Abstract A261: In vitro characterization of AMG 900, an orally active small molecule inhibitor of aurora kinases in phase 1 clinical trials

Abstract

Abstract Background: The aurora family of serine-threonine kinases (Aurora-A, -B, -C) regulate cell-cycle progression in mammalian cells. Aurora kinases A and B are essential for proper chromosome congression, segregation, and cytokinesis during mitosis, whereas aurora kinase C function appears restricted to male meiosis. Aurora kinase B is responsible for the direct phosphorylation of histone H3 on serine-10 (p-histone H3). Aurora kinase A and B expression is elevated in a variety of human cancers and is associated with advanced clinical staging and poor prognosis. The emergence of aurora kinases as key mitotic regulators and their potential role in tumorigenesis has focused substantial interest in developing selective small molecule inhibitors for the treatment of human cancers. Objective: The aim of this study was to characterize the in vitro effects of AMG 900 in tumor cell lines, including cell lines resistant to paclitaxel and three well-characterized aurora kinase inhibitors. Results: AMG 900 is a novel ATP competitive small molecule inhibitor that is highly potent and selective for aurora kinases A, B, and C. In cells, AMG 900 inhibits autophosphorylation of aurora kinases A and B as well as the phosphorylation of histone H3. The predominant cellular response of tumor cells to AMG 900 treatment is aborted cell division without a mitotic arrest, which leads to endoreduplication and cell death. The effect of AMG 900 was tested in a panel of 26 tumor cell lines to evaluate its potential to inhibit cell proliferation across multiple tumor types. AMG 900 inhibited the proliferation of tumor cell lines at low nanomolar concentrations (EC50 values 1–6 nM). Importantly, AMG 900 was equally potent against multidrugresistant (MDR) cell lines expressing ATP-binding cassette transporters (P-gp and BCRP1), whereas paclitaxel and three aurora kinase inhibitors (AZD1152, MK-0457, and PHA-739358) showed a loss of potency in these MDR-positive cell lines compared with matched parental cell lines. To further investigate potential mechanisms of resistance, an HCT116 cell line was adapted to grow in the presence of AZD1152, a selective inhibitor of aurora kinase B. The resulting AZD1152-resistant HCT116 subline harbors a mutation in one allele of the aurora kinase B gene (W221L substitution) and was negative for P-gp and BCRP1 expression. AMG 900 induced an accumulation of cells with ≥4N DNA content (EC50 value 5 nM) and inhibited colony formation in this AZD1152-resistant HCT116 subline. Conclusion: To our knowledge, AMG 900 is the first described inhibitor of aurora kinases A, B, and C that has uniform in vitro potency in MDR-positive tumor cell lines. AMG 900 is currently undergoing phase 1 clinical evaluation in patients with advanced solid tumors. Citation Information: Mol Cancer Ther 2009;8(12 Suppl):A261.