Lethal Activity of Camptothecin Sodium on Human Lymphoma Cells

The lethal effects of camptothecin sodium (CS) were studied with a human lymphoma cell line in order to compare activity in human and nonhuman cells. Differences in activity could explain the poor clinical results obtained thus far. No significant difference was observed. Asynchronous human lymphoma cells exposed to increasing concentrations of CS revealed a biphasic survival curve with an initial steep slope followed by a much more shallow one. Incubation for 24 and 48 hr increased the killing effect by more than 100-fold, but again biphasic curves were elicited. In synchronized lymphoma cells, CS is more effective on early and mid-S-phase cells, with an activity greater than 1 decade between the most and least-sensitive cells. It is suggested that CS is a phase-sensitive drug useful in combination regimens.