High affinity allosteric kinesin spindle protein (KSP) inhibitor (Ki app = 1.7 nM). Exhibits >10,000-fold selectivity for KSP over a range of other mitotic kinesins. Inhibits proliferation and induces apoptosis of prostate and breast cancer cells in vitro. Induces tumor regression of breast cancer cell xenografts in mice. Purity 98%. MW (observed): 517.06