Abstract 3467: Inhibition of AURKA targets gastrointestinal cancer cells with activated KRAS by inhibiting RPS6KB1
Authors: Chen Zheng , Bishop Lihong W. , Gomaa Ahmed , Lockhart Albert C. , Salaria Safia , Ecsedy Jeffrey , Washington Kay , Beauchamp Robert D. , El-Rifai Wael 
Published: August 2019

Abstract
Background & Aims: Amplifications and mutations of KRAS play essential roles in resistance to chemotherapeutics in luminal gastrointestinal cancers. We investigated the regulation of ribosomal protein S6 kinase B1 (RPS6KB1) by AURKA and the effects of knockdown AURKA or its inhibitions using alisertib, an AURKA inhibitor, in human gastrointestinal cancer cells with amplified or mutant activated forms of KRAS.
Methods: We performed CellTiter-Glo luminescence and clonogenic cell survival assays using 10 upper gastrointestinal or colon cancer cell lines with KRAS mutations or amplifications to test the effects of alisertib, AURKA overexpression or knock down. To determine protein co-localization, we used proximity ligation in situ and immunoprecipitation assays. Nude mice with xenograft tumors grown from HCT116, SNU-601, SW480, or SNU-1 cells were given oral alisertib (40 mg/kg, 5 times/week) for 4 weeks. Tumor samples were collected and analyzed by immunoblots and immunohistochemistry. In addition, immunohistochemistry was performed using AURKA antibody on tissue microarrays containing 151 paraffin-embedded human colon tumors with adjacent normal and adenomas.
Results: AURKA knockdown or inhibition with alisertib reduced Alisertib reduced proliferation and survival of cell lines tested. In addition, we detected a decrease in the levels of phosphorylated RPS6KB1 (at T389), and increased levels of proteins that induce apoptosis including BIM, cleaved PARP, and cleaved caspase 3. Proximity ligation assay and immunoprecipitation indicated that AURKA co-localized and interacted with RPS6KB1, mediating RPS6KB1 phosphorylation at T389. We detected AURKA-dependent phosphorylation of RPS6KB1 in cell lines with mutations in KRAS, but not in cells with wild-type Ras. Administration of alisertib to mice with xenograft tumors significantly reduced tumor volumes (P &lt; .001). These effects were associated with reduced phosphorylation of RPS6KB1 and Ki-67, and increased levels of cleaved caspase 3, in tumor xenograft tissues. The tissue microarrays demonstrated significant overexpression of AURKA in gastrointestinal tumor tissues compared with non-tumor tissues (P=.0003).
Conclusion: Our studies indicate that AURKA can phosphorylate RPS6KB1 in cancer cells with activated KRAS to promote cell proliferation and survival and growth of xenograft tumors in mice. AURKA inhibitors such as alisertib might slow the growth of gastrointestinal tumors with activation of KRAS.
Citation Format: Zheng Chen, Lihong W. Bishop, Ahmed Gomaa, Albert C. Lockhart, Safia Salaria, Jeffrey Ecsedy, Kay Washington, Robert D. Beauchamp, Wael El-Rifai. Inhibition of AURKA targets gastrointestinal cancer cells with activated KRAS by inhibiting RPS6KB1 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 3467.