Some gating potentiators, including VX-770, diminish ΔF508-CFTR functional expression

Abstract

Cystic fibrosis (CF) is caused by mutations in the CF transmembrane regulator (CFTR) that result in reduced anion conductance at the apical membrane of secretory epithelia. Treatment of CF patients carrying the G551D gating mutation with the potentiator VX-770 (ivacaftor) largely restores channel activity and has shown substantial clinical benefit. However, most CF patients carry the ΔF508 mutation, which impairs CFTR folding, processing, function, and stability. Studies in homozygous ΔF508 CF patients indicated little clinical benefit of monotherapy with the investigational corrector VX-809 (lumacaftor) or VX-770, whereas combination clinical trials show limited but significant improvements in lung function. We show that VX-770, as well as most other potentiators, reduces the correction efficacy of VX-809 and another investigational corrector, VX-661. To mimic the administration of VX-770 alone or in combination with VX-809, we examined its long-term effect in immortalized and primary human respiratory epithelia. VX-770 diminished the folding efficiency and the metabolic stability of ΔF508-CFTR at the endoplasmic reticulum (ER) and post-ER compartments, respectively, causing reduced cell surface ΔF508-CFTR density and function. VX-770–induced destabilization of ΔF508-CFTR was influenced by second-site suppressor mutations of the folding defect and was prevented by stabilization of the nucleotide-binding domain 1 (NBD1)–NBD2 interface. The reduced correction efficiency of ΔF508-CFTR, as well as of two other processing mutations in the presence of VX-770, suggests the need for further optimization of potentiators to maximize the clinical benefit of corrector-potentiator combination therapy in CF.

Correctors of mutant CFTR enhance subcortical cAMP–PKA signaling through modulating ezrin phosphorylation and cytoskeleton organization

“…Finally, the recent findings that chronic application of the potentiator VX-770 in combination with VX-809 resulted in a reduction of the correction efficacy of VX-809 due to destabilization of F508del CFTR and a consequent increase in its turnover rate (Cholon et al, 2014;Veit et al, 2014), highlight the need to identify new potential targets for therapeutically improving the formation of the multiprotein complex in order to favor the cAMP and PKA compartmentalization in the vicinity of F508del CFTR.…”

Molecular dynamics of the cryo-EM CFTR structure

“…Intense efforts have been made to correct the basic defect and restore the functional expression of the mutant by small molecules [2,3,4]. However, drug development is still hampered by lack of high resolution CFTR structures.…”

“…Currently four main conformations of Type I ABC exporter structures can be distinguished: (1) inward-facing, bottom-open (Fig. S1 a,b) and (2) inward-facing, bottom-closed conformations in the absence of ATP ( Fig. S1 c); (3) outward-facing, bottom-closed in the presence of ATP (Fig.…”

Cystic Fibrosis: The Dawn of a New Therapeutic Era

“…The CFTR corrector lumacaftor was developed specifically to repair this defect by increasing functional CFTR protein at the cell surface. Lumacaftor restores protein function in human F508del homozygous epithelial cells in vitro (36), and the combination therapy lumacaftor-ivacaftor was shown to moderately benefit patients, aged 12 years and older, with homozygous F508del CF despite in vitro evidence that the combination has a limited physiological effect in airway epithelial cells (37,38). Citing a 2.6-4.0% improvement in FEV 1 percent predicted and a reduction in pulmonary exacerbations by 30-39% (3), on July 2, 2015, lumacaftor-ivacaftor was approved by the U.S. Food and Drug Administration in this population.…”