Abstract
The high incidence of glioblastoma recurrence necessitates additional therapeutic strategies. Heterogeneous populations of cells, including glioma stem cells (GSC) have been implicated in disease recurrence. GSCs are able to survive irradiation and temozolomide (TMZ) treatment due to upregulation of DNA damage pathways. One potential strategy to target treatment-resistant tumor populations may be via the integrated stress response (ISR). Modulation of the ISR pathway also allows for sensitization of treatment-resistant cells to TRAIL. We generated a novel cell-based death receptor assay to identify potent inducers of ISR-dependent DR5 expression. We used this assay to screen compounds from three commercially available libraries, and identified 1-benzyl-3-cetyl-2-methylimidazolium iodide (NH125) as a potent inducer of DR5 expression. NH125 engages the EIF2α-ATF4-CHOP axis culminating in DR5 expression at low micromolar doses. Expression of CHOP plays a critical role in NH125-mediated TRAIL synergy. Treatment of GSC with NH125 produces a marked reduction in viability when compared with other cell lines. NH125-treated GSC also synergize with lower doses of TRAIL when compared with all other cell lines tested. Transcriptional analysis of NH125-treated GSC uncovers a unique profile that involves activation of ISR and GADD45 pathways. Treatment of GSC xenografts with encapsulated PEG-PCL-NH125 leads to a sustained decrease in tumor volume. IMPLICATIONS: Taken together, these data suggest that engaging the ISR pathway represents a promising strategy to target treatment refractory GSC that have been implicated in glioblastoma recurrence.