Antitumor effects of histone deacetylase inhibitor on Ewing's family tumors

The Chromatin Remodeler CHD4 Sustains Ewing Sarcoma Cell Survival by Controlling Global Chromatin Architecture

Ewing sarcoma is an aggressive cancer with a defective response to DNA damage leading to an enhanced sensitivity to genotoxic agents. Mechanistically, Ewing sarcoma is driven by the fusion transcription factor EWS-FLI1, which reprograms the tumor cell epigenome. The nucleosome remodeling and deacetylase (NuRD) complex is an important regulator of chromatin function, controlling both gene expression and DNA damage repair, and has been associated with EWS-FLI1 activity. Here, a NuRD-focused CRISPR/Cas9 inactivation screen identified the helicase CHD4 as essential for Ewing sarcoma cell proliferation. CHD4 silencing induced tumor cell death by apoptosis and abolished colony formation. Although CHD4 and NuRD colocalized with EWS-FLI1 at enhancers and super-enhancers, CHD4 promoted Ewing sarcoma cell survival not by modulating EWS-FLI1 activity and its oncogenic gene expression program but by regulating chromatin structure. CHD4 depletion led to a global increase in DNA accessibility and induction of spontaneous DNA damage, resulting in an increased susceptibility to DNA-damaging agents. CHD4 loss delayed tumor growth in vivo, increased overall survival, and combination with PARP inhibition by olaparib treatment further suppressed tumor growth. Collectively, these findings highlight the NuRD subunit CHD4 as a therapeutic target in Ewing sarcoma that can potentiate the antitumor activity of genotoxic agents.

SIGNIFICANCE

CRISPR/Cas9 screening in Ewing sarcoma identifies a dependency on CHD4, which is crucial for the maintenance of chromatin architecture to suppress DNA damage and a promising therapeutic target for DNA damage repair-deficient malignancies.

A Bifunctional PARP-HDAC Inhibitor with Activity in Ewing Sarcoma

PURPOSE

Histone deacetylase (HDAC) inhibition has been shown to induce pharmacologic "BRCAness" in cancer cells with proficient DNA repair activity. This provides a rationale for exploring combination treatments with HDAC and PARP inhibition in cancer types that are insensitive to single-agent PARP inhibitors (PARPi). Here, we report the concept and characterization of a novel bifunctional PARPi (kt-3283) with dual activity toward PARP1/2 and HDAC enzymes in Ewing sarcoma cells.

EXPERIMENTAL DESIGN

Inhibition of PARP1/2 and HDAC was measured using PARP1/2, HDAC activity, and PAR formation assays. Cytotoxicity was assessed by IncuCyte live cell imaging, CellTiter-Glo, and spheroid assays. Cell-cycle profiles were determined using propidium iodide staining and flow cytometry. DNA damage was examined by γH2AX expression and comet assay. Inhibition of metastatic potential by kt-3283 was evaluated via ex vivo pulmonary metastasis assay (PuMA).

RESULTS

Compared with FDA-approved PARP (olaparib) and HDAC (vorinostat) inhibitors, kt-3283 displayed enhanced cytotoxicity in Ewing sarcoma models. The kt-3283-induced cytotoxicity was associated with strong S and G2-M cell-cycle arrest in nanomolar concentration range and elevated DNA damage as assessed by γH2AX tracking and comet assays. In three-dimensional spheroid models of Ewing sarcoma, kt-3283 showed efficacy in lower concentrations than olaparib and vorinostat, and kt-3283 inhibited colonization of Ewing sarcoma cells in the ex vivo PuMA model.

CONCLUSIONS

Our data demonstrate the preclinical justification for studying the benefit of dual PARP and HDAC inhibition in the treatment of Ewing sarcoma in a clinical trial and provides proof-of-concept for a bifunctional single-molecule therapeutic strategy.

Targeting the Clear Cell Sarcoma Oncogenic Driver Fusion Gene EWSR1::ATF1 by HDAC Inhibition

Clear cell sarcoma (CCS), a rare but extremely aggressive malignancy with no effective therapy, is characterized by the expression of the oncogenic driver fusion gene EWSR1::ATF1. In this study, we performed a high-throughput drug screening, finding that the histone deacetylase inhibitor vorinostat exerted an antiproliferation effect with the reduced expression of EWSR1::ATF1. We expected the reduced expression of EWSR1::ATF1 to be due to the alteration of chromatin accessibility; however, assay for transposase-accessible chromatin using sequencing and a cleavage under targets and release using nuclease assay revealed that chromatin structure was only slightly altered, despite histone deacetylation at the EWSR1::ATF1 promoter region. Alternatively, we found that vorinostat treatment reduced the level of BRD4, a member of the bromodomain and extraterminal motif protein family, at the EWSR1::ATF1 promoter region. Furthermore, the BRD4 inhibitor JQ1 downregulated EWSR1::ATF1 according to Western blotting and qPCR analyses. In addition, motif analysis revealed that vorinostat treatment suppressed the transcriptional factor SOX10, which directly regulates EWSR1::ATF1 expression and is involved in CCS proliferation. Importantly, we demonstrate that a combination therapy of vorinostat and JQ1 synergistically enhances antiproliferation effect and EWSR1::ATF1 suppression. These results highlight a novel fusion gene suppression mechanism achieved using epigenetic modification agents and provide a potential therapeutic target for fusion gene-related tumors.

Significance

This study reveals the epigenetic and transcriptional suppression mechanism of the fusion oncogene EWSR1::ATF1 in clear cell sarcoma by histone deacetylase inhibitor treatment as well as identifying SOX10 as a transcription factor that regulates EWSR1::ATF1 expression.

Pathologic HDAC1/c-Myc signaling axis is responsible for angiotensinogen transcription and hypertension induced by high-fat diet

High-fat diet (HFD)-induced obesity is a cause of resistant hypertension. We have shown a possible link between histone deacetylases (HDACs) and renal angiotensinogen (Agt) upregulation in the HFD-induced hypertension, whereas the underlying mechanisms remain to be elucidated. Here, using a HDAC1/2 inhibitor romidepsin (FK228) and siRNAs, we determined roles of HDAC1 and HDAC2 in HFD-induced hypertension and found the pathologic signaling axis between HDAC1 and Agt transcription. Treatment with FK228 canceled the increased blood pressure of male C57BL/6 mice induced by HFD. FK228 also blocked upregulation of renal Agt mRNA, protein, angiotensin II (Ang II) or serum Ang II. Activation and nuclear accumulation of both HDAC1 and HDAC2 occurred in the HFD group. The HFD-induced HDAC activation was associated with an increase in deacetylated c-Myc transcription factor. Silencing of HDAC1, HDAC2 or c-Myc in HRPTEpi cells decreased Agt expression. However, only HDAC1 knockdown, but not HDAC2, increased c-Myc acetylation, suggesting selective roles in two enzymes. Chromatin immunoprecipitation assay revealed that HFD induced the binding of HDAC1 and deacetylated c-Myc at the Agt gene promoter. A putative c-Myc binding sequence in the promotor region was necessary for Agt transcription. Inhibition of c-Myc downregulated Agt and Ang II levels in kidney and serum, ameliorating HFD-induced hypertension. Thus, the abnormal HDAC1/2 in the kidney may be responsible for the upregulation of the Agt gene expression and hypertension. The results expose the pathologic HDAC1/c-myc signaling axis in kidney as a promising therapeutic target for obesity-associated resistant hypertension.

Cell cycle arrest and apoptosis are early events in radiosensitization of EWS::FLI1+ Ewing sarcoma cells by Mithramycin A

PURPOSE

The oncogenic fusion protein EWS::FLI1 is an attractive therapeutic target in Ewing sarcoma (ES). Mithramycin A (MithA) is a potent and specific inhibitor of EWS::FLI1 that can selectively radiosensitize ES cells through transcriptional inhibition of DNA double-strand break (DSB) repair. Here, we evaluate temporal changes in cell cycle progression and apoptosis in ES cells treated with MithA and/or ionizing radiation (RTx), testing the hypothesis that combining MithA with ionizing radiation would synergistically impair cell cycle progression and enhance apoptotic elimination to a greater extent than either agent alone.

MATERIALS AND METHODS

Four EWS::FLI1+ ES cell lines TC-71, RD-ES, SK-ES-1, and A673, and one EWS::ERG cell line (CHLA-25) were exposed to 10nM MithA or vehicle and followed 24 h later by exposure to 2 Gy x-radiation or sham irradiation. Reactive oxygen species (ROS) activity was evaluated by cytometric assay, and assay of antioxidant gene expression by RT-qPCR. Cell cycle changes were evaluated by flow cytometry of nuclei stained with propidium iodide. Apoptosis was assessed by cytometric assessment of Caspase-3/7 activity and by immunoblotting of PARP-1 cleavage. Radiosensitization was evaluated by clonogenic survival assay. Proliferation (EdU) and apoptosis (TUNEL) were evaluated in SK-ES-1 xenograft tumors following pretreatment with 1 mg/kg MithA, followed 24 h later by a single 4 Gy fraction of x-radiation.

RESULTS

MithA-treated cells showed reduced levels of ROS, and were associated with increased expression of antioxidant genes SOD1, SOD2, and CAT. It nonetheless induced persistent G0/G1 arrest and a progressive increase of the sub-G1 fraction, suggesting apoptotic degeneration. In vitro assays of Caspase-3/7 activity and immunoblotting of Caspase-3/7 dependent cleavage of PARP-1 indicated that apoptosis began as early as 24 h after MithA exposure, reducing clonogenic survival. Tumors from xenograft mice treated with either radiation alone, or in combination with MithA showed a significant reduction of tumor cell proliferation, while apoptosis was significantly increased in the group receiving the combination of MithA and RTx.

CONCLUSIONS

Taken together, our data show that the anti-proliferative and cytotoxic effects of MithA are the prominent components of radiosensitization of EWS::FLI1+ ES, rather than the result of acutely enhanced ROS levels.

Regulation of EWSR1-FLI1 Function by Post-Transcriptional and Post-Translational Modifications

Ewing sarcoma is the second most common bone tumor in childhood and adolescence. Currently, first-line therapy includes multidrug chemotherapy with surgery and/or radiation. Although most patients initially respond to chemotherapy, recurrent tumors become treatment refractory. Pathologically, Ewing sarcoma consists of small round basophilic cells with prominent nuclei marked by expression of surface protein CD99. Genetically, Ewing sarcoma is driven by a fusion oncoprotein that results from one of a small number of chromosomal translocations composed of a FET gene and a gene encoding an ETS family transcription factor, with ~85% of tumors expressing the EWSR1::FLI1 fusion. EWSR1::FLI1 regulates transcription, splicing, genome instability and other cellular functions. Although a tumor-specific target, EWSR1::FLI1-targeted therapy has yet to be developed, largely due to insufficient understanding of EWSR1::FLI1 upstream and downstream signaling, and the challenges in targeting transcription factors with small molecules. In this review, we summarize the contemporary molecular understanding of Ewing sarcoma, and the post-transcriptional and post-translational regulatory mechanisms that control EWSR1::FLI1 function.

Ewing Sarcoma Meets Epigenetics, Immunology and Nanomedicine: Moving Forward into Novel Therapeutic Strategies

Ewing Sarcoma (EWS) is an aggressive bone and soft tissue tumor that mainly affects children, adolescents, and young adults. The standard therapy, including chemotherapy, surgery, and radiotherapy, has substantially improved the survival of EWS patients with localized disease. Unfortunately, this multimodal treatment remains elusive in clinics for those patients with recurrent or metastatic disease who have an unfavorable prognosis. Consistently, there is an urgent need to find new strategies for patients that fail to respond to standard therapies. In this regard, in the last decade, treatments targeting epigenetic dependencies in tumor cells and the immune system have emerged into the clinical scenario. Additionally, recent advances in nanomedicine provide novel delivery drug systems, which may address challenges such as side effects and toxicity. Therefore, therapeutic strategies stemming from epigenetics, immunology, and nanomedicine yield promising alternatives for treating these patients. In this review, we highlight the most relevant EWS preclinical and clinical studies in epigenetics, immunotherapy, and nanotherapy conducted in the last five years.

Epigenetic modulation in sensitizing metastatic sarcomas to therapies and overcoming resistance

Sarcomas are a class of rare malignancies of mesenchymal origin with a heterogeneous histological spectrum. They are classically associated with poor outcomes, especially once metastasized. A path to improving clinical outcomes may be made through modifying the epigenome, where a variety of sarcomas demonstrate changes that contribute to their oncogenic phenotypes. This Perspective article identifies and describes changes in the sarcoma genome, while discussing specific epigenetic changes and their effect on clinical outcomes. Clinical attempts at modulating epigenetics in sarcoma are reviewed, as well as potential implications of these studies. Epigenetic targets to reverse and delay chemotherapy resistance are discussed. Future directions with primary next steps are proposed to invigorate the current understanding of epigenetic biomarkers to enact targeted therapies to epigenetic phenotypes of sarcoma subtypes. Modifications to prior studies, as well as proposed clinical steps, are also addressed.

Class I histone deacetylases (HDAC) critically contribute to Ewing sarcoma pathogenesis

Background

Histone acetylation and deacetylation seem processes involved in the pathogenesis of Ewing sarcoma (EwS). Here histone deacetylases (HDAC) class I were investigated.

Methods

Their role was determined using different inhibitors including TSA, Romidepsin, Entinostat and PCI-34051 as well as CRISPR/Cas9 class I HDAC knockouts and HDAC RNAi. To analyze resulting changes microarray analysis, qRT-PCR, western blotting, Co-IP, proliferation, apoptosis, differentiation, invasion assays and xenograft-mouse models were used.

Results

Class I HDACs are constitutively expressed in EwS. Patients with high levels of individual class I HDAC expression show decreased overall survival. CRISPR/Cas9 class I HDAC knockout of individual HDACs such as HDAC1 and HDAC2 inhibited invasiveness, and blocked local tumor growth in xenograft mice. Microarray analysis demonstrated that treatment with individual HDAC inhibitors (HDACi) blocked an EWS-FLI1 specific expression profile, while Entinostat in addition suppressed metastasis relevant genes. EwS cells demonstrated increased susceptibility to treatment with chemotherapeutics including Doxorubicin in the presence of HDACi. Furthermore, HDACi treatment mimicked RNAi of EZH2 in EwS. Treated cells showed diminished growth capacity, but an increased endothelial as well as neuronal differentiation ability. HDACi synergizes with EED inhibitor (EEDi) in vitro and together inhibited tumor growth in xenograft mice. Co-IP experiments identified HDAC class I family members as part of a regulatory complex together with PRC2.

Conclusions

Class I HDAC proteins seem to be important mediators of the pathognomonic EWS-ETS-mediated transcription program in EwS and in combination therapy, co-treatment with HDACi is an interesting new treatment opportunity for this malignant disease.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13046-021-02125-z.

Role of immunotherapy in Ewing sarcoma

Ewing sarcoma (ES) is thought to arise from mesenchymal stem cells and is the second most common bone sarcoma in pediatric patients and young adults. Given the dismal overall outcomes and very intensive therapies used, there is an urgent need to explore and develop alternative treatment modalities including immunotherapies. In this article, we provide an overview of ES biology, features of ES tumor microenvironment (TME) and review various tumor-associated antigens that can be targeted with immune-based approaches including cancer vaccines, monoclonal antibodies, T cell receptor-transduced T cells, and chimeric antigen receptor T cells. We highlight key reasons for the limited efficacy of various immunotherapeutic approaches for the treatment of ES to date. These factors include absence of human leukocyte antigen class I molecules from the tumor tissue, lack of an ideal surface antigen, and immunosuppressive TME due to the presence of myeloid-derived suppressor cells, F2 fibrocytes, and M2-like macrophages. Lastly, we offer insights into strategies for novel therapeutics development in ES. These strategies include the development of gene-modified T cell receptor T cells against cancer–testis antigen such as XAGE-1, surface target discovery through detailed profiling of ES surface proteome, and combinatorial approaches. In summary, we provide state-of-the-art science in ES tumor immunology and immunotherapy, with rationale and recommendations for future therapeutics development.

Selective inhibition of HDAC6 regulates expression of the oncogenic driver EWSR1-FLI1 through the EWSR1 promoter in Ewing sarcoma

Ewing sarcoma (EWS) is an aggressive bone and soft tissue tumor of children and young adults in which the principal driver is a fusion gene, EWSR1-FLI1. Although the essential role of EWSR1-FLI1 protein in the regulation of oncogenesis, survival, and tumor progression processes has been described in-depth, little is known about the regulation of chimeric fusion-gene expression. Here, we demonstrate that the active nuclear HDAC6 in EWS modulates the acetylation status of specificity protein 1 (SP1), consequently regulating the SP1/P300 activator complex binding to EWSR1 and EWSR1-FLI1 promoters. Selective inhibition of HDAC6 impairs binding of the activator complex SP1/P300, thereby inducing EWSR1-FLI1 downregulation and significantly reducing its oncogenic functions. In addition, sensitivity of EWS cell lines to HDAC6 inhibition is higher than other tumor or non-tumor cell lines. High expression of HDAC6 in primary EWS tumor samples from patients correlates with a poor prognosis in two independent series accounting 279 patients. Notably, a combination treatment of a selective HDAC6 and doxorubicin (a DNA damage agent used as a standard therapy of EWS patients) dramatically inhibits tumor growth in two EWS murine xenograft models. These results could lead to suitable and promising therapeutic alternatives for patients with EWS.

Pharmaceutical Interference of the EWS-FLI1-driven Transcriptome By Cotargeting H3K27ac and RNA Polymerase Activity in Ewing Sarcoma

The EWSR1-FLI1 t(11;22)(q24;q12) translocation is the hallmark genomic alteration of Ewing sarcoma, a malignancy of the bone and surrounding tissue, predominantly affecting children and adolescents. Although significant progress has been made for the treatment of localized disease, patients with metastasis or who relapse after chemotherapy have less than a 30% five-year survival rate. EWS-FLI1 is currently not clinically druggable, driving the need for more effective targeted therapies. Treatment with the H3K27 demethylase inhibitor, GSK-J4, leads to an increase in H3K27me and a decrease in H3K27ac, a significant event in Ewing sarcoma because H3K27ac associates strongly with EWS-FLI1 binding at enhancers and promoters and subsequent activity of EWS-FLI1 target genes. We were able to identify targets of EWS-FLI1 tumorigenesis directly inhibited by GSK-J4. GSK-J4 disruption of EWS-FLI1-driven transcription was toxic to Ewing sarcoma cells and slowed tumor growth in patient-derived xenografts (PDX) of Ewing sarcoma. Responses were markedly exacerbated by cotreatment with a disruptor of RNA polymerase II activity, the CDK7 inhibitor THZ1. This combination together suppressed EWS-FLI1 target genes and viability of ex vivo PDX Ewing sarcoma cells in a synergistic manner. In PDX models of Ewing Sarcoma, the combination shrank tumors. We present a new therapeutic strategy to treat Ewing sarcoma by decreasing H3K27ac at EWS-FLI1-driven transcripts, exacerbated by blocking phosphorylation of the C-terminal domain of RNA polymerase II to further hinder the EWS-FLI1-driven transcriptome.

Chondrosarcoma-from Molecular Pathology to Novel Therapies

Chondrosarcoma (CHS) is the second most common primary malignant bone sarcoma. Overall survival and prognosis of this tumor are various and often extreme, depending on histological grade and tumor subtype. CHS treatment is difficult, and surgery remains still the gold standard due to the resistance of this tumor to other therapeutic options. Considering the role of differentiation of CHS subtypes and the need to develop new treatment strategies, in this review, we introduced a multidisciplinary characterization of CHS from its pathology to therapies. We described the morphology of each subtype with the role of immunohistochemical markers in diagnostics of CHS. We also summarized the most frequently mutated genes and genome regions with altered pathways involved in the pathology of this tumor. Subsequently, we discussed imaging methods and the role of currently used therapies, including surgery and the limitations of chemo and radiotherapy. Finally, in this review, we presented novel targeted therapies, including those at ongoing clinical trials, which can be a potential future target in designing new therapeutics for patients with CHS.

Ewing Sarcoma-Diagnosis, Treatment, Clinical Challenges and Future Perspectives

Ewing sarcoma, a highly aggressive bone and soft-tissue cancer, is considered a prime example of the paradigms of a translocation-positive sarcoma: a genetically rather simple disease with a specific and neomorphic-potential therapeutic target, whose oncogenic role was irrefutably defined decades ago. This is a disease that by definition has micrometastatic disease at diagnosis and a dismal prognosis for patients with macrometastatic or recurrent disease. International collaborations have defined the current standard of care in prospective studies, delivering multiple cycles of systemic therapy combined with local treatment; both are associated with significant morbidity that may result in strong psychological and physical burden for survivors. Nevertheless, the combination of non-directed chemotherapeutics and ever-evolving local modalities nowadays achieve a realistic chance of cure for the majority of patients with Ewing sarcoma. In this review, we focus on the current standard of diagnosis and treatment while attempting to answer some of the most pressing questions in clinical practice. In addition, this review provides scientific answers to clinical phenomena and occasionally defines the resulting translational studies needed to overcome the hurdle of treatment-associated morbidities and, most importantly, non-survival.

Identification of Tumor Microenvironment-Related Prognostic Genes in Sarcoma

Aim

Immune cells that infiltrate the tumor microenvironment (TME) are associated with cancer prognosis. The aim of the current study was to identify TME related gene signatures related to the prognosis of sarcoma (SARC) by using the data from The Cancer Genome Atlas (TCGA).

Methods

Immune and stromal scores were calculated by estimation of stromal and immune cells in malignant tumor tissues using expression data algorithms. The least absolute shrinkage and selection operator (lasso) based cox model was then used to select hub survival genes. A risk score model and nomogram were used to predict the overall survival of patients with SARC.

Results

We selected 255 patients with SARC for our analysis. The Kaplan–Meier method found that higher immune (p = 0.0018) or stromal scores (p = 0.0022) were associated with better prognosis of SARC. The estimated levels of CD4+ (p = 0.0012) and CD8+ T cells (p = 0.017) via the tumor immune estimation resource were higher in patients with SARC with better overall survival. We identified 393 upregulated genes and 108 downregulated genes (p < 0.05, fold change >4) intersecting between the immune and stromal scores based on differentially expressed gene (DEG) analysis. The univariate Cox analysis of each intersecting DEG and subsequent lasso-based Cox model identified 11 hub survival genes (MYOC, NNAT, MEDAG, TNFSF14, MYH11, NRXN1, P2RY13, CXCR3, IGLV3-25, IGHV1-46, and IGLV2-8). Then, a hub survival gene-based risk score gene signature was constructed; higher risk scores predicted worse SARC prognosis (p < 0.0001). A nomogram including the risk scores, immune/stromal scores and clinical factors showed a good prediction value for SARC overall survival (C-index = 0.716). Finally, connectivity mapping analysis identified that the histone deacetylase inhibitors trichostatin A and vorinostat might have the potential to reverse the harmful TME for patients with SARC.

Conclusion

The current study provided new indications for the association between the TME and SARC. Lists of TME related survival genes and potential therapeutic drugs were identified for SARC.

Clinical efficiency of epigenetic drugs therapy in bone malignancies

A great interest in the scientific community is focused on the improvement of the cure rate in patients with bone malignancies that have a poor response to the first line of therapies. Novel treatments currently include epigenetic compounds or molecules targeting epigenetic-sensitive pathways. Here, we offer an exhaustive review of such agents in these clinical settings. Carefully designed preclinical studies selected several epigenetic drugs, including inhibitors of DNA methyltransferase (DNMTIs), such as Decitabine, histone deacetylase classes I-II (HDACIs), as Entinostat, Belinostat, lysine-specific histone demethylase (LSD1), as INCB059872 or FT-2102 (Olutasidenib), inhibitors of isocitrate dehydrogenases, and enhancer of zeste homolog 2 (EZH2), such as EPZ6438 (Tazemetostat) To enhance the therapeutic effect, the prevalent approach in phase II trial is the association of these epigenetic drug inhibitors, with targeted therapy or immune checkpoint blockade. Optimization of drug dosing and regimens of Phase II trials may improve the clinical efficiency of such novel therapeutic approaches against these devastating cancers.

Exploiting Signaling Pathways and Immune Targets Beyond the Standard of Care for Ewing Sarcoma

Ewing sarcoma (ES) family of tumors includes bone and soft tissue tumors that are often characterized by a specific translocation between chromosome 11 and 22, resulting in the EWS-FLI1 fusion gene. With the advent of multi-modality treatment including cytotoxic chemotherapy, surgery, and radiation therapy, the prognosis for patients with ES has substantially improved. However, a therapeutic plateau is now reached for both localized and metastatic disease over the last two decades. Burdened by the toxicity limits associated with the current frontline systemic therapy, there is an urgent need for novel targeted therapeutic strategies. In this review, we discuss the current treatment paradigm of ES, and explore preclinical evidence and emerging treatments directed at tumor signaling pathways and immune targets.

Targeted inhibition of histone deacetylase leads to suppression of Ewing sarcoma tumor growth through an unappreciated EWS-FLI1/HDAC3/HSP90 signaling axis

Ewing sarcoma (ES) are aggressive pediatric bone and soft tissue tumors driven by EWS-ETS fusion oncogenes, most commonly EWS-FLI1. Treatment of ES patients consists of up to 9 months of alternating courses of 2 chemotherapeutic regimens. Furthermore, EWS-ETS-targeted therapies have yet to demonstrate clinical benefit, thereby emphasizing a clinical responsibility to search for new therapeutic approaches. Our previous in silico drug screening identified entinostat as a drug hit that was predicted to reverse the ES disease signatures and EWS-FLI1-mediated gene signatures. Here, we establish preclinical proof of principle by investigating the in vitro and in vivo efficacy of entinostat in preclinical ES models, as well as characterizing the mechanisms of action and in vivo pharmacokinetics of entinostat. ES cells are preferentially sensitive to entinostat in an EWS-FLI1 or EWS-ERG-dependent manner. Entinostat induces apoptosis of ES cells through G₀/G₁ cell cycle arrest, intracellular reactive oxygen species (ROS) elevation, DNA damage, homologous recombination (HR) repair impairment, and caspase activation. Mechanistically, we demonstrate for the first time that HDAC3 is a transcriptional target of EWS-FLI1 and that entinostat inhibits growth of ES cells through suppressing a previously unexplored EWS-FLI1/HDAC3/HSP90 signaling axis. Importantly, entinostat significantly reduces tumor burden by 97.4% (89.5 vs. 3397.3 mm³ of vehicle, p < 0.001) and prolongs the median survival of mice (15.5 vs. 8.5 days of vehicle, p < 0.001), in two independent ES xenograft mouse models, respectively. Overall, our studies demonstrate promising activity of entinostat against ES, and support the clinical development of the entinostat-based therapies for children and young adults with metastatic/relapsed ES. KEY MESSAGES: • Entinostat potently inhibits ES both in vitro and in vivo. • EWS-FLI1 and EWS-ERG confer sensitivity to entinostat treatment. • Entinostat suppresses the EWS-FLI1/HDAC3/HSP90 signaling. • HDAC3 is a transcriptional target of EWS-FLI1. • HDAC3 is essential for ES cell viability and genomic stability maintenance.

Potential approaches to the treatment of Ewing's sarcoma

Ewing’s sarcoma (ES) is a highly aggressive and metastatic tumor in children and young adults caused by a chromosomal fusion between the Ewing sarcoma breakpoint region 1 (EWSR1) gene and the transcription factor FLI1 gene. ES is managed with standard treatments, including chemotherapy, surgery and radiation. Although the 5-year survival rate for primary ES has improved, the survival rate for ES patients with metastases or recurrence remains low. Several novel molecular targets in ES have recently been identified and investigated in preclinical and clinical settings, and targeting the function of receptor tyrosine kinases (RTKs), the fusion protein EWS-FLI1 and mTOR has shown promise. There has also been increasing interest in the immune responses of ES patients. Immunotherapies using T cells, NK cells, cancer vaccines and monoclonal antibodies have been considered for ES, especially for recurrent patients. Because understanding the pathogenesis of ES is extremely important for the development of novel treatments, this review focuses on the mechanisms and functions of targeted therapies and immunotherapies in ES. It is anticipated that integrating the knowledge obtained from basic research and translational and clinical studies will lead to the development of novel therapeutic strategies for the treatment of ES.

Targeting Histone Deacetylase Activity to Arrest Cell Growth and Promote Neural Differentiation in Ewing Sarcoma

There is an urgent need for advances in the treatment of Ewing sarcoma (EWS), an aggressive childhood tumor with possible neuroectodermal origin. Inhibition of histone deacetylases (HDAC) can revert aberrant epigenetic states and reduce growth in different experimental cancer types. Here, we investigated whether the potent HDAC inhibitor, sodium butyrate (NaB), has the ability to reprogram EWS cells towards a more differentiated state and affect their growth and survival. Exposure of two EWS cell lines to NaB resulted in rapid and potent inhibition of HDAC activity (1 h, IC₅₀ 1.5 mM) and a significant arrest of cell cycle progression (72 h, IC₅₀ 0.68-0.76 mM), marked by G0/G1 accumulation. Delayed cell proliferation and reduced colony formation ability were observed in EWS cells after long-term culture. NaB-induced effects included suppression of cell proliferation accompanied by reduced transcriptional expression of the EWS-FLI1 fusion oncogene, decreased expression of key survival and pluripotency-associated genes, and re-expression of the differentiation neuronal marker βIII-tubulin. Finally, NaB reduced c-MYC levels and impaired survival in putative EWS cancer stem cells. Our findings support the use of HDAC inhibition as a strategy to impair cell growth and survival and to reprogram EWS tumors towards differentiation. These results are consistent with our previous studies indicating that HDis can inhibit the growth and modulate differentiation of cells from other types of childhood pediatric tumors possibly originating from neural stem cells.

Therapeutic applications of histone deacetylase inhibitors in sarcoma

Sarcomas are a rare group of malignant tumors originating from mesenchymal stem cells. Surgery, radiation and chemotherapy are currently the only standard treatments for sarcoma. However, their response rates to chemotherapy are quite low. Toxic side effects and multi-drug chemoresistance make treatment even more challenging. Therefore, better drugs to treat sarcomas are needed. Histone deacetylase inhibitors (HDAC inhibitors, HDACi, HDIs) are epigenetic modifying agents that can inhibit sarcoma growth in vitro and in vivo through a variety of pathways, including inducing tumor cell apoptosis, causing cell cycle arrest, impairing tumor invasion and preventing metastasis. Importantly, preclinical studies have revealed that HDIs can not only sensitize sarcomas to chemotherapy and radiotherapy, but also increase treatment responses when combined with other chemotherapeutic drugs. Several phase I and II clinical trials have been conducted to assess the efficacy of HDIs either as monotherapy or in combination with standard chemotherapeutic agents or targeted therapeutic drugs for sarcomas. Combination regimen for sarcomas appear to be more promising than monotherapy when using HDIs. This review summarizes our current understanding and therapeutic applications of HDIs in sarcomas.

Macrothrombocytopenia and dense granule deficiency associated with FLI1 variants: ultrastructural and pathogenic features

Congenital macrothrombocytopenia is a family of rare diseases, of which a significant fraction remains to be genetically characterized. To analyze cases of unexplained thrombocytopenia, 27 individuals from a patient cohort of the Bleeding and Thrombosis Exploration Center of the University Hospital of Marseille were recruited for a high-throughput gene sequencing study. This strategy led to the identification of two novel FLI1 variants (c.1010G>A and c.1033A>G) responsible for macrothrombocytopenia. The FLI1 variant carriers’ platelets exhibited a defect in aggregation induced by low-dose adenosine diphosphate (ADP), collagen and thrombin receptor-activating peptide (TRAP), a defect in adenosine triphosphate (ATP) secretion, a reduced mepacrine uptake and release and a reduced CD63 expression upon TRAP stimulation. Precise ultrastructural analysis of platelet content was performed using transmission electron microscopy and focused ion beam scanning electron microscopy. Remarkably, dense granules were nearly absent in the carriers’ platelets, presumably due to a biogenesis defect. Additionally, 25–29% of the platelets displayed giant α-granules, while a smaller proportion displayed vacuoles (7–9%) and autophagosome-like structures (0–3%). In vitro study of megakaryocytes derived from circulating CD34⁺ cells of the carriers revealed a maturation defect and reduced proplatelet formation potential. The study of the FLI1 variants revealed a significant reduction in protein nuclear accumulation and transcriptional activity properties. Intraplatelet flow cytometry efficiently detected the biomarker MYH10 in FLI1 variant carriers. Overall, this study provides new insights into the phenotype, pathophysiology and diagnosis of FLI1 variant-associated thrombocytopenia.

Panobinostat-A Potential Treatment for Metastasized Ewing Sarcoma? A Case Report

Ewing sarcoma (ES) is a form of primary bone cancer, with few treatment options for patients who develop relapse with an overall 5-year survival of 13%. New treatment options are needed and histone deacetylase (HDAC) inhibitors show encouraging results in preclinical studies. Our patient developed inoperable progressive lung metastases and was treated with the HDAC inhibitor panobinostat. During 18 months of treatment, no new lesions appeared; the treatment was stopped due to progression. This clinical observation warrants further evaluation of HDAC inhibitors in ES. Combination with chemotherapy and biomarker studies could improve the therapeutic index of these classes of compounds.

High-throughput small molecule screen identifies inhibitors of aberrant chromatin accessibility

Mutations in chromatin-modifying proteins and transcription factors are commonly associated with a wide variety of cancers. Through gain- or loss-of-function, these mutations may result in characteristic alterations of accessible chromatin, indicative of shifts in the landscape of regulatory elements genome-wide. The identification of compounds that reverse a specific chromatin signature could lead to chemical probes or potential therapies. To explore whether chromatin accessibility could serve as a platform for small molecule screening, we adapted formaldehyde-assisted isolation of regulatory elements (FAIRE), a chemical method to enrich for nucleosome-depleted genomic regions, as a high-throughput, automated assay. After demonstrating the validity and robustness of this approach, we applied this method to screen an epigenetically targeted small molecule library by evaluating regions of aberrant nucleosome depletion mediated by EWSR1-FLI1, the chimeric transcription factor critical for the bone and soft tissue tumor Ewing sarcoma. As a class, histone deacetylase inhibitors were greatly overrepresented among active compounds. These compounds resulted in diminished accessibility at targeted sites by disrupting transcription of EWSR1-FLI1. Capitalizing on precise differences in chromatin accessibility for drug discovery efforts offers significant advantages because it does not depend on the a priori selection of a single molecular target and may detect novel biologically relevant pathways.

Sequencing Overview of Ewing Sarcoma: A Journey across Genomic, Epigenomic and Transcriptomic Landscapes

Ewing sarcoma is an aggressive neoplasm occurring predominantly in adolescent Caucasians. At the genome level, a pathognomonic EWSR1-ETS translocation is present. The resulting fusion protein acts as a molecular driver in the tumor development and interferes, amongst others, with endogenous transcription and splicing. The Ewing sarcoma cell shows a poorly differentiated, stem-cell like phenotype. Consequently, the cellular origin of Ewing sarcoma is still a hot discussed topic. To further characterize Ewing sarcoma and to further elucidate the role of EWSR1-ETS fusion protein multiple genome, epigenome and transcriptome level studies were performed. In this review, the data from these studies were combined into a comprehensive overview. Presently, classical morphological predictive markers are used in the clinic and the therapy is dominantly based on systemic chemotherapy in combination with surgical interventions. Using sequencing, novel predictive markers and candidates for immuno- and targeted therapy were identified which were summarized in this review.

The biology and management of cartilaginous tumors: a role for targeting isocitrate dehydrogenase

Chondrosarcomas are rare mesenchymal neoplasms defined by the production of abnormal cartilaginous matrix. Conventional chondrosarcoma is the most common histology. The management of primary conventional chondrosarcoma generally is surgical with the possible addition of radiation therapy. Treatment of conventional chondrosarcoma is problematic in unresectable or metastatic disease because the tumors tend to be resistant to standard sarcoma chemotherapy regimens. Previous attempts at targeted therapy, including inhibitors of Hedgehog signaling, the mTOR pathway, and platelet-derived growth factor receptor (PDGFR) have been largely disappointing. However, heterozygous mutations in isocitrate dehydrogenase (IDH) enzymes recently have been identified in chondrogenic neoplasms, with mutations reported in approximately 87% of benign enchondromas, 70% of conventional chondrosarcomas, and 54% of dedifferentiated chondrosarcomas. The normal IDH protein continues to produce alpha-ketoglutarate (alpha-KG) whereas the mutant IDH protein converts KG to the oncometabolite 2-hydroxyglutarate (2-HG). Clinical trials of novel IDH inhibitors are ongoing, with evidence of early activity in IDH-mutant leukemias. IDH inhibitors show antitumor effects against IDH-mutant chondrosarcoma cell lines, supporting the inclusion of patients with chondrosarcoma with IDH mutations on IDH inhibitor clinical trials for solid tumors. Targeting IDH mutations may offer hope of a novel antineoplastic strategy not only for patients with chondrosarcomas, but also for other solid tumors with aberrant IDH activity.

Anti-Epileptic Drug Targets Ewing Sarcoma

Ewing Sarcoma (ES) is a rare form of bone cancer that most commonly affects children and adolescents. Chromosomal translocations are fundamental to the development of Ewing Sarcoma, linked to the changes in gene expression affecting transcription factors. Histone acetyl transferases (HATs) and histone deacetylases (HDACs) regulate transcription by modifying acetylation of both histones and transcription factors. Despite the use of multimodal therapeutic approaches current therapies are associated with significant short and long-term side effects. Hence, new therapeutic approaches are needed. In this study, we show that ERG/EWS-ERG, inhibits transcriptional activation properties of RXRα. These results suggest that ERG/EWS-ERG/EWS-Fli-1 may target transcriptional co-activators and transcriptional repressors and thereby regulate RXRα transcriptional activity. To understand the molecular mechanism of action, how the fusion protein targets nuclear receptor function, and to provide a clue for the cancer health disparity seen in Ewing Sarcoma, we hypothesized that the aberrant fusion protein, EWS-ERG/EWS-Fli-1 regulates HDACs-mediated repressor complex and inhibits the binding of transcriptional activator complex causing transcriptional repression of RXRα activity. Since it is known that HDACs regulate nuclear receptors, we proposed that HDAC inhibitor, valproic acid (VPA), an anti-epileptic drug, may reverse the inhibitory properties of EWS-ERG/EWS-Fli-1 oncoprotein on RXRα transcriptional activity and might therefore be used as therapeutic agent in ES. We demonstrate that VPA reverses the inhibitory effect of EWSERG/EWS-Fli-1 on RXRα transcriptional activity and also inhibits the cell growth. Furthermore, VPA induces apoptosis and restored the expression of RXRα target genes RARβ, CRABPII and p21 activity and repressed the expression of aberrant fusion proteins, EWS-ERG and EWS-Fli-1 in Ewing Sarcoma cells. Thus, therapeutic regulation of transcriptional repressor properties of EWS-ERG/EWS-Fli-1 with an anti-epileptic drug with a promising new potential might have a profound impact on prevention, management and treatment of Ewing Sarcoma. Therapeutic use of VPA in minority patients may help reduce the health disparity.

Initial testing (stage 1) of the histone deacetylase inhibitor, quisinostat (JNJ-26481585), by the Pediatric Preclinical Testing Program

BACKGROUND

Quisinostat (JNJ-26481585) is a second-generation pyrimidyl-hydroxamic acid histone deacetylase (HDAC) inhibitor with high cellular potency towards Class I and II HDACs. Quisinostat was selected for clinical development as it showed prolonged pharmacodynamic effects in vivo and demonstrated improved single agent antitumoral efficacy compared to other analogs.

PROCEDURES

Quisinostat was tested against the PPTP in vitro panel at concentrations ranging from 1.0 nM to 10 μM and was tested against the PPTP in vivo panels at a dose of 5 mg/kg (solid tumors) or 2.5 mg/kg (ALL models) administered intraperitoneally daily × 21.

RESULTS

In vitro quisinostat demonstrated potent cytotoxic activity, with T/C% values approaching 0% for all of the cell lines at the highest concentration tested. The median relative IC50 value for the PPTP cell lines was 2.2 nM (range <1-19 nM). quisinostat induced significant differences in EFS distribution compared to control in 21 of 33 (64%) of the evaluable solid tumor xenografts and in 4 of 8 (50%) of the evaluable ALL xenografts. An objective response was observed in 1 of 33 solid tumor xenografts while for the ALL panel, two xenografts achieved complete response (CR) or maintained CR, and a third ALL xenograft achieved stable disease.

CONCLUSIONS

Quisinostat demonstrated broad activity in vitro, and retarded growth in the majority of solid tumor xenografts studied. The most consistent in vivo activity signals observed were for the glioblastoma xenografts and T-cell ALL xenografts.

In vitro antitumor effect of sodium butyrate and zoledronic acid combined with traditional chemotherapeutic drugs: a paradigm of synergistic molecular targeting in the treatment of Ewing sarcoma

Histone deacetylase inhibitors and bisphosphonates have a promising future in the treatment of cancer as targeted anticancer drugs, particularly when used together or in combination with other cytotoxic agents. However, the effects of these combined treatments have not yet been systematically evaluated in Ewing sarcoma. The in vitro effects on cellular proliferation, viability and survival were investigated in two Ewing sarcoma cell lines, SK-ES-1 and RD-ES. The cell lines were treated with sodium butyrate, a histone deacetylase inhibitor and zoledronic acid, a bisphosphonate, alone, together or in combination with chemotherapeutic drugs recommended for clinical treatment of Ewing sarcoma. The data demonstrated that the combination of sodium butyrate and zoledronic acid had a synergistic cytotoxic effect at 72 h following treatment, persisting for 10-14 days post-treatment, in both cell lines tested. All combinations between sodium butyrate or zoledronic acid and the traditional antineoplastic drugs (doxorubicin, etoposide and vincristine) demonstrated a synergistic cytotoxic effect at 72 h in SK-ES-1 and RD-ES cells, except for the combinations of sodium butyrate with vincristine and of zoledronic acid with doxorubicin, which showed only an additive effect in RD-ES cell lines as compared to each agent alone. These acute effects observed in both Ewing sarcoma cell lines were confirmed by the clonogenic assay. The present data suggest that combining histone deacetylase inhibitors and bisphosphonates with traditional chemotherapeutic drugs is a promising therapeutic strategy for the treatment of Ewing sarcoma, and provides a basis for further studies in this field.

Optimal management of Ewing sarcoma family of tumors: recent developments in systemic therapy

The Ewing sarcoma family of tumors (ESFT) is defined by cell surface expression of CD99 and a translocation involving EWS and an ETS partner. Cytotoxic chemotherapy remains the benchmark of first- and second-line therapy, and although the majority of patients with localized disease are cured, almost one third of patients relapse or progress from their disease. Moreover, cure remains elusive in most patients who present with distant metastases. In recent years, the ESFT literature has been dominated by reports of attempts at modulating the insulin-like growth factor (IGF) receptor (IGFR). Unfortunately, three phase II studies examining inhibiting antibodies to IGFR-1 published disappointing results. Whether these results were due to failure to modulate the pathway or other limitations in study design and/or patient selection remain unclear. Other novel strategies currently being investigated in ESFT include tyrosine kinase, mammalian target of rapamycin (mTOR), and poly(ADP-ribose) polymerase (PARP) inhibitors.

A phase II trial of panobinostat in patients with advanced pretreated soft tissue sarcoma. A study from the French Sarcoma Group

Background:

Soft tissue sarcomas (STS) are rare tumours for which treatment options are limited in the advanced setting. Histone deacetylase inhibitors have shown activity in preclinical models of STS.

Methods:

We conducted a single-arm, open-label, multicentre phase II study to assess the efficacy and tolerability of panobinostat given orally, 40 mg thrice weekly in patients with advanced pretreated STS. The primary endpoint was the 3-month progression-free rate.

Results:

Forty-seven STS patients were enrolled between January 2010 and December 2010. Median age was 59 (range 21–79) years, 22 (47%) patients were males. Panobinostat dose was lowered to 20 mg thrice weekly after nine patients were enrolled, based on the recommendation of an independent safety committee. The most common grade 3/4 adverse events were thrombocytopenia, fatigue, lymphopenia and anaemia. Forty-five patients were evaluable for the primary endpoint. Among them, nine patients (20%, 95% CI (10–35%)) were progression-free at 3 months. No partial response was seen, but 17 patients (36%) had stable disease (SD) as their best response. Six patients were progression-free at 6 months.

Conclusion:

Panobinostat was poorly tolerated at 40 mg thrice a week. Efficacy in unselected advanced STS was limited, although some patients had prolonged SD.

Targeted therapies for bone sarcomas

Bone sarcomas include a very large number of tumour subtypes, which originate form bone and more particularly from mesenchymal stem cell lineage. Osteosarcoma, Ewing's sarcoma and chondrosarcoma, the three main bone sarcoma entities develop in a favourable microenvironment composed by bone cells, blood vessels, immune cells, based on the 'seed and soil theory'. Current therapy associates surgery and chemotherapy, however, bone sarcomas remain diseases with high morbidity and mortality especially in children and adolescents. In the past decade, various new therapeutic approaches emerged and target the tumour niche or/and directly the tumour cells by acting on signalling/metabolic pathways involved in cell proliferation, apoptosis or drug resistance. The present review gives a brief overview from basic to clinical assessment of the main targeted therapies of bone sarcoma cells.

Bone sarcomas: from biology to targeted therapies

Primary malignant bone tumours, osteosarcomas, and Ewing sarcomas are rare diseases which occur mainly in adolescents and young adults. With the current therapies, some patients remain very difficult to treat, such as tumour with poor histological response to preoperative CT (or large initial tumour volume for Ewing sarcomas not operated), patients with multiple metastases at or those who relapsed. In order to develop new therapies against these rare tumours, we need to unveil the key driving factors and molecular abnormalities behind the malignant characteristics and to broaden our understanding of the phenomena sustaining the metastatic phenotype and treatment resistance in these tumours. In this paper, starting with the biology of these tumours, we will discuss potential therapeutic targets aimed at increasing local tumour control, limiting metastatic spread, and finally improving patient survival.

Acetylation Increases EWS-FLI1 DNA Binding and Transcriptional Activity

Ewing Sarcoma (ES) is associated with a balanced chromosomal translocation that in most cases leads to the expression of the oncogenic fusion protein and transcription factor EWS-FLI1. EWS-FLI1 has been shown to be crucial for ES cell survival and tumor growth. However, its regulation is still enigmatic. To date, no functionally significant post-translational modifications of EWS-FLI1 have been shown. Since ES are sensitive to histone deacetylase inhibitors (HDI), and these inhibitors are advancing in clinical trials, we sought to identify if EWS-FLI1 is directly acetylated. We convincingly show acetylation of the C-terminal FLI1 (FLI1-CTD) domain, which is the DNA binding domain of EWS-FLI1. In vitro acetylation studies showed that acetylated FLI1-CTD has higher DNA binding activity than the non-acetylated protein. Over-expression of PCAF or treatment with HDI increased the transcriptional activity of EWS-FLI1, when co-expressed in Cos7 cells. However, our data that evaluates the acetylation of full-length EWS-FLI1 in ES cells remains unclear, despite creating acetylation specific antibodies to four potential acetylation sites. We conclude that EWS-FLI1 may either gain access to chromatin as a result of histone acetylation or undergo regulation by direct acetylation. These data should be considered when patients are treated with HDAC inhibitors. Further investigation of this phenomenon will reveal if this potential acetylation has an impact on tumor response.

New therapeutic targets in soft tissue sarcoma

Soft tissue sarcomas are an uncommon and diverse group of more than 50 mesenchymal malignancies. The pathogenesis of many of these is poorly understood, but others have begun to reveal the secrets of their underlying mechanisms. With considerable effort over recent years, soft tissue sarcomas have increasingly been classified on the basis of underlying molecular alterations. In turn, this has allowed the development and application of targeted agents in several specific, molecularly defined, sarcoma subtypes. This review will focus on the rationale for targeted therapy in sarcoma, with emphasis on the relevance of specific molecular factors and pathways in both translocation-associated sarcomas and in genetically complex tumors. In addition, we will address some of the early successes in sarcoma-targeted therapy as well as a few challenges and disappointments in this field. Finally, we will discuss several possible opportunities represented by poorly understood, but potentially promising new therapeutic targets, as well as several novel biological agents currently in preclinical and early phase I/II trials. This will provide the reader with the context for understanding the current state of this field and a sense of where it may be headed in the coming years.

Small-molecule screen identifies modulators of EWS/FLI1 target gene expression and cell survival in Ewing's sarcoma

Ewing's sarcoma family of tumors (EFT) is characterized by the presence of chromosomal translocations leading to the expression of oncogenic transcription factors such as, in the majority of cases, EWS/FLI1. Because of its key role in Ewing's sarcoma development and maintenance, EWS/FLI1 represents an attractive therapeutic target. Here, we characterize PHLDA1 as a novel direct target gene whose expression is repressed by EWS/FLI1. Using this gene and additional specific well-characterized target genes such as NROB1, NKX2.2 and CAV1, all activated by EWS/FLI1, as a read-out system, we screened a small-molecule compound library enriched for FDA-approved drugs that modulated the expression of EWS/FLI1 target genes. Among a hit-list of nine well-known drugs such as camptothecin, fenretinide, etoposide and doxorubicin, we also identified the kinase inhibitor midostaurin (PKC412). Subsequent experiments demonstrated that midostaurin is able to induce apoptosis in a panel of six Ewing's sarcoma cell lines in vitro and can significantly suppress xenograft tumor growth in vivo. These results suggest that midostaurin might be a novel drug that is active against Ewing's cells, which might act by modulating the expression of EWS/FLI1 target genes.

Histone deacetylase inhibitors enhance expression of NKG2D ligands in Ewing sarcoma and sensitize for natural killer cell-mediated cytolysis

Background

Ewing sarcoma patients have a poor prognosis despite multimodal therapy. Integration of combination immunotherapeutic strategies into first-/second-line regimens represents promising treatment options, particularly for patients with intrinsic or acquired resistance to conventional therapies. We evaluated the susceptibility of Ewing sarcoma to natural killer cell-based combination immunotherapy, by assessing the capacity of histone deacetylase inhibitors to improve immune recognition and sensitize for natural killer cell cytotoxicity.

Methods

Using flow cytometry, ELISA and immunohistochemistry, expression of natural killer cell receptor ligands was assessed in chemotherapy-sensitive/-resistant Ewing sarcoma cell lines, plasma and tumours. Natural killer cell cytotoxicity was evaluated in Chromium release assays. Using ATM/ATR inhibitor caffeine, the contribution of the DNA damage response pathway to histone deacetylase inhibitor-induced ligand expression was assessed.

Results

Despite comparable expression of natural killer cell receptor ligands, chemotherapy-resistant Ewing sarcoma exhibited reduced susceptibility to resting natural killer cells. Interleukin-15-activation of natural killer cells overcame this reduced sensitivity. Histone deacetylase inhibitor-pretreatment induced NKG2D-ligand expression in an ATM/ATR-dependent manner and sensitized for NKG2D-dependent cytotoxicity (2/4 cell lines). NKG2D-ligands were expressed in vivo, regardless of chemotherapy-response and disease stage. Soluble NKG2D-ligand plasma concentrations did not differ between patients and controls.

Conclusion

Our data provide a rationale for combination immunotherapy involving immune effector and target cell manipulation in first-/second-line treatment regimens for Ewing sarcoma.

Molecular pathogenesis and targeted therapeutics in Ewing sarcoma/primitive neuroectodermal tumours

BACKGROUND

Ewing sarcoma/PNET is managed with treatment paradigms involving combinations of chemotherapy, surgery, and sometimes radiation. Although the 5-year survival rate of non-metastatic disease approaches 70%, those cases that are metastatic and those that recur have 5-year survival rates of less than 20%. Molecularly targeted treatments offer the potential to further improve treatment outcomes.

METHODS

A PUBMED search was performed from 1997 to 2011. Published literature that included the topic of the Ewing sarcoma/PNET was also referenced.

RESULTS

Insulin-like growth factor-1 receptor (IGF-1R) antagonists have demonstrated modest single agent efficacy in phase I/II clinical trials in Ewing sarcoma/PNET, but have a strong preclinical rationale. Based on in vitro and animal data, treatment using antisense RNA and cDNA oligonucleotides directed at silencing the EWS-FLI chimera that occurs in most Ewing sarcoma/PNET may have potential therapeutic importance. However drug delivery and degradation problems may limit this therapeutic approach. Protein-protein interactions can be targeted by inhibition of RNA helicase A, which binds to EWS/FLI as part of the transcriptional complex. Tumour necrosis factor related apoptosis inducing ligand induction using interferon has been used in preclinical models. Interferons may be incorporated into future chemotherapeutic treatment paradigms. Histone deacetylase inhibitors can restore TGF-β receptor II allowing TFF-β signalling, which appears to inhibit growth of Ewing sarcoma/PNET cell lines in vitro. Immunotherapy using allogeneic natural killer cells has activity in Ewing sarcoma/PNET cell lines and xenograft models. Finally, cyclin dependent kinase inhibitors such as flavopiridol may be clinically efficacious in relapsed Ewing sarcoma/PNET.

CONCLUSION

Preclinical evidence exists that targeted therapeutics may be efficacious in the ESFT. IGF-1R antagonists have demonstrated efficacy in phase I/II clinical trials, although predicting responses remains a challenge. The future treatment of Ewing sarcoma/PNET is likely to be improved by these scientific advances.

Histone deacetylase 1 and 2 in mesenchymal tumors

Histone deacetylases (HDACs) have a critical role in epigenetic gene silencing, rendering a compact chromatin structure by removing acetyl groups from lysine residues within the tails of core histones, thereby repressing gene expression. Epigenetic transcriptional dysregulation is an important oncogenic mechanism in some sarcomas associated with translocations, for which antitumor activity by HDAC inhibitors has been shown in preclinical studies. Nevertheless, the expression of the protein targets of these drugs has not yet been broadly surveyed in this neoplasia. In this study, we assess the expression of HDAC1 and 2 by immunohistochemistry in a tissue microarray series of 1332 cases, representing 44 categories of malignant and borderline mesenchymal tumors. HDAC2 was the more highly expressed isoform, and was more strongly expressed in translocation-associated sarcomas than in other mesenchymal tumors or normal tissues. HDAC1, in contrast, displayed lower expression in translocation-associated sarcomas than in other mesenchymal tumors or in normal tissues. These results indicate that HDAC1 and HDAC2 are differentially expressed in mesenchymal neoplasms, and suggest that HDAC2 is the isoform more likely contributing to the pathogenesis of many translocation-associated sarcomas and to their response to HDAC inhibitors.

Sodium butyrate-induced DAPK-mediated apoptosis in human gastric cancer cells

Epigenetic mechanisms of histone acetylation/deacetylation play an important role in the regulation of gene expression associated with the cell cycle and apoptosis. Recently, sodium butyrate, a histone deacetylase (HDAC) inhibitor, has been shown to exhibit anticancer effects via differentiation and apoptosis of cancer cells. Sodium butyrate may be a potential anticancer chemotherapeutic drug; however, the precise mechanism underlying the anticancer effects of sodium butyrate has not been clearly elucidated. In the present study, we investigated the role of death-associated protein kinase (DAPK) on the apoptosis of human gastric cancer cells induced by sodium butyrate. We observed that sodium butyrate induced apoptosis in human gastric cancer cells. Treatment with the HDAC inhibitor sodium butyrate increased the expression of caspase-3 and DAPK1/2 genes but decreased the expression of Bcl-2 in human gastric cancer cells. The expression of DAPK3, p53 and p21 were not altered by sodium butyrate treatment. Analysis of the general expression patterns revealed that sodium butyrate increased the expression of DAPK1/2 but decreased the expression of FAK and induced changes in the proliferation of apoptosis-related genes in human gastric cancer cells. These data suggest that DAPK expression prompts apoptosis by reducing the FAK protein level in sodium butyrate-induced apoptosis of human gastric cancer cells.

CD99/MIC2 Constitutes a Differentiation Antigen of a Human Osteoblast Cell Line

BACKGROUND

The histological origin of the Ewing's family of tumors (EFT) is still not clear. Since these small cell bone tumors may originate from osteogenic stem cells, the presence of the CD99/MIC2 antigen, known to be overexpressed in EFT, was studied in a human osteoblast cell line in response to differentiation inducers.

METHODS

The HBA-71 monoclonal antibody directed to the CD99/MIC2 antigen was used to stain a human osteoblast cell line as well as the two EFT cell lines KAL and EW-2 after pretreatment of the cells with the differentiation inducers calcitriol and the histone deacetylase (HDAC) inhibitors sodium butyrate (NaB), sodium phenylacetate (NaPA) as well as N, N'-hexamethylen-bis-acetamide (HMBA). Alkaline phosphatase (ALP) levels were determined as cellular differentiation marker.

RESULTS

Significant expression of the CD99/MIC2 antigen, yielding a molecular weight of 32 kD in Western blotting, was found in the human osteoblast cell line. Pretreatment of the osteoblasts with calcitriol and HMBA increased ALP content and suppressed the CD99/MIC2 antigen. Calcitriol had no major effect on CD99/MIC2 expression of both EFT cell lines, but HMBA enhanced ALP activity in KAL cells and downregulated CD99/MIC2. EW-2 cells exhibited reduced levels of both CD99/MIC2 and ALP.

CONCLUSIONS

This study supports the role of CD99/MIC2 as differentiation antigen of osteoblasts and a Ewing's sarcoma cell line with neuroectodermal phenotype. Response to calcitriol is absent or low in the two EFT cell lines tested.

Review of therapeutic strategies for osteosarcoma, chondrosarcoma, and Ewing's sarcoma

The most prevalent forms of bone cancer are osteosarcoma, chondrosarcoma, and Ewing’s sarcoma. Although chemotherapy and radiotherapy have replaced traditional surgical treatments, survival rates have undergone only marginal improvements. Current knowledge of the molecular pathways involved in each type of cancer has led to better approaches in cancer treatment. A number of cell signaling molecules are involved in tumorigenesis, and specific targets have been identified based on these signal transducers. This review highlights some of the important cellular pathways and potential therapeutic targets, tumor site-specific irradiation techniques, and novel drug delivery systems used to administer these drugs.