Histone deacetylase inhibitors in cancer therapy. A review

A Case Study from the Past: "The RGC-5 vs. the 661W Cell Line: Similarities, Differences and Contradictions-Are They Really the Same?"

In the pursuit of identifying the underlying pathways of ocular diseases, the use of cell lines such as (retinal ganglion cell-5) RGC-5 and 661W became a valuable tool, including pathologies like retinal degeneration and glaucoma. In 2001, the establishment of the RGC-5 cell line marked a significant breakthrough in glaucoma research. Over time, however, concerns arose about the true nature of RGC-5 cells, with conflicting findings in the literature regarding their identity as retinal ganglion cells or photoreceptor-like cells. This study aimed to address the controversy surrounding the RGC-5 cell line's origin and properties by comparing it with the 661W cell line, a known cone photoreceptor model. Both cell lines were differentiated according to two prior published redifferentiation protocols under the same conditions using 500 nM of trichostatin A (TSA) and investigated for their morphological and neuronal marker properties. The results demonstrated that both cell lines are murine, and they exhibited distinct morphological and neuronal marker properties. Notably, the RGC-5 cells showed higher expression of the neuronal marker β-III tubulin and increased Thy-1-mRNA compared with the 661W cells, providing evidence of their different properties. The findings emphasize the importance of verifying the authenticity of cell lines used in ocular research and highlight the risks of contamination and altered cell properties.

Molecular Target Interactions of Quinoline Derivatives as Anticancer Agents: A Review

One of the leading causes of death worldwide is cancer, which poses substantial risks to both society and an individual's life. Cancer therapy is still challenging, despite developments in the field and continued research into cancer prevention. The search for novel anticancer active agents with a broader cytotoxicity range is therefore continuously ongoing. The benzene ring gets fused to a pyridine ring at two carbon atoms close to one another to form the double ring structure of the heterocyclic aromatic nitrogen molecule known as quinoline (1-azanaphthalene). Quinoline derivatives contain a wide range of pharmacological activities, including antitubercular, antifungal, antibacterial, and antimalarial properties. Quinoline derivatives have also been shown to have anticancer properties. There are many quinoline derivatives widely available as anticancer drugs that act via a variety of mechanisms on various molecular targets, such as inhibition of topoisomerase, inhibition of tyrosine kinases, inhibition of heat shock protein 90 (Hsp90), inhibition of histone deacetylases (HDACs), inhibition of cell cycle arrest and apoptosis, and inhibition of tubulin polymerization.

Establishment, immunological analysis, and drug prediction of a prognostic signature of ovarian cancer related to histone acetylation

In recent years, epigenetic modifications have been increasingly regarded as an important hallmark of cancer. Histone acetylation, as an important part of epigenetic modification, plays a key role in the progress, treatment, and prognosis of many cancers. In this study, based on the TCGA database, we performed LASSO regression and the Cox algorithm to establish a prognostic signature of ovarian cancer associated with histone acetylation modulator genes and verified it externally in the GEO database. Subsequently, we performed an immunological bioinformatics analysis of the model from multiple perspectives using the CIBERSORT algorithm, ESTIMATE algorithm, and TIDE algorithm to verify the accuracy of the model. Based on the prognostic model, we divided ovarian cancer patients into high-risk and low-risk groups, and assessed survival and the efficacy of accepting immunosuppressive therapy. In addition, based on the analysis of characteristics of the model, we also screened targeted drugs for high-risk patients and predicted potential drugs that inhibit platinum resistance through the connectivity map method. We ultimately constructed a histone acetylation modulator-related signature containing 10 histone acetylation modulators, among which HDAC1, HDAC10, and KAT7 can act as independent prognostic factors for ovarian cancer and are related to poor prognosis. In the analysis of the tumor microenvironment, the proportion of the B-infiltrating cells and the macrophages was significantly different between the high- and low-risk groups. Also, the samples with high-risk scores had higher tumor purity and lower immune scores. In terms of treatment, patients in the high-risk group who received immunotherapy had a higher likelihood of immune escape or rejection and were less likely to respond to platinum/paclitaxel therapy. Finally, we screened 20 potential drugs that could target the model for reference.

Radiosensitization to γ-Ray by Functional Inhibition of APOBEC3G

The radiosensitization of tumor cells is one of the promising approaches for enhancing radiation damage to cancer cells and limiting radiation effects on normal tissue. In this study, we performed a comprehensive screening of radiosensitization targets in human lung cancer cell line A549 using an shRNA library and identified apolipoprotein B mRNA editing enzyme catalytic subunit 3G (APOBEC3G: A3G) as a candidate target. APOBEC3G is an innate restriction factor that inhibits HIV-1 infection as a cytidine deaminase. APOBEC3G knockdown with siRNA showed an increased radiosensitivity in several cancer cell lines, including pancreatic cancer MIAPaCa2 cells and lung cancer A549 cells. Cell cycle analysis revealed that APOBEC3G knockdown increased S-phase arrest in MIAPaCa2 and G2/M arrest in A549 cells after γ-irradiation. DNA double-strand break marker γH2AX level was increased in APOBEC3G-knocked-down MIAPaCa2 cells after γ-irradiation. Using a xenograft model of A549 in mice, enhanced radiosensitivity by a combination of X-ray irradiation and APOBEC3G knockdown was observed. These results suggest that the functional inhibition of APOBEC3G sensitizes cancer cells to radiation by attenuating the activation of the DNA repair pathway, suggesting that APOBEC3G could be useful as a target for the radiosensitization of cancer therapy.

Blocking autophagy overcomes resistance to dual histone deacetylase and proteasome inhibition in gynecologic cancer

Histone deacetylase (HDAC) inhibitors and proteasome inhibitors have been approved by the FDA for the treatment of multiple myeloma and lymphoma, respectively, but have not achieved similar activity as single agents in solid tumors. Preclinical studies have demonstrated the activity of the combination of an HDAC inhibitor and a proteasome inhibitor in a variety of tumor models. However, the mechanisms underlying sensitivity and resistance to this combination are not well-understood. This study explores the role of autophagy in adaptive resistance to dual HDAC and proteasome inhibition. Studies focus on ovarian and endometrial gynecologic cancers, two diseases with high mortality and a need for novel treatment approaches. We found that nanomolar concentrations of the proteasome inhibitor ixazomib and HDAC inhibitor romidepsin synergistically induce cell death in the majority of gynecologic cancer cells and patient-derived organoid (PDO) models created using endometrial and ovarian patient tumor tissue. However, some models were not sensitive to this combination, and mechanistic studies implicated autophagy as the main mediator of cell survival in the context of dual HDAC and proteasome inhibition. Whereas the combination of ixazomib and romidepsin reduces autophagy in sensitive gynecologic cancer models, autophagy is induced following drug treatment of resistant cells. Pharmacologic or genetic inhibition of autophagy in resistant cells reverses drug resistance as evidenced by an enhanced anti-tumor response both in vitro and in vivo. Taken together, our findings demonstrate a role for autophagic-mediated cell survival in proteasome inhibitor and HDAC inhibitor-resistant gynecologic cancer cells. These data reveal a new approach to overcome drug resistance by inhibiting the autophagy pathway.

Phase Ia dose escalation study of OBP-801, a cyclic depsipeptide class I histone deacetylase inhibitor, in patients with advanced solid tumors

Background Dysregulation of histone deacetylases (HDACs) is common in cancer and is critical to the development and progression of the majority of tumors. This first-in-human Phase Ia study assessed the safety, efficacy, and pharmacokinetics (PK) of OBP-801, a cyclic depsipeptide class I HDAC inhibitor. Methods Adult patients with advanced solid tumors were treated in 3 dose cohorts (1.0 mg/m², 2.0 mg/m² or 2.8 mg/m²) of OBP-801 that was administered via intravenous infusion weekly. Initially, an accelerated titration design was used that was followed by a 3 + 3 dose escalation strategy. Primary objective was assessment of safety. Secondary objectives included determination of PK and objective response rate. Results Seventeen patients were enrolled, of which 8 patients were evaluable for efficacy. Drug-related ≥ Grade 3 treatment-emergent adverse events included abdominal pain, anemia, fatigue, gamma glutamyl-transferase increase, hypertriglyceridemia and vomiting. No dose-limiting toxicity was observed in the 1.0 mg/m² cohort. The PK data showed that OBP-801 and its active metabolite OBP-801-SH exposure increased proportionally and more than proportionally, respectively. No accumulation of either agent was noticed after repeat administration. Best response was stable disease (37.5%), with one patient each in the three cohorts. Conclusion Further investigations of the OBP-801 1.0 mg/m² dose will be needed to better understand the efficacy of the agent, either alone or in combination. Trial registration: NCT02414516 (ClinicalTrials.gov) registered on April 10, 2015.

Discovery of novel class of histone deacetylase inhibitors as potential anticancer agents

Selective inhibition of histone deacetylases (HDACs) is an important strategy in the field of anticancer drug discovery. However, lack of inhibitors that possess high selectivity toward certain HDACs isozymes is associated with adverse side effects that limits their clinical applications. We have initiated a collaborative initiatives between multi-institutions aimed at the discovery of novel and selective HDACs inhibitors. To this end, a phenotypic screening of an in-house pilot library of about 70 small molecules against various HDAC isozymes led to the discovery of five compounds that displayed varying degrees of HDAC isozyme selectivity. The anticancer activities of these molecules were validated using various biological assays including transcriptomic studies. Compounds 15, 14, and 19 possessed selective inhibitory activity against HDAC5, while 28 displayed selective inhibition of HDAC1 and HDAC2. Compound 22 was found to be a selective inhibitor for HDAC3 and HDAC9. Importantly, we discovered a none-hydroxamate based HDAC inhibitor, compound 28, representing a distinct chemical probe of HDAC inhibitors. It contains a trifluoromethyloxadiazolyl moiety (TFMO) as a non-chelating metal-binding group. The new compounds showed potent anti-proliferative activity when tested against MCF7 breast cancer cell line, as well as increased acetylation of histones and induce cells apoptosis. The new compounds apoptotic effects were validated through the upregulation of proapoptotic proteins caspases3 and 7 and downregulation of the antiapoptotic biomarkers C-MYC, BCL2, BCL3 and NFĸB genes. Furthermore, the new compounds arrested cell cycle at different phases, which was confirmed through downregulation of the CDK1, 2, 4, 6, E2F1 and RB1 proteins. Taken together, our findings provide the foundation for the development of new chemical probes as potential lead drug candidates for the treatment of cancer.

Epigenomics and immunotherapeutic advances in pediatric brain tumors

Brain tumors are the leading cause of childhood cancer-related deaths. Similar to adult brain tumors, pediatric brain tumors are classified based on histopathological evaluations. However, pediatric brain tumors are often histologically inconsistent with adult brain tumors. Recent research findings from molecular genetic analyses have revealed molecular and genetic changes in pediatric tumors that are necessary for appropriate classification to avoid misdiagnosis, the development of treatment modalities, and the clinical management of tumors. As many of the molecular-based therapies developed from clinical trials on adults are not always effective against pediatric brain tumors, recent advances have improved our understanding of the molecular profiles of pediatric brain tumors and have led to novel epigenetic and immunotherapeutic treatment approaches currently being evaluated in clinical trials. In this review, we focus on primary malignant brain tumors in children and genetic, epigenetic, and molecular characteristics that differentiate them from brain tumors in adults. The comparison of pediatric and adult brain tumors highlights the need for treatments designed specifically for pediatric brain tumors. We also discuss the advancements in novel molecularly targeted drugs and how they are being integrated with standard therapy to improve the classification and outcomes of pediatric brain tumors in the future.

Histone Deacetylases (HDACs) in Gastric Cancer: An Update of their Emerging Prognostic and Therapeutic Role

Chemotherapy resistance is a rising concern in Gastric Cancer (GC) and has led to the investigation of various cellular compounds. Α functional equilibrium of histone acetylation and deacetylation was discovered in all cells, regulated by Histone Acetyltransferases and Deacetylases (HDACs), controlling chromatin coiling status and changing gene expression appropriately. In accordance with recent research, this equilibrium can be dysregulated in cancer cells aiding in the process of carcinogenesis and tumor progression by altering histone and non-histone proteins affecting gene expression, cell cycle control, differentiation, and apoptosis in various malignancies. In addition, increased HDAC expression in GC cells has been associated with increased stage, tumor invasion, nodal metastases, increased distant metastatic potential, and decreased overall survival. HDAC inhibitors could be used as treatment regimens for GC patients and could develop important synergistic interactions with chemotherapy drugs. The aim of this article is to review the molecular identity and mechanism of action of HDAC inhibitors, as well as highlight their potential utility as anti-cancer agents in GC.

[Mechanisms of cytotoxic action of a series of directionally synthesized heterocyclic hydroxamic acids]

Cyclic hydroxamic acids based on quinazoline-4(3H)-one and dihydroquinazoline-4(1H)-one have been synthesized. The antioxidant and iron-chelating properties of these compounds, their effect on the activity of the histone deacetylase enzyme, and their cytotoxic effect on cells of various tumor lines have been investigated. We have identified two compounds-hits, which exhibit the multipharmacological type of the antineoplastic activity. Their cytotoxic effect on cells of human lung carcinoma A549 and breast adenocarcinoma MCF-7 is obviously associated with their ability to modulate the level of reactive oxygen species and to chelate Fe(II) ions, as well as to inhibit the metalloenzymes, histone deacetylases, involved in the epigenetic regulation of tumor genesis. Thus, the synthesized hydroxamic acids may be considered as a promising basis for creating potential oncolytics.

Histone modifications in epigenetic regulation of cancer: Perspectives and achieved progress

Epigenetic changes associated with histone modifications play an important role in the emergence and maintenance of the phenotype of various cancer types. In contrast to direct mutations in the main DNA sequence, these changes are reversible, which makes the development of inhibitors of enzymes of post-translational histone modifications one of the most promising strategies for the creation of anticancer drugs. To date, a wide variety of histone modifications have been found that play an important role in the regulation of chromatin state, gene expression, and other nuclear events. This review examines the main features of the most common and studied epigenetic histone modifications with a proven role in the pathogenesis of a wide range of malignant neoplasms: acetylation / deacetylation and methylation / demethylation of histone proteins, as well as the role of enzymes of the HAT / HDAC and HMT / HDMT families in the development of oncological pathologies. The data on the relationship between histone modifications and certain types of cancer are presented and discussed. Special attention is devoted to the consideration of various strategies for the development of epigenetic inhibitors. The main directions of the development of inhibitors of histone modifications are analyzed and effective strategies for their creation are identified and discussed. The most promising strategy is the use of multitarget drugs, which will affect multiple molecular targets of cancer. A critical analysis of the current status of approved epigenetic anticancer drugs has also been performed.

Promising Molecular Targets for Pharmacological Therapy of Neurodegenerative Pathologies

Drug development for the treatment of neurodegenerative diseases has to confront numerous problems occurring, in particular, because of attempts to address only one of the causes of the pathogenesis of neurological disorders. Recent advances in multitarget therapy research are gaining momentum by utilizing pharmacophores that simultaneously affect different pathological pathways in the neurodegeneration process. The application of such a therapeutic strategy not only involves the treatment of symptoms, but also mainly addresses prevention of the fundamental pathological processes of neurodegenerative diseases and the reduction of cognitive abilities. Neuroinflammation and oxidative stress, mitochondrial dysfunction, dysregulation of the expression of histone deacetylases, and aggregation of pathogenic forms of proteins are among the most common and significant pathological features of neurodegenerative diseases. In this review, we focus on the molecular mechanisms and highlight the main aspects, including reactive oxygen species, the cell endogenous antioxidant system, neuroinflammation triggers, metalloproteinases, α-synuclein, tau proteins, neuromelanin, histone deacetylases, presenilins, etc. The processes and molecular targets discussed in this review could serve as a starting point for screening leader compounds that could help prevent or slow down the development of neurodegenerative diseases.

xCT Inhibition Increases Sensitivity to Vorinostat in a ROS-Dependent Manner

As histone deacetylase inhibitors (HDACIs) have limited efficacy against solid tumors, we investigated whether and how oxidative stress is involved in sensitivity to HDACIs to develop a novel therapeutic option of HDACIs treatment. We first tested whether a reduction of the antioxidant glutathione (GSH) by glutamine deprivation affects sensitivity to a commercially available HDACI vorinostat and reactive oxygen species (ROS) accumulation. Next we investigated the relationship between a glutamate-cystine transporter xCT and the efficacy of vorinostat using siRNA of xCT and bioinformatic analyses. Finally, we verified the combinatory effects of vorinostat and the xCT inhibitor salazosulfapyridine (SASP) on ROS accumulation, cell death induction, and colony formation. Glutamine deprivation increased vorinostat-mediated cell death with ROS accumulation. Genetic ablation of xCT improved the efficacy of vorinostat, consistent with the results of public data analyses demonstrating that xCT expressions positively correlate with insensitivity to HDACIs in many types of cancer cell lines. Vorinostat caused ROS accumulation when combined with SASP, possibly resulting in synergistic ferroptosis. Our study provides a novel mechanistic insight into the mechanism underlying sensitivity to HDACIs involving xCT, suggesting xCT to be a promising predictive marker of HDACIs and rationalizing combinatory therapy of HDACIs with xCT inhibitors to induce ferroptosis.

In silico Design of Novel Histone Deacetylase 4 Inhibitors: Design Guidelines for Improved Binding Affinity

Histone deacetylases (HDAC) are being targeted for a number of diseases such as cancer, inflammatory disease, and neurological disorders. Within this family of 18 isozymes, HDAC4 is a prime target for glioma, one of the most aggressive brain tumors reported. Thus, the development of HDAC4 inhibitors could present a novel therapeutic route for glioma. In this work, molecular docking studies on cyclopropane hydroxamic acid derivatives identified five novel molecular interactions to the HDAC4 receptor that could be harnessed to enhance inhibitor binding. Thus, design guidelines for the optimization of potent HDAC4 inhibitors were developed which can be utilized to further the development of HDAC4 inhibitors. Using the developed guidelines, eleven novel cyclopropane hydroxamic acid derivatives were designed that outcompeted all original cyclopropane hydroxamic acids HDAC4 inhibitors studied in silico. The results of this work will be an asset to paving the way for further design and optimization of novel potent HDAC4 inhibitors for gliomas.

Histone Deacetylases and Histone Deacetylase Inhibitors: Molecular Mechanisms of Action in Various Cancers

Epigenetic modifications such as histone modification play an important role in tumorigenesis. There are several evidence that histone deacetylases (HDACs) play a key role in cancer induction and progression by histone deacetylation. Besides, histone acetylation is being accessed as a therapeutic target because of its role in regulating gene expression. HDAC inhibitors (HDACIs) are a family of synthetic and natural compounds that differ in their target specificities and activities. They affect markedly cancer cells, inducing cell differentiation, cell cycle arrest and cell death, reduction of angiogenesis, and modulation of the immune system. Here, we summarize the mechanisms of HDACs and the HDACIs in several cancers. An online search of different sources such as PubMed, ISI, and Scopus was performed to find available data on mechanisms and pathways of HDACs and HDACIs in different cancers. The result indicated that HDACs induce cancer through multiple mechanisms in various tissues. This effect can be inhibited by HDACIs which affect cancer cell by different pathways such as cell differentiation, cell cycle arrest, and cell death. In conclusion, these findings indicate that the HDACs play a major role in carcinogenesis through various pathways, and HDACIs can inhibit HDAC activity by multiple mechanisms resulting in cell cycle arrest, cell growth inhibition, and apoptosis induction.

Suberoylanilide hydroxamic acid upregulates histone acetylation and activates endoplasmic reticulum stress to induce apoptosis in HepG2 liver cancer cells

Suberoylanilide hydroxamic acid (SAHA) is a histone deacetylase inhibitor that has demonstrated clinical activity against various solid tumors. The aim of the present study was to explore the effects of SAHA on the apoptosis of HepG2 liver cancer cells, as well as the potential mechanisms involved in histone acetylation and endoplasmic reticulum (ER) stress. HepG2 cells were treated with various doses of SAHA (0, 1, 6 and 12 µM), and apoptosis was measured by flow cytometry. The levels of ER stress-associated molecules, including 78 kDa glucose-regulated protein (GRP78), PRKR-like endoplasmic reticulum kinase (PERK), phosphorylated (p)-PERK, activating transcription factor 4 (ATF4) and C/EBP-homologous protein (CHOP), were quantitated by western blot analysis and reverse transcription-quantitative PCR assay. The expression levels of acetylated histone H4 (acH4, acH4 lysine (K)5 and acH4K12) were detected by western blot analysis. The effects of SAHA on the acetylation of H4 in the promoter regions of GRP78, ATF4 and CHOP were evaluated by chromatin immunoprecipitation assays. Following treatment with higher doses of SAHA (6 and 12 µM) for 48 h, the proliferation of HepG2 cells was significantly suppressed. SAHA induced dose-dependent apoptosis and increased both protein and mRNA expression levels of GRP78, ATF4 and CHOP in HepG2 cells. The protein expression of PERK was markedly decreased by treatment with SAHA, whereas the p-PERK expression level was notably increased, which resulted in increased p-PERK/PERK ratio. Furthermore, the acetylation levels of H4 in the promoter regions of GRP78, ATF4 and CHOP were significantly increased in HepG2 cells exposed to 6 µM SAHA for 36 h. Thus, SAHA induces apoptosis in HepG2 cells by activating the ER stress-mediated apoptotic signaling pathway, at least partially by enhancing the acetylation of histone H4 on the promoter regions of ER-stress associated genes, including GRP78, ATF4 and CHOP.

Chidamide suppresses the glycolysis of triple negative breast cancer cells partially by targeting the miR‑33a‑5p‑LDHA axis

Triple negative breast cancer (TNBC) is one of the most aggressive types of breast cancer and has a poor prognosis. Therefore, the development of novel drugs and understanding the molecular mechanisms that may contribute to the initiation and development of TNBC are urgently required. Chidamide, a histone deacetylase inhibitor, has been reported as possessing anti‑cancer properties in several cancers, however, the function of chidamide in TNBC remains to be elucidated. The present study revealed that chidamide inhibited the proliferation, colony formation and migration of TNBC cells. Experiments investigating the underlying mechanism revealed that chidamide upregulated the expression of microRNA (miR)‑33a‑5p in TNBC cells via RT‑qPCR. Luciferase reporter assay demonstrated that miR‑33a‑5p was bound to the 3'‑untranslated region of lactate dehydrogenase A (LDHA) and decreased the expression of LDHA in TNBC cells. In addition, chidamide suppressed the expression of LDHA and significantly decreased the glycolysis of TNBC cells. Collectively, the results of the present study demonstrated that chidamide reprogramed glucose metabolism, partially by targeting the miR‑33a‑5p/LDHA pathway, in TNBC. These findings indicate that chidamide may be a promising novel drug in the treatment of patients with TNBC.

Understanding Apoptosis and Apoptotic Pathways Targeted Cancer Therapeutics

Various physiological processes involve appropriate tissue developmental process and homeostasis - the pathogenesis of several diseases connected with deregulatory apoptosis process. Apoptosis plays a crucial role in maintaining a balance between cell death and division, evasion of apoptosis results in the uncontrolled multiplication of cells leading to different diseases such as cancer. Currently, the development of apoptosis targeting anticancer drugs has gained much interest since cell death induced by apoptosis causes minimal inflammation. The understanding of complexities of apoptosis mechanism and how apoptosis is evolved by tumor cells to oppose cell death has focused research into the new strategies designed to induce apoptosis in cancer cells. This review focused on the underlying mechanism of apoptosis and the dysregulation of apoptosis modulators involved in the extrinsic and intrinsic apoptotic pathway, which include death receptors (DRs) proteins, cellular FLICE inhibitory proteins (c-FLIP), anti-apoptotic Bcl-2 proteins, inhibitors of apoptosis proteins (IAPs), tumor suppressor (p53) in cancer cells along with various current clinical approaches aimed to selectively induce apoptosis in cancer cells.

Histone deacetylase enzymes and selective histone deacetylase inhibitors for antitumor effects and enhancement of antitumor immunity in glioblastoma

Glioblastoma multiforme (GBM), which is the most common primary central nervous system malignancy in adults, has long presented a formidable challenge to researchers and clinicians alike. Dismal 5-year survival rates of the patients with these tumors and the ability of the recurrent tumors to evade primary treatment strategies have prompted a need for alternative therapies in the treatment of GBM. Histone deacetylase (HDAC) inhibitors are currently a potential epigenetic therapy modality under investigation for use in GBM with mixed results. While these agents show promise through a variety of proposed mechanisms in the pre-clinical realm, only several of these agents have shown this same promise when translated into the clinical arena, either as monotherapy or for use in combination regimens. This review will examine the current state of use of HDAC inhibitors in GBM, the mechanistic rationale for use of HDAC inhibitors in GBM, and then examine an exciting new mechanistic revelation of certain HDAC inhibitors that promote antitumor immunity in GBM. The details of this antitumor immunity will be discussed with an emphasis on application of this antitumor immunity towards developing alternative therapies for treatment of GBM. The final section of this article will provide an overview of the current state of immunotherapy targeted specifically to GBM.

Therapeutic potential and functional interaction of carfilzomib and vorinostat in T-cell leukemia/lymphoma

We previously showed that the proteasome inhibitor carfilzomib and the histone deacetylase inhibitor (HDACI) vorinostat cooperated to induce cell apoptosis in one T-cell leukemia cell line in vitro, implying the possibility of the combination treatment of carfilzomib and vorinostat as a potential therapeutic strategy in human T-cell leukemia/lymphoma. Here we report that combination treatment of carfilzomib and vorinostat enhanced cell apoptosis and induced a marked increase in G2-M arrest, reactive oxygen species (ROS) generation, and activated the members of mitogen-activated protein kinases (MAPK) family, including the stress-activated kinases JNK, p38MAPK, and ERK1/2. Carfilzomib/vorinostat-mediated apoptosis was blocked by the ROS scavenger N-acetylcysteine (NAC). The JNK inhibitor SP600125 and the p38MAPK inhibitor SB203580 but not the MEK1/2 inhibitor U0126 significantly attenuated carfilzomib/vorinostat-induced apoptosis, suggesting that p38MAPK and JNK activation contribute to carfilzomib and vorinostat-induced apoptosis. This was further confirmed via short hairpin (shRNA) RNA knockdown of p38MAPK and JNK. Interestingly, the ROS scavenger NAC attenuated carfilzomib/vorinostat-mediated activation of p38MAPK and JNK. However, p38MAPK shRNA but not JNK shRNA diminished carfilzomib/vorinostat-mediated ROS generation. In contrast, overexpression of p38MAPK significantly increased carfilzomib/vorinostat-mediated ROS generation, suggesting that an amplification loop exists between ROS and p38MAPK pathway. Combination treatment of carfilzomib and vorinostat enhanced their individual antitumor activity in both a human xenograft model as well as human primary T-cell leukemia/lymphoma cells. These data suggest the potential clinical benefit and underlying molecular mechanism of combining carfilzomib with vorinostat in the treatment of human T-cell leukemia/lymphoma.

The Histone Deacetylase Inhibitor Valproic Acid Exerts a Synergistic Cytotoxicity with the DNA-Damaging Drug Ellipticine in Neuroblastoma Cells

Neuroblastoma (NBL) originates from undifferentiated cells of the sympathetic nervous system. Chemotherapy is judged to be suitable for successful treatment of this disease. Here, the influence of histone deacetylase (HDAC) inhibitor valproate (VPA) combined with DNA-damaging chemotherapeutic, ellipticine, on UKF-NB-4 and SH-SY5Y neuroblastoma cells was investigated. Treatment of these cells with ellipticine in combination with VPA led to the synergism of their anticancer efficacy. The effect is more pronounced in the UKF-NB-4 cell line, the line with N-myc amplification, than in SH-SY5Y cells. This was associated with caspase-3-dependent induction of apoptosis in UKF-NB-4 cells. The increase in cytotoxicity of ellipticine in UKF-NB-4 by VPA is dictated by the sequence of drug administration; the increased cytotoxicity was seen only after either simultaneous exposure to these drugs or after pretreatment of cells with ellipticine before their treatment with VPA. The synergism of treatment of cells with VPA and ellipticine seems to be connected with increased acetylation of histones H3 and H4. Further, co-treatment of cells with ellipticine and VPA increased the formation of ellipticine-derived DNA adducts, which indicates an easier accessibility of ellipticine to DNA in cells by its co-treatment with VPA and also resulted in higher ellipticine cytotoxicity. The results are promising for in vivo studies and perhaps later for clinical studies of combined treatment of children suffering from high-risk NBL.

Trichostatin A decreases the levels of MeCP2 expression and phosphorylation and increases its chromatin binding affinity

MeCP2 binds to methylated DNA in a chromatin context and has an important role in cancer and brain development and function. Histone deacetylase (HDAC) inhibitors are currently being used to palliate many cancer and neurological disorders. Yet, the molecular mechanisms involved are not well known for the most part and, in particular, the relationship between histone acetylation and MeCP2 is not well understood. In this paper, we study the effect of the HDAC inhibitor trichostatin A (TSA) on MeCP2, a protein whose dysregulation plays an important role in these diseases. We find that treatment of cells with TSA decreases the phosphorylation state of this protein and appears to result in a higher MeCP2 chromatin binding affinity. Yet, the binding dynamics with which the protein binds to DNA appear not to be significantly affected despite the chromatin reorganization resulting from the high levels of acetylation. HDAC inhibition also results in an overall decrease in MeCP2 levels of different cell lines. Moreover, we show that miR132 increases upon TSA treatment, and is one of the players involved in the observed downregulation of MeCP2.

Novel Class IIa-Selective Histone Deacetylase Inhibitors Discovered Using an in Silico Virtual Screening Approach

Histone deacetylases (HDAC) contain eighteen isoforms that can be divided into four classes. Of these isoform enzymes, class IIa (containing HDAC4, 5, 7 and 9) target unique substrates, some of which are client proteins associated with epigenetic control. Class IIa HDACs are reportedly associated with some neuronal disorders, making HDACs therapeutic targets for treating neurodegenerative diseases. Additionally, some reported HDAC inhibitors contain hydroxamate moiety that chelates with zinc ion to become the cofactor of HDAC enzymes. However, the hydroxamate functional group is shown to cause undesirable effects and has poor pharmacokinetic profile. This study used in silico virtual screening methodology to identify several nonhydroxamate compounds, obtained from National Cancer Institute database, which potentially inhibited HDAC4. Comparisons of the enzyme inhibitory activity against a panel of HDAC isoforms revealed these compounds had strong inhibitory activity against class IIa HDACs, but weak inhibitory activity against class I HDACs. Further analysis revealed that a single residue affects the cavity size between class I and class IIa HDACs, thus contributing to the selectivity of HDAC inhibitors discovered in this study. The discovery of these inhibitors presents the possibility of developing new therapeutic treatments that can circumvent the problems seen in traditional hydroxamate-based drugs.

Chromatin remodeling modulates radiosensitivity of the daughter cells derived from cell population exposed to low- and high-LET irradiation

Radiation effects are dependent of linear energy transfer (LET), but it is still obscure whether the daughter cells (DCs) derived from irradiated population are radioresistance and much less the underlying mechanism. With the measurements of survival, proliferation and γH2AX foci, this study shows that the DCs from γ-ray irradiated cells (DCs-γ) became more radioresistant than its parent control without irradiation, but the radiosensitivity of DCs from α-particle irradiated cells (DCs-α) was not altered. After irradiation with equivalent doses of γ-rays and α-particles, the foci number of histone H3 lysine 9 dimethylation (H3K9me3) and the activity of histone deacetylase (HDAC) in DCs-γ was extensively higher than these in DCs-α and its parent control, indicating that a higher level of heterochromatin was formed in DCs-γ but not in DCs-α. Treatment of cells with SAHA (an inhibitor of HDAC) decreased the level of heterochromatin domains by inhibiting the expressions of H3K9m3 and HP-1a proteins and triggering the expression of acetylated core histone H3 (Ac-H3). When cells were treated with SAHA, the radioresistance phenotype of DCs-γ was eliminated so that the radiosensitivities of DCs-γ, DCs-α and their parent cells approached to same levels. Our current results reveal that γ-rays but not α-particles could induce chromatin remodeling and heterochromatinization which results in the occurrence of radioresistance of DCs, indicating that the combination treatment of irradiation and HDAC inhibitor could serve as a potential cancer therapy strategy, especially for the fraction radiotherapy of low-LET irradiation.

Potential of apoptotic pathway-targeted cancer therapeutic research: Where do we stand?

Underneath the intricacy of every cancer lies mysterious events that impel the tumour cell and its posterity into abnormal growth and tissue invasion. Oncogenic mutations disturb the regulatory circuits responsible for the governance of versatile cellular functions, permitting tumour cells to endure deregulated proliferation, resist to proapoptotic insults, invade and erode normal tissues and above all escape apoptosis. This disruption of apoptosis has been highly implicated in various malignancies and has been exploited as an anticancer strategy. Owing to the fact that apoptosis causes minimal inflammation and damage to the tissue, apoptotic cell death-based therapy has been the centre of attraction for the development of anticancer drugs. Increased understanding of the molecular pathways underlying apoptosis has enabled scientists to establish unique approaches targeting apoptosis pathways in cancer therapeutics. In this review, we reconnoitre the two major pathways (intrinsic and extrinsic) targeted cancer therapeutics, steering toward chief modulators of these pathways, such as B-cell lymphoma 2 protein family members (pro- and antiapoptotic), inhibitor of apoptosis proteins, and the foremost thespian of extrinsic pathway regulator, tumour necrosis factor-related apoptosis-inducing agent. Together, we also will have a look from clinical perspective to address the agents (drugs) and therapeutic strategies adopted to target these specific proteins/pathways that have entered clinical trials.

The Therapeutic Potential of AN-7, a Novel Histone Deacetylase Inhibitor, for Treatment of Mycosis Fungoides/Sezary Syndrome Alone or with Doxorubicin

The 2 histone deacetylase inhibitors (HDACIs) approved for the treatment of cutaneous T-cell lymphoma (CTCL) including mycosis fungoides/sezary syndrome (MF/SS), suberoylanilide hydroxamic acid (SAHA) and romidepsin, are associated with low rates of overall response and high rates of adverse effects. Data regarding combination treatments with HDACIs is sparse. Butyroyloxymethyl diethylphosphate (AN-7) is a novel HDACI, which was found to have selective anticancer activity in several cell lines and animal models. The aim of this study was to compare the anticancer effects of AN-7 and SAHA, either alone or combined with doxorubicin, on MF/SS cell lines and peripheral blood lymphocytes (PBL) from patients with Sezary syndrome (SPBL). MyLa cells, Hut78 cells, SPBL, and PBL from healthy normal individuals (NPBL) were exposed to the test drugs, and the findings were analyzed by a viability assay, an apoptosis assay, and Western blot. AN-7 was more selectively toxic to MyLa cells, Hut78 cells, and SPBL (relative to NPBL) than SAHA and also acted more rapidly. Both drugs induced apoptosis in MF/SS cell lines, SAHA had a greater effect on MyLa cell line, while AN-7 induced greater apoptosis in SPBL; both caused an accumulation of acetylated histone H₃, but AN-7 was associated with earlier kinetics; and both caused a downregulation of the HDAC1 protein in MF/SS cell lines. AN-7 acted synergistically with doxorubicin in both MF/SS cell lines and SPBL, and antagonistically with doxorubicin in NPBL. By contrast, SAHA acted antagonistically with doxorubicin on MF/SS cell lines, SPBL, and NPBL, leaving <50% viable cells. In conclusion, AN-7 holds promise as a therapeutic agent in MF/SS and has several advantages over SAHA. Our data provide a rationale for combining AN-7, but not SAHA, with doxorubicin to induce the cell death in MF/SS.

Indomethacin-guided cancer selective prodrug conjugate activated by histone deacetylase and tumour-associated protease

Indomethacin-guided cancer selective prodrug system activated by histone deacetylase and tumour-associated protease.

A comprehensive analysis of radiosensitization targets; functional inhibition of DNA methyltransferase 3B radiosensitizes by disrupting DNA damage regulation

A comprehensive genome-wide screen of radiosensitization targets in HeLa cells was performed using a shRNA-library/functional cluster analysis and DNMT3B was identified as a candidate target. DNMT3B RNAi increased the sensitivity of HeLa, A549 and HCT116 cells to both γ-irradiation and carbon-ion beam irradiation. DNMT3B RNAi reduced the activation of DNA damage responses induced by γ-irradiation, including HP1β-, γH2AX- and Rad51-foci formation. DNMT3B RNAi impaired damage-dependent H2AX accumulation and showed a reduced level of γH2AX induction after γ-irradiation. DNMT3B interacted with HP1β in non-irradiated conditions, whereas irradiation abrogated the DNMT3B/HP1β complex but induced interaction between DNMT3B and H2AX. Consistent with radiosensitization, TP63, BAX, PUMA and NOXA expression was induced after γ-irradiation in DNMT3B knockdown cells. Together with the observation that H2AX overexpression canceled radiosensitization by DNMT3B RNAi, these results suggest that DNMT3B RNAi induced radiosensitization through impairment of damage-dependent HP1β foci formation and efficient γH2AX-induction mechanisms including H2AX accumulation. Enhanced radiosensitivity by DNMT3B RNAi was also observed in a tumor xenograft model. Taken together, the current study implies that comprehensive screening accompanied by a cluster analysis enabled the identification of radiosensitization targets. Downregulation of DNMT3B, one of the targets identified using this method, radiosensitizes cancer cells by disturbing multiple DNA damage responses.

Molecular Mechanism of the Cell Death Induced by the Histone Deacetylase Pan Inhibitor LBH589 (Panobinostat) in Wilms Tumor Cells

Background

Wilms tumor (WT) is an embryonic kidney cancer, for which histone acetylation might be a therapeutic target. LBH589, a novel targeted agent, suppresses histone deacetylases in many tumors. This study investigated the antitumor activity of LBH589 in SK-NEP-1 and G401 cells.

Methods

SK-NEP-1 and G401 cell growth was assessed by CCK-8 and in nude mice experiments. Annexin V/propidium iodide staining followed by flow cytometry detected apoptosis in cell culture. Gene expressions of LBH589-treated tumor cells were analyzed using an Arraystar Human LncRNA Array. The Multi Experiment View cluster software analyzed the expression data. Differentially expressed genes from the cluster analyses were imported into the Ingenuity Pathway Analysis tool.

Results

LBH589 inhibited cell proliferation of SK-NEP-1 and G401 cells in a dose-dependent manner. Annexin V, TUNEL and Hochest 33342 staining analysis showed that LBH589-treated cells showed more apoptotic features compared with the control. LBH589 treatment inhibited the growth of SK-NEP-1 xenograft tumors in nude mice. Arraystar Human LncRNA Array analysis of genes and lncRNAs regulated by LBH589 identified 6653 mRNAs and 8135 lncRNAs in LBH589-treated SK-NEP-1 cells. The most enriched gene ontology terms were those involved in nucleosome assembly. KEGG pathway analysis identified cell cycle proteins, including CCNA2, CCNB2, CCND1, CCND2, CDK4, CDKN1B and HDAC2, etc. Ingenuity Pathway Analysis identified important upstream molecules: HIST2H3C, HIST1H4A, HIST1A, HIST1C, HIST1D, histone H1, histone H3, RPRM, HSP70 and MYC.

Conclusions

LBH589 treatment caused apoptosis and inhibition of cell proliferation of SK-NEP-1and G401 cells. LBH589 had a significant effect and few side effects on SK-NEP-1 xenograft tumors. Expression profiling, and GO, KEGG and IPA analyses identified new targets and a new “network” of genes responding to LBH589 treatment in SK-NEP-1 cells. RPRM, HSP70 and MYC may be important regulators during LBH589 treatment. Our results provide new clues to the proapoptotic mechanism of LBH589.

The synergistic effects of DNA-damaging drugs cisplatin and etoposide with a histone deacetylase inhibitor valproate in high-risk neuroblastoma cells

High-risk neuroblastoma remains one of the most important therapeutic challenges for pediatric oncologists. New agents or regimens are urgently needed to improve the treatment outcome of this fatal tumor. We examined the effect of histone deacetylase (HDAC) inhibitors in a combination with other chemotherapeutics on a high-risk neuroblastoma UKF-NB-4 cell line. Treatment of UKF-NB-4 cells with DNA-damaging chemotherapeutics cisplatin or etoposide combined with the HDAC inhibitor valproate (VPA) resulted in the synergistic antitumor effect. This was associated with caspase-3-dependent induction of apoptosis. Another HDAC inhibitor trichostatin A and a derivative of VPA that does not exhibit HDAC inhibitory activity, valpromide, lacked this effect. The synergism was only induced when VPA was combined with cytostatics targeted to cellular DNA; VPA does not potentiate the cytotoxicity of the anticancer drug vincristine that acts by a mechanism different from that of DNA damage. The VPA-mediated sensitization of UKF-NB-4 cells to cisplatin or etoposide was dependent on the sequence of drug administration; the potentiating effect was only produced either by simultaneous treatment with these drugs or when the cells were pretreated with cisplatin or etoposide before their exposure to VPA. The synergistic effects of VPA with cisplatin or etoposide were associated with changes in the acetylation status of histones H3 and H4. The results of this study provide a rationale for clinical evaluation of the combination of VPA and cisplatin or etoposide for treating children suffering from high-risk neuroblastoma.

NBM-T-BBX-OS01, Semisynthesized from Osthole, Induced G1 Growth Arrest through HDAC6 Inhibition in Lung Cancer Cells

Disrupting lung tumor growth via histone deacetylases (HDACs) inhibition is a strategy for cancer therapy or prevention. Targeting HDAC6 may disturb the maturation of heat shock protein 90 (Hsp90) mediated cell cycle regulation. In this study, we demonstrated the effects of semisynthesized NBM-T-BBX-OS01 (TBBX) from osthole on HDAC6-mediated growth arrest in lung cancer cells. The results exhibited that the anti-proliferative activity of TBBX in numerous lung cancer cells was more potent than suberoylanilide hydroxamic acid (SAHA), a clinically approved pan-HDAC inhibitor, and the growth inhibitory effect has been mediated through G1 growth arrest. Furthermore, the protein levels of cyclin D1, CDK2 and CDK4 were reduced while cyclin E and CDK inhibitor, p21^Waf1/Cip1, were up-regulated in TBBX-treated H1299 cells. The results also displayed that TBBX inhibited HDAC6 activity via down-regulation HDAC6 protein expression. TBBX induced Hsp90 hyper-acetylation and led to the disruption of cyclin D1/Hsp90 and CDK4/Hsp90 association following the degradation of cyclin D1 and CDK4 proteins through proteasome. Ectopic expression of HDAC6 rescued TBBX-induced G1 arrest in H1299 cells. Conclusively, the data suggested that TBBX induced G1 growth arrest may mediate HDAC6-caused Hsp90 hyper-acetylation and consequently increased the degradation of cyclin D1 and CDK4.

Methamphetamine promotes α-tubulin deacetylation in endothelial cells: the protective role of acetyl-l-carnitine

Methamphetamine (METH) is a powerful psychostimulant drug used worldwide for its reinforcing properties. In addition to the classic long-lasting monoaminergic-disrupting effects extensively described in the literature, METH has been consistently reported to increase blood brain barrier (BBB) permeability, both in vivo and in vitro, as a result of tight junction and cytoskeleton disarrangement. Microtubules play a critical role in cell stability, which relies on post-translational modifications such as α-tubulin acetylation. As there is evidence that psychostimulants drugs modulate the expression of histone deacetylases (HDACs), we hypothesized that in endothelial cells METH-mediation of cytoplasmatic HDAC6 activity could affect tubulin acetylation and further contribute to BBB dysfunction. To validate our hypothesis, we exposed the bEnd.3 endothelial cells to increasing doses of METH and verified that it leads to an extensive α-tubulin deacetylation mediated by HDACs activation. Furthermore, since we recently reported that acetyl-l-carnitine (ALC), a natural occurring compound, prevents BBB structural loss in a context of METH exposure, we reasoned that ALC could also preserve the acetylation of microtubules under METH action. The present results confirm that ALC is able to prevent METH-induced deacetylation providing effective protection on microtubule acetylation. Although further investigation is still needed, HDACs regulation may become a new therapeutic target for ALC.

Histone deacetylases: structural determinants of inhibitor selectivity

Histone deacetylases (HDACs) are epigenetic targets with an important role in cancer, neurodegeneration, inflammation, and metabolic disorders. Although clinically effective HDAC inhibitors have been developed, the design of inhibitors with the desired isoform(s) selectivity remains a challenge. Selective inhibitors could help clarify the function of each isoform, and provide therapeutic agents having potentially fewer adverse effects. Crystal structures of several HDACs have been reported, enabling structure-based drug design and providing important information to understand enzyme function. Here, we provide a comprehensive review of the structural information available on HDACs, discussing both conserved and isoform-specific structural and mechanistic features. We focus on distinctive aspects that help rationalize inhibitor selectivity, and provide structure-based recommendations for achieving the desired selectivity.

Histone deacetylase inhibitor suberoyl bis-hydroxamic acid suppresses cell proliferation and induces apoptosis in breast cancer cells

Suberoyl bis‑hydroxamic acid (SBHA) is a histone deacetylase inhibitor that has shown anticancer activity against numerous types of human cancer. The aim of the current study was to explore the effects of SBHA on the proliferation and apoptosis of breast cancer cells. MCF‑7 breast cancer cells were treated with different concentrations of SBHA and tested for cell viability, apoptosis and gene expression changes. The results showed that SBHA significantly inhibited the proliferation of MCF‑7 cells in a concentration‑dependent manner, as determined using a Cell Counting kit‑8 assay. SBHA‑treated MCF‑7 cells showed G0/G1 cell‑cycle arrest, coupled with elevated expression levels of p21 and p27 proteins. Hoechst 33258 staining revealed cell shrinkage, chromosomal condensation and nuclear fragmentation in MCF‑7 cells treated with SBHA. Flow cytometric analysis of Annexin V‑stained cells showed that SBHA treatment induced apoptotic cell death in a concentration‑dependent manner. Western blot analysis confirmed the upregulation of Bax and the downregulation of Bcl‑2 by SBHA. In conclusion, these results indicate that SBHA exerts cytotoxic effects against human breast cancer cells, which involves the modulation of p21, p27 and Bcl‑2 family proteins, consequently leading to cell‑cycle arrest and apoptosis.

HDAC-inhibition counteracts everolimus resistance in renal cell carcinoma in vitro by diminishing cdk2 and cyclin A

Background

Targeted therapies have improved therapeutic options of treating renal cell carcinoma (RCC). However, drug response is temporary due to resistance development.

Methods

Functional and molecular changes in RCC Caki-1 cells, after acquired resistance to the mammalian target of rapamycin (mTOR)-inhibitor everolimus (Caki^res), were investigated with and without additional application of the histone deacetylase (HDAC)-inhibitor valproic acid (VPA). Cell growth was evaluated by MTT assay, cell cycle progression and apoptosis by flow cytometry. Target molecules of everolimus and VPA, apoptotic and cell cycle regulating proteins were investigated by western blotting. siRNA blockade was performed to evaluate the functional relevance of the proteins.

Results

Everolimus resistance was accompanied by significant increases in the percentage of G2/M-phase cells and in the IC₅₀. Akt and p70S6K, targets of everolimus, were activated in Caki^res compared to drug sensitive cells. The most prominent change in Caki^res cells was an increase in the cell cycle activating proteins cdk2 and cyclin A. Knock-down of cdk2 and cyclin A caused significant growth inhibition in the Caki^res cells. The HDAC-inhibitor, VPA, counteracted everolimus resistance in Caki^res, evidenced by a significant decrease in tumor growth and cdk2/cyclin A.

Conclusion

It is concluded that non-response to everolimus is characterized by increased cdk2/cyclin A, driving RCC cells into the G2/M-phase. VPA hinders everolimus non-response by diminishing cdk2/cyclin A. Therefore, treatment with HDAC-inhibitors might be an option for patients with advanced renal cell carcinoma and acquired everolimus resistance.