Modulation of neovascularization and metastasis by species of heparin.

Abstract

We have characterized the importance of size, sulfation and anticoagulant activity of heparin in: i) release of basic fibroblast growth factor (bFGF) from the subendothelial extracellular matrix (ECM), and ii) inhibition of heparanase (endo-β-D-glucuronidase) and tumor metastasis. Oligosaccharides derived from depolymerized heparin and containing as little as 8–10 sugar units were, on a molar basis, equivalent to whole heparin in their ability to release bFGF from ECM. Low sulfate oligosaccharides were less effective than medium and high sulfate oligosaccharides. N-desulfation or N-acetylation resulted in an almost complete inhibition of bFGF release. Heparin fractions with high and low affinity to antithrombin III exhibited the same high bFGF releasing activity. Similar requirements were observed for release of 125I-bFGF sequestered by the luminal surface of blood vessels. Heparanase expressed by intact cells (i.e. platelets, mast cells, neutrophils, lymphoma cells) released active bFGF from ECM and basement membranes. Heparanase activity also correlated with the ability of blood-borne tumor cells to extravasate and metastasize. Unlike release of bFGF, efficient inhibition of both heparanase and tumor metastasis was best achieved by heparin species containing 16 sugar units or more and was only slightly affected by substitution of N-sulfates with acetyl groups. These results indicate that various non-anticoagulant heparin species of different size, sulfation and substituted groups can be designed to elicit specific effects such as release of bFGF and inhibition of heparanase, resulting in induction of neovascularization and inhibition of tumor metastasis, respectively.