A novel small molecule, LLL12, inhibits STAT3 phosphorylation and activities and exhibits potent growth-suppressive activity in human cancer cells

Recent advances in the discovery of small molecules targeting glioblastoma

Glioblastoma (GBM) is one of the most common central nervous system cancers. It is characterized as a fast-growing tumor that arises from multiple cell types with neural stem-cell-like properties. Additionally, GBM tumors are highly invasive, which is attributed to the presence of glioblastoma stem cells that makes surgery ineffective in most cases. Currently, temozolomide is the unique chemotherapy option approved by the U.S. Food and Drug Administration for GBM treatment. This review analyzes the emergence and development of new synthetic small molecules discovered as promising anti-glioblastoma agents. A number of compounds were described herein and grouped according to the main chemical class used in the drug discovery process. Importantly, we focused only on synthetic compounds published in the last 10 years, thus excluding natural products. Furthermore, we included in this review only those most biologically active compounds with proven in vitro and/or in vivo efficacy.

NAMPT signaling is critical for the proangiogenic activity of tumor-associated neutrophils

Tumor-associated neutrophils (TANs) regulate many processes associated with tumor progression, and depending on the microenvironment, they can exhibit pro- or antitumor functions. However, the molecular mechanisms regulating their tumorigenicity are not clear. Using transplantable tumor models, we showed here that nicotinamide phosphoribosyltransferase (NAMPT), a molecule involved in CSF3R downstream signaling, is essential for tumorigenic conversion of TANs and their pro-angiogenic switch. As a result tumor vascularization and growth are strongly supported by these cells. Inhibition of NAMPT in TANs leads to their antitumor conversion. Adoptive transfer of such TANs into B16F10-tumor bearing mice attenuates tumor angiogenesis and growth. Of note, we observe that the regulation of NAMPT signaling in TANs, and its effect on the neutrophil tumorigenicity, are analogous in mice and human. NAMPT is up-regulated in TANs from melanoma and head-and-neck tumor patients, and its expression positively correlates with tumor stage. Mechanistically, we found that targeting of NAMPT suppresses neutrophil tumorigenicity by inhibiting SIRT1 signaling, thereby blocking transcription of pro-angiogenic genes. Based on these results, we propose that NAMPT regulatory axis is important for neutrophils to activate angiogenic switch during early stages of tumorigenesis. Thus, identification of NAMPT as the critical molecule priming protumor functions of neutrophils provides not only mechanistic insight into the regulation of neutrophil tumorigenicity, but also identifies a potential pathway that may be targeted therapeutically in neutrophils. This, in turn, may be utilized as a novel mode of cancer immunotherapy.

A new synthetic derivative of cryptotanshinone KYZ3 as STAT3 inhibitor for triple-negative breast cancer therapy

Silencing STAT3 is confirmed as a promising therapeutic strategy for triple-negative breast cancer (TNBC) therapy to address the issue of its poor prognosis. In this study, the natural product cryptotanshinone was firstly remodeled and modified as a more effective STAT3 inhibitor by structure-based strategy. The synthetic derivative KYZ3 had 22-24-fold increase in antitumor activity than cryptotanshinone on two TNBC cell lines but had little effect on normal breast epithelial MCF-10A cells. Further investigation showed that KYZ3 inhibited persistent STAT3 phosphorylation. It also prevented the STAT3 protein nuclear translocation to regulate the expressions of the target oncogenes including Bax and Bcl-2. Furthermore, KYZ3 inhibited TNBC cell metastasis by decreasing the levels of MMP-9 which were directly regulated by activated STAT3. A STAT3 plasmid transfecting assay suggested that KYZ3 induced tumor cell apoptosis mainly by targeting STAT3. Finally, KYZ3 suppressed the growth of tumors resulting from subcutaneous implantation of MDA-MB-231 cells in vivo. Taken together, KYZ3 may be a promising cancer therapeutic agent for TNBC.

Targeting signal-transducer-and-activator-of-transcription 3 sensitizes human cutaneous melanoma cells to BRAF inhibitor

Melanoma treatment with the BRAF V600E inhibitor vemurafenib provides therapeutic benefits but the common emergence of drug resistance remains a challenge. To define molecular mechanisms of vemurafenib resistance, we generated A375-R, WM35-R cell lines resistant to vemurafenib and show that the phosphorylated (p)-STAT3 was upregulated in these cells in vitro and in vivo. In particular, activation of the Signal-transducer-and-activator-of-transcription 3 (STAT3) pathway was associated with vemurafenib resistance. Inhibition of this pathway with STAT3-specific siRNA (shRNA) sensitized A375-R, WM35-R cells to vemurafenib and induced apoptosis in vitro and in vivo. Moreover, targeting STAT3 induced expression of miR-579-3p and elicited resistance to vemurafenib. However, targeting microRNA (miR)-579-3p with anti-miR-579-3p reversed the resistance to vemurafenib. Together, these results indicated that STAT3-mediated downexpression of miR-579-3p caused resistance to vemurafenib. Our findings suggest novel approaches to overcome resistance to vemurafenib by combining vemurafenib with STAT3 sliencing or miR-579-3p overexpression.

YL064 directly inhibits STAT3 activity to induce apoptosis of multiple myeloma cells

Aberrant activation of signal transducer and activator of transcription 3 (STAT3) plays a critical role in the proliferation and survival of multiple myeloma. And inactivation of STAT3 is considered a promising strategy for the treatment of multiple myeloma. Here we show that the sinomenine derivative YL064 could selectively reduce the cell viability of multiple myeloma cell lines and primary multiple myeloma cells. Moreover, YL064 also induces cell death of myeloma cells in the presence of stromal cells. Western blot analysis showed that YL064 inhibited the constitutive activation and IL-6-induced activation of STAT3, reflected by the decreased phosphorylation of STAT3 on Tyr705. Consistent with this, YL064 inhibited the nuclear translocation of STAT3 and the expression of STAT3 target genes, such as cyclin D1 and Mcl-1. Using biotin- and FITC-labeled YL064, we found that YL064 could pull-down STAT3 from myeloma cells and colocalized with STAT3, suggesting that YL064 directly targets STAT3. Cellular thermal shift assay further demonstrated the engagement of YL064 to STAT3 in cells. Molecular docking studies indicated that YL064 may interact with STAT3 in its SH2 domain, thereby inhibiting the dimerization of STAT3. Finally, YL064 inhibited the growth of human myeloma xenograft in vivo. Taken together, this study demonstrated that YL064 may be a promising candidate compound for the treatment of multiple myeloma by directly targeting STAT3.

A high-throughput fluorescence polarization assay for discovering inhibitors targeting the DNA-binding domain of signal transducer and activator of transcription 3 (STAT3)

Anti-cancer drug discovery efforts to directly inhibit the signal transducer and activator of transcription 3 (STAT3) have been active for over a decade following the discovery that 70% of cancers exhibit elevated STAT3 activity. The majority of research has focused on attenuating STAT3 activity through preventing homo-dimerization by targeting the SH2 or transcriptional activation domains. Such dimerization inhibitors have not yet reached the market. However, an alternative strategy focussed on preventing STAT3 DNA-binding through targeting the DNA-binding domain (DBD) offers new drug design opportunities. Currently, only EMSA and ELISA-based methods have been implemented with suitable reliability to characterize STAT3 DBD inhibitors. Herein, we present a new orthogonal, fluorescence polarization (FP) assay suitable for high-throughput screening of molecules. This assay, using a STAT3^127-688 construct, was developed and optimized to screen molecules that attenuate the STAT3:DNA association with good reliability (Z’ value > 0.6) and a significant contrast (signal-to-noise ratio > 15.0) at equilibrium. The assay system was stable over a 48 hour period. Significantly, the assay is homogeneous and simple to implement for high-throughput screening compared to EMSA and ELISA. Overall, this FP assay offers a new way to identify and characterize novel molecules that inhibit STAT3:DNA association.

A novel small inhibitor, LLL12, targets STAT3 in non-small cell lung cancer in vitro and in vivo

Lung cancer is the leading cause of cancer-associated mortality worldwide. Despite the development of novel molecular therapies, the prognosis for patients with locally advanced or metastatic lung cancer remains poor. Therefore, the identification of novel therapeutic approaches is required. In numerous types of cancer, the constitutive activation of signal transducer and activator of transcription 3 (STAT3) signaling serves as a potent therapeutic target. The present study aimed to characterize the suppressive role of LLL12, a STAT3 small molecule inhibitor, in lung cancer cell proliferation and tumor growth. The mechanism of STAT3 signaling modulation by LLL12 was also investigated. The antitumor activity of LLL12 was revealed to take place via inhibition of lung cancer cell proliferation and migration in vitro. High and low doses of LLL12 significantly reduced tumor volume and weight in xenograft mice compared with that in the control group. Furthermore, LLL12 was demonstrated to reduce the level of STAT3 phosphorylation. These results suggested that LLL12 inhibited the proliferation and migration of A549 cells, and the increase in tumor volume in nude mice with lung cancer. This may be associated with the inhibitory effect of STAT3 phosphorylation and the expression of STAT3. The results of the present study suggest that constitutive STAT3 signaling is required for lung cancer cell survival and migration, and tumor growth in vivo. It is also indicated that LLL12 has clinical potential as a novel targeted therapy.

RNAi screening identifies a mechanosensitive ROCK-JAK2-STAT3 network central to myofibroblast activation

Myofibroblasts play key roles in wound healing and pathological fibrosis. Here, we used an RNAi screen to characterize myofibroblast regulatory genes, using a high-content imaging approach to quantify α-smooth muscle actin stress fibers in cultured human fibroblasts. Screen hits were validated on physiological compliance hydrogels, and selected hits tested in primary fibroblasts from patients with idiopathic pulmonary fibrosis. Our RNAi screen led to the identification of STAT3 as an essential mediator of myofibroblast activation and function. Strikingly, we found that STAT3 phosphorylation, while responsive to exogenous ligands on both soft and stiff matrices, is innately active on a stiff matrix in a ligand/receptor-independent, but ROCK- and JAK2-dependent fashion. These results demonstrate how a cytokine-inducible signal can become persistently activated by pathological matrix stiffening. Consistent with a pivotal role for this pathway in driving persistent fibrosis, a STAT3 inhibitor attenuated murine pulmonary fibrosis when administered in a therapeutic fashion after bleomycin injury. Our results identify novel genes essential for the myofibroblast phenotype, and point to STAT3 as an important target in pulmonary fibrosis and other fibrotic diseases.

Targeting STAT3 restores BRAF inhibitor sensitivity through miR-759-3p in human cutaneous melanoma cells

Melanoma treatment with the BRAF V600E inhibitor vemurafenib provides therapeutic benefits, but the common emergence of drug resistance remains a challenge. To define molecular mechanisms of vemurafenib resistance, we generated A375-R, WM35-R cell lines resistant to vemurafenib and found that the p-STAT3 was upregulated in these cells in vitro and in vivo. In particular, activation of the STAT3 pathway was associated with vemurafenib resistance. Inhibition of this pathway with STAT3-specific siRNA (shRNA) sensitized A375-R, WM35-R cells to vemurafenib and induced apoptosis in vitro and in vivo. Moreover, targeting STAT3 induced expression of miR-579-3p and elicited resistance to vemurafenib. However, targeting miR-579-3p with anti- miR-579-3p reversed the resistance to vemurafenib. Together, these results indicate that STAT3-mediated downexpression of miR-579-3p caused resistance to vemurafenib. Our findings suggest novel approaches to overcome resistance to vemurafenib by combining vemurafenib with STAT3 silencing or miR-579-3p overexpression.

Silibinin is a direct inhibitor of STAT3

We herein combined experimental and computational efforts to delineate the mechanism of action through which the flavonolignan silibinin targets STAT3. Silibinin reduced IL-6 inducible, constitutive, and acquired feedback activation of STAT3 at tyrosine 705 (Y705). Silibinin attenuated the inducible phospho-activation of Y705 in GFP-STAT3 genetic fusions without drastically altering the kinase activity of the STAT3 upstream kinases JAK1 and JAK2. A comparative computational study based on docking and molecular dynamics simulation over 14 different STAT3 inhibitors (STAT3i) predicted that silibinin could directly bind with high affinity to both the Src homology-2 (SH2) domain and the DNA-binding domain (DBD) of STAT3. Silibinin partially overlapped with the cavity occupied by other STAT3i in the SH2 domain to indirectly prevent Y705 phosphorylation, yet showing a unique binding mode. Moreover, silibinin was the only STAT3i predicted to establish direct interactions with DNA in its targeting to the STAT3 DBD. The prevention of STAT3 nuclear translocation, the blockade of the binding of activated STAT3 to its consensus DNA sequence, and the suppression of STAT3-directed transcriptional activity confirmed silibinin as a direct STAT3i. The unique characteristics of silibinin as a bimodal SH2- and DBD-targeting STAT3i make silibinin a promising lead for designing new, more effective STAT3i.

Targeted inhibition of STATs and IRFs as a potential treatment strategy in cardiovascular disease

Key factors contributing to early stages of atherosclerosis and plaque development include the pro-inflammatory cytokines Interferon (IFN)α, IFNγ and Interleukin (IL)-6 and Toll-like receptor 4 (TLR4) stimuli. Together, they trigger activation of Signal Transducer and Activator of Transcription (STAT) and Interferon Regulatory Factor (IRF) families. In particular, STAT1, 2 and 3; IRF1 and 8 have recently been recognized as prominent modulators of inflammation, especially in immune and vascular cells during atherosclerosis. Moreover, inflammation-mediated activation of these STATs and IRFs coordinates a platform for synergistic amplification leading to pro-atherogenic responses.

Searches for STAT3-targeting compounds, exploring the pTyr-SH2 interaction area of STAT3, yielded many small molecules including natural products. Only a few inhibitors for other STATs, but none for IRFs, are described. Promising results for several STAT3 inhibitors in recent clinical trials predicts STAT3-inhibiting strategies may find their way to the clinic. However, many of these inhibitors do not seem STAT-specific, display toxicity and are not very potent. This illustrates the need for better models, and screening and validation tools for novel STAT and IRF inhibitors.

This review presents a summary of these findings. It postulates STAT1, STAT2 and STAT3 and IRF1 and IRF8 as interesting therapeutic targets and targeted inhibition could be a potential treatment strategy in CVDs. In addition, it proposes a pipeline approach that combines comparative in silico docking of STAT-SH2 and IRF-DBD models with in vitro STAT and IRF activation inhibition validation, as a novel tool to screen multi-million compound libraries and identify specific inhibitors for STATs and IRFs.

The role of STAT3 in leading the crosstalk between human cancers and the immune system

The development and progression of human cancers are continuously and dynamically regulated by intrinsic and extrinsic factors. As a converging point of multiple oncogenic pathways, signal transducer and activator of transcription 3 (STAT3) is constitutively activated both in tumor cells and tumor-infiltrated immune cells. Activated STAT3 persistently triggers tumor progression through direct regulation of oncogenic gene expression. Apart from its oncogenic role in regulating gene expression in tumor cells, STAT3 also paves the way for human cancer growth through immunosuppression. Activated STAT3 in immune cells results in inhibition of immune mediators and promotion of immunosuppressive factors. Therefore, STAT3 modulates the interaction between tumor cells and host immunity. Accumulating evidence suggests that targeting STAT3 may enhance anti-cancer immune responses and rescue the suppressed immunologic microenvironment in tumors. Taken together, STAT3 has emerged as a promising target in cancer immunotherapy.

A novel small molecule STAT3 inhibitor, LY5, inhibits cell viability, colony formation, and migration of colon and liver cancer cells

Signal Transducer and Activator of Transcription 3 (STAT3) is persistently activated in human liver and colon cancer cells and is required for cancer cell viability, survival and migration. Therefore, inhibition of STAT3 signaling may be a viable therapeutic approach for these two cancers. We recently designed a non-peptide small molecule STAT3 inhibitor, LY5, using in silico site-directed Fragment-based drug design (FBDD). The inhibitory effect on STAT3 phosphorylation, cell viability, migration and colony forming ability by LY5 were examined in human liver and colon cancer cells. We demonstrated that LY5 inhibited constitutive Interleukin-6 (IL-6)-induced STAT3 phosphorylation, STAT3 nuclear translocation, decreased STAT3 downstream targeted gene expression and induced apoptosis in liver and colon cancer cells. LY5 had little effect on STAT1 phosphorylation mediated by IFN-γ. Inhibition of persistent STAT3 phosphorylation by LY5 also inhibited colony formation, cell migration, and decreased the viability of liver cancer and colon cancer cells. Furthermore, LY5 inhibited STAT3 phosphorylation and suppressed colon tumor growth in a mouse model in vivo. Our results suggest that LY5 is a potent STAT3 inhibitor and may be a potential drug candidate for liver and colon cancer therapy.

Drug sensitivity profiling identifies potential therapies for lymphoproliferative disorders with overactive JAK/STAT3 signaling

Constitutive JAK/STAT3 signaling contributes to disease progression in many lymphoproliferative disorders. Recent genetic analyses have revealed gain-of-function STAT3 mutations in lymphoid cancers leading to hyperactivation of STAT3, which may represent a potential therapeutic target. Using a functional reporter assay, we screened 306 compounds with selective activity against various target molecules to identify drugs capable of inhibiting the cellular activity of STAT3. Top hits were further validated with additional models including STAT3-mutated natural killer (NK)-cell leukemia/lymphoma cell lines and primary large granular lymphocytic (LGL) leukemia cells to assess their ability to inhibit STAT3 phosphorylation and STAT3 dependent cell viability. We identified JAK, mTOR, Hsp90 and CDK inhibitors as potent inhibitors of both WT and mutant STAT3 activity. The Hsp90 inhibitor luminespib was highly effective at reducing the viability of mutant STAT3 NK cell lines and LGL leukemia patient samples. Luminespib decreased the phosphorylation of mutant STAT3 at Y705, whereas JAK1/JAK2 inhibitor ruxolitinib had reduced efficacy on mutant STAT3 phosphorylation. Additionally, combinations involving Hsp90, JAK and mTOR inhibitors were more effective at reducing cell viability than single agents. Our findings show alternative approaches to inhibit STAT3 activity and suggest Hsp90 as a therapeutic target in lymphoproliferative disorders with constitutively active STAT3.

MicroRNA-218 functions as a tumor suppressor in lung cancer by targeting IL-6/STAT3 and negatively correlates with poor prognosis

Background

Aberrant expression of microRNAs in different human cancer types has been widely reported. MiR-218 acts as a tumor suppressor in diverse human cancer types impacting regulation of multiple genes in oncogenic pathways. Here, we evaluated the expression and function of miR-218 in human lung cancer and ALDH positive lung cancer cells to understand the potential mechanisms responsible for disease pathology. Also, the association between its host genes and the target genes could be useful towards the better understanding of prognosis in clinical settings.

Methods

Publicly-available data from The Cancer Genome Atlas (TCGA) was mined to compare the levels of miR-218 and its host gene SLIT2/3 between lung cancer tissues and normal lung tissues. Transfection of miR-218 to investigate its function in lung cancer cells was done and in vivo effects were determined using miR-218 expressing lentiviruses. Aldefluor assay and Flow cytometry was used to quantify and enrich ALDH positive lung cancer cells. Levels of miR-218, IL-6R, JAK3 and phosphorylated STAT3 were compared in ALDH1A1 positive and ALDH1A1 negative cells. Overexpression of miR-218 in ALDH positive cells was carried to test the survival by tumorsphere culture. Finally, utilizing TCGA data we studied the association of target genes of miR-218 with the prognosis of lung cancer.

Results

We observed that the expression of miR-218 was significantly down-regulated in lung cancer tissues compared to normal lung tissues. Overexpression of miR-218 decreased cell proliferation, invasion, colony formation, and tumor sphere formation in vitro and repressed tumor growth in vivo. We further found that miR-218 negatively regulated IL-6 receptor and JAK3 gene expression by directly targeting the 3′-UTR of their mRNAs. In addition, the levels of both miR-218 host genes and the components of IL-6/STAT3 pathway correlated with prognosis of lung cancer patients.

Conclusions

MiR-218 acts as a tumor suppressor in lung cancer via IL-6/STAT3 signaling pathway regulation.

Electronic supplementary material

The online version of this article (doi:10.1186/s12943-017-0710-z) contains supplementary material, which is available to authorized users.

The role of STAT3 in glioblastoma progression through dual influences on tumor cells and the immune microenvironment

Glioblastoma multiforme (GBM) is the most aggressive form of cancer that begins within the brain; generally, the patient has a dismal prognosis and limited therapeutic options. Signal transducer and activator of transcription 3 (STAT3) is a critical mediator of tumorigenesis, tumor progression, and suppression of anti-tumor immunity in GBM. In a high percentage of GBM cells and tumor microenvironments, persistent activation of STAT3 induces cell proliferation, anti-apoptosis, glioma stem cell maintenance, tumor invasion, angiogenesis, and immune evasion. This makes STAT3 an attractive therapeutic target and a prognostic indicator in GBM. Targeting STAT3 affords an opportunity to disrupt multiple pro-oncogenic pathways at a single molecular hub. Unfortunately, there are no successful STAT3 inhibitors currently in clinical trials. However, strong clinical evidence implicating STAT3 as a major factor in GBM justifies the identification of safe and effective strategies for inhibiting STAT3.

Inhibition of STAT3 signaling pathway by ursolic acid suppresses growth of hepatocellular carcinoma

The signal transducer and activator of transcription 3 (STAT3) has been found to be constitutively active in liver cancer. There is no STAT3 inhibitors approved to be used clinically for the treatment or prevention of liver cancer. Some dietary compounds including ursolic acid (UA) have been reported to inhibit the growth of cancer cells. However, whether UA could inhibit STAT3 phosphorylation in hepatocellular carcinoma has not been reported. The inhibitory effects of UA on STAT3 phosphorylation, along with cell viability, migration, colony formation in vitro, as well as tumor growth in vivo were examined in human liver cancer cell lines. Our data showed that UA inhibited the P-STAT3 induced by interleukin-6 (IL-6) in Hep3B liver cancer cells which express very low basal level of P-STAT3. The constitutive STAT3 phosphorylation was also inhibited by UA in HEPG2, 7721 and Huh7 human liver cancer cell lines. UA decreased the expression of downstream target genes of STAT3, such as Bcl-2, Bcl-xl and survivin in general, with difference in these cell lines. UA also suppressed cell viability, cell migration and colony formation in liver cancer cells. Furthermore, UA suppressed STAT3 phosphorylation and HEPG2 tumor growth by oral daily treatment in vivo. UA, which exists widely in fruits and herbs, could inhibit STAT3 activation and the growth of human liver cancer cells in vitro and in vivo. It might be a potential health care product that could be used daily for prevention, as well as a promising candidate for chemotherapy of liver cancer.

Inhibition of IL-6/STAT3 signaling in human cancer cells using Evista

Persistent activation of IL-6/STAT3 signaling pathway has been frequently detected in human cancer including breast cancer, colon cancer and multiple myeloma. IL-6/STAT3 can be a promising target for cancer prevent and treatment. However, few STAT3 inhibitors with high efficiency, specificity and safety is available for present clinical cancer therapy. Evista (Raloxifene·HCl) is known as selective estrogen receptor modulator which has been used for the prevention and treatment of osteoporosis and was approved for reducing the risk of invasive breast cancer. Our previous study found that Raloxifene inhibited IL-6/GP130 interaction, resulting in blockade of STAT3 phosphorylation. In our present study, we examined the effect on IL-6/GP130/STAT3 signaling pathway and cancer cell viability with Evista. We first demonstrated Evista inhibited constitutive activation of STAT3 in breast cancer cell line MDB-MB-231, colon cancer cell line HCT116 and multiple myeloma cancer cell line U266. Evista also inhibited phosphorylation of STAT3 induced by IL-6 in MCF-7, HT29 and MM.1S cancer cell lines. Induction of apoptosis was exerted in MDA-MB-231, HCT116 and U266 as evidenced by increased caspase-3 cleavage. However, Evista did not inhibit STAT1, STAT2, STAT4 or STAT6 phosphorylation elicited by IFN-α, IFN-γ and IL-4, nor phosphorylation of STAT3 induced by LIF in MCF-7 cell lines. Evista attenuated STAT3 phosphorylation, decreased STAT3 transcriptional activity but much less in pGL3 and AP1 transcriptional luciferase activity, and decreased cell viability in vitro. These results suggest that it may be possible for Evista to emerge as a chemoprevention agent for breast cancer and other cancers such as colon cancer or multiple myeoloma by targeting IL-6/STAT3 signaling.

HIV-1 Infection Primes Macrophages Through STAT Signaling to Promote Enhanced Inflammation and Viral Replication

Macrophages play important roles in HIV-1 pathogenesis as targets for viral replication and mediators of chronic inflammation. Similar to IFNγ-priming, HIV-1 primes macrophages, resulting in hyperresponsiveness to subsequent toll-like receptor (TLR) stimulation and increased inflammatory cytokine production. However, the specific molecular mechanism of HIV-1 priming and whether cells must be productively infected or if uninfected bystander cells also are primed by HIV-1 remains unclear. To explore these questions, human macrophages were primed by IFNγ or infected with HIV-1 before activation by TLR ligands. Transcriptome profiling by microarray revealed a gene expression profile for IFNγ-primed cells that was further modulated by the addition of lipopolysaccharide (LPS). HIV-1 infection elicited a gene expression profile that correlated strongly with the profile induced by IFNγ (r = .679, p = .003). Similar to IFNγ, HIV-1 enhanced TLR ligand-induced tumor necrosis factor (TNF) protein expression and release. Increased TNF production was limited to productively infected cells. Specific signal transducer and activator of transcription (STAT)1 and STAT3 inhibitors suppressed HIV-1-mediated enhancement of TLR-induced TNF expression as well as HIV-1 replication. These findings indicate that viral replication and inflammation are linked through a common IFNγ-like, STAT-dependent pathway and that HIV-1-induced STAT1 and STAT3 signaling are involved in both inflammation and HIV-1 replication. Systemic innate immune activation is a hallmark of active HIV-1 replication. Our study shows that inflammation may develop as a consequence of HIV-1 triggering STAT-IFN pathways to support viral replication.

Discovery of monocarbonyl curcumin-BTP hybrids as STAT3 inhibitors for drug-sensitive and drug-resistant breast cancer therapy

Signal transducer and activator of transcription 3 (STAT3) is a well-known antitumor target. Exogenous ROS insult can lead to selective cytotoxicity against cancer cells. A combination of STAT3 inhibition and “oxidation therapy” may be a new strategy to address the multidrug-resistance issue due to their important roles in the survival and drug resistance of cancer cells. Here, a series of novel curcumin-BTP hybrids were designed and evaluated as STAT3 inhibitors with ROS production activity. Compound 6b exerted the best antitumor activity and selectivity for MCF-7 and MCF-7/DOX cells (IC₅₀ = 0.52 μM and 0.40 μM, respectively), while its IC₅₀ value for MCF-10A breast epithelial cells was 7.72 μM. Furthermore, compound 6b suppressed STAT3 phosphorylation, nuclear translocation and DNA-binding activity and the expression of STAT3 specific oncogenes. Increases in the level of IL-6-induced p-STAT3 were also inhibited by 6b without influencing IFN-γ-induced p-STAT1 expression. Additionally, 6b effectively promoted intracellular ROS accumulation, induced cancer cell apoptosis and cell cycle arrest, abolished the colony formation ability of breast cancer cells, and inhibited P-gp expression in MCF-7/DOX cells. Finally, 6b suppressed the growth of implanted human breast cancer in vivo. Our findings highlight that 6b may be a promising therapeutic agent for drug-sensitive and drug-resistant breast cancers.

Endogenously Expressed IL-4Rα Promotes the Malignant Phenotype of Human Pancreatic Cancer In Vitro and In Vivo

Exogenous interleukin-4 (IL-4) has been demonstrated to affect the growth of different human malignancies including pancreatic cancer cells. The aim of our study was to determine the role of endogenously expressed IL-4-receptor-α-chain (IL-4Rα) in pancreatic cancer cells. IL-4Rα-suppression was achieved by generating Capan-1 cells stably expressing shRNA targeting IL-4Rα. The malignant phenotype was characterized by assessing growth properties, directional and non-directional cell movement in vitro and tumor growth in vivo. Signaling pathways were analyzed upon IL-4 and IL-13 stimulation of wildtype (WT) and control-transfected cells compared to IL-4Rα-knockdown cells. Silencing of IL-4Rα resulted in reduced anchorage-dependent cell growth (p < 0.05) and reduced anchorage-independent colony size (p < 0.001) in vitro. Moreover, cell movement and migration was inhibited. IL-4 and IL-13 stimulation of Capan-1-WT cells induced activation of similar pathways like stimulation with Insulin-like growth factor (IGF)-I. This activation was reduced after IL-4Rα downregulation while IGF-I signaling seemed to be enhanced in knockdown-clones. Importantly, IL-4Rα silencing also significantly suppressed tumor growth in vivo. The present study indicates that endogenously expressed IL-4 and IL-4Rα contribute to the malignant phenotype of pancreatic cancer cells by activating diverse pro-oncogenic signaling pathways. Addressing these pathways may contribute to the treatment of the disease.

Ultrasound mediated delivery of oxygen and LLL12 loaded stimuli responsive microdroplets for the treatment of hypoxic cancer cells

LLL12 exhibits high specificity for inhibiting STAT3 phosphorylation and dimerization, and inducing apoptosis to constitutively activated STAT3 cancer cells without cytotoxicity to normal cells with dormant STAT3. However, clinical deployment of LLL12 in cancer treatment is hindered by its low bioavailability and hypoxia-induced resistance. To overcome these limitations, we encapsulate both oxygen and LLL12 in stimuli responsive microdroplets (SRMs) by a gas-driven coaxial flow focusing (CFF) process for ultrasound mediated treatment of hypoxic cancer cells. Our benchtop experiments demonstrate that the CFF process is able to produce SRMs with uniform size distribution, large oxygen loading capacity, high LLL12 encapsulation efficiency, well protection of bioactivity, and steadily long shelf time. The in vitro therapeutic studies in pancreatic cancer cells (PANC-1 and CAPAN-1) demonstrate the immediate release of oxygen and LLL12 in exposure to therapeutic ultrasound pulses as well as the improved anticancer effects under hypoxic conditions. The findings suggest that the proposed oxygen and LLL12 loaded SRMs provide a promising drug delivery strategy for more effective treatment of hypoxic cancer cells.

The Antiproliferative and Colony-suppressive Activities of STAT3 Inhibitors in Human Cancer Cells Is Compromised Under Hypoxic Conditions

Constitutive activation of signal transducer and activator of transcription 3 (STAT3) has been indicated as a novel cancer drug target, since it plays an important role in diverse oncogenic processes including survival, cell proliferation and migration. Emerging STAT3 inhibitors have demonstrated efficacy in cancer cells and animal tumor models. It is well known that most solid tumors are characterized by hypoxia, but it is not clear if hypoxic conditions affect activity of STAT3 inhibitors. To examine this, two STAT3 inhibitors were tested to investigate their inhibitory efficacy in cancer cells grown under hypoxic conditions compared with those without hypoxia. Cell proliferation, colony formation and western blot assays were performed to examine the differences in the cell viability, proliferation and proteins in the STAT3 pathway. Under hypoxic conditions, the half-maximal inhibitory concentration values for both STAT3 inhibitors were increased compared to normoxic conditions in human pancreatic cancer, medulloblastoma and sarcoma cell lines. In addition, the ability of both STAT3 inhibitors to inhibit colony formation in pancreatic cancer, medulloblastoma and sarcoma cell lines was reduced under hypoxic conditions when compared to cells under normoxic conditions. Furthermore, there was an increase in phosphorylated STAT3 levels in cancer cells under hypoxic conditions, suggesting this may be one of the mechanisms of resistance. In summary, the results presented here provide a novel finding of STAT3 inhibitor activity under hypoxic conditions and indicate that under such low oxygen conditions, the anticancer efficacy of STAT3 inhibitors was indeed hampered. These results highlight the need to develop new therapeutic strategies to overcome the resistance of cancer cells to STAT3 inhibitors under hypoxic conditions.

Evaluation of quantitative assays for the identification of direct signal transducer and activator of transcription 3 (STAT3) inhibitors

In many forms of cancer the signal transducer and activator of transcription 3 (STAT3) transcription factor remains constitutively active, driving cancer survival and progression. The critical role of STAT3 in tumorigenesis has prompted a campaign of drug discovery programs to identify small molecules that disrupt the function of STAT3, with more recent efforts focusing on direct STAT3 inhibition. There are two target binding sites for direct STAT3 inhibitors: the SH2 dimerization domain and the DNA-binding domain. An in vitro fluorescence polarization assay, using recombinant STAT3 protein, has successfully identified compounds that target the SH2 domain; however, no assay has been reported to identify inhibitors that bind the DNA-binding domain. The lack of such a quantitative assay has limited the identification and development of STAT3 DNA-binding domain inhibitors. Here, we report a modified DNA-binding ELISA to incorporate recombinant STAT3 protein to evaluate small molecules that prevent STAT3-DNA binding. The concomitant use of the ELISA and fluorescence polarization assay enables the classification of direct STAT3 inhibitors by their site of action. Our data provide further support that niclosamide inhibits STAT3 through interaction with the DNA-binding domain. Furthermore, the ELISA can support medicinal chemistry efforts by identifying DNA-binding domain inhibitors and allowing the determination of an IC50 value, supporting the ranking of inhibitors and development of structure-activity relationships. Therefore, we propose a tandem evaluation approach to identify small molecules that target the SH2 domain or the DNA-binding domain of STAT3, which allows for quantitative evaluation of candidate STAT3 inhibitors.

STAT3 as a potential therapeutic target in ALDH+ and CD44+/CD24+ stem cell-like pancreatic cancer cells

Persistent activation of signal transducers and activators of transcription 3 (STAT3) is commonly detected in many types of cancer including pancreatic cancer. Whether STAT3 is activated in stem cell-like pancreatic cancer cells and the effect of STAT3 inhibition, is still unknown. Flow cytometry was used to isolate pancreatic cancer stem-like cells which are identified by both aldehyde dehydrogenase (ALDH)-positive (ALDH⁺) as well as cluster of differentiation (CD) 44-positive/CD24-positive subpopulations (CD44⁺/CD24⁺). STAT3 activation and the effects of STAT3 inhibition by STAT3 inhibitors, LLL12, FLLL32, and Stattic in ALDH⁺ and CD44⁺/CD24⁺ cells were examined. Our results showed that ALDH⁺ and CD44⁺/CD24⁺ pancreatic cancer stem-like cells expressed higher levels of phosphorylated STAT3, an active form of STAT3, compared to ALDH-negative (ALDH⁻) and CD44-negative/CD24-negative (CD44⁻/CD24⁻) pancreatic cancer cells, suggesting that STAT3 is activated in pancreatic cancer stem-like cells. Small molecular STAT3 inhibitors inhibited STAT3 phosphorylation, STAT3 downstream target gene expression, cell viability, and tumorsphere formation in ALDH⁺ and CD44⁺/CD24⁺ cells. Our results indicate that STAT3 is a novel therapeutic target in pancreatic cancer stem-like cells and inhibition of activated STAT3 in these cells by STAT3 inhibitors may offer an effective treatment for pancreatic cancer.

4-Carbonyl-2,6-dibenzylidenecyclohexanone derivatives as small molecule inhibitors of STAT3 signaling pathway

Inhibition of STAT3 signaling pathway is proposed to be a promising strategy for cancer treatment. In this study, a series of 4-carbonyl-2,6-dibenzylidenecyclohexanone derivatives were prepared and evaluated as anticancer agents. The most potent compound 13r was discovered to exhibit antiproliferative activity against a broad rang of cancer cell lines and relatively low cytotoxicity against normal human cells. Besides, 13r effectively suppressed STAT3 expression as well as phosphorylation, and surface plasmon resonance analysis confirmed the direct interaction of 13r with STAT3. Docking simulation showed that 13r could inhibit STAT3 by targeting SH2 domain. This study provided evidence for these compounds to be further developed as antitumor agents through inhibition of the STAT3 pathway.

Antagonizing STAT3 activation with benzo[b]thiophene 1, 1-dioxide based small molecules

STAT3 is an attractive therapeutic target for cancer therapy. However, due to low potency or poor druggability, none of its inhibitors are clinically available. Herein, a series of aminobenzo[b]thiophene 1, 1-dioxides with good drug-likeness properties were designed, synthesized and evaluated as STAT3 inhibitors. Most of them exhibited higher antitumor activity than the small-molecule STAT3 inhibitor, Stattic. Compound 15 was the most potent and had an IC₅₀ range in 0.33-0.75 μM in various cancer cell lines. The overexpressed and IL-6 induced phosphorylation levels of STAT3 were both inhibited by 15 without influencing the phosphorylation levels of the upstream kinases Src and Jak2. 15 also suppressed the expressions of STAT3 downstream gene, Bcl-2. 15 effectively increased the ROS levels of cancer cells, induced cancer cell apoptosis and abolished the colony formation ability of cancer cells without affecting bypass kinase p-Erk. Furthermore, 15in vivo induced significant antitumor responses, and exhibited less toxicity than Doxorubicin. Together, this study described a class of new STAT3 inhibitors as antitumor agents.

Protective effect of suppressing STAT3 activity in LPS-induced acute lung injury

Acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) are diseases with high mortality. Macrophages and neutrophils are responsible for inflammatory responses in ALI and ARDS, which are characterized by excessive production of proinflammatory mediators in bronchoalveolar lavage fluid (BALF) and plasma. Aberrant activation of the JAK/STAT pathway is critical for persistent inflammation in many conditions such as infection and autoimmunity. Given the importance of the STAT3 transcription factor in activating macrophages and neutrophils and augmenting inflammation, we investigated the therapeutic potential of inhibiting STAT3 activity using the small-molecule STAT3 inhibitor, LLL12. Our results demonstrate that LPS induces STAT3 activation in macrophages in vitro and in CD45⁺CD11b⁺ cells from BALF in the LPS-induced ALI model in vivo. LLL12 treatment inhibits LPS-induced lung inflammation in the ALI model, which is accompanied by suppression of LPS-induced STAT3 activation and an inhibition of macrophage and inflammatory cell infiltration in lung and BALF. LLL12 treatment also suppresses expression of proinflammatory genes including IL-1β, IL-6, TNF-α, iNOS, CCL2, and MHC class II in macrophages and inflammatory cells from BALF and serum as determined by ELISA. Furthermore, hyperactivation of STAT3 in LysMCre-SOCS3^fl/fl mice accelerates the severity of inflammation in the ALI model. Both pre- and post-LPS treatment with LLL12 decrease LPS-induced inflammatory responses in mice with ALI. Importantly, LLL12 treatment attenuates STAT3 phosphorylation in human peripheral blood mononuclear cells induced by plasma from patients with ARDS, which suggests the feasibility of targeting the STAT3 pathway therapeutically for patients with ALI and ARDS.

Multilayer OMIC Data in Medullary Thyroid Carcinoma Identifies the STAT3 Pathway as a Potential Therapeutic Target in RETM918T Tumors

Purpose: Medullary thyroid carcinoma (MTC) is a rare disease with few genetic drivers, and the etiology specific to each known susceptibility mutation remains unknown. Exploiting multilayer genomic data, we focused our interest on the role of aberrant DNA methylation in MTC development.Experimental Design: We performed genome-wide DNA methylation profiling assessing more than 27,000 CpGs in the largest MTC series reported to date, comprising 48 molecularly characterized tumors. mRNA and miRNA expression data were available for 33 and 31 tumors, respectively. Two human MTC cell lines and 101 paraffin-embedded MTCs were used for validation.Results: The most distinctive methylome was observed for RET^M918T-related tumors. Integration of methylation data with mRNA and miRNA expression data identified genes negatively regulated by promoter methylation. These in silico findings were confirmed in vitro for PLCB2, DKK4, MMP20, and miR-10a, -30a, and -200c. The mutation-specific aberrant methylation of PLCB2, DKK4, and MMP20 was validated in 25 independent MTCs by bisulfite pyrosequencing. The methylome and transcriptome data underscored JAK/Stat pathway involvement in RET^M918T MTCs. Immunostaining [immunohistochemistry (IHC)] for the active form of signaling effector STAT3 was performed in a series of 101 MTCs. As expected, positive IHC was associated with RET^M918T-bearing tumors (P < 0.02). Pharmacologic inhibition of STAT3 activity increased the sensitivity to vandetanib of the RET^M918T-positive MTC cell line, MZ-CRC-1.Conclusions: Multilayer OMIC data analysis uncovered methylation hallmarks in genetically defined MTCs and revealed JAK/Stat signaling effector STAT3 as a potential therapeutic target for the treatment of RET^M918T MTCs. Clin Cancer Res; 23(5); 1334-45. ©2016 AACR.

Proteomic level changes associated with S3I201 treated U87 glioma cells

Glioblastoma multiforme is Grade IV brain tumor associated with high mortality and limited therapeutics. Signal Transducer and Activator of Transcription 3 (STAT3) is persistently active in several cancers including gliomas, and plays a major role in disease progression and survival of glioma patients, thus being a potential therapeutic target for treatment. S3I201 and its analogs inhibit the transcriptional functions of STAT3 and reduce growth of tumor tissues. Here we have studied proteomic alteration associated with S3I201 treated U87 cells using 2-DE and Isobaric tags for relative and absolute quantitation coupled with mass spectrometry. This analysis revealed 136 differentially expressed proteins which were functionally classified with gene ontology analysis. Results showed metabolism, apoptosis, cytoskeletal behaviour, cell redox homeostasis and immune response as the most affected biological processes on S3I201 treatment. Apoptosis-inducing factor 1 mitochondrial, cyclophilin A and chloride intra-cellular channel protein 1 were found to be up-regulated which possibly contributes to its anti-tumorigenic function. Several glycolytic enzymes like phosphoglycerate mutase 1 were also found to be up-regulated and its expression was validated using immunoblot. Conclusively, our study shows the downstream effects of S3I201 in U87 glioma cells and suggests its therapeutic potential.

SIGNIFICANCE

Gliomas with constitutive expression can be treated with STAT3 inhibitors. S3I201, a STAT3 inhibitor, reduces the growth of glioma cells thus could be studied further for its application as anti-glioma agent. This study investigated proteomic alteration associated with S3I201 in U87 cells using complementary proteomic approaches, and our findings suggest that S3I201 influences central metabolism, apoptosis, cytoskeletal behaviour, cell redox homeostasis and immune response as the most affected biological processes which altogether contribute to its anti-tumorigenic activity. Several proteins were identified which may serve as prognostic or predictive markers in GBM. Apoptosis-inducing factor 1 mitochondrial and cyclophilin A were identified as potential therapeutic targets and further investigations on these candidates may facilitate therapeutic development and suggests that GBM therapy can be improved by targeting cellular metabolism and by using immunotherapy.

Signal transducer and activator of transcription 3 as a therapeutic target for cancer and the tumor microenvironment

Signal transducer and activator of transcription 3 (STAT3) is a cytoplasmic transcription factor that modulates the transcription of a variety of genes to regulate important biological functions, including cell proliferation, differentiation, survival, angiogenesis, and immune response. Constitutive activation of STAT3 is important in oncogenic signaling and occurs at high frequency in human cancers, including diverse solid tumors and hematologic malignancies. Moreover, it is associated with a poor prognosis. The tumor microenvironment has recently been recognized as a key condition for cancer progression, invasion, angiogenesis, metastasis, and drug resistance by activation of STAT3 signaling. Therefore, understanding the biology associated with STAT3-mediated signaling cascades in the tumor microenvironment may offer the therapeutic potential to treat human cancers. This review presents an overview of the critical roles of STAT3 in the tumor microenvironment related to cancer biology and discusses recent advancements in the development of anticancer drugs that therapeutically inhibit STAT3 signaling cascades.

Rational combination of MEK inhibitor and the STAT3 pathway modulator for the therapy in K-Ras mutated pancreatic and colon cancer cells

K-Ras mutations are frequently detected in pancreatic and colon cancers, which are associated with the resistance to MEK inhibitors targeting the Ras pathway. Identifying the underlying mechanisms for the acquired resistance is essential for the future clinical development of MEK inhibitors. Here, we identified that Signal Transducer and Activator of Transcription 3 (STAT3) was significantly activated following the MEK inhibition using AZD6244, PD98059 and Trametinib in K-Ras mutant pancreatic and colon cancer cells. The STAT3 activation may be important for the MEK inhibitor resistance in these K-Ras mutant cancer cells. We have shown that dual inhibition of STAT3 and MEK using the STAT3 inhibitor LY5 and MEK inhibitor Trametinib exerts significant anti-tumor cell efficacy in K-Ras mutant pancreatic and colon cancer cells in vitro. In addition, Trametinib showed increased suppression on tumor growth in vivo in STAT3 knockdown pancreatic cancer cells compared with tumor growth of control cells without STAT3 knockdown. Taken together, our results suggest the induced STAT3 activation as a possible mechanism for the resistance to MEK inhibitor and demonstrate the potentials of a combination therapy using MEK and STAT3 inhibitors in pancreatic and colon cancers harboring K-Ras mutant proteins.

Strategies and Approaches of Targeting STAT3 for Cancer Treatment

Signal transducer and activator of transcription 3 (STAT3) is a transcription factor that regulates the expression of genes related to cell cycle, cell survival, and immune response associated with cancer progression and malignancy in a number of cancer types. Once activated, STAT3 forms a homodimer and translocates to the nucleus where it binds DNA promoting the translation of target genes associated with antiapoptosis, angiogenesis, and invasion/migration. In normal cells, levels of activated STAT3 remain transient; however, STAT3 remains constitutively active in approximately 70% of human solid tumors. The pivotal role of STAT3 in tumor progression has promoted a campaign in drug discovery to identify small molecules that disrupt the function of STAT3. A range of approaches have been used to identify novel small molecule inhibitors of STAT3, including high-throughput screening of chemical libraries, computational-based virtual screening, and fragment-based design strategies. The most common approaches in targeting STAT3 activity are either via the inhibition of tyrosine kinases capable of phosphorylating and thereby activating STAT3 or by preventing the formation of functional STAT3 dimers through disruption of the SH2 domains. However, the targeting of the STAT3 DNA-binding domain and disruption of binding of STAT3 to its DNA promoter have not been thoroughly examined, mainly due to the lack of adequate assay systems. This review summarizes the development of STAT3 inhibitors organized by the approach used to inhibit STAT3, the current inhibitors of each class, and the assay systems used to evaluate STAT3 inhibition and offers an insight into future approaches for small molecule STAT3 inhibitor development.

Erdr1 Suppresses Murine Melanoma Growth via Regulation of Apoptosis

Melanoma, one of the aggressive cancers, is known to be resistant to chemotherapy. Because of its aggressive nature, effectively inducing apoptosis is necessary to treat melanoma. Erythroid differentiation regulator 1 (Erdr1) is known to be a stress-related survival factor exhibiting anti-cancer effects in several cancers. However, little is known about the functions and underlying mechanisms of Erdr1 so far. To demonstrate the effect of Erdr1 in melanoma apoptosis, recombinant murine Erdr1 was injected into mice implanted with B16F10 melanoma cells. In vivo tumor growth was significantly inhibited in mice injected with Erdr1 compared to the control. In addition, the tumor from Erdr1-injected mice showed an increased level of apoptosis. Accordingly, apoptosis-regulating factors including anti-apoptotic marker Bcl-2 and pro-apoptotic marker Bax in the tumor tissues were examined. As expected, the decreased level of Bcl-2 and increased level of Bax were detected in tumors within the mice injected with Erdr1. Based on the in vivo study, the role of Erdr1 in tumor apoptosis was further tested by incubating it with cells of the murine melanoma cell line B16F10. Erdr1-induced apoptosis in B16F10 cells was observed. Additionally, Erdr1 downregulated STAT3 activity, inhibiting apoptosis via regulation of the Bcl-2 family. Overall, data demonstrate that Erdr1 induced murine melanoma apoptosis through the regulation of Bcl-2 and Bax. These findings suggest that Erdr1 is a novel regulator of apoptosis in melanoma.

Feedback Activation of STAT3 as a Cancer Drug-Resistance Mechanism

Signal transducer and activator of transcription 3 (STAT3) plays crucial roles in several cellular processes such as cell proliferation and survival, and has been found to be aberrantly activated in many cancers. Much research has explored the leading mechanisms for regulating the STAT3 pathway and its role in promoting tumorigenesis. We focus here on recent evidence suggesting that feedback activation of STAT3 plays a prominent role in mediating drug resistance to a broad spectrum of targeted cancer therapies and chemotherapies. We highlight the potential of co-targeting STAT3 and its primary target to overcome drug resistance, and provide perspective on repurposing clinically approved drugs as STAT3 pathway inhibitors, in combination with the FDA-approved receptor tyrosine kinase (RTK) inhibitors, to improve clinical outcome of cancer treatment.

Dogs as a Model for Cancer

Spontaneous cancers in client-owned dogs closely recapitulate their human counterparts with respect to clinical presentation, histological features, molecular profiles, and response and resistance to therapy, as well as the evolution of drug-resistant metastases. In several instances the incorporation of dogs with cancer into the preclinical development path of cancer therapeutics has influenced outcome by helping to establish pharmacokinetic/pharmacodynamics relationships, dose/regimen, expected clinical toxicities, and ultimately the potential for biologic activity. As our understanding regarding the molecular drivers of canine cancers has improved, unique opportunities have emerged to leverage this spontaneous model to better guide cancer drug development so that therapies likely to fail are eliminated earlier and therapies with true potential are optimized prior to human studies. Both pets and people benefit from this approach, as it provides dogs with access to cutting-edge cancer treatments and helps to insure that people are given treatments more likely to succeed.

Salinomycin Promotes Anoikis and Decreases the CD44+/CD24- Stem-Like Population via Inhibition of STAT3 Activation in MDA-MB-231 Cells

Triple-negative breast cancer (TNBC) is an aggressive tumor subtype with an enriched CD44⁺/CD24^- stem-like population. Salinomycin is an antibiotic that has been shown to target cancer stem cells (CSC); however, the mechanisms of action involved have not been well characterized. The objective of the present study was to investigate the effect of salinomycin on cell death, migration, and invasion, as well as CSC-like properties in MDA-MB-231 breast cancer cells. Salinomycin significantly induced anoikis-sensitivity, accompanied by caspase-3 and caspase-8 activation and PARP cleavage, during anchorage-independent growth. Salinomycin treatment also caused a marked suppression of cell migration and invasion with concomitant downregulation of MMP-9 and MMP-2 mRNA levels. Notably, salinomycin inhibited the formation of mammospheres and effectively reduced the CD44⁺/CD24^- stem-like population during anchorage-independent growth. These observations were associated with the inhibition of STAT3 phosphorylation (Tyr705). Furthermore, interleukin-6 (IL-6)-induced STAT3 activation was strongly suppressed by salinomycin challenge. These findings support the notion that salinomycin may be potentially efficacious for targeting breast cancer stem-like cells through the inhibition of STAT3 activation.

A STAT inhibitor patent review: progress since 2011

INTRODUCTION

The clinical utility of effective direct STAT inhibitors, particularly STAT3 and STAT5, for treating cancer and other diseases is well studied and known.

AREAS COVERED

This review will highlight the STAT inhibitor patent literature from 2011 to 2015 inclusive. Emphasis will be placed on inhibitors of the STAT3, STAT5a/b, and STAT1 proteins for cancer treatment. The review will, where suitably investigated, describe the mode and the site of inhibition, list indications that were evaluated, and rank the inhibitor's relative potency among compounds in the same class. The reader will gain an understanding of the diverse set of approaches, used both in academia and industry, to target STAT proteins.

EXPERT OPINION

There is still much work to be done to directly target the STAT3 and STAT5 proteins. As yet, there is still no direct STAT3 inhibitor in the clinic. While the SH2 domain remains a popular target for therapeutic intervention, the DNA-binding domain and N-terminal region are now attracting attention as possible sites for inhibition. Multiple putative STAT3 and STAT5 inhibitors have now been patented across a broad spectrum of chemotypes, each with their own advantages and limitations.

Hirsutinolide Series Inhibit Stat3 Activity, Alter GCN1, MAP1B, Hsp105, G6PD, Vimentin, TrxR1, and Importin α-2 Expression, and Induce Antitumor Effects against Human Glioma

We report that hirsutinolide series, 6, 7, 10, 11, 20, and 22, and the semisynthetic analogues, 30, 31, 33, and 36, inhibit constitutively active signal transducer and activator of transcription (Stat)3 and malignant glioma phenotype. A position 13 lipophilic ester group is required for activity. Molecular modeling and nuclear magnetic resonance structural analyses reveal direct hirsutinolide:Stat3 binding. One-hour treatment of cells with 6 and 22 also upregulated importin subunit α-2 levels and repressed translational activator GCN1, microtubule-associated protein (MAP)1B, thioredoxin reductase (TrxR)1 cytoplasmic isoform 3, glucose-6-phosphate 1-dehydrogenase isoform a, Hsp105, vimentin, and tumor necrosis factor α-induced protein (TNAP)2 expression. Active hirsutinolides inhibited anchorage-dependent and three-dimensional spheroid growth, survival, and migration of human glioma lines and glioma patients' tumor-derived xenograft cells harboring constitutively active Stat3. Oral gavage delivery of 6 or 22 inhibited human glioma tumor growth in subcutaneous mouse xenografts. The inhibition of Stat3 signaling represents part of the hirsutinolide-mediated mechanisms to induce antitumor effects.

Novel 2-Carbonylbenzo[b]thiophene 1,1-Dioxide Derivatives as Potent Inhibitors of STAT3 Signaling Pathway

Signal transducer and activator of transcription 3 (STAT3) is considered to be an attractive therapeutic target for cancer therapy. In this study, a series of 2-carbonylbenzo[b]thiophene 1,1-dioxide derivatives (CBT) were designed to inhibit the STAT3 SH2 domain phosphorylation site Try 705. We demonstrated that incorporation of basic flexible groups through amide bond linkage to benzo[b]thiophene 1,1-dioxide (BTP) achieved compounds with higher antiproliferative potency than BTP itself. The most potent compound 6o, as indicated from luciferase reporter gene assay, inhibited the STAT3 pathway by decreasing the phosphorylation level of STAT3 Tyr705, while the phosphorylation level of other upstream tyrosine kinases in this pathway was not significantly inhibited. Compound 6o was also shown to trigger ROS generation and accumulation, thus consequently attributed partially to the observed cell apoptosis. This study provided important structural information for the development of inhibitors targeting the STAT3 pathway.

Characterization of STAT3 expression, signaling and inhibition in feline oral squamous cell carcinoma

Background

Signal transducer and activator of transcription 3 (STAT3) plays a critical role in tumor development by regulating signaling pathways involved in cell proliferation, survival, metastasis and angiogenesis. STAT3 is activated in many cancers, including head and neck squamous cell carcinoma (HNSCC) in people. Feline oral squamous cell carcinoma (OSCC) is similar to advanced or recurrent HNSCC as it is poorly responsive to traditional therapies and carries a poor long-term prognosis. The purpose of this study was to characterize expression and activation of STAT3 in feline OSCC cell lines and tumor samples and to investigate the biologic activity of a novel, allosteric STAT3 inhibitor, LLL12, in feline OSCC cell lines.

Results

We evaluated 3 feline OSCC cell lines and one of these (SCCF2) exhibited high levels of constitutive STAT3 phosphorylation and high sensitivity to LLL12 treatment. Exposure of SCCF2 cells to LLL12 resulted in decreased expression of pSTAT3 and total STAT3, apoptosis as assessed by caspase 3/7 activation, inhibition of colony formation and reduced expression of the STAT3 transcriptional target survivin. In contrast, the STAT3 transcriptional targets VEGF and MCL-1 increased after LLL12 treatment. This was, in part, likely due to LLL12 mediated upregulation of HIF-1α, which is known to drive VEGF and MCL-1 expression. The OSCC cell lines with low basal STAT3 phosphorylation did not exhibit these effects, suggesting that STAT3 inhibition was responsible for the observed results. Lastly, immunohistochemistry for pSTAT3 was performed using a feline OSCC tissue microarray, demonstrating expression in 48 % of samples tested.

Conclusions

These data demonstrate that LLL12 has biologic activity against a feline OSCC cell line expressing pSTAT3 and that STAT3 represents a target for therapeutic intervention in this disease. However, given the up-regulation of several STAT3 transcriptional targets following treatment, further investigation of STAT3 and its related signaling pathways in OSCC is warranted.

Electronic supplementary material

The online version of this article (doi:10.1186/s12917-015-0505-7) contains supplementary material, which is available to authorized users.

Identification of Lead Compounds as Inhibitors of STAT3: Design, Synthesis and Bioactivity

STAT3 belongs to the signal transducers and activators of transcription (STAT) family. It has been demonstrated that STAT3 is constitutively activated in many tumors, playing a role in carcinogenesis and tumor progression. For this reason, it has being considered a potential target for cancer therapy. In this context, we have designed, synthesized and evaluated 1,4-dimethyl-carbazole derivatives, targeting the STAT3 protein. Moreover, MTT assay performed on A375 and HeLa, showed significant antiproliferative activity of some of synthesized compounds (3-5). The same compounds (3-5) considerably reduced STAT3 expression, as demonstrated by Western blot analysis. Our multidisciplinary approach shows that 1,4-dimethyl-carbazoles are potential building blocks to develop more affinity ligands of STAT3.