Anti-neuroblastoma activity of Helminthosporium carbonum (HC)-toxin is superior to that of other differentiating compounds in vitro

Large-scale and high-resolution mass spectrometry-based proteomics profiling defines molecular subtypes of esophageal cancer for therapeutic targeting

Esophageal cancer (EC) is a type of aggressive cancer without clinically relevant molecular subtypes, hindering the development of effective strategies for treatment. To define molecular subtypes of EC, we perform mass spectrometry-based proteomic and phosphoproteomics profiling of EC tumors and adjacent non-tumor tissues, revealing a catalog of proteins and phosphosites that are dysregulated in ECs. The EC cohort is stratified into two molecular subtypes-S1 and S2-based on proteomic analysis, with the S2 subtype characterized by the upregulation of spliceosomal and ribosomal proteins, and being more aggressive. Moreover, we identify a subtype signature composed of ELOA and SCAF4, and construct a subtype diagnostic and prognostic model. Potential drugs are predicted for treating patients of S2 subtype, and three candidate drugs are validated to inhibit EC. Taken together, our proteomic analysis define molecular subtypes of EC, thus providing a potential therapeutic outlook for improving disease outcomes in patients with EC.

Histone Deacetylases and Histone Deacetylase Inhibitors in Neuroblastoma

Histone deacetylases (HDACs) are enzymes that play a key role in regulating gene expression by remodeling chromatin structure. An imbalance of histone acetylation caused by deregulated HDAC expression and activity is known to promote tumor progression in a number of tumor types, including neuroblastoma, the most common solid tumor in children. Consequently, the inhibition of HDACs has emerged as a potential strategy to reverse these aberrant epigenetic changes, and several classes of HDAC inhibitors (HDACi) have been shown to inhibit tumor proliferation, or induce differentiation, apoptosis and cell cycle arrest in neuroblastoma. Further, the combined use of HDACi with other chemotherapy agents, or radiotherapy, has shown promising pre-clinical results and various HDACi have progressed to different stages in clinical trials. Despite this, the effects of HDACi are multifaceted and more work needs to be done to unravel their specific mechanisms of actions. In this review, we discuss the functional role of HDACs in neuroblastoma and the potential of HDACi to be optimized for development and use in the clinic for treatment of patients with neuroblastoma.

Epoxide containing molecules: A good or a bad drug design approach

Functional group modification is one of the main strategies used in drug discovery and development. Despite the controversy of being identified for many years as a biologically hazardous functional group, the introduction of an epoxide function in a structural backbone is still one of the possible modifications being implemented in drug design. In this manner, it is our intention to prove with this work that epoxides can have significant interest in medicinal chemistry, not only as anticancer agents, but also as important drugs for other pathologies. Thus, this revision paper aims to highlight the biological activity and the proposed mechanisms of action of several epoxide-containing molecules either in preclinical studies or in clinical development or even in clinical use. An overview of the chemistry of epoxides is also reported. Some of the conclusions are that effectively most of the epoxide-containing molecules referred in this work were being studied or are in the market as anticancer drugs. However, some of them in preclinical studies, were also associated with other different activities such as anti-malarial, anti-arthritic, insecticidal, antithrombotic, and selective inhibitory activity of FXIII-A (a transglutaminase). As for the epoxide-containing molecules in clinical trials, some of them are being tested for obesity and schizophrenia. Finally, drugs containing epoxide groups already in the market are mostly used for the treatment of different types of cancer, such as breast cancer and multiple myeloma. Other diseases for which the referred drugs are being used include heart failure, infections and gastrointestinal disturbs. In summary, epoxides can be a suitable option in drug design, particularly in the design of anticancer agents, and deserve to be better explored. However, and despite the promising results, it is imperative to explore the mechanisms of action of these compounds in order to have a better picture of their efficiency and safety.

Natural Products and Chemical Biology Tools: Alternatives to Target Epigenetic Mechanisms in Cancers

DNA methylation and histone acetylation are widely studied epigenetic modifications. They are involved in numerous pathologies such as cancer, neurological disease, inflammation, obesity, etc. Since the discovery of the epigenome, numerous compounds have been developed to reverse DNA methylation and histone acetylation aberrant profile in diseases. Among them several were inspired by Nature and have a great interest as therapeutic molecules. In the quest of finding new ways to target epigenetic mechanisms, the use of chemical tools is a powerful strategy to better understand epigenetic mechanisms in biological systems. In this review we will present natural products reported as DNMT or HDAC inhibitors for anticancer treatments. We will then discuss the use of chemical tools that have been used in order to explore the epigenome.

Gene expression profiling coupled with Connectivity Map database mining reveals potential therapeutic drugs for Hirschsprung disease

BACKGROUND

Hirschsprung disease (HD) is a congenital intestinal anomaly resulting from a failure to form enteric ganglia in the lower bowel. Surgery is the main therapeutic strategy, although neural stem cell transplantation has recently shown promise. However, HD remains a challenging disorder to treat. Our aim was to identify drugs that could counteract the dysregulated pathways in HD and could thus be potential novel therapies.

METHODS

We used microarray analysis to identify genes differentially expressed in ganglionic and aganglionic bowel samples from eight children with HD. The signature of differentially expressed genes was then used as a search query to explore the Connectivity Map (cMAP), a transcriptional expression database that catalogs gene signatures elicited by chemical perturbagens.

RESULTS

We uncovered several dysregulated signaling pathways, and in particular regulation of neuron development, in HD. The cMAP search identified some compounds with the potential to counteract the effects of the dysregulated molecular signature in this disease. One of these, pepstatin A, was recently shown to rescue the migration defects observed in a mouse model of HD, providing strong support for our findings.

CONCLUSIONS

This study advances our understanding of the molecular changes in HD and identifies several potential pharmacological interventions. Further testing of the identified compounds is warranted.

Targeting of epigenetic regulators in neuroblastoma

Approximately 15,000 new cases of pediatric cancer are diagnosed yearly in Europe, with 8–10% corresponding to neuroblastoma, a rare disease with an incidence of 8–9 cases per million children <15 years of age. Although the survival rate for low-risk and intermediate-risk patients is excellent, half of children with high-risk, refractory, or relapsed tumors will be cured, and two-thirds of the other half will suffer major side effects and life-long disabilities. Epigenetic therapies aimed at reversing the oncogenic alterations in chromatin structure and function are an emerging alternative against aggressive tumors that are or will become resistant to conventional treatments. This approach proposes targeting epigenetic regulators, which are proteins that are involved in the creation, detection, and interpretation of epigenetic signals, such as methylation or histone post-translational modifications. In this review, we focused on the most promising epigenetic regulators for targeting and current drugs that have already reached clinical trials.

Treatments that target chromatin, the combination of DNA and proteins, are emerging as alternative ways to treat aggressive neuroblastomas, cancers of neural tissue. Altering the structure and function of chromatin is a form of “epigenetic therapy”, treatment that affects inheritable molecular signals controlling the activity of genes, rather than targeting the genes directly. Researchers in Spain led by Miguel Segura at the Vall d’Hebron Research Institute in Barcelona review progress in developing epigenetic therapies for neuroblastomas. A growing body of fundamental research and evidence from clinical trials suggest this approach could open promising new avenues to treating aggressive and drug-resistant cancers. The authors recommend an increased effort to identify and explore the activities of small molecules that could form the basis of effective epigenetic therapies for various cancers.

MYCN and HDAC5 transcriptionally repress CD9 to trigger invasion and metastasis in neuroblastoma

The systemic and resistant nature of metastatic neuroblastoma renders it largely incurable with current multimodal treatment. Clinical progression stems mainly from the increasing burden of metastatic colonization. Therapeutically inhibiting the migration-invasion-metastasis cascade would be of great benefit, but the mechanisms driving this cycle are as yet poorly understood. In-depth transcriptome analyses and ChIP-qPCR identified the cell surface glycoprotein, CD9, as a major downstream player and direct target of the recently described GRHL1 tumor suppressor. CD9 is known to block or facilitate cancer cell motility and metastasis dependent upon entity. High-level CD9 expression in primary neuroblastomas correlated with patient survival and established markers for favorable disease. Low-level CD9 expression was an independent risk factor for adverse outcome. MYCN and HDAC5 colocalized to the CD9 promoter and repressed transcription. CD9 expression diminished with progressive tumor development in the TH-MYCN transgenic mouse model for neuroblastoma, and CD9 expression in neuroblastic tumors was far below that in ganglia from wildtype mice. Primary neuroblastomas lacking MYCN amplifications displayed differential CD9 promoter methylation in methyl-CpG-binding domain sequencing analyses, and high-level methylation was associated with advanced stage disease, supporting epigenetic regulation. Inducing CD9 expression in a SH-EP cell model inhibited migration and invasion in Boyden chamber assays. Enforced CD9 expression in neuroblastoma cells transplanted onto chicken chorioallantoic membranes strongly reduced metastasis to embryonic bone marrow. Combined treatment of neuroblastoma cells with HDAC/DNA methyltransferase inhibitors synergistically induced CD9 expression despite hypoxic, metabolic or cytotoxic stress. Our results show CD9 is a critical and indirectly druggable suppressor of the invasion-metastasis cycle in neuroblastoma.

Occurrence, biochemistry and biological effects of host-selective plant mycotoxins

Host-selective mycotoxins (HSTs) are various secondary metabolites or proteinaceous compounds secreted by pathogenic necrotrophic fungi that feed off on dead tissues of certain plants. Research on the HSTs has not only fundamental but also practical importance. On one hand they are implicated in the onset of devastating crop diseases. On the other hand, they have been studied as a good model for revealing the intricate mechanisms of plant-pathogen interactions. At the cellular level, HSTs target different compartments and in most instances induce programmed cell death (PCD) by a wide range of mechanisms. Often the responses provoked by HSTs resemble the effector-triggered immunity used by plant cells to combat biotrophic pathogens, which suggests that HST-producing fungi exploit the plants' own defensive systems to derive benefits. Although by definition HSTs are active only in tissues of susceptible plant genotypes, it has been demonstrated that some of them are able to influence animal cells as well. The possible effects, like cytotoxicity or cytostasis, can be harmful or beneficial and thus HSTs may either pose a health risk for humans and livestock, or be of prospective use in the fields of pharmacology, medicine and agriculture.

Acetazolamide potentiates the anti-tumor potential of HDACi, MS-275, in neuroblastoma

BACKGROUND

Neuroblastoma (NB), a tumor of the primitive neural crest, despite aggressive treatment portends a poor long-term survival for patients with advanced high stage NB. New treatment strategies are required.

METHODS

We investigated coordinated targeting of essential homeostatic regulatory factors involved in cancer progression, histone deacetylases (HDACs) and carbonic anhydrases (CAs).

RESULTS

We evaluated the antitumor potential of the HDAC inhibitor (HDACi), pyridylmethyl-N-{4-[(2-aminophenyl)-carbamoyl]-benzyl}-carbamate (MS-275) in combination with a pan CA inhibitor, acetazolamide (AZ) on NB SH-SY5Y, SK-N-SH and SK-N-BE(2) cells. The key observation was that the combination AZ + MS-275 significantly inhibited growth, induced cell cycle arrest and apoptosis, and reduced migration capacity of NB cell line SH-SY5Y. In addition, this combination significantly inhibited tumor growth in vivo, in a pre-clinical xenograft model. Evidence was obtained for a marked reduction in tumorigenicity and in the expression of mitotic, proliferative, HIF-1α and CAIX. NB xenografts of SH-SY5Y showed a significant increase in apoptosis.

CONCLUSION

MS-275 alone at nanomolar concentrations significantly reduced the putative cancer stem cell (CSC) fraction of NB cell lines, SH-SY5Y and SK-N-BE(2), in reference to NT2/D1, a teratocarcinoma cell line, exhibiting a strong stem cell like phenotype in vitro. Whereas stemness genes (OCT4, SOX2 and Nanog) were found to be significantly downregulated after MS-275 treatment, this was further enhanced by AZ co-treatment. The significant reduction in initial tumorigenicity and subsequent abrogation upon serial xenografting suggests potential elimination of the NB CSC fraction. The significant potentiation of MS-275 by AZ is a promising therapeutic approach and one amenable for administration to patients given their current clinical utility.

Histone deacetylase inhibitor screening identifies HC toxin as the most effective in intrahepatic cholangiocarcinoma cells

Histone deacetylases (HDACs) are highly expressed in intrahepatic cholangiocarcinoma (ICC) and are associated with poor prognosis of these patients. The aim of the present study was to explore the inhibitory effects of HDAC inhibitors on ICC cells and identify effective and sensitive drugs for ICC. Effects of 34 HDAC inhibitors were screened through two rounds of cell viability assays, and HC toxin, a cyclic tetrapeptide first isolated from the secondary metabolite of Helminthosporium carbonum, exhibited an antitumor activity superior to that of the other HDAC inhibitors and gemcitabine. The mechanisms involved in the inhibitory effects of HC toxin on CCLP-1 cells were investigated by cell counting, colony formation assay, cell morphological observation, real-time PCR, western blotting and flow cytometry. It was demonstrated that HC toxin inhibited the cell proliferation and clone formation ability of the CCLP-1 cells. HC toxin increased the acetyl-histone H4 level and this was associated with the inhibitory effect of HC toxin on the CCLP-1 cells. We also found that HC toxin reduced the level of HDAC1 protein in a post-transcriptional manner. Morphological observation showed multiple morphological changes and indicated the possibility of cell differentiation owing to HC toxin. With increasing concentration of HC toxin, the cell cycle was gradually arrested at the G0/G1 stage and the percentage of apoptotic cells increased which was not mainly through the caspase-3-dependent ways. These results indicated that HC toxin was the most effective among the various HDAC inhibitors with multiple functions in the suppression of ICC in vitro. Thus, HC may be a potential chemotherapeutic for ICC.

Polyploid giant cancer cells with budding and the expression of cyclin E, S-phase kinase-associated protein 2, stathmin associated with the grading and metastasis in serous ovarian tumor

BACKGROUND

We previously reported that polyploid giant cancer cells (PGCCs) exhibit cancer stem cell properties and express cell cycle-related proteins. HEY PGCCs induced by cobalt chloride generated daughter cells and the daughter cells had a strong migratory and invasive ability. This study is to compare the expression of cyclin E, S-phase kinase-associated protein 2 (SKP2), and stathmin between PGCCs with budding and control HEY cells, and determine the clinicopathological significance of cell cycle-related protein expression in ovarian tumors.

METHODS

We used western blot and immunocytochemical staining to compare the expression levels of cyclin E, SKP2 and stathmin between PGCC with budding daughter cells and control HEY cells. In addition, immunohistochemical staining for cyclin E, SKP2 and stathmin was performed on a total of 80 paraffin-embedded serous ovarian tumor tissue samples. The samples included 21 cases of primary high-grade carcinoma (group I) and their metastatic tumors (group II), 26 cases of primary low-grade carcinoma without metastasis (group III), and 12 cases of serous borderline cystadenoma (group IV).

RESULTS

Single PGCC with budding in the stroma showed high correlation with the metastasis of ovarian carcinoma. Group I had a significantly higher number of single PGCCs with budding in the stroma than group III (85.71% [18/21] vs. 23.08% [6/26] cases; χ2 = 18.240, P = 0.000). The expression of cyclin E, SKP2, and stathmin was compared among the four groups. The expression levels of cyclin E, SKP2, and stathmin increased with the malignant grade of ovarian tumors and group II had the highest expression levels. The expression of cyclin E (χ2 = 17.985, P = 0.000), SKP2 (χ2 = 12.384, P = 0.000), and stathmin (χ2 = 20.226, P = 0.000) was significantly different among the 4 groups.

CONCLUSIONS

These data suggest that the cell cycle-related proteins cyclin E, SKP2, and stathmin may be valuable biomarkers to evaluate the metastasis in patients with ovarian serous carcinoma.

Effects of the epigenetic drug MS-275 on the release and function of exosome-related immune molecules in hepatocellular carcinoma cells

Background

Tumor-derived exosomes have been viewed as a source of tumor antigens that can be used to induce anti-tumor immune responses. In the current study, we aim to investigate the regulatory effect of the epigenetic drug MS-275 on hepatoma G2 (HepG2) cell-derived exosomes, especially for their immunostimulatory properties and alteration of some non-specific immune protein expression, such as heat shock protein (HSP) 70, major histocompatibility complex (MHC) class I polypeptide-related sequence A (MICA) and MICB.

Methods

MS-275 was used to modulate the secretion of exosomes in human HepG2 cells, and exosomes from untreated HepG2 cells served as negative controls. RT-PCR was used to test the expression of HSP70, MICA and MICB in HepG2 cells. Immunogold labeling of exosomes and western blotting analysis were carried out to compare the expression of HSP70, MICA and MICB proteins in exosomes with or without MS-275 treatment. A natural killer (NK) cell cytotoxicity assay and peripheral blood mononuclear cell (PBMC) proliferation assay were used to evaluate the effect of MS-275 on the immunostimulatory ability of exosomes.

Results

Immunogold labeling and western blot analysis showed that modification of MS-275 increased the expression of HSP70 and MICB in exosomes. RT-PCR showed the mRNA levels of HSP70 and MICB were upregulated in HepG2 cells and were consistent with their protein levels in exosomes. The exosomes modified by MS-275 could significantly increase the cytotoxicity of NK cells and proliferation of PBMC (P < 0.05).

Conclusions

The non-specific immune response of exosomes derived from HepG2 cells could be enhanced with treatment by the histone deacetylase inhibitor (HDACi) drug MS-275; this could provide a potential tumor vaccine strategy against liver cancer.

Conservation of the genes for HC-toxin biosynthesis in Alternaria jesenskae

Background

HC-toxin, a cyclic tetrapeptide, is a virulence determinant for the plant pathogenic fungus Cochliobolus carbonum. It was recently discovered that another fungus, Alternaria jesenskae, also produces HC-toxin.

Results

The major genes (collectively known as AjTOX2) involved in the biosynthesis of HC-toxin were identified from A. jesenskae by genomic sequencing. The encoded orthologous proteins share 75-85% amino acid identity, and the genes for HC-toxin biosynthesis are duplicated in both fungi. The genomic organization of the genes in the two fungi show a similar but not identical partial clustering arrangement. A set of representative housekeeping proteins show a similar high level of amino acid identity between C. carbonum and A. jesenskae, which is consistent with the close relatedness of these two genera within the family Pleosporaceae (Dothideomycetes).

Conclusions

This is the first report that the plant virulence factor HC-toxin is made by an organism other than C. carbonum. The genes may have moved by horizontal transfer between the two species, but it cannot be excluded that they were present in a common ancestor and lost from other species of Alternaria and Cochliobolus.

p53, SKP2, and DKK3 as MYCN Target Genes and Their Potential Therapeutic Significance

Neuroblastoma is the most common extra-cranial solid tumor of childhood. Despite significant advances, it currently still remains one of the most difficult childhood cancers to cure, with less than 40% of patients with high-risk disease being long-term survivors. MYCN is a proto-oncogene implicated to be directly involved in neuroblastoma development. Amplification of MYCN is associated with rapid tumor progression and poor prognosis. Novel therapeutic strategies which can improve the survival rates whilst reducing the toxicity in these patients are therefore required. Here we discuss genes regulated by MYCN in neuroblastoma, with particular reference to p53, SKP2, and DKK3 and strategies that may be employed to target them.

The impact of plant-pathogen studies on medicinal drug discovery

The pharmaceutical industry is reliant on a constant supply of new chemical entities and molecular targets for disease intervention. In this tutorial review, we want to illustrate that basic research studies on the biological function of natural products involved in plant-pathogen interactions can serve as an inspiring source for the identification of new bioactive entities as well as of strategies on how to achieve small molecule manipulation of biological systems. An application of findings from plant-pathogen interaction studies might therefore display a significant impact on drug discovery.

Discovery and preclinical validation of drug indications using compendia of public gene expression data

The application of established drug compounds to new therapeutic indications, known as drug repositioning, offers several advantages over traditional drug development, including reduced development costs and shorter paths to approval. Recent approaches to drug repositioning use high-throughput experimental approaches to assess a compound's potential therapeutic qualities. Here, we present a systematic computational approach to predict novel therapeutic indications on the basis of comprehensive testing of molecular signatures in drug-disease pairs. We integrated gene expression measurements from 100 diseases and gene expression measurements on 164 drug compounds, yielding predicted therapeutic potentials for these drugs. We recovered many known drug and disease relationships using computationally derived therapeutic potentials and also predict many new indications for these 164 drugs. We experimentally validated a prediction for the antiulcer drug cimetidine as a candidate therapeutic in the treatment of lung adenocarcinoma, and demonstrate its efficacy both in vitro and in vivo using mouse xenograft models. This computational method provides a systematic approach for repositioning established drugs to treat a wide range of human diseases.

CAMTA1, a 1p36 tumor suppressor candidate, inhibits growth and activates differentiation programs in neuroblastoma cells

A distal portion of human chromosome 1p is often deleted in neuroblastomas and other cancers and it is generally assumed that this region harbors one or more tumor suppressor genes. In neuroblastoma, a 261 kb region at 1p36.3 that encompasses the smallest region of consistent deletion pinpoints the locus for calmodulin binding transcription activator 1 (CAMTA1). Low CAMTA1 expression is an independent predictor of poor outcome in multivariate survival analysis, but its potential functionality in neuroblastoma has not been explored. In this study, we used inducible cell models to analyze the impact of CAMTA1 on neuroblastoma biology. In neuroblastoma cells that expressed little endogenous CAMTA1, its ectopic expression slowed cell proliferation, increasing the relative proportion of cells in G(1)/G(0) phases of the cell cycle, inhibited anchorage-independent colony formation, and suppressed the growth of tumor xenografts. CAMTA1 also induced neurite-like processes and markers of neuronal differentiation in neuroblastoma cells. Further, retinoic acid and other differentiation- inducing stimuli upregulated CAMTA1 expression in neuroblastoma cells. Transciptome analysis revealed 683 genes regulated on CAMTA1 induction and gene ontology analysis identified genes consistent with CAMTA1-induced phenotypes, with a significant enrichment for genes involved in neuronal function and differentiation. Our findings define properties of CAMTA1 in growth suppression and neuronal differentiation that support its assignment as a 1p36 tumor suppressor gene in neuroblastoma.

Targeting of HDAC8 and investigational inhibitors in neuroblastoma

Histone deacetylase (HDAC) inhibitors are an emerging class of promising novel anticancer drugs. However, little is known which one of the 11 classical HDAC family members is the most relevant drug target for therapy. The first Phase I/II trials show that unselective inhibition of HDACs causes a variety of side effects. Therefore, identification and selective targeting of the most critical tumor entity-relevant HDAC family member may reduce unspecific effects and increase antitumor efficacy in the future. Here, we review the clinical relevance of a particular HDAC family member, HDAC8, in neuroblastoma biology, a highly malignant embryonal childhood cancer. HDAC8 expression correlates with poor outcome in neuroblastoma and selective HDAC8 inhibition induces differentiation. In contrast, the targeting of other HDAC family members results in a completely different phenotype. Because HDAC8-selective inhibitors are available, HDAC8 may be a potential drug target for neuroblastoma differentiation therapy using selective inhibitors, avoiding unspecific side effects.

Biosynthesis and role in virulence of the histone deacetylase inhibitor depudecin from Alternaria brassicicola

Depudecin, an eleven-carbon linear polyketide made by the pathogenic fungus Alternaria brassicicola, is an inhibitor of histone deacetylase (HDAC). A chemically unrelated HDAC inhibitor, HC toxin, was earlier shown to be a major virulence factor in the interaction between Cochliobolus carbonum and its host, maize. In order to test whether depudecin is also a virulence factor for A. brassicicola, we identified the genes for depudecin biosynthesis and created depudecin-minus mutants. The depudecin gene cluster contains six genes (DEP1 to DEP6), which are predicted to encode a polyketide synthase (AbPKS9 or DEP5), a transcription factor (DEP6), two monooxygenases (DEP2 and DEP4), a transporter of the major facilitator superfamily (DEP3), and one protein of unknown function (DEP1). The involvement in depudecin production of DEP2, DEP4, DEP5, and DEP6 was demonstrated by targeted gene disruption. DEP6 is required for expression of DEP1 through DEP5 but not the immediate flanking genes, thus defining a coregulated depudecin biosynthetic cluster. The genes flanking the depudecin gene cluster but not the cluster itself are conserved in the same order in the related fungi Stagonospora nodorum and Pyrenophora tritici-repentis. Depudecin-minus mutants have a small (10%) but statistically significant reduction in virulence on cabbage (Brassica oleracea) but not on Arabidopsis. The role of depudecin in virulence is, therefore, less dramatic than that of HC toxin.

Histone deacetylase 8 in neuroblastoma tumorigenesis

PURPOSE

The effects of pan-histone deacetylase (HDAC) inhibitors on cancer cells have shown that HDACs are involved in fundamental tumor biological processes such as cell cycle control, differentiation, and apoptosis. However, because of the unselective nature of these compounds, little is known about the contribution of individual HDAC family members to tumorigenesis and progression. The purpose of this study was to evaluate the role of individual HDACs in neuroblastoma tumorigenesis.

EXPERIMENTAL DESIGN

We have investigated the mRNA expression of all HDAC1-11 family members in a large cohort of primary neuroblastoma samples covering the full spectrum of the disease. HDACs associated with disease stage and survival were subsequently functionally evaluated in cell culture models.

RESULTS

Only HDAC8 expression was significantly correlated with advanced disease and metastasis and down-regulated in stage 4S neuroblastoma associated with spontaneous regression. High HDAC8 expression was associated with poor prognostic markers and poor overall and event-free survival. The knockdown of HDAC8 resulted in the inhibition of proliferation, reduced clonogenic growth, cell cycle arrest, and differentiation in cultured neuroblastoma cells. The treatment of neuroblastoma cell lines as well as short-term-culture neuroblastoma cells with an HDAC8-selective small-molecule inhibitor inhibited cell proliferation and clone formation, induced differentiation, and thus reproduced the HDAC8 knockdown phenotype. Global histone 4 acetylation was not affected by HDAC8 knockdown or by selective inhibitor treatment.

CONCLUSIONS

Our data point toward an important role of HDAC8 in neuroblastoma pathogenesis and identify this HDAC family member as a specific drug target for the differentiation therapy of neuroblastoma.

HKI 46F08, a novel potent histone deacetylase inhibitor, exhibits antitumoral activity against embryonic childhood cancer cells

Embryonic childhood cancer such as neuroblastoma and medulloblastoma are still a therapeutic challenge requiring novel treatment approaches. Here, we investigated the antitumoral effects of HKI 46F08, a novel trifluoromethyl ketone histone deacetylase (HDAC) inhibitor with a nonhydroxamic acid type structure. HKI 46F08 inhibits in-vitro HDAC activity in cell-free assays with a half maximal inhibitory concentration of 0.6 micromol/l and intracellular HDAC activity with a half maximal inhibitory concentration of 1.8 micromol/l. The compound reduces viability of both cultured neuroblastoma and medulloblastoma cells with an EC50 of 0.1-4 micromol/l. HKI 46F08 efficiently arrests tumor cell proliferation, represses clonogenic growth and induces differentiation and apoptosis in both MYCN-amplified and nonamplified neuroblastoma cells. In summary, we identified HKI 48F08 as a structural novel, potent HDAC inhibitor with strong antitumoral activity against embryonic childhood cancer cells in the low micromolar range.

HDAC family: What are the cancer relevant targets?

Histone deacetylases comprise a family of 18 genes, which are grouped into classes I-IV based on their homology to their respective yeast orthologues. Classes I, II, and IV consist of 11 family members, which are referred to as "classical" HDACs, whereas the 7 class III members are called sirtuins. Classical HDACs are a promising novel class of anti-cancer drug targets. First HDAC inhibitors have been evaluated in clinical trials and show activity against several cancer diseases. However, these compounds act unselectively against several or all 11 HDAC family members. As a consequence, clinical phase I trials document a wide range of side effects. Therefore, the current challenge in the field is to define the cancer relevant HDAC family member(s) in a given tumor type and to design selective inhibitors, which target cancer cells but leave out normal cells. Knockout of single HDAC family members in mice produces a variety of phenotypes ranging from early embryonic death to viable animals with only discrete alterations, indicating that potential side effects of HDAC inhibitors depend on the selectivity of the compounds. Recently, several studies have shown that certain HDAC family members are aberrantly expressed in several tumors and have non-redundant function in controlling hallmarks of cancer cells. The aim of this review is to discuss individual HDAC family members as drug targets in cancer taking into consideration their function under physiological conditions and their oncogenic potential in malignant disease.