Synthesis and preliminary anticancer evaluation of photo-responsive prodrugs of hydroxymethylene bisphosphonate alendronate

The antitumoral activity of hydroxymethylene bisphosphonates (HMBP) such as alendronate or zoledronate is hampered by their exceptional bone-binding properties and their short plasmatic half-life which preclude their accumulation in non-skeletal tumors. In this context, the use of lipophilic prodrugs represents a simple and straightforward strategy to enhance the biodistribution of bisphosphonates in these tissues. We describe in this article the synthesis of light-responsive prodrugs of HMBP alendronate. These prodrugs include lipophilic photo-removable nitroveratryl groups which partially mask the highly polar alendronate HMBP scaffold. Photo-responsive prodrugs of alendronate are stable in physiological conditions and display reduced toxicity compared to alendronate against MDA-MB-231 cancer cells. However, the antiproliferative effect of these prodrugs is efficiently restored after cleavage of their nitroveratryl groups upon exposure to UV light. In addition, substitution of alendronate with such photo-responsive substituents drastically reduces its bone-binding properties, thereby potentially improving its biodistribution in soft tissues after i.v. administration. The development of such lipophilic photo-responsive prodrugs is a promising approach to fully exploit the anticancer effect of HMBPs on non-skeletal tumors.

α-Amino bisphosphonate triazoles serve as GGDPS inhibitors

Depletion of cellular levels of geranylgeranyl diphosphate by inhibition of the enzyme geranylgeranyl diphosphate synthase (GGDPS) is a potential strategy for disruption of protein transport by limiting the geranylgeranylation of the Rab proteins that regulate intracellular trafficking. As such, there is interest in the development of GGDPS inhibitors for the treatment of malignancies characterized by abnormal protein production, including multiple myeloma. Our previous work has explored the structure-function relationship of a series of isoprenoid triazole bisphosphonate-based GGDPS inhibitors, with modifications having impact on enzymatic, cellular and in vivo activities. We have synthesized a new series of α-amino bisphosphonates to understand the impact of modifying the alpha position with a moiety that is potentially linkable to other agents. Bioassays evaluating the enzymatic and cellular activities of these compounds demonstrate that incorporation of the α-amino group affords compounds with GGDPS inhibitory activity which is modulated by isoprenoid tail chain length and olefin stereochemistry. These studies provide further insight into the complexity of the structure-function relationship and will enable future efforts focused on tumor-specific drug delivery.

Structural Diversity in Antiosteolytic Bisphosphonates: Deciphering Structure-Activity Trends in Ultra Long Controlled Release Phenomena

Bisphosphonate (BP)-based treatments have been extensively prescribed for bone-related conditions, particularly for osteoporosis. Their low bioavailability creates the need for prescribed dosage increase to reach therapeutic levels but generates a plethora of undesirable side effects. A viable approach to alleviating these issues is to design and exploit controlled release strategies. Herein, the controlled release profiles of 15 structurally characterized BPs (actual drugs and structural analogs) were thoroughly studied from tablets containing three (cellulose, lactose, and silica) or two (cellulose, and silica) excipients in human stomach-simulated pH conditions. The BPs were of two types, alkyl-BPs and amino-BPs. Alkyl-BPs included four derivatives of etidronate (acid, disodium, tetra-sodium, and monopotassium forms), medronic acid, and three analogs of etidronate, in which the -CH3 group was replaced by the moieties -H, -CH2CH2CH3, and -CH2CH2CH2CH2CH3. Amino-BPs included the commercial drugs pamidronate, alendronate, neridronate, and ibandronate, as well as three analog compounds. Release curves were constructed based on data taken from 1H NMR peak integration and were expressed as "% BP release" vs time. The controlled release profiles (initial release rate, plateau value, etc.) were correlated with certain structural features (number of hydrogen and metal-oxygen bonds), showing that the molecular and crystal lattice features of each BP profoundly influence its release characteristics. It was concluded that for all BPs, in general, the initial rate became lower as the total number of lattice interactions increased. For the alkyl-BPs elongation of the alkyl side chain seems to decelerate the release. Amino-BPs, in general, show slower release than the alkyl-BPs. No adverse effects of alkyl- and amino-BP drugs on NIH3T3 cell viability were noted.

A Facile Crystallization Strategy to Turn Calcium Bisphosphonates into Novel Osteogenesis-Inducing Biomaterials

Insoluble metal bisphosphonates (BPs) are considered an ideal alternative to the soluble counterparts in regenerative medicine due to their increased BP release profile, but still present undesired properties (e.g., low stability, uncontrolled degradation, and poor biocompatibility). Through a simple crystallization on a solid calcium hydroxyapatite (HA)-based substrate from a BP precursor solution in 30 days, a series of insoluble calcium BP (CaBP) crystals are developed. These crystals, including calcium alendronate (CaAln), calcium pamidronate (CaPam), calcium incadronate (CaInc), calcium risedronate (CaRis), calcium zoledronate (CaZol), and calcium di-minodronate (Ca(Min)2 ), present high purity, regular morphologies and excellent biodegradability. It is demonstrated that these CaBPs can induce osteogenic differentiation of adipose-derived mesenchymal stem cells in vitro in the absence of other osteogenic inducers. It is further found that CaBP induces bone formation more effectively in a femur defect rabbit model in three months but with a lower in vivo hematotoxicity than the clinically used HA during osteogenesis. It is believed that these desired biological properties arise from the capability of the insoluble CaBPs in releasing BPs in a sustained manner for stimulating osteogenesis. This work provides a significant strategy for turning CaBPs into novel biomaterials for tissue regeneration and demonstrates their great potential in the clinic.

A bifunctional zoledronate sustained-release system in scaffold: Tumor therapy and bone repair

It is of great challenges to repair bone defect and prevent tumor recurrence in bone tumors postoperative treatment. Bone scaffolds loaded with zoledronate (ZOL) are expected to solve these issues due to its osteogenesis and anti-tumor ability. Furthermore, ZOL needs to be sustained release to meet the requirement of long-term therapy. In this study, ZOL was loaded into amination functionalized mesoporous silicon (SBA15NH₂), and then incorporated into poly (L-lactic acid) to prepare PLLA/SBA15NH₂-ZOL scaffold via selective laser sintering technology. On one hand, ZOL of local release not only can inhibit growth and proliferation of bone tumor cells but also inhibit osteoclast differentiation through competitive binding of receptor activator of nuclear factor (NF)-kB (RANK) in osteoclast precursors. On the other hand, amination function could change the surface charge of mesoporous silica to positive charge to enhance the absorption of ZOL, mesoporous structure and abundant amino groups of SBA15NH₂ play a barrier role and form hydrogen bond with phosphate groups of ZOL, respectively, thereby achieving its sustained release. The results showed that the loading amount of ZOL was 236.53 mg/g, and the scaffold could sustainedly release ZOL for more than 6 weeks. The scaffold inhibited proliferation of osteosarcoma cells through inducing apoptosis and cell cycle arrest. TRAP staining and F-actin ring formation experiment showed the scaffold inhibited differentiation and mature of osteoclast. Pit formation assay indicated that bone resorption activity was inhibited strongly.

Drug-Inclusive Inorganic–Organic Hybrid Systems for the Controlled Release of the Osteoporosis Drug Zoledronate

Bisphosphonates (BPs) are common pharmaceutical treatments used for calcium- and bone-related disorders, the principal one being osteoporosis. Their antiresorptive action is related to their high affinity for hydroxyapatite, the main inorganic substituent of bone. On the other hand, the phosphonate groups on their backbone make them excellent ligands for metal ions. The combination of these properties finds potential application in the utilization of such systems as controlled drug release systems (CRSs). In this work, the third generation BP drug zoledronate (ZOL) was combined with alkaline earth metal ions (e.g., Sr²⁺ and Ba²⁺) in an effort to synthesize new materials. These metal–ZOL compounds can operate as CRSs when exposed to appropriate experimental conditions, such as the low pH of the human stomach, thus releasing the active drug ZOL. CRS networks containing Sr²⁺ or Ba² and ZOL were physicochemically and structurally characterized and were evaluated for their ability to release the free ZOL drug during an acid-driven hydrolysis process. Various release and kinetic parameters were determined, such as initial rates and release plateau values. Based on the drug release results of this study, there was an attempt to correlate the ZOL release efficiency with the structural features of these CRSs.

Bisphosphonates as Potential Inhibitors of Calcification in Bioprosthetic Heart Valves (Review)

As early as 50 years ago, bisphosphonates turned from a water treatment agent into one of the most widely used groups of drugs for the treatment of various diseases of calcium metabolism (bone tissue resorption, oncological complications of neurodegenerative diseases and others). Years of research on bisphosphonates have contributed to the understanding of their molecular and cellular pathways of their action. All bisphosphonates have a similar structure and common properties, however, there are obvious chemical, biochemical, and pharmacological differences between them. Each bisphosphonate has its own unique profile. This review summarizes data on the mechanisms of action of bisphosphonates, demonstrates the experience and prospects for their use for the modification of cardiovascular bioprostheses, since the issue of preventing bisphosphonate calcification has not been settled yet.

Structure-activity relationships of pyrimidine nucleotides containing a 5'-α,β-methylene diphosphonate at the P2Y6 receptor

The Gq-coupled P2Y6 receptor (P2Y6R) is a component of the purinergic signaling system and functions in inflammatory, cardiovascular and metabolic processes. UDP, the native P2Y6R agonist and P2Y14R partial agonist, is subject to hydrolysis by ectonucleotidases. Therefore, we have synthesized UDP/CDP analogues containing a stabilizing α,β-methylene bridge as P2Y6R agonists and identified compatible affinity-enhancing pyrimidine modifications. A distal binding region on the receptor was explored with 4-benzyloxyimino cytidine 5'-diphosphate analogues and their potency determined in a calcium mobilization assay. A 4-trifluoromethyl-benzyloxyimino substituent in 25 provided the highest human P2Y6R potency (MRS4554, 0.57 µM), and a 5-fluoro substitution of the cytosine ring in 28 similarly enhanced potency, with >175- and 39-fold selectivity over human P2Y14R, respectively. However, 3-alkyl (31-33, 37, 38), β-d-arabinofuranose (39) and 6-aza (40) substitution prevented P2Y6R activation. Thus, we have identified new α,β-methylene bridged N4-extended CDP analogues as P2Y6R agonists that are highly selective over the P2Y14R.

[68Ga]Ga-THP-Pam: A Bisphosphonate PET Tracer with Facile Radiolabeling and Broad Calcium Mineral Affinity

Calcium minerals such as hydroxyapatite (HAp) can be detected noninvasively in vivo using nuclear imaging agents such as [18F]NaF (available from cyclotrons), for positron emission tomography (PET) and 99mTc-radiolabeled bisphosphonates (BP; available from 99mTc generators for single photon emission computed tomography (SPECT) or scintigraphy). These two types of imaging agents allow detection of bone metastases (based on the presence of HAp) and vascular calcification lesions (that contain HAp and other calcium minerals). With the aim of developing a cyclotron-independent PET radiotracer for these lesions, with broad calcium mineral affinity and simple one-step radiolabeling, we developed [68Ga]Ga-THP-Pam. Radiolabeling with 68Ga is achieved using a mild single-step kit (5 min, room temperature, pH 7) to high radiochemical yield and purity (>95%). NMR studies demonstrate that Ga binds via the THP chelator, leaving the BP free to bind to its biological target. [68Ga]Ga-THP-Pam shows high stability in human serum. The calcium mineral binding of [68Ga]Ga-THP-Pam was compared in vitro to two other 68Ga-BPs which have been successfully evaluated in humans, [68Ga]Ga-NO2APBP and [68Ga]Ga-BPAMD, as well as [18F]NaF. Interestingly, we found that all 68Ga-BPs have a high affinity for a broad range of calcium minerals implicated in vascular calcification disease, while [18F]NaF is selective for HAp. Using healthy young mice as a model of metabolically active growing calcium mineral in vivo, we compared the pharmacokinetics and biodistribution of [68Ga]Ga-THP-Pam with [18F]NaF as well as [68Ga]NO2APBP. These studies revealed that [68Ga]Ga-THP-Pam has high in vivo affinity for bone tissue (high bone/muscle and bone/blood ratios) and fast blood clearance (t1/2 < 10 min) comparable to both [68Ga]NO2APBP and [18F]NaF. Overall, [68Ga]Ga-THP-Pam shows high potential for clinical translation as a cyclotron-independent calcium mineral PET radiotracer, with simple and efficient radiochemistry that can be easily implemented in any radiopharmacy.

Effect of nitrogen-containing bisphosphonates on osteoclasts and osteoclastogenesis: an ultrastructural study

We have previously indicated that a single injection of alendronate, one of the nitrogen-containing bisphosphonates (NBPs), affects murine hematopoietic processes, such as the shift of erythropoiesis from bone marrow (BM) to spleen, disappearance of BM-resident macrophages, the increase of granulopoiesis in BM and an increase in the number of osteoclasts. NBPs induce apoptosis and the formation of giant osteoclasts in vitro and/or in patients undergoing long-term NBP treatment. Therefore, the time-kinetic effect of NBPs on osteoclasts needs to be clarified. In this study, we examined the effect of alendronate on mouse osteoclasts and osteoclastogenesis. One day after the treatment, osteoclasts lost the clear zone and ruffled borders, and the cell size decreased. After 2 days, the cytoplasm of osteoclasts became electron dense and the nuclei became pyknotic. Some of the cells had fragmented nuclei. After 4 days, osteoclasts had euchromatic nuclei attached to the bone surface. Osteoclasts had no clear zones or ruffled borders. After 7 days, osteoclasts formed giant osteoclasts via the fusion of multinuclear and mononuclear osteoclasts. These results indicate that NBPs affect osteoclasts and osteoclastogenesis via two different mechanisms.

Nonbisphosphonate inhibitors of Plasmodium falciparum FPPS/GGPPS

A series of novel thiazole-containing amides were synthesized. A structure-activity relationship study of these compounds led to the identification of potent and selective PfFPPS/GGPPS inhibitors with good in vitro ADME profiles. The most promising candidate molecules were progressed to mouse in vivo PK studies and demonstrated adequate free drug exposure to warrant further investigation.

Mannose-Functionalized Biodegradable Nanoparticles Efficiently Deliver DNA Vaccine and Promote Anti-tumor Immunity

Cancer vaccines have attracted increasing attention for their application in tumor immunotherapy. DNA vaccines are one of them that have been proven very promising with the advantages of safety, rapid design, and low cost. However, the low stability, ineffective cell internalization, and low immunostimulation hinder their wide application. Thus, developing targeted and safe systems to effectively deliver DNA vaccines becomes a vital step. In this study, we report the development of mannose- and bisphosphonate (BP)-modified calcium phosphate (CP) nanoparticles (NPs) as efficient vaccine delivery vehicles by targeting C-type lectin receptors (CLRs) on antigen-presenting cells (APCs). Using a model antigen ovalbumin (OVA)-encoded plasmid DNA (pOVA) as a model vaccine, we demonstrate that mannose-modified and BP-stabilized CP (MBCP) nanoparticles are mono-dispersed for enhanced uptake by APCs and subsequently induce OVA antigen presentation and immunostimulation. Mice immunized with MBCP-pOVA nanovaccines show a significantly stronger anti-OVA antibody response with a quicker IgG1 and IgG2a antibody production than unmodified NPs. Moreover, MBCP-pOVA immunization significantly inhibits the growth of OVA-expressing E.G7 tumor cells in C57BL/6J mice. Our data collectively suggest that the modifications to enhance the stability and targeting ability of MBCP NPs are essential for effective delivery of DNA vaccines and promote robust anti-tumor immunity.

In silico exploration of binding of selected bisphosphonate derivatives to placental alkaline phosphatase via docking and molecular dynamics

Bisphosphonates constitute a group of pyrophosphate analogues therapeutically active against bone diseases. Numerous studies confirm their anticancer and antimetastatic potential as well as ability to relieve pathological pain. Although this is a known class of compounds, many aspects of their action remain unexplained and their new interaction partners are still being discovered. Due to the structural similarity to pyrophosphate, their interaction with pyrophosphate-recognizing enzymes seems to be feasible. In current work, the placental alkaline phosphatase (PLAP) is considered as a potential target for these class of compounds. PLAP is one of the enzymes responsible for degradation of pyrophosphate with high clinical significance. An elevation of PLAP level are considered as a potential cancer marker. An in silico study of complexes formed between selected phosphate derivatives and PLAP was performed. It indicates that all tested compounds: alendronic acid, clodronic acid, etidronic acid, zoledronic acid, imidodiphosphoric acid, pyrophosphoric acid, medronic acid, chloromethylenediphosphonic acid and hypophosphoric acid form a complexes with PLAP, stabilized by hydrogen bonds, hydrophobic and van der Waals interactions. Zoledronic acid, drug used in prevention of bone complications during cancer treatment was found to have the lowest estimated energy of binding (-6.6 kcal/mol). In silico study yielded very low energy of binding also for hypophosphate, equal -6.4 kcal/mol, despite having no identified hydrogen bonds. Subsequent molecular dynamic simulations, followed by molecular mechanics generalized-born surface area with pairwise decomposition calculations confirmed the stability of protein-ligand complexes. The results indicate that selected phosphate derivatives may potentially interact with the enzyme, changing its function, what should be investigated during in vitro studies.

Bisphosphonate-based surface biofunctionalization improves titanium biocompatibility

Novel-biofunctionalized surfaces are required to improve the performance of endosseous implants, which are mainly related to the resistance against biocorrosion, as well as for the consideration of osteoinductive phenomena. Among different strategies, the use of bisphosphonate molecules as linkers between titanium dioxide (TiO₂) surfaces and proteins is a distinctive approach, one in which bisphosphonate could play a role in the osseointegration. Thus, to address this issue, we proposed a novel biofunctionalization of TiO₂ surfaces using sodium alendronate (ALN) as a linker and bovine serum albumin as the protein. Physicochemical analysis of the functionalized surfaces was performed using contact angle analyses and surface roughness measurements, which indicated an efficient functionalization. The biocompatibility of the functionalized surfaces was analyzed through the adhesion behavior of the pre-osteoblasts onto the samples. Overall, our data showed a significant improvement concerning the cell adhesion by modulating the adhesion cell-related set of genes. The obtained results show that for modified surfaces there is an increase of up to 100 times in the percentage of cells adhered when compared to the control, besides the extracellular matrix remodeling seemed to be an essential prerequisite for the early stages of cell adhesion on to the biomaterials, which was assayed by evaluating the matrix metalloproteinase activities as well as the gene activations. In the expressions of the Bsp and Bglap2 genes, for the group containing ALN (TiO₂ + ALN), it was observed an increase in expression (approximately sixfold change) when compared to the control. Altogether, our data clearly showed that the bisphosphonate-biofunctionalized surface enhanced the biocompatibility of titanium and claims to further progress preclinical in vivo experimentation.

Empowering the Medicinal Applications of Bisphosphonates by Unveiling their Synthesis Details

Bisphosphonates (BPs), well-known medicinal compounds used for osteoporosis management, are currently the target of intensive research, from basic pre-formulation studies to more advanced stages of clinical practice. The high demand by the pharmaceutical industry inherently requires an easy, efficient and quick preparation of BPs. Current synthetic procedures are, however, still far from ideal. This work presents a comprehensive compilation of reports on the synthesis of the commercially available bisphosphonates that are pharmaceutical active ingredients. Current limitations to the conventional synthesis are assessed, and paths towards their improvement are described, either through the use of alternative solvents and/or by selecting appropriate ratios of the reactants. Innovative processes, such as microwave-assisted synthesis, are presented as more environmental-friendly and effective methods. The main advantages and setbacks of all syntheses are provided as a way to clarify and promote the development of simpler and improved procedures. Only in this way one will be able to efficiently respond to the future high demand of BPs, mostly due to the increase in life span in occidental countries.

Surface design of photon-upconversion nanoparticles for high-contrast immunocytochemistry

Immunohistochemistry (IHC) and immunocytochemistry (ICC) are routinely employed for the microscopic identification and diagnosis of cancerous cells in histological tissues and cell cultures. The maximally attainable contrast of conventional histological staining techniques, however, is low. While the anti-Stokes emission of photon-upconversion nanoparticles (UCNP) can efficiently eliminate optical background interference, excluding non-specific interactions of the label with the histological sample is equally important for specific immunolabeling. To address both requirements, we have designed and characterized several UCNP-based nanoconjugates as labels for the highly specific detection of the cancer biomarker HER2 on various breast cancer cell lines. An optimized streptavidin-PEG-neridronate-UCNP conjugate provided an unsurpassed signal-to-background ratio of 319, which was 50-fold better than conventional fluorescent labeling under the same experimental conditions. In combination, the absence of optical interference and non-specific binding lays the foundation for computer-based data evaluation in digital pathology.

Potentiating bisphosphonate-based coordination complexes to treat osteolytic metastases

The hydrothermal reaction between bioactive metal (Ca2+, Zn2+, and Mg2+) salts and a clinically utilized bisphosphonate, alendronate (ALEN), promotes the formation of several materials denominated as bisphosphonate-based coordination complexes (BPCCs). The systematic exploration of the effect of three variables, M2+/ALEN molar ratio, temperature, and pH, on the reaction yielded an unprecedented number of materials of enough crystal quality for structural elucidation. Five crystal structures were unveiled by single crystal X-ray diffraction (ALEN-Ca forms I and II, ALEN-Zn forms I and II, and ALEN-Mg) and their solid-state properties revealed in tandem with other techniques. The dissolution of these BPCCs was tested and contrasted to that of the commercially employed generic form of Fosamax® Alendronate Sodium, using fasted-state simulated gastric fluid and phosphate-buffered saline solution. Quantification of ALEN content was performed by derivatization with Cu2+, which produced a soluble complex suitable for quantification. The results show that these materials present a pH-dependent degradation. Moreover, a phase inversion temperature (PIT) nano-emulsion method was applied to the synthesis of ALEN-Ca form II. Size distribution analysis demonstrated the efficiency of the PIT-nano-emulsion method to decrease the particle size of this BPCC from ∼60 μm to ∼438 d nm. The cytotoxicity of ALEN, ALEN-Ca form II (bulk crystals), and nano-Ca@ALEN (nanocrystals) against the MDA-MB-231 cell line was investigated. Nano-Ca@ALEN form II presents higher cytotoxicity effects than ALEN and ALEN-Ca form II (bulk crystals), showing inhibition of cell proliferation at 7.5 μM. These results provide evidence of the structure, stability, dissolution and cytotoxicity properties of ALEN-based BPCCs and pave the way for better formulation strategies for this drug through the design of nano-sized BPCCs for the treatment of bone-related diseases.

Metal-Organic Framework Nanoparticles for Ameliorating Breast Cancer-Associated Osteolysis

Breast cancer metastases to bone poses a significant challenge for the administration of treatment strategies. The bone microenvironment, metastatic tumor cells, osteoclasts, and tumor-associated macrophages (TAMs) all play crucial and synergistic roles in creating a favorable environment for the proliferation, progression, and survival of the metastatic tumor, which in turn induces osteoclast-mediated bone destruction. In this study, we functionalized immunostimulatory cytosine-phosphate-guanosine (CpG)-loaded metal-organic framework (MOF) nanoparticles with bone targeting capabilities by surface modification with FDA approved antiresorptive bisphosphonate, zoledronic acid (ZOL). The functionalized bone targeting immunostimulatory MOF (BT-isMOF) nanoparticles demonstrates strong binding to calcium phosphate in vitro and exhibits specific targeting and accumulation in bone tissues in vivo. In vitro cellular and biochemical analyses demonstrated that the BT-isMOF nanoparticles could potently inhibit osteoclast formation and concomitantly induce macrophages polarization toward the M1 pro-inflammatory phenotype. Finally, using the intratibial murine model of breast cancer bone metastasis, we showed that the administration of BT-isMOF nanoparticles significantly suppressed osteoclast-mediated bone destruction and enhanced polarization of tumor-resident macrophages to M1 phenotype. Together, our data provides promising evidence for the potential therapeutic application of the BT-isMOF nanoparticles in the treatment of breast cancer bone metastases.

Quantification evaluation of 99mTc-MDP concentration in the lumbar spine with SPECT/CT: compare with bone mineral density

BACKGROUND

Despite recent technological advances allowing for quantitative single-photon emission computed tomography (SPECT), quantitative SPECT has not been widely used in the clinical practice of osteoporosis. The aim of this study is to evaluate the feasibility of quantitative bone SPECT/CT for measuring lumbar standard uptake value (SUV) in patients with different bone-mineral density (BMD), and investigate the correlation between SUV measured with ^99mTc-methylene diphosphonate (MDP) SPECT/CT and BMD assessment by dual-energy X-ray absorptiometry (DXA).

METHODS

A retrospective analysis of 62 cases ^99mTc-MDP whole-body bone imaging and local lumbar SPECT/CT tomography were performed. According to the results of dual-energy X-ray bone density examination, they were divided into normal group, osteopenic group, and osteoporosis group. The raw SPECT data were reconstructed using flash3D which includes attenuation correction, scatter compensation, and collimator resolution recovery, SPECT images from this algorithm were calibrated for SUV analysis. Comparing difference of lumbar SUV in different BMD subjects, and investigating the correlation between lumbar SUV and BMD. Data were analyzed by one-way ANOVA and Pearson regression analysis using SPSS 17.0 software.

RESULTS

The maximum SUV (SUV_max) and mean SUV (SUV_mean) of L1-L4 vertebral in 62 subjects were 7.39 ± 1.84 and 4.90 ± 1.27, respectively. The average BMD was 0.85 ± 0.15 (g/cm²), and the average CT value was 145.88 ± 53.99 (HU). The SUV_max, SUV_mean, BMD, and CT values of the lumbar spine were statistically significantly different among the three groups (F = 24.089, 30.501, 94.847, 30.241, all p < 0.001), and the osteopenic group was significantly lower than the normal group (all p < 0.001), the osteoporosis group was significantly lower than the normal group and the osteopenic group (all p < 0.001). Lumbar SUV_max, SUV_mean, and BMD were significantly negatively correlated with age (r = - 0.328 to - 0.442, all p < 0.05), and positively correlated with body weight and CT value (r = 0.299-0.737, all p < 0.05), but no significant correlation with height (r = 0.006-0.175, all p > 0.05). Lumbar SUV_max and SUV_mean increased significantly with the increase of BMD (r = 0.638, 0.632, p < 0.001).

CONCLUSION

The SUV of lumbar spine in ^99mTc-MDP bone SPECT/CT was significantly different among subjects with different BMD, and the SUV was positively correlated with BMD. These findings justify that quantitative bone SPECT/CT is an applicable tool for clinical quantification of bone metabolism in osteoporosis patients.

Alkaline Earth Metal-Organic Frameworks with Tailorable Ion Release: A Path for Supporting Biomineralization

An innovative application of metal-organic frameworks (MOFs) is in biomedical materials. To treat bone demineralization, which is a hallmark of osteoporosis, biocompatible MOFs (bioMOFs) have been proposed in which various components, such as alkaline-earth cations and bisphosphonate molecules, can be delivered to maintain normal bone density. Multicomponent bioMOFs that release several components simultaneously at a controlled rate thus offer an attractive solution. We report two new bioMOFs, comprising strontium and calcium ions linked by p-xylylenebisphosphonate molecules that release these three components and display no cytotoxic effects on human osteosarcoma cells. Varying the Sr²⁺/Ca²⁺ ratio in these bioMOFs causes the rate of ions dissolving into simulated body fluid to be unique; along with the ability to adsorb proteins, this property is crucial for future efforts in drug-release control and promotion of mineral formation. The one-pot synthesis of these bioMOFs demonstrates the utility of MOF design strategies.

Novel bisphosphonate compound FYB-931 preferentially inhibits aortic calcification in vitamin D3-treated rats

In patients with chronic kidney disease (CKD) or those undergoing hemodialysis, pathological calcific deposition known as ectopic calcification occurs in soft tissue, resulting in a life-threatening disorder. A potent and effective inhibitor of ectopic calcification is eagerly expected. In the current study, the effects of FYB-931, a novel bisphosphonate compound synthesized for the prevention of ectopic calcification, were compared with those of etidronate using both in vitro and in vivo models. In vitro, FYB-931 inhibited calcification of human aortic smooth muscle cells induced by high phosphate medium in a concentration-dependent manner, and the effect was slightly more potent than that of etidronate. In vivo, rats were administered with three subcutaneous injections of vitamin D3 to induce vascular calcification, and were given FYB-931 (1.5, 5, or 10 mg/kg) or etidronate (9, 30, or 60 mg/kg) orally once daily for 14 days. The increased aortic phosphorus content as an index of vascular calcification was inhibited by both FYB-931 and etidronate in a dose-dependent manner; however, FYB-931 was 10 times more potent than etidronate. FYB-931 inhibited serum tartrate-resistant acid phosphatase (TRACP) activity as a bone resorption marker 5.2 times more potently than etidronate. FYB-931, but not etidronate, significantly decreased serum phosphorus levels. The preferential inhibition of aortic calcification by FYB-931 suggested that possible additional effect including a decline in serum phosphorus may lead to an advantage in terms of its efficacy.

Composite Membranes of Poly(ε-caprolactone) with Bisphosphonate-Loaded Bioactive Glasses for Potential Bone Tissue Engineering Applications

Poly(ε-caprolactone) (PCL) is a bioresorbable synthetic polyester with numerous biomedical applications. PCL membranes show great potential in guided tissue regeneration because they are biocompatible, occlusive and space maintaining, but lack osteoconductivity. Therefore, two different types of mesoporous bioactive glasses (SiO2-CaO-P2O5 and SiO2-SrO-P2O5) were synthesized and incorporated in PCL thin membranes by spin coating. To enhance the osteogenic effect of resulting membranes, the bioglasses were loaded with the bisphosphonate drug ibandronate prior to their incorporation in the polymeric matrix. The effect of the composition of the bioglasses as well as the presence of absorbed ibandronate on the physicochemical, cell attachment and differentiation properties of the PCL membranes was evaluated. Both fillers led to a decrease of the crystallinity of PCL, along with an increase in its hydrophilicity and a noticeable increase in its bioactivity. Bioactivity was further increased in the presence of a Sr substituted bioglass loaded with ibandronate. The membranes exhibited excellent biocompatibility upon estimation of their cytotoxicity on Wharton's Jelly Mesenchymal Stromal Cells (WJ-SCs), while they presented higher osteogenic potential in comparison with neat PCL after WJ-SCs induced differentiation towards bone cells, which was enhanced by a possible synergistic effect of Sr and ibandronate.

[Osteoporosis and chronic kidney disease: review and new therapeutic strategies]

Osteoporosis affects a segment of the population in which Chronic Kidney Disease is also greatly represented. Nephropathic patients may present peculiar biochemical abnormalities related to Chronic Kidney Disease, defining the Mineral and Bone Disorder. This kind of anomalies, in the worst scenarios, configure the typical histomorphology patterns of Renal Osteodystrophy. Scientific Societies of Endocrinology have established therapy guidelines for patients with osteoporosis only based on the glomerular filtration rate and recommend avoiding the use of some drugs for the more advanced classes of nephropathy. However, there is no clear therapeutic approach for patients with advanced nephropathy and bone abnormalities. In this paper we propose a systematic review of the literature and present our proposal for managing patients with advanced nephropathy, based on eGFR and on presence of Mineral and Bone Disorder.

Synthesis and modification of uniform PEG-neridronate-modified magnetic nanoparticles determines prolonged blood circulation and biodistribution in a mouse preclinical model

Magnetite (Fe3O4) nanoparticles with uniform sizes of 10, 20, and 31 nm were prepared by thermal decomposition of Fe(III) oleate or mandelate in a high-boiling point solvent (>320 °C). To render the particles with hydrophilic and antifouling properties, their surface was coated with a PEG-containing bisphosphonate anchoring group. The PEGylated particles were characterized by a range of physicochemical methods, including dynamic light scattering, transmission electron microscopy, thermogravimetric analysis, Fourier transform infrared spectroscopy, and magnetization measurements. As the particle size increased from 10 to 31 nm, the amount of PEG coating decreased from 28.5 to 9 wt.%. The PEG formed a dense brush-like shell on the particle surface, which prevented particles from aggregating in water and PBS (pH 7.4) and maximized the circulation time in vivo. Magnetic resonance relaxometry confirmed that the PEG-modified Fe3O4 nanoparticles had high relaxivity, which increased with increasing particle size. In the in vivo experiments in a mouse model, the particles provided visible contrast enhancement in the magnetic resonance images. Almost 70% of administrated 20-nm magnetic nanoparticles still circulated in the blood stream after four hours; however, their retention in the tumor was rather low, which was likely due to the antifouling properties of PEG.

Non-Viral Delivery System and Targeted Bone Disease Therapy

Skeletal systems provide support, movement, and protection to the human body. It can be affected by several life suffering bone disorders such as osteoporosis, osteoarthritis, and bone cancers. It is not an easy job to treat bone disorders because of avascular cartilage regions. Treatment with non-specific drug delivery must utilize high doses of systemic administration, which may result in toxicities in non-skeletal tissues and low therapeutic efficacy. Therefore, in order to overcome such limitations, developments in targeted delivery systems are urgently needed. Although the idea of a general targeted delivery system using bone targeting moieties like bisphosphonates, tetracycline, and calcium phosphates emerged a few decades ago, identification of carrier systems like viral and non-viral vectors is a recent approach. Viral vectors have high transfection efficiency but are limited by inducing immunogenicity and oncogenicity. Although non-viral vectors possess low transfection efficiency they are comparatively safe. A number of non-viral vectors including cationic lipids, cationic polymers, and cationic peptides have been developed and used for targeted delivery of DNA, RNA, and drugs to bone tissues or cells with successful consequences. Here we mainly discuss such various non-viral delivery systems with respect to their mechanisms and applications in the specific targeting of bone tissues or cells. Moreover, we discuss possible therapeutic agents that can be delivered against various bone related disorders.

A Carboxyl-Terminated Dendrimer Enables Osteolytic Lesion Targeting and Photothermal Ablation of Malignant Bone Tumors

Malignant bone tumor accompanied by tumor-associated osteolysis remains a challenging task in clinical practice. Nanomedicines engineered with bone-targeting ligands, such as alendronate and pamidronate, are developed for targeted delivery of therapeutic agents to bone tumors. However, these targeting strategies usually show relatively poor selectivity toward the healthy skeletons and the osteolytic lesions because of the high binding affinity of bisphosphonates with all the bone tissues. Here, we reported a carboxyl-terminated dendrimer as the candidate to preferentially deliver therapeutic nanoparticles to the osteolytic lesions in a malignant bone tumor model. The high density of carboxyl groups on dendrimer surface endow the polymer with natural bone-binding capability. The dendrimer encapsulated with platinum nanoparticle predominantly accumulates at the osteolytic lesions around bone tumors rather than at healthy bone tissues in vivo. The therapeutic experiments reveal that the dendrimer-mediated photothermal therapy efficiently suppresses bone tumors and osteolysis, and the anionic polymer exhibits minimal cytotoxicity and hematologic toxicity. The results suggest that the carboxyl-terminated dendrimer is a promising candidate for selective delivery of therapeutics to the osteolytic lesions and photothermal treatment of malignant bone tumors.

[ASBMR topics from clinical research(osteoporosis and sarcopenia).]

There are a lot of progressive topics about osteoporosis and sarcopenia in 2018 ASBMR Annual Meeting, involving an association between diabetes and bone microarchitecture, associations between atypical femoral fractures and bisphosphonate drug holidays as well as pre-treatment bone mineral density, an effect of combined denosumab and high-dose teriparatide on bone parameters, and relationships between muscle and deuterated creatine, a selective androgen receptor modulator, and high-dose vitamin D supplementation.

Novel structures of platinum complexes bearing N‑bisphosphonates and study of their biological properties

Novel bisphosphonate platinum complexes: [Pt(isopropylamine)₂(BP)]NO₃ (BP = pamidronate and alendronate) have been synthesized and characterized. Their monomeric structure contains a bisphosphonate acting as chelate ligand through its oxygen atom donors, conferring the compound's cationic structure with a good solubility in water. The study of the compounds in solution showed high stability up to 24 h. The cytotoxicity in cancer cell lines has been assessed. We also present preliminary studies on the evaluation of the affinity towards biological targets such as DNA (both calf thymus DNA and supercoiled plasmid DNA) and hydroxyapatite where the complexes showed a low DNA interaction, but a clear affinity for hydroxyapatite comparing to their precursors.

Bisphosphonate-Generated ATP-Analogs Inhibit Cell Signaling Pathways

Bisphosphonates are a major class of drugs used to treat osteoporosis, Paget's disease, and cancer. They have been proposed to act by inhibiting one or more targets including protein prenylation, the epidermal growth factor receptor, or the adenine nucleotide translocase. Inhibition of the latter is due to formation in cells of analogs of ATP: the isopentenyl ester of ATP (ApppI) or an AppXp-type analog of ATP, such as AMP-clodronate (AppCCl2p). We screened both ApppI as well as AppCCl2p against a panel of 369 kinases finding potent inhibition of some tyrosine kinases by AppCCl2p, attributable to formation of a strong hydrogen bond between tyrosine and the terminal phosphonate. We then synthesized bisphosphonate preprodrugs that are converted in cells to other ATP-analogs, finding low nM kinase inhibitors that inhibited cell signaling pathways. These results help clarify our understanding of the mechanisms of action of bisphosphonates, potentially opening up new routes to the development of bone resorption, anticancer, and anti-inflammatory drug leads.

α-Methylation enhances the potency of isoprenoid triazole bisphosphonates as geranylgeranyl diphosphate synthase inhibitors

Disruption of protein geranylgeranylation via inhibition of geranylgeranyl diphosphate synthase (GGDPS) represents a novel therapeutic strategy for a variety of malignancies, especially those characterized by excessive protein secretion such as multiple myeloma. Our work has demonstrated that some isoprenoid triazole bisphosphonates are potent and selective inhibitors of GGDPS. Here we present the synthesis and biological evaluation of a new series of isoprenoid triazoles modified by incorporation of a methyl group at the α-carbon. These studies reveal that incorporation of an α-methyl substituent enhances the potency of these compounds as GGDPS inhibitors, and, in the case of the homogeranyl/homoneryl series, abrogates the effects of olefin stereochemistry on inhibitory activity. The incorporation of the methyl group allowed preparation of a POM-prodrug, which displayed a 10-fold increase in cellular activity compared to the corresponding salt. These studies form the basis for future preclinical studies investigating the anti-myeloma activity of these novel α-methyl triazole bisphosphonates.

A simple neridronate-based surface coating strategy for upconversion nanoparticles: highly colloidally stable 125I-radiolabeled NaYF4:Yb3+/Er3+@PEG nanoparticles for multimodal in vivo tissue imaging

In this report, monodisperse upconversion NaYF₄:Yb³⁺/Er³⁺ nanoparticles with superior optical properties were synthesized by the oleic acid-stabilized high-temperature co-precipitation of lanthanide chlorides in octadec-1-ene as a high-boiling organic solvent. To render the particles with biocompatibility and colloidal stability in bioanalytically relevant phosphate buffered saline (PBS), they were modified by using in-house synthesized poly(ethylene glycol)-neridronate (PEG-Ner), a bisphosponate. The NaYF₄:Yb³⁺/Er³⁺@PEG nanoparticles showed excellent long-term stability in PBS and/or albumin without any aggregation or morphology transformation. The in vitro cytotoxicity of the nanoparticles was evaluated using primary fibroblasts (HF) and a cell line derived from human cervical carcinoma (HeLa). The particles were subsequently modified by using Bolton-Hunter-hydroxybisphosphonate to enable radiolabeling with ¹²⁵I for single-photon emission computed tomography/computed tomography (SPECT/CT) bimodal imaging to monitor the biodistribution of the nanoparticles in non-tumor mice. The bimodal upconversion ¹²⁵I-radiolabeled NaYF₄:Yb³⁺/Er³⁺@PEG nanoparticles are prospective for near-infrared (NIR) photothermal/photodynamic and SPECT/CT cancer theranostics.

Crystallographic and thermodynamic characterization of phenylaminopyridine bisphosphonates binding to human farnesyl pyrophosphate synthase

Human farnesyl pyrophosphate synthase (hFPPS) catalyzes the production of the 15-carbon isoprenoid farnesyl pyrophosphate. The enzyme is a key regulator of the mevalonate pathway and a well-established drug target. Notably, it was elucidated as the molecular target of nitrogen-containing bisphosphonates, a class of drugs that have been widely successful against bone resorption disorders. More recently, research has focused on the anticancer effects of these inhibitors. In order to achieve increased non-skeletal tissue exposure, we created phenylaminopyridine bisphosphonates (PNP-BPs) that have bulky hydrophobic side chains through a structure-based approach. Some of these compounds have proven to be more potent than the current clinical drugs in a number of antiproliferation assays using multiple myeloma cell lines. In the present work, we characterized the binding of our most potent PNP-BPs to the target enzyme, hFPPS. Co-crystal structures demonstrate that the molecular interactions designed to elicit tighter binding are indeed established. We carried out thermodynamic studies as well; the newly introduced protein-ligand interactions are clearly reflected in the enthalpy of binding measured, which is more favorable for the new PNP-BPs than for the lead compound. These studies also indicate that the affinity of the PNP-BPs to hFPPS is comparable to that of the current drug risedronate. Risedronate forms additional polar interactions via its hydroxyl functional group and thus exhibits more favorable binding enthalpy; however, the entropy of binding is more favorable for the PNP-BPs, owing to the greater desolvation effects resulting from their large hydrophobic side chains. These results therefore confirm the overall validity of our drug design strategy. With a distinctly different molecular scaffold, the PNP-BPs described in this report represent an interesting new group of future drug candidates. Further investigation should follow to characterize the tissue distribution profile and assess the potential clinical benefits of these compounds.

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.

Smart, programmable and responsive injectable hydrogels for controlled release of cargo osteoporosis drugs

Easy-to-prepare drug delivery systems, based on smart, silica gels have been synthesized, characterized, and studied as hosts in the controlled release of bisphosphonates. They exhibit variable release rates and final % release, depending on the nature of bisphosphonate (side-chain length, hydro-philicity/-phobicity, water-solubility), cations present, pH and temperature. These gels are robust, injectable, re-loadable and re-usable.

Pamidronate-Conjugated Biodegradable Branched Copolyester Carriers: Synthesis and Characterization

The need for development of comprehensive therapeutic systems, (e.g., polymer-apatite composites) as a bone substitute material has previously been highlighted in many scientific reports. The aim of this study was to develop a new multifunctional composite based on hydroxyapatite porous granules doped with selenite ions (SeO₃^2-) and a biodegradable branched copolymer-bisphosphonate conjugate as a promising bone substitute material for patients with bone tumours or bone metastasis. A series of biodegradable and branched copolymer matrices, adequate for delivery of bisphosphonate in the bone-deficient area were synthesized and physico-chemically and biologically (cyto- and genotoxicity assays) characterized. Branched copolymers were obtained using a hyperbranched bis-MPA polyester-16-hydroxyl initiator and Sn(Oct)₂, a (co)catalyst of the ring-opening polymerization (ROP) of l,l-lactide (LLA) and ε-caprolactone (CL). A new amide bond was formed between the hydroxyl end groups of the synthesized copolymer carriers and an amine group of pamidronate (PAM)-the drug inhibiting bone resorption and osteoclast activity in bone. The dependence of the physico-chemical properties of the copolymer matrices on the kinetic release of PAM from the synthesized branched copolymer conjugate-coated hydroxyapatite granules doped with selenite ions was observed. Moreover, the correlation of these results with the hydrolytic degradation data of the synthesized matrices was evidenced. Therefore, the developed composite porous hydroxyapatite doped with SeO₃^2- ions/biodegradable copolymer-PAM conjugate appears most attractive as a bone substitute material for cancer patients.

Antiresorptive and anti-angiogenetic octacalcium phosphate functionalized with bisphosphonates: An in vitro tri-culture study

Development of new materials for the local administration of bisphosphonates (BPs) is aimed to avoid the negative side effects of prolonged systemic use of these potent drugs. In this work, we synthesized octacalcium phosphate (OCP) in the presence of two potent BPs and obtained a single crystalline phase up to a zoledronate and alendronate content of 3.5wt% and 5.2wt%, respectively. Both BPs provoke minor structural modifications and a reduction of the crystal dimensions of OCP, which suggests a preferential interaction of the BPs with the structure of the calcium phosphate. Alendronate containing samples display increased values of zeta potential with respect to that of OCP, and an initial burst release of the BP in solution. At variance, the zeta potential of zoledronate functionalized samples decreases on increasing the content of zoledronate, which is not appreciably released in solution. Bone microenvironment response to the composite materials was investigated in vitro using a triculture model. BP functionalized samples downregulate the viability of the cells, sustain osteoblast differentiation and accelerate the production of collagen type I and osteocalcin. At variance, they inhibit monocyte differentiation into osteoclast and provoke a dose dependent reduction of VEGF production, exhibiting antiresorptive and anti-angiogenetic properties that can be usefully exploited for the local treatment of abnormal bone losses.

STATEMENT OF SIGNIFICANCE

Bisphosphonates (BPs) are powerful drugs for the treatment of bone diseases. However, BPs systemic administration suffers several undesirable side effects, which stimulate the development of suitable systems for their local administration. In this study we functionalized octacalcium phosphate (OCP) with alendronate and zoledronate in order to get biomaterials able to couple the good biological performance of OCP with the therapeutic properties of the BPs. The results provide novel information on the interaction between these two potent BPs and octacalcium phosphate. Moreover, the triculture in vitro study indicates that the synthesized composite materials stimulate the production of bone extracellular matrix, inhibit monocytes differentiation into osteoclasts and downregulate the release of Vascular Endothelial Growth Factor (VEGF) in a dose dependent way. The data allow to state that the new composite materials can be usefully employed for the local treatment of diseases involving abnormally high bone resorption.

In vivo distribution of zoledronic acid in a bisphosphonate-metal complex-based nanoparticle formulation synthesized by a reverse microemulsion method

Bisphosphonates are used to treat bone diseases such as osteoporosis and cancer-induced bone pain and fractures. It is thought that modifying the pharmacokinetics and biodistribution profiles of bisphosphonates (i.e. rapid renal clearance and extensive bone absorption) will not only reduce their side effects, but also expand their clinical applications to extraskeletal tissues. In the present work, using zoledronic acid (Zol) and calcium as model bisphosphonate and metal molecules, respectively, we prepared DOPA (an anionic lipid)-coated spherical Zol-Ca nanocomposites (Zol-Ca@DOPA) and developed Zol-nanoparticle formulations (i.e. Zol-Ca@bi-lipid NPs) based on the nanocomposites. The influence of the inputted weight ratio of Zol-Ca@DOPA to DSPE-PEG_2k on the properties (e.g. size, size distribution, loading efficiency, encapsulation efficiency, zeta potential, and polydispersity) of Zol-Ca@bi-lipid NPs was investigated, and a type of Zol-Ca@bi-lipid NPs with size around 25nm was selected for further studies. In a mouse model, the Zol-Ca@bi-lipid NPs significantly reduced the bone distribution of Zol, increased the blood circulating time of Zol, and altered the distribution of Zol in major organs, as compared to free Zol. It is expected that similar nanoparticles prepared with bisphosphonate-metal complexes can be explored to expand the applications to bisphosphonates in extraskeletal tissues.

Bishomoisoprenoid triazole bisphosphonates as inhibitors of geranylgeranyl diphosphate synthase

Protein geranylgeranylation reactions are dependent on the availability of geranylgeranyl diphosphate (GGDP), which serves as the isoprenoid donor. Inhibition of GGDP synthase (GGDPS) is of interest from a drug development perspective as GGDPS inhibition results in impaired protein geranylgeranylation, which in multiple myeloma, disrupts monoclonal protein trafficking and induces apoptosis. We have recently reported a series of isoprenoid triazole bisphosphonates and have demonstrated that a 3:1 mixture of homogeranyl and homoneryl isomers potently, and in a synergistic manner, inhibits GGDPS. We now present the synthesis and biological evaluation of a novel series of bishomoisoprenoid triazoles which furthers our understanding of the structure-function relationship of this class. These studies demonstrate the importance of chain length and olefin stereochemistry on inhibitory activity.

Preparation and evaluation of rhenium-188-pamidronate as a palliative treatment in bone metastasis

OBJECTIVE

Rhenium-188-hydroxyethylidene diphosphonate (¹⁸⁸Re-HEDP) as a first generation bisphosphonate has been widely used for bone seeking radiopharmaceutical in cases of metastatic bone disease. No study has been yet reported on preparing a complex of ¹⁸⁸Re with pamidronate (3-aminohydroxypropylidene-1,1-bisphosphonic acid) (PMA) as a second generation bisphosphonate. Based on this fact, it was hypothesized that a bone-seeking ¹⁸⁸Re-PMA radiopharmaceutical could be developed as an agent for palliative radiotherapy of bone pain due to skeletal metastases.

METHODS

Pamidronate was labeled with ¹⁸⁸ReO₄^- eluted from the alumina based ¹⁸⁸W/¹⁸⁸Re generator. Labeling was optimized, and radiochemical analysis was performed by thin layer chromatography (TLC) and high performance liquid chromatography (HPLC). Biodistribution of this radioconjugate was evaluated and verified further in mice.

RESULTS

¹⁸⁸Re-PMA was prepared successfully in a high labeling yield (˃95%) corresponding to a specific activity of 124MBq/μmol and good in vitro stability, but it is likely to consist of multiple species. In biodistribution studies selective uptake and retention of activity in the skeletal system (0.81±0.25% ID/g and 0.57±0.16 at 4 and 48h in bone post injection respectively) followed by clearance in the soft tissues were observed.

CONCLUSION

These results show that due to its biological capabilities it would be advantageous to use ¹⁸⁸Re-PMA for bone pain palliation therapy.

Orderly Layered Zr-Benzylphosphonate Nanohybrids for Efficient Acid-Base-Mediated Bifunctional/Cascade Catalysis

The development of functional metal-organic materials that are robust and active for bifunctional/cascade catalysis is of great significance. Herein, a series of mesoporous and orderly layered nanohybrids were synthesized for the first time through simple and template-free assembly of ortho-, meta-, or para-xylylenediphosphonates (o-, p-, or m-PhP) containing zirconium. It was found that m-PhPZr nanoparticles (20-50 nm) with mesopores centered at 7.9 nm and high Lewis acid-base site ratio (1:0.7) showed excellent performance under mild conditions (as low as 82 °C) in transfer hydrogenation of carbonyl compounds, including bioaldehydes and alcohols, with near quantitative yields and little Zr leaching. Isotopic labeling studies indicated the occurrence of direct hydrogen transfer rather than metal hydride route by bifunctional catalysis. Lewis acidic (Zr) and basic (PO₃ ) centers of the heterogeneous catalyst were further revealed to play a synergistic role in one-pot cascade transformations, for example, of ethyl levulinate to γ-valerolactone and glucose to 5-hydroxymethylfurfural.

Targeted drug delivery of near IR fluorescent doxorubicin-conjugated poly(ethylene glycol) bisphosphonate nanoparticles for diagnosis and therapy of primary and metastatic bone cancer in a mouse model

BACKGROUND

Most primary and metastatic bone tumors demonstrate increased osteoclast activity and bone resorption. Current treatment is based on a combination of surgery, radiotherapy and chemotherapy. Severe side effects are associated with chemotherapy due to use of high dosage and nonspecific uptake. Bisphosphonates have a strong affinity to Ca2+ ions and are widely used in the treatment of bone disorders.

RESULTS

We have engineered a unique biodegradable bisphosphonate nanoparticle (NPs) bearing two functional surface groups: (1) primary amine groups for covalent attachment of a dye/drug (e.g. NIR dye Cy 7 or doxorubicin); (2) bisphosphonate groups for targeting and chelation to bone hydroxyapatite. In addition, these engineered NPs contain high polyethyleneglycol (PEG) concentration in order to increase their blood half life time. In vitro experiments on Saos-2 human osteosarcoma cell line, demonstrated that at a tenth of the concentration, doxorubicin-conjugated bisphosphonate NPs achieved a similar uptake to free doxorubicin. In vivo targeting experiments using the NIR fluorescence bisphosphonate NPs on both Soas-2 human osteosarcoma xenograft mouse model and orthotopic bone metastases mCherry-labeled 4T1 breast cancer mouse model confirmed specific targeting. In addition, therapeutic in vivo experiments using doxorubicin-conjugated bisphosphonate NPs demonstrated a 40% greater inhibition of tumor growth in Saos-2 human osteosarcoma xenograft mouse model when compared to free doxorubicin.

CONCLUSIONS

In this research we have shown the potential use of doxorubicin-conjugated BP NPs for the targeting and treatment of primary and metastatic bone tumors. The targeted delivery of doxorubicin to the tumor significantly increased the efficacy of the anti-cancer drug, thus enabling the effective use of a lower concentration of doxorubicin. Furthermore, the targeting ability of the BP NPs in an orthotopic xenograft mouse model reinforced our findings that these BP NPs have the potential to be used for the treatment of primary and metastatic bone cancer.

Stereoselective Synthesis of Homoneryl and Homogeranyl Triazole Bisphosphonates

Isoprenoid-substituted bisphosphonates are known to serve as inhibitors of the enzyme geranylgeranyl diphosphate synthase, and their activity can be highly sensitive to olefin stereochemistry. A mixture of homogeranyl and homoneryl triazole bisphosphonates has previously demonstrated potent activity, and thus stereocontrolled syntheses of the individual isomers have been developed.

Bone-Targeted Mesoporous Silica Nanocarrier Anchored by Zoledronate for Cancer Bone Metastasis

Once bone metastasis occurs, the chances of survival and quality of life for cancer patients decrease significantly. With the development of nanomedicine, nanocarriers loading bisphosphonates have been built to prevent cancer metastasis based on their enhanced permeability and retention (EPR) effects; however, as a passive mechanism, the EPR effects cannot apply to the metastatic sites because of their lack of leaky vasculature. In this study, we fabricated 40 nm-sized mesoporous silica nanoparticles (MSNs) anchored by zoledronic acid (ZOL) for targeting bone sites and delivered the antitumor drug doxorubicin (DOX) in a spatiotemporally controlled manner. The DOX loading and release behaviors, bone-targeting ability, cellular uptake and its mechanisms, subcellular localization, cytotoxicity, and the antimigration effect of this drug delivery system (DDS) were investigated. The results indicated that MSNs-ZOL had better bone-targeting ability compared with that of the nontargeted MSNs. The maximum loading capacity of DOX into MSNs and MSNs-ZOL was about 1671 and 1547 mg/g, with a loading efficiency of 83.56 and 77.34%, respectively. DOX@MSNs-ZOL had obvious pH-sensitive DOX release behavior. DOX@MSNs-ZOL entered into cells through an ATP-dependent pathway and then localized in the lysosome to achieve effective intracellular DOX release. The antitumor results indicated that DOX@MSNs-ZOL exhibited the best cytotoxicity against A549 cells and significantly decreased cell migration in vitro. This DDS is promising for the treatment of cancer bone metastasis in the future.

Synthesis of Hydroxymethylenebisphosphonic Acid Derivatives in Different Solvents

The syntheses of hydroxymethylenebisphosphonic acid derivatives (dronic acid derivatives) starting from the corresponding substituted acetic acids and P-reagents, mainly phosphorus trichloride and phosphorous acid are surveyed according to the solvents applied. The nature of the solvent is a critical point due to the heterogeneity of the reaction mixtures. This review sheds light on the optimum choice and ratio of the P-reactants, and on the optimum conditions.

A DOTA based bisphosphonate with an albumin binding moiety for delayed body clearance for bone targeting

Radiolabeled bisphosphonates are commonly used in the diagnosis and therapy of bone metastases. Blood clearance of bisphosphonates is usually fast and only 30%-50% of the injected activity is retained in the skeleton, while most of the activity is excreted by the urinary tract. A longer blood circulation may enhance accumulation of bisphosphonate compounds in bone metastases. Therefore, a chemically modified macrocyclic bisphosphonate derivative with an additional human albumin binding entity was synthesized and pharmacokinetics of its complex was evaluated. The DOTA-bisphosphonate conjugate BPAMD was compared against the novel DOTAGA-derived albumin-binding bisphosphonate DOTAGA(428-d-Lys)M^BP (L1). The ligands were labeled with ⁶⁸Ga(III) and were evaluated in in vitro binding studies to hydroxyapatite (HA) as well as to human serum albumin. The compounds were finally compared in in vivo PET and ex vivo organ distribution studies in small animals over 6h. Binding studies revealed a consistent affinity of both bisphosphonate tracers to HA. Small animal PET and ex vivo organ distribution studies showed longer blood retention of [⁶⁸Ga]L1. [⁶⁸Ga]BPAMD is initially more efficiently bound to the bone but skeletal accumulation of the modified compound and [⁶⁸Ga]BPAMD equalized at 6h p.i. Ratios of femur epiphyseal plate to ordinary bone showed to be more favorable for [⁶⁸Ga]L1 than for [⁶⁸Ga]BPAMD due to the longer circulation time of the new tracer. Thus, the chemical modification of BPAMD toward an albumin-binding bisphosphonate, L1, resulted in a novel PET tracer which conserves advantages of both functional groups within one and the same molecule. The properties of this new diagnostic tracer are expected to be preserved in ¹⁷⁷Lu therapeutic agent with the same ligand (a theranostic pair).

Transferrin-Targeted Nanoparticles Containing Zoledronic Acid as a Potential Tool to Inhibit Glioblastoma Growth

The treatment of glioblastoma (GBM) is a challenge for the biomedical research since cures remain elusive. Its current therapy, consisted on surgery, radiotherapy, and concomitant chemotherapy with temozolomide (TMZ), is often uneffective. Here, we proposed the use of zoledronic acid (ZOL) as a potential agent for the treatment of GBM. Our group previously developed self-assembling nanoparticles, also named PLCaPZ NPs, to use ZOL in the treatment of prostate cancer. Here, we updated the previously developed nanoparticles (NPs) by designing transferrin (Tf)-targeted self-assembling NPs, also named Tf-PLCaPZ NPs, to use ZOL in the treatment of brain tumors, e.g., GBM. The efficacy of Tf-PLCaPZ NPs was evaluated in different GBM cell lines and in an animal model of GBM, in comparison with PLCaPZ NPs and free ZOL. Tf-PLCaPZ NPs were characterized by a narrow size distribution and a high incorporation efficiency of ZOL. Moreover, the presence of Tf significantly reduced the hemolytic activity of the formulation. In vitro, in LN229 cells, a significant uptake and cell growth inhibition after treatment with Tf-PLCaPZ NPs was achieved. Moreover, the sequential therapy of TMZ and Tf-PLCaPZ NPs lead to a superior therapeutic activity compared to their single administration. The results obtained in mice xenografted with U373MG, revealed a significant anticancer activity of Tf-PLCaPZ NPs, while the tumors remained unaffected with free TMZ. These promising results introduce a novel type of easy-to-obtain NPs for the delivery of ZOL in the treatment of GBM tumors.

Potential Applications of Biphosphonates in Dental Surgical Implants

Biphosphonates are largely used for their unquestionable properties of inhibiting bone resorption by osteoclast in the treatment of various osteometabolic illnesses such as osteoporosis, multiple myeloma, tumors which metastasize to the bone and malignant hypercalcemia. In this literature review the physico-chemical properties, biologic activities and the mechanisms of action of biphosphonates are described. The use of these drugs is discussed, analyzing the quantity of results which have emerged through in vitro and in vivo experiments on animal models. In this study the efficiency of these drugs is demonstrated in contrasting the osteolitic processes of the alveolar bone, in promoting the neoformation and in bettering the quality of bone implants. However, it is important to draw attention to a worrying correlation which has emerged during the last 3–4 years, between osteonecrosis of the jaw (ONJ) and the systemic administration of aminobiphosphonates. This collateral effect did not emerge following the use of non-aminobiphosphonates. The aim of this revie w is to identify the guidelines for the use of biphosphonates in oral implant surgery.

Self-assembling bisphosphonates into nanofibers to enhance their inhibitory capacity on bone resorption

Osteoporosis (OP) is an important aging-related disease and the effective prevention/treatment of this disease remains challenging. Considering the acidic microenvironment of bone resorption lacunae, herein, we rationally designed two pamidronate (Pami)-derivative and alendronate (Alen)-derivative hydrogelators and which self-assemble into nanofibers to form supramolecular hydrogels under acidic conditions. Cell viability assay, osteoclastogenesis, osteoclastic gene expression, and in vitro bone resorption results indicated that both and have better inhibitory effects on osteoclastic formation and bone resorption than Pami and Alen, respectively. We anticipate that our new drugs and could "smartly" self-assemble and locally concentrate the drugs at bone resorption lacunae in vivo and subsequently prevent/treat osteoporosis more efficiently.

Targeted delivery to bone and mineral deposits using bisphosphonate ligands

The high concentration of mineral present in bone and pathological calcifications is unique compared with all other tissues and thus provides opportunity for targeted delivery of pharmaceutical drugs, including radiosensitizers and imaging probes. Targeted delivery enables accumulation of a high local dose of a therapeutic or imaging contrast agent to diseased bone or pathological calcifications. Bisphosphonates (BPs) are the most widely utilized bone-targeting ligand due to exhibiting high binding affinity to hydroxyapatite mineral. BPs can be conjugated to an agent that would otherwise have little or no affinity for the sites of interest. This article summarizes the current state of knowledge and practice for the use of BPs as ligands for targeted delivery to bone and mineral deposits. The clinical history of BPs is briefly summarized to emphasize the success of these molecules as therapeutics for metabolic bone diseases. Mechanisms of binding and the relative binding affinity of various BPs to bone mineral are introduced, including common methods for measuring binding affinity in vitro and in vivo. Current research is highlighted for the use of BP ligands for targeted delivery of BP conjugates in various applications, including (1) therapeutic drug delivery for metabolic bone diseases, bone cancer, other bone diseases, and engineered drug delivery platforms; (2) imaging probes for scintigraphy, fluorescence, positron emission tomography, magnetic resonance imaging, and computed tomography; and (3) radiotherapy. Last, and perhaps most importantly, key structure-function relationships are considered for the design of drugs with BP ligands, including the tether length between the BP and drug, the size of the drug, the number of BP ligands per drug, cleavable tethers between the BP and drug, and conjugation schemes.

Synthesis, Characterization, and Application of Core-Shell Co0.16Fe2.84O4@NaYF4(Yb, Er) and Fe3O4@NaYF4(Yb, Tm) Nanoparticle as Trimodal (MRI, PET/SPECT, and Optical) Imaging Agents

Multimodal nanoparticulate materials are described, offering magnetic, radionuclide, and fluorescent imaging capabilities to exploit the complementary advantages of magnetic resonance imaging (MRI), positron emission tomography/single-photon emission commuted tomography (PET/SPECT), and optical imaging. They comprise Fe3O4@NaYF4 core/shell nanoparticles (NPs) with different cation dopants in the shell or core, including Co0.16Fe2.84O4@NaYF4(Yb, Er) and Fe3O4@NaYF4(Yb, Tm). These NPs are stabilized by bisphosphonate polyethylene glycol conjugates (BP-PEG), and then show a high transverse relaxivity (r2) up to 326 mM(-1) s(-1) at 3T, a high affinity to [(18)F]-fluoride or radiometal-bisphosphonate conjugates (e.g., (64)Cu and (99m)Tc), and fluorescent emissions from 500 to 800 nm under excitation at 980 nm. The biodistribution of intravenously administered particles determined by PET/MR imaging suggests that negatively charged Co0.16Fe2.84O4@NaYF4(Yb, Er)-BP-PEG (10K) NPs cleared from the blood pool more slowly than positively charged NPs Fe3O4@NaYF4(Yb, Tm)-BP-PEG (2K). Preliminary results in sentinel lymph node imaging in mice indicate the advantages of multimodal imaging.