A Novel, Uniquely Efficacious Type of CFTR Corrector with Complementary Mode of Action

Three distinct pharmacological corrector types (I, II, III) with different binding sites and additive behaviour only partially rescue the F508del-CFTR folding and trafficking defect observed in cystic fibrosis. Here, we describe novel, uniquely effective, macrocyclic CFTR correctors that were additive to the known corrector types, thus exerting a new, complementary "type-IV" corrector mechanism. Macrocycles achieved wildtype-like folding efficiency of F508del-CFTR at the endoplasmic reticulum and normalized CFTR currents in reconstituted patient-derived bronchial epithelium. Using photo-activatable macrocycles, docking studies and site-directed mutagenesis a highly probable binding site and pose for type-IV correctors was identified in a cavity between lasso helix-1 (Lh1) and transmembrane helix-1 of membrane spanning domain-1 (MSD1), distinct from the known corrector binding sites. Since only F508del-CFTR fragments spanning from Lh1 until MSD2 responded to type-IV correctors, these likely promote co-translational assembly of Lh1, MSD1, and MSD2. Remarkably, previously corrector-resistant CFTR folding mutations were also robustly rescued, suggesting substantial therapeutic potential for this novel type-IV corrector mechanism. TeaserA novel type of macrocyclic CFTR corrector with new binding site, complementary mode of action and unique folding / trafficking efficacy is described.