Optimizing\nLigand\nValency to Maximize Tendon Accumulation\nof Peptide-Targeted Nanoparticles

In many tissues, including musculoskeletal\ntissues such\nas tendon,\nsystemic delivery typically results in poor targeting of free drugs.\nHence, we previously developed a targeted drug delivery nanoparticle\n(NP) system for tendon healing, leveraging a tartrate resistant acid\nphosphatase (TRAP) binding peptide (TBP) ligand. The greatest tendon\ntargeting was observed with NPs functionalized with 30 000\nTBP ligands per NP at day 7 during the proliferative healing phase,\nrelative to the inflammatory (day 3) and early remodeling (day 14)\nphases of healing. Nevertheless, TRAP activity varies throughout healing\nand, therefore, may offer an opportunity for optimizing temporal therapeutic\ntargeting through multivalent interactions. Hence, in this study,\nwe hypothesized that the ligand density (9000–55,000 TBPs per\nNP) can optimize tendon accumulation on the basis of variable TRAP\nlevels. The multivalent nanoparticles were loaded with three different\nfluorophores. In vitro, the ligand density and fluorophore had no\neffect on the physicochemical properties of the NPs, including size,\ncharge, polydispersity index, or dye loading efficiency; however,\nthe TRAP binding affinity correlated positively with the ligand density.\nIn vivo, the ligand density correlated positively with NP homing and\nretention in the tendon, establishing opportunities to leverage ligand\ndensity for tendon targeting across the tendon healing cascade, during\naging, and in other tendon pathologies, including tendinopathies.