Antibody-directed therapy for human hepatocellular carcinoma.

The goals of our research are to develop high-affinity and high-stability antibodies and fragments thereof for targeting tumor-specific antigens in an attempt to develop new therapeutic agents for human hepatocellular carcinoma (HCC). Tumor-associated antigens are excellent targets for drug and gene delivery, and offer the advantage of high cellular specificity. We have explored the use of a monoclonal antibody (Mab) AF-20 raised against a human hepatoma cell line (FOCUS) as a model system. This antibody binds to a 180-kDa homodimeric cell surface glycoprotein with high affinity. The antigen is uniformly expressed in HCC-derived cell lines and human tumors, including those with distant metastasis. There is minimal expression in nontumor tissues, and none detectable in normal liver. Because the AF-20 antigen antibody interactions on the cell surface is rapidly internalized at 37 degrees C, there is an opportunity to deliver cytotoxic payloads to tumor cells. In addition, high-affinity single-chain monoclonal antibody fragments (scFv) have been created using a novel yeast display system. Drug conjugates with AF-20 monoclonal antibodies have been prepared for gene targeting of HCC both in vitro and in vivo using preclinical animal model systems. These studies show that it is possible to generate high-affinity intact scFv antibody fragments that will allow specific tumor targeting of adenoviruses containing suicide genes, chemotherapeutic agents such as methotrexate, and cytotoxic peptides to produce antitumor effects. Therefore, specific antibody targeting of antitumor agents to HCC cells has the potential for therapeutic application in this devastating disease.