MCL1 and plasma cell myeloma: It has been found that in cells arrested by KSP inhibitors, an anti-apoptotic protein known as myeloid cell leukemia 1 (Mcl-1) is rapidly depleted resulting in cell death.34 Therefore, cells that are dependent on this pro-survival protein, Mcl-1, such as myeloma cells, are especially sensitive to filanesib.35 Filanesib is one of a several KSP inhibitors currently being studied in clinical trials as a novel anticancer chemotherapeutic drug.