Abstract
Purpose :
Manipulation of the parasympathetic nervous system of the eye has been implicated in regulating intraocular pressure (IOP). In particular, the activation of M3 muscarinic acetylcholine receptor (M3R) has been shown to induce pupillary muscle contraction, which pulls on the trabecular meshwork and improves aqueous outflow. Topical pilocarpine (PLC), an FDA-approved M3R agonist for glaucoma, faces limitations, like frequent doses and adverse cholinergic effects. This study aims to identify novel M3R agonists capable of regulating IOP using in silico and in vivo assays.
Methods :
First, we constructed a homology model of human M3R (hM3R) using Homology Modeling in Maestro (Schrodinger Inc., USA), and high-throughput virtual screening (HTVS) was performed with 6 hM3R agonists and 15 hM3R antagonists using Glide in Maestro. Triplicate molecular dynamics simulations validated nuanced binding mode differences between agonist and antagonist using Desmond in Maestro. Structural insights from in silico assays guided another HTVS, screening 1,667 FDA-approved drugs, identifying rivastigmine and edrophonium as potential hM3R agonists. The compounds' in vivo impact on IOP were assessed in six C57BL/6J mice using an iCare tonometer.
Results :
Initial HTVS with 21 hM3R ligands discovered crucial cation-π interactions common to agonists and antagonists, along with a unique π-π stacking interaction exclusive to antagonists. Subsequent in vivo studies revealed comparable IOP reductions among rivastigmine, edrophonium, and PLC but longer durations of action for rivastigmine (% IOP reduction = 21.04; time to return to baseline IOP = 5 hours) and edrophonium (% IOP reduction = 21.96; time to return to baseline IOP = 5.5 hours) compared to PLC (% IOP reduction = 22.13; time to return to baseline IOP = 4.4 hours). Notably, mild cholinergic adverse effects, like salivation, defecation, and urination, were observed with PLC and rivastigmine but absent with edrophonium.
Conclusions :
The study unveils structural insights into distinguishing M3R agonists and antagonists, emphasizing the importance of the ligand's nitrogen group and identifying exclusive π-π interactions in antagonists. Rivastigmine and edrophonium, identified as potential M3R agonists, present promising avenues for developing targeted medications with improved duration of action and fewer side effects than PLC in glaucoma patients.
This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.