Inhibition of Src phosphorylation alters metastatic potential of osteosarcoma in vitro but not in vivo

Purpose: Pulmonary metastasis remains the major cause of mortality in osteosarcoma. Src tyrosine kinase is a key player involved in metastatic pathways in multiple human cancers. c-Src has been shown to be expressed and phosphorylated in osteosarcoma cell lines and inhibiting Src phosphorylation in these cells causes inhibition of the metastatic phenotype in vitro. We studied the effect of inhibition of Src phosphorylation in preventing the growth and development of pulmonary metastases in osteosarcoma. Experimental Design: Dasatinib, a dual Src-Abl kinase inhibitor, was used to study the effect of Src kinase inhibition on proliferation, adhesion, and invasion of osteosarcoma cell lines in vitro and in preventing the development of pulmonary metastases in a spontaneously metastatic mouse model. Results: In vitro, phosphorylation of Src and its downstream signaling molecules such as focal adhesion kinase, Crk-associated substrate, and c-Jun was inhibited at nanomolar concentrations of dasatinib. Dasatinib was not cytotoxic against the osteosarcoma cells with the IC₅₀ ranging from 10 to 20 μmol/L but effectively inhibited the adhesion and migration of osteosarcoma cells at 10 to 100 nmol/L. However, in vivo, dasatinib did not inhibit the development of pulmonary metastases despite complete inhibition of Src phosphorylation in the primary tumors. No effect was seen in the primary tumor growth and the degree of apoptosis. Conclusions: These results suggest that Src kinase activation might not be the primary pathway involved in the development of pulmonary metastases in osteosarcoma.