The most frequent mutation in cystic fibrosis, F508del, causes the arrest of the maturation of CFTR protein. Correctors are able to rescue F508del-CFTR acting directly on CFTR or by modulating other proteins leading to beneficial effects on CFTR maturation. Among these proteins, one of the most promising is the ligase RNF5, whose inhibition is crucial for CFTR rescuing. By using a computational approach, in their previous FFC project identified one compound, called 2A2 that efficiently inhibits RNF5 ligase activity in immortalized human bronchial cells. The aim of this proposal is now to identify optimized RNF5 inhibitors and to evaluate their efficacy in epithelia from CF patients. Improved RNF5 inhibitors will be developed by screening of commercially available analogs and by synthesizing novel analogs; their efficacy on rescuing mutant CFTR will be assessed by electrophysiological techniques on bronchial epithelial derived from patients with one/two copies of F508del or other mutations with trafficking defect. Optimized RNF5 inhibitors may become part of combined drugs required to maximize F508del-CFTR rescue.