Targeted therapies in Ewing's sarcoma

Ewing's sarcoma, the second most common malignant bone tumor, is an extremely aggressive neoplasm, mainly occurring in children and adolescents. Ewing's sarcoma shows a low survival rate despite the adoption of multimodal treatments, including local control of the disease by surgery and/or radiotherapy and multidrug adjuvant chemotherapy. No new effective drugs have been recently described and proposed for sarcomas and, therefore, innovative treatment modalities are very welcome and needed. In this respect, two new entry sites for therapeutic intervention may derive from tailored therapies against the insulin-like growth factor receptor I (IGF-IR) or CD99, a cell surface transmembrane protein highly expressed in Ewing's sarcoma. Neutralizing IGF-IR functions was shown to significantly affect Ewing's sarcoma malignancy. However, it is only recently that new clinically applicable drugs targeting IGF-IR are available and represent a concrete opportunity. Engagement of CD99 induces massive apoptosis of Ewing's sarcoma cells through caspase-independent mechanisms and reduces their malignant potential. Since the apoptotic functions of this molecule are of potential clinical interest, the effects of a tailored therapy triggering CD99 were analyzed against Ewing's sarcoma local tumors and distal (lung and bone) metastases in athymic mice. The effects of targeted therapies against CD99 or IGF-IR were evaluated in combination with conventional chemotherapeutic agents to assess best drug-drug interactions and treatment schedule. Toxic effects of these tailored therapies were also considered to offer the necessary rationale for the application of possible forthcoming clinical trials.