To test the DNA-damaging effects of QST in GBM cells, we treated 2 independent GSC lines with QST for 72 hours at the IC50 and analyzed changes in the levels of phosphorylated histone H2AX (γ-H2AX), a marker for DNA double-strand breaks (DSBs) (27). This evidence concerns the gene H2AX and glioblastoma.