STAT3 isoforms: Alternative fates in cancer?

Effects of SB939 are mediated by STAT3 to inhibit breast cancer cell metastasis-related genes

The histone deacetylase inhibitor pracinostat (SB939) may inhibit metastasis of triple-negative breast cancer by downregulating fibronectin (FN1) expression through the STAT3 signaling pathway. SB939 exhibits low cytotoxicity and is a potential targeted agent against breast cancer. The present study investigated the value of STAT3 and FN1 as breast cancer treatment targets and integrated cancer databases and bioinformatics tools to evaluate the effect of SB939 on breast cancer metastasis. Gene Set Enrichment Analysis, Gene Expression Profiling Interactive Analysis, Gene Expression Database of Normal and Tumor Tissues 2, The University of Alabama at Birmingham Cancer data analysis portal, GeneMANIA, Search Tool for the Retrieval of Interacting Genes/Proteins, LinkedOmics and Tumor Immune Estimation Resource databases were used in the present study. SB939 inhibited enrichment of the STAT3 pathway and decreased the expression of FN1. FN1 and STAT3 expression was markedly higher in breast cancer tissues compared with normal tissues. Kaplan-Meier curves demonstrated that increased expression of STAT3 and FN1 was associated with low survival in patients with breast cancer with overall, recurrence-free and disease-specific survival and FN1 having the strongest association with MMP2, which facilitating extracellular matrix degradation and metastatic niche formation. Furthermore, MMP2 exhibits crosstalk STAT3 to induce metastasis of breast cancer cells. To conclude, SB939 may be used as a small molecule compound for the clinical treatment of breast cancer.

Novel inhibitors of STAT3: an updated patent review (2022-present)

INTRODUCTION

Signal transducer and activator of transcription 3 (STAT3), a member of the STAT protein family, serves as both a signal transducer and a transcription factor. Previous studies have highlighted its pivotal roles in regulating cell proliferation, differentiation, apoptosis, as well as immune and inflammatory responses. Consequently, targeting STAT3 has emerged as a promising therapeutic strategy for addressing related diseases.

AREAS COVERED

This review offers a comprehensive summary of the progress in discovering STAT3 inhibitors, with a focus on their structural diversity and structure-activity relationships as presented in patent literature from 2022 to the present.

EXPERT OPINION

Over the past decades, significant progress has transformed STAT3 into a target of interest for drug development. Despite these advances, no STAT3-targeting drugs have successfully progressed through late-phase clinical trials, largely due to challenges such as limited selectivity and undesirable side effects. These obstacles highlight the inherent complexity of developing safe and effective STAT3 inhibitors. Nevertheless, STAT3 remains a highly promising therapeutic target, and ongoing advancements in this field hold the potential to unlock novel strategies for addressing STAT3-related diseases.

Atovaquone and selinexor as a novel combination treatment option in acute myeloid leukemia

Acute myeloid leukemia (AML) is the most common acute leukemia and is predominantly affecting the elderly. It is a heterogenous disease, showing a broad spectrum of genomic alterations and mutations that influence the clinical outcome and treatment options. The expression of the signal transducer and activator of transcription 3 (STAT3) is often dysregulated in AML and its constitutive activation is associated with poor outcome. Thus, STAT3 became an attractive therapeutic target but until now drugs targeting STAT3 only had moderate efficacy. This phenomenon might be related to the expression ratio of the two alternatively spliced isoforms: the full-length isoform STAT3α and the truncated version STAT3β, which play opposite roles in AML. In this study, we investigated the potential of selected, well-established drugs to impact the STAT3β/α ratio, as a higher STAT3β/α ratio is associated with better disease outcome. Atovaquone and selinexor independently elevated the STAT3β/α ratio and led to an upregulation of the STAT3β target gene SELL (CD62L). The combined treatment with atovaquone and selinexor entailed synergistic killing of AML cells in vitro and impaired the leukemic cell infiltration in vivo. Moreover, CD62L overexpression in a human AML cell line resulted in significantly prolonged survival in a xenograft mouse model. We propose that targeting the STAT3β/α ratio could be a promising new strategy for treating patients with AML and that the combination of selinexor and atovaquone could offer enhanced treatment outcomes.

Pyrimethamine treatment in breast cancer lysate-loaded dendritic cells promotes autologous T cells' anti-tumor responses in vitro

BACKGROUND

Suppressing inhibitory molecules such as signal transducer and activator of transcription (STAT) 3 in dendritic cells (DCs) and eliciting an effective immune response via T cells against antigens (Ags) produced exclusively by malignant cells represents the major method in the process of DC-based vaccines. Pyrimethamine (Pyri), a potential STAT3 inhibitor, is an antimalarial drug that is employed for ameliorating various cancers, including breast cancer. The present study aimed to investigate T cell-mediated responses after DCs and T cells co-culturing using breast cancer lysate (BCL) and Pyri to inhibit STAT3 protein in the DCs for the first time.

METHOD

Employing the Magnetic Activated Cell Sorting (MACS) technique, monocytes were separated from peripheral blood mononuclear cells (PBMCs). After monocytes were differentiated into DCs, they were divided into two groups: mature dendritic cells (mDCs) (received lipopolysaccharide (LPS) and BCL) and Pyrimethamine-treated mature dendritic cells (Pyri-mDCs) (incubated with LPS, BCL, and Pyri). Flow cytometry was used to examine the surface markers related to DC phenotype in both groups of DCs. Consequently, RT-PCR was employed to investigate the expression of genes linked to inflammatory and anti-inflammatory cytokines in mDCs and Pyri-mDCs as well as related genes to T cell response after DC/T cell co-culturing.

RESULTS

Our outcomes revealed that Pyri-mediated STAT3 inhibition in DCs upregulates and downregulates the expression of inflammatory and anti-inflammatory cytokines' genes. Furthermore, co-culture of Pyri-mDCs with autologous T cells downregulated T helper (Th) 2 and regulatory T cell (Treg) responses and augmented Th1 activation compared to T cell cultured along with mDCs.

CONCLUSION

Overall, our research points to Pyri-mediated STAT3 suppression in DCs loaded with BCL as a potentially effective therapeutic method for inducing effective T cell responses; nevertheless, additional investigation is required to evaluate the effectiveness of this approach especially in pre-clinical settings.

Advances of signal transducer and activator of transcription 3 inhibitors in acute myeloid leukemia (Review)

Signal transducer and activator of transcription 3 (STAT3), a crucial transcription factor, exerts a notable influence by hyperactivating or acquiring functional mutations in the occurrence and progression of cancers. Hyperactive STAT3 is also implicated in a range of hematopoietic malignancies, especially acute myeloid leukemia (AML). The function of STAT3 is associated with the phosphorylated parallel dimer structure, enabling them to stimulate the transcription of specific genes. AML is a highly heterogeneous hematological malignancy, which is challenging in terms of therapy. The current efficacy of chemotherapy and targeted therapy remains suboptimal. Targeted inhibition of STAT3 has the potential to enhance the efficacy of AML treatment, thereby possibly improving the prognosis of individuals suffering from AML. The present review summarizes the development of inhibitors against STAT3 and discusses their applicability as AML therapeutics, which could inspire new possibilities for enhancing AML treatment strategies.

Fructosyl-mangiferin ameliorates dextran sulfate sodium-induced colitis in mice via the STAT3/M1/Th17 axis

BACKGROUND

Inflammatory bowel disease (IBD), a chronic inflammatory condition categorized into ulcerative colitis (UC) and Crohn's disease (CD), affects a growing global patient population. Despite the prevalence, clinically there is a scarcity of effective therapeutic agents.

PURPOSE

This study investigated the therapeutic effects of fructosyl mangiferin (FM) on UC and elucidated its underlying mechanisms through in vivo and in vitro experiments.

METHODS

In vivo, a UC model of C57BL/6J mice was established via dextran sulfate sodium (DSS) induction, and the therapeutic effects were assessed through intragastric administration. In vitro, the murine macrophage cell line RAW264.7 was stimulated with lipopolysaccharide (LPS) to establish an M1 polarization model and introduced to explore the role of FM in immune cells. Molecular docking was further employed to investigate the specific molecular mechanisms of FM.

RESULTS

In vivo experimental findings indicate that FM, like mangiferin (M), preserves mucin secretion and the expression of occludin protein, and both significantly impede the progression of fibrosis associated with colitis. Additionally, FM effectively suppresses M1 macrophage polarization and exerts a pronounced inhibitory effect on the adaptive immune response, outperforming M in mitigating UC. In vitro results corroborate FM's inhibitory action on M1 polarization. Molecular docking studies identified FM as a potential signal transducer and activator of transcription 3 (STAT3) inhibitor, aligning with western blot analyses from both in vivo and in vitro experiments.

CONCLUSION

In conclusion, following fructosylation, FM exhibits remarkable anti-inflammatory and colonic protective effects. FM's ability to control the progression of UC offers a novel strategy for its potential treatment, warranting further investigation into its clinical application.

RNA binding protein CUGBP2/ETR-3 regulates STAT3 alternative splicing

Signal transducer and activator of transcription 3 (STAT3) is a multifactorial regulator involved in many biological responses. Alternative splicing of STAT3 pre-mRNA leads to an internal 50-nucleotide deletion of exon 23 selecting an alternative 3' acceptor site, resulting in the generation of two splicing isoforms, STAT3α and STAT3β. STAT3β lacks 55 amino acid-residue transactivation domain at the C-terminal of STAT3α replacing seven unique amino acids. Although STAT3β was originally thought to be a dominant negative isoform of STAT3α, accumulating evidence have shown that STAT3β possesses both its unique functions and those that overlap with STAT3α in fundamental cellular processes. However, much remains unknown about STAT3 pre-mRNA alternative splicing in determining the balance between STAT3 isoforms. In this study, we identified cis-regulatory elements and CUGBP2/ETR-3 as a novel trans-acting factor that regulates STAT3 alternative splicing. Our findings demonstrate that STAT3 splicing can be modulated by CUGBP2 via association with UG-rich elements of intron 22, providing a novel insight into the mechanism of STAT3 alternative splicing. CUGBP2 would be a crucial molecule regulating the balance of STAT3 isoform expression, thus targeting CUGBP2 and its recognition sequences in intron 22 of STAT3 might impact on various biological processes regulated by STAT3 signaling pathway.

Overactivation of Signal Transducer and Activator of Transcription 3 in Canine Hepatocellular Carcinoma and Its Prognostic Significance

Phosphorylated signal transducer and activator of transcription 3 (pSTAT3), which is related to anti-apoptosis, cellular proliferation, invasion and migration of tumours, has prognostic significance in malignant tumours in humans as well as in canine melanoma. However, the significance of pSTAT3 in canine liver tissues has not yet been evaluated. This study's objective was to compare its expression in canine normal, non-neoplastic hepatic disease and hepatocellular carcinoma (HCC) tissues by immunohistochemical analysis. Furthermore, the association between pSTAT3 immunostaining and clinicopathological factors was investigated. Overall, 68 canine liver tissues, including 10 normal liver tissues, 30 non-neoplastic hepatic disease tissues and 28 HCC tissues were examined, revealing distinct differences in pSTAT3 immunostaining among the groups. (p < 0.001). Additionally, high pSTAT3 immunostaining was significantly associated with increased tumour size (5 > cm) (p = 0.041), and metastasis (p = 0.046). Furthermore, Kaplan-Meier survival curve analysis revealed a correlation between high pSTAT3 immunostaining and poor disease-free survival (p = 0.013) and overall survival (p = 0.011). These findings suggest that overactivation of STAT3 is associated with poor prognosis in canine HCC. Therefore, pSTAT3 is considered a potential prognostic marker and therapeutic target for canine HCC.

Curcumin: A Potential Weapon in the Prevention and Treatment of Head and Neck Cancer

Head and neck cancers (HNC) are aggressive, difficult-to-treat tumors that can be caused by genetic factors but mainly by lifestyle or infection caused by the human papillomavirus. As the sixth most common malignancy, it presents a formidable therapeutic challenge with limited therapeutic modalities. Curcumin, a natural polyphenol, is appearing as a promising multitarget anticancer and antimetastatic agent. Numerous studies have shown that curcumin and its derivatives have the potential to affect signaling pathways (NF-κB, JAK/STAT, and EGFR) and molecular mechanisms that are crucial for the growth and migration of head and neck tumors. Furthermore, its ability to interact with the tumor microenvironment and trigger the immune system may significantly influence the organism's immune response to the tumor. Combining curcumin with conventional therapies such as chemotherapy or radiotherapy may improve the efficacy of treatment and reduce the side effects of treatment, thereby increasing its therapeutic potential. This review is a comprehensive overview that discusses both the benefits and limitations of curcumin and its therapeutic effects in the context of tumor biology, with an emphasis on molecular mechanisms in the context of HNC. This review also includes possibilities to improve the limiting properties of curcumin both in terms of the development of new derivatives, formulations, or combinations with conventional therapies that have potential as a new type of therapy for the treatment of HNC and subsequent use in clinical practice.

The Induction of Drug Uptake Transporter Organic Anion Transporting Polypeptide 1A2 by Radiation Is Mediated by the Nonreceptor Tyrosine Kinase v-YES-1 Yamaguchi Sarcoma Viral Oncogene Homolog 1

Organic anion transporting polypeptides (OATP, gene symbol SLCO) are well-recognized key determinants for the absorption, distribution, and excretion of a wide spectrum of endogenous and exogenous compounds including many antineoplastic agents. It was therefore proposed as a potential drug target for cancer therapy. In our previous study, it was found that low-dose X-ray and carbon ion irradiation both upregulated the expression of OATP family member OATP1A2 and in turn, led to a more dramatic killing effect when cancer cells were cotreated with antitumor drugs such as methotrexate. In the present study, the underlying mechanism of the phenomenon was explored in breast cancer cell line MCF-7. It was found that the nonreceptor tyrosine kinase v-YES-1 Yamaguchi sarcoma viral oncogene homolog 1 (YES-1) was temporally coordinated with the change of OATP1A2 after irradiation. The overexpression of YES-1 significantly increased OATP1A2 both at the mRNA and protein level. The signal transducer and activator of transcription 3 (STAT3) pathway is likely the downstream target of YES-1 because phosphorylation and nuclear accumulation of STAT3 were both enhanced after overexpressing YES-1 in MCF-7 cells. Further investigation revealed that there are two possible binding sites of STAT3 localized at the upstream sequence of SLCO1A2, the encoding gene of OATP1A2. Electrophoretic mobility shift assay and chromatin immunoprecipitation analysis suggested that these two sites bound to STAT3 specifically and the overexpression of YES-1 significantly increased the association of the transcription factor with the putative binding sites. Finally, inhibition or knockdown of YES-1 attenuated the induction effect of radiation on the expression of OATP1A2. SIGNIFICANCE STATEMENT: The present study found that the effect of X-rays on v-YES-1 Yamaguchi sarcoma viral oncogene homolog 1 (YES-1) and organic anion transporting polypeptides (OATP)1A2 was temporally coordinated. YES-1 phosphorylates and increases the nuclear accumulation of signal transducer and activator of transcription 3, which in turn binds to the upstream regulatory sequences of SLCO1A2, the coding gene for OATP1A2. Hence, inhibitors of YES-1 may suppress the radiation induction effect on OATP1A2.

The "Heater" of "Cold" Tumors-Blocking IL-6

The resolution of inflammation is not simply the end of the inflammatory response but rather a complex process that involves various cells, inflammatory factors, and specialized proresolving mediators following the occurrence of inflammation. Once inflammation cannot be cleared by the body, malignant tumors may be induced. Among them, IL-6, as an immunosuppressive factor, activates a variety of signal transduction pathways and induces tumorigenesis. Monitoring IL-6 can be used for the diagnosis, efficacy evaluation and prognosis of tumor patients. In terms of treatment, improving the efficacy of targeted and immunotherapy remains a major challenge. Blocking IL-6 and its mediated signaling pathways can regulate the tumor immune microenvironment and enhance immunotherapy responses by activating immune cells. Even transform "cold" tumors that are difficult to respond to immunotherapy into immunogenic "hot" tumors, acting as a "heater" for "cold" tumors, restarting the tumor immune cycle, and reducing immunotherapy-related toxic reactions and drug resistance. In clinical practice, the combined application of IL-6 inhibition with targeted therapy and immunotherapy may produce synergistic results. Nevertheless, additional clinical trials are imperative to further validate the safety and efficacy of this therapeutic approach.

Splicing analysis of STAT3 tandem donor suggests non-canonical binding registers for U1 and U6 snRNAs

Tandem donor splice sites (5'ss) are unique regions with at least two GU dinucleotides serving as splicing cleavage sites. The Δ3 tandem 5'ss are a specific subclass of 5'ss separated by 3 nucleotides which can affect protein function by inserting/deleting a single amino acid. One 5'ss is typically preferred, yet factors governing particular 5'ss choice are not fully understood. A highly conserved exon 21 of the STAT3 gene was chosen as a model to study Δ3 tandem 5'ss splicing mechanisms. Based on multiple lines of experimental evidence, endogenous U1 snRNA most likely binds only to the upstream 5'ss. However, the downstream 5'ss is used preferentially, and the splice site choice is not dependent on the exact U1 snRNA binding position. Downstream 5'ss usage was sensitive to exact nucleotide composition and dependent on the presence of downstream regulatory region. The downstream 5'ss usage could be best explained by two novel interactions with endogenous U6 snRNA. U6 snRNA enables the downstream 5'ss usage in STAT3 exon 21 by two mechanisms: (i) binding in a novel non-canonical register and (ii) establishing extended Watson-Crick base pairing with the downstream regulatory region. This study suggests that U6:5'ss interaction is more flexible than previously thought.

A novel function of STAT3β in suppressing interferon response improves outcome in acute myeloid leukemia

Signal transducer and activator of transcription 3 (STAT3) is frequently overexpressed in patients with acute myeloid leukemia (AML). STAT3 exists in two distinct alternatively spliced isoforms, the full-length isoform STAT3α and the C-terminally truncated isoform STAT3β. While STAT3α is predominantly described as an oncogenic driver, STAT3β has been suggested to act as a tumor suppressor. To elucidate the role of STAT3β in AML, we established a mouse model of STAT3β-deficient, MLL-AF9-driven AML. STAT3β deficiency significantly shortened survival of leukemic mice confirming its role as a tumor suppressor. Furthermore, RNA sequencing revealed enhanced STAT1 expression and interferon (IFN) signaling upon loss of STAT3β. Accordingly, STAT3β-deficient leukemia cells displayed enhanced sensitivity to blockade of IFN signaling through both an IFNAR1 blocking antibody and the JAK1/2 inhibitor Ruxolitinib. Analysis of human AML patient samples confirmed that elevated expression of IFN-inducible genes correlated with poor overall survival and low STAT3β expression. Together, our data corroborate the tumor suppressive role of STAT3β in a mouse model in vivo. Moreover, they provide evidence that its tumor suppressive function is linked to repression of the STAT1-mediated IFN response. These findings suggest that the STAT3β/α mRNA ratio is a significant prognostic marker in AML and holds crucial information for targeted treatment approaches. Patients displaying a low STAT3β/α mRNA ratio and unfavorable prognosis could benefit from therapeutic interventions directed at STAT1/IFN signaling.

Terpenoid-Mediated Targeting of STAT3 Signaling in Cancer: An Overview of Preclinical Studies

Cancer has become one of the most multifaceted and widespread illnesses affecting human health, causing substantial mortality at an alarming rate. After cardiovascular problems, the condition has a high occurrence rate and ranks second in terms of mortality. The development of new drugs has been facilitated by increased research and a deeper understanding of the mechanisms behind the emergence and advancement of the disease. Numerous preclinical and clinical studies have repeatedly demonstrated the protective effects of natural terpenoids against a range of malignancies. Numerous potential bioactive terpenoids have been investigated in natural sources for their chemopreventive and chemoprotective properties. In practically all body cells, the signaling molecule referred to as signal transducer and activator of transcription 3 (STAT3) is widely expressed. Numerous studies have demonstrated that STAT3 regulates its downstream target genes, including Bcl-2, Bcl-xL, cyclin D1, c-Myc, and survivin, to promote the growth of cells, differentiation, cell cycle progression, angiogenesis, and immune suppression in addition to chemotherapy resistance. Researchers viewed STAT3 as a primary target for cancer therapy because of its crucial involvement in cancer formation. This therapy primarily focuses on directly and indirectly preventing the expression of STAT3 in tumor cells. By explicitly targeting STAT3 in both in vitro and in vivo settings, it has been possible to explain the protective effect of terpenoids against malignant cells. In this study, we provide a complete overview of STAT3 signal transduction processes, the involvement of STAT3 in carcinogenesis, and mechanisms related to STAT3 persistent activation. The article also thoroughly summarizes the inhibition of STAT3 signaling by certain terpenoid phytochemicals, which have demonstrated strong efficacy in several preclinical cancer models.

Unraveling the complexity of STAT3 in cancer: molecular understanding and drug discovery

Signal transducer and activator of transcription 3 (STAT3) is a transcriptional factor involved in almost all cancer hallmark features including tumor proliferation, metastasis, angiogenesis, immunosuppression, tumor inflammation, metabolism reprogramming, drug resistance, cancer stemness. Therefore, STAT3 has become a promising therapeutic target in a wide range of cancers. This review focuses on the up-to-date knowledge of STAT3 signaling in cancer. We summarize both the positive and negative modulators of STAT3 together with the cancer hallmarks involving activities regulated by STAT3 and highlight its extremely sophisticated regulation on immunosuppression in tumor microenvironment and metabolic reprogramming. Direct and indirect inhibitors of STAT3 in preclinical and clinical studies also have been summarized and discussed. Additionally, we highlight and propose new strategies of targeting STAT3 and STAT3-based combinations with established chemotherapy, targeted therapy, immunotherapy and combination therapy. These efforts may provide new perspectives for STAT3-based target therapy in cancer.

Detection of early prognostic biomarkers for metastasis of Ewing's sarcoma in pediatric patients

AIMS

Ewing's Sarcoma is an extremely aggressive tumor in children. The disease is associated with highly metastatic rate, especially at the time of diagnosis, contributing to a lower survival rate and poor prognosis. The study aimed to identify predictive biomarkers for metastatic Ewing's sarcoma through in-depth analysis of the plasma proteome profile of pediatric Ewing's sarcoma patients.

MAIN METHODS

Plasma samples from Ewing's sarcoma patients and control individuals were profiled using both shotgun and dimethyl-labeled proteomics analysis. Subsequently, Ewing's sarcoma patients were further stratified according to their metastatic state and chemotherapy response. Western blot was used for validation. Univariate and multivariate analyses were performed to determine proteome metastasis predictors. Receiver operating characteristic (ROC) analysis was done to assess the diagnostic significance of the potential plasma Ewing's sarcoma biomarkers.

KEY FINDINGS

Our results revealed a set of proteins significantly associated with the metastatic Ewing's sarcoma disease profile. These proteins include ceruloplasmin and several immunoglobulins. Additionally, our study disclosed significant differentially expressed proteins in pediatric Ewing's sarcoma, including CD5 antigen-like, clusterin, and dermcidin. Stable isotope dimethyl labeling and western blot further confirmed our results, strengthening the impact of such proteins in disease development. Furthermore, an unbiased ROC curve evaluated and confirmed the predictive power of these biomarker candidates.

SIGNIFICANCE

This study presented potential empirical predictive circulating biomarkers for determining the disease status of pediatric Ewing's sarcoma, which is vital for early prediction.

Fibronectin Type III Domain Containing 3B as a Potential Prognostic and Therapeutic Biomarker for Glioblastoma

Glioblastoma (GBM) is a representative malignant brain tumor characterized by a dismal prognosis, with survival rates of less than 2 years and high recurrence rates. Despite surgical resection and several alternative treatments, GBM remains a refractory disease due to its aggressive invasiveness and resistance to anticancer therapy. In this report, we explore the role of fibronectin type III domain containing 3B (FNDC3B) and its potential as a prognostic and therapeutic biomarker in GBM. GBM exhibited a significantly higher cancer-to-normal ratio compared to other organs, and patients with high FNDC3B expression had a poor prognosis (p < 0.01). In vitro studies revealed that silencing FNDC3B significantly reduced the expression of Survivin, an apoptosis inhibitor, and also reduced cell migration, invasion, extracellular matrix adhesion ability, and stem cell properties in GBM cells. Furthermore, we identified that FNDC3B regulates PTEN/PI3K/Akt signaling in GBM cells using MetaCore integrated pathway bioinformatics analysis and a proteome profiler phospho-kinase array with sequential western blot analysis. Collectively, our findings suggest FNDC3B as a potential biomarker for predicting GBM patient survival and for the development of treatment strategies for GBM.

Noncoding RNAs as regulators of STAT3 pathway in gastrointestinal cancers: Roles in cancer progression and therapeutic response

Gastrointestinal (GI) tumors (cancers of the esophagus, gastric, liver, pancreas, colon, and rectum) contribute to a large number of deaths worldwide. STAT3 is an oncogenic transcription factor that promotes the transcription of genes associated with proliferation, antiapoptosis, survival, and metastasis. STAT3 is overactivated in many human malignancies including GI tumors which accelerates tumor progression, metastasis, and drug resistance. Research in recent years demonstrated that noncoding RNAs (ncRNAs) play a major role in the regulation of many signaling pathways including the STAT3 pathway. The major types of endogenous ncRNAs that are being extensively studied in oncology are microRNAs, long noncoding RNAs, and circular RNAs. These ncRNAs can either be tumor-promoters or tumor-suppressors and each one of them imparts their activity via different mechanisms. The STAT3 pathway is also tightly modulated by ncRNAs. In this article, we have elaborated on the tumor-promoting role of STAT3 signaling in GI tumors. Subsequently, we have comprehensively discussed the oncogenic as well as tumor suppressor functions and mechanism of action of ncRNAs that are known to modulate STAT3 signaling in GI cancers.

JAKs and STATs from a Clinical Perspective: Loss-of-Function Mutations, Gain-of-Function Mutations, and Their Multidimensional Consequences

The JAK/STAT signaling pathway plays a key role in cytokine signaling and is involved in development, immunity, and tumorigenesis for nearly any cell. At first glance, the JAK/STAT signaling pathway appears to be straightforward. However, on closer examination, the factors influencing the JAK/STAT signaling activity, such as cytokine diversity, receptor profile, overlapping JAK and STAT specificity among non-redundant functions of the JAK/STAT complexes, positive regulators (e.g., cooperating transcription factors), and negative regulators (e.g., SOCS, PIAS, PTP), demonstrate the complexity of the pathway's architecture, which can be quickly disturbed by mutations. The JAK/STAT signaling pathway has been, and still is, subject of basic research and offers an enormous potential for the development of new methods of personalized medicine and thus the translation of basic molecular research into clinical practice beyond the use of JAK inhibitors. Gain-of-function and loss-of-function mutations in the three immunologically particularly relevant signal transducers STAT1, STAT3, and STAT6 as well as JAK1 and JAK3 present themselves through individual phenotypic clinical pictures. The established, traditional paradigm of loss-of-function mutations leading to immunodeficiency and gain-of-function mutation leading to autoimmunity breaks down and a more differentiated picture of disease patterns evolve. This review is intended to provide an overview of these specific syndromes from a clinical perspective and to summarize current findings on pathomechanism, symptoms, immunological features, and therapeutic options of STAT1, STAT3, STAT6, JAK1, and JAK3 loss-of-function and gain-of-function diseases.

Differential silencing of STAT3 isoforms leads to changes in STAT3 activation

Signal transducer and activator of transcription 3 (STAT3) is a transcription factor involved in multiple fundamental biological processes and a key player in cancer development and progression. STAT3 is activated upon tyrosine phosphorylation and is constitutively active in various malignancies; therefore, the expression of pSTAT3 has been recognized as a predictor of poor survival. STAT3 encodes two alternatively-spliced STAT3 isoforms: the full-length STAT3α isoform and the truncated STAT3β isoform. These isoforms have been suggested as the reason for the occasionally observed opposing roles of STAT3 in cancer: an oncogene, on one hand, and a tumor suppressor on the other. To investigate their roles in aggressive breast cancer, we separately silenced each isoform and found that they affect each other's activation, impacting cell viability, cytokine expression, and migration. Silencing specific isoforms can lead to a more favorable balance of activated STAT3 proteins in the cell. Distinguishing between the two isoforms and their active forms is crucial for STAT3-related cancer diagnosis and therapy.

Drosophila Stat92E Signaling Following Pre-exposure to Ethanol

Repeated exposure to alcohol alters neuromolecular signaling that influences acute and long-lasting behaviors underlying Alcohol Use Disorder (AUD). Recent animal model research has implicated changes in the conserved JAK/STAT pathway, a signaling pathway classically associated with development and the innate immune system. How ethanol exposure impacts STAT signaling within neural cells is currently unclear. Here, we investigated the role of Drosophila Stat92E in ethanol-induced locomotion, signaling activity, and downstream transcriptional responses. Findings suggest that expressing Stat92E-RNAi causes enhanced ethanol-induced hyperactivity in flies previously exposed to ethanol. Furthermore, alternative splicing of Stat92E itself was detected after repeated ethanol exposure, although no changes were found in downstream transcriptional activity. This work adds to our growing understanding of altered neuromolecular signaling following ethanol exposure and suggests that STAT signaling may be a relevant target to consider for AUD treatment.

Prognostic significance of STAT3 gene expression in patients with glioblastoma tumors: a study from Western India

Abstract

Objective

Glioblastoma Multiforme (GBM), a devastating the most common primary malignant intracranial brain tumors. In India, the incidence of this malignancy is escalating, however, there are very few studies on this tumor entity from Indian population. The present study sought to investigate the prevalence and prognostic significance of Signal Transducer and Activator of Transcription 3 (STAT3) gene expression in GBM patients from Western India.

Method

STAT3 gene expression using real-time PCR was detected in total 55 GBM patients. The impact of STAT3 aberrant expression on progression-free survival (PFS) and overall (OS) was analysed using univariate and multivariate survival analysis. The data were analysed using SPSS statistical software and p value ≤0.05 was considered as significant.

Results

The aberrant STAT3 expression was found in 85% (47/55) of patients with -1.12 fold change down-regulation in 49% (23/47) and 3.36 fold change up-regulation was noted in 51% (24/47) of patients. In wild type IDH tumors (n=30), down regulation and up regulation of STAT3 was noted in 63% and 27% of patients, respectively, whereas, for IDH mutant GBM tumors (n=25), the incidence of low expression and high expression of STAT3 was noted in 16% and 68% of patients, respectively. Thus, we found that incidence of STAT3 down regulation was significantly high in patients with IDH wild type tumors, whereas, in IDH mutant GBM tumors, the incidence of up-regulated STAT3 was significantly high (P=0.021, χ2=12.81, r=+0.310). In Kaplan-Meier univariate survival analysis, a part from age (P=0.006), tumor location (P=0.025), and KPS score (P=0.002), co-detection of STAT3 up regulation and presence of IDH mutation (P=0.030) remained significant prognostic factors for PFS and OS. In multivariate survival analysis also, co-detection of STAT3 high expression and presence of IDH mutation remained independent prognosticators for PFS (HR=6.45, 95% CI=1.32-31.40, P=0.021) and OS (HR=8.69, 95% CI=1.66-45.51, P=0.010).

Conclusion

For GBM tumors, STAT3 up-regulation and presence of IDH mutations together predicts better survival. This reflects unique molecular etiology for GBM patients. Therefore, they would be useful in the future for targeted therapy and for clinicians they would be useful for better patient management. However, study on a larger sample size is required for validation.

The Role of IL-6 in Cancer Cell Invasiveness and Metastasis-Overview and Therapeutic Opportunities

Interleukin 6 (IL-6) belongs to a broad class of cytokines involved in the regulation of various homeostatic and pathological processes. These activities range from regulating embryonic development, wound healing and ageing, inflammation, and immunity, including COVID-19. In this review, we summarise the role of IL-6 signalling pathways in cancer biology, with particular emphasis on cancer cell invasiveness and metastasis formation. Targeting principal components of IL-6 signalling (e.g., IL-6Rs, gp130, STAT3, NF-κB) is an intensively studied approach in preclinical cancer research. It is of significant translational potential; numerous studies strongly imply the remarkable potential of IL-6 signalling inhibitors, especially in metastasis suppression.

STAT family of transcription factors in breast cancer: Pathogenesis and therapeutic opportunities and challenges

Breast cancer is the most commonly diagnosed cancer and second-leading cause of cancer deaths in women. Breast cancer stem cells (BCSCs) promote metastasis and therapeutic resistance contributing to tumor relapse. Through activating genes important for BCSCs, transcription factors contribute to breast cancer metastasis and therapeutic resistance, including the signal transducer and activator of transcription (STAT) family of transcription factors. The STAT family consists of six major isoforms, STAT1, STAT2, STAT3, STAT4, STAT5, and STAT6. Canonical STAT signaling is activated by the binding of an extracellular ligand to a cell-surface receptor followed by STAT phosphorylation, leading to STAT nuclear translocation and transactivation of target genes. It is important to note that STAT transcription factors exhibit diverse effects in breast cancer; some are either pro- or anti-tumorigenic while others maintain dual, context-dependent roles. Among the STAT transcription factors, STAT3 is the most widely studied STAT protein in breast cancer for its critical roles in promoting BCSCs, breast cancer cell proliferation, invasion, angiogenesis, metastasis, and immune evasion. Consequently, there have been substantial efforts in developing cancer therapeutics to target breast cancer with dysregulated STAT3 signaling. In this comprehensive review, we will summarize the diverse roles that each STAT family member plays in breast cancer pathobiology, as well as, the opportunities and challenges in pharmacologically targeting STAT proteins and their upstream activators in the context of breast cancer treatment.

Targeting the transcriptional activity of STAT3 by a novel fusion protein

BACKGROUND

The continuous activation of transcription factors drives many diseases, including tumors, autoimmune disease, neurodegenerative disease, and male infertility. Thus, Blocking the transcriptional activity of these proteins may inhibit disease progression. In this study, we developed a new method to specifically inhibit the activity of the transcription factor STAT3.

METHODS

Fusing the transcriptional inhibitory domain KRAB with STAT3 successfully blocked the transcription activity of STAT3 in cancer cells without affecting its function in the mitochondria and lysosomes.

RESULTS

the expression of KRAB-STAT3 fusion protein inhibited the growth of tumor cells.

CONCLUSIONS

The KRAB-STAT3 fusion protein provides a novel approach for drug development for the treatment of cancer or autoimmune diseases.

The Multifaceted Role of STAT3 in NK-Cell Tumor Surveillance

Signal transducer and activator of transcription 3 (STAT3) is a member of the Janus kinase (JAK)-STAT pathway, which is one of the key pathways contributing to cancer. STAT3 regulates transcription downstream of many cytokines including interleukin (IL)-6 and IL-10. In cancer, STAT3 is mainly described as a tumor promoter driving tumor cell proliferation, resistance to apoptosis, angiogenesis and metastasis and aberrant activation of STAT3 is associated with poor prognosis. STAT3 is also an important driver of immune evasion. Among many other immunosuppressive mechanisms, STAT3 aids tumor cells to escape natural killer (NK) cell-mediated immune surveillance. NK cells are innate lymphocytes, which can directly kill malignant cells but also regulate adaptive immune responses and contribute to the composition of the tumor microenvironment. The inborn ability to lyse transformed cells renders NK cells an attractive tool for cancer immunotherapy. Here, we provide an overview of the role of STAT3 in the dynamic interplay between NK cells and tumor cells. On the one hand, we summarize the current knowledge on how tumor cell-intrinsic STAT3 drives the evasion from NK cells. On the other hand, we describe the multiple functions of STAT3 in regulating NK-cell cytotoxicity, cytokine production and their anti-tumor responses in vivo. In light of the ongoing research on STAT3 inhibitors, we also discuss how targeting STAT3 would affect the two arms of STAT3-dependent regulation of NK cell-mediated anti-tumor immunity. Understanding the complexity of this interplay in the tumor microenvironment is crucial for future implementation of NK cell-based immunotherapies.

Novel STAT3 Inhibitors Targeting STAT3 Dimerization by Binding to the STAT3 SH2 Domain

Our drug discovery model has identified two novel STAT3 SH2 domain inhibitors 323–1 and 323–2 (delavatine A stereoisomers) in a series of experiments. In silico computational modeling, drug affinity responsive target stability (DARTS), and fluorescence polarization (FP) assays altogether determined that 323–1 and 323–2 directly target the STAT3 SH2 domain and inhibited both phosphorylated and non-phosphorylated STAT3 dimerization. Computational docking predicted that compound 323s bind to three subpockets of the STAT3 SH2 domain. The 323s inhibition of STAT3 dimerization was more potent than the commercial STAT3 SH2 domain inhibitor S3I-201 in the co-immunoprecipitation assay, correlating with computational docking data. The fluorescence polarization assay further confirmed that the compound 323s target the STAT3 SH2 domain by competitively abrogating the interaction between STAT3 and the SH2-binding peptide GpYLPQTV. Compared with S3I-201, the 323 compounds exhibited stronger inhibition of STAT3 and reduced the level of IL-6-stimulated phosphorylation of STAT3 (Tyr705) in LNCaP cells over the phosphorylation of STAT1 (Tyr701) induced by IFN-ɣ in PC3 cells or the phosphorylation of STAT1 (Ser727) in DU145 cells. Both compounds downregulated STAT3 target genes MCL1 and cyclin D1. Thus, the two compounds are promising lead compounds for the treatment of cancers with hyper-activated STAT3.

IL-6 Responsiveness of CD4+ and CD8+ T Cells after Allogeneic Stem Cell Transplantation Differs between Patients and Is Associated with Previous Acute Graft versus Host Disease and Pretransplant Antithymocyte Globulin Therapy

Graft-versus-host disease (GVHD), one of the most common and serious complications after allogeneic stem cell transplantation, is mediated by allocative T cells. IL-6 mediates both pro- and anti-inflammatory effects and modulates T cell response through classical signaling and trans-signaling. We investigated the effects on the mTOR and JAK/STAT pathways after various types of IL-6 signaling for circulating T cells were derived from 31 allotransplant recipients 90 days post-transplant. Cells were stimulated with IL-6 alone, hyper-IL-6 (trans-signaling), IL-6+IL-6 receptor (IL-6R; classical + trans-signaling) and IL-6+IL-6R+soluble gp130-Fc (classical signaling), and flow cytometry was used to investigate the effects on phosphorylation of AKT (Thr308), mTOR (Ser2442), STAT3 (Ser727) and STAT3 (Tyr705). CD3⁺CD4⁺ and CD3⁺C8⁺ T cells responded to classical and trans IL-6 stimulation with increased STAT3 (Tyr705) phosphorylation; these responses were generally stronger for CD3⁺CD4⁺ cells. STAT3 (Tyr705) responses were stronger for patients with previous acute GVHD; CD3⁺CD4⁺ cells from GVHD patients showed an additional STAT3 (Ser727) response, whereas patients without acute GVHD showed additional mTOR (Ser2448) responses. Furthermore, treatment with antithymocyte globulin as a part of GVHD prophylaxis was associated with generally weaker STAT3 (Tyr705) responses and altered STAT3 (Ser727) responsiveness of CD3⁺CD4⁺ cells together with increased mTOR (Ser2448) responses for the CD3⁺CD8⁺ cells. Thus, early post-transplant CD3⁺CD4⁺ and CD3⁺ CD8⁺ T cell subsets differ in their IL-6 responsiveness; this responsiveness is modulated by antithymocyte globulin and differs between patients with and without previous acute GVHD. These observations suggest that allotransplant recipients will be heterogeneous with regard to the effects of post-transplant IL-6 targeting.

Structure-activity relationship studies on O-alkylamino-tethered salicylamide derivatives with various amino acid linkers as potent anticancer agents

In our continued SAR study efforts, a series of O-alkylamino-tethered salicylamide derivatives with various amino acid linkers has been designed, synthesized, and biologically evaluated as potent anticancer agents. Five selected compounds with different representative chemical structures were found to show broad anti-proliferative activities, effective against all tested ER-positive breast cancer (BC) and triple-negative breast cancer (TNBC) cell lines with low micromolar IC₅₀ values. Among these compounds, compound 9a (JMX0293) maintained good potency against MDA-MB-231 cell line (IC₅₀ = 3.38 ± 0.37 μM) while exhibiting very low toxicity against human non-tumorigenic breast epithelial cell line MCF-10A (IC₅₀ > 60 μM). Further mechanistic studies showed that compound 9a could inhibit STAT3 phosphorylation and contribute to apoptosis in TNBC MDA-MB-231 cells. More importantly, compound 9a significantly suppressed MDA-MB-231 xenograft tumor growth in vivo without significant toxicity, indicating its great potential as a promising anticancer drug candidate for further clinical development.

The Role of Janus Kinase/STAT3 Pathway in Hematologic Malignancies With an Emphasis on Epigenetics

The Janus kinase (JAK)/signal transducer and activator of transcription (STAT) signaling pathway has been known to be involved in cell growth, cellular differentiation processes development, immune cell survival, and hematopoietic system development. As an important member of the STAT family, STAT3 participates as a major regulator of cellular development and differentiation-associated genes. Prolonged and persistent STAT3 activation has been reported to be associated with tumor cell survival, proliferation, and invasion. Therefore, the JAK-STAT pathway can be a potential target for drug development to treat human cancers, e.g., hematological malignancies. Although STAT3 upregulation has been reported in hematopoietic cancers, protein-level STAT3 mutations have also been reported in invasive leukemias/lymphomas. The principal role of STAT3 in tumor cell growth clarifies the importance of approaches that downregulate this molecule. Epigenetic modifications are a major regulatory mechanism controlling the activity and function of STAT3. So far, several compounds have been developed to target epigenetic regulatory enzymes in blood malignancies. Here, we discuss the current knowledge about STAT3 abnormalities and carcinogenic functions in hematopoietic cancers, novel STAT3 inhibitors, the role of epigenetic mechanisms in STAT3 regulation, and targeted therapies, by focusing on STAT3-related epigenetic modifications.

Structural exploration with AlphaFold2-generated STAT3α structure reveals selective elements in STAT3α-GRIM-19 interactions involved in negative regulation

STAT3, an important transcription factor constitutively activated in cancers, is bound specifically by GRIM-19 and this interaction inhibits STAT3-dependent gene expression. GRIM-19 is therefore, considered as an inhibitor of STAT3 and may be an effective anti-cancer therapeutic target. While STAT3 exists in a dimeric form in the cytoplasm and nucleus, it is mostly present in a monomeric form in the mitochondria. Although GRIM-19-binding domains of STAT3 have been identified in independent experiments, yet the identified domains are not the same, and hence, discrepancies exist. Human STAT3-GRIM-19 complex has not been crystallised yet. Dictated by fundamental biophysical principles, the binding region, interactions and effects of hotspot mutations can provide us a clue to the negative regulatory mechanisms of GRIM-19. Prompted by the very nature of STAT3 being a challenging molecule, and to understand the structural basis of binding and interactions in STAT3α-GRIM-19 complex, we performed homology modelling and ab-initio modelling with evolutionary information using I-TASSER and avant-garde AlphaFold2, respectively, to generate monomeric, and subsequently, dimeric STAT3α structures. The dimeric form of STAT3α structure was observed to potentially exist in an anti-parallel orientation of monomers. We demonstrate that during the interactions with both unphosphorylated and phosphorylated STAT3α, the NTD of GRIM-19 binds most strongly to the NTD of STAT3α, in direct contrast to the earlier works. Key arginine residues at positions 57, 58 and 68 of GRIM-19 are mainly involved in the hydrogen-bonded interactions. An intriguing feature of these arginine residues is that these display a consistent interaction pattern across unphosphorylated and phosphorylated monomers as well as unphosphorylated dimers in STAT3α-GRIM-19 complexes. MD studies verified the stability of these complexes. Analysing the binding affinity and stability through free energy changes upon mutation, we found GRIM-19 mutations Y33P and Q61L and among GRIM-19 arginines, R68P and R57M, to be one of the top-most major and minor disruptors of binding, respectively. The proportionate increase in average change in binding affinity upon mutation was inclined more towards GRIM-19 mutants, leading to the surmise that GRIM-19 may play a greater role in the complex formation. These studies propound a novel structural perspective of STAT3α-GRIM-19 binding and inhibitory mechanisms in both the monomeric and dimeric forms of STAT3α as compared to that observed from the earlier experiments, these experimental observations being inconsistent among each other.

Anti-Tumor Functions of Prelatent Antithrombin on Glioblastoma Multiforme Cells

Antithrombin, the main physiological inhibitor of the coagulation cascade, exerts anti-tumor effects on glioblastoma multiforme cells. Antithrombin has different conformations: native, heparin-activated, prelatent, latent, and cleaved. The prelatent form has an intermediate affinity between latent and native antithrombin, although it is the most antiangiogenic form. Herein, we investigate the effect of this conformation on the tumorigenic processes of glioblastoma multiforme cells. Antithrombin forms were purified by chromatography. Chromogenic/fluorogenic assays were carried out to evaluate enteropeptidase and hepsin inhibition, two serine proteases involved in these processes. Wound healing, Matrigel invasion and BrdU incorporation assays were performed to study migration, invasion and proliferation. E-cadherin, Vimentin, VEGFA, pAKT, STAT3, pSTAT3, and pERK1/2 expression was assessed by Western blot and/or qRT-PCR. Prelatent antithrombin inhibited both enteropeptidase and hepsin, although it was less efficient than the native conformation. Exposure to prelatent antithrombin significantly reduced migration and invasion but not proliferation of U-87 MG, being the conformation most efficient on migration. Prelatent antithrombin down-regulated VEGFA, pSTAT3, and pERK1/2 expression in U-87 MG cells. Our work elucidates that prelatent antithrombin has surprisingly versatile anti-tumor properties in U-87 MG glioblastoma multiforme cells. This associates with resistance pathway activation, the decreased expression of tumorigenic proteins, and increased angiogenesis, postulating the existence of a new, formerly unknown receptor with potential therapeutic implications.

Targeting STAT3: A crucial modulator of sepsis

Signal transducer and activator of transcription 3 (STAT3) is a cellular signal transcription factor that has recently attracted a great deal of attention. It can trigger a variety of genes transcription in response to cytokines and growth factors stimulation, which plays an important role in many cellular biological processes involved in anti/proinflammatory responses. Sepsis is a life-threatening organ dysfunction resulting from dysregulated host responses to infection. As a converging point of multiple inflammatory responses pathways, accumulating studies have presented the elaborate network of STAT3 in sepsis pathophysiology; these results generally indicate a promising therapeutic application for targeting STAT3 in the treatment of sepsis. In the present review, we evaluated the published literature describing the use of STAT3 in the treatment of experimental and clinical sepsis. The information presented here may be useful for the design of future studies and may highlight the potential of STAT3 as a future biomarker and therapeutic target for sepsis.

STAT3 phosphorylation in central leptin resistance

Mechanism exploitation of energy homeostasis is urgently required because of the worldwide prevailing of obesity-related metabolic disorders in human being. Although it is well known that leptin plays a central role in regulating energy balance by suppressing food intake and promoting energy expenditure, the existence of leptin resistance in majority of obese individuals hampers the utilization of leptin therapy against these disorders. However, the mechanism of leptin resistance is largely unknown in spite of the globally enormous endeavors. Current theories to interpret leptin resistance include the impairment of leptin transport, attenuation of leptin signaling, chronic inflammation, ER tress, deficiency of autophagy, as well as leptin itself. Leptin-activated leptin receptor (LepRb) signals in hypothalamus via several pathways, in which JAK2-STAT3 pathway, the most extensively investigated one, is considered to mediate the major action of leptin in energy regulation. Upon leptin stimulation the phosphorylation of STAT3 is one of the key events in JAK2-STAT3 pathway, followed by the dimerization and nuclear translocation of this molecule. Phosphorylated STAT3 (p-STAT3), as a transcription factor, binds to and regulates its target gene such as POMC gene, playing the physiological function of leptin. Regarding POMC gene in hypothalamus however little is known about the detail of its interaction with STAT3. Moreover the status of p-STAT3 and its significance in hypothalamus of DIO mice needs to be well elucidated. This review comprehends literatures on leptin and leptin resistance and especially discusses what STAT3 phosphorylation would contribute to central leptin resistance.

Napabucasin Induces Mouse Bone Loss by Impairing Bone Formation via STAT3

The novel small molecule Napabucasin (also known as BBI608) was shown to inhibit gene transcription driven by Signal Transducer and Activator of Transcription 3 (STAT3), which is considered a promising anticancer target. Many preclinical studies have been conducted in cancer patients examining the selective targeting of cancer stem cells by Napabucasin, but few studies have examined side effects of Napabucasin in the skeleton system. In the present study, we found treating bone marrow mesenchymal stem cells (BMSCs) with Napabucasin in vitro impaired their osteogenic differentiation. In terms of mechanisms, Napabucasin disrupted differentiation of BMSCs by inhibiting the transcription of osteogenic gene osteocalcin (Ocn) through STAT3. Moreover, through micro-CT analysis we found 4 weeks of Napabucasin injections induced mouse bone loss. Histological analysis revealed that Napabucasin-induced bone loss in mice was the result of impaired osteogenesis. In conclusion, this study provided evidence for the effect of Napabucasin on mouse bone homeostasis and revealed its underlying mechanisms in vivo and in vitro.

STAT3β Enhances Sensitivity to Concurrent Chemoradiotherapy by Inducing Cellular Necroptosis in Esophageal Squamous Cell Carcinoma

Concurrent chemoradiotherapy (CCRT), especially platinum plus radiotherapy, is considered to be one of the most promising treatment modalities for patients with advanced esophageal cancer. STAT3β regulates specific target genes and inhibits the process of tumorigenesis and development. It is also a good prognostic marker and a potential marker for response to adjuvant chemoradiotherapy (ACRT). We aimed to investigate the relationship between STAT3β and CCRT. We examined the expression of STAT3α and STAT3β in pretreatment tumor biopsies of 105 ESCC patients who received CCRT by immunohistochemistry. The data showed that ESCC patients who demonstrate both high STAT3α expression and high STAT3β expression in the cytoplasm have a significantly better survival rate, and STAT3β expression is an independent protective factor (HR = 0.424, p = 0.003). Meanwhile, ESCC patients with high STAT3β expression demonstrated a complete response to CCRT in 65 patients who received platinum plus radiation therapy (p = 0.014). In ESCC cells, high STAT3β expression significantly inhibits the ability of colony formation and cell proliferation, suggesting that STAT3β enhances sensitivity to CCRT (platinum plus radiation therapy). Mechanistically, through RNA-seq analysis, we found that the TNF signaling pathway and necrotic cell death pathway were significantly upregulated in highly expressed STAT3β cells after CCRT treatment. Overall, our study highlights that STAT3β could potentially be used to predict the response to platinum plus radiation therapy, which may provide an important insight into the treatment of ESCC.

STAT3 and its targeting inhibitors in osteosarcoma

Signal transducer and activator of transcription 3 (STAT3) is one of seven STAT family members involved with the regulation of cellular growth, differentiation and survival. STAT proteins are conserved among eukaryotes and are important for biological functions of embryogenesis, immunity, haematopoiesis and cell migration. STAT3 is widely expressed and located in the cytoplasm in an inactive form. STAT3 is rapidly and transiently activated by tyrosine phosphorylation by a range of signalling pathways, including cytokines from the IL‐6 family and growth factors, such as EGF and PDGF. STAT3 activation and subsequent dimer formation initiates nuclear translocation of STAT3 for the regulation of target gene transcription. Four STAT3 isoforms have been identified, which have distinct biological functions. STAT3 is considered a proto‐oncogene and constitutive activation of STAT3 is implicated in the development of various cancers, including multiple myeloma, leukaemia and lymphomas. In this review, we focus on recent progress on STAT3 and osteosarcoma (OS). Notably, STAT3 is overexpressed and associated with the poor prognosis of OS. Constitutive activation of STAT3 in OS appears to upregulate the expression of target oncogenes, leading to OS cell transformation, proliferation, tumour formation, invasion, metastasis, immune evasion and drug resistance. Taken together, STAT3 is a target for cancer therapy, and STAT3 inhibitors represent potential therapeutic candidates for the treatment of OS.

STAT3 isoforms differentially affect ACE2 expression: A potential target for COVID-19 therapy

The SARS‐coronavirus 2 is the aetiologic agent COVID‐19. ACE2 has been identified as a cell entry receptor for the virus. Therefore, trying to understand how the gene is controlled has become a major goal. We silenced the expression of STAT3α and STAT3β, and found that while silencing STAT3α causes an increase in ACE2 expression, silencing STAT3β causes the opposite effect. Studying the role of STAT3 in ACE2 expression will shed light on the molecular events that contribute to the progression of the disease and that the different roles of STAT3α and STAT3β in that context must be taken in consideration. Our results place STAT3 in line with additional potential therapeutic targets for treating COVID‐19 patients.

STAT1 Isoforms Differentially Regulate NK Cell Maturation and Anti-tumor Activity

Natural killer (NK) cells are important components of the innate immune defense against infections and cancers. Signal transducer and activator of transcription 1 (STAT1) is a transcription factor that is essential for NK cell maturation and NK cell-dependent tumor surveillance. Two alternatively spliced isoforms of STAT1 exist: a full-length STAT1α and a C-terminally truncated STAT1β isoform. Aberrant splicing is frequently observed in cancer cells and several anti-cancer drugs interfere with the cellular splicing machinery. To investigate whether NK cell-mediated tumor surveillance is affected by a switch in STAT1 splicing, we made use of knock-in mice expressing either only the STAT1α (Stat1α/α) or the STAT1β (Stat1β/β ) isoform. NK cells from Stat1α/α mice matured normally and controlled transplanted tumor cells as efficiently as NK cells from wild-type mice. In contrast, NK cells from Stat1β/β mice showed impaired maturation and effector functions, albeit less severe than NK cells from mice that completely lack STAT1 (Stat1-/- ). Mechanistically, we show that NK cell maturation requires the presence of STAT1α in the niche rather than in NK cells themselves and that NK cell maturation depends on IFNγ signaling under homeostatic conditions. The impaired NK cell maturation in Stat1β/β mice was paralleled by decreased IL-15 receptor alpha (IL-15Rα) surface levels on dendritic cells, macrophages and monocytes. Treatment of Stat1β/β mice with exogenous IL-15/IL-15Rα complexes rescued NK cell maturation but not their effector functions. Collectively, our findings provide evidence that STAT1 isoforms are not functionally redundant in regulating NK cell activity and that the absence of STAT1α severely impairs, but does not abolish, NK cell-dependent tumor surveillance.

STAT3, the Challenge for Chemotherapeutic and Radiotherapeutic Efficacy

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

STAT3: Versatile Functions in Non-Small Cell Lung Cancer

Signal Transducer and Activator of Transcription 3 (STAT3) activation is frequently found in non-small cell lung cancer (NSCLC) patient samples/cell lines and STAT3 inhibition in NSCLC cell lines markedly impairs their survival. STAT3 also plays a pivotal role in driving tumor-promoting inflammation and evasion of anti-tumor immunity. Consequently, targeting STAT3 either directly or by inhibition of upstream regulators such as Interleukin-6 (IL-6) or Janus kinase 1/2 (JAK1/2) is considered as a promising treatment strategy for the management of NSCLC. In contrast, some studies also report STAT3 being a tumor suppressor in a variety of solid malignancies, including lung cancer. Here, we provide a concise overview of STAT3‘s versatile roles in NSCLC and discuss the yins and yangs of STAT3 targeting therapies.

Type 3 IP3 receptors: The chameleon in cancer

Inositol 1,4,5-trisphosphate (IP₃) receptors (IP₃Rs), intracellular calcium (Ca²⁺) release channels, fulfill key functions in cell death and survival processes, whose dysregulation contributes to oncogenesis. This is essentially due to the presence of IP₃Rs in microdomains of the endoplasmic reticulum (ER) in close proximity to the mitochondria. As such, IP₃Rs enable efficient Ca²⁺ transfers from the ER to the mitochondria, thus regulating metabolism and cell fate. This review focuses on one of the three IP₃R isoforms, the type 3 IP₃R (IP₃R3), which is linked to proapoptotic ER-mitochondrial Ca²⁺ transfers. Alterations in IP₃R3 expression have been highlighted in numerous cancer types, leading to dysregulations of Ca²⁺ signaling and cellular functions. However, the outcome of IP₃R3-mediated Ca²⁺ transfers for mitochondrial function is complex with opposing effects on oncogenesis. IP₃R3 can either suppress cancer by promoting cell death and cellular senescence or support cancer by driving metabolism, anabolic processes, cell cycle progression, proliferation and invasion. The aim of this review is to provide an overview of IP₃R3 dysregulations in cancer and describe how such dysregulations alter critical cellular processes such as proliferation or cell death and survival. Here, we pose that the IP₃R3 isoform is not only linked to proapoptotic ER-mitochondrial Ca²⁺ transfers but might also be involved in prosurvival signaling.

Effects of evodiamine on PI3K/Akt and MAPK/ERK signaling pathways in pancreatic cancer cells

The effective antitumor drug evodiamine (EVO) is attracting increased attention. Therefore, the present study aimed to investigate the effects of EVO on the proliferation, apoptosis and autophagy of human pancreatic cancer (PC) cell lines in vitro and in vivo. Human PANC-1 and SW1990 PC cell lines were treated with different concentrations of EVO and proliferation was detected using a Cell Counting Kit (CCK)-8 assay. Colony formation and wound-healing assays showed that EVO inhibited PC cell viability and migration, and apoptosis was detected using flow cytometry. Western blotting and immunofluorescence detected the expression of proteins in PANC-1 and SW1990 cells. The PANC-1 cells were used to establish an orthotopic pancreatic tumor model in nude mice. Tumor-bearing nude mice were administered with different concentrations of EVO, and growth was monitored. High-resolution positron emission tomography and fluorine-18-labeled fluorodeoxyglucose were used to monitor the tumor/non-tumor (T/NT) ratio and standard uptake value (SUV) of the mice, which were subsequently sacrificed to measure the transplanted tumor weight. Apoptosis increased with increasing EVO concentration. The EVO-treated PC cells exhibited significantly higher expression of LC3II than the controls cells. EVO decreased LC3II, enhanced P62 and inhibited the expression of Akt, extracellular-signal-regulated protein kinase (ERK)1/2 and p38. Compared with the control group, the T/NT ratio, SUV and tumor weight decreased more markedly in the EVO-treated group. The tumor expression of phosphorylated AKT, detected using immunohistochemistry, decreased with increasing EVO doses in vivo. EVO induced PC cell apoptosis by inhibiting phosphoinositide 3-kinase/AKT and mitogen-activated protein kinase/ERK and inhibiting the phosphorylation of signal transducer and activator of transcription activator 3 in PC cells to inhibit autophagy, suggesting that EVO may be considered as a novel PC treatment.

STAT3 Activation and Oncogenesis in Lymphoma

Signal transducer and activator of transcription 3 (STAT3) is an important and the most studied transcription factor in the Janus kinase (JAK)/STAT signaling pathway. STAT3 mediates the expression of various genes that play a critical role in many cellular and biological processes, such as cell proliferation, survival, differentiation, migration, angiogenesis, and inflammation. STAT3 and associated JAKs are activated and tightly regulated by a variety of cytokines and growth factors and their receptors in normal immune responses. However, abnormal expression of STAT3 leads to its constitutive activation, which promotes malignant transformation and tumor progression through oncogenic gene expression in numerous human cancers. Human lymphoma is a heterogeneous malignancy of T and B lymphocytes. Constitutive signaling by STAT3 is an oncogenic driver in several types of B-cell lymphoma and most of T-cell lymphomas. Aberrant STAT3 activation can also induce inappropriate expression of genes involved in tumor immune evasion such as PD-L1. In this review, we focus on the oncogenic role of STAT3 in human lymphoma and highlight potential therapeutic intervention by targeting JAK/STAT3 signaling.

STAT3 Activation Is Associated with Interleukin-10 Expression and Survival in Primary Central Nervous System Lymphoma

BACKGROUND

The findings from several studies have confirmed that signal transducer and activator of transcription 3 (STAT3) is constitutively phosphorylated in primary central nervous system lymphoma (PCNSL). However, the underlying mechanism and prognostic significance of STAT3 activation have not yet been clarified.

METHODS

The expression of STAT3, phosphorylated STAT3 (p-STAT3), and interleukin (IL)-10 was examined in 32 PCNSL samples using immunohistochemistry. The relationship between IL-10 expression and STAT3 phosphorylation was determined. In addition, the associations of the expression of these proteins with the clinical factors and survival were analyzed.

RESULTS

Expression of STAT3, p-STAT3, and IL-10 was detected in 28 (87.5%), 17 (53.1%), and 25 (78.1%) samples, respectively. IL-10 expression was significantly associated with STAT3 phosphorylation in PCNSL (P = 0.033). STAT3 phosphorylation and IL-10 expression were associated with the presence of multiple brain lesions (P = 0.004 and P = 0.027, respectively), suggesting that STAT3 activation might enhance the intracranial spread of tumors in PCNSL. The 2-year overall survival and progression-free survival (PFS) rates were 67.8% and 35.5%, respectively. Kaplan-Meier survival analysis demonstrated that STAT3 phosphorylation, IL-10 expression, and multiple brain lesions were significantly associated with PFS in those with PCNSL (P = 0.009, P = 0.030, and P = 0.040, respectively). However, Cox regression analysis indicated that only STAT3 phosphorylation was significantly associated with shorter PFS (hazard ratio, 3.22; 95% confidence interval, 1.24-8.37; P = 0.016).

CONCLUSION

Our results have indicated that STAT3 activation is closely related to IL-10 expression and that p-STAT3 might be a novel biomarker predictive of poor survival in those with PCNSL.

Repurposing of drugs as STAT3 inhibitors for cancer therapy

Drug repurposing is a valuable approach in delivering new cancer therapeutics rapidly into the clinic. Existing safety and patient tolerability data for drugs already in clinical use represent an untapped resource in terms of identifying therapeutic agents for off-label protein targets. The multicellular effects of STAT3 mediated by a range of various upstream signaling pathways make it an attractive therapeutic target with utility in a range of diseases including cancer, and has led to the development of a variety of STAT3 inhibitors. Moreover, heightened STAT3 transcriptional activation in tumor cells and within the cells of the tumor microenvironment contribute to disease progression. Consequently, there are many STAT3 inhibitors in preclinical development or under evaluation in clinical trials for their therapeutic efficacy predominantly in inflammatory diseases and cancer. Despite these advances, many challenges remain in ultimately providing STAT3 inhibitors to patients as cancer treatments, highlighting the need not only for a better understanding of the mechanisms associated with STAT3 activation, but also how various pharmaceutical agents suppress STAT3 activity in various cancers. In this review we discuss the importance of STAT3-dependent functions in cancer, review the status of compounds designed as direct-acting STAT3 inhibitors, and describe some of the strategies for repurposing of drugs as STAT3 inhibitors for cancer therapy.

STAT3: A Potential Drug Target for Tumor and Inflammation

STAT (Signal Transducers and Activators of Transcription) is a cellular signal transcription factor involved in the regulation of many cellular activities, such as cell differentiation, proliferation, angiogenesis in normal cells. During the study of the STAT family, STAT3 was found to be involved in many diseases, such as high expression and sustained activation of STAT3 in tumor cells, promoting tumor growth and proliferation. In the study of inflammation, it was found that it plays an important role in the anti-inflammatory and repairing of damage tissues. Because of the important role of STAT3, a large number of studies have been obtained. At the same time, after more than 20 years of development, STAT3 has also been used as a target for drug therapy. And the discovery of small molecule inhibitors also promoted the study of STAT3. Since STAT3 has been extensively studied in inflammation and tumor regulation, this review presents the current state of research on STAT3.

Transcriptional Regulation of Energy Metabolism in Cancer Cells

Cancer development, growth, and metastasis are highly regulated by several transcription regulators (TRs), namely transcription factors, oncogenes, tumor-suppressor genes, and protein kinases. Although TR roles in these events have been well characterized, their functions in regulating other important cancer cell processes, such as metabolism, have not been systematically examined. In this review, we describe, analyze, and strive to reconstruct the regulatory networks of several TRs acting in the energy metabolism pathways, glycolysis (and its main branching reactions), and oxidative phosphorylation of nonmetastatic and metastatic cancer cells. Moreover, we propose which possible gene targets might allow these TRs to facilitate the modulation of each energy metabolism pathway, depending on the tumor microenvironment.