Recent Advances in Medicinal Chemistry of Histone Deacetylase Inhibitors

Acylation or phosphorylation of hydroxyurea unexpectedly takes place on N rather than on O, leading to the formation of amides instead of the expected esters

Attempted acylation of the anticancer agent hydroxyurea (HU) with acyl chlorides or anhydrides led to acylation on the NH group rather than on the OH.

Drug targeting to monocytes and macrophages using esterase-sensitive chemical motifs

The therapeutic and toxic effects of drugs are often generated through effects on distinct cell types in the body. Selective delivery of drugs to specific cells or cell lineages would, therefore, have major advantages, in particular, the potential to significantly improve the therapeutic window of an agent. Cells of the monocyte-macrophage lineage represent an important target for many therapeutic agents because of their central involvement in a wide range of diseases including inflammation, cancer, atherosclerosis, and diabetes. We have developed a versatile chemistry platform that is designed to enhance the potency and delivery of small-molecule drugs to intracellular molecular targets. One facet of the technology involves the selective delivery of drugs to cells of the monocyte-macrophage lineage, using the intracellular carboxylesterase, human carboxylesterase-1 (hCE-1), which is expressed predominantly in these cells. Here, we demonstrate selective delivery of many types of intracellularly targeted small molecules to monocytes and macrophages by attaching a small esterase-sensitive chemical motif (ESM) that is selectively hydrolyzed within these cells to a charged, pharmacologically active drug. ESM versions of histone deacetylase (HDAC) inhibitors, for example, are extremely potent anticytokine and antiarthritic agents with a wider therapeutic window than conventional HDAC inhibitors. In human blood, effects on monocytes (hCE-1-positive) are seen at concentrations 1000-fold lower than those that affect other cell types (hCE-1-negative). Chemical conjugates of this type, by limiting effects on other cells, could find widespread applicability in the treatment of human diseases where monocyte-macrophages play a key role in disease pathology.

Use of polyamine derivatives as selective histone deacetylase inhibitors

Histone acetylation and deacetylation, mediated by histone acetyltransferase and the 11 isoforms of histone deacetylase, play an important role in gene expression. Histone deacetylase inhibitors have found utility in the treatment of cancer by promoting the reexpression of aberrantly silenced genes that code for tumor suppressor factors. It is unclear which of the 11 histone deacetylase isoforms are important in human cancer. We have designed a series of polyaminohydroxamic acid (PAHA) and polyaminobenzamide (PABA) histone deacetylase inhibitors that exhibit selectivity among four histone deacetylase isoforms. Although all of the active inhibitors promote reexpression of tumor suppressor factors, they produce variable cellular effects ranging from stimulation of growth to cytostasis and cytotoxicity. This chapter describes the procedures used to quantify the global and isoform-specific inhibition caused by these inhibitors, and techniques used to measure cellular effects such as reexpression of tumor suppressor proteins and hyperacetylation of histones H3 and H4. Procedures are also described to examine the ability of PAHAs and PABAs to utilize the polyamine transport system and to induce overexpression of the early apoptotic factor annexin A1.

Histone Deacetylase Inhibitors: Synthesis of Cyclic Tetrapeptides and their Triazole Analogues

Synthesis of nine macrocyclic peptide HDAC inhibitors and three triazole derivatives are described. HDAC inhibitory activity of these compounds against HeLa cell lysate is evaluated. The biological data demonstrates that incorporation of a triazole unit improves the HDAC inhibitory activity.

Pharmacophore modeling and virtual screening studies to design some potential histone deacetylase inhibitors as new leads

Histone deacetylase is one of the important targets in the treatment of solid tumors and hematological cancers. A total of 20 well-defined inhibitors were used to generate Pharmacophore models using and HypoGen module of Catalyst. These 20 molecules broadly represent 3 different chemotypes. The best HypoGen model consists of four-pharmacophore features--one hydrogen bond acceptor, one hydrophobic aliphatic and two ring aromatic centers. This model was validated against 378 known HDAC inhibitors with a correlation of 0.897 as well as enrichment factor of 2.68 against a maximum value of 3. This model was further used to retrieve molecules from NCI database with 238,819 molecules. A total of 4638 molecules from a pool of 238,819 molecules were identified as hits while 297 molecules were indicated as highly active. Also, a Similarity analysis has been carried out for set of 4638 hits with respect to most active molecule of each chemotypes which validated not only the Virtual Screening potential of the model but also identified the possible new Chemotypes. This type of Similarity analysis would prove to be efficient not only for lead generation but also for lead optimization.

Structure–activity relationships of aryloxyalkanoic acid hydroxyamides as potent inhibitors of histone deacetylase

Syntheses of aryloxyalkanoic acid hydroxyamides are described, all of which are potent inhibitors of histone deacetylase, some being more potent in vitro than trichostatin A (IC(50)=3 nM). Variation of the substituents on the benzene ring as well as fusion of a second ring have marked effects on potency, in vitro IC(50) values down to 1 nM being obtained.

Synthesis and cancer antiproliferative activity of new histone deacetylase inhibitors: hydrophilic hydroxamates and 2-aminobenzamide-containing derivatives

New series histone deacetylase inhibitors comprising a hydroxamic acid or 2-aminobenzamide group as a zinc-chelating function were synthesized and evaluated for antiproliferative activities against a panel of human cancer cells. The 2-aminobenzamide series inhibitors generally had the potency in cell growth inhibitions comparable to that of MS-275. Among them, the compound having a (3,4-difluorobenzyl)(2-hydroxyethyl)amino group at one end and a 2-aminobenzamide group at the other of molecule showed the most promising profile as an anticancer drug candidate, since it had a comparatively low toxicity as did MS-275 against a normal fibroblast cell CCD-1059SK. Additionally, the derivative exhibited a high recovery in human plasma stability test.