For NC-3000 assays, cells were fixed with 70% ethanol for 2 to 24 h at −20°C prior to permeabilization with 0.1% Triton X-100 and incubated with 1 μg/ml DAPI DNA stain for 5 min at 37°C. Exported FCS3 files were processed using Flowing software to delineate cell cycle phases and determine proportions of cells in each fraction.
For Accuri C6 flow cytometry, cells were fixed with 1% formaldehyde for 10 min at 37°C before being permeabilized with methanol (90% final concentration) at −20°C for 2 to 24 h. Cells were pelleted and washed with PBS before being incubated with 50 μM DRAQ5™ or 125 ng/ml DAPI DNA staining for 30–60 min in the dark at room temperature. More than 5000 events were collected with the Accuri C6 flow cytometer and cell cycle distributions were determined from histograms generated using the Accuri C6 analysis software.