Neuroblastoma, the most common extracranial solid tumor of children, arises from the sympathetic nervous system, is characterized by extensive genetic, morphologic, and clinical heterogeneity and presents as benign to highly aggressive forms in various stages. Hypoxia has been linked to tumor progression and increased malignancy. Like the most common malignant solid tumors, neuroblastomas contain zones of chronic or acute hypoxia reflecting poor oxygenation. Transient hypoxia and subsequent reoxygenation are common phenomena in solid tumors that greatly influence the outcome of therapies. Radiotherapy is commonly applied in higher stage neuroblastoma patients with MYCN oncogene amplification and metastases. The present study focuses how intermittent hypoxia modulates the effects of radiation treatment in human neuroblastoma cells. Intermittent hypoxia-conditioned cells were derived from human neuroblastoma cells that were exposed to 10 cycles of hypoxia and reoxygenation. Intermittent hypoxia stabilized the expression of HIF-l α in neuroblastoma cells. Cell survival to radiation treatment was assessed by the colony formation assay. The hypoxia-conditioned neuroblastoma cells exhibit increased survival to irradiation treatment compared with parental cells suggesting alterations in apoptotic pathways. The expression of selected genes associated with DNA damage as well as genes of BCL-2 family and caspase family were studied in parental and hypoxia-conditioned neuroblastoma cells in response to radiation treatment. Radiation caused an increase in the levels of proapoptotic proteins Bax, Bad, Bid and cleaved products of caspase-3 and −9 in parental tumor cells. Similar observations were not obtained in hypoxia-conditioned neuroblastoma cells upon radiation treatment demonstrating their increased radioresistance characteristics. We also assessed how hypoxia modulates radiation-induced in vitro angiogenesis. Human microvascular endothelial cells were exposed to conditioned medium from irradiated parental and irradiated hypoxia-conditioned tumor cells and capillary-like structure formation was studied. Further, tumor cell conditioned medium was also evaluated in chorioallantoic membrane assay for its angiogenic capabilities. These results suggest that intermittent hypoxia-conditioned neuroblastoma cells demonstrate increased survival, resistance to induction of apoptosis and angiogenic capabilities to radiation treatment.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 510.