Cellular thermal shift and clickable chemical probe assays for the determination of drug-target engagement in live cells

Abstract

Proof of drug-target engagement in physiologically-relevant contexts is a key pillar of successful therapeutic target validation. We developed two orthogonal technologies, the cellular thermal shift assay (CETSA) and a covalent chemical probe reporter approach (harnessing sulfonyl fluoride tyrosine labeling and subsequent click chemistry) to measure the occupancy of the mRNA-decapping scavenger enzyme DcpS by a small molecule inhibitor in live cells. Enzyme affinity determined using isothermal dose response fingerprinting (ITDRF_CETSA) and the concentration required to occupy 50% of the enzyme (OC₅₀) using the chemical probe reporter assay were very similar. In this case, the chemical probe method worked well due to the long offset kinetics of the reversible inhibitor (determined using a fluorescent dye-tagged probe). This work suggests that CETSA could become the first choice assay to determine in-cell target engagement due to its simplicity.