ATM and glioblastoma: Despite effective inhibition of Poly ADP-Ribosylation (PARylation) (Figure 4A), olaparib treatment failed to induce a discernable DNA damage response in GBM cells, whereas mono- or co-treatment with topotecan (TPT), a DNA strand break-inducing Topoisomerase-1 inhibitor, stimulated ATM-dependent KAP-1 phosphorylation, indicating DNA damage signaling activation (Figure 4A) [55].