Glioblastomas are highly aggressive brain tumors with a mean survival time of only 14 months. There is increasing evidence that brain tumors and glioblastomas in particular are driven by a subpopulation of cancer stem cells. It has recently been possible to isolate and maintain continuously in culture these putative tumor stem cells. These cells grow as neurospheres and retain the ability to differentiate into neurons and astrocytes despite being highly tumorigenic mouse xenografts. We have developed methods for high throughput screening of these GBM stem cells using RNAi. Here we propose to comprehensively identify kinases that are required for the growth and survival of glioblastoma stem cells under normoxic and hypoxic conditions. We will focus on kinases since they are druggable targets for which a great many inhibitors are already available and for which several have already been clinical successes.
Our first aim will be to perform shRNA screens of the human kinome to identify kinases commonly required for the growth and survival of glioblastoma stem cell lines. Our preliminary results indicate that the kinases required for tumor stem cell growth are distinct from the kinases required for growth of traditional serum grown cell lines. Thus, these screens are likely to uncover new kinase targets for glioblastoma therapy. Moreover, glioblastomas are known to be tumors that have hypoxic microenvironments that can limit the efficacy of traditional therapies. Our evidence indicates that glioblastoma stem cells actually thrive under hypoxia. Our preliminary data also indicates that there are kinases that are required for tumor stem cell growth under normoxic conditions, but not hypoxic conditions and vice versa. Identifying the kinases that are required for growth and survival under hypoxic conditions is thus critical for elimination of cancer stem cells in the tumor. Thus, we will screen these GBM stem cells under both hypoxic and normoxic conditions. In the second aim, we will investigate the cellular functions of kinases identified in the RNAi screens. In addition, we will determine whether key kinases identified in the screen are in fact activated in primary human glioblastomas, and determine whether inhibition of these kinases in mouse xenografts will inhibit tumor growth. Results of these studies should identify and prioritize new kinase targets for treatment of glioblastoma.
Glioblastoma is a highly aggressive brain tumor that typically causes death within two years of diagnosis. This research will identify key genes required for the growth of the critical tumor stem cells in glioblastoma. Therapies directed toward these genes may deplete the tumor stem cells and thereby improve treatment of glioblastoma.