Discovering FDA-approved drugs that can treat Long QT Syndrome caused by trafficking-deficient KV11.1 (hERG) variants
Background: The KV11.1 potassium channel, formerly the human Ether-a-go-go-Related Gene (hERG)-channel, is important for repolarization of cardiac action potentials. Loss-of-function (LOF) KV11.1 variants cause Long QT Syndrome (LQTS) type 2, which predisposes individuals to the fatal arrhythmia torsades de pointes. KV11.1 composes 30 35% of all clinical cases of LQTS and approximately 90% of LOF variants prevent KV11.1 intracellular transport (trafficking) to the plasma membrane. Multiple drugs can improve KV11.1 trafficking with ≥8-hour treatment and washout. Unfortunately, none are indicated for clinical treatment of LQTS due to side effects or direct KV11.1 channel block. Objective: Develop and utilize high-throughput screening (HTS) to identify new drugs that increase KV11.1 trafficking/function and could be used in patients with LQTS. Methods: Using an optimized Tl+-flux trafficking assay, we screened 1906 drugs in HEK-293 cells expressing trafficking-deficient KV11.1 variants (KV11.1-G601S-G965*X and KV11.1 N470D) for increased trafficking/function. 24-hours before experiments, cells were plated on 384-well plates with 10 µmol/L drug per well. On the day of experiments, drug was washed out, loaded with thallium-sensitive dye, and imaged using a 384-well fluorescent plate reader. The screen was performed in triplicate for each cell line. Positive hits were tested for WT inhibition using Tl+-flux. Concentration response (0.5 nmol/L to 25 µmol/L) for trafficking was tested for promising candidates. Patch clamp electrophysiology and immunoblotting were used to confirm Tl+-flux results. Results: The screen detected hundreds of drugs that increased KV11.1 trafficking. 214 hits were tested for wild-type KV11.1 inhibition, which eliminated >100 candidates. Concentration response of KV11.1 trafficking was tested in 40 candidates. Tl+-flux, patch clamp electrophysiology, and immunoblotting revealed that evacetrapib increased KV11.1 variant trafficking and activated KV11.1 currents acutely. Conclusion: We discovered evacetrapib’s dual function to increase membrane expression of trafficking deficient KV11.1 variants and activate the channel. Evacetrapib is a promising candidate for drug repurposing in LQTS and was well tolerated in clinical trials for a separate clinical indication.