Improved anti-cancer effect of interferon gene transfer by sustained expression using CpG-reduced plasmid DNA

Plasmid DNA (pDNA) expressing mouse interferon (IFN)-beta or IFN-gamma (pCMV-Mu beta and pCMV-Mu gamma, respectively) has been shown to be effective in inhibiting the growth of colon carcinoma CT-26 cells in the liver (Kobayashi et al., Molecular Therapy 2002;6:737-44). The therapeutic effect of such IFN gene transfer could be significantly increased by the sustained expression of IFNs. In the present study, CpG-reduced pDNA encoding IFN-beta or IFN-gamma (pGZB-Mu beta and pGZB-Mu gamma, respectively) was constructed. pCMV-Mu beta and pCMV-Mu gamma were used as conventional CpG-replete pDNAs. Each pDNA was injected into the tail vein of mice by the hydrodynamics-based procedure. An injection of pGZB-Mu beta resulted in very high IFN-beta activities in the serum for at least 24 hr after injection, whereas the IFN-beta activity after pCMV-Mu beta injection declined quickly. About a 14-fold greater amount of IFN-beta was produced from pGZB-Mu beta than from pCMV-Mu beta. pGZB-Mu beta markedly inhibited the pulmonary metastasis of CT-26 cells. Similar, but more marked results were obtained with pGZB-Mu gamma: it increased the area under the concentration-time curve by more than a 60-fold and the mean residence time of IFN-gamma 4-fold compared with pCMV-Mu gamma. The survival time of the pGZB-Mu gamma-treated mice was significantly (p<0.05) longer than that of the saline- or pCMV-Mu gamma-treated mice. These results indicate that long-term expression of IFN can be achieved by CpG-reduced pDNA and sustained IFN gene expression results in enhanced therapeutic effects of IFN gene transfer against tumor metastasis.