Histone Deacetylase Meets Protein Degradation: Accelerating Anticancer Drug Discovery

Histone deacetylases (HDACs) are key epigenetic regulators involved in a variety of cancers, rendering them attractive therapeutic targets. Although several HDAC inhibitors have achieved clinical success, challenges such as poor isoform selectivity, acquired resistance, and off-target toxicity limit their broader application. Proteolysis-targeting chimeras (PROTACs) represent an innovative therapeutic strategy that enables ubiquitin-proteasome-mediated degradation of HDACs. This approach enhances specificity, overcomes resistance mechanisms, including those resulting from point mutations or persistent target activity, and enables sustained suppression at low concentrations, owing to its catalytic and event-driven mode of action. This review summarizes the structural classification and biological functions of HDACs and surveys recent advances in the design of HDAC-directed PROTACs. Key emphasis is placed on rational warhead selection, linker optimization, and the strategic choice of E3 ligase recruiters to guide degradation efficiency and isoform specificity. Representative degraders are evaluated for their pharmacological characteristics and antitumor efficacy across diverse malignancies. Current challenges and future directions for the development of HDAC degraders as clinically viable agents are also discussed.