Silencing of the STAT3 signaling pathway reverses the inherent and induced chemoresistance of human ovarian cancer cells

Ovarian tumor microenvironment contributes to tumor progression and chemoresistance

Ovarian cancer is one of the deadliest gynecologic cancers affecting the female reproductive tract. This is largely attributed to frequent recurrence and development of resistance to the platinum-based drugs cisplatin and carboplatin. One of the major contributing factors to increased cancer progression and resistance to chemotherapy is the tumor microenvironment (TME). Extracellular signaling from cells within the microenvironment heavily influences progression and drug resistance in ovarian cancer. This is frequently done through metabolic reprogramming, the process where cancer cells switch between biochemical pathways to increase their chances of survival and proliferation. Here, we focus on how crosstalk between components of the TME and the tumor promotes resistance to platinum-based chemotherapy. We highlight the role of cancer-associated fibroblasts, immune cells, adipocytes, and endothelial cells in ovarian tumor progression, invasion, metastasis, and chemoresistance. We also highlight recent advancements in targeting components of the TME as a novel therapeutic avenue to combat chemoresistance in ovarian cancer.

Oligonucleotide-Based Therapeutics for STAT3 Targeting in Cancer-Drug Carriers Matter

High expression and phosphorylation of signal transducer and transcription activator 3 (STAT3) are correlated with progression and poor prognosis in various types of cancer. The constitutive activation of STAT3 in cancer affects processes such as cell proliferation, apoptosis, metastasis, angiogenesis, and drug resistance. The importance of STAT3 in cancer makes it a potential therapeutic target. Various methods of directly and indirectly blocking STAT3 activity at different steps of the STAT3 pathway have been investigated. However, the outcome has been limited, mainly by the number of upstream proteins that can reactivate STAT3 or the relatively low specificity of the inhibitors. A new branch of molecules with significant therapeutic potential has emerged thanks to recent developments in the regulatory function of non-coding nucleic acids. Oligonucleotide-based therapeutics can silence target transcripts or edit genes, leading to the modification of gene expression profiles, causing cell death or restoring cell function. Moreover, they can reach untreatable targets, such as transcription factors. This review briefly describes oligonucleotide-based therapeutics that found application to target STAT3 activity in cancer. Additionally, this review comprehensively summarizes how the inhibition of STAT3 activity by nucleic acid-based therapeutics such as siRNA, shRNA, ASO, and ODN-decoy affected the therapy of different types of cancer in preclinical and clinical studies. Moreover, due to some limitations of oligonucleotide-based therapeutics, the importance of carriers that can deliver nucleic acid molecules to affect the STAT3 in cancer cells and cells of the tumor microenvironment (TME) was pointed out. Combining a high specificity of oligonucleotide-based therapeutics toward their targets and functionalized nanoparticles toward cell type can generate very efficient formulations.

The role of microRNA-induced apoptosis in diverse radioresistant cancers

Resistance to cancer radiotherapy is one of the biggest concerns for success in treating and preventing recurrent disease. Malignant tumors may develop when they block genetic mutations associated with apoptosis or abnormal expression of apoptosis; Tumor treatment may induce the expression of apoptosis-related genes to promote tumor cell apoptosis. MicroRNAs have been shown to contribute to forecasting prognosis, distinguishing between cancer subtypes, and affecting treatment outcomes in cancer. Constraining these miRNAs may be an attractive treatment strategy to help overcome radiation resistance. The delivery of these future treatments is still challenging due to the excess downstream targets that each miRNA can control. Understanding the role of miRNAs brings us one step closer to attaining patient treatment and improving patient outcomes. This review summarized the current information on the role of microRNA-induced apoptosis in determining the radiosensitivity of various cancers.

The “Sweet Spot” of Targeting Tumor Metabolism in Ovarian Cancers

The objective of this review is to explore the metabolomic environment of epithelial ovarian cancer that contributes to chemoresistance and to use this knowledge to identify possible targets for therapeutic intervention. The Warburg effect describes increased glucose uptake and lactate production in cancer cells. In ovarian cancer, we require a better understanding of how cancer cells reprogram their glycogen metabolism to overcome their nutrient deficient environment and become chemoresistant. Glucose metabolism in ovarian cancer cells has been proposed to be influenced by altered fatty acid metabolism, oxidative phosphorylation, and acidification of the tumor microenvironment. We investigate several markers of altered metabolism in ovarian cancer including hypoxia-induced factor 1, VEGF, leptin, insulin-like growth factors, and glucose transporters. We also discuss the signaling pathways involved with these biomarkers including PI3K/AKT/mTOR, JAK/STAT and OXPHOS. This review outlines potential metabolic targets to overcome chemoresistance in ovarian cancer. Continued research of the metabolic changes in ovarian cancer is needed to identify and target these alterations to improve treatment approaches.

Comparing the Secretomes of Chemorefractory and Chemoresistant Ovarian Cancer Cell Populations

High-grade serous ovarian cancer (HGSOC) constitutes the majority of all ovarian cancer cases and has staggering rates of both refractory and recurrent disease. While most patients respond to the initial treatment with paclitaxel and platinum-based drugs, up to 25% do not, and of the remaining that do, 75% experience disease recurrence within the subsequent two years. Intrinsic resistance in refractory cases is driven by environmental stressors like tumor hypoxia which alter the tumor microenvironment to promote cancer progression and resistance to anticancer drugs. Recurrent disease describes the acquisition of chemoresistance whereby cancer cells survive the initial exposure to chemotherapy and develop adaptations to enhance their chances of surviving subsequent treatments. Of the environmental stressors cancer cells endure, exposure to hypoxia has been identified as a potent trigger and priming agent for the development of chemoresistance. Both in the presence of the stress of hypoxia or the therapeutic stress of chemotherapy, cancer cells manage to cope and develop adaptations which prime populations to survive in future stress. One adaptation is the modification in the secretome. Chemoresistance is associated with translational reprogramming for increased protein synthesis, ribosome biogenesis, and vesicle trafficking. This leads to increased production of soluble proteins and extracellular vesicles (EVs) involved in autocrine and paracrine signaling processes. Numerous studies have demonstrated that these factors are largely altered between the secretomes of chemosensitive and chemoresistant patients. Such factors include cytokines, growth factors, EVs, and EV-encapsulated microRNAs (miRNAs), which serve to induce invasive molecular, biophysical, and chemoresistant phenotypes in neighboring normal and cancer cells. This review examines the modifications in the secretome of distinct chemoresistant ovarian cancer cell populations and specific secreted factors, which may serve as candidate biomarkers for aggressive and chemoresistant cancers.

The implication of IL-6 in the invasiveness and chemoresistance of ovarian cancer cells. Systematic review of its potential role as a biomarker in ovarian cancer patients

Interleukin 6 (IL-6) is a pleiotropic cytokine that is strongly implicated in the development and progression of ovarian cancer. The most recognized actions of IL-6 in ovarian cancer (OC) cells are the induction of cell proliferation and inhibition of cell apoptosis. Equally important is its ability to enhance the migratory and invasive potential of OC cells. Moreover, the increased expression and secretion of this cytokine positively correlates with OC cell chemoresistance. Elevated concentrations of IL-6 are observed in the serum and ascites of ovarian cancer patients. Thus, its level is discussed in the literature as a potential biomarker that can help to discriminate malignant and nonmalignant ovarian tumors and allow for the prediction of the chemotherapy response. The importance of IL-6 in ovarian cancer is proved by the fact that this cytokine is a potential target to anti-cancer therapy. This review is divided into two parts. The first summarizes the general biological activity of IL-6, and overviews its impact on OC cells, as well as discusses the current proposition of IL-6 inclusion in combination of anti-OC therapy. The second part is a systematic review of IL-6 as a possible biomarker in ovarian cancer patients.

Oncogenic viruses and chemoresistance: What do we know?

Chemoresistance is often referred to as a major leading reason for cancer therapy failure, causing cancer relapse and further metastasis. As a result, an urgent need has been raised to reach a full comprehension of chemoresistance-associated molecular pathways, thereby designing new therapy methods. Many of metastatic tumor masses are found to be related with a viral cause. Although combined therapy is perceived as the model role therapy in such cases, chemoresistant features, which is more common in viral carcinogenesis, often get into way of this kind of therapy, minimizing the chance of survival. Some investigations indicate that the infecting virus dominates other leading factors, i.e., genetic alternations and tumor microenvironment, in development of cancer cell chemoresistance. Herein, we have gathered the available evidence on the mechanisms under which oncogenic viruses cause drug-resistance in chemotherapy.

Resveratrol protects against cisplatin-induced ovarian and uterine toxicity in female rats by attenuating oxidative stress, inflammation and apoptosis

Cisplatin is an important antineoplastic drug used in multiple chemotherapeutic regimens but unfortunately causes serious toxic effects as ovarian and uterine toxicity. This study aimed to investigate the potential protective effect of resveratrol (RSV) against cisplatin-induced ovarian and uterine toxicity in female rats. Thirty-two female Wistar rats were divided randomly into four groups (n = 8 in each). Control group received oral normal saline for 28 days; RSV group received RSV (10 mg/kg; daily) via oral gavage; CIS group received a single dose of CIS (7 mg/kg; i.p.) on the 21st day; (CIS + RSV) group received both RSV and CIS by the same schedules and doses of RSV and CIS groups, respectively. Results demonstrated a significant decrease in MDA level and a significant increase in both glutathione content and activity of the antioxidant enzymes GPx, SOD, and CAT in the tissues of the ovary and uterus of CIS + RSV group in comparison to that of CIS group (P<0.05), also there are significantly decreased tissue levels of the proinflammatory cytokines and enzymes (NF-κB, IL-1β, IL-6, TNF-α, COX-2, and iNOS), increased estradiol, progesterone, prolactin and decreased FSH serum levels in CIS + RSV group compared to CIS group (P < 0.05). Moreover, there is downregulation of tissues Cleaved Caspase-3, NF-κB and Cox-2 proteins as shown in Western blot analysis, also apoptosis was significantly inhibited, evidenced by downregulation of Bax and upregulation of Bcl-2 proteins, and the ovarian and uterine histological architecture and integrity were maintained in CIS + RSV group compared to CIS group. In conclusion, these findings indicate that RSV has beneficial effects in ameliorating cisplatin-induced oxidative stress, inflammation, and apoptosis in the ovarian and uterine tissues of female rats.

FSTL1 increases cisplatin sensitivity in epithelial ovarian cancer cells by inhibition of NF-κB pathway

OBJECTIVE

To investigate the effects of FSTL1-mediated NF-κB signaling pathway on cisplatin (DDP) sensitivity of EOC cells.

METHODS

FSTL1 expression was determined in epithelial ovarian cancer (EOC) tissues and corresponding adjacent tissues using immunohistochemistry. SKOV3 and SKOV3/DDP cells were transfected and grouped into Blank, Vector, and FSTL1 groups. The sensitivity and 50% inhibitory concentration (IC50) of cells treated with different concentrations of DDP were detected by MTT assay. SKOV3/DDP cells were treated with 20 μM DDP, followed by evaluation of cell proliferation, cell apoptosis and determination of NF-κB pathway-related proteins while SKOV3 cells without.

RESULTS

FSTL1 expression in EOC tissues and cells was significantly down-regulated, especially decreased in DDP-resistant EOC cells SKOV3/DDP. In SKOV3 cells and SKOV3/DDP cells, the cell viability was reduced and the DDP sensitivity was improved with the decreased IC50 after over-expressing FSTL1. Compared with Blank group, FSTL1 group had declined number of SKOV3 cell colonies and increased cell apoptosis, with obvious up-regulations of FSTL1, Bax/Bcl-2 and cleaved caspase-3 expression and the down-regulations of p-IκBα, p-p65 and survivin expression. Combination of up-regulation of FSTL1 and DDP treatment can also effectively reduce cell colony forming, increase cell apoptosis, and inhibit NF-κB pathway activity of SKOV3/DDP cells. Moreover, this combination can also significantly suppress the growth of subcutaneous xenograft tumors in nude mice.

CONCLUSION

FSTL1 may inhibit NF-κB signaling pathway to suppress the growth and promote the apoptosis of epithelial ovarian cancer cells, and thereby enhancing its DDP sensitivity.

Role of STAT3 signaling transduction pathways in cancer stem cell-associated chemoresistance

Chemoresistance resulting from cancer stem cells (CSCs) and epithelial-mesenchymal transition (EMT) results in inconsistent chemotherapeutic efficacy. The co-existence of CSCs and the EMT allows cancer cells to interconvert between differentiated and stem-like states, a phenomenon known as cellular plasticity. Phosphorylated signal transducer and activator of transcription 3 (pSTAT3) has been increasingly identified as a major contributor to CSCs and the EMT, as evidenced from preclinical studies that reversed chemoresistance through STAT3 pathway inhibition. In this review, we discuss mechanisms that center on STAT3 and its target genes responsible for regulating the EMT. We also highlight the current status of clinical trials using STAT3 pathway inhibitors.

CD44 in Ovarian Cancer Progression and Therapy Resistance-A Critical Role for STAT3

Despite significant progress in cancer therapy over the last decades, ovarian cancer remains the most lethal gynecologic malignancy worldwide with the five-year overall survival rate less than 30% due to frequent disease recurrence and chemoresistance. CD44 is a non-kinase transmembrane receptor that has been linked to cancer metastatic progression, cancer stem cell maintenance, and chemoresistance development via multiple mechanisms across many cancers, including ovarian, and represents a promising therapeutic target for ovarian cancer treatment. Moreover, CD44-mediated signaling interacts with other well-known pro-tumorigenic pathways and oncogenes during cancer development, such as signal transducer and activator of transcription 3 (STAT3). Given that both CD44 and STAT3 are strongly implicated in the metastatic progression and chemoresistance of ovarian tumors, this review summarizes currently available evidence about functional crosstalk between CD44 and STAT3 in human malignancies with an emphasis on ovarian cancer. In addition to the role of tumor cell-intrinsic CD44 and STAT3 interaction in driving cancer progression and metastasis, we discuss how CD44 and STAT3 support the pro-tumorigenic tumor microenvironment and promote tumor angiogenesis, immunosuppression, and cancer metabolic reprogramming in favor of cancer progression. Finally, we review the current state of therapeutic CD44 targeting and propose superior treatment possibilities for ovarian cancer.

Isolinderalactone Induces Cell Death via Mitochondrial Superoxide- and STAT3-Mediated Pathways in Human Ovarian Cancer Cells

The mortality rate of ovarian cancer (OC) worldwide increases with age. OC is an often fatal cancer with a curative rate of only 20-30%, as symptoms often appear after disease progression. Studies have reported that isolinderalactone (ILL), a furanosesquiterpene derivative extracted from the dried root of Lindera aggregata, can inhibit several cancer cell lines' growth. However, the molecular mechanisms underlying ILL activities in human OC cells remain unexplored. This study investigated the antitumor activities of ILL in human OC cells by inducing mitochondrial superoxide (mtSO) and JAK-signal transducer and activator of transcription 3 (STAT3)-dependent cell death. ILL caused cell death in SKOV-3 and OVCAR-3 cells and increased the cell proportion in the subG1 phase. Additionally, ILL significantly induced mtSO production and reduced ROS production. Moreover, ILL downregulated mitochondrial membrane potential and the expression levels of anti-apoptotic Bcl-2 family proteins and superoxide dismutase (SOD)2. Results showed that ILL decreased phosphorylation of serine 727 and tyrosine 705 of STAT3 and expression of survivin, a STAT3-regulated gene. Furthermore, ILL-induced cell death was reversed by pretreatment of Mito-TEMPO, a mitochondria-specific antioxidant. These results suggest that ILL induces cell death by upregulation of mtSO, downregulation of mitochondrial SOD2, and inactivation of the STAT3-mediated pathway.

STAT3, the Challenge for Chemotherapeutic and Radiotherapeutic Efficacy

Chemoradiotherapy is one of the most effective and extensively used strategies for cancer treatment. Signal transducer and activator of transcription 3 (STAT3) regulates vital biological processes, such as cell proliferation and cell growth. It is constitutively activated in various cancers and limits the application of chemoradiotherapy. Accumulating evidence suggests that STAT3 regulates resistance to chemotherapy and radiotherapy and thereby impairs therapeutic efficacy by mediating its feedback loop and several target genes. The alternative splicing product STAT3β is often identified as a dominant-negative regulator, but it enhances sensitivity to chemotherapy and offers a new and challenging approach to reverse therapeutic resistance. We focus here on exploring the role of STAT3 in resistance to receptor tyrosine kinase (RTK) inhibitors and radiotherapy, outlining the potential of targeting STAT3 to overcome chemo(radio)resistance for improving clinical outcomes, and evaluating the importance of STAT3β as a potential therapeutic approach to overcomes chemo(radio)resistance. In this review, we discuss some new insights into the effect of STAT3 and its subtype STAT3β on chemoradiotherapy sensitivity, and we explore how these insights influence clinical treatment and drug development for cancer.

STAT3 as a predictive biomarker in head and neck cancer: A validation study

Locally advanced head and neck squamous cell carcinoma (LAHNSCC) treatment consists of radiotherapy (RT) alone or cisplatin-based concomitant chemoradiotherapy (CCRT). CCRT is accompanied by substantially more toxicity than RT alone. A previous retrospective cohort study found that LAHNSCC patients with tumors negative for nuclear expression of the signal transducer and activator of transcription 3 (STAT3) protein might not benefit from the addition of cisplatin to radiotherapy (RT) treatment. We set out to validate these results in a new cohort. We found that in patients with both STAT3 positive and negative tumors, disease-free survival (DFS) and overall survival (OS) did not differ significantly between treatment with cisplatin-based concomitant chemoradiotherapy (CCRT) and radiotherapy alone. Therefore, our validation study does not confirm that STAT3 is a potential biomarker to predict the effectiveness of the addition of cisplatin to RT in LAHNSCC patients.

Transcription Factors in Cancer Development and Therapy

Cancer is a multi-step process and requires constitutive expression/activation of transcription factors (TFs) for growth and survival. Many of the TFs reported so far are critical for carcinogenesis. These include pro-inflammatory TFs, hypoxia-inducible factors (HIFs), cell proliferation and epithelial-mesenchymal transition (EMT)-controlling TFs, pluripotency TFs upregulated in cancer stem-like cells, and the nuclear receptors (NRs). Some of those, including HIFs, Myc, ETS-1, and β-catenin, are multifunctional and may regulate multiple other TFs involved in various pro-oncogenic events, including proliferation, survival, metabolism, invasion, and metastasis. High expression of some TFs is also correlated with poor prognosis and chemoresistance, constituting a significant challenge in cancer treatment. Considering the pivotal role of TFs in cancer, there is an urgent need to develop strategies targeting them. Targeting TFs, in combination with other chemotherapeutics, could emerge as a better strategy to target cancer. So far, targeting NRs have shown promising results in improving survival. In this review, we provide a comprehensive overview of the TFs that play a central role in cancer progression, which could be potential therapeutic candidates for developing specific inhibitors. Here, we also discuss the efforts made to target some of those TFs, including NRs.

Transcription Factors in Cancer Development and Therapy

Cancer is a multi-step process and requires constitutive expression/activation of transcription factors (TFs) for growth and survival. Many of the TFs reported so far are critical for carcinogenesis. These include pro-inflammatory TFs, hypoxia-inducible factors (HIFs), cell proliferation and epithelial-mesenchymal transition (EMT)-controlling TFs, pluripotency TFs upregulated in cancer stem-like cells, and the nuclear receptors (NRs). Some of those, including HIFs, Myc, ETS-1, and β-catenin, are multifunctional and may regulate multiple other TFs involved in various pro-oncogenic events, including proliferation, survival, metabolism, invasion, and metastasis. High expression of some TFs is also correlated with poor prognosis and chemoresistance, constituting a significant challenge in cancer treatment. Considering the pivotal role of TFs in cancer, there is an urgent need to develop strategies targeting them. Targeting TFs, in combination with other chemotherapeutics, could emerge as a better strategy to target cancer. So far, targeting NRs have shown promising results in improving survival. In this review, we provide a comprehensive overview of the TFs that play a central role in cancer progression, which could be potential therapeutic candidates for developing specific inhibitors. Here, we also discuss the efforts made to target some of those TFs, including NRs.

A novel small molecule STAT3 inhibitor SLSI-1216 suppresses proliferation and tumor growth of triple-negative breast cancer cells through apoptotic induction

Triple-negative breast cancer (TNBC) is the most aggressive type of breast cancer, characterized by the lack of expression of estrogen receptor, progesterone receptor, and human epidermal growth factor receptor 2. Owing to the absence of molecular targets, there are limited treatment options, and TNBC patients exhibit high mortality rates. Signal transducer and activator of transcription 3 (STAT3) is overexpressed and aberrantly activated in TNBC cells. Therefore, inhibition of STAT3-mediated signaling provides a potential strategy for the treatment of TNBC. In this study, A series of synthetic derivatives of SLSI-1 (a STAT3 inhibitor) were designed and evaluated for antitumor activity in TNBC cells. A novel derivative (SLSI-1216) exhibited the most potent anti-proliferative activity. SLSI-1216 effectively inhibited STAT3 activity and activation of STAT3, leading to the downregulation of AXL, a downstream target of STAT3 and epithelial-mesenchymal transition (EMT) progression. The inhibition of EMT by SLSI-1216 was associated with modulation of E-cadherin and N-cadherin. Furthermore, SLSI-1216 induced apoptosis by targeting STAT3 and effectively inhibited tumor growth in vivo. These findings suggest that SLSI-1216, as a potential inhibitor of STAT3, may be a promising therapeutic agent for TNBC.

STAT3 signaling in ovarian cancer: a potential therapeutic target

Accumulating evidence has shown that Signal Transducer and Activator of Transcription 3 (STAT3) is thought to be a promising target for cancer therapy as STAT3 is frequently overexpressed in a wide range of cancer cells as well as clinical specimens, promoting tumor progression. It is widely accepted that STAT3 regulates a variety of cellular processes, such as tumor cell growth, survival, invasion, cancer stem cell-like characteristic, angiogenesis and drug-resistance. In this review, we focus on the role of STAT3 in tumorigenesis in ovarian cancer and discuss the existing inhibitors of STAT3 signaling that can be promisingly developed as the strategies for ovarian cancer therapy.

Pectasol-C Modified Citrus Pectin targets Galectin-3-induced STAT3 activation and synergize paclitaxel cytotoxic effect on ovarian cancer spheroids

Here we sought to determine the relationship between STAT3 activity and Galectin‐3 (Gal‐3) and to investigate the cytotoxic effect of PectaSol‐C Modified Citrus Pectin (Pect‐MCP) as a specific competitive inhibitor of Galectin‐3 (Gal‐3) in combination with Paclitaxel (PTX) to kill the ovarian cancer cell SKOV‐3 multicellular tumor spheroid (MCTS). To this order, SKOV‐3 cells in 2D and 3D cultures were treated with exogenous Gal‐3 for the assessment of STAT3 activity. Two‐way ANOVA main effect and IC₅₀ of each drug Paclitaxel (PTX) and Pect‐MCP or in combination were obtained from MTT assay results. The phosphorylated STAT3 levels, migration, invasion, integrin mRNA and p‐AKTser⁴⁷³ levels were assessed in the absence or presence of each drug alone or in combination. Gal‐3 expression levels were assessed in human serous ovarian cancer (SOC) specimens and its correlation with different integrin mRNA levels was further assessed. Our results showed that Gal‐3 expression level was significantly increased in MCTS compared to monolayer SKOV‐3 cells which triggered STAT3 phosphorylation. Moreover, Pect‐MCP synergized with PTX to kill SKOV3 MCTS through abrogation of STAT3 activity and reduced expression of its downstream target HIF‐1α, reduced integrin mRNA levels, and subsequently decreased AKT activity. There were higher expression levels of Gal‐3 in human high‐grade SOC specimens compared to the normal ovary and borderline SOC which positively and significantly correlated with α5, β2 and β6 integrin mRNA levels. Together, these results revealed for the first time that Pect‐MCP could be considered as a potential drug to enhance the PTX effect on ovarian cancer cells MCTS through inhibition of STAT3 activity.

[Silencing RRM1 gene reverses paclitaxel resistance in human breast cancer cell line MCF- 7/R by inducing cell apoptosis]

OBJECTIVE

To investigate the effects of ribonucleotide reductase catalytic subunit M1 (RRM1) gene silencing on drug resistance of human breast cancer cell line MCF-7/R.

METHODS

We established a paclitaxel-resistant breast cancer MCF-7 cell line (MCF-7/R) by exposing the cells to high-concentration paclitaxel in a short time. Small interfering RNAs (siRNAs) targeting RRM1 were designed to silence RRM1 expression in human breast cancer MCF-7/R cells. MTT assay was used to detect the IC₅₀ values and the sensitivity to paclitaxel in the cells with or without siRNA transfection. The changes in the proliferative activity of MCF7 and MCF-7/R cells following RRM1 gene silencing were evaluated using EdU assay. Flow cytometry was used to analyze the cell apoptosis and cell cycle changes. We assessed the effect of RRM1 gene silencing and paclitaxel on the tumor growth in a nude mouse model bearing subcutaneous xenografts with or without siRNA transfection.

RESULTS

We detected significantly higher expressions of RRM1 at both the mRNA and protein levels in the drug-resistant MCF- 7/R cells than in the parental MCF-7 cells (P &lt; 0.01). Transfection with the specific siRNAs significantly reduced the expression of RRM1 in MCF-7/R cells (P &lt; 0.05), which showed a significantly lower IC₅₀ value of paclitaxel than the cells transfected with the negative control siRNA (P &lt; 0.05). RRM1 silencing significantly inhibited the proliferation (P &lt; 0.01) and enhanced the apoptosis-inducing effect of paclitaxel in MCF-7/R cells (P &lt; 0.001); RRM1 silencing also resulted in obviously reduced Akt phosphorylation, suppressed Bcl-2 expression and promoted the expression of p53 protein in MCF-7/R cells. In the tumor-bearing nude mice, the volume of subcutaneously transplanted tumors was significantly smaller in MCF-7/R/siRNA+ PTX group than in the other groups (P &lt; 0.001).

CONCLUSIONS

RRM1 gene silencing can reverse paclitaxel resistance in human breast cancer cell line MCF-7/R by promoting cell apoptosis.

Cisplatin, glutathione and the third wheel: a copper-(1,10-phenanthroline) complex modulates cisplatin-GSH interactions from antagonism to synergism in cancer cells resistant to cisplatin

The antagonistic effect of glutathione (GSH) against the cytotoxicity of cisplatin was observed in both wild type and cisplatin-resistant human leukaemia and ovarian carcinoma cell lines. The simultaneous presence of the cytotoxic copper complex [Cu(phen)2(OH2)](ClO4)2 (C0) restored the sensitivity of the cells to cisplatin, and, at selected concentrations, led to strong synergistic effects. The C0-cisplatin-glutathione system showed a synergistic toxic effect even in the presence of 1000 μM GSH. The three-drug cocktail exerted a higher potency against leukemic cells than against freshly isolated lymphocytes from healthy donors. Compared to actively proliferating normal lymphocytes, leukaemia cells were much more susceptible to the cytocide effect of the three-drug combination and underwent the dying process(es) much faster. When the ovarian carcinoma cells were treated with cisplatin, alone or in combination with C0, late apoptotic effects were mainly observed, suggesting that DNA interactions with the C0-cisplatin complex trigger a process of programmed cell death. In contrast, the ternary combination induced apoptotic effects similar to that shown by C0 in single treatment, that is, early apoptosis. One possible explanation is that C0 and cisplatin compete for GSH-binding in the culture medium. GSH in combination with C0 and cisplatin caused a significant induction of the apoptotic process(es), through a pathway which does not compromise the integrity of the plasma membrane of cells.

IL-6 mediates platinum-induced enrichment of ovarian cancer stem cells

In high-grade serous ovarian cancer (OC), chemotherapy eliminates the majority of tumor cells, leaving behind residual tumors enriched in OC stem cells (OCSC). OCSC, defined as aldehyde dehydrogenase-positive (ALDH+), persist and contribute to tumor relapse. Inflammatory cytokine IL-6 is elevated in residual tumors after platinum treatment, and we hypothesized that IL-6 plays a critical role in platinum-induced OCSC enrichment. We demonstrate that IL-6 regulates stemness features of OCSC driven by ALDH1A1 expression and activity. We show that platinum induces IL-6 secretion by cancer-associated fibroblasts in the tumor microenvironment, promoting OCSC enrichment in residual tumors after chemotherapy. By activating STAT3 and upregulating ALDH1A1 expression, IL-6 treatment converted non-OCSC to OCSC. Having previously shown altered DNA methylation in OCSC, we show here that IL-6 induces DNA methyltransferase 1 (DNMT1) expression and the hypomethylating agent (HMA) guadecitabine induced differentiation of OCSC and reduced - but did not completely eradicate - OCSC. IL-6 neutralizing antibody (IL-6-Nab) combined with HMA fully eradicated OCSC, and the combination blocked IL-6/IL6-R/pSTAT3-mediated ALDH1A1 expression and eliminated OCSC in residual tumors that persisted in vivo after chemotherapy. We conclude that IL-6 signaling blockade combined with an HMA can eliminate OCSC after platinum treatment, supporting this strategy to prevent tumor recurrence after standard chemotherapy.

Chemoresistance and the Self-Maintaining Tumor Microenvironment

The progression of cancer is associated with alterations in the tumor microenvironment, including changes in extracellular matrix (ECM) composition, matrix rigidity, hypervascularization, hypoxia, and paracrine factors. One key malignant phenotype of cancer cells is their ability to resist chemotherapeutics, and elements of the ECM can promote chemoresistance in cancer cells through a variety of signaling pathways, inducing changes in gene expression and protein activity that allow resistance. Furthermore, the ECM is maintained as an environment that facilitates chemoresistance, since its constitution modulates the phenotype of cancer-associated cells, which themselves affect the microenvironment. In this review, we discuss how the properties of the tumor microenvironment promote chemoresistance in cancer cells, and the interplay between these external stimuli. We focus on both the response of cancer cells to the external environment, as well as the maintenance of the external environment, and how a chemoresistant phenotype emerges from the complex signaling network present.

Kinome-Wide siRNA Screening Identifies Src-Enhanced Resistance of Chemotherapeutic Drugs in Triple-Negative Breast Cancer Cells

Background: Chemotherapy is the main treatment for triple-negative breast cancer (TNBC), which lack molecular markers for diagnosis and therapy. Cancer cells activate chemoresistant pathways and lead to therapeutic failure for patients with TNBC. Several kinases have been identified as chemoresistant genes. However, the involvement of kinases in the chemoresistance in TNBC cells is not fully understood.

Methods: We employed a kinome siRNA library to screen whether targeting any kinases could increase the chemosensitivity of TNBC cell lines. The effects of kinase on cell viability in various breast cancer cells were validated with ATP level and colony formation. Protein expression and phosphorylation were determined by immunoblotting. The Cancer Genome Atlas (TCGA) dataset was collected to analyze the correlation of Src expression with prognosis of TNBC patients.

Results: Primary screening and validation for the initial hits showed that Src kinase was a potential doxorubicin-resistant kinase in the TNBC cell lines MDA-MB-231 and Hs578T. Both siRNA against Src and the Src inhibitor dasatinib enhanced the cytotoxic effects of doxorubicin in TNBC cells. Moreover, phosphorylation of AKT and signal transducer and activator of transcription 3 (STAT3), downstream effectors of Src, were accordingly decreased in Src-silenced or -inhibited TNBC cells. Additionally, TCGA data analysis indicated that Src expression levels in tumor tissues were higher than those in tumor-adjacent normal tissues in patients with TNBC. High co-expression level of Src and STAT3 was also significantly correlated with poor prognosis in patients.

Conclusion: Our results showed that Src-STAT3 axis might be involved in chemoresistance of TNBC cells.

MSCs inhibit tumor progression and enhance radiosensitivity of breast cancer cells by down-regulating Stat3 signaling pathway

The acquisition of radioresistance by breast cancer cells during radiotherapy may lead to cancer recurrence and poor survival. Signal transducer and activator of transcription 3 (Stat3) is activated in breast cancer cells and, therefore, may be an effective target for overcoming therapeutic resistance. Mesenchymal stem cells (MSCs) have been investigated for use in cancer treatment. Here, we investigated the potential of MSC conditioned medium (MSC-CM) in sensitizing breast cancer to radiotherapy. It was found that MSC-CM could inhibit the level of activated Stat3, suppress cancer growth, and exhibit synergetic effects with radiation treatment in vitro and in vivo. Furthermore, MSC-CM reduced the ALDH-positive cancer stem cells (CSCs) population, modulated several potential stem cell markers, and decreased tumor migration, as well as metastasis. These results demonstrate that MSC-CM suppresses breast cancer cells growth and sensitizes cancer cells to radiotherapy through inhibition of the Stat3 signaling pathway, thus, providing a novel strategy for breast cancer therapy by overcoming radioresistance.

Growth of ovarian cancer xenografts causes loss of muscle and bone mass: a new model for the study of cancer cachexia

BACKGROUND

Cachexia frequently occurs in women with advanced ovarian cancer (OC), along with enhanced inflammation. Despite being responsible for one third of all cancer deaths, cachexia is generally under-studied in OC due to a limited number of pre-clinical animal models. We aimed to address this gap by characterizing the cachectic phenotype in a mouse model of OC.

METHODS

Nod SCID gamma mice (n = 6-10) were injected intraperitoneally with 1 × 107 ES-2 human OC cells to mimic disseminated abdominal disease. Muscle size and strength, as well as bone morphometry, were assessed. Tumour-derived effects on muscle fibres were investigated in C2C12 myotube cultures. IL-6 levels were detected in serum and ascites from tumour hosts, as well as in tumour sections.

RESULTS

In about 2 weeks, ES-2 cells developed abdominal tumours infiltrating omentum, mesentery, and adjacent organs. The ES-2 tumours caused severe cachexia with marked loss of body weight (-12%, P < 0.01) and ascites accumulation in the peritoneal cavity (4.7 ± 1.5 mL). Skeletal muscles appeared markedly smaller in the tumour-bearing mice (approximately -35%, P < 0.001). Muscle loss was accompanied by fibre atrophy, consistent with reduced muscle cross-sectional area (-34%, P < 0.01) and muscle weakness (-50%, P < 0.001). Body composition assessment by dual-energy X-ray absorptiometry revealed decreased bone mineral density (-8%, P < 0.01) and bone mineral content (-19%, P < 0.01), also consistent with reduced trabecular bone in both femurs and vertebrae, as suggested by micro-CT imaging of bone morphometry. In the ES-2 mouse model, cachexia was also associated with high tumour-derived IL-6 levels in plasma and ascites (26.3 and 279.6 pg/mL, respectively) and with elevated phospho-STAT3 (+274%, P < 0.001), reduced phospho-AKT (-44%, P < 0.001) and decreased mitochondrial proteins, as well as with increased protein ubiquitination (+42%, P < 0.001) and expression of ubiquitin ligases in the skeletal muscle of tumour hosts. Similarly, ES-2 conditioned medium directly induced fibre atrophy in C2C12 mouse myotubes (-16%, P < 0.001), consistent with elevated phospho-STAT3 (+1.4-fold, P < 0.001) and altered mitochondrial homoeostasis and metabolism, while inhibition of the IL-6/STAT3 signalling by means of INCB018424 was sufficient to restore the myotubes size.

CONCLUSIONS

Our results suggest that the development of ES-2 OC promotes muscle atrophy in both in vivo and in vitro conditions, accompanied by loss of bone mass, enhanced muscle protein catabolism, abnormal mitochondrial homoeostasis, and elevated IL-6 levels. Therefore, this represents an appropriate model for the study of OC cachexia. Our model will aid in identifying molecular mediators that could be effectively targeted in order to improve muscle wasting associated with OC.

Targeting tumor microenvironment to curb chemoresistance via novel drug delivery strategies

INTRODUCTION

Tumor is a heterogeneous mass of malignant cells co-existing with non-malignant cells. This co-existence evolves from the initial developmental stages of the tumor and is one of the hallmarks of cancer providing a protumorigenic niche known as tumor microenvironment (TME). Proliferation, invasiveness, metastatic potential and maintenance of stemness through cross-talk between tumors and its stroma forms the basis of TME.

AREAS COVERED

The article highlights the developmental phases of a tumor from dysplasia to the formation of clinically detectable tumors. The authors discuss the mechanistic stages involved in the formation of TME and its contribution in tumor outgrowth and chemoresistance. The authors have reviewed various approaches for targeting TME and its hallmarks along with their advantages and pitfalls. The authors also highlight cancer stem cells (CSCs) that are resistant to chemotherapeutics and thus a primary reason for tumor recurrence thereby, posing a challenge for the oncologists.

EXPERT OPINION

Recent understanding of the cellular and molecular mechanisms involved in acquired chemoresistance has enabled scientists to target the tumor niche and TME and modulate and/or disrupt this communication leading to the transformation from a tumor-supportive niche environment to a tumor-non-supporting environment and give synergistic results towards an effective management of cancer.

miR-199a modulates cisplatin resistance in ovarian cancer by targeting Hif1α

Resistance to chemotherapy is a primary problem for the effective treatment of ovarian cancer. Recently, increasing evidence has demonstrated that miRNAs modulate many important molecular pathways involved in chemotherapy. Previous studies demonstrated that miR-199a affected ovarian cancer cell resistance to cisplatin (DDP). However, the role of miR-199a and its target genes in determination of ovarian cancer sensitivity to DDP remains unclear. Quantitative reverse transcription polymerase chain reaction was used to detect the expression levels of miR-199a in ovarian cancer tissues and C13* and OV2008 cell lines. After transfection of miR-199a mimic or inhibitor, flow cytometry was used to detect cell apoptosis exposed to DDP. Enzyme-linked immunosorbent assay and Western blot assay were applied to detect tumor necrosis factor-α levels and protein expression levels of Bax, Fas, Fas-associated death domain, and caspase-8. The results indicated that the expression of miR-199a was downregulated and hypoxia-inducible factor 1α (Hif1α) upregulated in the ovarian tumors compared with those in the corresponding normal tissues. Besides, the expression levels of miR-199a were significantly higher in OV2008 cells compared with those in C13* cells. Moreover, suppression of Hif1α reversed the inhibiting function of miR-199a inhibitor on DDP-induced apoptosis in the OV2008 cells. However, overexpression of both miR-199a and Hif1α reduced DDP-induced apoptosis in C13* cells. In conclusion, miR-199a may change DDP resistance in ovarian cancer by regulating Hif1α.

MicroRNA-519a inhibits the proliferation and promotes the apoptosis of ovarian cancer cells through targeting signal transducer and activator of transcription 3

Ovarian cancer is a highly prevalent cancer among women. Recent studies have indicated that microRNAs (miRs) may serve important roles in the pathogenesis of ovarian cancer. miR-519a was observed to be downregulated in tissue samples of patients with ovarian cancer; however, its role in ovarian cancer requires further investigation. The aim of the present study was to examine the role of miR-519a in the pathogenesis of ovarian cancer and determine its direct target. Reverse transcription-quantitative polymerase chain reaction (RT-qPCR) was performed to examine the expression of miR-519a in 20 patients ovarian cancer and 20 normal ovarian tissue samples. Subsequently, SKOV3 cells were cultured and transfected with miR-519a mimics, while MTT and Annexin V assays were performed to investigate the role of miR-519a in the proliferation and apoptosis of SKOV3 cells. In addition, RT-qPCR and western blotting were used to determine the expression levels of miR-519a, signal transducer and activator of transcription 3 (STAT3), myeloid cell leukemia 1 (Mcl-1) and B-cell lymphoma-extra large (Bcl-xl) in untransfected and miR-519a mimic-transfected SKOV3 cells. Dual-luciferase reporter assay was also performed to confirm whether STAT3 was a direct target of miR-519a. The results revealed that miR-519a was significantly downregulated in tissue samples of patients with ovarian cancer as compared with the normal ovarian tissues. Furthermore, transient overexpression of miR-519a inhibited the proliferation and promoted the apoptosis of SKOV3 cells, as well as decreased the mRNA and protein expression levels of STAT3, Mcl-1 and Bcl-xl. Finally, dual-luciferase reporter assay confirmed that STAT3 was a direct target of miR-519a. In conclusion, the present study proved for the first time that miR-519a functions as a tumor suppressor by targeting STAT3 in ovarian cancer, suggesting that miR-519a may be a potential biomarker for the diagnosis and treatment of ovarian cancer.

Physapubescin B inhibits tumorgenesis and circumvents taxol resistance of ovarian cancer cells through STAT3 signaling

Ovarian cancer is the most lethal gynaecological malignancy. Recurrence and subsequent resistance to chemotherapy have become major obstacles to treating these diseases. In the present study, we showed that a natural withanolide isolated from the plant Physalis pubescens L. (Solanaceae), Physapubescin B, exhibited potent anti-tumor activity against ovarian cancer cells. Physapubescin B promoted apoptosis, induced cell-cycle arrest and inhibited invasion of ES-2 and A2780 cells. Physapubescin B treatment also resulted in suppression of the transcriptional activity of STAT3, an oncogenic transcription factor activated in many human malignancies including ovarian cancer, through disturbing the dimerization of STAT3, and thereby inhibited the nuclear translocation of Tyr705/Ser727-phosphorylated STAT3. The IL-6-stimulated activation of STAT3 and its downstream genes Cyclin D1, survivin, and Bcl-xL was also repressed by Physapubescin B. Furthermore, Physapubescin B sensitizes A2780 cells to taxol-induced cell growth inhibition in vitro. These findings strongly suggest that Physapubescin B has potential antitumor activity and may circumvent taxol resistance in human ovarian cancer cells through inhibition of aberrant activation of STAT3.

Sphingosine-1-Phosphate Receptor-1 Promotes Environment-Mediated and Acquired Chemoresistance

Drug resistance is a major barrier for the development of effective and durable cancer therapies. Overcoming this challenge requires further defining the cellular and molecular mechanisms underlying drug resistance, both acquired and environment-mediated drug resistance (EMDR). Here, using neuroblastoma (NB), a childhood cancer with high incidence of recurrence due to resistance to chemotherapy, as a model we show that human bone marrow-mesenchymal stromal cells induce tumor expression of sphingosine-1-phosphate receptor-1 (S1PR1), leading to their resistance to chemotherapy. Targeting S1PR1 by shRNA markedly enhances etoposide-induced apoptosis in NB cells and abrogates EMDR, while overexpression of S1PR1 significantly protects NB cells from multidrug-induced apoptosis via activating JAK-STAT3 signaling. Elevated S1PR1 expression and STAT3 activation are also observed in human NB cells with acquired resistance to etoposide. We show in vitro and in human NB xenograft models that treatment with FTY720, an FDA-approved drug and antagonist of S1PR1, dramatically sensitizes drug-resistant cells to etoposide. In summary, we identify S1PR1 as a critical target for reducing both EMDR and acquired chemoresistance in NB. Mol Cancer Ther; 16(11); 2516-27. ©2017 AACR.

Dovitinib enhances temozolomide efficacy in glioblastoma cells

The multikinase inhibitor and FDA‐approved drug dovitinib (Dov) crosses the blood–brain barrier and was recently used as single drug application in clinical trials for GB patients with recurrent disease. The Dov‐mediated molecular mechanisms in GB cells are unknown. We used GB patient cells and cell lines to show that Dov downregulated the stem cell protein Lin28 and its target high‐mobility group protein A2 (HMGA2). The Dov‐induced reduction in pSTAT3^Tyr705 phosphorylation demonstrated that Dov negatively affects the STAT3/LIN28/Let‐7/HMGA2 regulatory axis in GB cells. Consistent with the known function of LIN28 and HMGA2 in GB self‐renewal, Dov reduced GB tumor sphere formation. Dov treatment also caused the downregulation of key base excision repair factors and O⁶‐methylguanine‐DNA‐methyltransferase (MGMT), which are known to have important roles in the repair of temozolomide (TMZ)‐induced alkylating DNA damage. Combined Dov/TMZ treatment enhanced TMZ‐induced DNA damage as quantified by nuclear γH2AX foci and comet assays, and increased GB cell apoptosis. Pretreatment of GB cells with Dov (‘Dov priming’) prior to TMZ treatment reduced GB cell viability independent of p53 status. Sequential treatment involving ‘Dov priming’ and alternating treatment cycles with TMZ and Dov substantially reduced long‐term GB cell survival in MGMT+ patient GB cells. Our results may have immediate clinical implications to improve TMZ response in patients with LIN28⁺/HMGA2⁺GB, independent of their MGMT methylation status.

The anti-oxidant and pro-oxidant dichotomy of Bcl-2

Across a wide spectrum of cellular redox status, there emerges a dichotomy of responses in terms of cell survival/proliferation and cell death. Of note, there is emerging evidence that the anti-apoptotic protein, Bcl-2, in addition to its conventional activity of titrating the pro-apoptotic effects of proteins such as Bax and Bak at the mitochondria, also impacts cell fate decisions via modulating cellular redox metabolism. In this regard, both pro- and anti-oxidant effects of Bcl-2 overexpression have been described under different conditions and cellular contexts. In this short review, we attempt to analyze existing observations and present a probable explanation for the seemingly conflicting redox regulating activity of Bcl-2 from the standpoint of its pro-survival function. The consequential effect(s) of the dual redox functions of Bcl-2 are also discussed, particularly from the viewpoint of developing novel therapeutic strategies against cancers rendered refractory due to the aberrant expression of Bcl-2.

Molecular diagnosis and molecular profiling to detect treatment-resistant ovarian cancer

INTRODUCTION

Epithelial ovarian cancer remains the gynecologic tumor with the highest rate of recurrence after initial optimal cytoreductive surgery followed by adjuvant chemotherapy. Unfortunately, with the development of recurrent ovarian cancer often comes the discovery of chemo-resistant disease. The absence of improvement in long term survival, notwithstanding the use of newer agents as is seen in other cancers, emphasizes the need for improved understanding of the processes that lead to chemo-resistant disease.

AREAS COVERED

This review will cover the following topics: 1. Molecular and cellular mechanisms in platinum and paclitaxel resistance 2. Other molecular mediators of chemo-resistance 3. Expression of stem cell markers in ovarian cancer and relationship to chemo-resistance 4. MicroRNA and long non-coding RNA expression in chemo-resistant ovarian cancer 5. Determination of chromosomal aberrations as markers of chemo-resistance 6. Molecular profiling in chemo-resistant disease. A standard MEDLINE search was performed using the key words; ovarian cancer, chemo-resistant disease, molecular profiling, cancer stem cells and chemotherapy. Expert Commentary: Over the next few years the challenge remains to precisely determine the mechanisms responsible for the onset and maintenance of chemo-resistance and to effectively target these mechanisms.

A STAT3-NFkB/DDIT3/CEBPβ axis modulates ALDH1A3 expression in chemoresistant cell subpopulations

Here we studied the relevance and modulation of aldehyde dehydrogenase (ALDH) expression in malignant pleural mesothelioma (MPM) chemoresistant cell subpopulations (ALDH^bright cells), which survive pemetrexed + cisplatin treatment in vitro and in vivo. Expression of the ALDH1A3 isoform was invariably enriched in purified ALDH^bright cells from multiple MPM cell lines and accounted for the enzymatic activity of those cells. RNAi mediated downregulation of ALDH1A3 reduced the survival of the ALDH^bright cells at steady state and, much more, after pemetrexed + cisplatin treatment. We demonstrated, for the first time, that a pSTAT3(tyr705)-NFkB(p65) complex is required for the repression of DDIT3 mRNA and this ensures high levels of CEBPβ-dependent ALDH1A3 promoter activity. Inhibition of STAT3-NFkB activity allowed high levels of DDIT3 expression with increased formation of a DDIT3-CEBPβ complex. This reduced the occupancy of the ALDH1A3 promoter by CEBPβ, thus largely reducing the ALDH1A3 expression. Consequently, survival of ALDH^bright cells in pemetrexed + cisplatin-treated cultures was impaired, following increased apoptosis. We show that such a mechanism is relevant in vivo and underlies the action of butein, a dual STAT3-NFkB inhibitor capable of abating the chemoresistance of mesothelioma cells in vivo. The possible broad translational relevance of the described mechanism is discussed.

Cisplatin-induced CCL5 secretion from CAFs promotes cisplatin-resistance in ovarian cancer via regulation of the STAT3 and PI3K/Akt signaling pathways

Currently, acquired resistance to cisplatin (DDP) is a substantial obstacle to reducing the morbidity and mortality due to ovarian malignant tumors. Nevertheless, cisplatin plays a vital role in killing the tumor cells while it may also be a 'primer' involved in chemotherapy resistance. We found that the cisplatin-induced chemokine (C-C motif) ligand 5 (CCL5) secretion derived from cancer-associated fibroblasts (CAFs) promoted ovarian cancer cell resistance to cisplatin. Via a cytokine chip assay, we identified a spectrum of secreted proteins that were derived from the CAFs through cisplatin-induced treatment. Among these, CCL5 significantly attenuated the cytotoxic effect of cisplatin chemotherapy in vitro and in vivo. Additionally, CCL5 expression was also detected in 62 serous ovarian cancer patient tissue specimens using IHC, and the results demonstrated that chemotherapy resistant patients displayed higher expression of CCL5 than the chemo-sensitive patients (P<0.05). Mechanistically, we found that CCL5 notably increased STAT3 and Akt phosphorylation levels in ovarian cancer cells. These results indicated that cisplatin- induced CCL5 secretion derived from the CAFs may promote cisplatin resistance, which was mediated by regulation of the STAT3 and PI3K/Akt signal pathways.

Significance of Interleukin-6 in Papillary Thyroid Carcinoma

This study sought to reveal the significance of IL-6 in papillary thyroid carcinoma by determining its circulating levels, tumoral protein, and mRNA expressions. As compared to the healthy individuals, serum IL-6 was significantly higher in patients with benign thyroid diseases and PTC. Further, its level was significantly higher in PTC patients as compared to patients with benign thyroid diseases. ROC curves also confirmed a good discriminatory efficacy of serum IL-6 between healthy individuals and patients with benign thyroid diseases and PTC. The circulating IL-6 was significantly associated with poor overall survival in PTC patients. IL-6 immunoreactivity was significantly high in PTC patients as compared to the benign thyroid disease patients. Significantly higher IL-6 mRNA expression was also observed in the primary tumour tissues of PTC patients than the adjacent normal tissues. The protein expression of IL-6 at both the circulating and tissue level correlated with disease aggressiveness in PTC patients. Moreover, a significant positive correlation was observed between the IL-6 protein and mRNA expression in the primary tumours of PTC patients. Finally in conclusion, IL-6 has an important role in thyroid cancer progression. Thus targeting IL-6 signalling can help in clinical management of thyroid carcinoma patients.

Mitochondrial Stat3, the Need for Design Thinking

Stat3 has been studied extensively as a transcription factor, however the finding that Stat3 also localizes to mitochondria has opened a new area to discover non-classical functions. Here we review the current knowledge of mitochondrial Stat3 as a regulator of the electron transport chain (ETC) and its impact on mitochondrial production of ATP and ROS. We also describe recent findings identifying Stat3 as a regulator of mitochondrial Ca(2+) homeostasis through its effect on the ETC. It is becoming evident that these non-classical functions of Stat3 can have a major impact on cancer progression, cardiovascular diseases, and inflammatory diseases. Therefore, mitochondrial Stat3 functions challenge the current design of therapies that solely target Stat3 as a transcription factor and suggest the need for "design thinking," which leads to the development of novel strategies, to intervene the Stat3 pathway.

Cancer-associated fibroblasts attenuate Cisplatin-induced apoptosis in ovarian cancer cells by promoting STAT3 signaling

One of the main reasons for treatment failure in ovarian cancer is acquired drug resistance. Cancer associated fibroblasts (CAFs) are known to enhance chemoresistance in many human tumors. However, its contributions to chemoresistance acquisition in ovarian cancer are not well understood. Here, we provide the first evidence that the conditioned medium of CAFs (CAFs-CM) could attenuate the sensitivity to Cisplatin in A2780 and ES2 ovarian cancer cells and protect them from Cisplatin-induced apoptosis. We found the expression level of two anti-apoptotic proteins, Bcl-2 and Survivin, as well as their upstream controller p-STAT3 were significantly increased when ovarian cancer cells were exposed to CAFs-CM. Furthermore, inhibition of STAT3 signaling with Cryptotanshinone could down-regulate the expression of Bcl-2 and Survivin, thus weaken the post-target resistance to Cispaltin mediating by CAFs-CM in ovarian cancer cells. In conclusion, our data suggested that CAFs could activate the anti-apoptotic STAT3 signaling, thereby decrease the Cisplatin-induced apoptosis and promote chemoresistance in ovarian cancer.

Leukotriene B4 receptor-2 contributes to chemoresistance of SK-OV-3 ovarian cancer cells through activation of signal transducer and activator of transcription-3-linked cascade

Inflammation and inflammatory mediators are intimately linked with chemoresistance through complex pathways in the tumor microenvironment. However, the mechanism by which inflammatory mediators (e.g., eicosanoids) contribute to chemoresistance remains elusive. In this study, we found that the low-affinity leukotriene B4 receptor-2 (BLT2) and its ligand leukotriene B4 were highly up-regulated in cisplatin-resistant SK-OV-3 ovarian cancer cells and play critical roles in mediating the chemoresistance through the activation of signal transducer and activator of transcription-3 (STAT-3) and the subsequent up-regulation of interleukin-6 (IL-6). BLT2 depletion with siRNA clearly abolished the chemoresistance to cisplatin in SK-OV-3 ovarian cancer cells and further increased cell sensitivity to cisplatin chemotherapy by down-regulating the 'STAT-3-IL-6' cascade. Enlarged tumor formation due to the cisplatin resistance of SK-OV-3 cells in cisplatin-treated athymic mice was also substantially reduced by co-treatment with the BLT2 inhibitor in vivo. Our study demonstrates that BLT2 is a novel contributor to cisplatin resistance in SK-OV-3 ovarian cancer cells and thus may be a potential therapeutic target for the treatment of cisplatin-resistant ovarian cancer.

Overcoming Chemoresistance of Pediatric Ependymoma by Inhibition of STAT3 Signaling

The long-term clinical outcome of pediatric intracranial epepdymoma is poor with a high rate of recurrence. One of the main reasons for this poor outcome is the tumor’s inherent resistance to chemotherapy. Signal transducer and activator of transcription 3 (STAT3) is overactive in many human cancers, and inhibition of STAT3 signaling is an emerging area of interest in oncology. In this study, the possibility of STAT3 inhibition as a treatment was investigated in pediatric intracranial ependymoma tissues and cell lines. STAT3 activation status was checked in ependymoma tissues. The responses to conventional chemotherapeutic agents and a STAT3 inhibitor WP1066 in primarily cultured ependymoma cells were measured by cell viability assay. Apoptosis assays were conducted to reveal the cytotoxic mechanism of applied agents. Knockdown of STAT3 was tried to confirm the effects of STAT3 inhibition in ependymoma cells. High levels of phospho-STAT3 (p-STAT3) expression were observed in ependymoma tissue, especially in the anaplastic histology group. There was no cytotoxic effect of cisplatin, ifosfamide, and etoposide. Both brain tumor-initiating cells (BTICs) and bulk tumor cells (BCs) showed considerably decreased viability after WP1066 treatment. However, BTICs had fewer responses than BCs. No additive or synergistic effect was observed for combination therapy of WP1066 and cisplatin. WP1066 effectively abrogated p-STAT3 expression. An increased apoptosis and decreased Survivin expression were observed after WP1066 treatment. Knockdown of STAT3 also decreased cell survival, supporting the critical role of STAT3 in sustaining ependymoma cells. In this study, we observed a cytotoxic effect of STAT3 inhibitor on ependymoma BTICs and BCs. There is urgent need to develop new therapeutic agents for pediatric ependymoma. STAT3 inhibitors may be a new group of drugs for clinical application.