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Colorectal cancer (CRC) is the second leading cause of cancer deaths in the US. Despite progress in earlier stage disease, survival has only minimally improved in patients with systemic metastases (Stage IV), which occur primarily to the liver; therefore, more effective and targeted therapies are required. Small interfering RNA (siRNA) provides a highly selective method to target mutated pathways; however, its use is complicated by the inability to specifically target tumor cells. The purpose of this study was to: i) develop a novel murine model of portal vein catheterization for the chronic delivery of therapeutic agents to liver metastases, and ii) determine the utility of epithelial cell adhesion molecule (EpCAM) as a selective target for siRNA delivery to CRC metastases.

Methods: i) To establish a chronic portal vein catheterization model, a midline laparotomy was performed in 2 mo-old Balb/C mice and a 1.2F catheter inserted into the portal vein. Distribution of portal venous flow and catheter patency was evaluated using fluorescently-labeled microspheres. Uptake of siRNA within the liver was tested using DY-547-labeled siRNA followed by IVIS imaging 4h post injection. For metastatic studies, splenic injection of CT26 murine colon cancer cells, transfected with a luciferase vector, was performed and metastasis confirmed 10d later by IVIS imaging; siRNA delivery to liver metastases was confirmed using DY547-labeled siRNA and fluorescent microscopy. ii) The presence of EpCAM was evaluated using IHC staining of microarrays containing a total of 89 normal colon samples, 129 primary CRCs, 4 liver metastases and a normal liver specimen.

Results: i) Fluorescence was noted throughout the majority of the liver following injection of the microspheres thereby confirming excellent distribution; microsphere injection at 2 wks confirmed catheter patency. Portal venous injection of DY547-labeled siRNA demonstrated a high level of fluorescence throughout the entire liver. In the metastatic model, fluorescent microscopy confirmed the presence of siRNA within the liver metastases demonstrating effective delivery to metastatic lesions. ii) EpCAM staining was absent in normal hepatocytes; mild staining was present in the biliary radicals. All primary CRCs and liver metastases stained strongly for EpCAM.

Conclusions: Liver directed therapy provides an effective method for the delivery of siRNA to CRC metastases. Furthermore, the presence of EpCAM on the cell surface of CRC metastases, but not normal liver, may provide a method to selectively target hepatic metastases of epithelial origin. This targeted delivery, combined with the specific effects of siRNA, would provide a highly selective therapeutic strategy for treatment of CRC metastasis.