The Release of Inflammatory Mediators from Acid-Stimulated Mesenchymal Stromal Cells Favours Tumour Invasiveness and Metastasis in Osteosarcoma

Abstract

Osteosarcoma is the most frequent primary malignant bone tumour with an impressive tendency to metastasise. Highly proliferative tumour cells release a remarkable amount of protons into the extracellular space that activates the NF-kB inflammatory pathway in adjacent stromal cells. In this study, we further validated the correlation between tumour glycolysis/acidosis and its role in metastases. In patients, at diagnosis, we found high circulating levels of inflammatory mediators (IL6, IL8 and miR-136-5p-containing extracellular vesicles). IL6 serum levels significantly correlated with disease-free survival and 18F-FDG PET/CT uptake, an indirect measurement of tumour glycolysis and, hence, of acidosis. In vivo subcutaneous and orthotopic models, co-injected with mesenchymal stromal (MSC) and osteosarcoma cells, formed an acidic tumour microenvironment (mean pH 6.86, as assessed by in vivo MRI-CEST pH imaging). In these xenografts, we enlightened the expression of both IL6 and the NF-kB complex subunit in stromal cells infiltrating the tumour acidic area. The co-injection with MSC also significantly increased lung metastases. Finally, by using 3D microfluidic models, we directly showed the promotion of osteosarcoma invasiveness by acidosis via IL6 and MSC. In conclusion, osteosarcoma-associated MSC react to intratumoural acidosis by triggering an inflammatory response that, in turn, promotes tumour invasiveness at the primary site toward metastasis development.

Advantages and limitations of using cell viability assays for 3D bioprinted constructs

“…To analyze the advantages of confocal microscopy for this assay and model, we used a bioprinted osteosarcoma model. We chose AD-MSCs and osteocytes as representative stromal cells in the bone microenvironment, where they modulate tumors progression [29][30][31][32]. Reconstructing their 3D context in vitro may clarify the role of intercellular interactions for drug resistance and help in identifying new targets.…”

Biological evidence of cancer stem-like cells and recurrent disease in osteosarcoma

“…(8) As osteosarcoma is a form of cancer that originates in the mesenchyme, can we use the fibrogenic reprogramming of CSCs as a therapeutic option [138] ? Even whether sarcomas being considered as an immune desert explaining the current poor clinical efficacy of immune therapies needs more research [1,128] , macrophage and stromal cells contribute to the establishment of drug resistance and may be identified as therapeutic target in osteosarcoma [139] . For instance, M2 macrophage may be associated with tumor angiogenesis.…”

“…For instance, M2 macrophage may be associated with tumor angiogenesis. Tumor cells release a high number of protons that induce local acidosis, favoring the release of inflammatory mediators by local stromal cells, which in turn facilitates tumor invasiveness and metastasis in osteosarcoma [ 140 ] . Overall, it has been demonstrated that stromal cells significantly contribute to increase the stemness properties of osteosarcoma cells by inducing metabolic reprogramming of cancer cells [ 141 , 142 ] .…”

Exosomes in the tumor microenvironment of sarcoma: from biological functions to clinical applications

“…Liquid biopsy profiling of plasma exosomes in sarcoma has been found to show great potential for tumor detection, and stage and grade assessment (Table 3). High serum levels of exosomes containing specific microRNAs are related to sarcoma status [67,[74][75][76][77][78][79][80][81]. High-throughput sequencing identified that 57 micorRNAs in serum exosomes were differentially expressed in osteosarcoma patients and controls with 20 expression being up-regulated and 37 being downregulated [77].…”