Evidence for activation of KIT, PDGFRα, and PDGFRβ receptors in the Ewing sarcoma family of tumors

Abstract

BACKGROUND. The Ewing sarcoma family of tumors (ESFT) is one of the most common malignant neoplasms of children and adolescents, characterized by nonrandom translocations involving the Ewing sarcoma (EWS) gene. Over the years the adoption of intensive multimodality treatment approaches has led to a gradual improvement in the survival of patients with ESFT. The prognosis is still unsatisfactory for high‐risk patients, however, and novel therapeutic approaches are desirable. The aim of the study was to investigate the expression/activation of KIT, PDGFRα, and PDGFRβ receptor tyrosine kinases (RTKs) as potential therapeutic targets in ESFT. METHODS. RNA and proteins were extracted from 20 frozen ESFT specimens to ascertain the state activation of KIT, PDGFRα, and PDGFRβ. RESULTS. No mutations were found, whereas the cognate ligands were detected in all cases by polymerase chain reaction (PCR). The expression and activation of KIT, PDGFRα, and PDGFRβ were confirmed by quantitative PCR, immunohistochemistry, and immunoprecipitation and/or Western blot analysis. In particular, when compared with a protein pool obtained from normal adult tissues, PDGFRβ showed a greater protein expression and/or a stronger phosphorylation signal. CONCLUSIONS. The results are consistent with an autocrine/paracrine loop activation of the KIT, PDGFRα, and PDGFRβ receptors and suggest a rationale for the use of RTK inhibitors, either alone or in combination with chemotherapy. Cancer 2007. © 2007 American Cancer Society.