Synthesis of new serotonin 5-HT7 receptor ligands. Determinants of 5-HT7/5-HT1A receptor selectivity

Neuroprotective and Neurite Outgrowth Stimulating Effects of New Low-Basicity 5-HT7 Receptor Agonists: In Vitro Study in Human Neuroblastoma SH-SY5Y Cells

There is some evidence that the serotonin receptor subtype 7 (5-HT7) could be new therapeutic target for neuroprotection. The aim of this study was to compare the neuroprotective and neurite outgrowth potential of new 5-HT7 receptor agonists (AH-494, AGH-238, AGH-194) with 5-CT (5-carboxyamidotryptamine) in human neuroblastoma SH-SY5Y cells. The results revealed that 5-HT7 mRNA expression was significantly higher in retinoic acid (RA)-differentiated cells when compared to undifferentiated ones and it was higher in cell cultured in neuroblastoma experimental medium (DMEM) compared to those placed in neuronal (NB) medium. Furthermore, the safety profile of compounds was favorable for all tested compounds at concentration used for neuroprotection evaluation (up to 1 μM), whereas at higher concentrations (above 10 μM) the one of the tested compounds, AGH-194 appeared to be cytotoxic. While we observed relatively modest protective effects of 5-CT and AH-494 in UN-SH-SY5Y cells cultured in DMEM, in UN-SH-SY5Y cells cultured in NB medium we found a significant reduction of H2O2-evoked cell damage by all tested 5-HT7 agonists. However, 5-HT7-mediated neuroprotection was not associated with inhibition of caspase-3 activity and was not observed in RA-SH-SY5Y cells exposed to H2O2. Furthermore, none of the tested 5-HT7 agonists altered the damage induced by 6-hydroxydopamine (6-OHDA), 1-methyl-4-phenylpyridinium ion (MPP +) and doxorubicin (Dox) in UN- and RA-SH-SY5Y cells cultured in NB. Finally we showed a stimulating effect of AH-494 and AGH-194 on neurite outgrowth. The obtained results provide insight into neuroprotective and neurite outgrowth potential of new 5-HT7 agonists.

Design, synthesis and antimicrobial assessments of aminoacetylenic-piperazine nitroimidazole hybrid compounds

A new series of aminoacetylenic nitroimidazole piperazine hybrid compounds were prepared via three-component reaction. Mannich-type reaction was utilized to couple the nitroimidazole containing propargylic moiety with secondary amines and formaldehyde in the presence of Cu (I) catalyst. The newly synthesized molecules 10a-10w, were characterized an ambiguously through NMR and mass spectrometry. The prepared compounds were assessed in vitro for their antibacterial activity against selected gram-positive and gram-negative bacteria. All of the compounds had shown insignificant activities toward gram-negative bacteria. While compounds 10m, 10q, 10s and 10t had shown moderate activities against the gram-positive bacteria Staphylococcus aureus, Bacillus subtilis and against fungi Escherichia coli and Proteus vulgaris.

Mind the Gap—Deciphering GPCR Pharmacology Using 3D Pharmacophores and Artificial Intelligence

G protein-coupled receptors (GPCRs) are amongst the most pharmaceutically relevant and well-studied protein targets, yet unanswered questions in the field leave significant gaps in our understanding of their nuanced structure and function. Three-dimensional pharmacophore models are powerful computational tools in in silico drug discovery, presenting myriad opportunities for the integration of GPCR structural biology and cheminformatics. This review highlights success stories in the application of 3D pharmacophore modeling to de novo drug design, the discovery of biased and allosteric ligands, scaffold hopping, QSAR analysis, hit-to-lead optimization, GPCR de-orphanization, mechanistic understanding of GPCR pharmacology and the elucidation of ligand–receptor interactions. Furthermore, advances in the incorporation of dynamics and machine learning are highlighted. The review will analyze challenges in the field of GPCR drug discovery, detailing how 3D pharmacophore modeling can be used to address them. Finally, we will present opportunities afforded by 3D pharmacophore modeling in the advancement of our understanding and targeting of GPCRs.

Radioligand and computational insight in structure - Activity relationship of saccharin derivatives being ipsapirone and revospirone analogues

Schizophrenia and depression are diseases that significantly impede human functioning in society. Current antidepressant drugs are not fully effective. According to literature data, the effect on D₂R or 5-HT_1AR can effectively reduce the symptoms of depression or schizophrenia. Recent research hypothetized that the synergism of both of these receptors can improve the effectiveness of therapy. Ipsapirone, a representative of long-chain arylpiperazines, is a known 5-HT_1AR ligand that has antidepressant effect. This compound has no affinity for the D₂R. Bearing in mind, we decided to design ligands with improved affinity to D₂R and confirmed that in some cases elongation of the carbon linker or arylpiperazine exchange may have beneficial influence on the binding to D2R and 5-HT1AR. Four groups of ligands being ipsapirone analogues with butyl, pentyl, hexyl and stiffened xylene chains were designed. All compounds were obtained in solvent-free reactions supported by a microwave irradiation with an efficiency mainly above 60%. All ligands containing 1-(2-pyrimidinyl)piperazine exhibited high affinity to 5-HT_1AR. In this case, chemical modifications within the chain did not affect the affinity to D₂R. In the case of ligands containing 1-phenylpiperazine, 1-(3-trifluoromethylphenyl)piperazine, 1-(1-naphthyl)piperazine, and 1-(4-chlorophenyl)piperazine, elongation of carbon linker increases of affinity to D₂R. For ligands containing 1- (2-pyridyl) piperazine, and 1-(2,3-dichlorophenyl)piperazine, we observed an opposite effect. For ligands containing 1-phenylpiperazine, 1-(2-methoxyphenyl)piperazine and 1-(2-pyridyl)piperazine, chain elongation had no effect on 5-HT_1AR binding. In turn of ligands containing 1-(3-trifluoromethylphenyl)piperazine and 1- (2,3-dichlorophenyl)piperazine, we observed that elongation of carbon linker has a positive influence to 5-HT_1AR. Molecular modelling was used to support the SAR study.

Aerobic Dehydrogenation of N-Heterocycles with Grubbs Catalyst: Its Application to Assisted-Tandem Catalysis to Construct N-Containing Fused Heteroarenes

An aerobic dehydrogenation of nitrogen-containing heterocycles catalyzed by Grubbs catalyst is developed. The reaction is applicable to various nitrogen-containing heterocycles. The exceptionally high functional group compatibility of this method was confirmed by the oxidation of an unprotected dihydroindolactam V to indolactam V. Furthermore, by taking advantage of the oxygen-mediated structural change of the Grubbs catalyst, we integrated ring-closing metathesis and subsequent aerobic dehydrogenation to develop the novel assisted-tandem catalysis using molecular oxygen as a chemical trigger. The utility of the assisted-tandem catalysis was demonstrated by the concise synthesis of N-containing fused heteroarenes including a natural antibiotic, pyocyanine.

Impact of N-Alkylamino Substituents on Serotonin Receptor (5-HTR) Affinity and Phosphodiesterase 10A (PDE10A) Inhibition of Isoindole-1,3-dione Derivatives

In this study, a series of compounds derived from 4-methoxy-1H-isoindole-1,3(2H)-dione, potential ligands of phosphodiesterase 10A and serotonin receptors, were investigated as potential antipsychotics. A library of 4-methoxy-1H-isoindole-1,3(2H)-dione derivatives with various amine moieties was synthesized and examined for their phosphodiesterase 10A (PDE10A)-inhibiting properties and their 5-HT_1A and 5-HT₇ receptor affinities. Based on in vitro studies, the most potent compound, 18 (2-[4-(1H-benzimidazol-2-yl)butyl]-4-methoxy-1H-isoindole-1,3(2H)-dione), was selected and its safety in vitro was evaluated. In order to explain the binding mode of compound 18 in the active site of the PDE10A enzyme and describe the molecular interactions responsible for its inhibition, computer-aided docking studies were performed. The potential antipsychotic properties of compound 18 in a behavioral model of schizophrenia were also investigated.

Privileged scaffold-based design to identify a novel drug-like 5-HT7 receptor-preferring agonist to target Fragile X syndrome

Recent preclinical studies have shown that activation of the serotonin 5-HT₇ receptor has the potential to treat neurodevelopmental disorders such as Fragile X syndrome, a rare disease characterized by autistic features. With the aim to provide the scientific community with diversified drug-like 5-HT₇ receptor-preferring agonists, we designed a set of new long-chain arylpiperazines by exploiting structural fragments present in clinically approved drugs or in preclinical candidates (privileged scaffolds). The new compounds were synthesized, tested for their affinity at 5-HT₇ and 5-HT_1A receptors, and screened for their in vitro stability to microsomal degradation and toxicity. Selected compounds were characterized as 5-HT₇ receptor-preferring ligands, endowed with high metabolic stability and low toxicity. Compound 7g emerged as a drug-like 5-HT₇ receptor-preferring agonist capable to rescue synaptic plasticity and attenuate stereotyped behavior in a mouse model of Fragile X syndrome.

Serotonin Type 6 and 7 Receptors as a Novel Therapeutic Target for the Treatment of Schizophrenia

Schizophrenia is a serious disease of the central nervous system that affects a person's ability to think, feel and behave clearly. Even though the pathophysiological hypothesis of the disease is not clearly understood, dysfunction of dopamine, glutamate, serotonin and other neurotransmitters is widely believed to be involved. Serotonin within the synaptic vesicles functions as neurotransmitter and neurohormone in regulation of emotion, learning, memory, hormone release, cognition and motor function. Dysfunction of normal brain activity of serotonin is associated with schizophrenia. The role of serotonin 6 and 7 receptors in schizophrenia, interaction with neurotransmitters and the effect of drugs on those receptors in schizophrenia are the goal of this review. The aim of this review was to provide information for researchers and other scholars to identify the possible intervention points in the management of schizophrenia. The serotonin 6 and 7 receptors are associated with schizophrenia via modulating cyclic adenosine monophosphate, regulation of Fyn kinase and induction of structural plasticity. The above modulatory effects affect cholinergic, dopaminergic, glutamatergic, adrenergic and GABAergic systems. Recently, diverse numbers of selective agonist and antagonist ligands were developed for both receptors. SGS-518, ABT-354, Lu AE58054, SB-742,457, S-518, AVN-211, AVN-322, SYN-114 and SYN-120 are serotonin 6 receptor antagonists and aripiprazole-controlled release serotonin 7 receptor agonists under clinical trial for schizophrenia. Thus, research on novel drugs that act on serotonin 6 and 7 receptors likely facilitates the intervention into schizophrenia patients seeking better quality of life in the future.

Combined approach of homology modeling, molecular dynamics, and docking: computer-aided drug discovery

With the continuous development in software, algorithms, and increase in computer speed, the field of computer-aided drug design has been witnessing reduction in the time and cost of the drug designing process. Structure based drug design (SBDD), which is based on the 3D structure of the enzyme, is helping in proposing novel inhibitors. Although a number of crystal structures are available in various repositories, there are various proteins whose experimental crystallization is difficult. In such cases, homology modeling, along with the combined application of MD and docking, helps in establishing a reliable 3D structure that can be used for SBDD. In this review, we have reported recent works, which have employed these three techniques for generating structures and further proposing novel inhibitors, for cytoplasmic proteins, membrane proteins, and metal containing proteins. Also, we have discussed these techniques in brief in terms of the theory involved and the various software employed. Hence, this review can give a brief idea about using these tools specifically for a particular problem.

Pharmacology and Therapeutic Potential of the 5-HT7 Receptor

It is well-documented that serotonin (5-HT) exerts its pharmacological effects through a series of 5-HT receptors. The most recently identified member of this family, 5-HT₇, was first identified in 1993. Over the course of the last 25 years, this receptor has been the subject of intense investigation, and it has been demonstrated that 5-HT₇ plays an important role in a wide range of pharmacological processes. As a result of these findings, modulation of 5-HT₇ activity has been the focus of numerous drug discovery and development programs. This review provides an overview of the roles of 5-HT₇ in normal physiology and the therapeutic potential of this interesting drug target.

Structure-Activity Relationships and Therapeutic Potentials of 5-HT7 Receptor Ligands: An Update

Serotonin 5-HT₇ receptor (5-HT₇R) has been the subject of intense research efforts because of its presence in brain areas such as the hippocampus, hypothalamus, and cortex. Preclinical data link the 5-HT₇R to a variety of central nervous system processes including the regulation of circadian rhythms, mood, cognition, pain processing, and mechanisms of addiction. 5-HT₇R blockade has antidepressant effects and may ameliorate cognitive deficits associated with schizophrenia. 5-HT₇R has been recently shown to modulate neuronal morphology, excitability, and plasticity, thus contributing to shape brain networks during development and to remodel neuronal wiring in the mature brain. Therefore, the activation of 5-HT₇R has been proposed as a therapeutic approach for neurodevelopmental and neuropsychiatric disorders associated with abnormal neuronal connectivity. This Perspective celebrates the silver jubilee of the discovery of 5-HT₇R by providing a survey of recent studies on the medicinal chemistry of 5-HT₇R ligands and on the neuropharmacology of 5-HT₇R.

Design, physico-chemical and pre-clinical evaluation of a homo-bivalent 99mTc-(BTZ)2DTPA radioligand for targeting dimeric 5-HT1A/5-HT7 receptors

A ^99mTc-labelled bis-benzothiazolone-DTPA radio-complex as a SPECT neuroimaging agent.

The Effect of Carboxamide/Sulfonamide Replacement in Arylpiperazinylalkyl Derivatives on Activity to Serotonin and Dopamine Receptors

A series of carboxamide and sulfonamide alkyl (p-xylyl and benzyl) 1-(2-methoxyphenyl)piperazine (o-OMe-PhP) and 1-(2,3-dichlorophenyl)piperazine (2,3-DCPP) analogs were prepared and tested for their affinity to bind to serotonin 5-HT_1A /5-HT₆ /5-HT₇ and dopamine D₂ receptors. This chemical modification let us explore the impact of the replacement of the carboxamide by the sulfonamide group on the affinity changes. In both the o-OMe-PhP and 2,3-DCPP series, the relative activities of the carboxamides versus sulfonamides toward the 5-HT_1A /5-HT₆ /5-HT₇ and D₂ receptors show similar trends. Varied or similar activities for particular receptors were found for the carboxamides/sulfonamides with p-xylyl spacer, while of the two classes of carboxamides and sulfonamides examined, benzyl derivatives of the sulfonamides displayed the highest serotoninergic affinity, in particular to the 5-HT₇ receptors (K_i 8-85 nM). The K_i values revealed that, irrespective of the carboxamide/sulfonamide zone, both p-xylyl and benzyl derivatives had the highest affinity for the dopamine D₂ receptor (i.e., 16 out of 24 compounds investigated have an affinity below 100 nM). A molecular modeling study of carboxamide 9a and sulfonamide 9b showed that their binding effects to each of 5-HT_1A R and D₂ R created binding modes interaction with different conserved receptors residues. Structural similarities of carboxamide 9a in complexes with a 5-HT_1A R (9aI) and D₂ R (9aII) are over 83%, while the respective similarities of sulfonamide 9b structures (9bI/9bII) are only about 40%.

Improvising 5-HT7R homology model for design of high affinity ligands: model validation with docking, embrace minimization, MM-GBSA, and molecular dynamic simulations

The subtype, 5-HT₇R has been implicated in neurological disorders and presents itself as a promising target for antidepressant drugs. Design of targeted selective ligands, require a sound knowledge of 3D-receptor structure. In absence of receptor structure, structure-based design of targeted ligands relies on generation of 5-HT₇R homology model. In this study, the impact of template choice, alignment, and model building methods on the homology model of 5-HT₇R is addressed. The compactness and model quality due to the presence of cholesterol (lipidic receptor) have also been observed. The results suggest good stereochemical quality of the final model. Ramachandran Plot Analysis indicated more than 97.5% amino acid residues in the favorable region. The overall quality factor was 91.8% using ERRAT. The Z-score for backbone confirmation and packing quality were -1.248 and -1.427, respectively, using WHATCHECK. The RMS Z-score for side chain planarity was .711. Other validation results for the final model include binding site analysis in which Asp162, Val163, Phe343, Phe344, Arg350, Arg367, and Leu370 conserved residues were found in the active site, correlation coefficient of .82 in ligand-based screening and .85 in embrace minimization. Further, the model showed good correlation for agonist and antagonist in docking ([Formula: see text] ≈ .76, [Formula: see text] ≈ .82), embrace minimization ([Formula: see text] ≈ .73, [Formula: see text] ≈ .72), and MM-GBSA ([Formula: see text] ≈ .69, [Formula: see text] ≈ .75) studies. The model was subjected to Molecular Dynamics (MD) simulation of 20 ns both in ligand-free and ligand-bound receptor (agonist and antagonist) system in order to assess its stability.

Synthesis and evaluation of the structural elements in alkylated tetrahydroisoquinolines for binding to CNS receptors

Diseases of the CNS are often complex and involve multiple receptor systems and thus, the treatment options for these diseases must focus on targeting the multiple receptors implicated in the various disorders. Schizophrenia and depression are examples of such diseases and their pharmacotherapy thus depends on agents which target multiple receptors including the dopamine, serotonin and even cholinergic receptors at the same time. In our previous campaign to find multi-receptor ligands, we have identified the benzothiazole 1a as an initial lead molecule. In the current work, we have expanded the structure affinity relationship (SAFIR) of 1a resulting in the identification of a partially restrained butyrophenone 3j as a potent and selective dual 5-HT1A and 5-HT7 receptor ligand. It is expected that compound 3j may serve as a new lead for further development in our search for newer and novel ligands with the potential to treat diseases of CNS origin.

An Algorithm to Identify Target-Selective Ligands - A Case Study of 5-HT7/5-HT1A Receptor Selectivity

A computational procedure to search for selective ligands for structurally related protein targets was developed and verified for serotonergic 5-HT7/5-HT1A receptor ligands. Starting from a set of compounds with annotated activity at both targets (grouped into four classes according to their activity: selective toward each target, not-selective and not-selective but active) and with an additional set of decoys (prepared using DUD methodology), the SVM (Support Vector Machines) models were constructed using a selective subset as positive examples and four remaining classes as negative training examples. Based on these four component models, the consensus classifier was then constructed using a data fusion approach. The combination of two approaches of data representation (molecular fingerprints vs. structural interaction fingerprints), different training set sizes and selection of the best SVM component models for consensus model generation, were evaluated to determine the optimal settings for the developed algorithm. The results showed that consensus models with molecular fingerprints, a larger training set and the selection of component models based on MCC maximization provided the best predictive performance.

In vitro and in silico evaluation of twelve newly-synthesized 1-acetamide-5-methoxy-2-oxindoles as 5-Ht₇ receptor ligands

Based on in vitro studies of twelve newly-synthesized 1-acetamide-5-methoxy-2-oxindoles as 5-Ht7 receptor ligands, Structure Affinity Relationship (SAR) and Quantitative Structure Affinity Relationship model (QSAR) are provided. Also, a ligand-based pharmacophore model is proposed through molecular docking techniques and Nucleus Independent Chemical Shift DFT calculations (NICS).

Novel arylsulfonamide derivatives with 5-HT₆/5-HT₇ receptor antagonism targeting behavioral and psychological symptoms of dementia

In order to target behavioral and psychological symptoms of dementia (BPSD), we used molecular modeling-assisted design to obtain novel multifunctional arylsulfonamide derivatives that potently antagonize 5-HT(6/7/2A) and D2 receptors, without interacting with M1 receptors and hERG channels. In vitro studies confirmed their antagonism of 5-HT(7/2A) and D2 receptors and weak interactions with key antitargets (M1R and hERG) associated with side effects. Marked 5-HT6 receptor affinities were also observed, notably for 6-fluoro-3-(piperidin-4-yl)-1,2-benzoxazole derivatives connected by a 3-4 unit alkyl linker with mono- or bicyclic, lipophilic arylsulfonamide moieties. N-[4-[4-(6-Fluoro-1,2-benzoxazol-3-yl)piperidin-1-yl]butyl]benzothiophene-2-sulfonamide (72) was characterized in vitro on 14 targets and antitargets. It displayed dual blockade of 5-HT6 and D2 receptors and negligible interactions at hERG and M1 receptors. Unlike reference antipsychotics, 72 displayed marked antipsychotic and antidepressant activity in rats after oral administration, in the absence of cognitive or motor impairment. This profile is particularly attractive when targeting a fragile, elderly BPSD patient population.

New arylpiperazines with flexible versus partly constrained linker as serotonin 5-HT(1A)/5-HT(7) receptor ligands

A series of new long-chain arylpiperazine (LCAP) derivatives with flexible and partly constrained alkyl linker were synthesized and investigated in vitro as potential serotonin 5-HT(1A) and 5-HT(7) receptor ligands. The compounds were prepared by a two-step procedure using naphthalimide and 2H-1,3-benzoxazine-2,4(3H)-dione as imides, and 1-(2-methoxyphenyl)piperazine (o-OMe-PhP) and 1,2,3,4-tetrahydroisoquinoline (THIQ) as amine pharmacophores. Modifications of the spacer structure included introduction of flexible penta- and hexamethylene chains as well as partly constrained m- and p-xylyl moieties. In general, the new compounds were more active at the 5-HT(1A) than at the 5-HT(7) receptor, and the o-OMe-PhP derivatives displayed higher affinities than their respective THIQ analogs. The spacer modifications had little effect on the observed in vitro activities. Within the o-OMe-PhP series, except for a small binding reduction for ligands containing the m-xylyl moiety, there was no substantial change in the compounds' potency at both receptors, while for the THIQ derivatives a clear structure-activity relationship was visible only for the interaction of the compounds with the 5-HT(7) receptor, which strongly favored flexible analogs.

4-Aminoethylpiperazinyl aryl ketones with 5-HT₁A/5-HT₇ selectivity

The well-known 5-HT(1A)/5-HT(7) selectivity issue was tackled by a new series of 4-aminoethylpiperazinyl aryl ketones (1a-1l) specifically designed to distinguish the two hydrophobic sites centered at the anchoring salt bridge. The 4-aminoethylpiperazinyl aryl ketones showed a wide spectrum of activity and selectivity for the 5-HT receptors depending on the type of the hydrophobic groups attached at the aryl piperazinyl ketone scaffold. Docking study of the most active compounds against 5-HT(7)R and 5-HT(1A)R revealed that both receptors have two hydrophobic pockets around the anchoring salt bridge. These two binding sites are perpendicular to each other in 5-HT(7)R but parallel in 5-HT(1A)R, and this observation is well matched with the previous report which claimed that 5-HT(7)R affinity arises from bent conformation of the bound ligand whereas an extended one is best suited for 5-HT(1A)R selectivity. Also, as these pockets have different size and shape, inhibitory activity as well as selectivity of the 4-aminoethylpiperazinyl aryl ketones against 5-HT(7)R and 5-HT(1A)R seemed to be determined by combination of two hydrophobic substituents attached at both ends of the title compounds.

Serotonin 5-HT7 receptor agents: Structure-activity relationships and potential therapeutic applications in central nervous system disorders

Since its discovery in the 1940s in serum, the mammalian intestinal mucosa, and in the central nervous system, serotonin (5-HT) has been shown to be involved in virtually all cognitive and behavioral human functions, and alterations in its neurochemistry have been implicated in the etiology of a plethora of neuropsychiatric disorders. The cloning of 5-HT receptor subtypes has been of importance in enabling them to be classified as specific protein molecules encoded by specific genes. The 5-HT(7) receptor is the most recently classified member of the serotonin receptor family. Since its identification, it has been the subject of intense research efforts driven by its presence in functionally relevant regions of the brain. The availability of some selective antagonists and agonists, in combination with genetically modified mice lacking the 5-HT(7) receptor, has allowed for a better understanding of the pathophysiological role of this receptor. This paper reviews data on localization and pharmacological properties of the 5-HT(7) receptor, and summarizes the results of structure-activity relationship studies aimed at the discovery of selective 5-HT(7) receptor ligands. Additionally, an overview of the potential therapeutic applications of 5-HT(7) receptor agonists and antagonists in central nervous system disorders is presented.

Phe369(7.38) at human 5-HT(7) receptors confers interspecies selectivity to antagonists and partial agonists

BACKGROUND AND PURPOSE

Human and rat 5-HT(7) receptors were studied with a particular emphasis on the molecular interactions involved in ligand binding, searching for an explanation to the interspecies selectivity observed for a set of compounds. We performed affinity studies, molecular modelling and site-directed mutagenesis, with special focus on residue Phe(7.38) of the human 5-HT(7) receptor [Cys(7.38) in rat].

EXPERIMENTAL APPROACH

Competition binding studies were performed for seven 5-HT(7) receptor ligands at three different 5-HT(7) receptors. The functional behaviour was evaluated by measuring 5-carboxytryptamine-stimulated cAMP production. Computational simulations were carried out to explore the structural bases in ligand binding observed for these compounds.

KEY RESULTS

Competition experiments showed a remarkable selectivity for the human receptor when compared with the rat receptor. These results indicate that mutating Cys to Phe at position 7.38 profoundly affects the binding affinities at the 5-HT(7) receptor. Computational simulations provide a structural interpretation for this key finding. Pharmacological characterization of compounds mr25020, mr25040 and mr25053 revealed a competitive antagonistic behaviour. Compounds mr22423, mr22433, mr23284 and mr25052 behaved as partial agonists.

CONCLUSIONS AND IMPLICATIONS

We propose that the interspecies difference in binding affinities observed for the compounds at human and rat 5-HT(7) receptors is due to the nature of the residue at position 7.38. Our molecular modelling simulations suggest that Phe(7.38) in the human receptor is integrated in the hydrophobic pocket in the central part of the binding site [Phe(6.51)-Phe(6.52)] and allows a tighter binding of the ligands when compared with the rat receptor.