Cells of origin in osteosarcoma: mesenchymal stem cells or osteoblast committed cells?

Osteocytes and Cancer

PURPOSE OF REVIEW

While the function of osteocytes under physiologic conditions is well defined, their role and involvement in cancer disease remains relatively unexplored, especially in a context of non-bone metastatic cancer. This review will focus on describing the more advanced knowledge regarding the interactions between osteocytes and cancer.

RECENT FINDINGS

We will discuss the involvement of osteocytes in the onset and progression of osteosarcoma, with the common bone cancers, as well as the interaction that is established between osteocytes and multiple myeloma. Mechanisms responsible for cancer dissemination to bone, as frequently occur with advanced breast and prostate cancers, will be reviewed. While a role for osteocytes in the stimulation and proliferation of cancer cells has been reported, protective effects of osteocytes against bone colonization have been described as well, thus increasing ambiguity regarding the role of osteocytes in cancer progression and dissemination. Lastly, supporting the idea that skeletal defects can occur also in the absence of direct cancer dissemination or osteolytic lesions directly adjacent to the bone, our recent findings will be presented showing that in the absence of bone metastases, the bone microenvironment and, particularly, osteocytes, can manifest a clear and dramatic response to the distant, non-metastatic tumor. Our observations support new studies to clarify whether treatments designed to preserve the osteocytes can be combined with traditional anticancer therapies, even when bone is not directly affected by tumor growth.

Ubiquitin-specific proteases as therapeutic targets in paediatric primary bone tumours?

In children and young adults, primary malignant bone tumours are mainly composed of osteosarcoma and Ewing's sarcoma. Despite advances in treatments, nearly 40% of patients succumb to these diseases. In particular, the clinical outcome of metastatic osteosarcoma or Ewing's sarcoma remains poor, with less than 30% of patients who develop metastases surviving five years after initial diagnosis. Over the last decade, the cancer research community has shown considerable interest in the processes of protein ubiquitination and deubiquitination. In particular, a growing number of studies show the relevance to target the ubiquitin-specific protease (USP) family in various cancers. This review provides an update on the current knowledge regarding the implication of these USPs in the progression of bone sarcoma: osteosarcoma and Ewing's sarcoma.

Machine-Learning-Based m5C Score for the Prognosis Diagnosis of Osteosarcoma

Background

Osteosarcoma is a common and highly metastatic malignant tumor, and m5C RNA methylation regulates various biological processes. The purpose of this study was to explore the prognostic role of m5C in osteosarcoma using machine learning.

Methods

Osteosarcoma gene data and the corresponding clinical information were downloaded from the GEO database. Machine learning methods were used to screen m5C-related genes and construct m5C scores. In addition, the clusterProfiler package was used to predict the m5C-related functional pathways. xCell and CIBERSORT were used to calculate the immune microenvironment cells. GSVA was applied to analyze different categories of m5C genes, and the correlation between the GSVA and m5C scores was evaluated.

Results

Twenty m5C genes were identified, and 54 related genes were screened. The m5C score was constructed based on the PCA score. With an increase in the m5C score, the expression of m5C genes and their related genes changed. Functional analysis indicated that the focal adhesion, cell-substrate adherens junction, cell adhesion molecule binding, and E2F targets might change with the m5C score. The naive B cells and CD4⁺ memory T cell also changed with the m5C score. The results of the correlation analysis showed that the m5C score was significantly correlated with the reader and eraser genes.

Conclusion

The m5C score might be a prognostic index for osteosarcoma.

Suppression of Estrogen Receptor Alpha Inhibits Cell Proliferation, Differentiation and Enhances the Chemosensitivity of P53-Positive U2OS Osteosarcoma Cell

Osteosarcoma is a highly malignant musculoskeletal tumor that is commonly noticed in adolescent children, young children, and elderly adults. Due to advances in surgery, chemotherapy and imaging technology, survival rates have improved to 70–80%, but chemical treatments do not enhance patient survival; in addition, the survival rate after chemical treatments is still low. The most obvious clinical feature of osteosarcoma is new bone formation, which is called “sun burst”. Estrogen receptor alpha (ERα) is an essential feature of osteogenesis and regulates cell growth in various tumors, including osteosarcoma. In this study, we sought to investigate the role of ERα in osteosarcoma and to determine if ERα can be used as a target to facilitate the chemosensitivity of osteosarcoma to current treatments. The growth rate of each cell clone was assayed by MTT and trypan blue cell counting, and cell cycle analysis was conducted by flow cytometry. Osteogenic differentiation was induced by osteogenic induction medium and quantified by ARS staining. The effects of ERα on the chemoresponse of OS cells treated with doxorubicin were evaluated by colony formation assay. Mechanistic studies were conducted by examining the levels of proteins by Western blot. The role of ERα on OS prognosis was investigated by an immunohistochemical analysis of OS tissue array. The results showed an impaired growth rate and a decreased osteogenesis ability in the ERα-silenced P53(+) OS cell line U2OS, but not in P53(−) SAOS2 cells, compared with the parental cell line. Cotreatment with tamoxifen, an estrogen receptor inhibitor, increased the sensitivity to doxorubicin, which decreased the colony formation of P53(+) U2OS cells. Cell cycle arrest in the S phase was observed in P53(+) U2OS cells cotreated with low doses of doxorubicin and tamoxifen, while increased levels of apoptosis factors indicated cell death. Moreover, patients with ER−/P53(+) U2OS showed better chemoresponse rates (necrosis rate > 90%) and impaired tumor sizes, which were compatible with the findings of basic research. Taken together, ERα may be a potential target of the current treatments for osteosarcoma that can control tumor growth and improve chemosensitivity. In addition, the expression of ERα in osteosarcoma can be a prognostic factor to predict the response to chemotherapy.

Mesenchymal Stem Cells and Extracellular Vesicles in Osteosarcoma Pathogenesis and Therapy

Osteosarcoma (OS) is an aggressive bone tumor that mainly affects children and adolescents. OS has a strong tendency to relapse and metastasize, resulting in poor prognosis and survival. The high heterogeneity and genetic complexity of OS make it challenging to identify new therapeutic targets. Mesenchymal stem cells (MSCs) are multipotent stem cells that can differentiate into adipocytes, osteoblasts, or chondroblasts. OS is thought to originate at some stage in the differentiation process of MSC to pre-osteoblast or from osteoblast precursors. MSCs contribute to OS progression by interacting with tumor cells via paracrine signaling and affect tumor cell proliferation, invasion, angiogenesis, immune response, and metastasis. Extracellular vesicles (EVs), secreted by OS cells and MSCs in the tumor microenvironment, are crucial mediators of intercellular communication, driving OS progression by transferring miRNAs/RNA and proteins to other cells. MSC-derived EVs have both pro-tumor and anti-tumor effects on OS progression. MSC-EVs can be also engineered to deliver anti-tumor cargo to the tumor site, which offers potential applications in MSC-EV-based OS treatment. In this review, we highlight the role of MSCs in OS, with a focus on EV-mediated communication between OS cells and MSCs and their role in OS pathogenesis and therapy.

Kaposi's sarcoma herpesvirus is associated with osteosarcoma in Xinjiang populations

Osteosarcoma is the most common malignant tumor of bone predominately affecting adolescents and young adults. Based on animal studies, a viral etiology of osteosarcoma was proposed more than a half-century ago, but no viral association with human osteosarcoma has been found. The Uyghur ethnic population in Xinjiang, China, has an unusually high prevalence of Kaposi's sarcoma-associated herpesvirus (KSHV) infection and elevated incidence of osteosarcoma. In the current study, we explored the possible association of KSHV infection and osteosarcoma occurrence. Our seroepidemiological study revealed that KSHV prevalence was significantly elevated in Uyghur osteosarcoma patients versus the general Uyghur population (OR, 10.23; 95%CI, 4.25, 18.89). The KSHV DNA genome and viral latent nuclear antigen LANA were detected in most osteosarcoma tumor cells. Gene expression profiling analysis showed that KSHV-positive osteosarcoma represents a distinct subtype of osteosarcomas with viral gene-activated signaling pathways important for osteosarcoma development. We conclude that KSHV infection is a risk factor for osteosarcoma, and KSHV is associated with some osteosarcomas, representing a newly identified viral-associated endemic cancer.

Innovative Biomaterials for the Treatment of Bone Cancer

Bone cancer is a demanding challenge for contemporary medicine due to its high frequency of presentation and significant heterogeneity of malignant lesions developing within the bone. To date, available treatments are rarely curative and are primarily aimed at prolonging patients' survival and ameliorating their quality of life. Furthermore, both pharmacological and surgical therapies are aggravated by a consistent burden of adverse events and subsequent disability due to the loss of healthy bone structural and functional properties. Therefore, great research efforts are being made to develop innovative biomaterials able to selectively inhibit bone cancer progression while reducing the loss of bone structural properties secondary to local tissue invasion. In this review, we describe the state of the art of innovative biomaterials for the treatment of bone cancer. Along with physiological bone remodeling, the development of bone metastasis and osteosarcoma will be depicted. Subsequently, recent advances on nanocarrier-based drug delivery systems, as well as the application of novel, multifunctional biomaterials for the treatment of bone cancer will be discussed. Eventually, actual limitations and promising future perspectives regarding the employment of such approaches in the clinical scenario will be debated.

Single-Cell Transcriptomics Reveals the Complexity of the Tumor Microenvironment of Treatment-Naive Osteosarcoma

Osteosarcoma (OS), which occurs most commonly in adolescents, is associated with a high degree of malignancy and poor prognosis. In order to develop an accurate treatment for OS, a deeper understanding of its complex tumor microenvironment (TME) is required. In the present study, tissues were isolated from six patients with OS, and then subjected to single-cell RNA sequencing (scRNA-seq) using a 10× Genomics platform. Multiplex immunofluorescence staining was subsequently used to validate the subsets identified by scRNA-seq. ScRNA-seq of six patients with OS was performed prior to neoadjuvant chemotherapy, and data were obtained on 29,278 cells. A total of nine major cell types were identified, and the single-cell transcriptional map of OS was subsequently revealed. Identified osteoblastic OS cells were divided into five subsets, and the subsets of those osteoblastic OS cells with significant prognostic correlation were determined using a deconvolution algorithm. Thereby, different transcription patterns in the cellular subtypes of osteoblastic OS cells were reported, and key transcription factors associated with survival prognosis were identified. Furthermore, the regulation of osteolysis by osteoblastic OS cells via receptor activator of nuclear factor kappa-B ligand was revealed. Furthermore, the role of osteoblastic OS cells in regulating angiogenesis through vascular endothelial growth factor-A was revealed. C3_TXNIP⁺ macrophages and C5_IFIT1⁺ macrophages were found to regulate regulatory T cells and participate in CD8⁺ T cell exhaustion, illustrating the possibility of immunotherapy that could target CD8⁺ T cells and macrophages. Our findings here show that the role of C1_osteoblastic OS cells in OS is to promote osteolysis and angiogenesis, and this is associated with survival prognosis. In addition, T cell depletion is an important feature of OS. More importantly, the present study provided a valuable resource for the in-depth study of the heterogeneity of the OS TME.

The Immune Landscape of Osteosarcoma: Implications for Prognosis and Treatment Response

Osteosarcoma (OS) is a high-grade malignant stromal tumor composed of mesenchymal cells producing osteoid and immature bone, with a peak of incidence in the second decade of life. Hence, although relatively rare, the social impact of this neoplasm is particularly relevant. Differently from carcinomas, molecular genetics and the role of the tumor microenvironment in the development and progression of OS are mainly unknown. Indeed, while the tumor microenvironment has been widely studied in other solid tumor types and its contribution to tumor progression has been definitely established, tumor-stroma interaction in OS has been quite neglected for years. Only recently have new insights been gained, also thanks to the availability of new technologies and bioinformatics tools. A better understanding of the cross-talk between the bone microenvironment, including immune and stromal cells, and OS will be key not only for a deeper knowledge of osteosarcoma pathophysiology, but also for the development of novel therapeutic strategies. In this review, we summarize the current knowledge about the tumor microenvironment in OS, mainly focusing on immune cells, discussing their role and implication for disease prognosis and treatment response.

Molecular mechanisms underpinning sarcomas and implications for current and future therapy

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

Alterations of epigenetic regulators and P53 mutations in murine mesenchymal stem cell cultures: A possible mechanism of spontaneous transformation

BACKGROUND

Recent studies demonstrated the involvement of mesenchymal stem/stromal cells (MSCs) in carcinogenesis, but the molecular mechanism behind this transformation is still obscured.

OBJECTIVE

To screen both the expression levels of polycomb and trithorax epigenetic regulators and TrP53 mutations in early and late MSC culture passages in an attempt to decipher the mechanism of spontaneous transformation.

METHODS

The study was conducted on early and late passages of MSC culture model from C57BL/6J mice. The expression profile of 84 epigenetic regulators was examined using RT2 profiler PCR array. TrP53 mutations in the DNA binding domain was screened. Codons, amino acids positions and the corresponding human variants were detected in P53 sequences.

RESULTS

Sixty-two epigenetic regulators were dysregulated. Abnormalities were detected starting the third passage. Nine regulators were dysregulated in all passages. (C>G) substitution P53 mutation was detected in passage 3 resulting in Ser152Arg substitution. Passages 6, 9, 12 and the last passage showed T>C substitution resulting in Cys235Arg substitution. The last passage had T deletion and A insertion resulting in frame shift mutations changing the p.Phe286Ser and p.Asn103Lys respectively.

CONCLUSION

In vitro expanded MSCs undergo transformation through alteration of epigenetic regulators which results in genomic instability and frequent P53 mutations.

Curcumin-Loaded Nanoparticles Impair the Pro-Tumor Activity of Acid-Stressed MSC in an In Vitro Model of Osteosarcoma

In the tumor microenvironment, mesenchymal stromal cells (MSCs) are key modulators of cancer cell behavior in response to several stimuli. Intratumoral acidosis is a metabolic trait of fast-growing tumors that can induce a pro-tumorigenic phenotype in MSCs through the activation of the NF-κB-mediated inflammatory pathway, driving tumor clonogenicity, invasion, and chemoresistance. Recent studies have indicated that curcumin, a natural ingredient extracted from Curcuma longa, acts as an NF-κB inhibitor with anti-inflammatory properties. In this work, highly proliferating osteosarcoma cells were used to study the ability of curcumin to reduce the supportive effect of MSCs when stimulated by acidosis. Due to the poor solubility of curcumin in biological fluids, we used spherical polymeric nanoparticles as carriers (SPN-curc) to optimize its uptake by MSCs. We showed that SPN-curc inhibited the release of inflammatory cytokines (IL6 and IL8) by acidity-stimulated MSCs at a higher extent than by free curcumin. SPN-curc treatment was also successful in blocking tumor stemness, migration, and invasion that were driven by the secretome of acid-stressed MSCs. Overall, these data encourage the use of lipid–polymeric nanoparticles encapsulating NF-κB inhibitors such as curcumin to treat cancers whose progression is stimulated by an activated mesenchymal stroma.

New drug candidates for osteosarcoma: Drug repurposing based on gene expression signature

Osteosarcoma (OS) is an aggressive bone malignancy and the third most common cancer in adolescence. Since the late 1970s, OS therapy and prognosis had only modest improvements, making it appealing to explore new tools that could help ameliorate the treatment. We present a meta-analysis of the gene expression signature of primary OS, and propose small molecules that could reverse this signature. The meta-analysis was performed using GEO microarray series. We first compared gene expression from eleven primary OS against osteoblasts to obtain the differentially expressed genes (DEGs). We later filtered those DEGs by verifying which ones had a concordant direction of differential expression in a validation group of 82 OS samples versus 30 bone marrow mesenchymal stem cells (BM-MSC) samples. A final gene expression signature of 266 genes (98 up and 168 down regulated) was obtained. The L1000CDS² engine was used for drug repurposing. The top molecules predicted to reverse the signature were afatinib (PubChem CID 10184653), BRD-K95196255 (PubChem CID 3242434), DG-041 (PubChem CID 11296282) and CA-074 Me (PubChem CID 23760717). Afatinib (Gilotrif™) is currently used for metastatic non-small-cell lung cancer with EGFR mutations, and in vitro evidence shows antineoplastic potential in OS cells. The other three molecules have reports of antineoplastic effects, but are not currently FDA-approved. Further studies are necessary to establish the potential of these drugs in OS treatment. We believe our results can be an important contribution for the investigation of new therapeutic genetic targets and for selecting new drugs to be tested for OS.

The EMT transcription factor ZEB1 blocks osteoblastic differentiation in bone development and osteosarcoma

Osteosarcoma is an often-fatal mesenchyme-derived malignancy in children and young adults. Overexpression of EMT-transcription factors (EMT-TFs) has been associated with poor clinical outcome. Here, we demonstrated that the EMT-TF ZEB1 is able to block osteoblastic differentiation in normal bone development as well as in osteosarcoma cells. Consequently, overexpression of ZEB1 in osteosarcoma characterizes poorly differentiated, highly metastatic subgroups and its depletion induces differentiation of osteosarcoma cells. Overexpression of ZEB1 in osteosarcoma is frequently associated with silencing of the imprinted DLK-DIO3 locus, which encodes for microRNAs targeting ZEB1. Epigenetic reactivation of this locus in osteosarcoma cells reduces ZEB1 expression, induces differentiation, and sensitizes to standard treatment, thus indicating therapeutic options for ZEB1-driven osteosarcomas. © 2021 The Authors. The Journal of Pathology published by John Wiley & Sons, Ltd. on behalf of The Pathological Society of Great Britain and Ireland.

Translational cell biology of highly malignant osteosarcoma

Highly malignant osteosarcoma (HMO) is the most frequent malignant bone tumor preferentially occurring in adolescents and children with a second more flat peak in patients over the age of 60. The younger patients benefit from combined neoadjuvant chemotherapy with 65-70% 5-year survival rate. In patients with metastatic HMO the 5-year survival rate is consistently poor with approximately 30%. In the last several years strategies for target therapies have been developed by using next generation sequencing (NGS) for defining targetable molecular factors. However, it has so far been challenging to establish an effective target therapy for so-called 'orphan tumors' without recognizable driver mutations, including HMO. The molecular genetic studies using NGS have shown that HMOs are genomically unstable tumors with highly complex chaotic karyotypes. Before the background of this genetic complexity more investigations should be performed in the future for defining targetable biological factors. As the prognosis could not be improved for 40 years one may expect improvements for patients only by gaining a deeper understanding of the cell and molecular biology of HMO. The cell of origin of HMO is being clarified now. The majority of studies indicate that an osteoblastic progenitor cell is probably the cell of origin of HMO and not an undifferentiated mesenchymal stem cell. This means that the established histopathological definition of HMO through verification of osteoid production by the osteoblastic cells is well justified and will probably be the cornerstone for a precise differential diagnosis of HMO also in the years to come.

Cold Atmospheric Plasma: A New Strategy Based Primarily on Oxidative Stress for Osteosarcoma Therapy

Osteosarcoma is the most common primary bone tumor, and its first line of treatment presents a high failure rate. The 5-year survival for children and teenagers with osteosarcoma is 70% (if diagnosed before it has metastasized) or 20% (if spread at the time of diagnosis), stressing the need for novel therapies. Recently, cold atmospheric plasmas (ionized gases consisting of UV-Vis radiation, electromagnetic fields and a great variety of reactive species) and plasma-treated liquids have been shown to have the potential to selectively eliminate cancer cells in different tumors through an oxidative stress-dependent mechanism. In this work, we review the current state of the art in cold plasma therapy for osteosarcoma. Specifically, we emphasize the mechanisms unveiled thus far regarding the action of plasmas on osteosarcoma. Finally, we review current and potential future approaches, emphasizing the most critical challenges for the development of osteosarcoma therapies based on this emerging technique.

ER Stress-Sensor Proteins and ER-Mitochondrial Crosstalk-Signaling Beyond (ER) Stress Response

Recent studies undoubtedly show the importance of inter organellar connections to maintain cellular homeostasis. In normal physiological conditions or in the presence of cellular and environmental stress, each organelle responds alone or in coordination to maintain cellular function. The Endoplasmic reticulum (ER) and mitochondria are two important organelles with very specialized structural and functional properties. These two organelles are physically connected through very specialized proteins in the region called the mitochondria-associated ER membrane (MAM). The molecular foundation of this relationship is complex and involves not only ion homeostasis through the shuttling of calcium but also many structural and apoptotic proteins. IRE1alpha and PERK are known for their canonical function as an ER stress sensor controlling unfolded protein response during ER stress. The presence of these transmembrane proteins at the MAM indicates its potential involvement in other biological functions beyond ER stress signaling. Many recent studies have now focused on the non-canonical function of these sensors. In this review, we will focus on ER mitochondrial interdependence with special emphasis on the non-canonical role of ER stress sensors beyond ER stress.

Sex differences in expression of immune elements emerge in children, young adults and mice with osteosarcoma

BACKGROUND

Males < 40 years old are more likely to be diagnosed with and die from osteosarcoma (OS). The underlying mechanisms may depend on sex differences in immune response.

METHODS

We used SEER data to estimate survival differences between males and females aged < 40 years at OS diagnosis. In NCI TARGET-OS cases, we determined sex differences in gene expression, conducted Gene Set Enrichment Analysis (GSEA), and applied the LM22 signature to identify biologic sex differences. We compared sex differences in gene expression profiles in TARGET-OS to those observed in Sleeping Beauty (SB) transposon mutagenesis accelerated Trp53R270H-mutant mouse-OS and healthy adult osteoblasts.

RESULTS

Males had worse 17-year overall survival than females (SEER p < 0.0001). From 87 TARGET-OS cases, we observed 1018 genes and 69 pathways that differed significantly by sex (adjusted p < 0.05). Pathway and gene lists overlapped with those from mice (p = 0.03) and healthy osteoblasts (p = 0.017), respectively. Pathways that differed significantly by sex were largely immune-based and included the PD-1/PD-L1 immunotherapy pathway. We observed sex differences in M2 macrophages (LM22; p = 0.056) and M1-M2 macrophage transition (GSEA; p = 0.037) in TARGET-OS. LM22 trends were similar in mice. Twenty-four genes differentially expressed by sex in TARGET-OS had existing cancer therapies.

CONCLUSIONS

Sex differences in OS gene expression were similar across species and centered on immune pathways. Identified sex-specific therapeutic targets may improve outcomes in young individuals with OS.

STAT3 and its targeting inhibitors in osteosarcoma

Signal transducer and activator of transcription 3 (STAT3) is one of seven STAT family members involved with the regulation of cellular growth, differentiation and survival. STAT proteins are conserved among eukaryotes and are important for biological functions of embryogenesis, immunity, haematopoiesis and cell migration. STAT3 is widely expressed and located in the cytoplasm in an inactive form. STAT3 is rapidly and transiently activated by tyrosine phosphorylation by a range of signalling pathways, including cytokines from the IL‐6 family and growth factors, such as EGF and PDGF. STAT3 activation and subsequent dimer formation initiates nuclear translocation of STAT3 for the regulation of target gene transcription. Four STAT3 isoforms have been identified, which have distinct biological functions. STAT3 is considered a proto‐oncogene and constitutive activation of STAT3 is implicated in the development of various cancers, including multiple myeloma, leukaemia and lymphomas. In this review, we focus on recent progress on STAT3 and osteosarcoma (OS). Notably, STAT3 is overexpressed and associated with the poor prognosis of OS. Constitutive activation of STAT3 in OS appears to upregulate the expression of target oncogenes, leading to OS cell transformation, proliferation, tumour formation, invasion, metastasis, immune evasion and drug resistance. Taken together, STAT3 is a target for cancer therapy, and STAT3 inhibitors represent potential therapeutic candidates for the treatment of OS.

LncRNA SOX21-AS1 Promotes the Growth and Invasiveness of Osteosarcoma Cells Through miR-7-5p/IRS2 Regulatory Network

BACKGROUND

Osteosarcoma (OS) is commonly known as a bone malignancy, causing a mass of lethality worldwide. Long coding RNAs (lncRNAs) have been widely reported by documents that they exert important functions in the development of cancers. However, the relative mechanism of lncRNA SOX21-AS1 needs to be fully discovered in OS, as it has never been studied in the past.

AIM OF THE STUDY

To find out how SOX21-AS1 materializes its function in OS.

METHODS

qRT-PCR detected RNA expression, and western blot tested the protein level. CCK8 and TUNEL assays were performed to assess cell viability and apoptosis. Next, Transwell analyses were applied to identify OS cell migration and invasion. Luciferase reporter, RIP and RNA pull-down experiments were employed for investigating the relationships among RNAs.

RESULTS

SOX21-AS1 had high expression in OS, and its presence accelerated OS cell proliferation, migration and invasion. Interestingly, we evidenced that SOX21-AS1 sponged miR-7-5p, which then targeted IRS2 in OS cells. SOX21-AS1 competed with IRS2 in binding to miR-7-5p, which formulated the ceRNA signaling in OS. SOX21-AS1 could negatively regulate miR-7-5p expression. Rescue experiments certified that the enhancement of IRS2 would neutralize the inhibition of SOX21-AS1 depletion on OS cell proliferation and metastasis.

CONCLUSIONS

SOX21-AS1 enhances IRS2 level by absorbing miR-7-5p, so as to boost the progression of OS.

Single-cell RNA landscape of intratumoral heterogeneity and immunosuppressive microenvironment in advanced osteosarcoma

Osteosarcoma is the most frequent primary bone tumor with poor prognosis. Through RNA-sequencing of 100,987 individual cells from 7 primary, 2 recurrent, and 2 lung metastatic osteosarcoma lesions, 11 major cell clusters are identified based on unbiased clustering of gene expression profiles and canonical markers. The transcriptomic properties, regulators and dynamics of osteosarcoma malignant cells together with their tumor microenvironment particularly stromal and immune cells are characterized. The transdifferentiation of malignant osteoblastic cells from malignant chondroblastic cells is revealed by analyses of inferred copy-number variation and trajectory. A proinflammatory FABP4+ macrophages infiltration is noticed in lung metastatic osteosarcoma lesions. Lower osteoclasts infiltration is observed in chondroblastic, recurrent and lung metastatic osteosarcoma lesions compared to primary osteoblastic osteosarcoma lesions. Importantly, TIGIT blockade enhances the cytotoxicity effects of the primary CD3+ T cells with high proportion of TIGIT+ cells against osteosarcoma. These results present a single-cell atlas, explore intratumor heterogeneity, and provide potential therapeutic targets for osteosarcoma.

PRRX1 promotes malignant properties in human osteosarcoma

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PRRX1 is a poor-prognosis marker of human osteosarcoma.

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PRRX1 promotes proliferation, invasion, and drug resistance in human osteosarcoma.

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Forskolin was identified using RNA expression signatures of PRRX1 knockdown.

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Forskolin decreased proliferation and migration in human osteosarcoma.

Paired related homeobox 1 (PRRX1) is a marker of limb bud mesenchymal cells, and deficiency of p53 or Rb in Prrx1-positive cells induces osteosarcoma in several mouse models. However, the regulatory roles of PRRX1 in human osteosarcoma have not been defined. In this study, we performed PRRX1 immunostaining on 35 human osteosarcoma specimens to assess the correlation between PRRX1 level and overall survival. In patients with osteosarcoma, the expression level of PRRX1 positively correlated with poor prognosis or the ratio of lung metastasis. Additionally, we found PRRX1 expression on in 143B cells, a human osteosarcoma line with a high metastatic capacity. Downregulation of PRRX1 not only suppressed proliferation and invasion but also increased the sensitivity to cisplatin and doxorubicin. When 143B cells were subcutaneously transplanted into nude mice, PRRX1 knockdown decreased tumor sizes and rates of lung metastasis. Interestingly, forskolin, a chemical compound identified by Connectivity Map analysis using RNA expression signatures during PRRX1 knockdown, decreased tumor proliferation and cell migration to the same degree as PRRX1 knockdown. These results demonstrate that PRRX1 promotes tumor malignancy in human osteosarcoma.

Autophagy in Osteosarcoma Cancer Stem Cells Is Critical Process which Can Be Targeted by the Antipsychotic Drug Thioridazine

Simple Summary

Cancer stem cells (CSCs) represent a minor population of cancer cells with stem cell-like properties and appear as a crucial target in oncology as they are the origin of relapses and resistance to current treatments. Autophagy, which allows the degradation and recycling of cellular components for survival purposes, has been shown to be upregulated in some CSCs, participating in the resistance of these cells. The aim of our study was to analyze the autophagy level and the consequences of targeting this process in osteosarcoma CSCs. Our results indicate that autophagy is a critical process in osteosarcoma CSCs and that targeting this pathway allows to switch their fate from survival to death.

Abstract

Cancer stem cells (CSCs) represent a minor population of cancer cells with stem cell-like properties which are able to fuel tumor growth and resist conventional treatments. Autophagy has been described to be upregulated in some CSCs and to play a crucial role by maintaining stem features and promoting resistance to both hostile microenvironments and treatments. Osteosarcoma (OS) is an aggressive bone cancer which mainly affects children and adolescents and autophagy in OS CSCs has been poorly studied. However, this is a very interesting case because autophagy is often deregulated in this cancer. In the present work, we used two OS cell lines showing different autophagy capacities to isolate CSC-enriched populations and to analyze the autophagy in basal and nutrient-deprived conditions. Our results indicate that autophagy is more efficient in CSCs populations compared to the parental cell lines, suggesting that autophagy is a critical process in OS CSCs. We also showed that the antipsychotic drug thioridazine is able to stimulate, and then impair autophagy in both CSC-enriched populations, leading to autosis, a cell death mediated by the Na+/K⁺ ATPase pump and triggered by dysregulated accumulation of autophagosomes. Taken together, our results indicate that autophagy is very active in OS CSCs and that targeting this pathway to switch their fate from survival to death could provide a novel strategy to eradicate these cells in osteosarcoma.

Creating In Vitro Three-Dimensional Tumor Models: A Guide for the Biofabrication of a Primary Osteosarcoma Model

Osteosarcoma (OS) is a highly aggressive primary bone tumor. The mainstay for its treatment is multiagent chemotherapy and surgical resection, with a 50-70% 5-year survival rate. Despite the huge effort made by clinicians and researchers in the past 30 years, limited progress has been made to improve patient outcomes. As novel therapeutic approaches for OS become available, such as monoclonal antibodies, small molecules, and immunotherapies, the need for OS preclinical model development becomes equally pressing. Three-dimensional (3D) OS models represent an alternative system to study this tumor: In contrast to two-dimensional monolayers, 3D matrices can recapitulate key elements of the tumor microenvironment (TME), such as the cellular interaction with the bone mineralized matrix. The advancement of tissue engineering and biofabrication techniques enables the incorporation of specific TME aspects into 3D models, to investigate the contribution of individual components to tumor progression and enhance understanding of basic OS biology. The use of biomaterials that mimic the extracellular matrix could also facilitate the testing of drugs targeting the TME itself, allowing a larger range of therapeutics to be tested, while averting the ethical implications and high cost associated with in vivo preclinical models. This review aims at serving as a practical guide by delineating the OS TME ("what it is like") and, in turn, propose various biofabrication strategies to create a 3D model ("how to recreate it"), to improve the in vitro representation of the OS tumor and ultimately generate more accurate drug response profiles.

COLEC12 regulates apoptosis of osteosarcoma through Toll-like receptor 4-activated inflammation

OBJECTIVE

To investigate the role of COLEC12 in osteosarcoma and observe the relationship between COLEC12 knockdown and the inflammation of osteosarcoma. Then, further explore whether the process is regulated by TLR4.

METHOD

GEPIA and TCGA systems were used to predict the potential function of COLEC12. Western blot and RT-PCR were used to analyze the protein expression, or mRNA level, of COLEC12 in different tissue or cell lines. The occurrence and development of osteosarcoma were observed by using COLEC12 knockdown lentivirus. The inflammation indexes of osteosarcoma, in vitro and in vivo, were explored. TLR4 knockdown lentivirus was applied to the relationship between COLEC12 and TLR4.

RESULTS

COLEC12 expression in SARC tumor tissue was higher than in normal, and a high expression of COLEC12 in SARC patients had a worse prognostic outcome. Pairwise gene correlation analysis revealed a potential relationship between COLEC12 and TLR4. The COLEC12 expression and mRNA level in the tumor or Saos-2 cells were increased. COLEC12 knockdown lentivirus could inhibit osteosarcoma development, in vivo and vitro, through reducing tumor volume and weight, weakening tumor proliferation, migration, and invasion, and enhancing apoptosis. Furthermore, COLEC12 knockdown could increase inflammation of osteosarcoma, in vivo and in vitro, through inducing myeloperoxidase (MPO), TLR4, NF-κB, and C3, and expression of related inflammatory factors. Finally, TLR4 knockdown lentivirus inhibits the progress of inflammation after COLEC12 regulation, in vivo and vitro.

CONCLUSION

COLEC12 may be able to regulate apoptosis and inflammation of osteosarcoma, and TLR4 may be the downstream target factor of COLEC12 in inflammation.

LRP8 activates STAT3 to induce PD-L1 expression in osteosarcoma

PURPOSE

Targeting programmed death-ligand 1 (PD-L1) may be an effective intervention for osteosarcoma and PD-L1 expression is controlled by diverse regulatory factors. Low-density lipoprotein receptor-related protein 8 (LRP8) regulates osteoblast differentiation and it is unclear whether and how LRP8 could contribute to osteosarcoma pathogenesis. In this study, we investigated the LRP8/signal transducer and activator of transcription 3 (STAT3)/PD-L1 network in osteosarcoma.

METHODS

The expression of LRP8, STAT3, and PD-L1 was measured in osteosarcoma tissues and paired normal tissues. The effects of LRP8 on STAT3 and PD-L1 expression were investigated in an osteosarcoma cell line. The effects on immunosuppression were investigated in an in vitro co-culture system with Jurkat cell line and osteosarcoma cell line. The effects of LRP8 were blocked by a LRP8 neutralizing antibody, dominant-negative STAT3, or STAT3 inhibitor.

RESULTS

LRP8 was overexpressed in osteosarcoma compared to normal tissues and its level was correlated with phospho-STAT3 (p-STAT3) level in osteosarcoma tissues. In osteosarcoma cell lines, LRP8 increased p-STAT3 level and promoted nuclear translocation of STAT3. STAT3 activation also increased PD-L1 mRNA, protein, and promoter activity. In addition, LRP8 enhanced PD-L1 expression via STAT3. In a co-culture system, LRP8 overexpression in an osteosarcoma cell line impaired viability and interleukin-2 secretion of Jurkat cells and induced apoptosis of Jurkat cells. The effects of LRP8 could be blocked by neutralizing LRP8 antibody or STAT3 inhibitor. Blocking LRP8 inhibits proliferation and induces apoptosis of osteosarcoma cells.

CONCLUSIONS

Our results provide evidence for a novel regulation network of LRP8/STAT3/PD-L1 in osteosarcoma and LRP8 may be a potential therapeutic target in osteosarcoma.

Targeting Mechanotransduction in Osteosarcoma: A Comparative Oncology Perspective

Mechanotransduction is the process in which cells can convert extracellular mechanical stimuli into biochemical changes within a cell. While this a normal process for physiological development and function in many organ systems, tumour cells can exploit this process to promote tumour progression. Here we summarise the current state of knowledge of mechanotransduction in osteosarcoma (OSA), the most common primary bone tumour, referencing both human and canine models and other similar mesenchymal malignancies (e.g., Ewing sarcoma). Specifically, we discuss the mechanical properties of OSA cells, the pathways that these cells utilise to respond to external mechanical cues, and mechanotransduction-targeting strategies tested in OSA so far. We point out gaps in the literature and propose avenues to address them. Understanding how the physical microenvironment influences cell signalling and behaviour will lead to the improved design of strategies to target the mechanical vulnerabilities of OSA cells.

Targeting Molecular Mechanisms Underlying Treatment Efficacy and Resistance in Osteosarcoma: A Review of Current and Future Strategies

Osteosarcoma is the most common primary malignant bone tumour in children and adolescents. Due to micrometastatic spread, radical surgery alone rarely results in cure. Introduction of combination chemotherapy in the 1970s, however, dramatically increased overall survival rates from 20% to approximately 70%. Unfortunately, large clinical trials aiming to intensify treatment in the past decades have failed to achieve higher cure rates. In this review, we revisit how the heterogenous nature of osteosarcoma as well as acquired and intrinsic resistance to chemotherapy can account for stagnation in therapy improvement. We summarise current osteosarcoma treatment strategies focusing on molecular determinants of treatment susceptibility and resistance. Understanding therapy susceptibility and resistance provides a basis for rational therapy betterment for both identifying patients that might be cured with less toxic interventions and targeting resistance mechanisms to sensitise resistant osteosarcoma to conventional therapies.

Stearoyl-CoA Desaturase-1 Attenuates the High Shear Force Damage Effect on Human MG63 Osteosarcoma Cells

Mechanical regulation is known as an important regulator in cancer progression and malignancy. High shear force has been found to inhibit the cell cycle progression and result in cell death in various cancer cells. Stearoyl-CoA desaturase (SCD)-1, one of the important lipogenic enzymes, has recently been indicated as a potential pharmaceutical target in cancer therapy. In this study, we determined whether the cell fate control of shear force stimulation is through regulating the SCD-1 expression in cancer cells. Human MG63 osteosarcoma cells were used in this study. 2 and 20 dynes/cm² shear forces were defined as low and high intensities, respectively. A SCD-1 upregulation in human MG63 osteosarcoma cells under 20, but not 2, dynes/cm² shear force stimulation was shown, and this induction was regulated by Smad1/5 and peroxisome proliferator-activated receptor δ (PPARδ) signaling. Moreover, gene knockdown of PPARδ and SCD-1 in human MG63 osteosarcoma cells attenuated the differentiation inhibition and resulted in much more cell death of high shear force initiation. The present study finds a possible auto-protective role of SCD-1 upregulation in high shear force-damaged human MG63 osteosarcoma cells. However, its detailed regulation in the cancer fate decision of high shear force should be further examined.

Modeling the Tumor Microenvironment and Pathogenic Signaling in Bone Sarcoma

Investigations of cancer biology and screening of potential therapeutics for efficacy and safety begin in the preclinical laboratory setting. A staple of most basic research in cancer involves the use of tissue culture plates, on which immortalized cell lines are grown in monolayers. However, this practice has been in use for over six decades and does not account for vital elements of the tumor microenvironment that are thought to aid in initiation, propagation, and ultimately, metastasis of cancer. Furthermore, information gleaned from these techniques does not always translate to animal models or, more crucially, clinical trials in cancer patients. Osteosarcoma (OS) and Ewing sarcoma (ES) are the most common primary tumors of bone, but outcomes for patients with metastatic or recurrent disease have stagnated in recent decades. The unique elements of the bone tumor microenvironment have been shown to play critical roles in the pathogenesis of these tumors and thus should be incorporated in the preclinical models of these diseases. In recent years, the field of tissue engineering has leveraged techniques used in designing scaffolds for regenerative medicine to engineer preclinical tumor models that incorporate spatiotemporal control of physical and biological elements. We herein review the clinical aspects of OS and ES, critical elements present in the sarcoma microenvironment, and engineering approaches to model the bone tumor microenvironment. Impact statement The current paradigm of cancer biology investigation and therapeutic testing relies heavily on monolayer, monoculture methods developed over half a century ago. However, these methods often lack essential hallmarks of the cancer microenvironment that contribute to tumor pathogenesis. Tissue engineers incorporate scaffolds, mechanical forces, cells, and bioactive signals into biological environments to drive cell phenotype. Investigators of bone sarcomas, aggressive tumors that often rob patients of decades of life, have begun to use tissue engineering techniques to devise in vitro models for these diseases. Their efforts highlight how critical elements of the cancer microenvironment directly affect tumor signaling and pathogenesis.

Novel agent DMAMCL suppresses osteosarcoma growth and decreases the stemness of osteosarcoma stem cell

Osteosarcoma (OS) is the most common primary malignancy of bone that mostly affects children, adolescents, and young people. Despite advances have been made in multimodal therapy of OS, the long-term survival rate has reached a plateau, and the main obstacles are bad response to chemotherapy and gained chemoresistance. In this study, we tested the therapeutic effect of a newly reported drug, DMAMCL, on OS. Five human OS cell lines (143B, MNNG, MG63, Saos-2, U-2OS), and the mouse fibroblast cell line (NIH3T3) and human retinal epithelial cell (ARPE19) were used. The anti-tumor effect of DMAMCL was studied by MTS assay or IncuCyte-Zoom (in vitro), and Xenograft-mice-model (in vivo). Changes of cell cycle, apoptotic cells, caspase3/7 activities, and stemness after DMAMCL treatment were investigated. BAX siRNAs were used to knockdown the expression of BAX. Expressions of CyclinB1, CDC2, BCL-2 family, PARP, CD133, and Nanog were measured by Western Blotting. DMAMCL-induced dose-dependent OS cell death in vitro, and suppressed tumor growth and extended the survival of xenograft-bearing mice. DMAMCL-induced G2/M phase arrest in vitro, and apoptosis both in vitro and in vivo. Down-regulation of BAX expression attenuated the DMAMCL-induced OS cell death in vitro. We also found that DMAMCL inhibited the stemness in OS cells. These results indicated that DMAMCL possess therapeutic value in OS and may be a promising candidate for the new drug discovery for OS therapy.

The YAP/TAZ Pathway in Osteogenesis and Bone Sarcoma Pathogenesis

YAP and TAZ are intracellular messengers communicating multiple interacting extracellular biophysical and biochemical cues to the transcription apparatus in the nucleus and back to the cell/tissue microenvironment interface through the regulation of cytoskeletal and extracellular matrix components. Their activity is negatively and positively controlled by multiple phosphorylation events. Phenotypically, they serve an important role in cellular plasticity and lineage determination during development. As they regulate self-renewal, proliferation, migration, invasion and differentiation of stem cells, perturbed expression of YAP/TAZ signaling components play important roles in tumorigenesis and metastasis. Despite their high structural similarity, YAP and TAZ are functionally not identical and may play distinct cell type and differentiation stage-specific roles mediated by a diversity of downstream effectors and upstream regulatory molecules. However, YAP and TAZ are frequently looked at as functionally redundant and are not sufficiently discriminated in the scientific literature. As the extracellular matrix composition and mechanosignaling are of particular relevance in bone formation during embryogenesis, post-natal bone elongation and bone regeneration, YAP/TAZ are believed to have critical functions in these processes. Depending on the differentiation stage of mesenchymal stem cells during endochondral bone development, YAP and TAZ serve distinct roles, which are also reflected in bone tumors arising from the mesenchymal lineage at different developmental stages. Efforts to clinically translate the wealth of available knowledge of the pathway for cancer diagnostic and therapeutic purposes focus mainly on YAP and TAZ expression and their role as transcriptional co-activators of TEAD transcription factors but rarely consider the expression and activity of pathway modulatory components and other transcriptional partners of YAP and TAZ. As there is a growing body of evidence for YAP and TAZ as potential therapeutic targets in several cancers, we here interrogate the applicability of this concept to bone tumors. To this end, this review aims to summarize our current knowledge of YAP and TAZ in cell plasticity, normal bone development and bone cancer.

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.

Implication of the p53-Related miR-34c, -125b, and -203 in the Osteoblastic Differentiation and the Malignant Transformation of Bone Sarcomas

The formation of the skeleton occurs throughout the lives of vertebrates and is achieved through the balanced activities of two kinds of specialized bone cells: the bone-forming osteoblasts and the bone-resorbing osteoclasts. Impairment in the remodeling processes dramatically hampers the proper healing of fractures and can also result in malignant bone diseases such as osteosarcoma. MicroRNAs (miRNAs) are a class of small non-coding single-strand RNAs implicated in the control of various cellular activities such as proliferation, differentiation, and apoptosis. Their post-transcriptional regulatory role confers on them inhibitory functions toward specific target mRNAs. As miRNAs are involved in the differentiation program of precursor cells, it is now well established that this class of molecules also influences bone formation by affecting osteoblastic differentiation and the fate of osteoblasts. In response to various cell signals, the tumor-suppressor protein p53 activates a huge range of genes, whose miRNAs promote genomic-integrity maintenance, cell-cycle arrest, cell senescence, and apoptosis. Here, we review the role of three p53-related miRNAs, miR-34c, -125b, and -203, in the bone-remodeling context and, in particular, in osteoblastic differentiation. The second aim of this study is to deal with the potential implication of these miRNAs in osteosarcoma development and progression.

[Osteoid-forming bone tumors : Morphology and current translational cell biology]

Osteoid osteoma and osteoblastoma are the most important benign osteoid-forming tumors. They grow slowly and are well differentiated. Histologically, the tumor cells show no atypia and no increased mitoses. In typical cases, they can be clearly diagnosed. However, the rare cases on the dividing line between osteoblastoma and osteosarcoma are extremely problematic. In these cases, molecular genetic investigations should contribute to finding the correct diagnosis in the future.Juvenile highly malignant osteosarcoma is the most important malignant osteoid-forming tumor. About 40 years ago, neoadjuvant chemotherapy was introduced for the mostly young patients. This therapy highly significantly improved prognosis. However, a plateau phase was quickly reached and the last several decades have seen no further progress in conventional therapeutic approaches. There is no doubt that further progress can only be achieved on the basis of new molecular genetic and cell biological findings. The target-therapeutic strategies derived from these findings will be discussed in this review.The rare parosteal osteosarcoma and the even rarer periosteal osteosarcoma are mostly not highly malignant tumors that are located on the surface of bone. The parosteal osteosarcoma is usually G1 and the periosteal osteosarcoma G2. Occasionally, the differential diagnosis between a parosteal osteosarcoma and a fibrous dysplasia is difficult. In such rare cases, the detection of GNAS mutations in fibrous dysplasia can prove useful. In contrast to chondromas and chondrosarcomas, periosteal osteosarcomas do not contain IDH1 and IDH2 mutations.

Acquisition of stem associated-features on metastatic osteosarcoma cells and their functional effects on mesenchymal stem cells

BACKGROUND

Osteosarcoma (OS) is the most frequent malignant bone tumor, affecting predominantly children and young adults. Metastases are a major clinical challenge in OS. In this context, 20% of OS patients are diagnosed with metastatic OS, but near 80% of all OS patients could present non-detectable micrometastases at the moment of diagnosis.

METHODS

Osteogenic differentiation; doxorubicin exclusion assay; fluorescence microscopy; RT-qPCR; proteomic analysis.

RESULTS

Our results suggest that metastatic OS cells possess a diminished osteoblastic differentiation potential with a gain of metastatic traits like the capacity to modify intracellular localization of chemodrugs and higher levels of expression of stemness-related genes. On the opposite hand, non-metastatic OS cells possess bone-associated traits like higher osteoblastic differentiation and also an osteoblastic-inducer secretome. OS cells also differ in the nature of their interaction with mesenchymal stem cells (MSCs), with opposites impacts on MSCs phenotype and behavior.

CONCLUSIONS

All this suggests that a major trait acquired by metastatic cells is a switch into a stem-like state that could favor its survival in the pulmonary niche, opening new possibilities for personalized chemotherapeutic schemes.

GENERAL SIGNIFICANCE

Our work provides new insights regarding differences among metastatic and non-metastatic OS cells, with particular emphasis on differentiation potential, multidrug resistance and interaction with MSCs.

Biology and pathogenesis of human osteosarcoma

Osteosarcoma (OS) is a bone tumor of mesenchymal origin, most frequently occurring during the rapid growth phase of long bones, and usually located in the epiphyseal growth plates of the femur or the tibia. Its most common feature is genome disorganization, aneuploidy with chromosomal alterations, deregulation of tumor suppressor genes and of the cell cycle, and an absence of DNA repair. This suggests the involvement of surveillance failures, DNA repair or apoptosis control during osteogenesis, allowing the survival of cells which have undergone alterations during differentiation. Epigenetic events, including DNA methylation, histone modifications, nucleosome remodeling and expression of non-coding RNAs have been identified as possible risk factors for the tumor. It has been reported that p53 target genes or those genes that have their activity modulated by p53, in addition to other tumor suppressor genes, are silenced in OS-derived cell lines by hypermethylation of their promoters. In osteogenesis, osteoblasts are formed from pluripotent mesenchymal cells, with potential for self-renewal, proliferation and differentiation into various cell types. This involves complex signaling pathways and multiple factors. Any disturbance in this process can cause deregulation of the differentiation and proliferation of these cells, leading to the malignant phenotype. Therefore, the origin of OS seems to be multifactorial, involving the deregulation of differentiation of mesenchymal cells and tumor suppressor genes, activation of oncogenes, epigenetic events and the production of cytokines.

Mechanically tunable coaxial electrospun models of YAP/TAZ mechanoresponse and IGF-1R activation in osteosarcoma

Current in vitro methods for assessing cancer biology and therapeutic response rely heavily on monolayer cell culture on hard, plastic surfaces that do not recapitulate essential elements of the tumor microenvironment. While a host of tumor models exist, most are not engineered to control the physical properties of the microenvironment and thus may not reflect the effects of mechanotransduction on tumor biology. Utilizing coaxial electrospinning, we developed three-dimensional (3D) tumor models with tunable mechanical properties in order to elucidate the effects of substrate stiffness and tissue architecture in osteosarcoma. Mechanical properties of coaxial electrospun meshes were characterized with a series of macroscale testing with uniaxial tensile testing and microscale testing utilizing atomic force microscopy on single fibers. Calculated moduli in our models ranged over three orders of magnitude in both macroscale and microscale testing. Osteosarcoma cells responded to decreasing substrate stiffness in 3D environments by increasing nuclear localization of Hippo pathway effectors, YAP and TAZ, while downregulating total YAP. Additionally, a downregulation of the IGF-1R/mTOR axis, the target of recent clinical trials in sarcoma, was observed in 3D models and heralded increased resistance to combination chemotherapy and IGF-1R/mTOR targeted agents compared to monolayer controls. In this study, we highlight the necessity of incorporating mechanical cues in cancer biology investigation and the complexity in mechanotransduction as a confluence of stiffness and culture architecture. Our models provide a versatile, mechanically variable substrate on which to study the effects of physical cues on the pathogenesis of tumors. STATEMENT OF SIGNIFICANCE: The tumor microenvironment plays a critical role in cancer pathogenesis. In this work, we engineered 3D, mechanically tunable, coaxial electrospun environments to determine the roles of the mechanical environment on osteosarcoma cell phenotype, morphology, and therapeutic response. We characterize the effects of varying macroscale and microscale stiffnesses in 3D environments on the localization and expression of the mechanoresponsive proteins, YAP and TAZ, and evaluate IGF-1R/mTOR pathway activation, a target of recent clinical trials in sarcoma. Increased nuclear YAP/TAZ was observed as stiffness in 3D was decreased. Downregulation of the IGF-1R/mTOR cascade in all 3D environments was observed. Our study highlights the complexity of mechanotransduction in 3D culture and represents a step towards controlling microenvironmental elements in in vitro cancer investigations.

Osteosarcoma in the Post Genome Era: Preclinical Models and Approaches to Identify Tractable Therapeutic Targets

PURPOSE OF REVIEW

Osteosarcoma (OS) is the most common cancer of bone, yet is classified as a rare cancer. Treatment and outcomes for OS have not substantively changed in several decades. While the decoding of the OS genome greatly advanced the understanding of the mutational landscape of OS, immediately actionable therapeutic targets were not apparent. Here we describe recent preclinical models that can be leveraged to identify, test, and prioritize therapeutic candidates.

RECENT FINDINGS

The generation of multiple high fidelity murine models of OS, the spontaneous disease that arises in pet dogs, and the establishment of a diverse collection of patient-derived OS xenografts provide a robust preclinical platform for OS. These models enable evidence to be accumulated across multiple stages of preclinical evaluation. Chemical and genetic screening has identified therapeutic targets, often demonstrating cross species activity. Clinical trials in both PDX models and in canine OS have effectively tested new therapies for prioritization. Improving clinical outcomes in OS has proven elusive. The integrated target discovery and testing possible through a cross species platform provides validation of a putative target and may enable the rigorous evaluation of new therapies in models where endpoints can be rapidly assessed.

Advances in differentiation therapy for osteosarcoma

Differentiation therapy involves the use of agents that can induce differentiation in cancer cells, with the irreversible loss of tumour phenotype. The application of differentiation therapy in osteosarcoma has made progress because of a better understanding of the potential links between differentiation defects and tumorigenesis. Here, we review recent studies on differentiation therapy for osteosarcoma, describing a variety of differentiation inducers. By highlighting these examples of drug-induced osteosarcoma cell differentiation, we can acquire unique insights into not only osteosarcoma treatment, but also novel approaches to transform differentiating drugs into more effective therapies for other solid tumours.

The Heterogeneity of Osteosarcoma: The Role Played by Cancer Stem Cells

Osteosarcoma is the most common bone sarcoma and is one of the cancer entities characterized by the highest level of heterogeneity in humans. This heterogeneity takes place not only at the macroscopic and microscopic levels, with heterogeneous micro-environmental components, but also at the genomic, transcriptomic and epigenetic levels. Recent investigations have revealed the existence in osteosarcoma of cancer cells with stemness properties. Cancer stem cells are characterized by their specific phenotype and low cycling capacity, and are linked to drug resistance, tumour growth and the metastatic process. In addition, cancer stem cells contribute to the enrichment of tumour heterogeneity. The present manuscript will describe the main characteristic features of cancer stem cells in osteosarcoma and will discuss their impact on maintaining tumour heterogeneity. Their clinical implications will also be briefly addressed.

Anticancer Effects of Constituents of Herbs Targeting Osteosarcoma

Osteosarcoma is a rare primary malignancy of bone that is prone to early metastasis. Resection surgery and chemotherapeutic regimens are current standard treatments for osteosarcoma. However, the long-term survival rate of patients with osteosarcoma is low due to a high risk of metastasis. Hence, a new approach is urgently needed to improve the treatment of osteosarcoma. Compared with chemotherapy, natural active constituents isolated from herbs exhibit less adverse effects and better anti-tumor effects. This study aimed to summarize the anticancer effects of constituents of herbs on the progression and metastasis of osteosarcoma cells. It showed that many constituents of herbs inhibited osteosarcoma by targeting proliferation, matrix metalloproteinases, integrin and cadherin, and angiogenesis. The findings might be beneficial for the development of new drugs and treatment strategies.

Epigenetic alterations in mesenchymal stem cells by osteosarcoma-derived extracellular vesicles

Extracellular vesicles (EVs) are central to intercellular communication and play an important role in cancer progression and development. Osteosarcoma (OS) is an aggressive bone tumour, characterized by the presence of malignant mesenchymal cells. The specific tumour-driving genetic alterations that are associated with OS development are currently poorly understood. Mesenchymal stem cells (MSCs) of osteogenic lineage have been postulated as likely candidates as the cells of origin for OS, thus indicating that MSCs and OS stroma cells may be related cell types. Therefore, this study set out to examine the EV-mediated intercellular crosstalk of MSCs and OS. MSCs and pre-osteoblasts were treated with OS-EVs at different time points, and the epigenetic signature of OS-EVs was assessed by methylation analysis of LINE-1 (long interspersed element) and tumour suppressor genes. In addition, surface markers and expression of specific genes were also evaluated. Our data indicated that OS-EVs mediated LINE-1 hypomethylation in MSCs, whereas an opposite effect was seen in pre-osteoblasts, indicating that MSCs but not pre-osteoblasts were susceptible to epigenetic transformation. Thus, OS-EVs modulated the fate of MSCs by modulating the epigenetic status, and also influenced the expression of genes related to bone microenvironment remodelling. Overall, this study provided evidence that epigenetic regulation appears to be an early event in the transformation of MSCs during the development of OS. Elucidating the mechanisms of EV-mediated communication may lead to new avenues for therapeutic exploitation.

Insulin/IGF-1R, SIRT1, and FOXOs Pathways-An Intriguing Interaction Platform for Bone and Osteosarcoma

Aging is a substantial risk factor for the development of osteoarthritis (OA) and, probably, an essential substrate for the development of neoplastic disease of the bone, such as osteosarcoma, which is the most common malignant mesenchymal primary bone tumor. Genetic studies have established that the insulin/insulin-like growth factor 1 (IGF-1)/phosphatidylinositol-3 kinase (PI3K)/AKT (Protein Kinase B) signal transduction pathway is involved across species, including nematodes, fruit flies, and mammals. SIRT1, a phylogenetically-conserved family of deacetylases, seems to play pleiotropic effects in epithelial malignancies of the liver and interact with the IGF-1/PI3K/AKT signal transduction pathway. Some of the most critical processes in degenerative conditions may indeed include the insulin/IGF1R and SIRT1 signaling pathways as well as some specific transcription factors. The Forkhead box O (FOXO) transcription factors (FOXOs) control diverse cellular functions, such as metabolism, longevity, and cell death. FOXOs play a critical role in the IGF-1/PI3K/AKT signal transduction pathway. FOXOs can indeed be modulated to reduce age-related diseases. FOXOs have advantageous inhibitory effects on fibroblast and myofibroblast activation, which are accompanied by a subsequent excessive production of extracellular matrix. FOXOs can block or decrease the fibrosis levels in numerous organs. Previously, we observed a correlation between nuclear FOXO3 and high caspase-8 expression, which induces cellular apoptosis in response to harmful external stimuli. In this perspective, we emphasize the current advances and interactions involving the insulin/IGF1R, SIRT1, and FOXOs pathways in the bone and osteosarcoma for a better understanding of the mechanisms potentially underpinning tissue degeneration and tumorigenesis.

Lkb1 deletion in periosteal mesenchymal progenitors induces osteogenic tumors through mTORC1 activation

Bone osteogenic sarcoma has a poor prognosis as the exact cell of origin and the signaling pathways underling tumor formation remain undefined. Here, we report an osteogenic tumor mouse model based on the conditional knockout of liver kinase b1 (Lkb1; also known as Stk11) in Cathepsin K (Ctsk)-Cre expressing cells. Lineage tracing studies demonstrated that Ctsk-Cre could label a population of periosteal cells. The cells functioned as mesenchymal progenitors with regard to markers and functional properties. LKB1 deficiency increased proliferation and osteoblast differentiation of Ctsk+ periosteal cells, while downregulation of mTORC1 activity, using Raptor genetic mouse model or mTORC1 inhibitor treatment, ameliorated tumor progression of Ctsk-Cre Lkb1fllfl mice. Xenograft mouse models, using human osteosarcoma cell lines, also demonstrated that LKB1 deficiency promoted tumor formation, while mTOR inhibition suppressed xenograft tumor growth. In summary, we identified periosteum-derived Ctsk-Cre expressing cells as a cell of origin for osteogenic tumor and suggested the LKB1-mTORC1 pathway as a promising target for treatment of osteogenic tumor.

c-Fos induces chondrogenic tumor formation in immortalized human mesenchymal progenitor cells

Mesenchymal progenitor cells (MPCs) have been hypothesized as cells of origin for sarcomas, and c-Fos transcription factor has been showed to act as an oncogene in bone tumors. In this study, we show c-Fos is present in most sarcomas with chondral phenotype, while multiple other genes are related to c-Fos expression pattern. To further define the role of c-Fos in sarcomagenesis, we expressed it in primary human MPCs (hMPCs), immortalized hMPCs and transformed murine MPCs (mMPCs). In immortalized hMPCs, c-Fos expression generated morphological changes, reduced mobility capacity and impaired adipogenic- and osteogenic-differentiation potentials. Remarkably, immortalized hMPCs or mMPCs expressing c-Fos generated tumors harboring a chondrogenic phenotype and morphology. Thus, here we show that c-Fos protein has a key role in sarcomas and that c-Fos expression in immortalized MPCs yields cell transformation and chondrogenic tumor formation.