Dualsteric GPCR targeting and functional selectivity: the paradigmatic M2 muscarinic acetylcholine receptor

Muscarinic acetylcholine receptors belong to Class A seven transmembrane helical receptors and serve as important drug targets in the treatment of various diseases such as chronic obstructive pulmonary disease, overactive bladder, bronchial asthma and glaucoma. Despite intensive research the discovery of experimental ligands which activate or block specific muscarinic receptor subtypes has only been successful for the M1 and M4 subtypes but remains a challenging task at the other subtypes. In recent years, ligands have been introduced which bind simultaneously to the acetylcholine binding site, that is, the orthosteric site, and to an allosteric binding site. These so-called dualsteric ligands display M2 subtype preference due to the addressing of the allosteric binding site. As proven recently, dualsteric receptor activation goes along with a pronounced signaling bias which follows clear structure–bias-relationships. Dualsteric receptor targeting might represent a common strategy to generate functional selectivity.