199. Efficient Inhibition of Bone Metastasis Via Systemic Delivery of siRNA Using Atelocollagen-Mediated Delivery System

RNA interference has been one of the most powerful tool for genetic analysis, and much research on the development of siRNA for therapeutic use has progressed. Since siRNA shows a very low efficiency in gene silencing in vivo, various delivery methods have been investigated. However, there are no reports of efficient treatment of bone metastatic cancer by a systemic delivery of siRNA. We have demonstrated the excellent properties of an atelocollagen-mediated delivery system for nucleic acid medicines such as plasmids, antisense DNA and siRNA. Atelocollagen has been widely used because of its high biocompatibility and biodegradability. Last year, we reported that atelocollagen forms a complex with siRNA, and intratumor injection of the complex containing siRNA against FGF 4 mRNA inhibits growth of an orthotropically xenografted human nonseminomatous germ cell tumor. In this study, we demonstrated that the delivery system markedly enhanced the efficiency of siRNA in inhibiting bone metastasis through systemic administration. The siRNA/atelocollagen complex was formed by mixing siRNA with atelocollagen. The formation of the complex was confirmed by gel electrophoresis, and the complex can be administrated by conventional methods. To facilitate the detection of metastatic lesions and tumor regression as the effect of the caused by the complex, noninvasive optical imaging technologies and the bioluminescent human prostate carcinoma cell line PC-3M-luc-C6 were employed. An intracardiac injection of PC-3M-luc-C6 induced metastasis to the thorax, jaws and/or legs of mice. Prior to a metastasis inhibition study, we tested whether a systemic administration of the complex induces a gene silencing effect on metastatic sites. When the complex containing siRNA against luciferase mRNA was administered via the tail vein, bioluminescence was inhibited by 80–90% in the entire body including bone metastatic sites. In contrast, treatment with siRNA alone did not changed or slightly suppressed photon emission from tumor cells. The findings indicate that the complex delivered siRNA with high integrity and inhibited gene expression in metastatic sites including the bone. To inhibit bone metastasis, siRNAs against mRNAs related to cell growth were complexed with atelocollagen, and the complexes administered via the tail vein. When atelocollagen alone, siRNA alone or a non specific siRNA/atelocollagen complex was administered, a high metastasis was observed. On the other hand, bioluminescence intensity in mice administered the complexes of siRNA that inhibits cell growth was inhibited by 40–50% in the entire body including the bone. These findings indicate that the atelocollagen-mediated systemic delivery of siRNA could be a novel strategy for the inhibition of bone-metastatic prostate tumor growth. Furthermore, we confirmed that thecomplex did not induce an interferon response. In summary, an atelocollagen-mediated delivery system has great potential in significantly advancing the practical therapeutic applications of gene suppression using siRNAs.