Rigosertib sodium (ON-01910), a non-ATP-competitive inhibitor of PLK1(IC50=9 nM), exhibits 30-fold higher specificity activity over Plk2 and no effect on Plk3.

CDK1:260 nM (IC50), Fyn:182 nM (IC50), PDGFR:18 nM (IC50), FLK1:42 nM (IC50), PLK1:9 nM (IC50), PLK2:260 nM (IC50), BCR-ABL:32 nM (IC50), Src:155 nM (IC50)

In vitro enzyme assays for PLK1: Recombinant PLK1 (10 ng) is incubated with different concentrations of Rigosertib in a 15 μL reaction mixture (50 mM HEPES, 10 mM MgCl2, 1 mM EDTA, 2 mM Dithiothreitol, 0.01% NP-40 [pH 7.5]) for 30 min at room temperature. Kinase reactions are performed for 20 min at 30 °C in a volume of 20 μL (15 μL enzyme + inhibitor, 2 μL 1 mM ATP), 2 μL of γ32P-ATP (40 μCi), and 1 μL of recombinant Cdc25C (100 ng) or casein (1 μg) substrates. Reactions are terminated by boiling for 2 min in 20 μL of 2× Laemmli buffer. Phosphorylated substrates are separated by 18% SDS-PAGE. The gels are dried and exposed to X-ray film for 3-10 min.

Cells are grown in either DMEM or RPMI supplemented with 10% fetal bovine serum and 1 unit/mL penicillin-streptomycin solution. Tumor cells are plated into six-well dishes at a density of 1 × 105cells/mL/well, and Rigosertib is added 24 hours later at various concentrations. Cell counts are determined from duplicate wells after 96-hour of treatment. The total number of viable cells is determined by trypan blue exclusio(Only for Reference)