Glioblastoma (GBM) ranks among the most lethal of human cancers with conventional therapy offering only palliation. Great strides have been made in understanding GBM genetics and modeling these tumors, and new targeted therapies are being tested. Unfortunately, these advances have not substantially translated into improved patient outcomes. Multiple chemotherapeutic agents and radiation therapy have been developed to kill cancer cells. However, the response to chemotherapy and radiation in GBM is modest. There is clearly an unmet clinical need to develop either a novel treatment strategy or an adjuvant strategy to enhance efficacy of existing treatments. While no single mechanism provides for the failure of current GBM therapies, several laboratories including our own have shown that GBM tumors contain stem cell-like cells termed cancer stem cells (CSCs). The cancer stem cell hypothesis posits that tumor cells are organized in a hierarchy with CSCs at the apex. CSCs are resistant to cytotoxic therapies (Bao et al. Nature 2006) and promote tumor angiogenesis (Bao et al. Cancer Research 2006) supporting a direct clinical relevance. Our group and others have shown that CSCs reside in specific functional niches in perivascular and hypoxic niches (Li et al. Cancer Cell 2009; Lathia et al. Cell Stem Cell 2010), and targeting these niches may disrupt tumor maintenance and therapeutic resistance. Notably, our group has found that the microenvironment directly reprograms differentiated tumor cells into CSCs through the induction of epigenetic regulators (Heddleston et al. Cell Death Diff. 2012). While several therapies targeting epigenetic regulation in cancer have long been developed and in the clinic (e.g. HDAC inhibitors and Azacitidine) there has been a renewed interest in targeting this class of molecules based on the large amount of accumulating evidence that epigenetic regulation plays a central role in many diseases, particularly cancer. Major pharmaceutical companies and research agencies have developed large programs to try to target these moecules. With this resurgence of epigenetic drug development and evidence that epigenetic regulation controls cell state, I set out to identify novel epigenetic targets that are critical regulators of the CSC state in GBM. I conducted a targeted RNAi screen that focused on histone demethylases, a key class of epigenetic modifying genes. As epigenetic modifications, and therefore cell state are at least partially determined by the microenvironment, I utilized state-of-the-art RNAi screening technology to conduct the screen in vivo in the presence of a functional orthotopic microenvironment. Out of 31 histone demethylase genes screened, three candidate targets were identified, and clinical survival and gene expression data supports their potential as therapeutic targets. How CSC and normal neural progenitor biology is affect by targeting these hits will now be evaluated.
Glioblastoma multiforme is the most prevalent primary malignant brain tumor. Its resistance to conventional therapies, rapid growth and highly infiltrative nature necessitate the use of highly aggressive therapies including tumor resection, radiation, and chemotherapy. Even with such therapies, prognosis is dismal with the median patient survival between 14-16 months. Targeting cancer stem cells, a relatively resilient and drug resistant type of cell found within these cancers is a new potential therapeutic approach for treatment of these brain tumors. This study aims to discover new targets for therapy which will be effective against the cancer stem cell population.
