An in vivo pharmacological evaluation of pardoprunox (SLV308)--a novel combined dopamine D(2)/D(3) receptor partial agonist and 5-HT(1A) receptor agonist with efficacy in experimental models of Parkinson's disease

Synthesis and Biological Evaluation of a Series of Novel 1-(3-((6-Fluoropyridin-3-yl)oxy)propyl)piperazines as Dopamine/Serotonin Receptor Agonists

Evidence suggested that the use of partial dopamine D2/D3 receptor agonists may be a better choice for the treatment of Parkinson's disease (PD), and the stimulation of 5-HT1A receptors (mainly via nondopaminergic mechanisms) alleviates motor and nonmotor disorders of PD, implying that the multitarget approach may provide a double bonus for the treatment of the disease. In this study, 20 novel 1-(3-((6-fluoropyridin-3-yl)oxy)propyl)piperazine derivatives were designed and synthesized using a bioisosterism approach, and their activities for D2/D3/5-HT1A receptors were further tested. The results showed that several compounds exhibited a multitarget combination of D2/5-HT1A agonism. Compounds 7b and 34c showed agonistic activities on D2/D3/5-HT1A receptor. The EC50 value of 7b for D2/D3/5-HT1A receptor were 0.9/19/2.3 nmol/L, respectively; and the EC50 value of 34c for D2/D3/5-HT1A receptor were 3.3/10/1.4 nmol/L, respectively. In addition, 34c exhibited good metabolic stability (the half-life T 1/2 = 159.7 minutes) in vitro, which is of great significance for the further exploration of multitarget anti-PD drugs.

A Review on the Arylpiperazine Derivatives as Potential Therapeutics for the Treatment of Various Neurological Disorders

Abstract:

Neurological disorders are disease conditions related to the neurons and central nervous system (CNS). Any kind of structural, electrical, biochemical and functional abnormalities in neurons can lead to various types of disorders like Alzheimer’s disease (AD), depression, Parkinson’s disease (PD), epilepsy, stroke, etc. Currently available medicines are symptomatic and do not treat the disease state. Thus, novel CNS active agents with the potential of complete treatment of an illness are highly desired. A range of small organic molecules are being explored as potential drug candidates for the cure of different neurological disorders. In this context, arylpiperazine has been found to be a versatile scaffold and indispensable pharmacophore in many CNS active agents. A number of molecules with arylpiperazine nucleus have been developed as potent leads for the treatment of AD, PD, depression and other disorders. The arylpiperazine nucleus can be optionally substituted at different chemical structures and offer flexibility for the synthesis of large number of derivatives. In the current review article, we have explored the role of various arylpiperazine containing scaffolds against different neurological disorders, including AD, PD, and depression. The structure-activity relationship studies were conducted for recognizing potent lead compounds. This review article may provide important clues on the structural requirements for the design and synthesis of effective molecules as curative agents for different neurological disorders.

Cannabinoid-induced lower lip retraction in rats

RATIONALE

Lower lip retraction (LLR) in rats has been described as a distinctive effect of 5-HT_1A agonists. In the course of evaluating behavioral effects of cannabinoid agonists in rats, LLR effects were evident following injection of several cannabinoid agonists.

OBJECTIVES

To pharmacologically characterize cannabinoid-induced LLR in rats.

METHODS

Lower lip retraction was scored using a 3-point scale for up to 6 h after injection of the cannabinoid agonists Δ⁹-tetrahydrocannabinol (Δ⁹-THC, 1-10 mg/kg), AM7499 (0.01-1.0 mg/kg), or AM2389 (0.003-0.1 mg/kg), or, for comparison, the 5-HT_1A agonist 8-OH-DPAT (0.01-0.3 mg/kg). Next, antagonist effects of rimonabant (1-10 mg/kg) and WAY100635 (0.3 mg/kg) on LLR produced by cannabinoid or 5-HT_1A agonists were evaluated. Lastly, effects of 8-OH-DPAT were determined following pretreatment with AM2389 (0.003-0.01 mg/kg) or Δ⁹-THC (1 mg/kg).

RESULTS

All three cannabinoid agonists produced LLR. Effects of AM2389 were attenuated by both rimonabant and WAY100635 whereas effects of 8-OH-DPAT were antagonized by WAY 100635 but not by rimonabant. Pretreatment with 1 mg/kg Δ⁹-THC or 0.01 mg/kg AM2389 shifted the 8-OH-DPAT dose-effect function for LLR to the left and isobolographic analysis of the data indicates CB1 and 5-HT_1A interactions can be supraadditive.

CONCLUSIONS

Cannabinoid agonists produce LLR in rats, an effect heretofore ascribed only to activity at 5-HT_1A receptors, via CB1 receptor-mediated actions. Co-administration of a cannabinoid agonist and the 5-HT_1A agonist 8-OH-DPAT results in a synergistic effect on LLR.

Behavior, PET and histology in novel regimen of MPTP marmoset model of Parkinson's disease for long-term stem cell therapy

Stem cell technologies are particularly attractive in Parkinson's disease (PD) research although they occasionally need long-term treatment for anti-parkinsonian activity. Unfortunately, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) widely used as a model for PD has several limitations, including the risk of dose-dependent mortality and the difficulty of maintenance of PD symptoms during the whole experiment period. Therefore, we tested if our novel MPTP regimen protocol (2 mg/kg for 2 consecutive days and 1 mg/kg for next 3 consecutive days) can be maintained stable parkinsonism without mortality for long-term stem cell therapy. For this, we used small-bodied common marmoset monkeys (Callithrix jacchus) among several nonhuman primates showing high anatomical, functional, and behavioral similarities to humans. Along with no mortality, the behavioral changes involved in PD symptoms were maintained for 32 weeks. Also, the loss of jumping ability of the MPTP-treated marmosets in the Tower test was not recovered by 32 weeks. Positron emission tomography (PET) analysis revealed that remarkable decreases of bindings of 18F-FP-CIT were observed at the striatum of the brains of the marmosets received MPTP during the full period of the experiment for 32 weeks. In the substantia nigra of the marmosets, the loss of tyrosine hydroxylase (TH) immunoreactivity was also observed at 32 weeks following the MPTP treatment. In conclusion, our low-dose MPTP regimen protocol was found to be stable parkinsonism without mortality as evidenced by behavior, PET, and TH immunohistochemistry. This result will be useful for evaluation of possible long-term stem cell therapy for anti-parkinsonian activity.

Divergent effects of the 'biased' 5-HT1 A receptor agonists F15599 and F13714 in a novel object pattern separation task

BACKGROUND AND PURPOSE

Pattern separation, that is, the formation of distinct representations from similar inputs, is an important hippocampal process implicated in cognitive domains like episodic memory. A deficit in pattern separation could lead to memory impairments in several psychiatric and neurological disorders. Hence, mechanisms by which pattern separation can be increased are of potential therapeutic interest.

EXPERIMENTAL APPROACH

5-HT1A receptors are involved in spatial memory. Herein we tested the 'biased' 5-HT1A receptor agonists F15599, which preferentially activates post-synaptic heteroreceptors, and F13714, which preferentially activates raphe-located autoreceptors, in rats in a novel spatial task assessing pattern separation, the object pattern separation (OPS) task.

KEY RESULTS

The acetylcholinesterase inhibitor donepezil, which served as a positive control, significantly improved spatial pattern separation at a dose of 1 mg·kg(-1) , p.o. F15599 increased pattern separation at 0.04 mg·kg(-1) , i.p., while F13714 decreased pattern separation at 0.0025 mg·kg(-1) , i.p. The selective 5-HT1A receptor antagonist WAY-100635 (0.63 mg·kg(-1) , s.c.) counteracted the effects of both agonists. These data suggest that acute preferential activation of post-synaptic 5-HT1A heteroreceptors improves spatial pattern separation, whereas acute preferential activation of raphe-located 5-HT1A autoreceptors impairs performance.

CONCLUSIONS AND IMPLICATIONS

We successfully established and validated a novel, simple and robust OPS task and observed a diverging profile of response with 'biased' 5-HT1A receptor agonists based on their targeting of receptors in distinct brain regions. Our data suggest that the post-synaptic 5-HT1A receptor consists of a potential novel molecular target to improve pattern separation performance.

(6aR)-11-amino-N-propyl-noraporphine, a new dopamine D2 and serotonin 5-HT1A dual agonist, elicits potent antiparkinsonian action and attenuates levodopa-induced dyskinesia in a 6-OHDA-lesioned rat model of Parkinson's disease

Parkinson's disease (PD) drug therapy remains a challenge. Dual modulation of dopamine and 5-HT receptors has emerged as a promising approach in anti-PD drug development. Taking advantage of the newly discovered aporphine analogue(s), (6aR)-11-amino-N-propyl-noraporphine (SOMCL-171), which exhibited dual D2/5-HT1A receptor agonistic activity, we studied the effects of the compound on levodopa-induced dyskinesia (LID) in a PD animal model. The results demonstrated that SOMCL-171 elicited a potent anti-PD effect in a 6-OHDA-lesioned rat model. Chronic use of SOMCL-171 reduced LID without compromising the antiparkinsonian efficacy. Furthermore, we found that the antidyskinesia effect of SOMCL-171 is associated with its 5-HT1A agonistic activity and the up-regulation of the striatal 5-HT1A receptor. The present data indicated that chronic SOMCL-171 alone produced potent antiparkinsonian effects with weak dyskinesia, compared with that of levodopa. In addition, chronic SOMCL-171 application attenuated the development of levodopa-induced LID at no expense to the antiparkinsonian efficacy. Taken together, our data suggested that dual modulation of D2/5-HT1A receptors may provide a novel approach for drug development in PD and LID.

Treatment of Parkinson's disease: what's in the non-dopaminergic pipeline?

Dopamine depletion resulting from degeneration of nigrostriatal dopaminergic neurons is the primary neurochemical basis of the motor symptoms of Parkinson's disease (PD). While dopaminergic replacement strategies are effective in ameliorating these symptoms early in the disease process, more advanced stages of PD are associated with the development of treatment-related motor complications and dopamine-resistant symptoms. Other neurotransmitter and neuromodulator systems are expressed in the basal ganglia and contribute to the extrapyramidal refinement of motor function. Furthermore, neuropathological studies suggest that they are also affected by the neurodegenerative process. These non-dopaminergic systems provide potential targets for treatment of motor fluctuations, levodopa-induced dyskinesias, and difficulty with gait and balance. This review summarizes recent advances in the clinical development of novel pharmacological approaches for treatment of PD motor symptoms. Although the non-dopaminergic pipeline has been slow to yield new drugs, further development will likely result in improved treatments for PD symptoms that are induced by or resistant to dopamine replacement.

Dopamine receptor agonists for Parkinson's disease

INTRODUCTION

Prolonged administration of l-3,4-dihydroxyphenylalanine (l-DOPA) for Parkinson's disease (PD) is hampered by motor complications related to the progressive incapacity of residual nigrostriatal neurons to properly utilize the drug. Direct stimulation of dopaminergic (DAergic) receptors with specific compounds (DA agonists) has, therefore, become an additional therapeutic tool for PD.

AREAS COVERED

DA agonists have considerable anti-parkinsonian symptomatic efficacy, although they are less potent than l-DOPA. This review summarizes pre-clinical and clinical data on DA agonists and their role in treating PD. Specific focus was put on second-generation, first-line non-ergolinic DA agonists and their motor, non-motor and putative neuroprotective effects. The anti-parkinsonian potential of recently developed DA agonists that reached Phase II and III clinical trials was also addressed.

EXPERT OPINION

DA agonists can be useful along the whole natural course of PD, as monotherapy in the initial phase or combined with l-DOPA in advanced PD. Extended-release formulations have been developed for second-generation DA agonists, which are better appreciated by patients. Neuroprotective properties have been proposed for DA agonists, based on pre-clinical studies, but never convincingly demonstrated in patients. New DA agonists, with better symptomatic efficacy and devoid of the side effects that characterize current compounds, are needed.

Synthesis of 3-alkylbenzoxazolones from N-alkyl-N-arylhydroxylamines by contiguous O-trichloroacetylation, trichloroacetoxy ortho-shift, and cyclization sequence

Benzoxazolone pharmacophore is present in clinical pharmaceuticals, drug candidates, and many compounds having a wide spectrum of biological activities. The methods available for the synthesis of benzoxazolones have limited diversity due to problems in accessibility and air-sensitivity of diversely substituted o-aminophenols from which they are generally prepared by cyclocarbonylation with phosgene or its equivalents. The present paper describes a mild method for the synthesis of 3-alkylbenzoxazolones from easily accessible and air-stable nitroarenes. Nitroarenes were converted to N-alkyl-N-arylhydroxylamines in two steps involving partial reduction to arylhydroxylamines followed by selective N-alkylation. Treatment of N-alkyl-N-arylhydroxylamines with trichloroacetyl chloride and triethylamine afforded 3-alkylbenzoxazolones generally in good yields through an uninterrupted three-step sequence involving O-trichloroacetylation, N→C(ortho) trichloroacetoxy shift, and cyclization in a single pot at ambient temperatures. The present method is mild, wide in scope, economical, and regioselective. Many sensitive groups like alkyl and aryl esters, amide, cyano, and the carbon-carbon double bond survive the reaction.

Clinical utility of neuroprotective agents in neurodegenerative diseases: current status of drug development for Alzheimer's, Parkinson's and Huntington's diseases, and amyotrophic lateral sclerosis

INTRODUCTION

According to the definition of the Committee to Identify Neuroprotective Agents in Parkinson's Disease (CINAPS), "neuroprotection would be any intervention that favourably influences the disease process or underlying pathogenesis to produce enduring benefits for patients" [Meissner W, et al. Trends Pharmacol Sci 2004;25:249-253]. Preferably, neuroprotective agents should be used before or eventually during the prodromal phase of the diseases that could start decades before the appearance of symptoms. Although several symptomatic drugs are available, a disease-modifying agent is still elusive.

AREAS COVERED

The aim of the present review is to give an overview of neuroprotective agents being currently investigated for the treatment of AD, PD, HD and ALS in clinical phases.

EXPERT OPINION

Development of effective neuroprotective therapies resulting in clinically meaningful results is hampered by several factors in all research stages, both conceptual and methodological. Novel solutions might be offered by evaluation of new targets throughout clinical studies, therapies emerging from drug repositioning approaches, multi-target approaches and network pharmacology.

Animal models of Parkinson's disease: a source of novel treatments and clues to the cause of the disease

Animal models of Parkinson's disease (PD) have proved highly effective in the discovery of novel treatments for motor symptoms of PD and in the search for clues to the underlying cause of the illness. Models based on specific pathogenic mechanisms may subsequently lead to the development of neuroprotective agents for PD that stop or slow disease progression. The array of available rodent models is large and ranges from acute pharmacological models, such as the reserpine- or haloperidol-treated rats that display one or more parkinsonian signs, to models exhibiting destruction of the dopaminergic nigro-striatal pathway, such as the classical 6-hydroxydopamine (6-OHDA) rat and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) mouse models. All of these have provided test beds in which new molecules for treating the motor symptoms of PD can be assessed. In addition, the emergence of abnormal involuntary movements (AIMs) with repeated treatment of 6-OHDA-lesioned rats with L-DOPA has allowed for examination of the mechanisms responsible for treatment-related dyskinesia in PD, and the detection of molecules able to prevent or reverse their appearance. Other toxin-based models of nigro-striatal tract degeneration include the systemic administration of the pesticides rotenone and paraquat, but whilst providing clues to disease pathogenesis, these are not so commonly used for drug development. The MPTP-treated primate model of PD, which closely mimics the clinical features of PD and in which all currently used anti-parkinsonian medications have been shown to be effective, is undoubtedly the most clinically-relevant of all available models. The MPTP-treated primate develops clear dyskinesia when repeatedly exposed to L-DOPA, and these parkinsonian animals have shown responses to novel dopaminergic agents that are highly predictive of their effect in man. Whether non-dopaminergic drugs show the same degree of predictability of response is a matter of debate. As our understanding of the pathogenesis of PD has improved, so new rodent models produced by agents mimicking these mechanisms, including proteasome inhibitors such as PSI, lactacystin and epoximycin or inflammogens like lipopolysaccharide (LPS) have been developed. A further generation of models aimed at mimicking the genetic causes of PD has also sprung up. Whilst these newer models have provided further clues to the disease pathology, they have so far been less commonly used for drug development. There is little doubt that the availability of experimental animal models of PD has dramatically altered dopaminergic drug treatment of the illness and the prevention and reversal of drug-related side effects that emerge with disease progression and chronic medication. However, so far, we have made little progress in moving into other pharmacological areas for the treatment of PD, and we have not developed models that reflect the progressive nature of the illness and its complexity in terms of the extent of pathology and biochemical change. Only when this occurs are we likely to make progress in developing agents to stop or slow the disease progression. The overarching question that draws all of these models together in the quest for better drug treatments for PD is how well do they recapitulate the human condition and how predictive are they of successful translation of drugs into the clinic? This article aims to clarify the current position and highlight the strengths and weaknesses of available models.

Differential effects of activating D1 and D2 receptors on electrophysiology of neostriatal neurons in a rat model of Parkinson's disease induced by paraquat and maneb

Neostriatum plays an important role in the pathophysiology of Parkinson's disease (PD). However, the changes of sensitivity of dopamine receptors of neostriatal neurons in PD have been less addressed in vivo. In the present study, systemic exposure to paraquat and maneb induced Parkinsonian symptoms and neuronal loss of substantia nigra pars compacta. Using single-unit recording methods, three types of neostriatal neurons were recorded including medium spiny-like neurons, large aspiny-like neurons and fast-spiking interneurons. In the exposed rats, increased firing activity of neostriatal neurons was revealed when compared to control rats. Following D1 receptor agonist, SKF38393 and D2 receptor agonist, LY171555 iontophoretically administrated respectively, effects of increase and decrease in firing activity were both observed in neostriatal neurons. However, stronger inhibitory effects of activating D1 receptors and weaker excitatory effects of activating D2 receptors were found in the exposed rats as compared to controls. It indicated that differential changes of sensitivity of D1 and D2 receptors in Parkinson's disease were related to the modulation of the imbalance between D1-receptor-dependent striatonigral direct pathway and D2-receptor-dependent striatopallidal indirect pathway. Our results illustrate the electrophysiological changes of in vivo neostriatal neurons in Parkinson's disease, thereby providing insight into the regulatory mechanisms of dopamine-mediated physiology.

The serotonergic system in Parkinson's disease

Although the cardinal manifestations of Parkinson's disease (PD) are attributed to a decline in dopamine levels in the striatum, a breadth of non-motor features and treatment-related complications in which the serotonergic system plays a pivotal role are increasingly recognised. Serotonin (5-HT)-mediated neurotransmission is altered in PD and the roles of the different 5-HT receptor subtypes in disease manifestations have been investigated. The aims of this article are to summarise and discuss all published preclinical and clinical studies that have investigated the serotonergic system in PD and related animal models, in order to recapitulate the state of the current knowledge and to identify areas that need further research and understanding.

The partial dopamine agonist pardoprunox (SLV308) administered in combination with l-dopa improves efficacy and decreases dyskinesia in MPTP treated common marmosets

Dopamine agonist treatment in early Parkinson's disease (PD) induces less dyskinesia than l-dopa. However, once dyskinesia has developed, dopamine agonists administered with l-dopa exacerbate involuntary movements. The dopamine partial D2/D3 agonist pardoprunox reverses motor deficits in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine hydrochloride (MPTP)-treated primates without hyperactivity, indicating that pardoprunox may alleviate dyskinesia without compromising l-dopa's beneficial actions. This study examines a clinical scenario in which pardoprunox was introduced, in an l-dopa sparing strategy, to existing l-dopa treatment in MPTP-treated marmosets previously primed to express dyskinesia. l-Dopa (5-10 mg/kg) produced effects, which were stable over the 13 treatment days, of increased locomotor activity, reversed motor disability and marked dyskinesia. Pardoprunox (SLV308; 0.0125-0.025 mg/kg) plus l-dopa (3-10 mg/kg) administration increased locomotor activity over the same treatment period and initially produced an equivalent reversal of motor disability compared to l-dopa, however this effect was enhanced as treatment progressed. This reflected the prolonged duration of effect of pardoprunox compared to that of l-dopa. While pardoprunox plus l-dopa treatment initially produced dyskinesia to the same extent as l-dopa alone, the intensity diminished as treatment progressed and it was significantly different at the end of the study. On subsequent l-dopa challenge there was no difference in motor disability reversal between those animals previously treated with pardoprunox plus l-dopa compared to l-dopa alone but the combination treatment produced significantly less dyskinesia. These data suggest that pardoprunox may provide therapeutic benefit in mid to late stage PD by reducing dyskinesia while maintaining efficacy when used with concomitant l-dopa treatment.