RESUMEN
Structure-activity relationship studies on the phenyl ring of 3-(5-pyridin-2-yl-2H-tetrazol-2-yl)benzonitrile 2 led to the discovery that small, non-hydrogen bond donor substituents at the 3-position led to a substantial increase in in vitro potency. In particular, 3-fluoro-5-(5-pyridin-2-yl-2H-tetrazol-2-yl)benzonitrile (7) is a highly potent and selective mGlu5 receptor antagonist with good rat pharmacokinetics, brain penetration, and in vivo receptor occupancy.
Asunto(s)
Antagonistas de Aminoácidos Excitadores/síntesis química , Antagonistas de Aminoácidos Excitadores/farmacología , Nitrilos/química , Nitrilos/farmacología , Piridinas/química , Receptores de Glutamato Metabotrópico/antagonistas & inhibidores , Tetrazoles/química , Animales , Encéfalo/efectos de los fármacos , Encéfalo/metabolismo , Antagonistas de Aminoácidos Excitadores/química , Cinética , Ratones , Estructura Molecular , Ratas , Receptor del Glutamato Metabotropico 5 , Receptores de Glutamato Metabotrópico/metabolismo , Sensibilidad y Especificidad , Relación Estructura-Actividad , Especificidad por SustratoRESUMEN
Structure-activity relationship studies on 3-(5-pyridin-2-yl-2H-tetrazol-2-yl)benzonitrile 2 led to the discovery of 2-(2-[3-(pyridin-3-yloxy)phenyl]-2H-tetrazol-5-yl)pyridine (10)-a highly potent and selective mGlu5 receptor antagonist with good brain penetration and in vivo receptor occupancy in rat and cross-species oral bioavailability.
Asunto(s)
Ansiolíticos/farmacocinética , Nitrilos/farmacocinética , Piridinas/química , Receptores de Glutamato Metabotrópico/antagonistas & inhibidores , Tetrazoles/química , Tetrazoles/farmacocinética , Administración Oral , Animales , Ansiolíticos/administración & dosificación , Ansiolíticos/química , Disponibilidad Biológica , Perros , Relación Dosis-Respuesta a Droga , Haplorrinos , Estructura Molecular , Nitrilos/química , Piridinas/farmacocinética , Ratas , Receptor del Glutamato Metabotropico 5 , Relación Estructura-ActividadRESUMEN
Structure-activity relationship studies performed around 3-fluoro-5-(5-pyridin-2-yl-2H-tetrazol-2-yl)benzonitrile for the purpose of developing novel mGlu5 receptor antagonists are described. Synthesis of a series of four-ring tetrazoles led to the discovery of 3-[3-fluoro-5-(5-pyridin-2-yl-2H-tetrazol-2-yl)phenyl]-4-methylpyridine, a highly potent, brain penetrant, azole-based mGlu5 receptor antagonist.
Asunto(s)
Ansiolíticos/farmacocinética , Nitrilos/síntesis química , Piridinas/síntesis química , Receptores de Glutamato Metabotrópico/antagonistas & inhibidores , Tetrazoles/síntesis química , Administración Oral , Animales , Ansiolíticos/administración & dosificación , Ansiolíticos/síntesis química , Disponibilidad Biológica , Estructura Molecular , Nitrilos/química , Nitrilos/farmacocinética , Piridinas/química , Piridinas/farmacocinética , Ratas , Receptor del Glutamato Metabotropico 5 , Relación Estructura-Actividad , Tetrazoles/química , Tetrazoles/farmacocinéticaRESUMEN
In vivo receptor occupancy of mGlu5 receptor antagonists was quantified in rat and mouse brain using the mGlu5 receptor selective antagonist [3H]3-methoxy-5-(pyridin-2-ylethynyl)pyridine) ([3H]methoxy-PEPy). Administration of [3H]methoxy-PEPy (50 microCi/kg i.v.) to mGlu5 receptor-deficient mice revealed binding at background levels in forebrain, whereas wild-type mice exhibited 14-fold higher binding in forebrain relative to cerebellum. Systemic administration of the mGlu5 receptor antagonists 2-methyl-6-(phenylethynyl)pyridine (MPEP) and 3-[(2-methyl-1,3-thiazol-4-yl)ethynyl]pyridine (MTEP) reduced the binding of [3H]methoxy-PEPy in rats and mice, reflecting mGlu5 receptor occupancy by these compounds. MPEP (10 mg/kg i.p.) and MTEP (3 mg/kg i.p.) maintained >75% receptor occupancy for 2 h in rats, while in mice MPEP and MTEP achieved >75% occupancy for only 30 and 15 min, respectively. Compound levels in plasma were substantially lower in mice suggesting species differences in receptor occupancy result from differences in absorption or metabolism of the compounds. These findings demonstrate that [3H]methoxy-PEPy is useful for determining the occupancy of mGlu5 receptors in the brain.
Asunto(s)
Piridinas/farmacología , Receptores de Glutamato Metabotrópico/antagonistas & inhibidores , Receptores de Glutamato Metabotrópico/metabolismo , Animales , Sitios de Unión , Hipocampo/metabolismo , Inyecciones Intraperitoneales , Inyecciones Intravenosas , Ligandos , Masculino , Ratones , Ratones Endogámicos C57BL , Prosencéfalo/metabolismo , Piridinas/metabolismo , Ensayo de Unión Radioligante/métodos , Ratas , Ratas Sprague-Dawley , Receptor del Glutamato Metabotropico 5 , Receptores de Glutamato Metabotrópico/genética , Especificidad de la Especie , Tiazoles/metabolismo , Tiazoles/farmacología , Factores de Tiempo , TritioRESUMEN
The binding of [3H]methoxymethyl-3-[(2-methyl-1,3-thiazol-4-yl)ethynyl]pyridine (methoxymethyl-MTEP), a potent and selective antagonist for metabotropic glutamate (mGlu)5 receptors, was characterized in rat brain both in vitro and in vivo. Nonspecific binding, as defined with 10 microM 2-methyl-6-(phenylethynyl)-pyridine (MPEP), was less than 10% of total binding in rat brain membranes. The binding of [3H]methoxymethyl-MTEP was of high affinity (K(d) = 20 +/- 2.7 nM), saturable (B(max) = 487 +/- 48 fmol/mg protein), and to a single site. The mGlu5 antagonists methoxymethyl-MTEP and MPEP displaced [3H]methoxymethyl-MTEP binding with IC50 values of 30 and 15 nM, respectively. In vivo administration of [3H]methoxymethyl-MTEP (50 microCi/kg i.v.) revealed 12-fold higher binding in hippocampus (an area enriched in mGlu5 receptors) relative to cerebellum (an area with few mGlu5 receptors) in rats. Similarly, administration of [3H]methoxymethyl-MTEP to mGlu5-deficient mice demonstrated binding at background levels in forebrain, whereas wild-type littermates exhibited 17-fold higher binding in forebrain relative to cerebellum. Systemic administration of unlabeled mGlu5 antagonists methoxymethyl-MTEP and MPEP to rats reduced the binding of [3H]methoxymethyl-MTEP with ID50 values of 0.8 and 2 mg/kg i.p., respectively, 1 h post-treatment. The mGlu5 agonist 2-chloro-5-hydroxyphenylglycine (CHPG) (0.3, 1, and 3 micromol) dose-dependently increased phosphoinositide (PI) hydrolysis in the hippocampus after i.c.v. administration in rats. CHPG-evoked increases in PI hydrolysis were blocked with MPEP at a dose (10 mg/kg i.p.) that markedly reduced [3H]methoxymethyl-MTEP binding in vivo. These results indicate that [3H]methoxymethyl-MTEP is a selective radioligand for labeling mGlu5 and is useful for studying the binding of mGlu5 receptors in rat brain in vitro and in vivo.