Osteoporosis is a systemic disease where bones become weak and porous due to low bone mass and deteriorated microarchitecture, significantly increasing fracture risk. A key player in this process is sclerostin (SOST). SOST inhibits the bone-building Wnt signaling pathway by binding to LRP5/6 receptors. While blocking sclerostin is a promising treatment strategy, the clinically approved monoclonal antibody Romosozumab, despite effectively treating postmenopausal osteoporosis, carries elevated cardiovascular risks. Therefore, developing new sclerostin inhibitors that maintain cardiovascular safety is crucial.
The structure of SOST features three loops with flexible termini. Loop 2 mediates Wnt inhibition by binding with LRP5/6 and triggers cardiovascular risks. Approved antibody Romosozumab blocking both Loop 2 and Loop 3 gain bone-strengthening effects at the cost of cardiovascular safety. In contrast, a Loop 3-specific aptamer reduces osteoporosis without inducing cardiovascular compromise. However, its therapeutic potential is hampered by excessive size, poor bone targeting, and costly production.
Our study aims to develop a SOST Loop 3-specific peptide inhibitor designed to reverse osteoporosis while protecting cardiovascular health. Using AI-based drug design, we generated a peptide pool. Subsequent biolayer interferometry (BLI) screening identified four Loop 3-binding candidates. Among these, pep54 exhibited the highest affinity for Loop 3 and the lowest affinity for Loop 2. Cellular assays in osteoblasts demonstrated that pep54 activated the Wnt/β-catenin pathway and enhanced bone formation. These findings position pep54 as a highly promising candidate for further development. Critically, our strategy of targeting SOST Loop 3 with peptides not only overcomes the cardiovascular risks associated with current antibody therapies and the limitations of aptamers, but also establishes a novel framework for developing safer, more targeted therapeutics for osteoporosis that specifically uncouple bone anabolism from adverse cardiovascular effects.