SUPPRESSION OF VEGF-INDUCED ANGIOGENESIS BY THE PROTEIN-TYROSINE KINASE INHIBITOR, LAVENDUSTIN-A

1 Vascular endothelial growth factor (VEGF) is a heparin-binding angio genic factor which specifically acts on endothelial cells via distinct membrane-spanning tyrosine kinase receptors. Here we used the rat spo nge implant model to test the hypothesis that the angiogenic activity of VEGF can be suppressed by protein tyrosine kinase (PTK) inhibitors. 2 Neovascular responses in subcutaneous sponge implants were determin ed by measurements of relative sponge blood flow by use of a Xe-133 cl earance technique, and confirmed by histological studies and morphomet ric analysis. 3 Daily local administration of 250 ng VEGF(165) acceler ated the rate of Xe-133 clearance from the sponges and induced an inte nse neovascularisation. This VEGF(165)-induced angiogenesis was inhibi ted by daily co-administration of the selective PTK inhibitor, lavendu stin A (10 mu g), but not its negative control, lavendustin B (10 mu g ). Blood flow measurements and morphometric analysis of 8-day-old spon ges showed that lavendustin A reduced the Xe-133 clearance of VEGF165- treated sponges from 32.9 +/- 1.5% to 20.9 +/- 1.6% and the total fibr ovascular growth area from 62.4 +/- 6.1% to 21.6 +/- 6.8% (n = 12, P < 0.05). 4 Co-injection of suramin (3 mg), an inhibitor of heparin-bind ing growth factors, also suppressed the VEGF165-elicited neovascular r esponse. In contrast, neither lavendustin A nor suramin produced any e ffect on the basal sponge-induced angiogenesis. 5 When given alone, lo w doses of VEGF165 (25 ng) or basic fibroblast growth factor (bFGF; 10 ng) did not modify the basal sponge-induced neovascularisation. Howev er, co-administration of these two peptides to a single sponge togethe r caused a significant increase in the rate of Xe-133 clearance and an giogenesis similar to that seen with the high dose of VEGF165 (250 ng) acting alone. This VEGF/bFGF neovascular response was also blocked by daily co-administration of lavendustin A (10 mu g), suramin (3 mg) or a monoclonal anti-bFGF antibody (DG2, 1 mu g), but not lavendustin B (10 mu g). 6 These results suggest that selective inhibition of PTK co uld have therapeutic potential in angiogenic diseases where VEGF plays a dominant role. Furthermore, blockade of the angiogenic activity of VEGF and VEGF/bFGF by suramin reveals an alternative strategy in angio suppression.