Response of neuroblastoma cells to ionizing radiation: modulation of in vitro invasiveness and angiogenesis of human microvascular endothelial cells.

Neuroblastomas are the most common extra-cranial tumors of childhood and well known for their heterogeneous clinical behavior associated with certain genetic aberrations. Radiation therapy is an important modality for the treatment of high-risk neuroblastomas. In this study, we investigated whether ionizing irradiation modulate the migration and invasiveness of human neuroblastoma cells and expression of proangiogenic molecules known to be involved in tumor progression and metastasis. Irradiation of neuroblastoma cells resulted in increased migration and invasion as measured by spheroid migration and matrigel invasion assay respectively. Zymographic analysis revealed an increase in enzyme activity of MMP-9 and uPA in conditioned medium of irradiated neuroblastoma cells compared with non-irradiated cells. An increase in VEGF levels was also found in lysates of irradiated neuroblastoma cells. The up-regulation of uPA, MMP-9 and VEGF transcripts was also confirmed by RT-PCR analysis. Next, we examined the irradiated tumor cell-mediated modulation of endothelial cell behavior. Conditioned media from irradiated neuroblastoma cells enhanced capillary-like structure formation of microvascular endothelial cells. In a coculture system, irradiation of neuroblastoma cells enhanced endothelial cell invasiveness through Matrigel matrix. Endothelial cells treated with irradiated tumor cell conditioned medium were also analyzed for expression of uPA, MMP-9 and VEGF and compared to cells treated with non-irradiated tumor cell conditioned medium. These findings suggest that the irradiation effects of tumor cells could influence endothelial angiogenesis present in non-irradiated fields.