Bone metastases are the most common cause of cancer-related pain and often lead to complication such as bone fractures and spinal cord injury, all of which can severely erode patient’s quality of life. Even tumors such as breast cancer that can be now early diagnosed, leading to a positive resolution, may present increased morbidity and mortality if they metastasize to bone. The development of models allowing the study of cause mechanisms and new therapies represent a great challenge in cancer research. Animal models are essential for the study and characterization of these mechanisms. The ideal model should be clinically relevant and reproducible and should recapitulate human pathology. Different models are already available, each one with its own advantages and disadvantages. However a unique and standardized model has not been defined yet.
Our aim was to use a tissue engineering approach to create a mouse model, which allows to obtain a suitable environment for bone metastasis, starting from human cancer cells deriving from breast cancer. Human mesenchymal stromal cells (hMSCs) were seeded on a biocompatible and porous scaffold based on hydroxyapatite and β-tricalcium phosphate (MBCP+). The constructs were implanted subcutaneously in nude mice, to induce human bone growth. Once human ossicle was obtained in this “foreign” environment, human breast cancer cells were inoculated directly on the implant site, or intravenously through the tail. We injected luciferase-expressing breast cancer cells and the colonization and metastases formation were followed by IVIS. After two weeks mice were sacrificed, and the explants analysed by histology or processed to recover the colonizing cells. Selection of tumor cells was performed thanks to the expression of resistance gene for zeocine antibiotic. Culturing explants in selection medium (in presence of zeocine), only tumor cells which colonized the tissue will be able to attach and grow.
MDA-MB-231 metastatic breast cancer cells or MCF-7 cells were injected intravenously in mice previously implanted with MBCP+± hMSCs to obtain human bone. At first, MDA-MB-231 colonized the lungs, but they were able to reach the human bone within two weeks, and colonizing cells can be easily harvested from the explants. No colonization was observed in mouse skeleton. Interestingly, in mice implanted with MBCP+ alone (empty control), cancer cells did not reach the scaffold, suggesting a species-specific mechanism. MCF-7 cells were not able to metastasize, and no cells were recovered after explants.
Discussion and conclusions:
This system allows to study the mechanism by which breast cancer metastasizes to the bone, creating a species-specific environment. It could be an excellent tool for testing new combinations of drugs and, by using the patient’s cells directly, it could become a tool for the development of personalized therapies. Further investigations are required to characterize the metastatic cells on molecular level to shed light on the mechanism of action.