Selective Adenosine A2A Antagonist Research Articles

Effects of Selen on the Antidepressant-like Activity of Agents Affecting the Adenosinergic Neurotransmission.

The main goal of this study was to determine the antidepressant-like potential of the co-administration of sodium selenite (Se) and the selective adenosine A1 and A2A antagonists DPCPX and istradefylline (IST), respectively, in mice despair tests. Biochemical studies were performed to elucidate the action mechanisms of the investigated treatment strategies. The results confirmed that, when administered by itself, Se exerts an antidepressant-like effect in the FST and TST and that this activity is dose-dependent. Further experiments demonstrated that Se (0.25 mg/kg) significantly enhanced the activity of mice in both tests when co-administered with DPCPX (1 mg/kg) and IST (0.5 mg/kg) at doses which would be ineffective if administered individually. Our research revealed that neither DPCPX, IST, nor Se or combinations of the tested substances induced significant changes in the brain-derived neurotrophic factor (BDNF) levels in mice serum vs. the NaCl-treated group. However, we observed a decrease in the mRNA level of antioxidant defense enzymes. Molecular studies also showed changes in the expression of the Slc6a15, Comt, and Adora1 genes, particularly after exposure to the combination of Se and DPCPX, which indicates a beneficial effect and may help to explain the key mechanism of the antidepressant effect. The combination of Se with substances attenuating adenosine neurotransmission may become a new therapeutic strategy for patients with depression.

Orchestration of Dopamine Neuron Population Activity in the Ventral Tegmental Area by Caffeine: Comparison With Amphetamine.

BackgroundAmong psychostimulants, the dopamine transporter ligands amphetamine and cocaine display the highest addictive potential; the adenosine receptor antagonist caffeine is most widely consumed but less addictive. Psychostimulant actions of amphetamine were correlated with its ability to orchestrate ventral tegmental dopamine neuron activity with contrasting shifts in firing after single vs repeated administration. Whether caffeine might impinge on dopamine neuron activity has remained elusive.MethodsPopulation activity of ventral tegmental area dopamine neurons was determined by single-unit extracellular recordings and set in relation to mouse behavior in locomotion and conditioned place preference experiments, respectively.ResultsA single dose of caffeine reduced population activity as did amphetamine and the selective adenosine A2A antagonist KW-6002, but not the A1 antagonist DPCPX. Repeated administration of KW-6002 or amphetamine led to drug-conditioned place preference and to unaltered or even enhanced population activity. Recurrent injection of caffeine or DPCPX, in contrast, failed to cause conditioned place preference and persistently reduced population activity. Subsequent to repetitive drug administration, re-exposure to amphetamine or KW-6002, but not to caffeine or DPCPX, was able to reduce population activity.ConclusionsBehavioral sensitization to amphetamine is attributed to persistent activation of ventral tegmental area dopamine neurons via the ventral hippocampus. Accordingly, a switch from acute A2A receptor-mediated reduction of dopamine neuron population activity to enduring A1 receptor-mediated suppression is correlated with tolerance rather than sensitization in response to repeated caffeine intake.

Do caffeine and more selective adenosine A2A receptor antagonists protect against dopaminergic neurodegeneration in Parkinson's disease?

The adenosine A2A receptor is a major target of caffeine, the most widely used psychoactive substance worldwide. Large epidemiological studies have long shown caffeine consumption is a strong inverse predictor of Parkinson's disease (PD). In this review, we first examine the epidemiology of caffeine use vis-à-vis PD and follow this by looking at the evidence for adenosine A2A receptor antagonists as potential neuroprotective agents. There is a wealth of accumulating biological, epidemiological and clinical evidence to support the further investigation of selective adenosine A2A antagonists, as well as caffeine, as promising candidate therapeutics to fill the unmet need for disease modification of PD.

The non-selective adenosine antagonist theophylline reverses the effects of dopamine antagonism on tremor, motor activity and effort-based decision-making

Considerable evidence indicates that adenosine and dopamine systems interact in the regulation of basal ganglia function. Nonselective adenosine antagonists such as the methylxanthine caffeine as well as selective adenosine A2A antagonists have been shown to produce antiparkinsonian and antidepressant effects in animal models. The present studies were conducted to assess if another methylxantine, theophylline, can reverse motor and motivational impairments induced by dopamine antagonism in rats. ResultsTheophylline (3.75–30.0 mg/kg, IP) reversed tremulous jaw movements (TJMs), catalepsy, and locomotor suppression induced by the dopamine D2 antagonist pimozide. It also reversed TJMs induced by the muscarinic receptor agonist pilocarpine, which is a well-known tremorogenic agent. Parallel studies assessed the ability of theophylline (5.0–20.0 mg/kg, IP) to reverse the changes in effort-related choice behavior induced by the dopamine D1 antagonist ecopipam (0.2 mg/kg, IP) and the D2 antagonist haloperidol (0.1 mg/kg, IP). Rats were tested on two different operant choice tasks which assess the tendency to work for a preferred reinforcer by lever pressing (for palatable pellets or a high 5% sucrose solution) vs. approaching and consuming a less preferred reinforcer (freely available lab chow or a less concentrated 0.3% sucrose solution). Theophylline restored food and sucrose-reinforced lever pressing in animals treated with the D2 antagonist. However, it was unable to reverse the effects of the D1 antagonist. Overall, the effects of theophylline resembled those previously reported for adenosine A2A antagonists, and suggest that theophylline could be clinically useful for the treatment of motor and motivational symptoms in humans.

Intracellular adenosine released from THP-1 differentiated human macrophages is involved in an autocrine control of Leishmania parasitic burden, mediated by adenosine A2A and A2B receptors

Leishmania infected macrophages have conditions to produce adenosine. Despite its known immunosuppressive effects, no studies have yet established whether adenosine alter Leishmania parasitic burden upon macrophage infection. This work aimed at investigating whether endogenous adenosine exerts an autocrine modulation of macrophage response towards Leishmania infection, identifying its origin and potential pharmacological targets for visceral leishmaniasis (VL), using THP-1 differentiated macrophages. Adenosine deaminase treatment of infected THP-1 cells reduced the parasitic burden (29.1 ± 2.2%, P < 0.05). Adenosine A2A and A2B receptor subtypes expression was confirmed by RT-qPCR and by immunocytochemistry and their blockade with selective adenosine A2A and A2B antagonists reduced the parasitic burden [14.5 ± 3.1% (P < 0.05) and 12.3 ± 3.1% (P < 0.05), respectively; and 24.9 ± 2.8% (P < 0.05), by the combination of the two antagonists)], suggesting that adenosine A2 receptors are tonically activated in infected THP-1 differentiated macrophages. The tonic activation of adenosine A2 receptors was dependent on the release of intracellular adenosine through equilibrative nucleoside transporters (ENT1/ENT2): NBTI or dipyridamole reduced (~25%) whereas, when ENTs were blocked, adenosine A2 receptor antagonists failed to reduce and A2 agonists increase parasitic burden. Effects of adenosine A2 receptors antagonists and ENT1/2 inhibitor were prevented by L-NAME, indicating that nitric oxide production inhibition prevents adenosine from increasing parasitic burden. Results suggest that intracellular adenosine, released through ENTs, elicits an autocrine increase in parasitic burden in THP-1 macrophages, through adenosine A2 receptors activation. These observations open the possibility to use well-established ENT inhibitors or adenosine A2 receptor antagonists as new therapeutic approaches in VL.

Dopamine depletion shifts behavior from activity based reinforcers to more sedentary ones and adenosine receptor antagonism reverses that shift: Relation to ventral striatum DARPP32 phosphorylation patterns

The mesolimbic dopamine (DA) system plays a critical role in behavioral activation and effort-based decision-making. DA depletion produces anergia (shifts to low effort options) in animals tested on effort-based decision-making tasks. Caffeine, the most consumed stimulant in the world, acts as an adenosine A1/A2A receptor antagonist, and in striatal areas DA D1 and D2 receptors are co-localized with adenosine A1 and A2A receptors respectively. In the present work, we evaluated the effect of caffeine on anergia induced by the VMAT-2 inhibitor tetrabenazine (TBZ), which depletes DA. Anergia was evaluated in a three-chamber T-maze task in which animals can chose between running on a wheel (RW) vs. sedentary activities such as consuming sucrose or sniffing a neutral odor. TBZ-caffeine interactions in ventral striatum were evaluated using DARPP-32 phosphorylation patterns as an intracellular marker of DA-adenosine receptor interaction. In the T-maze, control mice spent more time running and much less consuming sucrose or sniffing. TBZ (4.0 mg/kg) reduced ventral striatal DA tissue levels as measured by HPLC, and also shifted preferences in the T-maze, reducing selection of the reinforcer that involved vigorous activity (RW), but increasing consumption of a reinforcer that required little effort (sucrose), at doses that had no effect on independent measures of appetite or locomotion in a RW. Caffeine at doses that had no effect on their own reversed the effects of TBZ on T-maze performance, and also suppressed TBZ-induced pDARPP-32(Thr34) expression as measured by western blot, suggesting a role for D2-A2A interactions. These results support the idea that DA depletion produces anergia, but does not affect the primary motivational effects of sucrose. Caffeine, possibly by acting on A2A receptors in ventral striatum, reversed the DA depletion effects. It is possible that caffeine, like selective adenosine A2A antagonists, could have some therapeutic benefit for treating effort-related symptoms.

Deletion of Soluble Epoxide Hydrolase Modulates Coronary Reactive Hyperemia in Isolated Mouse Heart

Coronary reactive hyperemia (RH) is impaired in hypertrophic hearts. Epoxyeicosatrienoic acids (EETs) exert cardioprotective effects in ischemia / reperfusion injury. Soluble epoxide hydrolase (sEH) is the main enzyme responsible for EETs breakdown. EETs level is increased in sEH knock‐out mice (sEH‐/‐). We hypothesized that in the absence of sEH, isolated mouse heart exhibits increased RH through increased generation of EETs in response to no‐flow ischemia compared to wild type (sEH+/+). Coronary flow (CF) in isolated sEH+/+ and sEH‐/‐ mouse heart was measured using Langendorff system. Perfused isolated heart was exposed to 15 second ischemia and RH was assessed. Following ischemia, flow repayment volume (RV) was significantly higher in sEH‐/‐ compared to sEH+/+ (7.6 ± 0.5 in sEH‐/‐ vs. 5.9 ± 0.7 in sEH+/+, p&lt;0.05). Moreover, sEH‐/‐ exhibited significantly higher repayment to debt ratio when compared to sEH+/+ hearts (2.1 ± 0.2 in sEH‐/‐ vs. 1.5 ± 0.1 in sEH+/+, p&lt;0.05). Upstream of EETs; the increased in RV in sEH‐/‐ was significantly decreased by SCH‐58261 (a selective adenosine A2A antagonist, 1.0 mM) (6.8 ± 0.8 in sEH‐/‐ without SCH‐58261 vs. 3.5 ± 0.3 with SCH‐58261, p&lt;0.05). Also, downstream of EETs; T‐0070907 (a selective PPARg antagonist, 10.0 mM) significantly decreased RV in sEH‐/‐ (7.7 ± 1.2 in sEH‐/‐ without T‐0070907 vs. 5.4 ± 0.8 with T‐0070907, p&lt;0.05).Our results demonstrate that deletion of sEH increases RH compared to WT and that the enhanced RH is significantly decreased by SCH‐58261 and T‐0070907. These data suggest that targeting or silencing sEH may have a beneficial effect on myocardial recovery from ischemia. Supported by HL‐114559 to MAN and z01‐ES025034 to DCZ

Synthesis, molecular structure, NMR spectroscopic and computational analysis of a selective adenosine A2A antagonist, ZM 241385

Herein, we describe the synthesis of the adenosine A2A antagonist ZM 241385 (9) starting from commercially available 2-furanhydrazide (1) and including a comprehensive structural characterization of all the intermediates and the final product. In addition, extensive NMR analysis, including temperature and concentration-dependent experiments, are reported as well as the first single-crystal structure of the compound ZM 241385 (9) as the trihydrate. Furthermore, an extensive structural comparison of the single-crystal structure with the published protein bound X-ray structures is reported.

Increased Orbitofrontal Brain Activation after Administration of a Selective Adenosine A2A Antagonist in Cocaine Dependent Subjects

Background: Positron Emission Tomography imaging studies provide evidence of reduced dopamine function in cocaine dependent subjects in the striatum, which is correlated with prefrontal cortical glucose metabolism, particularly in the orbitofrontal cortex. However, whether enhancement of dopamine in the striatum in cocaine dependent subjects would be associated with changes in prefrontal cortical brain activation is unknown. One novel class of medications that enhance dopamine function via heteromer formation with dopamine receptors in the striatum is the selective adenosine A2A receptor antagonists. This study sought to determine the effects administration of the selective adenosine A2A receptor antagonist SYN115 on brain function in cocaine dependent subjects. Methodology/Principle Findings: Twelve cocaine dependent subjects underwent two fMRI scans (one after a dose of placebo and one after a dose of 100 mg of SYN115) while performing a working memory task with three levels of difficulty (3, 5, and 7 digits). fMRI results showed that for 7-digit working memory activation there was significantly greater activation from SYN115 compared to placebo in portions of left (L) lateral orbitofrontal cortex, L insula, and L superior and middle temporal pole. Conclusion/Significance: These findings are consistent with enhanced dopamine function in the striatum in cocaine dependent subjects via blockade of adenosine A2A receptors producing increased brain activation in the orbitofrontal cortex and other cortical regions. This suggests that at least some of the changes in brain activation in prefrontal cortical regions in cocaine dependent subjects may be related to altered striatal dopamine function, and that enhancement of dopamine function via adenosine A2A receptor blockade could be explored further for amelioration of neurobehavioral deficits associated with chronic cocaine use.

Istradefylline for the treatment of Parkinson's disease

Introduction: Despite several available therapeutic options to treat the symptoms of Parkinson's disease (PD), there are currently no agents that halt or slow the progression of disease. Istradefylline is a selective adenosine A2A antagonist that is currently of interest for the treatment of motor complications in PD.Areas covered: This paper reviews the limitations of currently available treatment options and discusses the results seen in both animal models and human clinical trials that have explored the benefits of istradefylline in PD.Expert opinion: The studies outlined continue to suggest that istradefylline may be a promising non-dopaminergic therapy for the treatment of PD. It has not been proven to be more efficacious than other currently available dopaminergic drugs, nor has it been shown to be of significant benefit as monotherapy; however, it seems to be a safe and well-tolerated drug that may help with wearing-off fluctuations. Istradefylline is not yet an FDA-approved drug. At this time, the potential for approval in the US or through the European Medical Agency remains unknown.

Effects of Adenosine Receptor Antagonists on Survival in Amitriptyline-poisoned Mice

Objective: We investigated the effects of adenosine receptor antagonists on survival rates in a mouse model of amitriptyline poisoning.Materials and Methods: In the preliminary study, amitriptyline was given at doses of 75, 100, and 125 mg/ kg to mice intraperitoneally (i.p.; n = 20 for each dose) to determine the lethal dose at 50% (LD50). Different doses (1, 3, and 5 mg/kg) of DPCPX (selective adenosine A1 antagonists, n = 10 for each dose, total n = 30) or CSC (selective adenosine A2a antagonists, n = 10 for each dose, total n = 30) were given i.p. to find the nonlethal dose. After the administration of the LD50 dose of amitriptyline (125 mg/kg), mice were treated with DPCPX (3 mg/kg), CSC (3 mg/kg), saline, or DMSO (dimethyl sulfoxide) (n = 25 for each group). Mice were observed during a 24-hour period.Results: Kaplan-Meier estimates of the 24-hour survival rate was 52% (13/25) for saline and 68% (17/25), 52% (13/25), and 40% (10/25) for the DPCPX, CSC, and DMSO groups, respectively. There was no statistically significant difference in survival rates among the groups (P > 0.05).Conclusions: Adenosine antagonists failed to increase the survival rates of amitriptyline-poisoned mice. Further studies are needed with repeated doses of adenosine antagonists.

Caffeine and a selective adenosine A2A receptor antagonist induce sensitization and cross-sensitization behavior associated with increased striatal dopamine in mice

BackgroundCaffeine, a nonselective adenosine A1 and A2A receptor antagonist, is the most widely used psychoactive substance in the world. Evidence demonstrates that caffeine and selective adenosine A2A antagonists interact with the neuronal systems involved in drug reinforcement, locomotor sensitization, and therapeutic effect in Parkinson's disease (PD). Evidence also indicates that low doses of caffeine and a selective adenosine A2A antagonist SCH58261 elicit locomotor stimulation whereas high doses of these drugs exert locomotor inhibition. Since these behavioral and therapeutic effects are mediated by the mesolimbic and nigrostriatal dopaminergic pathways which project to the striatum, we hypothesize that low doses of caffeine and SCH58261 may modulate the functions of dopaminergic neurons in the striatum.MethodsIn this study, we evaluated the neuroadaptations in the striatum by using reverse-phase high performance liquid chromatography (HPLC) to quantitate the concentrations of striatal dopamine and its metabolites, dihydroxylphenylacetic acid (DOPAC) and homovanilic acid (HVA), and using immunoblotting to measure the level of phosphorylation of tyrosine hydroxylase (TH) at Ser31, following chronic caffeine and SCH58261 sensitization in mice. Moreover, to validate further that the behavior sensitization of caffeine is through antagonism at the adenosine A2A receptor, we also evaluate whether chronic pretreatment with a selective adenosine A2A antagonist SCH58261 or a selective adenosine A1 antagonist DPCPX can sensitize the locomotor stimulating effects of caffeine.ResultsChronic treatments with low dose caffeine (10 mg/kg) or SCH58261 (2 mg/kg) increased the concentrations of dopamine, DOPAC and HVA, concomitant with increased TH phosphorylation at Ser31 and consequently enhanced TH activity in the striatal tissues in both caffeine- and SCH58261-sensitized mice. In addition, chronic caffeine or SCH58261 administration induced locomotor sensitization, and locomotor cross-sensitization to caffeine was observed following chronic treatment of mice with SCH58261 but not with DPCPX.ConclusionsOur study demonstrated that low dosages of caffeine and a selective adenosine A2A antagonist SCH58261 elicited locomotor sensitization and cross-sensitization, which were associated with elevated dopamine concentration and TH phosphorylation at Ser31 in the striatum. Blockade of adenosine A2A receptor may play an important role in the striatal neuroadaptations observed in the caffeine-sensitized and SCH58261-sensitized mice.

Effects of the adenosine A2A antagonist KW 6002 (istradefylline) on pimozide-induced oral tremor and striatal c-Fos expression: comparisons with the muscarinic antagonist tropicamide

Typical antipsychotic drugs, including haloperidol and pimozide, have been shown to produce parkinsonian motor effects such as akinesia and tremor. Furthermore, there is an antagonistic interaction between adenosine A2A and dopamine D2 receptors in the basal ganglia, which is important for motor functions related to the production of parkinsonian symptoms. Several experiments were conducted to assess the effects of the selective adenosine A2A antagonist KW 6002 on both the motor and cellular effects of subchronic administration of pimozide. The motor test employed was tremulous jaw movements, which is used as a model of parkinsonian tremor. In addition, c-Fos expression in the ventrolateral neostriatum, which is the striatal area most associated with tremulous jaw movements, was used as a marker of striatal cell activity in animals that were tested in the behavioral experiments. Repeated administration of 1.0 mg/kg pimozide induced tremulous jaw movements and increased ventrolateral striatal c-Fos expression, while administration of 20.0 mg/kg of the atypical antipsychotic quetiapine did not. The tremulous jaw movements induced by pimozide were significantly reduced by co-administration of either the adenosine A2A antagonist KW 6002 or the muscarinic antagonist tropicamide. Pimozide-induced increases in ventrolateral striatal c-Fos expression were reduced by a behaviorally effective dose of KW 6002, but c-Fos expression in pimozide-treated rats was actually increased by tropicamide. These results indicate that two different drug manipulations that act to reduce tremulous jaw movements can have different effects on DA antagonist-induced c-Fos expression, suggesting that adenosine A2A antagonism and muscarinic receptor antagonism exert their motor effects by acting on different striatal circuits.

2,6-Diaryl-4-phenacylaminopyrimidines as potent and selective adenosine A2A antagonists with reduced hERG liability

In this report, the design and synthesis of a series of pyrimidine based adenosine A(2A) antagonists are described. The strategy and outcome of expanding SAR exploration to attenuate hERG and improve selectivity over A(1) are discussed. Compound 33 exhibited excellent potency, selectivity over A(1), and reduced hERG liability.

P.4.039 In vivo characterization of a novel compound 2-butyl-9-methyl-8-(2H-1,2,3-triazol-2-yl)-9H-purin-6-ylamine (ST 1535), a selective adenosine A2A antagonist

Despite its increasing use as an animal model of memory deficit in human dementia, relatively few studies have attempted to assess the memory processes involved in the anticholinergic-induced impairment of passive avoidance retention. In the present experiments, the influence of scopolamine administered prior to or immediately following training on 24-h retention of step-through passive avoidance was studied in NMRI mice. In low doses (0.3–3.0 mg/kg ip) pretraining administration (−5 min) of scopolamine induced a very strong amnesia. Post-training scopolamine induced a significant effect only at the highest dose tested (30 mg/kg). In a retention test of longer than normal duration (600 vs 180 s), which resulted in a more favorable comparison value in the control group, an intermediate post-training dose (10 mg/kg) induced a small effect which approached significance; a finding which may account for conflicting reports in the literature concerning the ability of scopolamine to induce a post-training deficit. The pretraining effect does not appear to have been solely the result of state-dependent learning; scopolamine (3 mg/kg) administered before both the training and test sessions induced a deficit of approximately the same magnitude as that found when administered before training or before testing only. The results indicate that scopolamine can induce a small post-trial effect, presumably through an influence on consolidation processes. The much larger effect of pretrial scopolamine, however, indicates a primary influence on processes related to information acquisition. Together with findings from the literature, the present experiments suggest that scopolamine-induced amnesia partially, but not completely, models the memory deficits of human dementia.

7-Substituted 5-amino-2-(2-furyl)pyrazolo[4,3-e]-1,2,4-triazolo[1,5-c]pyrimidines as A2A adenosine receptor antagonists: a study on the importance of modifications at the side chain on the activity and solubility.

It was demonstrated in the early 1990s that adenosine exerts many physiological functions through the interaction with four different receptors, named A1, A2A, A2B, and A3. In the past few years, our group has been involved in the development of A2A antagonists, which led to the synthesis of SCH 58261 (1), the first potent and selective adenosine A2A antagonist, which has been widely used as a reference compound. In this paper, we present an extended series of pyrazolotriazolopyrimidines synthesized with the aim to investigate the influence of the substitutions on the pyrazole ring. The choice of the substituents was based on their capability to improve water solubility while retaining high affinity and selectivity at the human A2A adenosine receptor subtype. In this series, some structural characteristics that are important for activity, i.e., tricyclic structure, free amino group at 5-position, furan ring, and substituent at 7-position on the pyrazole moiety, have been maintained. We focused our attention on the nature of the phenyl ring substituent to improve water solubility. Following this strategy, we developed new compounds with good affinity and selectivity for A2A adenosine receptors, such as 8d (K(i) 0.12 nM; hA1/hA2A ratio = 1025; R(m) = 2.8), 8h (K(i) 0.22; hA1/hA2A ratio = 9818; R(m) = 3.4), 8i (K(i) 0.18 nM; hA1/hA2A ratio = 994; R(m) = 2.8), 8k (K(i) 0.13 nM; hA1/hA2A ratio = 4430; R(m) = 3.6), and 14b (K(i) 0.19 nM; hA1/hA2A ratio = 2273; R(m) = 2.7). All the new synthesized compounds have no significant interaction with either A2B or A3 receptor subtypes. This new series of compounds deeply enlightens some structural requirements to display high affinity and selectivity for the A2A adenosine receptor subtype, although our goal of identifying new compounds with increased water solubility was not completely achieved. On this basis, other strategies will be devised to improve this class of compounds with a profile that appears to be promising for treatment of neurodegenerative disorders, such as Parkinson's disease.

Signaling via A2A adenosine receptor in four PC12 cell clones.

PC12 cells are genetically labile and so-called wild-type cells comprise multiple subclones. We have examined the A2A adenosine receptor signal transduction pathways in four such clones (denoted clones 1, 19, 21 and 27) of PC12 cells. Adenosine A2A, A2B and A1 receptor mRNAs were detected in all four clones by RT-PCR, whereas no A3 receptor mRNA was found. A2A receptors were quantitated by radioligand binding using the antagonist radioligand [3H]SCH 58261 ([3H]-5-amino-7(2-phenylethyl)-2-(2-furyl)-pyrazolo[4,3-e]-1,2,4 triazolo [1,5-c] pyrimidine). The Bmax was highest in clone 1 followed by clones 21, 19 and 27. Whereas the amount of G(i) protein appeared similar in all four clones, the amount of G(s) protein was higher in clones 21 and 27 than in the other two clones. Maximal responses to the non-selective adenosine analogue NECA (5'-N-ethylcarboxamidoadenosine) were similar to those observed with the selective adenosine A2A receptor agonist CGS 21680 (2-[p-(2-carbonylethyl) phenylethylamino]-5'-N-ethylcarboxamidoadenosine), and were approximately equal in clones I and 21, but lower in clone 19 and very low in clone 27. For both compounds EC50 was significantly higher in clone 27 than in clone 1. In both clones the response to NECA could be competitively antagonized by a selective adenosine A2A antagonist, SCH 58261. The present results show that different clones of PC 12 cells differ widely in the cAMP increase induced by adenosine analogues and that this is due to differences in the amount of adenosine A2A receptor, G protein and effector. A large difference in receptor number resulted in differences in potency of an agonist.

Selective adenosine antagonists for mapping central nervous system adenosine receptors with positron emission tomography: Carbon-11 labeled KF15372 (A1) and KF17837 (A2A)

During the past decade, many neuroreceptors in humans and other animals have been visualized in vivo by positron emission tomography (PET) with corresponding radioligands. Because adenosine is a neuromodulator, PET assessment of the adenosine receptor system offers us an opportunity to understand the neurotransmission system in general. The 11C-labeled selective adenosine A1 antagonists KF15372 ([3-propyl-11C]8-dicyclopropylmethyl-1, 3-dipropylxanthine) and a 11C-methyl derivative [11C]KF26345 and selective adenosine A2A antagonist KF17837 ([7-methyl-11C]-(E)-8-(3,4-dimethoxystyryl)-1,3-dipropyl-7-methylxanthine) and KF18446 ([7-methyl-11C]-(E)-8-3,4,5-trimethoxystyryl)-1,3,7-trimethylxanthine were evaluated in vivo as potential PET ligands for mapping CNS adenosine A1 and A2A receptors. [11C]KF15372 and [11C]KF263345: Tissue sampling and ex vivo autoradiography (ARG) suggest that the regional brain distribution of [11C]KF15372 and [11C]KF26345 is consistent with that of the adenosine A1 receptors found in mice and rats. The brain uptake was competitively reduced by the coadministration of A1, but not by A2A antagonists. The ex vivo ARG on the rat model with unilateral orbital enucleation, visualized the A1 receptor deficiency in the presynaptic terminals. PET with these ligands visualized the A1 receptors in the monkey and cat brain. [11C]KF17837 and [11C]KF18446: In mice, a high uptake of two ligands was found in the striatum in which A2A receptors are highly enriched. The uptake was decreased by coinjection of carrier KF17837 or other xanthine-type A2A antagonists, but not by four nonxanthine-type A2A antagonists or A1 antagonists. In the rat brain, ex vivo ARG showed the A2A receptor-specific uptake of two ligands in the striatum. In PET studies of the monkey and cat brain, the A2A receptors in the striatum was clearly visualized. These pieces of evidence demonstrated the potential of 11C-labeled selective xanthine-type adenosine antagonists as PET ligands for mapping CNS adenosine A1 and A2A receptors. Drug Dev. Res. 45:312–323, 1998. © 1998 Wiley-Liss, Inc.

Adenosine A2A receptors modify motor function in MPTP-treated common marmosets.

Both adenosine A1 and A2 receptor populations are located in the striatum and can modify locomotor activity, and they may form a therapeutic target for Parkinson's disease (PD). Administration of the selective adenosine A2A antagonist (E)-1,3-diethyl-8-(3,4-dimethoxystyryl)-7-methyl-3,7-dihydro-1H-pu rine-2,6-dione (KW-6002) to MPTP-treated common marmosets increased locomotor activity. In contrast, administration of the selective A1 receptor antagonist 1,3-dipropyl-8-cyclopentylxantine (DPCPX) had no effect on locomotion. Administration of the adenosine A2A receptor agonist 2-[p-[2-(2-aminoethylamino) carbonylethyl] phenethyl amino]-5'-N-ethylcarboxamidoadenosine (APEC) dose dependently suppressed basal locomotor activity. A minimally effective dose of APEC (0.62 mg/kg, i.p) completely reversed the increase in locomotor activity produced by administration of KW-6002. The adenosine A2A receptor appears to be an important target for the treatment of basal ganglia disorders, particularly PD.

Synthesis and preliminary evaluation of [11C]KF17837, a selective adenosine A2A antagonist.

An 11C-labeled selective adenosine A2A antagonist, (E)-8-(3,4-dimethoxystyryl)-1,3-dipropyl-7-[11C]-methylxanthine ([11C]KF17837), was prepared by reaction of (E)-8-(3,4-dimethoxystyryl)-1,3-dipropylxanthine and [11C]methyl iodide with decay-corrected radiochemical yield of 19-50%, radiochemical purity of > 99%, sp. act. of 17-100 GBq/mumol and preparation time of 20-25 min. In mice, the myocardium showed the highest (13.4% ID/g) at 5 min after i.v. injection, which decreased gradually with time. The specific myocardial uptake was visualized by gamma-camera. In the brain region the radioactivity level was higher in the A2A receptors-rich striatum than in the cortex and cerebellum. The specific striatal uptake in rats was clearly demonstrated by PET. These results have shown that [11C]KF17837 is a potential PET radioligand for mapping the adenosine A2A receptors in the heart and brain.