O⁶-methylguanine DNA methyltransferase (MGMT)

O⁶-methylguanine DNA methyltransferase (MGMT) is a specialized DNA repair protein responsible for the direct reversal of DNA damage caused by alkylating agents (UniProt P16455). It specifically targets O⁶-methylguanine adducts, which are highly mutagenic and cytotoxic, by transferring the alkyl group to its own internal cysteine residue (PubMed: 21548706). This reaction is stoichiometric and leads to the permanent inactivation and subsequent degradation of the MGMT molecule, often referred to as a suicide mechanism (StatPearls: NBK559274). In the context of oncology, MGMT expression is a primary determinant of resistance to alkylating chemotherapies such as temozolomide and dacarbazine. Tumors with high MGMT activity can efficiently repair drug-induced DNA damage, whereas those with MGMT promoter methylation (resulting in gene silencing) show significantly better responses to treatment (PubMed: 15758003). Therapeutic efforts have focused on using MGMT inhibitors like O⁶-benzylguanine to sensitize resistant tumors, although this can also increase the risk of bone marrow toxicity.

Other names

Methylated-DNA--protein-cysteine methyltransferase6-O-methylguanine-DNA methyltransferaseO6-alkylguanine-DNA alkyltransferaseAGTAGAT

MGMT acts as a suicide enzyme that stoichiometrically transfers alkyl groups from the O6-position of guanine in DNA to a cysteine residue (Cys145) in its own active site, resulting in irreversible protein inactivation (UniProt P16455). Inhibitors like O6-benzylguanine act as pseudo-substrates that the enzyme repairs, thereby depleting the cellular pool of MGMT and enhancing the efficacy of alkylating chemotherapeutic agents (PubMed: 11134448).