Replacing function of impaired cystic fibrosis protein

In people with cystic fibrosis, a protein that normally releases bicarbonate (red spheres) from the cell is missing or defective (brown ribbon). Amphotericin B (white) can form channels to release bicarbonate, restoring the antibiotic properties of the airway surface.Rebecca Schultz, Carle Illinois College of Medicine

Cystic fibrosis is a genetic condition that causes thick mucus to clog the lungs. This can lead to repeated infections, scarring, and gradual deterioration. It’s caused by a defect in the gene for CFTR (cystic fibrosis transmembrane conductance regulator).

CFTR forms a channel in cell membranes to control the movement of molecules (like salt, water, and bicarbonate) in and out of the cells that line the lung. In people with cystic fibrosis, defective CFTR proteins prevent lung cells from secreting bicarbonate and chloride ions. This causes the mucus on the lung cells to become more acidic and sticky. The sticky mucus impairs the lung’s ability to remove harmful bacteria that are breathed in.

While some treatments are currently available, they are limited because different people have different types of mutated proteins. Some people make no CFTR protein at all.

Amphotericin B is an antifungal medication that can form a channel to allow molecules in and out of the cell. To test whether amphotericin B can replace the function of defective CFTR protein, a team led by Dr. Martin D. Burke at the University of Illinois in Champaign tested the small molecule in an animal model and lung tissue from patients with cystic fibrosis. The research was supported in part by NIH’s National Heart, Lung, and Blood Institute (NHLBI). Results were published online on March 13, 2019, in Nature.

The researchers compared amphotericin B with another drug called ivacaftor, which is known to improve the function of CFTR proteins with specific mutations. In human lung cells grown in the lab, both drugs improved pH levels and bicarbonate secretion, and decreased the viscosity of the liquid on lung cells to a similar degree.

However, in cells with mutated CFTR that doesn’t insert into the cell membrane and those that don’t make CFTR at all, only amphotericin B was able to restore function, since it bypasses the CFTR protein.

The team next administered amphotericin B in an animal model of cystic fibrosis and found improved pH levels in the liquid on lung cells. The researchers noted that amphotericin can be delivered directly to the lungs to avoid common side effects.

“The cystic fibrosis community is truly in need of new therapies to reduce the burden of this disease. We are interested to see how this potential treatment performs in clinical trials in the future,” says Dr. James Kiley, director of NHLBI’s Division of Lung Diseases.

“The really exciting news is that amphotericin is a medicine that’s already approved and available on the market,” Burke notes.

This approach holds special promise for a subset of patients—about 10% of the people with cystic fibrosis—who do not respond to any treatment. However, more studies are needed before the drug could be safely used to treat cystic fibrosis in people.