Abstract 1622: the AKT Inhibitor Reverses Protein Trafficking and Inhibits Tumor Cell Motility of P27-Mislocalized Osteosarcoma Cells

Abstract Osteosarcoma is the most common malignant bone tumor in children. The development of metastasis remains to be the leading cause of death in osteosarcoma. This clinical challenge urges the development of a novel therapeutic strategy to improve the survival of the metastatic patients. mTOR has recently been regarded as a potential target for metastatic osteosarcoma. However, because of its feedback loop in the pathway, it has become clear that inhibition of mTOR alone would not yield effective therapeutics. More importantly, it is still not clear if the mTOR upstream kinases phosphorylate other important molecules that can also promote metastasis. Our lab has recently demonstrated that a vast majority of osteosarcoma cases harbor cytoplasmic mislocalization of p27. p27 is a tumor suppressor gene that regulates normal cell cycle progression when it is localized in the nucleus. We and others have indicated that p27 acquires a new pro-metastatic function in the cytoplasm of osteosarcoma and other tumors. To evaluate if this observation has any therapeutic significance, our lab has created a set of p27 phosphomutants and found that specific phosphorylations (S10 and T198) are important for the pro-metastatic function in the cytoplasm. Furthermore, shRNA-mediated gene silencing experiments showed that knocking down the expression of p27 decreased the motility of metastatic LM7 cells. Since AKT, the upstream kinase of mTOR, has shown to phosphorylate p27, we tested if AKT inhibitors have any effect on the migration/invasion ability of three osteosarcoma cell lines (LM7, MG63 and G292) that harbor the p27 mislocalization. The results showed that both the AKT1/2 inhibitor and the PI3K/mTOR dual inhibitor PP242, but not mTORC1 inhibitor rapamycin, reduced the tumor cell migration/invasion ability. Interestingly, the inhibitors could also reverse the protein trafficking of p27 into the nucleus. These results suggest that the inhibitors may be able to inhibit the pro-metastatic function and restore the cell cycle inhibitory function of p27. Our long-term goal is to develop a precision medicine approach that will ultimately improve the outcome of metastatic osteosarcoma. By targeting the p27 mislocalization, we believe that we will develop a novel and clinically applicable therapeutic strategy that would eradicate metastatic osteosarcoma and improve the outcome of children affected by this tumor. Citation Format: Xiang Chen, Yiting Li, Manjula Nakka, Tsz Kwong Man. The AKT inhibitor reverses protein trafficking and inhibits tumor cell motility of p27-mislocalized osteosarcoma cells. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 1622. doi:10.1158/1538-7445.AM2015-1622