Abstract 633: Tumor cell resistance mechanisms to aurora kinase inhibitors

Abstract Aurora kinase inhibitors are being developed as anti-cancer drugs and more than 10 small molecules are currently undergoing clinical trials. CYC116, an Aurora kinase inhibitor, discovered and developed by Cyclacel Ltd. is currently in phase I clinical trial in patients with advanced solid tumors. CYC116 showed significant anti-proliferative activity in preclinical studies. However tumor cell resistance mechanisms towards this Aurora kinase inhibitor have not been yet established. We developed several HCT116 p53 wild-type and HCT116 p53 null resistant clones towards CYC116 by exposing the cells to high drug concentrations. In order to compare resistance mechanisms, another Aurora kinase inhibitor, ZM447439, was used as a reference compound. Here we present the preliminary data characterizing CYC116-resistant clones. In MTT cytotoxicity assays all the clones showed CYC116 resistance and cross resistance to other Aurora kinase inhibitors, and to some anticancer drugs, which suggest a multidrug resistance phenotype. However the degree of resistance is variable between the clones. All CYC116-resistant clones irrespective of their p53 background became tetraploid. This was not observed for the ZM447439-resistant clones. PH3 (ser10), an Aurora kinase B phosphorylation site, was not inhibited in all resistant clones, suggesting that this kinase is still active. DNA and RNA synthesis were also not inhibited in these clones. Flow cytometry based studies revealed no up regulation of PgP drug transporter in all CYC116-resistant clones, whereas two HCT116 p53 null ZM447439-resistant clones displayed an increase in PgP levels. Up regulation of MRP was only detected in one HCT116 p53 null CYC116-resistant clone, which expressed high levels of this drug transporter. From the initial data it is obvious that there were no common resistance mechanisms towards the studied Aurora kinase inhibitors. We are continuing the characterization of these resistant clones, which include microarray gene expression studies, 2-D electrophoresis and mass spectrometry studies, Aurora A and B sequencing (target mutations), and other drug transporter (e.g. BCRP & LRP) expression studies. These will further help the understanding of the molecular basis of acquired tumor resistance to CYC116 and will aid us in predicting the clinical response as well as in designing combination treatment regimens for overcoming resistance hence furthering clinical development. This work was kindly supported by the Czech ministry of education. Grant number: MSM6198959216 and LC07017. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 633.