A synthetic kinesin spindle protein (KSP) inhibitor with potential antineoplastic activity. KSP inhibitor AZD4877 selectively inhibits microtubule motor protein KSP (also called kinesin-5 or Eg5), which may result in the inhibition of mitotic spindle assembly; activation of the spindle assembly checkpoint; induction of cell cycle arrest during the mitotic phase; and cell death in tumor cells that are actively dividing. Because KSP is not involved in postmitotic processes, such as neuronal transport, this agent may be less likely to cause the peripheral neuropathy often associated with the tubulin-targeting agents. Eg5 is essential for the formation of bipolar spindles and the proper segregation of sister chromatids during mitosis.