Cellular mechanisms of organ-specific metastasis of Ewing's sarcoma

Abstract

Ewing's sarcoma is the second most common bone tumour in children and adolescents. The prognosis is mainly influenced by the occurrence of primary metastasis. Although great improvement in treatment has been achieved, still only 2/3 of patients with localized disease can be cured. Furthermore, the 3-year event free survival in patients with lung metastases is only ~50%, and is less than 20% in patients with bony metastases. Metastatic models of Ewing’s sarcoma developed in this study using cell lines in immunocompromised mice show a pattern of disease spread similar to that found in patients, providing a suitable system for studying the metastatic process likely occurring in the course of Ewing’s sarcoma. The comparison of microarray gene expression patterns revealed interesting candidate genes for diagnosis and identified putative metastasis-specific targets that might be exploited in the development of new treatment approaches. However, it will be necessary to additionally analyse these patterns in primary material. One gene that formerly has been shown to play a role in the metastasis to bones in a variety of cancer types is CXCR4, which encodes for the cytokine receptor of CXCL12 (SDF-1), and which plays a role in the metastasis to bones in a variety of other cancer types. As Ewing’s sarcoma cells express CXCR4, a shRNA vector was constructed, transduced and stably expressed to investigate the role of the CXCR4/CXCL12 axis in Ewing’s sarcoma cells via RNA interference. This stability provides the possibility of an in vitro and furthermore an in vivo use for investigations. In order to investigate the biology of bone malignancy and especially the interaction of tumour cells with cells of the microenvironment of the bone directly, an orthotopic model for Ewing’s sarcoma was developed. Additionally, osteosarcoma as a further primary bone sarcoma and prostate carcinoma as a cancer type with frequent bone metastases were tested in this model. The previously described technique of intrafemoral transplantation was used in this model. Using small animal imaging techniques such as nano computed tomography and magnetic resonance imaging in combination with histology it could be shown that the transplanted cells led to the development of orthotopic tumours presenting a comparable picture to the clinical situation. This model will be further used for research projects performed in the Northern Institute for Cancer Research on the effectiveness of drugs targeting Ewing’s sarcoma cells.