gms | German Medical Science

Objective: Recent meta-analyses demonstrated that there has been no significant increase in survival rates in patients with osteosarcoma since the late 1980es. This highlights the urgent need to develop new approaches for the clinical management of the disease. Unfortunately, efforts towards this have been hampered by the lack of suitable animal models that recapitulate the human disease. To address this challenge, we have developed the first humanized xenograft model of osteosarcoma.

Method: The study protocol was approved by the ethics committees of the Queensland University of Technology and the Prince Charles Hospital Brisbane (no. 130/025 and 060/232). Human bone fragments and marrow were obtained from a healthy donor. Samples were subcutaneously implanted into male NOD/Scid mice (n=12) along with rhBMP-7 embedded within a fibrin matrix. Twelve additional mice received human bone and marrow without growth factor support and served as a control. After 8 weeks of in vivo bone formation, 6 mice from each group were euthanized to quantify mineralized tissue formation via MicroCT and to analyse the cellular composition of the newly formed ossicles via flow cytometry and immunohistochemistry. The ossicles of the remaining mice were injected with 5x105 luciferase-transduced human osteosarcoma cells (Saos-2). Six additional mice were injected intratibially to control the effect of the humanized niche on tumor formation. Tumor growth and metastasis were longitudinally assessed for the subsequent 4 weeks using bioluminescence imaging.

Results and conclusion: Human samples implanted together with rhBMP-7 trapped within a fibrin matrix successfully recapitulated a vital humanized bone organ. MicroCT analysis showed a trabecular network surrounded by a cortex-like outer structure. Flow cytometry and immunohistochemistry (using human-specific antibodies for nuclear mitotic apparatus protein-1, collagen type 1, CD146, CD34 and CD45) demonstrated that the newly formed ossicle was a human-mouse chimera, containing functionally and morphologically intact vascular and endosteal hematopoietic stem cell niches. Human bone fragments implanted without growth factor support were necrotic and did not harbour any hematopoietic cell clusters. Histology and bioluminescence imaging after Saos-2 injection demonstrated that lung metastases were only present in mice carrying vital humanized bone organs.

This model makes it for the first time possible to analyse human osteosarcoma growth within a humanized vital microenvironment in vivo. We have demonstrated that human tumors developed lung metastasis only when grown in a vital humanized niche, which emphasizes the key role of the surrounding milieu in the process of tumor progression. This model represents a readily translatable platform, which allows us to identify promising new drug candidates for patients with osteosarcoma.