The effects of 1-methyl-1-nitrosourea on the survival pattern of cycling and noncycling HeLa cells.

The biological behavior of HeLa cells exposed to 1-methyl-1-nitrosourea was examined by determining the survival fraction in asynchronous and synchronous cultures. Asynchronous cell population exposed to 1-methyl-1-nitrosourea for 1 h exhibited a shoulder type survival curve, indicating that damage must be accumulated before the lethal effect occurs. A fraction of 25% of cells survives the concentration of 100 micrograms/ml. The duration of treatment with the drug did not have a significant effect on the cell survival. The experiments with synchronized cells showed that MNU exhibits the killing in all phases of the cell age, but the most sensitive are these in S phase. However, they are still six times more resistant at the same concentration than the culture in plateau phase. At the concentration of 100 micrograms/ml nondividing plateau cells are about 35 times more sensitive than exponentially growing cells. We can conclude that MNU acts as the most acting killing agents on the cells which are in nondividing plateau phase.