Effects of (−)-OSU6162 and ACR16 on motor activity in rats, indicating a unique mechanism of dopaminergic stabilization

Genetic liability for anxiety and treatment response to the monoamine stabilizer OSU6162 in alcohol dependence: a retrospective secondary analysis

BACKGROUND

OSU6162, a monoamine stabilizer, has demonstrated efficacy in reducing alcohol and anxiety-related behaviors in preclinical settings. In a previous randomized, double-blind, placebo-controlled trial involving patients with alcohol dependence (AD), OSU6162 significantly reduced craving for alcohol but did not alter drinking behaviors. This retrospective secondary analysis explores whether genetic predispositions related to AD and associated traits might influence the response to OSU6162 treatment in original trial participants.

METHODS

Polygenic risk scores (PRSs) were calculated for 48 AD patients using PRSice-2 and genome-wide association study (GWAS) data for (i) alcohol use disorder and alcohol consumption, (ii) problematic alcohol use, (iii) drinks per week, (iv) major depression, and (v) anxiety (case-control comparisons and quantitative anxiety factor scores). Linear regression analyses, adjusted for population stratification, assessed interaction effects between PRSs and treatment type (OSU6162 or placebo) on various clinical outcomes.

RESULTS

Significant interactions were found between treatment type and anxiety factor score PRS at the genome-wide significance threshold. In the OSU6162-treated group, a higher anxiety PRS was associated with reductions in the number of drinks consumed (FDR = 0.0017), percentage of heavy drinking days (FDR = 0.0060), and percentage of drinking days (FDR = 0.0017), with a trend toward reduced blood phosphatidylethanol (PEth) levels (FDR = 0.068). These associations were absent in the placebo group.

CONCLUSIONS

These preliminary findings suggest that anxiety PRS may help predict response to OSU6162 treatment in AD. Further research with larger cohorts and more comprehensive genetic data is needed to confirm these results and advance personalized medicine approaches for alcohol use disorder.

Relapse after electric barrier-induced voluntary abstinence: A review

Relapse to drug use during abstinence is a defining feature of addiction. To date, however, results from studies using rat relapse/reinstatement models have yet to result in FDA-approved medications for relapse prevention. To address this translational gap, we and others have developed rat models of relapse after voluntary abstinence from drug self-administration. One of these models is the electric barrier conflict model. Here, we introduce the model, and then review studies on behavioral and neuropharmacological mechanisms of cue-induced relapse and incubation of drug seeking (time-dependent increase in drug seeking during abstinence) after electric barrier-induced abstinence. We also briefly discuss future directions and potential clinical implications. One major conclusion of our review is that the brain mechanisms controlling drug relapse after electrical barrier-induced voluntary abstinence are likely distinct from those controlling relapse after homecage forced abstinence.

The Efficacy and Safety of Pridopidine on Treatment of Patients with Huntington's Disease: A Systematic Review and Meta-Analysis

BACKGROUND

Pridopidine is a novel drug that helps stabilize psychomotor function in patients with Huntington's disease (HD) by activating the cortical glutamate pathway. It promises to achieve the unmet needs of current therapies of HD without worsening other symptoms.

OBJECTIVE

To review the literature discussing the efficacy of pridopidine in alleviating motor symptoms and its safety in patients with HD.

METHODS

We searched Scopus, Web of Science, the Cochrane Library, Wiley, and PubMed for randomized controlled trials (RCTs) of pridopidine on HD. Data from eligible studies were extracted and pooled as mean differences for efficacy and risk ratios (RRs) for safety using RevMan software version 5.3.

RESULTS

A total of 4 relevant RCTs with 1130 patients were selected (816 in the pridopidine group and 314 in the placebo group). The pooled effect size favored pridopidine over placebo insignificantly in the Unified Huntington's Disease Rating Scale Total Motor Score (mean difference [MD], -0.93; 95% confidence interval [CI], -2.01 to 0.14; P = 0.09), whereas the effect size of 3 studies significantly favored pridopidine over placebo in the Unified Huntington's Disease Rating Scale Modified Motor Score (MD, -0.81; 95% CI, -1.48 to -0.13; P = 0.02). Pridopidine generally was well tolerated. None of the adverse effects were considerably higher in the case of pridopidine compared with placebo in overall adverse events (RR, 1.03; 95% CI, 0.94-1.13; P = 0.49) and serious adverse events (RR, 1.62; 95% CI, 0.88-2.99; P = 0.12).

CONCLUSION

The effects of pridopidine on motor functions (especially voluntary movements) in patients with HD are encouraging and provide a good safety profile that motivates further clinical trials on patients to confirm its effectiveness and safety.

Animal Models of Drug Relapse and Craving after Voluntary Abstinence: A Review

Relapse to drug use during abstinence is a defining feature of addiction. During the last several decades, this clinical scenario has been studied at the preclinical level using classic relapse/reinstatement models in which drug seeking is assessed after experimenter-imposed home-cage forced abstinence or extinction of the drug-reinforced responding in the self-administration chambers. To date, however, results from studies using rat relapse/reinstatement models have yet to result in Food and Drug Administration-approved medications for relapse prevention. The reasons for this state of affairs are complex and multifaceted, but one potential reason is that, in humans, abstinence is often self-imposed or voluntary and occurs either because the negative consequences of drug use outweigh the drug's rewarding effects or because of the availability of nondrug alternative rewards that are chosen over the drug. Based on these considerations, we and others have recently developed rat models of relapse after voluntary abstinence, achieved either by introducing adverse consequences to drug taking (punishment) or seeking (electric barrier) or by providing mutually exclusive choices between the self-administered drug and nondrug rewards (palatable food or social interaction). In this review, we provide an overview of these translationally relevant relapse models and discuss recent neuropharmacological findings from studies using these models. We also discuss sex as a biological variable, future directions, and clinical implications of results from relapse studies using voluntary abstinence models. Our main conclusion is that the neuropharmacological mechanisms controlling relapse to drug seeking after voluntary abstinence are often different from the mechanisms controlling relapse after home-cage forced abstinence or reinstatement after extinction. SIGNIFICANCE STATEMENT: This review describes recently developed rat models of relapse after voluntary abstinence, achieved either by introducing adverse consequences to drug taking or seeking or by providing mutually exclusive choices between the self-administered drug and nondrug rewards. This review discusses recent neuropharmacological findings from studies using these models and discusses future directions and clinical implications.

The monoamine stabilizer OSU6162 has anxiolytic-like properties and reduces voluntary alcohol intake in a genetic rat model of depression

Alcohol use disorders (AUD) often co-occur with anxiety and depressive disorders, and anxiety often drives relapse during alcohol abstinence. Optimal AUD pharmacotherapies may thus need to target both excessive alcohol intake and elevated anxiety. (−)-OSU6162 (OSU) is a monoamine stabilizer that attenuates alcohol-mediated behaviors in both preclinical and clinical settings. However, OSU’s effect on anxiety-like behavior following long-term drinking remains unknown. To this end, we utilized a genetic rat model that exhibits increased anxiety- and depression-like behaviors (Flinders Sensitive Line; FSL) and their controls (Flinders Resistant Line; FRL). Using the novelty suppressed feeding (NSF) test, we evaluated anxiety-like behaviors (1) at baseline, (2) following long-term voluntary drinking and after 24 h of alcohol deprivation, and (3) following OSU administration in the same animals. At baseline, FSL animals displayed significantly elevated anxiety-like characteristics compared to FRL. Compared to alcohol-naïve animals, long-term drinking significantly reduced anxiety-like behaviors in FSL, without any significant effects in FRL animals. Compared to vehicle, OSU administration significantly reduced anxiety-like behaviors in alcohol-naïve FSL and long-term drinking FRL animals. While there was no significant difference in alcohol intake between FSL and FRL, OSU attenuated alcohol intake in both strains. Conclusively, in addition to the compound’s previously identified ability to suppress alcohol-mediated behaviors, OSU may also possess anxiolytic properties, warranting further clinical evaluation in both AUD and anxiety disorder settings.

Pridopidine for the Improvement of Motor Function in Patients With Huntington's Disease: A Systematic Review and Meta-Analysis of Randomized Controlled Trials

Background: Huntington's disease (HD) is a progressive neurodegenerative disorder. Generally, it is characterized by deficits in cognition, behavior, and movement. Recent studies have shown that pridopidine is a potential and effective drug candidate for the treatment of HD. In the present study, we performed a meta-analysis to evaluate the efficacy and safety of pridopidine in HD.

Methods: The MEDLINE, EMBASE, CENTRAL, and Clinicaltrials.gov databases were searched for randomized controlled trials (RCTs) which had that evaluated pridopidine therapy in HD patients.

Results: We pooled data from 1,119 patients across four RCTs. Patients in the pridopidine group had a significantly lower Unified Huntington's Disease Rating Scale (UHDRS)-modified Motor Score (mMS) (MD −0.79, 95% CI = −1.46 to −0.11, p = 0.02) than those in the placebo group. Additionally, no differences were observed in the UHDRS-Total Motor Score (TMS) (MD −0.91. 95% CI = −2.03 to 0.21, p = 0.11) or adverse events (RR 1.06, 95% CI = 0.96 to 1.16, p = 0.24) in the pridopidine and placebo groups. In the subgroup analysis, the short-term (≤12 weeks) and long-term (>12 weeks) subgroups exhibited similar efficacy and safety with no statistical significance in TMS, mMS, or adverse events. However, TMS (MD −1.50, 95% CI = −2.87 to −0.12, p = 0.03) and mMS (MD −1.03, 95% CI = −1.87 to −0.19, p = 0.02) were observed to be improved significantly when the dosage of pridopidine ≥90 mg/day. Additionally, pridopidine (≥90 mg/day) increased total adverse events (RR 1.11, 95% CI = 1.00 to 1.22, p = 0.04) compared with placebo. On this basis, we analyzed the incidence of various adverse events when the dosage was ≥90 mg/day. Nonetheless, these results were within the acceptable threshold, although patients developed symptoms, such as nasopharyngitis and insomnia.

Conclusion: Pridopidine improved mMS and had no statistical significance in association with TMS or adverse events. Pridopidine (≥90 mg/day) improved TMS and mMS but increased adverse events, such as nasopharyngitis and insomnia. More RCTs were expected to assess pridopidine in HD.

Open-label study with the monoamine stabilizer (-)-OSU6162 in myalgic encephalomyelitis/chronic fatigue syndrome

OBJECTIVES

The purpose of the present study was to investigate the safety and tolerability of the monoaminergic stabilizer (-)-OSU6162 in patients with myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS). In addition, a potential therapeutic effect of (-)-OSU6162 in ME/CFS was evaluated by means of observer-rated scales and self-assessment rating scales.

MATERIALS AND METHODS

In the current study using an open-label single-arm design ME/CFS patient received treatment with (-)-OSU6162 during 12 weeks. The patients received the following doses of (-)-OSU6162: 15 mg b.i.d. during the first 4-week period, up to 30 mg b.i.d. during the second 4-week period and up to 45 mg b.i.d. during the third 4-week period, with follow-up visits after 16 and 20 weeks.

RESULTS

Out of 33 included patients, 28 completed the 12 weeks treatment period. (-)-OSU6162 was well tolerated; only one patient discontinued due to an adverse event. Vital signs and physical examinations showed no abnormal changes. Blood analyses showed an increase in serum prolactin. Therapeutically, improvements were seen on the Clinical Global Impression of Change scale, the FibroFatigue scale, the Mental Fatigue Scale, the Fatigue Severity Scale, Beck Depression Inventory, and the Short Form 36 Health Survey Questionnaire.

CONCLUSIONS

(-)-OSU6162 is well tolerated in ME/CFS patients and shows promise as a novel treatment to mitigate fatigue and improve mood and health-related quality of life in ME/CFS. Obviously, the present results need to be confirmed in future placebo-controlled double-blind trials.

Effects of the monoamine stabilizer, (-)-OSU6162, on cocaine-induced locomotion and conditioned place preference in mice

Cocaine addiction is a severe mental disorder for which few treatment options are available. The underlying mechanisms include facilitation of monoamine-neurotransmission, particularly dopamine. Here, we tested the hypothesis that the monoamine stabilizers, (-)-OSU6162 ((3S)-3-(3-methylsulfonylphenyl)-1-propylpiperidine) and aripiprazole (7-[4-[4-(2,3-dichlorophenyl)piperazin-1-yl]butoxy]-3,4-dihydro-1H-quinolin-2-one), prevent cocaine-induced behaviors. Male Swiss mice received injections of (-)-OSU6162 or aripiprazole and cocaine and were tested for cocaine-induced hyperlocomotion, locomotor sensitization, and acquisition and expression of conditioned place preference (CPP). The increase in the distance traveled induced by cocaine (20 mg/kg) was prevented by pretreatment with aripiprazole (1 and 10 mg/kg), whereas (-)-OSU6162 (3 mg/kg) exerted a minor effect. Aripiprazole, however, also impaired spontaneous locomotion. Neither (-)-OSU6162 nor aripiprazole interfered with the locomotor sensitization and expression of CPP induced by cocaine (15 mg/kg). (-)-OSU6162 (3 mg/kg), but not aripiprazole, prevented the acquisition of CPP induced by cocaine (15 mg/kg). (-)-OSU6162 exerts a minor effect in reducing cocaine-induced stimulatory activity and context-related memories, which are responsible for triggering drug seeking. Further studies are required to establish whether (-)-OSU6162 could be a candidate drug for the treatment of cocaine addiction.

Effect of the monoaminergic stabiliser (-)-OSU6162 on mental fatigue following stroke or traumatic brain injury

OBJECTIVE

The purpose of the present study was to evaluate the efficacy and safety of (-)-OSU6162 in doses up to 30 mg b.i.d. in patients suffering from mental fatigue following stroke or traumatic brain injury (TBI).

METHODS

This 4 + 4 weeks double-blind randomised cross-over study included 30 patients afflicted with mental fatigue following a stroke or head trauma occurring at least 12 months earlier. Efficacy was assessed using the Mental Fatigue Scale (MFS), the Self-rating Scale for Affective Syndromes [Comprehensive Psychopathological Rating Scale (CPRS)], the Frenchay Activity Index (FAI), and a battery of neuropsychological tests. Safety was evaluated by recording spontaneously reported adverse events (AEs).

RESULTS

There were significant differences on the patients' total FAI scores (p = 0.0097), the subscale FAI outdoor scores (p = 0.0243), and on the trail making test (TMT-B) (p = 0.0325) in favour of (-)-OSU6162 treatment. Principal component analysis showed a clear overall positive treatment effect in 10 of 28 patients; those who responded best to treatment had their greatest improvements on the MFS. Reported AEs were mild or moderate in severity and did not differ between the (-)-OSU6162 and the placebo period.

CONCLUSION

The most obvious beneficial effects of (-)-OSU6162 were on the patients' activity level, illustrated by the improvement on the FAI scale. Moreover, a subgroup of patients showed substantial improvements on the MFS. Based on these observed therapeutic effects, in conjunction with the good tolerability of (-)-OSU6162, this compound may offer promise for treating at least part of the symptomatology in patients suffering from stroke- or TBI-induced mental fatigue.

Sigma-1 and dopamine D2/D3 receptor occupancy of pridopidine in healthy volunteers and patients with Huntington disease: a [18F] fluspidine and [18F] fallypride PET study

PURPOSE

Pridopidine is an investigational drug for Huntington disease (HD). Pridopidine was originally thought to act as a dopamine stabilizer. However, pridopidine shows highest affinity to the sigma-1 receptor (S1R) and enhances neuroprotection via the S1R in preclinical studies. Using [¹⁸F] fluspidine and [¹⁸F] fallypride PET, the purpose of this study was to assess in vivo target engagement/receptor occupancy of pridopidine to the S1R and dopamine D2/D3 receptor (D2/D3R) at clinical relevant doses in healthy volunteers (HVs) and as proof-of-concept in a small number of patients with HD.

METHODS

Using [¹⁸F] fluspidine PET (300 MBq, 0-90 min), 11 male HVs (pridopidine 0.5 to 90 mg; six dose groups) and three male patients with HD (pridopidine 90 mg) were investigated twice, without and 2 h after single dose of pridopidine. Using [¹⁸F] fallypride PET (200 MBq, 0-210 min), four male HVs were studied without and 2 h following pridopidine administration (90 mg). Receptor occupancy was analyzed by the Lassen plot.

RESULTS

S1R occupancy as function of pridopidine dose (or plasma concentration) in HVs could be described by a three-parameter Hill equation with a Hill coefficient larger than one. A high degree of S1R occupancy (87% to 91%) was found throughout the brain at pridopidine doses ranging from 22.5 to 90 mg. S1R occupancy was 43% at 1 mg pridopidine. In contrast, at 90 mg pridopidine, the D2/D3R occupancy was only minimal (~ 3%).

CONCLUSIONS

Our PET findings indicate that at clinically relevant single dose of 90 mg, pridopidine acts as a selective S1R ligand showing near to complete S1R occupancy with negligible occupancy of the D2/D3R. The dose S1R occupancy relationship suggests cooperative binding of pridopidine to the S1R. Our findings provide significant clarification about pridopidine's mechanism of action and support further use of the 45-mg twice-daily dose to achieve full and selective targeting of the S1R in future clinical trials of neurodegenerative disorders. Clinical Trials.gov Identifier: NCT03019289 January 12, 2017; EUDRA-CT-Nr. 2016-001757-41.

Pharmaco-fMRI in Patients With Traumatic Brain Injury: A Randomized Controlled Trial With the Monoaminergic Stabilizer (-)-OSU6162

OBJECTIVE

To examine the effects of monoaminergic stabilizer (-)-OSU6162 on brain activity, as measured by blood-oxygen-level-dependent (BOLD) functional magnetic resonance imaging (fMRI), in patients in the chronic phase of traumatic brain injury suffering from fatigue.

SETTING

Neurorehabilitation clinic.

PARTICIPANTS

Patients with traumatic brain injury received either placebo (n = 24) or active treatment (n = 28). Healthy controls (n = 27) went through fMRI examination at one point and were used in sensitivity analysis on normalization of BOLD response.

DESIGN

Randomized, double-blinded, placebo-controlled design.

MAIN MEASURES

Effects on BOLD signal changes from before to after treatment during performance of a fatiguing attention task.

RESULTS

The fMRI results revealed treatment effects within the right occipitotemporal cortex and the right orbitofrontal cortex. In these regions, the BOLD response was normalized relative to healthy controls at the postintervention fMRI session. No effects were seen in regions in which we previously observed activity differences between patients and healthy controls while performing this fMRI task, such as the striatum.

CONCLUSION

(-)-OSU6162 treatment had influences on functional brain activity, although the normalized regional BOLD response was observed in regions that were not a priori hypothesized to be sensitive to this particular treatment, and was not accompanied by any effects on in-scanner test performance or on fatigue.

Effect of the dopamine stabilizer (-)-OSU6162 on potentiated incubation of opioid craving after electric barrier-induced voluntary abstinence

In the classical incubation of drug craving rat model, drug seeking is assessed after homecage forced abstinence. However, human abstinence is often voluntary because negative consequences of drug seeking outweigh the desire for the drug. Here, we developed a rat model of incubation of opioid craving after electric barrier-induced voluntary abstinence and determined whether the dopamine stabilizer (-)-OSU6162 would decrease this new form of incubation. We trained male and female rats to self-administer oxycodone (0.1 mg/kg/infusion, 6 h/day) for 14 days. We then exposed them to either homecage forced abstinence or voluntary abstinence induced by an electric barrier of increasing intensity near the drug-paired lever. On abstinence days 1, 15, or 30, we tested the rats for oxycodone seeking without shock and drug. We also examined the effect of (-)-OSU6162 (7.5 and 15 mg/kg) on oxycodone seeking on abstinence day 1 or after 15 days of either voluntary or forced abstinence. Independent of sex, the time-dependent increase in oxycodone seeking after cessation of opioid self-administration (incubation of opioid craving) was stronger after voluntary abstinence than after forced abstinence. In males, (-)-OSU6162 decreased incubated (day 15) but not non-incubated (day 1) oxycodone seeking after either voluntary or forced abstinence. In females, (-)-OSU6162 modestly decreased incubated oxycodone seeking after voluntary but not forced abstinence. Results suggest that voluntary abstinence induced by negative consequences of drug seeking can paradoxically potentiate opioid craving and relapse. We propose the dopamine stabilizer (-)-OSU6162 may serve as an adjunct pharmacological treatment to prevent relapse in male opioid users.

Effects of the monoamine stabilizer (-)OSU6162 on cognitive function in alcohol dependence

INTRODUCTION

Alcohol dependence (AD) is associated with a dysregulated mesolimbocortical dopamine system-a pathway which is also implicated in both reward and cognition. The monoamine stabilizer (-)-OSU6162 (OSU) is a novel pharmacological compound with the ability to reduce ethanol intake and ethanol seeking in long-term drinking rats as well as reducing alcohol craving in AD patients. Dopaminergic drugs can both impair and improve cognitive functions, and the aim of the current study was to investigate the effect of OSU treatment on cognitive functioning in AD patients.

METHOD

In a randomized double-blind placebo-controlled study, 56 individuals with AD received 14 days of OSU or placebo treatment. Neuropsychological tasks from the Cambridge Automated Neuropsychological Test Battery (CANTAB®) and other tasks were used to evaluate treatment effect on executive function/impulsivity, working memory, attention, emotional recognition, and divergent thinking.

RESULTS

Treatment with OSU did not impair neuropsychological function in any of the cognitive domains investigated (all p > 0.1). In fact, OSU treatment did, compared to placebo, improve future planning ability (F_(1,46) = 6.9; p = 0.012; Cohen's d = 0.54), verbal divergent thinking (F_(1,44) = 10.1; p = 0.003; d = 0.96), and response time for emotional recognition (F_(1,47) = 6.7; p = 0.013; d = 0.44).

CONCLUSION

OSU treatment did not cause short-term cognitive side effects, further supporting the potential of OSU as a clinically feasible pharmacological treatment in AD patients. OSU treatment might improve future planning, verbal divergent thinking, and emotional recognition latency, which in turn may have a beneficial impact on alcohol use outcomes. Future studies are needed to confirm these preliminary findings.

Neuronal Sigma-1 Receptors: Signaling Functions and Protective Roles in Neurodegenerative Diseases

Sigma-1 receptor (S1R) is a multi-functional, ligand-operated protein situated in endoplasmic reticulum (ER) membranes and changes in its function and/or expression have been associated with various neurological disorders including amyotrophic lateral sclerosis/frontotemporal dementia, Alzheimer's (AD) and Huntington's diseases (HD). S1R agonists are broadly neuroprotective and this is achieved through a diversity of S1R-mediated signaling functions that are generally pro-survival and anti-apoptotic; yet, relatively little is known regarding the exact mechanisms of receptor functioning at the molecular level. This review summarizes therapeutically relevant mechanisms by which S1R modulates neurophysiology and implements neuroprotective functions in neurodegenerative diseases. These mechanisms are diverse due to the fact that S1R can bind to and modulate a large range of client proteins, including many ion channels in both ER and plasma membranes. We summarize the effect of S1R on its interaction partners and consider some of the cell type- and disease-specific aspects of these actions. Besides direct protein interactions in the endoplasmic reticulum, S1R is likely to function at the cellular/interorganellar level by altering the activity of several plasmalemmal ion channels through control of trafficking, which may help to reduce excitotoxicity. Moreover, S1R is situated in lipid rafts where it binds cholesterol and regulates lipid and protein trafficking and calcium flux at the mitochondrial-associated membrane (MAM) domain. This may have important implications for MAM stability and function in neurodegenerative diseases as well as cellular bioenergetics. We also summarize the structural and biochemical features of S1R proposed to underlie its activity. In conclusion, S1R is incredibly versatile in its ability to foster neuronal homeostasis in the context of several neurodegenerative disorders.

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

BACKGROUND

Pridopidine, in development for Huntington's disease, may modulate aberrant l-dopa-induced effects including l-dopa-induced dyskinesia (LID).

OBJECTIVE

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.

METHODS

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.

RESULTS

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.

CONCLUSIONS

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.

Pridopidine Induces Functional Neurorestoration Via the Sigma-1 Receptor in a Mouse Model of Parkinson's Disease

Pridopidine is a small molecule in clinical development for the treatment of Huntington's disease. It was recently found to have high binding affinity to the sigma-1 receptor, a chaperone protein involved in cellular defense mechanisms and neuroplasticity. Here, we have evaluated the neuroprotective and neurorestorative effects of pridopidine in a unilateral 6-hydroxydopamine (6-OHDA) lesion model of parkinsonism in mice. By 5 weeks of daily administration, a low dose of pridopidine (0.3 mg/kg) had significantly improved deficits in forelimb use (cylinder test, stepping test) and abolished the ipsilateral rotational bias typical of hemiparkinsonian animals. A higher dose of pridopidine (1 mg/kg) significantly improved only the rotational bias, with a trend towards improvement in forelimb use. The behavioral recovery induced by pridopidine 0.3 mg/kg was accompanied by a significant protection of nigral dopamine cell bodies, an increased dopaminergic fiber density in the striatum, and striatal upregulation of GDNF, BDNF, and phosphorylated ERK1/2. The beneficial effects of pridopidine 0.3 mg/kg were absent in 6-OHDA-lesioned mice lacking the sigma-1 receptor. Pharmacokinetic data confirmed that the effective dose of pridopidine reached brain concentrations sufficient to bind S1R. Our results are the first to show that pridopidine promotes functional neurorestoration in the damaged nigrostriatal system acting via the sigma-1 receptor.

Pridopidine stabilizes mushroom spines in mouse models of Alzheimer's disease by acting on the sigma-1 receptor

There is evidence that cognitive decline in Alzheimer's disease (AD) results from deficiencies in synaptic communication (e.g., loss of mushroom-shaped 'memory spines') and neurodegenerative processes. This might be treated with sigma-1 receptor (S1R) agonists, which are broadly neuroprotective and modulate synaptic plasticity. For example, we previously found that the mixed muscarinic/S1R agonist AF710B prevents mushroom spine loss in hippocampal cultures from APP knock-in (APP-KI) and presenilin-1-M146 V knock-in (PS1-KI) mice. We also found that the "dopaminergic stabilizer" pridopidine (structurally similar to the S1R agonist R(+)-3-PPP), is a high-affinity S1R agonist and is synaptoprotective in a mouse model of Huntington disease. Here we tested whether pridopidine and R(+)-3-PPP are synaptoprotective in models of AD and whether this requires S1R. We also examined the effects of pridopidine on long-term potentiation (LTP), endoplasmic reticulum calcium and neuronal store-operated calcium entry (nSOC) in spines, all of which are dysregulated in AD, contributing to synaptic pathology. We report here that pridopidine and 3-PPP protect mushroom spines from Aβ42 oligomer toxicity in primary WT hippocampal cultures from mice. Pridopidine also reversed LTP defects in hippocampal slices resulting from application of Aβ42 oligomers. Pridopidine and 3-PPP rescued mushroom spines in hippocampal cultures from APP-KI and PS1-KI mice. S1R knockdown from lenti-viral shRNA expression destabilized WT mushroom spines and prevented the synaptoprotective effects of pridopidine in PS1-KI cultures. Knockout of PS1/2 destabilized mushroom spines and pridopidine was unable to prevent this. Pridopidine lowered endoplasmic reticulum calcium levels in WT, PS1-KO, PS1-KI and PS2 KO neurons, but not in PS1/2 KO neurons. S1R was required for pridopidine to enhance spine nSOC in PS1-KI neurons. Pridopidine was unable to rescue PS1-KI mushroom spines during pharmacological or genetic inhibition of nSOC. Oral pridopidine treatment rescued mushroom spines in vivo in aged PS1-KI-GFP mice. Pridopidine stabilizes mushroom spines in mouse models of AD and this requires S1R, endoplasmic reticulum calcium leakage through PS1/2 and nSOC. Thus, pridopidine may be useful to explore for the treatment of AD.

Safety and efficacy of pridopidine in patients with Huntington's disease (PRIDE-HD): a phase 2, randomised, placebo-controlled, multicentre, dose-ranging study

BACKGROUND

Previous trials have shown that pridopidine might reduce motor impairment in patients with Huntington's disease. The aim of this study was to ascertain whether higher doses of pridopidine than previously tested reduce motor symptoms in a dose-dependent manner while maintaining acceptable safety and tolerability.

METHODS

PRIDE-HD was a randomised, placebo-controlled, phase 2, dose-ranging study in adults (aged ≥21 years) with Huntington's disease at outpatient clinics in 53 sites across 12 countries (Australia, Austria, Canada, Denmark, France, Germany, Italy, Poland, Russia, the Netherlands, the UK, and the USA). Eligible patients had clinical onset after age 18 years, 36 or more cytosine-adenine-guanine repeats in the huntingtin gene, motor symptoms (Unified Huntington's Disease Rating Scale total motor score [UHDRS-TMS] ≥25 points), and reduced independence (UHDRS independence score ≤90%). Patients were randomly assigned (1:1:1:1:1) with centralised interactive-response technology to receive one of four doses of pridopidine (45, 67·5, 90, or 112·5 mg) or placebo orally twice a day for 52 weeks. Randomisation was stratified within centres by neuroleptic drug use. The primary efficacy endpoint was change in the UHDRS-TMS from baseline to 26 weeks, which was assessed in all randomised patients who received at least one dose of study drug and had at least one post-baseline efficacy assessment (full analysis set). Participants and investigators were masked to treatment assignment. This trial is registered with EudraCT (2013-001888-23) and ClinicalTrials.gov (NCT02006472).

FINDINGS

Between Feb 13, 2014, and July 5, 2016, 408 patients were enrolled and randomly assigned to receive placebo (n=82) or pridopidine 45 mg (n=81), 67·5 mg (n=82), 90 mg (n=81), or 112·5 mg (n=82) twice daily for 26 weeks. The full analysis set included 397 patients (81 in the placebo group, 75 in the 45 mg group, 79 in the 67·5 mg group, 81 in the 90 mg group, and 81 in the 112·5 mg group). Pridopidine did not significantly change the UHDRS-TMS at 26 weeks compared with placebo at any dose. The most frequent adverse events across all groups were diarrhoea, vomiting, nasopharyngitis, falls, headache, insomnia, and anxiety. The most common treatment-related adverse events were insomnia, diarrhoea, nausea, and dizziness. Serious adverse events occurred in the pridopidine groups only and were most frequently falls (n=5), suicide attempt (n=4), suicidal ideation (n=3), head injury (n=3), and aspiration pneumonia (n=3). No new safety or tolerability concerns emerged in this study. One death in the pridopidine 112·5 mg group due to aspiration pneumonia was considered to be possibly related to the study drug.

INTERPRETATION

Pridopidine did not improve the UHDRS-TMS at week 26 compared with placebo and, thus, the results of secondary or tertiary analyses in previous trials were not replicated. A potentially strong placebo effect needs to be ruled out in future studies.

FUNDING

Teva Pharmaceutical Industries.

Open study with (-)-OSU6162 in multiple sclerosis-related fatigue

OBJECTIVES

The main objective of this study was to investigate the tolerability and safety of the monoaminergic stabilizer (-)-OSU6162 in patients with multiple sclerosis (MS). In addition, a potential therapeutic effect of (-)-OSU6162 with focus on MS-related fatigue was estimated by means of various self-assessment rating scales as well as a clinical investigator-rated scale.

MATERIALS AND METHODS

In this open-label, single-arm study, 30 MS patients received treatment with the monoaminergic stabilizer (-)-OSU6162 during 12 weeks. The dose of (-)-OSU6162 was 15 mg twice daily during the first 4-week period, up to 30 mg twice daily during the second 4-week period and up to 45 mg twice daily during the third 4-week period, with follow-up visits after 16 and 20 weeks. MS-related fatigue was rated by the clinical investigator or by self-assessments, using mainly established rating scales. Twenty-five patients completed the study.

RESULTS

(-)-OSU6162 was well tolerated by all patients, and no serious adverse events were observed. Therapeutically, improvements were observed with respect to fatigue and mood, as judged by ratings on the Mental Fatigue Scale (MFS), Short Form-36 (SF-36) scale and Beck Depression Inventory (BDI). Furthermore, the large majority of patients were rated as globally improved in the medical observers' rating scale Clinical Global Impression of Change (CGI-C).

CONCLUSIONS

In view of its good tolerability, (-)-OSU6162 may offer a new treatment option for alleviating mental fatigue, as well as depression, in MS. Larger, randomized double-blind controlled trials are warranted to confirm the present preliminary observations.

The Effects of the Monoamine Stabilizer (-)-OSU6162 on Binge-Like Eating and Cue-Controlled Food-Seeking Behavior in Rats

Binge-eating disorder (BED) is characterized by recurring episodes of excessive consumption of palatable food and an increased sensitivity to food cues. Patients with BED display an addiction-like symptomatology and the dopamine system might be a potential treatment target. The clinically safe monoamine stabilizer (-)-OSU6162 (OSU6162) restores dopaminergic dysfunction in long-term alcohol-drinking rats and shows promise as a novel treatment for alcohol use disorder. Here, the effects of OSU6162 on consummatory (binge-like eating) and appetitive (cue-controlled seeking) behavior motivated by chocolate-flavored sucrose pellets were evaluated in non-food-restricted male Lister Hooded rats. OSU6162 significantly reduced binge-like intake of chocolate-flavored sucrose pellets without affecting prior chow intake. Furthermore, OSU6162 significantly reduced the cue-controlled seeking of chocolate-flavored sucrose pellets under a second-order schedule of reinforcement before, but not after, the delivery and ingestion of reward, indicating a selective effect on incentive motivational processes. In contrast, the dopamine D2/D3 receptor antagonist raclopride reduced the seeking of chocolate-flavored sucrose pellets both pre- and post reward ingestion and also reduced responding under simpler schedules of seeking behavior. The D1/5 receptor antagonist SCH23390 had no effect on instrumental behavior under any reinforcement schedule tested. Finally, local administration of OSU6162 into the nucleus accumbens core, but not dorsolateral striatum, selectively reduced cue-controlled sucrose seeking. In conclusion, the present results show that OSU6162 reduces binge-like eating behavior and attenuates the impact of cues on seeking of palatable food. This indicates that OSU6162 might serve as a novel BED medication.

The sigma-1 receptor mediates the beneficial effects of pridopidine in a mouse model of Huntington disease

The tri-nucleotide repeat expansion underlying Huntington disease (HD) results in corticostriatal synaptic dysfunction and subsequent neurodegeneration of striatal medium spiny neurons (MSNs). HD is a devastating autosomal dominant disease with no disease-modifying treatments. Pridopidine, a postulated "dopamine stabilizer", has been shown to improve motor symptoms in clinical trials of HD. However, the target(s) and mechanism of action of pridopidine remain to be fully elucidated. As binding studies identified sigma-1 receptor (S1R) as a high-affinity receptor for pridopidine, we evaluated the relevance of S1R as a therapeutic target of pridopidine in HD. S1R is an endoplasmic reticulum - (ER) resident transmembrane protein and is regulated by ER calcium homeostasis, which is perturbed in HD. Consistent with ER calcium dysregulation, we observed striatal upregulation of S1R in aged YAC128 transgenic HD mice and HD patients. We previously demonstrated that dendritic MSN spines are lost in aged corticostriatal co-cultures from YAC128 mice. We report here that pridopidine and the chemically similar S1R agonist 3-PPP prevent MSN spine loss in aging YAC128 co-cultures. Spine protection was blocked by neuronal deletion of S1R. Pridopidine treatment suppressed supranormal ER Ca2+ release, restored ER calcium levels and reduced excessive store-operated calcium (SOC) entry in spines, which may account for its synaptoprotective effects. Normalization of ER Ca2+ levels by pridopidine was prevented by S1R deletion. To evaluate long-term effects of pridopidine, we analyzed expression profiles of calcium signaling genes. Pridopidine elevated striatal expression of calbindin and homer1a, whereas their striatal expression was reduced in aged Q175KI and YAC128 HD mouse models compared to WT. Pridopidine and 3-PPP are proposed to prevent calcium dysregulation and synaptic loss in a YAC128 corticostriatal co-culture model of HD. The actions of pridopidine were mediated by S1R and led to normalization of ER Ca2+ release, ER Ca2+ levels and spine SOC entry in YAC128 MSNs. This is a new potential mechanism of action for pridopidine, highlighting S1R as a potential target for HD therapy. Upregulation of striatal proteins that regulate calcium, including calbindin and homer1a, upon chronic therapy with pridopidine, may further contribute to long-term beneficial effects of pridopidine in HD.

Polypharmacology of dopamine receptor ligands

Most neurological diseases have a multifactorial nature and the number of molecular mechanisms discovered as underpinning these diseases is continuously evolving. The old concept of developing selective agents for a single target does not fit with the medical need of most neurological diseases. The development of designed multiple ligands holds great promises and appears as the next step in drug development for the treatment of these multifactorial diseases. Dopamine and its five receptor subtypes are intimately involved in numerous neurological disorders. Dopamine receptor ligands display a high degree of cross interactions with many other targets including G-protein coupled receptors, transporters, enzymes and ion channels. For brain disorders like Parkinsońs disease, schizophrenia and depression the dopaminergic system, being intertwined with many other signaling systems, plays a key role in pathogenesis and therapy. The concept of designed multiple ligands and polypharmacology, which perfectly meets the therapeutic needs for these brain disorders, is herein discussed as a general ligand-based concept while focusing on dopaminergic agents and receptor subtypes in particular.

Novel targets for Huntington's disease: future prospects

Huntington's disease (HD) is an incurable, inherited, progressive, neurodegenerative disorder that is characterized by a triad of motor, cognitive, and psychiatric problems. Despite the noticeable increase in therapeutic trials in HD in the last 20 years, there have, to date, been very few significant advances. The main hope for new and emerging therapeutics for HD is to develop a neuroprotective compound capable of slowing down or even stopping the progression of the disease and ultimately prevent the subtle early signs from developing into manifest disease. Recently, there has been a noticeable shift away from symptomatic therapies in favor of more mechanistic-based interventions, a change driven by a better understanding of the pathogenesis of this disorder. In this review, we discuss the status of, and supporting evidence for, potential novel treatments of HD that are currently under development or have reached the level of early Phase I/II clinical trials.

The monoamine stabilizer (-)-OSU6162 counteracts downregulated dopamine output in the nucleus accumbens of long-term drinking Wistar rats

We recently established that the monoamine stabilizer (−)‐OSU6162 (OSU6162) decreased voluntary alcohol‐mediated behaviors, including alcohol intake and cue/priming‐induced reinstatement, in long‐term drinking rats, while blunting alcohol‐induced dopamine output in the nucleus accumbens (NAc) of alcohol‐naïve rats. Therefore, we hypothesized that OSU6162 attenuates alcohol‐mediated behaviors by blunting alcohol's rewarding effects. Here, we evaluated the effects of long‐term drinking and OSU6162 treatment (30 mg/kg, sc) on basal and alcohol‐induced (2.5 g/kg, ip) NAc dopamine outputs in Wistar rats after 10 months of intermittent access to 20% alcohol. The results showed that basal and alcohol‐induced NAc dopamine outputs were significantly lower in long‐term drinking rats, compared with alcohol‐naïve rats. In the long‐term drinking rats, OSU6162 slowly increased and maintained the dopamine output significantly elevated compared with baseline for at least 4 hours. Furthermore, OSU6162 pre‐treatment did not blunt the alcohol‐induced output in the long‐term drinking rats, a finding that contrasted with our previous results in alcohol‐naïve rats. Finally, OSU6162 did not induce conditioned place preference (CPP) in either long‐term drinking or alcohol‐naïve rats, indicating that OSU6162 has no reinforcing properties. To verify that the CPP results were not due to memory acquisition impairment, we demonstrated that OSU6162 did not affect novel object recognition. In conclusion, these results indicate that OSU6162 attenuates alcohol‐mediated behaviors by counteracting NAc dopamine deficits in long‐term drinking rats and that OSU6162 is not rewarding on its own. Together with OSU6162's beneficial side‐effect profile, the present study merits evaluation of OSU6162's clinical efficacy to attenuate alcohol use in alcohol‐dependent patients.

The effects of the dopamine stabilizer (-)-OSU6162 on aggressive and sexual behavior in rodents

The dopamine stabilizer (-)-OSU61612 dampens locomotion in rodents rendered hyperactive by exposure to a novel environment or treatment with amphetamine, but stimulates locomotion in habituated animals displaying low motor activity, tentatively exerting this profile by selectively blocking extrasynaptic D2 receptors. The major aim of the present study was to explore the possible usefulness of (-)-OSU61612 as an anti-aggressive drug. To this end, the effect of (-)-OSU61612 on isolation-induced aggression in male mice and estrous cycle-dependent aggression in female rats were studied using the resident intruder test; in addition, the possible influence of (-)-OSU61612 on sexual behavior in male mice and on elevated plus maze (EPM) performance in male rats were assessed. (-)-OSU61612 at doses influencing neither locomotion nor sexual activity reduced aggression in male mice. The effect was observed also in serotonin-depleted animals and is hence probably not caused by the antagonism of serotonin receptors displayed by the drug; refuting the possibility that it is due to 5-HT1B activation, it was also not counteracted by isamoltane. (-)-OSU61612 did not display the profile of an anxiogenic or anxiolytic drug in the EPM but caused a general reduction in activity that is well in line with the previous finding that it reduces exploratory behavior of non-habituated animals. In line with the observations in males, (-)-OSU61612 reduced estrus cycle-related aggression in female Wistar rats, a tentative animal model of premenstrual dysphoria. By stabilizing dopaminergic transmission, (-)-OSU61612 may prove useful as a well-tolerated treatment of various forms of aggression and irritability.

The effects of the monoamine stabilizer (-)-OSU6162 on craving in alcohol dependent individuals: A human laboratory study

Alcohol dependence is associated with a dysregulated dopamine system modulating reward, craving and cognition. The monoamine stabilizer (-)-OSU6162 (OSU6162) can counteract both hyper- and hypo-dopaminergic states and we recently demonstrated that it attenuates alcohol-mediated behaviors in long-term drinking rats. The present Phase II exploratory human laboratory study investigated to our knowledge for the first time the effects of OSU6162 on cue- and priming-induced craving in alcohol dependent individuals. Fifty-six alcohol dependent individuals were randomized to a 14-day-treatment period of OSU6162 or placebo after their baseline impulsivity levels had been determined using the Stop Signal Task. On Day 15, participants were subjected to a laboratory alcohol craving test comprised of craving sessions induced by: i) active - alcohol specific cues, ii) neutral stimuli and iii) priming - intake of an alcoholic beverage (0.20g ethanol/kg bodyweight). Subjective ratings of alcohol craving were assessed using the shortened version of the Desire for Alcohol Questionnaire and visual analog scales (VAS). OSU6162 treatment had no significant effect on cue-induced alcohol craving, but significantly attenuated priming-induced craving. Exploratory analysis revealed that this effect was driven by the individuals with high baseline impulsivity. In addition, OSU6162 significantly blunted the subjective liking of the consumed alcohol (VAS). Although the present 14-day-treatment period, showed that OSU6162 was safe and well tolerated, this exploratory human laboratory study was not designed to evaluate the efficacy of OSU6162 to affect alcohol consumption. Thus a larger placebo-controlled efficacyclinical trial is needed to further investigate the potential of OSU6162 as a novel medication for alcohol dependence.

Profile of pridopidine and its potential in the treatment of Huntington disease: the evidence to date

Huntington disease (HD) is a chronic, genetic, neurodegenerative disease for which there is no cure. The main symptoms of HD are abnormal involuntary movements (chorea and dystonia), impaired voluntary movements (ie, incoordination and gait balance), progressive cognitive decline, and psychiatric disturbances. HD is caused by a CAG-repeat expanded mutation in the HTT gene, which encodes the huntingtin protein. The inherited mutation results in the production of an elongated polyQ mutant huntingtin protein (mHtt). The cellular functions of the Htt protein are not yet fully understood, but the functions of its mutant variant are thought to include alteration of gene transcription and energy production, and dysregulation of neurotransmitter metabolism, receptors, and growth factors. The phenylpiperidines pridopidine (4-[3-methanesulfonyl-phenyl]-1-propyl-piperidine; formerly known as ACR16) and OSU6162 ([S]-[-]-3-[3-methane [sulfonyl-phenyl]-1-propyl-piperidine) are members of a new class of pharmacologic agents known as “dopamine stabilizers”. Recent clinical trials have highlighted the potential of pridopidine for symptomatic treatment of patients with HD. More recently, the analysis of HD models (ie, in vitro and in mice) highlighted previously unknown effects of pridopidine (increase in brain-derived neurotrophic factor, reduction in mHtt levels, and σ-1 receptor binding and modulation). These additional functions of pridopidine suggest it might be a neuroprotective and disease-modifying drug. Data from ongoing clinical trials of pridopidine will help define its place in the treatment of HD. This commentary examines the available preclinical and clinical evidence regarding the use of pridopidine in HD.

Pridopidine selectively occupies sigma-1 rather than dopamine D2 receptors at behaviorally active doses

RATIONALE

Dopamine stabilizers have stimulatory actions under low dopamine tone and inhibitory actions under high dopamine tone without eliciting catalepsy. These compounds are dopamine D2 receptor (D2R) antagonists or weak partial agonists and may have pro-mnemonic and neuroprotective effects. The mechanism underlying their stimulatory and neuroprotective actions is unknown but could involve sigma-1R binding.

OBJECTIVES

The present study examined sigma-1R and D2R occupancy by the dopamine stabilizer pridopidine (ACR16) at behaviorally relevant doses in living rats.

METHODS

Rats were administered 3 or 15 mg/kg pridopidine, or saline, before injection of the radiotracer (11)C-SA4503 (sigma-1R) or (11)C-raclopride (D2R). Some animals received 60 mg/kg pridopidine and were only scanned with (11)C-raclopride. Cerebral (11)C-SA4503 binding was quantified using metabolite-corrected plasma input data and distribution volume (V T) calculated by Logan graphical analysis. (11)C-raclopride binding was quantified using striatum-to-cerebellum ratios and binding potentials calculated with a simplified reference tissue model.

RESULTS

Cunningham-Lassen plots indicated sigma-1R occupancies of 57 ± 2 and 85 ± 2% after pretreatment of animals with 3 and 15 mg/kg pridopidine. A significant (44-66%) reduction of (11)C-raclopride binding was only observed at 60 mg/kg pridopidine.

CONCLUSIONS

At doses shown to elicit neurochemical and behavioral effects, pridopidine occupied a large fraction of sigma-1Rs and a negligible fraction of D2Rs. Significant D2R occupancy was only observed at a dose 20-fold higher than was required for sigma-1R occupancy. The characteristics of dopamine stabilizers may result from the combination of high sigma-1R and low D2R affinity.

New treatments for the motor symptoms of Parkinson's disease

Levodopa remains the most potent drug to treat motor symptoms in Parkinson's disease (PD); however, motor fluctuations and levodopa-induced dyskinesia that occur with long-term use restrict some of its therapeutic value. Despite these limitations, the medical treatment of PD strives for continuous relief of symptoms using different strategies throughout the course of the illness: increasing the half-life of levodopa, using 'levodopa-sparing agents' and adding non-dopaminergic drugs. New options to 'improve' delivery of levodopa are under investigation, including long-acting levodopa, nasal inhalation and continuous subcutaneous or intrajejunal administration of levodopa. Long-acting dopamine agonists were recently developed and are undergoing further comparative studies to investigate potential superiority over the immediate-release formulations. Non-dopaminergic drugs acting on adenosine receptors, cholinergic, adrenergic, serotoninergic and glutamatergic pathways are newly developed and many are being evaluated in Phase II and Phase III trials. This article focuses on promising novel therapeutic approaches for the management of PD motor symptoms and motor complications. We will provide an update since 2011 on new formulations of current drugs, new drugs with promising results in Phase II and Phase III clinical trials, old drugs with new possibilities and some new potential strategies that are currently in Phase I and II of development (study start date may precede 2011 but are included as study is still ongoing or full data have not yet been published). Negative Phase II and Phase III clinical trials published since 2011 will also be briefly mentioned.

The dopamine stabilizer (-)-OSU6162 occupies a subpopulation of striatal dopamine D2/D3 receptors: an [(11)C]raclopride PET study in healthy human subjects

(-)-OSU6162 is a dopamine stabilizer that can counteract both hyperdopaminergic and hypodopaminergic states. In this study, D2/D3 receptor occupancy of (-)-OSU6162 in the human brain was investigated using positron emission tomography (PET). Twelve male healthy volunteers underwent [(11)C]raclopride PET scanning before and 1 h after a single oral dose of (-)-OSU6162 (15-90 mg). Blood samples for determination of (-)-OSU6162 and prolactin plasma levels were collected at Tmax. Parametric images of [(11)C]raclopride binding potential relative to nondisplaceable tissue (cerebellar grey matter) uptake (BPND) at baseline and after (-)-OSU6162 administration were generated using the simplified reference tissue model. MRI-based regions of interest were defined for the striatum, composed of caudate nucleus and putamen, and projected onto the co-registered parametric [(11)C]raclopride BPND image. Furthermore, three striatal subregions, ie, anterior dorsal caudate, anterior dorsal putamen, and ventral striatum, were defined manually and additionally analyzed. Plasma concentrations of (-)-OSU6162, ranging from 0.01 to 0.9 μM, showed a linear relationship with prolactin levels, reflecting blockade of pituitary D2 receptors. A concentration-dependent increase in striatal D2/D3 receptor occupancy was observed, reaching a value of about 20% at an (-)-OSU6162 plasma level of 0.2 μM, and which for higher concentrations leveled off to a maximal occupancy of about 40%. Findings were similar in the striatal subregions. The present data corroborate the notion that (-)-OSU6162 binds preferentially to a subpopulation of D2/D3 receptors, possibly predominantly extrasynaptic, and this may form the basis for the dopamine-stabilizing properties of (-)-OSU6162.

Update on the Mechanism of Action of Aripiprazole: Translational Insights into Antipsychotic Strategies Beyond Dopamine Receptor Antagonism

Dopamine partial agonism and functional selectivity have been innovative strategies in the pharmacological treatment of schizophrenia and mood disorders and have shifted the concept of dopamine modulation beyond the established approach of dopamine D2 receptor (D2R) antagonism. Despite the fact that aripiprazole was introduced in therapy more than 12 years ago, many questions are still unresolved regarding the complexity of the effects of this agent on signal transduction and intracellular pathways, in part linked to its pleiotropic receptor profile. The complexity of the mechanism of action has progressively shifted the conceptualization of this agent from partial agonism to functional selectivity. From the induction of early genes to modulation of scaffolding proteins and activation of transcription factors, aripiprazole has been shown to affect multiple cellular pathways and several cortical and subcortical neurotransmitter circuitries. Growing evidence shows that, beyond the consequences of D2R occupancy, aripiprazole has a unique neurobiology among available antipsychotics. The effect of chronic administration of aripiprazole on D2R affinity state and number has been especially highlighted, with relevant translational implications for long-term treatment of psychosis. The hypothesized effects of aripiprazole on cell-protective mechanisms and neurite growth, as well as the differential effects on intracellular pathways [i.e. extracellular signal-regulated kinase (ERK)] compared with full D2R antagonists, suggest further exploration of these targets by novel and future biased ligand compounds. This review aims to recapitulate the main neurobiological effects of aripiprazole and discuss the potential implications for upcoming improvements in schizophrenia therapy based on dopamine modulation beyond D2R antagonism.

Update on Huntington's disease: advances in care and emerging therapeutic options

INTRODUCTION

Huntington's disease (HD) is the most common hereditary neurodegenerative disorder. Despite the fact that both the gene and the mutation causing this monogenetic disorder were identified more than 20 years ago, disease-modifying therapies for HD have not yet been established.

REVIEW

While intense preclinical research and large cohort studies in HD have laid foundations for tangible improvements in understanding HD and caring for HD patients, identifying targets for therapeutic interventions and developing novel therapeutic modalities (new chemical entities and advanced therapies using DNA and RNA molecules as therapeutic agents) continues to be an ongoing process. The authors review recent achievements in HD research and focus on approaches towards disease-modifying therapies, ranging from huntingtin-lowering strategies to improving huntingtin clearance that may be promoted by posttranslational HTT modifications.

CONCLUSION

The nature and number of upcoming clinical studies/trials in HD is a reason for hope for HD patients and their families.

Tolerability and efficacy of the monoaminergic stabilizer (-)-OSU6162 (PNU-96391A) in Huntington's disease: a double-blind cross-over study

OBJECTIVE

To evaluate the safety (primary objective) and efficacy (secondary objective) of (-)-OSU6162 in Huntington's disease (HD).

METHODS

In a double-blind, cross-over trial, patients with HD were randomly assigned to start treatment on either (-)-OSU6162 or placebo. After 4 weeks, those patients who initially received active drug were switched to placebo for another 4 weeks, and vice versa. During the first week the (-)-OSU6162 dose was 15 mg twice daily, during the second week 30 mg twice daily, and during the last 2 weeks 45 mg twice daily. Motor, cognitive, mental and social functions were rated by the clinical investigator or by self-assessment, using established rating scales.

RESULTS

Fifteen patients fulfilling inclusion and exclusion criteria completed the study. (-)-OSU6162 was well tolerated by all patients and no adverse effects were observed. (-)-OSU6162 treatment significantly improved the Short Form 36 Vitality score, mainly due to an improvement of the individual item 'worn-out' (VT3). In addition, an improvement of depressive symptoms was found using Beck Depression Inventory. In contrast to a general trend of improvement in several non-motor variables only small and non-significant differences between (-)-OSU6162 and placebo were found regarding motor functions.

CONCLUSIONS

(-)-OSU6162 offers promise for the treatment of HD, as a drug with good tolerability, capable of improving the patients' experienced non-motor functions such as energy and mood and thus alleviating symptoms of great importance for their quality of life.

Caffeine's Attenuation of Cocaine-Induced Dopamine Release by Inhibition of Adenosine

Background: It is well known that the reinforcing properties of cocaine addiction are caused by the sharp increase of dopamine (DA) in the reward areas of the brain. However, other mechanisms have been speculated to contribute to the increase. Adenosine is one system that is associated with the sleep-wake cycle and is most important in regulating neuronal activity. Thus, more and more evidence is pointing to its involvement in regulating DA release. The current study set out to examine the role of adenosine in cocaine-induced DA release. Methods: Increasing doses of cocaine, caffeine, and their combination, as well as, 8-cyclopentyltheophylline (CPT), an adenosine A1 antagonist (alone and in combination with cocaine) were used to denote a response curve. A novel biosensor, the BRODERICK PROBE^® was implanted in the nucleus accumbens to image the drug-induced surge of DA release in vivo, in the freely moving animal in real time. Results: Combinations of cocaine and caffeine were observed to block the increased release of DA moderately after administration of the low dose (2.5 mg/kg cocaine and 12.5 mg/kg caffeine) and dramatically after administration of the high dose (10 mg/kg cocaine and 50 mg/kg caffeine), suggesting neuroprotection. Similarly, CPT and cocaine showed a decreased DA surge when administered in combination. Thus, the low and high dose of a nonselective adenosine antagonist, caffeine, and a moderate dose of a selective adenosine antagonist, CPT, protected against the cocaine-induced DA release. Conclusions: These results show a significant interaction between adenosine and DA release and suggest therapeutic options for cocaine addiction and disorders associated with DA dysfunction.

Therapeutic Strategies for Huntington's Disease

Huntington's disease (HD) is a devastating autosomal dominant neurodegenerative disease, caused by expansion of the CAG repeat in the huntingtin (HTT) gene and characterized pathologically by the loss of pyramidal neurons in several cortical areas, of striatal medium spiny neurons, and of hypothalamic neurons. Clinically, a distinguishing feature of the disease is uncontrolled involuntary movements (chorea, dyskensias) accompanied by progressive cognitive, motor, and psychiatric impairment. This review focuses on the current state of therapeutic development for the treatment of HD, including the preclinical and clinical development of small molecules and molecular therapies.

The monoamine stabilizer (-)-OSU6162 attenuates voluntary ethanol intake and ethanol-induced dopamine output in nucleus accumbens

BACKGROUND

New medications for alcohol use disorder (AUD) are needed. Long-term alcohol consumption leads to a dysregulated dopamine system. A novel approach to normalize these dysregulations might be treatment with "monoamine stabilizers," a novel class of compounds characterized by the ability to either suppress, stimulate, or not influence dopamine activity depending on the prevailing dopaminergic tone.

METHODS

The effects of the monoamine stabilizer (-)-OSU6162 (OSU6162) on voluntary ethanol intake and ethanol withdrawal symptoms were evaluated in rats voluntarily consuming ethanol for at least 3 months before testing. Furthermore, effects of OSU6162 on ethanol seeking behavior were evaluated with the progressive ratio and cue-induced reinstatement paradigms. Finally, the interaction of OSU6162 with ethanol on dopamine output and metabolism was studied with microdialysis.

RESULTS

The OSU6162 attenuated several ethanol-mediated behaviors, including voluntary ethanol consumption, ethanol withdrawal symptoms, operant ethanol self-administration under progressive ratio schedule, and cue-induced reinstatement of ethanol seeking in rats that had voluntarily consumed ethanol for at least 3 months before treatment. In addition, OSU6162 blunted ethanol-induced dopamine output in nucleus accumbens of ethanol-naïve rats.

CONCLUSIONS

These results highlight the ability of OSU6162 to stabilize dopamine activity depending on the prevailing dopaminergic tone and indicate that OSU6162 might decrease ethanol intake by attenuating the acute rewarding properties of ethanol. In addition, OSU6162 might have potential to prevent relapse triggered by alcohol craving, alcohol related cues, and or an urge to relieve abstinence symptoms. The present study is to our knowledge the first indicating that OSU6162 might serve as a novel medication for AUD.

Placebo-controlled cross-over study of the monoaminergic stabiliser (-)-OSU6162 in mental fatigue following stroke or traumatic brain injury

Objective: Mental fatigue occurring after a stroke or traumatic brain injury (TBI) often results in difficulties returning to work and pursuing social activities. No effective treatment of this condition is available today. In this study, we have tested a novel pharmacological strategy using the monoaminergic stabiliser (−)-OSU6162.

Methods: (−)-OSU6162 was given orally for 4 weeks in doses increasing from 15 to 45 mg b.i.d. to 12 patients suffering from mental fatigue, following upon stroke (n=6) or TBI (n=6). (−)-OSU6162 was compared with placebo using a double-blind, randomised cross-over design. Patients included were well rehabilitated physically with no gross impairment in cognitive functions other than those related to the mental fatigue.

Results: (−)-OSU6162 caused a remarkable improvement in mental stamina, as evaluated by a self-assessment scale on mental fatigue. Statistical significance was reached on the primary endpoint (Mental Fatigue Scale). There was a trend towards improvement in the secondary endpoints processing speed and attention. Principal component analysis showed an overall positive treatment effect in 7 of 12 patients. Beneficial responses were seen already during the first few days of active drug treatment. Increasing dosage caused no further improvement. Adverse reactions consisted of short-lasting mild nausea and attenuated appetite. These side effects disappeared upon dose reduction.

Conclusion: The monoaminergic stabiliser (−)-OSU6162 offers promise as a candidate for treatment of mental fatigue after a stroke or TBI.

Analysis of the actions of the novel dopamine receptor-directed compounds (S)-OSU6162 and ACR16 at the D2 dopamine receptor

BACKGROUND AND PURPOSE; The two phenylpiperidines, OSU6162 and ACR16, have been proposed as novel drugs for the treatment of brain disorders, including schizophrenia and Huntington's disease, because of their putative dopamine stabilizing effects. Here we evaluated the activities of these compounds in a range of assays for the D(2) dopamine receptor in vitro.

EXPERIMENTAL APPROACH

The affinities of these compounds for the D(2) dopamine receptor were evaluated in competition with [(3) H]spiperone and [(3) H]NPA. Agonist activity of these compounds was evaluated in terms of their ability to stimulate [(35) S]GTPγS binding.

KEY RESULTS

Both compounds had low affinities for inhibition of [(3) H]spiperone binding (pK(i) vs. [(3) H]spiperone, ACR16: <5, OSU6162: 5.36). Neither compound was able to stimulate [(35) S]GTPγS binding when assayed in the presence of Na(+) ions, but if the Na(+) ions were removed, both compounds were low-affinity, partial agonists (E(max) relative to dopamine: ACR16: 10.2%, OSU6162:54.3%). Schild analysis of the effects of OSU6162 to inhibit dopamine-stimulated [(35) S]GTPγS binding indicated Schild slopes of ∼0.9, suggesting little deviation from competitive inhibition. OSU6162 was, however, able to accelerate [(3) H]NPA dissociation from D(2) dopamine receptors, indicating some allosteric effects of this compound.

CONCLUSIONS AND IMPLICATIONS

The two phenylpiperidines were low-affinity, low-efficacy partial agonists at the D(2) dopamine receptor in vitro, possibly exhibiting some allosteric effects. Comparing their in vitro and in vivo effects, the in vitro affinities were a reasonable guide to potencies in vivo. However, the lack of in vitro-in vivo correlation for agonist efficacy needs to be further addressed.

LINKED ARTICLES

This article is part of a themed section on Analytical Receptor Pharmacology in Drug Discovery. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2010.161.issue-6.

I. In vivo evidence for partial agonist effects of (-)-OSU6162 and (+)-OSU6162 on 5-HT2A serotonin receptors

The locomotor effects of (-)- and (+)-OSU6162 were evaluated in 'low activity' animals (reserpinized mice and habituated rats) and 'high activity' animals (drug-naive mice and non-habituated rats). Both enantiomers of OSU6162 had dual effects on behavior, stimulating locomotor activity in 'low activity' animals and inhibiting locomotor activity in 'high activity' animals. There were also certain differences between the two enantiomers in their behavioral profiles. The stimulatory effects of both enantiomers in reserpinized mice were blocked by the 5-HT2A selective antagonist M100907, but not by the D2-selective antagonists haloperidol or raclopride, or by the D1-selective antagonists SCH23390 or SCH39166. The stimulatory effect in mice was more pronounced for (+)- than for (-)-OSU6162. In drug-naive mice, both enantiomers of OSU6162 produced head twitches, albeit to a much lesser extent than DOI, and both enantiomers inhibited DOI-induced head twitches, the (-)-form more effectively so than the (+)-form. These results suggest that (-)- and (+)-OSU6162 are partial agonists on 5-HT2A receptors and that the (+)-form has a higher intrinsic activity than the (-)-form. At high doses, both enantiomers inhibited locomotor activity in drug-naive mice, with (-)-OSU6162 being more potent than (+)-OSU6162. Similarly, in high-active rats, both enantiomers inhibited locomotor activity, with the (-)-enantiomer being more potent than the (+)-enantiomer. Conversely, in habituated rats, both enantiomers stimulated locomotor activity, and here, as opposed to the case in low-active mice, (-)-OSU6162 was more effective than (+)-OSU6162. The stimulatory effects in habituated rats of both enantiomers could be antagonized with either haloperidol or M100907. Overall, these results indicate that the dual effects on behavior of (-)- and (+)-OSU6162 are mediated through D2 and 5-HT2A receptors, consistent with their in vitro functional selectivity profiles (see Burstein et al., accompanying paper). Thus, both enantiomers of OSU6162 seem to act as stabilizers not only on dopaminergic, but also on serotonergic brain signaling. These discoveries have important implications for the potential clinical utility of both compounds, as well as for several of their congeners.

II. In vitro evidence that (-)-OSU6162 and (+)-OSU6162 produce their behavioral effects through 5-HT2A serotonin and D2 dopamine receptors

(-)-OSU6162 has promise for treating Parkinson's disease, Huntington's disease and schizophrenia. Behavioral tests evaluating the locomotor effects of (-) and (+)-OSU6162 on 'low activity' animals (reserpinized mice and habituated rats) and 'high activity' animals (drug naive mice and non-habituated rats) revealed that both enantiomers of OSU6162 had dual effects on behavior, stimulating locomotor activity in 'low activity' animals and inhibiting locomotor activity in 'high activity' animals. To elucidate a plausible mechanism of action for their behavioral effects, we evaluated the intrinsic actions of (-)- and (+)-OSU6162, and a collection of other antipsychotic and antiparkinsonian agents at 5-HT2A and D2 receptors in functional assays with various degrees of receptor reserve, including cellular proliferation, phosphatidyl inositol hydrolysis, GTPγS and beta-arrestin recruitment assays. We also tested for possible allosteric actions of (-)-OSU6162 at D2 receptors. Both enantiomers of OSU6162 were medium intrinsic activity partial agonists at 5-HT2A receptors and low intrinsic activity partial agonists at D2 receptors. (+)-OSU6162 had higher efficacy at 5-HT2A receptors, which correlated with its greater stimulatory activity in vivo, but (-)-OSU6162 had higher potency at D2 receptors, which correlated with its greater inhibitory activity in vivo. (-)-OSU6162 did not display any convincing allosteric properties. Both (+)- and (-)-OSU6162 were significantly less active at 27 other monoaminergic receptors and reuptake transporters tested suggesting that D2 and 5-HT2A receptors play crucial roles in mediating their behavioral effects. Compounds with balanced effects on these two receptor systems may offer promise for treating neuropsychiatric diseases.

Effects of the dopamine stabilizers (S)-(-)-OSU6162 and ACR16 on prolactin secretion in drug-naive and monoamine-depleted rats

Dopaminergic stabilizers may be conceptualized as drugs with normalizing effects on dopamine-mediated behaviours and neurochemical events. (S)-(-)-OSU6162 (OSU6162) and ACR16 are two structurally related compounds ascribed such properties, principally because of their stabilizing effects on motor activity in rodents. Reports in the literature indicate possible partial D2 receptor agonist effects using various in vitro systems. This study aimed to measure D2 receptor antagonist and agonist effects of OSU6162 and ACR16 in vivo. To address this, we have studied the effects of both compounds on prolactin secretion in drug-naive and dopamine-depleted rats; dopamine depletion was induced by pretreatment with reserpine plus α-methyl-DL: -p-tyrosine. We find that OSU6162 and ACR16 both stimulate prolactin secretion in drug-naive rats with OSU6162 being considerably more potent and efficacious. Both compounds show a non-significant trend towards reversal of the increased secretion caused by dopamine depletion, whereas the D2 receptor antagonist haloperidol further increased prolactin secretion. Thus, this study suggests that OSU6162 and ACR16 act as D2 receptor antagonists under normal conditions in vivo, possibly with minor agonist effects in a state of dopamine depletion.

The tetrahydroisoquinoline derivative SB269,652 is an allosteric antagonist at dopamine D3 and D2 receptors

In view of the therapeutic importance of dopamine D(3) and D(2) receptors, there remains considerable interest in novel ligands. Herein, we show that the tetrahydroisoquinoline 1H-indole-2-carboxylic acid {4-[2-(cyano-3,4-dihydro-1H-isoquinolin-2-yl)-ethyl]-cyclohexyl}-amide (SB269,652) behaves as an atypical, allosteric antagonist at D(3) and D(2) receptors. Accordingly, SB269,652 potently (low nanomolar range) abolished specific binding of [(3)H]nemanopride and [(3)H]spiperone to Chinese hamster ovary-transfected D(3) receptors when radioligands were used at 0.2 and 0.5 nM, respectively. However, even at high concentrations (5 μM), SB269,652 only submaximally inhibited the specific binding of these radioligands when they were employed at 10-fold higher concentrations. By analogy, although SB269,652 potently blocked D(3) receptor-mediated activation of Gα(i3) and phosphorylation of extracellular-signal-regulated kinase (ERK)1/2, when concentrations of dopamine were increased by 10-fold, from 1 μM to 10 μM, SB269,652 only submaximally inhibited dopamine-induced stimulation of Gα(i3). SB269,652 (up to 10 μM) only weakly and partially (by approximately 20-30%) inhibited radioligand binding to D(2) receptors. Likewise, SB269,652 only submaximally suppressed D(2) receptor-mediated stimulation of Gα(i3) and Gα(qi5) (detected with the aequorin assay) and phosphorylation of ERK1/2 and Akt. Furthermore, SB269,652 only partially (35%) inhibited the dopamine-induced recruitment of β-arrestin2 to D(2) receptors. Finally, Schild analysis using Gα(i3) assays, and studies of radioligand association and dissociation kinetics, supported allosteric actions of SB269,652 at D(3) and D(2) receptors.

Corticostriatal circuit dysfunction in Huntington's disease: intersection of glutamate, dopamine and calcium

Huntington's disease (HD) is a noncurable and progressive autosomal-dominant neurodegenerative disorder that results from a polyglutamine expansion in the amino-terminal region of the huntingtin protein. The generation of rodent HD models has revealed that cellular dysfunction, rather than cell death alone, occurs early in the disease progression, appearing even before overt symptom onset. Much evidence has now established that dysfunction of the corticostriatal circuit is key to HD symptomology. In this article, we summarize the most current findings that implicate glutamate, dopamine and calcium signaling in this system and discuss how they work in concert to disrupt corticostriatal function. In addition, we highlight therapeutic strategies related to altered corticostriatal signaling in HD.

Synthesis and evaluation of a set of 4-phenylpiperidines and 4-phenylpiperazines as D2 receptor ligands and the discovery of the dopaminergic stabilizer 4-[3-(methylsulfonyl)phenyl]-1-propylpiperidine (huntexil, pridopidine, ACR16)

Modification of the partial dopamine type 2 receptor (D(2)) agonist 3-(1-benzylpiperidin-4-yl)phenol (9a) generated a series of novel functional D(2) antagonists with fast-off kinetic properties. A representative of this series, pridopidine (4-[3-(methylsulfonyl)phenyl]-1-propylpiperidine; ACR16, 12b), bound competitively with low affinity to D(2) in vitro, without displaying properties essential for interaction with D(2) in the inactive state, thereby allowing receptors to rapidly regain responsiveness. In vivo, neurochemical effects of 12b were similar to those of D(2) antagonists, and in a model of locomotor hyperactivity, 12b dose-dependently reduced activity. In contrast to classic D(2) antagonists, 12b increased spontaneous locomotor activity in partly habituated animals. The "agonist-like" kinetic profile of 12b, combined with its lack of intrinsic activity, induces a functional state-dependent D(2) antagonism that can vary with local, real-time dopamine concentration fluctuations around distinct receptor populations. These properties may contribute to its unique "dopaminergic stabilizer" characteristics, differentiating 12b from D(2) antagonists and partial D(2) agonists.

Tetrabenazine is neuroprotective in Huntington's disease mice

Background

Huntington's disease (HD) is a neurodegenerative disorder caused by a polyglutamine (polyQ) expansion in Huntingtin protein (Htt). PolyQ expansion in Httexp causes selective degeneration of striatal medium spiny neurons (MSN) in HD patients. A number of previous studies suggested that dopamine signaling plays an important role in HD pathogenesis. A specific inhibitor of vesicular monoamine transporter (VMAT2) tetrabenazine (TBZ) has been recently approved by Food and Drug Administration for treatment of HD patients in the USA. TBZ acts by reducing dopaminergic input to the striatum.

Results

In previous studies we demonstrated that long-term feeding with TBZ (combined with L-Dopa) alleviated the motor deficits and reduced the striatal neuronal loss in the yeast artificial chromosome transgenic mouse model of HD (YAC128 mice). To further investigate a potential beneficial effects of TBZ for HD treatment, we here repeated TBZ evaluation in YAC128 mice starting TBZ treatment at 2 months of age ("early" TBZ group) and at 6 months of age ("late" TBZ group). In agreement with our previous studies, we found that both "early" and "late" TBZ treatments alleviated motor deficits and reduced striatal cell loss in YAC128 mice. In addition, we have been able to recapitulate and quantify depression-like symptoms in TBZ-treated mice, reminiscent of common side effects observed in HD patients taking TBZ.

Conclusions

Our results further support therapeutic value of TBZ for treatment of HD but also highlight the need to develop more specific dopamine antagonists which are less prone to side-effects.