Abstract 3106: Design, synthesis, and screening of niclosamide analogs as androgen receptor degraders for hepatocellular carcinoma

Hepatocellular Carcinoma (HCC) is the leading form of liver cancer, the 6th most common type, and the 4th leading cause of cancer death worldwide. Interestingly, HCC occurs two to four times more in males than females. A possible explanation for this sexual dimorphism is the implication of androgen and the Androgen Receptor (AR). However, previous clinical trials among HCC patients have shown no significant survival benefit after the administration of antiandrogen drugs (e.g. Enzalutamide) that block the Ligand-Binding Domain (LBD) of the Full-length Androgen Receptor (AR-FL). Instead, our lab has developed a novel approach using small molecular analogs of the previously FDA-approved drug, Niclosamide, to degrade full-length AR and its spliced variants within HCC cell lines. The primary goal of this project was to evaluate the minimal necessary pharmacophores for the biological activity of the Niclosamide scaffold. To do so, 23 analogs were synthesized and tested on three different HCC cell lines (SNU 475, 423, and LM3) using a CCK8 cell viability assay. Preliminary results have shown that only Niclosamide analogs with i.) electron-withdrawing groups on the aniline ring; ii) a conserved hydroxy group on the salicylic ring, and iii) a free amide group in the middle have cytotoxic activity. Further work will be completed using western blot to determine if there’s any correlation between androgen receptor degradation and in vitro potency. In conclusion, Niclosamide analogs have indicated promising potential to inhibit HCC cell lines by targeting the Androgen Receptor.

Citation Format: Jeffrey Cheng, Enming Xing, Shabber Mohammed, Emma Montgomery, Lauren Granchie, Christopher Coss, Pui-Kai Li. Design, synthesis, and screening of niclosamide analogs as androgen receptor degraders for hepatocellular carcinoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 3106.

BET Bromodomain Inhibitors: Novel Design Strategies and Therapeutic Applications

The mammalian bromodomain and extra-terminal domain (BET) family of proteins consists of four conserved members (Brd2, Brd3, Brd4, and Brdt) that regulate numerous cancer-related and immunity-associated genes. They are epigenetic readers of histone acetylation with broad specificity. BET proteins are linked to cancer progression due to their interaction with numerous cellular proteins including chromatin-modifying factors, transcription factors, and histone modification enzymes. The spectacular growth in the clinical development of small-molecule BET inhibitors underscores the interest and importance of this protein family as an anticancer target. Current approaches targeting BET proteins for cancer therapy rely on acetylation mimics to block the bromodomains from binding chromatin. However, bromodomain-targeted agents are suffering from dose-limiting toxicities because of their effects on other bromodomain-containing proteins. In this review, we provided an updated summary about the evolution of small-molecule BET inhibitors. The design of bivalent BET inhibitors, kinase and BET dual inhibitors, BET protein proteolysis-targeting chimeras (PROTACs), and Brd4-selective inhibitors are discussed. The novel strategy of targeting the unique C-terminal extra-terminal (ET) domain of BET proteins and its therapeutic significance will also be highlighted. Apart from single agent treatment alone, BET inhibitors have also been combined with other chemotherapeutic modalities for cancer treatment demonstrating favorable clinical outcomes. The investigation of specific biomarkers for predicting the efficacy and resistance of BET inhibitors is needed to fully realize their therapeutic potential in the clinical setting.

Development of Murine Leukemia Virus Integrase-Derived Peptides That Bind Brd4 Extra-Terminal Domain as Candidates for Suppression of Acute Myeloid Leukemia

The bromodomain and extra-terminal (BET) domain family of proteins, which include its prototypical member Brd4, is implicated in a variety of cancers and viral infections due to their interaction with cellular and viral proteins. BET proteins contain two bromodomains, a common protein motif that selectively binds acetylated lysine on histones. However, they are structurally distinct from other bromodomain-containing proteins because they encode a unique C-terminal extra-terminal (ET) domain that is important for the protein-protein interactions including jumonji C-domain-containing protein 6 (JMJD6) and histone-lysine N-methyltransferase NSD3 (NSD3). Brd4 functions primarily during transcription as a passive scaffold linking cellular and viral proteins to chromatin. The rapid development of clinical inhibitors targeting Brd4 highlights the importance of this protein as an anticancer target. Current therapeutic approaches focus on the development of small molecule acetylated lysine mimics of histone marks that block the ability of the bromodomains to bind their chromatin marks. Thus far, bromodomain-targeted agents have shown dose-limiting toxicities due to off-target effects on other bromodomain-containing proteins. Here, we exploited a viral-host protein interaction interface to design peptides for the disruption of BET protein function. A murine leukemia virus (MLV) integrase-derived peptide (ET binding motif, EBM) and its shorter minimal binding motif (pentapeptide LKIRL) were sufficient to directly bind the Brd4 ET domain and reduce cellular proliferation of an acute myeloid leukemia cell line. Using computational and biochemical approaches, we identified the minimal essential contacts between EBM and LKIRL peptides and the Brd4 ET domain. Our findings provide a structural foundation for inhibiting BET/Brd4-mediated cancers by targeting the ET domain with small peptide-based inhibitors.

ARVib suppresses growth of advanced prostate cancer via inhibition of androgen receptor signaling

Targeting androgen signaling with the second-generation anti-androgen drugs, such as enzalutamide (Enza), abiraterone (Abi), apalutamide (Apal), and darolutamide (Daro), is the mainstay for the treatment of castration-resistant prostate cancer (CRPC). While these treatments are effective initially, resistance occurs frequently. Continued expression of androgen receptor (AR) and its variants such as AR-V7 despite AR-targeted therapy contributes to treatment resistance and cancer progression in advanced CRPC patients. This highlights the need for new strategies blocking continued AR signaling. Here, we identify a novel AR/AR-V7 degrader (ARVib) and found that ARVib effectively degrades AR/AR-V7 protein and attenuates AR/AR-V7 downstream target gene expression in prostate cancer cells. Mechanistically, ARVib degrades AR/AR-V7 protein through the ubiquitin-proteasome pathway mediated by HSP70/STUB1 machinery modulation. ARVib suppresses HSP70 expression and promotes STUB1 nuclear translocation, where STUB1 binds to AR/AR-V7 and promotes its ubiquitination and degradation. ARVib significantly inhibits resistant prostate tumor growth and improves enzalutamide treatment in vitro and in vivo. These data suggest that ARVib has potential for development as an AR/AR-V7 degrader to treat resistant CRPC.

Mechanistic Insights into the Allosteric Inhibition of Androgen Receptors by Binding Function 3 Antagonists from an Integrated Molecular Modeling Study

An androgen receptor (AR) is an intensively studied treatment target for castration-resistant prostate cancer that is irresponsive to conventional antiandrogen therapeutics. Binding function 3 (BF3) inhibitors with alternative modes of action have emerged as a promising approach to overcoming antiandrogen resistance. However, how these BF3 inhibitors modulate AR function remains elusive, hindering the development of BF3-targeting agents. Here, we performed an integrated computational study to interrogate the binding mechanism of several known BF3 inhibitors with ARs. Our results show that the inhibitory effect of the BF3 antagonists arises from their allosteric modulation of the activation function (AF2) site, which alters the dynamic coupling between the BF3 and AF2 sites as well as the AF2-coactivator (SRC2-3) interaction. Moreover, the per-residue binding energy analyses reveal the "anchor" role of the linker connecting the phenyl ring and benzimidazole/indole in these BF3 inhibitors. Furthermore, the allosteric driver-interacting residues are found to include both "positive", e.g., Phe673 and Asn833, and "negative" ones, e.g., Phe826, and the differential interactions with these residues provide an explanation why stronger binding does not necessarily result in higher inhibitory activities. Finally, our allosteric communication pathway analyses delineate how the allosteric signals triggered by BF3 binding are propagated to the AF2 pocket through multiple short- and/or long-ranged transmission pathways. Collectively, our combined computational study provides a comprehensive structural mechanism underlying how the selected set of BF3 inhibitors modulate AR function, which will help guide future development of BF3 antagonists.

Rationally Designed ACE2-Derived Peptides Inhibit SARS-CoV-2

Severe acute respiratory syndrome coronavirus (SARS-CoV)-2 is a novel and highly pathogenic coronavirus and is the causative agent of the coronavirus disease 2019 (COVID-19). The high morbidity and mortality associated with COVID-19 and the lack of an approved drug or vaccine for SARS-CoV-2 underscores the urgent need for developing effective antiviral therapies. Therapeutics that target essential viral proteins are effective at controlling virus replication and spread. Coronavirus Spike glycoproteins mediate viral entry and fusion with the host cell, and thus are essential for viral replication. To enter host cells, the Spike proteins of SARS-CoV-2 and related coronavirus, SARS-CoV, bind the host angiotensin-converting enzyme 2 (ACE2) receptor through their receptor binding domains (RBDs). Here, we rationally designed a panel of ACE2-derived peptides based on the RBD-ACE2 binding interfaces of SARS-CoV-2 and SARS-CoV. Using SARS-CoV-2 and SARS-CoV Spike-pseudotyped viruses, we found that a subset of peptides inhibits Spike-mediated infection with IC50 values in the low millimolar range. We identified two peptides that bound Spike RBD in affinity precipitation assays and inhibited infection with genuine SARS-CoV-2. Moreover, these peptides inhibited the replication of a common cold causing coronavirus, which also uses ACE2 as its entry receptor. Results from the infection experiments and modeling of the peptides with Spike RBD identified a 6-amino-acid (Glu37-Gln42) ACE2 motif that is important for SARS-CoV-2 inhibition. Our work demonstrates the feasibility of inhibiting SARS-CoV-2 with peptide-based inhibitors. These findings will allow for the successful development of engineered peptides and peptidomimetic-based compounds for the treatment of COVID-19.

Steroid Sulfatase Stimulates Intracrine Androgen Synthesis and is a Therapeutic Target for Advanced Prostate Cancer

PURPOSE

Most patients with prostate cancer receiving enzalutamide or abiraterone develop resistance. Clinical evidence indicates that serum levels of dehydroepiandrosterone sulfate (DHEAS) and biologically active DHEA remain in the high range despite antiandrogen treatment. The conversion of DHEAS into DHEA by steroid sulfatase (STS) may contribute to sustained intracrine androgen synthesis. Here, we determine the contribution of STS to treatment resistance and explore the potential of targeting STS to overcome resistance in prostate cancer.

EXPERIMENTAL DESIGN

STS expression was examined in patients and cell lines. In vitro, STS activity and expression were modulated using STS-specific siRNA or novel STS inhibitors (STSi). Cell growth, colony formation, androgen production, and gene expression were examined. RNA-sequencing analysis was conducted on VCaP cells treated with STSi. Mice were treated with STSis with or without enzalutamide to determine their effects in vivo.

RESULTS

STS is overexpressed in patients with castration-resistant prostate cancer (CRPC) and resistant cells. STS overexpression increases intracrine androgen synthesis, cell proliferation, and confers resistance to enzalutamide and abiraterone. Inhibition of STS using siRNA suppresses prostate cancer cell growth. Targeting STS activity using STSi inhibits STS activity, suppresses androgen receptor transcriptional activity, and reduces the growth of resistant C4-2B and VCaP prostate cancer cells. STSis significantly suppress resistant VCaP tumor growth, decrease serum PSA levels, and enhance enzalutamide treatment in vitro and in vivo.

CONCLUSIONS

These studies suggest that STS drives intracrine androgen synthesis and prostate cancer proliferation. Targeting STS represents a therapeutic strategy to treat CRPC and improve second-generation antiandrogen therapy.

Mechanism of interference by hemoglobin in the determination of total bilirubin. I. Method of Malloy-Evelyn

Oxyhemoglobin is the species of hemoglobin in erythrocyte hemolysates that inhibits the diazo reaction. Ferric hemoglobin derivatives and species with relatively low molecular mass do not interfere. Conversion of oxyhemoglobin to acid hematin under assay reaction conditions is associated with rapid destruction of bilirubin, which accounts for the diazo reaction error. The most probable mechanism for this destruction of bilirubin is an oxidative reaction involving H2O2, formed in the oxidation of hemoglobin, and acid hematin acting as a pseudoperoxidase. We could find no evidence for other mechanisms of interference such as spectral error or azobilirubin destruction. Addition of potassium iodide, 4.0 mmol/L final concentration in the reaction mixture, eliminates interference from hemoglobin added to give concentrations as great as 10 g/L. It also eliminated the effects of hemolysis in the method of Ertingshausen et al. (Clin. Chem. 19: 1366, 1973), in which ethylene glycol is used as the accelerator.

Mechanism of interference by hemoglobin in the determination of total bilirubin. II. Method of Jendrassik-Grof

Oxyhemoglobin in erythrocyte hemolysates interferes with the Jendrassik-Grof assay. Destruction of azobilirubin occurs when oxyhemoglobin is oxidized to methemoglobin during diazotization or to alkaline hematin with addition of alkaline tartrate. The most probable mechanism is by oxidation with an agent such as hydrogen peroxide or a related species resulting from hemoglobin oxidation. Methemoglobin also appears to cause some destruction of azobilirubin during diazotization. Methemoglobin forms during diazotization because of reactions of oxyhemoglobin with both diazo reagent and nitrite ion. Formation of methemoglobin is, therefore, more rapid in the test than in the blank mixture and, under reaction conditions, its absorbance is less than that of oxyhemoglobin. This results in spectral interference when neutral azobilirubin is assayed. Alkaline tartrate abolishes this spectral error by causing rapid formation of alkaline hematin in both test and blank.

Therapeutic Effects of a Novel Phenylphthalimide Analog for Corneal Neovascularization and Retinal Vascular Leakage

Purpose

Neovascularization (NV) and retinal vascular leakage are major causes of impaired vision in ocular diseases. The purpose of this study was to identify novel phenylphthalimide analogs with therapeutic effects on NV and vascular leakage and to explore the mechanism of action.

Methods

Antiangiogenic activities of novel phenylphthalimide analogs were assessed in vitro by using VEGF ELISA and endothelial cell proliferation assay. Their efficacies on retinal vascular leakage were evaluated using rat models of oxygen-induced retinopathy (OIR) and streptozotocin (STZ)-induced diabetes. The in vivo antiangiogenic activity was evaluated using topical administration in the alkali burn-induced corneal NV model. The expression of VEGF and intercellular adhesion molecule-1 (ICAM-1) were measured using ELISA.

Results

Thalidomide and three novel analogs all showed inhibitory effects on endothelial cell proliferation and VEGF expression in vitro. Through intravitreal injection, all of the compounds reduced retinal vascular leakage in the OIR and STZ-induced diabetic models. Among these compounds, (2,6-diisopropylphenyl)-5-amino-1H-isoindole-1,3-dione (DAID) displayed the most potent efficacy and reduced retinal vascular leakage in a dose-dependent manner in both the OIR and STZ-diabetes models. Topical administration of DAID also inhibited alkali burn-induced corneal NV. Furthermore, DAID attenuated the overexpression of VEGF and ICAM-1 in the retina of the OIR model. Intravitreal injection of DAID did not result in any detectable side effects, as shown by electroretinogram and retinal histological analysis.

Conclusions

DAID is a novel phenylphthalimide analog with potent effects on NV and retinal vascular leakage through downregulation of VEGF and inflammatory factors and has therapeutic potential.

Structure-Activity Relationship of Niclosamide Derivatives

BACKGROUND/AIM

Cancer is a leading cause of death. Hence, this study aimed at the optimization of niclosamide derivatives for the development of new potential anticancer agents.

MATERIALS AND METHODS

Niclosamide derivatives were synthesized and tested against a panel of human cancer cells: MDA and MCF7 breast cancer cells, PC3 and DU-145 prostate cancer cells, Hela cervical cancer cells, and HL-60 acute promyelocytic leukemia cells. They were also tested in nuclear factor-ĸappa B (NFĸB), V-Ki-ras2 Kirsten rat sarcoma viral oncogene (KRAS), and mitochondria transmembrane potential (MTP) assays.

RESULTS

N-(3,5-Bis(trifluoromethyl)phenyl)-5-chloro-2-hydroxybenzamide exhibited the most significant cytotoxicity against HL-60 cells, while 5-chloro-N-(2-chlorophenyl)-2-hydroxybenzamide was the most active in the NFĸB assay and 5-chloro-N-(3,5-difluorophenyl)-2-hydroxybenzamide in the MTP assay. 5-chloro-N-(2-chloro-4-(trifluoromethyl) phenyl)-2-hydroxybenzamide and 5-chloro-2-hydroxy-N-(4-hydroxyphenyl)benzamide inhibited both HL-60 cell proliferation and NFĸB.

CONCLUSION

In-depth study of the most promising compounds is highly encouraged to further develop into potential anticancer agents those derivatives found to be significantly active.

Novel pyrrolopyrimidines as Mps1/TTK kinase inhibitors for breast cancer

New targeted therapy approaches for certain subtypes of breast cancer, such as triple-negative breast cancers and other aggressive phenotypes, are desired. High levels of the mitotic checkpoint kinase Mps1/TTK have correlated with high histologic grade in breast cancer, suggesting a potential new therapeutic target for aggressive breast cancers (BC). Novel small molecules targeting Mps1 were designed by computer assisted docking analyses, and several candidate compounds were synthesized. These compounds were evaluated in anti-proliferative assays of a panel of 15 breast cancer cell lines and further examined for their ability to inhibit a variety of Mps1-dependent biological functions. The results indicate that the lead compounds have strong anti-proliferative potential through Mps1/TTK inhibition in both basal and luminal BC cell lines, exhibiting IC₅₀ values ranging from 0.05 to 1.0μM. In addition, the lead compounds 1 and 13 inhibit Mps1 kinase enzymatic activity with IC₅₀ values from 0.356μM to 0.809μM, and inhibited Mps1-associated cellular functions such as centrosome duplication and the spindle checkpoint in triple negative breast cancer cells. The most promising analog, compound 13, significantly decreased tumor growth in nude mice containing Cal-51 triple negative breast cancer cell xenografts. Using drug discovery technologies, computational modeling, medicinal chemistry, cell culture and in vivo assays, novel small molecule Mps1/TTK inhibitors have been identified as potential targeted therapies for breast cancers.

Niclosamide and its analogs are potent inhibitors of Wnt/β-catenin, mTOR and STAT3 signaling in ovarian cancer

Epithelial ovarian cancer (EOC) is the leading cause of gynecologic cancer mortality worldwide. Platinum-based therapy is the standard first line treatment and while most patients initially respond, resistance to chemotherapy usually arises. Major signaling pathways frequently upregulated in chemoresistant cells and important in the maintenance of cancer stem cells (CSCs) include Wnt/β-catenin, mTOR, and STAT3. The major objective of our study was to investigate the treatment of ovarian cancer with targeted agents that inhibit these three pathways. Here we demonstrate that niclosamide, a salicylamide derivative, and two synthetically manufactured niclosamide analogs (analog 11 and 32) caused significant inhibition of proliferation of two chemoresistant ovarian cancer cell lines (A2780cp20 and SKOV3Trip2), tumorspheres isolated from the ascites of EOC patients, and cells from a chemoresistant patient-derived xenograft (PDX). This work shows that all three agents significantly decreased the expression of proteins in the Wnt/β-catenin, mTOR and STAT3 pathways and preferentially targeted cells that expressed the ovarian CSC surface protein CD133. It also illustrates the potential of drug repurposing for chemoresistant EOC and can serve as a basis for pathway-oriented in vivo studies.

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.

Attitudes about Organ and Tissue Donation among the General Public and Blood Donors in Hong Kong

Context

The cadaveric organ and tissue donation rate in Hong Kong is not satisfactory; 1 million blood donors are registered and more than 300 000 are active. However, the current attitudes toward organ and tissue donation in the general public and blood donors of Hong Kong are unknown.

Methods

Random general public (n = 1018) and blood donors (n = 1227) of Chinese origin, with age ranging from 16 to 60 years, were interviewed using a standard verified questionnaire that examines attitudes and knowledge of organ and tissue donation.

Results

The mean age of the general public and blood donors were 32.6 and 28.9 years, respectively. Of the general public, 44.4% were men and among blood donors, 60% were men. About 56% of both groups thought that organ donation is an obligation of citizens. Blood donors were more aware than the general public about the types of organs that can be donated. When compared with the general public, a significantly higher percentage of blood donors were willing to donate their organs (81% vs 53%), had heard about organ donation cards (98.3% vs 89.5%), and had signed the cards (49.9% vs 22.6%). About 70% of both groups who had signed a card were carrying it. Thirty-nine percent of the general public and 17% of blood donors had not decided whether they would donate. For blood donors, 49.7% were willing to donate their relatives' organs, compared with 41.8% of the general public. Most individuals in both groups would not object to their relatives' decision to donate. About two thirds of individuals in both groups disagreed with the concept of an opt-out law, though only 20% of the general public and 14.4% of blood donors would refuse donation if an opt-out law were in practice.

Conclusions

This study shows that blood donors have better knowledge of organ donation and are more willing to donate their organs and sign an organ donation card than the general public. However, a substantial proportion of blood donors have not signed a donor card. It would be useful to design promotion programs to facilitate blood donors' participation in organ donation.

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.

Abstract POSTER-THER-1402: Overcoming platinum resistance in ovarian cancer with niclosamide

Objective: Niclosamide, a salicyclamide derivative and FDA approved teniacide, exhibits potent effects against ovarian cancer in vitro by inhibiting the Wnt/β-catenin, STAT3, and mTOR pathways. Unfortunately, its low bioavailability as a chemotherapeutic agent in vivo necessitates investigation of analogs with improved pharmacokinetics and pharmacodynamics. The objective of this study was to investigate the role of targeting the Wnt/β-catenin and STAT3 pathways with niclosamide and niclosamide analogs (C-11 and C-32) in platinum-sensitive and -resistant ovarian cancer cell lines, primary ovarian cancer ascites cell populations, and tumor tissues. In addition, carboplatin and/or LLL12, a novel STAT3 inhibitor effective against ovarian cancer, were used in combination with niclosamide and its analogs to test for synergistic cytotoxicity. Methods: Two ovarian cancer cell lines A2780, SKOV3ip1 and their chemo-resistant derivatives, A2780.cp20 and SKOV3ip2.TRip2, were treated with niclosamide or C-11 or C-32 (0.1 to 5 μM) alone or in combination with carboplatin (5 to 150 μM) or LLL12 (0.1 nM - 10 µM). Tumorspheres were isolated from the ascites of ovarian cancer patients who underwent surgery. Tumor slices were prepared from freshly obtained ovarian cancer specimens. ATPLite assay was performed to measure cytotoxicity in cell lines, tumorspheres, and tumor slices. Western blot was used to assess expression of proteins implicated in the Wnt, mTOR, and STAT3 pathways. β-catenin signaling activity was measured using the TOPflash reporter assay. Results: All four cell lines were sensitive to niclosamide, C-11, and C-32 with similar IC50 values. Additive cytotoxicity was seen when niclosamide or its analogs were combined with carboplatin or LLL12 in the cell lines, tumorspheres, and tumor tissues. Ex vivo and in vitro samples from the same patient demonstrated similar cytotoxicity with niclosamide, C-11, and C-32 treatment. Synergism was also seen between carboplatin and LLL12 in vitro. The TOPflash assay showed that the combination of niclosamide (0.4 μM) and LLL12 (0.25 μM) decreased β-catenin activity more than either agent alone, suggesting that there is crosstalk between the STAT3 and Wnt/β-catenin pathways. Wnt/β-catenin, STAT3, and mTOR pathway target proteins (LRP6, pLRP6, Axin2, and Survivin) were downregulated with niclosamide and C-32 treatment, and to a greater degree with C-11. Conclusion: Combination treatment with niclosamide, or its analogs, with carboplatin or LLL12 induced greater cytotoxicity than either agent alone in ovarian cancer cell lines, primary tumorspheres, and tumor slices. The synergistic cytotoxicity seen in platinum-resistant cell lines with niclosamide, or its analogs, in combination with carboplatin suggest that targeting the Wnt/ β-catenin and STAT3 pathways may prove effective in overcoming chemoresistance in patients with platinum resistant ovarian cancer.

Citation Format: Rebecca C. Arend, MD, Abhishek Gangrade, Christen L. Walters Haygood, MD, Chandrika Kurpad, Brandon J. Metge, Rajeev S. Samant, PhD, Pui-Kai Li, PhD, Yonghe Li, PhD, Deepak Bhasin, PhD, Charles Landen, MD, Ronald Alvarez, MD, J. Michael Straughn, MD, Donald J. Buchsbaum, PhD. Overcoming platinum resistance in ovarian cancer with niclosamide [abstract]. In: Proceedings of the 10th Biennial Ovarian Cancer Research Symposium; Sep 8-9, 2014; Seattle, WA. Philadelphia (PA): AACR; Clin Cancer Res 2015;21(16 Suppl):Abstract nr POSTER-THER-1402.

Abstract 2517: STAT3 inhibition by LLL12 in combination with niclosamide and chemotherapy in ovarian cancer

Objective:

Chemoresistance and recurrence invariably develop in the treatment of ovarian cancer, despite initial response to chemotherapy. Recent studies have shown that signal transducer and activator of transcription-3 (STAT3) signaling is associated with recurrence and development of chemoresistance in ovarian cancer. A novel small molecule, LLL12, has been shown to inhibit STAT3 in many solid tumors including colon, breast, and glioma. Niclosamide, an FDA approved salicyclamide derivative used for the treatment of tapeworm infections, has also been shown to inhibit STAT3 and other pathways including mTOR, Wnt, NfkB. Therefore, the objective of this study was to investigate LLL12 alone and in combination with niclosamide and/or chemotherapy as a potential treatment for ovarian cancer.

Methods:

Ovarian cancer cell lines A2780 and SKOV3ip2 and their carboplatin and paclitaxel chemoresistant derivatives A2780.cp20, SKOV3ip2.TR were initially treated with LLL12 alone (0.1 nM - 10 µM). These cell lines were treated with the IC50 values for LLL12 alone in combination with niclosamide (0.1 - 5 µM). Ascites was collected from a patient undergoing surgery for ovarian cancer and treated concurrently with LLL12 (0.5 - 10 μM) and carboplatin (25 - 100 μM). Cell viability was assessed using the ATP-lite assay. All samples were assayed in quadruplicate and reported as the mean ± SE.

Results:

Combination treatment with LLL12 and niclosamide produced increased cytotoxicity compared to LLL12 alone in all ovarian cancer cell lines. Treatment with chemotherapy and LLL12 showed additive cytotoxicity in the patient-derived tumorspheres. The IC50 dose of LLL12 against A2780 cells was 0.2 ± .06 but when this dose was combined with 1 µM of niclosamide, 100% cytotoxicity was achieved; 1 µM of niclosamide alone produced 80% cytotoxicity. With the A2780.cp20 cell line, LLL12 had an IC50 of 0.79 ± µM, but with 1 µM of niclosamide there was 100% cell kill, and 80% with niclosamide alone. Both SKOV3 and SKOV3ip2.TR cell lines had higher IC50 values for LLL12 (4.25 µM ± 2.1 and 2.29 µM ± 1.4, respectively) and an additive effect was achieved in both cell lines when LLL12 was combined with niclosamide. In the patient sample, a dose of 50 µM of carboplatin alone killed 10% of cells, and 10 µM of LLL12 killed 50%, The combination of 10 µM of LLL12 and 50 µM of carboplatin killed 80% of the cells; therefore an additive cytotoxicity was seen with carboplatin and LLL12.

Conclusion:

This study demonstrates that the STAT3 inhibitor, LLL12, is active against ovarian cancer cell lines and tumorspheres from a patient sample. Future animal xenograft studies will elucidate more about its activity in combination with other agents such as niclosamide and chemotherapy.

Citation Format: Rebecca C. Arend, Christen L. Walters Haygood, Chandrika Kurpad, Abhishek Gangrade, Pui-Kai Li, Yonghi Li, Deepak Bhasin, J. Michael Straughn, Donald J. Buchsbaum. STAT3 inhibition by LLL12 in combination with niclosamide and chemotherapy in ovarian cancer. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 2517. doi:10.1158/1538-7445.AM2014-2517

Abstract 4073: STAT3 inhibitors elicit direct anti-tumor effects against human biliary caner cell lines and limit release of immune suppressive cytokines in vitro

Biliary cancer (BC), or cholangiocarcinoma originates from the malignant transformation of epithelial cells in the bile ducts. This deadly cancer is typically refractory to standard therapies and has a 3 year survival rate of only 10%. Therefore, novel treatment strategies are desparately needed against this malignancy. One important feature of BC cells is their ability to secrete interleukin-6 (IL-6) in an autocrine manner. This characteristic affords them an opportunity to activate numerous pro-oncogenic signaling pathways including MAPK, and STAT3 within the tumor cell, while simultaneously promoting immunologic changes in patients with advanced disease. We hypothesized that inhibitors of Signal-Transducer and Activator of Transcription-3 (STAT3) pathway may elicit a dual effect by promoting apoptosis of human BC cell lines, and limiting the secretion of immunosuppressive cytokines from these cells. A panel of human BC cell lines with various genotypic profiles was utilized, and all demonstrated secretion of IL-6 (range 5149-68pg/mL) and had constitutively phosphorylated STAT3 as determined by western blot. Similar to positive control conditions with IL-6 + GM-CSF (10 ng/mL each), exposure of human peripheral blood mononuclear cells to 5% or 10% BC culture supernatants induced in vitro differentiation into myeloid derived suppressor cells (MDSC). These data indicate that BC cells have robust activation of the IL-6/STAT3 signaling axis, and that culture supernatants contain factors capable of promoting expansion of immune suppressive cell subsets. A novel small molecule inhibitor FLLL100, could directly inhibit Tyr705 phosphorylation within the SH2 domain of STAT3, and induce apoptosis in the BC cell lines regardless of genotypic profile. Both growth inhibitory (by MTT assay) and pro-apoptotic effects (by Annexin V/PI staining) were observed within 24-48 hours of drug exposure at micromolar concentrations. Apoptosis was confirmed after drug exposure by assessment of PARP cleavage by immunoblot. Exposure of BC cell lines to FLLL100 resulted in significantly reduced secretion of immunomodulatory cytokines including IL-6 (p<0.05) and GM-CSF (p<0.05) in culture supernatants. Together, these data indicate that the IL-6/STAT3 signaling axis plays a role in human BC survival and that targeting this pathway can limit immune suppressive factors derived from BC cell lines.

Citation Format: Jennifer Yang, Kaitlin Keenan, Thomas Mace, Tanios Bekaii-Saab, James Fuchs, Eric Schwartz, Chenglong Li, Jiayuh Lin, Pui-Kai Li, Gregory Lesinski. STAT3 inhibitors elicit direct anti-tumor effects against human biliary caner cell lines and limit release of immune suppressive cytokines in vitro. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 4073. doi:10.1158/1538-7445.AM2014-4073

Abstract 4677: Niclosamide analogs for treatment of ovarian cancer

Objective: Niclosamide has shown promising activity against ovarian cancer in vitro;, however, it has low bioavailability in vivo. Thus, we investigated the cytotoxicity of niclosamide analogs in combination with carboplatin in ovarian cancer cell lines and against ovarian cancer patient ascites cells.

Methods: Tumorspheres were isolated from ascites collected from 8 patients undergoing ovarian cancer surgery at UAB. Tumorspheres were plated at 10,000 cells per 50 µL into low attachment plates. Eight patient samples were treated concurrently with niclosamide analog 11 (0.1 µM - 5 µM) and carboplatin (5 - 150 μM), while four 4 patient samples were treated with analog 32 (0.1 µM - 5 µM) and carboplatin (5 - 100 μM). After 48 hours, cells were analyzed for viability using the ATPlite assay. Analogs 11 and 32 were also assayed in combination with carboplatin against ovarian cancer cell lines, A2780, A2780.cp20, SKOV3ip2, and SKOV3ip2.TR.

Results: IC50 values for analog 11 ranged from 0.5 - 1 μM in the 8 patient ascites samples. With 150 μM carboplatin alone, patient samples had 40-80% cytotoxicity. In combination with analog 11 at 1 μM, 100% of cells were killed with 100 μM carboplatin in the 8 patient ascites samples. In the established ovarian cancer cell lines, cytotoxicity approached 100% at a dose of 3 - 5 μM of analog 11. In the 4 patient samples treated with analog 32, IC50 values ranged from 0.4 μM - 3 μM. With 100 μM carboplatin alone, patient samples had 40-80% cytotoxicity. In combination with 100 μM carboplatin, nearly 100% of cells were killed at a dose of 1 μM of analog 32. In the cell lines, IC50 values for analog 32 ranged from 0.9 - 2.5 μM. With combination treatment, there was increased cytotoxicity in the chemoresistant cells, A2780.cp20 and SKOV3ip2, compared to carboplatin alone.

Conclusion: These niclosamide analogs produced cytotoxicity both alone and in combination with carboplatin against ovarian cancer cells and tumorspheres from patient ascites. Future studies will evaluate the PK/PD of the analogs.

Citation Format: Christen L. Walters Haygood, Rebecca C. Arend, Pui-Kai Li, Yonghe Li, Chandrika Kurpad, Abhishek Gangrade, John M. Straughn, Donald Buchsbaum. Niclosamide analogs for treatment of ovarian cancer. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 4677. doi:10.1158/1538-7445.AM2014-4677

Biological Activity of 1-Aryl-3-phenethylamino-1-propanone Hydrochlorides and 3-Aroyl-4-aryl-1-phenethyl-4-piperidinols on PC-3 Cells and DNA Topoisomerase I Enzyme

A number of studies reported Mannich bases to manifest antimicrobial, cytotoxic, anticancer, anti-inflammatory, and anticonvulsant activities. A considerable number of therapeutically important cytotoxic compounds are active on DNA topoisomerases that regulate the DNA topology. In the present study we evaluated the biological activity of mono- Mannich bases, 1-aryl-3-phenethylamino-1-propanone hydrochlorides (- 10a), and semicyclic mono- Mannich bases, 3-aroyl-4-aryl-1-phenethyl-4-piperidinols (1b - 9b), synthesized in our laboratory. We employed androgen-independent human prostate cancer cells (PC-3) to assess the cytotoxicity of the compounds and extended the biological activity evaluation to cover supercoil relaxation assays of mammalian type I topoisomerases. Our results showed that the compounds had cytotoxicity within the 8.2 - 32.1 μM range, while two compounds gave rise to a comparable average value in topo I interference of 42% and 40% for 10a (with a hydroxy substituent on the phenyl ring from mono-Mannich bases) and 5b (with a fluoro substituent on the phenyl ring from the semicyclic mono-Mannich base series, piperidinols), respectively

Pro-growth role of the JMJD2C histone demethylase in HCT-116 colon cancer cells and identification of curcuminoids as JMJD2 inhibitors

Colon tumors are a major cause of cancer death, yet their molecular intricacies are not fully understood. We demonstrate that the histone demethylases JMJD2A, JMJD2B and JMJD2C are overexpressed in colon cancer cell lines, whereas another related protein, JMJD2D, is not. Interestingly, despite their high homology, the intracellular localization of JMJD2A-C is different in colon and other cancer cells, with JMJD2A being present comparably in the cytoplasm and nucleus, JMJD2B more prevalent in the nucleus and JMJD2C strongly associated with chromatin. This suggests that each of these three proteins performs different, non-redundant functions. Moreover, we show that JMJD2C (also called KDM4C) forms complexes with β-catenin, an oncoprotein whose overexpression is crucial for the development of most colonic tumors. In addition, JMJD2C downregulation reduced both growth and clonogenic capacity of HCT-116 colon cancer cells. Further, JMJD2C was required for efficient expression of the growth stimulatory proteins FRA1 and cyclin D1 as well as the survival factor BCL2. Lastly, we identified derivatives of curcumin as in vitro inhibitors of JMJD2 enzymes, suggesting that these curcuminoids could be useful for decreasing JMJD2 activity in vivo. In conclusion, our data highlight that overexpression of JMJD2C confers a pro-growth effect on colon cancer cells and, therefore, its inhibition by curcuminoids or other small molecules could be beneficial as an adjuvant therapy for colon cancer patients.

Multi-targeted therapy of cancer by niclosamide: A new application for an old drug

The rapid development of new anticancer drugs that are safe and effective is a common goal shared by basic scientists, clinicians and patients. The current review discusses one such agent, namely niclosamide, which has been used in the clinic for the treatment of intestinal parasite infections. Recent studies repeatedly identified niclosamide as a potential anticancer agent by various high-throughput screening campaigns. Niclosamide not only inhibits the Wnt/β-catenin, mTORC1, STAT3, NF-κB and Notch signaling pathways, but also targets mitochondria in cancer cells to induce cell cycle arrest, growth inhibition and apoptosis. A number of studies have established the anticancer activities of niclosamide in both in vitro and in vivo models. Moreover, the inhibitory effects of niclosamide on cancer stem cells provide further evidence for its consideration as a promising drug for cancer therapy. This article reviews various aspects of niclosamide as they relate to its efficacy against cancer and associated molecular mechanisms.

Tumor-induced STAT3 signaling in myeloid cells impairs dendritic cell generation by decreasing PKCβII abundance

A major mechanism by which cancers escape control by the immune system is by blocking the differentiation of myeloid cells into dendritic cells (DCs), immunostimulatory cells that activate antitumor T cells. Tumor-dependent activation of signal transducer and activator of transcription 3 (STAT3) signaling in myeloid progenitor cells is thought to cause this block in their differentiation. In addition, a signaling pathway through protein kinase C βII (PKCβII) is essential for the differentiation of myeloid cells into DCs. We found in humans and mice that breast cancer cells substantially decreased the abundance of PKCβII in myeloid progenitor cells through a mechanism involving the enhanced activation of STAT3 signaling by soluble, tumor-derived factors (TDFs). STAT3 bound to previously undescribed negative regulatory elements within the promoter of PRKCB, which encodes PKCβII. We also found a previously undescribed counter-regulatory mechanism through which the activity of PKCβII inhibited tumor-dependent STAT3 signaling by decreasing the abundance of cell surface receptors, such as cytokine and growth factor receptors, that are activated by TDFs. Together, these data suggest that a previously unrecognized cross-talk mechanism between the STAT3 and PKCβII signaling pathways provides the molecular basis for the tumor-induced blockade in the differentiation of myeloid cells, and suggest that enhancing PKCβII activity may be a therapeutic strategy to alleviate cancer-mediated suppression of the immune system.

Evaluation of STAT3 signaling in ALDH+ and ALDH+/CD44+/CD24- subpopulations of breast cancer cells

BACKGROUND

STAT3 activation is frequently detected in breast cancer and this pathway has emerged as an attractive molecular target for cancer treatment. Recent experimental evidence suggests ALDH-positive (ALDH(+)), or cell surface molecule CD44-positive (CD44(+)) but CD24-negative (CD24(-)) breast cancer cells have cancer stem cell properties. However, the role of STAT3 signaling in ALDH(+) and ALDH(+)/CD44(+)/CD24(-) subpopulations of breast cancer cells is unknown.

METHODS AND RESULTS

We examined STAT3 activation in ALDH(+) and ALDH(+)/CD44(+)/CD24(-) subpopulations of breast cancer cells by sorting with flow cytometer. We observed ALDH-positive (ALDH(+)) cells expressed higher levels of phosphorylated STAT3 compared to ALDH-negative (ALDH(-)) cells. There was a significant correlation between the nuclear staining of phosphorylated STAT3 and the expression of ALDH1 in breast cancer tissues. These results suggest that STAT3 is activated in ALDH(+) subpopulations of breast cancer cells. STAT3 inhibitors Stattic and LLL12 inhibited STAT3 phosphorylation, reduced the ALDH(+) subpopulation, inhibited breast cancer stem-like cell viability, and retarded tumorisphere-forming capacity in vitro. Similar inhibition of STAT3 phosphorylation, and breast cancer stem cell viability were observed using STAT3 ShRNA. In addition, LLL12 inhibited STAT3 downstream target gene expression and induced apoptosis in ALDH(+) subpopulations of breast cancer cells. Furthermore, LLL12 inhibited STAT3 phosphorylation and tumor cell proliferation, induced apoptosis, and suppressed tumor growth in xenograft and mammary fat pad mouse models from ALDH(+) breast cancer cells. Similar in vitro and tumor growth in vivo results were obtained when ALDH(+) cells were further selected for the stem cell markers CD44(+) and CD24(-).

CONCLUSION

These studies demonstrate an important role for STAT3 signaling in ALDH(+) and ALDH(+)/CD44(+)/CD24(-) subpopulations of breast cancer cells which may have cancer stem cell properties and suggest that pharmacologic inhibition of STAT3 represents an effective strategy to selectively target the cancer stem cell-like subpopulation.

Structure-activity relationship studies of thalidomide analogs with a taxol-like mode of action

Anti-microtubule agents such as paclitaxel and docetaxel have played an important role in the treatment of cancer for many years. Recently, a small molecule that has a taxol-like mode of action (5HPP-33) was reported. Herein, the detailed structure-activity relationship (SAR) studies of 5HPP-33 analogs that are substituted at the isoindole and phenyl rings are described. Bulky substitutions (such as di-isopropyl groups) on the phenyl ring result in the isoindole and phenyl rings being perpendicular to each other. It was found that this conformation is critical for anti-microtubule activity. These studies have provided valuable information, which will be helpful in the design of more potent analogs.

Phosphoproteomic analysis of anaplastic lymphoma kinase (ALK) downstream signaling pathways identifies signal transducer and activator of transcription 3 as a functional target of activated ALK in neuroblastoma cells

Activation of the anaplastic lymphoma kinase (ALK) receptor tyrosine kinase is a key oncogenic mechanism in a growing number of tumor types. In the majority of cases, ALK is activated by fusion with a dimerizing partner protein as a result of chromosomal translocation events, most studied in the case of the nucleophosmin–ALK and echinoderm microtubule-associated protein-like 4–ALK oncoproteins. It is now also appreciated that the full-length ALK receptor can be activated by point mutations and by deletions within the extracellular domain, such as those observed in neuroblastoma. Several studies have employed phosphoproteomics approaches to find substrates of ALK fusion proteins. In this study, we used MS-based phosphotyrosine profiling to characterize phosphotyrosine signaling events associated with the full-length ALK receptor. A number of previously identified and novel targets were identified. One of these, signal transducer and activator of transcription 3 (STAT3), has previously been observed to be activated in response to oncogenic ALK signaling, but the significance of this in signaling from the full-length ALK receptor has not been explored further. We show here that activated ALK robustly activates STAT3 on Tyr705 in a number of independent neuroblastoma cell lines. Furthermore, knockdown of STAT3 by RNA interference resulted in a reduction in myelocytomatosis neuroblastom (MYCN) protein levels downstream of ALK signaling. These observations, together with a decreased level of MYCN and inhibition of neuroblastoma cell growth in the presence of STAT3 inhibitors, suggest that activation of STAT3 is important for ALK signaling activity in neuroblastoma.

Design, synthesis and biological studies of survivin dimerization modulators that prolong mitotic cycle

Survivin, a member of the inhibitor of apoptosis protein (IAP) family proteins, has essential roles in cell division and inhibition of apoptosis. Several clinical studies in cancer patients have shown that the elevated levels of survivin correlate with aggressiveness of the disease and resistance to radiation and chemotherapeutic treatments. Survivin is an integral component of chromosomal passenger complex (CPC) where it binds to borealin and INCENP through its dimerization interface. Thus, disruption of functional survivin along its dimer interface with a small molecule is hypothesized to inhibit the proliferation of cancer cells and sensitize them to therapeutic agents and radiation. Recently, a small molecule (Abbott8) was reported to bind at the dimerization interface of survivin. Further development of this compound was accomplished by computational modeling of the molecular interactions along the dimerization interface, which has led to the design of promising survivin dimerization modulators. Two of the most potent survivin modulators, LLP3 and LLP9 at concentrations between 50 and 100nM, caused delay in mitotic progression and major mitotic defects in proliferating human umbilical vein endothelial cells (HUVEC) and prostate cancer cells (PC3).

JAK-STAT blockade inhibits tumor initiation and clonogenic recovery of prostate cancer stem-like cells

Interleukin (IL)-6 overexpression and constitutive STAT3 activation occur in many cancers, including prostate cancer. However, their contribution to prostate stem and progenitor cells has not been explored. In this study, we show that stem-like cells from patients with prostate cancer secrete higher levels of IL-6 than their counterparts in non-neoplastic prostate. Tumor grade did not influence the levels of expression or secretion. Stem-like and progenitor cells expressed the IL-6 receptor gp80 with concomitant expression of pSTAT3. Blockade of activated STAT3, by either anti-IL-6 antibody siltuximab (CNTO 328) or LLL12, a specific pSTAT3 inhibitor, suppressed the clonogenicity of the stem-like cells in patients with high-grade disease. In a murine xenograft model used to determine the in vivo effects of pSTAT3 suppression, LLL12 treatment effectively abolished outgrowth of a patient-derived castrate-resistant tumor. Our results indicate that the most primitive cells in prostate cancer require pSTAT3 for survival, rationalizing STAT3 as a therapeutic target to treat advanced prostate cancer.

Anticancer activity and SAR studies of substituted 1,4-naphthoquinones

In this paper, we report the structure-activity relationship studies of substituted 1,4-naphthoquinones for its anticancer properties. 1,4-Naphthoquinone, Juglone, Menadione, Plumbagin and LLL12.1 were used as lead molecules to design PD compounds. Most of the PD compounds showed improved antiproliferative activity in comparison to the lead molecule in prostate (DU-145), breast (MDA-MB-231) and colon (HT-29) cancer cell lines. PD9, PD10, PD11, PD13, PD14 and PD15 were found to be the most potent compound with an IC₀ value of 1-3 μM in all cancer cell lines. Fluorescent polarization assay was employed to study the inhibition of STAT3 dimerization by PD compounds. PD9 and PD18 were found to be potent STAT3 dimerization inhibitors.

Structurally modified curcumin analogs inhibit STAT3 phosphorylation and promote apoptosis of human renal cell carcinoma and melanoma cell lines

The Janus kinase-2 (Jak2)-signal transducer and activator of transcription-3 (STAT3) pathway is critical for promoting an oncogenic and metastatic phenotype in several types of cancer including renal cell carcinoma (RCC) and melanoma. This study describes two small molecule inhibitors of the Jak2-STAT3 pathway, FLLL32 and its more soluble analog, FLLL62. These compounds are structurally distinct curcumin analogs that bind selectively to the SH2 domain of STAT3 to inhibit its phosphorylation and dimerization. We hypothesized that FLLL32 and FLLL62 would induce apoptosis in RCC and melanoma cells and display specificity for the Jak2-STAT3 pathway. FLLL32 and FLLL62 could inhibit STAT3 dimerization in vitro. These compounds reduced basal STAT3 phosphorylation (pSTAT3), and induced apoptosis in four separate human RCC cell lines and in human melanoma cell lines as determined by Annexin V/PI staining. Apoptosis was also confirmed by immunoblot analysis of caspase-3 processing and PARP cleavage. Pre-treatment of RCC and melanoma cell lines with FLLL32/62 did not inhibit IFN-γ-induced pSTAT1. In contrast to FLLL32, curcumin and FLLL62 reduced downstream STAT1-mediated gene expression of IRF1 as determined by Real Time PCR. FLLL32 and FLLL62 significantly reduced secretion of VEGF from RCC cell lines in a dose-dependent manner as determined by ELISA. Finally, each of these compounds inhibited in vitro generation of myeloid-derived suppressor cells. These data support further investigation of FLLL32 and FLLL62 as lead compounds for STAT3 inhibition in RCC and melanoma.

First-in-human trial of a STAT3 decoy oligonucleotide in head and neck tumors: implications for cancer therapy

Despite evidence implicating transcription factors, including STAT3, in oncogenesis, these proteins have been regarded as "undruggable." We developed a decoy targeting STAT3 and conducted a phase 0 trial. Expression levels of STAT3 target genes were decreased in head and neck cancers following injection with the STAT3 decoy compared with tumors receiving saline control. Decoys have not been amenable to systemic administration due to instability. To overcome this barrier, we linked the oligonucleotide strands using hexaethylene glycol spacers. This cyclic STAT3 decoy bound with high affinity to STAT3 protein, reduced cellular viability, and suppressed STAT3 target gene expression in cancer cells. Intravenous injection of the cyclic STAT3 decoy inhibited xenograft growth and downregulated STAT3 target genes in the tumors. These results provide the first demonstration of a successful strategy to inhibit tumor STAT3 signaling via systemic administration of a selective STAT3 inhibitor, thereby paving the way for broad clinical development.

SIGNIFICANCE

This is the fi rst study of a STAT3-selective inhibitor in humans and the fi rst evidence that a transcription factor decoy can be modifi ed to enable systemic delivery. These findings have therapeutic implications beyond STAT3 to other “undruggable” targets in human cancers.

Creating diverse target-binding surfaces on FKBP12: synthesis and evaluation of a rapamycin analogue library

FK506 and rapamycin are immunosuppressive drugs with a unique mode of action. Prior to binding to their protein targets, these drugs form a complex with an endogenous chaperone FK506-binding protein 12 (FKBP12). The resulting composite FK506-FKBP and rapamycin-FKBP binding surfaces recognize the relatively flat target surfaces of calcineurin and mTOR, respectively, with high affinity and specificity. To test whether this mode of action may be generalized to inhibit other protein targets, especially those that are challenging to inhibit by conventional small molecules, we have developed a parallel synthesis method to generate a 200-member library of bifunctional cyclic peptides as FK506 and rapamycin analogues, which were referred to as "rapalogs". Each rapalog consists of a common FKBP-binding moiety and a variable effector domain. The rapalogs were tested for binding to FKBP12 by a fluorescence polarization competition assay. Our results show that FKBP12 binds to most of the rapalogs with high affinity (K(I) values in the nanomolar to low micromolar range), creating a large repertoire of composite surfaces for potential recognition of macromolecular targets such as proteins.

STAT3 is necessary for proliferation and survival in colon cancer-initiating cells

STAT3 is constitutively activated in colon cancer but its contributions in cancer-initiating cells have not been explored. In this study, we characterized STAT3 in aldehyde dehydrogenase (ALDH)-positive (ALDH(+)) and CD133-positive (CD133(+)) subpopulations of human colon tumor cells that exhibited more potent tumor-initiating ability than ALDH(-)/CD133(-) cells in tumor xenograft assays in mice. We found that ALDH(+)/CD133(+) cells expressed higher levels of the active phosphorylated form of STAT3 than either ALDH(-)/CD133(-) or unfractionated colon cancer cells. STAT3 inhibition by RNA interference-mediated knockdown or small-molecule inhibitors LLL12 or Stattic blocked downstream target gene expression, cell viability, and tumorsphere-forming capacity in cancer-initiating cells. Similarly, treatment of mouse tumor xenografts with STAT3 short hairpin RNA (shRNA), interleukin 6 shRNA, or LLL12 inhibited tumor growth. Our results establish that STAT3 is constitutively activated in colon cancer-initiating cells and that these cells are sensitive to STAT3 inhibition. These findings establish a powerful rationale to develop STAT3 inhibitory strategies for treating advanced colorectal cancers.

A small molecule, LLL12 inhibits constitutive STAT3 and IL-6-induced STAT3 signaling and exhibits potent growth suppressive activity in human multiple myeloma cells

We characterized the effects of a newly developed signal transducers and activators of transcription 3 (STAT3) inhibitor, LLL12 in multiple myeloma (MM) cells. LLL12 specifically inhibited STAT3 phosphorylation, nuclear localization, DNA binding activity, down-regulated STAT3 downstream genes, and induced apoptosis in MM cells. Importantly, LLL12 significantly inhibited STAT3 phosphorylation, induced apoptosis in primary MM cells which came from patients that were clinically resistant to lenalidomide and bortezomib. LLL12 is a potent inhibitor of cell proliferation with IC50 values ranging between 0.26 and 1.96 μM in MM and primary MM cells. LLL12 also inhibited STAT3 phosphorylation induced by interleukin-6 (IL-6) and interferon-α but not STAT1, STAT2, STAT4 and STAT6 phosphorylation induced by interferon-α, interferon-γ and IL-4 indicating the selectivity of LLL12 for STAT3. The selectively of LLL12 on STAT3 was further demonstrated on 21 protein kinases, which LLL12 had IC50 values ≥ 73.92 μM. In addition, the pretreatment of LLL12 blocked the promotion of the cell proliferation and resistance to lenalidomide by IL-6. Furthermore, LLL12 significantly blocked tumor growth of MM cells in mouse model. Our results indicate that LLL12 blocks constitutive STAT3 and IL-6 induced STAT3 signaling and may be a potential therapeutic agent for MM.

LLL12 inhibits endogenous and exogenous interleukin-6-induced STAT3 phosphorylation in human pancreatic cancer cells

Pancreatic cancer is one of the most serious types of cancer, with a five-year survival rate at only 6%. There is a critical need to develop more effective treatments for pancreatic cancer. Growing evidence shows that chronic inflammation plays a crucial role in tumor initiation and progression. Here we demonstrated that the endogenous expression of the inflammatory cytokine interleukin-6 (IL-6) correlates with signal transducer and activator of transcription 3 (STAT3) phosphorylation in human pancreatic cancer cells. Inhibition of the endogenous IL-6/STAT3 pathway reduces cell viability. Exogenous IL-6 induces STAT3 phosphorylation, but differently induces phosphorylation of STAT3 upstream kinases, Janus kinase 1(JAK1), JAK2, and tyrosine kinase 2 (TYK2). Interestingly, LLL12, a nonpeptide, cell-permeable small molecule, selectively blocked exogenous IL-6-induced STAT3 phosphorylation and nuclear translocation in both PANC-1 and ASPC-1 pancreatic cancer cell lines independently of the phosphorylation of JAK1, JAK2, and TYK2. These results suggest that the inhibition of endogenous and exogenous IL-6-mediated STAT3 signaling may be a potential therapeutic approach for pancreatic cancer.

The small molecule, LLL12, inhibits STAT3 phosphorylation and induces apoptosis in medulloblastoma and glioblastoma cells

Tumors of the central nervous system represent a major source of cancer-related deaths, with medulloblastoma and glioblastoma being the most common malignant brain tumors in children and adults respectively. While significant advances in treatment have been made, with the 5-year survival rate for medulloblastoma at 70-80%, treating patients under 3 years of age still poses a problem due to the deleterious effects of radiation on the developing brain, and the median survival for patients with glioblastoma is only 15 months. The transcription factor, STAT3, has been found constitutively activated in a wide variety of cancers and in recent years it has become an attractive therapeutic target. We designed a non-peptide small molecule STAT3 inhibitor, LLL12, using structure-based design. LLL12 was able to inhibit STAT3 phosphorylation, decrease cell viability and induce apoptosis in medulloblastoma and glioblastoma cell lines with elevated levels of p-STAT3 (Y705). IC(50) values for LLL12 were found to be between 1.07 µM and 5.98 µM in the five cell lines expressing phosphorylated STAT3. STAT3 target genes were found to be downregulated and a decrease in STAT3 DNA binding was observed following LLL12 treatment, indicating that LLL12 is an effective STAT3 inhibitor. LLL12 was also able to inhibit colony formation, wound healing and decreased IL-6 and LIF secretion. Our results suggest that LLL12 is a potent STAT3 inhibitor and that it may be a potential therapeutic treatment for medulloblastoma and glioblastoma.

Abstract 2444: STAT3 is necessary for proliferation and survival in pancreatic cancer-initiating cells

In recent years, cancer-initiating cells or cancer stem cells have been demonstrated in a variety of solid tumors including pancreatic cancer. This subpopulation of cancer cells has the ability to initiate and perpetuate tumor growth, and may be highly resistant to radiation or chemotherapy. Therefore, this subpopulation could be a very important and novel target for cancer therapy. Persistent activation of STAT3 is detected in many types of cancer including in pancreatic cancer. However, whether STAT3 is activated in pancreatic cancer-initiating cells and what role STAT3 signaling may play in them is still unknown. It has been reported that pancreatic cancer stem cells can be identified and isolated with several cancer stem cell markers, such as ALDH1, CD44, and CD24. Therefore, we examined STAT3 phosphorylation and ALDH1, CD44, CD24 expression in 30 cases of human pancreatic cancer tissues using tissue microarray slides. We observed there is a significant association between the nuclear staining of STAT3 phosphorylation and ALDH1 (p<0.01). In addition, the tumor samples express elevated levels of phosphorylated STAT3 also associated with CD44+ and CD24+ (p<0.01). These results indicate constitutive STAT3 signaling may be a novel therapeutic target in pancreatic cancer initiating cells. We next separated pancreatic cancer-initiating cells from human pancreatic cancer cell lines using ALDH1, CD44, and CD24 markers by flow cytometry. We found ALDH+ or CD44+/CD24+ pancreatic cells had more potent tumorspheres formation ability than ALDH− or CD44−/CD24− cells. Interestingly, we observed the ALDH+ and CD44+/CD24+ subpopulation of pancreatic cancer cells expressed higher levels of phosphorylated STAT3, compared to ALDH− or CD44−/CD24− subpopulation of pancreatic cancer cells. These results are consistent to the data using pancreatic cancer tissues from cancer patients suggesting that STAT3 is activated in pancreatic cancer-initiating cells. Furthermore, we demonstrated that three small molecular STAT3 inhibitors, LLL12, FLLL32, and Stattic inhibited STAT3 phosphorylation, cell viability, tumorsphere growth and induced apoptosis in pancreatic cancer-initiating cells. The inhibitory efficacy of the novel STAT3 inhibitor on pancreatic cancer-initiating cells in mouse tumor model will be examined. In conclusion, this is the first report to demonstrate that persistent STAT3 phosphorylation is expressed in pancreatic cancer-initiating cells. Our study is also the first attempt to target STAT3 in pancreatic cancer-initiating cells and we demonstrated for the first time that pancreatic cancer stem cells are indeed sensitive to the inhibition by three small molecular STAT3 inhibitors. Our results suggest STAT3 is a novel therapeutic target in pancreatic cancer-initiating cells and inhibition of activated STAT3 in cancer-initiating cells may offer an effective therapy approach for pancreatic cancer.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 2444. doi:10.1158/1538-7445.AM2011-2444

Abstract 933: The expression of PRMT5 methyltransferase mediates cell survival and metastatic phenotype in malignant melanoma

Post-translational modification of proteins is involved at all levels of cellular regulation. The PRMT5 enzyme is a type II arginine methyltransferase that catalyzes the transfer of a methyl group to two of three guanidino nitrogen atoms within the arginine molecule. This enzyme has been shown to methylate histone H3 at arginine 8 (H3R8) and H4R3 to trigger silencing of tumor suppressor genes. In addition, PRMT5 has been shown to interact with p53, TRAIL receptor, and the CDK4 complex to regulate the cell cycle or apoptosis. Although prior studies have provided insight into these mechanistic features of the PRMT enzymes, most data are derived from a limited panel of cell lines. PRMT5 over-expression has recently been shown to influence progression of leukemia and lymphoma. However, few, if any publications exist which document the role of PRMT enzymes in melanoma. We hypothesized that PRMT5 expression promotes metastasis and contributes to reduced immunologic recognition of melanoma cells. Immunoblot analysis and confocal microscopy revealed that PRMT5 is expressed in a panel of melanoma cell lines regardless of the mutational status of B-Raf, NRas, or p53. siRNA-mediated inhibition of PRMT5 led to apoptosis and restored CXCL10 chemokine expression. PRMT5 expression was next determined by immunohistochemical (IHC) analysis of formalin-fixed samples from patients with melanoma (n=56 primary; n=20 metastases) or benign nevi (n=24). The specimens were obtained as a commercially-available tissue microarray, or procured as de-identified primary patient samples (IRB #20100071; P.I. Lesinski; OSU IRB # 2002H0089; co-PI: Peters). PRMT5 expression was significantly increased in the nucleus of melanoma cells as compared to normal epidermis or benign nevi (p=0.001). The level of cytoplasmic PRMT5 expression was also elevated in melanoma lesions, however its distribution in benign tissues was bimodal, and expressed in a subset of benign samples. Notably, nuclear PRMT5 expression increased as melanoma cells invaded the dermis or in melanoma lesions exhibiting pagetoid spread. Finally, we have identified a specific inhibitor of PRMT5 arginine methyltransferase activity from a small molecule library. This lead compound (BLL-1) blocked the dimethylation of arginine 3 on histone H4 (H4R3me2s). A series of titration experiments revealed reduction of both H4R3me2s and proliferation rate. Treatment of multiple melanoma cell lines with BLL-1 (24 hr) led to significantly increased apoptosis. These data represent the first report of PRMT5 and its inhibition in melanoma. Together, this suggests PRMT5 inhibition as a potential therapeutic strategy by virtue of its ability to promote apoptosis and restore immunomodulatory gene expression.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 933. doi:10.1158/1538-7445.AM2011-933

The novel curcumin analog FLLL32 decreases STAT3 DNA binding activity and expression, and induces apoptosis in osteosarcoma cell lines

Background

Curcumin is a naturally occurring phenolic compound shown to have a wide variety of antitumor activities; however, it does not attain sufficient blood levels to do so when ingested. Using structure-based design, a novel compound, FLLL32, was generated from curcumin. FLLL32 possesses superior biochemical properties and more specifically targets STAT3, a transcription factor important in tumor cell survival, proliferation, metastasis, and chemotherapy resistance. In our previous work, we found that several canine and human osteosarcoma (OSA) cell lines, but not normal osteoblasts, exhibit constitutive phosphorylation of STAT3. Compared to curcumin, we hypothesized that FLLL32 would be more efficient at inhibiting STAT3 function in OSA cells and that this would result in enhanced downregulation of STAT3 transcriptional targets and subsequent death of OSA cells.

Methods

Human and canine OSA cells were treated with vehicle, curcumin, or FLLL32 and the effects on proliferation (CyQUANT^®), apoptosis (SensoLyte^® Homogeneous AMC Caspase- 3/7 Assay kit, western blotting), STAT3 DNA binding (EMSA), and vascular endothelial growth factor (VEGF), survivin, and matrix metalloproteinase-2 (MMP2) expression (RT-PCR, western blotting) were measured. STAT3 expression was measured by RT-PCR, qRT- PCR, and western blotting.

Results

Our data showed that FLLL32 decreased STAT3 DNA binding by EMSA. FLLL32 promoted loss of cell proliferation at lower concentrations than curcumin leading to caspase-3- dependent apoptosis, as evidenced by PARP cleavage and increased caspase 3/7 activity; this could be inhibited by treatment with the pan-caspase inhibitor Z-VAD-FMK. Treatment of OSA cells with FLLL32 decreased expression of survivin, VEGF, and MMP2 at both mRNA and protein levels with concurrent decreases in phosphorylated and total STAT3; this loss of total STAT3 occurred, in part, via the ubiquitin-proteasome pathway.

Conclusions

These data demonstrate that the novel curcumin analog FLLL32 has biologic activity against OSA cell lines through inhibition of STAT3 function and expression. Future work with FLLL32 will define the therapeutic potential of this compound in vivo.

Two small molecule compounds, LLL12 and FLLL32, exhibit potent inhibitory activity on STAT3 in human rhabdomyosarcoma cells

Signal transducers and activators of transcription 3 (STAT3) signaling is persistently activated in many types of cancer cells, and represents a valid target for anticancer drug design. However, few reports have described the constitutive activation of STAT3 in human sarcoma cells. In this study, we demonstrate that the STAT3 signaling pathway is constitutively activated in human rhabodomyosarcoma cells (RH28, RH30, and RD2). We also investigated the inhibitory effects of two newly developed small molecules, LLL12 and FLLL32, on the STAT3 signaling pathway in human rhabodomyosarcoma cells. Both LLL12 and FLLL32 downregulated STAT3 constitutively and interleukin-6 (IL-6) stimulated phosphorylated STAT3 (p-STAT3). The inhibition of STAT3 via LLL12 and FLLL32 was confirmed by the inhibition of STAT3 DNA binding activity. The downstream targets of STAT3, cyclin D1, Bcl-xL, and survivin were also downregulated by LLL12 and FLLL 32 at both messenger RNA and protein levels. The potency of LLL12 and FLLL32 to inhibit proliferation/viability in human rhabodomyosarcoma cells (RH28, RH30, and RD2) was higher than that of the 5 previously reported Janus kinase 2 (JAK2)/STAT3 inhibitors (LLL3, WP1066, Stattic, S3I-201, and AG490) and curcumin. Thus, in this study, we investigated the inhibitory effects of two STAT3 inhibitors, LLL12 and FLLL32, on the STAT3 signaling pathway in human rhabodomyosarcoma cells; we also demonstrated their higher potency in inhibiting proliferation on human rhabodomyosarcoma cells as compared to other five JAK2/STAT3 inhibitors and curcumin.

Abstract A100: STAT3 as a novel cancer prevention target in colorectal cancer stem cells

Constitutive activation of signal transducers and activators of transcription 3 (STAT3) signaling is frequently detected in human cancer including colon cancer, and has emerged as an attractive molecular target for cancer prevention. Recent experimental evidence suggests that the existence of a small population of tumorigenic stem/progenitor cells may be responsible for tumor initiation, chemotherapy and radiation resistance, invasion, recurrence, and metastasis. An increasing body of evidence suggests that the cancer stem cell concept is also relevant to colorectal cancer. To date, however, whether STAT3 is activated in colon cancer stem cells or cancer-initiating cells and what the role of STAT3 signaling may play in these cancer stem cells is still unknown. If STAT3 is activated in colorectal cancer stem cells, inhibiting STAT3 may offer a promising opportunity to target colorectal cancer stem cells and prevent the recurrence of cancer. We utilized the colon cancer stem cells, which are characterized by an aldehyde dehydrogenase (ALDH)-positive (ALDH+) and CD133-positive (CD133+) subpopulation. We demonstrated that ALDH+/CD133+ cells have capacity than ALDH-/CD133- cells to form more tumorspheres and to exhibit more potent tumor-initiating ability in mice. We then examined the STAT3 activation in these colon cancer cells. Interestingly, we observed that the ALDH+/CD133+ subpopulation of colon cancer cells expressed higher levels of phosphorylated STAT3, an active form of STAT3, compared to the ALDH-/CD133- subpopulation and un-separated colon cancer cells, suggesting that STAT3 is activated in colon cancer stem cells. We demonstrated that dietary agent, curcumin and a new curcumin analog, GO-Y030 can inhibit STAT3 phosphorylation, cell viability, and induced apoptosis in colon cancer stem cells. The inhibition of STAT3 was confirmed using a novel STAT3-selecitve curcumin analog, FLLL32, STAT3 ShRNA, as well as STAT3 inhibitors, LLL12 and Stattic. All these STAT3 inhibitors, inhibited STAT3 phosphorylation, cell viability, and tumorsphere growth in colon cancer stem cells. Furthermore, both GO-Y030 and LLL12 inhibited tumor growth of colon cancer stem cells in NOD/SCID mouse model in vivo. In Summary, this is the first report to demonstrate that persistent STAT3 phosphorylation is expressed in colon cancer stem cells. Our study is also the first attempt to target STAT3 in colon cancer stem cells and we demonstrated for the first time that colon cancer stem cells are indeed sensitive to the inhibition by small molecular STAT3 inhibitors, FLLL32, LLL12, Stattic, STAT3 shRNA, and curcumin analog, GO-Y030. Our results suggest that STAT3 is a novel prevention target in colon cancer stem cells and inhibition of activated STAT3 in cancer stem cells may offer an effective preventive approach for colorectal carcinoma.

Citation Information: Cancer Prev Res 2010;3(12 Suppl):A100.

Sorafenib overcomes TRAIL resistance of hepatocellular carcinoma cells through the inhibition of STAT3

PURPOSE

Recombinant tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is a promising antitumor agent. However, many hepatocellular carcinoma (HCC) cells show resistance to TRAIL-induced apoptosis. Here, we report that sorafenib improves the antitumor effect of TRAIL-related agents in resistant HCC.

EXPERIMENTAL DESIGN

HCC cell lines (PLC5, Huh-7, Hep3B, and Sk-Hep1) were treated with sorafenib and/or TRAIL-related agents (TRAIL or LBY135) and analyzed in terms of apoptosis and signal transduction. In vivo efficacy was determined in nude mice with PLC5 xenografts.

RESULTS

Sorafenib, the only approved drug for HCC, sensitizes resistant HCC cells to an agonistic DR5 antibody (LBY135) and TRAIL-induced apoptosis in TRAIL-resistant HCC cells. We found that STAT3 played a significant role in mediating TRAIL sensitization. Our data showed that sorafenib downregulated phospho-STAT3 (pSTAT3) and subsequently reduced the expression levels of STAT3-related proteins (Mcl-1, survivin, and cyclin D1) in a dose- and time-dependent manner in TRAIL-treated HCC cells. Knockdown of STAT3 by RNA interference overcame apoptotic resistance to TRAIL in HCC cells, and ectopic expression of STAT3 in HCC cells abolished the TRAIL-sensitizing effect of sorafenib. Moreover, SHP-1 inhibitor reversed downregulation of pSTAT3 and apoptosis induced by sorafenib, and silencing of SHP-1 by RNA interference abolished the effects of sorafenib on pSTAT3. Notably, sorafenib increased SHP-1 activity in PLC5 cells. Finally, sorafenib plus LBY135 significantly suppressed PLC5 xenograft tumor growth.

CONCLUSIONS

Sorafenib sensitizes resistant HCC cells to TRAIL-induced apoptosis at clinical achievable concentrations, and this effect is mediated via the inhibition of STAT3.

Sorafenib overcomes TRAIL resistance of hepatocellular carcinoma cells through the inhibition of STAT3

PURPOSE

Recombinant tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is a promising antitumor agent. However, many hepatocellular carcinoma (HCC) cells show resistance to TRAIL-induced apoptosis. Here, we report that sorafenib improves the antitumor effect of TRAIL-related agents in resistant HCC.

EXPERIMENTAL DESIGN

HCC cell lines (PLC5, Huh-7, Hep3B, and Sk-Hep1) were treated with sorafenib and/or TRAIL-related agents (TRAIL or LBY135) and analyzed in terms of apoptosis and signal transduction. In vivo efficacy was determined in nude mice with PLC5 xenografts.

RESULTS

Sorafenib, the only approved drug for HCC, sensitizes resistant HCC cells to an agonistic DR5 antibody (LBY135) and TRAIL-induced apoptosis in TRAIL-resistant HCC cells. We found that STAT3 played a significant role in mediating TRAIL sensitization. Our data showed that sorafenib downregulated phospho-STAT3 (pSTAT3) and subsequently reduced the expression levels of STAT3-related proteins (Mcl-1, survivin, and cyclin D1) in a dose- and time-dependent manner in TRAIL-treated HCC cells. Knockdown of STAT3 by RNA interference overcame apoptotic resistance to TRAIL in HCC cells, and ectopic expression of STAT3 in HCC cells abolished the TRAIL-sensitizing effect of sorafenib. Moreover, SHP-1 inhibitor reversed downregulation of pSTAT3 and apoptosis induced by sorafenib, and silencing of SHP-1 by RNA interference abolished the effects of sorafenib on pSTAT3. Notably, sorafenib increased SHP-1 activity in PLC5 cells. Finally, sorafenib plus LBY135 significantly suppressed PLC5 xenograft tumor growth.

CONCLUSIONS

Sorafenib sensitizes resistant HCC cells to TRAIL-induced apoptosis at clinical achievable concentrations, and this effect is mediated via the inhibition of STAT3.

A novel small molecule inhibits STAT3 phosphorylation and DNA binding activity and exhibits potent growth suppressive activity in human cancer cells

Background

Targeting Signal Transducer and Activator of Transcription 3 (STAT3) signaling is an attractive therapeutic approach for most types of human cancers with constitutively activated STAT3. A novel small molecular STAT3 inhibitor, FLLL32 was specifically designed from dietary agent, curcumin to inhibit constitutive STAT3 signaling in multiple myeloma, glioblastoma, liver cancer, and colorectal cancer cells.

Results

FLLL32 was found to be a potent inhibitor of STAT3 phosphorylation, STAT3 DNA binding activity, and the expression of STAT3 downstream target genes in vitro, leading to the inhibition of cell proliferation as well as the induction of Caspase-3 and PARP cleavages in human multiple myeloma, glioblastoma, liver cancer, and colorectal cancer cell lines. However, FLLL32 exhibited little inhibition on some tyrosine kinases containing SH2 or both SH2 and SH3 domains, and other protein and lipid kinases using a kinase profile assay. FLLL32 was also more potent than four previously reported JAK2 and STAT3 inhibitors as well as curcumin to inhibit cell viability in these cancer cells. Furthermore, FLLL32 selectively inhibited the induction of STAT3 phosphorylation by Interleukin-6 but not STAT1 phosphorylation by IFN-γ.

Conclusion

Our findings indicate that FLLL32 exhibits potent inhibitory activity to STAT3 and has potential for targeting multiple myeloma, glioblastoma, liver cancer, and colorectal cancer cells expressing constitutive STAT3 signaling.