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

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.

Preclinical Studies of a Rare CF-Causing Mutation in the Second Nucleotide Binding Domain (c.3700A>G) Show Robust Functional Rescue in Primary Nasal Cultures by Novel CFTR Modulators

“…Lukacs and group have demonstrated that VX-661 and VX-809 are type I correctors that stabilize the MSD2-NBD1 interface, and other correctors stabilize NBD1 (type III) or NBD2 (type II) [ 20 , 37 ]. VX-445 synergistically rescues F508del-CFTR folding with type I and II correctors but not with a type III corrector, suggesting that it may be a class III corrector that stabilizes NBD1 [ 38 ], which may not be as advantageous in the c.3700A>G NBD2 mutation.…”

DNAJB12 and Hsp70 Facilitate the Conformation Specific Degradation of Arrested N1303K-CFTR Intermediates by ER Associated-Autophagy

“…Class-II modulators appear to act synergistically with Class I modulators restore assembly of F508del-NBD1 with CL4 in MSD2 of CFTR. (Rosser, Grove et al 2008, Grove, Rosser et al 2009, Ren, Grove et al 2013, Veit, Roldan et al 2020). Modulators act on arrested intermediates of CFTR but cannot rescue the function of off-pathway and misfolded conformers of CFTR mutants {Van Goor, 2014 #8219}.…”

“…The Class I modulator VX-809 does increase the accumulation of N1303K-CFTR, but not proper folding. Treatment with VX-809 alone, or in combination with the tool compounds in the Class II modulator family, or VX-441, which is used in combination with Class I modulators clinically, does not restore N1303K-CFTR function in heterozygous or homozygous native human airways cells from CF patients (Veit, Roldan et al 2020). However, we were able to fix the folding of a small fraction of N1303K-CFTR in cells that are cultured at low temperatures.…”

In silico drug repositioning on F508del-CFTR: A proof-of-concept study on the AIFA library

“…This approach has already led to the development of four compounds that are currently on the market: lumacaftor (VX809), ivacaftor (VX770), tezacaftor (VX661), elexacaftor (VX445) and their combinations [10], among which the recently approved Trikafta [11,12].…”