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Activation of metabotropic glutamate 2 (mGlu 2 ) receptors is a potential novel therapeutic approach for the treatment of parkinsonism. Thus, when administered as monotherapy or as adjunct to a low dose of L-3,4-dihydroxyphenylalanine (L-DOPA), the mGlu 2 positive allosteric modulator (PAM) LY-487,379 alleviated parkinsonism in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-lesioned primates. Here, we sought to investigate the effect of biphenyl-indanone A (BINA), a highly selective mGlu 2 PAM whose chemical scaffold is unrelated to LY-487,379, to determine if a structurally different mGlu 2 PAM would also confer anti-parkinsonian benefit. In monotherapy experiments, MPTP-lesioned marmosets were injected with either vehicle, L-DOPA/benserazide (15/3.75 mg/kg, positive control) or BINA (0.1, 1, 10 mg/kg). In adjunct to a low L-DOPA dose experiments, MPTP-lesioned marmosets were injected with L-DOPA/benserazide (7.5/1.875 mg/kg) in combination with vehicle or BINA (0.1, 1, 10 mg/kg). Parkinsonism, dyskinesia and psychosis-like behaviours (PLBs) were then quantified. When administered alone, BINA 1 and 10 mg/kg decreased parkinsonism severity by ~22% (p < 0.01) and ~47% (p < 0.001), when compared with vehicle, which was comparable with the global effect of a high L-DOPA dose. When administered in combination with a low L-DOPA dose, BINA 1 and 10 mg/kg decreased global parkinsonism by ~38% (p < 0.001) and ~53% (p < 0.001). BINA 10 mg/kg decreased global dyskinesia by ~94% (p < 0.01) and global PLBs by ~92% (p < 0.01). Our results provide additional evidence that mGlu 2 positive allosteric modulation elicits anti-parkinsonian effects. That this benefit is not related to a particular chemical scaffold suggests that it may be a class effect rather than the effect of a specific molecule., (© 2024 The Author(s). European Journal of Neuroscience published by Federation of European Neuroscience Societies and John Wiley & Sons Ltd.)

Purpose: Antagonising serotonin (5-HT) type 2A receptors (5-HT 2A R) is an effective strategy to alleviate both dyskinesia and psychosis in Parkinson's disease (PD). We have recently shown that activation of metabotropic glutamate 2 receptors (mGluR 2 ), via either orthosteric stimulation or positive allosteric modulation, enhances the anti-dyskinetic and anti-psychotic effects of 5-HT 2A R antagonism. Here, we investigated if greater therapeutic efficacy would be achieved by combining 5-HT 2A R antagonism with concurrent mGluR 2 orthosteric stimulation and mGluR 2 positive allosteric modulation., Methods: Five 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-lesioned marmosets exhibiting dyskinesia and psychosis-like behaviours (PLBs) were administered L-3,4-dihydroxyphenylalanine (L-DOPA) in combination with vehicle or the 5-HT 2A R antagonist EMD-281,014. EMD-281,014 was itself administered alone or with the mGluR 2 orthosteric agonist (OA) LY-354,740, the mGluR 2 positive allosteric modulator (PAM) LY-487,379 and combination thereof, after which the severity of dyskinesia, PLBs and parkinsonism was rated., Results: EMD-281,014 reduced dyskinesia and PLBs by up to 47% and 40%, respectively (both P < 0.001). The addition of LY-354,740, LY-487,379 and LY-354,740/LY-487,379 decreased dyskinesia by 56%, 65% and 77%, while PLBs were diminished by 55%, 63% and 71% (all P < 0.001). All treatment combinations provided anti-dyskinetic and anti-psychotic benefits significantly greater than those conferred by EMD-281,014 alone (all P < 0.05). The combination of EMD-281,014/LY-354,740/LY-487,379 resulted in anti-dyskinetic and anti-psychotic effects significantly greater than those conferred by EMD-281,014 with either LY-354,740 or LY-487,379 (both P < 0.05). No deleterious effects on L-DOPA anti-parkinsonian action were observed., Conclusion: Our results suggest that combining 5-HT 2A R antagonism with mGluR 2 activation results in greater reduction of L-DOPA-induced dyskinesia and PD psychosis. They also indicate that further additive effect can be achieved when a mGluR 2 OA and a mGluR 2 PAM are combined with a 5-HT 2A R antagonist than when a mGluR 2 OA or a mGluR 2 PAM are added to a 5-HT 2A R antagonist., (© 2021. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Dyskinesia and psychosis are complications encountered in advanced Parkinson's disease (PD) following long-term therapy with L-3,4-dihydroxyphenylalanine (L-DOPA). Disturbances in the glutamatergic system have been associated with both dyskinesia and psychosis, making glutamatergic modulation a potential therapeutic approach for these. Treatments thus far have sought to dampen glutamatergic transmission, for example through blockade of N-methyl-D-aspartate (NMDA) receptors or modulation of metabotropic glutamate receptors 5. In contrast, activation of the glycine-binding site on NMDA receptors is required for their physiological response. Here, we investigated whether indirectly enhancing glutamatergic transmission through inhibition of glycine re-uptake would be efficacious in diminishing both dyskinesia and psychosis-like behaviours (PLBs) in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-lesioned common marmoset. Six marmosets were rendered parkinsonian by MPTP injection. Following repeated administration of L-DOPA to induce dyskinesia and PLBs, they underwent acute challenges of the glycine transporter 1 (GlyT 1 ) inhibitor ALX-5407 (0.01, 0.1 and 1 mg/kg) or vehicle, in combination with L-DOPA, after which the severity of dyskinesia, PLBs and parkinsonian disability was evaluated. In combination with L-DOPA, ALX-5407 0.1 and 1 mg/kg significantly reduced the severity of dyskinesia, by 51% and 41% (both P < 0.001), when compared to vehicle. ALX-5407 0.01, 0.1 and 1 mg/kg also decreased the severity of global PLBs, by 25%, 51% and 38% (all P < 0.001), when compared to vehicle. The benefits on dyskinesia and PLBs were achieved without compromising the therapeutic effect of L-DOPA on parkinsonism. Our results suggest that GlyT 1 inhibition may be a novel strategy to attenuate dyskinesia and PLBs in PD, without interfering with L-DOPA anti-parkinsonian action., (Copyright © 2021 Elsevier B.V. All rights reserved.)

Parkinson's disease (PD) psychosis afflicts over half of patients and poses a significant burden on quality of life. The aetiology of PD psychosis is multifactorial and likely arises from the complex interaction between dopamine replacement therapy and disease state. The 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-lesioned common marmoset is a validated model to predict the efficacy of therapeutic compounds for treatment-related complications, including PD psychosis. In this model, psychosis-like behaviours (PLBs) encompass stereotypies that are idiosyncratic in nature and reproducible with each L-3,4-dihydroxyphenylanaline (L-DOPA) administration. In the present study, we sought to expand upon the existing repertoire of PLBs through the characterisation of novel stereotypical behaviours that appear dependent on the environment. We then discuss our findings in the context of clinical reports on stereotypical behaviours termed "punding" in subjects with PD, which consists of stereotypical repetitive and senseless behaviours. The poor understanding of the pathophysiology governing punding and consequent lack of effective therapies stand to benefit from enhanced characterisation of these stereotypical behaviours in a validated pre-clinical model. We hope that further characterisation of PLBs in the MPTP-lesioned marmoset will be helpful in the evaluation of interventions that seek to alleviate PD psychosis symptoms., (© 2021. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Whereas monoamine oxidase (MAO) type B inhibitors are used as adjunct to L-3,4-dihydroxyphenylalanine (L-DOPA) in the treatment of Parkinson's disease (PD), the enzyme MAO type A (MAO-A) also participates in the metabolism of dopamine in the human and primate striatum. Here, we sought to assess the effect of the selective reversible MAO-A inhibitor moclobemide on L-DOPA anti-parkinsonian in the gold standard animal model of PD, the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-lesioned primate. We also assessed the effect of moclobemide on L-DOPA-induced dyskinesia and psychosis-like behaviours (PLBs). Experiments were performed in six MPTP-lesioned marmosets chronically treated with L-DOPA and exhibiting stable dyskinesia and PLBs upon each administration. In a randomised within-subject design, animals were administered a therapeutic dose of L-DOPA in combination with moclobemide (0.1, 1 and 10 mg/kg) or its vehicle, after which the severity of parkinsonism, dyskinesia, and PLBs was rated by an experienced blinded rater. Moclobemide significantly reduced the global parkinsonian disability (- 36% with 0.1 mg/kg, P < 0.05; - 38% with 1 mg/kg, P < 0.01; - 47% with 10 mg/kg, P < 0.01), when compared with its vehicle. This reduction of parkinsonism was not accompanied by an exacerbation of dyskinesia or PLBs. Reversible MAO-A inhibition with moclobemide appears as an effective way to increase the anti-parkinsonian action of L-DOPA, without negatively affecting dyskinesia or dopaminergic psychosis.

Monoamine oxidase (MAO) type B (MAO-B) inhibition was shown to confer anti-parkinsonian benefit as monotherapy and adjunct to L-3,4-dihydroxyphenylalanine (L-DOPA) in clinical trials. Here, we explore the anti-parkinsonian effect of MAO type A (MAO-A) inhibition as monotherapy, as the enzyme MAO-A is also encountered within the primate and human basal ganglia, where it metabolises dopamine, albeit to a lesser extent than MAO-B. In six 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-lesioned marmosets, we assessed the anti-parkinsonian effect of the reversible MAO-A inhibitor moclobemide (0.1 and 1 mg/kg) as monotherapy and compared it to that of L-DOPA and vehicle treatments. Moclobemide significantly reversed parkinsonism (by 39%, P < 0.01), while eliciting only mild dyskinesia and psychosis-like behaviours (PLBs). In contrast, L-DOPA anti-parkinsonian effect was accompanied by marked dyskinesia and PLBs. MAO-A inhibition with moclobemide may provide anti-parkinsonian benefit when administered without L-DOPA and might perhaps be considered as monotherapy for the treatment of Parkinson's disease in the early stages of the condition.

Selective blockade of serotonin 2A (5-HT 2A ) receptors is a promising strategy to reduce L-3,4-dihydroxyphenylalanine (l-DOPA)-induced dyskinesia and has shown efficacy in a Phase III clinical trial for dopaminergic psychosis in Parkinson's disease (PD). However, pre-clinical and clinical evidence suggest that, while this approach may be effective and well tolerated, there might be a ceiling beyond which no further therapeutic benefit might be achieved. There is mounting evidence that 5-HT 2A receptors form a functional hetero-complex with metabotropic glutamate 2 (mGlu 2 ) receptors, with antagonism of 5-HT 2A receptors and activation of mGlu 2 receptors producing similar effects on the Gi/Gq signalling ratio at the intra-cellular level. Based on this interaction between 5-HT 2A and mGlu 2 receptors, we hypothesised that activation of mGlu 2 receptors would alleviate dyskinesia and psychosis in PD. LY-354,740 is a selective mGlu 2/3 orthosteric agonist that was previously tested in the clinic. In experiments conducted in the 6-hydroxydopamine (6-OHDA)-lesioned rat and the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-lesioned marmoset, we found that mGlu 2/3 activation with LY-354,740 significantly reduced the expression of dyskinesia and psychosis-like behaviours, while simultaneously enhancing l-DOPA therapeutic benefit. Moreover, mGlu 2/3 activation with LY-354,740 attenuated the development of dyskinesia. These data indicate that activation of mGlu 2/3 receptors is a therapeutic strategy that may provide relief for both motor and-non-motor treatment-related complications in PD., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

Nefazodone is an anti-depressant that interacts with a wealth of pharmacological targets, including some that may exert anti-dyskinetic and anti-psychotic effects in Parkinson's disease (PD), notably serotonin 1A and 2A receptors. In this study, we sought to determine the effect of nefazodone on L-3,4-dihydroxyphenylalanine (L-DOPA)-induced dyskinesia and psychosis-like behaviours (PLBs) in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-lesioned primate. Six common marmosets developed parkinsonism following administration of MPTP, after which they were treated chronically with L-DOPA to induce stable dyskinesia and PLBs. In behavioural experiments, nefazodone (0.01, 0.1 and 1 mg/kg) or vehicle was administered in combination with L-DOPA and its effects on dyskinesia, PLBs and parkinsonian disability were assessed. The addition of nefazodone 0.01, 0.1 and 1 mg/kg to L-DOPA reduced the severity of peak dose dyskinesia by ≈ 21%, ≈ 39% and ≈ 42% (all P < 0.05), while it did not have any significant effect on PLBs, when compared to L-DOPA/vehicle. Parkinsonian disability was not affected by any dose of nefazodone. Our results suggest that nefazodone may be effective to alleviate L-DOPA-induced dyskinesia in PD, while it may not exert any beneficial effect on dopaminergic psychosis.

Trazodone is a clinically available anti-depressant that exhibits affinity for serotonin 1A and 2A receptors, as well as for alpha-adrenoceptors, suggesting that it may be useful to treat L-3,4-dihydroxyphenylalanine (L-DOPA)-induced dyskinesia and psychosis that are encountered in advanced Parkinson's disease (PD). Here, we investigated the anti-dyskinetic and anti-psychotic effects of trazodone in the parkinsonian non-human primate. 6 common marmosets were rendered parkinsonian by administration of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). Following repeated administration of L-DOPA to induce stable dyskinesia and psychosis-like behaviours (PLBs), trazodone (0.1, 1 and 10 mg/kg) or vehicle was administered in combination with L-DOPA and its effects on dyskinesia, PLBs and parkinsonism were determined. The addition of trazodone 10 mg/kg to L-DOPA reduced peak dose dyskinesia by ≈ 39% (P < 0.01) and peak dose PLBs by ≈ 17% (P < 0.01). However, parkinsonian disability was significantly worsened by trazodone 10 mg/kg (P < 0.05) and duration of anti-parkinsonian action was diminished by ≈ 21% (P < 0.05). Our results suggest that trazodone may be effective in alleviating L-DOPA-induced dyskinesia and psychosis in PD, but its deleterious effect on motor function is a concern and may limit its tolerability and usefulness in clinical settings.

Blockade of serotonin 2A (5-HT 2A ) receptors is regarded as an anti-dyskinetic and anti-psychotic strategy in Parkinson's disease (PD). However, the 5-HT 2A antagonists tested so far exhibited affinity for other receptors, which might have played a role in their action. EMD-281,014 is the most selective 5-HT 2A antagonist available, with approximately 2,000-fold selectivity over serotonin 2C (5-HT 2C ) receptors. EMD-281,014 was previously tested in the clinic and has high translational potential. In the present study, we assessed the effect of EMD-281,014 on dyskinesia and psychosis in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-lesioned common marmoset. We first determined the pharmacokinetic profile of EMD-281,014 in the marmoset, after which doses leading to clinically-relevant plasma levels (0.01, 0.03 and 0.1 mg/kg) or vehicle were administered to MPTP-lesioned marmosets, in combination with L-3,4-dihydroxyphenylalanine (l-DOPA). The effects of EMD-281,014 on dyskinesia, psychosis-like behaviours (PLBs) and parkinsonism were then evaluated. When added to l-DOPA, EMD-281,014 (0.03 and 0.1 mg/kg) reduced peak dose dyskinesia, by 41.8% and 54.5% (P < 0.05 and P < 0.001), when compared to l-DOPA/vehicle. EMD-281,014 (0.03 and 0.1 mg/kg) also significantly reduced the severity of peak dose PLBs, by 42.5% and 45.9% (P < 0.05 and P < 0.001), when compared to vehicle. The anti-dyskinetic and anti-psychotic effects of EMD-281,014 were achieved without interfering with l-DOPA anti-parkinsonian action. Our results suggest that highly-selective 5-HT 2A receptor blockade with EMD-281,014 is an effective way to alleviate both dyskinesia and psychosis in PD, without adversely affecting parkinsonian disability., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

Parkinson's disease (PD) has long been seen as a disorder caused by degeneration of the dopaminergic system, leading to the classic motor manifestations of the disease. However, there is now overwhelming evidence that PD is more than a disease merely caused by dopamine depletion. It is well-known that a myriad of other neurotransmitters are affected by the disease process. One such neurotransmitter is serotonin (5-HT). 5-HT has been shown to play a role in several motor and nonmotor manifestations of PD, including tremor, cognition, depression and psychosis. 5-HT also seems to play a critical role in L-3,4-dihydroxyphenylalanine (L-DOPA)-induced dyskinesia. A breadth of preclinical studies and clinical trials have been conducted that aimed at modulating the 5-HT system in order to alleviate depression, cognitive deficits, psychosis, and dyskinesia. In this Review, we summarize recent advances in the 5-HT field in PD, but with a translational emphasis. We start by presenting a novel nonhuman primate model of PD that presents with dual dopamine and 5-HT lesions. We then present preclinical and clinical data that introduce new concepts, such as the use of biased and partial agonists, as well as molecules recently introduced to the field of PD, such as eltoprazine, pimavanserin, nelotanserin, and SYN-120, to enhance therapeutic benefit while minimizing adverse events, notably on parkinsonian disability.

Background: Parkinson's disease (PD) psychosis is encountered in as many as 50% of patients with advanced disease. Treatment options for PD psychosis are few. In fact, only clozapine and pimavanserin have shown efficacy in randomised controlled trials. Clinicians are often reluctant to prescribe the former, due to the risk of agranulocytosis, while the latter is not widely available yet. Because it is already clinically available and exhibits high affinity for serotonin 2A receptors, a target with which both clozapine and pimavanserin interact, we hypothesised that the anti-depressant mirtazapine might be effective to alleviate PD psychosis., Methods: Here, we tested the anti-psychotic potential of mirtazapine in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-lesioned common marmoset. Five MPTP-lesioned marmosets exhibiting psychosis-like behaviours were administered L-3,4-dihydroxyphenylalanine (L-DOPA) in combination with mirtazapine (0.1, 1 and 10 mg/kg) or vehicle. We also tested the effect of mirtazapine on L-DOPA-induced dyskinesia., Results: The addition of mirtazapine 10 mg/kg to L-DOPA reduced psychosis-like behaviours by 50% (P < 0.05) and dyskinesia by 29% (P < 0.01), when compared to L-DOPA/vehicle. Importantly, the antipsychotic and antidyskinetic effects of mirtazapine were achieved without hindering L-DOPA anti-parkinsonian action., Conclusions: Our results suggest that mirtazapine may be effective to alleviate PD psychosis and, because the drug is clinically available, clinical trials that would assess its anti-psychotic efficacy in PD could be rapidly undertaken, hopefully leading to a new treatment option for this debilitating condition.

L-3,4-dihydroxyphenylalanine (L-DOPA) is the most effective anti-parkinsonian agent available, but upon chronic administration, patients with Parkinson's disease (PD) experience abnormal involuntary movements, dyskinesia. Modulation of serotonin 1A (5-HT1A) receptors is regarded as an effective way to alleviate dyskinesia, yet this approach has been marred by a reduction of the therapeutic effectiveness of L-DOPA. We hypothesised that highly-selective 5-HT1A stimulation might be a way to alleviate dyskinesia without compromising L-DOPA anti-parkinsonian action. F15599 (also known as NLX-101) is a highly-selective 5-HT1A agonist that displays over 1000 × selectivity over off-target receptors. Seven cynomolgus macaques were administered MPTP and developed severe parkinsonism. Following chronic administration of L-DOPA, they developed severe and reproducible dyskinesia. F15599 (0.003, 0.01, 0.03 and 0.1 mg/kg) or vehicle was administered in combination with L-DOPA and its effect on dyskinesia and L-DOPA anti-parkinsonian was assessed. In combination with L-DOPA, F15599 (0.1 mg/kg) reduced the severity of peak-dose dyskinesia, by ≈45% (P < 0.001), compared to L-DOPA alone. F15599 (any dose) had no effect on duration of on-time or motor activity counts compared to L-DOPA alone. F15599 at 0.03 and 0.1 mg/kg significantly reduced duration of on-time with disabling dyskinesia (by ≈49% and ≈71%, P < 0.05 and P < 0.001, respectively). These results suggest that F15599, a highly-selective 5-HT1A receptor agonist, alleviates dyskinesia without exerting a deleterious effect on L-DOPA anti-parkinsonian action., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

In this pilot study, pioglitazone, an agonist of the peroxisome proliferator-activated receptor gamma (PPAR-γ) used in the treatment of diabetes mellitus, was administered to dyskinetic parkinsonian macaques. Pioglitazone alleviated L-DOPA-induced dyskinesia, but impaired L-DOPA anti-parkinsonian efficacy. These results suggest caution when administering pioglitazone to patients with advanced Parkinson's disease., (© 2015 Wiley Periodicals, Inc.)

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., (Copyright © 2014. Published by Elsevier Ltd.)

3,4-Dihydroxyphenylalanine (L-DOPA) treatment of Parkinson's disease (PD) is compromised by motor side effects, such as dyskinesia and non-motor problems, including psychosis. Because of the marked reduction in brain dopamine in PD and the resultant dopamine D2 receptor supersensitivity, it is impossible to use standard potent dopamine D2 receptor antagonists such as haloperidol to alleviate side effects without compromising the anti-parkinsonian benefits of L-DOPA. Haloperidol antagonizes D2 receptors with high affinity and slowly dissociates from D2 receptors (50% dissociation at 38min). We hypothesized that a rapidly dissociating D2 antagonist might allow some functional dopaminergic transmission and thus have a profile, with respect to reduction of dyskinesia and anti-parkinsonian effects, that was more useful therapeutically. The present study tested the principle of using a fast-off-D2 drug, CLR151 (50% dissociation at 23s) to modify L-DOPA actions in cynomolgus macaques with MPTP-parkinsonism. CLR151 (100mg/kg p.o.) reduced L-DOPA-induced dyskinesia and activity in the parkinsonian macaque by 86% and 52% respectively during peak action. CLR151 (100mg/kg) also reduced psychosis-like behaviour (i.e. reduced apparent visual hallucinations by 78%). Nevertheless, this dose of CLR151 significantly reduced the duration of anti-parkinsonian action of L-DOPA, ON-time (by 90%), and increased parkinsonian disability (by 57%). These data suggest that fast-off-D2 dopamine receptor antagonists, with D2-off-rate values close to those for CLR151, are unlikely to be useful in the treatment of dyskinesia and psychosis in PD. However, fast-off-D2 drugs could provide benefit if new congeners would have an even faster dissociation rate. Such drugs are now becoming available., (Copyright © 2013 Elsevier Inc. All rights reserved.)

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 45 mg/kg). The duration of antiparkinsonian benefit (ON-time), parkinsonism and dyskinesia were determined. The ON-time after LDh was ∼170 min and the ON-time after LDl alone (∼98 min) was not significantly different to vehicle (∼37 min). In combination with LDl, entacapone significantly increased the ON-time (5, 15 and 45 mg/kg being ∼123, ∼148 and ∼180 min, respectively). The ON-time after LDl/entacapone 45 mg/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 45 mg/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., (© 2013 Federation of European Neuroscience Societies and Blackwell Publishing Ltd.)

L-3,4-Dihydroxyphenylalanine (L-DOPA) remains the most effective symptomatic treatment of Parkinson's disease (PD). However, long-term administration of L-DOPA is marred by the emergence of abnormal involuntary movements, i.e., L-DOPA-induced dyskinesia (LID). Years of intensive research have yielded significant progress in the quest to elucidate the mechanisms leading to the development and expression of dyskinesia and maintenance of the dyskinetic state, but the search for a complete understanding is still ongoing. Herein, we summarize the current knowledge of the pharmacology of LID in PD. Specifically, we review evidence gathered from postmortem and pharmacological studies, both preclinical and clinical, and discuss the involvement of dopaminergic and nondopaminergic systems, including glutamatergic, opioid, serotonergic, γ-aminobutyric acid (GABA)-ergic, adenosine, cannabinoid, adrenergic, histaminergic, and cholinergic systems. Moreover, we discuss changes occurring in transcription factors, intracellular signaling, and gene expression in the dyskinetic phenotype. Inasmuch as a multitude of neurotransmitters and receptors play a role in the etiology of dyskinesia, we propose that to optimally alleviate this motor complication, it may be necessary to develop combined treatment approaches that will target simultaneously more than one neurotransmitter system. This could be achieved via three ways as follows: 1) by developing compounds that will interact simultaneously to a multitude of receptors with the required agonist/antagonist effect at each target, 2) by targeting intracellular signaling cascades where the signals mediated by multiple receptors converge, and/or 3) to regulate gene expression in a manner that has effects on signaling by multiple pathways.

Objective: The 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-lesioned non-human primate is widely used to model Parkinson's disease (PD) and to evaluate the efficacy of new therapies. However, some doubts have been raised about the translatability of findings in the MPTP-lesioned monkey, because the doses of L-3,4-dihydroxyphenylalanine (L-DOPA) required to alleviate parkinsonism and elicit dyskinesia are high, on a mg/kg basis, when compared to clinical practice. Thus, in the MPTP-lesioned macaque, doses ranging from 20 to 40 mg/kg might be used, while in the clinic single L-DOPA administrations ranging from 100 to 200 mg are more typical. However, bioavailability of drugs varies between species and it is unknown how plasma L-DOPA levels providing therapeutic benefit in the non-human primate compare to those having similar actions in PD patients., Methods: We administered acute challenges of L-DOPA 30 mg/kg orally to MPTP-lesioned macaques with established dyskinesia, and determined plasma, brain and cerebrospinal fluid (CSF) levels of L-DOPA using high-performance liquid chromatography-mass spectrometry/mass spectrometry., Results: The maximal plasma concentration of L-DOPA (C(max)) was 18.2 ± 3.8 nmol/ml and was achieved 1.6 ± 0.3 h after administration (t(max)). Half-life was 58.8 ± 22.7 min. L-DOPA levels in the caudate nucleus at peak behavioural effect were 3.3 ± 0.7 μg/g tissue protein while they were 1.5 ± 0.1 nmol/ml in the CSF., Conclusions: Although therapeutically-active doses of L-DOPA administered to the MPTP-lesioned macaque are higher on a mg/kg basis than those administered in clinical settings, they lead to L-DOPA C(max) similar to those achieved with 200 mg L-DOPA in clinic. L-DOPA t(max) and half-life are also similar to those reported in human., (Copyright © 2012. Published by Elsevier Ltd.)

L-DOPA-induced dyskinesia remains an unmet challenge in the treatment of Parkinson's disease (PD). Here, we investigate the potential antidyskinetic efficacy of 3-([4-(4-chlorophenyl)piperazin-1-yl]methyl)-1H-pyrrolo[2,3-b]pyridine (L-745,870), a potent and selective dopamine D(4) receptor antagonist with a good toxicology profile and an excellent safety and tolerability record in phase I/II clinical studies, for non-PD indications. Six macaques were rendered parkinsonian by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine administration. After induction of stable and marked dyskinesia, animals were administered acute challenges of L-745,870 in combination with L-DOPA. To guarantee D(4) selectivity at the doses used in the study, we determined the plasma, cerebrospinal fluid, and brain levels of L-745,870. Coadministration of L-745,870 (1 mg/kg) and L-DOPA significantly reduced the severity of dyskinesia, by up to 59%, in comparison with L-DOPA alone (P < 0.01). L-745,870 had no effect on the duration of antiparkinsonian benefit (ON-time) (P > 0.05). However, L-745,870 (1 mg/kg) significantly increased the duration of ON-time without disabling dyskinesia (+204%; P < 0.001) and decreased duration of ON-time with disabling dyskinesia compared with L-DOPA alone (-56%; P < 0.01). Brain levels of L-745,870 (∼600 ng/g) were within the range at which L-745,870 provides selective D(4) receptor antagonism. Plasma levels were comparable with those demonstrated to be well tolerated in human studies. These data suggest that selective D(4) receptor antagonists represent a potential therapeutic approach for L-DOPA-induced dyskinesia. It is noteworthy that L-745,870 has already undergone significant clinical development, has an excellent profile for a therapeutic candidate, and could be advanced rapidly to phase IIa clinical studies for dyskinesia in PD.

Treatment of Parkinson's disease with dopaminergic agents, such as l-DOPA, is frequently compromised by disabling side effects, particularly dyskinesia and a shortening in duration of antiparkinsonian action. Studies in animal models and anecdotal evidence from a patient with Parkinson's disease show that the illicit drug ecstasy (MDMA) can alleviate these side effects, though with many drawbacks (e.g., psychoactivity). MDMA itself thus has little therapeutic potential. On the basis of known structure-psychoactivity relationships, we designed a series of α-substituted MDMA analogues, one of which, bearing an α-cyclopropyl substituent (UWA-101), enhanced the quality of l-DOPA actions in animal models. Indeed, UWA-101 was more effective than MDMA. Unlike MDMA, UWA-101 did not reduce viability of serotonergic cells, exhibit psychoactive properties, or reduce food intake, and did not substitute for MDMA in drug discrimination assays. UWA-101 displayed a unique receptor/transporter binding profile relative to MDMA, with a >5-fold decrease in affinity for NET and 5-HT(2A) receptors and a 10-fold increase in affinity for DAT. Furthermore, in a functional reuptake assay, UWA-101 inhibited both 5-HT and dopamine reuptake, while having no effect on the reuptake of noradrenaline. UWA-101 is the first selective DAT/SERT inhibitor described with comparable affinities for these two sites. These data identify a new class of therapeutic in Parkinson's disease and highlight the potential benefits of studying illicit drugs that in themselves would never be considered safe for long-term therapy.

L-DOPA remains the most effective treatment for Parkinson's disease (PD). However, long-term administration of L-DOPA is compromised by complications, particularly dyskinesia. Serotonergic type 1A (5-HT(1A)) receptor agonists and serotonergic type 2A (5-HT(2A)) receptor antagonists were, until recently, considered to be promising therapies against dyskinesia. However, there have been some recent high-profile failures in clinical trials, notably with sarizotan, and it seems that these classes of drugs may also impair l-DOPA antiparkinsonian efficacy. A simple explanation for the loss of antiparkinsonian benefit might be lack of good selectivity of these compounds for their respective targets, particularly with respect to off-target actions on dopaminergic receptors or poor dose selection in clinical studies. However, such explanations do not hold broadly when considering the actions of all compounds studied to date, whether in animal models or clinical trials. Here, we review 5-HT(1A) and 5-HT(2A) receptor function in PD and provide an anatomically based rationale as to why in some instances 5-HT(1A)- and 5-HT(2A)-modulating drugs might worsen parkinsonism, in addition to reducing dyskinesia. We propose that, in addition to selectivity for specific receptor subtypes, to target 5-HT(1A) and 5-HT(2A) receptors to alleviate dyskinesia, without worsening parkinsonism, it will be necessary to develop compounds that display anatomical selectivity, targeting corticostriatal transmission, while avoiding 5-HT receptors on ascending serotonergic and dopaminergic inputs from the raphe and substantia nigra, respectively.

l-3,4-dihydroxyphenylalanine (l-DOPA) is the most effective treatment for Parkinson's disease, but long-term l-DOPA administration is marred by the emergence of motor complications, namely, dyskinesia and a shortening of antiparkinsonian benefit (wearing-OFF). 3,4-methylenedioxymethamphetamine (MDMA) is unique in that it exerts antidyskinetic effects and may enhance antiparkinsonian actions of l-DOPA. MDMA is composed of two enantiomers with different pharmacological profiles; here, we describe a novel enantiospecific synthesis of the two enantiomers and expand on the previous characterization of their pharmacology. R-MDMA (rectus-MDMA) is relatively selective for 5-HT(2A) receptors, whereas S-MDMA (sinister-MDMA) inhibits both serotonin (SERT) and dopamine transporters (DAT; SERT/DAT ratio of 10 to 1). R- or S-MDMA (1, 3, and 10 mg/kg, s.c.) was administered in combination with l-DOPA (15 mg/kg, s.c.) to six female common marmosets (Callithrix jacchus) rendered parkinsonian by MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) administration. Motor disability, including parkinsonism and dyskinesia, and duration of antiparkinsonian benefit (ON-time) were evaluated. After the administration of R-MDMA (3 and 10 mg/kg), the severity of peak-dose dyskinesia was decreased (by 33 and 46%, respectively; p < 0.05); although total ON-time was unchanged (approximately 220 min), the duration of ON-time with disabling dyskinesia was decreased by 90 min when compared to l-DOPA alone (69% reduction; p < 0.05). S-MDMA (1 mg/kg) increased the total ON-time by 88 min compared to l-DOPA alone (34% increase; p < 0.05), though dyskinesia were exacerbated. These data suggest that racemic MDMA exerts simultaneous effects, reducing dyskinesia and extending ON-time, by 5-HT(2A) antagonism and SERT-selective mixed monoamine uptake inhibition, which arise from its R and S enantiomers, respectively.

Objectives: Neuropsychiatric symptoms are increasingly recognised as a significant problem in patients with Parkinson's disease (PD). These symptoms may be due to 'sensitisation' following repeated levodopa treatment or a direct effect of dopamine on the disease state. The levodopa-treated MPTP-lesioned marmoset was used as a model of neuropsychiatric symptoms in PD patients. Here we compare the time course of levodopa-induced motor fluctuations and neuropsychiatric-like behaviors to determine the relationship between duration of treatment and onset of symptoms., Methods: Marmosets were administered 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (2.0 mg/kg s.c.) for five days, resulting in stable parkinsonism. Levodopa (15 mg/kg and benserazide, 3.75 mg/kg) p.o. b.i.d, was administered for 30 days. Animals were evaluated for parkinsonian disability, dyskinesia and on-time (motor fluctuations) and neuropsychiatric-like behaviors on Day 0 (prior to levodopa) and on Days 1, 7, 13, 27 and 30 of treatment using post hoc DVD analysis by a trained rater, blind to the treatment day., Results: The neuropsychiatric-like behavior rating scale demonstrated high interrater reliability between three trained raters of differing professional backgrounds. As anticipated, animals exhibited a progressive increase in levodopa-induced motor fluctuations, dyskinesia and wearing-off, that correlated with the duration of levodopa therapy. In contrast, levodopa-induced neuropsychiatric-like behaviors were present on Day 1 of levodopa treatment and their severity did not correlate with duration of treatment., Conclusions: The data suggest that neuropsychiatric disorders in PD are more likely an interaction between levodopa and the disease state than a consequence of sensitisation to repeated dopaminergic therapy.