Targeting Agents Used in Specific Bone-Targeting Drug Delivery Systems: A Review

Bone-targeting agent–based specific drug delivery has attracted increasing attention in current research involving bone-related diseases because of its ability to effectively reduce the administered dose of drugs and subsequent systemic toxicity. Bone-targeting agents determine the targeting characteristics of the drug delivery system and are the key components of the system. In this review, we summarize the most commonly used bone-targeting agents for bone drug delivery, including bisphosphonates, tetracyclines, peptides, and aptamers. We discuss the mechanisms by which these moieties bind to the bone matrix and specific bone cells and analyze the advantages and disadvantages of various targeting agents, such as the inflexible drug release time of small molecules and the poor biological stability of peptide agents. Furthermore, we introduce current specific bone-targeting drug delivery systems that utilize bone-targeting agents to provide a reference for the prospect and development of these delivery systems.