Drug Discovery for Histone Deacetylase Inhibition: Past, Present and Future of Zinc-Binding Groups

Histone deacetylases (HDACs) are key regulators of gene expression, influencing chromatin remodeling and playing a crucial role in various physiological and pathological processes. Aberrant HDAC activity has been linked to cancer, neurodegenerative disorders, and inflammatory diseases, making these enzymes attractive therapeutic targets. HDAC inhibitors (HDACis) have gained significant attention, particularly those containing zinc-binding groups (ZBGs), which interact directly with the catalytic zinc ion in the enzyme's active site. The structural diversity of ZBGs profoundly impacts the potency, selectivity, and pharmacokinetics of HDACis. While hydroxamic acids remain the most widely used ZBGs, their limitations, such as metabolic instability and off-target effects, have driven the development of alternative scaffolds, including ortho-aminoanilides, mercaptoacetamides, alkylhydrazides, oxadiazoles, and more. This review explores the structural and mechanistic aspects of different ZBGs, their interactions with HDAC isoforms, and their influence on inhibitor selectivity. Advances in structure-based drug design have allowed the fine-tuning of HDACi pharmacophores, leading to more selective and efficacious compounds with improved drug-like properties. Understanding the nuances of ZBG interactions is essential for the rational design of next-generation HDACis, with potential applications in oncology, neuroprotection, and immunotherapy.