Antiparkinsonian Benefit Research Articles

Positive allosteric mGluR2 modulation with BINA alleviates dyskinesia and psychosis-like behaviours in the MPTP-lesioned marmoset.

There is mounting evidence that positive allosteric modulation of metabotropic glutamate type 2 receptors (mGluR2) is an efficacious approach to reduce the severity of L-3,4-dihydroxyphenylalanine (L-DOPA)-induced dyskinesia, psychosis-like behaviours (PLBs), while conferring additional anti-parkinsonian benefit. However, the mGluR2 positive allosteric modulators (PAMs) tested so far, LY-487,379 and CBiPES, share a similar chemical scaffold. Here, we sought to assess whether similar benefits would be conferred by a structurally-distinct mGluR2 PAM, biphenylindanone A (BINA). Six 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-lesioned marmosets exhibiting dyskinesia and PLBs were administered L-DOPA with either vehicle or BINA (0.1, 1, and 10mg/kg) in a randomised within-subject design and recorded. Behaviour was analysed by a blinded rater who scored the severity of each of parkinsonism, dyskinesia and PLBs. When added to L-DOPA, BINA 0.1mg/kg, 1mg/kg, and 10mg/kg all significantly reduced the severity of global dyskinesia, by 40%, 52% and 53%, (all P < 0.001) respectively. BINA similarly attenuated the severity of global PLBs by 35%, 48%, and 50%, (all P < 0.001) respectively. Meanwhile, BINA did not alter the effect of L-DOPA on parkinsonism exhibited by the marmosets. The results of this study provide incremental evidence of positive allosteric modulation of mGluR2 as an effective therapeutic strategy for alleviating dyskinesia and PLBs, without hindering the anti-parkinsonian action of L-DOPA. Furthermore, this therapeutic benefit does not appear to be confined to a particular chemical scaffold.

Activation of mGlu 2/3 receptors with the orthosteric agonist LY-404,039 alleviates dyskinesia in experimental parkinsonism.

LY-404,039 is an orthosteric agonist at metabotropic glutamate 2 and 3 (mGlu 2/3 ) receptors, with a possible additional agonist effect at dopamine D 2 receptors. LY-404,039 and its pro-drug, LY-2140023, have previously been tested in clinical trials for psychiatric indications and could therefore be repurposed if they were shown to be efficacious in other conditions. We have recently demonstrated that the mGlu 2/3 orthosteric agonist LY-354,740 alleviated L-3,4-dihydroxyphenylalanine (L-DOPA)-induced abnormal involuntary movements (AIMs) in the 6-hydroxydopamine (6-OHDA)-lesioned rat without hampering the anti-parkinsonian action of L-DOPA. Here, we seek to take advantage of a possible additional D 2 -agonist effect of LY-404,039 and see if an anti-parkinsonian benefit might be achieved in addition to the antidyskinetic effect of mGlu 2/3 activation. To this end, we have administered LY-404,039 (vehicle, 0.1, 1 and 10 mg/kg) to 6-OHDA-lesioned rats, after which the severity of axial, limbs and oro-lingual (ALO) AIMs was assessed. The addition of LY-404,039 10 mg/kg to L-DOPA resulted in a significant reduction of ALO AIMs over 60-100 min (54%, P < 0.05). In addition, LY-404,039 significantly enhanced the antiparkinsonian effect of L-DOPA, assessed through the cylinder test (76%, P < 0.01). These results provide further evidence that mGlu 2/3 orthosteric stimulation may alleviate dyskinesia in PD and, in the specific case of LY-404,039, a possible D 2 -agonist effect might also make it attractive to address motor fluctuations. Because LY-404,039 and its pro-drug have been administered to humans, they could possibly be advanced to Phase IIa trials rapidly for the treatment of motor complications in PD.

The MPTP-lesioned marmoset model of Parkinson's disease: proposed efficacy thresholds that may potentially predict successful clinical trial results.

The 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-lesioned common marmoset has been used extensively to model Parkinson's disease, L-3,4-dihydroxyphenylalanine (L-DOPA)-induced dyskinesia and, more recently, dopaminergic psychosis. Whereas several experimental drugs have been tested in this primate, many of which subsequently underwent clinical trials, efficacy thresholds in the marmoset that would predict efficacy in the clinic are lacking. Here, we aimed to determine such efficacy end points that would be indicative of likely efficacy in clinical studies. To do so, we used the evidence-based medicine reviews published by the International Parkinson and Movement Disorder Society (IPMDS) to select drugs that were rated as clinically efficacious, likely efficacious or not efficacious for the treatment of parkinsonism, dyskinesia and psychosis. We then reviewed the literature in the MPTP-lesioned marmoset and identified articles reporting the effects of drugs that were included in the IPMDS recommendations, following which we estimated efficacy thresholds in the marmoset that would predict efficacy at the clinical level. We propose that, when drugs are administered as monotherapy, ≥ 50% reduction of global parkinsonism may be necessary to predict the possibility of clinical efficacy. As adjunct to a low dose of L-DOPA, we propose that an additional reduction of global parkinsonism ≥ 25% might predict clinical efficacy. As adjunct to an optimal dose of L-DOPA, we propose that additional anti-parkinsonian benefit ≥ 20%, with global parkinsonism as the end point, might predict clinical efficacy. For the treatment of dyskinesia, we suggest that the predictability threshold be set at ≥ 25% reduction of peak dose dyskinesia, while we believe that this threshold should be > 50% reduction of peak dose psychosis-like behaviours for psychosis-related end points. This article represents the first step in determining what efficacy might be necessary to achieve in pre-clinical studies in the MPTP-lesioned marmoset prior to confidently advancing drugs to clinical trials. We hope that it will help in the drug discovery and development process, notably by avoiding exposing patients to drugs that have little probability of clinical efficacy based upon pre-clinical experiments.

The selective 5-HT1A receptor agonist, NLX-112, exerts anti-dyskinetic effects in MPTP-treated macaques

BackgroundLong-term treatment of Parkinson's disease (PD) with l-DOPA typically leads to development of l-DOPA induced dyskinesia (LID). Amantadine, an NMDA antagonist, attenuates LID, but with limited efficacy and considerable side-effects. NLX-112 (also known as befiradol or F13640), a highly selective and efficacious 5-HT1A receptor agonist, reduced LID when tested in rodent and marmoset models of PD. MethodsThe effects of NLX-112 (0.03, 0.1 and 0.3 mg/kg PO) on established LID evoked by acute challenge with l-DOPA (27.5 ± 3.8 mg/kg PO) were assessed in MPTP-treated cynomolgus macaques. Amantadine (10 mg/kg PO) was tested as a positive control. Plasma exposure of NLX-112 (0.1 mg/kg PO) was determined. ResultsNLX-112 significantly and dose-dependently reduced median LID levels by up to 96% during the first hour post-administration (0.3 mg/kg). Moreover, NLX-112 reduced the duration of ‘bad on-time’ associated with disabling LID by up to 48% (0.3 mg/kg). In contrast, NLX-112 had negligible impact on the anti-parkinsonian benefit of l-DOPA. NLX-112 exposure peaked at ~50 ng/ml at 30 min post-administration but decreased to ~15 ng/ml at 2h. Amantadine reduced by 42% ‘bad on-time’ associated with l-DOPA, thereby validating the model. ConclusionThese data show that, in MPTP-lesioned cynomolgus macaques, NLX-112 exerts robust anti-dyskinetic effects, without reducing the anti-parkinsonian benefit of l-DOPA. These observations complement previous findings and suggest that selective and high efficacy activation of 5-HT1A receptors by NLX-112 may constitute a promising approach to combat LID in PD, providing an alternative for patients in whom amantadine is poorly tolerated or without useful effect.

NYX-458 Improves Cognitive Performance in a Primate Parkinson's Disease Model.

NYX-458 is a N-methyl-d-aspartate receptor (NMDAR) modulator that enhances synaptic plasticity. Dopaminergic cell loss in Parkinson's disease (PD) leads to NMDAR dysregulation in the cortico-striato-pallidal-thalmo-cortical network and altered plasticity in brain regions important to cognitive function. We hypothesize that targeting the NMDAR may be an efficacious approach to treating cognitive impairment in PD. NYX-458 was evaluated in 2 nonhuman primate models of PD. The first, a chronic low-dose 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-administration model, was used to assess the effects of NYX-458 on cognitive domains impacted early in PD including attention, working memory, executive function, and visuospatial learning. The second, a high-dose MPTP-administration model, was used to assess potential for NYX-458 induced change in motor symptoms. NYX-458 was evaluated in the chronic low-dose MPTP model using the variable delayed response measure to assess attention and working memory and simple discrimination reversal to assess executive function. NYX-458 was also assessed in the high-dose MPTP model as a monotherapy and in combination with low-dose or high-dose levodopa to assess potential impact on motor symptoms. NYX-458 administration resulted in rapid and long-lasting improvement in cognitive function across the domains of attention, working memory, and executive function. Dose levels effective in improving cognitive performance had no effect on PD motor symptoms, the antiparkinsonian benefit of levodopa, or dyskinesia. NYX-458 provides benefit in specific domains known to be impaired in PD in a dopamine depletion model of PD-like cognitive impairment. These data support the continued evaluation of NYX-458 as a potential therapeutic for cognitive decline in PD. © 2020 International Parkinson and Movement Disorder Society.

Gold Standard of Symptomatic treatment in Parkinson disease: Carbidopa / Levodopa

Parkinson's disease (PD) is one of the most common neurologic disorders, affecting approximately 1% of individuals older than 60 years and causing progressive disability that can be slowed but not halted, by treatment. The goal of the medical management of Parkinson's disease is to provide control of signs and symptoms for as long as possible while minimizing adverse effects. Levodopa coupled with a peripheral decarboxylase inhibitor (PDI), such as carbidopa, remains the gold standard of symptomatic treatment of motor features of Parkinson's disease. It provides the greatest antiparkinsonian benefit with the fewest adverse effects in the short term. However, its long-term use is associated with the development of fluctuations and dyskinesias. This review article is written to summarize the clinical and pharmacological data of carbidopa and levodopa which will be helpful to neurologists and physicians.

Pridopidine, a clinic-ready compound, reduces 3,4-dihydroxyphenylalanine-induced dyskinesia in Parkinsonian macaques.

Pridopidine, in development for Huntington's disease, may modulate aberrant l-dopa-induced effects including l-dopa-induced dyskinesia (LID). This study investigated whether pridopidine could reduce LID in the MPTP macaque model of Parkinson's disease and characterized the observed behavioral effects in terms of receptor occupancy. The pharmacokinetic profile and effects of pridopidine (15-30 mg/kg) on parkinsonism, dyskinesia, and quality of on-time, in combination with l-dopa, were assessed in MPTP macaques with LID. Pridopidine receptor occupancy was estimated using known in vitro binding affinities to σ1 and dopamine D2 receptors, in vivo PET imaging, and pharmacokinetic profiling across different species. Pridopidine produced a dose-dependent reduction in dyskinesia (up to 71%, 30 mg/kg) and decreased the duration of on-time with disabling dyskinesia evoked by l-dopa by 37% (20 mg/kg) and 60% (30 mg/kg). Pridopidine did not compromise the anti-parkinsonian benefit of l-dopa. Plasma exposures following the ineffective dose (15 mg/kg) were associated with full σ1 occupancy (>80%), suggesting that σ1 engagement alone is unlikely to account for the antidyskinetic benefits of pridopidine. Exposures following effective doses (20-30 mg/kg), while providing full σ1 occupancy, provide only modest dopamine D2 occupancy (<40%). However, effective pridopidine doses clearly engage a range of receptors (including adrenergic-α2C , dopamine-D3 , and serotoninergic-5-HT1A sites) to a higher degree than D2 and might contribute to the antidyskinetic actions. In MPTP macaques, pridopidine produced a significant decrease in LID without compromising the antiparkinsonian benefit of l-dopa. Although the actions of pridopidine were associated with full σ1 occupancy, effective exposures are more likely associated with occupancy of additional, non-sigma receptors. This complex pharmacology may underlie the effectiveness of pridopidine against LID. © 2018 International Parkinson and Movement Disorder Society.

Effect of the selective 5-HT2A receptor antagonist EMD-281,014 on L-DOPA-induced abnormal involuntary movements in the 6-OHDA-lesioned rat.

L-3,4-Dihydroxyphenylalanine (L-DOPA) is the most effective therapy for motor symptoms of Parkinson's disease (PD); however, with repeated administration, as many as 94% of PD patients develop complications such as L-DOPA-induced dyskinesia. We previously demonstrated that EMD-281,014, a highly selective serotonin 2A (5-HT2A) receptor antagonist, reduces the severity of dyskinesia in the parkinsonian marmoset, without interfering with L-DOPA anti-parkinsonian benefit. Here, we assessed the effects of EMD-281,014 on L-DOPA-induced abnormal involuntary movements (AIMs) in the 6-hydroxydopamine (6-OHDA)-lesioned rat. We first determined the pharmacokinetic profile of EMD-281,014, to administer doses leading to clinically relevant plasma levels in the behavioural experiments. Dyskinetic 6-OHDA-lesioned rats were then administered EMD-281,014 (0.01, 0.03 and 0.1mg/kg) or vehicle in combination with L-DOPA and AIMs severity was evaluated. We also assessed the effect of EMD-281,014 on L-DOPA anti-parkinsonian action with the cylinder test. We found that the addition of EMD-281,014 (0.01, 0.03 and 0.1mg/kg) to L-DOPA did not reduce AIMs severity (P > 0.05), when compared to vehicle. EMD-281,014 did not compromise L-DOPA anti-parkinsonian action. Our results suggest that the highly selective 5-HT2A receptor antagonist EMD-281,014 is well-tolerated by parkinsonian rats, but does not attenuate L-DOPA-induced AIMs. Our results highlight differences between rodent and primate models of PD when it comes to determining the anti-dyskinetic action of 5-HT2A receptor antagonists.

Inferring the long duration response to levodopa in Parkinson’s disease

IntroductionThe long duration response to levodopa in Parkinson's disease outlasts drug elimination by days to weeks. Though a substantive part of anti-parkinsonian motor benefit, it cannot easily be observed. ObjectivesTo infer the magnitude of the long duration response during the first decade of Parkinson's disease and identify factors that influence it. MethodsSerial practically defined off scores of 24 patients from a longitudinal study of levodopa short duration response were used to establish their rate of motor progression. A line of notional untreated disability (as if drug treatment had never been given) with the same progression gradient was the basis for calculation of the long duration response. Predictors of mean long duration response amplitude were identified using a multiple linear regression model. ResultsOver a mean treatment period of 16.6 ± 4.4 years, annual increase in motor disability was 2.3% of the maximum score. The long duration response composed 49% of total levodopa response during the first decade of treatment, and this proportion was significantly higher soon after commencing levodopa (p = 0.001). Higher pre-treatment motor score (r = 0.60) and lower MMSE (r = 0.60) were the main predictors of a larger long duration response. There was little correlation between long and short duration responses. ConclusionsLong duration responses contribute almost half of the total levodopa benefit during the first decade of treatment. An appreciation of both long and short duration components of drug symptomatic effects is important in clinical trial design to investigate possible neuroprotective treatments.

DPI-289, a novel mixed delta opioid agonist / mu opioid antagonist (DAMA), has L-DOPA-sparing potential in Parkinson's disease.

L-DOPA-induced dyskinesia (LID) remains a significant problem in the management of Parkinson's disease (PD). In rodent and macaque models of PD, delta opioid receptor agonists have anti-parkinsonian actions while mu opioid antagonists can reduce the expression of LID. DPI-289 is a novel molecule with a unique combination of opioid receptor DAMA actions: delta agonist (Ki: 0.73 nM); mu antagonist (Ki: 12 nM). We demonstrated that DPI-289 has oral bioavailability and established its pharmacokinetic profile in both rat and primate. We hypothesised that these combined DAMA actions would provide an enhancement of L-DOPA effect without an associated increase in dyskinesia. In parkinsonian 6-OHDA lesioned rats and MPTP-lesioned macaques, DPI-289 provided anti-parkinsonian actions as monotherapy and an enhancement of L-DOPA benefit. Thus, acute administration of DPI-289 (3 mg/kg, p.o.) to 6-OHDA-lesioned rats produced a significant reduction in forelimb asymmetry (by 48%) that was maintained throughout the fifteen-day repeat-treatment period. Importantly, and in contrast to L-DOPA administration (6 mg/kg, i.p.), these benefits were not compromised by the development of abnormal involuntary movements. In the macaque, as monotherapy, DPI-289 (10 and 20 mg/kg) had significant, though incomplete, anti-parkinsonian actions lasting approximately 4 h. These benefits were not associated with dyskinesia. In fact, over the 6 h period of observation, DPI-289 (20 mg/kg) decreased parkinsonism by 19% and increased activity by 67% compared to vehicle treatment. By contrast, while high-dose L-DOPA (LDh) alone alleviated parkinsonism (for 3 h) this benefit was accompanied by significant dyskinesia that was disabling in nature. LDh provided a 50% reduction in parkinsonism over 6 h and 151% increase in activity. The combination of DPI-289 (20 mg/kg) and a low-dose of L-DOPA (LDl) provided anti-parkinsonian benefits greater than LDl alone without eliciting any significant dyskinesia. Treatment with LDl alone provided only transient statistically significant anti-parkinsonian benefit. However, the combination of LDl and DPI-289 reduced parkinsonism for 6 h (duration of monitoring), with parkinsonism being reduced by 35% and activity increased by 90% but with no increase in dyskinesia over that observed with LDl alone. Thus, DPI-289 has potential to improve the benefits of dopaminergic therapy in Parkinson's disease.

Parkinsonian monkeys with prior levodopa-induced dyskinesias followed by fetal dopamine precursor grafts do not display graft-induced dyskinesias.

Clinical trials testing the hypothesis that fetal dopamine grafts would provide antiparkinsonian benefit in patients who had already developed side effects from their long-term use of L-dopa revealed, in some cases, the presence of dyskinesias even in the absence of L-dopa. The form, intensity, and frequency of these dyskinesias were quite variable, but their manifestation slowed the clinical development of cell replacement therapies. Rodent models of graft-induced dyskinesias (GIDs) have been proposed, but their accuracy in modeling GIDs has been questioned because they usually require amphetamine for their presentation. The present study attempted to model GIDs in parkinsonian monkeys and, for the first time, to test the effect of grafts on previously dyskinetic monkeys. Toward this end, monkeys were rendered parkinsonian with n-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and dyskinetic with levodopa. They then received intraputamenal grafts of fetal dopaminergic cells, control cerebellar cells, or vehicle bilaterally and were studied for 18 months. Dopaminergic cells were grafted in a manner designed to produce either "hot spot" or "widespread" striatal innervation. Although levodopa-induced dyskinesias could be elicited postoperatively, GIDs were never observed in any animal at any time after grafting. Grafted monkeys were also challenged with levodopa but did not show any greater responses to these challenges than before grafting. These studies support the development of future dopamine neuron cell transplantation therapy-based approaches, indicating that in relevant primate models with appropriate cell preparation methodology, with successful graft survival and putamenal dopamine innervation, there is no evidence of graft-induced dyskinesias. J. Comp. Neurol. 525:498-512, 2017. © 2016 Wiley Periodicals, Inc.

Stimulation sites in the subthalamic nucleus and clinical improvement in Parkinson's disease: a new approach for active contact localization.

OBJECTIVE Deep brain stimulation (DBS) of the subthalamic nucleus (STN) is widely used in patients with Parkinson's disease (PD). However, which target area of this region results in the highest antiparkinsonian efficacy is still a matter of debate. The aim of this study was to develop a more accurate methodology to locate the electrodes and the contacts used for chronic stimulation (active contacts) in the subthalamic region, and to determine the position at which stimulation conveys the greatest clinical benefit. METHODS The study group comprised 40 patients with PD in whom bilateral DBS electrodes had been implanted in the STN. Based on the Morel atlas, the authors created an adaptable 3D atlas that takes into account individual anatomical variability and divides the STN into functional territories. The locations of the electrodes and active contacts were obtained from an accurate volumetric assessment of the artifact using preoperative and postoperative MR images. Active contacts were positioned in the 3D atlas using stereotactic coordinates and a new volumetric method based on an ellipsoid representation created from all voxels that belong to a set of contacts. The antiparkinsonian benefit of the stimulation was evaluated by the reduction in the Unified Parkinson's Disease Rating Scale Part III (UPDRS-III) score and in the levodopa equivalent daily dose (LEDD) at 6 months. A homogeneous group classification for contact position and the respective clinical improvement was applied using a hierarchical clustering method. RESULTS Subthalamic stimulation induced a significant reduction of 58.0% ± 16.5% in the UPDRS-III score (p < 0.001) and 64.9% ± 21.0% in the LEDD (p < 0.001). The greatest reductions in the total and contralateral UPDRS-III scores (64% and 76%, respectively) and in the LEDD (73%) were obtained when the active contacts were placed approximately 12 mm lateral to the midline, with no influence of the position being observed in the anteroposterior and dorsoventral axes. In contrast, contacts located about 10 mm from the midline only reduced the global and contralateral UPDRS-III scores by 47% and 41%, respectively, and the LEDD by 33%. Using the ellipsoid method of location, active contacts with the highest benefit were positioned in the rostral and most lateral portion of the STN and at the interface between this subthalamic region, the zona incerta, and the thalamic fasciculus. Contacts placed in the most medial regions of the motor STN area provided the lowest clinical efficacy. CONCLUSIONS The authors report an accurate new methodology to assess the position of electrodes and contacts used for chronic subthalamic stimulation. Using this approach, the highest antiparkinsonian benefit is achieved when active contacts are located within the rostral and the most lateral parts of the motor region of the STN and at the interface of this region and adjacent areas (zona incerta and thalamic fasciculus).

L-745,870 reduces the expression of abnormal involuntary movements in the 6-OHDA-lesioned rat.

L-3,4-Dihydroxyphenylalanine (L-DOPA) is the most effective treatment for Parkinson's disease, but chronic administration is complicated by the development of dyskinesia. We have previously demonstrated that the dopamine D4 receptor antagonist L-745,870 reduces the severity of L-DOPA-induced dyskinesia in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-lesioned macaque without compromising L-DOPA antiparkinsonian benefits. In the current study, we have addressed the effects of L-745,870 on the expression of L-DOPA-induced abnormal involuntary movements (AIMs) in the 6-hydroxydopamine-lesioned rat. Rats were primed with repeated L-DOPA administration, after which acute challenges of L-DOPA/L-745,870 (vehicle, 0.1, 0.3 and 1 mg/kg) were administered, and AIMs were assessed. Rotarod performance and AIMs were assessed. In L-DOPA-primed rats, L-745,870 (1 mg/kg, but not lower doses) alleviated previously established AIMs (by 84%, P<0.001). Whereas rotarod performance was significantly improved by L-DOPA/vehicle treatment, L-DOPA/L-745,870 failed to improve rotarod performance (P>0.05), suggesting that, in contrast to the MPTP-lesioned macaque, L-745,870 reduces L-DOPA antiparkinsonian benefit in the rat model. Overall, these data suggest that L-745,870 may have a narrow therapeutic window as an antidyskinetic agent in advanced Parkinson's disease.

Can levodopa-induced dyskinesias go beyond the motor circuit?

This scientific commentary refers to ‘A network centred on the inferior frontal cortex is critically involved in levodopa-induced dyskinesias’ by Cerasa et al. (doi: 10.1093/brain/awu329). Pioneers of levodopa treatment for Parkinson’s disease in the 1960s quickly realized that the dramatic motor improvement was often clouded by the occurrence of involuntary movements never previously seen in the disorder (Lees et al. , 2015). Levodopa-induced dyskinesias (LIDs) have been a common problem ever since and are one of the main reasons for recommending surgical treatment in advanced cases of Parkinson’s disease. In this issue of Brain , Cerasa and colleagues test the hypothesis that LIDs arise not only from the compromised basal ganglia motor circuit at the heart of Parkinson’s disease but from disturbances in areas of frontal cortex (Cerasa et al. , 2015). LIDs comprise a range of abnormal movements that may be distinguished according to presentation and type. The most common are choreic and sometimes dystonic movements that coincide with high plasma levodopa levels and maximal anti-parkinsonian benefit; hence, these are referred to as ‘peak dose’ or ‘ON’ period dyskinesia (Fahn, 2000). Experimental models are limited to such ‘peak dose’ presentation, which is the most studied type of LID. However, the pathophysiological mechanisms that cause LIDs are still incompletely understood. Classically, it has been proposed that LIDs are related to the degree of nigrostriatal neurodegeneration and striatal changes associated with chronic levodopa therapy (Obeso et al. , 2000). These interact to induce plastic synaptic abnormalities in striatal medium spiny neurons, which has the effect …

Gene therapy for Parkinson's disease: still a hot topic?

Parkinson's disease is a synucleinopathy with widespread degeneration within the peripheral nervous system and across a variety of brains regions. The best studied and understood region of neural degeneration is the dopaminergic nigrostriatal system. Striatal dopamine insufficiency and nigral neuronal loss underlie the cardinal motor symptoms of PD. Levodopa and deep brain stimulation (DBS) are the most potent therapies for these symptoms. However, they have side effects that warrant the investigation of new therapies. One novel therapy is gene transfer (or therapy), in which, for the most part, viruses are used to deliver therapeutic molecules. Gene therapy methodologies can be divided into two general types: symptomatic and disease modifying (for review, see Kordower and Bjorklund, 2013). The first gene therapy clinical trial for PD was the delivery of aromatic amino decarboxylase (AADC) (Mittermeyer et al, 2012). This approach was aimed at symptomatic benefit. AADC is the enzyme that converts levodopa to dopamine and AADC gene delivery attempts to make the conversion of the exogenous levodopa to dopamine more efficient. In animal studies, lower doses of levodopa result in the same antiparkinsonian benefit as high doses when it is combined with gene delivery of AADC. Lower doses would also obviate or delay the emergence of dopa-induced dyskinesias. AADC gene delivery was safe and well tolerated in a Phase 1 clinical trial (Mittermeyer et al, 2012). An open-label assessment demonstrated some benefit in a small number of patients. Oxford Biomedica employed a equine lentivirus to deliver tyrosine hydroxylase, AADC, and GTP cyclohydrolase, the combination of which makes dopamine. Preclinical studies in rodents and monkeys delivering lenti-dopamine demonstrated significant antiparkinsonian benefit. A Phase 1/2 clinical trial has been completed again demonstrating safety and tolerability with some measure of efficacy as determined via open-label assessments (Palfi et al, 2014). Another series of studies models gene therapy after deep brain stimulation (DBS). In PD, the subthalamic nucleus is hyperactive and DBS blocks that hyperactivity. Glutamic acid decarboxylase (GAD) reduces cellular activity and reverses motor dysfunction in rodent and nonhuman primate models of PD. A Phase 2 randomized sham controlled trial was performed and met the primary endpoint (LeWitt et al, 2011). However, the magnitude of the effect was small and it is unclear whether this approach is going forward. Disease-modifying gene therapy strategies have focused on the glial cell family of ligands (GFLs), namely, GDNF and neurturin. Gene delivery of both of these trophic factors protects nigrostriatal circuitry and motor function in numerous rodent and nonhuman primate models of PD (Kordower and Bjorklund, 2013). A new clinical trial using gene delivery of GDNF is currently underway. Unfortunately, two Phase 2 clinical trials testing neurturin failed (Marks et al, 2010; Olanow et al, manuscript in preparation). Why is this molecule so potent in preclinical models but ineffective in patients with PD? We have postulated that the failure is due to the extensive degeneration of the nigrostriatal system at the time the patients were treated (Kordower et al, 2013). Furthermore, the few fibers that are remaining are defective in axonal transport mechanisms and thus the trophic factor fails to be efficiently transported, either retrogradely or anterogradely, to nigral perikary. Gene therapy for PD still has great promise. Multiple approaches are safe and well tolerated. However, at this time, no study has demonstrated robust clinical benefit using rigorous double-blind assessments. However, it is possible that a resolution of delivery issues, which will maximize the spread of the vector to the target area, as well as moving to a less-impaired patient population, might unlock the potential of this strategy. Additionally, as currently practiced, gene therapy for PD only addressed the cardinal motor symptoms, and other signs, including potentially disabling psychiatric symptoms, require a different gene therapy approach.

UWA-121, a mixed dopamine and serotonin re-uptake inhibitor, enhances l-DOPA anti-parkinsonian action without worsening dyskinesia or psychosis-like behaviours in the MPTP-lesioned common marmoset

L-3,4-Dihydroxyphenylalanine (l-DOPA) is the most effective treatment for Parkinson's disease (PD), but its long-term administration is complicated by wearing-off and dyskinesia. UWA-101, a dual, equipotent inhibitor of dopamine (DAT) and serotonin (SERT) transporters, has previously been shown to successfully extend duration of anti-parkinsonian benefit of l-DOPA (ON-time), without exacerbating dyskinesia, in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-lesioned marmoset. However, UWA-101 is racemic and it is unclear whether one or both enantiomers contribute to its actions, and whether a better therapeutic effect might be attained by using a single antipode. In the current study, we synthesised the two enantiomers of UWA-101, R-101 (UWA-121) and S-101 (UWA-122), characterised their pharmacological profiles and administered them to MPTP-lesioned marmosets. Parkinsonism, dyskinesia, psychosis-like behaviours and duration of ON-time were evaluated. UWA-121 is a dual DAT > SERT inhibitor, with an approximate 10:1 DAT:SERT affinity ratio (inhibitory constants (Ki) of 307 and 3830 nM, respectively). In combination with l-DOPA, UWA-121 extended duration of ON-time when compared to l-DOPA/vehicle treatment (by 40%, P < 0.01). UWA-121 also extended duration of ON-time without dyskinesia (by 215%, P < 0.05) and ON-time without psychosis-like behaviours when compared to l-DOPA/vehicle treatment (by 345%, P < 0.01). UWA-121 did not worsen the severity of dyskinesia or psychosis-like behaviours (P > 0.05). UWA-122 is a selective SERT inhibitor (Ki 120 nM, Ki at DAT > 50 μM) and, in combination with l-DOPA, had no effect on ON-time, dyskinesia or psychosis-like behaviours (P > 0.05). These data indicate that dual DAT and SERT inhibitors effectively enhance l-DOPA anti-parkinsonian action without worsening dyskinesia and that compounds with such a pharmacological profile represent promising agents against wearing-off in PD.

Rotigotine polyoxazoline conjugate SER‐214 provides robust and sustained antiparkinsonian benefit

Currently available dopaminergic drugs such as levodopa and dopamine (DA) receptor agonists impart considerable improvement in Parkinson's disease (PD) motor symptoms but often lead to significant motor complications including "wearing-off" and dyskinesia. Such complications are believed to stem from the pulsatile nature of dopaminergic stimulation with these agents. Continuous dopaminergic drug delivery using polyoxazoline (POZ) polymer conjugation may improve motor symptoms, while avoiding development of side effects. The purposes of the current study are to characterize the in vitro and in vivo pharmacokinetics of POZ conjugation of a U.S. Food and Drug Administration (FDA)-approved DA agonist, rotigotine, and to evaluate their effects in an established rat model of PD. After determination of release profiles of several POZ-conjugated constructs ("fast": SER-212; "moderate": SER-213; and "slow": SER-214) using in vitro hydrolysis, normal male Sprague-Dawley rats were used for determination of the pharmacokinetic profile of both acute and chronic exposure. Finally, a separate group of rats was rendered hemiparkinsonian using intracranial 6-hydroxydopamine (6-OHDA) infusions, treated acutely with POZ-rotigotine, and assessed for rotational behavior and antiparkinsonian benefit using the cylinder test. POZ-rotigotine formulations SER-213 and SER-214 led to substantial pharmacokinetic improvement compared to unconjugated rotigotine. In addition, SER-214 led to antiparkinsonian effects in DA-lesioned rats that persisted up to 5 days posttreatment. Repeated weekly dose administration of SER-214 to normal rats for up to 12 weeks demonstrated highly reproducible pharmacokinetic profiles. The continuous dopaminergic stimulation profile afforded by SER-214 could represent a significant advance in the treatment of PD, with potential to be a viable, once-per-week therapy for PD patients.

Single or combined treatment with l-DOPA and quinpirole differentially modulate expression and phosphorylation of key regulatory kinases in neuroblastoma cells

In the past decades, the clinical use of dopamine agonists has expanded from adjunct therapy in patients with a deteriorating response to l-3,4-dihydroxyphenylalanine (l-DOPA) to monotherapy for the treatment of early PD. Dopamine agonists provide their antiparkinsonian benefit through stimulation of brain postsynaptic type 2 dopamine receptors that exert their effect through classical cAMP-dependent mechanisms, as well as cAMP-independent cellular signaling cascades, including the Akt/glycogen synthase kinase 3 (GSK3) pathway. Alterations of Akt/GSK3 have been observed and may contribute to the neurodegenerative processes and the development of l-DOPA-induced dyskinesia. The effects l-DOPA and quinpirole, a dopamine agonist, on the two key regulatory kinases, Akt and GSK3, were evaluated in neuroblastoma cell line. l-DOPA and dopamine agonist dose-dependently and differentially modulated Akt and GSK3 expression and phosphorylation when added alone or combined. The combined treatment inverted or potentiated the modulatory properties of the single compound. The drug- and concentration-dependent balance of dopamine receptor stimulation over auto-oxidation may distinctively modulate GSK3 isoforms and Akt. Our results indicate that particular attention must be given to drug concentration and combination when multiple therapies are applied for the clinical treatment of PD patients

TC-8831, a nicotinic acetylcholine receptor agonist, reduces l-DOPA-induced dyskinesia in the MPTP macaque

Long-term l-DOPA treatment for Parkinson's disease (PD) is limited by motor complications, particularly l-DOPA-induced dyskinesia (LID). A therapy with the ability to ameliorate LID without reducing anti-parkinsonian benefit would be of great value. We assessed the ability of TC-8831, an agonist at nicotinic acetylcholine receptors (nAChR) containing α6β2/α4β2 subunit combinations, to provide such benefits in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine- (MPTP) lesioned macaques with established LID.Animals were treated orally for consecutive 14-day periods with twice-daily vehicle (weeks 1–2) or TC-8831 (0.03, 0.1 or 0.3 mg/kg, weeks 3–8). l-DOPA was also administered, once-daily, (weeks 1–12, median-dose 30 mg/kg, p.o.). For the following two-weeks (weeks 9–10), TC-8831 was washed out, while once-daily l-DOPA treatment was maintained. The effects of once-daily amantadine (3 mg/kg, p.o.) were then assessed over weeks 11–12. LID, parkinsonism, duration and quality of ON-time were assessed weekly by a neurologist blinded to treatment.TC-8831 reduced the duration of ‘bad’ ON-time (ON-time with disabling dyskinesia) by up to 62% and decreased LID severity (median score 18 cf. 34 (vehicle), 0.1 mg/kg, 1–3 h period). TC-8831 also significantly reduced choreiform and dystonic dyskinesia (median scores 6 and 31 cf. 19 and 31 respectively (vehicle), both 0.03 mg/kg, 1–3 h). At no time did TC-8831 treatment result in a reduction in anti-parkinsonian benefit of l-DOPA. By comparison, amantadine also significantly reduced dyskinesia and decreased ‘bad’ ON-time (up to 61%) but at the expense of total ON-time (reduced by up to 23%).TC-8831 displayed robust anti-dyskinetic actions and improved the quality of ON-time evoked by l-DOPA without any reduction in anti-parkinsonian benefit.

Use of catechol‐O‐methyltransferase inhibition to minimize L‐3,4‐dihydroxyphenylalanine‐induced dyskinesia in the 1‐methyl‐4‐phenyl‐1,2,3,6‐tetrahydropyridine‐lesioned macaque

L-3,4-dihydroxyphenylalanine (L-DOPA)-induced dyskinesia is a complication of dopaminergic treatment in Parkinson's disease. Lowering the L-DOPA dose reduces dyskinesia but also reduces the antiparkinsonian benefit. A therapy that could enhance the antiparkinsonian action of low-dose L-DOPA (LDl) without exacerbating dyskinesia would thus be of considerable therapeutic benefit. This study assessed whether catechol-O-methyltransferase (COMT) inhibition, as an add-on to LDl, might be a means to achieve this goal. Cynomolgus macaques were administered 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine. Dyskinesia was established by chronic treatment with L-DOPA. Two doses of L-DOPA were identified - high-dose L-DOPA (LDh), which provided good antiparkinsonian benefit but was compromised by disabling dyskinesia, and LDl, which was sub-threshold for providing significant antiparkinsonian benefit, without dyskinesia. LDh and LDl were administered in acute challenges in combination with vehicle and, for LDl, with the COMT inhibitor entacapone (5, 15 and 45mg/kg). The duration of antiparkinsonian benefit (ON-time), parkinsonism and dyskinesia were determined. The ON-time after LDh was ∼170min and the ON-time after LDl alone (∼98min) was not significantly different to vehicle (∼37min). In combination with LDl, entacapone significantly increased the ON-time (5, 15 and 45mg/kg being ∼123, ∼148 and ∼180min, respectively). The ON-time after LDl/entacapone 45mg/kg was not different to that after LDh. However, whereas the percentage ON-time that was compromised by disabling dyskinesia was ∼56% with LDh, it was only ∼31% with LDl/entacapone 45mg/kg. In addition to the well-recognized action of COMT inhibition to reduce wearing-OFF, the data presented suggest that COMT inhibition in combination with low doses of L-DOPA has potential as a strategy to alleviate dyskinesia.