Histone deacetylases (HDACs) play an important role in gene transcription. Inhibitors of HDACs induce cell differentiation and suppress cell proliferation in tumor cells. Although many HDAC inhibitors have been designed and synthesized, selective inhibition for class I HDAC isoforms is a goal that has yet to be achieved. To understand the difference between class I HDAC isoforms that could be exploited for the design of isoform-specific HDAC inhibitors, we have built three-dimensional models of four class I histone deacetylases, HDAC1, HDAC2, HDAC3, and HDAC8. Comparison of the homology model of HDAC8 with the recently published X-ray structure shows excellent agreement and validates the approach. A series of HDAC inhibitors were docked to the homology models to understand the similarities and differences between the binding modes. Molecular dynamic simulations of these HDAC-inhibitor complexes indicate that the interaction between the protein surface and inhibitor is playing an important role; also some active site residues show some flexibility, which is usually not included in routine docking protocols. The implications of these results for the design of isoform-selective HDAC inhibitors are discussed.

Histone deacetylases (HDACs) play an important role in gene transcription. Inhibitors of HDACs induce cell differentiation and suppress cell proliferation in tumor cells. AutoDock calculations of known and novel HDAC inhibitors as well as of several probe molecules to histone deacetylase-like protein (HDLP), using a modified scoring function for metalloproteins, demonstrate excellent agreement (R = 0.92) between experimental and computed binding constants. Analysis of the docked structures allows a determination of the different binding motifs in known inhibitors. Such calculations are a useful tool for the prediction of binding constants for new HDAC inhibitors. Exploration of the 14 A long internal cavity adjacent to the active site by docking of small molecular probes suggest that it plays a crucial role by accepting the cleaved acetate and releasing it at the far side of the cavity. The importance of the findings for the design of new inhibitors is discussed.

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The dynamics of gene expression are regulated by histone acetylases (HATs) and histone deacetylases (HDACs) that control the acetylation state of lysine side chains of the histone proteins of chromatin. The catalytic activity of these two enzymes remodels chromatin to control gene expression without altering gene sequence. Treatment of cancer has been the primary target for the clinical development of HDAC inhibitors, culminating in approval for the first HDAC inhibitor for the treatment of cutaneous T cell lymphoma. Beyond cancer, HDAC inhibition has potential for the treatment of many other diseases. The HDAC inhibitors phenylbutyric acid, valproic acid, and suberoylanilide hydroxamic acid (SAHA) have been shown to correct errant gene expression, ameliorate the progression of disease, and restore absent synthetic or metabolic activities for a diverse group of non-cancer disorders. These benefits have been found in patients with sickle cell anemia, HIV, and cystic fibrosis. In vitro and in vivo models of spinal muscular atrophy, muscular dystrophy, and neurodegenerative, and inflammatory disorders also show response to HDAC inhibitors. This review examines the application of HDAC inhibition as a treatment for a wide-range of non-cancer disorders, many of which are rare diseases that urgently need therapy. Inhibition of the HDACs has general potential as a pharmacological epigenetic approach for gene therapy.