Engineered nanostructures within sol-gel bioactive glass for enhanced bioactivity and modulated drug delivery

The engineering of nanocrystalline phase in amorphous oxide materials such as bioactive glass is emerging as a new area of great technological and scientific interest in the field of biomaterials. This study reports for the first time the infusion of apatite nanocrystals in sol-gel-derived bioactive glass using P123 as the structure-directing agent. The synthesis of a multicomponent 80SiO₂-15CaO-5P₂O₅ bioactive glass material having a hierarchically ordered mesoporous structure with uniformly grown nanocrystals of apatite was achieved through a sono-assisted surfactant-templated sol-gel method. The bulk crystallographic analysis together with microstructural characterizations shows that the nanocrystalline apatite domains are uniformly dispersed as well as embedded along the mesopores. These nanocrystalline domains were found to influence the textural properties. In addition, macroscopic evidence for higher signs of bonelike matrix formation was observed by the biomineralization study in simulated body fluids. Osteostimulatory effects of these glass samples were evident by cultures in a osteogenic and non-osteogenic mediums with human osteosarcoma cells and a higher osteopromotive potential was authenticated by the alkaline phosphatase activity and alizarin red staining. Further, this study shows a new strategy to prolong the drug release period on account of the nanocrystalline phase and hierarchically positioned mesopores, thus making it a better drug delivery matrix as well.

Calcium Phosphate-Based Biomaterials for Bone Repair

Traumatic, tumoral, and infectious bone defects are common in clinics, and create a big burden on patient's families and society. Calcium phosphate (CaP)-based biomaterials have superior properties and have been widely used for bone defect repair, due to their similarities to the inorganic components of human bones. The biological performance of CaPs, as a determining factor for their applications, are dependent on their physicochemical properties. Hydroxyapatite (HAP) as the most thermally stable crystalline phase of CaP is mostly used in the form of ceramics or composites scaffolds with polymers. Nanostructured CaPs with large surface areas are suitable for drug/gene delivery systems. Additionally, CaP scaffolds with hierarchical nano-/microstructures have demonstrated excellent ability in promoting bone regeneration. This review focuses on the relationships and interactions between the physicochemical/biological properties of CaP biomaterials and their species, sizes, and morphologies in bone regeneration, including synthesis strategies, structure control, biological behavior, and the mechanisms of CaP in promoting osteogenesis. This review will be helpful for scientists and engineers to further understand CaP-based biomaterials (CaPs), and be useful in developing new high-performance biomaterials for bone repair.

Toward a doxorubicin-loaded bioinspired bone cement for the localized treatment of osteosarcoma

Aims: Osteosarcoma represents the second most common cause of death in children and young adults. No biomaterial allowing local drug delivery has been specifically developed. However, a biocompatible bioactive implantable material could prevent some amputations, and the local release of an antitumor agent could limit risks of relapse and metastasis. Methods: We propose a proof of concept of a self-setting paste combining amorphous calcium phosphate and doxorubicin-loaded particles of bone-like carbonated nanocrystalline apatite, as a means of local release. Results: The cement formulation and doping, first with folic acid and then with doxorubicin, was successful. Its physicochemistry was scrutinized. Preliminary in vivo data on an invasive osteosarcoma rat model suggest a limiting effect on metastatic events in the lungs without signs of toxicity.

Advanced Materials Based on Nanosized Hydroxyapatite

The development of new materials based on hydroxyapatite has undergone a great evolution in recent decades due to technological advances and development of computational techniques. The focus of this review is the various attempts to improve new hydroxyapatite-based materials. First, we comment on the most used processing routes, highlighting their advantages and disadvantages. We will now focus on other routes, less common due to their specificity and/or recent development. We also include a block dedicated to the impact of computational techniques in the development of these new systems, including: QSAR, DFT, Finite Elements of Machine Learning. In the following part we focus on the most innovative applications of these materials, ranging from medicine to new disciplines such as catalysis, environment, filtration, or energy. The review concludes with an outlook for possible new research directions.

Platinum-loaded, selenium-doped hydroxyapatite nanoparticles selectively reduce proliferation of prostate and breast cancer cells co-cultured in the presence of stem cells

Chemotherapeutic treatment of patients with bone tumors or bone metastases often leads to severe side effects such as high drug toxicity, lack of tumor specificity and induced drug resistance. A novel strategy to treat early stages of bone metastases involves local co-delivery of multiple chemotherapeutic agents to synergistically improve the curative effect and overcome shortcomings of traditional chemotherapy. Herein we show that selenite-doped hydroxyapatite nanoparticles loaded with a hydroxyapatite-binding anti-tumor platinum complex (PtPP-HASe) selectively reduce proliferation of cancer cells without reducing proliferation of bone marrow stem cells. These PtPP-HASe particles were nanocrystalline with selenium (Se) and platinum (Pt) contents ranging between 0-10 and 1.5-3 wt%, respectively. Release kinetics of Se and Pt from PtPP-HASe nanoparticles resulted in a cumulative release of ∼10 and ∼66 wt% after 7 days, respectively. At a Pt/Se ratio of 8, released Pt and Se species selectively reduced cell number of human prostate (PC3) and human breast cancer cells (MDA-MB-231) by a factor of >10 with limited effects on co-cultured human bone marrow stem cells (hBMSc). These novel nanoparticles demonstrate high anti-cancer selectivity, which offers ample opportunities for the design of novel biomaterials with potent and selective chemotherapeutic efficacy against cancer cells.

Nanotechnological approach and bio-inspired materials to face degenerative diseases in aging

The aging of the world population is increasingly claimed as an alarming situation, since an ever-raising number of persons in advanced age but still physically active is expected to suffer from invalidating and degenerative diseases. The impairment of the endogenous healing potential provoked by the aging requires the development of more effective and personalized therapies, based on new biomaterials and devices able to direct the cell fate to stimulate and sustain the regrowth of damaged or diseased tissues. To obtain satisfactory results, also in cases where the cell senescence, typical of the elderly, makes the regeneration process harder and longer, the new solutions have to possess excellent ability to mimic the physiological extracellular environment and thus exert biomimetic stimuli on stem cells. To this purpose, the "biomimetic concept" is today recognized as elective to fabricate bioactive and bioresorbable devices such as hybrid osteochondral scaffolds and bioactive bone cements closely resembling the natural hard tissues and with enhanced regenerative ability. The review will illustrate some recent results related to these new biomimetic materials developed for application in different districts of the musculoskeletal system, namely bony, osteochondral and periodontal regions, and the spine. Further, it will be shown how new bioactive and superparamagnetic calcium phosphate nanoparticles can give enhanced results in cardiac regeneration and cancer therapy. Since tissue regeneration will be a major demand in the incoming decades, the high potential of biomimetic materials and devices is promising to significantly increase the healing rate and improve the clinical outcomes even in aged patients.

Bone tumor-targeted delivery of theranostic 195mPt-bisphosphonate complexes promotes killing of metastatic tumor cells

Platinum-based drugs such as cisplatin are very potent chemotherapeutics, whereas radioactive platinum (195mPt) is a rich source of low-energy Auger electrons, which kills tumor cells by damaging DNA. Auger electrons damage cells over a very short range. Consequently, 195mPt-based radiopharmaceuticals should be targeted toward ​tumors to maximize radiotherapeutic efficacy and minimize Pt-based systemic toxicity. Herein, we show that systemically administered radioactive bisphosphonate-functionalized platinum (195mPt-BP) complexes specifically accumulate in intratibial bone metastatic lesions in mice. The 195mPt-BP complexes accumulate 7.3-fold more effectively in bone 7 days after systemic delivery compared to 195mPt-cisplatin lacking bone-targeting bisphosphonate ligands. Therapeutically, 195mPt-BP treatment causes 4.5-fold more γ-H2AX formation, a biomarker for DNA damage in metastatic tumor cells compared to 195mPt-cisplatin. We show that systemically administered 195mPt-BP is radiotherapeutically active, as evidenced by an 11-fold increased DNA damage in metastatic tumor cells compared to non-radioactive Pt-BP controls. Moreover, apoptosis in metastatic tumor cells is enhanced more than 3.4-fold upon systemic administration of 195mPt-BP vs. radioactive 195mPt-cisplatin or non-radioactive Pt-BP controls. These results provide the first preclinical evidence for specific accumulation and strong radiotherapeutic activity of 195mPt-BP in bone metastatic lesions, which offers new avenues of research on radiotherapeutic killing of tumor cells in bone metastases by Auger electrons.

Selenium-doped hydroxyapatite nanoparticles for potential application in bone tumor therapy

In the present study we have studied the incorporation and release of selenite ions (SeO₃^2-) in hydroxyapatite nanoparticles for the treatment of bone tumors. Two types of selenium-doped hydroxyapatite (HASe) nanoparticles (NPs) with a nominal Se/(P + Se) molar ratio ranging from 0.01 up to 0.40 have been synthesized by a new and mild wet method. The two series of samples were thoroughly characterized and resulted to be slightly different in chemical composition, but they had similar properties in terms of morphology and degree of crystallinity. Selenium release from HASe was investigated under neutral and acidic conditions to simulate both healthy tissues and the low-pH environment surrounding a tumor mass, respectively. The comparison of the release profiles at two pH values clearly showed the possibility of modulating the Se release by simply changing the amount of Se in the HASe particles. The correlation between the physicochemical properties of HASe and their dissolution as a function of pH has been also investigated to facilitate future application of the NPs as chemotherapeutic adjuvant agents. Finally, the cytotoxic activity of HASe was evaluated using prostate (PC3) and breast (MDA-MB-231) cancer cells as well as healthy human bone marrow stem cells (hBMSc). HASe NPs exerted a good cytocompatibility at low concentration of Se but, with high Se doping concentration, they displayed strong cytotoxicity.

Preclinical evaluation of platinum-loaded hydroxyapatite nanoparticles in an embryonic zebrafish xenograft model

Hydroxyapatite (HA) nanoparticles are commonly used as building blocks in the design of bone-substituting biomaterials. Recently, these nanoparticles have been considered for the treatment of metastasis disease, since their pH-dependent dissolution behavior allows for precise tuning of release kinetics of loaded cargo. Herein we show that the capacity of drug-loaded nanoparticles stabilized with citrate ions reduce cancer cell survival in an embryonic zebrafish xenograft model. In particular, in vitro studies demonstrate that PtPP-loaded HA nanoparticles exhibit anti-proliferative activity against breast cancer cells at reduced pH. In vivo studies using an embryonic zebrafish xenograft model reveal that PtPP co-delivered with human breast cancer cells strongly reduce cancer cell survival. Similarly, co-injection of breast cancer cells with citrate-functionalized and PtPP-loaded HA nanoparticles into zebrafish significantly reduces survival of cancer cells due to release of chemotherapeutically active kiteplatin species. These results demonstrate the preclinical efficacy of drug-loaded nanoparticles against human breast cancer cells in a xenogenic embryonic in vivo model.

Targeting of radioactive platinum-bisphosphonate anticancer drugs to bone of high metabolic activity

Platinum-based chemotherapeutics exhibit excellent antitumor properties. However, these drugs cause severe side effects including toxicity, drug resistance, and lack of tumor selectivity. Tumor-targeted drug delivery has demonstrated great potential to overcome these drawbacks. Herein, we aimed to design radioactive bisphosphonate-functionalized platinum (^195mPt-BP) complexes to confirm preferential accumulation of these Pt-based drugs in metabolically active bone. In vitro NMR studies revealed that release of Pt from Pt BP complexes increased with decreasing pH. Upon systemic administration to mice, Pt-BP exhibited a 4.5-fold higher affinity to bone compared to platinum complexes lacking the bone-seeking bisphosphonate moiety. These Pt-BP complexes formed less Pt-DNA adducts compared to bisphosphonate-free platinum complexes, indicating that in vivo release of Pt from Pt-BP complexes proceeded relatively slow. Subsequently, radioactive ^195mPt-BP complexes were synthesized using ^195mPt(NO₃)₂(en) as precursor and injected intravenously into mice. Specific accumulation of ^195mPt-BP was observed at skeletal sites with high metabolic activity using micro-SPECT/CT imaging. Furthermore, laser ablation-ICP-MS imaging of proximal tibia sections confirmed that ^195mPt BP co-localized with calcium in the trabeculae of mice tibia.

Calcium Phosphate Nanoparticles for Therapeutic Applications in Bone Regeneration

Bone injuries and diseases constitute a burden both socially and economically, as the consequences of a lack of effective treatments affect both the patients' quality of life and the costs on the health systems. This impended need has led the research community's efforts to establish efficacious bone tissue engineering solutions. There has been a recent focus on the use of biomaterial-based nanoparticles for the delivery of therapeutic factors. Among the biomaterials being considered to date, calcium phosphates have emerged as one of the most promising materials for bone repair applications due to their osteoconductivity, osteoinductivity and their ability to be resorbed in the body. Calcium phosphate nanoparticles have received particular attention as non-viral vectors for gene therapy, as factors such as plasmid DNAs, microRNAs (miRNA) and silencing RNA (siRNAs) can be easily incorporated on their surface. Calcium phosphate nanoparticles loaded with therapeutic factors have also been delivered to the site of bone injury using scaffolds and hydrogels. This review provides an extensive overview of the current state-of-the-art relating to the design and synthesis of calcium phosphate nanoparticles as carriers for therapeutic factors, the mechanisms of therapeutic factors' loading and release, and their application in bone tissue engineering.

Copper Nanocluster-Doped Luminescent Hydroxyapatite Nanoparticles for Antibacterial and Antibiofilm Applications

Novel strategies in the field of nanotechnology for the development of suitable multifunctional drug delivery vehicles have been pursued with promising upshots. Luminescent copper nanocluster-doped hydroxyapatite nanoparticles (HAP NPs) were synthesized and applied for the delivery of antibacterial drug kanamycin. The negatively charged doped HAP NPs could electrostatically interact with the positively charged kanamycin. The kanamycin-loaded doped HAP NPs showed pronounced activity in the case of Gram-negative bacteria compared to that in Gram-positive bacteria. Upon interaction with the bacteria, kanamycin could probably generate harmful agents such as hydroxyl radical that leads to bacterial cell damage. After being incorporated with copper nanoclusters (Cu NCs), the doped HAP NPs were applied for the bioimaging of bacterial cells. The biocompatibility of doped HAP NPs was also studied in HeLa cells. As compared to copper nanoclusters, the doped HAP NPs showed excellent biocompatibility even at higher concentrations of copper. The kanamycin-loaded doped HAP NPs were further applied toward Pseudomonas aeruginosa biofilm eradication. Thus, the as-synthesized copper nanocluster-doped HAP NPs were applied as nanocarriers for antibiotic drug delivery, bioimaging, and antibiofilm applications.

Nano-Based Systems and Biomacromolecules as Carriers for Metallodrugs in Anticancer Therapy

Since the discovery of cisplatin and its potency in anticancer therapy, the development of metallodrugs has been an active area of research. The large choice of transition metals, oxidation states, coordinating ligands, and different geometries, allows for the design of metal-based agents with unique mechanisms of action. Many metallodrugs, such as titanium, ruthenium, gallium, tin, gold, and copper-based complexes have been found to have anticancer activities. However, biological application of these agents necessitates aqueous solubility and low systemic toxicity. This minireview highlights the emerging strategies to facilitate the in vivo application of metallodrugs, aimed at enhancing their solubility and bioavailability, as well as improving their delivery to tumor tissues. The focus is on encapsulating the metal-based complexes into nanocarriers or coupling to biomacromolecules, generating efficacious anticancer therapies. The delivery systems for complexes of platinum, ruthenium, copper, and iron are discussed with most recent examples.

(μ-Methylenediphosphonato-κ4 O,O':O'',O''')bis[(ethyl-ene-diamine-κ2 N,N')palladium(II)] tetra-hydrate

The title compound, [Pd2(C2H8N2)2(CH2O6P2)]·4H2O, comprises of a binuclear mol-ecule (point group symmetry 2), with a twofold rotation axis running through the central C atom of the methyl-enedi-phospho-nate (MDP) anion. The PdII atom has a square-planar coordination environment defined by the N atoms of a bidentate ethyl-enedi-amine (en) ligand and two O atoms of the bridging MDP anion. In the crystal structure, metal complexes are arranged in layers parallel (001) and are sandwiched between layers containing disordered water mol-ecules of crystallization. Extensive intra-layer hydrogen bonds of the type N-H⋯O in the metal complex layer and O-H⋯O in the water layer, as well as O-H⋯O hydrogen bonds between the two types of layers, lead to the formation a three-dimensional network structure. The two lattice water mol-ecules are each equally disordered over two positions.

Functionalization of a nanostructured hydroxyapatite with Cu(II) compounds as a pesticide: in situ transmission electron microscopy and environmental scanning electron microscopy observations of treated Vitis vinifera L. leaves

BACKGROUND

The present study evaluated a biocompatible material for plant protection with the aim of reducing the amount of active substance applied. We used a synthetic hydroxyapatite (HA) that has been studied extensively as a consequence of its bioactivity and biocompatibility. An aggregation between HA nanoparticles and four Cu(II) compounds applied to Vitis vinifera L. leaves as a pesticide was studied. Formulations were characterized by X-ray diffraction (XRD), dynamic light scattering (DLS) and electron microscopy and applied in planta to verify particle aggregation and efficiency in controlling the pathogen Plasmopara viticola.

RESULTS

The XRD patterns showed different crystalline phases dependig on the Cu(II) compound formulated with HA particles, DLS showed that nanostructured particles are stable as aggregates out of the nanometer range and, in all formulations, transmission electron microscopy (TEM) and environmental scanning electron microscopy (ESEM) microscopy showed large aggregates which were partially nanostructured and were recognized as stable in their micrometric dimensions. Such particles did not show phytotoxic effects after their application in planta.

CONCLUSION

A formulation based on HA and a soluble Cu(II) compound showed promising results in the control of the fungal pathogen, confirming the potential role of HA as an innovative delivery system of Cu(II) ions. The present work indicates the possibility of improving the biological activity of a bioactive substance by modifying its structure through an achievable formulation with a biocompatible material. © 2018 Society of Chemical Industry.

The Cooperative Effect of Size and Crystallinity Degree on the Resorption of Biomimetic Hydroxyapatite for Soft Tissue Augmentation

Two kinds of hydroxyapatite (HA) crystals were studied as subcutaneous fillers in order to evaluate how their different degree of crystallinity and dimensions influence in vivo resorption. By appropriately adjusting the synthesis temperature, poorly crystalline HA (HApc) and highly crystalline HA (HAhc) were synthesized into clusters of needle-shaped crystals of about 50 nm and plate-shaped crystals of about 100 nm, respectively. The clusters of HApc had larger dimensions (30 μm) than those of HAhc (3 μm). Subcutaneous in vivo inoculations were performed in ten 6-month-old FVB female mice. HAhc underwent complete macroscopic resorption already 4 weeks after the implantation while HApc still showed agglomerates at the eighth week. This unexpected finding may be ascribed to the different size and morphology of the HAhc nanocrystals responsible for a lower aggregation and microcluster dimension than HApc nanocrystals.

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.

Hydroxyapatite nanocrystals as a smart, pH sensitive, delivery system for kiteplatin

Hydroxyapatite (HA) nanocrystals are important inorganic constituents of biological hard tissues in vertebrates and have been proposed as a bone substitute or a coating material for prostheses in biomedicine. Hydroxyapatite is also amenable for its capacity to bind to a great variety of biomolecules and therapeutic agents. As drug carriers, apatite nanoparticles also have the advantage of pH dependent solubility and low toxicity. Thus HA nanoparticles are negligibly soluble at physiological pH but their dissolution is accelerated at lower pH such as that typically found in the vicinity of tumors. In the present study we have investigated the adsorption on and the release from biomimetic HA nanoparticles of two platinum derivatives of cis-1,4-diaminocyclohexane ([PtX2(cis-1,4-DACH)], X2 = Cl2 (1) and 1,1-cyclobutanedicarboxylate (CBDCA, 2)). The first of the two compounds proved to be active against colon cancer cells also resistant to oxaliplatin. The release has been investigated as a function of pH to mimic the different physiological environments of healthy tissues and tumors, and the in vitro cytotoxicity of the releasates from the HA matrices has been assessed against various human cancer cell lines. The results fully confirmed the potential of 1-loaded HA nanoparticles as bone-specific drug delivery devices.

Calcium-based biomaterials for diagnosis, treatment, and theranostics

Calcium-based biomaterials with good biosafety and bio-absorbability are promising for biomedical applications such as diagnosis, treatment, and theranostics.

Novel Kiteplatin Pyrophosphate Derivatives with Improved Efficacy

Two new Pt(II) derivatives of kiteplatin ([PtCl₂(cis-1,4-DACH)]) with pyrophosphate as carrier ligand, one mononuclear (1) and one dinuclear (2), were synthesized with the aim of potentiating the efficacy of kiteplatin. Complex 1 resulted to be remarkably stable at physiological pH, but it undergoes a fast hydrolysis reaction at acidic pH releasing free pyrophosphate and (aquated) kiteplatin. The dinuclear compound 2 resulted to be less stable than 1 at both neutral and acidic pH forming 1 and (aquated) kiteplatin as first step. Both compounds (1 and 2) do not react as such with 5'-GMP, whereas their hydrolysis products readily form adducts with the nucleotide. The in vitro cytotoxicity assays against a panel of six human cancer cell lines showed that complex 2 affects cancer cell viability even at nanomolar concentrations. The cytotoxic activity of 2 is greater (up to 2 orders of magnitude) than that of cisplatin, oxaliplatin, and kiteplatin, whereas the mononuclear complex 1 has shown a cytotoxic activity comparable to that of oxaliplatin and kiteplatin, but higher than cisplatin. The latter result is not surprising, since the presence of two negative charges reduces the uptake of 1 into the tumor cells as compared to the neutral compound 2. The remarkable activity of 2 against the pancreatic cell line BxPC3 (average IC₅₀ = 0.07 μM) deserves further investigation.

Calcium Phosphate Bioceramics: A Review of Their History, Structure, Properties, Coating Technologies and Biomedical Applications

Calcium phosphate (CaP) bioceramics are widely used in the field of bone regeneration, both in orthopedics and in dentistry, due to their good biocompatibility, osseointegration and osteoconduction. The aim of this article is to review the history, structure, properties and clinical applications of these materials, whether they are in the form of bone cements, paste, scaffolds, or coatings. Major analytical techniques for characterization of CaPs, in vitro and in vivo tests, and the requirements of the US Food and Drug Administration (FDA) and international standards from CaP coatings on orthopedic and dental endosseous implants, are also summarized, along with the possible effect of sterilization on these materials. CaP coating technologies are summarized, with a focus on electrochemical processes. Theories on the formation of transient precursor phases in biomineralization, the dissolution and reprecipitation as bone of CaPs are discussed. A wide variety of CaPs are presented, from the individual phases to nano-CaP, biphasic and triphasic CaP formulations, composite CaP coatings and cements, functionally graded materials (FGMs), and antibacterial CaPs. We conclude by foreseeing the future of CaPs.

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

Because of the peculiarity of the bone microstructure, the uptake of chemotherapeutics often happens at non-targeted sites, which induces side effects. In order to solve this problem, we designed a bone-targeting drug delivery system that can release drug exclusively in the nidus of the bone. Alendronate (ALN), which has a high ability to target to hydroxyapatite, was used to fabricate double ALN-conjugated poly (ethylene glycol) 2000 material (ALN-PEG_2k-ALN). The ALN-PEG_2k-ALN was characterized using ¹H NMR and ³¹P NMR and FTIR. ALN-PEG_2k-ALN-modified calcium phosphate nanoparticles (APA-CPNPs) with an ALN targeting moiety and hydrophilic poly (ethylene glycol) arms tiled on the surface was prepared for bone-targeted drug delivery. The distribution of ALN-PEG_2k-ALN was tested by X-ray photoelectron spectroscopy. Isothermal titration calorimetry data indicated that similar to free ALN, both ALN-PEG_2k-ALN and APA-CPNPs can bind to calcium ions. The bone-binding ability of APA-CPNPs was verified via ex vivo imaging of bone fragments. An in vitro release experiment demonstrated that APA-CPNPs can release drug faster in an acid environment than a neutral environment. Cell viability experiments indicated that blank APA-CPNPs possessed excellent biocompatibility with normal cells. Methotrexate (MTX) loaded APA-CPNPs have the same ability to inhibit cancer cells as free drug at high concentrations, while they are slightly weaker at low concentrations. All of these experiments verified the prospective application of APA-CPNPs as a bone-targeting drug delivery system.

Dual-functionalisation of gelatine nanoparticles with an anticancer platinum(ii)–bisphosphonate complex and mineral-binding alendronate

Mineral-binding gelatine nanoparticles can be loaded with tailored amounts of anticancer molecules, which may benefit the development of bone-seeking carriers for targeted delivery of drugs to treat bone tumours.

Metalated nucleotide chemisorption on hydroxyapatite

The experiments here reported evidence on the importance of the residual charge of a nucleotide derivative, for the adsorption on nHAP (hydroxyapatite nanocrystals), in water solution. We found that the simple presence of phosphates on the nucleotide derivative does not guarantee adsorption on nHAP. On the other hand, we demonstrated that a cationic or neutral charge on a nucleotide derivative produces a strongly reduced chemical adsorption (chemisorption) whereas, in the presence of a net negative charge, relevant adsorption on nHAP is observed. The number of phosphates can only modulate the adsorption efficiency of a molecule provided that this latter bears an overall negative charge. The neutral zwitterionic nucleotide Pt(II) complexes, bearing negatively charged phosphates, are unable to give stable chemisorption. Previous considerations are important to model the binding ability of phosphate bearing nucleotide derivatives or molecules on hydroxyapatite. The findings reported in the present paper could be relevant in bone tissue targeting or nHAP mediated drug delivery.

Pros and cons of bifunctional platinum(IV) antitumor prodrugs: two are (not always) better than one

This article evaluates the efficacy and applicability of bifunctional prodrugs consisting of a six-coordinate Pt(iv) octahedral core and one or more bioactive molecules. The platinum(iv) complexes release upon reduction the corresponding cytotoxic Pt(ii) agents and the bioactive molecules, able to inhibit some biochemical mechanisms of cancer growth and/or prevent the deactivation of the Pt(ii) metabolites.

Anti-cancer applications of titanocene-functionalised nanostructured systems: an insight into cell death mechanisms

A series of alkenyl-substituted titanocene compounds have been supported on the mesoporous silica-based material KIT-6. The corresponding functionalised materials were completely characterised by different techniques (solid-state multinuclear NMR spectroscopy, IR spectroscopy, N2 adsorption-desorption isotherms, X-ray fluorescence and diffraction, SEM and TEM) to observe the incorporation of the titanocene derivatives on the external surface of the material KIT-6. Both the titanocene compounds and the materials were tested in vitro against a wide variety of human cancer and normal cell lines. A very high cytotoxicity of the synthesised titanocene derivatives (IC50 values in the range of those described in the literature for the most active cytotoxic titanocene compounds), with selectivity towards cancer cell lines was observed. The cytotoxic activity of the materials is the highest reported to date for titanocene-functionalised materials. In addition, higher Ti uptake (from 4 to 23% of the initial amount of Ti) of the cells treated with materials was observed with respect to those treated with "free" titanocene derivatives (which gave Ti uptake values from 0.4 to 4.6% of the initial amount of Ti). Additional experiments with the titanocene derivatives and the functionalised materials revealed that changes to the morphological and functional dynamics of apoptosis occurred when the active titanocene species were incorporated into mesoporous materials. In addition, the materials could induce programmed cell death in tumour cell populations by impairing the damaged DNA repair mechanisms and by upregulation of intrinsic and extrinsic apoptotic signalling pathways.

Enzyme-functionalized biomimetic apatites: concept and perspectives in view of innovative medical approaches

Biomimetic nanocrystalline calcium-deficient apatite compounds are particularly attractive for the setup of bioactive bone-repair scaffolds due to their high similarity to bone mineral in terms of chemical composition, structural and substructural features. As such, along with the increasingly appealing development of moderate temperature engineered routes for sample processing, they have widened the armamentarium of orthopedic and maxillofacial surgeons in the field of bone tissue engineering. This was made possible by exploiting the exceptional surface reactivity of biomimetic apatite nanocrystals, capable of easily exchanging ions or adsorbing (bio)molecules, thus leading to highly-versatile drug delivery systems. In this contribution we focus on the preparation of hybrid materials combining biomimetic nanocrystalline apatites and enzymes (lysozyme and subtilisin). This paper reports physico-chemical data as well as cytotoxicity evaluations towards Cal-72 osteoblast-like cells and finally antimicrobial assessments towards selected strains of interest in bone surgery. Biomimetic apatite/enzyme hybrids could be prepared in varying buffers. They were found to be non-cytotoxic toward osteoblastic cells and the enzymes retained their biological activity (e.g. bond cleavage or antibacterial properties) despite the immobilization and drying processes. Release properties were also examined. Beyond these illustrative examples, the concept of biomimetic apatites functionalized with enzymes is thus shown to be useable in practice, e.g. for antimicrobial purposes, thus widening possible therapeutic perspectives.

Cell surface receptor targeted biomimetic apatite nanocrystals for cancer therapy

Nanosized drug carriers functionalized with moieties specifically targeting tumor cells are promising tools in cancer therapy, due to their ability to circulate in the bloodstream for longer periods and their selectivity for tumor cells, enabling the sparing of healthy tissues. Because of its biocompatibility, high bioresorbability, and responsiveness to pH changes, synthetic biomimetic nanocrystalline apatites are used as nanocarriers to produce multifunctional nanoparticles, by coupling them with the chemotherapeutic drug doxorubicin (DOXO) and the DO-24 monoclonal antibody (mAb) directed against the Met/Hepatocyte Growth Factor receptor (Met/HGFR), which is over-expressed on different types of carcinomas and thus represents a useful tumor target. The chemical-physical features of the nanoparticles are fully investigated and their interaction with cells expressing (GTL-16 gastric carcinoma line) or not expressing (NIH-3T3 fibroblasts) the Met/HGFR is analyzed. Functionalized nanoparticles specifically bind to and are internalized in cells expressing the receptor (GTL-16) but not in the ones that do not express it (NIH-3T3). Moreover they discharge DOXO in the targeted GTL-16 cells that reach the nucleus and display cytotoxicity as assessed in an MTT assay. Two different types of ternary nanoparticles are prepared, differing for the sequence of the functionalization steps (adsorption of DOXO first and then mAb or vice versa), and it is found that the ones in which mAb is adsorbed first are more efficient under all the examined aspects (binding, internalization, cytotoxicity), possibly because of a better mAb orientation on the nanoparticle surface. These multifunctional nanoparticles could thus be useful instruments for targeted local or systemic drug delivery, allowing a reduction in the therapeutic dose of the drug and thus adverse side effects. Moreover, this work opens new perspectives in the use of nanocrystalline apatites as a new platform for theranostic applications in nanomedicine.

Preparation of core-shell poly(L-lactic) acid-nanocrystalline apatite hollow microspheres for bone repairing applications

In this paper, hybrid inorganic-organic core-shell hollow microspheres, made of poly(L-lactic acid) (PLLA) and biomimetic nano apatites (HA), were prepared from biodegradable and biocompatible substances, suitable for bone tissue applications. Preparation is started from Pickering emulsification, i.e., solid particle-stabilized emulsions in the absence of any molecular surfactant, where solid particles adsorbed to an oil-water interface. Stable oil-in-water emulsions were produced using biomimetic 20 nm sized HA nanocrystals as particulate emulsifier and a dichloromethane (CH(2)Cl(2)) solution of PLLA as oil phase. Hybrid hollow PLLA microspheres at three different HA nanocrystals surface coverage, ranging from 10 to 50 μm, were produced. The resulting materials were completely characterized with spectroscopic, calorimetric and microscopic techniques and the cytocompatibility was established by indirect contact tests with both fibroblasts and osteoblasts and direct contact with these latter. They displayed a high level of cytocompatibility and thus represent promising materials for drug delivery systems, cell carriers and scaffolds for regeneration of bone useful in the treatment of orthopaedic, maxillofacial and dental fields.

Dinuclear Pt(II)-bisphosphonate complexes: a scaffold for multinuclear or different oxidation state platinum drugs

Geminal bisphosphonates (BPs), used in the clinic for the treatment of hypercalcaemia and skeletal metastases, have been also exploited for promoting the specific accumulation of platinum antitumor drugs in bone tissue. In this work, the platinum dinuclear complex [{Pt(en)}(2)(μ-AHBP-H(2))](+) (1) (the carbon atom bridging the two phosphorous atoms carrying a 2-ammonioethyl and a hydroxyl group, AHBP-H(2)) has been used as scaffold for the synthesis of a Pt(II) trinuclear complex, [{Pt(en)}(3)(μ-AHBP)](+) (2), and a Pt(IV) adamantane-shaped dinuclear complex featuring an oxo-bridge, [{Pt(IV)(en)Cl}(2)(μ-O)(μ-AHBP-H(2))](+) (3) (X-ray structure). Compound 2 undergoes a reversible, pH dependent, rearrangement with a neat switch point around pH = 5.4. Compound 3 undergoes a one-step electrochemical reduction at E(pc) = -0.84 V affording compound 1. Such a potential is far lower than that of glutathione (-0.24 V), nevertheless compound 3 can undergo chemical reduction to 1 by GSH, most probably through a different (inner-sphere) mechanism. In vitro cytotoxicity of the new compounds, tested against murine glioma (C6) and human cervix (HeLa) and hepatoma (HepG2) cell lines, has shown that, while the Pt(IV) dimer 3 is inactive up to a concentration of 50 μM, the two Pt(II) polynuclear compounds 1 and 2 have a cytotoxicity comparable to that of cisplatin with the trinuclear complex 2 generally more active than the dinuclear complex 1.

Silica xerogels and hydroxyapatite nanocrystals for the local delivery of platinum-bisphosphonate complexes in the treatment of bone tumors: a mini-review

The present review focuses on the "drug targeting and delivery" approach of the selective transportation of cisplatin to bone tumors and bone metastases. This aim is realized by binding cisplatin to (bis)phosphonate ligands or their derivatives. Geminal bisphosphonates are in clinical use in the treatment of several bone-related diseases because of their high affinity for calcium ions and hence for bones. Platinum-bisphosphonate complexes may be easily loaded onto calcium-containing inorganic matrices, such as calcium-doped sol-gel derived silica xerogels and hydroxyapatite nanocrystals, for local administration at the site of the bone malignancy. The composites may be used as bone-filler materials that, in addition to their action as bone substitutes, can also act as controlled platinum-drug releasing agents. The release kinetics of the drug can be tailored for specific therapeutic applications modulating the physico-chemical features of the inorganic matrices. Moreover, apatite nanocrystals loaded with platinum-bisphosphonate prodrugs can be used as injectable material for nanomedical applications (e.g. intracellular drug delivery).

Coordination chemistry of Ca sites at the surface of nanosized hydroxyapatite: interaction with H₂O and CO

The affinity towards water of a selection of well-defined, nanostructured hydroxyapatite (HA) samples was investigated by H(2)O vapour adsorption microcalorimetry and infrared (IR) spectroscopy. A large hydrophilicity of all investigated materials was confirmed. The surface features of hydrated HA were investigated on the as-synthesized samples pre-treated in mild conditions at T=303 K, whereas dehydrated HA features were characterized on samples activated at T=573 K. The relatively large hydrophilicity of the hydrated surface (-Δ(ads)H~100-50 kJ mol(-1)) was due to the interaction of water with the highly polarized H(2)O molecules strongly coordinated to the surface Ca(2+) cations. At the dehydrated surface, exposing coordinatively unsaturated (cus) Ca(2+) cations, H(2)O was still molecularly adsorbed but more strongly (-Δ(ads)H~120-90 kJ mol(-1)). The use of CO adsorption to quantify the Lewis acidic strength of HA surface sites revealed only a moderate strength of cus Ca(2+) cations, as confirmed by both microcalorimetric and IR spectroscopic measurements and ab initio calculations. This result implies that the large HA/H(2)O interaction energy is due to the interplay between cus Ca(2+) sites and nearby hydrophilic PO(4) groups, not revealed by the CO probe. The lower density of cus Ca(2+) cations at the 573 K activated HA surface with respect to the pristine one did not affect the whole hydrophilicity of the surface, as the polarizing effect of Ca sites is so strong to extend up to the fourth hydrated layer, as confirmed by both high-coverage microcalorimetric and IR spectroscopic data. No specific effects due to the investigated specimen preparation method and/or different morphology were observed.

Nanocrystalline carbonate-apatites: role of Ca/P ratio on the upload and release of anticancer platinum bisphosphonates

In the present study two nanocrystalline apatites have been investigated as bone-specific drug delivery devices to be used for treatment of bone tumors either by local implantation or by injection. In order to assess how the Ca/P ratio can influence the adsorption and release of anticancer platinum-bisphosphonate complexes, two kinds of apatite nanocrystals having different Ca/P ratios but similar morphologies, degree of crystallinity, and surface areas have been synthesized and characterized. The two platinum-bisphosphonate complexes considered were the bis-{ethylenediamineplatinum(ii)}-2-amino-1-hydroxyethane-1,1-diyl-bisphosphonate and the bis-{ethylenediamineplatinum(ii)}medronate. The Ca/P ratio plays an important role in the adsorption as well as in the release of the two drugs. In fact, the apatite with a higher Ca/P ratio showed greater affinity for both platinum complexes. Also the chemical structure of the two Pt complexes appreciably affects their affinity towards as well as their release from the two kinds of apatites. In particular, the platinum complex whose bisphosphonate contains a free aminic group showed greater upload and smaller release. The cytotoxicity of the Pt complexes released from the apatite was tested against human cervical, colon, and lung cancer cells as well as against osteosarcoma cells. In agreement with previous work, the Pt complexes released were found to be more cytotoxic than the unmodified complexes.

Transplantable delivery systems for in situ controlled release of bisphosphonate in orthopedic therapy

IMPORTANCE OF THE FIELD

Bisphosphonates (BPs), structurally similar to pyrophosphates and functionally superior in restraining osteoclast-induced bone resorption, have been widely used as clinical drugs in the treatment of osteoporosis, bone voids and associated inflammation. However, owing to their high aqueous solubility and the consequently high rate of loss during oral administration, the loading and targeting of BPs pose major challenges in practice. Alternative delivery routes such as nasal, subcutaneous/intramuscular injection have contributed little to improving the bioavailiability and efficacy of BPs. To improve and optimize the delivery efficiency and efficacy of BPs, numerous strategies have been developed and adopted. Studies on controlled release of BPs provide important information on the fabrication of BP delivery systems for in situ treatment. As BPs play an important therapeutic role in osteoporosis and similar diseases, it has become essential and vital to survey various reported fabrication methodologies of these systems and the consequential orthopedic treatments so as to keep abreast with advances in their clinical use.

AREAS COVERED IN THIS REVIEW

Transplantable delivery systems for controlled release of BP are reviewed from literature published since 2000. The fabrication pathways and the release of BPs from various material systems are discussed in case studies. Recent progress in CaP models based on the strong and specific chelation between BPs and calcium phosphate crystals is highlighted.

WHAT THE READER WILL GAIN

This review offers an outline of the advances in BP controlled release and delivery systems for orthopedic therapy.

TAKE HOME MESSAGE

Understanding the cutting-edge BP controlled release and delivery systems for in situ treatment is key to the successful design of a more promising and perfect delivery system for orthopedic therapy. Moreover, developing such delivery systems incorporating the numerous advantages of BPs and controlled release environment requires substantially more flexible models to control better the fate of BP drugs.