CSIG-22. REGULATION OF GLIOMA STEM CELL SELF-RENEWAL AND TUMORIGENESIS BY CARBOHYDRATE BINDING PROTEINS

Abstract

Abstract Glioma Stem Cells (GSC) are a population of malignant self-renewing stem cells in glioblastoma (GBM) tumors, the most common and aggressive primary brain tumor in the adult brain. GSC promote tumor growth and recurrence and acquire resistance to therapy. Strategies to target GSC in the tumor bulk are urgently needed in order to develop more effective therapeutic strategies for GBM. EGFRvIII/STAT3 signaling is a major oncogenic pathway in GBM. Here, we report our discovery that Galectin1, a family member of carbohydrate-binding proteins with affinity for b-galactosides, promotes GSC self-renewal and tumor growth in EGFRvIII-expressing subset of tumors. Analysis of RNA-Seq data shows that LGALS1, the gene encoding Galectin1, is highly expressed in human EGFRvIII-expressing GSC and its expression correlates with the expression of transcription factor STAT3. Importantly, STAT3 directly binds the promoter of LGALS1 to upregulate its expression and knockdown of STAT3 significantly attenuates LGALS1 mRNA levels. Genetic knockdown of LGALS1 impairs the ability of GSC to form spheres, as assayed in limiting dilution assay, suggesting that LGALS1-STAT3 signaling regulates glioma stem cell fate in EGFRvIII tumor subset. Strikingly, we employed genetic and pharmacological approaches in patient derived xenografts and found that LGALS1/Galectin1 impairs gliomas stem cell growth and tumorigenesis. Subcutaneous and stereotactic intracranial implantation of CRISPR knockout LGALS1 EGFRvIII-expressing GSC into SCID mice showed significantly reduced in vivo tumor xenografts growth and increased survival rate compared with controls. Treatment of GSC with OTX008, a specific inhibitor of galectin-1, significantly attenuates the self-renewal ability of these cells and impairs tumorigenesis. Together, our findings suggest that targeting LGALS1/Galectin1 in combination with current standards of care may provide an effective strategy for the future treatment of these deadly brain tumors.