Open-Label, Multicenter, Phase I/II, First-in-Human Trial of TK216: A First-Generation EWS::FLI1 Fusion Protein Antagonist in Ewing Sarcoma.

PURPOSE: Ewing Sarcoma (ES), a rare cancer with a pathognomonic translocation resulting in the Ewing sarcoma gene (EWS)::FLI1 oncoprotein, has a poor prognosis in the relapsed/refractory (R/R) setting. Tokalas (TK)216 was designed to bind EWS::FLI1 proteins directly, disrupt protein-protein interactions, and inhibit transcription factor function. TK216 plus vincristine showed synergistic activity in preclinical tumor models. To our knowledge, we report the results of a first-in-class, first-in-human phase I/II trial of TK216 in R/R ES. PATIENTS AND METHODS: TK216 was administered intravenously as a continuous infusion to patients with R/R ES in 11 cohorts. The dosing duration of 7 days was later extended to 10, 14, and 28 days. Vincristine could be added on day 1 after cycle 2, per investigators' choice. The trial used a 3 + 3 design with an expansion cohort at the recommended phase II dose (RP2D). RESULTS: A total of 85 patients with a median age of 27 years (range, 11-77) were enrolled. The maximum tolerated dose for the 14-day infusion of TK216, 200 mg/m2 once daily, was determined in cohort 9 and selected as the RP2D. The median previous number of systemic therapies regimens was three (range, 1-10). The most frequent-related adverse events in patients treated at the RP2D included neutropenia (44.7%), anemia (29.4%), leukopenia (29.4%), febrile neutropenia (15.3%), thrombocytopenia (11.8%), and infections (17.6%). In cohorts 9 and 10, two patients had a complete response, one had a partial response, and 14 had stable disease; the 6-month progression-free survival was 11.9%. There were no responses among the eight patients in cohort 11. CONCLUSION: TK216 administered as 14-day continuous infusion with or without vincristine was well tolerated and showed limited activity at the RP2D in R/R ES.

Piperacetazine Directly Binds to the PAX3::FOXO1 Fusion Protein and Inhibits Its Transcriptional Activity.

The tumor-specific chromosomal translocation product, PAX3::FOXO1, is an aberrant fusion protein that plays a key role for oncogenesis in the alveolar subtype of rhabdomyosarcoma (RMS). PAX3::FOXO1 represents a validated molecular target for alveolar RMS and successful inhibition of its oncogenic activity is likely to have significant clinical applications. Even though several PAX3::FOXO1 function-based screening studies have been successfully completed, a directly binding small-molecule inhibitor of PAX3::FOXO1 has not been reported. Therefore, we screened small-molecule libraries to identify compounds that were capable of directly binding to PAX3::FOXO1 protein using surface plasmon resonance technology. Compounds that directly bound to PAX3::FOXO1 were further evaluated in secondary transcriptional activation assays. We discovered that piperacetazine can directly bind to PAX3::FOXO1 protein and inhibit fusion protein-derived transcription in multiple alveolar RMS cell lines. Piperacetazine inhibited anchorage-independent growth of fusion-positive alveolar RMS cells but not embryonal RMS cells. On the basis of our findings, piperacetazine is a molecular scaffold upon which derivatives could be developed as specific inhibitors of PAX3::FOXO1. These novel inhibitors could potentially be evaluated in future clinical trials for recurrent or metastatic alveolar RMS as novel targeted therapy options. SIGNIFICANCE: RMS is a malignant soft-tissue tumor mainly affecting the pediatric population. A subgroup of RMS with worse prognosis harbors a unique chromosomal translocation creating an oncogenic fusion protein, PAX3::FOXO1. We identified piperacetazine as a direct inhibitor of PAX3::FOXO1, which may provide a scaffold for designing RMS-specific targeted therapy.

Widespread hypertranscription in aggressive human cancers.

Cancers are often defined by the dysregulation of specific transcriptional programs; however, the importance of global transcriptional changes is less understood. Hypertranscription is the genome-wide increase in RNA output. Hypertranscription's prevalence, underlying drivers, and prognostic significance are undefined in primary human cancer. This is due, in part, to limitations of expression profiling methods, which assume equal RNA output between samples. Here, we developed a computational method to directly measure hypertranscription in 7494 human tumors, spanning 31 cancer types. Hypertranscription is ubiquitous across cancer, especially in aggressive disease. It defines patient subgroups with worse survival, even within well-established subtypes. Our data suggest that loss of transcriptional suppression underpins the hypertranscriptional phenotype. Single-cell analysis reveals hypertranscriptional clones, which dominate transcript production regardless of their size. Last, patients with hypertranscribed mutations have improved response to immune checkpoint therapy. Our results provide fundamental insights into gene dysregulation across human cancers and may prove useful in identifying patients who would benefit from novel therapies.

An international working group consensus report for the prioritization of molecular biomarkers for Ewing sarcoma.

The advent of dose intensified interval compressed therapy has improved event-free survival for patients with localized Ewing sarcoma (EwS) to 78% at 5 years. However, nearly a quarter of patients with localized tumors and 60-80% of patients with metastatic tumors suffer relapse and die of disease. In addition, those who survive are often left with debilitating late effects. Clinical features aside from stage have proven inadequate to meaningfully classify patients for risk-stratified therapy. Therefore, there is a critical need to develop approaches to risk stratify patients with EwS based on molecular features. Over the past decade, new technology has enabled the study of multiple molecular biomarkers in EwS. Preliminary evidence requiring validation supports copy number changes, and loss of function mutations in tumor suppressor genes as biomarkers of outcome in EwS. Initial studies of circulating tumor DNA demonstrated that diagnostic ctDNA burden and ctDNA clearance during induction are also associated with outcome. In addition, fusion partner should be a pre-requisite for enrollment on EwS clinical trials, and the fusion type and structure require further study to determine prognostic impact. These emerging biomarkers represent a new horizon in our understanding of disease risk and will enable future efforts to develop risk-adapted treatment.

Coupling Lipid Labeling and Click Chemistry Enables Isolation of Extracellular Vesicles for Noninvasive Detection of Oncogenic Gene Alterations.

Well-preserved molecular cargo in circulating extracellular vesicles (EVs) offers an ideal material for detecting oncogenic gene alterations in cancer patients, providing a noninvasive diagnostic solution for detection of disease status and monitoring treatment response. Therefore, technologies that conveniently isolate EVs with sufficient efficiency are desperately needed. Here, a lipid labeling and click chemistry-based EV capture platform ("Click Beads"), which is ideal for EV message ribonucleic acid (mRNA) assays due to its efficient, convenient, and rapid purification of EVs, enabling downstream molecular quantification using reverse transcription digital polymerase chain reaction (RT-dPCR) is described and demonstrated. Ewing sarcoma protein (EWS) gene rearrangements and kirsten rat sarcoma viral oncogene homolog (KRAS) gene mutation status are detected and quantified using EVs isolated by Click Beads and matched with those identified in biopsy specimens from Ewing sarcoma or pancreatic cancer patients. Moreover, the quantification of gene alterations can be used for monitoring treatment responses and disease progression.

Comprehensive profiling of mRNA splicing indicates that GC content signals altered cassette exon inclusion in Ewing sarcoma.

Ewing sarcoma (EwS) is a small round blue cell tumor and is the second most frequent pediatric bone cancer. 85% of EwS tumors express the fusion oncoprotein EWS-FLI1, the product of a t(11;22) reciprocal translocation. Prior work has indicated that transcription regulation alone does not fully describe the oncogenic capacity of EWS-FLI1, nor does it provide an effective means to stratify patient tumors. Research using EwS cell lines and patient samples has suggested that EWS-FLI1 also disrupts mRNA biogenesis. In this work we both describe the underlying characteristics of mRNA that are aberrantly spliced in EwS tumor samples as well as catalogue mRNA splicing events across other pediatric tumor types. Here, we also use short- and long-read sequencing to identify cis-factors that contribute to splicing profiles we observe in Ewing sarcoma. Our analysis suggests that GC content upstream of cassette exons is a defining factor of mRNA splicing in EwS. We also describe specific splicing events that discriminate EwS tumor samples from the assumed cell of origin, human mesenchymal stem cells derived from bone marrow (hMSC-BM). Finally, we identify specific splicing factors PCBP2, RBMX, and SRSF9 by motif enrichment and confirm findings from tumor samples in EwS cell lines.

O-Linked-N-Acetylglucosaminylation of the RNA-Binding Protein EWS N-Terminal Low Complexity Region Reduces Phase Separation and Enhances Condensate Dynamics.

Many membraneless organelles are thought to be biomolecular condensates formed by phase separation of proteins and other biopolymers. Post-translational modifications (PTMs) can impact protein phase separation behavior, although for many PTMs this aspect of their function is unknown. O-linked ß-D-N-acetylglucosaminylation (O-GlcNAcylation) is an abundant form of intracellular glycosylation whose roles in regulating biomolecular condensate assembly and dynamics have not been delineated. Using an in vitro approach, we found that O-GlcNAcylation reduces the phase separation propensity of the EWS N-terminal low complexity region (LCRN) under different conditions, including in the presence of the arginine- and glycine-rich RNA-binding domains (RBD). O-GlcNAcylation enhances fluorescence recovery after photobleaching (FRAP) within EWS LCRN condensates and causes the droplets to exhibit more liquid-like relaxation following fusion. Following extended incubation times, EWS LCRN+RBD condensates exhibit diminished FRAP, indicating a loss of fluidity, while condensates containing the O-GlcNAcylated LCRN do not. In HeLa cells, EWS is less O-GlcNAcylated following OGT knockdown, which correlates with its increased accumulation in a filter retardation assay. Relative to the human proteome, O-GlcNAcylated proteins are enriched with regions that are predicted to phase separate, suggesting a general role of O-GlcNAcylation in regulation of biomolecular condensates.

Clofarabine induces ERK/MSK/CREB activation through inhibiting CD99 on Ewing sarcoma cells.

Clofarabine, an FDA approved purine analog, is used in the treatment of relapsed or refractory acute lymphoblastic leukemia. Clofarabine acts by inhibiting DNA synthesis. We demonstrated that clofarabine may have a novel function though inhibiting CD99, a transmembrane protein highly expressed on Ewing Sarcoma (ES) cells. CD99 is a validated target in ES whose inhibition may lead to a high therapeutic index for patients. Here we present additional data to support the hypothesis that clofarabine acts on CD99 and regulates key signaling pathways in ES. Cellular thermal shift assay indicated a direct interaction between clofarabine and CD99 in ES cell lysates. Clofarabine induced ES cell death does not require clofarabine's conversion to its active form by deoxycytidine kinase. A phosphokinase array screen with clofarabine and a CD99 blocking antibody identified alterations in signaling pathways. CD99 inhibition with clofarabine in ES cells caused rapid and sustained phosphorylation of ERK, MSK, and CREB. However, activation of this pathway did not correlate with clofarabine induced ES cell death. In summary, we demonstrated that clofarabine may activate ERK, MSK, and CREB phosphorylation through CD99 within minutes, however this paradoxical activation and subsequent ES cell death requires additional investigation.

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

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

Coupling Nanostructured Microchips with Covalent Chemistry Enables Purification of Sarcoma-Derived Extracellular Vesicles for Downstream Functional Studies.

Tumor-derived extracellular vesicles (EVs) play essential roles in intercellular communication during tumor growth and metastatic evolution. Currently, little is known about the possible roles of tumor-derived EVs in sarcoma because the lack of specific surface markers makes it technically challenging to purify sarcoma-derived EVs. In this study, a specific purification system is developed for Ewing sarcoma (ES)-derived EVs by coupling covalent chemistry-mediated EV capture/ release within a nanostructure-embedded microchip. The purification platform-ES-EV Click Chip-takes advantage of specific anti-LINGO-1 recognition and sensitive click chemistry-mediated EV capture, followed by disulfide cleavage-driven EV release. Since the device is capable of specific and efficient purification of intact ES EVs with high purity, ES-EV Click Chip is ideal for conducting downstream functional studies of ES EVs. Absolute quantification of the molecular hallmark of ES (i.e., EWS rearrangements) using reverse transcription Droplet Digital PCR enables specific quantification of ES EVs. The purified ES EVs can be internalized by recipient cells and transfer their mRNA cargoes, exhibiting their biological intactness and potential role as biological shuttles in intercellular communication.

EWS-FLI1 modulated alternative splicing of ARID1A reveals novel oncogenic function through the BAF complex.

Connections between epigenetic reprogramming and transcription or splicing create novel mechanistic networks that can be targeted with tailored therapies. Multiple subunits of the chromatin remodeling BAF complex, including ARID1A, play a role in oncogenesis, either as tumor suppressors or oncogenes. Recent work demonstrated that EWS-FLI1, the oncogenic driver of Ewing sarcoma (ES), plays a role in chromatin regulation through interactions with the BAF complex. However, the specific BAF subunits that interact with EWS-FLI1 and the precise role of the BAF complex in ES oncogenesis remain unknown. In addition to regulating transcription, EWS-FLI1 also alters the splicing of many mRNA isoforms, but the role of splicing modulation in ES oncogenesis is not well understood. We have identified a direct connection between the EWS-FLI1 protein and ARID1A isoform protein variant ARID1A-L. We demonstrate here that ARID1A-L is critical for ES maintenance and supports oncogenic transformation. We further report a novel feed-forward cycle in which EWS-FLI1 leads to preferential splicing of ARID1A-L, promoting ES growth, and ARID1A-L reciprocally promotes EWS-FLI1 protein stability. Dissecting this interaction may lead to improved cancer-specific drug targeting.

The ETS Inhibitors YK-4-279 and TK-216 Are Novel Antilymphoma Agents.

PURPOSE: Transcription factors are commonly deregulated in cancer, and they have been widely considered as difficult to target due to their nonenzymatic mechanism of action. Altered expression levels of members of the ETS-transcription factors are often observed in many different tumors, including lymphomas. Here, we characterized two small molecules, YK-4-279 and its clinical derivative, TK-216, targeting ETS factors via blocking the protein-protein interaction with RNA helicases, for their antilymphoma activity. EXPERIMENTAL DESIGN: The study included preclinical in vitro activity screening on a large panel of cell lines, both as single agent and in combination; validation experiments on in vivo models; and transcriptome and coimmunoprecipitation experiments. RESULTS: YK-4-279 and TK-216 demonstrated an antitumor activity across several lymphoma cell lines, which we validated in vivo. We observed synergistic activity when YK-4-279 and TK-216 were combined with the BCL2 inhibitor venetoclax and with the immunomodulatory drug lenalidomide. YK-4-279 and TK-216 interfere with protein interactions of ETS family members SPIB, in activated B-cell-like type diffuse large B-cell lymphomas, and SPI1, in germinal center B-cell-type diffuse large B-cell lymphomas. CONCLUSIONS: The ETS inhibitor YK-4-279 and its clinical derivative TK-216 represent a new class of agents with in vitro and in vivo antitumor activity in lymphomas. Although their detailed mechanism of action needs to be fully defined, in DLBCL they might act by targeting subtype-specific essential transcription factors.

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

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

Rearrangement bursts generate canonical gene fusions in bone and soft tissue tumors.

Sarcomas are cancers of the bone and soft tissue often defined by gene fusions. Ewing sarcoma involves fusions between EWSR1, a gene encoding an RNA binding protein, and E26 transformation-specific (ETS) transcription factors. We explored how and when EWSR1-ETS fusions arise by studying the whole genomes of Ewing sarcomas. In 52 of 124 (42%) of tumors, the fusion gene arises by a sudden burst of complex, loop-like rearrangements, a process called chromoplexy, rather than by simple reciprocal translocations. These loops always contained the disease-defining fusion at the center, but they disrupted multiple additional genes. The loops occurred preferentially in early replicating and transcriptionally active genomic regions. Similar loops forming canonical fusions were found in three other sarcoma types. Chromoplexy-generated fusions appear to be associated with an aggressive form of Ewing sarcoma. These loops arise early, giving rise to both primary and relapse Ewing sarcoma tumors, which can continue to evolve in parallel.

Author Correction: EWS-FLI1 increases transcription to cause R-loops and block BRCA1 repair in Ewing sarcoma.

In this Letter, the sentence beginning "This work was funded…." in the Acknowledgements should have read "CPRIT (RP140105) to J.C.R." rather than "CPRIT (RP150445) to J.C.R." This error has been corrected online.

A probable primary malignant bone tumor in a pre-Columbian human humerus from Cerro Brujo, Bocas del Toro, Panamá.

We present a rare case of primary bone cancer principally affecting the right humerus of a skeleton from the pre-Columbian site of Cerro Brujo (1265-1380 CE) in Bocas del Toro, on the Caribbean coast of Panamá, excavated in the early 1970s. The humerus contains a dense, calcified sclerotic mass with associated lytic lesions localized around the midshaft of the diaphysis. Evidence of systemic inflammation and anemia, likely caused by the cancer, are visible in the form of severe porotic hyperostosis of the cranial vault and bilateral periosteal reactions in the tibiae. Differential diagnosis and future probes of the tumor are discussed. A tooth from the individual yielded a radiocarbon date 150 years later than those of the domestic occupation at the site. Given that it was the only formal burial recovered from the site, and as the individual had such a visible, painful, and rare pathology, this likely constitutes a ritual burial.

EWS-FLI1 increases transcription to cause R-loops and block BRCA1 repair in Ewing sarcoma.

Ewing sarcoma is an aggressive paediatric cancer of the bone and soft tissue. It results from a chromosomal translocation, predominantly t(11;22)(q24:q12), that fuses the N-terminal transactivation domain of the constitutively expressed EWSR1 protein with the C-terminal DNA binding domain of the rarely expressed FLI1 protein. Ewing sarcoma is highly sensitive to genotoxic agents such as etoposide, but the underlying molecular basis of this sensitivity is unclear. Here we show that Ewing sarcoma cells display alterations in regulation of damage-induced transcription, accumulation of R-loops and increased replication stress. In addition, homologous recombination is impaired in Ewing sarcoma owing to an enriched interaction between BRCA1 and the elongating transcription machinery. Finally, we uncover a role for EWSR1 in the transcriptional response to damage, suppressing R-loops and promoting homologous recombination. Our findings improve the current understanding of EWSR1 function, elucidate the mechanistic basis of the sensitivity of Ewing sarcoma to chemotherapy (including PARP1 inhibitors) and highlight a class of BRCA-deficient-like tumours.

Clofarabine inhibits Ewing sarcoma growth through a novel molecular mechanism involving direct binding to CD99.

Ewing sarcoma (ES) is an aggressive bone and soft tissue malignancy that predominantly affects children and adolescents. CD99 is a cell surface protein that is highly expressed on ES cells and is required to maintain their malignancy. We screened small molecule libraries for binding to extracellular domain of recombinant CD99 and subsequent inhibition of ES cell growth. We identified two structurally similar FDA-approved compounds, clofarabine and cladribine that selectively inhibited the growth of ES cells in a panel of 14 ES vs. 28 non-ES cell lines. Both drugs inhibited CD99 dimerization and its interaction with downstream signaling components. A membrane-impermeable analog of clofarabine showed similar cytotoxicity in culture, suggesting that it can function through inhibiting CD99 independent of DNA metabolism. Both drugs drastically inhibited anchorage-independent growth of ES cells, but clofarabine was more effective in inhibiting growth of three different ES xenografts. Our findings provide a novel molecular mechanism for clofarabine that involves direct binding to a cell surface receptor CD99 and inhibiting its biological activities.