New drugs are needed to enhance premature termination codon (PTC) suppression to treat the underlying cause of cystic fibrosis (CF) and other diseases caused by nonsense mutations. We tested the lead compounds for PTC suppression in a series of complementary CF models. Using a dual-luciferase reporter system containing the four most prevalent CFTR nonsense mutations (G542X, R553X, R1162X and W1282X) within their local sequence contexts (the three codons on either side of the PTC), we found that NB124, promoted the most read-through of G542X, R1162X and W1282X PTCs. NB124 also restored full-length CFTR expression and chloride transport in FRT cells stably transduced with a CFTR-G542X cDNA transgene, and was superior to gentamicin and other aminoglycosides tested. NB124 restored CFTR function to ~7% of wild type activity in primary human bronchial epithelial CF cells (G542X/delF508), a highly relevant preclinical model with endogenous CFTR expression. Efficacy was further enhanced by addition of the CFTR potentiator ivacaftor (VX-770) to airway cells expressing CFTR PTCs. NB124 treatment rescued CFTR function in a CF mouse model expressing a human CFTR-G542X transgene; efficacy was superior to gentamicin and exhibited favorable pharmacokinetic properties, suggesting in vitro results translated to clinical benefit in vivo. NB124 was also less cytotoxic than gentamicin in a tissue-based model for ototoxicity. These results provide evidence that NB124 and other synthetic aminoglycosides provide a 10-fold improvement in therapeutic index over gentamicin and other first generation aminoglycosides, providing a promising treatment for a wide array of CFTR nonsense mutations.
