Resistance to chemotherapy via Stat3-dependent overexpression of Bcl-2 in metastatic breast cancer cells

A novel small molecular STAT3 inhibitor, LY5, inhibits cell viability, cell migration, and angiogenesis in medulloblastoma cells

Signal transducers and activators of transcription 3 (STAT3) signaling is persistently activated and could contribute to tumorigenesis of medulloblastoma. Numerous studies have demonstrated that inhibition of the persistent STAT3 signaling pathway results in decreased proliferation and increased apoptosis in human cancer cells, indicating that STAT3 is a viable molecular target for cancer therapy. In this study, we investigated a novel non-peptide, cell-permeable small molecule, named LY5, to target STAT3 in medulloblastoma cells. LY5 inhibited persistent STAT3 phosphorylation and induced apoptosis in human medulloblastoma cell lines expressing constitutive STAT3 phosphorylation. The inhibition of STAT3 signaling by LY5 was confirmed by down-regulating the expression of the downstream targets of STAT3, including cyclin D1, bcl-XL, survivin, and micro-RNA-21. LY5 also inhibited the induction of STAT3 phosphorylation by interleukin-6 (IL-6), insulin-like growth factor (IGF)-1, IGF-2, and leukemia inhibitory factor in medulloblastoma cells, but did not inhibit STAT1 and STAT5 phosphorylation stimulated by interferon-γ (IFN-γ) and EGF, respectively. In addition, LY5 blocked the STAT3 nuclear localization induced by IL-6, but did not block STAT1 and STAT5 nuclear translocation mediated by IFN-γ and EGF, respectively. A combination of LY5 with cisplatin or x-ray radiation also showed more potent effects than single treatment alone in the inhibition of cell viability in human medulloblastoma cells. Furthermore, LY5 demonstrated a potent inhibitory activity on cell migration and angiogenesis. Taken together, these findings indicate LY5 inhibits persistent and inducible STAT3 phosphorylation and suggest that LY5 is a promising therapeutic drug candidate for medulloblastoma by inhibiting persistent STAT3 signaling.

Trefoil factor 3 promotes metastatic seeding and predicts poor survival outcome of patients with mammary carcinoma

Introduction

Recurrence or early metastasis remains the predominant cause of mortality in patients with estrogen receptor positive (ER+) mammary carcinoma (MC). However, the molecular mechanisms underlying the initial progression of ER+ MC to metastasis remains poorly understood. Trefoil factor 3 (TFF3) is an estrogen-responsive oncogene in MC. Herein, we provide evidence for a functional role of TFF3 in metastatic progression of ER+ MC.

Methods

The association of TFF3 expression with clinicopathological parameters and survival outcome in a cohort of MC patients was assessed by immunohistochemistry. The expression of TFF3 in MCF7 and T47D cells was modulated by forced expression or siRNA-mediated depletion of TFF3. mRNA and protein levels were determined using qPCR and western blot. The functional effect of modulation of TFF3 expression in MC cells was determined in vitro and in vivo. Mechanistic analyses were performed using reporter constructs, modulation of signal transducer and activator of transcription 3 (STAT3) expression, and pharmacological inhibitors against c-SRC and STAT3 activity.

Results

TFF3 protein expression was positively associated with larger tumour size, lymph node metastasis, higher stage, and poor survival outcome. Forced expression of TFF3 in ER+ MC cells stimulated colony scattering, cell adhesion to a Collagen I-coated matrix, colony formation on a Collagen I- or Matrigel-coated matrix, endothelial cell adhesion, and transmigration through an endothelial cell barrier. In vivo, forced expression of TFF3 in MCF7 cells stimulated the formation of metastatic nodules in animal lungs. TFF3 regulation of the mRNA levels of epithelial, mesenchymal, and metastatic-related genes in ER+ MC cells were consistent with the altered cell behaviour. Forced expression of TFF3 in ER+ MC cells stimulated phosphorylation of c-SRC that subsequently increased STAT3 activity, which lead to the downregulation of E-cadherin. siRNA-mediated depletion of TFF3 reduced the invasiveness of ER+ MC cells.

Conclusions

TFF3 expression predicts metastasis and poor survival outcome of patients with MC and functionally stimulates cellular invasion and metastasis of ER+ MC cells. Adjuvant functional inhibition of TFF3 may therefore be considered to ameliorate outcome of ER+ MC patients.

Electronic supplementary material

The online version of this article (doi:10.1186/s13058-014-0429-3) contains supplementary material, which is available to authorized users.

Novel carbazole inhibits phospho-STAT3 through induction of protein-tyrosine phosphatase PTPN6

The aberrant activation of STAT3 occurs in many human cancers and promotes tumor progression. Phosphorylation of a tyrosine at amino acid Y705 is essential for the function of STAT3. Synthesized carbazole derived with fluorophore compound 12 was discovered to target STAT3 phosphorylation. Compound 12 was found to inhibit STAT3-mediated transcription as well as to reduce IL-6 induced STAT3 phosphorylation in cancer cell lines expressing both elevated and low levels of phospho-STAT3 (Y705). Compound 12 potently induced apoptosis in a broad number of TNBC cancer cell lines in vitro and was effective at inhibiting the in vivo growth of human TNBC xenograft tumors (SUM149) without any observed toxicity. Compound 12 also effectively inhibited the growth of human lung tumor xenografts (A549) harboring aberrantly active STAT3. In vitro and in vivo studies showed that the inhibitory effects of 12 on phospho-STAT3 were through up-regulation of the protein-tyrosine phosphatase PTPN6. Our present studies strongly support the continued preclinical evaluation of compound 12 as a potential chemotherapeutic agent for TNBC and cancers with constitutive STAT3 signaling.

Deconstructing breast cancer cell biology and the mechanisms of multidrug resistance

Cancer complexity constantly challenges the way that clinicians manage breast cancer therapy. Tumor heterogeneity and intratumoral stroma characteristics allow cells with different phenotypes and deregulated apoptotic, proliferative and migration abilities to co-exist contributing to a disappointing therapeutic response. While new approaches are being associated with conventional chemotherapy, such as hormonal therapy or target monoclonal antibodies, recurrence and metastasization are still observed. Membrane transporters are the cell's first line of contact with anticancer drugs having a major role in multidrug resistance events. This structural-based activity enables the cell to be drug-resistant by decreasing drug intracellular concentration through an efflux-transport mechanism, mainly associated with overexpression of ATP-binding cassette (ABC) proteins. This review focuses on some of the important structural and biological properties of the malignant cell and tumor microenvironment, addressing the role of the membrane ABC transporters in therapeutic outcomes, and highlighting related molecular pathways that may represent meaningful target therapies.

SC-2001 overcomes STAT3-mediated sorafenib resistance through RFX-1/SHP-1 activation in hepatocellular carcinoma

Hepatocellular carcinoma is the fifth most common solid cancer worldwide. Sorafenib, a small multikinase inhibitor, is the only approved therapy for advanced HCC. The clinical benefit of sorafenib is offset by the acquisition of sorafenib resistance. Understanding of the molecular mechanism of STAT3 overexpression in sorafenib resistance is critical if the clinical benefits of this drug are to be improved. In this study, we explored our hypothesis that loss of RFX-1/SHP-1 and further increase of p-STAT3 as a result of sorafenib treatment induces sorafenib resistance as a cytoprotective response effect, thereby, limiting sorafenib sensitivity and efficiency. We found that knockdown of RFX-1 protected HCC cells against sorafenib-induced cell apoptosis and SHP-1 activity was required for the process. SC-2001, a molecule with similar structure to obatoclax, synergistically suppressed tumor growth when used in combination with sorafenib in vitro and overcame sorafenib resistance through up-regulating RFX-1 and SHP-1 resulting in tumor suppression and mediation of dephosphorylation of STAT3. In addition, sustained sorafenib treatment in HCC led to increased p-STAT3 which was a key mediator of sorafenib sensitivity. The combination of SC-2001 and sorafenib strongly inhibited tumor growth in both wild-type and sorafenib-resistant HCC cell bearing xenograft models. These results demonstrate that inactivation of RFX/SHP-1 induced by sustained sorafenib treatment confers sorafenib resistance to HCC through p-STAT3 up-regulation. These effects can be overcome by SC-2001 through RFX-1/SHP-1 dependent p-STAT3 suppression. In conclusion, the use of SC-2001 in combination with sorafenib may constitute a new strategy for HCC therapy.

Association of toxicity of sorafenib and sunitinib for human keratinocytes with inhibition of signal transduction and activator of transcription 3 (STAT3)

Hand–foot skin reaction is a most common multi-kinase inhibitor-related adverse event. This study aimed to examine whether the toxicity of sorafenib and sunitinib for human keratinocytes was associated with inhibiting signal transduction and activator of transcription 3 (STAT3). We studied whether STAT3 activity affects sorafenib- and sunitinib-induced cell growth inhibition in HaCaT cells by WST-8 assay. Stattic enhanced the cell-growth inhibitory and apoptotic effects of sorafenib and sunitinib. HaCaT cells transfected with constitutively-active STAT3 (STAT3C) were resistant to the sorafenib- and sunitinib-induced cell growth inhibition. STAT3 activity decreased after short-term treatment with sorafenib and sunitinib in a dose-dependent manner and recovered after long-term treatment with sorafenib and sunitinib at low doses. Moreover, the expression of survivin and bcl-2 decreased after treatment with sorafenib and sunitinib was concomitant with variations in STAT3 activity. Sorafenib-induced STAT3 inhibition was mediated by regulation via MAPK pathways in HaCaT cells, while sunitinib-induced STAT3 inhibition was not. Thus, STAT3 activation mediating apoptosis suppressors may be a key factor in sorafenib and sunitinib-induced keratinocyte cytotoxicity.

STAT3 inhibitor NSC74859 radiosensitizes esophageal cancer via the downregulation of HIF-1α

Radiotherapy is the main therapy for inoperable and locally advanced esophageal squamous cell carcinoma (ESCC). However, radioresistance in ESCC remains a challenge. The aim of this study is to investigate the radiosensitizing effects of STAT3 inhibitor NSC74859 on ESCC and explore the underlying mechanisms. ECA109 and TE13 cells were exposed to hypoxia, and treated with NSC74859 or radiation, alone or in combination. Cell proliferation, survival, apoptosis, and double-stranded DNA breaks (DSBs) were examined. Nude mice model of ECA109 xenograft was treated with radiation and/or NSC74859. The levels of STAT3, p-STAT3, HIF-1α, and VEGF were detected by Western blot analysis. NSC74859 efficiently radiosensitized ESCC cells and xenografts in nude mice, and inhibited hypoxia-/radiation-induced activation of STAT3 and upregulation of HIF-1α and VEGF expression. NSC74859 confers radiosensitivity in ESCC via the inhibition of STAT3 activation and the downregulation of HIF-1α and VEGF expression. NSC74859 may become a promising radiosensitizer for ESCC radiotherapy.

A novel miR-219-SMC4-JAK2/Stat3 regulatory pathway in human hepatocellular carcinoma

BACKGROUND

To understand the involvement of structural maintenance of chromosome 4 (SMC4) in the development and progression of hepatocellular carcinoma (HCC).

METHODS

Real-time quantitative PCR and Western Blotting were applied to measure the expression of SMC4 in HCC samples and cell lines. The tumor-promoting effect of SMC4 was determined by WST-1, soft agar colony formation, cell motility and invasion assays. The SMC4 target signal pathway was identified by luciferase reporter and real-time quantitative PCR assays.

RESULTS

The upregulation of SMC4 was frequently detected in HCC samples and cell lines. Functional assays demonstrated that SMC4 could effectively promote tumor cell growth rate, colony formation in soft agar, wound-healing and invasion. Further studies showed that increased miR-219 levels caused a significant decrease in the SMC4 expression, and SMC4 inhibitor downregulated JAK2/Stat3 expression at both the mRNA and protein levels.

CONCLUSIONS

Our findings provide new insight into SMC4 function and the mechanisms of growth and invasion of HCC.

STAT3 regulation by S-nitrosylation: implication for inflammatory disease

AIMS

S-nitrosylation and S-glutathionylation, redox-based modifications of protein thiols, are recently emerging as important signaling mechanisms. In this study, we assessed S-nitrosylation-based regulation of Janus-activated kinase 2/signal transducer and activator of transcription 3 (JAK2/STAT3) pathway that plays critical roles in immune/inflammatory responses and tumorigenesis.

RESULTS

Our studies show that STAT3 in stimulated microglia underwent two distinct redox-dependent modifications, S-nitrosylation and S-glutathionylation. STAT3 S-nitrosylation was associated with inducible nitric oxide synthase (iNOS)-produced nitric oxide (NO) and S-nitrosoglutathione (GSNO), whereas S-glutathionylation of STAT3 was associated with cellular oxidative stress. NO produced by iNOS or treatment of microglia with exogenous GSNO inhibited STAT3 activation via inhibiting STAT3 phosphorylation (Tyr(705)). Consequently, the interleukin-6 (IL-6)-induced microglial proliferation and associated gene expressions were also reduced. In cell-free kinase assay using purified JAK2 and STAT3, STAT3 phosphorylation was inhibited by its selective preincubation with GSNO, but not by preincubation of JAK2 with GSNO, indicating that GSNO-mediated mechanisms inhibit STAT3 phosphorylation through S-nitrosylation of STAT3 rather than JAK2. In this study, we identified that Cys(259) was the target Cys residue of GSNO-mediated S-nitrosylation of STAT3. The replacement of Cys(259) residue with Ala abolished the inhibitory role of GSNO in IL-6-induced STAT3 phosphorylation and transactivation, suggesting the role of Cys(259) S-nitrosylation in STAT3 phosphorylation.

INNOVATION

Microglial proliferation is regulated by NO via S-nitrosylation of STAT3 (Cys(259)) and inhibition of STAT3 (Tyr(705)) phosphorylation.

CONCLUSION

Our results indicate the regulation of STAT3 by NO-based post-translational modification (S-nitrosylation). These findings have important implications for the development of new therapeutics targeting STAT3 for treating diseases associated with inflammatory/immune responses and abnormal cell proliferation, including cancer.

Linifanib (ABT-869), enhances cytotoxicity with poly (ADP-ribose) polymerase inhibitor, veliparib (ABT-888), in head and neck carcinoma cells

OBJECTIVES

PARP inhibitors (PARPi) may provide an opportunity to gain selective killing of tumor cells which have deficiencies in cellular DNA repair systems. We previously demonstrated linifanib (ABT-869), a multi-receptor tyrosine kinase inhibitor of VEGF and PDGF receptor families, radiosensitized Head and Neck Squamous Cell Carcinoma cells (HNSCC) via inhibiting STAT3 activation. Given that STAT3 can modulate DNA damage response (DDR) pathway, in this study, we evaluate the effects of linifanib to enhance cytotoxicity with the PARPi, veliparib (ABT-888), in HNSCC.

MATERIALS AND METHODS

UMSCC-22A and UMSCC-22B cells were treated with linifanib (ABT-869) and veliparib (ABT-888). Cell viability, cytotoxicity, apoptosis induction, DNA single strand break (SSB) and double strand break (DSB) damages were examined by MTT assay, colony formation assay, flow cytometry and comet assay. In addition, the expression of DNA homologous recombination repair protein Rad51, γH2AX, a double strand break marker and cleaved PARP, an apoptotic cell death marker, were assessed using western immunoblotting.

RESULTS

Combination treatment resulted in more cell growth inhibition, induction of apoptosis, DNA damages and double strand breaks, lower expression of Rad51, increase γH2AX expression and PARP cleavage.

CONCLUSION

These data suggest the possibility of combining targeted therapeutic such as linifanib with veliparib to augment the inhibition of cell growth and apoptosis via synthetic lethality in HNSCC cells. Thus, it may provide a novel therapeutic strategy and improve efficacy and outcome in HNSCC.

HIF-1α activation under glucose deprivation plays a central role in the acquisition of anti-apoptosis in human colon cancer cells

A poor vascular network development in a tumor mass leads to poor oxygen and nutrient supply. To adapt to a hypoxic microenvironment, it is well-known that cancer cells activate the transcription factor hypoxia-inducible factor-1α (HIF-1α). HIF-1α plays a central role in hypoxia-induced metabolic switching, anti-apoptosis, angiogenesis and drug resistance. Glucose deprivation, another major stressful microenvironment, protects cancer cells from drug-induced apoptosis. However, the molecular mechanisms by which cancer cells adapt to poor nutrient conditions remain poorly understood. In this study, we focused on HIF-1α, signal transducer and activator of transcription 3 (STAT3) and trans-cription factor 4 (TCF4), which are involved in cell survival, anti-apoptosis and drug resistance. We examined their activities and the relationships among these transcription factors under glucose deprivation. Our results showed that glucose deprivation increased HIF-1α, STAT3 and TCF4 DNA-binding activity, as well as the expression levels of their target genes OCT4, BCL-2 and VEGF. HIF-1α knockdown significantly increased poly(ADP-ribose) polymerase 1 (PARP-1) cleavage at higher levels than STAT3 knockdown under glucose deprivation. Furthermore, HIF-1α knockdown led to a significant decrease in the expression levels of both STAT3 and TCF4, although STAT3 knockdown decreased only HIF-1α expression level. Our data indicated that activation of the HIF-1α signaling pathway under glucose deprivation leads to the acquisition of anti-apoptotic properties in human colon cancer cells, and targeting the HIF-1α signaling pathway may provide an effective avenue for treating cancers resistant to conventional therapy.

A novel curcumin analog (H-4073) enhances the therapeutic efficacy of cisplatin treatment in head and neck cancer

Chemotherapy constitutes the standard modality of treatment for localized head and neck squamous cell carcinomas (HNSCC). However, many patients fail to respond and relapse after this treatments due to the acquisition of chemo-resistance. Therefore, there is an urgent need to develop novel drugs that could reverse the resistant phenotype. Curcumin, the constituent of the spice turmeric has been shown to have anti-inflammatory, anti-oxidant and anti-proliferative properties in several tumor types. However, use of curcumin has been limited due to its poor bio-absorption. Recently, a novel class of curcumin analogs, based on diarylidenylpiperidones (DAP), has been developed by incorporating a piperidone link to the beta-diketone structure and fluoro substitutions on the phenyl groups. In this study, we evaluated the effectiveness of H-4073, a parafluorinated variant of DAP, using both in vitro and in vivo head and neck cancer models. Our results demonstrate that H-4073 is a potent anti-tumor agent and it significantly inhibited cell proliferation in all the HNSCC cell lines tested in a dose-dependent manner. In addition, pretreatment of cisplatin-resistant HNSCC cell lines with H-4073 significantly reversed the chemo-resistance as observed by cell viability assay (MTT), apoptosis assay (Annexin V binding) and cleaved caspase-3 (Western blot). H-4073 mediated its anti-tumor effects by inhibiting JAK/STAT3, FAK, Akt and VEGF signaling pathways that play important roles in cell proliferation, migration, survival and angiogenesis. In the SCID mouse xenograft model, H-4073 significantly enhanced the anti-tumor and anti-angiogenesis effects of cisplatin, with no added systemic toxicity. Interestingly, H-4073 inhibited tumor angiogenesis by blocking VEGF production by tumor cells as well as directly inhibiting endothelial cell function. Taken together, our results suggest that H-4073 is a potent anti-tumor agent and it can be used to overcome chemotherapy resistance in HNSCC.

Nicotine promotes apoptosis resistance of breast cancer cells and enrichment of side population cells with cancer stem cell-like properties via a signaling cascade involving galectin-3, α9 nicotinic acetylcholine receptor and STAT3

Nicotine, a main addictive compound in tobacco smoke, has been linked to promotion and progression of lung, head and neck, pancreatic, and breast cancers, but the detailed mechanisms of cancer progression remain elusive. Here, we show that nicotine induces the expression of galectin-3 (an anti-apoptotic β-galactoside-binding lectin) in breast cancer cell line and in primary tumors from breast cancer patients. Nicotine-induced up regulation of galectin-3 is due to an increased expression of α9 isoform of nicotinic acetylcholine receptor (α9nAChR), which activates transcription factor STAT3 that in turn, physically binds to galectin-3 (LGALS3) promoter and induces transcription of galectin-3. Intracellular galectin-3 increased mitochondrial integrity and suppressed chemotherapeutic-induced apoptosis of breast cancer cell. Moreover, nicotine-induced enrichment of side population cells with cancer stem cell-like properties was modulated by galectin-3 expression and could be significantly reduced by transient knock down of LGALS3 and its upstream signaling molecules STAT3 and α9nAChR. Thus, galectin-3 or its upstream signaling molecule STAT3 or α9nAChR could be a potential target to prevent nicotine-induced chemoresistance in breast cancer.

IL-6 and related cytokines as the critical lynchpins between inflammation and cancer

Inflammatory responses play pivotal roles in cancer development, including tumor initiation, promotion, progression, and metastasis. Cytokines are now recognized as important mediators linking inflammation and cancer, and are therefore potential therapeutic and preventive targets as well as prognostic factors. The interleukin (IL)-6 family of cytokines, especially IL-6 and IL-11, is highly up-regulated in many cancers and considered as one of the most important cytokine families during tumorigenesis and metastasis. This review discusses molecular mechanisms linking the IL-6 cytokine family to solid malignancies and their treatment.

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.

A perylene derivative regulates HIF-1α and Stat3 signaling pathways

It is becoming increasingly evident that improving the cure rate of many cancers will require treatment regimens hit more than one validated tumor targets. Developing an anti-cancer agent that targets two oncoproteins simultaneously is a promising strategy for accomplishing this goal. It would be expected to promote drug efficacy, reduce therapy-resistant without introducing additional toxic side effects. HIF-1α is a key regulator of the cellular response to hypoxia and is involved in tumor angiogenesis and cancer cell survival, glucose metabolism, and invasion. Stat3 has several oncogenic functions, including suppression of anti-tumor immune responses and promotion of inflammation. Recently, we have identified the perylene derivative, TEL03, as a dual inhibitor that targets both HIF-1α and Stat3. TEL03 blocks the expression of both HIF-1α and Stat3, regulated oncogenes (e.g., Bcl-2, VEGF, Glut1, and others) in cancer cells, and induces cancer cell apoptosis. The results demonstrated that: (i) TEL03 blocks Stat3 phosphorylation, and inhibits Stat3 transcriptional activity; and (ii) interferes the binding of HIF-1α to p300/CBP inducing its degradation by proteasomes under hypoxic conditions. Our in vivo tests showed that as a dual inhibitor, TEL03 dramatically inhibited tumor growth, and provided the evidence that targeting both HIF-1α and Stat3 simultaneously could be a promising strategy for breast and pancreatic cancer therapies.

Critical analysis of the potential for targeting STAT3 in human malignancy

The signal transducer and activator of transcription (STAT) family of proteins was originally discovered in the context of normal cell biology where they function to transduce intracellular and extracellular signals to the nucleus, ultimately leading to transcription of specific target genes and downstream phenotypic effects. It was quickly appreciated that the STATs, especially STAT3, play a fundamental role in human malignancy. In contrast to normal biology in which transient STAT3 signaling is strictly regulated by a tightly coordinated network of activators and deactivators, STAT3 is constitutively activated in human malignancies. Constitutive STAT3 signaling has been associated with many cancerous phenotypes across nearly all human cancers, including the upregulation of cell growth, proliferation, survival, and motility, among others. Studies involving candidate preclinical STAT3 inhibitors have further demonstrated that the reversal of these phenotypes results from pharmacologic or genetic inhibition of STAT3, suggesting that STAT3 may be a promising target for clinical interventions. Indeed, a Phase 0 clinical trial involving a STAT3 decoy oligonucleotide demonstrated that STAT3 is a drug-gable target in human tumors. Because of the ubiquity of overactive STAT3 in cancer, its role in promoting a wide variety of cancerous phenotypes, and the strong clinical and preclinical studies performed to date, STAT3 represents a promising target for the development of inhibitors for the treatment of human cancers.

BST-2 is a potential activator of invasion and migration in tamoxifen-resistant breast cancer cells

Bone marrow stromal cell antigen 2 (BST-2) is a type II transmembrane protein that is known to be a therapeutic target in several types of cancer. However, despite its clinical importance, the roles of BST-2 expression have remained elusive. Here, we found that BST-2 expression is up-regulated in tamoxifen-resistant MCF-7 human breast cancer (TRM-7) cells, resulting in enhanced invasiveness and migration. Matrigel and wound healing assays also showed that overexpression of BST-2 increased invasion and migration in MCF-7 cells, whereas invasion and migration were decreased by the silencing of BST-2 in TRM-7 cells. In addition, B16F10 cells expressing BST-2 showed increased metastatic melanoma nodule growth in a lung metastasis mouse model. Furthermore, BST-2 expression and promoter activity were regulated by activated signal transducer and activator of transcription 3 (STAT3). Taken together, our results indicate that BST-2 is an important factor in the invasiveness and motility of tamoxifen-resistant breast cancer cells, and that its expression and activity are regulated by activated STAT3. Therefore, regulation of BST-2 is a potential therapeutic target for tamoxifen-resistant breast cancer.

CD147 mediates chemoresistance in breast cancer via ABCG2 by affecting its cellular localization and dimerization

CD147 and ABCG2 both have been reported to mediate Multidrug resistance (MDR) in breast cancer. Recent study demonstrates that CD147 could form a complex with ABCG2 on the cell membrane in primary effusion lymphoma. However, whether these two molecules regulate each other in breast cancer and result in MDR is not clear. We established four MCF-7 cell lines transfected with CD147 and/or ABCG2 and found that CD147 could increase the expression and dimerization of ABCG2, affect its cellular localization and regulate its drug transporter function. The findings derived from cells were confirmed subsequently in clinic samples of chemotherapy-sensitive/resistant breast cancer.

p42/p44 MAPK-mediated Stat3Ser727 phosphorylation is required for progestin-induced full activation of Stat3 and breast cancer growth

Stat3 is a signaling node for multiple oncogenic pathways and is therefore frequently active in breast cancer. As experimental and clinical evidence reveals that progestins are key players in controlling mammary gland tumorigenesis, we studied Stat3 participation in this event. We have previously shown that progestins induce Stat3Tyr705 phosphorylation and its transcriptional activation in breast cancer cells. In this study, we demonstrate that progestins also induce Stat3 phosphorylation at Ser727 residue, which occurs via activation of c-Src/p42/p44 MAPK pathways in murine progestin-dependent C4HD cells and in T-47D cells. Expression of a Stat3S727A vector, which carries a serine-to-alanine substitution at codon 727, shows that Stat3Ser727 phosphorylation is required for full transcriptional activation of cyclin D1 gene expression by progestins and for in vivo Stat3 recruitment on cyclin D1 promoter. Transfection of Stat3S727A in murine and human breast cancer cells abolished progestin-induced in vitro and in vivo growth. Moreover, we found a positive correlation between progesterone receptor expression and nuclear localization of Stat3Ser727 phosphorylation in breast cancer biopsies. These data highlight Stat3 phosphorylation in Ser727 residue as a nongenomic action by progestins, necessary to promote breast cancer growth.

Linifanib (ABT-869) enhances radiosensitivity of head and neck squamous cell carcinoma cells

OBJECTIVES

Novel targeted therapeutic strategies to overcome radio-resistance of cancer cells traditionally treated with radiation may improve patient survival with the added benefit of reduced systemic toxicity. Herein, we tested the feasibility of Linifanib (ABT-869), a multi-receptor tyrosine kinase inhibitor of members of vascular endothelial growth factor (VEGF) and platelet derived growth factor (PDGF) receptor families, on radio-sensitization of Head and Neck Squamous Cell Carcinoma (HNSCC).

MATERIALS AND METHODS

UMSCC-22A and UMSCC-22B cells were treated with Linifanib and γ-radiation response was determined. Cell viability, cytotoxicity, apoptosis induction and cell cycle distribution were examined by MTT assay, colony formation assay and flow cytometry. In addition, expression of STAT3 and downstream signaling proteins were assessed using western immunoblotting.

RESULTS

Treatment with Linifanib resulted in cell growth inhibition, G2/M cell cycle arrest, induction of cell death via apoptosis, reduced phosphorylation of STAT3, which has been linked to radio-resistance, lower expression of cyclin D1, survivin and increased PARP cleavage. In addition, Linifanib overcame the radio-resistance of the cell lines and significantly enhanced radiation-induced cytotoxicity (p<0.05).

CONCLUSION

These data suggest the possibility of combining targeted therapeutic such as Linifanib with radiation to enhance inhibition of cell growth and apoptosis in HNSCC cells. Thus, it may provide a novel therapeutic strategy and improve efficacy of radiation against HNSCC in the future.

Biomarkers of residual disease, disseminated tumor cells, and metastases in the MMTV-PyMT breast cancer model

Cancer metastases arise in part from disseminated tumor cells originating from the primary tumor and from residual disease persisting after therapy. The identification of biomarkers on micro-metastases, disseminated tumors, and residual disease may yield novel tools for early detection and treatment of these disease states prior to their development into metastases and recurrent tumors. Here we describe the molecular profiling of disseminated tumor cells in lungs, lung metastases, and residual tumor cells in the MMTV-PyMT breast cancer model. MMTV-PyMT mice were bred with actin-GFP mice, and focal hyperplastic lesions from pubertal MMTV-PyMT;actin-GFP mice were orthotopically transplanted into FVB/n mice to track single tumor foci. Tumor-bearing mice were treated with TAC chemotherapy (docetaxel, doxorubicin, cyclophosphamide), and residual and relapsed tumor cells were sorted and profiled by mRNA microarray analysis. Data analysis revealed enrichment of the Jak/Stat pathway, Notch pathway, and epigenetic regulators in residual tumors. Stat1 was significantly up-regulated in a DNA-damage-resistant population of residual tumor cells, and a pre-existing Stat1 sub-population was identified in untreated tumors. Tumor cells from adenomas, carcinomas, lung disseminated tumor cells, and lung metastases were also sorted from MMTV-PyMT transplant mice and profiled by mRNA microarray. Whereas disseminated tumors cells appeared similar to carcinoma cells at the mRNA level, lung metastases were genotypically very different from disseminated cells and primary tumors. Lung metastases were enriched for a number of chromatin-modifying genes and stem cell-associated genes. Histone analysis of H3K4 and H3K9 suggested that lung metastases had been reprogrammed during malignant progression. These data identify novel biomarkers of residual tumor cells and disseminated tumor cells and implicate pathways that may mediate metastasis formation and tumor relapse after therapy.

Delivery of the co-expression plasmid pEndo-Si-Stat3 by attenuated Salmonella serovar typhimurium for prostate cancer treatment

OBJECTIVES

To investigate the therapeutic utility of an attenuated bacterium carrying a plasmid that co-expresses Endostatin, an inhibitor of tumor neovasculogenesis, and a shRNA that targets Stat3 to suppress prostate cancer growth.

METHODS

Plasmid pEndo-Si-Stat3 was constructed and introduced into an attenuated strain of Salmonella enterica serovar typhimurium. The resultant recombinant bacterium was used as a vector to deliver the plasmid to tumor cells growing in vivo. Tumor-associated gene and protein expression changes were measured by using RT-PCR and Western blot analyses. Expression of Endostatin in tumor tissue was detected by ELISA. The presence of vector bacteria in tissues was monitored and tumor destruction was assessed by using TUNEL and H&E staining assays.

RESULTS

Bacterially delivered pEndo-Si-Stat3 decreased Stat3 levels and increased Endostatin expression in mouse tumors, resulting in a significant suppression of tumor growth (P < 0.01). Expression of Bcl-2 and PCNA was down-regulated and Caspase3 expression was up-regulated to promote apoptosis of tumor cells.

CONCLUSIONS

Successful delivery by attenuated Salmonella of the combination therapeutic plasmid simultaneously knocked down the expression of Stat3 and resulted in over-expression of Endostatin, which synergistically inhibited prostate cancer growth.

Stat3 inhibitor Stattic exhibits potent antitumor activity and induces chemo- and radio-sensitivity in nasopharyngeal carcinoma

Nasopharyngeal carcinoma (NPC) is an Epstein-Barr virus-associated malignancy most common in East Asia, Africa and Alaska. Radiotherapy and cisplatin-based chemotherapy are the main treatment options. Unfortunately, disease response to concurrent chemoradiotherapy varies among patients with NPC, and many cases are resistant to cisplatin and radiotherapy. Signal transducer and activator of transcription 3 (Stat3) has been implicated in the development and progression of various solid tumors. In this study, we assessed the activation and expression of Stat3 in NPC cells. We found that Stat3 was activated and could be blocked by the small molecule inhibitor Stattic. The inhibition of Stat3 in NPC cells by Stattic decreased the expression of cyclin D1 in a dose- and time-dependent manner. Thus, Stattic was used to target Stat3 in NPC cell lines. We found that Stattic could inhibit cell viability and proliferation in NPC cells and significantly induced apoptosis. Additionally, Stat3 transfection attenuated, whereas Stat3 knockdown enhanced, the effects of Stattic upon cell viability inhibition and apoptosis induction. Furthermore, Stattic sensitized NPC cells to cisplatin and ionizing radiation (IR) by preventing cell proliferation and inducing apoptosis. Taken together, Stattic inhibit Stat3 and display antitumor effect in NPC, and enhanced chemosensitivity and radiosensitivity in NPC. Therefore, our findings provide the base for more rational approaches to treat NPC in the clinic.

IL-27 enhances the survival of tumor antigen-specific CD8+ T cells and programs them into IL-10-producing, memory precursor-like effector cells

IL-27 is a member of the IL-12 family of cytokines that is comprised of an IL-12 p40-related protein subunit, EBV-induced gene 3, and a p35-related subunit, p28. IL-27 functions through IL-27R and has been shown to have potent antitumor activity via activation of a variety of cellular components, including antitumor CD8(+) T-cell responses. However, the exact mechanisms of how IL-27 enhances antitumor CD8(+) T-cell responses remain unclear. Here we show that IL-27 significantly enhances the survival of activated tumor antigen-specific CD8(+) T cells in vitro and in vivo, and programs tumor antigen-specific CD8(+) T cells into memory precursor-like effector cells, characterized by upregulation of Bcl-6, SOCS3, Sca-1, and IL-10. While STAT3 activation and the CTL survival-enhancing effects can be independent of CTL IL-10 production, we show here that IL-27-induced CTL IL-10 production contributes to memory precursor cell phenotype induction, CTL memory, and tumor rejection. Thus, IL-27 enhances antitumor CTL responses via programming tumor antigen-specific CD8(+) T cells into a unique memory precursor type of effector cells characterized by a greater survival advantage. Our results have important implications for designing immunotherapy against human cancer.

Regulation of AKT gene expression by cisplatin

The use of chemotherapy drugs for the treatment of cancer is an effective therapeutic measure. However, chemoresistance affects the effectiveness of the treatment. AKT overexpression has been observed in chemoresistance. AKT expression in colon cells induced cisplatin resistance. The present study demonstrated the role of reactive oxygen species (ROS) in the induction of AKT regulation by cisplatin through the activation of JAK2/STAT3 at the transcriptional level in colon cancer cells. HCT-116 cells treated with cisplatin exhibited increased JAK2 and STAT3 activities. Reducing the expression of JAK2 in colon cancer cells using small interfering RNA (siRNA) decreased AKT expression. The present study demonstrated that AKT activation is closely associated with chemoresistance in human tumors. The inhibition of ROS decreased the levels of AKT in colon cancer cell lines. The JAK2/STAT3 pathway was also shown to mediate AKT expression and represents a potential target for overcoming cisplatin resistance in human tumors.

FACS analysis of Stat3/5 signaling reveals sensitivity to G-CSF and IL-6 as a significant prognostic factor in pediatric AML: a Children's Oncology Group report

Signal transducer and activator of transcription 3 (Stat3) and Stat5 are critical signaling intermediates that promote survival in myeloid leukemias. We examined Stat3 and Stat5 activation patterns in resting and ligand-stimulated primary samples from pediatric patients with acute myeloid leukemia. Phosphorylated Stats were measured by FACS before and after stimulation with increasing doses of granulocyte-colony stimulating factor or IL-6. We also measured positive and negative regulators of Stat signaling, and we compared the variation in multiple parameters to identify biologic relationships. Levels of constitutively phosphorylated Stats were variable and did not correlate with survival. In terms of induced phospho-Stats, 15 of 139 specimens (11%) phosphorylated Stat3 in response to moderate doses of both granulocyte-colony stimulating factor and IL-6. Compared with groups that were resistant to 1 or both ligands, this pattern of dual sensitivity was associated with a superior outcome, with a 5-year event-free survival of 79% (P = .049) and 5-year overall survival of 100% (P = .006). This study provides important and novel insights into the biology of Stat3 and Stat5 signaling in acute myeloid leukemia. Patterns of ligand sensitivity may be valuable for improving risk identification, and for developing new agents for individualized therapy.

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.

Tissue microarray-based study of patients with lymph node-positive breast cancer shows tyrosine phosphorylation of signal transducer and activator of transcription 3 (tyrosine705-STAT3) is a marker of good prognosis

BACKGROUND

Although lymph node-positive breast cancers are associated with poorer prognosis, individual patients may have different clinical outcomes. Signal transducer and activator of transcription 3 (STAT3) is a point of convergence for numerous oncogenic signalling pathways. The goal of this study was to determine the prognostic value of phosphorylated (tyrosine705)-STAT3 in node-positive breast cancer patients.

METHODS

Immunohistochemical analysis of Phospho- STAT3 was performed on a tissue microarray of breast cancer specimens. The expression pattern of Phospho-STAT3 was correlated with survival outcome, and clinical and pathological parameters.

RESULTS

Out of 125 interpretable tumours, positive Phospho- STAT3 nuclear expression was seen in 35 (28%) of tumours. There was no significant relationship between Phospho-STAT3 expression and clinical-pathological parameters including age, hormonal receptor status, grade and tumour size. Interestingly positive tumours had a significantly improved disease-free survival at 5 years (p=0.035). Additionally, positive Phospho-STAT3 nuclear expression was correlated with significantly improved survival at both 5 years (p=0.023) and 10 years (p=0.026). Finally, in multivariate analyses Phospho-STAT3 was found to be an independent prognostic marker of overall survival in node-positive breast cancer patients.

CONCLUSION

These findings support the role of Phospho- STAT3 as an important independent prognostic marker in node-positive breast cancer patients.

miR-337-3p and its targets STAT3 and RAP1A modulate taxane sensitivity in non-small cell lung cancers

NSCLC (non-small cell lung cancer) often exhibits resistance to paclitaxel treatment. Identifying the elements regulating paclitaxel response will advance efforts to overcome such resistance in NSCLC therapy. Using in vitro approaches, we demonstrated that over-expression of the microRNA miR-337-3p sensitizes NCI-H1155 cells to paclitaxel, and that miR-337-3p mimic has a general effect on paclitaxel response in NSCLC cell lines, which may provide a novel adjuvant strategy to paclitaxel in the treatment of lung cancer. By combining in vitro and in silico approaches, we identified STAT3 and RAP1A as direct targets that mediate the effect of miR-337-3p on paclitaxel sensitivity. Further investigation showed that miR-337-3p mimic also sensitizes cells to docetaxel, another member of the taxane family, and that STAT3 levels are significantly correlated with taxane resistance in lung cancer cell lines, suggesting that endogenous STAT3 expression is a determinant of intrinsic taxane resistance in lung cancer. The identification of a miR-337-3p as a modulator of cellular response to taxanes, and STAT3 and RAP1A as regulatory targets which mediate that response, defines a novel regulatory pathway modulating paclitaxel sensitivity in lung cancer cells, which may provide novel adjuvant strategies along with paclitaxel in the treatment of lung cancer and may also provide biomarkers for predicting paclitaxel response in NSCLC.

Elevated serum IL-10 levels in diffuse large B-cell lymphoma: a mechanism of aberrant JAK2 activation

Cytokines are deregulated in cancers and can contribute to tumor growth. In patients with diffuse large-cell lymphoma (DLBCL), we observed higher levels of JAK/STAT pathway-related serum cytokines (ie, IL-6, IL-10, epidermal growth factor, and IL-2) compared with controls. Of these, only IL-10 activated the JAK2 pathway in lymphoma cells in vitro. Patients with high serum IL-10 had shorter event-free survival (EFS) than patients with low levels (P > .01) and high IL-10 was correlated with high lactase dehydrogenase (P = .0085) and higher International Prognostic Index scores (P = .01). To explore the mechanism by which IL-10 may contribute to an inferior EFS, we investigated the effect of IL-10 on the JAK2 pathway and found that the IL-10/IL-10 receptor complex up-regulated JAK2 signaling. Neutralizing Ab to IL-10 inhibited constitutive and IL-10-induced JAK2/STAT3 phosphorylation. JAK2 inhibition dephosphorylated JAK2 and STAT3 and caused an inhibitory effect on phospho-JAK2-positive DLBCL cells; there was a minimal effect on phospho-JAK2-negative cells. Apoptosis induced by JAK2 inhibition was dependent on inhibition of autocrine IL-10 and c-myc expression and independent of Bcl-2 family expression. These results provide the rationale for testing JAK2 inhibitors in DLBCL patients, and indicate that serum IL-10 may be a biomarker to identify patients more likely to respond to JAK2-targeted therapy.

Thymoquinone decreases F-actin polymerization and the proliferation of human multiple myeloma cells by suppressing STAT3 phosphorylation and Bcl2/Bcl-XL expression

Background

Thymoquinone (TQ), the major active component of the medicinal herb Nigella sativa Linn., has been described as a chemopreventive and chemotherapeutic compound.

Methods

In this study, we investigated the effect of TQ on survival, actin cytoskeletal reorganization, proliferation and signal transduction in multiple myeloma (MM) cells.

Results

We found that TQ induces growth arrest in both MDN and XG2 cells in a dose- and time-dependent manner. TQ also inhibited CXC ligand-12 (CXCL-12)-mediated actin polymerization and cellular proliferation, as shown by flow cytometry. The signal transducer and activator of transcription (STAT) and B-cell lymphoma-2 (Bcl-2) signaling pathways may play important roles in the malignant transformation of a number of human malignancies. The constitutive activation of the STAT3 and Bcl-2 pathways is frequently observed in several cancer cell lines, including MM cells. Using flow cytometry, we found that TQ markedly decreased STAT3 phosphorylation and Bcl-2 and Bcl-_XL expression without modulating STAT5 phosphorylation in MM cells. Using western blotting, we confirmed the inhibitory effect of TQ on STAT3 phosphorylation and Bcl-2 and Bcl-_XL expression.

Conclusions

Taken together, our data suggests that TQ could potentially be applied toward the treatment of MM and other malignancies.

The curcumin analogue hydrazinocurcumin exhibits potent suppressive activity on carcinogenicity of breast cancer cells via STAT3 inhibition

Curcumin, the active component of turmeric, has been shown to protect against carcinogenesis and prevent tumor development in cancer. In our study, we tested the efficacy of a synthetic curcumin analogue, known as hydrazinocurcumin (HC), in breast cancer cells. The results demonstrated that compared to curcumin, HC was more effective in inhibiting STAT3 phosphorylation and downregulation of an array of STAT3 downstream targets which contributed to suppression of cell proliferation, loss of colony formation, depression of cell migration and invasion as well as induction of cell apoptosis. It was concluded that HC is a potent agent in the inhibition of STAT3 with more favorable pharmacological activity than curcumin, and HC may have translational potential as an effective cancer therapeutic or preventive agent for human breast carcinoma.

Cosmomycin C inhibits signal transducer and activator of transcription 3 (STAT3) pathways in MDA-MB-468 breast cancer cell

The signal transducer and activator of transcription 3 (STAT3) is constitutively activated in cancer cells. Therefore, blocking the aberrant activity of STAT3 in tumor cells is a validated therapeutic strategy. To discover novel inhibitors of STAT3 activity, we screened against microbial natural products using a dual-luciferase assay. Using the microbial metabolome library, we identified cosmomycin C (CosC), which was isolated from the mycelium extract of Streptomyces sp. KCTC19769, as a STAT3 pathway inhibitor. CosC inhibited STAT3 (Tyr705) phosphorylation and subsequent nuclear translocation in MDA-MB-468 breast cancer cells. CosC-mediated inhibition of STAT3 signaling pathway was confirmed by suppressed expression of STAT3 downstream target proteins including cyclin D1, Bcl-xL, survivin, Mcl-1, and VEGF in CosC-treated MDA-MB-468 cells. Flow cytometry showed that CosC caused accumulation in the G(0)-G(1) phase of the cell cycle and induced apoptosis via PARP cleavage and caspase-3 activation. Based on these findings, CosC may be a potential candidate for modulation of STAT3 pathway.

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.

XZH-5 inhibits STAT3 phosphorylation and causes apoptosis in human hepatocellular carcinoma cells

Growing evidence has demonstrated that signal transducer and activator of transcription 3 (STAT3), which is constitutively activated in patients with hepatocellular carcinoma (HCC), plays an important role in HCC development, progression, and prognosis. Interleukin-6 (IL-6) is a multifunctional inflammatory cytokine, which may induce STAT3 activation in a variety of human cancers. In this study, we demonstrated that blocking STAT3 phosphorylation with STAT3 small molecule inhibitors SD-1029 and Stattic caused apoptosis in HCC cells. Then we characterized the inhibitory effects of a novel small molecule XZH-5 on STAT3 phosphorylation in HCC cell lines. XZH-5 reduced constitutive STAT3 phosphorylation at Tyr705 and the expression of STAT3 downstream genes. The inhibition of STAT3 in HCC cells resulted in the induction of apoptosis and reduction of colony forming ability. In addition, XZH-5 also inhibited IL-6-induced STAT3 phosphorylation, nuclear translocation and STAT3 DNA binding activity. In contrast, it had no effect on IFN-γ-induced STAT1 phosphorylation, indicating the more selective effects on STAT3. These results suggested that XZH-5 may serve as a lead compound for further development of STAT3 specific small molecule inhibitors for HCC therapy.