title: O(6)-methylguanine DNA-methyltransferase (MGMT) overexpression in melanoma cells induces resistance to nitrosoureas and temozolomide but sensitizes to mitomycin C.
abstract: Alkylating agents play an important role in the chemotherapy of malignant melanomas. The activity of alkylating agents depends on their capacity to form alkyl adducts with DNA, in some cases causing cross-linking of DNA strands. However, the use of these agents is limited by cellular resistance induced by the DNA repair enzyme O(6)-methylguanine DNA-methyltransferase (MGMT) which removes alkyl groups from alkylated DNA strands. To determine to what extent the expression of MGMT in melanoma cells induces resistance to alkylating agents, the human cell line CAL77 Mer- (i.e., MGMT deficient) were transfected with pcMGMT vector containing human MGMT cDNA. Several clones expressing MGMT at a high level were selected to determine their sensitivity to chemotherapeutic drugs. Melanoma-transfected cells were found to be significantly less sensitive to nitrosoureas (carmustine, fotemustine, streptozotocin) and temozolomide with an increase of IC(50) values between 3 and 14 when compared to parent cells. No difference in cell survival rates between MGMT-proficient and -deficient cells was observed for melphalan, chlorambucil, busulphan, thiotepa and cisplatin which preferentially induce N(7) guanine lesions. Surprisingly, MGMT overexpression increased the sensitivity of CAL77 cells to mitomycin C by approximately 10-fold. Treatment of clonal cell lines with buthionine-[S,R]-sulfoximine (BSO), an inhibitor of gamma-glutamylcysteine synthetase which depletes cellular glutathione, completely reversed this unexpected increase in sensitivity to mitomycin C. This observation suggests that glutathione is involved in the sensitivity of MGMT-transfected cells to mitomycin C and may act synergistically with MGMT via an unknown mechanism.
authors.affiliation: Department of Toxicology, EA 2994, School of Pharmacy, Montpellier I University, 15, Avenue Charles Flahault BP 14491, 34093 Montpellier Cedex 05, France.
authors.forename: Isabelle
authors.initials: I
authors.lastname: Passagne
authors.forename: Alexandre
authors.initials: A
authors.lastname: Evrard
authors.forename: Philippe
authors.initials: P
authors.lastname: Depeille
authors.forename: Pierre
authors.initials: P
authors.lastname: Cuq
authors.forename: Didier
authors.initials: D
authors.lastname: Cupissol
authors.forename: Laurence
authors.initials: L
authors.lastname: Vian
mesh_terms: D000970:Antineoplastic Agents / Q000633:toxicity; D019328:Buthionine Sulfoximine / Q000494:pharmacology; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000187:drug effects / Q000235:genetics; D003606:Dacarbazine / Q000031:analogs & derivatives* / Q000633:toxicity; D004305:Dose-Response Relationship, Drug; D019008:Drug Resistance, Neoplasm / Q000235:genetics; D015971:Gene Expression Regulation, Enzymologic; D015972:Gene Expression Regulation, Neoplastic; D005978:Glutathione / Q000378:metabolism; D006801:Humans; D020128:Inhibitory Concentration 50; D008545:Melanoma / Q000201:enzymology / Q000235:genetics / Q000473:pathology; D016685:Mitomycin / Q000633:toxicity*; D009607:Nitrosourea Compounds / Q000633:toxicity*; D019853:O(6)-Methylguanine-DNA Methyltransferase / Q000235:genetics* / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D000077204:Temozolomide; D014162:Transfection
chemical_list: D000970:Antineoplastic Agents; D009607:Nitrosourea Compounds; D012333:RNA, Messenger; D019328:Buthionine Sulfoximine; D016685:Mitomycin; D003606:Dacarbazine; D019853:O(6)-Methylguanine-DNA Methyltransferase; D005978:Glutathione; D000077204:Temozolomide