TAK-960 hydrochloride is an orally available, selective inhibitor of polo-like kinase 1 (PLK1), with an IC50 of 0.8 nM at 10 μM ATP; TAK-960 hydrochloride also shows inhibitory activities against PLK2 and PLK3, with IC50s of 16.9 and 50.2 nM, respectively. PLK1|0.8 nM (IC50)|PLK2|16.9 nM (IC50)|PLK3|50.2 nM (IC50)|FAK/PTK2|19.6 nM (IC50)|MLCK/MYLK|25.6 nM (IC50)|FES/FPS|58.2 nM (IC50) TAK-960 inhibits full-length PLK1 protein with IC50 of 0.8 nM, wich is 20-fold lower than the next lowest IC50 value (PLK2: 16.9 nM). TAK-960 (2-1000 nM) causes accumulation of G2-M cells in HT-29 cells. TAK-960 inhibits proliferation of multiple cancer cell lines, with mean EC50 values ranging from 8.4 to 46.9 nM, but not in nondividing normal cells. TAK-960 (8 nM) leads to G2/M cell cycle arrest without significant cytotoxicity in HeLa cells. TAK-960 does not sensitize cancer cells to radiation when an insufficient amount of time is provided to induce mitotic arrest. The overexpression of a PLK1 mutant, PLK1-R136G&T210D, which is confirmed to cancel the TAK-960-mediated increase in the proportion of mitotic cells, abrogates the radiosensitizing effects of TAK-960. TAK-960 (7.5 mg/kg, p.o.) shows a significant increase in median survival compared with vehicle in MV4-11 human leukemia model. TAK-960 (10 mg/kg, p.o.) inhibits tumor growth in the MDR1-expressing K562ADR-bearing leukemia xenograft model. TAK-960 (10 mg/kg) significantly suppresses tumor growth when combined with IR in tumor xenografts.