Signal transducer and activator of transcription 3 is a major kinase-independent target of sorafenib in hepatocellular carcinoma

YC-1 enhances the anti-tumor activity of sorafenib through inhibition of signal transducer and activator of transcription 3 (STAT3) in hepatocellular carcinoma

Background

Traditional systemic chemotherapy does not provide survival benefits in patients with hepatocellular carcinoma (HCC). Molecular targeted therapy shows promise for HCC treatment, however, the duration of effectiveness for targeted therapies is finite and combination therapies offer the potential for improved effectiveness.

Methods

Sorafenib, a multikinase inhibitor, and YC-1, a soluble guanylyl cyclase (sGC) activator, were tested in HCC by proliferation assay, cell cycle analysis and western blot in vitro and orthotopic and ectopic HCC models in vivo.

Results

In vitro, combination of sorafenib and YC-1 synergistically inhibited proliferation and colony formation of HepG2, BEL-7402 and HCCLM3 cells. The combination also induced S cell cycle arrest and apoptosis, as observed by activated PARP and caspase 8. Sorafenib and YC-1 respectively suppressed the expression of phosphorylated STAT3 (p-STAT3) (Y705) in a dose- and time-dependent manner. Combination of sorafenib and YC-1 significantly inhibited the expression of p-STAT3 (Y705) (S727), p-ERK1/2, cyclin D1 and survivin and SHP-1 activity compared with sorafenib or YC-1 used alone in all tested HCC cell lines. In vivo, sorafenib-YC-1 combination significantly suppressed the growth of HepG2 tumor xenografts with decreased cell proliferation and increased apoptosis observed by PCNA and PARP. Similar results were also confirmed in a HCCLM3 orthotopic model. There was a reduction in CD31-positive blood vessels and reduced VEGF expression, which suggested a combinational effect of sorafenib and YC-1 on angiogenesis. The reduced expression of p-STAT3, cyclin D1 and survivin was also observed with the combination of sorafenib and YC-1.

Conclusions

Our data show that sorafenib-YC-1 combination is a novel potent therapeutic agent that can target the STAT3 signaling pathway to inhibit HCC tumor growth.

Discovery of novel Src homology region 2 domain-containing phosphatase 1 agonists from sorafenib for the treatment of hepatocellular carcinoma

Sorafenib is the first approved targeted therapeutic reagent for hepatocellular carcinoma (HCC). Here, we report that Src homology region 2 (SH2) domain-containing phosphatase 1 (SHP-1) is a major target of sorafenib and generates a series of sorafenib derivatives to search for potent SHP-1 agonists that may act as better anti-HCC agents than sorafenib. Sorafenib increases SHP-1 activity by direct interaction and impairs the association between the N-SH2 domain and the catalytic protein tyrosine phosphatase domain of SHP-1. Deletion of the N-SH2 domain (dN1) or point mutation (D61A) of SHP-1 abolished the effect of sorafenib on SHP-1, phosphorylated signal transducer and activator of transcription 3 (p-STAT3), and apoptosis, suggesting that sorafenib may affect SHP-1 by triggering a conformational switch relieving its autoinhibition. Molecular docking of SHP-1/sorafenib complex confirmed our findings in HCC cells. Furthermore, novel sorafenib derivatives SC-43 and SC-40 displayed more potent anti-HCC activity than sorafenib, as measured by enhanced SHP-1 activity, inhibition of p-STAT3, and induction of apoptosis. SC-43 induced substantial apoptosis in sorafenib-resistant cells and showed better survival benefits than sorafenib in orthotopic HCC tumors.

CONCLUSION

In this study, we identified SHP-1 as a major target of sorafenib. SC-43 and SC-40, potent SHP-1 agonists, showed better anti-HCC effects than sorafenib in vitro and in vivo. Further clinical investigation is warranted.

BCRP/ABCG2 inhibition sensitizes hepatocellular carcinoma cells to sorafenib

The multikinase inhibitor, sorafenib (Nexavar®, BAY43-9006), which inhibits both the Raf/MEK/ERK pathway and several receptor tyrosine kinases (RTKs), has shown significantly therapeutic benefits in advanced hepatocellular carcinoma (HCC). However, not all HCC patients respond to sorafenib well and new therapeutic strategies to optimize the efficacy of sorafenib are urgently required. Overexpression of breast cancer resistance protein (BCRP/ABCG2) mediates the drug-efflux of several tyrosine kinase inhibitors (TKIs) to attenuate their efficacy. This study aimed to investigate the role of BCRP/ABCG2 in the sensitivity of HCC to sorafenib. Our data showed that BCRP/ABCG2 mediated the efflux of sorafenib. Co-treatment with a BCRP/ABCG2 inhibitor greatly augmented the cytotoxicity of sorafenib in HCC cells. Similar results were also achieved by the competitive inhibitor of BCRP/ABCG2, gefitinib, in combination with sorafenib. These results suggest not only that BCRP/ABCG2 is a potential predictor for the sorafenib sensitivity in HCC, but also that blockage of BCRP/ABCG2 may be a potential strategy to increase the response of HCC cells to sorafenib.

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.

Signal transducer and activator of transcription 3 is a proviral host factor for hepatitis C virus

Host factors play an important role in all facets of the hepatitis C virus (HCV) life cycle and one such host factor is signal transducer and activator of transcription 3 (STAT3). The HCV core protein has been shown to directly interact with and activate STAT3, while oxidative stress generated during HCV replication in a replicon-based model also induced STAT3 activation. However, despite these findings the precise role of STAT3 in the HCV life cycle remains unknown. We have established that STAT3 is actively phosphorylated in the presence of replicating HCV. Furthermore, expression of a constitutively active form of STAT3 leads to marked increases in HCV replication, whereas, conversely, chemical inhibition and small interfering RNA (siRNA) knockdown of STAT3 leads to significant decreases in HCV RNA levels. This strongly implicates STAT3 as a proviral host factor. As STAT3 is a transcription factor, up-regulation of a distinct set of STAT3-dependent genes may create an environment that is favorable for HCV replication. However, STAT3 has recently been demonstrated to positively regulate microtubule (MT) dynamics, by way of a direct sequestration of the MT depolymerizing protein Stathmin 1 (STMN1), and we provide evidence that STAT3 may exert its effect on the HCV life cycle by way of positive regulation of MT dynamics.

CONCLUSION

We have demonstrated that STAT3 plays a role in the life cycle of HCV and have clarified the role of STAT3 as a proviral host factor.

The tyrosine phosphatase SHP-1 inhibits proliferation of activated hepatic stellate cells by impairing PDGF receptor signaling

The dimerization and auto-transphosphorylation of platelet-derived growth factor receptor (PDGFR) upon engagement by platelet-derived growth factor (PDGF) activates signals promoting the mitogenic response of hepatic stellate cells (HSCs) due to liver injury, thus contributing to the development of hepatic fibrosis. We demonstrate that the tyrosine phosphatases Src homology 2 domain-containing phosphatase 1 and 2 (SHP-1 and SHP-2) act as crucial regulators of a complex signaling network orchestrated by PDGFR activation in a spatio-temporal manner with diverse and opposing functions in HSCs. In fact, silencing of either phosphatase shows that SHP-2 is committed to PDGFR-mediated cell proliferation, whereas SHP-1 dephosphorylates PDGFR hence abrogating the downstream signaling pathways that result in HSC activation. In this regard, SHP-1 as an off-switch of PDGFR signaling appears to emerge as a valuable molecular target to trigger as to prevent HSC proliferation and the fibrogenic effects of HSC activation. We show that boswellic acid, a multitarget compound with potent anti-inflammatory action, exerts an anti-proliferative effect on HSCs, as in other cell models, by upregulating SHP-1 with subsequent dephosphorylation of PDGFR-β and downregulation of PDGF-dependent signaling after PDGF stimulation. Moreover, the synergism resulting from the combined use of boswellic acid and imatinib, which directly inhibits PDGFR-β activity, on activated HSCs offers new perspectives for the development of therapeutic strategies that could implement molecules affecting diverse players of this molecular circuit, thus paving the way to multi-drug low-dose regimens for liver fibrosis.

Sunitinib versus sorafenib in advanced hepatocellular cancer: results of a randomized phase III trial

PURPOSE

Open-label, phase III trial evaluating whether sunitinib was superior or equivalent to sorafenib in hepatocellular cancer.

PATIENTS AND METHODS

Patients were stratified and randomly assigned to receive sunitinib 37.5 mg once per day or sorafenib 400 mg twice per day. Primary end point was overall survival (OS).

RESULTS

Early trial termination occurred for futility and safety reasons. A total of 1,074 patients were randomly assigned to the study (sunitinib arm, n = 530; sorafenib arm, n = 544). For sunitinib and sorafenib, respectively, median OS was 7.9 versus 10.2 months (hazard ratio [HR], 1.30; one-sided P = .9990; two-sided P = .0014); median progression-free survival (PFS; 3.6 v 3.0 months; HR, 1.13; one-sided P = .8785; two-sided P = .2286) and time to progression (TTP; 4.1 v 3.8 months; HR, 1.13; one-sided P = .8312; two-sided P = .3082) were comparable. Median OS was similar among Asian (7.7 v 8.8 months; HR, 1.21; one-sided P = .9829) and hepatitis B-infected patients (7.6 v 8.0 months; HR, 1.10; one-sided P = .8286), but was shorter with sunitinib in hepatitis C-infected patients (9.2 v 17.6 months; HR, 1.52; one-sided P = .9835). Sunitinib was associated with more frequent and severe adverse events (AEs) than sorafenib. Common grade 3/4 AEs were thrombocytopenia (29.7%) and neutropenia (25.7%) for sunitinib; hand-foot syndrome (21.2%) for sorafenib. Discontinuations owing to AEs were similar (sunitinib, 13.3%; sorafenib, 12.7%).

CONCLUSION

OS with sunitinib was not superior or equivalent but was significantly inferior to sorafenib. OS was comparable in Asian and hepatitis B-infected patients. OS was superior in hepatitis C-infected patients who received sorafenib. Sunitinib-treated patients reported more frequent and severe toxicity.

Schedule-dependent antitumor effects of 5-fluorouracil combined with sorafenib in hepatocellular carcinoma

Background

Recently, a phase II clinical trial in hepatocellular carcinoma (HCC) has suggested that the combination of sorafenib and 5-fluorouracil (5-FU) is feasible and side effects are manageable. However, preclinical experimental data explaining the interaction mechanism(s) are lacking. Our objective is to investigate the anticancer efficacy and mechanism of combined sorafenib and 5-FU therapy in vitro in HCC cell lines MHCC97H and SMMC-7721.

Methods

Drug effects on cell proliferation were evaluated by cell viability assays. Combined-effects analyses were conducted according to the median-effect principle. Cell cycle distribution was measured by flow cytometry. Expression levels of proteins related to the RAF/MEK/ERK and STAT3 pathways and to cell cycle progression (cyclin D1) were determined by western blot analysis.

Results

Sorafenib and 5-FU alone or in combination showed significant efficacy in inhibiting cell proliferation in both cell lines tested. However, a schedule-dependent combined effect, associated with the order of compound treatments, was observed. Efficacy was synergistic with 5-FU pretreatment followed by sorafenib, but it was antagonistic with the reverse treatment order. Sorafenib pretreatment resulted in a significant increase in the half inhibitory concentration (IC50) of 5-FU in both cell lines. Sorafenib induced G1-phase arrest and significantly decreased the proportion of cells in S phase when administrated alone or followed by 5-FU. The RAF/MEK/ERK and STAT3 pathways were blocked and cyclin D1 expression was down regulated significantly in both cell lines by sorafenib; whereas, the kinase pathways were hardly affected by 5-FU, and cyclin D1 expression was up regulated.

Conclusions

Antitumor activity of sorafenib and 5-FU, alone or in combination, is seen in HCC cell lines. The nature of the combined effects, however, depends on the particular cell line and treatment order of the two compounds. Sorafenib appears to reduce sensitivity to 5-FU through down regulation of cyclin D1 expression by inhibiting RAF/MEK/ERK and STAT3 signaling, resulting in G1-phase arrest and reduction of the S-phase cell subpopulation when 5-FU is administrated after sorafenib, in which situation, combination treatment of the two agents results in antagonism; on the other hand, when sorafenib is administrated afterward, it can continue to work since it is not cell cycle specific, as a result, combination treatment of the two agents shows an additive-to-synergistic effect.

Mechanisms of resistance to sorafenib and the corresponding strategies in hepatocellular carcinoma

Sorafenib, the unique drug as first-line treatment for advanced hepatocellular carcinoma (HCC), has opened a window of hope after searching for effective agents to combat HCC for decades. However, the overall outcomes are far from satisfactory. One of the explanations is the genetic heterogeneity of HCC, which has led to identifying predictive biomarkers for primary resistance to sorafenib, and then applying the concept of personalized medicine, or seeking therapeutic strategies such as combining sorafenib with other anticancer agents. Some of the combinations have demonstrated a better effectiveness than sorafenib alone, with good tolerance. The acquired resistance to sorafenib has also drawn attention. As a multikinase inhibitor, sorafenib targets several cellular signaling pathways but simultaneously or sequentially the addiction switches and compensatory pathways are activated. Several mechanisms are involved in the acquired resistance to sorafenib, such as crosstalks involving PI3K/Akt and JAK-STAT pathways, hypoxia-inducible pathways, epithelial-mesenchymal transition, etc. Based on the investigated mechanisms, some other molecular targeted drugs have been applied as second-line treatment for treat HCC after the failure of sorafenib therapy and more are under evaluation in clinical trials. However, the exact mechanisms accounting for sorafenib resistance remains unclear. Further investigation on the crosstalk and relationship of associated pathways will better our understanding of the mechanisms and help to find effective strategies for overcoming sorafenib resistance in HCC.

Sorafenib and its derivative SC-49 sensitize hepatocellular carcinoma cells to CS-1008, a humanized anti-TNFRSF10B (DR5) antibody

BACKGROUND AND PURPOSE

Previously, we have shown that sorafenib sensitizes hepatocellular carcinoma (HCC) to apoptosis induced by TNF-related apoptosis-inducing ligand (TNFSF10; TRAIL). Here, we report that sorafenib and SC-49 sensitize HCC cells to CS-1008, a novel anti-human death receptor 5 (TNFRSF10B) antibody.

EXPERIMENTAL APPROACH

HCC cell lines (PLC5, Huh-7, and Hep3B) were treated with CS-1008 and/or sorafenib and analysed in terms of apoptosis and signal transductions.

KEY RESULTS

SC-49 is a sorafenib derivative, which is devoid of kinase inhibitory activity. Both sorafenib and SC-49 down-regulated the phosphorylation of STAT3 at Tyr(705) and subsequently reduced the levels of STAT3-regulated proteins, Mcl-1, survivin and cylcin D1, in CS-1008-treated HCC cells. Knockdown of STAT3 by RNA interference overcame apoptotic resistance to CS-1008 in HCC cells, and ectopic expression of STAT3 in HCC cells abolished the sensitizing effects of sorafenib and SC-49 on CS-1008-induced apoptosis, indicating that inhibition of STAT3 mediates the enhancing effects of these compounds when combined with CS-1008. Importantly, inhibition of SHP-1 by adding a specific SHP-1 inhibitor reduced the effects of SC-49 and CS-1008 on p-STAT3 and apoptosis, whereas co-treatment of CS-1008 with SC-49 increased the activity of SHP-1. These data indicate that the combined effects of CS-1008 and SC-49 on HCC are mediated by SHP-1. Moreover, the combination of CS-1008 and SC-49 inhibited HCC xenograft tumour growth in vivo.

CONCLUSIONS AND IMPLICATIONS

Sorafenib and its derivative SC-49 sensitize HCC cells to the antitumour effects of CS-1008 through SHP-1-dependent inactivation of STAT3.

Potentiating the efficacy of molecular targeted therapy for hepatocellular carcinoma by inhibiting the insulin-like growth factor pathway

Insulin-like growth factor (IGF) signaling pathway is an important regulatory mechanism of tumorigenesis and drug resistance in many cancers. The present study explored the potential synergistic effects between IGF receptor (IGFR) inhibition and other molecular targeted agents (MTA) in HCC cells. HCC cell lines (Hep3B, PLC5, and SK-Hep1) and HUVECs were tested. The MTA tested included sorafenib, sunitinib, and the IGFR kinase inhibitor NVP-AEW541. The potential synergistic antitumor effects were tested by median dose effect analysis and apoptosis assay in vitro and by xenograft models in vivo. The activity and functional significance of pertinent signaling pathways and expression of apoptosis-related proteins were measured by RNA interference and Western blotting. We found that IGF can activate IGFR and downstream AKT signaling activities in all the HCC cells tested, but the growth-stimulating effect of IGF was most prominent in Hep3B cells. NVP-AEW541 can abrogate IGF-induced activation of IGFR and AKT signaling in HCC cells. IGF can increase the resistance of HCC cells to sunitinib. The apoptosis-inducing effects of sunitinib, but not sorafenib, were enhanced when IGFR signaling activity was inhibited by NVP-AEW541 or IGFR knockdown. Chk2 kinase activation was found contributory to the synergistic anti-tumor effects between sunitinib and IGFR inhibition. Our data indicate that the apoptosis-potentiating effects of IGFR inhibition for HCC may be drug-specific. Combination therapy of IGFR inhibitors with other MTA may improve the therapeutic efficacy in HCC.

Interaction of signal transducer and activator of transcription 3 polymorphisms with hepatitis B virus mutations in hepatocellular carcinoma

Hepatitis B virus (HBV) mutations and signal transducer and activator of transcription 3 (STAT3) activation are closely associated with hepatocellular carcinoma (HCC). However, single nucleotide polymorphisms (SNPs) of STAT3 have not been implicated in HCC susceptibility. This study was designed to evaluate the effect of STAT3 SNPs and their interactions with HBV mutations on HCC risk. A total of 2,011 HBV-infected subjects (including 1,021 HCC patients) and 1,012 healthy controls were involved in this study. SNPs rs4796793 (-1697, C>G), rs2293152 (intron 11, C>G), and rs1053004 (3' untranslated region, T>C) were genotyped using quantitative polymerase chain reaction. HBV mutations were determined via direct sequencing. It was found that rs2293152 (GG versus CC) was significantly associated with HCC risk compared with the subjects without HCC, adjusting for age and sex (adjusted odds ratio [AOR], 1.30; 95% confidence interval [CI], 1.04-1.62). The impact of rs2293152 was greater in women compared with men. Compared with HCC-free HBV-infected subjects, rs2293152 GG was solely associated with HCC in women (AOR, 2.04; 95% CI, 1.15-3.61). rs2293152 GG was significantly associated with high viral load (≥1 × 10(4) copies/mL) (AOR, 1.37; 95%, CI 1.01-1.88) and increased frequencies of T1674C/G (AOR, 1.61; 95% CI, 1.06-2.46) and A1762T/G1764A (AOR, 1.64; 95% CI, 1.14-2.35). In multivariate regression analyses, multiplicative interaction of rs1053004 with T1674C/G significantly increased HCC risk, whereas rs2293152 and A1726C interaction reduced it, adjusting for covariates including HBV mutations in the enhancer II/basal core promoter/precore region; the interaction of rs4796793 with preS2 start codon mutation significantly increased HCC risk, adjusting for covariates including HBV mutations in the preS region.

CONCLUSION

STAT3 SNPs appear to predispose the host with HBV mutations to hepatocarcinogenesis, and this effect may differ in men versus women. STAT3 SNPs may have applicability in future HCC surveillance algorithms. (Hepatology 2013;57:2369-2377).

The evolving landscape of therapeutic drug development for hepatocellular carcinoma

Currently, only one drug, sorafenib, is FDA approved for the treatment of advanced hepatocellular carcinoma (HCC), achieving modest objective response rates while still conferring an overall survival benefit. Unlike other solid tumors, no oncogenic addiction loops have been validated as clinically actionable targets in HCC. Outcomes of HCC could potentially be improved if critical molecular subclasses with distinct therapeutic vulnerabilities can be identified, biomarkers that predict recurrence or progression early can be determined and key epigenetic, genetic or microenvironment drivers that determine best response to a specific targeting treatment can be uncovered. Our group and others have examined the molecular heterogeneity of hepatocellular carcinoma. We have developed a panel of patient derived xenograft models to enable focused pre-clinical drug development of rationally designed therapies in specific molecular subgroups. We observed unique patterns, including synergies, of drug activity across our molecularly diverse HCC xenografts, pointing to specific therapeutic vulnerabilities for individual tumors. These efforts inform clinical trial designs and catalyze therapeutic development. It also argues for efficient strategic allocation of patients into appropriate enriched clinical trials. Here, we will discuss some of the recent important therapeutic studies in advanced HCC and also some of the potential strategies to optimize clinical therapeutic development moving forward.

Sorafenib enhances radiation-induced apoptosis in hepatocellular carcinoma by inhibiting STAT3

PURPOSE

Hepatocellular carcinoma (HCC) is one of the most common and lethal human malignancies. Lack of efficient therapy for advanced HCC is a pressing problem worldwide. This study aimed to determine the efficacy and mechanism of combined sorafenib and radiation therapy treatment for HCC.

METHODS AND MATERIALS

HCC cell lines (PLC5, Huh-7, Sk-Hep1, and Hep3B) were treated with sorafenib, radiation, or both, and apoptosis and signal transduction were analyzed.

RESULTS

All 4 HCC cell lines showed resistance to radiation-induced apoptosis; however, this resistance could be reversed in the presence of sorafenib. Inhibition of phospho-STAT3 was found in cells treated with sorafenib or sorafenib plus radiation and subsequently reduced the expression levels of STAT3-related proteins, Mcl-1, cyclin D1, and survivin. Silencing STAT3 by RNA interference overcame apoptotic resistance to radiation in HCC cells, and the ectopic expression of STAT3 in HCC cells abolished the radiosensitizing effect of sorafenib. Moreover, sorafenib plus radiation significantly suppressed PLC5 xenograft tumor growth.

CONCLUSIONS

These results indicate that sorafenib sensitizes resistant HCC cells to radiation-induced apoptosis via downregulating phosphorylation of STAT3 in vitro and in vivo.

Suppression of natural killer cells by sorafenib contributes to prometastatic effects in hepatocellular carcinoma

Sorafenib, a multi-tyrosine kinase inhibitor, is a standard treatment for advanced hepatocellular carcinoma (HCC). The present study was undertaken to determine whether the growth and metastasis of HCC were influenced in mice receiving sorafenib prior to implantation with tumors, and to investigate the in-vivo and in-vitro effect of sorafenib on natural killer (NK) cells. In sorafenib-pretreated BALB/c nu/nu mice and C57BL/6 mice, tumor growth was accelerated, mouse survival was decreased, and lung metastasis was increased. However, the depletion of NK1.1⁺ cells in C57BL/6 mice eliminated sorafenib-mediated pro-metastatic effects. Sorafenib significantly reduced the number of NK cells and inhibited reactivity of NK cells against tumor cells, in both tumor-bearing and tumor-free C57BL/6 mice. Sorafenib down-regulated the stimulatory receptor CD69 in NK cells of tumor-bearing mice, but not in tumor-free mice, and inhibited proliferation of NK92-MI cells, which is associated with the blocking of the PI3K/AKT pathway, and inhibited cytotoxicity of NK cells in response to tumor targets, which was due to impaired ERK phosphorylation. These results suggest immunotherapeutic approaches activating NK cells may enhance the therapeutic efficacy of sorafenib in HCC patients.

Mcl-1-dependent activation of Beclin 1 mediates autophagic cell death induced by sorafenib and SC-59 in hepatocellular carcinoma cells

We investigated the molecular mechanisms underlying the effect of sorafenib and SC-59, a novel sorafenib derivative, on hepatocellular carcinoma (HCC). Sorafenib activated autophagy in a dose- and time-dependent manner in the HCC cell lines PLC5, Sk-Hep1, HepG2 and Hep3B. Sorafenib downregulated phospho-STAT3 (P-STAT3) and subsequently reduced the expression of myeloid cell leukemia-1 (Mcl-1). Inhibition of Mcl-1 by sorafenib resulted in disruption of the Beclin 1-Mcl-1 complex; however, sorafenib did not affect the amount of Beclin 1, suggesting that sorafenib treatment released Beclin 1 from binding with Mcl-1. Silencing of SHP-1 by small interference RNA (siRNA) reduced the effect of sorafenib on P-STAT3 and autophagy. Ectopic expression of Mcl-1 abolished the effect of sorafenib on autophagy. Knockdown of Beclin 1 by siRNA protected the cells from sorafenib-induced autophagy. Moreover, SC-59, a sorafenib derivative, had a more potent effect on cancer cell viability than sorafenib. SC-59 downregulated P-STAT3 and induced autophagy in all tested HCC cell lines. Furthermore, our in vivodata showed that both sorafenib and SC-59 inhibited tumor growth, downregulated P-STAT3, enhanced the activity of SHP-1 and induced autophagy in PLC5 tumors, suggesting that sorafenib and SC-59 activate autophagy in HCC. In conclusion, sorafenib and SC-59 induce autophagy in HCC through a SHP-1-STAT3-Mcl-1-Beclin 1 pathway.

SC-1, a sorafenib derivative, shows anti-tumor effects in osteogenic sarcoma cells

Despite significant advances in the treatment of osteosarcoma (OS), overall survival rate of OS patients has remained relatively constant for over two decades and novel approaches are needed to further improve prognosis. Here, we report the anti-tumor effect of SC-1, a novel sorafenib derivative that closely resembles sorafenib structurally but is devoid of kinase inhibitory activity, on OS cells through mediation of signal transducer and activator of transcription 3 (STAT3). SC-1 showed similar effects to sorafenib on growth inhibition and apoptosis, and downregulated phospho-STAT3 (p-STAT3) at tyrosine 705 in all tested OS cell lines (U2OS, HOS, and 143B). Expression of STAT3-driven genes, including cylcin D1 and c-myc, were also repressed by SC-1. Ectopic expression of STAT3 in 143B cells abolished apoptosis in SC-1-treated cells. Inhibition of SHP-1 decreased SC-1-induced apoptosis. SC-1 upregulated the activity of SHP-1 in tested OS cell lines in a dose-dependent manner. Finally, SC-1 reduced 143B tumor growth significantly in vivo, which was associated with downregulation of p-STAT3 and upregulation of SHP-1 activity. These data demonstrate that SC-1 has clinical potential for the treatment of OS patients.

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.

STAT proteins - key regulators of anti-viral responses, inflammation, and tumorigenesis in the liver

Since its discovery in the early 1990s, the Janus kinase (JAK)-signal transducer and activator of transcription (STAT) signaling pathway has been found to play key roles in regulating many key cellular processes such as survival, proliferation, and differentiation. There are seven known mammalian STAT family members: STAT1, 2, 3, 4, 5a, 5b, and 6. In the liver, activation of these STAT proteins is critical for anti-viral defense against hepatitis viral infection and for controlling injury, repair, inflammation, and tumorigenesis. The identification of functions for these STAT proteins has increased our understanding of liver disease pathophysiology and treatments, while also suggesting new therapeutic modalities for managing liver disease.

Molecular mechanisms of sorafenib action in liver cancer cells

Sorafenib, a multikinase inhibitor, recently received FDA approval for the treatment of advanced hepatocellular carcinoma (HCC). However, as the clinical application of sorafenib evolves, there is increasing interest in defining the mechanisms underlying its anti-tumor activity. Considering that this specific inhibitor could target unexpected molecules depending on the biologic context, a precise understanding of its mechanism of action could be critical to maximize its treatment efficacy, while minimizing adverse effects. Two human HCC cell lines (HepG2 and Huh7), carrying different biological and genetic characteristics, were used in this study to examine the intracellular events leading to sorafenib-induced HCC cell-growth inhibition. Sorafenib inhibited cell growth in both cell lines in a dose- and time-dependent manner and significantly altered expression levels of 826 and 2011 transcripts in HepG2 and Huh7 cells, respectively. Genes functionally involved in angiogenesis, apoptosis, transcription regulation, signal transduction, protein biosynthesis and modification were predominantly upregulated, while genes implicated in cell cycle control, DNA replication recombination and repair, cell adhesion, metabolism and transport were mainly downregulated upon treatment. However, each sorafenib-treated HCC cell line displayed specificity in the expression and activity of crucial factors involved in hepatocarcinogenesis. The altered expression of some of these genes was confirmed by semiquantitative and quantitative RT-PCR and by western blotting. Many novel genes emerged from our transcriptomics analysis that had not previously been reported to be effected by sorafenib. Further functional analyses may determine whether these genes can serve as potential molecular targets for more effective anti-HCC strategies.

Blockade of STAT3 activation by sorafenib derivatives through enhancing SHP-1 phosphatase activity

Previously, we demonstrated that the multiple kinase inhibitor sorafenib mediates the repression of phospho-STAT3 in hepatocellular carcinoma cells. In this study, we used this kinase-independent mechanism as a molecular basis to use sorafenib as scaffold to develop a novel class of SHP-1-activating agents. The proof of principle of this premise was provided by SC-1, which on replacement of N-methylpicolinamide by a phenylcyano group showed abolished kinase activity while retaining phospho-STAT3 repressive activity. Structural optimization of SC-1 led to compound 6, which repressed phospho-STAT3 through SHP-1 activation and inhibited PLC5 cell proliferation at sub-micromolar potency. In light of the pivotal role of phospho-STAT3 in promoting tumorigenesis and drug resistance, this novel SHP-1-activating agent may have therapeutic relevance in cancer therapy.

NSC 74859 enhances doxorubicin cytotoxicity via inhibition of epithelial-mesenchymal transition in hepatocellular carcinoma cells

Doxorubicin-based therapy is not effective for the treatment of hepatocellular carcinomas (HCCs), which often undergo epithelial-mesenchymal transition (EMT) during tumor progression. Activation of signal transducer and activator of transcription 3 (STAT3) is associated with chemosensitivity and may contribute to EMT during HCC chemotherapy. Low doses of NSC 78459 (a novel STAT3 inhibitor) have little effect on HCC cell proliferation, but efficiently inhibit STAT3. HuH-7, Hep3B, and HepG2 cells, with epithelial phenotypes, show significantly enhanced doxorubicin cytotoxicity following co-treatment with NSC 74859, whereas mesenchymal SNU-449 cells show no such enhancement. NSC 74859 inhibits STAT3 activity and suppressed doxorubicin-induced EMT in epithelial HCC cells. siRNA-mediated STAT3 knockdown resulted in EMT inhibition, which led to attenuation of NSC 74859-mediated chemosensitivity. Our data indicate NSC 74859 co-administration enhances doxorubicin cytotoxicity by inhibiting STAT3 in epithelial HCC cells. STAT3 deactivation and associated EMT attenuation contribute to the synergistic anti-tumor effects of combined NSC 74859/doxorubicin therapy.

Epidermal growth factor receptor and HER-3 restrict cell response to sorafenib in hepatocellular carcinoma cells

BACKGROUND & AIMS

Sorafenib is the standard of care for the treatment of advanced hepatocellular carcinoma (HCC). However, primary and acquired resistance is observed in patients. We examined whether gefitinib, which inhibits both epidermal growth factor receptor (EGFR) and HER-3 phosphorylation, could improve HCC cell response to sorafenib.

METHODS

Sorafenib and gefitinib were tested in HCC tumor xenografts and in sorafenib-sensitive and sorafenib-resistant HCC cell lines. Biomarkers relevant to the HER system were analyzed by Western blotting and ELISA. RNA interference was used to downregulate the HER system. Amphiregulin concentrations were measured by ELISA in sera from patients under sorafenib treatment.

RESULTS

Sorafenib combined with gefitinib significantly inhibited tumor growth in mice and reduced cell viability in vitro compared to single agents. In cell lines cultured in 10% serum or treated with EGF, sorafenib alone inhibited phospho-STAT3 while it maintained or even increased phospho-ERK and/or phospho-AKT. The paradoxical effects of sorafenib were prevented by gefitinib or by downregulation of EGFR and HER-3 expression. In cells with acquired resistance to sorafenib, aberrant activation of EGFR/HER-3 receptors as well as overexpression of several EGFR ligands were observed. These enhanced autocrine/paracrine loops led to the constitutive activation of ERK and AKT and conferred increased sensitivity to gefitinib. Increased serum concentrations of amphiregulin were observed in 10 out of 14 patients under sorafenib treatment compared to baselines.

CONCLUSIONS

Signaling pathways controlled by EGFR and HER-3 restrict sorafenib effects both in naive and sorafenib-resistant HCC cells. Consequently, gefitinib cooperates with sorafenib to increase antiproliferative response and to prevent resistance.

Combined anti-tumor effects of IFN-α and sorafenib on hepatocellular carcinoma in vitro and in vivo

Hepatocellular carcinoma (HCC) is among the most common and aggressive cancers worldwide, and novel therapeutic strategies are urgently required to improve clinical outcome. Interferon-alpha (IFN-α) and sorafenib are widely used as anti-tumor agents against various malignancies. In this study, we investigated the combined effects of IFN-α and sorafenib against HCC. We demonstrated that the combination therapy synergistically suppressed HCC cellular viability, arrested cell cycle propagation and induced apoptosis in HCC cells. Further research revealed that IFN-α and sorafenib collaboratively regulated the expression levels of cell cycle-related proteins Cyclin A and Cyclin B as well as the pro-survival Bcl-2 family proteins Mcl-1, Bcl-2 and Bcl-X(L). Moreover, sorafenib inhibited IFN-α induced oncogenic signaling of STAT3, AKT and ERK but not the activation of the tumor suppressor STAT1. Xenograft experiments also confirmed the combined effects of IFN-α and sorafenib on tumor growth inhibition and apoptosis induction in vivo. In conclusion, these results provide rationale for the clinical application of IFN-α and sorafenib combination therapy in HCC treatment.

Inhibition of Bcl-2 improves effect of LCL161, a SMAC mimetic, in hepatocellular carcinoma cells

In this study, we investigated the effect of LCL161, a SMAC mimetic, in hepatocellular carcinoma (HCC). LCL161 showed differential effects on apoptosis in four HCC cell lines, and the endogenous level of Bcl-2 determined the sensitivity of HCC cells to LCL161. Cytotoxicity and apoptosis were observed in sensitive PLC5 and Hep3B cells that express lower levels of Bcl-2, but not in resistant Huh-7 and SK-Hep1 cells with higher Bcl-2 expression. Down regulation of Bcl-2 by small interference RNA overcame the resistance to LCL161 in Huh-7, and the apoptotic effect was rescued in Bcl-2-expressing Hep3B. To test the hypothesis that Bcl-2 determines the sensitivity of HCC cells to LCL161, we assayed the biological effect of SC-2001, a novel Bcl-2 inhibitor derived from obatoclax, in LCL161-resistant cell lines. Huh-7 cells co-treated with LCL161 and SC-2001 showed a significant dose-dependent apoptotic effect demonstrated by sub-G1 assay and cleavage of PARP. Furthermore, the combination index (CI) of LCL161 and SC-2001 showed a convincing synergism in resistant Huh-7. In addition, the combinational therapy showed significant growth inhibition in Huh-7-bearing xenograft tumors. Notably, down regulation of Bcl-2 was observed in a tumor sample treated with LCL161 and SC-2001. In conclusion, targeting Bcl-2 with SC-2001 overcomes drug resistance to LCL161 in HCC cells thus suggesting a new anti-IAP combinational therapy for HCC.

Targeted therapy of hepatocellular carcinoma: present and future

Following the encouraging results of sorafenib in advanced hepatocellular carcinoma (HCC), targeted therapy has become a new direction of research in the treatment of HCC. Emerging data provide evidence that the pathogenesis and progression of HCC are mediated by a number of molecular defects and dysregulated pathways. Novel targeted therapies are designed to inhibit the aberrant pathways at a molecular level with an aim to improve the clinical outcome. For the past few years, an increasing number of targeted agents have been tested in HCC in the clinical setting. This review aims to summarize the current status of clinical development of targeted therapy in HCC, with focus on novel agents targeting angiogenesis, signal transduction and epigenetic dysregulation of tumors. The review also discusses the lessons learned from outcomes of completed clinical trials and provides perspectives on future clinical trials in HCC.

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.

Sorafenib sensitizes hepatocellular carcinoma cells to physiological apoptotic stimuli

Sorafenib increases survival rate of patients with advanced hepatocellular carcinoma (HCC). The mechanism underlying this effect is not completely understood. In this work we have analyzed the effects of sorafenib on autocrine proliferation and survival of different human HCC cell lines. Our results indicate that sorafenib in vitro counteracts autocrine growth of different tumor cells (Hep3B, HepG2, PLC-PRF-5, SK-Hep1). Arrest in S/G2/M cell cycle phases were observed coincident with cyclin D1 down-regulation. However, sorafenib's main anti-tumor activity seems to occur through cell death induction which correlated with caspase activation, increase in the percentage of hypodiploid cells, activation of BAX and BAK and cytochrome c release from mitochondria to cytosol. In addition, we observed a rise in mRNA and protein levels of the pro-apoptotic "BH3-domain only" PUMA and BIM, as well as decreased protein levels of the anti-apoptotic MCL1 and survivin. PUMA targeting knock-down, by using specific siRNAs, inhibited sorafenib-induced apoptotic features. Moreover, we obtained evidence suggesting that sorafenib also sensitizes HCC cells to the apoptotic activity of transforming growth factor-β (TGF-β) through the intrinsic pathway and to tumor necrosis factor-α (TNF) through the extrinsic pathway. Interestingly, sensitization to sorafenib-induced apoptosis is characteristic of liver tumor cells, since untransformed hepatocytes did not respond to sorafenib inducing apoptosis, either alone or in combination with TGF-β or TNF. Indeed, sorafenib effectiveness in delaying HCC late progression might be partly related to a selectively sensitization of HCC cells to apoptosis by disrupting autocrine signals that protect them from adverse conditions and pro-apoptotic physiological cytokines.

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.

Dovitinib induces apoptosis and overcomes sorafenib resistance in hepatocellular carcinoma through SHP-1-mediated inhibition of STAT3

The multiple kinase inhibitor dovitinib is currently under clinical investigation for hepatocellular carcinoma (HCC). Here, we investigated the mechanistic basis for the effects of dovitinib in HCCs. Dovitinib showed significant antitumor activity in HCC cell lines PLC5, Hep3B, Sk-Hep1, and Huh-7. Dovitinib downregulated phospho-STAT3 (p-STAT3) at tyrosine 705 and subsequently reduced the levels of expression of STAT3-related proteins Mcl-1, survivin, and cyclin D1 in a time-dependent manner. Ectopic expression of STAT3 abolished the apoptotic effect of dovitinib, indicating that STAT3 is indispensable in mediating the effect of dovitinib in HCC. SHP-1 inhibitor reversed downregulation of p-STAT3 and apoptosis induced by dovitinib, and silencing of SHP-1 by RNA interference abolished the effects of dovitinib on p-STAT3, indicating that SHP-1, a protein tyrosine phosphatase, mediates the effects of dovitinib. Notably, dovitinib increased SHP-1 activity in HCC cells. Incubation of dovitinib with pure SHP-1 protein enhanced its phosphatase activity, indicating that dovitinib upregulates the activity of SHP-1 via direct interactions. In addition, dovitinib induced apoptosis in two sorafenib-resistant cell lines through inhibition of STAT3, and sorafenib-resistant cells showed significant activation of STAT3, suggesting that targeting STAT3 may be a useful approach to overcome drug resistance in HCC. Finally, in vivo, dovitinib significantly suppressed growth of both Huh-7 and PLC5 xenograft tumors and downregulated p-STAT3 by increasing SHP-1 activity. In conclusion, dovitinib induces significant apoptosis in HCC cells and sorafenib-resistant cells via SHP-1-mediated inhibition of STAT3.