Mechanical Property of Hydrogels and the Presence of Adipose Stem Cells in Tumor Stroma Affect Spheroid Formation in the 3D Osteosarcoma Model

Osteosarcoma is one of the most common metastatic bone cancers, which results in significant morbidity and mortality. Unfolding of effectual therapeutic strategies against osteosarcoma is impeded because of the absence of adequate animal models, which can truly recapitulate disease biology of humans. Tissue engineering provides an opportunity to develop physiologically relevant, reproducible, and tunable in vitro platforms to investigate the interactions of osteosarcoma cells with its microenvironment. Adipose-derived stem cells (ASCs) are detected adjacent to osteosarcoma masses and are considered to have protumor effects. Hence, the present study focuses on investigating the role of reactive ASCs in formation of spheroids of osteosarcoma cells (Saos 2) within a three-dimensional (3D) niche, which is created using gellan gum (GG)-silk fibroin. By modifying the blending ratio of GG-silk, the optimum stiffness of the resultant hydrogels such as GG and GG75: S25 is obtained for cancer spheroid formation. This work indicates that the co-existence of cancer and stem cells can form a spheroid, the hallmark of cancer, only in particular microenvironment stiffness. The incorporation of fibrillar silk fibroin within the hydrophilic network of GG in GG75: S25 spongy-like hydrogels closely mimics the stiffness of commercially established cancer biomaterials (e.g., Matrigel, HyStem). The GG75: S25 hydrogel maintains the metabolically active construct for a longer time with elevated expression of osteopontin, osteocalcin, RUNX 2, and bone sialoprotein genes, the biomarkers of osteosarcoma, compared to GG. The GG75: S25 construct also exhibits intense alkaline phosphatase expression in immunohistochemistry compared to GG, indicating itspotentiality to serve as biomimetic niche to model osteosarcoma. Taken together, the GG-silk fibroin-blended spongy-like hydrogel is envisioned as an alternative low-cost platform for 3D cancer modeling.