In vitro activity: OTS514 strongly suppressed the growth of TOPK-positive cancer cells. It also shows significant growth-inhibitory effect on ovarian cancer cell lines with IC50 values of 3.0 to 46 nM. OTS514 has growth inhibitory effect on five kidney cancer cell lines, VMRC-RCW, Caki-1, Caki-2, 769-P and 786-O, in which TOPK was highly expressed. The IC50 values range from 19.9 to 44.1 nM

Cell Assay: Cells were cultured in RPMI supplemented with 20% fetal bovine serum and 1×StemSpan CC100. Cells were treated with OTS514 (20 or 40 nM) or OTS964 (100 or 200 nM) for 48 hours. Collected cells were washed with PBS and resuspended in 100 ml of PBS followed by staining with CD41a antibody for 20 min at room temperature. Finally, the cells were washed with PBS again and then analyzed for CD41a staining by flow cytometry. Expression of STAT5 was examined by Western blot with an anti-STAT5 antibody.