HIF-1α activation mediates resistance to anti-angiogenic therapy in neuroblastoma xenografts

Introduction: The anti-tumor activity of angiogenesis inhibitors is often limited by the development of resistance to these drugs. Here we establish HIF-1 alpha as a major factor in the development of this resistance in neuroblastoma xenografts. Methods: Neuroblastoma xenografts were established by injecting unmodified SKNAS or NB-1691 cells (2x10(6) cells), or cells in which HIF-1 alpha expression had been knocked down with shRNA, into the retroperitoneal space of SCID mice. Treatment of established tumors included bevacizumab (5 mg/kg q2wk), sunitinib (40 mg/kg qd), or topotecan (0.5 mg/kg qd) alone or in combination for a total of two weeks. Results: NB-1691 xenografts showed no difference in relative growth in HIF-1 alpha knockdowns compared to control tumors (73.33+/-7.90 vs 79.94+/-6.15, p=0.528). However, HIF-1 alpha knockdowns demonstrated relative final volumes that were significantly lower than unmodified tumors when both were treated with bevacizumab (35.88+/-4.24 vs 53.57+/-6.61, p=0.0544) or sunitinib (12.46+/-2.59 vs 36.36+/-4.82, p=0.0024). Monotherapy of unmodified xenografts with bevacizumab, sunitinib, or topotecan was largely ineffective. Relative final volumes of NB-1691 xenografts were significantly less in cohorts treated with sunitinib+topotecan (4.78+/-0.77 vs 39.17+/-2.44 [sunitinib alone], p=0.011) and bevacizumab+topotecan (13.63+/-1.55 vs 48.16+/-9.94 [bevacizumab alone], p=0.014). Conclusion: Upregulation of HIF-1 alpha appears to be a significant mechanism of resistance to antiangiogenic therapies in neuroblastoma. Suppressing HIF-1 alpha with low-dose topotecan potentiates the effects of the antiangiogenic drugs in a mouse model. (C) 2013 Elsevier Inc. All rights reserved.