APEX1 and neoplasm: To explore the role of Chk2 in Ape1-mediated cellular responses in glioblastoma tumor model, we exposed U251-MG cells to temozolomide, a DNA alkylating agent that is currently used as an effective adjuvant therapy in glioblastoma patients33, and observed that clonogenic survival of Ape1-depleted cells was markedly reduced in response to TMZ (Fig. 2F).