Recent studies have revealed that the targeting therapy using monoclonal antibody against tumor associated antigens did not have a clinically satisfactory effect due to various physiological characters of tumor. We propose a novel approach targeting tumor vascular endothelium to solve the inefficiency of common tumor missile therapy. In this study, the tissue distribution of anti-tumor vascular endothelium monoclonal antibody (TES-23) produced by immunizing with plasma membrane vesicles obtained from isolated rat tumor-derived endothelial cells (TECs) was assessed in various tumor-bearing animals. Radiolabeled TES-23 dramatically accumulated in KMT-17 fibrosarcoma, a source of isolated TECs after intravenous injection. In Meth-A fibrosarcoma, Colon-26 adenocarcinoma in BALB/c mice and HT-1080 human tumor tissue in nude mice, radioactivities of I-125-TES-23 were also up to fifty times higher than those of control antibody with little distribution to normal tissues. Furthermore, immunostaining of human tissue sections showed specific binding of TES-23 on endothelium in esophagus and colon cancers. These results indicate that tumor vascular endothelial cells express a common antigen in different tumor types of various animal species. In order to clarify the efficacy of TES-23 as a drug carrier, an immunoconjugate, composed of TES-23 and neocarzinostatin, was tested for its antitumor effect in vivo. The immunoconjugate (TES-23-NCS) caused a marked regression of the tumor, KMT-17 in rats and Meth-A in mice. Thus, from a clinical view, TES-23 would be a novel drug carrier because of its high specificity to tumor vascular endothelium and its application to many types of cancer.
