The proliferative activity of human neoplasms may be an important determinant for therapeutic management. The advent of automated flow- through systems measuring cellular DNA content by means of fluorescence has considerably facilitated the analysis of cellular kinetics. Using a pulse cytophotometer ICP-11 (Phywe Co., Gottingen, Germany), three different fluorescent staining techniques for DNA histogram measurement on human hemopoietic cells were tested: mithramycin, ethidium bromide, and a combination of ethidium bromide and mithramycin. Employing the tritiated thymidine labeling index as reference standard for comparison with the DNA histogram-derived S-phase fractions, linear correlations were obtained using ethidium bromide alone and ethidium bromide in combination with mithramycin as staining techniques. The fluorescence intensity was increased fourfold to fivefold by the use of the two-dye combination, resulting in a substantial decrease in the coefficient of variation of DNA histograms to 1.5%-2%. This augmented histogram resolution is an important codition for detecting small-degree numeric chromosomal aberrations and discrete drug perturbation effects.

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