A critical open question in regenerative medicine is how to create successful stem cell therapies that yield regenerative growth healing the patient but without giving them cancers which are thought to be the most likely side effect of these types of therapies. One step toward achieving this goal of having human embryonic stem cells (hESC) that are as effective and safe as possible is to identify (1) the stem cell factors that promote the properties of stem cells to regrow organs and (2) the factors that promote cancer formation. With this information we can "customize" hESC to be more functional but not cause cancer. Unfortunately because cancer is a highly related process to regenerative organ growth, the prediction is that the same factors that would tend to enhance the ability of stem cells to mediate regenerative growth are also likely to promote cancer. One example of such factors is the myc family of proto-oncogenes. The main objective of this proposal is to test the hypothesis that the concentration of Myc in hESC determines their regenerative and cancer capacities. We predict that we can identify an optimum amount of Myc that will yield hESC that have enhanced regenerative medicine properties without increased risk of cancer. To this end, we will conduct studies where we selectively raise or lower the amount of Myc in hESC and follow the properties of the "low Myc" hESC, "medium Myc" hESC, and "high Myc" hESC using in vitro assays as well as in vivo assays in mice for regenerative growth in injury models and for tumorigenesis. Our broader goal is to test the novel and risky hypothesis, that we can harness an oncogene to work in a beneficial manner in hESC to promote better regenerative medicine.
Statement of Benefit to California:
There is great promise in the potential use of human embryonic stem cells (hESC) for regenerative medicine therapies to treat a number of serious medical disorders such as liver disease, blood disorders, neurological disorders, diabetes, heart disease and other conditions. An important place to begin building a foundation for such therapies is to increase our understanding of how hESC function, specifically what makes them more likely to mediate regenerative organ growth and what makes them more likely to cause the unacceptable side effect of cancer. The proposed research, investigating the master regulators of hESC normal and cancerous function, will be of great benefit to the State of California. These studies will promote our ability to use hESC in a safe and effective manner and may allow us to customize hESC lines with an optimum amount of Myc that promotes their beneficial activity while eliminating the risk of cancer.
SYNOPSIS: The investigator will evaluate the role of c-myc and N-myc in the proliferation, differentiation and potential tumorigenesis of human embryonic stem cells (hESC). In the first specific aim, the investigator will analyze the biology of myc-deficient hESC by using lentiviral vector medicated gene transfer to introduce shRNA expression cassettes targeted to N-myc and/or c-myc. In the second aim, the investigator will modulate myc levels by using a tet-on promoter system. The investigator anticipates that myc over-expression will stimulate proliferation, confer growth factor independence, inhibit differentiation as well as promote retention of pluripotency. In the 3rd aim, the investigator will test regulation of the in vivo behavior of hESC by myc in tumorigenisis and regeneration in injury models. He proposes to use NOD/SCID/MPSVII mice so that the behavior of hESC can be tracted by virtue of their expression of GUSB. Marrow damage induced by irradiation or liver damage induced by CCL4 will be studied in mice that receive hESC. INNOVATION AND SIGNIFICANCE: The overall hypothesis being tested asks whether the expression level of myc determines a regenerative versus an oncogenic phenotype. The investigator's specific hypothesis that the myc proteins have important roles in hESC is plausible and based on data already available in the mouse system. He proposes complex, state of the art methodology to modulate myc expression levels using lentiviral vector mediated gene transfer. As such, the proposal is moderately inovative although one reviewer noted that the hypothesis is not a novel idea and that the work breaks no new ground. The proposal's significance reflects the critical need to understand the function of specific genes in hESC biology. It's narrow focus, while laudable with respect to scientific design, may limit the mechanistic understanding that emerges from these studies. Thus, the results of this study are not expected to provide significant new insight into the problem of carcinogenic potential of ESC derived cell therapies. STRENGTHS: This is new project for a recently appointed assistent professor who was highly productive as a graduate student and who had a long and productive post-docotral fellow with the myc guru, Robert Eissenman. Based on this experience and the thoughtfulness of his proposal, we can infer that he understands the complexities of myc biology. He has formed colloborations with Dr. Nolta who is an expert in xenograft models and with Dr. Li who has experience in working with lentiviral vectors and hESC. Overall the enviroment seems optimal for the proposed work. WEAKNESSES: The proposal utilizes complex methodology which is relatively new to the investigator and which may require substantial effort to implement. The collaborative team has no track record of working together. The biological endpoints may be difficult to quantify precisely and to interpret in biological terms. Also, while the investigator acknowledges the role of myc as a modulator of transcription, he does not propose to attempt to define downstream targets of myc. DISCUSSION: There was no further discussion following reviewers' comments.