Despite several decades of progress, bone-specific drug delivery is still a major challenge. Current bone-acting drugs require high-dose systemic administration which decreases therapeutic efficacy and increases off-target tissue effects. Here, a bone-targeted nanoparticle (NP) delivery system for a β-catenin agonist, 3-amino-6-(4-((4-methylpiperazin-1-yl)-sulfonyl)phenyl)-N-(pyridin-3-yl)pyrazine-2-carboxamide, a glycogen synthase kinase 3 beta (GSK-3β) inhibitor, was developed to enhance fracture healing. The GSK-3β inhibitor loading capacity was found to be 15 wt % within highly stable poly(styrene-alt-maleic anhydride)-b-poly(styrene) NPs, resulting in ~50 nm particles with ~ −30 mV surface charge. A peptide with high affinity for tartrate-resistant acid phosphatase (TRAP), a protein deposited by osteoclasts on bone resorptive surfaces, was introduced to the NP corona to achieve preferential delivery to fractured bone. Targeted NPs showed improved pharmacokinetic profiles with greater accumulation at fractured bone, accompanied by significant uptake in regenerative cell types (mesenchymal stem cells (MSCs) and osteoblasts). MSCs treated with drug-loaded NPs in vitro exhibited 2-fold greater β-catenin signaling than free drug that was sustained for 5 days. To verify similar activity in vivo, TOPGAL reporter mice bearing fractures were treated with targeted GSK-3β inhibitor-loaded NPs. Robust β-galactosidase activity was observed in fracture callus and periosteum treated with targeted carriers versus controls, indicating potent β-catenin activation during the healing process. Enhanced bone formation and microarchitecture were observed in mice treated with GSK-3β inhibitor delivered via TRAP-binding peptide-targeted NPs. Specifically, increased bone bridging, ~4-fold greater torsional rigidity, and greater volumes of newly deposited bone were observed 28 days after treatment, indicating expedited fracture healing.

Leukemias are challenging diseases to treat due, in part, to interactions between leukemia cells and the bone marrow microenvironment (BMME) that contribute significantly to disease progression. Studies have shown that leukemic cells secrete C-chemokine (C-C motif) ligand 3 (CCL3), to disrupt the BMME resulting in loss of hematopoiesis and support of leukemic cell survival and proliferation. In this study, a murine model of blast crisis chronic myelogenous leukemia (bcCML) that expresses the translocation products BCR/ABL and Nup98/HoxA9 was used to determine the role of CCL3 in BMME regulation. Leukemic cells derived from CCL3 −/− mice were shown to minimally engraft in a normal BMME, thereby demonstrating that CCL3 signaling was necessary to recapitulate bcCML disease. Further analysis showed disruption in hematopoiesis within the BMME in the bcCML model. To rescue the altered BMME, therapeutic inhibition of CCL3 signaling was investigated using bone-targeted nanoparticles (NP) to deliver Maraviroc, an inhibitor of 2 of 14 | ACKUN-FARMMER Et Al.

Despite efforts to achieve tissue selectivity, the majority of systemically administered drug delivery systems (DDSs) are cleared by the mononuclear phagocyte system (MPS) before reaching target tissues regardless of disease or injury pathology. Previously, we showed that while tartrate‐resistant acid phosphatase (TRAP) binding peptide (TBP)‐targeted polymeric nanoparticles (TBP‐NP) delivering a bone regenerative Wnt agonist improved NP fracture accumulation and expedited healing compared with controls, there was also significant MPS accumulation. Here we show that TBP‐NPs are taken up by liver, spleen, lung, and bone marrow macrophages (Mϕ), with 76 ± 4%, 49 ± 11%, 27 ± 9%, and 92 ± 5% of tissue‐specific Mϕ positive for NP, respectively. Clodronate liposomes (CLO) significantly depleted liver and spleen Mϕ, resulting in 1.8‐fold and 3‐fold lower liver and spleen and 1.3‐fold and 1.6‐fold greater fracture and naïve femur accumulation of TBP‐NP. Interestingly, depletion and saturation of MPS using 10‐fold greater TBP‐NP doses also resulted in significantly higher TBP‐NP accumulation at lungs and kidneys, potentially through compensatory clearance mechanisms. The higher NP dose resulted in greater TBP‐NP accumulation at naïve bone tissue; however, other MPS tissues (i.e., heart and lungs) exhibited greater TBP‐NP accumulation, suggesting uptake by other cell types. Most importantly, neither Mϕ depletion nor saturation strategies improved fracture site selectivity of TBP‐NPs, possibly due to a reduction of Mϕ‐derived osteoclasts, which deposit the TRAP epitope. Altogether, these data support that MPS‐mediated clearance is a key obstacle in robust and selective fracture accumulation for systemically administered bone‐targeted DDS and motivates the development of more sophisticated approaches to further improve fracture selectivity of DDS.