Could istradefylline be a treatment option for postural abnormalities in mid-stage Parkinson's disease?

Novel and experimental therapeutics for the management of motor and non-motor Parkinsonian symptoms

BACKGROUND  : Both motor and non-motor symptoms of Parkinson's disease (PD) have a substantial detrimental influence on the patient's quality of life. The most effective treatment remains oral levodopa. All currently known treatments just address the symptoms; they do not completely reverse the condition.

METHODOLOGY

In order to find literature on the creation of novel treatment agents and their efficacy for PD patients, we searched PubMed, Google Scholar, and other online libraries.

RESULTS

According to the most recent study on Parkinson's disease (PD), a great deal of work has been done in both the clinical and laboratory domains, and some current scientists have even been successful in developing novel therapies for PD patients.

CONCLUSION

The quality of life for PD patients has increased as a result of recent research, and numerous innovative medications are being developed for PD therapy. In the near future, we will see positive outcomes regarding PD treatment.

Newly Approved and Investigational Drugs for Motor Symptom Control in Parkinson's Disease

Motor symptoms are a core feature of Parkinson's disease (PD) and cause a significant burden on patients' quality of life. Oral levodopa is still the most effective treatment, however, the motor benefits are countered by inherent pharmacologic limitations of the drug. Additionally, with disease progression, chronic levodopa leads to the appearance of motor complications including motor fluctuations and dyskinesia. Furthermore, several motor abnormalities of posture, balance, and gait may become less responsive to levodopa. With these unmet needs and our evolving understanding of the neuroanatomic and pathophysiologic underpinnings of PD, several advances have been made in defining new therapies for motor symptoms. These include newer levodopa formulations and drug delivery systems, refinements in adjunctive medications, and non-dopaminergic treatment strategies. Although some are in early stages of development, these novel treatments potentially widen the available options for the management of motor symptoms allowing clinicians to provide an individually tailored care for PD patients. Here, we review the existing and emerging interventions for PD with focus on newly approved and investigational drugs for motor symptoms, motor fluctuations, dyskinesia, and balance and gait dysfunction.

Istradefylline for OFF Episodes in Parkinson’s Disease: A US Perspective of Common Clinical Scenarios

The effective management of OFF episodes remains an important unmet need for patients with Parkinson’s disease (PD) who develop motor complications with long-term levodopa therapy. Istradefylline is a selective adenosine A_2A receptor antagonist for the treatment of patients with PD experiencing OFF episodes while on levodopa/decarboxylase inhibitor. Originally approved in Japan, istradefylline was recently approved in the USA. In this article, we provide a specific review of the four clinical studies that the FDA included in the approval of istradefylline in the USA, and discuss common clinical scenarios, based on our experience, where treatment with istradefylline may benefit patients experiencing motor fluctuations.

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.

Adenosine A1 and A2A receptors are involved on guanosine protective effects against oxidative burst and mitochondrial dysfunction induced by 6-OHDA in striatal slices

6-Hydroxydopamine (6-OHDA) is the most used toxin in experimental Parkinson's disease (PD) models. 6-OHDA shows high affinity for the dopamine transporter and once inside the neuron, it accumulates and undergoes non-enzymatic auto-oxidation, promoting reactive oxygen species (ROS) formation and selective damage of catecholaminergic neurons. In this way, our group has established a 6-OHDA in vitro protocol with rat striatal slices as a rapid and effective model for screening of new drugs with protective effects against PD. We have shown that co-incubation with guanosine (GUO, 100 μM) prevented the 6-OHDA-induced damage in striatal slices. As the exact GUO mechanism of action remains unknown, the aim of this study was to investigate if adenosine A1 (A1R) and/or A2A receptors (A2AR) are involved on GUO protective effects on striatal slices. Pre-incubation with DPCPX, an A1R antagonist prevented guanosine effects on 6-OHDA-induced ROS formation and mitochondrial membrane potential depolarization, while CCPA, an A1R agonist, did not alter GUO effects. Regarding A2AR, the antagonist SCH58261 had similar protective effect as GUO in ROS formation and mitochondrial membrane potential. Additionally, SCH58261 did not affect GUO protective effects. The A2AR agonist CGS21680, although, completely blocked GUO effects. Finally, the A1R antagonist DPCPX, and the A2AR agonist CGS21680 also abolished the preventive guanosine effect on 6-OHDA-induced ATP levels decrease. These results reinforce previous evidence for a putative interaction of GUO with A1R-A2AR heteromer as its molecular target and clearly indicate a dependence on adenosine receptors modulation to GUO protective effect.

Balance response to levodopa predicts balance improvement after bilateral subthalamic nucleus deep brain stimulation in Parkinson's disease

The effect of subthalamic nucleus deep brain stimulation (STN-DBS) on balance function in patients with Parkinson’s disease (PD) and the potential outcome predictive factors remains unclear. We retrospectively included 261 PD patients who underwent STN-DBS and finished the 1-month follow-up (M1) assessment in the explorative set for identifying postoperative balance change predictors, and 111 patients who finished both the M1 and 12-month follow-up (M12) assessment in the validation set for verifying the identified factors. Motor and balance improvement were evaluated through the UPDRS-III and the Berg balance scale (BBS) and pull test (PT), respectively. Candidate predictors of balance improvement included age, disease duration, motor subtypes, baseline severity of PD, cognitive status, motor and balance response to levodopa, and stimulation parameters. In the off-medication condition, STN-DBS significantly improved BBS and PT performance in both the M1 and M12, in both datasets. While in the on-medication condition, no significant balance improvement was observed. Higher preoperative BBS response to levodopa was significantly associated with larger postoperative off-medication, but not on-medication, BBS (p < 0.001) and PT (p < 0.001) improvement in both the M1 and M12. BBS subitems 8, 9, 11, 13, and 14 were the major contributors to the prediction of balance improvement after STN-DBS. STN-DBS improves short-term off-medication, but not on-medication, balance function assessed through BBS and PT. Preoperative BBS response to levodopa best predicts postoperative off-medication balance improvement. For patients who manifested severe balance problems, a levodopa challenge test on BBS or the short version of BBS is recommended.

Effect of dopaminergic medication on adenosine 2A receptor availability in patients with Parkinson's disease

OBJECTIVE

To assess the necessity of withdrawing dopaminergic medication in Parkinson's disease (PD) patients for accurate estimation of adenosine 2A receptor (A_2AR) availability using [¹¹C]TMSX PET imaging. This was accomplished by studying the short-term effect of the cessation of dopaminergic medication on A_2AR availability in non-dyskinetic patients with PD treated with dopaminergic medication.

METHODS

Eight PD patients (age 67.9 ± 5.6 years; 6 men, 2 women) without dyskinesia were enrolled in this study. A_2AR availability was measured using PET imaging with a [7-methyl-¹¹C]-(E)-8-(3,4,5-trimethoxystyryl)-1,3,7-trimethylxanthine ([¹¹C]TMSX) radioligand after a short term cessation of dopaminergic medication (12hrs for levodopa, 24hrs for dopamine agonists and MAO-B inhibitors). Repeated PET imaging was performed while the patients were back 'on' their regular dopaminergic medication (median 13 days after first imaging). Conventional MRI was acquired for anatomical reference. Specific binding of [¹¹C]TMSX was quantified as distribution volume ratios (DVR) for caudate, pallidum and putamen using Logan graphical method with clustered gray matter reference region.

RESULTS

No significant differences were observed for the DVRs in all three striatal regions between 'on' and 'off' medication states. Strong correlations were also observed between the two states. Statistical equivalence was found in pallidum (TOST equivalence test, p = 0.045) and putamen (TOST equivalence test, p = 0.022), but not in caudate DVR (TOST equivalence test, p = 0.201) between the two medication states.

CONCLUSIONS

Our results show that dopaminergic medication has no significant short-term effect on the availability of A_2A receptors in putamen and pallidum of patients with PD. However, relatively poor repeatability was demonstrated in the caudate.

Istradefylline - a first generation adenosine A2A antagonist for the treatment of Parkinson's disease

Introduction It is now accepted that Parkinson's disease (PD) is not simply due to dopaminergic dysfunction, and there is interest in developing non-dopaminergic approaches to disease management. Adenosine A_2A receptor antagonists represent a new way forward in the symptomatic treatment of PD.Areas covered In this narrative review, we summarize the literature supporting the utility of adenosine A_2A antagonists in PD with a specific focus on istradefylline, the most studied and only adenosine A_2A antagonist currently in clinical use.Expert opinion: At this time, the use of istradefylline in the treatment of PD is limited to the management of motor fluctuations as supported by the results of randomized clinical trials and evaluation by Japanese and USA regulatory authorities. The relatively complicated clinical development of istradefylline was based on classically designed studies conducted in PD patients with motor fluctuations on an optimized regimen of levodopa plus adjunctive dopaminergic medications. In animal models, there is consensus that a more robust effect of istradefylline in improving motor function is produced when combined with low or threshold doses of levodopa rather than with high doses that produce maximal dopaminergic improvement. Exploration of istradefylline as a 'levodopa sparing' strategy in earlier PD would seem warranted.

How do adenosine A2A receptors regulate motor function?

Adenosine A_2A receptor antagonism is a new therapeutic strategy in the symptomatic treatment of Parkinson's disease (PD). This review addresses how adenosine A_2A receptors are involved with the control of motor function via the basal ganglia-thalamocortical circuit, and considers the anatomical localization and physiological function of the receptor, along with its ultrastructural localization in critical areas/neurons of the circuit. Based on this understanding of the functional significance of the adenosine A_2A receptor in the basal ganglia, the mode of action of A_2A receptor antagonists is explored in terms of the dynamic functioning of the basal ganglia and the activity of the internal circuits of the striatum in PD. Finally, the pathophysiological differences between the normal and PD states are examined to emphasize the importance of the adenosine A_2A receptor.

Istradefylline to Treat Patients with Parkinson's Disease Experiencing "Off" Episodes: A Comprehensive Review

Parkinson’s disease (PD) is a common neurodegenerative disorder that leads to significant morbidity and disability. PD is caused by a loss of dopaminergic, cholinergic, serotonergic, and noradrenergic neurons in the central nervous system (CNS), and peripherally; the syndromic parkinsonism symptoms of movement disorder, gait disorder, rigidity and tremor are mostly driven by the loss of these neurons in the basal ganglia. Unfortunately, a significant proportion of patients taking levodopa, the standard of care treatment for PD, will begin to experience a decrease in effectiveness at varying times. These periods, referred to as “off episodes”, are characterized by increased symptoms and have a detrimental effect on quality of life and disability. Istradefylline, a novel adenosine A2A receptor antagonist, is indicated as a treatment addition to levodopa/carbidopa in patients experiencing “off episodes”. It promotes dopaminergic activity by antagonizing adenosine in the basal ganglia. This review will discuss istradefylline as a treatment for PD patients with off episodes.

Involvement of adenosine A1 and A2A receptors on guanosine-mediated anti-tremor effects in reserpinized mice

Parkinson's disease (PD) signs and symptoms regularly include tremor. Interestingly, the nucleoside guanosine (GUO) has already proven to be effective in reducing reserpine-induced tremulous jaw movements (TJMs) in rodent models, thus becoming a promising antiparkinsonian drug. Here, we aimed at revealing the mechanism behind GUO antiparkinsonian efficacy by assessing the role of adenosine A₁ and A_2A receptors (A₁R and A_2AR) on GUO-mediated anti-tremor effects in the reserpinized mouse model of PD. Reserpinized mice showed elevated reactive oxygen species (ROS) production and cellular membrane damage in striatal slices assessed ex vivo and GUO treatment reversed ROS production. Interestingly, while the simultaneous administration of sub-effective doses of GUO (5 mg/kg) and SCH58261 (0.01 mg/kg), an A_2AR antagonist, precluded reserpine-induced TJMs, these were ineffective on reverting ROS production in ex vivo experiments. Importantly, GUO was able to reduce TJM and ROS production in reserpinized mouse lacking the A_2AR, thus suggesting an A_2AR-independent mechanism of GUO-mediated effects. Conversely, the administration of DPCPX (0.75 mg/kg), an A₁R antagonist, completely abolished both GUO-mediated anti-tremor effects and blockade of ROS production. Overall, these results indicated that GUO anti-tremor and antioxidant effects in reserpinized mice were A₁R dependent but A_2AR independent, thus suggesting a differential participation of adenosine receptors in GUO-mediated effects.

Efficacy of istradefylline for gait disorders with freezing of gait in Parkinson's disease: A single-arm, open-label, prospective, multicenter study

Background: Gait disorders are common in Parkinson's disease patients who respond poorly to dopaminergic treatment. Blockade of adenosine A_2A receptors is expected to improve gait disorders. Istradefylline is a first-in-class selective adenosine A_2A receptor antagonist with benefits for motor complications associated with Parkinson's disease. Research design and methods: This multicenter, open-label, single-group, prospective interventional study evaluated changes in total gait-related scores of the Part II/III Movement Disorder Society-Unified Parkinson's Disease Rating Scale (MDS-UPDRS) and Freezing of Gait Questionnaire (FOG-Q) in 31 Parkinson's disease patients treated with istradefylline. Gait analysis by portable gait rhythmogram was performed. Results: MDS-UPDRS Part III gait-related total scores significantly decreased at Weeks 4-12 from baseline with significant improvements in gait, freezing of gait, and postural stability. Significant decreases in MDS-UPDRS Part II total scores and individual item scores at Week 12 indicated improved daily living activities. At Week 12, there were significant improvements in FOG-Q, new FOG-Q, and overall movement per 48 h measured by portable gait rhythmogram. Adverse events occurred in 7/31 patients. Conclusions: Istradefylline improved gait disorders in Parkinson's disease patients complicated with freezing of gait, improving their quality of life. No unexpected adverse drug reactions were identified. Trial registration: UMIN-CTR (UMIN000020288).

Chemical management of levodopa-induced dyskinesia in Parkinson's disease patients

INTRODUCTION

Levodopa-induced dyskinesias (LID) appears in more than 50% of Parkinson's disease patients after 5 years of treatment and clinicians always have to ensure that there is a balance between the beneficial effect of the treatment and the potential complications.

AREAS COVERED

In this review, the authors discuss the treatment of LID. Treatment can be divided into strategies for preventing their occurrence, modification of dopaminergic therapy, and providing more continuous dopaminergic stimulation as well as the use of nondopaminergic drugs.

EXPERT OPINION

Amantadine is currently considered the most effective drug for the treatment of LID. Several compounds developed to target adenosine, adrenergic, glutamatergic, and serotonergic receptors have shown to significantly decrease dyskinesias in animal models. However, despite promising preclinical results, translation to clinical practice remains challenging and majority of these compounds failed to decrease LID in randomized controlled trials with moderate-to-advanced parkinsonian patients. Despite promising results with nondopaminergic drugs, treatment of dyskinesias is still challenging and largely due to their side effects. Future research should focus on developing treatments that can provide continuous dopaminergic delivery throughout the day in a noninvasive manner. Studies on the impact of the early administration of long-acting formulations of levo-3,4-dihydroxy-phenylalanine on dyskinesias are also necessary.