Hormonal-like modulation of growth of moloney virus-induced tumors by interferon and platelet-derived growth factor.

Continued intramuscular (i.m.) administration of highly purified preparations of mouse interferon (MuIFN) and/or bovine platelet-derived growth factor (PDGF) to the Moloney sarcoma virus (MSV) infected Balb/c mice resulted in a hormonal-like modulation of growth of tumors. Large dose MuIFN treatment (10(5) units per mouse daily, for 14 days) inhibited the MSV-induced tumors. On the other hand, small-dose MuIFN treatment (100 units per mouse daily, for 14 days or 10(4) units per mouse, every second day in 3-4 doses) enhanced the tumor growth. The simultaneous administration of large doses of MuIFN and PDGF significantly diminished the antitumor effect of IFN. The results suggest that the negative and positive interaction between IFN and PDGF takes place in vivo.