Novel pyrazole compounds for pharmacological discrimination between receptor‐operated and store‐operated Ca 2+ entry pathways

Abstract

Background and purpose: Pyrazole derivatives have recently been suggested as selective blockers of transient receptor potential cation ( TRPC ) channels but their ability to distinguish between the TRPC and O rai pore complexes is ill‐defined. This study was designed to characterize a series of pyrazole derivatives in terms of TRPC / O rai selectivity and to delineate consequences of selective suppression of these pathways for mast cell activation. Experimental approach: Pyrazoles were generated by microwave‐assisted synthesis and tested for effects on Ca 2+ entry by F ura‐2 imaging and membrane currents by patch‐clamp recording. Experiments were performed in HEK 293 cells overexpressing TRPC 3 and in RBL ‐2 H 3 mast cells, which express classical store‐operated Ca 2+ entry mediated by O rai channels. The consequences of inhibitory effects on Ca 2+ signalling in RBL ‐2 H 3 cells were investigated at the level of both degranulation and nuclear factor of activated T‐cells activation. Key Results: P yr3, a previously suggested selective inhibitor of TRPC 3, inhibited Orai1‐ and TRPC 3‐mediated Ca 2+ entry and currents as well as mast cell activation with similar potency. By contrast, P yr6 exhibited a 37‐fold higher potency to inhibit O rai1‐mediated Ca 2+ entry as compared with TRPC 3‐mediated Ca 2+ entry and potently suppressed mast cell activation. The novel pyrazole P yr10 displayed substantial selectivity for TRPC 3‐mediated responses (18‐fold) and the selective block of TRPC 3 channels by P yr10 barely affected mast cell activation. Conclusions and Implications: The pyrazole derivatives P yr6 and P yr10 are able to distinguish between TRPC and O rai‐mediated Ca 2+ entry and may serve as useful tools for the analysis of cellular functions of the underlying Ca 2+ channels.