Reagents
Sorafenib (Nexavar, Bayer, 43-9006) was purchased from the American LC LAB Company and was dissolved in 12.5% ethanol, 12.5% Cremophor, and 75% water (1:1:6) (20). The dissolved Sorafenib was used at the concentration of 30 mg/kg/day in the animal model, which is in accordance with the range of respective dosage used for human (400 mg, twice daily) (26). Antibodies against CD56 (PE, EXBIO, Czech Republic) and CD3 (FITC, Beckman Coulter, US) were used for flow cytometric analysis. Human recombinant interleukin-2 (specific activity of greater than or equal to 5.7 x 10e6 Units/mg) was purchased from eBioscience (US).
Cell Lines and Animals
Human HCC cell line (HepG2) was purchased from the Iranian Biological Resource Center and cultured in high glucose DMEM media (Gibco D5796, USA), supplemented with 10% fetal bovine serum (Gibco,USA) and penicillin and streptomycin (100 μg/ml). The cells were then incubated in a 37°C, 95% humidified atmosphere containing 5% CO2. Cells at second or third passages were used for xenograft injection to immunodeficient mice and creation of a suitable HepG2 mouse model. Male athymic C57BL/6 nu/nu mice (mean weight: 20 g; age: 4 -6 weeks) were purchased from the Pasteur Institute of Iran. (27). All experimental procedures were performed according to the National Institutes of Health (NIH) guide for the care and use of Laboratory animals and were approved by the Institutional Ethical Committee of Tehran University (IECTU) of Medical Sciences (IR.TUMS.VCR.REC.1397.181) (28).
Isolation, expansion and activation of NK Cells
Primary NK cell was collected from buffy coats of healthy donors under the approval of the IECTU of Medical Sciences and then expanded and activated under specific condition as detailed in our previous article (29). Briefly, Peripheral Blood Mononuclear Cells (PBMCs) were isolated by density gradient centrifugation on Ficoll-Hypaque (GE Healthcare, GE17-5442-02Sigma, and Sweden). NK cell was isolated from PB using the NK Cell Isolation Kit and MACS columns (Miltenyi Biotec, Germany) by negative selection kits, according to the manufacturer’s procedures. The purified NK cells were cultured in SCGM medium (CellGenix, Freiburg, Germany), containing anti-CD3 Antibody (OKT3) (Cytomatin Gene, Iran) (10 ng/ml), penicillin (100 IU/mL), 10% FBS, and streptomycin (100 mg/mL) with irradiated autologous PBMCs as feeder layer. The activation process was performed by human recombinant interleukin-2 (hrIL-2) (eBioscience™, US) (1,000 IU/mL) and hrIL-15 (eBioscience™, US) (10 ng/ml) (30). Purity of the isolated and expanded human CD3-, CD56+ NK cells were determined using Attune NxT acoustic focusing flow cytometer. On average, purity of the isolated and expanded NK cells were more than 95% in all experiments.
HepG2 xenograft model and treatment
To implant heterotopic HepG2 tumors, as described in our previous studies (27, 31). Briefly, 1 × 107 human HepG2 cells suspended in 200 μl of a 1:1 ratio of serum-free medium and Matrigel (Corning, product number: 354230, USA) were injected subcutaneously into the two flanks of each animal. Tumor formation was monitored twice a week until day 40 p.i of HepG2 cells. Tumor volume was calculated with the means of Vernier calipers using a standard formula (length × width2 × 0.5) followed by drawing the growth curves (32). When the average of tumor volumes approximately reached to 200 mm3 (12th day), which is equivalent to advanced stage (27), the mice were randomly assigned to four experimental groups (control, Sor, NK cells and Sor plus NK cells) with three mice in each group. Sor (30 mg kg−1, daily) was intraperitoneally (IP) injected (33) while human IL-2 activated NK cells (5×106 cells/100µl/mouse) were injected IP (30) into the tumor margins twice with one-week interval. An equal volume of carrier solution was injected in the CG. Four weeks after the onset of treatment, the mice were sacrificed followed by collecting their blood samples and tumor tissues (30, 34). Some of tumor tissues were fast frozen in liquid nitrogen and then stored at −80 °C and the rest tissue was fixed in 10% neutral buffered formalin (NBF) followed by paraffin embedding for IHC analysis.
Analysis of biochemical factors for safety assay
To evaluate the in vivo safety of either of the NKC alone or its combination with Sor, body weight of each mouse as well as its liver and kidney functions were analyzed. The blood sample of each mouse was centrifuged at 1500g for 10 min followed by collecting the serum and measuring the levels of various biochemical factors, including alanine aminotransferase (ALT), aspartate aminotransferase (AST), urea and cratinin, using an automated biochemical analyzer (Mindray, Shenzhen, China).
Histopathology study
The mice were euthanized on day 28 post-treatment and the obtained tissues (tumor mass) were fixed in the 10% NBF (PH= 7.26), followed by being processed and embedded in paraffin. Tumor tissue were sectioned at a thickness of 5µm and were stained with heamtoxylin and eosin (H&E). The histological sections were evaluated by two expert pathologists, using light microscopy (Olympus, Japan). Histopathological examination was performed using the Edmondson-Steiner grading system (1954) for HCC. Moreover, any changes, including coagulative necrosis, inflammatory response, hemorrhage, and hyperemia, were comparatively evaluated in tumor sections of different groups.
Immunohistochemistry
Paraffin-embedded tumoral sections (4 μm) were applied for immunohistochemistry (IHC) evaluation of proliferating cell nuclear antigen (Ki67) using a monoclonal primary mouse anti-human Ki67 antibody (Biocare, CA, USA). The proliferative index was determined by counting the number of positive stained cells amongst 100 nuclei (Percentage) which were randomly counted from five high magnification microscopic fields (200× magnification) using the Image-Pro Plus®V.6 software (Media Cybernetics, Inc,Silver Spring, USA).
To assess the angiogenesis index (AI) of HCC tumor, the sections were stained using a monoclonal mouse anti-human CD34 antibody (Biocare, CA, USA). The AI was defined by counting the number of positive stained cells for CD34 in five high magnification microscopic fields (200× magnification). The results of angiogenesis were reported as the mean number of vessels ± SEM. The negative control sections were prepared by omitting the primary antibody for Ki67 and CD34.
TUNEL assay
TUNEL Assay Kit (Abcam, UK) was used to detect apoptotic DNA fragmentation. To compare the anti-tumor efficacy of each treatment via enhancing the number of apoptotic tumor cells in vivo, the tumor tissue sections were stained using TUNEL according to manufacturer’s procedure and were visualized using a fluorescence microscope . The TUNEL positive cells were counted in three microscopic fields per section and reported as the mean percentage of the total apoptotic index.
Determination of serum TNF-α and IFN-γ
The serum sample was harvested from each mouse and analyzed by ELISA kits to detect the contents of mouse interferon gamma (IFNG) (ab100689, Abcam, UK) and Mouse TNF alpha (ab208348, Abcam, UK).
Quantitative Real-Time PCR assay
The expression levels of intended inflammatory factors, including TNF-α, IFN-γ, ILs 1-6 and 10 and cytoplasmic granules (Perforin and Granzyme-B), were quantified using qRT-PCR. Total RNA was extracted from the treated xenograft HCC tumor tissues using a total RNA extraction kit (Takara, Japan) according to the manufacturer’s procedure. Isolated RNA with a 260/280 ratio of ~2 (1µg) was reverse-transcribed to cDNA by using a PrimeScript RT reagent Kit (Takara, Japan). Gene expression was determined by ABI-7000 Detection System thermal cycler (Applied Biosystems, USA) using SYBR Premix Ex Taq (Takara, Japan). The Real-Time PCP reaction mixture was prepared using 10 pM of each of the primers, 100 ng cDNA (2 µl), SYBR Green I Master Mix (2X) (BioFact, Korea) and nuclease-free H2O. The real-time PCR cycle consisted of 95°C for 5 minutes followed by 40 cycles of 95°C for 30 seconds, 60°C for 30 seconds, 72 °C for 30 seconds and a cycle of melt curve consisted of 95 °C for 15 seconds, 60 ºC for 1 minute and 95 °C for 15 seconds. Glyceraldehyde 3-phosphate dehydrogenase (GAPDH) mRNA was used as the internal comparator in parallel with the control sample. All the qRT-PCR experiments were performed in duplicates. qRT-PCR results were analyzed using the comparative Ct, 2−ΔΔCT, method.
Statistical analysis
The results are reported as the mean ± SEM. Two-way analysis of variance (Two-way ANOVA) was used to compare the mean values obtained from all experimental groups, followed by post-hoc Tukey test. The paired data were analyzed using the 2-tailed paired Student’s t test. The charts were drawn using GraphPad Prism and the statistical differences were considered to be significant at P<0.05 (p<0.05 *, p<0.01 ** and p<0.001 ***).