Poster Sessions

C-39

Adam Tai Chi Cheuk

A. Cheuk, J. Taylor, P. Tsang, J. Chung, Y. Song, K. Desai, Y. Yu, Q. Chen, K. Shah, J. Wei, A. Mendoza, C. Khanna, S. Hewitt, G. Merlino, S. Chanock, J. Khan

The identification of activating mutations in the Fibroblast Growth Factor Receptor 4 promotes metastasis in rhabdomyosarcoma

Rhabdomyosarcoma (RMS) is the most common soft tissue sarcoma in childhood in which metastatic disease remains incurable despite aggressive therapy. Fibroblast growth factor receptor 4 (FGFR4) is a tyrosine receptor kinase that regulates survival, motility and angiogenesis, and we have previously reported it to be over expressed in RMS by microarray analysis. We thus hypothesized that over expression or mutations of the FGFR4 gene may lead to a more aggressive phenotype. We found that over expression of the FGFR4 was associated with advanced disease and an significant increase in the overall mortality (p<0.05). We next sequenced all FGFR4 coding exons from RMS tumor DNA samples from over 100 RMS tumors, and found eight missense mutations in the protein tyrosine kinase (PTK) domain. These PTK domain variants represent true mutations as none were present among the 1030 healthy controls. Predictive analysis of the PTK domain mutations suggests they disrupt protein function, which is consistent with their presence adjacent to the ATP binding pocket within FGFR crystal structures. To examine the function of these PTK domain mutations, we transduced either wild type FGFR4 or selected FGFR4 mutants N535K or V550E into two murine RMS cell lines. These cell lines have previously been reported to have low metastatic potential and undetectable Fgfr4 protein levels. Cells expressing the mutated human FGFR4 were to be more resistant to apoptosis and growth arrest in serum free medium. To investigate the metastatic potential of these transfectants, we injected these teansfectants into nude mice through tail vein injection. Intravital videomicroscopy of the lungs demonstrated the persistence of cells expressing the PTK mutations compared to wild type or vector control. In addition after three weeks post intravenous injection of these cell lines, we found mice injected with murine RMS cell lines expressing human FGFR4 with N535K or V550E had significantly more lung metastases. Moreover we found that cell lines harboring these mutations or overexpressing this gene were more sensitive to a FGFR inhibitor PD174074. This is the first report of activating mutations in RMS that promote metastasis. Thus this gene represents a potential target for therapy and the identification mutations may allow for selection of candidates for personalized therapy in patients with metastatic RMS.