TC 2559 difumarate

5-I A-85380 and TC-2559 differentially activate heterologously expressed alpha4beta2 nicotinic receptors.[Pubmed:16674940]

Eur J Pharmacol. 2006 Jun 6;539(1-2):10-7.

The neuronal nicotinic acetylcholine receptor alpha4 and beta2 subunits expressed in heterologous expression systems assemble into at least two distinct subunit stoichiometries of alpha4beta2 receptor. The (alpha4)2(beta2)3 stoichiometry is about 100-fold more sensitive to acetylcholine than the (alpha4)3(beta2)2 stoichiometry. In order to investigate if agonists in general distinguish high- and low-affinity alpha4beta2 nicotinic acetylcholine receptors, we have expressed human alpha4 and beta2 nicotinic acetylcholine receptor subunits in two different expression systems. The relative amounts of alpha4beta2 nicotinic acetylcholine receptors with high- and low-affinity for acetylcholine were manipulated by (a) injecting the subunit cDNAs at different alpha:beta ratios into Xenopus oocytes and (b) by culturing HEK-293 cells stably expressing alpha4beta2 nicotinic acetylcholine receptors overnight at different temperatures. The sensitivities of the alpha4beta2 nicotinic acetylcholine receptors to the agonists acetylcholine, 5-I A-85380, and TC-2559 were investigated using the voltage-clamp technique on Xenopus oocytes and using a fluorescent imaging plate reader to measure calcium responses from HEK-293 cells. Like acetylcholine, 5-I A-85380 produced biphasic concentration-response curves and the high-affinity component became larger when the cells were manipulated to produce a greater proportion of (alpha4)2(beta2)3 nicotinic acetylcholine receptors. Interestingly, under all circumstances, TC-2559 produced monophasic concentration-response curves. In oocytes injected with alpha4 and beta2 subunits in the 1:1 ratio the maximum effect of TC-2559 was 28% of that of acetylcholine. The EC50 for TC-2559 was not changed when oocytes were manipulated to express exclusively (alpha4)2(beta2)3 nicotinic acetylcholine receptors, however, the maximum effect of TC-2559 was dramatically enhanced. These results suggest that TC-2559 is a selective agonist of the (alpha4)2(beta2)3 nicotinic acetylcholine receptor stoichiometry.

The nicotinic alpha 4 beta 2 receptor selective agonist, TC-2559, increases dopamine neuronal activity in the ventral tegmental area of rat midbrain slices.[Pubmed:12871651]

Neuropharmacology. 2003 Sep;45(3):334-44.

The ability of alpha4beta2 nicotinic acetylcholine receptors to modulate dopaminergic (DA) cell activity in the ventral tegmental area (VTA) in rat midbrain slices was assessed using a selective alpha4beta2 receptor agonist, TC-2559 ((E)-N-methyl-4-[3-(5-ethoxypyridin)y1]-3-buten-1-amine). The selectivity of TC-2559 was characterized across 6 recombinant human nicotinic receptors (alpha4beta2, alpha2beta4, alpha4beta4, alpha3beta4, alpha3beta2 and alpha7) stably expressed in mammalian cell lines. Using a fluorescent imaging plate reader and fluo-3 to monitor changes in intracellular calcium, TC-2559 was found to be at least 69 fold more potent on alpha4beta2 than on other heteromeric subtypes, with an efficacy of 33%. No activity on the homomeric alpha7 subtype was detected. TC-2559 also showed selectivity for alpha4beta2 over the alpha4beta4 and alpha7 subtypes expressed in Xenopus oocytes. When bath applied to VTA slices, TC-2559 increased the firing of DA cells in a dose-dependent manner, in the same concentration range that activates alpha4beta2 receptors in recombinant cell lines or oocytes. The effect of TC-2559 was blocked by 2 microM dihydro-beta-erythroidine (an alpha4beta2-preferring antagonist), but not by 10 nM methyllycaconitine (an alpha7 antagonist). Glutamate receptor antagonists (6-cyano-7-nitroquinoxaline-2,3-dione and D(-)-2-amino-5-phosphonopentanoic acid) did not reduce TC-2559-induced responses, suggesting that the increase in DA cell firing induced by TC-2559 is caused by direct postsynaptic depolarisation via the activation of alpha4beta2 receptors and not by enhancement of glutamate release.

TC-2559: a novel orally active ligand selective at neuronal acetylcholine receptors.[Pubmed:11099699]

Eur J Pharmacol. 2000 Dec 1;409(1):45-55.

TC-2559 [(E)-N-Methyl-4-[3-(5-ethoxypyridin)yl]-3-buten-1-amine] is a novel nicotinic agonist markedly more selective than recently reported novel nicotinic receptor ligands (selectivity ratio for central nervous system (CNS) to peripheral nervous system (PNS)>4000). TC-2559 competes effectively with [3H]-nicotine binding (K(i)=5 nM) but not with [125I]-bungarotoxin (>50,000 nM). Dopamine release from striatal synaptosomes and ion flux from thalamic synaptosomes indicate that TC-2559 is potent and efficacious in the activation of CNS receptors and significantly reduced glutamate-induced neurotoxicity in vitro. TC-2559 has no detectable effects on muscle and ganglion-type nicotinic acetylcholine receptors at concentrations up to 1 mM. TC-2559 significantly attenuates scopolamine-induced cognitive deficits in a step-through passive avoidance task. Acute and repeated oral dosing of TC-2559 enhances performance in a radial arm maze task. In contrast to the effects of equimolar concentrations of (-) nicotine, TC-2559 does not induce hypothermia and locomotor activity is not enhanced following repeated daily administration of 14 days. TC-2559 has a markedly enhanced CNS-PNS selectivity ratio and an intra-CNS selectivity as evidenced by the improved cognition without increased locomotor activity. The in vitro and in vivo studies in the present study suggest that TC-2559 has the desired profile to be further evaluated as a potential therapeutic agent for neurodegenerative diseases.