Kinase experiment:

The human PLK1 enzymatic reaction totaled 30 μL contains 50 mM Tris-HCl (pH 8.0), 10 mM MgCl2, 0.02% BSA, 10% glycerol, 1 mM DTT, 100 mM NaCl, 3.3% DMSO, 50 μM ATP, 2 μM peptide substrate (Biotin-AHX-LDETGHLDSSGLQEVHLA-CONH2), and 0.3 nM recombinant human PLK1[2-369]T210D. The enzymatic reaction mixture, with or without PLK inhibitors, is incubated 90 min at room temperature before termination with 50 μL of STOP buffer containing 1% BSA, 0.05% Tween 20, 100 mM EDTA. Then 50 μL of the stopped enzyme reaction mixture is transferred to a Neutravidin-coated 384-well plate and incubated at room temperature for 60 min. The wells are washed with wash buffer (25 mM Tris, 150 mM sodium chloride, and 0.1% Tween 20) and incubated for 1 h with 50 μL of antibody reaction mixture containing 1% BSA, 0.05% Tween 20, antiphospho-cdc25c rabbit monoclonal antibody (325 pM), and europium labeled antirabbit IgG (2 nM). The wells are washed, and then the bound europium is liberated using 50 μL of Enhancement Solution. Quantification of europium is done using a Pherastar[1].

Cell experiment:

Eight μL of serially diluted test compounds are added to75 μL of HT29 (2.66×104 cells/well) cells in McCoy’s 5A media supplemented with 10% Fetal Calf Serum in Biocoat Poly-D lysine 384 well Black/Clear plates. Cells are incubated for 72 h at 37℃. Supernatant is aspirated from the wells, leaving 25 μL in each well. ATP-lite 1 step reagent (25 μL) is added to each well, and luminescence for each plate is read on the LeadSeeker. Percent inhibition is calculated using the values from a DMSO control set to 100%[1].

Animal experiment:

HT29 cells are obtained from ATCC and are cultured in McCoy’s 5A medium supplemented with 10% FBS. HT29 cells (2×106) are resuspended in Hanks buffer and injected subcutaneously into the flanks of female Nude mice. Mice (10 animals/group) are treated orally with 12c (MLN0905) for 21 days at doses based on tolerability results: QD (6.25 and 12.5 mg/kg), QD×1/week (50 mg/kg), and QD×3/week (25 mg/kg). Tumor growth is monitored using vernier calipers, and the mean tumor volume is calculated using the formula V = W2 × L/2. When the mean tumor volume reaches approximately 200 mm3, the animals are randomized into treatment groups (n = 10 animals/group). Tumor growth and body weights are measured twice per week[1].

MLN0905 is a potent inhibitor of PLK1 with IC50 value ranges from 3 to 24 nM [1].

Polo-like kinase 1 (PLK1) is a family of conserved serine/threonine kinases and plays an important role in regulating cell cycle. It has been revealed that PLK1 drives cell cycle progression by triggerting G2/M transition and is considered as a pro-oncogene which overexpressed in tumor cells [2].

MLN0905 is a selective PLK1 inhibitor and has similar effect as RNAi hnockdown. When tested with HT-29 cells, MLN0905 treatment significantly increased pHisH3 expression which indicated that cells were arrested in G2/M phase by inhibiting PLK1 expression [1].

In mouse model with human diffuse large B-cell lymphoma (DLBCL) cell line OCILY-19 subcutaneous xenograft, co-administration of MLN0905 and rituximab markedly reduced tumor volume and increased survival time through inhibiting PLK1 which resulted in mitotic arrest [1]. And the same result was achieved when using nude mice model with human colon tumor HT29 xenograft, MLN0905 treatment significantly inhibited tumor growth or progression [3].

References:
[1].  Shi, J.Q., et al., MLN0905, a small-molecule plk1 inhibitor, induces antitumor responses in human models of diffuse large B-cell lymphoma. Mol Cancer Ther, 2012. 11(9): p. 2045-53.
[2].  Espeut, J., et al., Natural Loss of Mps1 Kinase in Nematodes Uncovers a Role for Polo-like Kinase 1 in Spindle Checkpoint Initiation. Cell Rep, 2015.
[3].   Duffey, M.O., et al., Discovery of a potent and orally bioavailable benzolactam-derived inhibitor of Polo-like kinase 1 (MLN0905). J Med Chem, 2012. 55(1): p. 197-208.