A monoclonal antibody directed against the receptor activator of nuclear factor kappa beta ligand (RANKL) with potential antiosteoclast and antineoplastic activities. Upon administration, anti-RANKL monoclonal antibody GB-223 specifically binds to RANKL and blocks the interaction of RANKL with RANK, a receptor located on osteoclast cell surfaces. This results in the inhibition of osteoclast activity, a decrease in bone resorption, and a potential increase in bone mineral density. By blocking the activation of the RANK/RANKL-mediated signaling pathway, GB-223 may also reduce tumor-associated bone destruction and may result in tumor regression in bone tumors with high RANK and RANKL expressions. RANKL, a protein expressed by osteoblastic cells, plays an important role in osteoclastic differentiation and activation. Both RANKL and RANK are overexpressed in certain bone tumors, and the RANK/RANKL-mediated signaling pathway plays an important role in certain bone tumors.