Development of Polyethylene Glycol-Conjugated Alendronate, a Novel Nitrogen-Containing Bisphosphonate Derivative: Evaluation of Absorption, Safety, and Effects After Intrapulmonary Administration in Rats

DSPE-PEG polymers for improving pulmonary absorption of poorly absorbed macromolecules in rats and relative mechanism

OBJECTIVE

This study aims to investigate the potential of DSPE-PEG polymers (DSPE-PEG-OH and DSPE-PEG-SH) on improving absorption of poorly absorbable macromolecules via intrapulmonary administration and underlying mechanism.

METHODS

In situ pulmonary absorption experiments were performed to investigate the absorption of model compounds after intrapulmonary administration to rats. The local membrane damage induced by these DSPE-PEG polymers were evaluated based on morphological observation of lung tissues and measurement of biological toxic markers in bronchoalveolar lavage fluid (BALF) postintrapulmonary delivery of DSPE-PEG polymers to rats. The underlying enhancement mechanism of these polymers was explored by investigating their effects on the pulmonary membrane fluidity and gene expression of tight junction associated proteins with fluorescence polarization and western blotting, respectively.

RESULTS

Intrapulmonary delivery of these DSPE-PEG polymers significantly enhanced absorptions of poorly absorbed model drugs and did not induce serious damage to the pulmonary membranes of rats. Mechanistic studies demonstrated unaffected pulmonary membrane fluidity and up-regulated expression levels of tight junction-associated proteins by DSPE-PEG polymers, thus indicating that paracellular pathways might be included in the underlying mechanisms by which DSPE-PEG polymers exerted their enhancing actions on drug absorption.

CONCLUSIONS

These findings suggested that these DSPE-PEG polymers are potential for promoting absorptions of poorly absorbable macromolecules with no evidence of damage to the local pulmonary membranes of rats.Novelty statementIn this study, DSPE-PEG-OH and DSPE-PEG-SH polymers, two DSPE-PEG2000 conjugates with different terminal groups demonstrated significant promoting effects on the absorption of poorly absorbed macromolecular drugs after intrapulmonary delivery to rats, and did not induce serious damage to the pulmonary membranes of rats. These DSPE-PEG polymers could statistically downregulate expression levels of tight junction-associated proteins (ZO-1 and occludin), indicating the underlying mechanism by which these polymers exerted their absorption enhancing actions through pulmonary epithelial paracellular pathways. Thus, this study exhibited prospective potential of these DSPE-PEG polymers in developing into dosage forms with the aim to improve the poor bioavailability of some poorly absorbed macromolecular drugs.

Alendronate Sodium Intercalation in Layered Double Hydroxide/Poly (ε-caprolactone): Application in Osteoporosis Treatment

Background:

Osteoporosis is a bone disease alters the amount and variety of proteins in bone tissue and increases the potential of bone fracture. Antiresorptive therapy is one of the most popular treatment methods for osteoporosis. To reduce side effects and enhance the bioavailability of drug agents, the controlled delivery of drug is commonly utilized.

Objectives:

We investigated the controlled release of Alendronate in different composites of layered double hydroxide (LDH) using poly (ε-caprolactone) (PCL) as a matrix.

Materials and Methods:

We prepared different microsphere composites of ALD intercalated in various amounts of LDH, using PCL as a matrix. The controlled release of ALD from these composites is subsequently investigated. Samples are characterized and in vitro cell cytotoxicity, attachment, osteogenic activity including alkaline phosphatase activity and mineralization are examined using MG-63 human osteosarcoma cells.

Results:

The results showed that the release of ALD is more desirable and controlled in the samples having a higher amount of LDH incorporated into the PCL matrix. MG63 cells show a significant increase in viability, attachment, and mineralization while alkaline phosphatase activity remains almost at a constant level after 3 weeks.

Conclusions:

Overall, the findings showed that by incorporation of 15 wt% of LDH, the composite microsphere is capable of holding the antiresorptive drug longer and release it in a more controlled manner. This is an advantageous and promising characteristic for a carrier that could be used as a potential candidate for osteoporosis treatment.

CREB activation affects mesenchymal stem cell migration and differentiation in periodontal tissues due to orthodontic force

During the orthodontic tooth movement, cells in periodontal ligament could differentiate into osteoblasts to synthesize alveolar bone as well as affect the proliferation, migration and differentiation of mesenchymal stem cells, which also contribute to bone remodeling. However, the mechanism is still largely elusive. Here, we evaluated the expression of CREB at the tension site of mouse periodontal ligament under orthodontic mechanical strain and in the cyclic tension strain treated human periodontal ligament cells. Then, through gain and loss of function analysis, we revealed that CREB in PDLCs promotes SDF-1 and FGF2 secretion, which enhance the migration and osteoblastic differentiation of BMSCs. We further discovered that CREB transcriptionally activates FGF2 and SDF-1 expressions by binding to the promoter regions.In conclusion, this study confirms that CREB is an upregulated gene in periodontal ligament under orthodontic tension strain stimulation and plays an important role in regulating BMSCs' physiological activity in orthodontic tension strain-induced bone formation.

Development of Zoledronic Acid-Based Nanoassemblies for Bone-Targeted Anticancer Therapy

Bone metastasis occurs in the majority of cancer patients, which hampers quality of life and significantly decreases survival. Aggressive chemotherapy is a traditional treatment regimen that induces severe systemic toxicities. Therefore, bone-directed therapies are highly warranted. We report a novel nanoparticle formulation that is composed of poly(vinylpyrrolidone) and tannic acid core nanoparticles (PVT NPs) that forms self-assembly with zoledronic acid (ZA@PVT NPs). The construction of ZA@PVT NPs was confirmed by particle size, zeta potential, transmission electron microscopy, and spectral analyses. An optimized bone-targeted ZA@PVT NPs formulation showed greater binding and internalization in in vitro with metastasis prostate and breast cancer cells. ZA@PVT NPs were able to deliver ZA more efficiently to tumor cells, which inhibited proliferation of human prostate and breast cancer cells. In addition, ZA@PVT NPs were capable of targeting mouse bones and prostate tumor microarray tissues (ex vivo) while sparing all other vital organs. More importantly, ZA@PVT NPs induce chemo sensitization to docetaxel treatment in cancer cells. Overall, the study results confirm that ZA-based, bone-targeted NPs have great potential for the treatment of bone metastasis in the near future.

In Situ In Vivo radiolabeling of polymer-coated hydroxyapatite nanoparticles to track their biodistribution in mice

The imaging of healthy tissues and solid tumors benefits from the application of nanoparticle probes with altered pharmacokinetics, not available to low molecular weight compounds. However, the distribution and accumulation of nanoprobes in vivo typically take at least tens of hours to be efficient. For nanoprobes bearing a radioactive label, this is contradictory to the requirement of minimizing the radiation dose for patients by using as-short-as-feasible half-life radionuclides in diagnostics. Thus, we developed a two-stage diagnostic concept for monitoring long-lasting targeting effects with short-lived radioactive labels using bone-mimicking biocompatible polymer-coated and colloidally fully stabilized hydroxyapatite nanoparticles (HAP NPs) and bone-seeking radiopharmaceuticals. Within the pretargeting stage, the nonlabeled nanoparticles are allowed to circulate in the blood. Afterward, ^99mTc-1-hydroxyethylidene-1.1-diphosphonate (^99mTc-HEDP) is administered intravenously for in situ labeling of the nanoparticles and subsequent single-photon emission computed tomography/computed tomography (SPECT/CT) visualization. The HAP NPs, stabilized with tailored hydrophilic polymers, are not cytotoxic in vitro, as shown by several cell lines. The polymer coating prolongs the circulation of HAP NPs in the blood. The nanoparticles were successfully labeled in vivo with ^99mTc-HEDP, 1 and 24 h after injection, and they were visualized by SPECT/CT over time in healthy mice.

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.

Development of Bone Targeting Drugs

The skeletal system, comprising bones, ligaments, cartilage and their connective tissues, is critical for the structure and support of the body. Diseases that affect the skeletal system can be difficult to treat, mainly because of the avascular cartilage region. Targeting drugs to the site of action can not only increase efficacy but also reduce toxicity. Bone-targeting drugs are designed with either of two general targeting moieties, aimed at the entire skeletal system or a specific cell type. Most bone-targeting drugs utilize an affinity to hydroxyapatite, a major component of the bone matrix that includes a high concentration of positively-charged Ca²⁺. The strategies for designing such targeting moieties can involve synthetic and/or biological components including negatively-charged amino acid peptides or bisphosphonates. Efficient delivery of bone-specific drugs provides significant impact in the treatment of skeletal related disorders including infectious diseases (osteoarthritis, osteomyelitis, etc.), osteoporosis, and metabolic skeletal dysplasia. Despite recent advances, however, both delivering the drug to its target without losing activity and avoiding adverse local effects remain a challenge. In this review, we investigate the current development of bone-targeting moieties, their efficacy and limitations, and discuss future directions for the development of these specific targeted treatments.

Tocilizumab-Alendronate Conjugate for Treatment of Rheumatoid Arthritis

An autoimmune disease of rheumatoid arthritis (RA) causes severe inflammation on the synovial membrane, which results in the destruction of articular cartilage and bone. Here, Tocilizumab (TCZ)-Alendronate (ALD) conjugate is synthesized for the early intervention of RA. A humanized monoclonal antibody of TCZ shows an immunosuppressive effect, targeting interleukin-6 (IL-6) receptor in the RA pathogenesis. ALD is an anti-inflammatory bisphosphonate drug which can bind to the exposed bone surface. ALD is conjugated selectively to N-glycan on Fc region of TCZ using a chemical linker of 3-(2-pyridyldithio)propionyl hydrazide (PDPH)-poly(ethylene glycol)-N-hydroxysuccinimide (PDPH-PEG-NHS). The successful synthesis of TCZ-ALD conjugate is corroborated by ¹H NMR, the purpald assay, mass spectrometry (MS), and high performance liquid chromatography (HPLC). In vitro binding affinity and cell viability tests confirmed the biological activity of TCZ-ALD conjugate. Furthermore, in vivo efficacy of TCZ-ALD conjugate is confirmed by microcomputed tomography (CT), histology, and Western blot analyses for the treatment of RA.

Design and Biological Evaluation of Delivery Systems Containing Bisphosphonates

Bisphosphonates have found application in the treatment of reoccurrence of bone diseases, breast cancer, etc. They have also been found to exhibit antimicrobial, anticancer and antimalarial activities. However, they suffer from pharmacological deficiencies such as toxicity, poor bioavailability and low intestinal adsorption. These shortcomings have resulted in several researchers developing delivery systems that can enhance their overall therapeutic effectiveness. This review provides a detailed overview of the published studies on delivery systems designed for the delivery of bisphosphonates and the corresponding in vitro/in vivo results.

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.

Pharmacokinetic and therapeutic efficacy of intrapulmonary administration of zoledronate for the prevention of bone destruction in rheumatoid arthritis

Zoledronate, a third-generation nitrogen-containing bisphosphonate, is a new therapeutic agent for the prevention of joint destruction in rheumatoid arthritis (RA). Due to the poor oral absorption of zoledronate, the intravenous route has been the preferred method of administration. To evaluate whether the lung is a promising alternative route of zoledronate administration for the prevention of joint destruction in RA, we examined the pharmacokinetics, safety and therapeutic potential of zoledronate after intrapulmonary administration. The bioavailability of zoledronate was 55% after intrapulmonary administration in rats. In a collagen-induced RA mouse model, an intrapulmonary administration of zoledronate given 7 d before the 2nd collagen immunization effectively suppressed bone loss and joint destruction to a level similar to that achieved with intravenous injection at 21 d after the 2nd collagen immunization. Zoledronate only slightly affected lactate dehydrogenase activity in bronchoalveolar lavage fluid 4 h after intrapulmonary administration of the therapeutic dose in rats. Moreover, zoledronate only slightly changed the plasma level of creatinine after intrapulmonary administration while creatinine significantly increased after intravenous injection of zoledronate in mice. These results indicate that the lung is a promising alternative route of zoledronate administration for the treatment and prevention of joint destruction in RA.

The potential impact of new effervescent alendronate formulation on compliance and persistence in osteoporosis treatment

Osteoporotic fractures are a public health problem and their incidence and subsequent economic and social costs are expected to rise in the next future. Different drugs have been developed to reduce osteoporosis and the risk of osteoporotic fractures, and among them, antiresorptive agents, and in particular oral alendronate, are the most widely utilized. However, one of the most common problems with antiresorptive drugs is poor adherence to treatment, which is associated with a high fracture incidence and with an increase in hospitalization costs. One of the main reasons of poor adherence to these treatments is the occurrence of adverse events, mainly at gastrointestinal (GI) level, including dyspepsia, dysphagia, and esophageal ulcers. In light of these considerations the aim of this paper is to perform a literature review to show the pathophysiologic bases of GI alendronate-induced adverse events and how new bisphosphonate formulations like effervescent alendronate can improve compliance and persistence to treatment and decrease the fracture rate incidence in osteoporotic patients.

Bisphosphonate-modified biomaterials for drug delivery and bone tissue engineering

INTRODUCTION

Bisphosphonates (BPs) were introduced 45 years ago as anti-osteoporotic drugs and during the last decade have been utilized as bone-targeting groups in systemic treatment of bone diseases. Very recently, strategies of chemical immobilization of BPs in hydrogels and nanocomposites for bone tissue engineering emerged. These strategies opened new applications of BPs in bone tissue engineering.

AREAS COVERED

Conjugates of BPs to different drug molecules, imaging agents, proteins and polymers are discussed in terms of specific targeting to bone and therapeutic affect induced by the resulting prodrugs in comparison with the parent drugs. Conversion of these conjugates into hydrogel scaffolds is also presented along with the application of the resulting materials for bone tissue engineering.

EXPERT OPINION

Calcium-binding properties of BPs can be successfully extended via different conjugation strategies not only for purposes of bone targeting, but also in supramolecular assembly affording either new nanocarriers or bulk nanocomposite scaffolds. Interaction between carrier-linked BPs and drug molecules should also be considered for the control of release of these molecules and their optimized delivery. Bone-targeting properties of BP-functionalized nanomaterials should correspond to bone adhesive properties of their bulk analogs.

Synthesis, characterization and in vitro evaluation of new composite bisphosphonate delivery systems

In this study, new composite bisphosphonate delivery systems were obtained from polyurethanes (PUs) and nanocrystalline hydroxyapatite (HA). The biodegradable PUs were first synthesized from poly(ε-caprolactone) diols (PCL diols), poly(ethylene adipate) diol, 1,6-hexamethylene diisocyanate, 1,4-butanediol and HA. Moreover, the PCL diols were synthesized by the ring-opening polymerization catalysed by the lipase from Candida antarctica. Next, composite drug delivery systems for clodronate were prepared. The mechanical properties of the obtained biomaterials were determined. The cytotoxicity of the synthesized polymers was tested. The preliminary results show that the obtained composites are perspective biomaterials and they can be potentially applied in the technology of implantation drug delivery systems.

Biomedical applications of bisphosphonates

Since their discovery over 100 years ago, bisphosphonates have been used industrially as corrosion inhibitors and complexing agents. With the discovery of their pharmacological activity in the late 1960s, implicating their high affinity for hydroxyapatite, bisphosphonates have been employed in the treatment of bone diseases and as targeting agents for colloids and drugs. They have notably been investigated for the treatment of Paget's disease, osteoporosis, bone metastases, malignancy-associated hypercalcemia, and pediatric bone diseases. Currently, they are first-line medications for several of these diseases and are taken by millions of patients worldwide, mostly postmenopausal women. A major problem associated with their use is their low oral bioavailability. Several delivery systems have been proposed to improve their absorption and to direct them to sites other than bone tissues. Beyond their important pharmacological role, the medical applications of bisphosphonates are numerous. In addition, their metal-chelating properties have been exploited to coat and stabilize implants, nanoparticulates, and contrast agents. In this contribution, we review the pharmacological and clinical uses of bisphosphonates and highlight their novel applications in the pharmaceutical and biomedical fields.

siRNA transfection with calcium phosphate nanoparticles stabilized with PEGylated chelators

Despite the enormous therapeutic potential of siRNAs, their delivery is still problematic due to unfavorable biodistribution profiles and poor intracellular bioavailability. Calcium phosphate co-precipitate has been used for nearly 40 years for in vitro transfection due to its non-toxic nature and simplicity of preparation. However, rapid particle growth has largely prevented the translation of this method for in vivo purposes. It has recently been shown that bisphosphonate derivatives can physically stabilize calcium phosphate nanoparticles while still allowing for efficient cell transfection with plasmid DNA. Herein, two novel PEGylated chelating agents (PEG-alendronate and PEG-inositolpentakisphosphate) with enhanced stabilizing properties are introduced, and it is demonstrated that the bisphosphonate-stabilized nanoparticles can efficiently deliver siRNA in vitro. The nanoparticles are mainly taken up by clathrin-dependent endocytosis, and acidification of the endosomal compartment is required to release the entrapped siRNA into the cytosol. Furthermore, particle uptake enhances the inhibition of the mevalonate pathway by the bisphosphonate in macrophages.

Development of a novel self-dissolving microneedle array of alendronate, a nitrogen-containing bisphosphonate: evaluation of transdermal absorption, safety, and pharmacological effects after application in rats

Alendronate is a nitrogen-containing bisphosphonate that is widely used for the treatment of osteoporosis. In this study, we developed a novel self-dissolving micron-size needle array (microneedle array) containing alendronate, which was fabricated by micromodeling technologies using hyaluronic acid as a basic material. Micron-scale pores in the skin were seen after the application of the alendronate-loaded microneedle array, verifying establishment of transdermal pathways for alendronate. The absorption of alendronate after the application of alendronate-loaded microneedle array was almost equivalent to that after subcutaneous administration, and the bioavailability of alendronate was approximately 90% in rats. Furthermore, delivery of alendronate via this strategy effectively suppressed the decrease in the width of the growth plate in a rat model of osteoporosis. Although mild cutaneous irritation was observed after the application of the alendronate-loaded microneedle array, it resolved by day 15. These findings indicate that this alendronate-loaded microneedle array is a promising transdermal formulation for the treatment of osteoporosis.