MGMT and glioblastoma: Ten patient-derived GSC lines (Table 1) and two GBM cell lines (U87 and SJGBM-2) were characterized for the expression of the MMR components MLH1, MSH2 and MSH6, involved in the processing and toxicity of O6-methylguanine, and of MGMT, responsible for the removal of the O6-methyl adduct.