Abstract Body (Do not enter title and authors here): Background: Long QT syndrome (LQTS) is a potentially lethal cardiac channelopathy that stems primarily from pathogenic variants in KCNQ1 (LQT1), KCNH2 (LQT2), or SCN5A (LQT3) and is characterized by prolongation of the cardiac action potential duration (APD) at the cellular level. Despite current therapeutic options, there is a pressing need for novel, precision medicine-based, effective pharmacological therapies for LQTS, particularly for LQT2 and LQT3.
Goal: To develop a high-throughput drug screening platform to identify novel therapeutics for LQTS using induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs).
Methods: iPSC-CMs were made for patients with LQT2 (p.G604S) or LQT3 (p.P1332L). Voltage dye assays were performed using a kinetic image cytometer (KIC) in a 96 well format. The APD at 90% repolarization (APD90) was measured in treated/untreated iPSC-CMs. Cyteseer image analysis software was used for optical APD analysis. SCN5A-P1332L iPSC-CMs were treated with 10 uM mexiletine (MEX) as a positive control. 114 compounds from a commercially available library of FDA-approved drugs were tested in triplicate to assess their APD shortening efficacy. Whole-cell patch clamp was used to confirm the lead compound’s effect in KCNH2-G604S iPSC-CMs.
Results: MEX significantly shortened the APD90 of SCN5A-P1332L iPSC-CMs by 13% (669 ± 5 to 586 ± 10 ms; p<0.0001; n=50). Of the 114 tested compounds, 6 shortened the APD90 of SCN5A-P1332L iPSC-CMs by greater than 20%. The lead compound shortened the APD90 of SCN5A-P1332L iPSC-CMs by 32% (571 ± 2 ms; n=314, to 387 ± 4 ms; n=80; p<0.0001). All 6 candidate compounds also shortened the APD90 of KCNH2-G604S iPSC-CMs by greater than 20% in KIC screening assays. Whole-cell patch clamp confirmed APD shortening by the lead compound in KCNH2-G604S iPSC-CMs (759 ± 35 ms; n=13, to 599 ± 89 ms; n=9; p<0.03).
Conclusion: The high-throughput KIC screen confirmed mexiletine’s APD shortening effects in SCN5A-P1332L iPSC-CMs, validating the assay's potential for efficient, large-scale drug screening. In a pilot screen, we identified 6 novel LQTS drug candidates which shortened the APD90 in SCN5A-P1332L (LQT3) and KCNH2-G604S (LQT2) iPSC-CMs more than mexiletine. The lead compound’s APD shortening effects in KCNH2-G604S iPSC-CMs were confirmed with whole cell patch clamp. The KIC platform offers a robust method for identifying novel QT shortening compounds by enabling reproducible APD measurements in a high-throughput format.