Angiogenesis as a target for cancer therapy has received a great deal of attention since tumor growth and maintenance is dependent upon a tumors ability to stimulate angiogenesis. Vascular endothelial growth factor (VEGF) promotes angiogenesis in vivo by binding to its receptor (Flk1/KDR) on endothelial cells, which results in subsequent phosphorylation of the kinase domain, ultimately inducing downstream signaling for cell differentiation. The use of tyrosine kinase inhibitors (TKIs) to block the intracellular signaling process that follows receptor activation is a relatively new approach for cancer therapy. The tyrosine kinase inhibitor ZD6474, an orally available small synthetic molecule, is a 4-anilinoquinazoline that has activity against both Flk1/KDR and EGFR tyrosine kinase activity in the nanomolar range. Studies have shown that the use of TKIs in combination with cytotoxic agents improved tumor regression and decreased vascular density. For this reason we have begun to investigate the utility of TKIs alone and in combination with low-dose cytotoxics to inhibit tumor angiogenesis. We are currently using commercially available transformed murine endothelial cells (bEnd.3, ATCC) and primary mouse lung endothelial cells to investigate the cell inhibitory growth effects of ZD6474 and ZD6474 in combination with docetaxel in vitro. We show similar results with bEnd.3 and primary endothelial cells with IC50 values for ZD6474 in the low micromolar range (1–5μM). ZD6474 in combination with docetaxel dramatically enhances the inhibitory growth effects as determined by cell proliferation assays. Cell cycle kinetics and apoptosis have also been evaluated with ZD6474 alone and in combination with docetaxel. Results from these studies will be used in combination with pharmacokinetic modeling to design dosing regimens that optimize the anti-endothelial effects of combined ZD6474 and docetaxel which will be evaluated in xenograft models.
[Proc Amer Assoc Cancer Res, Volume 45, 2004]