Cordycepin or 3'-Deoxyadenosine (Purity >98.0%) from /of Cordycepin militaris purchased from TCI chemicals. RPMI-1640 and FBS were purchased from Gibco by life technologies™. MTT (3-(4, 5-dimethylthiazol-2-yl)-2,5diphenyltetrazolium bromide) and DMSO were purchased from Himedia India. Thermo Fisher Scientific was the source of Acridine Orange (AO), Ethidium bromide (EB),4′, 6-diamidino-2-phenylindole Dihydrochloride(DAPI), and Rhodamine-123. DCFDA/H2DCFDA-Cellular ROS Assay Kit was obtained from Abcam US, while FITC tagged Annexin V and PI, were procured from Sigma Aldrich. All other chemicals and reagents used in experiments were of the standard purity grade.
The population of BALB/c (H2d) strain was allowed inbreeding under standard laboratory hygienic conditions. Dalton's lymphoma cells (1.0 ×106) were injected intraperitoneally(i.p.) in either male or female for the development and progression of Dalton’s Lymphoma(DL) in mice peritoneum. DL was continuously maintained by in vitro passaging in culture and serial transplantation in mice. All experiments were carried out as per instructions approved by the institutional Animal Ethics Committee of the Department of Zoology, Banaras Hindu University, India.
2.1 Cell Culture-
BALB/c mice containing Dalton’s lymphoma were used as a model system for growing and harvesting DL cells. Tumor cells were isolated from peritoneum DL-bearing mice via intraperitoneal injection, washed with PBS, cultured in RPMI-1640 complete medium added with 10% FBS and placed inside 5 % CO2 incubator.
2.2 MTT Assay for Cellular Toxicity-
MTT assay was used to determine the cytotoxicity of cordycepin against DL Cells [15]. DL cells were seeded in RPMI 1640 complete medium (10% FBS and antibiotics) in a culture plate and treated with various concentrations (25,50,100,150,200,250,300,600µg/ml) of cordycepin along with a untreated group. Culture plates were placed in 5% CO2 incubator( shel lab model-2406-ZZMFG) for 24 h and 48 h Thereafter MTT solution (5mg/ml) was mixed into each well and it was again incubated for additional four hrs at 37˚C to enable intracellular reduction of the soluble yellow MTT to insoluble purple formazan crystal. In this sequence, Culture plates were subjected to centrifugation to remove media and cell debris. Absorbance was taken at 595 nm with the help of a microplate plate (Bio-Rad) reader after adding 100µL DMSO into each well. The cell viability percentage of the treated cells was calculated concerning untreated cells by the following equation-
% Cell Viability = [Absorbance in the treated group]/ [Absorbance in the untreated group] × 100.
2.3 Wright-Giemsa, DAPI staining for Cellular and Nuclear morphology
The morphological attributes of apoptotic cells include chromatin condensation, abnormal cell shape as well as disrupted nuclear symmetry [16]. These characteristics were taken as criteria to evaluate apoptosis after cordycepin treatment. DL cells were treated with cordycepin (0,125,250,500𝜇g/ml) after 24 h of culture when cell confluency was maintained. After 24 hrs treatment cells were washed with PBS fixed and stained with Wright-Giemsa (5mg/ml) for 5 min at room temperature. Furthermore, DAPI staining was done to investigate alteration in nuclear structure. Treated and control cells were washed with PBS and fixed in 4%paraformaldehyde for 15 min at room temperature. DAPI Staining of cells was done after permeabilization with methanol.
The Cells of both groups (DAPI and Wright- Giemsa stained) were observed under the fluorescence microscope (evos XL digital inverted micrpscope) at magnification 20X.
2.4 Evaluation of apoptosis and necrosis
Criteria of apoptosis include initiation of apoptotic body formation, condensation of chromatin, cell shrinkage [17]. We used AO/EB dual staining to evaluate above stated apoptotic attributes. DL cells were seed in a 6- well culture plate and treated with cordycepin for 24hrs. Further Cells were washed with PBS and resuspended in staining solution (5mg/ml of AO and 3mg/ml of EB) for 15min. The stained cell was visualized under the fluorescent microscope (Nikon ECLIPSE 90i) using band FITC and TRITC.
Moreover, we used AnnexinV/ Propidium iodide staining method to accurately enumerate apoptotic or necrotic mode of cell death. In nutshell, the DL cells (1×106 cells per well) were exposed to different concentrations of cordycepin for 24 h. The cells were washed with PBS and resuspended in 250𝜇L of an annexin-binding buffer followed by adding of FITC-tagged Annexin-V and PI into it and kept 15 in dark. After incubation with FITC tagged annexin and PI, the cells were subjected to flow cytometry analysis (BD FACS Calibur flow cytometer). Analysis of apoptosis and necrosis of at least 10,000 cells in each apoptotic phase was performed by FlowJo software. The apoptotic and necrotic death was further confirmed by microscopic observation of the control, and Cordycepin treated DL cell.
2.5 Cell cycle analysis- Flow cytometry was employed for quantification of cellular DNA content and the analysis of the cell cycle [18]. DL cells were seeded (1 × 106 cells per well) in 6 well culture plates and treated with cordycepin for 24 hrs. Successively treated and control cells were washed with PBS and fixed with chilled methanol (70%) before treatment with RNase A. The DNA content of cells was stained with Propidium Iodide. Finally, the cells were subjected to flow cytometry analysis .The cell quest software (Becton Dickinson) was used to interpret flow cytometry data.
2.6 Estimation of Reactive Oxygen Species-
ROS estimation was done by using the standard protocol of H2DCFDA staining [19]. Briefly the control and treated DL cells (1 × 106 cells per well) were stained with 10 μM H2DCFDA for 1 h in the dark. FL-1H channel was set in Flow cytometry (BD FACSCalibur) to capture green fluorescence per cell emitted by 2’7 dichlorofluorescein, a product formed after oxidation H2DCFDA by ROS. The control and treated DL cells stained with the dye (H2DCFDA) were also visualized under a fluorescence microscope (EVOS) at magnification 20X and photographed.
2.7 Estimation of Mitochondrial Membrane potential (MMP) – Mitochondrial mediated apoptosis is recognised by the kinetics of mitochondrial membrane potential. We used the standard protocol of Flow cytometry for analysis of MMP in Rhodamine-123 stained DL cells [20]. Treated and untreated cells were washed with PBS followed by incubation with Rh-123 (5 μg/ml) for 10 min in the dark at room temperature. Further, the DL cells were subjected to flow cytometry(BD FACSCalibur) analysis using the FL2-H channel to collect red fluorescence emitted by Rh-123. MMP were further confirmed visualized of Rh-123 stained DL cells under a fluorescence microscope at magnification 20X and photographed.
2.8 Statistical Analysis-All results are representative of mean ± SD from experiments in triplicate. GraphPad Prism and Excel2013 were used for statistical analysis. The significance of differences between two groups and analysis of variance (two-way ANOVA) was done by an unpaired t-Test.