A home away from bone: development of an organotypic in vitro model of human osteosarcoma

Osteosarcoma (OS) is a rare primary bone sarcoma that occurs primarily in children and young adults. Treatment strategies and event-free survival rate have not changed significantly in over 20 years, and standard treatments can often cause life-altering side effects. A significant deficiency in most preclinical models of OS is that they do not accurately recreate the tumour microenvironment, which is implicated to play a critical role in tumour development and treatment resistance, and use of these incomplete models may contribute to the high failure rate of new treatments in clinical trials. Herein, I describe a modular, 3D in vitro model of the OS microenvironment that may be used to better understand and model tumour-stromal interactions and provide a more biologically-relevant preclinical model. The model exploits a 3D gelatin sponge scaffold containing bone-native mesenchymal stem cells (MSCs) and calcified extracellular matrix (ECM) that is naturally deposited by osteoblasts. The model is simple to use, amenable to a wide range of analysis techniques, and supports the assessment of individual aspects of the tumour microenvironment as well as combinations thereof. I found that the model supports the natural deposition of calcified ECM in a 3D bone-like structure, supports a co-culture of at least three different aspects of the OS tumour microenvironment and allows the functional analysis of tumour cells within the model. I also found that the presence of calcified ECM, osteoblasts and MSCs within the model leads to a significant decrease in OS tumour cell proliferation that does not appear to be related to the induction of tumour cell dormancy. Further development of this model could lead to a better understanding of the role that individual stromal components play in tumour progression and treatment resistance in osteosarcoma, which could lead to the development of novel treatment strategies.