Osteoprotegerin inhibits osteolysis and decreases skeletal tumor burden in syngeneic and nude mouse models of experimental bone metastasis

Certain malignancies, including breast cancer, frequently metastasize to bone, where the tumor cells induce osteoclasts to locally destroy bone. Osteoprotegerin (OPG), a member of the tumor necrosis factor receptor family, is a negative regulator of osteoclast differentiation, activation, and survival, We tested the ability of recombinant OPG to inhibit tumor-induced osteoclastogenesis, osteolysis, and skeletal tumor burden in two animal models. In a syngeneic model, mouse colon adenocarcinoma (Colon-26) cells were injected into the left ventricle of mice. Treatment with OPG dose-dependently decreased the number and area of radiographically evident lytic bone lesions, which, at the highest dose, were undetectable. Histologically, OPG also decreased skeletal tumor burden and tumor-associated osteoclasts, In a nude mouse model, OPG treatment completely prevented radiographic osteolytic lesions caused by human MDA-MB-231 breast cancer cells. Histologically, OPG decreased skeletal tumor burden by 75% and completely eradicated MDA tumor-associated osteoclasts. In both models, OPG had no effect on metastatic tumor burden in a panel of soft tissue organs. These data indicate that OPG may be an effective therapy for preventing osteolysis and decreasing skeletal tumor burden in patients with bone metastasis.