In vitro activity: Ivacaftor (10 μM) significantly increases the forskolin-stimulated Cl- secretion (IT) by ~4-fold with an EC50 of 100 nM in the recombinant Fisher rat thyroid (FRT) cells expressing G551D gating mutation of CFTR, and by ~6-fold with an EC50 of 25 nM in the recombinant cells expressing temperature-corrected F508del processing mutation of CFTR. Consistent with the increases in the forskolin-stimulated IT, Ivacaftor (10 μM) increases the open probability (Po) of G551D-, F508del-, and wild-type CFTR by ~6-fold, ~5-fold and ~2-fold, respectively, indicating that Ivacaftor acts directly on CFTR to increase its gating activity. In primary cultured human CF bronchial epithelia (HBE) carrying the G551D and F508del CFTR mutations, Ivacaftor (10 μM) potently increases the forskolin-stimulated IT by ~10-fold from 5% to a maximum level of 48% of that measured in non-CF HBE, with an EC50 of 236 nM displaying ~70-fold more potency compared with the commonly used CFTR potentiator genistein, which has an EC50 of 16 μM. In HBE with F508del homozygous CFTR, Ivacaftor causes a significant increase in the forskolin-stimulated IT with an EC50 of 22 nM, to a less extent from 4% to 16% of non-CF HBE compared with the effect in G551D/F508del HBE. Due to CFTR potentiation, Ivacaftor inhibits excessive ENaC-mediated Na+ and fluid absorption with an IC50 of 43 nM, and decreases the amiloride response, resulting in an increase in the surface fluid and cilia beat frequency (CBF) in G551D/F508del HBE.

Kinase Assay: Ivacaftor (10 μM) increases the PC secretion activity by 3-fold for ABCB4-G535D, 13.7-fold for ABCB4-G536R, 6.7-fold for ABCB4-S1076C, 9.4-fold for ABCB4-S1176L, and 5.7-fold for ABCB4-G1178S. Ivacaftor corrects the functional defect of ABCB4 mutants[1]. Ivacaftor (10 μM) significantly increases CFTR activity in W1282X-expressing cells compared to R1162X CFTR cells[2]. Ivacaftor shows no significant activity against 160 targets tested including the GABAA benzodiazepine receptor. Ivacaftor increases the chloride secretion with an EC50 of 0.236 ± 0.200 μM, a 10-fold shift in potency compared to the F508del HBEs[3]. In recombinant cells, VX-770 increases CFTR channel open probability (Po) in both the F508del processing mutation and the G551D gating mutation. VX-770 increases forskolin-stimulated IT in temperature-corrected F508del-FRT cells by appr 6-fold with an EC50 of 25 nM.

Cell Assay: In CHO-G551D cells, VX-770 activated G551D-CFTR channel, and OAG + VX-770 increased G551D-CFTR activity by 58%.