Discovery of potent, selective and insurmountable MRGPRX2 antagonists for mast cell-driven disorders 2308475

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Abstract Introduction Mas-related G protein—coupled receptor X2 (MRGPRX2) is an important mediator of non-IgE—dependent mast cell activation and has emerged as a key target in pseudo-allergic reactions and chronic inflammatory diseases. Yet, drugs targeting this mechanism remain limited. We report the discovery and characterization of novel series of potent, selective, and insurmountable MRGPRX2 oral small-molecule antagonists. Methods Compounds were evaluated in vitro using CHO-K1 and HEK293 cells overexpressing human MRGPRX2, LAD2 human mast cells, and mast cells differentiated from mobilized CD34+ hematopoietic progenitor cells. Functional activity was assessed across multiple assay platforms – including calcium flux, β-arrestin recruitment, inositol monophosphate (IP1) accumulation and mast cell degranulation assays – using different MRGPRX2 agonists. Selectivity against the closest human homologs MRGPRX1 and MRGPRX4, dog and monkey MRGPRX2 orthologs, and a broad panel of G protein-coupled receptor proteins were tested to ensure high target specificity. Lead molecules were further evaluated in vivo in a humanized MRGPRX2 mouse model of cutaneous anaphylaxis for efficacy. Results Lead antagonists demonstrated potent and insurmountable inhibition of MRGPRX2-mediated responses across all cellular models and were active against all MRGPRX2 agonists tested. They exhibited minimal off-target activity, no cross-reactivity with dog and monkey orthologs, and no activity against MRGPRX1 and MRGPRX4, underscoring their high target selectivity. In vivo, lead compounds showed favorable pharmacokinetics and significantly reduced mast cell—dependent vascular leakage in a dose-dependent manner. Conclusion These findings highlight the therapeutic promise of those insurmountable MRGPRX2 antagonists for the treatment of mast cell—driven disorders. Funding Source Blueprint Medicines Corporation Topic Categories Translational and Interventional Immunology (TI)

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