Prognostic role of hypoxia-inducible factor-1 alpha expression in osteosarcoma: a meta-analysis

Protein Stability Regulation in Osteosarcoma: The Ubiquitin-like Modifications and Glycosylation as Mediators of Tumor Growth and as Targets for Therapy

The identification of new therapeutic targets and the development of innovative therapeutic approaches are the most important challenges for osteosarcoma treatment. In fact, despite being relatively rare, recurrence and metastatic potential, particularly to the lungs, make osteosarcoma a deadly form of cancer. In fact, although current treatments, including surgery and chemotherapy, have improved survival rates, the disease's recurrence and metastasis are still unresolved complications. Insights for analyzing the still unclear molecular mechanisms of osteosarcoma development, and for finding new therapeutic targets, may arise from the study of post-translational protein modifications. Indeed, they can influence and alter protein structure, stability and function, and cellular interactions. Among all the post-translational modifications, ubiquitin-like modifications (ubiquitination, deubiquitination, SUMOylation, and NEDDylation), as well as glycosylation, are the most important for regulating protein stability, which is frequently altered in cancers including osteosarcoma. This review summarizes the relevance of ubiquitin-like modifications and glycosylation in osteosarcoma progression, providing an overview of protein stability regulation, as well as highlighting the molecular mediators of these processes in the context of osteosarcoma and their possible targeting for much-needed novel therapy.

Multi-Anticancer Activities of Phytoestrogens in Human Osteosarcoma

Phytoestrogens are plant-derived bioactive compounds with estrogen-like properties. Their potential health benefits, especially in cancer prevention and treatment, have been a subject of considerable research in the past decade. Phytoestrogens exert their effects, at least in part, through interactions with estrogen receptors (ERs), mimicking or inhibiting the actions of natural estrogens. Recently, there has been growing interest in exploring the impact of phytoestrogens on osteosarcoma (OS), a type of bone malignancy that primarily affects children and young adults and is currently presenting limited treatment options. Considering the critical role of the estrogen/ERs axis in bone development and growth, the modulation of ERs has emerged as a highly promising approach in the treatment of OS. This review provides an extensive overview of current literature on the effects of phytoestrogens on human OS models. It delves into the multiple mechanisms through which these molecules regulate the cell cycle, apoptosis, and key pathways implicated in the growth and progression of OS, including ER signaling. Moreover, potential interactions between phytoestrogens and conventional chemotherapy agents commonly used in OS treatment will be examined. Understanding the impact of these compounds in OS holds great promise for developing novel therapeutic approaches that can augment current OS treatment modalities.

Hypoxia-Inducible Factor-2α Signaling in the Skeletal System

Hypoxia-inducible factors (HIFs) are oxygen-dependent heterodimeric transcription factors that mediate molecular responses to reductions in cellular oxygen (hypoxia). HIF signaling involves stable HIF-β subunits and labile, oxygen-sensitive HIF-α subunits. Under hypoxic conditions, the HIF-α subunit is stabilized, complexes with nucleus-confined HIF-β subunit, and transcriptionally regulates hypoxia-adaptive genes. Transcriptional responses to hypoxia include altered energy metabolism, angiogenesis, erythropoiesis, and cell fate. Three isoforms of HIF-α-HIF-1α, HIF-2α, and HIF-3α-are found in diverse cell types. HIF-1α and HIF-2α serve as transcriptional activators, whereas HIF-3α restricts HIF-1α and HIF-2α. The structure and isoform-specific functions of HIF-1α in mediating molecular responses to hypoxia are well established across a wide range of cell and tissue types. The contributions of HIF-2α to hypoxic adaptation are often unconsidered if not outrightly attributed to HIF-1α. This review establishes what is currently known about the diverse roles of HIF-2α in mediating the hypoxic response in skeletal tissues, with specific focus on development and maintenance of skeletal fitness. © 2023 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.

KCNJ2/HIF1α positive-feedback loop promotes the metastasis of osteosarcoma

BACKGROUND

Early metastasis is a hallmark of osteosarcoma (OS), a highly common type of malignant tumor. Members of the potassium inwardly rectifying channel family exert oncogenic effects in various cancers. However, the role of the potassium inwardly rectifying channel subfamily J member 2 (KCNJ2) in OS is unclear.

METHODS

The expression of KCNJ2 in OS tissues and cell lines was measured using bioinformatic analysis, immunohistochemistry, and western blotting. Wound-healing assays, Transwell assays, and lung metastasis models were used to analyze the effects of KCNJ2 on mobility of OS cells. The molecular mechanisms linking KCNJ2 and HIF1α in OS were explored by mass spectrometry analysis, immunoprecipitation, ubiquitination detection, and chromatin-immunoprecipitation quantitative real-time polymerase chain reaction.

RESULTS

KCNJ2 was found to be overexpressed in advanced-stage OS tissues, as well as in cells with high metastatic potential. High expression of KCNJ2 was associated with a shorter survival rate of OS patients. KCNJ2-inhibition repressed the metastasis of OS cells, whereas KCNJ2-elevation induced the opposite effects. Mechanistically, KCNJ2 binds to HIF1α and inhibits its ubiquitination, thus increasing the expression of HIF1α. Interestingly, HIF1α binds directly to the KCNJ2 promoter and increases its transcription under hypoxic conditions.

CONCLUSION

Taken together, our results indicated that a KCNJ2/HIF1α positive feedback loop exists in OS tissues, which significantly promotes OS cell metastasis. This evidence may contribute to the diagnosis and treatment of OS. Video Abstract.

Association of hypoxia-inducible factor 1 expressions with prognosis role as a survival prognostic biomarker in the patients with osteosarcoma: a meta-analysis

BACKGROUND

Osteosarcoma, the most prevalent primary bone cancer, tends to relapse or metastasize quickly. Hypoxia-inducible factor-1 alpha (HIF-1α) affects tumor metabolism, differentiation, angiogenesis, proliferation, and metastasis. Many studies have investigated the possible inconsistent prognostic value of HIF-1 α. This study evaluated the correlation between HIF-1 α expression and prognosis in osteosarcoma patients.

METHODS

: A total of 978 patients from 12 studies were followed up. A meta-analysis was conducted on articles investigating HIF-1 α prognostic value in osteosarcoma patients. The authors excluded articles with overlapping data, duplicate data, reviews, case reports, and letters that did not provide original data. Calculation of the hazard ratios (HR) and pooled risk ratios (RR) with corresponding 95% confidence intervals were used to determine the association degree (CIs).

RESULTS

It was determined that HIF-1 α in osteosarcoma patients had a prognostic value based on the RRs and HRs. The results showed that high HIF-1 α expression was associated with a worse prognosis when compared to low or undetectable HIF-1 α expression.

CONCLUSION

HIF-1 α overexpression was found to predict poor outcomes in osteosarcomas. The present study suggests that HIF-1α is a useful prognostic biomarker to predict OS in patients with osteosarcoma.

Sphingosine Kinase-1 Is Overexpressed and Correlates with Hypoxia in Osteosarcoma: Relationship with Clinicopathological Parameters

The Sphingosine kinase-1/Sphingosine 1-Phosphate (SphK1/S1P) signaling pathway is overexpressed in various cancers, and is instrumental for the adaptation to hypoxia in a number of solid tumor models, but no data are available in osteosarcoma. Here we report that SphK1 and the S1P₁ receptor are involved in HIF-1α accumulation in hypoxic osteosarcoma cells. FTY720 (Fingolimod), which targets SphK1 and S1P_1, prevented HIF-1α accumulation, and also inhibited cell proliferation in both normoxia and hypoxia unlike conventional chemotherapy. In human biopsies, a significant increase of SphK1 activity was observed in cancer compared with normal bones. In all sets of TMA samples (130 cases of osteosarcoma), immunohistochemical analysis showed the hypoxic marker GLUT-1, SphK1 and S1P₁ were expressed in tumors. SphK1 correlated with the GLUT-1 suggesting that SphK1 is overexpressed and correlates with intratumoral hypoxia. No correlation was found between GLUT-1 or SphK1 and response to chemotherapy, but a statistical difference was found with increased S1P₁ expression in patients with poor response in long bone osteosarcomas. Importantly, multivariate analyses showed that GLUT-1 was associated with an increased risk of death in flat bone, whereas SphK1 and S1P₁ were associated with an increased risk of death in long bones.

Hypoxia stimulates the migration and invasion of osteosarcoma via up-regulating the NUSAP1 expression

Osteosarcoma is a highly aggressive malignant tumor, which most commonly occurs in children and adolescents. This study aims to reveal that hypoxia promotes the invasion of osteosarcoma cells by up-regulating the expression of NUSAP1. The expression of HIF-1α and NUSAP1 was significantly up-regulated in MG63 cells cultured in hypoxia for 6–36 h. Furthermore, hypoxia induced the migration and invasion of MG63 cells and regulated the level of E-cad, N-cad, Vimentin, Snail, Slug, MMP2, and MMP9 proteins. Importantly, knockdown of NUSAP1 inhibited hypoxia-induced cell migration and invasion. In the hypoxia microenvironment, the addition of HIF-1α inhibitor or the transfection of siRNA specifically targeting HIF-1α significantly reduced the expression of HIF-1α and NUSAP1 and markedly inhibited the migration and invasion of MG63 cells under the hypoxia microenvironment. In conclusion, hypoxia induced the expression of NUSAP1 in a HIF-1α-dependent manner, stimulating the migration and invasion of MG63 cells.

The effect of 900 MHz electromagnetic fields on biological pathways induced by electrochemotherapy

Electrochemotherapy (ECT) is a new and promising treatment strategy for cancer treatment. The aim of this work is to investigate the effect of 900 MHz radiofrequency electromagnetic fields (RF-EMFs) on the mechanisms of ECT (low voltage, high frequency) including cell permeability in vitro, and tumor hypoxia, immune system response in vivo, and on volume of tumors treated with ECT (70 V/cm, 5 kHz). The 4T1 cells were exposed to RF-EMFs at 17, 162, or 349 µW/cm2 power densities, using GSM900 simulator, 10 min. The cells were then put in individual groups, comprising of no treatment, chemotherapy, electric pulses (EPs), or ECT. The cell viability was evaluated. The mice with 4T1 tumor cells were exposed to RF field 10 min/day until the tumor volume reached about 8 mm. Then, the mice tumors were treated with ECT. Tumor hypoxia and immune system response was analyzed through immunohistochemistry (IHC) assay and ELISA technique, respectively. The volume of tumors was also calculated for 24 days following the treatment. The results showed that RF fields at 349 µW/cm2 could increase tumor hypoxia induced by ECT and cause a significant increase of Interferon-gamma (IFN-γ) in comparison with group ECT alone. However, 900 MHz radiations did not affect the volume of tumors treated to ECT (70 V/cm, 5 kHz) significantly. In this study, 900 MHz EMF could improve some biological pathways induced by ECT. Such a positive effect could utilize in some other treatments to increase efficacy, which should be investigated in further research.

Distinct roles for the hypoxia-inducible transcription factors HIF-1α and HIF-2α in human osteoclast formation and function

Bone homeostasis is maintained by a balance between osteoblast-mediated bone formation and osteoclast-driven bone resorption. Hypoxia modulates this relationship partially via direct and indirect effects of the hypoxia-inducible factor-1 alpha (HIF-1α) transcription factor on osteoclast formation and bone resorption. Little data is available on the role(s) of the HIF-2α isoform of HIF in osteoclast biology. Here we describe induction of HIF-1α and HIF-2α during the differentiation of human CD14+ monocytes into osteoclasts. Knockdown of HIF-1α did not affect osteoclast differentiation but prevented the increase in bone resorption that occurs under hypoxic conditions. HIF-2α knockdown did not affect bone resorption but moderately inhibited osteoclast formation. Growth of osteoclasts in 3D gels reversed the effect of HIF-2α knockdown; HIF-2α siRNA increasing osteoclast formation in 3D. Glycolysis is the main HIF-regulated pathway that drives bone resorption. HIF knockdown only affected glucose uptake and bone resorption in hypoxic conditions. Inhibition of glycolysis with 2-deoxy-d-glucose (2-DG) reduced osteoclast formation and activity under both basal and hypoxic conditions, emphasising the importance of glycolytic metabolism in osteoclast biology. In summary, HIF-1α and HIF-2α play different but overlapping roles in osteoclast biology, highlighting the importance of the HIF pathway as a potential therapeutic target in osteolytic disease.

A lineage-tracing tool to map the fate of hypoxic tumour cells

Intratumoural hypoxia is a common characteristic of malignant treatment-resistant cancers. However, hypoxia-modification strategies for the clinic remain elusive. To date, little is known on the behaviour of individual hypoxic tumour cells in their microenvironment. To explore this issue in a spatial and temporally controlled manner, we developed a genetically encoded sensor by fusing the O2-labile hypoxia-inducible factor 1α (HIF-1α) protein to eGFP and a tamoxifen-regulated Cre recombinase. Under normoxic conditions, HIF-1α is degraded but, under hypoxia, the HIF-1α-GFP-Cre-ERT2 fusion protein is stabilised and in the presence of tamoxifen activates a tdTomato reporter gene that is constitutively expressed in hypoxic progeny. We visualise the random distribution of hypoxic tumour cells from hypoxic or necrotic regions and vascularised areas using immunofluorescence and intravital microscopy. Once tdTomato expression is induced, it is stable for at least 4 weeks. Using this system, we could show in vivo that the post-hypoxic cells were more proliferative than non-labelled cells. Our results demonstrate that single-cell lineage tracing of hypoxic tumour cells can allow visualisation of their behaviour in living tumours using intravital microscopy. This tool should prove valuable for the study of dissemination and treatment response of post-hypoxic tumour cells in vivo at single-cell resolution.This article has an associated First Person interview with the joint first authors of the paper.

The role of 217-Hz ELF magnetic fields emitted from GSM mobile phones on electrochemotherapy mechanisms

Electrochemotherapy (ECT), the combination of electric pulses (EPs) and an anticancer drug, is a type of cancer treatment method. We investigated the effect of 217-Hz magnetic fields (MFs) similar to that generated by GSM900 mobile phones, as intervening factors, on proposed mechanisms of ECT including permeability, tumor hypoxia and immune system response. The 4T1 cells were exposed to extremely low-frequency (ELF)-MFs at 93, 120 or 159 µT intensities, generated by Helmholtz coils 10 min, and then put in individual groups, comprising no treatment, chemotherapy, EPs or ECT. The cell viability was evaluated. Then, two treatment protocols were selected for in vivo experiments. The mice with 4T1 tumor cells were exposed to ELF-MFs 10 min/day until the day their tumors reached 8 mm in diameter. Then, the tumors were treated to ECT. Tumor hypoxia and immune system response were analyzed through immunohistochemistry assay and enzyme-linked immunosorbent assay technique, respectively. The results in vitro indicated a significant decreased ECT efficacy of 60 V/cm, 5 kHz at the flux density of 93 µT. The results in vivo showed that pre-exposure to ELF-MFs could increase tumor hypoxia induced by ECT. In addition, exposure to ELF-MFs before ECT caused a significant increase in interferon-γ/interleukin-4 in comparison with ECT alone. More studies, including studies on the effect of ELF-MFs emitted from mobile phones on tumor volume changes induced by ECT, are needed to elucidate how the process of ECT is influenced by the MFs.

New Insights about the Wnt/β-Catenin Signaling Pathway in Primary Bone Tumors and Their Microenvironment: A Promising Target to Develop Therapeutic Strategies?

Osteosarcoma and Ewing sarcoma are the most common malignant primary bone tumors mainly occurring in children, adolescents and young adults. Current standard therapy includes multidrug chemotherapy and/or radiation specifically for Ewing sarcoma, associated with tumor resection. However, patient survival has not evolved for the past decade and remains closely related to the response of tumor cells to chemotherapy, reaching around 75% at 5 years for patients with localized forms of osteosarcoma or Ewing sarcoma but less than 30% in metastatic diseases and patients resistant to initial chemotherapy. Despite Ewing sarcoma being characterized by specific EWSR1-ETS gene fusions resulting in oncogenic transcription factors, currently, no targeted therapy could be implemented. It seems even more difficult to develop a targeted therapeutic strategy in osteosarcoma which is characterized by high complexity and heterogeneity in genomic alterations. Nevertheless, the common point between these different bone tumors is their ability to deregulate bone homeostasis and remodeling and divert them to their benefit. Therefore, targeting different actors of the bone tumor microenvironment has been hypothesized to develop new therapeutic strategies. In this context, it is well known that the Wnt/β-catenin signaling pathway plays a key role in cancer development, including osteosarcoma and Ewing sarcoma as well as in bone remodeling. Moreover, recent studies highlight the implication of the Wnt/β-catenin pathway in angiogenesis and immuno-surveillance, two key mechanisms involved in metastatic dissemination. This review focuses on the role played by this signaling pathway in the development of primary bone tumors and the modulation of their specific microenvironment.

Clinicopathological and prognostic value of hypoxia-inducible factor-1α in patients with bone tumor: a systematic review and meta-analysis

Background

Recently, many studies have shown the role of hypoxia-inducible factor-1α (HIF-1α) expression in the outcome of bone tumor. However, the results remain inconclusive. It is necessary to carry out a meta-analysis of all the current available data to clarify the relationship between HIF-1α and survival or clinicopathological features of bone tumor.

Methods

PubMed, Cochrane Library, Web of Science, China National Knowledge Internet, and Wanfang databases were used to search the relationship between HIF-1α and bone tumor. Articles investigating clinicopathological and prognostic value of HIF-1α in bone tumor patients were enrolled in this meta-analysis. Overlapping articles, duplicate data, reviews, case reports, and letters without original data were excluded. The pooled risk ratios (RRs) and hazard ratios (HRs) were used to evaluate the clinicopathological and prognostic value of HIF-1α on bone tumor patients, respectively.

Results

A total of 28 studies including 1443 patients were included in this meta-analysis, which were involved in three different types of bone tumor including 3 chondrosarcomas, 2 giant cell tumors of bone, and 23 osteosarcomas. Our results showed that high expression levels of HIF-1α were associated with poorer OS (overall survival) (HR = 2.61, 95% CI 2.11–3.23, P <  0.001) and shorter DFS (disease-free survival) (HR = 2.02, 95% CI 1.41–2.89, P <  0.001) in bone tumor. In addition, this study also analyzed the role of HIF-1α expression in clinicopathological features, which were closely related with the severity of bone tumor, including differentiation, clinical stage, metastasis, and microvessel density. Our results indicated that HIF-1α overexpression was significantly associated with differentiation (RR = 1.56, 95% CI 1.00–2.43, P = 0.049), clinical stage (RR = 1.75, 95% CI 1.25–2.45, P = 0.001), metastasis (RR = 1.78, 95% CI 1.58–2.00, P <  0.001), and microvessel density (SMD = 2.34, 95% CI 1.35–3.34, P <  0.001) of bone tumor.

Conclusions

HIF-1α overexpression indicated an unfavorable factor for OS and DFS in bone tumor, suggesting that HIF-1α may serve as a potential prognostic marker for bone tumor.

Electronic supplementary material

The online version of this article (10.1186/s13018-019-1101-5) contains supplementary material, which is available to authorized users.

Prognostic Role of Hypoxia-Inducible Factor-2α Tumor Cell Expression in Cancer Patients: A Meta-Analysis

Hypoxia-inducible factor-2α (HIF-2α) plays an important role in tumor progression and metastasis. A number of studies have evaluated the correlation between HIF-2α overexpression and clinical outcome in cancer patients but yielded inconsistent results. To comprehensively and quantitatively summarize the evidence on the capability of HIF-2α to predict the prognosis of cancer patients with solid tumors, a meta-analysis was carried out. Renal cell carcinoma (CC-RCC) was separately analyzed due to an alternative mechanism of regulation. Systematic literature searches were performed in PubMed and Embase databases for relevant original articles until February 2018. Forty-nine studies with 6,052 patients were included in this study. The pooled hazard ratios (HRs) with corresponding confidence intervals were calculated to assess the prognostic value of HIF-2α protein expression in tumor cells. The meta-analysis revealed strong significant negative associations between HIF-2α expression and five endpoints: overall survival [HR = 1.69, 95% confidence interval (95% CI) 1.39-2.06], disease-free survival (HR = 1.87, 95% CI 1.2-2.92), disease-specific survival (HR = 1.57, 95% CI 1.06-2.34), metastasis-free survival (HR = 2.67, 95% CI 1.32-5.38), and progression-free survival (HR = 2.18, 95% CI 1.25-3.78). Subgroup analyses revealed similar associations in the majority of tumor sites. Overall, these data demonstrate a negative prognostic role of HIF-2α in patients suffering from different types of solid tumors.

Hypoxia-inducible factor-1 promotes cancer progression through activating AKT/Cyclin D1 signaling pathway in osteosarcoma

OBJECTIVE

Osteosarcoma is an aggressive malignant neoplasm, which commonly afflicts patients of 20-30 years of age, and its morbidity has increased markedly in recent years. Certain genes and signal pathways have been identified to exert key roles in osteosarcoma progression. Here, we set out to characterize in more detail of the role of HIF-1/AKT/Cyclin D1 pathway in the progression of osteosarcoma.

METHODS

Immunohistochemistry, western blot and qPCR were used to test the protein or mRNA levels of HIF-1 in osteosarcoma tissues or adjacent nontumor tissues. MTT, clone formation, wound healing, Transwell, in vivo tumorigenesis, flow cytometry and western blot analysis were used to determine cell proliferation, clone formation ability, migration, invasion, tumorigenesis, and cell apoptosis in MG63 and U2OS cells, respectively. Immunoprecipitation and immunofluorescence assays were performed to investigate the protein-protein interaction between HIF-1α and proteins related to signal pathways.

RESULTS

HIF-1 was overexpressed in osteosarcoma tissues and cell lines, which promoted cell proliferation, clone formation, migration, invasion and inhibited cell apoptosis. Results also demonstrated that HIF-1 combined with AKT, and there might be a positive loop between the two proteins of HIF-1 and AKT, then the protein-protein interaction up-regulated the expression of Cyclin D1 in protein level, but not mRNA level, made Cyclin D1 protein more stable, triggered cell proliferation, clone formation, tumorigenesis, but inhibited cell apoptosis.

CONCLUSIONS

The present study showed that HIF-1 modulated Cyclin D1 expression might through shaping a positive loop with AKT proteins. Additionally, HIF-1α promoted the tumor cells growth, migration and invasion in osteosarcoma through the activation of the AKT/Cyclin D1 signal cascade. We proposed that HIF-1 could be served as a marker for distinguishing osteosarcoma and an effective therapeutic target for osteosarcoma.

The effect of pathological fractures on the prognosis of patients with osteosarcoma: a meta-analysis of 14 studies

Osteosarcoma is a leading cause of malignant tumor related death. We conducted a meta-analysis to evaluate the association between pathological fractures and prognosis in patients with osteosarcoma. We searched PubMed, Web of Science, and Embase for studies published until May 15, 2017. Crude and adjusted relative risk (RR) with 95% confidence intervals were used to compare data between the case and control groups. Fourteen studies and 3910 patients were included in the final meta-analysis. No statistically significant difference was detected between the pathological fracture and non-pathological fracture groups in local recurrences analysis (RR = 1.102, 95% CI: 0.813–1.495, P = 0.531); however, a statistically significant difference was found between group in distant metastasis (RR = 1.424, 95% CI: 1.089–1.862, P = 0.01). For survival rates, the following RRs were calculated: 3-year overall survival (OS) (RR = 0.736, 95% CI: 0.593–0.912, P = 0.005); 5-year OS (RR = 0.889, 95% CI: 0.791–0.999, P = 0.049); 3-year event-free survival (EFS) (RR = 0.812, 95% CI: 0.682–0.966, P = 0.018); and 5-year EFS (RR = 0.876, 95% CI: 0.785–0.978, P = 0.019). The pooled estimate of RR was 0.673 (95% CI: 0.364–1.244, P = 0.206) for local recurrence in the amputation and limb salvage groups. In conclusion, our analysis indicated that there were no differences in local recurrence and local recurrence after limb salvage between patients with or without a fracture. Additionally, the patients with pathological fracture had a higher risk of distant metastasis and lower 3-year OS, 5-year OS, 3-year EFS, and 5-year EFS. Considering the limitations of this study, we believe that future large-scale studies should be performed to confirm our conclusions.

Tetrahydrocurcumin induces mesenchymal-epithelial transition and suppresses angiogenesis by targeting HIF-1α and autophagy in human osteosarcoma

Human osteosarcoma is considered a malignant tumor with poor prognosis that readily metastasizes. Tetrahydrocurcumin (THC) has been reported to have anti-tumor activity in numerous tumors. In addition, hypoxia-inducible factor-1α (HIF-1α) has been demonstrated to be associated with tumor metastasis by regulating epithelial-mesenchymal transition (EMT). However, the role of THC in osteosarcoma remains uncertain. Therefore, this study aimed to elucidate the potential mechanisms. We found that THC significantly reduced the growth of osteosarcoma cells and suppressed migration and invasion, as tested in a nude mouse lung metastasis model. Additionally, the mesenchymal-epithelial transition (MET) process was facilitated by THC. Mechanistically, our study showed that HIF-1α had a pivotal role in the anti-metastatic effect of THC. Importantly, HIF-1α expression was downregulated by THC by inhibiting Akt/mTOR and p38 MAPK pathways. Moreover, THC exhibited a remarkable inhibitory effect on HIF-1α expression and angiogenesis under hypoxic conditions. Furthermore, THC activated autophagy and induced MET and suppressed angiogenesis in a HIF-1α-related manner. Taken together, our findings suggest that THC suppresses metastasis and invasion and this may be associated with HIF-1α and autophagy, which would potentially provide therapeutic strategies for human osteosarcoma.

Mesenchymal stroma: Role in osteosarcoma progression

The initiation and progression of malignant tumors are supported by their microenvironment: cancer cells per se cannot explain growth and formation of the primary or metastasis, and a combination of proliferating tumor cells, cancer stem cells, immune cells mesenchymal stromal cells and/or cancer-associated fibroblasts all contribute to the tumor bulk. The interaction between these multiple players, under different microenvironmental conditions of biochemical and physical stimuli (i.e. oxygen tension, pH, matrix mechanics), regulates the production and biological activity of several soluble factors, extracellular matrix components, and extracellular vesicles that are needed for growth, maintenance, chemoresistance and metastatization of cancer. In osteosarcoma, a very aggressive cancer of young adults characterized by the extensive need for more effective therapies, this aspect has been only recently explored. In this view, we will discuss the role of stroma, with a particular focus on the mesenchymal stroma, contributing to osteosarcoma progression through inherent features for homing, neovascularization, paracrine cross-feeding, microvesicle secretion, and immune modulation, and also by responding to the changes of the microenvironment that are induced by tumor cells. The most recent advances in the molecular cues triggered by cytokines, soluble factors, and metabolites that are partially beginning to unravel the axis between stromal elements of mesenchymal origin and osteosarcoma cells, will be reviewed providing insights likely to be used for novel therapeutic approaches against sarcomas.