Ispinesib is a potent, allosteric, reversible, and specific inhibitor of KSP, which changes the binding property of KSP to microtubules and disturbs its movement by inhibiting ADP
release without altering the release of the KSP-ADP complex from the microtubule. Ispinesib shows potent cytotoxic activity in a panel of tumor cell lines, including Colo205, Colo201, HT-29, M5076,
Madison-109, and MX-1, with IC50 of 1.2 nM to 9.5 nM.