Cross-Site Reliability of Human Induced Pluripotent stem cell-derived Cardiomyocyte Based Safety Assays Using Microelectrode Arrays: Results from a Blinded CiPA Pilot Study.

Recent in vitro cardiac safety studies demonstrate the ability of human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) to detect electrophysiologic effects of drugs. However, variability contributed by unique approaches, procedures, cell lines, and reagents across laboratories makes comparisons of results difficult, leading to uncertainty about the role of hiPSC-CMs in defining proarrhythmic risk in drug discovery and regulatory submissions. A blinded pilot study was conducted to evaluate the electrophysiologic effects of 8 well-characterized drugs on 4 cardiomyocyte lines using a standardized protocol across 3 microelectrode array platforms (18 individual studies). Drugs were selected to define assay sensitivity of prominent repolarizing currents (E-4031 for IKr, JNJ303 for IKs) and depolarizing currents (nifedipine for ICaL, mexiletine for INa) as well as drugs affecting multichannel block (flecainide, moxifloxacin, quinidine, and ranolazine). Inclusion criteria for final analysis was based on demonstrated sensitivity to IKr block (20% prolongation with E-4031) and L-type calcium current block (20% shortening with nifedipine). Despite differences in baseline characteristics across cardiomyocyte lines, multiple sites, and instrument platforms, 10 of 18 studies demonstrated adequate sensitivity to IKr block with E-4031 and ICaL block with nifedipine for inclusion in the final analysis. Concentration-dependent effects on repolarization were observed with this qualified data set consistent with known ionic mechanisms of single and multichannel blocking drugs. hiPSC-CMs can detect repolarization effects elicited by single and multichannel blocking drugs after defining pharmacologic sensitivity to IKr and ICaL block, supporting further validation efforts using hiPSC-CMs for cardiac safety studies.

Molecular Phenotyping Combines Molecular Information, Biological Relevance, and Patient Data to Improve Productivity of Early Drug Discovery.

Today, novel therapeutics are identified in an environment which is intrinsically different from the clinical context in which they are ultimately evaluated. Using molecular phenotyping and an in vitro model of diabetic cardiomyopathy, we show that by quantifying pathway reporter gene expression, molecular phenotyping can cluster compounds based on pathway profiles and dissect associations between pathway activities and disease phenotypes simultaneously. Molecular phenotyping was applicable to compounds with a range of binding specificities and triaged false positives derived from high-content screening assays. The technique identified a class of calcium-signaling modulators that can reverse disease-regulated pathways and phenotypes, which was validated by structurally distinct compounds of relevant classes. Our results advocate for application of molecular phenotyping in early drug discovery, promoting biological relevance as a key selection criterion early in the drug development cascade.

Phenotypic screening with human iPS cell-derived cardiomyocytes: HTS-compatible assays for interrogating cardiac hypertrophy.

A major hurdle for cardiovascular disease researchers has been the lack of robust and physiologically relevant cell-based assays for drug discovery. Derivation of cardiomyocytes from human-induced pluripotent stem (iPS) cells at high purity, quality, and quantity enables the development of relevant models of human cardiac disease with source material that meets the demands of high-throughput screening (HTS). Here we demonstrate the utility of iPS cell-derived cardiomyocytes as an in vitro model of cardiac hypertrophy. Exposure of cardiomyocytes to endothelin 1 (ET-1) leads to reactivation of fetal genes, increased cell size, and robust expression of B-type natriuretic peptide (BNP). Using this system, we developed a suite of assays focused on BNP detection, most notably a high-content imaging-based assay designed for phenotypic screening. Miniaturization of this assay to a 384-well format enabled the profiling of a small set of tool compounds known to modulate the hypertrophic response. The assays described here provide consistent and reliable results and have the potential to increase our understanding of the many mechanisms underlying this complex cardiac condition. Moreover, the HTS-compatible workflow allows for the incorporation of human biology into early phases of drug discovery and development.

Multiparameter in vitro assessment of compound effects on cardiomyocyte physiology using iPSC cells.

A large percentage of drugs fail in clinical studies due to cardiac toxicity; thus, development of sensitive in vitro assays that can evaluate potential adverse effects on cardiomyocytes is extremely important for drug development. Human cardiomyocytes derived from stem cell sources offer more clinically relevant cell-based models than those presently available. Human-induced pluripotent stem cell-derived cardiomyocytes are especially attractive because they express ion channels and demonstrate spontaneous mechanical and electrical activity similar to adult cardiomyocytes. Here we demonstrate techniques for measuring the impact of pharmacologic compounds on the beating rate of cardiomyocytes with ImageXpress Micro and FLIPR Tetra systems. The assays employ calcium-sensitive dyes to monitor changes in Ca(2+) fluxes synchronous with cell beating, which allows monitoring of the beat rate, amplitude, and other parameters. We demonstrate here that the system is able to detect concentration-dependent atypical patterns caused by hERG inhibitors and other ion channel blockers. We also show that both positive and negative chronotropic effects on cardiac rate can be observed and IC(50) values determined. This methodology is well suited for safety testing and can be used to estimate efficacy and dosing of drug candidates prior to clinical studies.

Comparative gene expression profiling in human-induced pluripotent stem cell--derived cardiocytes and human and cynomolgus heart tissue.

Cardiotoxicity is one of the leading causes of drug attrition. Current in vitro models insufficiently predict cardiotoxicity, and there is a need for alternative physiologically relevant models. Here we describe the gene expression profile of human-induced pluripotent stem cell-derived cardiocytes (iCC) postthaw over a period of 42 days in culture and compare this profile to human fetal and adult as well as adult cynomolgus nonhuman primate (NHP, Macaca fascicularis) heart tissue. Our results indicate that iCC express relevant cardiac markers such as ion channels (SCN5A, KCNJ2, CACNA1C, KCNQ1, and KCNH2), tissue-specific structural markers (MYH6, MYLPF, MYBPC3, DES, TNNT2, and TNNI3), and transcription factors (NKX2.5, GATA4, and GATA6) and lack the expression of stem cell markers (FOXD3, GBX2, NANOG, POU5F1, SOX2, and ZFP42). Furthermore, we performed a functional evaluation of contractility of the iCC and showed functional and pharmacological correlations with myocytes isolated from adult NHP hearts. These results suggest that stem cell-derived cardiocytes may represent a novel in vitro model to study human cardiac toxicity with potential ex vivo and in vivo translation.

Characterization of human-induced pluripotent stem cell-derived cardiomyocytes: bioenergetics and utilization in safety screening.

Cardiotoxicity remains the number one reason for drug withdrawal from the market, and Food and Drug Administration issued black box warnings, thus demonstrating the need for more predictive preclinical safety screening, especially early in the drug discovery process when much chemical substrate is available. Whereas human-ether-a-go-go related gene screening has become routine to mitigate proarrhythmic risk, the development of in vitro assays predicting additional on- and off-target biochemical toxicities will benefit from cellular models exhibiting true cardiomyocyte characteristics such as native tissue-like mitochondrial activity. Human stem cell-derived tissue cells may provide such a model. This hypothesis was tested using a combination of flux analysis, gene and protein expression, and toxicity-profiling techniques to characterize mitochondrial function in induced pluripotent stem cell (iPSC) derived human cardiomyocytes in the presence of differing carbon sources over extended periods in cell culture. Functional analyses demonstrate that iPSC-derived cardiomyocytes are (1) capable of utilizing anaerobic or aerobic respiration depending upon the available carbon substrate and (2) bioenergetically closest to adult heart tissue cells when cultured in galactose or galactose supplemented with fatty acids. We utilized this model to test a variety of kinase inhibitors with known clinical cardiac liabilities for their potential toxicity toward these cells. We found that the kinase inhibitors showed a dose-dependent toxicity to iPSC cardiomyocytes grown in galactose and that oxygen consumption rates were significantly more affected than adenosine triphosphate production. Sorafenib was found to have the most effect, followed by sunitinib, dasatinib, imatinib, lapatinib, and nioltinib.

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. Long QT syndrome diagnosis is hindered by reduced penetrance, as the long QT phenotype is absent on baseline electrocardiogram (ECG) in about 30%. METHODS: Fifty-two family members were phenotyped by baseline QTc, QTc maximum on serial ECGs (Ser QTc-max), and on exercise ECGs (Ex QTc-max) and by T-wave patterns. Linkage analysis tested association of the intronic change with phenotype. The consequences of T1945+6C on splicing was studied using a minigene system and on function by heterologous expression. RESULTS: Expanded phenotype/pedigree criteria identified 23 affected and 29 unaffected. Affected versus unaffected had baseline QTc 484 +/- 48 ms versus 422 +/- 20 ms, Ser QTc-max 508 +/- 48 ms versus 448 +/- 10 ms, Ex QTc-max 513 +/- 54 ms versus 444 +/- 11 ms, and LQT2 T waves in 87% versus 0%. Linkage analysis demonstrated a logarithm of odds score of 10.22. Splicing assay showed T1945+6C caused downstream intron retention. Complementary deoxyribonucleic acid with retained intron 7 failed to produce functional channels. CONCLUSIONS: T1945+6C is a disease-causing mutation. It alters KCNH2 splicing and cosegregates with the LQT2 phenotype. Expanded ECG criteria plus pedigree analysis provided accurate clinical diagnosis of all carriers including those with reduced penetrance. Intronic mutations may be responsible for LQTS in some families with otherwise negative mutation screening.