Combined therapy with the RANKL inhibitor RANK-Fc and rhApo2L/TRAIL/dulanermin reduces bone lesions and skeletal tumor burden in a model of breast cancer skeletal metastasis

In bone metastases, tumor cells interact with the bone microenvironment to induce osteoclastogenesis, leading to bone destruction and the growth factor release. RANK ligand (RANKL) is essential for osteoclast formation, function, and survival. Tumor cell-mediated osteolysis is thought to occur ultimately via induction of RANKL within the bone stroma, and inhibition of RANKL in models of breast cancer bone metastases blocks tumor-induced osteolysis and reduces skeletal tumor burden. In addition, the skeleton is co-opted by tumor cells and functions as a supportive tumor microenvironment. Inhibition of RANKL, by reducing tumor-induced osteoclastogenesis, may reduce the local release of growth factors and calcium which may potentially enhance the anti-tumor activity of cytotoxic or direct tumor apoptotic agents. Recombinant human Apo2 ligand/ TNF-related apoptosis-inducing ligand (rhApo2L/TRAIL/dulanermin) is a dual pro-apoptotic receptor agonist that preferentially induces apoptosis in cancer cells versus normal cells. We therefore examined RANKL inhibition (using RANK-Fc) in combination with rhApo2L/TRAIL on tumor-induced osteolysis and skeletal tumor burden in a murine intracardiac injection model of MDA-MB-231 breast carcinoma bone metastasis. rhApo2L/TRAIL treatment resulted in a rapid reduction of skeletal tumor burden. Treatment with RANK-Fc prevented osteolytic lesions and reduced skeletal tumor burden. Combining RANK-Fc with rhApo2L/TRAIL was superior to either rhApo2L/TRAIL or RANK-Fc alone at reducing skeletal tumor burden in the bone metastasis model. Our findings show that RANKL inhibition effectively inhibits pathologic osteolysis induced by human breast adenocarcinoma MDA-MB-231 cells in animals with established tumors, and also enhances the ability of rhApo2L/TRAIL to reduce skeletal tumor burden in vivo.