Pharmacological evidence that 5‐HT1D activation induces renal vasodilation by NO pathway in rats

5‐HT is a powerful vasoconstrictor substance in renal vasculature (mainly by 5‐HT₂ activation). Nevertheless, 5‐HT is notable for its dual cardiovascular effects, producing both vasodilator and vasoconstrictor actions. This study aimed to investigate whether, behind the predominant serotonergic vasoconstrictor action, THE 5‐HT system may exert renal vasodilator actions, and, if so, characterize the 5‐HT receptors and possible indirect pathways. Renal perfusion pressure (PP), systemic blood pressure (SBP) and heart rate (HR) measurement in in situ autoperfused rat kidney was determined in phenylephrine infused rats. Intra arterial (i.a.) bolus administration of 5‐HT (0.00000125–0.1 μg/kg) decreased renal PP in the presence of a phenylephrine continuous infusion (phenylephrine‐infusion group), without modifying SBP or HR. These vasodilator responses were potentiated by 5‐HT₂ antagonism (ritanserin, 1 mg/kg i.v.), whereas the responses were abolished by 5‐HT_1/7 antagonist (methiothepin, 100 μg/kg i.v.) or 5‐HT_1D antagonist (LY310762, 1 mg/kg i.v.). The i.a. administration (0.00000125 to 0.1 μg/kg) of 5‐CT or L‐694,247 (5‐HT_1D agonist) mimicked 5‐HT vasodilator effect, while other agonists (1‐PBG, α‐methyl‐5‐HT, AS‐19 (5‐HT₇), 8‐OH‐DPAT (5‐HT_1A) or CGS‐12066B (5‐HT_1B)) did not alter baseline haemodynamic variables. L‐694,247 vasodilation was abolished by i.v. bolus of antagonists LY310762 (5‐HT_1D, 1 mg/kg) or L‐NAME (nitric oxide, 10 mg/kg), but not by i.v. bolus of indomethacin (cyclooxygenase, 2 mg/kg) or glibenclamide (ATP‐dependent K⁺ channel, 20 mg/kg). These outcomes suggest that 5‐HT_1D activation produces a vasodilator effect in the in situ autoperfused kidney of phenylephrine‐infusion rats mediated by the NO pathway.     

Quinolinesulfonamides of Aryloxy‐/Arylthio‐ethyl Piperidines: Influence of an Arylether Fragment on 5‐HT1A/5‐HT7 Receptor Selectivity

The solid‐phase synthesis of a new series of 19 biomimetics of long‐chain arylpiperazines, namely flexible quinoline sulfonamides of aryl(heteroaryl)oxy‐/heteroarylthio‐ethyl 4‐aminomethylpiperidines, is reported. Various structural modifications applied followed by biological evaluation for 5‐HT_1A, 5‐HT₆, and 5‐HT₇ receptors gave further support of a possible replacement of arylpiperazine with aryloxy‐/arylthio‐ethyl derivatives of alicyclic amines and control of receptor selectivity upon diversification in the aryl(heteroaryl)oxy‐/heteroarylthio‐ethyl fragment.     

Synthesis,pharmacological evaluations,and molecular docking studies on a new 1,3,4,11b‐tetrahydro‐1H‐fluoreno[9,1‐cd]azepine framework: Rigidification of D1 receptor selective 1‐phenylbenzazepines and discovery of a new 5‐HT6 receptor scaffold

The novel 1,3,4,11b‐tetrahydro‐1H‐fluoreno[9,1‐cd]azepine framework, a structurally rigidified variant of the 1‐phenylbenzazepine template, was synthesized via direct arylation as a key reaction. Evaluation of the binding affinities of the rigidified compounds across a battery of serotonin, dopamine, and adrenergic receptors indicates that this scaffold unexpectedly has minimal affinity for D₁ and other dopamine receptors and is selective for the 5‐HT₆ receptor. The affinity of these systems at the 5‐HT₆ receptor is significantly influenced by electronic and hydrophobic interactions as well as the enhanced rigidity of the ligands. Molecular docking studies indicate that the reduced D₁ receptor affinity of the rigidified compounds may be due in part to weaker H‐bonding interactions between the oxygenated moieties on the compounds and specific receptor residues. Key receptor–ligand H‐bonding interactions, salt bridges, and π–π interactions appear to be responsible for the 5‐HT₆ receptor affinity of the compounds. Compounds 10 (6,7‐dimethoxy‐2,3,4,11b‐tetrahydro‐1H‐fluoreno[9,1‐cd]azepine) and 12 (6,7‐dimethoxy‐2‐methyl‐2,3,4,11b‐tetrahydro‐1H‐fluoreno[9,1‐cd]azepine) have been identified as structurally novel, high affinity (K_i = 5 nM), selective 5‐HT₆ receptor ligands.     

New Arylpiperazines with Flexible versus Partly Constrained Linker as Serotonin 5‐HT1A/5‐HT7 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‐HT₇ 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‐HT₇ 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‐HT₇ receptor, which strongly favored flexible analogs.     

Synthesis of 3H‐ and 14C‐labeled AR‐A000002, a new and selective 5‐HT1B/1D ligand

AR‐A000002 is a novel and selective high‐affinity 5‐HT_1B/1D receptor antagonist. The compound has been shown to enhance 5‐HT turnover in the guinea pig brain in vivo and to increase the extracellular concentration of 5‐HT and the metabolite 5‐hydroxyindoleacetic acid (5‐HIAA) in guinea pig frontal cortex. The observed effects suggest that the compound could be used for the treatment of affective disorders. The syntheses of labeled AR‐A000002 analogues as needed for the further pharmacological evaluation of this selective 5‐HT_1B/1D antagonist, are described. Copyright © 2004 John Wiley & Sons, Ltd.     

Solid‐Supported Synthesis and 5‐HT7/5‐HT1A Receptor Affinity of Arylpiperazinylbutyl Derivatives of 4,5‐dihydro‐1,2,4‐triazine‐6‐(1H)‐one

A series of arylpiperazinylbutyl derivatives of 4,5‐dihydro‐1,2,4‐triazine‐6(1H)‐ones was designed and synthesized according to the new solid‐supported methodology. In this approach, triazinone scaffold was constructed from the Fmoc‐protected glycine. The library representatives showed different levels of affinity for 5‐HT₇ and 5‐HT_1A receptors; compounds 13 , 14 and 18 – 20 were classified as dual 5‐HT₇/5‐HT_1A receptors ligands. The structure–affinity relationship analysis revealed that the receptor affinity and selectivity of the tested compounds depended on the kind of substituent in position 3 of triazinone fragment as well as substitution pattern of the phenylpiperazine moiety.     

The 5-HT1-like receptors mediating inhibition of sympathetic vasopressor outflow in the pithed rat: operational correlation with the 5-HT1A, 5-HT1B and 5-HT1D subtypes

1. It has been suggested that the inhibition of sympathetically-induced vasopressor responses produced by 5-hydroxytryptamine (5-HT) in pithed rats is mediated by 5-HT₁-like receptors. The present study has re-analysed this suggestion with regard to the classification schemes recently proposed by the NC-IUPHAR subcommittee on 5-HT receptors.
2. Intravenous (i.v.) continuous infusions of 5-HT and the 5-HT₁ receptor agonists, 8-OH-DPAT (5-HT_1A), indorenate (5-HT_1A), CP 93,129 (5-HT_1B) and sumatriptan (5-HT_1B/1D), resulted in a dose-dependent inhibition of sympathetically-induced vasopressor responses.
3. The sympatho-inhibitory responses induced by 5-HT, 8-OH-DPAT, indorenate, CP 93,129 or sumatriptan were analysed before and after i.v. treatment with blocking doses of the putative 5-HT receptor antagonists, WAY 100635 (5-HT_1A), cyanopindolol (5-HT_1A/1B) or GR 127935 (5-HT_1B/1D). Thus, after WAY 100635, the responses to 5-HT and indorenate, but not to 8-OH-DPAT, CP 93,129 and sumatriptan, were blocked. After cyanopindolol, the responses to 5-HT, indorenate and CP 93,129 were abolished, whilst those to 8-OH-DPAT and sumatriptan (except at the lowest frequency of stimulation) remained unaltered. In contrast, after GR 127935, the responses to 5-HT, CP 93,129 and sumatriptan, but not to 8-OH-DPAT and indorenate, were abolished.
4. In additional experiments, the inhibition induced by 5-HT was not modified after 5-HT₇ receptor blocking doses of mesulergine.
5. The above results suggest that the 5-HT₁-like receptors, which inhibit the sympathetic vasopressor outflow in pithed rats, display the pharmacological profile of the 5-HT_1A, 5-HT_1B and 5-HT_1D, but not that of 5-HT₇, receptors.

     

Novel Mannich Bases, 5‐Arylimidazolidine‐2,4‐dione Derivatives with Dual 5‐HT1A Receptor and Serotonin Transporter Affinity

A computer aided ligand design study of imidazolidine‐2,4‐dione derivatives was conducted in order to obtain compounds with dual 5‐HT_1A receptor and serotonin transporter (SERT) affinity. According to molecular modeling results, series of Mannich bases were chosen and synthesized. Investigated compounds were tested for 5‐HT_1A, 5‐HT_2A, α₁ and SERT affinity. Two selected compounds ( 5 , 9 ) were characterized in functional experiments and possessed a pharmacological profile which may enhance SERT blocking efficacy – 5‐HT_1A partial agonism and 5‐HT_2A antagonism in one molecule. Furthermore these compounds displayed satisfactory selectivity over adrenergic α₁ receptors. The most promising compounds, 5‐arylimidazolidine‐2,4‐dione derivatives with 4‐(3‐chlorophenyl)piperazinylmethyl moiety were tested for antidepressant and anxiolytic activity. In particular, compound 5 (5‐(2‐methoxyphenyl)‐3‐{1‐[4‐(3‐chlorophenyl)piperazin‐1‐yl]methyl}‐imidazolidine‐2,4‐dione), tested in the forced swim test in mice, exhibited a favorable antidepressant‐like profile without affecting spontaneous locomotor activity.     

5‐HT2C receptor antagonists: Potential in schizophrenia

The therapeutic success of clozapine and other so‐called atypical antipsychotics has focused attention on the serotonin (5‐hydroxytryptamine; 5‐HT) system and its interaction with the dopaminergic system as a treatment for psychotic illnesses. Clozapine has been shown to display high affinity for the 5‐HT₂ receptor family and it has been suggested that this, together with evidence that dopamine D₂ receptor blockade following clozapine treatment is lower than typical antipsychotics, contributes to the therapeutic profile of clozapine and, in particular, its efficacy in treating the negative symptoms of schizophrenia. Much attention has concentrated on the interaction of clozapine and atypical antipsychotics with the 5‐HT_2A receptor. In this review, we focus on the role of the 5‐HT_2C receptor in both the therapeutic profile of atypical antipsychotics and in the regulation of the dopaminergic system. We further suggest that 5‐HT_2C receptor antagonists may have therapeutic utility in the treatment of psychotic illnesses. Drug Dev. Res. 54:88–94, 2001. © 2001 Wiley‐Liss, Inc.     

In Search of Potent 5‐HT6 Receptor Inverse Agonists

A series of non‐sulfonamide/non‐sulfone derived potent 5‐HT₆ receptor inverse agonists has been disclosed. Representative compound 9 ( K _i = 14 nm ) displayed selectivity against a set of family members as well as brain permeability 6 h post‐oral administration. In addition, the separated enantiomers of compound 9 displayed difference in activity indicating the influence of chirality on potency.     

Cardiovascular effects of novel esters and alcohol analogs of the 5‐HT1A receptor ligand,indorenate

The cardiovascular pharmacological profiles of a series of novel indorenate analogs, including methyl 3‐amino‐(1H‐indol‐3‐yl) propanoate hydrochloride and 3‐amino‐2‐(1H‐indol‐3‐yl)propanol oxalate 5‐substituted analogs, were evaluated. The antihypertensive effects in anesthetized spontaneously hypertensive rats (SHR), direct action on blood pressure in the pithed rat preparation, on canine basilar artery vascular tone, and on the tension develop by rat aortic rings were assessed for the 5‐methoxy, 5‐fluor and 5 benzyloxy esters, and alcohol derivatives. 5‐Alkoxytryptamine derivatives caused a short‐lasting, dose‐dependent immediate antihypertensive response, after which blood pressure returned to baseline. Ester derivatives induced both a significant long‐lasting and dose‐dependent increase in arterial blood pressure and elicited concentration‐dependent contractions of the canine basilar artery. This last response was potently blocked by selective 5‐HT_1B/1D antagonist GR 127935 (1 nM). Unlike the canine basilar artery, the rat aorta was almost insensitive to these alcohols and ester indorenate derivatives. Fluoro derivative 4 and the benzyloxy compounds 5 and 6 significantly inhibited phenylephrine‐induced contractions of rat aorta rings at high concentrations. It is concluded that: 1) substitution of a 5‐fluoro group instead of a 5‐alcoxyl group increases affinity for 5‐HT₁ subtype receptors; 2) the 5‐alcoxy group is an important requirement for the antihypertensive effect; and 3) a β‐carbomethoxy group in the lateral chain increases potency. Drug Dev. Res. 48:130–137, 1999. © 1999 Wiley‐Liss, Inc.     

PM2.5 upregulates rat mesenteric arteries 5‐HT2A receptor via inflammatory‐mediated mitogen‐activated protein kinases signaling pathway

Fine particulate matter (PM_2.5) is an important environmental risk factor for cardiovascular diseases. However, little is known about the effects of PM_2.5 on arteries. The present study investigated whether PM_2.5 alters 5‐hydroxytryptamine (5‐HT) receptor expression and inflammatory mediators on rat mesenteric arteries, and examined the underlying mechanisms. Isolated rat mesenteric arteries segments were cultured with PM_2.5 in the presence or absence of ERK1/2, JNK, and p38 pathway inhibitors. Contractile reactivity was monitored by a sensitive myograph. The expression of 5‐HT_2A/1B receptors and inflammatory mediators were studied by a real‐time polymerase chain reaction and/or by immunohistochemistry. The phosphorylation of mitogen‐activated protein kinases (MAPK) pathway was detected by Western blot. Compared with the fresh or culture alone groups, 1.0 μg/mL PM_2.5 cultured for 16 hours significantly enhanced contractile response induced by 5‐HT and increased 5‐HT_2A receptor mRNA and protein expressions, indicating PM_2.5 upregulates 5‐HT_2A receptor. SB203580 (p38 inhibitor) and U0126 (ERK1/2 inhibitor) significantly decreased PM_2.5‐induced elevated contraction and mRNA and protein expression of 5‐HT_2A receptor. Cultured with PM_2.5 significantly increased the mRNA expression of inflammatory mediators (NOS2, IL‐1β, and TNF‐α), while SB203580 decreased mRNA expression level of NOS2, IL‐1β, and TNF‐α. SP600125 (JNK inhibitor) decreased mRNA expression level of TNF‐α and IL‐1β. After PM_2.5 exposure, the phosphorylation of p38 and ERK1/2 protein were increased. SB203580 and U0126 inhibited the PM_2.5 caused increased phosphorylation protein of p38 and ERK1/2. In conclusion, PM_2.5 induces inflammatory‐mediated MAPK pathway in artery which subsequently results in enhanced vascular contraction responding to 5‐HT via the upregulated 5‐HT_2A receptors.     

N‐[3‐[4‐(2‐methoxyphenyl) piperaziny‐1‐yl]propyl]cyclam: synthesized as a potential 5‐HT1A receptor ligand and labelled with 99mTc‐nitrido core

This paper reports the synthesis of new potential 5‐HT_1A receptor ligand N‐[3‐[4‐(2‐methoxyphenyl)piperaziny‐1‐yl]propyl]cyclam (MPPC) and radiolabelling of it with ^99mTc‐nitrido core. The novel neutral complex ^99mTcN‐MPPC combines 1,4,8,11‐tetraazacyclotetradecane (cyclam) ligand as chelate moiety for ^99mTc‐nitrido with a 1‐(2‐methoxyphenyl)piperazine moiety derived from WAY 100635 via a 3‐carbon alkyl chain. This provided a reliable and reproducible method for attaching the technetium to the pharmacophore moiety of WAY 100635. ^99mTcN‐MPPC was prepared by a two‐step procedure and the radiochemical purity was found to be greater than 95%. It was hydrophilic and stable for at least 4 h at room temperature. In vivo stability study in normal rats showed that no degradation of ^99mTcN‐MPPC was found in deproteinated blood samples at 2 h post‐injection. This effective ^99mTc‐labelling strategy for obtaining neutral ^99mTc nitrido complexes would be a useful tool to prepare new SPECT agents to image 5‐HT_1A receptor with cyclam conjugated ligands. Copyright © 2008 John Wiley & Sons, Ltd.     

2‐Amino‐3‐(1‐(4‐(4‐(2‐methoxyphenyl) piperazine‐1‐yl)butyl)‐1H‐1,2,3‐triazol‐4‐yl) propanoic acid: synthesized, 99mTc‐tricarbonyl labeled,and bioevaluated as a potential 5HT1A receptor ligand

To develop a novel 5HT_1A receptor imaging agent, a new methoxyphenyl piperazine derivative was synthesized and radiolabeled with ^99mTc‐tricarbonyl precursor. We used the Cu (I)‐catalyzed cycloaddition of azide and terminal alkynes to synthesize 1, 2, 3 triazole as the metal chelating system. This synthesis provided reliable and reproducible method to attach technetium to the methoxyphenyl piperazine moiety. ^99mTc‐tricabonyl labeling of ligand was performed at high radiochemical purity (greater than 95%). The radiolabeled compound was stable at least 24 h in room temperature. In vitro stability study in human serum albumin showed more than 90% stability in 37 °C incubation for 6 h. Biodistribution studies in rat have shown brain hippocampus uptake of 0.31 ± 0.02 %ID/g at 5‐min post‐injection. The favorable in vitro/in vivo stability, lipophilicity, and biodistribution profiles suggest that this radioconjugate is a good candidate for further exploration of its potential clinical application. Copyright © 2012 John Wiley & Sons, Ltd.     

RU24969-induced behavioural syndrome requires activation of both 5HT1A and 5HT1B receptors

The behavioural profiles of the mixed 5HT_1A/B agonist RU24969 and the more selective 5HT_1B agonist anpirtoline were compared. Both compounds induce an increase in activity as measured in photocell activity cages. The behaviours displayed by the rats receiving each treatment differed markedly, with RU24969 inducing flat body posture and circling of the cage perimeter (1.25−10 mg/kg SC), whereas anpirtoline increased ambulation characterised by a hopping motion (1.25−5.0 mg/kg SC). The effects of RU24969 were attenuated by both the 5HT_1A antagonist WAY100635 (0.03−1.25 mg/kg SC) and the 5HT_1B/D antagonist GR127935 (1.0−5.0 mg/kg SC). Anpirtoline-induced behaviour was attenuated by GR127935 across the same dose range but was largely unaffected by WAY100635 even at doses above those which had blocked the effects of RU24969. Coadministration of the selective 5HT_1A agonist 8-OH-DPAT (0.03−1.25  mg/kg SC) with anpirtoline (2.5 mg/kg) induced a dramatic increase in locomotor activity and a behavioural syndrome identical to that produced by RU24969. Thus it would appear that a synergistic effect of stimulation of both 5HT_1A and 5HT_1B receptors underlies the behavioural effects of RU24969, while anpirtoline acts mainly via stimulation of 5HT_1B receptors only. Received: 31 October 1996/Final version: 24 February 1997     

1-cinnamyl-4-(2-methoxyphenyl)piperazines: synthesis, binding properties, and docking to dopamine (D(2)) and serotonin (5-HT(1A)) receptors

Clinical properties of atypical antipsychotics are based on their interaction with D(2) dopamine receptor and serotonin 5-HT(1A) and 5-HT(2A) receptors. As a part of our research program on new antipsychotics, we synthesized various derivatives of 1-cinnamyl-4-(2-methoxyphenyl)piperazines, and evaluated their affinities for D(2), 5-HT(1A), 5-HT(2A), and adrenergic (alpha(1)) receptors using radioligand-binding assays. In addition, we performed docking analysis using models for the D(2) and 5-HT(1A) receptors. All compounds exhibited low to moderate affinity to 5-HT(1A) and 5-HT(2A) receptors, high affinity to the D(2 )receptor and large variability in affinities for the alpha(1) receptor. Docking analysis indicated that the binding to D(2) and 5-HT(1A) receptors is based on (i) interaction between protonated N1 of the piperazine ring and various aspartate residues, (ii) hydrogen bonds between various moieties of the ligand and the residues of threonine, serine, histidine or tryptophane, and (iii) edge-to-face interactions of the aromatic ring of the arylpiperazine moiety with phenylalanine or tyrosine residues. Docking data for the D(2) receptor can account for the binding properties obtained in binding assays, suggesting that the model is reliable and robust. However, docking data for the 5-HT(1A) receptor cannot account for actual binding properties, suggesting that further refinement of the model is required.     

Synthesis,radiosynthesis and preliminary in vivo evaluation of [123I]‐(4‐fluorophenyl) {1‐[2‐(2‐iodophenyl)ethyl]piperidin‐4‐yl}methanone,a potential 5‐HT2A‐antagonist for SPECT brain imaging

Many people suffer from psychiatric illnesses like depression and anorexia. Relevant to these diseases is amongst others a malfunctioning of brain 5‐HT_2A‐receptors. To allow in vivo quantification of these receptors with Single Photon Emission Computerized Tomography (SPECT), a radiolabelled ligand with high 5‐HT_2A affinity is needed. This work reports the radiosynthesis of [¹²³I]‐(4‐fluorophenyl) {1‐[2‐(2‐iodophenyl)ethyl]piperidin‐4‐yl}methanone, the synthesis of its precursor, (4‐fluorophenyl) {1‐[2‐(2‐bromophenyl)ethyl]piperidin‐4‐yl}methanone, and the preliminary in vivo evaluation of the tracer. The precursor was synthesized with a total yield of 40%. Radiolabelling was performed using a halogen exchange reaction and the yield was 70%. Radiochemical purity was >95%, and specific activity was at least 2.4 Ci/µmol. Log P was measured to be 2.52. The tracer showed uptake in mice brain (3.5% I.D./g tissue at 3 min post injection) and therefore will be evaluated further by regional brain biodistribution and displacement studies in rabbits. Copyright © 2004 John Wiley & Sons, Ltd.