In vitro activity: GSK923295 is the first potent and selective inhibitor of the mitotic kinesin centromere-associated protein-E (CENP-E). GSK923295 is uncompetitive with both ATP and microtubules (MT), inhibiting CENP-E MT-stimulated ATPase activity with a Ki of 3.2 nM, highly selective over other kinesins. GSK923295 inhibits release of inorganic phosphate and stabilizes CENP-E motor domain interaction with microtubules, reduces the rate of ATP-promoted dissociation of CENP-E from MT (koff, MT) by more than 50-fold. GSK923295 causes failure of metaphase chromosome alignment and induces mitotic arrest. GSK923295 is a potent inhibitor of tumor cell growth, with an average GI50 of 253 nM and a median GI50 of 32 nM for 237 tumor cell lines. GSK923295 inhibits tumor cell growth more effectively when mitogen-activated protein kinase (MEK/ERK) signaling is also inhibited.

Kinase Assay: Kinesin motor domains are expressed in Escherichia coli BL21(DE3) and purified. CENP-E proteins includes residues 2–340 with a carboxyl-terminal 6-his tag. All studies using MT are conducted in PEM25 buffer [25mM PipesK+ (pH 6.8), 2mM MgCl2, 1mM EGTA] supplemented with 10 μM paclitaxel. The IC50 for steady-state inhibition is determined at 500 μM ATP, 5 μM MT, and 1 nM CENP-E in PEM25 buffer.

Cell Assay: Cell-growth inhibition assays are performed by MDS in 384-well plates, and DNA content of fixed cells stained with DAPI using an Incell 1000 is analyzed. DNA content is determined 24 h after seeding (T0) and after exposure to varying concentrations of drug for an additional 72 h (T72). All T72 measurements are normalized to T0. Curves are analyzed using the XLfit curve-fitting tool to determine the concentration of GSK923295 yielding 50% growth inhibition relative to T0 and Ymax values (GI50).

Proc Natl Acad Sci U S A. 2010 Mar 30;107(13):5839-44; Pediatr Blood Cancer. 2012 Jun;58(6):916-23.