The histone deacetylase inhibitor MS-275 interacts synergistically with fludarabine to induce apoptosis in human leukemia cells

Nanocarrier mediated entinostat and oxaliplatin combination therapy displayed enhanced efficacy against pancreatic cancer

Pancreatic cancer is the third leading cause of cancer-related death in the United States, with a 5-year survival rate of only 12%. The poor prognosis of pancreatic cancer is primarily attributed to the lack of early detection, the aggressiveness of the disease, and its resistance to conventional chemotherapeutics. The use of combination chemotherapy targeting different key pathways has emerged as a potential strategy to minimize drug resistance while improving therapeutic outcomes. Here, we evaluated a novel approach to treating pancreatic cancer using entinostat (ENT), a selective class I and IV HDAC inhibitor, and oxaliplatin (OXP) administered at considerably lower dosages. Combination therapy exhibited strong synergistic interaction against human (PANC-1) and murine (KPC) pancreatic cancer cells. As expected, ENT treatment enhanced acetylated histone H3 and H4 expression in treated cells, which was even augmented in the presence of OXP. Similarly, cells treated with a combination therapy showed higher expression of cleaved caspase 3 and increased apoptosis compared to monotherapy. To further improve the efficacy of the combination treatment, we encapsulated OXP and ENT into bovine serum albumin and poly(lactic-co-glycolic) acid nanoparticles. Both nanocarriers showed suitable physicochemical properties with respect to size, charge, polydispersity index, and loading. Besides, the combination of OXP and ENT nanoparticles showed similar or even better synergistic effects compared to free drugs during in vitro cytotoxicity and colony formation assays towards pancreatic cancer cells.

Discovery of novel benzohydroxamate-based histone deacetylase 6 (HDAC6) inhibitors with the ability to potentiate anti-PD-L1 immunotherapy in melanoma

In this study, a novel series of histone deacetylases 6 (HDAC6) inhibitors containing polycyclic aromatic rings were discovered and evaluated for their pharmacological activities. The most potent compound 10c exhibited high HDAC6 inhibitory activity (IC₅₀ = 261 nM) and excellent HDAC6 selectivity (SI = 109 for HDAC6 over HDAC3). 10c also showed decent antiproliferative activity in vitro with IC₅₀ of 7.37-21.84 μM against four cancer cell lines, comparable to that of tubastatin A (average IC₅₀ = 6.10 μM). Further mechanism studies revealed that 10c efficiently induced apoptosis and S-phase arrest in B16-F10 cells. In addition, 10c markedly increased the expression of acetylated-α-tubulin both in vitro and in vivo, without affecting the levels of acetylated-H3 (marker of HDAC1 inhibition). Furthermore, 10c (80 mg/kg) exhibited moderate antitumor efficacy in a melanoma tumour model with a tumour growth inhibition (TGI) of 32.9%, comparable to that (TGI = 31.3%) of tubastatin A. Importantly, the combination of 10c with NP19 (a small molecule PD-L1 inhibitor discovered by us before) decreased tumour burden substantially (TGI% = 60.1%) as compared to monotherapy groups. Moreover, the combination of 10c with NP19 enhanced the anti-tumour immune response, mediated by a decrease of PD-L1 expression levels and increased infiltration of anti-tumour CD8⁺ T cells in tumour tissues. Collectively, 10c represents a novel HDAC6 inhibitor deserving further investigation as a potential anti-cancer agent.

The Class IIA Histone Deacetylase (HDAC) Inhibitor TMP269 Downregulates Ribosomal Proteins and Has Anti-Proliferative and Pro-Apoptotic Effects on AML Cells

Acute myeloid leukemia (AML) is a hematopoietic malignancy characterized by altered myeloid progenitor cell proliferation and differentiation. As in many other cancers, epigenetic transcriptional repressors such as histone deacetylases (HDACs) are dysregulated in AML. Here, we investigated (1) HDAC gene expression in AML patients and in different AML cell lines and (2) the effect of treating AML cells with the specific class IIA HDAC inhibitor TMP269, by applying proteomic and comparative bioinformatic analyses. We also analyzed cell proliferation, apoptosis, and the cell-killing capacities of TMP269 in combination with venetoclax compared to azacitidine plus venetoclax, by flow cytometry. Our results demonstrate significantly overexpressed class I and class II HDAC genes in AML patients, a phenotype which is conserved in AML cell lines. In AML MOLM-13 cells, TMP269 treatment downregulated a set of ribosomal proteins which are overexpressed in AML patients at the transcriptional level. TMP269 showed anti-proliferative effects and induced additive apoptotic effects in combination with venetoclax. We conclude that TMP269 exerts anti-leukemic activity when combined with venetoclax and has potential as a therapeutic drug in AML.

What we have learnt from Drosophila model organism: the coordination between insulin signaling pathway and tumor cells

Cancer development is related to a variety of signaling pathways which mediate various cellular processes including growth, survival, division and competition of cells, as well as cell-cell interaction. The insulin signaling pathway interacts with different pathways and plays a core role in the regulations of all these processes. In this study, we reviewed recent studies on the relationship between the insulin signaling pathway and tumors using the Drosophila melanogaster model. We found that on one hand, the insulin pathway is normally hyperactive in tumor cells, which promotes tumor growth, and on the other hand, tumor cells can suppress the growth of healthy tissues via inhibition of their insulin pathway. Moreover, systematic disruption in glucose homeostasis also facilitates cancer development by different mechanisms. The studies on how the insulin network regulates the behaviors of cancer cells may help to discover new therapeutic treatments for cancer.

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

PURPOSE

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

EXPERIMENTAL DESIGN

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

RESULTS

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

CONCLUSION

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

Fludarabine modulates expression of type VII collagen during haematopoietic stem cell transplantation for recessive dystrophic epidermolysis bullosa

BACKGROUND

Recessive dystrophic epidermolysis bullosa (RDEB) is a severe, complicated inherited blistering skin disease with few treatment options currently available. Recently, haematopoietic stem cell transplantation (HCT) has been used as an alternative therapy that can improve skin integrity, but it is not known if the preparative HCT regimen also contributes to the therapeutic response.

OBJECTIVES

To determine whether chemotherapy drugs used in the HCT preparative regimen influence type VII collagen (C7) expression, which is inherently reduced or absent in RDEB skin, and to explore the pathomechanisms of such responses, if present.

METHODS

Drugs from the HCT preparative regimen (busulfan, cyclophosphamide, ciclosporin A, fludarabine and mycophenolate) with inhibitors (PD98059, U0126, LY294002, SR11302, SIS3 and N-acetyl-l-cysteine) were added to normal human dermal and human RDEB fibroblasts. C7 expression was measured using reversetranscription polymerase chain reaction and immunoblotting.

RESULTS

We uncovered a previously unknown consequence of fludarabine whereby dermal fibroblasts exposed to fludarabine upregulate C7. This effect is mediated, in part, through activation of the mitogen-activated protein kinase/extracellular signal-regulated kinase, phosphoinositide 3-kinase/protein kinase B and transforming growth factor-β pathways. Activation of these pathways leads to activation of downstream transcription factors, including activator protein 1 (AP-1) and SMAD. Subsequently, both AP-1 and SMAD bind the COL7A1 promoter and increase COL7A1 expression.

CONCLUSIONS

Fludarabine influences the production of type VII collagen in RDEB fibroblasts.

In situ exploring Chidamide, a histone deacetylase inhibitor, induces molecular changes of leukemic T-lymphocyte apoptosis using Raman spectroscopy

Though it has been demonstrated that Chidamide (CS055/HBI-8000), a novel benzamide class of histone deacetylase (HDAC) subtype-selectively inhibitor, reveals better anticancer effect in acute leukemia, but it remains unknown about the precise mechanism of Chidamide-induced acute leukemia cell apoptosis due to the lack of in situ molecular changes information. Based on Raman spectral analysis, we find that the action of Chidamide on Jurkat cell will lead to an addition of an acetyl group to a specific lysine residue at the end of histone amino acid, and greatly enhance the acetylation of histones H1, H2A, H2B, H3, and H4, and then destroy the electrostatic force between the alkaline terminal of the positive charged arginine side chain and the negative charged DNA of phosphate group, finally cause the depolymerization of DNA and histone octamer in chromatin nucleosome depolymerization and the relaxation of chromatin. Accordingly, the accumulation of reactive oxygen species (ROS) and the decreasing of mitochondrial membrane potential (MMP) are observed. For comparison, we also present the corresponding results of suberoylanilide hydroxamic acid (SAHA) and MS-275 inhibitors. The achieved results show that proliferation of Chidamide-treated Jurkat cells is low relative to MS-275 or SAHA, and the action of Chidamide or MS-275 on Jurkat cells lead to obvious increasing in histones H1, H2A, H2B, H3, and H4, whereas the action effect of SAHA is mainly observed in histones H1, H2A, H2B, H3 but weak in histone H4. Moreover, it is found that Chidamide-induced histone H3 acetylation in Jurkat cells is stronger than MS-275 and SAHA. Collectively, by Raman spectral analysis, we achieve the dynamic behavior of biochemical components, molecular conformation and morphological changes of HDAC inhibitors-treated Jurkat cells. Importantly, our research is the first to demonstrate that the action site of HDAC inhibitors on Jurkat cell is located in the DNA minor groove. Most importantly, the application of Raman spectrum in exploring in-situ molecular changes information, histone acetylation modification in epigenetics, drug action sites and cell cycle affected by HDAC inhibitors will supply new idea and reference for the design and modification of HDAC inhibitors.

Dual-Target Inhibitors Based on HDACs: Novel Antitumor Agents for Cancer Therapy

Histone deacetylases (HDACs) play an important role in regulating target gene expression. They have been highlighted as a novel category of anticancer targets, and their inhibition can induce apoptosis, differentiation, and growth arrest in cancer cells. In view of the fact that HDAC inhibitors and other antitumor agents, such as BET inhibitors, topoisomerase inhibitors, and RTK pathway inhibitors, exert a synergistic effect on cellular processes in cancer cells, the combined inhibition of two targets is regarded as a rational strategy to improve the effectiveness of these single-target drugs for cancer treatment. In this review, we discuss the theoretical basis for designing HDAC-involved dual-target drugs and provide insight into the structure-activity relationships of these dual-target agents.

Research Advances in the Use of Histone Deacetylase Inhibitors for Epigenetic Targeting of Cancer

The causes and progression of cancer are controlled by epigenetic processes. The mechanisms involved in epigenetic regulation of cancer development, gene expression, and signaling pathways have been studied. Histone deacetylases (HDACs) have a major impact on chromatin remodeling and epigenetics, making their inhibitors a very interesting area of cancer research. This review comprehensively summarizes the literature regarding HDAC inhibitors (HDACis) as an anticancer treatment published in the past few years. In addition, we explain the mechanisms of their therapeutic effects on cancer. An analysis of the beneficial characteristics and drawbacks of HDACis also is presented, which will assist preclinical and clinical researchers in the design of future experiments to improve the therapeutic efficacy of these drugs and circumvent the challenges in the path of successful epigenetic therapy. Future therapeutic strategies may include a combination of HDACis and chemotherapy or other inhibitors to target multiple oncogenic signaling pathways.

p53 at the Crossroads between Different Types of HDAC Inhibitor-Mediated Cancer Cell Death

Cancer is a complex genetic and epigenetic-based disease that has developed an armada of mechanisms to escape cell death. The deregulation of apoptosis and autophagy, which are basic processes essential for normal cellular activity, are commonly encountered during the development of human tumors. In order to assist the cancer cell in defeating the imbalance between cell growth and cell death, histone deacetylase inhibitors (HDACi) have been employed to reverse epigenetically deregulated gene expression caused by aberrant post-translational protein modifications. These interfere with histone acetyltransferase- and deacetylase-mediated acetylation of both histone and non-histone proteins, and thereby exert a wide array of HDACi-stimulated cytotoxic effects. Key determinants of HDACi lethality that interfere with cellular growth in a multitude of tumor cells are apoptosis and autophagy, which are either mutually exclusive or activated in combination. Here, we compile known molecular signals and pathways involved in the HDACi-triggered induction of apoptosis and autophagy. Currently, the factors that determine the mode of HDACi-elicited cell death are mostly unclear. Correspondingly, we also summarized as yet established intertwined mechanisms, in particular with respect to the oncogenic tumor suppressor protein p53, that drive the interplay between apoptosis and autophagy in response to HDACi. In this context, we also note the significance to determine the presence of functional p53 protein levels in the cancer cell. The confirmation of the context-dependent function of autophagy will pave the way to improve the benefit from HDACi-mediated cancer treatment.

Inhibition of BET Proteins and Histone Deacetylase (HDACs): Crossing Roads in Cancer Therapy

Histone DeACetylases (HDACs) are enzymes that remove acetyl groups from histones and other proteins, regulating the expression of target genes. Pharmacological inhibition of these enzymes re-shapes chromatin acetylation status, confusing boundaries between transcriptionally active and quiescent chromatin. This results in reinducing expression of silent genes while repressing highly transcribed genes. Bromodomain and Extraterminal domain (BET) proteins are readers of acetylated chromatin status and accumulate on transcriptionally active regulatory elements where they serve as scaffold for the building of transcription-promoting complexes. The expression of many well-known oncogenes relies on BET proteins function, indicating BET inhibition as a strategy to counteract their activity. BETi and HDACi share many common targets and affect similar cellular processes to the point that combined inhibition of both these classes of proteins is regarded as a strategy to improve the effectiveness of these drugs in cancer. In this work, we aim to discuss the molecular basis of the interplay between HDAC and BET proteins, pointing at chromatin acetylation as a crucial node of their functional interaction. We will also describe the state of the art of their dual inhibition in cancer therapy. Finally, starting from their mechanism of action we will provide a speculative perspective on how these drugs may be employed in combination with standard therapies to improve effectiveness and/or overcome resistance.

Epigenetic Targeting of Autophagy via HDAC Inhibition in Tumor Cells: Role of p53

Tumor development and progression is the consequence of genetic as well as epigenetic alterations of the cell. As part of the epigenetic regulatory system, histone acetyltransferases (HATs) and deacetylases (HDACs) drive the modification of histone as well as non-histone proteins. Derailed acetylation-mediated gene expression in cancer due to a delicate imbalance in HDAC expression can be reversed by histone deacetylase inhibitors (HDACi). Histone deacetylase inhibitors have far-reaching anticancer activities that include the induction of cell cycle arrest, the inhibition of angiogenesis, immunomodulatory responses, the inhibition of stress responses, increased generation of oxidative stress, activation of apoptosis, autophagy eliciting cell death, and even the regulation of non-coding RNA expression in malignant tumor cells. However, it remains an ongoing issue how tumor cells determine to respond to HDACi treatment by preferentially undergoing apoptosis or autophagy. In this review, we summarize HDACi-mediated mechanisms of action, particularly with respect to the induction of cell death. There is a keen interest in assessing suitable molecular factors allowing a prognosis of HDACi-mediated treatment. Addressing the results of our recent study, we highlight the role of p53 as a molecular switch driving HDACi-mediated cellular responses towards one of both types of cell death. These findings underline the importance to determine the mutational status of p53 for an effective outcome in HDACi-mediated tumor therapy.

Use of a genome-wide haploid genetic screen to identify treatment predicting factors: a proof-of-principle study in pancreatic cancer

The ability to develop a comprehensive panel of treatment predicting factors would significantly improve our ability to stratify patients for cytotoxic or targeted therapies, and prevent patients receiving ineffective treatments. We have investigated if a recently developed genome-wide haploid genetic screen can be used to reveal the critical mediators of response to anticancer therapy. Pancreatic cancer is known to be highly resistant to systemic therapy. Recently epigenetic changes have been shown to be a key determinant in the maintenance of subpopulations of cancer cells with high-level resistance to cytotoxic therapy. We show that in human pancreatic cancer cell lines, treatment with the potent class I histone deacetylase inhibitor, entinostat, synergistically enhances gemcitabine-induced inhibition of cell proliferation and apoptosis. Using a genome-wide haploid genetic screen, we identified deoxycytidine kinase (DCK) as one of the genes with the highest degree of insertional enrichment following treatment with gemcitabine and entinostat; DCK is already known to be the rate-limiting activating enzyme for gemcitabine. Immunoblotting confirmed loss of DCK protein expression in the resistant KBM7 cells. CRISPR/Cas-9 inactivation of DCK in pancreatic cancer cell lines resulted in resistance to gemcitabine alone and in combination with entinostat. We have identified gemcitabine and entinostat as a potential new combination therapy in pancreatic cancer, and in this proof-of-principle study we have demonstrated that a recently developed haploid genetic screen can be used as a novel approach to identify the critical genes that determine treatment response.

Histone Deacetylase Inhibitor-Induced Autophagy in Tumor Cells: Implications for p53

Autophagy is an essential process of the eukaryotic cell allowing degradation and recycling of dysfunctional cellular components in response to either physiological or pathological changes. Inhibition of autophagy in combination with chemotherapeutic treatment has emerged as a novel approach in cancer treatment leading to cell cycle arrest, differentiation, and apoptosis. Suberoyl hydroxamic acid (SAHA) is a broad-spectrum histone deacetylase inhibitor (HDACi) suppressing family members in multiple HDAC classes. Increasing evidence indicates that SAHA and other HDACi can, in addition to mitochondria-mediated apoptosis, also promote caspase-independent autophagy. SAHA-induced mTOR inactivation as a major regulator of autophagy activating the remaining autophagic core machinery is by far the most reported pathway in several tumor models. However, the question of which upstream mechanisms regulate SAHA-induced mTOR inactivation that consequently initiate autophagy has been mainly left unexplored. To elucidate this issue, we recently initiated a study clarifying different modes of SAHA-induced cell death in two human uterine sarcoma cell lines which led to the conclusion that the tumor suppressor protein p53 could act as a molecular switch between SAHA-triggered autophagic or apoptotic cell death. In this review, we present current research evidence about HDACi-mediated apoptotic and autophagic pathways, in particular with regard to p53 and its therapeutic implications.

Histone deacetylases inhibitors (HDACis) as novel therapeutic application in various clinical diseases

Accumulating evidence suggests that histone hypoacetylation which is partly mediated by histone deacetylase (HDAC), plays a causative role in the etiology of various clinical disorders such as cancer and central nervous diseases. HDAC inhibitors (HDACis) are natural or synthetic small molecules that can inhibit the activities of HDACs and restore or increase the level of histone acetylation, thus may represent the potential approach to treating a number of clinical disorders. This manuscript reviewed the progress of the most recent experimental application of HDACis as novel potential drugs or agents in a large number of clinical disorders including various brain disorders including neurodegenerative and neurodevelopmental cognitive disorders and psychiatric diseases like depression, anxiety, fear and schizophrenia, and cancer, endometriosis and cell reprogramming in somatic cell nuclear transfer in human and animal models of disease, and concluded that HDACis as potential novel therapeutic agents could be used alone or in adjunct to other pharmacological agents in various clinical diseases.

Multiplexed, targeted profiling of single-cell proteomes and transcriptomes in a single reaction

We present a scalable, integrated strategy for coupled protein and RNA detection from single cells. Our approach leverages the DNA polymerase activity of reverse transcriptase to simultaneously perform proximity extension assays and complementary DNA synthesis in the same reaction. Using the Fluidigm C1™ system, we profile the transcriptomic and proteomic response of a human breast adenocarcinoma cell line to a chemical perturbation, benchmarking against in situ hybridizations and immunofluorescence staining, as well as recombinant proteins, ERCC Spike-Ins, and population lysate dilutions. Through supervised and unsupervised analyses, we demonstrate synergies enabled by simultaneous measurement of single-cell protein and RNA abundances. Collectively, our generalizable approach highlights the potential for molecular metadata to inform highly-multiplexed single-cell analyses.

Tumor suppressive functions of ceramide: evidence and mechanisms

Studies over the past two decades have identified ceramide as a multifunctional central molecule in the sphingolipid biosynthetic pathway. Given its diverse tumor suppressive activities, molecular understanding of ceramide action will produce fundamental insights into processes that limit tumorigenesis and may identify key molecular targets for therapeutic intervention. Ceramide can be activated by a diverse array of stresses such as heat shock, genotoxic damage, oxidative stress and anticancer drugs. Ceramide triggers a variety of tumor suppressive and anti-proliferative cellular programs such as apoptosis, autophagy, senescence, and necroptosis by activating or repressing key effector molecules. Defects in ceramide generation and metabolism in cancer contribute to tumor cell survival and resistance to chemotherapy. The potent and versatile anticancer activity profile of ceramide has motivated drug development efforts to (re-)activate ceramide in established tumors. This review focuses on our current understanding of the tumor suppressive functions of ceramide and highlights the potential downstream targets of ceramide which are involved in its tumor suppressive action.

Histone acetylation: novel target for the treatment of acute lymphoblastic leukemia

Acute lymphoblastic leukemia (ALL) has been generally considered a genetic disease (disorder) with an aggressive tumor entity of highly proliferative malignant lymphoid cells. However, in recent years, significant advances have been made in the elucidation of the ALL-associated processes. Thus, we understand that histone acetylation is involved in the permanent changes of gene expression controlling ALL developmental outcomes. In this article, we will focus on histone acetylation associated with ALL, their implications as biomarkers for prognostic, and their preclinical and clinical applications.

A Novel High-Content Immunofluorescence Assay as a Tool to Identify at the Single Cell Level γ-Globin Inducing Compounds

The identification of drugs capable of reactivating γ-globin to ameliorate β-thalassemia and Sickle Cell anemia is still a challenge, as available γ-globin inducers still have limited clinical indications. High-throughput screenings (HTS) aimed to identify new potentially therapeutic drugs require suitable first-step-screening methods combining the possibility to detect variation in the γ/β globin ratio with the robustness of a cell line. We took advantage of a K562 cell line variant expressing β-globin (β-K562) to set up a new multiplexed high-content immunofluorescence assay for the quantification of γ- and β-globin content at single-cell level. The assay was validated by using the known globin inducers hemin, hydroxyurea and butyric acid and further tested in a pilot screening that confirmed HDACs as targets for γ-globin induction (as proved by siRNA-mediated HDAC3 knockdown and by treatment with HDACs inhibitors entinostat and dacinostat) and identified Heme-oxygenases as novel candidate targets for γ-globin induction. Indeed, Heme-oxygenase2 siRNA knockdown as well as its inhibition by Tin protoporphyrin-IX (TinPPIX) greatly increased γ-globin expression. This result is particularly interesting as several metalloporphyrins have already been developed for clinical uses and could be tested (alone or in combination with other drugs) to improve pharmacological γ-globin reactivation for the treatment of β-hemoglobinopathies.

Histone Modifications, Modifiers and Readers in Melanoma Resistance to Targeted and Immune Therapy

The treatment of melanoma has been revolutionized by new therapies targeting MAPK signaling or the immune system. Unfortunately these therapies are hindered by either primary resistance or the development of acquired resistance. Resistance mechanisms involving somatic mutations in genes associated with resistance have been identified in some cases of melanoma, however, the cause of resistance remains largely unexplained in other cases. The importance of epigenetic factors targeting histones and histone modifiers in driving the behavior of melanoma is only starting to be unraveled and provides significant opportunity to combat the problems of therapy resistance. There is also an increasing ability to target these epigenetic changes with new drugs that inhibit these modifications to either prevent or overcome resistance to both MAPK inhibitors and immunotherapy. This review focuses on changes in histones, histone reader proteins and histone positioning, which can mediate resistance to new therapeutics and that can be targeted for future therapies.

Phosphodiesterase inhibitor, pentoxifylline enhances anticancer activity of histone deacetylase inhibitor, MS-275 in human breast cancer in vitro and in vivo

MS-275, a histone deacetylase inhibitor (HDACi), is undergoing clinical trials for treatment of various cancers. Pentoxifylline, a nonselective phosphodiesterase (PDE) inhibitor, has been shown to increase the effectiveness of antitumor chemotherapy. In the present study, the potential anti-cancer activity of MS-275 in combination with pentoxifylline in panel of cell lines and human breast cancer xenograft model were examined. A Panel of cancer cell lines were treated with MS-275 and pentoxifylline to determine their impact on cellular proliferation, cell cycle regulation, apoptosis, anti-angiogenesis. The in vivo activities of MS-275 and pentoxifylline were assessed in a Matrigel plug angiogenesis model and human breast cancer (MDA-MB-231) xenograft model. Combination of MS-275 with pentoxifylline showed enhanced anti-proliferative activity in a panel of cancer cell lines (HCT 116, MCF-7, PC3 and MDA-MB-231). Apoptotic studies performed using, Hoechst staining and cell cycle analysis reveal that this combination at the lower concentrations induces apoptosis downstream of the HDAC inhibition and PDE regulation. Further, combination showed enhanced antiangiogenic activity in Matrigel tube formation assay using HUVECs and in Matrigel plug assay in vivo. A significant inhibition (P<0.001) of tumor growth was observed in mice bearing MDA-MB-231 breast cancer xenograft treated with the combination of MS-275 (5mg/kg p.o.) and pentoxifylline (60 mg/kg i.p.) than treatments alone, without much signs of toxicity. Taken together, our study demonstrated enhanced anticancer activity of MS-275 and pentoxifylline combination both in vitro and in vivo with reduced toxicity. However, further studies are required to understand the mechanism for this combination effect.

Histone deacetylase inhibitors and cell death

Histone deacetylases (HDACs) are a vast family of enzymes involved in chromatin remodeling and have crucial roles in numerous biological processes, largely through their repressive influence on transcription. In addition to modifying histones, HDACs also target many other non-histone protein substrates to regulate gene expression. Recently, HDACs have gained growing attention as HDAC-inhibiting compounds are being developed as promising cancer therapeutics. Histone deacetylase inhibitors (HDACi) have been shown to induce differentiation, cell cycle arrest, apoptosis, autophagy and necrosis in a variety of transformed cell lines. In this review, we mainly discuss how HDACi may elicit a therapeutic response to human cancers through different cell death pathways, in particular, apoptosis and autophagy.

Histone deacetylase inhibitor (HDACI) mechanisms of action: emerging insights

Initially regarded as "epigenetic modifiers" acting predominantly through chromatin remodeling via histone acetylation, HDACIs, alternatively referred to as lysine deacetylase or simply deacetylase inhibitors, have since been recognized to exert multiple cytotoxic actions in cancer cells, often through acetylation of non-histone proteins. Some well-recognized mechanisms of HDACI lethality include, in addition to relaxation of DNA and de-repression of gene transcription, interference with chaperone protein function, free radical generation, induction of DNA damage, up-regulation of endogenous inhibitors of cell cycle progression, e.g., p21, and promotion of apoptosis. Intriguingly, this class of agents is relatively selective for transformed cells, at least in pre-clinical studies. In recent years, additional mechanisms of action of these agents have been uncovered. For example, HDACIs interfere with multiple DNA repair processes, as well as disrupt cell cycle checkpoints, critical to the maintenance of genomic integrity in the face of diverse genotoxic insults. Despite their pre-clinical potential, the clinical use of HDACIs remains restricted to certain subsets of T-cell lymphoma. Currently, it appears likely that the ultimate role of these agents will lie in rational combinations, only a few of which have been pursued in the clinic to date. This review focuses on relatively recently identified mechanisms of action of HDACIs, with particular emphasis on those that relate to the DNA damage response (DDR), and discusses synergistic strategies combining HDACIs with several novel targeted agents that disrupt the DDR or antagonize anti-apoptotic proteins that could have implications for the future use of HDACIs in patients with cancer.

Valproic acid, an anti-epileptic drug and a histone deacetylase inhibitor, in combination with proteasome inhibitors exerts antiproliferative, pro-apoptotic and chemosensitizing effects in human colorectal cancer cells: underlying molecular mechanisms

Although the therapeutic efficacy of valproic acid (VPA) has been observed in patients with solid tumors, the very high concentration required to induce antitumor activity limits its clinical utility. The present study focused on the development of combined molecular targeted therapies using VPA and proteasome inhibitors (PIs: MG132, PI-1 and PR-39) to determine whether this combination of treatments has synergistic anticancer and chemosensitizing effects against colorectal cancer. Furthermore, the potential molecular mechanisms of action of the VPA/PI combinations were evaluated. The effects of VPA in combination with PIs on the growth of colorectal cancer cells were assessed with regard to proliferation, cell cycle, apoptosis, reactive oxygen species (ROS) generation and the expression of genes that control the cell cycle, apoptosis and pro-survival/stress-related pathways. Treatment with combinations of VPA and PIs resulted in an additive/synergistic decrease in colorectal cancer cell proliferation compared to treatment with VPA or PIs alone. The combination treatment was associated with a synergistic increase in apoptosis and in the number of cells arrested in the S phase of the cell cycle. These events were associated with increased ROS generation, pro-apoptotic gene expression and stress-related gene expression. These events were also associated with the decreased expression of anti-apoptotic genes and pro-survival genes. The combination of VPA with MG132 or PI-1 enhanced the chemosensitivity of the SW1116 (29-185‑fold) and SW837 (50-620-fold) colorectal cancer cells. By contrast, the combination of VPA/PR-39 induced a pronounced increase in the chemosensitivity of the SW837 (16-54-fold) colorectal cancer cells. These data provide a rational basis for the clinical use of this combination therapy for the treatment of colorectal cancer.

Development of histone deacetylase inhibitors for cancer treatment

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

Utility of a histone deacetylase inhibitor (PXD101) for thyroid cancer treatment

Background

We evaluated the therapeutic effects of the histone deacetylase inhibitor PXD101 alone and in combination with conventional chemotherapy in treating thyroid cancer.

Methodology/Principal Findings

We studied eight cell lines from four types of thyroid cancer (papillary, follicular, anaplastic and medullary). The cytotoxicity of PXD101 alone and in combination with three conventional chemotherapeutic agents (doxorubicin, paclitaxel and docetaxel) was measured using LDH assay. Western blot assessed expression of acetylation of histone H3, histone H4 and tubulin, proteins associated with apoptosis, RAS/RAF/ERK and PI3K/AKT/mTOR signaling pathways, DNA damage and repair. Apoptosis and intracellular reactive oxygen species (ROS) were measured by flow cytometry. Mice bearing flank anaplastic thyroid cancers (ATC) were daily treated with intraperitoneal injection of PXD101 for 5 days per week. PXD101 effectively inhibited thyroid cancer cell proliferation in a dose-dependent manner. PXD101 induced ROS accumulation and inhibited RAS/RAF/ERK and PI3K/mTOR pathways in sensitive cells. Double-stranded DNA damage and apoptosis were induced by PXD101 in both sensitive and resistant cell lines. PXD101 retarded growth of 8505C ATC xenograft tumors with promising safety. Combination therapy of PXD101with doxorubicin and paclitaxel demonstrated synergistic effects against four ATC lines invitro.

Conclusions

PXD101 represses thyroid cancer proliferation and has synergistic effects in combination with doxorubicin and paclitaxel in treating ATC. These findings support clinical trials using PXD101 for patients with this dismal disease.

Epigenetic priming of AML blasts for all-trans retinoic acid-induced differentiation by the HDAC class-I selective inhibitor entinostat

All-trans retinoic acid (ATRA) has only limited single agent activity in AML without the PML-RARα fusion (non-M3 AML). In search of a sensitizing strategy to overcome this relative ATRA resistance, we investigated the potency of the HDAC class-I selective inhibitor entinostat in AML cell lines Kasumi-1 and HL-60 and primary AML blasts. Entinostat alone induced robust differentiation of both cell lines, which was enhanced by the combination with ATRA. This "priming" effect on ATRA-induced differentiation was at least equivalent to that achieved with the DNA hypomethylating agent decitabine, and could overall be recapitulated in primary AML blasts treated ex vivo. Moreover, entinostat treatment established the activating chromatin marks acH3, acH3K9, acH4 and H3K4me3 at the promoter of the RARβ2 gene, an essential mediator of retinoic acid (RA) signaling in different solid tumor models. Similarly, RARβ2 promoter hypermethylation (which in primary blasts from 90 AML/MDS patients was surprisingly infrequent) could be partially reversed by decitabine in the two cell lines. Re-induction of the epigenetically silenced RARβ2 gene was achieved only when entinostat or decitabine were given prior to ATRA treatment. Thus in this model, reactivation of RARβ2 was not necessarily required for the differentiation effect, and pharmacological RARβ2 promoter demethylation may be a bystander phenomenon rather than an essential prerequisite for the cellular effects of decitabine when combined with ATRA. In conclusion, as a "priming" agent for non-M3 AML blasts to the differentiation-inducing effects of ATRA, entinostat is at least as active as decitabine, and both act in part independently from RARβ2. Further investigation of this treatment combination in non-M3 AML patients is therefore warranted, independently of RARβ2 gene silencing by DNA methylation.

Improvement of the boron neutron capture therapy (BNCT) by the previous administration of the histone deacetylase inhibitor sodium butyrate for the treatment of thyroid carcinoma

We have shown that boron neutron capture therapy (BNCT) could be an alternative for the treatment of poorly differentiated thyroid carcinoma (PDTC). Histone deacetylase inhibitors (HDACI) like sodium butyrate (NaB) cause hyperacetylation of histone proteins and show capacity to increase the gamma irradiation effect. The purpose of these studies was to investigate the use of the NaB as a radiosensitizer of the BNCT for PDTC. Follicular thyroid carcinoma cells (WRO) and rat thyroid epithelial cells (FRTL-5) were incubated with 1 mM NaB and then treated with boronophenylalanine ¹⁰BPA (10 μg ¹⁰B ml⁻¹) + neutrons, or with 2, 4-bis (α,β-dihydroxyethyl)-deutero-porphyrin IX ¹⁰BOPP (10 μg ¹⁰B ml⁻¹) + neutrons, or with a neutron beam alone. The cells were irradiated in the thermal column facility of the RA-3 reactor (flux = (1.0 ± 0.1) × 10¹⁰ n cm⁻² s⁻¹). Cell survival decreased as a function of the physical absorbed dose in both cell lines. Moreover, the addition of NaB decreased cell survival (p < 0.05) in WRO cells incubated with both boron compounds. NaB increased the percentage of necrotic and apoptotic cells in both BNCT groups (p < 0.05). An accumulation of cells in G2/M phase at 24 h was observed for all the irradiated groups and the addition of NaB increased this percentage. Biodistribution studies of BPA (350 mg kg⁻¹ body weight) 24 h after NaB injection were performed. The in vivo studies showed that NaB treatment increases the amount of boron in the tumor at 2-h post-BPA injection (p < 0.01). We conclude that NaB could be used as a radiosensitizer for the treatment of thyroid carcinoma by BNCT.

Interdiction of sphingolipid metabolism to improve standard cancer therapies

Non-surgical therapies for human malignancies must negotiate complex cell signaling pathways to impede cancer cell growth, ideally promoting death of cancer cells while sparing healthy tissue. For most of the past half century, medical approaches for treating cancer have relied primarily on cytotoxic chemotherapeutics that interfere with DNA replication and cell division, susceptibilities of rapidly dividing cancer cells. As a consequence, these therapies exert considerable cell stress, promoting the generation of ceramide through de novo synthesis and recycling of complex glycosphingolipids and sphingomyelin into apoptotic ceramide. Radiotherapy of cancer exerts similar geno- and cytotoxic cell stresses, and generation of ceramide following ionizing radiation therapy is a well-described feature of radiation-induced cell death. Emerging evidence now describes sphingolipids as mediators of death in response to newer targeted therapies, cementing ceramide generation as a common mechanism of cell death in response to cancer therapy. Many studies have now shown that dysregulation of ceramide accumulation-whether by reduced generation or accelerated metabolism-is a common mechanism of resistance to standard cancer therapies. The aims of this chapter will be to discuss described mechanisms of cancer resistance to therapy related to dysregulation of sphingolipid metabolism and to explore clinical and preclinical approaches to interdict sphingolipid metabolism to improve outcomes of standard cancer therapies.

Resveratrol sensitizes acute myelogenous leukemia cells to histone deacetylase inhibitors through reactive oxygen species-mediated activation of the extrinsic apoptotic pathway

Histone deacetylase inhibitors (HDACIs) activate the prosurvival nuclear factor-κB (NF-κB) pathway by hyperacetylating RelA/p65, whereas the chemopreventive agent resveratrol inhibits NF-κB by activating the class III histone deacetylase Sirt1. Interactions between resveratrol and pan-HDACIs (vorinostat and panobinostat) were examined in human acute myelogenous leukemia (AML) cells. Pharmacologically achievable resveratrol concentrations (25-50 μM) synergistically potentiated HDACI lethality in AML cell lines and primary AML blasts. Resveratrol antagonized RelA acetylation and NF-κB activation in HDACI-treated cells. However, short hairpin RNA Sirt1 knockdown failed to modify HDACI sensitivity, which suggests that factors other than or in addition to Sirt1 activation contribute to resveratrol/HDACI interactions. These interactions were associated with death receptor 5 (DR5) up-regulation and caspase-8 activation, whereas cells expressing dominant-negative caspase-8 were substantially protected from resveratrol/HDACI treatment, which suggests a significant functional role for the extrinsic apoptotic pathway in lethality. Exposure to resveratrol with HDACI induced sustained reactive oxygen species (ROS) generation, which was accompanied by increased levels of DNA double-strand breaks, as reflected in γH2A.X and comet assays. The free radical scavenger Mn(III)tetrakis(4-benzoic acid)porphyrin chloride blocked ROS generation, DR5 up-regulation, caspase-8 activation, DNA damage, and apoptosis, which indicates a primary role for oxidative injury in lethality. Analyses of cell-cycle progression and 5-ethynyl-2'-deoxyuridine incorporation through flow cytometry revealed that resveratrol induced S-phase accumulation; this effect was abrogated by HDACI coadministration, which suggests that cells undergoing DNA synthesis may be particularly vulnerable to HDACI lethality. Collectively, these findings indicate that resveratrol interacts synergistically with HDACIs in AML cells through multiple ROS-dependent actions, including death receptor up-regulation, extrinsic apoptotic pathway activation, and DNA damage induction. They also raise the possibility that S-phase cells may be particularly susceptible to these actions.

CS055 (Chidamide/HBI-8000), a novel histone deacetylase inhibitor, induces G1 arrest, ROS-dependent apoptosis and differentiation in human leukaemia cells

CS055 (Chidamide/HBI-8000) is a novel benzamide-type HDACi (histone deacetylase inhibitor), which has entered Phase I clinical trials in the U.S. and Phase II/III in China. In the present study, we investigated the effects of CS055 on proliferation, differentiation and apoptosis in human leukaemia cell lines and primary myeloid leukaemia cells. The results showed that at low concentrations (<1 μM), CS055 induced G1 arrest. At moderate concentrations (0.5 μM–2 μM), CS055 induced differentiation, as determined by the increased expression of the myeloid differentiation marker CD11b. At relatively high concentrations (2 μM–4 μM), CS055 potently induced caspase-dependent apoptosis. Co-treatment with the ROS (reactive oxygen species) scavengers N-acetyl-L-cysteine or Tiron blocked CS055-induced cell differentiation and apoptosis, suggesting an essential role for ROS in these effects. Cytochrome c release and ROS-mediated mitochondrial dysfunction are involved in CS055-induced apoptosis of leukaemia. In addition to cell lines, CS055 also exhibits therapeutic effects in human primary leukaemia cells. Moreover, daily oral CS055 treatment of nude mice bearing HL60 cell xenografts suppressed tumour growth, induced tumour cell apoptosis and prolonged the survival of tumour-bearing mice. In conclusion, our findings demonstrate that CS055 is a novel HDACi with potential chemotherapeutic value in several haematological malignancies, especially leukaemia.

HDAC modulation and cell death in the clinic

Histone acetyltransferases (HATs) and histone deacetylases (HDACs) are two opposing classes of enzymes, which finely regulate the balance of histone acetylation affecting chromatin packaging and gene expression. Imbalanced acetylation has been associated with carcinogenesis and cancer progression. In contrast to genetic mutations, epigenetic changes are potentially reversible. This implies that epigenetic alterations are amenable to pharmacological interventions. Accordingly, some epigenetic-based drugs (epidrugs) have been approved by the Food and Drug Administration (FDA) and the European Medicines Agency (EMA) for cancer treatment. Here, we focus on the biological features of HDAC inhibitors (HDACis), analyzing the mechanism(s) of action and their current use in clinical practice.

Valproic acid combined with cytosine arabinoside in elderly patients with acute myeloid leukemia has in vitro but limited clinical activity

Elderly patients with acute myeloid leukemia (AML) have a poor prognosis. The authors examined the in vitro and clinical activity of the histone deacetylase inhibitor valproic acid (VA) combined with cytosine arabinoside (AraC) in elderly patients with AML unsuited to intensive therapy. For the in vitro studies, primary AML cells from 11 patients were treated with AraC and VA and analyzed for apoptosis, cytostatic effects, differentiation and acetyl histone H3 induction. VA (alone and with AraC) enhanced apoptosis and induced acetyl histone H3. VA inhibited cell proliferation. For the clinical trial, 15 patients were treated with VA and subcutaneous AraC and assessed for toxicity and response. No complete or partial remissions were achieved. In conclusion, VA has in vitro activity against AML and has additional activity with AraC. However, in this study, this combination demonstrated limited clinical activity in elderly patients with AML.

Concerted functions of HDAC1 and microRNA-574-5p repress alternatively spliced ceramide synthase 1 expression in human cancer cells

Histone deacetylases (HDACs) and microRNAs (miRs) have pro-survival roles, but the mechanism behind this is unclear. Repression of ceramide synthase 1 (CerS1), altering C(18) -ceramide generation, was linked to drug resistance and metastasis. Here we report that the CerS1 promoter was repressed by HDAC1-dependent inhibition of Sp1 recruitment to two specific GC-boxes spanning the -177 and -139 region. Moreover, an alternatively spliced variant CerS1 mRNA (CerS1-2) was detected mainly in cancer cells or primary tumour tissues compared to controls, which was targeted by miR-574-5p for degradation. A specific 3'UTR-targeting site, localized within the retained intron between exons 6 and 7, was identified, and its mutation, or miR-574-5p knockdown prevented the degradation of CerS1-2 mRNA. Interference with HDAC1 and miR-574-5p reconstituted CerS1-2 expression and C(18) -ceramide generation in multiple human cancer cell lines, which subsequently inhibited proliferation and anchorage-independent growth. Accordingly, knockdown of CerS1 partially protected cancer cells from MS-275/miR-574-5p siRNA-mediated growth inhibition. Thus, these data suggest that the HDAC1/miR-574-5p axis might provide a novel therapeutic target to reconstitute tumour suppressor CerS1/ceramide signalling.

LBH-589 (panobinostat) potentiates fludarabine anti-leukemic activity through a JNK- and XIAP-dependent mechanism

Effects of the HDAC inhibitor LBH-589 (panobinostat) on fludarabine lethality toward acute myeloid leukemia (AML) cells were examined in vitro and in vivo. LBH-589 pretreatment sensitized U937, HL-60, and primary leukemia cells to fludarabine while blocking NF-κB activation accompanied by XIAP down-regulation and JNK activation. Pharmacologic or genetic JNK inhibition significantly attenuated LBH-589/fludarabine lethality, whereas XIAP over-expression diminished JNK activation and apoptosis. Combined in vivo treatment abrogated leukemia growth in a U937 xenograft murine model and substantially increased animal survival. These studies highlight the interplay between NF-κB activation, XIAP down-regulation, and JNK activation in anti-leukemic synergism between fludarabine and LBH-589.

Effects and mechanisms of the combination of suberoylanilide hydroxamic acid and bortezomib on the anticancer property of gemcitabine in pancreatic cancer

OBJECTIVES

Earlier studies that dealt with the combination therapy of gemcitabine and histone deacetylation inhibitors for pancreatic cancer revealed unsatisfactory results. The activation of nuclear factor κB (NF-κB) was referred as one of the attributable causes, and we attempted to overcome this resistance by the addition of a proteasome inhibitor.

METHODS

The influences of suberoylanilide hydroxamic acid (vorinostat, SAHA), a histone deacetylase inhibitor, and bortezomib, a novel selective antagonist of 26S proteasome, with or without gemcitabine on cell growth and apoptosis and the expressions of related proteins were observed in pancreatic cancer cell lines (MiaPaCa-2 and ASPC-1). The xenograft model of pancreatic cancer was used to notice effects in vivo.

RESULTS

Vorinostat and bortezomib had independent inhibitory effects and potentiated the antitumor property of gemcitabine in vitro. In the xenograft model, more augmented effects were achieved when bortezomib was combined with gemcitabine than gemcitabine alone. The down-regulation of pAkt and suppression of NF-κB activity was induced by the triple combination.

CONCLUSIONS

The triple combination of vorinostat, bortezomib, and gemcitabine resulted in the strongest antitumor effects both in vitro and in vivo and pAkt and NF-κB seems to be involved in this process.

The role of HDACs inhibitors in childhood and adolescence acute leukemias

Acute leukemia is the most common type of childhood and adolescence cancer, characterized by clonal proliferation of variably differentiated myeloid or lymphoid precursors. Recent insights into the molecular pathogenesis of leukemia have shown that epigenetic modifications, such as deacetylation of histones and DNA methylation, play crucial roles in leukemogenesis, by transcriptional silencing of critical genes. Histone deacetylases (HDACs) are potential targets in the treatment of leukaemia, and, as a consequence, inhibitors of HDACs (HDIs) are being studied for therapeutic purposes. HDIs promote or enhance several different anticancer mechanisms, such as apoptosis, cell cycle arrest, and cellular differentiation and, therefore, are in evidence as promising treatment for children and adolescents with acute leukemia, in monotherapy or in association with other anticancer drugs. Here we review the main preclinical and clinical studies regarding the use of HDIs in treating childhood and adolescence leukemia.

The DAC system and associations with acute leukemias and myelodysplastic syndromes

Imbalances of histone acetyltransferase (HAT) and deacetylase activity (DAC) that result in deregulated gene expression are commonly observed in leukemias. These alterations provide the basis for novel therapeutic approaches that target the epigenetic mechanisms implicated in leukemogenesis. As the acetylation status of histones has been linked to transcriptional regulation of genes involved particularly in differentiation and apoptosis, DAC inhibitors (DACi) have attracted considerable attention for treatment of hematologic malignancies. DACi encompass a structurally diverse family of compounds that are being explored as single agents as well as in combination with chemotherapeutic drugs, small molecule inhibitors of signaling pathways and hypomethylating agents. While DACi have shown clear evidence of activity in acute myeloid leukemia, myelodysplastic syndromes and lymphoid malignancies, their precise role in treatment of these different entities remain to be elucidated. Successful development of these compounds as elements of novel targeted treatment strategies for leukemia will require that clinical studies be performed in conjunction with translational research including efforts to identify predictive biomarkers.

Selenium-containing analogs of SAHA induce cytotoxicity in lung cancer cells

Cancer therapy has moved beyond conventional chemotherapeutics to more mechanism-based targeted approaches. Studies demonstrate that histone deacetylase (HDAC) is a promising target for anticancer agents. Numerous, structurally diverse, hydroxamic acid derivative, HDAC inhibitors have been reported and have been shown to induce growth arrest, differentiation, autophagy, and/or apoptotic cell death by inhibiting multiple signaling pathways in cancer cells. Suberoylanilide hydroxamic acid (SAHA) has emerged as an effective anticancer therapeutic agent and was recently approved by the FDA for the treatment of advanced cutaneous T-cell lymphoma. In our previous study, we reported the development of the novel, potent, selenium-containing HDAC inhibitors (SelSA-1 and SelSA-2). In this study, the effects of SelSA-1 and SelSA-2 on signaling pathways and cytotoxicity were compared with the known HDAC inhibitor, SAHA, in lung cancer cell lines. After 24 h of treatment, SelSA-1 and SelSA-2 inhibited lung cancer cell growth to a greater extent than SAHA in a dose-dependent manner with IC(50) values at low micromolar concentrations. SelSA-1 and SelSA-2 inhibited ERK and PI3K-AKT signaling pathways while simultaneously increasing in autophagy in A549 cells in a time dependent manner. This preliminary study demonstrates the effectiveness of the selenium-containing analogs of SAHA, SelSA-1, and SelSA-2, as HDAC inhibitors and provides insight into the improvement and/or development of these analogs as a therapeutic approach for the treatment of lung cancer.

Rationale for possible targeting of histone deacetylase signaling in cancer diseases with a special reference to pancreatic cancer

There is ongoing interest to identify signaling pathways and genes that play a key role in carcinogenesis and the development of resistance to antitumoral drugs. Given that histone deacetylases (HDACs) interact with various partners through complex molecular mechanims leading to the control of gene expression, they have captured the attention of a large number of researchers. As a family of transcriptional corepressors, they have emerged as important regulators of cell differentiation, cell cycle progression, and apoptosis. Several HDAC inhibitors (HDACis) have been shown to efficiently protect against the growth of tumor cells in vitro as well as in vivo. The pancreatic cancer which represents one of the most aggressive cancer still suffers from inefficient therapy. Recent data, although using in vitro tumor cell cultures and in vivo chimeric mouse model, have shown that some of the HDACi do express antipancreatic tumor activity. This provides hope that some of the HDACi could be potential efficient anti-pancreatic cancer drugs. The purpose of this review is to analyze some of the current data of HDACi as possible targets of drug development and to provide some insight into the current problems with pancreatic cancer and points of interest for further study of HDACi as potential molecules for pancreatic cancer adjuvant therapy.

ROS-mediated upregulation of Noxa overcomes chemoresistance in chronic lymphocytic leukemia

In recent years considerable progress has been made in treatment strategies for chronic lymphocytic leukemia (CLL). However, the disease remains incurable because of the development of chemoresistance. Strategies to overcome resistance mechanisms are therefore highly needed. At least two mechanisms contribute to the development of resistance to drugs; acquired mutations resulting in a dysfunctional p53 response and shifts in the balance between apoptosis-regulating proteins. Platinum-based compounds have been successfully applied in relapsed lymphoma and recently also in high-risk CLL. In this study we investigated the efficacy and mechanism of action of cisplatinum (CDDP) in chemorefractory CLL. Independent of p53-functional status, CDDP acted synergistically with fludarabine (F-ara-A). The response involved generation of reactive oxygen species (ROS), which led to specific upregulation of the proapoptotic BH3-only protein Noxa. Induction of Noxa resulted in cell death by apoptosis as inhibition of caspase activation completely abrogated cell death. Furthermore, drug-resistance upon CD40-ligand stimulation, a model for the protective stimuli provided in lymph nodes, could also be overcome by CDDP/F-ara-A. ROS accumulation resulted in Noxa upregulation mainly at the transcriptional level and this was, at least in part, mediated by the mitogen-activated protein kinase p38. Finally, Noxa RNA-interference markedly decreased sensitivity to CDDP/F-ara-A, supporting a key role for Noxa as mediator between ROS signaling and apoptosis induction. Our data indicate that interference in the cellular redox balance can be exploited to overcome chemoresistance in CLL.

Combinations of DNA methyltransferase and histone deacetylase inhibitors induce DNA damage in small cell lung cancer cells: correlation of resistance with IFN-stimulated gene expression

Because epigenetic inhibitors can reduce cancer cell proliferation, we tested the hypothesis that concurrent inhibition of histone acetylation and DNA methylation could synergistically reduce the viability of small cell lung cancer (SCLC) cells. Sub-IC(50) concentrations of the DNA methyltransferase (DNMT) inhibitor decitabine (5-AZA-dC) and the histone deacetylase (HDAC) inhibitors (LBH589 or MGCD0103) synergistically reduced the proliferation of five of nine SCLC cell lines. Loss of viability of sensitive SCLC cells did not correlate with the inhibition of either DNMT1 or HDACs, suggesting nonepigenetic mechanisms for synergy between these two classes of epigenetic modulators. Because combinations of 5-AZA-dC and HDAC inhibitors had marginal effects on the apoptosis index, Comet assay was undertaken to assess DNA damage. MGCD0103 and 5AZA-dC cotreatment augmented DNA damage in SCLC cells, resulting in increased tail length and moment in Comet assays by 24 hours in sensitive cell lines (P < 0.01). Consistent with augmented DNA damage, combination of a DNMT and HDAC inhibitor markedly increased the levels of phospho-H2A.X in sensitive cells but not in resistant ones. Comparison of basal gene expression between resistant and sensitive cells identified markedly higher basal expression of IFN-stimulated genes in the resistant cell lines, suggesting that IFN-stimulated gene expression may determine SCLC cell sensitivity to epigenetic modulators or other DNA damaging agents.

Histone deacetylase inhibitors and 15-deoxy-Delta12,14-prostaglandin J2 synergistically induce apoptosis

PURPOSE

The clinically relevant histone deacetylase inhibitors (HDI) valproic acid (VPA) and suberoylanilide hydroxamic acid exert variable antitumor activities but increase therapeutic efficacy when combined with other agents. The natural endogenous ligand of peroxisome proliferator-activated receptor gamma 15-deoxy-Delta(12,14)-prostaglandin J(2) (15d-PGJ(2)) is a potent antineoplastic agent. Therefore, we investigated whether these HDIs in combination with 15d-PGJ(2) could show synergistic antitumor activity in colon cancer DLD-1 cells.

EXPERIMENTAL DESIGN

Cell viability was determined using a Cell Counting Kit-8 assay. Apoptosis and reactive oxygen species (ROS) generation were determined using flow cytometry analysis. Western blotting and real-time reverse transcription-PCR analysis were carried out to investigate the expression of apoptosis-related molecules. Mice bearing DLD-1 xenograft were divided into four groups (n = 5) and injected everyday (i.p.) with diluent, VPA (100 mg/kg), 15d-PGJ(2) (5 mg/kg), or a combination for 25 days.

RESULTS

HDI/15d-PGJ(2) cotreatments synergistically induced cell death through caspase-dependent apoptosis in DLD-1 cells. Moreover, HDIs/15d-PGJ(2) caused histone deacetylase inhibition, leading to subsequent ROS generation and endoplasmic reticulum stress to decrease the expression of antiapoptotic molecules Bcl-X(L) and XIAP and to increase that of proapoptotic molecules CAAT/enhancer binding protein homologous protein and death receptor 5. Additionally, VPA/15d-PGJ(2) cotreatment induced ROS-dependent apoptosis in other malignant tumor cells and was more effective than a VPA or 15d-PGJ(2) monotherapy in vivo.

CONCLUSIONS

Cotreatments with the clinically relevant HDIs and the endogenous peroxisome proliferator-activated receptor gamma ligand 15d-PGJ(2) are promising for the treatment of a broad spectrum of malignant tumors.

Histone Deacetylase Inhibitor M344 Inhibits Cell Proliferation and Induces Apoptosis in Human THP-1 Leukemia Cells

Histone acetylation plays an important role in the silencing and activation of genes involved in tumoregenesis. Trichostatin A, originally identified as an anti-fungal drug, is a potent inhibitor of histone deacetylase (HDAC) with potential anti-tumor activity. In this study, we investigated the effect of M344, an amide analogues of trichostatin A, on the growth and differentiation of THP-1 human leukemia cells. We showed that at low doses, (< 0.2 muM), M344 could inhibit the growth of THP-1 cells at G1 phase in vitro with low cytotoxic effect. Low dose of M344 exerted some differentiating effect on THP-1 cells as judged by the expression of c-fms proto-oncogene (M-CSF receptor) and appearance of adherent cells. Growth arrest induced by M344 is associated with increased levels of cyclin-dependent protein kinase inhibitor p21 and cyclin E, in agreement with G1 phase arrest. At higher doses (2 muM), M344 could induce THP-1 cells to undergo apoptosis, which was associated with the cleavage of PARP, cytochrome c release and activation of both caspases-8, -9, followed by the activation of caspase-3. In addition, M344 could increase the levels of pro-apoptotic protein Bax but decreased the levels of anti-apoptotic protein XIAP. M344 is a potent activator of NF-kappaB transcription factor. RT-PCR assay showed that the M344 could transiently increase IL-1 expression yet markedly decreased TNF-alpha expression. Our results show that M344 is a potent growth inhibitor and inducer of apoptosis in human leukemia cells and suggest potential therapeutic strategies of HDAC inhibitors for patients with leukemias.