Gustave Bergnes

Antitumor activity of an allosteric inhibitor of centromere-associated protein-E

Centromere-associated protein-E (CENP-E) is a kinetochore-associated mitotic kinesin that is thought to function as the key receptor responsible for mitotic checkpoint signal transduction after interaction with spindle microtubules. We have identified GSK923295, an allosteric inhibitor of CENP-E kinesin motor ATPase activity, and mapped the inhibitor binding site to a region similar to that bound by loop-5 inhibitors of the kinesin KSP/Eg5. Unlike these KSP inhibitors, which block release of ADP and destabilize motor-microtubule interaction, GSK923295 inhibited release of inorganic phosphate and stabilized CENP-E motor domain interaction with microtubules. Inhibition of CENP-E motor activity in cultured cells and tumor xenografts caused failure of metaphase chromosome alignment and induced mitotic arrest, indicating that tight binding of CENP-E to microtubules is insufficient to satisfy the mitotic checkpoint. Consistent with genetic studies in mice suggesting that decreased CENP-E function can have a tumor-suppressive effect, inhibition of CENP-E induced tumor cell apoptosis and tumor regression.

Mitotic Kinesins: Prospects for Antimitotic Drug Discovery

Kinesins, mechanochemical enzymes that utilize the energy of ATP to translocate along or destabilize microtubules, are essential for accurate completion of cell division. Recently, small moleculer inhibitors of one kinesin, kinesin spindle protein (KSP/Eg5/kinesin5), have been shown to be efficacious in pre-clinical studies, with one quinazolinone-based inhibitor advancing to Phase II clinical trials as a potential anticancer chemotherapeutic agent. This highlights the potential of KSP and other mitotic kinesins as targets for chemotherapeutic intervention. Ten other kinesins have been shown to play essential roles in cell division and thus may provide additional therapeutic opportunities. In this review, the biological roles of these proteins are described with emphasis on their importance to cell proliferation. In addition, kinesin motor domain structure and mechanism are described with particular attention given to the conformational changes that offer opportunities for chemical inhibition. Finally, a current list of KSP inhibitor classes is described in the context of their potential as clinical leads.

Discovery of the First Potent and Selective Inhibitor of Centromere-Associated Protein E: GSK923295.

Inhibition of mitotic kinesins represents a novel approach for the discovery of a new generation of anti-mitotic cancer chemotherapeutics. We report here the discovery of the first potent and selective inhibitor of centromere-associated protein E (CENP-E) 3-chloro-N-{(1S)-2-[(N,N-dimethylglycyl)amino]-1-[(4-{8-[(1S)-1-hydroxyethyl]imidazo[1,2-a]pyridin-2-yl}phenyl)methyl]ethyl}-4-[(1-methylethyl)oxy]benzamide (GSK923295; 1), starting from a high-throughput screening hit, 3-chloro-4-isopropoxybenzoic acid 2. Compound 1 has demonstrated broad antitumor activity in vivo and is currently in human clinical trials.

Mitotic Kinesin Inhibitors as Novel Anti-cancer Agents

Publisher Summary This chapter discusses the biological roles and characteristics of mitotic kinesins. Mitosis is divided into several phases, each characterized by specific mechanical events. The integrity of mitosis is monitored and enforced by the mitotic checkpoint. This checkpoint prevents sister chromatid separation and anaphase onset until all chromosomes are attached to spindle microtubules and aligned at the spindle midzone. Mitotic spindle dysfunction in prometaphase results in failure to satisfy this checkpoint, resulting in prolonged cell cycle arrest and eventual cell death. Mitotic kinesins have been shown to play important roles in nearly all aspects of mitotic spindle function. Mitotic kinesins also include substantial additional regions responsible for protein–protein interaction, including regions responsible for dimerization, for localization to intracellular cargo and for interaction with upstream regulators. The variety of inhibitory mechanisms that may be identified in small molecule discovery screening efforts may vary greatly depending on the specific protein fragment used and the functional or binding event monitored. Discovery efforts reported to date have been grounded in both biochemical and cell-based approaches. Biochemical screens have focused on motor domain function. One mitotic kinesin, known as KSP or Hs Eg 5, has seen significant attention as a drug target, yielding several classes of inhibitors.

Progress on Mitotic Kinesin Inhibitors as Anti-cancer Therapeutics

Publisher Summary Kinesin spindle protein (KSP), also known as Hs Eg5, is a mitotic kinesin required in early mitosis for the formation of a bipolar mitotic spindle. This chapter discusses various KSP inhibitors. The KSP inhibitor, ispinesib, has been studied in Phase II clinical trials against locally advanced or metastatic breast cancer (in which it has demonstrated anticancer activity), platinum-refractory and -sensitive nonsmall cell lung cancer, ovarian cancer, hepatocellular cancer, colorectal cancer, head and neck cancer, hormone-refractory prostate cancer, and melanoma. In addition, a number of other potent and structurally diverse structures are in preclinical development, most of which bind to the same induced-fit, allosteric pocket as monastrol. With another 13 proteins designated as mitotic kinesins, efforts against this target class are still at an early stage.

Discovery of Tirasemtiv, the First Direct Fast Skeletal Muscle Troponin Activator

The identification and optimization of the first activators of fast skeletal muscle are reported. Compound 1 was identified from high-throughput screening (HTS) and subsequently found to improve muscle function via interaction with the troponin complex. Optimization of 1 for potency, metabolic stability, and physical properties led to the discovery of tirasemtiv (25), which has been extensively characterized in clinical trials for the treatment of amyotrophic lateral sclerosis.