The GPCR superfamily of ligand regulated receptors has proven to be a rich source of targets for development of therapeutics for a myriad of human diseases. The orexin 1 and orexin 2 receptors are class A GPCR?s differentially expressed in the central nervous system. The orexin 1 receptor is most abundantly expressed in the locus coeruleus and is thought to control aspects of emotion, reward, and the autonomic nervous system, whereas the orexin 2 receptor is expressed in regions controlling arousal such as the tubermammillary nucleus, an important site for the regulation of sleep/wakefulness. Almost 20 years after their initial discovery, the first potent dual orexin 1 / orexin 2 receptor antagonist therapeutic has been brought to market for insomnia (Belsomera , suvorexant, Merck). Despite a massive effort to identify antagonists of the the orexin receptor, almost no reports of small molecule agonists appear in the primary or patent literature. Elegant genetic ablation experiments using orexin knock-out animals and experiments with intracerebroventricular dosing of orexin A or orexin B peptides suggests a role for orexin receptor agonists or potentiators for a number of potential indications including: 1) depression; 2) learning and memory (cognition); 3) attention deficit hyperactivity disorder (ADHD); 4) treatment for colon cancer; and 5) sleep disorders including narcolepsy. While the orexin peptides are potent agonists of both orexin receptors, they are not selective nor do they cross the blood brain barrier well, making them poor probe substrates for in vivo pharmacology studies. This provides the impetus to identify small molecule, brain penetrant activators of the orexin receptors to interrogate the receptors function in the context of disease states. We have optimized a cell-based high-throughput screening compatible primary assay that specifically measures the functional activity of orexin 1 and orexin 2. A preliminary 10k pilot screen was performed leading to the identification of a number of small molecule agonists of these receptors demonstrating this assay to be robust and reproducible. A full HTS screening campaign of the Scripps Institutional Drug Discovery Library (~640k compounds) will lead to the identification of multiple classes of orexin receptor agonists and potentiators for further development. In an iterative process, these validated hits will be characterized through a cascade of in vitro cell-based assays to determine potency, selectivity and mechanism of action. Preliminary medicinal chemistry lead optimization will identify early structure activity relationships and in vitro drug metabolism will be assessed to confirm tractibility of early leads. These efforts will provide first in-class chemical tools to be used to further probe orexin receptor function in animal models of disease.
The orexin 1 receptor is most abundantly expressed in the locus coeruleus and is thought to control aspects of emotion, reward, and the autonomic nervous system, whereas the orexin 2 receptor is expressed in regions controlling arousal such as the tubermammillary nucleus, an important site for the regulation of sleep/wakefulness. An intense effort to develop antagonists for this class of receptors for numerous CNS indications has ensued over the past decade identifying the orexin receptors as highly tractable therapeutic targets, however little effort has been spent to identify agonists or positive allosteric modulators. The identification of novel, small molecule non- peptide activators of the orexin receptors will provide pharmacological tools to interrogate the function of the orexin receptors in the context of disease including cognition, ADHD, narcolepsy, depression and cancer.
