Regional Delivery of an Adenovirus Vector Containing the Escherichia coli Cytosine Deaminase Gene to Provide Local Activation of 5-Fluorocytosine to Suppress the Growth of Colon Carcinoma Metastatic to Liver

Abstract

To evaluate the hypothesis that regional delivery of an adenovirus vector containing the Escherichia coli cytosine deaminase gene (AdCMV.CD) together with systemic 5-FC could suppress the growth of metastatic colon cancer in the liver, the AdCMV.CD vector was injected 0.8–1 cm from the site of a human colon cancer tumor in the livers of nude mice. The growth of the human colon cancer cells was quantified by dot blot analysis of genomic DNA extracted from tumor-bearing liver, hybridized with a human-specific Alu probe. The combination of regional AdCMV.CD plus systemic 5-fluorocytosine (5-FC) suppressed the growth of the metastatic tumors over the 21 days of evaluation following vector administration. Histologic evaluation showed necrosis at the site of the tumor in the livers of mice treated with AdCMV.CD/5-FC, but not in control groups. Evaluation of the potential toxicity of AdCMV.CD plus 5-FC on the normal liver showed only mild, self-limited dose-related inflammation, with no deaths. These data suggest that the regional administration of AdCMV.CD together with systemic 5-FC may be a safe and effective strategy to suppress the growth of metastases of colorectal carcinoma in the liver.

Overview summary

These studies explore the potential for regional gene therapy of colon carcinoma metastatic to the liver using an adenovirus vector to deliver the Escherichia coli cytosine deaminase gene (AdCMV.CD) to hepatic parenchyma in an experimental metastasis model. It is hypothesized that mice expressing the gene within hepatocytes convert systemically administered 5-fluorocytosine (5-FC) to 5-fluorouracil locally. Injection of the vector AdCMV.CD into hepatic parenchyma directs expression of mRNA transcript within the liver and produces a functional intracellular protein that is most highly concentrated in the injected lobe. The combination of intraparenchymal AdCMV.CD and 5-FC in tumor-bearing mice effectively suppresses growth of intrahepatic tumor. Safety evaluations show no mortality and indicate only mild, self-limited inflammation associated with the vector delivery, independent of the prodrug administration. These studies collectively suggest this approach may be both therapeutic and safe and serve as a paradigm for treating micrometastasis or areas with multiple metastases within the liver.