Of clinically importance is that this kinase is frequently overexpressed in varieties of human cancers. Several in vitro experiments support that elevated expression of Aurora-A is oncogenic since transfection of fibroblasts with Aurora-A results in cell transformation. These observations provide foundation that inhibition of this kinase could A 1070722 contribute to tumor suppression. We have previously generated transgenic mice, in which Aurora-A is highly expressed in mammary gland. Although Aurora-A causes cell transformation rapidly in vitro, tumorigenesis in these mice is not frequent and its latency is quite long. These results strongly suggest that increased levels of Aurora- A are not an immediate driving force, but additional oncogenic pathway needs to be activated for tumor development. In fact, immunohistochemistry analysis of mammary tumors developed in our mice indicated that phosphorylation of Akt and mTOR is increased, suggesting that activation of Akt/mTOR pathway collaborates with Aurora-A, leading to cell transformation. Roles of Akt/mTOR pathway in Aurora-A transformation have also been implicated from our and other��s previous studies. Intrinsic roles of Akt/mTOR pathway in cell proliferation have also been well illustrated previously. We discovered that Aurora-A cells contain phosphorylated Akt/mTOR demonstrated after long-term cell culture, compared to those in short term cell AC 4 culture and that those Akt/mTOR active cells show much aggressive colony forming abilities than those without Akt/mTOR phosphorylation. Roles of p53 pathway in Akt/mTOR activation in Aurora-A��s transformation are further demonstrated in the current studies. Thus, Akt and mTOR are phosphorylated in variants of HCT116 cell lines that are resistant to VX680 or MK- 8745 in xenograft assay. Importantly, these cells undergo apoptosis when treated with Akt/mTOR inhibitors. These results suggest that combination therapy with inhibitors of Aurora-A, mTOR and Akt could inhibit Aurora-A tumor malignancy, although integrity of p53 pathway is crucial for induction of apoptosis. Although our data indicates functional collaboration between Aurora-A and Akt/mTOR, the mechanism of how phosphorylation of Akt and mTOR is induced in tumors remains to be elucidated. It is possible that Akt/mTOR pathway become activated in the course of tumorigenesis and provides growth advantage to Aurora-A cells in vivo. However, it is also possible that original pool of Aurora-A cells are heterogeneous and that Akt and mTOR are already activated in a small fraction of cells in this pool. In that sense, these small numbers of Aurora-A positive cells containing activated Akt/mTOR could survive when VX680 or MK-8745 is provided into mice. This hypothesis that cells�� sensitivities to Aurora-A inhibitors is determined by activities of Akt/mTOR is supported by our previous results indicating that Aurora-A inhibitors cause apoptosis only when Akt/mTOR pathway is not activated.