Induced pluripotent stem cells used to reveal drug actions in a long QT syndrome family with complex genetics

Abstract

Understanding the basis for differential responses to drug therapies remains a challenge despite advances in genetics and genomics. Induced pluripotent stem cells (iPSCs) offer an unprecedented opportunity to investigate the pharmacology of disease processes in therapeutically and genetically relevant primary cell types in vitro and to interweave clinical and basic molecular data. We report here the derivation of iPSCs from a long QT syndrome patient with complex genetics. The proband was found to have a de novo SCN5A LQT-3 mutation (F1473C) and a polymorphism (K897T) in KCNH2, the gene for LQT-2. Analysis of the biophysics and molecular pharmacology of ion channels expressed in cardiomyocytes (CMs) differentiated from these iPSCs (iPSC-CMs) demonstrates a primary LQT-3 (Na+ channel) defect responsible for the arrhythmias not influenced by the KCNH2 polymorphism. The F1473C mutation occurs in the channel inactivation gate and enhances late Na+ channel current (INaL) that is carried by channels that fail to inactivate completely and conduct increased inward current during prolonged depolarization, resulting in delayed repolarization, a prolonged QT interval, and increased risk of fatal arrhythmia. We find a very pronounced rate dependence of INaL such that increasing the pacing rate markedly reduces INaL and, in addition, increases its inhibition by the Na+ channel blocker mexiletine. These rate-dependent properties and drug interactions, unique to the proband’s iPSC-CMs, correlate with improved management of arrhythmias in the patient and provide support for this approach in developing patient-specific clinical regimens.

Mexiletine rescues a mixed biophysical phenotype of the cardiac sodium channel arising from the SCN5A mutation, N406K, found in LQT3 patients

“…Preliminary experimental and clinical evidences claim that mexiletine, a sodium channel blocker targeted in the inactivated state [26], could preferentially reduce the elevated late I Na [27] and shorten the APD in a cellular model of LQT3 [28,29] and the QT interval in LQT3 patients [30,31]. Liu et al reported that mexiletine produces more significant QRS widening when APD prolongation is induced by late I Na enhancer than I Kr blocker in the rabbit ventricular wedges, which indicates that the enhanced late I Na may be the consequence due to the failure of fast Na channel inactivation [32].…”

Integrating cardiomyocytes from human pluripotent stem cells in safety pharmacology: has the time come?

“…Examples include long‐QT syndrome (Terrenoire et al , 2013; Malan et al , 2016), catecholaminergic polymorphic ventricular tachycardia (Penttinen et al , 2015) and heart failure with preserved ejection fraction (Raphael et al , 2016). The cardiotoxic effects of anthracyclines in cardio‐oncology (Burridge et al , 2016) have also been recently validated (Avior et al , 2016).…”

Induced pluripotent stem cells: at the heart of cardiovascular precision medicine

“…In a LQT3 patient with both a de novo F1473C SCN5A mutation and a K897T KCNH2 gene polymorphism, the APDs of LQT3 hiPSC-CMs via a current clamp were not measurable because of a relatively depolarized diastolic membrane potential in these immature hiPSC-CMs. 66 Fatima et al likewise had difficulty showing increased ADP in LQT3 hiPSC-CMs derived from patients carrying different SCN5A mutations (p.V240M and p.R535Q) because of variations in the EP parameters among individual hiPSC-CMs. 68 These findings underscored the current limitations of hiPSC models, including the inability to accurately recapitulate all clinical disease thus far.…”