Bone is a very common metastatic site for
breast cancer. In bone
metastasis, there is a vicious circle wherein bone-residing metastatic cells stimulate osteoclast-mediated
bone resorption, and bone-derived
growth factors released from resorbed bone promote
tumor growth. The contribution of
tumor angiogenesis in the growth of bone
metastases is, however, unknown. By using an experimental model of bone
metastasis caused by MDA-MB-231/B02
breast cancer cells that quite closely mimics the conditions likely to occur in naturally arising metastatic human breast
cancers, we demonstrate here that when MDA-MB-231/B02 cells were engineered to produce at the bone metastatic site an
angiogenesis inhibitor,
angiostatin, there was a marked inhibition in the extent of skeletal lesions. Inhibition of skeletal lesions came with a pronounced reduction in
tumor burden in bone. However, although
angiostatin produced by MDA-MB-231/B02 cells was effective at inhibiting in vitro endothelial cell proliferation and in vivo angiogenesis in a
Matrigel implant model, we have shown that it inhibited
cancer-induced bone destruction through a direct inhibition of osteoclast activity and generation. Overall, these results indicate that, besides its well known anti-angiogenic activity,
angiostatin must also be considered as a very effective inhibitor of
bone resorption, broadening its potential clinical use in
cancer therapy.