Ispinesib is a potent, specific and reversible inhibitor of kinesin spindle protein (KSP) with Ki app of 1.7 nM, no inhibition to CENP-E, RabK6, MCAK, MKLP1, KHC or Kif1A.

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. In PC-3 prostate cancer cells, Ispinesib (15 nM and 30 nM) blocks cell proliferation and induces apoptosis by regulating the expression levels of genes that controls apoptosis, cell proliferation, cell cycle, and cell signaling, such as EGFR, p27, p15, and IL-11. In a panel of 53 breast cell lines, Ispinesib (7.4 nM–600 nM) demonstrates broad inhibitory activity. In BT-474 and MDA-MB-468 cells, Ispinesib (150 nM) induces apoptosis, as revealed by a higher proportion of apoptotic cells, lower antiapoptotic Bcl-XL level, and higher proapoptotic Bax and Bid levels.