Allosteric folding correction of F508del and rare CFTR mutants by elexacaftor-tezacaftor-ivacaftor (Trikafta) combination.

Guido Veit,Mark A Hancock,Haijin Xu,Saul Frenkiel,Elias Matouk,Gergely L Lukacs,Tony Velkov,Ariel Roldan,Dillon F Da Fonte,Maytham Hussein

doi:10.1172/jci.insight.139983

Abstract

Based on its clinical benefits, Trikafta — the combination of folding correctors VX-661 (tezacaftor), VX-445 (elexacaftor), and the gating potentiator VX-770 (ivacaftor) — was FDA approved for treatment of patients with cystic fibrosis (CF) carrying deletion of phenylalanine at position 508 (F508del) of the CF transmembrane conductance regulator (CFTR) on at least 1 allele. Neither the mechanism of action of VX-445 nor the susceptibility of rare CF folding mutants to Trikafta are known. Here, we show that, in human bronchial epithelial cells, VX-445 synergistically restores F508del-CFTR processing in combination with type I or II correctors that target the nucleotide binding domain 1 (NBD1) membrane spanning domains (MSDs) interface and NBD2, respectively, consistent with a type III corrector mechanism. This inference was supported by the VX-445 binding to and unfolding suppression of the isolated F508del-NBD1 of CFTR. The VX-661 plus VX-445 treatment restored F508del-CFTR chloride channel function in the presence of VX-770 to approximately 62% of WT CFTR in homozygous nasal epithelia. Substantial rescue of rare misprocessing mutations (S13F, R31C, G85E, E92K, V520F, M1101K, and N1303K), confined to MSD1, MSD2, NBD1, and NBD2 of CFTR, was also observed in airway epithelia, suggesting an allosteric correction mechanism and the possible application of Trikafta for patients with rare misfolding mutants of CFTR.

Highlights

Cystic fibrosis (CF), one of the most common lethal autosomal-recessive diseases in the White population, is a multiorgan disease caused by loss of function of the CF transmembrane conductance regulator (CFTR), an anion channel expressed at the apical membrane of secretory epithelia [1]
Since VX-445 synergizes with class I and II correctors in rescuing the processing defect of both F508del-CFTR and rare folding mutants in a human bronchial cell model and primary human nasal epithelia (HNE), these findings suggest that VX-445 is potentially the first FDA-approved type III corrector with possible utility for a wide range of folding mutants
Synergistic rescue of F508del-CFTR misprocessing with VX-445 and type I and II correctors

Summary

Introduction

Cystic fibrosis (CF), one of the most common lethal autosomal-recessive diseases in the White population, is a multiorgan disease caused by loss of function of the CF transmembrane conductance regulator (CFTR), an anion channel expressed at the apical membrane of secretory epithelia [1]. F508del impairs the NBD1 stability and the coupled or cooperative domain folding of the channel [9,10,11]. This leads to a combination of defects, consisting of severely impaired processing, plasma membrane (PM) expression, and stability, as well as defective gating of the F508del-CFTR [12,13,14]

Methods

Results

Conclusion