Identification of β-Escin as a Novel Inhibitor of Signal Transducer and Activator of Transcription 3/Janus-Activated Kinase 2 Signaling Pathway that Suppresses Proliferation and Induces Apoptosis in Human Hepatocellular Carcinoma Cells

Abstract

The activation of signal transducer and activator of transcription 3 (STAT3) has been linked with the proliferation, survival, invasion, and angiogenesis of a variety of human cancer cells, including hepatocellular carcinoma (HCC). Agents that can suppress STAT3 activation have potential for the prevention and treatment of HCC. In this study, we tested an agent, ␤-escin, for its ability to suppress STAT3 activation. We found that ␤-escin, a pentacyclic triterpenoid, inhibited both constitutive and interleukin-6-inducible STAT3 activation in a doseand time-dependent manner in HCC cells. The suppression was mediated through the inhibition of activation of upstream kinases c-Src, Janus-activated kinase 1, and Janus-activated kinase 2. Vanadate treatment reversed the ␤-escin-induced down-regulation of STAT3, suggesting the involvement of a tyrosine phosphatase. Indeed, we found that ␤-escin induced the expression of tyrosine phosphatase Src homology phosphatase 1 that correlated with the down-regulation of constitutive STAT3 activation. ␤-Escin also down-regulated the expression of STAT3-regulated gene products, such as cyclin D1, Bcl-2, Bcl-xL, survivin, Mcl-1, and vascular endothelial growth factor. Finally, ␤-escin inhibited proliferation and also substantially potentiated the apoptotic effects of paclitaxel and doxorubicin in HCC cells. Overall, these results suggest that ␤-escin is a novel blocker of STAT3 activation that may have potential in the suppression of proliferation and chemosensitization in HCC.Hepatocellular carcinoma (HCC) is one of the most common solid tumors, ranking fifth in incidence and third in mortality worldwide (Bruix et al., 2004). Although epidemiologic studies have shown that chronic viral infections and hepatotoxic agents are the major risk factors, the molecular pathogenesis of HCC is quite complex with the involvement of several oncogenes and tumor suppressor genes . Surgery remains the first choice for treatment of HCC; however, tumor size, hepatic functional reserve, and/or portal hypertension all may restrict surgical ablation (Kerr and Kerr, 2009). Currently, first-line drugs used for HCC include doxorubicin, fuorouracil, cisplatin, and mitomycin, but most of them are nonselective cytotoxic molecules with significant side effects (Kerr and Kerr, 2009). Hence, novel agents that are cheap, nontoxic, and efficacious are urgently needed.STAT proteins were originally discovered as latent cytoplasmic transcription factors more than a decade ago (Ihle, 1996). There are seven known mammalian STAT proteins,

β-Escin Inhibits NNK-Induced Lung Adenocarcinoma and ALDH1A1 and RhoA/Rock Expression in A/J Mice and Growth of H460 Human Lung Cancer Cells

“…This study is consistent with the earlier observations that support possible antitumorigenic effects of b-escin in in vitro and in vivo models (6)(7)(8)(9)(10). Previously, we showed that b-escin, at 250 and 500 ppm in the diet, inhibited colon carcinogen-induced preneoplastic foci in rat colon in a dose-dependent manner (6).…”

“…Studies from our laboratory showed that b-escin inhibits the growth of colon cancer cells and inhibits chemically induced colon carcinogenesis in rats (6). In recent years, several studies have shown that b-escin possesses anticancer activity by inhibiting growth and inducing apoptosis in various human cancer cell lines derived from lung (7), pancreatic (8), and liver (9) cancers and in leukemia and multiple myeloma (10).…”

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

“…Interestingly, a clear link between hepatitis C virus (HCV), STAT3 activation and HCC development has been reported (Waris and Siddiqui 2005;Yoshida et al 2002). As described by many studies, STAT3 represents a good candidate as a target in HCC patients for therapeutic agents including natural compounds Rajendran et al 2011a, b;Tan et al 2010). …”

“…Therefore, it is very important to identify new effective drugs. Among natural compounds from a variety of plants, diosgenin , b-escin (Tan et al 2010), butein ) and c-tocotrienol (Rajendran et al 2011a) were reported to inhibit proliferation and to induce apoptosis of HCC cells concomitantly in order to downregulate various STAT3-regulated gene products, including cyclin D1, Bcl-2, Bcl-xL, survivin, Mcl-1 and VEGF. These four natural molecules inhibited constitutive and inducible activation of STAT3 through the inhibition of c-Src, JAK1 and JAK2 activation.…”

Targeted inhibition of tumor proliferation, survival, and metastasis by pentacyclic triterpenoids: Potential role in prevention and therapy of cancer

“…We found that b-escin downregulated the expression of various STAT3 regulated gene products, such as cyclin D1, Bcl-2, Bcl-xL, survivin, Mcl-1, and VEGF. b-escin, in combination with paclitaxel or doxorubicin, potentiated the apoptotic effects of the chemotherapeutic compounds, thus its potent suppression of proliferation and chemosensitization of hepatocellular carcinoma [113,114]. In combination with 5-FU, b-escin showed a synergistic cytotoxic effect in human hepatocellular carcinoma SMMC-7721 by inhibiting induction of apoptosis, cell cycle arrest, activation of caspases-3, 8 and 9, and down-regulation Bcl-2 expression [115].…”