title: Carmustine-resistant cancer cells are sensitized to temozolomide as a result of enhanced mismatch repair during the development of carmustine resistance.
abstract: The cytotoxicity of the monofunctional alkylator temozolomide (TMZ) is mediated by mismatch repair (MMR) triggered by O(6)-alkylguanine, whereas MMR protects cells against bifunctional alkylators, including carmustine (BCNU). Therefore, TMZ may be cytotoxic to BCNU-resistant cancer cells because MMR affects sensitivity to TMZ and BCNU in a converse way. We evaluated TMZ cytotoxicity on BCNU-resistant variant (CEM-R) compared with the parental CCRF-CEM cell line (CEM-S). The mechanisms of its BCNU-resistance involved DNA repairs including nucleotide excision repair, base excision repair, alkylguanine alkyltransferase, MMR, and apoptotic and survival pathways. In particular, transcript levels of MMR-related hMLH1 and hMSH2 were enhanced in CEM-R cells. CEM-R cells were 8-fold more BCNU-resistant but surprisingly 9-fold more TMZ-sensitive than were CEM-S cells. Although TMZ-induced adducts include N-alkylated purines and O(6)-alkylguaine, DNA excision repair was enhanced in CEM-R cells, suggesting the efficient repair of N-alkylation adducts. Cotreatment with methoxyamine, a base excision repair inhibitor, did not sensitize CEM-R cells to TMZ, suggesting little or no contribution of N-alkylation to TMZ-induced cytotoxicity. Cotreatment with O(6)-benzylguanine, an alkylguanine alkyltransferase inhibitor, further sensitized CEM-R cells to TMZ, confirming the cytotoxic impact of O(6)-alkylguanine. Cotreatment with cadmium chloride, an MMR inhibitor, disrupted the sensitivity of CEM-R cells to TMZ. The sensitivity to TMZ was reversed in the CEM-R variant clone that had been established by transfecting CEM-R cells with short hairpin hRNA against hMLH1, suggesting the critical role of MMR on sensitization to TMZ. In conclusion, BCNU-resistant CEM-R cells were sensitized to TMZ as a result of enhanced MMR during the development of BCNU resistance.
authors.affiliation: Department of Hematology and Oncology, University of Fukui, 23 Shimoaizuki, Matsuoka, Eiheiji, Fukui 910-1193, Japan. tyamauch@u-fukui.ac.jp
authors.forename: Takahiro
authors.initials: T
authors.lastname: Yamauchi
authors.forename: Masami
authors.initials: M
authors.lastname: Ogawa
authors.forename: Takanori
authors.initials: T
authors.lastname: Ueda
mesh_terms: D018906:Antineoplastic Agents, Alkylating / Q000008:administration & dosage / Q000494:pharmacology*; D000971:Antineoplastic Combined Chemotherapy Protocols / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects; D019256:Cadmium Chloride / Q000008:administration & dosage; D002330:Carmustine / Q000494:pharmacology; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D020552:Comet Assay; D053843:DNA Mismatch Repair / Q000187:drug effects*; D003606:Dacarbazine / Q000031:analogs & derivatives* / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D019008:Drug Resistance, Neoplasm / Q000502:physiology; D006147:Guanine / Q000008:administration & dosage / Q000031:analogs & derivatives; D006801:Humans; D006898:Hydroxylamines / Q000008:administration & dosage; D015376:Nimustine / Q000008:administration & dosage; D054198:Precursor Cell Lymphoblastic Leukemia-Lymphoma / Q000188:drug therapy* / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D000077204:Temozolomide
chemical_list: D018906:Antineoplastic Agents, Alkylating; D006898:Hydroxylamines; C064976:O(6)-benzylguanine; D015376:Nimustine; D006147:Guanine; D003606:Dacarbazine; C005214:methoxyamine; D019256:Cadmium Chloride; D002330:Carmustine; D000077204:Temozolomide