Bevacizumab and Aflibercept Activate Platelets via FcγRIIa

PURPOSE: To confirm the formation of a drug-growth factor complex and investigate the effects of three VEGF inhibitors in the activation of platelets. METHODS: Growth factors and individual drugs were mixed and incubated. Scattered light intensity was measured by dynamic light scattering (DLS) to monitor the formation of drug-growth factor complex. Blood samples were obtained from 16 subjects (5 AMD patients and 11 healthy volunteers). Platelets obtained from the platelet-rich fraction by centrifugation were washed and resuspended in HEPES/Tyrode buffer. Platelet aggregability was assessed using a light transmission aggregometer in the presence of VEGF inhibitors and growth factors. RESULTS: In DLS study, a mixture of bevacizumab and VEGF-A showed one peak with a relatively gentle slope, indicating a heterogeneous mixture of multimeric bevacizumab-VEGF-A complexes. In aggregation study, no detectable aggregation was observed in the presence of ranibizumab, while significant aggregation was observed in the presence of VEGF-A and bevacizumab in five cases (one AMD patient and four healthy volunteers), VEGF-B and aflibercept in two cases (two volunteers), and placental growth factor (PlGF) and aflibercept in one case (one volunteer). No aggregation was observed when FcγRIIa antibody was added beforehand. CONCLUSIONS: A complex composed of bevacizumab or aflibercept, but not ranibizumab, and growth factors activates platelets via FcγRIIa.