In vitro characterization of the catalytic domain of human histone deacetylase 5.

Both histone acetyltransferases (HATs) and histone deacetylases (HDACs) control the acetylation state of conserved lysine residues in histone tails. Thereby, modulating chromatin structure and gene transcription. Disturbance of this precisely balanced acetylation state contributes to neuronal, cardiovascular, muscle degenerative, autoimmune diseases and cancer. To restore this delicate balance, HDAC inhibitors (HDACi) are employed. However, employing pan-HDAC inhibitors, that target a broad spectrum of HDACs, often leads to significant side effects. Therefore, the development of isoform specific inhibitors is urgently needed. Among the HDAC family, class IIa HDACs, particularly HDAC5, have emerged as promising drug targets due to their tissue-specific expression patterns and presence in large regulatory complexes. Recent progress in selective class IIa HDAC inhibition has led to the development of novel HDACi that contain a 5-(trifluoromethyl)-1,2,4-oxadiazole (TFMO) zinc-binding group (ZBG) to interact with the Zn²⁺ ion in the active site, avoiding the drawbacks associated with promiscuous hydroxamic acid–based HDACi. This study focuses on the in vitro characterization of the catalytic domain of human HDAC5 and its inhibition by the TFMO-based HDACi FFK24 and NT160. Our findings contribute to a better biochemical understanding of the kinetic parameters of HDAC5 activity and support the development of selective inhibitors targeting class IIa HDACs.