Heparin–Avastin Complexes Show Enhanced VEGF Binding and Inhibition of VEGF-Mediated Cell Migration

Bevacizumab (known by the tradename Avastin) is an antibody that binds VEGF and blocks its binding to VEGF receptors on endothelial cells, and is used to treat cancers and other diseases associated with excessive vascular growth. Our previous findings showed enhanced VEGF binding to Avastin in the presence of heparin, indicating that colocalizing heparin with Avastin could enhance VEGF inhibitory activity. Thus, the aim of the present study was to determine if conjugating Avastin and heparin to one another would lead to enhanced anti-VEGF activity. Avastin was conjugated to either biotin or streptavidin, and biotin–heparin was used to bring the two molecules into close proximity via biotin–streptavidin binding. Radioligand binding assays with 125 I-VEGF and cell migration assays using human umbilical vein endothelial cells were used to evaluate the impact of heparin on Avastin binding and activity. We found that bringing Avastin and heparin together, either on a surface or through streptavidin conjugation of Avastin, led to increased VEGF binding compared to that with each molecule alone. The heparin-mediated increase in VEGF binding was also noted at acidic pH where Avastin showed decreased VEGF binding. Conditions where Avastin and heparin showed enhanced VEGF binding also showed reduced VEGF-induced migration of human umbilical vein endothelial cells. These findings suggest design principles for a modified Avastin-based inhibitor of angiogenesis.