PROJECT SUMMARY Osteoarthritis (OA) is a leading cause of disability in the United States and is presently without a cure. Despite advances in drug discovery and cell based therapies, disease-modifying therapies have remained elusive. OA is a complex disease involving maladaptive remodeling throughout the joint, including cartilage erosion, synovitis, and bone remodeling. The continuum of joint damage creates a chronic pro-inflammatory and catabolic joint environment, which ultimately destroys the joint's anatomy and physiologic function. There is a critical need for an OA therapy to address multiple disease mechanisms in multiple locations throughout the joint. While numerous drugs and factors have been identified for promoting cartilage repair and blocking various OA disease mechanisms, rapid joint clearance and poor tissue targeting limit their clinical application. This proposal lays the foundation for a comprehensive approach to treating OA that focuses on delivering the right drug in the right place at the right time in the joint. Specifically, this proposal aims to design drug carriers that can simultaneously delivery chondroprotective signals to the cartilage and immunomodulatory signals to synovial macrophages. We hypothesize that site-specific drug delivery that targets multiple disease processes will improve cartilage protection and prevent/reduce chronic joint inflammation, synergistically slowing/stopping OA progression. Specific Aim 1 focuses on the development of nanoparticle-based drug carriers that bind to and penetrate cartilage tissue, enabling sustained release of the chondroprotective drug, kartogenin, within the cartilage itself. Nanoparticle biodistribution and cartilage retention will be evaluated, as will the chondroprotective effects of site-specific kartogenin delivery in rodent models of OA. Specific Aim 2 focuses on the development of biocompatible particles that localize to the inflamed synovium and deliver a potent immunomodulatory signal, CD200, to macrophages. The influence of CD200 delivery on macrophage polarization, inflammatory cytokine production, and PTOA progression will be determined. Specific Aim 3 will study the combination the cartilage protecting and immune cell modulating drug delivery systems, and evaluate therapeutic effectiveness compared to each individual system alone. These studies will be performed in rodent model of OA that simulate many of the features observed in human patients. Therapeutic efficacy will be determined by comprehensive evaluation of structural, biochemical, and behavioral (pain and gait) metrics of the disease. Overall, the proposed work will advance knowledge and technologies for targeted drug delivery within the joint. Moreover, this work will also reveal new insights on the role of chondroprotection and macrophage immunomodulation on joint structure and function. By providing site-specific localization of OA drugs that simultaneously target multiple, synergistic pathways in the joint, we hope to overcome some of the limitations with existing treatment paradigms and move closer towards a cure for OA.