Novel STAT 3 inhibitors for treating gastric cancer

Targeting STAT3 potentiates CDK4/6 inhibitors therapy in head and neck squamous cell carcinoma

Anti-CDK4/6 therapy has been employed for the treatment for head and neck squamous cell carcinoma (HNSCC) with CDK4/6 hyperactivation, but the response rate is relatively low. In this study, we first showed that CDK4 and CDK6 was over-expressed and conferred poor prognosis in HNSCC. Moreover, in RB-positive HNSCC, STAT3 signaling was activated induced by CDK4/6 inhibition and STAT3 promotes RB deficiency by upregulation of MYC. Thirdly, the combination of Stattic and CDK4/6 inhibitor results in striking anti-tumor effect in vitro and in Cal27 derived animal models. Additionally, phospho-STAT3 level negatively correlates with RB expression and predicts poor prognosis in patients with HNSCC. Taken together, our findings suggest an unrecognized function of STAT3 confers to CDK4/6 inhibitors resistance and presenting a promising combination strategy for patients with HNSCC.

Synthesis, characterization, and evaluation of the anticancer properties of pH-responsive carvacrol-zinc oxide quantum dots on breast cancer cell line (MDA-MB-231)

Since most solid tumors have a low pH value, a pH-responsive drug delivery system may offer a broad method for tumor-targeting treatment. The present study is used to analyze the anticancer activity of carvacrol-zinc oxide quantum dots (CVC-ZnO QDs) against breast cancer cells (MDA-MB-231). CVC-ZnO QDs demonstrate pH responsive and are specifically released within the acidic pH tumor microenvironment. This property enables targeted drug delivery exclusively to cancer cells while minimizing the impact on normal cells. To the synthesized ZnO QDs, the CVC was loaded and then examined by X-ray diffraction, ultraviolet-visible, Fourier transform infrared spectrophotometer, scanning electron microscopy-energy dispersive X-ray, and transmission electron microscopy. For up to 20 h, CVC release was examined in different pH-buffered solutions. The results showed that carvacrol release was stable in an acidic pH solution. Further, cytotoxicity assay, antioxidant, and lipid peroxidation activity, reactive oxygen species, mitochondrial membrane potential, nuclear damage, and the ability of CVC-ZnO QDs to cause apoptosis were all examined. Apoptosis markers such as Bcl2, Bax, caspase-3, and caspase-9, were also studied. In conclusion, the CVC-ZnO QDs destabilized the MDA-MB-231cells under its acidic tumor microenvironment and regulated apoptosis.

The oncogenic mechanisms of the Janus kinase-signal transducer and activator of transcription pathway in digestive tract tumors

Digestive tract tumors are heterogeneous and involve the dysregulation of multiple signaling pathways. The Janus kinase-signal transducer and activator of transcription (JAK-STAT) pathway plays a notable role in the oncogenesis of digestive tract tumors. Typically activated by pro-inflammatory cytokines, it regulates important biological processes, such as cell growth, differentiation, apoptosis, immune responses, and inflammation. The aberrant activation of this pathway manifests in different forms, including mutations in JAKs, overexpression of cytokine receptors, and sustained STAT activation, and contributes to promoting the malignant characteristics of cancer cells, including uncontrolled proliferation, resistance to apoptosis, enhanced invasion and metastasis, angiogenesis, acquisition of stem-like properties, and drug resistance. Numerous studies have shown that aberrant activation of the JAK-STAT pathway is closely related to the development and progression of digestive tract tumors, contributing to tumor survival, angiogenesis, changes in the tumor microenvironment, and even immune escape processes. In addition, this signaling pathway also affects the sensitivity of digestive tract tumors to chemotherapy and targeted therapy. Therefore, it is crucial to comprehensively understand the oncogenic mechanisms underlying the JAK-STAT pathway in order to develop effective therapeutic strategies against digestive tract tumors. Currently, several JAK-STAT inhibitors are undergoing clinical and preclinical trials as potential treatments for various human diseases. However, further investigation is required to determine the role of this pathway, as well as the effectiveness and safety of its inhibitors, especially in the context of digestive tract tumors. In this review, we provide an overview of the structure, classic activation, and negative regulation of the JAK-STAT pathway. Furthermore, we discuss the pathogenic mechanisms of JAK-STAT signaling in different digestive tract tumors, with the aim of identifying potential novel therapeutic targets. Video Abstract.

Discovery, Optimization, and Evaluation of Novel N-(Benzimidazol-5-yl)-1,3,4-thiadiazol-2-amine Analogues as Potent STAT3 Inhibitors for Cancer Treatment

Signal transducer and activator of transcription 3 (STAT3) is an attractive target for cancer therapy. However, identifying potent and selective STAT3 small-molecule inhibitors with drug-like properties remains challenging. Based on a scaffold combination strategy, compounds with a novel N-(benzimidazol-5-yl)-1,3,4-thiadiazol-2-amine scaffold were designed and their inhibition of the interleukin-6 (IL-6)/JAK/STAT3 pathway was tested in HEK-Blue IL-6 reporter cells. After optimization of lead compound 12, compound 40 was identified as a selective STAT3 inhibitor that directly binds the SH2 domain to inhibit STAT3 phosphorylation, translocation, and downstream gene transcription. Compound 40 exhibited antiproliferative activities against STAT3-overactivated DU145 (IC50 value = 2.97 μM) and MDA-MB-231 (IC50 value = 3.26 μM) cancer cells and induced cell cycle arrest and apoptosis. In the DU145 xenograft model, compound 40 showed in vivo antitumor efficacy following intraperitoneal administration, with a tumor growth inhibition rate of 65.3% at 50 mg/kg, indicating promise for further development.

Bioactive compound C498-0670 alleviates LPS-induced sepsis via JAK/STAT and NFκB signaling pathways

The JAK/STAT and NFκB signaling pathways are two major inflammatory signaling pathways that are usually activated simultaneously in the body's inflammatory response to bacterial or viral infections. Hyperactivation of these two prominent signaling pathways is associated with various immune-related diseases and mortality, pointing to an urgent need for drug development targeting JAK/STAT and/or NFκB signaling. In this study, we screened 18,840 compounds using our well-established dual STAT-NFκB driven luciferase reporter based high-throughput screening system and identified a bioactive compound C498-0670, which inhibits both JAK/STAT and NFκB signaling. C498-0670 inhibits the activation of STATs and p-IKKα/β in both the immortalized cell lines and primary peritoneal macrophages, while suppressing the expression of LPS-induced inflammatory mediators in vitro. In addition, the overall anti-inflammatory effects of C498-0670 were investigated using transcriptome sequencing and bioinformatics approaches. C498-0670 was predicted to alleviate sepsis/septic shock by disease/function analysis using IPA software, which was further verified in the LPS-induced mouse sepsis model in vivo. C498 reduced LPS-induced liver and kidney damage, myeloid cell infiltration, and pro-inflammatory cytokine and chemokine production in vivo. Furthermore, the SPR-HPLC-MS-based target fishing approach was used to identify the putative drug targets, and the high affinities of JAK2 (JAK/STAT signaling), NFKBIA (NFκB signaling), and IL-1β, NLRP1b (inflammasome signaling) for C498-0670 were verified by molecular docking approach. These results suggest that C498-0670 can be used as a dual-target inhibitor of JAK/STAT and NFκB signaling pathways for the treatment of various inflammatory diseases, especially septic shock.

A Narrative Review of STAT Proteins in Diabetic Retinopathy: From Mechanisms to Therapeutic Prospects

Diabetic retinopathy (DR), a blinding disease, is one of the high-incidence chronic complications of diabetes. However, the current treatment for DR is mainly based on advanced pathological changes, which cannot reverse pre-existing retinal tissue damage and visual impairment. Signal transducer and activator of transcription (STAT) proteins are essential in DR through early and late stages. They participate in the early stage of DR through multiple mechanisms and have a strong proangiogenic effect in the late stage. Inhibiting STAT proteins activity has also achieved a significant effect in reversing the pathological changes of DR. Thus, STAT proteins are expected to be an effective therapeutic target in the early stage of DR and can make up for inadequate late treatment. This review introduces the structure, signal transduction mode, and biological functions of STAT proteins in detail and focuses on their role in the mechanism of DR. We also summarize the current research on STAT-related biological agents in DR, aiming to provide a theoretical basis for the treatment of DR.

Boronic Acid: A Novel Pharmacophore Targeting Src Homology 2 (SH2) Domain of STAT3

SH2 domains have been recognized as promising targets for various human diseases. However, targeting SH2 domains with phosphopeptides or small-molecule inhibitors derived from bioisosteres of the phosphate group is still challenging. Identifying novel bioisosteres of the phosphate group to achieve favorable in vivo potency is urgently needed. Here, we report the feasibility of targeting the STAT3-SH2 domain with a boronic acid group and the identification of a highly potent inhibitor compound 7 by replacing the carboxylic acid of compound 4 with a boronic acid. Compound 7 shows higher binding affinity, better cellular potency, more favorable PK profiles, and higher in vivo antitumor activity than 4. The stronger anticancer effect of 7 partially stems from its covalent binding mode with the SH2 domain, verified by the washout experiments. The relatively high level of sequence conservation among SH2 domains makes the results presented here of general significance.

Propofol induces ferroptosis and inhibits malignant phenotypes of gastric cancer cells by regulating miR-125b-5p/STAT3 axis

BACKGROUND

Gastric cancer is a common malignancy with poor prognosis, in which ferroptosis plays a crucial function in its development. Propofol is a widely used anesthetic and has antitumor potential in gastric cancer. However, the effect of propofol on ferroptosis during gastric cancer progression remains unreported.

AIM

To explore the function of propofol in the regulation of ferroptosis and malignant phenotypes of gastric cancer cells.

METHODS

MTT assays, colony formation assays, Transwell assays, wound healing assay, analysis of apoptosis, ferroptosis measurement, luciferase reporter gene assay, and quantitative reverse transcription polymerase chain reaction were used in this study.

RESULTS

Our data showed that propofol was able to inhibit proliferation and induce apoptosis of gastric cancer cells. Meanwhile, propofol markedly repressed the invasion and migration of gastric cancer cells. Importantly, propofol enhanced the erastin-induced inhibition of growth of gastric cancer cells. Consistently, propofol increased the levels of reactive oxygen species, iron, and Fe²⁺ in gastric cancer cells. Moreover, propofol suppressed signal transducer and activator of transcription (STAT)3 expression by upregulating miR-125b-5p and propofol induced ferroptosis by targeting STAT3 in gastric cancer cells. The miR-125b-5p inhibitor or STAT3 overexpression reversed propofol-attenuated malignant phenotypes of gastric cancer cells.

CONCLUSION

Propofol induced ferroptosis and inhibited malignant phenotypes of gastric cancer cells by regulating the miR-125b-5p/STAT3 axis. Propofol may serve as a potential therapeutic candidate for gastric cancer.

Gastrokine 2 Regulates the Antitumor Effect of JAK2/STAT3 Pathway in Gastric Cancer

GKN2 (gastrokine 2) mainly plays a regulatory role in gastric mucosal defense and cell protection mechanisms, and its role in gastric cancer has not been thoroughly elucidated. Immunohistochemistry was used to detect GKN2 and TFF1 expressions in 90 gastric cancer tissues, 48 neoplastic resection margins, and 22 normal gastric mucosa epithelia. It showed that the downregulation of GKN2 and TFF1 expressions in gastric cancer tissues was significantly different from that in adjacent normal gastric tissues and distal gastric mucosal tissues. Nevertheless, correlation analysis showed that GKN2 expression in gastric cancer tissues was independent of TFF1 expression. After overexpression of GKN2 was constructed in human gastric cancer cell line MKN28 with the Ad-GFP-GKN2 transfected, cell viability was measured by CCK-8 assay, and migration and invasion ability were analyzed by transwell migration assay and transwell invasion assay. It indicated that overexpression of GKN2 significantly reduced the viability of MKN28 and SGC7901 cells. Overexpression of GKN2 could also inhibit the migration and invasion ability in MKN28 and SGC7901 cells. In addition, upregulation of GKN2 can inactivate the JAK2/STAT3 pathway. Our data suggest that GKN2 and TFF1 play the antitumor role in gastric carcinoma, and TFF1 may not interact or cooperate with GKN2. GKN2 overexpression can inhibit the growth and metastasis by downregulating the JAK2/STAT3 pathway in gastric cancer cells.

Dihydrotanshinone Inhibits Hepatocellular Carcinoma by Suppressing the JAK2/STAT3 Pathway

Liver cancer is the sixth most commonly diagnosed cancer and the fourth leading cause of cancer death. Most (75–85%) primary liver cancers occurring worldwide are hepatocellular carcinoma (HCC). The development of resistance and other drug related side effects are the prime reasons for the failure of treatment. Therefore, developing high-efficacy and low-toxicity natural anticancer agents is greatly needed in the treatment of HCC. Dihydrotanshinone (DHTS) is widely used for promoting blood circulation and antitumor. The aim of the present study was to investigate the effect and mechanism of DHTS-induced apoptosis of HCC, both in vitro and in vivo. We found that DHTS inhibited the growth of several HCC cells (HCCLM3, SMMC7721, Hep3B and HepG2). DHTS induced the apoptosis of SMMC7721 cells. Immunofluorescence results have showed that DHTS decreased STAT3 nuclear translocation. Moreover, Western blot results have demonstrated that DHTS suppressed the activation of JAK2/STAT3 signaling pathway. In addition, xenograft results have showed that DHTS suppressed tumor growth of SMMC7721 cells in vivo by inhibiting the p-STAT3. Thus, we demonstrated that DHTS could inhibit HCC by suppressing the JAK2/STAT3 pathway. DHTS has potential to be a chemotherapeutic agent in HCC and merits further clinical investigation.

My 60-Year Love Affair with Natural Products

The author describes his 60-year career in studying the chemistry of natural products, which includes structural, synthetic, and biosynthetic studies of natural products ranging from insect pigments, antibiotics, and fecal mutagens to taxol and other anticancer natural products as well as antimalarial natural products. One of the compounds discussed, napabucasin, is now an anticancer drug in phase III clinical trials.

MicroRNA-140-5p regulates the proliferation, apoptosis and inflammation of RA FLSs by repressing STAT3

Ectopic expression of microRNA (miRNA) in rheumatoid arthritis (RA) fibroblast-like synoviocyte (RA FLS) is associated with the development of rheumatoid arthritis. The present study aimed to evaluate the effects of miRNA-140-5p (miR-140) on the properties of RA FLSs. It was found that miR-140 expression was decreased in 33 RA patients and extracted RA FLS samples, when compared to the corresponding healthy controls. Abnormally increased miR-140 expression in RA FLSs attenuated cell proliferation and increased cell apoptosis. Additionally, reduced pro-inflammatory cytokine production was observed in RA FLSs transfected with a miR-140 precursor. Furthermore, the 3'-UTR of the signal transducer and activator of transcription (STAT) 3 gene was identified as a target of miR-140. Notably, restoration of STAT3 expression rescued the regulatory effect of miR-140 on the proliferation, apoptosis and inflammatory cytokine production of RA FLSs. Therefore, the current findings indicated that miR-140 is a crucial modulator of both proliferation and apoptosis, shedding light on the etiology behind RA FLS viability, which is modulated by an interplay between miR-140 and STAT3 in the context of RA.

Cancer Stem Cell (CSC) Inhibitors in Oncology-A Promise for a Better Therapeutic Outcome: State of the Art and Future Perspectives

Cancer stem cells (CSCs), a subpopulation of cancer cells endowed with self-renewal, tumorigenicity, pluripotency, chemoresistance, differentiation, invasive ability, and plasticity, reside in specialized tumor niches and are responsible for tumor maintenance, metastasis, therapy resistance, and tumor relapse. The new-age "hierarchical or CSC" model of tumor heterogeneity is based on the concept of eradicating CSCs to prevent tumor relapse and therapy resistance. Small-molecular entities and biologics acting on various stemness signaling pathways, surface markers, efflux transporters, or components of complex tumor microenvironment are under intense investigation as potential anti-CSC agents. In addition, smart nanotherapeutic tools have proved their utility in achieving CSC targeting. Several CSC inhibitors in clinical development have shown promise, either as mono- or combination therapy, in refractory and difficult-to-treat cancers. Clinical investigations with CSC marker follow-up as a measure of clinical efficacy are needed to turn the "hype" into the "hope" these new-age oncology therapeutics have to offer.

Targeting kinases with thymoquinone: a molecular approach to cancer therapeutics

Kinases are enzymes that are important for cellular functions, but their overexpression has strong connections with carcinogenesis, rendering them important targets for anticancer drugs. Thymoquinone (TQ) is a natural compound with proven anticancer activities, at least in preclinical studies. TQ can target several kinases, including phosphoinositide 3-kinase (PI3K), mitogen-activated protein kinase (MAPK), Janus kinase/signal transducers and activators of transcription (JAK/STAT), polo-like kinase 1 (PLK1), and tyrosine kinase in different cancer cells and animal models. Inhibiting the activity of kinases or suppressing their expression might be among the mechanisms of TQ anticancer activity. In this review, we discuss the role of TQ in kinase regulation in different cancer models.

Suppression of FAK by nexrutine inhibits gastric cancer progression

AIM

Nexrutine, an herbal extract of Phellodendron amurense, has been found to play a tumor-suppressive role in many cancers. However, its role in the pathogenesis of gastric cancer remains unclear.

MATERIALS AND METHODS

Gastric cancer cells (SGC-7901 and MGC-803) were treated with nexrutine, and cell proliferation, invasion and apoptosis were analyzed. And the MGC-803 cells-derived xenograft mouse models were fed pelleted diet containing 600 mg/kg nexrutine for 21 days after inoculation. Mechanically, we focused on the influences of nexrutine on the levels and activation of STAT3 and NF-κB as well as their upstream regulator FAK. Additionally, we further verified whether nexrutine affected the proliferation, invasion and apoptosis of gastric cancer cells via FAK by upregulating FAK expression before nexrutine treatment.

KEY FINDINGS

We found nexrutine inhibited the viability, invasion, and expression levels of PCNA, CyclinD1 and Bcl-2, promoted the apoptosis and Bax expression, decreased levels of STAT3, phospho-STAT3, NF-κB p65, phospho-p65, FAK and phospho-FAK in gastric cancer cells. Overexpression of FAK reversed the impacts of nexrutine on the levels of STAT3, phospho-STAT3, NF-κB p65, phospho-p65, as well as the malignant characteristics of gastric cancer cells. Moreover, nexrutine suppressed tumor volumes and weights, and decreased expression and phosphorylation of FAK, STAT3 and NF-κB p65 in vivo.

SIGNIFICANCE

Nexrutine inhibited the malignant progression of gastric cancer via negatively regulating STAT3/NF-κB signaling pathway by suppressing FAK expression and activation.

MiR-126 promotes esophageal squamous cell carcinoma via inhibition of apoptosis and autophagy

MiRNA-126 (miR-126) has been shown to be involved in various malignancies as well as other biological processes. However, currently, its role in esophageal squamous cell carcinoma (ESCC) is not well understood. The present study is focused on the mechanisms that underlie the effect of miR-126 on cell survival and death (apoptosis and autophagy) in ESCC cells. MiR-126 expression was found to be enhanced in ESCC cells and tissues. Downregulation of miR-126 suppressed cell survival, and TUNEL staining indicated that miR-126 inhibition promoted ESCC cell death. In addition, the production of LC3B and p62 proteins, two autophagy signals, was reduced following miR-126 inhibition. A dual luciferase reporter assay demonstrated that the STAT3 3’-UTR is a direct target of miR-126. Furthermore, STAT3 knock-down rescued the effects on autophagy and apoptosis caused by miR-126 inhibition in ESCC cells. The results of this study may provide some insight into the molecular and biological mechanisms underlying ESCC generation and contribute to the development of novel therapeutic approaches for ESCC.

Antitumor functions and mechanisms of nitidine chloride in human cancers

Nitidine chloride (NC), a quaternary ammonium alkaloid, exhibits multiple biological activities, including antimalarial, antifungal, and antiangiogenesis. Recently, NC has been characterized to perform antitumor activity in a variety of malignancies. NC has been identified to suppress cell proliferation, stimulate apoptosis, and induce cell cycle arrest, retard migration, invasion and metastasis. Moreover, NC is reported to sensitize cancer cells to chemotherapeutic drugs. In this review article, we describe the functions of NC in human cancers and discuss the molecular insight into NC-involved antitumor feature. This review article will stimulate the deeper investigation for using NC as a potent agent for the management of cancer patients.

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.

lncRNA CCAT1 contributes to the growth and invasion of gastric cancer via targeting miR-219-1

Gastric cancer (GC) is one of the most malignant tumors that seriously threaten human health. Increased reports have indicated that long noncoding RNAs (lncRNAs) are associated with GC. This study aims to investigate the regulatory role of colon cancer-associated transcript-1 (CCAT1) in GC. The results exhibited the fact that CCAT1 was expressed higher in 57 GC tissue samples than in 57 paired adjacent normal tissue samples. The expression of CCAT1 was also increased in GC cell lines (MKN45, Hs746T, and SGC-7901) compared with the gastric epithelial cell line GES-1. Besides this, decreased cell proliferation with increased cell apoptosis was detected in SGC-7902 cells transfected with CCAT1 short hairpin RNA (shRNA). At the same time, a lower cell invasion ability was measured in SCG-7901 cells transfected with CCAT1 shRNA.In addition, miR-219-1 was predicted and convinced a direct target of CCAT1. The expression of miR-219-1 was decreased in GC tissues and GC cell lines. Further studies demonstrated that the roles of CCAT1 in cell proliferation, apoptosis, and invasion were inhibited by miR-219-1. Finally, in vivo experiment indicated that tumor growth of GC was suppressed through knockdown of CCAT1. In conclusion, these results suggested that CAT1 promotes the tumorigenesis and progression of GC by negatively regulating miR-219-1.

Selective Acetogenins and Their Potential as Anticancer Agents

The Kingdom Plantae has provided several successful drugs for the treatment of different diseases, including cancer, and continues to be a source of new possible therapeutic molecules. For example, the annonaceous acetogenins (AAs) are secondary metabolites found in the Annonaceae family, which are plants employed in traditional medicine for the treatment of cancer and various other diseases. These polyketides are inhibitors of Complex I in the respiratory chain of tumor cells, a process that is closely related to tumor metabolism, cell death, apoptosis, and autophagy. The goal of this review is to update readers on the role of the AAs as antitumor agents using in vitro and in vivo studies to demonstrate their importance in the area of oncology drug discovery. For this purpose, we performed a literature search in the PubMed scientific database using a range of keywords, including acetogenins and cancer, acetogenins antitumor activity, acetogenins and cytotoxicity, and acetogenins mechanism of action, among others. As a result, we found that the AAs are cytotoxic compounds that can induce apoptosis, cell cycle arrest, and autophagy in vitro, in addition to exhibiting tumor growth inhibition in vivo. The functional group related to their antineoplastic activity is suggested to be the mono or bis tetrahydrofuran ring accompanied by two or more hydroxy groups. The versatility of the AA bioactivity therefore renders them potential therapeutic agents for cancer treatment. It is therefore apparent that nature is worth further examination to aid in the discovery of more effective, accurate, and less harmful therapies in the fight against cancer.

Activation of IGF1R by DARPP-32 promotes STAT3 signaling in gastric cancer cells

Dopamine and cAMP-regulated phosphoprotein, Mr 32000 (DARPP-32), is frequently overexpressed in early stages of gastric cancers. We utilized in vitro assays, 3D gastric gland organoid cultures, mouse models, and human tissue samples to investigate the biological and molecular impact of DARPP-32 on activation of IGF1R and STAT3 signaling and gastric tumorigenesis. DARPP-32 enhanced phosphorylation of IGF1R (Y1135), a step that was critical for STAT3 phosphorylation at Y705, nuclear localization, and transcription activation. By using proximity ligation and co-immunoprecipitation assays, we found that IGF1R and DARPP-32 co-existed in the same protein complex. Binding of DARPP-32 to IGF1R promoted IGF1R phosphorylation with subsequent activation of downstream SRC and STAT3. Analysis of gastric tissues from the TFF1 knockout (KO) mouse model of gastric neoplasia, demonstrated phosphorylation of STAT3 in the early stages of gastric tumorigenesis. By crossing the TFF1 KO mice with DARPP-32 (DP) knockout (KO) mice, that have normal stomach, we obtained double knockout (TFF1 KO/DP KO). The gastric mucosa from the double KO mice did not show phosphorylation of IGF1R or STAT3. In addition, the TFF1 KO/DP KO mice had a significant delay in developing neoplastic gastric lesions. Analysis of human gastric cancer tissue microarrays, showed high levels of DARPP-32 and positive immunostaining for nuclear STAT3 in cancer tissues, as compared to non-cancer histologically normal tissues. In summary, the DARPP-32-IGF1R signaling axis plays a key role in regulating the STAT3 signaling, a critical step in gastric tumorigenesis.

miR-337 suppresses cutaneous T-cell lymphoma via the STAT3 pathway

Cutaneous T-cell lymphoma (CTCL) is associated with the downregulation of miR-337 expression, although the exact underlying mechanism is unknown. In the present work, we investigated the molecular mechanism and function of miR-337 in regulating CTCL cell viability and invasion. We observed that miR-337 expression was downregulated in both CTCL tumors and cell lines. Furthermore, CCK assay, BrdU incorporation assay, and flow cytometry revealed that transfection with the miR-337 mimic resulted in decreased proliferation and increased apoptotic levels in CTCL cells. Results of the Transwell migration assay indicated that the miR-337 mimic decreased CTCL cell invasion in vitro. Both bioinformatics prediction and the dual-luciferase reporter assay revealed that miR-337 targets the 3'-UTR of STAT3 for silencing. Overexpression of STAT3 counteracted the pro-apoptotic influence of miR-337 in CTCL cell lines and restored their invasion properties. The results thus indicate that the miR-337-STAT3 axis inhibits the proliferation of malignant T cells and that miR-337 may serve as a promising therapeutic target for CTCL.

Dietary Phytochemicals Targeting Cancer Stem Cells

There is an increasing awareness of the importance of a diet rich in fruits and vegetables for human health. Cancer stem cells (CSCs) are characterized as a subpopulation of cancer cells with aberrant regulation of self-renewal, proliferation or apoptosis leading to cancer progression, invasiveness, metastasis formation, and therapy resistance. Anticancer effects of phytochemicals are also directed to target CSCs. Here we provide a comprehensive review of dietary phytochemicals targeting CSCs. Moreover, we evaluate and summarize studies dealing with effects of dietary phytochemicals on CSCs of various malignancies in preclinical and clinical research. Dietary phytochemicals have a significant impact on CSCs which may be applied in cancer prevention and treatment. However, anticancer effects of plant derived compounds have not yet been fully investigated in clinical research.

BP‑1‑102 exerts an antitumor effect on the AGS human gastric cancer cell line through modulating the STAT3 and MAPK signaling pathways

BP-1-102, a novel inhibitor of signal transducer and activator of transcription 3 (STAT3), exhibits significant antitumor effects in several malignancies in vitro and in vivo. However, its role in gastric cancer (GC) remains to be elucidated. In the present study, the effect and potential molecular mechanisms of BP-102 in human GC cell lines were investigated. The results showed that BP-1-02 dose-dependently inhibited the proliferation of AGS cells, whereas it had little effect on HGC-27 cells. Flow cytometric analysis indicated that BP-1-102 induced apoptosis, but had minimal effect on cell cycle distribution. In addition, cells treated with BP-1-102 demonstrated markedly suppressed migration and invasion capacities. Western blot analysis revealed that BP-1-102 inhibited the phosphorylation of STAT3 and its target genes, including c-Myc, cyclin D1 and survivin, in a time- and dose-dependent manner. Furthermore, it was found that BP-1-102 induced the phosphorylation of c-Jun N-terminal kinase and p38 mitogen-activated protein kinase (MAPK) and inhibited the activation of extracellular signal-related kinases. Taken together, these results demonstrated that BP-1-102 may be a potent antitumor agent that acts through modulating the STAT3 and MAPK signaling pathways in GC cells.

Knockdown of RNF6 inhibits gastric cancer cell growth by suppressing STAT3 signaling

Background and objective

RNF6, an E3 ligase, has been reported to play an important role in the tumorigenesis in several tissues, but its role in gastric cancer is still unknown. In this study, we aimed to investigate the biological function and molecular mechanisms of RNF6 in gastric cancer.

Materials and methods

The expression levels of RNF6 were detected by quantitative real-time PCR (qRT-PCR) and immunoblotting in gastric cancer tissues and cell lines. Cell Counting Kit-8 assay was performed to evaluate cell proliferation. Cell apoptosis was analyzed by flow cytometer and immunoblotting. Luciferase assay, immunoblotting and qRT-PCR were performed to explore the activation of STAT3. Immunoprecipitation was performed to evaluate the ubiquitination of SHP-1.

Results

In this study, RNF6 was found to be upregulated in both primary tissues and cell lines of gastric cancer. Knockdown or overexpression of RNF6 inhibited or promoted cell growth of gastric cancer cells. Knockdown of RNF6 also induced the cleavage of PARP and promoted cell apoptosis in gastric cancer cells. In addition, knockdown of RNF6 also increased the cytotoxicity of doxorubicin against gastric cancer. Moreover, knockdown of RNF6 inhibited STAT3-derived luciferase activity and downregulated the phosphorylation of STAT3, but upregulated the protein level of SHP-1. Knockdown of RNF6 downregulated the expression of MCL1 and XIAP, which are target genes of STAT3. Further studies showed that RNF6 regulated the stability of SHP-1 by inducing its polyubiquitination.

Conclusion

These results demonstrated that RNF6 was highly expressed in gastric cancer and regulated the growth of gastric cancer cells by affecting SHP-1/STAT3 signaling, which suggested that RNF6 could be a novel target for gastric cancer therapy.

Napabucasin and Related Heterocycle-Fused Naphthoquinones as STAT3 Inhibitors with Antiproliferative Activity against Cancer Cells

Napabucasin (6) and its angularly anellated isomer (7), for which the synthesis is described, together with related plant-derived naphthoquinones, were evaluated in vitro against human breast cancer (MDA-MB-231) and chronic myelogenous leukemia (K562) cells. As observed for β-lapachone (3), the active naphthoquinones all induced apoptosis in a cell-cycle-independent fashion. In contrast to the pyran-fused β-lapachone (3), however, the most potent furan-fused naphthoquinones were able to redox cycle and generate superoxide in cell-based assays, which was independent of NAD(P)H:quinone oxido-reductase 1. In a homogeneous time-resolved fluorescence (HTRF) assays with MDA-MB-231 cells, both napabucasin (6) and isonapabucasin (7) were identified as targeting STAT3 phosphorylation. In addition, drug affinity responsive target stability assays were performed to validate a direct interaction of the naphthoquinones with STAT3. Isonapabucasin (7) turned out to be twice as potent against STAT3 as napabucasin (6) in the HTRF assay, with an EC₅₀ in the submicromolar range, which was in excellent agreement with the potency of both agents to inhibit the growth of MDA-MB-231 cells. Moreover, molecular docking experiments predicted different binding modes to the STAT3 SH2 domain for the linearly anellated napabucasin (6) and its angularly anellated isomer (7).

Plant-Derived Anticancer Agents: Lessons from the Pharmacology of Geniposide and Its Aglycone, Genipin

For centuries, plants have been exploited by mankind as sources of numerous cancer chemotherapeutic agents. Good examples of anticancer compounds of clinical significance today include the taxanes (e.g., taxol), vincristine, vinblastine, and the podophyllotoxin analogues that all trace their origin to higher plants. While all these drugs, along with the various other available therapeutic options, brought some relief in cancer management, a real breakthrough or cure has not yet been achieved. This critical review is a reflection on the lessons learnt from decades of research on the iridoid glycoside geniposide and its aglycone, genipin, which are currently used as gold standard reference compounds in cancer studies. Their effects on tumour development (carcinogenesis), cancer cell survival, and death, with particular emphasis on their mechanisms of actions, are discussed. Particular attention is also given to mechanisms related to the dual pro-oxidant and antioxidant effects of these compounds, the mitochondrial mechanism of cancer cell killing through reactive oxygen species (ROS), including that generated through the uncoupling protein-2 (UCP-2), the inflammatory mechanism, and cell cycle regulation. The implications of various studies for the evaluation of glycosidic and aglycone forms of natural products in vitro and in vivo through pharmacokinetic scrutiny are also addressed.

Knockdown of long non-coding RNA HOXD-AS1 inhibits the progression of osteosarcoma

Long non-coding RNA HOXD-AS1 (HOXD-AS1) has recently been shown to be involved in the development and progression of multiple cancers. However, the expression, significance, and biological function of HOXD-AS1 in osteosarcoma (OS) remain unknown. Here, we found that the expression level of HOXD-AS1 was significantly upregulated in OS tissues and cells. Furthermore, high expression of HOXD-AS1 was positively associated with the clinical and pathological characteristics of OS, including tumor stage and lymph node metastasis, and negatively correlated with overall survival rate. in vitro assays confirmed that knockdown of HOXD-AS1 suppressed cell proliferation, colony formation, migration, and invasion, and promoted cell cycle arrest at G1 stage and apoptosis in OS cells. in vivo assays confirmed that knockdown of HOXD-AS1 significantly decreased tumor growth in xenograft mice, and decreased tumor size and weight. Importantly, we also showed that knockdown of HOXD-AS1 significantly reduced signal transducer and activator of transcription 3 and its target protein (CyclinD1, Bcl-2, and MMP-2) expression in vitro and in vivo. Moreover, overexpression of STAT3 could reverse the suppression of proliferation ability induced by sh-HOXD-AS1 in U2OS cells. Collectively, our data indicated that HOXD-AS1 might be an oncogenic long non-coding RNA (lncRNA) and might be a potential attractive therapeutic target for OS.

Current therapeutic landscape for advanced gastroesophageal cancers

Treatment of advanced gastroesophageal cancers remains challenging for clinicians, patients, and caregivers alike. Despite considerable research, the therapeutic armamentarium is restricted and hardly personalized. In the first-line setting, trastuzumab with a fluoropyrimidine and platinum agent is the standard-of-care in patients with HER2-positive tumor. For the others, a platinum-based doublet (preferably with oxaliplatin) is recommended. Three-drug cytotoxic regimens should be reserved for exceptional cases where patients have good performance status. Triple combinations produce higher toxicity and provide marginal advantage. In the second line setting, the combination of paclitaxel and ramucirumab is preferred over all others. Currently, nothing is approved in the 3rd or later line. Nivolumab has resulted in an improved benefit in an Asian trial. Early trials of TAS-102, STAT3 inhibitors, anti-claudin 18.2 and other immune checkpoint inhibitors (alone or in combination) are ongoing. However, development of reproducible biomarkers for patient enrichment is critical for future progress.

Thymoquinone Augments Cisplatin-Induced Apoptosis on Esophageal Carcinoma Through Mitigating the Activation of JAK2/STAT3 Pathway

BACKGROUND

Thymoquinone (TQ) is the major constituent of Nigella sativa seed and has shown biological activity in various human carcinomas. However, few studies have reported its effect on esophageal carcinoma (EC).

AIMS

To explore the chemosensitive effect and mechanism of TQ in augmentation of cisplatin (DDP)-induced apoptosis of EC, both in vitro and in vivo.

METHODS

The viability and apoptosis of esophageal carcinoma cells were detected by the Cell Counting Kit-8 assay, flow cytometry, and Hoechst 33258 staining. The expression levels of JAK2, p-JAK2, STAT3, p-STAT3, Bax, Bcl-2, Cyclin D1, Survivin, and caspase-3, 7, 9 were evaluated by western blot analysis. The histological changes were examined by TUNEL technique and immunohistochemical analysis.

RESULTS

TQ enhanced the proapoptotic effect of DDP in human esophageal carcinoma cell line Eca-109, while blocking the activation of JAK2/STAT3 signaling pathway. The apoptosis of esophageal carcinoma cells was induced via blocking the activation of JAK2/STAT3 by using a molecular inhibitor (WP1066). Consistent with the in vivo and in vitro results, TQ increased cellular apoptosis and enriched the chemosensitivity of DDP.

CONCLUSIONS

TQ along with DDP may regulate the progression of EC and has potential to be a chemotherapeutic agent in EC.

MicroRNA-29a inhibits proliferation and induces apoptosis in rheumatoid arthritis fibroblast-like synoviocytes by repressing STAT3

Rheumatoid arthritis-fibroblast-like synoviocytes (RA-FLS) with aberrant expression of microRNA (miRNA) have been reported to be involved in the initiation, progression, and perpetuation of rheumatoid arthritis (RA). In this study, we explored the biological function and underlying mechanism of microRNA-29a (miR-29a) in cultured RA-FLS from RA patients. The expression of miR-29a in serum, synovial tissues, and FLS from RA patients and health donors was detected by real-time quantitative RT-PCR (qRT-PCR). The effects of miR-29a on cell proliferation, apoptosis, and inflammatory cytokine levels in RA-FLS were also determined using Counting Assay Kit-8 (CCK-8), flow cytometry, and enzyme-linked immunosorbent assay (ELISA) respectively. Luciferase reporter assay was carried out to identify the target genes of miR-29a. We observed that expression of miR-29a was markedly downregulated in serum, synovial tissues and FLS of RA patients. miR-29a overexpression in RA-FLS significantly inhibited proliferation, promoted apoptosis, and suppressed expression of inflammatory cytokines. Signal transducer and activator of transcription 3 (STAT3) was identified to be a direct target of miR-29a in RA-FLS. miR-29a overexpression suppressed the expression of STAT3, as well as phosphorylated STAT3(p-STAT3) and its downstream targets protein (Cyclin D1 and Bcl-2). In addition, the levels of miR-29a were inversely correlated with that of STAT3 in synovial tissues. Rescue experiments showed that overexpression of STAT3 effectively reversed the effect of miR-29a on proliferation and apoptosis in RA-FLS. These data indicate that miR-29a inhibits proliferation and induces apoptosis in RA-FLS by targeting STAT3, suggesting that promoting miR-29a expression may yield therapeutic benefits in the treatment of RA.

Naphthoquinones: A continuing source for discovery of therapeutic antineoplastic agents

Naturally occurring naphthoquinones, usually in forms of botanical extracts, have been implicated with human life since ancient time, far earlier than their isolation and identification in modern era. The long use history of naphthoquinones has witnessed their functional shift from the original purposes as dyes and ornaments toward medicinal benefits. Hitherto, numerous studies have been carried out to elucidate the pharmacological profile of both natural and artificial naphthoquinones. A number of entities have been identified with promising therapeutic potential. Apart from the traditional effects of wound healing, anti-inflammatory, hemostatic, antifertility, insecticidal and antimicrobial, etc., the anticancer potential of naphthoquinones either in combination with other treatment approaches or on their own is being more and more realized. The molecular mechanisms of naphthoquinones in cells mainly fall into two categories as inducing oxidant stress by ROS (reactive oxygen species) generation and directly interacting with traditional therapeutic targets in a non-oxidant mechanism. Based on this knowledge, optimized agents with naphthoquinones scaffold have been acquired and further tested. Hereby, we summarize the explored biological mechanisms of naphthoquinones in cells and review the application perspective of promising naphthoquinones in cancer therapies.

Napabucasin: An Update on the First-in-Class Cancer Stemness Inhibitor

Napabucasin (BBI608) is an orally administered small molecule that blocks stem cell activity in cancer cells by targeting the signal transducer and activator of transcription 3 pathway. The signal transducer and activator of transcription 3 pathway is over-activated in many types of cancer and has been shown to be an important pathway in cancer stem cell-mediated propagation of cancer. Cancer stem cells are a subpopulation of cancer cells considered to be the primary source of tumor growth, metastasis, and resistance to conventional therapies, and thus, responsible for cancer relapse. This review describes the clinical development program of this first-in-class cancer stemness inhibitor, including preclinical discovery, early clinical trials, current phase III clinical trial evaluation, and future therapeutic combinations. The therapeutic potential of napabucasin was first reported in a preclinical study that demonstrated the potent anti-tumor and anti-metastatic activity of napabucasin in several different cancer types, both in vitro and in vivo. In mouse models, napabucasin was effective both as a monotherapy and in combination with other agents; in particular, synergy was observed with paclitaxel in vivo. Napabucasin clinical trials have demonstrated encouraging anti-tumor activity as monotherapy and in combination with conventional therapeutics, with no significant pharmacokinetic interactions when used in combination therapies. Adverse events attributed to napabucasin have been predominantly mild, although some patients have experienced grade 3 gastrointestinal adverse events. More severe adverse events required reduced or discontinued dosing of napabucasin or medication to reverse or manage symptoms. In conclusion, napabucasin may prove useful in targeting cancer stem cells, with the potential to suppress metastasis and prevent relapse in patients with varying cancer types.

Small molecules to the rescue: Inhibition of cytokine signaling in immune-mediated diseases

Cytokines are small, secreted proteins associated with the maintenance of immune homeostasis but also implicated with the pathogenesis of several autoimmune and inflammatory diseases. Biologic agents blocking cytokines or their receptors have revolutionized the treatment of such pathologies. Nonetheless, some patients fail to respond to these drugs or do not achieve complete remission. The signal transduction originating from membrane-bound cytokine receptors is an intricate network of events that lead to gene expression and ultimately regulate cellular functionality. Our understanding of the intracellular actions that molecules such as interleukins, interferons (IFNs) and tumor necrosis factor (TNF) set into motion has greatly increased in the past few years, making it possible to interfere with cytokines' signaling cascades. The Janus kinase (JAK)/signal transducer and activator of transcription (STAT), the nuclear factor kappa-light-chain-enhancer of activated B cells (NF-kB), the mitogen activated protein kinase (MAPK) and the Phosphatidylinositol-3'-kinases (PI3K) pathways have all been intensively studied and key steps as well as molecules have been identified. These research efforts have led to the development of a new generation of small molecule inhibitors. Drugs capable of blocking JAK enzymatic activity or interfering with the proteasome-mediated degradation of intermediates in the NF-kB pathway have already entered the clinical arena confirming the validity of this approach. In this review, we have recapitulated the biochemical events downstream of cytokine receptors and discussed some of the drugs which have already been successfully utilized in the clinic. Moreover, we have highlighted some of the new molecules that are currently being developed for the treatment of immune-mediated pathologies and malignancies.

Alteration of SHP-1/p-STAT3 Signaling: A Potential Target for Anticancer Therapy

The Src homology 2 (SH2) domain-containing protein tyrosine phosphatase 1 (SHP-1), a non-receptor protein tyrosine phosphatase, has been reported as a negative regulator of phosphorylated signal transducer and activator of transcription 3 (STAT3) and linked to tumor development. In this present review, we will discuss the importance and function of SHP-1/p-STAT3 signaling in nonmalignant conditions as well as malignancies, its cross-talk with other pathways, the current clinical development and the potential role of inhibitors of this pathway in anticancer therapy and clinical relevance of SHP-1/p-STAT3 in cancers. Lastly, we will summarize and highlight work involving novel drugs/compounds targeting SHP-1/p-STAT3 signaling and combined strategies that were/are discovered in our and our colleagues’ laboratories.

Exploiting the Ref-1-APE1 node in cancer signaling and other diseases: from bench to clinic

Reduction-oxidation factor 1-apurinic/apyrimidinic endonuclease (Ref-1/APE1) is a critical node in tumor cells, both as a redox regulator of transcription factor activation and as part of the DNA damage response. As a redox signaling protein, Ref-1/APE1 enhances the transcriptional activity of STAT3, HIF-1α, nuclear factor kappa B, and other transcription factors to promote growth, migration, and survival in tumor cells as well as inflammation and angiogenesis in the tumor microenvironment. Ref-1/APE1 is activated in a variety of cancers, including prostate, colon, pancreatic, ovarian, lung and leukemias, leading to increased aggressiveness. Transcription factors downstream of Ref-1/APE1 are key contributors to many cancers, and Ref-1/APE1 redox signaling inhibition slows growth and progression in a number of tumor types. Ref-1/APE1 inhibition is also highly effective when paired with other drugs, including standard-of-care therapies and therapies targeting pathways affected by Ref-1/APE1 redox signaling. Additionally, Ref-1/APE1 plays a role in a variety of other indications, such as retinopathy, inflammation, and neuropathy. In this review, we discuss the functional consequences of activation of the Ref-1/APE1 node in cancer and other diseases, as well as potential therapies targeting Ref-1/APE1 and related pathways in relevant diseases. APX3330, a novel oral anticancer agent and the first drug to target Ref-1/APE1 for cancer is entering clinical trials and will be explored in various cancers and other diseases bringing bench discoveries to the clinic.

Identification of New Shikonin Derivatives as Antitumor Agents Targeting STAT3 SH2 Domain

Signal transducer and activator of transcription 3 (STAT3) is hyper-activated in diversiform human tumors and has been validated as an attractive therapeutic target. Current research showed that a natural product, shikonin, along with its synthetic analogues, is able to inhibit the activity of STAT3 potently. The potential space of shikonin in developing novel anti-cancer agents encouraged us to carry out the investigation of the probable binding mode with STAT3. From this foundation, we have designed new types of STAT3 SH2 inhibitors. Combined simulations were performed to filter for the lead compound, which was then substituted, synthesized and evaluated by a variety of bioassays. Among the entities, PMM-172 exhibited the best anti-proliferative activity against MDA-MB-231 cells with IC₅₀ value 1.98 ± 0.49 μM. Besides, it was identified to decrease luciferase activity, induce cell apoptosis and reduce mitochondrial transmembrane potential in MDA-MB-231 cells. Also, PMM-172 inhibited constitutive/inducible STAT3 activation without affecting STAT1 and STAT5 in MDA-MB-231 cells, and had no effect in non-tumorigenic MCF-10A cells. Moreover, PMM-172 suppressed STAT3 nuclear localization and STAT3 downstream target genes expression. Overall, these results indicate that the antitumor activity of PMM-172 is at least partially due to inhibition of STAT3 in breast cancer cells.

Genome-wide expression profiling and bioinformatics analysis of deregulated genes in human gastric cancer tissue after gastroscopy

AIM

The aim of this study was to analyze the gene expression profile and biological processes enriched in gastric cancer.

METHODS

We collected five human advanced gastric cancer tissues by gastroscopy and five peritumor normal tissues as controls and examined the gene expression changes by microarray. KEGG Orthology Based Annotation System annotation was used to identify pathways and biological processes regulated by the deregulated genes. Protein-protein interaction network analysis identified protein complex and functional modules. We also selected 14 genes for further verification by real-time quantitative Polymerase Chain Reaction (PCR).

RESULTS

Human gene expression profile analysis showed that 2028 deregulated genes were detected in gastric cancer compared with the control group (at least a 2.0-fold change and P < 0.05), among which there were 689 upregulated and 1339 downregulated genes. Interestingly, we identified some important genes, such as CXCL17, OTX1 and CCDC125, which have not previously been reported in gastric cancer. Real-time quantitative PCR results verified that CXCL8, OTX1, CEBPB, FOSL1, FOXS1, ARFRP1 and IRF9 were upregulated in gastric cancer and CCDC125, PPP1R36, SOX2, JUN and MIA2 were downregulated. Moreover, bioinformatics analysis demonstrated that the biological processes of inflammatory response, angiogenesis, cell migration and pathways of chemokine signaling pathway, TNF signaling pathway were enriched. We also selected the top 30 significant Gene Ontology terms and select pathways for a brief summary.

CONCLUSION

We performed a global analysis of the mRNA landscape in gastric cancer. Our results may stimulate a deeper understanding of the disease, and lead to the development of potential therapies and the identification of novel biomarkers.

Emerging Novel Therapeutic Agents in the Treatment of Patients with Gastroesophageal and Gastric Adenocarcinoma

With further understanding of the biology of gastric and gastroesophageal adenocarcinomas, strides are being made to find effective treatments through novel trial designs. This article focuses on the ongoing trials of drugs targeting specific hallmarks of gastric and gastroesophageal cancers, including oncogene addiction proliferative pathways (fibroblast growth factor receptor 2 amplified tumors), stem cell inhibition, apoptotic induction through claudin inhibitors, and matrix metalloproteinase inhibition. In developing novel therapeutics in treatment of patients with gastroesophageal adenocarcinomas, parallel research efforts to refine target population and biomarkers are crucial, and targeting the tumor genomics and microenvironment may be key in improving overall survival.

Epigenetic silencing of the NR4A3 tumor suppressor, by aberrant JAK/STAT signaling, predicts prognosis in gastric cancer

While aberrant JAK/STAT signaling is crucial to the development of gastric cancer (GC), its effects on epigenetic alterations of its transcriptional targets remains unclear. In this study, by expression microarrays coupled with bioinformatic analyses, we identified a putative STAT3 target gene, NR4A3 that was downregulated in MKN28 GC daughter cells overexpressing a constitutively activated STAT3 mutant (S16), as compared to an empty vector control (C9). Bisulphite pyrosequencing and demethylation treatment showed that NR4A3 was epigenetically silenced by promoter DNA methylation in S16 and other GC cell lines including AGS cells, showing constitutive activation of STAT3. Subsequent experiments revealed that NR4A3 promoter binding by STAT3 might repress its transcription. Long-term depletion of STAT3 derepressed NR4A3 expression, by promoter demethylation, in AGS GC cells. NR4A3 re-expression in GC cell lines sensitized the cells to cisplatin, and inhibited tumor growth in vitro and in vivo, in an animal model. Clinically, GC patients with high NR4A3 methylation, or lower NR4A3 protein expression, had significantly shorter overall survival. Intriguingly, STAT3 activation significantly associated only with NR4A3 methylation in low-stage patient samples. Taken together, aberrant JAK/STAT3 signaling epigenetically silences a potential tumor suppressor, NR4A3, in gastric cancer, plausibly representing a reliable biomarker for gastric cancer prognosis.