In vitro activity: BI 2536 blocks the activities of Plk2 and Plk3 to a slightly lesser extent with IC50 of 3.5 nM and 9.0 nM, respectively. In HeLa cells, BI 2536 treatment ranging from 10-100 nM leads to the blocking of the recruitment of γ-tubulin and phosphorylation of Apc6 at mitotic centrosomes, inhibition of cohesin release from chromosome arms, induction of monopolar spindles, as well as a range of other mitotic processes that are known to depend on Plk1. BI 2536 treatment leads to the HeLa cells arrested in G2/M, subsequently a sub-G1 DNA peak indicative of DNA breakdown and apoptosis, and accumulated cleaved PARP p85 fragments in a concentration-dependent manner. BI 2536 inhibits the growth of a panel of 32 human cancer cell lines with EC50 of 2-25 nM, while blocking the proliferation of exponentially growing hTERT-RPE1, human umbilical vein endothelial cells (HUVECs), and normal rat kidney (NRK) cells with EC50 of 12-31 nM. Plk1 inhibition by BI 2536 reduces the growth and viability of anaplastic thyroid carcinoma (ATC) cells such as CAL62, OCUT-1, SW1736, 8505C, and ACT-1 with EC50 values of 1.4-5.6 nM.

Kinase Assay: Recombinant human Plk1 (residues 1-603) is expressed as N-terminal, GST-tagged fusion protein with a baculoviral expression system and purified by affinity chromatography with Glutathione-agarose. Enzyme activity assays for Plk1 are performed in the presence of serially diluted BI 2536 with 20 ng of recombinant kinase and 10 μg casein from bovine milk as the substrate. Kinase reactions are performed in a final volume of 60 μL for 45 minutes at 30 °C (15 mM MgCl2, 25 mM MOPS [pH 7.0], 1 mM DTT, 1% DMSO, 7.5 mM ATP, 0.3 μCi γ-33P-ATP). Reactions are terminated by the addition of 125 μL of ice-cold 5% TCA. After transfer of the precipitates to Multi-Screen mixed ester cellulose filter plates, plates are washed with 1% TCA and quantified radiometrically. Dose-response curve is used for calculating IC50 value.

Cell Assay: Cells (HeLa, A43, SKOV-3, HT-29, K562, A549, Saos-2, MCF7, HCT116, COLO 205, Hep G2, Raji and PC-3 cells, etc.) are exposed to various concentrations of BI 2536 for 24, and 72 hours. Cell growth is assessed by the measurement of Alamar Blue dye conversion in a fluorescence spectrophotometer. For determining the DNA content of the cultures, cell suspensions are fixed in 80% ethanol, treated for 5 minutes with 0.25% Triton X-100 in PBS, and incubated with 0.1% RNase and 10 μg/mL propidium iodide (PI) in PBS for 20 minutes at RT. Cell-cycle profiles are determined by flow cytometric analysis.

Curr Biol. 2007 Feb 20;17(4):316-22; Cancer Res. 2009 Mar 1;69(5):1916-23.