Histone deacetylase inhibitors: a novel class of anti-cancer agents on its way to the market

A Review on Molecular Docking on HDAC Isoforms: Novel Tool for Designing Selective Inhibitors

Research into histone deacetylases (HDACs) has experienced a remarkable surge in recent years. These enzymes are key regulators of several fundamental biological processes, often associated with severe and potentially fatal diseases. Inhibition of their activity represents a promising therapeutic approach and a prospective strategy for the development of new therapeutic agents. A critical aspect of their inhibition is to achieve selectivity in terms of enzyme isoforms, which is essential to improve treatment efficacy while reducing undesirable pleiotropic effects. The development of computational chemistry tools, particularly molecular docking, is greatly enhancing the precision of designing molecules with inherent potential for specific activity. Therefore, it was considered necessary to review the molecular docking studies conducted on the major isozymes of the enzyme in order to identify the specific interactions associated with each selective HDAC inhibitor. In particular, the most critical isozymes of HDAC (1, 2, 3, 6, and 8) have been thoroughly investigated within the scope of this review.

The Impact of Histone Modifications in Endometriosis Highlights New Therapeutic Opportunities

Endometriosis is a chronic disorder of the female reproductive system which afflicts a great number of women worldwide. Histone deacetylases (HDACs) prevent the relaxation of chromatin, thereby positively or negatively modulating gene transcription. The current review aims at studying the impact of histone modifications and their therapeutic targeting in endometriosis. In order to identify relevant studies, a literature review was conducted using the MEDLINE and LIVIVO databases. The current manuscript represents the most comprehensive, up-to-date review of the literature focusing on the particular role of HDACs and their inhibitors in the context of endometriosis. HDAC1, HDAC2, HDAC3, Sirtuin 1, and Sirtuin 3, are the five most studied HDAC enzymes which seem to, at least partly, influence the pathophysiology of endometriosis. Both well-established and novel HDACIs could possibly represent modern, efficacious anti-endometriotic drug agents. Altogether, histone modifications and their therapeutic targeting have been proven to have a strong impact on endometriosis.

In search of constrained FTY720 and phytosphingosine analogs as dual acting anticancer agents targeting metabolic and epigenetic pathways

A series of compounds containing pyrrolidine and pyrrolizidine cores with appended hydrophobic substituents were prepared as constrained analogs of FTY720 and phytosphingosine. The effect of these compounds on the viability of cancer cells, on downregulation of the nutrient transport systems, and on their ability to cause vacuolation was studied. An attempt to inhibit HDACs with some phosphate esters of our analogs was thwarted by our failure to reproduce the reported inhibitory action of FTY720-phosphate.

Novel hybrid molecule overcomes the limited response of solid tumours to HDAC inhibitors via suppressing JAK1-STAT3-BCL2 signalling

Despite initial progress in preclinical models, most known histone deacetylase inhibitors (HDACis) used as a single agent have failed to show clinical benefits in nearly all types of solid tumours. Hence, the efficacy of HDACis in solid tumours remains uncertain. Herein, we developed a hybrid HDAC inhibitor that sensitized solid tumours to HDAC-targeted treatment. Methods: A hybrid molecule, Roxyl-zhc-84 was designed and synthesized with novel architecture. The pharmacokinetics and toxicity of Roxyl-zhc-84 were analysed. The antitumour effects of Roxyl-zhc-84 on solid tumours were investigated by assessing cell growth, apoptosis and cell cycle in vitro and in three in vivo mouse models and compared to those of corresponding control inhibitors alone or in combination. Gene set enrichment analysis was performed, and relevant JAK1-STAT3-BCL2 signalling was identified in vitro and in vivo in mechanistic studies. Results: Roxyl-zhc-84 showed excellent pharmacokinetics and low toxicity. The novel hybrid inhibitor Roxyl-zhc-84 induced cell apoptosis and G1-phase arrest in breast cancer and ovarian cancer cell lines. In three mouse models, oral administration of Roxyl-zhc-84 led to significant tumour regression without obvious toxicity. Moreover, Roxyl-zhc-84 dramatically improved the limited response of traditional HDAC inhibitors in solid tumours via overcoming JAK1-STAT3-BCL2-mediated drug resistance. Roxyl-zhc-84 treatment exhibited vastly superior efficacy than the combination of HDAC and JAK1 inhibitors both in vitro and in vivo. Conclusion: Concurrent inhibition of HDAC and CDK using Roxyl-zhc-84 with additional JAK1 targeting resolved the limited response of traditional HDAC inhibitors in solid tumours via overcoming JAK1-STAT3-BCL2-mediated drug resistance, providing a rational multi-target treatment to sensitize solid tumours to HDACi therapy.

Design, synthesis, docking, and biological evaluation of novel diazide-containing isoxazole- and pyrazole-based histone deacetylase probes

The design, synthesis, docking, and biological evaluation of novel potent HDAC3 and HDAC8 isoxazole- and pyrazole-based diazide probes suitable for binding ensemble profiling with photoaffinity labeling (BEProFL) experiments in cells is described. Both the isoxazole- and pyrazole-based probes exhibit low nanomolar inhibitory activity against HDAC3 and HDAC8, respectively. The pyrazole-based probe 3f appears to be one of the most active HDAC8 inhibitors reported in the literature with an IC(50) of 17 nM. Our docking studies suggest that unlike the isoxazole-based ligands the pyrazole-based ligands are flexible enough to occupy the second binding site of HDAC8. Probes/inhibitors 2b, 3a, 3c, and 3f exerted the antiproliferative and neuroprotective activities at micromolar concentrations through inhibition of nuclear HDACs, indicating that they are cell permeable and the presence of an azide or a diazide group does not interfere with the neuroprotection properties, or enhance cellular cytotoxicity, or affect cell permeability.

Binding ensemble profiling with photoaffinity labeling (BEProFL) approach: mapping the binding poses of HDAC8 inhibitors

A binding ensemble profiling with (f)photoaffinity labeling (BEProFL) approach that utilizes photolabeling of HDAC8 with a probe containing a UV-activated aromatic azide, mapping of the covalent modifications by liquid chromatography-tandem mass spectrometry, and a computational method to characterize the multiple binding poses of the probe is described. By use of the BEProFL approach, two distinct binding poses of the HDAC8 probe were identified. The data also suggest that an "upside-down" pose with the surface binding group of the probe bound in an alternative pocket near the catalytic site may contribute to the binding.