Tubacin suppresses proliferation and induces apoptosis of acute lymphoblastic leukemia cells

Role of HDAC6-STAT3 in immunomodulatory pathways in Colorectal cancer cells

Colorectal cancer (CRC) is one of the most common malignant neoplasms and the second leading cause of death from tumors worldwide. Therefore, there is a great need to study new therapeutical strategies, such as effective immunotherapies against these malignancies. Unfortunately, many CRC patients do not respond to current standard immunotherapies, making it necessary to search for adjuvant treatments. Histone deacetylase 6 (HDAC6) is involved in several processes, including immune response and tumor progression. Specifically, it has been observed that HDAC6 is required to activate the Signal Transducer and Activator of Transcription 3 (STAT3), a transcription factor involved in immunogenicity, by activating different genes in these pathways, such as PD-L1. Over-expression of immunosuppressive pathways in cancer cells deregulates T-cell activation. Therefore, we focused on the pharmacological inhibition of HDAC6 in CRC cells because of its potential as an adjuvant to avoid immunotolerance in immunotherapy. We investigated whether HDAC6 inhibitors (HDAC6is), such as Nexturastat A (NextA), affected STAT3 activation in CRC cells. First, we found that NextA is less cytotoxic than the non-selective HDACis panobinostat. Then, NextA modified STAT3 and decreased the mRNA and protein expression levels of PD-L1. Importantly, transcriptomic analysis showed that NextA treatment affected the expression of critical genes involved in immunomodulatory pathways in CRC malignancies. These results suggest that treatments with NextA reduce the functionality of STAT3 in CRC cells, impacting the expression of immunomodulatory genes involved in the inflammatory and immune responses. Therefore, targeting HDAC6 may represent an interesting adjuvant strategy in combination with immunotherapy.

HDACs alters negatively to the tumor immune microenvironment in gynecologic cancers

The role of histone deacetylases (HDACs) in the tumor immune microenvironment of gynecologic tumors remains unexplored. We integrated data from The Cancer Genome Atlas and Human Protein Atlas to examine HDAC expression in breast, cervical, ovarian, and endometrial cancers. Elevated HDAC expression correlated with poor prognosis and highly malignant cancer subtypes. Gene Set Enrichment Analysis revealed positive associations between HDAC expression and tumor proliferation signature, while negative associations were found with tumor inflammation signature. Increased HDAC expression was linked to reduced infiltration of natural killer (NK), NKT, and CD8+ T cells, along with negative associations with the expression of PSMB10, NKG7, CCL5, CD27, HLA-DQA1, and HLA-DQB1. In a murine 4T1 breast cancer model, treatment with suberoylanilide hydroxamic acid (SAHA; HDAC inhibitor) and PD-1 antibody significantly inhibited tumor growth and infiltration of CD3+ and CD8+ T cells. Real-time polymerase chain reaction revealed upregulated expressions of Psmb10, Nkg7, Ccl5, Cd8a, Cxcr6, and Cxcl9 genes, while Ctnnb1 and Myc genes were inhibited, indicating tumor suppression and immune microenvironment activation. Our study revealed that HDACs play tumor-promoting and immunosuppressive roles in gynecologic cancers, suggesting HDAC inhibitors as potential therapeutic agents for these cancers.

HDAC inhibitors: Promising agents for leukemia treatment

The essential role of epigenetic modification in the pathogenesis of a series of cancers have gradually been recognized. Histone deacetylase (HDACs), as well-known epigenetic modulators, are responsible for DNA repair, cell proliferation, differentiation, apoptosis and angiogenesis. Studies have shown that aberrant expression of HDACs is found in many cancer types. Thus, inhibition of HDACs has provided a promising therapeutic approach alternative for these patients. Since HDAC inhibitor (HDACi) vorinostat was first approved by the Food and Drug Administration (FDA) for treating cutaneous T-cell lymphoma (CTCL) in 2006, the combination of HDAC inhibitors with other molecules such as chemotherapeutic drugs has drawn much attention in current cancer treatment, especially in hematological malignancies therapy. Up to now, there have been more than twenty HDAC inhibitors investigated in clinic trials with five approvals being achieved. Indeed, Histone deacetylase inhibitors promote or enhance several different anticancer mechanisms and therefore are in evidence as potential antileukemia agents. In this review, we will focus on possible mechanisms by how HDAC inhibitors exert therapeutic benefit and their clinical utility in leukemia.

Neomenthol prevents the proliferation of skin cancer cells by restraining tubulin polymerization and hyaluronidase activity

Introduction

Neomenthol, a cyclic monoterpenoid, is a stereoisomer of menthol present in the essential oil of Mentha spp. It is used in food as a flavoring agent, in cosmetics and medicines because of its cooling effects. However, neomenthol has not been much explored for its anticancer potential. Additionally, targeting hyaluronidase, Cathepsin-D, and ODC by phytochemicals is amongst the efficient approach for cancer prevention and/or treatment.

Objectives

To investigate the molecular and cell target-based antiproliferative potential of neomenthol on human cancer (A431, PC-3, K562, A549, FaDu, MDA-MB-231, COLO-205, MCF-7, and WRL-68) and normal (HEK-293) cell lines.

Methods

The potency of neomenthol was evaluated on human cancer and normal cell line using SRB, NRU and MTT assays. The molecular target based study of neomenthol was carried out in cell-free and cell-based test systems. Further, the potency of neomenthol was confirmed by quantitative real-time PCR analysis and molecular docking studies. The in vivo anticancer potential of neomenthol was performed on mice EAC model and the toxicity examination was accomplished through in silico, ex vivo and in vivo approaches.

Results

Neomenthol exhibits a promising activity (IC₅₀ 17.3 ± 6.49 μM) against human epidermoid carcinoma (A431) cells by arresting the G2/M phase and increasing the number of sub-diploid cells. It significantly inhibits hyaluronidase activity (IC₅₀ 12.81 ± 0.01 μM) and affects the tubulin polymerization. The expression analysis and molecular docking studies support the in vitro molecular and cell target based results. Neomenthol prevents EAC tumor formation by 58.84% and inhibits hyaluronidase activity up to 10% at 75 mg/kg bw, i.p. dose. The oral dose of 1000 mg/kg bw was found safe in acute oral toxicity studies.

Conclusion

Neomenthol delayed the growth of skin carcinoma cells by inhibiting the tubulin polymerization and hyaluronidase activity, which are responsible for tumor growth, metastasis, and angiogenesis.

The Role of ARID1A in Tumors: Tumor Initiation or Tumor Suppression?

Genes encoding subunits of SWItch/Sucrose Non-Fermenting (SWI/SNF) chromatin remodeling complexes are collectively mutated in 20% of all human cancers, among which the AT-rich interacting domain-containing protein 1A (ARID1A, also known as BAF250a, B120, C1orf4, Osa1) that encodes protein ARID1A is the most frequently mutated, and mutations in ARID1A have been found in various types of cancer. ARID1A is thought to play a significant role both in tumor initiation and in tumor suppression, which is highly dependent upon context. Recent molecular mechanistic research has revealed that ARID1A participates in tumor progression through its effects on control of cell cycle, modulation of cellular functions such as EMT, and regulation of various signaling pathways. In this review, we synthesize a mechanistic understanding of the role of ARID1A in human tumor initiation as well as in tumor suppression and further discuss the implications of these new discoveries for potential cancer intervention. We also highlight the mechanisms by which mutations affecting the subunits in SWI/SNF complexes promote cancer.

Off-target toxicity is a common mechanism of action of cancer drugs undergoing clinical trials

Ninety-seven percent of drug-indication pairs that are tested in clinical trials in oncology never advance to receive U.S. Food and Drug Administration approval. While lack of efficacy and dose-limiting toxicities are the most common causes of trial failure, the reason(s) why so many new drugs encounter these problems is not well understood. Using CRISPR-Cas9 mutagenesis, we investigated a set of cancer drugs and drug targets in various stages of clinical testing. We show that-contrary to previous reports obtained predominantly with RNA interference and small-molecule inhibitors-the proteins ostensibly targeted by these drugs are nonessential for cancer cell proliferation. Moreover, the efficacy of each drug that we tested was unaffected by the loss of its putative target, indicating that these compounds kill cells via off-target effects. By applying a genetic target-deconvolution strategy, we found that the mischaracterized anticancer agent OTS964 is actually a potent inhibitor of the cyclin-dependent kinase CDK11 and that multiple cancer types are addicted to CDK11 expression. We suggest that stringent genetic validation of the mechanism of action of cancer drugs in the preclinical setting may decrease the number of therapies tested in human patients that fail to provide any clinical benefit.

Recent Progress in Histone Deacetylase Inhibitors as Anticancer Agents

Histone Deacetylase (HDAC) inhibitors are a relatively new class of anti-cancer agents that play important roles in epigenetic or non-epigenetic regulation, inducing death, apoptosis, and cell cycle arrest in cancer cells. Recently, their use has been clinically validated in cancer patients resulting in the approval by the FDA of four HDAC inhibitors, vorinostat, romidepsin, belinostat and panobinostat, used for the treatment of cutaneous/peripheral T-cell lymphoma and multiple myeloma. Many more HDAC inhibitors are at different stages of clinical development for the treatment of hematological malignancies as well as solid tumors. Also, clinical trials of several HDAC inhibitors for use as anti-cancer drugs (alone or in combination with other anti-cancer therapeutics) are ongoing. In the intensifying efforts to discover new, hopefully, more therapeutically efficacious HDAC inhibitors, molecular modelingbased rational drug design has played an important role. In this review, we summarize four major structural classes of HDAC inhibitors (hydroxamic acid derivatives, aminobenzamide, cyclic peptide and short-chain fatty acids) that are in clinical trials and different computer modeling tools available for their structural modifications as a guide to discover additional HDAC inhibitors with greater therapeutic utility.

The application of histone deacetylases inhibitors in glioblastoma

The epigenetic abnormality is generally accepted as the key to cancer initiation. Epigenetics that ensure the somatic inheritance of differentiated state is defined as a crucial factor influencing malignant phenotype without altering genotype. Histone modification is one such alteration playing an essential role in tumor formation, progression, and resistance to treatment. Notably, changes in histone acetylation have been strongly linked to gene expression, cell cycle, and carcinogenesis. The balance of two types of enzyme, histone acetyltransferases (HATs) and histone deacetylases (HDACs), determines the stage of histone acetylation and then the architecture of chromatin. Changes in chromatin structure result in transcriptional dysregulation of genes that are involved in cell-cycle progression, differentiation, apoptosis, and so on. Recently, HDAC inhibitors (HDACis) are identified as novel agents to keep this balance, leading to numerous researches on it for more effective strategies against cancers, including glioblastoma (GBM). This review elaborated influences on gene expression and tumorigenesis by acetylation and the antitumor mechanism of HDACis. Besdes, we outlined the preclinical and clinical advancement of HDACis in GBM as monotherapies and combination therapies.

Histone Deacetylase 6 as a Therapeutic Target in B cell-associated Hematological Malignancies

B lymphocytes play a critical role in humoral immunity. Abnormal B cell development and function cause a variety of hematological malignancies such as myeloma, B cell lymphoma, and leukemia. Histone deacetylase 6 (HDAC6) inhibitors alone or in combination with other drugs have shown efficacy in several hematological malignancies, including those resistant to targeted therapies. Mechanistically, HDAC6 inhibitors promote malignant tumor cell apoptosis by inhibiting protein degradation, reinvigorating anti-tumor immunity, and inhibiting cell survival signaling pathways. Due to their specificity, HDAC6 inhibitors represent a very promising and feasible new development pipeline for high-efficacy drugs with limited side effects. This article reviews recent progress in the mechanisms of action of HDAC6 inhibitors for the treatment of B cell-associated hematological malignancies, such as multiple myeloma and B cell non-Hodgkin lymphoma, which are often resistant to targeted therapies.

HDAC6-an Emerging Target Against Chronic Myeloid Leukemia?

Imatinib became the standard treatment for chronic myeloid leukemia (CML) about 20 years ago, which was a major breakthrough in stabilizing the pathology and improving the quality of life of patients. However, the emergence of resistance to imatinib and other tyrosine kinase inhibitors leads researchers to characterize new therapeutic targets. Several studies have highlighted the role of histone deacetylase 6 (HDAC6) in various pathologies, including cancer. This protein effectively intervenes in cellular activities by its primarily cytoplasmic localization. In this review, we will discuss the molecular characteristics of the HDAC6 protein, as well as its overexpression in CML leukemic stem cells, which make it a promising therapeutic target for the treatment of CML.

HDAC6‑selective inhibitor synergistically enhances the anticancer activity of immunomodulatory drugs in multiple myeloma

Nonselective histone deacetylase (HDAC) inhibitors have therapeutic effects, but exhibit dose‑limiting toxicities in patients with multiple myeloma (MM). The present study investigated the interaction between the HDAC6 inhibitor, A452, and immunomodulatory drugs (IMiDs) on dexamethasone (Dex)‑sensitive and ‑resistant MM cells compared with the current clinically tested HDAC6 inhibitor, ACY‑1215. It was shown that the combination of the HDAC6‑selective inhibitor, A452, with either of the IMiDs tested (lenalidomide or pomalidomide) led to the synergistic inhibition of cell growth, a decrease in the viability of MM cells and in an increase in the levels of apoptosis. Furthermore, enhanced cell death was associated with the inactivation of AKT and extracellular signal‑regulated kinase (ERK)1/2. Of note, A452 in combination with IMiDs induced synergistic MM cytotoxicity without altering the expression of cereblon and thereby, the synergistic downregulation of IKAROS family zinc finger (IKZF)1/3, c‑Myc and interferon regulatory factor 4 (IRF4). Furthermore, combined treatment with A452 and IMiDs induced the synergistic upregulation of PD‑L1. More importantly, this combination treatment was effective in the Dex‑resistant MM cells. Overall, the findings of this study indicate that A452 is more effective as an anticancer agent than ACY‑1215. Taken together, these findings suggest that a combination of the HDAC6‑selective inhibitor, A452, and IMiDs may prove to be beneficial in the treatment of patients with MM.

Structure-based design generated novel hydroxamic acid based preferential HDAC6 lead inhibitor with on-target cytotoxic activity against primary choroid plexus carcinoma

Histone deacetylase 6 (HDAC6) is an attractive target for cancer therapeutic intervention. Selective HDAC6 inhibitors is important to minimise the side effects of pan inhibition. Thus, new class of hydroxamic acid-based derivatives were designed on structural basis to perform preferential activity against HDAC6 targeting solid tumours. Interestingly, 1-benzylbenzimidazole-2-thio-N-hydroxybutanamide 10a showed impressive preference with submicromolar potency against HDAC6 (IC₅₀ = 510 nM). 10a showed cytotoxic activity with interesting profile against CCHE-45 at (IC₅₀ = 112.76 µM) when compared to standard inhibitor Tubacin (IC₅₀ = 20 µM). Western blot analysis of acetylated-α-tubulin verified the HDAC6 inhibiting activity of 10a. Moreover, the insignificant difference in acetylated-α-tubulin induced by 10a and Tubacin implied the on-target cytotoxic activity of 10a. Docking of 10a in the binding site of HDAC6 attributed the activity of 10a to π-π stacking with the amino acids of the hydrophobic channel of HDAC6 and capture of zinc metal in bidentate fashion. The therapeutic usefulness besides the on-target activity may define 10a as an interesting safe-lead inhibitor for future development.

Histone Deacetylase Inhibitors Sensitize TRAIL-Induced Apoptosis in Colon Cancer Cells

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is considered as a promising anti-cancer therapeutic. However, many cancers have been found to be or to become inherently resistant to TRAIL. A combination of epigenetic modifiers, such as histone deacetylase inhibitors (HDACi's), with TRAIL was effective to overcome TRAIL resistance in some cancers. Broad spectrum HDACi's, however, show considerable toxicity constraining clinical use. Since overexpression of class I histone deacetylase (HDAC) has been found in colon tumors relative to normal mucosa, we have focused on small spectrum HDACi's. We have now tested agonistic receptor-specific TRAIL variants rhTRAIL 4C7 and DHER in combination with several class I specific HDACi's on TRAIL-resistant colon cancer cells DLD-1 and WiDr. Our data show that TRAIL-mediated apoptosis is largely improved in WiDr cells by pre-incubation with Entinostat-a HDAC1, 2, and 3 inhibitor- and in DLD-1 cells by RGFP966-a HDAC3-specific inhibitor- or PCI34051-a HDAC8-specific inhibitor. We are the first to report that using RGFP966 or PCI34051 in combination with rhTRAIL 4C7 or DHER represents an effective cancer therapy. The intricate relation of HDACs and TRAIL-induced apoptosis was confirmed in cells by knockdown of HDAC1, 2, or 3 gene expression, which showed more early apoptotic cells upon adding rhTRAIL 4C7 or DHER. We observed that RGFP966 and PCI34051 increased DR4 expression after incubation on DLD-1 cells, while RGFP966 induced more DR5 expression on WiDr cells, indicating a different role for DR4 or DR5 in these combinations. At last, we show that combined treatment of RGFP966 with TRAIL variants (rhTRAIL 4C7/DHER) increases apoptosis on 3D tumor spheroid models.

The HDAC6-selective inhibitor is effective against non-Hodgkin lymphoma and synergizes with ibrutinib in follicular lymphoma

Follicular lymphoma (FL) is the most common indolent B-cell non-Hodgkin lymphoma (NHL) with genetic alterations of BCL-2, KMT2B, and KMT6. FL is refractory to conventional chemotherapy and is still incurable in most patients. Thus, new drugs and/or novel combination treatment strategies are needed to further improve FL patient outcome. We investigated the efficacy of the histone deacetylase 6 (HDAC6) inhibitor A452 combined with a Bruton's tyrosine kinase (BTK) inhibitor ibrutinib on NHL and the underlying mechanisms compared with the current clinically tested HDAC6 inhibitor ACY-1215. We first showed that FL is the most sensitive to HDAC6 inhibitor. We showed that combining A452 with ibrutinib led to the synergistic inhibition of cell growth and decreased viability of FL cells, as well as increased levels of apoptosis. Similar synergistic interactions occur in chronic lymphocytic leukemia (CLL) and germinal center diffuse large B-cell lymphoma cells (DLBCL). Enhanced cell death is associated with AKT and ERK1/2 inactivation and increased DNA damage (induction of γH2A.X and reduction of pChk1/2). In addition, A452 downregulates c-Myc, an effect significantly enhanced by ibruninib. Although ACY-1215 is less potent than A452, it displays synergism with ibrutinib. Overall, our results suggest that A452 is more effective as an anticancer agent than ACY-1215 in FL. These findings suggest that a combination of HDAC6-selective inhibitor and ibrutinib is a potent therapeutic strategy for NHL including FL.

[On the road to deciphering the tubulin code: focus on acetylation and detyrosination]

Microtubules are cytoskeletal fibers formed by the assembly of α- and β-tubulin heterodimers. They contribute to cell morphology, mobility and polarity, as well as to cellular transport processes and cell division. The microtubular network constantly adapts to cellular needs and may be composed of very dynamic or more stable microtubules. To regulate their diverse functions in a spatio-temporal manner, microtubules are subjected to numerous reversible post-translational modifications, which generate the "tubulin code". This review focuses on two modifications characteristic of stable microtubules - acetylation and detyrosination of α-tubulin - and their deregulation in certain pathologies.

FAM65B controls the proliferation of transformed and primary T cells

Cell quiescence is controlled by regulated genome-encoded programs that actively express genes which are often down-regulated or inactivated in transformed cells. Among them is FoxO1, a transcription factor that imposes quiescence in several cell types, including T lymphocytes. In these cells, the FAM65B encoding gene is a major target of FOXO1. Here, we show that forced expression of FAM65B in transformed cells blocks their mitosis because of a defect of the mitotic spindle, leading to G2 cell cycle arrest and apoptosis. Upon cell proliferation arrest, FAM65B is engaged in a complex containing two proteins well known to be involved in cell proliferation i.e. the HDAC6 deacetylase and the 14.3.3 scaffolding protein. In primary T cells, FAM65B is down-regulated upon T cell receptor engagement, and maintaining its expression blocks their proliferation, establishing that the decrease of FAM65B expression is required for proliferation. Conversely, inhibiting FAM65B expression in naive T lymphocytes decreases their activation threshold. These results identify FAM65B as a potential new target for controlling proliferation of both transformed and normal cells.

Anti-cancer effects of naturally derived compounds targeting histone deacetylase 6-related pathways

Alterations of the epigenetic machinery, affecting multiple biological functions, represent a major hallmark enabling the development of tumors. Among epigenetic regulatory proteins, histone deacetylase (HDAC)6 has emerged as an interesting potential therapeutic target towards a variety of diseases including cancer. Accordingly, this isoenzyme regulates many vital cellular regulatory processes and pathways essential to physiological homeostasis, as well as tumor multistep transformation involving initiation, promotion, progression and metastasis. In this review, we will consequently discuss the critical implications of HDAC6 in distinct mechanisms relevant to physiological and cancerous conditions, as well as the anticancer properties of synthetic, natural and natural-derived compounds through the modulation of HDAC6-related pathways.

HDACs and HDAC Inhibitors in Cancer Development and Therapy

Over the last several decades, it has become clear that epigenetic abnormalities may be one of the hallmarks of cancer. Posttranslational modifications of histones, for example, may play a crucial role in cancer development and progression by modulating gene transcription, chromatin remodeling, and nuclear architecture. Histone acetylation, a well-studied posttranslational histone modification, is controlled by the opposing activities of histone acetyltransferases (HATs) and histone deacetylases (HDACs). By removing acetyl groups, HDACs reverse chromatin acetylation and alter transcription of oncogenes and tumor suppressor genes. In addition, HDACs deacetylate numerous nonhistone cellular substrates that govern a wide array of biological processes including cancer initiation and progression. This review will discuss the role of HDACs in cancer and the therapeutic potential of HDAC inhibitors (HDACi) as emerging drugs in cancer treatment.

Epi-reevesioside F inhibits Na+/K+-ATPase, causing cytosolic acidification, Bak activation and apoptosis in glioblastoma

Epi-reevesioside F, a new cardiac glycoside isolated from the root of Reevesia formosana, displayed potent activity against glioblastoma cells. Epi-reevesioside F was more potent than ouabain with IC₅₀ values of 27.3±1.7 vs. 48.7±1.8 nM (P < 0.001) and 45.0±3.4 vs. 81.3±4.3 nM (P < 0.001) in glioblastoma T98 and U87 cells, respectively. However, both Epi-reevesioside F and ouabain were ineffective in A172 cells, a glioblastoma cell line with low Na⁺/K⁺-ATPase α3 subunit expression. Epi-reevesioside F induced cell cycle arrest at S and G2 phases and apoptosis. It also induced an increase of intracellular concentration of Na⁺ but not Ca²⁺, cleavage and exposure of N-terminus of Bak, loss of mitochondrial membrane potential, inhibition of Akt activity and induction of caspase cascades. Potassium supplements significantly inhibited Epi-reevesioside F-induced effects. Notably, Epi-reevesioside F caused cytosolic acidification that was highly correlated with the anti-proliferative activity. In summary, the data suggest that Epi-reevesioside F inhibits Na⁺/K⁺-ATPase, leading to overload of intracellular Na⁺ and cytosolic acidification, Bak activation and loss of mitochondrial membrane potential. The PI3-kinase/Akt pathway is inhibited and caspase-dependent apoptosis is ultimately triggered in Epi-reevesioside F-treated glioblastoma cells.

HDAC6 deficiency or inhibition blocks FGFR3 accumulation and improves bone growth in a model of achondroplasia

Mutations that cause increased and/or inappropriate activation of FGFR3 are responsible for a collection of short-limbed chondrodysplasias. These mutations can alter receptor trafficking and enhance receptor stability, leading to increased receptor accumulation and activity. Here, we show that wildtype and mutant activated forms of FGFR3 increase expression of the cytoplasmic deacetylase HDAC6 (Histone Deacetylase 6) and that FGFR3 accumulation is compromised in cells lacking HDAC6 or following treatment of fibroblasts or chondrocytes with small molecule inhibitors of HDAC6. The reduced accumulation of FGFR3 was linked to increased FGFR3 degradation that occurred through a lysosome-dependent mechanism. Using a mouse model of Thanatophoric Dysplasia Type II (TDII) we show that both HDAC6 deletion and treatment with the small molecule HDAC6 inhibitor tubacin reduced FGFR3 accumulation in the growth plate and improved endochondral bone growth. Defective endochondral growth in TDII is associated with reduced proliferation and poor hypertrophic differentiation and the improved bone growth was associated with increased chondrocyte proliferation and expansion of the differentiation compartment within the growth plate. These findings further define the mechanisms that control FGFR3 accumulation and contribute to skeletal pathology caused by mutations in FGFR3.

An immediate transcriptional signature associated with response to the histone deacetylase inhibitor Givinostat in T acute lymphoblastic leukemia xenografts

Despite some success with certain hematological malignancies and in contrast with the strong pro-apoptotic effects measured in vitro, the overall response rate of acute lymphoblastic leukemia (ALL) to histone deacetylase inhibitors (HDACis) is low. With the aim to improve the understanding of how HDACis work in vivo, we investigated the therapeutic efficacy of the clinically approved HDACi Givinostat in a collection of nine pediatric human T-ALL engrafted systemically in NOD/SCID mice. We observed highly heterogeneous antileukemia responses to Givinostat, associated with reduction of the percentage of infiltrating blasts in target organs, induction of apoptosis and differentiation. These effects were not associated with the T-ALL cytogenetic subgroup. Transcriptome analysis disclosed an immediate transcriptional signature enriched in genes involved in cell-cycle regulation and DNA repair, which was validated by quantitative RT-PCR and was associated with in vivo response to this HDACi. Increased phospho-H2AX levels, a marker of DNA damage, were measured in T-ALL cells from Givinostat responders. These results indicate that the induction of the DNA damage response could be an early biomarker of the therapeutic effects of Givinostat in T-ALL models. This information should be considered in the design of future clinical trials with HDACis in acute leukemia.

HDAC6 activity is not required for basal autophagic flux in metastatic prostate cancer cells

Histone deacetylase 6 is a multifunctional lysine deacetylase that is recently emerging as a central facilitator of response to stress and may play an important role in cancer cell proliferation. The histone deacetylase 6-inhibitor tubacin has been shown to slow the growth of metastatic prostate cancer cells and sensitize cancer cells to chemotherapeutic agents. However, the proteins histone deacetylase 6 interacts with, and thus its role in cancer cells, remains poorly characterized. Histone deacetylase 6 deacetylase activity has recently been shown to be required for efficient basal autophagic flux. Autophagy is often dysregulated in cancer cells and may confer stress resistance and allow for cell maintenance and a high proliferation rate. Tubacin may therefore slow cancer cell proliferation by decreasing autophagic flux. We characterized the histone deacetylase 6-interacting proteins in LNCaP metastatic prostate cancer cells and found that histone deacetylase 6 interacts with proteins involved in several cellular processes, including autophagy. Based on our interaction screen, we assessed the impact of the histone deacetylase 6-inhibitor tubacin on autophagic flux in two metastatic prostate cancer cell lines and found that tubacin does not influence autophagic flux. Histone deacetylase 6 therefore influences cell proliferation through an autophagy-independent mechanism.

Histone acetyltransferases and histone deacetylases in B- and T-cell development, physiology and malignancy

The development of B and T cells from hematopoietic precursors and the regulation of the functions of these immune cells are complex processes that involve highly regulated signaling pathways and transcriptional control. The signaling pathways and gene expression patterns that give rise to these developmental processes are coordinated, in part, by two opposing classes of broad-based enzymatic regulators: histone acetyltransferases (HATs) and histone deacetylases (HDACs). HATs and HDACs can modulate gene transcription by altering histone acetylation to modify chromatin structure, and by regulating the activity of non-histone substrates, including an array of immune-cell transcription factors. In addition to their role in normal B and T cells, dysregulation of HAT and HDAC activity is associated with a variety of B- and T-cell malignancies. In this review, we describe the roles of HATs and HDACs in normal B- and T-cell physiology, describe mutations and dysregulation of HATs and HDACs that are implicated lymphoma and leukemia, and discuss HAT and HDAC inhibitors that have been explored as treatment options for leukemias and lymphomas.

Cancer stem cells from epithelial ovarian cancer patients privilege oxidative phosphorylation, and resist glucose deprivation

We investigated the metabolic profile of cancer stem cells (CSC) isolated from patients with epithelial ovarian cancer. CSC overexpressed genes associated with glucose uptake, oxidative phosphorylation (OXPHOS), and fatty acid β-oxidation, indicating higher ability to direct pyruvate towards the Krebs cycle. Consistent with a metabolic profile dominated by OXPHOS, the CSC showed higher mitochondrial reactive oxygen species (ROS) production and elevated membrane potential, and underwent apoptosis upon inhibition of the mitochondrial respiratory chain. The CSC also had a high rate of pentose phosphate pathway (PPP) activity, which is not typical of cells privileging OXPHOS over glycolysis, and may rather reflect the PPP role in recharging scavenging enzymes. Furthermore, CSC resisted in vitro and in vivo glucose deprivation, while maintaining their CSC phenotype and OXPHOS profile. These observations may explain the CSC resistance to anti-angiogenic therapies, and indicate this peculiar metabolic profile as a possible target of novel treatment strategies.

Histone deacetylase 6 represents a novel drug target in the oncogenic Hedgehog signaling pathway

Uncontrolled Hedgehog (Hh) signaling is the cause of several malignancies, including the pediatric cancer medulloblastoma, a neuroectodermal tumor affecting the cerebellum. Despite the development of potent Hh pathway antagonists, medulloblastoma drug resistance is still an unresolved issue that requires the identification of novel drug targets. Following up on our observation that histone deacetylase 6 (HDAC6) expression was increased in Hh-driven medulloblastoma, we found that this enzyme is essential for full Hh pathway activation. Intriguingly, these stimulatory effects of HDAC6 are partly integrated downstream of primary cilia, a known HDAC6-regulated structure. In addition, HDAC6 is also required for the complete repression of basal Hh target gene expression. These contrasting effects are mediated by HDAC6's impact on Gli2 mRNA and GLI3 protein expression. As a result of this complex interaction with Hh signaling, global transcriptome analysis revealed that HDAC6 regulates only a subset of Smoothened- and Gli-driven genes, including all well-established Hh targets such as Ptch1 or Gli1. Importantly, medulloblastoma cell survival was severely compromised by HDAC6 inhibition in vitro and pharmacologic HDAC6 blockade strongly reduced tumor growth in an in vivo allograft model. In summary, our data describe an important role for HDAC6 in regulating the mammalian Hh pathway and encourage further studies focusing on HDAC6 as a novel drug target in medulloblastoma.

Misfolded proteins: from little villains to little helpers in the fight against cancer

The application of cytostatic drugs targeting the high proliferation rates of cancer cells is currently the most commonly used treatment option in cancer chemotherapy. However, severe side effects and resistance mechanisms may occur as a result of such treatment, possibly limiting the therapeutic efficacy of these agents. In recent years, several therapeutic strategies have been developed that aim at targeting not the genomic integrity and replication machinery of cancer cells but instead their protein homeostasis. During malignant transformation, the cancer cell proteome develops vast aberrations in the expression of mutated proteins, oncoproteins, drug- and apoptosis-resistance proteins, etc. A complex network of protein quality-control mechanisms, including chaperoning by heat shock proteins (HSPs), not only is essential for maintaining the extravagant proteomic lifestyle of cancer cells but also represents an ideal cancer-specific target to be tackled. Furthermore, the high rate of protein synthesis and turnover in certain types of cancer cells can be specifically directed by interfering with the proteasomal and autophagosomal protein recycling and degradation machinery, as evidenced by the clinical application of proteasome inhibitors. Since proteins with loss of their native conformation are prone to unspecific aggregations and have proved to be detrimental to normal cellular function, specific induction of misfolded proteins by HSP inhibitors, proteasome inhibitors, hyperthermia, or inducers of endoplasmic reticulum stress represents a new method of cancer cell killing exploitable for therapeutic purposes. This review describes drugs - approved, repurposed, or under investigation - that can be used to accumulate misfolded proteins in cancer cells, and particularly focuses on the molecular aspects that lead to the cytotoxicity of misfolded proteins in cancer cells.

Toward isozyme-selective inhibitors of histone deacetylase as therapeutic agents for the treatment of cancer

Since post-translational modifications of proteins are key mechanisms for controlling cellular function, targeting the machinery involved in these modifications offers new opportunities for the development of therapeutic agents.The histone deacetylases (HDACs) represent an important family of enzymes that are involved in controlling the acetylation state of key lysine residues in histones and other proteins. The development of HDAC inhibitors for the treatment of several diseases, most notably cancer, has proceeded rapidly. Recent attention has turned towards the development of isozyme-specific inhibitors that will provide selective targeting. It is believed that the ability to target-specific HDACs rather than all family members will lead to superior therapeutics with better efficacy and lower toxicity. A review of recent patents shows that researchers are targeting a wide range of isozymes and that key advances in the structural biology of HDACs are providing important design information.

Reevesioside A, a cardenolide glycoside, induces anticancer activity against human hormone-refractory prostate cancers through suppression of c-myc expression and induction of G1 arrest of the cell cycle

In the past decade, there has been a profound increase in the number of studies revealing that cardenolide glycosides display inhibitory activity on the growth of human cancer cells. The use of potential cardenolide glycosides may be a worthwhile approach in anticancer research. Reevesioside A, a cardenolide glycoside isolated from the root of Reevesia formosana, displayed potent anti-proliferative activity against human hormone-refractory prostate cancers. A good correlation (r² = 0.98) between the expression of Na⁺/K⁺-ATPase α₃ subunit and anti-proliferative activity suggested the critical role of the α₃ subunit. Reevesioside A induced G1 arrest of the cell cycle and subsequent apoptosis in a thymidine block-mediated synchronization model. The data were supported by the down-regulation of several related cell cycle regulators, including cyclin D1, cyclin E and CDC25A. Reevesioside A also caused a profound decrease of RB phosphorylation, leading to an increased association between RB and E2F1 and the subsequent suppression of E2F1 activity. The protein and mRNA levels of c-myc, which can activate expression of many downstream cell cycle regulators, were dramatically inhibited by reevesioside A. Transient transfection of c-myc inhibited the down-regulation of both cyclin D1 and cyclin E protein expression to reevesioside A action, suggesting that c-myc functioned as an upstream regulator. Flow cytometric analysis of JC-1 staining demonstrated that reevesioside A also induced the significant loss of mitochondrial membrane potential. In summary, the data suggest that reevesioside A inhibits c-myc expression and down-regulates the expression of CDC25A, cyclin D1 and cyclin E, leading to a profound decrease of RB phosphorylation. G1 arrest is, therefore, induced through E2F1 suppression. Consequently, reevesioside A causes mitochondrial damage and an ultimate apoptosis in human hormone-refractory prostate cancer cells.

Proteasome inhibitors exert cytotoxicity and increase chemosensitivity via transcriptional repression of Notch1 in T-cell acute lymphoblastic leukemia

The Notch signaling pathway has been recognized as a key factor for the pathogenesis of T-cell acute lymphoblastic leukemia (T-ALL), because of the high incidence of activating mutations of Notch1. Notch inhibition could serve as a new treatment strategy for T-ALL; however, the attempts to perturb Notch signaling pathways have been unsuccessful so far. In this study, we found that proteasome inhibitors exert cytotoxic effects on T-ALL cells with constitutive activation of Notch1 to a similar extent as myeloma cells. The proteasome inhibitor bortezomib repressed the transcription of Notch1 and downstream effectors including Hes1, GATA3, RUNX3 and nuclear factor-κB (NF-κB) (p65 and p50), coincided with downregulation of the major transactivator Sp1 and its dissociation from Notch1 promoter. Overexpression of the Notch1 intracellular domain (NICD) significantly ameliorated bortezomib-induced cytotoxicity against T-ALL cells. Drug combination studies revealed that bortezomib showed synergistic or additive effects with key drugs for the treatment of T-ALL such as dexamethasone (DEX), doxorubicin and cyclophosphamide, which were readily abolished by NICD overexpression. The synergy of bortezomib and DEX was confirmed in vivo using a murine xenograft model. Our findings provide a molecular basis and rationale for the inclusion of proteasome inhibitors in treatment strategies for T-ALL.

Combined treatment with SAHA, bortezomib, and clarithromycin for concomitant targeting of aggresome formation and intracellular proteolytic pathways enhances ER stress-mediated cell death in breast cancer cells

The ubiquitin-proteasome pathway and the autophagy-lysosome pathway are two major intracellular protein degradation systems. We previously reported that clarithromycin (CAM) blocks autophagy flux, and that combined treatment with CAM and proteasome inhibitor bortezomib (BZ) enhances ER-stress-mediated apoptosis in breast cancer cells, whereas treatment with CAM alone results in almost no cytotoxicity. Since HDAC6 is involved in aggresome formation, which is recognized as a cytoprotective response serving to sequester misfolded proteins and facilitate their clearance by autophagy, we further investigated the combined effect of vorinostat (suberoylanilide hydroxamic acid (SAHA)), which has a potent inhibitory effect for HDAC6, with CAM and BZ in breast cancer cell lines. SAHA exhibited some cytotoxicity along with an increased acetylation level of α-tubulin, a substrate of HDAC6. Combined treatment of SAHA, CAM, and BZ potently enhanced the apoptosis-inducing effect compared with treatment using each reagent alone or a combination of two of the three. Expression levels of ER-stress-related genes, including the pro-apoptotic transcription factor CHOP (GADD153), were maximally induced by the simultaneous combination of three reagents. Like breast cancer cell lines, a wild-type murine embryonic fibroblast (MEF) cell line exhibited enhanced cytotoxicity and maximally up-regulated Chop after combined treatment with SAHA, CAM, and BZ; however, a Chop knockout MEF cell line almost completely canceled this enhanced effect. The specific HDAC6 inhibitor tubacin also exhibited a pronounced cytocidal effect with a combination of CAM plus BZ. These data suggest that simultaneous targeting of intracellular proteolytic pathways and HDAC6 enhances ER-stress-mediated apoptosis in breast cancer cells.

The effects of a histone deacetylase inhibitor on biological behavior of diffuse large B-cell lymphoma cell lines and insights into the underlying mechanisms

Background

Epigenetic control using histone deacetylase (HDAC) inhibitors is a promising therapy for lymphomas. Insights into the anti-proliferative effects of HDAC inhibitors on diffuse large B-cell lymphoma (DLBCL) and further understanding of the underlying mechanisms, which remain unclear to date, are of great importance.

Methods

Three DLBCL cell lines (DoHH2, LY1 and LY8) were used to define the potential epigenetic targets for Trichostatin A (TSA)-mediated anti-proliferative effects via CCK-8 assay. Cell cycle distribution and apoptosis were detected by flow cytometry. We further investigated the underlying molecular mechanisms by examining expression levels of relevant proteins using western blot analysis.

Results

TSA treatment inhibited the growth of all three DLBCL cell lines and enhanced cell cycle arrest and apoptosis. Molecular analysis revealed upregulated acetylation of histone H3, α-tubulin and p53, and dephosphorylation of pAkt with altered expression of its main downstream effectors (p21, p27, cyclin D1 and Bcl-2). HDAC profiling revealed that all three cell lines had varying HDAC1–6 expression levels, with the highest expression of all six isoforms, in DoHH2 cells, which displayed the highest sensitivity to TSA.

Conclusion

Our results demonstrated that the HDAC inhibitor TSA inhibited DLBCL cell growth, and that cell lines with higher expression of HDACs tended to be more sensitive to TSA. Our data also suggested that inhibition of pAkt and activation of p53 pathway are the main molecular events involved in inhibitory effects of TSA.

Development and therapeutic implications of selective histone deacetylase 6 inhibitors

This Perspective provides an in depth look at the numerous disease states in which histone deacetylase 6 (HDAC6) has been implicated. The physiological pathways, protein-protein interactions, and non-histone substrates relating to different pathological conditions are discussed with regard to HDAC6. Furthermore, the compounds and methods used to modulate HDAC6 activity are profiled. The latter half of this Perspective analyzes reported HDAC6 selective inhibitors in terms of structure, potency, and selectivity over the other HDAC isoforms with the intent of providing a comprehensive overview of the molecular tools available. Potential obstacles and future directions of HDAC6 research are also presented.

Could interleukin-15 potentiate histone deacetylase inhibitor effects in haematological malignancy?

Despite significant progress in cancer therapy, prognosis in acute leukaemia remains dismal, and the development of new therapies is urgently warranted: in acute myeloid leukaemia, the current cure rate is of 30-40% in younger and much less in older patients. Chromatin remodeling through histone acetylation is one of the major mechanisms of transcriptional control of genes, and is involved in 'gene silencing' of antioncogenes in various tumour cells. Chromatin remodeling is also involved in transcriptional control of other genes, such as NKG2D ligand genes. Histone deacetylases and acetyltransferases are involved in the epigenetic regulation of gene expression, and increased/decreased activity of histone deacetylases has been reported in several cancer types. Histone deacetylase inhibitors were reportedly active in many cancers including hematological malignancies, and have been shown in numerous experiments to reduce cancer cell growth and enhance cell differentiation, growth arrest and apoptosis. In acute myeloid leukaemia, histone deacetylase inhibitors alone had limited efficacy, but their combination with other anticancer agents yielded promising results. Interleukin (IL)-15 is regarded with great hope in the immunotherapy of cancer, and IL-15-activated cytokine-induced killer cells showed potent antileukemic activity both in vitro and in vivo. IL-15 increases expression of NKG2D and its ligands and can increase natural killer cell mediated cytotoxicity against tumour cells. The administration of IL-15 was recently shown to be safe in preclinical models, and there are ongoing clinical trials of IL-15 in patients with cancer and HIV infection. We hypothesise that IL-15 will synergise with histone deacetylase inhibitors in increasing the levels of activatory NKG2D receptors on natural killer and CD8(+) T cells and of their ligands, the MHC class I related molecule A and B, on tumor cells, and will enhance innate immune antitumour responses in acute myeloid leukaemia and other haematological malignancies. Up-regulation of NKG2D-NKG2D-ligand antitumour immune response by combining histone deacetylase inhibitors with IL-15 has the potential to improve the efficacy of acute myeloid leukaemia treatment.

Histone deacetylases as targets for treatment of multiple diseases

HDACs (histone deacetylases) are a group of enzymes that deacetylate histones as well as non-histone proteins. They are known as modulators of gene transcription and are associated with proliferation and differentiation of a variety of cell types and the pathogenesis of some diseases. Recently, HDACs have come to be considered crucial targets in various diseases, including cancer, interstitial fibrosis, autoimmune and inflammatory diseases, and metabolic disorders. Pharmacological inhibitors of HDACs have been used or tested to treat those diseases. In the present review, we will examine the application of HDAC inhibitors in a variety of diseases with the focus on their effects of anti-cancer, fibrosis, anti-inflammatory, immunomodulatory activity and regulating metabolic disorders.

Histone deacetylases and cancer

Reversible acetylation of histone and non-histone proteins is one of the most abundant post-translational modifications in eukaryotic cells. Protein acetylation and deacetylation are achieved by the antagonistic actions of two families of enzymes, histone acetyltransferases (HATs) and histone deacetylases (HDACs). Aberrant protein acetylation, particularly on histones, has been related to cancer while abnormal expression of HDACs has been found in a broad range of cancer types. Therefore, HDACs have emerged as promising targets in cancer therapeutics, and the development of HDAC inhibitors (HDIs), a rapidly evolving area of clinical research. However, the contributions of specific HDACs to a given cancer type remain incompletely understood. The aim of this review is to summarize the current knowledge concerning the role of HDACs in cancer with special emphasis on what we have learned from the analysis of patient samples.

A novel class of small molecule inhibitors of HDAC6

Histone deacetylases (HDACs) are a family of enzymes that play significant roles in numerous biological processes and diseases. HDACs are best known for their repressive influence on gene transcription through histone deacetylation. Mapping of nonhistone acetylated proteins and acetylation-modifying enzymes involved in various cellular pathways has shown protein acetylation/deacetylation also plays key roles in a variety of cellular processes including RNA splicing, nuclear transport, and cytoskeletal remodeling. Studies of HDACs have accelerated due to the availability of small molecule HDAC inhibitors, most of which contain a canonical hydroxamic acid or benzamide that chelates the metal catalytic site. To increase the pool of unique and novel HDAC inhibitor pharmacophores, a pharmacological active compound screen was performed. Several unique HDAC inhibitor pharmacophores were identified in vitro. One class of novel HDAC inhibitors, with a central naphthoquinone structure, displayed a selective inhibition profile against HDAC6. Here we present the results of a unique class of HDAC6 inhibitors identified using this compound library screen. In addition, we demonstrated that treatment of human acute myeloid leukemia cell line MV4-11 with the selective HDAC6 inhibitors decreases levels of mutant FLT-3 and constitutively active STAT5 and attenuates Erk phosphorylation, all of which are associated with the inhibitor's selective toxicity against leukemia.