Lack of antitumor activity of recombinant endostatin in a human neuroblastoma xenograft model

Patients with metastatic neuroblastoma are rarely curable with currently av ailable therapy, and the search for new treatment options, which include th e use of inhibitors of tumor angiogenesis, is warranted. Here, we have eval uated the efficacy of one of the most promising natural inhibitors of angio genesis described to date, endostatin, in a human neuroblastoma xenograft m odel in nude mice. Murine endostatin cDNA was cloned in a bacterial express ion vector, expressed as a polyHis-Endostatin fusion protein and purified o n Ni2+-NTA beads. The in vitro activity of soluble endostatin was confirmed on bovine capillary endothelial cells and human umbilical vein endothelial cells. The human neuroblastoma cell line SKNAS was injected subcutaneously in the flank of nude mice and administration of the recombinant angiogenes is inhibitor started when tumors reached the size of 100 mum(3). Twenty mg/ kg of recombinant precipitated endostatin or PBS was subcutaneously injecte d daily for 12 days. Serum endostatin levels were measured using a competit ive enzyme immunoassay. Tumor growth was only slowed down in endostatin-tre ated mice when compared to control mice, and no statistically significant d ifference in serum levels of endostatin was observed between endostatin-tre ated and control groups. The lack of correlation between serum concentratio n and tumor response raises concern regarding the mechanism of action of en dostatin.