In vitro activity: Semaxanib inhibits VEGF-dependent phosphorylation of the Flk-1 receptor in Flk-1-overexpressing NIH 3T3 cells with IC50 of 1.04 μM. Semaxanib inhibits PDGF-dependent autophosphorylation in NIH 3T3 cells with IC50 of 20.3 μM. Semaxanib inhibits VEGF- and FGF-driven mitogenesis in a dose-dependent manner with IC50 of 0.04 and 50 μM, respectively. Semaxanib treatment has no effect on the in vitro growth of C6 glioma, Calu 6 lung carcinoma, A375 melanoma, A431 epidermoid carcinoma, and SF767T glioma cells (all IC50s> 20 μM).

Kinase Assay: Solubilized membranes from 3T3 Flk-1 cells are added to polystyrene ELISA plates that had been precoated with a monoclonal antibody that recognizes Flk-1. After an overnight incubation with lysate at 4 ℃, serial dilutions of SU5416 are added to the immunolocalized receptor. To induce autophosphorylation of the receptor, various concentrations of ATP are added to the ELISA plate wells containing serially diluted solutions of SU5416. The autophosphorylation is allowed to proceed for 60 min at room temperature and then stopped with EDTA. The amount of phosphotyrosine present on the Flk-1 receptors in the individual wells is determined by incubating the immunolocalized receptor with a biotinylated monoclonal antibody directed against phosphotyrosine. After removal of the unbound anti-phosphotyrosine antibody, avidin-conjugated horseradish pero-idase H is added to the wells. A stabilized form of 3,3 9,5,5 9-tetramethyl benzidine dihydrochloride and H2O2 is added to the wells. The color readout of the assay is allowed to develop for 30 min, and the reaction is stopped with H2SO4.

Cell Assay: HUVECs are plated in 96-well, flat-bottomed plates (1×104 cells/100 μL/well) in F-12K media containing 0.5% heat-inactivated FBS and cultured at 37 ℃ for 24 h to quiesce the cells. Serial dilutions of compounds prepared in medium containing 1% DMSO are then added for 2 h, followed by the addition of mitogenic concentrations of either VEGF at 5 ng/mL or 20 ng/mL or acidic fibroblast growth factor at 0.25–5 ng/mL in media. The final concentration of DMSO in the assay is 0.25%. After 24 h, either [3H]thymidine (1 μCi/well) or BrdUrd is added, and the cell monolayers are incubated for another 24 h. The uptake of either [3H]thymidine or BrdUrd into cells is quantitated using a liquid scintillation counter or a BrdUrd ELISA, respectively.

Cancer Res. 1999 Jan 1;59(1):99-106; Neoplasia. 1999 Apr;1(1):31-41.