Stem-20. Radio-Sensitizing Glioblastoma Cancer Stem Cells by Inhibition of Fact

Abstract

Glioblastoma (GBM) has a particularly high rate of recurrence with a 5-year overall survival rate of approximately 5%. This is in part due to a sub-population of cancer stem cells (CSC), which are both radioresistant and chemotherapeutically resistant to conventional treatments. Here we investigated CBL0137, a small molecule form of curaxin, in combination with radiotherapy as a means to radiosensitize CSCs. CBL0137 sequesters FACT (facilitates chromatin transcription) complex to chromatin, which leads to activation of p53 and inhibition of NF-κB. This sequestering of FACT results in cytotoxicity especially within tumor cells and prevents FACT from performing its primary role as a histone chaperone, as well as inhibits its part in the DNA damage response pathway. We show that when combined with radiotherapy, CBL0137 administration limited the ability of CSCs to identify and repair damaged DNA. CSCs treated in vitro with CBL0137 and irradiation showed an increased inhibition of cancer cell growth and decreased viability compared to irradiation or drug alone. Combination therapy also showed more DNA damage in the CSCs than with either agent alone. Based on our in vitro evidence for the efficacy of combination therapy to target CSCs, we moved forward to test the treatment in vivo. Using a subcutaneous model, we show that the amount of CD133+ cells (a marker for GMB CSCs) was reduced in irradiation plus CBL0137 compared to either treatment alone. Survival studies demonstrated that irradiation plus CBL0137 compared to irradiation alone or CBL0137 alone increase lifespan. Here we show the ability of CBL0137, in combination with irradiation, to target patient GBM CSCs both in vitro and in vivo. This work establishes a new treatment paradigm for GBM that inclusively targets CSCs and may ultimately reduce tumor recurrence.