Live Cell CDK Inhibitor Profiling Confirms Selectivity for Key Drugs and Reveals Opportunities for Inhibitor Repurposing
Vasta, J. D. et al., Promega Corporation
AACR 2020 Abstract #5808
Cyclin-dependent kinases (CDK) play key roles in diverse cellular functions including cell cycle control, cell proliferation, and transcriptional regulation. Due to these important roles, CDKs have been targeted for cancer therapeutic development, which has resulted in hundreds of small molecule inhibitors. However, conflicting data of CDK inhibitor potency has been reported and a rigorous comparison of inhibitor affinity and selectivity for intracellular CDKs is lacking.
To address this need, we have developed a panel of cell-permeable energy transfer probes or tracers to enable comprehensive quantitation of inhibitor target occupancy and affinity for CDKs in live cells via a bioluminescent energy transfer (BRET) method. Specifically, the quantitative BRET-based capability is achieved via energy transfer from cell-permeable fluorescent tracers reversibly engaged to NanoLuc luciferase-tagged CDK proteins expressed in live cells. An untagged cyclin can be introduced into the cells at the same time as the NanoLuc-CDK, allowing for the interrogation of a specific CDK-cyclin pair. The BRET-based method can be used in equilibrium binding analysis. In addition, time-dependent target-compound occupancy (or residence time) can also be obtained with this method. We will present a comprehensive evaluation of intracellular isozyme potency and selectivity for a collection of clinically-advanced CDK inhibitors and chemical probes across the CDK family. We observed unexpected intracellular activity profiles for some clinically-advanced CDK inhibitors. We further evaluated mechanisms for achieving target selectivity through target residence time under non-equilibrium cell culture conditions. This BRET-based method is broadly applicable for evaluating the occupancy, affinity, and selectivity of chemical matter for CDKs in live cells.
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