Comprehensive Characterization of Bruton's Tyrosine Kinase Inhibitor Specificity, Potency, and Biological Effects: Insights into Covalent and Noncovalent Mechanistic Signatures.

Uncovering a drug's mechanism of action and possible adverse effects are critical components in drug discovery and development. Moreover, it provides evidence for why some drugs prove more effective than others and how to design better drugs altogether. Here, we demonstrate the utility of a high-throughput screening platform along with a comprehensive panel to aid in the characterization of 15 Bruton's tyrosine kinase (BTK) inhibitors that are either approved by the FDA or presently under clinical evaluation. To compare the potency of these drugs, we measured the binding affinity of each to wild-type BTK as well as a clinically relevant resistance mutant of BTK (BTK C481S). In doing so, we discovered a considerable difference in the selectivity and potency of these BTK inhibitors to the wild-type and mutant proteins. Some of this potentially contributes to the adverse effects experienced by patients undergoing therapy using these drugs. Overall, noncovalent BTK inhibitors showed stronger potency for both the wild-type and mutant BTK when compared with that of covalent inhibitors, with the majority demonstrating a higher specificity and less off-target modulation. Additionally, we compared biological outcomes for four of these inhibitors in human cell-based models. As expected, we found different phenotypic profiles for each inhibitor. However, the two noncovalent inhibitors had fewer off-target biological effects when compared with the two covalent inhibitors. This and similar in-depth preclinical characterization of drug candidates can provide critical insights into the efficacy and mechanism of action of a compound that may affect its safety in a clinical setting.