Orexin receptor


The orexin receptor is a G-protein-coupled receptor that binds the neuropeptide orexin. There are two variants, OX1 and OX2, each encoded by a different gene.
Both orexin receptors exhibit a similar pharmacology - the 2 orexin peptides, orexin-A and orexin-B, bind to both receptors and, in each case, agonist binding results in an increase in intracellular calcium levels. However, orexin-B shows a 10-fold selectivity for orexin receptor type 2, whilst orexin-A is equipotent at both receptors.
Several orexin receptor antagonists are in development for potential use in sleep disorders. The first of these, Suvorexant, has been on the market in the United States since 2015. There are two orexin agonists under development.

Synthetic ligands

Several drugs acting on the orexin system are under development, either orexin agonists for the treatment of conditions such as narcolepsy, or orexin antagonists for insomnia. No neuropeptide agonists are yet available, although synthetic Orexin-A polypeptide has been made available as a nasal spray and tested on monkeys. One non-peptide antagonist is currently available in the U.S., Merck's suvorexant,; two additional agents are in development: SB-649,868 by GlaxoSmithKline, for sleep disorders, and ACT-462206, currently in human clinical trials. Another drug in development, almorexant by Actelion, was abandoned due to adverse effects.
Most ligands acting on the orexin system so far are polypeptides modified from the endogenous agonists Orexin-A and Orexin-B, however there are some subtype-selective non-peptide antagonists available for research purposes.