Therapeutic approaches for nonsense mutations in CFTR.

This manuscript reviews recent developments in suppressing nonsense mutations in the CFTR gene. Nonsense mutations lead to premature termination codons (PTCs)-UAG, UGA, or UAA- that cause the production of truncated, non-functional proteins and result in the degradation of transcripts by the nonsense-mediated decay (NMD) pathway, and in some cases exon skipping. Readthrough approaches facilitate incorporation of amino acids at nonsense codons, enabling the synthesis of a functional full-length protein. We focus on three readthrough strategies that may lead to therapeutics. First, high-throughput screens yield novel small-molecule compounds, such as aminoglycoside derivatives, with reduced off-target effects compared to previously tested molecules. Second, suppressor tRNAs-exogenous tRNAs designed to directly decode PTCs-and their delivery strategies are active areas of study which promise to achieve high levels of readthrough. Finally, recently introduced readthrough-inducing antisense oligonucleotides (R-ASOs) can readthrough disease-causing mRNAs by targeting the complementary region downstream of the PTC, taking advantage of structural differences between elongation and termination processes. Preclinical results demonstrate the feasibility of these three strategies to readthrough nonsense mutations in CFTR, necessitating their translation to humans. Future steps include the optimization of their delivery, pharmacokinetics, and minimization of off-target effects, such as the possibility of readthrough at normal stop codons.