Pharmacophore Model To Discover OX₁ and OX₂ Orexin Receptor Ligands

Small molecule agonists and antagonists of the orexinergic system have key implications for research and therapeutic purposes. We report a pharmacophore model trained on ∼200 antagonists and prospectively validated by screening a collection of ∼137,000 compounds. The resulting hit list, 395 compounds, was tested for OX₁ and OX₂ receptor activity using calcium mobilization assay in recombinant cell lines. Validation was conducted using both calcium mobilization and [¹²⁵I]-orexin‑A competition binding. Compounds 4–7 have weak agonist activity and K_i’s in the 1–30 μM range; compounds 8–14 are antagonists with K_i’s in the 0.1–10 μM range for OX₂ and 1–50 μM for the OX₁ receptor. Docking simulations were used to devise a working hypothesis where two subpockets are important for activation, one between TM5 and TM6 lined by Phe5.42, Tyr5.47, and Tyr6.48 and another above the orthosteric pocket lined by Asp2.65 and Tyr7.32.