The antimigraine drugs ergotamine and dihydroergotamine are potent 5-HT1C receptor agonists in piglet choroid plexus

One-pot multicomponent synthesis of novel pyridine derivatives for antidiabetic and antiproliferative activities

Background: Due to the close relationship of diabetes with hypertension reported in various research, a set of pyridine derivatives with US FDA-approved drug cores were designed and integrated by artificial intelligence. Methods: Novel pyridines were designed and synthesized. Compounds MNS-1-MNS-4 were evaluated for their structure and were screened for their in vitro antidiabetic (α-amylase) activity and anticancer (HepG2) activity by methyl thiazolyl tetrazolium assay. Comparative 3D quantitative structure-activity relationship analysis and pharmacophore generation were carried out. Results: The study revealed MNS-1 and MNS-4 as good alternatives to acarbose as antidiabetic agents, and MNS-2 as a more viable, better alternative to doxorubicin in the methyl thiazolyl tetrazolium assay. Conclusion: This combination of studies identifies new and more active analogs of existing FDA-approved drugs for the treatment of diabetes.

A Short Review on Structural Concepts of Metal Complexes of Proton Transfer Salts of Pyridine-2-Carboxylic Acid

In this study, a brief review of the proton transfer salts synthesized from the reaction of piperazine with pyridine-2-carboxylic acid and their metal complexes since 2009 was made. The metals in the studied compounds are mostly d-block metals. In complexes, the anionic component of the salt is coordinated to the metal, while the cationic component is present only as a complementary ion in a complex.

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

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

DABCO bond cleavage for the synthesis of piperazine derivatives

The applications of DABCO (1,4-diazabicyclo[2.2.2]octane) in the synthesis of piperazine derivatives including biologically active compounds via C–N bond cleavage are investigated in this review. Different reagents such as alkyl halides, aryl(heteroary) halides, carboxylic acids, diaryliodonium salts, tosyl halides, activated alkynes, benzynes etc. were applied for the preparation of the corresponding quaternary ammonium salts of DABCO, which are very good electrophiles for various nucleophiles such as phenols, thiophenols, thiols, alcohols, aliphatic and aromatic amines, sulfinates, phthalimide, indoles, NaN₃, triazole and terazoles, NaCN, enols and enolates, halides, carboxylic acid salts etc. Besides preactivated DABCO salts, the in situ activation of DABCO in multicomponent reactions is also an efficient tactic in synthetic organic chemistry for the diversity oriented synthesis of drug-like piperazine derivatives.

The applications of DABCO (1,4-diazabicyclo[2.2.2]octane) in the synthesis of piperazine derivatives including biologically active compounds via C–N bond cleavage are investigated in this review.

Ictal lack of binding to brain parenchyma suggests integrity of the blood-brain barrier for 11C-dihydroergotamine during glyceryl trinitrate-induced migraine

See Dreier (doi: 10.1093/aww112 ) for a scientific commentary on this article.

For many decades a breakdown of the blood–brain barrier has been postulated to occur in migraine. Hypothetically this would facilitate access of medications, such as dihydroergotamine or triptans, to the brain despite physical properties otherwise restricting their entry. We studied the permeability of the blood–brain barrier in six migraineurs and six control subjects at rest and during acute glyceryl trinitrate-induced migraine attacks using positron emission tomography with the novel radioligand ¹¹ C-dihydroergotamine, which is chemically identical to pharmacologically active dihydroergotamine. The influx rate constant K _i , average dynamic image and time activity curve were assessed using arterial blood sampling and served as measures for receptor binding and thus blood–brain barrier penetration. At rest, there was binding of ¹¹ C-dihydroergotamine in the choroid plexus, pituitary gland, and venous sinuses as expected from the pharmacology of dihydroergotamine. However, there was no binding to the brain parenchyma, including the hippocampus, the area with the highest density of the highest-affinity dihydroergotamine receptors, and the raphe nuclei, a postulated brainstem site of action during migraine, suggesting that dihydroergotamine is not able to cross the blood–brain barrier. This binding pattern was identical in migraineurs during glyceryl trinitrate-induced migraine attacks as well as in matched control subjects. We conclude that ¹¹ C-dihydroergotamine is unable to cross the blood–brain barrier interictally or ictally demonstrating that the blood–brain barrier remains tight for dihydroergotamine during acute glyceryl trinitrate-induced migraine attacks.

Agonist actions of dihydroergotamine at 5-HT2B and 5-HT2C receptors and their possible relevance to antimigraine efficacy

1. The pharmaceutical compound, dihydroergotamine (DHE) is dispensed to prevent and reduce the occurrence of migraine attacks. Although still controversial, the prophylactic effect of this drug is believed to be caused through blockade and/or activation of numerous receptors including serotonin (5-HT) receptors of the 5-HT2 subtype. 2. To elucidate if 5-HT2 receptors (5-HT2Rs) may be involved in DHE prophylactic effect, we performed investigations aimed to determine the respective pharmacological profile of DHE and of its major metabolite 8'-hydroxy-DHE (8'-OH-DHE) at the 5-HT2B and 5-HT2CRs by binding, inositol triphosphate (IP3) or cyclic GMP (cGMP) coupling studies in transfected fibroblasts. 3. DHE and 8'-OH-DHE are competitive compounds at 5-HT2B and 5-HT2CRs. 8'-OH-DHE interaction at (5-HT2BRs) was best fitted by a biphasic competition curve and displayed the highest affinity with a Ki of 5 nm. These two compounds acted as agonists for both receptors in respect to cGMP production with pEC50 of 8.32+/-0.09 for 8'-OH-DHE at 5-HT2B and 7.83+/-0.06 at 5-HT2CRs. 4. Knowing that the antimigraine prophylactic effect of DHE is only observed after long-term treatment, we chronically exposed the recombinant cells to DHE and 8'-OH-DHE. The number of 5-HT2BR-binding sites was always more affected than 5-HT2CRs. At 5-HT2BRs, 8'-OH-DHE was more effective than DHE, with an uncoupling that persisted for more than 40 h for IP3 or cGMP. By contrast, the 5-HT2CR coupling was reversible after either treatment. 5. Chronic exposure to 8'-OH-DHE caused a persistent agonist-mediated desensitisation of 5-HT2B, but not 5-HT2CRs. This may be of relevance to therapeutic actions of the compound.

A review of the role of serotonin receptors in psychiatric disorders

Serotonin (5-hydroxytryptamine, 5-HT) mediates a wide variety of physiological functions by activating multiple receptors, and abnormalities of these receptor systems has been implicated in many psychiatric disorders including anxiety, depression, psychosis, migraine, disorders of sexual functioning, sleep, cognition, and feeding. Many of the currently used treatments for these disorders act by affecting the serotonergic system. Observation of serotonin receptor alterations, before and following effective treatments, may yield important insights into the aetiology of these psychiatric disorders and may ultimately lead to more selective and effective therapies. Copyright 2000 John Wiley & Sons, Ltd.

Effects of PNU-109,291, a selective 5-HT1D receptor agonist, on electrically induced dural plasma extravasation and capsaicin-evoked c-fos immunoreactivity within trigeminal nucleus caudalis

We studied the effects of PNU-109291 [(S)-(-)-1-[2-[4-(4-methoxyphenyl)-1-piperazinyl]ethyl]-N-methyl-isoc hroman-6-carboxamide], a receptor agonist showing 5000-fold selectivity for primate 5-HT1D versus 5-HT1B receptors (Ennis et al., J. Med. Chem. 41, 2180-2183), on dural neurogenic inflammation and on c-fos like immunoreactivity within trigeminal nucleus caudalis evoked by electrical and chemical activation of trigeminal afferents, respectively. Subcutaneous injection of PNU-109291 in male guinea pigs dose-dependently reduced dural extravasation of [125I]-labeled bovine serum albumin evoked by trigeminal ganglion stimulation with an IC50 of 4.2 nmol kg(-1). A dose of 73.3 nmol kg(-1) blocked the response completely. The selective 5-HT1B/1D receptor antagonist GR-127935 (> or = 2 micromol kg(-1) i.v.) prevented this effect. In addition, the number of c-fos immunoreactive cells within guinea pig trigeminal nucleus caudalis induced by chemical meningeal stimulation (intracisternally administered capsaicin) was reduced by more than 50% with PNU-109291 (> or = 122.2 nmol kg(-1) administered s.c. 45 min before and 15 min after capsaicin). These data indicate that the 5-HT1D receptor subtype plays a significant role in suppressing meningeal neurogenic inflammation and attenuating trigeminal nociception in these guinea pig models. Since 5-HT1D receptor mRNA and protein are expressed in trigeminal ganglia but not vascular smooth muscle, the 5-HT1D receptor subtype may become a useful therapeutic target for migraine and related headaches.

Simple O-acylated derivatives of lysergol and dihydrolysergol-I: synthesis and interaction with 5-HT2A, 5-HT2C and 5-HT1B receptors, and alpha1 adrenergic receptors

A series of simple O-acylated derivatives of the naturally occurring clavine alkaloids lysergol and dihydrolysergol-I were synthesized and tested in-vitro for their ability to interact with 5-HT2A receptors in rat tail artery, 5-HT2C receptors in piglet choroid plexus, 5-HT1B receptors in guinea-pig iliac artery and alpha1-adrenergic receptors in rat aorta. In contrast to the classical ergoline 5-HT2A receptor antagonists methysergide and LY53857, the compounds produced competitive antagonism of the 5-HT response in rat tail artery. Affinities of ergolines 3-14 were higher (pA2 values of 7.33-8.40) than those of the parent alcohols lysergol (1) and dihydrolysergol-I (2), respectively. The introduction of an isopropyl substituent at the N(1) position of the compounds failed to enhance 5-HT2A receptor affinity. Compounds 3-14 exhibited lower affinities for alpha1-adrenergic receptors than for 5-HT2A receptors. In particular, those lysergol derivatives that had an isopropyl substituent at the N(1) position were highly specific 5-HT2A receptor antagonists (ratio 5-HT2A/alpha1 = 302-3548). Selected derivatives of lysergol (3-5, 9-11) which were assayed for radioligand binding at 5-HT2C receptors in piglet choroid plexus had affinities that were similar to those found in rat tail artery. Additionally, lysergol and its N(1)-unsubstituted derivatives were found to be partial agonists (alpha of 0.2-0.4) for 5-HT2C receptor-mediated inositol phosphate accumulation in piglet choroid plexus. On the other hand, analogues with an isopropyl substituent at N(1) showed no measurable agonist activity. The observation that N(1)-unsubstituted derivatives of lysergol possessed agonist properties at 5-HT2C receptors whereas their agonist activity at 5-HT2A receptors was marginal (alpha of 0.05 for compound 3 at 1 microM) or not measurable, suggests that these compounds have different abilities to cause conformational change at the two receptor types. Selected derivatives of lysergol (3-5, 9-11) which were examined as ligands for 5-HT1B receptors in guinea-pig iliac artery caused insurmountable blockade of the contractile effect of 5-HT. N(1)-isopropyl derivatives had 30-50-fold lower affinities for 5-HT1B receptors of this tissue than their N(1)-unsubstituted analogues. It is concluded that O-acylated derivatives of the clavine alkaloids lysergol and dihydrolysergol-I mimic therapeutically relevant ergolines due to the complexity of their pharmacological profile as partial agonists and antagonists at 5-HT2A, 5-HT2C and 5-HT1B receptors, and at alpha1-adrenergic receptors.

Headache induced by serotonergic agonists--a key to the interpretation of migraine pathogenesis?

Serotonergic agonists such as m-chlorophenylpiperazine (m-CPP) and fenfluramine may induce migraine attacks. This has led to opposing theories concerning the role of 5-hydroxytryptamine (5HT) in triggering migraine attacks; is there hyperfunction or hypofunction of the central serotonergic system. Our review of the literature strongly suggests that m-CPP and fenfluramine provoke migraine attacks by stimulating, directly or indirectly, the 5HT2C/5HT2B receptors, although there is no total agreement with this interpretation. Central 5HT hypersensitivity in migraine patients, probably due to 5HT neuronal depletion, is proposed on the basis of review of electrophysiological tests and neuroendocrine challenge paradigms.

Endothelial 5-HT receptors mediate relaxation of porcine pulmonary arteries in response to ergotamine and dihydroergotamine

1. The aim of the present study was to investigate whether antimigraine ergot compounds may act at endothelial 5-hydroxytryptamine (5-HT) receptors which trigger the release of endothelium-derived relaxing factor (EDRF). Changes in tone of porcine isolated pulmonary arteries were measured isometrically. The integrity of the endothelium was assessed by the bradykinin-induced relaxation of prostaglandin F2 alpha (PGF2 alpha, 3 microM)-precontracted vessels. 2. The ergot derivatives ergotamine, dihydroergotamine (DHE) and dihydroergocristine, as well as 5-HT and (+/-)-alpha-methyl-5-HT, elicited a reversible endothelium-dependent relaxation of PGF2 alpha-precontracted arterial ring segments. The relaxation to both ergotamine and 5-HT was associated with an increase in cyclic GMP. After pretreatment of the vessels with NG-nitro-L-arginine methyl ester (200 microM), or removal of endothelium by mechanical rubbing, the relaxant responses were abolished. 3. The mean pEC50 values for relaxant responses followed the order: (+/-)-alpha-methyl-5-HT (8.80) > 5-HT (8.75) > ergotamine (8.17) > DHE (7.70) > 5-carboxamidotryptamine (7.62) > dihydroergocristine (7.17). 4. The relaxant effects of both ergotamine and dihydroergotamine were resistant to block by indomethacin (3 microM), prazosin (1 microM) and ketanserin (1 microM). However, the ergotamine-induced relaxation was highly susceptible to block by pizotifen (pA2 = 8.23), norclozapine (pA2 = 8.20), methiothepin (-log IC50 = 7.26), rauwolscine (pA2 = 7.24) and mesulergine (pA2 = 6.64). Each antagonist inhibited the relaxant responses to (+/-)-alpha-methyl-5-HT in the same manner with similar potency as that determined against ergotamine. 5. Recently, mRNA transcripts for 5-HT1D beta and 5-HT2B receptors have been demonstrated in porcine pulmonary arteries. The rank order of potencies of agonists and antagonists in the present study suggests that the relaxant responses to 5-HT and ergot derivatives are mediated through activation of endothelial 5-HT receptors which are similar to the 5-HT2B receptor subtypes.

In vitro and in vivo profile of SB 206553, a potent 5-HT2C/5-HT2B receptor antagonist with anxiolytic-like properties

1. SB 206553 (5-methyl-1-(3-pyridylcarbamoyl)-1,2,3,5-tetrahydropyrrolo[2 ,3-f]indole) displays a high affinity (pK1 7.9) for the cloned human 5-HT2C receptor expressed in HEK 293 cells and the 5-HT2B receptor (pA2 8.9) as measured in the rat stomach fundus preparation. SB 206553 has low affinity for cloned human 5-HT2A receptors expressed in HEK 293 cells (pK1 5.8) and (pK1 < 6) for a wide variety of other neurotransmitter receptors. 2. SB 206553 appears to be a surmountable antagonist of 5-HT-stimulated phosphoinositide hydrolysis in HEK 293 cells expressing the human 5-HT2C receptor (pKB 9.0). 3. The compound potently (ID50 5.5 mg kg-1, p.o., 0.27 mg kg-1, i.v.) inhibited the hypolocomotor response to m-chlorophenylpiperazine (mCPP), a putative model of 5-HT2C/5-HT2B receptor function in vivo. 4. At similar doses (2-20 mg kg-1, p.o.) SB 206553 increased total interaction scores in a rat social interaction test and increased punished responding in a rat Geller-Seifter conflict test. These effects are consistent with the possession of anxiolytic properties. 5. SB 206553 also increased suppressed responding in a marmoset conflict model of anxiety at somewhat higher doses (15 and 20 mg kg-1, p.o.) but also reduced unsuppressed responding. 6. These results suggest that SB 206553 is a potent mixed 5-HT2C/5-HT2B receptor antagonist with selectivity over the 5-HT2A and all other sites studied and possesses anxiolytic-like properties.

An investigation of the mechanism responsible for fluoxetine-induced hypophagia in rats

The effect of fluoxetine on feeding in p-chlorophenylalanine (PCPA) pretreated rats and the nature of its interaction with 5-HT2C receptors have been investigated. Animals that received 3 days PCPA (150 mg/kg i.p.) pretreatment and vehicle on the test day consumed a similar amount as control, saline pretreated animals under the test paradigm used in this study. Fluoxetine (20 and 30 mg/kg p.o.) significantly reduced food intake in PCPA and control pretreated animals to a similar extent, despite an approximately 90% reduction in the levels of brain 5-hydroxytryptamine (5-HT) and 5-hydroxyindole acetic acid (5-HIAA) in the PCPA-pretreated animals. Thus, hypophagia is unlikely to be caused by inhibition of 5-HT reuptake. In the pig choroid plexus in vitro, fluoxetine and norfluoxetine inhibited specific [3H] mesulergine binding with pKI's (+/- S.E.M.) of 6.45 +/- 0.09 (n = 4) and 6.05 +/- 0.05 (n = 3), and slope factors (+/- S.E.M.) of 1.06 +/- 0.14 and 0.99 +/- 0.13, respectively. In slices of piglet choroid plexus fluoxetine (1, 10 and 33 microM) caused a rightward shift in the dose-response curve produced by 5-HT with no effect on the maximal response, and a mean pKB of 5.94 +/- 0.09. Norfluoxetine (10 microM) also produced a rightward shift in the 5-HT dose-response curve with no effect on the maximal response, and a pKB of 6.20. Thus, both compounds acted as surmountable antagonists with no agonist efficacy at 5-HT2C receptors present in choroid plexus. The hypophagic effect of fluoxetine (20 mg/kg p.o.) was also unaffected by the non-specific 5-HT2C receptor antagonist metergoline (2 and 5 mg/kg i.p.). These findings suggest that the hypophagic effect of fluoxetine is not likely to be dependent upon intact brain 5-hydroxytryptaminergic presynaptic function, nor is it mediated by an agonist action at the 5-HT2C receptor, but by an additional, unknown mechanism.

Serotonin receptors: subtypes, functional responses and therapeutic relevance

Recent, rapid progress in the molecular biology of serotonin (5-HT) receptors requires conceptual re-thinking with respect to receptor classification. Thus, based on operational criteria (agonist and antagonist rank order), as well as transduction mechanisms involved and the structure of the receptor protein, the Nomenclature Committee of the Serotonin Club has proposed the following classification and nomenclature: the main receptor types 5-HT1 to 5-HT4, recombinant receptors (e.g. 5-ht5 to 5-ht7) and 'orphan' receptors. The aim of the present review is to discuss the events leading to this classification, the criteria for and functional responses mediated by various 5-HT receptors, as well as the therapeutic possibilities with 5-HT ligands.

Effect of SB 200646A, a 5-HT2C/5-HT2B receptor antagonist, in two conflict models of anxiety

SB 200646A is the first selective 5-HT2C/5-HT2B receptor antagonist and has previously been observed to have anxiolytic-like properties in the rat social interaction test. In the present study the effects of the compound in two conflict models of anxiety, the rat Geller-Seifter and marmoset conflict test, were examined. In the rat Geller-Seifter test, suppressed responding was increased by all doses of SB 200646A between 5 and 40 mg/kg PO when given 1 h pretest. Unsuppressed responding was slightly increased only at 10 mg/kg PO. Suppressed responding was also increased by the benzodiazepine anxiolytic, chlordiazepoxide, at 1, 2.5 and 5 mg/kg PO 1 h pretest. Unsuppressed responding was modestly increased by chlordiazepoxide only at 5 mg/kg PO. In the marmoset conflict test marmosets were trained to lever press for a palatable food reward. Lever pressing was subsequently suppressed by air puffs. In this procedure suppressed responding was increased by both the benzodiazepine anxiolytic diazepam at 2 and 5 mg/kg PO and SB 200646A after 10 and 20 mg/kg PO. Both treatments caused small increases in unsuppressed responding at 2 and 20 mg/kg PO respectively. Taken together with the previous effects of SB 200646A in the rat social interaction test, this is compelling evidence that 5-HT2C/2B receptor antagonists may possess anxiolytic properties.

The effects of 5-HT and m-chlorophenylpiperazine (m-CPP) on the efflux of [3H]-5-HT from human perfused platelets

1. m-Chlorophenylpiperazine (m-CPP), a 5-HT1c-receptor agonist, induces migraine-like headaches when taken orally by migraine sufferers. The present study was undertaken to see what effects m-CPP had on 5-HT function in platelets. 2. Platelets from healthy male volunteers were loaded with [3H]-5-HT and continuously perfused in vitro with carboxygenated Krebs solution at 37 degrees C. After 30 min washout the effects of m-CPP, thrombin, 5-HT and ADP on the efflux of [3H]-5-HT were recorded. 3. m-CPP (0.5-500 microM) did not evoke an increase in the efflux of [3H]-5-HT over that occurring spontaneously whereas thrombin, unlabelled 5-HT and ADP did. The effects of 5-HT were potentiated by ADP. The results were identical whether or not the 5-HT reuptake blocker paroxetine (1 microM) was present. 4. m-CPP inhibited the increase in the efflux of [3H]-5-HT evoked by different concentrations of unlabelled 5-HT in the presence of ADP (2.5 microM) and displaced the 5-HT log concentration response curve to the right. A similar result was obtained with the 5-HT2-receptor antagonist ketanserin. 5. We conclude that m-CPP is a 5-HT2-receptor antagonist on human platelets, which is unlikely to account for its headache-inducing property, as many drugs effective in migraine prophylaxis have this action.