Possible role of FLICE-like inhibitory protein (FLIP) in chemoresistant ovarian cancer cells in vitro

Chemoresistance is a major therapeutic problem and the current knowledge on cellular mechanisms involved is incomplete. In the present study, we have investigated the possible involvement of Fas-associated death domain-like interleukin-1beta-converting enzyme (FLICE)-like inhibitory protein (FLIP) in ovarian cancer resistance by comparing chemosensitive (OV2008) and chemoresistant (C13*) ovarian cancer cells treated with cisplatin in vitro, and/or transfected with FLIP sense cDNA or FLIP small interfering RNA (siRNA) and determining FLIP protein content, cleavage of caspase-8 and caspase-3 and apoptosis. Cisplatin significantly decreased FLIP protein level, induced cleavage of caspase-8 and caspase-3 and apoptosis in a concentration-dependent manner in cisplatin-sensitive but not -resistant cells. While overexpression of FLIP-attenuated cisplatin-induced cleavage of caspase-8 and caspase-3 and apoptosis in chemosensitive cells, downregulation of FLIP in chemoresistant cells by siRNA increased apoptosis induced by cisplatin. These results suggest that FLIP plays a significant role in the regulation of apoptosis in human ovarian cancer cells and their sensitivity to cisplatin. This cell survival factor may be an important determinant in chemoresistance in ovarian cancer and may serve as a molecular target for the development of novel therapy for chemoresistant ovarian cancer.     

Gelsolin regulates cisplatin sensitivity in human head‐and‐neck cancer

Chemoresistance is a major challenge in cancer therapy. Cisplatin is commonly used for chemotherapy in patients with head‐and‐neck cancer (HNC), but it increases control of the disease by only 10–15%. Downregulation of proapoptotic pathways is a key determinant for chemoresistance in which gelsolin (GSN) is critically involved. We analyzed the association between GSN expression and cisplatin resistance in HNC cell lines, animals with HNC and cancer tissue samples from 58 cisplatin‐treated patients with HNC. GSN expression levels were positively associated with chemoresistance in vitro and in vivo. Cisplatin‐induced GSN downregulation was associated with the cleavage of GSN and the promotion of apoptosis. GSN silencing facilitated cisplatin‐induced apoptosis in chemoresistant cells. In contrast, intact gelsolin was prosurvival in the presence of cisplatin by interacting with X‐linked inhibitor of apoptosis protein (XIAP). In chemosensitive cells, cisplatin suppressed GSN–XIAP interaction, promoted translocation of XIAP from the perinuclear region to the nucleus and induced apoptosis. In chemoresistant cells, GSN was highly expressed, and cisplatin had no significant effect on GSN–XIAP interaction and apoptosis. We conclude that GSN is important for chemoresistance in HNC and may be an appropriate therapeutic target in chemoresistant cancers.     

Sensitization of ovarian cancer cells to cisplatin by gold nanoparticles

Recently we reported that gold nanoparticles (AuNPs) inhibit ovarian tumor growth and metastasis in mice by reversing epithelial-mesenchymal transition (EMT). Since EMT is known to confer drug resistance to cancer cells, we wanted to investigate whether anti-EMT property of AuNP could be utilized to sensitize ovarian cancer cells to cisplatin. Herein, we report that AuNPs prevent cisplatin-induced acquired chemoresistance and stemness in ovarian cancer cells and sensitize them to cisplatin. AuNPs inhibit cisplatin induced EMT, decrease the side population cells and key stem cell markers such as ALDH1, CD44, CD133, Sox2, MDR1 and ABCG2 in ovarian cancer cells. Mechanistically, AuNPs prevent cisplatin-induced activation of Akt and NF-κB signaling axis in ovarian cancer cells that are critical for EMT, stem cell maintenance and drug resistance. In vivo, AuNPs sensitize orthotopically implanted ovarian tumor to a low dose of cisplatin and significantly inhibit tumor growth via facilitated delivery of both AuNP and cisplatin. These findings suggest that by depleting stem cell pools and inhibiting key molecular pathways gold nanoparticles sensitize ovarian cancer cells to cisplatin and may be used in combination to inhibit tumor growth and metastasis in ovarian cancer.     

Akt promotes cisplatin resistance in human ovarian cancer cells through inhibition of p53 phosphorylation and nuclear function

Resistance to cisplatin-based chemotherapy is a major cause of treatment failure in human ovarian cancer. Wild-type TP53 status is often, but not always, associated with cisplatin sensitivity, suggesting that additional factors may be involved. Overexpression/activation of the phosphatidylinositol-3-kinase/Akt pathway is commonly observed in ovarian cancer, and Akt activation is a determinant of chemoresistance in ovarian cancer cells, an effect that may be due, in part, to its inhibitory actions on p53-dependent apoptosis. To that end, we examined the role and regulation of p53 in chemosensitive ovarian cancer cells, as well as in their chemoresistant counterparts, and investigated if and how Akt influences this pathway. Cisplatin induced apoptosis in chemosensitive, but not chemoresistant cells, and this was inhibited by downregulation of p53. Cisplatin upregulated PUMA in a p53-dependent manner, and the presence of PUMA was necessary, but not sufficient for cisplatin-induced apoptosis. p53 was phosphorylated on numerous N-terminal residues, including Ser15, Ser20, in response to cisplatin in chemosensitive, but not chemoresistant cells. Furthermore, activation of Akt inhibited the cisplatin-induced upregulation of PUMA, and suppressed cisplatin-induced p53 phosphorylation, while inhibition of Akt increased total and phospho-p53 contents and sensitized p53 wild-type, chemoresistant cells to cisplatin-induced apoptosis. Finally, mutation of Ser15 and/or Ser20, but not of Ser37, to alanine significantly attenuated the ability of p53 to facilitate CDDP-induced apoptosis, and this was independent of PUMA expression. These results support the hypothesis that p53 is a determinant of CDDP sensitivity, and suggest that Akt contributes to chemoresistance, in part, by attenuating p53-mediated PUMA upregulation and phosphorylation of p53, which are essential, but independent determinants of sensitivity to CDDP-induced apoptosis.     

Repeated cisplatin treatment can lead to a multiresistant tumor cell population with stem cell features and sensitivity to 3-bromopyruvate

Cisplatin is used in treatment of several types of cancer, including epithelial ovarian carcinoma (EOC). In order to mimic clinical treatment and to investigate longterm effects of cisplatin in surviving cancer cells, two EOC cell lines were repeatedly treated with low doses. In the SKOV-3 cell line originating from malignant ascites, but not in A2780 cells from a primary tumor, this led to emergence of a stable population (SKOV-3-R) which in the absence of cisplatin showed increased motility, epithelial-mesenchymal transition (EMT) and expression of cancer stem cell markers CD117, CD44 and ALDH1. Accordingly, the cells formed self-renewing spheres in serum-free stem cell medium. Despite upregulation of mitochondrial mass and cytochrome c, and no upregulation of Bcl-2/Bcl-xL, SKOV-3-R were multiresistant to antineoplastic drugs. Cancer stem cells, or tumor-initiating cells (TICs) are highly chemoresistant and are believed to cause relapse into disseminated and resistant EOC. Our second aim was therefore to target resistance in these TIC-like cells. Resistance could be correlated with upregulation of hexokinase-II and VDAC, which are known to form a survival-promoting mitochondrial complex. The cells were thus sensitive to 3-bromopyruvate, which dissociates hexokinase-II from this complex, and were particularly sensitive to combination treatment with cisplatin at doses down to 0.1 x IC₅₀. 3-bromopyruvate might thus be of use in targeting the especially aggressive TIC populations.     

Acquisition of chemoresistance in a human ovarian carcinoma cell line is linked to a defect in cell cycle control

Chemoresistance is a major concern in cancer erradication; it involves various mechanisms, including defects in the apoptosis program induced by anticancer drugs. In order to further explore the mechanisms underlying the development of chemoresistance in ovarian carcinoma after cisplatin treatment, we established an in vitro model, mimicking a clinical protocol of administration of cisplatin. Therefore, IGROV1 ovarian carcinoma cells were exposed for 2 hr to the drug and allowed to recover for several weeks; this way of exposure was reiterated with escalating doses. We followed changes in cytotoxicity of the drug, cell cycle kinetics and long-term survival of cells after cisplatin treatment, and found that resistance to cisplatin was not associated with altered apoptosis pathway, since both cisplatin sensitive and resistant cells underwent apoptosis in a similar way. Acquisition of resistance to cisplatin was associated with the ability of the treated cells to progress through the cell cycle beyond the G₁/S checkpoint; although most cells died by apoptosis, a few surviving cells proliferated and recolonized the cultures. Compared to sensitive cells, the chemoresistant variants were able to override the G₁/S checkpoint whatever the dose, and the recurrent cells recolonized the cultures much faster. Analysis of alterations in gene expression suggests that the defect in cell cycle regulation could take place at the level of the cdk inhibitor p21^CIP1/WAF1. Int. J. Cancer 78:454–463, 1998. © 1998 Wiley-Liss, Inc.     

蛋白激酶B调控的p53蛋白直接线粒体转移与卵巢癌细胞顺铂耐药的关系

目的 探讨蛋白激酶B(PKB,又称Akt)调控的p53蛋白直接线粒体转移在顺铂诱导的卵巢癌细胞凋亡中的作用及与卵巢癌顺铂耐药的关系.方法 应用Western blot检测顺铂作用前后卵巢癌顺铂敏感细胞OV2008、A2780s和顺铂耐药细胞C13*、A2780cp中线粒体和全细胞中p53含量.分离纯化线粒体,检测卵巢癌敏感细胞与耐药细胞p53直接线粒体作用的差异;应用Hoechst染色法检测卵巢癌细胞的凋亡率,将Akt1/2 siRNA导入耐药细胞C13*细胞中,观察p53线粒体转移作用和细胞凋亡率的改变.结果 顺铂能引起p53进入OV2008和A2780s细胞的线粒体中,但不能进入C13*和A2780cP细胞的线粒体.过度表达活化的Akt2能抑制p53进入A2780s细胞的线粒体;下调Akt后,可使p53进入C13*细胞的线粒体,同时C13*细胞对顺铂的敏感性增加.结论 顺铂能引起卵巢癌敏感细胞中p53转移至线粒体,Akt导致的卵巢癌化疗耐药在一定程度上是Akt对p53直接线粒体作用的抑制.下调Akt的表达能使卵巢癌化疗耐药细胞的p53直接线粒体作用增强,耐药性得到一定程度的逆转.

Abstract：

Objective To explore Akt-regulated direct p53 mitochondrial translocation in cisplatininduced apoptosis in ovarian cancer cells and the relationship between this and chemoresistance in ovarian cancer. Methods Chemosensitive ovarian cancer cell lines(0V2008 and A2780s) and chemoresistant cells(C13* and A2780cp) were treated with cisplatin and whole cell and mitochondrial p53 contents were determined by Western blot.The p53 accumulation in mitochondria was determined in purified mitochondrial fractions in cisplatin-sensitive and -resistant ovarian cancer cells.Akt1/2 siRNA were transfected into C13*cells.Cisplatin-induced apoptosis was measured by Hoechst staining and p53 translocation was determined by Western blot.ResultsCisplatin induced mitochondrial p53 accumulation and apoptosis in chemosensitive cells(P ＜0.05 ),but not in resistant cells(P ＞ 0.05 ).Over-expression of active Akt2 inhibited p53 directly translocate to mitochondria,and downregulation of Akt by Akt1/2 siRNA increased p53 mitochondrial accumulation and sensitize C13* cells to cisplatin treatment. Conclusions Cisplatin induces direct p53 mitochondrial accumulation in chemosensitive cells,and Akt confers resistance in ovarian cancer cells,in part,by regulating the direct action of p53 in mitochondrial death pathway.     

Programmed cell death 4 enhances chemosensitivity of ovarian cancer cells by activating death receptor pathway in vitro and in vivo

Chemoresistance is a major cause of treatment failure in ovarian cancer. Therefore, it is necessary to explore alternative therapeutic methods to overcome drug resistance for ovarian cancer treatment. We previously reported that programmed cell death 4 (PDCD4), a tumor suppressor, significantly suppresses the malignant phenotype of ovarian cancer cells and its lost or low expression in ovarian cancer is associated with unfavorable prognosis of patients. Here we show that PDCD4 improves the sensitivity of ovarian cancer cells to platinum‐based chemotherapy. Overexpression of PDCD4 enhanced chemosensitivity in SKOV3 and CAOV3 cells with low levels of PDCD4, whereas knockdown of PDCD4 reduced chemosensitivity in OVCAR3 cells with high levels of PDCD4. Subsequently, the combination of enforced PDCD4 expression with cisplatin treatment significantly suppressed ovarian tumor growth in a xenograft animal model. The PDCD4 effect appears to be specific for cisplatin and carboplatin, not affecting cyclophosphamide, etoposide, or paclitaxel. Mechanistically, PDCD4 significantly increased cisplatin‐induced cleavage of caspase‐3 and caspase‐8, but had only a slight impact on caspase‐9 cleavage and the expression of Bax and Bcl‐2 in vitro and in vivo. A specific caspase‐8 inhibitor, Z‐ITED‐FMK, attenuated cisplatin‐induced apoptosis in PDCD4‐overexpressing ovarian cancer cells. Taken together, our results indicate that PDCD4 enhances cisplatin‐induced apoptosis by mainly activating the death receptor pathway, and PDCD4 gene transfer in combination with cisplatin therapy may break the resistance of ovarian cancer cells to chemotherapy. (Cancer Sci 2010)     

Ganoderma lucidum exerts anti-tumor effects on ovarian cancer cells and enhances their sensitivity to cisplatin

Ganoderma lucidum is a herbal mushroom known to have many health benefits, including the inhibition of tumor cell growth. However, the effect of Ganoderma lucidum on epithelial ovarian cancer (EOC), the most fatal gynecological malignancy, has not yet been reported. In this study, we determined whether Ganoderma lucidum regulates EOC cell activity. Using several cell lines derived from EOC, we found that Ganoderma lucidum strongly decreased cell numbers in a dose-dependent manner. Ganoderma lucidum also inhibited colony formation, cell migration and spheroid formation. In particular, Ganoderma lucidum was effective in inhibiting cell growth in both chemosensitive and chemoresistant cells and the treatment with Ganoderma lucidum significantly enhanced the effect of cisplatin on EOC cells. Furthermore, Ganoderma lucidum induced cell cycle arrest at the G2/M phase and also induced apoptosis by activating caspase 3. Finally, Ganoderma lucidum increased p53 but inhibited Akt expression. Taken together, these findings suggest that Ganoderma lucidum exerts multiple anti-tumor effects on ovarian cancer cells and can enhance the sensitivity of EOC cells to cisplatin.     

Cisplatin resistance in an ovarian carcinoma is associated with a defect in programmed cell death control through XIAP regulation

Chemoresistance is a major impediment to the successful treatment of cancer. It involves various mechanisms, including defects in the apoptosis program that is induced by anticancer drugs. To further explore the mechanisms underlying the development of chemoresistance in ovarian carcinoma after cisplatin (CDDP) treatment, we compared the effect of CDDP on expression of X-linked inhibitor of apoptosis protein (XIAP), a direct inhibitor of caspase-3, -7, and -9, Fas, Fas-ligand (Fas-L), and pro- and antiapoptotic proteins in a CDDP-sensitive human ovarian carcinoma cell line (2008) and its CDDP-resistant subclone (2008C13). In this article, we show that cisplatin treatment led to a differential expression of distinct apoptotic targets in the CDDP-sensitive cell line (2008) and its CDDP-resistant subclone (2008C13). The acquisition of cisplatin resistance was associated with the ability of the treated cells to enhanced expression of XIAP, whereas the death inducer Fas-L was abrogated in 2008C13 following treatment with CDDP. However, the CDDP-sensitive cells failed to activate XIAP but increased Fas-L expression, indicating that distinct regulatory mechanisms are operative. These findings suggest that the expression of XIAP and downregulation of Fas-L are linked to chemoresistance in ovarian carcinoma cells and may represent one of the potential antiapoptotic mechanisms involved during this process.     

Critical role of Wnt/β-catenin signaling in driving epithelial ovarian cancer platinum resistance

Resistance to platinum-based chemotherapy is the major barrier to treating epithelial ovarian cancer. To improve patient outcomes, it is critical to identify the underlying mechanisms that promote platinum resistance. Emerging evidence supports the concept that platinum-based therapies are able to eliminate the bulk of differentiated cancer cells, but are unable to eliminate cancer initiating cells (CIC). To date, the relevant pathways that regulate ovarian CICs remain elusive. Several correlative studies have shown that Wnt/β-catenin pathway activation is associated with poor outcomes in patients with high-grade serous ovarian cancer (HGSOC). However, the functional relevance of these findings remain to be delineated. We have uncovered that Wnt/β-catenin pathway activation is a critical driver of HGSOC chemotherapy resistance, and targeted inhibition of this pathway, which eliminates CICs, represents a novel and effective treatment for chemoresistant HGSOC. Here we show that Wnt/β-catenin signaling is activated in ovarian CICs, and targeted inhibition of β-catenin potently sensitized cells to cisplatin and decreased CIC tumor sphere formation. Furthermore, the Wnt/β-catenin specific inhibitor iCG-001 potently sensitized cells to cisplatin and decreased stem-cell frequency in platinum resistant cells. Taken together, our data is the first report providing evidence that the Wnt/β-catenin signaling pathway maintains stem-like properties and drug resistance of primary HGSOC PDX derived platinum resistant models, and therapeutic targeting of this pathway with iCG-001/PRI-724, which has been shown to be well tolerated in Phase I trials, may be an effective treatment option.     

The E3 ubiquitin ligase EDD is an adverse prognostic factor for serous epithelial ovarian cancer and modulates cisplatin resistance in vitro

Despite a high initial response rate to first-line platinum/paclitaxel chemotherapy, most women with epithelial ovarian cancer relapse with recurrent disease that becomes refractory to further cytotoxic treatment. We have previously shown that the E3 ubiquitin ligase, EDD, a regulator of DNA damage responses, is amplified and overexpressed in serous ovarian carcinoma. Given that DNA damage pathways are linked to platinum resistance, the aim of this study was to determine if EDD expression was associated with disease recurrence and platinum sensitivity in serous ovarian cancer. High nuclear EDD expression, as determined by immunohistochemistry in a cohort of 151 women with serous ovarian carcinoma, was associated with an approximately two-fold increased risk of disease recurrence and death in patients who initially responded to first-line chemotherapy, independently of disease stage and suboptimal debulking. Although EDD expression was not directly correlated with relative cisplatin sensitivity of ovarian cancer cell lines, sensitivity to cisplatin was partially restored in platinum-resistant A2780-cp70 ovarian cancer cells following siRNA-mediated knockdown of EDD expression. These results identify EDD as a new independent prognostic marker for outcome in serous ovarian cancer, and suggest that pathways involving EDD, including DNA damage responses, may represent new therapeutic targets for chemoresistant ovarian cancer.     

核苷酸切除修复交叉互补基因1与卵巢癌顺铂耐药的关系

目的 探讨核苷酸切除修复交叉互补基因1(ERCC1)与卵巢癌顺铂(DDP)耐药的关系.方法 分别应用免疫组化、逆转录聚合酶链反应(RT-PCR)和Western blot检测58例卵巢癌组织和ES-2、SKOV3、COC1、COC1/DDP 4株卵巢癌细胞系中ERCC1基因的表达,分析该基因与DDP化疗耐药的关系,并观察应用RNA干扰技术干扰了ERCC1基因后卵巢癌细胞对DDP敏感性的变化.结果 58例卵巢癌组织中,ERCC1表达阳性者22例,阳性率为37.9%.ERCC1的表达与DDP化疗敏感性有关(P＜0.05),DDP耐药者ERCC1表达的阳性率(57.89%)显著高于敏感者(28.21%,P=0.029).ES-2、SKOV3、COC1、COC1/DDP 4株卵巢癌细胞ERCC1基因的表达与DDP IC50正相关(r=0.932,P＜0.05).RNA干扰ERCC1基因后,ES-2、SKOV3、COC1/DDP细胞对DDP的敏感性分别增加了53.88、5.07、3.75倍.结论 ERCC1基因与卵巢癌DDP耐药有关,RNA干扰ERCC1基因可增强卵巢癌细胞对DDP的敏感性.     

人卵巢癌细胞系干/祖细胞分离及其鉴定

目的:自人卵巢癌细胞系SK-OV-3中分离干/祖细胞并进行鉴定。方法:采用无血清球形体形成法从SKOV-3中分离培养卵巢癌干/祖细胞;采用实时定量PCR和蛋折质印迹法测定球形体细胞干/祖细胞相关标志ABCG2、Oct-4、Nanog基因和蛋白的表达;流式细胞仪检测其耐药性;双层软琼脂检测其克隆形成能力;NOD/SCID小鼠检测其体内致瘤性。结果:球形体细胞表达干/祖细胞相关标志Oct-4、ABCG2、Nanog;对顺铂高耐药;在双层软琼脂上克隆形成率达(13.67±1.48)%;1 000个球形体形成细胞就能在NOD/SCID鼠中成瘤。结论:采用无血清培养基中球形体形成法从SKOV-3细胞系中可以分离出具有干/祖特性的卵巢癌细胞,可为今后研究卵巢癌的发生、发展、复发及其化疗药物筛选提供简便实用的体外模型。     

SOX8 regulates cancer stem‐like properties and cisplatin‐induced EMT in tongue squamous cell carcinoma by acting on the Wnt/β‐catenin pathway

A sub‐population of chemoresistant cells exhibits biological properties similar to cancer stem cells (CSCs), and these cells are believed to be a main cause for tumor relapse and metastasis. In our study, we explored the role of SOX8 and its molecular mechanism in the regulation of the stemness properties and the epithelial mesenchymal transition (EMT) of cisplatin‐resistant tongue squamous cell carcinoma (TSCC) cells. We found that SOX8 was upregulated in cisplatin‐resistant TSCC cells, which displayed CSC‐like properties and exhibited EMT. SOX8 was also overexpressed in chemoresistant patients with TSCC and was associated with higher lymph node metastasis, advanced tumor stage and shorter overall survival. Stable knockdown of SOX8 in cisplatin‐resistant TSCC cells inhibited chemoresistance, tumorsphere formation, and EMT. The Wnt/β‐catenin pathway mediated the cancer stem‐like properties in cisplatin‐resistant TSCC cells. Further studies showed that the transfection of active β‐catenin in SOX8 stable‐knockdown cells partly rescued the SOX8 silencing‐induced repression of stem‐like features and chemoresistance. Through chromatin immunoprecipitation and luciferase assays, we observed that SOX8 bound to the promoter region of Frizzled‐7 (FZD7) and induced the FZD7‐mediated activation of the Wnt/β‐catenin pathway. In summary, SOX8 confers chemoresistance and stemness properties and mediates EMT processes in chemoresistant TSCC via the FZD7‐mediated Wnt/β‐catenin pathway.     

β-Elemene Effectively Suppresses the Growth and Survival of Both Platinum-sensitive and -resistant Ovarian Tumor Cells

The development of cisplatin drug resistance remains a chief concern in ovarian cancer chemotherapy. β-Elemene is a natural plant product with broad-spectrum antitumor activity towards many types of carcinomas. This study aimed to define the biological and therapeutic significance of β-elemene in chemoresistant ovarian cancer. In the present study, β-elemene significantly inhibited cell growth and proliferation of both the cisplatin-sensitive human ovarian cancer cell line A2780 and its cisplatin-resistant counterpart A2780/CP. β-Elemene also suppressed the growth of several other chemosensitive and chemoresistant ovarian cancer cell lines, including ES-2, MCAS, OVCAR-3, and SKOV-3, with the half maximal inhibitory concentration (IC(50)) values ranging from 54 to 78 μg/ml. In contrast, the IC(50) values of β-elemene for the human ovarian epithelial cell lines IOSE-386 and IOSE-397 were 110 and 114 μg/ml, respectively, which are almost two-fold those for the ovarian cancer cell lines. Cell cycle analysis demonstrated that β-elemene induced a persistent block of cell cycle progression at the G(2)/M phase in A2780 and A2780/CP cells. This was mediated by alterations in cyclin and cyclin-dependent kinase expression, including the down-regulation of CDC2, cyclin A, and cyclin B1, and the up-regulation of p21(WAF1/CIP1) and p53 proteins. Moreover, β-elemene triggered apoptosis and irreversible cell death in both sensitive and resistant ovarian cancer cells via the activation of caspase-3, -8 and 9; the loss of mitochondrial membrane potential (δΨm); the release of cytochrome c into the cytosol; and changes in the expression of BCL-2 family proteins. All of these molecular changes were associated with β-elemene-induced growth inhibition and cell death of ovarian cancer cells. Our results demonstrate that β-elemene has antitumor activity against both platinum-sensitive and resistant ovarian cancer cells, and thus has the potential for development as a chemotherapeutic agent for cisplatin-resistant ovarian cancer.     

Abrogation of constitutive Stat3 activity circumvents cisplatin resistant ovarian cancer

The aim of the present study was to investigate the role of Stat3 in cisplatin resistant ovarian cancer. It was first demonstrated that higher activated Stat3 was detected in cisplatin-resistant ovarian cancer cell lines. To provide evidence that supported the hypothesis that phosphorylated-Stat3 expression may promote cisplatin resistance, ectopic Stat3 was expressed by IL-6 stimulation that partially abrogates Stat3, as opposed to the knock-down of Stat3 by specific siRNA that restores cisplatin sensitivity against ovarian cancer cells. This hypothesis was further confirmed by clinical tumor specimens of ovarian cancer obtained from patients with cisplatin-resistance. Based on these premises, Stattic [1], an effective small molecular inhibitor of Stat3, was used to inhibit Stat3 activation. The data presented here show that Stattic restored the sensitivity to cisplatin in chemoresistant ovarian cancer by significant reductions in the expression of the anti-apoptosis protein Bcl-2, Bcl-X_L, Survivin protein and phosphorylated-Akt levels. Consistent with these observations, this experiment demonstrated the first evidence of Stattic circumvented cisplatin resistance of orthotopic xenograft ovarian cancer in vivo. Altogether, these findings emphasize the importance of Stat3 in cisplatin resistance in ovarian cancer and provide a further impetus to clinically evaluate biological modifiers that may circumvent cisplatin resistance in patients with chemoresistant ovarian cancer.