New approach for treating cystic fibrosis shows success in mice

Researchers have developed a potential strategy to treat cystic fibrosis, using oligonucleotides to correct certain gene defects.

Cystic fibrosis

University of North Carolina (UNC) School of Medicine, US, scientists have led a collaboration of researchers to demonstrate a potential new strategy for treating cystic fibrosis (CF) and a range of other diseases. The new method involves oligonucleotides that can correct some of the gene defects that underlie CF but are not addressed by existing modulator therapies. The researchers also used a new delivery method that overcomes traditional obstacles of getting oligonucleotides into lung cells.

The team demonstrated the effectiveness of their approach in cells derived from a CF patient and in mice.

“With our oligonucleotide delivery platform, we were able to restore the activity of the protein that does not work normally in CF and we saw a prolonged effect with just one modest dose, so we are really excited about the potential of this strategy,” said study senior author Dr Silvia Kreda.

The researchers say that CF is an inherited disorder in which gene mutations cause the functional absence of a protein called CFTR. Absent CFTR causes the mucus lining the lungs and upper airways to become dehydrated and highly susceptible to bacterial infections, which occur frequently and lead to progressive lung damage.

Treatments for CF now include CFTR modulator drugs, which effectively restore partial CFTR function in many cases. However, CFTR modulators cannot help roughly ten percent of CF patients, often because the underlying gene defect is of the type known as a splicing defect. Splicing is a process that occurs when genes are transcribed into temporary strands of RNA. A complex of enzymes and other molecules then chops up the RNA strand and reassembles them. However, defects in splicing can lead to many diseases – including CF when CFTR’s gene transcript is mis-spliced.

In principle, properly designed oligonucleotides can correct some kinds of splicing defects. In practice, however, getting oligonucleotides into cells and to the locations within cells where they can correct RNA splicing defects, has been extremely challenging for some organs.

“It has been especially difficult to get significant concentrations of oligonucleotides into the lungs to target pulmonary diseases,” Kreda said.

Even when oligonucleotides get into cells, the most usually are trapped within endosomes and are sent back outside the cell or degraded by enzymes before they can ever do their work.

The new strategy developed by the researchers overcomes these obstacles by adding two new features to splice switching oligonucleotides. Firstly, the oligonucleotides are connected to peptides that are designed to help them to distribute in the body and enter cells. Secondly, there is a separate treatment with small molecules called OECs which help the therapeutic oligonucleotides escape their entrapment within endosomes.

The researchers demonstrated this combined approach in cultured airway cells from a human CF patient with a common splicing-defect mutation.

“Adding it just once to these cells, at a relatively low concentration, essentially corrected CFTR to a normal level of functioning, with no evidence of toxicity to the cells,” Kreda said.

The team found the results were much better with than without OECs and improved with OEC dose.

The researchers successfully tested their approach using a different oligonucleotide in a mouse model of a splicing defect affecting a reporter gene. In these experiments, the researchers observed that the correction of the splicing defect in the mouse lungs lasted for at least three weeks after a single treatment – hinting that patients taking such therapies might need only sporadic dosing.

The team now plan further pre-clinical studies of their potential CF treatment in preparation for possible clinical trials.

The study was published in Nucleic Acids Research.