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RC1-00126-1: Constructing a library of custom-tailored human embryonic stem cell-derived cardiomyocytes for specific heart therapies

Recommendation: Not recommended for funding 

Public Abstract (provided by applicant)

Malfunctions or significant loss of heart cells due to aging or diseases can lead to lethal consequences (e.g. heart attack, heart failure and various forms of irregular heart rhythms). Since heart cells normally lack the ability to regenerate, transplantation is the last resort for patients with end-stage heart failure. However, this option is severely limited by the number of donor organs available. Cell replacement therapy is an alternative for myocardial repair but is similarly hampered by the availability of transplantable cells (e.g. human fetal cardiomyocytes). Non-cardiac cells such as skeletal muscle myoblasts have thus been sought as alternatives, but potentially lethal side effects arise due to the fact that they are not genuine heart cells.

Human embryonic stem cells (hESCs), isolated from the inner cell mass of blastocysts, can self-renew and propagate indefinitely while maintaining their ability to become all cell types, including heart cells. Therefore, hESCs may provide an unlimited cell source. However, current methods for differentiating hESCs into specific heart cell types (e.g. pacemaker cells that are specialized for generating electrical heart rhythms, and cardiac atrial and ventricular muscles for the mechanical action of blood pumping) are stochastic. Furthermore, unlike the adult counterparts, hESC-derived CMs have embryonic-like properties. Indeed, some of these immature properties can even cause lethal electrical disturbances, making them unsafe for transplantation. Therefore, it is necessary to improve the yields of chamber-specific CMs and maturate their properties. Engineering of hESCs to create “custom-tailored” CMs can present a novel and flexible solution.

Using a combination of cell- and gene-based approaches, we have demonstrated, at the preclinical level, in both small (guinea pigs) and large (swines) animal disease models that the various biological alternatives that we developed are superior to such conventional treatments as device-based therapies (e.g. biological versus electronic pacemakers for sick sinus syndrome). These scientific progresses of ours have been reported by various public news media (e.g. WebMD, Forbes, etc). With such an established in-house platform, here we propose to employ a range of state-of-the-art scientific techniques that are uniquely available to us a) to construct a library of customized hESC-derived cardiomyocytes for specific heart therapies (e.g. pacemaker for rhythm generation disorders, and cardiac muscles for myocardial repair), and b) to test that cardiac function(s) of our animal disease models can be improved after transplantation of engineered hESC-derived cells. Collectively, this proposal serves to obtain a better understanding of the basic biology of hESC-derived heart cells, as well as to provide a unique translational platform for developing hESC-based heart therapies

Statement of Benefit to California (provided by applicant)

Human ESCs have been a hot topic because of their potential of curing numerous currently untreatable human diseases. The proposed project to be executed in CA has the following long-term visions: 1) to extend the human lifespan and to improve the quality of life via successful hESC research, 2) to provide a collegial and intellectually stimulating environment in CA for hESC research, 3) to make important, long half-life fundamental discoveries in the hESC field of high academic value, 4) to develop novel commercially-viable, therapeutic approaches that can directly benefit patients and our state’s economy via translational hESC research, 5) to offer excellent training opportunities and education for the next-generation scientists, clinicians and academians. During the requested funding period, our specific mission is to build in CA a unique internationally renowned hESC research program that specializes in the proposed discipline. According to a recent article in 2006 (Nat. Biotech 24, 391), only a total of 132 hESC research articles from the entire medical literature were published during 1998-2004. To date, merely ~10 of all published hESC articles studied the heart and 5 were on ion channels and pumps. Clearly, such a low productivity in the fields of cardiovascular sciences and electrophysiology is not because they are less important than others. Instead, it reflects the associated technical difficulties. In fact, only 5 labs worldwide, including our own, have reported the successful derivation of heart cells from hESCs. In particular, we specifically focuses on genetic engineering of hESCs and their bioelectrical properties. This unique marriage (of hESC biology and quantitative sciences) enables us to employ a broad range of state-of-the-art techniques to investigate the focused topic of engineering hESC-derived heart cells. In fact, we have already gained the necessary momentum: 1) In the past year alone, we have filed in CA a total of 6 related patents. We have been approached by various companies (e.g. Bioheart, Japan Tobacco, Bayer, etc) for potential licensing activities. 3) While the core science focuses on the heart, our experimental design and platform are highly scalable and of general utility to multiple disciplines. For instance, our efforts have led to preliminary data for supporting 6 other CIRM seed grants from our institution (c.f. Collaboration). Overall, we anticipate that our program will contribute to both the scholastic and economical developments in CA. This will be accomplished by training new stem cell scientists (for the academia and the biotech industry) and by creating new jobs (e.g. via extramural funding and licensing activities). Since our hESC work is not currently extramurally supported, receiving a comprehensive grant from CIRM is crucial for us to maintain our momentum, and to make further progresses for facilitating both basic discovery and translation.

Review

SYNOPSIS: The purpose of this grant application is to generate “custom tailored cardiomyocytes (CMs) as a solution to modify and repair injured myocardium”. The author proposes to obtain customized human pacemakers that are engineered to fire at different rates for possible application for rhythm generation disorders. When cardiomyocytes are derived from human embryonic stem cells (hESCs), they maintain the electrical properties of the embryonic cell type. In order for these cells to become suitable for transplantation into adults, maturation of their rhythm is required. The authors propose to develop rhythmically mature cells from hESCs and test the function and efficacy of hESC-CMs as donor cells. The proof of principle will be established in guinea pigs and swine.

IMPACT AND SIGNIFICANCE: The proposal has scientific significance related to the development of hESCs as models to study the formation of human conduction system cells. The clinical significance is not as compelling, given that conventional pacemakers work quite well and the only potential niche for a biological pacemaker might relate to infants with congenital heart block, a relatively rare entity. However, there is insufficient preliminary data to support this potential therapeutic direction at the present time.

The applicant proposes to improve on existing methods for preparing hESC-derived cardiomyocytes. The logic is three-fold: limitations of “stochastic” differentiation, the electrophysiological immaturity of conventional hESC-derived cardiomyocytes, and the proposed utility of biological pacemakers. Modifying the cells’ rate of electrical firing in defined ways is quite interesting, in terms of understanding more concretely how cardiac automaticity is established, but the clinical need for biological pacemakers is not at all convincing, by comparison to other priorities in the field. Several of the needs appear to be exaggerated, alternative approaches are minimized, and potential hazards including integration events and tumorigenicity are disregarded.

QUALITY OF THE RESEARCH PLAN: This proposal is poorly written and full of unnecessary jargon. The same proposal could have been conveyed in a much simpler, cleaner fashion. Aspects of the design are appropriate, but the underlying assumption that expression of modified pacemaker channels in hESCs will somehow lead to the increased formation of ES-derived cardiomyocytes is unclear. Pacemaker channels are actually expressed throughout the early embryonic heart in most cardiomyocytes, and later become restricted to pacemaker and other conduction system cells during subsequent steps of heart maturation. Another potential problem is that there is extreme heterogeneity of the cardiomyocytes that are derived from differentiating ESCs, that include atrial, ventricular, and conduction system cells. Expression of these modified pacemaker channels are likely to have differential effects on each of these cell types and it may be difficult to unequivocally identify the original cardiac cell type which is being interrogated, resulting in a large scatter of data.

Cell “maturation” on the basis of forcibly expressed exogenous channels alone does not adequately take into account many potential kinds of cell heterogeneity, within the cardiomyocyte lineage. The entire selection strategy is disappointingly superficial and even naive.

The applicant proposes to find key proteins for maturation and differentiation by a proteomic screen. A screen alone, without functional validation, is a poor choice for a project of 4 years’ overall duration. Insufficient indication is given about how positive hits would be prioritized, for later functional testing, or the exact form such testing would involve, if the proposed approach was uninformative.

STRENGTHS: The investigator has extensive experience in cardiac biology in general, and electrophysiology of cardiac channels in particular. The applicant has hands-on experience with WiCell and HES2 hESCs, experienced collaborators for many aspects of the work, and excellent publications. The proposal has some interesting aspects, and the goal of understanding hESC-derived cardiomyocytes as a system to study conduction system cells has potential value.

WEAKNESSES: There are many weaknesses in this proposal, but perhaps the most important one is the complete lack of appreciation for where the field currently stands. For example, the author states that it is relatively straightforward to derive cardiomyocytes from hESCs. The applicant cites up to 90% from HES4. This is simply not correct. We are far away from even the basic understanding of how you derive cardiomyocytes from hESCs to start with, before we need to worry about changing their rhythm. The answer to questions such as how many transition states it takes for an hESC to become a cardiomyocyte are neither addressed nor appreciated. Do the cells need to undergo first a change to dorsal mesodermal fate in cardiac lineages? It is not clear how the specific cardiac cell types will be isolated.

Additional weaknesses include the emphasis on biological pacemakers (a clinical need of uncertain value), the excessively narrow focus on electrical maturation, the superficial use of genetic selection, the failure to explore alternative approaches, and the failure to test systematically for tumorigenicity.

Furthermore, the author proposes a comparative proteomic approach among cells of varied stages in development toward cardiac myocytes that does not consider the magnitude with which it would need to be carried out if using the appropriate statistical controls. Are cardiac progenitors derived from hESCs a homogeneous population? If they are not, what would that proteomic analysis mean?

DISCUSSION: The PI is a bright, young, aggressive individual, but the proposal is not well thought out and presented with an amazing amount of unnecessary jargon. The clinical need is not competitive (designing biologic pacemakers over electronic pacemakers). Even if the rationale were strong, the scientific aspects are naïve. The applicant is taking a lot for granted technically. Collectively, the aim is to get cardiomyocytes but it is not easy to get a homogeneous population of these. The study is not comprehensive for the field, and the clinical significance is virtually nil. The PI is well-trained, but the PI’s knowledge of hESCs is not strong.

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:

• Feit, Marcy
• Lansing, Sherry
• Rosen, Michael