Targeting polymer therapeutics to bone

Pectolinarigenin ameliorates osteoporosis via enhancing Wnt signaling cascade in PPARβ-dependent manner

BACKGROUND

Osteoporosis is a prevalent metabolic bone disease in older adults. Peroxisome proliferator-activated receptor β (PPARβ), the most abundant PPAR isotype expressed in bone tissues, plays a critical role in regulating the energy metabolism of osteoblasts. However, the botanical compounds targeting PPARβ for the treatment of osteoporosis remain largely unexplored.

PURPOSE

To discover a potent PPARβ agonist from botanical compounds, as well as to investigate the anti-osteoporosis effects and to elucidate the underlying mechanisms of the newly identified PPARβ agonist.

METHODS

The PPARβ agonist effects of botanical compounds were screened by an in vitro luciferase reporter gene assay. The PPARβ agonist effects of pectolinarigenin (PEC) in bone marrow mesenchymal stromal cells (BMSCs) were validated by Western blotting. RNA-seq transcriptome analyses were conducted to reveal the underlying osteoporosis mechanisms of PEC in BMSCs. The PPARβ antagonist (GSK0660) and Wnt signaling inhibitor (XAV969) were used to explore the role of the PPARβ and Wnt signaling cascade in the anti-osteoporosis effects of PEC. PEC or the PEG-PLGA nanoparticles of PEC (PEC-NP) were intraperitoneally administrated in both wild-type mice and ovariectomy-induced osteoporosis mice to examine its anti-osteoporotic effects in vivo.

RESULTS

PEC, a newly identified naturally occurring PPARβ agonist, significantly promotes osteogenic differentiation and up-regulates the osteogenic differentiation-related genes (Runx2, Osterix, and Bmp2) in BMSCs. RNA sequencing and functional gene enrichment analysis suggested that PEC could activate osteogenic-related signaling pathways, including Wnt and PPAR signaling pathways. Further investigations suggested that PEC could enhance Wnt/β-catenin signaling in a PPARβ-dependent manner in BMSCs. Animal tests showed that PEC-NP promoted bone mass and density, increased the bone cell matrix protein, and accelerated bone formation in wild-type mice, while PEC-NP also played a preventive role in ovariectomy-induced osteoporosis mice via maintaining the expression level of bone cell matrix protein, balancing the rate of bone formation, and slowing down bone loss. Additionally, PEC-NP did not cause any organ injury and body weight loss after long-term use (11 weeks).

CONCLUSION

PEC significantly promotes bone formation and reduces bone loss in both BMSCs and ovariectomy-induced osteoporosis mice via enhancing the Wnt signaling cascade in a PPARβ-dependent manner, providing a new alternative therapy for preventing estrogen deficiency-induced osteoporotic diseases.

Hydrophilic biomaterials: From crosslinked and self-assembled hydrogels to polymer-drug conjugates and drug-free macromolecular therapeutics

This "Magnum Opus" accentuates my lifelong belief that the future of science is in the interdisciplinary approach to hypotheses formulation and problem solving. Inspired by the invention of hydrogels and soft contact lenses by my mentors, my six decades of research have continuously proceeded from the synthesis of biocompatible hydrogels to the development of polymer-drug conjugates, then generation of drug-free macromolecular therapeutics (DFMT) and finally to multi-antigen T cell hybridizers (MATCH). This interdisciplinary journey was inspiring; the lifetime feeling that one is a beginner in some aspects of the research is a driving force that keeps the enthusiasm high. Also, I wanted to illustrate that systematic research in one wide area can be a life-time effort without the need to jump to areas that are temporarily en-vogue. In addition to generating general scientific knowledge, hydrogels from my laboratory have been transferred to the clinic, polymer-drug conjugates to clinical trials, and drug-free macromolecular systems have an excellent potential for personalizing patient therapies. There is a limit to life but no limit to imagination. I anticipate that systematic basic research will contribute to the expansion of our knowledge and create a foundation for the design of new paradigms based on the comprehension of mechanisms of physiological processes. The emerging novel platform technologies in biomaterial-based devices and implants as well as in personalized nanomedicines will ultimately impact clinical practice.

Engineering small-molecule and protein drugs for targeting bone tumors

Bone cancer is common and severe. Both primary (e.g., osteosarcoma, Ewing sarcoma) and secondary (e.g., metastatic) bone cancers lead to significant health problems and death. Currently, treatments such as chemotherapy, hormone therapy, and radiation therapy are used to treat bone cancer, but they often only shrink or slow tumor growth and do not eliminate cancer completely. The bone microenvironment contributes unique signals that influence cancer growth, immunogenicity, and metastasis. Traditional cancer therapies have limited effectiveness due to off-target effects and poor distribution on bones. As a result, therapies with improved specificity and efficacy for treating bone tumors are highly needed. One of the most promising strategies involves the targeted delivery of pharmaceutical agents to the site of bone cancer by introduction of bone-targeting moieties, such as bisphosphonates or oligopeptides. These moieties have high affinities to the bone hydroxyapatite matrix, a structure found exclusively in skeletal tissue, and can enhance the targeting ability and efficacy of anticancer drugs when combating bone tumors. This review focuses on the engineering of small molecules and proteins with bone-targeting moieties for the treatment of bone tumors.

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.

TC and LDL-C are negatively correlated with bone mineral density in patients with osteoporosis

OBJECTIVE

To investigate the relationships of multiple lipid metabolism indicators and bone turnover markers (BTMs) with bone mineral density (BMD) and osteoporosis, in order to identify high-risk populations.

METHODS

A total of 380 patients were recruited and their general information was collected. Linear and logistic regression models were used to analyze the correlation of these indicators with BMD and osteoporosis.

RESULTS

Lipid metabolism indices and BTMs exhibited varying degrees of positive or negative correlation with BMD. Elevated levels of triglycerides (r = -0.204, P = 0.004), total cholesterol (TC) (r = -0.244, P < 0.001), low-density lipoprotein cholesterol (LDL-C) (r = -0.256, P < 0.001), apoprotein B (r = -0.292, P < 0.001) and lipoprotein-associated phospholipase A2 (Lp-PLA2) (r = -0.221, P = 0.002) in women were associated with a reduction in BMD. This relationship persisted even after adjusting for confounding factors and in the subgroup analysis of elderly women. In males, TC (r = 0.159, P = 0.033), LDL-C (r = 0.187, P = 0.012), apoprotein B (r = 0.157, P = 0.035), and Lp-PLA2 (r = 0.168, P = 0.024) exhibited a positive correlation with BMD, while free fatty acid (FFA) (r = -0.153, P = 0.041) was negatively correlated with BMD. However, after adjusting for confounding factors, only FFA remained negatively correlated with BMD, which was not observed in the age subgroup analysis. Furthermore, elevated levels of TC and LDL-C in elderly women were positively associated with the risk of osteoporosis or low bone mass.

CONCLUSION

Elevated levels of TC and LDL-C not only indicate a decrease in BMD in females but also positively correlate with the occurrence of osteoporosis and low bone mass in elderly females.

Effect of phosphodiester composition in polyphosphoesters on the inhibition of osteoclastic differentiation of murine bone marrow mononuclear cells

Osteoporosis is a common bone disorder characterized by reduced bone density and increased risk of fractures. The modulation of bone cell functions, particularly the inhibition of osteoclastic differentiation, plays a crucial role in osteoporosis treatment. Polyphosphoesters (PPEs) have shown the potential in reducing the function of osteoclast cells, but the effect of their chemical structure on osteoclastic differentiation remains largely unexplored. In this study, we evaluated the effect of PPE's chemical structure on the inhibition of osteoclastic differentiation of murine bone marrow mononuclear cells (BMNCs). PPEs containing phosphotriester and phosphodiester units at varying compositions were synthesized. Cytotoxicity testing confirmed the biocompatibility of the copolymers at concentrations below 0.5 mg/mL. Isolated from long bones, BMNCs were cultured in a differentiation medium supplemented with different PPE concentrations. Osteoclast formation was assessed through tartrate-resistant acid phosphatase and phalloidin staining. A significant decrease in the size of osteoclast cells formed upon BMNC contact with PPEs was observed, with a more pronounced effect observed at higher PPE concentrations. In addition, an increased composition of phosphodiester units in the PPEs yielded a decreased density of differentiated osteoclasts. Furthermore, real-time PCR analysis of major osteoclastic markers provided gene expression data that correlated with microscopic observations, confirming the effect of phosphodiester units in suppressing osteoclast differentiation of BMNCs from the early stages. These findings highlight the potential of PPEs as polymers are capable of modulating bone cell functions through their chemical structures.

Bone-targeting polyphosphodiesters that promote osteoblastic differentiation

Polymers for pharmaceutical use have been attractive in medical treatments because of the conjugation of multifunctional components and their long circulation time in the blood stream. Bone-targeted drug delivery systems are also no exceptional, and several polymers have been proposed for the treatment of bone diseases, such as cancer metastasis and osteoporosis. Herein, we report that polyphosphodiesters (PPDEs) have a potential to enhance osteoblastic differentiation, and they have a targeting ability to bone tissues in vivo. Two types of PPDEs, poly (ethylene sodium phosphate) (PEP•Na) and poly (propylene sodium phosphate) (PPP•Na), have been synthesized. Regardless of the alkylene structure in the main chain of PPDEs, the gene expression of osteoblast-specific transcription factors and differentiation markers of mouse osteoblastic-like cells (MC3T3-E1 cells) cultured in a differentiation medium was significantly upregulated by the addition of PPDEs. Moreover, it was also clarified that the signaling pathway related to cytoplasmic calcium ions was activated by PPDEs. The mineralization of MC3T3-E1 cells has a similar trend with its gene expression and is synergistically enhanced by PPDEs with β-glycerophosphate. The biodistribution of fluorescence-labeled PPDEs was also determined after intravenous injection in mice. PPDEs accumulated well in the bone through the blood stream, whereas polyphosphotriesters (PPTEs) tended to be excreted from the kidneys. Hydrophilic PEP•Na showed a superior bone affinity as compared with PPP•Na. PPDEs could be candidate polymers for the restoration of bone remodeling and bone-targeting drug delivery platforms.

Naringin: Nanotechnological Strategies for Potential Pharmaceutical Applications

Polyphenols comprise a number of natural substances, such as flavonoids, that show interesting biological effects. Among these substances is naringin, a naturally occurring flavanone glycoside found in citrus fruits and Chinese medicinal herbs. Several studies have shown that naringin has numerous biological properties, including cardioprotective, cholesterol-lowering, anti-Alzheimer’s, nephroprotective, antiageing, antihyperglycemic, antiosteoporotic and gastroprotective, anti-inflammatory, antioxidant, antiapoptotic, anticancer and antiulcer effects. Despite its multiple benefits, the clinical application of naringin is severely restricted due to its susceptibility to oxidation, poor water solubility, and dissolution rate. In addition, naringin shows instability at acidic pH, is enzymatically metabolized by β-glycosidase in the stomach and is degraded in the bloodstream when administered intravenously. These limitations, however, have been overcome thanks to the development of naringin nanoformulations. This review summarizes recent research carried out on strategies designed to improve naringin’s bioactivity for potential therapeutic applications.

Targeting Intratibial Osteosarcoma Using Water-Soluble Copolymers Conjugated to Collagen Hybridizing Peptides

Osteosarcoma (OS) is the most common form of primary malignant bone cancer in adolescents. Over the years, OS prognosis has greatly improved due to adjuvant and neoadjuvant (preoperative) chemotherapeutic treatment, increasing the chances of successful surgery and reducing the need for limb amputation. However, chemotherapeutic treatment to treat OS is limited by off-target toxicities and requires improved localization at the tumor site. Collagen, the main constituent of bone tissue, is extensively degraded and remodeled in OS, leading to an increased availability of denatured (monomeric) collagen. Collagen hybridizing peptides (CHPs) comprise a class of peptides rationally designed to selectively bind to denatured collagen. In this work, we have conjugated CHPs as targeting moieties to water-soluble N-(2-hydroxypropyl)methacrylamide (HPMA) copolymers to target OS tumors. We demonstrated increased accumulation of collagen-targeted HPMA copolymer-CHP conjugates compared to nontargeted HPMA copolymers, as well as increased retention compared to both nontargeted copolymers and CHPs, in a murine intratibial OS tumor model. Furthermore, we used microcomputed tomography analysis to evaluate the bone microarchitecture and correlated bone morphometric parameters (porosity, bone volume, and surface area) with maximum accumulation (Smax) and accumulation at 168 h postinjection (S168) of the copolymers at the tumor. Our results provide the foundation for the use of HPMA copolymer-CHP conjugates as targeted drug delivery systems in OS tumors.

Molecular Complex of HSIM-loaded Polymeric Nanoparticles: Potential Carriers in Osteoporosis

BACKGROUND

Statins, especially simvastatin promote bone formation by stimulating the activity of osteoblasts and suppressing osteoclast activity via the BMP-Smad signaling pathway. Statins present the liver first-pass metabolism. This study attempts to fabricate and evaluate simvastatin functionalized hydroxyapatite encapsulated in poly(lactic-co-glycolic) acid (PLGA) nanoparticles (HSIM-PLGA NPs) administered subcutaneously with sustained release properties for effective management of osteoporosis.

METHODS

Simvastatin functionalized hydroxyapatite (HSIM) was prepared by stirring and validated by docking studies, Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and X-ray diffraction (XRD). Further, HSIM-loaded PLGA nanoparticles (HSIM-PLGA NPs) were developed via the solvent emulsification method. The nanoparticles were evaluated for zeta potential, particle size, entrapment efficiency, stability studies, and in vitro drug release studies. in vitro binding affinity of nanoparticles for hydroxyapatite was also measured. Bone morphology and its effect on bone mineral density were examined by using a glucocorticoid-induced osteoporosis rat model.

RESULTS

The optimized nanoparticles were found to be amorphous and showed no drug-polymer interaction. The particle size of formulated nanoparticles varied from 196.8 ± 2.27nm to 524.8 ± 5.49 nm and the entrapment efficiency of nanoparticles varied from 41.9 ± 3.44% to 70.8 ± 4.46%, respectively. The nanoparticles showed sustained release behaviour (75% in 24 hr) of the drug followed by non-fickian drug release. The nanoparticles exhibited high binding affinity to bone cell receptors, increasing bone mineral density. A significant difference in calcium and phosphorous levels was observed in disease and treatment rats. Porous bone and significant improvement in porosity were observed in osteoporotic rats and treated rats, respectively (P < 0.05).

CONCLUSION

Bone-targeting nanoparticles incorporating functionalized simvastatin can target bone. Thus, in order to distribute simvastatin subcutaneously for the treatment of osteoporosis, the developed nanoparticles may act as a promising approach.

Modification and Functionalization of Polymers for Targeting to Bone Cancer and Bone Regeneration

Bone is one of the most complex, inaccessible body structures, responsible for calcium storage and haematopoiesis. The second highest cause of death across the world is cancer. Amongst all the types of cancers, bone cancer treatment modalities are limited due to the structural complexity and inaccessibility of bones. The worldwide incidence of bone diseases and bone defects due to cancer, infection, trauma, age-related bone degeneration is increasing. Currently different conventional therapies are available for bone cancer such as chemotherapy, surgery and radiotherapy, but they have several disadvantages associated with them. Nanomedicine is being extensively researched as viable therapeutics to mitigate drug resistance in cancer therapy and promote bone regeneration. Several natural polymers such as chitosan, dextran, alginate, hyaluronic acid, and synthetic polymers like polyglycolic acid, poly(lactic-co-glycolic acid), polycaprolactone are investigated for their application in nanomedicine for bone cancer treatment and bone regeneration. Nanocarriers have shown promising results in preclinical experimental studies. However, they still face a major drawback of inadequate targetability. The paper summarizes the status of research and the progress made so far in modifications and functionalization of natural polymers for improving their site specificity and targeting for effective treatment of bone cancer and enhancing bone regeneration.

Pluronic® triblock copolymer-based nanoformulations for cancer therapy: A 10-year overview

This paper provides a review of the literature on the use of Pluronic® triblock copolymers for drug encapsulation over the last 10 years. A special focus is given to the progress of drug delivery systems (e.g., micelles, liposomes, micro/nanoemulsions, hydrogels and nanogels, and polymersomes and niosomes); the beneficial aspects of Pluronic® triblock copolymers as biological response modifiers and as pharmaceutical additives, adjuvants, and stabilizers, are also discussed. The advantages and limitations encountered in developing site-specific targeting approaches based on Pluronic-based nanostructures in cancer treatment are highlighted, in addition to innovative examples for improving tumor cytotoxicity while reducing side effects.

Tetracycline-grafted mPEG-PLGA micelles for bone-targeting and osteoporotic improvement

Aim: We aimed to create a nano drug delivery system with tetracycline (TC)-grafted methoxy poly-(ethylene-glycol)‒poly-(D, L-lactic-co-glycolic acid) (mPEG‒PLGA) micelles (TC‒mPEG‒PLGA) with TC and mPEG‒PLGA for potential bone targeting. Prospectively, TC‒mPEG‒PLGA aims to deliver bioactive compounds, such as astragaloside IV (AS), for osteoporotic therapy.

Methods: Preparation and evaluation of TC‒mPEG‒PLGA were accomplished via nano-properties, cytotoxicity, uptake by MC3T3-E1 cells, ability of hydroxyapatite targeting and potential bone targeting in vivo, as well as pharmacodynamics in a rat model.

Results: The measured particle size of AS-loaded TC‒mPEG‒PLGA micelles was an average of 52.16 ± 2.44 nm, which exhibited a sustained release effect compared to that by free AS. The TC‒mPEG‒PLGA demonstrated low cytotoxicity and was easily taken by MC3T3-E1 cells. Through assaying of bone targeting in vitro and in vivo, we observed that TC‒mPEG‒PLGA could effectively increase AS accumulation in bone. A pharmacodynamics study in mice suggested potentially increased bone mineral density by AS-loaded TC‒mPEG‒PLGA in ovariectomized rats compared to that by free AS.

Conclusion: The nano drug delivery system (TC‒mPEG‒PLGA) could target bone in vitro and in vivo, wherein it may be used as a novel delivery method for the enhancement of therapeutic effects of drugs with osteoporotic activity.

Research progress of bone-targeted drug delivery system on metastatic bone tumors

Bone metastases are common in malignant tumors and the effect of conventional treatment is limited. How to effectively inhibit tumor bone metastasis and deliver the drug to the bone has become an urgent issue to be solved. While bone targeting drug delivery systems have obvious advantages in the treatment of bone tumors. The research on bone-targeted anti-tumor therapy has made significant progress in recent years. We introduced the related tumor pathways of bone metastases. The tumor microenvironment plays an important role in metastatic bone tumors. We introduce a drug-loading systems based on different environment-responsive nanocomposites for anti-tumor and anti-metastatic research. According to the process of bone metastases and the structure of bone tissue, we summarized the information on bone-targeting molecules. Bisphosphate has become the first choice of bone-targeted drug delivery carrier because of its affinity with hydroxyapatite in bone. Therefore, we sought to summarize the bone-targeting molecule of bisphosphate to identify the modification effect on bone-targeting. And this paper discusses the relationship between bisphosphate bone targeting molecular structure and drug delivery carriers, to provide some new ideas for the research and development of bone-targeting drug delivery carriers. Targeted therapy will make a more outstanding contribution to the treatment of tumors.

Sorption Studies of Tetracycline Antibiotics on Hydroxyapatite (001) Surface-A First-Principles Insight

Owing to the limitations of traditional systemic drug delivery in the treatment of bone diseases with side effects on normal cells, the selection of materials with high affinities for bones, as targeting ligands to modify drug carriers, has become an important research topic. Tetracyclines (TCs) have an adsorption effect on hydroxyapatite (HAp). Thus, they can be used as bone-targeting ligands and combined with drug carriers. In this study, density functional theory is used to analyze the interaction mechanism of TC, oxytetracycline (OTC), chlortetracycline, and HAp. We calculate the electrostatic potential (ESP) and molecular orbitals to predict the possible binding sites of TCs on the HAp surface. The adsorption energy is used to compare the affinities of the three TCs to HAp. An independent gradient model analysis is performed to study the weak interaction between TCs and HAp. The coordination bond between TCs and the HAp surface is evaluated by conducting a charge density difference analysis. The results show that OTC has the highest affinity to HAp because the introduction of hydroxyl groups change the adsorption configuration of OTC. Thus, OTC adsorbed on HAp in a broken-line shape exposes more binding sites. This study provides a theoretical basis for TCs as bone-targeting ligands in treating bone diseases and in improving the safety of treatment by selecting different bone-targeting ligands.

Decoration of Squalenoyl-Gemcitabine Nanoparticles with Squalenyl-Hydroxybisphosphonate for the Treatment of Bone Tumors

Therapeutic perspectives of bone tumors such as osteosarcoma remain restricted due to the inefficacy of current treatments. We propose here the construction of a novel anticancer squalene‐based nanomedicine with bone affinity and retention capacity. A squalenyl‐hydroxybisphosphonate molecule was synthetized by chemical conjugation of a 1‐hydroxyl‐1,1‐bisphosphonate moiety to the squalene chain. This amphiphilic compound was inserted onto squalenoyl‐gemcitabine nanoparticles using the nanoprecipitation method. The co‐assembly led to nanoconstructs of 75 nm, with different morphology and colloidal properties. The presence of squalenyl‐hydroxybisphosphonate enhanced the nanoparticles binding affinity for hydroxyapatite, a mineral present in the bone. Moreover, the in vitro anticancer activity was preserved when tested in commercial and patient‐treated derived pediatric osteosarcoma cells. Further in vivo studies will shed light on the potential of these nanomedicines for the treatment of bone sarcomas.

Polyethylenimine-Bisphosphonate-Cyclodextrin Ternary Conjugates: Supramolecular Systems for the Delivery of Antineoplastic Drugs

Bisphosphonates (BPs) are bone-binding molecules that provide targeting capabilities to bone cancer cells when conjugated with drug-carrying polymers. This work reports the design, synthesis, and biological evaluation of polyethyleneimine-BP-cyclodextrin (PEI-BP-CD) ternary conjugates with supramolecular capabilities for the loading of antineoplastic drugs. A straightforward, modular, and versatile strategy based on the click aza-Michael addition reaction of vinyl sulfones (VSs) allows the grafting of BPs targeting ligands and βCD carrier appendages to the PEI polymeric scaffold. The in vitro evaluation (cytotoxicity, cellular uptake, internalization routes, and subcellular distribution) for the ternary conjugates and their doxorubicin inclusion complexes in different bone-related cancer cell lines (MC3T3-E1 osteoblasts, MG-63 sarcoma cells, and MDA-MB-231 breast cancer cells) confirmed specificity, mitochondrial targeting, and overall capability to mediate a targeted drug transport to those cells. The in vivo evaluation using xenografts of MG-63 and MDA-MB-231 cells on mice also confirmed the targeting of the conjugates.

Strategies for transdermal drug delivery against bone disorders: A preclinical and clinical update

The transdermal drug delivery system is an exceptionally safe and well-tolerable therapeutic approach that has immense potential for delivering active components against bone-related pathologies. However, its use is limited in the current clinical practices due to the low skin permeability of most active drugs in the formulation. Thus, innovations in the methodologies of skin permeation enhancement techniques are suggested to overcome this limitation. Although various transdermal drug delivery systems are studied to date, there are insufficient studies comparing the therapeutic efficacy of transdermal delivery systems to oral delivery systems. Thus, creating a decision-making dilemma between oral or transdermal therapies. Therefore, a timely review is inevitable to develop a platform for future researchers to develop next-generation transdermal drug delivery strategies against skeletal diseases that must be convenient and cost-effective for the patients with improved therapeutic efficacy. Here, we will outline the most recent strategies that can overcome the choice limitation of the drug and enhance the transdermal adsorption of various types of drugs to treat bone disorders. For the first time, in this review paper, we will highlight the preclinical and clinical studies on the different transdermal delivery methods. Thus, providing insight into the current therapeutic approaches and suggesting new directions for the advancements in transdermal drug delivery systems against bone disorders.

Controlled biointerfaces with biomimetic phosphorus-containing polymers

Phosphorus is a ubiquitous and one of the most common elements found in living organisms. Almost all molecules containing phosphorus in our body exist as analogs of phosphate salts or phosphoesters. Their functions are versatile and important, being responsible for forming the genetic code, cell membrane, and mineral components of hard tissue. Several materials inspired from these phosphorus-containing biomolecules have been recently developed. These materials have shown unique properties at the biointerface, such as nonfouling ability, blood compatibility, lubricity, mineralization induction capability, and bone affinity. Several unfavorable events occur at the interface of materials and living organisms because most of these materials have not been designed while taking host responses into account. These unfavorable events are directly linked to reducing functions and shorten the usable periods of medical devices. Biomimetic phosphorus-containing polymers can improve the reliability of materials in biological systems. In addition, phosphorus-containing biomimetic polymers are useful not only for improving the biocompatibility of material surfaces but also for adding new functions due to the flexibility in molecular design. In this review, we describe the recent advances in the control of biointerfacial phenomena with phosphorus-containing polymers. We especially focus on zwitterioninc phosphorylcholine polymers and polyphosphoesters.

Drug Delivery to the Bone Microenvironment Mediated by Exosomes: An Axiom or Enigma

The increasing incidence of bone-related disorders is causing a burden on the clinical scenario. Even though bone is one of the tissues that possess tremendous regenerative potential, certain bone anomalies need therapeutic intervention through appropriate delivery of a drug. Among several nanosystems and biologics that offer the potential to contribute towards bone healing, the exosomes from the class of extracellular vesicles are outstanding. Exosomes are extracellular nanovesicles that, apart from the various advantages, are standing out of the crowd for their ability to conduct cellular communication. The internal cargo of the exosomes is leading to its potential use in therapeutics. Exosomes are being unraveled in terms of the mechanism as well as application in targeting various diseases and tissues. Through this review, we have tried to understand and review all that is already established and the gap areas that still exist in utilizing them as drug delivery vehicles targeting the bone. The review highlights the potential of the exosomes towards their contribution to the drug delivery scenario in the bone microenvironment. A comparison of the pros and cons of exosomes with other prevalent drug delivery systems is also done. A section on the patents that have been generated so far from this field is included.

Review of a new bone tumor therapy strategy based on bifunctional biomaterials

Bone tumors, especially those in osteosarcoma, usually occur in adolescents. The standard clinical treatment includes chemotherapy, surgical therapy, and radiation therapy. Unfortunately, surgical resection often fails to completely remove the tumor, which is the main cause of postoperative recurrence and metastasis, resulting in a high mortality rate. Moreover, bone tumors often invade large areas of bone, which cannot repair itself, and causes a serious effect on the quality of life of patients. Thus, bone tumor therapy and bone regeneration are challenging in the clinic. Herein, this review presents the recent developments in bifunctional biomaterials to achieve a new strategy for bone tumor therapy. The selected bifunctional materials include 3D-printed scaffolds, nano/microparticle-containing scaffolds, hydrogels, and bone-targeting nanomaterials. Numerous related studies on bifunctional biomaterials combining tumor photothermal therapy with enhanced bone regeneration were reviewed. Finally, a perspective on the future development of biomaterials for tumor therapy and bone tissue engineering is discussed. This review will provide a useful reference for bone tumor-related disease and the field of complex diseases to combine tumor therapy and tissue engineering.

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.

Targeting reactive oxygen species in stem cells for bone therapy

Reactive oxygen species (ROS) have emerged as key players in regulating the fate and function of stem cells from both non-hematopoietic and hematopoietic lineages in bone marrow, and thus affect the osteoblastogenesis-osteoclastogenesis balance and bone homeostasis. Accumulating evidence has linked ROS and associated oxidative stress with the progression of bone disorders, and ROS-based therapeutic strategies have appeared to achieve favorable outcomes in bone. We review current knowledge of the multifactorial roles and mechanisms of ROS as a target in bone pathology. In addition, we discuss emerging ROS-based therapeutic strategies that show potential for bone therapy. Finally, we highlight the opportunities and challenges facing ROS-targeted stem cell therapeutics for improving bone health.

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.

Targeted nanomedicines for the treatment of bone disease and regeneration

Targeted delivery by either passive or active targeting of therapeutics to the bone is an attractive treatment for various bone related diseases such as osteoporosis, osteosarcoma, multiple myeloma, and metastatic bone tumors. Engineering novel drug delivery carriers can increase therapeutic efficacy and minimize the risk of side effects. Developmnet of nanocarrier delivery systems is an interesting field of ongoing studies with opportunities to provide more effective therapies. In addition, preclinical nanomedicine research can open new opportunities for preclinical bone-targeted drug delivery; nevertheless, further research is needed to progress these therapies towards clinical applications. In the present review, the latest advancements in targeting moieties and nanocarrier drug delivery systems for the treatment of bone diseases are summarized. We also review the regeneration capability and effective delivery of nanomedicines for orthopedic applications.

Osteoblast-n-Osteoclast: Making Headway to Osteoporosis Treatment

Background:

Bone is a dynamic tissue that continuously undergoes the modeling and remodeling process to maintain its strength and firmness. Bone remodeling is determined by the functioning of osteoblast and osteoclast cells. The imbalance between the functioning of osteoclast and osteoblast cells leads to osteoporosis. Osteoporosis is divided into primary and secondary osteoporosis. Generally, osteoporosis is diagnosed by measuring bone mineral density (BMD) and various osteoblast and osteoclast cell markers.

Methods:

Relevant literature reports have been studied and data has been collected using various search engines like google scholar, scihub, sciencedirect, pubmed, etc. A thorough understanding of the mechanism of bone targeting strategies has been discussed and related literature has been studied and compiled.

Results:

Bone remodeling process has been described in detail including various approaches for targeting bone. Several bone targeting moieties have been stated in detail along with their mechanisms. Targeting of osteoclasts and osteoblasts using various nanocarriers has been discussed in separate sections. The toxicity issues or Biosafety related to the use of nanomaterials have been covered.

Conclusion:

The treatment of osteoporosis targets the inhibition of bone resorption and the use of agents that promote bone mineralization to slow disease progression. Current osteoporosis therapy involves the use of targeting moieties such as bisphosphonates and tetracyclines for targeting various drugs. Nanotechnology has been used for targeting various drug molecules such as RANKLinhibitors, parathyroid hormone analogues, estrogen agonists and antagonists, Wnt signaling enhancer and calcitonin specifically to bone tissue (osteoclast and osteoblasts). So, a multicomponent treatment strategy targeting both the bone cells will be more effective rather than targeting only osteoclasts and it will be a potential area of research in bone targeting used to treat osteoporosis. The first section of the review article covers various aspects of bone targeting. Another section comprises details of various targeting moieties such as bisphosphonates, tetracyclines; and various nanocarriers developed to target osteoclast and osteoblast cells and summarized data on in vivo models has been used for assessment of bone targeting, drawbacks of current strategies and future perspectives.

Water/pH dual responsive in situ calcium supplement collaborates simvastatin for osteoblast promotion mediated osteoporosis therapy via oral medication

Calcium supplement is the most commonly adopted treatment for osteoporosis but usually requires high dose and frequency. The modality of calcium supplement is therefore overlooked by current nanomedicine-based osteoporosis therapies without proper oral formulations. Herein, we proposed a tetracycline (Tc) modified and monostearin (MS) coated amorphous calcium carbonate (ACC) platform (TMA) as oral bone targeted and osteoporosis microenvironment (water/pH) responsive carrier for in situ calcium supplement. Moreover, current osteoporosis therapies also fall short of finding suitable molecular target and effective therapeutic regimen to further increase the therapeutic efficacy over available treatment means. As a result, the simvastatin (Sim) was loaded into TMA to construct drug delivery system (TMA/Sim) capable of synergistically activating the bone morphogenetic proteins (BMPs)-Smad pathway to provide a novel therapeutic regimen for osteoblast promotion mediated osteoporosis therapy. Our results revealed that optimized TMA showed high accessibility and oral availability with targeted drug delivery to bone tissue. Most importantly, benefit from the effective in situ calcium supplement and targeted Sim delivery, this therapeutic regime (TMA/Sim) achieved better synergetic effects than conventional combination strategies with promising osteoporosis reversion performance under low calcium dosage (1/10 of commercial calcium carbonate tablet) and significantly attenuated side effects.

Bone-Specific Drug Delivery for Osteoporosis and Rare Skeletal Disorders

PURPOSE OF REVIEW

The skeletal system provides an important role to support body structure and protect organs. The complexity of its architecture and components makes it challenging to deliver the right amount of the drug into bone regions, particularly avascular cartilage lesions. In this review, we describe the recent advance of bone-targeting methods using bisphosphonates, polymeric oligopeptides, and nanoparticles on osteoporosis and rare skeletal diseases.

RECENT FINDINGS

Hydroxyapatite (HA), a calcium phosphate with the formula Ca10(PO4)6(OH)2, is a primary matrix of bone mineral that includes a high concentration of positively charged calcium ion and is found only in the bone. This unique feature makes HA a general targeting moiety to the entire skeletal system. We have applied bone-targeting strategy using acidic amino acid oligopeptides into lysosomal enzymes, demonstrating the effects of bone-targeting enzyme replacement therapy and gene therapy on bone and cartilage lesions in inherited skeletal disorders. Virus or no-virus gene therapy using techniques of engineered capsid or nanomedicine has been studied preclinically for skeletal diseases. Efficient drug delivery into bone lesions remains an unmet challenge in clinical practice. Bone-targeting therapies based on gene transfer can be potential as new candidates for skeletal diseases.

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.

Polymer nanomedicines

Polymer nanomedicines (macromolecular therapeutics, polymer-drug conjugates, drug-free macromolecular therapeutics) are a group of biologically active compounds that are characterized by their large molecular weight. This review focuses on bioconjugates of water-soluble macromolecules with low molecular weight drugs and selected proteins. After analyzing the design principles, different structures of polymer carriers are discussed followed by the examination of the efficacy of the conjugates in animal models and challenges for their translation into the clinic. Two innovative directions in macromolecular therapeutics that depend on receptor crosslinking are highlighted: a) Combination chemotherapy of backbone degradable polymer-drug conjugates with immune checkpoint blockade by multivalent polymer peptide antagonists; and b) Drug-free macromolecular therapeutics, a new paradigm in drug delivery.

Calcium Supplement by Tetracycline guided amorphous Calcium Carbonate potentiates Osteoblast promotion for Synergetic Osteoporosis Therapy

Background: The calcium supplement is a clinically approved approach for osteoporosis therapy but usually requires a large dosage without targetability and with poor outcome. This modality is not fully explored in current osteoporosis therapy due to the lack of proper calcium supplement carrier.

Methods: In this study, we constructed a tetracycline (Tc) modified and simvastatin (Sim) loaded phospholipid-amorphous calcium carbonate (ACC) hybrid nanoparticle (Tc/ACC/Sim).

Results: The resulted Tc/ACC/Sim was able to enhance its accumulation at the osteoporosis site. Most importantly, the combination of calcium supplement and Sim offered synergetic osteoblast promotion therapy of osteoporosis with advanced performance than non-targeted system or mono therapy.

Conclusion: This platform provides an alternative approach to stimulate bone formation by synergetic promotion of osteoblast differentiation using calcium supplement and Sim.

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.

Nanocapsule pH Regulator: Sustained Continuous Alkali Release from Thermosensitive Liposomes Reduces Acid Erosion

Thermosensitive liposomes are major drug delivery carriers, which enable targeting of drugs and burst release of the drugs from the liposomes at the site of action by applying a local heat stimulation above body temperature. Although the burst release is significant for a one-shot high-rate release of drugs at the target site, this type of release has a limited sustained action of the drugs. In this study, we report the alkali-encapsulating thermosensitive liposomes enabling environment pH regulation by sustained continuous cargo release at human body temperature. The liposomes encapsulating alkalis successfully neutralized the environmental acids for hours by releasing the alkalis and prevented acid erosion of hydroxyapatite matrix. Taken together, the present liposomes are effective for the sustained release of cargo at body temperature, specifically the alkali-encapsulating liposomes can be a preventing agent for dental caries in the oral cavity. The sustained release under endogenous body heat characteristics of thermosensitive liposomes showcased in this study can also be extended for prolonged intravenous drug exposure from targeted liposomal drug nanotherapeutics in the near future.

Bone-targeting phospholipid polymers to solubilize the lipophilic anticancer drug

Current chemotherapy methods have limited effectiveness in eliminating bone metastasis, which leads to a poor prognosis associated with severe bone disorders. To provide regional chemotherapy for this metastatic tumor, a bone-targeting drug carrier was produced by introducing the osteotropic bisphosphonate alendronate (ALN) units into an amphiphilic phospholipid polymer, poly(2-methacryloyloxyethyl phosphorylcholine-co-n-butyl methacrylate). The polymer can form nanoparticles with a diameter of less than 30 nm; ALN units were exposed to the outer layer of the particle. A simple mixing procedure was used to encapsulate a hydrophobic anticancer drug, known as docetaxel (DTX), in the polymer nanoparticle, providing a uniform solution of a polymer-DTX complex in the aqueous phase. The complex showed anticancer activities against several breast cancer cell lines, and the complex formation did not hamper the pharmacological effect of DTX. The fluorescence observations evaluated by an in vivo imaging system and fluorescence microscopy showed that the addition of ALN to the polymer-DTX complex enhanced bone accumulation. Bone-targeting phospholipid polymers are potential solubilizing excipients used to formulate DTX and deliver the hydrophobic drug to bone tissues by blood administration.

Bone-targeted PAMAM nanoparticle to treat bone metastases of lung cancer

Aim: To prepare pH-sensitive nanoparticle composed of alendronate (ALN) and poly(amidoamine) (PAMAM) to treat bone metastases of lung cancer. Methods: The solvent evaporation method was used to prepare docetaxel (DTX)-loaded ALN-PAMAM nanoparticles (DTX@ALN-PAMAM). Results: The in vitro results showed DTX@ALN-PAMAM significantly enhanced the anticancer activity of DTX and inhibited the formation of osteoclasts. DTX@ALN-PAMAM concentrated at bone metastasis site in mice, which resulted in the suppression of bone resorption, pain response and growth of bone metastases. Eventually, the therapeutic effect of DTX on bone metastases of lung cancer was obviously improved. Conclusion: ALN modified PAMAM nanoparticle could be an effective platform for the treatment of bone metastases of lung cancer.

Tuning Ligand Density To Optimize Pharmacokinetics of Targeted Nanoparticles for Dual Protection against Tumor-Induced Bone Destruction

Breast cancer patients are at high risk for bone metastasis. Metastatic bone disease is a major clinical problem that leads to a reduction in mobility, increased risk of pathologic fracture, severe bone pain, and other skeletal-related events. The transcription factor Gli2 drives expression of parathyroid hormone-related protein (PTHrP), which activates osteoclast-mediated bone destruction, and previous studies showed that Gli2 genetic repression in bone-metastatic tumor cells significantly reduces tumor-induced bone destruction. Small molecule inhibitors of Gli2 have been identified; however, the lipophilicity and poor pharmacokinetic profile of these compounds have precluded their success in vivo. In this study, we designed a bone-targeted nanoparticle (BTNP) comprising an amphiphilic diblock copolymer of poly[(propylene sulfide)-block-(alendronate acrylamide-co-N,N-dimethylacrylamide)] [PPS-b-P(Aln-co-DMA)] to encapsulate and preferentially deliver a small molecule Gli2 inhibitor, GANT58, to bone-associated tumors. The mol % of the bisphosphonate Aln in the hydrophilic polymer block was varied in order to optimize BTNP targeting to tumor-associated bone by a combination of nonspecific tumor accumulation (presumably through the enhanced permeation and retention effect) and active bone binding. Although 100% functionalization with Aln created BTNPs with strong bone binding, these BTNPs had highly negative zeta-potential, resulting in shorter circulation time, greater liver uptake, and less distribution to metastatic tumors in bone. However, 10 mol % of Aln in the hydrophilic block generated a formulation with a favorable balance of systemic pharmacokinetics and bone binding, providing the highest bone/liver biodistribution ratio among formulations tested. In an intracardiac tumor cell injection model of breast cancer bone metastasis, treatment with the lead candidate GANT58-BTNP formulation decreased tumor-associated bone lesion area 3-fold and increased bone volume fraction in the tibiae of the mice 2.5-fold. Aln conferred bone targeting to the GANT58-BTNPs, which increased GANT58 concentration in the tumor-associated bone relative to untargeted NPs, and also provided benefit through the direct antiresorptive therapeutic function of Aln. The dual benefit of the Aln in the BTNPs was supported by the observations that drug-free Aln-containing BTNPs improved bone volume fraction in bone-tumor-bearing mice, while GANT58-BTNPs created better therapeutic outcomes than both unloaded BTNPs and GANT58-loaded untargeted NPs. These findings suggest GANT58-BTNPs have potential to potently inhibit tumor-driven osteoclast activation and resultant bone destruction in patients with bone-associated tumor metastases.

Recent advances in bone-targeted therapy

The coordination between bone resorption and bone formation plays an essential role in keeping the mass and microstructure integrity of the bone in a steady state. However, this balance can be disturbed in many pathological conditions of the bone. Nowadays, the classical modalities for treating bone-related disorders are being challenged by severe obstacles owing to low tissue selectivity and considerable safety concerns. Moreover, as a highly mineralized tissue, the bone shows innate rigidity, low permeability, and reduced blood flow, features that further hinder the effective treatment of bone diseases. With the development of bone biology and precision medicine, one novel concept of bone-targeted therapy appears to be promising, with improved therapeutic efficacy and minimized systematic toxicity. Here we focus on the recent advances in bone-targeted treatment based on the unique biology of bone tissues. We summarize commonly used bone-targeting moieties, with an emphasis on bisphosphonates, tetracyclines, and biomimetic bone-targeting moieties. We also introduce potential bone-targeting strategies aimed at the bone matrix and major cell types in the bone. Based on these bone-targeting moieties and strategies, we discuss the potential applications of targeted therapy to treat bone diseases. We expect that this review will put together useful insights to help with the search for therapeutic efficacy in bone-related conditions.

A novel biocompatible, simvastatin-loaded, bone-targeting lipid nanocarrier for treating osteoporosis more effectively

An insufficient drug concentration at the target site and drug efflux resulting in poor efficacy are recognized as important obstacles in osteoporosis treatment. Simvastatin (SIM), which can treat osteoporosis by promoting osteoblast differentiation and mineralization through the bone morphogenetic proteins (BMP)-Smad signaling pathway, has lower bioavailability, and less bone tissue distribution. Herein, novel lipid nanoparticles (LNPs) delivering SIM (SIM/LNPs) for osteoporosis therapy were developed with aspartic oligopeptide (ASP_n, here ASP₆)-based bone-targeting moieties grafted to the nanoparticles (SIM/ASP₆-LNPs) in an attempt to increase the concentration of SIM in bones with a relatively low dose to minimize adverse effects. In vivo experiments indicated that the ASP₆-LNPs exhibited ideal bone-targeting characteristics, and in vitro cell evaluation experiments showed LNPs have good biocompatibility with MC3T3-E1 cells. The cell mineralization experiment revealed that the SIM-loaded LNPs induced osteoblast differentiation and the formation of mineralized nodules in MC3T3-E1 cells, achieving the same efficacy as that of SIM. Pharmacodynamic experiments revealed that SIM/ASP₆-LNPs improved the efficacy of SIM on the recovery of bone mineral density when compared to SIM/LNPs or to SIM alone. Therefore, SIM/ASP₆-LNPs may represent a potential bone-targeting drug delivery system (DDS) that contributes to the development of a novel osteoporosis treatment.

A scheme of the preparation of SIM/ASP₆-LNPs and a mechanism which indicated that SIM/ASP₆-LNPs could improve the efficacy of SIM on the recovery of osteoporosis under the action of bone-targeting moieties ASP₆.

A light-triggered self-reinforced nanoagent for targeted chemo-photodynamic therapy of breast cancer bone metastases via ER stress and mitochondria mediated apoptotic pathways

Current therapeutic strategies for the treatment of bone metastases are often limited by the lack of selectivity, severe systemic toxicity and suboptimal efficacy. Nanomedicine meditated chemo-photodynamic therapy provides a promising therapeutic opportunity for enhanced cancer therapy. Herein, we constructed an alendronate (ALN)-functionalized bone-seeking nanoagent (BTZ@ZnPc-ALN) to co-deliver the proteasome inhibitor bortezomib (BTZ) and the photosensitizer Zinc phthalocyanine (ZnPc) for synergistic chemo-photodynamic therapy of bone metastases. Results showed that BTZ@ZnPc-ALN possessed favorable bone affinity both in vitro and in vivo and could release drug in a pH-responsive manner. Under irradiation, BTZ@ZnPc-ALN could generate reactive oxygen species (ROS) to cause mitochondrial damage, and increase the cytosolic Ca²⁺ levels and the expression of GRP78 protein to induce excessive endoplasmic reticulum (ER) stress, thereby synergistically inhibiting cell proliferation. More importantly, BTZ@ZnPc-ALN could prolong blood circulation time and preferentially navigate to the bone affected site. As a result, tumor growth was significantly inhibited by bone targeted chemo-photodynamic therapy, with tumor volume cut down by 85% compared with PBS group and bone remained undamaged. Besides, the systemic toxicity of BTZ was significantly reduced. Therefore, the versatile nanoagent is expected to be a promising nanoplatform to concern multiple intracellular stress for remarkable synergistic chemo-photodynamic therapy of bone metastases.

Cathepsin-sensitive nanoscale drug delivery systems for cancer therapy and other diseases

Cathepsins are an important category of enzymes that have attracted great attention for the delivery of drugs to improve the therapeutic outcome of a broad range of nanoscale drug delivery systems. These proteases can be utilized for instance through actuation of polymer-drug conjugates (e.g., triggering the drug release) to bypass limitations of many drug candidates. A substantial amount of work has been witnessed in the design and the evaluation of Cathepsin-sensitive drug delivery systems, especially based on the tetra-peptide sequence (Gly-Phe-Leu-Gly, GFLG) which has been extensively used as a spacer that can be cleaved in the presence of Cathepsin B. This Review Article will give an in-depth overview of the design and the biological evaluation of Cathepsin-sensitive drug delivery systems and their application in different pathologies including cancer before discussing Cathepsin B-cleavable prodrugs under clinical trials.

Hydroxyapatite-binding micelles for the detection of vascular calcification in atherosclerosis

Atherosclerosis is a chronic disease characterized by the formation of calcified, arterial plaques. Microcalcifications (5 μm to 100 μm), mainly composed of hydroxyapatite (HA, Ca₅(PO₄)₃(OH)), develop in the fibrous caps of atherosclerotic plaques and can trigger plaque rupture due to the loss of compliance and elasticity. Ultimately, plaque rupture can cause arterial occlusion and embolization and result in ischemic events such as strokes and myocardial infarctions. Unfortunately, current imaging technologies used to detect calcifications are limited by low signal-to-noise ratio or use invasive procedures that pose risk of arterial dissection. To mitigate these drawbacks, in our study, we developed a novel, fluorescently-labeled peptide amphiphile micelle (PAM) that uses a 12 amino acid HA-binding peptide (HABP) [SVSVGMKPSPRP] to target and detect atherosclerotic calcification (HA PAM). Our results show HA PAMs can successfully target HA microcrystals with a strong binding affinity (K_D = 6.26 ± 1.2 μM) in vitro. In addition, HA PAMs detected HA mineralization (HA PAM vs. non-targeting micelle, p≤ 0.001; HA PAM vs. scrambled HABP PAM, p≤ 0.01) formed by calcifying mouse aortic vascular smooth muscle cells (MOVAS). Moreover, HA PAMs successfully detected calcifications in atherosclerotic mouse models as well as in patient-derived arteries. Our studies show that HA PAMs show promise as calcium-targeting nanoparticles for the detection of calcifications in atherosclerosis.