ANTIPROLIFERATIVE EFFECTS OF NATURAL INTERFERON-BETA ALONE AND IN COMBINATION WITH NATURAL INTERFERON-GAMMA ON HUMAN BREAST CARCINOMAS IN NUDE-MICE

Nude mice bearing bilateral xenografts of human breast carcinoma cells (MCF-7 and BT20) were treated with 2 or 4 5-day cycles of intralesional (i.l.) injections of human natural interferon beta (nIFN-β) alone or in combination with human natural interferon gamma (nIFN-γ). The injections were administered to only 1 of the 2 tumors in each animal, thus making it possible to assess at the same time local therapeutic effects in the injected tumors and systemic effects in the contralateral ones. When n-IFN-β was used as a single agent only mild local antitumor effects and virtually no systemic effects were observed. In contrast, the combined administration of nIFN-β/nIFN-γ produced marked antiproliferative effects, presumably as a result of the synergistic action of type I and type II IFNs. These effects ranged from complete regression documented histologically in 2 MCF-7 tumors to varying degrees of growth inhibition with persistence of residual microscopic or grossly detectable tumor. Local effects were more pronounced than systemic effects. The therapeutic efficacy of nIFN-β proved to be greater than that of recombinant interferon beta (rIFN-β). In MCF-7 tumors nIFN-β appeared to be less effective than nIFN-α, whereas the opposite was true for BT 20 tumors. © 1990 Kluwer Academic Publishers.