Background

• Hyperactivity of muscarinic acetylcholine receptor mAChR3 is involved in pathogenesis of Bronchial asthma and Chronic obstructive pulmonary disease (COPD) by causing abnormal airway contraction and mucus secretion.
• Current non-selective therapeutic drugs exhibit severe adverse effects.
• There's a pressing need for more selective drugs against COPD.
• This study aims at discovering highly selective inhibitors of mAChR3 with minimal side effects

‍Methodology

• Full-length mAChR3 model was obtained by homology modeling.
• Using the ICM Pocket Finder algorithm orthosteric binding site has been identified.
• Molecular docking of the pre-selected focused library was performed.
• Top 2% of compounds were selected by docking score followed by the human triage by visual inspection.
• 23 candidates were selected.
• The reaction of tracheal preparations to the application of acetylcholine (100 uM) was used to test the potency of selected compounds.

Results

• 3 compounds appeared to be the most promising.
• The compound THPT-1 demonstrated the IC50 of 162 nM.
• Selectivity was assessed by testing the impact of THPT-1/4 on mAChR2, nicotinic cholinergic and adrenergic receptors.
• No off-target effects were detected.
• THPT-1 shares the binding mode with highly active non-selective antagonist of mAChRs tiotropium, which explains its high activity.
• The selectivity can be explained by additional interactions of THPT-1 with the binding pocket.
• 7 derivatives of THPT-1 were selected for further evaluation.
• The compliance of the compounds with the binding mode was enforced.
• 3 compounds were active and selective.
• The best one THPO-4 had the highest activity with IC50 of 3.09 nM.