title: Glioblastoma resistance to anti-VEGF therapy is associated with myeloid cell infiltration, stem cell accumulation, and a mesenchymal phenotype.
abstract: Vascular endothelial growth factor (VEGF) is a critical regulator of angiogenesis. Inhibiting the VEGF-VEGF receptor (R) signal transduction pathway in glioblastoma has recently been shown to delay progression, but the relative benefit and mechanisms of response and failure of anti-VEGF therapy and VEGFR inhibitors are not well understood. The purpose of our study was to evaluate the relative effectiveness of VEGF sequestration and/or VEGFR inhibition on orthotopic tumor growth and the mechanism(s) of treatment resistance. We evaluated, not only, the effects of anti-VEGF therapy (bevacizumab), anti-VEGFR therapy (sunitinib), and the combination on the survival of mice bearing orthotopic gliomas, but also the differential effects of the treatments on tumor vascularity, cellular proliferation, mesenchymal and stem cell markers, and myeloid cell infiltration using flow cytometry and immunohistochemistry. Bevacizumab significantly prolonged survival compared with the control or sunitinib alone. Both antiangiogenic agents initially reduced infiltration of macrophages and tumor vascularity. However, multitargeted VEGFR inhibition, but not VEGF sequestration, rapidly created a vascular gradient and more rapidly induced tumor hypoxia. Re-infiltration of macrophages was associated with the induction of hypoxia. Combination treatment with bevacizumab and sunitinib improved animal survival compared with bevacizumab therapy alone. However, at the time of tumor progression, a significant increase in CD11b(+)/Gr1(+) granulocyte infiltration was observed, and tumors developed aggressive mesenchymal features and increased stem cell marker expression. Collectively, our results demonstrate a more prolonged decrease in tumor vascularity with bevacizumab than with sunitinib, associated with a delay in the development of hypoxia and sustained reduction of infiltrated myeloid cells.
authors.affiliation: Brain Tumor Center, Department of Neuro-Oncology, Genitourinary Medical Oncology, The University of Texas MD Anderson Cancer Center, Houston, Texas 77030, USA.
authors.forename: Yuji
authors.initials: Y
authors.lastname: Piao
authors.forename: Ji
authors.initials: J
authors.lastname: Liang
authors.forename: Lindsay
authors.initials: L
authors.lastname: Holmes
authors.forename: Amado J
authors.initials: AJ
authors.lastname: Zurita
authors.forename: Verlene
authors.initials: V
authors.lastname: Henry
authors.forename: John V
authors.initials: JV
authors.lastname: Heymach
authors.forename: John F
authors.initials: JF
authors.lastname: de Groot
mesh_terms: D000818:Animals; D061067:Antibodies, Monoclonal, Humanized / Q000008:administration & dosage; D000970:Antineoplastic Agents / Q000008:administration & dosage*; D000068258:Bevacizumab; D015687:Cell Hypoxia / Q000187:drug effects; D045744:Cell Line, Tumor; D019008:Drug Resistance, Neoplasm / Q000187:drug effects*; D005434:Flow Cytometry; D005909:Glioblastoma / Q000473:pathology*; D006801:Humans; D007150:Immunohistochemistry; D007211:Indoles / Q000008:administration & dosage; D008648:Mesoderm / Q000187:drug effects / Q000473:pathology; D051379:Mice; D008819:Mice, Nude; D022423:Myeloid Cells / Q000187:drug effects / Q000473:pathology*; D009389:Neovascularization, Pathologic / Q000188:drug therapy / Q000473:pathology; D010641:Phenotype; D011758:Pyrroles / Q000008:administration & dosage; D060888:Real-Time Polymerase Chain Reaction; D040262:Receptors, Vascular Endothelial Growth Factor / Q000037:antagonists & inhibitors; D013234:Stem Cells / Q000187:drug effects / Q000473:pathology*; D000077210:Sunitinib; D059016:Tumor Microenvironment / Q000187:drug effects*; D042461:Vascular Endothelial Growth Factor A / Q000037:antagonists & inhibitors; D023041:Xenograft Model Antitumor Assays
chemical_list: D061067:Antibodies, Monoclonal, Humanized; D000970:Antineoplastic Agents; D007211:Indoles; D011758:Pyrroles; D042461:Vascular Endothelial Growth Factor A; D000068258:Bevacizumab; D040262:Receptors, Vascular Endothelial Growth Factor; D000077210:Sunitinib