Acquired resistance to 6-thioguanine in melanoma cells involves the repair enzyme O6-methylguanine-DNA methyltransferase (MGMT). 2010

Nir Gefen, and Gordana Brkic, and Dalia Galron, and Esther Priel, and Janet Ozer, and Daniel Benharroch, and Jacob Gopas
Dept. of Microbiology and Immunology, Faculty of Health Sciences, Ben Gurion University, Beer Sheva, Israel.

O(6)-methylguanine-DNA methyltransferase (MGMT), is a DNA repair enzyme that recognizes O(6)-alkylated guanine, a base analog resulting from treatment with alkylating agents. O(6)-6-thioguanine (6-TG) is used clinically to treat malignant as well as inflammatory diseases. Although MGMT participates in resistance to alkylating agents, it has not been shown to be involved in resistance of tumors to 6-TG. In this study we used a human melanoma cell line (GA) and its selected 6-TG drug resistant variant (GA-6-TG) to investigate whether MGMT plays a role in determining the drug resistant phenotype of GA-6-TG cells. We showed that GA-6-TG resistant cells express about three fold more MGMT protein and mRNA than GA cells. Treatment with 6-TG diminishes significantly MGMT amounts in both cell lines. Increased amounts of MGMT in resistant cells, are consistent with hypermethylation of the MGMT gene coding-region. Pretreatment of cells with the MGMT inhibitor O6 benzyl guanine, resulted in sensitization of GA-6-TG cells to 6-TG. Taken together, our data suggests that MGMT is associated with 6-TG drug resistance. In analogy to patients treated with alkylating agents, patients with tumors containing increased MGMT amounts, may be more resistant to 6-TG and therefore may benefit from treatment with MGMT inhibitors.

UI MeSH Term Description Entries
D008545 Melanoma A malignant neoplasm derived from cells that are capable of forming melanin, which may occur in the skin of any part of the body, in the eye, or, rarely, in the mucous membranes of the genitalia, anus, oral cavity, or other sites. It occurs mostly in adults and may originate de novo or from a pigmented nevus or malignant lentigo. Melanomas frequently metastasize widely, and the regional lymph nodes, liver, lungs, and brain are likely to be involved. The incidence of malignant skin melanomas is rising rapidly in all parts of the world. (Stedman, 25th ed; from Rook et al., Textbook of Dermatology, 4th ed, p2445) Malignant Melanoma,Malignant Melanomas,Melanoma, Malignant,Melanomas,Melanomas, Malignant
D004305 Dose-Response Relationship, Drug The relationship between the dose of an administered drug and the response of the organism to the drug. Dose Response Relationship, Drug,Dose-Response Relationships, Drug,Drug Dose-Response Relationship,Drug Dose-Response Relationships,Relationship, Drug Dose-Response,Relationships, Drug Dose-Response
D006147 Guanine
D006801 Humans Members of the species Homo sapiens. Homo sapiens,Man (Taxonomy),Human,Man, Modern,Modern Man
D013866 Thioguanine An antineoplastic compound which also has antimetabolite action. The drug is used in the therapy of acute leukemia. 6-Thioguanine,2-Amino-6-Purinethiol,Lanvis,Tabloid,Thioguanin-GSK,Thioguanine Anhydrous,Thioguanine Hemihydrate,Thioguanine Monosodium Salt,Thioguanine Tabloid,Tioguanina Wellcome,Tioguanine,2 Amino 6 Purinethiol,6 Thioguanine,Anhydrous, Thioguanine,Thioguanin GSK,ThioguaninGSK
D045744 Cell Line, Tumor A cell line derived from cultured tumor cells. Tumor Cell Line,Cell Lines, Tumor,Line, Tumor Cell,Lines, Tumor Cell,Tumor Cell Lines
D018906 Antineoplastic Agents, Alkylating A class of drugs that differs from other alkylating agents used clinically in that they are monofunctional and thus unable to cross-link cellular macromolecules. Among their common properties are a requirement for metabolic activation to intermediates with antitumor efficacy and the presence in their chemical structures of N-methyl groups, that after metabolism, can covalently modify cellular DNA. The precise mechanisms by which each of these drugs acts to kill tumor cells are not completely understood. (From AMA, Drug Evaluations Annual, 1994, p2026) Alkylating Agents, Antineoplastic,Alkylating Antineoplastic Agents,Alkylating Antineoplastic Drugs,Alkylating Antineoplastics,Alkylating Drugs, Antineoplastic,Antineoplastic Alkylating Agents,Antineoplastic Drugs, Alkylating,Antineoplastics, Alkylating,Antineoplastic Alkylating Drugs,Drugs, Antineoplastic Alkylating
D019175 DNA Methylation Addition of methyl groups to DNA. DNA methyltransferases (DNA methylases) perform this reaction using S-ADENOSYLMETHIONINE as the methyl group donor. DNA Methylations,Methylation, DNA,Methylations, DNA
D019853 O(6)-Methylguanine-DNA Methyltransferase An enzyme that transfers methyl groups from O(6)-methylguanine, and other methylated moieties of DNA, to a cysteine residue in itself, thus repairing alkylated DNA in a single-step reaction. EC 2.1.1.63. Methylated-DNA-Protein-Cysteine S-Methyltransferase,O(6)-AGT,O(6)-Methylguanine Methyltransferase,DNA Repair Methyltransferase I,DNA Repair Methyltransferase II,Guanine-O(6)-Alkyltransferase,O(6)-Alkylguanine-DNA Alkyltransferase,O(6)-MeG-DNA Methyltransferase,O(6)-Methylguanine DNA Transmethylase,Methylated DNA Protein Cysteine S Methyltransferase,S-Methyltransferase, Methylated-DNA-Protein-Cysteine

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