Alternate channel therapy for cystic fibrosis lung disease

Abstract

Cystic Fibrosis (CF) is the most common, severe, autosomal recessive disease in the Caucasian population, and is caused by mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene. A triple-combination drug therapy that restores CFTR function is now available for around 85-90% of the CF population. However, the remaining 10-15% carry rare and poorly characterized mutations that cannot benefit from this treatment. An alternative approach for this group is to use a CFTR-independent therapy, exploiting alternative ion channels and transporters (AICTs), to restore anion and fluid secretion. The main aim of this work was to identify drug candidates that target AICTs, and to determine if increasing the activity of the specific AICTs, TMEM16A, SLC26A9 and SLC26A4, could restore the airways environment in CF cells. 1400 FDA-approved drugs were screened on nasal airway organoids derived from CF patients with different mutations for their ability to boost fluid secretion. From the screen, the most promising 13 ‘hit’ compounds, that induced fluid secretion, were further evaluated on fully differentiated monolayers from three CF donors with rare CF mutations. Electrophysiological and ASL pH assays, combined with CRISPR-Cas gene knock-out of selective AICTs, showed that SLC26A9 was not active under the conditions tested, and none of the FDA compounds modulated TMEM16A activity, even when overexpressed under inflammatory conditions. However, under inflammatory conditions, TMEM16A regulated ASL pH after sustained calcium stimuli. Furthermore, SLC26A4 also regulated ASL pH in response to cAMP agonists and was the target of 2 FDA compounds. However, significant donor variability was observed in these functional measurements. Overall, this study clearly demonstrates that patients-derived airway organoids are a suitable in vitro model to screen compound libraries, which encourages a personalised approach to identify new therapies for orphan mutations. The results also support the use of AICTs as an alternative therapy for CF.