Inhibition of RANK/RANKL signal transduction pathway: a promising approach for osteoporosis treatment.

Osteoporosis is a bone disease causing impaired bone strength. It is characterized by increased osteoclast formation or enhanced bone resorption, leading to an increased risk of fragility fractures. Its prevalence increases with age. The advent of an aging population suggests that progressively more individuals will develop this disease in the aging population. A number of drugs for the prevention and treatment of osteoporosis act by inhibiting bone resorption. However, the effectiveness of osteoporosis treatment in clinical practice is limited. Since the osteoclast is the only cell in the body that is capable of resorbing bone, understanding its biology will be necessary for developing a new therapeutic approach for osteoporosis. Recently, it was discovered that the receptor activator of nuclear factor kappaB (RANK)/RANK ligand (RANKL)/osteoprotegerin (OPG) system is an important signal transduction pathway that regulates osteoclast formation. The binding of OPG to RANKL inhibits the binding between RANKL and RANK; this, in turn, prevents osteoclast precursors from differentiating and fusing to form mature osteoclasts. Therefore, the inhibition of the RANK/RANKL pathway inhibits osteoclast formation, differentiation, activation, and bone resorption. A potential clinical antiresorptive therapy can be developed by using an anti-RANKL monoclonal antibody, such as denosumab, that binds to RANKL with high affinity and specificity and blocks RANKL-RANK interactions.