For example, an in vitro chemical screen targeting Plk1 identified the small molecule BI2536.6 BI2536 was not only used to define novel roles for Plk1 during cell division, it was further developed into an anti-cancer drug whose efficacy is being evaluated in clinical trials.7 Therefore, beyond their therapeutic potential, inhibitors can be used as molecular probes for dissecting the function of enzymes critical for cell cycle progression in an acute and temporal manner. Here, PLK1 is linked to cancer.