γ-Tocotrienol is a novel inhibitor of constitutive and inducible STAT3 signalling pathway in human hepatocellular carcinoma: potential role as an antiproliferative, pro-apoptotic and chemosensitizing agent

Improved antitumor activity and reduced cardiotoxicity of epirubicin using hepatocyte-targeted nanoparticles combined with tocotrienols against hepatocellular carcinoma in mice

Hepatocellular carcinoma (HCC) is the third most common cause of cancer death worldwide. Epirubicin (EPI), an anthracycline derivative, is one of the main line treatments for HCC. However, serious side effects including cardiomyopathy and congestive heart failure limit its long term administration. Our main goal is to develop a delivery strategy that ensures improved efficacy of the chemotherapeutic agent together with reduced cardiotoxicity. In this context, EPI was loaded in chitosan-PLGA nanoparticles linked with asialofetuin (EPI-NPs) selectively targeting hepatocytes. In an attempt to reduce cardiotoxicity, targeted EPI-NPs were coadministered with tocotrienols. EPI-NPs significantly enhanced the antiproliferative effect compared to free EPI as studied on Hep G2 cell line. Nanoencapsulated EPI injected in HCC mouse model revealed higher p53-mediated apoptosis and reduced angiogenesis in the tumor. Combined therapy of EPI-NPs with tocotrienols further enhanced apoptosis and reduced VEGF level in a dose dependent manner. Assessment of cardiotoxicity indicated that EPI-NPs diminished the high level of proinflammatory cytokine tumor necrosis factor-α (TNF-α) as well as oxidative stress-induced cardiotoxicity as manifested by reduced level of lipid peroxidation products (TBARS) and nitric oxide (NO). EPI-NPs additionally restored the diminished level of superoxide dismutase (SOD) and reduced glutathione (GSH) in the heart. Interestingly, tocotrienols provided both antitumor activity and higher protection against oxidative stress and inflammation induced by EPI in the heart. This hepatocyte-targeted biodegradable nanoparticle/tocotrienol combined therapy represents intriguing therapeutic strategy for EPI providing not only superior efficacy but also higher safety levels.

Abrogation of STAT3 signaling cascade by zerumbone inhibits proliferation and induces apoptosis in renal cell carcinoma xenograft mouse model

Persistent activation of signal transducer and activator of transcription 3 (STAT3) is one of the characteristic features of renal cell carcinoma (RCC) and often linked to its deregulated proliferation, survival, and angiogenesis. In the present report, we investigated whether zerumbone, a sesquiterpene, exerts its anticancer effect through modulation of STAT3 activation pathway. The pharmacological effect of zerumbone on STAT3 activation, associated protein kinases and phosphatase, and apoptosis was investigated using both RCC cell lines and xenograft mouse model. We observed that zerumbone suppressed STAT3 activation in a dose- and time-dependent manner in RCC cells. The suppression was mediated through the inhibition of activation of upstream kinases c-Src, Janus-activated kinase 1, and Janus-activated kinase 2. Pervanadate treatment reversed zerumbone-induced downregulation of STAT3, suggesting the involvement of a tyrosine phosphatase. Indeed, we found that zerumbone induced the expression of tyrosine phosphatase SHP-1 that correlated with its ability to inhibit STAT3 activation. Interestingly, deletion of SHP-1 gene by siRNA abolished the ability of zerumbone to inhibit STAT3 activation. The inhibition of STAT3 activation by zerumbone also caused the suppression of the gene products involved in proliferation, survival, and angiogenesis. Finally, when administered i.p., zerumbone inhibited STAT3 activation in tumor tissues and the growth of human RCC xenograft tumors in athymic nu/nu mice without any side effects. Overall, our results suggest for the first time that zerumbone is a novel blocker of STAT3 signaling cascade and thus has an enormous potential for the treatment of RCC and other solid tumors.

Gö6976, a FLT3 kinase inhibitor, exerts potent cytotoxic activity against acute leukemia via inhibition of survivin and MCL-1

Mutations of the FMS-like tyrosine kinase 3 (FLT3) have been reported in about a third of patients with acute myeloid leukemia (AML). The presence of FLT3 mutations confers a poor prognosis. Thus, pharmacological inhibitors of FLT3 are of therapeutic interest for AML. Gö6976 is an indolocarbazole with a similar structural backbone to staurosporine. In the present study, we demonstrated that Gö6976 displays a potent inhibitory activity against recombinant FLT3 using an in vitro kinase assay, with an IC50 value of 0.7nM. Gö6976 markedly inhibited the proliferation of human leukemia cells having FLT3-ITD such as MV4-11 and MOLM13. We also observed that Gö6976 showed minimal toxicity for human normal CD34(+) cells. Gö6976 suppressed the phosphorylation of FLT3 and downstream signaling molecules such as STAT3/5, Erk1/2, and Akt in MV4-11 and MOLM13 cells. Interestingly, induction of apoptosis by Gö6976 was associated with rapid and pronounced down-regulation of the anti-apoptotic protein survivin and MCL-1. Suppression of survivin protein expression by Gö6976 was due to the inhibition of transcription via the suppression of STAT3/5. On the other hand, Gö6976 induced proteasome-mediated degradation of MCL-1. Previously described FLT3 inhibitors such as PKC412 are bound by the human plasma protein, α1-acid glycoprotein, resulting in diminished inhibitory activity against FLT3. In contrast, we found that Gö6976 potently inhibited phosphorylation of FLT3 and exerted cytotoxicity in the presence of human serum. In conclusion, Gö6976 is a potent FLT3 inhibitor that displays a significant antiproliferative activity against leukemia cells with FLT3-ITD through the profound down-regulation of survivin and MCL-1.

Effect of vitamin E supplementation on aminotransferase levels in patients with NAFLD, NASH, and CHC: results from a meta-analysis

OBJECTIVE

The antioxidant vitamin E has been extensively employed to treat chronic liver diseases. The aim of this study was to assess the effect of vitamin E supplementation in lowering alanine aminotransferase (ALT) and aspartate aminotransferase (AST) levels in patients with nonalcoholic fatty liver disease (NAFLD), nonalcoholic steatohepatitis (NASH), and chronic hepatitis C (CHC).

METHODS

We searched all publications in PubMed, Web of Science, and Cochrane Library databases up to June 2013. In total, eight articles met the eligibility criteria, among which, two studies about NAFLD, four studies about NASH, and three studies about CHC, were identified and included in the meta-analysis.

RESULTS

According to standardized mean difference and 95% confidence interval, 12.19 (-4.08 to 28.46) for ALT and 6.84 (-3.18 to 16.86) for AST in patients with NAFLD, 4.54 (1.62-7.46) for ALT and 3.55 (1.39-5.71) for AST in patients with NASH, and 0.61 (0.20-1.02) for ALT and 0.68 (0.07-1.29) for AST in patients with CHC, vitamin E supplementation could optimize ALT and AST levels in patients with NASH and CHC, although it was not statistically significantly associated with reduced ALT and AST levels in patients with NAFLD.

CONCLUSION

To summarize, the evidence currently available supported the theory that vitamin E supplementation can optimize aminotransferase levels for patients with NAFLD, NASH, and CHC, and more well-designed, large-scale clinical trials are encouraged to examine the therapeutic effect of vitamin E for these disorders.

Therapeutic modulators of STAT signalling for human diseases

The signal transducer and activator of transcription (STAT) proteins have important roles in biological processes. The abnormal activation of STAT signalling pathways is also implicated in many human diseases, including cancer, autoimmune diseases, rheumatoid arthritis, asthma and diabetes. Over a decade has passed since the first inhibitor of a STAT protein was reported and efforts to discover modulators of STAT signalling as therapeutics continue. This Review discusses the outcomes of the ongoing drug discovery research endeavours against STAT proteins, provides perspectives on new directions for accelerating the discovery of drug candidates, and highlights the noteworthy candidate therapeutics that have progressed to clinical trials.

γ-Tocotrienol induces paraptosis-like cell death in human colon carcinoma SW620 cells

Colorectal cancer is one of the most serious illnesses among diagnosed cancer. As a new type of anti-cancer composition from tocotrienol-rich fraction of palm oil, γ-tocotrienol is widely used in anti-cancer research. The objectives of this study were to investigate the effects of γ-tocotrienol on human colon cancer SW620 and HCT-8 cells. We showed that treatment with different concentrations of γ-tocotrienol resulted in a dose dependent inhibition of cell growth. Cell death induced by γ-tocotrienol was mediated by a paraptosis-like cell death in SW620 and HCT-8 cells. Real-time RT-PCR and western blot analyses showed that γ-tocotrienol inhibited the expression level of β-catenin, cyclin D1 and c-jun. These data suggest that a paraptosis-like cell death induced by γ-tocotrienol in SW620 cells is associated with the suppression of the Wnt signaling pathway, which offers a novel tool for treating apoptosis-resistance colon cancer.

Potential role of signal transducer and activator of transcription (STAT)3 signaling pathway in inflammation, survival, proliferation and invasion of hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is one of the most lethal malignancies, and is also the fourth most common cancer worldwide with around 700,000 new cases each year. Currently, first line chemotherapeutic drugs used for HCC include fluorouracil, cisplatin, doxorubicin, paclitaxel and mitomycin, but most of these are non-selective cytotoxic molecules with significant side effects. Sorafenib is the only approved targeted therapy by the U.S. Food and Drug Administration for HCC treatment, but patients suffer from various kinds of adverse effects, including hypertension. The signal-transducer-and-activator-of-transcription 3 (STAT3) protein, one of the members of STATs transcription factor family, has been implicated in signal transduction by different cytokines, growth factors and oncogenes. In normal cells, STAT3 activation is tightly controlled to prevent dysregulated gene transcription, whereas constitutively activated STAT3 plays an important role in tumorigenesis through the upregulation of genes involved in anti-apoptosis, proliferation and angiogenesis. Thus, pharmacologically safe and effective agents that can block STAT3 activation have the potential both for the prevention and treatment of HCC. In the present review, we discuss the possible role of STAT3 signaling cascade and its interacting partners in the initiation of HCC and also analyze the role of various STAT3 regulated genes in HCC progression, inflammation, survival, invasion and angiogenesis.

A novel obatoclax derivative, SC-2001, induces apoptosis in hepatocellular carcinoma cells through SHP-1-dependent STAT3 inactivation

We investigated the effects of a novel compound, SC-2001, on hepatocellular carcinoma (HCC). SC-2001, which is structurally related to the Mcl-1 inhibitor obatoclax, showed better antitumor effects than obatoclax in HCC cell lines, including HepG2, PLC5 and Huh-7. Like obatoclax, SC-2001 inhibited the protein-protein interactions between Mcl-1 and Bak. However, SC-2001 downregulated the protein levels of Mcl-1 by reducing its transcription whereas obatoclax had no significant effect on Mcl-1 expression. As Mcl-1 is regulated by signal transducers and activators of transcription 3 (STAT3), we found that SC-2001 downregulated the phosphorylation of STAT3 (Tyr 705) and subsequently inhibited transcriptional activities of STAT3 in a dose-dependent manner. In addition to Mcl-1, STAT3-regulated proteins, including survivin and cyclin D1, were also repressed by SC-2001. Notably, SC-2001 reduced IL-6-induced STAT3 activation in HepG2 and PLC5 cells. Ectopic expression of STAT3 abolished the prominent apoptotic death in SC-2001-treated PLC5 cells, indicating that STAT3 is indispensable in mediating the effects of SC-2001. Importantly, SC-2001 enhanced the expression of SHP1, a negative regulator of STAT3. Inhibition of SHP-1 by either specific inhibitor or small interference RNA reduced the apoptotic effects of SC-2001, indicating that SHP-1 plays a key role in mediating SC2001-induced cell death. SC-2001 enhanced the activity of SHP-1 in all tested HCC cells including HepG2, PLC5 and Huh-7. Finally, SC-2001 reduced PLC5 tumor growth, downregulated p-STAT3 and upregulated SHP-1 expression and activity in vivo. In conclusion, our results suggest that SC-2001 induces apoptosis in HCC, and that this effect is mediated through SHP-1-dependent STAT3 inactivation.

First evidence that γ-tocotrienol inhibits the growth of human gastric cancer and chemosensitizes it to capecitabine in a xenograft mouse model through the modulation of NF-κB pathway

PURPOSE

Because of poor prognosis and development of resistance against chemotherapeutic drugs, the existing treatment modalities for gastric cancer are ineffective. Hence, novel agents that are safe and effective are urgently needed. Whether γ-tocotrienol can sensitize gastric cancer to capecitabine in vitro and in a xenograft mouse model was investigated.

EXPERIMENTAL DESIGN

The effect of γ-tocotrienol on proliferation of gastric cancer cell lines was examined by mitochondrial dye uptake assay, apoptosis by esterase staining, NF-κB activation by DNA-binding assay, and gene expression by Western blotting. The effect of γ-tocotrienol on the growth and chemosensitization was also examined in subcutaneously implanted tumors in nude mice.

RESULTS

γ-Tocotrienol inhibited the proliferation of various gastric cancer cell lines, potentiated the apoptotic effects of capecitabine, inhibited the constitutive activation of NF-κB, and suppressed the NF-κB-regulated expression of COX-2, cyclin D1, Bcl-2, CXCR4, VEGF, and matrix metalloproteinase-9 (MMP-9). In a xenograft model of human gastric cancer in nude mice, we found that administration of γ-tocotrienol alone (1 mg/kg body weight, intraperitoneally 3 times/wk) significantly suppressed the growth of the tumor and this effect was further enhanced by capecitabine. Both the markers of proliferation index Ki-67 and for microvessel density CD31 were downregulated in tumor tissue by the combination of capecitabine and γ-tocotrienol. As compared with vehicle control, γ-tocotrienol also suppressed the NF-κB activation and the expression of cyclin D1, COX-2, intercellular adhesion molecule-1 (ICAM-1), MMP-9, survivin, Bcl-xL, and XIAP.

CONCLUSIONS

Overall our results show that γ-tocotrienol can potentiate the effects of capecitabine through suppression of NF-κB-regulated markers of proliferation, invasion, angiogenesis, and metastasis.

Dietary compounds as potent inhibitors of the signal transducers and activators of transcription (STAT) 3 regulatory network

Signal transducers and activators of transcription (STAT) proteins were described as a family of latent cytosolic transcription factors whose activation is dependent on phosphorylation via growth factor- and cytokine-membrane receptors including interferon and interleukin, or by non-receptor intracellular tyrosine kinases, including Src. A vast majority of natural substances are capable of modulating mitogenic signals, cell survival, apoptosis, cell cycle regulation, angiogenesis as well as processes involved in metastasis development. The inhibition of STAT3 phosphorylation by natural and dietary compounds leads to decreased protein expression of STAT3 targets essentially involved in regulation of the cell cycle and apoptotic cell death. This review details the cell signaling pathways involving STAT transcription factors as well as the corresponding compounds from nature able to interfere with this regulatory system in human cancer.

Dovitinib sensitizes hepatocellular carcinoma cells to TRAIL and tigatuzumab, a novel anti-DR5 antibody, through SHP-1-dependent inhibition of STAT3

Hepatocellular carcinoma (HCC) often displays resistance to recombinant tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-induced apoptosis. Dovitinib, a multiple tyrosine kinase inhibitor, and tigatuzumab, a novel humanized anti-human death receptor 5 (DR5) agonistic antibody, are both under clinical investigations in HCC. Here, we report that dovitinib sensitizes resistant HCC cells to TRAIL- and tigatuzumab-induced apoptosis through inhibition of signal transducers and activators of transcription 3 (STAT3). Our data indicate that HCC cells showed significant resistance to TRAIL- and tigatuzumab-induced apoptosis. The combination of dovitinib and tigatuzumab restored the sensitivity of HCC cells to TRAIL- and tigatuzumab-induced apoptosis. Dovitinib down-regulated phospho-STAT3 (Tyr705) (p-STAT3) and subsequently reduced the protein levels of STAT3-regulated proteins, Mcl-1, survivin and cylcin D1, 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 sensitizing effect of dovitinib on TRAIL-induced apoptosis. Importantly, silencing SHP-1 by RNA-interference reduced the effects of dovitinib and TRAIL on p-STAT3 and apoptosis, whereas co-treatment of TRAIL and dovitinib increased the activity of SHP-1. Moreover, in vivo the combination of tigatuzumab and dovitinib inhibited Huh-7 xenograft tumor growth. In conclusion, dovitinib sensitizes resistant HCC cells to TRAIL- and tigatuzumab-induced apoptosis through a novel machinery: SHP-1 dependent STAT3 inhibition.