Abstract
Cystic fibrosis (CF) is a fatal, autosomal and recessive genetic disease that is mainly due to inactivating mutations in the chloride channel CF transmembrane conductance regulator (CFTR). Sodium hyperabsorption by the airways, mediated by the epithelial Na+ channel (ENaC), profound lung inflammation and dysregulation of the calcium homeostasis are presumably causally related to loss of CFTR-dependent chloride function in CF patients. One strategy for development of CF therapeutics is the identification of pharmacological agents that correct processing defect of F508del-CFTR and/or stimulate the channel activity of mutated proteins. The protein-repair therapy is based on several observations showing that in the presence of a pharmacological corrector, tailored to the specific F508del genotype, the misfolded protein escapes the ER and targeted to the plasma membrane. We have identified numerous F508del correctors with a CF drug discovery program using a robotic cell-based assay combined to molecular, biochemical and electrophysiological approaches. Among them, we identified miglustat, an orally bioavailable N-alkylated imino sugar (N-butyldeoxynojirimycin, Zavesca?). We investigated effects of high concentration (100 ?M) of miglustat on several CF characteristics and demonstrated after short-term (2-4 h) treatment of CF cells, a partial rescue of the defective F508del-CFTR trafficking and function [1], an improvement of the altered Ca2+ homeostasis [2], a down-regulation of ENaC-dependent Na+ hyperabsorption [3] and an anti-inflammatory effect of miglustat [4]. We suggested that the mechanism by which miglustat corrects the defective F508del-CFTR trafficking is correlated to a disturbance of the ER quality control system in CF cells. In support of that, miglustat is an ?1,2-glucosidase inhibitor preventing the interaction between F508del-CFTR and calnexin in the ER. More recently, we explored the concentration- and time-dependence of miglustat-induced correction of ionic transports in the human respiratory CF epithelial cells. The most salient result is the demonstration that a daily treatment for 2 months with low concentration of miglustat (3?M) resulted in progressive, stable, reversible and sustained correction of the F508del-CFTR deficient trafficking [5]. Then by investigating different biological and cellular aspects of cystic fibrosis such as Na+ hyperabsorption and dysregulation of the Ca2+ homeostasis, we were able to show paralleled normalization of these parameters correlated with the restoration of the F508del-CFTR function. In conclusion, we provided the first evidence that a respiratory CF cell can acquire a non-CF like phenotype when chronically treated with low-concentration of a pharmacological drug resulting in progressive, stable, reversible and sustained correction of F508del-CFTR trafficking, down-regulation of sodium hyperabsorption and regulation of the calcium homeostasis. This body of information makes the use of miglustat attractive as a potential pharmacologic therapy for those CF patients who have at least one F508del-CFTR allele. Miglustat, a medicament already prescribed in another orphan disease, is now evaluated in CF patients within a pilot phase 2a clinical trial.