Abstract A57: Glutathione depletion overcomes chemotherapy resistance in aggressive medulloblastoma stem-like cells

Abstract

Abstract Drug resistance is one of the main limiting steps for the successful treatment of most cancers. Additionally, the presence of cancer cells with stem cell traits favors the process of treatment resistance, tumor recurrence, and spreading. Glutathione (GSH) is a major antioxidant intracellular molecule and has been positively correlated with the development of drug resistance. The purpose of this study was to verify whether GSH depletion potentiates the effect of chemotherapy in stem-like cells from the medulloblastoma cell line Daoy. Cells expressing normal (control tumor cells) or high levels of the pluripotency factor OCT4A (stem-like cells) were treated with a combination of BSO (glutathione inhibitor), cisplatin, and temozolomide (TMZ). Cell viability was assessed through MTT and apoptosis assays. Initially, the concentration of BSO required to deplete the GSH in both Daoy and Daoy-OCT4A cells was established (50 and 58 μM, respectively), as well as the IC50 of each chemotherapeutic drug. Both cells were sensitive to cisplatin (IC50 = 0.494 μM for Daoy and 0.215 μM for Daoy-OCT4A), but resistant to TMZ. The highest dose of TMZ used (500 μM) reduced the viability of Daoy cells to 56%, but only to 80% in Daoy-OCT4A cells, denoting the chemoresistant phenotype of these cancer stem-like cells. Next, the ideal combination of the three compounds was defined. For Daoy cells, it was BSO 50 μM + cisplatin 0.8 μM + TMZ 0.8 μM. As for Daoy-OCT4A cells, it was BSO 58 μM + cisplatin 0.215 μM + TMZ 500 μM. Daoy-OCT4A cells required a higher dose of TMZ than control Daoy cells to attain similar death rates; however, the combined treatment was effective for both cells. When combining these three drugs, a synergistic effect was observed for Daoy-OCT4A cells, reducing cell viability to ~17%, in comparison with treatment of cisplatin+TMZ alone. As for Daoy cells, an additive effect was observed and viability was reduced to ~15%, in comparison with cisplatin+TMZ alone. This indicates that the use of a glutathione inhibitor in combination with cisplatin and TMZ may be useful in the treatment of medulloblastoma, even in the case of aggressive tumors. Similarly, this approach may also be useful in the development of therapeutic strategies for other chemoresistant tumors. Citation Format: Beatriz Dias Barbieri, Marina Marçola, Clarissa Rocha, Oswaldo Keith Okamoto. Glutathione depletion overcomes chemotherapy resistance in aggressive medulloblastoma stem-like cells [abstract]. In: Proceedings of the AACR International Conference held in cooperation with the Latin American Cooperative Oncology Group (LACOG) on Translational Cancer Medicine; May 4-6, 2017; São Paulo, Brazil. Philadelphia (PA): AACR; Clin Cancer Res 2018;24(1_Suppl):Abstract nr A57.