Off-Target Decoding of a Multitarget Kinase Inhibitor by Chemical Proteomics

Since the approval of the first selective tyrosine:kinase inhibitor, imatinib, various drugs have been developed to target protein kinases. However, due to a high degree, of structural conservation of the ATP binding site, off-target effects, have been reported for several drugs. Here, we report on off target decoding for a multitarget protein kinase inhibitor. by chemical proteomics, by focusing on interactions with. nonprotein kinases. We tested two different routes for the immobibilization of the inhibitor on a carrier matrix, and thus identified,off-targets that interact with distinct compound moieties. Besides several of the kinases known to bind to the compound, the pyridoxal kinase (PDXK), which has been described to interact with the CDK inhibitor R-roscovitine, was captured. The PDXK-inhibitor interaction was shown to occur at the substrate binding site rather than at the ATP binding site. In addition, carbonic anhydrase 2 (CA2) binding was demonstrated, and the determination of the IC50, revealed an enzyme inhibition in the submicromolar range. The data demonstrate that different compound immobilization routes for chemical proteomics approaches are a valuable method to improve the knowledge about the off-target profile of a compound.