Side Groups Convert the α7 Nicotinic Receptor Agonist Ether Quinuclidine into a Type I Positive Allosteric Modulator

Area of Science:

• Medicinal Chemistry
• Neuroscience
• Pharmacology

Background:

• The quinuclidine scaffold is crucial for developing nicotinic acetylcholine receptor (nAChR) agonists.
• Hydrophobic substituents at position 3 of quinuclidine enhance selectivity for α7 nAChRs.

Purpose of the Study:

• Synthesize and characterize novel 3-(pyridin-3-yloxy)quinuclidine ligands (ether quinuclidines).
• Investigate the structure-activity relationships of these ligands at the α7 nAChR.
• Identify new modulators of α7 nAChR function.

Main Methods:

• Chemical synthesis of six new ligands (compounds 4-9).
• Two-electrode voltage-clamp electrophysiology to assess receptor activation and potentiation.
• Single-channel recordings to analyze channel gating.
• Computational modeling to predict binding sites and interactions.

Main Results:

• Ligand 4 activated the α7 nAChR.
• Ligands 6, 8, and 9 potentiated acetylcholine (ACh)-evoked currents.
• Ligand 6 demonstrated the highest potency and efficacy as a potentiator (EC50 = 12.6 μM).
• Ligand 6 increased maximal ACh responses without altering current kinetics.
• Single-channel analysis revealed prolonged opening bursts with ligand 6.
• Computational studies identified an intersubunit binding site and key interactions, with Met276 mutation abolishing ligand 6's effect.

Conclusions:

• Ligand 6 represents a novel type I positive allosteric modulator (PAM-I) of the α7 nAChR.
• Structural features of ether quinuclidines influence their interaction with the α7 nAChR.
• The findings provide insights into the allosteric modulation of nAChRs.