Histone deacetylase (HDAC) inhibitors are epigenetic compounds that block the activity of enzymes responsible for removing acetyl groups from histones and other proteins. By preventing deacetylation, they promote a more open chromatin state and can alter gene expression patterns. These agents are widely studied because they can influence cell growth, differentiation, apoptosis, and stress responses.

Mechanism of Action

HDAC inhibitors increase histone acetylation, which generally reduces chromatin compaction and makes DNA more accessible to transcriptional machinery. They also affect non-histone proteins, so their effects extend beyond chromatin remodeling alone. This broader substrate range helps explain why HDAC inhibitors can produce diverse cellular outcomes depending on cell type and disease context.

Major Classes

HDACs are commonly grouped into multiple classes based on sequence and functional properties, and classical HDAC inhibitors generally target classes I, II, and IV rather than the NAD⁺-dependent class III enzymes. Well-known examples include hydroxamic acid-based compounds such as vorinostat, which has been used in clinical settings and investigated for both hematologic and solid cancers. Other HDAC inhibitors under study differ in selectivity, potency, and pharmacological behavior.

Biological Effects

In cancer cells, HDAC inhibition can trigger cell-cycle arrest, apoptosis, senescence, oxidative stress-related death, or autophagy. Normal cells are often more resistant to these effects, which is one reason HDAC inhibitors are considered attractive anticancer agents. Their activity can also influence differentiation and immune signaling, adding to their therapeutic relevance.