Abstract 225: Chemoproteomic evaluation of target engagement in clinical samples

One of the challenges during the clinical development of kinase inhibitors is understanding whether or not a compound is actually binding the kinase of interest, in the appropriate tissue, during the course of compound treatment. While compound concentration in blood can be determined from pharmacodynamics, there are very few approaches that directly measure whether or not the compound is binding the target kinase. Herein, we apply a chemoproteomics platform (KiNativ®) using a desthiobiotin ATP acyl phosphate probe (ATP probe), to monitor target engagement in clinical samples. As a proof of concept, we demonstrate that compound can be added to whole blood, after which peripheral blood mononuclear cells (PBMCs) are isolated, lysed, labeled with the ATP probe, and analyzed by mass spectrometry to determine whether or not compound treatment blocks the probe-labeling of the target. We successfully applied this approach in the analysis of both the reversible JNK inhibitor CC-930, as well as the covalent BTK inhibitor Ibrutinib (Imbruvica®). We then extended the study to monitor the inhibition of BTK by Ibrutinib in PBMCs isolated from patients undergoing drug treatment. Finally, we demonstrate that in addition to profiling kinases in PBMCs isolated from whole blood, this method can also be used to profile kinases in solid tumors. Thus, the chemoproteomics approach described here could be applied as a general method to monitor target engagement for inhibitors developed against a variety of different kinases in clinical samples. Citation Format: Tyzoon K. Nomanbhoy. Chemoproteomic evaluation of target engagement in clinical samples [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 225. doi:10.1158/1538-7445.AM2017-225