Efficacy of selective 5-HT6 receptor ligands determined by monitoring 5-HT6 receptor-mediated cAMP signaling pathways.
1. Two novel selective 5-HT6 receptor ligands E-6801 (6-chloro-N-(3-(2-(dimethylamino)ethyl)-1H-indol-5-yl)imidazo[2,1-b]thiazole-5-sulfonamide) and E-6837 (5-chloro-N-(3-(2-(dimethylamino)ethyl)-1H-indol-5-yl)naphthalene-2-sulfonamide) were investigated and compared to the putative 5-HT6 receptor antagonists SB-271046 (5-chloro-N-(4-methoxy-3-(piperazin-1-yl)phenyl)-3-methylbenzo[b]thiophene-2-sulfonamide) and Ro 04-06790 (N-(2,6-bis(methylamino)pyrimidin-4-yl)-4-aminobenzenesulfonamide) using a cAMP-mediated pathway. 2. Forskolin stimulation, to increase the magnitude of agonist cAMP responses, and site-directed mutagenesis of the 5-HT6 receptor, in order to yield constitutively active receptor, were applied. 3. 5-HT (E(max), % over basal: 200), E-6801 (120) and E-6837 (23) induced cAMP formation at the rat 5-HT6 receptor. In the copresence of forskolin, cAMP responses were more potent and enhanced to 294 (5-HT, % over forskolin), 250 (E-6801) and 207 (E-6837), respectively. 5-HT-mediated cAMP formation was dose-dependently blocked by SB-271046 (pA(2): 8.76+/-0.22) and Ro 04-6790 (pA(2): 7.89+/-0.10) and not affected by the copresence of forskolin. Both E-6801 and E-6837 yielded partial antagonism of the 5-HT response in the absence of forskolin, whereas antagonism was either completely absent (E-6801) or attenuated (E-6837) in the copresence of forskolin. Intrinsic activity of these 5-HT6 receptor ligands at a constitutively active human S267K 5-HT6 receptor in Cos-7 cells indicated similar efficacy (E(max), % over basal) for 5-HT (97), E-6801 (91) and E-6837 (100), while Ro 04-6790 (-33) and SB-271046 (-39) were equi-efficacious inverse agonists. 4. The use of either forskolin or a constitutively active S267K 5-HT6 receptor enhances the resolution for monitoring the efficacy of 5-HT6 receptor ligands. E-6801 and E-6837 are potent partial agonists at the 5-HT6 receptor. Ro 04-6790 and SB-271046 appear to act as inverse agonists/antagonists.
Romero
Gonzalo
G
Laboratorios Dr Esteve SA, Av. Mare de Déu de Montserrat 221, 08041 Barcelona, Spain.
Sánchez
Elisabeth
E
Pujol
Marta
M
Pérez
Pilar
P
Codony
Xavier
X
Holenz
Jörg
J
Buschmann
Helmut
H
Pauwels
Petrus J
PJ
D000818:Animals; D001483:Base Sequence; D002460:Cell Line; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000378:metabolism*; D017931:DNA Primers; D006801:Humans; D008024:Ligands; D010957:Plasmids; D051381:Rats; D011985:Receptors, Serotonin / Q000187:drug effects / Q000378:metabolism*; D017366:Serotonin Receptor Agonists / Q000494:pharmacology; D015398:Signal Transduction
D017931:DNA Primers; D008024:Ligands; D011985:Receptors, Serotonin; D017366:Serotonin Receptor Agonists; C097216:serotonin 6 receptor; D005576:Colforsin; D000242:Cyclic AMP