Authors
Jude Canon, Rebecca Bryant, Martine Roudier, Tao Osgood, Jon Jones, Robert Miller, Angela Coxon, Robert Radinsky, William C. Dougall
Abstract
Bone metastases cause severe skeletal complications and are associated with osteoclast-mediated bone destruction. RANKL is essential for osteoclast formation, function, and survival, and is the primary effector of tumor-induced osteoclastogenesis and osteolysis. RANKL inhibition by its soluble decoy receptor osteoprotegerin (OPG) prevents tumor-induced osteolysis and decreases skeletal tumor burden. Because
osteoclast-mediated bone resorption releases growth factors from the bone matrix, the host bone micro-environment induces a vicious cycle of bone destruction and tumor proliferation and survival. A prediction of
this vicious cycle hypothesis is that targeting the host bone microenvironment by osteoclast inhibition would reduce tumor growth and survival and may enhance the anti-tumor effects of targeted therapies. The
epidermal growth factor receptor (EGFR) pathway regulates critical processes such as cell growth and survival, and anti-EGFR therapies can cause tumor cell arrest and apoptosis. We evaluated whether reduction
of osteolysis by RANKL inhibition could enhance the anti-tumor effects of an anti-EGFR antibody (panitumumab) in a novel murine model of human A431 epidermoid carcinoma bone metastasis. Skeletal tumor progression was assessed longitudinally by bioluminescence imaging. RANKL inhibition by OPG-Fc treatment resulted in a reduction in tumor progression in bony sites. OPG-Fc treatment also caused a dose-
dependent reduction in tumor-induced osteolysis, supporting the essential role of RANKL in this process. In combination, RANKL inhibition increased the anti-tumor efficacy of an anti-EGFR antibody, and completely blocked tumor-induced bone breakdown, demonstrating that addition of the indirect anti-tumor effect of RANKL inhibition increases the anti-tumor efficacy of panitumumab, a targeted anti-EGFR antibody.