PF-956980 is a selective inhibitor of JAK3, related in structure to CP-690550, a compound being evaluated in clinical trials for rheumatoid arthritis and prevention of allograft rejection. PF-956980 has been evaluated against a panel of 30 kinases, and found to have nanomolar potency against only JAK3. Cellular and whole blood activity of this compound parallels its potency and selectivity in enzyme assays. It was effective in vivo at inhibiting the delayed type hypersensivity reaction in mice. We compared 2 commercially available JAK3 inhibitors (WHI-P131 and WHI-P154) in the same panel of biochemical and cellular assays and found them to be neither potent nor selective for JAK3. Both were found to be nanomolar inhibitors of the EGF receptor family of kinases. As these compounds have been used in numerous publications in the transplant and autoimmune disease literature, their specificity should be considered when interpreting these results.

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Kinases represent attractive targets for drug discovery. Eight small-molecule kinase inhibitors are currently marketed in the area of oncology, and numerous others are in clinical trials. Characterization of the selectivity profiles of these compounds is important to target appropriate patient populations and to reduce the potential of toxicity due to off-target effects. The authors describe the development, validation, and utilization of a biochemical kinase assay panel for the selectivity profiling of inhibitors. The panel was developed as 29 radiometric Flashplate assays, and then an initial 13 were transitioned to a nonradiometric Caliper mobility shift assay format. Generation of high-quality data from the panel is detailed along with a comparison of the assay formats. Both assay technologies were found to be suitable for panel screening, but mobility shift assays yielded higher data quality. The selectivity data generated here should be useful in computational modeling and help facilitate, in conjunction with sequence and structural information, the rational design of inhibitors with well-defined selectivity profiles.

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Kinases are involved in a variety of diseases such as cancer, diabetes, and arthritis. In recent years, many kinase small molecule inhibitors have been developed as potential disease treatments. Despite the recent advances, selectivity remains one of the most challenging aspects in kinase inhibitor design. To interrogate kinase selectivity, a panel of 45 kinase assays has been developed in-house at Pfizer. Here we present an application of in silico quantitative structure activity relationship (QSAR) models to extract rules from this experimental screening data and make reliable selectivity profile predictions for all compounds enumerated from virtual libraries. We also propose the construction of R-group selectivity profiles by deriving their activity contribution against each kinase using QSAR models. Such selectivity profiles can be used to provide better understanding of subtle structure selectivity relationships during kinase inhibitor design.

Glycogen synthase kinase 3 (GSK3) is an essential component of the Wnt signaling pathway and plays important roles in regulating cell proliferation, differentiation, and apoptosis. As GSK3 is abnormally upregulated in several diseases including type II diabetes, Alzheimer's disease and cancer, it has been regarded as a potential drug target. During zebrafish development, inhibition of GSK3 leads to ectopic activation of the Wnt pathway, resulting in a headless embryo. Using this phenotype as an assay we screened a chemical library of 4000 compounds and identified one novel compound, 3F8, which specifically inhibits eye and forebrain formation in zebrafish embryos, resembling a typical Wnt overexpression phenotype. Cell reporter assays, chemical informatics analysis and in vitro kinase experiments revealed that 3F8 is a selective GSK3 inhibitor, which is more potent than SB216763, a commonly used GSK3 inhibitor. Based on the structure of 3F8, a new generation of compounds inhibiting GSK3 was synthesized and validated by biological assays. Together, 3F8 and its derivatives could be useful as new reagents and potential therapeutic candidates for GSK3 related diseases.

Background: Designing small-molecule kinase inhibitors with desirable selectivity profiles is a major challenge in drug discovery. A high-throughput screen for inhibitors of a given kinase will typically yield many compounds that inhibit more than one kinase. A series of chemical modifications are usually required before a compound exhibits an acceptable selectivity profile. Rationalizing the selectivity profile for a small-molecule inhibitor in terms of the specificitydetermining kinase residues for that molecule can be an important step toward the goal of developing selective kinase inhibitors.