SLV313 (1-(2,3-dihydro-benzo[1,4]dioxin-5-yl)-4- [5-(4-fluoro-phenyl)-pyridin-3-ylmethyl]-piperazine monohydrochloride): a novel dopamine D2 receptor antagonist and 5-HT1A receptor agonist potential antipsychotic drug

International Union of Basic and Clinical Pharmacology. CX. Classification of Receptors for 5-hydroxytryptamine; Pharmacology and Function

5-HT receptors expressed throughout the human body are targets for established therapeutics and various drugs in development. Their diversity of structure and function reflects the important role 5-HT receptors play in physiologic and pathophysiological processes. The present review offers a framework for the official receptor nomenclature and a detailed understanding of each of the 14 5-HT receptor subtypes, their roles in the systems of the body, and, where appropriate, the (potential) utility of therapeutics targeting these receptors. SIGNIFICANCE STATEMENT: This review provides a comprehensive account of the classification and function of 5-hydroxytryptamine receptors, including how they are targeted for therapeutic benefit.

Evaluation of SYA16263 as a new potential antipsychotic agent without catalepsy

SYA16263 exhibited moderate radioligand binding affinity at the D₂ receptor and produced inhibition of apomorphine-induced climbing behavior in mice with an ED₅₀ value of 3.88 mg/kg IP, predicting potential antipsychotic effects in humans. Analysis of plasma and brains from rats injected IP with SYA16263 over the course of 24 h revealed a log [brain]/[plasma] (log BB) at Cmax observed equal to 1.08, indicating that SYA16263 enters the brain and is predicted to cross the blood brain barrier (BBB) readily. When tested in animal behavior tests for catalepsy, SYA16263 did not produce catalepsy at doses up to 19 times the apomorphine ED₅₀ value predicting little or no extra-pyramidal (EPS) side effects in humans. This is similar to aripiprazole, which is associated with a low incidence of EPS in humans, but unlike haloperidol which is known to cause severe EPS in humans. Functional activities for SYA16263 show that it acts as a D₂ agonist at both the Gi and β-arrestin pathways, similar to, but better than aripiprazole, which could account for the absence of the catalepsy observed. Taken together, the receptor binding profile, the functional status, the animal behavioral tests and the log BB value, all provide evidence for further pre-clinical testing of SYA16263 as a potential antipsychotic agent with an interesting profile and a unique mechanism of action resulting in no EPS even up to 19 times the ED₅₀ value.

Molecular targets of atypical antipsychotics: From mechanism of action to clinical differences

The introduction of atypical antipsychotics (AAPs) since the discovery of its prototypical drug clozapine has been a revolutionary pharmacological step for treating psychotic patients as these allow a significant recovery not only in terms of hospitalization and reduction in symptoms severity, but also in terms of safety, socialization and better rehabilitation in the society. Regarding the mechanism of action, AAPs are weak D₂ receptor antagonists and they act beyond D₂ antagonism, involving other receptor targets which regulate dopamine and other neurotransmitters. Consequently, AAPs present a significant reduction of deleterious side effects like parkinsonism, hyperprolactinemia, apathy and anhedonia, which are all linked to the strong blockade of D₂ receptors. This review revisits previous and current findings within the class of AAPs and highlights the differences in terms of receptor properties and clinical activities among them. Furthermore, we propose a continuum spectrum of "atypia" that begins with risperidone (the least atypical) to clozapine (the most atypical), while all the other AAPs fall within the extremes of this spectrum. Clozapine is still considered the gold standard in refractory schizophrenia and in psychoses present in Parkinson's disease, though it has been associated with adverse effects like agranulocytosis (0.7%) and weight gain, pushing the scientific community to find new drugs as effective as clozapine, but devoid of its side effects. To achieve this, it is therefore imperative to characterize and compare in depth the very complex molecular profile of AAPs. We also introduce relatively new concepts like biased agonism, receptor dimerization and neurogenesis to identify better the old and new hallmarks of "atypia". Finally, a detailed confrontation of clinical differences among the AAPs is presented, especially in relation to their molecular targets, and new means like therapeutic drug monitoring are also proposed to improve the effectiveness of AAPs in clinical practice.

Serotonergic Approaches in Parkinson's Disease: Translational Perspectives, an Update

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

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.

Serotonergic modulation of the activity of mesencephalic dopaminergic systems: Therapeutic implications

Since their discovery in the mammalian brain, it has been apparent that serotonin (5-HT) and dopamine (DA) interactions play a key role in normal and abnormal behavior. Therefore, disclosure of this interaction could reveal important insights into the pathogenesis of various neuropsychiatric diseases including schizophrenia, depression and drug addiction or neurological conditions such as Parkinson's disease and Tourette's syndrome. Unfortunately, this interaction remains difficult to study for many reasons, including the rich and widespread innervations of 5-HT and DA in the brain, the plethora of 5-HT receptors and the release of co-transmitters by 5-HT and DA neurons. The purpose of this review is to present electrophysiological and biochemical data showing that endogenous 5-HT and pharmacological 5-HT ligands modify the mesencephalic DA systems' activity. 5-HT receptors may control DA neuron activity in a state-dependent and region-dependent manner. 5-HT controls the activity of DA neurons in a phasic and excitatory manner, except for the control exerted by 5-HT_2C receptors which appears to also be tonically and/or constitutively inhibitory. The functional interaction between the two monoamines will also be discussed in view of the mechanism of action of antidepressants, antipsychotics, anti-Parkinsonians and drugs of abuse.

Bioactive benzofuran derivatives: An insight on lead developments, radioligands and advances of the last decade

Benzofuran core is a highly versatile, presents in many important natural products and natural drugs. Many benzofuran containing synthetic drugs and clinical candidates have been derived from natural products. The present review will provide an insight on lead design-developments of the decade, clinical candidates and PET tracer radio-ligands containing benzofuran core along with brief target biology. Brief of the all approved drugs containing benzofuran core also have been enclosed. Main therapeutic areas covered are Cancer, Neurological disorders including anti-psychotic agent and diabetes.

Further evaluation of the tropane analogs of haloperidol

Previous work from our labs has indicated that a tropane analog of haloperidol with potent D2 binding but designed to avoid the formation of MPP(+)-like metabolites, such as 4-(4-chlorophenyl)-1-(4-(4-fluorophenyl)-4-oxobutyl)pyridin-1-ium (BCPP(+)) still produced catalepsy, suggesting a strong role for the D2 receptor in the production of catalepsy in rats, and hence EPS in humans. This study tested the hypothesis that further modifications of the tropane analog to produce compounds with less potent binding to the D2 receptor than haloperidol, would produce less catalepsy. These tests have now revealed that while haloperidol produced maximum catalepsy, these compounds produced moderate to low levels of catalepsy. Compound 9, with the least binding affinity to the D2R, produced the least catalepsy and highest Minimum Adverse Effective Dose (MAED) of the analogs tested regardless of their affinities at other receptors including the 5-HT1AR. These observations support the hypothesis that moderation of the D2 binding of the tropane analogs could reduce catalepsy potential in rats and consequently EPS in man.

(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.

Evaluation of the potential of antipsychotic agents to induce catalepsy in rats: assessment of a new, commercially available, semi-automated instrument

Haloperidol induced catalepsy was determined using the classic bar test and a new MED Associates Catalepsy Test Chamber instrument. The dose that produced an adverse effect in 50% of rats (AED50) for haloperidol was calculated using the instrument data as 0.29 mg/kg. Hand scoring of the video recordings gave AED50 values of 0.30 and 0.31 mg/kg, both well within the 95% CL of the instrument data. Clozapine was also evaluated and catalepsy was not detected up to 40 mg/kg. No significant difference was found between the instrument and hand scoring data. The instrument was useful for testing haloperidol and clozapine, relieving much of the tedium and variability experienced without its use. It was especially valuable at measuring shorter time periods, where the researcher cannot react as quickly. Finally, olanzapine was also evaluated. However, clenched forepaws and hind paws prevented the use of the instrument alone at higher doses. A backup stopwatch was used for the bar test in these cases. Some of the advantages and limitations are discussed. Results are also compared to the crossed-legs position (CLP) test for all three antipsychotics. While haloperidol gave similar results at all concentrations tested, clozapine deviated significantly at the highest dose (40 mg/kg) displaying catalepsy in the CLP test but not in the bar test. Olanzapine displayed catalepsy in rats significantly different from vehicle at 40 mg/kg in both the bar and CLP tests. However, the CLP test may be more suited to compounds with gripping problems which prevent the consistent grasping of the bar. Overall, the instrument was found to be a useful aid in conducting the bar test for catalepsy. The CLP test was found to complement the bar test under certain conditions and could provide additional data that might be missed by the bar test for compounds producing grasping problems.

The role of dopamine in schizophrenia from a neurobiological and evolutionary perspective: old fashioned, but still in vogue

Dopamine is an inhibitory neurotransmitter involved in the pathology of schizophrenia. The revised dopamine hypothesis states that dopamine abnormalities in the mesolimbic and prefrontal brain regions exist in schizophrenia. However, recent research has indicated that glutamate, GABA, acetylcholine, and serotonin alterations are also involved in the pathology of schizophrenia. This review provides an in-depth analysis of dopamine in animal models of schizophrenia and also focuses on dopamine and cognition. Furthermore, this review provides not only an overview of dopamine receptors and the antipsychotic effects of treatments targeting them but also an outline of dopamine and its interaction with other neurochemical models of schizophrenia. The roles of dopamine in the evolution of the human brain and human mental abilities, which are affected in schizophrenia patients, are also discussed.

Synthesis and dual D2 and 5-HT1A receptor binding affinities of 5-piperidinyl and 5-piperazinyl-1H-benzo[d]imidazol-2(3H)-ones

A series of new 5-piperidinyl and 5-piperazinyl-1H-benzo[d]imidazol-2(3H)-ones have been synthesized and evaluated for dual D2 and 5-HT1A receptor binding affinities. The synthesized ligands are structurally related to bifeprunox, a potential atypical antipsychotic, having potent D2 receptor antagonist and 5-HT1A receptor agonist properties. The Suzuki-Miyaura reaction of cyclic vinyl boronate with appropriate aryl halide yielded arylpiperidine, which was eventually transformed to piperidinyl-1H-benzo[d]imidazol-2(3H)-one. The reductive amination of the latter with appropriate biarylaldehdyes rendered the synthesis of 5-piperidinyl-1H-benzo[d]imidazol-2(3H)-ones. Likewise, the Buchwald-Hartwig coupling reactions of 1-boc-piperazine with appropriate aryl halide and subsequent removal of the boc group rendered arylpiperazine. The reductive amination of the latter with appropriate biarylaldehdyes accomplished the synthesis of 5-piperazinyl-1H-benzo[d]imidazol-2(3H)-ones. The structure-activity relationship studies showed that cyclopentenylpyridine and cyclopentenylbenzyl groups contribute significantly to the dual D2 and 5-HT1A receptor binding affinities of these compounds.

Evaluation of the behavioral and pharmacokinetic profile of SYA013, a homopiperazine analog of haloperidol in rats

SYA013, a homopiperazine analog of haloperidol, was further evaluated for antipsychotic potential using additional animal models. Previously, SYA013 was tested in mice with an antipsychotic screening model in which it inhibited apomorphine induced climbing behavior, indicating antagonism of the dopaminergic system and the potential for use in the treatment of schizophrenia. In this study, SYA013 was shown to inhibit both d-amphetamine-induced locomotor activity in rats and conditioned avoidance response (CAR) in rats in a dose dependent manner and in the case of CAR, without producing any escape failure responses (EFRs), two tests predictive of antipsychotic action. The selective 5HT(1A) antagonist WAY100,635 was used to determine if binding of SYA013 to the 5HT(1A) receptor contributed to suppression of CAR. The results indicated that 0.63mg/kg WAY100,635 did not have a significant effect on the inhibition of CAR by SYA013. Pharmacokinetic parameters in brain and plasma were determined for SYA013. A log brain/plasma concentration ratio at a t(max) of 1.48 suggests that SYA013 readily crosses the blood brain barrier (BBB). The hypothesis that binding of SYA013 to the 5HT(1A) receptor contributed to the lack of significant catalepsy was investigated using the 5HT(1A) antagonist WAY100,635. The results of acute and semi-chronic tests suggest that binding to the 5HT(1A) receptor alone did not significantly account for the lack of catalepsy. Lack of catalepsy was preserved after the semi-chronic challenge with SYA013. These tests further indicate that SYA013 has a pharmacological profile with the potential for use in the treatment of neuropsychiatric diseases. In addition, the 5HT(1A) receptor does not appear to play a significant role in the pharmacological profile of SYA013.

Synthesis and antidepressant activity of arylalkanol-piperidine derivatives as triple reuptake inhibitors

A series of arylalkanol-piperidine derivatives was synthesized, and their triple reuptake inhibition and in vivo activities have been evaluated. Among them, compounds 2a, 2j, 2k, 2m and 2n exhibited high potency for 5-HT, NA and DA transporters. Optimized compounds 2j and 2m showed significant reduction of immobility time compared to that of vehicle in the mouse tail suspension test (TST) test at doses ranging from 10 to 50 mg/kg po, and were not generally motor stimulants at 50 mg/kg dose. In addition, compounds 2j and 2m displayed desirable pharmacokinetic properties in SD rats.

The effects of PRX-07034, a novel 5-HT6 antagonist, on cognitive flexibility and working memory in rats

RATIONALE

Accumulating evidence indicates that schizophrenia and autism spectrum disorder patients are marked by cognitive deficits in working memory and strategy switching. There is accumulating evidence that 5-hydroxytryptamine (5-HT)(6) receptors may serve as a useful target to improve cognitive functioning.

OBJECTIVES

In the present experiments, the novel 5-HT(6) antagonist, PRX-07034, was examined for its selectivity of the 5-HT(6) receptor, as well as its effect on delayed spontaneous alternation and strategy switching.

METHODS

The binding affinity of PRX-07034 to the 5-HT(6) receptor, other 5-HT receptors, as well as other G-protein coupled receptors, ion channels, and transporters was evaluated. Cyclic AMP production was measured from transfected HEK-293 cells. In separate behavioral experiments, rats received different doses of PRX-07034 (0.1, 1, or 3 mg/kg, i.p.) 30 min prior to delayed spontaneous alternation testing or prior to the acquisition and switch phases in a place-response switch test.

RESULTS

The results indicated that PRX-07034 is both a potent (Ki = 4-8 nM) and highly selective 5-HT(6) receptor antagonist (≥100-fold selectivity for the 5-HT(6) receptor compared to 68 other GPCRs, ion channels, and transporters, except D(3) (Ki = 71 nM) and 5-HT(1B) (Ki = 260 nM) receptors. For cyclic AMP quantification, PRX-07034 demonstrated antagonist activity (IC(50) = 19 nM) without an effect on basal levels and did not show any agonist activity up to 10 μM. PRX-07034 at 1 and 3 mg/kg (but not 0.1 mg/kg) significantly enhanced delayed spontaneous alternation. The drug at 1 and 3 mg/kg also enhanced switching between a place and response strategy, but did not affect initial learning of either a place or response discrimination.

CONCLUSIONS

These findings demonstrate that PRX-07034 is a selective 5-HT(6) receptor antagonist that may represent a novel treatment for enhancing working memory and cognitive flexibility.

Spontaneous object recognition and its relevance to schizophrenia: a review of findings from pharmacological, genetic, lesion and developmental rodent models

RATIONALE

Spontaneous (novel) object recognition (SOR) is one of the most widely used rodent behavioural tests. The opportunity for rapid data collection has made SOR a popular choice in studies that explore cognitive impairment in rodent models of schizophrenia, and that test the efficacy of drugs intended to reverse these deficits.

OBJECTIVES

We provide an overview of the many recent studies that have used SOR to explore the mnemonic effects of manipulation of the key transmitter systems relevant to schizophrenia-the dopamine, glutamate, GABA, acetylcholine, serotonin and cannabinoid systems-alone or in combination. We also review the use of SOR in studying memory in genetically modified mouse models of schizophrenia, as well as in neurodevelopmental and lesion models. We end by discussing the construct and predictive validity, and translational relevance, of SOR with respect to cognitive impairment in schizophrenia.

RESULTS

Perturbation of the dopamine or glutamate systems can generate robust and reliable impairment in SOR. Impaired performance is also seen following antagonism of the muscarinic acetylcholine system, or exposure to cannabinoid agonists. Cognitive enhancement has been reported using alpha7-nicotinic acetylcholine receptor agonists and 5-HT(6) antagonists. Among non-pharmacological models, neonatal ventral hippocampal lesions and maternal immune activation can impair SOR, while mixed results have been obtained with mice carrying mutations in schizophrenia risk-associated genes, including neuregulin and COMT.

CONCLUSIONS

While SOR is not without its limitations, the task represents a useful method for studying manipulations with relevance to cognitive impairment in schizophrenia, as well as the interactions between them.

Comparative pharmacology of antipsychotics possessing combined dopamine D2 and serotonin 5-HT1A receptor properties

RATIONALE

There is increasing interest in antipsychotics intended to manage positive symptoms via D(2) receptor blockade and improve negative symptoms and cognitive deficits via 5-HT(1A) activation. Such a strategy reduces side-effects such as the extrapyramidal syndrome (EPS), weight gain, and autonomic disturbance liability.

OBJECTIVE

This study aims to review pharmacological literature on compounds interacting at both 5-HT(1A) and D(2) receptors (as well as at other receptors), including aripiprazole, perospirone, ziprasidone, bifeprunox, lurasidone and cariprazine, PF-217830, adoprazine, SSR181507, and F15063.

METHODS

We examine data on in vitro binding and agonism and in vivo tests related to (1) positive symptoms (e.g., psychostimulant-induced hyperactivity or prepulse inhibition deficit), (2) negative symptoms (e.g., phencyclidine-induced social interaction deficits and cortical dopamine release), and (3) cognitive deficits (e.g., phencyclidine or scopolamine-induced memory deficits). EPS liability is assessed by measuring catalepsy and neuroendocrine impact by determining plasma prolactin, glucose, and corticosterone levels.

RESULTS

Compounds possessing "balanced" 5-HT(1A) receptor agonism and D(2) antagonism (or weak partial agonism) and, in some cases, combined with other beneficial properties, such as 5-HT(2A) receptor antagonism, are efficacious in a broad range of rodent pharmacological models yet have a lower propensity to elicit EPS or metabolic dysfunction.

CONCLUSIONS

Recent compounds exhibiting combined 5-HT(1A)/D(2) properties may be effective in treating a broader range of symptoms of schizophrenia and be better tolerated than existing antipsychotics. Nevertheless, further investigations are necessary to evaluate recent compounds, notably in view of their differing levels of 5-HT(1A) affinity and efficacy, which can markedly influence activity and side-effect profiles.

The role of serotonin receptors in the action of atypical antipsychotic drugs

The main class of atypical antipsychotic drugs (APDs) in current use includes the protypical atypical APD, clozapine, as well as aripiprazole, asenapine, iloperidone, lurasidone, olanzapine, quetiapine, risperidone, and ziprasidone. At clinically effective doses, these agents produce extensive blockade of serotonin (5-HT)(2A) receptors, direct or indirect stimulation of 5-HT(1A) receptors, and to a lesser extent, reduction in dopamine (DA) D(2) receptor-mediated neurotransmission. This contrasts with typical APDs, for example haloperidol and perphenazine, which are mainly DA D(2/)D(3) receptor antagonists and have weaker, if any, potency as 5-HT(2A) receptor antagonists. Some, but not all, atypical APDs are also effective 5-HT(2C) receptor inverse agonists or neutral antagonists, 5-HT(6) or 5-HT(7) receptor antagonists. This diverse action on 5-HT receptors may contribute to significant differences in efficacy and tolerability among the atypical APDs. There is considerable preclinical and some clinical evidence that effects on 5-HT receptors contribute to the low risk of producing extrapyramidal side effects, which is the defining characteristic of an atypical APD, the lack of elevation in plasma prolactin levels (with risperidone and 9-hydroxyrisperidone being exceptions), antipsychotic action, and ability to improve some domains of cognition in patients with schizophrenia. The serotonergic actions of the atypical APDs, especially 5-HT(2A) receptor antagonism, are particularly important to the differential effects of typical and atypical APDs to overcome the effects of acute or subchronic administration of N-methyl-d-aspartate (NMDA) receptor antagonists, such as phencyclidine, ketamine, and dizocipline (MK-801). 5-HT(1A) receptor stimulation and 5-HT(6) and 5-HT(7) receptor antagonism may contribute to beneficial effects of these agents on cognition. In particular, 5-HT(7) receptor antagonism may be the basis for the pro-cognitive effects of the atypical APD, amisulpride, a D(2)/D(3) receptor antagonist, which has no effect on other 5-HT receptor. 5-HT(2C) receptor antagonism appears to contribute to the weight gain produced by some atypical APDs and may also affect cognition and psychosis via its influence on cortical and limbic dopaminergic activity.

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

Partial D(2/3) dopamine (DA) receptor agonists provide a novel approach to the treatment of the motor symptoms of Parkinson's disease (PD) that may avoid common dopaminergic side-effects, including dyskinesia and psychosis. The present study focussed on the in vivo pharmacological and therapeutic characterisation of the novel D(2/3) receptor partial agonist and full 5-HT(1A) receptor agonist pardoprunox (SLV308; 7-[4-methyl-1-piperazinyl]-2(3H)-benzoxazolone monochloride). Pardoprunox induced contralateral turning behaviour in rats with unilateral 6-hydroxydopamine-induced lesions of the substantia nigra pars compacta (SNpc) (MED=0.03mg/kg; po). In 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated common marmosets, pardoprunox dose-dependently increased locomotor activity (MED=0.03mg/kg; po) and decreased motor disability (MED=0.03mg/kg; po). The effects of pardoprunox were reversed by the D(2) antagonist sulpiride. In contrast pardoprunox attenuated novelty-induced locomotor activity (MED=0.01mg/kg; po), (+)-amphetamine-induced hyperlocomotion (MED=0.3mg/kg; po) and apomorphine-induced climbing (MED=0.6mg/kg; po) in rodents. Pardoprunox also induced 5-HT(1A) receptor-mediated behaviours, including flat body posture and lower lip retraction (MED=0.3mg/kg; po) and these were reversed by the 5-HT(1A) receptor antagonist WAY100635. Collectively, these findings demonstrate that pardoprunox possesses dopamine D2/3 partial agonist effects, 5-HT1A agonist effects and reduces parkinsonism in animal models. functional DA D(2) receptor partial agonist activity and is effective in experimental models predictive of efficacy in PD. The presence of functional 5-HT(1A) agonist activity might confer anti-dyskinetic activity and have effects that control neuropsychiatric components of PD.

Role of serotonin in central dopamine dysfunction

The interaction between serotonin (5-HT) and dopamine (DA)-containing neurons in the brain is a research topic that has raised the interest of many scientists working in the field of neuroscience since the first demonstration of the presence of monoamine-containing neurons in the mid 1960. The bulk of neuroanatomical data available clearly indicate that DA-containing neurons in the brain receive a prominent innervation from serotonin (5-hydroxytryptamine, 5-HT) originating in the raphe nuclei of the brainstem. Compelling electrophysiological and neurochemical data show that 5-HT can exert complex effects on the activity of midbrain DA neurons mediated by its various receptor subtypes. The main control seems to be inhibitory, this effect being more marked in the mesocorticolimbic DA system as compared to the DA nigrostriatal system. In spite of a direct effect of 5-HT by its receptors located on DA cells, 5-HT can modulate their activity indirectly, modifying gamma-aminobutyric (GABA)-ergic and glutamatergic input to the ventral tegmental area (VTA) and substantia nigra pars compacta (SNc). Although 5-HT/DA interaction in the brain has been extensively studied, much work remains to be done to clarify this issue. The recent development of subtype-selective ligands for 5-HT receptors will not only allow a detailed understanding of this interaction but also will lead to the development of new treatment strategies, appropriate for those neuropsychiatric disorders in which an alteration of the 5-HT/DA balance is supposed.

Comparison of the mGlu(5) receptor positive allosteric modulator ADX47273 and the mGlu(2/3) receptor agonist LY354740 in tests for antipsychotic-like activity

Recently, it has been proposed that activation of either metabotropic glutamate receptors e.g. mGlu(5) by positive allosteric modulators or stimulation of mGluR(2/3) receptors by agonists may offer new strategy in schizophrenia treatment. The aim of the present study was to compare the effect of mGlu(5) receptor positive allosteric modulator, ADX47273 (S-(4-Fluoro-phenyl)-{3-[3-(4-fluoro-phenyl)-[1,2,4]oxadiazol-5-yl]-piperidin-1-yl}-methanone), mGluR(2/3) agonist, LY354740 ((1S,2S,5R,6S)-2-aminobicyclo[3.1.0]hexane-2,6-dicarboxylate monohydrate) and selected neuroleptics in animal models for positive schizophrenia symptoms. ADX47273 (3 and 10mg/kgi.p.), the typical antipsychotic haloperidol (0.1 and 0.2mg/kgi.p.), the atypical antipsychotics aripiprazole (1.25-5mg/kgi.p.) and olanzapine (2.5 and 5mg/kgi.p.) all reduced amphetamine-induced hyperlocomotion in Sprague-Dawley rats, unlike the mGlu(2/3) receptor agonist LY354740 (1-10mg/kgi.p.). Interestingly, haloperidol (0.1 and 0.2mg/kgi.p.), aripiprazole (1.25-5mg/kgi.p.) and olanzapine (1.25-5mg/kgi.p.), but not ADX47273 (1-10mg/kgi.p.), all reduced spontaneous locomotion and rearings at doses effective against amphetamine-induced hyperlocomotion. This indicates that the effect of ADX47273 in combination with amphetamine may be specific, and also suggests a lack of sedative side effects. Moreover, ADX47273 (30mg/kgi.p.), haloperidol (0.1 and 0.2mg/kgi.p.) and aripiprazole (5 and 10mg/kgi.p.) reversed apomorphine (0.5mg/kgs.c.)-induced deficits of prepulse inhibition, whereas neither LY354740 (1-10mg/kgi.p.) nor olanzapine (1.25-5mg/kgi.p.) produced this effect. Lack of effect of olanzapine was unexpected and at present no convincing explanation can be provided. In conclusion, in selected rodent models for positive schizophrenia symptoms, ADX47273 showed better efficacy than LY354740.

Serotonin1A receptors in the pathophysiology of schizophrenia: development of novel cognition-enhancing therapeutics

Serotonin (5-HT) receptors have been suggested to play key roles in psychosis, cognition, and mood via influence on neurotransmitters, synaptic integrity, and neural plasticity. Specifically, genetic evidence indicates that 5-HT(1A), 5-HT(2A), and 5-HT(2C) receptor single-nucleotide polymorphisms (SNPs) are related to psychotic symptoms, cognitive disturbances, and treatment response in schizophrenia. Data from animal research suggest the role of 5-HT in cognition via its influence on dopaminergic, cholinergic, glutamatergic, and GABAergic function. This article provides up-to-date findings on the role of 5-HT receptors in endophenotypic variations in schizophrenia and the development of newer cognition-enhancing medications, based on basic science and clinical evidence. Imaging genetics studies on associations of polymorphisms of several 5-HT receptor subtypes with brain structure, function, and metabolism suggest a role for the prefrontal cortex and the parahippocampal gyrus in cognitive impairments of schizophrenia. Data from animal experiments to determine the effect of agonists/antagonists at 5-HT(1A), 5-HT(2A), and 5-HT(2C) receptors on behavioral performance in animal models of schizophrenia based on the glutamatergic hypothesis provide useful information. For this purpose, standard as well as novel cognitive tasks provide a measure of memory/information processing and social interaction. In order to scrutinize mixed evidence for the ability of 5-HT(1A) agonists/antagonists to improve cognition, behavioral data in various paradigms from transgenic mice overexpressing 5-HT(1A) receptors provide valuable insights. Clinical trials reporting the advantage of 5-HT(1A) partial agonists add to efforts to shape pharmacologic perspectives concerning cognitive enhancement in schizophrenia by developing novel compounds acting on 5-HT receptors. Overall, these lines of evidence from translational research will facilitate the development of newer pharmacologic strategies for the treatment of cognitive disturbances of schizophrenia.

The antipsychotics clozapine and olanzapine increase plasma glucose and corticosterone levels in rats: comparison with aripiprazole, ziprasidone, bifeprunox and F15063

Several novel antipsychotics activate serotonin 5-HT1A receptors as well as antagonising dopamine D2/3 receptors. Such a pharmacological profile is associated with a lowered liability to produce extrapyramidal side effects and enhanced efficacy in treating negative and cognitive symptoms of schizophrenia. However, 5-HT1A receptor agonists increase plasma corticosterone and many antipsychotics disturb the regulation of glucose. Here, we compared the influence on plasma glucose and corticosterone of acute treatments with 'new generation' antipsychotics which target dopamine D2/3 receptors and 5-HT1A receptors, with that of atypical antipsychotics, and with haloperidol. Olanzapine and clozapine, antipsychotics that are known to produce weight gain and diabetes in humans, both at 10 mg/kg p.o., substantially increased plasma glucose (from 0.8 to 1.7 g/l) at 1 h after administration, an effect that returned to control levels after 4 h. In comparison, F15063 (40 mg/kg p.o.) was without effect at any time point. Olanzapine and clozapine dose-dependently increased plasma glucose concentrations as did SLV313 and SSR181507. Haloperidol and risperidone had modest effects whereas aripiprazole, ziprasidone and bifeprunox, antipsychotics that are not associated with metabolic dysfunction in humans, and F15063 had little or no influence on plasma glucose. The same general pattern of response was found for plasma corticosterone levels. The present data provide the first comparative study of conventional, atypical and 'new generation' antipsychotics on glucose and corticosterone levels in rats. A variety of mechanisms likely underlie the hyperglycemia and corticosterone release observed with clozapine and olanzapine, whilst the balance of dopamine D2/3/5-HT1A interaction may contribute to the less favourable impact of SLV313 and SSR181507 compared with that of bifeprunox and F15063.

Identification of a butyrophenone analog as a potential atypical antipsychotic agent: 4-[4-(4-chlorophenyl)-1,4-diazepan-1-yl]-1-(4-fluorophenyl)butan-1-one

The synthesis and exploration of novel butyrophenones have led to the identification of a diazepane analogue of haloperidol, 4-[4-(4-chlorophenyl)-1,4-diazepan-1-yl]-1-(4-fluorophenyl)butan-1-one (compound 13) with an interesting multireceptor binding profile. Compound 13 was evaluated for its binding affinities at DA subtype receptors, 5HT subtype receptors, H-1, M-1 receptors and at NET, DAT, and SERT transporters. At each of these receptors, compound 13 was equipotent or better than several of the standards currently in use. In in vivo mouse and rat models to evaluate its efficacy and propensity to elicit catalepsy and hence EPS in humans, compound 13 showed similar efficacy as clozapine and did not produce catalepsy at five times its ED(50) value.

Agonist and antagonist properties of antipsychotics at human dopamine D4.4 receptors: G-protein activation and K+ channel modulation in transfected cells

Interaction at dopamine D4 receptors may improve cognitive function, which is highly impaired in individuals with schizophrenia, but comparative studies of recent antipsychotics in cellular models of D4 receptor activation are lacking. Here, we report the in-vitro profile of over 30 ligands at recombinant hD4.4 receptors. In [35S]GTPgammaS binding experiments using membranes of CHO-hD4.4 cells, apomorphine, preclamol and the selective D4 agonists, ABT724, CP226269, Ro-10-5824 and PD168077, behaved as partial agonists (Emax 20-60% vs. dopamine), whereas L745870 and RBI257, displayed antagonist properties. The 'conventional' antipsychotic, haloperidol and the 'atypicals', clozapine and risperidone, exhibited antagonist properties, while 'third generation' compounds bifeprunox, SLV313 and F15063, acted as partial agonists (10-30%). Aripiprazole and SSR181507 slightly stimulated [35S]GTPgammaS binding at micromolar concentrations. In Xenopus laevis oocytes co-expressing hD4.4 receptors with G-protein-coupled inwardly rectifying potassium (GIRK) channels, apomorphine, preclamol, ABT724, CP226269, and PD168077 stimulated GIRK currents (Emax 70-80%). The 5-HT1A receptor ligands, WAY100635 and flibanserin, also exhibited partial agonist activity (30% and 15%, respectively). Haloperidol, clozapine, olanzapine and nemonapride did not stimulate GIRK currents, whereas aripiprazole, bifeprunox, SLV313 and F15063, but not SSR181507, exhibited partial agonism (Emax 20-35%). In-vitro responses depended on experimental conditions: increasing NaCl concentration (30 mm to 100 mm) reduced agonist efficacy in [35S]GTPgammaS binding, whereas decreasing the amount of hD4.4 cRNA injected into oocytes (from 2.0 to 0.5 ng/oocyte) reduced agonist efficacy of several compounds. These data indicate that, unlike conventional or 'atypical' antipsychotics, several 'third generation' agents display D4 receptor partial agonism that may be sufficient to influence physiological D4 receptor activity in vivo.

Antipsychotics differ in their ability to internalise human dopamine D2S and human serotonin 5-HT1A receptors in HEK293 cells

Antipsychotic drugs act preferentially via dopamine D(2) receptor blockade, but interaction with serotonin 5-HT(1A) receptors has attracted interest as additional target for antipsychotic treatment. As receptor internalisation is considered crucial for drug action, we tested the propensity of antipsychotics to internalise human (h)D(2S) receptors and h5-HT(1A) receptors. Agonist-induced internalisation of hemaglutinin (HA)-tagged hD(2S) and HA-h5-HT(1A) receptors expressed in HEK293 cells was increased by coexpression of G-protein coupled receptor kinase 2 and beta-arrestin2. At the HA-hD(2S) receptor, dopamine, quinpirole and bromocriptine behaved as full agonists, while S(-)-3-(3-hydroxyphenyl)-N-n-propylpiperidine [(-)-3PPP] and sarizotan were partial agonists. The typical antipsychotic, haloperidol, and the atypical compounds, olanzapine, nemonapride, ziprasidone and clozapine did not internalise HA-hD(2S) receptors, whereas aripiprazole potently internalised these receptors (>50% relative efficacy). Among antipsychotics with combined D(2)/5-HT(1A) properties, bifeprunox and (3-exo)-8-benzoyl-N-[[(2S)7-chloro-2,3-dihydro-1,4-benzodioxin-1-yl]methyl]-8-azabicyclo-[3.2.1]octane-3-methanamine (SSR181507) partially internalised HA-hD(2S) receptors, piperazine, 1-(2,3-dihydro-1,4-benzodioxin-5-yl)-4-[[5-(4-fluorophenyl)-3-pyridinyl]methyl (SLV313) and N-[(2,2-dimethyl-2,3-dihydro-benzofuran-7-yloxy)ethyl]-3-(cyclopent-1-enyl)-benzylamine (F15063) were inactive. At the HA-h5-HT(1A) receptor, serotonin, (+)-8-hydroxy-2-(di-n-propylamino)tetralin [(+)-8-OH-DPAT] and sarizotan were full agonists, buspirone acted as partial agonist. (-)-Pindolol showed little activity and no internalising properties were manifested for the 5-HT(1A) receptor antagonist N-[2-[4-(2-methoxyphenyl)-1-piperazinyl]-ethyl]-N-(2-pyridinyl)cyclohexanecarboxamide (WAY100635). Most antipsychotics induced HA-h5-HT(1A) receptor internalisation, with an efficacy rank order: nemonapride>F15063>SSR181507>bifeprunox approximately SLV313 approximately ziprasidone>aripiprazole and potencies: SLV313>SSR181507 approximately F15063>bifeprunox approximately nemonapride approximately aripiprazole>ziprasidone. Interestingly, the internalisation induced by clozapine was only minimal, whereas aripirazole and bifeprunox were more potent for internalisation than for G-protein activation. These different profiles of antipsychotics for receptor internalisation may help to evaluate their potential therapeutic impact in the treatment of schizophrenia.

Principal Component Analysis Differentiates the Receptor Binding Profiles of Three Antipsychotic Drug Candidates from Current Antipsychotic Drugs

The receptor binding affinities of the three drug candidates 1 (SLV310), 2 (SLV313), and 3 (SLV314) were positioned against the results from nine (a)typical antipsychotic drugs. The receptor binding data from sixteen monoaminergic receptors served as the input in a principal component analysis (PCA). The PCA outcome revealed a unique binding profile of 1, 2, and 3 as compared with the reference compounds 4-8 and 10-12. The weight gain inducing antipsychotics 6-8 clustered in the PCA by scoring strongly negative for factor 1. The hyperprolactinaemia related antipsychotics 4, 5, 10, and 12 clustered by their negative scores for factor 2.

Differential profile of typical, atypical and third generation antipsychotics at human 5-HT7a receptors coupled to adenylyl cyclase: detection of agonist and inverse agonist properties

5-HT(7) receptors are present in thalamus and limbic structures, and a possible role of these receptors in the pathology of schizophrenia has been evoked. In this study, we examined binding affinity and agonist/antagonist/inverse agonist properties at these receptors of a large series of antipsychotics, i.e., typical, atypical, and third generation compounds preferentially targeting D(2) and 5-HT(1A) sites. Adenylyl cyclase (AC) activity was measured in HEK293 cells stably expressing the human (h) 5-HT(7a) receptor isoform. 5-HT and 5-CT increased cyclic adenosine monophosphate level by about 20-fold whereas (+)-8-OH-DPAT, the antidyskinetic agent sarizotan, and the novel antipsychotic compound bifeprunox exhibited partial agonist properties at h5-HT(7a) receptors stimulating AC. Other compounds antagonized 5-HT-induced AC activity with pK (B) values which correlated with their pK (i) as determined by competition binding vs [(3)H]5-CT. The selective 5-HT(7) receptor ligand, SB269970, was the most potent antagonist. For antipsychotic compounds, the following rank order of antagonism potency (pK (B)) was ziprasidone > tiospirone > SSR181507 > or = clozapine > or = olanzapine > SLV-314 > SLV-313 > or = aripiprazole > or = chlorpromazine > nemonapride > haloperidol. Interestingly, pretreatment of HEK293-h5-HT(7a) cells with forskolin enhanced basal AC activity and revealed inverse agonist properties for both typical and atypical antipsychotics as well as for aripiprazole. In contrast, other novel antipsychotics exhibited diverse 5-HT(7a) properties; SLV-313 and SLV-314 behaved as quasi-neutral antagonists, SSR181507 acted as an inverse agonist, and bifeprunox as a partial agonist, as mentioned above. In conclusion, the differential properties of third generation antipsychotics at 5-HT(7) receptors may influence their antipsychotic profile.

Effects of the serotonin 5-HT7 receptor antagonist SB-269970 on the inhibition of dopamine neuronal firing induced by amphetamine

Using extracellular unitary recordings in anaesthetized rats, this study examined the implication of the serotonin 7 (5-HT(7)) receptors in the inhibitory effect of amphetamine on ventral tegmental area and substantia nigra pars compacta dopamine neuronal activity. The acute administration of the selective 5-HT(7) receptor antagonist, SB-269970 (0.1, 0.5 and 1 mg/kg, i.p.), did not alter the firing activity of dopamine neurons. Interestingly, this antagonist prevented significantly the inhibition of dopamine neuronal firing activity induced by amphetamine (1 mg/kg, i.v.) in the ventral tegmental area, but not in the substantia nigra pars compacta. The present results suggest that 5-HT(7) receptors modulate the dopamine firing activity in the ventral tegmental area, thus affecting preferentially the mesocorticolimbic pathway.

Induction by antipsychotics of "win-shift" in the drug discrimination paradigm

In a two-lever, food-rewarded drug discrimination paradigm, behavior seems to be governed by a win-stay/lose-shift rule; rats continue to press the lever that yields food, and, when not rewarded, they shift responding to the alternative lever. Here, we report on the effects that antipsychotics and further neuropharmacological agents exert in those conditions. At higher doses, antipsychotics disrupt most or all behavioral parameters in this paradigm. However, at lower doses, rats may select the appropriate lever with normal latency and accuracy, obtain a first food pellet (i.e., "win"), and then, remarkably, shift responding to the alternative lever ("win-shift"). This suggests that antipsychotics can block the effects of reward selectively, i.e., at doses where the initial, secondarily reinforced behavior including the initiation of lever pressing, remains intact. Indeed, saline-treated rats that are given no reward (i.e., "lose") after having selected a lever, also press the alternative lever ("lose-shift"). The induction of selective win-shift is specific to antipsychotics, but it varies greatly among them. Perhaps relating to its alleged "incisive" action on delirium and hallucinations, and, surprisingly, in view of its extrapyramidal actions, acutely administered haloperidol (0.04-0.08 mg/kg) demonstrates win-shift to an exceptional extent, shared only with the newly proposed agent (3-cyclopent-1-enyl-benzyl)-[2-(2,2-dimethyl-2,3-dihydro-benzofuran-7-yloxy)-ethyl]-amine fumarate (F 15063; 0.31-0.63 mg/kg); the more sedative antipsychotic chlorpromazine demonstrated little selectivity. The paradigm offers a novel tool to characterize antipsychotics with regard to presumably pathogenic motivational processes; mixed D(2)-antagonist/5-hydroxytryptamine(1A)-agonist agents such as F 15063 may conceivably share the powerful antipsychotic action of haloperidol while avoiding the sensitization that develops to extrapyramidal effects of haloperidol and consequent negative symptoms.

Differential agonist and inverse agonist profile of antipsychotics at D2L receptors coupled to GIRK potassium channels

The D(2) dopaminergic receptor represents a major target of antipsychotic drugs. Using the coupling of the human D(2long) (hD(2L)) receptor to G protein-coupled inward rectifier potassium (GIRK) channels in Xenopus laevis oocytes, we examined the activity of antipsychotic agents of different classes - typical, atypical, and a "new generation" of compounds, exhibiting a preferential D(2) and 5-HT(1A) receptor profile. When the hD(2L) receptor was coexpressed with GIRK channels, a series of reference compounds exhibited full agonist (dopamine, and quinpirole), partial agonist (apomorphine, (-)3-PPP, and (+)-UH232) or inverse agonist (raclopride, and L741626) properties. Sarizotan exhibited only very weak partial agonist action. At higher levels of receptor cRNA injected per oocyte, both partial agonist activity and inverse agonist properties were generally more pronounced. The inverse agonist action of L741626 was reversed by interaction with sarizotan, thus confirming the constitutive activity of wild-type hD(2L) receptors in the oocyte expression system. When antipsychotic agents were tested for their actions at the hD(2L) receptor, typical (haloperidol) as well as atypical (nemonapride, ziprasidone, and clozapine) compounds acted as inverse agonists. In contrast, among D(2)/5-HT(1A) antipsychotics, only SLV313 and F15063 behaved as inverse agonists, whilst the other members of this group (bifeprunox, SSR181507 and the recently marketed antipsychotic, aripiprazole) exhibited partial agonist properties. Thus, the X. laevis oocyte expression system highlights markedly different activity of antipsychotics at the hD(2L) receptor. These differential properties may translate to distinct therapeutic potential of these compounds.

In vivo occupancy of dopamine D2 receptors by antipsychotic drugs and novel compounds in the mouse striatum and olfactory tubercles

Interaction with dopamine D2-like receptors plays a major role in the therapeutic effects of antipsychotic drugs. We examined in vivo dopamine D2 receptor occupancy of various established and potential antipsychotics in mouse striatum and olfactory tubercles 1 h after administration of the compound, using [3H]nemonapride as a ligand. All the compounds reduced in vivo binding of [3H]nemonapride in the striatum. When administered systemically, conventional antipsychotics, D2 antagonists, nemonapride (ID50: 0.034 mg/kg), eticlopride (0.047), haloperidol (0.11) and raclopride (0.11) potently inhibited [3H]nemonapride binding. The 'atypical' antipsychotics, risperidone (0.18), ziprasidone (0.38), aripiprazole (1.6), olanzapine (0.99), and clozapine (11.1) were less potent for occupying D2-like receptors. New compounds, displaying marked agonism at 5-HT1A receptors in addition to D2 receptor affinity, exhibited varying D2 receptor occupancy: bifeprunox (0.25), SLV313 (0.78), SSR181507 (1.6) and sarizotan (6.7). ID50 values for inhibition of [3H]nemonapride binding in the striatum correlated with those in the olfactory tubercles (r=0.95, P<0.0001). These values also correlated with previously-reported in vitro affinity of the compounds at rat D2 receptors (r=0.85, P=0.0001) and with inhibition of apomorphine-induced climbing in mice (r=0.79 P=0.0005). In contrast, there was no significant correlation between ID50 values herein and previously-reported ED50 values for catalepsy in mice. These data indicate that: (1) there is no difference in D2 receptor occupancy in limbic versus striatal regions between most classical and atypical or potential antipsychotics; and (2) high occupancy of D2 receptors can be dissociated from catalepsy, if the drugs also activate 5-HT1A receptors. Taken together, these data support the strategy of simultaneously targeting D2 receptor blockade and 5-HT1A receptor activation for new antipsychotics.