1. ¹Cancer Epigenetics Laboratory, Molecular Pathology Program, Spanish National Cancer Center (CNIO), Melchor Fernandez Almagro 3, Madrid 28029, Spain
2. ²Sidney Kimmel Comprehensive Cancer Center at Johns Hopkins, Johns Hopkins School of Medicine, Bunting-Blaustein Cancer Research Building, 1650 Orleans, Room 543, Baltimore, MD 21231, USA

Correspondence: M Esteller, E-mail: mesteller@cnio.es or hermanji@jhmi.edu

Abstract

O⁶-methylguanine DNA methyltransferase (MGMT) is a key enzyme in the DNA repair network. MGMT removes mutagenic and cytotoxic adducts from O⁶-guanine in DNA, the preferred point of attack of many carcinogens (i.e. methylnitrosourea) and alkylating chemotherapeutic agents (i.e. BCNU, temozolamide, etc.). Hypermethylation of the CpG island located in the promoter region of MGMT is primarily responsible for the loss of MGMT function in many tumor types. The methylation-mediated silencing of MGMT has two consequences for cancer. First, tumors with MGMT methylation have a new mutator phenotype characterized by the generation of transition point mutations in genes involved in cancer etiology, such as the tumor suppressor p53 and the oncogene K-ras. Second, MGMT hypermethylation demonstrates the possibility of pharmacoepigenomics: methylated tumors are more sensitive to the killing effects of alkylating drugs used in chemotherapy. These recent results underscore the importance of MGMT in basic and translational cancer research.