gms | German Medical Science

Objective: The EphrinB2 system has been linked to organ specific metastasis formation by mediating both tumor cell - endothelial cell interactions and angiogenesis. It was the aim to determine the influence of endothelial EphrinB2 depletion on tumor cell – endothelial cell interactions in osseous tissue and to characterize the effects on spinal metastasis angiogenesis.

Methods: Luciferin expressing B16 melanoma cell (1*10⁵ cells) were injected retrograde into the left CCA in control (efnb2^lox/lox) and endothelial EphrinB2 knock-out mice (efnb2^i△EC, N≥5). Spinal bone histology was performed in efnb2^lox/lox and efnb2^i△EC animals using endomucin and CD31 staining. Cell dissemination (3 hours after injection) experiments and calvae fluorescence intravital microscopy (IVM) were performed to identify efnb2 related endothelial - tumor cell interactions during tumor cell dissemination.

Results: In non-tumor bearing efnb2^i△EC animals endomucin positive spinal sinusoids were significantly reduced compared to controls (65±14% vs. 39±20%) whereas CD31 positive sinusoids were comparable between groups. In spinal metastasis bearing efnb2^i△EC animals, this vascular phenotype changed to a significant increase of CD31 pos. spinal sinusoids (21±19% vs. 41±21%), whereas no difference was observed in Endomucin pos. vessels. IVM demonstrated a significantly increased number of trapped tumor cells in bone microvessels after intraarterial tumor cell injection in efnb^2i△EC animals (31±28 cells/ROI vs 69±18 cells/ROI; 3 hours after injection)

Conclusion: Endothelial EphrinB2 depletion leads to increased tumor cell – endothelial cell interactions during hematogenous metastatic dissemination to the spine and supports a proangiogenic response in spinal metastasis angiogenesis.