O⁶-methylguanine DNA-methyltransferase (MGMT) overexpression in melanoma cells induces resistance to nitrosoureas and temozolomide but sensitizes to mitomycin C

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• 作者：Isabelle Passagne ; Alexandre Evrard ; Philippe Depeille ; Pierre Cuq ; Didier Cupissol and Laurence Vian
• 关键词：O⁶-methylguanine DNA-methyltransferase ; Alkylating agents ; Mitomycin C ; Glutathione ; Chemoresistance ; Melanoma
• 刊名：Toxicology and Applied Pharmacology
• 出版年：2006
• 出版时间：1 March 2006
• 年：2006
• 卷：211
• 期：2
• 页码：97-105
• 全文大小：351 K

文摘

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 O⁶-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 IC₅₀ 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 N⁷ 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 γ-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.