Correction of delF508-CFTR activity with benzo(c)quinolizinium compounds through facilitation of its processing in cystic fibrosis airway cells

A number of genetic diseases, including cystic fibrosis, have been identifi ed as disorders of protein trafficking associated with retention of mutant protein within the endoplasmic reticulum. In the presence of the benzo(c)qu inolizinium drugs, MPB-07 and its congener MPB-91, we show the activation o f cystic fibrosis transmembrane conductance regulator (CFTR) delF508 channe ls in IB3-1 human cells, which express endogenous levels of delF508-CFTR. T hese drugs were without effect on the Ca2+-activated Cl- transport, whereas the swelling-activated Cl- transport was found altered in MPB-treated cell s. Immunoprecipitation and in vitro phosphorylation shows a 20% increase of the band C form of delF508 after MPB treatment. We then investigated the e ffect of these drugs on the extent of mislocalisation of delF508-CFTR in na tive airway cells from cystic fibrosis patients. We first showed that delF5 08 CFTR was characteristically restricted to an endoplasmic reticulum locat ion in approximately 80% of untreated cells from CF patients homozygous for the delF508-CFTR mutation. By contrast, 60-70% of cells from non-CF patien ts showed wild-type CFTR in an apical location. MPB-07 treatment caused dra matic relocation of delF508-CFTR to the apical region such that the majorit y of delF508/delF508 CF cells showed a similar CFTR location to that of wil d-type. MPB-07 had no apparent effect on the distribution of wild-type CFTR , the apical membrane protein CD59 or the ER membrane Ca2+,Mg-ATPase. We al so showed a similar pharmacological effect in nasal cells freshly isolated from a delF508/G551D CF patient. The results demonstrate selective redirect ion of a mutant membrane protein using cell-permeant small molecules of the benzo(c)quinolizinium family and provide a major advance towards developme nt of a targetted drug treatment for cystic fibrosis and other disorders of protein trafficking.