The acronym for the CCN family was recently revised to represent “cellular communication network”. These six, small, cysteine-enriched and evolutionarily conserved proteins are secreted matricellular proteins, that convey and modulate intercellular communication by interacting with structural proteins, signalling factors and cell surface receptors. Their role in the development and physiology of musculoskeletal system, constituted by connective tissues where cells are interspersed in the cellular matrix, has been broadly studied. Previous research has highlighted a crucial balance of CCN proteins in mesenchymal stem cell commitment and a pivotal role for CCN1, CCN2 and their alter ego CCN3 in chondrogenesis and osteogenesis; CCN4 plays a minor role and the role of CCN5 and CCN6 is still unclear. CCN proteins also participate in osteoclastogenesis and myogenesis. In adult life, CCN proteins serve as mechanosensory proteins in the musculoskeletal system providing a steady response to environmental stimuli and participating in fracture healing. Substantial evidence also supports the involvement of CCN proteins in inflammatory pathologies, such as osteoarthritis and rheumatoid arthritis, as well as in cancers affecting the musculoskeletal system and bone metastasis. These matricellular proteins indeed show involvement in inflammation and cancer, thus representing intriguing therapeutic targets. This review discusses the current understanding of CCN proteins in the musculoskeletal system as well as the controversies and challenges associated with their multiple and complex roles, and it aims to link the dispersed knowledge in an effort to stimulate and guide readers to an area that the writers consider to have significant impact and relevant potentialities.

Musculoskeletal sarcomas pose major challenges to researchers and clinicians due to their rarity and heterogeneity. Xenografting human cells or tumor fragments in rodents is a mainstay for the generation of cancer models and for the preclinical trial of novel drugs. Lately, though, technical, intrinsic and ethical concerns together with stricter regulations have significantly curbed the employment of murine patient-derived xenografts (mPDX). In alternatives to murine PDXs, researchers have focused on embryonal systems such as chorioallantoic membrane (CAM) and zebrafish embryos. These systems are time- and cost-effective hosts for tumor fragments and near-patient cells. The CAM of the chick embryo represents a unique vascularized environment to host xenografts with high engraftment rates, allowing for ease of visualization and molecular detection of metastatic cells. Thanks to the transparency of the larvae, zebrafish allow for the tracking of tumor development and metastatization, enabling high-throughput drug screening. This review will focus on xenograft models of musculoskeletal sarcomas to highlight the intrinsic and technically distinctive features of the different hosts, and how they can be exploited to elucidate biological mechanisms beneath the different phases of the tumor’s natural history and in drug development. Ultimately, the review suggests the combination of different models as an advantageous approach to boost basic and translational research.

Bone metastases from osteosarcoma occur in only 10% of patients, and related preclinical models are lacking. A patient diagnosed with pelvic osteosarcoma developed a metachronous scapular metastasis and was treated with multi-agent chemotherapy and surgery. Patient-derived tissue fragments (PDTFs) were obtained from leftover material after diagnosis and biobanking. PDTFs were grown on chick chorioallantoic membrane, establishing an in vivo-like predictive model. Additionally, we obtained a patient-derived cell culture, OS-MET-R-092, which has been maintained in vitro for nearly one year. OS-MET-R-092 cells were authenticated based on short tandem repeats and on their morphology when grown on commercial 3D scaffolds. Using U-2 OS and SaOS-2 as controls, we characterized growth, clonogenic potential, ability to form spheroids, migration, osteogenic differentiation, and expression of related genes. OS-MET-R-092 cells showed a low proliferation rate, impaired differentiation potential, and migratory abilities comparable to SaOS-2, while expressing higher levels of some MMPs and CD44. Functionally, OS-MET-R-092 cells demonstrated a resistant phenotype to doxorubicin, cisplatin, gemcitabine, and docetaxel, corroborated by higher expression of chemo-resistance-related genes. Collectively, OS-MET-R-092 represents a valuable tool for studying bone metastasis from osteosarcoma across various experimental settings and serves as the foundational building block for composite and translatable 3D models.