Figure 3.

PTI-CH improves the functional rescue of F508del–cystic fibrosis transmembrane conductance regulator (CFTR) conferred by approved CFTR modulators. (A) PTI-CH shows a concentration-dependent increase in the activity of the combination of ivacaftor and lumacaftor in Ussing chamber short-circuit current measurements. (B) Representative Ussing chamber Isc traces are shown for the indicated treatments. Acute additions (10 µM forskolin, 1 µM ivacaftor, 20 µM CFTRinh172) during the Ussing assay are shown with arrows indicating the time of addition. All other compound incubations (3 µM lumacaftor with or without 3 µM PTI-CH) were for 24 h prior to the assay. Not shown is the 10 µM benzamil addition at the beginning of the assay to inhibit ENaC activity. (C) Summary of PTI-CH–mediated increases in F508del-CFTR CFTRinh172-sensitive current relative to other treatments. Concentrations as in panel B. Data are presented relative to the ivacaftor and lumacaftor combination. Solid bars represent means and black error bars represent the standard error of the mean (SEM) of three biological replicates. Open bars represent calculated values for expected additivity of PTI-CH with the indicated treatment, and gray error bars are drawn from the experimentally observed combinations. EXP, expected activity if PTI-CH were additive to the without PTI-CH condition; OBS, observed functional activity. See Methods for details. ns, non-significant. *p < 0.05, ****p < 0.0001 by two-way ANOVA with Tukey’s multiple comparisons test.