Abstract 5226: Glioma stem cells internalize perivascular bevacizumab via a non-canonical pathway and target it for recycling or degradation

Abstract

Abstract Antiangiogenic therapy shows great promise for treatment of cancer. Bevacizumab is a humanized mAb that blocks VEGF-A, thereby inhibiting angiogenesis. It has received FDA approval for patients with recurrent glioblastoma (GBM); however, approximately 30% of patients are non-responsive and the underlying mechanism for the lack of response is not known. It has been assumed that Bevacizumab solely targets circulating VEGF-A; however, VEGF-A found in the perivascular space of GBM tumors could also be an important target. We hypothesized that Bevacizumab is transcytosed across brain endothelial cells (ECs), gains access to the perivascular niche containing glioma stem cells (GSCs), and that differences in GSC endocytosis and trafficking of Bevacizumab to either a recycling or degradation compartment determines a patients’ response. We found that Bevacizumab is internalized by normal and tumor-isolated brain ECs in a time-dependent manner. ECs transcytose 20% of Bevacizumab after 30 minutes, and 40% after 120 minutes. Importantly, we found that 95% of GSCs internalize Bevacizumab within 30 minutes. Internalized Bevacizumab in GSCs can be recycled to the extracellular space via a Rab4+ fast recycling compartment, or degraded via trafficking to the LAMP1+ compartment (late endosome/lysosome). Furthermore, Bevacizumab internalization in GSCs was partially inhibited by a macropinocytosis inhibitor (EIPA) suggesting macropinocytosis is one mechanism of internalization. GSCs do not internalize Bevacizumab via the canonical IgG internalization pathway since they do not express the neonatal Fc Receptor (FcRn). Supporting our in vitro data, we found a gradient of Bevacizumab extending from the vessel into the tumor in an orthotopic xenograft mouse model of GBM administered Bevacizumab, and Bevacizumab was readily detected within perivascular tumor cells. Our data suggest that the transcytosis of Bevacizumab by brain and tumor-associated ECs, and the endocytosis and trafficking of Bevacizumab by perivascular GSCs influences Bevacizumab effectiveness in patients with GBM. Citation Format: Gaelle Muller-Greven, Cathleen Carlin, Justin Lathia, Richard Prayson, Manmeet Ahluwalia, Steven Toms, Markus Bredel, Jeremy Rich, Petra Hamerlik, Candece L. Gladson. Glioma stem cells internalize perivascular bevacizumab via a non-canonical pathway and target it for recycling or degradation. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 5226. doi:10.1158/1538-7445.AM2015-5226