Characterisation of aurora kinase inhibitors derived from fragment based lead discovery

4915 The protein kinases Aurora A and B have been associated with the incidence and severity of several cancers. As a consequence they have been the focus of a significant amount of drug discovery activity. We describe here a series of Aurora A and B inhibitors that have been developed using a fragment based lead discovery approach which couples high throughput x-ray crystallography of the target protein with fragment soaks from the Astex fragment library. The Aurora kinases regulate mitosis and are only expressed in cells that are actively dividing, making them ideal targets for therapeutic intervention. Inhibition of Aurora-B induces a polyploid phenotype, via abnormal cytokinesis in cells progressing through mitosis and results ultimately in apoptosis. We have profiled a series of compounds for anti-tumour activity in in-vitro kinase assays, in cells and in animals. We tested a number of compounds from the series in a number of leukemic cell lines and showed sensitivity in each case to the Aurora inhibitor. We also tested the therapeutic window for the compound by comparing the cell cycle effects in tumour lines to normal mammary epithelial cells. Following successful profiling of the series in DMPK experiments we also wanted to show how PD effects might translate to efficacy in animal models. Thus, we analysed xenograft tumours using single doses of active compound shown to be efficacious in-vivo for inhibition of surrogate markers. The markers tested included phosphorylation on serine 10 of histone H3, a known Aurora substrate after single doses and p53 stabilisation in tumour xenografts after multiple doses of active compound using IHC as well as the polyploidy phenotype in the tumour sections from later timepoints post dosing. The activity of our series has been tested in a number of different human tumour xenograft models. We anticipate initiation of clinical development for a compound from this series in the near future.