The histone deacetylase inhibitor ITF2357 has anti-leukemic activity in vitro and in vivo and inhibits IL-6 and VEGF production by stromal cells

Abnormal histone methylation is responsible for increased vascular endothelial growth factor 165a secretion from airway smooth muscle cells in asthma

Vascular endothelial growth factor (VEGF), a key angiogenic molecule, is aberrantly expressed in several diseases including asthma where it contributes to bronchial vascular remodeling and chronic inflammation. Asthmatic human airway smooth muscle cells hypersecrete VEGF, but the mechanism is unclear. In this study, we defined the mechanism in human airway smooth muscle cells from nonasthmatic and asthmatic patients. We found that asthmatic cells lacked a repression complex at the VEGF promoter, which was present in nonasthmatic cells. Recruitment of G9A, trimethylation of histone H3 at lysine 9 (H3K9me3), and a resultant decrease in RNA polymerase II at the VEGF promoter was critical to repression of VEGF secretion in nonasthmatic cells. At the asthmatic promoter, H3K9me3 was absent because of failed recruitment of G9a; RNA polymerase II binding, in association with TATA-binding protein-associated factor 1, was increased; H3K4me3 was present; and Sp1 binding was exaggerated and sustained. In contrast, DNA methylation and histone acetylation were similar in asthmatic and nonasthmatic cells. This is the first study, to our knowledge, to show that airway cells in asthma have altered epigenetic regulation of remodeling gene(s). Histone methylation at genes such as VEGF may be an important new therapeutic target.

Developing histone deacetylase inhibitors in the therapeutic armamentarium of pancreatic adenocarcinoma

INTRODUCTION

Histone deacetylases (HDACs) are commonly dysregulated in pancreatic adenocarcinoma (PA) and have a central role in the development and progression of the disease. HDAC is a family of enzymes involved in deacetylation of lysine residues on histone and non-histone proteins. Deacetylation of histone proteins leads to compaction of the DNA/histone complex resulting in inhibition of gene expression. Deacetylation of non-histone proteins can affect the stability and function of key proteins leading to dysregulation of cellular signaling pathways. HDAC inhibitors have been shown to potentiate the antiproliferative and proapoptotic effects of several cytotoxic agents, in vitro and in vivo PA xenograft models.

AREAS COVERED

The areas covered include the biology and function of the HDAC isoenzymes and their significant role in multiple oncogenic pathways in PA. Preclinical and clinical trials evaluating HDAC inhibitors are also reviewed.

EXPERT OPINION

Despite discouraging early phase clinical trials evaluating HDAC inhibitors in PA, this strategy deserves further evaluation guided by better preclinical studies in identifying the role of specific HDAC isoenzyme inhibitors in PA. Evaluation of the effects of HDAC inhibitors on PA stem cell function and epithelial to mesenchymal transformation is also an evolving area that holds future potential for these agents. Such preclinical studies will yield insight into the functionality of HDAC isoenzymes, which can then be translated into rationally designed clinical trials. One such strategy could focus on HDAC inhibition employed in combination with proteasome inhibition targeting the aggresome pathway in PA.

Efficacy of vorinostat in a murine model of polycythemia vera

The discovery of the JAK2V617F mutation in most patients with Ph-negative myeloproliferative neoplasms has led to the development of JAK2 kinase inhibitors. However, JAK2 inhibitor therapy has shown limited efficacy and dose-limiting hematopoietic toxicities in clinical trials. In the present study, we describe the effects of vorinostat, a small-molecule inhibitor of histone deacetylase, against cells expressing JAK2V617F and in an animal model of polycythemia vera (PV). We found that vorinostat markedly inhibited proliferation and induced apoptosis in cells expressing JAK2V617F. In addition, vorinostat significantly inhibited JAK2V617F-expressing mouse and human PV hematopoietic progenitors. Biochemical analyses revealed significant inhibition of phosphorylation of JAK2, Stat5, Stat3, Akt, and Erk1/2 in vorinostat-treated, JAK2V617F-expressing human erythroleukemia (HEL) cells. Expression of JAK2V617F and several other genes, including GATA1, KLF1, FOG1, SCL, C/EPBα, PU.1, and NF-E2, was significantly down-regulated, whereas the expression of SOCS1 and SOCS3 was up-regulated by vorinostat treatment. More importantly, we observed that vorinostat treatment normalized the peripheral blood counts and markedly reduced splenomegaly in Jak2V617F knock-in mice compared with placebo treatment. Vorinostat treatment also decreased the mutant allele burden in mice. Our results suggest that vorinostat may have therapeutic potential for the treatment of PV and other JAK2V617F-associated myeloproliferative neoplasms.

Antileukemic activity of the HSP70 inhibitor pifithrin-μ in acute leukemia

Heat shock protein (HSP) 70 is aberrantly expressed in different malignancies and has emerged as a promising new target for anticancer therapy. Here, we analyzed the in vitro antileukemic effects of pifithrin-μ (PFT-μ), an inhibitor of inducible HSP70, in acute myeloid leukemia (AML) and acute lymphoblastic leukemia (ALL) cell lines, as well as in primary AML blasts. PFT-μ significantly inhibited cell viability at low micromolar concentrations in all cell lines tested, with IC50 values ranging from 2.5 to 12.7 μ, and was highly active in primary AML blasts with a median IC50 of 8.9 μ (range 5.7–37.2). Importantly, higher IC50 values were seen in normal hematopoietic cells. In AML and ALL, PFT-μ induced apoptosis and cell cycle arrest in a dose-dependent fashion. PFT-μ also led to an increase of the active form of caspase-3 and reduced the intracellular concentrations of AKT and ERK1/2 in NALM-6 cells. Moreover, PFT-μ enhanced cytotoxicity of cytarabine, 17-(allylamino)-17-desmethoxygeldanamycin, suberoylanilide hydroxamic acid, and sorafenib in NALM-6, TOM-1 and KG-1a cells. This is the first study demonstrating significant antileukemic effects of the HSP70 inhibitor PFT-μ, alone and in combination with different antineoplastic drugs in both AML and ALL. Our results suggest a potential therapeutic role for PFT-μ in acute leukemias.

Myeloproliferative neoplasms: new translational therapies

The myeloproliferative neoplasms represent a diverse group of hematologic malignancies that have been the subject of intense investigation over the last decade. Although clinical trials of the much anticipated small molecule inhibitors of Janus kinase 2 have shown that these experimental agents are successful in palliating many of the symptoms associated with the myeloproliferative neoplasms, they have not been reported to affect the disease initiating hematopoietic stem cell population or to alter the natural history of these disorders. Investigators remain optimistic that new information about the genetic and cellular origins gained from the efforts of numerous laboratories will ultimately translate in to the identification of new drug targets and more effective therapies. We hypothesize that ultimately, the use of combinations of drugs including chromatin modifying agents, immunomodulatory agents, anti-apoptotic agents, cellular therapies and monoclonal antibodies will be required to effectively treat patients with myeloproliferative neoplasms.

Interpreting clinical assays for histone deacetylase inhibitors

As opposed to genetics, dealing with gene expressions by direct DNA sequence modifications, the term epigenetics applies to all the external influences that target the chromatin structure of cells with impact on gene expression unrelated to the sequence coding of DNA itself. In normal cells, epigenetics modulates gene expression through all development steps. When "imprinted" early by the environment, epigenetic changes influence the organism at an early stage and can be transmitted to the progeny. Together with DNA sequence alterations, DNA aberrant cytosine methylation and microRNA deregulation, epigenetic modifications participate in the malignant transformation of cells. Their reversible nature has led to the emergence of the promising field of epigenetic therapy. The efforts made to inhibit in particular the epigenetic enzyme family called histone deacetylases (HDACs) are described. HDAC inhibitors (HDACi) have been proposed as a viable clinical therapeutic approach for the treatment of leukemia and solid tumors, but also to a lesser degree for noncancerous diseases. Three epigenetic drugs are already arriving at the patient's bedside, and more than 100 clinical assays for HDACi are registered on the National Cancer Institute website. They explore the eventual additive benefits of combined therapies. In the context of the pleiotropic effects of HDAC isoforms, more specific HDACi and more informative screening tests are being developed for the benefit of the patients.

Histone deacetylase inhibitors for treating a spectrum of diseases not related to cancer

This issue of Molecular Medicine contains 14 original research reports and state-of-the-art reviews on histone deacetylase inhibitors (HDACi's), which are being studied in models of a broad range of diseases not related to the proapoptotic properties used to treat cancer. The spectrum of these diseases responsive to HDACi's is for the most part due to several antiinflammatory properties, often observed in vitro but importantly also in animal models. One unifying property is a reduction in cytokine production as well as inhibition of cytokine postreceptor signaling. Distinct from their use in cancer, the reduction in inflammation by HDACi's is consistently observed at low concentrations compared with the higher concentrations required for killing tumor cells. This characteristic makes HDACi's attractive candidates for treating chronic diseases, since low doses are well tolerated. For example, low oral doses of the HDACi givinostat have been used in children to reduce arthritis and are well tolerated. In addition to the antiinflammatory properties, HDACi's have shown promise in models of neurodegenerative disorders, and HDACi's also hold promise to drive HIV-1 out of latently infected cells. No one molecular mechanism accounts for the non-cancer-related properties of HDACi's, since there are 18 genes coding for histone deacetylases. Rather, there are mechanisms unique for the pathological process of specific cell types. In this overview, we summarize the preclinical data on HDACi's for therapy in a wide spectrum of diseases unrelated to the treatment of cancer. The data suggest the use of HDACi's in treating autoimmune as well as chronic inflammatory diseases.

The clinical development of histone deacetylase inhibitors as targeted anticancer drugs

IMPORTANCE OF THE FIELD

Histone deacetylase (HDAC) inhibitors are being developed as a new, targeted class of anticancer drugs.

AREA COVERED IN THIS REVIEW

This review focuses on the mechanisms of action of the HDAC inhibitors, which selectively induce cancer cell death.

WHAT THE READER WILL GAIN

There are 11 zinc-dependent HDACs in humans and the biological roles of these lysine deacetylases are not completely understood. It is clear that these different HDACs are not redundant in their activity. This review focuses on the mechanisms by which HDAC inhibitors can induce transformed cell growth arrest and cell death, inhibit cell mobility and have antiangiogenesis activity. There are more than a dozen HDAC inhibitors, including hydroxamates, cyclic peptides, benzamides and fatty acids, in various stages of clinical trials and many more compounds in preclinical development. The chemically different HDAC inhibitors may target different HDACs.

TAKE HOME MESSAGE

There are extensive preclinical studies with transformed cells in culture and tumor-bearing animal models, as well as limited clinical studies reported to date, which indicate that HDAC inhibitors will be most useful when used in combination with cytotoxic or other targeted anticancer agents.

The novel histone deacetylase inhibitor, AR-42, inhibits gp130/Stat3 pathway and induces apoptosis and cell cycle arrest in multiple myeloma cells

Multiple myeloma (MM) remains incurable with current therapy, indicating the need for continued development of novel therapeutic agents. We evaluated the activity of a novel phenylbutyrate-derived histone deacetylase inhibitor, AR-42, in primary human myeloma cells and cell lines. AR-42 was cytotoxic to MM cells at a mean LC(50) of 0.18 ± 0.06 μmol/l at 48 hr and induced apoptosis with cleavage of caspases 8, 9 and 3, with cell death largely prevented by caspase inhibition. AR-42 downregulated the expression of gp130 and inhibited activation of STAT3, with minimal effects on the PI3K/Akt and MAPK pathways, indicating a predominant effect on the gp130/STAT-3 pathway. AR-42 also inhibited interleukin (IL)-6-induced STAT3 activation, which could not be overcome by exogenous IL-6. AR-42 also downregulated the expression of STAT3-regulated targets, including Bcl-xL and cyclin D1. Overexpression of Bcl-xL by a lentivirus construct partly protected against cell death induced by AR-42. The cyclin dependent kinase inhibitors, p16 and p21, were also significantly induced by AR-42, which together with a decrease in cyclin D1, resulted in G(1) and G(2) cell cycle arrest. In conclusion, AR-42 has potent cytotoxicity against MM cells mainly through gp130/STAT-3 pathway. The results provide rationale for clinical investigation of AR-42 in MM.

Histone deacetylase (HDAC) inhibitors in recent clinical trials for cancer therapy

Heritable changes in gene expression that are not based upon alterations in the DNA sequence are defined as epigenetics. The most common mechanisms of epigenetic regulation are the methylation of CpG islands within the DNA and the modification of amino acids in the N-terminal histone tails. In the last years, it became evident that the onset of cancer and its progression may not occur only due to genetic mutations but also because of changes in the patterns of epigenetic modifications. In contrast to genetic mutations, which are almost impossible to reverse, epigenetic changes are potentially reversible. This implies that they are amenable to pharmacological interventions. Therefore, a lot of work in recent years has focussed on the development of small molecule enzyme inhibitors like DNA-methyltransferase inhibitors or inhibitors of histone-modifying enzymes. These may reverse misregulated epigenetic states and be implemented in the treatment of cancer or other diseases, e.g., neurological disorders. Today, several epigenetic drugs are already approved by the FDA and the EMEA for cancer treatment and around ten histone deacetylase (HDAC) inhibitors are in clinical development. This review will give an update on recent clinical trials of the HDAC inhibitors used systemically that were reported in 2009 and 2010 and will present an overview of different biomarkers to monitor the biological effects.

A pilot study of the Histone-Deacetylase inhibitor Givinostat in patients with JAK2V617F positive chronic myeloproliferative neoplasms

A phase II A study was conducted to evaluate the safety and efficacy of Givinostat, a novel Histone-Deacetylases inhibitor, in patients with Polycythaemia Vera (PV, n = 12), Essential Thrombocythaemia (ET, n = 1) and Myelofibrosis (n = 16), bearing the JAK2V617F mutation. The study was approved by the local ethics committees and all human participants gave written informed consent. Givinostat was given orally for 24 weeks at a starting dose of 50 mg twice daily. The median treatment duration was 20 weeks. Reasons for treatment discontinuation were disease progression (n = 6), grade 2 thrombocytopenia (n = 1), psychiatric symptoms (n = 1) and withdrawn consent (n = 2). A dose reduction was applied in 10 patients while a temporary interruption occurred in 15. Among 13 PV/ET patients, 1 complete, 6 partial and 4 no responses were documented at study end while 2 patients went off-study, prematurely. Three major responses were registered among 16 MF patients. Pruritus disappeared in most patients and reduction of splenomegaly was observed in 75% of PV/ET and 38% of MF patients. Reverse transcription polymerase chain reaction identified a trend to reduction of the JAK2V617F allele burden. Givinostat was well tolerated and could induce haematological response in most PV and some MF patients.

The histone deacetylase inhibitor ITF2357 decreases surface CXCR4 and CCR5 expression on CD4(+) T-cells and monocytes and is superior to valproic acid for latent HIV-1 expression in vitro

OBJECTIVES

Chromatin-associated repression is one mechanism that maintains HIV-1 latency. Inhibition of histone deacetylases (HDAC) reverses this repression resulting in viral expression from quiescently infected cells. Clinical studies with the HDAC inhibitor valproic acid (VPA) failed to substantially decrease the latent pool within resting CD4(+) cells. Here we compared the efficacy of ITF2357, an orally active and safe HDAC inhibitor, with VPA for HIV-1 expression from latently infected cells in vitro. We also evaluated the effect of ITF2357 on the surface expression of CXCR4 and CCR5.

METHODS

Latently infected cell lines were incubated with either ITF2357 or VPA and p24 levels were measured. Peripheral blood mononuclear cells of uninfected donors were treated with ITF2357 and HIV-1 coreceptors expression was assessed by flow cytometry.

RESULTS

At clinically relevant concentrations, ITF2357 increased p24 by 15-fold in ACH2 cells and by 9-fold in U1 cells, whereas VPA increased expression less than 2-fold. Analogues of ITF2357 primarily targeting HDAC-1 increased p24 up to 30-fold. In CD4(+) T cells treated with ITF2357, CXCR4 expression decreased by 54% (P < 0.001).

CONCLUSION

ITF2357 is superior to VPA in inducing HIV-1 from latently infected cells. Safely used in humans, ITF2357 is an attractive candidate for HIV-1 clinical purging.

Therapy of myelofibrosis (excluding JAK2 inhibitors)

Myelofibrosis shows a progressive clinical course and usually a poor, lethal prognosis. Allogeneic transplantation is an effective, potentially curable treatment approach although only a minority of patients may currently benefit from it. New effective treatment strategies are becoming available for this disease, including not only JAK2 inhibitors, but also other innovative drugs, targeting more general oncogenic mechanisms and the epigenetic control of cell proliferation and differentiation.

Therapeutic efficacy of the pan-cdk inhibitor PHA-793887 in vitro and in vivo in engraftment and high-burden leukemia models

OBJECTIVE

The aim of the work was to determine and characterize, in vitro and in vivo, the therapeutic activity of PHA-793887, a new potent pan-cdk inhibitor, in the context of hematopoietic neoplasms.

MATERIALS AND METHODS

Thirteen leukemic cell lines bearing different cytogenetic abnormalities and normal hematopoietic cells were used in cytotoxicity and colony assays. The drug activity at the molecular level was analyzed by Western blotting. PHA-793887 was also tested in vivo in several leukemia xenograft models.

RESULTS

PHA-793887 was cytotoxic for leukemic cell lines in vitro, with IC(50) ranging from 0.3 to 7 microM (mean: 2.9 microM), regardless of any specific chromosomal aberration. At these doses, the drug was not cytotoxic for normal unstimulated peripheral blood mononuclear cells or CD34(+) hematopoietic stem cells. Interestingly, in colony assays PHA-793887 showed very high activity against leukemia cell lines, with an IC(50) <0.1 microM (mean: 0.08 microM), indicating that it has efficient and prolonged antiproliferative activity. PHA-793887 induced cell-cycle arrest, inhibited Rb and nucleophosmin phosphorylation, and modulated cyclin E and cdc6 expression at low doses (0.2-1 microM) and induced apoptosis at the highest dose (5 microM). It was also effective in vivo in both subcutaneous xenograft and primary leukemic disseminated models that better mimic naturally occurring human disease. Interestingly, in one disseminated model derived from a relapsed Philadelphia-positive acute lymphoid leukemia patient, PHA-793887 showed strong therapeutic activity also when treatment was started after establishment of high disease burden.

CONCLUSIONS

We conclude that PHA-793887 has promising therapeutic activity against acute leukemias in vitro and in vivo.

Novel histone deacetylase inhibitors in clinical trials as anti-cancer agents

Histone deacetylases (HDACs) can regulate expression of tumor suppressor genes and activities of transcriptional factors involved in both cancer initiation and progression through alteration of either DNA or the structural components of chromatin. Recently, the role of gene repression through modulation such as acetylation in cancer patients has been clinically validated with several inhibitors of HDACs. One of the HDAC inhibitors, vorinostat, has been approved by FDA for treating cutaneous T-cell lymphoma (CTCL) for patients with progressive, persistent, or recurrent disease on or following two systemic therapies. Other inhibitors, for example, FK228, PXD101, PCI-24781, ITF2357, MGCD0103, MS-275, valproic acid and LBH589 have also demonstrated therapeutic potential as monotherapy or combination with other anti-tumor drugs in CTCL and other malignancies. At least 80 clinical trials are underway, testing more than eleven different HDAC inhibitory agents including both hematological and solid malignancies. This review focuses on recent development in clinical trials testing HDAC inhibitors as anti-tumor agents.

The potential role of epigenetic therapy in multiple myeloma

This review describes the role that epigenetic changes play in the pathogenesis of cancer, concentrating on the plasma cell malignancy multiple myeloma, and highlights recent findings regarding the efficacy of epigenetic therapeutic agents in laboratory studies and clinical trials. DNA methylation is altered in a wide range of cancers with hypermethylation of CpG islands associated with silencing of tumour suppressor genes. Genes found to be silenced by methylation in myeloma samples include VHL, TP53, CDKN2A, and TGFBR2. Myeloma is linked to the overexpression of a histone methylatransferase (MMSET) and inactivating mutations of a histone demethylase (UTX), suggesting that the regulation of histone methylation is a potential therapeutic target. Abnormal expression of histone deacetylases (HDACs) has been widely described in solid tumours and haematological malignancies. In myeloma, histone deacetylase inhibitors show promising results both in laboratory-based cell culture studies and in clinical trials, where they demonstrate particularly good therapeutic outcome when administered in combination with other standard chemotherapeutic agents. The study of epigenetics shows great promise for understanding the alterations in gene expression that underlie malignancies and provides exciting novel drugable targets.

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.

Pleiotropic anti-myeloma activity of ITF2357: inhibition of interleukin-6 receptor signaling and repression of miR-19a and miR-19b

BACKGROUND

The histone deacetylase inhibitor ITF2357 has potent cytotoxic activity in multiple myeloma in vitro and has entered clinical trials for this disease.

DESIGN AND METHODS

In order to gain an overall view of the activity of ITF2357 and identify specific pathways that may be modulated by the drug, we performed gene expression profiling of the KMS18 multiple myeloma cell line treated with the drug. The modulation of several genes and their biological consequence were verified in a panel of multiple myeloma cell lines and cells freshly isolated from patients by using polymerase chain reaction analysis and western blotting.

RESULTS

Out of 38,500 human genes, we identified 140 and 574 up-regulated genes and 102 and 556 down-modulated genes at 2 and 6 h, respectively, with a significant presence of genes related to transcription regulation at 2 h and to cell cycling and apoptosis at 6 h. Several of the identified genes are particularly relevant to the biology of multiple myeloma and it was confirmed that ITF2357 also modulated their encoded proteins in different multiple myeloma cell lines. In particular, ITF2357 down-modulated the interleukin-6 receptor alpha (CD126) transcript and protein in both cell lines and freshly isolated patients' cells, whereas it did not significantly modify interleukin-6 receptor beta (CD130) expression. The decrease in CD126 expression was accompanied by decreased signaling by interleukin-6 receptor, as measured by STAT3 phosphorylation in the presence and absence of inter-leukin-6. Finally, the drug significantly down-modulated the MIRHG1 transcript and its associated microRNA, miR-19a and miR-19b, known to have oncogenic activity in multiple myeloma.

CONCLUSIONS

ITF2357 inhibits several signaling pathways involved in myeloma cell growth and survival.

Epigenetic therapy in myeloproliferative neoplasms: evidence and perspectives

The classic Philadelphia chromosome-negative myeloproliferative neoplasms (MPNs), which include polycythaemia vera, essential thrombocythaemia and primary myelofibrosis, originate from a stem cell-derived clonal myeloproliferation that manifests itself with variable haematopoietic cell lineage involvement; they are characterized by a high degree of similarities and the chance to transform each to the other and to evolve into acute leukaemia. Their molecular pathogenesis has been associated with recurrent acquired mutations in janus kinase 2 (JAK2) and myeloproliferative leukemia virus oncogene (MPL). These discoveries have simplified the diagnostic approach and provided a number of clues to understanding the phenotypic expression of MPNs; furthermore, they represented a framework for developing and/or testing in clinical trials small molecules acting as tyrosine kinase inhibitors. On the other hand, evidence of abnormal epigenetic gene regulation as a mechanism potentially contributing to the pathogenesis and the phenotypic diversity of MPNs is still scanty; however, study of epigenetics in MPNs represents an active field of research. The first clinical trials with epigenetic drugs have been completed recently, whereas others are still ongoing; results have been variable and at present do not allow any firm conclusion. Novel basic and translational information concerning epigenetic gene regulation in MPNs and the perspectives for therapy will be critically addressed in this review.

HDAC inhibitor-based therapies and haematological malignancy

Reversible acetylation mediated by histone deacetylase (HDAC) influences a broad repertoire of physiological processes, many of which are aberrantly controlled in tumour cells. Since HDAC inhibition prompts tumour cells to enter apoptosis, small-molecule HDAC inhibitors have been developed as a new class of mechanism-based anticancer agent, many of which have entered clinical trials. While the clinical picture is evolving and the precise utility of HDAC inhibitors remains to be determined, it is noteworthy that certain tumour types undergo a favourable response, in particular haematological malignancies. Vorinostat (suberoylanilide hydroxamic acid) has been approved for treating cutaneous T-cell lymphoma in patients with progressive, persistent or recurrent disease. Here, we discuss developments in our understanding of molecular events that underlie the anticancer effects of HDAC inhibitors and relate this information to the emerging clinical picture for the application of HDAC inhibitors in haematological malignancies.

Increased signaling through p62 in the marrow microenvironment increases myeloma cell growth and osteoclast formation

Adhesive interactions between multiple myeloma (MM) cells and marrow stromal cells activate multiple signaling pathways including nuclear factor kappaB (NF-kappaB), p38 mitogen-activated protein kinase (MAPK), and Jun N-terminal kinase (JNK) in stromal cells, which promote tumor growth and bone destruction. Sequestosome-1 (p62), an adapter protein that has no intrinsic enzymatic activity, serves as a platform to facilitate formation of signaling complexes for these pathways. Therefore, we determined if targeting only p62 would inhibit multiple signaling pathways activated in the MM microenvironment and thereby decrease MM cell growth and osteoclast formation. Signaling through NF-kappaB and p38 MAPK was increased in primary stromal cells from MM patients. Increased interleukin-6 (IL-6) production by MM stromal cells was p38 MAPK-dependent while increased vascular cell adhesion molecule-1 (VCAM-1) expression was NF-kappaB-dependent. Knocking-down p62 in patient-derived stromal cells significantly decreased protein kinase Czeta (PKCzeta), VCAM-1, and IL-6 levels as well as decreased stromal cell support of MM cell growth. Similarly, marrow stromal cells from p62(-/-) mice produced much lower levels of IL-6, tumor necrosis factor-alpha (TNF-alpha), and receptor activator of NF-kappaB ligand (RANKL) and supported MM cell growth and osteoclast formation to a much lower extent than normal cells. Thus, p62 is an attractive therapeutic target for MM.

Antitumor effects of a novel sulfur-containing hydroxamate histone deacetylase inhibitor H40

Histone deacetylase (HDAC) inhibitors are among the most promising targeted anticancer agents and are potent inducers of growth arrest, differentiation, and/or apoptotic cell death of transformed cells. In this study, antitumor effects of a novel sulfur-containing hydroxamate HDAC inhibitor, H40, were observed and compared with a typical HDAC inhibitor SAHA. In biochemical HDAC assay, H40 showed a potent HDAC inhibition. It induced histone H3 hyperacetylation, correlating with inhibition of cancer cell proliferation, induction of cell differentiation and cell cycle blockage. A broad cytotoxicity was observed across cell lines from different tumor entities. The autophagy rather than apoptosis inducing activity for both H40 and SAHA was observed in prostate cancer PC-3M cells. HDAC inhibitor-induced p21(CIP/WAF1) expression was evident in PC-3M and HL-60 cell lines. The in vivo efficacy of H40 against a murine prostate carcinoma TRAMP-C2 was compared with that of SAHA, which showed that H40 exerted a favorable antitumor action when only administered twice a week. We conclude that H40 might have clinical value in cancer chemotherapy and warrants further investigation in this regard.

Blocking TH17-polarizing cytokines by histone deacetylase inhibitors in vitro and in vivo

Histone deacetylase (HDAC) inhibitors are small molecules inducing cell-cycle arrest, differentiation, and apoptosis, currently undergoing clinical trials as anticancer drugs. In addition, emerging evidence suggests HDAC inhibitors may have anti-inflammatory and immunomodulatory properties as well, although the molecular mechanisms remain poorly defined. Given the central role of dendritic cells (DC) in the induction and maintenance of the inflammatory and immune response, we investigated the effects of HDAC inhibitors on the maturation and activation of human monocyte-derived DC in the presence of LPS and IFN-gamma. Our results show that the production of T(H)1- and T(H)17-inducing cytokines, namely IL-12 and IL-23, was inhibited by trichostatin A (72% and 52%, respectively) and suberoylanilide hydroxamic acid (86% and 83%). Strikingly, HDAC inhibitors were effective if added simultaneously as well as after the proinflammatory challenge, and their effect was not associated to a reduction of expression or function of LPS/IFN-gamma receptors. These findings were confirmed in two different murine models. In addition, HDAC inhibitors selectively blocked the production of T(H)1-attracting chemokines CXCL9, CXCL10, and CXCL11. The reduction of T(H)1- and T(H)17-inducing cytokines as well as T(H)1-attracting chemokines may represent relevant mechanisms through which HDAC inhibitors at nonproapoptotic doses exert their immunomodulatory properties.

Histone deacetylase inhibitors in cancer therapy

PURPOSE OF REVIEW

The purpose of this review is to provide an overview of recent advances in the development of histone deacetylase inhibitors (HDACi) for the treatment of cancer.

RECENT FINDINGS

Recently, there has been a dramatic expansion of HDACi clinical investigation. There are now 11 HDACi in clinical trial, including inhibitors with a broad spectrum of HDAC isoform inhibitory activity as well as drugs with isoform selectivity. Over 70 combination therapy trials are in progress. Major areas of progress covered include the entry of new HDAC inhibitors into clinical development, recent progress in understanding of molecular mechanisms of HDACi anticancer activity, and a preclinical and clinical update on HDACi in combination.

SUMMARY

In the period under review there have been advances in understanding of HDACi mechanisms of action, identification of rational combinations that address increased efficacy and overcoming resistance, and greatly expanded clinical development of pan-HDAC-inhibitory and isoform-selective inhibitors in monotherapy and combination therapy protocols.

The bone marrow microenvironment as a tumor sanctuary and contributor to drug resistance

The bone marrow microenvironment facilitates the survival, differentiation, and proliferation of hematopoietic cells. These cells are supported by fibroblast-like bone marrow stromal cells, osteoblasts, and osteoclasts which secrete soluble factors and extracellular matrix proteins that mediate these functions. This rich environment serves as a safe haven not only for normal and malignant hematopoietic cells, but also for epithelial tumor cells that metastasize to bone, offering protection from chemotherapeutic agents by common mechanisms. Soluble factors produced in the bone marrow, such as stromal cell-derived factor-1 and interleukin-6, mediate homing, survival, and proliferation of tumor cells, and integrin-mediated adhesion sequesters tumor cells to this protective niche. Environment-mediated drug resistance includes a combination of soluble factors and adhesion, and can be subdivided into soluble factor-mediated drug resistance and cell adhesion-mediated drug resistance. Because it is induced immediately by the microenvironment and is independent of epigenetic or genetic changes caused by the selective pressure of drug exposure, environment-mediated drug resistance is a form of de novo drug resistance. In this form of drug resistance, tumor cells are transiently and reversibly protected from apoptosis induced by both chemotherapy and physiologic mediators of cell death. This protection allows tumor cells to survive the insult of chemotherapy, leading to minimal residual disease, and thereby increases the probability for the development of acquired drug resistance.

From palliation to epigenetic therapy in myelofibrosis

Myelofibrosis shows a progressive clinical course and usually a poor, lethal prognosis. The molecular pathogenesis of this disease largely remains to be fully understood but the identification of the JAK2V617F mutation in more than half of patients was a major improvement in our understanding of the disease biology and may represent the first biologic marker useful for risk stratification, independently from conventional clinical predictors. After many elusive efforts, new effective treatment strategies are becoming available for this disease. Allogeneic transplantation following reduced-intensity conditioning programs, at least in some patients, may induce not only a hematologic response but also a molecular remission, thus supporting the hope of a possible, definitive eradication of the disease. Moreover, new innovative drugs, targeting either the JAK2V617F mutation or more general oncogenic mechanisms, may provide widely applicable, effective treatments to many patients for whom allogeneic transplantation is not feasible.

The histone deacetylase inhibitor ITF2357 selectively targets cells bearing mutated JAK2(V617F)

We investigated the activity of ITF2357, a novel histone deacetylase inhibitor (HDACi) with antitumor activity, on cells carrying the JAK2(V617F) mutation obtained from polycythemia vera (PV) and essential thrombocythemia (ET) patients as well as the HEL cell line. The clonogenic activity of JAK2(V617F) mutated cells was inhibited by low concentrations of ITF2357 (IC(50) 0.001-0.01 microM), 100- to 250-fold lower than required to inhibit growth of normal or tumor cells lacking this mutation. Under these conditions, ITF2357 allowed a seven fold increase in the outgrowth of unmutated over mutated colonies. By western blotting we showed that in HEL cells, ITF2357 led to the disappearance of total and phosphorylated JAK2(V617F) as well as pSTAT5 and pSTAT3, but it did not affect the wild-type JAK2 or STAT proteins in the control K562 cell line. By real-time PCR, we showed that, upon exposure to ITF2357, JAK2(V617F) mRNA was not modified in granulocytes from PV patients while the expression of the PRV-1 gene, a known target of JAK2, was rapidly downmodulated. Altogether, the data presented suggest that ITF2357 inhibits proliferation of cells bearing the JAK2(V617F) mutation through a specific downmodulation of the JAK2(V617F) protein and inhibition of its downstream signaling.