Inhibition of Polo-like Kinase 1 by Small Molecules Targeting the Polo-Box Domain

The serine/threonine kinase Polo-like kinase 1 (Plk1) is a key regulator of multiple stages of mitosis. It is overexpressed in many types of human cancers and has been implicated as an adverse prognostic marker for tumor patients. All currently reported strategies for interference with Plk1 functions ultimately target the kinase's catalytic activity. This thesis introduces a new approach to the inhibition of Plk1. A fluorescence polarization-based high-throughput screen led to the identification of Poloxin and its core structure, the natural product Thymoquinone (TQ), as the first small-molecule inhibitors of the protein-interaction domain of Plk1, the polo-box domain (PBD). Both compounds arrested cancer cells in mitosis with chromosome congression defects and mislocalized endogenous Plk1. These date provide a molecular explanation for the well-documented anti-cancer activity of TQ, and have implications for analysis of the role of the PBD in mammalian cells and the future design of anti-cancer drugs.