Novel peptidomimetic inhibitors of signal transducer and activator of transcription 3 dimerization and biological activity

Interleukin-6 serves as a critical factor in various cancer progression and therapy

Interleukin-6 (IL-6), a pro-inflammatory cytokine, plays a crucial role in host immune defense and acute stress responses. Moreover, it modulates various cellular processes, including proliferation, apoptosis, angiogenesis, and differentiation. These effects are facilitated by various signaling pathways, particularly the signal transducer and activator of transcription 3 (STAT3) and Janus kinase 2 (JAK2). However, excessive IL-6 production and dysregulated signaling are associated with various cancers, promoting tumorigenesis by influencing all cancer hallmarks, such as apoptosis, survival, proliferation, angiogenesis, invasiveness, metastasis, and notably, metabolism. Emerging evidence indicates that selective inhibition of the IL-6 signaling pathway yields therapeutic benefits across diverse malignancies, such as multiple myeloma, prostate, colorectal, renal, ovarian, and lung cancers. Targeting key components of IL-6 signaling, such as IL-6Rs, gp130, STAT3, and JAK via monoclonal antibodies (mAbs) or small molecules, is a heavily researched approach in preclinical cancer studies. The purpose of this study is to offer an overview of the role of IL-6 and its signaling pathway in various cancer types. Furthermore, we discussed current preclinical and clinical studies focusing on targeting IL-6 signaling as a therapeutic strategy for various types of cancer.

JAK2/STAT3 as a new potential target to manage neurodegenerative diseases: An interactive review

Neurodegenerative diseases (NDDs) are a collection of incapacitating disorders in which neuroinflammation and neuronal apoptosis are major pathological consequences due to oxidative stress. Neuroinflammation manifests in the impacted cerebral areas as a result of pro-inflammatory cytokines stimulating the Janus Kinase2 (JAK2)/Signal Transducers and Activators of Transcription3 (STAT3) pathway via neuronal cells. The pro-inflammatory cytokines bind to their respective receptor in the neuronal cells and allow activation of JAK2. Activated JAK2 phosphorylates tyrosines on the intracellular domains of the receptor which recruit the STAT3 transcription factor. The neuroinflammation issues are exacerbated by the active JAK2/STAT3 signaling pathway in conjunction with additional transcription factors like nuclear factor kappa B (NF-κB), and the mammalian target of rapamycin (mTOR). Neuronal apoptosis is a natural process made worse by persistent neuroinflammation and immunological responses via caspase-3 activation. The dysregulation of micro-RNA (miR) expression has been observed in the consequences of neuroinflammation and neuronal apoptosis. Neuroinflammation and neuronal apoptosis-associated gene amplification may be caused by dysregulated miR-mediated aberrant phosphorylation of JAK2/STAT3 signaling pathway components. Therefore, JAK2/STAT3 is an attractive therapeutic target for NDDs. Numerous synthetic and natural small molecules as JAK2/STAT3 inhibitors have therapeutic advances against a wide range of diseases, and many are now in human clinical studies. This review explored the interactive role of the JAK2/STAT3 signaling system with key pathological factors during the reinforcement of NDDs. Also, the clinical trial data provides reasoning evidence about the possible use of JAK2/STAT3 inhibitors to abate neuroinflammation and neuronal apoptosis in NDDs.

Use of phosphotyrosine-containing peptides to target SH2 domains: Antagonist peptides of the Crk/CrkL-p130Cas axis

Protein-protein interactions between SH2 domains and segments of proteins that include a post-translationally phosphorylated tyrosine residue (pY) underpin numerous signal transduction cascades that allow cells to respond to their environment. Dysregulation of the writing, erasing, and reading of these posttranslational modifications is a hallmark of human disease, notably cancer. Elucidating the precise role of the SH2 domain-containing adaptor proteins Crk and CrkL in tumor cell migration and invasion is challenging because there are no specific and potent antagonists available. Crk and CrkL SH2s interact with a region of the docking protein p130Cas containing 15 potential pY-containing tetrapeptide motifs. This chapter summarizes recent efforts toward peptide antagonists for this Crk/CrkL-p130Cas interaction. We describe our protocol for recombinant expression and purification of Crk and CrkL SH2s for functional assays and our procedure to determine the consensus binding motif from the p130Cas sequence. To develop a more potent antagonist, we employ methods often associated with structure-based drug design. Computational docking using Rosetta FlexPepDock, which accounts for peptides having a greater number of conformational degrees of freedom than small organic molecules that typically constitute libraries, provides quantitative docking metrics to prioritize candidate peptides for experimental testing. A battery of biophysical assays, including fluorescence polarization, differential scanning fluorimetry and saturation transfer difference nuclear magnetic resonance spectroscopy, were employed to assess the candidates. In parallel, GST pulldown competition assays characterized protein-protein binding in vitro. Taken together, our methodology yields peptide antagonists of the Crk/CrkL-p130Cas axis that will be used to validate targets, assess druggability, foster in vitro assay development, and potentially serve as lead compounds for therapeutic intervention.

Design, synthesis, and anti-hepatocellular carcinoma of thiopyrimidine/chalcone hybrids as dual STAT3/STAT5 inhibitors

Among the promising therapeutic targets for treating cancer are the continuously active STAT proteins, which are important in the progression of many malignancies. Here, we detail the STAT3/5 inhibitory action and thiopyrimidine/chalcone hybrid design, production, and anti-hepatocellular carcinoma activity. The prepared hybrids were assessed for their cytotoxic effect on HepG2 and Huh7 liver cancer cells. The most active compounds 5e and 5h (IC50 range from 0.55 to 2.58 μM) were further evaluated against normal THLE cells to examine their safety profiles. The hybrids 5e and 5h were additionally tested for their potential to inhibit STAT3 and STAT5a. They showed dual inhibitory action, with a decrease in the level of STAT3 by 65 and 87 times, respectively, and a decrease in the level of STAT5 by 60 and 79.5 times, respectively, compared to the control. Additionally, western blot analysis of compound 5h revealed inhibition of STAT3 and STAT5 phosphorylation at Tyr705 and Tyr694, respectively, with only a slight decrease in the total expression of STAT3 and STAT5 proteins. And lastly, molecular docking research provided additional insight on the 5h binding mechanism in the STAT3 and STAT5 SH2 domains.

Lung cancer treatment potential and limits associated with the STAT family of transcription factors

Lung cancer is one of the mortal cancers and the leading cause of cancer-related mortality, with a cancer survival rate of fewer than 5% in developing nations. This low survival rate can be linked to things like late-stage detection, quick postoperative recurrences in patients receiving therapy, and chemoresistance developing against various lung cancer treatments. Signal transducer and activator of transcription (STAT) family of transcription factors are involved in lung cancer cell proliferation, metastasis, immunological control, and treatment resistance. By interacting with specific DNA sequences, STAT proteins trigger the production of particular genes, which in turn result in adaptive and incredibly specific biological responses. In the human genome, seven STAT proteins have been discovered (STAT1 to STAT6, including STAT5a and STAT5b). Many external signaling proteins can activate unphosphorylated STATs (uSTATs), which are found inactively in the cytoplasm. When STAT proteins are activated, they can increase the transcription of several target genes, which leads to unchecked cellular proliferation, anti-apoptotic reactions, and angiogenesis. The effects of STAT transcription factors on lung cancer are variable; some are either pro- or anti-tumorigenic, while others maintain dual, context-dependent activities. Here, we give a succinct summary of the various functions that each member of the STAT family plays in lung cancer and go into more detail about the advantages and disadvantages of pharmacologically targeting STAT proteins and their upstream activators in the context of lung cancer treatment.

Regulation of the JAK/STAT signaling pathway: The promising targets for cardiovascular disease

Individuals have known that Janus kinase (JAK) signal transducer and activator of transcription (STAT) signaling pathway was involved in the growth of the cell, cell differentiation courses advancement, immune cellular survival, as well as hematopoietic system advancement. Researches in the animal models have already uncovered a JAK/STAT regulatory function in myocardial ischemia-reperfusion injury (MIRI), acute myocardial infarction (MI), hypertension, myocarditis, heart failure, angiogenesis and fibrosis. Evidences originating in these studies indicate a therapeutic JAK/STAT function in cardiovascular diseases (CVDs). In this retrospection, various JAK/STAT functions in the normal and ill hearts were described. Moreover, the latest figures about JAK/STAT were summarized under the background of CVDs. Finally, we discussed the clinical transformation prospects and technical limitations of JAK/STAT as the potential therapeutic targets for CVDs. This collection of evidences has essential meanings for the clinical application of JAK/STAT as medicinal agents for CVDs. In this retrospection, various JAK/STAT functions in the normal and ill hearts were described. Moreover, the latest figures about JAK/STAT were summarized under the background of CVDs. Finally, we discussed the clinical transformation prospects and toxicity of JAK/STAT inhibitors as potential therapeutic targets for CVDs. This collection of evidences has essential meanings for the clinical application of JAK/STAT as medicinal agents for CVDs.

Mst1-mediated phosphorylation of Nur77 improves the endometrial receptivity in human and mice

BACKGROUND

Successful embryo implantation requires the attachment of a blastocyst to the receptive endometrial epithelium, which was disturbed in the women with recurrent implantation failure (RIF). Endometrial β3-integrin was the most important adhesion molecule contributing to endometrial receptivity in both humans and mice. Nur77 has been proven indispensable for fertility in mice, here we explore the role of Nur77 on embryo-epithelial adhesion and potential treatment to embryo implantation failure.

METHODS

The expression and location of Mst1 and Nur77 in endometrium from fertile women and RIF patients were examined by IHC, qRT-PCR and Western blotting. In vitro kinase assay following with LC-MS/MS were used to identify the phosphorylation site of Nur77 activated by Mst1. The phosphorylated Nur77 was detected by phos-tag SDS-PAGE assay and specific antibody against phospho-Nur77-Thr366. The effect of embryo-epithelium interaction was determined in the BeWo spheroid or mouse embryo adhesion assay, and delayed implantation mouse model. RNA-seq was used to explore the mechanism by which Nur77 derived peptide promotes endometrial receptivity.

FINDINGS

Endometrial Mammalian sterile 20 (STE20)-like kinase 1 (Mst1) expression level was decreased in the women with RIF than that in the fertile control group, while Mst1 activation in the epithelial cells promoted trophoblast-uterine epithelium adhesion. The effect of Nur77 mediated trophoblast-uterine epithelium adhesion was facilitated by active Mst1. Mechanistically, mst1 promotes the transcription activity of Nur77 by phosphorylating Nur77 at threonine 366 (T366), and consequently increased downstream target β3-integrin expression. Furthermore, a Nur77-derived peptide containing phosphorylated T366 markedly promoted mouse embryo attachment to Ishikawa cells ([4 (2-4)] vs [3 (2-4)]) and increased the embryo implantation rate (4 vs 1.4) in a delayed implantation mouse model by regulating integrin signalling. Finally, it is observed that the endometrial phospho-Nur77 (T366) level is decreased by 80% in the women with RIF.

INTERPRETATION

In addition to uncovering a potential regulatory mechanism of Mst1/Nur77/β3-integrin signal axis involved in the regulation of embryo-epithelium interaction, our finding provides a novel marker of endometrial receptivity and a potential therapeutic agent for embryo implantation failure.

FUNDING

National Key Research and Development Program of China (2018YFC1004400), the National Natural Science Foundation of China (82171653, 82271698, 82030040, 81971387 and 30900727), and National Institutes of Health grants (R01HL103869).

Precision medicine: The use of tailored therapy in primary immunodeficiencies

Primary immunodeficiencies (PID) are rare, complex diseases that can be characterised by a spectrum of phenotypes, from increased susceptibility to infections to autoimmunity, allergy, auto-inflammatory diseases and predisposition to malignancy. With the introduction of genetic testing in these patients and wider use of next-Generation sequencing techniques, a higher number of pathogenic genetic variants and conditions have been identified, allowing the development of new, targeted treatments in PID. The concept of precision medicine, that aims to tailor the medical interventions to each patient, allows to perform more precise diagnosis and more importantly the use of treatments directed to a specific defect, with the objective to cure or achieve long-term remission, minimising the number and type of side effects. This approach takes particular importance in PID, considering the nature of causative defects, disease severity, short- and long-term complications of disease but also of the available treatments, with impact in life-expectancy and quality of life. In this review we revisit how this approach can or is already being implemented in PID and provide a summary of the most relevant treatments applied to specific diseases.

Natural product preferentially targets redox and metabolic adaptations and aberrantly active STAT3 to inhibit breast tumor growth in vivo

Dysregulated gene expression programs and redox and metabolic adaptations allow cancer cells to survive under high oxidative burden. These mechanisms also represent therapeutic vulnerabilities. Using triple-negative breast cancer (TNBC) as a model, we show that compared to normal human breast epithelial cells, the TNBC cells, MDA-MB-231 and MDA-MB-468 that harbor constitutively active STAT3 also express higher glucose-6-phosphate dehydrogenase (G6PD), thioredoxin reductase (TrxR)1, NADPH, and GSH levels for survival. Present studies discover that the natural product, R001, targets these adaptation mechanisms. Treatment of TNBC cells with R001 inhibited constitutively active STAT3, STAT3-regulated gene expression, and the functions of G6PD and TrxR1. Consequently, in the TNBC, but not normal cells, R001 suppressed GSH levels, but raised NADPH levels, reflective of a loss of mitochondrial respiration and which led to reactive oxygen species (ROS) induction, all of which led to loss of viable cells and inhibition of anchorage-dependent and independent growth. R001 treatment further led to early pyroptosis and late DNA damage, cell cycle arrest, and apoptosis only in the TNBC cells. Oral administration of 5 mg/kg R001 inhibited MDA-MB-468 xenografts growth in mice, with reduced pY705-STAT3, G6PD, TrxR1, and GSH levels. R001 serves as a therapeutic entity that targets the vulnerabilities of TNBC cells to inhibit tumor growth in vivo.

STAT3 pathway in cancers: Past, present, and future

Signal transducer and activator of transcription 3 (STAT3), a member of the STAT family, discovered in the cytoplasm of almost all types of mammalian cells, plays a significant role in biological functions. The duration of STAT3 activation in normal tissues is a transient event and is strictly regulated. However, in cancer tissues, STAT3 is activated in an aberrant manner and is induced by certain cytokines. The continuous activation of STAT3 regulates the expression of downstream proteins associated with the formation, progression, and metastasis of cancers. Thus, elucidating the mechanisms of STAT3 regulation and designing inhibitors targeting the STAT3 pathway are considered promising strategies for cancer treatment. This review aims to introduce the history, research advances, and prospects concerning the STAT3 pathway in cancer. We review the mechanisms of STAT3 pathway regulation and the consequent cancer hallmarks associated with tumor biology that are induced by the STAT3 pathway. Moreover, we summarize the emerging development of inhibitors that target the STAT3 pathway and novel drug delivery systems for delivering these inhibitors. The barriers against targeting the STAT3 pathway, the focus of future research on promising targets in the STAT3 pathway, and our perspective on the overall utility of STAT3 pathway inhibitors in cancer treatment are also discussed.

PIM1/STAT3 axis: a potential co-targeted therapeutic approach in triple-negative breast cancer

Triple-negative breast cancer lacks an expression of ER, PR, and Her-2, has a poor prognosis, and there are no target therapies available. Therapeutic options to treat TNBC are limited and urgently needed. Strong evidence indicates that molecular signaling pathways have a significant function to regulate biological mechanisms and their abnormal expression endows with the development of cancer. PIM kinase is overexpressed in various human cancers including TNBC which is regulated by various signaling pathways that are crucial for cancer cell proliferation and survival and also make PIM kinase as an attractive drug target. One of the targets of the STAT3 signaling pathway is PIM1 that plays a key role in tumor progression and transformation. In this review, we accumulate the current scenario of the PIM-STAT3 axis that provides insights into the PIM1 and STAT3 inhibitors which can be developed as potential co-inhibitors as prospective anticancer agents.

Recent Developments in Oxazole Derivatives as Anticancer Agents: Review on Synthetic Strategies, Mechanism of Action and SAR studies

BACKGROUND

Cancer is the world's third deadliest disease. Despite the availability of numerous treatments, researchers are focusing on the development of new drugs lacking resistance and toxicity issues. Many newly synthesized drugs fail to reach clinical trials due to poor pharmacokinetic properties. Therefore, there is an imperative requisite to expand novel anticancer agents with in vivo efficacy.

OBJECTIVE

This review emphasizes synthetic methods, contemporary strategies used for the inclusion of oxazole moiety, mechanistic targets along with comprehensive structure-activity relationship studies to provide perspective into the rational design of highly efficient oxazole-based anticancer drugs.

METHODS

Literature related to oxazole derivatives engaged in cancer research is reviewed. This article gives a detailed account of synthetic strategies, targets of oxazole in cancer, including STAT3, Microtubules, G-quadruplex, DNA topoisomerases, DNA damage, Protein kinases, miscellaneous targets, in vitro studies, and some SAR studies.

RESULTS

Oxazole derivatives possess potent anticancer activity by inhibiting novel targets such as STAT3 and G-quadruplex. Oxazoles also inhibit tubulin protein to induce apoptosis in cancer cells. Some other targets such as DNA topoisomerase enzyme, protein kinases, and miscellaneous targets including Cdc25, mitochondrial enzymes, HDAC, LSD1, HPV E2 TAD, NQO1, Aromatase, BCl-6, Estrogen receptor, GRP-78, and Keap-Nrf2 pathway are inhibited by oxazole derivatives Many derivatives showed excellent potencies on various cancer cell lines with IC50 values in nanomolar concentrations.

CONCLUSION

Oxazole is a five-membered heterocycle, with oxygen and nitrogen at 1 and 3 positions respectively. It is often combined with other pharmacophores in the expansion of novel anticancer drugs. In summary, oxazole is a promising entity to develop new anticancer drugs.

Novel STAT3 small-molecule inhibitors identified by structure-based virtual ligand screening incorporating SH2 domain flexibility

Efforts to develop STAT3 inhibitors have focused on its SH2 domain starting with short phosphotyrosylated peptides based on STAT3 binding motifs, e.g. pY₉₀₅LPQTV within gp130. Despite binding to STAT3 with high affinity, issues regarding stability, bioavailability, and membrane permeability of these peptides, as well as peptidomimetics such as CJ-887, have limited their further clinical development and led to interest in small-molecule inhibitors. Some small molecule STAT3 inhibitors, identified using structure-based virtual ligand screening (SB-VLS); while having favorable drug-like properties, suffer from weak binding affinities, possibly due to the high flexibility of the target domain. We conducted molecular dynamic (MD) simulations of the SH2 domain in complex with CJ-887, and used an averaged structure from this MD trajectory as an "induced-active site" receptor model for SB-VLS of 110,000 compounds within the SPEC database. Screening was followed by re-docking and re-scoring of the top 30% of hits, selection for hit compounds that directly interact with pY + 0 binding pocket residues R609 and S613, and testing for STAT3 targeting in vitro, which identified two lead hits with good activity and favorable drug-like properties. Unlike most small-molecule STAT3 inhibitors previously identified, which contain negatively-charged moieties that mediate binding to the pY + 0 binding pocket, these compounds are uncharged and likely will serve as better candidates for anti-STAT3 drug development. IMPLICATIONS: SB-VLS, using an averaged structure from molecular dynamics (MD) simulations of STAT3 SH2 domain in a complex with CJ-887, a known peptidomimetic binder, identify two highly potent, neutral, low-molecular weight STAT3-inhibitors with favorable drug-like properties.

STAT Signaling in Glioma Cells

STAT (signal transducers and activators of transcription) are latent cytoplasmic transcription factors that function as downstream effectors of cytokine and growth factor receptor signaling. The canonical JAK/STAT signaling pathway involves the activation of Janus kinases (JAK) or growth factors receptor kinases, phosphorylation of STAT proteins, their dimerization and translocation into the nucleus where STATs act as transcription factors with pleiotropic downstream effects. STAT signaling is tightly controlled with restricted kinetics due to action of its negative regulators. While STAT1 is believed to play an important role in growth arrest and apoptosis, and to act as a tumor suppressor, STAT3 and 5 are involved in promoting cell cycle progression, cellular transformation, and preventing apoptosis. Aberrant activation of STATs, in particular STAT3 and STAT5, have been found in a large number of human tumors, including gliomas and may contribute to oncogenesis. In this chapter, we have (1) summarized the mechanisms of STAT activation in normal and malignant signaling; (2) discussed evidence for the critical role of constitutively activated STAT3 and STAT5 in glioma pathobiology; (3) disclosed molecular and pharmacological strategies to interfere with STAT signaling for potential therapeutic intervention in gliomas.

Phosphotyrosine prodrugs: design, synthesis and anti-STAT3 activity of ISS-610 aryloxy triester phosphoramidate prodrugs

Unmasked phohate groups of phosphotyrosine-containing molecules carry two negative charges at physiological pH, which compromise their (passive) cellular uptake. Also, these phosphate groups are often cleaved off by phosphatases. Together, these ultimately limit the pharmacological efficacy of the phosphotyrosine-containing compounds. To address these drawbacks, we herein present the application of the aryloxy triester phosphoramidate prodrug technology, a monophosphate prodrug technology, to the phosphotyrosine-containing compound ISS-610-Met, an analogue of the anticancer STAT3 dimerization inhibitor ISS-610. Our data shows that the generated ISS-610-Met prodrugs exhibited enhanced pharmacological activity and inhibition of STAT3 downstream signaling compared to the parent compound ISS-610-Met and the known STAT3 dimerization inhibitor ISS-610. These encouraging results provide a compelling proof of concept for the potential of the aryloxy triester phosphoramidate prodrug technology in the discovery of novel therapeutics that contain phosphotyrosine and its phospho mimics.

Protein biomarker for psoriasis: A systematic review on their role in the pathomechanism, diagnosis, potential targets and treatment of psoriasis

Psoriasis is defined as a long-lasting multifactorial inflammatory autoimmune skin condition precisely characterized by delimited, erythematic papules with adherent shiny scales. The conditions are led by hyperproliferative responses of epidermis due to hyperactivation and immature keratinocytes production. The psoriatic skin consists of the thickened epidermal layer, in concurrence with inflammatory exudates in the dermis mainly of dendritic cells, neutrophils, T cells, and macrophages, contributing to the distinct manifestation of psoriatic lesions. It consents to multifaceted and discrete pathology due to the genetic and immunological alteration resulting from abnormal expression of various regulatory and structural proteins. These proteins are associated with various cellular and sub-cellular activities. Therefore, the presence of protein in a pathological cellular environment in the psoriatic lesions as well as in serum could be a great avenue for the insight of pathomechanism, anticipation and diagnosis of psoriasis. Research of protein biomarker in psoriasis is yet a developing realm to be explored by both fundamental and clinical researchers. This review is an attempt to assimilate the current discoveries and revelations of different proteins as a biomarker and their importance in pathogenesis, diagnosis, treatment, and anticipation of both the inflammatory and other dermatological aspects of psoriasis.

The Role of Signal Transducer and Activator of Transcription 3 (STAT3) and Its Targeted Inhibition in Hematological Malignancies

Signal transducer and activator of transcription 3 (STAT3), a member of the STAT protein family, can be phosphorylated by receptor-associated Janus kinases (JAKs) in response to stimulation by cytokines and growth factors. It forms homo- or heterodimers that can translocate to the cell nucleus where they act as transcription activators. Constitutive activation of STAT3 has been found to be associated with initiation and progression of various cancers. It can exert proliferative as well as anti-apoptotic effects. This review focuses on the role of STAT3 in pathogenesis i.e., proliferation, differentiation, migration, and apoptosis of hematological malignancies viz. leukemia, lymphoma and myeloma, and briefly highlights the potential therapeutic approaches developed against STAT3 activation pathway.

A New Perspective: Mitochondrial Stat3 as a Regulator for Lymphocyte Function

Stat3 as a transcription factor regulating gene expression in lymphocytes during the immune response is well known. However, since the pioneering studies discovering the presence of Stat3 in mitochondria and its role in regulating mitochondrial metabolism, only a few studies have investigated this non-conventional function of Stat3 in lymphocytes. From this perspective, we review what is known about Stat3 as a transcription factor and what is known and unknown about mitochondrial Stat3 (mitoStat3) in lymphocytes. We also provide a framework to consider how some of the functions previously assigned to Stat3 as regulator of gene transcription could be mediated by mitoStat3 in lymphocytes. The goal of this review is to stimulate interest for future studies investigating mitoStat3 in the immune response that could lead to the generation of alternative pharmacological inhibitors of mitoStat3 for the treatment of chronic inflammatory diseases.

Targeting the IL-6/JAK/STAT3 signalling axis in cancer

The IL-6/JAK/STAT3 pathway is aberrantly hyperactivated in many types of cancer, and such hyperactivation is generally associated with a poor clinical prognosis. In the tumour microenvironment, IL-6/JAK/STAT3 signalling acts to drive the proliferation, survival, invasiveness, and metastasis of tumour cells, while strongly suppressing the antitumour immune response. Thus, treatments that target the IL-6/JAK/STAT3 pathway in patients with cancer are poised to provide therapeutic benefit by directly inhibiting tumour cell growth and by stimulating antitumour immunity. Agents targeting IL-6, the IL-6 receptor, or JAKs have already received FDA approval for the treatment of inflammatory conditions or myeloproliferative neoplasms and for the management of certain adverse effects of chimeric antigen receptor T cells, and are being further evaluated in patients with haematopoietic malignancies and in those with solid tumours. Novel inhibitors of the IL-6/JAK/STAT3 pathway, including STAT3-selective inhibitors, are currently in development. Herein, we review the role of IL-6/JAK/STAT3 signalling in the tumour microenvironment and the status of preclinical and clinical investigations of agents targeting this pathway. We also discuss the potential of combining IL-6/JAK/STAT3 inhibitors with currently approved therapeutic agents directed against immune-checkpoint inhibitors.

Crispenes F and G, cis-Clerodane Furanoditerpenoids from Tinospora crispa, Inhibit STAT3 Dimerization

Two new cis-clerodane-type furanoditerpenes, crispenes F and G (1 and 2), together with seven known compounds, were isolated from the stems of Tinospora crispa. Crispenes F and G (1 and 2) inhibited STAT3 dimerization in a cell-free fluorescent polarization assay and were found to have significant cytotoxicity against a STAT3-dependent MDA-MB 231 breast cancer cell line, while being inactive in a STAT3-null A4 cell line. These two compounds share structural similarities with a previously reported STAT3 inhibitor, crispene E, isolated from the same plant. Molecular docking studies suggested that the molecules inhibit STAT3 by interacting with its SH2 domain.

B Cell Lymphoma Immunotherapy Using TLR9-Targeted Oligonucleotide STAT3 Inhibitors

Growing evidence links the aggressiveness of non-Hodgkin’s lymphoma, especially the activated B cell-like type diffuse large B cell lymphomas (ABC-DLBCLs) to Toll-like receptor 9 (TLR9)/MyD88 and STAT3 transcription factor signaling. Here, we describe a dual-function molecule consisting of a clinically relevant TLR9 agonist (CpG7909) and a STAT3 inhibitor in the form of a high-affinity decoy oligodeoxynucleotide (dODN). The CpG-STAT3dODN blocked STAT3 DNA binding and activity, thus reducing expression of downstream target genes, such as MYC and BCL2L1, in human and mouse lymphoma cells. We further demonstrated that injections (i.v.) of CpG-STAT3dODN inhibited growth of human OCI-Ly3 lymphoma in immunodeficient mice. Moreover, systemic CpG-STAT3dODN administration induced complete regression of the syngeneic A20 lymphoma, resulting in long-term survival of immunocompetent mice. Both TLR9 stimulation and concurrent STAT3 inhibition were critical for immune-mediated therapeutic effects, since neither CpG7909 alone nor CpG7909 co-injected with unconjugated STAT3dODN extended mouse survival. The CpG-STAT3dODN induced expression of genes critical to antigen-processing/presentation and Th1 cell activation while suppressing survival signaling. These effects resulted in the generation of lymphoma cell-specific CD8/CD4-dependent T cell immunity protecting mice from tumor rechallenge. Our results suggest that CpG-STAT3dODN as a systemic/local monotherapy or in combination with PD1 blockade can provide an opportunity for treating patients with B cell NHL.

Mitochondrial GRIM-19 as a potential therapeutic target for STAT3-dependent carcinogenesis of gastric cancer

Aberrant STAT3 activation occurs in most human gastric cancers (GCs) and contributes to the malignant progression of GC, but mechanism(s) underlying aberrant STAT3 remain largely unknown. Here we demonstrated that the gene associated with retinoid interferon-induced mortality 19 (GRIM-19) was severely depressed or lost in GC and chronic atrophic gastritis (CAG) tissues and its loss contributed to GC tumorigenesis partly by activating STAT3 signaling. In primary human GC tissues, GRIM-19 was frequently depressed or lost and this loss correlated with advanced clinical stage, lymph node metastasis, H. pylori infection and poor overall survival of GC patients. In CAG tissues, GRIM-19 was progressively decreased along with its malignant transformation. Functionally, we indentified an oncogenic role of GRIM-19 loss in promoting GC tumorigenesis. Ectopic GRIM-19 expression suppressed GC tumor formation in vitro and in vivo by inducing cell cycle arrest and apoptosis. Moreover, we revealed that GRIM-19 inhibited STAT3 transcriptional activation and its downstream targets by reducing STAT3 nuclear distribution. Conversely, knockdown of GRIM-19 induced aberrant STAT3 activation and accelerated GC cell growth in vitro and in vivo, and this could be partly attenuated by the blockage of STAT3 activation. In addition, we observed subcellular redistributions of GRIM-19 characterized by peri-nuclear aggregates, non-mitochondria cytoplasmic distribution and nuclear invasion, which should be responsible for reduced STAT3 nuclear distribution. Our studies suggest that mitochondrial GRIM-19 could not only serve as an valuable prognostic biomarker for GC development, but also as a potential therapeutic target for STAT3-dependent carcinogenesis of GC.

SHP2 associates with nuclear localization of STAT3: significance in progression and prognosis of colorectal cancer

Tyrosine phosphatase SHP2, encoded by PTPN11, has been implicated in many physiologic and pathologic processes in neoplastic progression. However, controversies are emerging from many studies, indicating SHP2 has a dual role in different types of tumors. We aimed to explore the role of SHP2 in progression and prognosis of colorectal cancer (CRC). SHP2 inhibited CRC cell proliferation and migration, and the phosphorylation of STAT3 was negatively regulated by SHP2 in CRC. SHP2 and nuclear STAT3 were examined in 270 CRC tissues. SHP2 was significantly correlated with nuclear STAT3 (Spearman’s rho = −0.408, P ≤ 0.001). Based on Cox regression analysis, patients with high levels of SHP2 and low levels of nuclear STAT3 had longer disease-specific survival (DSS) (HR, 0.362; 95% CI, 0.165–0.794) and disease-free survival (DFS) (HR, 0.447; 95% CI, 0.227–0.877). Further, low levels of SHP2 and high levels of nuclear STAT3 were independently associated with adverse outcomes in the whole cohort (DFS; HR, 2.353; 95% CI, 1.199–4.619). These results suggest that combination of SHP2 and nuclear STAT3 is a strong prognostic predictor in CRC.

The role of STAT3 in leading the crosstalk between human cancers and the immune system

The development and progression of human cancers are continuously and dynamically regulated by intrinsic and extrinsic factors. As a converging point of multiple oncogenic pathways, signal transducer and activator of transcription 3 (STAT3) is constitutively activated both in tumor cells and tumor-infiltrated immune cells. Activated STAT3 persistently triggers tumor progression through direct regulation of oncogenic gene expression. Apart from its oncogenic role in regulating gene expression in tumor cells, STAT3 also paves the way for human cancer growth through immunosuppression. Activated STAT3 in immune cells results in inhibition of immune mediators and promotion of immunosuppressive factors. Therefore, STAT3 modulates the interaction between tumor cells and host immunity. Accumulating evidence suggests that targeting STAT3 may enhance anti-cancer immune responses and rescue the suppressed immunologic microenvironment in tumors. Taken together, STAT3 has emerged as a promising target in cancer immunotherapy.

Silibinin sensitizes chemo-resistant breast cancer cells to chemotherapy

CONTEXT

Multiple drug resistance is the major obstacle to conventional chemotherapy. Silibinin, a nontoxic naturally occurring compound, has anticancer activity and can increase the cytotoxic effects of chemotherapy in various cancer models.

OBJECTIVE

To evaluate the effects of silibinin on enhancing the sensitivity of chemo-resistant human breast cell lines to doxorubicin (DOX) and paclitaxel (PAC).

MATERIALS AND METHODS

The cells were treated with silibinin (at 50 to 600 μM concentrations) and/or chemo drugs for 24 and 48 h, then cell viability and changes in oncogenic proteins were determined by MTT assay and Western blotting/RT-PCR, respectively. Flow cytometry was used to study apoptosis in the cells receiving different treatments. The antitumorigenic effects of silibinin (at 200 to 400 μM concentration) were evaluated by mammosphere assay.

RESULTS

Silibinin exerted significant growth inhibitory effects with IC₅₀ ranging from 200 to 570 μM in different cell lines. Treatment of DOX-resistant MDA-MB-435 cells with silibinin at 200 μM reduced DOX IC₅₀ from 71 to 10 μg/mL and significantly suppressed the key oncogenic pathways including STAT3, AKT, and ERK in these cells. Interestingly treatment of DOX-resistant MDA-MB-435 cells with silibinin at 400 μM concentration for 48 h induced a 50% decrease in the numbers of colonies as compared with DMSO-treated cells. Treatment of PAC-resistant MCF-7 cells with silibinin at 400 μM concentration generated synergistic effects when it was used in combination with PAC at 250 nM concentration (CI = 0.81).

CONCLUSION

Silibinin sensitizes chemo-resistant cells to chemotherapeutic agents and can be useful in treating breast cancers.

Emerging therapeutic targets in myeloproliferative neoplasms and peripheral T-cell leukemia and lymphomas

Introduction: Hematopoietic neoplasms are often driven by gain-of-function mutations of the JAK-STAT pathway together with mutations in chromatin remodeling and DNA damage control pathways. The interconnection between the JAK-STAT pathway, epigenetic regulation or DNA damage control is still poorly understood in cancer cell biology.

Areas covered: Here, we focus on a broader description of mutational insights into myeloproliferative neoplasms and peripheral T-cell leukemia and lymphomas, since sequencing efforts have identified similar combinations of driver mutations in these diseases covering different lineages. We summarize how these pathways might be interconnected in normal or cancer cells, which have lost differentiation capacity and drive oncogene transcription.

Expert opinion: Due to similarities in driver mutations including epigenetic enzymes, JAK-STAT pathway activation and mutated checkpoint control through TP53, we hypothesize that similar therapeutic approaches could be of benefit in these diseases. We give an overview of how driver mutations in these malignancies contribute to hematopoietic cancer initiation or progression, and how these pathways can be targeted with currently available tools.

Androgen receptor-dependent and -independent mechanisms driving prostate cancer progression: Opportunities for therapeutic targeting from multiple angles

Despite aggressive treatment for localized cancer, prostate cancer (PC) remains a leading cause of cancer-related death for American men due to a subset of patients progressing to lethal and incurable metastatic castrate-resistant prostate cancer (CRPC). Organ-confined PC is treated by surgery or radiation with or without androgen deprivation therapy (ADT), while options for locally advanced and disseminated PC include radiation combined with ADT, or systemic treatments including chemotherapy. Progression to CRPC results from failure of ADT, which targets the androgen receptor (AR) signaling axis and inhibits AR-driven proliferation and survival pathways. The exact mechanisms underlying the transition from androgen-dependent PC to CRPC remain incompletely understood. Reactivation of AR has been shown to occur in CRPC despite depletion of circulating androgens by ADT. At the same time, the presence of AR-negative cell populations in CRPC has also been identified. While AR signaling has been proposed as the primary driver of CRPC, AR-independent signaling pathways may represent additional mechanisms underlying CRPC progression. Identification of new therapeutic strategies to target both AR-positive and AR-negative PC cell populations and, thereby, AR-driven as well as non-AR-driven PC cell growth and survival mechanisms would provide a two-pronged approach to eliminate CRPC cells with potential for synthetic lethality. In this review, we provide an overview of AR-dependent and AR-independent molecular mechanisms which drive CRPC, with special emphasis on the role of the Jak2-Stat5a/b signaling pathway in promoting castrate-resistant growth of PC through both AR-dependent and AR-independent mechanisms.

Signal transducer and activator of transcription 3 as a therapeutic target for cancer and the tumor microenvironment

Signal transducer and activator of transcription 3 (STAT3) is a cytoplasmic transcription factor that modulates the transcription of a variety of genes to regulate important biological functions, including cell proliferation, differentiation, survival, angiogenesis, and immune response. Constitutive activation of STAT3 is important in oncogenic signaling and occurs at high frequency in human cancers, including diverse solid tumors and hematologic malignancies. Moreover, it is associated with a poor prognosis. The tumor microenvironment has recently been recognized as a key condition for cancer progression, invasion, angiogenesis, metastasis, and drug resistance by activation of STAT3 signaling. Therefore, understanding the biology associated with STAT3-mediated signaling cascades in the tumor microenvironment may offer the therapeutic potential to treat human cancers. This review presents an overview of the critical roles of STAT3 in the tumor microenvironment related to cancer biology and discusses recent advancements in the development of anticancer drugs that therapeutically inhibit STAT3 signaling cascades.

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.

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.

Bioactive sesquiterpene lactones and other compounds isolated from Vernonia cinerea

Four new sesquiterpene lactones, 8α-(2'Z-tigloyloxy)-hirsutinolide (1), 8α-(2'Z-tigloyloxy)-hirsutinolide-13-O-acetate (2), 8α-(4-hydroxytigloyloxy)-hirsutinolide (3), and 8α-hydroxy-13-O-tigloyl-hirsutinolide (4), along with seven known derivatives (5-11), three norisoprenoids (12-14), a flavonoid (15), and a linoleic acid derivative (16), were isolated from the chloroform partition of a methanol extract from the combined leaves and stems of Vernonia cinerea. Their structures were established by 1D and 2D NMR, UV, and MS analyses. Compounds 1-16 were evaluated for their inhibitory effects against the viability of U251MG glioblastoma and MDA-MB-231 breast cancer cells that harbour aberrantly-active STAT3, compared to normal NIH3T3 mouse fibroblasts that show no evidence of activated STAT3. Among the isolates, compounds 2 and 7 inhibited the aberrant STAT3 activity in glioblastoma or breast cancer cells. Further, compounds 7 and 8 inhibited viability of all three cell lines, compounds 2, 4, and 9 predominantly inhibited the viability of the U251MG glioblastoma cell line.

Stat3 inhibition augments the immunogenicity of B-cell lymphoma cells, leading to effective antitumor immunity

Mantle cell lymphoma (MCL) is an aggressive and incurable subtype of B-cell non-Hodgkin lymphomas. Although patients often respond initially to first-line treatment with chemotherapy plus monoclonal antibodies, relapse and decreased response to further lines of treatment eventually occurs. Harnessing the immune system to elicit its exquisite specificity and long-lasting protection might provide sustained MCL immunity that could potentially eradicate residual malignant cells responsible for disease relapse. Here, we show that genetic or pharmacologic disruption of Stat3 in malignant B cells augments their immunogenicity leading to better activation of antigen-specific CD4(+) T cells and restoration of responsiveness of tolerized T cells. In addition, treatment of MCL-bearing mice with a specific Stat3 inhibitor resulted in decreased Stat3 phosphorylation in malignant B cells and anti-lymphoma immunity in vivo. Our findings therefore indicate that Stat3 inhibition may represent a therapeutic strategy to overcome tolerance to tumor antigens and elicit a strong immunity against MCL and other B-cell malignancies.

Triterpenoid CDDO-methyl ester inhibits the Janus-activated kinase-1 (JAK1)-->signal transducer and activator of transcription-3 (STAT3) pathway by direct inhibition of JAK1 and STAT3

The C-28 methyl ester of the oleane triterpenoid 2-cyano-3,12-dioxooleana-1,9-dien-28-oic acid (CDDO-Me) induces apoptosis of human cancer cells by disrupting redox balance and is in clinical trials. CDDO-Me contains alpha,beta-unsaturated carbonyl groups that form reversible adducts with thiol nucleophiles. The present studies show that CDDO-Me blocks interleukin-6 (IL-6)-induced and constitutive activation of the Janus-activated kinase 1 (JAK1) in cells. In support of a direct mechanism, CDDO-Me forms adducts with JAK1 at Cys(1077) in the kinase domain and inhibits JAK1 activity. In concert with these results, CDDO-Me blocked IL-6-induced and constitutive activation of signal transducer and activator of transcription 3 (STAT3). Moreover, we show that CDDO-Me (a) binds directly to STAT3 by a mechanism dependent on the alkylation of Cys(259) and (b) inhibits the formation of STAT3 dimers. These findings indicate that CDDO-Me inhibits activation of the JAK1-->STAT3 pathway by forming adducts with both JAK1 and STAT3.

Transcription factor signal transducer and activator of transcription 5 promotes growth of human prostate cancer cells in vivo

PURPOSE

Signal transducer and activator of transcription 5a/b (Stat5a/b) is the key mediator of prolactin effects in prostate cancer cells via activation of Janus-activated kinase 2. Prolactin is a locally produced growth factor in human prostate cancer. Prolactin protein expression and constitutive activation of Stat5a/b are associated with high histologic grade of clinical prostate cancer. Moreover, activation of Stat5a/b in primary prostate cancer predicts early disease recurrence. Here, we inhibited Stat5a/b by several different methodologic approaches. Our goal was to establish a proof of principle that Stat5a/b is critical for prostate cancer cell viability in vitro and for prostate tumor growth in vivo.

EXPERIMENTAL DESIGN

We inhibited Stat5a/b protein expression by antisense oligonucleotides or RNA interference and transcriptional activity of Stat5a/b by adenoviral expression of a dominant-negative mutant of Stat5a/b in prostate cancer cells in culture. Moreover, Stat5a/b activity was suppressed in human prostate cancer xenograft tumors in nude mice. Stat5a/b regulation of Bcl-X(L) and cyclin D1 protein levels was shown by antisense suppression of Stat5a/b protein expression followed by Western blotting.

RESULTS AND CONCLUSIONS

We show here that inhibition of Stat5a/b by antisense oligonucleotides, RNA interference, or adenoviral expression of dominant-negative Stat5a/b effectively kills prostate cancer cells. Moreover, we show that Stat5a/b is critical for human prostate cancer xenograft growth in nude mice. The effects of Stat5a/b on the viability of prostate cancer cells involve Stat5a/b regulation of Bcl-X(L) and cyclin D1 protein levels but not the expression or activation of Stat3. This work establishes Stat5a/b as a therapeutic target protein for prostate cancer. Pharmacologic inhibition of Stat5a/b in prostate cancer can be achieved by small-molecule inhibitors of transactivation, dimerization, or DNA binding of Stat5a/b.

Abrogation of signal transducer and activator of transcription 3 reactivation after Src kinase inhibition results in synergistic antitumor effects

PURPOSE

The Src family of kinases (SFKs) regulate multiple signal transduction cascades and influence proliferation, motility, survival, and angiogenesis. Dasatinib inhibits SFKs, which leads to cytotoxicity, cell cycle arrest, apoptosis, and decreased invasion of cancer cells. Signal transducer and activator of transcription 3 (STAT3) is a latent transcription factor that regulates survival and proliferation. Dasatinib results in rapid and durable inhibition of c-Src, whereas STAT3 undergoes only transient inactivation. We hypothesized that the reactivation of STAT3 after dasatinib treatment represents the engagement of a compensatory signal for cell survival that blocks the antitumor effects of SFK inhibition.

EXPERIMENTAL DESIGN

The effects of upstream inhibitors on STAT3 activation were assessed with western blotting and a quantitative bioplex phosphoprotein assay. We used the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay to determine the cytotoxicity and propidium iodine/annexin V staining with fluorescence-activated cell sorting (FACS) analysis to evaluate cell cycle change and apoptosis. The combination index was calculated by the Chou-Talalay equation. Cytokines were quantitated using a multiplexed, particle-based FACS analysis.

RESULTS

C-Src and several downstream molecules were rapidly and durably inhibited by dasatinib. However, STAT3 was reactivated by 24 h. The addition of JAK inhibitors during dasatinib incubation resulted in sustained inhibition of STAT3, although JAK activation by dasatinib was not shown. Combined SFK and JAK inhibition resulted in synergistic cytotoxicity due to increased apoptosis.

CONCLUSIONS

The reactivation of STAT3 during dasatinib treatment is caused by the engagement of a compensatory pathway that suppresses the antitumor effects of SFK inhibition and allows cancer cell survival. Abrogation of this pathway resulted in synergistic cytotoxicity. Given that STAT3 reactivation occurred in 14 of 15 solid tumor cell lines, dasatinib combined with Janus-activated kinase inhibitors may have widespread application in cancer treatment.

Resveratrol inhibits Src and Stat3 signaling and induces the apoptosis of malignant cells containing activated Stat3 protein

Resveratrol is a naturally occurring phytoalexin with antioxidant and antiinflammatory properties. Recent studies suggest that resveratrol possesses anticancer effects, although its mechanism of action is not well understood. We now show that resveratrol inhibits Src tyrosine kinase activity and thereby blocks constitutive signal transducer and activator of transcription 3 (Stat3) protein activation in malignant cells. Analyses of resveratrol-treated malignant cells harboring constitutively-active Stat3 reveal irreversible cell cycle arrest of v-Src-transformed mouse fibroblasts (NIH3T3/v-Src), human breast (MDA-MB-231), pancreatic (Panc-1), and prostate carcinoma (DU145) cell lines at the G0-G1 phase or at the S phase of human breast cancer (MDA-MB-468) and pancreatic cancer (Colo-357) cells, and loss of viability due to apoptosis. By contrast, cells treated with resveratrol, but lacking aberrant Stat3 activity, show reversible growth arrest and minimal loss of viability. Moreover, in malignant cells harboring constitutively-active Stat3, including human prostate cancer DU145 cells and v-Src-transformed mouse fibroblasts (NIH3T3/v-Src), resveratrol treatment represses Stat3-regulated cyclin D1 as well as Bcl-xL and Mcl-1 genes, suggesting that the antitumor cell activity of resveratrol is in part due to the blockade of Stat3-mediated dysregulation of growth and survival pathways. Our study is among the first to identify Src-Stat3 signaling as a target of resveratrol, further defining the mechanism of antitumor cell activity of resveratrol and raising its potential application in tumors with an activated Stat3 profile.

Cyclooxygenase-2-dependent activation of signal transducer and activator of transcription 3 by interleukin-6 in non-small cell lung cancer

PURPOSE

Cyclooxygenase-2 (COX-2), phosphorylated signal transducers and activators of transcription 3 (STAT3), and interleukin-6 (IL-6) are elevated in non-small cell lung cancer (NSCLC). These molecules affect numerous cellular pathways, including angiogenesis and apoptosis resistance, and, therefore, may act in concert in NSCLC.

EXPERIMENTAL DESIGN

We examined IL-6 and phosphorylated STAT3 in COX-2-overexpressing [COX-2 sense-oriented (COX-2-S)] NSCLC cells and control cells. The effect of IL-6, STAT3, phosphatidylinositol 3-kinase, and mitogen-activated protein/extracellular signal-regulated kinase kinase on vascular endothelial growth factor (VEGF) production and apoptosis resistance was assessed in COX-2-overexpresing cells.

RESULTS

We report that NSCLC cells overexpressing COX-2 (COX-2-S) have increased IL-6 and phosphorylated STAT3 expression compared with control cells. IL-6 induced expression of VEGF in NSCLC cells. Moreover, blocking IL-6, mitogen-activated protein/extracellular signal-regulated kinase kinase, or phosphatidylinositol 3-kinase decreased VEGF production in COX-2-S cells. The addition of IL-6 to NSCLC cells resulted in increased apoptosis resistance. Furthermore, the inhibition of STAT3 or IL-6 induced apoptosis and reduced survivin expression, a member of the inhibitor of apoptosis protein family in COX-2-S cells.

CONCLUSIONS

Overall, these findings suggest a novel pathway in which COX-2 activates STAT3 by inducing IL-6 expression. This pathway could contribute to tumor formation by promoting survivin-dependent apoptosis resistance and VEGF production. These findings provide a rationale for the future development of STAT3, IL-6, and/or COX-2-targeted therapies for the treatment of lung cancer.

Persistent activation of stat3 signaling induces survivin gene expression and confers resistance to apoptosis in human breast cancer cells

PURPOSE

Signal transducer and activator of transcription 3 (Stat3) protein is persistently activated in breast cancer and promotes tumor cell survival. To gain a better understanding of the role of constitutive Stat3 signaling in breast cancer progression, we evaluated the expression profile of potential Stat3-regulated genes that may confer resistance to apoptosis.

EXPERIMENTAL DESIGN

Stat3 signaling was blocked with antisense oligonucleotides in human MDA-MB-435s breast cancer cells and Affymetrix GeneChip microarray analysis was done. The candidate Stat3 target gene Survivin was further evaluated in molecular assays using cultured breast cancer cells and immunohistochemistry of breast tumor specimens.

RESULTS

Survivin, a member of the inhibitor of apoptosis protein family, was identified as a potential Stat3-regulated gene by microarray analysis. This was confirmed in Survivin gene promoter studies and chromatin immunoprecipitation assays showing that Stat3 directly binds to and regulates the Survivin promoter. Furthermore, direct inhibition of Stat3 signaling blocked the expression of Survivin protein and induced apoptosis in breast cancer cells. Direct inhibition of Survivin expression also induced apoptosis. Increased Survivin protein expression correlates significantly (P = 0.001) with elevated Stat3 activity in primary breast tumor specimens from high-risk patients who were resistant to chemotherapy treatment.

CONCLUSIONS

We identify Survivin as a direct downstream target gene of Stat3 in human breast cancer cells that is critical for their survival in culture. Our findings suggest that activated Stat3 signaling contributes to breast cancer progression and resistance to chemotherapy by, at least in part, inducing expression of the antiapoptotic protein, Survivin.

STAT1: a modulator of chemotherapy-induced apoptosis

The anthracyclines, such as doxorubicin, are widely used in the treatment of breast cancer. Previously, we showed that these drugs could activate the transcription factor, nuclear factor kappaB, in a DNA damage-dependent manner. We now show that these drugs can potentiate the activation of signal transducer and activator of transcription 1 (STAT1) in MDA-MB 435 breast cancer cells treated with IFN-gamma. We observed that key markers of STAT1 activation, including tyrosine 701 and serine 727 phosphorylation, were enhanced in the presence of doxorubicin. This potentiation resulted in enhanced nuclear localization of activated STAT1 and led to an increase in the nuclear binding of activated STAT complexes. The observed potentiation was specific for STAT1 and IFN-gamma, as no effects were observed with either STAT3 or STAT5. Furthermore, the type I IFNs (alpha and beta) had little or no effect. The observed effects on STAT1 phosphorylation have previously been linked with maximal transcriptional activation and apoptosis. Cell viability was assessed by crystal violet staining followed by analysis with CalcuSyn to determine combination index values, a measure of synergy. We confirmed that significant synergy existed between IFN-gamma and doxorubicin (combination index = 0.34) at doses lower than IC(50) values for this drug (0.67 micromol/L). In support of this, we observed that apoptotic cell death was also enhanced by measuring poly(ADP-ribose) polymerase and caspase-3 cleavage. Finally, suppression of STAT1 expression by small-interfering RNA resulted in a loss of synergistic apoptotic cell death compared with cells, where no suppression of STAT1 expression was attained with scrambled small-interfering RNA control. We conclude that doxorubicin potentiates STAT1 activation in response to IFN-gamma, and that this combination results in enhanced apoptosis in breast cancer cells.