Rescue of CF airway epithelial cell function in vitro by a CFTR potentiator, VX-770

Abstract

Cystic fibrosis (CF) is a fatal genetic disease caused by mutations in the gene encoding the CF transmembrane conductance regulator (CFTR), a protein kinase A (PKA)-activated epithelial anion channel involved in salt and fluid transport in multiple organs, including the lung. Most CF mutations either reduce the number of CFTR channels at the cell surface (e.g., synthesis or processing mutations) or impair channel function (e.g., gating or conductance mutations) or both. There are currently no approved therapies that target CFTR. Here we describe the in vitro pharmacology of VX-770, an orally bioavailable CFTR potentiator in clinical development for the treatment of CF. In recombinant cells VX-770 increased CFTR channel open probability (Po) in both the F508del processing mutation and the G551D gating mutation. VX-770 also increased Cl ؊ secretion in cultured human CF bronchial epithelia (HBE) carrying the G551D gating mutation on one allele and the F508del processing mutation on the other allele by Ϸ10-fold, to Ϸ50% of that observed in HBE isolated from individuals without CF. Furthermore, VX-770 reduced excessive Na ؉ and fluid absorption to prevent dehydration of the apical surface and increased cilia beating in these epithelial cultures. These results support the hypothesis that pharmacological agents that restore or increase CFTR function can rescue epithelial cell function in human CF airway.

Correction of the F508del-CFTR protein processing defect in vitro by the investigational drug VX-809

“…Confocal microscopy was used to test if VX-809 increased the airway surface liquid (ASL) height in cultured F508del-HBE. To activate CFTR, vasoactive intestinal peptide was added to the basolateral surface throughout the treatment period (9). Addition of VX-809 to the basolateral surface for 5 d increased the ASL height from 4.5± 0.2 μm to 6.7 ± 0.5 μm, indicating less fluid absorption, more secretion, or both.…”

“…To enhance chloride transport through F508del-CFTR corrected by VX-809, the CFTR potentiator VX-770 (ivacaftor) (9) was added to maximize the P o of the CFTR channel. Acute application of 1 μM VX-770 increased forskolin-stimulated chloride transport in cultured F508del-HBE pretreated with VX-809 for 48 h (Fig.…”

“…Electrophysiology. Ussing chamber techniques with FRT and HBE cells were used to record the transepithelial current (I T ) resulting from CFTR-mediated chloride transport (9). The single-channel activity of CFTR was measured by using excised inside-out membrane patch recordings (9) Further details are provided in SI Materials and Methods.…”

Efficacy and Safety of Ivacaftor in Patients Aged 6 to 11 Years with Cystic Fibrosis with a G551D Mutation

“…This report shows efficacy with this small-molecule CFTR potentiator in this age group and underscores the clinical improvements that can be achieved even in a population with low disease burden at baseline. reabsorption in cultured human CF bronchial epithelial cells carrying one G551D allele (7). By addressing the underlying protein defect, ivacaftor may help to maintain adequate airway hydration, and may be able to modify disease progression (8,9).…”

Protein Quality Control in Health and Disease

“…These cases stem from the mutation G551D in the sequence of the CF transmembrane conductance regulator (CFTR), which does not affect the protein's localization but impedes its activity. Ivacaftor binds the mutated CFTR molecules, modulates their spatial structure, enhances their activity, and alleviates CFTR symptoms (Van Goor et al 2009). Recently, Ivacaftor was approved for the treatment of CF patients who carry additional mutations that impair CF folding (Carter et al 2015).…”