Cystic Fibrosis

Cystic Fibrosis (CF) is an autosomal recessive genetic disease affecting more than 100,000 people world-wide. CF is caused by mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene which encodes an anion channel that, when mutated, results in the buildup of mucus in tissues such as the lung and pancreas, disrupting proper organ function. There are over 2000 known mutations in the CFTR gene but most CF therapies in the clinic or in development target only the most abundant CFTR mutations, leaving patients with rare mutations in need of more personalized therapies. A large portion of these rarer mutations include those that alter CFTR gene expression by disrupting pre-mRNA splicing or introducing premature termination codons. Due to their effect on CFTR expression, insufficient CFTR protein is produced which hinders the efficacy of protein-targeted therapeutics approved for use in CF patients. Splice-switching antisense oligonucleotides (ASOs) have emerged as effective therapeutic molecules that can modify gene expression by modulating pre-mRNA splicing. There is potential for ASO-based targeting of a wide range of these mutations including the 3849+10kb C>T, which creates a de novo splice site resulting in the inclusion of a cryptic exon with a premature stop codon. In addition, for terminating mutation, ASOs can be used to disrupt splicing to exons with these mutations such as W1282X in exon 23. Skipping of exon 23 results in a stable, in-frame mRNA that encodes a partially functional protein isoform. We have designed and tested ASOs that block the desired splicing reaction in each of these mutations and show that ASO-treatment of bronchial epithelial cells isolated from patients with these mutations have elevated CFTR chloride channel activity at a level predicted to be clinically relevant. ASO-based splice-switching strategies have the potential to improve the expression and function of many additional forms of mutated CFTR, which we and others are exploring as therapeutics for CF patients.