New Assay Could Help Researchers Discover Promising CF Therapeutics for ΔF508-CFTR

Discovering new compounds to treat cystic fibrosis is now more feasible as a result of work in the collaborative laboratory of Dr. Aleksander Edelman at INSERM in France. The research team identified new compounds using their novel functional assay that tests the function of the CFTR protein following the application of candidate compounds to cells.

The team was specifically looking at the case of the ΔF508-CFTR mutant, where Phe508 is deleted from the CFTR protein. This mutation is the most common of the 2,000 gene mutations that affect patients with cystic fibrosis, with 70% of cases of cystic fibrosis having ΔF508. It results in improperly folded CFTR proteins that are eventually degraded by proteosomes rather than function in cells.

As described by the team’s article published in EMBO Molecular Medicine, “Discovery of Novel Potent ΔF508-CFTR Correctors That Target the Nucleotide Binding Domain,” they screened 200,000 compounds for the ability to interact with the first nucleotide binding domain (NBD1) of CFTR that contains the ΔF508 mutation. The team hypothesized that low molecular weight compounds that bind to ΔF508-NBD1 interfere with protein-protein interactions that usually carry ΔF508-CFTR proteins to the plasma membrane.

First the team used the National Cancer Institute diversity set 1 (NCIDS) database of chemical structures to identify out of 140,000 available compounds a set of testable molecules. They used a computer simulation to explore binding of candidate molecules to NBD1 and narrowed their list of candidates down to twelve molecules. Then, using HeLa cells and bronchial cells from cystic fibrosis patients, the team applied the compounds in silico and noticed an increase in expression of functional ΔF508-CFTR protein when four of the candidate compounds were applied.

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One compound (“407882”) was then selected for in vivo use in mice with the ΔF508 mutation. The team administered the most water soluble molecule to the nostrils of mice and measured the nasal potential difference two to three days later. There was higher activity in treated mice than untreated mice.

“In conclusion, the chemical compounds identified by us as correctors of ΔF508‐CFTR are very promising as potential therapeutic agents,” wrote Dr. Edelman. “A correction level between 10% and 30% of the [normal CFTR protein] activity has been estimated as the threshold required eo ameliorate the symptoms of cystic fibrosis. In our study, this correction threshold is obtained even by treatment with a single molecule, something that has been attainable with VX-809 [lumacaftor from Vertex Pharmaceuticals].”