RESUMEN
The dopamine transporter (DAT), located presynaptically on dopamine neurons, provides a marker for Parkinson's disease (Pd) and attention deficit hyperactivity disorder (ADHD). In ADHD, DAT density levels are elevated, while in Pd these levels are depleted. The depletion of DAT levels also corresponds with the loss of dopamine. We now describe the design, synthesis, biology, and SPECT imaging in nonhuman primates of second-generation (99m)technetium-based tropane ligands that bind potently and selectively to the DAT. We demonstrate that improved selectivity and biological stability allows sufficient agent to enter the brain and label the DAT in vivo to provide a quantitative measure of DAT density in nonhuman primates. We introduce FLUORATEC (N-[(2-((3'-N'-propyl-(1"R)-3"alpha-(4-fluorophenyl)tropane-2"beta-1-propanoyl)(2-mercaptoethyl)amino)acetyl)-2-aminoethanethiolato]technetium(V) oxide), a DAT imaging agent that has emerged from these studies and is now in phase 1 clinical trials in the U.S.
Asunto(s)
Encéfalo/metabolismo , Dopamina/metabolismo , Glicoproteínas de Membrana , Proteínas de Transporte de Membrana/metabolismo , Proteínas del Tejido Nervioso , Compuestos de Organotecnecio/síntesis química , Radiofármacos/síntesis química , Tropanos/síntesis química , Animales , Encéfalo/diagnóstico por imagen , Proteínas de Transporte de Dopamina a través de la Membrana Plasmática , Femenino , Técnicas In Vitro , Ligandos , Macaca fascicularis , Masculino , Compuestos de Organotecnecio/química , Compuestos de Organotecnecio/farmacocinética , Unión Proteica , Radiofármacos/química , Radiofármacos/farmacocinética , Estereoisomerismo , Tomografía Computarizada de Emisión de Fotón Único , Tropanos/química , Tropanos/farmacocinéticaRESUMEN
Methylphenidate (Ritalin) binds stereoselectively and enantioselectively to the dopamine transporter (DAT) and inhibits dopamine reuptake with in vitro and in vivo potency similar to that of cocaine. Unlike cocaine, it manifests little, if any, tolerance or addiction liability. Since this compound has a substantial clinical history, it provides an excellent template from which to design potential medications for cocaine abuse. It has long been assumed that a nitrogen, such as exists in cocaine and methylphenidate, is essential for interaction with monoamine transporters. We previously demonstrated that an amine nitrogen in phenyltropane analogues of cocaine is not necessary for conferring high DAT binding affinity. We now report the synthesis of oxacyclic and carbacyclic analogues of methylphenidate, including the four enantiomerically pure isomers of 2-(3,4-dichlorophenyl)-2-(tetrahydropyran-2-yl)acetic acid methyl ester. The threo isomers are potent and selective inhibitors of the DAT. This is the first generalization of the principle that the presence of nitrogen is not a necessity for DAT inhibition.
Asunto(s)
Proteínas Portadoras/antagonistas & inhibidores , Inhibidores de Captación de Dopamina/síntesis química , Glicoproteínas de Membrana/antagonistas & inhibidores , Moduladores del Transporte de Membrana , Proteínas de Transporte de Membrana/antagonistas & inhibidores , Metilfenidato/análogos & derivados , Metilfenidato/síntesis química , Proteínas del Tejido Nervioso , Fenilacetatos/síntesis química , Piranos/síntesis química , Inhibidores Selectivos de la Recaptación de Serotonina/síntesis química , Animales , Unión Competitiva , Núcleo Caudado/metabolismo , Dopamina/metabolismo , Proteínas de Transporte de Dopamina a través de la Membrana Plasmática , Inhibidores de Captación de Dopamina/química , Inhibidores de Captación de Dopamina/farmacología , Femenino , Técnicas In Vitro , Macaca fascicularis , Macaca mulatta , Masculino , Metilfenidato/química , Metilfenidato/farmacología , Fenilacetatos/química , Fenilacetatos/farmacología , Putamen/metabolismo , Piranos/química , Piranos/farmacología , Ensayo de Unión Radioligante , Serotonina/metabolismo , Proteínas de Transporte de Serotonina en la Membrana Plasmática , Inhibidores Selectivos de la Recaptación de Serotonina/química , Inhibidores Selectivos de la Recaptación de Serotonina/farmacología , Estereoisomerismo , Relación Estructura-ActividadRESUMEN
Cocaine is a powerful reinforcer and stimulant that binds to specific recognition sites associated with monoamine transporters in the mammalian brain. The search for a functional antagonist to the addictive properties of cocaine has focused on the discovery of a molecule that can inhibit cocaine binding to the dopamine transporter (DAT) but continue to allow dopamine transport by the DAT. No such dopamine-sparing cocaine antagonist has been reported and it is becoming evident that dopamine-sparing antagonism of the pharmacological effects of cocaine by a classical antagonist may not be possible. Herein we present a new concept for the design of dopamine-sparing cocaine antagonists. A unique approach is utilized to deliver an inhibitor that binds irreversibly to the DAT, then cleaves and leaves behind a small fragment attached to the DAT that blocks access by cocaine but permits dopamine transport. The design of these compounds takes advantage of a cysteinyl sulfhydryl group in the DAT. This group is hypothesized to attack the incoming inhibitor and lead to selective inhibition of the cocaine binding site while sparing dopamine transport. This concept of a mechanism based irreversible dopamine-sparing cocaine antagonist has now been demonstrated to be viable and, as example, the unsaturated 6 showed inhibition of cocaine (63%) at the DAT after 24h incubation, while at that point considerably less inhibition of dopamine is manifested (23%). In contrast, the epoxide 7 showed a greater inhibition of dopamine reuptake than cocaine binding at 24h (68% versus 18%).
Asunto(s)
Cocaína/antagonistas & inhibidores , Dopamina/fisiología , Proteínas de Transporte de Membrana/química , Proteínas del Tejido Nervioso , Proteínas Portadoras/efectos de los fármacos , Proteínas Portadoras/metabolismo , Línea Celular , Proteínas de Transporte de Dopamina a través de la Membrana Plasmática , Diseño de Fármacos , Humanos , Indicadores y Reactivos , Riñón/efectos de los fármacos , Riñón/metabolismo , Ligandos , Espectroscopía de Resonancia Magnética , Glicoproteínas de Membrana/efectos de los fármacos , Glicoproteínas de Membrana/metabolismo , Proteínas de Transporte de Membrana/efectos de los fármacos , Conformación Molecular , Proteínas de Transporte de Serotonina en la Membrana Plasmática , Relación Estructura-Actividad , Reactivos de SulfhidriloRESUMEN
The four 2,2,5-regioisomer counterparts of SCH 51048 were synthesized and evaluated. As with the parent series, only the two cis isomers possessed any in vitro activity, and only the activity of the isomer with the R-configuration at the tetrahydrofuran 2-carbon was significant. The activity data suggests that oxygen at only one of the two possible ring positions benzylic to the difluorobenzene participates usefully in active site binding.