Specimen collection
The specimens used in this study were obtained with written informed consent from a 68-year-old Chinese male patient who underwent surgical resection at the First Affiliated Hospital of Xiamen University (Xiamen, P.R. China) for gastric cancer in the fundal junction of the stomach. The size of the original tumour was 3.5×4.3 cm. No distant metastasis was detected at the time of surgical resection. The tumour was histopathologically classified as a poorly differentiated gastric adenocarcinoma.
BALB/C nude mice
BALB/C nude mice were purchased from Shanghai Slac Laboratory Animals Co., Ltd., and kept in the animal experiment centre of Xiamen University.
The animal experiments were carried out according to the requirements of the Xiamen University Experimental Animal Care Commission. If an animal became severely ill during the experiment, the animal was humanely killed by CO2 inhalation combined with cervical dislocation to confirm death and prevent animal suffering. Pathogen-free BALB/C nude mice aged 4 weeks old were housed in filter-top cages, and sterile water and food were given ad libitum. The mice weighed 15–18 g at the beginning of the experiment. All manipulations were conducted aseptically inside a laminar flow hood.
The following methods were similar or identical to those employed in previous studies [12, 20].
Establishment of the XGC-1 cell line
Tumour specimens were rinsed twice with sterile phosphate-buffered saline (PBS) containing antibiotics. Then, the samples were enzymatically disaggregated after incubation with collagenase type II and neutral protease solution at 37°C in a humidified atmosphere containing 5% CO2. After the samples were incubated for approximately 0.5 h, 5 ml of foetal calf serum (FBS) (Gibco, Grand Island, NY, USA) was added to terminate the digestion. Then, the digested tumour fragments and fluid were filtered through a 200 mesh sieve, and the filtrate was centrifuged at 1,000 rpm for 5 min. The supernatant was removed, and the remaining cells were resuspended in Dulbecco’s modified Eagle’s medium (DMEM) and Ham’s F-12 medium (1:1) (Gibco) supplemented with penicillin (100 U/ml), streptomycin (100 μg/ml), heat-inactivated 2% FBS, hEGF (0.1 ng/ml), bFGF (0.1 ng/ml), hydrocortisone (25 μg/ml), fluconazole (40 μg/ml) (Gibco), and M-plasmocin (25 μg/ml) (Invitrogen); seeded in 12-well culture plates; and cultivated at 37°C in a humidified atmosphere of 5% CO2 in air. The growth medium was replaced every 2–3 days, and the plate was regularly assessed for epithelial cell and fibroblast outgrowth. When the cells completely covered the bottom of the plate, they were passaged. Currently, the cell line has been cultured for >90 passages. The cells were tested for mycoplasma contamination, and the result was negative. The cell line was designated XGC-1 (Xiamen gastric cancer-1).
Short tandem repeat analysis for authentication
To authenticate the established cell line, we analyzed short tandem repeats (STRs) of the XGC-1 cells and the original tumor tissue. The data were analyzed, and the STR profiles were compared with those recorded in public cell banks, such as the ATCC, CCTCC, and JRCB, for reference matching.
Morphology of the XGC-1 cell line
XGC-1 cells were seeded in 6-well plates and incubated at 37°C in a humidified atmosphere containing 5% CO2 for 2 weeks. Every day, the cells were placed under an inverted microscope to observe their general morphology. Cell ultrastructure was observed under a transmission electron microscope.
Cell growth properties
Cells were plated in 96-well plates at 1,000 cells/well and cultured in DMEM/F12 containing 10% FBS for various durations. Cell numbers were measured by MTT assays, which were performed according to the manufacturer’s protocol. The doubling times were determined from the growth curve.
Colony-forming efficiency
Colony formation of different cell clones in soft agar was used to assess their growth capabilities. A single-cell suspension (1×104 cells/ml) was prepared. Agar (0.6%) was mixed with DMEM/F12 and added to 6-well plates as the lower layer. Then, 0.3% agar was mixed with the cell suspension, and the mixture was added to the same 6-well plate as the upper layer. Every well contained 1,000 cells. The plates were incubated at 37°C in a humidified incubator containing 5% CO2. Fourteen days later, cell colonies were counted with a microscope, and the colony formation rates were calculated using the following formula: colony formation rate (%)=(number of colonies/number of cells inoculated)×100%.
Chromosome analysis
Cells were karyotyped using a standard air-drying method after treatment with a final concentration of 0.05 mg/ml colcemid for 2 h when the cells were in the exponential growth phase. The cells were analysed using trypsin G banding. A total of 200 metaphase spreads were examined to determine the modal number. Karyotyping was performed according to the International System for Human Cytogenetic Nomenclature (2005). Chromosome analysis was carried out on the cell line at passage 40.
Tumourigenicity in BALB/C nude mice
The study protocol for mice was approved by the Xiamen University Experimental Animal Care Commission. Briefly, cells at passage 45 were prepared to determine their tumourigenicity in BALB/C nude mice. Cultured cells (1×106 cells/ml) were harvested, washed, resuspended in 0.1 ml of complete DMEM/F12, and injected subcutaneously into the right flanks of three 4-week-old female BALB/C nude mice. The animals were examined every week for the development of tumours. Tumour-bearing mice were sacrificed. Tumour tissue was excised, fixed in 10% formalin, and processed for routine histopathological examination.
Immunohistochemistry
Cell monolayers at passage 35 were subcultured and grown on sterile microscope slides. After confluent growth was observed, the slides were washed with PBS, fixed in 4% paraformaldehyde for 15 min, air-dried and treated with 0.5% Triton X-100 for 20 min. PBS was used as the negative control, and the slides were then overlaid with the following antibodies: a mouse monoclonal antibody directed against human cytokeratin, a rabbit monoclonal antibody directed against Ki-67, and a mouse monoclonal antibody directed against human vimentin, mouse monoclonal antibody directed against human carcinoembryonic antigen, mouse monoclonal antibody directed against human cancer antigen 19-9. The slides were incubated with the antibodies for 60 min and thoroughly washed with PBS. Biotinylated rabbit anti-mouse IgG was subsequently applied for 15–20 min, and the samples were washed. Then, a solution of DAB was added to the slides, and the slides were incubated for 1–5 min at room temperature. Finally, the slides were rinsed with distilled water, counterstained with haematoxylin and eosin (H&E) and examined by light microscopy.
Statistical analysis
The statistical significance of differences between experimental groups and controls was determined by Student's t-test. Values of P≤0.05 were considered statistically significant.