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A Chemoproteomic Strategy for Direct and Proteome-Wide Covalent Inhibitor Target-Site Identification

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posted on 06.12.2018, 00:00 by Christopher M. Browne, Baishan Jiang, Scott B. Ficarro, Zainab M. Doctor, Jared L. Johnson, Joseph D. Card, Sindhu Carmen Sivakumaren, William M. Alexander, Tomer M. Yaron, Charles J. Murphy, Nicholas P. Kwiatkowski, Tinghu Zhang, Lewis C. Cantley, Nathanael S. Gray, Jarrod A. Marto
Despite recent clinical successes for irreversible drugs, potential toxicities mediated by unpredictable modification of off-target cysteines represents a major hurdle for expansion of covalent drug programs. Understanding the proteome-wide binding profile of covalent inhibitors can significantly accelerate their development; however, current mass spectrometry strategies typically do not provide a direct, amino acid level readout of covalent activity for complex, selective inhibitors. Here we report the development of CITe-Id, a novel chemoproteomic approach that employs covalent pharmacologic inhibitors as enrichment reagents in combination with an optimized proteomic platform to directly quantify dose-dependent binding at cysteine-thiols across the proteome. CITe-Id analysis of our irreversible CDK inhibitor THZ1 identified dose-dependent covalent modification of several unexpected kinases, including a previously unannotated cysteine (C840) on the understudied kinase PKN3. These data streamlined our development of JZ128 as a new selective covalent inhibitor of PKN3. Using JZ128 as a probe compound, we identified novel potential PKN3 substrates, thus offering an initial molecular view of PKN3 cellular activity. CITe-Id provides a powerful complement to current chemoproteomic platforms to characterize the selectivity of covalent inhibitors, identify new, pharmacologically addressable cysteine-thiols, and inform structure-based drug design programs.