Isoliensinine, a Bioactive Alkaloid Derived from Embryos of Nelumbo

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Isoliensinine, a bioactive alkaloid derived from embryos of Nelumbo nucifera, induces hepatocellular carcinoma cell apoptosis through suppression of NF-#B signaling Guangwen Shu, Ling Yue, Wenhao Zhao, Chan Xu, Jing Yang, Shaobing Wang, and Xinzhou Yang J. Agric. Food Chem., Just Accepted Manuscript • DOI: 10.1021/acs.jafc.5b02993 • Publication Date (Web): 21 Sep 2015 Downloaded from http://pubs.acs.org on September 24, 2015

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Journal of Agricultural and Food Chemistry

Isoliensinine, a bioactive alkaloid derived from embryos of Nelumbo nucifera, induces

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hepatocellular carcinoma cell apoptosis through suppression of NF-κB signaling

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Guangwen Shu, Ling Yue,§ Wenhao Zhao, Chan Xu, Jing Yang, Shaobing Wang, and

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Xinzhou Yang*,

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College of Pharmacy, South-Central University for Nationalities, Wuhan, PR China

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§

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Wuhan, PR China

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*To whom correspondence can be addressed.

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Department of Endocrinology, Wuhan General Hospital of Guangzhou Military Command,

Phone/Fax: + 86 27 6784 1196. E-mail address: [email protected]

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ABSTRACT:

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Isoliensinine (isolie) is an alkaloid produced by the edible plant Nelumbo nucifera. Here,

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we unveiled that isolie was able to provoke HepG2, Huh-7 and H22 hepatocellular carcinoma

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(HCC) cell apoptosis. Isolie decreased NF-κB activity and constitutive phosphorylation of

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NF-κB p65 subunit at Ser536 in HCC cells. Overexpression of p65 Ser536 phosphorylation

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mimics abrogated isolie-mediated HCC cell apoptosis. Furthermore, intraperitoneal injection

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of isolie inhibited the growth of Huh-7 xenografts in nude mice. Additionally, isolie given by

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both intraperitoneal injection and gavage diminished the proliferation of transplanted H22

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cells in Kunming mice. Reduced tumor growth in vivo was associated with inhibited p65

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phosphorylation at Ser536 and declined NF-κB activity in tumor tissues. Finally, we revealed

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that isolie was bioavailable in the blood of mice and exhibited no detectable toxic effects on

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tumor-bearing mice. Our data provided strong evidence for the anti-HCC effect of isolie.

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KEYWORDS:

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Nelumbo nucifera; Isoliensinine; Hepatocellular carcinoma; Apoptosis; NF-κB

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INTRODUCTION

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Hepatocellular carcinoma (HCC) is one of the most prevalent malignancies and is the third

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most frequent cause of cancer-related mortality worldwide.1 Surgical resection is considered

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to be the standard strategy for treatment of HCC. However, only a small proportion of HCC

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patients are eligible for surgical intervention, since HCC is often diagnosed in later stages due

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to the extended length of time it takes for HCC to begin and develop.2 Therefore, the majority

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of HCC patients must rely on systemic chemotherapies. Though compounds such as sorafenib,

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5-fluorouracil and cisplatin are approved for clinical HCC treatment, they only provide

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limited benefit due to toxic side effects in patients and chemoresistance in HCC cells. Thus, it

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is imperative to discover and develop new chemotherapy reagents that are capable of inducing

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HCC cell death but have low or no toxic side effects in patients.

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Nuclear factor κB (NF-κB) is a family of widely expressed and structurally related homo-

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or heterodimeric DNA-binding proteins that control the transcription of NF-κB responsive

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genes and participate in a multitude of important biological processes.3 Aberrant activation of

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NF-κB is involved in the pathogenesis of HCC.4 The heterodimer p65/p50 is a representative

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form of NF-κB. Phosphorylation of the p65 subunit of NF-κB is an important mechanism

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modulating NF-κB activity. For instance, phosphorylation of p65 at Ser536 enhances NF-κB

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transcriptional potential.5 In cancer cells of different origins, such as myeloma cells, stomach

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cancer cells and embryonic carcinoma cells, reduction of p65 phosphorylation at Ser536 is

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associated with cancer cell apoptosis induced by potential chemotherapeutic reagents.6-8

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However, the role of p65 dephosphorylation at Ser536 in HCC cell apoptosis remains to be

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fully elucidated.

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In recent years, natural products have garnered a lot of attentions from pharmaceutical

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researchers and clinicians owing to their efficiency, safety, and immediate availability.9-11

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During the past 30 years, more than 70% of the drugs approved by the U.S. Food and Drug

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Administration originated from natural products.12 Nelumbo nucifera (N. nucifera),

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commonly known as lotus, is a well-known edible plant. Food related to N. nucifera is

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popular in some areas of East Asia, especially China. Embryos of N. nucifera contain

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structurally related bioactive alkaloids including liensinine, isoliensinine (isolie) and neferine

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(chemical structures shown in Figure 1A). In previous pilot studies in our lab, liensinine,

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isolie and neferine were prepared from embryos of N. nucifera and tested for cytotoxic

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activity in a series of human HCC cell lines. Isolie displayed stronger cytotoxic activity on

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HCC cells compared to liensinine or neferine. Interestingly, the cytotoxic effect of isolie on

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untransformed hepatocytes, including human HL-7702 hepatocytes and primary mouse

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hepatocytes, was much lower than the cytotoxic effects of neferine or liensinine (Table 1). In

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the current study, we demonstrate that isolie provokes HCC cell apoptosis both in vitro and in

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vivo. Mechanistically, dephosphorylation of p65 at Ser536 which inhibits NF-κB activity is a

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crucial molecular event mediating isolie-induced HCC cell apoptosis. The bioavailability and

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toxic impact of isolie were also assessed on tumor-bearing mice.

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MATERIALS AND METHODS

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Isolation and purification of isolie

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The embryos of N. nucifera were purchased from Jointown Pharmaceutical Group Co. Ltd.

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(Wuhan, Hubei Province, PR China) in September 2011 and identified by Prof. Dingrong

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Wan from the College of Pharmacy, South-Central University for Nationalities, Wuhan,

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China. Voucher specimens (2011009N) were deposited in the Herbarium of the College of

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Pharmacy, South-Central University for Nationalities. Air-dried embryos of N. nucifera (1.0

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kg) were ground into powder and extracted using 90% EtOH (4 × 3.0 L). After evaporation of

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the collected percolate, the crude extract was acidified with diluted HCl (5%) to a pH of 1-2

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and partitioned between hexane (3 × 1.5 L) and the acid water layer. The aqueous part was

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basified with aqueous NH3 to a pH of 9-10 and extracted with CHCl3 to yield 14.5 g of crude

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alkaloid. A portion of the crude alkaloid (14 g) was then subjected to column chromatography

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over silica gel (300-400 mesh) and eluted with the isocratic gradient solvent system of CH2Cl2,

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methanol and diethylamide (100: 5: 2) to yield five major fractions (F1-F5) (F1, 1.8 L; F2, 2.4

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L; F3, 1. 7 L; F4, 2.6 L; F5, 3.5 L). After evaporation under vacuum, crude isolie (1.8 g) was

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obtained from F4 and then dissolved in anhydrous acetone (50 mL). The solution was

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acidified with drops of diluted HClO4 (10%) to a pH of 2-3. The acidized isolie solution was

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kept in 4 °C to crystallize and yielded 1.9 g of pure isolie perchloride. The isolie perchloride

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(1.8 g) was dissolved in 50 mL of water, and this solution was basified with aqueous NH3 to a

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pH of 9-10. The solution was extracted with CHCl3 to give 1.3 g of the free isolie. 1H,

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NMR and LC-ESIMS data were obtained to support the identification of isolie (Supporting

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Information, Supplementary Figure 1). The isolie were analyzed by high-performance liquid

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chromatography (HPLC) on a Waters 1525 HPLC instrument by a single injection of 20 µL

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with an analytical C18 HPLC column (Betasil 150 × 4.6 mm, 5 µm) detected at 254 nm;

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Gradient conditions: 90% H2O (0.1% TFA) + 10% MeCN (0.1% TFA) → 100% MeCN

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(0.1% TFA), 20 min, 100% MeCN (0.1% TFA), 25 min; flow rate: 1.0 mL/min. The purity of

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the isolie was above 95% as detected by HPLC and UV spectrum analysis (Figure 1A).

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Cells, reagents, kits and antibodies

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Human HL-7702 untransformed hepatocytes and murine H22 ascitic hepatoma cells were

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supplied by the China Center for Type Culture Collection. HepG2 and Hep3B human HCC

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cells were from the American Type Culture Collection. Huh-7 HCC cells, Panc-1 pancreatic

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carcinoma cells and HT-29 colon carcinoma cells were got from the Cell Bank of Shanghai

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Institute of Biological Sciences. Primary mouse hepatocytes were separated and cultured as

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described previously.13 Dulbecco’s Modified Eagle Medium (DMEM) was got from Hyclone

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(Logan, UT, USA). Fetal calf serum (FCS), penicillin and streptomycin for cell culture and

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Trizol reagents for RNA extraction were purchased from Invitrogen (Carlsbad, CA, USA).

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FuGENE reagents for cell transfection were purchased from Roche (Penzberg, Germany).

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3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazoliunbromide (MTT) and propidium iodine

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were purchased from Wolsen Biotechnology (Xi’an, Shanxi Province, PR China). Caspase-3

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activity assay kits, BCA protein quantification kits and JC-1 which is a fluorescent probe for

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mitochondria membrane potential were purchased from Beyotime Biotechnology (Nantong,

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Jiangsu Province, PR China). NF-κB-dependent luciferase reporters, pRL-TK plasmids and

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Dual Reporter assay systems for the determination of intercellular luciferase activity were got

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from Promega (Fitchburg, WI, USA). The pRL-TK plasmid encodes the Renilla luciferase

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gene driven by the promoter of herpes simplex virus thymidine kinase gene and is used as an

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internal control in luciferase activity assays. Reverse transcriptase ReverTra Ace-α were got

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from Toyobo (Osaka, Japan). Primary antibodies against Bcl-2 (SC-492), Bcl-xL (SC-8392),

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MMP9 (SC-6841), p65 (SC-372) and IκBα (SC-371), and secondary antibodies conjugated

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with horseradish peroxidase were from Santa Cruz Biotechnology (Santa Cruz, CA, USA).

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Antibodies against Ser536-phosphorylated p65 (No. 13346), myc tag (No. 2278) and β-actin

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(No. 3700) were got from Cell Signaling Technology (Danvers, MA, USA).

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Cells culture and transfection

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Cells were maintained in DMEM containing 10% FCS, 100 U/mL penicillin and 100

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µg/mL streptomycin at 37 °C in a humidified atmosphere with 5% CO2. To overexpress p65

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phosphorylation mimics in which Ser536 is mutated into an Asp (p65-S536D), the encoding

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gene of human p65-S536D was cloned into the vector pcDNA3.1A. Plasmids were transected

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into HCC cells using FuGENE reagents, according to the manufacturer’s instructions.

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Cell viability assay and calculation of IC50 value

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Cells were incubated with different concentrations of the indicated compounds. After 48 h,

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MTT cell viability assays were performed as described previously.14 The IC50 value of a

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compound is defined as the concentration at which cell viability was reduced by 50% as

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determined by MTT cell viability assays and calculated by using the Origin Software.

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Flow cytometry analysis (FACS)

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FACS was performed as described previously.15 Briefly, after undergoing treatment as

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indicated in the text, the cells were trypsinized and fixed with cold 70% ethanol (stored at

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-20 °C) for at least 2 h. Samples were then pelleted and washed with PBS containing 20 mM

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EDTA. Intracellular RNA was removed by incubating samples with 1 mg/mL RNaseA at

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37 °C for more than 2 h. Finally, cells were stained with 30 µg/mL propidium iodine and

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subjected to FACS (Becton Dickinson FACSCalibur, Franklin Lakes, NJ, USA). Cells in Sub

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G1 phase were considered to be apoptotic.

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Caspase-3 activity assay Caspase-3 activity assay kits were used to measure caspase-3 activity in the total lysates of cultured cells or tumors tissues, according to the manufacturer’s instructions.

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NF-κB luciferase reporter assay

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Cells were cultured for 24 h in 24-well plates prior to transfection. Then, NF-κB luciferase

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reporters and pRL-TK plasmids were co-transfected into HCC cells using FuGENE reagents.

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After 24 h, the media was replaced and cells were incubated with various stimuli as indicated

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in the text. The Dual Reporter assay system was used to measure luciferase activity in cell

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lysates, according to the manufacturer’s instructions.

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RNA isolation, reverse transcription and real-time polymerase chain reaction (PCR)

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RNA was extracted from cultured HCC cells or in vivo tumors tissues by Trizol reagent,

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according to the manufacturer’s instructions. To get cDNA from each sample, 3 µg of total

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RNA was reverse transcribed at 42 °C for 30 min using ReverTra Ace-α. mRNA levels of

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indicated genes were analyzed by real-time PCR. Glyceraldehyde-3-phosphate dehydrogenase

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(GAPDH) was used as the loading control.

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Chromatin immunoprecipitation (ChIP) ChIP assay was performed as previously described.16 Relative binding of p65 to promoter regions of Bcl-2 and Bcl-xL encoding genes was measured by real-time PCR.

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Assessment of mitochondria dysfunction by JC-1 staining

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JC-1 is a fluorescent dye which forms aggregates in normal mitochondrias and emits red

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fluorescence. However, JC-1 monomers emit green fluorescence in cells with mitochondria

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dysfunction. Cells were seeded in 24-well plates and stimulated as indicated in the text. After

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the treatment, the medium was discarded and replaced by 500 µL of fresh medium containing

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5 µg/mL JC-1. After incubating for 1 h, cells were washed twice with PBS and photographed

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at a magnification of 100 × under a fluorescence microscope.

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Animals

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Male athymic nude mice (6 weeks old) and Kunming mice, weighting between 18 and 22 g,

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were obtained from the Center of Experimental Animals, Institute of Health and Epidemic

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Prevention (Wuhan, PR China) and housed under standard specific pathogen-free conditions

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with access to sterilized water and food ad libitum. All of the animal experimental procedures

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were performed in accordance with the terms approved by the Experimental Animal Care and

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Use Committee of South-Central University for Nationalities (Wuhan, PR China).

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Huh-7 xenograft tumor growth in nude mice

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Huh-7 cells (1 × 106) were suspended in 0.2 mL of serum-free DMEM with 50% Matrigel

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(BD Biosciences, Bedford, MA, USA) and subcutaneously injected into the dorsal flanks of

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nude mice. Mice were randomly divided into groups of 6 mice each. When the xenograft

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tumor volume reached about 200 mm3, isolie was administrated at the indicated dosages once

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daily, for 3 weeks, via intraperitoneal (i. p.) injection; normal saline (0.9% NaCl) was used as

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the negative control. Tumor volumes were monitored every 3 days by the following formula:

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tumor volume = length × width × width / 2. Blood samples were collected from animals

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anesthetized with diethyl ether. All mice were then euthanized and the livers and xenograft

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tumors were immediately resected for further analysis.

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H22 transplanted tumor establishment and isolie administration

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H22 cells (1 × 106) were subcutaneously transplanted into the dorsal flanks of Kunming

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mice. Mice were randomly divided into groups of 10 mice each. Drug treatment began 24

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hours later. Drugs were administrated once daily, for 10 days, via i. p. injection or gavage as

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indicated in the text. Isolie groups received different dosages (3 and 10 mg/kg). The vehicle

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control group received normal saline. A group of mice without tumor transplantation was also

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included. Tumor volumes were monitored every 2 days. At last, blood samples were collected

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under diethyl ether anesthesia. Immediately after euthanizing all animals, transplanted tumors

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and corresponding organs were resected for further analysis. The organ index was calculated

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using the following formula: Organ index = organ weight (g) / body weight (g) × 1000.

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Blood and serum physiochemical indexes determination

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An automatic blood cell count apparatus (Mindray, Shenzhen, Guangdong Province, PR

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China) was used to record the amount of white blood cells (WBC), red blood cells (RBC),

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hemoglobins (HGB) and platelets (PLT). Serum was prepared by centrifuging blood samples

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at 4500 × g for 10 min. Serum hepatic and renal function parameters, including aspartate

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aminotransferace (AST), alanine aminotransferace (ALT), blood urea nitrogen (BUN), uric

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acid (UA) and creatinine (CRE), were measured by an automatic biochemical analyzer

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(Sysmex, Kobe, Japan) according to the manufacturer’s instructions.

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Statistical analysis

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Data shown in this study are representatives or statistics (mean value ± standard deviation)

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of the results from at least three independent experiments or all mice of each group. One-way

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analysis of variance (ANOVA) was performed to determine the statistical significance. If the

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treatment involved more than one concentration or dosage, Dunnett’s t tests were further

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conducted to determine the statistical significance of each concentration/dosage group

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compared to the negative control. A p value of < 0.05 was considered to be statistically

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significant and indicated by “*”. A p value of < 0.01 was considered to be statistically very

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significant and indicated by “**”.

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More detailed materials and methods are provided as Supplementary Materials and Methods in Supporting Information.

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RESULTS

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Isolie induced HCC cell apoptosis in vitro

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To assess the ability of isolie to provoke HCC cell apoptosis, human HepG2 and Huh-7

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HCC cells were treated with 3 and 10 µg/mL isolie. After 48 h, ratios of Sub-G1 DNA in the

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cell populations were quantified by FACS. The result showed that 48-hour isolie treatment

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dose-dependently increased the ratio of Sub-G1 DNA (Figure 1B, left and middle). In

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addition, caspase-3 activity was dose-dependently elevated in HCC cells by isolie (Figure 1B,

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right). Similarly, as shown by FACS and caspase-3 activity assay, isolie time-dependently

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triggered HepG2 and Huh-7 cell apoptosis (Figure 1C). Moreover, isolie dose-dependently

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induced murine H22 ascitic hepatoma cell apoptosis (Figure 1D). These data demonstrated

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that isolie is capable of provoking HCC cell apoptosis in vitro.

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Isolie suppressed NF-κB activity in HCC cells

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To understand the molecular mechanisms underlying isolie-mediated HCC cell apoptosis,

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we firstly evaluated the impacts of isolie on an array of signaling pathways that regulate cell

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apoptosis including p53, STAT3, Foxo3a and NF-κB using corresponding luciferase reporter

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assays. Isolie showed few effects on the activity of p53, STAT3 or Foxo3a (data not shown),

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but substantially decreased the basal level of NF-κB activity in both HepG2 and Huh-7 HCC

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cells (Figure 2A). Consistently, mRNA and protein levels of typical NF-κB target genes, such

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as Bcl-2, Bcl-xL and MMP9, in HCC cells were also downregulated by isolie (Figure 2B and

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C). ChIP assay confirmed that isolie suppressed the interaction between NF-κB p65 subunit

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and promoter regions of Bcl-2 and Bcl-xL encoding genes (Figure 2D). In HepG2 and Huh-7

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cells without isolie treatment, mitochondrias were intact and emitted red fluorescence after

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JC-1 staining. Isolie reduced the red fluorescence signal emitted by JC-1, but elevated the

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green fluorescence signal, indicating that isolie induced mitochondria dysfunction in HCC

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cells (Figure 2E). In murine H22 HCC cells, isolie dose-dependently inhibited transcription

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and translation of NF-κB responsive genes (Figure 2F and G). Interactions between p65

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proteins and promoter regions of Bcl-2 and Bcl-xL were also reduced by isolie (Figure 2H).

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These data suggested that isolie suppresses NF-κB activity in HCC cells.

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Isolie provoked dephosphorylation of p65 protein at Ser536

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Degradation of IκBα protein is an important molecular event that activates NF-κB signaling.

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However, IκBα remained unchanged in response to isolie (Figure 3A). Phosphorylation of

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NF-κB p65 subunit at Ser536 plays important roles in promoting NF-κB-dependent gene

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transcription. Isolie dose-dependently suppressed p65 Ser536 phosphorylation in HCC cells

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(Figure 3A). To confirm the role of p65 dephosphorylation at Ser536 in isolie-induced HCC

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cell apoptosis, plasmids encoding myc-tagged p65-S536D which is a p65 phosphorylation

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mimic at Ser536 were transfected into HCC cells (Figure 3B). Overexpressing p65-S536D

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dramatically alleviated isolie-induced mitochondria dysfunction (Figure 3C). Accordingly,

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isolie-induced HCC cell apoptosis was also considerably abrogated (Figure 3D and E). These

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findings suggested that p65 dephosphorylation at Ser536 is a critical molecular event

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accounting for isolie-induced NF-κB inhibition and apoptosis in HCC cells.

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Isolie suppressed Huh-7 xenograft tumor growth in nude mice

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To explore whether the pro-apoptotic activity of isolie on HCC cells lines has any potential

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clinical implications, we evaluated the in vivo impacts of isolie on the proliferation of Huh-7

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HCC xenograft tumors. Isolie substantially attenuated the proliferation of xenograft tumors as

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compared to vehicle (Figure 4A). Isolie-induced HCC cell apoptosis in vivo was verified by

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caspase-3 activity assay (Figure 4B). To assess side impacts of isolie on normal hepatocytes

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of tumor-bearing mice, its effects on host liver indexes and serum makers of liver function

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including ALT and AST were tested immediately at the end of the treatment. There was no

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significant change in any of these parameters in response to i. p. injection of isolie (Figure

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4C). To correlate the tumor-suppressing activity in vivo with mechanisms of action identified

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in vitro, effects of isolie on p65 phosphorylation and NF-κB activity in Huh-7 xenograft

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tumors were detected. Isolie dose-dependently decreased p65 Ser536 phosphorylation (Figure

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4E, left and middle). Moreover, mRNA and protein levels of NF-κB responsive genes were

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dose-dependently declined in xenograft tumors as shown by real-time PCR (Figure 4D) and

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immunoblotting (Figure 4E, left and right). These data suggested that in Huh-7 xenograft

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HCC tumors, isolie provokes p65 dephosphorylation at Ser536 that reduces NF-κB activity

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and leads to cell apoptosis. Toxic impacts of isolie on normal livers were undetectable.

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Effects of isolie on transplanted H22 HCC cell growth in Kunming mice

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To explore the anti-HCC activity of isolie in hosts with intact immune systems that is closer

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to clinical situations, effects of isolie on the proliferation of H22 HCC cells subcutaneously

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transplanted into the dorsal flanks of Kunming mice were evaluated. Two routes of drug

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administration, including i. p. injection and gavage, were both tested in this model. As shown

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in Figure 5A and B, isolie given by both routes dose-dependently reduced the growth of H22

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transplanted tumors and elevated caspase-3 activity in tumor tissues. Additionally, gavage of

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isolie dose-dependently reduced constitutive phosphorylation of p65 at Ser536 in transplanted

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tumor tissues (Figure 5D, left and middle). There were also dramatic decreases in mRNA and

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protein levels of NF-κB target genes (Figure 5C and D, left and right). To understand isolie

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uptake by mice, the concentration of isolie in the blood was quantified by ultra-performance

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liquid chromatography tandem mass spectrometry (UPLC-MS/MS). After i. p. injection of

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isolie at the dosage of 10 mg/kg, the maximum absorption peak of isolie appeared at 15 min

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with the concentration of 1356.3 ng/mL in plasma. The concentration of isolie in plasma

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declined to 469.1 ng/mL at 30 min, and further to 95.5 ng/mL at 2 h (Supporting Information,

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Supplementary Figure 2). These data provided more evidences to support the capacity of

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isolie to inhibit NF-κB signaling and induce apoptosis in HCC cells in vivo.

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Effects of isolie on tumor-bearing mice

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Finally, we evaluated toxic impacts of i. p. injection of isolie on Kunming mice. We found

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that i. p. injection of isolie (10 mg/kg) showed few effects on body weights of tumor-bearing

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mice (data not shown). Moreover, amounts of WBC, RBC, HGB and PLT were comparable

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among all experimental groups (Table 2). In addition, effects of isolie on serum levels of liver

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function parameters including ALT and AST were unobvious. BUN, UA, and CRE are serum

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renal function indicators. These parameters remained almost unchanged after i. p. injection of

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isolie (Table 3). Moreover, isolie showed little influence on indexes of thymus, spleens, and

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livers of tumor-bearing mice (Table 4). These data suggested that toxic effects of isolie at the

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dosage of 10 mg/kg on vital organs of tumor-bearing mice are undetectable.

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DISSCUSSION In this study, we prepared isolie from embryos of N. nucifera. The 1H,

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C NMR and

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LC-ESIMS data of isolie we isolated are as followed. 1H NMR data (CDCl3, 500 MHz): δH

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3.65 (1H, m, H-1), 3.73 (1H, m, H-1'), 2.46 (1H, s, 2-NCH3), 2.56 (1H, s, 2'-NCH3), 3.12 (1H,

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m, H1-3), 2.76 (1H, m, H1-3), 3.18 (1H, m, H1-3'), 3.00 (1H, m, H1-3'), 2.73 (2H, m, H-4),

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2.74 (1H, m, H1-4'), 2.72 (1H, m, H1-4'), 6.65 (1H, s, H-5), 6.48 (1H, s, H-5'), 3.80 (3H, s,

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6-OCH3), 3.82 (3H, s, 6'-OCH3), 6.25 (1H, s, H-8), 6.29 (1H, s, H-8'), 2.89 (1H, dd, J = 12.0,

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8.7 Hz, H1-9), 2.81 (1H, J = 12.0, 5.1 Hz, H2-9), 3.12 (1H, m, H1-9'), 2.72 (1H, J = 13.8, 6.9

323

Hz, H2-9'), 6.90 (1H, d, J = 8.6 Hz, H-11, H-15), 6.43 (1H, d, J =1.8 Hz, H-15'), 6.70 (1H, d, J

324

=8.6 Hz, H-12, H-14), 3.73 (3H, s, 13-OCH3), 6.83 (1H, d, J =8.2 Hz, H-14'), 6.76 (1H, 1H,

325

dd, J =8.2, 1.8 Hz, H-11'). 13C NMR data (CDCl3, 125 MHz): δ 64.3 (C-1), 64.5 (C-1'), 42.3

326

(2-NCH3, 2'-NCH3), 47.1 (C-3), 46.6 (C-3'), 25.7 (C-4), 24.9 (C-4'), 130.1 (C-4a), 130.5

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(C-4a'), 112.4 (C-5), 110.6 (C-5'), 149.2 (C-6), 145.4 (C-6'), 55.8 (6-OCH3), 56.0 (6'-OCH3),

328

142.9 (C-7), 143.7 (C-7'), 120.0 (C-8), 113.9 (C-8'), 130.1 (C-8a), 125.4 (C-8a'), 40.4 (C-9),

329

39.1 (C-9'), 130.8 (C-10), 131.0 (C-10'), 130.5 (C-11, C-15), 125.4 (C-11'), 113.6 (C-12,

330

C-14), 144.5 (C-12'), 157.9 (C-13), 145.4 (C-13'), 55.2 (13-OCH3), 115.5 (C-14'), 119.1

331

(C-15'). ESI-MS: m/z 611 [M + H]+. Compared with the spectroscopic data of isolie reported

332

in the previous literature,17 this compound we purified from embryos of N. nucifera could be

333

unambiguously determined as isolie. Although isolie has been recognized for decades, it still

334

remains poorly understood whether it possesses any pro-apoptotic activity against HCC cells.

335

Here, we showed that isolie time- and dose-dependently induced apoptosis in HepG2, Huh-7

336

and H22 HCC cells in vitro. Additionally, isolie also displayed strong cytotoxic effects on

337

HT-29 colon carcinoma cells and Panc-1 pancreatic carcinoma cells (Supporting Information,

338

Supplementary Figure 3). These data suggested that isolie is able to inhibit other cancer cells

339

such as colon and pancreatic cancer cells.

340

On the basis of its favorable in vitro pro-apoptotic activity against HCC cells, effects of

341

isolie on Huh-7 xenograft tumors in nude mice were assessed. It was revealed that i. p.

342

injection of isolie dramatically decreased growth of xenografted Hun-7 tumors. Caspase-3

343

activity assay further demonstrated that isolie has the capacity of provoking apoptosis in

344

xenografted HCC tissues in vivo. Similarly, i. p. injection of isolie inhibited transplanted H22

345

tumor growth and induced H22 HCC cell apoptosis in Kunming mice. Gavage is a safer and

346

more convenient route than i. p. injection. We thus also tested the anti-HCC activity of isolie

347

given by gavage. Excitingly, isolie gavage achieved a similar tumor-suppressing effect as

348

compared to that of i. p. injection, implying a possibility that this compound is stable in the

349

digestive tract of animals and can be efficiently absorbed into the circulatory system.

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350

An important part of cancer chemotherapy is that the agent used should induce malignant

351

cell death with low toxic effects on their normal counterparts. Cisplatin is a conventional

352

chemotherapeutic anticancer drug with a high tumor-suppressing activity. However, it exhibits

353

severe hepatotoxicity and nephrotoxicity in patients, leading to a very poor prognosis.18

354

Sorafenib is one of few targeted therapeutic reagents for treating advanced HCC approved by

355

the US Food and Drug Administration. Unfortunately, sorafenib has also been shown to exert

356

side effects on some vital organs including the liver itself.19, 20 In this study, isolie exerted its

357

in vivo anti-HCC effects at the dosage of 10 mg/kg. At this dosage, i. p. injection of isolie

358

showed few changes in liver indexes and serum parameters of liver function in nude mice.

359

Toxic effects of i. p. injection of isolie at 10 mg/kg on Kunming mice were unobvious as well.

360

Consistently, our unpublished data showed that the Median Lethal Dosage of isolie given by i.

361

p. injection is greater than 1.2 g/kg for mice. These observations can be supported by the fact

362

that the plant N. nucifera is widely consumed as food. Pervious studies showed that the mass

363

fraction of isolie in the crude extract of embryos of N. nucifera was 45.7 mg/g. In their report,

364

the yield of the crude extract from embryos of N. nucifera was 593 g / 10 kg = 5.93%.21 The

365

mass fraction of isolie in the raw plant material was thereby 2.71 mg/g. Hence, the dosage of

366

isolie (10 mg/kg) in our in vivo experiment should be equivalent to an intake of about 3.69

367

g/kg embryos of N. nucifera for mice. According to the notion of animal surface area, this

368

dosage is equivalent to 0.3 g/kg for human.22 Thus, a person weighting 65 kg would need to

369

consume about 20 g of embryos of N. nucifera every day, which is in fact a feasible dosage.

370

Among three alkaloids including liensinine, isolie and neferine, isolie exhibited the most

371

prominent cytotoxic activity on HCC cells. Cytotoxic activity of neferine on HCC cells was

372

less potent than that of isolie, but stronger than that of liensinine. Similar to our observations,

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a very recent study reported that, among these three alkaloids, cytotoxic activity of isolie on

374

MDA-MB-231 breast cancer cells was the most potent and liensinine was the least potent.23

375

Based on these data, structure-activity relationships of these three alkaloids can be summed

376

up as follows (Positions R1 and R2 are indicated in Figure 1A). Replacing the hydrogen atom

377

at the R2 position by a methyl group is conducive to enhancing the cytotoxic potency of the

378

compound. But the same substitution at the R1 position can potentially decline its cytotoxic

379

potency. Mechanistically, neferine-mediated malignant cell death is associated with the

380

inhibition of Akt signaling,24,

381

through DNM1L-mediated mitochondrial fission.26 Here, we reported that suppression of

382

NF-κB signaling is the key molecular event mediating isolie-induced HCC cell apoptosis.

25

while liensinine sensitizes cancer cells to chemotherapy

383

Epidemiological studies revealed that viral infection and steatohepatitis are significant risk

384

factors of HCC. Both of them have the potential to activate hepatic NF-κB, suggesting the

385

important role of persistently activated NF-κB in hepatocarcinogenesis.27, 28 At molecular

386

level, activation of NF-κB has the potential to promote transcription of genes antagonizing

387

apoptosis such as Bcl-2 and Bcl-xL as well as enzymes degrading extracellular matrix such as

388

MMP9.29, 30 These NF-κB-responsive genes are important contributors to the survival and

389

metastasis of HCC. Our current study clearly displayed that in HCC cells, isolie dramatically

390

declined their transcription and translation both in vitro and in vivo. These data suggested that

391

isolie inhibited NF-κB in HCC cells. Similarly, previous studies reported that an array of

392

reagent with the capacity of suppressing NF-κB signaling induced HCC cell apoptosis.31-34

393

These findings not only supported the feasibility of considering NF-κB as a potential target in

394

HCC chemotherapy, but also implied a possible participation of hyperactivated NF-κB for

395

maintaining HCC cell survival.

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Declined p65 phosphorylation at Ser536 was implicated in isolie-mediated inhibition of

397

NF-κB, which could be supported by lines of evidences in this study. First, isolie suppressed

398

p65 phosphorylation at Ser536 both in vitro and in vivo, and p65 dephosphorylation at Ser536

399

was associated with HCC cell apoptosis. Second, transfection of p65 Ser536 phosphorylation

400

mimics abrogated isolie-induced mitochondria injury and apoptosis in HCC cells. It has been

401

reported by previous studies that p65 phosphorylation at Ser536 plays critical roles in the

402

proliferation and invasion of cancer cells of different origins.35-37 In addition, aberrant p65

403

phosphorylation at Ser536 has been detected in some other malignant tissues dissected from

404

human cancers and correlates with cancer progression.38-41 A series of kinases are involved in

405

the phosphorylation of p65 protein at Ser536. For example, activation of kinases, such as Akt

406

and IKK, is positively associated with elevated p65 protein phosphorylation at Ser536.42-44

407

Dysregulation of Akt and IKK are increasingly implicated in the pathogenesis of HCC.45, 46 In

408

addition, Akt- and IKK-related signaling pathways have been considered as potential targets

409

for the clinical management of HCC.47, 48 It is thus reasonable to speculate that the possible

410

interaction between isolie and these pathways in HCC cells plays roles in isolie-mediated

411

dephosphorylation of p65 at Ser536.

412

For a brief summary, in this study, pro-apoptotic effects of isolie on HCC cells were tested

413

and possible molecular mechanisms underlying isolie-induced HCC cell apoptosis were

414

explored. It was unveiled that isolie dose- and time-dependently provoked HepG2, Huh-7 and

415

H22 HCC cell apoptosis. Mechanistically, isolie gave rise to a substantial decrease in NF-κB

416

activity in HCC cells. Isolie dramatically declined constitutive phosphorylation of NF-κB p65

417

subunit at Ser536. Overexpressing p65 Ser536 phosphorylation mimics abrogated HCC cell

418

apoptosis induced by isolie. Moreover, i. p. injection of isolie inhibited the growth of Huh-7

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419

xenografts in nude mice. In Huh-7 xenografts, isolie triggered p65 Ser536 dephosphorylation

420

and inhibited NF-κB activity. In addition, isolie given by both i. p. injection and gavage had

421

the capacity of diminishing in vivo proliferation of transplanted H22 cells in Kunming mice.

422

Toxic effects of isolie on tumor-bearing mice were undetectable. Our findings provided strong

423

evidence for the potential anti-HCC capacity of isolie. Suppression of NF-κB via p65

424

dephosphorylation at Ser536 is implicated in isolie-induced HCC cell apoptosis.

425 426

ASSOCIATED CONTENT

427

Supporting Information

428

Supporting Information associated with this article includes Supplementary Materials and

429

Methods, Supplementary Figure 1, 2 and 3 and their captions. This material is available free

430

of charge via the Internet at http://pbs.acs.org.

431 432

AUTHOR INFORMATION

433

Corresponding Author

434

Tel./Fax: + 86 27 6784 1196. E-mail: [email protected] (Xinzhou Yang)

435

Funding

436 437 438

This work is supported by the Natural Science Foundation of China (31301147, 81573561). Notes The authors declare no conflicts of interest.

439 440 441

ABBREVIATIONS USED Isolie, Isoliensinine; HCC, hepatocellular carcinoma; NF-κB, nuclear factor κB

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588 589

Figure captions

590

Figure 1. Isolie dose- and time-dependently provoked human and murine HCC cell apoptosis

591

in vitro. (A) Chemical structures of liensinine, isolie and neferine are shown. The purity of

592

isolie was determined by both HPLC and UV spectrum analysis. (B) HCC cells were treated

593

with indicated concentrations of isolie. After 48 h, cell apoptosis was examined by FACS (left

594

and middle, both representative FACS diagrams and statistics are shown) and caspase-3

595

activity assay (right). (C) HepG2 and Huh-7 cells were treated with 10 µg/mL isolie for

596

indicated times. Then, cell apoptosis was examined by FACS (left and middle) and caspase-3

597

activity assay (right). (D) H22 cells were incubated with indicated concentrations of isolie.

598

Cell apoptosis was examined by FACS (left and middle) and caspase-3 activity assay (right)

599

48 h later. * p < 0.05 and ** p < 0.01 versus HCC cells without isolie treatment.

600

Figure 2. Isolie inhibited NF-κB activity in HCC cells. (A) Plasmids encoding Renilla

601

luciferase and NF-κB-dependent luciferase reporter were cotransfected into HepG2 and

602

Huh-7 cells. After 24 h, these cells were treated with indicated concentrations of isolie, using

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Journal of Agricultural and Food Chemistry

603

vehicle as the negative control. Cells were subjected to luciferase activity assay 24 h later. (B,

604

C and D) HCC cells were treated with different concentrations of isolie. After 24 h, mRNA

605

and protein levels of NF-κB target genes were determined by real-time PCR (B) and

606

immunoblotting (C, left). Density values of immunoreactive bands of Bcl-2, Bcl-xL and

607

MMP9 were normalized to those of β-actin (C, middle and right). Association between p65

608

protein and promoter regions of indicated genes was detected by ChIP (D). (E) HepG2 and

609

Huh-7 cells were treated with indicated concentrations of isolie for 24 h, and then subjected to

610

JC-1 staining assays. (F, G and H) H22 cells were treated with indicated concentrations of

611

isolie for 24 h. Then, mRNA and protein levels of Bcl-2, Bcl-xL and MMP9 were determined

612

by real-time PCR (F) and immunoblotting (G). Association between p65 and promoter

613

regions of Bcl-2 and Bcl-xL were quantified by ChIP (H). * p < 0.05 and ** p < 0.01 versus

614

HCC cells without isolie treatment.

615

Figure 3. Isolie decreased constitutive phosphorylation of p65 protein at Ser536. (A) Effects

616

of 24-hour isolie treatment on protein levels of phosphorylated p65 (Ser536), p65 and IκBα in

617

HCC cells were detected by immunoblotting (left). Density values of immunoreactive bands

618

of Ser536-phosphorylated p65 were normalized to those of total p65 (right) (B) Myc-tagged

619

p65-S536D was transfected into indicated HCC cells. After 24 h, exogenous p65-S536D

620

proteins were determined by immunoblotting using the primary antibody against myc tag. (C)

621

Cells transfected with indicated plasmids were incubated with or without 10 µg/mL isolie, and

622

subjected to JC-1 staining assays after 24 h. (D and E) Empty or p65-S536D encoding

623

plasmids were transfected into HepG2 and Huh-7 cells. After 24 h, HCC cells were incubated

624

with or without 10 µg/mL isolie. Cell apoptosis was examined 48 h later by FACS (D) and

625

caspase-3 activity assay (E). * p < 0.05 and ** p < 0.01 versus the indicated control.

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626

Figure 4. Isolie suppressed the growth of Huh-7 xenografts in nude mice. (A) Vehicle or

627

indicated dosages of isolie were intraperitoneally injected into tumor-bearing nude mice for 3

628

weeks, and tumor growth was monitored every 3 days. (B) At the end of the study, tumor

629

lysates were prepared and subjected to caspase-3 activity assay. (C) Serum and livers were

630

collected from tumor-bearing mice. Serum activities of ALT and AST were detected, and liver

631

indexes were calculated. Values were normalized to those from the vehicle control group. (D

632

and E) At the end of isolie treatment, transcription levels of indicated genes were detected by

633

real-time PCR (D). Levels of indicated proteins were detected by immunoblotting (E, left).

634

Densitometric values of phosphorylated p65 at Ser536 were normalized to those of total p65

635

(E, middle). Densitometric values of Bcl-2, Bcl-xL and MMP9 were normalized to those of

636

β-actin (E, right). ** p < 0.01 versus tumors dissected from mice treated with saline.

637

Figure 5. Effects of isolie on transplanted H22 HCC cells in Kunming mice. (A and B)

638

Kunming mice bearing H22 tumors were treated with indicated dosages of isolie by i. p.

639

injection (left) or gavage (right) for 10 d, and tumor growth was monitored every day (A). At

640

the end of isolie treatment, tumor lysates were prepared and subjected to caspase-3 activity

641

assay (B). (C and D) Tumor-bearing mice were treated with indicated dosages of isolie by

642

gavage for 10 d. At the end of the study, mRNA levels of Bcl-2, Bcl-xL and MMP9 were

643

detected by reverse transcription real-time PCR (C). Indicated proteins were examined by

644

immunoblotting (D). Densitometric values of phosphorylated p65 at Ser536 were normalized

645

to those of total p65 (D, middle). Densitometric values of Bcl-2, Bcl-xL and MMP9 were

646

normalized to those of β-actin (D, right). ** p < 0.01 versus tumors dissected from mice

647

treated with saline.

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Tables Table 1 Cytotoxic effects of liensinine, isolie and neferine on HCC cells and untransformed hepatocytes IC50 (µg/mL) a Compound PMH b

HL-7702

Huh-7

HepG2

Hep3B

Bel-7402

liensinine

53.7

49.3

9.7

11.7

14.1

15.5

isolie

72.9

70.1

4.5

4.2

6.0

5.7

neferine

23.2

20.8

6.2

8.3

10.1

9.8

a

IC50, the concentration of a compound at which cell viability was reduced by 50%

b

PMH, primary mouse hepatocytes

Table 2 Effects of i. p. injection of isolie on WBC, RBC, HGB, and PLT in Kunming mice Dosage

Concentrations of blood cells (L -1)

Group (mg/kg)

WBC (109)

RBC (1012)

HGB (g)

PLT (109)

Non-tumor

-

6.62 ± 0.47

5.57 ± 0.73

109 ± 11

666 ± 63

vehicle

-

6.35 ± 0.55

6.48 ± 0.66

121 ± 12

680 ± 70

isolie

3

7.07 ± 0.58

5.91 ± 0.73

115 ± 12

662 ± 69

isolie

10

6.83 ± 0.62

6.61 ± 0.69

117 ± 13

692 ± 66

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Table 3 Effects of i. p. injection of isolie on serum parameters of liver and kidney functions in Kunming mice Dosage

Serum parameters of hepatic and renal functions (U/L)

Group (mg/kg)

BUN

UA

CRE

ALT

AST

non-tumor

-

6.5 ± 0.49

140 ± 8.8

45.8 ± 5.4

121 ± 13

589 ± 48

vehicle

-

6.7 ± 0.53

139 ± 9.4

44.7 ± 4.7

133 ± 17

611 ± 52

isolie

3

6.6 ± 0.55

135 ± 8.9

46.4 ± 5.1

118 ± 16

618 ± 46

isolie

10

6.6 ± 0.47

136 ± 9.5

47.1 ± 4.9

126 ± 15

577 ± 49

Table 4 Effects of i. p. injection of isolie on organ indexes of Kunming mice Organ indexes (mg/g)

Dosage Group (mg/kg)

Thymus

Spleen

Liver

non-tumor

-

2.72 ± 0.12

8.60 ± 0.40

48.2 ± 5.2

vehicle

-

2.70 ± 0.09

8.95 ± 0.35

47.9 ± 4.2

isolie

3

2.82 ± 0.11

8.90 ± 0.37

48.6 ± 4.8

isolie

10

2.84 ± 0.11

8.97 ± 0.42

48.1 ± 5.1

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