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

Plasmid DNA (pDNA) expressing mouse interferon (IFN)‐β or IFN‐γ (pCMV‐Muβ and pCMV‐Muγ, 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‐β or IFN‐γ (pGZB‐Muβ and pGZB‐Muγ, respectively) was constructed. pCMV‐Muβ and pCMV‐Muγ 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‐Muβ resulted in very high IFN‐β activities in the serum for at least 24 hr after injection, whereas the IFN‐β activity after pCMV‐Muβ injection declined quickly. About a 14‐fold greater amount of IFN‐β was produced from pGZB‐Muβ than from pCMV‐Muβ. pGZB‐Muβ markedly inhibited the pulmonary metastasis of CT‐26 cells. Similar, but more marked results were obtained with pGZB‐Muγ: it increased the area under the concentration‐time curve by more than a 60‐fold and the mean residence time of IFN‐γ 4‐fold compared with pCMV‐Muγ. The survival time of the pGZB‐Muγ‐treated mice was significantly (p < 0.05) longer than that of the saline‐ or pCMV‐Muγ‐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. © 2007 Wiley‐Liss, Inc.