Histone Deacetylase Inhibitors: Advancing Therapeutic Strategies in Hematological and Solid Malignancies

Mechanistic Sequence of Histone Deacetylase Inhibitors and Radiation Treatment: An Overview

Histone deacetylases inhibitors (HDACis) have shown promising therapeutic outcomes in haematological malignancies such as leukaemia, multiple myeloma, and lymphoma, with disappointing results in solid tumours when used as monotherapy. As a result, combination therapies either with radiation or other deoxyribonucleic acid (DNA) damaging agents have been suggested as ideal strategy to improve their efficacy in solid tumours. Numerous in vitro and in vivo studies have demonstrated that HDACis can sensitise malignant cells to both electromagnetic and particle types of radiation by inhibiting DNA damage repair. Although the radiosensitising ability of HDACis has been reported as early as the 1990s, the mechanisms of radiosensitisation are yet to be fully understood. This review brings forth the various protocols used to sequence the administration of radiation and HDACi treatments in the different studies. The possible contribution of these various protocols to the ambiguity that surrounds the mechanisms of radiosensitisation is also highlighted.

Discovery of novel isoform-selective histone deacetylases 5 and 9 inhibitors through combined ligand-based pharmacophore modeling, molecular mocking, and molecular dynamics simulations for cancer treatment

Class IIa histone deacetylases (HDACs) 5 and 9 play crucial roles in several human disorders such as cancer, making them important targets for drug design. Continuous research is pursed to overcome the cytotoxicity side effect that comes with the currently available broad-spectrum HDACs inhibitors. Herein, common features of active HDACs inhibitors in clinical trials and use have been calculated to generate the best pharmacophore hypothesis. Guner-Henry scoring system was used to validate the generated hypotheses. Hypo1 of HDAC5 and Hypo2 of HDAC9 exhibited the most statistically significance hypotheses. Compounds with fit value of 3 and more were examined by QuickVina 2 docking tool to calculate their binding affinity toward all class IIa HDACs. A total of 6 potential selective compounds were subjected to 100 molecular dynamics (MD) simulation to examine their binding modes. The free binding energy calculations were computed according to the MM-PBSA method. Proposed selective compounds displayed good stability with their targets and thus they may offer potent leads for the designing of HDAC5 and HDAC9 isoform selective inhibitors.

Current status of histone deacetylase inhibitors in cutaneous T-cell lymphoma

Cutaneous T cell lymphoma (CTCL) is a non-Hodgkin's lymphoma with a heterogenous presentation and highly variable disease course. The most common subtypes of CTCL are mycosis fungoides (MF) and Sézary Syndrome (SS). Treatment varies based on the stage of the disease with skin directed therapies typically utilized for early stage disease, and systemic therapies employed for more advanced disease. There are few highly effective treatments available, and systemic therapies have limited response rates. Histone deacetylase inhibitors have emerged as mainstream treatments for MF/SS over the past several years. Here, we discuss the mechanism of action of histone deacetylase inhibitors in relation to the pathogenesis of MF/SS, evaluate the clinical trials that led to Food and Drug Administration approval of two of the histone deacetylase inhibitors for MF/SS and describe the results for those still under investigation. Additionally, we discuss the potential for combination therapies in order to optimize outcomes of treatment with histone deacetylase inhibitors.

Synthesis of N-Substituted Benzamide Derivatives and their Evaluation as Antitumor Agents

BACKGROUND

Histone deacetylases inhibitors (HDACIs) with different chemical structures have been reported to play an important role in the treatment of cancer.

OBJECTIVE

The study aims to modify the structure of Entinostat (MS-275) to discover new compounds with improved anti-proliferative activities and perform SAR studies on this class of bioactive compounds.

METHODS

Fourteen N-substituted benzamide derivatives were synthesized and their antiproliferative activities were tested with four cancer cell lines (MCF-7, A549, K562 and MDA-MB- 231) by MTT assay.

RESULTS

Compared with MS-275, six compounds exhibited comparable or even better antiproliferative activities against specific/certain cancer cell lines.

CONCLUSION

The preliminary SARs showed that (ⅰ) the 2-substituent of the phenyl ring in the R group and heteroatoms of amide which can chelate with zinc ion are critical to the antiproliferative activity and (ⅱ) chlorine atom or nitro-group on the same benzene ring largely decreases their anti-proliferative activity. Molecular docking study illustrated the interaction (binding affinity) between the synthesized compounds and HDAC2 was observed to be similar to that of MS-275.

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.

Histone deacetylase inhibitors upregulate Snail via Smad2/3 phosphorylation and stabilization of Snail to promote metastasis of hepatoma cells

Hepatocellular carcinoma (HCC) remains the third most common cause of cancer-related mortality. Resection and transplantation are the only curative treatments available, but are greatly hampered by high recurrence rates. Histone deacetylase inhibitors (HDACIs) are considered to be promising anticancer agents in drug development. Currently, four HDACIs have been granted Food and Drug Administration (FDA) approval for cancer. HDACIs have shown significant efficacy in hematological malignancies. However, they have limited effects in epithelial cell-derived cancers, including HCC, and the mechanisms of these are not elucidated. In this study, our results demonstrated that HDACIs were able to induce epithelial-mesenchymal transitions (EMT) in hepatoma cells which are believed to trigger tumor cell invasion and metastasis. We found that HDACIs promoted the expression of Snail and Snail-induced EMT was critical for HDACI-initiated invasion and metastasis. We indicated that HDACIs upregulated Snail in two ways. Firstly, HDACIs upregulated Snail at the transcriptional level by promoting Smad2/3 phosphorylation and nuclear translocation, then combined with the promoter to activate the transcription of Snail. Secondly, we showed that HDACIs regulated the stabilization of Snail via upregulating the expression of COP9 signalosome 2 (CSN2), which combined with Snail and exposed its acetylation site, then promoted acetylation of Snail, thereby inhibiting its phosphorylation and ubiquitination to repress the degradation of Snail. All these results highlighted that HDACIs have limited effects in HCC, and the use of HDACIs combined with other targeted strategies to inhibit EMT, which explored in this study is a promising treatment method for treating HCC.

A novel HDAC inhibitor, CG200745, inhibits pancreatic cancer cell growth and overcomes gemcitabine resistance

Pancreatic cancer is predominantly lethal, and is primarily treated using gemcitabine, with increasing resistance. Therefore, novel agents that increase tumor sensitivity to gemcitabine are needed. Histone deacetylase (HDAC) inhibitors are emerging therapeutic agents, since HDAC plays an important role in cancer initiation and progression. We evaluated the antitumor effect of a novel HDAC inhibitor, CG200745, combined with gemcitabine/erlotinib on pancreatic cancer cells and gemcitabine-resistant pancreatic cancer cells. Three pancreatic cancer-cell lines were used to evaluate the antitumor effect of CG200745 combined with gemcitabine/erlotinib. CG200745 induced the expression of apoptotic proteins (PARP and caspase-3) and increased the levels of acetylated histone H3. CG200745 with gemcitabine/erlotinib showed significant growth inhibition and synergistic antitumor effects in vitro. In vivo, gemcitabine/erlotinib and CG200745 reduced tumor size up to 50%. CG200745 enhanced the sensitivity of gemcitabine-resistant pancreatic cancer cells to gemcitabine, and decreased the level of ATP-binding cassette-transporter genes, especially multidrug resistance protein 3 (MRP3) and MRP4. The novel HDAC inhibitor, CG200745, with gemcitabine/erlotinib had a synergistic anti-tumor effect on pancreatic cancer cells. CG200745 significantly improved pancreatic cancer sensitivity to gemcitabine, with a prominent antitumor effect on gemcitabine-resistant pancreatic cancer cells. Therefore, improved clinical outcome is expected in the future.

The histone deacetylase inhibitor sodium butyrate improves insulin signalling in palmitate-induced insulin resistance in L6 rat muscle cells through epigenetically-mediated up-regulation of Irs1

Dietary administration of the histone deacetylase (HDAC) inhibitor butyric acid - a short chain fatty acid present in milk products and also bacterially produced in the intestine - has been shown to increase energy expenditure and favour insulin sensitivity in mice through induction of PGC1α (peroxisome proliferator-activated receptor gamma co-activator 1α) and AMPK (AMP-activated protein kinase) in skeletal muscle, and a consequential increase of mitochondrial fatty acid oxidation. Here, we investigate whether such physiological improvements are associated to epigenetic effects dependent on increased histone acetylation and whether butyrate exerts a direct action on skeletal muscle insulin signalling. We show that sodium butyrate (NaBut) ameliorates the insulin-resistant phenotype, induced in L6 myotubes by prolonged exposure to palmitate, by i) increasing the insulin-induced phosphorylation of both PKB (protein kinase B) and MAPK (mitogen activated protein kinase), the two branches of insulin signalling and ii) increasing histone H3 acetylation - even in the presence of palmitate - on chromatin in proximity of the Irs1 (insulin receptor substrate 1) transcriptional start site. Consequently, NaBut induced Irs1 mRNA and protein overexpression, which in turn relayed higher insulin-stimulated IRS1 tyrosine phosphorylation and PI 3-kinase (phosphoinositide 3-kinase) association, suggesting that the increased IRS1 expression may mediate the insulin-sensitizing effects of NaBut. Furthermore, downstream of PKB, NaBut induced GSK3β gene upregulation. Our observations indicate that NaBut - through its action as HDAC inhibitor - can promote insulin responsiveness in L6 myotubes under conditions of lipid-induced insulin resistance.

Analysis of the interplay between all-trans retinoic acid and histone deacetylase inhibitors in leukemic cells

The treatment of acute promyelocytic leukemia (APL) with all-trans retinoic acid (ATRA) induces granulocytic differentiation. This process renders APL cells resistant to cytotoxic chemotherapies. Epigenetic regulators of the histone deacetylases (HDACs) family, which comprise four classes (I-IV), critically control the development and progression of APL. We set out to clarify the parameters that determine the interaction between ATRA and histone deacetylase inhibitors (HDACi). Our assays included drugs against class I HDACs (MS-275, VPA, and FK228), pan-HDACi (LBH589, SAHA), and the novel HDAC6-selective compound Marbostat-100. We demonstrate that ATRA protects APL cells from cytotoxic effects of SAHA, MS-275, and Marbostat-100. However, LBH589 and FK228, which have a superior substrate-inhibitor dissociation constant (Ki) for the class I deacetylases HDAC1, 2, 3, are resistant against ATRA-dependent cytoprotective effects. We further show that HDACi evoke DNA damage, measured as induction of phosphorylated histone H2AX and by the comet assay. The ability of ATRA to protect APL cells from the induction of p-H2AX by HDACi is a readout for the cytoprotective effects of ATRA. Moreover, ATRA increases the fraction of cells in the G1 phase, together with an accumulation of the cyclin-dependent kinase inhibitor p21 and a reduced expression of thymidylate synthase (TdS). In contrast, the ATRA-dependent activation of the transcription factors STAT1, NF-κB, and C/EBP hardly influences the responses of APL cells to HDACi. We conclude that the affinity of HDACi for class I HDACs determines whether such drugs can kill naïve and maturated APL cells.

Epigenetic and miRNAs Dysregulation in Prostate Cancer: The role of Nutraceuticals

The control of cancer onset and progression is recognized to benefit from specific molecular targeting. MiRNAs are increasingly being implicated in prostate cancer, and the evidence suggests they are possible targets for molecular therapy and diagnosis. In cancer cells, growing attention has been dedicated to novel molecular mechanisms linking the epigenetic scenario to miRNA dysregulation. Currently, the rising evidence shows that nutritional and natural agents, the so-called nutraceuticals, could modulate miRNAs expression, and, as a consequence, might influence cellular responses in health or diseases conditions, including cancer. Among dietary components, plant-derived polyphenols are receiving wide interest, either for their anti-aging and anti-oxidant properties, or for their more general "cell-protective" effects. Above all, their role in preventing the occurrence/recurrence of cancer and, in particular, their potentiality in nutritional intervention for modulating the functions of miRNAs and the epigenetic mechanisms, is still under active debate. This review is focused on the more recent highlights of the impact of miRNAs dysregulation on the onset and progression of prostate cancer, their interplay with epigenetic control and their modulation by natural agents.

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

PURPOSE

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

MHY218-induced apoptotic cell death is enhanced by the inhibition of autophagy in AGS human gastric cancer cells

We previously reported the anticancer effects of MHY218, which is a hydroxamic acid derivative, in HCT116 human colon cancer cells. In the present study, the involvement of autophagy in the MHY218-induced apoptotic cell death of AGS human gastric cancer cells was investigated. MHY218 treatment induced growth inhibition and apoptotic cell death in a concentration- and time-dependent manner. The induction of apoptosis was confirmed by observations of decreased viability, DNA fragmentation, and an increase in late apoptosis and sub-G1 DNA, which were detected with a flow cytometric analysis. Western blot analyses showed that MHY218 treatment resulted in decreased protein levels of procaspase-8, -9, and -3; cleavage of poly(ADP-ribose) polymerase (PARP); and alterations in the ratio of Bax/Bcl-2 protein expression. Apoptosis induced by MHY218 was involved in the activation of caspase-8, -9, and -3, and it was blocked by the addition of Z-VAD‑FMK, a pan-caspase inhibitor. In addition, autophagy-inducing effects of MHY218 were indicated by cytoplasmic vacuolation, the accumulation of acidic vesicular organelles, the appearance of green fluorescent protein-light-chain 3 (LC3) punctate dots, and increased levels of Beclin-1 and LC3-II protein expression. Pretreatment with the autophagy inhibitors LY294002, 3-methyladenine, chloroquine, and bafilomycin A1 enhanced the induction of apoptosis by MHY218, and this was accompanied by an increase in PARP cleavage. Taken together, these results provide new insights into the role of MHY218 as a potential antitumor agent. The combination of MHY218 with an autophagy inhibitor might be a useful candidate for the chemoprevention and/or treatment of gastric cancer.

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.

Trichostatin A, a histone deacetylase inhibitor, suppresses proliferation and promotes apoptosis of esophageal squamous cell lines

Histone deacetylase (HDAC)‑mediated epigenetic modification plays crucial roles in numerous biological processes, including cell cycle regulation, cell proliferation and apoptosis. HDAC inhibitors demonstrate antitumor effects in various cancers, including glioblastoma and breast cancer. HDAC inhibitors are therefore promising antitumor drugs for these tumors. The tumorigenesis and development of esophageal squamous cell carcinoma (ESCC) involve genetic and epigenetic mechanisms. However, the effects of the HDAC inhibitor on ESCC are not fully investigated. In the present study, ESCC cells were treated with trichostatin A (TSA) and its antitumor effects and related mechanisms were investigated. The results indicated that TSA suppressed the proliferation of ESCCs and caused G1 phase arrest by inducing the expression of p21 and p27. TSA also induced cell apoptosis by enhancing the expression of pro‑apoptotic protein Bax and decreasing the expression of anti‑apoptotic protein Bcl‑2. Furthermore, TSA inhibited the expression of phosphatidylinositol‑3‑kinase (PI3K) and reduced the phosphorylation of Akt and extracellular signal‑regulated kinase (ERK)1/2 in EC9706 and EC1 cell lines. High levels of acetylated histone H4 were detected in TSA‑treated ESCC cell lines. Overall, these results indicate that TSA suppresses ESCC cell growth by inhibiting the activation of the PI3K/Akt and ERK1/2 pathways. TSA also promotes cell apoptosis through epigenetic regulation of the expression of apoptosis‑related protein.

Combinatorial antitumor effect of HDAC and the PI3K-Akt-mTOR pathway inhibition in a Pten defecient model of prostate cancer

Increased expression of histone deacetylases (HDACs) and activation of the PI3K-Akt-mTORC1 pathway are common aberrations in prostate cancer (PCa). For this reason, inhibition of such targets is an exciting avenue for the development of novel therapeutic strategies to treat patients with advanced PCa. Previous reports demonstrated that HDAC inhibitors (HDACi) increases DNA damage and induce greater apoptosis in PCa cell lines that express androgen receptor (AR). In this study we utilized the AR negative PCa cell line and observed that re-expression of AR (PC3-AR) results in greater levels of apoptosis when treated with the pan-DACi, panobinostat (PAN). PAN mediated apoptosis in PC3 and PC3-AR cells was associated with increased levels of double strand DNA breaks, indicated by p-ɣH2AX. Further, PAN treatment in PC3-AR cells resulted in moderate attenuation of the ATM-Akt-ERK DNA damage response pathway. For this reason, we combined PAN with the dual PI3K-mTOR inhibitor, BEZ235. Combination of PAN with BEZ235 resulted in significant attenuation of the DNA damage repair protein ATM and significantly increased anti-tumor activity compared to each single treatment. Overall, superior anti-tumor activity with combination of PAN with BEZ235 was independent of AR status. These findings suggest that this therapeutic strategy should be further developed in clinical trials.

Epigenetic approaches for chemosensitization of refractory diffuse large B-cell lymphomas

Diffuse large B-cell lymphoma (DLBCL) is the most common form of non-Hodgkin lymphoma, with the greatest challenge for improving patient survival being the management of chemorefractory disease upon relapse. Epigenetic dysregulation has been correlated with more-aggressive malignancies and chemoresistance. In this issue of Cancer Discovery, Clozel and colleagues show the potential for low-dose DNA methyltransferase inhibitors as both a rational and an effective neoadjuvant approach for chemosensitization in DLBCL.

Synergistic anticancer activity of valproate combined with nicotinamide enhances anti-proliferation response and apoptosis in MIAPaca2 cells

Histone deacetylase is strongly associated with epigenetic regulation and carcinogenesis, and its inhibitors can induce cell cycle arrest and apoptosis of the cancer cells. In this study we aimed to examine the antiproliferative effects a combination of the valproate with nicotinamide in MIAPaca2 cell line. We revealed that valproate acted in a synergistic/additive with nicotinamide to inhibit the proliferation and induction of apoptosis in MIAPaca2 cancer cell line. MIAPaca2 was treated with various concentrations of valproate. The MTT assay and colony formation in soft agar indicated that valproate at 0.5 mM, when used alone weakly, suppressed proliferation of cells (37 ± 3.02%) whereas the combination treatment of valproate + nicotinamide significantly suppressed cell proliferation (58 ± 3.5%). The effect of nicotinamide at 25 mM on cell proliferation and cell colonization induced 50% apoptosis of MIAPaca2 cells. To identify the anti-proliferation and apoptotic effects of valproate and nicotinamide we performed flow cytometric and microscopic analyses. The results indicated significant apoptosis induction and nuclear morphological alterations greater than when valproate was used alone. Furthermore, western blot analyses was performed to study the role of acetyl-histone H3 levels, and quantitative RNA expression analyses were performed on expression of thrombospondin (TSP) and maspin genes in MIAPaca2. We found that the combination treatment of valproate + nicotinamide enhanced the expression of maspin and TSP genes and the biological response of the cell line was correlated with the increase of histone H3 acetylation after nicotinamide and valproate application. Together our findings indicate that valproate which act as inhibitor of cell proliferation and inducer of apoptosis in human cancer MIAPaca2 cells when used in combination with nicotinamide makes it a potentially good candidate for new anticancer drug development.

Therapeutic potential of histone deacetylase inhibitors in pancreatic cancer

Pancreatic cancer is a devastating disease with a dismal prognosis. Surgical resection is the only curative option but is heavily hampered by delayed diagnosis. Due to few therapeutic treatments available, novel and efficacious therapy is urgently needed. Histone deacetylase inhibitors (HDACIs) are emerging as a prominent class of therapeutic agents for pancreatic cancer and have exhibited significant anticancer potential with negligible toxicity in preclinical studies. Clinical evaluations of HDACIs are currently underway. HDACIs as monotherapy in solid tumors have proven less effective than hematological malignancies, the combination of HDACIs with other anticancer agents have been assessed for advanced pancreatic cancer. In this review, we describe the molecular mechanism underpin the anticancer effect of HDACIs in pancreatic cancer and summarize the recent advances in the rationale for the combination strategies incorporating HDACIs. In addition, we discuss the importance of identifying predictors of response to HDACI-based therapy.

The anti-tumor activity of E1A and its implications in cancer therapy

The adenovirus type 5 E1A protein (E1A) plays a critical role in anti-cancer gene therapy and has been tested in clinical trials. The expression of E1A significantly reduces tumorigenesis, promotes cell death, and inhibits cancer cell mobility. Chemosensitization is one of the anti-tumor effects of E1A, increasing in vitro and in vivo sensitization of anti-cancer drugs, including cisplatin, gemcitabine, etoposide, doxorubicin, paclitaxel, and tumor necrosis factor-related apoptosis-inducing ligand and histone deacetylase inhibitors in different types of cancer cells. E1A also demonstrates anti-metastasis activity through various molecular mechanisms such as the repression of protease expression, suppression of HER2/neu and downregulation of microRNA (miR-520h). Moreover, E1A has been reported to reprogram transcription in tumor cells and stabilize tumor suppressors such as PP2A/C, p21 and p53. Because E1A plays a potentially significant role in anti-tumor therapy, there exists an urgent need to study the anti-cancer activities of E1A. This paper presents a review of our current understanding of the tumor-suppressive functions and molecular regulation of E1A, as well as the potential clinical applications of E1A.

Activation of p53 by the MDM2 inhibitor RG7112 impairs thrombopoiesis

The tumor suppressor p53 is thought to play a role in megakaryocyte (MK) development. To assess the influence of the p53 regulatory pathway further, we studied the effect of RG7112, a small molecule MDM2 antagonist that activates p53 by preventing its interaction with MDM2, on normal megakaryocytopoiesis and platelet production. This drug has been previously been evaluated in clinical trials of cancer patients where thrombocytopenia was one of the major dose-limiting toxicities. In this study, we demonstrated that administration of RG7112 in vivo in rats and monkeys results in thrombocytopenia. In addition, we identified two distinct mechanisms by which RG7112-mediated activation of p53 affected human megakaryocytopoiesis and platelet production in vitro. RG7112 promoted apoptosis of MK progenitor cells, resulting in a reduction of their numbers and RG7112 affected mature MK by blocking DNA synthesis during endomitosis and impairing platelet production. Together, the disruption of these events provides an explanation for RG7112-induced thrombocytopenia and insight into the role of the p53-MDM2 auto-regulatory loop in normal megakaryocytopoiesis.

The enhanced apoptosis and antiproliferative response to combined treatment with valproate and nicotinamide in MCF-7 breast cancer cells

Acetylation of histone is a major player in epigenetic modifications, resulting in open chromatin structures and, hence, permissive conditions for transcription-factor recruitment to the promoters, followed by initiation of transcription. Histone deacetylase inhibitors arrest cancer cell growth and cause apoptosis with low toxicity thereby constituting a promising treatment for cancer. In this study, we examined the antiproliferative effects of valproate with a combination of nicotinamide in the MCF-7 cell line. MCF-7 was treated with various concentrations of valproate. The MTT assay showed that the viability of MCF-7 cells was inhibited and the cell activity was decreased. Viability percent of valproate and nicotinamide combined treatment cells (28 ± 2) was 1.78 times increased compared with the valproate-alone (0.5 mM) treated cells (50 ± 2). Colony formation in soft agar indicated that valproate at 0.3 mM, when used alone, weakly suppressed proliferation of cells (82 ± 3) and the combination treatment of valproate + nicotinamide strongly suppressed cell proliferation (51 ± 3). The flow cytometric and microscopic analyses of HDACI combined with treated cells indicated strong apoptosis induction and nuclear morphological alterations greater than those of valproate alone. Real-time reverse transcriptase-polymerase chain reaction (RT-PCR) analysis confirmed the efficiency of the HDAC inhibitor combination, revealing the effectively upregulated p16 and p21. Furthermore, to investigate the role of acetyl-histone H3 levels, western blot analyses have been performed and high levels of acetylated histone H3 were detected in valproate- and nicotinamide-treated cells. These results suggest that the combination treatment of valproate with nicotinamide exerts significant antitumor activity and could be a promising therapeutic candidate to treat human breast cancer.

The novel HDAC inhibitor NDACI054 sensitizes human cancer cells to radiotherapy

BACKGROUND AND PURPOSE

Inhibition of histone deacetylases (HDACs) has preclinically and clinically shown promise to overcome radio- and chemoresistance of tumor cells. NDACI054 is a novel HDAC inhibitor, which has been evaluated here for its effects on cell survival and radiosensitization of human tumor cell lines from different origins cultured under more physiological three-dimensional (3D), extracellular matrix (ECM)-based conditions.

MATERIAL AND METHODS

A549 lung, DLD-1 colorectal, MiaPaCa2 pancreatic and UT-SCC15 head and neck squamous cell carcinoma cells were treated with increasing NDACI054 concentrations (0-50 nM, 24 h) either alone or in combination with X-rays (single dose, 0-6 Gy). Subsequently, 3D clonogenic cell survival, HDAC activity, histone H3 acetylation, apoptosis, residual DNA damage (γH2AX/p53BP1 foci assay 24h post irradiation) and phosphorylation kinetics of Ataxia telangiectasia mutated (ATM), DNA-dependent protein kinase (DNA-PK), Caspase-3 and Poly(ADP-ribose)-Polymerase 1 (PARP 1) cleavage were analyzed.

RESULTS

NDACI054 potently decreased HDAC activity with concomitant increase in acetyl-histone H3 levels, mediated significant cytotoxicity and radiosensitization. These effects were accompanied by a significant increase of residual γH2AX/p53BP1-positive foci, slightly elevated levels of Caspase-3 and PARP 1 cleavage but no induction of apoptosis.

CONCLUSIONS

Our data show potent antisurvival and radiosensitizing effects of the novel HDAC inhibitor NDACI054 encouraging further preclinical examinations on this compound for future clinical use.

The anti-tumor effect of HDAC inhibition in a human pancreas cancer model is significantly improved by the simultaneous inhibition of cyclooxygenase 2

Pancreatic ductal adenocarcinoma is the fourth leading cause of cancer death worldwide, with no satisfactory treatment to date. In this study, we tested whether the combined inhibition of cyclooxygenase-2 (COX-2) and class I histone deacetylase (HDAC) may results in a better control of pancreatic ductal adenocarcinoma. The impact of the concomitant HDAC and COX-2 inhibition on cell growth, apoptosis and cell cycle was assessed first in vitro on human pancreas BxPC-3, PANC-1 or CFPAC-1 cells treated with chemical inhibitors (SAHA, MS-275 and celecoxib) or HDAC1/2/3/7 siRNA. To test the potential antitumoral activity of this combination in vivo, we have developed and characterized, a refined chick chorioallantoic membrane tumor model that histologically and proteomically mimics human pancreatic ductal adenocarcinoma. The combination of HDAC1/3 and COX-2 inhibition significantly impaired proliferation of BxPC-3 cells in vitro and stalled entirely the BxPC-3 cells tumor growth onto the chorioallantoic membrane in vivo. The combination was more effective than either drug used alone. Consistently, we showed that both HDAC1 and HDAC3 inhibition induced the expression of COX-2 via the NF-kB pathway. Our data demonstrate, for the first time in a Pancreatic Ductal Adenocarcinoma (PDAC) model, a significant action of HDAC and COX-2 inhibitors on cancer cell growth, which sets the basis for the development of potentially effective new combinatory therapies for pancreatic ductal adenocarcinoma patients.

Combining histone deacetylase inhibitors with MDA-7/IL-24 enhances killing of renal carcinoma cells

In the present study we show that histone deacetylase inhibitors (HDACIs) enhance the anti-tumor effects of melanoma differentiation associated gene-7/interleukin 24 (mda-7/IL-24) in human renal carcinoma cells. Similar data were obtained in other GU tumor cells. Combination of these two agents resulted in increased autophagy that was dependent on expression of ceramide synthase 6, with HDACIs enhancing MDA-7/IL-24 toxicity by increasing generation of ROS and Ca²⁺. Knock down of CD95 protected cells from HDACI and MDA-7/IL-24 lethality. Sorafenib treatment further enhanced (HDACI + MDA-7/IL-24) lethality. Anoikis resistant renal carcinoma cells were more sensitive to MDA-7/IL-24 that correlated with elevated SRC activity and tyrosine phosphorylation of CD95. We employed a recently constructed serotype 5/3 adenovirus, which is more effective than a serotype 5 virus in delivering mda-7/IL-24 to renal carcinoma cells and which conditionally replicates (CR) in tumor cells expressing MDA-7/IL-24 by virtue of placing the adenoviral E1A gene under the control of the cancer-specific promoter progression elevated gene-3 (Ad.5/3-PEG-E1A-mda-7; CRAd.5/3-mda-7, Ad.5/3-CTV), to define efficacy in renal carcinoma cells. Ad.5/3-CTV decreased the growth of renal carcinoma tumors to a significantly greater extent than did a non-replicative virus Ad.5/3-mda-7. In contralateral uninfected renal carcinoma tumors Ad.5/3-CTV also decreased the growth of tumors to a greater extent than did Ad.5/3-mda-7. In summation, our data demonstrates that HDACIs enhance MDA-7/IL-24-mediated toxicity and tumor specific adenoviral delivery and viral replication of mda-7/IL-24 is an effective pre-clinical renal carcinoma therapeutic.

The in vitro apoptotic effects of A248 and A1659, newly synthetic histone deacetylase inhibitors in oral cancer cells

OBJECTIVES

Histone deacetylase (HDAC) inhibitors represent potential therapeutic agents against various cancers. In this study, we attempt to identify whether newly synthesized HDAC inhibitors, A248 and A1659, can be effective anti-cancer drug candidates for oral cancer.

MATERIALS AND METHODS

The anti-cancer activities of A248 and A1659 in MC-3 and HN22 human oral cancer cells were evaluated by 3-(4,5-dimethylthiazol-20yl)-(3-carboxymethoxyphenyl)-2-(4-sulphophenyl)-2H-tetrazolium (MTS) assay, 4'-6-diamidino-2-phenylindole (DAPI) staining, Western blot analysis, immunocytochemistry, and small interference RNA (siRNA) technology.

RESULTS

A248 and A1659 enhanced histone acetylation and decreased the viability of MC-3 and HN22 cells. A248 and A1659 also induced apoptosis, as evidenced by altered nuclear features and poly(ADP-ribose)polymerase (PARP) cleavage. A248 and A1659 markedly decreased Sp1 expression in a concentration- or time-dependent manner and blocked nuclear translocation of Sp1 protein from the cytosol, which contributed to an increase in p27 expression and a decrease in cyclin D1 expression. Furthermore, the knockdown of Sp1 protein with siRNA caused marked alteration of p27 and cyclin D1 expression to induce apoptosis. The most popular HDAC inhibitor, trichostatin A (TSA) also induced apoptosis and reduced the expression level of Sp1 protein.

CONCLUSION

These results suggest that A248 and A1659, two new HDAC inhibitors, may be attractive therapeutic drug candidates for targeting Sp1 in human oral cancer cells.

Belinostat and panobinostat (HDACI): in vitro and in vivo studies in thyroid cancer

Purpose

Advanced thyroid cancer responds poorly to most therapies. New therapies and combinations are needed. The aim of this study was to examine both in vitro and in vivo activity of two relatively new histone deacetylase inhibitors (HDACIs), belinostat and panobinostat, and a variety of tyrosine kinase inhibitors (TKIs) against a panel of nine human thyroid cancer cell lines.

Methods

The anti-proliferative activity and the effects of HDACIs, TKIs and their combinations on thyroid cancer cells were determined by cytotoxicity assays, microarray and immunoblot analyses. Synergism between HDACIs and TKIs was assessed by the median effects model of Chou-Talalay (Calcusyn^®).

Results

Belinostat and panobinostat were active against the thyroid cancer cell lines irrespective of their mutational composition, and belinostat was effective in preventing growth of human thyroid cancer xenografts in immunodeficient mice. Further studies showed that both HDACIs induced apoptosis. HDACI also elevated acetylated histone 3, p21^Waf, and PARP, and decreased levels of phosphorylated ERK and AKT (Ser473). RNA assay analysis suggested both HDACIs modulated genes associated with the cell cycle, DNA damage and apoptosis. Most of the TKI (pazopanib, motesanib, sorafenib and dasatinib) were either inactive in vitro or were active only at high doses. However, the novel combinations of either pazopanib or dasatinib TKIs with either belinostat or panobinostat synergistically inhibited cell growth of thyroid cancer cells in vitro.

Conclusions

In summary, these HDACIs either alone or combined with selected TKIs may have a role in treatment of aggressive thyroid cancer.

Electronic supplementary material

The online version of this article (doi:10.1007/s00432-013-1465-6) contains supplementary material, which is available to authorized users.

Histone deacetylase inhibitors interact with melanoma differentiation associated-7/interleukin-24 to kill primary human glioblastoma cells

We presently demonstrate that histone deacetylase inhibitors (HDACIs) enhance toxicity of melanoma differentiation-associated gene-7/interleukin 24 (mda-7/IL-24) in invasive primary human glioblastoma multiforme (GBM) cells. Additionally, a method is described to augment the efficacy of adenoviral delivery of mda-7/IL-24 in these cells. HDACIs synergized with melanoma differentiation-associated (MDA)-7/IL-24 killing GBM cells. Enhanced lethality correlated with increased autophagy that was dependent on the expression of ceramide synthase 6. HDACIs interacted with MDA-7/IL-24 prolonging generation of reactive oxygen species and Ca(2+). Quenching of reactive oxygen species and Ca(2+) blocked HDACI and MDA-7/IL-24 killing. In vivo MDA-7/IL-24 prolonged the survival of animals carrying orthotopic tumors, and HDACIs enhanced survival further. A serotype 5/3 adenovirus more effectively delivers mda-7/IL-24 to GBM tumors than a serotype 5 virus. Hence, we constructed a serotype 5/3 adenovirus that conditionally replicates in tumor cells expressing MDA-7/IL-24, in which the adenoviral early region 1A (E1A) gene was driven by the cancer-specific promoter progression elevated gene-3 [Ad.5/3 (INGN 241)-PEG-E1A-mda-7; also called Ad.5/3-CTV (cancer terminator virus)]. Ad.5/3-CTV increased the survival of mice carrying GBM tumors to a significantly greater extent than did a nonreplicative virus Ad.5/3-mda-7. Ad.5/3-CTV exhibited no toxicity in the brains of Syrian hamsters. Collectively our data demonstrate that HDACIs enhance MDA-7/IL-24 lethality, and adenoviral delivery of mda-7/IL-24 combined with tumor-specific viral replication is an effective preclinical GBM therapeutic.

Trichostatin A induces apoptotic cell death of HeLa cells in a Bcl-2 and oxidative stress-dependent manner

Trichostatin A (TSA) as a HDAC inhibitor can regulate many biological properties including apoptosis and cell proliferation in various cancer cells. Here, we evaluated the effect of TSA on the growth and death of HeLa cervical cancer cells in relation to reactive oxygen species (ROS) and glutathione (GSH) levels. Dose- and time-dependent growth inhibition was observed in HeLa cells with an IC50 of approximately 20 nM at 72 h. This agent also induced apoptotic cell death, as evidenced by annexin V-FITC staining cells, caspase-3 activation and the loss of mitochondrial membrane potential (MMP; ∆ψm). In addition, the administration of Bcl-2 siRNA intensified TSA-induced HeLa cell death. All of the tested caspase inhibitors significantly rescued some cells from TSA-induced HeLa cell death. TSA increased O2•- level and induced GSH depletion in HeLa cells. Caspase inhibitors significantly attenuated O2•- level and GSH depletion in TSA-treated HeLa cells. In addition, N-acetyl cysteine (NAC; a well known antioxidant) significantly prevented cell death and GSH depletion in TSA-treated HeLa cells via decreasing O2•- level. In conclusion, TSA inhibited the growth of HeLa cells via Bcl-2-mediated apoptosis, which was closely related to O2•- and GSH content levels.

Vorinostat, an HDAC inhibitor attenuates epidermoid squamous cell carcinoma growth by dampening mTOR signaling pathway in a human xenograft murine model

Histone deacetylase (HDAC) inhibitors are potent anticancer agents and show efficacy against various human neoplasms. Vorinostat is a potent HDAC inhibitor and has shown potential to inhibit growth of human xenograft tumors. However, its effect on the growth of skin neoplasm remains undefined. In this study, we show that vorinostat (2 μM) reduced expression of HDAC1, 2, 3, and 7 in epidermoid carcinoma A431 cells. Consistently, it increased acetylation of histone H3 and p53. Vorinostat (100mg/kg body weight, IP) treatment reduced human xenograft tumor growth in highly immunosuppressed nu/nu mice. Histologically, the vorinostat-treated tumor showed features of well-differentiation with large necrotic areas. Based on proliferating cell nuclear antigen (PCNA) staining and expression of cyclins D1, D2, E, and A, vorinostat seems to impair proliferation by down-regulating the expression of these proteins. However, it also induced apoptosis. The mechanism by which vorinostat blocks proliferation and makes tumor cells prone to apoptosis, involved inhibition of mTOR signaling which was accompanied by reduction in cell survival AKT and extracellular-signal regulated kinase (ERK) signaling pathways. Our data provide a novel mechanism-based therapeutic intervention for cutaneous squamous cell carcinoma (SCC). Vorinostat may be utilized to cure skin neoplasms in organ transplant recipient (OTR). These patients have high morbidity and surgical removal of these lesions which frequently develop in these patients, is difficult.

Early prediction of response to Vorinostat in an orthotopic rat glioma model

Glioblastoma is the most common primary brain tumor and is uniformly fatal despite aggressive surgical and adjuvant therapy. As survival is short, it is critical to determine the value of therapy early on in treatment. Improved early predictive assessment would allow neuro-oncologists to personalize and adjust or change treatment sooner to maximize the use of efficacious therapy. During carcinogenesis, tumor suppressor genes can be silenced by aberrant histone deacetylation. This epigenetic modification has become an important target for tumor therapy. Suberoylanilide hydroxamic acid (SAHA, Vorinostat, Zolinza) is an orally active, potent inhibitor of histone deacetylase (HDAC) activity. A major shortcoming of the use of HDAC inhibitors in the treatment of patients with brain tumors is the lack of reliable biomarkers to predict and determine response. Histological evaluation may reflect tumor viability following treatment, but is an invasive procedure and impractical for glioblastoma. Another problem is that response to SAHA therapy is associated with tumor redifferentiation and cytostasis rather than tumor size reduction, thus limiting the use of traditional imaging methods. A noninvasive method to assess drug delivery and efficacy is needed. Here, we investigated whether changes in (1)H MRS metabolites could render reliable biomarkers for an early response to SAHA treatment in an orthotopic animal model for glioma. Untreated tumors exhibited significantly elevated alanine and lactate levels and reduced inositol, N-acetylaspartate and creatine levels, typical changes reported in glioblastoma relative to normal brain tissues. The (1)H MRS-detectable metabolites of SAHA-treated tumors were restored to those of normal-like brain tissues. In addition, reduced inositol and N-acetylaspartate were found to be potential biomarkers for mood alteration and depression, which may also be alleviated with SAHA treatment. Our study suggests that (1)H MRS can provide reliable metabolic biomarkers at the earliest stage of SAHA treatment to predict the therapeutic response.

Synergistic induction of apoptosis and chemosensitization of human colorectal cancer cells by histone deacetylase inhibitor, scriptaid, and proteasome inhibitors: potential mechanisms of action

Histone deacetylase inhibitors (HDACIs) exhibit modest results as single agents in preclinical and clinical studies against solid tumors; they often fall short and activate nuclear factor kappa-B (NFκB). Co-administration of HDACI with proteasome inhibitors (PIs), which interrupt NFκB pathways, may enhance HDACI-lethality. The goal of this study was to determine whether PIs could potentiate HDACI, scriptaid (SCP)-mediated lethality, to unravel the associated mechanisms and to assess the effects of the combined inhibition of HDAC and proteasome on chemotherapy response in human colorectal cancer cells. Cancer cells were exposed to agents alone or in combination; cell growth inhibition was determined by MTT and colony formation assays. HDAC-, proteasome-, NFκB-activities, and reactive oxygen species (ROS) were quantified. Induction of apoptosis and cell cycle alterations were monitored by flow cytometry. Expression of cell cycle/apoptosis and cytoprotective/stress-related genes was determined by real-time qRT-PCR and EIA, respectively. Potentiation of cancer cell sensitivity to chemotherapies by SCP/PIs was also evaluated. SCP and PIs: MG132, PI-1, or epoxomicin interact synergistically to potently inhibit cancer cell growth, alter cell cycle, induce apoptosis, reduce NFκB activity, and increase ROS generation. These events are associated with multiple perturbations in the expression of cell cycle, apoptosis, cytoprotective, and stress-related genes. Co-administration of SCP and PIs strikingly increases the chemosensitivity of cancer cells (122-2 × 10(5)-fold) in a drug and SCP/PIs-dependent manner. This combination regimen markedly reduced the doses of chemotherapies with potent anticancer effects and less toxicity. A strategy combining HDAC/proteasome inhibition with chemotherapies warrants further investigation in colorectal cancer.

HDAC inhibitors for the treatment of cutaneous T-cell lymphomas

Epigenetic modification by small-molecule histone deacetylase inhibitors (HDAC-Is) has been a promising new antineoplastic approach for various solid and hematological malignancies, particularly for cutaneous T-cell lymphoma (CTCL). Vorinostat, a pan-HDAC-I and, most recently, romidepsin, a bicyclic pan-HDAC-I, have been US FDA approved for treatment of relapsed or refractory CTCL. However, because many patients do not reach the 50% partial response mark and response is not always sustainable, overcoming HDAC-I resistance by adding other agents or finding more selective molecules is an important clinical problem in realizing the full clinical potential of HDAC-Is. In this review, we discuss the molecular basis for HDAC-I function in cancer, the clinical response and side-effect profile experienced by CTCL patients, and the progress made in attempting to identify biomarkers of response and resistance, as well as synergistic combination therapies.

Molecular pathways: old drugs define new pathways: non-histone acetylation at the crossroads of the DNA damage response and autophagy

Histone deacetylases (HDAC) modulate acetylation and the function of histone and non-histone proteins. HDAC inhibitors have been developed to block the aberrant action of HDACs in cancer, and several are in clinical use (vorinostat, romidepsin, and valproic acid). Detailed understanding of their action is lacking, however, and their clinical activity is limited in most cases. Recently, HDACs have been involved in the control of the DNA damage response (DDR) at several levels and in directly regulating the acetylation of a number of DDR proteins (including CtIP and Exo1). Mechanistically, acetylation leads to the degradation of double-strand break repair enzymes through autophagy, providing a novel, direct link between DDR and autophagy. These observations, obtained in yeast cells, should now be translated to mammalian model systems and cancer cells to reveal whether this acetylation link is maintained in mammals, and if and how it is deregulated in cancer. In addition to HDACs, DDR and autophagy have been addressed pharmacologically, suggesting that the acetylation link, if involved in cancer, can be exploited for the design of new anticancer treatments.

DNMT inhibitors and HDAC inhibitors regulate E-cadherin and Bcl-2 expression in endometrial carcinoma in vitro and in vivo

BACKGROUND

The effect of histone deacetylase inhibitors (HDACIs) and DNA methyltransferase inhibitors (DNMTIs) on proliferation of endometrial cancer (EC) cells in vitro and in vivo was investigated.

METHODS

Changes in methylation of the CDH1 promoter in HDACI- and DNMTI-treated HEC-1-B and RL-952 EC cells were detected. Nude mice with xenografted implants of human EC HEC-1-B cells were treated with valproic acid (VPA) and decitabine (DAC) and evaluated for tumor growth, CDH1 and Bcl-2 mRNA levels.

RESULTS

DAC, VPA and suberoylanilide hydroxamic acid (SAHA) inhibited proliferation, induced cell cycle arrest and enhanced the apoptotic index in both cell lines, DAC, VPA and SAHA upregulated E-cadherin mRNA and protein levels and downregulated Bcl-2 mRNA levels in vitro. DAC and VPA inhibited tumor growth, upregulated CDH1 mRNA and downregulated Bcl-2 mRNA levels in vivo.

CONCLUSIONS

A combination of HDACIs and DNMTIs suppresses the growth of EC, which is likely mediated by upregulation of E-cadherin and downregulation of Bcl-2.

Trichostatin A reduced phospholipase C gamma-1 transcript and protein contents in MCF-7 breast cancer cells

It has recently been demonstrated that phospholipase C gamma-1 (PLCγ1) activation may contribute to breast carcinoma cell motility and their metastasis. Employing MCF-7 breast cancer cells, we showed the effect of trichostatin A (TSA) on the cellular contents of the PLCγ1 molecule. Using reverse transcription, real-time quantitative PCR and western blot analysis, we demonstrated that TSA reduced the PLCγ1 transcript and protein levels in MCF-7 cells. We also found that TSA decreased the half-life of the PLCγ1 transcript from approximately 7hours to 5hours. Moreover, we observed that protein synthesis appears to be essential in the TSA reduction of PLCγ1 mRNA stability. Since PLCγ1 activation is considered a key factor in the initiation of events that increase malignant cell motility, our observations may support the validity of TSA in anticancer studies.

Emerging therapeutic targets for soft tissue sarcoma

Soft tissue sarcomas (STS) are malignancies of mesenchymal origin that represent approximately 1% of cancers in adults. Systematic research into the treatment of STS is challenging given its rarity and disease heterogeneity. Despite the ability to histologically subtype STS, only recently has our approach to therapy begun to differentiate along these lines. The purpose of this review is to highlight emerging therapeutic targets and therapies that hold the potential to add to the current state of systemic treatment for STS.

Combined histone deacetylase and cyclooxygenase inhibition achieves enhanced antiangiogenic effects in lung cancer cells

Prostaglandin E2 (PGE2) is an important pro-angiogenic and pro-proliferative cytokine and the key enzymes modulating its levels, cyclooxygenase (COX)-2 and 15-hydroxyprostaglandin dehydrogenase (15-PGDH) play important opposing roles in carcinogenesis. Previously we found loss of 15-PGDH expression in lung cancer and its reactivation leads to strong in vivo tumor-suppressive effect via an antiangiogenic mechanism. Here, we find that HDAC inhibitors (HDACI), such as trichostatin A (TSA) and vorinostat could reactivate 15-PGDH expression but overall induce PGE2 generation and this is the result of concomitant induction of COX-1 and -2 leading to functional promotion of endothelial cell proliferation and capillary formation. Direct TSA treatment inhibits endothelial cell proliferation and capillary formation in our study in line with prior reports as HDACIs have been shown to directly inhibit angiogenesis. The elevation of PGE2 levels induced by HDACI is potently neutralized by indomethacin (INN) or Celecoxib co-treatment and accordingly, angiogenesis is more effectively inhibited when using conditioned medium of co-treatment than either alone confirming that this effect is mediated via the PGE2 axis. Accordingly, blockage of EP2/4 receptors mitigates the stimulation of angiogenesis by excessive PGE2 generation mediated by TSA. In this study, we identify a potentially adverse effect of HDACIs through induction of both 15-PGDH and COX-2 leading to elevated PGE2 levels and thereby stimulation of angiogenesis. Co-treatment of TSA and INN shows more potent anti-angiogenic effects by inducing 15-PGDH and inhibiting COX-2. Overall, our results suggest that combined HDACI and COX inhibition should be explored clinically to achieve more meaningful benefits from HDACI therapy in lung cancer.

Epigenetic modifications: novel therapeutic strategies for systemic sclerosis?

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

Concurrent HDAC and mTORC1 inhibition attenuate androgen receptor and hypoxia signaling associated with alterations in microRNA expression

Specific inhibitors towards Histone Deacetylases (HDACs) and Mammalian Target of Rapamycin Complex 1 (mTORC1) have been developed and demonstrate potential as treatments for patients with advanced and/or metastatic and castrate resistant prostate cancer (PCa). Further, deregulation of HDAC expression and mTORC1 activity are documented in PCa and provide rational targets to create new therapeutic strategies to treat PCa. Here we report the use of the c-Myc adenocarcinoma cell line from the c-Myc transgenic mouse with prostate cancer to evaluate the in vitro and in vivo anti-tumor activity of the combination of the HDAC inhibitor panobinostat with the mTORC1 inhibitor everolimus. Panobinostat/everolimus combination treatment resulted in significantly greater antitumor activity in mice bearing androgen sensitive Myc-CaP and castrate resistant Myc-CaP tumors compared to single treatments. We identified that panobinostat/everolimus combination resulted in enhanced anti-tumor activity mediated by decreased tumor growth concurrent with augmentation of p21 and p27 expression and the attenuation of angiogenesis and tumor proliferation via androgen receptor, c-Myc and HIF-1α signaling. Also, we observed altered expression of microRNAs associated with these three transcription factors. Overall, our results demonstrate that low dose concurrent panobinostat/everolimus combination therapy is well tolerated and results in greater anti-tumor activity compared to single treatments in tumor bearing immuno-competent mice. Finally, our results suggest that response of selected miRs could be utilized to monitor panobinostat/everolimus in vivo activity.

Autophagic and apoptotic effects of HDAC inhibitors on cancer cells

Because epigenetic alterations are believed to be involved in the repression of tumor suppressor genes and the promotion of tumorigenesis in cancers, novel compounds endowed with histone deacetylase (HDAC) inhibitory activity are an attractive therapeutic approach. Indeed, the potential of HDAC inhibitors for cancer therapy has been explored in preclinical models, and some agents approved for hematologic malignancies have reached the clinical setting. HDAC inhibitors are able to mediate the induction of both apoptosis and autophagy, which are related to anticancer activity in a variety of cancer cell lines. Given the inherent resistance to apoptosis that characterizes cancer, the targeting of alternative pathways is an attractive strategy to improve anti-tumor therapy. The activation of autophagy represents novel cancer treatment targets. This paper aims to critically discuss how the anticancer potential of HDAC inhibitors may elicit a response to human cancers through different cell pathways leading to cell death.