P11.30 Special VEGF90kDa form in exosome from GBM cells activates TAZ in endothelial cells to promote angiogenesis and contributes bevacizumab resistance

Abstract

Abstract BACKGROUND Glioblastoma (GBM) has obvious blood vessels proliferation, which is one of the important histological diagnostic criteria. Bevacizumab, VEGF targeted inhibitor, is found inefficient in 2/3 cases after the clinical trial. Here, we found a specific 90kDa form of VEGF (VEGF90K) in exosomes of GBM could activate TAZ expression in endothelial cells to promote angiogenesis, which might also contribute to Bevacizumab treatment resistance. MATERIAL AND METHODS Exosomes were isolated from U87, LN229 GBM cell culture medium and characterized using transmission electron microscopy, nanoparticle analysis, and western blotting. VEGF expression in GBM and TAZ expression in human umbilical vein endothelial cells (HUVEC) are inhibited by shRNA. In vitro migration, proliferation, and tube formation assays were used to assess the angiogenic potential of HUVEC cells. Western blotting was used to analysis TAZ expression in HUVEC. Bevacizumab or exosome inhibitor GW4869 were used separately or together to evaluation their blocking effects on angiogenic functions of GBM cells. RESULTS we found a unique 90kDa form of VEGF (VEGF90K) from exosome of GBM cells could activate TAZ expression in HUVEC cells which correlated with higher levels of cellular migration, proliferation, and tube formation. Knockdown VEGF expression in GBM exosomes or TAZ expression in HUVEC cells could decrease the angiogenic function of GBM cells. GW4869 combine Bevacizumab had significantly inhibited the angiogenic ability of GBM cells in vivo and in vitro. CONCLUSION A specific exosome-associated VEGF from GBM can promote angiogenesis by activating TAZ expression in endothelial cells. Targeted inhibition of exosome secretion can significantly inhibit tumor angiogenesis and restore bevacizumab effect. Our study highlights the unique properties of VEGF in exosome which might help to explore new treatment strategies of GBM.