Fracture-Targeted Delivery of β-Catenin Agonists via Peptide-Functionalized Nanoparticles Augments Fracture Healing

Development of a nanoparticle-based tendon-targeting drug delivery system to pharmacologically modulate tendon healing

Satisfactory healing following acute tendon injury is marred by fibrosis. Despite the high frequency of tendon injuries and poor outcomes, there are no pharmacological therapies in use to enhance the healing process. Moreover, systemic treatments demonstrate poor tendon homing, limiting the beneficial effects of potential tendon therapeutics. To address this unmet need, we leveraged our existing tendon healing spatial transcriptomics dataset and identified an area enriched for expression of Acp5 (TRAP) and subsequently demonstrated robust TRAP activity in the healing tendon. This unexpected finding allowed us to refine and apply our existing TRAP binding peptide (TBP) functionalized nanoparticle (NP) drug delivery system (DDS) to facilitate improved delivery of systemic treatments to the healing tendon. To demonstrate the translational potential of this DDS, we delivered niclosamide (NEN), an S100a4 inhibitor. While systemic delivery of free NEN did not alter healing, TBP-NPNEN enhanced both functional and mechanical recovery, demonstrating the translational potential of this approach to enhance the tendon healing process.

Advancing Bone-Targeted Drug Delivery: Leveraging Biological Factors and Nanoparticle Designs to Improve Therapeutic Efficacy

Designing targeted drug delivery systems to effectively treat bone diseases ranging from osteoporosis to nonunion bone defects remains a significant challenge. Previously, nanoparticles (NPs) self-assembled from diblock copolymers of poly(styrene-alt-maleic anhydride)-b-poly(styrene) (PSMA-b-PS) delivering a Wnt agonist were shown to effectively target bone and improve healing via the introduction of a peptide with high affinity to tartrate-resistant acid phosphatase (TRAP), an enzyme deposited by the osteoclasts during bone remodeling. Despite these promising results, the underlying biological factors governing targeting and subsequent drug delivery system (DDS) design parameters have not been examined to enable the rational design to improve bone selectivity. Therefore, this work investigated the effect of target ligand density, the treatment window after injury, specificity of TRAP binding peptide (TBP), the extent of TRAP deposition, and underlying genetic factors (e.g., mouse strain differences) on TBP-NP targeting. Data based on in vitro binding studies and in vivo biodistribution analyses using a murine femoral fracture model suggest that TBP-NP-TRAP interactions and TBP-NP bone accumulation were ligand-density-dependent; in vitro, TRAP affinity was correlated with ligand density up to the maximum of 200,000 TBP ligands/NP, while NPs with 80,000 TBP ligands showed 2-fold increase in fracture accumulation at day 21 post injury compared with that of untargeted or scrambled controls. While fracture accumulation exhibited similar trends when injected at day 3 compared to that at day 21 postfracture, there were no significant differences observed between TBP-functionalized and control NPs, possibly due to saturation of TRAP by NPs at day 3. Leveraging a calcium-depletion diet, TRAP deposition and TBP-NP bone accumulation were positively correlated, confirming that TRAP-TBP binding leads to TBP-NP bone accumulation in vivo. Furthermore, TBP-NP exhibited similar bone accumulation in both C57BL/6 and BALB/c mouse strains versus control NPs, suggesting the broad applicability of TBP-NP regardless of the underlying genetic differences. These studies provide insight into TBP-NP design, mechanism, and therapeutic windows, which inform NP design and treatment strategies for fractures and other bone-associated diseases that leverage TRAP, such as marrow-related hematologic diseases.

Bone Targeting Nanoparticles for the Treatment of Osteoporosis

Osteoporosis (OP) affects millions of people worldwide, especially postmenopausal women and the elderly. Although current available anti-OP agents can show promise in slowing down bone resorption, most are not specifically delivered to the hard tissue, causing significant toxicity. A bone-targeted nanodrug delivery system can reduce side effects and precisely deliver drug candidates to the bone. This review focuses on the progress of bone-targeted nanoparticles in OP therapy. We enumerate the existing OP medications, types of bone-targeted nanoparticles and categorize pairs of the most common bone-targeting functional groups. Finally, we summarize the potential use of bone-targeted nanoparticles in OP treatment. Ongoing research into the development of targeted ligands and nanocarriers will continue to expand the possibilities of OP-targeted therapies into clinical application.

Bone-Targeted Nanoparticle Drug Delivery System-Mediated Macrophage Modulation for Enhanced Fracture Healing

Despite decades of progress, developing minimally invasive bone-specific drug delivery systems (DDS) to improve fracture healing remains a significant clinical challenge. To address this critical therapeutic need, nanoparticle (NP) DDS comprised of poly(styrene-alt-maleic anhydride)-b-poly(styrene) (PSMA-b-PS) functionalized with a peptide that targets tartrate-resistant acid phosphatase (TRAP) and achieves preferential fracture accumulation has been developed. The delivery of AR28, a glycogen synthase kinase-3 beta (GSK3β) inhibitor, via the TRAP binding peptide-NP (TBP-NP) expedites fracture healing. Interestingly, however, NPs are predominantly taken up by fracture-associated macrophages rather than cells typically associated with fracture healing. Therefore, the underlying mechanism of healing via TBP-NP is comprehensively investigated herein. TBP-NPAR28 promotes M2 macrophage polarization and enhances osteogenesis in preosteoblast-macrophage co-cultures in vitro. Longitudinal analysis of TBP-NPAR28 -mediated fracture healing reveals distinct spatial distributions of M2 macrophages, an increased M2/M1 ratio, and upregulation of anti-inflammatory and downregulated pro-inflammatory genes compared to controls. This work demonstrates the underlying therapeutic mechanism of bone-targeted NP DDS, which leverages macrophages as druggable targets and modulates M2 macrophage polarization to enhance fracture healing, highlighting the therapeutic benefit of this approach for fractures and bone-associated diseases.

Integrating osteoimmunology and nanoparticle-based drug delivery systems for enhanced fracture healing

Fracture healing is a complex interplay of molecular and cellular mechanisms lasting from days to weeks. The inflammatory phase is the first stage of fracture healing and is critical in setting the stage for successful healing. There has been growing interest in exploring the role of the immune system and novel therapeutic strategies, such as nanoparticle drug delivery systems in enhancing fracture healing. Advancements in nanotechnology have revolutionized drug delivery systems to the extent that they can modulate immune response during fracture healing by leveraging unique physiochemical properties. Therefore, understanding the intricate interactions between nanoparticle-based drug delivery systems and the immune response, specifically macrophages, is essential for therapeutic efficacy. This review provides a comprehensive overview of the relationship between the immune system and nanoparticles during fracture healing. Specifically, we highlight the influence of nanoparticle characteristics, such as size, surface properties, and composition, on macrophage activation, polarization, and subsequent immune responses. IMPACT STATEMENT: This review provides valuable insights into the interplay between fracture healing, the immune system, and nanoparticle-based drug delivery systems. Understanding nanoparticle-macrophage interactions can advance the development of innovative therapeutic approaches to enhance fracture healing, improve patient outcomes, and pave the way for advancements in regenerative medicine.

Multi-Functional Small Molecule Alleviates Fracture Pain and Promotes Bone Healing

Bone injuries such as fractures are one major cause of morbidities worldwide. A considerable number of fractures suffer from delayed healing, and the unresolved acute pain may transition to chronic and maladaptive pain. Current management of pain involves treatment with NSAIDs and opioids with substantial adverse effects. Herein, we tested the hypothesis that the purine molecule, adenosine, can simultaneously alleviate pain and promote healing in a mouse model of tibial fracture by targeting distinctive adenosine receptor subtypes in different cell populations. To achieve this, a biomaterial-assisted delivery of adenosine is utilized to localize and prolong its therapeutic effect at the injury site. The results demonstrate that local delivery of adenosine inhibited the nociceptive activity of peripheral neurons through activation of adenosine A1 receptor (ADORA1) and mitigated pain as demonstrated by weight bearing and open field movement tests. Concurrently, local delivery of adenosine at the fracture site promoted osteogenic differentiation of mesenchymal stromal cells through adenosine A2B receptor (ADORA2B) resulting in improved bone healing as shown by histological analyses and microCT imaging. This study demonstrates the dual role of adenosine and its material-assisted local delivery as a feasible therapeutic approach to treat bone trauma and associated pain.

Development of a Nanoparticle-Based Tendon-Targeting Drug Delivery System to Pharmacologically Modulate Tendon Healing

Tendon regeneration following acute injury is marred by a fibrotic healing response that prevents complete functional recovery. Despite the high frequency of tendon injuries and the poor outcomes, including functional deficits and elevated risk of re-injury, there are currently no pharmacological therapies in clinical use to enhance the healing process. Several promising pharmacotherapies have been identified; however, systemic treatments lack tendon specificity, resulting in poor tendon biodistribution and perhaps explaining the largely limited beneficial effects of these treatments on the tendon healing process. To address this major unmet need, we leveraged our existing spatial transcriptomics dataset of the tendon healing process to identify an area of the healing tendon that is enriched for expression of Acp5. Acp5 encodes tartrate-resistant acid phosphatase (TRAP), and we demonstrate robust TRAP activity in the healing tendon. This unexpected finding allowed us to refine and apply our existing TRAP binding peptide (TBP) functionalized nanoparticle (NP) drug delivery system (DDS) to facilitate improved delivery of systemic treatments to the healing tendon. To demonstrate the translational potential of this drug delivery system, we delivered the S100a4 inhibitor, Niclosamide to the healing tendon. We have previously shown that genetic knockdown of S100a4 enhances tendon healing. While systemic delivery of Niclosamide did not affect the healing process, relative to controls, TBP-NP delivery of Niclosamide enhanced both functional and mechanical outcome measures. Collectively, these data identify a novel tendon-targeting drug delivery system and demonstrate the translational potential of this approach to enhance the tendon healing process.

Drug Delivery Approaches to Improve Tendon Healing

Tendon injuries disrupt the transmission of forces from muscle to bone, leading to chronic pain, disability, and a large socioeconomic burden. Tendon injuries are prevalent; there are over 300,000 tendon repair procedures a year in the United States to address acute trauma or chronic tendinopathy. Successful restoration of function after tendon injury remains challenging clinically. Despite improvements in surgical and physical therapy techniques, the high complication rate of tendon repair procedures motivates the use of therapeutic interventions to augment healing. While many biological and tissue engineering approaches have attempted to promote scarless tendon healing, there is currently no standard clinical treatment to improve tendon healing. Moreover, the limited efficacy of systemic delivery of several promising therapeutic candidates highlights the need for tendon-specific drug delivery approaches to facilitate translation. This review article will synthesize the current state-of-the-art methods that have been used for tendon-targeted delivery through both systemic and local treatments, highlight emerging technologies used for tissue-specific drug delivery in other tissue systems, and outline future challenges and opportunities to enhance tendon healing through targeted drug delivery.

Smart Strategies to Overcome Drug Delivery Challenges in the Musculoskeletal System

The musculoskeletal system (MSKS) is composed of specialized connective tissues including bone, muscle, cartilage, tendon, ligament, and their subtypes. The primary function of the MSKS is to provide protection, structure, mobility, and mechanical properties to the body. In the process of fulfilling these functions, the MSKS is subject to wear and tear during aging and after injury and requires subsequent repair. MSKS diseases are a growing burden due to the increasing population age. The World Health Organization estimates that 1.71 billon people suffer from MSKS diseases worldwide. MSKS diseases usually involve various dysfunctions in bones, muscles, and joints, which often result in pain, disability, and a decrease in quality of life. The most common MSKS diseases are osteoporosis (loss of bone), osteoarthritis (loss of cartilage), and sarcopenia (loss of skeletal muscle). Because of the disease burden and the need for treatment, regenerative drug therapies for MSKS disorders are increasingly in demand. However, the difficulty of effective drug delivery in the MSKS has become a bottleneck for developing MSKS therapeutics. The abundance of extracellular matrix and its small pore size in the MSKS present a formidable barrier to drug delivery. Differences of vascularity among various MSKS tissues pose complications for drug delivery. Novel strategies are necessary to achieve successful drug delivery in different tissues composing the MSKS. Those considerations include the route of administration, mechanics of surrounding fluids, and biomolecular interactions, such as the size and charge of the particles and targeting motifs. This review focuses on recent advances in challenges to deliver drugs to each tissue of the MSKS, current strategies of drug delivery, and future ideas of how to overcome drug delivery challenges in the MSKS.

Impact of Nanoparticle Physicochemical Properties on Protein Corona and Macrophage Polarization

Macrophages, the major component of the mononuclear phagocyte system, uptake and clear systemically administered nanoparticles (NPs). Therefore, leveraging macrophages as a druggable target may be advantageous to enhance NP-mediated drug delivery. Despite many studies focused on NP-cell interactions, NP-mediated macrophage polarization mechanisms are still poorly understood. This work aimed to explore the effect of NP physicochemical parameters (size and charge) on macrophage polarization. Upon exposure to biological fluids, proteins rapidly adsorb to NPs and form protein coronas. To this end, we hypothesized that NP protein coronas govern NP-macrophage interactions, uptake, and subsequent macrophage polarization. To test this hypothesis, model polystyrene NPs with various charges and sizes, as well as NPs relevant to drug delivery, were utilized. Data suggest that cationic NPs potentiate both M1 and M2 macrophage markers, while anionic NPs promote M1-to-M2 polarization. Additionally, anionic polystyrene nanoparticles (APNs) of 50 nm exhibit the greatest influence on M2 polarization. Proteomics was pursued to further understand the effect of NPs physicochemical parameters on protein corona, which revealed unique protein patterns based on NP charge and size. Several proteins impacting M1 and M2 macrophage polarization were identified within cationic polystyrene nanoparticles (CPNs) corona, while APNs corona included fewer M1 but more M2-promoting proteins. Nevertheless, size impacts protein corona abundance but not identities. Altogether, protein corona identities varied based on NP surface charge and correlated to dramatic differences in macrophage polarization. In contrast, NP size differentially impacts macrophage polarization, which is dominated by NP uptake level rather than protein corona. In this work, specific corona proteins were identified as a function of NP physicochemical properties. These proteins are correlated to specific macrophage polarization programs and may provide design principles for developing macrophage-mediated NP drug delivery systems.

Targeting Agents in Biomaterial-Mediated Bone Regeneration

Bone diseases are a global public concern that affect millions of people. Even though current treatments present high efficacy, they also show several side effects. In this sense, the development of biocompatible nanoparticles and macroscopic scaffolds has been shown to improve bone regeneration while diminishing side effects. In this review, we present a new trend in these materials, reporting several examples of materials that specifically recognize several agents of the bone microenvironment. Briefly, we provide a subtle introduction to the bone microenvironment. Then, the different targeting agents are exposed. Afterward, several examples of nanoparticles and scaffolds modified with these agents are shown. Finally, we provide some future perspectives and conclusions. Overall, this topic presents high potential to create promising translational strategies for the treatment of bone-related diseases. We expect this review to provide a comprehensive description of the incipient state-of-the-art of bone-targeting agents in bone regeneration.

Nanomaterial-assisted theranosis of bone diseases

Bone-related diseases refer to a group of skeletal disorders that are characterized by bone and cartilage destruction. Conventional approaches can regulate bone homeostasis to a certain extent. However, these therapies are still associated with some undesirable problems. Fortunately, recent advances in nanomaterials have provided unprecedented opportunities for diagnosis and therapy of bone-related diseases. This review provides a comprehensive and up-to-date overview of current advanced theranostic nanomaterials in bone-related diseases. First, the potential utility of nanomaterials for biological imaging and biomarker detection is illustrated. Second, nanomaterials serve as therapeutic delivery platforms with special functions for bone homeostasis regulation and cellular modulation are highlighted. Finally, perspectives in this field are offered, including current key bottlenecks and future directions, which may be helpful for exploiting nanomaterials with novel properties and unique functions. This review will provide scientific guidance to enhance the development of advanced nanomaterials for the diagnosis and therapy of bone-related diseases.

Pathobiology and Therapeutic Relevance of GSK-3 in Chronic Hematological Malignancies

Glycogen synthase kinase-3 (GSK-3) is an evolutionarily conserved, ubiquitously expressed, multifunctional serine/threonine protein kinase involved in the regulation of a variety of physiological processes. GSK-3 comprises two isoforms (α and β) which were originally discovered in 1980 as enzymes involved in glucose metabolism via inhibitory phosphorylation of glycogen synthase. Differently from other proteins kinases, GSK-3 isoforms are constitutively active in resting cells, and their modulation mainly involves inhibition through upstream regulatory networks. In the early 1990s, GSK-3 isoforms were implicated as key players in cancer cell pathobiology. Active GSK-3 facilitates the destruction of multiple oncogenic proteins which include β-catenin and Master regulator of cell cycle entry and proliferative metabolism (c-Myc). Therefore, GSK-3 was initially considered to be a tumor suppressor. Consistently, GSK-3 is often inactivated in cancer cells through dysregulated upstream signaling pathways. However, over the past 10–15 years, a growing number of studies highlighted that in some cancer settings GSK-3 isoforms inhibit tumor suppressing pathways and therefore act as tumor promoters. In this article, we will discuss the multiple and often enigmatic roles played by GSK-3 isoforms in some chronic hematological malignancies (chronic myelogenous leukemia, chronic lymphocytic leukemia, multiple myeloma, and B-cell non-Hodgkin’s lymphomas) which are among the most common blood cancer cell types. We will also summarize possible novel strategies targeting GSK-3 for innovative therapies of these disorders.

pH-Responsive Liposomes Loaded with Targeting Procoagulant Proteins as Potential Embolic Agents for Solid Tumor-Targeted Therapy

Selectively inducing tumor thrombosis and subsequent necrosis is a novel and promising antitumor strategy. We have previously designed a targeting procoagulant protein, called tTF-EG3287, which is a fusion of a truncated tissue factor (tTF) with EG3287, a short peptide against the neuropilin-1 (NRP1) binding site of vascular endothelial growth factor-A 165 (VEGF-A 165). However, off-target effects and high-dose requirements limit the further use of tTF-EG3287 in antitumor therapy. Therefore, we encapsulated tTF-EG3287 into poly(2-ethyl-2-oxazoline)-distearoyl phosphatidyl ethanolamine (PEOz-DSPE)-modified liposomes to construct pH-responsive liposomes as a novel vascular embolization agent, called tTF-EG3287@Liposomes. The liposomes had an average particle size of about 100 nm and showed considerable drug-loading capacity, encapsulation efficiency, and biocompatibility. Under the stimulation of acidic microenvironments (pH 6.5), the lipid membrane of tTF-EG3287@Liposomes collapsed, and the cumulative drug release rate within 72 h was 83 ± 1.26%. When administered to a mouse model of hepatocellular carcinoma (HCC), tTF-EG3287@Liposomes showed prolonged retention and enhanced accumulation in the tumor as well as a superior antitumor effec, compared with tTF-EG3287. This study demonstrates the potential of tTF-EG3287@Liposomes as a novel embolic agent for solid tumors and provides a new strategy for tumor-targeted infarction therapy.

Semiparametric mixed-effects model for analysis of non-invasive longitudinal hemodynamic responses during bone graft healing

When dealing with longitudinal data, linear mixed-effects models (LMMs) are often used by researchers. However, LMMs are not always the most adequate models, especially if we expect a nonlinear relationship between the outcome and a continuous covariate. To allow for more flexibility, we propose the use of a semiparametric mixed-effects model to evaluate the overall treatment effect on the hemodynamic responses during bone graft healing and build a prediction model for the healing process. The model relies on a closed-form expectation–maximization algorithm, where the unknown nonlinear function is estimated using a Lasso-type procedure. Using this model, we were able to estimate the effect of time for individual mice in each group in a nonparametric fashion and the effect of the treatment while accounting for correlation between observations due to the repeated measurements. The treatment effect was found to be statistically significant, with the autograft group having higher total hemoglobin concentration than the allograft group.

Macrophage depletion increases target specificity of bone-targeted nanoparticles

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.

Nanoparticle-Mediated Delivery of Micheliolide Analogs to Eliminate Leukemic Stem Cells in the Bone Marrow

Micheliolide (MCL) is a naturally occurring sesquiterpene lactone that selectively targets leukemic stem cells (LSCs), which persist after conventional chemotherapy for myeloid leukemias, leading to disease relapse. To overcome modest MCL cytotoxicity, analogs with ≈two-threefold greater cytotoxicity against LSCs are synthesized via late-stage chemoenzymatic C-H functionalization. To enhance bone marrow delivery, MCL analogs are entrapped within bone-targeted polymeric nanoparticles (NPs). Robust drug loading capacities of up to 20% (mg drug mg-1 NP) are obtained, with release dominated by analog hydrophobicity. NPs loaded with a hydrolytically stable analog are tested in a leukemic mouse model. Median survival improved by 13% and bone marrow LSCs are decreased 34-fold following NPMCL treatments versus controls. Additionally, selective leukemic cell and LSC cytotoxicity of the treatment versus normal hematopoietic cells is observed. Overall, these studies demonstrate that MCL-based antileukemic agents combined with bone-targeted NPs offer a promising strategy for eradicating LSCs.

Biomaterials for Orthopaedic Diagnostics and Theranostics

Despite widespread use of conventional diagnostic methods in orthopaedic applications, limitations still exist in detection and diagnosing many pathologies especially at early stages when intervention is most critical. The use of biomaterials to develop diagnostics and theranostics, including nanoparticles and scaffolds for systemic or local applications, has significant promise to address these shortcomings and enable successful clinical translation. These developments in both modular and holistic design of diagnostic and theranostic biomaterials may improve patient treatments for myriad orthopaedic applications ranging from cancer to fractures to infection.

Potential Privilege of Maltodextrin-α-Tocopherol Nano-Micelles in Seizing Tacrolimus Renal Toxicity, Managing Rheumatoid Arthritis and Accelerating Bone Regeneration

Background

Tacrolimus (TAC) is a powerful immunosuppressive agent whose therapeutic applicability is confined owing to its systemic side effects.

Objective

Herein, we harnessed a natural polymer based bioconjugate composed of maltodextrin and α-tocopherol (MD-α-TOC) to encapsulate TAC as an attempt to overcome its biological limitations while enhancing its therapeutic anti-rheumatic efficacy.

Methods

The designed TAC loaded maltodextrin-α-tocopherol nano-micelles (TAC@MD-α-TOC) were assessed for their physical properties, safety, toxicological behavior, their ability to combat arthritis and assist bone/cartilage formation.

Results

In vitro cell viability assay revealed enhanced safety profile of optimized TAC@MD-α-TOC with 1.6- to 2-fold increase in Vero cells viability compared with free TAC. Subacute toxicity study demonstrated a diminished nephro- and hepato-toxicity accompanied with optimized TAC@MD-α-TOC. TAC@MD-α-TOC also showed significantly enhanced anti-arthritic activity compared with free TAC, as reflected by improved clinical scores and decreased IL-6 and TNF-α levels in serum and synovial fluids. Unique bone formation criteria were proved with TAC@MD-α-TOC by elevated serum and synovial fluid levels of osteocalcin and osteopontin mRNA and proteins expression. Chondrogenic differentiation abilities of TAC@MD-α-TOC were proved by increased serum and synovial fluid levels of SOX9 mRNA and protein expression.

Conclusion

Overall, our designed bioconjugate micelles offered an excellent approach for improved TAC safety profile with enhanced anti-arthritic activity and unique bone formation characteristics.

Growth factor delivery using extracellular matrix-mimicking substrates for musculoskeletal tissue engineering and repair

Therapeutic approaches for musculoskeletal tissue regeneration commonly employ growth factors (GFs) to influence neighboring cells and promote migration, proliferation, or differentiation. Despite promising results in preclinical models, the use of inductive biomacromolecules has achieved limited success in translation to the clinic. The field has yet to sufficiently overcome substantial hurdles such as poor spatiotemporal control and supraphysiological dosages, which commonly result in detrimental side effects. Physiological presentation and retention of biomacromolecules is regulated by the extracellular matrix (ECM), which acts as a reservoir for GFs via electrostatic interactions. Advances in the manipulation of extracellular proteins, decellularized tissues, and synthetic ECM-mimetic applications across a range of biomaterials have increased the ability to direct the presentation of GFs. Successful application of biomaterial technologies utilizing ECM mimetics increases tissue regeneration without the reliance on supraphysiological doses of inductive biomacromolecules. This review describes recent strategies to manage GF presentation using ECM-mimetic substrates for the regeneration of bone, cartilage, and muscle.

Transcription Factor β-Catenin Plays a Key Role in Fluid Flow Shear Stress-Mediated Glomerular Injury in Solitary Kidney

Increased fluid flow shear stress (FFSS) in solitary kidney alters podocyte function in vivo. FFSS-treated cultured podocytes show upregulated AKT-GSK3β-β-catenin signaling. The present study was undertaken to confirm (i) the activation of β-catenin signaling in podocytes in vivo using unilaterally nephrectomized (UNX) TOPGAL mice with the β-galactosidase reporter gene for β-catenin activation, (ii) β-catenin translocation in FFSS-treated mouse podocytes, and (iii) β-catenin signaling using publicly available data from UNX mice. The UNX of TOPGAL mice resulted in glomerular hypertrophy and increased the mesangial matrix consistent with hemodynamic adaptation. Uninephrectomized TOPGAL mice showed an increased β-galactosidase expression at 4 weeks but not at 12 weeks, as assessed using immunofluorescence microscopy (p < 0.001 at 4 weeks; p = 0.16 at 12 weeks) and X-gal staining (p = 0.008 at 4 weeks; p = 0.65 at 12 weeks). Immunofluorescence microscopy showed a significant increase in phospho-β-catenin (Ser552, p = 0.005) at 4 weeks but not at 12 weeks (p = 0.935) following UNX, and the levels of phospho-β-catenin (Ser675) did not change. In vitro FFSS caused a sustained increase in the nuclear translocation of phospho-β-catenin (Ser552) but not phospho-β-catenin (Ser675) in podocytes. The bioinformatic analysis of the GEO dataset, #GSE53996, also identified β-catenin as a key upstream regulator. We conclude that transcription factor β-catenin mediates FFSS-induced podocyte (glomerular) injury in solitary kidney.

Reduction of leukemic burden via bone-targeted nanoparticle delivery of an inhibitor of C-chemokine (C-C motif) ligand 3 (CCL3) signaling

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 C-C chemokine receptor type 5 (CCR5), a CCL3 receptor. NP-mediated Maraviroc delivery partially restored the BMME, significantly reduced leukemic burden, and improved survival. Overall, our results demonstrate that inhibiting CCL3 via CCR5 antagonism is a potential therapeutic approach to restore normal hematopoiesis as well as reduce leukemic burden within the BMME.

An oligopeptide/aptamer-conjugated dendrimer-based nanocarrier for dual-targeting delivery to bone

Bone targeting is one of the most potentially valuable therapeutic methods for medically treating bone diseases, such as osteoarthritis, osteoporosis, nonunion bone defects, bone cancer, and myeloma-related bone disease, but its efficacy remains a challenge due to unfavorable bone biodistribution, off-target effects, and the lack of cell specificity. To address these problems, we synthesized a new dual-targeting nanocarrier for delivery to bone by covalently modifying the G4.0 PAMAM dendrimer with the C11 peptide and the CH6 aptamer (CH6-PAMAM-C11). The molecular structure was confirmed using ¹H-NMR and FT-IR spectroscopy. CLSM results showed that the novel nanocarrier could successfully accumulate in the targeted cells, mineralized areas and tissues. DLS and TEM demonstrated that CH6-PAMAM-C11 was approximately 40-50 nm in diameter. In vitro targeting experiments confirmed that the C11 ligand had a high affinity for HAP, while the CH6 aptamer had a high affinity for osteoblasts. The in vivo biodistribution analysis showed that CH6-PAMAM-C11 could rapidly accumulate in bone within 4 h and 12 h and then deliver drugs to sites of osteoblast activity. The components of CH6-PAMAM-C11 were well excreted via the kidneys. The accumulation of many more CH6-PAMAM-C11 dual-targeting nanocarriers than single-targeting nanocarriers was observed in the periosteal layer of the rat skull, along with aggregation at sites of osteoblast activity. All of these results indicate that CH6-PAMAM-C11 may be a promising nanocarrier for the delivery of drugs to bone, particularly for the treatment of osteoporosis, and our research strategy may serve as a reference for research in targeted drug, small molecule drug and nucleic acid delivery.

Aminocellulose-grafted-polycaprolactone coated gelatin nanoparticles alleviate inflammation in rheumatoid arthritis: A combinational therapeutic approach

Rheumatoid arthritis (RA) is a chronic autoimmune disorder and serious cause of disability. Despite considerable advances in RA management, challenges like extensive drug metabolism and rapid clearance causes poor bioavailability. Core-shell nanocarriers for co-delivery of glycyrrhizic acid (GA) and budesonide against RA were developed. GA-loaded gelatin nanoparticles (NPs) were synthesized and coated with budesonide encapsulated aminocellulose-grafted polycaprolactone (PCL-AC). GA- and budesonide-loaded PCL-AC-gel NPs had diameter of 200-225 nm. Dual drug-loaded (DDL) NPs reduced joint swelling and erythema in rats while markedly ameliorating bone erosion evidenced by radiological analysis, suppressed collagen destruction, restored synovial tissue, bone and cartilage histoarchitecture with reduced inflammatory cells infiltration. NPs also reduced various inflammatory biomarkers such as TNF-α, IL-1β, COX-2, iNOS. Results of this study suggest that dual NPs exerted superior therapeutic effects in RA compared to free drugs which may be attributed to slow and sustained drug release and NPs' ability to inhibit inflammatory mediators.

Analysis of the bone fracture targeting properties of osteotropic ligands

PURPOSE

Although more than 18,000,000 fractures occur each year in the US, methods to promote fracture healing still rely primarily on fracture stabilization, with use of bone anabolic agents to accelerate fracture repair limited to rare occasions when the agent can be applied to the fracture surface. Because management of broken bones could be improved if bone anabolic agents could be continuously applied to a fracture over the entire course of the healing process, we undertook to identify strategies that would allow selective concentration of bone anabolic agents on a fracture surface following systemic administration. Moreover, because hydroxyapatite is uniquely exposed on a broken bone, we searched for molecules that would bind with high affinity and specificity for hydroxyapatite. We envisioned that by conjugating such osteotropic ligands to a bone anabolic agent, we could acquire the ability to continuously stimulate fracture healing.

RESULTS

Although bisphosphonates and tetracyclines were capable of localizing small amounts of peptidic payloads to fracture surfaces 2-fold over healthy bone, their specificities and capacities for drug delivery were significantly inferior to subsequent other ligands, and were therefore considered no further. In contrast, short oligopeptides of acidic amino acids were found to localize a peptide payload to a bone fracture 91.9 times more than the control untargeted peptide payload. Furthermore acidic oligopeptides were observed to be capable of targeting all classes of peptides, including hydrophobic, neutral, cationic, anionic, short oligopeptides, and long polypeptides. We further found that highly specific bone fracture targeting of multiple peptidic cargoes can be achieved by subcutaneous injection of the construct.

CONCLUSIONS

Using similar constructs, we anticipate that healing of bone fractures in humans that have relied on immobilization alone can be greately enhanced by continuous stimulation of bone growth using systemic administration of fracture-targeted bone anabolic agents.

Matrix metalloproteinase (MMP)-degradable tissue engineered periosteum coordinates allograft healing via early stage recruitment and support of host neurovasculature

Despite serving as the clinical "gold standard" treatment for critical size bone defects, decellularized allografts suffer from long-term failure rates of ~60% due to the absence of the periosteum. Stem and osteoprogenitor cells within the periosteum orchestrate autograft healing through host cell recruitment, which initiates the regenerative process. To emulate periosteum-mediated healing, tissue engineering approaches have been utilized with mixed outcomes. While vascularization has been widely established as critical for bone regeneration, innervation was recently identified to be spatiotemporally regulated together with vascularization and similarly indispensable to bone healing. Notwithstanding, there are no known approaches that have focused on periosteal matrix cues to coordinate host vessel and/or axon recruitment. Here, we investigated the influence of hydrogel degradation mechanism, i.e. hydrolytic or enzymatic (cell-dictated), on tissue engineered periosteum (TEP)-modified allograft healing, especially host vessel/nerve recruitment and integration. Matrix metalloproteinase (MMP)-degradable hydrogels supported endothelial cell migration from encapsulated spheroids whereas no migration was observed in hydrolytically degradable hydrogels in vitro, which correlated with increased neurovascularization in vivo. Specifically, ~2.45 and 1.84-fold, and ~3.48 and 2.58-fold greater vessel and nerve densities with high levels of vessel and nerve co-localization was observed using MMP degradable TEP (MMP-TEP) -modified allografts versus unmodified and hydrolytically degradable TEP (Hydro-TEP)-modified allografts, respectively, at 3 weeks post-surgery. MMP-TEP-modified allografts exhibited greater longitudinal graft-localized vascularization and endochondral ossification, along with 4-fold and 2-fold greater maximum torques versus unmodified and Hydro-TEP-modified allografts after 9 weeks, respectively, which was comparable to that of autografts. In summary, our results demonstrated that the MMP-TEP coordinated allograft healing via early stage recruitment and support of host neurovasculature.

Ligand Density Controls C-Type Lectin-Like Molecule-1 Receptor-Specific Uptake of Polymer Nanoparticles

The newest generation of drug delivery systems (DDSs) exploits ligands to mediate specific targeting of cells and/or tissues. However, studies investigating the link between ligand density and nanoparticle (NP) uptake are limited to a small number of ligand-receptor systems. C-type lectin-like molecule-1 (CLL1) is uniquely expressed on myeloid cells, which enables the development of receptors specifically targeting treat various diseases. This study aims to investigate how NPs with different CLL1 targeting peptide density impact cellular uptake. To this end, poly(styrene-alt-maleic anhydride)-b-poly(styrene) NPs are functionalized with cyclized CLL1 binding peptides (cCBP) ranging from 240 ± 12 to 31 000 ± 940 peptides per NP. Unexpectedly, the percentage of cells with internalized NPs is decreased for all cCBP-NP designs regardless of ligand density compared to unmodified NPs. Internalization through CLL1 receptor-mediated processes is further investigated without confounding the effects of NP size and surface charge. Interestingly, high density cCBP-NPs (>7000 cCBP per NP) uptake is dominated by CLL1 receptor-mediated processes while low density cCBP-NPs (≈200 cCBP per NP) and untargeted NP occurred through non-specific clathrin and caveolin-mediated endocytosis. Altogether, these studies show that ligand density and uptake mechanism should be carefully investigated for specific ligand-receptor systems for the design of targeted DDSs to achieve effective drug delivery.

Unleashing β-catenin with a new anti-Alzheimer drug for bone tissue regeneration

The Wnt/β-catenin signaling pathway is critical for bone differentiation and regeneration. Tideglusib, a selective FDA approved glycogen synthase kinase-3β (GSK-3β) inhibitor, has been shown to promote dentine formation, but its effect on bone has not been examined. Our objective was to study the effect of localized Tideglusib administration on bone repair. Bone healing between Tideglusib treated and control mice was analysed at 7, 14 and 28 days postoperative (PO) with microCT, dynamic histomorphometry and immunohistology. There was a local downregulation of GSK-3β in Tideglusib animals, resulting in a significant increase in the amount of new bone formation with both enhanced cortical bone bridging and medullary bone deposition. The bone formation in the Tideglusib group was characterized by early osteoblast differentiation with down-regulation of GSK-3β at day 7 and 14, and higher accumulation of active β-catenin at day 14. Here, for the first time, we show a positive effect of Tideglusib on bone formation through the inactivation of GSK-3β. Furthermore, the findings suggest that Tideglusib does not interfere with precursor cell recruitment and commitment, contrary to other GSK-3β antagonists such as lithium chloride. Taken together, the results indicate that Tideglusib could be used directly at a fracture site during the initial intraoperative internal fixation without the need for further surgery, injection or drug delivery system. This FDA-approved drug may be useful in the future for the prevention of non-union in patients presenting with a high risk for fracture-healing.

Bone-Targeting Systems to Systemically Deliver Therapeutics to Bone Fractures for Accelerated Healing

PURPOSE OF REVIEW

Compared with the current standard of implanting bone anabolics for fracture repair, bone fracture-targeted anabolics would be more effective, less invasive, and less toxic and would allow for control over what phase of fracture healing is being affected. We therefore sought to identify the optimal bone-targeting molecule to allow for systemic administration of therapeutics to bone fractures.

RECENT FINDINGS

We found that many bone-targeting molecules exist, but most have been developed for the treatment of bone cancers, osteomyelitis, or osteoporosis. There are a few examples of bone-targeting ligands that have been developed for bone fractures that are selective for the bone fracture over the body and skeleton. Acidic oligopeptides have the ideal half-life, toxicity profile, and selectivity for a bone fracture-targeting ligand and are the most developed and promising of these bone fracture-targeting ligands. However, many other promising ligands have been developed that could be used for bone fractures.

Targeting nanoparticles for diagnosis and therapy of bone tumors: Opportunities and challenges

A variety of targeted nanoparticles were developed for the diagnosis and therapy of orthotopic and metastatic bone tumors during the past decade. This critical review will focus on principles and methods in the design of these bone-targeted nanoparticles. Ligands including bisphosphonates, aspartic acid-rich peptides and synthetic polymers were grafted on nanoparticles such as PLGA nanoparticles, liposomes, dendrimers and inorganic nanoparticles for bone targeting. Besides, other ligands such as monoclonal antibodies, peptides and aptamers targeting biomarkers on tumor/bone cells were identified for targeted diagnosis and therapy. Examples of targeted nanoparticles for the early detection of bone metastatic tumors and the ablation of cancer via chemotherapy, photothermal therapy, gene therapy and combination therapy will be intensively reviewed. The development of multifunctional nanoparticles to break down the "vicious" cycle between tumor cell proliferation and bone resorption, and the challenges and perspectives in this area will be discussed.

Wnt modulation in bone healing

Genetic studies have been instrumental in the field of orthopaedics for finding tools to improve the standard management of fractures and delayed unions. The Wnt signaling pathway that is crucial for development and maintenance of many organs also has a very promising pathway for enhancement of bone regeneration. The Wnt pathway has been shown to have a direct effect on stem cells during bone regeneration, making Wnt a potential target to stimulate bone repair after trauma. A more complete view of how Wnt influences animal bone regeneration has slowly come to light. This review article provides an overview of studies done investigating the modulation of the canonical Wnt pathway in animal bone regeneration models. This not only includes a summary of the recent work done elucidating the roles of Wnt and β-catenin in fracture healing, but also the results of thirty transgenic studies, and thirty-eight pharmacological studies. Finally, we discuss the discontinuation of sclerostin clinical trials, ongoing clinical trials with lithium, the results of Dkk antibody clinical trials, the shift into combination therapies and the future opportunities to enhance bone repair and regeneration through the modulation of the Wnt signaling pathway.

Nanoscale perfluorocarbon expediates bone fracture healing through selectively activating osteoblastic differentiation and functions

Background and rationale

Fracture incidence increases with ageing and other contingencies. However, the strategy of accelerating fracture repair in clinical therapeutics remain a huge challenge due to its complexity and a long-lasting period. The emergence of nano-based drug delivery systems provides a highly efficient, targeted and controllable drug release at the diseased site. Thus far, fairly limited studies have been carried out using nanomedicines for the bone repair applications. Perfluorocarbon (PFC), FDA-approved clinical drug, is received increasing attention in nanomedicine due to its favorable chemical and biologic inertness, great biocompatibility, high oxygen affinity and serum-resistant capability. In the premise, the purpose of the current study is to prepare nano-sized PFC materials and to evaluate their advisable effects on promoting bone fracture repair.

Results

Our data unveiled that nano-PFC significantly enhanced the fracture repair in the rabbit model with radial fractures, as evidenced by increased soft callus formation, collagen synthesis and accumulation of beneficial cytokines (e.g., vascular endothelial growth factor (VEGF), matrix metalloprotein 9 (MMP-9) and osteocalcin). Mechanistic studies unraveled that nano-PFC functioned to target osteoblasts by stimulating their differentiation and activities in bone formation, leading to accelerated bone remodeling in the fractured zones. Otherwise, osteoclasts were not affected upon nano-PFC treatment, ruling out the potential target of nano-PFC on osteoclasts and their progenitors.

Conclusions

These results suggest that nano-PFC provides a potential perspective for selectively targeting osteoblast cell and facilitating callus generation. This study opens up a new avenue for nano-PFC as a promising agent in therapeutics to shorten healing time in treating bone fracture.

Delivery of RNAi-Based Therapeutics for Bone Regeneration

PURPOSE OF REVIEW

The clinical significance, target pathways, recent successes, and challenges that preclude translation of RNAi bone regenerative approaches are overviewed.

RECENT FINDINGS

RNA interference (RNAi) is a promising new therapeutic approach for bone regeneration by stimulating or inhibiting critical signaling pathways. However, RNAi suffers from significant delivery challenges. These challenges include avoiding nuclease degradation, achieving bone tissue targeting, and reaching the cytoplasm for mRNA inhibition. Many drug delivery systems have overcome stability and intracellular localization challenges but suffer from protein adsorption that results in clearance of up to 99% of injected dosages, thus severely limiting drug delivery efficacy. While RNAi has myriad promising attributes for use in bone regenerative applications, delivery challenges continue to plague translation. Thus, a focus on drug delivery system development is critical to provide greater delivery efficiency and bone targeting to reap the promise of RNAi.

Nanocomposites drug delivery systems for the healing of bone fractures

The skeletal system is fundamental for the structure and support of the body consisting of bones, cartilage, and connective tissues. Poor fracture healing is a chief clinical problem leading to disability, extended hospital stays and huge financial liability. Even though most fractures are cured using standard clinical methods, about 10% of fractures are delayed or non-union. Despite decades of progress, the bone-targeted delivery system is still restricted due to the distinctive anatomical bone features. Recently, various novel nanocomposite systems have been designed for the cell-specific targeting of bone, enhancing drug solubility, improving drug stability and inhibiting drug degradation so that it can reach its target site without being removed in the systemic circulation. Such targeting systems could consist of biological compounds i.e. bone marrow stem cells (BMSc), growth factors, RNAi, parathyroid hormone or synthetic compounds, i.e. bisphosphonates (BPs) and calcium phosphate cement. Hydrogels and nanoparticles are also being employed for fracture healing. In this review, we discussed the normal mechanism of bone healing and all the possible drug delivery systems being employed for the healing of the bone fracture.

Adjuvant Drug-Assisted Bone Healing: Advances and Challenges in Drug Delivery Approaches

Bone defects of critical size after compound fractures, infections, or tumor resections are a challenge in treatment. Particularly, this applies to bone defects in patients with impaired bone healing due to frequently occurring metabolic diseases (above all diabetes mellitus and osteoporosis), chronic inflammation, and cancer. Adjuvant therapeutic agents such as recombinant growth factors, lipid mediators, antibiotics, antiphlogistics, and proangiogenics as well as other promising anti-resorptive and anabolic molecules contribute to improving bone healing in these disorders, especially when they are released in a targeted and controlled manner during crucial bone healing phases. In this regard, the development of smart biocompatible and biostable polymers such as implant coatings, scaffolds, or particle-based materials for drug release is crucial. Innovative chemical, physico- and biochemical approaches for controlled tailor-made degradation or the stimulus-responsive release of substances from these materials, and more, are advantageous. In this review, we discuss current developments, progress, but also pitfalls and setbacks of such approaches in supporting or controlling bone healing. The focus is on the critical evaluation of recent preclinical studies investigating different carrier systems, dual- or co-delivery systems as well as triggered- or targeted delivery systems for release of a panoply of drugs.

Systemically Administered, Target-Specific, Multi-Functional Therapeutic Recombinant Proteins in Regenerative Medicine

Growth factors, chemokines and cytokines guide tissue regeneration after injuries. However, their applications as recombinant proteins are almost non-existent due to the difficulty of maintaining their bioactivity in the protease-rich milieu of injured tissues in humans. Safety concerns have ruled out their systemic administration. The vascular system provides a natural platform for circumvent the limitations of the local delivery of protein-based therapeutics. Tissue selectivity in drug accumulation can be obtained as organ-specific molecular signatures exist in the blood vessels in each tissue, essentially forming a postal code system ("vascular zip codes") within the vasculature. These target-specific "vascular zip codes" can be exploited in regenerative medicine as the angiogenic blood vessels in the regenerating tissues have a unique molecular signature. The identification of vascular homing peptides capable of finding these unique "vascular zip codes" after their systemic administration provides an appealing opportunity for the target-specific delivery of therapeutics to tissue injuries. Therapeutic proteins can be "packaged" together with homing peptides by expressing them as multi-functional recombinant proteins. These multi-functional recombinant proteins provide an example how molecular engineering gives to a compound an ability to home to regenerating tissue and enhance its therapeutic potential. Regenerative medicine has been dominated by the locally applied therapeutic approaches despite these therapies are not moving to clinical medicine with success. There might be a time to change the paradigm towards systemically administered, target organ-specific therapeutic molecules in future drug discovery and development for regenerative medicine.

Roles of mTOR Signaling in Tissue Regeneration

The mammalian target of rapamycin (mTOR), is a serine/threonine protein kinase and belongs to the phosphatidylinositol 3-kinase (PI3K)-related kinase (PIKK) family. mTOR interacts with other subunits to form two distinct complexes, mTORC1 and mTORC2. mTORC1 coordinates cell growth and metabolism in response to environmental input, including growth factors, amino acid, energy and stress. mTORC2 mainly controls cell survival and migration through phosphorylating glucocorticoid-regulated kinase (SGK), protein kinase B (Akt), and protein kinase C (PKC) kinase families. The dysregulation of mTOR is involved in human diseases including cancer, cardiovascular diseases, neurodegenerative diseases, and epilepsy. Tissue damage caused by trauma, diseases or aging disrupt the tissue functions. Tissue regeneration after injuries is of significance for recovering the tissue homeostasis and functions. Mammals have very limited regenerative capacity in multiple tissues and organs, such as the heart and central nervous system (CNS). Thereby, understanding the mechanisms underlying tissue regeneration is crucial for tissue repair and regenerative medicine. mTOR is activated in multiple tissue injuries. In this review, we summarize the roles of mTOR signaling in tissue regeneration such as neurons, muscles, the liver and the intestine.

MicroRNA-92a-1-5p influences osteogenic differentiation of MC3T3-E1 cells by regulating β-catenin

Osteoblastic differentiation is a complex process that is critical for proper bone formation. An increasing number of studies have suggested that microRNAs (miRNAs) are pivotal regulators in various physiological and pathological processes, including osteogenesis. Here, we discuss the influence of miRNA-92a-1-5p on osteogenic differentiation. We found that miR-92a-1-5p was obviously downregulated during osteogenic differentiation of MC3T3-E1 cells. Gain-of-function and loss-of-function experiments revealed that miR-92a-1-5p was a negative regulator of osteogenic differentiation. Experimental validation demonstrated that β-catenin, which acts as a positive regulator of osteogenic differentiation, was negatively regulated by miR-92a1-5p. The findings of this study provide new insights into the possibility of miR-92a1-5p being a potential therapeutic target in the management of bone regeneration-related diseases.

l-Peptide functionalized dual-responsive nanoparticles for controlled paclitaxel release and enhanced apoptosis in breast cancer cells

Nanoparticles and macromolecular carriers have been widely used to increase the efficacy of chemotherapeutics, largely through passive accumulation provided by their enhanced permeability and retention effect. However, the therapeutic efficacy of nanoscale anticancer drug delivery systems is severely truncated by their low tumor-targetability and inefficient drug release at the target site. Here, the design and development of novel l-peptide functionalized dual-responsive nanoparticles (l-CS-g-PNIPAM-PTX) for active targeting and effective treatment of GRP78-overexpressing human breast cancer in vitro and in vivo are reported. l-CS-g-PNIPAM-PTX NPs have a relative high drug loading (13.5%) and excellent encapsulation efficiency (74.3%) and an average diameter of 275 nm. The release of PTX is slow at pH 7.4 and 25 °C but greatly accelerated at pH 5.0 and 37 °C. MTT assays and confocal experiments showed that the l-CS-g-PNIPAM-PTX NPs possessed high targetability and antitumor activity toward GRP78 overexpressing MDA-MB-231 human breast cancer cells. As expected, l-CS-g-PNIPAM-PTX NPs could effectively treat mice bearing MDA-MB-231 human breast tumor xenografts with little side effects, resulting in complete inhibition of tumor growth and a high survival rate over an experimental period of 60 days. These results indicate that l-peptide-functionalized acid - and thermally activated - PTX prodrug NPs have a great potential for targeted chemotherapy in breast cancer.

Scaffolds as Structural Tools for Bone-Targeted Drug Delivery

Although bone has a high potential to regenerate itself after damage and injury, the efficacious repair of large bone defects resulting from resection, trauma or non-union fractures still requires the implantation of bone grafts. Materials science, in conjunction with biotechnology, can satisfy these needs by developing artificial bones, synthetic substitutes and organ implants. In particular, recent advances in materials science have provided several innovations, underlying the increasing importance of biomaterials in this field. To address the increasing need for improved bone substitutes, tissue engineering seeks to create synthetic, three-dimensional scaffolds made from organic or inorganic materials, incorporating drugs and growth factors, to induce new bone tissue formation. This review emphasizes recent progress in materials science that allows reliable scaffolds to be synthesized for targeted drug delivery in bone regeneration, also with respect to past directions no longer considered promising. A general overview concerning modeling approaches suitable for the discussed systems is also provided.

Bone Targeted Delivery of SDF-1 via Alendronate Functionalized Nanoparticles in Guiding Stem Cell Migration

Stem cells are well-known for their great capacity for tissue regeneration. This provides a promising source for cell-based therapies in treating various bone degenerative disorders. However, the major hurdles for their application in transplantation are the poor bone marrow homing and engraftment efficiencies. Stromal cell-derived factor 1 (SDF-1) has been identified as a major stem cell homing factor. With the aims of bone targeted SDF-1 delivery and regulating MSCs migration, alendronate modified liposomal nanoparticles (Aln-Lipo) carrying SDF-1 gene were developed in this study. Alendronate modification significantly increased the mineral binding affinity of liposomes, and facilitated the gene delivery to osteoblastic cells. Up-regulated SDF-1 expression in osteoblasts triggered MSCs migration. Systemic infusion of Aln-Lipo-SDF-1 with fluorescence labeling in mice showed the accumulation in osseous tissue by biophotonic imaging. Corresponding to the delivered SDF-1, the transplanted GFP⁺ MSCs were attracted to bone marrow and contributed to bone regeneration. This study may provide a useful technique in regulating stem cell migration.

In Vivo Translation of Peptide-Targeted Drug Delivery Systems Discovered by Phage Display

Therapeutic compounds with narrow therapeutic windows and significant systemic side effects benefit from targeted drug delivery strategies. Peptide-protein interactions are often exploited for targeting, with phage display a primary method to identify high-affinity peptide ligands that bind cell surface and matrix bound receptors preferentially expressed in target tissues. After isolating and sequencing high-binding phages, peptides are easily synthesized and chemically modified for incorporation into drug delivery systems, including peptide-drug conjugates, polymers, and nanoparticles. This review describes the phage display methodology to identify targeting peptide sequences, strategies to functionalize drug carriers with phage-derived peptides, specific examples of drug carriers with in vivo translation, and limitations and future applications of phage display to drug delivery.

Retroductal Nanoparticle Injection to the Murine Submandibular Gland

Two common goals of salivary gland therapeutics are prevention and cure of tissue dysfunction following either autoimmune or radiation injury. By locally delivering bioactive compounds to the salivary glands, greater tissue concentrations can be safely achieved versus systemic administration. Furthermore, off target tissue effects from extra-glandular accumulation of material can be dramatically reduced. In this regard, retroductal injection is a widely used method for investigating both salivary gland biology and pathophysiology. Retroductal administration of growth factors, primary cells, adenoviral vectors, and small molecule drugs has been shown to support gland function in the setting of injury. We have previously shown the efficacy of a retroductally injected nanoparticle-siRNA strategy to maintain gland function following irradiation. Here, a highly effective and reproducible method to administer nanomaterials to the murine submandibular gland through Wharton's duct is detailed (Figure 1). We describe accessing the oral cavity and outline the steps necessary to cannulate Wharton's duct, with further observations serving as quality checks throughout the procedure.

Development of controlled drug delivery systems for bone fracture-targeted therapeutic delivery: A review

Impaired fracture healing is a major clinical problem that can lead to patient disability, prolonged hospitalization, and significant financial burden. Although the majority of fractures heal using standard clinical practices, approximately 10% suffer from delayed unions or non-unions. A wide range of factors contribute to the risk for nonunions including internal factors, such as patient age, gender, and comorbidities, and external factors, such as the location and extent of injury. Current clinical approaches to treat nonunions include bone grafts and low-intensity pulsed ultrasound (LIPUS), which realizes clinical success only to select patients due to limitations including donor morbidities (grafts) and necessity of fracture reduction (LIPUS), respectively. To date, therapeutic approaches for bone regeneration rely heavily on protein-based growth factors such as INFUSE, an FDA-approved scaffold for delivery of bone morphogenetic protein 2 (BMP-2). Small molecule modulators and RNAi therapeutics are under development to circumvent challenges associated with traditional growth factors. While preclinical studies has shown promise, drug delivery has become a major hurdle stalling clinical translation. Therefore, this review overviews current therapies employed to stimulate fracture healing pre-clinically and clinically, including a focus on drug delivery systems for growth factors, parathyroid hormone (PTH), small molecules, and RNAi therapeutics, as well as recent advances and future promise of fracture-targeted drug delivery.

Re-education begins at home: an overview of the discovery of in vivo-active small molecule modulators of endogenous stem cells

INTRODUCTION

Degenerative diseases, such as Alzheimer's disease, heart disease and arthritis cause great suffering and are major socioeconomic burdens. An attractive treatment approach is stem cell transplantation to regenerate damaged or destroyed tissues. However, this can be problematic. For example, donor cells may not functionally integrate into the host tissue. An alternative methodology is to deliver bioactive agents, such as small molecules, directly into the diseased tissue to enhance the regenerative potential of endogenous stem cells. Areas covered: In this review, the authors discuss the necessity of developing these small molecules to treat degenerative diseases and survey progress in their application as therapeutics. They describe both the successes and caveats of developing small molecules that target endogenous stem cells to induce tissue regeneration. This article is based on literature searches which encompass databases for biomedical research and clinical trials. These small molecules are also categorized per their target disease and mechanism of action. Expert opinion: The development of small molecules targeting endogenous stem cells is a high-profile research area. Some compounds have made the successful transition to the clinic. Novel approaches, such as modulating the stem cell niche or targeted delivery to disease sites, should increase the likelihood of future successes in this field.

Functional peptide-based nanoparticles for photodynamic therapy

Photodynamic therapy as a non-invasive approach has obtained great research attention during the last decade.