Activity of etoposide (VP-16) in human tumor cells under different growth conditions

The effect of etoposide (VP-16) on a human epidermoid carcinoma cell line (HEp3) has been evaluated under different growth conditions. A significant increase in resistance to this agent from exponential to unfed plateau cells has been observed. Variations in the cell cycle distribution appear not to be sufficient to explain the difference in cell killing. Rather, our studies suggest the presence of an important proportion of quiescent (Q) cells in the plateau phase cultures which may determine the treatment outcome.