Identification of Drug-Drug Interactions In Vitro: A Case Study Evaluating the Effects of Sofosbuvir and Amiodarone on hiPSC-Derived Cardiomyocytes.

Drug-drug interactions pose a difficult drug safety problem, given the increasing number of individuals taking multiple medications and the relative complexity of assessing the potential for interactions. For example, sofosbuvir-based drug treatments have significantly advanced care for hepatitis C virus-infected patients, yet recent reports suggest interactions with amiodarone may cause severe symptomatic bradycardia and thus limit an otherwise extremely effective treatment. Here, we evaluated the ability of human induced pluripotent stem cell derived cardiomyocytes (hiPSC-CMs) to recapitulate the interaction between sofosbuvir and amiodarone in vitro, and more generally assessed the feasibility of hiPSC-CMs as a model system for drug-drug interactions.

Development and Characterization of a Scaffold-Free 3D Spheroid Model of Induced Pluripotent Stem Cell-Derived Human Cardiomyocytes.

Cardiomyocytes (CMs) are terminally differentiated cells in the adult heart, and ischemia and cardiotoxic compounds can lead to cell death and irreversible decline of cardiac function. As testing platforms, isolated organs and primary cells from rodents have been the standard in research and toxicology, but there is a need for better models that more faithfully recapitulate native human biology. Hence, a new in vitro model comprising the advantages of 3D cell culture and the availability of induced pluripotent stem cells (iPSCs) of human origin was developed and characterized.

High purity human-induced pluripotent stem cell-derived cardiomyocytes: electrophysiological properties of action potentials and ionic currents.

Human-induced pluripotent stem cells (hiPSCs) can differentiate into functional cardiomyocytes; however, the electrophysiological properties of hiPSC-derived cardiomyocytes have yet to be fully characterized. We performed detailed electrophysiological characterization of highly pure hiPSC-derived cardiomyocytes. Action potentials (APs) were recorded from spontaneously beating cardiomyocytes using a perforated patch method and had atrial-, nodal-, and ventricular-like properties.

Stem cells and their derivatives: a renaissance in cardiovascular translational research.

Moving from the bench to the bedside is an expensive and arduous journey with a high risk of failure. One roadblock on the path of translational medicine is the paucity of predictive in vitro models available during preclinical drug development. The ability of human embryonic stem (ES) and induced pluripotent stem (iPS) cells to generate virtually any tissue of the body, in vitro, makes these cells an obvious choice for use in drug discovery and translational medicine.

Properties of WT and mutant hERG K(+) channels expressed in neonatal mouse cardiomyocytes.

Mutations in human ether-a-go-go-related gene 1 (hERG) are linked to long QT syndrome type 2 (LQT2). hERG encodes the pore-forming alpha-subunits that coassemble to form rapidly activating delayed rectifier K(+) current in the heart. LQT2-linked missense mutations have been extensively studied in noncardiac heterologous expression systems, where biogenic (protein trafficking) and biophysical (gating and permeation) abnormalities have been postulated to underlie the loss-of-function phenotype associated with LQT2 channels.

Most LQT2 mutations reduce Kv11.1 (hERG) current by a class 2 (trafficking-deficient) mechanism.

Background: The KCNH2 or human ether-a-go-go related gene (hERG) encodes the Kv11.1 alpha-subunit of the rapidly activating delayed rectifier K+ current (IKr) in the heart. Type 2 congenital long-QT syndrome (LQT2) results from KCNH2 mutations that cause loss of Kv11.

Comparison of HERG channel blocking effects of various beta-blockers-- implication for clinical strategy.

beta-Blockers are widely used in the treatment of cardiovascular diseases. However, their effects on HERG channels at comparable conditions remain to be defined. We investigated the direct acute effects of beta-blockers on HERG current and the molecular basis of drug binding to HERG channels with mutations of putative common binding site (Y652A and F656C).

Specific serine proteases selectively damage KCNH2 (hERG1) potassium channels and I(Kr).

KCNH2 (hERG1) encodes the alpha-subunit proteins for the rapidly activating delayed rectifier K+ current (I(Kr)), a major K+ current for cardiac myocyte repolarization. In isolated myocytes I(Kr) frequently is small in amplitude or absent, yet KCNH2 channels and I(Kr) are targets for drug block or mutations to cause long QT syndrome. We hypothesized that KCNH2 channels and I(Kr) are uniquely sensitive to enzymatic damage.

Intragenic suppression of trafficking-defective KCNH2 channels associated with long QT syndrome.

Mutations in the KCNH2 or human ether-a-go-go-related gene-encoded K(+) channel reduce functional KCNH2 current (I(KCNH2)) to cause long QT syndrome (LQT2) by multiple mechanisms, including defects in intracellular transport (trafficking). Trafficking-deficient, or class 2, LQT2 mutations reduce the Golgi processing and surface membrane expression of KCNH2 channel proteins. Drugs that associate with pore-S6 intracellular drug binding domain of KCNH2 channel proteins to cause high-affinity block of I(KCNH2) also can increase the processing of class 2 LQT2 channel proteins through the secretory pathway.

Blockade of HERG channels by HIV protease inhibitors.

The HIV protease inhibitor class of antiretroviral drug causes unpredicted adverse effects by changing elements of normal cellular metabolism. A case of QT prolongation in a patient receiving protease inhibitors made us question whether these drugs might be responsible. We identified 24 patients with QT prolongation or torsade de pointes, or both, associated with protease inhibitors, using the Food and Drug Administration's voluntary adverse event reporting system.

An intronic mutation causes long QT syndrome.

Objectives: The purpose of this research was to determine whether an intronic variant (T1945+6C) in KCNH2 is a disease-causing mutation, and if expanded phenotyping criteria produce improved identification of long QT syndrome (LQTS) patients.

Background: Long QT syndrome is usually caused by mutations in conserved coding regions or invariant splice sites, yet no mutation is found in 30% to 50% of families. In one such family, we identified an intronic variant in KCNH2.

Biology of cardiac arrhythmias: ion channel protein trafficking.

The mechanisms underlying normal and abnormal cardiac rhythms are complex and incompletely understood. Through the study of uncommon inheritable arrhythmia syndromes, including the long QT and Brugada syndromes, new insights are emerging. At the cellular and tissue levels, we now recognize that ion channel current is the sum of biophysical (gating, permeation), biochemical (phosphorylation, etc), and biogenic (biosynthesis, processing, trafficking, and degradation) properties.

Molecular and functional characterization of common polymorphisms in HERG (KCNH2) potassium channels.

Long QT syndrome (LQTS) is a cardiac repolarization disorder that can lead to arrhythmias and sudden death. Chromosome 7-linked inherited LQTS (LQT2) is caused by mutations in human ether-a-go-go-related gene (HERG; KCNH2), whereas drug-induced LQTS is caused primarily by HERG channel block. Many common polymorphisms are functionally silent and have been traditionally regarded as benign and without physiological consequence.

Thapsigargin selectively rescues the trafficking defective LQT2 channels G601S and F805C.

Several mutations in the human ether-a-go-go-related K+ channel gene (HERG or KCNH2) cause long QT syndrome (LQT2) by reducing the intracellular transport (trafficking) of the channel protein to the cell surface. Drugs that bind to and block HERG channels (i.e.

Molecular characterization, functional expression, and developmental profile of an ether à-go-go K+ channel in the tobacco hornworm Manduca sexta.

A very large number of evolutionarily conserved potassium channels have been identified but very little is known about their function or modulation in vivo. Metamorphosis of the tobacco hornworm, Manduca sexta, is a compelling model system for such studies because it permits analysis to be conducted at the level of identified neurons whose roles in simple behaviors and endocrine regulation are known. We present here the characterization of the first ion channel to be cloned from this animal.

Genetic basis for the origin of cardiac arrhythmias: implications for therapy.

The recognition of the role that genetic abnormalities play in the generation of cardiac arrhythmias and sudden cardiac death has evolved enormously over the past decade. One result is new insight into underlying physiologic and pathophysiologic mechanisms. New therapies based on this evolving insight are being developed.

Pharmacological rescue of human K(+) channel long-QT2 mutations: human ether-a-go-go-related gene rescue without block.

Background: Defective protein trafficking is a consequence of gene mutations. Human long-QT (LQT) syndrome results from mutations in several genes, including the human ether-a-go-go-related gene (HERG), which encodes a delayed rectifier K(+) current. Trafficking-defective mutant HERG protein is a mechanism for reduced delayed rectifier K(+) current in LQT2, and high-affinity HERG channel-blocking drugs can result in pharmacological rescue.