The tumor necrosis factor family ligand, tumor necrosis factor-related activation-induced cytokine (TRANCE), and its receptors, receptor activator of nuclear factor-B (RANK) and osteoprotegerin (OPG), are known to be regulators of development and activation of osteoclasts in bone remodeling. Sustained osteoclast activation that occurs through TRANCE-RANK causes osteopenic disorders such as osteoporosis and contributes to osteolytic metastases. Here, we report a rationally designed small molecule mimic of osteoprotegerin to inhibit osteoclast formation in vitro and limit bone loss in an animal model of osteoporosis. One of the mimetics, OP3-4, significantly inhibited osteoclast formation in vitro (IC 50 ‫؍‬ 10 M) and effectively inhibited total bone loss in ovariectomized mice at a dosage of 2 mg/kg/day. Unlike soluble OPG receptors, which preclude TRANCE binding to RANK, OP3-4 shows the ability to modulate RANK-TRANCE signaling pathways and alters the biological functions of the RANK-TRANCE receptor complex by facilitating a defective receptor complex. These features suggest that OPG-derived small molecules can be used as a probe to understand complex biological functions of RANK-TRANCE-OPG receptors and also can be used as a platform to develop more useful therapeutic agents for inflammation and bone disease. TRANCE,1 a TNF family member, also known as OPGL, RANKL, ODF, and OCIF, plays a key role in the development of osteoclasts and in modulating their bone resorbing activity (1-4). Increased osteoclast activity has been reported in many osteopenic disorders, including postmenopausal osteoporosis, Paget's disease, bone metastases, and rheumatoid arthritis (5-7). TRANCE interacts with two receptors: a secreted decoy receptor osteoprotegerin, OPG (8), and a transmembrane receptor, RANK (9 -11). The interaction between TRANCE and RANK is essential for osteoclastogenesis because RANK is activated by TRANCE and then associates with TNF receptorassociated family members to trigger downstream signaling (11) events. OPG, on the other hand, plays an opposite role by preventing TRANCE from binding and activating RANK and thus is considered a "decoy" receptor. In this way, the interaction between TRANCE and OPG or TRANCE and RANK represents a complex network required for normal bone development, and any imbalance in the system potentially leads to bone disorders. Thus it is well recognized that this receptor complex network is an interesting drug development target for the treatment of bone disorders such as osteoporosis (12), and there is considerable interest in developing ways to modulate RANK functions which may prove beneficial for bone-related pathologies.To date there is no three-dimensional structural information available for the RANK receptor complex. However, it is believed that the complex should resemble that of the TNF receptor as a member of TNF superfamily. The TNF-␤⅐TNFR1 co-crystal structure has been solved, thus facilitating rational drug design based on the receptor-ligand interaction sites coupled wi...

Tumor necrosis factor (TNF) and TNF receptor (TNFR) family proteins play important roles in many biological processes. Recently, the TNF-family molecule, RANKL (also called TRANCE, ODF, and OPGL), and its receptors, RANK and OPG, were found to be regulators of the development and activation of osteoclasts in bone remodeling. TNFalphaalso activates osteoclasts both by themselves and in synergy with RANKL. We used structure-based design to create peptidomimetics and organic therapeutics that inhibit osteoclastogenesis by inhibiting the interaction of ligands and receptors. Here we show for the first time that blocking TNFalpha by these small molecules effectively inhibited osteoclast formation in vitro. These mimetics can be used as a probe to understand the molecular basis of osteoclastogenesis and also as a platform to create useful therapeutic agent.