Divergent kinetics differentiate the mechanism of action of two HDAC inhibitors.

Histone deacetylases (HDACs) play diverse roles in many diseases including cancer, sarcopenia, and Alzheimer's. Different isoforms of HDACs appear to play disparate roles in the cell and are associated with specific diseases; as such, a substantial effort has been made to develop isoform-selective HDAC inhibitors. Our group focused on developing HDAC1/HDAC2-specific inhibitors as a cancer therapeutic. In the course of characterizing the mechanism of inhibition of a novel HDAC1/2-selective inhibitor, it was determined that it did not exhibit classical Michaelis-Menten kinetic behavior; this result is in contrast to the seminal HDAC inhibitor SAHA. Enzymatic assays, along with a newly developed binding assay, were used to determine the rates of binding and the affinities of both the HDAC1/2-selective inhibitor and SAHA. The mechanism of action studies identified a potential conformational change required for optimal binding by the selective inhibitor. A model of this putative conformational change is proposed.