Kinobead/LC-MS Phosphokinome Profiling Enables Rapid Analyses of Kinase-Dependent Cell Signaling Networks.

Kinase-catalyzed protein phosphorylation is fundamental to eukaryotic signal transduction, regulating most cellular processes. Kinases are frequently dysregulated in cancer, inflammation, and degenerative diseases, and because they can be inhibited with small molecules, they became important drug targets. Accordingly, analytical approaches that determine kinase activation states are critically important to understand kinase-dependent signal transduction and to identify novel drug targets and predictive biomarkers. Multiplexed inhibitor beads (MIBs or kinobeads) efficiently enrich kinases from cell lysates for liquid chromatography-mass spectrometry (LC-MS) analysis. When combined with phosphopeptide enrichment, kinobead/LC-MS can also quantify the phosphorylation state of kinases, which determines their activation state. However, an efficient kinobead/LC-MS kinase phospho-profiling protocol that allows routine analyses of cell lines and tissues has not yet been developed. Here, we present a facile workflow that quantifies the global phosphorylation state of kinases with unprecedented sensitivity. We also found that our kinobead/LC-MS protocol can measure changes in kinase complex composition and show how these changes can indicate kinase activity. We demonstrate the utility of our approach in specifying kinase signaling pathways that control the acute steroidogenic response in Leydig cells; this analysis establishes the first comprehensive framework for the post-translational control of steroid biosynthesis.

Pyrrolopyrimidine Bumped Kinase Inhibitors for the Treatment of Cryptosporidiosis.

Bumped kinase inhibitors (BKIs) that target Cryptosporidium parvum calcium-dependent protein kinase 1 have been well established as potential drug candidates against cryptosporidiosis. Recently, BKI-1649, with a 7H-pyrrolo[2,3-d]pyrimidin-4-amine, or "pyrrolopyrimidine", central scaffold, has shown improved efficacy in mouse models of Cryptosporidium at substantially reduced doses compared to previously explored analogs of the pyrazolopyrimidine scaffold. Here, two pyrrolopyrimidines with varied substituent groups, BKI-1812 and BKI-1814, were explored in several in vitro and in vivo models and show improvements in potency over the previously utilized pyrazolopyrimidine bumped kinase inhibitors while maintaining equivalent results in other key properties, such as toxicity and efficacy, with their pyrazolopyrimidine isosteric counterparts.

Pharmacoproteomics Identifies Kinase Pathways that Drive the Epithelial-Mesenchymal Transition and Drug Resistance in Hepatocellular Carcinoma.

Hepatocellular carcinoma (HCC) is a complex and deadly disease lacking druggable genetic mutations. The limited efficacy of systemic treatments for advanced HCC implies that predictive biomarkers and drug targets are urgently needed. Most HCC drugs target protein kinases, indicating that kinase-dependent signaling networks drive HCC progression. To identify HCC signaling networks that determine responses to kinase inhibitors (KIs), we apply a pharmacoproteomics approach integrating kinome activity in 17 HCC cell lines with their responses to 299 KIs, resulting in a comprehensive dataset of pathway-based drug response signatures. By profiling patient HCC samples, we identify signatures of clinical HCC drug responses in individual tumors. Our analyses reveal kinase networks promoting the epithelial-mesenchymal transition (EMT) and drug resistance, including a FZD2-AXL-NUAK1/2 signaling module, whose inhibition reverses the EMT and sensitizes HCC cells to drugs. Our approach identifies cancer drug targets and molecular signatures of drug response for personalized oncology.

Development of a Chemical Toolset for Studying the Paralog-Specific Function of IRE1.

The dual kinase endoribonuclease IRE1 is a master regulator of cell fate decisions in cells experiencing endoplasmic reticulum (ER) stress. In mammalian cells, there are two paralogs of IRE1: IRE1α and IRE1ß. While IRE1α has been extensively studied, much less is understood about IRE1ß and its role in signaling. In addition, whether the regulation of IRE1ß's enzymatic activities varies compared to IRE1α is not known. Here, we show that the RNase domain of IRE1ß is enzymatically active and capable of cleaving an XBP1 RNA mini-substrate in vitro. Using ATP-competitive inhibitors, we find that, like IRE1α, there is an allosteric relationship between the kinase and RNase domains of IRE1ß. This allowed us to develop a novel toolset of both paralog specific and dual-IRE1α/ß kinase inhibitors that attenuate RNase activity (KIRAs). Using sequence alignments of IRE1α and IRE1ß, we propose a model for paralog-selective inhibition through interactions with nonconserved residues that differentiate the ATP-binding pockets of IRE1α and IRE1ß.

Kinome chemoproteomics characterization of pyrrolo[3,4-c]pyrazoles as potent and selective inhibitors of glycogen synthase kinase 3.

Glycogen synthase kinase 3 has evolutionarily conserved roles in cell signaling and metabolism and is a recognized drug target in neurological pathologies, most prominently bipolar disorder. More recently it has been suggested that GSK3 may be a target for the treatment of trypanosomatid parasite infections, e.g. with T. brucei, due to the lethal phenotype observed in parasite GSK3 short RNAi knockdown experiments. Here we investigated the kinome selectivity of a library of pyrrolo[3,4-c]pyrazol inhibitors that were developed against T. brucei GSK3 but that also interact with the human orthologue and other protein kinases. We applied label-free MS-based kinome chemoproteomics profiling with kinobeads to obtain the selectivity profiles of all 39 library members against 217 human protein and lipid kinases. This allowed us to study the structure-activity relationship of the library members as well as the chemical genetic relationships between kinase targets. As a result, we identified a novel and highly selective HsGSK3 inhibitor containing a 2-chloroaniline-substituted squaric acid amide pharmacophore that confers low nanomolar (IC50 = 2.8 nM) and sub-micromolar potency against purified and cellular HsGSK3. The inhibitor will be useful as a new lead for GSK3 inhibitor development and as a chemical genetic probe to study roles of GSK3 in cell signaling.