The role of eukaryotic initiation factor 4E (eIF4E) in osteosarcoma metastasis

The most significant problem for cancer patients is the dissemination of cancer cells and the formation of metastatic disease. Emblematic of the problem is the clinical progression seen in most patients with osteosarcoma, where metastasis to the lung is the most common cause of death. The primary research need in the field is to understand the biology of metastasis in osteosarcoma so as to improve outcomes for future patients. Unraveling the complexity of metastasis demands a focus on new tools, reagents, and biology in order to investigate hypotheses. Accordingly, this body of work introduces an outcome-linked human ostoesarcoma tissue microarray (new tool) used to detect and validate protein biomarkers across a variety of patients and an ex vivo pulmonary metastasis assay (new reagent) that allows real-time assessment of metastatic progression in a relevant microenvironment. Furthermore, cancer cells are believed to efficiently regulate protein translation at specific times and locations in a cell in response to changes in their environment. Preventing the dynamic regulation of these proteins (many of which have been associated with cancer/metastasis) may be an effective treatment strategy in the management of metastasis. Within the process of protein translation the abundance and activation of the mRNA cap-binding phosphoprotein, eukaryotic initiation factor 4E (eIF4E) is considered to be both rate and process limiting. We describe for the first time, the biological role of eIF4E (new biology) in metastatic osteosarcoma. We employed a comparative approach to study the biology of metastasis in osteosarcoma by using tissues and reagents from murine and human osteosarcomas. Using overexpression and knockdown techniques we modulated eIF4E expression in murine and human osteosarcoma cell lines and then evaluated the consequences at various steps within the metastatic cascade in vitro and in vivo. We found that suppression of eIF4E significantly delayed migration and reduced the number and size of colonies that formed in soft agar. Additionally, suppression of eIF4E inhibited spontaneous pulmonary metastases. eIF4E overexpression did not change the phenotype of previously nonmetastatic cells. These results suggest eIF4E may be a necessary, but not sufficient, requirement for metastasis in osteosarcoma. The goals of this research were to utilize these new tools and reagents to identify proteins and/or processes that define the metastatic phenotype of osteosarcoma and to use our newfound understanding of eIF4E in osteosarcoma metastasis to develop novel therapeutic strategies to prevent growth of metastases and improve treatment outcomes for patients.