Systems biology analysis of a novel Aurora kinase inhibitor: CYC116
Authors: Christophe Chassagnole, Eric Fernandez, Frederic Scaerou, Christopher Snell, Daniella Zheleva, David Glover, Robert Jackson, David Fell
Journal: Cancer Research (2008)

1645    Introduction  Aurora kinases are known to play a role in mitotic entry, progression and exit. These kinases represent attractive targets for anticancer drug development because they regulate both genomic integrity and cell cycle progression in cancer.  Cyclacel and Physiomics entered a collaboration to model the action of Aurora kinase (AK) inhibitors, focusing on describing the effects of the dual Aurora A and B inhibitor CYC116 and other Cyclacel inhibitors on cell cycle progression. Using both published data and data supplied by Cyclacel for its proprietary compounds, a dynamic and accurate cell cycle simulation was extended to include the key actions of AKs, in order to simulate the various aspects of their inhibition. Whereas AK-A regulates centrosome cohesion and separation, AK-B is responsible for maintaining active the spindle checkpoint (SCP) and triggering cytokinesis.   Histone H3 as a biomarker of AKB inhibition   We initially focused on the effects of AK-B and polyploidy. One of the best known targets of AK-B is Histone H3 (HisH3), which participates to chromosome condensation in prophase. We calibrated the cell cycle model with published Vertex VX-680 and proprietary CYC116 data so that the level of phosphorylation of HisH3, controlled by AK-B, triggers polyploidy in A549 cells. The model was then able to predict the experimental HisH3 phosphorylation IC50 for a series of Cyclacel compounds from the measured Ki for AK-A and AK-B.  These results confirm that HisH3 is a good biomarker of AK-B activity and polyploid status, as well as validate the accuracy of the model.   Cell population simulation and VirtualFACS  SystemCell® technology is a cell population simulator which can be used to simulate the fate of a cancer cell population under the effect of various drugs (US patent: 6,446,055; www.physiomics-plc.com).   SystemCell® technology was used to analyze the effects of the inhibition of AK-A and AK-B on a culture of A549 cancer cells. We have been able to reproduce the effects of various AK inhibitor compounds, in particular CYC116, and to predict the effect of others in a wide concentration range.  SystemCell® technology was extended in order to study the effect of combining Nocodazole and AK inhibitors. This lead to simulating the mitotic slippage effect, i.e. exit from mitosis after a fixed period due to degradation of cyclin B. The cell cycle model was able to predict in advance the mitotic slippage mechanism which is due to an incomplete inactivation of APC-CDC20 complex by the SCP. The model was able to reproduce the results obtained for two AK inhibitors. CYC116 triggers a SCP override (faster mitotic slippage) due to the AK-B inhibition for this range of inhibitor concentrations, whereas a “pure” AK-A inhibitor shows no effects on mitotic slippage.  Systems biology modeling is a useful method to predict the cell cycle and cell population outcomes which may result from inhibiting cell cycle kinases to different degrees with small molecule inhibitors.