Abstract

The main objective of this dissertation was to gain an understanding of orexin receptor activation at the molecular level and apply it in discovery of novel orexin receptor ligands. As non-peptide orexin receptor activators were almost completely unknown at the start of this study, attention was focused on them. To accomplish these goals, I utilized a combination of molecular modelling and pharmacological in vitro studies. First, I studied the known orexin receptor ligands by structure- and ligand-based computational methods, and assembled the hypothesized activation features for a pharmacophore model. The model was utilized in a virtual screening, and a hit list of 395 compounds continued to a pharmacological screening phase, wherein I assessed their activities in a functional Ca2+-based screening assay developed particularly for that purpose. I validated the screening hits in the competition binding and Ca2+ elevation assays; six compounds showed weak agonist activity and Ki’s in the 1−30 µM range (Publication I). Antagonists with sub-micromolar binding affinities were also identified. Retrospective docking simulations of these agonistic hits and known non-peptide orexin receptor agonists (Nag26 and Yan7874, the latter of which was pharmacologically characterized in Publication II) were used to devise a working hypothesis of the binding pocket regions important for orexin receptor activation. Interactions in the antagonist binding region and two additional sub-pockets—one between TM5 and TM6, and the other approximately one helical turn above the antagonist binding site close to TM7—would be needed for orexin receptor activation (Publication I). Relying on this, I constructed a targeted azulene-based combinatory compound library accessible to in-house chemistry. The azulene library was virtually screened at the crystal structure of OX2 receptor, and compounds selected from the hit list were synthesized and screened in vitro. I validated the hits as above, and novel antagonists, weak agonists and compounds potentiating the actions of orexin-A were identified (Publications III and IV). The literature review focuses on the concept of GPCR activation and the orexin system: its structure, functions, and pharmaceutical applications thereof.
Original languageEnglish
Supervisors/Advisors
  • Xhaard, Henri, Supervisor
  • Kukkonen, Jyrki (P), Supervisor
Place of PublicationHelsinki
Publisher
Print ISBNs978-951-51-4354-9
Publication statusPublished - 2018
MoE publication typeG5 Doctoral dissertation (article)

Fields of Science

  • Orexins
  • Orexin Receptors
  • +agonists
  • Ligands
  • Azulenes
  • Binding Sites
  • Binding, Competitive
  • Protein Binding
  • Sleep Wake Disorders
  • Drug Design
  • Small Molecule Libraries
  • 317 Pharmacy

Cite this

Turku, A. (2018). Discovery of OX1 and OX2 orexin receptor ligands. Helsinki: Helsingin yliopisto.