RT Journal Article
SR Electronic
T1 Biochemical and Electrophysiological Characterization of Almorexant, a Dual Orexin 1 Receptor (OX<sub>1</sub>)/Orexin 2 Receptor (OX<sub>2</sub>) Antagonist: Comparison with Selective OX<sub>1</sub> and OX<sub>2</sub> Antagonists
JF Molecular Pharmacology
JO Mol Pharmacol
FD American Society for Pharmacology and Experimental Therapeutics
SP 618
OP 631
DO 10.1124/mol.109.055152
VO 76
IS 3
A1 Pari Malherbe
A1 Edilio Borroni
A1 Emmanuel Pinard
A1 Joseph G. Wettstein
A1 Frédéric Knoflach
YR 2009
UL http://molpharm.aspetjournals.org/content/76/3/618.abstract
AB Recent preclinical and clinical research has shown that almorexant promotes sleep in animals and humans without disrupting the sleep architecture. Here, the pharmacology and kinetics of [3H]almorexant binding to human orexin 1 receptor (OX1)- and human orexin 2 receptor (OX2)-human embryonic kidney 293 membranes were characterized and compared with those of selective OX1 and OX2 antagonists, including 1-(5-(2-fluoro-phenyl)-2-methyl-thiazol-4-yl)-1-((S)-2-(5-phenyl-(1,3,4)oxadiazol-2-ylmethyl)-pyrrolidin-1-yl)-methanone (SB-674042), 1-(6,8-difluoro-2-methyl-quinolin-4-yl)-3-(4-dimethylamino-phenyl)-urea (SB-408124), and N-ethyl-2-[(6-methoxy-pyridin-3-yl)-(toluene-2-sulfonyl)-amino]-N-pyridin-3-ylmethyl-acetamide (EMPA). The effect of these antagonists was also examined in vitro on the spontaneous activity of rat ventral tegmental area (VTA) dopaminergic neurons. [3H]Almorexant bound to a single saturable site on hOX1 and hOX2 with high affinity (Kd of 1.3 and 0.17 nM, respectively). In Schild analyses using the [3H]inositol phosphates assay, almorexant acted as a competitive antagonist at hOX1 and as a noncompetitive-like antagonist at hOX2. In binding kinetic analyses, [3H]almorexant had fast association and dissociation rates at hOX1, whereas it had a fast association rate and a remarkably slow dissociation rate at hOX2. In the VTA, orexin-A potentiated the basal firing frequency to 175 ± 17% of control in approximately half of the neurons tested. In the presence of 1 μM SB-674042 or SB-408124, the effect of orexin-A was only partially antagonized. However, in the presence of 1 μM EMPA or 1 μM almorexant, the effect of orexin-A was completely antagonized. In conclusion, almorexant exhibited a noncompetitive and long-lasting pseudo-irreversible mode of antagonism as a result of its very slow rate of dissociation from OX2. The electrophysiology data suggest that OX2 might be more important than OX1 in mediating the effect of orexin-A on slow-firing of VTA dopaminergic neurons.