SPECTRAMAX APPLICATION NOTE
Cathy Olsen, Ph.D., Molecular Devices Corporation, 1311 Orleans Dr., Sunnyvale, CA 94089.
Quantitation of cell proliferation using fluorescence allows one to easily monitor the effects of drugs and other experimental treatments on cell growth. The CyQUANT Cell Proliferation Assay Kit from Molecular Probes is a sensitive, rapid and convenient way to quantitate cell growth using a fluorescence microplate reader. CyQUANT GR dye binds to cellular nucleic acids, allowing cell numbers to be calculated from a standard curve. Because DNA-to-RNA ratios can vary over the course of the cell cycle, the CyQUANT kit allows users to determine cell numbers using RNase-digested cell lysates and a nucleic acid standard curve.
This application note describes how to use the CyQUANT kit with the SpectraMax M5, M2 and Gemini microplate readers and SoftMax Pro software from Molecular Devices. Two methods are detailed. In the first, cellular proliferation is quantitated using a cell-based standard curve. In the second, cellular proliferation is quantitated using RNase-treated cell samples and a DNA standard curve.
Note: Lysis Buffer and CyQUANT GR should be used within a few hours of being diluted. Be sure to protect the CyQUANT GR solution from light.
Table 1. Cell Concentration (Number Of Cells) Prepared In A Microplate Well 1 2 3 4 5 6 7 8 9 10 11 12 A 50,000 25,000 12,500 6,250 3,125 1,562 391 195 98 49 24 no cells B 50,000 25,000 12,500 6,250 3,125 1,562 391 195 98 49 24 no cells C 50,000 25,000 12,500 6,250 3,125 1,562 391 195 98 49 24 no cells D 50,000 25,000 12,500 6,250 3,125 1,562 391 195 98 49 24 no cells
Step 2. Incubate the microplate at 37C for the desired time after which proliferation will be assayed. The incubation time will depend on the type of proliferation assay being performed, the cell type being used and the users particular experimental design.
Step 3. Gently aspirate culture medium from wells. The wells may be washed gently with phosphate buffered saline (PBS), but this is not essential and is not recommended for very dense cultures where cells may dislodge.
Step 4. Freeze the cells in the microplate at -70C until ready to assay (at least one hour, up to four weeks). This freezing step ensures complete lysis of cell samples.
Step 1. Detach adherent cells from the culture plate using trypsin or EDTA solution, and prepare a concentrated cell suspension in culture medium. Cells should be at a density of about 105 to 106 cells/mL.
Step 2. Centrifuge 1.0 mL of the cell suspension for 5 minutes at about 200 x g (approximately 1500 rpm in a microcentrifuge). Discard the supernatant and freeze the cell pellet at -70C until ready to assay. This freezing step ensures complete lysis of the cells.
Step 2. Prepare 1X working solution of CyQUANT GR dye/cell-lysis buffer by diluting the concentrated CyQUANT GR stock solution 1:400 with 1X cell-lysis buffer. This solution should be prepared in a plastic container rather than glass (see CyQUANT product insert).
Step 2. Generate a dilution series in the wells of a microplate, starting at 50,000 cells/well and making serial 1:2 dilutions down to 24 cells/well. se CyQUANT GR dye/cell-lysis buffer to make dilutions such that the desired cell number is in a volume of 200 l. Prepare four replicates of each standard, and include a set of replicates without cells as a control (you can omit one of the standards, e.g., 781 cells/well, to make room on the microplate).
Step 3. Incubate the microplate at room temperature for 2-5 minutes, protected from light.
Step 2. Click the Setup button in the Plate section to launch the Instrument Settings dialogue box as shown in Table 2. After setting all of the parameters, click OK to proceed.
Table 2. Instrument Settings Dialog
Step 3. Create a template of the assay indicating the location of standards (cell numbers for each dilution), blanks (no cell lysate) and unknowns in the microplate. Click the Template button in the Plate section to set up the template. An example of a template with standards and unknowns is shown in Figure 1. Please note that this is the view of the template setup window that appears when the Ctrl and Shift keys are held down simultaneously to display the values assigned to each well. The assigned names of unknowns (Un01-Un12) do not appear in this view.
Step 4. Place the microplate in the microplate reader. Use the appropriate adapter to correctly position the microplate for top reading.
Step 5. Click the softwares Read button. The instrument will read the plate, then the relative fluorescence units (RFUs) will be displayed in the Plate section of SoftMax Pro.
Step 2. In the Graph section, plot the Mean RFU Value versus Concentration (number of cells/well) from the Standards group. Configuration of the Graph Options and Edit dialog boxes is shown in Figure 2.
Step 3. Choose the appropriate curve fit from the drop-down Curve Fit menu in the Graph sections tool bar. When plotting the standard curve for this application note, we used a log-log curve fit. (See Figure 3.) The quadratic curve fit may also be suitable.
Step 4. Determine the number of cells per well for experimental cell samples (unknowns). The SoftMax Pro CyQUANT assay protocol calculates these values from the cell-based standard curve and lists them in the Concentration column of the Unknowns group section.
Table 3 shows sample cell proliferation assay results for CHO-K1 cells plated according to the scheme in Table 1 and allowed to proliferate in culture for two days. Cells/well on day two were calculated with SoftMax Pro using the cell-based standard curve.
Table 3. Example Of Unknowns Group
# Cells Plated
* Mean concentration (cells/well) of cells two days after plating is calculated.
Step 2. Prepare 1X and 2X working solutions (100 L per well) of CyQUANT GR dye/ cell-lysis buffer by diluting the concentrated CyQUANT GR stock solution 1:400 or 1:200, respectively, with working strength cell-lysis buffer. This solution should be prepared in a plastic container rather than glass, as recommended by Molecular Probes.
Step 2. Dilute the 1 g/mL stock solution further to make a dilution series as shown in Table 4.
Table 4: Preparation Of Dilutions For DNA Standard
Curve For The CyQUANT Cell Proliferation Assay
Note: The CyQUANT kit includes a l bacteriophage DNA standard. The data shown in this application note were generated using this standard, prepared in serial dilutions. Depending upon the assay you are running, you may wish to use the kits DNA standard or another DNA that is more appropriate for your sample, prepared according to the instructions in the Molecular Probes Product Information sheet MP-7026.
Step 2. Pre-treat the cells with RNase by adding 100 L 1X cell-lysis buffer containing 180 mM NaCl and 1 mM EDTA to each well and to four wells without cells (blanks). If using previously pelleted cells, resuspend each sample in 100 L and transfer to the wells of a microplate. Add 4 L of RNase (two units per well; see note below) into each well containing cells as well as the control wells without cells. Incubate at room temperature for one hour.
Note: DNase-free RNase should be used at a concentration such that no more than 10 L contains the full number of units needed to treat a sample. For example, the RNase Cocktail from Ambion has 500 U/ mL activity, so 4 L per well equals two units per well.
Step 3. Add 100 L of 2X CyQUANT GR dye/ cell-lysis buffer to each of the microplate wells, including the control wells without cells.
Step 4. Prepare the DNA standard curve by transferring the previously prepared DNA serial dilutions into the appropriate wells of the microplate, as defined in the template editor. The plate should contain two controls: a digest control prepared following the same steps as the cellular samples, but without cells (no DNA), and a standard curve control/plate blank containing only 200 L 1X CyQUANT GR dye/cell-lysis buffer (no DNA and no RNase).
Step 5. Incubate the samples for 2-5 minutes.
Step 2. Set up the Instrument Settings dialog box as shown in Table 2.
Step 3. Create a template of the assay showing where standards, unknowns (cells treated with RNase), and plate blanks will be located on the microplate. To access the Template Editor, click the Template button in the tool bar of the Plate section.
Step 2. Read the plate. RFUs will be displayed in the Plate section.
Step 3. After the microplate has been read, the RFUs will be displayed in the Plate section. The data will be analyzed in the Group tables that you created while setting up the template.
Step 4. Plot the mean RFU of the Standards group versus the concentration of the Standards group in the Graph section for the DNA standard curve.
Step 5. Choose the appropriate curve fit from the drop-down Curve Fit menu in the Graph sections tool bar. We used a log-log curve fit for this experiment.
Step 6. Calculate the cellular DNA values in RNase-treated cells from the DNA standard curve using the built-in formula in SoftMax Pro. An example of the Graph Options and Edit dialogue boxes are shown in Figure 2.
* Replicates are not presented in this view of the group table.
Figure 5 shows the average cellular DNA in each set of samples versus the number of cells/well. The linear range of the assay under these conditions is from 50 to 50,000 cells, as expected based on Molecular Probes Product Information sheet MP 7026. A comparison of RFUs in RNase-treated and untreated cell samples is shown in Figure 6 and demonstrates that RNase treatment reduces the amount of fluorescence in the cell lysates.