A2A Adenosine Receptor Antagonists and their Potential in Neurological Disorders

GPCR-mediated natural products and compounds: Potential therapeutic targets for the treatment of neurological diseases

G protein-coupled receptors (GPCRs), widely expressed in the human central nervous system (CNS), perform numerous physiological functions and play a significant role in the pathogenesis of diseases. Consequently, identifying key therapeutic GPCRs targets for CNS-related diseases is garnering immense interest in research labs and pharmaceutical companies. However, using GPCRs drugs for treating neurodegenerative diseases has limitations, including side effects and uncertain effective time frame. Recognizing the rich history of herbal treatments for neurological disorders like stroke, Alzheimer's disease (AD), and Parkinson's disease (PD), modern pharmacological research is now focusing on the understanding of the efficacy of traditional Chinese medicinal herbs and compounds in modulating GPCRs and treatment of neurodegenerative conditions. This paper will offer a comprehensive, critical review of how certain natural products and compounds target GPCRs to treat neurological diseases. Conducting an in-depth study of herbal remedies and their efficacies against CNS-related disorders through GPCRs targeting will augment our strategies for treating neurological disorders. This will not only broaden our understanding of effective therapeutic methodologies but also identify the root causes of altered GPCRs signaling in the context of pathophysiological mechanisms in neurological diseases. Moreover, it would be informative for the creation of safer and more effective GPCR-mediated drugs, thereby establishing a foundation for future treatment of various neurological diseases.

Effects of the adenosine A2A receptor antagonist KW6002 on the dopaminergic system, motor performance, and neuroinflammation in a rat model of Parkinson's disease

Adenosine A2A-receptors (A2AR) and dopamine D2-receptors (D2R) are known to work together in a synergistic manner. Inhibiting A2ARs by genetic or pharmacological means can relief symptoms and have neuroprotective effects in certain conditions. We applied PET imaging to evaluate the impact of the A2AR antagonist KW6002 on D2R availability and neuroinflammation in an animal model of Parkinson's disease. Male Wistar rats with 6-hydroxydopamine-induced damage to the right striatum were given 3 mg/kg of KW6002 daily for 20 days. Motor function was assessed using the rotarod and cylinder tests, and neuroinflammation and dopamine receptor availability were measured using PET scans with the tracers [11C]PBR28 and [11C]raclopride, respectively. On day 7 and 22 following 6-OHDA injection, rats were sacrificed for postmortem analysis. PET scans revealed a peak in neuroinflammation on day 7. Chronic treatment with KW6002 significantly reduced [11C]PBR28 uptake in the ipsilateral striatum [normalized to contralateral striatum] and [11C]raclopride binding in both striata when compared to the vehicle group. These imaging findings were accompanied by an improvement in motor function. Postmortem analysis showed an 84% decrease in the number of Iba-1+ cells in the ipsilateral striatum [normalized to contralateral striatum] of KW6002-treated rats compared to vehicle rats on day 22 (p = 0.007), corroborating the PET findings. Analysis of tyrosine hydroxylase levels showed less dopaminergic neuron loss in the ipsilateral striatum of KW6002-treated rats compared to controls on day 7. These findings suggest that KW6002 reduces inflammation and dopaminergic neuron loss, leading to less motor symptoms in this animal model of Parkinson's disease.

A2AR and traumatic brain injury

Accumulating evidence has revealed the adenosine 2A receptor is a key tuner for neuropathological and neurobehavioral changes following traumatic brain injury by experimental animal models and a few clinical trials. Here, we highlight recent data involving acute/sub-acute and chronic alterations of adenosine and adenosine 2A receptor-associated signaling in pathological conditions after trauma, with an emphasis of traumatic brain injury, including neuroinflammation, cognitive and psychiatric disorders, and other severe consequences. We expect this would lead to the development of therapeutic strategies for trauma-related disorders with novel mechanisms of action.

Dual Anta-Inhibitors Targeting Protein Kinase CK1δ and A2A Adenosine Receptor Useful in Neurodegenerative Disorders

Currently, the number of patients with neurodegenerative pathologies is estimated at over one million, with consequences also on the economic level. Several factors contribute to their development, including overexpression of A_2A adenosine receptors (A_2AAR) in microglial cells and up-regulation and post-translational alterations of some casein kinases (CK), among them, CK-1δ. The aim of the work was to study the activity of A_2AAR and CK1δ in neurodegeneration using in-house synthesized A_2A/CK1δ dual anta-inhibitors and to evaluate their intestinal absorption. Experiments were performed on N13 microglial cells, which were treated with a proinflammatory CK cocktail to simulate an inflammatory state typical of neurodegenerative diseases. Results showed that the dual anta-inhibitors have the ability to counteract the inflammatory state, even if compound 2 is more active than compound 1. In addition, compound 2 displayed an important antioxidant effect similar to the reference compound ZM241385. Since many known kinase inhibitors are very often unable to cross lipid bilayer membranes, the ability of A_2A/CK1δ double anta-inhibitors to cross the intestinal barrier was investigated by an everted gut sac assay. HPLC analysis revealed that both compounds are able to cross the intestinal barrier, making them promising candidates for oral therapy.

A2AR antagonist treatment for multiple sclerosis: Current progress and future prospects

Emerging evidence suggests that both selective and non-selective Adenosine A2A receptor (A2AR) antagonists could effectively protect mice from experimental autoimmune encephalomyelitis (EAE), which is the most commonly used animal model for multiple sclerosis (MS) research. Meanwhile, the recent FDA approval of Nourianz® (istradefylline) in 2019 as an add-on treatment to levodopa in Parkinson's disease (PD) with "OFF" episodes, along with its proven clinical safety, has prompted us to explore the potential of A2AR antagonists in treating multiple sclerosis (MS) through clinical trials. However, despite promising findings in experimental autoimmune encephalomyelitis (EAE), the complex and contradictory role of A2AR signaling in EAE pathology has raised concerns about the feasibility of using A2AR antagonists as a therapeutic approach for MS. This review addresses the potential effect of A2AR antagonists on EAE/MS in both the peripheral immune system (PIS) and the central nervous system (CNS). In brief, A2AR antagonists had a moderate effect on the proliferation and inflammatory response, while exhibiting a potent anti-inflammatory effect in the CNS through their impact on microglia, astrocytes, and the endothelial cells/epithelium of the blood-brain barrier. Consequently, A2AR signaling remains an essential immunomodulator in EAE/MS, suggesting that A2AR antagonists hold promise as a drug class for treating MS.

"Dual Anta-Inhibitors" of the A2A Adenosine Receptor and Casein Kinase CK1delta: Synthesis, Biological Evaluation, and Molecular Modeling Studies

Based on a screening of a chemical library of A2A adenosine receptor (AR) antagonists, a series of di- and tri-substituted adenine derivatives were synthesized and tested for their ability to inhibit the activity of the enzyme casein kinase 1 delta (CK1δ) and to bind adenosine receptors (ARs). Some derivatives, here called "dual anta-inhibitors", demonstrated good CK1δ inhibitory activity combined with a high binding affinity, especially for the A2AAR. The N6-methyl-(2-benzimidazolyl)-2-dimethyamino-9-cyclopentyladenine (17, IC50 = 0.59 μM and KiA2A = 0.076 μM) showed the best balance of A2AAR affinity and CK1δ inhibitory activity. Computational studies were performed to simulate, at the molecular level, the protein-ligand interactions involving the compounds of our series. Hence, the dual anta-inhibitor 17 could be considered the lead compound of new therapeutic agents endowed with synergistic effects for the treatment of chronic neurodegenerative and cancer diseases.

Design, Synthesis and Assay of Novel Methylxanthine-Alkynylmethylamine Derivatives as Acetylcholinesterase Inhibitors

Xanthine derivatives have been a great area of interest for the development of potent bioactive agents. Thirty-eight methylxanthine derivatives as acetylcholinesterase inhibitors (AChE) were designed and synthesized. Suzuki-Miyaura cross-coupling reactions of 8-chlorocaffeine with aryl(hetaryl)boronic acids, the CuAAC reaction of 8-ethynylcaffeine with several azides, and the copper(I) catalyzed one-pot three-component reaction (A³-coupling) of 8-ethynylcaffeine, 1-(prop-2-ynyl)-, or 7-(prop-2-ynyl)-dimethylxanthines with formaldehyde and secondary amines were the main approaches for the synthesis of substituted methylxanthine derivatives (yield 53-96%). The bioactivity of all new compounds was evaluated by Ellman's method, and the results showed that most of the synthesized compounds displayed good and moderate acetylcholinesterase (AChE) inhibitory activities in vitro. The structure-activity relationships were also discussed. The data revealed that compounds 53, 59, 65, 66, and 69 exhibited the most potent inhibitory activity against AChE with IC₅₀ of 0.25, 0.552, 0.089, 0.746, and 0.121 μM, respectively. The binding conformation and simultaneous interaction modes were further clarified by molecular docking studies.

A2A Adenosine Receptor Antagonists: Are Triazolotriazine and Purine Scaffolds Interchangeable?

The A_2A adenosine receptor (A_2AAR) 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_2AAR 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_2AAR, 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.