Histone deacetylase inhibitor

Histone deacetylase inhibitors (HDAC inhibitors, HDACi, HDIs) are chemical compounds that inhibit histone deacetylases. HDIs have a long history of use in psychiatry and neurology as mood stabilizers and anti-epileptics. More recently they are being investigated as possible treatments for cancers, parasitic and inflammatory diseases. To carry out gene expression, a cell must control the coiling and uncoiling of DNA around histones. This is accomplished with the assistance of histone acetyl transferases (HAT), which acetylate the lysine residues in core histones leading to a less compact and more transcriptionally active euchromatin, and, on the converse, the actions of histone deacetylases (HDAC), which remove the acetyl groups from the lysine residues leading to the formation of a condensed and transcriptionally silenced chromatin. Reversible modification of the terminal tails of core histones constitutes the major epigenetic mechanism for remodeling higher-order chromatin structure and controlling gene expression. HDAC inhibitors (HDI) block this action and can result in hyperacetylation of histones, thereby affecting gene expression. The open chromatin resulting from inhibition of histone deacetylases can result in either the up-regulation or the repression of genes. The histone deacetylase inhibitors are a new class of cytostatic agents that inhibit the proliferation of tumor cells in culture and in vivo by inducing cell cycle arrest, differentiation and/or apoptosis. Histone deacetylase inhibitors exert their anti-tumour effects via the induction of expression changes of oncogenes or tumour suppressors, through modulating the acetylation/deacetylation of histones and/or non-histone proteins such as transcription factors. Histone acetylation and deacetylation play important roles in the modulation of chromatin topology and the regulation of gene transcription. Histone deacetylase inhibition induces the accumulation of hyperacetylated nucleosome core histones in most regions of chromatin but affects the expression of only a small subset of genes, leading to transcriptional activation of some genes, but repression of an equal or larger number of other genes.