title: Kinetic properties of "dual" orexin receptor antagonists at OX1R and OX2R orexin receptors.
abstract: Orexin receptor antagonists represent attractive targets for the development of drugs for the treatment of insomnia. Both efficacy and safety are crucial in clinical settings and thorough investigations of pharmacokinetics and pharmacodynamics can predict contributing factors such as duration of action and undesirable effects. To this end, we studied the interactions between various "dual" orexin receptor antagonists and the orexin receptors, OX1R and OX2R, over time using saturation and competition radioligand binding with [(3)H]-BBAC ((S)-N-([1,1'-biphenyl]-2-yl)-1-(2-((1-methyl-1H-benzo[d]imidazol-2-yl)thio)acetyl)pyrrolidine-2-carboxamide). In addition, the kinetics of these compounds were investigated in cells expressing human, mouse and rat OX1R and OX2R using FLIPR® assays for calcium accumulation. We demonstrate that almorexant reaches equilibrium very slowly at OX2R, whereas SB-649868, suvorexant, and filorexant may take hours to reach steady state at both orexin receptors. By contrast, compounds such as BBAC or the selective OX2R antagonist IPSU ((2-((1H-Indol-3-yl)methyl)-9-(4-methoxypyrimidin-2-yl)-2,9-diazaspiro[5.5]undecan-1-one) bind rapidly and reach equilibrium very quickly in binding and/or functional assays. Overall, the "dual" antagonists tested here tend to be rather unselective under non-equilibrium conditions and reach equilibrium very slowly. Once equilibrium is reached, each ligand demonstrates a selectivity profile that is however, distinct from the non-equilibrium condition. The slow kinetics of the "dual" antagonists tested suggest that in vitro receptor occupancy may be longer lasting than would be predicted. This raises questions as to whether pharmacokinetic studies measuring plasma or brain levels of these antagonists are accurate reflections of receptor occupancy in vivo.
authors.affiliation: Department of Pharmacology and Therapeutics, Faculty of Medicine, Dentistry and Health Sciences, School of Medicine, The University of Melbourne Parkville, VIC, Australia ; The Florey Institute of Neuroscience and Mental Health, The University of Melbourne Parkville, VIC, Australia.
authors.forename: Gabrielle E
authors.initials: GE
authors.lastname: Callander
authors.affiliation: Department of Neuroscience, Novartis Institutes for Biomedical Research Basel, Switzerland.
authors.forename: Morenike
authors.initials: M
authors.lastname: Olorunda
authors.affiliation: Department of Neuroscience, Novartis Institutes for Biomedical Research Basel, Switzerland.
authors.forename: Dominique
authors.initials: D
authors.lastname: Monna
authors.affiliation: Department of Neuroscience, Novartis Institutes for Biomedical Research Basel, Switzerland.
authors.forename: Edi
authors.initials: E
authors.lastname: Schuepbach
authors.affiliation: Department of Neuroscience, Novartis Institutes for Biomedical Research Basel, Switzerland.
authors.forename: Daniel
authors.initials: D
authors.lastname: Langenegger
authors.affiliation: Global Discovery Chemistry, Novartis Institutes for Biomedical Research Basel, Switzerland.
authors.forename: Claudia
authors.initials: C
authors.lastname: Betschart
authors.affiliation: Global Discovery Chemistry, Novartis Institutes for Biomedical Research Basel, Switzerland.
authors.forename: Samuel
authors.initials: S
authors.lastname: Hintermann
authors.affiliation: Global Discovery Chemistry, Novartis Institutes for Biomedical Research Basel, Switzerland.
authors.forename: Dirk
authors.initials: D
authors.lastname: Behnke
authors.affiliation: Global Discovery Chemistry, Novartis Institutes for Biomedical Research Basel, Switzerland.
authors.forename: Simona
authors.initials: S
authors.lastname: Cotesta
authors.affiliation: Department of Neuroscience, Novartis Institutes for Biomedical Research Basel, Switzerland.
authors.forename: Markus
authors.initials: M
authors.lastname: Fendt
authors.affiliation: Metabolism and Pharmacokinetics, Novartis Institutes for Biomedical Research Basel, Switzerland.
authors.forename: Grit
authors.initials: G
authors.lastname: Laue
authors.affiliation: Global Discovery Chemistry, Novartis Institutes for Biomedical Research Basel, Switzerland.
authors.forename: Silvio
authors.initials: S
authors.lastname: Ofner
authors.affiliation: Global Discovery Chemistry, Novartis Institutes for Biomedical Research Basel, Switzerland.
authors.forename: Emmanuelle
authors.initials: E
authors.lastname: Briard
authors.affiliation: Department of Neuroscience, Novartis Institutes for Biomedical Research Basel, Switzerland ; Centre for Neurobiology Hamburg, Institute for Synaptic Physiology Hamburg, Germany.
authors.forename: Christine E
authors.initials: CE
authors.lastname: Gee
authors.affiliation: Department of Neuroscience, Novartis Institutes for Biomedical Research Basel, Switzerland.
authors.forename: Laura H
authors.initials: LH
authors.lastname: Jacobson
authors.affiliation: Department of Pharmacology and Therapeutics, Faculty of Medicine, Dentistry and Health Sciences, School of Medicine, The University of Melbourne Parkville, VIC, Australia ; The Florey Institute of Neuroscience and Mental Health, The University of Melbourne Parkville, VIC, Australia ; Department of Neuroscience, Novartis Institutes for Biomedical Research Basel, Switzerland.
authors.forename: Daniel
authors.initials: D
authors.lastname: Hoyer
keywords: dual orexin receptor antagonists; kinetics; orexin receptor antagonists; radioligands