Beyond Antiresorptive Activity: Risedronate-Based Coordination Complexes To Potentially Treat Osteolytic Metastases

Coordination of clinically employed bisphosphonate, risedronate (RISE), to bioactive metals, Ca²⁺, Mg²⁺, and Zn²⁺, allowed the formation of bisphosphonate-based coordination complexes (BPCCs). Three RISE-based BPCCs, RISE-Ca, RISE-Mg, and RISE-Zn, were produced, and their structures were elucidated by single crystal X-ray diffraction. Interestingly, the addition of an auxiliary ligand, etidronic acid (HEDP), resulted in the recrystallized protonated form of the ligand, H-RISE. The pH-dependent structural stability of the RISE-based BPCCs was measured by means of dissolution profiles under neutral and acidic simulated physiological conditions (PBS and FaSSGF, respectively). In comparison to RISE (Actonel), the complexes showed a lower equilibrium solubility (∼70-85% in 18-24 h) in PBS, while a higher equilibrium solubility (∼100% in 3 h) in acidic media. The results point to the capacity to release this BP in a pH-dependent manner from the RISE-based BPCCs. Subsequently, the particle size of RISE-Ca was reduced, from 300 μm to ∼350 d.nm, employing the phase inversion temperature (PIT)-nanoemulsion method, resulting in nano-Ca@RISE. Aggregation measurements of nano-Ca@RISE in 1% fetal bovine serum (FBS):H₂O was monitored after 24, 48, and 72 h to study the particle size longevity in physiological media, showing that the suspended material has the potential to maintain its particle size over time. Furthermore, binding assays were performed to determine the potential binding of nano-Ca@RISE to the bone, where results show higher binding (∼1.7×) for the material to hydroxyapatite (HA, 30%) when compared to RISE (17%) in 1 d. The cytotoxicity effects of nano-Ca@RISE were compared to those of RISE against the human breast cancer MDA-MB-231 and normal osteoblast-like hFOB 1.19 cell lines by dose-response curves and relative cell viability assays in an in vitro setting. The results demonstrate that nano-Ca@RISE significantly decreases the viability of MDA-MB-231 with high specificity, at concentrations ∼2-3× lower than the ones reported employing other third-generation BPs. This is supported by the fact that when normal osteoblast cells (hFOB 1.19), which are part of the tissue microenvironment at metastatic sites, were treated with nano-Ca@RISE no significant decrease in viability was observed. This study expands on the therapeutic potential of RISE beyond its antiresorptive activity through the design of BPCCs, specifically nano-Ca@RISE, that bind to the bone and degrade in a pH-dependent manner under acidic conditions.

Functionalization of Titanium Dioxide by In Situ Surface Crystallization of Bisphosphonate-Based Coordination Complexes

Functionalization of highly pure rutile phase titanium dioxide (TiO2) particles with a selected bisphosphonate-based coordination complex (BPCC), ZOLE-Ca form II, was achieved through in situ surface crystallization. The hydrothermal reaction of the selected BPCC was carried out in the presence of photoactivated rutile phase TiO2 by ultraviolet irradiation. The reaction time was varied to control the crystal growth of the BPCC around the TiO2 core, resulting in a functionalized material with different shell thicknesses: TiO2-core:nano-Ca@ZOLE-shell-† (5 min) and TiO2-core:nano-Ca@ZOLE-shell-‡ (10 min). The crystal phase assessment of the BPCC and the polymorphic phase purity of the metal oxide were determined after immobilization through Raman spectroscopy and powder X-ray diffraction. The results initially suggested that the crystallization of a shell comprising the selected BPCC surrounding a highly pure rutile phase TiO2 core was achieved through controlled in situ surface crystallization. Morphological changes, elemental composition and exact atomic distribution in the functionalized materials were addressed employing scanning electron microscopy coupled with energy-dispersive spectroscopy. These analyses unambiguously confirmed that after 5 min, successful incorporation of a thin BPCC shell on the surface of the metal oxide particles was achieved. Particle size distribution measurements revealed an average particle size of 495 d.nm for the functionalized material after the immobilization process. Quantitative determination of the BPCC shell content in TiO2-core:nano-Ca@ZOLE-shell-† was determined through thermogravimetric analysis, estimating a ratio of ∼1:3 (TiO2:BPCC). The cytotoxicity of TiO2-core:nano-Ca@ZOLE-shell-† against MDA-MB-231 (cancer cell model) and hFOB 1.19 (normal osteoblast-like cell model) cell lines was investigated. The results demonstrated significant cell growth inhibition for TiO2-core:nano-Ca@ZOLE-shell-† against MDA-MB-231, specifically at a concentration of 7.5 μM (% RCL = 46 ± 2%, 72 h). Under the same conditions, the functionalized material did not present cytotoxicity against hFOB 1.19 (% RCL ∼ 100%). These important outcomes provide evidence of the surface crystallization of BPCCs onto rutile phase TiO2 for the development of a novel functionalized material with the potential to treat and prevent osteolytic metastases.

High affinity zoledronate-based metal complex nanocrystals to potentially treat osteolytic metastases

Formation of several materials, denoted as bisphosphonate-based coordination complexes (BPCCs), resulted from the reaction between clinically employed bisphosphonate, zoledronate (ZOLE) and bioactive metals (M²⁺ = Ca²⁺, Mg²⁺ and Zn²⁺). Six ZOLE-based BPCCs were synthesized using different variables (M²⁺ : ZOLE molar ratio, temperature, pH, and anion) and their structures were elucidated by single crystal X-ray diffraction (ZOLE-Ca forms I and II, ZOLE-Mg forms I and II, and ZOLE-Zn forms I and II). The dissolution of the ZOLE-based BPCCs was compared to that of ZOLE (Reclast®). Most of the ZOLE-based BPCCs (60-85%, in 18-24 h) present a lower dissolution and equilibrium solubility than ZOLE (∼100%, 30 min) in phosphate buffered saline (PBS), while a significantly higher dissolution is observed in acidic media (88% in 1 h). This suggests the ability to release the ZOLE content in a pH-dependent manner. Moreover, a phase inversion temperature (PIT)-nano-emulsion synthesis was performed, which demonstrated the ability to significantly decrease the crystal size of ZOLE-Ca form II from a micron-range (∼200 μm) to a nano-range (∼150 d nm), resulting in nano-Ca@ZOLE. Furthermore, low aggregation of nano-Ca@ZOLE in 10% fetal bovine serum (FBS) : PBS after 0, 24 and 48 h was demonstrated. Additionally, nano-Ca@ZOLE showed an ∼2.5x more binding to hydroxyapatite (HA, 36%) than ZOLE (15%) in 1 d. The cytotoxicity of nano-Ca@ZOLE against MDA-MB-231 (cancer cell model) and hFOB 1.19 (normal osteoblast-like cell model) cell lines was investigated. The results demonstrated significant cell growth inhibition for nano-Ca@ZOLE against MDA-MB-231, specifically at a low concentration of 3.8 μM (%RCL = 55 ± 1%, 72 h). Under the same conditions, the nanocrystals did not present cytotoxicity against hFOB 1.19 (%RCL = 100 ± 2%). These results evidence that nano-ZOLE-based BPCCs possess viable properties in terms of structure, dissolution, stability, binding, and cytotoxicity, which render them suitable for osteolytic metastasis therapy.

An oligopeptide/aptamer-conjugated dendrimer-based nanocarrier for dual-targeting delivery to bone

Bone targeting is one of the most potentially valuable therapeutic methods for medically treating bone diseases, such as osteoarthritis, osteoporosis, nonunion bone defects, bone cancer, and myeloma-related bone disease, but its efficacy remains a challenge due to unfavorable bone biodistribution, off-target effects, and the lack of cell specificity. To address these problems, we synthesized a new dual-targeting nanocarrier for delivery to bone by covalently modifying the G4.0 PAMAM dendrimer with the C11 peptide and the CH6 aptamer (CH6-PAMAM-C11). The molecular structure was confirmed using ¹H-NMR and FT-IR spectroscopy. CLSM results showed that the novel nanocarrier could successfully accumulate in the targeted cells, mineralized areas and tissues. DLS and TEM demonstrated that CH6-PAMAM-C11 was approximately 40-50 nm in diameter. In vitro targeting experiments confirmed that the C11 ligand had a high affinity for HAP, while the CH6 aptamer had a high affinity for osteoblasts. The in vivo biodistribution analysis showed that CH6-PAMAM-C11 could rapidly accumulate in bone within 4 h and 12 h and then deliver drugs to sites of osteoblast activity. The components of CH6-PAMAM-C11 were well excreted via the kidneys. The accumulation of many more CH6-PAMAM-C11 dual-targeting nanocarriers than single-targeting nanocarriers was observed in the periosteal layer of the rat skull, along with aggregation at sites of osteoblast activity. All of these results indicate that CH6-PAMAM-C11 may be a promising nanocarrier for the delivery of drugs to bone, particularly for the treatment of osteoporosis, and our research strategy may serve as a reference for research in targeted drug, small molecule drug and nucleic acid delivery.

Influence of Polyvinyl Alcohol (PVA) on PVA-Poly-N-hydroxyethyl-aspartamide (PVA-PHEA) Microcrystalline Solid Dispersion Films

This study was conducted to formulate buccal films consisting of polyvinyl alcohol (PVA) and poly-N-hydroxyethyl-aspartamide (PHEA), to improve the dissolution of the drug through the oral mucosa. Ibuprofen sodium salt was used as a model drug, and the buccal film was expected to enhance its dissolution rate. Two different concentrations of PVA (5% w/v and 7.5% w/v) were used. Solvent casting was used to prepare films, where a solution consisting of drug and polymer was cast and allowed to dry. Attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR), differential scanning calorimetry (DSC), and scanning electron microscopy (SEM) were used to investigate the properties of films. In vitro dissolution studies were also conducted to investigate drug release. SEM studies showed that films containing a higher concentration of PVA had larger particles in microrange. FTIR studies confirmed the presence of the drug in films and indicated that ibuprofen sodium did not react with polymers. DSC studies confirmed the crystalline form of ibuprofen sodium when incorporated within films. In vitro dissolution studies found that the dissolution percentage of ibuprofen sodium alone was increased when incorporated within the film from 59 to 74%. This study led to the development of solid microcrystalline dispersion as a buccal film with a faster dissolution rate than the drug alone overcoming problem of poor solubility.

Integration of iron oxide nanoparticles and polyaspartamide biopolymer for MRI image contrast enhancement and an efficient drug-delivery system in cancer therapy

We integrate superparamagnetic iron oxide nanoparticles with polyaspartamide (PA) biopolymer to form a biological construct that functions as a tracking, targeting and drug-delivery system for cancer diagnosis and therapy. Iron oxide nanoparticles with uniformly distributed average spherical diameters of around 10 nm and superparamagnetic characteristics play a key role in increasing the transverse 1/T ₂ relaxation rate or darkening the T ₂-weighted MR image for cancer diagnosis using MRI. In in vitro MRI testing on cancer cells, the MR images of samples with the bio-constructshow a much clearer contrast effect than those of controls. The PA biopolymer plays an essential role in enhancing the hydrophilicity and biocompatibility of the bio-construct. In addition, as a multifunctional polymer, PA is conjugated with biotin and doxorubicin (Dox) functional groups to enhance targeting and impairment of cancer cells. In in vivo testing on cancer tumors, injection with the bio-construct decreased the magnitude of cancer tumor volume growth by three times compared with that of uninjected controls. The physicochemical characteristics of the bio-construct and the roles of biotin and Dox functional groups are examined and discussed in detail.

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.

Bone-targeting carbon dots: effect of nitrogen-doping on binding affinity

Novel fluorescent carbon dots (CDs) for bone imaging were fabricated via a facile hydrothermal method using alendronate in the absence of a nitrogen-doping precursor to enhance bone affinity. One-step synthesized alendronate-based CDs (Alen-CDs) had strong binding activity for calcium-deficient hydroxyapatite (CDHA, the mineral component of bones) scaffold, rat femur, and bone structures of live zebrafish. This was attributed to the bisphosphonate group present on the CD surface, even after carbonization. For comparison, the surface effects of nitrogen-doped CDs obtained using ethylenediamine (EDA), i.e., Alen-EDA-CDs, were also investigated, focusing on the targeting ability of distinct surface functional groups when compared with Alen-CDs. An in vivo study to assess the impact on bone affinity revealed that Alen-CDs effectively accumulated in the bone structures of live zebrafish larvae after microinjections, as well as in the bone tissues of femur extracted from rats. Moreover, Alen-CD-treated zebrafish larvae had superior toleration, retaining skeletal fluorescence for 7 days post-injection (dpi). The sustainable capability, surpassing that of Alizarin Red S, suggests that Alen-CDs have the potential for targeted drug delivery to damaged bone tissues and provides motivation for additional in vivo investigations. To our knowledge, this is the first in vitro, ex vivo, and in vivo demonstration of direct bone-targeted deliveries, supporting the use of fluorescent CDs in the treatment of various bone diseases such as osteoporosis, Paget's disease, and metastatic bone cancer.

Fluorescent carbon dots selectively bind to skull tissues with high affinity, including a strong binding activity for calcium deficient hydroxyapatite, and rat femur, for bone targeted imaging.

Near-Infrared Light Responsive Folate Targeted Gold Nanorods for Combined Photothermal-Chemotherapy of Osteosarcoma

Folate-targeted gold nanorods (GNRs) are proposed as selective theranostic agents for osteosarcoma treatment. An amphiphilic polysaccharide based graft-copolymer (INU-LA-PEG-FA) and an amino derivative of the α,β-poly(N-2-hydroxyethyl)-d,l-aspartamide functionalized with folic acid (PHEA-EDA-FA), have been synthesized to act as coating agents for GNRs. The obtained polymer-coated GNRs were characterized in terms of size, shape, zeta potential, chemical composition, and aqueous stability. They protected the anticancer drug nutlin-3 and were able to deliver it efficiently in different physiological media. The ability of the proposed systems to selectively kill tumor cells was tested on U2OS cancer cells expressing high levels of FRs and compared with human bronchial epithelial cells (16HBE) and human dermal fibroblasts (HDFa). The property of the nanosystems of efficiently controlling drug release upon NIR laser irradiation and of acting as an excellent hyperthermia agent as well as Two Photon Luminescence imaging contrast agents was demonstrated. The proposed folate-targeted GNRs have also been tested in terms of chemoterapeutic and thermoablation efficacy on tridimensional (3-D) osteosarcoma models.

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.

Physiologic Activity of Bisphosphonates – Recent Advances

Background:

Bisphosphonates are drugs commonly used for the medication and prevention of diseases caused by decreased mineral density. Despite such important medicinal use, they display a variety of physiologic activities, which make them promising anti-cancer, anti-protozoal, antibacterial and antiviral agents.

Objective:

To review physiological activity of bisphosphonates with special emphasis on their ongoing and potential applications in medicine and agriculture.

Method:

Critical review of recent literature data.

Results:

Comprehensive review of activities revealed by bisphosphonates.

Conclusion:

although bisphosphonates are mostly recognized by their profound effects on bone physiology their medicinal potential has not been fully evaluated yet. Literature data considering enzyme inhibition suggest possibilities of far more wide application of these compounds. These applications are, however, limited by their low bioavailability and therefore intensive search for new chemical entities overcoming this shortage are carried out.

Bone-targeted delivery of nanodiamond-based drug carriers conjugated with alendronate for potential osteoporosis treatment

This paper describes the design of alendronate-conjugated nanodiamonds (Alen-NDs) and evaluation of their feasibility for bone-targeted delivery. Alen-NDs exhibited a high affinity to hydroxyapatite (HAp, the mineral component of bone) due to the presence of Alen. Unlike NDs (without Alen), Alen-NDs were preferentially taken up by MC3T3-E1 osteoblast-like cells, compared to NIH3T3 and HepG2 cells, suggesting their cellular specificity. In addition, NDs itself increased ALP activity of MC3T3-E1 cells, compared to control group (osteogenic medium) and Alen-NDs exhibited more enhanced ALP activity. In addition, an in vivo study revealed that Alen-NDs effectively accumulated in bone tissues after intravenous tail vein injection. These results confirm the superior properties of Alen-NDs with advantages of high HAp affinity, specific uptake for MC3T3-E1 cells, positive synergistic effect for ALP activity, and in vivo bone targeting ability. The Alen-NDs can potentially be employed for osteoporosis treatment by delivering both NDs and Alen to bone tissue.