RESUMEN
In this Letter, we present the results of a hit-finding and lead optimization programme against the EP4 receptor (EP4R). In a short time period, we were able to discover five structurally diverse series of hit compounds using a combination of virtual screening methods. The most favoured hit, compound 6, was demonstrated to be a competitive antagonist of the EP4R. Compound 73 was identified following several rounds of optimization, which centred on improving both the primary EP4R affinity and selectivity against the related EP2R as well as the aqueous solubility. This work culminated in the preparation of PGN-1531, the sodium salt of 73, which showed a marked improvement in solubility (>10 mg/mL). PGN-1531 is a potent and selective antagonist at EP4Rs in vitro and in vivo, with the potential to alleviate the symptoms of migraine that result from cerebral vasodilatation.
Asunto(s)
Descubrimiento de Drogas , Subtipo EP4 de Receptores de Prostaglandina E/antagonistas & inhibidores , Encéfalo/irrigación sanguínea , Células HEK293 , Humanos , Ligandos , Trastornos Migrañosos/tratamiento farmacológico , Modelos Moleculares , Subtipo EP4 de Receptores de Prostaglandina E/metabolismo , Vasodilatación/efectos de los fármacosRESUMEN
Using a human Prostaglandin E(2) (PGE(2)) model of headache, we examined whether a novel potent and selective EP(4) receptor antagonist, BGC20-1531, may prevent headache and dilatation of the middle cerebral (MCA) and superficial temporal artery (STA). In a three-way cross-over trial, eight healthy volunteers were randomly allocated to receive 200 and 400 mg BGC20-1531 and placebo, followed by a 25-min infusion of PGE(2). We recorded headache intensity on a verbal rating scale, MCA blood flow velocity and STA diameter. There was no difference in headache response or prevention of the dilation of the MCA or the STA (P > 0.05) with either dose of BGC20-1531 relative to placebo, although putative therapeutic exposures were not reached in all volunteers. In conclusion, these data suggest that the other EP receptors may be involved in PGE(2) induced headache and dilatation in normal subjects.
Asunto(s)
Analgésicos/uso terapéutico , Cefalea/tratamiento farmacológico , Piridinas/uso terapéutico , Subtipo EP4 de Receptores de Prostaglandina E/antagonistas & inhibidores , Sulfonamidas/uso terapéutico , Adulto , Analgésicos/farmacocinética , Circulación Cerebrovascular/efectos de los fármacos , Estudios Cruzados , Dinoprostona/toxicidad , Método Doble Ciego , Femenino , Cefalea/inducido químicamente , Humanos , Masculino , Piridinas/farmacocinética , Sulfonamidas/farmacocinética , Vasodilatación/efectos de los fármacos , Adulto JovenRESUMEN
3-tert-Butyl-7-(5-methylisoxazol-3-yl)-2-(1-methyl-1H-1,2,4-triazol-5-ylmethoxy)-pyrazolo[1,5-d][1,2,4]triazine (MRK-016) is a pyrazolotriazine with an affinity of between 0.8 and 1.5 nM for the benzodiazepine binding site of native rat brain and recombinant human alpha1-, alpha2-, alpha3-, and alpha5-containing GABA(A) receptors. It has inverse agonist efficacy selective for the alpha5 subtype, and this alpha5 inverse agonism is greater than that of the prototypic alpha5-selective compound 3-(5-methylisoxazol-3-yl)-6-[(1-methyl-1,2,3-triazol-4-hdyl)methyloxy]-1,2,4-triazolo[3,4-a]phthalazine (alpha5IA). Consistent with its greater alpha5 inverse agonism, MRK-016 increased long-term potentiation in mouse hippocampal slices to a greater extent than alpha5IA. MRK-016 gave good receptor occupancy after oral dosing in rats, with the dose required to produce 50% occupancy being 0.39 mg/kg and a corresponding rat plasma EC(50) value of 15 ng/ml that was similar to the rhesus monkey plasma EC(50) value of 21 ng/ml obtained using [(11)C]flumazenil positron emission tomography. In normal rats, MRK-016 enhanced cognitive performance in the delayed matching-to-position version of the Morris water maze but was not anxiogenic, and in mice it was not proconvulsant and did not produce kindling. MRK-016 had a short half-life in rat, dog, and rhesus monkey (0.3-0.5 h) but had a much lower rate of turnover in human compared with rat, dog, or rhesus monkey hepatocytes. Accordingly, in human, MRK-016 had a longer half-life than in preclinical species ( approximately 3.5 h). Although it was well tolerated in young males, with a maximal tolerated single dose of 5 mg corresponding to an estimated occupancy in the region of 75%, MRK-016 was poorly tolerated in elderly subjects, even at a dose of 0.5 mg, which, along with its variable human pharmacokinetics, precluded its further development.
Asunto(s)
Agonistas del GABA/farmacología , Agonistas de Receptores de GABA-A , Isoxazoles/farmacología , Triazinas/farmacología , Animales , Ansiedad/psicología , Conducta Animal/efectos de los fármacos , Convulsivantes/farmacología , Perros , Relación Dosis-Respuesta a Droga , Estimulación Eléctrica , Electrofisiología , Potenciales Postsinápticos Excitadores/efectos de los fármacos , Fibroblastos , Flumazenil/metabolismo , Agonistas del GABA/metabolismo , Agonistas del GABA/farmacocinética , Moduladores del GABA/metabolismo , Hepatocitos/metabolismo , Hipocampo/efectos de los fármacos , Hipocampo/metabolismo , Humanos , Macaca mulatta , Masculino , Aprendizaje por Laberinto/efectos de los fármacos , Ratones , Técnicas de Placa-Clamp , Equilibrio Postural/efectos de los fármacos , Ratas , Ratas Sprague-Dawley , Receptores de GABA-A/metabolismo , Adulto JovenRESUMEN
Substance P receptor [neurokinin 1 (NK1] antagonists (SPAs) represent a novel mechanistic approach to antidepressant therapy with comparable clinical efficacy to selective serotonin reuptake inhibitors (SSRIs). Because SSRIs are thought to exert their therapeutic effects by enhancing central serotonergic function, we have examined whether SPAs regulate neuronal activity in the dorsal raphe nucleus (DRN), the main source of serotonergic projections to the forebrain. Using in vivo electrophysiological techniques in the guinea pig, we found that administration of the highly selective NK1 receptor antagonist 1-(5-[[(2R,3S)-2-([(1R)-1-[3,5-bis(trifluoromethyl)phenyl]ethyl]oxy)-3-(4-phenyl)morpholin-4-yl]methyl]-2H-1,2,3-triazol-4-yl)-N,N-dimethylmethanamine (L-760735) caused an increase in DRN neuronal firing rate. However, unlike chronic treatment with fluoxetine, there was no detectable 5-HT1A autoreceptor desensitization. In vitro electrophysiological investigation showed that these effects were not mediated by a direct action in the DRN, an observation supported by immunocytochemical analysis that identified the lateral habenula (LHb) as a more likely site of action. Subsequently, we found that local application of L-760735 into the LHb increased firing in the DRN, which, together with our data showing that L-760735 increased metabolic activity in the cingulate cortex, amygdala, LHb, and DRN, indicates that the effects of L-760735 may be mediated by disinhibition of forebrain structures acting via a habenulo raphe projection. These findings support other evidence for an antidepressant profile of SPAs and suggest that regulation of DRN neuronal activity may contribute to their antidepressant mechanism of action but in a manner that is distinct from monoamine reuptake inhibitors.
Asunto(s)
Morfolinas/farmacología , Antagonistas del Receptor de Neuroquinina-1 , Neuronas/efectos de los fármacos , Núcleos del Rafe/efectos de los fármacos , Receptores de Neuroquinina-1/metabolismo , 8-Hidroxi-2-(di-n-propilamino)tetralin/farmacología , Animales , Autorradiografía , Desoxiglucosa/metabolismo , Desoxiglucosa/farmacocinética , Relación Dosis-Respuesta a Droga , Electrofisiología , Cobayas , Habénula/efectos de los fármacos , Habénula/fisiología , Inmunohistoquímica , Técnicas In Vitro , Iontoforesis , Masculino , Red Nerviosa/efectos de los fármacos , Red Nerviosa/fisiología , Inhibición Neural/efectos de los fármacos , Inhibición Neural/fisiología , Neuronas/metabolismo , Prosencéfalo/efectos de los fármacos , Prosencéfalo/metabolismo , Ensayo de Unión Radioligante , Núcleos del Rafe/citología , Núcleos del Rafe/metabolismo , Receptores de Serotonina/efectos de los fármacos , Agonistas de Receptores de Serotonina/farmacología , Inhibidores Selectivos de la Recaptación de Serotonina/farmacologíaRESUMEN
The alpha5 subunit of the GABA(A) receptor is localized mainly to the hippocampus of the mammalian brain. The significance of this rather distinct localization and the function of alpha5-containing GABA(A) receptors has been explored by targeted disruption of the alpha5 gene in mice. The alpha5 -/- mice showed a significantly improved performance in a water maze model of spatial learning, whereas the performance in non-hippocampal-dependent learning and in anxiety tasks were unaltered in comparison with wild-type controls. In the CA1 region of hippocampal brain slices from alpha5 -/- mice, the amplitude of the IPSCs was decreased, and paired-pulse facilitation of field EPSP (fEPSP) amplitudes was enhanced. These data suggest that alpha5-containing GABA(A) receptors play a key role in cognitive processes by controlling a component of synaptic transmission in the CA1 region of the hippocampus.
Asunto(s)
Hipocampo/fisiología , Aprendizaje , Memoria , Receptores de GABA-A/fisiología , Transmisión Sináptica , Animales , Reacción de Prevención , Conducta Animal , Conductividad Eléctrica , Potenciales Postsinápticos Excitadores , Femenino , Cinética , Potenciación a Largo Plazo , Masculino , Aprendizaje por Laberinto , Ratones , Ratones Noqueados , Subunidades de Proteína , Receptores de GABA-A/genética , Ácido gamma-Aminobutírico/metabolismoRESUMEN
Screening of the Merck compound collection identified 6 as an unusually simple, low molecular weight hit with moderate affinity for GABAA receptors. The structural novelty of 6, compared to our advanced series of GABAA alpha5 inverse agonists, made it an attractive molecule for further exploration. This paper will describe the evolution of 6 into a new series of ligands with nanomolar affinity and functional selectivity for GABAA alpha5 receptor subtypes.
Asunto(s)
Piridazinas/síntesis química , Receptores de GABA-A/efectos de los fármacos , Animales , Línea Celular , Humanos , Técnicas In Vitro , Ligandos , Masculino , Ratones , Microsomas Hepáticos/efectos de los fármacos , Microsomas Hepáticos/metabolismo , Técnicas de Placa-Clamp , Subunidades de Proteína/fisiología , Piridazinas/farmacocinética , Piridazinas/farmacología , Ensayo de Unión Radioligante , Ratas , Ratas Sprague-Dawley , Receptores de GABA-A/fisiología , Proteínas Recombinantes/metabolismo , Relación Estructura-ActividadRESUMEN
Currently the treatment of Alzheimer's disease (AD) and Mild Cognitive Impairment (MCI) is largely unrealised, with no preventive or curative therapies. The marketed acetylcholinesterase inhibitors (eg. donepezil, Aricept) are directed toward temporary symptomatic relief from impaired cognition, but have prominent adverse effects with minimal efficacy. In pursuit of novel cognition enhancers, the observation that classical benzodiazepines (BZ, eg. diazepam) are amnesic, coupled with the preservation of GABA(A) receptors in brain areas most affected by AD, highlighted the GABA(A) receptor as a potential therapeutic target. In contrast to the amnesic BZ agonists, the BZ inverse agonists (eg. DMCM) which attenuate GABA(A) receptor function, have been shown to improve performance in animal models of learning and memory. Unfortunately, such non-selective ligands also induce anxiety and convulsions. More recently, novel ligands have been developed (eg. 6,6-dimethyl-3-(2-hydroxyethyl)thio-1-(thiazol-2-yl)-6,7-dihydro-2-benzothiophen-4(5H)-one) that demonstrate binding selectivity and high inverse agonism for the alpha5 GABA(A) receptor subtype, which is preferentially located in the hippocampus, a region of the brain associated with learning and memory. Pre-clinical results are encouraging, since these alpha5 selective inverse agonists enhance memory in animal models, such as spatial learning in the Morris water-maze, but are devoid of the adverse effects associated with activity at other GABA(A) receptor subtypes in other brain regions. If the efficacy and safety profiles of alpha5 inverse agonists in humans prove to be similar to those seen in pre-clinical studies, these compounds would offer significant benefit to AD and MCI patients.
Asunto(s)
Benzodiazepinas/farmacología , Trastornos del Conocimiento/tratamiento farmacológico , Cognición/efectos de los fármacos , Agonistas del GABA/farmacología , Receptores de GABA-A/efectos de los fármacos , Enfermedad de Alzheimer/tratamiento farmacológico , Animales , Modelos Animales de Enfermedad , Haplorrinos , Hipocampo/efectos de los fármacos , Humanos , Ratones , Ratones Transgénicos , Receptores de GABA-A/clasificación , Tiazoles/farmacología , Tiofenos/farmacologíaRESUMEN
In pursuit of a GABA(A) alpha5-subtype-selective inverse agonist to enhance cognition, a series of 6,7-dihydro-2-benzothiophen-4(5H)-ones has been identified as a novel class of GABA(A) receptor ligands. These thiophenes have higher binding affinity for the GABA(A) alpha5 receptor subtype compared to the GABA(A) alpha1, alpha2, and alpha3 subtypes, and several analogues exhibit high GABA(A) alpha5 receptor inverse agonism. 6,6-Dimethyl-3-(2-hydroxyethyl)thio-1-(thiazol-2-yl)-6,7-dihydro-2-benzothiophen-4(5H)-one (43) has been identified as a full inverse agonist at the GABA(A) alpha5 receptor and is functionally selective over the other major GABA(A) receptor subtypes. 43 readily penetrates into the CNS to give selective occupancy of GABA(A) alpha5 receptors. In addition, 43 enhances cognitive performance in rats in the delayed 'matching-to-place' Morris water maze test-a hippocampal-dependent memory task-without the convulsant or proconvulsant activity associated with nonselective, GABA(A) receptor inverse agonists.
Asunto(s)
Cognición/efectos de los fármacos , Agonistas del GABA/síntesis química , Nootrópicos/síntesis química , Receptores de GABA-A/efectos de los fármacos , Tiazoles/síntesis química , Tiofenos/síntesis química , Animales , Encéfalo/metabolismo , Línea Celular , Femenino , Agonistas del GABA/efectos adversos , Agonistas del GABA/farmacología , Hipocampo/fisiología , Humanos , Técnicas In Vitro , Ligandos , Masculino , Aprendizaje por Laberinto/efectos de los fármacos , Memoria/efectos de los fármacos , Ratones , Nootrópicos/efectos adversos , Nootrópicos/farmacología , Oocitos/efectos de los fármacos , Oocitos/fisiología , Técnicas de Placa-Clamp , Subunidades de Proteína , Ensayo de Unión Radioligante , Ratas , Convulsiones/inducido químicamente , Relación Estructura-Actividad , Tiazoles/efectos adversos , Tiazoles/farmacología , Tiofenos/efectos adversos , Tiofenos/farmacología , Xenopus laevisRESUMEN
Nonselective inverse agonists at the benzodiazepine binding site on the GABA-A chloride ion channel enhance cognitive performance in animals but cannot be used in the treatment of cognitive disorders because of anxiogenic and convulsant side effects. We have identified a novel series of GABA-A alpha5 receptor ligands during our search for alpha5 receptor inverse agonists as potential cognition enhancers. In particular, 6,6-dimethyl-3-(2-hydroxyethyl)thio-1-(thiazol-2-yl)-6,7-dihydro-2-benzothiophen-4(5H)-one (26) has been identified as a functionally selective GABA-A alpha5 inverse agonist.
Asunto(s)
Agonistas de Receptores de GABA-A , Cetonas/síntesis química , Tiofenos/síntesis química , Animales , Células Cultivadas , Cognición , Humanos , Cetonas/farmacología , Ratones , Tiazoles/síntesis química , Tiazoles/farmacología , Tiofenos/farmacología , Xenopus laevisRESUMEN
This new conference on Psychiatric Drug Research was organised by the Strategic Research Institute and was chaired by P McGonigle (Wyeth Research, USA) and D Schoepp (Eli Lilly, USA). The 2-day meeting featured presentations from an international assembly of industrial and academic experts who have significantly contributed to the current body of knowledge in the field of psychotherapeutics. D Weinberger (NIMH, USA) gave an elegant keynote lecture on the application of genomics in psychopharmacology. Other presentations covered the latest technological advances, animal models and mechanistic approaches utilised in drug discovery for neuropsychiatric disorders and reviewed the current status of numerous novel targets resulting from these strategies.
Asunto(s)
Antipsicóticos/farmacología , Animales , Antipsicóticos/uso terapéutico , Modelos Animales de Enfermedad , Sistemas de Liberación de Medicamentos , Diseño de Fármacos , Humanos , Trastornos Mentales/tratamiento farmacológicoRESUMEN
Benzodiazepines are sedative hypnotics that produce marked anterograde amnesia in humans. These pharmacological properties are thought to result from the potentiation of GABA-A receptor function and subsequent attenuation of long-term potentiation (LTP), however many reports have suggested this is not the case for triazolam. Using electrophysiological recordings in a cell line expressing recombinant GABA-A receptors, we confirm that triazolam is an efficacious positive allosteric modulator of GABA-A receptors. Triazolam also slowed the decay of spontaneous inhibitory synaptic currents, reduced the amplitude of fEPSPs elicited during a theta burst and reduced the magnitude of LTP in hippocampal CA1 neurones in vitro. These data show that triazolam modifies LTP induction consistent with an enhancement of GABA-A receptor function via activation of the allosteric benzodiazepine-site.