STAT proteins: novel molecular targets for cancer drug discovery

Assessment of drug delivery and anticancer potentials of nanoparticles-loaded siRNA targeting STAT3 in lung cancer, in vitro and in vivo

Activation of signal transducer and activator of transcription3 (STAT3) is a hallmark of several types of cancer. Failure to inhibit STAT3 expression by injection of siRNA for STAT3 directly to Balb/c mice led us to adopt alternative means. We formulated nanoparticle-based encapsulation of siRNA (NsiRNA) with polyethylenimine (PEI) and poly(lactide-co-glycolide) (PLGA) and characterized them. The siRNA treated and NsiRNA-treated cells were subjected separately to different assay systems. We also checked if NsiRNA could cross the blood brain barrier (BBB). Cell viability reduced dramatically in A549 cells after NsiRNA administration (23.89% at 24 h), thereby implicating considerable silencing of STAT3 by NsiRNA, but not after siRNA administration. Compared to controls, a significant decrease in expression of IL-6 and the angiogenic factor (VEGF) and increase in Caspase 3 activity was observed with corresponding regression in tumor growth in mice treated with NsiRNA. NsiRNA induced apoptosis of cells and arrested cells at G1/G0 stage, both in vitro and in vivo. Apoptosis was also verified by Annexin-V-FITC/Propidium-iodide staining. NsiRNA could cross blood brain barrier. Overall results revealed PEI-PLGA to be a promising carrier for delivery of siRNA targeting STAT3 expression, which can be utilized as an effective strategy for cancer therapy.

Novel inhibitors of signal transducer and activator of transcription 3 signaling pathway: an update on the recent patent literature

INTRODUCTION

The signal transducer and activator of transcription 3 (STAT3) is a transcription factor that plays a key role in normal cell growth and is constitutively activated in about 70% of solid and hematological cancers. Thus, the development of potent and selective inhibitors that target STAT3 is of interest especially in the cancer therapeutic area.

AREAS COVERED

This review updates new patents claiming STAT3 inhibitors and their uses published from 2011 to 2013. Pre-2011 patents have been extensively covered in previous reviews. Comments on the context of each chemical series are given where applicable to orientate the readers on the bewildering array of molecular designs now available.

EXPERT OPINION

The growing number of preclinical studies in numerous malignances as well as the first clinical trials of STAT3 inhibitors suggest that STAT3 remains a valid target for the treatment of human cancers as well as inflammatory diseases and/or autoimmune disorders. So, the future looks bright for patients because many new drugs are being developed and now combinations of STAT3 inhibitors with other targeted agents can diminish the resistance to traditional chemotherapy. These advances are expected to lead to further significant progress improving patient outcomes and quality of life.

Honokiol inhibits epithelial-mesenchymal transition in breast cancer cells by targeting signal transducer and activator of transcription 3/Zeb1/E-cadherin axis

Epithelial-mesenchymal transition (EMT), a critical step in the acquisition of metastatic state, is an attractive target for therapeutic interventions directed against tumor metastasis. Honokiol (HNK) is a natural phenolic compound isolated from an extract of seed cones from Magnolia grandiflora. Recent studies from our lab show that HNK impedes breast carcinogenesis. Here, we provide molecular evidence that HNK inhibits EMT in breast cancer cells resulting in significant downregulation of mesenchymal marker proteins and concurrent upregulation of epithelial markers. Experimental EMT induced by exposure to TGFβ and TNFα in spontaneously immortalized nontumorigenic human mammary epithelial cells is also completely reversed by HNK as evidenced by morphological as well as molecular changes. Investigating the downstream mediator(s) that may direct EMT inhibition by HNK, we found functional interactions between HNK, Stat3, and EMT-signaling components. In vitro and in vivo analyses show that HNK inhibits Stat3 activation in breast cancer cells and tumors. Constitutive activation of Stat3 abrogates HNK-mediated activation of epithelial markers whereas inhibition of Stat3 using small molecule inhibitor, Stattic, potentiates HNK-mediated inhibition of EMT markers, invasion and migration of breast cancer cells. Mechanistically, HNK inhibits recruitment of Stat3 on mesenchymal transcription factor Zeb1 promoter resulting in decreased Zeb1 expression and nuclear translocation. We also discover that HNK increases E-cadherin expression via Stat3-mediated release of Zeb1 from E-cadherin promoter. Collectively, this study reports that HNK effectively inhibits EMT in breast cancer cells and provide evidence for a previously unrecognized cross-talk between HNK and Stat3/Zeb1/E-cadherin axis.

Targeting the STAT3 signaling pathway in cancer: role of synthetic and natural inhibitors

Signal transducers and activators of transcription (STATs) comprise a family of cytoplasmic transcription factors that mediate intracellular signaling that is usually generated at cell surface receptors and thereby transmit it to the nucleus. Numerous studies have demonstrated constitutive activation of STAT3 in a wide variety of human tumors, including hematological malignancies (leukemias, lymphomas, and multiple myeloma) as well as diverse solid tumors (such as head and neck, breast, lung, gastric, hepatocellular, colorectal and prostate cancers). There is strong evidence to suggest that aberrant STAT3 signaling promotes initiation and progression of human cancers by either inhibiting apoptosis or inducing cell proliferation, angiogenesis, invasion, and metastasis. Suppression of STAT3 activation results in the induction of apoptosis in tumor cells, and accordingly its pharmacological modulation by tyrosine kinase inhibitors, antisense oligonucleotides, decoy nucleotides, dominant negative proteins, RNA interference and chemopreventive agents have been employed to suppress the proliferation of various human cancer cells in culture and tumorigenicity in vivo. However, the identification and development of novel drugs that can target deregulated STAT3 activation effectively remains an important scientific and clinical challenge. This review presents the evidence for critical roles of STAT3 in oncogenesis and discusses the potential for development of novel cancer therapies based on mechanistic understanding of STAT3 signaling cascade.

Constitutive activation of STAT3 signaling regulates hTERT and promotes stem cell-like traits in human breast cancer cells

Mounting clinical data suggest that high telomerase activity is tightly associated with cancer progression and poor outcomes. Constitutively activated STAT3 is found in ∼60% of human malignancies and shows a dismal prognosis. We previously reported that activated STAT3 promoted epithelial-mesenchymal transition (EMT) and cancer stem cell phenotype in human breast cancer. However, little is known how STAT3 is regulated in the cancer stem cell and by which mechanisms STAT3 contributes to poor prognosis in aggressive breast cancer. Here we demonstrate that STAT3 physically interacts with CD44 and NF-kB and activates the catalytic subunit of telomerase (hTERT) in human breast cancer stem cells. STAT3 plays a role as a signal transducing molecule between CD44 and NF-kB. In addition to functioning as a catalytic subunit of telomerase, hTERT has been reported to function as a transcription co-factor which drives EMT and cancer stem cell phenotype in human cancer. We observed that activated hTERT increases CD44 (+) subpopulation, whereas targeted knock-down of hTERT abolished cancer stem cell phenotype. Targeted STAT3 knock-down cells also down-regulated hTERT and decreased CD44 subpopulation. Finally, CD44 knock-down resulted in the abrogation of cancer stem cell phenotype and concurrent down-regulation of pSTAT3 and hTERT. Our study delineates the signaling pathway where STAT3 functions as a modulator for CD44 and hTERT, promoting a cancer stem cell phenotype. The constitutive activation of STAT3 signaling that leads to regulation of hTERT pathway may provide novel therapeutic targets for human breast cancer stem cells.

Evaluation of STAT3 signaling in ALDH+ and ALDH+/CD44+/CD24- subpopulations of breast cancer cells

BACKGROUND

STAT3 activation is frequently detected in breast cancer and this pathway has emerged as an attractive molecular target for cancer treatment. Recent experimental evidence suggests ALDH-positive (ALDH(+)), or cell surface molecule CD44-positive (CD44(+)) but CD24-negative (CD24(-)) breast cancer cells have cancer stem cell properties. However, the role of STAT3 signaling in ALDH(+) and ALDH(+)/CD44(+)/CD24(-) subpopulations of breast cancer cells is unknown.

METHODS AND RESULTS

We examined STAT3 activation in ALDH(+) and ALDH(+)/CD44(+)/CD24(-) subpopulations of breast cancer cells by sorting with flow cytometer. We observed ALDH-positive (ALDH(+)) cells expressed higher levels of phosphorylated STAT3 compared to ALDH-negative (ALDH(-)) cells. There was a significant correlation between the nuclear staining of phosphorylated STAT3 and the expression of ALDH1 in breast cancer tissues. These results suggest that STAT3 is activated in ALDH(+) subpopulations of breast cancer cells. STAT3 inhibitors Stattic and LLL12 inhibited STAT3 phosphorylation, reduced the ALDH(+) subpopulation, inhibited breast cancer stem-like cell viability, and retarded tumorisphere-forming capacity in vitro. Similar inhibition of STAT3 phosphorylation, and breast cancer stem cell viability were observed using STAT3 ShRNA. In addition, LLL12 inhibited STAT3 downstream target gene expression and induced apoptosis in ALDH(+) subpopulations of breast cancer cells. Furthermore, LLL12 inhibited STAT3 phosphorylation and tumor cell proliferation, induced apoptosis, and suppressed tumor growth in xenograft and mammary fat pad mouse models from ALDH(+) breast cancer cells. Similar in vitro and tumor growth in vivo results were obtained when ALDH(+) cells were further selected for the stem cell markers CD44(+) and CD24(-).

CONCLUSION

These studies demonstrate an important role for STAT3 signaling in ALDH(+) and ALDH(+)/CD44(+)/CD24(-) subpopulations of breast cancer cells which may have cancer stem cell properties and suggest that pharmacologic inhibition of STAT3 represents an effective strategy to selectively target the cancer stem cell-like subpopulation.

Therapeutic modulators of STAT signalling for human diseases

The signal transducer and activator of transcription (STAT) proteins have important roles in biological processes. The abnormal activation of STAT signalling pathways is also implicated in many human diseases, including cancer, autoimmune diseases, rheumatoid arthritis, asthma and diabetes. Over a decade has passed since the first inhibitor of a STAT protein was reported and efforts to discover modulators of STAT signalling as therapeutics continue. This Review discusses the outcomes of the ongoing drug discovery research endeavours against STAT proteins, provides perspectives on new directions for accelerating the discovery of drug candidates, and highlights the noteworthy candidate therapeutics that have progressed to clinical trials.

Mild oxidative stress induces S-glutathionylation of STAT3 and enhances chemosensitivity of tumoural cells to chemotherapeutic drugs

STAT3 is a transcription factor constitutively activated in a variety of cancers that has a critical role in the inhibition of apoptosis and induction of chemoresistance. Inhibition of the STAT3 signaling pathway suppresses cell survival signals and leads to apoptosis in cancer cells, suggesting that direct inhibition of STAT3 function is a viable therapeutic approach. Herein, we identify the naturally occurring sesquiterpene lactone cynaropicrin as a potent inhibitor of both IL-6-inducible and constitutive STAT3 activation (IC50=12 μM). Cynaropicrin, which contains an α-β-unsaturated carbonyl moiety and acts as potent Michael reaction acceptor, induces a rapid drop in intracellular glutathione (GSH) concentration, thereby triggering S-glutathionylation of STAT3. Furthermore, glutathione ethylene ester, the cell permeable form of GSH, reverts the inhibitory action of cynaropicrin on STAT3 tyrosine phosphorylation. These findings suggest that this sesquiterpene lactone is able to induce redox-dependent post-translational modification of cysteine residues of STAT3 protein to regulate its function. STAT3 inhibition led to the suppression of two anti-apoptotic genes, Bcl-2 and survivin, in DU145 cells that constitutively express active STAT3. This event may be responsible for the decline in cell viability after cynaropicrin treatment. As revealed by PI/annexin-V staining, PARP cleavage, and DNA ladder formation, cynaropicrin cytotoxicity is mediated by apoptosis. Finally, cynaropicrin displayed a slight to strong synergism with two well-established chemotherapeutic drugs, cisplatin and docetaxel. Taken together our studies suggest that cynaropicrin suppresses the STAT3 pathway, leading to the down-regulation of STAT3-dependent gene expression and chemosensitization of tumour cells to chemotherapy.

PAK-dependent STAT5 serine phosphorylation is required for BCR-ABL-induced leukemogenesis

The transcription factor STAT5 (signal transducer and activator of transcription 5) is frequently activated in hematological malignancies and represents an essential signaling node downstream of the BCR-ABL oncogene. STAT5 can be phosphorylated at three positions, on a tyrosine and on the two serines S725 and S779. We have investigated the importance of STAT5 serine phosphorylation for BCR-ABL-induced leukemogenesis. In cultured bone marrow cells, expression of a STAT5 mutant lacking the S725 and S779 phosphorylation sites (STAT5(SASA)) prohibits transformation and induces apoptosis. Accordingly, STAT5(SASA) BCR-ABL(+) cells display a strongly reduced leukemic potential in vivo, predominantly caused by loss of S779 phosphorylation that prevents the nuclear translocation of STAT5. Three distinct lines of evidence indicate that S779 is phosphorylated by group I p21-activated kinase (PAK). We show further that PAK-dependent serine phosphorylation of STAT5 is unaffected by BCR-ABL tyrosine kinase inhibitor treatment. Interfering with STAT5 phosphorylation could thus be a novel therapeutic approach to target BCR-ABL-induced malignancies.

Targeting apoptosis pathways in cancer with alantolactone and isoalantolactone

Alantolactone and isoalantolactone, main bioactive compounds that are present in many medicinal plants such as Inula helenium, L. Inula japonica, Aucklandia lappa, Inula racemosa, and Radix inulae, have been found to have various pharmacological actions including anti-inflammatory, antimicrobial, and anticancer properties, with no significant toxicity. Recently, the anticancer activity of alantolactone and isoalantolactone has been extensively investigated. Here, our aim is to review their natural sources and their anticancer activity with specific emphasis on mechanism of actions, by which these compounds act on apoptosis pathways. Based on the literature and also on our previous results, alantolactone and isoalantolactone induce apoptosis by targeting multiple cellular signaling pathways that are frequently deregulated in cancers and suggest that their simultaneous targeting by these compounds could result in efficacious and selective killing of cancer cells. This review suggests that alantolactone and isoalantolactone are potential promising anticancer candidates, but additional studies and clinical trials are required to determine their specific intracellular sites of actions and derivative targets in order to fully understand the mechanisms of therapeutic effects to further validate in cancer chemotherapy.

Effective down-regulation of signal transducer and activator of transcription 3 (STAT3) by polyplexes of siRNA and lipid-substituted polyethyleneimine for sensitization of breast tumor cells to conventional chemotherapy

Signal transducer and activator of transcription 3 (STAT3) is a transcription factor that plays a major role in the development of resistance to conventional anti-cancer drugs in many types of cancer, when constitutively activated. Inhibition of STAT3 is considered as a promising strategy for inhibition of tumor growth and overcoming the drug resistance manifested. In this study, the capability of STAT3 knockdown by lipid substituted low molecular weight (2 kDa) polyethyleneimine (PEI2) complexes of STAT3-siRNA was assessed. The efficiency of PEI/STAT3-siRNA polyplexes in the induction of STAT3 associated cell death in wild type and drug-resistant MDA-MB-435 breast cancer cells as monotherapy and upon combination with chemotherapeutic agents, doxorubicin and paclitaxel, was also investigated. Our results identified linoleic acid-substituted (PEI-LA) polymer as the most efficient carrier among different lipid substituted PEI2 for siRNA delivery, leading to most STAT3 associated loss of cell viability in MDA-MB-435 cells. STAT3-siRNA delivery by the PEI-LA polymer resulted in efficient down-regulation of STAT3 at both mRNA and protein levels. Furthermore, pre-treatment of cancer cells with STAT3-siRNA formulation increased the cytotoxic effect of doxorubicin and paclitaxel in both wild type and drug resistant MDA-MB-435 cells. The results of this study point to the potential of PEI-LA polyplexes of STAT3-siRNA as inhibitors of STAT3 expression in breast tumor cells. The results also demonstrate an improved efficacy for chemotherapeutic drugs in combination with lipid-substituted low molecular weight PEI-LA/STAT3-siRNA complexes in comparison to drug therapy alone.

Trichosanthes kirilowii Ethanol Extract and Cucurbitacin D Inhibit Cell Growth and Induce Apoptosis through Inhibition of STAT3 Activity in Breast Cancer Cells

Trichosanthes kirilowii tuber is a traditional medicine which exhibits various medicinal effects including antidiabetic and anticancer activities in several cancer cells. Recently, it was reported that Cucurbitacin D (CuD) isolated from Trichosanthes kirilowii also induces apoptosis in several cancer cells. Constitutive signal transducer and activator of transcription 3 (STAT3), which is an oncogenic transcription factor, is often observed in many human malignant tumor, including breast cancer. In the present study, we tested whether Trichosanthes kirilowii ethanol extract (TKE) or CuD suppresses cell growth and induces apoptosis through inhibition of STAT3 activity in breast cancer cells. We found that both TKE and CuD suppressed proliferation and induced apoptosis and G2/M cell cycle arrest in MDA-MB-231 breast cancer cells by inhibiting STAT3 phosphorylation. In addition, both TKE and CuD inhibited nuclear translocation and transcriptional activity of STAT3. Taken together, our results indicate that TKE and its derived compound, CuD, could be potent therapeutic agents for breast cancer, blocking tumor cell proliferation and inducing apoptosis through suppression of STAT3 activity.

PIAS3 activates the intrinsic apoptotic pathway in non-small cell lung cancer cells independent of p53 status

Protein inhibitor of activated signal transducer and activator of transcription 3 (STAT3) (PIAS3) is an endogenous inhibitor of STAT3 that negatively regulates STAT3 transcriptional activity and cell growth and demonstrates limited expression in the majority of human squamous cell carcinomas of the lung. In this study, we sought to determine whether PIAS3 inhibits cell growth in non-small cell lung cancer cell lines by inducing apoptosis. Our results demonstrate that overexpression of PIAS3 promotes mitochondrial depolarization, leading to cytochrome c release, caspase 9 and 3 activation and poly (ADP-ribose) polymerase cleavage. This intrinsic pathway activation was associated with decreased Bcl-xL expression and increased Noxa expression and was independent of p53 status. Furthermore, PIAS3 inhibition of STAT3 activity was also p53 independent. Microarray experiments were performed to discover STAT3-independent mediators of PIAS3-induced apoptosis by comparing the apoptotic gene expression signature induced by PIAS3 overexpression with that induced by STAT3 siRNA. The results showed that a subset of apoptotic genes was uniquely expressed only after PIAS3 expression. Thus, PIAS3 may represent a promising lung cancer therapeutic target because of its p53-independent efficacy and its potential to synergize with Bcl-2 targeted inhibitors.

Prosapogenin A induces apoptosis in human cancer cells in vitro via inhibition of the STAT3 signaling pathway and glycolysis

Signal transducer and activator of transcription 3 (STAT3) is considered to be an oncogene. Blocking STAT3 signaling may induce growth arrest and apoptosis in different types of tumors. Cancer cells utilize the glycolytic pathway to maintain cell growth even when adequate oxygen is present. Glycolysis inhibition is a potential therapeutic modality. In the present study, the effects of Prosapogenin A (PSA) from the traditional Chinese medicine, Veratrum, on apoptosis, the STAT3 signaling pathway and glycometabolism in cancer cells were investigated. The results indicated that PSA induced growth inhibition and apoptosis in HeLa, HepG2 and MCF-7 cells. PSA inhibited the STAT3 signaling pathway and modulated the expression of glycometabolism-related genes. The results indicate that the inhibition of the STAT3 signaling and glycometabolism pathways contributes to the PSA-mediated apoptosis of HeLa, HepG2 and MCF-7 cells.

Protein kinase C zeta regulates human pancreatic cancer cell transformed growth and invasion through a STAT3-dependent mechanism

Pancreatic cancer is a very aggressive disease with few therapeutic options. In this study, we investigate the role of protein kinase C zeta (PKCζ) in pancreatic cancer cells. PKCζ has been shown to act as either a tumor suppressor or tumor promoter depending upon the cellular context. We find that PKCζ expression is either maintained or elevated in primary human pancreatic tumors, but is never lost, consistent with PKCζ playing a promotive role in the pancreatic cancer phenotype. Genetic inhibition of PKCζ reduced adherent growth, cell survival and anchorage-independent growth of human pancreatic cancer cells in vitro. Furthermore, PKCζ inhibition reduced orthotopic tumor size in vivo by inhibiting tumor cell proliferation and increasing tumor necrosis. In addition, PKCζ inhibition reduced tumor metastases in vivo, and caused a corresponding reduction in pancreatic cancer cell invasion in vitro. Signal transducer and activator of transcription 3 (STAT3) is often constitutively active in pancreatic cancer, and plays an important role in pancreatic cancer cell survival and metastasis. Interestingly, inhibition of PKCζ significantly reduced constitutive STAT3 activation in pancreatic cancer cells in vitro and in vivo. Pharmacologic inhibition of STAT3 mimicked the phenotype of PKCζ inhibition, and expression of a constitutively active STAT3 construct rescued the transformed phenotype in PKCζ-deficient cells. We conclude that PKCζ is required for pancreatic cancer cell transformed growth and invasion in vitro and tumorigenesis in vivo, and that STAT3 is an important downstream mediator of the pro-carcinogenic effects of PKCζ in pancreatic cancer cells.

Structural properties of non-traditional drug targets present new challenges for virtual screening

Traditional drug targets have historically included signaling proteins that respond to small molecules and enzymes that use small molecules as substrates. Increasing attention is now being directed toward other types of protein targets, in particular those that exert their function by interacting with nucleic acids or other proteins rather than small-molecule ligands. Here, we systematically compare existing examples of inhibitors of protein-protein interactions to inhibitors of traditional drug targets. While both sets of inhibitors bind with similar potency, we find that the inhibitors of protein-protein interactions typically bury a smaller fraction of their surface area upon binding to their protein targets. The fact that an average atom is less buried suggests that more atoms are needed to achieve a given potency, explaining the observation that ligand efficiency is typically poor for inhibitors of protein-protein interactions. We then carried out a series of docking experiments and found a further consequence of these relatively exposed binding modes is that structure-based virtual screening may be more difficult: such binding modes do not provide sufficient clues to pick out active compounds from decoy compounds. Collectively, these results suggest that the challenges associated with such non-traditional drug targets may not lie with identifying compounds that potently bind to the target protein surface, but rather with identifying compounds that bind in a sufficiently buried manner to achieve good ligand efficiency and, thus, good oral bioavailability. While the number of available crystal structures of distinct protein interaction sites bound to small-molecule inhibitors is relatively small at present (only 21 such complexes were included in this study), these are sufficient to draw conclusions based on the current state of the field; as additional data accumulate it will be exciting to refine the viewpoint presented here. Even with this limited perspective however, we anticipate that these insights, together with new methods for exploring protein conformational fluctuations, may prove useful for identifying the "low-hanging fruit" among non-traditional targets for therapeutic intervention.

Constitutive activation of signal transducer and activator of transcription 3 (STAT3) and nuclear factor κB signaling in glioblastoma cancer stem cells regulates the Notch pathway

Malignant gliomas are locally aggressive, highly vascular tumors that have a dismal prognosis, and present therapies provide little improvement in the disease course and outcome. Many types of malignancies, including glioblastoma, originate from a population of cancer stem cells (CSCs) that are able to initiate and maintain tumors. Although CSCs only represent a small fraction of cells within a tumor, their high tumor-initiating capacity and therapeutic resistance drives tumorigenesis. Therefore, it is imperative to identify pathways associated with CSCs to devise strategies to selectively target them. In this study, we describe a novel relationship between glioblastoma CSCs and the Notch pathway, which involves the constitutive activation of STAT3 and NF-κB signaling. Glioma CSCs were isolated and maintained in vitro using an adherent culture system, and the biological properties were compared with the traditional cultures of CSCs grown as multicellular spheres under nonadherent culture conditions. Interestingly, both adherent and spheroid glioma CSCs show constitutive activation of the STAT3/NF-κB signaling pathway and up-regulation of STAT3- and NF-κB-dependent genes. Gene expression profiling also identified components of the Notch pathway as being deregulated in glioma CSCs, and the deregulated expression of these genes was sensitive to treatment with STAT3 and NF-κB inhibitors. This finding is particularly important because Notch signaling appears to play a key role in CSCs in a variety of cancers and controls cell fate determination, survival, proliferation, and the maintenance of stem cells. The constitutive activation of STAT3 and NF-κB signaling pathways that leads to the regulation of Notch pathway genes in glioma CSCs identifies novel therapeutic targets for the treatment of glioma.

The role of cancer stem cells in the anti-carcinogenicity of curcumin

Many cancers contain cell subpopulations that display characteristics of stem cells. These cells are characterised by their ability to self-renew, form differentiated progeny and develop resistance to chemotherapeutic strategies. Cancer stem cells may utilise many of the same signalling pathways as normal stem cells including Wnt, Notch and Hedgehog. The dietary agent curcumin exerts a plethora of anti-carcinogenic effects both in vitro and in vivo, and can also inhibit many of the signalling pathways associated with stem cell biology. Emerging evidence suggests that curcumin can exert its anti-carcinogenic activity via targeting cancer stem cells through the disruption of stem cell signalling pathways. In this review we summarise the ability of curcumin to interfere with signalling pathways Wnt, Hedgehog, Notch, Signal Transducers and Activator (STAT) and interleukin-8, and report curcumin-induced changes in function and properties of cancer stem cells. We present evidence that the effects of curcumin on cancer stem cells mediate, or contribute to, its anti-carcinogenic activity.

Inhibitory effects of STAT3 decoy oligodeoxynucleotides on human epithelial ovarian cancer cell growth in vivo

The signal transducer and activator of transcription 3 (STAT3) regulates target gene expression by binding to a consensus DNA sequence within the promoter of the target genes. The constitutive activation of STAT3 has been shown to contribute to tumorigenesis in ovarian cancer and it has been reported to be a key factor for drug resistance in ovarian cancer. STAT3-specific decoy oligodeoxynucleotides (ODNs) (STAT3 decoy ODNs) that contain a consensus DNA sequence inhibit the transcriptional activity of STAT3, leading to cancer cell death. However, their mechanisms of action are unclear and little information is available as to the effects and the toxicity of STAT3 decoy ODNs in vivo. In this study, we established subcutaneous xenografts of SKOV3 human ovarian cancer cells in nude mice, evaluated the antitumor effects of STAT3 decoy ODNs on xenografted nude mice, and investigated the mechanisms behind the antitumor effects of STAT3 decoy ODNs targeting the STAT3 signaling pathway in vivo. The results revealed that the STAT3 decoy ODN inhibited ovarian cancer cell growth and promoted ovarian cancer cell apoptosis in vivo. Western blot analysis indicated that the STAT3 decoy ODN downregulated the protein expression levels of matrix metalloproteinase (MMP)-2, MMP-9 and Bcl-2, and upregulated the protein expression levels of caspase-3 in vivo. H&E staining was used to detect the side-effects of the STAT3 decoy ODN in the vital organs of the nude mice. We found that there were no significant abnormalities in the vital organs of the nude mice apart from slight inflammation and necrosis in parts of the hepatic lobule. The data from the present study suggest that decoy ODNs targeting STAT3 may be an effective therapeutic approach for the treatment of ovarian cancer in vivo.

Deguelin action involves c-Met and EGFR signaling pathways in triple negative breast cancer cells

Background

Treatment of breast cancer patients with antiestrogens and aromatase inhibitor(s) or Herceptin have shown significant success in steroid receptor positive or Her-2+ breast cancers respectively. However, choice of treatments for breast cancer patients with negative status for estrogen, progesterone receptors and HER2/neu is limited. As a result, search for appropriate therapy regimen for these triple negative breast cancers (TNBC) has become a major focus of investigations for many laboratories. Recently, Deguelin, a natural product isolated from African plant Mundulea sericea (Leguminossae) has shown both antiproliferative actions in various cancers including breast as well as chemoprenventive activity against carcinogen induced experimental cancers. In this report we evaluated efficacy and mechanism of action of Deguelin in triple negative breast cancer cell lines.

Methods/Findings

In vitro, Deguelin in a dose and time dependent manner inhibited the growth of MDA-MB-231, MDA-MB-468, BT-549 and BT-20 cells. Deguelin (2 or 4 mg/kg body weight), when injected intraperitoneally, reduced the in vivo tumor growth of MDA-MB-231 cells transplanted subcutaneously in athymic mice. Moreover it was nontoxic as evident from daily observations on mobility, food and water consumption and comparison of bodyweight and other visceral organ weights with those in control animals at the termination of the study. The western blot analyses and immunostaining studies indicated that the deguelin effects may be mediated through EGFR-PAKT/c-Met p-ERK and NF-κB by down regulating their downstream targets such as p-STAT3, c-Myc, Survivin.

Conclusion/Significance

These results suggest that Deguelin may have a significant therapeutic value for the treatment of TNBC patients.

Kaposi's sarcoma-associated herpesvirus kaposin B induces unique monophosphorylation of STAT3 at serine 727 and MK2-mediated inactivation of the STAT3 transcriptional repressor TRIM28

Kaposi's sarcoma-associated herpesvirus (KSHV) is the etiologic agent of primary effusion lymphoma (PEL), multicentric Castleman's disease (MCD), and the inflammation-driven neoplasm Kaposi's sarcoma (KS). A triad of processes, including abnormal proliferation of endothelial cells, aberrant angiogenesis, and chronic inflammation, characterize KS lesions. STAT3 is a key transcription factor governing these processes, and deregulation of STAT3 activity is linked to a wide range of cancers, including PEL and KS. Using primary human endothelial cells (ECs), I demonstrate that KSHV infection modulated STAT3 activation in two ways: (i) KSHV induced uncoupling of canonical tyrosine (Y) and serine (S) phosphorylation events while (ii) concomitantly inducing the phosphorylation and inactivation of TRIM28 (also known as KAP-1 or TIF-1β), a newly identified negative regulator of STAT3 activity. KSHV infection of primary ECs induced chronic STAT3 activation characterized by a shift from the canonical dual P-STAT3 Y705 S727 form to a mono P-STAT3 S727 form. Expression of the latent protein kaposin B promoted the unique phosphorylation of STAT3 at S727, in the absence of Y705, activated the host kinase mitogen-activated protein kinase-activated protein (MAPKAP) kinase 2 (MK2), and stimulated increased expression of STAT3-dependent genes, including CCL5, in ECs. TRIM28-mediated repression of STAT3 is relieved by phosphorylation of S473, and in vitro kinase assays identified TRIM28 S473 as a bona fide target of MK2. Together, these data suggest that kaposin B significantly contributes to the chronic inflammatory environment that is a hallmark of KS by unique activation of the proto-oncogene STAT3, coupled with MK2-mediated inactivation of the STAT3 transcriptional repressor TRIM28.

Central role of liver in anticancer and radioprotective activities of Toll-like receptor 5 agonist

Vertebrate Toll-like receptor 5 (TLR5) recognizes bacterial flagellin proteins and activates innate immune responses to motile bacteria. In addition, activation of TLR5 signaling can inhibit growth of TLR5-expressing tumors and protect normal tissues from radiation and ischemia-reperfusion injuries. To understand the mechanisms behind these phenomena at the organismal level, we assessed nuclear factor kappa B (NF-κB) activation (indicative of TLR5 signaling) in tissues and cells of mice treated with CBLB502, a pharmacologically optimized flagellin derivative. This identified the liver and gastrointestinal tract as primary CBLB502 target organs. In particular, liver hepatocytes were the main cell type directly and specifically responding to systemic administration of CBLB502 but not to that of the TLR4 agonist LPS. To assess CBLB502 impact on other pathways, we created multireporter mice with hepatocytes transduced in vivo with reporters for 46 inducible transcription factor families and found that along with NF-κB, CBLB502 strongly activated STAT3-, phenobarbital-responsive enhancer module (PREM), and activator protein 1 (AP-1-) -driven pathways. Livers of CBLB502-treated mice displayed induction of numerous immunomodulatory factors and massive recruitment of various types of immune cells. This led to inhibition of growth of liver metastases of multiple tumors regardless of their TLR5 status. The changed liver microenvironment was not, however, hepatotoxic, because CBLB502 induced resistance to Fas-mediated apoptosis in normal liver cells. Temporary occlusion of liver blood circulation prevented CBLB502 from protecting hematopoietic progenitors in lethally irradiated mice, indicating involvement of a factor secreted by responding liver cells. These results define the liver as the key mediator of TLR5-dependent effects in vivo and suggest clinical applications for TLR5 agonists as hepatoprotective and antimetastatic agents.

Role of stat3 in skin carcinogenesis: insights gained from relevant mouse models

Signal transducer and activator of transcription 3 (Stat3) is a cytoplasmic protein that is activated in response to cytokines and growth factors and acts as a transcription factor. Stat3 plays critical roles in various biological activities including cell proliferation, migration, and survival. Studies using keratinocyte-specific Stat3-deficient mice have revealed that Stat3 plays an important role in skin homeostasis including keratinocyte migration, wound healing, and hair follicle growth. Use of both constitutive and inducible keratinocyte-specific Stat3-deficient mouse models has demonstrated that Stat3 is required for both the initiation and promotion stages of multistage skin carcinogenesis. Further studies using a transgenic mouse model with a gain of function mutant of Stat3 (Stat3C) expressed in the basal layer of the epidermis revealed a novel role for Stat3 in skin tumor progression. Studies using similar Stat3-deficient and gain-of-function mouse models have indicated its similar roles in ultraviolet B (UVB) radiation-mediated skin carcinogenesis. This paper summarizes the use of these various mouse models for studying the role and underlying mechanisms for the function of Stat3 in skin carcinogenesis. Given its significant role throughout the skin carcinogenesis process, Stat3 is an attractive target for skin cancer prevention and treatment.

Versatile DNAzyme-based amplified biosensing platforms for nucleic acid, protein, and enzyme activity detection

DNAzymes have been widely applied as signal amplifiers for enzyme-free and highly sensitive detection of DNA. A few of them have also been employed for amplified detection of other biomolecules via a target-triggered assembly of split or mutated DNAzyme strategy. However, most of these designs adopt Mg(2+)-dependent DNAzyme as the catalytic unit, which suffered from low catalytic cleavage activity. Meanwhile, some DNAzymes with high catalytic activity are not suitable for these designs because the slight modification of the catalytic core might results in remarkably decreased or even no catalytic activity of these DNAzymes. On the basis of DNAzyme topological effect or the terminal protection of small-molecule-linked DNA, we developed two versatile sensing platforms for amplified detection of different biotargets. Since no modification is necessary for the catalytic core of the DNAzyme in these designs, they can employ any DNAzyme with high catalytic activity as amplified unit, which affords a high amplified efficiency for the sensing platform. A catalytic and molecular beacon design was further employed to realize the true enzymatic multiple turnover of DNAzyme. These designs together allow a high sensitivity for the biotargets, resulting in a detection limit of 20 pM, 0.2 U/mL, and 1 ng/mL for target DNA, DNA adenine methylation methyltransferase (Dam MTase), and streptavidin, respectively, much lower than previously reported biosensors. In addition, the proposed sensing strategy is versatile. By conjugating with various recognition units, it can be employed to detect a wide range of biotargets, varying from nucleic acids to proteins with high sensitivity.

Discovery of O-Alkylamino Tethered Niclosamide Derivatives as Potent and Orally Bioavailable Anticancer Agents

Niclosamide has been identified to potently inhibit the activation, nuclear translocation, and transactivation of STAT3. Nevertheless, the poor aqueous solubility and bioavailability of niclosamide has hindered its further clinical development for cancer therapy. To discover new molecules with enhanced drug-like properties, a series of novel O-alkylamino tethered derivatives of niclosamide have been designed, synthesized, and biologically evaluated. Among them, compound 11 (HJC0152) has been demonstrated to significantly suppress MDA-MB-231 xenograft tumor growth in vivo (i.p. & p.o.), indicating its great potential as efficacious and orally bioavailable therapeutics for human cancer.

OPB-31121, a novel small molecular inhibitor, disrupts the JAK2/STAT3 pathway and exhibits an antitumor activity in gastric cancer cells

We investigated the mechanisms of action and antitumor effects of OPB-31121, a novel STAT3 inhibitor, in gastric cancer cells. OPB-31121 downregulated JAK2 and gp130 expression and inhibited JAK2 phosphorylation which leads to inhibition of STAT3 phosphorylation. OPB-31121 inhibited constitutively activated and IL-6-induced JAK/STAT signaling pathway. OPB-31121 decreased cell proliferation in both gastric cancer cells and in a xenograft model, induced the apoptosis of gastric cancer cells, inhibited the expression of antiapoptotic proteins, and showed synergism with 5-fluorouracil and cisplatin. Taken together, our study suggests that STAT3 inhibition with OPB-31121 can be tested in patients with gastric cancer.

Plant sterols as anticancer nutrients: evidence for their role in breast cancer

While many factors are involved in the etiology of cancer, it has been clearly established that diet significantly impacts one’s risk for this disease. More recently, specific food components have been identified which are uniquely beneficial in mitigating the risk of specific cancer subtypes. Plant sterols are well known for their effects on blood cholesterol levels, however research into their potential role in mitigating cancer risk remains in its infancy. As outlined in this review, the cholesterol modulating actions of plant sterols may overlap with their anti-cancer actions. Breast cancer is the most common malignancy affecting women and there remains a need for effective adjuvant therapies for this disease, for which plant sterols may play a distinctive role.

Fragment-based drug design and identification of HJC0123, a novel orally bioavailable STAT3 inhibitor for cancer therapy

Fragment-based drug design (FBDD) is a promising approach for the generation of lead molecules with enhanced activity and especially drug-like properties against therapeutic targets. Herein, we report the fragment-based drug design, systematic chemical synthesis and pharmacological evaluation of novel scaffolds as potent anticancer agents by utilizing six privileged fragments from known STAT3 inhibitors. Several new molecules such as compounds 5, 12, and 19 that may act as advanced chemical leads have been identified. The most potent compound 5 (HJC0123) has demonstrated to inhibit STAT3 promoter activity, downregulate phosphorylation of STAT3, increase the expression of cleaved caspase-3, inhibit cell cycle progression and promote apoptosis in breast and pancreatic cancer cells with low micromolar to nanomolar IC50 values. Furthermore, compound 5 significantly suppressed estrogen receptor (ER)-negative breast cancer MDA-MB-231 xenograft tumor growth in vivo (p.o.), indicating its great potential as an efficacious and orally bioavailable drug candidate for human cancer therapy.

Preliminary evaluation of safety of conditionally replication adenovirus M4

Conditionally replication adenovirus M4, which was constructed in our lab, was proved to have good clinical application prospect for its good anti-tumor and anti-metastasis effect. However, clinically applying M4 faces many problems. One of the most important is the safety of M4. In this study, we investigated the safety of M4 by comparing with Adv-TK, which was proved to be safe in I-III phase clinical trials. M4 and Adv-TK were injected into mice via the tail vein separately, and the mice were sacrificed at the indicated time. Blood was collected for biochemical tests, the liver was harvested for hematoxylin and eosin (H&E) staining and viral quantification, and splenic lymphocytes were separated for adenovirus specific cellular immune response. Our results showed that M4 had no obvious effect on mouse general symptoms. A transient reversible infiltration of inflammatory cells in collect abbacy was only observed in M4 group, and a transient slight increase in Cr level was detected both after M4 and Adv-TK injection. The adenovirus specific cellular immune response induced by M4 was similar to that by Adv-TK, and the distribution and metabolism of M4 in the mouse liver were also similar to those of Adv-TK. It was concluded that conditionally replication adenovirus M4 had the same safety as Adv-TK. The study provides safety basis for the coming clinical trials of M4.

Stat3 is required to maintain the full differentiation potential of mammary stem cells and the proliferative potential of mammary luminal progenitors

Stat3 has a defined role in mammary gland where it is a critical mediator of cell death during post-lactational regression. On the other hand, Stat3 is required for the self-renewal of embryonic stem cells and is sufficient for the induction of a naïve pluripotent state in epiblast stem cells. Mammary stem cells (MaSCs) have a high capacity for self-renewal and can grow robustly in transplantation experiments in vivo. However, a role for Stat3 in MaSCs has not been investigated. Here we show that depletion of Stat3 from basal cells results in reduced primary transplantation efficiency and diminishes the potential to generate ductal, but not alveolar, outgrowths. In addition, Stat3 is required for maximal proliferation of luminal progenitors.

Synthesis and biological evaluation of new N-alkylcarbazole derivatives as STAT3 inhibitors: preliminary study

The signalling pathway of Janus tyrosine Kinases-Signal Transducers and Activators of Transcription (JAK-STAT) is activated by a number of cytokines, hormones (GH, erythropoietin and prolactin), and growth factors. JAK-STAT signalling is involved in regulation of cell proliferation, differentiation and apoptosis. These activities are due to different members of JAK-STAT family consisting of: JAK1, JAK2, JAK3, Tyk2 and STAT1, STAT2, STAT3, STAT4, STAT5a, STAT5b, STAT6. Recent studies suggest a key role for STAT family proteins, in particular for STAT3, in selectively inducing and maintaining a pro-carcinogenic inflammatory microenvironment, that promote tumour cells transformation. Moreover, a striking correlation between cancer development/progression and STAT3 persistent activation exists, probably due to STAT3 promoting of the pro-oncogenic inflammatory pathways, like NF-kB, IL-6 and JAK family kinases. Recent study demonstrated that carbazoles can inhibit STAT3 mediated transcription. From these evidences, STAT3 represents a therapeutic target, so we have synthesized a new set of N-alkylcarbazole derivatives substituted in positions 2, 4 and 6, to evaluate their activity on STAT3. Some of these compounds showed an interesting activity as STAT3 selective inhibitors; in particular, compounds 9a 9b and 9c revealed to inhibit the STAT3 activation for the 50%, 90% and 95%, respectively.

Novel therapy for liver regeneration by increasing the number of platelets

Platelets are the smallest blood constitutes which contain three types of granules; alpha granules, dense granules, and lysosomal granules. Each granule contains various biophysiological substances such as growth factors, cytokines, etc. Platelets have been conventionally viewed as a trigger of inflammatory responses and injury in the liver. Some studies revealed that platelets have strong effects on promoting liver regeneration. This review presents experimental evidence of platelets in accelerating liver regeneration and describes three different mechanisms involved; (1) the direct effect on hepatocytes, where platelets translocate to the space of Disse and release growth factors through direct contact with hepatocytes, (2) the cooperative effect with liver sinusoidal endothelial cells, where the dense concentration of sphingosine-1-phosphate in platelets induces excretion of interleukin-6 from liver sinusoidal endothelial cells, and (3) the collaborative effect with Kupffer cells, where the functions of Kupffer cells are enhanced by platelets.

Luteolin induces carcinoma cell apoptosis through binding Hsp90 to suppress constitutive activation of STAT3

Background

Abnormal activity of STAT3 is associated with a number of human malignancies. Hsp90 plays a central role in stabilizing newly synthesized proteins and participates in maintaining the functional competency of a number of signaling transducers involved in cell growth, survival and oncogenesis, such as STAT3. Hsp90 interacts with STAT3 and stabilizes Tyr-phosphorylated STAT3. It has been reported that luteolin possesses anticancer activity through degradation of Tyr⁷⁰⁵-phosphorylated STAT3.

Methodology/Principal Findings

We found that overexpression of Hsp90 inhibited luteolin-induced degradation of Tyr⁷⁰⁵-phosphorylated STAT3 and luteolin also reduced the levels of some other Hsp90 interacting proteins. Results from co-immunoprecipitation and immunoblot analysis demonstrated that luteolin prevented the association between Hsp90 and STAT3 and induced both Tyr⁷⁰⁵- and Ser⁷²⁷-phosphorylated STAT3 degradation through proteasome-dependent pathway. The molecular modeling analysis with CHARMm–Discovery Studio 2.1(DS 2.1) indicated that luteolin could bind to the ATP-binding pocket of Hsp90. SPR technology-based binding assay confirmed the association between luteolin and Hsp90. ATP-sepharose binding assay displayed that luteolin inhibited Hsp90-ATP binding.

Conclusions/Significance

Luteolin promoted the degradation of Tyr⁷⁰⁵- and Ser⁷²⁷-phosphorylated STAT3 through interacting with Hsp90 and induced apoptosis of cancer cells. This study indicated that luteolin may act as a potent HSP90 inhibitor in antitumor strategies.

Molecular docking studies on inhibition of Stat3 dimerization by curcumin natural derivatives and its conjugates with amino acids

Stat3 is a mammalian transcription factor which regulates various genes involved in cell growth, proliferation, cell survival and other biological processes. Its constitutive activation promotes dysregulated growth, survival and immune responses which contribute to tumor progression and carcinogenesis. Inhibition of Stat3 dimerization which prevents its binding to DNA is a rational strategy that could be translated to potential therapeutic applications. The present computational study provides insights into the inhibition of Stat3 dimerization by curcumin natural derivatives and its conjugates with amino acids. The involvement of residues like LYS-591, ARG-609, SER-611, GLU-612, SER-613, SER-636 and VAL-637 seems to play an important role in binding of curcumin natural derivatives and its amino acids conjugates with Src Homology (SH2) domain of Stat3 monomer. Demethoxycurcumin followed by hexahydrocurcuminol were predicted to be the most potent inhibitors amongst all the curcumin natural derivatives and known inhibitors (FLLL32, Sta21 and Stattic). Curcumin-proline conjugate (1,7-Bis(4-O-L-prolinoyl-3- methoxyphenyl)-1,4,6-heptatriene-5-ol-3-one) was predicted to be the most potent inhibitor of Stat3 dimerization amongst the curcumin-amino acid conjugates and known peptide based inhibitor (Phpr-pTYR-LEU-cis-3,4-methanoPRO-GLN-NHBn).

STAT3 protein up-regulates Gα-interacting vesicle-associated protein (GIV)/Girdin expression, and GIV enhances STAT3 activation in a positive feedback loop during wound healing and tumor invasion/metastasis

Gα-interacting vesicle-associated protein (GIV) is a guanine nucleotide exchange factor that modulates key signaling pathways during a diverse set of biological processes, e.g. wound healing, macrophage chemotaxis, tumor angiogenesis, vascular repair, and cancer invasion/metastasis. We recently demonstrated that GIV is a metastasis-related protein, which serves both as a therapeutic target and as a biomarker for prognostication in cancer patients. Here we report the discovery that GIV is a direct target of the transcription factor signal transducer and activator of transcription-3 (STAT3), which is commonly known as a central regulator of tumor metastasis. We identified a single STAT3-binding site on the GIV promoter that was necessary and sufficient for transcriptional activation of GIV during wound healing and cancer invasion. Immunohistochemical analysis of breast carcinomas showed significant correlation between STAT3 activation and elevated GIV expression. Furthermore, we provide evidence that GIV positively autoregulates its own transcription by enhancing STAT3 activation via its guanine nucleotide exchange factor activity. Our findings provide mechanistic insights into how STAT3 activation is directly integrated with the receptor tyrosine kinase-GIV-G protein signaling axis. The forward feedback regulation we describe here between GIV and STAT3 may have profound therapeutic implications for cancer and epithelial regeneration/repair and could help invent novel approaches in treating and prognosticating cancer.

XZH-5 inhibits STAT3 phosphorylation and enhances the cytotoxicity of chemotherapeutic drugs in human breast and pancreatic cancer cells

Constitutive activation of Signal Transducers and Activators of Transcription 3 (STAT3) signaling is frequently detected in breast and pancreatic cancer. Inhibiting constitutive STAT3 signaling represents a promising molecular target for therapeutic approach. Using structure-based design, we developed a non-peptide cell-permeable, small molecule, termed as XZH-5, which targeted STAT3 phosphorylation. XZH-5 was found to inhibit STAT3 phosphorylation (Tyr705) and induce apoptosis in human breast and pancreatic cancer cell lines expressing elevated levels of phosphorylated STAT3. XZH-5 could also inhibit interleukin-6-induced STAT3 phosphorylation in cancer cell lines expressing low phosphorylated STAT3. Inhibition of STAT3 signaling by XZH-5 was confirmed by the down-regulation of downstream targets of STAT3, such as Cyclin D1, Bcl-2, and Survivin at mRNA level. In addition, XZH-5 inhibited colony formation, cell migration, and enhanced the cytotoxicity of chemotherapeutic drugs when combined with Doxorubicin or Gemcitabine. Our results indicate that XZH-5 may be a potential therapeutic agent for breast and pancreatic cancers with constitutive STAT3 signaling.

Selective small molecule Stat3 inhibitor reduces breast cancer tumor-initiating cells and improves recurrence free survival in a human-xenograft model

Metastasis and disease relapse are hypothesized to result from tumor initiating cells (TICs). Previously, we have defined a CD44+/CD24−/low mammosphere-forming tumorigenic 493-gene signature in breast cancer. Stat3 was identified as a critical node in self-renewal based on an ongoing lentiviral shRNA screen being conducted in two breast cancer cell lines SUM159 and BT549. In corroborating work, targeting the SH2 domain of Stat3 with a novel small molecule decreased the percentage of cells expressing TIC markers (CD44+/CD24−/low and ALDH+) and mammosphere formation in p-Stat3 overexpressing human breast cancer xenografts in SCID-beige mice. Importantly, we observed a four-fold improvement in the 30-day recurrence-free survival relative to docetaxel alone with the addition of the Stat3 inhibitor in the chemoresistant tumor model. Thus, these findings provide a strong impetus for the development of selective Stat3 inhibitors in order to improve survival in patients with p-Stat3 overexpressing tumors.

STAT3 inhibition, a novel approach to enhancing targeted therapy in human cancers (review)

Signal transducer and activator of transcription 3 (STAT3) regulates many critical functions in human normal and malignant tissues, such as differentiation, proliferation, survival, angiogenesis and immune function. Constitutive activation of STAT3 is implicated in a wide range of human cancers. As such, STAT3 has been studied as a tumour therapeutic target. This review aimed principally to summarise the updated research on STAT3 inhibition studies and their therapeutic potential in solid tumours. Recent literature associated with STAT3 inhibition was reviewed through PubMed and Medline database, followed by critical comparison and analysis. Constitutive activation of STAT3 has been identified as abnormal and oncogenic. The pathway of STAT3 activation and signal transduction identifies 3 approaches for inhibition: modulating upstream positive or negative regulators, regulating RNA (DN-STAT3, anti-sense RNA, siRNA and microRNA) or targeting STAT3 protein at different domains. The last approach using small molecule STAT3 inhibitors has been the most examined so far with both preclinical and clinical studies. Targeting STAT3 using a specific inhibitor may be a useful cancer treatment approach, with the potential for a broad clinical impact.

Potential use of STAT3 inhibitors in targeted prostate cancer therapy: future prospects

In 2012, prostate cancer will once again be the second-leading cause of cancer death of American males. Although initially treatable, prostate cancer can recur in a hormone refractory form that is not responsive to current available therapies. The mortality rate associated with hormone refractory prostate cancer is high, and there is an urgent need for new therapeutic agents to treat prostate cancer. A common feature of prostate cancer is the dependence on activated signal transducer and activator of transcription 3 (STAT3), a transcription factor, for survival. More important, inhibition of STAT3 has been shown to induce apoptosis in prostate cancer cells. In recent years, inhibitors of STAT3 have emerged as promising molecular candidates for targeted prostate cancer therapy. The aim of this review is to examine the role of STAT3 in prostate cancer and how inhibitors of STAT3 could advance the quest for treatment of the disease. Janus kinase 2 (JAK2)-targeted therapy appears very promising in the treatment of prostate cancer. It has been shown to decrease symptoms associated with myeloproliferative disorders and increase overall survival of patients compared with the best available therapy. In addition to improved outcome, many JAK2 inhibitors have been found to be tolerable with no adverse impact on quality of life. As such, JAK2 inhibitors may play an important role in the management of patients with prostate cancer. Current studies are evaluating the role of JAK2 inhibitors in solid tumors. Pending clinical trial results will determine the future direction of JAK2 inhibitors in the treatment of patients with prostate cancer.

STAT3 activation by IL-6 from mesenchymal stem cells promotes the proliferation and metastasis of osteosarcoma

We previously demonstrated that human mesenchymal stem cells (MSCs) promote the growth of osteosarcoma in the bone microenvironment. The aim of the present study was to further determine the effect of IL-6/STAT3 signaling on the progression of osteosarcoma. First, conditioned medium from MSCs was used to stimulate the growth of osteosarcoma cells (Saos-2) in vitro. We found that STAT3 was activated and that the activation could be blocked by an IL-6-neutralizing antibody. The inhibition of STAT3 in Saos-2 cells by siRNA or AG490 decreased cell proliferation, migration and invasion, down-regulated the mRNA expression of Cyclin D, Bcl-xL and Survivin and enhanced the apoptotic response. Furthermore, a nude mouse osteosarcoma model was established by injecting luciferase-labeled Saos-2 cells into the tibia, and the effect of STAT3 on tumor growth was determined by treating the mice with AG490. In vivo bioluminescence images showed that tumor growth was dramatically reduced in the AG490 group. In addition, STAT3 inhibition decreased the lung metastasis rate and prolonged the survival of these mice. After treatment with AG490, the protein levels of IL-6, p-STAT3 and PCNA were decreased, and the level of apoptosis in the tumor was increased. Altogether, these data indicate that MSCs in the bone microenvironment might promote the progression of osteosarcoma and protect tumor cells from drug-induced apoptosis through IL-6/STAT3 signaling.

A small molecule, LLL12 inhibits constitutive STAT3 and IL-6-induced STAT3 signaling and exhibits potent growth suppressive activity in human multiple myeloma cells

We characterized the effects of a newly developed signal transducers and activators of transcription 3 (STAT3) inhibitor, LLL12 in multiple myeloma (MM) cells. LLL12 specifically inhibited STAT3 phosphorylation, nuclear localization, DNA binding activity, down-regulated STAT3 downstream genes, and induced apoptosis in MM cells. Importantly, LLL12 significantly inhibited STAT3 phosphorylation, induced apoptosis in primary MM cells which came from patients that were clinically resistant to lenalidomide and bortezomib. LLL12 is a potent inhibitor of cell proliferation with IC50 values ranging between 0.26 and 1.96 μM in MM and primary MM cells. LLL12 also inhibited STAT3 phosphorylation induced by interleukin-6 (IL-6) and interferon-α but not STAT1, STAT2, STAT4 and STAT6 phosphorylation induced by interferon-α, interferon-γ and IL-4 indicating the selectivity of LLL12 for STAT3. The selectively of LLL12 on STAT3 was further demonstrated on 21 protein kinases, which LLL12 had IC50 values ≥ 73.92 μM. In addition, the pretreatment of LLL12 blocked the promotion of the cell proliferation and resistance to lenalidomide by IL-6. Furthermore, LLL12 significantly blocked tumor growth of MM cells in mouse model. Our results indicate that LLL12 blocks constitutive STAT3 and IL-6 induced STAT3 signaling and may be a potential therapeutic agent for MM.