CHEMBL5736692

MELK Inhibitor Library Screening assay: MELK and its substrate, Bcl-G were both recombinantly expressed and purified for use in screening assays (See Methods). 752 compounds from an in-house curated inhibitor library were subjected to a p81-based kinase assay. 10 nM MELK 340 and 10 μM Bcl-GL in kinase assay buffer (50 mM HEPES pH 7.5, 100 mM KCl, 0.1 mM EDTA, 0.1 mM EGTA, 10 mM MgCl2, 10 μg/mL BSA) with 10 mM DTT were added to either 10 μM or 1 μM inhibitor aliquoted into 96 well plates (final 1% DMSO). The mixture was incubated at room temperature for 30 minutes prior to initiation of the assay with 40 μM γ-32P-ATP (100-1000 CPM/pmol). 40 μL aliquots were spotted onto a p81 96 well filter plate (Unifilter, Whatman), quenched, and washed with 75 mM O-phosphoric acid 8 times, followed by a final wash with acetone for drying. Wells were then filled with scintillation fluid, sealed, and quantified using a MicroBeta TriLux liquid scintillation counter (PerkinElmer). Each inhibitor plate was assayed in duplicate, with at least 4 wells without MELK to establish background and at least 4 wells without inhibitor as a negative control. All readings were corrected for background signal based on the average counts from the wells without enzyme. Percent inhibition, defined as [100−(CPM+inhibitor/average CPM of positive controls)*100], was determined first at 10 μM inhibitor. The top 50 inhibitors were then re-screened in duplicate at 1 μM.