Constitutively activated STAT3 plays a pivotal role in oncogenesis and metastasis in many human cancers, and STAT3 has been validated as a novel anticancer drug target. Thus, the identification of small molecules that modulate STAT3 activity could be of great therapeutic importance. The aim of this study was to isolate novel modulators of the STAT3 signaling pathway from the roots of Polygonum cuspidatum by bioassay-guided fractionation using a STAT3 reporter gene assay. 2-Methoxystypandrone (1), as well as three anthraquinones (2–4), were identified as major active components of P. cuspidatum. Compound 1 demonstrated a potent inhibitory effect on STAT3 activation and significantly inhibited cell proliferation of human breast cancer cells, especially those with constitutively activated STAT3 (IC₅₀ = 2.7–3.1 µM). The SAR analysis of quinone analogues suggested that the phenolic and carbonyl groups are the key structures contributing to their inhibitory activities against the STAT3 signaling. ^* These authors contributed equally to this work.

Neuraminidase (NA) is one of the key surface protein of the influenza virus, and has been established as a primary drug target for anti-influenza therapies. This study aimed to screen bioactive herbal extracts from some medicinal plants traditionally used in Lingnan Chinese Medicines by NA activity high-throughput screening assay. One hundred ninety herbal extracts from 95 medicinal plants collected in Guangzhou were screened for their potential inhibitory activities against A (H1N1) influenza neuraminidase, and the most active extracts were further evaluated for their anti-influenza virus activities using virus-induced cytopathic effect (CPE). Among the tested 190 herbal extracts, 14 extracts inhibited significantly NA activity (IC50 < 40 μg/mL), and the extracts 1–5, which were obtained from Amomurn villosum Lour, Melaphis chinensis (Bell) Baker, Sanguisorba officinalis and Flos Caryophylli, showed potent inhibitory activity against NA with IC50 values ranging from 4.1 to 9.6 μg/mL. Moreover, the most bioactive extracts 1–5 were found to protect MDCK cells from A (H1N1) influenza virus infection with very low cytotoxicity to the host cells (EC50 values ranged from 1.8 to 14.1 μg/mL, CC50 values ranged from 97.0 to 779.2 μg/mL, SI values ranged from 14 to 438). In addition, quantitative RT-PCR analysis showed that the extracts 1–5 inhibited viral RNA synthesis in a dose-dependent manner. We performed in vitro screening of anti-neuraminidase activities of herbal extracts from medicinal plants used in Lingnan Chinese Medicines, and the results indicate that some bioactive extracts are worth further studies to identify the bioactive components responsible for anti-influenza virus activities, to elucidate their modes of action and finally determine their clinical potentials.

Signal transducer and activator of transcription 3 (STAT3) is an oncogene constitutively activated in hepatocellular carcinoma (HCC) cells and HCC cancer stem cells (CSCs). Constitutively activated STAT3 plays a pivotal role in holding cancer stemness of HCC CSCs, which are essential for hepatoma initiation, relapse, metastasis and drug resistance. Therefore, STAT3 has been validated as a novel anti-cancer drug target and the strategies targeting HCC CSCs may bring new hopes to HCC therapy. This study aimed to isolate and identify small-molecule STAT3 signaling inhibitors targeting CSCs from the ethyl acetate (EtOAc) extract of the roots of Polygonum cuspidatum and to evaluate their in vitro anti-cancer activities. The chemical components of the EtOAc extract and the subfractions of P. cuspidatum were isolated by using various column chromatographies on silical gel, Sephadex LH-20, and preparative HPLC. Their chemical structures were then determined on the basis of spectroscopic data including NMR, MS and IR analysis and their physicochemical properties. The inhibitory effects of the isolated compounds against STAT3 signaling were screened by a STAT3-dependent luciferase reporter gene assay. The tyrosine phosphorylation of STAT3 was examined by Western Blot analysis. In vitro anti-cancer effects of the STAT3 pathway inhibitor were further evaluated on cell growth of human HCC cells by a MTT assay, on self-renewal capacity of HCC CSCs by the tumorsphere formation assay, and on cell cycle and apoptosis by flow cytometry analysis, respectively. The EtOAc extract of the roots of P. cuspidatum was investigated and a novel juglone analogue 2-ethoxystypandrone (1) along with seven known compounds (2–8) was isolated. Among the eight isolated compounds 1–8, 2-ethoxystypandrone was a novel and potent STAT3 signaling inhibitor (IC50 = 7.75 ± 0.18 μM), and inhibited the IL-6-induced and constitutive activation of phosphorylation of STAT3 in HCC cells. Moreover, 2-ethoxystypandrone inhibited cell survival of HCC cells (IC50 = 3.69 ± 0.51 μM ~ 20.36 ± 2.90 μM), blocked the tumorspheres formation (IC50 = 2.70 ± 0.28 μM), and induced apoptosis of HCC CSCs in a dose-dependent manner. A novel juglone analogue 2-ethoxystypandrone was identified from the EtOAc extract of the roots of P. cuspidatum and was demonstrated to be a potent small-molecule STAT3 signaling inhibitor, which strongly blocked STAT3 activation, inhibited proliferation, and induced cell apoptosis of HCC cells and HCC CSCs. 2-Ethoxystypandrone as a STAT3 signaling inhibitor might be a promising lead compound for further development into an anti-CSCs drug.

Background: 2-Methoxystypandrone (2-MS), isolated from the roots of Polygonum cuspidatum, is a potent dual inhibitor of the STAT3 and NF-κB pathways. Objective: To investigate the molecular targets and mechanisms of 2-MS. Method: A biotin-conjugated 2-MS analog, named 2-MS-Biotin, was designed and synthesized. The effects of 2-MS-Biotin on the STAT3 and NF-κB pathways were examined by Western blotting. The cytotoxicity of 2- MS-Biotin was evaluated using real-time cell analysis system. Proteins directly bound to 2-MS-Biotin were pulled down through streptavidin agarose beads and were detected using Western blotting. Results: 2-MS-Biotin retained the inhibition activities of the parent compound 2-MS on the STAT3 and NF-κB pathways as well as on cancer cell growth. Also, JAK2 and IKK proteins can be effectively pulled down by 2- MS-Biotin. Conclusion: Using 2-MS-Biotin as a tool, both JAK2 and IKK were identified as the targets of 2-MS.