Abstract 3727: Overcoming of radiochemoresistance in glioblastoma stem cells via inhibition of lipid catabolism and SIRT1 deacetylase.
Authors: zhang yibei , Liu Yue , Menjivar Jimmy Christian , Tso Jonathan , Tian Jane , Yong William H. , Liau Linda M. , McBride William , Tso Cho-Lea 
Published: August 2014

Abstract
Glioblastoma remain resistant to radiotherapy (RT) and chemotherapy. To elucidate the cellular and molecular basis of glioblastoma resistance to standard treatment, we isolated and characterized cellular and molecular properties of glioblastoma stem cell clones (GC) resistance to RT (4Gy x 3) with and without 10 μM temozolomide (TMZ) (TRGC-RT, TRGC-RT+TMZ) and compared to those of treatment-sensitive GSC clones (TSGC). To explore the protective strategies which drive the super-survivability of TRGC, we performed comparative analysis of genome-wide gene expression profiles in TRGC and TSGC (n=3 patients) and have identified 56 defense genes significantly overexpressed in TRGC that mainly associated with metabolic stress, suppression of growth, differentiation and inflammation, and activation of cellular and genomic maintenance and repair networks. Functional assays confirmed the association of treatment resistance with reduced glucose uptake, fatty acid oxidation-dependent ATP maintenance, and increased AMPK activation, NAD+ levels and autophagic activity accompanied by upregulated mRNA levels of SIRT1/PGC-1α axis and DNA repair genes. The association of metabolic gene pathways and radiochemoresisatnce of TRGC were further confirmed by the treatment of TRGC with three potent inhibitors that blocking of SIRT1/SIRT2 pathway (tenovin-6), autophagy (3-MA) and fatty acid oxidation (Etomoxir). Uniquely, all three inhibitors promoted cell apoptosis in a higher degree in TRGC than that of TSGC, and the combination of inhibitors with RT further enhance treatment efficacy when compared to RT or RT+TMZ. To further explore additional gene pathways which contribute to radiochemoresistance, we performed a loss-of-function RNA interference (RNAi) screen against 56 genes and had discovered that knockdown of ribosomal proteins, RPL27A, RPS11, or RPL38, or a spliceosome-associated protein, SF3B1 alone without RT showed the significantly higher apoptosis levels by which render in to loss of tumor sphere-initiating ability. Moreover, combined siRNA therapy with RT further showed the enhancement of cell depletion, in contrast to RT or RT+TMZ which showed the return of full-grown tumor spheres. Coincidently, both RPL38 and SF3B1 have a role in repression of Hox gene expression. These data therefore support the view that treatment resistance may arise from GSC exhibiting glucose restriction, lipid catabolism-dependent and cellular quiescent phenotype and suggest that targeting metabolic pathways and stemness of TRGC may provide a novel strategy in combination with standard treatment for glioblastoma.
Citation Format: yibei zhang, Yue Liu, Jimmy Christian Menjivar, Jonathan Tso, Jane Tian, William H. Yong, Linda M. Liau, William McBride, Cho-Lea Tso. Overcoming of radiochemoresistance in glioblastoma stem cells via inhibition of lipid catabolism and SIRT1 deacetylase. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 3727. doi:10.1158/1538-7445.AM2013-3727