EWS/ETS-Driven Ewing Sarcoma Requires BET Bromodomain Proteins

Bromodomain inhibitor treatment leads to overexpression of multiple kinases in cancer cells

The bromodomain and extraterminal (BET) family of proteins show altered expression across various cancers. The members of the bromodomain (BRD) family contain epigenetic reader domains that bind to acetylated lysine residues in both histone and non-histone proteins. Since BRD proteins are involved in cancer initiation and progression, therapeutic targeting of these proteins has recently been an area of interest. In experimental settings, JQ1, a commonly used BRD inhibitor, is the first known inhibitor to target BRD-containing protein 4 (BRD4), a ubiquitously expressed BRD and extraterminal family protein. BRD4 is necessary for a normal cell cycle, and its aberrant expression activates pro-inflammatory cytokines, leading to tumor initiation and progression. Various BRD4 inhibitors have been developed recently and tested in preclinical settings and are now in clinical trials. However, as with many targeted therapies, BRD inhibitor treatment can lead to resistance to treatment. Here, we investigated the kinases up-regulated on JQ1 treatment that may serve as target for combination therapy along with BRD inhibitors. To identify kinase targets, we performed a comparative analysis of gene expression data using RNA from BRD inhibitor-treated cells or BRD-modulated cells and identified overexpression of several kinases, including FYN, NEK9, and ADCK5. We further validated, by immunoblotting, the overexpression of FYN tyrosine kinase; NEK9 serine/threonine kinase and ADCK5, an atypical kinase, to confirm their overexpression after BRD inhibitor treatment. Importantly, our studies show that targeting FYN or NEK9 along with BRD inhibitor effectively reduces proliferation of cancer cells. Therefore, our research emphasizes a potential approach of utilizing inhibitors targeting some of the overexpressed kinases in conjunction with BRD inhibitors to enhance therapeutic effectiveness.

EWS-FLI1 and Activator Protein-1 (AP-1) Reciprocally Regulate Extracellular-Matrix Proteins in Ewing sarcoma Cells

Ribonucleotide reductase (RNR) is the rate-limiting enzyme in the synthesis of deoxyribonucleotides and the target of multiple chemotherapy drugs, including gemcitabine. We previously identified that inhibition of RNR in Ewing sarcoma tumors upregulates the expression levels of multiple members of the activator protein-1 (AP-1) transcription factor family, including c-Jun and c-Fos, and downregulates the expression of c-Myc. However, the broader functions and downstream targets of AP-1, which are highly context- and cell-dependent, are unknown in Ewing sarcoma tumors. Consequently, in this work, we used genetically defined models, transcriptome profiling, and gene-set -enrichment analysis to identify that AP-1 and EWS-FLI1, the driver oncogene in most Ewing sarcoma tumors, reciprocally regulate the expression of multiple extracellular-matrix proteins, including fibronectins, integrins, and collagens. AP-1 expression in Ewing sarcoma cells also drives, concurrent with these perturbations in gene and protein expression, changes in cell morphology and phenotype. We also identified that EWS-FLI1 dysregulates the expression of multiple AP-1 proteins, aligning with previous reports demonstrating genetic and physical interactions between EWS-FLI1 and AP-1. Overall, these results provide novel insights into the distinct, EWS-FLI1-dependent features of Ewing sarcoma tumors and identify a novel, reciprocal regulation of extracellular-matrix components by EWS-FLI1 and AP-1.

Peptide Inhibitor Targeting the Extraterminal Domain in BRD4 Potently Suppresses Breast Cancer Both In Vitro and In Vivo

BRD4 is associated with a variety of human diseases, including breast cancer. The crucial roles of amino-terminal bromodomains (BDs) of BRD4 in binding with acetylated histones to regulate oncogene expression make them promising drug targets. However, adverse events impede the development of the BD inhibitors. BRD4 adopts an extraterminal (ET) domain, which recruits proteins to drive oncogene expression. We discovered a peptide inhibitor PiET targeting the ET domain to disrupt BRD4/JMJD6 interaction, a protein complex critical in oncogene expression and breast cancer. The cell-permeable form of PiET, TAT-PiET, and PROTAC-modified TAT-PiET, TAT-PiET-PROTAC, potently inhibits the expression of BRD4/JMJD6 target genes and breast cancer cell growth. Combination therapy with TAT-PiET/TAT-PiET-PROTAC and JQ1, iJMJD6, or Fulvestrant exhibits synergistic effects. TAT-PiET or TAT-PiET-PROTAC treatment overcomes endocrine therapy resistance in ERα-positive breast cancer cells. Taken together, we demonstrated that targeting the ET domain is effective in suppressing breast cancer, providing a therapeutic avenue in the clinic.

Discovery, classification and application of the CPISPR-Cas13 system

BACKGROUND

The clustered regularly interspaced short palindromic repeats (CRISPR)-Cas system is an acquired immune system of bacteria and archaea. Continued research has resulted in the identification of other Cas13 proteins.

OBJECTIVE

This review briefly describes the discovery, classification, and application of the CRISPR-Cas13 system, including recent technological advances in addition to factors affecting system performance.

METHODS

Cas13-based molecular therapy of human, animal, and plant transcriptomes was discussed, including regulation of gene expression to combat pathogenic RNA viruses. In addition, the latest progress, potential shortcomings, and challenges of the CRISPR-Cas system for treatment of animal and plant diseases are reviewed.

RESULTS

The CRISPR-Cas system VI is characterized by two RNA-guided higher eukaryotes and prokaryotes nucleotide-binding domains. CRISPR RNA can cleave specific RNA through the interaction between the stem-loop rich chain of uracil residues and the Cas13a protein. The CRISPR-Cas13 system has been applied for gene editing in animal and plant cells, in addition to biological detection via accurate targeting of single-stranded RNA.

CONCLUSION

The CRISPR-Cas13 system offers a high-throughput and convenient technology for detection of viruses and potentially the development of anti-cancer drugs in the near future.

Establishment and functional testing of a novel ex vivo extraskeletal osteosarcoma cell model (USZ20-ESOS1)

Extraskeletal osteosarcoma (ESOS) is a rare malignant mesenchymal tumor that originates in the soft tissue. ESOS accounts for less than 1% of all soft tissue sarcomas and exhibits an aggressive behavior with a high propensity for local recurrence and distant metastasis. Despite advances in treatment, the prognosis for ESOS remains poor, with a five-year survival rate of less than 50% and 27% for metastatic patients. Ex vivo models derived from patient samples are critical tools for studying rare diseases with poor prognoses, such as ESOS, and identifying potential new treatment strategies. In this work, we established a novel ESOS ex vivo sarco-sphere model from a metastatic lesion to the dermis for research and functional testing purposes. The ex vivo cell model accurately recapitulated the native tumor, as evidenced by histomorphology and molecular profiles. Through a functional screening approach, we were able to identify novel individual anti-cancer drug sensitivities for different drugs such as romidepsin, miverbresib and to multiple kinase inhibitors. Overall, our new ESOS ex vivo cell model represents a valuable tool for investigating disease mechanisms and answering basic and translational research questions.

PROTAC-Based Protein Degradation as a Promising Strategy for Targeted Therapy in Sarcomas

Sarcomas are heterogeneous bone and soft tissue cancers representing the second most common tumor type in children and adolescents. Histology and genetic profiling discovered more than 100 subtypes, which are characterized by peculiar molecular vulnerabilities. However, limited therapeutic options exist beyond standard therapy and clinical benefits from targeted therapies were observed only in a minority of patients with sarcomas. The rarity of these tumors, paucity of actionable mutations, and limitations in the chemical composition of current targeted therapies hindered the use of these approaches in sarcomas. Targeted protein degradation (TPD) is an innovative pharmacological modality to directly alter protein abundance with promising clinical potential in cancer, even for undruggable proteins. TPD is based on the use of small molecules called degraders or proteolysis-targeting chimeras (PROTACs), which trigger ubiquitin-dependent degradation of protein of interest. In this review, we will discuss major features of PROTAC and PROTAC-derived genetic systems for target validation and cancer treatment and focus on the potential of these approaches to overcome major issues connected to targeted therapies in sarcomas, including drug resistance, target specificity, and undruggable targets. A deeper understanding of these strategies might provide new fuel to drive molecular and personalized medicine to sarcomas.

CRISPR-Cas9 knockout screening identifies KIAA1429 as an essential gene in Ewing sarcoma

BACKGROUND

Ewing sarcoma (ES) is an aggressive childhood bone and soft tissue cancer. KIAA1429 is one type of N6-methyladenosine (m6A) writer that plays a tumor-progressive role in various cancers, but the role of KIAA1429 in ES remains to be elucidated. The aim of the study was to investigate the role of KIAA1429 in ES.

METHODS

We performed a multi-omic screen including CRISPR-Cas9 functional genomic and transcriptomic approaches, and identified that KIAA1429 played a significant role in ES progression. Gene knockdown, quantitative real-time PCR (Q-RT-PCR), immunoblotting, CellTiter-Glo assays, clonogenic assays, a subcutaneous xenograft model and immunohistochemistry were used to assess the functional role of KIAA1429 in ES. We mainly conducted RNA sequencing (RNA-seq) in ES cells to analyze the downstream regulatory mechanism of KIAA1429. An integrative analysis of chromatin immunoprecipitation sequencing (ChIP-seq) and RNA-seq indicated the upstream regulatory mechanism of KIAA1429.

RESULTS

In vitro and in vivo CRISPR-Cas9 knockout screening identified KIAA1429 as an ES-dependent gene. Genetic suppression of KIAA1429 inhibited ES cell proliferation and tumorigenicity both in vitro and in vivo. Further studies revealed that KIAA1429 promotes ES tumorigenesis by regulating the ribosome-associated cell cycle and cancer-related inflammation. Interestingly, we found that STAT3 was a target of KIAA1429 and that a STAT3 inhibitor reduced KIAA1429 transcript levels, indicating positive feedback between KIAA1429 and STAT3. Finally, we found that NKX2-2 bound to the KIAA1429 promoter and transactivated KIAA1429.

CONCLUSION

Our study systematically analyzed ES-dependent epigenetic/transcriptional regulatory genes and identified KIAA1429 as a biomarker of tumor progression in ES, providing a potential therapeutic target for treating ES.

Targeted Therapy for EWS-FLI1 in Ewing Sarcoma

Ewing sarcoma (EwS) is a rare and predominantly pediatric malignancy of bone and soft tissue in children and adolescents. Although international collaborations have greatly improved the prognosis of most EwS, the occurrence of macrometastases or relapse remains challenging. The prototypic oncogene EWS-FLI1 acts as an aberrant transcription factor that drives the cellular transformation of EwS. In addition to its involvement in RNA splicing and the DNA damage response, this chimeric protein directly binds to GGAA repeats, thereby modifying the transcriptional profile of EwS. Direct pharmacological targeting of EWS-FLI1 is difficult because of its intrinsically disordered structure. However, targeting the EWS-FLI1 protein complex or downstream pathways provides additional therapeutic options. This review describes the EWS-FLI1 protein partners and downstream pathways, as well as the related target therapies for the treatment of EwS.

Ewing sarcoma treatment: a gene therapy approach

Ewing sarcoma (ES) is an aggressive malignant tumor, characterized by non-random chromosomal translocations that produce fusion genes. Fusion genes and fusion protein products are promising targets for gene therapy. Therapeutic approaches and strategies vary based on target molecules (nucleotides, proteins) of interest. We present an extensive literature review of active molecules for gene therapy and methods of gene therapy delivery, both of which are necessary for successful treatment.

Epigenetic Control of Translation Checkpoint and Tumor Progression via RUVBL1-EEF1A1 Axis

Epigenetic dysregulation is reported in multiple cancers including Ewing sarcoma (EwS). However, the epigenetic networks underlying the maintenance of oncogenic signaling and therapeutic response remain unclear. Using a series of epigenetics- and complex-focused CRISPR screens, RUVBL1, the ATPase component of NuA4 histone acetyltransferase complex, is identified to be essential for EwS tumor progression. Suppression of RUVBL1 leads to attenuated tumor growth, loss of histone H4 acetylation, and ablated MYC signaling. Mechanistically, RUVBL1 controls MYC chromatin binding and modulates the MYC-driven EEF1A1 expression and thus protein synthesis. High-density CRISPR gene body scan pinpoints the critical MYC interacting residue in RUVBL1. Finally, this study reveals the synergism between RUVBL1 suppression and pharmacological inhibition of MYC in EwS xenografts and patient-derived samples. These results indicate that the dynamic interplay between chromatin remodelers, oncogenic transcription factors, and protein translation machinery can provide novel opportunities for combination cancer therapy.

Polycomb-like Proteins in Gene Regulation and Cancer

Polycomb-like proteins (PCLs) are a crucial group of proteins associated with the Polycomb repressive complex 2 (PRC2) and are responsible for setting up the PRC2.1 subcomplex. In the vertebrate system, three homologous PCLs exist: PHF1 (PCL1), MTF2 (PCL2), and PHF19 (PCL3). Although the PCLs share a similar domain composition, they differ significantly in their primary sequence. PCLs play a critical role in targeting PRC2.1 to its genomic targets and regulating the functionality of PRC2. However, they also have PRC2-independent functions. In addition to their physiological roles, their dysregulation has been associated with various human cancers. In this review, we summarize the current understanding of the molecular mechanisms of the PCLs and how alterations in their functionality contribute to cancer development. We particularly highlight the nonoverlapping and partially opposing roles of the three PCLs in human cancer. Our review provides important insights into the biological significance of the PCLs and their potential as therapeutic targets for cancer treatment.

Shifting from a Biological-Agnostic Approach to a Molecular-Driven Strategy in Rare Cancers: Ewing Sarcoma Archetype

Sarcomas of the thoracic cavity are rare entities that predominantly affect children and young adults. They can be very heterogeneous encompassing several different histological entities. Ewing Sarcoma (ES) can potentially arise from every bone, soft tissue, or visceral site in the body. However, it represents an extremely rare finding when it affects the thoracic cavity. It represents the second most frequent type of thoracic sarcoma, after chondrosarcoma. ES arises more frequently in sites that differ from the thoracic cavity, but it displays the same biological features and behavior of extra-thoracic ones. Current management of ES often requires a multidisciplinary treatment approach including surgery, radiotherapy, and systemic therapy, as it can guarantee local and distant disease control, at least transiently, although the long-term outcome remains poor. Unfortunately, due to the paucity of clinical trials purposely designed for this rare malignancy, there are no optimal strategies that can be used for disease recurrence. As a result of its complex biological features, ES might be suitable for emerging biology-based therapeutic strategies. However, a deeper understanding of the molecular mechanisms driving tumor growth and treatment resistance, including those related to oncogenic pathways, epigenetic landscape, and immune microenvironment, is necessary in order to develop new valid therapeutic opportunities. Here, we provide an overview of the most recent therapeutic advances for ES in both the preclinical and clinical settings. We performed a review of the current available literature and of the ongoing clinical trials focusing on new treatment strategies, after failure of conventional multimodal treatments.

BET proteins: Biological functions and therapeutic interventions

Bromodomain and extra-terminal (BET) family member proteins (BRD2, BRD3, BRD4 and BRDT) play a pivotal role in interpreting the epigenetic information of histone Kac modification, thus controlling gene expression, remodeling chromatin structures and avoid replicative stress-induced DNA damages. Abnormal activation of BET proteins is tightly correlated to various human diseases, including cancer. Therefore, BET bromodomain inhibitors (BBIs) were considered as promising therapeutics to treat BET-related diseases, raising >70 clinical trials in the past decades. Despite preliminary effects achieved, drug resistance and adverse events represent two major challenges for current BBIs development. In this review, we will introduce the biological functions of BET proteins in both physiological and pathological conditions; and summarize the progress in current BBI drug development. Moreover, we will also discuss the major challenges in the front of BET inhibitor development and provide rational strategies to overcome these obstacles.

FLI1 and FRA1 transcription factors drive the transcriptional regulatory networks characterizing muscle invasive bladder cancer

Bladder cancer is mostly present in the form of urothelium carcinoma, causing over 150,000 deaths each year. Its histopathological classification as muscle invasive (MIBC) and non-muscle invasive (NMIBC) is the most prominent aspect, affecting the prognosis and progression of this disease. In this study, we defined the active regulatory landscape of MIBC and NMIBC cell lines using H3K27ac ChIP-seq and used an integrative approach to combine our findings with existing data. Our analysis revealed FRA1 and FLI1 as two critical transcription factors differentially regulating MIBC regulatory landscape. We show that FRA1 and FLI1 regulate the genes involved in epithelial cell migration and cell junction organization. Knock-down of FRA1 and FLI1 in MIBC revealed the downregulation of several EMT-related genes such as MAP4K4 and FLOT1. Further, ChIP-SICAP performed for FRA1 and FLI1 enabled us to infer chromatin binding partners of these transcription factors and link this information with their target genes. Finally, we show that knock-down of FRA1 and FLI1 result in significant reduction of invasion capacity of MIBC cells towards muscle microenvironment using IC-CHIP assays. Our results collectively highlight the role of these transcription factors in selection and design of targeted options for treatment of MIBC.

Therapeutic targeting the oncogenic driver EWSR1::FLI1 in Ewing sarcoma through inhibition of the FACT complex

EWS/ETS fusion transcription factors, most commonly EWSR1::FLI1, drives initiation and progression of Ewing sarcoma (EwS). Even though direct targeting EWSR1::FLI1 is a formidable challenge, epigenetic/transcriptional modulators have been proved to be promising therapeutic targets for indirectly disrupting its expression and/or function. Here, we identified structure-specific recognition protein 1 (SSRP1), a subunit of the Facilitates Chromatin Transcription (FACT) complex, to be an essential tumor-dependent gene directly induced by EWSR1::FLI1 in EwS. The FACT-targeted drug CBL0137 exhibits potent therapeutic efficacy against multiple EwS preclinical models both in vitro and in vivo. Mechanistically, SSRP1 and EWSR1::FLI1 form oncogenic positive feedback loop via mutual transcriptional regulation and activation, and cooperatively promote cell cycle/DNA replication process and IGF1R-PI3K-AKT-mTOR pathway to drive EwS oncogenesis. The FACT inhibitor drug CBL0137 effectively targets the EWSR1::FLI1-FACT circuit, resulting in transcriptional disruption of EWSR1::FLI1, SSRP1 and their downstream effector oncogenic signatures. Our study illustrates a crucial role of the FACT complex in facilitating the expression and function of EWSR1::FLI1 and demonstrates FACT inhibition as a novel and effective epigenetic/transcriptional-targeted therapeutic strategy against EwS, providing preclinical support for adding EwS to CBL0137's future clinical trials.

The importance of fusion protein activity in Ewing sarcoma and the cell intrinsic and extrinsic factors that regulate it: A review

Accumulating evidence shows that despite clonal origins tumors eventually become complex communities comprised of phenotypically distinct cell subpopulations. This heterogeneity arises from both tumor cell intrinsic programs and signals from spatially and temporally dynamic microenvironments. While pediatric cancers usually lack the mutational burden of adult cancers, they still exhibit high levels of cellular heterogeneity that are largely mediated by epigenetic mechanisms. Ewing sarcomas are aggressive bone and soft tissue malignancies with peak incidence in adolescence and the prognosis for patients with relapsed and metastatic disease is dismal. Ewing sarcomas are driven by a single pathognomonic fusion between a FET protein and an ETS family transcription factor, the most common of which is EWS::FLI1. Despite sharing a single driver mutation, Ewing sarcoma cells demonstrate a high degree of transcriptional heterogeneity both between and within tumors. Recent studies have identified differential fusion protein activity as a key source of this heterogeneity which leads to profoundly different cellular phenotypes. Paradoxically, increased invasive and metastatic potential is associated with lower EWS::FLI1 activity. Here, we review what is currently understood about EWS::FLI1 activity, the cell autonomous and tumor microenvironmental factors that regulate it, and the downstream consequences of these activity states on tumor progression. We specifically highlight how transcription factor regulation, signaling pathway modulation, and the extracellular matrix intersect to create a complex network of tumor cell phenotypes. We propose that elucidation of the mechanisms by which these essential elements interact will enable the development of novel therapeutic approaches that are designed to target this complexity and ultimately improve patient outcomes.

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.

AT-hook DNA-binding motif-containing protein one knockdown downregulates EWS-FLI1 transcriptional activity in Ewing's sarcoma cells

Ewing's sarcoma is the second most common bone malignancy in children or young adults and is caused by an oncogenic transcription factor by a chromosomal translocation between the EWSR1 gene and the ETS transcription factor family. However, the transcriptional mechanism of EWS-ETS fusion proteins is still unclear. To identify the transcriptional complexes of EWS-ETS fusion transcription factors, we applied a proximal labeling system called BioID in Ewing's sarcoma cells. We identified AHDC1 as a proximal protein of EWS-ETS fusion proteins. AHDC1 knockdown showed a reduced cell growth and transcriptional activity of EWS-FLI1. AHDC1 knockdown also reduced BRD4 and BRG1 protein levels, both known as interacting proteins of EWS-FLI1. Our results suggest that AHDC1 supports cell growth through EWS-FLI1.

Oncofusion-driven de novo enhancer assembly promotes malignancy in Ewing sarcoma via aberrant expression of the stereociliary protein LOXHD1

Ewing sarcoma (EwS) is a highly aggressive tumor of bone and soft tissues that mostly affects children and adolescents. The pathognomonic oncofusion EWSR1::FLI1 transcription factor drives EwS by orchestrating an oncogenic transcription program through de novo enhancers. By integrative analysis of thousands of transcriptomes representing pan-cancer cell lines, primary cancers, metastasis, and normal tissues, we identify a 32-gene signature (ESS32 [Ewing Sarcoma Specific 32]) that stratifies EwS from pan-cancer. Among the ESS32, LOXHD1, encoding a stereociliary protein, is the most highly expressed gene through an alternative transcription start site. Deletion or silencing of EWSR1::FLI1 bound upstream de novo enhancer results in loss of the LOXHD1 short isoform, altering EWSR1::FLI1 and HIF1α pathway genes and resulting in decreased proliferation/invasion of EwS cells. These observations implicate LOXHD1 as a biomarker and a determinant of EwS metastasis and suggest new avenues for developing LOXHD1-targeted drugs or cellular therapies for this deadly disease.

Insights into high-risk multiple myeloma from an analysis of the role of PHF19 in cancer

Despite  improvements in outcome, 15-25% of newly diagnosed multiple myeloma (MM) patients have treatment resistant high-risk (HR) disease with a poor survival. The lack of a genetic basis for HR has focused attention on the role played by epigenetic changes. Aberrant expression and somatic mutations affecting genes involved in the regulation of tri-methylation of the lysine (K) 27 on histone 3 H3 (H3K27me3) are common in cancer. H3K27me3 is catalyzed by EZH2, the catalytic subunit of the Polycomb Repressive Complex 2 (PRC2). The deregulation of H3K27me3 has been shown to be involved in oncogenic transformation and tumor progression in a variety of hematological malignancies including MM. Recently we have shown that aberrant overexpression of the PRC2 subunit PHD Finger Protein 19 (PHF19) is the most significant overall contributor to HR status further focusing attention on the role played by epigenetic change in MM. By modulating both the PRC2/EZH2 catalytic activity and recruitment, PHF19 regulates the expression of key genes involved in cell growth and differentiation. Here we review the expression, regulation and function of PHF19 both in normal and the pathological contexts of solid cancers and MM. We present evidence that strongly implicates PHF19 in the regulation of genes important in cell cycle and the genetic stability of MM cells making it highly relevant to HR MM behavior. A detailed understanding of the normal and pathological functions of PHF19 will allow us to design therapeutic strategies able to target aggressive subsets of MM.

One oncogene, several vulnerabilities: EWS/FLI targeted therapies for Ewing sarcoma

EWS/FLI is the defining mutation of Ewing sarcoma. This oncogene drives malignant transformation and progression and occurs in a genetic background characterized by few other recurrent cooperating mutations. In addition, the tumor is absolutely dependent on the continued expression of EWS/FLI to maintain the malignant phenotype. However, EWS/FLI is a transcription factor and therefore a challenging drug target. The difficulty of directly targeting EWS/FLI stems from unique features of this fusion protein as well as the network of interacting proteins required to execute the transcriptional program. This network includes interacting proteins as well as upstream and downstream effectors that together reprogram the epigenome and transcriptome. While the vast number of proteins involved in this process challenge the development of a highly specific inhibitors, they also yield numerous therapeutic opportunities. In this report, we will review how this vast EWS-FLI transcriptional network has been exploited over the last two decades to identify compounds that directly target EWS/FLI and/or associated vulnerabilities.

Tilting MYC toward cancer cell death

MYC oncoprotein promotes cell proliferation and serves as the key driver in many human cancers; therefore, considerable effort has been expended to develop reliable pharmacological methods to suppress its expression or function. Despite impressive progress, MYC-targeting drugs have not reached the clinic. Recent advances suggest that within a limited expression range unique to each tumor, MYC oncoprotein can have a paradoxical, proapoptotic function. Here we introduce a counterintuitive idea that modestly and transiently elevating MYC levels could aid chemotherapy-induced apoptosis and thus benefit the patients as much, if not more than MYC inhibition.

The oncogenic transcription factor FUS-CHOP can undergo nuclear liquid-liquid phase separation

Myxoid liposarcoma is caused by a chromosomal translocation resulting in a fusion protein comprised of the N terminus of FUS (fused in sarcoma) and the full-length transcription factor CHOP (CCAAT/enhancer-binding protein homologous protein, also known as DDIT3). FUS functions in RNA metabolism, and CHOP is a stress-induced transcription factor. The FUS-CHOP fusion protein causes unique gene expression and oncogenic transformation. Although it is clear that the FUS segment is required for oncogenic transformation, the mechanism of FUS-CHOP-induced transcriptional activation is unknown. Recently, some transcription factors and super enhancers have been proposed to undergo liquid-liquid phase separation and form membraneless compartments that recruit transcription machinery to gene promoters. Since phase separation of FUS depends on its N terminus, transcriptional activation by FUS-CHOP could result from the N terminus driving nuclear phase transitions. Here, we characterized FUS-CHOP in cells and in vitro, and observed novel phase-separating properties relative to unmodified CHOP. Our data indicate that FUS-CHOP forms phase-separated condensates that colocalize with BRD4, a marker of super enhancer condensates. We provide evidence that the FUS-CHOP phase transition is a novel oncogenic mechanism and potential therapeutic target for myxoid liposarcoma. This article has an associated First Person interview with the first author of the paper.

Unraveling the IGF System Interactome in Sarcomas Exploits Novel Therapeutic Options

Aberrant bioactivity of the insulin-like growth factor (IGF) system results in the development and progression of several pathologic conditions including cancer. Preclinical studies have shown promising anti-cancer therapeutic potentials for anti-IGF targeted therapies. However, a clear but limited clinical benefit was observed only in a minority of patients with sarcomas. The molecular complexity of the IGF system, which comprises multiple regulators and interactions with other cancer-related pathways, poses a major limitation in the use of anti-IGF agents and supports the need of combinatorial therapeutic strategies to better tackle this axis. In this review, we will initially highlight multiple mechanisms underlying IGF dysregulation in cancer and then focus on the impact of the IGF system and its complexity in sarcoma development and progression as well as response to anti-IGF therapies. We will also discuss the role of Ephrin receptors, Hippo pathway, BET proteins and CXCR4 signaling, as mediators of sarcoma malignancy and relevant interactors with the IGF system in tumor cells. A deeper understanding of these molecular interactions might provide the rationale for novel and more effective therapeutic combinations to treat sarcomas.

SPOP and OTUD7A Control EWS-FLI1 Protein Stability to Govern Ewing Sarcoma Growth

Chromosomal translocation results in development of an Ewing sarcoma breakpoint region 1-Friend leukemia integration 1 (EWS-FLI1) fusion oncogene in the majority of Ewing sarcoma. The persistent dependence of the tumor for this oncoprotein points to EWS-FLI1 as an ideal drug target. Although EWS-FLI1 transcriptional targets and binding partners are evaluated, the mechanisms regulating EWS-FLI1 protein stability remain elusive. Speckle-type POZ protein (SPOP) and OTU domain-containing protein 7A (OTUD7A) are identified as the bona fide E3 ligase and deubiquitinase, respectively, that control EWS-FLI1 protein turnover in Ewing sarcoma. Casein kinase 1-mediated phosphorylation of the VTSSS degron in the FLI1 domain enhances SPOP activity to degrade EWS-FLI1. Opposing this process, OTUD7A deubiquitinates and stabilizes EWS-FLI1. Depletion of OTUD7A in Ewing sarcoma cell lines reduces EWS-FLI1 protein abundance and impedes Ewing sarcoma growth in vitro and in mice. Performing an artificial-intelligence-based virtual drug screen of a 4-million small molecule library, 7Ai is identified as a potential OTUD7A catalytic inhibitor. 7Ai reduces EWS-FLI1 protein levels and decreases Ewing sarcoma growth in vitro and in a xenograft mouse model. This study supports the therapeutic targeting of OTUD7A as a novel strategy for Ewing sarcoma bearing EWS-FLI1 and related fusions, and may also be applicable to other cancers dependent on aberrant FLI1 expression.

Molecular mechanisms underpinning sarcomas and implications for current and future therapy

Sarcomas are complex mesenchymal neoplasms with a poor prognosis. Their clinical management is highly challenging due to their heterogeneity and insensitivity to current treatments. Although there have been advances in understanding specific genomic alterations and genetic mutations driving sarcomagenesis, the underlying molecular mechanisms, which are likely to be unique for each sarcoma subtype, are not fully understood. This is in part due to a lack of consensus on the cells of origin, but there is now mounting evidence that they originate from mesenchymal stromal/stem cells (MSCs). To identify novel treatment strategies for sarcomas, research in recent years has adopted a mechanism-based search for molecular markers for targeted therapy which has included recapitulating sarcomagenesis using in vitro and in vivo MSC models. This review provides a comprehensive up to date overview of the molecular mechanisms that underpin sarcomagenesis, the contribution of MSCs to modelling sarcomagenesis in vivo, as well as novel topics such as the role of epithelial-to-mesenchymal-transition (EMT)/mesenchymal-to-epithelial-transition (MET) plasticity, exosomes, and microRNAs in sarcomagenesis. It also reviews current therapeutic options including ongoing pre-clinical and clinical studies for targeted sarcoma therapy and discusses new therapeutic avenues such as targeting recently identified molecular pathways and key transcription factors.

Enhancer rewiring in tumors: an opportunity for therapeutic intervention

Enhancers are cis-regulatory sequences that fine-tune expression of their target genes in a spatiotemporal manner. They are recognized by sequence-specific transcription factors, which in turn recruit transcriptional coactivators that facilitate transcription by promoting assembly and activation of the basal transcriptional machinery. Their functional importance is underscored by the fact that they are often the target of genetic and nongenetic events in human disease that disrupt their sequence, interactome, activation potential, and/or chromatin environment. Dysregulation of transcription and addiction to transcriptional effectors that interact with and modulate enhancer activity are common features of cancer cells and are amenable to therapeutic intervention. Here, we discuss the current knowledge on enhancer biology, the broad spectrum of mechanisms that lead to their malfunction in tumor cells, and recent progress in developing drugs that efficaciously target their dependencies.

Bromodomain and extra-terminal inhibitors-A consensus prioritisation after the Paediatric Strategy Forum for medicinal product development of epigenetic modifiers in children-ACCELERATE

Based on biology and pre-clinical data, bromodomain and extra-terminal (BET) inhibitors have at least three potential roles in paediatric malignancies: NUT (nuclear protein in testis) carcinomas, MYC/MYCN-driven cancers and fusion-driven malignancies. However, there are now at least 10 BET inhibitors in development, with a limited relevant paediatric population in which to evaluate these medicinal products. Therefore, a meeting was convened with the specific aim to develop a consensus among relevant biopharmaceutical companies, academic researchers, as well as patient and family advocates, about the development of BET inhibitors, including prioritisation and their specific roles in children. Although BET inhibitors have been in clinical trials in adults since 2012, the first-in-child study (BMS-986158) only opened in 2019. In the future, when there is strong mechanistic rationale or pre-clinical activity of a class of medicinal product in paediatrics, early clinical evaluation with embedded correlative studies of a member of the class should be prioritised and rapidly executed in paediatric populations. There is a strong mechanistic and biological rationale to evaluate BET inhibitors in paediatrics, underpinned by substantial, but not universal, pre-clinical data. However, most pan-BET inhibitors have been challenging to administer in adults, since monotherapy results in only modest anti-tumour activity and provides a narrow therapeutic index due to thrombocytopenia. It was concluded that it is neither scientifically justified nor feasible to undertake simultaneously early clinical trials in paediatrics of all pan-BET inhibitors. However, there is a clinical need for global access to BET inhibitors for patients with NUT carcinoma, a very rare malignancy driven by bromodomain fusions, with proof of concept of clinical benefit in a subset of patients treated with BET inhibitors. Development and regulatory pathway in this indication should include children and adolescents as well as adults. Beyond NUT carcinoma, it was proposed that further clinical development of other pan-BET inhibitors in children should await the results of the first paediatric clinical trial of BMS-986158, unless there is compelling rationale based on the specific agent of interest. BDII-selective inhibitors, central nervous system-penetrant BET inhibitors (e.g. CC-90010), and those dual-targeting BET/p300 bromodomain are of particular interest and warrant further pre-clinical investigation. This meeting emphasised the value of a coordinated and integrated strategy to drug development in paediatric oncology. A multi-stakeholder approach with multiple companies developing a consensus with academic investigators early in the development of a class of compounds, and then engaging regulatory agencies would improve efficiency, productivity, conserve resources and maximise potential benefit for children with cancer.

Applications of CRISPR/Cas9 in the research of malignant musculoskeletal tumors

Background

Malignant tumors of the musculoskeletal system, especially osteosarcoma, Ewing sarcoma and rhabdomyosarcoma, pose a major threat to the lives and health of adolescents and children. Current treatments for musculoskeletal tumors mainly include surgery, chemotherapy, and radiotherapy. The problems of chemotherapy resistance, poor long-term outcome of radiotherapy, and the inherent toxicity and side effects of chemical drugs make it extremely urgent to seek new treatment strategies.

Main text

As a potent gene editing tool, the rapid development of CRISPR/Cas9 technology in recent years has prompted scientists to apply it to the study of musculoskeletal tumors. This review summarizes the application of CRISPR/Cas9 technology for the treatment of malignant musculoskeletal tumors, focusing on its essential role in the field of basic research.

Conclusion

CRISPR, has demonstrated strong efficacy in targeting tumor-related genes, and its future application in the clinical treatment of musculoskeletal tumors is promising.

The E-Twenty-Six Family in Hepatocellular Carcinoma: Moving into the Spotlight

Hepatocellular carcinoma (HCC) is a major cause of morbidity and mortality worldwide. Although therapeutic strategies have recently advanced, tumor metastasis and drug resistance continue to pose challenges in the treatment of HCC. Therefore, new molecular targets are needed to develop novel therapeutic strategies for this cancer. E-twenty-six (ETS) transcription family has been implicated in human malignancies pathogenesis and progression, including leukemia, Ewing sarcoma, gastrointestinal stromal tumors. Recently, increasing studies have expanded its great potential as functional players in other cancers, including HCC. This review focuses primarily on the key functions and molecular mechanisms of ETS factors in HCC. Elucidating these molecular details may provide novel potential therapeutic strategies for cancers.

RING1B recruits EWSR1-FLI1 and cooperates in the remodeling of chromatin necessary for Ewing sarcoma tumorigenesis

Ewing sarcoma (EwS) is an aggressive tumor that affects adolescents and young adults. EwS is defined by a chromosomal translocation, EWSR1-FLI1 being the most common, that causes genome reprogramming through remodeling of enhancers. Here, we describe an unexpected function of RING1B, which is highly expressed in EwS. While retaining its repressive activity at Polycomb developmental regulated genes, RING1B colocalizes with EWSR1-FLI1 at active enhancers. We demonstrate that RING1B is necessary for the expression of key EWSR1-FLI1 targets by facilitating oncogene recruitment to their enhancers. Knockdown of RING1B impairs growth of tumor xenografts and expression of genes regulated by EWSR1-FLI1 bound enhancers. Pharmacological inhibition of AURKB with AZD1152 increases H2Aub levels causing down-regulation of RING1B/EWSR1-FLI1 common targets. Our findings demonstrate that RING1B is a critical modulator of EWSR1-FLI1-induced chromatin remodeling, and its inhibition is a potential therapeutic strategy for the treatment of these tumors.

Rapid and direct control of target protein levels with VHL-recruiting dTAG molecules

Chemical biology strategies for directly perturbing protein homeostasis including the degradation tag (dTAG) system provide temporal advantages over genetic approaches and improved selectivity over small molecule inhibitors. We describe dTAGV-1, an exclusively selective VHL-recruiting dTAG molecule, to rapidly degrade FKBP12F36V-tagged proteins. dTAGV-1 overcomes a limitation of previously reported CRBN-recruiting dTAG molecules to degrade recalcitrant oncogenes, supports combination degrader studies and facilitates investigations of protein function in cells and mice.

Photocontrolled activation of small molecule cancer therapeutics

Cancer remains one of the leading causes of death worldwide. Conventional treatment of the disease is comprised of chemotherapy, radiation and surgery among other treatment approaches. Chemotherapy is plagued by multiple side-effects caused due to non-specific drug action. Light-based therapies offer an alternative treatment approach that can be fine tuned to achieve the desired effect to treat the disease and address challenges posed by chemotherapeutic side-effects. Photodynamic therapy (PDT) is one of the light mediated treatment modalities that has been successfully applied to treat superficial malignancies with high-efficiency, although its dependence on normoxic conditions limits its efficiency to treat deep-seated tumors. On the other hand, light-sensitive drug-mimetics and drug-release platforms have been deemed efficient in preclinical settings to induce cancer cell death with minimal collateral damage. Drawing from about a decade's worth of examples, we highlight the application of photosensitive molecules as an alternative therapeutic option to PDT and describe their designs that influence the biology of the cancer cells, in turn affecting their viability with high spatio-temporal control.

CDK9 as a Valuable Target in Cancer: From Natural Compounds Inhibitors to Current Treatment in Pediatric Soft Tissue Sarcomas

Cyclin-Dependent Kinases (CDKs) are well-known reliable targets for cancer treatment being often deregulated. Among them, since the transcription-associated CDK9 represents the sentry of cell transcriptional homeostasis, it can be a valuable target for managing cancers in which the transcriptional machinery is dysregulated by tumor-driver oncogenes. Here we give an overview of some natural compounds identified as CDK inhibitors with reported activity also against CDK9, that were taken as a model for the development of highly active synthetic anti-CDK9 agents. After, we summarize the data on CDK9 inhibition in a group of rare pediatric solid tumors such as rhabdomyosarcoma, Ewing’s sarcoma, synovial sarcoma and malignant rhabdoid tumors (soft tissue sarcomas), highlighting the more recent results in this field. Finally, we discuss the perspective and challenge of CDK9 modulation in cancer.

Management of Refractory Pediatric Sarcoma: Current Challenges and Future Prospects

Paediatric sarcomas are a heterogeneous group of disorders constituting bone sarcoma and various soft tissue sarcomas. Almost one-third of these presents with metastasis at baseline and another one-third recur after initial curative treatment. There is a huge unmet need in this cohort in terms of curative options and/or prolongation of survival. In this review, we have discussed the current treatment options, challenges and future strategies of managing relapsed/refractory paediatric sarcomas. Upfront risk-adapted treatment with multidisciplinary management remains the main strategy to prevent future recurrence or relapse of the disease. In the case of limited local and/or systemic relapse or late relapse, initial multimodality management can be administered. In treatment-refractory cases or where cure is not feasible, the treatment options are limited to novel therapeutics, immunotherapeutic approach, targeted therapies, and metronomic therapies. A better understanding of disease biology, mechanism of treatment refractoriness, identifications of driver mutation, the discovery of novel targeted therapies, cellular vaccine and adapted therapies should be explored in relapsed/refractory cases. Close national and international collaboration for translation research is needed to fulfil the unmet need.

LAMB3 promotes tumour progression through the AKT-FOXO3/4 axis and is transcriptionally regulated by the BRD2/acetylated ELK4 complex in colorectal cancer

Aberrant expression of laminin-332 promotes tumour growth and metastasis in multiple cancers. However, the dysregulated expression and mechanism of action of LAMB3, which encodes the β3 subunit of laminin-332, and the mechanism underlying dysregulated LAMB3 expression in CRC remain obscure. Here, we show that LAMB3 is overexpressed in CRC and that this overexpression is correlated with tumour metastasis and poor prognosis. Overexpression of LAMB3 promoted cell proliferation and cell migration in vitro and tumour growth and metastasis in vivo, while knockdown of LAMB3 elicited opposing effects. LAMB3 inhibited the tumour suppressive function of FOXO3/4 by activating AKT in CRC. Both the BET inhibitor JQ1 and the MEK inhibitor U0126 decreased the mRNA level of LAMB3 in multiple CRC cells. Mechanistically, ELK4 cooperated with BRD2 to regulate the transcription of LAMB3 in CRC by directly binding to the ETS binding motifs in the LAMB3 promoter. ELK4 was as acetylated at K125, which enhanced the interaction between ELK4 and BRD2. JQ1 disrupted the interaction between ELK4 and BRD2, resulting in decreased binding of BRD2 to the LAMB3 promoter and downregulation of LAMB3 transcription. Both ELK4 and BRD2 expression was associated with LAMB3 expression in CRC. LAMB3 expression was also negatively correlated with FOXO3/4 in CRC. Our study reveals the pro-tumorigenic role of LAMB3 through the AKT-FOXO3/4 axis and the transcriptional mechanism of LAMB3 in CRC, demonstrating that LAMB3 is a potential therapeutic target that can be targeted by BET inhibitors and MEK inhibitors.

The CRISP(Y) Future of Pediatric Soft Tissue Sarcomas

The RNA-guided clustered regularly interspaced palindromic repeats (CRISPR)/associated nuclease 9 (Cas9)-based genome editing technology has increasingly become a recognized method for translational research. In oncology, the ease and versatility of CRISPR/Cas9 has made it possible to obtain many results in the identification of new target genes and in unravel mechanisms of resistance to therapy. The majority of the studies have been made on adult tumors so far. In this mini review we present an overview on the major aspects of CRISPR/Cas9 technology with a focus on a group of rare pediatric malignancies, soft tissue sarcomas, on which this approach is having promising results.

The Optimal Outcome of Suppressing Ewing Sarcoma Growth in vivo With Biocompatible Bioengineered miR-34a-5p Prodrug

Being the second most common type of primary bone malignancy in children and adolescents, Ewing Sarcoma (ES) encounters the dilemma of low survival rate with a lack of effective treatments. As an emerging approach to combat cancer, RNA therapeutics may expand the range of druggable targets. Since the genome-derived oncolytic microRNA-34a (miR-34a) is down-regulated in ES, restoration of miR-34a-5p expression or function represents a new therapeutic strategy which is, however, limited to the use of chemically-engineered miRNA mimics. Very recently we have developed a novel bioengineering technology using a stable non-coding RNA carrier (nCAR) to achieve high-yield production of biocompatible miRNA prodrugs, which is a great addition to current tools for the assessment of RNA therapeutics. Herein, for the first time, we investigated the biochemical pharmacology of bioengineered miR-34a-5p prodrug (nCAR/miR-34a-5p) in the control of ES using human ES cells and xenograft mouse models. The bioengineered nCAR/miR-34a-5p was precisely processed to mature miR-34a-5p in ES cells and subsequently suppressed cell proliferation, attributable to the enhancement of apoptosis and induction of G2 cell cycle arrest through downregulation of SIRT-1, BCL-2 and CDK6 protein levels. Furthermore, systemic administration of nCAR/miR-34a-5p dramatically suppressed the ES xenograft tumor growth in vivo while showing biocompatibility. In addition, the antitumor effect of bioengineered nCAR/miR-34a-5p was associated with a lower degree of tumoral cell proliferation and greater extent of apoptosis. These findings demonstrate the efficacy of bioengineered miR-34a-5p prodrug for the treatment of ES and support the development of miRNA therapeutics using biocompatible bioengineered miRNA prodrugs.

Combined Inhibition of Epigenetic Readers and Transcription Initiation Targets the EWS-ETS Transcriptional Program in Ewing Sarcoma

Background: Previously, we used inhibitors blocking BET bromodomain binding proteins (BRDs) in Ewing sarcoma (EwS) and observed that long term treatment resulted in the development of resistance. Here, we analyze the possible interaction of BRD4 with cyclin-dependent kinase (CDK) 9. Methods: Co-immunoprecipitation experiments (CoIP) to characterize BRD4 interaction and functional consequences of inhibiting transcriptional elongation were assessed using drugs targeting of BRD4 or CDK9, either alone or in combination. Results: CoIP revealed an interaction of BRD4 with EWS-FLI1 and CDK9 in EwS. Treatment of EwS cells with CDKI-73, a specific CDK9 inhibitor (CDK9i), induced a rapid downregulation of EWS-FLI1 expression and block of contact-dependent growth. CDKI-73 induced apoptosis in EwS, as depicted by cleavage of Caspase 7 (CASP7), PARP and increased CASP3 activity, similar to JQ1. Microarray analysis following CDKI-73 treatment uncovered a transcriptional program that was only partially comparable to BRD inhibition. Strikingly, combined treatment of EwS with BRD- and CDK9-inhibitors re-sensitized cells, and was overall more effective than individual drugs not only in vitro but also in a preclinical mouse model in vivo. Conclusion: Treatment with BRD inhibitors in combination with CDK9i offers a new treatment option that significantly blocks the pathognomonic EWS-ETS transcriptional program and malignant phenotype of EwS.

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).

Management of recurrent Ewing sarcoma: challenges and approaches

Although many patients with newly diagnosed Ewing sarcoma can become long-term survivors, relapse remains an important clinical problem for which there is no standard approach. Several prognostic factors have been identified, and these may help guide patient counseling and therapy decisions. A variety of chemotherapy regimens have produced responses in patients with recurrent Ewing sarcoma, but no comparative studies have been completed to show superiority of any one particular approach. In addition, the optimum length of therapy for salvage regimens and use of local control measures remains unknown. The likelihood of cure remains low and the gaps in our knowledge are great, and so enrollment on clinical trials should be strongly encouraged for these patients when feasible. Because Ewing sarcoma is relatively rare, some pediatric and adult oncologists may be less familiar with the management of relapsed patients. In this review, we address common questions facing the clinician and patient, and provide an update on new strategies for therapy.

Bromodomain and extraterminal proteins foster the core transcriptional regulatory programs and confer vulnerability in liposarcoma

Liposarcomas (LPSs) are a group of malignant mesenchymal tumors showing adipocytic differentiation. Here, to gain insight into the enhancer dysregulation and transcriptional addiction in this disease, we chart super-enhancer structures in both LPS tissues and cell lines. We identify a bromodomain and extraterminal (BET) protein-cooperated FUS-DDIT3 function in myxoid LPS and a BET protein-dependent core transcriptional regulatory circuitry consisting of FOSL2, MYC, and RUNX1 in de-differentiated LPS. Additionally, SNAI2 is identified as a crucial downstream target that enforces both proliferative and metastatic potentials to de-differentiated LPS cells. Genetic depletion of BET genes, core transcriptional factors, or SNAI2 mitigates consistently LPS malignancy. We also reveal a compelling susceptibility of LPS cells to BET protein degrader ARV-825. BET protein depletion confers additional advantages to circumvent acquired resistance to Trabectedin, a chemotherapy drug for LPS. Moreover, this study provides a framework for discovering and targeting of core oncogenic transcriptional programs in human cancers.

Liposarcoma (LPS) is a rare cancer that can acquire resistance to chemotherapy. Here, the authors map super-enhancers in LPS, finding BET-protein dependent mechanisms that can be targeted by a BET protein degrader, which also can overcome acquired resistance to chemotherapy in LPS.

Discovery of ARD-69 as a Highly Potent Proteolysis Targeting Chimera (PROTAC) Degrader of Androgen Receptor (AR) for the Treatment of Prostate Cancer

We report herein the discovery of highly potent PROTAC degraders of androgen receptor (AR), as exemplified by compound 34 (ARD-69). ARD-69 induces degradation of AR protein in AR-positive prostate cancer cell lines in a dose- and time-dependent manner. ARD-69 achieves DC₅₀ values of 0.86, 0.76, and 10.4 nM in LNCaP, VCaP, and 22Rv1 AR+ prostate cancer cell lines, respectively. ARD-69 is capable of reducing the AR protein level by >95% in these prostate cancer cell lines and effectively suppressing AR-regulated gene expression. ARD-69 potently inhibits cell growth in these AR-positive prostate cancer cell lines and is >100 times more potent than AR antagonists. A single dose of ARD-69 effectively reduces the level of AR protein in xenograft tumor tissue in mice. Further optimization of ARD-69 may ultimately lead to a new therapy for AR+, castration-resistant prostate cancer.