Multiple receptor tyrosine kinases promote the in vitro phenotype of metastatic human osteosarcoma cell lines

The survival rate for osteosarcoma patients with localized disease is 70% and only 25% for patients with metastases. Therefore, novel therapeutic and prognostic tools are needed. In this study, extensive screening and validation strategies identified Axl, EphB2, FGFR2, IGF-1R and Ret as specific receptor tyrosine kinases (RTKs) that are activated and promote the in vitro phenotype of two genetically different metastatic osteosarcoma cell lines. Initial phosphoproteomic screening identified twelve RTKs that were phosphorylated in 143B and/or LM7 metastatic human osteosarcoma cells. A small interfering RNA (siRNA) screen demonstrated that siRNA pools targeting ten of the twelve RTKS inhibited the in vitro phenotype of one or both cell lines. To validate the results, we individually tested the four siRNA duplexes that comprised each of the effective siRNA pools from the initial screen. The pattern of phenotype inhibition replicated the pattern of mRNA knockdown by the individual duplexes for seven of the ten RTKs, indicating the effects are consistent with on-target silencing. Five of those seven RTKs were further validated using independent approaches including neutralizing antibodies (IGF-1R), antisense-mediated knockdown (EphB2, FGFR2, and Ret) or small molecule inhibitors (Axl), indicating that those specific RTKs promote the in vitro behavior of metastatic osteosarcoma cell lines and are potential therapeutic targets for osteosarcoma. Immunohistochemistry demonstrated that Axl is frequently activated in osteosarcoma patient biopsy samples, further supporting our screening and validation methods to identify RTKs that may be valuable targets for novel therapies for osteosarcoma patients.