Proliferative response of human venous endothelial cells to medium conditioned by human tumour cells

Serum-free medium conditioned by the prior cultivation of cells of the IPT line (derived from a poorly differentiated carcinoma of the lung) contained material of a high MW which stimulated proliferation in cultures of endothelial cells from human umbilical vein. A response was shown by cells seeded on plastic, gelatin or collagen of type I or type IV, at densities of 25 to 200/mm2, and in media with serum concentrations ranging from 0.5 to 20% v/v. Cells plated on biological substrata showed a greater response than those on plastic.