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Abstract Aims This research developed a prognostic model for OS patients based on the Mechanistic Target of Rapamycin Complex 1 (mTORC1) signature. Background The mTORC1 signaling pathway has a critical role in the maintenance of cellular homeostasis and tumorigenesis and development through the regulation of cell growth, metabolism and autophagy. However, the mechanism of action of this signaling pathway in Osteosarcoma (OS) remains unclear. Objective The datasets including the TARGET-OS and GSE39058, and 200 mTORC1 genes were collected. Methods The mTORC1 signaling-related genes were obtained based on the Molecular Signatures Database (MSigDB) database, and the single sample gene set enrichment analysis (ssGSEA) algorithm was utilized in order to calculate the mTORC1 score. Then, the WGCNA were performed for the mTORC1-correlated gene module, the un/multivariate and lasso Cox regression analysis were conducted for the RiskScore model. The immune infiltration analysis was performed by using the ssGSEA method, ESTIMATE tool and MCP-Count algorithm. KM survival and Receiver Operating Characteristic (ROC) Curve analysis were performed by using the survival and timeROC package. Results The mTORC1 score and WGCNA with β = 5 screened the mTORC1 positively correlated skyblue2 module that included 67 genes, which are also associated with the metabolism and hypoxia pathways. Further narrowing of candidate genes and calculating the regression coefficient, we developed a useful and reliable RiskScore model, which can classify the patients in the training and validation set into high and low-risk groups based on the median value of RiskScore as an independent and robust prognostic factor. High-risk patients had a significantly poor prognosis, lower immune infiltration level of multiple immune cells and prone to cancer metastasis. Finally, we a nomogram model incorporating the metastasis features and RiskScore showed excellent prediction accuracy and clinical practicability. Conclusion We developed a useful and reliable risk prognosis model based on the mTORC1 signaling signature.

Aims: This research developed a prognostic model for OS patients based on the Mechanistic Target of Rapamycin Complex 1 (mTORC1) signature. Background: The mTORC1 signaling pathway has a critical role in the maintenance of cellular homeostasis and tumorigenesis and development through the regulation of cell growth, metabolism and autophagy. However, the mechanism of action of this signaling pathway in Osteosarcoma (OS) remains unclear. Objective: The datasets including the TARGET-OS and GSE39058, and 200 mTORC1 genes were collected. Methods: The mTORC1 signaling-related genes were obtained based on the Molecular Signatures Database (MSigDB) database, and the single sample gene set enrichment analysis (ssGSEA) algorithm was utilized in order to calculate the mTORC1 score. Then, the WGCNA were performed for the mTORC1-correlated gene module, the un/multivariate and lasso Cox regression analysis were conducted for the RiskScore model. The immune infiltration analysis was performed by using the ssGSEA method, ESTIMATE tool and MCP-Count algorithm. KM survival and Receiver Operating Characteristic (ROC) Curve analysis were performed by using the survival and timeROC package. Results: The mTORC1 score and WGCNA with β = 5 screened the mTORC1 positively correlated skyblue2 module that included 67 genes, which are also associated with the metabolism and hypoxia pathways. Further narrowing of candidate genes and calculating the regression coefficient, we developed a useful and reliable RiskScore model, which can classify the patients in the training and validation set into high and low-risk groups based on the median value of RiskScore as an independent and robust prognostic factor. High-risk patients had a significantly poor prognosis, lower immune infiltration level of multiple immune cells and prone to cancer metastasis. Finally, we a nomogram model incorporating the metastasis features and RiskScore showed excellent prediction accuracy and clinical practicability. Conclusion: We developed a useful and reliable risk prognosis model based on the mTORC1 signaling signature. [ABSTRACT FROM AUTHOR]

Cisplatin (CDDP) is a commonly used chemotherapeutic for osteosarcoma (OS) patients, and drug resistance remains as a major hurdle to undermine the treatment outcome. Here, we investigated the potential involvement of FoxG1 and BNIP3 in CDDP resistance of OS cells. FoxG1 and BNIP3 expression levels were detected in the CDDP‐sensitive and CDDP‐resistant OS tumors and cell lines. Mitophagy was observed through transmission electron microscope analysis. The sensitivity to CDDP in OS cells upon FoxG1 overexpression was examined in cell and animal models. We found that FoxG1 and BNIP3 showed significant downregulation in the CDDP‐resistant OS tumor samples and cell lines. CDDP‐resistant OS tumor specimens and cells displayed impaired mitophagy. FoxG1 overexpression promoted BNIP3 expression, enhanced mitophagy in CDDP‐resistant OS cells, and resensitized the resistant cells to CDDP treatment in vitro and in vivo. Our data highlighted the role of the FoxG1/BNIP3 axis in regulating mitophagy and dictating CDDP resistance in OS cells, suggesting targeting FoxG1/BNIP3‐dependent mitophagy as a potential strategy to overcome CDDP resistance in OS. [ABSTRACT FROM AUTHOR]

Background: The involvement of neutrophil-related genes (NRGs) in patients with osteosarcoma (OS) has not been adequately explored. In this study, we aimed to examine the association between NRGs and the prognosis as well as the tumor microenvironment of OS. Methods: The OS data were obtained from the TARGET-OS and GEO database. Initially, we extracted NRGs by intersecting 538 NRGs from single-cell RNA sequencing (scRNA-seq) data between aneuploid and diploid groups, as well as 161 up-regulated differentially expressed genes (DEGs) from the TARGET-OS datasets. Subsequently, we conducted Least Absolute Shrinkage and Selection Operator (Lasso) analyses to identify the hub genes for constructing the NRG-score and NRG-signature. To assess the prognostic value of the NRG signatures in OS, we performed Kaplan–Meier analysis and generated time-dependent receiver operating characteristic (ROC) curves. Gene enrichment analysis (GSEA) and gene set variation analysis (GSVA) were utilized to ascertain the presence of tumor immune microenvironments (TIMEs) and immunomodulators (IMs). Additionally, the KEGG neutrophil signaling pathway was evaluated using ssGSEA. Subsequently, PCR and IHC were conducted to validate the expression of hub genes and transcription factors (TFs) in K7M2-induced OS mice. Results: FCER1G and C3AR1 have been identified as prognostic biomarkers for overall survival. The findings indicate a significantly improved prognosis for OS patients. The effectiveness and precision of the NRG signature in prognosticating OS patients were validated through survival ROC curves and an external validation dataset. The results clearly demonstrate that patients with elevated NRG scores exhibit decreased levels of immunomodulators, stromal score, immune score, ESTIMATE score, and infiltrating immune cell populations. Furthermore, our findings substantiate the potential role of SPI1 as a transcription factor in the regulation of the two central genes involved in osteosarcoma development. Moreover, our analysis unveiled a significant correlation and activation of the KEGG neutrophil signaling pathway with FCER1G and C3AR1. Notably, PCR and IHC demonstrated a significantly higher expression of C3AR1, FCER1G, and SPI1 in Balb/c mice induced with K7M2. Conclusions: Our research emphasizes the significant contribution of neutrophils within the TIME of osteosarcoma. The newly developed NRG signature could serve as a good instrument for evaluating the prognosis and therapeutic approach for OS. [ABSTRACT FROM AUTHOR]

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Primary bone tumors (PBT), although rare, could pose significant mortality and morbidity risks due to their high incidence of lung metastasis. Survival rates of patients with PBTs may vary based on the tumor type, therapeutic interventions, and the time of diagnosis. Despite advances in the management of patients with these tumors over the past four decades, the survival rates seem not to have improved significantly, implicating the need for novel therapeutic interventions. Surgical resection with wide margins, radiotherapy, and systemic chemotherapy are the main lines of treatment for PBTs. Neoadjuvant and adjuvant chemotherapy, along with emerging immunotherapeutic approaches such as chimeric antigen receptor (CAR)-T cell therapy, have the potential to improve the treatment outcomes for patients with PBTs. CAR-T cell therapy has been introduced as an option in hematologic malignancies, with FDA approval for several CD19-targeting CAR-T cell products. This review aims to highlight the potential of immunotherapeutic strategies, specifically CAR T cell therapy, in managing PBTs.

Background: Osteosarcoma (OS) is the most common bone malignant tumor in children and adolescents. Recent research indicates that non-coding RNAs (ncRNAs) have been associated with OS occurrence and development, with significant progress made in this field. However, there is no intelligent structure prediction and literature visualization analysis in this research field. From the perspective of intelligent knowledge structure construction and bibliometrics, this study will comprehensively review the role of countries, institutions, journals, authors, literature citation relationships and subject keywords in the field of ncRNAs in OS. Based on this analysis, we will systematically analyze the characteristics of the knowledge structure of ncRNAs in OS disease research and identify the current research hotspots and trends. Methods: The Web of Science Core Collection (WoSCC) database was searched for articles on ncRNAs in OS between 2001 and 2023. This bibliometric analysis was performed using VOSviewers, CiteSpace, and Pajek. Results: This study involved 15,631 authors from 2,631 institutions across 57 countries/regions, with a total of 3,642 papers published in 553 academic journals. China has the highest number of published papers in this research field. The main research institutions include Nanjing Medical University (n = 129, 3.54%), Shanghai Jiao Tong University (n = 128, 3.51%), Zhengzhou University (n = 110, 3.02%), and China Medical University (n = 109, 2.99%). Oncology Letters (n =139, 3.82%), European Review for Medical Pharmacological Sciences (120, 3.31%), and Molecular Medicine Reports (n = 95, 2.61%) are the most popular journals in this field, with Oncotarget being the most co-cited journal (Co-Citation = 4,268). Wei Wang, Wei Liu, and Zhenfeng Duan published the most papers, with Wang Y being the most co-cited author. "miRNA", "lncRNA" and "circRNA" are the main focuses of ncRNAs in OS studies. Key themes include "migration and invasion", "apoptosis and proliferation", "prognosis", "biomarkers" and "chemoresistance". Since 2020, hotspots and trends in ncRNA research in OS include "tumor microenvironment", "immune" and "exosome". Conclusion: This study represents the first comprehensive bibliometric analysis of the knowledge structure and development of ncRNAs in OS. These findings highlight current research hotspots and frontier directions, offering valuable insights for future studies on the role of ncRNAs in OS [ABSTRACT FROM AUTHOR]

Abstract Background Osteosarcoma (OS) is the most prevalent primary malignant bone tumor. However, single-agent chemotherapy exhibits limited efficacy against OS and often encounters tumor resistance. Therefore, we designed and constructed an integrated treatment strategy of photothermal therapy (PTT) combined with chemotherapy and used a surface-encapsulated platelet-osteosarcoma hybrid membrane (OPM) that enhances circulation time and enables OS-specific targeting. Results The OPM functions as a shell structure, encapsulating multiple drug-loaded nanocores (BPQDs-DOX) and controlling the release rate of doxorubicin (DOX). Moreover, near-infrared light irradiation accelerates the release of DOX, thereby extending circulation time and enabling photostimulation-responsive release. The OPM encapsulation system improves the stability of BPQDs, enhances their photothermal conversion efficiency, and augments PTT efficacy. In vitro and ex vivo experiments demonstrate that BPQDs-DOX@OPM effectively delivers drugs to tumor sites with prolonged circulation time and specific targeting, resulting in superior anti-tumor activity compared to single-agent chemotherapy. Furthermore, these experiments confirm the favorable biosafety profile of BPQDs-DOX@OPM. Conclusions Compared to single-agent chemotherapy, the combined therapy using BPQDs-DOX@OPM offers prolonged circulation time, targeted drug delivery, enhanced anti-tumor activity, and high biosafety, thereby introducing a novel approach for the clinical treatment of OS.

Background: The involvement of neutrophil-related genes (NRGs) in patients with osteosarcoma (OS) has not been adequately explored. In this study, we aimed to examine the association between NRGs and the prognosis as well as the tumor microenvironment of OS. Methods: The OS data were obtained from the TARGET-OS and GEO database. Initially, we extracted NRGs by intersecting 538 NRGs from single-cell RNA sequencing (scRNA-seq) data between aneuploid and diploid groups, as well as 161 up-regulated differentially expressed genes (DEGs) from the TARGET-OS datasets. Subsequently, we conducted Least Absolute Shrinkage and Selection Operator (Lasso) analyses to identify the hub genes for constructing the NRG-score and NRG-signature. To assess the prognostic value of the NRG signatures in OS, we performed Kaplan–Meier analysis and generated time-dependent receiver operating characteristic (ROC) curves. Gene enrichment analysis (GSEA) and gene set variation analysis (GSVA) were utilized to ascertain the presence of tumor immune microenvironments (TIMEs) and immunomodulators (IMs). Additionally, the KEGG neutrophil signaling pathway was evaluated using ssGSEA. Subsequently, PCR and IHC were conducted to validate the expression of hub genes and transcription factors (TFs) in K7M2-induced OS mice. Results: FCER1G and C3AR1 have been identified as prognostic biomarkers for overall survival. The findings indicate a significantly improved prognosis for OS patients. The effectiveness and precision of the NRG signature in prognosticating OS patients were validated through survival ROC curves and an external validation dataset. The results clearly demonstrate that patients with elevated NRG scores exhibit decreased levels of immunomodulators, stromal score, immune score, ESTIMATE score, and infiltrating immune cell populations. Furthermore, our findings substantiate the potential role of SPI1 as a transcription factor in the regulation of the two central genes involved in osteosarcoma development. Moreover, our analysis unveiled a significant correlation and activation of the KEGG neutrophil signaling pathway with FCER1G and C3AR1. Notably, PCR and IHC demonstrated a significantly higher expression of C3AR1, FCER1G, and SPI1 in Balb/c mice induced with K7M2. Conclusions: Our research emphasizes the significant contribution of neutrophils within the TIME of osteosarcoma. The newly developed NRG signature could serve as a good instrument for evaluating the prognosis and therapeutic approach for OS.

Cisplatin (CDDP) is a mainstay chemotherapeutic agent for OS treatment, but drug resistance has become a hurdle to limit its clinical effect. Autophagy plays an important role in CDDP resistance in OS, and in the present study we explored the role of ANXA2 and Rac1 in dictating CDDP sensitivity in OS cells. ANXA2 and Rac1 expression levels were examined by Western blot and autophagy induction was detected by transmission electron miscroscope (TEM) in the clinical samples and OS cell lines. CDDP resistant cells were established by exposing OS cells to increasing doses of CDDP. The effects of ANXA2 and Rac1 knockdown on CDDP sensitivity were evaluated in the cell and animal models. Reduced autophagy was associated with the increased expression of ANXA2 and Rac1 in CDDP resistant OS tumor samples and cells. Autophagy suppression promoted CDDP resistance and inducing autophagy re-sensitized the resistant cells to CDDP treatment in vitro and in vivo. Further, knocking down ANXA2 or Rac1 re-activated autophagy and attenuated CDDP resistance in OS cells. We further demonstrated that CDDP resistant OS cells displayed a poorer osteogenic differentiation state when compared to the parental cell lines, which was significantly reversed by autophagy re-activation and ANXA2 or Rac1 silencing. Our findings revealed a complicated interplay of ANXA2/Rac1, autophagy induction, and osteogenic differentiation in dictating CDDP resistance in OS cells, suggesting ANXA2 and Rac1 as promising targets to modulate autophagy and overcome CDDP resistance in OS cells. • Autophagy is suppressed in CDDP resistant OS cells. • ANXA2 and Rac1 are upregulated in CDDP resistant OS cells. • Silencing ANXA2 or Rac1 re-activates autophagy and increases CDDP sensitivity. • ANXA2 and Rac1 modulate the osteogenic differentiation of OS cells. [ABSTRACT FROM AUTHOR]

Aim: To establish a p53-negative osteosarcoma (OS) SaOS-2 cellular subline exhibiting resistance to specific chemotherapeutic agents, including topoisomerase II inhibitors, taxanes, and vinca alkaloids. Methods: The OS subline exhibiting resistance to the chemotherapeutic agents indicated above was generated by the stepwise treatment of the parental SaOS-2 cell line with increasing concentrations of doxorubicin (Dox) for 5 months. Half-inhibitory concentrations (IC50) for Dox, vinblastine (Vin), and paclitaxel (PTX) were calculated by a colorimetric MTS-based assay. Crystal violet staining was used to assess cellular viability, whereas the proliferation capacities of cancer cells were monitored in real-time by the i-Celligence system. Expression of apoptotic markers (e.g., cleaved PARP and caspase-3), DNA repair proteins (e.g., ATM, DNA-PK, Nbs1, Rad51, MSH2, etc.), and certain ABC transporters (P-glycoprotein, MRP1, ABCG2, etc.) was assessed by western blotting and real-time PCR. Flow cytometry was used to examine the fluorescence intensity of Dox and ABC-transporter substrates (e.g., Calcein AM and CMFDA) and to assess their excretion to define the activity of specific ABC-transporters. To confirm OS resistance to Dox in vivo, xenograft experiments were performed. Results: An OS subline generated by a stepwise treatment of the parental SaOS-2 cell line with increasing concentrations of Dox resulted in an increase in the IC50 for Dox, Vin, and PTX (~6-, 4-, and 30-fold, respectively). The acquisition of chemoresistance in vitro was also evidenced by the lack of apoptotic markers (e.g., cleaved PARP and caspase-3) in resistant OS cells treated with the chemotherapeutic agents indicated above. The development of the multidrug resistance (MDR) phenotype in this OS subline was due to the overexpression of ABCB1 (i.e., P-glycoprotein) and ABCC1 (i.e., multidrug resistance protein-1, MRP-1), which was evidenced on both mRNA and protein levels. Due to increased expression of MDR-related proteins, resistant OS exhibited an excessive efflux of Dox. Moreover, decreased accumulation of calcein AM, a well-known fluorescent substrate for both ABCB1 and ABCC1, was observed for resistant OS cells compared to their parental SaOS-2 cell line. Importantly, tariquidar and cyclosporin, well-known ABC inhibitors, retained the intensity of Dox-induced fluorescence in resistant SAOS-2 cells. Furthermore, in addition to the increased efflux of the chemotherapeutic agents from Dox-resistant OS cells, we found higher expression of several DNA repair proteins (e.g., Rad51 recombinase, Mre11, and Nbs1, activated forms of ATM, DNA-PK, Chk1, and Chk2, etc.), contributing to the chemoresistance due to the excessive DNA repair. Lastly, the in vivo study indicated that Dox has no impact on the SaOS-2 Dox-R xenograft tumor growth in a nude mouse model. Conclusions: An acquired resistance of OS to the chemotherapeutic agents might be due to the several mechanisms undergoing simultaneously on the single-cell level. This reveals the complexity of the mechanisms involved in the secondary resistance of OS to chemotherapies. [ABSTRACT FROM AUTHOR]

Novel therapeutic approaches are much needed for the treatment of osteosarcoma. Targeted radionuclide therapy (TRT) and radioimmunotherapy (RIT) are promising approaches that deliver therapeutic radiation precisely to the tumor site. We have previously developed a fully human antibody, named IF3, that binds to insulin-like growth factor 2 receptor (IGF2R). IF3 was used in TRT to effectively inhibit tumor growth in osteosarcoma preclinical models. However, IF3's relatively short half-life in mice raised the need for improvement. We generated an Fc-engineered version of IF3, termed IF3δ, with amino acid substitutions known to enhance antibody half-life in human serum. In this study, we confirmed the specific binding of IF3δ to IGF2R with nanomolar affinity, similar to wild-type IF3. Additionally, IF3δ demonstrated binding to human and mouse neonatal Fc receptors (FcRn), indicating the potential for FcRn-mediated endocytosis and recycling. Biodistribution studies in mice showed a higher accumulation of IF3δ in the spleen and bone than wild-type IF3, likely attributed to abnormal spleen expression of IGF2R in mice. Therefore, the pharmacokinetics data from mouse xenograft models may not precisely reflect their behavior in canine and human patients. However, the findings suggest both IF3 and IF3δ as promising options for the RIT of osteosarcoma. [ABSTRACT FROM AUTHOR]

Background: Osteosarcoma (OS) is the most prevalent primary malignant bone tumor. However, single-agent chemotherapy exhibits limited efficacy against OS and often encounters tumor resistance. Therefore, we designed and constructed an integrated treatment strategy of photothermal therapy (PTT) combined with chemotherapy and used a surface-encapsulated platelet-osteosarcoma hybrid membrane (OPM) that enhances circulation time and enables OS-specific targeting. Results: The OPM functions as a shell structure, encapsulating multiple drug-loaded nanocores (BPQDs-DOX) and controlling the release rate of doxorubicin (DOX). Moreover, near-infrared light irradiation accelerates the release of DOX, thereby extending circulation time and enabling photostimulation-responsive release. The OPM encapsulation system improves the stability of BPQDs, enhances their photothermal conversion efficiency, and augments PTT efficacy. In vitro and ex vivo experiments demonstrate that BPQDs-DOX@OPM effectively delivers drugs to tumor sites with prolonged circulation time and specific targeting, resulting in superior anti-tumor activity compared to single-agent chemotherapy. Furthermore, these experiments confirm the favorable biosafety profile of BPQDs-DOX@OPM. Conclusions: Compared to single-agent chemotherapy, the combined therapy using BPQDs-DOX@OPM offers prolonged circulation time, targeted drug delivery, enhanced anti-tumor activity, and high biosafety, thereby introducing a novel approach for the clinical treatment of OS. [ABSTRACT FROM AUTHOR]

Osteosarcoma is a primary malignant tumor found mainly in teenagers and young adults. Patients have very little long-term survival. MYC controls tumor initiation and progression by regulating the expression of its target genes; thus, constructing a risk signature of osteosarcoma MYC target gene set will benefit the evaluation of both treatment and prognosis. In this paper, we used GEO data to download the ChIP-seq data of MYC to obtain the MYC target gene. Then, a risk signature consisting of 10 MYC target genes was developed using Cox regression analysis. The signature indicates that patients in the high-risk group performed poorly. After that, we verified it in the GSE21257 dataset. In addition, the difference in tumor immune function among the low- and high-risk populations was compared by single sample gene enrichment analysis. Immunotherapy and prediction of response to the anticancer drug have shown that the risk signature of the MYC target gene set was positively correlated with immune checkpoint response and drug sensitivity. Functional analysis has demonstrated that these genes are enriched in malignant tumors. Finally, STX10 was selected for functional experimentation. STX10 silence has limited osteosarcoma cell migration, invasion, and proliferation. Therefore, these findings indicated that the MYC target gene set risk signature could be used as a potential therapeutic target and prognostic indicator in patients with osteosarcoma. [ABSTRACT FROM AUTHOR]

Background: Osteosarcoma typically occurs in adolescents, and the survival rate of patients with metastatic and recurrent osteosarcoma remains low. Abnormal regulation of alternative splicing is associated with the development of osteosarcoma. However, there is no genome-wide analysis of the function and regulatory mechanisms of aberrant alternative splicing associated with osteosarcoma. Methods: Published transcriptome data on osteosarcoma (GSE126209) derived from osteosarcoma patient tissue were downloaded. Gene expression profiling by high-throughput sequencing was performed on 9 normal samples and 10 tumor samples for genome-wide identification of osteosarcoma-related alternative splicing events. The potential function of osteosarcoma-associated alternative splicing events was examined by immune infiltration and correlation analysis. Regulation of aberrantly expressed RNA-binding proteins (RBPs) related to alternative splicing in osteosarcoma was clarified by co-expression analysis. Results: A total of 63 alternative splicing events, which are highly credible and dominant, were identified. GO enrichment analysis indicated that alternative splicing may be closely related to the immune response process. Immune infiltration analysis showed significant changes in the percentages of CD8 T cells, resting memory CD4 T cells, activated memory CD4 T cells, monocytes, resting dendritic cells, and activated mast cells in tumors compared to normal tissues, indicating the involvement of these immune cell types in the occurrence of osteosarcoma. Moreover, the analysis identified alternative splicing events that were co-altered with resting memory CD4 T cells, resting dendritic cells, and activated mast cells, events that may be associated with regulation of the osteosarcoma immune microenvironment. In addition, a co-regulatory network (RBP-RAS-immune) of osteosarcoma-associated RBPs with aberrant alternative splicing and altered immune cells was established. These RBPs include NOP58, FAM120C, DYNC1H1, TRAP1, and LMNA, which may serve asmolecular targets for osteosarcoma immune regulation. Conclusion: These findings allow us to further understand the causes of osteosarcoma development and provide a new research direction for osteosarcoma immunotherapy or targeted therapy. [ABSTRACT FROM AUTHOR]

Bone contributes to the maintenance of vital biological activities. At the cellular level, multiple types of skeletal cells, including skeletal stem and progenitor cells (SSPCs), osteoblasts, chondrocytes, marrow stromal cells, and adipocytes, orchestrate skeletal events such as development, aging, regeneration, and tumorigenesis. Osteosarcoma (OS) is a primary malignant tumor and the main form of bone cancer. Although it has been proposed that the cellular origins of OS are in osteogenesis-related skeletal lineage cells with cancer suppressor gene mutations, its origins have not yet been fully elucidated because of a poor understanding of whole skeletal cell diversity and dynamics. Over the past decade, the advent and development of single-cell RNA sequencing analyses andmouse lineage-tracing approaches have revealed the diversity of skeletal stem and its lineage cells. Skeletal stem cells (SSCs) in the bone marrow endoskeletal region have now been found to efficiently generate OS and to be robust cells of origin under p53 deletion conditions. The identification of SSCs may lead to a more limited redefinition of bone marrow mesenchymal stem/stromal cells (BM-MSCs), and this population has been thought to contain cells from which OS originates. In this mini-review, we discuss the cellular diversity and dynamics of multiple skeletal cell types and the origin of OS in the native in vivo environment in mice. We also discuss future challenges in the study of skeletal cells and OS. [ABSTRACT FROM AUTHOR]

Simple Summary: Solid tumors account for ~60% of pediatric, as well as adolescent and young adult (AYA), cancers, and outcomes for patients with these progressive diseases remain poor. This highlights the critical need to develop tumor models from patients with aggressive cancers so that oncogenic signatures can be identified for therapeutic testing. Thus, patient-derived xenografts (PDXs) were established from sarcoma and Wilms tumor patients at diagnosis or following treatment. Overall, the molecular landscape of serially passaged PDXs recapitulated the original tumor based on an integrated multi-OMICS pipeline that cross-validated cancer-associated pathways. Actionable mechanisms of tumor progression were identified. CDK4/6 and BETs were prioritized as biomarkers of therapeutic response for in vivo validation. In osteosarcoma PDXs harboring pertinent molecular signatures, inhibition of CDK4/6 or BETs decreased growth. This systematic approach that links patient disease history to data generated from its corresponding PDX provides a foundation to discover improved therapies for patients with high-risk cancers. Establishment of clinically annotated, molecularly characterized, patient-derived xenografts (PDXs) from treatment-naïve and pretreated patients provides a platform to test precision genomics-guided therapies. An integrated multi-OMICS pipeline was developed to identify cancer-associated pathways and evaluate stability of molecular signatures in a panel of pediatric and AYA PDXs following serial passaging in mice. Original solid tumor samples and their corresponding PDXs were evaluated by whole-genome sequencing, RNA-seq, immunoblotting, pathway enrichment analyses, and the drug–gene interaction database to identify as well as cross-validate actionable targets in patients with sarcomas or Wilms tumors. While some divergence between original tumor and the respective PDX was evident, majority of alterations were not functionally impactful, and oncogenic pathway activation was maintained following serial passaging. CDK4/6 and BETs were prioritized as biomarkers of therapeutic response in osteosarcoma PDXs with pertinent molecular signatures. Inhibition of CDK4/6 or BETs decreased osteosarcoma PDX growth (two-way ANOVA, p < 0.05) confirming mechanistic involvement in growth. Linking patient treatment history with molecular and efficacy data in PDX will provide a strong rationale for targeted therapy and improve our understanding of which therapy is most beneficial in patients at diagnosis and in those already exposed to therapy. [ABSTRACT FROM AUTHOR]

Osteosarcoma (OS) is a highly malignant tumor, and chemotherapy resistance is a major challenge in the treatment of this disease. This study aims to explore the role of the CLTC-VMP1 gene fusion in the mechanism of chemotherapy resistance in OS and investigate its molecular mechanisms in mediating energy metabolism reprogramming by regulating autophagy and apoptosis balance. Using single-cell transcriptome analysis, the heterogeneity of OS cells and their correlation with resistance to platinum drugs were revealed. Cisplatin-resistant cell lines were established in human OS cell lines for subsequent experiments. Based on transcriptomic analysis, the importance of VMP1 in chemotherapy resistance was confirmed. Lentiviral vectors overexpressing or interfering with VMP1 were used, and it was observed that inhibiting VMP1 could reverse cisplatin resistance, promote cell apoptosis, and inhibit autophagy, and mitochondrial respiration and glycolysis. Furthermore, the presence of CLTC-VMP1 gene fusion was validated, and its ability to regulate autophagy and apoptosis balance, promote mitochondrial respiration, and glycolysis was demonstrated. Mouse model experiments further confirmed the promoting effect of CLTC-VMP1 on tumor growth and chemotherapy resistance. In summary, the CLTC-VMP1 gene fusion mediates energy metabolism reprogramming by regulating autophagy and apoptosis balance, which promotes chemotherapy resistance in OS. NEW & NOTEWORTHY This study identifies the CLTC-VMP1 gene fusion as a key driver of chemotherapy resistance in osteosarcoma by regulating autophagy and reprogramming cellular energy metabolism. Through single-cell transcriptomics, the research reveals the heterogeneity of tumor cells and the role of VMP1 in promoting resistance to cisplatin. The findings suggest that targeting the CLTC-VMP1 fusion gene may offer new therapeutic strategies to overcome chemotherapy resistance in osteosarcoma.

Abstract Backgrounds Osteosarcomas are one of the most common primary malignant tumors of bone. It primarily occurs in children and adolescents, with the second highest incidence among people over 50 years old. Although there were immense improvements in the survival of patients with osteosarcoma in the past 30 years, targetable mutations and agents of osteosarcomas still have been generally not satisfactory. Therefore, it is of great importance to further explore the highly specialized immune environment of bone, genes related to macrophage infiltration and potential therapeutic biomarkers and targets. Methods The 11 expression data sets of OS tissues and the 11 data sets of adjacent non-tumorous tissues available in the GEO database GSE126209 were used to conduct immune infiltration analysis. Then, through WGCNA analysis, we acquired the co-expression modules related to Mast cells activated and performed the GO and KEGG enrichment analysis. Next, we did the survival prognosis analysis and plotted a survival curve. Finally, we analyzed the COX multivariate regression of gene expression on clinical parameters and drew forest maps for visualization by the forest plot package. Results OS disease-related immune cell populations, mainly Mast cells activated, have higher cell content (p = 0.006) than the normal group. Then, we identified co-expression modules related to Mast cells activated. In sum, a total of 822 genes from the top three strongest positive correlation module MEbrown4, MEdarkslateblue and MEnavajowhite2 and the strongest negative correlation module MEdarkturquoise. From that, we identified nine genes with different levels in immune cell infiltration related to osteosarcoma, eight of which including SORBS2, BAIAP2L2, ATAD2, CYGB, PAMR1, PSIP1, SNAPC3 and ZDHHC21 in their low abundance have higher disease-free survival probability than the group in their high abundances. Conclusion These results could assist clinicians to select targets for immunotherapies and individualize treatment strategies for patients with OS.

Osteosarcoma (OS) is a primary malignant tumor of the bone characterized by poor prognosis due to chemotherapy resistance and high recurrence rates. DJ-1 (PARK7) is known as an oncogene and its abnormal expression is related to the poor prognosis of various types of malignant tumors. It was found in this study that upregulated expression of DJ-1 was closely correlated with the prognosis of OS patients by promoting the proliferation, migration and chemotherapy resistance of OS cells in vitro through regulating the activity of CDK4 but not through the oxidation mechanism or AKT pathway. The combination of DJ-1 and CDK4 promoted RB phosphorylation, leading to the dissociation of E2F1 into the nucleus to regulate the expression of cell cycle-related genes. The tumor xenograft mouse model demonstrated that DJ-1 knockout suppressed tumor growth in vivo. All these findings indicate that DJ-1 can affect the occurrence and progression of OS by regulating the CDK/ RB/E2F1axis, suggesting a novel therapeutic opportunity for OS patients. [ABSTRACT FROM AUTHOR]

[Display omitted] • Primary bone tumors (PBTs) have a low incidence, but cause significant patient burden. • CAR T-cell therapy has been used in treating hematological malignancies. • CAR T-cells may be used in solid tumors to improve survival in patients with PBTs. • This review summarizes findings on CAR T-cell therapy for PBTs. Primary bone tumors (PBT), although rare, could pose significant mortality and morbidity risks due to their high incidence of lung metastasis. Survival rates of patients with PBTs may vary based on the tumor type, therapeutic interventions, and the time of diagnosis. Despite advances in the management of patients with these tumors over the past four decades, the survival rates seem not to have improved significantly, implicating the need for novel therapeutic interventions. Surgical resection with wide margins, radiotherapy, and systemic chemotherapy are the main lines of treatment for PBTs. Neoadjuvant and adjuvant chemotherapy, along with emerging immunotherapeutic approaches such as chimeric antigen receptor (CAR)-T cell therapy, have the potential to improve the treatment outcomes for patients with PBTs. CAR-T cell therapy has been introduced as an option in hematologic malignancies, with FDA approval for several CD19-targeting CAR-T cell products. This review aims to highlight the potential of immunotherapeutic strategies, specifically CAR T cell therapy, in managing PBTs. [ABSTRACT FROM AUTHOR]

Cao K, Fang Y, Wang H, Jiang Z, Guo L, Hu Y. Cancer Manag Res. 2019;11:4505–4518. The authors have advised due to an error at the time of figure assembly, Figure 3B on page 4512 is incorrect. The correct Figure 3 is shown in Download Article. The authors apologize for this error and advise it does not affect the results of the paper. Read the original article

Chaofan Xie,1,* Guanzhao Liang,2,* Yinfeng Xu,1 Erhu Lin3 1Department of Orthopaedics, The First Affiliated Hospital of Sun Yat-Sen University, Guangzhou, Guangdong Province, People’s Republic of China; 2Department of Emergency, The First Affiliated Hospital of Sun Yat-Sen University, Guangzhou, Guangdong Province, People’s Republic of China; 3Department of Spine Surgery, Shenzhen People’s Hospital, Shenzhen, Guangdong Province, People’s Republic of China*These authors contributed equally to this workCorrespondence: Erhu Lin Department of Spine SurgeryShenzhen People’s Hospital, 1017 Dongmen North Road, Luohu District, Shenzhen, Guangdong Province 518020, People’s Republic of ChinaTel +86-13760341589Email jiqbzbb@163.comBackground: Osteosarcoma (OS) is the most common primary malignancy of bone with a high incidence in children. Circular RNAs (circRNAs) play crucial roles in the carcinogenesis and chemoresistance of OS. In the current work, we focused on the function and mechanism of hsa_circ_0003496 (circ_0003496) in OS progression and chemoresistance.Materials and Methods: The expression levels of circ_0003496, miR-370 and Krüppel-like factor 12 (KLF12) mRNA were measured by quantitative real-time polymerase chain reaction (qRT-PCR). The Cell Counting Kit-8 (CCK-8) assay was used to assess the 50% inhibitory concentration (IC50) value and cell proliferation. Cell migration, invasion and apoptosis were detected by transwell assay and flow cytometry, respectively. Western blot analysis was performed to assess the protein level. Targeted relationships among circ_0003496, miR-370 and KLF12 were validated by dual-luciferase reporter, RNA immunoprecipitation (RIP) and RNA pull-down assays. Animal studies were carried out to observe the role of circ_0003496 in vivo.Results: Our results indicated that circ_0003496 up-regulation was associated with doxorubicin (DXR) resistance of OS. Circ_0003496 knockdown repressed DXR-resistant OS cell proliferation, migration and invasion, and enhanced apoptosis and DXR sensitivity. Circ_0003496 functioned as a sponge of miR-370, and miR-370 mediated the regulatory effect of circ_0003496 depletion on DXR-resistant OS cell progression and DXR sensitivity. KLF12 was a direct target of miR-370, and miR-370 overexpression suppressed cell progression and enhanced DXR sensitivity by KLF12. Moreover, circ_0003496 protected against KLF12 repression through sponging miR-370. Additionally, circ_0003496 knockdown hampered tumor growth and promoted DXR sensitivity in vivo.Conclusion: Our present work suggested that the knockdown of circ_0003496 suppressed OS progression and enhanced DXR sensitivity at least partially through modulating KLF12 expression via functioning as a miR-370 sponge, highlighting new opportunities for OS management.Keywords: osteosarcoma, OS, circ_0003496, miR-370, Krüppel-like factor 12, KLF12, chemoresistance

Abstract Background Cancer stem cell (CSC) is identified in osteosarcoma (OS) and considered resistant to chemotherapeutic agents. However, the mechanism of osteosarcoma stem cell (OSC) resistant to chemotherapy remains debatable and vague, and the metabolomics feature of OSC is not clarified. Materials and methods OSC was isolated by using sphere forming assay and identified. Untargeted LC–MS/MS analysis was performed to reveal the metabolomics feature of OSC and underlying mechanisms of OSC resistant to methotrexate (MTX). Results OSC was efficiently isolated and identified from human OS 143B and MG63 cell lines with enhanced chemo-resistance to MTX. The untargeted LC–MS analysis revealed that OSC showed differential metabolites and perturbed signaling pathways, mainly involved in metabolisms of fatty acid, amino acid, carbohydrate metabolism and nucleic acid. After treated with MTX, metabolomics feature of OSC was mainly involved metabolisms of amino acid, fatty acid, energy and nucleic acid. Moreover, compared with their parental OS cells response to MTX, the differential metabolites and perturbed signaling pathways were mainly involved in metabolism of amino acid, fatty acid and nucleic acid. What’s more, Rap1 signaling pathway and Ras signaling pathway were involved in OS cells and their SCs response to MTX. Conclusion Sphere-forming assay was able to efficiently isolate OSC from human OS cell lines and the untargeted LC–MS/MS analysis was suggested a sufficient methodology to investigate metabolomics features of OS cells and OSCs. Moreover, the metabolomics features of OSCs response to MTX might reveal a further understanding of chemotherapeutic resistance in OS.

Osteosarcoma (OS) is the most common primary malignant tumor of bone. The aim of this study was to investigate the regulatory mechanisms of M2 macrophage exosomes (M2-Exos) in ferroptosis in OS. A mouse model was established to investigate the in vivo role of M2-Exos. We investigated their effects on ferroptosis in OS using erastin, a ferroptosis activator, and deferoxamine mesylate, an iron chelator. In vitro, we investigated whether the Apoc1/Acyl-CoA Synthetase Family Member 2 (ACSF2) axis mediates these effects, using shApoc1 and shACSF2. The mechanisms whereby Apoc1 regulates ACSF2 were examined using cyclohexanone, a protein synthesis inhibitor, and MG132, a proteasomal inhibitor. M2-Exos reversed the inhibitory effects of erastin on OS cells, thus enhancing their viability, migration, invasion, proliferation, and reducing ferroptosis. Apoc1 was highly expressed in M2-Exos, and interfering with this expression reversed the effects of M2-Exos on OS cells. ACSF2 mediated the effects of M2-Exos-derived Apoc1. Apoc1 interacted with ACSF2, which, in turn, interacted with USP40. Apoc1 overexpression increased ACSF2 ubiquitination, promoting its degradation, whereas USP40 overexpression inhibited ACSF2 ubiquitination and promoted its expression. Apoc1 overexpression inhibited ACSF2 binding to USP40. M2-Exos-derived Apoc1 promoted ferroptosis resistance by inhibiting USP40 binding to ACSF2 and promoting ACSF2 ubiquitination and degradation, thus enhancing OS development., (© 2024 Wiley Periodicals LLC.)

Backgrounds: Osteosarcomas are one of the most common primary malignant tumors of bone. It primarily occurs in children and adolescents, with the second highest incidence among people over 50 years old. Although there were immense improvements in the survival of patients with osteosarcoma in the past 30 years, targetable mutations and agents of osteosarcomas still have been generally not satisfactory. Therefore, it is of great importance to further explore the highly specialized immune environment of bone, genes related to macrophage infiltration and potential therapeutic biomarkers and targets.Methods: The 11 expression data sets of OS tissues and the 11 data sets of adjacent non-tumorous tissues available in the GEO database GSE126209 were used to conduct immune infiltration analysis. Then, through WGCNA analysis, we acquired the co-expression modules related to Mast cells activated and performed the GO and KEGG enrichment analysis. Next, we did the survival prognosis analysis and plotted a survival curve. Finally, we analyzed the COX multivariate regression of gene expression on clinical parameters and drew forest maps for visualization by the forest plot package.Results: OS disease-related immune cell populations, mainly Mast cells activated, have higher cell content (p = 0.006) than the normal group. Then, we identified co-expression modules related to Mast cells activated. In sum, a total of 822 genes from the top three strongest positive correlation module MEbrown4, MEdarkslateblue and MEnavajowhite2 and the strongest negative correlation module MEdarkturquoise. From that, we identified nine genes with different levels in immune cell infiltration related to osteosarcoma, eight of which including SORBS2, BAIAP2L2, ATAD2, CYGB, PAMR1, PSIP1, SNAPC3 and ZDHHC21 in their low abundance have higher disease-free survival probability than the group in their high abundances.Conclusion: These results could assist clinicians to select targets for immunotherapies and individualize treatment strategies for patients with OS. [ABSTRACT FROM AUTHOR]

Kun Cao,1 Yueyang Fang,1 Hao Wang,1 Zheng Jiang,1 Li Guo,2 Yong Hu11Department of Orthopaedics, The First Hospital Of Anhui Medical University, Hefei, People’s Republic of China; 2Department of Orthopaedics, The Second Hospital Of Shanxi Medical University, Taiyuan, People’s Republic of ChinaObjective: Many studies have shown that long non-coding RNAs (lncRNAs) are closely related to various cancers. This study aims to explore the roles of lncRNA HOXA11-AS in the development and progression of osteosarcoma (OS).Methods: The expression levels of HOXA11-AS and miR-125a-5p in tumor tissues and the adjacent tissues were detected by RT-PCR method. The proliferation, migration and invasion of MG-63 and KHOS cells were determined.Results: It was found that HOXA11-AS expression levels in OS tissues and OS cell lines were higher than those in OS adjacent tissues and normal human osteoblast cell lines. The higher expression level of HOXA11-AS was positively correlated with more severe clinical stage, distant metastasis and poor prognosis of OS. Inhibition of HOXA11-AS expression could reduce metastasis and invasion of OS cell lines. In addition, HOXA11-AS was found to be an endogenous inhibitor of miR-125a-5p, it down regulated the expression level of miR-125a-5p, and this process could promote the expression of Rab3D, the target gene of miR-125a-5p.Conclusion: Our study elucidated the role of a new HOXA11-AS/miR-125a-5p/Rab3D regulatory pathway in promoting OS metastasis.Keywords: osteosarcoma (OS), long non-coding RNAs (lncRNAs), HOXA11-AS, miR-125a-5p, Rab3D

Osteosarcoma (OS) is the most common primary malignant bone tumour in adolescence. Lately, light‐emitting diodes (LED)‐based therapy has emerged as a new promising approach for several diseases. However, it remains unknown in human OS. Here, we found that the blue LED irradiation significantly suppressed the proliferation, migration and invasion of human OS cells, while we observed blue LED irradiation increased ROS production through increased NADPH oxidase enzymes NOX2 and NOX4, as well as decreased Catalase (CAT) expression levels. Furthermore, we revealed blue LED irradiation‐induced autophagy characterized by alterations in autophagy protein markers including Beclin‐1, LC3‐II/LC3‐I and P62. Moreover, we demonstrated an enhanced autophagic flux. The blockage of autophagy displayed a remarkable attenuation of anti‐tumour activities of blue LED irradiation. Next, ROS scavenger N‐acetyl‐L‐cysteine (NAC) and NOX inhibitor diphenyleneiodonium (DPI) blocked suppression of OS cell growth, indicating that ROS accumulation might play an essential role in blue LED‐induced autophagic OS cell death. Additionally, we observed blue LED irradiation decreased EGFR activation (phosphorylation), which in turn led to Beclin‐1 release and subsequent autophagy activation in OS cells. Analysis of EGFR colocalization with Beclin‐1 and EGFR‐immunoprecipitation (IP) assay further revealed the decreased interaction of EGFR and Beclin‐1 upon blue LED irradiation in OS cells. In addition, Beclin‐1 down‐regulation abolished the effects of blue LED irradiation on OS cells. Collectively, we concluded that blue LED irradiation exhibited anti‐tumour effects on OS by triggering ROS and EGFR/Beclin‐1‐mediated autophagy signalling pathway, representing a potential approach for human OS treatment. [ABSTRACT FROM AUTHOR]

Osteosarcoma (OS) is the most common bone malignant tumor. However, the genetic basis of OS pathogenesis is still not understood, and occurrence of chemo-resistance is a major reason for the high morbidity of OS patients. Recently, chromodomain helicase/ATPase DNA binding protein 1-like gene (CHD1L) has been identified as a gene related to malignant tumor progression. Unfortunately, its effects on OS development and drug resistance are still not understood. In the study, we attempted to investigate the effects of CHD1L on tumorigenesis and chemoresistance in OS. We found that CHD1L expression was markedly up-regulated in OS samples, especially in cisplatin (cDDP)-resistant patients. We also showed that OS cells with CHD1L knockdown were more sensitive to cDDP treatment with lower IC 50 values. In addition, we found that CHD1L deletion markedly reduced cell proliferation and induced apoptosis in OS cells with cDDP resistance. Moreover, the properties of cancer stem cells were highly suppressed in cDDP-resistant OS cells following CHD1L knockdown. Furthermore, multidrug resistance protein 1 (MDR-1) expression levels were dramatically decreased in OS cells with cDDP resistance when CHD1L was suppressed. Functional analysis indicated that CHD1L knockdown clearly restrained the activation of ERK1/2, protein kinase B (AKT) and NF-κB signaling pathways in cDDP-resistant OS cells. Consistently, animal experiments suggested that CHD1L suppression mitigated cDDP resistance in the generated in vivo xenografts. Collectively, CHD1L could modulate chemoresistance of OS cells to cDDP, and thus may be inspiring findings for overcoming drug resistance in OS. • CHD1L expression is increased in osteosarcoma and in cDDP-resistant patients. • CHD1L inhibition induces apoptosis and represses cancer stem like properties in osteosarcoma in vitro. • CHD1L knockdown reduces MDR-1, p-ERK1/2, p-AKT and p-NF-κB signals in drug-resistant osteosarcoma cells. • CHD1L suppression alleviates cDDP resistance in osteosarcoma in vivo. [ABSTRACT FROM AUTHOR]

Background: Osteosarcoma (OS) poses significant challenges in treatment and lacks reliable prognostic markers. Epigenetic alterations play a crucial role in disease progression. This study aimed to develop an accurate prognostic signature for OS using epigenetic modification genes (EMGs)., Methods: The Therapeutically Applicable Research to Generate Effective Treatments (TARGET)-OS cohort was analyzed. Univariate Cox analysis identified survival-associated EMGs. Based on least absolute shrinkage and selection operator (LASSO) regression and multivariate analysis, a 6-gene prognostic signature termed the epigenetic modification-related prognostic signature (EMRPS) was derived in the testing cohort. Kaplan-Meier and receiver operating characteristic (ROC) curve analysis confirmed predictive accuracy through internal and external validation (GEO accession GSE21257). A prognostic nomogram incorporating EMRPS and clinical features was constructed. Transcriptomic analysis including differential gene expression, Gene Ontology (GO), gene set enrichment analysis (GSEA), and immune infiltration analysis was conducted to explore mechanisms linking EMRPS to OS prognosis. Additionally, EMRPS impact on drug sensitivity was predicted., Results: A 6-gene EMRPS comprising DDX24 , DNAJC1 , HDAC4 , SIRT7 , SP140 and UHRF2 was successfully developed. The high-risk group showed significantly shorter survival, consistently observed in both internal and external validation. EMRPS demonstrated high predictive efficacy for 1-, 3-, and 5-year overall survival, with area under curve (AUC) >0.85 in training and ~0.7 in testing. The nomogram integrating age, gender, metastasis status, and EMRPS exhibited high predictive performance based on concordance index analysis. Mechanistic analysis indicated the low-risk group had increased immune infiltration and activity with higher immune checkpoint expression, reflecting an immune-activated tumor microenvironment (TME) suitable for immunotherapy. Drug sensitivity analysis revealed the low-risk group had increased sensitivity to cisplatin, a first-line OS chemotherapy., Conclusions: Our study successfully established an efficient EMRPS and nomogram, highlighting their potential as novel prognostic markers and indicators for selecting appropriate immunotherapy and chemotherapy candidates in OS treatment., Competing Interests: Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://tcr.amegroups.com/article/view/10.21037/tcr-23-2300/coif). The authors have no conflicts of interest to declare., (2024 Translational Cancer Research. All rights reserved.)

Background: Osteosarcoma (OS) is a malignancy originating from mesenchymal tissue. Microfibril-associated protein 2 ( MFAP2 ) plays a crucial role in cancer, notably promoting epithelial-mesenchymal transition (EMT). However, its involvement in OS remains unexplored., Methods: MFAP2 was silenced in U2OS cells using shRNA targeting MFAP2 (sh-MFAP2) and validated by quantitative real-time polymerase chain reaction (qRT-PCR). We extracted gene chip data of MFAP2 from multiple databases (GSE28424, GSE42572, and GSE126209). Correlation analyses between MFAP2 and the Notch1 pathway identified through the gene set variation analysis (GSVA) enrichment analysis were conducted using the Pearson correlation method. Cellular behaviors (viability, migration, and invasion) were assessed via the Cell Counting Kit-8 (CCK-8), wound healing, and Transwell assays. EMT markers (N-cadherin, vimentin, and β-catenin) and Notch1 levels were examined by western blotting and qRT-PCR. Cell morphology was observed microscopically to evaluate EMT. Finally, the role of MFAP2 in OS was validated through a xenograft tumor model., Results: OS cell lines exhibited higher MFAP2 mRNA expression than normal osteoblasts. MFAP2 knockdown in U2OS cells significantly reduced viability, migration, and invasion, along with downregulation of N-cadherin and vimentin, as well as upregulation of β-catenin. MFAP2 significantly correlated with the Notch1 pathway in OS and its knockdown inhibited Notch1 protein expression. Furthermore, Notch1 activation reversed the inhibitory effects of MFAP2 knockdown on the malignant characteristic of U2OS cells. Additionally, MFAP2 knockdown inhibited tumor growth, expression levels of EMT markers, and Notch1 expression in OS tumor tissues., Conclusions: Our study revealed that MFAP2 was an upstream regulator of the Notch1 signaling pathway to promote EMT in OS. These findings suggested MFAP2 as a potential OS therapy target., Competing Interests: Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://tcr.amegroups.com/article/view/10.21037/tcr-23-2035/coif). The authors have no conflicts of interest to declare., (2024 Translational Cancer Research. All rights reserved.)

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. [ABSTRACT FROM AUTHOR]

Background: Osteosarcoma (OS) is one of the most common malignant bone tumors with a poor overall prognosis. MiR-1224-5p plays an important role in cancer, but its function and mechanism in OS have not been studied. Materials and Methods: The expression of miR-1224-5p and PLK1 was detected by qRT-PCR in OS cells, adjacent tissues, and cell lines. Dual-luciferase reporter gene assay was used to verify the interaction between miR-1224-5p and PLK1. The expression of miR-1224-5p and PLK1 was intervened by transfection with miR-1224-5p mimic, NC mimic, pc-NC and PLK1, respectively. MTT, colony formation assay, Transwell and flow cytometry were used to observe the cell proliferation, invasion and apoptosis. Western blot was used to detect the expression levels of PLK1, PI3K/AKT/mTOR signaling pathway-related proteins, autophagy-related proteins, and epithelial-mesenchymal transition (EMT)-related proteins in the cells. Results: We found that miR-1224-5p was down-regulated and PLK1 expression was up-regulated in OS tissues and cells. On the other hand, it is further confirmed that PLK1 was a target gene of miR-1224-5p. Overexpression of miR-1224-5p inhibited the proliferation, invasion while promoted the apoptosis of OS cells, whereas overexpression of PLK1 promoted the proliferation, invasion and inhibited the apoptosis of OS cells. In the miR-1224-5p group (overexpression of miR-1224-5p), PI3K, AKT, and mTOR protein phosphorylation levels were significantly reduced, while autophagic activity was significantly activated, and the degree of EMT was significantly reduced. But the results in the PLK1 group (overexpression of PLK1) were the opposite. In addition, overexpression of miR-1224-5p reversed the effect of PLK1 upregulation on OS cells. Conclusion: MiR-1224-5p targets PLK1 to inhibit PI3K/AKT/mTOR signaling pathway, thus mediating the proliferation, invasion, apoptosis, autophagy and EMT in OS cells. [ABSTRACT FROM AUTHOR]

Background: Cancer stem cell (CSC) is identified in osteosarcoma (OS) and considered resistant to chemotherapeutic agents. However, the mechanism of osteosarcoma stem cell (OSC) resistant to chemotherapy remains debatable and vague, and the metabolomics feature of OSC is not clarified. Materials and methods: OSC was isolated by using sphere forming assay and identified. Untargeted LC–MS/MS analysis was performed to reveal the metabolomics feature of OSC and underlying mechanisms of OSC resistant to methotrexate (MTX). Results: OSC was efficiently isolated and identified from human OS 143B and MG63 cell lines with enhanced chemo-resistance to MTX. The untargeted LC–MS analysis revealed that OSC showed differential metabolites and perturbed signaling pathways, mainly involved in metabolisms of fatty acid, amino acid, carbohydrate metabolism and nucleic acid. After treated with MTX, metabolomics feature of OSC was mainly involved metabolisms of amino acid, fatty acid, energy and nucleic acid. Moreover, compared with their parental OS cells response to MTX, the differential metabolites and perturbed signaling pathways were mainly involved in metabolism of amino acid, fatty acid and nucleic acid. What's more, Rap1 signaling pathway and Ras signaling pathway were involved in OS cells and their SCs response to MTX. Conclusion: Sphere-forming assay was able to efficiently isolate OSC from human OS cell lines and the untargeted LC–MS/MS analysis was suggested a sufficient methodology to investigate metabolomics features of OS cells and OSCs. Moreover, the metabolomics features of OSCs response to MTX might reveal a further understanding of chemotherapeutic resistance in OS. [ABSTRACT FROM AUTHOR]

Purpose: Osteosarcoma (OS) is the most common primary bone tumor, with high morbidity in infants and adolescents. Long noncoding RNA LINC00313 has been found to modulate papillary thyroid cancer tumorigenesis and to be dysregulate in lung cancer. However, the role of LINC00313 in OS has not yet been addressed. Materials and Methods: We evaluated mRNA and protein expression using real-time quantitative PCR and Western blotting. Cell proliferation was evaluated using MTT; apoptosis and autophagy were assessed with flow cytometry, Western blotting, and/or GFP-LC3 assay. Transwell assay was conducted to measure cell migration and invasion. Potential target sites for LINC00313 and miR-342-3p were predicted with starBase v.2.0 and TargetScan Human, and verified using luciferase reporter assay, RNA immunoprecipitation, and RNA pull-down assay. In vivo, xenogeneic tumors were induced with U2OS and MG-63 cells, separately. Results: LINC00313 was upregulated and miR-342-3p was downregulated in OS tissues and cells. High expression of LINC00313 was associated with shorter overall survival. FOSL2 downregulation and miR-342-3p overexpression suppressed cell proliferation and migratory and invasive abilities while promoting apoptosis and autophagy, all of which were consistent with the effects of LINC00313 knockdown. miR-342-3p, sponged by LINC00313, inversely modulated FOSL2 by targeting MG-63 cells, and FOSL2 expression was positively controlled by LINC00313. LINC00313 knockdown suppressed tumor growth in vivo. Conclusion: LINC00313 is upregulated in OS, and LINC00313 knockdown plays a vital anti-tumor role in OS cell progression through a miR-342-3p/FOSL2 axis. Our study suggests that LINC00313 may be a novel, promising biomarker for diagnosis and prognosis of OS. [ABSTRACT FROM AUTHOR]

Osteosarcoma (OS) is closely related to the dysregulation of various intracellular signaling pathways, especially the PI3K/Akt signaling pathway. Reportedly, HSP90 was responsible for phospho-Akt stabilization, and both AKT1 and HSP90 were upregulated within osteosarcoma. Herein, we demonstrated that AKT1 and HSP90 mRNA and protein expression were upregulated within osteosarcoma tissues and cells; AKT1 knockdown significantly inhibited OS cell viability. HSP90 knockdown suppressed the phosphorylation of AKT1, decreased ki-67 and Vimentin protein levels, enhanced p21 and E-cadherin protein levels, and inhibited OS cell proliferation and migration; AKT1 overexpression exerted opposing effects and significantly attenuated the effects of HSP90 knockdown. miR-485-5p targeted AKT1 and HSP90 3′-UTR to inhibit AKT1 and HSP90 expression. miR-485-5p overexpression dramatically reduced AKT1, HSP90, and ki-67 proteins, increased E-cadherin protein levels, and inhibited OS cell proliferation and migration. In conclusion, HSP90 knockdown blocked the phosphorylation of AKT1 suppressing the proliferation and migration capacity of OS cells via the PI3K/AKT pathway; miR-485-5p binds to HSP90 and AKT1 in their 3′-UTR to inhibit HSP90 and AKT1 expression, therefore exerting a tumor suppressor function within osteosarcoma. [ABSTRACT FROM AUTHOR]

Osteosarcoma (OS), the most common bone cancer, causes high morbidity in children and young adults. TRIM46 is a member of the family of tripartite motif (TRIM)-containing proteins that serve as important regulators of tumorigenesis. Here we investigate the possible role of TRIM46 in OS and the underlying molecular mechanism. We report an increase in the expression of TRIM46 in OS and its association with tumor size, Ennekings stage, and patient prognosis. TRIM46 knockdown inhibits OS cell viability and cell cycle progression and induces apoptosis, while TRIM46 overexpression exerts inverse effects, which are inhibited by peroxisome proliferator-activated receptor alpha (PPAR) overexpression and the nuclear factor kappa B (NF-B) inhibitor, pyrrolidine dithiocarbamate (PDTC). Furthermore, TRIM46 negatively regulates PPAR expression via ubiquitination-mediated protein degradation and modification. PPAR overexpression also inactivates NF-B signaling and NF-B promoter activity in OS cells overexpressing TRIM46. Moreover, TRIM46 knockdown inhibits tumor growth and induces apoptosis of OS cells in vivo. TRIM46 acts as an oncogene in OS by interacting with and ubiquitinating PPAR, resulting in the activation of NF-B signaling pathway. Thus, TRIM46 may be a potential biomarker of carcinogenesis. [ABSTRACT FROM AUTHOR]

[Display omitted] • The scRNA-seq and bulk-seq was combined to uncover the CAFs heterogeneity in OS. • CAFs related risk score, prognostic values and targeting medication were explored. • CAFs identified by bioinformatics were in accordance with validation experiments. Osteosarcoma (OS), with a peak incidence during the adolescent growth spurt, is correlated with poor prognosis for its high malignancy. The tumor microenvironment (TME) is highly complicated, with frequent interactions between tumor and stromal cells. The cancer-associated fibroblasts (CAFs) in the TME have been considered to actively involve in the progression, metastasis, and drug resistance of OS. This study aimed to characterize cellular heterogeneity and molecular characterization in CAFs subtypes and explore the potential targeting therapeutic strategies to improve the prognosis of OS patients. The single-cell atlas of human OS tumor lesions were constructed from the GEO database. Then significant marker genes and potential biological functions for each CAFs subtype were identified and explored using the Seurat R package. Next, by performing the survival analyses and constructing the risk scores for CAFs subtypes, we aimed to identify and characterize the prognostic values of specific marker genes and different CAFs subtypes. Furthermore, we explored the therapeutic targets and innovative drugs targeting different CAFs subtypes based on the GDSC database. Finally, prognoses related CAFs subtypes were further validated through immunohistochemistry (IHC) on clinical OS specimens. Overall, nine main cell clusters and five subtypes of CAFs were identified. The differentially expressed marker genes for each CAFs clusters were then identified. Moreover, through Gene Ontology (GO) enrichment analysis, we defined the CAFs_2 (upregulated CXCL14 and C3), which was closely related to leukocyte migration and chemotaxis, as inflammatory CAFs (iCAFs). Likewise, we defined the CAFs_4 (upregulated CD74, HLA-DRA and HLA-DRB1), which was closely related to antigen process and presentation, as antigen-presenting CAFs (apCAFs). Furthermore, Kaplan-Meier analyses showed that CAFs_2 and CAFs_4 were correlated with poor clinical prognosis of OS patients. Meanwhile, therapeutic drugs targeting CAFs_2 and CAFs_4, such as 17-AAG/Docetaxel/Bleomycin and PHA-793887/NG-25/KIN001-102, were also explored, respectively. Finally, IHC assay confirmed the abundant CAFs_2 and CAFs_4 subtypes infiltration in the OS microenvironment compared with adjacent tissues. Our study revealed the diversity, complexity, and heterogeneity of CAFs in OS, and complemented the single-cell atlas in OS TME. [ABSTRACT FROM AUTHOR]

Background/Aims: MicroRNAs (miRNAs) play an essential role in the tumorigenesis of osteosarcoma (OS). However, the effects of miR-1248 on chemo-resistant potential of OS have not been studied. Here, we addressed this question. Methods: The levels of miR-1248 and apoptotic protein angiotensin II type 1 receptor (AGTR1) in OS specimens were examined by RT-qPCR and Western blotting, respectively. The relationship between miR-1248 and AGTR1 was determined by analysis of Spearman’s Rank Correlation Coefficients. The patient survival was determined with Kaplan-Meier curves. Bioinformatics analyses were done to predict microRNAs (miRNAs) that target AGTR1. The functional binding of miRNAs to AGTR1 mRNA was examined by a dual luciferase reporter assay. Cell viability was determined by an CCK-8 assay. Apoptosis was determined by a fluorescence-based apoptosis assay. Results: The levels of miR-1248 were significantly elevated while the levels of AGTR1 were significantly decreased in OS specimens than in paired adjacent normal tissue. The levels of miR-1248 were negatively correlated to the levels of AGTR1. Moreover, the patients with high miR-1248 levels had poorer survival than those with low MiR-1248 levels, and the patients with low AGTR1 levels had poorer survival than those with high AGTR1 levels. MiR-1248 inhibited protein translation of AGTR1, through binding to the 3’-UTR of the AGTR1 mRNA. The AGTR1-mediated cell apoptosis was suppressed by overexpressing miR-1248, and was augmented by depleting miR-1248. Conclusion: Increased miR-1248 expression in OS may inhibit AGTR1-mediated cancer cell death in chemotherapy. The outcome of chemotherapy may be improved by the suppression of miR-1248 in OS cells.

Background/Aims: Osteosarcoma (OS) is the most common primary malignant bone tumor in children and adolescents. However, the molecular mechanisms regulating osteosarcoma tumorigenesis and progression are still poorly understood. Circular RNAs (circRNAs) have been identified as microRNA sponges and are involved in many important biological processes. This study aims to investigate the global changes in the expression pattern of circRNAs in osteosarcoma and provide a comprehensive understanding of differentially expressed circRNAs. Methods: Microarray based circRNA expression was determined in osteosarcoma cell lines and compared with hFOB1.19, which was used as the normal control. We confirmed the microarray data by real time-qPCR in both osteosarcoma cell lines and tissues. The circRNA/microRNA/mRNA interaction network was predicted using bioinformatics. Gene Ontology analysis and 4 annotation tools for pathway analysis (KEGG, Biocarta, PANTHER and Reactome) were used to predict the functions of differentially expressed circRNAs. Results: We revealed a number of differentially expressed circRNAs and 12 of them were confirmed, which suggests a potential role of circRNAs in OS. Among these differentially expressed circRNAs, hsa_circRNA_103801 was up-regulated in both osteosarcoma cell lines and tissues, while hsa_circRNA_104980 was down-regulated. The most likely potential target miRNAs for hsa_circRNA_103801 include hsa-miR-370-3p, hsa-miR-338-3p and hsa-miR-877-3p, while the most potential target miRNAs of hsa_circRNA_104980 consist of hsa-miR-1298-3p and hsa-miR-660-3p. Functional analysis found that hsa_circRNA_103801 was involved in pathways in cancer, such as the HIF-1, VEGF and angiogenesis pathway, the Rap1 signaling pathway and the PI3K-Akt signaling pathway, while hsa_circRNA_104980 was related to some pathways such as the tight junction pathway. Conclusions: This study has identified the comprehensive expression profile of circRNAs in osteosarcoma for the first time. And the ceRNA network prediction and bioinformatics functional analysis could provide a comprehensive understanding of hsa_circRNA_103801 and hsa_circRNA_104980, which may be involved in the initiation and progression of osteosarcoma. The present study indicates that circRNAs may play important roles in osteosarcoma and thus serve as biomarkers of osteosarcoma diagnosis and treatment.

Background: Osteosarcoma (OS) is an exceptionally aggressive bone neoplasm that predominantly impacts the paediatric and adolescent population, exhibiting unfavourable prognosis. The importance of RNA binding motif protein 14 ( RBM14 ) in the aetiology of OS is not well understood, despite its established involvement in several other types of cancer., Methods: In this study, we conducted an analysis of the expression profiles of RBM14 in cancer tissues and cell lines. To achieve this, we will utilised data obtained from various databases including The Cancer Genome Atlas Program (TCGA) project, The Genotype-Tissue Expression (GTEx) Project, Gene Expression Omnibus (GEO) database, and cancer cell line encyclopedia (CCLE) data. Furthermore, this study also aims to examine the effects of RBM14 on the proliferation, migration, and invasive properties of OS cells using cell functional gain and loss studies. In this study, we carried out an in-depth investigation to explore possible molecular pathways that underlie the regulation of the malignant phenotype found in OS by RBM14 . This investigation involved integrating data from RBM14 overexpression, RBM14 knockdown RNA-seq experiments, and an array comprising 6,096 perturbed genes obtained from the Genetic Perturbation Similarity Analysis Database (GPSAdb). This research offers an opportunity to build a robust conceptual framework for the potential advancement of novel therapeutic approaches that are especially aimed at attacking OS., Results: RBM14 plays an active role in OS by significantly contributing to the enhancement of cellular proliferation, migration, and invasion. At the molecular level, it is probable that RBM14 exerts control over the malignant characteristics of OS through its modulation of the Hippo signalling system., Conclusions: The above-mentioned findings underscore the significant importance of RBM14 as an intriguing target for therapy for the mitigation and management of OS. This particular protein holds an excellent opportunity for the development of novel and efficacious therapeutic approaches that possess the potential to yield favorable results for patients affected with OS., Competing Interests: Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://tcr.amegroups.com/article/view/10.21037/tcr-23-2070/coif). The authors have no conflicts of interest to declare., (2024 Translational Cancer Research. All rights reserved.)

Osteosarcoma (OS), a primary malignant bone tumor, poses significant challenges in diagnosis and prognosis. It is a painful medical burden, and treating it is still a difficult issue. Osteopontin (OPN), a multifunctional extracellular matrix protein, has emerged as a promising biomarker in this context. This systematic review explores the role of OPN as a diagnostic and prognostic marker in OS, highlighting its potential in enhancing early detection, monitoring disease progression, and predicting patient outcomes. Various studies have demonstrated elevated levels of OPN in OS patients, correlating with tumor aggressiveness, metastatic potential, and poor prognosis. In addition, OPN's involvement in tumor microenvironment regulation and metastatic processes underscores its clinical relevance as a biomarker. For this systematic review, comprehensive literature searches were conducted in the PubMed databases for research published between the database's establishment and November 11, 2022. Out of the nine studies that were available for analysis, a higher level of OPN in primary osteogenic sarcoma patients indicates a poorer prognosis and higher incidence of metastasis. OS has not shown commensurable progress with concerns to treatment approches and survical outcomes. However, the discovery of a biological marker that can predict metastasis and severity will be a groundbreaking development for advancements in OS diagnosis and treatment. Therefore, understanding the intricate interplay between OPN and OS pathogenesis holds promise for improving patient management and developing targeted therapeutic strategies., Competing Interests: The authors have declared that no competing interests exist., (Copyright © 2024, Agrawal et al.)

Osteosarcoma (OS) accounts for 9 percent of cancer-related deaths in young people. The PI3K/Akt signaling, a well-known carcinogenic signaling pathway in human cancer, cooperates with other signaling pathways such as Wnt signaling to promote cancer progression. Wnt7b, as a transforming member of the Wnt family, could activate mTORC1 through PI3K-AKT signaling and is upregulated in OS. In the present study, we found that miR-342-5p inhibits Wnt7b expression via direct binding to Wnt7b 3′-UTR. miR-342-5p overexpression remarkably suppressed the viability and invasion while enhanced the apoptosis of OS cells; meanwhile, Wnt7b, β-catenin, c-myc, and cyclin D1 proteins were reduced while E-cadherin protein showed to be increased. Consistent with its expression pattern, Wnt7b exerted oncogenic effects on OS cells. Wnt7b could significantly attenuate the impacts of miR-342-5p. In conclusion, we demonstrated a miR-342-5p/Wnt7b axis that regulates the capacity of OS cells to proliferate and to invade through Wnt/β-catenin signaling. The miR-342-5p/Wnt7b axis might be novel targets for OS targeted therapy, which needs further in vivo and clinical investigations. [ABSTRACT FROM AUTHOR]

A growing amount of evidence has shown that long noncoding RNAs (lncRNAs) play crucial roles in osteosarcoma (OS). However, little knowledge is available about the functional roles and molecular mechanisms of lncRNA Alu‐mediated p21 transcriptional regulator (APTR) in OS. Herein, APTR expression was demonstrated to be significantly upregulated in OS tumor tissues and four OS cell lines (including MG63, 143B, Saos‐2, and HOS) compared with the adjacent tissues and human osteoblast cell line hFOB1.19, respectively. We confirmed miR‐132‐3p to be a target for APTR, and its expression was demonstrated to be inhibited by APTR. In functional terms, knockdown of APTR and overexpression of miR‐132‐3p both, remarkably repressed human OS cell proliferation, invasion and migration, and induced apoptosis. Also, Yes‐associated protein 1 (YAP1) was determined as an inhibitory target of miR‐132‐3p. Moreover, our findings demonstrated that the repression of YAP1 protein expression and the suppression of Ki‐67, MMP9, and Bcl2 expression induced by APTR knockdown required increased miR‐132‐3p. Thus, APTR contributed to OS progression through repression of miR‐132‐3p and upregulation of YAP1 expression. Therefore, we have uncovered a novel regulatory mechanism by which the APTR/miR‐132‐3p/YAP1 axis can regulate OS progression. In summary, our study was the first to establish that Alu‐mediated p21 transcriptional regulator (APTR) can function as an oncogenic long noncoding RNA in osteosarcoma (OS). Most importantly, we explored a new regulatory mechanism of the APTR/miR‐132‐3p/Yes‐associated protein 1 axis in the regulation of OS cells, which could be a potential therapeutic biomarker for OS. [ABSTRACT FROM AUTHOR]

Osteosarcoma (OS), as the most frequent primary malignancy of bone, is characterized by the presence of malignant mesenchymal cells. In the current study, our aim was to explore the possible effects Fos‐like antigen‐1 (FOSL1) had on the silencing regarding OS cell proliferation, invasion, and migration through the activation of the extracellular‐signal‐regulated kinase (ERK)/activator protein‐1 (AP‐1) signaling pathway. After the collection of OS on top of already having the adjacent normal tissue samples, the protein positive expression rate of FOSL1 was then measured by implementing the use of immunohistochemistry and discovered that FOSL1 was robustly expressed in OS. Later, to better grasp the impact FOSL1 projects on OS and its underlying mechanism, we determined the OS related genes as well as the ERK/AP‐1 signaling pathway related genes expression by using a reverse‐transcription quantitative polymerase chain reaction and western blot assay techniques. The results of the aforementioned two experiments revealed that the FOSL1 depletion had downregulated the expression of OS related genes by simultaneously downregulating the ERK/AP‐1 signaling pathway. Moreover, cell proliferation, cycle, apoptosis, invasion, and migration of FOS1 were all tested by using a cell counting kit‐8 assay, flow cytometry, Transwell assay, and scratch test, and these results presented that silencing of the FOSL1 gene inhibited OS cell proliferation, invasion, and migration. Our findings revealed a novel mechanism by which FOSL1 depletion played a significantly negative role in the OS progression through the regulation of the ERK/AP‐1 signaling pathway. Functional suppression of FOSL1 might be a future therapeutic strategy regarding OS. Our findings revealed a novel mechanism by which Fos‐like antigen‐1 (FOS1) depletion played a significantly negative role in the osteosarcoma (OS) progression through the regulation of the extracellular‐signal‐regulated kinase/activator protein‐1 signaling pathway. Functional suppression of FOSL1 might be a future therapeutic strategy regarding OS. [ABSTRACT FROM AUTHOR]

Background: The proteasome exists in all eukaryotic cells and provides the main route of intracellular proteins degradation involved in cell growth and apoptosis. Proteasome inhibition could block protein degradation pathways and disturb regulatory networks, possibly leading to profound effects on cell growth, particularly in cancer cells. A proteasome inhibitor with an appropriate toxicity index for malignant cells rather than normal cells would be an attractive anticancer therapy. Methods: The human osteosarcoma (OS) cell lines MG-63 and Saos-2 and normal osteoblast cells were used to study the antitumour activity of the proteasome inhibitor MLN9708/2238. Results: MLN2238 inhibited cell growth, induced cell cycle arrest and apoptosis, and attenuated the invasion abilities of MG-63 and Saos-2 cells, with little cytotoxicity to normal cells. In addition, MLN2238 promoted antitumour mechanisms including the accumulation of E2F1, P53, P21 and other negative G2/M checkpoint proteins; up-regulated the relative expression ratio of BAX/BCL-2, APAF-1 and pro-apoptotic proteins of the BCL-2 family; triggered mitochondrial outer membrane permeabilization (MOMP); down-regulated BCL-2 and XIAP; activated caspase3/8/9; and suppressed MMP2/9 expression and secretion levels. Conclusions: The proteasome may be a novel biochemical target for OS treatment in vitro. Our study provides a promising mechanistic framework for MLN9708/2238 in OS treatment, supporting its clinical development.