Identification and characterisation of selective antagonists for TMEM16A(acd) isoform for the treatment of obstructive respiratory diseases

Abstract

TMEM16A protein is a Ca²⁺ activated Cl^- channel associated with multiple diseases, including respiratory disease, for which it has become an attractive drug target. The channel is upregulated and over-activated in Airway Smooth Muscle (ASM) of asthmatic patients, leading to abnormal constriction of bronchi associated with severe Asthma¹. Relaxing ASM with antagonists of TMEM16A was proposed to serve as a novel mechanism of bronchodilation and an alternative to β-agonist treatment to improve lung function. Different isoforms are generated by alternative splicing, with two major splicing variants known as TMEM16A(abc), predominant in goblet cells and possibly involved in mucus secretion, and TMEM16A(acd), mainly expressed in human ASM². The aim of this study was to identify new chemical matter to antagonise TMEM16A. To that end, we established a FLIPR high throughput screening assay to identify novel chemotypes using a TMEM16A(acd)-expressing cell line. Surprisingly, we uncovered some chemotypes selective for TMEM16A(acd) over TMEM16A(abc), as confirmed by electrophysiological measurements. Measuring bronchodilation of mouse tracheal rings with the wire myograph, we showed that TMEM16A(acd) selective antagonists were not able to relax rodent tracheal rings as opposed to non-selective antagonists. We also showed that TMEM16A(acd) selective antagonists were unable to block TMEM16A short-circuit current of human bronchial epithelium. In conclusion, to our knowledge, this is the first report of small molecules able to selectively block TMEM16A(acd) while sparing TMEM16A(abc).

1- Wang et al, vol 141,1259, 2018.

2- Miner et al,vol 10, 2019.