RDR01752 rescues F508del-CFTR processing, PM traffic and channel function
Incubation of CFBE cells expressing F508del-CFTR with the RDR01752 compound rescued F508del-CFTR processing, resulting in the appearance of the fully-glycosylated form of CFTR (~180 kDa, band C) in a dose-dependent manner with the maximal correction achieved at 10 µM (Fig. 1A,B). This effect was comparable to that obtained for VX-809 or VX-661, and in contrast to that obtained for DMSO (vehicle), which only led to the appearance of the core-glycosylated form of CFTR (~140 kDa, band B). This result was also confirmed by the immunofluorescence detection of the Flag-tag of mCherry-Flag-F508del-CFTR expressed in CFBE cells without cell permeabilization, only in cells treated with RDR01752 or VX-809, but not DMSO (Fig. 1C,D).
To assess the ability of RDR01752 to restore F508del-CFTR function, we first measured the rate of HS-YFP quenching induced by iodide influx into cells in CFBE cells stably co-expressing F508del-CFTR and the HS-YFP (Fig. 2A,B). Both RDR01752 (10 µM) and VX-809 demonstrated rescue of F508del-CFTR function, although the efficacy of RDR01752 was lower than that of VX-809. In order to confirm these findings, we then investigated rescue of F508del-CFTR function by RDR01752 in polarized CFBE cells in the Ussing chamber (Fig. 2C-F). A significant increase in equivalent short-circuit current (ΔIsceq) was observed upon Fsk/IBMX stimulation in cells incubated with either RDR01752 or VX-809 and stimulated with potentiator genistein (Gen) versusthose incubated with DMSO alone. These data are consistent with the rate of HS-YFP quenching.