gms | German Medical Science

Objective: The skeleton is a preferred site for breast cancer metastasis. To date, treatment options for patients with bone metastases are at best palliative and the disease is still incurable. Indeed key mechanisms involved in breast cancer osteotropism are still only partially understood due to the lack of suitable animal models. Recently, humanized xenograft models have been developed where human bone was implanted subcutaneously into immunodeficient mice to serve as a target site for metastasis by human cancer cells. However there are practical issues associated with this approach, including reliance on donor tissue, patient-related variability and low viability of the human bone implants. Tissue engineered bone constructs may provide more reproducible and functional implants. In the presented study we investigate a novel humanized xenograft model to mimic bone metastasis by breast cancer using a tissue engineering approach.

Methods: Electrospun polycaprolactone scaffolds coated with calcium phosphate were seeded with primary human osteoblasts and cultured in vitro under osteogenic conditions for 10 weeks. The human tissue engineered bone constructs (hTEBC) were then loaded with fibrin glue and rhBMP-7 and implanted in the flanks of 5 week-old NOD/SCID mice. After 10 weeks to allow ectopic bone formation, luciferase-expressing human breast cancer cell lines MDA-MB-231 and MDA-MB-231BO were injected into the mice via the intracardiac route. Non-tumorigenic MCF10A cells served as controls. Cancer cell dissemination was monitored over 4 weeks by in vivo bioluminescent imaging using the Xenogen IVIS spectrum. After euthanasia, the hTEBC specimens were analysed by ex vivo bioluminescent imaging and micro-CT. Histology and immunohistochemistry analysis are underway.

Results and conclusion: Micro-CT analysis revealed mineralised tissue deposition in the constructs (7.9 ± 1.2 mm3). Preliminary immunohistochemical results show the formation of ectopic bone incorporating mineralised bone matrix, an interconnected vascular network and a bone marrow compartment in the hTEBC. Bioluminescent imaging indicated respectively a 85.7% and 50% homing rate to the hTEBC for the MDA-MB-231BO and MDA-MB-231 cell groups. Both cell lines also disseminated to several mice organs including to the skeleton. No metastases were detected in the control group.

We demonstrate here that the hTEBC is a controllable system to obtain ectopic human bone formation in a mouse model and that it can be applied as a target tissue for the dissemination of human breast cancer cells injected into the circulatory system. In conclusion, we developed a highly suitable model to investigate species-specific mechanisms of human breast cancer related bone metastasis in vivo.