Osteosarcoma Microenvironment Research Articles

Comprehensive Analysis of a Ferroptosis-Related lncRNA Signature for Predicting Prognosis and Immune Landscape in Osteosarcoma

Research on the implications of ferroptosis in tumors has increased rapidly in the last decades. There are evidences that ferroptosis is involved in several aspects of cancer biology, including tumor progression, metastasis, immunomodulation, and therapeutic response. Nonetheless, the interaction between ferroptosis-related lncRNAs (FRLs) and the osteosarcoma immune microenvironment is poorly understood. In this study, a risk model composed of FRLs was developed using univariate and LASSO Cox regression analyses. On the basis of this model, FRL scores were calculated to systematically explore the role of the model in predicting the prognosis and immune characteristics of osteosarcoma patients. Survival analysis showed that osteosarcoma samples with lower FRL-score had better overall survival. After predicting the abundance of immune cells in osteosarcoma microenvironment by single-sample gene-set enrichment analysis (ssGSEA) and ESTIMATE analysis, we found that the FRL-score could distinguish immune function, immune score, stromal score, tumor purity, and tumor infiltration of immune cells in different osteosarcoma patients. In addition, FRL-score was also associated with immune checkpoint gene expression and half-maximal inhibitory concentration of chemotherapeutic agents. Finally, we confirmed that knockdown of RPARP-AS1 suppressed the malignant activity of osteosarcoma cells in vitro experiments. In general, the FRL-based prognostic signature could promote our understanding of the immune microenvironment characteristics of osteosarcoma and guide more effective treatment regimens.

Single-Cell Profiling of Tumor Microenvironment Heterogeneity in Osteosarcoma Identifies a Highly Invasive Subcluster for Predicting Prognosis.

Osteosarcoma is the most common malignant bone tumor in adolescents, and metastasis is the key reason for treatment failure and poor prognosis. Once metastasis occurs, the 5-year survival rate is only approximately 20%, and assessing and predicting the risk of osteosarcoma metastasis are still difficult tasks. In this study, cellular communication between tumor cells and nontumor cells was identified through comprehensive analysis of osteosarcoma single-cell RNA sequencing (scRNA-seq) and bulk RNA-seq data, illustrating the complex regulatory network in the osteosarcoma microenvironment. In line with the heterogeneity of osteosarcoma, we found subpopulations of osteosarcoma cells that highly expressed COL6A1, COL6A3 and MIF and were closely associated with lung metastasis. Then, BCDEG, a reliable risk regression model that could accurately assess the metastasis risk and prognosis of patients, was established, providing a new strategy for the diagnosis and treatment of osteosarcoma.

Immune Infiltrate and Tumor Microenvironment Transcriptional Programs Stratify Pediatric Osteosarcoma into Prognostic Groups at Diagnosis

These findings indicate that the osteosarcoma microenvironment composition is a major feature to identify hard-to-treat patient tumors at diagnosis and define the biological pathways and potential actionable targets associated with these tumors.

MerTK-mediated efferocytosis promotes immune tolerance and tumor progression in osteosarcoma through enhancing M2 polarization and PD-L1 expression

ABSTRACT The poor progress of immunotherapy on osteosarcoma patients requires deeper delineation of immune tolerance mechanisms in the osteosarcoma microenvironment and a new therapeutic strategy. Clearance of apoptotic cells by phagocytes, a process termed “efferocytosis,” is ubiquitous in tumors and mediates the suppression of innate immune inflammatory response. Considering the massive infiltrated macrophages in osteosarcoma, efferocytosis probably serves as a potential target, but is rarely studied in osteosarcoma. Here, we verified M2 polarization and PD-L1 expression of macrophages following efferocytosis. Pharmacological inhibition and genetic knockdown were used to explore the underlying pathway. Moreover, tumor progression and immune landscape were evaluated following inhibition of efferocytosis in osteosarcoma model. Our study indicated that efferocytosis promoted PD-L1 expression and M2 polarization of macrophages. Ëfferocytosis was mediated by MerTK receptor in osteosarcoma and regulated the phenotypes of macrophages through the p38/STAT3 pathway. By establishing the murine osteosarcoma model, we emphasized that inhibition of MerTK suppressed tumor growth and enhanced the T cell cytotoxic function by increasing the infiltration of CD8+ T cells and decreasing their exhaustion. Our findings demonstrate that MerTK-mediated efferocytosis promotes osteosarcoma progression by enhancing M2 polarization of macrophages and PD-L1-induced immune tolerance, which were regulated through the p38/STAT3 pathway.

Destabilization of macrophage migration inhibitory factor by 4-IPP reduces NF-κB/P-TEFb complex-mediated c-Myb transcription to suppress osteosarcoma tumourigenesis.

BackgroundAs an inflammatory factor and oncogenic driver protein, the pleiotropic cytokine macrophage migration inhibitory factor (MIF) plays a crucial role in the osteosarcoma microenvironment. Although 4‐iodo‐6‐phenylpyrimidine (4‐IPP) can inactivate MIF biological functions, its anti‐osteosarcoma effect and molecular mechanisms have not been investigated. In this study, we identified the MIF inhibitor 4‐IPP as a specific double‐effector drug for osteosarcoma with both anti‐tumour and anti‐osteoclastogenic functions.MethodsThe anti‐cancer effects of 4‐IPP were evaluated by wound healing assay, cell cycle analysis, colony formation assay, CCK‐8 assay, apoptosis analysis, and Transwell migration/invasion assays. Through the application of a luciferase reporter, chromatin immunoprecipitation assays, and immunofluorescence and coimmunoprecipitation analyses, the transcriptional regulation of the NF‐κB/P‐TEFb complex on c‐Myb‐ and STUB1‐mediated proteasome‐dependent MIF protein degradation was confirmed. The effect of 4‐IPP on tumour growth and metastasis was assessed using an HOS‐derived tail vein metastasis model and subcutaneous and orthotopic xenograft tumour models.ResultsIn vitro, 4‐IPP significantly reduced the proliferation and metastasis of osteosarcoma cells by suppressing the NF‐κB pathway. 4‐IPP hindered the binding between MIF and CD74 as well as p65. Moreover, 4‐IPP inhibited MIF to interrupt the formation of downstream NF‐κB/P‐TEFb complexes, leading to the down‐regulation of c‐Myb transcription. Interestingly, the implementation of 4‐IPP can mediate small molecule‐induced MIF protein proteasomal degradation via the STUB1 E3 ligand. However, 4‐IPP still interrupted MIF‐mediated communication between osteosarcoma cells and osteoclasts, thus promoting osteoclastogenesis. Remarkably, 4‐IPP strongly reduced HOS‐derived xenograft osteosarcoma tumourigenesis and metastasis in an in vivo mouse model.ConclusionsOur findings demonstrate that the small molecule 4‐IPP targeting the MIF protein exerts an anti‐osteosarcoma effect by simultaneously inactivating the biological functions of MIF and promoting its proteasomal degradation. Direct destabilization of the MIF protein with 4‐IPP may be a promising therapeutic strategy for treating osteosarcoma.

A Contemporary Assessment of Osteosarcoma: Lessons from a Comparative Approach

This review will describe more than two decades of comparative research on primary bone cancer (osteosarcoma). Osteosarcoma is a chaotic disease present in a complex and variable microenvironment composed of many different cell types which interact with each other and lead to high transcriptional heterogeneity. Despite this heterogeneity, common transcriptional patterns can be observed in the bulk transcriptomes of these tumors; additionally, these patterns are associated with outcome, indicating their importance to the molecular biology of the disease. Work from our group and others has led to our current understanding of osteosarcoma as a disease where multiple pathological processes appear to converge into a limited array of tissue organizations with distinct biology. Recurrent as well as distinct events can lead to these states of tissue organization, explaining the heterogeneity of osteosarcoma that is observed among and within species. Yet, despite their chaotic genomes, osteosarcomas seem to be (relatively) genetically stable, with persistent maintenance of essentially the same chromothriptic karyotype throughout the developmental lifetime of the tumor. Importantly, the transcriptional variance between tumors can highlight the underlying biology of the malignant cells themselves, as well as the composition of the osteosarcoma microenvironment and the host response, both of which are prognostically significant for this disease. Initial single cell RNA-seq reports provide further evidence of the importance of the osteosarcoma microenvironment for tumor characterization. Our data suggest that improving patient outcomes in immunologically barren or “cold” osteosarcomas, necessitates generating immune permissive or “warmer” microenvironments within the tumor. Furthermore, the aging bone microenvironment may create specific niches that predispose to cancer, and identification of the drivers that lead to these variable transcriptional patterns will be essential to identify personalized, effective genomic therapy for osteosarcoma.

Prognostic Value of a Pyroptosis-Related Long Noncoding RNA Signature Associated with Osteosarcoma Microenvironment.

Background Osteosarcoma is the most prevalent bone cancer that affects young adults and adolescents. It is the most frequent malignancy of the bone. In spite of the fact that complete surgical resection and chemotherapy have increased the overall survival of osteosarcoma patients considerably, the prognosis remains dismal in patients with recurring and/or metastasized osteosarcoma. Thus, finding predictive biomarkers representing osteosarcoma's biological variability may result in more effective treatment for osteosarcoma patients. Methods In this research, RNA data and clinical information were obtained from TARGET database. The risk score was calculated using a technique that incorporated both univariate and multivariate Cox regression. A variety of statistical methods were employed to assess the risk score's accuracy. These included ROC curves, nomograms, and Kaplan-Meier curves. Following that, bioinformatics studies were carried out in order to investigate the possible biological processes that influence the prognosis of osteosarcoma patients. GSEA was used to investigate the variations in pathway enrichment among the different groups of genes. To examine the disparities in the immune microenvironment, the analytical methods CIBERSORT and ssGSEA were employed. Results We discovered three differentially expressed lncRNAs (RPARP-AS1, AC009159.3, and AC124312.3) that are linked to osteosarcoma prognosis. Kaplan-Meier analysis showed the presence of a signature of high-risk lncRNAs linked with a poor prognosis for osteosarcoma. Furthermore, the AUC of the lncRNAs signature was 0.773, indicating that they are useful in predicting osteosarcoma prognosis in certain cases. In predicting osteosarcoma prognosis, our risk assessment approach outperformed conventional clinicopathological characteristics. In the high-risk group of people, GSEA showed the presence of tumor-related pathways as well as immune-related pathways. Furthermore, TARGET revealed that immune-related functions such as checkpoint, T-cell coinhibition, and costimulation were significantly different between the high-risk and low-risk groups. LAIR1, LAG3, CD44, and CD22, as well as other immune checkpoints, were shown to be expressed differentially across the two risk groups. Conclusion This study established that pyroptosis-derived lncRNAs had a significant predictive value for osteosarcoma patients' survival, indicating that they may be a viable target for future therapy.

Tumor-associated macrophages in osteosarcoma.

Osteosarcoma (OS) is the most common primary bone tumor in children and adolescents. It is an aggressive tumor with a tendency to spread to the lung, which is the most common site of metastasis. Patients with advanced OS with metastases have poor prognoses despite the application of chemotherapy, thus highlighting the need for novel therapeutic targets. The tumor microenvironment (TME) of OS is confirmed to be essential for and supportive of tumor growth and dissemination. The immune component of the OS microenvironment is mainly composed of tumor-associated macrophages (TAMs). In OS, TAMs promote tumor growth and angiogenesis and upregulate the cancer stem cell-like phenotype. However, TAMs inhibit the metastasis of OS. Therefore, much attention has been paid to investigating the mechanism of TAMs in OS development and the progression of immunotherapy for OS. In this article, we aim to summarize the roles of TAMs in OS and the major findings on the application of TAMs in OS treatment.

LncRNA MALAT1 Promotes Tumor Angiogenesis by Regulating MicroRNA-150-5p/VEGFA Signaling in Osteosarcoma: In-Vitro and In-Vivo Analyses.

The present study aims to analyze the expression of long noncoding RNA (lncRNA) metastasis-associated lung adenocarcinoma transcript 1 (MALAT1) in human osteosarcoma (OS) cells and to investigate its role in OS-induced angiogenesis. MALAT1 expression in OS cells was significantly higher than in normal osteoblasts. The functional analysis indicated that MALAT1 appears to enhance OS-induced angiogenesis, in vitro and in vivo analyses, endothelial cell proliferation and migration, chick embryo angiogenesis assay, and zebrafish xenograft model. Mechanistically, silencing MALAT1 downregulated vascular endothelial growth factor A (VEGFA) expression and upregulated miR-150-5p expression in OS cells, and MALAT1-mediated angiogenic induction by VEGFA in OS microenvironment. Moreover, MALAT1 directly targeted miR-150-5p and miR-150-5p directly target VEGFA in OS. Overexpression of miR-150-5p downregulates VEGFA expression in OS. More notably, we showed that MALAT1 induced angiogenesis in OS microenvironment by upregulating the expression of VEGFA via targeting miR-150-5p. Overall, our findings suggest that MALAT1 promotes angiogenesis by regulating the miR-150-5p/VEGFA signaling in OS microenvironment. The findings of the molecular mechanisms of MALAT1 in tumor angiogenesis offer a new viewpoint on OS treatment.

Investigating Optimal Chemotherapy Options for Osteosarcoma Patients through a Mathematical Model.

Simple SummaryOsteosarcoma is a rare type of cancer with poor prognoses. However, to the best of our knowledge, there are no mathematical models that study the impact of chemotherapy treatments on the osteosarcoma microenvironment. In this study, we developed a data driven mathematical model to analyze the dynamics of the important players in three groups of osteosarcoma tumors with distinct immune patterns in the presence of the most common chemotherapy drugs. The results indicate that the treatments’ start times and optimal dosages depend on the unique growth rate of the tumor, which implies the necessity of personalized medicine. Furthermore, the developed model can be extended by others to build models that can recommend individual-specific optimal dosages.Since all tumors are unique, they may respond differently to the same treatments. Therefore, it is necessary to study their characteristics individually to find their best treatment options. We built a mathematical model for the interactions between the most common chemotherapy drugs and the osteosarcoma microenvironments of three clusters of tumors with unique immune profiles. We then investigated the effects of chemotherapy with different treatment regimens and various treatment start times on the behaviors of immune and cancer cells in each cluster. Saliently, we suggest the optimal drug dosages for the tumors in each cluster. The results show that abundances of dendritic cells and HMGB1 increase when drugs are given and decrease when drugs are absent. Populations of helper T cells, cytotoxic cells, and IFN- grow, and populations of cancer cells and other immune cells shrink during treatment. According to the model, the MAP regimen does a good job at killing cancer, and is more effective than doxorubicin and cisplatin combined or methotrexate alone. The results also indicate that it is important to consider the tumor’s unique growth rate when deciding the treatment details, as fast growing tumors need early treatment start times and high dosages.

MicroRNA-432-5p regulates sprouting and intussusceptive angiogenesis in osteosarcoma microenvironment by targeting PDGFB

Osteosarcoma (OS) is a type of bone tumor conferred with high metastatic potential. Attainable growth of tumors necessitates functional vasculature mediated by sprouting angiogenesis (SA) and intussusceptive angiogenesis (IA). However, the regulation of IA and SA is still unclear in OS. To understand the mechanisms adopted by OS to induce angiogenesis, initially, we assessed the expression profile of a set of miRNAs' in both OS cells (SaOS2 and MG63) and normal bone cells. Amongst them, miR-432-5p was found to be highly downregulated in OS. The functional role of miR-432-5p in OS was further analyzed using miR-432-5p mimic/inhibitor. Platelet-derived growth factor-B (PDGFB) was found to be a putative target of miR-432-5p and it was further confirmed that the PDGFB 3′UTR is directly targeted by miR-432-5p using the luciferase reporter gene system. PDGFB was found to be secreted by OS to regulate angiogenesis by targeting the cells in its microenvironment. The conditioned medium obtained from miR-432-5p mimic transfected MG63 and SaOS2 cells decreased cell viability, proliferation, migration, and aorta ring formation in endothelial cells. The miRNA mimic/inhibitor transfected MG63 and SaOS2 cells were placed on SA (day 6) and IA (day 9) phase of CAM development to analyze SA and IA mechanisms. It was found that miR-432-5p mimic transfection in OS promotes the transition of SA to IA which was documented by the angiogenic parameters and SA and IA-associated gene expression. Interestingly, this outcome was also supported by the zebrafish tumor xenograft model. Corroborating these results, it is clear that miR-432-5p expression in OS cells regulates SA and IA by targeting PDGFB genes. We conclude that targeting miR-432-5p/PDGFB signaling can be a potential therapeutic strategy to treat OS along with other existing strategies.MicroRNA-432-5p expression in osteosarcoma cells regulates sprouting and intussusceptive angiogenesis by targeting PDGFB genes. MicroRNA-432-5p/PDGFB signaling can be targeted to treat angiogenesis in osteosarcoma along with other strategies which will further strengthen the effectiveness of antiangiogenic therapy.

A Hypoxia Gene-Based Signature to Predict the Survival and Affect the Tumor Immune Microenvironment of Osteosarcoma in Children.

Osteosarcoma is a quickly developing, malignant cancer of the bone, which is associated with a bad prognosis. In osteosarcoma, hypoxia promotes the malignant phenotype, which results in a cascade of immunosuppressive processes, poor prognosis, and a high risk of metastasis. Nonetheless, additional methodologies for the study of hyperoxia in the tumor microenvironment also need more analysis. We obtained 88 children patients with osteosarcoma from the Therapeutically Applicable Research to Generate Effective Treatment (TARGET) database and 53 children patients with RNA sequence and clinicopathological data from the Gene Expression Omnibus (GEO). We developed a four-gene signature related to hypoxia to reflect the immune microenvironment in osteosarcoma that predicts survival. A high-risk score indicated a poor prognosis and immunosuppressive microenvironment. The presence of the four-gene signature related to hypoxia was correlated with clinical and molecular features and was an important prognostic predictor for pediatric osteosarcoma patients. In summary, we established and validated a four-gene signature related to hypoxia to forecast recovery and presented an independent prognostic predictor representing overall immune response strength within the osteosarcoma microenvironment.

Data-Driven Mathematical Model of Osteosarcoma.

Simple SummaryOsteosarcoma is the most common primary bone tumor and has a poor prognosis. Therefore, it is important to understand the mechanism of the development of osteosarcoma to overcome therapy resistance. Several mathematical models have been developed to study the initiation and progression of many cancer types. However, there are currently no mathematical models for the progression of osteosarcoma, to the best of our knowledge. In this work, we develop a data-driven mathematical model to analyze the impact of the immune cell interactions on the growth of osteosarcoma tumors that have distinct immune patterns. Our model provides a foundation for investigating the effect of various treatments on the dynamics of key players in the primary tumor, including immune cells and cytokines, and ultimately the whole tumor.As the immune system has a significant role in tumor progression, in this paper, we develop a data-driven mathematical model to study the interactions between immune cells and the osteosarcoma microenvironment. Osteosarcoma tumors are divided into three clusters based on their relative abundance of immune cells as estimated from their gene expression profiles. We then analyze the tumor progression and effects of the immune system on cancer growth in each cluster. Cluster 3, which had approximately the same number of naive and M2 macrophages, had the slowest tumor growth, and cluster 2, with the highest population of naive macrophages, had the highest cancer population at the steady states. We also found that the fastest growth of cancer occurred when the anti-tumor immune cells and cytokines, including dendritic cells, helper T cells, cytotoxic cells, and IFN-, switched from increasing to decreasing, while the dynamics of regulatory T cells switched from decreasing to increasing. Importantly, the most impactful immune parameters on the number of cancer and total cells were the activation and decay rates of the macrophages and regulatory T cells for all clusters. This work presents the first osteosarcoma progression model, which can be later extended to investigate the effectiveness of various osteosarcoma treatments.

Local administration of IL-12 with an HC vector results in local and metastatic tumor control in pediatric osteosarcoma

Osteosarcoma is the most frequent and aggressive bone tumor in children and adolescents, with a long-term survival rate of 30%. Interleukin-12 (IL-12) is a potent cytokine that bridges innate and adaptive immunity, triggers antiangiogenic responses, and achieves potent antitumor effects. In this work, we evaluated the antisarcoma effect of a high-capacity adenoviral vector encoding mouse IL-12. This vector harbored a mifepristone-inducible system for controlled expression of IL-12 (High-Capacity adenoviral vector enconding the EF1α promoter [HCA-EFZP]-IL-12). We found that local administration of the vector resulted in a reduction in the tumor burden, extended overall survival, and tumor eradication. Moreover, long-term survivors exhibited immunological memory when rechallenged with the same tumor cells. Treatment with HCA-EFZP-IL-12 also resulted in a significant decrease in lung metastasis. Immunohistochemical analyses showed profound remodeling of the osteosarcoma microenvironment with decreases in angiogenesis and macrophage and myeloid cell numbers. In summary, our data underscore the potential therapeutic value of IL-12 in the context of a drug-inducible system that allows controlled expression of this cytokine, which can trigger a potent antitumor immune response in primary and metastatic pediatric osteosarcoma.

Information Transfer and Biological Significance of Neoplastic Exosomes in the Tumor Microenvironment of Osteosarcoma.

Osteosarcoma is a highly invasive kind of malignant bone tumor. Exosomes are a type of extracellular vesicles that play an important role in intercellular communication in the microenvironment. Tumor cell progression is promoted through the interaction between exosomes and cells in the microenvironment (including immune cells, mesenchymal cells, and endothelial cells) during tumor development. Neoplastic exosomes can carry a variety of biological information molecules, such as proteins, lipids, and nucleic acids. These molecules play an important clinical role, not only being able domesticate the recipient cells but also being recognized as tumor specific markers. At the same time, exosomes secreted by osteosarcoma can also cooperate with antigen-presenting cells to activate the body’s immune response and then to exert anti-tumor effects. Studies on exosomes may be a breakthrough in the search for a new osteosarcoma treatment. In this study, we review the role of neoplastic exosomes in the osteosarcoma microenvironment, summarize their potential as tumor markers, and investigate their clinical application prospects.

The Role of Pre-Clinical 3-Dimensional Models of Osteosarcoma.

Treatment for osteosarcoma (OS) has been largely unchanged for several decades, with typical therapies being a mixture of chemotherapy and surgery. Although therapeutic targets and products against cancer are being continually developed, only a limited number have proved therapeutically active in OS. Thus, the understanding of the OS microenvironment and its interactions are becoming more important in developing new therapies. Three-dimensional (3D) models are important tools in increasing our understanding of complex mechanisms and interactions, such as in OS. In this review, in vivo animal models, in vitro 3D models and in ovo chorioallantoic membrane (CAM) models, are evaluated and discussed as to their contribution in understanding the progressive nature of OS, and cancer research. We aim to provide insight and prospective future directions into the potential translation of 3D models in OS.

Identification of Immune-Related Prognostic Genes and LncRNAs Biomarkers Associated With Osteosarcoma Microenvironment.

Osteosarcoma (OS) is the most common malignancy of the bone that occurs majorly in young people and adolescents. Although the survival of OS patients markedly improved by complete surgical resection and chemotherapy, the outcome is still poor in patients with recurrent and/or metastasized OS. Thus, identifying prognostic biomarkers that reflect the biological heterogeneity of OS could lead to better interventions for OS patients. Increasing studies have indicated the association between immune-related genes (IRGs) and cancer prognosis. In the present study, based on the data concerning OS obtained from TARGET (Therapeutically Applicable Research to Generate Effective Treatments) database, we constructed a classifier containing 12 immune-related (IR) long non-coding RNAs (lncRNAs) and 3 IRGs for predicting the prognosis of OS by using the least absolute shrinkage and selection operation Cox regression. Besides, based on the risk score calculated by the classifier, the samples were divided into high- and low-risk groups. We further investigated the tumor microenvironment of the OS samples by ESTIMATE and CIBERSORT algorithms between the two groups. Finally, we identified three small molecular drugs with potential therapeutic value for OS patients with high-risk score. Our results suggest that the IRGs and IR-lncRNAs–based classifier could be used as a reliable prognostic predictor for OS survival.

Abstract A34: Hypoxia signaling pathway is frequently involved in pediatric osteosarcoma microenvironment, as diagnostic and prognostic biomarkers, but also as new therapeutic targets

Abstract Osteosarcoma is the first bone cancer diagnosed in adolescent and young adults. Multiple studies involved a deregulation of osteoblast, osteoclast, or microenvironment genes in their development and progression. Nevertheless, no focus was already done in the oxygen-modulated environment of those cancers. Our objectives in this study were to determine, first, the presence of hypoxia deregulation in a cohort of pediatric osteosarcomas (pOS at diagnosis) and in 4 PDCLs (patient-derived cell lines from diagnostic samples). For this purpose, we performed CGHarray for 67 samples and a validation by semiquantitative PCR in another cohort of 20 samples. We also explored by immunohistochemistry in 30 tumor specimens protein expressions of key biomarkers from the hypoxic signaling pathway. Those biomarkers were validated and assessed functionally by immunofluorescence and Western blotting in PDCLs and paired xenografts. All those results in the pOS collections were correlated to survivals and response to first-line therapies. Secondly, the role of hypoxia modulation in PDCLs was determined using variations of oxygen levels from 21% to 5% on cell proliferation characteristics and protein parameters. Finally, to understand how the process of hypoxia is a potential target for pOS treatment, we inhibited different targets of the mTor/HIF1alpha pathway in those PDCLs. As expected, the hypoxia signaling pathway was highly expressed in pOS (tumor samples and PDCLs). Several biomarkers (for example, ULK1, USP33, VEGFR2, CCL7, etc.) were overexpressed in specific groups, linking them significantly to prognosis and a response to chemotherapy. Most of them were involved in the metabolism, autophagy, or angiogenic processes. The PDCLs also expressed in vitro and in xenografts several proteins of this hypoxic pathway as in tumors themselves (pS6, phosphor-mTor, pAKT, HIF1alpha, HIF2alpha). The induction of HIF1alpha during oxygen decrease is early and constant in PDCLs. mTor and HIF2alpha were not induced by the variation of oxygen and were constantly expressed in the cells. Surprisingly, most of the PDCLs increase their proliferation rate in hypoxic conditions, but do not change their microscopic aspects. Finally, the inhibition of mTor and HIF1alpha with rapamycine and irinotecan, respectively, decreases the cell proliferation with a complete inhibition of the targets. In conclusion, hypoxia seems to be frequently involved in pOS through different downstream signaling processes and might be a new potential way of treatment. Citation Format: Marina Pierrevelcin, Audrey Grain, Aurelien Tripp, Adeline Obrecht, Benoit Lhermitte, Noelle Weingertner, Nathalie Gaspar, Pascal Villa, Isabelle Lelong-Rebel, Françoise Redini, Monique Dontenwill, Natacha Entz-Werlé. Hypoxia signaling pathway is frequently involved in pediatric osteosarcoma microenvironment, as diagnostic and prognostic biomarkers, but also as new therapeutic targets [abstract]. In: Proceedings of the AACR Special Conference on the Advances in Pediatric Cancer Research; 2019 Sep 17-20; Montreal, QC, Canada. Philadelphia (PA): AACR; Cancer Res 2020;80(14 Suppl):Abstract nr A34.

Exosomes Secreted by Adipose-Derived Mesenchymal Stem Cells Foster Metastasis and Osteosarcoma Proliferation by Increasing COLGALT2 Expression.

ObjectivesHomosapien collagen beta (1-O) galactosyl transferase 2 (COLGALT2) is an important enzyme during collagen glycosylation, yet its biological functions in cancer are incompletely understood. Our previous study revealed that in the osteosarcoma microenvironment, adipose-derived mesenchymal stem cells (ADSCs) demonstrate cancer-promoting effects, but the exact mechanisms remain unclear. The aim of this study was to investigate the role of COLGALT2 in the osteosarcoma-fostering effects of ADSCs.Materials and MethodsIn this study, we compared COLGALT2 expression between primary and metastatic osteosarcoma tissues and found that metastatic tissues expressed significantly higher COLGALT2 levels. Then, we isolated and identified exosomes secreted by ADSCs. Additionally, we assessed the roles of ADSC exosomes and COLGALT2 in the osteosarcoma-promoting effects of ADSCs.ResultsOur results showed that ADSC exosomes could foster the invasion, migration, and proliferation of osteosarcoma cells, together with increasing COLGALT2 expression. COLGALT2 inhibition in MG63 cells suppressed the ADSC exosome-mediated fostering of osteosarcoma cell invasion, migration and proliferation in vitro. Conversely, COLGALT2 overexpression promoted U-2OS cell invasion, migration and proliferation in vitro. Additionally, COLGALT2 inhibition attenuated metastasis and tumor growth, and ADSC exosomes promoted tumor progression, as demonstrated in a nude mouse model of osteosarcoma.ConclusionAccording to these data, ADSC exosomes foster osteosarcoma progression by increasing COLGALT2 expression in osteosarcoma cells.

The Osteosarcoma Microenvironment: A Complex But Targetable Ecosystem.

Osteosarcomas are the most frequent primary bone sarcomas, affecting mainly children, adolescents, and young adults, and with a second peak of incidence in elderly individuals. The current therapeutic management, a combined regimen of poly-chemotherapy and surgery, still remains largely insufficient, as patient survival has not improved in recent decades. Osteosarcomas are very heterogeneous tumors, both at the intra- and inter-tumor level, with no identified driver mutation. Consequently, efforts to improve treatments using targeted therapies have faced this lack of specific osteosarcoma targets. Nevertheless, these tumors are inextricably linked to their local microenvironment, composed of bone, stromal, vascular and immune cells and the osteosarcoma microenvironment is now considered to be essential and supportive for growth and dissemination. This review describes the different actors of the osteosarcoma microenvironment and gives an overview of the past, current, and future strategies of therapy targeting this complex ecosystem, with a focus on the role of extracellular vesicles and on the emergence of multi-kinase inhibitors.