Glioblastoma (GBM), the most common primary malignant brain tumor, is amongst the deadliest types for cancer with a five year survival rate of less than 5%. Epigenetically based cancer therapeutics have shown great promise for the treatment of other cancers, and notably the FDA approved histone deacetylase inhibitor (HDACi), vorinostat, shows activity in multiple in vitro and in vivo GBM models and can cross the blood brain barrier. Recently published data from clinical trials in GBM indicate that vorinostat is well-tolerated and that biological activity (i.e. histone hyperacetylation) is demonstrable. However 51% of these patients experienced disease progression, indicating that strategies that enhance HDACi action are warranted. Published data from our lab demonstrates that histone deacetylase inhibitor (HDACi) treatment leads to an increase in histone H3 lysine 4 methylation, a modification regulated by the lysine specific demethylase 1 (LSD1/KDM1A) enzyme. We further found that protein levels of LSD1 are aberrantly higher in glioblastoma: in patient derived cell lines compared to normal human astrocytes and in glioblastoma patient derived stem cells compared to normal neural stem cells. Based on these observations, we tested effects of inhibition of LSD1 with either chemical means or with RNAi in combination with HDACi. Dual targeting of LSD1 and HDACs resulted in synergistic apoptotic cell death in GBM cell lines, but not in normal human astrocytes, indicating that this therapeutic strategy has potential to be lethal to tumor cells while sparing healthy brain cells. Little is known regarding how LSD1 inhibition contributes to HDACi mediated induction of apoptosis. To gain insight into this question we have conducted RNA-Seq and have validated gene alterations using additional array based assays. We hypothesize that LSD1 and HDAC inhibition activates a gene expression profile that promotes a selective mode of killing GBM cells in vivo. RNA-Seq and subsequent validation indicates that amongst the genes altered by this combination are the pro-apoptotic gene, Hrk and tumor suppressors, p53 and p73. Since mutations in p53 or in the p53 pathway are seen in over 45% of GBM patients13, highlighting a population that may benefit moreso from this treatment. We will define gene signatures of sensitivity versus resistance. Alterations of these genes will be evaluated in vivo using an orthotopic GBM mouse model as biomarkers of efficacy. To test our hypothesis we will: 1 - Determine the significance of gene expression changes by LSD1 on sensitivity to combined inhibition of LSD1 and HDACs. 2 - Assess the in vivo efficacy of dual HDAC and LSD1 targeting in invasive GBM patient derived stem cell based orthotopic brain tumor models.
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