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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

Manganese superoxide disumutase (MnSOD) expression in OSE and ovarian cancer cells. (A) Whole-cell lysates from different ovarian cell lines containing equal amounts of protein (50 μg) were loaded in each lane and analysed for expression of MnSOD by western blotting. β-Actin was also blotted as a protein-loading control. (B) O2•− level was measured by flow cytometry analysis using dihydroethidium. Solid histogram, CaOV-3 and SKOV-3 cells; open histogram, OVCAR-3.
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fig1: Manganese superoxide disumutase (MnSOD) expression in OSE and ovarian cancer cells. (A) Whole-cell lysates from different ovarian cell lines containing equal amounts of protein (50 μg) were loaded in each lane and analysed for expression of MnSOD by western blotting. β-Actin was also blotted as a protein-loading control. (B) O2•− level was measured by flow cytometry analysis using dihydroethidium. Solid histogram, CaOV-3 and SKOV-3 cells; open histogram, OVCAR-3.

Mentions: It has been shown in earlier studies that the majority of ovarian cancer tissues exhibited higher levels of MnSOD expression as compared with normal or benign ovary tissues (Ishikawa et al, 1990; Hileman et al, 2004; Hu et al, 2005). In the present study, we compared the expression level of MnSOD in three ovarian carcinoma cell lines (CaOV-3, SKOV-3, and OVCAR-3) against immortalised, non-tumourigenic OSE cell lines (IOSE-29, IOSE-80, IOSE-397, and IOSE-398). As shown in Figure 1A, OSE cells exhibited only a weak MnSOD signal. In contrast, all of the ovarian cancer cell lines, with the exception of OVCAR-3, showed substantially higher levels of MnSOD. As MnSOD catalyses the elimination of O2•− in the mitochondria where a large portion of cellular ROS is generated, we measured the O2•− content by flow cytometry using the ROS-sensitive probe dihydroethidium. Consistently, CaOV-3 and SKOV-3 exhibited relatively lower levels of fluorescence (cellular O2•− level) compared with OVCAR-3 (Figure 1B).


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)

Manganese superoxide disumutase (MnSOD) expression in OSE and ovarian cancer cells. (A) Whole-cell lysates from different ovarian cell lines containing equal amounts of protein (50 μg) were loaded in each lane and analysed for expression of MnSOD by western blotting. β-Actin was also blotted as a protein-loading control. (B) O2•− level was measured by flow cytometry analysis using dihydroethidium. Solid histogram, CaOV-3 and SKOV-3 cells; open histogram, OVCAR-3.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2480972&req=5

fig1: Manganese superoxide disumutase (MnSOD) expression in OSE and ovarian cancer cells. (A) Whole-cell lysates from different ovarian cell lines containing equal amounts of protein (50 μg) were loaded in each lane and analysed for expression of MnSOD by western blotting. β-Actin was also blotted as a protein-loading control. (B) O2•− level was measured by flow cytometry analysis using dihydroethidium. Solid histogram, CaOV-3 and SKOV-3 cells; open histogram, OVCAR-3.
Mentions: It has been shown in earlier studies that the majority of ovarian cancer tissues exhibited higher levels of MnSOD expression as compared with normal or benign ovary tissues (Ishikawa et al, 1990; Hileman et al, 2004; Hu et al, 2005). In the present study, we compared the expression level of MnSOD in three ovarian carcinoma cell lines (CaOV-3, SKOV-3, and OVCAR-3) against immortalised, non-tumourigenic OSE cell lines (IOSE-29, IOSE-80, IOSE-397, and IOSE-398). As shown in Figure 1A, OSE cells exhibited only a weak MnSOD signal. In contrast, all of the ovarian cancer cell lines, with the exception of OVCAR-3, showed substantially higher levels of MnSOD. As MnSOD catalyses the elimination of O2•− in the mitochondria where a large portion of cellular ROS is generated, we measured the O2•− content by flow cytometry using the ROS-sensitive probe dihydroethidium. Consistently, CaOV-3 and SKOV-3 exhibited relatively lower levels of fluorescence (cellular O2•− level) compared with OVCAR-3 (Figure 1B).

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