A group of cationic amphiphilic drugs activates MRGPRX2 and induces scratching behavior in mice

Background: Mas gene-related G protein-coupled receptors (MRGPRs) are a G protein-coupled receptor family responsive to various exogenous and endogenous agonists, playing a fundamental role in pain and itch sensation. The primate specific family member MRGPRX2 and its murine orthologue MRGPRB2 are expressed by mast cells mediating IgEindependent signaling and pseudoallergic drug reactions. Objectives: Our aim was to increase knowledge about the function and regulation of MRGPRX2/MRGPRB2, which is of major importance in prevention of drug hypersensitivity reactions and drug-induced pruritus. Methods: To identify novel MRGPR (ant)agonists, we screened a library of pharmacologically active compounds by utilizing a high-throughput calcium mobilization assay. The identified hit compounds were analyzed for their pseudoallergic and pruritogenic effects in mice and human. Results: We found a class of commonly used drugs activating MRGPRX2 that, to a large extent, consists of antidepressants, antiallergic drugs, and antipsychotics. Three-dimensional pharmacophore modeling revealed structural similarities of the identified agonists, classifying them as cationic amphiphilic drugs. Mast cell activation was investigated by using the 3 representatively selected antidepressants clomipramine, paroxetine, and desipramine. Indeed, we were able to show a concentration-dependent activation and MRGPRX2-dependent degranulation of the human mast cell line LAD2 (Laboratory of Allergic Diseases-2). Furthermore, clomipramine, paroxetine, and desipramine were able to induce degranulation of human skin and murine peritoneal mast cells. These substances elicited dose-dependent scratching behavior following intradermal injection into C57BL/6 mice but less so in MRGPRB2-mutant mice, as well as wheal-and-flare reactions following intradermal injections in humans. Conclusion: Our results contribute to the characterization of structure-activity relationships and functionality of MRGPRX2 ligands and facilitate prediction of adverse reactions such as drug-induced pruritus to prevent severe drug hypersensitivity reactions. (J Allergy Clin Immunol 2021;148:506-22.)

Automated summary

Mas gene-related G protein-coupled receptors (MRGPRs) play a fundamental role in pain and itch sensation, with MRGPRX2 and its murine orthologue MRGPRB2 mediating pseudoallergic drug reactions. The study identified a class of commonly used drugs that activate MRGPRX2, primarily consisting of cationic amphiphilic drugs, leading to degranulation of mast cells and scratching behavior in both human and mice models. This research contributes to understanding the structure-activity relationships and functionality of MRGPRX2 ligands to predict and prevent adverse reactions such as drug-induced pruritus.