Plk1 Inhibitor BI 2536 is a small molecule compound with potential antineoplastic activities. BI 2536 binds to and inhibits Polo-like kinase 1 (Plk1), resulting in mitotic arrest, disruption of cytokinesis, and apoptosis in susceptible tumor cell populations. Plk1, a serine/threonine-protein kinase, is a key regulator of multiple processes fundamental to mitosis and cell division.