Optimization of activity-based probes for proteomic profiling of histone deacetylase complexes.

Histone deacetylases (HDACs) are key enzymatic regulators of the epigenome and serve as promising targets for anticancer therapeutics. Recently, we developed a photoreactive "clickable" probe, SAHA-BPyne, to report on HDAC activity and complex formation in native biological systems. Here, we investigate the selectivity, sensitivity, and inhibitory properties of SAHA-BPyne and related potential activity-based probes for HDACs. While we identified several probes that are potent HDAC inhibitors and label HDAC complex components in native proteomic preparations, SAHA-BPyne was markedly superior for profiling HDAC activities in live cells. Interestingly, the enhanced performance of SAHA-BPyne as an in situ activity-based probe could not be solely ascribed to potency in HDAC binding, implying that other features of the molecule were key to efficient active site-directed labeling in living systems. Finally, we demonstrate the value of in situ profiling of HDACs by comparing the activity and expression of HDAC1 in cancer cells treated with the cytotoxic agent parthenolide. These results underscore the utility of activity-based protein profiling for studying HDAC function and may provide insight for the future development of click chemistry-based photoreactive probes for the in situ analysis of additional enzyme activities.