Integrity of p53 associated pathways determines induction of apoptosis of tumor cells resistant to Aurora-A kinase inhibitors.

We have previously shown that mammary tumorigenesis in MMTV-Aurora-A mice is further enhanced when p53 is inactivated, demonstrating that integrity of p53 pathway determines phenotypes induced by this oncogenic kinase. In this study, we investigated the roles of genes involved in p53 pathway (p53, Puma, p21, Bax, and Chk2) in response to Aurora-A inhibitors, VX680 and MK-8745, and explored whether chemoresistant tumor cells would further undergo apoptosis with other therapeutic agents. Isogenic HCT116 cell lines were treated with VX680 or MK-8745. Cell cycle analysis, apoptosis, and tumorigenesity were studied. Chemoresistant cells were recovered from xenograft, and further induction of apoptosis was studied. Induction of apoptosis and aneuploidy with VX680 is much stronger than MK-8745. Xenograft assay indicates that tumor growth of HCT116 and HCT116 p53(-) cells are strongly inhibited by VX680, while that of other cell types are similarly inhibited by two compounds. Among the established cell lines recovered from xenografts, MK-8745-resistant clones contain elevated phosphorylation of mTOR and Akt. When further treated with inhibitors of both mTOR and Akt, those cells undergo apoptosis. These results indicate that p53-associated pathway plays a crucial role in regulating growth inhibition of tumor cells when treated with Aurora-A inhibitors. Combined treatment with Akt/mTOR inhibitors can further induce apoptosis of Aurora-A tumors.