Preferential Activity of Wild‐type and Mutant Tumor Necrosis Factor‐α against Tumor‐derived Endothelial‐like Cells

Tumor‐derived endothelial‐like cells (tEC) were prepared by culturing human umbilical vein endothelial cells (HUVEC) in the presence of HT1080 human fibrosarcoma‐conditioned medium. tEC showed higher permeability and less cell‐adhesion activity than normal HUVEC (nEC). Tumor necrosis factor‐α (TNF) is known to have tumor‐vasculature disrupting activity. tEC showed higher cytotoxicity to recombinant human TNF (rhTNF) than nEC, and was not observed using HUVEC cultured with WI38 human diploid cell‐conditioned medium as a medium‐control. These results demonstrate that tEC acquire physiological properties of tumor‐associated vasculature, and may be a useful model system for the study of the mechanisms of TNF antitumor action. The TNF‐mutant RGD‐V29 (code No. F4614), which has an inserted (4)Arg‐Gly‐Asp sequence and an (29)Arg→Val replacement, was found to induce greater preferential destruction of tEC compared to rhTNF. When the preferential activities were evaluated in terms of 30% cytotoxicity (IC(30)) ratio (nEC/tEC), the ratio was 460 for RGD‐V29 compared to 4.2 for rhTNF. RGD‐V29 also exhibited cell‐adhesive function and bound preferentially to the p55 TNF‐receptor. Both these properties of RGD‐V29 contributed to the tEC selective cytotoxicity, indicating that the RGD ligands and selective p55 receptor binding on the cells, although uncharacterized, are involved in tEC targeting. Therefore, the TNF mutant RGD‐V29 may show greater selectivity toward tumor vasculature than wild‐type TNF.