text: In 2009, researchers developed siRNAs capable of targeting both polo-like kinase 1(PLK1) and kinesin spindle protein(KSP).  Both proteins are important to the cell-cycle of tumor cells, PLK1 involved with phosphorylation of a variety of proteins and KSP integral to chromosome segregation during mitosis.  Specifically, bipolar mitotic spindles are unable to form when KSP is inhibited, leading to arrest of the cell cycle and, eventually, apoptosis.  Likewise, inhibition of PLK1 facilitates mitotic arrests and cell apoptosis.  According to the study, a 2 mg/kg dose of PLK1-specific siRNA administered for 3 weeks to mice implanted with tumors resulted in increased survival times and obvious reduction of tumors.  In fact, the median survival time of treated mice was 51 days as opposed to 32 days for the controls.  Further, only 2 of the 6 mice treated had noticeable tumors around the implantation site.  Even so, GAPDH, a tumor-derived signal, was present at low levels, indicating significant suppression of tumor growth but not complete elimination.  Still, the results suggested minimal toxicity and no significant dysfunction of the bone marrow.  Animals treated with KSP-specific siRNA, too, exhibited increased survival times of 28 days compared to 20 days in the controls.