PARP-1 inhibition as a targeted strategy to treat Ewing's sarcoma

Expression of DNA Repair Genes in Ewing Sarcoma

Background/Aim

Ewing sarcoma is an aggressive mesenchymal malignancy commonly affecting children and young adolescents. The molecular basis of this neoplasia is well reported with the formation of the EWSR1/FLI1 fusion gene being the most common genetic finding. However, this fusion gene has not been targeted therapeutically nor is being used as a prognostic marker. Its relevance regarding the molecular steps leading to Ewing sarcoma genesis are yet to be defined. The generation of the oncogenic EWSR1/FLI1 fusion gene, can be attributed to the simultaneous introduction of two DNA double-strand breaks (DSBs). The scope of this study is to detect any association between DNA repair deficiency and the clinicopathological aspects of Ewing's sarcoma disease.

Patients and Methods

We have conducted an expression analysis of 35 patients diagnosed with Ewing sarcoma concerning the genes involved in non-homologous end joining (NHEJ) and homologous recombination (HR) repair pathways. We have analyzed the expression levels of 6 genes involved in NHEJ (XRCC4, XRCC5, XRCC6, POLλ, POLμ) and 9 genes involved in HR (RAD51, RAD52, RAD54, BRCA1, BRCA2, FANCC, FANCD, DNTM1, BRIT1) using real time PCR. Age, sex, location of primary tumor, tumor size, KI67, mitotic count, invasion of adjacent tissues and treatment were the clinicopathological parameters included in the statistical analysis.

Results

Our results show that both these DNA repair pathways are deregulated in Ewing sarcoma. In addition, low expression of the xrcc4 gene has been associated with better overall survival probability (p=0.032).

Conclusion

Our results, even though retrospective and in a small number of patients, highlight the importance of DSBs repair and propose a potential therapeutic target for this type of sarcoma.

Therapeutic Targeting of DNA Repair Pathways in Pediatric Extracranial Solid Tumors: Current State and Implications for Immunotherapy

DNA damage is fundamental to tumorigenesis, and the inability to repair DNA damage is a hallmark of many human cancers. DNA is repaired via the DNA damage repair (DDR) apparatus, which includes five major pathways. DDR deficiencies in cancers give rise to potential therapeutic targets, as cancers harboring DDR deficiencies become increasingly dependent on alternative DDR pathways for survival. In this review, we summarize the DDR apparatus, and examine the current state of research efforts focused on identifying vulnerabilities in DDR pathways that can be therapeutically exploited in pediatric extracranial solid tumors. We assess the potential for synergistic combinations of different DDR inhibitors as well as combinations of DDR inhibitors with chemotherapy. Lastly, we discuss the immunomodulatory implications of targeting DDR pathways and the potential for using DDR inhibitors to enhance tumor immunogenicity, with the goal of improving the response to immune checkpoint blockade in pediatric solid tumors. We review the ongoing and future research into DDR in pediatric tumors and the subsequent pediatric clinical trials that will be critical to further elucidate the efficacy of the approaches targeting DDR.

MOF@COF Nanocapsules Enhance Soft Tissue Sarcoma Treatment: Synergistic Effects of Photodynamic Therapy and PARP Inhibition on Tumor Growth Suppression and Immune Response Activation

Soft tissue sarcomas (STS) are highly malignant tumors with limited treatment options owing to their heterogeneity and resistance to conventional therapies. Photodynamic therapy (PDT) and poly-ADP-ribose polymerase (PARP) inhibitors (PARPi) have shown potential for STS treatment, with PDT being effective for sarcomas located on the extremities and body surface and PARPi targeting defects in homologous recombination repair. To address the limitations of PDT and harness the potential of PARPi, herein, a novel therapeutic approach for STS treatment combining nanocapsules bearing integrated metal-organic frameworks (MOFs) and covalent organic frameworks (COFs), i.e., MOF@COF, with PDT and PARPi is proposed. Nanocapsules are designed, referred to as ZTN@COF@poloxamer, which contain a Zr-based MOF and tetrakis (4-carbethoxyphenyl) porphyrin as a photosensitizer, are coated with a COF to improve the sensitizing properties, and are loaded with niraparib to inhibit DNA repair. Experiments demonstrate that this new nanocapsules treatment significantly inhibits STS growth, promotes tumor cell apoptosis, exhibits high antitumor activity with minimal side effects, activates the immune response of the tumor, and inhibits lung metastasis in vivo. Therefore, MOF@COF nanocapsules combined with PARPi offer a promising approach for STS treatment, with the potential to enhance the efficacy of PDT and prevent tumor recurrence.

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

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

SIGNIFICANCE

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

PARP inhibitor combinations with high-dose vitamin C in the treatment of Ewing sarcoma: two case reports and mechanistic overview

Ewing's sarcoma (ES) is a bone and soft tissue tumor that mainly occurs at a young age. The underlying cause of Ewing's sarcoma is the formation of fusion proteins between FET family genes and ETS family genes. Tumors with FET/ETS fusion genes can have defects in the DNA damage response and are sensitive to PARP inhibitors (PARPi). However, several studies have shown that PARPi alone is not sufficient to induce a meaningful antitumor response and that combinations of DNA-damaging agents with PARPi are required to achieve efficacy. Accordingly, preclinical studies have reported dramatic responses to PARPi treatment in combination with DNA-damaging agents such as temozolomide or irinotecan. Similarly, it has been previously reported that by generating reactive oxygen species, high-dose intravenous vitamin C (IVC) can induce DNA damage. This suggests that the combination of IVC with PARPi may increase genotoxic stress and enhance the antitumor response. In addition, unlike chemotherapeutic agents, IVC induces DNA damage selectively in cancer cells, and the side effects are significantly milder than those of chemotherapy. As ETS fusion-positive ES is deficient in faithful DNA repair, partly due to the interaction between ETS fusion products and PARP1, a PARPi plus IVC seems to be a logical and effective combination for the treatment of ETS fusion-positive ES. This paper reports significant responses to IVC (1-1.5 g/kg) in combination with PARPi (olaparib 300 mg BID or talazoparib 1 mg/day) in two patients with metastatic Ewing's sarcoma. The observations highlight an unmet therapeutic need for patients with advanced metastatic ES. The combination of PARPi with a selective DNA-damaging agent was effective in these cases. This case experience suggests that IVC may be incorporated into PARPi-based therapeutic strategies. Further studies are needed to confirm the efficacy of this combination in the treatment of Ewing sarcoma with ETS fusions.

Small molecule tractable PARP inhibitors: Scaffold construction approaches, mechanistic insights and structure activity relationship

Diverse drug design strategies viz. molecular hybridization, substituent installation, scaffold hopping, isosteric replacement, high-throughput screening, induction and separation of chirality, structure modifications of phytoconstituents and use of structural templates have been exhaustively leveraged in the last decade to load the chemical toolbox of PARP inhibitors. Resultantly, numerous promising scaffolds have been pinpointed that in turn have led to the resuscitation of the credence to PARP inhibitors as cancer therapeutics. This review briefly presents the physiological functions of PARPs, the pharmacokinetics, and pharmacodynamics, and the interaction profiles of FDA-approved PARP inhibitors. Comprehensively covered is the section on the drug design strategies employed by drug discovery enthusiasts for furnishing PARP inhibitors. The impact of structural variations in the template of designed scaffolds on enzymatic and cellular activity (structure-activity relationship studies) has been discussed. The insights gained through the biological evaluation such as profiling of physicochemical properties andin vitroADME properties, PK assessments, and high-dose pharmacology are covered.

Bioinformatic Analysis of Recurrent Genomic Alterations and Corresponding Pathway Alterations in Ewing Sarcoma

Ewing Sarcoma (ES) is an aggressive, mesenchymal malignancy associated with a poor prognosis in the recurrent or metastatic setting with an estimated overall survival (OS) of <30% at 5 years. ES is characterized by a balanced, reciprocal chromosomal translocation involving the EWSR1 RNA-binding protein and ETS transcription factor gene (EWS-FLI being the most common). Interestingly, murine ES models have failed to produce tumors phenotypically representative of ES. Genomic alterations (GA) in ES are infrequent and may work synergistically with EWS-ETS translocations to promote oncogenesis. Aberrations in fibroblast growth factor receptor (FGFR4), a receptor tyrosine kinase (RTK) have been shown to contribute to carcinogenesis. Mouse embryonic fibroblasts (MEFs) derived from knock-in strain of homologous Fgfr4G385R mice display a transformed phenotype with enhanced TGF-induced mammary carcinogenesis. The association between the FGFRG388R SNV in high-grade soft tissue sarcomas has previously been demonstrated conferring a statistically significant association with poorer OS. How the FGFR4G388R SNV specifically relates to ES has not previously been delineated. To further define the genomic landscape and corresponding pathway alterations in ES, comprehensive genomic profiling (CGP) was performed on the tumors of 189 ES patients. The FGFR4G388R SNV was identified in a significant proportion of the evaluable cases (n = 97, 51%). In line with previous analyses, TP53 (n = 36, 19%), CDK2NA/B (n = 33, 17%), and STAG2 (n = 22, 11.6%) represented the most frequent alterations in our cohort. Co-occurrence of CDK2NA and STAG2 alterations was observed (n = 5, 3%). Notably, we identified a higher proportion of TP53 mutations than previously observed. The most frequent pathway alterations affected MAPK (n = 89, 24% of pathological samples), HRR (n = 75, 25%), Notch1 (n = 69, 23%), Histone/Chromatin remodeling (n = 57, 24%), and PI3K (n = 64, 20%). These findings help to further elucidate the genomic landscape of ES with a novel investigation of the FGFR4G388R SNV revealing frequent aberration.

Ewing sarcoma from molecular biology to the clinic

In Europe, with an incidence of 7.5 cases per million, Ewing sarcoma (ES) is the second most common primary malignant bone tumor in children, adolescents and young adults, after osteosarcoma. Since the 1980s, conventional treatment has been based on the use of neoadjuvant and adjuvant chemotherapeutic agents combined with surgical resection of the tumor when possible. These treatments have increased the patient survival rate to 70% for localized forms, which drops drastically to less than 30% when patients are resistant to chemotherapy or when pulmonary metastases are present at diagnosis. However, the lack of improvement in these survival rates over the last decades points to the urgent need for new therapies. Genetically, ES is characterized by a chromosomal translocation between a member of the FET family and a member of the ETS family. In 85% of cases, the chromosomal translocation found is (11; 22) (q24; q12), between the EWS RNA-binding protein and the FLI1 transcription factor, leading to the EWS-FLI1 fusion protein. This chimeric protein acts as an oncogenic factor playing a crucial role in the development of ES. This review provides a non-exhaustive overview of ES from a clinical and biological point of view, describing its main clinical, cellular and molecular aspects.

Poly(ADP-ribose) Polyremase-1 (PARP-1) Inhibition: A Promising Therapeutic Strategy for ETS-Expressing Tumours

ETS transcription factors are a highly conserved family of proteins involved in the progression of many cancers, such as breast and prostate carcinomas, Ewing's sarcoma, and leukaemias. This significant involvement can be explained by their roles at all stages of carcinogenesis progression. Generally, their expression in tumours is associated with a poor prognosis and an aggressive phenotype. Until now, no efficient therapeutic strategy had emerged to specifically target ETS-expressing tumours. Nevertheless, there is evidence that pharmacological inhibition of poly(ADP-ribose) polymerase-1 (PARP-1), a key DNA repair enzyme, specifically sensitises ETS-expressing cancer cells to DNA damage and limits tumour progression by leading some of the cancer cells to death. These effects result from a strong interplay between ETS transcription factors and the PARP-1 enzyme. This review summarises the existing knowledge of this molecular interaction and discusses the promising therapeutic applications.

B-cell lymphoma 2 family members and sarcomas: a promising target in a heterogeneous disease

Targeting the B-cell lymphoma 2 (Bcl-2) family proteins has been the backbone for hematological malignancies with overall survival improvements. The Bcl-2 family is a major player in apoptosis regulation and, has captured the researcher's interest in the treatment of solid tumors. Sarcomas are a heterogeneous group of diseases, comprising several entities, with high morbidity and mortality and with few specific therapies available. The treatment for sarcomas is based on platinum regimens, with variable results and poor outcomes, especially in advanced lesions. The high number of different sarcoma entities makes treatment standardization as well as the performance of clinical trials difficult. The use of Bcl-2 family members modifiers has revealed promising results in in vitro and in vivo models and may be a valid option, especially when used in combination with chemotherapy. In this article, a revision of these results and possibilities for the use of Bcl-2 family members inhibitors in sarcomas was performed.

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.

Clinical research with targeted drugs in paediatric oncology

The development of targeted drugs in paediatric oncology has been notoriously slow, in part due to the peculiarities of this rare and highly heterogeneous population. To provide therapeutic breakthroughs for the highest risk subgroups of childhood cancer, innovative research solutions have been implemented in the last several years by different international collaborative groups and regulators. Here, we discuss and summarise some of these approaches, as well as challenges and unmet needs that are still being addressed. A wide range of topics were covered in this review including molecular diagnosis optimisation, innovative research methodologies, big data approaches, trial enrolment strategies, and improvements in regulation and preclinical research platforms.

Paediatric Strategy Forum for medicinal product development of DNA damage response pathway inhibitors in children and adolescents with cancer: ACCELERATE in collaboration with the European Medicines Agency with participation of the Food and Drug Administration

DNA damage response inhibitors have a potentially important therapeutic role in paediatric cancers; however, their optimal use, including patient selection and combination strategy, remains unknown. Moreover, there is an imbalance between the number of drugs with diverse mechanisms of action and the limited number of paediatric patients available to be enrolled in early-phase trials, so prioritisation and a strategy are essential. While PARP inhibitors targeting homologous recombination-deficient tumours have been used primarily in the treatment of adult cancers with BRCA1/2 mutations, BRCA1/2 mutations occur infrequently in childhood tumours, and therefore, a specific response hypothesis is required. Combinations with targeted radiotherapy, ATR inhibitors, or antibody drug conjugates with DNA topoisomerase I inhibitor-related warheads warrant evaluation. Additional monotherapy trials of PARP inhibitors with the same mechanism of action are not recommended. PARP1-specific inhibitors and PARP inhibitors with very good central nervous system penetration also deserve evaluation. ATR, ATM, DNA-PK, CHK1, WEE1, DNA polymerase theta and PKMYT1 inhibitors are early in paediatric development. There should be an overall coordinated strategy for their development. Therefore, an academia/industry consensus of the relevant biomarkers will be established and a focused meeting on ATR inhibitors (as proof of principle) held. CHK1 inhibitors have demonstrated activity in desmoplastic small round cell tumours and have a potential role in the treatment of other paediatric malignancies, such as neuroblastoma and Ewing sarcoma. Access to CHK1 inhibitors for paediatric clinical trials is a high priority. The three key elements in evaluating these inhibitors in children are (1) innovative trial design (design driven by a clear hypothesis with the intent to further investigate responders and non-responders with detailed retrospective molecular analyses to generate a revised or new hypothesis); (2) biomarker selection and (3) rational combination therapy, which is limited by overlapping toxicity. To maximally benefit children with cancer, investigators should work collaboratively to learn the lessons from the past and apply them to future studies. Plans should be based on the relevant biology, with a focus on simultaneous and parallel research in preclinical and clinical settings, and an overall integrated and collaborative strategy.

The potential of PARP as a therapeutic target across pediatric solid malignancies

BACKGROUND

Pediatric cancer is the leading cause of disease-related death in children and the need for better therapeutic options remains urgent. Due to the limited number of patients, target and drug development for pediatrics is often supplemented by data from studies focused on adult cancers. Recent evidence shows that pediatric cancers possess different vulnerabilities that should be explored independently from adult cancers.

METHODS

Using the publicly available Genomics of Drug Sensitivity in Cancer database, we explore therapeutic targets and biomarkers specific to the pediatric solid malignancies Ewing sarcoma, medulloblastoma, neuroblastoma, osteosarcoma, and rhabdomyosarcoma. Results are validated using cell viability assays and high-throughput drug screens are used to identify synergistic combinations.

RESULTS

Using published drug screening data, PARP is identified as a drug target of interest across multiple different pediatric malignancies. We validate these findings, and we show that efficacy can be improved when combined with conventional chemotherapeutics, namely topoisomerase inhibitors. Additionally, using gene set enrichment analysis, we identify ribosome biogenesis as a potential biomarker for PARP inhibition in pediatric cancer cell lines.

CONCLUSION

Collectively, our results provide evidence to support the further development of PARP inhibition and the combination with TOP1 inhibition as a therapeutic approach in solid pediatric malignancies. Additionally, we propose ribosome biogenesis as a component to PARP inhibitor sensitivity that should be further investigated to help maximize the potential utility of PARP inhibition and combinations across pediatric solid malignancies.

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.

FLI1 regulates radiotherapy resistance in nasopharyngeal carcinoma through TIE1-mediated PI3K/AKT signaling pathway

BACKGROUND

Radiotherapy resistance is the main cause of treatment failure in nasopharyngeal carcinoma (NPC), which leads to poor prognosis. It is urgent to elucidate the molecular mechanisms underlying radiotherapy resistance.

METHODS

RNA-seq analysis was applied to five paired progressive disease (PD) and complete response (CR) NPC tissues. Loss-and gain-of-function assays were used for oncogenic function of FLI1 both in vitro and in vivo. RNA-seq analysis, ChIP assays and dual luciferase reporter assays were performed to explore the interaction between FLI1 and TIE1. Gene expression with clinical information from tissue microarray of NPC were analyzed for associations between FLI1/TIE1 expression and NPC prognosis.

RESULTS

FLI1 is a potential radiosensitivity regulator which was dramatically overexpressed in the patients with PD to radiotherapy compared to those with CR. FLI1 induced radiotherapy resistance and enhanced the ability of DNA damage repair in vitro, and promoted radiotherapy resistance in vivo. Mechanistic investigations showed that FLI1 upregulated the transcription of TIE1 by binding to its promoter, thus activated the PI3K/AKT signaling pathway. A decrease in TIE1 expression restored radiosensitivity of NPC cells. Furthermore, NPC patients with high levels of FLI1 and TIE1 were correlated with poor prognosis.

CONCLUSION

Our study has revealed that FLI1 regulates radiotherapy resistance of NPC through TIE1-mediated PI3K/AKT signaling pathway, suggesting that targeting the FLI1/TIE1 signaling pathway could be a potential therapeutic strategy to enhance the efficacy of radiotherapy in NPC.

Fli1 and Tissue Fibrosis in Various Diseases

Being initially described as a factor of virally-induced leukemias, Fli1 (Friend leukemia integration 1) has attracted considerable interest lately due to its role in both healthy physiology and a variety of pathological conditions. Over the past few years, Fli1 has been found to be one of the crucial regulators of normal hematopoiesis, vasculogenesis, and immune response. However, abnormal expression of Fli1 due to genetic predisposition, epigenetic reprogramming (modifications), or environmental factors is associated with a few diseases of different etiology. Fli1 hyperexpression leads to malignant transformation of cells and progression of cancers such as Ewing's sarcoma. Deficiency in Fli1 is implicated in the development of systemic sclerosis and hypertensive disorders, which are often accompanied by pronounced fibrosis in different organs. This review summarizes the initial findings and the most recent advances in defining the role of Fli1 in diseases of different origin with emphasis on its pro-fibrotic potential.

Molecularly Defined Subsets of Ewing Sarcoma Tumors Differ in Their Responses to IGF1R and WEE1 Inhibition

PURPOSE

Targeted cancer therapeutics have not significantly benefited patients with Ewing sarcoma with metastatic or relapsed disease. Understanding the molecular underpinnings of drug resistance can lead to biomarker-driven treatment selection.

EXPERIMENTAL DESIGN

Receptor tyrosine kinase (RTK) pathway activation was analyzed in tumor cells derived from a panel of Ewing sarcoma tumors, including primary and metastatic tumors from the same patient. Phospho-RTK arrays, Western blots, and IHC were used. Protein localization and the levels of key markers were determined using immunofluorescence. DNA damage tolerance was measured through PCNA ubiquitination levels and the DNA fiber assay. Effects of pharmacologic inhibition were assessed in vitro and key results validated in vivo using patient-derived xenografts.

RESULTS

Ewing sarcoma tumors fell into two groups. In one, IGF1R was predominantly nuclear (nIGF1R), DNA damage tolerance pathway was upregulated, and cells had low replication stress and RRM2B levels and high levels of WEE1 and RAD21. These tumors were relatively insensitive to IGF1R inhibition. The second group had high replication stress and RRM2B, low levels of WEE1 and RAD21, membrane-associated IGF1R (mIGF1R) signaling, and sensitivity to IGF1R or WEE1-targeted inhibitors. Moreover, the matched primary and metastatic tumors differed in IGF1R localization, levels of replication stress, and inhibitor sensitivity. In all instances, combined IGF1R and WEE1 inhibition led to tumor regression.

CONCLUSIONS

IGF1R signaling mechanisms and replication stress levels can vary among Ewing sarcoma tumors (including in the same patient), influencing the effects of IGF1R and WEE1 treatment. These findings make the case for using biopsy-derived predictive biomarkers at multiple stages of Ewing sarcoma disease management.

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

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

The Adaptability of Chromosomal Instability in Cancer Therapy and Resistance

Variation in chromosome structure is a central source of DNA damage and DNA damage response, together representinga major hallmark of chromosomal instability. Cancer cells under selective pressure of therapy use DNA damage and DNA damage response to produce newfunctional assets as an evolutionary mechanism. Recent efforts to understand DNA damage/chromosomal instability and elucidate its role in initiation or progression of cancer have also disclosed its vulnerabilities represented by inappropriate DNA damage response, chromatin changes, andinflammation. Understanding these vulnerabilities can provide important clues for predicting treatment response and for the development of novel strategies that prevent the emergence of therapy resistant tumors.

Nicaraven induces programmed cell death by distinct mechanisms according to the expression levels of Bcl-2 and poly (ADP-ribose) glycohydrolase in cancer cells

The PARP-1 expression level and poly (ADP-ribosyl)ation activity in cancer markedly affect the therapeutic outcome. Nicaraven, a free radical scavenger has been found to inhibit PARP, but the effect on cancer cells is still unclear. In this study, we investigated the potential role and molecular mechanism of nicaraven on cancer cells. Using U937 lymphoma cells and HCT-8 colorectal cancer cells, we found that nicaraven moderately reduced the cell viability of both cells in a dose-dependent manner. Interestingly, nicaraven significantly induced apoptosis of U937 cells that are dominantly expressing Bcl-2 but induced PAR-dependent cell death (parthanatos) of HCT-8 cells that are highly expressing poly (ADP-ribose) glycohydrolase (PARG). Based on our data, nicaraven seems to induce programmed cell death through distinct mechanisms, according to the expression levels of Bcl-2 and PARG in cancer cells.

The potential of PARP inhibitors in targeted cancer therapy and immunotherapy

DNA damage response (DDR) deficiencies result in genome instability, which is one of the hallmarks of cancer. Poly (ADP-ribose) polymerase (PARP) enzymes take part in various DDR pathways, determining cell fate in the wake of DNA damage. PARPs are readily druggable and PARP inhibitors (PARPi) against the main DDR-associated PARPs, PARP1 and PARP2, are currently approved for the treatment of a range of tumor types. Inhibition of efficient PARP1/2-dependent DDR is fatal for tumor cells with homologous recombination deficiencies (HRD), especially defects in breast cancer type 1 susceptibility protein 1 or 2 (BRCA1/2)-dependent pathway, while allowing healthy cells to survive. Moreover, PARPi indirectly influence the tumor microenvironment by increasing genomic instability, immune pathway activation and PD-L1 expression on cancer cells. For this reason, PARPi might enhance sensitivity to immune checkpoint inhibitors (ICIs), such as anti-PD-(L)1 or anti-CTLA4, providing a rationale for PARPi-ICI combination therapies. In this review, we discuss the complex background of the different roles of PARP1/2 in the cell and summarize the basics of how PARPi work from bench to bedside. Furthermore, we detail the early data of ongoing clinical trials indicating the synergistic effect of PARPi and ICIs. We also introduce the diagnostic tools for therapy development and discuss the future perspectives and limitations of this approach.

Harnessing immunomodulation during DNA damage in Ewing sarcoma

Ewing sarcoma is a fusion-oncoprotein-driven primary bone tumor most commonly diagnosed in adolescents. Given the continued poor outcomes for patients with metastatic and relapsed Ewing sarcoma, testing innovative therapeutic approaches is essential. Ewing sarcoma has been categorized as a 'BRCAness' tumor with emerging data characterizing a spectrum of DNA damage repair defects within individual Ewing tumors, including the presence of EWSR1::FLI1 itself, recurrent somatic mutations, and rare germline-based defects. It is critical to understand the cumulative impact of various DNA damage repair defects on an individual Ewing tumor's response to therapy. Further, in addition to DNA-damage-directed therapies, subsets of Ewing tumors may be more susceptible to DNA-damage/immunotherapy combinations given the significant cross-talk between DNA damage and inflammatory pathways in the tumor microenvironment. Here we review potential approaches utilizing DNA-damaging agents as modulators of the Ewing tumor immune microenvironment, with a focus on radiation and opportunities during disease metastasis and relapse.

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.

TrkC, a novel prognostic marker, induces and maintains cell survival and metastatic dissemination of Ewing sarcoma by inhibiting EWSR1-FLI1 degradation

Upregulation of EWSR1-FLI1 expression has been associated with invasiveness, induced cell survival, metastatic dissemination, and acquisition of self-renewal traits in Ewing sarcoma (ES). Although existing evidence implies that TrkC expression is linked to the pathogenesis of other cancer types, its role and the mechanism behind its correlation with EWSR1-FLI1 in the pathogenesis of ES remain unclear. In this study, we uncovered a novel physiological role of TrkC as a key regulator of EWSR1-FLI1 involved in the survival and metastatic dissemination of ES. TrkC was observed to be frequently overexpressed in human metastatic ES cells in vitro and in vivo, facilitating enhanced survival, tumorigenicity, and metastasis of ES cells. TrkC-mediated metastasis of ES cells was induced by the inhibition of the proteasomal degradation of EWSR1-FLI1 via the TrkC/EWSR1-FLI1 complex, which subsequently enabled the induction of the target proteins, EGR2 and NKX2.2. Moreover, TrkC significantly inhibited tumor suppressor activity of TGF-β through reduction of the mRNA expression of one of its receptors, TGFBR2 via TrkC-induced stabilization of EWSR1-FLI1. Furthermore, loss of TrkC expression inhibited tumor growth and metastasis in experimental mouse models. This study is the first to report the involvement and functional role of TrkC in the pathogenesis of ES, suggesting important implications for understanding the alterations of TrkC in Ewing tumors.

Targeting the DNA damage response in pediatric malignancies

INTRODUCTION

High levels of DNA damage and mutations in DNA damage response genes creates a high reliance on DNA damage repair in various tumors. This creates a vulnerability for new cancer therapies. Although there is extensive data for the use of these agents in adult tumors, the evaluation of these compounds in the pediatric population remains in the early stages.

AREAS COVERED

In this review, we discuss the role of the DNA damage response as a therapeutic vulnerability in pediatric malignancies, provide a summary of clinical data for the use of DNA damage response inhibitors in cancer, and review how these compounds can be extended to the pediatric population.

EXPERT OPINION

A number of pediatric cancers rely on robust DNA damage repair to maintain cell viability. This provides a therapeutic vulnerability in cancer cells resistant to other traditional therapies. Unfortunately, although clinical evaluation of inhibitors of various components of the DNA damage response has been done in adults, pediatric data remains limited. Further studies are needed to evaluate the efficacy of these compounds in the pediatric population.

Sacral Ewing sarcoma with rib, lung, and multifocal skull metastases: A rare case report and review of treatments

Ewing sarcoma (ES) rarely derives from the sacrum or mobile spine. The discovery of primary ES with multimetastatic involvements is exceedingly less frequent in clinical practice. A 23-year-old man with initial primary sacral ES developed metastases of rib, lung, and multifocal skull after receiving surgical intervention and series of adjuvant therapies. We provide this very rare case consisting of its clinical features, imaging findings, treatments, and outcomes. Therapeutic modalities of ES are also reviewed in previous published articles. The prognosis of metastatic ES remains dismal; effective therapeutic modalities for ES require multidisciplinary collaboration, with more high-quality clinical trials to promote the optimal protocols.

Review of various NAMPT inhibitors for the treatment of cancer

Nicotinamide phosphoribosyltransferase (NAMPT) is a rate-limiting enzyme in the NAD salvage pathway of mammalian cells and is overexpressed in numerous types of cancers. These include breast cancer, ovarian cancer, prostate cancer, gastric cancer, colorectal cancer, glioma, and b-cell lymphoma. NAMPT is also known to impact the NAD and NADPH pool. Research has demonstrated that NAMPT can be inhibited. NAMPT inhibitors are diverse anticancer medicines with significant anti-tumor efficacy in ex vivo tumor models. A few notable NAMPT specific inhibitors which have been produced include FK866, CHS828, and OT-82. Despite encouraging preclinical evidence of the potential utility of NAMPT inhibitors in cancer models, early clinical trials have yielded only modest results, necessitating the adaptation of additional tactics to boost efficacy. This paper examines a number of cancer treatment methods which target NAMPT, including the usage of individual inhibitors, pharmacological combinations, dual inhibitors, and ADCs, all of which have demonstrated promising experimental or clinical results. We intend to contribute further ideas regarding the usage and development of NAMPT inhibitors in clinical therapy to advance the field of research on this intriguing target.

A phase II trial of regorafenib in patients with advanced Ewing sarcoma and related tumors of soft tissue and bone: SARC024 trial results

BACKGROUND

Regorafenib is one of several FDA-approved cancer therapies targeting multiple tyrosine kinases. However, there are few subtype-specific data regarding kinase inhibitor activity in sarcomas. We report results of a single arm, phase II trial of regorafenib in advanced Ewing family sarcomas.

METHODS

Patients with metastatic Ewing family sarcomas (age ≥ 18, ECOG 0-2, good organ function) who had received at least one line of therapy and experienced progression within 6 months of registration were eligible. Prior kinase inhibitors were not allowed. The initial dose of regorafenib was 160 mg oral days 1-21 of a 28-day cycle. The primary endpoint was estimating progression-free rate (PFR) at 8 weeks employing RECIST 1.1.

RESULTS

Thirty patients (median age, 32 years; 33% women [10 patients]; bone primary, 40%; extraskeletal primary, 60%) enrolled at 14 sites. The most common grade 3 or higher toxicities were hypophosphatemia (5 grade 3, 1 grade 4), hypertension (2 grade 3), elevated ALT (2 grade 3). Sixteen patients required dose reductions, most often for hypophosphatemia (n = 7 reductions in 6 patients); two stopped regorafenib for toxicity. There was one death unrelated to treatment in the 30-day post-study period. Median progression-free survival (PFS) was 14.8 weeks (95% CI 7.3-15.9); PFR at 8 weeks by Kaplan-Meier analysis was 63% (95% CI 46-81%). The RECIST 1.1 response rate was 10%. Median OS was 53 weeks (95% CI 37-106 weeks).

CONCLUSIONS

Regorafenib has modest activity in the Ewing family sarcomas. Toxicity was similar to that seen in approval studies.

Clinical genomic profiling in the management of patients with soft tissue and bone sarcoma

There are more than 70 distinct sarcomas, and this diversity complicates the development of precision-based therapeutics for these cancers. Prospective comprehensive genomic profiling could overcome this challenge by providing insight into sarcomas' molecular drivers. Through targeted panel sequencing of 7494 sarcomas representing 44 histologies, we identify highly recurrent and type-specific alterations that aid in diagnosis and treatment decisions. Sequencing could lead to refinement or reassignment of 10.5% of diagnoses. Nearly one-third of patients (31.7%) harbor potentially actionable alterations, including a significant proportion (2.6%) with kinase gene rearrangements; 3.9% have a tumor mutational burden ≥10 mut/Mb. We describe low frequencies of microsatellite instability (<0.3%) and a high degree of genome-wide loss of heterozygosity (15%) across sarcomas, which are not readily explained by homologous recombination deficiency (observed in 2.5% of cases). In a clinically annotated subset of 118 patients, we validate actionable genetic events as therapeutic targets. Collectively, our findings reveal the genetic landscape of human sarcomas, which may inform future development of therapeutics and improve clinical outcomes for patients with these rare cancers.

Protein post-translational modifications in the regulation of cancer hallmarks

Posttranslational modifications (PTMs) of proteins, the major mechanism of protein function regulation, play important roles in regulating a variety of cellular physiological and pathological processes. Although the classical PTMs, such as phosphorylation, acetylation, ubiquitination and methylation, have been well studied, the emergence of many new modifications, such as succinylation, hydroxybutyrylation, and lactylation, introduces a new layer to protein regulation, leaving much more to be explored and wide application prospects. In this review, we will provide a broad overview of the significant roles of PTMs in regulating human cancer hallmarks through selecting a diverse set of examples, and update the current advances in the therapeutic implications of these PTMs in human cancer.

BRCA1-associated RING domain-1 (BARD1) loss and GBP1 expression enhance sensitivity to DNA damage in Ewing sarcoma

Ewing sarcoma is a fusion oncoprotein-driven primary bone tumor. A subset of patients (~10%) with Ewing sarcoma are known to harbor germline variants in a growing number of genes involved in DNA damage repair. We recently reported our discovery of a germline mutation in the DNA damage repair protein BARD1 (BRCA1-associated RING domain-1) in a patient with Ewing sarcoma. BARD1 is recruited to the site of DNA double stranded breaks via the poly(ADP-ribose) polymerase (PARP) protein and plays a critical role in DNA damage response pathways including homologous recombination. We thus questioned the impact of BARD1 loss on Ewing cell sensitivity to DNA damage and the Ewing sarcoma transcriptome. We demonstrate that PSaRC318 cells, a novel patient-derived cell line harboring a pathogenic BARD1 variant, are sensitive to PARP inhibition and by testing the effect of BARD1 depletion in additional Ewing sarcoma cell lines, we confirm that BARD1 loss enhances cell sensitivity to PARP inhibition plus radiation. Additionally, RNA-seq analysis revealed that loss of BARD1 results in the upregulation of GBP1 (guanylate-binding protein 1), a protein whose expression is associated with variable response to therapy depending on the adult carcinoma subtype examined. Here, we demonstrate that GBP1 contributes to the enhanced sensitivity of BARD1 deficient Ewing cells to DNA damage. Together, our findings demonstrate the impact of loss-of function mutations in DNA damage repair genes, such as BARD1, on Ewing sarcoma treatment response.

Systemic Treatment of Ewing Sarcoma: Current Options and Future Perspectives

Ewing sarcoma (ES) is an uncommon malignant neoplasm, mostly affecting young adults and adolescents. Surgical excision, irradiation, and combinations of multiple chemotherapeutic agents are currently used as a multimodal strategy for the treatment of local and oligometastatic disease. Although ES usually responds to the primary treatment, relapsed and primarily refractory disease remains a difficult therapeutic challenge. The growing understanding of cancer biology and the subsequent development of new therapeutic strategies have been put at the service of research in recurrent and refractory ES, generating a great number of ongoing studies with compounds that could find superior clinical outcomes in the years to come. This review gathers the current available information on the treatment and clinical investigation of ES and aims to be a point of support for future research.

Current approaches to management of bone sarcoma in adolescent and young adult patients

Bone tumors are a group of histologically diverse diseases that occur across all ages. Two of the commonest, osteosarcoma (OS) and Ewing sarcoma (ES), are regarded as characteristic adolescent and young adult (AYA) cancers with an incidence peak in AYAs. They are curable for some but associated with unacceptably high rates of treatment failure and morbidity. The introduction of effective new therapeutics for bone sarcomas is slow, and to date, complex biology has been insufficiently characterized to allow more rapid therapeutic exploitation. This review focuses on current standards of care, recent advances that have or may soon change that standard of care and challenges to the expert clinical research community that we suggest must be met.

Therapeutic vulnerability to PARP1,2 inhibition in RB1-mutant osteosarcoma

Loss-of-function mutations in the RB1 tumour suppressor are key drivers in cancer, including osteosarcoma. RB1 loss-of-function compromises genome-maintenance and hence could yield vulnerability to therapeutics targeting such processes. Here we demonstrate selective hypersensitivity to clinically-approved inhibitors of Poly-ADP-Polymerase1,2 inhibitors (PARPi) in RB1-defective cancer cells, including an extended panel of osteosarcoma-derived lines. PARPi treatment results in extensive cell death in RB1-defective backgrounds and prolongs survival of mice carrying human RB1-defective osteosarcoma grafts. PARPi sensitivity is not associated with canonical homologous recombination defect (HRd) signatures that predict PARPi sensitivity in cancers with BRCA1,2 loss, but is accompanied by rapid activation of DNA replication checkpoint signalling, and active DNA replication is a prerequisite for sensitivity. Importantly, sensitivity in backgrounds with natural or engineered RB1 loss surpasses that seen in BRCA-mutated backgrounds where PARPi have established clinical benefit. Our work provides evidence that PARPi sensitivity extends beyond cancers identifiable by HRd and advocates PARP1,2 inhibition as a personalised strategy for RB1-mutated osteosarcoma and other cancers.

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.

Targeting the DNA damage response: PARP inhibitors and new perspectives in the landscape of cancer treatment

Cancer derives from alterations of pathways responsible for cell survival, differentiation and proliferation. Dysfunctions of mechanisms protecting genome integrity can promote oncogenesis but can also be exploited as therapeutic target. Poly-ADP-Ribose-Polymerase (PARP)-inhibitors, the first approved targeted agents able to tackle DNA damage response (DDR), have demonstrated antitumor activity, particularly when homologous recombination impairment is present. Despite the relevant results achieved, a large proportion of patients fail to obtain durable responses. The development of innovative treatments, able to overcome resistance and ensure long-lasting benefit for a wider population is still an unmet need. Moreover, improvement in biomarker assays is necessary to properly identify patients who can benefit from DDR targeting agents. Here we summarize the main DDR pathways, explain the current role of PARP inhibitors in cancer therapy and illustrate new therapeutic strategies targeting the DDR, focusing on the combinations of PARP inhibitors with other agents and on cell-cycle checkpoint inhibitors.

PARP1 as a prognostic biomarker for human cancers: a meta-analysis

Aim: A comprehensive meta-analysis was carried out to evaluate the association between high PARP1 expression and clinical outcomes in diverse types of cancers. Materials & methods: The electronic databases for all articles about PARP1 expression and cancers were searched. Additionally, bioinformatics analysis was utilized to validate the results of the meta-analysis. Results: Fifty-two studies with a total of 7140 patients were included in the current meta-analysis. High PARP1 expression was found to be significantly associated with poor overall survival and recurrence in various cancers, which were further strengthened and complemented by the results of bioinformatic analysis. Furthermore, increased PAPR1 expression was also related to clinicopathological features. Conclusion: Our findings confirmed that PARP1 might be a promising biomarker for prognosis in human cancers.

Fanconi Anaemia, Childhood Cancer and the BRCA Genes

Fanconi anaemia (FA) is an inherited chromosomal instability disorder characterised by congenital and developmental abnormalities and a strong cancer predisposition. In less than 5% of cases FA can be caused by bi-allelic pathogenic variants (PGVs) in BRCA2/FANCD1 and in very rare cases by bi-allelic PGVs in BRCA1/FANCS. The rarity of FA-like presentation due to PGVs in BRCA2 and even more due to PGVs in BRCA1 supports a fundamental role of the encoded proteins for normal development and prevention of malignant transformation. While FA caused by BRCA1/2 PGVs is strongly associated with distinct spectra of embryonal childhood cancers and AML with BRCA2-PGVs, and also early epithelial cancers with BRCA1 PGVs, germline variants in the BRCA1/2 genes have also been identified in non-FA childhood malignancies, and thereby implying the possibility of a role of BRCA PGVs also for non-syndromic cancer predisposition in children. We provide a concise review of aspects of the clinical and genetic features of BRCA1/2-associated FA with a focus on associated malignancies, and review novel aspects of the role of germline BRCA2 and BRCA1 PGVs occurring in non-FA childhood cancer and discuss aspects of clinical and biological implications.

Role of immunotherapy in Ewing sarcoma

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

TRIM8 modulates the EWS/FLI oncoprotein to promote survival in Ewing sarcoma

Fusion-transcription factors (fusion-TFs) represent a class of driver oncoproteins that are difficult to therapeutically target. Recently, protein degradation has emerged as a strategy to target these challenging oncoproteins. The mechanisms that regulate fusion-TF stability, however, are generally unknown. Using CRISPR-Cas9 screening, we discovered tripartite motif-containing 8 (TRIM8) as an E3 ubiquitin ligase that ubiquitinates and degrades EWS/FLI, a driver fusion-TF in Ewing sarcoma. Moreover, we identified TRIM8 as a selective dependency in Ewing sarcoma compared with >700 other cancer cell lines. Mechanistically, TRIM8 knockout led to an increase in EWS/FLI protein levels that was not tolerated. EWS/FLI acts as a neomorphic substrate for TRIM8, defining the selective nature of the dependency. Our results demonstrate that fusion-TF protein stability is tightly regulated and highlight fusion oncoprotein-specific regulators as selective therapeutic targets. This study provides a tractable strategy to therapeutically exploit oncogene overdose in Ewing sarcoma and potentially other fusion-TF-driven cancers.

SLFN11 is Widely Expressed in Pediatric Sarcoma and Induces Variable Sensitization to Replicative Stress Caused By DNA-Damaging Agents

Pediatric sarcomas represent a heterogeneous group of malignancies that exhibit variable response to DNA-damaging chemotherapy. Schlafen family member 11 protein (SLFN11) increases sensitivity to replicative stress and has been implicated as a potential biomarker to predict sensitivity to DNA-damaging agents (DDA). SLFN11 expression was quantified in 220 children with solid tumors using IHC. Sensitivity to the PARP inhibitor talazoparib (TAL) and the topoisomerase I inhibitor irinotecan (IRN) was assessed in sarcoma cell lines, including SLFN11 knock-out (KO) and overexpression models, and a patient-derived orthotopic xenograft model (PDOX). SLFN11 was expressed in 69% of pediatric sarcoma sampled, including 90% and 100% of Ewing sarcoma and desmoplastic small round-cell tumors, respectively, although the magnitude of expression varied widely. In sarcoma cell lines, protein expression strongly correlated with response to TAL and IRN, with SLFN11 KO resulting in significant loss of sensitivity in vitro and in vivo Surprisingly, retrospective analysis of children with sarcoma found no association between SLFN11 levels and favorable outcome. Subsequently, high SLFN11 expression was confirmed in a PDOX model derived from a patient with recurrent Ewing sarcoma who failed to respond to treatment with TAL + IRN. Selective inhibition of BCL-xL increased sensitivity to TAL + IRN in SLFN11-positive resistant tumor cells. Although SLFN11 appears to drive sensitivity to replicative stress in pediatric sarcomas, its potential to act as a biomarker may be limited to certain tumor backgrounds or contexts. Impaired apoptotic response may be one mechanism of resistance to DDA-induced replicative stress.

Poly (ADP-Ribose) Polymerase Inhibitor, ABT888, Improved Cisplatin Effect in Human Oral Cell Carcinoma

Cisplatin is one of the chemotherapeutic drugs used for the management of oral carcinoma, in which combined therapies are estimated to exert superior therapeutic efficacy compared with monotherapy. It is known that poly(ADP-ribosyl)ation is implicated in a multiplicity of cellular activities, such as DNA repair and cell death. Based on these, PARP inhibitors are used for the treatment of cancers; however, the capacity of PARP inhibitors associated to anti-cancer drugs have not been completely assessed in oral carcinoma. Here, we evaluated the effects of PARPi veliparib (ABT888) in combination with cisplatin on the survival of three human oral cancer cell lines HSC-2, Ca9-22 and CAL27 and we observed the effects of ABT888 alone or in combination with cisplatin on apoptosis and DNA damage repair mechanism. The results obtained showed that ABT888 induces a cytotoxicity effect on cell viability increasing the apoptotic pathway as well as DNA strand break; moreover, our results displayed the effects with cisplatin in a dose-dependent manner. Therefore, our results indicate PARP inhibitors as adjuvants for therapeutic strategy of oral cancer.

Recent progress in the treatment of cancer in children

Although significant improvements have been made in the outcomes of children with cancer, the pace of improvement has slowed in recent years as the limits of therapy intensification may have been reached for many pediatric cancers. Furthermore, with increasing numbers of pediatric cancer survivors, the long-term side effects of treatment have become increasingly apparent. Therefore, attention has shifted to the use of molecularly targeted agents and immunotherapies to improve the outcomes of children who are not cured by traditional cytotoxic chemotherapies and to decrease exposure to cytotoxic chemotherapy and reduce late effects. This review describes the recent progress in the treatment of children with cancer, focusing in particular on diseases in which targeted and immunotherapeutic agents have made an impact.

Integrated Analysis of the Transcriptome Profile Reveals the Potential Roles Played by Long Noncoding RNAs in Immunotherapy for Sarcoma

Background

Long-term survival is still low for high-risk patients with soft tissue sarcoma treated with standard management options, including surgery, radiation, and chemotherapy. Immunotherapy is a promising new potential treatment paradigm. However, the application of immune checkpoint inhibitors for the treatment of patients with sarcoma did not yield promising results in a clinical trial. Therefore, there is a considerable need to identify factors that may lead to immune checkpoint inhibitor resistance.

Methods

In this study, we performed a bioinformatic analysis of The Cancer Genome Atlas (TCGA) to detect key long noncoding RNAs (lncRNAs) that were correlated with immune checkpoint inhibitory molecules in sarcoma. The expression levels of these lncRNAs and their correlation with patient prognosis were explored. The upstream long noncoding RNAs were also examined via 450K array data from the TCGA. The potential roles of these lncRNAs were further examined via KEGG and GO analysis using DAVID online software. Finally, the relationship between these lncRNAs and immune cell infiltration in tumors and their effect on immune checkpoint inhibitors were further explored.

Results

We identified lncRNAs correlated with tumor cell immune evasion in sarcoma. The expression of these lncRNAs was upregulated and correlated with worse prognosis in sarcoma and other human cancer types. Moreover, low DNA methylation occupation of these lncRNA loci was detected. Negative correlations between DNA methylation and lncRNA expression were also found in sarcoma and other human cancer types. KEGG and GO analyses indicated that these lncRNAs correlated with immune evasion and negative regulation of the immune response in sarcoma. Finally, high expression of these lncRNAs correlated with more suppressive immune cell infiltration and reduced sensitivity to immune checkpoint inhibitors in sarcoma and other human cancer types.

Conclusion

Our results suggest that long noncoding RNAs confer immune checkpoint inhibitor resistance in human cancer. Further characterization of these lncRNAs may help to elucidate the mechanisms underlying immune checkpoint inhibitor resistance and uncover a novel therapeutic intervention point for immunotherapy.

Ewing sarcoma: investigational mono- and combination therapies in clinical trials

INTRODUCTION

Over the last decades, multi-institutional clinical trials have resulted in significant improvements in the outcomes of patients with localized Ewing sarcoma; however, those with metastatic and recurrent diseases continue to fare poorly. More recently, advancements made in understanding the biology of the disease and mechanisms of response to therapy have opened the door for the incorporation of targeted therapies. Here we review the current state of treatment for Ewing sarcoma and the most recent preclinical advancements that have the potential to translate to improved care.

AREAS COVERED

This review provides a general overview of the most recent clinical trials completed in Ewing sarcoma, as well as the preclinical and translational data that has the potential to be incorporated into clinical trials. A PubMed review as well as a review of published meeting abstracts was used to compose this review.

EXPERT OPINION

While dose-intenstifying strategies have failed to lead to improvements in outcomes for patients with the highest-risk disease, recent preclinical advancements have shed light on potential new targeted strategies. The lack of early-phase clinical trial responses should not deter us from further developing these agents, but instead should guide us in designing novel combination strategies.

Dipyridamole induces the phosphorylation of CREB to promote cancer cell proliferation

Dipyridamole, a traditional anti-platelet drug, has been reported to inhibit the proliferation of cancer cells. The present study aimed to investigate the possibility of dipyridamole as an adjuvant of chemotherapy by enhancing the cytotoxicity of an anti-cancer drug. The cytotoxicity of colorectal cancer cells (HCT-8), CD133⁺/CD44⁺ stem-like subpopulation of HCT-8 cells and lymphoma cells (U937) to dipyridamole and/or doxorubicin was evaluated using MTT proliferation and colony forming assays. The expression levels of phosphorylated cAMP-regulatory element-binding protein (pCREB) and poly(ADP-ribose) polymerase-1 (PARP-1) in cells were analyzed via western blotting and immunofluorescence. The present study reported controversial data regarding the anti-cancer effect of dipyridamole. Dipyridamole increased, rather than inhibited, the proliferation of HCT-8 and U937 cells in a dose-dependent manner. Furthermore, it was found that dipyridamole significantly increased the expression levels of pCREB and PARP-1. However, the combined usage of dipyridamole significantly enhanced the cytotoxicity of doxorubicin to HCT-8 cells at particular doses. Based on the current findings, dipyridamole likely induces the phosphorylation of CREB to promote the proliferation of cancer cells, but may enhance the cytotoxicity of anti-cancer drugs at particular doses.

Systems Biology Analysis for Ewing Sarcoma

Ewing sarcoma (EwS) is a highly aggressive pediatric bone cancer that is defined by a somatic fusion between the EWSR1 gene and an ETS family member, most frequently the FLI1 gene, leading to expression of a chimeric transcription factor EWSR1-FLI1. Otherwise, EwS is one of the most genetically stable cancers. The situation when the major cancer driver is well known looks like a unique opportunity for applying the systems biology approach in order to understand the EwS mechanisms as well as to uncover some general mechanistic principles of carcinogenesis. A number of studies have been performed revealing the direct and indirect effects of EWSR1-FLI1 on multiple aspects of cellular life. Nevertheless, the emerging picture of the oncogene action appears to be highly complex and systemic, with multiple reciprocal influences between the immediate consequences of the driver mutation and intracellular and intercellular molecular mechanisms, including regulation of transcription, epigenome, and tumoral microenvironment. In this chapter, we present an overview of existing molecular profiling resources available for EwS tumors and cell lines and provide an online comprehensive catalogue of publicly available omics and other datasets. We further highlight the systems biology studies of EwS, involving mathematical modeling of networks and integration of molecular data. We conclude that despite the seeming simplicity, a lot has yet to be understood on the systems-wide mechanisms connecting the driver mutation and the major cellular phenotypes of this pediatric cancer. Overall, this chapter can serve as a guide for a systems biology researcher to start working on EwS.