Rescue of the CFTR chloride channel with nonsense mutations is markedly improved under inflammatory conditions

Loss of CFTR chloride channel function is the basic defect in cystic fibrosis (CF), a genetic disease that particularly affects the respiratory system, with bacterial infection and severe inflammation. People with CF carrying the most frequent mutation (F508del) or many types of missense mutations can be efficiently treated with drugs, named correctors and potentiators, that improve CFTR protein processing and channel activity. These treatments are ineffective on nonsense mutations that lead to nonsense-mediated RNA decay (NMD) and CFTR protein truncation. We tested the efficacy of a triple combination of small molecules including the readthrough agent ELX-02, the CFTR corrector VX-809, and the eRF3A degrader CC-90009, on cultured airway epithelia from patients carrying the G542X mutation. The treatment resulted in a significant but relatively modest (three-fold) increase in CFTR function. Importantly, the efficacy of the triple drug combination was greatly amplified under inflammatory conditions, i.e. by exposing the epithelia to IL-4 (15-fold increase) or to IL-17A/TNF-α (9-fold increase). Similar effects were also found in epithelia with the W1282X mutation. The large rescue of CFTR function under inflammatory conditions was paralleled by the appearance of full-length CFTR protein and by the increase in CFTR mRNA. The effect of inflammatory stimuli could be mediated by enhanced translational readthrough and/or reduced NMD. Our results suggest that rescue of CFTR with nonsense mutations could be more effective than expected in vivo . Our findings may also lead to the identification of novel targets to correct the effect of nonsense mutations in CF and other genetic diseases.