Monastrol is a potent and cell-permeable inhibitor of the mitotic kinesin Eg5 with an IC₅₀ value of 14 μM. IC50 & Target: IC50: 14 μM (Eg5)^[3] In Vitro: Monastrol is a small, cell-permeable molecule that arrests cells in mitosis by specifically inhibiting Eg5, a member of the Kinesin-5 family. Monastrol treatment of dividing cells results in spindle collapse and cell cycle arrest with a monoastral spindle, which is similar to the phenotype observed when Eg5 is inhibited by anti-Eg5 antibodies^[1]. Monastrol is an allosteric inhibitor of the mitotic kinesin Eg5 that exhibits an antiproliferative effect against several cell lines. Monastrol treatment can decrease cell viability in MCF-7 tumor cells. Real-time cell growth kinetic analysis showed a decrease in the proliferation of MCF-7 cells exposed to monastrol^[2].