Enhancement of the antitumor effect of 1,3-bis(2-chloroethyl)-1-nitrosourea by various psychotropic drugs in combination with caffeine.

Certain psychotropic drugs when combined with caffeine significantly enhanced the antitumor effect of 1,3-bis(2-chloroethyl)-1-nitrosourea in murine leukemia L1210. Enhancement required that all three drugs be given together and optimal results were obtained when the psychotropic drug was given 6 hours before 1,3-bis(2-chloroethyl)-1-nitrosourea and caffeine. Thus, 1,3-bis(2-chloroethyl)-1-nitrosourea alone or with caffeine resulted in 5% cures. Addition of chlorpromazine increased the cure rate to 51% while prochlorperazine gave 30% cures. Chlordiazepoxide produced 39% cures while the dibenzazepine compounds studied were ineffective. For the phenothiazine, benzodiazepine and dibenzazepine compounds studied, tentative conclusions could be drawn on the relationship of chemical structure to enhancing activity. For phenothiazines, the substituent in the R2 position of the phenothiazine ring determined activity to a greater extent than did the substituent in the R1 position. For the benzodiazepine compounds, chlordiazepoxide was superior to diazepam. Although the mechanism of action of psychotropic drugs in this system is unknown, these preliminary results suggest the possibility of a change transfer reaction between the free radical form of the psychotropic drug and one or more intracellular constituents.