In vitro activity: The most Aurora-selective CYC116 shows inhibitory effect on Aurora A and B kinases 50-fold more potently than any of the CDKs assayed. CYC116 is initially screened against a panel of human leukemia and solid tumor cell lines using an MTT antiproliferative assay. The results show that CYC116 has broad-spectrum antitumor activity and shows specific cytotoxicity against the acute myelogenous leukemia cell line MV4-11 with IC50 of 34 nM. In addition, anti-proliferative activity of CYC116 is found to be associated with Aurora A and B modulation such as, inhibition of Aurora autophosphorylation, reduction of histone H3 phosphorylation, polyploidy, followed by cell death, resulting from a failure in cytokinesis.

Kinase Assay: Aurora A kinase assays are performed using a 25 μL reaction volume (25 mM β-glycerophosphate, 20 mM Tris/HCl, pH 7.5, 5 mM EGTA, 1 mM DTT, 1 mM Na3VO4, 10 μg of kemptide (peptide substrate)). Recombinant Aurora A kinase is diluted in 20 mM Tris/HCl, pH 8, containing 0.5 mg/mL BSA, 2.5% glycerol, and 0.006% Brij-35. Reactions are started by the addition of 5 μL Mg/ATP mix (15 mM MgCl2, 100 μM ATP, with 18.5 kBq γ-32P-ATP per well) and incubated at 30°C for 30 minutes before termination with 25 μL of 75 mM H3PO4. Aurora B kinase assays are performed like Aurora A except that prior to use, Aurora B is activated in a separate reaction at 30°C for 60 minutes with inner centromere protein.

Cell Assay: Standard MTT assays are performed. In short, cells (HeLa, MCF7, MV4-11 and A2780 cells) are seeded into 96-well plates according to doubling time and incubated overnight at 37°C. Test compounds are made up in DMSO, a 3-fold dilution series is prepared in 100 μL of cell medium, added to cells (in triplicates) and incubated for 72 or 96 hours at 37°C. MTT is made up as a stock of 5 mg/mL in cell medium, and the solution is filter-sterilized. Medium is removed from the cells followed by a wash with PBS. MTT solution is then added at 20 μL/well and incubated in the dark at 37°C for 4 hours. MTT solution is removed and cells are again washed with 200 μL of PBS. MTT dye is solubilized with 200 μL/well of DMSO by agitation. Absorbance is read at 540 nm and data analyzed using curve-fitting software to determine IC50 values.

J Med Chem. 2010 Jun 10;53(11):4367-78