Design, synthesis, docking, and biological evaluation of novel diazide-containing isoxazole- and pyrazole-based histone deacetylase probes

The design, synthesis, docking, and biological evaluation of novel potent HDAC3 and HDAC8 isoxazole- and pyrazole-based diazide probes suitable for binding ensemble profiling with photoaffinity labeling (BEProFL) experiments in cells is described. Both the isoxazole- and pyrazole-based probes exhibit low nanomolar inhibitory activity against HDAC3 and HDAC8, respectively. The pyrazole-based probe 3f appears to be one of the most active HDAC8 inhibitors reported in the literature with an IC(50) of 17 nM. Our docking studies suggest that unlike the isoxazole-based ligands the pyrazole-based ligands are flexible enough to occupy the second binding site of HDAC8. Probes/inhibitors 2b, 3a, 3c, and 3f exerted the antiproliferative and neuroprotective activities at micromolar concentrations through inhibition of nuclear HDACs, indicating that they are cell permeable and the presence of an azide or a diazide group does not interfere with the neuroprotection properties, or enhance cellular cytotoxicity, or affect cell permeability.

Vorinostat modulates cell cycle regulatory proteins in glioma cells and human glioma slice cultures

Chromatin modification through histone deacetylase inhibition has shown evidence of activity against malignancies. The mechanism of action of such agents are pleiotropic and potentially tumor specific. In this study, we studied the mechanisms of vorinostat-induced cellular effects in gliomas. The effects of vorinostat on proliferation, induction of apoptosis and cell cycle effects were studied in vitro (D54, U87 and U373 glioma cell lines). To gain additional insights into its effects on human gliomas, vorinostat-induced changes were examined ex vivo using a novel organotypic human glioma slice model. Vorinostat treatment resulted in increased p21 levels in all glioma cells tested in a p53 independent manner. In addition, cyclin B1 levels were transcriptionally downregulated and resulted in reduced kinase activity of the cyclin B1/cdk1 complex causing a G2 arrest. These effects were associated with a dose- and time-dependent inhibition of cellular proliferation and anchorage-independent growth in association with hyperacetylation of core histones and induction of apoptosis. Of particular significance, we demonstrate histone hyperacetylation and increased p21 levels in freshly resected human glioma specimens maintained as organotypic slice cultures and exposed to vorinostat similar to cell lines suggesting that human glioma can be targeted by this agent. Our data suggest that the effects of vorinostat are associated with modulation of cell cycle related proteins and activation of a G2 checkpoint along with induction of apoptosis. These effects are mediated by both transcriptional and post-translational mechanisms which provide potential options that can be exploited to develop new therapeutic approaches against gliomas.

Parthenolide sensitizes hepatocellular carcinoma cells to TRAIL by inducing the expression of death receptors through inhibition of STAT3 activation

This article shows that HepG2, Hep3B, and SK-Hep1 cells, three lines of human hepatocellular carcinoma (HCC) cells, are resistant to apoptosis induced by tumor necrosis factor-related apoptosis-inducing ligand (TRAIL). Parthenolide, a sesquiterpene lactone found in European feverfew, has been shown to exert both anti-inflammatory and anti-cancer activities. This article demonstrates that co-treatment with parthenolide and TRAIL-induced apoptosis with synergistic interactions in the three lines of HCC cells. In order to explain these effects we ascertained that parthenolide increased either at protein or mRNA level the total content of death receptors TRAIL-R1 and -R2 as well as their surface expression. These effects were found in the three cell lines in the case of TRAIL-R2, while for TRAIL-R1 they were observed in HepG2 and SK-Hep1 cells, but not in Hep3B cells. We suggest that the effects of parthenolide on death receptors depend on the decrease in the level of phosphorylated and active forms of STAT proteins, an event which could be a consequence of the inhibitory effect exerted by parthenolide on the activation of JAK proteins. In agreement with this hypothesis treatment with STAT3 siRNA increased in HCC cells the effect of parthenolide on the expression of death receptors. Sensitization by parthenolide to TRAIL stimulated in the three cell lines the extrinsic mechanism of apoptosis with the activation of both caspases 8 and 3, whereas mitochondria were not involved in the process. Our results suggest that co-treatment with parthenolide and TRAIL could represent a new important therapeutic strategy for hepatic tumors.

Myelodysplastic syndrome and histone deacetylase inhibitors: “to be or not to be acetylated”. J Biomed Biotechnol. 2011;2011:214143. [PMID: 21629744 PMCID: PMC3100562 DOI: 10.1155/2011/214143]

Myelodysplastic syndrome (MDS) represents a heterogeneous group of diseases with clonal proliferation, bone marrow failure and increasing risk of transformation into an acute myeloid leukaemia. Structured guidelines are developed for selective therapy based on prognostic subgroups, age, and performance status. Although many driving forces of disease phenotype and biology are described, the complete and possibly interacting pathogenetic pathways still remain unclear. Epigenetic investigations of cancer and haematologic diseases like MDS give new insights into the pathogenesis of this complex disease. Modifications of DNA or histones via methylation or acetylation lead to gene silencing and altered physiology relevant for MDS. First clinical trials give evidence that patients with MDS could benefit from epigenetic treatment with, for example, DNA methyl transferase inhibitors (DNMTi) or histone deacetylase inhibitors (HDACi). Nevertheless, many issues of HDACi remain incompletely understood and pose clinical and translational challenges. In this paper, major aspects of MDS, MDS-associated epigenetics and the potential use of HDACi are discussed.

Mocetinostat (MGCD0103): a review of an isotype-specific histone deacetylase inhibitor

INTRODUCTION

HDAC inhibitors (HDACIs) have the potential to restore gene expression and display antitumor effects in vitro. As single agents, HDACIs have clinical activity in lymphoma. In myeloid leukemias, combinations of DNA methylation inhibitors and HDACIs are promising. Other combinations are being studied in solid tumors.

AREAS COVERED

This article covers basic information and an update on preclinical and clinical experience with the oral isotype-selective HDACI MGCD0103 (mocetinostat) in hematological malignancies and solid tumors. It also examines data concerning MGCD0103 from recent conferences and articles through to November 2010, including new data regarding responses in lymphoma and toxicities.

EXPERT OPINION

MGCD0103 is well-tolerated and exhibits favorable pharmacokinetic and pharmacodynamic profiles, demonstrating target inhibition and clinical responses. It induces cell death and autophagy, synergizes with proteasomal inhibitors and affects non-histone targets, such as microtubules. In 2008, new patient enrollment in trials was temporarily suspended due to potential cardiac complications. This restriction was lifted in 2009 as no correlation between MGCD0103 exposure and pericardial effusions was found. New patient enrollment in MGCD0103 clinical trials requires the exclusion of patients diagnosed with significant cardiac abnormalities prior to enrollment. Clinical and pharmacodynamic data support a three-times-weekly administration at a 90 mg fixed dose. MGCD0103 displays promising antitumor activity in several hematological diseases.

Combination of vorinostat and adenovirus-TRAIL exhibits a synergistic antitumor effect by increasing transduction and transcription of TRAIL in lung cancer cells

Soluble TRAIL and adenovirus (ad)-TRAIL exhibit a strong antitumor effect by inducing apoptosis. Vorinostat is the histone deacetylase (HDAC) inhibitor that induces cell death in cancer cell lines and regulates the expression of epigenetically silenced genes, such as Coxackie adenoviral receptor (CAR), the receptor for adenoviral entry. We propose a new strategy in which vorinostat will induce high expression of ad-TRAIL and a strong antitumor response, and investigated the mechanism involved. The effect of vorinostat on transcription and expression of TRAIL from ad-TRAIL-transduced lung cancer cells were confirmed by reverse transciption-PCR (RT-PCR), quantitative real time-PCR and western blot assay. Anti-tumor effects were measured after cotreatment of vorinostat and ad-TRAIL, and the drug interactions were analyzed. After combined treatment of vorinostat and ad-TRAIL, apoptosis and western blot assays for Akt, Bcl-2 and caspase were performed. Vorinostat increased the expression of CAR in lung cancer cell lines and increased the expression of luciferase (luc) from ad-luc-transduced cells and TRAIL from ad-TRAIL-transduced cells. RT-PCR and quantitative real time-PCR, after sequential vorinostat treatment, revealed that vorinostat may enhance TRAIL expression from ad-TRAIL by increasing transduction through enhanced CAR expression and increasing adenoviral transgene transcription. Combined vorinostat and ad-TRAIL treatment showed the synergistic anti-tumor effect in lung cancer cell lines. Combined vorinostat and ad-TRAIL induced stronger apoptosis induction, suppression of NF-κB activation and breakdown of the anti-apoptotic molecule Bcl-2. In conclusion, the vorinostat synergistically enhanced the anti-tumor effect of ad-TRAIL by (1) increasing adenoviral transduction through the increased expression of CAR and (2) increasing adenoviral transgene (TRAIL) transcription in lung cancer cell lines.

The synthesis and evaluation of N1-(4-(2-[18F]-fluoroethyl)phenyl)-N8-hydroxyoctanediamide ([18F]-FESAHA), a PET radiotracer designed for the delineation of histone deacetylase expression in cancer

INTRODUCTION

Given the significant utility of suberoylanilide hydroxamic acid (SAHA) in chemotherapeutic protocols, a PET tracer that mimics the histone deacetylase (HDAC) inhibition of SAHA could be a valuable tool in the diagnosis, treatment planning and treatment monitoring of cancer. Here, we describe the synthesis, characterization and evaluation of N(1)-(4-(2-[(18)F]-fluoroethyl)phenyl)-N(8)-hydroxyoctanediamide ([(18)F]-FESAHA), a PET tracer designed for the delineation of HDAC expression in cancer.

METHODS

FESAHA was synthesized and biologically characterized in vivo and in vitro. [(18)F]-FESAHA was then synthesized in high radiochemical purity, and the logP and serum stability of the radiotracer were determined. In vitro cellular uptake experiments and acute biodistribution and small-animal PET studies were performed with [(18)F]-FESAHA in mice bearing LNCaP xenografts.

RESULTS

[(18)F]-FESAHA was synthesized in high radiochemical purity via an innovative one-pot procedure. Enzymatic inhibition assays illustrated that FESAHA is a potent HDAC inhibitor, with IC(50) values from 3 nM to 1.7 μM against the 11 HDAC subtypes. Cell proliferation experiments revealed that the cytostatic properties of FESAHA very closely resemble those of SAHA in both LNCaP cells and PC-3 cells. Acute biodistribution and PET imaging experiments revealed tumor uptake of [(18)F]-FESAHA and substantially higher values in the small intestine, kidneys, liver and bone.

CONCLUSION

The significant non-tumor background uptake of [(18)F]-FESAHA presents a substantial obstacle to the use of the radiotracer as an HDAC expression imaging agent. The study at hand, however, does present a number of lessons critical to both the synthesis of hydroxamic acid containing PET radiotracers and imaging agents aimed at delineating HDAC expression.

Histone deacetylase inhibitors as therapeutic agents for acute central nervous system injuries

Histone deacetylase (HDAC) inhibitors are emerging as a novel class of potentially therapeutic agents for treating acute injuries of the central nervous system (CNS). In this review, we summarize data regarding the effects of HDAC inhibitor administration in models of acute CNS injury and discuss issues warranting clinical trials. We have previously shown that the pan-HDAC inhibitor ITF2357, a compound shown to be safe and effective in humans, improves functional recovery and attenuates tissue damage when administered as late as 24 h after injury. Using a well-characterized, clinically relevant mouse model of closed head injury, we demonstrated that a single dose of ITF2357 administered 24 h after injury improves neurobehavioral recovery and reduces tissue damage. ITF2357-induced functional improvement was found to be sustained up to 14 d after trauma and was associated with augmented histone acetylation. Single postinjury administration of ITF2357 also attenuated injury-induced inflammatory responses, as indicated by reduced glial accumulation and activation as well as enhanced caspase-3 expression within microglia/macrophages after treatment. Because no specific therapeutic intervention is currently available for treating brain trauma patients, the ability to affect functional outcome by postinjury administration of HDAC inhibitors within a clinically feasible timeframe may be of great importance. Furthermore, a growing body of evidence indicates that HDAC inhibitors are beneficial for treating various forms of acute CNS injury including ischemic and hemorrhagic stroke. Because HDAC inhibitors are currently approved for other use, they represent a promising new avenue of treatment, and their use in the setting of CNS injury warrants clinical evaluation.

Cell death and hepatocarcinogenesis: Dysregulation of apoptosis signaling pathways

Hepatocellular carcinoma (HCC) remains a disease with a poor prognosis despite recent advances in the pathophysiology and treatment. Although the disease is biologically heterogeneous, dysregulation of cellular proliferation and apoptosis both occur frequently and contribute to the malignant phenotype. Chronic liver disease is associated with intrahepatic inflammation which promotes dysregulation of cellular signaling pathways; this triggers proliferation and thus lays the ground for expansion of premalignant cells. Cancer emerges when immunological control fails and transformed cells develop resistance against cell death signaling pathways. The same mechanisms underlie the poor responsiveness of HCC towards chemotherapy. Only recently advances in understanding the signaling pathways involved has led to the development of an effective pharmacological therapy for advanced disease. The current review will discuss apoptosis signaling pathways and focus on apoptosis resistance of HCC involving derangements in cell death receptors (e.g. tumor necrosis factor-alpha [TNF], CD95/Apo-1, TNF-related apoptosis-inducing ligand [TRAIL]) and associated adapter molecules (e.g. FADD and FLIP) of apoptotic signaling pathways. In addition, the role of the transcription factor nuclear factor-kappaB (NFκB) and members of the B cell leukemia-2 (Bcl-2) family that contribute to the regulation of apoptosis in hepatocytes are discussed. Eventually, the delineation of cell death signaling pathways could contribute to the implementation of new therapeutic strategies to treat HCC.

Identification of histone deacetylase 3 as a biomarker for tumor recurrence following liver transplantation in HBV-associated hepatocellular carcinoma

BACKGROUND

Recent studies have shown that high expression levels of class I histone deacetylases (HDACs) correlate with malignant phenotype and poor prognosis in some human tumors. However, the expression patterns and prognostic role of class I HDAC isoforms in hepatocellular carcinoma (HCC) remain unclear.

METHODOLOGY/PRINCIPAL FINDINGS

The expression patterns and clinical significance of class I HDAC isoforms were assessed by immunohistochemistry in a cohort of 43 hepatitis B virus-associated HCC patients treated with liver transplantation. In addition, the effects of HDAC inhibition on HCC cell behavior were investigated by knockdown of the HDAC isoform with short interfering RNA. Class I HDACs were highly expressed in a subset of HCCs with positivity for HDAC1 in 51.2%, HDAC2 in 48.8%, and HDAC3 in 32.6% of cases. The expression levels of HDAC isoforms were significantly associated with the proliferation index of HCC. Kaplan-Meier curves showed that a high expression level of HDAC2 or HDAC3 implicated significantly reduced recurrence-free survival. Cox proportional hazards model analysis revealed HDAC3 overexpression was an unfavorable independent prognostic factor (P = 0.002; HR 3.907). In vitro, inhibition of HDAC2 and HDAC3, but not HDAC1, suppressed proliferation and the invasiveness of liver cancer cells.

CONCLUSIONS/SIGNIFICANCE

Our findings demonstrate that HDAC3 plays a significant role in regulating tumor cell proliferation and invasion, and it could be served as a candidate biomarker for predicting the recurrence of hepatitis B virus-associated HCC following liver transplantation and a potential therapeutic target.

Decitabine-induced apoptosis is derived by Puma and Noxa induction in chronic myeloid leukemia cell line as well as in PBL and is potentiated by SAHA

Restoration of cellular apoptotic pathways plays a crucial role in cancer therapy strategies. In a broad spectrum of anticancer drugs, epigenetic effectors are in the center of interest mostly because of potential reversibility of their action. Methylation status of the cells is influenced by methyltransferase inhibitor 2-deoxy-5'-azacytidine (decitabine, DAC), but higher concentrations of this agent cause a DNA-damage. In our study, tumor supressor p53-apoptotic pathway was activated in decitabine-induced cell death. Expression of p53-inducible BH3-only apoptotic proteins Puma and Noxa was elevated and large activation of executive caspases was observed. The extent of acetylation in the cell is affected by histonedeacetylase inhibitor suberoylanilide hydroxamic acid (SAHA). Combination of SAHA with decitabine brought synergistic effect on apoptosis triggering in CML-T1 cell line, but apoptosis as well as necrosis occurred also in normal peripheral blood lymphocytes. Therefore, promising potential of such combined therapy calls for more detailed investigation of unwanted effects in normal cells.

Overcoming resistance to histone deacetylase inhibitors in human leukemia with the redox modulating compound β-phenylethyl isothiocyanate

Mechanisms of action and resistance of histone deacetylase inhibitors (HDACIs) are not well understood. A gene expression analysis performed in a phase 1 trial of vorinostat in leukemia indicated that overexpression of genes involved in antioxidant defense was associated with clinical resistance. We hypothesized that nonepigenetic mechanisms may be involved in resistance to HDACI therapy in leukemia. Here we confirmed up-regulation of a series of antioxidants in a pan-HDACI-resistant leukemia cell line HL60/LR. Vorinostat induced reactive oxygen species (ROS) through nicotinamide adenine dinucleotide phosphate oxidase in leukemia cells. An increase in ROS resulted in translocation of nuclear factor E2-related factor 2 from cytosol to nucleus, leading to up-regulation of antioxidant genes, including a majority of glutathione-associated enzymes as a cellular protective mechanism. Addition of β-phenylethyl isothiocyanate, a natural compound capable of depleting cellular glutathione, significantly enhanced the cytotoxicity of vorinostat in leukemia cell lines and primary leukemia cells by inhibiting the cytoprotective antioxidant response. These results suggest that ROS plays an important role in action of vorinostat and that combination with a redox-modulating compound increases sensitivity to HDACIs and also overcomes vorinostat resistance. Such a combination strategy may be an effective therapeutic regimen and have potential clinical application in leukemia.

High mobility group box 1 release from hepatocytes during ischemia and reperfusion injury is mediated by decreased histone deacetylase activity

The mobilization and extracellular release of nuclear high mobility group box-1 (HMGB1) by ischemic cells activates inflammatory pathways following liver ischemia/reperfusion (I/R) injury. In immune cells such as macrophages, post-translational modification by acetylation appears to be critical for active HMGB1 release. Hyperacetylation shifts its equilibrium from a predominant nuclear location toward cytosolic accumulation and subsequent release. However, mechanisms governing its release by parenchymal cells such as hepatocytes are unknown. In this study, we found that serum HMGB1 released following liver I/R in vivo is acetylated, and that hepatocytes exposed to oxidative stress in vitro also released acetylated HMGB1. Histone deacetylases (HDACs) are a family of enzymes that remove acetyl groups and control the acetylation status of histones and various intracellular proteins. Levels of acetylated HMGB1 increased with a concomitant decrease in total nuclear HDAC activity, suggesting that suppression in HDAC activity contributes to the increase in acetylated HMGB1 release after oxidative stress in hepatocytes. We identified the isoforms HDAC1 and HDAC4 as critical in regulating acetylated HMGB1 release. Activation of HDAC1 was decreased in the nucleus of hepatocytes undergoing oxidative stress. In addition, HDAC1 knockdown with siRNA promoted HMGB1 translocation and release. Furthermore, we demonstrate that HDAC4 is shuttled from the nucleus to cytoplasm in response to oxidative stress, resulting in decreased HDAC activity in the nucleus. Together, these findings suggest that decreased nuclear HDAC1 and HDAC4 activities in hepatocytes following liver I/R is a mechanism that promotes the hyperacetylation and subsequent release of HMGB1.

Intervention of NF-κB activation inhibits the growth of human hepatocellular carcinoma HepG2 cells

AIM: To investigate the impact of intervention of nuclear factor-κB (NF-κB) activation with tumor necrosis factor-α (TNF-α) monoclonal antibody (TNF-α mab) on the proliferation of human hepatocellular carcinoma (HCC) HepG2 cells.

METHODS: HepG2 cells were cultured in vitro and incubated with TNF-α mab. The changes in cell cycle and apoptosis were detected by flow cytometry (FCM) and annexin-V/PI double staining assay, respectively. The expression of NF-κB and TNF-α in human liver cancer, tumor-adjacent liver tissue, and HepG2 cells were quantitatively analyzed by enzyme-linked immunosorbent assay (ELISA).

RESULTS: The expression level of NF-κB in human HCC was higher than that in tumor-adjacent liver tissue (P < 0.01). The percentage of apoptotic cells in HepG2 cells treated with TNF-α mab (5 mg/L) was higher than that in untreated HepG2 cells (21.45% ± 4.07% vs 5.63% ± 0.93%, q = 10.07, P < 0.01). The percentage of cells in G₀/G₁ phase was significantly higher in HepG2 cells treated with TNF-α mab than in untreated HepG2 cells (q = 10.98, P < 0.01) though no significant difference was noted in the percentage of cells in S phase between the two groups of cells. The level of NF-κB in HepG2 cells treated with TNF-α mab was lower than that in untreated HepG2 cells [59.00 ng/mg ± 1.02 ng/mg nuclear protein (NP) vs 73.88 ng/mg ± 7.41 ng/mg NP, q = 18.92, P < 0.01]. Increased NF-κB level is correlated with decreased TNF-α level in HepG2 cells treated with TNF-α mab (r = 0.89, P < 0.01). The inhibitory effect of TNF-α mab on TNF-α level is dose-dependent (P < 0.01).

CONCLUSION: Intervention of NF-κB activation by TNF-α mab inhibits the proliferation of HepG2 cells by inducing apoptosis and blocking the cells in G₀/G₁ phase.

Sorafenib activates CD95 and promotes autophagy and cell death via Src family kinases in gastrointestinal tumor cells

Sorafenib and vorinostat interact in a synergistic fashion to kill carcinoma cells by activating CD95; the present studies have determined how sorafenib and vorinostat individually contribute to CD95 activation. Sorafenib (3-6 micromol/L) promoted a dose-dependent increase in Src Y416, ERBB1 Y845 and CD95 Y232/Y291 phosphorylation, and Src Y527 dephosphorylation. Low levels of sorafenib-induced (3 micromol/L) CD95 tyrosine phosphorylation did not promote surface localization whereas sorafenib (6 micromol/L), or sorafenib (3 micromol/L) and vorinostat (500 nmol/L) treatment promoted higher levels of CD95 phosphorylation which correlated with DISC formation, receptor surface localization, and autophagy. CD95 (Y232F, Y291F) was not tyrosine phosphorylated and was unable to localize plasma membrane or induce autophagy. Knockdown/knockout of Src family kinases abolished sorafenib-induced CD95 tyrosine phosphorylation, DISC formation, and the induction of cell death and autophagy. Knockdown of platelet-ived growth factor receptor-beta enhanced Src Y416 and CD95 tyrosine phosphorylation, which correlated with elevated CD95 plasma membrane levels and autophagy, and with a reduced ability of sorafenib to promote CD95 membrane localization. Vorinostat increased reactive oxygen species levels, and in a delayed NF kappa B-dependent fashion, those of FAS ligand and CD95. Neutralization of FAS-L did not alter the initial rapid drug-induced activation of CD95; however, neutralization of FAS-L reduced sorafenib + vorinostat toxicity by approximately 50%. Thus, sorafenib contributes to CD95 activation by promoting receptor tyrosine phosphorylation, whereas vorinostat contributes to CD95 activation via the initial facilitation of reactive oxygen species generation and subsequently of FAS-L expression.

Histone deacetylase inhibitors enhance the anticancer activity of nutlin-3 and induce p53 hyperacetylation and downregulation of MDM2 and MDM4 gene expression

Nutlin-3, a small-molecule MDM2 inhibitor, restores p53 function and is, thus, an appealing candidate for the treatment of cancers retaining wild-type p53. However, nutlin-3 applied as single agent may be insufficient for cancer therapy. Therefore, we explored whether the anticancer activity of nutlin-3 could be enhanced by combination with histone deacetylase inhibitors (HDACi), i.e. vorinostat, sodium butyrate, MS-275 and apicidin. We found that nutlin-3 and HDACi cooperated to induce cell death in the p53 wild-type cell lines A549 and A2780, but not in the p53 null cell line PC-3, as assessed by Alamar Blue assay and flow cytometric analyses of propidium iodide uptake and mitochondrial depolarization. Combination index analysis showed that the effect was synergistic. For comparison, we tested nutlin-3 in combination with paclitaxel, revealing that nutlin-3 antagonized the cytotoxic activity of paclitaxel. To shed light on the underlying mechanism of the synergistic action of nutlin-3 and HDACi, we determined the acetylation status of p53 by immunoblotting and the mRNA levels of MDM2 and MDM4 by real-time RT-PCR. We observed vorinostat to induce p53 hyperacetylation, to reduce the constitutive gene expression of MDM2 and MDM4, and to counteract the nutlin-3-induced upregulation of MDM2 gene expression. In conclusion, our study shows that HDACi amplify the antitumor activity of nutlin-3-possibly by inducing p53 hyperacetylation and/or MDM2 and/or MDM4 downregulation-suggesting that treatment with a combination of nutlin-3 and HDACi may be an effective strategy for treating tumors with wild-type p53.

Combination therapy of bortezomib with novel targeted agents: an emerging treatment strategy

Clinical trials evaluating combinations of targeted agents with bortezomib, the first-in-class proteasome inhibitor, have been initiated, with the objective of enhancing its single agent activity in hematologic malignancies (myeloma, mantle cell lymphoma), as well as expanding its efficacy in solid tumors. In most cases, preclinical studies have provided a supportive rationale for designing these doublet combination studies. Novel, small molecule-targeted agents being investigated with bortezomib in clinical trials include protein deacetylase inhibitors, kinase inhibitors, farnesyltransferase inhibitors, heat-shock protein 90 inhibitors, pan-Bcl-2 family inhibitors, and other classes of targeted inhibitors. Preliminary clinical data, available from a number of ongoing trials, suggest that most of these combinations are well tolerated and some have promising clinical efficacy that will require subsequent confirmation. Translational studies, conducted as part of the trials, may provide important insights into the putative mechanism of action delineated by preclinical studies of the combinations. The emergence of novel proteasome inhibitors may also expand the opportunities for optimizing these combination therapies. There is potential for an increasingly broad clinical trials program to investigate this therapeutic approach in a range of tumor types, as well as to consider additional agents in sequence or in combination.

Combination of suberoylanilide hydroxamic acid and ritonavir is effective against renal cancer cells

OBJECTIVES

To investigate the combined effect of the histone deacetylase (HDAC) inhibitor suberoylanilide hydroxamic acid (SAHA) and the protease inhibitor ritonavir on renal cancer cells.

METHODS

Renal cancer cells (769P, 786O, A498, ACHN, Caki-1) and renal proximal tubule epithelial cells were treated with SAHA (0-5 μM) with or without ritonavir (0-50 μM). Cell viability, clonogenecity, and changes in cell cycle were evaluated. The expression of acetylated histone, retinoblastoma protein (Rb), phosphorylated Rb, histone deacetylases, X-linked inhibitor of apoptosis, survivin, and active caspase 3 was assessed using Western blot analysis.

RESULTS

SAHA induced histone acetylation and Rb dephosphorylation and inhibited cell growth in a time- and dose-dependent manner. SAHA and ritonavir combined inhibited cell proliferation effectively and promoted histone acetylation and Rb dephosphorylation but only slightly affected renal proximal tubule epithelial cell survival. The combination induced the accumulation of the sub-G(1) fraction, decreased the expression of X-linked inhibitor of apoptosis and survivin, and increased active caspase 3, thus inducing apoptosis. It also inhibited the expression of histone deacetylases.

CONCLUSIONS

Combination therapy using SAHA and ritonavir inhibited the proliferation of renal cancer cells effectively, perhaps by inhibiting both histone deacetylase function and expression. It might be a useful new regimen for treating renal cancer.

Deacetylase inhibitors - focus on non-histone targets and effects

Inhibitors of protein deacetylases have recently been established as a novel therapeutic principle for several human diseases, including cancer. The original notion of the mechanism of action of these compounds focused on the epigenetic control of transcriptional processes, especially of tumor suppressor genes, by interfering with the acetylation status of nuclear histone proteins, hence the name histone deacetylase inhibitors was coined. Yet, this view could not explain the high specificity for tumor cells and recent evidence now suggests that non-histone proteins represent major targets for protein deacetylase inhibitors and that the post-translational modification of the acetylome is involved in various cellular processes of differentiation, survival and cell death induction.

4-(4-Chloro-2-methylphenoxy)-N-hydroxybutanamide (CMH) targets mRNA of the c-FLIP variants and induces apoptosis in MCF-7 human breast cancer cells

Cellular FLICE (FADD-like IL-1beta-converting enzyme)-inhibitory protein (c-FLIP) is a major resistance factor for the tumor necrosis factor-related apoptosis-inducing ligand TRAIL and in drug resistance in human malignancies. c-FLIP is an antagonist of caspases-8 and -10, which inhibits apoptosis and is expressed as long (c-FLIP(L)) and short (c-FLIP(S)) splice forms. c-FLIP is often overexpressed in various human cancers, including breast cancer. Several studies have shown that silencing c-FLIP by specific siRNAs sensitizes cancer cells to TRAIL and anticancer agents. However, systemic use of siRNA as a therapeutic agent is not practical at present. In order to reduce or inhibit c-FLIP expression, small molecules are needed to allow targeting c-FLIP without inhibiting caspases-8 and -10. We used a small molecule inhibitor of c-FLIP, 4-(4-chloro-2-methylphenoxy)-N-hydroxybutanamide (CMH), and show that CMH, but not its inactive analog, downregulated c-FLIP(L) and c-FLIP(S) mRNA and protein levels, caused poly(ADP-ribose) polymerase (PARP) degradation, reduced cell survival, and induced apoptosis in MCF-7 breast cancer cells. These results revealed that c-FLIP is a critical apoptosis regulator that can serve as a target for small molecule inhibitors that downregulate its expression and serve as effective targeted therapeutics against breast cancer cells.

Anti-melanoma effects of vorinostat in combination with polyphenolic antioxidant (-)-epigallocatechin-3-gallate (EGCG)

PURPOSE

Melanoma is an aggressive neoplasm with a propensity for metastases and resistance to therapy. Previously, we showed that (-)-epigallocatechin-3-gallate (EGCG), the major polyphenolic antioxidant present in green tea, resulted in a significant decrease in the viability and growth of melanoma and induction of apoptosis via modulation of the cki-cdk-cyclin network and Bcl2 family proteins. Epigenetic regulation of gene transcription by histone deacetylase (HDAC) inhibitors is gaining momentum as a novel cancer therapy. SAHA-suberoylanilidine hydroxamic acid Zolinza (vorinostat) is the first HDAC inhibitor approved by the U.S. FDA. In this study, we determined if vorinostat alone or in combination with EGCG imparts anti-proliferative effects against human melanoma cells.

METHODS

Employing human melanoma cell lines A-375, Hs-294T and G-361, we determined the effect of vorinostat and/or EGCG on 1) growth/viability and colony formation, 2) apoptosis, and 3) the critical molecules involved in cell cycle and apoptosis regulation.

RESULTS

Our data demonstrated that the anti-proliferative effects of vorinostat were greater than or similar to those of EGCG among the cell lines tested. Furthermore, relative to monotherapy, the combination treatment resulted in significantly greater inhibition of cell proliferation, increased apoptosis, activation of p21, p27 and caspases (3, 7 and 9) and Bax as well as down-regulation of cdk2, cdk4, cyclin A, NF-kappaB protein p65/RelA and Bcl2 protein and transcript.

CONCLUSIONS

Our preclinical findings suggest that combination therapy with EGCG and vorinostat may be beneficial for the management of human melanoma.

Histone deacetylase inhibitor vorinostat suppresses the growth of uterine sarcomas in vitro and in vivo

Background

Uterine sarcomas are very rare malignancies with no approved chemotherapy protocols. Histone deacetylase (HDAC) inhibitors belong to the most promising groups of compounds for molecular targeting therapy. Here, we described the antitumor effects of suberoylanilide hydroxamic acid (SAHA; vorinostat) on MES-SA uterine sarcoma cells in vitro and in vivo. We investigated effects of vorinostat on growth and colony forming ability by using uterine sarcoma MES-SA cells. We analyzed the influence of vorinostat on expression of different HDACs, p21^WAF1 and activation of apoptosis. Finally, we examined the antitumor effects of vorinostat on uterine sarcoma in vivo.

Results

Vorinostat efficiently suppressed MES-SA cell growth at a low dosage (3 μM) already after 24 hours treatment. Decrease of cell survival was even more pronounced after prolonged treatment and reached 9% and 2% after 48 and 72 hours of treatment, respectively. Colony forming capability of MES-SA cells treated with 3 μM vorinostat for 24 and 48 hours was significantly diminished and blocked after 72 hours. HDACs class I (HDAC2 and 3) as well as class II (HDAC7) were preferentially affected by this treatment. Vorinostat significantly increased p21^WAF1 expression and apoptosis. Nude mice injected with 5 × 10⁶ MES-SA cells were treated for 21 days with vorinostat (50 mg/kg/day) and, in comparison to placebo group, a tumor growth reduction of more than 50% was observed. Results obtained by light- and electron-microscopy suggested pronounced activation of apoptosis in tumors isolated from vorinostat-treated mice.

Conclusions

Our data strongly indicate the high therapeutic potential of vorinostat in uterine sarcomas.

The synthetic cannabinoid WIN 55,212-2 sensitizes hepatocellular carcinoma cells to tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-induced apoptosis by activating p8/CCAAT/enhancer binding protein homologous protein (CHOP)/death receptor 5 (DR5) axis

In this article, we demonstrate that the synthetic cannabinoid R-(+)-(2,3-dihydro-5-methyl-3-[(4-morpholinyl)methyl]pyrol[1,2,3-de]-1,4-benzoxazin-6-yl)-(1-naphthalenyl) methanone mesylate (WIN 55,212-2) sensitizes human hepatocellular carcinoma (HCC) cells to apoptosis mediated by tumor necrosis-related apoptosis inducing ligand (TRAIL). The apoptotic mechanism induced by treatment with WIN/TRAIL combination involved the loss of the mitochondrial transmembrane potential and led to the activation of caspases. In HCC cells, WIN treatment induced the up-regulation of TRAIL death receptor DR5, an effect that seemed to be related to the increase in the level of p8 and CHOP, two factors implicated in cellular stress response and apoptosis. This relationship was suggested by the observation that the down-regulation of p8 or CHOP by specific small interfering RNAs attenuated both WIN-mediated DR5 up-regulation and the cytotoxicity induced by WIN/TRAIL cotreatment. Moreover, WIN induced a significant decrease in the levels of some survival factors (survivin, c-inhibitor of apoptosis protein 2, and Bcl-2) and in particular in that of the active phosphorylated form of AKT. This event seemed to be dependent on the transcription factor peroxisome proliferator-activated receptor-gamma whose level significantly increased after WIN treatment. Therefore, both the induction of DR5 via p8 and CHOP and the down-regulation of survival factors seem to be crucial for the marked synergistic effects induced by the two drugs in HCC cells. Taken together, the results reported in this article indicate that WIN/TRAIL combination could represent a novel important tool for the treatment of HCC.

Size-mediated cytotoxicity and apoptosis of hydroxyapatite nanoparticles in human hepatoma HepG2 cells

Hydroxyapatite nanoparticles (HAPN) have been discovered to exert cytotoxicity and apoptosis-induction in some cancer cells. But it is still not clear how tumor cells interact with HAPNs with various sizes. In this study, we investigated the effect of the particle size of the HAPN on the anti-tumor activity, apoptosis-induction and the levels of the apoptotic signaling proteins in human hepatoma HepG2 model cells. HAPNs within 20-180 nm size range were synthesized by a modified sol-gel method. The cellular internalization and biolocalization of the FITC-labeled HAPNs were also identified. The results showed that in HepG2 cells, the anti-tumor activity and HAPN-induced apoptosis strongly depended on the size of HAPNs, and the efficacies all decreased in the order of 45-nm>26-nm>78-nm>175-nm. HAPNs, ranging from 20 nm to 80 nm, were found to effectively activate caspase-3 and -9, decrease the Bcl-2 protein level, and increase the levels of Bax, Bid and the release of cytochrome c from mitochondria into cytoplasm, with the best efficiency from 45-nm HAPN. Correlating the cellular response with the cellular internalization, it can be inferred that the size of HAPN and thereby the cellular localization had predominant effect on the HAPN-induced cytotoxicity, apoptotis, and the levels of the apoptotic proteins in HepG2 cells. The findings presented here could provide new means to modulate the cellular behaviors of HAPN and to guide the design of HAPN-based delivery and therapeutic systems.

Hepatopoietin Cn suppresses apoptosis of human hepatocellular carcinoma cells by up-regulating myeloid cell leukemia-1

AIM: To investigate the role of hepatopoietin Cn (HPPCn) in apoptosis of hepatocellular carcinoma (HCC) cells and its mechanism.

METHODS: Two human HCC cell lines, SMMC7721 and HepG2, were used in this study. Immunostaining, Western blotting and enzyme linked immunosorbent assay were conducted to identify the expression of HPPCn and the existence of an autocrine loop of HPPCn/HPPCn receptor in SMMC7721 and HepG2. Apoptotic cells were detected using fluorescein isothiocyanate (FITC)-conjugated Annexin V and propidium iodide.

RESULTS: The HPPCn was highly expressed in human HCC cells and secreted into culture medium (CM). FITC-labeled recombinant human protein (rhHPPCn) could specifically bind to its receptor on HepaG2 cells. Treatment with 400 ng/mL rhHPPCn dramatically increased the viability of HCC-derived cells from 48.1% and 36.9% to 85.6% and 88.4%, respectively (P < 0.05). HPPCn silenced by small-interfering RNA reduced the expression and secretion of HPPCn and increased the apoptosis induced by trichostatin A. Additionally, HPPCn could up-regulate the expression of myeloid cell leukemia-1 (Mcl-1) in HCC cells via mitogen-activated protein kinase (MAPK) and sphingosine kinase-1.

CONCLUSION: HPPCn is a novel hepatic growth factor that can be secreted to CM and suppresses apoptosis of HCC cells by up-regulating Mcl-1 expression.

Histone deacetylase inhibitors: current status and overview of recent clinical trials

Histone deacetylase (HDAC) inhibitors are a new group of anticancer agents that have a potential role in the regulation of gene expression, induction of cell death, apoptosis and cell cycle arrest of cancer cells by altering the acetylation status of chromatin and other non-histone proteins. In clinical trials, HDAC inhibitors have demonstrated promising antitumour activity as monotherapy in cutaneous T-cell lymphoma and other haematological malignancies. In solid tumours, several HDAC inhibitors have been shown to be efficacious as single agents; however, results of most clinical trials were in favour of using HDAC inhibitors either prior to the initiation of chemotherapy or in combination with other treatments. Currently, the molecular basis of response to HDAC inhibitors in patients is not fully understood. In this review, we summarize the current status of HDAC inhibitors, as single agents or in combination with other agents in different phases of clinical trials. In most of the clinical trials, HDAC inhibitors were tolerable and exerted biological or antitumor activity. HDAC inhibitors have been studied in phase I, II and III clinical trials with variable efficacy. The combination of HDAC inhibitors with other anticancer agents including epigenetic or chemotherapeutic agents demonstrated favourable clinical outcome.

Histone deacetylase inhibitor ITF2357 is neuroprotective, improves functional recovery, and induces glial apoptosis following experimental traumatic brain injury

Despite efforts aimed at developing novel therapeutics for traumatic brain injury (TBI), no specific pharmacological agent is currently clinically available. Here, we show that the pan-histone deacetylase (HDAC) inhibitor ITF2357, a compound shown to be safe and effective in humans, improves functional recovery and attenuates tissue damage when administered as late as 24 h postinjury. Using a well-characterized, clinically relevant mouse model of closed head injury (CHI), we demonstrate that a single dose of ITF2357 administered 24 h postinjury improves neurobehavioral recovery from d 6 up to 14 d postinjury (improved neurological score vs. vehicle; P< or =0.05), and that this functional benefit is accompanied by decreased neuronal degeneration, reduced lesion volume (22% reduction vs. vehicle; P< or =0.01), and is preceded by increased acetylated histone H3 levels and attenuation of injury-induced decreases in cytoprotective heat-shock protein 70 kDa and phosphorylated Akt. Moreover, reduced glial accumulation and activation were observed 3 d postinjury, and total p53 levels at the area of injury and caspase-3 immunoreactivity within microglia/macrophages at the trauma area were elevated, suggesting enhanced clearance of these cells via apoptosis following treatment. Hence, our findings underscore the relevance of HDAC inhibitors for ameliorating trauma-induced functional deficits and warrant consideration of applying ITF2357 for this indication.

The histone deacetylase inhibitor suberoylanilide hydroxamic acid sensitises human hepatocellular carcinoma cells to TRAIL-induced apoptosis by TRAIL-DISC activation

This paper shows that the histone deacetylase inhibitor SAHA sensitised at sub-toxic doses human hepatocellular carcinoma cells (HepG2, Hep3B and SK-Hep1) to TRAIL-induced apoptosis, while it was ineffective in primary human hepatocytes (PHHs). In particular in HCC cells SAHA increased the expression of death receptor 5 (DR5) and caused a decrement of c-Flip. These two modifications provoked in the presence of TRAIL the rapid production of TRAIL-DISC and the activation of caspase-8. Consequently SAHA/TRAIL combination induced many apoptotic events, such as a cleavage of Bid into tBid, dissipation of mitochondrial membrane potential, activation of caspase-3 with the consequent cleavage of both NF-kB and Akt. The decrease in NF-kB level seemed to be responsible for the reduction in the content of IAP family antiapoptotic proteins while the decrease in Akt level caused a reduction in phospho-Bad. These events led to the activation of caspase-9, which contributed to the strong apoptotic activity of TRAIL. Sensitisation of human hepatocellular carcinoma cells to TRAIL-induced apoptosis by SAHA may suggest new strategies for the treatment of liver tumours.

Role of epigenetics in liver-specific gene transcription, hepatocyte differentiation and stem cell reprogrammation

Controlling both growth and differentiation of stem cells and their differentiated somatic progeny is a challenge in numerous fields, from preclinical drug development to clinical therapy. Recently, new insights into the underlying molecular mechanisms have unveiled key regulatory roles of epigenetic marks driving cellular pluripotency, differentiation and self-renewal/proliferation. Indeed, the transcription of genes, governing cell-fate decisions during development and maintenance of a cell's differentiated status in adult life, critically depends on the chromatin accessibility of transcription factors to genomic regulatory and coding regions. In this review, we discuss the epigenetic control of (liver-specific) gene-transcription and the intricate interplay between chromatin modulation, including histone (de)acetylation and DNA (de)methylation, and liver-enriched transcription factors. Special attention is paid to their role in directing hepatic differentiation of primary hepatocytes and stem cells in vitro.

Oxidative stress by targeted agents promotes cytotoxicity in hematologic malignancies

The past decade has seen an exponential increase in the number of cancer therapies with defined molecular targets. Interestingly, many of these new agents are also documented to raise levels of intracellular reactive oxygen species (ROS) in addition to inhibiting a biochemical target. In most cases, the exact link between the primary target of the drug and effects on cellular redox status is unknown. However, it is important to understand the role of oxidative stress in promoting cytotoxicity by these agents, because the design of multiregimen strategies could conceivably build on these redox alterations. Also, drug resistance mediated by antioxidant defenses could potentially be anticipated and circumvented with improved knowledge of the redox-related effects of these targeted agents. Given the large number of targeted chemotherapies, in this review, we focus on selected agents that have shown promise in hematologic malignancies: proteasome inhibitors, histone deacetylase inhibitors, Bcl-2-targeted agents, and a kinase inhibitor called adaphostin. Despite structural differences within classes of these compounds, a commonality of causing increased oxidative stress exists, which contributes to induction of cell death.

Emerging treatments for multiple myeloma: beyond immunomodulatory drugs and bortezomib

The successful clinical development of thalidomide, bortezomib, and lenalidomide not only transformed the therapeutic management of multiple myeloma (MM) but also catalyzed a renewed interest in the development of additional classes of novel agents for this disease. This review focuses on a series of new therapeutics that have shown promising preclinical results, as well as encouraging safety profiles and early evidence of anti-MM activity in clinical studies, either alone or in combination with other, conventional or novel, anti-MM treatments. These agents include second-generation proteasome inhibitors and immunomodulatory agents, as well as members of other therapeutic classes, such as histone deacetylase inhibitors (HDAC), heat shock protein 90 (Hsp90) inhibitors, and the alkylphospholipid Akt inhibitor perifosine.

Histone deacetylase inhibitors that target tubulin

Epigenetics is defined as heritable changes in gene expression that occur without changes in DNA sequence. Major mechanisms of epigenetics are post-translational histone modifications such as reversible acetylation. Histone deacetylases (HDACs) maintain the acetylation level of histones but also act on non-histone substrates that are involved in signal transduction or cellular transport processes. One important non-histone substrate is tubulin. The isotypes responsible for tubulin deacetylation are HDAC6 and the NAD(+)-dependent histone deacetylase (sirtuin) Sirt2. Here we review the action of those enzymes on tubulin and present an overview over existing inhibitors with a focus on their structural interaction with the targets.

Bortezomib arrests the proliferation of hepatocellular carcinoma cells HepG2 and JHH6 by differentially affecting E2F1, p21 and p27 levels

Despite the broad anti-tumour potential of the proteasome inhibitor bortezomib, partial information is available with regard to its effects on hepatocellular carcinoma (HCC) cells. Here we studied the effects of bortezomib on two human HCC cell lines displaying a different phenotype, hepatocyte-like for HepG2 and undifferentiated for JHH6. Bortezomib induced a dose- and time-dependent increase in cell toxicity and decrease of cell viability, with JHH6 being less sensitive than HepG2. Moreover, a differential influence on major cell cycle regulatory genes was responsible for the observed decrease of S and increase of G(2)-M phase cells. In HepG2, bortezomib induced a post-transcriptional increase of cyclin E1 together with a transcriptional-mediated decrease of the transcription factor E2F1. This in turn resulted in the reduction of the hyper-phosphorylated form of pRB and in the transcriptional down-regulation of the E2F1 targets cyclin D1, cyclin A2 and CdK2 but not cyclin E1. Up-regulation of LRH1, a liver specific cyclin E1 transcription factor, accounted for the unvaried cyclin E1 mRNA levels. Additionally, bortezomib induced both transcriptional and post-translational increase of p21(waf1/cip1) and p27(kip1). In JHH6, an overall more contained variation in cell cycle mediators was observed with the reduction of E2F1, cyclin A2, LRH1 and the increase of p21(waf1/cip1) being the most evident. In conclusion, the presented data show the mechanisms regulating cell proliferation inhibition by bortezomib in two different HCC cell lines. Despite a certain phenotype-dependent effect, the potent action exerted by bortezomib makes this drug attractive for future experimentation in animal models, possibly leading to novel treatments for HCC.

Development of vorinostat: current applications and future perspectives for cancer therapy

Vorinostat is a potent histone deacetylase inhibitor that blocks the catalytic site of these enzymes. A large number of cellular proteins are modified post-translationally by acetylation, leading to altered structure and/or function. Many of these proteins, such as core nucleosomal histones and transcription factors, function in key cellular processes and signal transduction pathways that regulate cell growth, migration, and differentiation. At concentrations that are non-toxic to normal cells, vorinostat dramatically alters cellular acetylation patterns and causes growth arrest and death and in a wide range of transformed cells, both in vitro and in animal tumor models. Vorinostat has shown promising clinical activity against hematologic and solid tumors at doses that have been well tolerated by patients. Recent non-clinical experiments that explored the effects of vorinostat in combination with other chemotherapeutic agents have begun to illuminate potential mechanisms of action for this histone deacetylase inhibitor and are providing guidance for new avenues of clinical investigation.

Caspase-8 dependent histone acetylation by a novel proteasome inhibitor, NPI-0052: a mechanism for synergy in leukemia cells

Combination studies of histone deacetylase inhibitors (HDACi) and proteasome inhibitors are providing preclinical framework to build better strategies against hematologic malignancies. Our previous work found that a novel proteasome inhibitor, NPI-0052, and HDACi synergistically induce apoptosis in leukemia cells in a caspase-8- and oxidant-dependent manner. Here we extend those observations to primary leukemia cells and identify novel mechanisms of synergy. Because the proximal targets of NPI-0052 and HDACi are inhibition of proteasome activity and histone acetylation, we initially examined those biochemical events. Increased acetylation of histone-H3 was detected in Jurkat and CLL primary cells treated with NPI-0052, alone or in combination with various HDACi (MS/SNDX-275 or vorinostat). Hyperacetylation by NPI-0052 occurred to a lesser extent in caspase-8-deficient cells and in cells treated with an antioxidant. These results indicate that NPI-0052 is eliciting caspase-8 and oxidative stress-dependent epigenetic alterations. In addition, real-time PCR revealed that MS/SNDX-275 repressed expression of the proteasomal beta5, beta2, and beta1 subunits, consequently inhibiting respective enzymatic activities. Overall, our results suggest that crosstalk by NPI-0052 and HDACi are contributing, along with caspase-8 activation and oxidative stress, to their synergistic cytotoxic effects in leukemia cells, reinforcing the potential clinical utility of combining these 2 agents.

Vorinostat and bortezomib exert synergistic antiproliferative and proapoptotic effects in colon cancer cell models

Despite the availability of several Food and Drug Administration-approved drugs, advanced inoperable colorectal cancer remains incurable. In this study, we focused on the development of combined molecular targeted therapies against colon cancer by testing the efficacy of the combination of the histone deacetylase inhibitor vorinostat with the proteasome inhibitor bortezomib to determine if this resulted in synergistic antitumor effects against colorectal cancer. The effects of the histone deacetylase inhibitor vorinostat in combination with the proteasome inhibitor bortezomib on the growth of two colorectal cancer cell lines were assessed with regard to proliferation, cell cycle arrest, and apoptosis. Treatment with the combination of vorinostat and bortezomib resulted in a synergistic decrease in proliferation of both colorectal cancer cell lines compared with treatment with single agents alone. This inhibition was associated with a synergistic increase in apoptosis as measured by caspase-3/7 activity and cleaved poly(ADP-ribose) polymerase. In addition, we observed an increase in the proapoptotic protein BIM and in the number of cells arrested in the G(2)-M phase of the cell cycle. Although p21 levels were significantly increased, short hairpin RNA knockdown of p21 did not lead to changes in proliferation in response to the combination of drugs, indicating that although p21 is a target of these drugs, it is not required to mediate their antiproliferative effects. These data indicate that combination treatment with vorinostat and bortezomib result in synergistic antiproliferative and proapoptotic effects against colon cancer cell lines, providing a rational basis for the clinical use of this combination for the treatment of colorectal cancer.

Is the focus moving toward a combination of targeted drugs?

The concept of combining targeted agents for the treatment of acute myeloid leukemia (AML) is a relatively new but potentially promising area of investigation. A number of targeted agents may have limited single-agent activity but could show significant promise when used in conjunction with other types of similar compounds. Combinations of targeted agents may effectively interrupt multiple pathways in either a linear or parallel fashion. There are currently numerous combination regimens under investigation at either the preclinical or clinical levels, including histone deacetylase (HDAC) and CDK inhibitors; HDAC and proteasome inhibitors; HDAC and NF-kappaB (IKKbeta) inhibitors; CHK1 and MEK1/2 inhibitors; and BCL-2 antagonists and CDK inhibitors. Although combinations of targeted agents will not displace conventional cytotoxic regimens in AML or related disorders in the foreseeable future, these combinations clearly warrant further attention.

Synergistic apoptosis induction in leukemic cells by the phosphatase inhibitor salubrinal and proteasome inhibitors

BACKGROUND

Cells adapt to endoplasmic reticulum (ER)-stress by arresting global protein synthesis while simultaneously activating specific transcription factors and their downstream targets. These processes are mediated in part by the phosphorylation-dependent inactivation of the translation initiation factor eIF2alpha. Following restoration of homeostasis protein synthesis is resumed when the serine/threonine-protein phosphatase PP1 dephosphorylates and reactivates eIF2alpha. Proteasome inhibitors, used to treat multiple myeloma patients evoke ER-stress and apoptosis by blocking the ER-associated degradation of misfolded proteins (ERAD), however, the role of eIF2alpha phosphorylation in leukemic cells under conditions of proteasome inhibitor-mediated ER stress is currently unclear.

METHODOLOGY AND PRINCIPAL FINDINGS

Bcr-Abl-positive and negative leukemic cell lines were used to investigate the functional implications of PP1-related phosphatase activities on eIF2alpha phosphorylation in proteasome inhibitor-mediated ER stress and apoptosis. Rather unexpectedly, salubrinal, a recently identified PP1 inhibitor capable to protect against ER stress in various model systems, strongly synergized with proteasome inhibitors to augment apoptotic death of different leukemic cell lines. Salubrinal treatment did not affect the phosphorlyation status of eIF2alpha. Furthermore, the proapoptotic effect of salubrinal occurred independently from the chemical nature of the proteasome inhibitor, was recapitulated by a second unrelated phosphatase inhibitor and was unaffected by overexpression of a dominant negative eIF2alpha S51A variant that can not be phosphorylated. Salubrinal further aggravated ER-stress and proteotoxicity inflicted by the proteasome inhibitors on the leukemic cells since characteristic ER stress responses, such as ATF4 and CHOP synthesis, XBP1 splicing, activation of MAP kinases and eventually apoptosis were efficiently abrogated by the translational inhibitor cycloheximide.

CONCLUSIONS

Although PP1 activity does not play a major role in regulating the ER stress response in leukemic cells, phosphatase signaling nevertheless significantly limits proteasome inhibitor-mediated ER-stress and apoptosis. Inclusion of specific phosphatase inhibitors might therefore represent an option to improve current proteasome inhibitor-based treatment modalities for hematological cancers.

SAHA induces caspase-independent, autophagic cell death of endometrial stromal sarcoma cells by influencing the mTOR pathway

Endometrial stromal sarcomas are rare and molecular mechanisms involved in their pathogenesis are poorly understood. Covalent modifications of histone proteins, in particular de/acetylation of lysine residues, play an important role in the regulation of gene transcription in normal and neoplastic cells, but there are only limited data about these processes in solid mesenchymal tumours. We treated endometrial stromal sarcoma cells (ESS-1) and non-malignant human endometrial stromal cells (HESCs) with suberoylanilide hydroxamic acid (SAHA), a histone deacetylase inhibitor. SAHA was able to mediate the cell cycle and expression of genes related to the malignant phenotype of endometrial stromal tumours, eg p21(WAF1) and HDAC7. SAHA led to dose-dependent differentiation and death of ESS-1 cells but not of HESCs. Exposure of HESCs to SAHA resulted only in slightly decreased cell proliferation. SAHA also increased the p21(WAF1) expression and caused significant changes in the cell cycle by inhibiting the G1/S transition in ESS-1 cells. Recovery experiments indicated that these changes became irreversible when the tumour cells were treated with SAHA for longer than 24 h. In our experimental system, not apoptotic but autophagic processes were responsible for the cell death. Monodansyl cadaverine accumulation in treated ESS-1 cells and decreased expression of the mTOR and phospho-S6 ribosomal protein (S6rp) additionally supported this observation. Taken together, our study indicates that HDACs might be considered as potential drug targets in the therapy of stromal sarcomas and that SAHA might be a promising therapeutic agent for endometrial stromal sarcoma.

Targeting histone deacetylases for the treatment of disease

The ‘histone code’ is a well-established hypothesis describing the idea that specific patterns of post-translational modifications to histones act like a molecular ‘code’ recognized and used by non-histone proteins to regulate specific chromatin functions. One modification, which has received significant attention, is that of histone acetylation. The enzymes that regulate this modification are described as lysine acetyltransferases or KATs, and histone deacetylases or HDACs. Due to their conserved catalytic domain HDACs have been actively targeted as a therapeutic target. The pro-inflammatory environment is increasingly being recognized as a critical element for both degenerative diseases and cancer. The present review will discuss the current knowledge surrounding the clinical potential and current development of histone deacetylases for the treatment of diseases for which a pro-inflammatory environment plays important roles, and the molecular mechanisms by which such inhibitors may play important functions in modulating the pro-inflammatory environment.

Valproic acid was well tolerated in heavily pretreated pediatric patients with high-grade glioma

Valproic acid (VPA) inhibits histone deacetylase and has been reported to induce apoptosis in glioma. We report 44 heavily pretreated pediatric patients with high-grade glioma or diffuse intrinsic pontine glioma who received VPA as oral continues maintenance treatment with individual dose adaptation. The tumor status when starting the drug was: no measurable disease in 12, measurable but stable disease in 12, and measurable progressive disease in 22 patients. Average trough blood levels of VPA were 99 mg/l. The most frequent complaint was somnolence (three patients), but no severe toxicity was reported. One relapse patient responded, early progression of disease was observed in three frontline patients and in six relapsed patients. Median overall survival duration for all patients was 1.33 years, with large differences between first-line (5-year overall survival, 44%) and relapse therapy (5-year overall survival, 14%). This shows that valproate is safe in this patient population. The moderate tumor efficacy encourages studying the drug further as an element of multi-agent protocols.