The use of layered double hydroxides as DNA vaccine delivery vector for enhancement of anti-melanoma immune response

Synthesis and characterization of layered double hydroxides and their potential as nonviral gene delivery vehicles

Layered double hydroxides (LDHs) exhibit characteristic anion-exchange chemistry making them ideal carriers of negatively charged molecules like deoxyribonucleic acid (DNA). In this study, hydrotalcite (Mg-Al) and hydrotalcite-like compounds (Mg-Fe, Zn-Al, and Zn-Fe), also known as LDHs, were evaluated for their potential application as a carrier of DNA. LDHs were prepared by coprecipitation at low supersaturation and characterized by Powder X-ray diffraction (XRD), infrared (IR), Raman, and inductively coupled plasma-optical emission spectroscopy, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). XRD patterns showed strong and sharp diffraction peaks for the (003) and (006) planes indicating well-ordered crystalline materials. TEM images yielded irregular circular to hexagonal-shaped particles of 50-250 nm in size. Varying degrees of DNA binding was observed for all the compounds, and nuclease digestion studies revealed that the LDHs afford some degree of protection to the bound DNA. Minimal toxicity was observed in human embryonic kidney (HEK293), cervical cancer (HeLa) and hepatocellular carcinoma (HepG2) cell lines with most showing a cell viability in excess of 80 %. All LDH complexes promoted significant levels of luciferase gene expression, with the DNA:Mg-Al LDHs proving to be the most efficient in all cell lines.

Size-tunable LDH–protein hybrids toward the optimization of drug nanocarriers

Stabilization of LDH nanoparticles containing chloride and dodecylsulfate with BSA points to optimization of drug nanocarriers based on these solids.

Highly biocompatible behaviour and slow degradation of a LDH (layered double hydroxide)-coating on implants in the middle ear of rabbits

Chronic inflammation can irreversibly damage components of the ossicular chain which may lead to sound conduction deafness. The replacement of impaired ossicles with prostheses does not reduce the risk of bacterial infections which may lead to loss of function of the implant and consequently to additional damage of the connected structures such as inner ear, meninges and brain. Therefore, implants that could do both, reconstruct the sound conduction and in addition provide antibacterial protection are of high interest for ear surgery. Layered double hydroxides (LDHs) are promising novel biomaterials that have previously been used as an antibiotic-releasing implant coating to curb bacterial infections in the middle ear. However, animal studies of LDHs are scarce and there exist only few additional data on the biocompatibility and hardly any on the biodegradation of these compounds. In this study, middle ear prostheses were coated with an LDH compound, using suspensions of nanoparticles of an LDH containing Mg and Al as well as carbonate ions. These coatings were characterized and implanted into the middle ear of healthy rabbits for 10 days. Analysis of the explanted prostheses showed only little signs of degradation. A stable health constitution was observed throughout the whole experiment in every animal. The results show that LDH-based implant coatings are biocompatible and dissolve only slowly in the middle ear. They, therefore, appear as promising materials for the construction of controlled drug delivery vehicles.

Dexamethasone sodium phosphate intercalated layered double hydroxides and their therapeutic efficacy in a murine asthma model

Schematic diagram showing the intercalation of Dexa into the MgAl–LDH interlayers.

Particulate inorganic adjuvants: recent developments and future outlook

Objectives

To review the state of the art and assess future potential in the use of inorganic particulates as vaccine adjuvants.

Key findings

An adjuvant is an entity added to a vaccine formulation to ensure that robust immunity to the antigen is inculcated. The inclusion of an adjuvant is typically vital for the efficacy of vaccines using inactivated organisms, subunit and DNA antigens. With increasing research efforts being focused on subunit and DNA antigens because of their improved safety profiles, the development of appropriate adjuvants is becoming ever more crucial. Despite this, very few adjuvants are licensed for use in humans (four by the FDA, five by the European Medicines Agency). The most widely used adjuvant, alum, has been used for nearly 90 years, yet its mechanism of action remains poorly understood. In addition, while alum produces a powerful antibody Th2 response, it does not provoke the cellular immune response required for the elimination of intracellular infections or cancers. New adjuvants are therefore needed, and inorganic systems have attracted much attention in this regard.

Summary

In this review, the inorganic adjuvants currently in use are considered, and the efforts made to date to understand their mechanisms of action are summarised. We then move on to survey the literature on inorganic particulate adjuvants, focusing on the most interesting recent developments in this area and their future potential.

In vitro antioxidant activity and in vivo antifatigue effect of layered double hydroxide nanoparticles as delivery vehicles for folic acid

Folic acid antioxidants were successfully intercalated into layered double hydroxides (LDH) nanoparticles according to a previous method with minor modification. The resultant folic acid-LDH constructs were then characterized by X-ray powder diffraction and transmission electron microscopy. The in vitro antioxidant activities, cytotoxicity effect, and in vivo antifatigue were examined by a series of assays. The results showed that folic acid-LDH antioxidant system can scavenge 1,1-diphenyl-2-picrylhydrazyl and hydroxyl free radicals and chelate pro-oxidative Cu²⁺. The in vitro cytotoxicity assays indicated that folic acid-LDH antioxidant system had no significant cytotoxic effect or obvious toxicity to normal cells. It also prolonged the forced swimming time of the mice by 32% and 51% compared to folic acid and control groups, respectively. It had an obvious effect on decreasing the blood urea nitrogen and blood lactic acid, while increasing muscle and hepatic glycogen levels. Therefore, folic acid-LDH might be used as a novel antioxidant and antifatigue nutritional supplement.

Nanohybrid based on antibiotic encapsulated layered double hydroxide as a drug delivery system

Nanohybrid of cefuroxime (CFO) with layered double hydroxide (LDH) has been prepared, and the rate of dissolution and bioavailability of CFO using nanohybrid as a drug delivery system has been broadly studied. The intercalation process was confirmed by X-ray diffraction, Fourier transform infrared spectroscopy, and thermogravimetric analysis. The CFO contents were found to be 19.0 wt% in the nanohybrid. The release mechanism of CFO was investigated with respect to anion and pH of the dissolution media such as gastric, intestinal and blood simulated media. The effect of pH was evaluated on the release of CFO from nanohybrid, and the dissolution of CFO from the nanohybrid was found to be a slow process at pH 4.0, 6.8, and 7.4. Further the addition of Cl ion and PAM in release media did not affect the release rate of drug at pH 4.0 and 6.8, while at pH 7.4, Cl ion and PAM have significant role on the drug release. At pH 1.2, the release study shows that LDH dissolved in the acidic medium and CFO released in its molecular form. The release behavior suggests two mechanisms that are responsible for the release of CFO from nanohybrid: weathering (dependent on the pH) and ion exchange (highly dependent on the anions). Surface reactions mediated by solid weathering ruled the release in gastric fluid, whereas anion exchange determined CFO release in lysosomal, intestinal, and blood medium. In order to evaluate the drug release mechanism, the released data were fitted by mathematical models describing various kinetic.

Influence of hydrothermal treatment on physicochemical properties and drug release of anti-inflammatory drugs of intercalated layered double hydroxide nanoparticles

The synthesis method of layered double hydroxides (LDHs) determines nanoparticles’ performance in biomedical applications. In this study, hydrothermal treatment as an important synthesis technique has been examined for its influence on the physicochemical properties and the drug release rate from drug-containing LDHs. We synthesised MgAl–LDHs intercalated with non-steroidal anti-inflammatory drugs (i.e., naproxen, diclofenac and ibuprofen) using a co-precipitation method with or without hydrothermal treatment (150 °C, 4 h). After being hydrothermally treated, LDH–drug crystallites increased in particle size and crystallinity, but did not change in the interlayer anion orientation, gallery height and chemical composition. The drug release patterns of all studied LDH–drug hybrids were biphasic and sustained. LDHs loaded with diclofenac had a quicker drug release rate compared with those with naproxen and ibuprofen, and the drug release from the hydrothermally-treated LDH–drug was slower than the freshly precipitated LDH–drug. These results suggest that the drug release of LDH–drugs is influenced by the crystallite size of LDHs, which can be controlled by hydrothermal treatment, as well as by the drug molecular physicochemical properties.

Immunity induced by a broad class of inorganic crystalline materials is directly controlled by their chemistry

There is currently no paradigm in immunology that enables an accurate prediction of how the immune system will respond to any given agent. Here we show that the immunological responses induced by members of a broad class of inorganic crystalline materials are controlled purely by their physicochemical properties in a highly predictable manner. We show that structurally and chemically homogeneous layered double hydroxides (LDHs) can elicit diverse human dendritic cell responses in vitro. Using a systems vaccinology approach, we find that every measured response can be modeled using a subset of just three physical and chemical properties for all compounds tested. This correlation can be reduced to a simple linear equation that enables the immunological responses stimulated by newly synthesized LDHs to be predicted in advance from these three parameters alone. We also show that mouse antigen-specific antibody responses in vivo and human macrophage responses in vitro are controlled by the same properties, suggesting they may control diverse responses at both individual component and global levels of immunity. This study demonstrates that immunity can be determined purely by chemistry and opens the possibility of rational manipulation of immunity for therapeutic purposes.

Potential for layered double hydroxides-based, innovative drug delivery systems

Layered Double Hydroxides (LDHs)-based drug delivery systems have, for many years, shown great promises for the delivery of chemical therapeutics and bioactive molecules to mammalian cells in vitro and in vivo. This system offers high efficiency and drug loading density, as well as excellent protection of loaded molecules from undesired degradation. Toxicological studies have also found LDHs to be biocompatible compared with other widely used nanoparticles, such as iron oxide, silica, and single-walled carbon nanotubes. A plethora of bio-molecules have been reported to either attach to the surface of or intercalate into LDH materials through co-precipitation or anion-exchange reaction, including amino acid and peptides, ATPs, vitamins, and even polysaccharides. Recently, LDHs have been used for gene delivery of small molecular nucleic acids, such as antisense, oligonucleotides, PCR fragments, siRNA molecules or sheared genomic DNA. These nano-medicines have been applied to target cells or organs in gene therapeutic approaches. This review summarizes current progress of the development of LDHs nanoparticle drug carriers for nucleotides, anti-inflammatory, anti-cancer drugs and recent LDH application in medical research. Ground breaking studies will be highlighted and an outlook of the possible future progress proposed. It is hoped that the layered inorganic material will open up new frontier of research, leading to new nano-drugs in clinical applications.

The induction of maturation on dendritic cells by TiO2 and Fe(3)O(4)@TiO(2) nanoparticles via NF-κB signaling pathway

Nanomaterials are increasingly used in many fields, including drug vectors and vaccine formulation. In this study, nano-TiO(2) and magnetic Fe(3)O(4)@TiO(2) were synthesized and their abilities to activate dendritic cells were investigated. The signaling pathway involved in their effects on the cellular functions was also explored. First, nano-TiO(2) and Fe(3)O(4)@TiO(2) were prepared with diameters of 82nm and 63nm, and zeta potentials of 41.5mV and 30.2mV, respectively. The magnetic property of Fe(3)O(4)@TiO(2) was detected to be 12.9emu/g. Both kinds of nanoparticles were proved to have good biocompatibility in vitro. Second, the exposure of nano-TiO2 and Fe(3)O(4)@TiO(2)caused an increased expression of TNF-α, CD86 and CD80, and besides, Fe(3)O(4)@TiO(2)showed a certain up-regulation on MHC-II. The cellular uptake of Ovalbumin on BMDCs could be strongly improved by nano-TiO2 and Fe(3)O(4)@TiO(2)as detected via flow cytometer and confocal observation. Further investigation revealed that nano-TiO(2) and Fe(3)O(4)@TiO(2)significantly increased the NF-κB expression in the nucleus, indicating that the NF-κB signaling pathway was involved in the dendritic cell maturation. Our results suggested that nano-TiO(2) and Fe(3)O(4)@TiO(2)may function as a useful vector to promote vaccine delivery in immune cells, and Fe(3)O(4)@TiO(2)provided a possibility to deliver and track vaccines via its magnetofection.

Pathogen-like particles: biomimetic vaccine carriers engineered at the nanoscale

Vaccine adjuvants are an essential component of vaccine design, helping to generate immunity to pathogen antigens in the absence of infection. Recent advances in nanoscale engineering have created a new class of particulate bionanotechnology that uses biomimicry to better integrate adjuvant and antigen. These pathogen-like particles, or PLPs, can come from a variety of sources, ranging from fully synthetic platforms to biologically derived, self-assembling systems. By employing molecularly engineered targeting and stimulation of key immune cells, recent studies utilizing PLPs as vaccine delivery platforms have shown great promise against high-impact, unsolved vaccine targets ranging from bacterial and viral pathogens to cancer and addiction.

The enhanced immune response of hepatitis B virus DNA vaccine using SiO2@LDH nanoparticles as an adjuvant

Various approaches have been used to improve systemic immune response to infectious disease or virus, and DNA vaccination has been demonstrated to be one of these effective ways to elicit protective immunity against pathogens. Our previous studies showed that layered double hydroxides (LDH) nanoparticles could be efficiently taken up by the MDDCs and had an adjuvant activity for DC maturation. To further enhance the immune adjuvant activity of LDH, core-shell structure SiO2@LDH nanoparticles were synthesized with an average diameter of about 210 nm. And its high transfection efficiency in vitro was demonstrated by using GFP expression plasmid as model DNA. Exposing SiO2@LDH nanoparticles to macrophages caused a higher dose-dependent expression of IFN-γ, IL-6, CD86 and MHC II, compared with SiO2 and LDH respectively. Furthermore, in vivo immunization of BALB/c mice indicated that, DNA vaccine loaded-SiO2@LDH nanoparticles not only induced much higher serum antibody response than naked DNA vaccine and plain nanoparticles, but also obviously promoted T-cell proliferation and skewed T helper to Th1 polarization. Additionally, it was proved that the caveolae-mediated uptake of SiO2@LDH nanoparticles by macrophage lead to macrophages activation via NF-κB signaling pathway. Our results indicate that SiO2@LDH nanoparticles could serve as a potential non-viral gene delivery system.

Applications of nanotechnology for melanoma treatment, diagnosis, and theranostics

Melanoma is the most aggressive type of skin cancer and has very high rates of mortality. An early stage melanoma can be surgically removed, with a survival rate of 99%. However, metastasized melanoma is difficult to cure. The 5-year survival rates for patients with metastasized melanoma are still below 20%. Metastasized melanoma is currently treated by chemotherapy, targeted therapy, immunotherapy and radiotherapy. The outcome of most of the current therapies is far from optimistic. Although melanoma patients with a mutation in the oncogene v-Raf murine sarcoma viral oncogene homolog B1 (BRAF) have an initially higher positive response rate to targeted therapy, the majority develop acquired drug resistance after 6 months of the therapy. To increase treatment efficacy, early diagnosis, more potent pharmacological agents, and more effective delivery systems are urgently needed. Nanotechnology has been extensively studied for melanoma treatment and diagnosis, to decrease drug resistance, increase therapeutic efficacy, and reduce side effects. In this review, we summarize the recent progress on the development of various nanoparticles for melanoma treatment and diagnosis. Several common nanoparticles, including liposome, polymersomes, dendrimers, carbon-based nanoparticles, and human albumin, have been used to deliver chemotherapeutic agents, and small interfering ribonucleic acids (siRNAs) against signaling molecules have also been tested for the treatment of melanoma. Indeed, several nanoparticle-delivered drugs have been approved by the US Food and Drug Administration and are currently in clinical trials. The application of nanoparticles could produce side effects, which will need to be reduced so that nanoparticle-delivered drugs can be safely applied in the clinical setting.

The in vitro sustained release profile and antitumor effect of etoposide-layered double hydroxide nanohybrids

Magnesium-aluminum layered double hydroxides intercalated with antitumor drug etoposide (VP16) were prepared for the first time using a two-step procedure. The X-ray powder diffraction data suggested the intercalation of VP16 into layers with the increased basal spacing from 0.84–1.18 nm was successful. Then, it was characterized by X-ray powder diffraction, Fourier transform infrared spectroscopy, thermogravimetry and differential thermal analysis, and transmission electron microscopy. The prepared nanoparticles, VP16-LDH, showed an average diameter of 62.5 nm with a zeta potential of 20.5 mV. Evaluation of the buffering effect of VP16-LDH indicated that the nanohybrids were ideal for administration of the drugs that treat human stomach irritation. The loading amount of intercalated VP16 was 21.94% and possessed a profile of sustained release. The mechanism of VP16-LDH release in the phosphate buffered saline solution at pH 7.4 is likely controlled by the diffusion of VP16 anions from inside to the surface of LDH particles. The in vitro cytotoxicity and antitumor assays indicated that VP16-LDH hybrids were less toxic to GES-1 cells while exhibiting better antitumor efficacy on MKN45 and SGC-7901 cells. These results imply that VP16-LDH is a potential antitumor drug for a broad range of gastric cancer therapeutic applications.

A facile synthesis of strong near infrared fluorescent layered double hydroxide nanovehicles with an anticancer drug for tumor optical imaging and therapy

In this work, a new multifunctional nanovehicle for tumor optical imaging and therapy was developed using Y2O3:Er(3+),Yb(3+) nanoparticles as near infrared fluorescent nanophosphors, and MgAl-layered double hydroxide (LDH) nanosheets as anticancer drug nanovehicles. Monodispersed Y2O3:Er(3+),Yb(3+) nanophosphors were readily synthesized by the urea assisted homogenous precipitation method. Hierarchically structured LDH nanosheets intercalated with an anticancer drug, fluorouracil (5FU), were deposited on the surface of Y2O3:Er(3+),Yb(3+)@SiO2 by a simple precipitation method followed by hydrothermal treatment. The resultant Y2O3:Er(3+),Yb(3+)@SiO2@LDH-5FU nanovehicles exhibit strong red upconversion fluorescence under the excitation of a 980 nm laser, which allows tracking of the nanovehicles after localization in cancer cells. A better anticancer efficiency was obtained over the nanovehicles than the free drug which can be attributed to their positively charged surfaces for favorable interaction with the negatively charged cell membranes. The multifunctional nanovehicles designed in this work are expected to be promising material candidates for simultaneous tumor optical imaging and therapy.

Layered double hydroxides as efficient drug delivery system of ciprofloxacin in the middle ear: an animal study in rabbits

Chronic otitis media is a common disease often accompanied by recurrent bacterial infections. These may lead to the destruction of the middle ear bones such that prostheses have to be implanted to restore sound transmission. Surface coatings with layered double hydroxides (LDHs) are evaluated here as a possibility for drug delivery systems with convenient advantages such as low cytotoxicity and easy synthesis. Male New Zealand White rabbits were implanted with Bioverit(®) II middle ear prostheses coated with the LDH Mg(4)Al(2)(OH)(12)(SO(4))(2)·6H(2)O impregnated with ciprofloxacin. 12 (group 1) were directly infected with Pseudomonas aeruginosa and another 12 (group 2) 1 week after the implantation. Clinical outcome, blood counts, histological analyses and microbiological examination showed an excellent antimicrobial activity for group 1, whereas this effect was attenuated in animals where infection was performed 1 week after implantation. This is the first study to demonstrate an efficient drug delivery system with an LDH coating on prostheses in the middle ear.

The improvement of the anticancer effect of a novel compound benzoic acid, 2-hydroxy-, 2-D-ribofuranosylhydrazide (BHR) loaded in solid lipid nanoparticles

A novel drug delivery system consisting of benzoic acid, 2-hydroxy-, 2-D-ribofuranosylhydrazide (BHR)-loaded solid lipid nanoparticles (BHR-SLNs) was prepared using the emulsification-evaporation technique. The mean particle size of the BHR-SLNs measured by photon correlation spectroscopy was about 75 nm. BHR-SLN morphology was assessed by transmission electron microscopy and atomic force microscopy. The drug entrapment efficiency was 70.2%, as determined via Sephadex gel chromatography and high-performance liquid chromatography. Drug release assessment in vitro showed that BHR was gradually released from SLNs in a time-dependent manner. Furthermore, treatment of 293T and Hela cells with BHR-SLNs demonstrated that BHR-SLNs were less toxic to normal cells while more effective in antitumor potency compared with the BHR drug alone. The results imply that BHR-SLNs could be considered as a promising antitumor drug system for a range of new therapeutic applications.

pH-sensitive strontium carbonate nanoparticles as new anticancer vehicles for controlled etoposide release

Strontium carbonate nanoparticles (SCNs), a novel biodegradable nanosystem for the pH-sensitive release of anticancer drugs, were developed via a facile mixed solvent method aimed at creating smart drug delivery in acidic conditions, particularly in tumor environments. Structural characterization of SCNs revealed that the engineered nanocarriers were uniform in size and presented a dumbbell-shaped morphology with a dense mass of a scale-like spine coating, which could serve as the storage structure for hydrophobic drugs. Chosen as a model anticancer agent, etoposide was effectively loaded into SCNs based on a simultaneous process that allowed for the formation of the nanocarriers and for drug storage to be accomplished in a single step. The etoposide-loaded SCNs (ESCNs) possess both a high loading capacity and efficient encapsulation. It was found that the cumulative release of etoposide from ESCNs is acid-dependent, and that the release rate is slow at a pH of 7.4; this rate increases significantly at low pH levels (5.8, 3.0). Meanwhile, it was also found that the blank SCNs were almost nontoxic to normal cells, and ESCN systems were evidently more potent in antitumor activity compared with free etoposide, as confirmed by a cytotoxicity test using an MTT assay and an apoptosis test with fluorescence-activated cell sorter (FACS) analysis. These findings suggest that SCNs hold tremendous promise in the areas of controlled drug delivery and targeted cancer therapy.

One-step bulk preparation of calcium carbonate nanotubes and its application in anticancer drug delivery

Bulk fabrication of ordered hollow structural particles (HSPs) with large surface area and high biocompatibility simultaneously is critical for the practical application of HSPs in biosensing and drug delivery. In this article, we describe a smart approach for batch synthesis of calcium carbonate nanotubes (CCNTs) based on supported liquid membrane (SLM) with large surface area, excellent structural stability, prominent biocompatibility, and acid degradability. The products were characterized by transmission electron micrograph, X-ray diffraction, Fourier transform infrared spectra, UV-vis spectroscopy, zeta potential, and particle size distribution. The results showed that the tube-like structure facilitated podophyllotoxin (PPT) diffusion into the cavity of hollow structure, and the drug loading and encapsulation efficiency of CCNTs for PPT are as high as 38.5 and 64.4 wt.%, respectively. In vitro drug release study showed that PPT was released from the CCNTs in a pH-controlled and time-dependent manner. The treatment of HEK 293T and SGC 7901 cells demonstrated that PPT-loaded CCNTs were less toxic to normal cells and more effective in antitumor potency compared with free drugs. In addition, PPT-loaded CCNTs also enhanced the apoptotic process on tumor cells compared with the free drugs. This study not only provides a new kind of biocompatible and pH-sensitive nanomaterial as the feasible drug container and carrier but more importantly establishes a facile approach to synthesize novel hollow structural particles on a large scale based on SLM technology.