Calcium phosphate nanoparticles functionalized with alendronate-conjugated polyethylene glycol (PEG) for the treatment of bone metastasis

Nanoparticles for the Treatment of Bone Metastasis in Breast Cancer: Recent Advances and Challenges

Although the frequency of bone metastases from breast cancer has increased, effective treatment is lacking, prompting the development of nanomedicine, which involves the use of nanotechnology for disease diagnosis and treatment. Nanocarrier drug delivery systems offer several advantages over traditional drug delivery methods, such as higher reliability and biological activity, improved penetration and retention, and precise targeting and delivery. Various nanoparticles that can selectively target tumor cells without causing harm to healthy cells or organs have been synthesized. Recent advances in nanotechnology have enabled the diagnosis and prevention of metastatic diseases as well as the ability to deliver complex molecular "cargo" particles to metastatic regions. Nanoparticles can modulate systemic biodistribution and enable the targeted accumulation of therapeutic agents. Several delivery strategies are used to treat bone metastases, including untargeted delivery, bone-targeted delivery, and cancer cell-targeted delivery. Combining targeted agents with nanoparticles enhances the selective delivery of payloads to breast cancer bone metastatic lesions, providing multiple delivery advantages for treatment. In this review, we describe recent advances in nanoparticle development for treating breast cancer bone metastases.

Nano-hydroxyapatite structures for bone regenerative medicine: Cell-material interaction

Bone tissue engineering holds great promise for the regeneration of damaged or severe bone defects. However, several challenges hinder its translation into clinical practice. To address these challenges, interdisciplinary efforts and advances in biomaterials, cell biology, and bioengineering are required. In recent years, nano-hydroxyapatite (nHA)-based scaffolds have emerged as a promising approach for the development of bone regenerative agents. The unique similarity of nHA with minerals found in natural bones promotes remineralization and stimulates bone growth, which are crucial factors for efficient bone regeneration. Moreover, nHA exhibits desirable properties, such as strong chemical interactions with bone and facilitation of tissue growth, without inducing inflammation or toxicity. It also promotes osteoblast survival, adhesion, and proliferation, as well as increasing alkaline phosphatase activity, osteogenic differentiation, and bone-specific gene expression. However, it is important to note that the effect of nHA on osteoblast behavior is dose-dependent, with cytotoxic effects observed at higher doses. Additionally, the particle size of nHA plays a crucial role, with smaller particles having a more significant impact. Therefore, in this review, we highlighted the potential of nHA for improving bone regeneration processes and summarized the available data on bone cell response to nHA-based scaffolds. In addition, an attempt is made to portray the current status of bone tissue engineering using nHA/polymer hybrids and some recent scientific research in the field.

Recent Advances in Nanotechnology-Based Strategies for Bone Tuberculosis Management

Bone tuberculosis, an extrapulmonary manifestation of tuberculosis, presents unique treatment challenges, including its insidious onset and complex pathology. While advancements in anti-tubercular therapy have been made, the efficacy is often limited by difficulties in achieving targeted drug concentrations and avoiding systemic toxicity. The intricate bone structure and presence of granulomas further impede effective drug delivery. Nano-drug delivery systems have emerged as a promising alternative, offering the enhanced targeting of anti-tubercular drugs. These systems, characterized by their minute size and adaptable surface properties, can be tailored to improve drug solubility, stability, and bioavailability, while also responding to specific stimuli within the bone TB microenvironment for controlled drug release. Nano-drug delivery systems can encapsulate drugs for precise delivery to the infection site. A significant innovation is their integration with prosthetics or biomaterials, which aids in both drug delivery and bone reconstruction, addressing the infection and its osteological consequences. This review provides a comprehensive overview of the pathophysiology of bone tuberculosis and its current treatments, emphasizing their limitations. It then delves into the advancements in nano-drug delivery systems, discussing their design, functionality, and role in bone TB therapy. The review assesses their potential in preclinical research, particularly in targeted drug delivery, treatment efficacy, and a reduction of side effects. Finally, it highlights the transformative promise of nanotechnology in bone TB treatments and suggests future research directions in this evolving field.

Design of Nanodrug Delivery Systems for Tumor Bone Metastasis

Tumor metastasis is a complex process that is controlled at the molecular level by numerous cytokines. Primary breast and prostate tumors most commonly metastasize to bone, and the development of increasingly accurate targeted nanocarrier systems has become a research focus for more effective anti-bone metastasis therapy. This review summarizes the molecular mechanisms of bone metastasis and the principles and methods for designing bone-targeted nanocarriers and then provides an in-depth review of bone-targeted nanocarriers for the treatment of bone metastasis in the context of chemotherapy, photothermal therapy, gene therapy, and combination therapy. Furthermore, this review also discusses the treatment of metastatic and primary bone tumors, providing directions for the design of nanodelivery systems and future research.

Biomaterials-enhanced bioactive agents to efficiently block spinal metastases of cancers

The spine is the most common site of bone metastases, as 20%-40% of cancer patients suffer from spinal metastases. Treatments for spinal metastases are scarce and palliative, primarily aiming at relieving bone pain and preserving neurological function. The bioactive agents-mediated therapies are the most effective modalities for treating spinal metastases because they achieve systematic and specific tumor regression. However, the clinical applications of some bioactive agents are limited due to the lack of targeting capabilities, severe side effects, and vulnerability of drug resistance. Fortunately, advanced biomaterials have been developed as excipients to enhance these treatments, including chemotherapy, phototherapy, magnetic hyperthermia therapy, and combination therapy, by improving tumor targeting and enabling sustaining and stimuli-responsive release of various therapeutic agents. Herein, the review summarizes the development of biomaterials-mediated bioactive agents for enhanced treatments of spinal metastases and predicts future research trends.

Development of tetracycline-modified nanoparticles for bone-targeted delivery of anti-tubercular drug

Background: Since the poor response to existing anti-tuberculosis drugs and low drug concentration in local bone tissues, the traditional drug therapy does not result in satisfactory treatment of osteoarticular tuberculosis. Thus, we report a rifapentine release system with imparted bone targeting potential using tetracycline (TC) -modified nanoparticles (NPs). Methods: TC was conjugated to PLGA-PEG copolymer via a DCC/NHS technique. Rifapentine-loaded NPs were prepared by premix membrane emulsification technique. The resulting NPs were characterized in terms of physicochemical characterization, hemolytic study, cytotoxicity, bone mineral binding ability, in vitro drug release, stability test and antitubercular activity. The pharmacokinetic and biodistribution studies were also performed in mice. Results: Rifapentine loaded TC-PLGA-PEG NPs were proved to be 48.8 nm in size with encapsulation efficiency and drug loading of 83.3% ± 5.5% and 8.1% ± 0.4%, respectively. The release of rifapentine from NPs could be maintained for more than 60 h. Most (68.0%) TC-PLGA-PEG NPs could bind to HAp powder in vitro. The cellular studies revealed that NPs were safe for intravenous administration. In vivo evaluations also revealed that the drug concentration of bone tissue in TC-PLGA-PEG group was significantly higher than that in other groups at all time (p < 0.05). Both NPs could improve pharmacokinetic parameters without evident organ toxicity. The minimal inhibitory concentration of NPs was 0.094 μg/mL, whereas this of free rifapentine was 0.25 μg/mL. Conclusion: Rifapentine loaded TC-PLGA-PEG NPs could increase the amount of rifapentine in bone tissue, prolong drug release in systemic circulation, enhance anti-tuberculosis activity, and thereby reducing dose and frequency of drug therapy for osteoarticular tuberculosis.

Functionalization of Octacalcium Phosphate Bone Graft with Cisplatin and Zoledronic Acid: Physicochemical and Bioactive Properties

Bones are the fourth most frequent site of metastasis from malignant tumors, including breast cancer, prostate cancer, melanoma, etc. The bioavailability of bone tissue for chemotherapy drugs is extremely low. This requires a search for new approaches of targeted drug delivery to the tumor growth zone after surgery treatment. The aim of this work was to develop a method for octacalcium phosphate (OCP) bone graft functionalization with the cytostatic drug cisplatin to provide the local release of its therapeutic concentrations into the bone defect. OCP porous ceramic granules (OCP ceramics) were used as a platform for functionalization, and bisphosphonate zoledronic acid was used to mediate the interaction between cisplatin and OCP and enhance their binding strength. The obtained OCP materials were studied using scanning electron and light microscopy, high-performance liquid chromatography, atomic emission spectroscopy, and real-time PCR. In vitro and in vivo studies were performed on normal and tumor cell lines and small laboratory animals. The bioactivity of initial OCP ceramics was explored and the efficiency of OCP functionalization with cisplatin, zoledronic acid, and their combination was evaluated. The kinetics of drug release and changes in ceramics properties after functionalization were studied. It was established that zoledronic acid changed the physicochemical and bioactive properties of OCP ceramics and prolonged cisplatin release from the ceramics. In vitro and in vivo experiments confirmed the biocompatibility, osteoconductivity, and osteoinductivity, as well as cytostatic and antitumor properties of the obtained materials. The use of OCP ceramics functionalized with a cytostatic via the described method seems to be promising in clinics when primary or metastatic tumors of the bone tissue are removed.

Bone targeted miRNA delivery system for miR-34a with enhanced anti-tumor efficacy to bone-associated metastatic breast cancer

Bone metastatic cancer is the most common occurrence in breast cancer, and the treatment is also facing great challenges. MicroRNA-34a (miRNA-34a) is a promising anti-cancer miRNA for gene therapy to bone metastatic cancer patients. However, the lack of specificity to bone and low accumulation at the site of bone tumor remains the major challenge when used bone-associated tumor. To solve this problem, a bone-targeted vector for delivery of miR-34a to bone metastatic breast cancer was constructed by using the commonly used gene vector branched polyethylenimine 25 k (BPEI 25 k) as the skeleton and linking with alendronate (ALN) moieties for bone targeting group. The constructed gene delivery system PCA/miR-34a can efficiently prevent miR-34a from degradation during blood circulation and enhance the specific bone delivery and distribution. PCA/miR-34a nanoparticles can be uptake into tumor cells through clathrin and caveolae-mediated endocytosis, and directly regulate the expression of oncogenes, thus promoting tumor cell apoptosis and relieving bone tissue erosion. The results of experiments in vitro and in vivo confirmed that the constructed bone-targeted miRNA delivery system PCA/miR-34a can enhance the anti-tumor efficacy in bone metastatic cancer, and provide a potential strategy for gene therapy in bone metastatic cancer.

Drug delivery systems based on polyethylene glycol hydrogels for enhanced bone regeneration

Drug delivery systems composed of osteogenic substances and biological materials are of great significance in enhancing bone regeneration, and appropriate biological carriers are the cornerstone for their construction. Polyethylene glycol (PEG) is favored in bone tissue engineering due to its good biocompatibility and hydrophilicity. When combined with other substances, the physicochemical properties of PEG-based hydrogels fully meet the requirements of drug delivery carriers. Therefore, this paper reviews the application of PEG-based hydrogels in the treatment of bone defects. The advantages and disadvantages of PEG as a carrier are analyzed, and various modification methods of PEG hydrogels are summarized. On this basis, the application of PEG-based hydrogel drug delivery systems in promoting bone regeneration in recent years is summarized. Finally, the shortcomings and future developments of PEG-based hydrogel drug delivery systems are discussed. This review provides a theoretical basis and fabrication strategy for the application of PEG-based composite drug delivery systems in local bone defects.

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.

Calcium Phosphate Functionalization and Applications in Dentistry

The oral and maxillofacial hard tissues support the maxillofacial shape and serve as the foundation for functional activities. Defects in these tissues not only impair patients’ ability to perform their normal physiological functions but also have a significant negative impact on their psychological well-being. Moreover, these tissues have a limited capacity for self-healing, necessitating the use of artificial materials to repair defects. Calcium phosphate is a fine-grained inorganic biomineral found in vertebrate teeth and bones that has a comparable composition to human hard tissues. Calcium phosphate materials are biocompatible, bioactive, and osteogenic for hard tissue repair, despite drawbacks such as poor mechanical qualities, limiting their clinical efficacy and application. With the advancement of materials science and technology, numerous techniques have been developed to enhance the characteristics of calcium phosphate, and one of them is functionalization. Calcium phosphate can be functionally modified by changing its size, morphology, or composition through various preparation processes to achieve multifunctionality and improve physical and chemical properties, biocompatibility, and osteogenic potential. The purpose of this review is to provide new ideas for the treatment of oralmaxillofacial hard tissue defects and deficiencies by summarizing the functionalization strategies of calcium phosphate materials and their applications in dentistry.

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.

Drug-delivery nanoparticles for bone-tissue and dental applications

The use of nanoparticles as biomaterials with applications in the biomedical field is growing every day. These nanomaterials can be used as contrast imaging agents, combination therapy agents, and targeted delivery systems in medicine and dentistry. Usually, nanoparticles are found as synthetic or natural organic materials, such as hydroxyapatite, polymers, and lipids. Besides that, they are could also be inorganic, for instance, metallic or metal-oxide-based particles. These inorganic nanoparticles could additionally present magnetic properties, such as superparamagnetic iron oxide nanoparticles. The use of nanoparticles as drug delivery agents has many advantages, for they help diminish toxicity effects in the body since the drug dose reduces significantly, increases drugs biocompatibility, and helps target drugs to specific organs. As targeted-delivery agents, one of the applications uses nanoparticles as drug delivery particles for bone-tissue to treat cancer, osteoporosis, bone diseases, and dental treatments such as periodontitis. Their application as drug delivery agents requires a good comprehension of the nanoparticle properties and composition, alongside their synthesis and drug attachment characteristics. Properties such as size, shape, core-shell designs, and magnetic characteristics can influence their behavior inside the human body and modify magnetic properties in the case of magnetic nanoparticles. Based on that, many different studies have modified the synthesis methods for these nanoparticles and developed composite systems for therapeutics delivery, adapting, and improving magnetic properties, shell-core designs, and particle size and nanosystems characteristics. This review presents the most recent studies that have been presented with different nanoparticle types and structures for bone and dental drug delivery.

Bone-targeted nanoplatform enables efficient modulation of bone tumor microenvironment for prostate cancer bone metastasis treatment

As there is currently no effective therapy for patients with prostate cancer (PCa) bone metastasis, it was stringent to explore the relevant treatment strategies. Actually, the interaction between cancer cells and bone microenvironment plays important role in prostate cancer bone metastasis, especially the Sonic hedgehog protein (SHH) signaling in the bone microenvironment. The SHH promotes osteoblast maturation and osteoblast then secretes RANKL to induce osteoclastogenesis. Herein, this study develops bone-targeting calcium phosphate lipid hybrid nanoparticles (NPs) loaded with docetaxel (DTXL) and SHH siRNA for PCa bone metastasis treatment. For bone targeting purposes, the nanoplatform was modified with alendronate (ALN). (DTXL + siRNA)@NPs-ALN NPs effectively change the bone microenvironment by inhibiting the SHH paracrine and autocrine signaling, enhancing the anti-tumor effects of DTXL. Besides showing good in vitro cellular uptake, the NPs-ALN also inhibited tumor growth both in vitro and in vivo by inducing apoptosis, cell cycle arrest, and autophagy. This DDS comprised of (DTXL + siRNA)-loaded NPs provides an excellent strategy to treat PCa bone metastasis.

Recent Progress in Nanostructured Smart Drug Delivery Systems for Cancer Therapy: A Review

Traditional treatment approaches for cancer involve intravenous chemotherapy or other forms of drug delivery. These therapeutic measures suffer from several limitations such as nonspecific targeting, poor biodistribution, and buildup of drug resistances. However, significant technological advancements have been made in terms of superior modes of drug delivery over the last few decades. Technical capability in analyzing the molecular mechanisms of tumor biology, nanotechnology─particularly the development of biocompatible nanoparticles, surface modification techniques, microelectronics, and material sciences─has increased. As a result, a significant number of nanostructured carriers that can deliver drugs to specific cancerous sites with high efficiency have been developed. This particular maneuver that enables the introduction of a therapeutic nanostructured substance in the body by controlling the rate, time, and place is defined as the nanostructured drug delivery system (NDDS). Because of their versatility and ability to incorporate features such as specific targeting, water solubility, stability, biocompatibility, degradability, and ability to reverse drug resistance, they have attracted the interest of the scientific community, in general, and nanotechnologists as well as biomedical scientists. To keep pace with the rapid advancement of nanotechnology, specific technical aspects of the recent NDDSs and their prospects need to be reported coherently. To address these ongoing issues, this review article provides an overview of different NDDSs such as lipids, polymers, and inorganic nanoparticles. In addition, this review also reports the challenges of current NDDSs and points out the prospective research directions of these nanocarriers. From our focused review, we conclude that still now the most advanced and potent field of application for NDDSs is lipid-based, while other significantly potential fields include polymer-based and inorganic NDDSs. However, despite the promises, challenges remain in practical implementations of such NDDSs in terms of dosage and stability, and caution should be exercised regarding biocompatibility of materials. Considering these aspects objectively, this review on NDDSs will be particularly of interest for small-to-large scale industrial researchers and academicians with expertise in drug delivery, cancer research, and nanotechnology.

MCP mediated active targeting calcium phosphate hybrid nanoparticles for the treatment of orthotopic drug-resistant colon cancer

BACKGROUND

Colon cancer is a most common malignant cancer in digestive system, and it is prone to develop resistance to the commonly used chemotherapy drugs, leading to local recurrence and metastasis. Paris saponin VII (PSVII) could not only inhibit the proliferation of colon cancer cells but also effectively induce apoptosis of drug-resistant colon cancer cells and reduce the metastasis of drug-resistant colon cancer cells as well. However, PSVII was insoluble in water and fat. It displayed no selective distribution in body and could cause severe hemolysis. Herein, colon cancer targeting calcium phosphate nanoparticles were developed to carry PSVII to treat drug-resistant colon cancer.

RESULTS

PSVII carboxymethyl-β-cyclodextrin inclusion compound was successfully encapsulated in colon cancer targeting calcium phosphate nanoparticles (PSVII@MCP-CaP) by using modified citrus pectin as stabilizer agent and colon cancer cell targeting moiety. PSVII@MCP-CaP significantly reduced the hemolysis of PSVII. Moreover, by specific accumulating in orthotopic drug-resistant colon cancer tissue, PSVII@MCP-CaP markedly inhibited the growth of orthotopic drug-resistant colon cancer in nude mice. PSVII@MCP-CaP promoted the apoptosis of drug-resistant colon cancer cells through mitochondria-mediated apoptosis pathway. Moreover, PSVII@MCP-CaP significantly inhibited the invasion and migration of drug-resistant colon cancer cells by increasing E-cadherin protein expression and reducing N-cadherin and MMP-9 protein expression.

CONCLUSION

PSVII@MCP-CaP has great potential in the treatment of drug-resistant colon cancer. This study also explores a new method to prepare active targeting calcium phosphate nanoparticles loaded with a fat and water insoluble compound in water.

Nano-Hydroxyapatite as a Delivery System for Promoting Bone Regeneration In Vivo: A Systematic Review

Nano-hydroxyapatite (nHA) has been widely used as an orthopedic biomaterial and vehicle for drug delivery owing to its chemical and structural similarity to bone minerals. Several studies have demonstrated that nHA based biomaterials have a potential effect for bone regeneration with very minimal to no toxicity or inflammatory response. This systematic review aims to provide an appraisal of the effectiveness of nHA as a delivery system for bone regeneration and whether the conjugation of proteins, antibiotics, or other bioactive molecules to the nHA further enhances osteogenesis in vivo. Out of 282 articles obtained from the literature search, only 14 articles met the inclusion criteria for this review. These studies showed that nHA was able to induce bone regeneration in various animal models with large or critical-sized bone defects, open fracture, or methicillin-resistant Staphylococcus aureus (MRSA)-induced osteomyelitis. The conjugations of drugs or bioactive molecules such as bone-morphogenetic protein-2 (BMP-2), vancomycin, calcitriol, dexamethasone, and cisplatin were able to enhance the osteogenic property of nHA. Thus, nHA is a promising delivery system for a variety of compounds in promoting bone regeneration in vivo.

The optimized drug delivery systems of treating cancer bone metastatic osteolysis with nanomaterials

Some cancers such as human breast cancer, prostate cancer, and lung cancer easily metastasize to bone, leading to osteolysis and bone destruction accompanied by a complicated microenvironment. Systemic administration of bisphosphonates (BP) or denosumab is the routine therapy for osteolysis but with non-negligible side effects such as mandibular osteonecrosis and hypocalcemia. Thus, it is imperative to exploit optimized drug delivery systems, and some novel nanotechnology and nanomaterials have opened new horizons for scientists. Targeted and local drug delivery systems can optimize biodistribution depending on nanoparticles (NPs) or microspheres (MS) and implantable biomaterials with the controllable property. Drug delivery kinetics can be optimized by smart and sustained/local drug delivery systems for responsive delivery and sustained delivery. These delicately fabricated drug delivery systems with special matrix, structure, morphology, and modification can minimize unexpected toxicity caused by systemic delivery and achieve desired effects through integrating multiple drugs or multiple functions. This review summarized recent studies about optimized drug delivery systems for the treatment of cancer metastatic osteolysis, aimed at giving some inspiration in designing efficient multifunctional drug delivery systems.

Alendronate/folic acid-decorated polymeric nanoparticles for hierarchically targetable chemotherapy against bone metastatic breast cancer

To considerably enhance treatment efficacy for bone metastatic breast cancer via dual bone/tumor-targeted chemotherapy, a nanoparticle-based delivery system comprising poly(lactic-co-glycolic acid) (PLGA) as the hydrophobic core coated with alendronate-modified d-α-tocopheryl polyethylene glycol succinate (ALN-TPGS) and folic acid-conjugated TPGS (FA-TPGS) was developed as a vehicle for paclitaxel (PTX) in this work. The ALN/FA-decorated nanoparticles not only showed superior ALN-mediated binding affinity for hydroxyapatite abundant in bone tissue but also promoted uptake of payloads by folate receptor-overexpressing cancer cells to significantly augment PTX cytotoxicity. Notably, through dual-targetable delivery to the bone matrix and folate receptor-overexpressing 4T1 tumors, the PTX-loaded nanoparticles substantially accumulated in bone metastases in vivo and inhibited 4T1 tumor growth and lung metastasis, leading to significant improvement of the survival rate of treated mice. Upon treatment with the ALN/FA-decorated PTX-loaded nanoparticles, the bone destruction and bone loss of the tumor-bearing mice were appreciably retarded, and the adverse effects on normal tissues were alleviated. These results demonstrate that the ALN/FA-decorated PTX-loaded delivery system developed in this study shows great promise for the effective treatment of bone metastatic breast cancer.

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.

Bone-Targeted Calcium Phosphate-Polymer Hybrid Nanoparticle Co-Deliver Zoledronate and Docetaxel to Treat Bone Metastasis of Prostate Cancer

Prostate cancer is the most common malignant tumor with bone metastasis, and there is still no ideal treatment for bone metastasis of prostate cancer. In this study, a pH and GSH dual sensitive calcium phosphate-polymer hybrid nanoparticle (DTX@Cap/HP) was prepared to co-deliver zoledronate (ZOL) and docetaxel (DTX) to treat bone metastasis of prostate cancer. DTX@Cap/HP exhibited high bone binding affinity and released more DTX and ZOL in acidic and high GSH concentration environment. A large amount of DTX@Cap/HP was uptaken by PC-3 cell in acidic medium than that in neutral medium. DTX@Cap/HP obviously reduced PC-3 cell proliferation and bone lesion in in-vitro 3D model of bone metastases of prostate cancer. Besides, DTX@Cap/HP also exhibited stronger anti bone metastases of prostate cancer activity in vivo as compared with the same dose of DTX + ZOL, which resulted from the co-delivery of DTX and ZOL to bone metastases of prostate cancer by DTX@Cap/HP and the synergistic effects of DTX and ZOL. DTX@Cap/HP has great potential in the treatment of bone metastases of prostate cancer.

Bone-seeking nanoplatform co-delivering cisplatin and zoledronate for synergistic therapy of breast cancer bone metastasis and bone resorption

The "vicious cycle" established between tumor growth and osteolysis aggravates the process of breast cancer bone metastasis, leading to life-threatening skeletal-related events that severely reduce survival and quality of life. To effectively interrupt the "vicious cycle", innovative therapeutic strategies that not only reduce osteolysis but also relieve tumor burden are urgently needed. Herein, a bone-seeking moiety, alendronate (ALN), functionalized coordination polymer nanoparticles (DZ@ALN) co-delivering cisplatin prodrug (DSP) and antiresorptive agent zoledronate (ZOL) via Zn²⁺ crosslinking for combination therapy was reported. The versatile DZ@ALN with a diameter of about 40 nm can cross the fissure in the bone marrow sinus capillaries, and possesses an excellent bone-seeking ability both in vitro and in vivo. Additionally, DZ@ALN could synergistically inhibit the proliferation of cancer cells, suppress the formation of osteoclast-like cells and induce the apoptosis of osteoclasts in vitro. Importantly, it could preferentially accumulate in bone affected site, remarkably inhibit the proliferation of tumor cells, relieving bone pain, and significantly inhibit the activation of osteoclasts, protecting the bone from destruction in vivo, eventually leading to the breakdown of "vicious cycle" without inducing obvious systemic toxicity. This innovative nanoagent combines chemotherapy and osteolysis inhibition, exhibiting an inspiring strategy for effective treatment of bone metastasis.

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.

Bone Diseases: Current Approach and Future Perspectives in Drug Delivery Systems for Bone Targeted Therapeutics

Bone diseases include a wide group of skeletal-related disorders that cause mobility limitations and mortality. In some cases, e.g., in osteosarcoma (OS) and metastatic bone cancer, current treatments are not fully effective, mainly due to low patient compliance and to adverse side effects. To overcome these drawbacks, nanotechnology is currently under study as a potential strategy allowing specific drug release kinetics and enhancing bone regeneration. Polymers, ceramics, semiconductors, metals, and self-assembled molecular complexes are some of the most used nanoscale materials, although in most cases their surface properties need to be tuned by chemical or physical reactions. Among all, scaffolds, nanoparticles (NPs), cements, and hydrogels exhibit more advantages than drawbacks when compared to other nanosystems and are therefore the object of several studies. The aim of this review is to provide information about the current therapies of different bone diseases focusing the attention on new discoveries in the field of targeted delivery systems. The authors hope that this paper could help to pursue further directions about bone targeted nanosystems and their application for bone diseases and bone regeneration.

Folate conjugation improved uptake and targeting of porous hydroxyapatite nanoparticles containing epirubicin to cancer cells

As hydroxyapatite (HAp) with the hexagonal crystal structure is biocompatible and bioactive. In the present study, HAp nanoparticles were synthesized and functionalized with polyethylene glycol and folic acid. The anticancer drug, epirubicin, was loaded to the folic acid-conjugated polyethylene glycol-coated HAp (FA-PEG-HAp) nanoparticles. The prepared nanoparticles were used for in vitro and in vivo experiments. Particle size analyzer showed that the hydrodynamic size of PEG-HAp and FA-PEG-HAp nanoparticles was 150.3 ± 1.5 nm and 217.2 ± 14.9 nm, respectively. The release behavior of epirubicin from nanoparticles showed an increase in the rate of release in acidic pH. The released drug in acidic pH was 2.5 fold more than pH 7.4. The results of in vitro study indicated an increase in cellular uptake of nanoparticles due to folate ligand. In vivo treatment with both PEG-HAp and FA-PEG-HAp nanoparticles had notably higher inhibition efficacy towards tumor growth than free epirubicin. In conclusion, folate conjugation provided higher uptake and better targeting of hydroxyapatite nanoparticles to cancer cells.

Interactions between cancer cells and bone microenvironment promote bone metastasis in prostate cancer

Bone metastasis is the leading cause of death in prostate cancer patients, for which there is currently no effective treatment. Since the bone microenvironment plays an important role in this process, attentions have been directed to the interactions between cancer cells and the bone microenvironment, including osteoclasts, osteoblasts, and bone stromal cells. Here, we explained the mechanism of interactions between prostate cancer cells and metastasis-associated cells within the bone microenvironment and further discussed the recent advances in targeted therapy of prostate cancer bone metastasis. This review also summarized the effects of bone microenvironment on prostate cancer metastasis and the related mechanisms, and provides insights for future prostate cancer metastasis studies.

Functionalized calcium orthophosphates (CaPO4) and their biomedical applications

Due to the chemical similarity to natural calcified tissues (bones and teeth) of mammals, calcium orthophosphates (abbreviated as CaPO₄) appear to be good biomaterials for creation of artificial bone grafts. However, CaPO₄ alone have some restrictions, which limit their biomedical applications. Various ways have been developed to improve the properties of CaPO₄ and their functionalization is one of them. Namely, since surfaces always form the interfaces between implanted grafts and surrounding tissues, the state of CaPO₄ surfaces plays a crucial role in the survival of bone grafts. Although the biomedically relevant CaPO₄ possess the required biocompatible properties, some of their properties could be better. For example, functionalization of CaPO₄ to enhance cell attachment and cell material interactions has been developed. In addition, to prepare stable formulations from nanodimensional CaPO₄ particles and prevent them from agglomerating, the surfaces of CaPO₄ particles are often functionalized by sorption of special chemicals. Furthermore, there are functionalizations in which CaPO₄ are exposed to various types of physical treatments. This review summarizes the available knowledge on CaPO₄ functionalizations and their biomedical applications.

Alendronate-Functionalized Poly(2-oxazoline)s with Tunable Affinity for Calcium Cations

A library of poly(2-oxazoline)s functionalized with controllable amounts of alendronate, hydroxyl, and carboxylic acid side groups was successfully synthesized to create novel polymers with tunable affinity for calcium cations. The affinity of alendronate-containing polymers for calcium cations was quantified using isothermal titration calorimetry. Thermodynamic measurements revealed that the Ca²⁺-binding affinity of these polymers increased linearly with the amount of alendronate functionalization, up to values (K_Ca²⁺ = 2.4 × 10⁵ M^–1) that were about 120-fold higher than those for previously reported polymers. The calcium-binding capacity of alendronate-functionalized poly(2-oxazoline)s was exploited to form robust hydrogel networks cross-linked using reversible physical bonds. Oscillatory rheology showed that these hydrogels recovered more than 100% of their initial storage modulus after severe network destruction. The versatile synthesis of alendronate-functionalized polymers and their strong and tunable affinity for calcium cations render these polymers promising candidates for various biomedical applications.

Bortezomib-catechol conjugated prodrug micelles: combining bone targeting and aryl boronate-based pH-responsive drug release for cancer bone-metastasis therapy

The treatment of metastatic tumors is highly desirable in clinics, which has also increased the interest in the design of nanoscale drug delivery systems. Bone metastasis is one of the most common pathways in the metastasis of breast cancer, and it is also an important cause for tumor recurrence and death. The aryl boronate group, as an acid-labile linker, has been introduced into nano-assemblies in recent years. Especially, as a proteasome inhibitor anticancer drug with a boric acid group, bortezomib can facilitate the formation of pH-sensitive aryl boric acid ester linkage with the catecholic group. In this study, bortezomib-loaded micelles with bone targeting properties were constructed for the treatment of breast cancer bone metastasis. The mixed micelles employed alendronate (ALN) as the bone-targeting ligand and encapsulated bortezomib-catechol conjugates as the cargo. In vitro and in vivo studies showed that compared with free drugs or control micelles, these prodrug micelles (ALN-NP) exhibited many favorable properties such as reduced systemic toxicity and improved therapeutic effects. Therefore, ALN-NP is promising as a nanovehicle for bone-targeting delivery of chemotherapeutic drugs. Furthermore, this study offers a novel strategy combining bone targeting and aryl boronate-based pH-responsive drug release for anti-metastasis therapy.

Calcium phosphate-based nanosystems for advanced targeted nanomedicine

Synthetic calcium phosphates (CaPs) are the most widely accepted bioceramics for the repair and reconstruction of bone tissue defects. The recent advancements in materials science have prompted a rapid progress in the preparation of CaPs with nanometric dimensions, tailored surface characteristics, and colloidal stability opening new perspectives in their use for applications not strictly related to bone. In particular, the employment of CaPs nanoparticles as carriers of therapeutic and imaging agents has recently raised great interest in nanomedicine. CaPs nanoparticles, as well as other kinds of nanoparticles, can be engineered to specifically target the site of the disease (cells or organs), thus minimizing their dispersion in the body and undesired organism-nanoparticles interactions. The most promising and efficient approach to improve their specificity is the 'active targeting', where nanoparticles are conjugated with a targeting moiety able to recognize and bind with high efficacy and selectivity to receptors that are highly expressed only in the therapeutic site. The aim of this review is to give an overview on advanced targeted nanomedicine with a focus on the most recent reports on CaP nanoparticles-based systems, specifically designed for the active targeting. The distinctive characteristics of CaP nanoparticles with respect to the other kinds of nanomaterials used in nanomedicine are also discussed.

Bone metastasis target redox-responsive micell for the treatment of lung cancer bone metastasis and anti-bone resorption

In order to inhibit the growth of lung cancer bone metastasis and reduce the bone resorption at bone metastasis sites, a bone metastasis target micelle DOX@DBMs-ALN was prepared. The size and the zeta potential of DOX@DBNs-ALN were about 60 nm and -15 mV, respectively. DOX@DBMs-ALN exhibited high binding affinity with hydroxyapatite and released DOX in redox-responsive manner. DOX@DBMs-ALN was effectively up taken by A549 cells and delivered DOX to the nucleus of A549 cells, which resulted in strong cytotoxicity on A549 cells. The in vivo experimental results indicated that DOX@DBMs-ALN specifically delivered DOX to bone metastasis site and obviously prolonged the retention time of DOX in bone metastasis site. Moreover, DOX@DBMs-ALN not only significantly inhibited the growth of bone metastasis tumour but also obviously reduced the bone resorption at bone metastasis sites without causing marked systemic toxicity. Thus, DOX@DBMs-ALN has great potential in the treatment of lung cancer bone metastasis.

Self-assembled CaP-based hybrid nanoparticles to enhance gene transfection efficiency in vitro and in vivo: beneficial utilization of PEGylated bisphosphate and nucleus locating signal

Calcium phosphate (CaP) nanoparticles have been considered as a non-viral gene delivery vehicle, but the weakness of inconsistent and low transfection efficiencies is limited to its progress.

Tumor acidity-activatable manganese phosphate nanoplatform for amplification of photodynamic cancer therapy and magnetic resonance imaging

Amorphous biodegradable metal phosphate nanomaterials are considered to possess great potential in cancer theranostic application due to their promise in providing ultra-sensitive pH-responsive therapeutic benefits and diagnostic functions simultaneously. Here we report the synthesis of photosensitising and acriflavine-carrying amorphous porous manganese phosphate (PMP) nanoparticles with ultra-sensitive pH-responsive degradability and their application for a photoactivable synergistic nanosystem that imparts reactive oxygen species (ROS) induced cytotoxicity in synchrony with hypoxia-inducible factor 1α/vascular endothelial growth factor (HIF1α/VEGF) inhibitor that suppresses tumor growth and treatment escape signalling pathway. Carboxymethyl dextran (CMD) is chemically anchored on the surface of porous manganese phosphate theranostic system through the pH-responsive boronate esters. Upon the stimulus of the tumor acid microenvironment, manganese phosphate disintegrates and releases Mn²⁺ ions rapidly, which are responsible for the magnetic resonance imaging (MRI) effect. Meanwhile, the released photosensitizer chlorin e6 (Ce6) produces ROS under irradiation while acriflavine (ACF) inhibits the HIF-1α/VEGF pathway during the burst release of VEGF in tumour induced by photodynamic therapy (PDT), resulting in increased therapeutic efficacy. Considering the strong pH responsivity, MRI signal amplification and drug release profile, the PMP nanoparticles offer new prospects for tumor acidity-activatable theranostic application by amplifying the PDT through inhibiting the HIF-1α /VEGF pathway timely while enhancing the MRI effect.

STATEMENT OF SIGNIFICANCE

In this study, we report the synthesis of the tumor acidity-activatable amorphous porous manganese phosphate nanoparticles and their application for a photoactivable synergistic nanosystem that imparts reactive oxygen species (ROS) induced cytotoxicity in synchrony with hypoxia-inducible factor 1α/vascular endothelial growth factor (HIF-1α/VEGF) inhibitor that suppresses tumor growth and treatment escape signalling pathway. Besides, upon the stimulus of the tumor acid microenvironment, the manganese phosphate nanoparticles finally disintegrate and release Mn²⁺ ions rapidly, which are responsible for the magnetic resonance imaging (MRI) effect. This nanoplatform is featured with distinctive advantages such as ultra pH-responsive drug release, MRI function and rational drug combination exploiting the blockage of the treatment escape signalling pathway.

Bisphosphonate-functionalized coordination polymer nanoparticles for the treatment of bone metastatic breast cancer

Bone is the most common organ affected by metastatic breast cancer. Targeting cancers within the bone remains a great challenge due to the inefficient delivery of therapeutic to bone. In this study, a polyethylene glycol (PEG) coated nanoparticles (NPs) made of a Zn²⁺ coordination polymer was linked with a bone seeking moiety, alendronate (ALN), to deliver cisplatin prodrug (DSP) to the bone. The particle sizes of this novel system, DSP-Zn@PEG-ALN NPs, were regulated by adjusting the volume ratio of water phase to oil phase in microemulsion. It was small enough (about 55nm) to extravasate through the clefts (80nm) of the bone's sinusoidal capillaries and localize into metastatic bones. DSP-Zn@PEG-ALN NPs showed much higher affinity for hydroxyapatite in vitro and bone in vivo than non-targeted DSP-Zn@PEG NPs and cisplatin. In addition, the in vivo biodistribution studies demonstrated that about 4-fold of platinum was delivered to the bone metastatic lesions than that in healthy bones by DSP-Zn@PEG-ALN NPs intravenously. Finally, DSP-Zn@PEG-ALN NPs not only inhibited the tumor growth efficiently but also reduced the osteocalastic bone destruction. Besides, DSP-Zn@PEG-ALN NPs showed significantly reduced toxicity of cisplatin. These results indicate that the DSP-Zn@PEG-ALN NPs have a great potential in enhancing chemotherapeutic efficacy for the treatment of bone metastatic breast cancer.

Targeting Osteocytes to Attenuate Early Breast Cancer Bone Metastasis by Theranostic Upconversion Nanoparticles with Responsive Plumbagin Release

The early detection and thus treatment of breast cancer bone metastasis remain a big challenge clinically. As the most abundant cells within bone tissue, osteocytes have been found to manipulate the activity of early cancer bone metastasis by its crosstalk with cancer cells and osteoclasts. However, conventional bone-targeting nanomedicine has limited bone-lesion specificity and ignores the vital role of osteocytes during breast cancer bone metastasis. Also, it lacks detailed insight into the therapeutic mechanisms, which hinders the following translational practice. Previously, we have shown that a combination of zoledronic acid (ZA) and plumbagin (PL) synergistically alleviates cancer-induced bone destruction. Herein, we further develop a pH-responsive bone-targeting drug delivery system, i.e., the ZA-anchored bimodal mesoporous slica covered gadolinium(III) upconversion nanoparticles loaded with PL, to detect and treat bone metastasis sensitively and specifically at an early stage. This multifunctional nanosystem can target osteocytes to release PL as controlled by pH, decreasing osteocytic RANKL expression synergistically through the structural simulation of adenosine phosphate, which competitively inhibits the phosphorylation of osteocytic protein kinase-a, cAMP-response element binding protein, extracellular regulated protein kinase, and c-Jun N-terminal kinase. More importantly, by establishing a breast cancer bone metastasis mice model via intracardiac injection, we show that tumoriogenesis and osteoclastogenesis can both be attenuated significantly. We thereby realize the effective theranostics of tiny bone metastasis in breast cancer bone metastasis. Our work highlights the significance of theranostic nanomedicine and osteocyte-targeting therapy in the treatment of early bone metastasis, which could be applied in achieving efficient theranostic effects for other bone diseases.

Coordination self-assembly of platinum-bisphosphonate polymer-metal complex nanoparticles for cisplatin delivery and effective cancer therapy

Cisplatin (CDDP) is a potent anti-carcinogen that is widely used for various solid tumors; however, its clinical application is limited by its severe nephrotoxicity. Novel platinum-bisphosphonate polymer-metal complex nanoparticles (Pt-bp NPs), based on platinum-bisphosphonate coordination, have been established. Three polymer carriers bearing alendronate (ALN) ligands, while containing different lengths of alkyl hydrophobic chains, were synthesized. Their structures were characterized by ¹H NMR, ³¹P NMR and FTIR. The ALN was used to coordinate to the CDDP precursor [Pt(NH₃)₂(OSO₃)(OH₂)], and the Pt-bp NPs were formed spontaneously. The Pt-bp NPs formed by the polymer carrier, ALN-PEG_2k-ASA_C18, which contained the poly(ethylene glycol) chain with ALN on one side and the octadecyl hydrophobic chain on the other side, was denoted as ALN-ASA_C18-CDDP; its diameter was within 200 nm. CDDP was released in a Cl^- or pH-dependent manner. The cytotoxic effects to the HeLa, A549 and MCF-7 cell lines were relatively weak, compared to CDDP. However, ALN-ASA_C18-CDDP showed significantly prolonged blood circulation time and tumor accumulation of platinum of 2.5-fold, compared to CDDP at 8 h. Besides, ALN-ASA_C18-CDDP was demonstrated to remarkably reduce systemic toxicity without compromising in vivo antitumor activity. These results indicate that the facilely prepared ALN-ASA_C18-CDDP has great utilization potential for CDDP delivery in a clinical setting.