Interferon and cis-DDP: Combination Chemotherapy for P388 Leukemia in CDF1 Mice

CDF1 mice were implanted with 10⁶ P388 leukemia cells. One day postimplantation, when interferon (IFN) therapy was begun, the tumor burden was ca. 4.8 × 10⁶ cells. Therapy consisted of nine consecutive daily intraperitoneal (i.p.) injections of 106 units of Ehrlich ascites tumor cell IFN (specific activity 5 × 10⁷ 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 × 10⁶ viable P388 cells were present on Day 9 when therapy was discontinued.

There was no evidence of toxicity in animals receiving 10⁶ 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 versus 15 days for animals receiving 10⁶ 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.