ABSTRACT
Epigenetic modifications such as acetylation and deacetylation of histone proteins play a decisive role in transcriptional alteration and expression of genes. Acetylation is catalysed by the histone acetyl transferases enzymes and activates expression of genes by converting chromatin into a less compact, transcriptionally active state. Histone deacetylases enzymes catalyze deacetylation that condenses chromatin into a closed structure .Consequently transcriptional factors are unable to access DNA and gene expression is suppressed. Balanced activity of HATs and HDACS is essential for normal gene expression. Increased HDAC activity can lead to imbalance in protein acetylation resulting in hypoacetylation, tight chromatin structure and suppression of various genes. This aberrant suppression of genes is the hallmark of several malignant and other diseases including neurodegenerative disorders. Histone Deacetylase Inhibitors (HDACIs) have potential to restore the balance of histone acetylation that reverses the silencing of pathological genes. Thus HDACIs modify expression of genes without affecting sequence of DNA and act as epigenetic modifiers. Vorinostat and romidepsin are FDA approved HDACIs. Valproic acid, belinostat and many others are in different phases of clinical trials. This review article explores the target based epigenetic mechanisms as well as existing and potential therapeutic role of HDACIs in various malignant and non-malignant diseases. Data sources were articles published in medical journals and bibliographic database Medline.