The Histone Deacetylase Inhibitor Trichostatin A Has Genotoxic Effects in Human Lymphoblasts In Vitro

Genomic and cellular context-dependent expression of the human ELMO1 gene transcript variants

Engulfment and cell motility protein 1 (Elmo1) forms a complex with Dedicator of cytokinesis (Dock) 1-5 and promotes GTP-loading of Rac1, the major agent of cell movement. While the pathophysiological roles of Elmo1 have expanded from apoptotic cell engulfment to cancer, inflammation, diabetic nephropathy and cardiomyopathy, little information is available on its transcriptional regulation. Genome databases indicate at least five transcript variants for human ELMO1: the variants V1, V4 and V5 encode a full-length 727 aa protein, whereas V2 and V3 encode a truncated Elmo1 of 247 aa that lacks N-terminal domains. A CpG island promoter drives the major V1 transcript, while an LTR12 drives V5 in intron 1, one of the three LTR12 family of retroviral elements in ELMO1. In contrast, the short-forms V2 and V3 contain CAT-TATA type promoters. Examination of various cell lines by RT-qPCR designed to detect individual transcripts showed that basal transcriptions of the variants were very low to undetectable in cultured cells. However, treatments with Trichostatin A, a histone deacetylase inhibitor, or with 5-Aza-2'-deoxycytidine, a DNA methyl transferase inhibitor, significantly upregulated V1, V4, V5 and V2 expression in a cell line-specific manner, indicating that these transcripts are epigenetically regulated. Another LTR12D transposon in intron 13 also drives an unannotated transcript stimulated by these inhibitors. Finally, we found the levels of V2 transcripts in the mouse and human brain exceed those of V1, suggesting a brain-specific regulation and role of V2 protein.

From Pipeline to Plant Protection Products: Using New Approach Methodologies (NAMs) in Agrochemical Safety Assessment

The human population will be approximately 9.7 billion by 2050, and food security has been identified as one of the key issues facing the global population. Agrochemicals are an important tool available to farmers that enable high crop yields and continued access to healthy foods, but the average new agrochemical active ingredient takes more than ten years, 350 million dollars, and 20,000 animals to develop and register. The time, monetary, and animal costs incentivize the use of New Approach Methodologies (NAMs) in early-stage screening to prioritize chemical candidates. This review outlines NAMs that are currently available or can be adapted for use in early-stage screening agrochemical programs. It covers new in vitro screens that are on the horizon in key areas of regulatory concern. Overall, early-stage screening with NAMs enables the prioritization of development for agrochemicals without human and environmental health concerns through a more directed, agile, and iterative development program before animal-based regulatory testing is even considered.

Novel Histone Deacetylase 6 Inhibitor Confers Anti-inflammatory Effects and Enhances Gut Barrier Function

Background/Aims

The purpose of the current study was to examine the anti-inflammatory effects of CKD-506, a novel histone deacetylase 6 inhibitor, on human peripheral blood mononuclear cells (PBMCs) and CD4+ T cells and to explore the relationship between CKD-506 and gut epithelial barrier function.

Methods

Lipopolysaccharide-stimulated human PBMCs from inflammatory bowel disease (IBD) patients were treated with CKD-506, and tumor necrosis factor (TNF)-α expression was measured using an enzyme-linked immunosorbent assay. The proliferation of CD4+ T cells from IBD patients was evaluated using flow cytometric analysis. The effects of CKD-506 on gut barrier function in a cell line and colon organoids, based on examinations of mRNA production, goblet cell differentiation, and E-cadherin recovery, were investigated using quantitative reverse transcription polymerase chain reaction, immunofluorescence, and a fluorescein isothiocyanate-dextran permeability assay.

Results

Secretion of TNF-α, a pivotal pro-inflammatory mediator in IBD, by lipopolysaccharide-triggered PBMCs was markedly decreased by CKD-506 treatment in a dose-dependent manner and to a greater extent than by tofacitinib or tubastatin A treatment. E-cadherin mRNA expression and goblet cell differentiation increased significantly and dose-dependently in HT-29 cells in response to CKD-506, and inhibition of E-cadherin loss after TNF-α stimulation was significantly reduced both in HT-29 cells and gut organoids. Caco-2 cells treated with CKD-506 showed a significant reduction in barrier permeability in a dose-dependent manner.

Conclusions

The present study demonstrated that CKD-506 has anti-inflammatory effects on PBMCs and CD4 T cells and improves gut barrier function, suggesting its potential as a small-molecule therapeutic option for IBD.

SIRT2 Inhibition Rescues Neurodegenerative Pathology but Increases Systemic Inflammation in a Transgenic Mouse Model of Alzheimer's Disease

Sirtuin 2 (SIRT2) has been proposed to have a central role on aging, inflammation, cancer and neurodegenerative diseases; however, its specific function remains controversial. Recent studies propose SIRT2 pharmacological inhibition as a therapeutic strategy for several neurodegenerative diseases including Alzheimer's disease (AD). Surprisingly, none of these published studies regarding the potential interest of SIRT2 inhibition has assessed the peripheral adverse side consequences of this treatment. In this study, we demonstrate that the specific SIRT2 inhibitor, the compound 33i, does not exhibit genotoxic or mutagenic properties. Moreover, pharmacological treatment with 33i, improved cognitive dysfunction and long-term potentiation, reducing amyloid pathology and neuroinflammation in the APP/PS1 AD mouse model. However, this treatment increased peripheral levels of the inflammatory cytokines IL-1β, TNF, IL-6 and MCP-1. Accordingly, peripheral SIRT2 inhibition with the blood brain barrier impermeable compound AGK-2, worsened the cognitive capacities and increased systemic inflammation. The analysis of human samples revealed that SIRT2 is increased in the brain but not in the serum of AD patients. These results suggest that, although SIRT2 pharmacological inhibition may have beneficial consequences in neurodegenerative diseases, its pharmacological inhibition at the periphery would not be recommended and the systemic adverse side effects should be considered. This information is essential to maximize the therapeutic potential of SIRT2 inhibition not only for AD but also for other neurodegenerative diseases.

Cytotoxic evaluation of YSL-109 in a triple negative breast cancer cell line and toxicological evaluations

Breast cancer (BC) is the leading cause of cancer-related death in women worldwide. Triple negative breast cancer (TNBC) is the most aggressive form of BC being with the worst prognosis and the worst survival rates. There is no specific pharmacological target for the treatment of TNBC; conventional therapy includes the use of non-specific chemotherapy that generally has a poor prognosis. Therefore, the search of effective therapies against to TNBC continues at both preclinical and clinical level. In this sense, the exploration of different pharmacological targets is a continue task that pave the way to epigenetic modulation using novel small molecules. Lately, the inhibition of histone deacetylases (HDACs) has been explored to treat different BC, including TNBC. HDACs remove the acetyl groups from the ɛ-amino lysine resides on histone and non-histone proteins. In particular, the inhibition of HDAC6 has been suggested to be useful for the treatment of TNBC due to it is overexpressed in TNBC. Therefore, in this work, an HDAC6 selective inhibitor, the (S)-4-butyl-N-(1-(hydroxyamino)-3-(naphthalen-1-yl)-1-oxopropan-2-yl) benzamide (YSL-109), was assayed on TNBC cell line (MDA-MB231) showing an antiproliferative activity (IC₅₀ = 50.34 ± 1.11 µM), whereas on fibroblast, it was lesser toxic. After corroborating the in vitro antiproliferative activity of YSL-109 in TNBC, the toxicological profile was explored using combined approach with in silico tools and experimental assays. YSL-109 shows moderate mutagenic activity on TA-98 strain at 30 and 100 µM in the Ames test, whereas YSL-109 did not show in vivo genotoxicity and its oral acute toxicity (LD₅₀) in CD-1 female mice was higher than 2000 mg/kg, which is in agreement with our in silico predictions. According to these results, YSL-109 represents an interesting compound to be explored for the treatment of TNBC under preclinical in vivo models.

Synergistic association of resveratrol and histone deacetylase inhibitors as treatment in amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease associated with motor neuron degeneration, progressive paralysis and finally death. Despite the research efforts, currently there is no cure for ALS. In recent years, multiple epigenetic mechanisms have been associated with neurodegenerative diseases. A pathological role for histone hypoacetylation and the abnormal NF-κB/RelA activation involving deacetylation of lysines, with the exclusion of lysine 310, has been established in ALS. Recent findings indicate that the pathological acetylation state of NF-κB/RelA and histone 3 (H3) occurring in the SOD1(G93A) murine model of ALS can be corrected by the synergistic combination of low doses of the AMP-activated kinase (AMPK)-sirtuin 1 pathway activator resveratrol and the histone deacetylase (HDAC) inhibitors MS-275 (entinostat) or valproate. The combination of the epigenetic drugs, by rescuing RelA and the H3 acetylation state, promotes a beneficial and sexually dimorphic effect on disease onset, survival and motor neurons degeneration. In this mini review, we discuss the potential of the epigenetic combination of resveratrol with HDAC inhibitors in the ALS treatment.

Pharmacological Properties of Trichostatin A, Focusing on the Anticancer Potential: A Comprehensive Review

Trichostatin A (TSA), a natural derivative of dienohydroxamic acid derived from a fungal metabolite, exhibits various biological activities. It exerts antidiabetic activity and reverses high glucose levels caused by the downregulation of brain-derived neurotrophic factor (BDNF) expression in Schwann cells, anti-inflammatory activity by suppressing the expression of various cytokines, and significant antioxidant activity by suppressing oxidative stress through multiple mechanisms. Most importantly, TSA exhibits potent inhibitory activity against different types of cancer through different pathways. The anticancer activity of TSA appeared in many in vitro and in vivo investigations that involved various cell lines and animal models. Indeed, TSA exhibits anticancer properties alone or in combination with other drugs used in chemotherapy. It induces sensitivity of some human cancers toward chemotherapeutical drugs. TSA also exhibits its action on epigenetic modulators involved in cell transformation, and therefore it is considered an epidrug candidate for cancer therapy. Accordingly, this work presents a comprehensive review of the most recent developments in utilizing this natural compound for the prevention, management, and treatment of various diseases, including cancer, along with the multiple mechanisms of action. In addition, this review summarizes the most recent and relevant literature that deals with the use of TSA as a therapeutic agent against various diseases, emphasizing its anticancer potential and the anticancer molecular mechanisms. Moreover, TSA has not been involved in toxicological effects on normal cells. Furthermore, this work highlights the potential utilization of TSA as a complementary or alternative medicine for preventing and treating cancer, alone or in combination with other anticancer drugs.

HDAC6 Inhibition Corrects Electrophysiological and Axonal Transport Deficits in a Human Stem Cell-Based Model of Charcot-Marie-Tooth Disease (Type 2D)

Charcot-Marie-Tooth disease type 2D (CMT2D), is a hereditary peripheral neuropathy caused by mutations in the gene encoding glycyl-tRNA synthetase (GARS1). Here, human induced pluripotent stem cell (hiPSC)-based models of CMT2D bearing mutations in GARS1 and their use for the identification of predictive biomarkers amenable to therapeutic efficacy screening is described. Cultures containing spinal cord motor neurons generated from this line exhibit network activity marked by significant deficiencies in spontaneous action potential firing and burst fire behavior. This result matches clinical data collected from a patient bearing a GARS1^P724H mutation and is coupled with significant decreases in acetylated α-tubulin levels and mitochondrial movement within axons. Treatment with histone deacetylase 6 inhibitors, tubastatin A and CKD504, improves mitochondrial movement and α-tubulin acetylation in these cells. Furthermore, CKD504 treatment enhances population-level electrophysiological activity, highlighting its potential as an effective treatment for CMT2D.

Inhibition of Histone Deacetylase 6 (HDAC6) as a therapeutic strategy for Alzheimer's disease: A review (2010-2020)

Alzheimer's disease (AD) is one of the most common neurodegenerative disorders, which is characterized by the primary risk factor, age. Several attempts have been made to treat AD, while most of them end in failure. However, with the deepening study of pathogenesis of AD, the expression of HDAC6 in the hippocampus, which plays a major role of the memory formation, is becoming worth of notice. Neurofibrillary tangles (NFTs), a remarkable lesion in AD, has been characterized in association with the abnormal accumulation of hyperphosphorylated Tau, which is mainly caused by the high expression of HDAC6. On the other hand, the hypoacetylated tubulin induced by HDAC6 is also fatal for the neuronal transport, which is the key impact of the formation of axons and dendrites. Overall, the significantly increased expression of HDAC6 in brain regions is deleterious to neuron survival in AD patients. Based on the above research, the inhibition of HDAC6 seems to be a potential therapeutic method for the treatment of AD. Up to now, various types of HDAC6 inhibitors have been discovered. This review mainly analyzes the HDAC6 inhibitors reported amid 2010-2020 in terms of their structure, selectivity and pharmacological impact towards AD. And we aim at facilitating the design and development of better HDAC6 inhibitors in the future.

Adolescent Intermittent Ethanol (AIE) Enhances the Dopaminergic Response to Ethanol within the Mesolimbic Pathway during Adulthood: Alterations in Cholinergic/Dopaminergic Genes Expression in the Nucleus Accumbens Shell

A consistent preclinical finding is that exposure to alcohol during adolescence produces a persistent hyperdopaminergic state during adulthood. The current experiments determine that effects of Adolescent Intermittent Ethanol (AIE) on the adult neurochemical response to EtOH administered directly into the mesolimbic dopamine system, alterations in dendritic spine and gene expression within the nucleus accumbens shell (AcbSh), and if treatment with the HDACII inhibitor TSA could normalize the consequences of AIE. Rats were exposed to the AIE (4 g/kg ig; 3 days a week) or water (CON) during adolescence, and all testing occurred during adulthood. CON and AIE rats were microinjected with EtOH directly into the posterior VTA and dopamine and glutamate levels were recorded in the AcbSh. Separate groups of AIE and CON rats were sacrificed during adulthood and Taqman arrays and dendritic spine morphology assessments were performed. The data indicated that exposure to AIE resulted in a significant leftward and upward shift in the dose-response curve for an increase in dopamine in the AcbSh following EtOH microinjection into the posterior VTA. Taqman array indicated that AIE exposure affected the expression of target genes (Chrna7, Impact, Chrna5). The data indicated no alterations in dendritic spine morphology in the AcbSh or any alteration in AIE effects by TSA administration. Binge-like EtOH exposure during adolescence enhances the response to acute ethanol challenge in adulthood, demonstrating that AIE produces a hyperdopaminergic mesolimbic system in both male and female Wistar rats. The neuroadaptations induced by AIE in the AcbSh could be part of the biological basis of the observed negative consequences of adolescent binge-like alcohol exposure on adult drug self-administration behaviors.

Development and validation of the TGx-HDACi transcriptomic biomarker to detect histone deacetylase inhibitors in human TK6 cells

Transcriptomic biomarkers can be used to inform molecular initiating and key events involved in a toxicant's mode of action. To address the limited approaches available for identifying epigenotoxicants, we developed and assessed a transcriptomic biomarker of histone deacetylase inhibition (HDACi). First, we assembled a set of ten prototypical HDACi and ten non-HDACi reference compounds. Concentration-response experiments were performed for each chemical to collect TK6 human lymphoblastoid cell samples after 4 h of exposure and to assess cell viability following a 20-h recovery period in fresh media. One concentration was selected for each chemical for whole transcriptome profiling and transcriptomic signature derivation, based on cell viability at the 24-h time point and on maximal induction of HDACi-response genes (RGL1, NEU1, GPR183) or cellular stress-response genes (ATF3, CDKN1A, GADD45A) analyzed by TaqMan qPCR assays after 4 h of exposure. Whole transcriptomes were profiled after 4 h exposures by Templated Oligo-Sequencing (TempO-Seq). By applying the nearest shrunken centroid (NSC) method to the whole transcriptome profiles of the reference compounds, we derived an 81-gene toxicogenomic (TGx) signature, referred to as TGx-HDACi, that classified all 20 reference compounds correctly using NSC classification and the Running Fisher test. An additional 4 HDACi and 7 non-HDACi were profiled and analyzed using TGx-HDACi to further assess classification performance; the biomarker accurately classified all 11 compounds, including 3 non-HDACi epigenotoxicants, suggesting a promising specificity toward HDACi. The availability of TGx-HDACi increases the diversity of tools that can facilitate mode of action analysis of toxicants using gene expression profiling.

Anticancer Therapy with HDAC Inhibitors: Mechanism-Based Combination Strategies and Future Perspectives

The increasing knowledge of molecular drivers of tumorigenesis has fueled targeted cancer therapies based on specific inhibitors. Beyond "classic" oncogene inhibitors, epigenetic therapy is an emerging field. Epigenetic alterations can occur at any time during cancer progression, altering the structure of the chromatin, the accessibility for transcription factors and thus the transcription of genes. They rely on post-translational histone modifications, particularly the acetylation of histone lysine residues, and are determined by the inverse action of histone acetyltransferases (HATs) and histone deacetylases (HDACs). Importantly, HDACs are often aberrantly overexpressed, predominantly leading to the transcriptional repression of tumor suppressor genes. Thus, histone deacetylase inhibitors (HDACis) are powerful drugs, with some already approved for certain hematological cancers. Albeit HDACis show activity in solid tumors as well, further refinement and the development of novel drugs are needed. This review describes the capability of HDACis to influence various pathways and, based on this knowledge, gives a comprehensive overview of various preclinical and clinical studies on solid tumors. A particular focus is placed on strategies for achieving higher efficacy by combination therapies, including phosphoinositide 3-kinase (PI3K)-EGFR inhibitors and hormone- or immunotherapy. This also includes new bifunctional inhibitors as well as novel approaches for HDAC degradation via PROteolysis-TArgeting Chimeras (PROTACs).

Anticancer Ruthenium Complexes with HDAC Isoform Selectivity

The histone deacetylase (HDAC) enzymes have emerged as an important class of molecular targets in cancer therapy, with five inhibitors in clinical use. Recently, it has been shown that a lack of selectivity between the 11 Zn-dependent HDAC isoforms may lead to unwanted side-effects. In this paper, we show that piano stool Ru complexes can act as HDAC inhibitors, and variation in the capping arene leads to differences in HDAC isoform selectivity.

Proteasome inhibitors trigger mutations via activation of caspases and CAD, but mutagenesis provoked by the HDAC inhibitors vorinostat and romidepsin is caspase/CAD-independent

Genotoxic anti-cancer therapies such as chemotherapy and radiotherapy can contribute to an increase in second malignancies in cancer survivors due to their oncogenic effects on non-cancerous cells. Inhibition of histone deacetylase (HDAC) proteins or the proteasome differ from chemotherapy in that they eliminate cancer cells by regulating gene expression or cellular protein equilibrium, respectively. As members of these drug classes have been approved for clinical use in recent times, we investigated whether these two drug classes exhibit similar mutagenic capabilities as chemotherapy. The HDAC inhibitors vorinostat/SAHA and romidepsin/FK288 were found to induce DNA damage, and mis-repair of this damage manifested into mutations in clonogenically viable surviving cells. DNA damage and mutations were also detected in cells treated with the proteasome inhibitor bortezomib. Exposure to both drug classes stimulated caspase activation consistent with apoptotic cell death. Inhibition of caspases protected cells from bortezomib-induced acute (but not clonogenic) death and mutagenesis, implying caspases were required for the mutagenic action of bortezomib. This was also observed for second generation proteasome inhibitors. Cells deficient in caspase-activated DNase (CAD) also failed to acquire DNA damage or mutations following treatment with bortezomib. Surprisingly, vorinostat and romidepsin maintained an equivalent level of killing and mutagenic ability regardless of caspase or CAD activity. Our findings indicate that both drug classes harbour mutagenic potential in vitro. If recapitulated in vivo, the mutagenicity of these agents may influence the treatment of cancer patients who are more susceptible to oncogenic mutations due to dysfunctional DNA repair pathways.

Design, Synthesis and Biological Evaluation of Novel Benzoylimidazole Derivatives as Raf and Histone Deacetylases Dual Inhibitors

In recent studies, combinations of histone deacetylases (HDACs) inhibitor with kinase inhibitor showed additive and synergistic effects. BRaf^V600E as an attractive target in many diseases treatments has been studied extensively. Herein, we present a novel design approach though incorporating the pharmacophores of BRaf^V600E inhibitor and HDACs inhibitor in one molecule. Several synthesized compounds exhibited distinct BRaf^V600E and HDAC1 inhibitory activities. The representative dual Raf/HDAC inhibitor, 7a, showed better antiproliferative activities against A549 and SK-Mel-2 in cellular assay than SAHA and sorafenib, with IC₅₀ values of 9.11 µM and 5.40 µM, respectively. This work may lay the foundation for the further development of dual Raf/HDAC inhibitors as potential anticancer agents.

Restoration of histone acetylation ameliorates disease and metabolic abnormalities in a FUS mouse model

Dysregulation of epigenetic mechanisms is emerging as a central event in neurodegenerative disorders, including amyotrophic lateral sclerosis (ALS). In many models of neurodegeneration, global histone acetylation is decreased in the affected neuronal tissues. Histone acetylation is controlled by the antagonistic actions of two protein families -the histone acetyltransferases (HATs) and the histone deacetylases (HDACs). Drugs inhibiting HDAC activity are already used in the clinic as anti-cancer agents. The aim of this study was to explore the therapeutic potential of HDAC inhibition in the context of ALS. We discovered that transgenic mice overexpressing wild-type FUS ("Tg FUS+/+"), which recapitulate many aspects of human ALS, showed reduced global histone acetylation and alterations in metabolic gene expression, resulting in a dysregulated metabolic homeostasis. Chronic treatment of Tg FUS+/+ mice with ACY-738, a potent HDAC inhibitor that can cross the blood-brain barrier, ameliorated the motor phenotype and substantially extended the life span of the Tg FUS+/+ mice. At the molecular level, ACY-738 restored global histone acetylation and metabolic gene expression, thereby re-establishing metabolite levels in the spinal cord. Taken together, our findings link epigenetic alterations to metabolic dysregulation in ALS pathology, and highlight ACY-738 as a potential therapeutic strategy to treat this devastating disease.

Differentiation of Aneugens and Clastogens in the In Vitro Micronucleus Test by Kinetochore Scoring Using Automated Image Analysis

The in vitro micronucleus test according to OECD Test Guideline 487 (TG 487) is widely used to investigate the genotoxic potential of drugs. Besides the identification of in vitro genotoxicants, the assay can be complemented with kinetochore staining for the differentiation between clastogens and aneugens. This differentiation constitutes a major contribution to risk assessment as especially aneugens show a threshold response. Thus, a novel method for automated MN plus kinetochore (k+) scoring by image analysis was developed based on the OECD TG 487. Compound-induced increases in MN frequency can be detected using the cytokinesis-block (cytochalasin B) method in V79 cells after 24 h in a 96-well format. Nuclei, MN, and kinetochores were labeled with nuclear counterstain and anti-kinetochore antibodies, respectively, to score MN in binuclear or multinuclear cells and to differentiate compound-induced MN by the presence of kinetochores. First, a reference data set was created by manual scoring using two clastogens and aneugens. After developing the automated scoring process, a set of 14 reference genotoxicants were studied. The automated image analysis yielded the expected results: 5/5 clastogens and 6/6 aneugens (sensitivity: 100%) as well as 3/3 non-genotoxicants (specificity: 100%) were correctly identified. Further, a threshold was determined for identifying aneugens. Based on the data for our internally characterized reference compounds, unknown compounds that induce ≥53.8% k+ MN are classified as aneugens. The current data demonstrate excellent specificity and sensitivity and the methodology is superior to manual microscopic analysis in terms of speed and throughput as well as the absence of human bias. Environ. Mol. Mutagen. 60:227-242, 2019. © 2018 Wiley Periodicals, Inc.

CKD-506, a novel HDAC6-selective inhibitor, improves renal outcomes and survival in a mouse model of systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is a chronic multisystemic autoimmune disease with an unknown etiology. Recently, it has been elucidated that dysregulated histone deacetylase (HDAC) activity is related to the pathogenesis of inflammatory and autoimmune diseases. Broad-spectrum HDAC inhibitors are effective for the treatment of allergy, cancer, and autoimmune diseases, but they have several adverse side effects. Thus, the purpose of this study was to evaluate the effects of a novel HDAC 6-specific inhibitor, CKD-506, in a murine SLE model. CKD-506 significantly improved survival rate and significantly decreased the incidence of severe proteinuria, blood urea nitrogen, kidney inflammation, and glomerular infiltration of IgG and C3. In addition, CKD 506 reduced the proportions of CD138⁺ plasma cells, CD4⁻CD8⁻ T cells, and CD25⁺ cells and the Th1/Th2 ratio in the spleen. CKD-506 significantly reduced inflammatory cytokines such as IL-10, IL-15, IL-17, TNF-α, and IFN-inducible protein (IP-10) and significantly increased TGF-β in serum. CKD-506 also significantly reduced IFN-γ, IL-1β, IL-4, IL-6, IP-10, MCP-1, and CCL4 levels in kidney. CKD-506 decreased the production of various pro-inflammatory cytokines and chemokines in the serum and kidneys, resulting in inhibition of cell migration and suppression of lupus nephritis without adverse effects.

Chromatin dynamics underlying latent responses to xenobiotics

Pleiotropic xenobiotics can trigger dynamic alterations in mammalian chromatin structure and function but many of these are likely non-adverse and simply reflect short-term changes in DNA transactions underlying normal homeostatic, adaptive and protective cellular responses. However, it is plausible that a subset of xenobiotic-induced perturbations of somatic tissue or germline epigenomes result in delayed-onset and long-lasting adverse effects, in particular if they occur during critical stages of growth and development. These could include reprogramming, dedifferentiation, uncontrolled growth, and cumulative toxicity effects through molecular memory of prior xenobiotic exposures or altered susceptibility to subsequent xenobiotic exposures. Here we discuss the current evidence for epigenetic mechanisms underlying latent responses to xenobiotics, and the potential for identifying molecular epigenetic changes that are prodromal to overt morphologic or functional toxicity phenotypes.

Lead Induces Genotoxicity via Oxidative Stress and Promoter Methylation of DNA Repair Genes in Human Lymphoblastoid TK6 Cells

Background

Lead (Pb) is a widely used metal in modern industry and is regarded as a health hazard. Although lead-induced genotoxicity has been confirmed, the direct evidence that lead induces genotoxicity in human cells and its related mechanisms has not been fully elucidated. In this study, for the first time, we evaluated the genotoxicity induced by lead in human lymphoblastoid TK6 cells.

Material/Methods

The TK6 cells were incubated with various concentrations of Pb(Ac)₂ for 6 h, 12 h, or 24 h. Cell viability was detected by CCK8 assay. Various biochemical markers were assessed by specific kits. Immunofluorescence assay was used to detect γ-H2AX foci formation. The promoter methylation was assessed by methylation-specific PCR. The protein levels were determined by Western blot assay.

Results

The results showed that after exposure to lead, cell viability was obviously decreased and γ-H2AX foci formation was significantly enhanced in TK6 cells. Moreover, the levels of 8-OHdG, ROS, MDA, and GSSG were increased, while the GSH level and SOD activity were decreased in lead-treated TK6 cells. The activation of the Nrf2-ARE signaling pathway was involved in lead-induced oxidative stress in TK6 cells. Finally, the expressions of DNA repair genes XRCC1, hOGG-1, BRCA1, and XPD were inhibited via enhancing their promoter methylation in TK6 cells after exposure to lead.

Conclusions

Taken together, our study provides the first published evidence that lead exposure results in DNA damage via promoting oxidative stress and the promoter methylation of DNA repair genes in human lymphoblastoid TK6 cells.

Synthesis of ST7612AA1, a Novel Oral HDAC Inhibitor, via Radical Thioacetic Acid Addition

Abstract: Background

In the expanding field of anticancer drugs, HDAC inhibitors are playing an increasingly important role. To date, four/five HDAC inhibitors have been approved by FDA. All these compounds fit the widely accepted HDAC inhibitors pharmacophore model characterized by a cap group, a linker chain and a zinc binding group (ZBG), able to bind the Zn²⁺ ion in a pocket of the HDAC active site. Romidepsin, a natural compound, is the only thiol derivative. We have selected a new class of synthetic HDAC inhibitors, the thio-ω(lactam-carboxamide) derivatives, with ST7612AA1 as drug candidate, pan-inhibitor active in the range of single- to two-digit nanomolar concentrations. Preliminary results of a synthetic optimization attempt towards a fast scale-up process are here proposed.

Methods

In the four steps of synthesis, from unsaturated amino acid intermediate to the final product, we explored different synthetic conditions in order to have a transferable process for a scale-up synthetic laboratory.

Results

In the first step, isobutyl chloroformate was used and, after a simple work up with 1M HCl, 2 (96% yield) was obtained as a white solid, which was used directly in the next step. For thioacetic acid addition to the double bond of intermediate 2, two different routes were possible, with addition reaction in the first (D’) or last step (D). Reactions of 2 to give 5 or of 4 to give ST7612AA1 were both performed in dioxane. Reactions were fast and did not need the usually advised radical quenching with cyclohexene. The corresponding products were obtained in good yields (step D’, 89%; step D, 81%) after a flash chromatography.

Conclusion: ST7612AA1

, a thiol derivative prodrug of ST7464AA1, is the first of a new generation of HDAC inhibitors, very potent, orally administered, and well tolerated. Here, we have identified a synthetic route, competitive, versatile and easily transferable to industrial processes.

Histone Deacetylase Inhibitors Delivery using Nanoparticles with Intrinsic Passive Tumor Targeting Properties for Tumor Therapy

Fast clearance, metabolism and systemic toxicity are major limits for the clinical use of anti-cancer drugs. Histone deacetylase inhibitors (HDACi) present these defects despite displaying promising anti-tumor properties on tumor cells in vitro and in in vivo model of cancers. Specific delivery of anti-cancer drugs into the tumor should improve their clinical benefit by limiting systemic toxicity and by increasing the anti-tumor effect. In this work, we describe a simple and flexible polymeric nanoparticle platform highly targeting the tumor in vivo and triggering impressive tumor weight reduction when functionalized with HDACi. Our nanoparticles were produced by Ring-Opening Metathesis Polymerization of azido-polyethylene oxide-norbornene macromonomers and functionalized using click chemistry. Using an orthotopic model of peritoneal invasive cancer, a highly selective accumulation of the particles in the tumor was obtained. A combination of epigenetic drugs involving a pH-responsive histone deacetylase inhibitor (HDACi) polymer conjugated to these particles gave 80% reduction of tumor weight without toxicity whereas the free HDACi has no effect. Our work demonstrates that the use of a nanovector with theranostic properties leads to an optimized delivery of potent HDACi in tumor and then, to an improvement of their anti-tumor properties in vivo.

HDAC and HDAC Inhibitor: From Cancer to Cardiovascular Diseases

Histone deacetylases (HDACs) are epigenetic regulators that regulate the histone tail, chromatin conformation, protein-DNA interaction, and even transcription. HDACs are also post-transcriptional modifiers that regulate the protein acetylation implicated in several pathophysiologic states. HDAC inhibitors have been highlighted as a novel category of anti-cancer drugs. To date, four HDAC inhibitors, Vorinostat, Romidepsin, Panobinostat, and Belinostat, have been approved by the United States Food and Drug Administration. Principally, these HDAC inhibitors are used for hematologic cancers in clinic with less severe side effects. Clinical trials are continuously expanding to address other types of cancer and also nonmalignant diseases. HDAC inhibition also results in beneficial outcomes in various types of neurodegenerative diseases, inflammation disorders, and cardiovascular diseases. In this review, we will briefly discuss 1) the roles of HDACs in the acquisition of a cancer's phenotype and the general outcome of the HDAC inhibitors in cancer, 2) the functional relevance of HDACs in cardiovascular diseases and the possible therapeutic implications of HDAC inhibitors in cardiovascular disease.

Why Hydroxamates May Not Be the Best Histone Deacetylase Inhibitors--What Some May Have Forgotten or Would Rather Forget?

Hydroxamate-based histone deacetylase inhibitors (HDACIs) have been approved as therapeutic agents by the US Food and Drug Administration for use in oncology applications. While the potential utility of such HDACIs in other areas of medicinal chemistry is tremendous, there are significant concerns that "pan-HDAC inhibitors" may be too broadly acting and/or toxic for clinical use beyond oncology. In addition to the isozyme selectivity challenge, the potential mutagenicity of hydroxamate-containing HDAC inhibitors represents a major hindrance in their application to other therapeutic areas. Herein we report on the mutagenicity of known hydroxamates, discuss the mechanisms responsible for their genotoxicity, and review some of the current alternatives to hydroxamates. We conclude that the hydroxamate group, while providing high-potency HDACIs, is not necessarily the best zinc-binding group for HDACI drug discovery.

Thiol-Based Potent and Selective HDAC6 Inhibitors Promote Tubulin Acetylation and T-Regulatory Cell Suppressive Function

Several new mercaptoacetamides were synthesized and studied as HDAC6 inhibitors. One compound, 2b, bearing an aminoquinoline cap group, was found to show 1.3 nM potency at HDAC6, with >3000-fold selectivity over HDAC1. 2b also showed excellent efficacy at increasing tubulin acetylation in rat primary cortical cultures, inducing a 10-fold increase in acetylated tubulin at 1 μM. To assess possible therapeutic effects, compounds were assayed for their ability to increase T-regulatory (Treg) suppressive function. Some but not all of the compounds increased Treg function, and thereby decreased conventional T cell activation and proliferation in vitro.

Role of chromatin structure modulation by the histone deacetylase inhibitor trichostatin A on the radio-sensitivity of ataxia telangiectasia

At present, a lot is known about biochemical aspects of double strand breaks (DBS) repair but how chromatin structure affects this process and the sensitivity of DNA to DSB induction is still an unresolved question. Ataxia telangiectasia (A-T) patients are characterised by very high sensitivity to DSB-inducing agents such as ionising radiation. This radiosensitivity is revealed with an enhancement of chromosomal instability as a consequence of defective DNA repair for a small fraction of breaks located in the heterochromatin, where they are less accessible. Besides, recently it has been reported that Ataxia Telangiectasia Mutated (ATM) mediated signalling modifies chromatin structure. In order to study the impact of chromatin compaction on the chromosomal instability of A-T cells, the response to trichostatin-A, an histone deacetylase inhibitor, in normal and A-T lymphoblastoid cell lines was investigated testing its effect on chromosomal aberrations, cell cycle progression, DNA damage and repair after exposure to X-rays. The results suggest that the response to both trichostatin-A pre- and continuous treatments is independent of the presence of either functional or mutated ATM protein, as the reduction of chromosomal damage was found also in the wild-type cell line. The presence of trichostatin-A before exposure to X-rays could give rise to prompt DNA repair functioning on chromatin structure already in an open conformation. Differently, trichostatin-A post-treatment causing hyperacetylation of histone tails and reducing the heterochromatic DNA content might diminish the requirement for ATM and favour DSBs repair reducing chromosomal damage only in A-T cells. This fact could suggest that trichostatin-A post-treatment is favouring the slow component of DSB repair pathway, the one impaired in absence of a functionally ATM protein. Data obtained suggest a fundamental role of chromatin compaction on chromosomal instability in A-T cells.

Down-regulation of sirtuin 3 is associated with poor prognosis in hepatocellular carcinoma after resection

Background

Sirtuin 3 (Sirt3), one of the seven Sirtuins family members, plays critical roles in the progression of multiple cancer types. However, its role in the prognosis of hepatocellular carcinoma (HCC) has not yet been investigated systematically.

Methods

The correlation of Sirtuins expression with prognosis of HCC was determined by immunohistochemistry (IHC) in a large HCC patient cohort (n = 342). Expression of Sirt3 in tumoral and peritumoral tissues of HCC patients were further determined by western blotting (WB).

Results

IHC and WB studies both showed a decreased expression of Sirt3 in tumoral tissues compared with peritumoral tissues (P = 0.003 for IHC, P = 0.0042 for WB). Decreased expression of Sirt3 in both tumoral and peritumoral tissues was associated with increased recurrence probability and decreased overall survival rate by univariate analyses (intratumoral Sirt3: P = 0.011 for TTR, P = 0.001 for OS; peritumoral Sirt3: P = 0.017 for TTR, P = 0.023 for OS), the prognostic value was strengthened by multivariate analyses (intratumoral Sirt3: P = 0.031 for TTR, P = 0.001 for OS; peritumoral Sirt3: P = 0.047 for TTR, P = 0.031 for OS). Intratumoral Sirt3 also showed a favorable prognostic value in patients with BCLC stage A (TTR, P = 0.011; OS, P < 0.001). In addition, we found that IHC studies of other sirtuin members showed a decreased expression of Sirt2, Sirt4 and Sirt5 and an increased expression of Sirt1, Sirt6 and Sirt7 in intratumoral tissues compared with peritumoral tissues. In contrast to Sirt3, other members did not showed a remarkable correlation with HCC prognosis.

Conclusions

Down-regulation of intratumoral and peritumoral Sirt3 were both associated with poor outcome in HCC, moreover, intratumoral Sirt3 was a favorable prognostic predictor in early stage patients.

Histone deacetylase inhibitors selectively target homology dependent DNA repair defective cells and elevate non-homologous endjoining activity

Background

We have previously used the ATAD5-luciferase high-throughput screening assay to identify genotoxic compounds with potential chemotherapeutic capabilities. The successful identification of known genotoxic agents, including the histone deacetylase inhibitor (HDACi) trichostatin A (TSA), confirmed the specificity of the screen since TSA has been widely studied for its ability to cause apoptosis in cancer cells. Because many cancers have acquired mutations in DNA damage checkpoints or repair pathways, we hypothesized that these cancers may be susceptible to treatments that target compensatory pathways. Here, we used a panel of isogenic chicken DT40 B lymphocyte mutant and human cell lines to investigate the ability of TSA to define selective pathways that promote HDACi toxicity.

Results

HDACi induced a DNA damage response and reduced viability in all repair deficient DT40 mutants although ATM-nulls were least affected. The most dramatic sensitivity was observed in mutants lacking the homology dependent repair (HDR) factor BLM or the non-homologous end-joining (NHEJ) and HDR factors, KU/RAD54, suggesting an involvement of either HDR or NHEJ in HDACi-induced cell death. To extend these findings, we measured the frequencies of HDR and NHEJ after HDACi treatment and monitored viability in human cell lines comparably deficient in HDR or NHEJ. Although no difference in HDR frequency was observed between HDACi treated and untreated cells, HDR-defective human cell lines were clearly more sensitive than wild type. Unexpectedly, cells treated with HDACis showed a significantly elevated NHEJ frequency.

Conclusions

HDACi targeting drugs induced significant increases in NHEJ activity in human cell lines but did not alter HDR frequency. Moreover, HDR is required for cellular resistance to HDACi therapy; therefore, NHEJ does not appear to be a critical axis for HDACi resistance. Rather, HDACi compounds induced DNA damage, most likely double strand breaks (DSBs), and HDR proficiency is correlated with cell survival.

Epigenetic reactivation of estrogen receptor-α (ERα) by genistein enhances hormonal therapy sensitivity in ERα-negative breast cancer

BACKGROUND

Estrogen receptor-α (ERα)-negative breast cancer is clinically aggressive and normally does not respond to conventional estrogen target-directed therapies. The soybean isoflavone, genistein (GE), has been shown to prevent and inhibit breast cancer and recent studies have suggested that GE can enhance the anticancer capacity of an estrogen antagonist, tamoxifen (TAM), especially in ERα-positive breast cancer cells. However, the role of GE in ERα-negative breast cancer remains unknown.

METHODS

We have evaluated the in vitro and in vivo epigenetic effects of GE on ERα reactivation by using MTT assay, real-time reverse transcription-polymerase chain reaction (RT-PCR) assay, western-blot assay, immunoprecipitation (ChIP) assay, immunohistochemistry and epigenetic enzymatic activity analysis. Preclinical mouse models including xenograft and spontaneous breast cancer mouse models were used to test the efficacy of GE in vivo.

RESULTS

We found that GE can reactivate ERα expression and this effect was synergistically enhanced when combined with a histone deacetylase (HDAC) inhibitor, trichostatin A (TSA), in ERα-negative MDA-MB-231 breast cancer cells. GE treatment also re-sensitized ERα-dependent cellular responses to activator 17β-estradiol (E2) and antagonist TAM. Further studies revealed that GE can lead to remodeling of the chromatin structure in the ERα promoter thereby contributing to ERα reactivation. Consistently, dietary GE significantly prevented cancer development and reduced the growth of ERα-negative mouse breast tumors. Dietary GE further enhanced TAM-induced anti-cancer efficacy due at least in part to epigenetic ERα reactivation.

CONCLUSIONS

Our studies suggest that soybean genistein can epigenetically restore ERα expression, which in turn increases TAM-dependent anti-estrogen therapeutic sensitivity in vitro and in vivo. The results from our studies reveal a novel therapeutic combination approach using bioactive soybean product and anti-hormone therapy in refractory ERα-negative breast cancer which will provide more effective options in breast cancer therapy.

Histone-deacetylase inhibitors produce positive results in the GADD45a-GFP GreenScreen HC assay

Histone-deacetylase inhibitors (HDACi) are able to induce cell-cycle arrest, apoptosis and differentiation in a variety of tumour cell lines. The mechanisms leading to these cellular outcomes are not fully understood, however, it is has been proposed that induction of cell-cycle arrest might be a result of genotoxic stress. Despite the potential for genotoxic activity of this class of compounds, there are very few data available to provide evidence for this, either in vitro or in vivo. In this study, four HDACi, viz. trichostatin A, sodium butyrate, APHA compound 8 and apicidin, were tested in the human lymphoblastoid TK6 cell line-hosted GADD45a-GFP assay, which has high sensitivity and specificity in the detection of genotoxic carcinogens and in vivo genotoxicants. All four compounds produced positive genotoxicity results within the acceptable toxic dose range of the assay, with APHA compound 8 producing the weakest response. Taken alongside recent evidence demonstrating that GADD45a is not induced by non-genotoxic apoptogens, this study suggests that genotoxicity contributes to the anti-tumour activity of HDACi drugs.

Primary hepatocyte cultures for pharmaco-toxicological studies: at the busy crossroad of various anti-dedifferentiation strategies

Continuously increasing understanding of the molecular triggers responsible for the onset of diseases, paralleled by an equally dynamic evolution of chemical synthesis and screening methods, offers an abundance of pharmacological agents with a potential to become new successful drugs. However, before patients can benefit of newly developed pharmaceuticals, stringent safety filters need to be applied to weed out unfavourable drug candidates. Cost effectiveness and the need to identify compound liabilities, without exposing humans to unnecessary risks, has stimulated the shift of the safety studies to the earliest stages of drug discovery and development. In this regard, in vivo relevant organotypic in vitro models have high potential to revolutionize the preclinical safety testing. They can enable automation of the process, to match the requirements of high-throughput screening approaches, while satisfying ethical considerations. Cultures of primary hepatocytes became already an inherent part of the preclinical pharmaco-toxicological testing battery, yet their routine use, particularly for long-term assays, is limited by the progressive deterioration of liver-specific features. The availability of suitable hepatic and other organ-specific in vitro models is, however, of paramount importance in the light of changing European legal regulations in the field of chemical compounds of different origin, which gradually restrict the use of animal studies for safety assessment, as currently witnessed in cosmetic industry. Fortunately, research groups worldwide spare no effort to establish hepatic in vitro systems. In the present review, both classical and innovative methodologies to stabilize the in vivo-like hepatocyte phenotype in culture of primary hepatocytes are presented and discussed.

Radioprotective effect of hypothermia on cells - a multiparametric approach to delineate the mechanisms

PURPOSE

Low temperature (hypothermia) during irradiation of cells has been reported to have a radioprotective effect. The mechanisms are not fully understood. This study further investigates the possible mechanisms behind hypothermia-mediated radioprotection.

MATERIALS AND METHODS

Human lymphoblastoid TK6 cells were incubated for 20 min at 0.8 or 37°C and subsequently exposed to 1 Gy of γ- or X-rays. The influence of ataxia telangiectasia mutated (ATM)-mediated double-strand break signalling and histone deacetylase-dependent chromatin condensation was investigated using the micronucleus assay. Furthermore, the effect of hypothermia was investigated at the level of phosphorylated histone 2AX (γH2AX) foci, clonogenic cell survival and micronuclei in sequentially-harvested cells.

RESULTS

The radioprotective effect of hypothermia (called the temperature effect [TE]) was evident only at the level of micronuclei at a single fixation time, was not influenced by the inhibition of ATM kinase activity and completely abolished by the histone deacetylase inhibition. No TE was seen at the level of γH2AX foci and cell survival.

CONCLUSIONS

We suggest that low temperature during irradiation can induce a temporary cell cycle shift, which could lead to a reduced micronucleus frequency. Future experiments focused on cell cycle progression are needed to confirm this hypothesis.

Epigenetic modifications: novel therapeutic strategies for systemic sclerosis?

Epigenetic modifications of gene expression comprise modifications of DNA by DNA methylation and modifications of the histone proteins by acetylation, methylation, SUMOylation or phosphorylation. DNA methylation in the promoter region of genes represses gene transcription. Histone modifications influence the structure of DNA and regulate gene expression by changing the availability of DNA for the transcriptional machinery or DNA-binding proteins. Histone modifications are mediated by enzymes and induce or repress gene expression. Aberrant expression of single enzymes disturb the normal balance of these modifiers leading to cancer or autoimmune diseases. We show in this article that epigenetic modifications contribute to the massive production of extracellular matrix proteins in systemic sclerosis skin fibroblasts. Both DNA methylation and histone modifications contribute to the activated phenotype of systemic sclerosis fibroblasts. In vitro and in vivo experiments demonstrate that the use of epigenetic-based drugs on these cells is able to reverse their activated phenotype.

Nonclinical safety assessment of the histone deacetylase inhibitor vorinostat

Vorinostat (SAHA, Zolinza), a histone deacetylase inhibitor, is assessed in nonclinical studies to support its approval for cutaneous T-cell lymphoma. Vorinostat is weakly mutagenic in the Ames assay; is clastogenic in rodent (ie, CHO) cells but not in normal human lymphocytes; and is weakly positive in an in vivo mouse micronucleus assay. No effects are observed on potassium ion currents in the hERG assay up to 300 microM (safety margin approximately 300-fold the approximately 1 microM serum concentration associated with the 400 mg/d maximum recommended human dose. No rat respiratory or central nervous system effects are found at 150 mg/kg (>2-fold maximum recommended human dose). No cardiovascular effects, including effects on QTc interval, are observed after a single oral dose (150 mg/kg) in dogs. Vorinostat is orally dosed daily in rats (controls, 20, 50, or 150 mg/kg/d) and dogs (controls, 60, 80, or 100/125/160 mg/kg/d) for 26 weeks with a 4-week recovery. Rat vorinostat-related adverse findings are decreased food consumption, weight loss, and hematologic changes; a no observed adverse effects level is not established. In dogs, adverse effects are primarily gastrointestinal; the no observed adverse effects level is 60 mg/kg/d (approximately 6-fold maximum recommended human dose). Toxicities are reversible and can be monitored in the clinic.

Identification of a kinase profile that predicts chromosome damage induced by small molecule kinase inhibitors

Kinases are heavily pursued pharmaceutical targets because of their mechanistic role in many diseases. Small molecule kinase inhibitors (SMKIs) are a compound class that includes marketed drugs and compounds in various stages of drug development. While effective, many SMKIs have been associated with toxicity including chromosomal damage. Screening for kinase-mediated toxicity as early as possible is crucial, as is a better understanding of how off-target kinase inhibition may give rise to chromosomal damage. To that end, we employed a competitive binding assay and an analytical method to predict the toxicity of SMKIs. Specifically, we developed a model based on the binding affinity of SMKIs to a panel of kinases to predict whether a compound tests positive for chromosome damage. As training data, we used the binding affinity of 113 SMKIs against a representative subset of all kinases (290 kinases), yielding a 113x290 data matrix. Additionally, these 113 SMKIs were tested for genotoxicity in an in vitro micronucleus test (MNT). Among a variety of models from our analytical toolbox, we selected using cross-validation a combination of feature selection and pattern recognition techniques: Kolmogorov-Smirnov/T-test hybrid as a univariate filter, followed by Random Forests for feature selection and Support Vector Machines (SVM) for pattern recognition. Feature selection identified 21 kinases predictive of MNT. Using the corresponding binding affinities, the SVM could accurately predict MNT results with 85% accuracy (68% sensitivity, 91% specificity). This indicates that kinase inhibition profiles are predictive of SMKI genotoxicity. While in vitro testing is required for regulatory review, our analysis identified a fast and cost-efficient method for screening out compounds earlier in drug development. Equally important, by identifying a panel of kinases predictive of genotoxicity, we provide medicinal chemists a set of kinases to avoid when designing compounds, thereby providing a basis for rational drug design away from genotoxicity.

Sodium arsenite modulates histone acetylation, histone deacetylase activity and HMGN protein dynamics in human cells

Extensive epidemiological data indicate that inorganic arsenic is associated with several types of human cancer. Nevertheless, the underlying mechanisms are poorly understood. Among its mode of action are the alterations on DNA methylation, which provoke aberrant gene expression. However, beyond DNA methylation, little is known about arsenic's effects on chromatin. In this study, we investigated the effects of sodium arsenite (NaAsO(2)) on global histone modifications and nucleosome-associated proteins. Our findings revealed that NaAsO(2) exposure significantly increases global histone acetylation. This effect was related to the inhibition of histone deacetylase (HDAC) activity because NaAsO(2) was able to inhibit HDACs comparable to the well-known HDAC inhibitor trichostatin A (TSA). Furthermore, analyses of the dynamic properties of the nucleosome-associated high mobility group N proteins demonstrate that NaAsO(2) elevates their mobility. Thus, our data suggest that NaAsO(2) induces chromatin opening by histone hyperacetylation due to HDAC inhibition and increase of the mobility of nucleosome-associated proteins. As the chromatin compaction is crucial for the regulation of gene expression as well as for genome stability, we propose that chromatin opening by NaAsO(2) may play a significant role to impart its genotoxic effects.

Inhibition of telomerase activity and human telomerase reverse transcriptase gene expression by histone deacetylase inhibitor in human brain cancer cells

The aim of the present study is to investigate the effect of histone deacetylase inhibitor, trichostatin A (TSA) on the cell growth, apoptosis, genomic DNA damage and the expression of telomerase and associated factors in human normal and brain cancer cells. Here, human normal un-transformed fibroblasts (MRC-5), human normal hTERT-immortalised fibroblasts (hTERT-BJ1) and human brain cancer cell lines (glioblastoma cell line, A-172 and medulloblastoma cell line, ONS-76) were treated with 0.5-3.0microM TSA for 24h. Exposure to TSA resulted in apoptosis in a dose-dependent manner in the brain cancer cells. Glioblastoma cell line (A-172) displayed higher sensitivity to TSA-induced cell killing effect and apoptosis than the medulloblastoma cell line (ONS-76). The brain cancer cell lines and hTERT-BJ1 cell line displayed significant inhibition in telomerase activity and hTERT mRNA level after 2microM TSA treatment. Elevated expressions of p53 and p21 with a decrease in cyclin-D level supported the observation on cell cycle arrest following TSA treatment. Upregulation of Bax and cytochrome c correlated with the apoptotic events in TSA-treated cells. This study suggests that telomerase and hTERT might be the primary targets of TSA which may have the potential to be used as a telomerase inhibitor in cancer therapy.

In vitro micronucleus assay scored by flow cytometry provides a comprehensive evaluation of cytogenetic damage and cytotoxicity

This laboratory has previously reported on the development of a flow cytometry-based method for scoring in vitro micronuclei in mouse lymphoma (L5178Y) cells [S.L. Avlasevich, S.M. Bryce, S.E. Cairns, S.D. Dertinger, In vitro micronucleus scoring by flow cytometry: differential staining of micronuclei versus apoptotic and necrotic chromatin enhances assay reliability, Environ. Molec. Mutagen. 47 (2006) 56-66]. With this method, necrotic and mid/late stage apoptotic cells are labeled with the fluorescent dye ethidium monoazide. Cells are then washed, stripped of their cytoplasmic membranes, and incubated with RNase plus a pan-nucleic acid dye (SYTOX Green). This process provides a suspension of free nuclei and micronuclei that are differentially stained relative to chromatin associated with dead/dying cells. The current report extends this line of investigation to include the human cell line TK6. Additionally, methods are described that facilitate simultaneous quantitative analysis of cytotoxicity, perturbations to the cell cycle, and what we hypothesize is aneuploidization. This comprehensive cytogenetic damage assay was evaluated with the following diverse agents: etoposide, ionizing radiation, methyl methanesulfonate, vinblastine, ethanol, and staurosporine. Cells were harvested after 30h of continuous treatment (in the case of chemicals), or following graded doses of radiation up to 1Gy. Key findings include the following: (1) Significant discrepancies in top dose selection were found for five of the six agents studied when relative survival measurements were based on Coulter counting versus flow cytometry. (2) Both microscopy- and flow cytometry-based scoring methods detected dose-dependent micronucleus formation for the four genotoxic agents studied, whereas no significant increases were observed for the presumed non-genotoxicants ethanol and staurosporine when top dose selection was based on flow cytometric indices of cytotoxicity. (3) SYTOX and ethidium monoazide fluorescence signals conveyed cell cycle and cell death information, respectively, and appear to represent valuable aids for interpreting micronucleus data. (4) The frequency of hypodiploid nuclei increased in response to each of the genotoxic agents studied, but not following exposure to ethanol or staurosporine. Collectively, these results indicate that a comprehensive assessment of genotoxicity and other test article-induced toxicities can be acquired simultaneously using a simple two-color flow cytometry-based technique.