-7-amine. Among the new compounds, a dual hA1/hA2A receptor antagonist was identified, namely the 5-(3-phenylpropyl) derivative 25, which shows high affinity both at human A1 (Ki = 5.31 nM) and A2A (Ki = 55 nM) receptors. We also obtained some potent and selective antagonists for the A1 receptor, such as the 5-(3-arylpropyl)-substituted compounds 26–31, whose affinities fall in the low nanomolar range (Ki = 0.15–18 nM). Through an in silico receptor-driven approach, the obtained binding data were rationalized and the molecular bases of the hA1 and hA2A AR affinity and selectivity of derivatives 25–31 are explained.

High-yield production of apoplast-directed human adenosine deaminase in transgenic tobacco BY-2 cell suspensions.

Adenosine deaminase (ADA) deficiency, where a deleterious mutation in the ADA gene of patients results in a dysfunctional immune system, is ultimately caused by an absence of ADA. Over the last 25 years the disease has been treated with PEG-ADA, made from purified bovine ADA coupled with polyethylene glycol (PEG). However, it is thought that an enzyme replacement therapy protocol based on recombinant human ADA would probably be a more effective treatment. With this end in mind, a human ADA cDNA was inserted into plant expression vectors used to transform tobacco plant cell suspensions. Transgenic calli expressing constructs containing apoplast-directing signals showed significantly higher levels of recombinant ADA expression than calli transformed with cytosolic constructs. The most significant ADA activities, however, were measured in the media of transgenic cell suspensions prepared from high expressing transformed calli: where incorporation of a signal for arabinogalactan addition to ADA led to a recombinant protein yield of approximately 16mgL(-1) , a 336-fold increase over ADA produced by cell suspensions transformed with a cytosolic construct.

Proteochemometric modeling in a Bayesian framework.

Proteochemometrics (PCM) is an approach for bioactivity predictive modeling which models the relationship between protein and chemical information. Gaussian Processes (GP), based on Bayesian inference, provide the most objective estimation of the uncertainty of the predictions, thus permitting the evaluation of the applicability domain (AD) of the model. Furthermore, the experimental error on bioactivity measurements can be used as input for this probabilistic model.In this study, we apply GP implemented with a panel of kernels on three various (and multispecies) PCM datasets. The first dataset consisted of information from 8 human and rat adenosine receptors with 10,999 small molecule ligands and their binding affinity. The second consisted of the catalytic activity of four dengue virus NS3 proteases on 56 small peptides. Finally, we have gathered bioactivity information of small molecule ligands on 91 aminergic GPCRs from 9 different species, leading to a dataset of 24,593 datapoints with a matrix completeness of only 2.43%.GP models trained on these datasets are statistically sound, at the same level of statistical significance as Support Vector Machines (SVM), with values on the external dataset ranging from 0.68 to 0.92, and RMSEP values close to the experimental error. Furthermore, the best GP models obtained with the normalized polynomial and radial kernels provide intervals of confidence for the predictions in agreement with the cumulative Gaussian distribution. GP models were also interpreted on the basis of individual targets and of ligand descriptors. In the dengue dataset, the model interpretation in terms of the amino-acid positions in the tetra-peptide ligands gave biologically meaningful results.

Overexpression of NUAK1 is associated with disease-free survival and overall survival in patients with gastric cancer.

Novel (nua) kinase family 1 (NUAK1) is a member of the human adenosine monophosphate-activated protein kinases family, which is overexpressed in multiple human malignancies and thought to be involved in tumor invasion and metastasis ability. Our study is to investigate the association of NUAK1 expression with clinicopathological parameters and prognostic significance of patients with gastric cancer. The expression patterns of the NUAK1 protein in 117 primary archival gastric cancer specimens and 46 adjacent normal epithelial tissues from patients were detected by immunohistochemistry assay. Staining evaluation results were analyzed statistically in relation to various clinicopathological characters, recurrence-free survival and overall survival. High level of NUAK1 expression was detected in gastric cancer, significantly more than in adjacent normal epithelial cells. In gastric cancer, NUAK1 was positively correlated with depth of invasion, lymph node metastasis, pathological stage, surgical resection and histological differentiation. However, no correlations between NUAK1 expression and patients' age, sex, tumor size, location, CA19-9 or CEA were detected. The recurrence-free survival and overall survival were significantly shorter for patients with NUAK1 higher scores than those with NUAK1 lower scores. Multivariate analysis identified NUAK1 was an independent prognostic factor for both recurrence-free survival and overall survival. Our findings provided convincing evidence for NUAK1 overexpression, which was tightly associated with more aggressive tumor behavior and a poor prognosis, indicating that NUAK1 is a valuable molecular biomarker for gastric cancer progression. It might also act as a promising target for both prognostic prediction and therapeutics.

Application of orthogonal L-shaped PLS to chemogenomic data and its chemical interpretation from predictive and orthogonal latent variables

We carried out a validation study of the orthogonal L-shaped PLS (OLPLS) method using chemogenomic data based on adenosine receptor inhibitor activity measurements. Using OLPLS, the ligand and protein descriptors could be connected to eight adenosine receptor inhibitor activities. The fingerprints representing specific chemical substructures on the ligands were used as the ligand descriptors, while z-scales were used as the protein descriptors. Three clusters were observed in the chemical and protein spaces from the predictive scores and loadings. From these, the predictive and orthogonal ligand structure fragments towards three adenosine receptors could be successfully elucidated. The predictive fragment for the human adenosine 2A receptor was confirmed by comparison to the X-ray crystal structure. As expected, the orthogonal fragments contained no physicochemical features required for specific interaction with the adenosine receptors.

A bimodular nuclear localization signal assembled via an extended double-stranded RNA-binding domain acts as an RNA-sensing signal for transportin 1.

The human RNA-editing enzyme adenosine deaminase acting on RNA (ADAR1) carries a unique nuclear localization signal (NLS) that overlaps one of its double-stranded RNA-binding domains (dsRBDs). This dsRBD-NLS is recognized by the nuclear import receptor transportin 1 (Trn1; also called karyopherin-β2) in an RNA-sensitive manner. Most Trn1 cargos bear a well-characterized proline-tyrosine-NLS, which is missing from the dsRBD-NLS. Here, we report the structure of the dsRBD-NLS, which reveals an unusual dsRBD fold extended by an additional N-terminal α-helix that brings the N- and C-terminal flanking regions in close proximity. We demonstrate experimentally that the atypical ADAR1-NLS is bimodular and is formed by the combination of the two flexible fragments flanking the folded domain. The intervening dsRBD acts only as an RNA-sensing scaffold, allowing the two NLS modules to be properly positioned for interacting with Trn1. We also provide a structural model showing how Trn1 can recognize the dsRBD-NLS and how dsRNA binding can interfere with Trn1 binding.

ChemInform Abstract: Synthesis of Novel Pyrido[3,2‐e][1,2,4]triazolo[1,5‐c]pyrimidine Derivatives: Potent and Selective Adenosine A3 Receptor Antagonists.

Abstract15 Title compounds of type (III) or (V) are prepared and 8 of them are evaluated for their affinity towards all four subtypes of human adenosine receptors.

Agonists for the Adenosine A1Receptor with Tunable Residence Time. A Case for Nonribose 4-Amino-6-aryl-5-cyano-2-thiopyrimidines

We report the synthesis and evaluation of previously unreported 4-amino-6-aryl-5-cyano-2-thiopyrimidines as selective human adenosine A1 receptor (hA1AR) agonists with tunable binding kinetics, this without affecting their nanomolar affinity for the target receptor. They show a very diverse range of kinetic profiles (from 1 min (compound 52) to 1 h (compound 43)), and their structure-affinity relationships (SAR) and structure-kinetics relationships (SKR) were established. When put in perspective with the increasing importance of binding kinetics in drug discovery, these results bring new evidence of the consequences of affinity-only driven selection of drug candidates, that is, the potential elimination of slightly less active compounds that may display preferable binding kinetics.

Dissecting the Mechanism of Histone Deacetylase Inhibitors to Enhance the Activity of Zinc Finger Nucleases Delivered by Integrase-Defective Lentiviral Vectors

Integrase-defective lentiviral vectors (IDLVs) have been of limited success in the delivery of zinc finger nucleases (ZFNs) to human cells, due to low expression. A reason for reduced gene expression has been proposed to involve the epigenetic silencing of vector genomes, carried out primarily by histone deacetylases (HDACs). In this study, we tested valproic acid (VPA), a known HDAC inhibitor (HDACi), for its ability to increase transgene expression from IDLVs, especially in the context of ZFN delivery. Using ZFNs targeting the human adenosine deaminase (ADA) gene in K562 cells, we demonstrated that treatment with VPA enhanced ZFN expression by up to 3-fold, resulting in improved allelic disruption at the ADA locus. Furthermore, three other U.S. Food and Drug Administration-approved HDACis (vorinostat, givinostat, and trichostatin-A) exhibited a similar effect on the activity of ZFN-IDLVs in K562 cells. In primary human CD34(+) cells, VPA- and vorinostat-treated cells showed higher levels of expression of both green fluorescent protein (GFP) as well as ZFNs from IDLVs. A major mechanism for the effects of HDAC inhibitors on improving expression was from their modulation of the cell cycle, and the influence of heterochromatinization was determined to be a lesser contributing factor.

Insights into Behavioral Vulnerability to Differential Sleep Pressure and Circadian Phase from a Functional ADA Polymorphism

Sleep loss affects human behavior in a nonuniform manner, depending on the cognitive domain and also the circadian phase. Besides, evidence exists about stable interindividual variations in sleep loss-related performance impairments. Despite this evidence, only a few studies have considered both circadian phase and neurobehavioral domain when investigating trait-like vulnerability to sleep manipulation. By applying a randomized, crossover design with 2 sleep pressure conditions (40 h sleep deprivation vs. 40 h multiple naps), we investigated the influence of a human adenosine deaminase (ADA) polymorphism (rs73598374) on several behavioral measures throughout nearly 2 circadian cycles. Confirming earlier studies, we observed that under sleep deprivation the previously reported vulnerable G/A-allele carriers felt overall sleepier than G/G-allele carriers. As expected, this difference was no longer present when sleep pressure was reduced by the application of multiple naps. Concomitantly, well-being was worse in the G/A genotype under sleep loss when compared to the nap protocol, and n-back working memory performance appeared to be specifically susceptible to sleep-wake manipulation in this genotype. When considering psychomotor vigilance performance, however, a higher sensitivity to sleep-wake manipulation was detected in homozygous participants, but specifically at the end of the night and only for optimal task performance. Although these data are based on a small sample size and hence require replication (12 G/A- and 12 G/G-allele carriers), they confirm the assumption that interindividual differences regarding the effect of sleep manipulation highly depend on the cognitive task and circadian phase, and thus emphasize the necessity of a multimethodological approach. Moreover, they indicate that napping might be suitable to counteract endogenously heightened sleep pressure depending on the neurobehavioral domain.

Agrobacterium-mediated transformation of tarwi (Lupinus mutabilis Sweet), a potential platform for the production of plant-made proteins

A robust, reproducible method of Agrobacterium-mediated transformation was developed for Lupinus mutabilis Sweet (tarwi), a large-seeded Andean legume. Initially, a regeneration and transformation protocol was developed using a plasmid which contained a bifunctional fusion gene conferring both β-glucuronidase (gus) and neomycin phosphotransferase activities, under the control of a constitutive 35S35SAMV promoter. The tissue explants consisted of longitudinal slices from embryonic axes of imbibed, mature seed. Using a series of tissue culture media for cocultivation, shoot initiation, shoot elongation, and rooting, kanamycin-resistant transgenic plants were recovered from approximately 1% of the explants. This transformation protocol was further used with a construct that contained the human adenosine deaminase (hADA) gene under the control of a legumin seed-specific promoter, also with a kanamycin resistance cassette for chemical selection. Changes made during the course of this study, which included adjustments to the antibiotic concentration during the shoot elongation and rooting phases plus the incorporation of techniques to improve ventilation in the tissue culture system, resulted in major improvements in shoot quality and, most significantly, rooting. The outcome was an increased frequency of transgenic plant recovery (7.4%), with a low (9.6%) rate of plants that escaped selection. The inheritance of the hADA gene was documented and showed the expected Mendelian segregation pattern. The produced hADA protein was a fully functional enzyme and localized only in the seed, as expected. Thus, this legume species is an excellent candidate for a nonfood plant host platform for the production of plant-made proteins.

Rehabilitating drug-induced long-QT promoters: In-silico design of hERG-neutral cisapride analogues with retained pharmacological activity

BackgroundThe human ether-a-go-go related gene 1 (hERG1), which codes for a potassium ion channel, is a key element in the cardiac delayed rectified potassium current, IKr, and plays an important role in the normal repolarization of the heart’s action potential. Many approved drugs have been withdrawn from the market due to their prolongation of the QT interval. Most of these drugs have high potencies for their principal targets and are often irreplaceable, thus “rehabilitation” studies for decreasing their high hERG1 blocking affinities, while keeping them active at the binding sites of their targets, have been proposed to enable these drugs to re-enter the market.MethodsIn this proof-of-principle study, we focus on cisapride, a gastroprokinetic agent withdrawn from the market due to its high hERG1 blocking affinity. Here we tested an a priori strategy to predict a compound’s cardiotoxicity using de novo drug design with molecular docking and Molecular Dynamics (MD) simulations to generate a strategy for the rehabilitation of cisapride.ResultsWe focused on two key receptors, a target interaction with the (adenosine) receptor and an off-target interaction with hERG1 channels. An analysis of the fragment interactions of cisapride at human A2A adenosine receptors and hERG1 central cavities helped us to identify the key chemical groups responsible for the drug activity and hERG1 blockade. A set of cisapride derivatives with reduced cardiotoxicity was then proposed using an in-silico two-tier approach. This set was compared against a large dataset of commercially available cisapride analogs and derivatives.ConclusionsAn interaction decomposition of cisapride and cisapride derivatives allowed for the identification of key active scaffolds and functional groups that may be responsible for the unwanted blockade of hERG1.

Discovery of simplified N2-substituted pyrazolo[3,4-d]pyrimidine derivatives as novel adenosine receptor antagonists: Efficient synthetic approaches, biological evaluations and molecular docking studies

In the present study, a molecular simplification approach was employed to design novel bicyclic pyrazolo[3,4-d]pyrimidine (PP) derivatives from tricyclic pyrazolo[4,3-e]-1,2,4-triazolo-[1,5-c]pyrimidines (PTP) as promising human A3 adenosine receptor (hA3AR) antagonists. All the target compounds were synthesized using novel and efficient synthetic schemes and the structure–activity relationship studies of these PPs were explored through the synthesis of a series of PTP analogues with various substituents. Substituents with different lipophilicity and steric hindrance (e.g., alkyl and aryl–alkyl) functions were introduced at N2 position of the pyrazole ring, while acyl groups with different electronic properties were introduced at C6 position of the bicyclic nucleus to probe both electronic and positional effects. Most of the synthesized derivatives of the PP series presented good affinity at the hA3AR, as indicated by the low micromolar range of Ki values and among them, compound 63 with N2 neopentyl substituents showed most potent hA3AR affinity with Ki value of 0.9μM and high selectivity (hA1AR/hA3AR=>111 & hA2AAR/hA3AR=>111) towards other adenosine receptor subtypes. Interestingly, small isopropyl groups at N2 position displayed high affinity at another receptor subtype (hA2AAR, e.g., compound 55, with Ki hA2AAR=0.8μM), while they were less favorable at the hA3AR. Molecular docking analysis was also performed to predict the possible binding mode of target compounds inside the hA3AR and hA2AAR. Overall, PP derivatives represent promising starting points for new AR antagonists.

A yeast screening method to decipher the interaction between the adenosine A2B receptor and the C-terminus of different G protein α-subunits

The expression of human G protein-coupled receptors (GPCRs) in Saccharomyces cerevisiae containing chimeric yeast/mammalian Gα subunits provides a useful tool for the study of GPCR activation. In this study, we used a one-GPCR-one-G protein yeast screening method in combination with molecular modeling and mutagenesis studies to decipher the interaction between GPCRs and the C-terminus of different α-subunits of G proteins. We chose the human adenosine A2B receptor (hA2BR) as a paradigm, a typical class A GPCR that shows promiscuous behavior in G protein coupling in this yeast system. The wild-type hA2BR and five mutant receptors were expressed in 8 yeast strains with different humanized G proteins, covering the four major classes: Gαi, Gαs, Gαq, and Gα12. Our experiments showed that a tyrosine residue (Y) at the C-terminus of the Gα subunit plays an important role in controlling the activation of GPCRs. Receptor residues R103(3.50) and I107(3.54) are vital too in G protein-coupling and the activation of the hA2BR, whereas L213(IL3) is more important in G protein inactivation. Substitution of S235(6.36) to alanine provided the most divergent G protein-coupling profile. Finally, L236(6.37) substitution decreased receptor activation in all G protein pathways, although to a different extent. In conclusion, our findings shed light on the selectivity of receptor/G protein coupling, which may help in further understanding GPCR signaling.

Short Chain Lipids Maintain Adenosine A2AR Ligand Binding in the Absence of Cholesterol

Evidence of preferential interactions between sphingolipids and cholesterol, and the identification of cholesterol binding pockets in some membrane proteins highlights the importance of lipids in the regulation of membrane protein function. However, the mechanism through which these lipid-protein interactions modify the conformation and activity of membrane proteins is not yet understood. In vitro, cholesterol is known to affect micelle physical properties and has been found to interact directly with some membrane proteins. Previous studies of a G protein-coupled receptor (GPCR), human adenosine A2A receptor (hA2AR), purified using the detergent dodecylmaltoside (DDM) showed that the presence of a cholesterol analog was critical for ligand binding and the structural stability of the receptor. Here, we present biophysical characterization and ligand binding studies of the hA2AR purified using a short chain lipid (1,2-dihexanoyl-sn-glycero-3-phosphocholine, DHPC), which indicate that cholesterol is not needed to maintain the functionality and stability of the hA2AR in this lipid system. Differences in stability and ligand binding affinity are observed when the receptor is purified using these detergent and lipid systems, emphasizing the importance of the solubilization environment on receptor functionality. We will highlight the use of fluorescence polarization in characterizing this stability, for example, following protein storage or lipid addition.

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 N6-position. In contrast, the adenosine-5′-N-ethyluronamide (NECA) analogs of 2-(ar)-alkynyladenosine derivatives are full A3 agonists. Molecular modeling analyses were performed considering both the conformational behavior of the ligands and the impact of 2- and 5′-substituents on ligand–target interaction. The results suggest an explanation for the different agonistic behavior of adenosine and NECA derivatives, respectively. A sub-pocket of the binding site was analyzed as a crucial interaction domain for receptor activation.

Discovery of a novel activator of 5-lipoxygenase from an anacardic acid derived compound collection

Lipoxygenases (LOXs) and cyclooxygenases (COXs) metabolize poly-unsaturated fatty acids into inflammatory signaling molecules. Modulation of the activity of these enzymes may provide new approaches for therapy of inflammatory diseases. In this study, we screened novel anacardic acid derivatives as modulators of human 5-LOX and COX-2 activity. Interestingly, a novel salicylate derivative 23a was identified as a surprisingly potent activator of human 5-LOX. This compound showed both non-competitive activation towards the human 5-LOX activator adenosine triphosphate (ATP) and non-essential mixed type activation against the substrate linoleic acid, while having no effect on the conversion of the substrate arachidonic acid. The kinetic analysis demonstrated a non-essential activation of the linoleic acid conversion with a KA of 8.65μM, αKA of 0.38μM and a β value of 1.76. It is also of interest that a comparable derivative 23d showed a mixed type inhibition for linoleic acid conversion. These observations indicate the presence of an allosteric binding site in human 5-LOX distinct from the ATP binding site. The activatory and inhibitory behavior of 23a and 23d on the conversion of linoleic compared to arachidonic acid are rationalized by docking studies, which suggest that the activator 23a stabilizes linoleic acid binding, whereas the larger inhibitor 23d blocks the enzyme active site.

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 N6-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.

Modulation of A2B adenosine receptor by 1-Benzyl-3-ketoindole derivatives

We have disclosed a series of 1-benzyl-3-ketoindole derivatives acting as either positive or negative modulators of the human A2B adenosine receptor (A2B AR) depending on small differences in their side chain. The new compounds were designed taking into account structural similarities between AR antagonists and ligands of the GABAA/benzodiazepine receptor. All compounds resulted totally inactive at A2A and A3 ARs and showed small (8a,b) or none (7a,b, 8c and 9a,b) affinity for A1 AR. When tested on A2B AR-transfected CHO cells, 7a,b and 8a acted as positive modulators, whereas 8b,c and 9a,b acted as negative modulators, enhancing or weakening the NECA-induced increase of cAMP levels, respectively. Compounds 7–9 might be regarded as useful biological and pharmacological tools to explore the therapeutic potential of A2B AR modulators, while their 3-ketoindole scaffold might be taken as a reference to design new analogs.