TP53 and glioblastoma: We also used a panel of established GBM cell lines with known p53 status and different MGMT protein levels: MGMT-positive mutp53 GBM cell lines LN-18 (high MGMT protein levels, p53 C238S substitution) and U138 (intermediate MGMT protein levels, p53 R273H substitution) [20, 54] as well as MGMT-negative U87MG and A172 cell lines (Table 1).