Redox Mechanisms of Human Neural Stem Cell Differentiation: Implications for Malignant Brain Tumor Treatment
New Faculty II
Brain tumors are a group of very severe diseases and currently more than 360,000 patients are diagnosed in the United States alone. The most common brain malignancy in children is medulloblastoma, a tumor which shares many characteristics with neuronal precursors. By contrast, older adults develop glioblastoma multiforme, a very aggressive tumor that shares many cellular characteristics with the support cells of the brain (astrocytic glia). The survival rates for these patients is abysmal; rarely more than one year despite surgery, radiation, and chemotherapy. Hence, there is a clear need to understand the reasons for which older adults, rather than children, develop this specific type of malignancy, in order to develop more specific diagnostic methods and effective treatment strategies, ultimately improving patient survival rates and quality of life. As the brain requires high levels of energy and oxygen in order to survive and function properly, it is exposed to chronically increased levels of harmful byproducts called free radicals. Cells use antioxidants to prevent oxidative stress and damage caused by free radicals, however this antioxidant activity decreases with aging. The oxidative damage has been long proposed as playing an important role in cancer development, which is further supported by new published data that suggests an inverse relationship between dietary intake of antioxidants and the risk of developing adult brain cancers. Using genetically engineered mice as models for human disease, we will test whether pharmacologically decreasing oxidative stress will retard the progression of brain tumor growth. Given that aging is associated with cumulative oxidative stress, healing becomes more difficult and the risk for cancer increases dramatically. We propose that under chronic oxidative stress, normal neural stem cells (which give rise to all types of cells in the mature brain and persist through life to play an important role in our ability to learn and heal) suffer changes that lead to the formation of tumor stem cells. Tumor stem cells have many features in common with normal stem cells, which include the ability to rapidly divide, allowing them to become the most invasive part of the tumor. With respect to this, we propose to test whether neural stem cells react to oxidative stress by preferentially increasing production of glial cells and decreasing production of neurons (which are required for maintaining normal brain functions), and thus perpetuating conditions that are conducive toward developing cancer. Successful completion of these studies will offer direct evidence that might be immediately moved into clinical practice. The ability to finally have an effective strategy for prevention and treatment of glioblastoma, as well as potential pharmacological intervention that can be used together with radiation and chemotherapy, will prove invaluable in the fight against this currently incurable disease.
Statement of Benefit to California:
Given the poor prognosis and survival rates typical of patients with malignant brain cancers such as glioblastoma multiforme, there is a strong sense of urgency to develop more effective treatment strategies for these patients. This is especially important, given the fact that this severe disease afflicts mostly older adults and that there is a growing aging population. The healthcare costs for the treatment of glioblastoma multiforme are staggering, and include the excessive costs of the new chemotherapy agents, the extensive need for acute hospitalization and the loss of years of life and income of the patients and families. In times of limited federal funding of medical research and increased stress on our health care resources, it is in the best interest of the State of California to invest tax payer dollars in research that is directly clinically applicable and in which the translation from the lab bench to the bed side is realistic, feasible, and less costly. Investment in this specific area of research will also bring additional intellectual payoffs, such as the development of a local translational program combining normal neural stem cell work and brain cancer research. As our goals strongly remain translational, and focused on finding better treatments for brain cancers, we will strive to offer a testing platform for other investigators in our field, as well as for the biomedical industry. Most of the clinical trials resulting from this work will be directly available to all of the patients in California, offering the benefit of local therapies instead of the added inconvenience of travel to other major medical centers located in the central and eastern part of the United States. This in turn will benefit the local and state economies by creating employment opportunities in California’s hospitals and clinics, thereby encouraging further investment in our local medical and biotechnological research.
This proposal is based on the hypothesis that oxidative stress predisposes multipotent neural stem cells (NSCs) to assume a glial lineage and increases genomic instability in normal NSCs. Such genomic instability is hypothesized to lead to malignant transformation such as in glioblastoma multiforme (GBM)-type tumors in older animals. Decreasing oxidative stress may therefore decrease glial differentiation and the incidence of malignant progression. In order to test this hypothesis, the applicant proposes two main specific aims. In Aim 1, the principal investigator (PI) will characterize the redox biology of human NSC, and brain tumor stem cells (SCs) and test in vitro the effects of oxidative stress exposure on the differentiation and propensity for malignant transformation of these cells. In Aim 2, the PI will test the in vivo differentiation and tumorigenicity of normal and tumor SCs in genetically engineered models of oxidative stress. In terms of the research plan, reviewers agreed that overall, this is a very ambitious proposal based on an interesting idea that addresses an area of research not well studied in the SC field. However, the research plan lacks a logical hypothesis driven flow and the applicant has not been able to translate it into productive experiments. Furthermore, there has been little consideration of how to interpret possible outcomes and of how such results would inform subsequent experiments. Some of the major weaknesses in the experimental plan are the following. In terms of the in vivo experiments, the PI proposes a transgenic model of oxidative stress to examine whether this will impact the transformation and growth of normal SCs subjected to chronic oxidative damage. Reviewers found the idea interesting but expressed concern about the time required to generate the model, the lack of experimental detail and potential caveats to the experiments not addressed by the PI. One of the essential components of this proposal is the careful experimental control of the redox state. While the PI mentions work by a collaborator on the differences of NSC behavior in different oxygen level conditions, this paradigm is not part of the experimental plan proposed and the collaborator’s preliminary data that is presented still needs to be reproduced in the applicant’s lab. Finally, the fact that the PI did not address the possibility that the most salient SCs may not necessarily express the proposed separation marker, was found to be too naïve from the reviewer’s perspective for this level of research. The applicant is a physician-scientist recently appointed Assistant Professor in the Department of Neurology at the host institution. Currently, the PI has no peer-reviewed funding. Reviewers expressed concern about the lack of expertise of the applicant on neural stem cells (NSCs) and a lack of familiarity with the relevant literature. In addition, the applicant’s lab has little transplant expertise. While she/he seems clearly dedicated to studying oxidative stress, reviewers found that the applicant has not accumulated much research experience/data since his/her last post-doctoral position. Moreover, the PI has an ambitious plan in matters of publication schedule, platform presentations and getting R01 funding. Unfortunately, the career development plan does not address very well how she/he will achieve these goals, which clearly exceeds his/her track record of publication to date. In terms of institutional commitment, reviewers had some concerns. The institutional funds received by the PI as a startup seem very modest as per today’s standards for a new starting investigator. The application is supported by a letter from the Vice Chancellor for Administration, but does not highlight what the institution will really do for the PI. However, reviewers also noted that the institution has made a very strong commitment to developing stem cell research with an endowed Stem Cell Research Center and a multi-million dollar commitment for the recruitment of new investigators over the next 10 years. A large number of other core facilities are listed which could facilitate success. In conclusion, reviewers found that the present application was interesting but weak and not well developed. Reviewers felt that the applicant would benefit from first generating some preliminary data from his/her own lab to support the hypotheses proposed and generate some publications out of his/her own lab. Once these milestones will be achieved the applicant will be in a stronger position to be competitive for funding. The applicant is encouraged to reapply with a more mature proposal in 1-2 years.