title: Inhibition of GSH synthesis potentiates temozolomide-induced bystander effect in glioblastoma.
abstract: Glioblastoma multiforme (GBM) is one of the most aggressive human tumors with poor prognosis. Current standard treatment includes chemotherapy using DNA alkylating agent temozolomide (TMZ) concomitant with surgical resection and/or irradiation. However, GBM patients exhibit various levels of the elevated expression of DNA repair enzyme, due to MGMT causing resistance to TMZ. Determination of the MGMT-positive population of primary tumor is important to evaluate the therapeutic efficacy of TMZ. Here we generated TMZ-resistant GBM cells by introducing MGMT into TMZ-sensitive GBM cell line KMG4, and established a model to assess the TMZ-induced bystander effect on TMZ-resistant cells. By mixing TMZ-resistant and -sensitive cells, GBM tumors with MGMT positivity as 50%, 10%, and 1% were generated in vivo. We could not observe any bystander effect of TMZ-induced cell death in tumor with 50% MGMT positivity. Although the bystander effect was observed within 20 days in the case of tumor with 1% MGMT positivity, final tumor size at day 28 was the same as control without sensitive cells. This bystander effect was observed in vitro using conditioned medium of TMZ-damaged GBM cells, and PCR array analysis indicated that the conditioned medium stimulated stress and toxicity pathway and upregulated anti-oxidants genes expression such as catalase and SOD2 in TMZ-resistant cells. In addition, the reduction of the activity of anti-stress mechanism by using inhibitor of GSH synthesis potentiated TMZ-induced bystander effect. These results suggest that GSH inhibitor might be one of the candidates for combination therapy with TMZ for TMZ-resistant GBM patients.
authors.affiliation: Department of Cancer Pathology, Hokkaido University Graduate School of Medicine, N15, W7, Kita-ku, Sapporo 060-8638, Japan.
authors.forename: Shinji
authors.initials: S
authors.lastname: Kohsaka
authors.forename: Kenta
authors.initials: K
authors.lastname: Takahashi
authors.forename: Lei
authors.initials: L
authors.lastname: Wang
authors.forename: Mishie
authors.initials: M
authors.lastname: Tanino
authors.forename: Taichi
authors.initials: T
authors.lastname: Kimura
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Nishihara
authors.forename: Shinya
authors.initials: S
authors.lastname: Tanaka
mesh_terms: D000818:Animals; D018906:Antineoplastic Agents, Alkylating / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects; D015153:Blotting, Western; D001932:Brain Neoplasms / Q000188:drug therapy* / Q000378:metabolism / Q000473:pathology; D024201:Bystander Effect; D002374:Catalase / Q000037:antagonists & inhibitors / Q000378:metabolism; D049109:Cell Proliferation / Q000187:drug effects; D017077:Culture Media, Conditioned / Q000494:pharmacology; D019175:DNA Methylation; D015254:DNA Modification Methylases / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D045643:DNA Repair Enzymes / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D003606:Dacarbazine / Q000031:analogs & derivatives* / Q000494:pharmacology; D019008:Drug Resistance, Neoplasm / Q000187:drug effects*; D005260:Female; D005909:Glioblastoma / Q000188:drug therapy* / Q000378:metabolism / Q000473:pathology; D005978:Glutathione / Q000378:metabolism*; D006801:Humans; D007124:Immunoenzyme Techniques; D051379:Mice; D008807:Mice, Inbred BALB C; D034741:RNA, Small Interfering / Q000235:genetics; D060888:Real-Time Polymerase Chain Reaction; D013482:Superoxide Dismutase / Q000037:antagonists & inhibitors / Q000378:metabolism; D000077204:Temozolomide; D014407:Tumor Cells, Cultured; D025521:Tumor Suppressor Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D023041:Xenograft Model Antitumor Assays; D000099156:Superoxide Dismutase 2
chemical_list: D018906:Antineoplastic Agents, Alkylating; D002374:Catalase; D017077:Culture Media, Conditioned; D015254:DNA Modification Methylases; D045643:DNA Repair Enzymes; D003606:Dacarbazine; D005978:Glutathione; D034741:RNA, Small Interfering; D013482:Superoxide Dismutase; D000077204:Temozolomide; D025521:Tumor Suppressor Proteins; D000099156:Superoxide Dismutase 2; C515491:MGMT protein, human