N7MeG and N3MeA are repaired by base-excision repair (BER) and contribute minimally to overall cytotoxicity of TMZ, while O6MeG is repaired by O6-methylguanine-DNA-methyl transferase (MGMT), found suppressed by promoter methylation in ~40% of GBM tumors. Here, MGMT is linked to glioblastoma.