Abstract 3008: IGF2 mRNA binding protein 1 drives growth, metastasis and chemoresistance in osteosarcoma.

Proceedings: AACR 104th Annual Meeting 2013; Apr 6-10, 2013; Washington, DC Osteosarcoma (OSA) is the most common bone tumor in children arising in the metaphyseal regions of the appendicular skeleton and frequently metastasizing to the lungs. Standard treatment for OSA of surgical resection with neoadjuvant and adjuvant chemotherapy using multi-agent dose intensive therapy has resulted in survival rates of 75%, however for patients with metastasis at diagnosis, the survival rate is only 20%. Consequently, increased understanding of the mechanisms that contribute to metastasis and resistance to therapy is needed. Unfortunately, the availability of OSA samples for study is extremely limited. However, over 10,000 canine patients spontaneously develop OSA annually and canine tumors share common histological features, genetic mutations and gene expression profiles with human OSA. To identify factors that contribute to metastasis and chemotherapeutic resistance of OSA, we assessed the gene expression signatures of normal bone and groups of primary canine OSA tumors surgically resected from dogs with short and long disease free intervals (DFI) following standard treatment of amputation and therapy with doxorubicin or platinum-based drugs. Since the average DFI following treatment in canine osteosarcoma is approximately 200 days, these groups included tumors from dogs with DFI 300 days. We identified IGF2 mRNA binding protein 1 (IGF2BP1) as a gene with elevated expression in osteosarcomas from patients with a DFI 300 group (7-fold, p=0.047) and normal bone (920-fold, p<0.001). IGF2BP1 is an oncofetal protein that binds multiple mRNA targets to regulate their nuclear transport, stability, translation and subcellular localization. In five human OSA cell lines we measured an average 14-fold increase in IGF2BP1 mRNA transcripts compared to normal human osteoblasts. More importantly, we measured elevated mRNA transcripts (five-fold, p=0.0368) and protein levels (seven-fold) in the MG63.2 cell line, a metastatic variant of the MG63 human OSA cell line, implicating IGF2BP1 in metastasis of osteosarcoma. IGF2BP1 knockdown in shRNA-expressing MG63.2 clones reduced cell invasion by 42% (p<0.05). In addition, IGF2BP1 knockdown in MG63.2 cells resulted in a three-fold (p<0.001) decrease in cellular proliferation compared to cells stably expressing a non-targeted shRNA construct. A similar experiment was performed in vivo using a subcutaneous model in nude mice (n=5/group) where the IGF2BP1 knockdown tumors from two independent shRNA constructs displayed significantly delayed tumor appearance and reduced tumor volume compared to control at days 9 (p<0.05), 12 and 14 (p<0.001) following tumor cell inoculation. Finally, IGF2BP1 knockdown resulted in a two-fold increase in doxorubicin sensitivity in MG63.2 cells (95% confidence interval). Overall, these data suggest IGF2BP1 drives OSA growth, metastasis and chemotherapeutic resistance. Citation Format: Brian T. Kalet, Liza E. O'Donoghue, Dawn L. Duval. IGF2 mRNA binding protein 1 drives growth, metastasis and chemoresistance in osteosarcoma. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 3008. doi:10.1158/1538-7445.AM2013-3008