CYSTIC FIBROSIS Sildenafil (Viagra) corrects DF508-CFTR location in nasal epithelial cells from patients with cystic fibrosis

Background: Most patients with cystic fibrosis (CF) have a DF508 mutation resulting in abnormal retention of mutant gene protein (DF508-CFTR) within the cell. This study was undertaken to investigate DF508-CFTR trafficking in native cells from patients with CF with the aim of discovering pharmacological agents that can move DF508-CFTR to its correct location in the apical cell membrane. Method: Nasal epithelial cells were obtained by brushing from individuals with CF. CFTR location was determined using immunofluorescence and confocal imaging in untreated cells and cells treated with sildenafil. The effect of sildenafil treatment on CFTR chloride transport function was measured in CF15 cells using an iodide efflux assay. Results: In most untreated CF cells DF508-CFTR was mislocalised within the cell at a site close to the nucleus. Exposure of cells to sildenafil (2 hours at 37 C̊) resulted in recruitment of DF508-CFTR to the apical membrane and the appearance of chloride transport activity. Sildenafil also increased DF508-CFTR trafficking in cells from individuals with CF with a single copy DF508 (DF508/4016ins) or with a newly described CF trafficking mutation (R1283M). Conclusions: The findings provide proof of principle for sildenafil as a DF508-CFTR trafficking drug and give encouragement for future testing of sildenafil and related PDE5 inhibitors in patients with CF.