Effects of levamisole administration on treatment with 6-mercaptopurine riboside of mice bearing L1210 leukemia cells.

DBA/3 mice and BALB/c X DBA/2 F1 mice were inoculated i.p. with 1 X 10(5) L1210 leukemia cells on Day 0. Beginning with Day 1 following inoculation, the animals were given injections of 6-mercaptopurine riboside (200 mg/kg i.p.) once daily for 5 consecutive days in combination with a single s.c. injection of levamisole (LMS) (10 mg/kg). In DBA/2 mice, a marked decrease in the total peritoneal cell count was achieved when LMS was given on any day from Day -2 to 3 as compared with therapy using 6-mercaptopurine riboside alone, although the survival time was not prolonged in these mice. When LMS was given on Day 1 or 3, a decrease was observed in the in vitro growth rate of the L1210 cells obtained on Day 11 from the peritoneal cavity. In BALB/c X DBA/2 F1 mice, no significant changes were observed in either the total peritoneal cell count or the in vitro growth rate when LMS was injected on Day 3 or daily from Day 3 to 5. Daily injection of LMS from Day 1 to 3 resulted in a conspicuous inhibition of the in vitro growth rate, although no significant changes were observed in the total peritoneal cell count. It seems reasonable to conclude from these results that LMS has a potentiating effect on the antitumor activity of 6-mercaptopurine riboside.