A potent and selective inhibitor of the mitotic kinesin CENP-E (GSK923295A), demonstrates a novel mechanism of inhibiting tumor cell proliferation and shows activity against a broad panel of human tumor cell lines in vitro

A111 The mitotic kinesin Centromere-associated protein E (CENP-E) integrates mitotic spindle mechanics with mitotic checkpoint signaling. CENP-E plays no known role outside of mitosis. CENP-E mRNA is over-expressed in a variety of human tumors relative to normal adjacent tissues suggesting it may play an important role in tumor cell proliferation. Inhibition of CENP-E in cultured human tumor cells leads to cell cycle arrest in mitosis with bipolar mitotic spindles and misaligned chromosomes and eventual cell death.
 GSK923295A, which is currently in Phase I clinical trials, is a novel and selective inhibitor of CENP-E ATPase activity with a Ki of 3.2nM. Treatment of many tumor cell lines with ~30nM GSK923295A caused a metaphase mitotic arrest with relatively normal microtubule morphology. Often, a small number of misaligned chromosomes were observed on the spindle. Timelapse microscopy and flow cytometry indicated that tumor cell death, indicated by propidium iodide positivity and PARP cleavage, occurs subsequent to the mitotic arrest. Clonogenic studies were conducted with HCT-116 cells to determine if transient exposure to GSK923295A could lead to cell death and to measure the minimal concentration and duration of exposure required for this effect. Exposure to approximately 140nM GSK923295A for 16h was sufficient to kill 90% of HCT-116 cells. This is within the exposure that can be achieved in vivo. To further study the potential utility of GSK923295A as a cancer therapeutic, it was tested for anti-proliferative activity against 214 solid and 85 hematological tumor cell lines. The large majority of cell lines were sensitive to GSK923295A (IC 50 for 204/214 solid tumor cell lines 50 values between 150 and 600nM and three were resistant up to 20μM GSK923295A. The median IC 50 for 83/85 hematological cell lines was 52nM (range 6 - 219nM). Of the two remaining cell lines, one had an IC 50 value of approximately 4μM and one was resistant up to 20μM GSK923295A. The activity of GSK923295A was also determined against normal primary human bone marrow progenitor cells using primary cultures. The IC 50 and IC 90 values were 133 and 219nM respectively. Overall, significant numbers of sensitive cell lines were observed for all tumor types suggesting the potential for this compound to be tested broadly in the clinic. Among the common solid tumor types, breast tumor lines were the most sensitive with an average IC 50 of 37nM and 15/17 lines with IC 50 50 of 68nM and only 17/25 with IC 50