Quantitative dose-response relations for the cytotoxic activity of chloroethylnitrosoureas in cell culture.

A dose-response relation for the cytotoxic activity of chloroethylnitrosourea cancer chemotherapeutic agents in cell culture has been developed. Data for the activity of 1,3-bis(2-chloroethyl)-1-nitrosourea, 1-(2-chloroethyl)-3-cyclohexyl-1-nitrosourea, 1-(2-chloroethyl)-3-(trans-4-methylcyclohexyl)-1-nitrosourea, and 1-(2-chloroethyl)-3-(piperidine-3,6-dion-3-yl)-1-nitrosourea against 9L rat brain tumor cells are presented. Cytotoxicity resulting from treatment schedules at different initial drug concentrations, exposure periods, and preincubation periods are correlated using a proposed dose function. Equations are presented that incorporate drug concentration, duration of exposure of cells, and the rate constant for conversion of the drug from an active intermediate into a single dose function. When compared in this way, all cell treatment schedules used were found to be equally effective in killing cells in culture. The cytotoxic activity of the four different chloroethyl-nitrosourea analogs were also found to be the same. These data demonstrate the application of quantitative dose-response relations to the activity of chloroethylnitrosoureas in cell culture and provide new insight into the mechanism of action and structure-activity relationships of these compounds.