Abstract LB-264: A novel therapeutic strategy to effectively target glioblastoma stem cells using biochemical mechanism-based drug combination

Abstract

Abstract Glioblastoma multiforme is the most common and aggressive type of primary brain tumor. Although this disease can be treated with surgery and radiotherapy/chemotherapy, the therapeutic outcomes for many patients are still unsatisfactory due in part to high incident of tumor recurrence. Recent studies suggest that glioblastoma stem cells (GSCs) are resistant to anticancer agents and may remain as residual cancer cells after therapy, leading to disease recurrence. Moreover, GSCs may reside in a hypoxic tissue vironment that induces survival signals such as HIF-1, rendering them more resistant to chemotherapy. Thus, developing new therapy to effectively eliminate GSCs is an important and challenging task. Based on our recent observations that cancer stem cells have low mitochondrial respiration and prefer hypoxic environment to maintain stemness, we hypothesized that GSCs might be more dependent on glycolytic pathway in cytosol for ATP generation due to their low ability to produce ATP in the mitochondria, and that inhibition of glycolysis would be highly effective in blocking energy supply in GSCs, rendering them sensitive to chemotherapeutic agents. To test this hypothesis, two GSC lines (GSC11 and GSC23) with a high expression of CD133, derived from the tumor tissues of glioblastoma patients by selection in stem cell culture, were used in this study. These two cell lines exhibited high resistance to conventional drugs such as temozolomide (TMZ) and carmustine (BCNU), even at high drug concentrations, as evidenced by a lack of growth inhibition in the MTS assay and absence of cell death in flowcytometry analysis (annexin-V/PI double staining) when they were treated with up to 500uM TMZ or 100uM BCNU. Such drug resistance was especially prominent under hypoxis. In contrast, these cancer stem cells were sensitive to glycolytic inhibition, which effectively kill GSCs, especially under hypoxia. Importantly, combination of a glycolytic inhibitor at a moderate toxic concentration significantly enhanced the cytotoxic activity of 100 uM BCNU and caused massive cell death in GSCs under hypoxia. This highly synergistic effect was consistently observed in both GSC11 and GSC23 cells. Interestingly, combination of glycolytic inhibition and TMZ did not show significant enhancement of cytotoxicity, suggesting that the synergy observed in case of BCNU was due to a mechanism unique to this drug that was enhanced by the ATP depletion induced by glycolytic inhibition. Our study has identified a novel strategy to effectively kill glioblastoma stem cells based on their metabolic features, and suggest that such mechanism-based drug combination may have significant therapeutic implication in treatment of cancer patients. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr LB-264.