Bone Abstracts

Roundabout receptors are crucial regulators of vessels and axons growth during development. A comparative transcriptomic study between the MDA-MB-231 breast cancer cell line and its osteotropic subpopulation, MDA-B02 cells, has shown an overexpression of ROBO4 receptor. Interestingly, a high ROBO4 expression in primary tumour from patients with breast cancer correlates with poor prognosis and increased risk of bone metastasis relapse. Inoculation of ROBO4 depleted cells in the mammary fat pad of mice led to a 50% reduction in tumour burden and a decrease of osteolytic lesions after injection of ROBO4-depleted tumour cells into caudal artery of mice. In vivo intra-tibial injection of ROBO4-depleted cells or MDA-B02 cells first incubated with an anti-ROBO4 antibody led to a decrease of the incidence and extent of tumour cell engraftment in the bone marrow. Altogether these results let us hypothesize that ROBO4 might facilitate the migration and engraftment of tumour cells in the bone marrow. In vitro, the co-culture of MDA-B02 cells with osteoblastic cell line MC3T3-E1 generated an increase in SLIT2 production, the ROBO receptor ligand, by MC3T3-E1 cells. Further, when we used an anti-ROBO4 or anti-SLIT2 antibody, MDA-B02 cell adhesion to MC3T3-E1 cell monolayer was dramatically reduced. These results suggest that anchoring of tumour cells in bone was driven by an interaction between ROBO4-expressing cancer cells and bone marrow osteoblasts. Furthermore, SLIT2 was involved in this interaction. Our findings suggest the use of an antibody directed against ROBO4 could lead to the development of innovative therapies to prevent bone metastatic niche formation.