Experimental parameters and a biological standard for acridine orange detection of drug-induced alterations in chromatin condensation.

We investigated a number of sample-preparative parameters for use of flow cytometry to detect chromatin condensation in cells stained with acridine orange after DNA in situ is partially denatured by acid treatment. Stability and data reproducibility for both control and drug-treated ME-180 and HT-29 cells were assessed over: a range of cell concentrations in 2.56 X 10(-5) M acridine orange; 15 days of storage in fixative; various times between RNase digestion and staining; and increasing times between staining and analysis. Listmode data for red and green fluorescence were collected and mean fluorescence intensities of G1, S, and G2 subpopulations of HT-29 and ME-180 cells were computed. These were normalized to data from HeLa-S3 cells and fluorescent microspheres to control for inter-experiment variations in staining and instrumental parameters, respectively. The normalized red and green fluorescence data were used to calculate alpha 1 for G1 cells [alpha t = red fluorescence/(total fluorescence)]. Exponentially growing HeLa-S3 cells were a very consistent and reproducible biological standard to control for fixation and staining variability. Mean fluorescence intensities of control and difluoromethylornithine-treated (i.e., polyamine depleted) cells remained stable and reproducible across all tested ranges for cell concentration, storage in fixative, and time after RNase digestion. This technique can thus be used to evaluate difluoromethylornithine-induced changes in chromatin condensation of samples stored for as long as 2 weeks and analyzed all on 1 day.