Modulation of Ca2+ -activated K+ channels by CFTR Correctors

Cystic fibrosis (CF) results from mutations in the CFTR Cl- channel resulting in diminished transepithelial Cl- secretion. The most common CFTR mutation, F508del, results in a channel that fails to correctly fold/traffic. Thus, compounds were sought to improve the folding/trafficking of this misfolded CFTR - referred to as

correctors. Vertex pioneered the identification of CFTR correctors, and in 2019 introduced Trikafta, consisting of the correctors, VX-661 (Tezacafor) and VX-445 (Elexacaftor), together with the CFTR potentiator VX-770 (Ivacaftor). This highly effective modulator therapy (HEMT) has proved to be highly efficacious. Unfortunately,

real-world studies have reported adverse events (AE) in a subset of CF patients taking these HEMT, including headache, hypertension and mental health issues, such as anxiety, low mood, insomnia and “brain fog”. The mechanisms by which HEMT induce these AE remain unknown and thus represent a critical gap in our

understanding of drug action. Herein, we demonstrate the CFTR corrector VX-445 (Elexacaftor) inhibits the intermediate (KCa3.1) conductance, Ca2+-activated K+ channel (KCa), resulting in an inhibition of Cl- secretion across WT and F508del CFTR-expressing primary human bronchial epithelial cells (HBEs). Further, we

demonstrate these CFTR correctors potentiate the large (BKCa; KCa1.1) conductance KCa. As KCa channels are widely expressed, including in neurons, where they control neuronal excitability, and vascular smooth muscle, where they regulate vascular reactivity, understanding how CFTR correctors modulate KCa activity is

crucial to understanding these AE. Thus, the rationale for our studies is by defining the mechanisms by which CFTR correctorsinhibit KCa3.1 and potentiate BKCa channels, and how this affectsthe physiology of cells where these channels are expressed, we will better understand the AE induced by HEMT. Based on this, we propose

the following aims: (1) Define the mechanism(s) by which CFTR correctors inhibit KCa3.1 and KCa2.x channels and the effects on HBE function. (2) Define the mechanism by which CFTR correctors potentiate BKCa channels and the effects on HBE function. (3) Define the effects of CFTR corrector-mediated KCa3.1/KCa2.x inhibition

and BKCa potentiation on vascular reactivity and neuronal action potential firing. To carry out these studies, we will utilize a combination of in vitro and ex vivo techniques, including electrophysiological, molecular, protein biochemical, live-cell fluorescence imaging, as well as wire- and pressure-myography on mouse aortic rings and

microvascular arteries, and patch-clampingon primary cultures of cortical and hippocampal neurons. Our studies will be the first to demonstrate CFTR correctors directly inhibit KCa2.x/KCa3.1 and potentiate BKCa channels and how this affects ion transport across HBEs, vascular reactivity and neuronal action potential firing. As HEMT

represent the standard of care for CF patients it is highly significant to understand the mechanisms underlying the AE reported, both in the short-term, so they may be mitigated, and in the long-term such that next-generation HEMT may be developed – improving the lives of CF patients.