Signal Transducer And Activator Of Transcription 3 Inhibitor Research Articles

Abstract PO1-25-08: Evaluating the role of CDK4/6 inhibition on STAT3 activation in a transgenic mouse model of HER2-positive breast cancer

Abstract Background: The human epidermal growth factor receptor 2 (HER2) is a receptor tyrosine kinase overexpressed in approximately 20-25% of breast cancers with varying biological differences according to hormone receptor (HR) positive status. Combination of chemotherapy with dual HER2 blockade and endocrine therapy (adjuvant) or CDK4/6 inhibitor (CDK4/6i) therapy (metastatic) is standard of care for HER2-positive/HR-positive breast cancer. However, de-escalation of chemotherapy remains of significant interest given associated toxicities and, as a result, alternative therapeutic strategies are needed. One such strategy is targeting the signal transducer and activator of transcription 3 (STAT3) which is constitutively activated in the HER-2 positive setting. Moreover, there is preclinical evidence to suggest that phosphorylated STAT3 (pSTAT3) induces overexpression of cyclin D1 (CCND1), which along with CDK4 may mediate resistance to targeted therapy for HER2-positive breast cancer. However, it is unclear if pSTAT3 plays a significant role in tumorigenesis or the development of resistance to therapy in HER2-positive disease. We aim to evaluate the effect of CDK4/6i therapy with palbociclib on tumor growth in an inducible transgenic HER2-positive mouse model and the impact on pSTAT3 and cyclin D1 levels. Methods: Using an inducible transgenic mouse mammary tumor virus (MMTV) model of HER2-positive breast cancer, we evaluated STAT3 phosphorylation in tumors driven by HER2 expression in addition to the impact of CDK4/6 inhibition with palbociclib on tumorigenesis and pSTAT3 activation. To model tumor recurrence, doxycycline was withdrawn from tumor bearing mice and tumor regression was observed. Subsequently, the mice developed recurrent mammary tumors. Given recurrent tumors in this model are driven by a HER2-independent mechanism, we examined expression of cell cycle proteins together with STAT3 phosphorylation to determine association with recurrence. Result: In addition to expressing HER2, the primary tumors expressed estrogen receptor (ERα), Rb, cyclin D1, and CDK4/6 proteins. STAT3 phosphorylation was also observed. Treatment with palbociclib decreased Rb phosphorylation and decreased tumor growth compared to vehicle treated mice (%TGI 79.37% after 21 days). Furthermore, pSTAT3 levels were not altered with palbociclib therapy. When recurrent tumors were analyzed, they lacked HER2 expression but expressed cyclin D1 and CDK4/6 supporting that tumor growth is driven by cyclin D1/CDK4 pathway. Recurrent tumors also demonstrated pSTAT3 despite lack of HER2 expression suggesting that STAT3 phosphorylation in the recurrent tumors is mediated by an alternative mechanism, potentially the CDK4/6 pathway. Conclusion: We demonstrate STAT3 activation in a mouse model of HER2 driven breast cancer and show persistent activation in recurrent tumors lacking HER2 expression rendering them resistant to HER2-targeted therapy. We also demonstrate the anti-tumor effect of palbociclib in primary tumors with HER2-dependent proliferation. Taken together, our findings suggest that pSTAT3 is a viable therapeutic target and provides the rationale for combination therapy with CDK4/6 inhibition using palbociclib and STAT3 inhibition with a novel STAT3 inhibitor in HER2-positive breast cancer. This therapeutic approach may represent a potential chemotherapy de-escalation strategy. Citation Format: Taiwo Adesoye, Linjie Luo, Tuyen Bui, Serena Kim, Hannah Wingate, Debu Tripathy, Kelly Hunt, Khandan Keyomarsi. Evaluating the role of CDK4/6 inhibition on STAT3 activation in a transgenic mouse model of HER2-positive breast cancer [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO1-25-08.

Identification of Novel STAT3 Dimerization Inhibitor Through Structure-Based Virtual Screening for Cancer Management

Background: Signal transducer and activator of transcription 3 (STAT3) is a transcription factor that controls cell proliferation, differentiation, angiogenesis, and immunological responses. In many human malignancies, abnormal STAT3 activation promotes tumor growth via oncogenic gene expression, resulting in tumor malignancy. Many drugs with clinically authorized analogues that are used as STAT3 inhibitors for cancer therapy have several drawbacks in terms of stability and toxicity.Methods: This study used PyRx 0.8 tool to screen the Traditional Chinese Medicine (TCM) database of about 32,364 commercially available natural compounds in order to identify new STAT3 inhibitors. Physicochemical and ADME properties of selected compounds were estimated using Datawarrior and SwissADME.Result: The top 20 compounds were initially chosen based on their strong binding affinities with STAT3. Lipinski and Vaber tools were used to filter the top 20 compounds, yielding the top 6 compounds. The compounds ZINC85542844, ZINC4098720, ZINC85543599, ZINC85593523, ZINC85593528, and ZINC85593537 were passed through these filters. These compounds were found to interact with active site STAT3 residues and have several amino acid interactions in common with the control compound (STX0119).Conclusion: This study suggests that the compounds ZINC85542844, ZINC4098720, ZINC85543599, ZINC85593523, ZINC85593528, and ZINC85593537 could be used as a lead for the development of novel STAT3 inhibitors. However, further experimental validation is required to optimized them as STAT3 inhibitors.Keywords: STAT3; Transcription factor; Natural compounds; Cancer; Virtual screening

The endonuclease FEN1 mediates activation of STAT3 and facilitates proliferation and metastasis in breast cancer.

The metastasis accounts for most deaths from breast cancer (BRCA). Understanding the molecular mechanisms of BRCA metastasis is urgently demanded. Flap Endonuclease 1 (FEN1), a pivotal factor in DNA metabolic pathways, contributes to tumor growth and drug resistance, however, little is known about the role of FEN1 in BRCA metastasis. In this study, FEN1 expression and its clinical correlation in BRCA were investigated using bioinformatics, showing being upregulated in BRCA samples and significant relationships with tumor stage, node metastasis, and prognosis. Immunohistochemistry (IHC) staining of local BRCA cohort indicated that the ratio of high FEN1 expression in metastatic BRCA tissues rose over that in non-metastatic tissues. The assays of loss-of-function and gain-of-function showed that FEN1 enhanced BRCA cell proliferation, migration, invasion, xenograft growth as well as lung metastasis. It was further found that FEN1 promoted the aggressive behaviors of BRCA cells via Signal Transducer and Activator of Transcription 3 (STAT3) activation. Specifically, the STAT3 inhibitor Stattic thwarted the FEN1-induced enhancement of migration and invasion, while the activator IL-6 rescued the decreased migration and invasion caused by FEN1 knockdown. Additionally, overexpression of FEN1 rescued the inhibitory effect of nuclear factor-κB (NF-κB) inhibitor BAY117082 on phosphorylated STAT3. Simultaneously, the knockdown of FEN1 attenuated the phosphorylation of STAT3 promoted by the NF-κB activator tumor necrosis factor α (TNF-α). These results indicate a novel mechanism that NF-κB-driven FEN1 contributes to promoting BRCA growth and metastasis by STAT3 activation.

Novel STAT3 oligonucleotide compounds suppress tumor growth and overcome the acquired resistance to sorafenib in hepatocellular carcinoma.

Signal transducer and activator of transcription 3 (STAT3) plays an important role in the occurrence and progression of tumors, leading to resistance and poor prognosis. Activation of STAT3 signaling is frequently detected in hepatocellular carcinoma (HCC), but potent and less toxic STAT3 inhibitors have not been discovered. Here, based on antisense technology, we designed a series of stabilized modified antisense oligonucleotides targeting STAT3 mRNA (STAT3 ASOs). Treatment with STAT3 ASOs decreased the STAT3 mRNA and protein levels in HCC cells. STAT3 ASOs significantly inhibited the proliferation, survival, migration, and invasion of cancer cells by specifically perturbing STAT3 signaling. Treatment with STAT3 ASOs decreased the tumor burden in an HCC xenograft model. Moreover, aberrant STAT3 signaling activation is one of multiple signaling pathways involved in sorafenib resistance in HCC. STAT3 ASOs effectively sensitized resistant HCC cell lines to sorafenib in vitro and improved the inhibitory potency of sorafenib in a resistant HCC xenograft model. The developed STAT3 ASOs enrich the tools capable of targeting STAT3 and modulating STAT3 activity, serve as a promising strategy for treating HCC and other STAT3-addicted tumors, and alleviate the acquired resistance to sorafenib in HCC patients. A series of novel STAT3 antisense oligonucleotide were designed and showed potent anti-cancer efficacy in hepatocellular carcinoma in vitro and in vivo by targeting STAT3 signaling. Moreover, the selected STAT3 ASOs enhance sorafenib sensitivity in resistant cell model and xenograft model.

STAT3 promotes cytoplasmic-nuclear translocation of RNA-binding protein HuR to inhibit IL-1β-induced IL-8 production

Signal transducer and activator of transcription 3 (STAT3) functions to regulate inflammation and immune response, but its mechanism is not fully understood. We report here that STAT3 inhibitors Stattic and Niclosamide up-regulated IL-1β-induced IL-8 production in C33A, CaSki, and Siha cervical cancer cells. As expected, IL-1β-induced IL-8 production was also up-regulated through the molecular inhibition of STAT3 by use of CRISPR/Cas9 technology. Unexpectedly, IL-1β induced IL-8 production via activating ERK and P38 signal pathways, but neither STAT3 inhibitors nor STAT3 knockout affected IL-1β-induced signal transduction, suggesting that STAT3 decreases IL-8 production not via inhibition of signal transduction. To our surprise, STAT3 inhibition increased the stabilization, and decreased the degradation of IL-8 mRNA, suggesting a post-transcriptional regulation of IL-1β-induced IL-8. Moreover, Dihydrotanshinone I, an inhibitor of RNA-binding protein HuR, down-regulated IL-1β-induced IL-8 dose-dependently. HuR inhibition by CRISPR/Cas9 also decreased IL-8 production induced by IL-1β. Mechanistically, co-immunoprecipitation results showed that STAT3 did not react with HuR directly, but STAT3 inhibition increased the protein levels of HuR in cytoplasm. And IL-6 activation of STAT3 induced HuR cytoplasmic-nuclear transport. Taken together, these results suggest that STAT3 contributes to HuR nuclear localization and inhibits Il-1β-induced IL-8 production through this non-transcriptional mechanism.

Abstract 3157: The crosstalk between STAT3 and p53/ERK signaling regulates brain metastasis

Abstract Brain metastasis (BM) affects approximately 10% of cancer patients with metastatic disease, representing a major cause of morbidity and mortality. BM is a complex multi-step process involving various immune checkpoint proteins. Mitogen-activated protein kinase (MAPK), particularly extracellular signal-regulated kinases 1/2 (ERK1/2), and signal transducer and activator of transcription 3 (STAT3) are implicated in tumorigenesis and are critical upstream regulators of Programmed Death Ligand 1 (PD-L1) expression, a common immunotherapy target. Tumor suppressor p53 is shown to regulate STAT3 and ERK1/2 signaling, which are dysregulated in various malignancies. We hypothesize that p53 along with STAT3 and ERK1/2 play a critical role in the initiation and maintenance of BM. Twenty-six BM tumors with various primary sites of origin were used following IRB guidelines. pSTAT3Tyr705, pERK1/2Thr202/Tyr204, mutant p53 (p53mt), and PD-L1 expression was determined by immunohistochemistry. Gene expression analysis of BM was performed on a cDNA microarray. Human brain metastatic breast cancer cells (MDA-MB-231) were treated with STAT3 inhibitor (NSC74859) or MAPK inhibitor (U0126) in regular or astrocytic media to determine cell proliferation and migration by MTT assay and scratch-wound, respectively. ERK1/2 signaling pathway status was determined by Western blotting. Results demonstrated: 1) pSTAT3Tyr705 and pERK1/2Thr202/Tyr204 were expressed profusely at tumor margins, while p53mt was uniformly expressed throughout. 81% of BM expressed p53mt while 86% and 63% expressed pERK1/2Thr202/Tyr204 and pSTAT3Tyr705, respectively. Venn analysis displayed significant overlap between expression, with 62% overlap between p53mt and pERK1/2Thr202/Tyr204 and a 50% overlap between both pSTAT3Tyr705 and pERK1/2Thr202/Tyr204 with p53mt. Expression of PD-L1 was seen in a majority of BM tumors. 2) Gene expression analysis demonstrated alterations in 32 STAT3- and MAPK-associated genes; these included upregulation of stathmin-1 and stathmin-like 3, which control microtubule dynamics in STAT3-related cell migration, and changes in cytokine-related genes, suggesting altered immune responses. 3) Cell proliferation showed augmented growth in astrocytic media (p≤0.05) and was significantly decreased following treatment with NSC74850 or U0126 (p≤0.01). While migration showed a trend towards significance in reduction following NSC74859 (p=0.08), migration stagnated following U0126 treatment in astrocytic media (p≤0.01). 4) pERK1/2Thr202/Tyr204 expression was reduced following U0126 or NSC74859 treatment. These findings suggest activation of STAT3 and ERK1/2 promote BM and suppression of these pathways may lead to a reduction in cell viability and motility. Therefore, this provides compelling evidence for the use of STAT3 and ERK1/2 along with p53 as potential targets for immunotherapy in brain metastatic disease. Citation Format: Sabrina L. Zeller, Eris Spirollari, John V. Wainwright, Simon J. Hanft, Chirag D. Gandhi, Meena Jhanwar-Uniyal. The crosstalk between STAT3 and p53/ERK signaling regulates brain metastasis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 3157.

Abstract 3049: Similarities between ovarian cancer and endometriosis: The role of STAT3

Abstract Endometriosis is a painful gynecological disease that affects over 190 million women worldwide. This disease is classified by the presence of endometrial-like cells growing in and around the female reproductive system. Instead of lining the uterus, these ectopic cells shed off and cluster together forming lesions that attach to different surfaces of the female reproductive system. In particular, endometriosis cells interact with and form lesions within the mesothelial cells that line the peritoneum. There is currently no cure, and many of the therapies aiming to help with pain management come with unfavorable tradeoffs. Our research on ovarian cancer led us to investigate potential overlapping characteristics with endometriosis. Growing ovarian cancer cells in 3D causes spheroids to form which mimic the physical features of tumors and are also able to better represent cell-cell and cell-environment interactions. Analysis of the endometriosis cell lines 12Z and hEM3 demonstrated that they could also form spheroids. As both ovarian cancer cells and endometriosis cells interact with mesothelial cells, we wanted to determine if endometriosis spheroids were able to clear the mesothelial layer comparable to ovarian cancer spheroids. Evaluation of 12Z and hEM3 cell lines demonstrated that endometriosis spheroids were able to undergo mesothelial clearance. While the exact cause of endometriosis is not known, different proteins have been identified as important factors in the progression of endometriosis. The Signal Transducer and Activator of Transcription 3 (STAT3) is a transcription factor involved in cell differentiation, proliferation, apoptosis resistance, angiogenesis, and metastasis. In endometriosis cell lines, STAT3 is constitutively active, which makes it a promising potential therapeutic target. To verify that STAT3 is important in endometriosis, siRNA was used to reduce the expression of STAT3 in two endometriosis cell lines, 12Z and hEM3. Both cell lines showed a decrease in cell viability. In addition, reducing the expression of STAT3 in the endometriosis cells appeared to decrease mesothelial clearance ability. Our lab previously identified statins as potential STAT3 inhibitors by using the Broad Institute’s CLUE tool. After statin treatment, 12Z and hEM3 spheroids showed a decrease in cell viability and clearance ability. Taken together, these data suggest that STAT3 plays a key role in endometriosis and that the repurposing of statins may provide a benefit to patients with endometriosis. Citation Format: Allison A. Kloeckner, Sarah R. Walker. Similarities between ovarian cancer and endometriosis: The role of STAT3 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 3049.

Enhanced STAT3/PIK3R1/mTOR signaling triggers tubular cell inflammation and apoptosis in septic-induced acute kidney injury: implications for therapeutic intervention.

Septic acute kidney injury (AKI) is a severe form of renal dysfunction associated with high morbidity and mortality rates. However, the pathophysiological mechanisms underlying septic AKI remain incompletely understood. Herein, we investigated the signaling pathways involved in septic AKI using the mouse models of lipopolysaccharide (LPS) treatment and cecal ligation and puncture (CLP). In these models, renal inflammation and tubular cell apoptosis were accompanied by the aberrant activation of the mechanistic target of rapamycin (mTOR) and the signal transducer and activator of transcription 3 (STAT3) signaling pathways. Pharmacological inhibition of either mTOR or STAT3 significantly improved renal function and reduced apoptosis and inflammation. Interestingly, inhibition of STAT3 with pharmacological inhibitors or small interfering RNA blocked LPS-induced mTOR activation in renal tubular cells, indicating a role of STAT3 in mTOR activation. Moreover, knockdown of STAT3 reduced the expression of the phosphoinositide-3-kinase regulatory subunit 1 (PIK3R1/p85α), a key subunit of the phosphatidylinositol 3-kinase for AKT and mTOR activation. Chromatin immunoprecipitation assay also proved the binding of STAT3 to PIK3R1 gene promoter in LPS-treated kidney tubular cells. In addition, knockdown of PIK3R1 suppressed mTOR activation during LPS treatment. These findings highlight the dysregulation of mTOR and STAT3 pathways as critical mechanisms underlying the inflammatory and apoptotic phenotypes observed in renal tubular cells during septic AKI, suggesting the STAT3/ PIK3R1/mTOR pathway as a therapeutic target of septic AKI.

Discovery of the Highly Selective and Potent STAT3 Inhibitor for Pancreatic Cancer Treatment.

Signal transducer and activator of transcription 3 (STAT3) is an attractive cancer therapeutic target. Unfortunately, targeting STAT3 with small molecules has proven to be very challenging, and for full activation of STAT3, the cooperative phosphorylation of both tyrosine 705 (Tyr705) and serine 727 (Ser727) is needed. Further, a selective inhibitor of STAT3 dual phosphorylation has not been developed. Here, we identified a low nanomolar potency and highly selective small-molecule STAT3 inhibitor that simultaneously inhibits both STAT3 Tyr705 and Ser727 phosphorylation. YY002 potently inhibited STAT3-dependent tumor cell growth in vitro and achieved potent suppression of tumor growth and metastasis in vivo. More importantly, YY002 exhibited favorable pharmacokinetics, an acceptable safety profile, and superior antitumor efficacy compared to BBI608 (STAT3 inhibitor that has advanced into phase III trials). For the mechanism, YY002 is selectively bound to the STAT3 Src Homology 2 (SH2) domain over other STAT members, which strongly suppressed STAT3 nuclear and mitochondrial functions in STAT3-dependent cells. Collectively, this study suggests the potential of small-molecule STAT3 inhibitors as possible anticancer therapeutic agents.

Molecular crosstalk between MUC1 and STAT3 influences the anti-proliferative effect of Napabucasin in epithelial cancers

MUC1 is a transmembrane glycoprotein that is overexpressed and aberrantly glycosylated in epithelial cancers. The cytoplasmic tail of MUC1 (MUC1 CT) aids in tumorigenesis by upregulating the expression of multiple oncogenes. Signal transducer and activator of transcription 3 (STAT3) plays a crucial role in several cellular processes and is aberrantly activated in many cancers. In this study, we focus on recent evidence suggesting that STAT3 and MUC1 regulate each other’s expression in cancer cells in an auto-inductive loop and found that their interaction plays a prominent role in mediating epithelial-to-mesenchymal transition (EMT) and drug resistance. The STAT3 inhibitor Napabucasin was in clinical trials but was discontinued due to futility. We found that higher expression of MUC1 increased the sensitivity of cancer cells to Napabucasin. Therefore, high-MUC1 tumors may have a better outcome to Napabucasin therapy. We report how MUC1 regulates STAT3 activity and provide a new perspective on repurposing the STAT3-inhibitor Napabucasin to improve clinical outcome of epithelial cancer treatment.

Abstract WP301: STAT3 Inhibition Reduces Infarct and Neuroinflammation in Experimental Stroke

Signal Transducer and Activator of Transcription 3 (STAT3) activation is increased in the brain following cerebral ischemia. STAT3, a transcription factor, is a positive regulator of cell survival and is implicated in cytoprotection following ischemia in multiple cell types, including neurons and endothelial cells. We hypothesized that pharmacological inhibition of STAT3 activation in mice during the reperfusion phase after middle cerebral artery occlusion (MCAO) will lead to increased infarct size. We subjected mice to 1-hour MCAO, following which they received STAT3 inhibitor Stattic (20 mg/kg), or vehicle, for 24 hours delivered subcutaneously via osmotic pump. Twenty-four hours later, infarct was measured by TTC and inflammatory cells were measured by flow cytometry. For experiments involving splenectomy, spleens were surgically removed 14 days prior to MCAO surgery. Surprisingly, we found that STAT3 inhibition reduces infarct after MCAO, with infarct in the hemisphere reducing from 49.90 ± 2.44 % in vehicle to 32.86 ± 1.55 % in Stattic-treated mice. Since STAT3 is involved in inflammatory processes, as well as cytoprotection, this led us to hypothesize that the reduction in infarct we observe may be due to decreased inflammation. We carried out FACS analysis and observed that Stattic inhibits MCAO-induced infiltration of B-, T- and dendritic cells into the brain. Neutrophil and monocyte infiltration into the brain were unaffected by Stattic. Since MCAO is known to induce splenic atrophy, with spleen size being inversely proportional to infarct volume, we measured spleen weights. Interestingly Stattic-treated mice had larger spleens (66.31 ± 5.40 g) compared to vehicle-treated mice (46.43 ± 4.60 g), indicating a dampened peripheral immune response upon inhibition of STAT3. Furthermore, Stattic was no longer effective in reducing infarct size in splenectomized mice. We conclude that pharmacological inhibition of STAT3 reduces infarct following MCAO, with the mechanism of protection involving differential regulation of the peripheral immune response.

Abstract B037: Utilizing GSK3β and integrin inhibitors to target STAT3 activity in triple negative breast cancer

Abstract Triple negative breast cancer (TNBC) is the most aggressive subtype of breast cancer known for its high rate of recurrence and metastatic ability. Patients face a poor prognosis and the five-year survival rate for those diagnosed with metastatic TNBC is very low. The transcription factor Signal Transducer and Activator of Transcription 3 (STAT3) is constitutively active in TNBC and functions to promote proliferation and metastasis. Therefore, it is a potential therapeutic target for TNBC. We used CLUE, an online bioinformatics tool from the Broad Institute, to identify potential STAT3 inhibitors. To do this, a STAT3 gene signature generated from TNBC cells was used to query the gene signatures from drug treatments in the CLUE dataset for compounds that caused a similar signature. The hypothesis is that a drug with a similar signature to the STAT3 inhibition signature would be a potential STAT3 inhibitor. Drugs were chosen based on high similarity rating and known function. One of the top drugs we chose to pursue was TWS-119, a GSK3β inhibitor. GSK3β is a serine/threonine kinase that regulates proliferation and cell survival. TWS-119 was found to decrease the viability of MDA-MB-231, MDA-MB-468, and Hs587T TNBC cell lines. To assess the ability of TWS-119 to inhibit STAT3 activity, we used a STAT3 responsive reporter and found that TWS-119 inhibited STAT3 activity in MDA-MB-468 cells. To determine the mechanism of inhibition of STAT3 activity, we analyzed the effects of TWS-119 on STAT3 tyrosine phosphorylation. Preliminary results suggest that TWS-119 inhibits STAT3 activity via inhibition of tyrosine phosphorylation. Having determined that TWS-119 inhibited STAT3 activity, we wanted to determine if TWS-119 had any effect on TNBC migration. We found that TWS-119 reduced the migratory ability of MDA-MB-231 cells. An additional drug identified from CLUE was Cilengitide, an inhibitor of integrin ⍺vβ3 which plays an important role in proliferation and migration. While Cilengitide only slightly decreased the viability of the three different TNBC cell lines (MDA-MB-231, MDA-MB-468, Hs587T), we found that combinations of Cilengitide and TWS-119 had synergistic effects on cell viability in the TNBC cells. Preliminary western blot analysis demonstrated that the combination of both drugs reduced the level of pY-STAT3. This suggests that this combination targeting STAT3 may be a viable treatment strategy for TNBC. However, the mechanism through which these drugs interact is unknown, and the cell signaling relationship between their known targets (GSK3β and integrin ⍺vβ3) and STAT3 is unclear. We are currently working to define the mechanism of action of these combination effects in TNBC cells. Using TWS-119 and Cilengitide, we can determine the connection between integrins, GSK3β, and STAT3 to better understand proliferation and metastasis and to identify new therapeutic options for TNBC patients. Citation Format: Emily A Pratt, Sarah R Walker. Utilizing GSK3β and integrin inhibitors to target STAT3 activity in triple negative breast cancer [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Advances in Breast Cancer Research; 2023 Oct 19-22; San Diego, California. Philadelphia (PA): AACR; Cancer Res 2024;84(3 Suppl_1):Abstract nr B037.

Exploring Novel Frontiers: Leveraging STAT3 Signaling for Advanced Cancer Therapeutics

Signal Transducer and Activator of Transcription 3 (STAT3) plays a significant role in diverse physiologic processes, including cell proliferation, differentiation, angiogenesis, and survival. STAT3 activation via phosphorylation of tyrosine and serine residues is a complex and tightly regulated process initiated by upstream signaling pathways with ligand binding to receptor and non-receptor-linked kinases. Through downstream deregulation of target genes, aberrations in STAT3 activation are implicated in tumorigenesis, metastasis, and recurrence in multiple cancers. While there have been extensive efforts to develop direct and indirect STAT3 inhibitors using novel drugs as a therapeutic strategy, direct clinical application remains in evolution. In this review, we outline the mechanisms of STAT3 activation, the resulting downstream effects in physiologic and malignant settings, and therapeutic strategies for targeting STAT3. We also summarize the pre-clinical and clinical evidence of novel drug therapies targeting STAT3 and discuss the challenges of establishing their therapeutic efficacy in the current clinical landscape.

Inhibition of STAT3 alleviates LPS-induced apoptosis and inflammation in renal tubular epithelial cells by transcriptionally down-regulating TASL

BackgroundSystemic lupus erythematosus (SLE) is a common autoimmune disease that impacts various organs. Lupus nephritis (LN) significantly contributes to death in children with SLE. Toll-like receptor (TLR) adaptor interacting with SLC15A4 on the lysosome (TASL) acts as an innate immune adaptor for TLR and is implicated in the pathogenesis of SLE. A transcription factor known as signal transducer and activator of transcription 3 (STAT3), which is known to be linked to autoimmune diseases, is also involved in the development of SLE.MethodsBioinformatics and real-time quantitative PCR (qRT-PCR) was used to detect the expression of STAT3 and TASL in peripheral blood of SLE patients and their correlation. Bioinformatics analysis, qRT-PCR, luciferase assay and chromatin immunoprecipitation (ChIP) were used to verify the regulation of transcription factor STAT3 on TASL. The expression levels of STAT3, TASL and apoptosis-related genes in LPS-induced HK2 cells were detected by qRT-PCR and Western blot. TUNEL staining were used to detect the apoptosis of HK2 cells after LPS stimulation. ELISA and qRT-PCR were used to detect the levels of inflammatory cytokines in the cell culture supernatant. TASL knockdown in HK2 cells was used to detect the changes in apoptosis-related genes and inflammatory factors. The expression level of TASL in LPS-stimulated HK2 cells and its effect on cell apoptosis and inflammatory factors were observed by knocking down and overexpressing STAT3, respectively. It was also verified in a rescue experiment.ResultsThe expressions of STAT3 and TASL were higher in SLE than in healthy children, and the expression of STAT3 was positively correlated with TASL. Transcription factor STAT3 can directly and positively regulate the expression of TASL through the promoter region binding site. The expression of STAT3, TASL and inflammatory cytokines was elevated, and the change of apoptosis was up-regulated in LPS-stimulated HK2 cells. Inhibition of STAT3 alleviates LPS-stimulated apoptosis and inflammatory response in HK2 cells through transcriptional regulation of TASL.ConclusionsThese findings provide new insights into the transcriptional regulation of TASL and provide new evidence of a direct regulatory relationship between signaling nodes in the lupus signaling network.Graphical

The Ethanolic Extract of Dictyopteris Divaricata Induces Apoptosis in Non-Small Cell Lung Cancer Cells by Inhibiting STAT3 Activity

Dictyopteris divaricata (DD) has been reported to exert diverse pharmacological activities, including anti-inflammatory, antioxidant, and anticancer effects. In this study, we aimed to investigate the anticancer potential of the ethanolic extract of DD (EDD) in non-small cell lung cancer (NSCLC) cells and to explore the underlying mechanism. EDD significantly suppressed cell proliferation in H1299, PC9, and H1975 NSCLC cells. EDD treatment increased the proportion of Annexin V-positive cells and cells in sub-G1 phase, indicating the induction of apoptosis. This observation was further supported by the presence of fragmented nuclei and increased expression of cleaved PARP and cleaved caspase-3 in NSCLC cells following EDD treatment. Mechanistically, EDD decreased the phosphorylation levels of signal transducer and activator of transcription 3 (STAT3) and Src. Transfection of constitutively activated STAT3 into H1975 cells partially attenuated EDD-induced apoptosis, highlighting the contribution of STAT3 inhibition to the anticancer activity of EDD. In addition, we identified fucosterol as a major constituent of EDD that exhibited similar anticancer potential in NSCLC cells. Taken together, our results demonstrate that EDD induces apoptosis in NSCLC cells by inhibiting STAT3 activity. We propose EDD as a potential candidate for the development of therapies targeting NSCLC.

Differential curcumin absorption and curcumin-induced STAT3 inhibition during 3T3-L1 cell adipogenesis in 2D and 3D cultures

It is increasingly considered that 3D cell culture systems are superior to 2D in evaluating health promoting effects of candidate molecules because they better mimic tissue-like structures, thus testing in such systems will increase their in vivo applicability. The present study sought to examine the potential usefulness of spheroid models for assessing the antiadipogenic effect of polyphenols. The major food polyphenols were compared for their antiadipogenic effects in 3T3-L1 cells grown in conventional 2D conditions and as 3D spheroids. Further, the study evaluated the effect of the cell culture environment on the inhibition of the adipogenesis-related signaling pathway mediated by curcumin (CUR), the most effective antiadipogenic polyphenol identified in 2D and 3D, and its cellular absorption rate. CUR treatment inhibited the activity of signal transducer and activator of transcription 3 (STAT3) in cells cultured in both conditions; however, it was more effective in 2D. Notably, 3T3-L1 preadipocytes in a 3D cell culture system maintained high STAT3 activity and CCAAT/enhancer-binding protein alpha (C/EBPα) expression compared with a 2D system. Additionally, the cellular absorption rate was lower in 3D cultures. Thus, different cellular absorption rates, innate STAT3 activity, and C/EBPα expression levels may contribute to the difference in CUR efficacy. This study demonstrated that the STAT3 inhibition at least partly contributes to antiadipogenic effect of CUR. Moreover, it showed that the presentation of cells in 3D significantly alters activation of intracellular signaling pathways and absorption rate of CUR. Therefore, 3D spheroid models are valuable tools to evaluate the anti-adipogenicity of candidate molecules.

Unveiling the STAT3-ACC1 axis: a key driver of lipid metabolism and tumor progression in non-small cell lung cancer.

Background and Objective: Lung cancer is a prevalent global malignancy, and investigating the metabolic reprogramming of tumor cells has significant therapeutic implications. This study aims to explore the molecular mechanism driving the progression of non-small cell lung cancer (NSCLC), with a specific emphasis on the STAT3-ACC1-FAS axis involved in fatty acid synthesis. Methods: The levels of Signal transducer and activator of transcription 3 (STAT3) and acetyl-CoA carboxylase 1 (ACC1) were determined in mouse NSCLC specimens and cell lines using Western blot and qPCR methods. Various assays such as CCK-8, colony formation, EDU, wound-healing, and transwell migration were employed to assess cancer cell proliferation, migration, and invasion. Additionally, a nude mouse xenograft model was utilized for in vivo tumor growth analysis. The interaction between STAT3 and ACC1 was examined through chromatin immunoprecipitation and dual-luciferase assays. Results: The study observed upregulation of STAT3 and ACC1 in NSCLC tissues. Notably, the suppression of STAT3 and ACC1 inhibited the in vitro progression and lipid synthesis of NSCLC cells. Furthermore, STAT3 enhanced lipid synthesis by upregulating ACC1 expression. Mechanistic assays revealed that this process occurred through direct activation of ACC1 transcription by STAT3. STAT3 played a vital role in regulating lipid metabolism and supporting NSCLC progression. Conclusion: The findings of this study underscore the significance of the STAT3-ACC1-FAS axis in NSCLC. The activation of ACC1 through STAT3-mediated transcription serves as a crucial mechanism for stimulating the progression of NSCLC tumors and promoting lipid synthesis. Consequently, targeting the STAT3-ACC1 axis may present a promising avenue for the diagnosis and treatment of NSCLC patients.

Exercise-induced vitamin D receptor and androgen receptor mediate inhibition of IL-6 and STAT3 in muscle

BackgroundSkeletal muscle produces interleukin-6 (IL-6) during exercise as a myokine. Although IL-6 is required for skeletal muscle regeneration, its action increases the expression of myostatin and other proteins involved in muscle atrophy, resulting in skeletal muscle atrophy. In this study, we clarified the effects exercise-induced vitamin D receptor (VDR) and androgen receptor (AR) expression on IL-6 and signal transducer and activator of transcription 3 (STAT3) in vivo and in vitro. MethodC2C12 myotubes were subjected to electric pulse stimulation (EPS) in vitro. To evaluate VDR and AR function, a VDR/AR agonist and antagonist were administered before EPS to C2C12 myotubes. C57BL6 mice underwent 4 weeks of exercise. The expression levels of proteolytic-associated genes, including CCAAT/enhancer-binding protein delta (C/EBPδ) and myostatin, were measured by quantitative real-time polymerase chain reaction, and phosphorylated and total STAT3 levels were measured by Western blot analysis. ResultThe expression of VDR and AR mRNA was induced following EPS in C2C12 myotubes. IL-6 mRNA expression was also increased with a peak at 6 h after EPS and p-STAT3/STAT3 ratio reciprocally decreased. Although VDR/AR agonist administration decreased IL-6 mRNA expression and p-STAT3/STAT3 ratio, these two endpoints increased after treatment with VDR/AR antagonist, respectively. Exercise in mice also increased the expression of VDR/AR and IL-6 mRNA and decreased p-STAT3/STAT3 ratio. ConclusionExercise-induced VDR and AR expression results in the suppression of IL-6 mRNA and STAT3 phosphorylation in skeletal muscle.

Natural bioactive compounds and STAT3 against hepatocellular carcinoma: An update

Hepatocellular carcinoma (HCC) is a challenging and very fatal liver cancer. The signal transducer and activator of transcription 3 (STAT3) pathway is a crucial regulator of tumor development and are ubiquitously active in HCC. Therefore, targeting STAT3 has emerged as a promising approach for preventing and treating HCC. Various natural bioactive compounds (NBCs) have been proven to target STAT3 and have the potential to prevent and treat HCC as STAT3 inhibitors. Numerous kinds of STAT3 inhibitors have been identified, including small molecule inhibitors, peptide inhibitors, and oligonucleotide inhibitors. Due to the undesirable side effects of the conventional therapeutic drugs against HCC, the focus is shifted to NBCs derived from plants and other natural sources. NBCs can be broadly classified into the categories of terpenes, alkaloids, carotenoids, and phenols. Most of the compounds belong to the family of terpenes, which prevent tumorigenesis by inhibiting STAT3 nuclear translocation. Further, through STAT3 inhibition, terpenes downregulate matrix metalloprotease 2 (MMP2), matrix metalloprotease 9 (MMP9) and vascular endothelial growth factor (VEGF), modulating metastasis. Terpenes also suppress the anti-apoptotic proteins and cell cycle markers. This review provides comprehensive information related to STAT3 abrogation by NBCs in HCC with in vitro and in vivo evidences.

Repurposing TAK875 as a novel STAT3 inhibitor for treating inflammatory bowel disease

Inflammatory bowel disease (IBD) is a chronic immune-mediated disease associated with a high recurrence rate and an elevated risk of colon cancer. In this study, we screened a bioactive compound library using a luciferase reporter assay and identified the compound TAK875 as a novel inhibitor of signal transducer and activator of transcription 3 (STAT3). Surface plasmon resonance analysis, differential scanning fluorimetry, and isothermal titration calorimetry demonstrated that TAK875 directly bound to recombinant STAT3. TAK875 suppressed the lipopolysaccharide (LPS)-induced release of nitric oxide, inducible nitric oxide synthase, and inflammatory factors in RAW264.7 cells, likely by inhibiting STAT3 phosphorylation. In addition, TAK875 inhibited the differentiation of CD4+ T cells into T-helper 17 cells, which may partially account for its anti-inflammatory effect. TAK875 also alleviated the LPS-induced accumulation of intracellular reactive oxygen species, thus displaying its antioxidant effects. Finally, we demonstrated its satisfactory anti-inflammatory effect in a dextran sulfate sodium-induced mouse model of ulcerative colitis. In conclusion, this study presented TAK875 as a novel STAT3 inhibitor and demonstrated its anti-inflammatory and antioxidant effects both in vitro and in vivo.