The fusion protein SS18-SSX1 employs core Wnt pathway transcription factors to induce a partial Wnt signature in synovial sarcoma

Advances of SS18-SSX fusion gene in synovial sarcoma: Emerging novel functions and therapeutic potentials

Synovial sarcoma is a rare type of soft tissue sarcoma that primarily affects adolescents and young adults, featured by aggressive behavior and a high potential for metastasis. Genetically, synovial sarcoma is defined by the fusion oncogene SS18-SSX arising from the translocation of t(X;18)(p11;q11). SS18-SSX fusion gene is the major driver of the oncogenic event in synovial sarcoma. SS18-SSX fusion protein, while not containing any DNA-binding motifs, binds to the SWI/SNF (BAF) complex, a major epigenetic regulator, leading to the disruption of gene expression which results in tumor initiation and progression. Emerging studies on the molecular mechanisms of SS18-SSX associated signaling pathway hold promise for developments in diagnosis and treatments. Advanced diagnostic methods facilitate early and precise detection of the tumor, enabling disease monitoring and prognostic improvements. Treatment of synovial sarcoma typically comprises local surgery, radiotherapy and chemotherapy, while novel managements such as immunotherapy, targeted therapies and epigenetic modifiers are explored. This review focuses on the recent studies of SS18-SSX fusion gene, epigenetic landscape, signaling pathways, diagnostic techniques, and relevant therapeutic advances, aiming to inhibit the oncogenic processes and improve outcomes for patients with synovial sarcoma.

Combination of HDAC and FYN inhibitors in synovial sarcoma treatment

The SS18-SSX fusion protein is an oncogenic driver in synovial sarcoma. At the molecular level, SS18-SSX functions as both an activator and a repressor to coordinate transcription of different genes responsible for tumorigenesis. Here, we identify the proto-oncogene FYN as a new SS18-SSX target gene and examine its relation to synovial sarcoma therapy. FYN is a tyrosine kinase that promotes cancer growth, metastasis and therapeutic resistance, but SS18-SSX appears to negatively regulate FYN expression in synovial sarcoma cells. Using both genetic and histone deacetylase inhibitor (HDACi)-based pharmacologic approaches, we show that suppression of SS18-SSX leads to FYN reactivation. In support of this notion, we find that blockade of FYN activity synergistically enhances HDACi action to reduce synovial sarcoma cell proliferation and migration. Our results support a role for FYN in attenuation of anti-cancer activity upon inhibition of SS18-SSX function and demonstrate the feasibility of targeting FYN to improve the effectiveness of HDACi treatment against synovial sarcoma.

CIC-DUX4 Chromatin Profiling Reveals New Epigenetic Dependencies and Actionable Therapeutic Targets in CIC-Rearranged Sarcomas

CIC-DUX4-rearranged sarcoma (CDS) is a rare and aggressive soft tissue tumor that occurs most frequently in young adults. The key oncogenic driver of this disease is the expression of the CIC-DUX4 fusion protein as a result of chromosomal rearrangements. CIC-DUX4 displays chromatin binding properties, and is therefore believed to function as an aberrant transcription factor. However, the chromatin remodeling events induced by CIC-DUX4 are not well understood, limiting our ability to identify new mechanism-based therapeutic strategies for these patients. Here, we generated a genome-wide profile of CIC-DUX4 DNA occupancy and associated chromatin states in human CDS cell models and primary tumors. Combining chromatin profiling, proximity ligation assays, as well as genetic and pharmacological perturbations, we show that CIC-DUX4 operates as a potent transcriptional activator at its binding sites. This property is in contrast with the repressive function of the wild-type CIC protein, and is mainly mediated through the direct interaction of CIC-DUX4 with the acetyltransferase p300. In keeping with this, we show p300 to be essential for CDS tumor cell proliferation; additionally, we find its pharmacological inhibition to significantly impact tumor growth in vitro and in vivo. Taken together, our study elucidates the mechanisms underpinning CIC-DUX4-mediated transcriptional regulation.

Transcriptome Profiling of the Hippocampal Seizure Network Implicates a Role for Wnt Signaling during Epileptogenesis in a Mouse Model of Temporal Lobe Epilepsy

Mesial temporal lobe epilepsy (mTLE) is a life-threatening condition characterized by recurrent hippocampal seizures. mTLE can develop after exposure to risk factors such as febrile seizure, trauma, and infection. Within the latent period between exposure and onset of epilepsy, pathological remodeling events occur that contribute to epileptogenesis. The molecular mechanisms responsible are currently unclear. We used the mouse intrahippocampal kainite model of mTLE to investigate transcriptional dysregulation in the ipsilateral and contralateral dentate gyrus (DG), representing the epileptogenic zone (EZ) and peri-ictal zone (PIZ). DG were analyzed after 3, 7, and 14 days by RNA sequencing. In both the EZ and PIZ, transcriptional dysregulation was dynamic over the epileptogenic period with early expression of genes representing cell signaling, migration, and proliferation. Canonical Wnt signaling was upregulated in the EZ and PIZ at 3 days. Expression of inflammatory genes differed between the EZ and PIZ, with early expression after 3 days in the PIZ and delayed expression after 7-14 days in the EZ. This suggests that critical gene changes occur early in the hippocampal seizure network and that Wnt signaling may play a role within the latent epileptogenic period. These findings may help to identify novel therapeutic targets that could prevent epileptogenesis.

Upregulation of ERK-EGR1-heparanase axis by HDAC inhibitors provides targets for rational therapeutic intervention in synovial sarcoma

BACKGROUND

Synovial sarcoma (SS) is an aggressive soft tissue tumor with limited therapeutic options in advanced stage. SS18-SSX fusion oncogenes, which are the hallmarks of SS, cause epigenetic rewiring involving histone deacetylases (HDACs). Promising preclinical studies supporting HDAC targeting for SS treatment were not reflected in clinical trials with HDAC inhibitor (HDACi) monotherapies. We investigated pathways implicated in SS cell response to HDACi to identify vulnerabilities exploitable in combination treatments and improve the therapeutic efficacy of HDACi-based regimens.

METHODS

Antiproliferative and proapoptotic effects of the HDACi SAHA and FK228 were examined in SS cell lines in parallel with biochemical and molecular analyses to bring out cytoprotective pathways. Treatments combining HDACi with drugs targeting HDACi-activated prosurvival pathways were tested in functional assays in vitro and in a SS orthotopic xenograft model. Molecular mechanisms underlying synergisms were investigated in SS cells through pharmacological and gene silencing approaches and validated by qRT-PCR and Western blotting.

RESULTS

SS cell response to HDACi was consistently characterized by activation of a cytoprotective and auto-sustaining axis involving ERKs, EGR1, and the β-endoglycosidase heparanase, a well recognized pleiotropic player in tumorigenesis and disease progression. HDAC inhibition was shown to upregulate heparanase by inducing expression of the positive regulator EGR1 and by hampering negative regulation by p53 through its acetylation. Interception of HDACi-induced ERK-EGR1-heparanase pathway by cell co-treatment with a MEK inhibitor (trametinib) or a heparanase inhibitor (SST0001/roneparstat) enhanced antiproliferative and pro-apoptotic effects. HDAC and heparanase inhibitors had opposite effects on histone acetylation and nuclear heparanase levels. The combination of SAHA with SST0001 prevented the upregulation of ERK-EGR1-heparanase induced by the HDACi and promoted caspase-dependent cell death. In vivo, the combined treatment with SAHA and SST0001 potentiated the antitumor efficacy against the CME-1 orthotopic SS model as compared to single agent administration.

CONCLUSIONS

The present study provides preclinical rationale and mechanistic insights into drug combinatory strategies based on the use of ERK pathway and heparanase inhibitors to improve the efficacy of HDACi-based antitumor therapies in SS. The involvement of classes of agents already clinically available, or under clinical evaluation, indicates the transferability potential of the proposed approaches.

Emerging Role of Chimeric RNAs in Cell Plasticity and Adaptive Evolution of Cancer Cells

Gene fusions can give rise to somatic alterations in cancers. Fusion genes have the potential to create chimeric RNAs, which can generate the phenotypic diversity of cancer cells, and could be associated with novel molecular functions related to cancer cell survival and proliferation. The expression of chimeric RNAs in cancer cells might impact diverse cancer-related functions, including loss of apoptosis and cancer cell plasticity, and promote oncogenesis. Due to their recurrence in cancers and functional association with oncogenic processes, chimeric RNAs are considered biomarkers for cancer diagnosis. Several recent studies demonstrated that chimeric RNAs could lead to the generation of new functionality for the resistance of cancer cells against drug therapy. Therefore, targeting chimeric RNAs in drug resistance cancer could be useful for developing precision medicine. So, understanding the functional impact of chimeric RNAs in cancer cells from an evolutionary perspective will be helpful to elucidate cancer evolution, which could provide a new insight to design more effective therapies for cancer patients in a personalized manner.

Comprehensive characterization of 536 patient-derived xenograft models prioritizes candidatesfor targeted treatment

Development of candidate cancer treatments is a resource-intensive process, with the research community continuing to investigate options beyond static genomic characterization. Toward this goal, we have established the genomic landscapes of 536 patient-derived xenograft (PDX) models across 25 cancer types, together with mutation, copy number, fusion, transcriptomic profiles, and NCI-MATCH arms. Compared with human tumors, PDXs typically have higher purity and fit to investigate dynamic driver events and molecular properties via multiple time points from same case PDXs. Here, we report on dynamic genomic landscapes and pharmacogenomic associations, including associations between activating oncogenic events and drugs, correlations between whole-genome duplications and subclone events, and the potential PDX models for NCI-MATCH trials. Lastly, we provide a web portal having comprehensive pan-cancer PDX genomic profiles and source code to facilitate identification of more druggable events and further insights into PDXs' recapitulation of human tumors.

The role of SYT-SSX fusion gene in tumorigenesis of synovial sarcoma

Synovial sarcoma (SS) is an aggressive malignancy of an unknown tissue origin that is characterized by biphasic differentiation. A possible basis of the pathogenesis of SS is pathognomonic t(X;18) (p11.2; q11.2) translocation, leading to the formation and expression of the SYT-SSX fusion gene. More than a quarter of the patients die of SS metastasis within 5 years after the diagnosis, but the pathogenic factors are unknown. Therefore, there is an urgent need to explore the pathogenesis, invasion, metastasis, and clinical treatment options for SS, especially molecular-targeted drug therapy. Recent studies have shown that the SYT-SSX fusion gene associated with SS may be regulated by different signaling pathways, microRNAs, and other molecules, which may produce stem cell characteristics or promote epithelial-mesenchymal transition, resulting in SS invasion and metastasis. This review article aims to show the relationship between the SYT-SSX fusion gene and the related pathway molecules as well as other molecules involved from different perspectives, which may provide a deeper and clearer understanding of the SYT-SSX fusion gene function. Therefore, this review may provide a more innovative and broader perspective of the current research, treatment options, and prognosis assessment of SS.

The chromatin landscape of primary synovial sarcoma organoids is linked to specific epigenetic mechanisms and dependencies

We have addressed the mechanisms by which the fusion protein SS18-SSX modifies the epigenome toward the development of synovial sarcoma and the establishment of its potentially targetable vulnerabilities.

Synovial sarcoma (SyS) is an aggressive mesenchymal malignancy invariably associated with the chromosomal translocation t(X:18; p11:q11), which results in the in-frame fusion of the BAF complex gene SS18 to one of three SSX genes. Fusion of SS18 to SSX generates an aberrant transcriptional regulator, which, in permissive cells, drives tumor development by initiating major chromatin remodeling events that disrupt the balance between BAF-mediated gene activation and polycomb-dependent repression. Here, we developed SyS organoids and performed genome-wide epigenomic profiling of these models and mesenchymal precursors to define SyS-specific chromatin remodeling mechanisms and dependencies. We show that SS18-SSX induces broad BAF domains at its binding sites, which oppose polycomb repressor complex (PRC) 2 activity, while facilitating recruitment of a non-canonical (nc)PRC1 variant. Along with the uncoupling of polycomb complexes, we observed H3K27me3 eviction, H2AK119ub deposition and the establishment of de novo active regulatory elements that drive SyS identity. These alterations are completely reversible upon SS18-SSX depletion and are associated with vulnerability to USP7 loss, a core member of ncPRC1.1. Using the power of primary tumor organoids, our work helps define the mechanisms of epigenetic dysregulation on which SyS cells are dependent.

B-ALL Complexity: Is Targeted Therapy Still A Valuable Approach for Pediatric Patients?

Simple Summary

B-ALL is the more frequent childhood malignancy. Even though significant improvements in patients’ survival, some pediatric B-ALL have still poor prognosis and novel strategies are needed. Recently, new genetic abnormalities and altered signaling pathways have been described, defining novel B-ALL subtypes.Innovative targeted therapeutic drugs may potentially show a great impact on the treatment of B-ALL subtypes, offering an important chance to block multiple signaling pathways and potentially improving the clinical management of B-ALL younger patients, especially for the new identified subtypes that lack efficient chemotherapeutic protocols. In this review, we shed light on the up-to-date knowledge of the novel childhood B-ALL subtypes and the altered signaling pathways that could become new druggable targets.

Abstract

B-cell acute lymphoblastic leukemia (B-ALL) is a hematologic malignancy that arises from the clonal expansion of transformed B-cell precursors and predominately affects childhood. Even though significant progresses have been made in the treatment of B-ALL, pediatric patients’ outcome has to be furtherly increased and alternative targeted treatment strategies are required for younger patients. Over the last decade, novel approaches have been used to understand the genomic landscape and the complexity of the molecular biology of pediatric B-ALL, mainly next generation sequencing, offering important insights into new B-ALL subtypes, altered pathways, and therapeutic targets that may lead to improved risk stratification and treatments. Here, we will highlight the up-to-date knowledge of the novel B-ALL subtypes in childhood, with particular emphasis on altered signaling pathways. In addition, we will discuss the targeted therapies that showed promising results for the treatment of the different B-ALL subtypes.

YJ5 as an immunohistochemical marker of osteogenic lineage

Overexpression of WLS, an upstream protein in the Wnt pathway, has been implicated in several non-osteogenic tumours. This study represents the first attempt at evaluating WLS expression in various bone and soft tissue tumours using YJ5, a monoclonal antibody specific to WLS, with the aim of elucidating its utility in discerning tumours with aberrant Wnt signalling and as a marker of osteogenic lineage in challenging cases. Tumour tissue sections of 144 bone mass lesions and 63 soft tissue mass lesions were immunostained with the YJ5 antibody following standardised protocols. Subsequent assessment of immunoreactivity segregated cases into one of three groups: absent/weak, moderate, or strong YJ5 immunoreactivity. For the bone tumours, strong YJ5 immunoreactivity was seen in almost all osteosarcomas and chondroblastomas, all osteoblastomas and osteoid osteomas. In contrast, all other cartilaginous tumours, chordomas, aneurysmal bone cysts, chondromyxoid fibromas, most fibrous dysplasias and most giant cell tumours exhibited absent/weak YJ5 immunostaining. For the soft tissue tumours, a more heterogeneous pattern of YJ5 immunoreactivity was observed. Because diffuse and strong YJ5 expression is identified in almost all benign and malignant bone tumours with osteoblastic activity, it can be potentially utilised as an immunohistochemical marker to support osteogenic lineage. If interpreted in the appropriate context, this marker is useful in determining whether a malignant bone tumour is an osteosarcoma, particularly in those subtypes with no or minimal osteoid or unusual morphological features. This marker can also complement SATB2 to denote osteogenic lineage.

Synovial Sarcoma: A Complex Disease with Multifaceted Signaling and Epigenetic Landscapes

PURPOSE OF REVIEW

Aside from a characteristic SS18-SSX translocation identified in almost all cases, no genetic anomalies have been reliably isolated yet to drive the pathogenesis of synovial sarcoma. In the following review, we explore the structural units of wild-type SS18 and SSX, particularly as they relate to the transcriptional alterations and cellular pathway changes imposed by SS18-SSX.

RECENT FINDINGS

Native SS18 and SSX contribute recognizable domains to the SS18-SSX chimeric proteins, which inflict transcriptional and epigenetic changes through selective protein interactions involving the SWI/SNF and Polycomb chromatin remodeling complexes. Multiple oncogenic and developmental pathways become altered, collectively reprogramming the cellular origin of synovial sarcoma and promoting its malignant transformation. Synovial sarcoma is characterized by complex epigenetic and signaling landscapes. Identifying the operational pathways and concomitant genetic changes induced by SS18-SSX fusions could help develop tailored therapeutic strategies to ultimately improve disease control and patient survivorship.

Impact of Wnt/β-Catenin Inhibition on Cell Proliferation through CDC25A Downregulation in Soft Tissue Sarcomas

Simple Summary

Growing evidence suggests that Wnt signaling may be crucial for tumorigenesis and progression of soft tissue sarcomas (STS). Inhibitors of this pathway are currently in clinical trials or pre-clinical studies in order to validate its utility in different neoplasia. One of this inhibitors, PRI-724, is showing promising results for advanced pancreatic adenocarcinoma or ovarian cancer. We found that PRI-724 is able to suppress cell viability/proliferation and to increase cell death rates of soft tissue sarcomas cells in vitro. CDC25A, a target gene of Wnt signaling pathway, is essential for STS proliferation because its downregulation via siRNA was able to mimic the effect of PRT-724 on cell cycle arrest and evaluation of NCBI/GenBank data confirmed its overexpression in STS patients’ samples. Moreover, in vitro administration of PRI-724 along with standard STS chemotherapeutic drugs improved the efficacy of chemotherapy, suggesting that Wnt inhibition could be a promising new therapeutic strategy in STS.

Abstract

The Wnt signaling pathway is an important cellular mechanism for regulating differentiation processes as well as cell cycle events, and different inhibitors of this pathway, for example, PRI-724, are showing promising results in clinical trials for treatment of advanced pancreatic adenocarcinoma or ovarian cancer. Growing evidence suggests that Wnt signaling may also be crucial for tumorigenesis and progression of soft tissue sarcomas (STS), a malignant neoplasm with few therapeutic options at an advanced state. Our study with several STS cell lines and primary cultures shows that inhibition of Wnt/β-catenin signaling with PRI-724 is able to suppress cell viability/proliferation and to increase cell death rates. TCF/β-catenin-mediated transcriptional activity is decreased in treated cells, leading to downregulation of its target genes CCND1 and CDC25A. The latter was critical because its downregulation via siRNA was able to mimic the effect of PRI-724 on cell cycle arrest and cell death induction. An evaluation of NCBI/GenBank data confirmed that CDC25A mRNA is elevated in STS patients. Importantly, PRI-724 in combination with standard STS chemotherapeutics doxorubicin or trabectedin enhanced their antitumoral effect in a synergistic manner according to isobolographic analysis, suggesting that Wnt inhibition through PRI-724 could be a beneficial combination regime in patients with advanced STS.

A Genetic Screen for Human Genes Suppressing FUS Induced Toxicity in Yeast

FUS is a nucleic acid binding protein that, when mutated, cause a subset of familial amyotrophic lateral sclerosis (ALS). Expression of FUS in yeast recapitulates several pathological features of the disease-causing mutant proteins, including nuclear to cytoplasmic translocation, formation of cytoplasmic inclusions, and cytotoxicity. Genetic screens using the yeast model of FUS have identified yeast genes and their corresponding human homologs suppressing FUS induced toxicity in yeast, neurons and animal models. To expand the search for human suppressor genes of FUS induced toxicity, we carried out a genome-scale genetic screen using a newly constructed library containing 13570 human genes cloned in an inducible yeast-expression vector. Through multiple rounds of verification, we found 37 human genes that, when overexpressed, suppress FUS induced toxicity in yeast. Human genes with DNA or RNA binding functions are overrepresented among the identified suppressor genes, supporting that perturbations of RNA metabolism is a key underlying mechanism of FUS toxicity.

Feasibility of Targeting Traf2-and-Nck-Interacting Kinase in Synovial Sarcoma

Background: The treatment of patients with metastatic synovial sarcoma is still challenging, and the development of new molecular therapeutics is desirable. Dysregulation of Wnt signaling has been implicated in synovial sarcoma. Traf2-and-Nck-interacting kinase (TNIK) is an essential transcriptional co-regulator of Wnt target genes. We examined the efficacy of a small interfering RNA (siRNA) to TNIK and a small-molecule TNIK inhibitor, NCB-0846, for synovial sarcoma. Methods: The expression of TNIK was determined in 20 clinical samples of synovial sarcoma. The efficacy of NCB-0846 was evaluated in four synovial sarcoma cell lines and a mouse xenograft model. Results: We found that synovial sarcoma cell lines with Wnt activation were highly dependent upon the expression of TNIK for proliferation and survival. NCB-0846 induced apoptotic cell death in synovial sarcoma cells through blocking of Wnt target genes including MYC, and oral administration of NCB-846 induced regression of xenografts established by inoculation of synovial sarcoma cells. Discussion: It has become evident that activation of Wnt signaling is causatively involved in the pathogenesis of synovial sarcoma, but no molecular therapeutics targeting the pathway have been approved. This study revealed for the first time the therapeutic potential of TNIK inhibition in synovial sarcoma.

Uncommon tumors of temporomandibular joint: An institutional experience and review

BACKGROUND

The temporomandibular joint (TMJ) harbors a myriad of pathologic alterations including arthritides and benign and malignant neoplasms.

METHODS

Herein, we describe our institutional experience of some uncommon and unusual synovial pathologies of the TMJ along with a review of literature. We searched through the archives of department of pathology and institutional electronic medical record for specimens of TMJ between 1999 and 2019. Hematoxylin and eosin slides were reviewed and data (final diagnosis, age, gender, clinical presentation, tumor size, treatment modality, recurrence, and vital status) were collected.

RESULTS

A total of seven cases were identified including four cases of synovial chrondromatosis; and one case each of tenosynovial giant cell tumor, localized type, tenosynovial giant cell tumor, diffuse type, and synovial sarcoma.

CONCLUSIONS

The article emphasizes on the clinical, radiologic, pathologic, and molecular features of these uncommon entities. The differential diagnosis of each entity is also discussed. Current updates in the management are also reviewed.

Targeting the undruggable: exploiting neomorphic features of fusion oncoproteins in childhood sarcomas for innovative therapies

While sarcomas account for approximately 1% of malignant tumors of adults, they are particularly more common in children and adolescents affected by cancer. In contrast to malignancies that occur in later stages of life, childhood tumors, including sarcoma, are characterized by a striking paucity of somatic mutations. However, entity-defining fusion oncogenes acting as the main oncogenic driver mutations are frequently found in pediatric bone and soft-tissue sarcomas such as Ewing sarcoma (EWSR1-FLI1), alveolar rhabdomyosarcoma (PAX3/7-FOXO1), and synovial sarcoma (SS18-SSX1/2/4). Since strong oncogene-dependency has been demonstrated in these entities, direct pharmacological targeting of these fusion oncogenes has been excessively attempted, thus far, with limited success. Despite apparent challenges, our increasing understanding of the neomorphic features of these fusion oncogenes in conjunction with rapid technological advances will likely enable the development of new strategies to therapeutically exploit these neomorphic features and to ultimately turn the "undruggable" into first-line target structures. In this review, we provide a broad overview of the current literature on targeting neomorphic features of fusion oncogenes found in Ewing sarcoma, alveolar rhabdomyosarcoma, and synovial sarcoma, and give a perspective for future developments. Graphical abstract Scheme depicting the different targeting strategies of fusion oncogenes in pediatric fusion-driven sarcomas. Fusion oncogenes can be targeted on their DNA level (1), RNA level (2), protein level (3), and by targeting downstream functions and interaction partners (4).

Pan-Cancer Landscape of Aberrant DNA Methylation across Human Tumors

The discovery of cancer-associated alterations has primarily focused on genetic variants. Nonetheless, altered epigenomes contribute to deregulate transcription and promote oncogenic pathways. Here, we designed an algorithmic approach (RESET) to identify aberrant DNA methylation and associated cis-transcriptional changes across >6,000 human tumors. Tumors exhibiting mutations of chromatin remodeling factors and Wnt signaling displayed DNA methylation instability, characterized by numerous hyper- and hypo-methylated loci. Most silenced and enhanced genes coalesced in specific pathways including apoptosis, DNA repair, and cell metabolism. Cancer-germline antigens (CG) were frequently epigenomically enhanced and their expression correlated with response to anti-PD-1, but not anti-CTLA4, in skin melanoma. Finally, we demonstrated the potential of our approach to explore DNA methylation changes in pediatric tumors, which frequently lack genetic drivers and exhibit epigenomic modifications. Our results provide a pan-cancer map of aberrant DNA methylation to inform functional and therapeutic studies.

HDAC2 Regulates Site-Specific Acetylation of MDM2 and Its Ubiquitination Signaling in Tumor Suppression

Histone deacetylases (HDACs) are promising targets for cancer therapy, although their individual actions remain incompletely understood. Here, we identify a role for HDAC2 in the regulation of MDM2 acetylation at previously uncharacterized lysines. Upon inactivation of HDAC2, this acetylation creates a structural signal in the lysine-rich domain of MDM2 to prevent the recognition and degradation of its downstream substrate, MCL-1 ubiquitin ligase E3 (MULE). This mechanism further reveals a therapeutic connection between the MULE ubiquitin ligase function and tumor suppression. Specifically, we show that HDAC inhibitor treatment promotes the accumulation of MULE, which diminishes the t(X; 18) translocation-associated synovial sarcomagenesis by directly targeting the fusion product SS18-SSX for degradation. These results uncover a new HDAC2-dependent pathway that integrates reversible acetylation signaling to the anticancer ubiquitin response.

Difference in transducin-like enhancer of split 1 protein expression between basal cell adenomas and basal cell adenocarcinomas - an immunohistochemical study

Background

Basal cell adenoma (BCA) and basal cell adenocarcinoma (BCAC) are benign and malignant, basaloid salivary gland neoplasms, respectively. These tumors show a dual-cell proliferation of inner luminal/ductal cells and outer abluminal/myoepithelial or basal cells. The only difference between them is defined as a malignant morphology such as invasion. Recently, the nuclear expression of β-catenin and a catenin beta-1 (CTNNB1) mutation were found in BCA. Transducin-like enhancer of split 1 (TLE1) belongs to the Groucho/TLE family, and it functions in the “off” state in the Wnt/β-catenin signaling pathway. We hypothesized that if the dysregulation of the Wnt/β-catenin signaling pathway could be attributed to the tumorigenesis of BCA/BCAC, there might be differences in TLE1 expression between BCA and BCAC.

Method

The study included 35 BCA and 4 BCAC cases. We performed immunohistochemistry to detect TLE1 and β-catenin and investigated the catenin beta-1 (CTNNB1) mutational profile among BCA and BCAC cases.

Results

In BCA, the expression of TLE1 was confined to luminal cells of glandular structures, in contrast to the expression of β-catenin in abluminal cells. The BCA cases harbored CTNNB1 gene mutations (12/35). In BCAC, luminal cell staining of TLE1 was identical to BCA in non-invasive areas (4/4) but indistinct in invasive areas (3/4). The BCAC cases were β-catenin positive for abluminal cells in both areas. The BCAC cases had CTNNB1 mutation (2/4) and the laser-captured microdissection allowed the separate collection of infiltrative and non-infiltrative areas to detect the same mutation.

Conclusions

Immunohistochemical analysis for TLE1 can identify BCA and BCAC by luminal cell staining difference, especially indistinct luminal cell expression for TLE1 in invasive areas of BCAC. Moreover, TLE1 can be luminal/ductal cell markers.

Identification of cytotoxic agents disrupting synovial sarcoma oncoprotein interactions by proximity ligation assay

Conventional cytotoxic therapies for synovial sarcoma provide limited benefit. Drugs specifically targeting the product of its driver translocation are currently unavailable, in part because the SS18-SSX oncoprotein functions via aberrant interactions within multiprotein complexes. Proximity ligation assay is a recently-developed method that assesses protein-protein interactions in situ. Here we report use of the proximity ligation assay to confirm the oncogenic association of SS18-SSX with its co-factor TLE1 in multiple human synovial sarcoma cell lines and in surgically-excised human tumor tissue. SS18-SSX/TLE1 interactions are disrupted by class I HDAC inhibitors and novel small molecule inhibitors. This assay can be applied in a high-throughput format for drug discovery in fusion-oncoprotein associated cancers where key effector partners are known.

Wnt Signaling in Ewing Sarcoma, Osteosarcoma, and Malignant Peripheral Nerve Sheath Tumors

PURPOSE OF REVIEW

Wnt signaling plays a central role in development and homeostasis, and its dysregulation is a common event in many types of human cancer. Here we explore in detail the contributions of Wnt signaling to the initiation and maintenance of three types of saroma: Ewing sarcoma, osteosarcoma, and malignant peripheral nerve sheath tumors. This review provides an overview of the Wnt signaling pathway and explores in detail the current knowledge about its role in the initiation or maintenance of three tumor types: Ewing sarcoma, osteosarcoma, and malignant peripheral nerve sheath tumors.

RECENT FINDINGS

Recent work has assessed the role(s) of Wnt signaling within these cell types. This review provides an overview of the mechanistic insights that have been gained from a number of recent studies to set the foundation for potential therapeutic applications. Wnt signaling has emerged as a potentially critical pathway in maintaining the growth of these types of tumors. Given the fact that many new inhibitors of the pathway have recently or will soon enter Phase 1 clinical trials, it is likely that assessment of their activity in these tumor types will occur in human patients.

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.

Disruption of TCF/β-Catenin Binding Impairs Wnt Signaling and Induces Apoptosis in Soft Tissue Sarcoma Cells

Soft tissue sarcomas (STS) are malignant tumors of mesenchymal origin and represent around 1% of adult cancers, being a very heterogeneous group of tumors with more than 50 different subtypes. The Wnt signaling pathway is involved in the development and in the regulation, self-renewal, and differentiation of mesenchymal stem cells, and plays a role in sarcomagenesis. In this study, we have tested pharmacologic inhibition of Wnt signaling mediated by disruption of TCF/β-catenin binding and AXIN stabilization, being the first strategy more efficient in reducing cell viability and downstream effects. We have shown that disruption of TCF/β-catenin binding with PKF118-310 produces in vitro antitumor activity in a panel of prevalent representative STS cell lines and primary cultures. At the molecular level, PKF118-310 treatment reduced β-catenin nuclear localization, reporter activity, and target genes, resulting in an increase in apoptosis. Importantly, combination of PKF118-310 with doxorubicin resulted in enhanced reduction of cell viability, suggesting that Wnt inhibition could be a new combination regime in these patients. Our findings support the usefulness of Wnt inhibitors as new therapeutic strategies for the prevalent STS. Mol Cancer Ther; 16(6); 1166–76. ©2017 AACR.

Targeting Cyclin-Dependent Kinases in Synovial Sarcoma: Palbociclib as a Potential Treatment for Synovial Sarcoma Patients

Background

In synovial sarcomas alterations in the cyclin D1-CDK4/6-Rb axis have been described. Also, β-catenin, a cyclin D1 regulator, is often overexpressed. Additionally, studies have shown that the t(X;18) translocation influences tumor behavior partly through cyclin D1 activation. We investigated how alterations in the cyclin D1-CDK4/6-Rb axis impact prognosis and studied effects of targeting this axis with the CDK4/6 inhibitor palbociclib.

Methods

Synovial sarcoma samples (n = 43) were immunohistochemically stained for β-catenin, cyclin D1, p16, p21, p27, Rb, and phospho-Rb. Fluorescent in situ hybridization (FISH) was performed to detect CCND1 amplification or translocation. In 4 synovial sarcoma cell lines sensitivity to palbociclib was investigated using cell viability assays, and effects on the sensitive cell lines were evaluated on protein level and by cell cycle arrest.

Results

Expression of nuclear phospho-Rb and nuclear β-catenin in the patient samples was associated with poor survival. FISH showed a sporadic translocation of CCND1 in a subset of tumors. An 8-fold CCND1 amplification was found in 1 cell line, but not in the patient samples investigated. Palbociclib effectively inhibited Rb-phosphorylation in 3 cell lines, resulting in an induction of a G1 arrest and proliferation block.

Conclusions

In this series nuclear phospho-Rb and nuclear β-catenin expression were negative prognostic factors. In vitro data suggest that palbociclib may be a potential treatment for a subset of synovial sarcoma patients. Whether this effect can be enhanced by combination treatment deserves further preclinical investigations.

Electronic supplementary material

The online version of this article (doi:10.1245/s10434-016-5341-x) contains supplementary material, which is available to authorized users.

Nuclear β-Catenin Expression is Frequent in Sinonasal Hemangiopericytoma and Its Mimics

Sinonasal hemangiopericytoma (HPC) is a tumor showing pericytic myoid differentiation and which arises in the nasal cavity and paranasal sinuses. CTNNB1 mutations appear to be a consistent aberration in sinonasal HPC, and nuclear expression of β-catenin has been reported. Our aim was to evaluate the frequency of β-catenin expression in sinonasal HPC and its histologic mimics in the upper aerodigestive tract. Cases were retrieved from the surgical pathology and consultation files. Immunohistochemical staining for β-catenin was performed on 50 soft tissue tumors arising in the sinonasal tract or oral cavity, and nuclear staining was recorded semiquantitatively by extent and intensity. Nuclear reactivity for β-catenin was present in 19/20 cases of sinonasal HPC; 17 showed moderate-to-strong multifocal or diffuse staining, and 2 had moderate focal nuclear reactivity. All solitary fibrous tumors (SFT) (10/10) showed focal-to-multifocal nuclear staining, varying from weak to strong in intensity. Most cases of synovial sarcoma (9/10) showed nuclear β-catenin expression in the spindle cell component, ranging from focal-weak to strong-multifocal. No cases of myopericytoma (0/10) showed any nuclear β-catenin expression. β-catenin expression is prevalent in sinonasal HPC, but is also frequent in SFT and synovial sarcoma. Our findings indicate that β-catenin is not a useful diagnostic tool in the evaluation of spindle cell tumors with a prominent hemangiopericytoma-like vasculature in the sinonasal tract and oral cavity, and that definitive diagnosis relies on the use of a broader immunohistochemical panel.