Discovery of a Fungal Metabolite as a Novel TMEM16a Inhibitor in Human Airway Epithelial Cells

Abstract

Transmembrane protein 16a (TMEM16a) is a Ca2+‐activated Cl‐ channel (CaCC) that expresses in various epithelia. Inhibition of TMEM16a has been reported as a potential strategy for attenuating severity and progression of asthma. The main objective of this study is to discover a novel TMEM16a inhibitor and mechanisms of its action. By screening, we found that N9, a fungal metabolite, inhibited UTP‐activated TMEM16a Cl‐ current in basolaterally permeabilized Calu‐3 cell monolayers with an IC50 of ~ 0.8 µM and maximal inhibitory effect being observed at 10 µM. Indeed, N9 had no cytotoxic effect and did not disrupt airway epithelial barrier function, suggesting that inhibitory effect of N9 on TMEM16a was not due to the disturbance of normal airway epithelial function. Electrophysiological analyses indicated that N9 suppressed both ionomycin‐ and thapsigargin‐activated TMEM16a Cl‐ current. In addition, N9 had no effect on elevated intracellular Ca2+ level induced by UTP and thapsigargin, suggesting that N9 reduced TMEM16a Cl‐ current in human airway epithelial cell monolayers in a Ca2+‐independent mechanism. Of particular importance, N9 also significantly suppressed TMEM16a‐mediated Cl‐ current induced by Eact, a direct activator of TMEM16a, indicating that N9 exerts a novel class of TMEM16a inhibitor in human airway epithelial cell monolayers. Hence, this study may lead to identification of a novel class of anti‐asthmatic drug from fungal metabolites.