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5-Chloro-N-(4-methoxy-3-piperazin-1-yl-phenyl)-3-methyl-2- benzothiophenesulfonamide (SB-271046): A potent, selective, and orally bioavailable 5-HT6 receptor antagonist [1]
... The serotoninergic subtype 6 receptors (5-HT6Rs) are mainly expressed in the central nervous system, particularly in brain regions involved in memory processes [1][2][3][4][5]. This distribution can support a role for these receptors in the treatment of memory disorders related to neuropsychiatric diseases such as those observed in schizophrenia. ...
... This study therefore aimed to functionally characterize the interplay between 5-HT6Rs and glutamatergic neurotransmission by assessing the effects of the 5-HT6Rs' antagonist SB-271046 on synaptic activity and plasticity of CA3/CA1 hippocampal synapses. SB-271046, whose structure and function have been initially described by Bromidge et al. (1999) [4] and Routledge et al. (2000) [5], is known to block the 5-HT6Rs, leading to a decrease in adenylyl-cyclase activation and a decrease in AMPc intracellular concentration. Our investigation was performed in both male and female mice, allowing us to take into consideration the sexual dimorphism that can be observed in healthy brains [43] but is also accentuated in diseases such as schizophrenia [44][45][46]. ...
... This study therefore aimed to functionally characterize the interplay between 5-HT6Rs and glutamatergic neurotransmission by assessing the effects of the 5-HT6Rs' antagonist SB-271046 on synaptic activity and plasticity of CA3/CA1 hippocampal synapses. SB-271046, whose structure and function have been initially described by Bromidge et al. (1999) [4] and Routledge et al. (2000) [5], is known to block the 5-HT6Rs, leading to a decrease in adenylyl-cyclase activation and a decrease in AMPc intracellular concentration. Our investigation was performed in both male and female mice, allowing us to take into consideration the sexual dimorphism that can be observed in healthy brains [43] but is also accentuated in diseases such as schizophrenia [44][45][46]. ...
The subtype 6 of the serotoninergic receptors (5-HT6Rs) is highly expressed in the hippocampus, and evidence indicates the beneficial effects of 5-HT6Rs blockade on short- and long-term memory in rodents. Nevertheless, the underlying functional mechanisms still need to be established. To this end, we performed electrophysiological extracellular recordings to assess the effects of the 5-HT6Rs antagonist SB-271046 on the synaptic activity and functional plasticity at the CA3/CA1 hippocampal connections of male and female mice slices. We found that basal excitatory synaptic transmission and isolated N-methyl-D-aspartate receptors (NMDARs) activation were significantly increased by SB-271046. The NMDARs-related improvement was prevented by the GABAAR antagonist bicuculline in male but not in female mice. Regarding synaptic plasticity, neither paired-pulse facilitation (PPF) nor NMDARs-dependent long-term potentiation (LTP) (induced either by high-frequency or theta-burst stimulation) was affected by the 5-HT6Rs blockade. Taken together, our results indicate a sex-dependent 5-HT6Rs effect on synaptic activity at the CA3/CA1 hippocampal connections through changes in the excitation/inhibition balance.
... Nowadays, Thiophene moiety have attracted great attention in medicinal field due to its diversified biological activities such as anti bacterial activity and anti fungal activity, [1][2][3][4][5][6][7][8][9][10] anti cancer activity, [11][12][13][14][15] phosphodiesterase-IV inhibitors, [16,17] anti amoebic and anti parasitic activity, [18,19] anti depressant and analgesic activity, [20,21] anti inflammatory and analgesic activity, [22][23][24][25] anti histaminic and anti cholinergic activity, [26][27][28] anti tubercular activity, [29][30][31] anti oxidant activity, [32][33][34][35] anti convulsant activity, [36][37][38] local anaesthetic activity, [39] anti arrhythmic activity, [40,41] anti allergy activity [42] and many more. ...
... B. A. El-Gazzar (22) et al synthesized (Substituted)-6-isopropyl-3H-thieno [2,3-d]pyrimidin analogues and evaluated them for anti-inflammatory and analgesic activity using acetyl salicylic acid as standard drug. Compound (28) showed good activity compared to standard drug acetyl salicylic acid. (28) et al synthesized 5-Chloro-N-(4-methoxy-3-piperazin-1-yl-phenyl)-3-methyl-2-benzothiophene sulfonamide as potent, selective, and orally bioavailable 5-HT 6 receptor antagonist. ...
... Compound (28) showed good activity compared to standard drug acetyl salicylic acid. (28) et al synthesized 5-Chloro-N-(4-methoxy-3-piperazin-1-yl-phenyl)-3-methyl-2-benzothiophene sulfonamide as potent, selective, and orally bioavailable 5-HT 6 receptor antagonist. Compound (34) was found to be a potent orally bioavailable 5-HT 6 receptor antagonist. ...
... Among the first reported selective antagonists are Ro-04-6790 (40) reported in 1998 [82,84], SB-271046 (29) in 1999 [82,85,86] and SB-399885 (41) in 2002 [87] (see Figure 13) showed a 200-fold selectivity for the 5-HT6R. Although selective antagonists have been developed, no 5-HT6R antagonist has reached the pharmacological market to date. ...
... In phase II, Idalopirdine (55) was given to AD patients already receiving donepezil (21, an AChE inhibitor). It was found that Idalopirdine (55) provided an inhibitory effect on CYP206, which is involved in the metabolism of donepezil (21), therefore, it cannot be ruled out that the initial positive results originated from an increase in donepezil bioavailability [85]. Three Phase III studies with idalopirdine were initiated in 2013 involving patients with mild to moderate AD. ...
Alzheimer’s disease (AD) is the most common form of dementia affecting millions of people worldwide and currently, the only possible treatment is the use of symptomatic drugs. Therefore, there is a need for new and disease-modifying approaches. Among the numbers of biological targets which are today explored in order to prevent or limit the progression of AD, the modulation of serotonin receptors the subtype 4 and 6 receptors (5-HT4R and 5-HT6R) has received increasing attention and has become a promising target for improving cognition and limit the amyloid pathology through modulation of the neurotransmitter system. A large number of publications describing the development of ligands for these serotonin receptors have emerged, and their pharmaceutical potential is now quite evident. However, 5-HT4R and 5-HT6R functionality is much more complex than initially defined. This chapter describes recent advances in the understanding of this modulation as well as the medicinal chemistry efforts towards development of selective 5-HT4R or 5-HT6R ligands.
... A different pharmacokinetics of both drugs, facing to the temporal implication of glutamate transmission in memory acquisition, consolidation and/or recall should receive a specific attention. Indeed, SB-271046, that has an half-time of 4.8 h [42], has been demonstrated to increase glutamate release in the frontal cortex and hippocampus at least for approximately 4 h [17], while CGS 19755 reveals a shorter central effect with a total reversal between 2 and 4 h [37]. These pharmacokinetic data could thus explain the deleterious effect of the combination of CGS 19755 and SB-271046 for the 2 h ISI and its absence for the 4 h ISI. ...
... Indeed, drugs administered before the training session of the place recognition test could impact acquisition, early and late consolidation as well as retrieval phases of memory processes with a short (e.g. 2 h) ISI but mainly affect acquisition and early consolidation with 4 h and 6 h ISI. SB-271046 is known to improve the consolidation and/or the storage but not retrieval processes, as demonstrated in recognition paradigms [31,33] , probably because of kinetic considerations (half-time of 4.8 h [42]). However, the inhibitory effects of CGS 19755 and NFPS have a half-time of approximately 2 h and 13 h respectively [27,37] and thus could differentially impact memory phases. ...
... These compounds were synthesized by condensation of the intermediate amines 8-10 with the corresponding carboxylic acids that contain the different tags (Scheme 1). With respect to the 5-HT 6 R, we selected the ligand developed by SmithKline Beecham SB-271046 [14] (13, K i = 1.2 nm, Scheme 2) as starting point. In this case, we were able to successfully replace the benzothiophene ring by a benzophenone (compound 14, K i = 1.6 nm, Scheme 2), so we ex- Alternatively, reaction of 20 with N-[3-(3-aminobenzoyl)phenyl]biotinamide (26) yielded, after deprotection of the trichloroacetyl group, final compound 17 (Scheme 2). ...
... [c] Value from reference [14]. 76 nm]. ...
Determination of the targets of a compound remains an essential aspect in drug discovery. A complete understanding of all binding interactions is critical to recognize in advance both therapeutic effects and undesired consequences. However, the complete polypharmacology of many drugs currently in clinical development is still unknown, especially in the case of G protein-coupled receptor (GPCR) ligands. In this work we have developed a chemoproteomic platform based on the use of chemical probes to explore the target profile of a compound in biological systems. As proof of concept, this methodology has been applied to selected ligands of the therapeutically relevant serotonin 5-HT1A and 5-HT6 receptors, and we have identified and validated some of their off-targets. This approach could be extended to other drugs of interest to study the targeted proteome in disease-relevant systems.
... Les échecs répétés des composés antagonistes des récepteurs 5-HT6 ne peuvent pas être expliqués par des biais méthodologiques des études cliniques mais probablement par des propriétés pharmacocinétiques espèce-dépendantes déjà illustrées avec le SB271046 ayant une plus faible pénétration de la barrière hémato-méningée chez l'homme que chez le rat, liée aux protéines d'efflux P-gp pour lesquelles le SB271046 était un bon substrat chez l'homme (Bromidge et al., 1999). Le composé SUVN-502 présenterait un profil pharmacocinétique, toxicologique et de sécurité favorable lorsque administré une fois par jour (Nirogi et al., 2009). ...
En France, la prévalence des douleurs neuropathiques est estimée à 6,9% de la population adulte. Ces douleurs ont un impact important sur la qualité de vie du patient et sont souvent associées à des comorbidités dépressives, anxieuses, cognitives et des troubles du sommeil. La prise en charge thérapeutique des douleurs neuropathiques demeure un défi médical majeur, l'efficacité des traitements de référence (antidépresseurs (tricycliques et inhibiteurs de la recapture de la sérotonine-noradrénaline) et anti-épileptiques (gabapentine / prégabaline)) étant peu satisfaisante. Malgré le rôle majeur de la sérotonine dans la modulation de la douleur, les inhibiteurs sélectifs de la recapture de la sérotonine (ISRS) sont peu efficaces alors qu’ils exposent à moins d’effets indésirables que les antidépresseurs tricycliques. Le récepteur 5-HT 6 , connu pour ses effets dans les fonctions cognitives, a récemment émergé comme un nouvel acteur de la modulation sérotoninergique de la douleur. Outre son couplage à la protéine Gs, le récepteur 5-HT 6 est physiquement associé à des partenaires protéiques intracellulaires dont mTOR (mammalian Target Of Rapamycin), également impliquée dans la douleur neuropathique et la régulation des fonctions cognitives. Les travaux présentés ont permis de caractériser la localisation sub-cellulaire du récepteur 5-HT 6 au niveau du cil primaire de neurones présents dans les couches superficielles de la corne dorsale de la moelle épinière suggérant l’implication de cette structure dans la modulation de la douleur. L’administration d’agonistes inverses du récepteur 5-HT 6 exerce un effet antiallodynique et prévient les déficits cognitifs associés chez le rat SNL, alors que des antagonistes neutres sont dépourvus d’effets, suggérant une activité constitutive du récepteur et son implication dans l’hypersensibilité douloureuse dans ce modèle de neuropathie. De même, l’administration de rapamycine, un inhibiteur de mTOR, réduit l’allodynie tactile et les déficits cognitifs associés chez les rats SNL. Ils ont également permis de démontrer le couplage entre le récepteur 5-HT 6 et mTOR in vitro et in vivo chez le rat douloureux. Ainsi, à l’aide d’un peptide interférant s’opposant à l’interaction physique du récepteur avec mTOR, injecté par voie intrathécale, une diminution des signes douloureux et des troubles cognitifs a été observée confirmant le rôle délétère de l’interaction entre le récepteur 5-HT 6 spinal et mTOR en condition de douleur neuropathique. L’ensemble de ces résultats expérimentaux permet une meilleure compréhension du rôle du récepteur 5-HT 6 et de son partenaire mTOR dans la douleur chronique et ouvre de nouvelles perspectives dans sa prise en charge avec, notamment, le développement de nouveaux agonistes inverses du récepteur 5-HT 6.
... SB258585 has a high affinity for 5-HT6R . It is a very potent and a selective 5-HT6R antagonist that displays 160-fold selectivity over other 5-HT receptor subtypes (Bromidge et al. 1999). Daily injections of either saline (0.9% saline) or SB258585 were performed with a 30-gauge injector cannula (1 mm below the tip of the guide cannula) and a Hamilton syringe (Hamilton Laboratory Products, Switzerland). ...
Alzheimer’s disease (AD) is a neurodegenerative disorder characterized by progressive memory decline. It has been suggested that 5-hydroxytryptamine receptor 6 (5-HT6R) might be involved in AD pathology. The aim of this study was to evaluate the effect of a 5-HT6R antagonist on cognition, learning, memory, and hippocampal apoptosis in an experimental rat model of AD. AD was induced by intracerebroventricular (icv) administration of streptozotocin (STZ; 3 mg/kg, 10 μL, twice). Adult, male rats were divided into the following groups: control, sham, AD (saline treatment, 1 μL icv for 30 days), and AD + SB258585 (5-HT6R antagonist, 1 μg/μL icv for 30 days). Following the treatment period, novel object recognition (NOR) and passive avoidance learning (PAL) tests were conducted to measure cognition, as well as learning and memory, respectively. TUNEL staining was used to evaluate apoptosis in the hippocampus. This study demonstrates that icv STZ injections induce apoptosis in hippocampal cells, decrease the NOR discrimination index, increase the number of trials needed to reach acquisition and the time spent in the dark compartment during PAL, as compared with sham and control groups. Subsequent administration of SB258585 in the STZ treated rats increased the NOR discrimination index, decreased the number of trials till acquisition and the time spent in the dark compartment during PAL, while decreasing neuronal apoptosis, as compared to the untreated AD group. Thus, we conclude that long-term administration of the 5-HT6R antagonist SB258585, ameliorates AD-associated cognitive and behavioral impairments through the suppression of apoptosis in the hippocampus.
... Additionally, three HTR6 antagonists tested in our experiment were also effective at reducing Aβ generation, although they showed differences in efficacy (Fig. 2D). Interestingly, among those antagonists, two compounds entering clinical phase III trials reduced Aβ generation to a smaller extent than SB271046, which had failed in a phase I clinical trial due to its poor ability to penetrate into the CNS after systemic dosing 35,36 . Considering the recent failure of idalopirdine in a phase III clinical trial, our data suggests that the Aβ-reducing activity may be worth considering when researchers design and modify the HTR6 antagonists for the development of AD drugs. ...
Alzheimer’s disease (AD) is a major and devastating neurodegenerative disease, and the amyloid-β (Aβ) hypothesis is still the central theory for AD pathogenesis. Meanwhile, another major mental illness, depression, is one of the risk factors for AD. From a high-throughput screening (HTS), amoxapine, a typical secondary amine tricyclic antidepressant (TCA), was identified to reduce Aβ production. A follow-up investigation on antidepressants showed that most of the TCAs harbour similar activity. Previous studies have indicated that TCAs improve cognitive function in AD mouse models as well as in preliminary clinical data; however, the underlying mechanism is controversial, and the effect on Aβ is elusive. Thus, we developed a secondary screening to determine the molecular target of amoxapine, and serotonin receptor 6 (HTR6) was identified. Knockdown of HTR6 reduced the amoxapine’s effect, while the HTR6 antagonist SB258585 mimicked the activity of amoxapine. Further mechanistic study showed that amoxapine and SB258585 reduced Aβ generation through multiple HTR6-mediated targets, including β-arrestin2 and CDK5. Taken together, our study suggests that amoxapine, though no longer a first-line drug for the treatment of depression, may be beneficial for AD and further structural modification of TCAs may lead to desirable therapeutic agents to treat both AD and depression.
... As 5HT 6 R antago nists remain the most studied and promising ligands in this therapeutic area, this chapter will concentrate on them. Ro 630563 11 [59] and SB271046 12 [60], pre senting a bisarylsulfonamide scaffold, were the first antagonists for the 5HT 6 R described in the late 1990s identified by highthroughput screening at Roche (Basel, Switzerland) and GlaxoSmithKline (Essex, UK) (Figure 7). More than a chemical tool, SB271046 was the first 5HT 6 R antagonist to enter Phase I clini cal development for the treatment of cognitive impair ment in AD. ...
Alzheimer's disease (AD) is the most common form of dementia affecting millions of patients worldwide which can only be treated with symptomatic drugs. Among the numbers of biological targets which are today explored in order to prevent or limit the progression of AD, the modulation of 5-HT6R and 5-HT4R appeared to be promising. This modulation has been proved to enhance the cognition in AD through modulation of the neurotransmitter system but could also be beneficial in order to limit the amyloid pathology. This review will describe recent advances in the understanding of this modulation as well as the medicinal chemistry of 5-HT6R or 5-HT4R ligands from synthesis to ongoing clinical trials.
... According to the literature, the first described antagonist, Ro 04-6790 (Hoyer et al. 2002), was identified in the late 1990s at Roche (Sleight et al. 1998;Leng et al. 2003). The first candidate for clinical development was the phenyl-piperazine SB-271046 (Russell & Dias 2002), which was developed by Glaxo Smith Kline and entered Phase 1 trials, but was discontinued (Bromidge et al. 1999). Several other compounds have entered clinical trials, such as SB-742457 (Kohen et al. 1996) and LY-483518 (Bourson et al. 1995), for the treatment of the cognitive dysfunction associated with Alzheimer's disease or of the cognitive impairment associated with schizophrenia. ...
This study aims to screen and identify the multi-mechanism antistress effects of an extract of Hippophae rhamnoides L. (HR) leaves on corticosterone (CORT)-induced injury, N-methyl-d-aspartate (NMDA) receptor and serotonin 6 (5-hydroxytryptamine 6, 5-HT6) receptor activity tests (in vitro), electric foot shock and forced swimming tests (FSTs) (in vivo), and tests for hippocampal CORT and monoamine levels (ex vivo), in search of active principles and underlying mechanisms of action. We confirmed that the water extract of HR (HRW) and various ethanol extracts of HR confer protective effects against CORT-induced impairments in SH-SY5Y cells and antagonistic effects on NMDA receptors and the 5-HT6 receptor by using primary cultured rat hippocampal neurons and a stable 5-HT6 receptor-expressing cell line, respectively. In addition, we confirmed the antistress effects of HRW in an electric foot shock stress model in mice and explored the underlying mechanisms of its action. We observed that HRW treatment significantly reversed the reduction in immobility times and increased climbing times in FSTs induced by electric foot shocks in the stress model. The levels of CORT, dopamine, and norepinephrine were increased, and the level of serotonin in the hippocampus was decreased in the electric foot shock stress model. The standardized HRW effectively restored abnormal CORT and monoamine levels in the hippocampus that were induced by stress. The results of the present study demonstrate that the standardized HRW produces novel multifunctional antistress effects.
... During this decade or so, there was a plenty of chemistry developed around different nuclei including the indole-based ones or even much simpler biphenyl sulfones and sulfonamides [16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33]34 ( Figure 2). Suven has reported several series of 1-sulfonylindoles bearing the amino group at 3 or 4 or 5 position of the central core [31][32][33] . ...
A series of 1-[3-(4-methyl piperazin-1-ylmethyl) phenylsulfonyl]-1H-indole and 1-[3-(4-ethyl piperazin-1-ylmethyl) phenylsulfonyl]-1H-indole derivatives were designed and synthesized as 5-HT6 receptor (5-HT6R) ligands. The lead compound 1-[4-methyl-3-(4-methyl piperazin-1-yl methyl) phenylsulfonyl]-1H-indole dihydrochloride (6b), in this series, has shown potent in vitro binding affinity, selectivity, good pharmacokinetics (PK) profile and activity in the animal models of cognition.
... Soon after the cloning of the receptor several antipsychotic and antidepressant drugs such as bromocriptine, clozapine, olanzapine, chlorpromazine, etc. were found to bind to it with moderate activity [19]. The first selective 5-HT 6 R antagonists were identified in the late 1990s by Roche and GlaxoSmithKline [20,21]. Since then hundreds of selective ligands have been identified, most of which contain a basic amine moiety positively charged at physiological pH and are based on bisaryl sulfone or sulfonamide scaffolds [16]. ...
In order to identify molecular models of the human 5-HT6 receptor suitable for virtual screening, homology modeling and membrane-embedded molecular dynamics simulations were performed. Structural requirements for robust enrichment were assessed by an unbiased chemometric analysis of enrichments from retrospective virtual screening studies. The two main structural features affecting enrichment are the outward movement of the second extracellular loop and the formation of a hydrophobic cavity deep in the binding site. These features appear transiently in the trajectories and furthermore the stretches of uniformly high enrichment may only last 4-10 ps. The formation of the inner hydrophobic cavity was also linked to the active-like to inactive-like transition of the receptor, especially the so-called connector region. The best structural models provided significant and robust enrichment over three independent ligand sets.
Herein, A series of novel 1-((4-methoxy-3-(piperazin-1-yl)phenyl)sulfonyl)- 1H-indole derivative were designed and synthesized via hybridization strategy of idalopirdine and SB-271046. The optimal compound C14 (Ki = 0.085 nM), with difluoromethyl on C3 position on indole scaffold, increased the affinity for the 5-HT6R up to 10-folds than idalopirdine (Ki = 0.83 nM). Additionally, C14 had good pharmacokinetic properties and in vitro metabolic properties. Finally, C14 could efficiently reverse the scopolamine induced emotional memory deficits in novel object recognition assay in rats. Thus, we propose C14 might be considered as a new cognition-enhancing agent and the further studies are now underway in our laboratory.
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.
Whereas the potential role of serotonin for the pathophysiology of irritable bowel syndrome (IBS) has since long been discussed, the possibility that 5-hydroxytryptamine 6 (5-HT6) receptors may serve as targets for the treatment of this condition has as yet not been explored. The aim of the current study was to assess to what extent defecation in rats is influenced by manipulation of 5-HT6 receptors. Reduced defecation following SB-399885 was observed in non-stressed animals assessed for 7 h after drug administration. While not impacting context-conditioned freezing, three 5-HT6 receptor antagonists (SB-399885, SB-271046 and SB-258585) also markedly reduced the number of faecal boli produced by rats exposed to context-conditioned fear. In contrast, a 5-HT6 receptor agonist, WAY-208466, influenced defecation neither in unstressed animals nor in rats experiencing conditioned fear stress. A clinical study on the possible effect of a 5-HT6 receptor antagonist in IBS with diarrhea appears warranted.
Monitor provides an insight into the latest developments in drug discovery through brief synopses of recent presentations and publications together with expert commentaries on the latest technologies. There are two sections: Molecules summarizes the chemistry and the pharmacological significance and biological relevance of new molecules reported in the literature and on the conference scene; Profiles offers commentary on promising lines of research, emerging molecular targets, novel technology, advances in synthetic and separation techniques and legislative issues.
The 5-hydroxytryptamine receptor 6 (5-HT6R) represents one of the most avowed targets for alleviating cognitive, learning, and memory deficits related to Alzheimer’s disease (AD). Ligand- and structure-based computational modeling methods serve as main tools at the initial stages of drug discovery projects to underlie and to understand small molecule targeting of the receptor. Here, we describe the currently known 5-HT6R antagonists in clinical trials and at discovery stages. We analyze existing ligand-based information and disposable pharmacophore models, quantitative structure-activity relationship methods, usable crystal structure templates, homology models, and molecular docking approaches. Our goal is to provide the reader with guidelines on how to utilize the existing knowledge and ligand- and structure-based methods for the design of new 5-HT6R antagonists and to highlight advantages and limitations of corresponding approaches and computational modeling tools in the field of 5-HT6R drug design.
We describe here the synthesis, antioxidant capacity, and biological activities on MAO, ChE, and selected GPCRs, of novel 1-(2,5-dimethoxybenzyl)-4-arylpiperazines 1–10, as well as known N-(2-(2-methyl-5-nitro-1H-imidazol-1-yl))-2-(4-arylpiperazin-1-yl) 11–20 and N-(5-nitrothiazol-2-yl)-2-(4-arylpiperazin-1-yl) 21–29. Some of the new 4-arylpiperazines were found to have low-micromolar affinities for the proteins tested. The most potent MAO inhibitor identified was compound 2-(4-(3-fluorophenyl)-yl)-N-(5-nitrothiazol-2-yl)(27), with an IC50 value of 4.14 ± 0.5 μM, whereas the most potent interaction with a GPCR was 1-(2,5-dimethoxybenzyl)-4-(4-trifluoromethylphenyl) (5) for the 5-HT6 serotonin receptor, with a Ki value of 0.7 μM. Interestingly, some of the compounds described here showed impressive antioxidant potential. Of mention, compounds 1, 6, 7, and 23 had trolox/equivalent ORAC values of 9.10, 8.80, 8.82, and 9.42, respectively, all of them being significantly higher than the TE determined for ferulic acid (3.74), a standard antioxidant. Among all molecules synthesized and tested, compound 23 can be regarded as an interesting low-micromolar MAO−B/5-HT6 dual inhibitor lead with potent antioxidant properties.
The work describes a discovery of new chemical family of potent ligands for the 5-HT6 serotonin receptors. During the search for new histamine H4 receptor antagonists among 1,3,5-triazine derivatives, compound 2 (4-benzyl-6-(4-methylpiperazin-1-yl)-1,3,5-triazin-2-amine) was found. Compound 2, weakly active for the H4 receptor but fitted in 3/4 of pharmacophore features of the 5-HT6R ligand, occurred to be a moderate 5-HT6R agent, useful as a lead structure for further modifications. A series of new derivatives (3–19) of the lead 2 was synthesized, evaluated in the radioligand binding assay (RBA) and explored in comprehensive molecular modelling, including both pharmacophore- and structure-based approaches with docking to the homology model of 5-HT6R. The most active compounds displayed a potent affinity for the 5-HT6R in the nanomolar range (Ki = 20–30 nM), some of them (4, 11 and 19) were tested in the rat forced swim test that revealed their antidepressant-like effect. SAR-analysis on the basis of both, RBA and docking results, indicated that action on the receptor is related to the hydrophobicity and the size of aromatic moiety substituted by a methylene linker at the position 4 of 1,3,5-triazine.
A facile protocol for synthesis of naphth-annulated thiophenes has been developed via benzo-DMTHFs/triflic acid-mediated annulation of thiophenes. Furthermore, this methodology was found to be successful with substituted benzo-DMTHFs as well as higher homologues of benzo-DMTHF.
Meta-C−H amination and meta-C−H alkynylation using a modified norbornene (methyl bicyclo[2.2.1]hept-2-ene-2-carboxylate) as a transient mediator has been developed for the first time. Both the identification of a mono-protected 3-amino-2-hydroxypyridine/pyridone type ligand and the use of methyl bicyclo[2.2.1]hept-2-ene-2-carboxylate as the mediator are crucial for realizing these two unprecedented meta-C−H transformations. A variety of substrates are compatible with both meta-C–H amination and meta-C–H alkynylation. Amination and alkynylation of heterocyclic substrates including indole, indoline, and indazole afford the desired products in moderate to high yields.
As a group of G protein-coupled receptors (GPCRs) and ligandgated ion channels (LGICs), the serotonin (5-HT) receptors are found in the central and peripheral nervous systems. After activated by the neurotransmitter serotonin, their natural ligand, 5-HT receptors mediate both excitatory and inhibitory neurotransmission by modulating the release of many neurotransmitters, including glutamate, GABA, dopamine, epinephrine/norepinephrine, and acetylcholine, as well as many hormones, including oxytocin, prolactin, vasopressin, cortisol, corticotropin, and substance P, among others. 5-HT receptors influence various biological and neurological processes such as aggression, anxiety, appetite, cognition, learning, memory, mood, nausea, sleep, and thermoregulation. Accordingly, 5-HT receptors are the target of a variety of pharmaceutical drugs, including many antidepressants, antipsychotics, anorectics, antiemetics, gastroprokinetic agents, antimigraine agents, hallucinogens, and entactogens. In order to help the potential readers to understand the complicated network of 5-HT receptors, here we try to summarize the comprehensive information on 5-HT receptors in a concise summary with detailed references, which may help the readers for further information excavation.
Within the past decade several novel targets have been indicated as key players in Alzheimer-type dementia and associated conditions, including a 'frightening' memory loss as well as severe cognitive impairments. These proteins are deeply implicated in crucial cell processes e.g. autophagy, growth and progression, apoptosis and metabolic equilibrium. Since recently, 5-HT6R has been considered as one of the most prominent biological targets in AD chemotherapy. Therefore, we investigated the potential pro-cognitive and neuroprotective effects of our novel selective 5-HT6R antagonist, AVN-211. During an extensive preclinical evaluation the lead compound demonstrated a relatively high therapeutic potential and absolutely the best selectivity as compared to reference drug candidates. It was thoroughly examined in different in vivo behavioral models directly related to AD and showed evident improvements in cognition and learning. In many cases, the observed effect was considerably greater than that determined for the reported drug molecules, including memantine, SB-742457 and PRX-07034, evaluated under the same conditions. In addition, AVN-211 showed a similar or better anxiolytic efficacy than fenobam, rufinamide, lorazepam and buspirone in an elevated plus-maze model, elevated platform and open field tests. The compound demonstrated low toxicity and side effects in vivo, an appropriate pharmacokinetic profile as well as stability. In conclusion, AVN-211 significantly delayed or partially halted the progressive decline in memory function associated with AD that makes it an attractive drug candidate for the treatment of neurodegenerative and psychiatric disorders. The advanced clinical trials following the title indication is currently under active discussion and in high priority.
The human brain is a uniquely complex organ, which has evolved a sophisticated protection system to avoid injury from external insults and toxins. Penetrating the blood-brain barrier (BBB) to achieve the drug concentrations required for efficacious target receptor occupancy in the brain region of interest is a unique and significant challenge facing medicinal chemists working on CNS targets. Prospective design of molecules with optimal brain exposure and safety profile requires in-depth understanding of the fundamental relationships between physicochemical properties and in vitro and in vivo outcomes. Following from the now widely accepted “rule of five” guidelines for the design of oral drugs, the physicochemical properties for brain penetration have been extensively studied in an effort to define the characteristics of successful CNS drug candidates. Several key physicochemical properties have been identified that influence the rate of brain permeability and extent of brain penetration, including H-bonding potential, molecular weight, lipophilicity, polar surface area (PSA), ionization state and rotatable bond count. The ability to process this information effectively and engage in multi-parameter prospective design ultimately determines the success in delivering high-quality drug candidates that are suitable robustly to test hypotheses in the clinic and have good probability of reaching the market. This chapter focuses on the medicinal chemistry aspects of drug candidate optimization particular to the CNS therapeutic area, such as crossing the blood-brain barrier (BBB), as well as safety-related issues frequently challenging CNS programs such as hERG selectivity and phospholipidosis.
The great majority of CNS drugs are small molecules that are designed to cross the blood–brain barrier (BBB) via the transcellular passive diffusion route. Achieving optimal brain exposure is a unique and major challenge for medicinal chemists working on the CNS targets. Design strategies toward such molecules and their physicochemical properties are the main foci of this chapter. The existence of the BBB renders classic pharmacokinetic (PK) parameters, such as oral bioavailability and plasma concentration, insufficient for assessing CNS drug candidates due to uncertainty regarding whether such parameters will reflect the time course or exposure levels in the brain. Several key physicochemical properties have been identified that influence the rate of brain permeability and the extent of brain penetration including H-bonding potential, molecular weights (MWs), lipophilicity, polar surface area (PSA), ionization state, and rotatable bond count.
It is often necessary to make changes in an active molecule. Indeed, the evolution of a hit to a lead or a lead to a preclinical candidate frequently requires adjustment. In addition to the activity and selectivity, one may have to modify some physicochemical parameters such as solubility, lipophilicity, or overcome unwanted interactions (hERG, CYP's ...), increase metabolic stability, and even adapt more specific parameters. It is possible, to some extent, to predict the impact that the introduction of certain substituents could have on some of these parameters and thus to perform more accurate research. The purpose of this chapter is to give information about the changes observed on the solubility, conformation, metabolism, bioavailability, toxicity ... when halogen, methyl groups, hydroxyl, acid or basic functions are introduced, thanks to concrete examples from the literature.
The first enantioselective epoxidation of readily available alkylidenemalononitriles has been developed by using a multifunctional cinchona derived thiourea as the organocatalyst and cumyl hydroperoxide as the oxidant. A new simple one-pot asymmetric epoxidation/SN2 ring-opening reaction with 1,2-diamines leading to important enantioenriched heterocycles, i.e. 3-substituted piperazin-2-ones, has been established.
N1-Benzenesulfonyl-5-methoxy-N,N-dimethyltryptamine (BS/5-OMe DMT, 2; Ki = 2.1 nM) binds at 5-HT6 receptors with enhanced affinity relative to 5-OMe DMT (Ki = 77 nM). The role of the benzenesulfonyl group was examined by replacing the sulfoxide portion with a methylene group or a carbonyl group, or by its complete elimination. Several different indole 2- and 5-positions substituents were also explored to a limited degree. Although the effect of N1 modifications are seemingly dependent upon other substituents present in the molecule, the N1-benzenesulfonyl moiety is generally optimal with respect to affinity enhancement.
It is widely recognized that cognitive dysfunction is among the most debilitating symptoms of many neuropsychiatric disorders, including Alzheimer's disease and schizophrenia. Accordingly, there is a critical need for new drugs with procognitive activity. Recently, the role of the neurotransmitter serotonin (5-HT) and its receptor subtypes in cognition has emerged, and as a result, the focus on 5-HT receptor subtypes as targets for memory enhancement has increased. Among the 5-HT subtypes, the 5-HT6 receptor may be a particularly attractive target given its almost exclusive localization in the brain and its expression in both limbic areas and other brain regions known to be critical to cognition. Novel ligands with selective affinity for 5-HT 6 receptors would be predicted to have a low incidence of peripheral side effects and to potentially address both cognitive and noncognitive symptoms (e.g., anxiety, depression) of neuropsychiatric disorders. To date, several preclinical studies of 5-HT6 antagonists in rodent models have indeed provided evidence of cognitive enhancement (especially in aged and pharmacologically impaired rats), as well as anxiolytic and antidepressant effects. Accordingly, several 5-HT6 antagonists are currently in clinical trials for the treatment of neuropsychiatric disorders. The purpose of this review is to provide a brief overview of the 5-HT6-related pharmacological approaches designed to enhance memory function. Copyright © 2009 Prous Science, S.A.U. or its licensors. All rights reserved.
The serotonin 5-HT6 receptor (5- HT6R) is amongst the recently discovered serotonergic receptors with almost exclusive localization in the brain. Hence, this receptor is fast emerging as a promising target for cognition enhancement in central nervous system (CNS) diseases such as Alzheimer's disease (cognitive function), obesity, schizophrenia and anxiety. The last decade has seen a surge of literature reports on the functional role of this receptor in learning and memory processes and investigations related to the chemistry and pharmacology of 5-HT6 receptor ligands, especially 5-HT6 receptor antagonists. Studies show the involvement of multiple neurotransmitter systems in cognitive enhancement by 5-HT6R antagonists including cholinergic, glutamatergic, and GABAergic systems. Several of the 5-HT6R ligands are indole based agents bearing structural similarity to the endogenous neurotransmitter serotonin. Based on the pharmacophoric models proposed for these agents, drug designing has been carried out incorporating various heterocyclic replacements for the indole nucleus. In this review, we have broadly summarized the medicinal chemistry and current status of this fairly recent class of drugs along with their potential therapeutic applications.
Rapid in silico selection of target focused libraries from commercial repositories is an attractive and cost effective approach. If structures of active compounds are available rapid 2D similarity search can be performed on multimillion compound databases but the generated library requires further focusing. We report here a combination of the 2D approach with pharmacophore matching which was used for selecting 5-HT6 antagonists. In the first screening round 12 compounds showed > 85% antagonist efficacy out of the 91 screened. For the second round (hit validation) screening phase pharmacophore models were built, applied and compared with the routine 2D similarity search. Three pharmacophore models were created based on the structure of the reference compounds and the 1st round hit compounds. The pharmacophore search resulted in a high hit rate (40%) and led to novel chemotypes, while 2D similarity search had slightly better hit rate (51%), but lacking the novelty. In order to demonstrate the power of the virtual screening cascade ligand efficiency indices were also calculated and their steady improvement was confirmed. This article is protected by copyright. All rights reserved.
This article is protected by copyright. All rights reserved.
A novel domino annulation strategy for the construction of benzo[b]thiophenes has been developed. In the presence of Cs2CO3 and Ag2CO3, a wide range of α-alkenoyl-α-alkynyl ketene dithioacetals readily react with cyanoacetates in CH3CN at 110 °C under N2 to afford multisubstituted benzo[b]thiophenes efficiently via tandem thien- and benzannulations. A plausible mechanism is also proposed.
The serotonin-6 (5-HT6) receptor is the most recently discovered serotonin receptor, and it represents an increasingly promising target for improving cognition in both normal and disease states. Recently, a new selective 5-HT6 receptor agonist, 2-(5 chloro-2-methyl-1H-indol-3-yl)-N,N-dimethylethanamine (ST1936), with nanomolar affinity for 5-HT6 receptors was described. We performed in-vivo electrophysiological studies to investigate the physiological role of 5-HT6 receptors in the control of the function of the substantia nigra pars compacta (SNc) and ventral tegmental area (VTA). Extracellular single-unit recordings were performed from putative dopamine-containing neurons in the SNc and VTA of anesthetised rats. In the SNc, acute systemic administration of ST1936 had no effects on basal firing activity of these dopamine neurons; however, in the VTA, ST1936 induced either dose-related increases (45% of cells) or decreases in basal activity of these dopaminergic neurons. Local application of ST1936 into the VTA caused excitation in all of the dopamine neurons, but had no effects on non-dopamine VTA neurons. Both effects of systemic and microiontophoretic ST1936 were completely reversed by the potent and selective 5-HT6 receptor antagonist 5-chloro-N-(4-methoxy-3-piperazin-1-ylphenyl)-3-methyl-2- benzothiophene-sulfonamide (SB271046). Systemic application of another 5-HT6 agonist, 2-(1-{6-chloroimidazo[2,1-b] [1,3]thiazole-5-sulfonyl}-1H-indol-3-yl)ethan-1-amine (WAY-181187), induced dose-dependent inhibition of these VTA dopaminergic neurons. ST1936 and WAY-181187 appear to have different effects on these VTA dopaminergic neurons, potentially due to different mechanisms of action or to the complexity of 5-HT6 receptor functions. Our data demonstrate the need for further investigations into the use of 5-HT6 receptor agonists to control cognitive disfunction, such as in schizophrenia and depression.
© The Author(s) 2015.
Enantiomerically-enriched trichloromethyl-containing alcohols, obtained by asymmetric reduction, can be transformed regioselectively into 1-substituted piperazinones by modified Jocic reactions with little or no loss of stereochemical integrity. This methodology can be easily used to synthesise important pharmaceutical compounds such as the fluorobenzyl intermediate of a known PGGTase-I inhibitor.
Fluorescent GPCR Ligands as New Tools in Pharmacology - update, years 2008- early 2014 The robust of fluorescent techniques to study the ligand-receptor interaction followed by rapidly developing fluorescence imaging techniques resulted in a burst of the novel fluorescent ligands development. Taking into consideration not only ligand's high affinity to the receptor, but also their fluorescent properties to visualize the interaction even in the single cell level, gives the researchers a strong impulse to investigate that field of GPCR ligands. Moreover, paying attention to the "non pharmacological" advantages of these ligands, as well as the techniques to be used, fluorescent ligands become commonly used pharmacological tools to study GPCRs. Herein we report on the results described in the literature since late 2007 in the field of the fluorescent GPCR small, non-peptide ligands according the receptor affinity, fluorophores that has been used to tag the molecules and their fluorescent properties as well as their application in GPCR research.
Alzheimer's disease (AD) is one of the most frequent causes of death and disability worldwide and has a significant clinical and socio-economic impact. In the search for novel therapeutic strategies, serotonin 5-HT6 receptor (5-HT6R) has been proposed as a promising drug target for cognition enhancement in AD. This perspective reviews the compelling evidence for the implication of this receptor in learning and memory processes. We have summarized the current status of the medicinal chemistry of 5-HT6R antagonists and the encouraging preclinical findings that demonstrate their significant pro-cognitive behavioral effects in a number of learning paradigms, probably acting through modulation of multiple neurotransmitter systems and signaling pathways. The results of the ongoing clinical trials are eagerly awaited to shed some light on the validation of 5-HT6R antagonists as a new drug class for the treatment of symptomatic cognitive impairment in AD, either as stand-alone therapy or in combination with established agents.
The Concise Guide to PHARMACOLOGY 2013/14 provides concise overviews of the key properties of over 2000 human drug targets with their pharmacology, plus links to an open access knowledgebase of drug targets and their ligands (www.guidetopharmacology.org), which provides more detailed views of target and ligand properties. The full contents can be found at http://onlinelibrary.wiley.com/doi/10.1111/bph.12444/full.
G protein-coupled receptors are one of the seven major pharmacological targets into which the Guide is divided, with the others being G protein-coupled receptors, ligand-gated ion channels, ion channels, catalytic receptors, nuclear hormone receptors, transporters and enzymes. These are presented with nomenclature guidance and summary information on the best available pharmacological tools, alongside key references and suggestions for further reading. A new landscape format has easy to use tables comparing related targets.
It is a condensed version of material contemporary to late 2013, which is presented in greater detail and constantly updated on the website www.guidetopharmacology.org, superseding data presented in previous Guides to Receptors and Channels. It is produced in conjunction with NC-IUPHAR and provides the official IUPHAR classification and nomenclature for human drug targets, where appropriate. It consolidates information previously curated and displayed separately in IUPHAR-DB and the Guide to Receptors and Channels, providing a permanent, citable, point-in-time record that will survive database updates.
High-throughput screening of a specific set (focused library) of heterocyclic compounds containing an alkylsulfonyl moiety (a total of 2827 compounds from 78 combinatorial libraries) was performed in order to discover highly effective 5-HT6 receptor antagonists. The screening identified several compounds that exhibited pronounced inhibiting properties for 5-HT6 receptors that enabled them to be used to develop new highly effective drugs for treating central nervous system disturbances. The structures of most antagonists corresponded to the PhM2 pharmacophore model, which confirmed its potential in the search for effective 5-HT6 receptor antagonists. It was established that the structure of the substituent introduced in the vicinity of the sulfonyl moiety in the PhM2 ligands could affect their pharmacological activity, including the ability to block serotonin-induced 5-HT6 receptor-mediated cell responses. In particular, bulky electron-donating substituents decreased the activity whereas a methylamino group increased statistically significantly the 5-HT6 antagonistic activity. Based on these findings, a new pharmacophore model for 5-HT6 antagonists, PhM3, was proposed. It was shown that compounds from the combinatorial libraries with a sulfonyl moiety separated from the heterocyclic and/or aromatic moiety by one (or more) methylenes and heterocyclic compounds containing an alkylsulfonyl moiety or endocyclic sulfonyl, (5-aryl-sulfonyl-3H-[1,2,3]triazol-4-yl)amines, and azoles substituted simultaneously by arylsulfonyl and alkylsulfonyl moieties all had low hit rates and were not promising for discovery of new 5-HT6 receptor antagonists.
In the present study we determined the role of spinal 5-hydroxytriptamine (5-HT) and 5-HT4/6/7 receptors in the long-term secondary mechanical allodynia and hyperalgesia induced by formalin in the rat. Formalin produced acute nociceptive behaviors (flinching and licking/lifting) followed by long-term secondary mechanical allodynia and hyperalgesia in both paws. In addition, formalin increased the tissue content of 5-HT in the ipsilateral, but not contralateral, dorsal part of the spinal cord compared to control animals. Intrathecal (i.t.) administration of 5,7-dihydroxytriptamine (5,7-DHT), a serotonergic neurotoxin, diminished tissue 5-HT content in the ipsilateral and contralateral dorsal parts of the spinal cord. Accordingly, i.t. 5,7-DHT prevented formalin-induced secondary allodynia and hyperalgesia in both paws. I.t. pre-treatment (−10 min) with ML-10302 (5-HT4 agonist), EMD-386088 (5-HT6 agonist) and LP-12 (5-HT7 agonist) significantly increased secondary mechanical allodynia and hyperalgesia in both paws. In contrast, i.t. pre-treatment (−20 min) with GR-125487 (5-HT4 antagonist), SB-258585 (5-HT6 antagonist) and SB-269970 (5-HT7 antagonist) significantly prevented formalin-induced long-term effects in both paws. In addition, these antagonists prevented the pro-nociceptive effect of ML-10302, EMD-386088 and LP-12, respectively. The i.t. post-treatment (6 days after formalin injection) with GR-125487, SB-258585 and SB-269970 reversed formalin-induced secondary allodynia and hyperalgesia in both paws. These results suggest that spinal 5-HT, released from the serotonergic projections in response to formalin injection, activates pre- or post-synaptic 5-HT4/6/7 receptors at the dorsal root ganglion/spinal cord promoting the development and maintenance of secondary allodynia and hyperalgesia.
Rapidly aSSembled: The combination of cobalt-catalyzed migratory arylzincation and copper-mediated/catalyzed chalcogenative cyclization allows the construction of benzothiophenes and benzoselenophenes from arylzinc reagents, alkynes, and elemental chalcogens. Benzothiophenes and benzoselenophenes diversely functionalized at the benzene ring moiety can be prepared, which are not readily accessible by conventional methods.
This chapter describes recent approaches to novel antidepressant therapy. Three basic improvements in antidepressant therapy; faster onset of action, improved efficacy in refractory patients, and an improved side-effect profile, remain the primary targets for new antidepressant research. Selective serotonin reuptake inhibitors (SSRIs) have been available since the 1980s for the treatment of depression. The most widely known SSRls are fluoxetine, sertraline, paroxetine, fluvoxamine, and citalopram. SSRIs possess a favorable side-effect profile relative to classical tricyclic antidepressants (TCAs). They are generally not more efficacious than the TCAs. In addition, they exhibit a marked delay in onset of antidepressant action, and are accompanied by their own particular set of side effects resulting from the non-selective stimulation of serotonergic receptor sites. The chapter highlights significant results in recent efforts to develop new pharmaceutical agents that could constitute a new generation of antidepressant therapy and discusses concepts related to monoamine reuptake inhibitors. A discussion on SSRIs is presented. Norepineohrine reuptake inhibitors are elaborated. Serotonin receptor ligands are discussed and other monoaminergic receptor ligands are described. Nonmonoaminergic receptor approaches are reviewed. Details of Hypericum and Mesembrine are also provided in the chapter.
Publisher Summary This chapter discusses the biology and medicinal chemistry of 5-HT 5A , 5-HT 6 and 5-HT 7 receptors. The cloning of the 5-HT 5 , 5-HT 6 and 5-HT 7 receptors has led to an increased research towards the development of selective agonists and antagonists. For example, the identification of the selective 5-HT 5A antagonist 1 should provide much needed insight into the role of the 5-HT 5A receptor in CNS-mediated processes. The variety and number of 5-HT 6 agonists and antagonists in clinical development for obesity or cognitive disorders is representative of a large research effort from numerous pharmaceutical and academic laboratories. While there is no 5-HT 7 antagonist or agonist reported to be in clinical development, the diversity of structures reported for this receptor indicates continued interest in the development of selective 5-HT 7 receptor ligands with suitable drug-like properties for pre-clinical validation.
Sulfonamide-focused compound libraries have been synthesized in our laboratories for biological evaluation using antitumor phenotypic screens such as cancer cell proliferation assay, flow cytometric cell cycle analysis, and rat aorta tube formation assay. Among thousands of sulfonamide compounds evaluated, E7010 (a microtubule depolymerizing agent), E7070 (a G1 phase cell cycle inhibitor), and E7820 (an antian-giogenesis agent) have progressed to clinical trials, thereby demonstrating some objective responses in cancer patients so far. The sequential discovery of these drug candidates allowed us to carry out a research approach of forward chemical genetics, in which phenotypically bioactive compounds are selected from a large collection of small molecules and then utilized for understanding the functions of their protein partners and relevant biological pathways via target identification. This paper describes our attempt using oligonucleotide microarray and quantitative proteomic analyses not only for identifying drug targets and downstream pathways applicable to biomarkers but also for exploring druggable chemical space in medicinal chemistry research.
The exclusive distribution of 5-HT6 receptors in the brain regions associated with learning and memory makes it an ideal target for cognitive disorders. A novel series of 5-piperazinyl methyl-N 1-aryl sulfonyl indoles were designed and synthesized as 5-HT6R ligands. Most of the synthesized compounds are potent when tested by in vitro radioligand binding assay. The lead compound from the series does not have the CYP liabilities and is active in an animal model of cognition.
This chapter summarizes the recent advances in identifying potent and selective serotonin receptor ligands. A multitude of non-selective ligands for the various serotonin and other monamine receptors have been identified in the past, some of which have found clinical use. Selective serotonin receptor modulators have been the focus of many research groups. The advances in molecular biology coupled with the advent of high throughput synthesis and progress seen in asymmetric chemistry in the last decade have given rise to a multitude of novel selective serotonin subtype ligands. Utilization of these agents is expected to enable a greater understanding of serotonin's role in the pathophysiology of various disease states. The increased focus on central nervous system (CNS) therapeutics, and serotonin mediated pathways in particular, is expected to fuel the progress of this research. The manifest goal of this effort is to develop selective serotonin therapeutics that holds improvements over current non-selective serotonergic agents with respect to efficacy, side-effect profile and safety margin.
3-Iodoindoles, 5-bromo-3-iodoindoles and 5-bromo-3-iodoindazoles have been studied with respect to their reactivity and selectivity in palladium catalyzed Sonogashira and Suzuki cross-coupling reactions. As a result, sequential Sonogashira-Sonogashira, Sonogashira-Suzuki, and Suzuki-Sonogashira reactions with 5-bromo-3-iodoindoles or indazoles were used to obtain a large range of new functionalized indoles and indazoles, which are potential 5-HT receptor ligands.
The purpose of the present study was to determine possible physiological functions of the 5-ht6 receptor using antisense oligonucleotides (AOs) in male rats. Repeated intracerebroventricular treatment with AOs but not with a scrambled form of the antisense sequence (SO) gave rise to a specific behavioral syndrome of yawning, stretching and chewing and caused a 30% reduction in the number of [3H]-lysergic acid diethylamide binding sites (measured in the presence of 300 nM spiperone). Neither sequence, however, had any effect on other parameters measured (e.g., locomotor activity, body weight, food intake, body temperature and nociception). The specific behavioral syndrome did not appear to be caused by modulation of dopaminergic neurotransmission since no changes in the tissue levels of either dopamine or its metabolites 3,4-dihydroxyphenylacetic acid and homovanillic acid were seen. Furthermore, haloperidol (0.03 mg/kg s.c.) did not reduce the number of yawns or stretches. An increase in cholinergic neurotransmission did appear to be involved since the behavioral syndrome was dose-dependently antagonized by atropine. The present study suggests that 5-ht6 receptors are functionally expressed in the rat brain, where one of their functions appears to be the control of cholinergic neurotransmission.
1. The potential of ketoconazole and sulphaphenazole to inhibit specific P450 enzyme activities (1A2, 2A6, 2B6, 2C9/8, 2C19, 2D6, 2E1, 3A and 4A) was investigated using human liver microsomes. 2. Ketoconazole demonstrated an inhibitory effect on cyclosporine oxidase and testosterone 6 beta-hydroxylase activities, with mean IC50's of 0.19 and 0.22 microM respectively. Ketoconazole inhibition of the other P450 activities investigated was significantly less, as illustrated by IC50's of at least a magnitude higher. 3. Sulphaphenazole was shown to have an inhibitory effect on tolbutamide hydroxylase activity, with a mean IC50 of 0.8 microM in incubations containing 100 microM tolbutamide. Sulphaphenazole (at concentrations of up to 100 microM) did not exhibit any significant inhibition of the other enzyme activities investigated. 4. Ketoconazole and sulphaphenazole are the respective selective inhibitors of P4503A and 2C9. Ketoconazole at 1 microM and sulphaphenazole at 10 microM can be used to establish the involvement of P4503A and 2C9 respectively in oxidative reactions in human liver microsomes.
We have used the polymerase chain reaction technique to selectively amplify a guanine nucleotide-binding protein-coupled receptor cDNA sequence from rat striatal mRNA that exhibits high homology to previously cloned serotonin receptors. Sequencing of a full length clone isolated from a rat striatal cDNA library revealed an open reading frame of 1311 base pairs, encoding a 437-residue protein with seven hydrophobic regions. Within these hydrophobic regions, this receptor was found to be 41-36% identical to the following serotonin [5-hydroxytryptamine (5-HT)] receptors: 5-HT2 > 5-HT1D > 5-HT1C > 5-HT1B > 5-HT1A > 5-HT1E. Northern blots revealed a approximately 4.2-kilobase transcript localized in various brain regions, with the following rank order of abundance: striatum > olfactory tubercle > cerebral cortex > hippocampus. Expression of this clone in COS-7 cells resulted in the appearance of high affinity, saturable binding of (+)-[2-125I] iodolysergic acid diethylamide ([125I]LSD) with a Kd of 1.26 nM. Among endogenous biogenic amines, only 5-HT completely inhibited [125I]LSD binding (Ki = 150 nM). The inhibition of [125I]LSD binding by other serotonergic agonists and antagonists revealed a pharmacological profile that does not correlate with that of any previously described serotonin receptor subtype. In addition, this receptor exhibits high affinity for a number of tricyclic antipsychotic and antidepressant drugs, including clozapine, amoxipine, and amitriptyline. In HEK-293 cells stably transfected with this receptor, serotonin elicits a potent stimulation of adenylyl cyclase activity, which is blocked by antipsychotic and antidepressant drugs. The distinct structural and pharmacological properties of this receptor site indicate that it represents a completely novel subtype of serotonin receptor. Based on its affinity for tricyclic psychotropic drugs and its localization to limbic and cortical regions of the brain, it is likely that this receptor may play a role in several neuropsychiatric disorders that involve serotonergic systems.
The serotonin receptor subtype 6, which raises intracellular cyclic AMP via stimulatory G-proteins, has recently been cloned and characterized. To determine the distribution of serotonin subtype 6 messenger RNA, in situ hybridization was performed in coronal sections of rat brain. 35S-labeled riboprobe, complementary to the 5' non-coding region of the serotonin subtype 6 messenger RNA, and a 33P-labeled riboprobe complementary to its 3' non-coding region, were used for hybridization. Serotonin subtype 6 receptor message was found in serotonin projection fields, rather than regions of serotonin-containing cell bodies, suggesting that the receptor is mainly postsynaptic. Hybridization signal was highest in olfactory tubercle, as well as prominent in the striatum, nucleus accumbens, dentate gyrus, and CA1, CA2 and CA3 of the hippocampus. Less intense hybridization was observed in cerebellum, some diencephalic nuclei, the amygdala, and layers 2, 3, 4 and 6 of the cortex. This pattern of hybridization was observed with both probes, but not when sense transcripts were used. Because the serotonin subtype 6 receptor has a high affinity for the atypical antipsychotic clozapine, and because striatum and nucleus accumbens are proposed sites of antipsychotic drug effects, the possibility is raised that this receptor may play an important role in mediating the effects of the atypical antipsychotic agents.
The authors examined the affinities of 36 typical and atypical antipsychotic agents for the cloned rat 5-hydroxytryptamine-6 (5-HT6) and rat 5-hydroxytryptamine-7 (5-HT7) receptors in transiently expressed COS-7 cells (5-HT7) or stably transfected HEK-293 cells (5-HT6 receptors). Clozapine and several related atypical antipsychotic agents (rilapine, olanzepine, tiospirone, fluperlapine, clorotepine and zotepine) had high affinities for the newly discovered 5-HT6 receptor (Kis < 20 nM). The 5-HT7 receptor bound clozapine, rilapine, fluperlapine, clorotepine, zotepine and risperidone but not tiospirone and olanzepine, with affinities less than 15 nM. In addition, several typical antipsychotic agents (chloroprothixene, chlorpromazine, clothiapine and fluphenazine) had high affinities for both the 5-HT6 and 5-HT7 receptors. Pimozide, a diphenylbutylpiperidine, had the highest affinity of all the typical antipsychotic agents tested for the 5-HT7 receptor (Ki = 0.5 nM). Three putative atypical antipsychotic agents melperone, amperozide and MDL 100907 did not bind with high affinities to either the 5-HT6 or 5-HT7 receptors (Kis > 50 nM). Several dopamine-selective antipsychotic agents (raclopride, rimcazole and penfluridol) had essentially no affinity for either the 5-HT6 or 5-HT7 receptors (Ki values > 5000 nM).(ABSTRACT TRUNCATED AT 250 WORDS)
It is evident that in the last decade or so, a vast amount of new information has become available concerning the various 5-HT receptor types and their characteristics. This derives from two main research approaches, operational pharmacology, using selective ligands (both agonists and antagonists), and, more recently, molecular biology. Although the scientific community continues to deliberate about the hierarchy of criteria for neurotransmitter receptor characterisation, there seems good agreement between the two approaches regarding 5-HT receptor classification. In addition, the information regarding transduction mechanisms and second messengers is also entirely consistent. Thus, on the basis of these essential criteria for receptor characterisation and classification, there are at least three main groups or classes of 5-HT receptor: 5-HT1, 5-HT2, and 5-HT3. Each group is not only operationally but also structurally distinct, with each receptor group having its own distinct transducing system. The more recently identified 5-HT4 receptor almost undoubtedly represents a fourth 5-HT receptor class on the basis of operational and transductional data, but this will only be definitively shown when the cDNA for the receptor has been cloned and the amino acid sequence of the protein is known. Although those 5-HT receptors that have been fully characterised and classified to date (and, hence, named with confidence) would seem to mediate the majority of the actions of 5-HT throughout the mammalian body, not all receptors for 5-HT are fully encompassed within our scheme of classification. These apparent anomalies must be recognised and need further study. They may or may not represent new groups of 5-HT receptor or subtypes of already known groups of 5-HT receptor. Even though the cDNAs for the 5-ht1E, 5-ht1F, 5-ht5, 5-ht6, and 5-ht7 receptors have been cloned and their amino acid sequence defined, more data are necessary concerning their operational and transductional characteristics before one can be confident of the suitability of their appellations. Therefore, it is important to rationalise in concert all of the available data from studies involving both operational approaches of the classical pharmacological type and those from molecular and cellular biology.(ABSTRACT TRUNCATED AT 400 WORDS)
Using a strategy based upon nucleotide sequence homology and starting from the sequence of the rat histamine H2 receptor (Ruat et al., Biochem. Biophys. Res. Commun. 1991, 179, 1470-1478), we have cloned a rat cDNA encoding a functional serotonin receptor (5-HT6). Its coding sequence corresponds to a glycoprotein of 436 amino acids displaying significant homology with other cloned monoaminergic receptors, e.g., various serotonin receptors. Genomic analysis of its gene indicated the presence of at least one intron. The major transcript of the 5-HT6 receptor gene has a size of approximately 4.1 kb but another minor 3.2 kb transcript was also evidenced. The highest expression, detected by Northern blot analysis as well as by in situ hybridization occurs in various serotoninergic areas of rat or guinea pig brain such as striatum, olfactory tubercle, nucleus accumbens and hippocampus, but a faint expression is also detectable in rat stomach. When transiently expressed in transfected COS-7 cells the 5-HT6 receptor appears to be positively coupled to cyclic AMP production.
We describe the cloning and characterization of a human 5-HT6 serotonin receptor. The open reading frame is interrupted by two introns in positions corresponding to the third cytoplasmic loop and the third extracellular loop. The human 5-HT6 cDNA encodes a 440-amino-acid polypeptide whose sequence diverges significantly from that published for the rat 5-HT6 receptor. Resequencing of the rat cDNA revealed a sequencing error producing a frame shift within the open reading frame. The human 5-HT6 amino acid sequence is 89% similar to the corrected rat sequence. The recombinant human 5-HT6 receptor is positively coupled to adenylyl cyclase and has pharmacological properties similar to the rat receptor with high affinity for several typical and atypical antipsychotics, including clozapine. The receptor is expressed in several human brain regions, most prominently in the caudate nucleus. The gene for the receptor maps to the human chromosome region 1p35-p36. This localization overlaps that established for the serotonin 5-HT1D alpha receptor, suggesting that these may be closely linked. Comparison of genomic and cDNA clones for the human 5-HT6 receptor also reveals an Rsal restriction fragment length polymorphism within the coding region.
The purpose of the present study was to determine whether the 5-ht6 receptor is functionally expressed in the rat brain by blocking its translation from mRNA with treatments of phosphorothioate antisense oligonucleotides. Rats were treated with either saline, antisense (AO) or scrambled oligonucleotides (SO) for 4 days. Treatment with AO reduced the number of [3H]LSD binding sites in the frontal lobes by 30% but had no significant effect on the number of 5-HT1A and 5-HT2A receptor binding sites in the cortex of the rats. A behavioural syndrome of yawning, stretching and chewing, however, was observed in AO treated rats but not in any of the other treatment groups. This AO-specific behaviour had returned to normal 5 days after cessation of the oligodeoxynucleotide treatment. These data suggest that the 5-ht6 receptor has a physiological function in the rat brain where it appears to be under the tonic control of endogenous 5-HT.
Possible adaptive changes of the recently cloned serotonin 5-HT6 receptor after the selective lesion of serotoninergic neurons by an intracerebral administration of 5,7-dihydroxytryptamine were investigated using competitive RT-PCR (reverse transcription followed by polymerase chain reaction) for the measurement of 5-HT6-mRNA in various areas of the rat central nervous system. In control rats, 5-HT6-mRNA was the most abundant in the nucleus accumbens, followed by the olfactory tubercle and the striatum. High levels of 5-HT6-mRNA were also found in the hypothalamus and the hippocampus, whereas the cerebral cortex, the substantia nigra, and the spinal cord contained moderate levels of the transcript. Low but easily quantifiable levels of 5-HT6-mRNA were measured in the ventral tegmental area, the anterior raphe area, and the cerebellum. In addition, moderate to low levels of this mRNA were also found in dorsal root ganglia and the pituitary gland. Three weeks after the microinfusion of 5,7-dihydroxytryptamine into the anteroventral vicinity of the dorsal raphe nucleus in nomifensine-pretreated rats, the levels of serotonin transporter-mRNA were reduced by 90% in the anterior raphe area, as expected of the extensive lesion of serotoninergic neurons. In contrast, quantitative determinations of the 5-HT6-mRNA in this area as well as in the nucleus accumbens, the striatum, and the hippocampus indicated that its levels were not significantly different in 5,7-dihydroxytryptamine-treated rats and in controls. These data showed that the 5-HT6 receptor: 1) is not an autoreceptor, and 2) exhibits probably no up regulation in postsynaptic target cells after the selective degeneration of serotoninergic projections.
Molecular biology has dramatically advanced our knowledge and understanding of receptors for 5-hydroxytryptamine (5-HT). The existence of multiple 5-HT receptors defined using traditional pharmacological and biochemical approaches has now been amply confirmed, but gene products encoding putative "new" 5-HT receptors have also been discovered. In some cases, the absence of suitably selective agonists and antagonists has hampered determination of a physiological role for these gene products. This makes their classification as formally recognised receptors premature.
This study describes the in vitro characterization of two potent and selective 5-HT6 receptor antagonists at the rat and human recombinant 5-HT6 receptor.
In binding assays with [3H]-LSD, 4-amino-N-(2,6 bis-methylamino-pyrimidin-4-yl)-benzene sulphonamide (Ro 04-6790) and 4-amino-N-(2,6 bis-methylamino-pyridin-4-yl)-benzene sulphonamide (Ro 63-0563) had mean pKi values ±s.e.mean at the rat 5-HT6 receptor of 7.35±0.04 and 7.83±0.01, respectively and pKi values at the human 5-HT6 receptor of 7.26±0.06 and 7.91±0.02, respectively.
Both compounds were found to be over 100 fold selective for the 5-HT6 receptor compared to 23 (Ro 04-6790) and 69 (Ro 63-0563) other receptor binding sites.
In functional studies, neither compound had any significant effect on basal levels of cyclicAMP accumulation in Hela cells stably expressing the human 5-HT6 receptor, suggesting that the compounds are neither agonists nor inverse agonists at the 5-HT6 receptor. However, both Ro 04-6790 and Ro 63-0563 behaved as competitive antagonists with mean ±s.e.mean pA2 values of 6.75±0.07 and 7.10±0.09, respectively.
In rats habituated to observation cages, Ro 04-6790 produced a behavioural syndrome similar to that seen following treatment with antisense oligonucleotides designed to reduce the expression of 5-HT6 receptors. This behavioural syndrome consisted of stretching, yawning and chewing.
Ro 04-6790 and Ro 63-0563 represent valuable pharmacological tools for the identification of 5-HT6 receptors in natural tissues and the study of their physiological function.
Cytochromes P450: Structure, Function and Mechanism
- D F Lewis
Lewis, D. F. V. Cytochromes P450: Structure, Function and Mechanism; Taylor and Francis Publishing: London, 1996.