Calcium-Sensing Receptor Negative Allosteric Modulators Oppose Contraction of Mouse Airways.

Abstract

Asthma is a heterogeneous chronic airways disease with an unmet need for improved therapeutics in uncontrolled severe disease. The calcium-sensing receptor (CaSR) is a G protein-coupled receptor upregulated in asthma. The CaSR agonist, spermine, is also increased in asthmatic airways and contributes to bronchoconstriction. CaSR negative allosteric modulators (NAMs) oppose chronic airway inflammation, remodelling and hyperresponsiveness in murine and guinea pig asthma models, but whether CaSR NAMs are effective acute bronchodilators compared to standard-of-care has not yet been established. Further, the ability of different classes of NAMs to inhibit spermine-induced CaSR signaling or MCh-induced airway contraction has not been quantified. Here, we show CaSR NAMs differentially inhibit spermine-induced intracellular calcium mobilisation and inositol monophosphate accumulation in HEK293 cells stably expressing the CaSR. NAMs reverse methacholine (MCh)-mediated airway contraction in mouse precision cut lung slices with similar maximal relaxation compared to the standard treatment, salbutamol. Of note, the bronchodilator effects of CaSR NAMs are maintained under conditions of β2 adrenergic receptor desensitization when salbutamol efficacy is abolished. Furthermore, overnight treatment with some, but not all, CaSR NAMs prevents MCh-mediated bronchoconstriction. These findings further support the CaSR as a putative drug target, and NAMs as alternative or adjunct bronchodilators, in asthma.