SH2 Domain Of Signal Transducer And Activator Of Transcription 3 Research Articles

The STAT3 inhibitor B9 alleviates lipopolysaccharide-induced acute lung injury through its anti-inflammatory effects

The development of acute lung injury (ALI), a common respiratory condition with multiple causes, is significantly influenced by the pro-inflammatory environment of signal transducer and activator of transcription 3 (STAT3) in macrophages. Our study aimed to evaluate the anti-inflammatory effects of B9 (N-(4-hydroxyphenyl)-9, 10-dioxo-9, 10-dihydroanthracene-2-sulfonamide), a novel inhibitor targeting the STAT3 SH2 domain, in macrophages and to assess its therapeutic potential for ALI using a mouse model of lipopolysaccharide (LPS)-induced ALI. We found that B9 (30 mg/kg) significantly reduced lung pathological damage and neutrophil infiltration caused by the intratracheal administration of LPS. Additionally, the high expression of pro-inflammatory cytokines (TNF-α, IL-1β, and IL-6) in alveolar lavage fluid was also inhibited by B9 treatment. The decreased expression of CD86 and increased CD206 in lung tissue demonstrated the anti-inflammatory effect of B9, which was due to its inhibition of the STAT3 signaling pathway in macrophages of ALI mice. Furthermore, B9 suppressed the activation of RAW264.7 cells induced by LPS, characterized by its ability to inhibit the activation of iNOS and STAT3 in a dose-dependent manner, as well as reduce the secretion of IL-6 and IL-1β. The in vivo preliminary safety evaluation indicated that B9 had a favorable safety profile at the administered doses. These results suggest that B9 exerts a therapeutic effect on LPS-induced ALI, potentially by preventing the phosphorylation of STAT3 Y705 and S727 without affecting the STAT3 protein level. Taken together, these findings provide a foundation for developing B9 as a novel anti-inflammatory agent for ameliorating LPS-induced ALI.

Discovery of Potential Natural STAT3 Inhibitors: An in silico Molecular Docking and Molecular Dynamics Study

Cancer is a mechanistically complex and diverse disease with a plethora of fundamental genetic and epigenetic factors. Signal transducer and activator of transcription-3 (STAT3) is a transcription factor, and its constitutive activation executes promotion of cellular proliferation, cell cycle, angiogenesis, metastasis, immunosuppression, and chemo-resistance in cancer cells. Here, we aimed to design natural potential STAT3 inhibitors. For this purpose, we investigated 92 phytochemical compounds by molecular docking studies because they are diversified, multitargeted, affordable, easily available, and less- or non-toxic. We selected only 6 compounds such as sarsasapogenin (L3), peiminine (L9), solasodine (L10), tormentic acid (L23), obacunone (L29), and echinocystic acid (L34) due to their greater binding affinity than reference STAT3 inhibitor (S3I-201) with STAT3. The study was further continued by molecular dynamic (MD) simulations and ADMET (absorption, distribution, metabolism, excretion, and toxicity) analysis. The results of molecular docking showed that all selected ligands exhibited binding affinity range from -9.3 Kcal/mol to -7.9 Kcal/mol and predicted inhibition constant ([Formula: see text].) values range from 0.14 [Formula: see text]M to 1.5 [Formula: see text]M. These compounds showed effective hydrogen bonding and hydrophobic interactions with DNA binding domain as well as SH2-domain of STAT3. The MD simulations performed by nanoscale molecular dynamics (NAMD) calculated root mean square deviations (RMSD), root mean square fluctuations (RMSF), radius of gyration ([Formula: see text]), solvent accessible surface area (SASA) and number of hydrogen bond dynamics. All selected ligands with protein exhibited stability over 120 ns by MD simulation. Moreover, these ligands showed favorable ADMET profiling and drug likeness. So, our current computational investigations showed that these novel drug candidates can be potential STAT3 inhibitors and evoke the scientific interest for their further verification by in vitro and in vivo studies.

Discovery of potent STAT3 inhibitors using structure-based virtual screening, molecular dynamic simulation, and biological evaluation.

Signal transducer and activator of transcription 3 (STAT3) is ubiquitously hyper-activated in numerous cancers, rendering it an appealing target for therapeutic intervention. In this study, using structure-based virtual screening complemented by molecular dynamics simulations, we identified ten potential STAT3 inhibitors. The simulations pinpointed compounds 8, 9, and 10 as forming distinct hydrogen bonds with the SH2 domain of STAT3. In vitro cytotoxicity assays highlighted compound 4 as a potent inhibitor of gastric cancer cell proliferation across MGC803, KATO III, and NCI-N87 cell lines. Further cellular assays substantiated the ability of compound 4 to attenuate IL-6-mediated STAT3 phosphorylation at Tyr475. Additionally, oxygen consumption rate assays corroborated compound 4's deleterious effects on mitochondrial function. Collectively, our findings position compound 4 as a promising lead candidate warranting further exploration in the development of anti-gastric cancer therapeutics.

An Isoxazoloquinone Derivative Inhibits Tumor Growth by Targeting STAT3 and Triggering Its Ubiquitin-Dependent Degradation.

Triple-negative breast cancer (TNBC) is the most aggressive breast cancer subtype, with shorter five-year survival than other breast cancer subtypes, and lacks targeted and hormonal treatment strategies. The signal transducer and activator of transcription 3 (STAT3) signaling is up-regulated in various tumors, including TNBC, and plays a vital role in regulating the expression of multiple proliferation- and apoptosis-related genes. By combining the unique structures of the natural compounds STA-21 and Aulosirazole with antitumor activities, we synthesized a class of novel isoxazoloquinone derivatives and showed that one of these compounds, ZSW, binds to the SH2 domain of STAT3, leading to decreased STAT3 expression and activation in TNBC cells. Furthermore, ZSW promotes STAT3 ubiquitination, inhibits the proliferation of TNBC cells in vitro, and attenuates tumor growth with manageable toxicities in vivo. ZSW also decreases the mammosphere formation of breast cancer stem cells (BCSCs) by inhibiting STAT3. We conclude that the novel isoxazoloquinone ZSW may be developed as a cancer therapeutic because it targets STAT3, thereby inhibiting the stemness of cancer cells.

Dual inhibition of MYC and SLC39A10 by a novel natural product STAT3 inhibitor derived from Chaetomium globosum suppresses tumor growth and metastasis in gastric cancer

Gastric cancer remains one of the most common deadly diseases and lacks effective targeted therapies. In the present study, we confirmed that the signal transducer and activator of transcription 3 (STAT3) is highly expressed and associated with a poor prognosis in gastric cancer. We further identified a novel natural product inhibitor of STAT3, termed XYA-2, which interacts specifically with the SH2 domain of STAT3 (Kd= 3.29 μM) and inhibits IL-6-induced STAT3 phosphorylation at Tyr705 and nuclear translocation. XYA-2 inhibited the viability of seven human gastric cancer cell lines with 72-h IC50 values ranging from 0.5 to 0.7 μΜ. XYA-2 at 1 μΜ inhibited the colony formation and migration ability of MGC803 (72.6% and 67.6%, respectively) and MKN28 (78.5% and 96.6%, respectively) cells. In the in vivo studies, intraperitoneal administration of XYA-2 (10 mg/kg/day, 7 days/week) significantly suppressed 59.8% and 88.8% tumor growth in the MKN28-derived xenograft mouse model and MGC803-derived orthotopic mouse model, respectively. Similar results were obtained in a patient-derived xenograft (PDX) mouse model. Moreover, XYA-2 treatment extended the survival of mice bearing PDX tumors. The molecular mechanism studies based on transcriptomics and proteomics analyses indicated that XYA-2 might exert its anticancer activity by synergistically inhibiting the expression of MYC and SLC39A10, two downstream genes of STAT3 in vitro and in vivo. Together, these findings suggested that XYA-2 may be a potent STAT3 inhibitor for treating gastric cancer, and dual inhibition of MYC and SLC39A10 may be an effective therapeutic strategy for STAT3-activated cancer.

Synthesis and evaluation of naphthalene derivatives as potent STAT3 inhibitors and agents against triple-negative breast cancer growth and metastasis.

Triple-negative breast cancer (TNBC) represents the worst prognostic subtype of breast cancer and lacks targeted therapeutic drugs. Signal transducer and activator of transcription 3 (STAT3) is overexpressed and constitutively activated in TNBCs and associated with poor patient outcomes. However, no agents targeting STAT3 have been successfully developed and marketed. Selective Estrogen Receptor Modulators (SERMs) have been reported as potential inhibitors of the IL-6/STAT3 signaling pathway. Naphthalene compounds have good pharmacological activity and significant anti-cancer activity. In this study, we synthesized a new series of naphthalene derivatives with the general structure of SERM and evaluated their effects on TNBC and STAT3 signals. A new series of compounds based on the scaffold of SERMs and an amino group were designed and screened based on the structure-activity relationship by MTT assay. The binding activity of SMY002 to STAT3 was predicted and validated by docking and SPR. The STAT3 signaling target and anti-cancer effects of SMY002 were evaluated with three TNBC cell lines and the mice transplanted tumor model. Among the compounds, SMY002 displayed the most potent activity, which could directly interact with STAT3 SH2-domain, and strongly inhibit the phosphorylation, dimerization, nuclear distribution, transcriptional activity, and target genes expression of STAT3. Furthermore, SMY002 markedly suppressed migration, invasion, survival, growth, and metastasis of TNBC cells in vitro and in vivo via down-regulating the expression of Cyclin D1 and MMP9. SMY002 can significantly inhibit the growth and metastasis of TNBC cells by targeting the STAT3 signal.

Cirsiliol regulates mitophagy in colon cancer cells via STAT3 signaling

BackgroundMitophagy is a type of selective autophagy for dysfunctional mitochondria and plays a key role in tumorigenesis and cancer progression. However, whether mitophagy plays a role in colon cancer remains unclear. Cirsiliol is a natural product and has been found to exert anti-cancer effects in multiple tumors. The effects of cirsiliol in the tumorigenesis and progression of colon cancer remain unknown.MethodsCCK8 assay, plate cloning assay, and cell scratch assay were performed to determine cell viability, colony formation, and wound healing abilities of HCT116 and SW480 cells. JC-1 staining, H2DCFDA staining, and Mito-Tracker Red staining were carried out to evaluate mitochondrial membrane potential (Δψm), intracellular reactive oxygen species (ROS) level, and mitochondrial morphology. Molecular docking technology was utilized to predict interaction of cirsiliol and signal transducer and activator of transcription 3 (STAT3). Immunofluorescence staining was used to measure nuclear translocation of STAT3. The protein levels of phosphorylated STAT3 (Y705), total STAT3, and mitophagy proteins were detected by western blot.ResultsIn this study, we first found that cirsiliol inhibited cell viability, colony formation, and wound healing abilities of HCT116 and SW480 colon cancer cells. Moreover, cirsiliol suppressed Δψm, increased ROS production, and disrupted mitochondrial morphology via inhibiting the levels of mitophagy proteins including PINK1, Parkin, BNIP3, and FUNDC1. Application of mitophagy activator improved the levels of mitophagy-related proteins, and ameliorated Δψm and ROS levels. According to the result of molecular docking, we found that cirsiliol potentially bound to the SH2 domain of STAT3, the key domain for the functional activation of STAT3. Moreover, it was found that cirsiliol inhibited constitutive and IL‑6‑induced STAT3 phosphorylation and nuclear translocation by western blot and immunofluorescence analysis. Comparing with cirsiliol group, we found that overexpression of STAT3 restored the expressions of mitophagy proteins.ConclusionsCirsiliol targets STAT3 to inhibit colon cancer cell proliferation by regulating mitophagy.

Inhibiting STAT3 signaling pathway by natural products for cancer prevention and therapy: In vitro and in vivo activity and mechanisms of action

Signal transducer and activator of transcription 3 (STAT3) plays a critical role in signal transmission from the plasma membrane to the nucleus, regulating the expression of genes involved in essential cell functions and controlling the processes of cell cycle progression and apoptosis. Thus, STAT3 has been elucidated as a promising target for developing anticancer drugs. Many natural products have been reported to inhibit the STAT3 signaling pathway during the past two decades and have exhibited significant anticancer activities in vitro and in vivo. However, there is no FDA-approved STAT3 inhibitor yet. The major mechanisms of these natural product inhibitors of the STAT3 signaling pathway include targeting the upstream regulators of STAT3, directly binding to the STAT3 SH2 domain and inhibiting its activation, inhibiting STAT3 phosphorylation and/or dimerization, and others. In the present review, we have systematically discussed the development of these natural product inhibitors of STAT3 signaling pathway as well as their in vitro and in vivo anticancer activity and mechanisms of action. Outlooks and perspectives on the associated challenges are provided as well.

S3I-201 derivative incorporating naphthoquinone unit as effective STAT3 inhibitors: Design, synthesis and anti-gastric cancer evaluation

Signal transducer and activator of transcription 3 (STAT3) is a key regulator of many human cancers and has been widely recognized as a promising target for cancer therapy. A variety of small-molecule inhibitors have been developed for targeting STAT3, and some of them are now undergoing clinical trials. S3I-201, a known STAT3 inhibitor, may block STAT3 function in cancer cells by binding to the STAT3 SH2 domain to disrupt STAT3 protein complex formation. Using S3I-201 as a starting point for drug development, we synthesized a series of new STAT3 inhibitors 9a-x in this study by introducing naphthoquinone unit, a privileged fragment in STAT3 inhibitors. Most of the compounds exhibited strong anti-proliferation activity of gastric cancer cells (MGC803, MKN28, MNK1, and AGS). The representative compound 9n (SIL-14) could effectively inhibit the colony formation and migration of gastric cancer cells MGC803, arrest the cell cycle and induce MGC803 cell apoptosis at low micromolar concentrations in vitro. In addition, SIL-14 can also inhibit the phosphorylation of STAT3 protein and significantly decrease the expression of total STAT3, suggesting that it may exert anticancer effects by blocking the STAT3 signaling pathway. These results support that SIL-14 may be a promising STAT3 inhibitor for the further development of potential anti-gastric cancer candidates.

The direct STAT3 inhibitor 6-ethoxydihydrosanguinarine exhibits anticancer activity in gastric cancer

Signal transducer and activator of transcription 3 (STAT3) plays a key role in promoting tumor malignant progression. Suppression of hyperactivated STAT3 signaling has emerged as a potential therapeutic strategy for many cancer types. In this study, the effect of 6-ethoxydihydrosanguinarine (6-EDS), a secondary transformation product formed from dihydrosanguinarine, isolated from Macleaya (Papaveraceae), was evaluated in gastric cancer (GC). We demonstrated that 6-EDS inhibited the survival, migration, and invasiveness of GC cells in vitro. Moreover, 6-EDS inhibited STAT3 phosphorylation and transcriptional activity, thus suppressing the mRNA expression of downstream target genes associated with the malignant survival, migration, and invasiveness of GC cells. Molecular docking indicated that 6-EDS directly bound the SH2 domain of STAT3. Molecular dynamics simulations suggested that 6-EDS inhibited the binding of phosphorylated and non-phosphorylated STAT3 to target DNA. Cellular thermal-shift assays and microscale thermophoresis further confirmed the direct binding of 6-EDS to STAT3. Site-directed mutagenesis indicated that the S611 residue in the SH2 domain of STAT3 is critical for 6-EDS binding. In vivo, 6-EDS decreased tumor growth in xenografted nude mice by blocking STAT3 signaling. These findings indicated that 6-EDS, a direct STAT3 inhibitor, may be a potent anticancer candidate for GC therapy.

Rational drug design of benzothiazole-based derivatives as potent signal transducer and activator of transcription 3 (STAT3) signaling pathway inhibitors.

The cumulative evidence supports STAT3, a transcriptional mediator of oncogenic signaling, as a therapeutic target in cancer. The development of STAT3 inhibitors remain an active area of research as no inhibitors have yet to be approved for cancer treatment. In a continuing effort to develop more potent STAT3 inhibitors based on our previously identified hit compound 16w, a series of benzothiazole derivatives with unique binding mode in SH2 domain of STAT3 were designed, synthesized and biologically evaluated. Of note, compound B19 demonstrated excellent activity against IL-6/STAT3 signaling pathway with the IC50 value as low as 0.067μM as determined by a luciferase reporter assay. Moreover, multiple compounds displayed potent antiproliferative activity against MDA-MB-468 and JAK2 mutant HEL cell lines. Further biochemical study using Western blot assay indicated that B19 blocked the phosphorylation of STAT3 at Tyr 705 and Ser 727 and thus suppressed STAT3-mediated gene expression of c-MYC and MCL-1. Simultaneously, it induced cancer cell G2/M phase arrest and apoptosis both in MDA-MB-468 and HEL cell lines. Finally, molecular docking study along with surface plasmon resonance (SPR) and fluorescence polarization (FP) assays disclosed the binding mode of B19 in STAT3 SH2 domain. Taken together, our finding suggests that B19 is a promising therapeutic STAT3 inhibitor for cancer treatment.

Identification of novel STAT3 inhibitors bearing 2-acetyl-7-phenylamino benzofuran scaffold for antitumour study

Signal transducer and activator of transcription 3 (STAT3) is identified as a promising target for multiple cancer therapy and attracts widespread concern. Herein, we reported the discovery of a series of 2-acetyl-7-phenylamino benzofuran derivatives as STAT3 inhibitors using scaffold fusion strategy. Further structure activity relationship study led to the discovery of compound C6, which displayed the most potent anti-proliferation activities against MDA-MB-468 cells (IC50 = 0.16 μM). Western blot assay demonstrated that C6 inhibited the activation of STAT3 (Tyr705) without influencing the phosphorylation of STAT1 (Tyr701). Further mechanistic studies indicated that C6 caused a notable G2/M cycle-arresting and early apoptosis in a concentration-dependent manner in MDA-MB-468 cells. Finally, molecular modelling study elucidated the binding mode of C6 in STAT3 SH2 domain.

Design, synthesis and biological evaluation of novel potent STAT3 inhibitors based on BBI608 for cancer therapy

Persistently activated signal transducer and activator of transcription 3 (STAT3) plays an important role in the development of multiple cancers, and therefore is a potential therapeutic target for cancer prevention. Herein, we report the rational design, synthesis, and biological evaluation of novel potent STAT3 inhibitors based on BBI608. Among them, compound A11 exhibited the most potent in vitro tumor cell growth inhibitory activities toward MDA-MB-231, MDA-MB-468 and HepG2 cells with IC50 values as low as 0.67 ± 0.02 μM, 0.77 ± 0.01 μM and 1.24 ± 0.16 μM, respectively. Fluorescence polarization (FP) assay validated the binding of compound A11 in STAT3 SH2 domain with the IC50 value of 5.18 μM. Further mechanistic studies indicated that A11 inhibited the activation of STAT3 (Y705), and thus reduced the expression of STAT3 downstream genes CyclinD1 and C-Myc. Simultaneously, it induced cancer cell S phase arrest and apoptosis in a concentration-dependent manner. An additional in vivo study revealed that A11 suppressed the MDA-MB-231 xenograft tumor growth in mice at the dose of 10 mg/kg (i.p.) without obvious body-weight loss. Finally, molecular docking study further elucidated the binding mode of A11 in STAT3 SH2 domain.

Trichothecin Inhibits Cancer-Related Features in Colorectal Cancer Development by Targeting STAT3.

Signal transducer and activator of transcription 3 (STAT3) is a transcription factor that contributes to cancer progression through multiple processes of cancer development, which makes it an attractive target for cancer therapy. The IL-6/STAT3 pathway is associated with an advanced stage in colorectal cancer patients. In this study, we identified trichothecin (TCN) as a novel STAT3 inhibitor. TCN was found to bind to the SH2 domain of STAT3 and inhibit STAT3 activation and dimerization, thereby blocking STAT3 nuclear translocation and transcriptional activity. TCN did not affect phosphorylation levels of STAT1. TCN significantly inhibited cell growth, arrested cell cycle at the G0/G1 phase, and induced apoptosis in HCT 116 cells. In addition, the capacities of colony formation, migration, and invasion of HCT 116 cells were impaired upon exposure to TCN with or without IL-6 stimulation. In addition, TCN treatment abolished the tube formation of HUVEC cells in vitro. Taken together, these results highlight that TCN inhibits various cancer-related features in colorectal cancer development in vitro by targeting STAT3, indicating that TCN is a promising STAT3 inhibitor that deserves further exploration in the future.

Imperatorin alleviates cancer cachexia and prevents muscle wasting via directly inhibiting STAT3

Skeletal muscle wasting is the most remarkable phenotypic feature of cancer cachexia that increases the risk of morbidity and mortality. Imperatorin (IMP), a main bioactive component of Angelica dahurica Radix, has been reported to possess several pharmacological effects including potential anti-colitis, anti-arthritis and anti-tumor activities. In this work, we demonstrated that IMP is a promising agent for the treatment of muscle wasting in cancer cachexia. IMP (5−20 μM) dose-dependently attenuated TCM-induced C2C12 myotube atrophy and prevented the induction of E3 ubiquitin ligases muscle RING-finger containing protein-1 (MuRF1) and muscle atrophy Fbox protein (Atrogin-1/MAFbx). Moreove, IMP administration significantly improved chief features of cancer cachexia in vivo, with significant prevention of the loss of body weight and deleterious wasting of multiple tissues, including skeletal muscle, fat and kidney and decreased expression of MuRF1 and Atrogin-1 in cachectic muscles. Cellular signaling pathway analysis showed that IMP selectively inhibited the phosphorylation of signal transducer and activator of transcription 3 (STAT3) in vitro and in vivo, and surface plasmon resonance (SPR) affinity experiments further demonstrated IMP bound to STAT3 in a concentration-dependent resonance manner. Molecular docking results revealed that IMP binds to the SH2 domain of STAT3, forming a hydrogen bond interaction with Arg-609, and a Sigma-Pi interaction with Lys-591. Mechanism analysis demonstrated that STAT3 overexpression markedly weakens the improvements of IMP on myotube atrophy and muscle wasting of cancer cachexia, indicating that STAT3 mediated the therapeutic effect of IMP. All these favorable results indicated that IMP is a new potential therapeutic candidate for cancer cachexia.

Structure-Based Discovery of SD-36 as a Potent, Selective, and Efficacious PROTAC Degrader of STAT3 Protein.

Signal transducer and activator of transcription 3 (STAT3) is a transcription factor and an attractive therapeutic target for cancer and other human diseases. Despite 20 years of persistent research efforts, targeting STAT3 has been very challenging. We report herein the structure-based discovery of potent small-molecule STAT3 degraders based upon the proteolysis targeting chimera (PROTAC) concept. We first designed SI-109 as a potent, small-molecule inhibitor of the STAT3 SH2 domain. Employing ligands for cereblon/cullin 4A E3 ligase and SI-109, we obtained a series of potent PROTAC STAT3 degraders, exemplified by SD-36. SD-36 induces rapid STAT3 degradation at low nanomolar concentrations in cells and fails to degrade other STAT proteins. SD-36 achieves nanomolar cell growth inhibitory activity in leukemia and lymphoma cell lines with high levels of phosphorylated STAT3. A single dose of SD-36 results in complete STAT3 protein degradation in xenograft tumor tissue and normal mouse tissues. SD-36 achieves complete and long-lasting tumor regression in the Molm-16 xenograft tumor model at well-tolerated dose-schedules. SD-36 is a potent, selective, and efficacious STAT3 degrader.

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.

Identification of a Novel Quinoxaline-Isoselenourea Targeting the STAT3 Pathway as a Potential Melanoma Therapeutic

The prognosis for patients with metastatic melanoma remains very poor. Constitutive signal transducer and activator of transcription 3 (STAT3) activation has been correlated to metastasis, poor patient survival, larger tumor size, and acquired resistance against vemurafenib (PLX-4032), suggesting its potential as a molecular target. We recently designed a series of isoseleno- and isothio-urea derivatives of several biologically active heterocyclic scaffolds. The cytotoxic effects of lead isoseleno- and isothio-urea derivatives (compounds 1 and 3) were studied in a panel of five melanoma cell lines, including B-RAFV600E-mutant and wild-type (WT) cells. Compound 1 (IC50 range 0.8–3.8 µM) showed lower IC50 values than compound 3 (IC50 range 8.1–38.7 µM) and the mutant B-RAF specific inhibitor PLX-4032 (IC50 ranging from 0.4 to >50 µM), especially at a short treatment time (24 h). These effects were long-lasting, since melanoma cells did not recover their proliferative potential after 14 days of treatment. In addition, we confirmed that compound 1 induced cell death by apoptosis using Live-and-Dead, Annexin V, and Caspase3/7 apoptosis assays. Furthermore, compound 1 reduced the protein levels of STAT3 and its phosphorylation, as well as decreased the expression of STAT3-regulated genes involved in metastasis and survival, such as survivin and c-myc. Compound 1 also upregulated the cell cycle inhibitor p21. Docking studies further revealed the favorable binding of compound 1 with the SH2 domain of STAT3, suggesting it acts through STAT3 inhibition. Taken together, our results suggest that compound 1 induces apoptosis by means of the inhibition of the STAT3 pathway, non-specifically targeting both B-RAF-mutant and WT melanoma cells, with much higher cytotoxicity than the current therapeutic drug PLX-4032.

Lycorine Displays Potent Antitumor Efficacy in Colon Carcinoma by Targeting STAT3.

Signal transducer and activator of transcription 3 (STAT3) is an attractive therapeutic target for cancer treatment. In this study, we identify lycorine is an effective inhibitor of STAT3, leading to repression of multiple oncogenic processes in colon carcinoma. Lycorine selectively inactivates phospho-STAT3 (Tyr-705), and subsequent molecular docking uncovers that lycorine directly binds to the SH2 domain of STAT3. Consequently, we find that lycorine exhibits anti-proliferative activity and induces cell apoptosis on human colorectal cancer (CRC) in vitro. Lycorine induces the activation of the caspase-dependent mitochondrial apoptotic pathway, as indicated by activation of caspase and increase of the ratio of Bax/Bcl-2 and mitochondrial depolarization. Overexpressing STAT3 greatly blocks these effects by lycorine in CRC cells. Finally, lycorine exhibits a potential therapeutic effect in xenograft colorectal tumors by targeting STAT3 without observed toxicity. Taken together, the present study indicates that lycorine acts as a promising inhibitor of STAT3, which blocks tumorigenesis in colon carcinoma.

Bt354 as a new STAT3 signaling pathway inhibitor against triple negative breast cancer

Inhibition of the signal transducer and activator of transcription 3 (STAT3) signalling pathway has been considered as a novel therapeutic strategy to treat human cancers with constitutively active STAT3. In this study, we screened 1563 compounds and identified Bt354 as a new small-molecule inhibitor of the STAT3 signalling pathway. The effect of Bt354 on STAT3 activity was initially screened and Bt354 significantly inhibited STAT3 activity in a dual luciferase assay. Bt354 inhibited the proliferation of cancer cells in a dose- and time-dependent manner. The phosphorylation of STAT3 at Y705 was suppressed without affecting the phosphorylation of STAT3 at S727 in breast cancer cells. Furthermore, Bt354 inhibited the nuclear translocation of STAT3 and consequently induced cell growth inhibition, apoptosis and cell cycle G2/M arrest in triple negative breast cancer cells. In vivo, Bt354 also inhibited tumour growth in MDA-MB-435 and MDA-MB-231 xenograft mice without affecting body weight. Computational modelling showed that Bt354 could bind to the SH2 domain of STAT3. These findings suggest that Bt354 may be a potent anticancer agent for STAT3-activated triple negative breast cancer cells.