VX-809

VX-809 is a CFTR corrector that partially restores the function of F508del-CFTR. In Fischer rat thyroid (FRT) cells, it increases F508del-CFTR maturation at EC50 of 0.1 μM, and elevates F508del-CFTR–mediated chloride transport at EC50 of 0.5 μM [1]. It has no effect of other ion channels (hERG), transporter (P-gp) and disease-causing mislocalized proteins (α1-antitrypsin Z mutant) [1]. VX-809 stabilizes N-terminal fragment of CFTR that contain MSD1 by altering its protein conformation [2, 3].

Homozygous F508del-CFTR is the most common mutation in cystic fibrosis (CF) patients, accounting for 66–70% of CF cases worldwide. In cultured human bronchial epithelial cells that are homozygous for F508del, VX-809 restored the CFTR function and improved chloride and fluid Transport [1]. The combination of CFTR potentiators and VX-809 further improved the function of F508del-CFTR [4].

VX-809 has been tested in several clinical trials. Although it had minimal benefit to F508del-CFTR homozygous patients as a monotherapy [4], the result of Phase 2 study of VX-809 and KALYDECO combination showed significant improvements in lung function in CF patients with homozygous F508del-CFTR [5]. VX-809 is currently under investigation in two phase 3 trials.

References:
[1]Van Goor F, Hadida S, Grootenhuis PD et al. Correction of the F508del-CFTR protein processing defect in vitro by the investigational drug VX-809. Proc Natl Acad Sci U S A 2011; 108: 18843-18848.[2] Ren HY, Grove DE, De La Rosa O et al. VX-809 corrects folding defects in cystic fibrosis transmembrane conductance regulator protein through action on membrane-spanning domain 1. Mol Biol Cell 2013; 24: 3016-3024.[3]Loo TW, Bartlett MC, Clarke DM. Corrector VX-809 stabilizes the first transmembrane domain of CFTR. Biochem Pharmacol 2013; 86: 612-619.[4]Clancy JP, Rowe SM, Accurso FJ et al. Results of a phase IIa study of VX-809, an investigational CFTR corrector compound, in subjects with cystic fibrosis homozygous for the F508del-CFTR mutation. Thorax 2012; 67: 12-18.[5]http://investors.vrtx.com/releasedetail.cfm?releaseid=687394

Restoration of R117H CFTR folding and function in human airway cells through combination treatment with VX-809 and VX-770.[Pubmed:27402691]

Am J Physiol Lung Cell Mol Physiol. 2016 Sep 1;311(3):L550-9.

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.

Increased efficacy of VX-809 in different cellular systems results from an early stabilization effect of F508del-CFTR.[Pubmed:26171232]

Pharmacol Res Perspect. 2015 Aug;3(4):e00152.

Cystic fibrosis (CF), the most common recessive autosomal disease among Caucasians, is caused by mutations in the gene encoding the CF transmembrane conductance regulator (CFTR) protein. The most common mutation, F508del, leads to CFTR impaired plasma membrane trafficking. Therapies modulating CFTR basic defect are emerging, such as VX-809, a corrector of F508del-CFTR traffic which just succeeded in a Phase III clinical trial. We recently showed that VX-809 is additive to two other correctors (VRT-325 and compound 4a). Here, we aimed to determine whether the differential rescuing by these compounds results from cell-specific factors or rather from distinct effects at the early biogenesis and/or processing. The rescuing efficiencies of the above three correctors were first compared in different cellular models (primary respiratory cells, cystic fibrosis bronchial epithelial and baby hamster kidney [BHK] cell lines) by functional approaches: micro-Ussing chamber and iodide efflux. Next, biochemical methods (metabolic labeling, pulse-chase and immunoprecipitation) were used to determine their impact on CFTR biogenesis / processing. Functional analyses revealed that VX-809 has the greatest rescuing efficacy and that the relative efficiencies of the three compounds are essentially maintained in all three cellular models tested. Nevertheless, biochemical data show that VX-809 significantly stabilizes F508del-CFTR immature form, an effect that is not observed for C3 nor C4. VX-809 and C3 also significantly increase accumulation of immature CFTR. Our data suggest that VX-809 increases the stability of F508del-CFTR immature form at an early phase of its biogenesis, thus explaining its increased efficacy when inducing its rescue.

Pseudomonas aeruginosa Reduces VX-809 Stimulated F508del-CFTR Chloride Secretion by Airway Epithelial Cells.[Pubmed:26018799]

PLoS One. 2015 May 27;10(5):e0127742.

BACKGROUND: P. aeruginosa is an opportunistic pathogen that chronically infects the lungs of 85% of adult patients with Cystic Fibrosis (CF). Previously, we demonstrated that P. aeruginosa reduced wt-CFTR Cl secretion by airway epithelial cells. Recently, a new investigational drug VX-809 has been shown to increase F508del-CFTR Cl secretion in human bronchial epithelial (HBE) cells, and, in combination with VX-770, to increase FEV1 (forced expiratory volume in 1 second) by an average of 3-5% in CF patients homozygous for the F508del-CFTR mutation. We propose that P. aeruginosa infection of CF lungs reduces VX-809 + VX-770- stimulated F508del-CFTR Cl secretion, and thereby reduces the clinical efficacy of VX-809 + VX-770. METHODS AND RESULTS: F508del-CFBE cells and primary cultures of CF-HBE cells (F508del/F508del) were exposed to VX-809 alone or a combination of VX-809 + VX-770 for 48 hours and the effect of P. aeruginosa on F508del-CFTR Cl secretion was measured in Ussing chambers. The effect of VX-809 on F508del-CFTR abundance was measured by cell surface biotinylation and western blot analysis. PAO1, PA14, PAK and 6 clinical isolates of P. aeruginosa (3 mucoid and 3 non-mucoid) significantly reduced drug stimulated F508del-CFTR Cl secretion, and plasma membrane F508del-CFTR. CONCLUSION: The observation that P. aeruginosa reduces VX-809 and VX-809 + VX-770 stimulated F508del CFTR Cl secretion may explain, in part, why VX-809 + VX-770 has modest efficacy in clinical trials.

Corrector VX-809 promotes interactions between cytoplasmic loop one and the first nucleotide-binding domain of CFTR.[Pubmed:28366727]

Biochem Pharmacol. 2017 Jul 15;136:24-31.

A large number of correctors have been identified that can partially repair defects in folding, stability and trafficking of CFTR processing mutants that cause cystic fibrosis (CF). The best corrector, VX-809 (Lumacaftor), has shown some promise when used in combination with a potentiator (Ivacaftor). Understanding the mechanism of VX-809 is essential for development of better correctors. Here, we tested our prediction that VX-809 repairs folding and processing defects of CFTR by promoting interactions between the first cytoplasmic loop (CL1) of transmembrane domain 1 (TMD1) and the first nucleotide-binding domain (NBD1). To investigate whether VX-809 promoted CL1/NBD1 interactions, we performed cysteine mutagenesis and disulfide cross-linking analysis of Cys-less TMD1 (residues 1-436) and DeltaTMD1 (residues 437-1480; NBD1-R-TMD2-NBD2) truncation mutants. It was found that VX-809, but not bithiazole correctors, promoted maturation (exited endoplasmic reticulum for addition of complex carbohydrate in the Golgi) of the DeltaTMD1 truncation mutant only when it was co-expressed in the presence of TMD1. Expression in the presence of VX-809 also promoted cross-linking between R170C (in CL1 of TMD1 protein) and L475C (in NBD1 of the DeltaTMD1 truncation protein). Expression of the DeltaTMD1 truncation mutant in the presence of TMD1 and VX-809 also increased the half-life of the mature protein in cells. The results suggest that the mechanism by which VX-809 promotes maturation and stability of CFTR is by promoting CL1/NBD1 interactions.