Targeting autophagy as a novel strategy for facilitating the therapeutic action of potentiators on Delta F508 cystic fibrosis transmembrane conductance regulator

Channel activators (potentiators) of cystic fibrosis (CF) transmembrane conductance regulator (CFTR), can be used for the treatment of the small subset of CF patients that carry plasma membrane-resident CFTR mutants. However, approximately 90% of CF patients carry the misfolded Delta F508-CFTR and are poorly responsive to potentiators, because Delta F508-CFTR is intrinsically unstable at the plasma membrane (PM) even if rescued by pharmacological correctors. We have demonstrated that human and mouse CF airways are autophagy deficient due to functional sequestration of BECN1 and that the tissue transglutaminase-2 inhibitor, cystamine, or antioxidants restore BECN1-dependent autophagy and reduce SQSTM1/p62 levels, thus favoring Delta F508-CFTR trafficking to the epithelial surface. Here, we investigated whether these treatments could facilitate the beneficial action of potentiators on Delta F508-CFTR homozygous airways. Cystamine or the superoxide dismutase (SO D)/catalase-mimetic EUK-134 stabilized Delta F508-CFTR at the plasma membrane of airway epithelial cells and sustained the expression of CFTR at the epithelial surface well beyond drug withdrawal, overexpressing BECN1 and depleting SQSTM1. This facilitates the beneficial action of potentiators in controlling inflammation in ex vivo Delta F508-CFTR homozygous human nasal biopsies and in vivo in mouse Delta F508-CFTR lungs. Direct depletion of Sqstm1 by shRNAs in vivo in Delta F508-CFTR mice synergized with potentiators in sustaining surface CFTR expression and suppressing inflammation. Cystamine pre-treatment restored Delta F508-CFTR response to the CFTR potentiators genistein, Vrx-532 or Vrx-770 in freshly isolated brushed nasal epithelial cells from Delta F508-CFTR homozygous patients. These findings delineate a novel therapeutic strategy for the treatment of CF patients with the Delta F508-CFTR mutation in which patients are first treated with cystamine and subsequently pulsed with CFTR potentiators.