Dualsteric muscarinic antagonists--orthosteric binding pose controls allosteric subtype selectivity

Area of Science:

• Pharmacology
• Molecular Biology
• Medicinal Chemistry

Background:

• Bivalent ligands can bind to adjacent receptors or bridge parts of a single receptor.
• Muscarinic receptor agonists can exhibit dual binding to orthosteric and allosteric sites.
• Extending bivalent ligand concepts to antagonism is an emerging area.

Purpose of the Study:

• To investigate the bitopic binding mode of novel bivalent antagonists for muscarinic receptors.
• To explore subtype selectivity and structure-activity relationships of these new antagonist hybrids.
• To demonstrate the feasibility of designing bitopic antagonists for G protein-coupled receptors.

Main Methods:

• Synthesis of bivalent ligands incorporating phthalimide/naphthalimide and atropine/scopolamine moieties linked by hexamethonium.
• Structure-activity relationship (SAR) studies.
• Site-directed mutagenesis, molecular docking, and molecular dynamics simulations.

Main Results:

• First demonstration of a bitopic binding mode for bivalent muscarinic receptor antagonist hybrids.
• Spatial orientation of the orthosteric tropane moiety influences M2/M5 subtype selectivity.
• SAR, mutagenesis, docking, and simulations support the proposed binding mode.

Conclusions:

• Bivalent antagonism at muscarinic receptors is achievable through a bitopic binding mode.
• Designed bitopic antagonists offer potential for subtype-selective targeting.
• This work expands the understanding of bivalent ligand design for GPCRs.