Potentiation of BKCa channels by cystic fibrosis transmembrane conductance regulator correctors VX-445 and VX-121
Aaron Kolski-Andreaco, Stefanie Taiclet, Michael M. Myerburg, John Sembrat, Robert J. Bridges, Adam C. Straub, Zachary P. Wills, Michael B. Butterworth, Daniel C. Devor
Aaron Kolski-Andreaco, Stefanie Taiclet, Michael M. Myerburg, John Sembrat, Robert J. Bridges, Adam C. Straub, Zachary P. Wills, Michael B. Butterworth, Daniel C. Devor
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Research Article

Potentiation of BKCa channels by cystic fibrosis transmembrane conductance regulator correctors VX-445 and VX-121

Abstract

Cystic fibrosis results from mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) anion channel, ultimately leading to diminished transepithelial anion secretion and mucociliary clearance. CFTR correctors are therapeutics that restore the folding/trafficking of mutated CFTR to the plasma membrane. The large-conductance calcium-activated potassium channel (BKCa, KCa1.1) is also critical for maintaining lung airway surface liquid (ASL) volume. Here, we show that the class 2 (C2) CFTR corrector VX-445 (elexacaftor) induces K+ secretion across WT and F508del CFTR primary human bronchial epithelial cells (HBEs), which was entirely inhibited by the BKCa antagonist paxilline. Similar results were observed with VX-121, a corrector under clinical evaluation. Whole-cell patch-clamp recordings verified that CFTR correctors potentiated BKCa activity from both primary HBEs and HEK cells stably expressing the α subunit (HEK-BK cells). Furthermore, excised patch-clamp recordings from HEK-BK cells verified direct action on the channel and demonstrated a significant increase in open probability. In mouse mesenteric artery, VX-445 induced a paxilline-sensitive vasorelaxation of preconstricted arteries. VX-445 also reduced firing frequency in primary rat hippocampal and cortical neurons. We raise the possibilities that C2 CFTR correctors gain additional clinical benefit by activation of BKCa in the lung yet may lead to adverse events through BKCa activation elsewhere.

Authors

Aaron Kolski-Andreaco, Stefanie Taiclet, Michael M. Myerburg, John Sembrat, Robert J. Bridges, Adam C. Straub, Zachary P. Wills, Michael B. Butterworth, Daniel C. Devor

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Figure 1

VX-445, VX-659, and VX-121 stimulate BKCa currents across WT CFTR HBEs.

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VX-445, VX-659, and VX-121 stimulate BKCa currents across WT CFTR HBEs. ...
Currents were recorded with a 125:5 mM K+ gradient (basolateral to apical). (A–C) Subsequent to amiloride, short-circuit current (Isc) was increased by the C2 CFTR correctors VX-445 (A, 10 μM), VX-659 (B, 10 μM), and VX-121 (C, 10 μM). (D and E) In contrast, the C1 CFTR corrector VX-661 (D, 10 μM) and the CFTR potentiator VX-770 (E, 10 μM) failed to increase Isc. Subsequent addition of either VX-445 (D) or VX-121 (E) stimulated Isc. In all experiments, the current was completely blocked by the specific BKCa inhibitor paxilline (10 μM). (F and G) Additional studies verified that both the VX-445–induced (F) and the VX-121–induced (G) currents were inhibited by the additional specific BKCa blocker IBTX (300 nM). (H) Subsequent to amiloride, 10 μM NS1619 failed to stimulate Isc, while further addition of 50 μM NS1619 induced a marked increase. This response was further increased by VX-445 (10 μM) and inhibited by paxilline. (I) Average responses (mean ± SEM, *P < 0.01; 1-way ANOVA) are represented as the change in K+ current (ΔIK). The magnitude of the K+ current was calculated as described in Methods. Nine donors were used in these studies. Experimental replicates are indicated in parentheses above each data set.