The fate of cancer cells has been well-linked to the mechanical robustness of their underlying niche, affecting the formation of cancer spheroid and malignant evolution . However, the critical modeling of mechanical dynamics of cancerous niche is limited to only animal-derived matrices, such as Matrigel (the chemical signature of the matrix is poorly defined)  and collagen type I (possesses less structural stability in prolong culture) . Hence, modular natural polymer-based low-cost hydrogel network with definite extracellular matrix component is developed to substitute the high-cost commercial animal derived matrices. The practicability of the designed hydrogel to serve as 3D extracellular matrix (ECM) of cancer is investigated using osteosarcoma cells (Saos 2). Adjacent to osteosarcoma mass, infiltration of adipose derived stem cells (ASCs) is observed at physiological disease niche, leading us to hypothesize that ASCs have regulatory role in osteosarcoma development. To explore this, reactive ASCs are further incorporated along with Saos 2 cells in designed dynamic hydrogel network of gellan-gum and silk fibroin. The present report demonstrates that the co-existence of ASCs and cancer cells can only lead to formation of cancer spheroid with particular ECM stiffness. The stiffness of designed hydrogel (~ 0.6 kPa) with a 3 to 1 blending ratio of gellan gum to silk fibroin (represented as GG75: S25) mimics closely the stiffness of conventional commercial cancer biomaterials (e.g., Matrigel) (0.98 ± 0.30 kPa). It also promotes the expression of osteocalcin, osteopontin, RUNX 2, and bone sialoprotein genes, the well-known biomarkers of osteosarcoma. In addition, the GG75: S25 construct demonstrates the augmented level of expression of alkaline phosphatase, the typical discrimination marker of osteosarcoma from other primary bone tumors. Thus, the present approach overcomes the current limitations of cheap, natural-based biomaterials to model cancer. The heterogeneity of the present model, both at structural and cellular level, greatly expands its applicability in basic and translational research. The principles undertaken here can also be extended to screen the efficacy of anti-cancer therapeutics.
ACKNOWLEDGEMENTS: European Union Framework Programme for Research and Innovation Horizon 2020 (nº 668983 —FoReCaST), FROnTHERA (NORTE-01-0145-FEDER-000023), Investigator FCT program IF/01214/2014 and IF/01285/2015.
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