In vitro evaluation of the 93 putative Plk1-PBD inhibitors.

A) Fluorescence polarization assay to measure the effect of DMSO (green bar), 100 µM Poloxin (red bar) or 100 µM of each of the 93 test compounds (blue bars) on the percent binding of Plk1-PBD to its substrate peptide 5-carboxyfluorescein-GPMQSpTPLNG. B) Chemical structure of Chemistry_28272 and Poloxin and their respective IC_50s for Plk1-PBD inhibition in fluorescence polarization assays described in A. C) Overlay of Hypo1 and the critical residues in the active site of the Plk1-PDB with hit lead compound Chemistry_28272. D) Zoomed view of ligand protein interaction showing that Chemistry_28272 forms hydrogen bond interactions with key residues (Trp414, Asp416, His538, and Lys540) in the Plk1-PBD active site.