Intracellular DNA and RNA in the course of tumor cell growth

We have investigated the intracellular levels of the nucleic acids, especially intracellular RNA to determine whether or not they could be used as indicators of cell proliferation kinetics and thereby enable an investigation into the biology of tumor cells. HeLa and COLO 205 were the cell lines used in this experiment, and normal human peripheral lymphocytes were used as the control. Cells were stained with acridine orange and subjected to flow cytometry. Based on the cytograms obtained, changes in the DNA and RNA contents in the cell lines were expressed as a ratio of the mean channel to that of the control. The intracellular RNA concentration was reflected in changes in the mean RNA channel ratio on the DNA and RNA cytograms. An increase in the mean RNA channel ratio represented a logarithmic proliferation of the tumor cells. Changes in the mean RNA channel ratio could be noted in cell samples containing as little as 20% logarithmic growth phase cells. There was a close correlation between the RNA content and the proliferative potential, and an increase in the RNA content was predictive of subsequent cellular proliferation. These results suggested that an increase in the intracellular RNA content on flow cytometry could be used as indicator of tumor proliferative potential, suggesting that this method could be useful for assessing the biological properties of tumor cells.