The present study was conducted to determine the effects of bone sialoprotein (BSP) in promoting vascular invasion of tumor cells in metastasis. We used a Matrigel system and the MDA-231 human breast cancer cells transfected with human BSP cDNA (MDA-231/BSP). Quantative analysis indicated an average of 1.7-fold increase in cell numbers that migrated through the endothelial cells in MDA-231/BSP cells compared with empty vector-transfected MDA-231 cells (MDA-231/EV). In an in vivo assay, the MDA-231 cells were incubated with or without BSP antibodies and were then inoculated onto the upper chorioallantoic membrane (CAM) of chicken embryos, in which the only route for the tumor cells to reach the lower CAM was to migrate through the embryonic vasculature. PCR amplification using human Alu primers and genomic DNA from harvested lower CAM showed an average reduction of 67% in the samples treated with BSP antibodies. These preliminary data suggest that, in metastasis, BSP may enhance the penetrating ability of tumor cells through endothelial cells and basement membrane into blood vessels. BSP antibodies can specifically hinder this effect in an in vivo system.

Bone sialoprotein (BSP) is synthesized and secreted by bone-, dentine- and cementum-forming cells and has been implicated in de novo bone formation and mineralization. In this study, we used histological sections of odontogenic neoplasms and performed immunohistochemical and in situ hybridization analyses. In ameloblastoma, BSP mRNA signals were seen in the neoplastic epithelial cells forming nests, strips and islands. BSP deposition was also seen in the stellate reticulum of the tumour masses revealed by immunohistochemistry using human BSP antibodies. In calcifying epithelial odontogenic tumour, the calcified masses demonstrated positive immunoreactivity to the human BSP antibodies, and the hybridization signals for BSP were located in the cells near the calcified particles. In the calcifying odontogenic cyst, strong BSP signals were seen in cells surrounding the characteristic nests of ghost cells, which often calcify subsequently. BSP protein was also found in these cells by immunohistochemistry. The active expression of BSP in the epithelial elements of the odontogenic tumours of adult patients suggests the activation of this matrix protein gene in the neoplastic process, and that BSP may play an important role in tumour formation and differentiation with respect to pathological calcification.