Abstract
INTRODUCTION: The anti-tumor activity of angiogenesis inhibitors is often limited by the development of resistance to these drugs. Here we establish HIF-1α 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 (2 × 10(6) cells), or cells in which HIF-1α expression had been knocked down with shRNA, into the retroperitoneal space of SCID mice. Treatment of established tumors included bevacizumab (5mg/kg q2wk), sunitinib (40 mg/kg qd), or topotecan (0.5mg/kg qd) alone or in combination for a total of two weeks. RESULTS: NB-1691 xenografts showed no difference in relative growth in HIF-1α knockdowns compared to control tumors (73.33 ± 7.90 vs 79.94 ± 6.15, p=0.528). However, HIF-1α 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-1α appears to be a significant mechanism of resistance to antiangiogenic therapies in neuroblastoma. Suppressing HIF-1α with low-dose topotecan potentiates the effects of the antiangiogenic drugs in a mouse model.