Cellular Context Influences Kinase Inhibitor Selectivity

A pivotal part of
kinase chemical probe and drug development
is
assessment of the selectivity of a putative lead compound. While there
is no consensus around the panel size or the type of assay(s) that
are most appropriate, there is concurrence that gauging the number
of on- and off-targets of a kinase inhibitor is essential. As pharmacology
takes place in cells, we have compared profiling results for ten kinase
inhibitors generated using the cell-free assays to those obtained
when a panel of cellular target engagement NanoBRET assays is used
to assess selectivity in intact cells. This is the first systematic
comparison of these two approaches across a broad kinase panel. Comparison
of the data sets demonstrates divergent results that can influence
chemical probe prioritization. We identify unanticipated kinase interactions
in cells for type II kinase inhibitors that are not observed in biochemical,
cell-free systems. Furthermore, we characterize TPKI-39 as a DDR1,
DDR2, and FLT1 chemical probe based on its in-cell selectivity profile.