Adenovirus vectors have many advantages for gene therapy. However, because of their lack of tumor tropism and their preference for liver infection following systemic administration, they cannot be utilized for systemic attack on metastatic disease. Liver is a major site of epithelial cancer metastasis, especially colorectal cancer (CRC), often resulting in death.

Cyclooxygenase 2 (COX-2) and carcinoembryonic antigen (CEA) genes are not expressed in liver, but are expressed in many epithelial tumors (e.g., colon, lung, and breast). We used a combination of adenovirus (Ad) transductional liver untargeting, Ad CEA-dependent tumor retargeting, and COX-2 transcriptional restriction to express the luciferase reporter transgene and the Herpes Virus Type 1 thymidine kinase (HSV1-tk) therapeutic transgene in hepatic CEA-positive, COX-2-positive epithelial tumor metastases.

A bispecific adapter protein fusing the coxsackie/adenovirus receptor (CAR) ectodomain (sCAR) and a single-chain anti-CEA antibody (MFE-23) "untargets" liver, reducing hepatic infection. sCAR-MFE also "retargets" adenovirus infection to CEA-expressing hepatic tumor xenografts, following intravenous Ad administration. A trimeric sCAR-MFE (sCARfMFE) was constructed via trimerization of monomeric sCAR-MFE (sCARhMFE). Trimeric sCARfMFE is substantially more efficient than is monomeric sCARhMFE both at untargeting CAR-dependent Ad infection and at retargeting CEA-dependent Ad infection to CEA-expressing tumor cells, both in cell culture and in vivo. In addition, trimerization of sCARfMFE substantially reduces competition by soluble CEA for sCARfMFE directed, CEA-dependent Adenovirus binding and infection. These data suggest that trimeric sCARfMFE may reduce or eliminate the problem caused by CEA shedding, which occurs in most colorectal cancers, for Ad transductional targeting.

Combining hepatic untargeting and tumor retargeting by sCAR-MFE with COX-2 promoter transcriptional restriction increases substantially tumor:liver infection ratios for hepatic epithelial tumor xenografts. Transcriptional Ad targeting therapy, transductional Ad targeting therapy or combined Ad targeting therapy, with the HSV1-tk gene and ganciclovir administration, can extensively decrease hepatic tumor burden and protect livers from being damaged, both by viral induced immunologic toxicity and by transgene product toxicity. Our data suggest that combined transductional retargeting/transcriptional restriction therapy is a therapeutic modality that effectively treats hepatic CRC metastases with reduced adverse effects, suggesting a practical avenue to advance therapy of unresectable hepatic metastases.