Antitumor Effects of Interferon Preparations In Mice

Abstract

Repeated daily intraperitoneal administration of preparations of mouse brain interferon increased the survival of BALB/c, C57BL/6, and DBA/2 mice inoculated intraperitoneally with several thousand Ehrlich ascites (EA), RC19, EL4, L1210, and E ♂ G 2 tumor cells. Antitumor effect was most marked in BALB/c mice inoculated with EA cells, and this experimental system was chosen for more detailed investigation: 1) Interferon treatment of mice before inoculation of EA cells was ineffective. 2) Subcutaneous administration of interferon increased mouse survival, but was probably less effective than intraperitoneal inoculation. 3) The efficacy of treatment in increasing mouse survival was directly related to its efficacy in inhibiting tumor growth and inversely proportional to the number of EA cells inoculated. One to ten EA cells constituted 1 LD50 for untreated mice, whereas 10⁴–10⁵ EA cells constituted 1 LD50 for interferon-treated mice. 4) Phagocytosis of tumor cells by macrophages was observed on smears obtained from the peritoneal cavities of mice treated with interferon, but not from untreated mice or mice treated with normal brain extract. 5) Interferon-treated mice surviving inoculation of EA cells had an enhanced resistance to reinoculation of EA cells. The mechanism of the antitumor effect in interferon-treated mice is still unknown.