title: Chemosensitisation by manganese superoxide dismutase inhibition is caspase-9 dependent and involves extracellular signal-regulated kinase 1/2.
abstract: Chemoresistance and therapeutic selectivity are major obstacles to successful chemotherapy of ovarian cancer. Manganese superoxide disumutase (MnSOD) is an important antioxidant enzyme responsible for the elimination of superoxide radicals. We reported here that MnSOD was significantly elevated in ovarian cancer cells and its overexpression was one of the mechanisms that increased resistance to apoptosis in cancer cells. Knockdown of MnSOD by small-interfering RNA (siRNA) led to an increase in superoxide generation and sensitisation of ovarian cancer cells to the two front-line anti-cancer agents doxorubicin and paclitaxel whose action involved free-radical generation. This synergistic effect was not observed in non-transformed ovarian surface epithelial cells. Furthermore, our results revealed that this combination at the cellular level augmented activation of caspase-3 and caspase-9, but not caspase-8, suggesting involvement of an intrinsic apoptotic pathway. Evaluation of signalling pathways showed that MnSOD siRNA enhanced doxorubicin- and paclitaxel-induced phosphorylation of extracellular signal-regulated kinase 1/2. Akt activation was not affected. These results identify a novel chemoresistance mechanism in ovarian cancer, and show that combination of drugs capable of suppressing MnSOD with conventional chemotherapeutic agents may provide a novel strategy with a superior therapeutic index and advantage for the treatment of refractory ovarian cancer.
authors.affiliation: School of Biological Sciences, The University of Hong Kong, Hong Kong, PR China.
authors.forename: B H Y
authors.initials: BH
authors.lastname: Yeung
authors.forename: K Y
authors.initials: KY
authors.lastname: Wong
authors.forename: M C
authors.initials: MC
authors.lastname: Lin
authors.forename: C K C
authors.initials: CK
authors.lastname: Wong
authors.forename: T
authors.initials: T
authors.lastname: Mashima
authors.forename: T
authors.initials: T
authors.lastname: Tsuruo
authors.forename: A S T
authors.initials: AS
authors.lastname: Wong
mesh_terms: D000975:Antioxidants / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects / Q000502:physiology; D053453:Caspase 9 / Q000235:genetics / Q000378:metabolism*; D061945:Caspase Inhibitors; D045744:Cell Line, Tumor; D004317:Doxorubicin / Q000494:pharmacology; D005260:Female; D006801:Humans; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism*; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism*; D009842:Oligopeptides / Q000494:pharmacology; D010051:Ovarian Neoplasms / Q000188:drug therapy* / Q000201:enzymology* / Q000235:genetics; D017239:Paclitaxel / Q000494:pharmacology; D034741:RNA, Small Interfering / Q000235:genetics; D017382:Reactive Oxygen Species / Q000378:metabolism; D013482:Superoxide Dismutase / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism; D014162:Transfection
chemical_list: D000975:Antioxidants; D061945:Caspase Inhibitors; D009842:Oligopeptides; D034741:RNA, Small Interfering; D017382:Reactive Oxygen Species; C403754:benzyloxycarbonyl-leucyl-glutamyl-histidyl-aspartic acid fluoromethyl ketone; D004317:Doxorubicin; D013482:Superoxide Dismutase; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D053453:Caspase 9; D017239:Paclitaxel