Potent kinesin spindle protein (KSP) inhibitor (IC50 = 6 nM); selective for KSP over >250 other receptors and kinases at a concentration of 10 μM. Displays robust antitumor activity in bortezomib-resistant xenografts either alone or in combination with bortezomib. Induces degradation of Mcl-1; exhibits comparable cytotoxic activity to taxol (Cat. No. 1097) in epithelial ovarian cancer cells. Active in vivo. Purity 98%. MW (observed): 420.48