Restoration of R117H CFTR folding and function in human airway cells through combination treatment with VX-809 and VX-770

Abstract

Cystic fibrosis (CF) is a lethal recessive genetic disease caused primarily by the F508del mutation in the CF transmembrane conductance regulator (CFTR). The potentiator VX-770 was the first CFTR modulator approved by the FDA for treatment of CF patients with the gating mutation G551D. Orkambi is a drug containing VX-770 and corrector VX809 and is approved for treatment of CF patients homozygous for F508del, which has folding and gating defects. At least 30% of CF patients are heterozygous for the F508del mutation with the other allele encoding for one of many different rare CFTR mutations. Treatment of heterozygous F508del patients with VX-809 and VX-770 has had limited success, so it is important to identify heterozygous patients that respond to CFTR modulator therapy. R117H is a more prevalent rare mutation found in over 2,000 CF patients. In this study we investigated the effectiveness of VX-809/VX-770 therapy on restoring CFTR function in human bronchial epithelial (HBE) cells from R117H/F508del CF patients. We found that VX-809 stimulated more CFTR activity in R117H/F508del HBEs than in F508del/F508del HBEs. R117H expressed exclusively in immortalized HBEs exhibited a folding defect, was retained in the ER, and degraded prematurely. VX-809 corrected the R117H folding defect and restored channel function. Because R117 is involved in ion conductance, VX-770 acted additively with VX-809 to restore CFTR function in chronically treated R117H/F508del cells. Although treatment of R117H patients with VX-770 has been approved, our studies indicate that Orkambi may be more beneficial for rescue of CFTR function in these patients.

Nasospheroids permit measurements of CFTR-dependent fluid transport

“…After washing with PBS at room temperature, nasospheroids were incubated with blocking buffer for 1 hour, followed by incubation with blocking buffer containing monoclonal antibody to CFTR that were produced, quality tested, and provided by J.R. Riordan (University of North Carolina-Chapel Hill) through a program of Cystic Fibrosis Foundation Therapeutics (NBD2 antibody 596 and 528; refs. [45][46][47][48][49] and incubated overnight at 4°C. After washing with PBS at room temperature, nasospheroids were incubated in the dark with secondary fluorescent antibodies (Alexa Fluor 488 goat anti-mouse IgG conjugate; Invitrogen/Thermo Fisher Scientific) and visualized.…”

Potentiation of the cystic fibrosis transmembrane conductance regulator Cl−channel by ivacaftor is temperature independent

“…In combination with the CFTR corrector lumacaftor, ivacaftor also has clinical benefit for patients with CF homozygous for the F508del mutation, albeit the health improvements are less than for individuals with G551D treated with ivacaftor (68,75). Nevertheless, laboratory studies suggest that lumacaftorivacaftor combination therapy is likely to be beneficial to patients with CF and a variety of rare missense mutations in CFTR (10,29,32).…”

Guanylate cyclase 2C agonism corrects CFTR mutants

“…prevalent CF mutations, which result in obliterated (G551D CFTR) or reduced (R117H CFTR) channel function at the cell surface, are responsive to CF potentiators such as VX-770 (ivacaftor) (17,18). Irrespective of their fundamental defects, both F508del CFTR and R117H CFTR mutant proteins would ideally derive more clinical benefit from the combining effects of a corrector and increased cell surfaceassociated function (15,(17)(18)(19).…”