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Chemosensitisation by manganese superoxide dismutase inhibition is caspase-9 dependent and involves extracellular signal-regulated kinase 1/2.

Yeung BH, Wong KY, Lin MC, Wong CK, Mashima T, Tsuruo T, Wong AS - Br. J. Cancer (2008)

Bottom Line: 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.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.

View Article: PubMed Central - PubMed

Affiliation: School of Biological Sciences, The University of Hong Kong, Hong Kong, PR China.

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.

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Related in: MedlinePlus

Inhibition of manganese superoxide disumutase (MnSOD) does not sensitise chemotherapy-induced apoptosis in non-transformed OSE cells. IOSE-29 and IOSE-398 cells were transfected with non-specific control (Ctrl small-interfering RNA, siRNA) or MnSOD siRNA in the presence or absence of doxorubicin (DOX, 5 μM) or paclitaxel (PTX, 0.1 μM) for 48 h. (A) Expression of MnSOD protein was analysed by western blotting. β-Actin serves as a protein-loading control. (B) Apoptosis was assessed by the terminal deoxynucleotidyl transferase-mediated dUTP nick-end labelling (TUNEL) assay. Experiments were repeated three times, and data are shown as mean±s.d. (C) O2•− level of DOX- and PTX-treated cells was measured by flow cytometry analysis using dihydroethidium. Solid histogram, untreated cells; open histogram, DOX- and PTX-treated cells.
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fig7: Inhibition of manganese superoxide disumutase (MnSOD) does not sensitise chemotherapy-induced apoptosis in non-transformed OSE cells. IOSE-29 and IOSE-398 cells were transfected with non-specific control (Ctrl small-interfering RNA, siRNA) or MnSOD siRNA in the presence or absence of doxorubicin (DOX, 5 μM) or paclitaxel (PTX, 0.1 μM) for 48 h. (A) Expression of MnSOD protein was analysed by western blotting. β-Actin serves as a protein-loading control. (B) Apoptosis was assessed by the terminal deoxynucleotidyl transferase-mediated dUTP nick-end labelling (TUNEL) assay. Experiments were repeated three times, and data are shown as mean±s.d. (C) O2•− level of DOX- and PTX-treated cells was measured by flow cytometry analysis using dihydroethidium. Solid histogram, untreated cells; open histogram, DOX- and PTX-treated cells.

Mentions: We also studied the combined effect of MnSOD siRNA and chemotherapeutic drugs in non-transformed OSE cells and did not find any synergistic effect. Figure 7A shows that a combination treatment of MnSOD siRNA with DOX and PTX induced 2.2 and 6.5% apoptosis respectively in OSE, which is almost the same as that by DOX or PTX alone. OSE showed only little, if any, increase of O2•− in response to DOX and PTX treatment (Figure 7B) than did ovarian cancer cells (Figure 6B). Taken together, the above results suggest that the active generation of O2•− in ovarian cancer cells by MnSOD inhibition renders these cells more susceptible to apoptosis induced by chemotherapeutic drugs.


Chemosensitisation by manganese superoxide dismutase inhibition is caspase-9 dependent and involves extracellular signal-regulated kinase 1/2.

Yeung BH, Wong KY, Lin MC, Wong CK, Mashima T, Tsuruo T, Wong AS - Br. J. Cancer (2008)

Inhibition of manganese superoxide disumutase (MnSOD) does not sensitise chemotherapy-induced apoptosis in non-transformed OSE cells. IOSE-29 and IOSE-398 cells were transfected with non-specific control (Ctrl small-interfering RNA, siRNA) or MnSOD siRNA in the presence or absence of doxorubicin (DOX, 5 μM) or paclitaxel (PTX, 0.1 μM) for 48 h. (A) Expression of MnSOD protein was analysed by western blotting. β-Actin serves as a protein-loading control. (B) Apoptosis was assessed by the terminal deoxynucleotidyl transferase-mediated dUTP nick-end labelling (TUNEL) assay. Experiments were repeated three times, and data are shown as mean±s.d. (C) O2•− level of DOX- and PTX-treated cells was measured by flow cytometry analysis using dihydroethidium. Solid histogram, untreated cells; open histogram, DOX- and PTX-treated cells.
© Copyright Policy
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC2480972&req=5

fig7: Inhibition of manganese superoxide disumutase (MnSOD) does not sensitise chemotherapy-induced apoptosis in non-transformed OSE cells. IOSE-29 and IOSE-398 cells were transfected with non-specific control (Ctrl small-interfering RNA, siRNA) or MnSOD siRNA in the presence or absence of doxorubicin (DOX, 5 μM) or paclitaxel (PTX, 0.1 μM) for 48 h. (A) Expression of MnSOD protein was analysed by western blotting. β-Actin serves as a protein-loading control. (B) Apoptosis was assessed by the terminal deoxynucleotidyl transferase-mediated dUTP nick-end labelling (TUNEL) assay. Experiments were repeated three times, and data are shown as mean±s.d. (C) O2•− level of DOX- and PTX-treated cells was measured by flow cytometry analysis using dihydroethidium. Solid histogram, untreated cells; open histogram, DOX- and PTX-treated cells.
Mentions: We also studied the combined effect of MnSOD siRNA and chemotherapeutic drugs in non-transformed OSE cells and did not find any synergistic effect. Figure 7A shows that a combination treatment of MnSOD siRNA with DOX and PTX induced 2.2 and 6.5% apoptosis respectively in OSE, which is almost the same as that by DOX or PTX alone. OSE showed only little, if any, increase of O2•− in response to DOX and PTX treatment (Figure 7B) than did ovarian cancer cells (Figure 6B). Taken together, the above results suggest that the active generation of O2•− in ovarian cancer cells by MnSOD inhibition renders these cells more susceptible to apoptosis induced by chemotherapeutic drugs.

Bottom Line: 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.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.

View Article: PubMed Central - PubMed

Affiliation: School of Biological Sciences, The University of Hong Kong, Hong Kong, PR China.

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.

Show MeSH
Related in: MedlinePlus