ABSTRACT
PURPOSE: Inhibition of vascular endothelial growth factor (VEGF) may effect transient "normalization" of tumor vasculature by pruning immature vessels, resulting in improved tumor perfusion and oxygenation. This may improve the efficacy of adjuvant ionizing radiation (IR). We tested this hypothesis using bevacizumab, an anti-VEGF antibody, in rhabdomyosarcoma (RMS) xenografts. METHODS: Mice bearing orthotopic alveolar RMS xenografts were treated with a single dose of bevacizumab, IR, or a combination of the two on different schedules. Tumors were then evaluated for changes in microvessel density, vessel maturity, vessel permeability, intratumoral oxygenation, as well as altered growth. RESULTS: After bevacizumab treatment, a significant decrease in tumor microvessel density and a significant increase in tumor vessel maturity, defined as the ratio of pericytes to endothelial cells, were observed, suggesting pruning of immature vessels lacking pericytes. Tumor vessel permeability was also significantly decreased and intratumoral oxygen tension increased 2 and 5 days after bevacizumab owing to a transient improvement in tumor perfusion. Treatment with IR 2 or 5 days after bevacizumab resulted in the greatest antitumor activity. CONCLUSION: Our findings support the hypothesis that VEGF inhibition with bevacizumab transiently normalizes the dysfunctional vasculature of RMS xenografts, improving tumor oxygenation and increasing tumor sensitivity to adjuvant IR.
Subject(s)
Blood Vessels/pathology , Muscle Neoplasms/blood supply , Neoplasms, Experimental/blood supply , Neovascularization, Physiologic/physiology , Rhabdomyosarcoma, Alveolar/blood supply , Actins/metabolism , Animals , Antibodies, Monoclonal/toxicity , Antibodies, Monoclonal, Humanized , Antigens, CD34/metabolism , Bevacizumab , Blood Vessels/drug effects , Blood Vessels/radiation effects , Capillary Permeability/radiation effects , Disease Progression , Humans , Immunohistochemistry , Mice , Mice, SCID , Muscle Neoplasms/metabolism , Muscle Neoplasms/radiotherapy , Neoplasms, Experimental/metabolism , Neoplasms, Experimental/radiotherapy , Neovascularization, Physiologic/radiation effects , Oxygen Consumption/drug effects , Oxygen Consumption/radiation effects , Radiation, Ionizing , Radiotherapy, Adjuvant , Rhabdomyosarcoma, Alveolar/metabolism , Rhabdomyosarcoma, Alveolar/radiotherapy , Transplantation, Heterologous , Vascular Endothelial Growth Factor A/antagonists & inhibitorsABSTRACT
BACKGROUND: We hypothesized that vascular endothelial growth factor (VEGF) contributes to autocrine stimulation of neuroblastoma and that inhibition of its signaling pathway contributes to the anticancer activity of bevacizumab, an anti-VEGF monoclonal antibody. METHODS: For in vitro studies, 2 neuroblastoma cell lines, CHLA-255 and NB1691, were treated with VEGF+/-bevacizumab. For in vivo studies, disseminated neuroblastoma was established by intravenous administration of luciferase-expressing tumor cells in SCID mice prior to bevacizumab treatment. RESULTS: Exogenous VEGF increased cell counts after 48 h (NB1691: 58,878 +/- 8279 vs 137,500 +/- 13,108 cells, P < .001; CHLA: 1.56 x 10(6) +/- 866 vs 1.81 x 10(6) +/- 2550 cells, P <.001); the addition of bevacizumab abrogated this stimulation. In vivo, mice with disseminated disease treated twice weekly with intraperitoneal bevacizumab had a decreased tumor burden at day 14 and prolonged survival (NB1691: 50 +/- 2 vs 43 +/- 2 days, P < .001; CHLA: 53 +/- 3 vs 42 +/- 1 days, P = .006). Interestingly, VEGF and basic fibroblast growth factor expression was increased in treated NB1691 tumors, which likely occurred in response to VEGF signaling inhibition. CONCLUSION: Our results suggest that VEGF has a role in neuroblastoma autocrine signaling. Maintenance therapy with bevacizumab may be useful for disease suppression after maximal cytoreductive therapy; however, upregulation of proangiogenic factors may provide resistance to this approach, which suggests that maximal antitumor efficacy may require combination therapy.
Subject(s)
Angiogenesis Inhibitors/therapeutic use , Antibodies, Monoclonal/therapeutic use , Antineoplastic Agents/therapeutic use , Neuroblastoma/pathology , Angiogenesis Inhibitors/pharmacology , Animals , Antibodies, Monoclonal/pharmacology , Antibodies, Monoclonal, Humanized , Antineoplastic Agents/pharmacology , Autocrine Communication , Bevacizumab , Cell Line, Tumor , Cell Proliferation/drug effects , Disease Progression , Fibroblast Growth Factor 2/metabolism , Humans , Mice , Mice, SCID , Neuroblastoma/drug therapy , Receptors, Vascular Endothelial Growth Factor/metabolism , Signal Transduction , Tumor Cells, Cultured , Vascular Endothelial Growth Factor A/immunology , Vascular Endothelial Growth Factor A/metabolism , Vascular Endothelial Growth Factor A/pharmacologyABSTRACT
BACKGROUND: Bortezomib is a proteasome inhibitor with pleiotropic antitumor activity. Here we investigate the antiangiogenic and antitumor efficacy of bortezomib against neuroblastoma both in vitro and in a murine model of localized and disseminated disease. METHODS: In vitro activity of bortezomib was assessed by evaluating its effect on cell proliferation and cell cycle status. Localized tumor burden was followed with caliper measurements and total-body bioluminescence in mice with disseminated disease. The antiangiogenic activity was evaluated with immunohistochemistry and human vascular endothelial growth factor (VEGF) enzyme-linked immunosorbent assay on tumor protein extracts. RESULTS: Bortezomib treatment resulted in dose and time-dependent decreases in cell proliferation and resulted in cell cycle arrest. In vivo, bortezomib restricted tumor growth in a model of localized disease and decreased bioluminescence in mice with disseminated disease. That decreased bioluminescence reflected decreased tumor burden was confirmed at necropsy by assessing disease in specific organs. In addition, treatment resulted in a decrease in intratumoral vessel counts and reduced tumor VEGF expression. CONCLUSION: Bortezomib shows significant activity against neuroblastoma in vitro, and it inhibits tumor growth and angiogenesis in vivo. These results suggest that clinical studies of bortezomib are warranted for the treatment of this difficult disease.
