Notch activation as a driver of osteogenic sarcoma

Targeting the Wnt/β-catenin cascade in osteosarcoma: The potential of ncRNAs as biomarkers and therapeutics

Osteosarcoma (OS) is a bone cancer which stems from several sources and presents with diverse clinical features, making evaluation and treatment difficult. Chemotherapy tolerance and restricted treatment regimens hinder progress in survival rates, requiring new and creative therapeutic strategies. The Wnt/β-catenin system has been recognised as an essential driver of OS development, providing potential avenues for therapy. Non-coding RNAs (ncRNAs), such as circular RNAs (circRNAs), long non-coding RNAs (lncRNAs), and microRNAs (miRNAs), are essential in modulating the Wnt/β-catenin cascade in OS. MiRNAs control the system by targeting vital elements, while lncRNAs and circRNAs interact with system genes, impacting OS growth and advancement. This paper thoroughly analyses the intricate interplay between ncRNAs and the Wnt/β-catenin cascade in OS. We examine how uncontrolled levels of miRNAs, lncRNAs, and circRNAs lead to an abnormal Wnt/β-catenin network, which elevates the development, spread, and susceptibility to the treatment of OS. We emphasise the potential of ncRNAs as diagnostic indicators and avenues for treatment in OS care. The review offers valuable insights for academics and clinicians studying OS aetiology and creating new treatment techniques for the ncRNA-Wnt/β-catenin cascade. Utilising the oversight roles of ncRNAs in the Wnt/β-catenin system shows potential for enhancing the outcomes of patients and progressing precision medicine in OS therapy.

Clinical, pathologic and molecular findings in 2 Rottweiler littermates with appendicular osteosarcoma

Appendicular osteosarcoma was diagnosed and treated in a pair of littermate Rottweiler dogs, resulting in distinctly different clinical outcomes despite similar therapy within the context of a prospective, randomized clinical trial (NCI-COTC021/022). Histopathology, immunohistochemistry, mRNA sequencing, and targeted DNA hotspot sequencing techniques were applied to both dogs' tumors to define factors that could underpin their differential response to treatment. We describe the comparison of their clinical, histologic and molecular features, as well as those from a companion cohort of Rottweiler dogs, providing new insight into potential prognostic biomarkers for canine osteosarcoma.

Emerging roles of long non-coding RNAs in osteosarcoma

Osteosarcoma (OS) is a highly aggressive and lethal malignant bone tumor that primarily afflicts children, adolescents, and young adults. However, the molecular mechanisms underlying OS pathogenesis remain obscure. Mounting evidence implicates dysregulated long non-coding RNAs (lncRNAs) in tumorigenesis and progression. These lncRNAs play a pivotal role in modulating gene expression at diverse epigenetic, transcriptional, and post-transcriptional levels. Uncovering the roles of aberrant lncRNAs would provide new insights into OS pathogenesis and novel tools for its early diagnosis and treatment. In this review, we summarize the significance of lncRNAs in controlling signaling pathways implicated in OS development, including the Wnt/β-catenin, PI3K/AKT/mTOR, NF-κB, Notch, Hippo, and HIF-1α. Moreover, we discuss the multifaceted contributions of lncRNAs to drug resistance in OS, as well as their potential to serve as biomarkers and therapeutic targets. This review aims to encourage further research into lncRNA field and the development of more effective therapeutic strategies for patients with OS.

Comprehensive analysis of the proximity-dependent nuclear interactome for the oncoprotein NOTCH1 in live cells

Notch signaling plays a critical role in cell fate decisions in all cell types. Furthermore, gain-of-function mutations in NOTCH1 have been uncovered in many human cancers. Disruption of Notch signaling has recently emerged as an attractive disease treatment strategy. However, the nuclear interaction landscape of the oncoprotein NOTCH1 remains largely unexplored. We therefore employed here a proximity-dependent biotin identification approach to identify in vivo protein associations with the nuclear Notch1 intracellular domain in live cells. We identified a large set of previously reported and unreported proteins that associate with NOTCH1, including general transcription and elongation factors, DNA repair and replication factors, coactivators, corepressors, and components of the NuRD and SWI/SNF chromatin remodeling complexes. We also found that Notch1 intracellular domain associates with protein modifiers and components of other signaling pathways that may influence Notch signal transduction and protein stability such as USP7. We further validated the interaction of NOTCH1 with histone deacetylase 1 or GATAD2B using protein network analysis, proximity-based ligation, in vivo cross-linking and coimmunoprecipitation assays in several Notch-addicted cancer cell lines. Through data mining, we also revealed potential drug targets for the inhibition of Notch signaling. Collectively, these results provide a valuable resource to uncover the mechanisms that fine-tune Notch signaling in tumorigenesis and inform therapeutic targets for Notch-addicted tumors.

Hdac1 and Hdac2 positively regulate Notch1 gain-of-function pathogenic signaling in committed osteoblasts of male mice

BACKGROUND

Skeletal development requires precise extrinsic and intrinsic signals to regulate processes that form and maintain bone and cartilage. Notch1 is a highly conserved signaling receptor that regulates cell fate decisions by controlling the duration of transcriptional bursts. Epigenetic molecular events reversibly modify DNA and histone tails by influencing the spatial organization of chromatin and can fine-tune the outcome of a Notch1 transcriptional response. Histone deacetylase 1 and 2 (HDAC1 and HDAC2) are chromatin modifying enzymes that mediate osteoblast differentiation. While an HDAC1-Notch interaction has been studied in vitro and in Drosophila, its role in mammalian skeletal development and disorders is unclear. Osteosclerosis is a bone disorder with an abnormal increase in the number of osteoblasts and excessive bone formation.

METHODS

Here, we tested whether Hdac1/2 contribute to the pathogenesis of osteosclerosis in a murine model of the disease owing to conditionally cre-activated expression of the Notch1 intracellular domain in immature osteoblasts.

RESULTS

Importantly, selective homozygous deletions of Hdac1/2 in osteoblasts partially alleviate osteosclerotic phenotypes (Col2.3kb-Cre; TGRosaN1ICD/+ ; Hdac1flox/flox ; Hdac2flox/flox ) with a 40% decrease in bone volume and a 22% decrease in trabecular thickness in 4 weeks old when compared to male mice with heterozygous deletions of Hdac1/2 (Col2.3 kb-Cre; TGRosaN1ICD/+ ; Hdac1flox/+ ; Hdac2flox/+ ). Osteoblast-specific deletion of Hdac1/2 in male and female mice results in no overt bone phenotype in the absence of the Notch1 gain-of-function (GOF) allele.

CONCLUSIONS

These results provide evidence that Hdac1/2 contribute to Notch1 pathogenic signaling in the mammalian skeleton. Our study on epigenetic regulation of Notch1 GOF-induced osteosclerosis may facilitate further mechanistic studies of skeletal birth defects caused by Notch-related GOF mutations in human patients, such as Adams-Oliver disease, congenital heart disease, and lateral meningocele syndrome.

Abrogation of stemness in osteosarcoma by the mithramycin analog EC-8042 is mediated by its ability to inhibit NOTCH-1 signaling

Osteosarcomas are frequently associated to a poor prognosis and a modest response to current treatments. EC-8042 is a well-tolerated mithramycin analog that has demonstrated an efficient ability to eliminate tumor cells, including cancer stem cell subpopulations (CSC), in sarcomas. In transcriptomic and protein expression analyses, we identified NOTCH1 signaling as one of the main pro-stemness pathways repressed by EC-8042 in osteosarcomas. Overexpression of NOTCH-1 resulted in a reduced anti-tumor effect of EC-8042 in CSC-enriched 3D tumorspheres cultures. On the other hand, the depletion of the NOTCH-1 downstream target HES-1 was able to enhance the action of EC-8042 on CSCs. Moreover, HES1 depleted cells failed to recover after treatment withdrawal and showed reduced tumor growth potential in vivo. In contrast, mice xenografted with NOTCH1-overexpressing cells responded worse than parental cells to EC-8042. Finally, we found that active NOTCH1 levels in sarcoma patients was associated to advanced disease and lower survival. Overall, these data highlight the relevant role that NOTCH1 signaling plays in mediating stemness in osteosarcoma. Moreover, we demonstrate that EC-8042 is powerful inhibitor of NOTCH signaling and that the anti-CSC activity of this mithramycin analog highly rely on its ability to repress this pathway.

Oncogenic signaling-mediated regulation of chromatin during tumorigenesis

Signaling pathways play critical roles in executing and controlling important biological processes within cells. Cells/organisms trigger appropriate signal transduction pathways in order to turn on or off intracellular gene expression in response to environmental stimuli. An orchestrated regulation of different signaling pathways across different organs and tissues is the basis of many important biological functions. Presumably, any malfunctions or dysregulation of these signaling pathways contribute to the pathogenesis of disease, particularly cancer. In this review, we discuss how the dysregulation of signaling pathways (TGF-β signaling, Hippo signaling, Wnt signaling, Notch signaling, and PI3K-AKT signaling) modulates chromatin modifications to regulate the epigenome, thereby contributing to tumorigenesis and metastasis.

Signal Pathways and microRNAs in Osteosarcoma Growth and the Dual Role of Mesenchymal Stem Cells in Oncogenesis

The major challenges in Osteosarcoma (OS) therapy are its heterogeneity and drug resistance. The development of new therapeutic approaches to overcome the major growth mechanisms of OS is urgently needed. The search for specific molecular targets and promising innovative approaches in OS therapy, including drug delivery methods, is an urgent problem. Modern regenerative medicine focuses on harnessing the potential of mesenchymal stem cells (MSCs) because they have low immunogenicity. MSCs are important cells that have received considerable attention in cancer research. Currently, new cell-based methods for using MSCs in medicine are being actively investigated and tested, especially as carriers for chemotherapeutics, nanoparticles, and photosensitizers. However, despite the inexhaustible regenerative potential and known anticancer properties of MSCs, they may trigger the development and progression of bone tumors. A better understanding of the complex cellular and molecular mechanisms of OS pathogenesis is essential to identify novel molecular effectors involved in oncogenesis. The current review focuses on signaling pathways and miRNAs involved in the development of OS and describes the role of MSCs in oncogenesis and their potential for antitumor cell-based therapy.

The Intricate Notch Signaling Dynamics in Therapeutic Realms of Cancer

The Notch pathway is remarkably simple without the interventions of secondary messengers. It possesses a unique receptor-ligand interaction that imparts signaling upon cleavage of the receptor followed by the nuclear localization of its cleaved intracellular domain. It is found that the transcriptional regulator of the Notch pathway lies at the intersection of multiple signaling pathways that enhance the aggressiveness of cancer. The preclinical and clinical evidence supports the pro-oncogenic function of Notch signaling in various tumor subtypes. Owing to its oncogenic role, the Notch signaling pathway assists in enhanced tumorigenesis by facilitating angiogenesis, drug resistance, epithelial to mesenchymal transition, etc., which is also attributed to the poor outcome in patients. Therefore, it is extremely vital to discover a suitable inhibitor to downregulate the signal-transducing ability of Notch. The Notch inhibitory agents, such as receptor decoys, protease (ADAM and γ-secretase) inhibitors, and monoclonal/bispecific antibodies, are being investigated as candidate therapeutic agents. Studies conducted by our group exemplify the promising results in ablating tumorigenic aggressiveness by inhibiting the constituents of the Notch pathway. This review deals with the detailed mechanism of the Notch pathways and their implications in various malignancies. It also bestows us with the recent therapeutic advances concerning Notch signaling in the context of monotherapy and combination therapy.

Cellular dynamics of distinct skeletal cells and the development of osteosarcoma

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 and mouse 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.

Self-Renewal and Pluripotency in Osteosarcoma Stem Cells' Chemoresistance: Notch, Hedgehog, and Wnt/β-Catenin Interplay with Embryonic Markers

Osteosarcoma is a highly malignant bone tumor derived from mesenchymal cells that contains self-renewing cancer stem cells (CSCs), which are responsible for tumor progression and chemotherapy resistance. Understanding the signaling pathways that regulate CSC self-renewal and survival is crucial for developing effective therapies. The Notch, Hedgehog, and Wnt/β-Catenin developmental pathways, which are essential for self-renewal and differentiation of normal stem cells, have been identified as important regulators of osteosarcoma CSCs and also in the resistance to anticancer therapies. Targeting these pathways and their interactions with embryonic markers and the tumor microenvironment may be a promising therapeutic strategy to overcome chemoresistance and improve the prognosis for osteosarcoma patients. This review focuses on the role of Notch, Hedgehog, and Wnt/β-Catenin signaling in regulating CSC self-renewal, pluripotency, and chemoresistance, and their potential as targets for anti-cancer therapies. We also discuss the relevance of embryonic markers, including SOX-2, Oct-4, NANOG, and KLF4, in osteosarcoma CSCs and their association with the aforementioned signaling pathways in overcoming drug resistance.

NOTCH Signaling in Osteosarcoma

The combination of neoadjuvant chemotherapy and surgery has been promoted for the treatment of osteosarcoma; however, the local recurrence and lung metastasis rates remain high. Therefore, it is crucial to explore new therapeutic targets and strategies that are more effective. The NOTCH pathway is not only involved in normal embryonic development but also plays an important role in the development of cancers. The expression level and signaling functional status of the NOTCH pathway vary in different histological types of cancer as well as in the same type of cancer from different patients, reflecting the distinct roles of the Notch pathway in tumorigenesis. Studies have reported abnormal activation of the NOTCH signaling pathway in most clinical specimens of osteosarcoma, which is closely related to a poor prognosis. Similarly, studies have reported that NOTCH signaling affected the biological behavior of osteosarcoma through various molecular mechanisms. NOTCH-targeted therapy has shown potential for the treatment of osteosarcoma in clinical research. After the introduction of the composition and biological functions of the NOTCH signaling pathway, the review paper discussed the clinical significance of dysfunction in osteosarcoma. Then the paper reviewed the recent relevant research progress made both in the cell lines and in the animal models of osteosarcoma. Finally, the paper explored the potential of the clinical application of NOTCH-targeted therapy for the treatment of osteosarcoma.

Loss of RanGAP1 drives chromosome instability and rapid tumorigenesis of osteosarcoma

Chromothripsis is a catastrophic event of chromosomal instability that involves intensive fragmentation and rearrangements within localized chromosomal regions. However, its cause remains unclear. Here, we show that reduction and inactivation of Ran GTPase-activating protein 1 (RanGAP1) commonly occur in human osteosarcoma, which is associated with a high rate of chromothripsis. In rapidly expanding mouse osteoprogenitors, RanGAP1 deficiency causes chromothripsis in chr1q, instant inactivation of Rb1 and degradation of p53, consequent failure in DNA damage repair, and ultrafast osteosarcoma tumorigenesis. During mitosis, RanGAP1 anchors to the kinetochore, where it recruits PP1-γ to counteract the activity of the spindle-assembly checkpoint (SAC) and prevents TOP2A degradation, thus safeguarding chromatid decatenation. Loss of RanGAP1 causes SAC hyperactivation and chromatid decatenation failure. These findings demonstrate that RanGAP1 maintains mitotic chromosome integrity and that RanGAP1 loss drives tumorigenesis through its direct effects on SAC and decatenation and secondary effects on DNA damage surveillance.

Multi-omics analysis identifies osteosarcoma subtypes with distinct prognosis indicating stratified treatment

Osteosarcoma (OS) is a primary malignant bone tumor that most commonly affects children, adolescents, and young adults. Here, we comprehensively analyze genomic, epigenomic and transcriptomic data from 121 OS patients. Somatic mutations are diverse within the cohort, and only TP53 is significantly mutated. Through unsupervised integrative clustering of the multi-omics data, we classify OS into four subtypes with distinct molecular features and clinical prognosis: (1) Immune activated (S-IA), (2) Immune suppressed (S-IS), (3) Homologous recombination deficiency dominant (S-HRD), and (4) MYC driven (S-MD). MYC amplification with HR proficiency tumors is identified with a high oxidative phosphorylation signature resulting in resistance to neoadjuvant chemotherapy. Potential therapeutic targets are identified for each subtype, including platinum-based chemotherapy, immune checkpoint inhibitors, anti-VEGFR, anti-MYC and PARPi-based synthetic lethal strategies. Our comprehensive integrated characterization provides a valuable resource that deepens our understanding of the disease, and may guide future clinical strategies for the precision treatment of OS.

Regulation of Molecular Targets in Osteosarcoma Treatment

The most prevalent malignant bone tumor, osteosarcoma, affects the growth plates of long bones in adolescents and young adults. Standard chemotherapeutic methods showed poor response rates in patients with recurrent and metastatic phases. Therefore, it is critical to develop novel and efficient targeted therapies to address relapse cases. In this regard, RNA interference technologies are encouraging options in cancer treatment, in which small interfering RNAs regulate the gene expression following RNA interference pathways. The determination of target tissue is as important as the selection of tissue-specific promoters. Moreover, small interfering RNAs should be delivered effectively into the cytoplasm. Lentiviral vectors could encapsulate and deliver the desired gene into the cell and integrate it into the genome, providing long-term regulation of targeted genes. Silencing overexpressed genes promote the tumor cells to lose invasiveness, prevents their proliferation, and triggers their apoptosis. The uniqueness of cancer cells among patients requires novel therapeutic methods that treat patients based on their unique mutations. Several studies showed the effectiveness of different approaches such as microRNA, drug- or chemotherapy-related methods in treating the disease; however, identifying various targets was challenging to understanding disease progression. In this regard, the patient-specific abnormal gene might be targeted using genomics and molecular advancements such as RNA interference approaches. Here, we review potential therapeutic targets for the RNA interference approach, which is applicable as a therapeutic option for osteosarcoma patients, and we point out how the small interfering RNA method becomes a promising approach for the unmet challenge.

Protein kinase CK2 phosphorylates a conserved motif in the Notch effector E(spl)-Mγ

Across metazoan animals, the effects of Notch signaling are mediated via the Enhancer of Split (E(spl)/HES) basic Helix-Loop-Helix-Orange (bHLH-O) repressors. Although these repressors are generally conserved, their sequence diversity is, in large part, restricted to the C-terminal domain (CtD), which separates the Orange (O) domain from the penultimate WRPW tetrapeptide motif that binds the obligate co-repressor Groucho. While the kinases CK2 and MAPK target the CtD and regulate Drosophila E(spl)-M8 and mammalian HES6, the generality of this regulation to other E(spl)/HES repressors has remained unknown. To determine the broader impact of phosphorylation on this large family of repressors, we conducted bioinformatics, evolutionary, and biochemical analyses. Our studies identify E(spl)-Mγ as a new target of native CK2 purified from Drosophila embryos, reveal that phosphorylation is specific to CK2 and independent of the regulatory CK2-β subunit, and identify that the site of phosphorylation is juxtaposed to the WRPW motif, a feature unique to and conserved in the Mγ homologues over 50 × 10⁶ years of Drosophila evolution. Thus, a preponderance of E(spl) homologues (four out of seven total) in Drosophila are targets for CK2, and the distinct positioning of the CK2 and MAPK sites raises the prospect that phosphorylation underlies functional diversity of bHLH-O proteins.

A novel necroptosis-related lncRNAs signature effectively predicts the prognosis for osteosarcoma and is associated with immunity

Background: Necroptosis is closely related to tumorigenesis and development. Accumulating evidence has revealed that long non-coding RNAs (lncRNAs) are also central players in osteosarcoma (OS). However, the role of necroptosis-related lncRNAs in OS remains unclear. In the present study, we aim to craft a prognostic signature based on necroptosis-related lncRNAs to improve the OS prognosis prediction.

Methods: The signature based on necroptosis-related lncRNAs was discovered using univariate Cox, least absolute shrinkage and selection operator (LASSO), and multivariate Cox regression analysis. The prognosis efficiency of the signature was then estimated by employing various bioinformatics methods. Subsequently, immunological analysis and Gene Set Enrichment Analysis (GSEA) were used to explore the association between necroptosis-related lncRNAs with clinical outcomes and immune status. More importantly, several necroptosis-related lncRNAs were validated with RT-qPCR.

Results: Consequently, a novel prognosis signature was successfully constructed based on eight necroptosis-related lncRNAs. Meanwhile, the novel necroptosis-related lncRNAs model could distribute OS patients into two risk groups with a stable and accurate predictive ability. Additionally, the GSEA and immune analysis revealed that the necroptosis-related lncRNAs signature affects the development and prognosis of OS by regulating the immune status. The necroptosis-related lncRNA signature was closely correlated with multiple anticancer agent susceptibility. Moreover, the RT-qPCR results indicated several necroptosis-related lncRNAs were significantly differently expressed in osteosarcoma and osteoblast cell lines.

Conclusion: In this summary, a novel prognostic signature integrating necroptosis-related lncRNAs was firstly constructed and could accurately predict the prognosis of OS. This study may increase the predicted value and guide the personalized chemotherapy treatment for OS.

EID3 Promotes Cancer Stem Cell-Like Phenotypes in Osteosarcoma through the Activation of PI3K-AKT Signaling Pathway

The aim of this study is to elucidate molecular mechanism by which E1A-like inhibitor of differentiation 3 (EID3) promotes cancer stem cell-like phenotypes in osteosarcoma. Overexpression of EID3 in osteosarcoma cells generated more spherical clones, enhanced the expression of stemness-associated genes, and promoted chemoresistance, invasion, and metastasis. Furthermore, osteosarcoma cells overexpressing EID3 had increased ability to grow in suspension as osteospheres with high expression of Sox2 and stem cell marker CD133. In addition, knockdown of EID3 reduced sphere formation and inhibited osteosarcoma cell migration and invasion. RNA sequencing and bioinformatics analysis revealed that PI3K-Akt signaling pathway and MAPK pathway­related genes were enriched in osteosarcoma cells with high expression of EID3. Taken together, EID3 promotes osteosarcoma, and EID3–PI3K-Akt axis is a potential therapeutic target for osteosarcoma treatment.

Non-classical Notch signaling by MDA-MB-231 breast cancer cell-derived small extracellular vesicles promotes malignancy in poorly invasive MCF-7 cells

Aberrant Notch signaling is implicated in breast cancer progression, and recent studies have demonstrated links between the Notch pathway components Notch1 and Notch1 intracellular domain (N1ICD) with poor clinical outcomes. Growing evidence suggests that Notch signaling can be regulated by small extracellular vesicles (SEVs). Here, we used breast cancer cell models to examine whether SEVs are involved in functional Notch signaling. We found that Notch components are packaged into MDA-MB-231- and MCF-7-derived SEVs, although higher levels of N1ICD were detected in SEVs from the more aggressive MDA-MB-231 cell line than from poorly invasive MCF-7 cells. SEV-Notch components were functional, as SEVs cargo from MDA-MB-231 cells induced the expression of Notch target genes in MCF-7 cells and triggered a more invasive and proliferative phenotype concomitant with the acquisition of mesenchymal features. Neutralization of the N1ICD cargo in MDA-MB-231-derived SEVs significantly reduced their potential to enhance the aggressiveness of MCF-7 cells in vitro and in a xenograft model. Overall, our results indicate that a SEV-mediated non-classical pathway of Notch signal transduction in breast cancer models bypasses the need for classical ligand-receptor interactions, which may have important implications in cancer.

RecQ Helicase Somatic Alterations in Cancer

Named the “caretakers” of the genome, RecQ helicases function in several pathways to maintain genomic stability and repair DNA. This highly conserved family of enzymes consist of five different proteins in humans: RECQL1, BLM, WRN, RECQL4, and RECQL5. Biallelic germline mutations in BLM, WRN, and RECQL4 have been linked to rare cancer-predisposing syndromes. Emerging research has also implicated somatic alterations in RecQ helicases in a variety of cancers, including hematological malignancies, breast cancer, osteosarcoma, amongst others. These alterations in RecQ helicases, particularly overexpression, may lead to increased resistance of cancer cells to conventional chemotherapy. Downregulation of these proteins may allow for increased sensitivity to chemotherapy, and, therefore, may be important therapeutic targets. Here we provide a comprehensive review of our current understanding of the role of RecQ DNA helicases in cancer and discuss the potential therapeutic opportunities in targeting these helicases.

MicroRNAs and osteosarcoma: Potential targets for inhibiting metastasis and increasing chemosensitivity

Osteosarcoma (OS) is the third most common cancer in young adults after lymphoma and brain cancer. Metastasis, like other cellular events, is dependent on signaling pathways; a series of changes in some proteins and signaling pathways pave the way for OS cells to invade and migrate. Ezrin, TGF-β, Notch, RUNX2, matrix metalloproteinases (MMPs), Wnt/β-catenin, and phosphoinositide 3-kinase (PI3K)/AKT are among the most important of these proteins and signaling pathways. Despite the improvements in treating OS, the overall survival of patients suffering from the metastatic disease has not experienced any significant change after surgical treatments and chemotherapy and 5-years overall survival in patients with metastatic OS is about 20%. Studies have shown that overexpression or inhibition of some microRNAs (miRNAs) has significant effects in limiting the invasion and migration of OS cells. The results of these studies highlight the potential of the clinical application of some miRNA mimics and miRNA inhibitors (antagomiRs) to inhibit OS metastasis in the future. In addition, some studies have shown that miRNAs are associated with the most important drug resistance mechanisms in OS, and some miRNAs are highly effective targets to increase chemosensitivity. The results of these studies suggest that miRNA mimics and antagomiRs may be helpful to increase the efficacy of conventional chemotherapy drugs in the treatment of metastatic OS. In this article, we discussed the role of various signaling pathways and the involved miRNAs in the metastasis of OS, attempting to provide a comprehensive review of the literature on OS metastasis and chemosensitivity.

Nanoengineering a metal-organic framework for osteosarcoma chemo-immunotherapy by modulating indoleamine-2,3-dioxygenase and myeloid-derived suppressor cells

Background

The high postoperative recurrence rate and refractoriness of relapsed tumors are still a conundrum for the clinical management of osteosarcoma (OS). New therapeutic options are urgently needed. Depriving the nourishment of myeloid-derived suppressor cells is a novel strategy to improve the immunosuppressive tumor microenvironment for enhanced OS therapy.

Methods

We synthesized a hyaluronic acid (HA)-modified metal–organic framework for combinational chemotherapy and immunotherapy of OS. Zeolitic Imidazolate Framework-8 (ZIF-8) was prepared by a one-pot synthetic method, Gemcitabine (Gem) and D-1-Methyltryptophan (D-1-MT) were loaded into the ZIF-8 during the synthesis process to make ZIF-8@Gem/D-1-MT nanoparticles (NPs). The end product (HA/ZIF-8@Gem/D-1-MT NPs) was obtained by HA modification on the surface of ZIF-8@Gem/D-1-MT NPs. The obtained HA/ZIF-8@Gem/D-1-MT NPs have excellent potential as a drug delivery vector for chemotherapy and immunotherapy in vitro and vivo.

Results

The results indicate that HA/ZIF-8@Gem/D-1-MT NPs were readily taken up by OS cells, and that the Gem and D-1-MT were effectively released into the acidic environment. The HA/ZIF-8@Gem/D-1-MT NPs could efficiently decrease OS cell viability (proliferation, apoptosis, cell cycle, migration and invasion). And HA/ZIF-8@Gem/D-1-MT NPs could reactivate antitumor immunity by inhibiting indoleamine 2,3 dioxygenase and myeloid-derived suppressor cells. Furthermore, animal experiments confirmed that HA/ZIF-8@Gem/D-1-MT NPs could induce intratumoral immune responses and inhibit tumor growth. Additionally, HA/ZIF-8@Gem/D-1-MT NPs have a good safety profile.

Conclusions

Our findings demonstrate that the combination of Gem with D-1-MT brings new hope for the improved treatment of OS, while the generation of the nanosystem has increased the application potential and flexibility of this strategy.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13046-022-02372-8.

Canine and murine models of osteosarcoma

Osteosarcoma (OS) is the most common malignant bone tumor in children. Despite efforts to develop and implement new therapies, patient outcomes have not measurably improved since the 1980s. Metastasis continues to be the main source of patient mortality, with 30% of cases developing metastatic disease within 5 years of diagnosis. Research models are critical in the advancement of cancer research and include a variety of species. For example, xenograft and patient-derived xenograft (PDX) mouse models provide opportunities to study human tumor cells in vivo while transgenic models have offered significant insight into the molecular mechanisms underlying OS development. A growing recognition of naturally occurring cancers in companion species has led to new insights into how veterinary patients can contribute to studies of cancer biology and drug development. The study of canine cases, including the use of diagnostic tissue archives and clinical trials, offers a potential mechanism to further canine and human cancer research. Advancement in the field of OS research requires continued development and appropriate use of animal models. In this review, animal models of OS are described with a focus on the mouse and tumor-bearing pet dog as parallel and complementary models of human OS.

miRNA ‐34c suppresses osteosarcoma progression in vivo by targeting Notch and E2F

The expression of microRNAs (miRNAs) is dysregulated in many types of cancers including osteosarcoma (OS) due to genetic and epigenetic alterations. Among these, miR‐34c, an effector of tumor suppressor P53 and an upstream negative regulator of Notch signaling in osteoblast differentiation, is dysregulated in OS. Here, we demonstrated a tumor suppressive role of miR‐34c in OS progression using in vitro assays and in vivo genetic mouse models. We found that miR‐34c inhibits the proliferation and the invasion of metastatic OS cells, which resulted in reduction of the tumor burden and increased overall survival in an orthotopic xenograft model. Moreover, the osteoblast‐specific overexpression of miR‐34c increased survival in the osteoblast specific p53 mutant OS mouse model. We found that miR‐34c regulates the transcription of several genes in Notch signaling (NOTCH1, JAG1, and HEY2) and in p53‐mediated cell cycle and apoptosis (CCNE2, E2F5, E2F2, and HDAC1). More interestingly, we found that the metastatic‐free survival probability was increased among a patient cohort from Therapeutically Applicable Research to Generate Effective Treatments (TARGET) OS, which has lower expression of direct targets of miR‐34c that was identified in our transcriptome analysis, such as E2F5 and NOTCH1. In conclusion, we demonstrate that miR‐34c is a tumor suppressive miRNA in OS progression in vivo. In addition, we highlight the therapeutic potential of targeting miR‐34c in OS. © 2022 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.

Selective Targeting of Class I Histone Deacetylases in a Model of Human Osteosarcoma

Dysregulation of histone deacetylases (HDACs) is associated with the pathogenesis of human osteosarcoma, which may present an epigenetic vulnerability as well as a therapeutic target. Domatinostat (4SC-202) is a next-generation class I HDAC inhibitor that is currently being used in clinical research for certain cancers, but its impact on human osteosarcoma has yet to be explored. In this study, we report that 4SC-202 inhibits osteosarcoma cell growth in vitro and in vivo. By analyzing cell function in vitro, we show that the anti-tumor effect of 4SC-202 involves the combined induction of cell-cycle arrest at the G2/M phase and apoptotic program, as well as a reduction in cell invasion and migration capabilities. We also found that 4SC-202 has little capacity to promote osteogenic differentiation. Remarkably, 4SC-202 revised the global transcriptome and induced distinct signatures of gene expression in vitro. Moreover, 4SC-202 decreased tumor growth of established human tumor xenografts in immunodeficient mice in vivo. We further reveal key targets regulated by 4SC-202 that contribute to tumor cell growth and survival, and canonical signaling pathways associated with progression and metastasis of osteosarcoma. Our study suggests that 4SC-202 may be exploited as a valuable drug to promote more effective treatment of patients with osteosarcoma and provide molecular insights into the mechanism of action of class I HDAC inhibitors.

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.

Genomic Analysis Revealed Mutational Traits Associated with Clinical Outcomes in Osteosarcoma

Objective

The limited understanding of correlation between genomic features and biological behaviors has impeded the therapeutic breakthrough in osteosarcoma (OS). This study aimed to reveal the correlation of mutational and evolutionary traits with clinical outcomes.

Methods

We applied a case-based targeted and whole exome sequencing of eleven matched primary, recurrent and metastatic samples from three OS patients characterized by different clinical behaviors in local recurrence or systematic progression pattern.

Results

Extensive OS-associated driver genes were detected including TP53, RB1, NF1, PTEN, SPEN, CDKN2A. Oncogenic signaling pathways including cell cycle, TP53, MYC, Notch, WNT, RTK-RAS and PI3K were determined. MYC amplification was observed in the patient with shortest disease-free interval. Linear, branched or mixed evolutionary models were constructed in the three OS cases. A branched evolution with limited root mutation was detected in patient with shorter survival interval. ADAM17 mutation and HEY1 amplification were identified in OS happening dedifferentiation. Signatures 21 associated with microsatellite instability (MSI) was identified in OS patient with extra-pulmonary metastases.

Conclusion

OS was characterized by complex genomic alterations. MYC aberration, limited root mutations, and a branched evolutionary model were observed in OS patient with relatively aggressive course. Extra-pulmonary metastases of OS might attribute to distinct mutational process pertaining to MSI. Further research in a larger number of people is needed to confirm these findings.

FOXP1 drives osteosarcoma development by repressing P21 and RB transcription downstream of P53

Osteosarcoma has a poor prognosis, and the poor understanding of the genetic drivers of osteosarcoma hinders further improvement in therapeutic approaches. Transcription factor forkhead box P1 (FOXP1) is a crucial modulator in skeletal development and aging. Here, we determined the role and regulatory mechanisms of FOXP1 in osteosarcoma. Higher FOXP1 expression correlated with malignancy in both osteosarcoma cell lines and clinical biopsies. FOXP1 overexpression and knockdown in osteosarcoma cell lines revealed that FOXP1 promoted proliferation, tumor sphere formation, migration and invasion, and inhibited anoikis. Mechanistically, FOXP1 acted as a repressor of P21 and RB (retinoblastoma protein) transcription, and directly interacted with the tumor suppressor p53 to inhibit its activity. Extracellular signal-regulated kinase/c-Jun N-terminal kinase (ERK/JNK) signaling and c-JUN/c-FOS transcription factors were found to be upstream activators of FOXP1. Moreover, FOXP1 silencing via lentivirus or adeno-associated virus (AAV)-mediated delivery of shRNA suppressed osteosarcoma development and progression in cell-derived and patient-derived xenograft animal models. Taken together, we demonstrate that FOXP1, which is transactivated by ERK/JNK-c-JUN/c-FOS, drives osteosarcoma development by regulating the p53-P21/RB signaling cascade, suggesting that FOXP1 is a potential target for osteosarcoma therapy.

Context Matters: NOTCH Signatures and Pathway in Cancer Progression and Metastasis

The Notch signaling pathway is a critical player in embryogenesis but also plays various roles in tumorigenesis, with both tumor suppressor and oncogenic activities. Mutations, deletions, amplifications, or over-expression of Notch receptors, ligands, and a growing list of downstream Notch-activated genes have by now been described for most human cancer types. Yet, it often remains unclear what may be the functional impact of these changes for tumor biology, initiation, and progression, for cancer therapy, and for personalized medicine. Emerging data indicate that Notch signaling can also contribute to increased aggressive properties such as invasion, tumor heterogeneity, angiogenesis, or tumor cell dormancy within solid cancer tissues; especially in epithelial cancers, which are in the center of this review. Notch further supports the “stemness” of cancer cells and helps define the stem cell niche for their long-term survival, by integrating the interaction between cancer cells and the cells of the tumor microenvironment (TME). The complexity of Notch crosstalk with other signaling pathways and its roles in cell fate and trans-differentiation processes such as epithelial-to-mesenchymal transition (EMT) point to this pathway as a decisive player that may tip the balance between tumor suppression and promotion, differentiation and invasion. Here we not only review the literature, but also explore genomic databases with a specific focus on Notch signatures, and how they relate to different stages in tumor development. Altered Notch signaling hereby plays a key role for tumor cell survival and coping with a broad spectrum of vital issues, contributing to failed therapies, poor patient outcome, and loss of lives.

A mutation in NOTCH2 gene first associated with Hajdu-Cheney syndrome in a Greek family: diversity in phenotype and response to treatment

INTRODUCTION

Hajdu-Cheney Syndrome (HCS) is a rare genetic autosomal dominant disorder, characterized by distinctive facial features, acroosteolysis, and severe osteoporosis. Very rarely HCS is associated with polycystic kidney disease, splenomegaly or Crohn's disease (CD). It is caused by gain-of-function mutations in NOTCH2 gene. Treatment with bisphosphonates or denosumab is reported to result in BMD increase.

OBJECTIVE

We report a mutation in exon 34 of NOTCH2 gene, in a Greek pedigree, with diverse phenotypes among members.

DESCRIPTION OF THE PEDIGREE

The 48-year-old mother had a history of a T12 vertebral fracture, postpartum at the age of 21 and two subsequent uneventful full-term pregnancies and never received treatment. Her 29-year-old son, presented with severe osteoporosis and multiple morphological vertebral fractures. Her 21-year-old daughter had recurrent vertebral fractures starting at 10 years of age. At 17 years, she developed severe CD, resistant to treatment with biologic agents, and functional hypothalamic hypogonadism. One male pedigree died of cystic fibrosis. All subjects bore the typical facial characteristics and acroosteolysis, while none had splenomegaly or renal defects. Zoledronate infusion led to BMD increase.

GENETIC TESTING

Mutation in c.6758 G > A (NM_008163.1), leading to a Trp2253Ter replacement. This mutation has been reported as possibly pathogenic (SCV000620308), but not in association with HCS.

CONCLUSIONS

Bone involvement can present with diverse severity in the same pedigree, ranging from low BMD to multiple fragility fractures. Antiresorptive therapy improves BMD, but its anti-fracture efficacy remains to be shown. The presence of CD might indicate the significant role of NOTCH2 signaling in different tissues.

Notch-1 promotes the malignant progression of osteosarcoma through the activation of cell division cycle 20

The molecular mechanism of osteosarcoma (OS) pathogenesis is poorly understood. The Notch signaling pathway has been shown to be critically involved in tumorigenesis, including OS. Therefore, we explored the molecular mechanism by which the Notch-1 signaling pathway is involved in OS progression. Several approaches were carried out to determine the biological function of Notch-1 in OS cells. The MTT results revealed that Notch-1 overexpression increased the viability of OS cells, whereas Notch-1 downregulation reduced cell viability. Consistently, modulation of Notch-1 regulated apoptosis and the migratory and invasive abilities of OS cells. Mechanistic studies showed that Notch-1 overexpression augmented cell division cycle 20 (Cdc20) expression in OS cells. Moreover, overexpression of Cdc20 alleviated the inhibitory effects of Notch-1 downregulation on the viability, migration and invasion of OS cells. Our study offers a promising OS treatment strategy by inhibiting Notch-1.

Role of microRNAs in the crosstalk between osteosarcoma cells and the tumour microenvironment

Osteosarcoma (OS) is the most common primary bone tumour, with a peak incidence in adolescents, and the five-year survival rate of patients with metastasis or recurrence is much lower than that of patients without metastasis and recurrence. OS is initiated and develops in a complex tumour microenvironment (TME) that contains many different components, such as osteoblasts, osteoclasts, mesenchymal stem cells, fibroblasts, immune cells, extracellular matrix (ECM), extracellular vesicles, and cytokines. The extensive interaction between OS and the TME underlies OS progression. Therefore, rather than targeting OS cells, targeting the key factors in the TME may yield novel therapeutic approaches. MicroRNAs (miRNAs) play multiple roles in the biological behaviours of OS, and recent studies have implied that miRNAs are involved in mediating the communication between OS cells and the surrounding TME. Here, we review the TME landscape and the miRNA dysregulation of OS, describe the role of the altered TME in OS development and highlight the role of miRNA in the crosstalk between OS cells and the TME.

Decreased long non-coding RNA lincFOXF1 indicates poor progression and promotes cell migration and metastasis in osteosarcoma

Long non‐coding RNAs have been demonstrated to be important regulators of various cancers, though the precise mechanisms remain unclear. Although lincFOXF1 has been reported to act as a tumour suppressor, its function and underlying mechanisms in osteosarcoma have not yet been explored. We employed quantitative real‐time polymerase chain reaction (qRT‐PCR) to evaluate the expression of lincFOXF1 and GAPDH in osteosarcoma tissues and cell lines, and colony‐formation, CCK8, wound‐healing, and transwell assays were conducted to analyse the proliferation, migration, and invasion capacity of osteosarcoma cells. Subcellular localization analysis by fractionation and RNA immunoprecipitation assays were performed to elucidate the mechanism responsible for lincFOXF1‐mediated phenotypes of osteosarcoma cells. The results revealed that lincFOXF1 expression is significantly decreased and strongly related to Enneking stage as well as metastasis in osteosarcoma patients. Further experiments showed that lincFOXF1 inhibits the migration, invasion and metastasis of cells in vitro and vivo. Mechanistic investigation demonstrated that lincFOXF1 physically binds to EZH2, a polycomb repressive complex 2 (PRC2) component, and a search for downstream targets suggested that G‐protein‐coupled receptor kinase‐interacting protein 1 (GIT1) is involved in the lincFOXF1‐mediated repression of osteosarcoma cells migration and invasion. Moreover, GIT1 expression is inversely correlated with lincFOXF1 in osteosarcoma. The present findings indicate that lincFOXF1 is involved in the progression of osteosarcoma through binding with EZH2, further regulating GIT1 expression. Our results suggest that lincFOXF1 may serve as a biomarker and therapeutic target for osteosarcoma patients.

Notch and the regulation of osteoclast differentiation and function

Notch 1 through 4 are transmembrane receptors that play a pivotal role in cell differentiation and function; this review addresses the role of Notch signaling in osteoclastogenesis and bone resorption. Notch receptors are activated following interactions with their ligands of the Jagged and Delta-like families. In the skeleton, Notch signaling controls osteoclast differentiation and bone-resorbing activity either directly acting on osteoclast precursors, or indirectly acting on cells of the osteoblast lineage and cells of the immune system. NOTCH1 inhibits osteoclastogenesis, whereas NOTCH2 enhances osteoclast differentiation and function by direct and indirect mechanisms. NOTCH3 induces the expression of RANKL in osteoblasts and osteocytes and as a result induces osteoclast differentiation. There is limited expression of NOTCH4 in skeletal cells. Selected congenital disorders and skeletal malignancies are associated with dysregulated Notch signaling and enhanced bone resorption. In conclusion, Notch signaling is a critical pathway that controls osteoblast and osteoclast differentiation and function and regulates skeletal homeostasis in health and disease.

Silencing hsa_circRNA_0008035 exerted repressive function on osteosarcoma cell growth and migration by upregulating microRNA-375

Traditionally, circular RAN hsa_circ_0008035 was proven to function as a tumor inhibitor in gastric cancer. Nevertheless, much less was known about hsa_circ_0008035 in osteosarcoma (OSA). This project was undertaken to assess the role of hsa_circ_0008035 in OSA. Hsa_circ_0008035 level in serum of OSA patients, OSA tissues and cell lines were measured by reverse transcription-quantitative PCR. After downregulation or overexpression of hsa_circ_0008035, cell proliferation, apoptosis and migration were tested in MG63, SAOS-2 or hFOB1.19 cells. Meanwhile, the expression level of miR-375 was analyzed. The binding between hsa_circ_0008035 and miR-375 was confirmed using bioinformatics and luciferase assay. Subsequently, the effects of miR-375 inhibition on MG63 cell growth and migratory potential were reevaluated. Eventually, the activating status of Notch pathway was assessed by Western blot. Our results demonstrated that hsa_circ_0008035 was overexpressed in serum of OSA patients, OSA tissues and cells. Silencing hsa_circRNA_0008035 impeded OSA cell growth and migration, while hsa_circ_0008035 facilitated cell behaviors of hFOB1.19 cells. Additionally, hsa_circ_0008035 negatively modulated miR-375 expression. Meanwhile, miR-375 inhibition overturned the suppressive effects of silencing hsa_circRNA_0008035 on OSA cell behaviors. Furthermore, silencing hsa_circ_0008035 perturbed Notch pathway by adjusting miR-375 expression. In conclusion, silencing hsa_circRNA_0008035 exerted repressive function on OSA cell growth and migration and Notch pathway by accelerating miR-375.

Molecular Biology of Osteosarcoma

Osteosarcoma (OS) is the most frequent primary bone cancer in children and adolescents and the third most frequent in adults. Many inherited germline mutations are responsible for syndromes that predispose to osteosarcomas including Li Fraumeni syndrome, retinoblastoma syndrome, Werner syndrome, Bloom syndrome or Diamond-Blackfan anemia. TP53 is the most frequently altered gene in osteosarcoma. Among other genes mutated in more than 10% of OS cases, c-Myc plays a role in OS development and promotes cell invasion by activating MEK-ERK pathways. Several genomic studies showed frequent alterations in the RB gene in pediatric OS patients. Osteosarcoma driver mutations have been reported in NOTCH1, FOS, NF2, WIF1, BRCA2, APC, PTCH1 and PRKAR1A genes. Some miRNAs such as miR-21, -34a, -143, -148a, -195a, -199a-3p and -382 regulate the pathogenic activity of MAPK and PI3K/Akt-signaling pathways in osteosarcoma. CD133+ osteosarcoma cells have been shown to exhibit stem-like gene expression and can be tumor-initiating cells and play a role in metastasis and development of drug resistance. Although currently osteosarcoma treatment is based on adriamycin chemoregimens and surgery, there are several potential targeted therapies in development. First of all, activity and safety of cabozantinib in osteosarcoma were studied, as well as sorafenib and pazopanib. Finally, novel bifunctional molecules, of potential imaging and osteosarcoma targeting applications may be used in the future.

Development and characterization of the novel human osteosarcoma cell line COS-33 with sustained activation of the mTOR pathway

Outcomes have not improved for metastatic osteosarcoma for several decades. In part, this failure to develop better therapies stems from a lack of understanding of osteosarcoma biology, given the rarity of the disease and the high genetic heterogeneity at the time of diagnosis. We report here the successful establishment of a new human osteosarcoma cell line, COS-33, from a patient-derived xenograft and demonstrate retention of the biological features of the original tumor. We found high mTOR signaling activity in the cultured cells, which were sensitive to a small molecule inhibitor, rapamycin, a suppressor of the mTOR pathway. Suppressed mTOR signaling after treatment with rapamycin was confirmed by decreased phosphorylation of the S6 ribosomal protein. Increasing concentrations of rapamycin progressively inhibited cell proliferation in vitro. We observed significant inhibitory effects of the drug on cell migration, invasion, and colony formation in the cultured cells. Furthermore, we found that only a strong osteogenic inducer, bone morphogenetic protein-2, promoted the cells to differentiate into mature mineralizing osteoblasts, indicating that the COS-33 cell line may have impaired osteoblast differentiation. Grafted COS-33 cells exhibited features typical of osteosarcoma, such as production of osteoid and tumorigenicity in vivo. In addition, we revealed that the COS-33 cell line retained a complex karyotype, a homozygous deletion of the TP53 gene, and typical histological features from its original tumor. Our novel cellular model may provide a valuable platform for studying the etiology and molecular pathogenesis of osteosarcoma as well as for testing novel drugs for future genome-informed targeted therapy.

Epidemiology and Risk Factors of Osteosarcoma

Osteosarcoma is a rare tumor diagnosed at any age; however younger age is a common risk factor. In addition, multiple factors are believed to contribute to higher rates of osteosarcoma, particularly race and gender. Although diagnosed worldwide, osteosarcoma is found to be more prevalent in Africa with high numbers of cases reported in Nigeria, Uganda, and Sudan. Additionally, higher rates are detected in African Americans, suggesting a genetic predisposition linked to race. This review focuses on identifying high risk factors of osteosarcoma with an emphasis on sarcoma epidemiology and risk factors in African countries.

The crucial p53-dependent oncogenic role of JAB1 in osteosarcoma in vivo

Osteosarcoma (OS) is the most common primary bone cancer and ranks amongst the leading causes of cancer mortality in young adults. Jun activation domain binding protein 1 (JAB1) is overexpressed in many cancers and has recently emerged as a novel target for cancer treatment. However, the role of JAB1 in osteosarcoma was virtually unknown. In this study, we demonstrate that JAB1-knockdown in malignant osteosarcoma cell lines significantly reduced their oncogenic properties, including proliferation, colony formation, and motility. We also performed RNA-sequencing analysis in JAB1-knockdown OS cells and identified 4110 genes that are significantly differentially expressed. This demonstrated for the first time that JAB1 regulates a large and specific transcriptome in cancer. We also found that JAB1 is overexpressed in human OS and correlates with a poor prognosis. Moreover, we generated a novel mouse model that overexpresses Jab1 specifically in osteoblasts upon a TP53 heterozygous sensitizing background. Interestingly, by 13 months of age, a significant proportion of these mice spontaneously developed conventional OS. Finally, we demonstrate that a novel, highly specific small molecule inhibitor of JAB1, CSN5i-3, reduces osteosarcoma cell viability and has specific effects on the ubiquitin-proteasome system in OS. Thus, we show for the first time that the overexpression of JAB1 in vivo can result in accelerated spontaneous tumor formation in a p53-dependent manner. In summary, JAB1 might be a unique target for the treatment of osteosarcoma and other cancers.

Targeted and sustained Sox9 expression in mouse hypertrophic chondrocytes causes severe and spontaneous osteoarthritis by perturbing cartilage homeostasis

Sox9 is the master transcription factor essential for cartilage development and homeostasis. To investigate the specific role of Sox9 during chondrocyte hypertrophy, we generated a novel Col10a1-Sox9 transgenic mouse model, in which Sox9 is specifically expressed in hypertrophic chondrocytes driven by a well-characterized 10-kb Col10a1 promoter. These mice were viable and fertile, and appeared normal at birth. However, they developed dwarfism by ten weeks of age. The histological analysis of the growth plates from these transgenic mice demonstrated an abnormal growth plate architecture and a significantly reduced amount of trabecular bone and mineral content in the primary spongiosa. Real-time qPCR analysis revealed the reduced expression of Col10a1, and increased expressions of adipogenic differentiation markers in primary hypertrophic chondrocytes isolated from transgenic mice. Concomitantly, the transgenic mouse chondrocyte cultures had increased lipid droplet accumulation. Unexpectedly, we also observed an increased incidence of spontaneous osteoarthritis (OA) development in the transgenic mice by X-ray analysis, micro-computed tomography scanning, and histological examination of knee joints. The manifestation of OA in Col10a1-Sox9 transgenic mice began by six-months of age, and worsened by eleven-months of age. In conclusion, we provide strong evidence that the proper spatiotemporal expression of Sox9 is necessary for normal adult hypertrophic cartilage homeostasis, and that the aberrant expression of Sox9 might lead to spontaneous OA development.

FAM64A Promotes Osteosarcoma Cell Growth and Metastasis and Is Mediated by miR-493

Aberrant expression of FAM64A was correlated with cell proliferation in various cancer types. We examined the expression of FAM64A and the upstream gene miR-493 in OS. The functions of miR-493 were revealed through extensive experiments. We found an increase of FAM64A gene and protein in OS tissues. Overexpression of FAM64A resulted in promoting tumor proliferation, migration, and invasion. The miR-493 targeted and negatively regulated FAM64A. Our data showed that upregulation of FAM64A in OS correlated with poor prognosis.

Notch Signaling in Skeletal Development, Homeostasis and Pathogenesis

Skeletal development is a complex process which requires the tight regulation of gene activation and suppression in response to local signaling pathways. Among these pathways, Notch signaling is implicated in governing cell fate determination, proliferation, differentiation and apoptosis of skeletal cells-osteoblasts, osteoclasts, osteocytes and chondrocytes. Moreover, human genetic mutations in Notch components emphasize the critical roles of Notch signaling in skeletal development and homeostasis. In this review, we focus on the physiological roles of Notch signaling in skeletogenesis, postnatal bone and cartilage homeostasis and fracture repair. We also discuss the pathological gain- and loss-of-function of Notch signaling in bone and cartilage, resulting in osteosarcoma and age-related degenerative diseases, such as osteoporosis and osteoarthritis. Understanding the physiological and pathological function of Notch signaling in skeletal tissues using animal models and human genetics will provide new insights into disease pathogenesis and offer novel approaches for the treatment of bone/cartilage diseases.

Emerging next-generation sequencing-based discoveries for targeted osteosarcoma therapy

Osteosarcoma (OS) is the most common primary bone malignancy and is frequently lethal via metastasis to the lung. While surgical techniques and adjuvant chemotherapies have emerged to combat this deadly cancer, the 5-year survival rate has plateaued over the past four decades. Therapeutic progress has been notably poor because past technologies have not been able to reveal obscured OS biomarkers and targets. With the advent and implementation of large-scale next-generation sequencing (NGS) studies, various somatic mutations and copy number changes involved in OS progression and metastasis have surfaced. These findings have significantly expanded the amount of genome-informed pathways and candidate genes suitable for targeting in pre-clinical models. Furthermore, NGS analyses comparing primary and matched pulmonary metastatic tumor tissues have catalogued previously unknown prognostic biomarkers in OS. In this review, we delineate the most recent findings in NGS for OS therapy and how this technology has advanced personalized therapy.

RECQ DNA Helicases and Osteosarcoma

The RECQ family of DNA helicases is a conserved group of enzymes that plays an important role in maintaining genomic stability. Humans possess five RECQ helicase genes, and mutations in three of them - BLM, WRN, and RECQL4 - are associated with the genetic disorders Bloom syndrome, Werner syndrome, and Rothmund-Thomson syndrome (RTS), respectively. These syndromes share overlapping clinical features, and importantly they are all associated with an increased risk of cancer. Patients with RTS have the highest specific risk of developing osteosarcoma compared to all other cancer predisposition syndromes; therefore, RTS serves as a relevant model to study the pathogenesis and molecular genetics of osteosarcoma. The "tumor suppressor" function of the RECQ helicases continues to be an area of active investigation. This chapter will focus primarily on the known cellular functions of RECQL4 and how these may relate to tumorigenesis, as well as ongoing efforts to understand RECQL4's functions in vivo using animal models. Understanding the RECQ pathways will provide insight into avenues for novel cancer therapies in the future.

Prospects for the involvement of cancer stem cells in the pathogenesis of osteosarcoma

Osteosarcoma (OS) is one of the most common bone tumors in children and adolescents that cause a high rate of mortality in this age group and tends to be metastatic, in spite of chemotherapy and surgery. The main reason for this can be returned to a small group of malignant cells called cancer stem cells (CSCs). OS-CSCs play a key role in the resistance to treatment and relapse and metastasis through self-renewal and differentiation abilities. In this review, we intend to go through the different aspects of this malignant disease, including the cancer stem cell-phenotype, methods for isolating CSCs, signaling pathways, and molecular markers in this disease, and drugs showing resistance in treatment efforts of OS.

MicroRNA-1296-5p suppresses the proliferation, migration, and invasion of human osteosarcoma cells by targeting NOTCH2

Osteosarcoma (OS) is a highly aggressive bone tumor with a poor prognosis. MicroRNAs are revealed to exerts essential roles in the carcinogenesis and tumor invasion of OS. But, the function of miR-1296-5p and its related mechanism in OS progression have not yet been studied. This study discovered the levels of miR-1296-5p in OS and corresponding noncancerous tissues, and we demonstrated that miR-1296-5p level was markedly downregulated in tumor specimens as compared with nontumor tissues. In addition, we discovered that miR-1296-5p was also underexpressed in OS cells compared with the hFOB1.19 osteoblast cells. Interestingly, the reduced expression of miR-1296-5p was confirmed to associated with large tumor size, advanced tumor stages, and distance metastasis, respectively. Patients with OS low-expressing miR-1296-5p showed a prominent shorter survival. In addition, gain-of-function assays verified that miR-1296-5p overexpression remarkably repressed OS cell proliferation, migration, and invasion. Conversely, depletion of miR-1296-5p facilitated the growth and mobility of OS cells. Notably, miR-1296-5p inversely modulated notch receptor 2 (NOTCH2) in OS cells. The level of NOTCH2 messenger RNA was negatively correlated with miR-1296-5p level in OS samples. NOTCH2 knockdown markedly suppressed the abilities of MG-63 cell proliferation and mobility. More importantly, the restoration of NOTCH2 prominently rescued miR-1296-5p-induced tumor-suppressive effects on MG-63 cells. In conclusion, our study identified the reduced expression of miR-1296-5p, which contributed to OS progression. miR-1296-5p might be a promising prognostic marker and therapeutic target in OS.

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.