Selective Enhancement by Tumor Necrosis Factor‐α of Vascular Permeability of New Blood Vessels Induced with Agarose Hydrogel‐entrapped Meth‐A Fibrosarcoma Cells

We have previously developed a simple and quantitative method for assessment of in vivo tumor cell‐induced angiogenesis by means of microencapsulation of tumor cells in agarose hydrogel and mouse hemoglobin ELISA (mHb‐ELISA). In this article, we report that the new blood vessels induced with agarose‐encapsulated tumor cells have the same sensitivity to tumor necrosis factor‐α (TNF‐α) as the original solid‐tumor vessels. Agarose beads (average diameter=200 μm), in which Meth‐A fibrosarcoma cells were microencapsulated, were subcutaneously implanted in non‐syngeneic ddY mice. Ten days later, extensive angiogenesis was observed on the implanted sites of Meth‐A agarose beads, whereas no new blood vessels were induced with cell‐free agarose beads. The vascular permeability of the new blood vessels induced with agarose‐microencapsulated Meth‐A cells was selectively and significantly enhanced by the i.v. injection of TNF‐α, and it reached the maximum level at 2 h after the injection of TNF‐α. At 4 h after the injection of TNF‐α, the vascular permeability was reduced to the basal level. This permeability profile in Meth‐A agarose beads in ddY mice is very similar to that in Meth‐A solid tumor in syngeneic BALB/c mice. On the other hand, TNF‐α‐treatment did not affect the vascular permeability of other normal tissues or inflammatory tissue in ddY mice. These results strongly suggest that the new blood vessels induced with agarose‐microencapsulated tumor cells have the specific characteristics of tumor vessels. Our in vivo angiogenesis assay system should be useful not only to screen anti‐angiogenetic agents, but also to elucidate the mechanism of tumor angiogenesis.