title: Inhibition of glutathione synthesis overcomes Bcl-2-mediated topoisomerase inhibitor resistance and induces nonapoptotic cell death via mitochondrial-independent pathway.
abstract: Bcl-2 protein plays a critical role in inhibiting anticancer drug-induced apoptosis. We found that Bcl-2 overexpression is associated with a nearly 3-fold increase in cellular glutathione levels and with increased resistance to cell death after treatment with etoposide or SN-38, a derivative of camptothecin, in leukemia 697 cells with wild-type p53. Treatment of Bcl-2-overexpressing 697 cells (697-Bcl-2) with buthionine sulfoximine (BSO), an inhibitor of glutathione synthesis, reduced cellular glutathione levels and completely abolished Bcl-2-mediated drug resistance. Morphologic studies revealed that nonapoptotic cell death was induced in 697-Bcl-2 cells after treatment with BSO plus etoposide or SN-38. Activation of caspase-3/7 and cytochrome c release could not be detected in 697-Bcl-2 cells after these drug treatments. Notably, we showed that proteasome-mediated down-regulation of Puma and Noxa proteins occurs in 697-Bcl-2 cells after treatment with BSO plus topoisomerase inhibitor, although there is an increase in the protein levels of p53 in these 697-Bcl-2 cells. In contrast, parental 697 cells underwent typical apoptosis with up-regulation of Puma and Noxa proteins, followed by cytochrome c release and caspase-3/7 activation after treatment with topoisomerase inhibitor in the presence or absence of BSO. Our data suggest that BSO may possess a unique activity to overcome Bcl-2-mediated drug resistance by stimulating the signals that can bypass mitochondrial process in Bcl-2-overexpressing cells.
authors.affiliation: First Department of Internal Medicine, Faculty of Medical Sciences, University of Fukui, Fukui, Japan. ayoshi@fmsrsa.fukui-med.ac.jp
authors.forename: Akira
authors.initials: A
authors.lastname: Yoshida
authors.forename: Haruyuki
authors.initials: H
authors.lastname: Takemura
authors.forename: Hitoshi
authors.initials: H
authors.lastname: Inoue
authors.forename: Toshiyuki
authors.initials: T
authors.lastname: Miyashita
authors.forename: Takanori
authors.initials: T
authors.lastname: Ueda
mesh_terms: D000971:Antineoplastic Combined Chemotherapy Protocols / Q000494:pharmacology; D051017:Apoptosis Regulatory Proteins / Q000096:biosynthesis / Q000235:genetics; D019328:Buthionine Sulfoximine / Q000008:administration & dosage / Q000494:pharmacology; D002166:Camptothecin / Q000008:administration & dosage / Q000031:analogs & derivatives / Q000494:pharmacology; D053148:Caspase 3; D053179:Caspase 7; D020169:Caspases / Q000378:metabolism; D016923:Cell Death / Q000187:drug effects / Q000502:physiology; D045744:Cell Line, Tumor; D004264:DNA Topoisomerases, Type I / Q000378:metabolism; D018432:Drug Resistance, Multiple; D019008:Drug Resistance, Neoplasm; D004789:Enzyme Activation; D005047:Etoposide / Q000008:administration & dosage / Q000494:pharmacology; D015973:Gene Expression Regulation, Leukemic / Q000187:drug effects; D005978:Glutathione / Q000037:antagonists & inhibitors* / Q000096:biosynthesis*; D006801:Humans; D000077146:Irinotecan; D015452:Precursor B-Cell Lymphoblastic Leukemia-Lymphoma / Q000188:drug therapy* / Q000201:enzymology / Q000378:metabolism* / Q000473:pathology; D011518:Proto-Oncogene Proteins / Q000096:biosynthesis / Q000235:genetics; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000037:antagonists & inhibitors / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D059004:Topoisomerase I Inhibitors; D016159:Tumor Suppressor Protein p53 / Q000096:biosynthesis / Q000235:genetics
chemical_list: D051017:Apoptosis Regulatory Proteins; C438378:BBC3 protein, human; C498702:PMAIP1 protein, human; D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; C495901:TP53 protein, human; D059004:Topoisomerase I Inhibitors; D016159:Tumor Suppressor Protein p53; D019328:Buthionine Sulfoximine; D005047:Etoposide; D000077146:Irinotecan; C505407:CASP3 protein, human; C505520:CASP7 protein, human; D053148:Caspase 3; D053179:Caspase 7; D020169:Caspases; D004264:DNA Topoisomerases, Type I; D005978:Glutathione; D002166:Camptothecin