Basic Biology II
Glioblastomas are the most common and lethal form of intracranial tumors. They account for approximately 70% of the 22,500 new cases of malignant primary brain tumors that are diagnosed in adults in the United States each year. These cancers exhibit a relentless malignant progression characterized by widespread invasion throughout the brain, resistance to traditional and newer targeted therapeutic approaches, destruction of normal brain tissue, and certain death. The median age of patients at the time of diagnosis is 64 years. Despite optimal treatment, and improving standard of care the median survival is only 12 to 15 months for patients with glioblastomas. Glioblastoma multiforme (GBM), the most malignant of all brain tumors resuls from the sequential accumulation of genetic aberrations. To understand the role of some or all of the altered genes found in the human gliomas, we have recently used a novel method of using viral vectors to introduce the mutated genes directly into the specific part or cells in the brain. Remarkably we are able to completely recapture the disease of GBM, found in humans. Thus we have an excellent model system to understand and mechanistically decipher the formation of cancer stem cells. In our mouse model systems and xenotransplantation with human GBM cells, as few as 10 cells can lead to the formation of gliomas. Thus on principle every GBM cell is potentially a cancer initiating stem cell. To understand the role of cancer stem cells in glioblastomas, in the next three years we would like to first recapitulate the genetic traits of human GBM in mouse models. We would then like to pursue the time course in which brain tumors develop to get an idea of how soon the tumors grow and more importantly if the different regions of the brain form the same or different tumors. Another important property of the GBMs is that they have very extensive blood supply; therefore it is a good candidate for treatment with drugs that inhibit blood vessel formation. Interestingly, the tumor cells have learned to transdifferentiate into cells that line the walls of blood vessels, thereby rendering the drugs effecting formation of blood vessels ineffective. Finally, since as few as 10-100 GBM tumor cells are capable of initiating new tumors, they offer an excellent opportunity to study the pluripotency of GBMs and their relationship to cancer stem cells We believe that the proposed experiments provide an excellent opportunity to help us understand the molecular mechanisms of formation of GBM and its relationship to formation of pluripotent cancer stem cells.
Statement of Benefit to California:
There is a growing body of scientific literature which suggests that many cancers have stem cells which, like pluripotent stem cells, have the ability to replicate and differentiate into specific cancer phenotypes. The clinical implications are that unless such cancer stem cells are not eliminated, tumors will grow back again leading to a relapse. The actual percentage of the stem cells in different types of tumors varies quite a bit. Our results, albeit preliminary, indicate that in glioblastoma multiforme (GBM)—one of the most devastating brain tumors with a life expectancy of just over 12-15 months—every tumor cell has the potential to induce gliomas. Moreover these gliomas undergo transdifferentiation to endothelial cells, lining the blood vessels, thus frustrating the use of anti-angiogenic drugs. The work proposed here in our CIRM Basic Biology Awards II application has the potential to not only identify the mechanism of gliomogenesis, but offers an excellent opportunity to generate therapeutic entities. The State of California has excellent academic and biotechnology institutions that will be very glad to further develop some of the genes that we identify in our pursuit to understand the mechanism of GBM formation. Cancer is a very big health burden on the state budget and takes a major toll on the families of cancer patients, especially something as malignant as GBM. Ever more, we need to spend state resources wisely, and finding ways to reduce the continually increasing cost of long-term medical care is critical. The work proposed here seeks to do just that by creating outright cures for diseases that if left untreated require substantial and prolonged medical expenditures and incredible suffering for the patients and their families. In other regards keeping the State of California at the forefront of medical breakthroughs and strengthening our biomedical and biotechnology industries. We are a leading force in these fields, not only across the nation but also worldwide.
EXECUTIVE SUMMARY The goal of this proposal is to study the brain cancer glioblastoma multiforme (GBM) in human and mouse to uncover relationships between cancer stem cells and pluripotent stem cells at a molecular level. Aim 1 will recapitulate human GBM in a mouse model using lentiviral vectors. Aim 2 will study the kinetics of glioma formation. In Aim 3, the vascularity and transdifferentiation of gliomas to endothelial cells will be investigated. Aim 4 examines the relationship between glioblastoma stem cells and pluripotency. The reviewers agreed that the proposal contains high significance as it addresses the molecular basis of glioblastoma tumorigenesis. They felt the proposal featured a number of exciting hypotheses and interesting experiments. Despite these strengths, the proposal suffered from a lack of a coherent, unifying hypothesis that addressed a major unresolved issue in stem cell biology. The proposal has minimal focus on mechanism of cancer stem cell origin, pluripotency, or the mechanisms of transdifferentiation, and as such, reviewers viewed the proposal as unresponsive to the RFA. Although reviewers appreciated many innovative ideas in the proposal, such as the suggested transdifferentiation of glioblastoma stem cells into endothelial cells, they found the proposal unfocused with many experiments having little relation to one another. Reviewers questioned the relevance to human disease of mouse xenograft experiments for studying transdifferentiation and felt that studies of the viral reprogramming of astrocytes and neurons to induced pluripotent stem cells (iPSCs) were not supported by a compelling rationale. The reviewers acknowledged the proposal’s feasibility and general strength of the experimental design. For example, reviewers valued the proposal’s novel method of GBM generation, the preliminary data concerning transdifferentiation of glioblastoma stem cell into endothelial cells, and the state of the art in vivo imaging facilities used to observe kinetics of tumor formation. However, the review panel raised several serious concerns about some experiments, which diminished their enthusiasm. For example, the possibility of exosomal transmission of tumor-derived RNAs was not adequately considered, and few experiments addressed the analysis of molecular or biochemical mechanisms underlying transdifferentiation. Reviewers were unconvinced that experiments outlined under the fourth aim would provide meaningful information or were scientifically connected to other parts of the project. Furthermore, the proposal provided very little elaboration on potential pitfalls and alternative approaches. Reviewers unanimously praised the PI’s expertise, experience, ingenuity, and productivity. They felt that the proposed research team was capable of completing the project successfully, and the research environment was judged as exceptional. In summary, this proposal studies GBM with several different approaches, including deriving mouse models of GBM, studying GBM kinetics in a mouse model, characterizing transdifferentiation of GBM cells into endothelial cells, and examining the relationship between pluripotency and GBM stem cells. Strengths of the proposal included the excellent PI and research team and the potential significance of the study. Weaknesses included a serious lack of cohesion of the project’s aims, an inadequate focus on stem cell mechanisms, and an overall lack of responsiveness to the goals of the RFA.