EFFECT OF CELL-DENSITY ON THE INHIBITION OF TUMOR-CELL ATTACHMENT ANDNUCLEIC-ACID SYNTHESIS BY SELENITE

The effect of cell density on the sensitivity of tumor cells to seleni te has been examined. The inhibitory effect of selenite on cellular DN A and RNA synthesis was significantly greater in higher density cultur es of HeLa cells and A2780 ovarian tumor cells. High-density cells wer e also more sensitive to the inhibitory effect of selenite on cell att achment. This difference could not be accounted for by a higher intrac ellular level of glutathione, since there was no significant differenc e between the cells at high or low density. The high-density cells wer e found to take up more selenium per cell during the exposure period; the resulting higher level of intracellular Se could explain their gre ater sensitivity to selenite. This hypothesis is supported by the obse rvation that DNA synthesis in nuclei isolated from high-density cells did not exhibit higher sensitivity to inhibition by selenite than synt hesis in nuclei isolated from low-density cells.