However, a major mechanism that counteracts this cytotoxicity is the DNA repair enzyme, O6-methylguanine DNA methyltransferase (MGMT), which sequesters the toxic methyl adducts from O6 guanine prior to DNA replication (Pegg et al., 1995; Esteller et al., 2000), rendering the cancer cells resistant to TMZ cytotoxicity. Here, MGMT is linked to cancer.