Acetylcholine receptors (muscarinic) (version 2019.4) in the IUPHAR/BPS Guide to Pharmacology Database

Comparative spasmolytic effect between Cinnamomum tamala and Cinnamomum verum leaf essential oils and eugenol through in vitro and in silico approaches

Cinnamomum tamala and Cinnamomum verum are known for their folk medicinal usage in treating gastrointestinal ailments. The spasmolytic activity of essential oils was studied using isolated rat ileum. The results indicate that C. tamala, despite having a lower content of eugenol (60%), shows a spasmolytic potential of 68.01 ± 2.63% (EC₅₀ = 110.12 ± 13.58 μg/mL) while C. verum with rich eugenol (80%) shows lesser spasmolytic potential (38.96 ± 0.63%) and fails to attain an EC₅₀ value. Upon comparison with standard eugenol's percentage of spasmolytic (35.68 ± 2.57%), it is evident that the action of these essential oils does not solely rely on the major component but the synergistic role in association with other components of the mixture influences the pharmacological action of the essential oils. In silico docking of phytochemicals of leaf essential oils with M₂ (M₂AChR) and M₃ muscarinic (M₃AChR) and nicotinic acetylcholine receptor (nAChR) was carried out to determine the type of receptors through which the essential oils had spasmolytic potential. The binding affinity for eugenol with nAChR shows a better docking score than M₂AChR and M₃AChR.

Discovery of [11C]MK-6884: A Positron Emission Tomography (PET) Imaging Agent for the Study of M4Muscarinic Receptor Positive Allosteric Modulators (PAMs) in Neurodegenerative Diseases

The measurement of receptor occupancy (RO) using positron emission tomography (PET) has been instrumental in guiding discovery and development of CNS directed therapeutics. We and others have investigated muscarinic acetylcholine receptor 4 (M4) positive allosteric modulators (PAMs) for the treatment of symptoms associated with neuropsychiatric disorders. In this article, we describe the synthesis, in vitro, and in vivo characterization of a series of central pyridine-related M4 PAMs that can be conveniently radiolabeled with carbon-11 as PET tracers for the in vivo imaging of an allosteric binding site of the M4 receptor. We first demonstrated its feasibility by mapping the receptor distribution in mouse brain and confirming that a lead molecule 1 binds selectively to the receptor only in the presence of the orthosteric agonist carbachol. Through a competitive binding affinity assay and a number of physiochemical properties filters, several related compounds were identified as candidates for in vivo evaluation. These candidates were then radiolabeled with ¹¹C and studied in vivo in rhesus monkeys. This research eventually led to the discovery of the clinical radiotracer candidate [¹¹C]MK-6884.