O6-methylguanine-DNA methyltransferase (MGMT) (MGMT)

O6-methylguanine-DNA methyltransferase (MGMT) is a unique DNA repair enzyme that provides a critical defense against the mutagenic and cytotoxic effects of alkylating agents by directly removing O6-alkylguanine lesions from DNA [1, 9]. The enzyme operates through a suicide mechanism, where it irreversibly transfers the alkyl group from the DNA to a cysteine residue in its own active site, leading to its own inactivation and subsequent degradation [9]. In oncology, MGMT is a major determinant of resistance to alkylating chemotherapies such as temozolomide and carmustine, as high levels of the protein can repair the DNA damage intended to kill tumor cells [4, 9]. Conversely, epigenetic silencing of the MGMT gene via promoter methylation is a well-established clinical biomarker, particularly in glioblastoma, where it predicts a significantly better response to treatment and improved patient survival [2, 5, 6]. Therapeutic strategies have focused on using MGMT inhibitors, such as O6-benzylguanine, to deplete the enzyme and sensitize tumors to chemotherapy [9]. However, the clinical application of these inhibitors is limited by severe safety concerns, primarily dose-limiting myelosuppression resulting from the increased toxicity of alkylating agents in normal bone marrow cells [9].

Other names

O6-alkylguanine-DNA alkyltransferaseAGTAGATMethylated-DNA--protein-cysteine methyltransferaseO-6-methylguanine-DNA methyltransferase

Drugs targeting MGMT, such as O6-benzylguanine, act as pseudosubstrates that undergo the same methyl-transfer reaction as O6-methylguanine, leading to the irreversible inactivation and depletion of the MGMT protein (suicide inhibition) [9]. This depletion sensitizes tumor cells to the cytotoxic effects of alkylating agents like temozolomide by preventing the repair of drug-induced DNA lesions [4, 9].