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RL1-00639-1: Induced Pluripotent Stem Cells for Cardiovascular Diagnostics

Recommendation: Recommended for funding
Scientific Score: 73

First Year Funds Requested: $569,520
Total Funds Requested: $1,708,560

Public Abstract (provided by applicant)

Our objective is to use induced pluripotent stem (iPS) cell technology to produce a cell-based test for long QT syndrome (LQTS), a major form of sudden cardiac death. Nearly 500,000 people in the US die of sudden cardiac death each year. LQTS can be triggered by drug exposure or stresses. Drug-induced LQTS is the single most common reason for drugs to be withdrawn from clinical trials, causing major setbacks to drug discovery efforts and exposing people to dangerous drugs. In most cases, the mechanism of drug-induced LQTS is unknown. However, there are genetic forms of LQTS that should allow us to make iPS cell–derived heart cells that have the key features of LQTS. Despite the critical need, current tests for drug-induced LQTS are far from perfect. As a result, potentially unsafe drugs enter clinical trials, endangering people and wasting millions of dollars in research funds. When drugs causing LQTS such as terfenadine (Seldane) enter the market, millions of people are put at serious risk. Unfortunately it is very difficult to know when a drug will cause LQTS, since most people who develop LQTS have no known genetic risk factors. The standard tests for LQTS use animal models or hamster cells that express human heart genes at high levels. Unfortunately, cardiac physiology in animal models (rabbits and dogs) differs from that in humans, and hamster cells lack many key features of human heart cells. Human embryonic stem cells (hESCs) can be differentiated into heart cells, but we do not know the culture conditions that would make the assay most similar to LQTS in a living person. These problems could be solved if we had a method to grow human heart cells from people with genetic LQTS mutations, so that we know the exact test conditions that would reflect the human disease. This test would be much more accurate than currently available tests and would help enable the development of safer human pharmaceuticals. Our long-term goal is to develop a panel of iPS cell lines that better represent the genetic diversity of the human population. Susceptibility to LQTS varies, and most people who have life-threatening LQTS have no known genetic risk factors. We will characterize iPS cells that have well-defined mutations that have clinically proven responses to drugs that cause LQTS. These iPS cell lines will be used to refine testing conditions. To validate the iPS cell–based test, the results will be directly compared to the responses in people. These studies will provide the foundation for an expanded panel of iPS cell lines from people with other genetic mutations and from people who have no genetically defined risk factor but still have potentially fatal drug-induced LQTS. This growing panel of iPS cell lines should allow for testing drugs for LQTS more effectively and accurately than any current test.

Statement of Benefit to California (provided by applicant)

Heart disease is the leading killer of adults in the Western world. Nearly 500,000 people in the US die of sudden cardiac death each year. Our goal is to develop a cell-based test to screen for drugs that can cause sudden cardiac death. Drug-induced cardiac side effects are the most common reason for withdrawal of drugs from clinical trials, causing major setbacks to drug discovery efforts. Therefore our test we will improve the safety of pharmaceuticals. Our test will also reduce the change that a drug in development will fail during clinical trials, thereby decreasing the financial risk for pharmaceutical companies. The results of our studies will help develop new technology that is likely to contribute to the California biotechnology industry. Our studies will develop multiple lines of iPS cells with unique genetic characteristics. These cell lines could be valuable for biotechnology companies and researchers who are screening for drug compounds. We are working closely with California companies to develop new microscopes, assay devices, and analytical software that could be the basis for new product lines or new businesses. If therapies do come to fruition, we anticipate that California medical centers will be leading the way. The most important contribution of this study will be to improve the health of Californians. Heart disease is a major cause of mortality and morbidity, resulting in billions of dollars in health care costs and lost days at work. Our goal is to contribute research that would ultimately improve the quality of life and increase productivity for millions of people who suffer from heart disease.

Review

This is an interesting proposal to develop new human induced pluripotent stem (iPS) cell lines derived from patients that present with long QT syndrome (LQTS). The goal is not to use these cells for regenerative medicine, but rather to use them to develop research reagents, specifically cellular assays that accurately reflect susceptibility to a form of drug-induced arrhythmia. The plan is to derive iPS cells from patients with LQTS, and demonstrate pluripotency. These iPS cells will be differentiated to cardiomyocytes, and the electrophysiologic profiles will be compared with normal iPS-derived cardiomyocytes. Finally, the principal investigator (PI) plans to adapt culture conditions of iPS cell-derived cardiomyocytes for high-throughput preclinical screening of drugs.

LQTS is a serious and potentially deadly condition that reflects an abnormal cardiac ventricular repolarization interval. It is a major cause of arrhythmia and sudden cardiac death, often in response to drug exposure or physiologic stresses. Genetic forms of LQTS result from mutations in ten genes, including a specific ion channel, which is the focus of this study. Drug-induced LQTS often also occurs in people with no detectable genetic mutation. The PI seeks to develop a panel of iPS cell lines constituting a range of LQTS susceptibility and to develop in vitro assays to better predict drug-induced responses. This is an important problem and significance is potentially very high, since drug-induced LQTS is a major reason that drugs are withdrawn from clinical trials.

There are several major strengths in this proposal. First, the team assembled to do the work appears to have the expertise and commitment to the project and notably includes a pioneer in the development of the iPS technology. Second, the PI will generate the iPS cells from patients with known mutations in a specific ion channel, and can compare the electrophysiologic findings with responses of the patients themselves, and possibly with cells from unaffected relatives. Finally, one underlying assumption in the proposal is well-founded: there is an imperfect relationship between electrophysiologic findings obtained by screening in conventionally-used in vitro assays, and animal models may carry similar liabilities. A leading hypothesis to explain this disconnect is failure of heterologous systems to express all cardiac proteins, some of which may interact with ion channels to produce a human phenotype. Thus, the incorporation of a mutant channel into an authentic human cardiomyocyte background could represent an important step to developing better models.

Reviewers identified some weaknesses with the proposal. The proposal lacked key preliminary data attesting to the ability to generate cardiomyocytes from these human fibroblasts. Work by this team in the mouse is reassuring, but one reviewer noted that mouse electrophysiology is different from humans, and myocytes derived from larger mammals display considerable heterogeneity within the same chamber. It was not clear to reviewers how the homogeneity and maturity of the derived cells will be validated. One reviewer felt this could also impact the third aim to develop high throughput assays, in which reproducibility and homogeneity of cell types, rather than efficiency, is key.

A final caveat from one reviewer is that the PI should carefully consider how to choose which cardiomyocytes to study. If the ultimate goal of the screen is to understand the underlying mechanism or to determine how a specific patient will respond to a drug, then cells with the mutations are appropriate. However, if the goal is to predict which drugs will cause abnormal effects in a population, the appropriate cells to study are those from normal individuals.

In summary, this is a proposal to establish a cell-based test for LQTS that can be used to identify drugs that cause LQTS and its attendant arrhythmias. The strengths are the investigative team, and the possibility that new reagents that would assist in understanding mechanisms underlying these arrhythmias would be developed. The proposal was felt to be responsive to the RFA and novel in seeking to develop a unique research toolkit, rather than regenerative protocols.

Programmatic Discussion
A motion was made to recommend that this application be moved to Tier 1 – Recommended for Funding. The panel highlighted the strength of the research team and the utility of the proposed screening system as reasons to recommend this application. Technical difficulties with the proposal were acknowledged, but the panel's sentiment was that this was the team that could accomplish the work. The motion to move this application to Tier 1 carried.

The following Working Group members had a conflict of interest with this application and were therefore recused from participating in review of, discussion of, and voting on the application:

• None