Binding of acridine orange to DNA in situ of cells from patients with acute leukemia

Fluorescence flow cytometry was used to generate DNA histograms of acridine orange stained leukemic cell populations in G0-G1 phase of the cell cycle. Complexes of the intercalating agent, acridine orange, with double-stranded DNA in situ, emit green fluorescence upon excitation with blue laser light. The histograms were evaluated by first determining the standard deviation of the fluorescence intensity relative to the mean channel of fluorescence, i.e., the coefficient of variation, and then dividing the coefficient of variation of a patient's sample by that of a control sample (rCV). The mean rCV of cell populations of acute lymphoblastic leukemia (31 patients) differed significantly from that of nonlymphoblastic leukemia (21 patients). When cells were treated with a solution of citric acid and magnesium sulfate prior to their staining with acridine orange, the mean rCV of cell populations of acute lymphoblastic leukemia increased while that of acute nonlymphoblastic leukemia decreased compared to their respective pretreatment values. The mean difference of rCVs between untreated and treated cells (rCVD) within each disease category was statistically significant. A logistic regression model, based on rCVD, confirmed the conventional classification of acute lymphoblastic leukemia and acute nonlymphoblastic leukemia cells in 90% of the cases.