{"type":"root","children":[{"type":"paragraph","children":[{"type":"text","value":"O-6-methylguanine-DNA methyltransferase (MGMT) is a DNA “suicide” repair enzyme. It repairs damaged guanine nucleotides by transferring the methyl at O6 site of guanine to its cysteine residues, thus avoiding gene mutation, cell death and tumorigenesis caused by alkylating agents. The expression of the MGMT gene is mainly regulated by epigenetic modification. Many studies have shown that the loss of MGMT expression is due to methylation of CpG island of MGMT promoter. In cancer cells, MGMT can repair DNA damage induced by alkylating chemotherapeutic drugs making cancer cells more resistant to treatment."}]}]}