Can adenosine A2A receptor antagonists modify motor behavior and dyskinesia in experimental models of Parkinson's disease?

Impact of istradefylline on motor and non-motor symptoms in patients with Parkinson's disease: Subanalysis of the ISTRA ADJUST PD

Introduction

Parkinson's disease (PD) presents with diverse motor and non-motor symptoms, some of which do not fully respond to dopamine replacement therapy. To clarify the effects of the adenosine A2A receptor antagonist istradefylline (IST) on PD symptoms, we conducted a subanalysis of the 37-week ISTRA ADJUST PD randomized controlled trial.

Methods

Patients with PD experiencing wearing-off with levodopa at 300-400 mg/day were randomized 1:1 to receive IST or no IST (control). Levodopa doses were titrated according to clinical severity throughout the study. PD symptoms were assessed using the Movement Disorder Society Unified Parkinson's Disease Rating Scale (MDS-UPDRS) and Parkinson's Disease Questionnaire-39 (PDQ-39).

Results

The efficacy analyses included 105 patients (IST, n = 52; control, n = 53). Regarding MDS-UPDRS subitems in patients in the IST group, significant improvements (p < 0.05) were observed at week 36 compared with baseline for both motor (e.g., facial expression, rigidity, finger tapping, toe tapping, time spent in the off state, and complexity of motor fluctuation) and non-motor (e.g., daytime sleepiness, fatigue, and doing hobbies and other activities) symptoms. In patients in the control group, significant improvements (p < 0.05) were observed for motor symptoms only. Regarding PDQ-39 subitems in patients in the IST group, significant improvements (p < 0.05) were observed at week 36 compared with baseline in doing up buttons or shoelaces, writing, feeling angry or bitter, and unexpectedly falling asleep during the day.

Conclusion

IST can improve motor and non-motor symptoms and quality of life suggesting that it provides more comprehensive improvement in PD symptoms than increasing the levodopa dose alone.

Clinical trial registration

Japan Registry of Clinical Trials; study ID: jRCTs031180248.

A2A Adenosine Receptor Antagonists and Their Efficacy in Rat Models of Parkinson's Disease

Parkinson's disease (PD) represents a growing challenge to global health, as it involves millions of people. The high grade of disability is due to the loss of dopaminergic neuron activity, and levodopa is the gold-standard therapy used to restore dopamine in the dopamine-denervated regions. Another therapeutic approach is the use of A2A adenosine receptor antagonists and, among them, istradefylline is the only one currently approved for therapy in association with levodopa. In this work, we synthesized A2A adenosine receptor antagonists represented by 9-ethyl-2,8-disubstituted adenine derivatives, which were tested at human adenosine receptors in binding and functional assays. These compounds showed A2A adenosine receptor-binding affinities in the low nanomolar range and 1, 4, and 5 exhibited good potency in the functional assays. Hence, they were evaluated in in vivo rat models of PD, where they were demonstrated to revert haloperidol-induced catalepsy and potentiate levodopa-induced contralateral rotations in 6-hydroxydopamine-lesioned rats. The most potent derivative, 4, was then evaluated in the tacrine model, where it reduced the tremulous jaw movements, therefore demonstrating an action on parkinsonian tremor. These data revealed 8-ethoxy-2-phenethoxy-9-ethyladenine (4) as an A2A adenosine receptor antagonist endowed with antiparkinsonian effects and as a good candidate to treat the disease.

Evolving Landscape of Parkinson's Disease Research: Challenges and Perspectives

Parkinson's disease (PD) is a progressive neurodegenerative disorder that primarily affects movement. It occurs due to a gradual deficit of dopamine-producing brain cells, particularly in the substantia nigra. The precise etiology of PD is not fully understood, but it likely involves a combination of genetic and environmental factors. The therapies available at present alleviate symptoms but do not stop the disease's advancement. Research endeavors are currently directed at inventing disease-controlling therapies that aim at the inherent mechanisms of PD. PD biomarker breakthroughs hold enormous potential: earlier diagnosis, better monitoring, and targeted treatment based on individual response could significantly improve patient outcomes and ease the burden of this disease. PD research is an active and evolving field, focusing on understanding disease mechanisms, identifying biomarkers, developing new treatments, and improving care. In this report, we explore data from the CAS Content Collection to outline the research progress in PD. We analyze the publication landscape to offer perspective into the latest expertise advancements. Key emerging concepts are reviewed and strategies to fight disease evaluated. Pharmacological targets, genetic risk factors, as well as comorbid diseases are explored, and clinical usage of products against PD with their production pipelines and trials for drug repurposing are examined. This review aims to offer a comprehensive overview of the advancing landscape of the current understanding about PD, to define challenges, and to assess growth prospects to stimulate efforts in battling the disease.

Small Molecules in Parkinson's Disease Therapy: From Dopamine Pathways to New Emerging Targets

Parkinson's disease (PD) is a chronic, progressive neurological disorder affecting approximately 10 million people worldwide, with prevalence expected to rise as the global population ages. It is characterized by the degeneration of dopamine-producing neurons in the substantia nigra pars compacta, leading to motor symptoms such as tremor, rigidity, bradykinesia, postural instability, and gait disturbances, as well as non-motor symptoms including olfactory disturbances, sleep disorders, and depression. Currently, no cure exists for PD, and most available therapies focus on symptom alleviation. This dopamine deficiency impairs motor control, and since dopamine itself cannot cross the blood-brain barrier (BBB), the precursor L-Dopa is commonly used in treatment. L-Dopa is administered with enzyme inhibitors to prevent premature conversion outside the brain, allowing it to cross the BBB and convert to dopamine within the central nervous system. Although these therapies have improved symptom management, recent research has revealed additional molecular factors in PD pathology, such as α-synuclein aggregation, mitochondrial dysfunction, and lysosomal abnormalities, contributing to its complexity. These discoveries open up possibilities for neuroprotective therapies that could slow disease progression. In this review, we categorize PD therapeutic targets into two main groups: currently used therapies and targets under active research. We also introduce promising small-molecule compounds studied between 2019 and 2023, which may represent future treatment options. By examining both established and emerging targets, we aim to highlight effective strategies and potential directions for future drug development in Parkinson's disease therapy.

Targeting the Adenosine A2A Receptor as a Novel Therapeutic Approach for Renal Cell Carcinoma: Mechanisms and Clinical Trial Review

Renal cell carcinoma (RCC) accounts for nearly 2% of cancers diagnosed worldwide. For metastatic RCC, targeted therapy is one of the most common treatment methods. It can include approaches that target vascular endothelial growth factor (VEGFR) or rely on immune checkpoint inhibitors or mTOR inhibitors. Adenosine A2A receptor (A2AR) is a type of widely distributed G-protein-coupled receptor (GPCR). Recently, an increasing number of studies suggest that the activation of A2AR can downregulate anti-tumor immune responses and prevent tumor growth. Currently, the data on A2AR antagonists in RCC treatment are still limited. Therefore, in this article, we further investigate the clinical trials investigating A2AR drugs in RCC. We also describe the epidemiology and current treatment of RCC, along with the physiological role of A2AR, and the types of A2AR drugs that are associated with tumor treatment.

Coffee and Parkinson's disease

Parkinson's disease (PD) is a prevalent neurodegenerative disease marked by dopaminergic neuronal loss and misfolded alpha-synuclein (α-syn) accumulation, which results in both motor and cognitive symptoms. Its occurrence grows with age, with a larger prevalence among males. Despite substantial study, effective medicines to reduce or stop the progression of diseases remain elusive. Interest has grown in examining dietary components, such as caffeine present in coffee, for potential medicinal effects. Epidemiological studies imply a lower incidence of PD with coffee drinking, attributable to caffeine's neuroprotective abilities. Beyond caffeine, coffee constituent like chlorogenic acid and cafestol have anti-Parkinsonian benefits. Moreover, coffee use has been related with variations in gut microbiota composition, which may reduce intestinal inflammation and prevent protein misfolding in enteric nerves, perhaps through the microbiota-gut-brain axis. This review gives a summary of the neuroprotective effects of coffee, investigating both its motor and non-motor advantages in individuals with PD as well as in experimental models of PD. We reviewed some bioactive constituents of coffee, their respective interactions with misfolded α-syn accumulation, and its emerging mechanisms associated to the gut microbiome.

Future Directions for Developing Non-dopaminergic Strategies for the Treatment of Parkinson's Disease

The symptomatic treatment of Parkinson's disease (PD) has been dominated by the use of dopaminergic medication, but significant unmet need remains, much of which is related to non-motor symptoms and the involvement of non-dopaminergic transmitter systems. As such, little has changed in the past decades that has led to milestone advances in therapy and significantly improved treatment paradigms and patient outcomes, particularly in relation to symptoms unresponsive to levodopa. This review has looked at how pharmacological approaches to treatment are likely to develop in the near and distant future and will focus on two areas: 1) novel non-dopaminergic pharmacological strategies to control motor symptoms; and 2) novel non-dopaminergic approaches for the treatment of non-motor symptoms. The overall objective of this review is to use a 'crystal ball' approach to the future of drug discovery in PD and move away from the more traditional dopamine-based treatments. Here, we discuss promising non-dopaminergic and 'dirty drugs' that have the potential to become new key players in the field of Parkinson's disease treatment.

Trends on Novel Targets and Nanotechnology-Based Drug Delivery System in the Treatment of Parkinson's disease: Recent Advancement in Drug Development

Parkinson's disease (PD) is a progressive neurodegenerative disorder that impacts a significant portion of the population. Despite extensive research, an effective cure for PD remains elusive, and conventional pharmacological treatments often face limitations in efficacy and management of symptoms. There has been a lot of discussion about using nanotechnology to increase the bioavailability of small- molecule drugs to target cells in recent years. It is possible that PD treatment might become far more effective and have fewer side effects if medication delivery mechanisms were to be improved. Potential alternatives to pharmacological therapy for molecular imaging and treatment of PD may lie in abnormal proteins such as parkin, α-synuclein, leucine-rich repeat serine and threonine protein kinase 2. Published research has demonstrated encouraging outcomes when nanomedicine-based approaches are used to address the challenges of PD therapy. So, to address the present difficulties of antiparkinsonian treatment, this review outlines the key issues and limitations of antiparkinsonian medications, new therapeutic strategies, and the breadth of delivery based on nanomedicine. This review covers a wide range of subjects, including drug distribution in the brain, the efficacy of drug-loaded nano-carriers in crossing the blood-brain barrier, and their release profiles. In PD, the nano-carriers are also used. Novel techniques of pharmaceutical delivery are currently made possible by vesicular carriers, which eliminate the requirement to cross the blood-brain barrier (BBB).

How and why the adenosine A2A receptor became a target for Parkinson's disease therapy

Dopaminergic therapy for Parkinson's disease has revolutionised the treatment of the motor symptoms of the illness. However, it does not alleviate all components of the motor deficits and has only limited effects on non-motor symptoms. For this reason, alternative non-dopaminergic approaches to treatment have been sought and the adenosine A2A receptor provided a novel target for symptomatic therapy both within the basal ganglia and elsewhere in the brain. Despite an impressive preclinical profile that would indicate a clear role for adenosine A2A antagonists in the treatment of Parkinson's disease, the road to clinical use has been long and full of difficulties. Some aspects of the drugs preclinical profile have not translated into clinical effectiveness and not all the clinical studies undertaken have had a positive outcome. The reasons for this will be explored and suggestions made for the further development of this drug class in the treatment of Parkinson's disease. However, one adenosine A2A antagonist, namely istradefylline has been introduced successfully for the treatment of late-stage Parkinson's disease in two major areas of the world and has become a commercial success through offering the first non-dopaminergic approach to the treatment of unmet need to be introduced in several decades.

Promising biomarkers and therapeutic targets for the management of Parkinson's disease: recent advancements and contemporary research

Parkinson's disease (PD) is one of the progressive neurological diseases which affect around 10 million population worldwide. The clinical manifestation of motor symptoms in PD patients appears later when most dopaminergic neurons have degenerated. Thus, for better management of PD, the development of accurate biomarkers for the early prognosis of PD is imperative. The present work will discuss the potential biomarkers from various attributes covering biochemical, microRNA, and neuroimaging aspects (α-synuclein, DJ-1, UCH-L1, β-glucocerebrosidase, BDNF, etc.) for diagnosis, recent development in PD management, and major limitations with current and conventional anti-Parkinson therapy. This manuscript summarizes potential biomarkers and therapeutic targets, based on available preclinical and clinical evidence, for better management of PD.

Adenosinergic Pathway in Parkinson's Disease: Recent Advances and Therapeutic Perspective

Parkinson's disease (PD) is a neurodegenerative disease characterized pathologically by α-synuclein (α-syn) aggregation. In PD, the current mainstay of symptomatic treatment is levodopa (L-DOPA)-based dopamine (DA) replacement therapy. However, the development of dyskinesia and/or motor fluctuations which is relevant to levodopa is restricting its long-term utility. Given that the ability of which is to modulate the striato-thalamo-cortical loops and function to modulate basal ganglia output, the adenosinergic pathway (AP) is qualified as a potential promising non-DA target. As an indispensable component of energy production pathways, AP modulates cellular metabolism and gene regulation in both neurons and neuroglia cells through the recognition and degradation of extracellular adenosine. In addition, AP is geared to the initiation, evolution, and resolution of inflammation as well. Besides the above-mentioned crosstalk between the adenosine and dopamine signaling pathways, the functions of adenosine receptors (A₁R, A_2AR, A_2BR, and A₃R) and metabolism enzymes in modulating PD pathological process have been extensively investigated in recent decades. Here we reviewed the emerging findings focused on the function of adenosine receptors, adenosine formation, and metabolism in the brain and discussed its potential roles in PD pathological process. We also recapitulated clinical studies and the preclinical evidence for the medical strategies targeting the Ado signaling pathway to improve motor dysfunction and alleviate pathogenic process in PD. We hope that further clinical studies should consider this pathway in their monotherapy and combination therapy, which would open new vistas to more targeted therapeutic approaches.

Modulation of adenosine signaling reverses 3-nitropropionic acid-induced bradykinesia and memory impairment in adult zebrafish

Huntington's disease (HD) is a neurodegenerative disorder, characterized by motor dysfunction, psychiatric disturbance, and cognitive decline. In the early stage of HD, occurs a decrease in dopamine D₂ receptors and adenosine A_2A receptors (A_2AR), while in the late stage also occurs a decrease in dopamine D₁ receptors and adenosine A₁ receptors (A₁R). Adenosine exhibits neuromodulatory and neuroprotective effects in the brain and is involved in motor control and memory function. 3-Nitropropionic acid (3-NPA), a toxin derived from plants and fungi, may reproduce HD behavioral phenotypes and biochemical characteristics. This study investigated the effects of acute exposure to CPA (A₁R agonist), CGS 21680 (A_2AR agonist), caffeine (non-selective of A₁R and A_2AR antagonist), ZM 241385 (A_2AR antagonist), DPCPX (A₁R antagonist), dipyridamole (inhibitor of nucleoside transporters) and EHNA (inhibitor of adenosine deaminase) in an HD pharmacological model induced by 3-NPA in adult zebrafish. CPA, CGS 21680, caffeine, ZM 241385, DPCPX, dipyridamole, and EHNA were acutely administered via i.p. in zebrafish after 3-NPA (at dose 60 mg/kg) chronic treatment. Caffeine and ZM 241385 reversed the bradykinesia induced by 3-NPA, while CGS 21680 potentiated the bradykinesia caused by 3-NPA. Moreover, CPA, caffeine, ZM 241385, DPCPX, dipyridamole, and EHNA reversed the 3-NPA-induced memory impairment. Together, these data support the hypothesis that A_2AR antagonists have an essential role in modulating locomotor function, whereas the activation of A₁R and blockade of A_2AR and A₁R and modulation of adenosine levels may reduce the memory impairment, which could be a potential pharmacological strategy against late-stage symptoms HD.

Glycolysis: The Next Big Breakthrough in Parkinson's Disease

Parkinson's disease (PD) is a common neurodegenerative disease characterized by the death of dopaminergic neurons. Its pathogenesis comprises defects in the physiological pathway of mitophagy and mutations in the genes involved in this process's regulatory mechanism. PD manifests itself with multiple motor and non-motor symptoms, and currently, there are multiple pharmacological treatments, and unconventional non-drug treatments available. The mainstay of Parkinson's disease treatment has centered around directly manipulating neural mechanisms to retain high dopamine levels, either by exogenous administration, increasing intrinsic production, or inhibiting the breakdown of dopamine. In this review, we highlight a new potential biochemical modality of treatment, treating PD through glycolysis. We highlight how terazosin (TZ), via PGK1, increases ATP levels and how enhanced glycolysis serves a neuroprotective role in PD, and compensates for damage caused by mitophagy. We also discuss the role of quercetin, a bioactive flavonoid, in preventing the development of PD, and reversing mitochondrial dysfunction but only so in diabetic patients. Thus, further research should be conducted on glycolysis as a protective target in PD that can serve to not just prevent, but also alleviate the non-dopaminergic signs and symptoms of PD.

Emerging Therapeutic Strategies for Parkinson’s Disease and Future Prospects: A 2021 Update

Parkinson’s disease (PD) is a neurodegenerative disorder pathologically distinguished by degeneration of dopaminergic neurons in the substantia nigra pars compacta. Muscle rigidity, tremor, and bradykinesia are all clinical motor hallmarks of PD. Several pathways have been implicated in PD etiology, including mitochondrial dysfunction, impaired protein clearance, and neuroinflammation, but how these factors interact remains incompletely understood. Although many breakthroughs in PD therapy have been accomplished, there is currently no cure for PD, only trials to alleviate the related motor symptoms. To reduce or stop the clinical progression and mobility impairment, a disease-modifying approach that can directly target the etiology rather than offering symptomatic alleviation remains a major unmet clinical need in the management of PD. In this review, we briefly introduce current treatments and pathophysiology of PD. In addition, we address the novel innovative therapeutic targets for PD therapy, including α-synuclein, autophagy, neurodegeneration, neuroinflammation, and others. Several immunomodulatory approaches and stem cell research currently in clinical trials with PD patients are also discussed. Moreover, preclinical studies and clinical trials evaluating the efficacy of novel and repurposed therapeutic agents and their pragmatic applications with encouraging outcomes are summarized. Finally, molecular biomarkers under active investigation are presented as potentially valuable tools for early PD diagnosis.

Efficacy and safety of istradefylline in patients with Parkinson's disease presenting with postural abnormalities: Results from a multicenter, prospective, and open-label exploratory study in Japan

Postural abnormalities in Parkinson's disease (PD) can devastatingly impair the quality of life, especially in patients with advanced disease, and are generally refractory to dopaminergic agents. The objective of this exploratory study was to investigate the efficacy and safety of istradefylline for the treatment of postural abnormalities in PD. In this open-label, 24-week, single-arm prospective trial, PD patients with postural abnormalities experiencing the wearing-off phenomenon on levodopa-containing therapies were enrolled and received a starting dose of 20 mg/day istradefylline orally for 4 weeks, which was then increased to 40 mg/day. The primary endpoint was the change from baseline to week 24 in the 14-item Unified Dystonia Rating Scale (UDRS) total score. Pivotal secondary endpoints were changes in the sub-items of UDRS, Movement Disorder Society-Unified Parkinson's Disease Rating Scale (MDS-UPDRS) part III, and adverse drug reactions (ADRs). Overall, 24/31 enrolled patients completed the study; mean (standard deviation) age and duration of motor complications were 73.3 (7.7) years and 3.2 (4.4) years, respectively. Mean (95% confidence interval [CI]) change in the UDRS total score was 4.84 (1.97, 7.71; P = 0.002), with significant improvements in the neck, right distal arm and hand, and trunk severity scores. Mean (95% CI) change in the MDS-UPDRS part III score was 7.84 (4.34, 11.34; P < 0.001). The most common ADRs were malaise, dyskinesia exacerbation, and visual hallucinations in 2 (6.5%) patients each. This exploratory study demonstrated that istradefylline could be efficacious for postural abnormalities and was generally well tolerated in patients with PD experiencing the wearing-off phenomenon with levodopa-containing therapies.

Novel therapeutic interventions for combating Parkinson's disease and prospects of Nose-to-Brain drug delivery

Parkinson disease (PD) is a progressive neurodegenerative disorder prevalent mainly in geriatric population. While, L-DOPA remains one of the major choices for the therapeutic management of PD, various motor and non-motor manifestations complicate the management of PD. In the last two decades, exhaustive research has been carried out to explore novel therapeutic approaches for mitigating motor and non-motor symptoms of PD. These approaches majorly include receptor-based, anti-inflammatory, stem-cell and nucleic acid based. The major limitations of existing therapeutic interventions (of commonly oral route) are low efficacy due to low brain bioavailability and associated side effects. Nanotechnology has been exploited and has gained wide attention in the recent years as an approach for enhancement of bioavailability of various small molecule drugs in the brain. To address the challenges associated with PD therapy, nose-to-brain delivery utilizing nanomedicine-based approaches has been found to be encouraging in published evidence. Therefore, the present work summarises the major challenges and limitations with antiparkinsonian drugs, novel therapeutic interventions, and scope of nanomedicine-based nose-to-brain delivery in addressing the current challenges of antiparkinsonian therapy. The manuscript tries to sensitize the researchers for designing brain-targeted nanomedicine loaded with natural/synthetic scaffolds, biosimilars, and nucleic acids that can bypass the first-pass effect for the effective management of PD.

How Are Adenosine and Adenosine A2A Receptors Involved in the Pathophysiology of Amyotrophic Lateral Sclerosis?

Adenosine is extensively distributed in the central and peripheral nervous systems, where it plays a key role as a neuromodulator. It has long been implicated in the pathogenesis of progressive neurogenerative disorders such as Parkinson’s disease, and there is now growing interest in its role in amyotrophic lateral sclerosis (ALS). The motor neurons affected in ALS are responsive to adenosine receptor function, and there is accumulating evidence for beneficial effects of adenosine A_2A receptor antagonism. In this article, we focus on recent evidence from ALS clinical pathology and animal models that support dynamism of the adenosinergic system (including changes in adenosine levels and receptor changes) in ALS. We review the possible mechanisms of chronic neurodegeneration via the adenosinergic system, potential biomarkers and the acute symptomatic pharmacology, including respiratory motor neuron control, of A_2A receptor antagonism to explore the potential of the A_2A receptor as target for ALS therapy.