MGMT Gene Editing    

O⁶-methylguanine-DNA methyltransferase (MGMT) is a DNA "suicide" repair enzyme. It can repair damaged guanine nucleotides by transferring the methyl at O⁶ site of guanine to its cysteine residues, so as to avoid gene mutation, cell death and tumorigenesis caused by alkylating agents. The expression of MGMT gene is mainly regulated by epigenetic modification. Somatic alterations of MGMT have been reported in a variety of tumor types including brain, ovarian, head and neck, non-small cell lung, stomach and colorectal tumors, being its inactivation mainly caused by promoter hypermethylation.

The Function of MGMT

MGMT is a highly evolutionarily conserved and widely expressed enzyme involved in DNA repair. It counteracts the lethal effects of alkylating agents by removing alkyl adducts from the O⁶ position of guanine, but is irreversibly inactivated by doing so—a process that is called suicide inhibition. The persistent O⁶-methylguanine adduct induced by DNA-alkylating agents (such as temozolomide and nitrosourea derivatives) leads to base mispairing, which manifests as mismatch repair during DNA replication and, according to the futile repair hypothesis, finally induces cell cycle arrest and cell death. The methylation damage induced by alkylating agents can be reversed by MGMT. This DNA repair activity provides resistance against the cytotoxic effects of DNA-alkylating drugs, further proved by small molecule inhibitors of MGMT that restore sensitivity to alkylating agents. However, the cytotoxic activity of O⁶-alkylguanine also requires intact mismatch repair machinery. Although many studies have suggested that deficiency of MGMT can increase the sensitivity of high-grade gliomas to alkylating agents, tumors with low levels of MGMT expression can still exhibit resistance to these drugs. Thus, other mechanisms might be involved in the resistance of some tumors to chemotherapy.

Figure 1. MGMT-mediated DNA repair. (Wick W, et al, 2014)

The Prediction and Prognostic Value of MGMT Promoter Status in Glioma

Some studies have shown that methylation of MGMT promoter can predict whether alkylating agents can be of benefit in glioblastoma and low-grade gliomas. Two other clinical trials have shown that methylation status of MGMT promoter can predict the prognosis of glioma patients. In these two studies, retrospective analysis of MGMT promoter methylation in elderly patients found that it could predict good prognosis in temozolomide (TMZ) group, but not in radiotherapy alone group. It was found that methylation of MGMT promoter in anaplastic oligodendroglioma patients predicted better overall survival (OS) and PFS, whether in radiotherapy alone or in sequential radiotherapy and chemotherapy group. But it had no prognostic value in glioblastoma patients. Another phase III randomized clinical trial, NOA-04, drew a similar conclusion that methylation of MGMT promoter and IDH1 mutation can reduce the risk of progression in anaplastic glioma patients, and patients with MGMT promoter methylation have a longer PFS in both radiotherapy and chemotherapy groups (PVC). Besides, results from a phase III clinical trial prospectively indicate that MGMT promoter methylation status can be used as a biomarker to predict good prognosis of glioblastoma patients treated with TMZ.

MGMT Gene Editing Services

CRISPR/Cas9 Platform^CB, one of the leading biotechnological companies specializing in gene editing, is dedicated to offering comprehensive CRISPR/Cas9 gene-editing services to a wide range of genomics researchers. Based on our platform, we can help you effectively MGMT gene deleted, inserted or point mutated in cells or animals by CRISPR/Cas9 technology.

• MGMT Gene Knockout: We offer MGMT gene knockout cell line and knockout animal model generation service with high quality. Typically, we develop CRISPR-mediated gene editing cell lines including HEK239T, Hela, HepG2, U87, but we can use other cell lines according to your requirements. Our one-stop KO animal model generation service covers from sgRNA design and construction, pronuclear microinjection to Founders genotyping and breeding.
• MGMT Gene Knockin: CRISPR/Cas9 Platform^CB provides the one-stop MGMT knock-in cell line and knockout animal model generation services, including point mutation and gene insertion. Our expert staff has succeeded in dozens of MGMT knock-in cell line generation projects, including stem cells, tumor cells and even difficult-to-handle cells. We also have extensive experience in incorporating CRISPR/Cas9 technology into animal models, which have been fully recognized by our clients.

If you have any questions, please feel free to contact us.

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