Cell-density Dependency in the Survival Kinetics of Neocarzinostatin-treated HeLa Cells in Monolayer Cultures and in Spheroids

Cell survival kinetics of HeLa cells grown exponentially in monolayers or grown in multicellular spheroids following neocarzinostatin (NCS) treatment was analyzed in vitro. The effect of NCS was markedly reduced when a large number of cells were plated as compared to a small number per dish. Cell survival kinetics for various combinations of factors: the cell number per dish, concentration of NCS and volume of the medium containing NCS showed that the extent, of cell killing by NCS was solely determined by the relative relation of cell density expressed as cells per unit volume of medium to the effective concentration of NCS; the effective total NCS available to each cell. The theoretical formulation in a controlled situation indicates that C37, the concentration of NCS required to reduce the surviving fraction to e-1, is directly proportional to the cell density. The experimental data points derived from all the combinations of factors essentially followed a linear regression line of the theoretical equation. Therefore, the cell-density dependency of drug-induced cell killing may not be due to a difference in cellular sensitivity or recovery capacity. The effect of NCS on cells in spheroids with central necroses can not be explained only on the basis of the cell-density dependency, but is likely to be reduced by hypoxic conditions, decreased reactivation and the limited penetration of NCS to the deeper layers.