Interferon and cis-DDP: combination chemotherapy for P388 leukemia in CDF1 mice.

CDF1 mice were implanted with 10(6) P388 leukemia cells. One day postimplantation, when interferon (IFN) therapy was begun, the tumor burden was ca. 4.8 X 10(6) cells. Therapy consisted of nine consecutive daily intraperitoneal (i.p.) injections of 10(6) units of Ehrlich ascites tumor cell IFN (specific activity 5 X 10(7) IU/mg). The median life span for control animals was 10.0 days versus 18.5 days for the treated animals. It was estimated that about 2 X 10(6) viable P388 cells were present on Day 9 when therapy was discontinued. There was no evidence of toxicity in animals receiving 10(6) units of IFN/day for nine consecutive days. In a separate experiment, control animals challenged as above had a median life span of 9.5 days of versus 15 days for animals receiving 10(6) units of IFN qd on Days 2-10. A third group of animals receiving a single injection of cis-DDP on Day 1 had a median survival of 18.5 days, while a fourth group receiving both cis-DDP on Day 1 and subsequent treatment with IFN survived 26 days. The results are discussed in terms of impact on tumor cell population.