Abstract A156: Mechanisms of resistance to Aurora kinase B inhibitors in leukemia: Development and characterization of in vitro models

Abstract

Abstract Aurora kinase inhibitors are generating great interest as new mitosis targeting drugs in cancer chemotherapy. Whilst these new agents are progressing through clinical trials against both solid and haematological malignancies, knowledge of the molecular factors that influence sensitivity and resistance remains limited. Development of optimal treatment modalities and the design of next generation Aurora inhibitors requires an understanding of processes and pathways of drug sensitivity mechanisms. In this study we report the development and characterisation of an in vitro derived leukaemia model of resistance to the Aurora B inhibitor ZM447439. CCRF-CEM cells were selected for resistance in 4uM ZM447439 and designated CEM/AKB4 cells. Cytotoxicity assays showed that CEM/AKB4 cells were 13.2 fold resistant to ZM44739 compared to parental CEM cells. Resistance was not associated with the multi-drug resistance phenotype and CEM/AKB4 cells showed no cross-resistance to a number of tubulin-targeting mitotic poisons or DNA-damaging agents. The CEM/AKB4 cells remained sensitive to the Aurora kinase A inhibitor, ENMD-2076. Cell cycle analysis revealed that exposure of CEM cells to ZM447439 (0.4–4 uM) caused extensive cell cycle disruption and cell death. In contrast, the cell cycle profiles of CEM/AKB4 cells at the same concentrations of drug were barely altered. Full length sequencing of the Aurora B gene revealed a single point mutation in the kinase domain corresponding to a G160E amino acid substitution. Molecular modelling of drug binding in Aurora B containing this mutation suggested that resistance is mediated by the glutamate substitution preventing formation of an active binding motif for Aurora B inhibitors. Moreover molecular docking of an Aurora B inhibitor with a novel binding motif was unchanged in the mutant enzyme suggesting this drug may abrogate resistance. Aurora kinase B inhibitor resistant cells are a valuable tool for identifying resistance mechanisms and the design of new kinase inhibitors active against Aurora kinase B mutations. Citation Information: Mol Cancer Ther 2009;8(12 Suppl):A156.