Vascular mimicry and neo-angiogenesis of Ewing Tumors explored based on the identification of angiogenetic target structures

Aims: Metastatic spread in Ewing Tumors (ET) is hematogenous and malignant features have been shown to correlate with hypoxia and angiogenesis. We confirmed the endothelial signature by microarray analysis. This analysis revealed 37 genes that are highly up-regulated or even specifically expressed in ET including genes that may play a central role in angiogenesis of this tumor: Chondromodulin-1 (CHM1), a cartilage glycoprotein with anti-angiogenic activity, is believed to be involved in vasculogenic mimicry of tumor cells. G-protein coupled receptor-64 (GPR64) is an orphan receptor with normal expression restricted to human epididymis, is highly induced in ET. Methods used: The role of CHM1 and GPR64 expression in tumorigenicity and phenotype of Ewing Tumors was analyzed by RNA interference. Summary of results: Down-regulation of CHM1 and GPR64 in ET reduced their ability for contact independent growth in colony forming assays, while plastic adherent proliferation was not affected. Similarly, inhibition of GPR64 expression suppressed the ability of ET to constitute endothelial loops in tube forming assays whereas CHM1 knockdown even increased this capacity. CHM1 and even more GPR64 suppression in ET lines inhibited tumor development in immunodeficient Rag2-/-γC-/- mice. Subsequent microarray analysis of GPR64 knock down in ET revealed a GPR64-mediated regulation of genes with presumed central role in tumor specific angiogenesis. Conclusion: CHM1 and GPR64 up-regulation may shape ET angiogenesis and play a central role in the pathogenesis of this tumor.