Role of Class I and Class II histone deacetylases in carcinoma cells using siRNA

Anticancer efficacy of Spiruchostatin A: current insights into histone deacetylase inhibition and oncologic applications

Spiruchostatin A also referred to as YM753 and OBP801, a cyclic peptide-based natural product derived from Pseudomonas sp., is distinguished by its potent inhibition of Class I histone deacetylases (HDACs). The modulation of epigenetic mechanisms by HDAC inhibitors is fundamental for altering gene expression related to cell growth, apoptosis, and differentiation, highlighting their potential in oncologic therapies. This updated review assesses the antitumor efficacy of Spiruchostatin A across diverse cellular and animal models, scrutinizing its viability as a therapeutic agent against various cancers. A systematic literature review was executed by searching databases such as PubMed/MedLine, Scopus, and Web of Science from October 2022 to February 2023. The inclusion criteria focused on studies involving Spiruchostatin A in the context of cancer treatment, including in vitro and in vivo models. The review concentrated on the compound's mechanistic action, biological activity, and clinical applicability. Spiruchostatin A has demonstrated significant antitumor activities, including inducing apoptosis and inhibiting tumor growth effectively in multiple models. Its therapeutic potential is particularly noted in synergistic applications with other anticancer agents, enhancing its efficacy. Mechanistically, the compound facilitates chromatin relaxation and transcriptional activation of key tumor suppressor genes through increased histone acetylation. Spiruchostatin A exhibits substantial potential as an anticancer agent through effective HDAC inhibition and subsequent epigenetic modifications of cancer cell biology. However, comprehensive clinical trials are imperative to validate its efficacy and safety profiles comprehensively. Future research is warranted to elucidate detailed molecular mechanisms and to develop biomarkers for predicting treatment response. Comprehensive longitudinal clinical studies are also critical to establish Spiruchostatin A's role within the broader oncological therapeutic regimen, along with the exploration of its analogs for improved therapeutic outcomes.

Discovery of novel anaplastic lymphoma kinase (ALK) and histone deacetylase (HDAC) dual inhibitors exhibiting antiproliferative activity against non-small cell lung cancer

A series of novel benzimidazole derivatives were designed and synthesised based on the structures of reported oral available ALK inhibitor and HDAC inhibitor, pracinostat. In enzymatic assays, compound 3b, containing a 2-acyliminobenzimidazole moiety and hydroxamic acid side chain, could inhibit both ALK and HDAC6 (IC50 = 16 nM and 1.03 µM, respectively). Compound 3b also inhibited various ALK mutants known to be involved in crizotinib resistance, including mutant L1196M (IC50, 4.9 nM). Moreover, 3b inhibited the proliferation of several cancer cell lines, including ALK-addicted H2228 cells. To evaluate its potential for treating cancers in vivo, 3b was used in a human A549 xenograft model with BALB/c nude mice. At 20 mg/kg, 3b inhibited tumour growth by 85% yet had a negligible effect on mean body weight. These results suggest a attracting route for the further research and optimisation of dual ALK/HDAC inhibitors.

Identification of structural fingerprints among natural inhibitors of HDAC1 to accelerate nature-inspired drug discovery in cancer epigenetics

Histone deacetylase 1 (HDAC1), a class I HDAC enzyme, is crucial for histone modification. Currently, it is emerged as one of the important biological targets for designing small molecule drugs through cancer epigenetics. Along with synthetic inhibitors different natural inhibitors are showing potential HDAC1 inhibitions. In order to gain insights into the relationship between the molecular structures of the natural inhibitors and HDAC1, different molecular modelling techniques (Bayesian classification, recursive partitioning, molecular docking and molecular dynamics simulations) have been applied on a dataset of 155 HDAC1 nature-inspired inhibitors with diverse scaffolds. The Bayesian study showed acceptable ROC values for both the training set and test sets. The Recursive partitioning study produced decision tree 1 with 6 leaves. Further, molecular docking study was processed for generating the protein ligand complex which identified some potential amino acid residues such as F205, H28, L271, P29, F150, Y204 for the binding interactions in case of natural inhibitors. Stability of these HDAC1-natutal inhibitors complexes has been also evaluated by molecular dynamics simulation study. The current modelling study is an attempt to get a deep insight into the different important structural fingerprints among different natural compounds modulating HDAC1 inhibition.Communicated by Ramaswamy H. Sarma.

Decrypting lysine deacetylase inhibitor action and protein modifications by dose-resolved proteomics

Lysine deacetylase inhibitors (KDACis) are approved drugs for cutaneous T cell lymphoma (CTCL), peripheral T cell lymphoma (PTCL), and multiple myeloma, but many aspects of their cellular mechanism of action (MoA) and substantial toxicity are not well understood. To shed more light on how KDACis elicit cellular responses, we systematically measured dose-dependent changes in acetylation, phosphorylation, and protein expression in response to 21 clinical and pre-clinical KDACis. The resulting 862,000 dose-response curves revealed, for instance, limited cellular specificity of histone deacetylase (HDAC) 1, 2, 3, and 6 inhibitors; strong cross-talk between acetylation and phosphorylation pathways; localization of most drug-responsive acetylation sites to intrinsically disordered regions (IDRs); an underappreciated role of acetylation in protein structure; and a shift in EP300 protein abundance between the cytoplasm and the nucleus. This comprehensive dataset serves as a resource for the investigation of the molecular mechanisms underlying KDACi action in cells and can be interactively explored online in ProteomicsDB.

Targeted Protein Degradation of Histone Deacetylases by Hydrophobically Tagged Inhibitors

There is a growing interest in alternative strategies for targeted protein degradation. In this work, we present the development of histone deacetylase (HDAC) degraders based on hydrophobic tagging technology. To this end, a library of hydrophobically tagged HDAC inhibitors was synthesized via efficient solid-phase protocols utilizing pre-loaded resins. The subsequent biological evaluation led to the identification of our best degrader, 1a, which significantly decreased HDAC1 levels in MM.1S multiple myeloma cells.

Curcuphenol possesses an unusual histone deacetylase enhancing activity that counters immune escape in metastatic tumours

Curcuphenol, a common component of the culinary spices, naturally found in marine invertebrates and plants, has been identified as a novel candidate for reversing immune escape by restoring expression of the antigen presentation machinery (APM) in invasive cancers, thereby resurrecting the immune recognition of metastatic tumours. Two synthetic curcuphenol analogues, were prepared by informed design that demonstrated consistent induction of APM expression in metastatic prostate and lung carcinoma cells. Both analogues were subsequently found to possess a previously undescribed histone deacetylase (HDAC)-enhancing activity. Remarkably, the H3K27ac ChIPseq analysis of curcuphenol-treated cells reveals that the induced epigenomic marks closely resemble the changes in genome-wide pattern observed with interferon-γ, a cytokine instrumental for orchestrating innate and adaptive immunity. These observations link dietary components to modifying epigenetic programs that modulate gene expression guiding poised immunity.

A toolbox for class I HDACs reveals isoform specific roles in gene regulation and protein acetylation

The class I histone deacetylases are essential regulators of cell fate decisions in health and disease. While pan- and class-specific HDAC inhibitors are available, these drugs do not allow a comprehensive understanding of individual HDAC function, or the therapeutic potential of isoform-specific targeting. To systematically compare the impact of individual catalytic functions of HDAC1, HDAC2 and HDAC3, we generated human HAP1 cell lines expressing catalytically inactive HDAC enzymes. Using this genetic toolbox we compare the effect of individual HDAC inhibition with the effects of class I specific inhibitors on cell viability, protein acetylation and gene expression. Individual inactivation of HDAC1 or HDAC2 has only mild effects on cell viability, while HDAC3 inactivation or loss results in DNA damage and apoptosis. Inactivation of HDAC1/HDAC2 led to increased acetylation of components of the COREST co-repressor complex, reduced deacetylase activity associated with this complex and derepression of neuronal genes. HDAC3 controls the acetylation of nuclear hormone receptor associated proteins and the expression of nuclear hormone receptor regulated genes. Acetylation of specific histone acetyltransferases and HDACs is sensitive to inactivation of HDAC1/HDAC2. Over a wide range of assays, we determined that in particular HDAC1 or HDAC2 catalytic inactivation mimics class I specific HDAC inhibitors. Importantly, we further demonstrate that catalytic inactivation of HDAC1 or HDAC2 sensitizes cells to specific cancer drugs. In summary, our systematic study revealed isoform-specific roles of HDAC1/2/3 catalytic functions. We suggest that targeted genetic inactivation of particular isoforms effectively mimics pharmacological HDAC inhibition allowing the identification of relevant HDACs as targets for therapeutic intervention.

Natural Bioactive Compounds Targeting Histone Deacetylases in Human Cancers: Recent Updates

Cancer is a complex pathology that causes a large number of deaths worldwide. Several risk factors are involved in tumor transformation, including epigenetic factors. These factors are a set of changes that do not affect the DNA sequence, while modifying the gene’s expression. Histone modification is an essential mark in maintaining cellular memory and, therefore, loss of this mark can lead to tumor transformation. As these epigenetic changes are reversible, the use of molecules that can restore the functions of the enzymes responsible for the changes is therapeutically necessary. Natural molecules, mainly those isolated from medicinal plants, have demonstrated significant inhibitory properties against enzymes related to histone modifications, particularly histone deacetylases (HDACs). Flavonoids, terpenoids, phenolic acids, and alkaloids exert significant inhibitory effects against HDAC and exhibit promising epi-drug properties. This suggests that epi-drugs against HDAC could prevent and treat various human cancers. Accordingly, the present study aimed to evaluate the pharmacodynamic action of different natural compounds extracted from medicinal plants against the enzymatic activity of HDAC.

Integrated Proteomic and Transcriptomic Analysis of Gonads Reveal Disruption of Germ Cell Proliferation and Division, and Energy Storage in Glycogen in Sterile Triploid Pacific Oysters (Crassostrea gigas)

Triploid oysters have poor gonadal development, which can not only bring higher economic benefits but also have a potential application in the genetic containment of aquaculture. However, the key factors that influence germ cell development in triploid oysters remain unclear. In this study, data-independent acquisition coupled to transcriptomics was applied to identify genes/proteins related to sterility in triploid Crassostrea gigas. Eighty-four genes were differentially expressed at both the protein and mRNA levels between fertile and sterile females. For male oysters, 207 genes were differentially expressed in the transcriptomic and proteomic analysis. A large proportion of downregulated genes were related to cell division, which may hinder germ cell proliferation and cause apoptosis. In sterile triploid females, a primary cause of sterility may be downregulation in the expression levels of certain mitotic cell cycle-related genes. In sterile triploid males, downregulation of genes related to cell cycle and sperm motility indicated that the disruption of mitosis or meiosis and flagella defects may be linked with the blocking of spermatogenesis. Additionally, the genes upregulated in sterile oysters were mainly associated with the biosynthesis of glycogen and fat, suggesting that sterility in triploids stimulates the synthesis of glycogen and energy conservation in gonad tissue.

Phase 1 study of the histone deacetylase inhibitor entinostat plus clofarabine for poor-risk Philadelphia chromosome-negative (newly diagnosed older adults or adults with relapsed refractory disease) acute lymphoblastic leukemia or biphenotypic leukemia

PURPOSE

Despite advances in immunotherapies, the prognosis for adults with Philadelphia chromosome-negative, newly diagnosed (ND) or relapsed/refractory (R/R) acute lymphoblastic leukemia/acute biphenotypic leukemia (ALL/ABL) remains poor. The benzamide derivative entinostat inhibits histone deacetylase and induces histone hyperacetylation. The purine nucleoside analogue clofarabine is FDA-approved for R/R ALL in children 1-21 years of age. Low doses of clofarabine have been reported to induce DNA hypomethylation. We conducted a phase 1 study of low dose clofarabine with escalating doses of entinostat in adults with ND or R/R ALL/ABL.

EXPERIMENTAL DESIGN

Adults ≥60 years with ND ALL/ABL or ≥21 years with R/R ALL/ABL received repeated cycles every 3 weeks of entinostat (4 mg, 6 mg or 8 mg orally days 1 and 8) and clofarabine (10 mg/m²/day IV for 5 days, days 3-7) (Arm A). Adults aged 40-59 years with ND ALL/ABL or age ≥21 years in first relapse received entinostat and clofarabine prior to traditional chemotherapy on day 11 (Arm B). Changes in DNA damage, global protein lysine acetylation, myeloid-derived suppressor cells and monocytes were measured in PBMCs before and during therapy.

RESULTS

Twenty-eight patients were treated at three entinostat dose levels with the maximum administered dose being entinostat 8 mg. The regimen was well tolerated with infectious and metabolic derangements more common in the older population versus the younger cohort. There was no severe hyperglycemia and no peripheral neuropathy in this small study. There were 2 deaths (1 sepsis, 1 intracranial bleed). Overall response rate was 32 %; it was 50 % for ND ALL/ABL. Entinostat increased global protein acetylation and inhibited immunosuppressive monocyte subpopulations, while clofarabine induced DNA damage in all cell subsets examined.

CONCLUSION

Entinostat plus clofarabine appears to be tolerable and active in older adults with ND ALL/ABL, but less active in R/R patients. Further evaluation of this regimen in ND ALL/ABL appears warranted.

EGFR phosphorylates HDAC1 to regulate its expression and anti-apoptotic function

HDAC1 is the prototypical human histone deacetylase (HDAC) enzyme responsible for catalyzing the removal of acetyl group from lysine residues on many substrate proteins. By deacetylating histones and non-histone proteins, HDAC1 has a profound effect on the regulation of gene transcription and many processes related to cell growth and cell death, including cell cycle progression, DNA repair, and apoptosis. Early studies reveal that, like most eukaryotic proteins, the functions and activities of HDAC1 are regulated by post-translational modifications. For example, serine phosphorylation of HDAC1 by protein kinase CK2 promotes HDAC1 deacetylase enzymatic activity and alters its interactions with proteins in corepressor complexes. Here, we describe an alternative signaling pathway by which HDAC1 activities are regulated. Specifically, we discover that EGFR activity promotes the tyrosine phosphorylation of HDAC1, which is necessary for its protein stability. A key EGFR phosphorylation site on HDAC1, Tyr72, mediates HDAC1's anti-apoptotic function. Given that HDAC1 overexpression and EGFR activity are strongly related with tumor progression and cancer cell survival, HDAC1 tyrosine phosphorylation may present a possible target to manipulate HDAC1 protein levels in future potential cancer treatment strategies.

The HDAC Inhibitor Domatinostat Promotes Cell-Cycle Arrest, Induces Apoptosis, and Increases Immunogenicity of Merkel Cell Carcinoma Cells

Merkel cell carcinoma (MCC) is a rare, highly aggressive skin cancer for which immune modulation by immune checkpoint inhibitors shows remarkable response rates. However, primary or secondary resistance to immunotherapy prevents benefits in a significant proportion of patients. For MCC, one immune escape mechanism is insufficient for recognition by T cells owing to the downregulation of major histocompatibility complex I surface expression. Histone deacetylase inhibitors have been demonstrated to epigenetically reverse the low major histocompatibility complex I expression caused by the downregulation of the antigen-processing machinery. Domatinostat, an orally available small-molecule inhibitor targeting histone deacetylase class I, is currently in clinical evaluation to overcome resistance to immunotherapy. In this study, we present preclinical data on domatinostat's efficacy and mode of action in MCC. Single-cell RNA sequencing revealed a distinct gene expression signature of antigen processing and presentation, cell-cycle arrest, and execution phase of apoptosis on treatment. Accordingly, functional assays showed that domatinostat induced G2M arrest and apoptosis. In the surviving cells, antigen-processing machinery component gene transcription and translation were upregulated, consequently resulting in increased major histocompatibility complex I surface expression. Altogether, domatinostat not only exerts direct antitumoral effects but also restores HLA class I surface expression on MCC cells, therefore, restoring surviving MCC cells' susceptibility to recognition and elimination by cognate cytotoxic T cells.

A novel HDAC1 inhibitor, CBUD‑1001, exerts anticancer effects by modulating the apoptosis and EMT of colorectal cancer cells

Colorectal cancer (CRC) is one of the most commonly diagnosed malignancies and is a leading cause of cancer‑related mortality worldwide. Histone deacetylases (HDACs) are a class of enzymes responsible for the epigenetic regulation of gene expression. Some HDAC inhibitors have been shown to be efficient agents for cancer treatment. The aim of the present study was to discover a novel, potent HDAC inhibitor and demonstrate its anticancer effect and molecular mechanisms in CRC cells. A novel fluorinated aminophenyl‑benzamide‑based compound, CBUD‑1001, was designed to specifically target HDAC1, and it was then synthesized and evaluated. CBUD‑1001 exerted a potent inhibitory effect on HDAC enzyme activity and exhibited anticancer potency against CRC cell lines. Molecular docking analysis rationalized the high potency of CBUD‑1001 by validating its conformation in the HDAC active site. Further investigation using CRC cells demonstrated that CBUD‑1001 inhibited HDAC activity by hyper‑acetylating histones H3 and H4, and it exerted an apoptotic effect by activating a mitochondrial‑dependent pathway. Of note, it was found that CBUD‑1001 attenuates the cell motility of CRC cells by downregulating the EMT signaling pathway. Thus, CBUD‑1001 may prove to be a promising novel drug candidate for CRC therapy.

Targeted therapy for mTORC1-driven tumours through HDAC inhibition by exploiting innate vulnerability of mTORC1 hyper-activation

BACKGOUND

The mechanistic target of rapamycin complex 1 (mTORC1) is important in the development and progression of many cancers. Targeted cancer therapy using mTORC1 inhibitors is used for treatment of cancers; however, their clinical efficacies are still limited.

METHODS

We recently created a new mouse model for human lymphangiosarcoma by deleting Tsc1 in endothelial cells and consequent hyper-activation of mTORC1. Using Tsc1iΔEC tumour cells from this mouse model, we assessed the efficacies of histone deacetylase (HDAC) inhibitors as anti-tumour agents for mTORC1-driven tumours.

RESULTS

Unlike the cytostatic effect of mTORC1 inhibitors, HDAC inhibitors induced Tsc1iΔEC tumour cell death in vitro and their growth in vivo. Analysis of several HDAC inhibitors suggested stronger anti-tumour activity of class I HDAC inhibitor than class IIa or class IIb inhibitors, but these or pan HDAC inhibitor SAHA did not affect mTORC1 activation in these cells. Moreover, HDAC inhibitor-induced cell death required elevated autophagy, but was not affected by disrupting caspase-dependent apoptosis pathways. We also observed increased reactive oxygen species and endoplasmic reticulum stress in SAHA-treated tumour cells, suggesting their contribution to autophagic cell death, which were dependent on mTORC1 hyper-activation.

CONCLUSION

These studies suggest a potential new treatment strategy for mTORC1-driven cancers like lymphangiosarcoma through an alternative mechanism.

Computer-Driven Development of an in Silico Tool for Finding Selective Histone Deacetylase 1 Inhibitors

Histone deacetylases (HDACs) are a class of epigenetic modulators overexpressed in numerous types of cancers. Consequently, HDAC inhibitors (HDACIs) have emerged as promising antineoplastic agents. Unfortunately, the most developed HDACIs suffer from poor selectivity towards a specific isoform, limiting their clinical applicability. Among the isoforms, HDAC1 represents a crucial target for designing selective HDACIs, being aberrantly expressed in several malignancies. Accordingly, the development of a predictive in silico tool employing a large set of HDACIs (aminophenylbenzamide derivatives) is herein presented for the first time. Software Phase was used to derive a 3D-QSAR model, employing as alignment rule a common-features pharmacophore built on 20 highly active/selective HDAC1 inhibitors. The 3D-QSAR model was generated using 370 benzamide-based HDACIs, which yielded an excellent correlation coefficient value (R² = 0.958) and a satisfactory predictive power (Q² = 0.822; Q²_F3 = 0.894). The model was validated (r²_{ext_ts} = 0.794) using an external test set (113 compounds not used for generating the model), and by employing a decoys set and the receiver-operating characteristic (ROC) curve analysis, evaluating the Güner-Henry score (GH) and the enrichment factor (EF). The results confirmed a satisfactory predictive power of the 3D-QSAR model. This latter represents a useful filtering tool for screening large chemical databases, finding novel derivatives with improved HDAC1 inhibitory activity.

Histone deacetylase (HDAC) inhibitors and doxorubicin combinations target both breast cancer stem cells and non-stem breast cancer cells simultaneously

PURPOSE

Breast cancer stem cells (CSCs) are a small subpopulation of cancer cells that have high capability for self-renewal, differentiation, and tumor initiation. CSCs are resistant to chemotherapy and radiotherapy, and are responsible for cancer recurrence and metastasis.

METHODS

By utilizing a panel of breast cancer cells and mammospheres culture as cell-based screening platforms, we performed high-throughput chemical library screens to identify agents that are effective against breast CSCs and non-CSCs. The hit molecules were paired with conventional chemotherapy to evaluate the combinatorial treatment effects on breast CSCs and non-CSCs.

RESULTS

We identified a total of 193 inhibitors that effectively targeting both breast CSCs and non-CSCs. We observed that histone deacetylase inhibitors (HDACi) synergized conventional chemotherapeutic agents (i.e., doxorubicin and cisplatin) in targeting breast CSCs and non-CSCs simultaneously. Further analyses revealed that quisinostat, a potent inhibitor for class I and II HDACs, potentiated doxorubicin-induced cytotoxicity in both breast CSCs and non-CSCs derived from the basal-like (MDA-MB-468 and HCC38), mesenchymal-like (MDA-MB-231), and luminal-like breast cancer (MCF-7). It was also observed that the basal-like breast CSCs and non-CSCs were more sensitive to the co-treatment of quisinostat with doxorubicin compared to that of the luminal-like breast cancer subtype.

CONCLUSION

In conclusion, this study demonstrates the potential of HDACi as therapeutic options, either as monotherapy or in combination with chemotherapeutics against refractory breast cancer.

Reconstitution of Mammalian Enzymatic Deacylation Reactions in Live Bacteria Using Native Acylated Substrates

Lysine deacetylases (KDACs) are enzymes that catalyze the hydrolysis of acyl groups from acyl-lysine residues. The recent identification of thousands of putative acylation sites, including specific acetylation sites, created an urgent need for biochemical methodologies aimed at better characterizing KDAC-substrate specificity and evaluating KDACs activity. To address this need, we utilized genetic code expansion technology to coexpress site-specifically acylated substrates with mammalian KDACs, and study substrate recognition and deacylase activity in live Escherichia coli. In this system the bacterial cell serves as a “biological test tube” in which the incubation of a single mammalian KDAC and a potential peptide or full-length acylated substrate transpires. We report novel deacetylation activities of Zn²⁺-dependent deacetylases and sirtuins in bacteria. We also measure the deacylation of propionyl-, butyryl-, and crotonyl-lysine, as well as novel deacetylation of Lys310-acetylated RelA by SIRT3, SIRT5, SIRT6, and HDAC8. This study highlights the importance of native interactions to KDAC-substrate recognition and deacylase activity.

Targeting Histone Deacetylases with Natural and Synthetic Agents: An Emerging Anticancer Strategy

Cancer initiation and progression are the result of genetic and/or epigenetic alterations. Acetylation-mediated histone/non-histone protein modification plays an important role in the epigenetic regulation of gene expression. Histone modification is controlled by the balance between histone acetyltransferase and (HAT) and histone deacetylase (HDAC) enzymes. Imbalance between the activities of these two enzymes is associated with various forms of cancer. Histone deacetylase inhibitors (HDACi) regulate the activity of HDACs and are being used in cancer treatment either alone or in combination with other chemotherapeutic drugs/radiotherapy. The Food and Drug Administration (FDA) has already approved four compounds, namely vorinostat, romidepsin, belinostat, and panobinostat, as HDACi for the treatment of cancer. Several other HDACi of natural and synthetic origin are under clinical trial for the evaluation of efficiency and side-effects. Natural compounds of plant, fungus, and actinomycetes origin, such as phenolics, polyketides, tetrapeptide, terpenoids, alkaloids, and hydoxamic acid, have been reported to show potential HDAC-inhibitory activity. Several HDACi of natural and dietary origin are butein, protocatechuic aldehyde, kaempferol (grapes, green tea, tomatoes, potatoes, and onions), resveratrol (grapes, red wine, blueberries and peanuts), sinapinic acid (wine and vinegar), diallyl disulfide (garlic), and zerumbone (ginger). HDACi exhibit their antitumor effect by the activation of cell cycle arrest, induction of apoptosis and autophagy, angiogenesis inhibition, increased reactive oxygen species generation causing oxidative stress, and mitotic cell death in cancer cells. This review summarizes the HDACs classification, their aberrant expression in cancerous tissue, structures, sources, and the anticancer mechanisms of HDACi, as well as HDACi that are either FDA-approved or under clinical trials.

Scriptaid cause histone deacetylase inhibition and cell cycle arrest in HeLa cancer cells: A study on structural and functional aspects

Scriptaid (SCR), a well-known histone deacetylase inhibitor, cause various cellular effects such as cell growth inhibition and apoptosis. In this study, we have evaluated the anti-cancer effects of Scriptaid in HeLa cells, IMR-32 and HepG2 cells. Scriptaid inhibited the growth of HeLa cells with IC₅₀ of 2μM at 48h in a dose-dependent manner. Flow-cytometric analysis indicated that SCR induced apoptosis. Scriptaid was found to inhibit HDAC-8 effectively than other HDAC inhibitor such as TSA as observed by HDAC-8 assay, Western blotting and modelling study. This observation was further strengthened by an artificial neuronal network (ANN) model.

HDAC Inhibitor-Induced Mitotic Arrest Is Mediated by Eg5/KIF11 Acetylation

Histone deacetylase 1 (HDAC1) is an epigenetic enzyme that regulates key cellular processes, such as cell proliferation, apoptosis, and cell survival, by deacetylating histone substrates. Aberrant expression of HDAC1 is implicated in multiple diseases, including cancer. As a consequence, HDAC inhibitors have emerged as effective anti-cancer drugs. HDAC inhibitor-induced G₀/G₁ cell-cycle arrest has been attributed to epigenetic transcriptional changes mediated by histone acetylation. However, the mechanism of G₂/M arrest remains poorly understood. Here, we identified mitosis-related protein Eg5 (KIF11) as an HDAC1 substrate using a trapping mutant strategy. HDAC1 colocalized with Eg5 during mitosis and influenced the ATPase activity of Eg5. Importantly, an HDAC1- and HDAC2-selective inhibitor caused mitotic arrest and monopolar spindle formation, consistent with a model in which Eg5 deacetylation by HDAC1 is critical for mitotic progression. These findings revealed a previously unknown mechanism of action of HDAC inhibitors involving Eg5 acetylation, and provide a compelling mechanistic hypothesis for HDAC inhibitor-mediated G₂/M arrest.

Design, synthesis and biological evaluation of novel hydroxamates and 2-aminobenzamides as potent histone deacetylase inhibitors and antitumor agents

Many studies have indicated that histone deacetylase (HDAC) inhibitors are promising agents for the treatment of cancer. With the aim to search for novel potent HDAC inhibitors, we designed and synthesized two series of hydroxamates and 2-aminobenzamides compounds as HDAC inhibitors and antitumor agents. Those compounds were investigated for their HDAC enzymatic inhibitory activities and in vitro anti-proliferation activities against diverse cancer cell line (A549, HepG2, MGC80-3 and HCT116). Most of the synthesized compounds displayed potent HDAC inhibitory activity and antiproliferative activity. In particular, Compound 12a, N-(2-aminophenyl)-4-[(4-fluorophenoxy)methyl]benzamide, was shown to have the most HDAC inhibitory activity (70.6% inhibition at 5 μM) and antitumor activity with IC50 value of as low as 3.84 μM against HepG2 human liver hepatocellular carcinoma cell line, more than 4.8-fold lower than CS055 and 5.9-fold lower than CI994. HDAC isoform selectivity assay indicated 12a is a potent HDAC2 inhibitor. Docking study of 12a suggested that it bound tightly to the binding pocket of HDAC2. Further investigation showed that 12a could inhibit the migration and colony formation of A549 cancer cells. Furthermore, 12a remarkably induced apoptosis and G2/M phase cell cycle arrest in A549 cancer cells. Those results indicated that compound 12a could be a promising candidate for treatment of cancer.

Histone deacetylases function as novel potential therapeutic targets for cancer

Diverse cellular functions, including tumor suppressor gene expression, DNA repair, cell proliferation and apoptosis, are regulated by histone acetylation and deacetylation. Histone deacetylases (HDACs) are enzymes involved in remodeling of chromatin by deacetylating the lysine residues. They play a pivotal role in epigenetic regulation of gene expression. Dysregulation of HDACs and aberrant chromatin acetylation and deacetylation have been implicated in the pathogenesis of various diseases, including cancer. Histone deacetylases have become a target for the development of drugs for treating cancer because of their major contribution to oncogenic cell transformation. Overexpression of HDACs correlates with tumorigenesis. Previous work showed that inhibition of HDACs results in apoptosis and the inhibition of cell proliferation in multiple cells. A significant number of HDAC inhibitors have been developed in the past decade. These inhibitors have strong anticancer effects in vitro and in vivo, inducing growth arrest, differentiation, and programmed cell death, inhibiting cell migration, invasion, and metastasis, and suppressing angiogenesis. In addition, HDAC-mediated deacetylation alters the transcriptional activity of nuclear transcription factors, including p53, E2F, c-Myc, and nuclear factor-κB, as well as the extracellular signal-regulated kinase1/2, phosphatidylinositol 3-kinase, Notch, and Wnt signaling pathways. This review highlights the role of HDACs in cancer pathogenesis and, more importantly, that HDACs are potential novel therapeutic targets.

LSD1 Substrate Binding and Gene Expression Are Affected by HDAC1-Mediated Deacetylation

Lysine Specific Demethylase 1 (LSD1) catalyzes the demethylation of histone 3 to regulate gene expression. With a fundamental role in gene regulation, LSD1 is involved in multiple cellular processes, including embryonic development, cell proliferation, and metastasis. Significantly, LSD1 is overexpressed in multiple cancers and has emerged as a potential anticancer drug target. LSD1 is typically found in association with another epigenetic enzyme, histone deacetylase (HDAC). HDAC and LSD1 inhibitor compounds have been tested as combination anticancer agents. However, the functional link between LSD1 and HDAC has yet to be understood in detail. Here, we used a substrate trapping strategy to identify cellular substrates of HDAC1. Using inactive HDAC1 mutants, we identified LSD1 as an HDAC1 substrate. HDAC1 mediated deacetylation of LSD1 at K374 in the substrate binding lobe, which affected the histone 3 binding and gene expression activity of LSD1. The mechanistic link between HDAC1 and LSD1 established here suggests that HDAC inhibitors influence LSD1 activity, which will ultimately guide drug design targeting epigenetic enzymes.

Cellular analysis of the action of epigenetic drugs and probes

Small molecule drugs and probes are important tools in drug discovery, pharmacology, and cell biology. This is of course also true for epigenetic inhibitors. Important examples for the use of established epigenetic inhibitors are the study of the mechanistic role of a certain target in a cellular setting or the modulation of a certain phenotype in an approach that aims toward therapeutic application. Alternatively, cellular testing may aim at the validation of a new epigenetic inhibitor in drug discovery approaches. Cellular and eventually animal models provide powerful tools for these different approaches but certain caveats have to be recognized and taken into account. This involves both the selectivity of the pharmacological tool as well as the specificity and the robustness of the cellular system. In this article, we present an overview of different methods that are used to profile and screen for epigenetic agents and comment on their limitations. We describe not only diverse successful case studies of screening approaches using different assay formats, but also some problematic cases, critically discussing selected applications of these systems.

Histone deacetylase 1 plays a predominant pro-oncogenic role in Eμ-myc driven B cell lymphoma

The two histone deacetylases (Hdacs), Hdac1 and Hdac2, are erasers of acetylation marks on histone tails, and are important regulators of gene expression that were shown to play important roles in hematological malignancies. However, several recent studies reported opposing tumor-suppressive or tumor-promoting roles for Hdac1 and Hdac2. Here, we investigated the functional role of Hdac1 and Hdac2 using the Eμ-myc mouse model of B cell lymphoma. We demonstrate that Hdac1 and Hdac2 have a pro-oncogenic role in both Eμ-myc tumorigenesis and tumor maintenance. Hdac1 and Hdac2 promote tumorigenesis in a gene dose-dependent manner, with a predominant function of Hdac1. Our data show that Hdac1 and Hdac2 impact on Eμ-myc B cell proliferation and apoptosis and suggest that a critical level of Hdac activity may be required for Eμ-myc tumorigenesis and proper B cell development. This provides the rationale for utilization of selective Hdac1 and Hdac2 inhibitors in the treatment of hematological malignancies.

Development of a gene carrier using a triblock co-polyelectrolyte with poly(ethylene imine)-poly(lactic acid)-poly(ethylene glycol)

The success of gene therapy mainly depends on the carriers for effective gene delivery. A non-viral vector using a cationic block co-polyelectrolyte, PEI-PLA-PEG polyethyleneimine-poly(lactic acid)-poly(ethylene glycol)) was developed as a potential gene carrier. The cationic PEI-PLA-PEG showed less toxicity compared to PEI and formed a gene nanocomplex (termed polyplex) by interaction with plasmid DNA or small interference RNA. The polyplex showed smaller particle size and greater positive zeta potential by increasing the high polymer nitrogen/DNA phosphate ratio. The polyplex with a nitrogen/DNA phosphate ratio of 16 or 32 demonstrated higher gene transfection by fluorescence imaging, flow cytometry measurement, and β-galactosidase activity. In particular, the polyplex with therapeutic histone deacetylase small interference RNA at nitrogen/DNA phosphate ratio 16 showed the most favorable properties with definite tumor growth inhibition. The synthetic PEI-PLA-PEG also showed less toxicity and would, therefore, be a great potential gene carrier, particularly given that small interference RNA delivery does not increase the charge density of small interference RNA due to the formation of a stable complex through conjugation with PLA-PEG.

Yakushinamides, Polyoxygenated Fatty Acid Amides That Inhibit HDACs and SIRTs, from the Marine Sponge Theonella swinhoei

Yakushinamides A (1) and B (2), prolyl amides of polyoxygenated fatty acids, have been isolated from the marine sponge Theonella swinhoei as inhibitors of HDACs and SIRTs. Their planar structures were determined by interpretation of the NMR data of the intact molecules and tandem FABMS data of the methanolysis products. For the assignment of the relative configurations of the three contiguous oxymethine carbons in 1 and 2, Kishi's universal NMR database was applied to the methanolysis products. During the assignments of relative configurations of the isolated 1-hydroxy-3-methyl moiety in 1 and the isolated 1-hydroxy-2-methyl moiety in 2, we found diagnostic NMR features to distinguish each pair of diastereomers. The absolute configurations of 1 and 2 were determined by a combination of the modified Mosher's method and Marfey's method. Although the modified Mosher's method was successfully applied to the methanolysis product of 1, this method gave an ambiguous result at C-20 when applied to the methanolysis product of 2, even after oxidative cleavage of the C-14 and C-15 bond.

Growth-suppressive effect of suberoylanilide hydroxamic acid (SAHA) on human oral cancer cells

PURPOSE

The histone deacetylase (HDAC) inhibitor suberoylanilide hydroxamic acid (SAHA) has been reported to exhibit anticancer activities in various cancer cell types, but as yet there are few reports on the anticancer effects of SAHA in oral squamous cell carcinoma (OSCC)-derived cells and xenograft models.

METHODS

The anti-proliferative and apoptotic activities of SAHA were assessed in human HSC-3 and HSC-4 (OSCC)-derived cell lines and JB6 normal mouse skin-derived epidermal cells using histone acetylation, soft agar colony formation, trypan blue exclusion, 4'-6-diamidino-2-phenylindole (DAPI) staining, Live/Dead viability/cytotoxicity and Western blot analyses.

RESULTS

We found that SAHA treatment resulted in hyperacetylation of histones H2A and H3 and a concomitant decrease in the viability of HSC-3 and HSC-4 cells. SAHA also significantly inhibited the neoplastic transformation of JB6 cells treated with TPA, whereas the viability of these cells was not affected by this treatment. Additionally, we found that SAHA suppressed the anchorage-independent growth (colony forming capacity in soft agar) of HSC-3 and HSC-4 cells. DAPI staining, Live/Dead and Western blot analyses revealed that SAHA can induce caspase-dependent apoptosis in HSC-3 and HSC-4 cells. We also found that SAHA treatment led to inhibition of ERK phosphorylation, and that two MEK inhibitors potentiated SAHA-mediated apoptosis. Okadaic acid treatment inhibited SAHA-mediated apoptosis in both the HSC-3 and HSC-4 cell lines, wheras SAHA induced a profound in vivo inhibition of tumor growth in HSC-3 xenografts.

CONCLUSIONS

Our results indicate that the ERK signaling pathway may constitute a critical denominator of SAHA-induced apoptosis in OSCC-derived cells and that SAHA may have therapeutic potential for OSCC.

TGF-β1 Reduces miR-29a Expression to Promote Tumorigenicity and Metastasis of Cholangiocarcinoma by Targeting HDAC4

Transforming growth factor β1 (TGF-β1) and miRNAs play important roles in cholangiocarcinoma progression. In this study, miR-29a level was found significantly decreased in both cholangiocarcinoma tissues and tumor cell lines. TGF-β1 reduced miR-29a expression in tumor cell lines. Furthermore, anti-miR-29a reduced the proliferation and metastasis capacity of cholangiocarcinoma cell lines in vitro, overexpression of miR-29a counteracted TGF-β1-mediated cell growth and metastasis. Subsequent investigation identified HDAC4 is a direct target of miR-29a. In addition, restoration of HDAC4 attenuated miR-29a-mediated inhibition of cell proliferation and metastasis. Conclusions: TGF-β1/miR-29a/HDAC4 pathway contributes to the pathogenesis of cholangiocarcinoma and our data provide new therapeutic targets for cholangiocarcinoma.

Histone Deacetylase 10 Regulates the Cell Cycle G2/M Phase Transition via a Novel Let-7-HMGA2-Cyclin A2 Pathway

Histone deacetylase (HDAC) inhibition leads to cell cycle arrest in G1 and G2, suggesting HDACs as therapeutic targets for cancer and diseases linked to abnormal cell growth and proliferation. Many HDACs are transcriptional repressors. Some may alter cell cycle progression by deacetylating histones and repressing transcription of key cell cycle regulatory genes. Here, we report that HDAC10 regulates the cell cycle via modulation of cyclin A2 expression, and cyclin A2 overexpression rescues HDAC10 knockdown-induced G2/M transition arrest. HDAC10 regulates cyclin A2 expression by deacetylating histones near the let-7 promoter, thereby repressing transcription. In HDAC10 knockdown cells, let-7f and microRNA 98 (miR-98) were upregulated and the let-7 family target, HMGA2, was downregulated. HMGA2 loss resulted in enrichment of the transcriptional repressor E4F at the cyclin A2 promoter. These findings support a role for HDACs in cell cycle regulation, reveal a novel mechanism of HDAC10 action, and extend the potential of HDACs as targets in diseases of cell cycle dysregulation.

Mechanisms of Histone Deacetylase Inhibitor-Regulated Gene Expression in Cancer Cells

SIGNIFICANCE

Class I and II histone deacetylase inhibitors (HDACis) are approved for the treatment of cutaneous T-cell lymphoma and are undergoing clinical trials as single agents, and in combination, for other hematological and solid tumors. Understanding their mechanisms of action is essential for their more effective clinical use, and broadening their clinical potential.

RECENT ADVANCES

HDACi induce extensive transcriptional changes in tumor cells by activating and repressing similar numbers of genes. These transcriptional changes mediate, at least in part, HDACi-mediated growth inhibition, apoptosis, and differentiation. Here, we highlight two fundamental mechanisms by which HDACi regulate gene expression—histone and transcription factor acetylation. We also review the transcriptional responses invoked by HDACi, and compare these effects within and across tumor types.

CRITICAL ISSUES

The mechanistic basis for how HDACi activate, and in particular repress gene expression, is not well understood. In addition, whether subsets of genes are reproducibly regulated by these agents both within and across tumor types has not been systematically addressed. A detailed understanding of the transcriptional changes elicited by HDACi in various tumor types, and the mechanistic basis for these effects, may provide insights into the specificity of these drugs for transformed cells and specific tumor types.

FUTURE DIRECTIONS

Understanding the mechanisms by which HDACi regulate gene expression and an appreciation of their transcriptional targets could facilitate the ongoing clinical development of these emerging therapeutics. In particular, this knowledge could inform the design of rational drug combinations involving HDACi, and facilitate the identification of mechanism-based biomarkers of response.

Design and Validation of FRESH, a Drug Discovery Paradigm Resting on Robust Chemical Synthesis

A method capable of identifying novel synthetic targets for small molecule lead optimization has been developed. The FRESH (FRagment-based Exploitation of modular Synthesis by vHTS) approach relies on a multistep synthetic route to a target series of compounds devised by a close collaboration between synthetic and computational chemists. It combines compound library generation, quantitative structure-acitvity relationship construction, fragment processing, virtual high throughput screening and display of results within the Pipeline Pilot framework. Outcomes enumerate tailored selection of novel synthetic targets with improved potency and optimized physical properties for an emerging compound series. To validate the application of FRESH, three retrospective case studies have been performed to pinpoint reported potent analogues. One prospective case study was performed to demonstrate that FRESH is able to capture additional potent analogues.

Targeting histone deacetylase 6 mediates a dual anti-melanoma effect: Enhanced antitumor immunity and impaired cell proliferation

The median survival for metastatic melanoma is in the realm of 8-16 months and there are few therapies that offer significant improvement in overall survival. One of the recent advances in cancer treatment focuses on epigenetic modifiers to alter the survivability and immunogenicity of cancer cells. Our group and others have previously demonstrated that pan-HDAC inhibitors induce apoptosis, cell cycle arrest and changes in the immunogenicity of melanoma cells. Here we interrogated specific HDACs which may be responsible for this effect. We found that both genetic abrogation and pharmacologic inhibition of HDAC6 decreases in vitro proliferation and induces G1 arrest of melanoma cell lines without inducing apoptosis. Moreover, targeting this molecule led to an important upregulation in the expression of tumor associated antigens and MHC class I, suggesting a potential improvement in the immunogenicity of these cells. Of note, this anti-melanoma activity was operative regardless of mutational status of the cells. These effects translated into a pronounced delay of in vivo melanoma tumor growth which was, at least in part, dependent on intact immunity as evidenced by the restoration of tumor growth after CD4+ and CD8+ depletion. Given our findings, we provide the initial rationale for the further development of selective HDAC6 inhibitors as potential therapeutic anti-melanoma agents.

Down-regulation of HDAC5 inhibits growth of human hepatocellular carcinoma by induction of apoptosis and cell cycle arrest

Histone deacetylases (HDACs) play a critical role in the proliferation, differentiation, and apoptosis of cancer cells. An obstacle for the application of HDAC inhibitors as effective anti-cancer therapeutics is that our current knowledge on the contributions of different HDACs in various cancer types remains scarce. The present study reported that the mRNA and protein levels of HDAC5 were up-regulated in human hepatocellular carcinoma (HCC) tissues and cells as shown by quantitative real-time PCR and Western blot. MTT assay and BrdU incorporation assay showed that the down-regulation of HDAC5 inhibited cell proliferation in HepG2, Hep3B, and Huh7 cell lines. Data from in vivo xenograft tumorigenesis model also demonstrated the anti-proliferative effect of HDAC5 depletion on tumor cell growth. Furthermore, the suppression of HDAC5 promoted cell apoptosis and induced G1-phase cell cycle arrest in HCC cells. On the molecular level, we observed altered expression of apoptosis-related proteins such as p53, bax, bcl-2, cyto C, and caspase 3 in HDAC5-shRNA-transfected cells. Knockdown of HDAC5 led to a significant up-regulation of p21 and down-regulation of cyclin D1 and CDK2/4/6. We also found that the down-regulation of HDAC5 substantially increased p53 stability and promoted its nuclear localization and transcriptional activity. Our study suggested that knockdown of HDAC5 could inhibit cancer cell proliferation by the induction of cell cycle arrest and apoptosis; thus, suppression of HDAC5 may be a viable option for treating HCC patients.

Histone deacetylase inhibitors in oral squamous cell carcinoma treatment

Introduction: The involvement of the histone deacetylases (HDACs) family in tumor development and progression is well demonstrated. HDAC inhibitors (HDACis) constitute a novel, heterogeneous family of highly selective anticancer agents that inhibit HDACs and present significant antitumor activity in several human malignancies, including oral squamous cell carcinoma (OSCC). Areas covered: This review summarizes the current research on the anticancer activity of HDACis against OSCC. The review also presents the molecular mechanisms of HDACis action and the existing studies evaluating their utilization in combined therapies of OSCC. Expert opinion: The currently available data support evidence that HDACis may provide new therapeutic options against OSCC, decreasing treatment side effects and allowing a more conservative therapeutic approach. Future research should be focused on in vivo and clinical evaluation of their utilization as combined therapies or monotherapies. Before HDACis can be brought into clinical practice as treatment options for OSCC, further evaluation is needed to determine their optimal dosage, the appropriate duration of treatment and whether they should be used in combination or as stand-alone therapeutics.

Histone deacetylase 3 promotes pancreatic cancer cell proliferation, invasion and increases drug-resistance through histone modification of P27, P53 and Bax

Pancreatic cancer is one of the most aggressive solid malignancies with a dismal survival rate. Recent studies have shown that high expression levels of histone deacetylase 3 (HDAC3) correlate with malignant phenotype. However, the expression patterns and biological role of HDAC3 in pancreatic cancer remain unclear. In this study, our data showed that a higher level of HDAC3 protein expression was found in pancreatic cancer as compared to paired paracancerous tissues. Consistently, higher expression level of HDAC3 was found in all of the eight pancreatic cancer cell lines relative to human pancreatic ductal epithelial cells (HPDE). In addition, further function analysis revealed that HDAC3 can function as oncogenic protein, which could promote pancreatic cancer cell proliferation, migration and invasion, and may increase drug resistance. Moreover, the functional involvement of HDAC3 was partially correlated with post-induction repression of P53, P27 and Bax gene transcription, acting via H3K9 deacetylation. Taken together, our data suggest that HDAC3 participates in the pathogenesis and progression of pancreatic cancer through histone modification, which might be a pivotal epigenetic target against this devastating disease.

The therapeutic potential of class I selective histone deacetylase inhibitors in ovarian cancer

Epithelial ovarian cancer remains the deadliest gynecologic malignancy. Despite advances in treatment, new approaches are needed. Histone deacetylases (HDACs) are a family of enzymes that regulate gene expression by removing acetyl groups from lysine residues on histones and non-histone proteins. Inhibition of HDACs with small molecules has led to the development of histone deacetylase inhibitors (HDACi) that are in clinical use, primarily for hematologic malignancies. Although clinical trials with HDACi as single agents in solid tumors have been disappointing, data from independent labs and recent work by our group show that class I selective HDACi have potent anti-tumor effects in pre-clinical models of ovarian cancer. This review summarizes the role of HDACs in ovarian cancer and the potential niche for selective class I HDACi, particularly HDAC3 in ovarian cancer therapy.

Class I HDAC activity is required for renal protection and regeneration after acute kidney injury

Activation of histone deacetylases (HDACs) is required for renal epithelial cell proliferation and kidney development. However, their role in renal tubular cell survival and regeneration after acute kidney injury (AKI) remains unclear. In this study, we demonstrated that all class I HDAC isoforms (1, 2, 3, and 8) were expressed in the renal epithelial cells of the mouse kidney. Inhibition of class I HDACs with MS-275, a highly selective inhibitor, resulted in more severe tubular injury in the mouse model of AKI induced by folic acid or rhabdomyolysis, as indicated by worsening renal dysfunction, increased neutrophil gelatinase-associated lipocalin expression, and enhanced apoptosis and caspase-3 activation. Blocking class I HDAC activity also impaired renal regeneration as evidenced by decreased expression of renal Pax-2, vimentin, and proliferating cell nuclear antigen. Injury to the kidney is accompanied by increased phosphorylation of epidermal growth factor receptor (EGFR), signal transducers and activators of transcription 3 (STAT3), and Akt. Inhibition of class I HDACs suppressed EGFR phosphorylation as well as reduced its expression. MS-275 was also effective in inhibiting STAT3 and Akt phosphorylation, but this treatment did not affect their expression levels. Taken together, these data suggest that the class I HDAC activity contributes to renal protection and functional recovery and is required for renal regeneration after AKI. Furthermore, renal EGFR signaling is subject to regulation by this class of HDACs.

Discovery of the first N-hydroxycinnamamide-based histone deacetylase 1/3 dual inhibitors with potent oral antitumor activity

In our previous study, we designed and synthesized a novel series of N-hydroxycinnamamide-based HDAC inhibitors (HDACIs), among which the representative compound 14a exhibited promising HDACs inhibition and antitumor activity. In this current study, we report the development of a more potent class of N-hydroxycinnamamide-based HDACIs, using 14a as lead, among which, compound 11r gave IC50 values of 11.8, 498.1, 3.9, 2000.8, 5700.4, 308.2, and 900.4 nM for the inhibition of HDAC1, HDAC2, HDAC3, HDAC8, HDAC4, HDAC6, and HDAC11, exhibiting dual HDAC1/3 selectivity. Compounds 11e, 11r, 11w, and 11y showed excellent growth inhibition in multiple tumor cell lines. In vivo antitumor assay in U937 xenograft model identified compound 11r as a potent, orally active HDACI. To the best of our knowledge, this work constitutes the first report of oral active N-hydroxycinnamamide-based HDACIs with dual HDAC1/3 selectivity.

Molecular epigenetics in the management of ovarian cancer: are we investigating a rational clinical promise?

Epigenetics is essentially a phenotypical change in gene expression without any alteration of the DNA sequence; the emergence of epigenetics in cancer research and mainstream oncology is fueling new hope. However, it is not yet known whether this knowledge will translate to improved clinical management of ovarian cancer. In this malignancy, women are still undergoing chemotherapy similar to what was approved in 1978, which to this day represents one of the biggest breakthroughs for treating ovarian cancer. Although liquid tumors are benefiting from epigenetically related therapies, solid tumors like ovarian cancer are not (yet?). Herein, we will review the science of molecular epigenetics, especially DNA methylation, histone modifications and microRNA, but also include transcription factors since they, too, are important in ovarian cancer. Pre-clinical and clinical research on the role of epigenetic modifications is also summarized. Unfortunately, ovarian cancer remains an idiopathic disease, for the most part, and there are many areas of patient management, which could benefit from improved technology. This review will also highlight the evidence suggesting that epigenetics may have pre-clinical utility in pharmacology and clinical applications for prognosis and diagnosis. Finally, drugs currently in clinical trials (i.e., histone deacetylase inhibitors) are discussed along with the promise for epigenetics in the exploitation of chemoresistance. Whether epigenetics will ultimately be the answer to better management in ovarian cancer is currently unknown; but we hope so in the future.

Liquid chromatography mass spectrometry determination of mocetinostat (MGCD0103) in rat plasma and its application to a pharmacokinetic study

Mocetinostat (MGCD0103) is a benzamide histone deacetylase inhibitor undergoing clinical trials for treatment of various cancers including Hodgkin's lymphoma, follicular lymphoma and acute myelogenous leukemia. A sensitive and selective liquid chromatography mass spectrometry method for determination of MGCD0103 in rat plasma was developed. After addition of midazolam as internal standard (IS), protein precipitation by acetonitrile was used as sample preparation. Chromatographic separation was achieved on a C18 (2.1 mm×50 mm, 3.5 µm) column with acetonitrile-0.1% formic acid in water as mobile phase with gradient elution. An electrospray ionization source was applied and operated in positive ion mode; selective ion monitoring (SIM) mode was used for quantification using target fragment ions m/z 397 for MGCD0103 and m/z 326 for the IS. Calibration plots were linear over the range of 5-5000 ng/mL for MGCD0103 in rat plasma. Mean recoveries of MGCD0103 in rat plasma were in the range of 89.7-96.1%. RSD of intra-day and inter-day precision were both<11%. The accuracy of the method ranged from 96.5% to 109.7%. The matrix effects for MGCD0103 were between 94.5% and 97.4%. The method was successfully applied to pharmacokinetic study of MGCD0103 after oral (15 mg/kg) and intravenous (3 mg/kg) administration in rats. The bioavailability of MGCD0103 was 29.3% in rats.

Development of histone deacetylase inhibitors for cancer treatment

Histone deacetylase (HDAC) inhibitors are an exciting new addition to the arsenal of cancer therapeutics. The inhibition of HDAC enzymes by HDAC inhibitors shifts the balance between the deacetylation activity of HDAC enzymes and the acetylation activity of histone acetyltransferases, resulting in hyperacetylation of core histones. Exposure of cancer cells to HDAC inhibitors has been associated with a multitude of molecular and biological effects, ranging from transcriptional control, chromatin plasticity, protein-DNA interaction to cellular differentiation, growth arrest and apoptosis. In addition to the antitumor effects seen with HDAC inhibitors alone, these compounds may also potentiate cytotoxic agents or synergize with other targeted anticancer agents. The exact mechanism by which HDAC inhibitors cause cell death is still unclear and the specific roles of individual HDAC enzymes as therapeutic targets has not been established. However, emerging evidence suggests that the effects of HDAC inhibitors on tumor cells may not only depend on the specificity and selectivity of the HDAC inhibitor, but also on the expression patterns of HDAC enzymes in the tumor tissue. In this review, the recent advances in the understanding and clinical development of HDAC inhibitors, as well as their current role in cancer therapy, will be discussed.

SAMSN1 is highly expressed and associated with a poor survival in glioblastoma multiforme

OBJECTIVES

To study the expression pattern and prognostic significance of SAMSN1 in glioma.

METHODS

Affymetrix and Arrystar gene microarray data in the setting of glioma was analyzed to preliminarily study the expression pattern of SAMSN1 in glioma tissues, and Hieratical clustering of gene microarray data was performed to filter out genes that have prognostic value in malignant glioma. Survival analysis by Kaplan-Meier estimates stratified by SAMSN1 expression was then made based on the data of more than 500 GBM cases provided by The Cancer Genome Atlas (TCGA) project. At last, we detected the expression of SAMSN1 in large numbers of glioma and normal brain tissue samples using Tissue Microarray (TMA). Survival analysis by Kaplan-Meier estimates in each grade of glioma was stratified by SAMSN1 expression. Multivariate survival analysis was made by Cox proportional hazards regression models in corresponding groups of glioma.

RESULTS

With the expression data of SAMSN1 and 68 other genes, high-grade glioma could be classified into two groups with clearly different prognoses. Gene and large sample tissue microarrays showed high expression of SAMSN1 in glioma particularly in GBM. Survival analysis based on the TCGA GBM data matrix and TMA multi-grade glioma dataset found that SAMSN1 expression was closely related to the prognosis of GBM, either PFS or OS (P<0.05). Multivariate survival analysis with Cox proportional hazards regression models confirmed that high expression of SAMSN1 was a strong risk factor for PFS and OS of GBM patients.

CONCLUSION

SAMSN1 is over-expressed in glioma as compared with that found in normal brains, especially in GBM. High expression of SAMSN1 is a significant risk factor for the progression free and overall survival of GBM.

Divergent roles of HDAC1 and HDAC2 in the regulation of epidermal development and tumorigenesis

The histone deacetylases HDAC1 and HDAC2 remove acetyl moieties from lysine residues of histones and other proteins and are important regulators of gene expression. By deleting different combinations of Hdac1 and Hdac2 alleles in the epidermis, we reveal a dosage-dependent effect of HDAC1/HDAC2 activity on epidermal proliferation and differentiation. Conditional ablation of either HDAC1 or HDAC2 in the epidermis leads to no obvious phenotype due to compensation by the upregulated paralogue. Strikingly, deletion of a single Hdac2 allele in HDAC1 knockout mice results in severe epidermal defects, including alopecia, hyperkeratosis, hyperproliferation and spontaneous tumour formation. These mice display impaired Sin3A co-repressor complex function, increased levels of c-Myc protein, p53 expression and apoptosis in hair follicles (HFs) and misregulation of HF bulge stem cells. Surprisingly, ablation of HDAC1 but not HDAC2 in a skin tumour model leads to accelerated tumour development. Our data reveal a crucial function of HDAC1/HDAC2 in the control of lineage specificity and a novel role of HDAC1 as a tumour suppressor in the epidermis.

Molecular and biologic analysis of histone deacetylase inhibitors with diverse specificities

Histone deacetylase inhibitors (HDACi) are anticancer agents that induce hyperacetylation of histones, resulting in chromatin remodeling and transcriptional changes. In addition, nonhistone proteins, such as the chaperone protein Hsp90, are functionally regulated through hyperacetylation mediated by HDACis. Histone acetylation is thought to be primarily regulated by HDACs 1, 2, and 3, whereas the acetylation of Hsp90 has been proposed to be specifically regulated through HDAC6. We compared the molecular and biologic effects induced by an HDACi with broad HDAC specificity (vorinostat) with agents that predominantly inhibited selected class I HDACs (MRLB-223 and romidepsin). MRLB-223, a potent inhibitor of HDACs 1 and 2, killed tumor cells using the same apoptotic pathways as the HDAC 1, 2, 3, 6, and 8 inhibitor vorinostat. However, vorinostat induced histone hyperacetylation and killed tumor cells more rapidly than MRLB-223 and had greater therapeutic efficacy in vivo. FDCP-1 cells dependent on the Hsp90 client protein Bcr-Abl for survival, were killed by all HDACis tested, concomitant with caspase-dependent degradation of Bcr-Abl. These studies provide evidence that inhibition of HDAC6 and degradation of Bcr-Abl following hyperacetylation of Hsp90 is likely not a major mechanism of action of HDACis as had been previously posited.

Histone deacetylase (HDAC) 10 suppresses cervical cancer metastasis through inhibition of matrix metalloproteinase (MMP) 2 and 9 expression

Aberrant expression of histone deacetylases (HDACs) is associated with carcinogenesis. Some HDAC inhibitors are widely considered as promising anticancer therapeutics. A major obstacle for development of HDAC inhibitors as highly safe and effective anticancer therapeutics is that our current knowledge on the contributions of different HDACs in various cancer types remains scant. Here we report that the expression level of HDAC10 was significantly lower in patients exhibiting lymph node metastasis compared with that in patients lacking lymph node metastasis in human cervical squamous cell carcinoma. Forced expression of HDAC10 in cervical cancer cells significantly inhibited cell motility and invasiveness in vitro and metastasis in vivo. Mechanistically, HDAC10 suppresses expression of matrix metalloproteinase (MMP) 2 and 9 genes, which are known to be critical for cancer cell invasion and metastasis. At the molecular level, HDAC10 binds to MMP2 and -9 promoter regions, reduces the histone acetylation level, and inhibits the binding of RNA polymerase II to these regions. Furthermore, an HDAC10 mutant lacking histone deacetylase activity failed to mimic the functions of full-length protein. These results identify a critical role of HDAC10 in suppression of cervical cancer metastasis, underscoring the importance of developing isoform-specific HDAC inhibitors for treatment of certain cancer types such as cervical squamous cell carcinoma.

Comparison of epigenetic profiles of human oral epithelial cells from HIV-positive (on HAART) and HIV-negative subjects

HIV-infected subjects on highly active antiretroviral therapy (HAART) are susceptible to comorbid microbial infections in the oral cavity. We observed that primary oral epithelial cells (POECs) isolated from HIV+ subjects on HAART grow more slowly and are less innate immune responsive to microbial challenge when compared with POECs from normal subjects. These aberrant cells also demonstrate epigenetic differences that include reduction in histone deacetylase 1 (HDAC-1) levels and reduced total DNA methyltransferase (DNMT) activity specific to enzymes DNMT1 and DNMT3A. The DNMT activity correlates well with global DNA methylation, indicating that aberrant DNMT activity in HIV+ (on HAART) POECs leads to an aberrantly methylated epithelial cell phenotype. Overall, our results lead us to hypothesize that, in patients with chronic HIV infection on HAART, epigenetic changes in key genes result in increased vulnerability to microbial infection in the oral cavity.