Abstract LB-340: Mechanism of bevacizumab internalization and fate by brain endothelial cells .

Abstract

Abstract Antiangiogenic immunotherapy shows great promise for treatment of malignancies, including cancer. Bevacizumab is a humanized monoclonal antibody that inactivates vascular endothelial growth factor-A (VEGF-A), thereby inhibiting angiogenesis. It has received FDA approval for patients with recurrent glioblastoma (GBM); however, more than 30% of patients are non-responsive. The internalization and fate of bevacizumab in endothelial cells (ECs) may play a critical role in the response to therapy, i.e., bevacizumab may be degraded, recycled to the vessel lumen, or transcytosed to the sub-basal EC where tumor cell VEGF-A is found. We examined the internalization of bevacizumab by normal brain ECs in different conditions and found that internalization increased in a time-dependent manner (30 min - 24 hrs). Epidermal growth factor (EGF) stimulated internalization, suggesting bevacizumab enters the cells by an endocytic pathway that is induced by growth factors, such as macropinocytosis. Also, internalized bevacizumab was compartmentalized into vesicles that in part co-localized with the EGF receptor. Treatment with Amiloride (inhibitor of macropinocytosis) decreased the number of bevacizumab-containing vesicles per cell, suggesting macropinocytosis may be one mechanism of internalization. Treatment with Bafilomycin A1 (inhibitor of lysosomal acidification) caused accumulation of bevacizumab, suggesting one fate is lysosomal degradation. Ongoing experiments will determine the endocytic compartment(s) containing bevacizumab, its trafficking, and whether it is transcytosed across normal brain and tumor-associated ECs. Understanding the mechanism of internalization and trafficking of bevacizumab in brain ECs will positively impact the design and modification of monoclonal antibody therapy for GBM patients and for other cancers. Citation Format: Gaelle M. Muller-Greven, Cathleen Carlin, Candece L. Gladson. Mechanism of bevacizumab internalization and fate by brain endothelial cells . [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr LB-340. doi:10.1158/1538-7445.AM2013-LB-340