D-AB17-05 - Disease Modeling And Lumacaftor Drug Efficacy Testing In Ipsc-cms Derived From A Patient With A Novel Kcnh2 Variant Of Uncertain Significance (ID 1415)
B.J. O'Hare: Nothing relevant to disclose.
Background: Pathogenic missense variants in the KCNH2-encoded Kv11.1 (hERG) potassium channel often render the channel trafficking defective, can prolong the action potential duration (APD), and cause long QT syndrome type 2 (LQT2). Lumacaftor (LUM), a clinically used cystic fibrosis treatment that functions as a protein chaperone, has been suggested as a new treatment option in LQT2.
Objective: To characterize a novel KCNH2 variant of uncertain significance (VUS) and test the efficacy of LUM as therapeutic option using patient-derived, induced pluripotent stem cell cardiomyocytes (iPSC-CMs).
Methods: iPSC-CMs from an 11-year-old female (QT ≥ 500ms) with a novel KCNH2-R685P VUS were generated. ANEPPS voltage sensing dye was used to assess APD in the patient’s iPSC-CMs and control iPSC-CMs before/after LUM (10µM) treatment. The KCNH2-R685P VUS was engineered using site-directed mutagenesis. Standard whole-cell patch clamp technique was used to measure KCNH2-WT and -R685P currents heterologously expressed in TSA201 cells. Immunofluorescence (IF) imaging and western blot (WB) were used for hERG membrane expression profiling.
Results: The APD90 was prolonged significantly in KCNH2-R685P iPSC-CMs vs. control iPSC-CMs at baseline (569 ± 29 ms vs 350 ± 9 ms, p < 0.0001), which was rescued with LUM treatment (372 ± 20 ms vs 330 ± 18 ms, p = 0.1). KCNH2-R685P revealed significant tail current reduction across the voltage from +20 to +60 mV. At +60 mV, tail current density was reduced by 58% from 155.2 ± 19.5 (n=16) to 90.7 ± 19.2 (n=17, p < 0.05 vs. KCNH2-WT). However, KCNH2-R685P did not significantly shift peak activation and tail deactivation curves. IF and WB demonstrated that KCNH2-R685P results in hERG channel trafficking deficiency in both iPSC-CM and TSA201 cell models. Reduced hERG membrane expression was rescued following LUM treatment in the KCNH2-R685P iPSC-CMs, but not in the TSA201 cell model.
Conclusion: Here, we demonstrate that the novel KCNH2-R685P VUS identified in our patient is a hERG channel trafficking defective variant that can be rescued by LUM treatment in the patient’s iPSC-CMs. Importantly, the efficacy of drug treatment strategies such as LUM should be performed in iPSC-CMs, not in the TSA201 heterologous expression systems.