David H. Drewry

Assessment of Chemical Coverage of Kinome Space and Its Implications for Kinase Drug Discovery

More than 500 compounds chosen to represent kinase inhibitor space have been screened against a panel of over 200 protein kinases. Significant results include the identification of hits against new kinases including PIM1 and MPSK1, and the expansion of the inhibition profiles of several literature compounds. A detailed analysis of the data through the use of affinity fingerprints has produced findings with implications for biological target selection, the choice of tool compounds for target validation, and lead discovery and optimization. In a detailed examination of the tyrosine kinases, interesting relationships have been found between targets and compounds. Taken together, these results show how broad cross-profiling can provide important insights to assist kinase drug discovery.

Solid-supported reagents in organic synthesis.

The current interest in solid‐phase organic synthesis has led to a renewed interest in a complementary technique in which solid supported reagents are used in solution phase chemistry. This technique obviates the need for attachment of the substrate to a solid‐support, and enables the chemist to monitor the reactions using familiar analytical techniques. The purpose of this review is to increase awareness of the wide range of useful transformations which can be accomplished using solid‐supported reagents.

Comprehensive characterization of the Published Kinase Inhibitor Set

Despite the success of protein kinase inhibitors as approved therapeutics, drug discovery has focused on a small subset of kinase targets. Here we provide a thorough characterization of the Published Kinase Inhibitor Set (PKIS), a set of 367 small-molecule ATP-competitive kinase inhibitors that was recently made freely available with the aim of expanding research in this field and as an experiment in open-source target validation. We screen the set in activity assays with 224 recombinant kinases and 24 G protein–coupled receptors and in cellular assays of cancer cell proliferation and angiogenesis. We identify chemical starting points for designing new chemical probes of orphan kinases and illustrate the utility of these leads by developing a selective inhibitor for the previously untargeted kinases LOK and SLK. Our cellular screens reveal compounds that modulate cancer cell growth and angiogenesis in vitro. These reagents and associated data illustrate an efficient way forward to increasing understanding of the historically untargeted kinome.

A public-private partnership to unlock the untargeted kinome

Chemical probes are urgently needed to functionally annotate hitherto-untargeted kinases and stimulate new drug discovery efforts to address unmet medical needs. The size of the human kinome combined with the high cost associated with probe generation severely limits access to new probes. We propose a large-scale public-private partnership as a new approach that offers economies of scale, minimized redundancy and sharing of risk and cost.

New Compound Sets Identified from High Throughput Phenotypic Screening Against Three Kinetoplastid Parasites: An Open Resource

Using whole-cell phenotypic assays, the GlaxoSmithKline high-throughput screening (HTS) diversity set of 1.8 million compounds was screened against the three kinetoplastids most relevant to human disease, i.e. Leishmania donovani, Trypanosoma cruzi and Trypanosoma brucei. Secondary confirmatory and orthogonal intracellular anti-parasiticidal assays were conducted, and the potential for non-specific cytotoxicity determined. Hit compounds were chemically clustered and triaged for desirable physicochemical properties. The hypothetical biological target space covered by these diversity sets was investigated through bioinformatics methodologies. Consequently, three anti-kinetoplastid chemical boxes of ~200 compounds each were assembled. Functional analyses of these compounds suggest a wide array of potential modes of action against kinetoplastid kinases, proteases and cytochromes as well as potential host–pathogen targets. This is the first published parallel high throughput screening of a pharma compound collection against kinetoplastids. The compound sets are provided as an open resource for future lead discovery programs, and to address important research questions.

SOLID-PHASE SYNTHESIS OF TRISUBSTITUTED GUANIDINES

Abstract The solid-phase synthesis of trisubsituted guanidines is reported via aza-Wittig coupling of a solid-supported alkyl iminophosphorane with an aryl or alkyl isothiocyanate to generate the corresponding solid-supported carbodiimide which is then reacted with a primary or secondary amine to afford the desired trisubstituted guanidines.

Discovery of GSK1070916, a Potent and Selective Inhibitor of Aurora B/C Kinase

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.

Discovery and Characterization of GSK2801, a Selective Chemical Probe for the Bromodomains BAZ2A and BAZ2B

Bromodomains are acetyl-lysine specific protein interaction domains that have recently emerged as a new target class for the development of inhibitors that modulate gene transcription. The two closely related bromodomain containing proteins BAZ2A and BAZ2B constitute the central scaffolding protein of the nucleolar remodeling complex (NoRC) that regulates the expression of noncoding RNAs. However, BAZ2 bromodomains have low predicted druggability and so far no selective inhibitors have been published. Here we report the development of GSK2801, a potent, selective and cell active acetyl-lysine competitive inhibitor of BAZ2A and BAZ2B bromodomains as well as the inactive control compound GSK8573. GSK2801 binds to BAZ2 bromodomains with dissociation constants (KD) of 136 and 257 nM for BAZ2B and BAZ2A, respectively. Crystal structures demonstrated a canonical acetyl-lysine competitive binding mode. Cellular activity was demonstrated using fluorescent recovery after photobleaching (FRAP) monitoring displacement of GFP-BAZ2A from acetylated chromatin. A pharmacokinetic study in mice showed that GSK2801 had reasonable in vivo exposure after oral dosing, with modest clearance and reasonable plasma stability. Thus, GSK2801 represents a versatile tool compound for cellular and in vivo studies to understand the role of BAZ2 bromodomains in chromatin biology.

Plasmodium kinases as targets for new-generation antimalarials

There is an urgent need for the development of new antimalarial drugs with novel modes of actions. The malarial parasite, Plasmodium falciparum, has a relatively small kinome of <100 kinases, with many members exhibiting a high degree of structural divergence from their host counterparts. A number of Plasmodium kinases have recently been shown by reverse genetics to be essential for various parts of the complex parasitic life cycle, and are thus genetically validated as potential targets. Implementation of mass spectrometry-based phosphoproteomics approaches has informed on key phospho-signalling pathways in the parasite. In addition, global phenotypic screens have revealed a large number of putative protein kinase inhibitors with antimalarial potency. Taken together, these investigations point to the Plasmodium kinome as a rich source of potential new targets. In this review, we highlight recent progress made towards this goal.

Seeding Collaborations to Advance Kinase Science with the GSK Published Kinase Inhibitor Set (PKIS)

To catalyze research on historically untargeted protein kinases, we created the PKIS, an annotated set of 367 small molecule kinase inhibitors. The set has been widely distributed to academic collaborators as an open access tool. It has been used to identify chemical starting points for development of chemical probes for orphan kinases and to investigate kinase signaling in high content phenotypic assays. Access to the set comes with few restrictions other than the requirement that assay results be released into the public domain for the benefit of the entire research community. Examples from the efforts of several collaborators are summarized.