title: Depletion of O6-methylguanine-DNA methyltransferase by O6-benzylguanine enhances 5-FU cytotoxicity in colon and oral cancer cell lines.
abstract: O6-methylguanine-DNA methyltransferase (MGMT) is a DNA repair enzyme whose expression is controlled by its promoter methylation. A cell that expresses a low amount of MGMT is known to be more sensitive to the antiproliferative effects of alkylating agents. We have previously shown that the colorectal cancer patients treated with 5-fluorouracil (5-FU) as adjuvant chemotherapy had a better prognosis when the tumor revealed hypermethylation in its MGMT promoter. Therefore, we sought to investigate the relationship between the expression levels of MGMT and the anti-tumor effect of 5-FU in vitro by using two colon adenocarcinoma and four oral cancer cell lines with a variety of MGMT expression. We also investigated the effects of MGMT depletion by O6-benzylguanine (O6-BG), a potent inhibitor of MGMT. The 5-FU treatment uniformly depleted protein and mRNA expression of MGMT in all cell lines examined. Cell lines expressing low levels of MGMT were sensitive to 5-FU. On the other hand, cells expressing high levels of MGMT were less sensitive to 5-FU. The 5-FU treatment exhibited a better antiproliferative effect on the cells expressing high levels of MGMT by the pretreatment of O6-BG. Depletion of MGMT by O6-BG enhanced the anti-tumor effect of 5-FU. Assessment of the levels of MGMT expression in cancer cells and the control of its expression could contribute to the effective chemotherapy by 5-FU especially in patients who previously were considered as low-responsive individuals whose tumors have high levels of MGMT.
authors.affiliation: Department of Oral and Maxillofacial Radiology, Field of Tumor Biology, Okayama University Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, Okayama 700-8558, Japan. jun-m@md.okayama-u.ac.jp
authors.forename: Jun
authors.initials: J
authors.lastname: Murakami
authors.forename: You-Jin
authors.initials: YJ
authors.lastname: Lee
authors.forename: Susumu
authors.initials: S
authors.lastname: Kokeguchi
authors.forename: Hidetsugu
authors.initials: H
authors.lastname: Tsujigiwa
authors.forename: Jun-Ichi
authors.initials: J
authors.lastname: Asaumi
authors.forename: Hitoshi
authors.initials: H
authors.lastname: Nagatsuka
authors.forename: Kazuhiro
authors.initials: K
authors.lastname: Fukui
authors.forename: Masahiro
authors.initials: M
authors.lastname: Kuroda
authors.forename: Noriaki
authors.initials: N
authors.lastname: Tanaka
authors.forename: Nagahide
authors.initials: N
authors.lastname: Matsubara
mesh_terms: D000970:Antineoplastic Agents / Q000494:pharmacology*; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D003110:Colonic Neoplasms / Q000201:enzymology*; D019008:Drug Resistance, Neoplasm / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D005472:Fluorouracil / Q000494:pharmacology*; D006147:Guanine / Q000031:analogs & derivatives* / Q000494:pharmacology; D006801:Humans; D009062:Mouth Neoplasms / Q000201:enzymology*; D019853:O(6)-Methylguanine-DNA Methyltransferase / Q000032:analysis / Q000037:antagonists & inhibitors* / Q000378:metabolism
chemical_list: D000970:Antineoplastic Agents; D004791:Enzyme Inhibitors; C064976:O(6)-benzylguanine; D006147:Guanine; D019853:O(6)-Methylguanine-DNA Methyltransferase; D005472:Fluorouracil