Semaxinib (SU5416) is a potent and selective VEGFR2 inhibitor (IC50: 1.23 μM), 20-fold more selective for VEGFR than PDGFRβ, lack of activity against InsR, EGFR, and FGFR. Semaxanib reversibly inhibits ATP binding to the tyrosine kinase domain of vascular endothelial growth factor receptor 2 (VEGFR2), which may inhibit VEGF-stimulated endothelial cell migration and proliferation and reduce the tumor microvasculature.

VEGFR2:1.23 μM

SU5416 inhibits VEGF-driven mitogenesis in a dose-dependent manner with an IC50 of 0.04±0.02 μM (n=3). In contrast, SU5416 blocked FGF-dependent mitogenesis of HUVECs with an IC50 of 50 μM (n=10). The selective activity of SU5416 on Flk-1 is supported by the fact that testing of SU5416 using NIH 3T3 cells overexpressing either the EGF or insulin receptors indicated a complete lack of activity (IC50>100 μM). This observation is confirmed by immunoblotting after ligand stimulation. An IC50 of 20.26±5.2 μM (n=7), which is about 20-fold less in potency on PDGF-dependent autophosphorylation, is observed when SU5416 is tested in NIH 3T3 cells overexpressing the human PDGF receptor β[1].

Daily administration of SU5416 (i.p., 3 mg/kg/day) inhibits the local growth of C6 tumors in the colon. A comparable level of growth inhibition (62% by day 16; P=0.001) is observed for tumors growing in the colon in comparison with ones growing in the hindflank region (54% by day 18; P=0.001). These results indicate that SU5416 could inhibit tumor growth at a site other than the subcutaneous implantation site, where the preexisting vasculature may be different[1]. Daily treatment with SU5416(25 mg/kg) results in a significantly lower tumor growth rate with tumor masses of up to 8% of that present in control animals by day 22 after implantation. Inhibition of tumor growth is clearly preceded by a marked reduction of the tissue area covered by the newly formed glioma microvasculature in the SU5416-treated group, indicating a reduced initial tumor vascularization[2].

Solubilized membranes from 3T3 Flk-1 cells are added to polystyrene ELISA plates that has been precoated with a monoclonal antibody that recognizes Flk-1. After an overnight incubation with lysate at 4°C, 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 peroxidase H is added to the wells. A stabilized form of 3,3′,5,5′-tetramethyl benzidine dihydrochloride and Water2 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. Parallel biochemical kinase assays are performed to measure autophosphorylation on EGFR and fibroblast growth factor receptor[1].

SU5416 is dissolved in DMSO and stored,and then diluted with appropriate media (DMSO<0.5%) before use[1] 3T3Her2 and 488 g2M2 are NIH3T3 fibroblast cell lines engineered to overexpress Her2 and to express human PDGF-BB and human PDGF receptor β.Both cell lines are cultured in DMEM supplemented with 2% CS and 2 mM L-glutamine.C6,Calu 6,A375,A431,and SF767T are plated in their respective growth medium at 2×103 cells/100 μL/well in 96-well,flat-bottomed plates.SU5416 is serially diluted in media containing DMSO (<0.5%) and added to cultures of tumor cells 1 day after the initiation of culture.Cell growth is measured after 96 h using the sulforhodamine B method.IC50s are calculated by curve fitting using four-parameter analysis[1].