Pharmacological rescue of specific long QT variants of KCNQ1/KCNE1 channels

Abstract

The congenital Long QT Syndrome (LQTS) is an inherited disorder in which cardiac ventricular repolarization is delayed and predisposes patients to cardiac arrhythmias and sudden cardiac death. LQT1 and LQT5 are LQTS variants caused by mutations in KCNQ1 or KCNE1 genes respectively. KCNQ1 and KCNE1 co-assemble to form critical IKS potassium channels. Beta-blockers are the standard of care for the treatment of LQT1, however, doing so based on mechanisms other than correcting the loss-of-function of K+ channels. ML277 and R-L3 are compounds that enhance IKS channels and slow channel deactivation in a manner that is dependent on the stoichiometry of KCNE1 subunits in the assembled channels. In this paper, we used expression of IKS channels in Chinese hamster ovary (CHO) cells and Xenopus oocytes to study the potential of these two drugs (ML277 and R-L3) for the rescue of LQT1 and LQT5 mutant channels. We focused on the LQT1 mutation KCNQ1-S546L, and two LQT5 mutations, KCNE1-L51H and KCNE1-G52R. We found ML277 and R-L3 potentiated homozygote LQTS mutations in the IKS complexes-KCNE1-G52R and KCNE1-L51H and in heterogeneous IKS channel complexes which mimic heterogeneous expression of mutations in patients. ML277 and R-L3 increased the mutant IKS current amplitude and slowed current deactivation, but not in wild type (WT) IKS. We obtained similar results in the LQT1 mutant (KCNQ1 S546L/KCNE1) with ML277 and R-L3. ML277 and R-L3 had a similar effect on the LQT1 and LQT5 mutants, however, ML277 was more effective than R-L3 in this modulation. Importantly we found that not all LQT5 mutants expressed with KCNQ1 resulted in channels that are potentiated by these drugs as the KCNE1 mutant D76N inhibited drug action when expressed with KCNQ1. Thus, our work shows that by directly studying the treatment of LQT1 and LQT5 mutations with ML277 and R-L3, we will understand the potential utility of these activators as options in specific LQTS therapeutics.

Impacts of gene variants on drug effects-the foundation of genotype-guided pharmacologic therapy for long QT syndrome and short QT syndrome

“…Interestingly, the KCNE1 -D76N variant had the greatest impact on the effects of both drugs. 131 It was discovered that KCNE1 subunits can interact with the putative binding site for R-L3 in the S6 domain of the KCNQ1 subunit, which is facing away from the central cavity. 132 Additionally, previous data indicated that KCNQ1 was more sensitive to R-L3 compared to the KCNQ1 plus KCNE1 channel.…”

Development of automated patch clamp assays to overcome the burden of variants of uncertain significance in inheritable arrhythmia syndromes

“…Similarly, if a disease is very rare, then there may be an insufficient number of definitely (likely) pathogenic variants available to calibrate the assay to achieve more than moderate evidence strength. Furthermore, not all assays have incorporated the potential for dominant-negative effects, and difficulties in co-expression of multiple sub-units in the correct stoichiometry ( Zou et al, 2022 ) need to be considered. There are also no assays yet developed for channels with more complex stoichiometries, e.g., L-type calcium channels which require co-expression of multiple subunits ( Dolphin, 2016 ).…”