Systemic RANK-Fc protein therapy is efficacious against primary osteosarcoma growth in a murine model via activity against osteoclasts.

OBJECTIVES: Osteosarcoma (OS) is the most common primary malignant bone tumour, and mainly affects adolescents and young adults. Although there has been substantial improvement in management of OS with surgery and chemotherapy, further survival increase has not been achieved over the past two decades.
METHODS: We focused on the receptor activator of nuclear factor kappaB ligand (RANKL)-osteoclast (OCL) system as a biological target for OS. RANKL is a critical factor for OCL formation and bone resorption activity. The primary lesion in bone and ensuing metastasis in OS both require the induction of OCLs. RANK-Fc is a potent RANKL antagonist and inhibitor of OCL formation and activity. KEY
FINDINGS: In an orthotopic model in Balb/c nu/nu mice, a twice weekly dosing regimen of 350 microg of RANK-Fc per mouse subcutaneously (n= 5) reduced lung metastasis (P > 0.05), preserved bone structure and reduced tartrate-resistant acid phosphatase (TRAP)(+) OCLs (P < 0.005) in OS-bearing bone. In vitro, RANK-Fc suppressed OCL formation (P < 0.005), bone resorption activity (P < 0.005) and RANKL-induced anti-apoptosis (P < 0.5) of OCLs.