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.

Remodeling the immune microenvironment for gastric cancer therapy through antagonism of prostaglandin E2 receptor 4.

Gastric cancer is highly prevalent among digestive tract tumors. Due to the intricate nature of the gastric cancer immune microenvironment, there is currently no effective treatment available for advanced gastric cancer. However, there is promising potential for immunotherapy targeting the prostaglandin E2 receptor subtype 4 (EP4) in gastric cancer. In our previous study, we identified a novel small molecule EP4 receptor antagonist called YY001. Treatment with YY001 alone demonstrated a significant reduction in gastric cancer growth and inhibited tumor metastasis to the lungs in a mouse model. Furthermore, administration of YY001 stimulated a robust immune response within the tumor microenvironment, characterized by increased infiltration of antigen-presenting cells, T cells, and M1 macrophages. Additionally, our research revealed that YY001 exhibited remarkable synergistic effects when combined with the PD-1 antibody and the clinically targeted drug apatinib, rather than fluorouracil. These findings suggest that YY001 holds great promise as a potential therapeutic strategy for gastric cancer, whether used as a standalone treatment or in combination with other drugs.

Selectively targeting BCL6 using a small molecule inhibitor is a potential therapeutic strategy for ovarian cancer.

Ovarian cancer is one of the tumors with the highest fatality rate among gynecological tumors. The current 5-year survival rate of ovarian cancer is <35%. Therefore, more novel alternative strategies and drugs are needed to treat ovarian cancer. The transcription factor B-cell lymphoma 6 (BCL6) is critically associated with poor prognosis and cisplatin resistance in ovarian cancer treatment. Therefore, BCL6 may be an attractive therapeutic target for ovarian cancer. However, the role of targeting BCL6 in ovarian cancer remains elusive. Here, we developed a novel BCL6 small molecule inhibitor, WK369, which exhibits excellent anti-ovarian cancer bioactivity, induces cell cycle arrest and causes apoptosis. WK369 effectively inhibits the growth and metastasis of ovarian cancer without obvious toxicity in vitro and in vivo. meanwhile, WK369 can prolong the survival of ovarian cancer-bearing mice. It is worth noting that WK369 also has significant anti-tumor effects on cisplatin-resistant ovarian cancer cell lines. Mechanistic studies have shown that WK369 can directly bind to the BCL6-BTB domain and block the interaction between BCL6 and SMRT, leading to the reactivation of p53, ATR and CDKN1A. BCL6-AKT, BCL6-MEK/ERK crosstalk is suppressed. As a first attempt, our study demonstrates that targeting BCL6 may be an effective approach to treat ovarian cancer and that WK369 has the potential to be used as a candidate therapeutic agent for ovarian cancer.

WB518, a novel STAT3 inhibitor, effectively alleviates IMQ and TPA-induced animal psoriasis by inhibiting STAT3 phosphorylation and Keratin 17.

OBJECTIVES: Psoriasis is a prevalent chronic inflammatory skin disease in humans that is characterized by frequent relapses and challenging to cure. WB518 is a novel small molecule compound with an undisclosed structure. Therefore, our study aimed to investigate the therapeutic potential of WB518 in vitro and in vivo for the treatment of psoriasis, specifically targeting the abnormal proliferation, aberrant differentiation of epidermal keratinocytes, and pathogenic inflammatory response. MATERIALS AND METHODS: We employed dual luciferase reporter assay to screen compounds capable of inhibiting STAT3 gene transcription. Flow cytometry was utilized to analyze CD3-positive cells. Protein and mRNA levels were assessed through Western blotting, immunofluorescence, immunohistochemistry, and real-time PCR. Cell viability was measured using the MTS assay, while in vivo models of psoriasis induced by IMQ and TPA were employed to study the anti-psoriasis effect of WB518. RESULTS: WB518 was found to significantly reduce the mRNA and protein levels of Keratin 17 (K17) in HaCaT cells by inhibiting the phosphorylation of STAT3 Tyr705 (Y705). In the IMQ and TPA-induced psoriasis mouse model, WB518 effectively improved scaling, epidermal hyperplasia, and inflammation. WB518 also suppressed the expression of inflammatory cytokines, such as interleukin (IL)-1ß, IL-6, IL-17, and IL-23. Furthermore, WB518 decreased the proportion of CD3-positive cells in the psoriatic skin of mice. CONCLUSIONS: WB518 exhibits promising potential as a treatment candidate for psoriasis.

Discovery of a Highly Potent and Selective MYOF Inhibitor with Improved Water Solubility for the Treatment of Gastric Cancer.

Myoferlin (MYOF) mediates the growth and metastasis of various cancers as an emerging therapeutic target by regulating exocytosis and endocytosis. However, the previously reported MYOF inhibitor, 6y, failed to be a favorable candidate agent due to its poor physicochemical properties, such as water solubility, in preclinical studies. Naturally, a novel range of MYOF inhibitors was synthesized and optimized based on the lead compound 6y. The optimal compound HJ445A potently repressed the proliferation of gastric cancer cells with IC50 values of 0.16 and 0.14 µM in MGC803 and MKN45, respectively. Moreover, HJ445A bound to the MYOF-C2D domain with a KD of 0.17 µM, and HJ445A prevented the migration of gastric cancer cells by reversing the epithelial-mesenchymal transition (EMT) process and inhibited the colony formation of the MKN45 cells in a concentration-dependent manner. Notably, the water solubility of HJ445A was significantly improved compared to 6y, with about 170-fold enhancement. Additionally, HJ445A also demonstrated superior antitumor efficacy in vivo.

A small molecule BCL6 inhibitor as chemosensitizers in acute myeloid leukemia.

BCL6 is a transcriptional repressor that regulates multiple genes involved in immune cell differentiation, DNA damage repair, cell cycle, and apoptosis, and is a carcinogenic factor in acute myeloid leukemia (AML). AML is one of the four major types of leukemia with the 5-year survival rate of patients is less than 20% and chemotherapy resistance remains the major obstacle to the treatment failure of AML. We identified WK499, a small molecule compound that can bind to BCL6BTB structure. Treatment with WK499 hinders the interactions between BCL6 with its corepressor proteins, resulting in a remarkable change of BCL6 downstream genes and anti-proliferative effects in AML cells, and inducing cell cycle arrest and apoptosis. We verified that AraC and DOXo could induce BCL6 expression in AML cells, and found that WK499 had a synergistic effect when combined with chemotherapeutic drugs. We further proved that WK499 and AraC could achieve a better result of inhibiting the growth of AML in vivo. These findings indicate that WK499, a small molecule inhibitor of BCL6, not only inhibits the proliferation of AML, but also provides an effective therapeutic strategy for increasing AML sensitivity to chemotherapy.

Preclinical characterization of WB737, a potent and selective STAT3 inhibitor, in natural killer/T-cell lymphoma.

Natural killer/T-cell lymphoma (NKTL) is an uncommon malignancy with poor prognosis and limited therapeutic options. Activating mutations of signal transducer and activator of transcription 3 (STAT3) are frequently found in patients with NKTL, suggesting that targeted inhibition of STAT3 is a potential therapeutic option for this disease. Here, we have developed a small molecule drug WB737 as a novel and potent STAT3 inhibitor that directly binds to the STAT3-Src homology 2 domain with high affinity. In addition, the binding affinity of WB737 to STAT3 is 250-fold higher than STAT1 and STAT2. Interestingly, WB737 is more selective for NKTL with STAT3-activating mutations in terms of growth inhibition and apoptotic induction when compared with Stattic. Mechanistically, WB737 inhibits both canonical and noncanonical STAT3 signaling via suppression of STAT3 phosphorylation at Tyr705 and Ser727, respectively, thereby inhibiting the expression of c-Myc and mitochondria-related genes. Moreover, WB737 inhibited STAT3 more potently than Stattic, resulting in a significant antitumor effect with undetectable toxicity, followed by almost complete tumor regression in an NKTL xenograft model harboring a STAT3-activating mutation. Taken together, these findings provide preclinical proof-of-concept for WB737 as a novel therapeutic strategy for the treatment of NKTL patients with STAT3-activating mutations.

Combined treatment of disulfiram with PARP inhibitors suppresses ovarian cancer.

Introduction: Due to the difficulty of early diagnosis, nearly 70% of ovarian cancer patients are first diagnosed at an advanced stage. Thus, improving current treatment strategies is of great significance for ovarian cancer patients. Fast-developing poly (ADP-ribose) polymerases inhibitors (PARPis) have been beneficial in the treatment of ovarian cancer at different stages of the disease, but PARPis have serious side effects and can result in drug resistance. Using PARPis in combination with other drug therapies could improve the efficacy of PRAPis.In this study, we identified Disulfiram as a potential therapeutic candidate through drug screening and tested its use in combination with PARPis. Methods: Cytotoxicity tests and colony formation experiments showed that the combination of Disulfiram and PARPis decreased the viability of ovarian cancer cells. Results: The combination of PARPis with Disulfiram also significantly increased the expression of DNA damage index gH2AX and induced more PARP cleavage. In addition, Disulfiram inhibited the expression of genes associated with the DNA damage repair pathway, indicating that Disulfiram functions through the DNA repair pathway. Discussion: Based on these findings, we propose that Disulfiram reinforces PARPis activity in ovarian cancer cells by improving drug sensitivity. The combined use of Disulfiram and PARPis provides a novel treatment strategy for patients with ovarian cancer.

Selectively Targeting STAT3 Using a Small Molecule Inhibitor is a Potential Therapeutic Strategy for Pancreatic Cancer.

PURPOSE: Pancreatic cancer is the worst prognosis among all human cancers, and novel effective treatments are urgently needed. Signal transducer and activator of transcription 3 (STAT3) has been demonstrated as a promising target for pancreatic cancer. Meanwhile, selectively targeted STAT3 with small molecule remains been challenging. EXPERIMENTAL DESIGN: To specifically identify STAT3 inhibitors, more than 1.3 million compounds were screened by structure-based virtual screening and confirmed with the direct binding assay. The amino acid residues that WB436B bound to were verified by induced-fit molecular docking simulation, RosettaLigand computations, and site-directed mutagenesis. On-target effects of WB436B were examined by microscale thermophoresis, surface plasmon resonance, in vitro kinase assay, RNA sequencing, and selective cell growth inhibition assessment. In vivo studies were performed in four animal models to evaluate effects of WB436B on tumor growth and metastasis. Kaplan-Meier analyses were used to assess survival. RESULTS: WB436B selectively bound to STAT3 over other STAT families protein, and in vitro antitumor activities were improved by 10 to 1,000 fold than the representative STAT3 inhibitors. WB436B selectively inhibits STAT3-Tyr705 phosphorylation, STAT3 target gene expression, and the viability of STAT3-dependent pancreatic cancer cells. WB436B significantly suppresses tumor growth and metastasis in vivo and prolongs survival of tumor-bearing mice. Mechanistic studies showed that WB436B have unique binding sites located in STAT3 Src homology 2 domain. CONCLUSIONS: Our work presents the first-in-class selective STAT3 inhibitor WB436B as a potential therapeutic candidate for the treatment of pancreatic cancer.

Discovery of a Highly Potent and Orally Bioavailable STAT3 Dual Phosphorylation Inhibitor for Pancreatic Cancer Treatment.

Increasing evidence has demonstrated that STAT3 phosphorylation at Tyr705 and Ser727 is closely associated with the progression and poor prognosis of pancreatic cancer. Herein, we report the function-based screening, SAR studies, and biological activity evaluation of a series of novel STAT3 dual phosphorylation inhibitors with an indole-containing tetra-aromatic heterocycle scaffold. Our efforts led to the discovery of optimal compound 4c among the investigated ones, showing desirable ADME properties and highly potent antitumor activities in vitro and in vivo. By targeting the STAT3 SH2 domain, 4c significantly blocked p-Tyr705 and p-Ser727 and caused the abrogation of the corresponding nuclear transcription and mitochondrial oxidative phosphorylation functions of STAT3 in the low nanomolar range. Except for nanomolar antiproliferation activities in vitro, oral treatment of 4c exhibited significant suppressive effects and tolerance in a pancreatic cancer xenograft model, indicating that 4c could be useful for pancreatic cancer treatment as a STAT3 dual phosphorylation inhibitor.

Discovery of 1,5-diaryl-1,2,4-triazole derivatives as myoferlin inhibitors and their antitumor effects in pancreatic cancer.

Aim: The first inhibitor targeting myoferlin (MYOF), WJ460, bears poor metabolic stability and water solubility. Therefore, this study aimed to improve the drug-like properties of WJ460. Materials & methods: The authors synthesized an array of 1,5-diaryl-1,2,4-triazole analogs and appraised the binding activities with MYOF and their antiproliferative and antimigratory activities against pancreatic cancer cells. Results: Molecular docking and surface plasmon resonance results showed that E4 was directly bound to the MYOF-C2D domain. E4 effectively inhibited the proliferation and migration of pancreatic cancer cells in vitro. An in silico study suggested that the water solubility of E4 was improved by about 22-times than that of WJ460. Conclusion: The findings suggested that the druglike ability of E4 was significantly improved.

Discovery of a Novel Potent STAT3 Inhibitor HP590 with Dual p-Tyr705/Ser727 Inhibitory Activity for Gastric Cancer Treatment.

Accumulating evidence has documented that STAT3 phosphorylation at Tyr705 and Ser727 jointly promotes the initiation and progression of gastric cancer. However, most reported STAT3 inhibitors have mainly focused on suppressing STAT3 phosphorylation at Tyr705 while ignoring the tumorigenic effects of phosphorylation at Ser727. Herein, we described the design, synthesis, and structure-activity relationship studies on a series of triaromatic heterocyclic derivatives as potent dual phosphorylation STAT3 inhibitors. These efforts led to the discovery of the best compound 3h (HP590) among the investigated ones, a novel, highly potent, and orally bioavailable STAT3 inhibitor possessing lower nanomolar inhibitory activity toward p-Tyr705 and p-Ser727. Target validation revealed that HP590 selectively targets STAT3 to remarkably inhibit its canonical and noncanonical activation and corresponding biological functions, thereby resulting in the growth inhibition of gastric cancer in vitro and in vivo, highlighting the therapeutic potential of dual phosphorylation STAT3 inhibitors for gastric cancer.

Discovery of 2-Amino-3-cyanothiophene Derivatives as Potent STAT3 Inhibitors for the Treatment of Osteosarcoma Growth and Metastasis.

Osteosarcoma is one of the most common malignant bone tumors. However, the treatment and clinical outcomes of osteosarcoma have hardly changed over the past three decades due to the comprehensive heterogeneity and higher rate of mutation of osteosarcoma. Recent studies have shown that STAT3 has the potential to suppress the proliferation and metastasis of osteosarcoma. In this study, a novel class of 2-amino-3-cyanothiophene derivatives were designed and synthesized to inhibit osteosarcoma by targeting STAT3. Representative compound 6f showed potent antiproliferative effects against osteosarcoma cells, directly bound to the STAT3 SH2 domain with a KD of 0.46 µM, and inhibited the phosphorylation of STAT3 Y705 in a dose-dependent manner. Furthermore, compound 6f promoted osteosarcoma cell apoptosis in vitro and significantly suppressed the growth and metastasis of osteosarcoma in vivo. These findings demonstrate that targeting STAT3 may be a feasible therapeutic strategy for the treatment of metastatic osteosarcoma.

A novel small-molecule activator of unfolded protein response suppresses castration-resistant prostate cancer growth.

Androgen receptor-targeted therapy improves survival in castration-resistant prostate cancer (CRPC). However, almost all patients with CRPC eventually develop secondary resistance to these drugs. Therefore, alternative therapeutic approaches for incurable metastatic CRPC are urgently needed. Unfolded protein response (UPR) is regarded as a cytoprotective mechanism that removes misfolded proteins in rapidly proliferating tumor cells. However, acute activation of the UPR directly leads to tumor cell death. This study has shown that WJ-644A, a novel small molecule activator of UPR, potently inhibited the proliferation of prostate cancer cells and caused tumor regression with a good safety profile in multiple animal models. Mechanistically, we have identified that WJ-644A induced cell methuosis and autophagy upon UPR activation. Our study not only identifies the UPR as an actionable target for CRPC treatment, but also establishes WJ-644A as a novel UPR activator that has potential therapeutic value for CRPC.

An orally available small molecule BCL6 inhibitor effectively suppresses diffuse large B cell lymphoma cells growth in vitro and in vivo.

The transcription factor B cell lymphoma 6 (BCL6) is an oncogenic driver of diffuse large B cell lymphoma (DLBCL) and mediates lymphomagenesis through transcriptional repression of its target genes by recruiting corepressors to its N-terminal broad-complex/tramtrack/bric-a-brac (BTB) domain. Blocking the protein-protein interactions of BCL6 and its corepressors has been proposed as an effective approach for the treatment of DLBCL. However, BCL6 inhibitors with excellent drug-like properties are rare. Hence, the development of BCL6 inhibitors is worth pursuing. We screened our internal chemical library by luciferase reporter assay and Homogenous Time Resolved Fluorescence (HTRF) assay and a small molecule compound named WK500B was identified. WK500B engaged BCL6 inside cells, blocked BCL6 repression complexes, reactivated BCL6 target genes, killed DLBCL cells and caused apoptosis as well as cell cycle arrest. In animal models, WK500B inhibited germinal center (GC) formation and DLBCL tumour growth without toxic and side effects. Moreover, WK500B displayed strong efficacy and favourable pharmacokinetics and presented superior druggability. Therefore, WK500B is a promising candidate that could be developed as an effective orally available therapeutic agent for DLBCL.

Single-Cell Analysis Reveals EP4 as a Target for Restoring T-Cell Infiltration and Sensitizing Prostate Cancer to Immunotherapy.

PURPOSE: Immunotherapies targeting immune checkpoint molecules have shown promising treatment for a subset of cancers; however, many "cold" tumors, such as prostate cancer, remain unresponsive. We aimed to identify a potential targetable marker relevant to prostate cancer and develop novel immunotherapy. EXPERIMENTAL DESIGN: Analysis of transcriptomic profiles at single-cell resolution was performed in clinical patients' samples, along with integrated analysis of multiple RNA-sequencing datasets. The antitumor activity of YY001, a novel EP4 antagonist, combined with anti-programmed cell death protein 1 (PD-1) antibody was evaluated both in vitro and in vivo. RESULTS: We identified EP4 (PTGER4) as expressed in epithelial cells and various immune cells and involved in modulating the prostate cancer immune microenvironment. YY001, a novel EP4 antagonist, inhibited the differentiation, maturation, and immunosuppressive function of myeloid-derived suppressor cells (MDSC) while enhancing the proliferation and anticancer functions of T cells. Furthermore, it reversed the infiltration levels of MDSCs and T cells in the tumor microenvironment by overturning the chemokine profile of tumor cells in vitro and in vivo. The combined immunotherapy demonstrated a robust antitumor immune response as indicated by the robust accumulation and activation of CD8+ cytotoxic T cells, with a significantly decreased MDSC ratio and reduced MDSC immunosuppression function. CONCLUSIONS: Our study identified EP4 as a specific target for prostate cancer immunotherapy and demonstrated that YY001 inhibited the growth of prostate tumors by regulating the immune microenvironment and strongly synergized with anti-PD-1 antibodies to convert completely unresponsive prostate cancers into responsive cancers, resulting in marked tumor regression, long-term survival, and lasting immunologic memory.

Regression of Castration-Resistant Prostate Cancer by a Novel Compound HG122.

Prostate cancer (PCa) is a common aggressive disease worldwide which usually progresses into incurable castration-resistant prostate cancer (CRPC) in most cases after 18-24 months treatment. Androgen receptor (AR) has been considered as a crucial factor involved in CRPC and the study of AR as a potential therapeutic target in CRPC may be helpful in disease control and life-cycle management. In this study, we identified a potent small molecule compound, HG122, that suppressed CRPC cells proliferation and metastasis, and inhibited tumor growth both in subcutaneous and orthotopic tumor model. In addition, HG122 reduced the mRNA expression of PSA and TMPRSS2 which are target genes of AR, resulting in cell growth inhibition and metastasis suppression of CRPC, without affecting the expression of AR mRNA level. Mechanically, HG122 promoted AR protein degradation through the proteasome pathway impairing the AR signaling pathway. In conclusion, HG122 overcomes enzalutamide (ENZ) resistance in CRPC both in vitro and in vivo, thus suggesting HG122 is a potential candidate for the clinical prevention and treatment of CRPC.

The natural product trienomycin A is a STAT3 pathway inhibitor that exhibits potent in vitro and in vivo efficacy against pancreatic cancer.

BACKGROUND AND PURPOSE: Pancreatic cancer is an exceptionally fatal disease. However, therapeutic drugs for pancreatic cancer have presented a serious shortage over the past few decades. Signal transducer and activator of transcription-3 (STAT3) is persistently activated in many human cancers where it promotes tumour development and progression. Natural products serve as an inexhaustible source of anticancer drugs. Here, we identified the natural product trienomycin A (TA), an ansamycin antibiotic, as a potential inhibitor of the STAT3 pathway with potent activity against pancreatic cancer. EXPERIMENTAL APPROACH: Effects of trienomycin A on transcriptional activity of STAT3 were assessed by the STAT3-luciferase (STAT3-luc) reporter system. In vitro and in vivo inhibitory activity of TA against pancreatic cancer made use of molecular docking, surface plasmon resonance (SPR) assay, MTS assay, colony formation assay, transwell migration/invasion assay, flow cytometric analysis, immunofluorescence staining, quantitative real-time polymerase chain reaction (PCR), western blotting, tumour xenograft model, haematoxylin and eosin (H&E) staining and immunohistochemistry. KEY RESULTS: Trienomycin A directly bound to STAT3 and inhibited STAT3 (Tyr705) phosphorylation, thus inhibiting the STAT3 pathway. Trienomycin A also inhibited colony formation, proliferation, migration and invasion of pancreatic cancer cell lines. Trienomycin A also markedly blocked pancreatic tumour growth in vivo. More importantly, trienomycin A did not show obvious toxicity at the effective dose in mice. CONCLUSIONS AND IMPLICATIONS: Trienomycin A exerted anti-neoplastic activity by suppressing STAT3 activation in pancreatic cancer. This natural product could be a novel therapeutic candidate for pancreatic cancer.

A potent and selective small molecule inhibitor of myoferlin attenuates colorectal cancer progression.

As a pivotal vesicular trafficking protein, Myoferlin (MYOF) has become an attractive target for cancer therapy. However, the roles of MYOF in colorectal cancer invasion remain enigmatic, and MYOF-targeted therapy in this malignancy has not been explored. In the present study, we provided the first functional evidence that MYOF promoted the cell invasion of colorectal cancer. Furthermore, we identified a novel small molecule inhibitor of MYOF (named YQ456) that showed high binding affinity to MYOF (KD  = 37 nM) and excellent anti-invasion capability (IC50  = 110 nM). YQ456 was reported for the first time to interfere with the interactions between MYOF and Ras-associated binding (Rab) proteins at low nanomolar levels. This interference disrupted several vesicle trafficking processes, including lysosomal degradation, exosome secretion, and mitochondrial dynamics. Further, YQ456 exhibited excellent inhibitory effects on the growth and invasiveness of colorectal cancer. As the first attempt, the anticancer efficacy of YQ456 in the patient-derived xenograft (PDX) mouse model indicated that targeting MYOF may serve as a novel and practical therapeutic approach for colorectal cancer.

Targeting STAT3 by a small molecule suppresses pancreatic cancer progression.

Pancreatic cancer is lethal in over 90% of cases since it is resistant to current therapeutic strategies. The key role of STAT3 in promoting pancreatic cancer progression has been proven, but effective interventions that suppress STAT3 activities are limited. The development of novel anticancer agents that directly target STAT3 may have potential clinical benefits for pancreatic cancer treatment. Here, we report a new small-molecule inhibitor (N4) with potent antitumor bioactivity, which inhibits multiple oncogenic processes in pancreatic cancer. N4 blocked STAT3 and phospho-tyrosine (pTyr) peptide interactions in fluorescence polarization (FP) assay, specifically abolished phosphor-STAT3 (Tyr705), and suppressed expression of STAT3 downstream genes. The mechanism involved the direct binding of N4 to the STAT3 SH2 domain, thereby, the STAT3 dimerization, STAT3-EGFR, and STAT3-NF-κB cross-talk were efficiently inhibited. In animal models of pancreatic cancer, N4 was well tolerated, suppressed tumor growth and metastasis, and significantly prolonged survival of tumor-bearing mice. Our results offer a preclinical proof of concept for N4 as a candidate therapeutic compound for pancreatic cancer.