Angiopoietin-2 inhibition using siRNA or the peptide antagonist L1–10 results in antitumor activity in human neuroblastoma

Abstract

The angiopoietin/Tie-2 system has been identified as a key role player in tumor angiogenesis. We investigated whether angiopoietin-2 could be a promising target in human neuroblastoma. Angiopoietin-2 down-regulation by siRNA or shRNA was evaluated in vitro in Kelly cells. Angiopoietin-2 shRNA-transfected Kelly cells were tested in a chorioallantoic membrane (CAM) assay to evaluate tumor growth and microvessel density. The effects of L1-10, a peptide-Fc fusion molecule blocking angiopoietin-2/Tie-2 interaction, administered 3 times/week were assessed in a murine neuroblastoma xenograft model. Angiopoietin-2 down-regulation by siRNA or shRNA in Kelly cells inhibited cell proliferation and migration. In vivo growth and microvessel density of angiopoietin-2 shRNA-transfected Kelly cells in the CAM assay were reduced. Therapy of advanced tumors with L1-10 did not stop tumor progression. However, starting L1-10 treatment at the same time as neuroblastoma cell injection significantly inhibited tumor growth (vehicule: 903±160mm(3); L1-10: 270±152mm(3) after 26days; P<0.05). Microvessel density was reduced in both L1-10-treated tumors, whereas expression of angiopoietin-2 and VEGF-A did not change. This first demonstration of beneficial angiopoietin-2 inhibition in neuroblastoma offers an additional approach for future therapy strategies, especially by using L1-10 in the setting of minimal residual disease.