Phosphotyrosyl peptides block Stat3-mediated DNA binding activity, gene regulation, and cell transformation

Hydroxamic Acid and Benzoic Acid-Based STAT3 Inhibitors Suppress Human Glioma and Breast Cancer Phenotypes In Vitro and In Vivo

STAT3 offers an attractive target for cancer therapy, but small-molecule inhibitors with appealing pharmacologic properties have been elusive. Here, we report hydroxamic acid-based and benzoic acid-based inhibitors (SH5-07 and SH4-54, respectively) with robust bioactivity. Both inhibitors blocked STAT3 DNA-binding activity in vitro and in human glioma, breast, and prostate cancer cells and in v-Src-transformed murine fibroblasts. STAT3-dependent gene transcription was blocked along with Bcl-2, Bcl-xL, Mcl-1, cyclin D1, c-Myc, and survivin expression. Nuclear magnetic resonance analysis of STAT3-inhibitor complexes defined interactions with the SH2 and DNA-binding domains of STAT3. Ectopic expression of the SH2 domain in cells was sufficient to counter the STAT3-inhibitory effects of SH4-54. Neither compound appreciably affected STAT1 or STAT5 DNA-binding activities, STAT3-independent gene transcription, or activation of a panel of oncogenic kinases in malignant cells. Each compound decreased the proliferation and viability of glioma, breast, and prostate cancer cells and v-Src-transformed murine fibroblasts harboring constitutively active STAT3. Further, in mouse xenograft models of glioma and breast cancer, administration of SH5-07 or SH4-54 effectively inhibited tumor growth. Our results offer preclinical proof of concept for SH5-07 and SH4-54 as candidates for further development as cancer therapeutics.

Small-molecule inhibitors targeting the DNA-binding domain of STAT3 suppress tumor growth, metastasis and STAT3 target gene expression in vivo

Signal transducer and activator of transcription 3 (STAT3) is constitutively activated in malignant tumors and has important roles in multiple aspects of cancer aggressiveness. Thus targeting STAT3 promises to be an attractive strategy for treatment of advanced metastatic tumors. Although many STAT3 inhibitors targeting the SH2 domain have been reported, few have moved into clinical trials. Targeting the DNA-binding domain (DBD) of STAT3, however, has been avoided due to its 'undruggable' nature and potentially limited selectivity. In a previous study, we reported an improved in silico approach targeting the DBD of STAT3 that resulted in a small-molecule STAT3 inhibitor (inS3-54). Further studies, however, showed that inS3-54 has off-target effect although it is selective to STAT3 over STAT1. In this study, we describe an extensive structure and activity-guided hit optimization and mechanistic characterization effort, which led to identification of an improved lead compound (inS3-54A18) with increased specificity and pharmacological properties. InS3-54A18 not only binds directly to the DBD and inhibits the DNA-binding activity of STAT3 both in vitro and in situ but also effectively inhibits the constitutive and interleukin-6-stimulated expression of STAT3 downstream target genes. InS3-54A18 is completely soluble in an oral formulation and effectively inhibits lung xenograft tumor growth and metastasis with little adverse effect on animals. Thus inS3-54A18 may serve as a potential candidate for further development as anticancer therapeutics targeting the DBD of human STAT3 and DBD of transcription factors may not be 'undruggable' as previously thought.

Current and future intratumoral targeted treatment for pancreatic cancer

Pancreatic cancer is an insidious type of cancer with its symptoms manifested upon extensive disease. The overall 5-year survival rates between 0.4 and 4%. Surgical resection is an option for only 10% of the patients with pancreatic cancer. Local recurrence and hepatic metastases occur within 2 years after surgery. There are currently several molecular pathways investigated and novel targeted treatments are on the market. However; the nature of pancreatic cancer with its ability to spread locally in the primary site and lymph nodes indicates that further experimentation with local interventional therapies could be a future treatment proposal as palliative care or adjunct to gene therapy and chemotherapy/radiotherapy. In the current review, we will summarize the molecular pathways and present the interventional treatment options for pancreatic cancer.

Phase I study of OPB-51602, an oral inhibitor of signal transducer and activator of transcription 3, in patients with relapsed/refractory hematological malignancies

We carried out a multicenter dose-escalation phase I study of oral OPB-51602, a signal transducer and activator of transcription 3 phosphorylation inhibitor, in patients with relapsed or refractory hematological malignancies to evaluate the safety, maximum tolerated dose (MTD), pharmacokinetics, and preliminary antitumor activity. Twenty patients were treated with OPB-51602 at doses of 1, 2, 3, 4, and 6 mg in the “3 + 3” dose escalation design. The most common treatment-related adverse events included nausea (55%), peripheral sensory neuropathy (45%), and diarrhea (40%). The most frequently observed grade 3 or 4 drug-related adverse events were neutropenia (20%), leukopenia (15%), lymphopenia (10%), and thrombocytopenia (10%). The MTD was 6 mg, with dose-limiting toxicities of grade 3 lactic acidosis and increased blood lactic acid levels observed in one of three patients and grade 1–2 peripheral neuropathy in three of three patients. The recommended dose was determined to be 4 mg. OPB-51602 was rapidly absorbed, and exposure tended to increase in a dose-dependent manner. Accumulation of OPB-51602 was seen with 4 weeks of multiple treatments. No clear therapeutic response was observed. Durable stable disease was observed in two patients with acute myeloid leukemia and one with myeloma. In conclusion, the MTD of OPB-51602 was 6 mg. OPB-51602 was safe and well tolerated in a dose range of 1–4 mg. However, long-term administration at higher doses was difficult with the daily dosing schedule, and no response was seen. Therefore, further clinical development of OPB-51602 for hematological malignancies with a daily dosing schedule was terminated.

STAT3 upregulation in pituitary somatotroph adenomas induces growth hormone hypersecretion

Pituitary somatotroph adenomas result in dysregulated growth hormone (GH) hypersecretion and acromegaly; however, regulatory mechanisms that promote GH hypersecretion remain elusive. Here, we provide evidence that STAT3 directly induces somatotroph tumor cell GH. Evaluation of pituitary tumors revealed that STAT3 expression was enhanced in human GH-secreting adenomas compared with that in nonsecreting pituitary tumors. Moreover, STAT3 and GH expression were concordant in a somatotroph adenoma tissue array. Promoter and expression analysis in a GH-secreting rat cell line (GH3) revealed that STAT3 specifically binds the Gh promoter and induces transcription. Stable expression of STAT3 in GH3 cells induced expression of endogenous GH, and expression of a constitutively active STAT3 further enhanced GH production. Conversely, expression of dominant-negative STAT3 abrogated GH expression. In primary human somatotroph adenoma-derived cell cultures, STAT3 suppression with the specific inhibitor S3I-201 attenuated GH transcription and reduced GH secretion in the majority of derivative cultures. In addition, S3I-201 attenuated somatotroph tumor growth and GH secretion in a rat xenograft model. GH induced STAT3 phosphorylation and nuclear translocation, indicating a positive feedback loop between STAT3 and GH in somatotroph tumor cells. Together, these results indicate that adenoma GH hypersecretion is the result of STAT3-dependent GH induction, which in turn promotes STAT3 expression, and suggest STAT3 as a potential therapeutic target for pituitary somatotroph adenomas.

Pharmacological manipulation of transcription factor protein-protein interactions: opportunities and obstacles

Much research on transcription factor biology and their genetic pathways has been undertaken over the last 30 years, especially in the field of developmental biology and cancer. Yet, very little is known about the molecular modalities of highly dynamic interactions between transcription factors, genomic DNA, and protein partners. Methodological breakthroughs such as RNA-seq (RNA-sequencing), ChIP-seq (chromatin immunoprecipitation sequencing), RIME (rapid immunoprecipitation mass spectrometry of endogenous proteins), and single-molecule imaging will dramatically accelerate the discovery rate of their molecular mode of action in the next few years. From a pharmacological viewpoint, conventional methods used to target transcription factor activity with molecules mimicking endogenous ligands fail to achieve high specificity and are limited by a lack of identification of new molecular targets. Protein-protein interactions are likely to represent one of the next major classes of therapeutic targets. Transcription factors, known to act mostly via protein-protein interaction, may well be at the forefront of this type of drug development. One hurdle in this field remains the difficulty to collate structural data into meaningful information for rational drug design. Another hurdle is the lack of chemical libraries meeting the structural requirements of protein-protein interaction disruption. As more attempts at modulating transcription factor activity are undertaken, valuable knowledge will be accumulated on the modality of action required to modulate transcription and how these findings can be applied to developing transcription factor drugs. Key discoveries will spawn into new therapeutic approaches not only as anticancer targets but also for other indications, such as those with an inflammatory component including neurodegenerative disorders, diabetes, and chronic liver and kidney diseases.

Investigational therapies targeting signal transducer and activator of transcription 3 for the treatment of cancer

INTRODUCTION

Signal transducer and activator of transcription 3 (STAT3) mediates the expression of a variety of genes in response to cell stimuli and thus plays a key role in several cellular processes such as cell growth and apoptosis. Deregulation of the STAT3 activity has been shown in many malignancies, including breast, head and neck, prostate, pancreas, ovarian and brain cancers and melanoma. Thus, STAT3 may represent an ideal target for cancer therapy.

AREAS COVERED

The authors review recent data on the role of STAT3 in tumor initiation and progression, as well as the ongoing clinical trials in cancer patients. The content includes information derived from trial databases, regulatory authorities and scientific literature.

EXPERT OPINION

Targeting STAT3 activation leads to the inhibition of tumor growth and metastasis both in vitro and in vivo without affecting normal cells; this suggests that STAT3 could be a valid molecular target for cancer therapy. Extensive clinical research is trying to find anti-STAT3 agents with high single-agent activity. The identification and development of novel drugs that can target deregulated STAT3 activation effectively is both a scientific and clinical challenge that needs to be addressed in the near future.

Effects of hnRNP A2/B1 Knockdown on Inhibition of Glioblastoma Cell Invasion, Growth and Survival

Heterogeneous nuclear ribonucleoprotein A2/B1 (hnRNP A2/B1) plays an important role in influence of pre-messenger RNA (pre-mRNA) processing and mRNA metabolism and transportation in cells. Increasing evidence indicates that hnRNP A2/B1 played an important role in development and progression of various human cancers. Forty cases of normal and human glioma tissue samples were analyzed using immunohistochemistry to reveal the expression of hnRNP A2/B1 protein in the samples. Then, knockdown of hnRNP A2/B1 expression induced by RNA interference (RNAi) method was used to analyze the role of hnRNP A2/B1 in glioblastoma cell viability, adhesion, migration, invasion, and chemoresistance for temozolomide (TMZ). The data showed that hnRNP A2/B1 protein was overexpressed in glioma tissue specimens and associated with advanced glioma grades. Knockdown of hnRNP A2/B1 could reduce glioblastoma cell viability, adhesion, migration, invasion, and chemoresistance for TMZ capacity, but induced tumor cells to apoptosis and reactive oxygen species (ROS) generation in glioma U251 and SHG44 cells. Molecularly, hnRNP A2/B1 knockdown reduced expression of phospho-STAT3 and MMP-2. Detection of hnRNP A2/B1 expression may be useful as a biomarker for prediction of glioma progression and knockdown of hnRNP A2/B1 expression as a novel strategy in future control of glioblastoma in clinic.

Ascochlorin, an isoprenoid antibiotic inhibits growth and invasion of hepatocellular carcinoma by targeting STAT3 signaling cascade through the induction of PIAS3

Deregulated activation of oncogenic transcription factors such as signal transducer and activator of transcription 3 (STAT3) plays a pivotal role in proliferation and survival of hepatocellular carcinoma (HCC). Thus, agents which can inhibit STAT3 activation may have an enormous potential for treatment of HCC patients. Hence, in the present report, we investigated the effect of ascochlorin (ASC), an isoprenoid antibiotic on STAT3 activation cascade in various HCC cell lines and orthotopic mouse model. We observed that ASC could substantially inhibit both constitutive and IL-6/EGF inducible STAT3 activation as well as reduce its DNA binding ability. ASC increased the expression of protein inhibitor of activated STAT3 (PIAS3) which could bind to STAT3 DNA binding domain and thereby down-regulate STAT3 activation. Deletion of PIAS3 gene by siRNA abolished the ability of ASC to inhibit STAT3 activation and induce apoptosis in HCC cells. ASC also modulated the expression of diverse STAT3-regulated oncogenic gene products. Finally, when administered intraperitoneally, ASC also inhibited tumor growth in an orthotopic HCC mouse model and reduced STAT3 activation in tumor tissues. Overall our results indicate that ASC mediates its anti-tumor effects predominantly through the suppression of STAT3 signaling cascade, and can form the basis of novel therapy for HCC patients.

Postsurgical adjuvant tumor therapy by combining anti-angiopoietin-2 and metronomic chemotherapy limits metastatic growth

Antiangiogenic tumor therapy has failed in the adjuvant setting. Here we show that inhibition of the Tie2 ligand angiopoietin-2 (Ang2) effectively blocks metastatic growth in preclinical mouse models of postsurgical adjuvant therapy. Ang2 antibody treatment combines well with low-dose metronomic chemotherapy (LDMC) in settings in which maximum-dose chemotherapy does not prove effective. Mechanistically, Ang2 blockade could be linked to quenching the inflammatory and angiogenic response of endothelial cells (ECs) in the metastatic niche. Reduced EC adhesion molecule and chemokine expression inhibits the recruitment of tumor-promoting CCR2(+)Tie2(-) metastasis-associated macrophages. Moreover, LDMC contributes to therapeutic efficacy by inhibiting the recruitment of protumorigenic bone marrow-derived myeloid cells. Collectively, these data provide a rationale for mechanism-guided adjuvant tumor therapies.

Upregulation of TPX2 by STAT3: identification of a novel STAT3 binding site

TPX2, a protein involved in mitosis, is considered a good marker for actively proliferating tissues, highly expressed in a number of cancer cells. We show the presence of high-affinity binding site for STAT3 in the 5'-flanking region of the Tpx2 gene, which is in vivo bound by activated STAT3. A specific STAT3 peptide inhibitor represses the expression of the Tpx2 gene and inhibits the binding of STAT3 to its consensus sequence in human cell lines where STAT3 is activated. These results indicate that activated STAT3 contributes to the over-expression of Tpx2 through the binding to an enhancer site.

Could signal transducer and activator of transcription 3 be a therapeutic target in obesity-related gastrointestinal malignancy?

INTRODUCTION

A large body of evidence has implicated the signal transducer and activator of transcription (STAT) family and particularly the ubiquitously expressed STAT3 protein in the pathogenesis of colorectal, hepatocellular, gastric and pancreatic carcinoma.

DISCUSSION

Concomitantly, an increasing body of epidemiological evidence has linked obesity and its associated pro-inflammatory state with the development of gastrointestinal cancers. Visceral adipose tissue is no longer considered inert and is known to secrete a number of adipocytokines such as leptin, interleukin (IL)-6, IL-8, IL-1β and tumour necrosis factor-alpha (TNF-α) into the surrounding environment. Interestingly, these adipocytokines are strongly linked with the Janus kinase (JAK)/STAT pathway of signal transduction and there is experimental evidence linking IL-1β, IL-8 and TNF-α to JAK/STAT signaling in other tissues. The result is an up-regulation of a wide range of anti-apoptotic, pro-metastatic and pro-angiogenic genes and processes. This is particularly relevant for gastrointestinal malignancy as these factors have the potential to signal adjacent endothelial cells in a paracrine manner.

CONCLUSION

This review examines the potential role of the STAT3 signaling pathway in the pathogenesis of obesity-related gastrointestinal malignancy and the potential therapeutic role of STAT3 blockade given its status as a signaling hub for a number of inflammatory adipocytokines.

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.

Dual-inhibitors of STAT5 and STAT3: studies from molecular docking and molecular dynamics simulations

Although molecularly targeted therapy with imatinib has improved treatments of chronic myeloid leukemia (CML), clinical resistance gradually develops in patients with accelerated or blast phase CML. The inability of imatinib to cure CML suggests that inactivation of BCR-ABL kinase activity alone is not sufficient to control the disease. Aberrant STAT signaling and constitutive STAT5 or STAT3 activation are frequently found in both acute and chronic leukemia. Constitutive activation of STAT5 and STAT3 are associated with imatinib resistance on leukemia cells. Development of drugs targeting SH2 domains of STAT5 and STAT3 provides a novel strategy for the treatment of the imatinib-resistant CML. Here, molecular docking and molecular dynamics simulations were used to investigate the interactions of the drugs targeting STAT3 and STAT5 receptors at molecular level. The calculated binding free energies are consistent with the ranking of the experimental affinities and our simulations also explained their differences in binding energy. Then virtual screening based on molecular docking and molecular dynamics was applied to screen a set of ~1500 compounds for dual inhibitors of the SH2 domains of STAT5 and STAT3. Three top score compounds obtained in virtual screening were compound 660, 304, and 561. Results show that the three predicted dual-inhibitors are well fitted within the two binding domains and are predicted to present improved STAT5 and STAT3 SH2 inhibitory activity.

STAT3 inhibitors for cancer therapy: Have all roads been explored?

The signal transducer and activator of transcription STAT3 is a transcription factor which plays a key role in normal cell growth and is constitutively activated in about 70% of solid and hematological cancers. Activated STAT3 is phosphorylated on tyrosine and forms a dimer through phosphotyrosine/src homology 2 (SH2) domain interaction. The dimer enters the nucleus via interaction with importins and binds target genes. Inhibition of STAT3 results in the death of tumor cells, this indicates that it is a valuable target for anticancer strategies; a view that is corroborated by recent findings of activating mutations within the gene. Yet, there is still only a small number of STAT3 direct inhibitors; in addition, the high similarity of STAT3 with STAT1, another STAT family member mostly oriented toward apoptosis, cell death and defense against pathogens, requires that STAT3-inhibitors have no effect on STAT1. Specific STAT3 direct inhibitors consist of SH2 ligands, including G quartet oligodeoxynucleotides (ODN) and small molecules, they induce cell death in tumor cells in which STAT3 is activated. STAT3 can also be inhibited by decoy ODNs (dODN), which bind STAT3 and induce cell death. A specific STAT3 dODN which does not interfere with STAT1-mediated interferon-induced cell death has been designed pointing to the STAT3 DBD as a target for specific inhibition. Comprehensive analysis of this region is in progress in the laboratory to design DBD-targeting STAT3 inhibitors with STAT3/STAT1 discriminating ability.

The consequences of selective inhibition of signal transducer and activator of transcription 3 (STAT3) tyrosine705 phosphorylation by phosphopeptide mimetic prodrugs targeting the Src homology 2 (SH2) domain

Herein we review our progress on the development of phosphopeptide-based prodrugs targeting the SH2 domain of STAT3 to prevent recruitment to cytokine and growth factor receptors, activation, nuclear translocation and transcription of genes involved in cancer. We developed high affinity phosphopeptides (K_I = 46–200 nM). Corresponding prodrugs inhibited constitutive and IL-6 induced Tyr705 phosphorylation at 0.5–1 μM in a variety of human cancer cell lines. They were not cytotoxic at 5 μM in vitro but they inhibited tumor growth in a human xenograft breast cancer model in mice, accompanied by reduced VEGF expression and angiogenesis.

Identification of a natural product-like STAT3 dimerization inhibitor by structure-based virtual screening

STAT3 regulates a variety of genes involved with cell proliferation, differentiation, apoptosis, angiogenesis, metastasis, inflammation, and immunity. The purpose of this study was to apply molecular docking techniques to identify STAT3 inhibitors from a database of over 90000 natural product and natural product-like compounds. The virtual screening campaign furnished 14 hit compounds, from which compound 1 emerged as a top candidate. Compound 1 inhibited STAT3 DNA-binding activity in vitro and attenuated STAT3-directed transcription in cellulo with selectivity over STAT1 and with comparable potency to the well-known STAT3 inhibitor S3I-201. Furthermore, compound 1 inhibited STAT3 dimerization and decreased STAT3 phosphorylation in cells without affecting STAT1 dimerization and phosphorylation. Compound 1 also exhibited selective anti-proliferative activity against cancer cells over normal cells in vitro. Molecular docking analysis suggested that compound 1 might putatively function as an inhibitor of STAT3 dimerization by binding to the SH2 domain. This study also validates the use of in silico techniques to identify inhibitors of protein-protein interactions, which are typically considered difficult to target with small molecules.

Transcription Factor STAT3 as a Novel Molecular Target for Cancer Prevention

Signal Transducers and Activators of Transcription (STATs) are a family of transcription factors that regulate cell proliferation, differentiation, apoptosis, immune and inflammatory responses, and angiogenesis. Cumulative evidence has established that STAT3 has a critical role in the development of multiple cancer types. Because it is constitutively activated during disease progression and metastasis in a variety of cancers, STAT3 has promise as a drug target for cancer therapeutics. Recently, STAT3 was found to have an important role in maintaining cancer stem cells in vitro and in mouse tumor models, suggesting STAT3 is integrally involved in tumor initiation, progression and maintenance. STAT3 has been traditionally considered as nontargetable or undruggable, and the lag in developing effective STAT3 inhibitors contributes to the current lack of FDA-approved STAT3 inhibitors. Recent advances in cancer biology and drug discovery efforts have shed light on targeting STAT3 globally and/or specifically for cancer therapy. In this review, we summarize current literature and discuss the potential importance of STAT3 as a novel target for cancer prevention and of STAT3 inhibitors as effective chemopreventive agents.

A specific STAT3-binding peptide exerts antiproliferative effects and antitumor activity by inhibiting STAT3 phosphorylation and signaling

STAT3 promotes the survival, proliferation, metastasis, immune escape, and drug resistance of cancer cells, making its targeting an appealing prospect. However, although multiple inhibitors of STAT3 and its regulatory or effector pathway elements have been developed, bioactive agents have been somewhat elusive. In this report, we report the identification of a specific STAT3-binding peptide (APTSTAT3) through phage display of a novel "aptide" library. APTSTAT3 bound STAT3 with high specificity and affinity (∼231 nmol/L). Addition of a cell-penetrating motif to the peptide to yield APTSTAT3-9R enabled uptake by murine B16F1 melanoma cells. Treatment of various types of cancer cells with APTSTAT3-9R blocked STAT3 phosphorylation and reduced expression of STAT targets, including cyclin D1, Bcl-xL, and survivin. As a result, APTSTAT3-9R suppressed the viability and proliferation of cancer cells. Furthermore, intratumoral injection of APTSTAT3-9R exerted potent antitumor activity in both xenograft and allograft tumor models. Our results offer a preclinical proof-of-concept for APTSTAT3 as a tractable agent for translation to target the broad array of cancers harboring constitutively activated STAT3.

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.

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.

STAT inhibitors for cancer therapy

Signal Transducer and Activator of Transcription (STAT) proteins are a family of cytoplasmic transcription factors consisting of 7 members, STAT1 to STAT6, including STAT5a and STAT5b. STAT proteins are thought to be ideal targets for anti-cancer therapy since cancer cells are more dependent on the STAT activity than their normal counterparts. Inhibitors targeting STAT3 and STAT5 have been developed. These included peptidomimetics, small molecule inhibitors and oligonucleotides. This review summarized advances in preclinical and clinical development of these compounds.

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.

Survivin Is a transcriptional target of STAT3 critical to estradiol neuroprotection in global ischemia

Transient global ischemia causes selective, delayed death of hippocampal CA1 pyramidal neurons in humans and animals. It is well established that estrogens ameliorate neuronal death in animal models of focal and global ischemia. However, the role of signal transducer and activator of transcription-3 (STAT3) and its target genes in estradiol neuroprotection in global ischemia remains unclear. Here we show that a single intracerebral injection of 17β-estradiol to ovariectomized female rats immediately after ischemia rescues CA1 neurons destined to die. Ischemia promotes activation of STAT3 signaling, association of STAT3 with the promoters of target genes, and STAT3-dependent mRNA and protein expression of prosurvival proteins in the selectively vulnerable CA1. In animals subjected to ischemia, acute postischemic estradiol further enhances activation and nuclear translocation of STAT3 and STAT3-dependent transcription of target genes. Importantly, we show that STAT3 is critical to estradiol neuroprotection, as evidenced by the ability of STAT3 inhibitor peptide and STAT3 shRNA delivered directly into the CA1 of living animals to abolish neuroprotection. In addition, we identify survivin, a member of the inhibitor-of-apoptosis family of proteins and known gene target of STAT3, as essential to estradiol neuroprotection, as evidenced by the ability of shRNA to survivin to reverse neuroprotection. These findings indicate that ischemia and estradiol act synergistically to promote activation of STAT3 and STAT3-dependent transcription of survivin in insulted CA1 neurons and identify STAT3 and survivin as potentially important therapeutic targets in an in vivo model of global ischemia.

Novel multiplexed assay for identifying SH2 domain antagonists of STAT family proteins

Some of the signal transducer and activator of transcription (STAT) family members are constitutively activated in a wide variety of human tumors. The activity of STAT depends on their Src homology 2 (SH2) domain-mediated binding to sequences containing phosphorylated tyrosine. Thus, antagonizing this binding is a feasible approach to inhibiting STAT activation. We have developed a novel multiplexed assay for STAT3- and STAT5b-SH2 binding, based on amplified luminescent proximity homogeneous assay (Alpha) technology. AlphaLISA and AlphaScreen beads were combined in a single-well assay, which allowed the binding of STAT3- and STAT5b-SH2 to phosphotyrosine peptides to be simultaneously monitored. Biotin-labeled recombinant human STAT proteins were obtained as N- and C-terminal deletion mutants. The spacer length of the DIG-labeled peptide, the reaction time, and the concentration of sodium chloride were optimized to establish a HTS system with Z' values of greater than 0.6 for both STAT3- and STAT5b-SH2 binding. We performed a HTS campaign for chemical libraries using this multiplexed assay and identified hit compounds. A 2-chloro-1,4-naphthalenedione derivative, Compound 1, preferentially inhibited STAT3-SH2 binding in vitro, and the nuclear translocation of STAT3 in HeLa cells. Initial structure activity relationship (SAR) studies using the multiplexed assay showed the 3-substituent effect on both the activity and selectivity of STAT3 and STAT5b inhibition. Therefore, this multiplexed assay is useful for not only searching for potential lead compounds but also obtaining SAR data for developing new STAT3/STAT5b inhibitors.

Immunoresponsive gene 1 augments bactericidal activity of macrophage-lineage cells by regulating β-oxidation-dependent mitochondrial ROS production

Evidence suggests the bactericidal activity of mitochondria-derived reactive oxygen species (mROS) directly contributes to killing phagocytozed bacteria. Infection-responsive components that regulate this process remain incompletely understood. We describe a role for the mitochondria-localizing enzyme encoded by Immunoresponsive gene 1 (IRG1) during the utilization of fatty acids as a fuel for oxidative phosphorylation (OXPHOS) and associated mROS production. In a zebrafish infection model, infection-responsive expression of zebrafish irg1 is specific to macrophage-lineage cells and is regulated cooperatively by glucocorticoid and JAK/STAT signaling pathways. Irg1-depleted macrophage-lineage cells are impaired in their ability to utilize fatty acids as an energy substrate for OXPHOS-derived mROS production resulting in defective bactericidal activity. Additionally, the requirement for fatty acid β-oxidation during infection-responsive mROS production and bactericidal activity toward intracellular bacteria is conserved in murine macrophages. These results reveal IRG1 as a key component of the immunometabolism axis, connecting infection, cellular metabolism, and macrophage effector function.

The self-renewal of mouse embryonic stem cells is regulated by cell-substratum adhesion and cell spreading

Mouse embryonic stem cells (mESCs) undergo self-renewal in the presence of the cytokine, leukaemia inhibitory factor (LIF). Following LIF withdrawal, mESCs differentiate, and this is accompanied by an increase in cell-substratum adhesion and cell spreading. The purpose of this study was to investigate the relationship between cell spreading and mESC differentiation. Using E14 and R1 mESC lines, we have restricted cell spreading in the absence of LIF by either culturing mESCs on chemically defined, weakly adhesive biomaterial substrates, or by manipulating the cytoskeleton. We demonstrate that by restricting the degree of spreading by either method, mESCs can be maintained in an undifferentiated and pluripotent state. Under these conditions, self-renewal occurs without the need for LIF and is independent of nuclear translocation of tyrosine-phosphorylated STAT3 or β-catenin, which have previously been implicated in self-renewal. We also demonstrate that the effect of restricted cell spreading on mESC self-renewal is not mediated by increased intercellular adhesion, as evidenced by the observations that inhibition of mESC adhesion using a function blocking anti E-cadherin antibody or siRNA do not promote differentiation. These results show that mESC spreading and differentiation are regulated both by LIF and by cell-substratum adhesion, consistent with the hypothesis that cell spreading is the common intermediate step in the regulation of mESC differentiation by either LIF or cell-substratum adhesion.

Curcumin ameliorates dextran sulfate sodium-induced experimental colitis by blocking STAT3 signaling pathway

BACKGROUND AND AIMS

Although a series of studies have shown that curcumin can exert anti-inflammatory effects in colitis by inhibiting NF-κB activation, whether these anti-inflammatory effects of curcumin are also attributed to its ability to inhibiting STAT3 pathway has never been tested in experimental colitis to date. The purpose of the study was to investigate whether curcumin could exert its therapeutic effects in experimental colitis by inhibiting STAT3 pathway.

MATERIALS AND METHODS

Curcumin was administered in experimental colitis induced by dextran sulfate sodium (DSS). The disease activity index (DAI) and histological score were observed. The phospho-STAT3 was assessed by western blot analysis. The DNA-binding activity of STAT3 dimers was evaluated by electrophoretic mobility shift assay (EMSA). The expression of tumor necrosis factor (TNF)-α and interleukin (IL)-1β was measured by enzyme-linked immunosorbent assay. Myeloperoxidase (MPO) activity was determined by using MPO assay kit.

RESULTS

A significant improvement was observed in DAI and histological score in mice with curcumin, and the increases in phospho-STAT3 activity, DNA-binding activity of STAT3 dimers, MPO activity, IL-1β, and TNF-α expression in mice with DSS-induced colitis were significantly reduced following treatment with curcumin.

CONCLUSION

Curcumin exerts beneficial effects in experimental colitis by the suppression of STAT3 pathway, which may therefore provide a better understanding of the mechanism of action for curcumin in treating colitis.

Reciprocal regulation by TLR4 and TGF-β in tumor-initiating stem-like cells

Tumor-initiating stem-like cells (TICs) are resistant to chemotherapy and associated with hepatocellular carcinoma (HCC) caused by HCV and/or alcohol-related chronic liver injury. Using HCV Tg mouse models and patients with HCC, we isolated CD133(+) TICs and identified the pluripotency marker NANOG as a direct target of TLR4, which drives the tumor-initiating activity of TICs. These TLR4/NANOG-dependent TICs were defective in the TGF-β tumor suppressor pathway. Functional oncogene screening of a TIC cDNA library identified Yap1 and Igf2bp3 as NANOG-dependent genes that inactivate TGF-β signaling. Mechanistically, we determined that YAP1 mediates cytoplasmic retention of phosphorylated SMAD3 and suppresses SMAD3 phosphorylation/activation by the IGF2BP3/AKT/mTOR pathway. Silencing of both YAP1 and IGF2BP3 restored TGF-β signaling, inhibited pluripotency genes and tumorigenesis, and abrogated chemoresistance of TICs. Mice with defective TGF-β signaling (Spnb2(+/-) mice) exhibited enhanced liver TLR4 expression and developed HCC in a TLR4-dependent manner. Taken together, these results suggest that the activated TLR4/NANOG oncogenic pathway is linked to suppression of cytostatic TGF-β signaling and could potentially serve as a therapeutic target for HCV-related HCC.

Large granular lymphocyte leukemia: from dysregulated pathways to therapeutic targets

Large granular lymphocyte (LGL) leukemia is a clonal lymphoproliferative disorder of cytotoxic lymphocytes characterized by an expansion of CD3(+) cytotoxic T lymphocytes or CD3(-) natural killer cells. Patients present with various cytopenias including neutropenia, anemia and thrombocytopenia. In addition, there is an association of T-cell large granular lymphocytic leukemia with rheumatoid arthritis. It is believed that LGL leukemia begins as an antigen-driven immune response with subsequent constitutive activation of cytotoxic T lymphocytes or natural killer cells through PDGF and IL-15 contributing to their survival. Consequently, this leads to a dysregulation of apoptosis and dysfunction of the activation-induced cell death pathway. Treatment of LGL leukemia is based on a low-dose immunosuppressive regimen using methotrexate or cyclophosphamide. However, no standard of therapy has been established, as large prospective trials have not been conducted. In addition, some patients are refractory to treatment. The lack of a curative therapy for LGL leukemia means that new treatment options are needed. Insight into the various dysregulated signaling pathways in LGL leukemia may provide novel therapeutic treatment modalities.

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.

A novel inhibitor of STAT3 homodimerization selectively suppresses STAT3 activity and malignant transformation

STAT3-STAT3 dimerization, which involves reciprocal binding of the STAT3-SH2 domain to phosphorylated tyrosine-705 (Y-705), is required for STAT3 nuclear translocation, DNA binding, and transcriptional regulation of downstream target genes. Here, we describe a small molecule S3I-1757 capable of disrupting STAT3-STAT3 dimerization, activation, and malignant transforming activity. Fluorescence polarization assay and molecular modeling suggest that S3I-1757 interacts with the phospho-Y-705-binding site in the SH2 domain and displaces fluorescein-labeled GpYLPQTV phosphotyrosine peptide from binding to STAT3. We generated hemagglutinin (HA)-tagged STAT3 and FLAG-tagged STAT3 and showed using coimmunoprecipitation and colocalization studies that S3I-1757 inhibits STAT3 dimerization and STAT3-EGF receptor (EGFR) binding in intact cells. Treatment of human cancer cells with S3I-1757 (but not a closely related analog, S3I-1756, which does not inhibit STAT3 dimerization), inhibits selectively the phosphorylation of STAT3 over AKT1 and ERK1/2 (MAPK3/1), nuclear accumulation of P-Y705-STAT3, STAT3-DNA binding, and transcriptional activation and suppresses the expression levels of STAT3 target genes, such as Bcl-xL (BCL2L1), survivin (BIRC5), cyclin D1 (CCND1), and matrix metalloproteinase (MMP)-9. Furthermore, S3I-1757, but not S3I-1756, inhibits anchorage-dependent and -independent growth, migration, and invasion of human cancer cells, which depend on STAT3. Finally, STAT3-C, a genetically engineered mutant of STAT3 that forms a constitutively dimerized STAT3, rescues cells from the effects of S3I-1757 inhibition. Thus, we have developed S3I-1757 as a STAT3-STAT3 dimerization inhibitor capable of blocking hyperactivated STAT3 and suppressing malignant transformation in human cancer cells that depend on STAT3.

Development of new N-Arylbenzamides as STAT3 Dimerization Inhibitors

The O-tosylsalicylamide S3I-201 (10) was used as a starting point for design and synthesis of novel STAT-3 dimerization inhibitors with improved drug-like qualities. The phosphonic acid 12d and salicylic acids 13f, 13g with a shorter amide linker lacking the O-tosyl group had improved STAT-3 inhibitory activity. The equivalent potencies observed by the replacement of phosphonic acid moiety of 12d with 5-amino-2-hydroxybenzoic acid group as in 13f further validates 5-amino-2-hydroxybenzoic acid as a phosphotyrosine mimic. The salicylic acid 13f displayed improved whole cell activity. The focused library of salicylic acids 13 with benzamide linker indicated that hydrophobic heptyl and cyclohexyl are the best tolerated R groups and a biphenyl ether (as the Ar group) significantly contributes to STAT3 inhibitory activity. Our docking studies indicated that the acidic groups of 12d, 13f and 13g interact in the p-Tyr-705 binding site in a broadly similar manner, while the phenoxybenzoyl group and the cyclohexylbenzyl group occupying pY+1 and pY-X hydrophobic pockets respectively. The in vitro and cell based potency of 13f warrants further development of this scaffold as STAT3 inhibitors.

Thymic stromal lymphopoietin promotes asthmatic airway remodelling in human lung fibroblast cells through STAT3 signalling pathway

This study aimed to identify the role and regulation of thymic stromal lymphopoietin (TSLP) in asthmatic airway remodelling. To identify the expression of TSLP, α smooth muscle actin (α-SMA) and collagen I in bronchial tissues, bronchial biopsy specimens were collected from patients with asthma and healthy controls and stained with specific antibodies, respectively. To characterize the signalling pathways regulated by TSLP, we silenced or overexpressed TSLP in human lung fibroblast (HLF-1) cells by shRNA approaches or transfection and detected the expression of TSLP receptor (TSLPR) by enzyme-linked immunosorbent assay and Western blot analysis. In TSLP signalling pathway, the protein expression of total signal transducer and activator of transcription 3 (STAT3), STAT5, the phosphorylation of STAT3 (pSTAT3) and STAT5 (pSTAT5), TSLP, α-SMA and collagen I were also detected by Western blotting. In addition, the α-SMA, collagen I and mRNA expression were determined by real-time reverse-transcription. To further confirm the TSLP-STAT3 signalling pathway in HLF-1 cells, we inhibited STAT3 activity by targeted small molecules and then detected TSLP-induced expression of α-SMA and collagen I in both mRNA and protein levels by quantitative real-time reverse-transcription and Western blotting, respectively. First, overexpression of TSLP, α-SMA and collagen I was detected in epithelium collected from patients with asthma. Second, STAT3 activity and the expression of α-SMA and collagen I were controlled, regulated by TSLP. Specifically, the pSTAT3, α-SMA and collagen I were induced by the introduction of TSLP in HLF-1 cells, and the repression of α-SMA and collagen I was detected after TSLP silencing. Third, no changes of pSTAT5 were found in the presence of the STAT3 inhibitor, and TSLP-induced α-SMA and collagen I upregulation is in a STAT3 dependent manner. If we inhibit STAT3 activity by STAT3 targeted small molecules, TSLP-induced α-SMA and collagen I upregulation cannot be detected. The functions of TSLP in asthmatic airway remodelling were performed through STAT3 signalling pathway.

Drugging the undruggable: transcription therapy for cancer

Transcriptional regulation is often the convergence point of oncogenic signaling. It is not surprising, therefore, that aberrant gene expression is a hallmark of cancer. Transformed cells often develop a dependency on such a reprogramming highlighting the therapeutic potential of rectifying cancer-associated transcriptional abnormalities in malignant cells. Although transcription is traditionally considered as undruggable, agents have been developed that target various levels of transcriptional regulation including DNA binding by transcription factors, protein-protein interactions, and epigenetic alterations. Some of these agents have been approved for clinical use or entered clinical trials. While artificial transcription factors have been developed that can theoretically modulate expression of any given gene, the emergence of reliable reporter assays greatly facilitates the search for transcription-targeted agents. This review provides a comprehensive overview of these developments, and discusses various strategies applicable for developing transcription-targeted therapeutic agents.

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).

Interleukin-6 induces S100A9 expression in colonic epithelial cells through STAT3 activation in experimental ulcerative colitis

Background

Intestinal epithelium is essential for maintaining normal intestinal homeostasis; its breakdown leads to chronic inflammatory pathologies, such as inflammatory bowel diseases (IBDs). Although high concentrations of S100A9 protein and interleukin-6 (IL-6) are found in patients with IBD, the expression mechanism of S100A9 in colonic epithelial cells (CECs) remains elusive. We investigated the role of IL-6 in S100A9 expression in CECs using a colitis model.

Methods

IL-6 and S100A9 expression, signal transducer and activator of transcription 3 (STAT3) phosphorylation, and infiltration of immune cells were analyzed in mice with dextran sulfate sodium (DSS)-induced colitis. The effects of soluble gp130-Fc protein (sgp130Fc) and S100A9 small interfering (si) RNA (si-S100A9) on DSS-induced colitis were evaluated. The molecular mechanism of S100A9 expression was investigated in an IL-6-treated Caco-2 cell line using chromatin immunoprecipitation assays.

Results

IL-6 concentrations increased significantly in the colon tissues of DSS-treated mice. sgp130Fc or si-S100A9 administration to DSS-treated mice reduced granulocyte infiltration in CECs and induced the down-regulation of S100A9 and colitis disease activity. Treatment with STAT3 inhibitors upon IL-6 stimulation in the Caco-2 cell line demonstrated that IL-6 mediated S100A9 expression through STAT3 activation. Moreover, we found that phospho-STAT3 binds directly to the S100A9 promoter. S100A9 may recruit immune cells into inflamed colon tissues.

Conclusions

Elevated S100A9 expression in CECs mediated by an IL-6/STAT3 signaling cascade may play an important role in the development of colitis.

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.

Molecular mechanisms of estrogen receptors' suppression of lipogenesis in pancreatic β-cells

The gonadal steroid, 17β-estradiol (E2), suppresses pancreatic islet fatty acid and glycerolipid synthesis and prevents β-cell failure in rodent models of type 2 diabetes. β-Cell estrogen receptors (ER) mediate these actions by suppressing the expression and enzymatic activity of fatty acid synthase (FAS). Here, we explored the mechanism of FAS suppression. We show that E2, and pharmacological agonists for ERα, ERβ, and the G protein-coupled ER, suppress mRNA and protein expression of the transcriptional regulators of FAS, namely, sterol regulatory element-binding protein 1c (SREBP1c) and carbohydrate response element binding protein (ChREBP) in insulin-secreting INS-1 cells. ER suppress SREBP1c and ChREBP mRNA and protein expression via an extranuclear localization. Using two mouse lines with pancreas-specific null deletion of either ERα or the signal transducer and activator of transcription 3 (STAT3), we show that ERα activation in vivo reduces SREBP1c and ChREBP mRNA expression via a direct islet action involving STAT3 activation. The master regulators of lipogenesis, liver X receptor (LXR) α and β, transcriptionally up-regulate SREBP1c and ChREBP. We find that activation of ERα, ERβ, and G protein-coupled ER suppresses LXR's mRNA expression in INS-1 cells. We also observe that activation of ERα in mouse islets in vivo suppresses LXR mRNA in a STAT3-dependent manner. Finally, we show that E2 also activates and uses AMP-activated protein kinase in INS-1 cells to suppress SREBP1c protein expression. This study identifies extranuclear ER pathways involving STAT3 and AMP-activated protein kinase in the genetic control of lipogenesis with therapeutic implications to protect β-cells in type 2 diabetes.

Targeting proliferation and survival pathways in head and neck cancer for therapeutic benefit

Head and neck squamous cell carcinomas (HNSCC) are common human malignancies with poor clinical outcomes. The 5-year survival rates for patients with advanced stage HNSCC have not changed appreciably in the past few decades, underscoring a dire need for improved therapeutic options. Recent studies have elucidated a key signaling axis, the EGFR-STAT3-Bcl-XL signaling axis, that is aberrantly activated in a majority of HNSCC and contributes to the proliferation and survival of malignant cells. Considerable effort is being placed on developing highly specific inhibitors of different components of this pathway. This review highlights the progress that is being made towards achieving potent inhibition of the EGFR-STAT3-Bcl-XL signaling axis in HNSCC and the promising therapeutic strategies that are currently under development for this disease.

NEUROG3 is a critical downstream effector for STAT3-regulated differentiation of mammalian stem and progenitor spermatogonia

Spermatogenesis relies on coordinated differentiation of stem and progenitor spermatogonia, and the transcription factor STAT3 is essential for this process in mammals. Here we studied the THY1+ spermatogonial population in mouse testes, which contains spermatogonial stem cells (SSC) and non-stem cell progenitor spermatogonia, to further define the downstream mechanism regulating differentiation. Transcript abundance for the bHLH transcription factor Neurog3 was found to be significantly reduced upon transient inhibition of STAT3 signaling in these cells and exposure to GDNF, a key growth factor regulating self-renewal of SSCs, suppressed activation of STAT3 and in accordance Neurog3 gene expression. Moreover, STAT3 was found to bind the distal Neurog3 promoter/enhancer region in THY1+ spermatogonia and regulate transcription. Transient inhibition of Neurog3 expression in cultures of proliferating THY1+ spermatogonia increased stem cell content after several self-renewal cycles without effecting overall proliferation of the cells, indicating impaired differentiation of SSCs to produce progenitor spermatogonia. Furthermore, cultured THY1+ spermatogonia with induced deficiency of Neurog3 were found to be incapable of differentiation in vivo following transplantation into testes of recipient mice. Collectively, these results establish a mechanism by which activation of STAT3 regulates the expression of NEUROG3 to subsequently drive differentiation of SSC and progenitor spermatogonia in the mammalian germline.

Orally bioavailable small-molecule inhibitor of transcription factor Stat3 regresses human breast and lung cancer xenografts

Computer-aided lead optimization derives a unique, orally bioavailable inhibitor of the signal transducer and activator of transcription (Stat)3 Src homology 2 domain. BP-1-102 binds Stat3 with an affinity (K(D)) of 504 nM, blocks Stat3-phospho-tyrosine (pTyr) peptide interactions and Stat3 activation at 4-6.8 μM, and selectively inhibits growth, survival, migration, and invasion of Stat3-dependent tumor cells. BP-1-102-mediated inhibition of aberrantly active Stat3 in tumor cells suppresses the expression of c-Myc, Cyclin D1, Bcl-xL, Survivin, VEGF, and Krüppel-like factor 8, which is identified as a Stat3 target gene that promotes Stat3-mediated breast tumor cell migration and invasion. Treatment of breast cancer cells with BP-1-102 further blocks Stat3-NF-κB cross-talk, the release of granulocyte colony-stimulating factor, soluble intercellular adhesion molecule 1, macrophage migration-inhibitory factor/glycosylation-inhibiting factor, interleukin 1 receptor antagonist, and serine protease inhibitor protein 1, and the phosphorylation of focal adhesion kinase and paxillin, while enhancing E-cadherin expression. Intravenous or oral gavage delivery of BP-1-102 furnishes micromolar or microgram levels in tumor tissues and inhibits growth of human breast and lung tumor xenografts.