O6-methylguanine DNA adduct (O6-MeG) (O6-MeG)

O6-guanine residues, specifically O6-methylguanine (O6-MeG), are critical DNA lesions formed by the action of alkylating chemotherapeutic agents like temozolomide and dacarbazine (StatPearls, NBK553089). These modifications occur when an alkyl group is covalently attached to the oxygen atom at the 6th position of the guanine base within the DNA double helix (PubMed, 15155833). If left unrepaired, O6-MeG is highly cytotoxic and mutagenic because it tends to pair with thymine instead of cytosine during DNA replication, leading to G:C to A:T transition mutations (Nature Reviews Cancer, nrc1551). The persistence of these residues triggers the mismatch repair (MMR) system, which, in the absence of a correct template, results in double-strand breaks and subsequent apoptosis (PubMed, 11412110). The therapeutic efficacy of drugs targeting these residues depends heavily on the relative lack of the repair enzyme O6-methylguanine-DNA methyltransferase (MGMT) in tumor cells (NIH, PMC3078526). MGMT acts as a suicide enzyme that removes the alkyl group, thereby restoring the DNA and causing resistance to alkylating therapies. Consequently, O6-guanine residues serve as the primary molecular trigger for the clinical activity of many frontline alkylating agents used in oncology, particularly for brain tumors and melanomas. Monitoring the status of these residues and their repair enzymes is a cornerstone of personalized oncology in neuro-oncology.

Other names

O6-alkylguanineO6-methylguanineO6-MeGO6-methyl-2'-deoxyguanosineDNA O6-guanine alkylationO6-alkylguanine DNA adduct

Alkylating agents deliver an alkyl group to the O6 position of guanine, creating a lesion that interferes with DNA replication and triggers mismatch repair-mediated apoptosis.