Phosphoinositide 3-kinase R (PI3KR) is a critical regulator of cell growth and transformation, and its signaling pathway is the most commonly mutated pathway in human cancers. The mammalian target of rapamycin (mTOR), a class IV PI3K protein kinase, is also a central regulator of cell growth, and mTOR inhibitors are believed to augment the antiproliferative efficacy of PI3K/AKT pathway inhibition. 2,4-Difluoro-N-{2-(methyloxy)-5-[4-(4-pyridazinyl)-6-quinolinyl]-3-pyridinyl}benzenesulfonamide (GSK2126458, 1) has been identified as a highly potent, orally bioavailable inhibitor of PI3KR and mTOR with in vivo activity in both pharmacodynamic and tumor growth efficacy models. Compound 1 is currently being evaluated in human clinical trials for the treatment of cancer. KEYWORDS GSK2126458, phosphoinositide 3-kinase R, mammalian target of rapamycin, PI3K/AKT pathway

The mitotic kinesin KSP (kinesin spindle protein, or Eg5) has an essential role in centrosome separation and formation of the bipolar mitotic spindle. Its exclusive involvement in the mitotic spindle of proliferating cells presents an opportunity for developing new anticancer agents with reduced side effects relative to antimitotics that target tubulin. Ispinesib is an allosteric small-molecule KSP inhibitor in phase 2 clinical trials. Mutations that attenuate ispinesib binding to KSP have been identified, which highlights the need for inhibitors that target different binding sites. We describe a new class of selective KSP inhibitors that are active against ispinesib-resistant forms of KSP. These ATP-competitive KSP inhibitors do not bind in the nucleotide binding pocket. Cumulative data from generation of resistant cells, site-directed mutagenesis and photo-affinity labeling suggest that they compete with ATP binding via a novel allosteric mechanism.

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Human fatty acid synthase (hFAS) is a complex, multifunctional enzyme that is solely responsible for the de novo synthesis of long chain fatty acids. hFAS is highly expressed in a number of cancers, with low expression observed in most normal tissues. Although normal tissues tend to obtain fatty acids from the diet, tumor tissues rely on de novo fatty acid synthesis, making hFAS an attractive metabolic target for the treatment of cancer. We describe here the identification of GSK2194069, a potent and specific inhibitor of the β-ketoacyl reductase (KR) activity of hFAS; the characterization of its enzymatic and cellular mechanism of action; and its inhibition of human tumor cell growth. We also present the design of a new protein construct suitable for crystallography, which resulted in what is to our knowledge the first co-crystal structure of the human KR domain and includes a bound inhibitor.

The Aurora kinases play critical roles in the regulation of mitosis and are frequently overexpressed or amplified in human tumors. Selective inhibitors may provide a new therapy for the treatment of tumors with Aurora kinase amplification. Herein we describe our lead optimization efforts within a 7-azaindole-based series culminating in the identification of GSK1070916 (17k). Key to the advancement of the series was the introduction of a 2-aryl group containing a basic amine onto the azaindole leading to significantly improved cellular activity. Compound 17k is a potent and selective ATP-competitive inhibitor of Aurora B and C with K(i)* values of 0.38 +/- 0.29 and 1.5 +/- 0.4 nM, respectively, and is >250-fold selective over Aurora A. Biochemical characterization revealed that compound 17k has an extremely slow dissociation half-life from Aurora B (>480 min), distinguishing it from clinical compounds 1 and 2. In vitro treatment of A549 human lung cancer cells with compound 17k results in a potent antiproliferative effect (EC(50) = 7 nM). Intraperitoneal administration of 17k in mice bearing human tumor xenografts leads to inhibition of histone H3 phosphorylation at serine 10 in human colon cancer (Colo205) and tumor regression in human leukemia (HL-60). Compound 17k is being progressed to human clinical trials.

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.

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Kinesin spindle protein (KSP), an ATPase responsible for spindle pole separation during mitosis that is present only in proliferating cells, has become a novel and attractive anticancer target with potential for reduced side effects compared to currently available therapies. We report herein the discovery of the first known ATP-competitive inhibitors of KSP, which display a unique activity profile as compared to the known loop 5 (L5) allosteric KSP inhibitors that are currently under clinical evaluation. Optimization of this series led to the identification of biphenyl sulfamide 20, a potent KSP inhibitor with in vitro antiproliferative activity against human cells with either wild-type KSP (HCT116) or mutant KSP (HCT116 D130V). In a murine xenograft model with HCT116 D130V tumors, 20 showed significant antitumor activity following intraperitoneal dosing, providing in vivo proof-of-principle of the efficacy of an ATP-competitive KSP inhibitor versus tumors that are resistant to the other known KSP inhibitors.