Therapeutic effect of intravenous delivery of lipoplexes containing the interferon-β gene and poly I: Poly C in a murine lung metastasis model

We have evaluated and compared the efficacy of systemic administration of lipoplex formulations containing plasmids encoding IFN-β or IFN-γ, and a synthetic double-strand RNA poly I:poly C (pI:pC), a type I IFN inducer, in a lung metastasis model in which colon carcinoma CT-26 cells were inoculated intravenously into immunocompatible mice. Injection of lipoplexes containing plasmid DNA, regardless of IFN gene insertion, stimulated a transient increase in the serum concentration of proinflammatory cytokines such as tumor necrosis factor (TNF)-α and IFN-γ, while injection of lipoplexes containing pI:pC led to a low level of TNF-α and undetectable IFN-γ production. Furthermore, injection of these lipoplexes containing plasmids resulted in the production of a mixture of type I and type II IFNs, partly derived from the inserted IFN genes, in lung tissue cultures. In tumor-prophylactic experiments, intravenous injection of lipoplexes containing plasmid, regardless of IFN gene insertion, showed a significant reduction in lung metastatic nodules probably due to proinflammatory cytokines such as TNF-α and IFN-γ nonspecifically induced by the CpG motifs in the plasmid and the type I IFNs produced. On the other hand, the antimetastatic effect of pI:pC-lipoplex seemed to be due mainly to IFN-β induced by pI:pC. In established lung metastasis experiments, a single intravenous administration of lipoplexes containing IFN-β gene or pI:pC, but not other lipoplexes, showed a significant therapeutic effect on the tumor metastasis: reduction in tumor nodules and prolongation of survival time of tumor-burden mice. The therapeutic effects were specifically impaired by anti-IFN-β antibody treatment, indicating that IFN-γ produced by the lipoplexes played an important role in the suppression of established metastatic lung tumors. Thus, the local IFN-β in the lung delivered by intravenous administration of lipoplex containing IFN-β gene or pI:pC may be a convenient and useful method of inhibiting established metastatic lung tumors.