Purpose:
Bevacizumab, a humanized
monoclonal antibody to
VEGF, is used routinely in the treatment of patients with recurrent
glioblastoma (GBM). However, very little is known regarding the effects of
bevacizumab on the cells in the perivascular space in
tumors.Experimental Design: Established orthotopic xenograft and syngeneic models of GBM were used to determine entry of monoclonal anti-
VEGF-A into, and uptake by cells in, the perivascular space. Based on the results, we examined CD133+ cells derived from GBM
tumors in vitro
Bevacizumab internalization, trafficking, and effects on cell survival were analyzed using multilabel confocal microscopy, immunoblotting, and cytotoxicity assays in the presence/absence of inhibitors.Results: In the GBM mouse models, administered anti-mouse-
VEGF-A entered the perivascular
tumor niche and was internalized by Sox2+/CD44+
tumor cells. In the perivascular
tumor cells,
bevacizumab was detected in the recycling compartment or the lysosomes, and increased autophagy was found.
Bevacizumab was internalized rapidly by CD133+/Sox2+-GBM cells in vitro through macropinocytosis with a fraction being trafficked to a recycling compartment, independent of FcRn, and a fraction to lysosomes.
Bevacizumab treatment of CD133+ GBM cells depleted
VEGF-A and induced autophagy thereby improving cell survival. An inhibitor of lysosomal acidification decreased
bevacizumab-induced autophagy and increased cell death. Inhibition of macropinocytosis increased cell death, suggesting macropinocytosis of
bevacizumab promotes CD133+ cell survival.Conclusions: We demonstrate that
bevacizumab is internalized by Sox2+/CD44+-GBM
tumor cells residing in the perivascular
tumor niche. Macropinocytosis of
bevacizumab and trafficking to the lysosomes promotes CD133+ cell survival, as does the autophagy induced by
bevacizumab depletion of
VEGF-A. Clin
Cancer Res; 23(22); 7059-71. ©2017 AACR.