Cell culture and antibodies. The chemicals for buffer preparation, including SDS, Tris base, DMSO, and NaCl, were obtained from Sigma-Aldrich (St. Louis, MO). Cell culture medium and supplements, such as RPMI-1640/DMEM medium and Fetal Bovine Serum (FBS) were purchased from Invitrogen (Grand Island, NY). Human oral squamous cell carcinoma (OSCC) cells, including SCC9 SCC15, SCC25, and CAL27, were purchased from American Type Culture Collection (ATCC, Manassas, VA). The immortalized epithelial and fibroblast cells, including HBE, NL20, MRC5, Het-1A, and FHC were purchased from ATCC. The immortalized non-tumorous cells LO2 was obtained from the Cell Bank of the Chinese Academy of Sciences (Shanghai, China). The immortalized oral epithelial cell hTERT-OME was purchased from Applied Biological Materials (ABM) Inc. (Richmond, BC, Canada). The cells were maintained in a 37 °C humidified incubator with 5% CO2 following the standard protocols, and mycoplasma test was performed every two months. Antibodies against Aurora B (#3094, 1:1000), cleaved-caspase 3 (#9661, 1:1000), β-actin (#3700, 1:10000), Histone H3 (#4499, 1:2000), p-Histone H3 Ser10 (#9701, 1:1000), and cleaved-PARP (#5625, 1:1000) were purchased from Cell Signaling Technology, Inc. (Beverly, MA). Antibodies against Ki67 (ab16667, 1:300) and p-Aurora B Thr232 (ab115793, 1:1000) were obtained from Abcam (Cambridge, UK). The ECL substrate (#32132, Thermo Fisher Scientific) was used for protein visualization.
MTS assay. The MTS assay was performed as described previously (15). Briefly, the cells were seeded (3 × 103/well/100 mL) into a 96-well plate and treated with Tanshinone IIA (Tan IIA) for various time points. The MTS reagent (Promega, Madison, WI) was added into the cell culture medium and incubated for 1 h according to the standard procedures.
Soft agar assay. The soft agar assay was performed as described previously (16). Briefly, OSCC Cells were counted and suspended at a concentration of 8 × 103 per well and seeded into a 6-well plate with 0.3% Basal Medium Eagle agar containing 10% FBS and Tan IIA. The cells were maintained at a 37 °C humidified incubator with 5% CO2 for 2 weeks. The colony was counted with a light microscope.
Clinical tissue sample collections. A total of 20 cases of OSCC tissues and matched adjacent non-tumor tissues were collected from 20 patients with written informed consent by the Department of pathology, Hunan Cancer Hospital of Central South University, Changsha, Hunan, China. All the patients received no treatment before surgery. The samples were frozen in liquid nitrogen, and protein was prepared for western blotting analysis.
Construction of Aurora B knockdown stable cell line. Construction of Aurora B knockdown stable cell line was performed as described previously (17). The guaranteed sh-Aurora B lentivirus plasmids (Cat#1:V3SH11240-230132624, Cat#1:V3SH11240-225176452) were purchased from GE Horizon (Lafayette, CO). For the virus package, the sh-Aurora B lentivirus plasmid, psPAX2, and pMD2.G were co-transfected into 293T cells. The virus-containing supernatant was collected at 48 h after transfection. After centrifuge, the supernatant was filtered through a 0.45 µm filter and infected with OSCC cells with 8 µg/mL polybrene overnight. The fresh medium containing 1 µg/mL puromycin was added into the virus-infected OSCC cells and maintained for 1 week for stable cell selection.
Molecular modeling. The Natural Product Library (Cat. No. L1400-01/02) is a product of Selleck Chemicals (Houston, TX), and the 74 compounds of interest (Table S1) used for screening were selected from this Natural Product Library. To find inhibitors against Aurora B, the x-ray crystal structure of Aurora B (PDB ID: 4C2V) was downloaded from Protein Data Bank1 (PDB). The protein structure was prepared using the Protein Preparation Wizard in Schrödinger Suite 2013, including filling in missing side chains, adding hydrogens, and minimizing heavy atoms with default parameters, before the corresponding protein grid files were generated for docking. Then the structure file of nature product was pretreated in the LigPrep module of Schrödinger Suite 2013, and docking was performed based on the standard precision mode of Glide with default settings. Prime was employed to refine the binding pose further and calculate binding free energy by the MM-GBSA method in Schrödinger Suite 2013. Residues with distances from the ligand less than 12.0 Å were set as flexible. Other settings were kept in default. The docking pose for the receptor-ligand complex was then submitted to binding mode analysis and figure generation using PyMOL2. Herein, we could obtain the top-scored representative list. Barasertib was used as a positive control. To further confirm which top-scored representative exhibited significant anti-tumor effect, the CAL27 cells were seeded in a 96-well plate and treated with a single dose of 2 µM natural compounds or DMSO (control) for 24 h. Cell viability was determined by MTS assay.
Immunoblotting (IB). IB analysis was performed as described previously (18). Briefly, cell lysate was prepared with RIPA buffer (#89900, Thermo Fisher Scientific) supplied with protease inhibitors and concentrated using the BCA protein assay kit (#23225, Thermo Fisher Scientific). Cell lysate (20 µg) was boiled with loading buffer at 95 °C for 5 min and subjected to SDS-PAGE electrophoresis. The protein was transferred onto polyvinylidene difluoride membranes and blocked with 5% non-fat milk at room temperature for 1 h, followed by subsequent incubation with primary antibody (overnight, 4 °C) and second antibody (1 h, room temperature). The target protein was visualized with the ECL chemiluminescence reagents (#32132, Thermo Fisher Scientific).
Immunofluorescence (IF). IF analysis was performed as described previously (19). OSCC cells seeded in chamber slides, treated with Tan IIA, and fixed in 4% paraformaldehyde and permeabilized in 0.5% Triton X-100 for 30 minutes. The cells were blocked with 50% goat serum albumin in PBS and incubated with the primary antibody in a humidified chamber overnight at 4 °C, followed by incubation with the fluorescence-labeled second antibody at room temperature for 40 min. DAPI was used for counterstaining. The stained cells were viewed and captured with the confocal fluorescence microscope system (Nikon C1si; NIKON Instruments Co.).
Ex vivo pull-down and in vitro ATP competitive binding assays. The ex vivo pull-down and in vitro ATP competitive binding assays were performed as described previously (20). Briefly, Tan IIA was conjugated with Sepharose 4B beads (GE Healthcare Biosciences) following the standard procedure. The control Sepharose 4B beads or Tan IIA conjugated Tan IIA-Sepharose 4B was incubated with CAL27 cell lysate (400 µg) overnight at 4 °C. The beads were raised with binding buffer and subjected to IB analysis. For in vitro ATP competitive binding assay, the active Aurora B kinase (Millipore, Burlington, MA) was incubated with various concentrations of ATP overnight at 4 °C, followed by the Sepharose 4B beads or Tan IIA–conjugated Sepharose 4B was added to the reaction and incubated for another 4 h at 4 °C. The beads were raised with wash buffer and subjected to IB analysis.
In vitro Aurora B kinase assay. The in vitro Aurora B kinase assay was performed as described previously (21). Briefly, 100 ng of active Aurora B kinase (Millipore) and 1 µg of the substrate (Histone H3 or Survivin, Millipore) were incubated with various doses of Tan IIA or barasertib (positive control) in a 20 µL reaction containing 100 µM ATP and 1 × kinase buffer (Cell Signaling Technology). The in vitro kinase assay was conducted at 30 °C for 30 min and stopped by boiling with the loading buffer at 95 °C for 5 min. Histone H3 phosphorylation was examined by IB analysis.
Flow cytometry. The flow cytometry assay for cell cycle and apoptosis analysis was performed as described previously (22). Briefly, the OSCC cells were treated with Tan IIA for 24 h and fixed with 70% ice-cold ethanol at 4 °C for 24 h. The cells were washed with PBS and stained with ribonuclease A contained Propidium Iodide (50 µg/ml). The cell cycle was analyzed by flow cytometry. For apoptotic cell analysis, the OSCC cells treated with Tan IIA for 72 h and suspended with 300 µl binding buffer and incubated with 5 µl Annexin V-FITC and Propidium Iodide contained staining buffer at room temperature for 15 min at dark. The apoptotic cell was analyzed by FACS.
Xenograft mouse model. The animal experiments were approved by the Institutional Animal Care and Use Committee of Central South University (Changsha, China). The OSCC xenograft models were constructed by s.c.injection of CAL27 (2 × 106) or SCC25 (3 × 106) cells into the right flank of 6-week-old athymic nude mice (n = 5). Tumor volume and mouse body weight were recorded every two days. The tumor-bearing mice were initiated with Tan IIA treatment when the tumor volume reached around 100 mm3. The control group was administrated vehicle control, whereas the compound-treated group was administrated Tanshinone IIA (low dose, 10 mg/kg; high dose, 30 mg/kg) every two days by i.p injection. For irradiation treatment, the tumor bearing mice were randomly divided into four groups (n = 6) when the tumor volume reached around 100 mm3: 1,vehicle control (0.5% dimethyl sulfoxide, 100 µL/every two days, i.p.); 2, local ionizing radiation (2 Gy/ twice per week, irradiated with X-rays using X-RAD 320, Precision X-ray, Inc.,); 3, Tan IIA (30 mg/kg/every two days, i.p.); 4, Tan IIA (30 mg/kg/every two days, i.p.) + local ionizing radiation (2 Gy/ twice per week). Tumor volume was determined according to the following formula: length × width × width/2. At the endpoint, tumor mass was fixed and subjected to IHC staining. IR
Immunohistochemistry. Immunohistochemistry (IHC) was performed as described previously (23). Briefly, the xenograft tumor tissue was fixed with formalin and embedded in paraffin. For IHC staining, the tissue was deparaffinized by baking at a 60 °C incubator for 1 h and subsequently immersing into xylene to complete removal of paraffin. Tumor tissue was rehydrated by a graded series of ethanol, and Antigen retrieval was performed by immersing into the sodium citrate buffer (10 mM, pH 6.0) and boiled for 10 min. The 3% H2O2 in methanol was used for deactivating the endogenous horseradish peroxidase. Tumor tissue was washed with PBS, blocked with 50% goat serum albumin, and incubated with the primary antibody overnight at 4 °C in a humidified chamber. After incubation with the secondary antibody for 45 min and washed with PBS, the target protein was visualized with the DAB substrate and counterstained with hematoxylin.
Blood analysis. Mouse blood was collected by cardiac puncture into the EDTA-coated tubes. The red blood cells (RBC), white blood cells (WBC), hemoglobin (Hb), alanine aminotransferase (ALT), aspartate aminotransferase (AST), and blood urea nitrogen (BUN) were analyzed at the Laboratory of the Third Xiangya Hospital of Central South University (Changsha, China).
Statistical Analysis. The SPSS 16.0 (SPSS, Inc, Chicago, IL) software was used for statistical analysis. All quantitative data were expressed as means ± SD as indicated. The significant differences between examined groups were determined by Student t-test or one-way ANOVA, and a probability value of less than 0.05 (p < 0.05) was used as the criterion for statistical significance.