Small Molecule Signal Transducer And Activator Of Transcription 3 Inhibitor Research Articles

TTI-101 targets STAT3/c-Myc signaling pathway to suppress cervical cancer progression: an integrated experimental and computational analysis

BackgroundCervical cancer (CC) is a significant global health concern, demanding the consideration of novel therapeutic strategies. The signal transducer and activator of transcription 3 (STAT3) pathway has been implicated in cancer progression and is a potential target for therapeutic intervention. This study aimed to explore the therapeutic potential of TTI-101, a small molecule STAT3 inhibitor, in CC and investigate its underlying mechanisms.MethodsMolecular docking studies and molecular dynamics simulations were performed to explore the binding interaction between TTI-101 and STAT3 and assess the stability of the STAT3-TTI-101 complex. Cell viability assays, wound healing assays, colony formation assays, flow cytometry analysis, and gene expression analysis were conducted. In vivo xenograft models were used to assess the antitumor efficacy of TTI-101.ResultsThe in silico analysis shows a stable binding interaction between TTI-101 and STAT3. TTI-101 treatment inhibits cell viability, clonogenic ability, and cell migration in CC cells. Furthermore, TTI-101 induces apoptosis and cell cycle arrest. Analysis of apoptosis-related markers demonstrated dysregulation of Bax, Bcl-2, and Caspase-3 upon TTI-101 treatment. Moreover, TTI-101 caused G2/M phase arrest accompanied by a decrease in CDK1 and Cyclin B1 at mRNA levels. In the xenograft model, TTI-101 significantly inhibited tumor growth without adverse effects on body weight.ConclusionTTI-101 exhibited anticancer effects by targeting the STAT3/c-Myc signaling pathway, inducing cell cycle arrest, and promoting apoptosis in CC cells. These findings provide valuable insights into the development of novel therapeutic strategies for cervical cancer. Further investigation is warranted to validate the clinical application of TTI-101.Graphical

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.

Stattic ameliorates the cecal ligation and puncture-induced cardiac injury in septic mice via IL-6-gp130-STAT3 signaling pathway

AimSepsis-induced cardiac dysfunction is the leading cause of higher morbidity and mortality with poor prognosis in septic patients. Our recent previous investigation provides evidence of the hallmarks of signal transducer and activator of transcription3 (STAT3) activation in sepsis and targeting of STAT3 with Stattic, a small-molecule inhibitor of STAT3, has beneficial effects in various septic tissues. We investigated the possible cardioprotective effects of Stattic on cardiac inflammation and dysfunction in mice with cecal ligation and puncture (CLP)-induced sepsis. Main methodsA polymicrobial sepsis model was induced by CLP in mice and Stattic (25 mg/kg) was intraperitoneally given at one and twelve hours after CLP operation. The cecum was exposed in sham-control mice without CLP. After 18 h of surgery, electrocardiogram (ECG) for anaesthized mice was registered followed by collecting of samples of blood and tissues for bimolecular and histopathological assessments. Myeloperoxidase, a marker of neutrophil infiltration, was assessed immunohistochemically. Key findingsCLP profoundly impaired cardiac functions as evidenced by ECG changes in septic mice as well as elevation of cardiac enzymes, and inflammatory markers with myocardial histopathological and immunohistochemical alterations. While, Stattic markedly reversed the CLP-induced cardiac abnormalities and restored the cardiac function by its anti-inflammatory activities. SignificanceStattic treatment had potential beneficial effects against sepsis-induced cardiac inflammation, dysfunction and damage. Its cardioprotective effects were possibly attributed to its anti-inflammatory activities by targeting STAT3 and downregulation of IL-6 and gp130. Our investigations suggest that Stattic could be a promising target for management of cardiac sepsis and inflammation-related cardiac damage.

STAT3 inhibitor Stattic and its analogues inhibit STAT3 phosphorylation and modulate cytokine secretion in senescent tumour cells.

Signal transducer and activator of transcription 3 (STAT3) signalling serves an important role in carcinogenesis and cellular senescence, and its inhibition in tumour cells represents an attractive therapeutic target. Premature cellular senescence, a process of permanent proliferative arrest of cells in response to various inducers, such as cytostatic drugs or ionizing radiation, is accompanied by morphological and secretory changes, and by altered susceptibility to chemotherapeutic agents, which can thereby complicate their eradication by cancer therapies. In the present study, the responsiveness of proliferating and docetaxel (DTX)‑induced senescent cancer cells to small molecule STAT3 inhibitor Stattic and its analogues was evaluated using tumour cell lines. These agents displayed cytotoxic effects in cell viability assays on both proliferating and senescent murine TRAMP‑C2 and TC‑1 cells; however, senescent cells were markedly more resistant. Western blot analysis revealed that Stattic and its analogues effectively inhibited constitutive STAT3 phosphorylation in both proliferating and senescent cells. Furthermore, whether the Stattic‑derived inhibitor K1836 could affect senescence induction or modulate the phenotype of senescent cells was evaluated. K1836 treatment demonstrated no effect on senescence induction by DTX. However, the K1836 compound significantly modulated secretion of certain cytokines (interleukin‑6, growth‑regulated oncogene α and monocyte chemoattractant protein‑1). In summary, the present study demonstrated differences between proliferating and senescent tumour cells in terms of their susceptibility to STAT3 inhibitors and demonstrated the ability of the new STAT3 inhibitor K1836 to affect the secretion of essential components of the senescence‑associated secretory phenotype. The present study may be useful for further development of STAT3 inhibitor‑based therapy of cancer or age‑related diseases.

The STAT3 inhibitor GPB730 enhances the sensitivity to enzalutamide in prostate cancer cells

Enzalutamide is a second-generation anti-androgen which has shown increased survival in patients with metastatic prostate cancer. However, some patients do not respond to this therapy or will develop resistance to treatment over time. Signal Transducer and Activator of Transcription 3 (STAT3) is known to be involved in castration-resistant prostate cancer and to interact with androgen receptor (AR)-signaling. This study aims to investigate the combination enzalutamide and the small molecule STAT3 inhibitor GPB730 for enhanced therapeutic effect in advanced prostate cancer in vitro. The prostate cancer cell lines LNCaP (androgen dependent) and C4–2 (androgen insensitive) were used. The effect of enzalutamide and GPB730, alone and in combination, was investigated on viability and IC50 values calculated. Enzalutamide and GPB730 treated LNCaP and C4–2 cells were subjected to western blot and QPCR analyses in order to investigate the expression of AR, STAT3 and down-stream targets. C4–2 were less sensitive to growth inhibition by enzalutamide than LNCaP cells. GPB730 enhanced the growth inhibitory effect of enzalutamide in LNCaP and C4–2 cells. The addition of GPB730 to enzalutamide decreased the IC50 values for enzalutamide by 3.3-fold for LNCaP and by 12-fold for C4–2. In C4–2 cells, GPB730 alone decreased PSA expression and enhanced the enzalutamide induced decrease in NKX3.1 expression. GPB730 and enzalutamide in combination enhanced inhibition of c-myc and survivin expression. This study suggests that enzalutamide may be combined with the STAT3 inhibitor GPB730 in order to enhance the efficacy of enzalutamide, offering a new therapeutic approach in advanced prostate cancer.

EXTH-08. STAT3 AT THE CROSSROADS OF INNATE IMMUNE ACTIVATION IN GLIOBLASTOMA

Abstract BACKGROUND Innate immune cells comprise the majority of the immune microenvironment in glioblastoma (GBM) tumors where they are chiefly thought to foster a hospitable environment for cancer cells by regulating immune suppression and driving resistance to immunotherapy. Of these, myeloid-derived suppressor cells (MDSCs) are regarded as one of the most potent contributors to immune suppression in GBM and thus have become a focus of targeted therapy. Signal transducer and activator of transcription 3 (STAT3) is a key phenotypic regulator of MDSCs. Therefore, we sought to examine if targeted STAT3 inhibition may augment the immunogenicity of these tumors. HYPOTHESIS: Targeted STAT3 inhibition reduces GBM tumor infiltration by MDSCs. METHODS Using syngeneic murine models of GBM, we performed pharmacological inhibition analyses using a specific small molecule inhibitor of STAT3, LLL12B. Circulating numbers of immune cells were assessed in tumor bearing animals with or without concomitant focal radiation. Treated tumors were examined for immune infiltrates, and additional phenotyping analyses were performed. Therapeutic responses to LLL12B alone and in combination with immune checkpoint blockade were evaluated. RESULTS STAT3 is activated in the bone marrow of tumor-bearing animals, preferentially by Gr-1 positive granulocytic myeloid cells. Increased circulating numbers of these cells were also detected. These observations were markedly enhanced in tumor-bearing animals following cranial irradiation. Therapeutic inhibition with LLL12B could mitigate these effects, indicating a dependency on STAT3. Within the tumor compartment, granulocytic myeloid cells that successfully infiltrated following treatment demonstrated a pro-inflammatory phenotype denoted by interferon-gamma expression. Improved survival was also observed following combination treatment with LLL12B and radiation or immune checkpoint blockade. CONCLUSIONS These findings advocate a critically important role for STAT3 in regulating granulocytic myeloid cell mobilization and trafficking to GBM tumors. It further illustrates the plasticity of these cells within these tumors, which may be useful in designing successful immunotherapeutic strategies.

The STAT3-MYC axis promotes survival of leukemia stem cells by regulating SLC1A5 and oxidative phosphorylation

AbstractAcute myeloid leukemia (AML) is characterized by the presence of leukemia stem cells (LSCs), and failure to fully eradicate this population contributes to disease persistence/relapse. Prior studies have characterized metabolic vulnerabilities of LSCs, which demonstrate preferential reliance on oxidative phosphorylation (OXPHOS) for energy metabolism and survival. In the present study, using both genetic and pharmacologic strategies in primary human AML specimens, we show that signal transducer and activator of transcription 3 (STAT3) mediates OXPHOS in LSCs. STAT3 regulates AML-specific expression of MYC, which in turn controls transcription of the neutral amino acid transporter gene SLC1A5. We show that genetic inhibition of MYC or SLC1A5 acts to phenocopy the impairment of OXPHOS observed with STAT3 inhibition, thereby establishing this axis as a regulatory mechanism linking STAT3 to energy metabolism. Inhibition of SLC1A5 reduces intracellular levels of glutamine, glutathione, and multiple tricarboxylic acid (TCA) cycle metabolites, leading to reduced TCA cycle activity and inhibition of OXPHOS. Based on these findings, we used a novel small molecule STAT3 inhibitor, which binds STAT3 and disrupts STAT3-DNA, to evaluate the biological role of STAT3. We show that STAT3 inhibition selectively leads to cell death in AML stem and progenitor cells derived from newly diagnosed patients and patients who have experienced relapse while sparing normal hematopoietic cells. Together, these findings establish a STAT3-mediated mechanism that controls energy metabolism and survival in primitive AML cells.

Signal Transducer and Activator of Transcription-3 Modulation of Cardiac Pathology in Chronic Chagasic Cardiomyopathy

Chronic Chagasic cardiomyopathy (CCC) is a severe clinical manifestation that develops in 30%–40% of individuals chronically infected with the protozoal parasite Trypanosoma cruzi and is thus an important public health problem. Parasite persistence during chronic infection drives pathologic changes in the heart, including myocardial inflammation and progressive fibrosis, that contribute to clinical disease. Clinical manifestations of CCC span a range of symptoms, including cardiac arrhythmias, thromboembolic disease, dilated cardiomyopathy, and heart failure. This study aimed to investigate the role of signal transducer and activator of transcription-3 (STAT3) in cardiac pathology in a mouse model of CCC. STAT3 is a known cellular mediator of collagen deposition and fibrosis. Mice were infected with T. cruzi and then treated daily from 70 to 91 days post infection (DPI) with TTI-101, a small molecule inhibitor of STAT3; benznidazole; a combination of benznidazole and TTI-101; or vehicle alone. Cardiac function was evaluated at the beginning and end of treatment by echocardiography. By the end of treatment, STAT3 inhibition with TTI-101 eliminated cardiac fibrosis and fibrosis biomarkers but increased cardiac inflammation; serum levels of interleukin-6 (IL-6), and IFN−γ; cardiac gene expression of STAT1 and nuclear factor-κB (NF-κB); and upregulation of IL-6 and Type I and Type II IFN responses. Concurrently, decreased heart function was measured by echocardiography and myocardial strain. These results indicate that STAT3 plays a critical role in the cardiac inflammatory–fibrotic axis during CCC.

Recent Update on Development of Small-Molecule STAT3 Inhibitors for Cancer Therapy: From Phosphorylation Inhibition to Protein Degradation.

Signal transducer and activator of transcription 3 (STAT3) is a transcription factor that regulates various biological processes, including proliferation, metastasis, angiogenesis, immune response, and chemoresistance. In normal cells, STAT3 is tightly regulated to maintain a transiently active state, while persistent STAT3 activation occurs frequently in cancers, associating with a poor prognosis and tumor progression. Targeting the STAT3 protein is a potentially promising therapeutic strategy for tumors. Although none of the STAT3 inhibitors has been marketed yet, a few of them have succeeded in entering clinical trials. This Review aims to systematically summarize the progress of the last 5 years in the discovery of directive STAT3 small-molecule inhibitors and degraders, focusing primarily on their structural features, design strategies, and bioactivities. We hope this Review will shed light on future drug design and inhibitor optimization to accelerate the discovery process of STAT3 inhibitors or degraders.

First-in-man phase I clinical trial evaluating TTI-101, an orally bioavailable, small molecule inhibitor of STAT3, in patients with advanced solid tumors.

TPS3158 Background: Signal transducer and activator of transcription 3 (STAT3) is a transcription factor that is a key signaling node and a master regulator of the key hallmarks of cancer, including tumor angiogenesis, resistance to apoptosis, metastasis, and immune evasion. STAT3 activation is observed in ̃70% of all cancers and up to 95% of hepatocellular carcinomas (HCC). Thus, inhibition of STAT3 signaling is expected to have a therapeutic effect against a wide range of cancers. TTI-101 is a first-in-class, orally bioavailable, selective small molecule that binds STAT3 and prevents phosphorylation, homodimerization, nuclear translocation, and ultimately, STAT3-mediated transcriptional activity. TTI-101 has demonstrated anti-tumor activity across a broad range of preclinical cancer models, including a Hep Pten- (hepatocyte-specific deletion of Pten) murine model of liver cancer, which recapitulates the pathogenesis of HCC in non-alcoholic fatty liver disease (NAFLD) with chronic inflammation and liver fibrosis leading to cancer at 11 months. TTI-101 treatment starting at 11 months arrested tumor growth as well as reversed liver injury and fibrosis (1). Given these findings, a clinical trial is being conducted examining the effect of this novel, targeted therapeutic agent in patients with advanced solid malignancies. Methods: This single-site Phase I trial (NCT03195699) is evaluating TTI-101 as monotherapy in patients with advanced solid tumors who are refractory to prior therapies. The primary objectives of this dose-escalation study include establishing tolerability and safety at each dose level, pharmacokinetics (PK), and establishing the recommended phase 2 dose (RP2D). The secondary and exploratory objectives include assessing clinical outcomes of patients and pharmacodynamics (PD) of TTI-101 via timed, paired tumor biopsies. The initial dose-escalation study is stratified by disease type (HCC and non-HCC) with independent dose-escalation schemas and will be followed by dose expansion cohorts where safety, PK and PD will be evaluated. TTI-101 is administered orally, twice daily for a 28-day cycle. Key eligibility criteria include: 18 years of age or older, having metastatic or unresectable solid tumor refractory to standard therapies, and measurable disease as defined by Response Evaluation Criteria in Solid Tumors (RECIST) version 1.1, an Eastern Cooperative Oncology Group (ECOG) score of 0-2, and normal organ function. Additional criteria are specified for patients with HCC including Child-Pugh class A. HCC cohorts 1-4 and non-HCC cohorts 1-3 have been completed without dose limiting toxicities (DLTs). Enrollment to the HCC dose expansion began in February 2021. 1. Jung KH, et al. Multifunctional Effects of a Small-Molecule STAT3 Inhibitor on NASH and Hepatocellular Carcinoma in Mice. Clin Cancer Res. 2017;23(18):5537-46. Clinical trial information: NCT03195699.

Inhibition of STAT3 prevents bone metastatic progression of prostate cancer in vivo.

Prostate cancer (PC) metastasizes to the skeleton forming predominantly sclerotic lesions, and there is currently no cure for bone metastatic disease. The transcription factor signal transducer and activator of transcription 3 (STAT3) is implicated as a metastatic driver, but its potential as therapeutic target in bone metastasis has not been investigated. In this study, we evaluated for the first time a STAT3 inhibitor, Napabucasin, as a therapeutic option for bone metastatic PC. Effects of STAT3 inhibitors, Stattic and Napabucasin, on metastatic potential in PC cells were studied in vitro by assessment of migration capacity, self-renewal potential, and tumorsphere formation. For evaluation of the role of STAT3 in initial skeletal establishment of PC cells as well as in progressed castration-resistant PC (CRPC) in bone, human VCaP prostate cancer cells were inoculated in the tibia of mice which subsequently were treated with the STAT3 inhibitor Napabucasin. Bone specimens were analyzed using computed tomography (CT), immunohistochemistry, and quantitative polymerase chain reaction. The small molecule STAT3 inhibitors Stattic and Napabucasin both effectively impaired metastatic potential of PC cells in vitro. Furthermore, treatment with Napabucasin prevented metastatic establishment in tibial bones in vivo and thereby also the tumor-induced sclerotic bone response seen in vehicle-treated VCaP xenografts. In addition, treatment with Napabucasin of established bone CRPC significantly decreased both tumor burden and tumor-induced trabecular bone volume compared with effects seen in vehicle-treated animals. Anti-mitotic effects were confirmed by decreased Ki67 staining in Napabucasin-treated xenografts compared with vehicle-treated xenografts. Alterations of gene expression in the femoral bone marrow (BM) niche towardthe maintenance of hematopoietic stem cells and the myeloid lineage were demonstrated by quantitative real-time polymerase chain reaction and were further reflected by a substantial increase in the number of erythrocytes in BM of Napabucasin-treated mice. Furthermore, a unique pattern of STAT3 phosphorylation in osteoblasts/stromal cells surrounding the areas of tumor cells was demonstrated immunohistochemically in bone xenograft models using several different PC cell lines. Inhibition of STAT3 activity disrupts the bone metastatic niche and targets both the skeletal establishment of PC and advanced bone metastatic CRPC in mice, suggesting STAT3 as a candidate for molecular targeted therapies of skeletal metastatic disease.

LLL12B, a small molecule STAT3 inhibitor, induces growth arrest, apoptosis, and enhances cisplatin-mediated cytotoxicity in medulloblastoma cells

Signal Transducer and Activator of Transcription 3 (STAT3) is a transcription factor and an oncogene product, which plays a pivotal role in tumor progression. Therefore, targeting persistent STAT3 signaling directly is an attractive anticancer strategy. The aim of this study is to test the efficacy of a novel STAT3 small molecule inhibitor, LLL12B, in suppressing medulloblastoma cells in vitro and tumor growth in vivo. LLL12B selectively inhibited the induction of STAT3 phosphorylation by interleukin-6 but not induction of STAT1 phosphorylation by INF-γ. LLL12B also induced apoptosis in human medulloblastoma cells. In addition, LLL12B exhibited good oral bioavailability in vivo and potent suppressive activity in tumor growth of medulloblastoma cells in vivo. Besides, combining LLL12B with cisplatin showed greater inhibition of cell viability and tumorsphere formation as well as induction of apoptosis comparing to single agent treatment in medulloblastoma cells. Furthermore, LLL12B and cisplatin combination exhibited greater suppression of medulloblastoma tumor growth than monotherapy in vivo. The present study supported that LLL12B is a novel therapeutic agent for medulloblastoma and the combination of LLL12B with a chemotherapeutic agent cisplatin may be an effective approach for medulloblastoma therapy.

Discovery of N-substituted sulfamoylbenzamide derivatives as novel inhibitors of STAT3 signaling pathway based on Niclosamide.

Signal transducer and activator of transcription 3 (STAT3) has been confirmed as an attractive therapeutic target for cancer therapy. Herein, we designed and synthesized a series of N-substituted Sulfamoylbenzamide STAT3 inhibitors based on small-molecule STAT3 inhibitor Niclosamide. Compound B12, the best active compound of this series, was identified as an inhibitor of IL-6/STAT3 signaling with an IC50 of 0.61-1.11μM in MDA-MB-231, HCT-116 and SW480 tumor cell lines with STAT3 overexpression, by inhibiting the phosphorylation of STAT3 of Tyr705 residue and the expression of STAT3 downstream genes, inducing apoptosis and inhibiting the migration of cancer cells. Furthermore, invivo study revealed that compound B12 suppressed the MDA-MB-231 xenograft tumor growth in nude mice at the dose of 30mg/kg (i.g.), which has better antitumor activity than the positive control Niclosamide. More importantly, B12 is an orally bioavailable anticancer agent as a promising candidate for further development.

HJC0416 Attenuates Fibrogenesis in Activated Hepatic Stellate Cells via STAT3 and NF-κB Pathways

BackgroundHepatic fibrosis is wound-healing response that is the result of hepatic stellate cell (HSC) activation and subsequent excess extracellular matrix deposition. HSCs can be activated by a variety of inflammatory stimuli as well as through the signal transducer and activator of transcription 3 (STAT3) pathway. HJC0416 is a novel, orally bioavailable small-molecule inhibitor of STAT3 that was developed by our team using a fragment-based drug design approach. Previously, our team has shown that HJC0416 has antifibrogenic effects in activated HSCs. Recently, increasing evidence suggests that nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) plays an important role in the activation of HSCs. In the present study, we examined the role of NF-κB inhibition of HSC activation by HJC0416. MethodsLX-2 (human) and HSC-T6 (rat) cell lines were used. Expression levels of extracellular proteins, NF-κB and STAT3 expression and DNA binding, and inflammatory cytokine levels were determined using western blot, ELISA, and immunofluorescence assay. ResultsHJC0416 decreased cell viability in a dose-dependent manner in both cell lines and arrested the cell cycle at the S phase. Increased apoptosis was seen in LX-2 cells through Yo-Pro-1 and propidium iodide immunofluorescent stating. HJC0416 significantly decreased expression of fibronectin and collagen I as well as markedly decreased α-SMA and laminin. HJC0416 inhibited the STAT3 pathway by decreasing phosphorylation of STAT3, as well as signal transduction pathway activation. Notably, HJC0416 also inhibited the classic and alternative pathways of NF-κB activation. HJC0416 inhibited LPS-induced p65 nuclear translocation and DNA binding, as well as prevented phosphorylation and degradation of inhibitory protein IκBα. HJC0416 also prevented phosphorylation of serine residue 536 on p65. ConclusionsHJC0416, an inhibitor of STAT3, was found to have antifibrogenic properties in activated hepatic stellate cell lines. In addition, HJC0416 was found to inhibit the NF-κB pathway. Owing to this double effect, HJC0416 demonstrates promise for in vivo experimentation as an antifibrosis treatment.

Napabucasin, a novel inhibitor of STAT3, inhibits growth and synergises with doxorubicin in diffuse large B-cell lymphoma.

Diffuse large B-cell lymphoma (DLBCL), the most common type of aggressive non-Hodgkin lymphoma (NHL), has highly heterogeneous molecular characteristics. Although some patients initially respond to standard R-CHOP therapy, 30-40% develop refractory disease or suffer relapse. Signal transducer and activator of transcription 3 (STAT3), which regulates multiple oncogenic processes, has been found to be constitutively activated in various cancers, including DLBCL, suggesting its potential as a therapeutic target. In this study, we determined that 34% (23/69) of DLBCL patients expressed pSTAT3 (Y705) in tumour tissues. Napabucasin, a novel STAT3 inhibitor, exhibited potent cytotoxicity against NHL cell lines in a dose-dependent manner. Mechanistic studies demonstrated that napabucasin induced intrinsic and extrinsic cell apoptosis, downregulated the expression of STAT3 target genes, including the antiapoptotic protein Mcl-1, and regulated the ROS-mediated mitogen-activated protein kinase (MAPK) pathway. Most importantly, in vivo studies revealed the suppressive efficacy of napabucasin as a monotherapy without obvious toxicity. Furthermore, preliminary combination studies of napabucasin with doxorubicin showed significant synergism both in vitro and in vivo. Thus, our studies provide evidence that napabucasin alone or in combination is a promising therapeutic candidate for DLBCL patients.

A novel small molecule STAT3 inhibitor SLSI-1216 suppresses proliferation and tumor growth of triple-negative breast cancer cells through apoptotic induction

Triple-negative breast cancer (TNBC) is the most aggressive type of breast cancer, characterized by the lack of expression of estrogen receptor, progesterone receptor, and human epidermal growth factor receptor 2. Owing to the absence of molecular targets, there are limited treatment options, and TNBC patients exhibit high mortality rates. Signal transducer and activator of transcription 3 (STAT3) is overexpressed and aberrantly activated in TNBC cells. Therefore, inhibition of STAT3-mediated signaling provides a potential strategy for the treatment of TNBC. In this study, A series of synthetic derivatives of SLSI-1 (a STAT3 inhibitor) were designed and evaluated for antitumor activity in TNBC cells. A novel derivative (SLSI-1216) exhibited the most potent anti-proliferative activity. SLSI-1216 effectively inhibited STAT3 activity and activation of STAT3, leading to the downregulation of AXL, a downstream target of STAT3 and epithelial-mesenchymal transition (EMT) progression. The inhibition of EMT by SLSI-1216 was associated with modulation of E-cadherin and N-cadherin. Furthermore, SLSI-1216 induced apoptosis by targeting STAT3 and effectively inhibited tumor growth in vivo. These findings suggest that SLSI-1216, as a potential inhibitor of STAT3, may be a promising therapeutic agent for TNBC.

Inhibition of STAT3 signaling induces apoptosis and suppresses growth of lung cancer: good and bad

Signal transducer and activator of transcription 3 (STAT3) modulates a variety of genes involved in the regulation of critical functions, including cell proliferation, differentiation, apoptosis, angiogenesis, metastasis, and immunity. For many cancers, elevated levels of STAT3 signaling have been associated with a poor prognosis and the development of chemotherapy resistance. In this study, we investigated the inhibitory effects of a novel small-molecule inhibitor of STAT3, STX-0119, on the cell viability and survival of human lung cancer cells. STX-0119 inhibited activated STAT3 and the expression of STAT3-regulated oncoproteins such as c-Myc, cyclin D1, and survivin in lung cancer cells. STX-0119 also decreased the amount of STAT3 in the nuclear fraction as well as induced apoptosis of these lung cancer cell lines as evidenced by increases in apoptotic cells (Annexin V positive) and poly (ADP-ribose) polymerase (PARP) cleavage. The efficacy of STX-0119 in a mouse xenograft model was confirmed. However, a hematological side effect, which had not been previously reported, was observed. The level of white blood cells was significantly lowered when treated at the dose at which STX-0119 alone showed a significant tumor-suppressive effect. In conclusion, we suggest that STX-0119 may be a potent therapeutic agent against lung cancer. Consideration of the side effect suggests, it is necessary to study whether low-dose STX-0119 is effective for lung treatment with a combination of classic lung cancer therapeutics.

LL1, a novel and highly selective STAT3 inhibitor, displays anti-colorectal cancer activities in vitro and in vivo.

Signal transducer and activator of transcription 3 (STAT3) factor is associated with the development and progression of numerous types of human cancer. STAT3 activation is involved in metastasis. However, no STAT3 inhibitor has been used therapeutically. Hence, we syntheised a novel, potent and small-molecule inhibitor of STAT3, LL1, and studied its antitumour effects and investigated its mechanism of action in two tumour models. Using structure-based drug design method, based on the crystal structure of STAT3 protein, we identified a potent STAT3 inhibitor (LL1) targeting STAT3 SH2 domain and characterized its therapeutic properties and potential toxicity in vitro and in vivo using the MTT assay, colony formation assay, histological, immunohistochemical, flow cytometric analysis, and tumour xenograft model. LL1 is highly selective among STATs family members and specifically inhibits phosphorylation of STAT3 Tyr-705 site, blocking the whole transmission process of STAT3 signalling. LL1 inhibited proliferation, colony formation, migration, and invasion of colonic cell lines. STAT3 is orally available to animals and suppresses tumour growth and metastasis in a dosage level compatible to clinical applications. Importantly, it does not cause significant toxicity at several times the effective dose. LL1 inhibits tumour growth and metastasis by blocking STAT3 signalling pathway. LL1 could be a promising therapeutic drug candidate for colorectal cancer by inhibiting the STAT3 activation.

STAT3 Plays a Critical Role in Mitochondrial Function and Survival of Primary AML Cells

Introduction: Acute myeloid leukemia (AML) is an aggressive disease with a dismal prognosis. This is largely due to high relapse rates, which stem from our inability to eliminate leukemia stem cells (LSCs) with conventional chemotherapy. As we have gained a deeper understanding of the biology of LSCs, new targets against these chemo-resistant cells have surfaced. One such example is treatment using venetoclax/azacititine, a therapy that has significantly improved the outcome for these patients. Notwithstanding, some patients show resistance to all treatments, and developing a larger repertoire of agents that target LSCs remains an unmet need in this disease. One key vulnerability of LSCs is their dependence on oxidative phosphorylation (OXPHOS). Although signal transducer and activator of transcription 3 (STAT3) has been classically studied as a transcription factor that regulates self-renewal and proliferation, it has also been shown to play an essential role in OXPHOS via regulation of the electron transport chain (ETC). Given that STAT3 is commonly overexpressed in AML, and LSCs are dependent on OXPHOS, we hypothesized that STAT3 may be an effective target for eradication of LSCs. Methods: We have developed a novel small molecule inhibitor of STAT3, SF25. This compound, as well as genetic knockdown of STAT3, was employed to test the functional role of STAT3 in primary AML specimens. Flow cytometry, colony-forming potential, and engraftment of primary samples in PDX mouse models were performed to assess therapeutic efficacy. RNA-seq, seahorse assays, and metabolomics experiments were also performed to determine molecular mechanisms linked to targeting STAT3. Results: Our data shows that inhibition of STAT3 in primary AML samples leads to decreased cell viability, colony-formation and engraftment potential in xenograft models, while not affecting normal hematopoietic stem cells. This effect appears to be a result of mitochondrial dysfunction in LSCs, as seen by a significant decrease in oxygen consumption rate of STAT3 depleted cells. The mitochondrial dysfunction and reduction in OXPHOS is mediated by the downregulation of several mitochondrial and nuclear encoded genes that are important for oxidative phosphorylation, including several electron transport chain complex genes. Inhibition of STAT3 also affects glutaminolysis, as noted by metabolomics analysis of leukemia stem cells treated with STAT3 inhibitor. We suspect this effect is mediated by down-regulation of Myc upon STAT3 inhibition, which blocks glutamine conversion to glutamate, and leads to further decrease in TCA cycle intermediates. Conclusions: Acute myeloid leukemia is an aggressive disease, largely due to the presence of a chemo-resistant population of leukemia stem cells. LSCs highly depend on proper mitochondrial function and OXPHOS, a process that is partly regulated by STAT3 via multiple mechanisms. We propose that inhibition of STAT3 is therefore an effective way of eliminating this population, making this a promising new target in the treatment of AML. Disclosures No relevant conflicts of interest to declare.

Small molecule STAT3 inhibitor, 6Br-6a suppresses breast cancer growth in vitro and in vivo

Signal transducer and activator of transcription 3 (STAT3) protein frequently overexpressed in many malignancies and plays an essential role in regulating proliferation, apoptosis, migration and invasion in cancer cells. However, No STAT3 inhibitor was used clinically. In this study, we evaluated the toxic potential of a novel STAT3 inhibitor, 6Br-6a in breast cancer cell lines. The anti-cancer effect and underlying mechanism of 6Br-6a on MDA-MB-231 and MCF-7 cells were determined in vitro and in xenograft mouse model. Our data demonstrated that 6Br-6a significantly induced cell cycle arrest and cell apoptosis in breast cancer via blocking the activation of STAT3. Finally, we verified these inhibitory effects of 6Br-6a in the MDA-MB-231 xenograft mouse model. In conclusion, 6Br-6a effectively inhibited activation of STAT3 and induced cell cycle arrest and apoptosis via regulating cyclin D1 and Bcl-2 expression. All of these data indicate that 6Br-6a could be a potential candidate for the treatment of breast cancer.