Abstract
Introduction and Aims: To investigate the expression of Vascular Endothelial Growth Factor (VEGF) and its receptors in bone metastases from primary breast tumors and further characterise its effects on osteoclasts in vitro.
Method and Results: Seventeen specimens of breast cancer metastases to bone were immunohistochemically stained for VEGF, its receptors VEGFR1 and 2, and the macrophage marker CD68. This demonstrated that breast cancer metastases express VEGF strongly and that surrounding osteoclasts express both VEGFR1 (12 of 14 specimens) and VEGFR2 (14 of 14 specimens).
To investigate osteoclastogenesis in vitro, Peripheral Blood Mononuclear Cells (PBMC) were isolated from healthy volunteers and cultured under stimulation by cytokines. Tartrate Resistant Acid Phophatase (TRAP) positive multinucleated cells were counted in duplicate per treatment and experiments repeated three times. VEGF and RANKL together induced differentiation of multinucleated TRAP-positive cells in similar numbers (22±4.7[SE]) per field of view to M-CSF and RANKL (27.3±7.2[SE]). Stimulation with PlGF (a specific ligand for VEGFR1) and RANKL induced osteoclastogenesis, but VEGF-D (a specific ligand for VEGFR2) with RANKL had little effect.
RAW 264.7 cells (mouse monocyte cell line) differentiated into osteoclast-like cells after stimulation with VEGF and RANKL similar to M-CSF and RANKL. Culture under the same conditions on ivory disks was performed and resorption of ivory by osteoclasts from both PBMC and RAW cells was identified.
Conclusion: VEGF, the angiogenic cytokine, is expressed highly by many solid tumors often correlating with poor prognosis. We have shown that VEGF induces monocytes to differentiate into osteoclast-like cells in the presence of RANKL and this seems to be mediated by VEGFR1. VEGF may therefore play a role in physiological bone resorption and in pathological situations, such as tumor osteolysis and consequently VEGF signalling may be a therapeutic target for osteoclast inhibition.
These abstracts were prepared by Editorial Secretary, George Sikorski. Correspondence should be addressed to Australian Orthopaedic Association, Ground Floor, The William Bland Centre, 229 Macquarie Street, Sydney, NSW 2000, Australia.
At least one of the authors is receiving or has received material benefits or support from a commercial source.
