Gliomas are the most common, and most fatal, primary brain tumors. Every year, about 24,000 new cases of glioma are diagnosed in the US, and about 18,000 of those people die within a year. The poor prognosis is because these cancers grow by invading the surrounding brain, rendering complete surgical removal possible only in few patients. As such, the development of a successful treatment requires devising means of eliminating every remaining invasive tumor cell left behind after surgery, at the same time protecting the functioning surrounding brain.
Our proposal addresses this great unmet medical need, and seeds a long-term goal, which is to discover novel therapeutics to treat the invasive brain cancer cell. This application is based on previous exciting studies by us and others, which has demonstrated that in animal models, neural stem cells (NSCs) move specifically towards invasive brain cancer cells and track down pockets of tumors within the brain. Importantly, NSCs can be used to deliver therapeutic agents directly to tumor cells, with significant therapeutic benefit in animals. Here, our goal is to advance the field of brain cancer stem cell therapy by establishing novel approaches to examine the mechanisms how NSCs move, or migrate, toward glioma. We expect this knowledge to translate into refinement of the processes used to generate tumor-tropic stem cells (=stem cells that specifically track tumor cells), so that this can be accomplished in a clinically practicable fashion. Specifically, the proposed studies will contribute to the development of stem cell therapy in two ways. First, we will establish rigorous "motility assays", which are laboratory tests that will facilitate an important comparison of the migratory capabilities of NSCs derived by two well-publicized but heretofore never compared routes: NSCs derived from human embryonic stem cells (hESCs) vs. NSCs isolated directly from the central nervous system. Thus, although NSC migration is an absolute requirement for the use and further development of NSCs in stem cell therapy, migratory capabilities of different NSCs are currently unknown. Second, rigorous motility tests are needed for the analysis of the detailed mechanisms (the inner workings) how NSCs move towards glioma. We will subsequently utilize various genetic, molecular and cell biological means to study these mechanisms in detail. Our goal is to identify and characterize the genes and proteins that regulate the process of NSC movement towards gliomas. We expect our knowledge on the molecular mechanisms how stem cells track infiltrating tumor cells to allow further refinement of this therapeutic modality, because specific stem cell populations could be purified or genetically engineered on the basis of enhanced motility characteristics, thereby improving the efficiency of this treatment strategy for glioma.
Statement of Benefit to California:
Each year more than 200,000 people in the United States are diagnosed with a primary or metastatic brain tumor; primary brain tumors comprise approximately 40,0000 of these diagnoses. Brain tumors are the leading cause of solid tumor cancer death in children under the age of 20, and they are the second leading cause of cancer death in male adults ages 20-29. In California alone, 1,500 people die of brain cancers annually. Due to the high mortality rate, malignant brain cancer remains the single most costly and morbid cancer per capita in the United States, and unfortunately, the overall prognosis of brain cancer patients has remained virtually unchanged over the past 20 years. Thus, there is a great unmet medical need to provide novel and more effective treatment strategies to the people affected by this disease.
Based on animal studies, human ES cell-derived neural stem cells represent an important step forward that may prove critical in the ultimate clinical implementation of a new treatment for glioma, the most common form of brain cancer. Our proposed studies in this application, once completed, are expected to greatly accelerate the path towards the generation and engineering of clinically useful stem cell therapies for this disease. If we are successful in this goal, our studies are anticipated to significantly reduce the human and economic costs of brain cancer in California and elsewhere, and also make adjuvant brain cancer therapy more readily available to the underserved population. In parallel, we expect that a successful completion of these studies will greatly invigorate stem cell therapy studies for other cancers, as well. This could open up unprecedented new opportunities for future oncology applications, and attract scientists from other states to California, all this having a positive effect on our State. Finally, the expansion of biotechnology industry (jobs, capital investments) that translates the scientific discoveries made under the auspices of CIRM to practical applications is also expected to have a significant positive economic impact on California.
Previous work in mice has shown that neural progenitors cells will migrate to, and track with, infiltrating glioblastoma cells in vivo. Furthermore, these neural progenitor cells have been used to deliver therapeutic agents to gliomas and prolong lifespan. This proposal further addresses the molecular mechanism of neural stem cell migration toward invasive gliomas, with the goal of translating these observations into more effective clinical therapies. In Aim 1 the applicant will compare the migratory abilities of neural stem cells derived from human ES cells in vitro to neural stem cells harvested directly from the CNS. In Aim 2 the molecular mechanism of neural stem cell migration will be studied by gene expression profiling, and by direct targeting of candidate regulators of cell motility.
SIGNIFICANCE AND INNOVATION: This proposal is significant because it will begin to explore the innovative idea that neural progenitors derived from human ES cells in vitro might be able to target glioma cells, as has already been demonstrated for neural progenitors harvested from fetal tissue. This could provide a more readily available and reproducible reagent with which to test whether this might be a useful new therapeutic approach.
STRENGTHS: This is an innovative proposal that brings together scientists with a broad range of expertise to approach a problem of substantial clinical importance. The application is based on observations and assays made by the principal investigators, and therefore is technically feasible.
WEAKNESSES: While this might be a very innovative approach to therapy, there are some aspects of this proposal are worrisome. One area of concern is the idea that RNA and epigenetic profiling of cells in vitro will provide insight into mechanisms that control stem cell motility and cell-cell recognition in vivo. I just don’t see how global datasets on epigenetic DNA modifications can be related to complex phenotypes like cell-cell interactions and cell migration. Also, the applicants assume, without any direct evidence, that the ability of a cell to migrate in vitro will be determined by its pattern of gene expression as opposed to post-translational regulation of protein abundance or activity. I am also troubled by the failure of the application to discuss any specific mechanisms that control cell migration and how they may relate to the in vivo phenomena that form the basis of the proposal. It seems that the applicants are completely in the dark here. Another problem is that although neural stem cells have been shown to migrate in the in vitro chemotaxis assay described here, it remains to be seen whether responsiveness in this assay corresponds to migratory and therapeutic activity in vivo. Some evidence that these are correlated would have been useful. It is also disappointing that the applicants do not propose to test ES cell derived neural progenitors for their ability to migrate to gliomas in vivo; only in vitro chemotaxis assays are proposed.
The migration assays may not clearly recapitulate migration in vivo, and genes that aid or suppress migration in in vitro assays may differ from those important in promoting migration in vivo.
The use of directly isolated glioma cells is a positive factor, but it also may limit the numbers of experiments one can do with a particular set of hNSCs. Establishing cell lines from the gliomas is one strategy, but that involves the possibility of selecting for subpopulations of the glioma cells. The glioma cells will be processed according to Lee et al. (2006), which involved growing cells from glioma tissues in growth factors. This must select for a subpopulation of cells that have many of the properties of NSCs.
It is certain that the environment in a glioma in vivo is far more complex than the environment created by the secreted molecules of glioma-derived NSC-like cells, and there is thus no a priori reason to think that all of the behavior of stem cells in vivo is regulated by glioma cells, rather than changes in the brain produced by the glioma. Nevertheless, this application begins in a reductionist mode, which has its logic.