Enhanced Transfection Efficiency into Macrophages and Dendritic Cells by a Combination Method Using Mannosylated Lipoplexes and Bubble Liposomes with Ultrasound Exposure

Stimuli-Responsive Biomaterials for Vaccines and Immunotherapeutic Applications

The immune system is the key target for vaccines and immunotherapeutic approaches aimed at blunting infectious diseases, cancer, autoimmunity, and implant rejection. However, systemwide immunomodulation is undesirable due to the severe side effects that typically accompany such strategies. In order to circumvent these undesired, harmful effects, scientists have turned to tailorable biomaterials that can achieve localized, potent release of immune-modulating agents. Specifically, "stimuli-responsive" biomaterials hold a strong promise for delivery of immunotherapeutic agents to the disease site or disease-relevant tissues with high spatial and temporal accuracy. This review provides an overview of stimuli-responsive biomaterials used for targeted immunomodulation. Stimuli-responsive or "environmentally responsive" materials are customized to specifically react to changes in pH, temperature, enzymes, redox environment, photo-stimulation, molecule-binding, magnetic fields, ultrasound-stimulation, and electric fields. Moreover, the latest generation of this class of materials incorporates elements that allow for response to multiple stimuli. These developments, and other stimuli-responsive materials that are on the horizon, are discussed in the context of controlling immune responses.

Biodegradable nanoparticles decorated with different carbohydrates for efficient macrophage-targeted gene therapy

Macrophages are attractive therapeutic targets due to their contributions to many pathological processes including cancers, atherosclerosis, obesity, diabetes and other inflammatory diseases. Macrophage-targeted gene therapy is an effective strategy for regulating macrophage function at the site of inflammation to treat related diseases. However, macrophages are recognized as difficult to transfect cells and non-specific delivery would inevitably cause unwanted systemic side effects. Herein, we prepared a series of macrophage-targeted nanoparticles (NPs) using cationic lipid-like compound G0-C14 and different carbohydrates-modified poly(lactide-co-glycolide) (PLGA) or poly(lactide-coglycolide)-b-poly(ethylene glycol) (PLGA-PEG) for gene delivery by a robust self-assembly method. The yielded NPs were decorated with carbohydrate-based targeting moieties including mannose, galactose, dextran, and a mixture of mannose and galactose. EGFP messenger RNA (mRNA) and GFP plasmid DNA (pDNA) were used as reporter genes to evaluate NP-mediated gene transfection in macrophages. Experimental results of macrophage phagocytosis demonstrated that more carbohydrate-decorated NPs were endocytosed by Raw 264.7 cells than the ones without carbohydrate modification. Mannose-decorated NPs showed better targeting ability to macrophages than NPs decorated with galactose only and a blended mixture of mannose and galactose. It is worth noting that polysaccharide dextran-modified NPs also exhibited evident targeting effects. CCK-8 assay revealed that no cytotoxicity was observed for all tested NP concentrations up to 2.8 mg/mL. The carbohydrate-decorated polymer/G0-C14 exhibited strong entrapment of mRNA and pDNA with an encapsulation efficiency of above 95%. The targeted NPs significantly improved cellular internalization and transfection efficiency in macrophages, depending on the type and content of the carbohydrate moieties presented on the NP surface. Interestingly, dextran-decorated NPs showing higher endocytosis at various concentrations in macrophages also demonstrated more efficient mRNA transfection, suggesting that the NP-mediated mRNA transfection efficiency was consistent with the endocytosis results.

Enhanced macrophage delivery to the colon using magnetic lipoplexes with a magnetic field

Magnetically guided cell delivery systems would be valuable to achieve effective macrophage-based cell therapy for colonic inflammatory diseases. In the current study, we developed a method for the efficient and simultaneous introduction of superparamagnetic iron oxide nanoparticles (SPIONs) and plasmid DNA (pDNA) into RAW264 murine macrophage-like cells using SPION-incorporated cationic liposome/pDNA complexes (magnetic lipoplexes). SPIONs and pDNA were introduced for magnetization and functionalization of the macrophages, respectively. We also evaluated the adhesive properties of magnetized RAW264 cells using magnetic lipoplexes in the murine colon under a magnetic field. Significant cellular association and gene expression without cytotoxicity were observed when magnetic cationic liposomes and pDNA were mixed at a weight ratio of 10:1, and SPION concentration and magnetic field exposure time was 0.1 mg/mL and 10 min, respectively. We also observed that cytokine production in magnetized RAW264 cells was similar to that in non-treated RAW264 cells, whereas nitric oxide production was significantly increased in magnetized RAW264 cells. Furthermore, magnetized RAW264 cells highly adhered to a Caco-2 cell monolayer and colon in mice, under a magnetic field. These results suggest that this magnetic cell delivery system can improve the colonic delivery of macrophages and its therapeutic efficacy against colonic inflammatory diseases.

Mannosylated nanocarriers mediated site-specific drug delivery for the treatment of cancer and other infectious diseases: A state of the art review

The non-modified nanocarriers-based therapies for the treatment of cancer and other infectious diseases enhanced the chemical stability of therapeutically active agents, protected them from enzymatic degradation and extended their blood circulation time. However, the lack of specificity and off-target effects limit their applications. Mannose receptors overexpressed on antigen presenting cells such as dendritic cells and macrophages are one of the most desirable targets for treating cancer and other infectious diseases. Therefore, the development of mannosylated nanocarrier formulation is one of the most extensively explored approaches for targeting these mannose receptors. The present manuscript gives readers the background information on C-type lectin receptors followed by the roles, expression, and distribution of the mannose receptors. It further provides a detailed account of different mannosylated nanocarrier formulations. It also gives the tabular information on most relevant and recently granted patents on mannosylated systems. The overview of mannosylated nanocarrier formulations depicted site-specific targeting, enhanced pharmacokinetic/pharmacodynamic profiles, and improved transfection efficiency of the therapeutically active agents. This suggests the bright future ahead for mannosylated nanocarriers in the treatment of cancer and other infectious diseases. Nevertheless, the mechanism behind the enhanced immune response by mannosylated nanocarriers and their thorough clinical and preclinical evaluation need to explore further.

Ultrasound-Targeted Microbubble Destruction (UTMD) Combined with Liposome Increases the Effectiveness of Suppressing Proliferation, Migration, Invasion, and Epithelial- Mesenchymal Transition (EMT) via Targeting Metadherin (MTDH) by ShRNA

Background

Reports show that ultrasound-targeted microbubble destruction (UTMD) is a promising method of gene therapy, and metadherin (MTDH) is related to the development of breast cancer. Thus, we investigated the role of MTDH in breast cancer and compared the effect of suppressing MTDH by shRNA using liposome, UTMD, or the combination of these 2 methods.

Material/Methods

Graphing of survival curves of MTDH was analyzed by bioinformatics. UTMD was conducted using an ultrasonic therapeutic apparatus. Cell counting kit-8 (CCK-8) assay was used to measure cell viability. Migration and invasion rates were measured by wound healing test and Transwell invasion assay, respectively. The expression of MTDH, E-cadherin, metastasis-associated protein-1 (MTA-1), matrix metalloproteinase (MMP)-2, and MMP-9 were measured by Western blot and qPCR.

Results

The prognosis of breast cancer can be decreased by the high expression of MTDH, and elevated expression of MTDH was discovered in MCF-7, MCF-10A, and T47D cell lines. UTMD combined with liposome is most efficient in transfecting shRNA, clearly suppressing the expression of MTDH and thereby decreasing cell viability, migration, invasion rate, and epithelial- mesenchymal transition (EMT) processes in the MCF-7 cell line.

Conclusions

UTMD combined with liposome could be used as a more efficient way to transfect shRNA into cells to suppress the expression of MTDH and thus lead to the downregulation of proliferation, migration, and EMT processes of the MCF-7 cell line, showing the potential for use in gene therapy.

Synthesis of high functionality and quality mannose-grafted lipids to produce macrophage-targeted liposomes

The mannose receptor, which is responsible for tumor invasion, proliferation, and metastasis in the tumor microenvironment, is overexpressed in tumor-associated macrophages. Mannose is commonly applied to PEGylated liposomes in macrophage-targeted cancer therapy. To develop a high functionality and quality (HFQ) lipid for macrophage-targeted liposomes, we designed a novel mannosylated lipid with improved mannose receptor binding affinity using serine-glycine repeats (SG)_n. We synthesized Man(S)-(SG)₅-SSK-K(Pal)₂ using only a fluorenylmethyloxycarbonyl (Fmoc) protecting group solid-phase peptide synthesis method, which produced a high-quality lipid at a moderately good yield. We then prepared Man-(SG)₅/PEGylated liposomes using a post-insertion technique to insert Man(S)-(SG)₅-SSK-K(Pal)₂ into the PEGylated liposomes. In vitro cell investigations revealed that the Man-(SG)₅/PEGylated liposomes effectively associated with mouse peritoneal macrophages by interacting with the mannose receptors. The results suggest that we produced a novel high-quality, highly functional mannosylated lipid that is suitable for clinical drug delivery applications.

Effective intraperitoneal gene transfection system using nanobubbles and ultrasound irradiation

In this study, we demonstrate the low toxicity and highly efficient and spatially improved transfection of plasmid DNA (pDNA) with liposomal nanobubbles (bubble liposomes [BLs]) using ultrasound (US) irradiation in mice. Naked pDNA with BLs was intraperitoneally injected, followed by US irradiation. The injection volume, the duration of US irradiation, and the dose of BLs were optimized. Both BLs and US irradiation were essential to achieve high transgene expression from naked pDNA. We observed transgene expression in the entire peritoneal tissues, including the peritoneal wall, liver, spleen, stomach and small and large intestines. The area of transfection could be controlled with focused US irradiation. There were few changes in the morphology of the peritoneum, the peritoneal function or serum alanine aminotransferase levels, suggesting the safety of BLs with US irradiation. Using a tissue-clearing method, the spatial distribution of transgene expression was evaluated. BLs with US irradiation delivered pDNA to the submesothelial layer in the peritoneal wall, whereas transgene expression was restricted to the surface layer in the liver and stomach. Therefore, BLs with US irradiation could be an effective and safe method of gene transfection to the peritoneum.

Stably engineered nanobubbles and ultrasound - An effective platform for enhanced macromolecular delivery to representative cells of the retina

Herein we showcase the potential of ultrasound-responsive nanobubbles in enhancing macromolecular permeation through layers of the retina, ultimately leading to significant and direct intracellular delivery; this being effectively demonstrated across three relevant and distinct retinal cell lines. Stably engineered nanobubbles of a highly homogenous and echogenic nature were fully characterised using dynamic light scattering, B-scan ultrasound and transmission electron microscopy (TEM). The nanobubbles appeared as spherical liposome-like structures under TEM, accompanied by an opaque luminal core and darkened corona around their periphery, with both features indicative of efficient gas entrapment and adsorption, respectively. A nanobubble +/- ultrasound sweeping study was conducted next, which determined the maximum tolerated dose for each cell line. Detection of underlying cellular stress was verified using the biomarker heat shock protein 70, measured before and after treatment with optimised ultrasound. Next, with safety to nanobubbles and optimised ultrasound demonstrated, each human or mouse-derived cell population was incubated with biotinylated rabbit-IgG in the presence and absence of ultrasound +/- nanobubbles. Intracellular delivery of antibody in each cell type was then quantified using Cy3-streptavidin. Nanobubbles and optimised ultrasound were found to be negligibly toxic across all cell lines tested. Macromolecular internalisation was achieved to significant, yet varying degrees in all three cell lines. The results of this study pave the way towards better understanding mechanisms underlying cellular responsiveness to ultrasound-triggered drug delivery in future ex vivo and in vivo models of the posterior eye.

Gene delivery systems by the combination of lipid bubbles and ultrasound

Gene therapy is promising for the treatment of many diseases including cancers and genetic diseases. From the viewpoint of safety, ultrasound (US)-mediated gene delivery with nano/ microbubbles was recently developed as a novel non-viral vector system. US-mediated gene delivery using nano/microbubbles are able to produce transient changes in the permeability of the cell membrane after US-induced cavitation while reducing cellular damage and enables the tissue-specific or the site-specific intracellular delivery of gene both in vitro and in vivo. We have recently developed novel lipid nanobubbles (Lipid Bubbles). These nanobubbles can also be used to enhance the efficacy of the US-mediated genes (plasmid DNA, siRNA, and miRNA etc.) delivery. In this review, we describe US-mediated delivery systems combined with nano/microbubbles and discuss their feasibility as non-viral vector systems.

A semi-synthetic whole parasite vaccine designed to protect against blood stage malaria

Although attenuated malaria parasitized red blood cells (pRBCs) are promising vaccine candidates, their application in humans may be restricted for ethical and regulatory reasons. Therefore, we developed an organic microparticle-based delivery platform as a whole parasite malaria-antigen carrier to mimic pRBCs. Killed blood stage parasites were encapsulated within liposomes that are targeted to antigen presenting cells (APCs). Mannosylated lipid core peptides (MLCPs) were used as targeting ligands for the liposome-encapsulated parasite antigens. MLCP-liposomes, but not unmannosylated liposomes, were taken-up efficiently by APCs which then significantly upregulated expression of MHC-ll and costimulatory molecules, CD80 and CD86. Two such vaccines using rodent model systems were constructed - one with Plasmodium chabaudi and the other with P. yoelii. MLCP-liposome vaccines were able to control the parasite burden and extended the survival of mice. Thus, we have demonstrated an alternative delivery system to attenuated pRBCs with similar vaccine efficacy and added clinical advantages. Such liposomes are promising candidates for a human malaria vaccine.

STATEMENT OF SIGNIFICANCE

Attenuated whole parasite-based vaccines, by incorporating all parasite antigens, are very promising candidates, but issues relating to production, storage and safety concerns are significantly slowing their development. We therefore developed a semi-synthetic whole parasite malaria vaccine that is easily manufactured and stored. Two such prototype vaccines (a P. chabaudi and a P. yoelii vaccine) have been constructed. They are non-infectious, highly immunogenic and give good protection profiles. This semi-synthetic delivery platform is an exciting strategy to accelerate the development of a licensed malaria vaccine. Moreover, this strategy can be potentially applied to a wide range of pathogens.

Targeted gene delivery to the synovial pannus in antigen-induced arthritis by ultrasound-targeted microbubble destruction in vivo

The purpose of this study was to optimize an ultrasound-targeted microbubble destruction (UTMD) technique to improve the in vivo transfection efficiency of the gene encoding enhanced green fluorescent protein (EGFP) in the synovial pannus in an antigen-induced arthritis rabbit model. A mixture of microbubbles and plasmids was locally injected into the knee joints of an antigen-induced arthritis (AIA) rabbits. The plasmid concentrations and ultrasound conditions were varied in the experiments. We also tested local articular and intravenous injections. The rabbits were divided into five groups: (1) ultrasound+microbubbles+plasmid; (2) ultrasound+plasmid; (3) microbubble+plasmid; (4) plasmid only; (5) untreated controls. EGFP expression was observed by fluorescent microscope and immunohistochemical staining in the synovial pannus of each group. The optimal plasmid dosage and ultrasound parameter were determined based on the results of EGFP expression and the present and absent of tissue damage under light microscopy. The irradiation procedure was performed to observe the duration of the EGFP expression in the synovial pannus and other tissues and organs, as well as the damage to the normal cells. The optimal condition was determined to be a 1-MHz ultrasound pulse applied for 5 min with a power output of 2 W/cm(2) and a 20% duty cycle along with 300 μg of plasmid. Under these conditions, the synovial pannus showed significant EGFP expression without significant damage to the surrounding normal tissue. The EGFP expression induced by the local intra-articular injection was significantly more increased than that induced by the intravenous injection. The EGFP expression in the synovial pannus of the ultrasound+microbubbles+plasmid group was significantly higher than that of the other four groups (P<0.05). The expression peaked on day 5, remained detectable on day 40 and disappeared on day 60. No EGFP expression was detected in the other tissues and organs. The UTMD technique can significantly enhance the in vivo gene transfection efficiency without significant tissue damage in the synovial pannus of an AIA model. Thus, this could become a safe and effective non-viral gene transfection procedure for arthritis therapy.

In vitro methods to study bubble-cell interactions: Fundamentals and therapeutic applications

Besides their use as contrast agents for ultrasound imaging, microbubbles are increasingly studied for a wide range of therapeutic applications. In particular, their ability to enhance the uptake of drugs through the permeabilization of tissues and cell membranes shows great promise. In order to fully understand the numerous paths by which bubbles can interact with cells and the even larger number of possible biological responses from the cells, thorough and extensive work is necessary. In this review, we consider the range of experimental techniques implemented in in vitro studies with the aim of elucidating these microbubble-cell interactions. First of all, the variety of cell types and cell models available are discussed, emphasizing the need for more and more complex models replicating in vivo conditions together with experimental challenges associated with this increased complexity. Second, the different types of stabilized microbubbles and more recently developed droplets and particles are presented, followed by their acoustic or optical excitation methods. Finally, the techniques exploited to study the microbubble-cell interactions are reviewed. These techniques operate over a wide range of timescales, or even off-line, revealing particular aspects or subsequent effects of these interactions. Therefore, knowledge obtained from several techniques must be combined to elucidate the underlying processes.

Co-administration of Microbubbles and Drugs in Ultrasound-Assisted Drug Delivery: Comparison with Drug-Carrying Particles

There are two alternative approaches to ultrasound-assisted drug delivery. First, the drug can be entrapped into or attached onto the ultrasound-responsive particles and administered in the vasculature, to achieve ultrasound-triggered drug release from the particles and localized tissue deposition in response to ultrasound treatment of the target zone. Second, the drug can be co-administered with the microbubbles or other sonosensitive particles. In this case, the action of ultrasound on the particles (which act as cavitation nuclei) results in the transient improvement of permeability of the physiological barriers, so that the circulating drug can exit the bloodstream and get into the target tissues and cells. We discuss and compare both of these approaches, their characteristic advantages and disadvantages for the specific drug delivery scenarios. Clearly, the system based on the off-label use of the existing approved microbubbles and drugs (or drug carriers) will have a chance of getting to clinical trials faster and with lesser resources spent. However, if a superior curative potential of a sonosensitive drug carrier is proven, and formulation stability problems are addressed properly, this approach may find its way to practical use, especially for nucleic acid delivery scenarios.

Nonviral gene delivery systems by the combination of bubble liposomes and ultrasound

The combination of therapeutic ultrasound (US) and nano/microbubbles is an important system for establishing a novel and noninvasive gene delivery system. Genes are delivered more efficiently using this system compared with a conventional nonviral vector system such as the lipofection method, resulting in higher gene expression. This higher efficiency is due to the gene being delivered into the cytosol and bypassing the endocytosis pathway. Many in vivo studies have demonstrated US-mediated gene delivery with nano/microbubbles, and several gene therapy feasibility studies for various diseases have been reported. In addition, nano/microbubbles can deliver genes site specifically by the control of US exposure site. In the present review, we summarize the gene delivery systems by the combination of nano/microbubbles and US, describe their properties, and assess applications and challenges of US theranostics.

Intraperitoneal administration of a tumor-associated antigen SART3, CD40L, and GM-CSF gene-loaded polyplex micelle elicits a vaccine effect in mouse tumor models

Polyplex micelles have demonstrated biocompatibility and achieve efficient gene transfection in vivo. Here, we investigated a polyplex micelle encapsulating genes encoding the tumor-associated antigen squamous cell carcinoma antigen recognized by T cells-3 (SART3), adjuvant CD40L, and granulocyte macrophage colony-stimulating factor (GM-CSF) as a DNA vaccine platform in mouse tumor models with different types of major histocompatibility antigen complex (MHC). Intraperitoneally administrated polyplex micelles were predominantly found in the lymph nodes, spleen, and liver. Compared with mock controls, the triple gene vaccine significantly prolonged the survival of mice harboring peritoneal dissemination of CT26 colorectal cancer cells, of which long-term surviving mice showed complete rejection when re-challenged with CT26 tumors. Moreover, the DNA vaccine inhibited the growth and metastasis of subcutaneous CT26 and Lewis lung tumors in BALB/c and C57BL/6 mice, respectively, which represent different MHC haplotypes. The DNA vaccine highly stimulated both cytotoxic T lymphocyte and natural killer cell activities, and increased the infiltration of CD11c⁺ DCs and CD4⁺/CD8a⁺ T cells into tumors. Depletion of CD4⁺ or CD8a⁺ T cells by neutralizing antibodies deteriorated the anti-tumor efficacy of the DNA vaccine. In conclusion, a SART3/CD40L+GM-CSF gene-loaded polyplex micelle can be applied as a novel vaccine platform to elicit tumor rejection immunity regardless of the recipient MHC haplotype.

Ultrasound induced cancer immunotherapy

Recently, the use of ultrasound (US) has been shown to have potential in cancer immunotherapy. High intensity focused US destruction of tumors may lead to immunity forming in situ in the body by immune cells being exposed to the tumor debris and immune stimulatory substances that are present in the tumor remains. Another way of achieving anti-cancer immune responses is by using US in combination with microbubbles and nanobubbles to deliver genes and antigens into cells. US leads to bubble destruction and the forces released to direct delivery of the substances into the cytoplasm of the cells thus circumventing the natural barriers. In this way tumor antigens and antigen-encoding genes can be delivered to immune cells and immune response stimulating genes can be delivered to cancer cells thus enhancing immune responses. Combination of bubbles with cell-targeting ligands and US provides an even more sophisticated delivery system whereby the therapy is not only site specific but also cell specific. In this review we describe how US has been used to achieve immunity and discuss the potential and possible obstacles in future development.

Macrophage mannose receptor-specific gene delivery vehicle for macrophage engineering

Macrophages are the most plastic cells in the hematopoietic system and they exhibit great functional diversity. They have been extensively applied in anti-inflammatory, anti-fibrotic and anti-cancer therapies. However, the application of macrophages is limited by the efficiency of their engineering. The macrophage mannose receptor (MMR, CD206), a C-type lectin receptor, is ubiquitously expressed on macrophages and has a high affinity for mannose oligosaccharides. In the present study, we developed a novel non-viral vehicle with specific affinity for MMR. Mannan was cationized with spermine at a grafted ratio of ∼12% to deliver DNA and was characterized as a stable system for delivery. This spermine-mannan (SM)-based delivery system was evaluated as a biocompatible vehicle with superior transfection efficiency on murine macrophages, up to 28.5-fold higher than spermine-pullulan, 11.5-fold higher than polyethylenimine and 3.0-fold higher than Lipofectamine™ 2000. We confirmed that the SM-based delivery system for macrophages transfection was MMR-specific and we described the intracellular transport of the delivery system. To our knowledge, this is the first study using SM to demonstrate a mannose receptor-specific gene delivery system, thereby highlighting the potential of a novel specific non-viral delivery vehicle for macrophage engineering.

Development of therapeutic microbubbles for enhancing ultrasound-mediated gene delivery

Ultrasound (US)-mediated gene delivery has emerged as a promising non-viral method for safe and selective gene delivery. When enhanced by the cavitation of microbubbles (MBs), US exposure can induce sonoporation that transiently increases cell membrane permeability for localized delivery of DNA. The present study explores the effect of generalizable MB customizations on MB facilitation of gene transfer compared to Definity®, a clinically available contrast agent. These modifications are 1) increased MB shell acyl chain length (RN18) for elevated stability and 2) addition of positive charge on MB (RC5K) for greater DNA associability. The MB types were compared in their ability to facilitate transfection of luciferase and GFP reporter plasmid DNA in vitro and in vivo under various conditions of US intensity, MB dosage, and pretreatment MB-DNA incubation. The results indicated that both RN18 and RC5K were more efficient than Definity®, and that the cationic RC5K can induce even greater transgene expression by increasing payload capacity with prior DNA incubation without compromising cell viability. These findings could be applied to enhance MB functions in a wide range of therapeutic US/MB gene and drug delivery approach. With further designs, MB customizations have the potential to advance this technology closer to clinical application.

Tumour-associated macrophages targeted transfection with NF-κB decoy/mannose-modified bubble lipoplexes inhibits tumour growth in tumour-bearing mice

Tumour-associated macrophages (TAM) exhibit an M2 phenotype that promotes tumour progression, and conversion of M2 TAM toward a tumouricidal M1 phenotype is a promising anti-cancer therapy. As NF-κB is a key regulator of macrophage polarization, we developed an in vivo TAM-targeting delivery system that combines mannose-modified bubble liposomes/NF-κB decoy complexes (Man-PEG bubble lipoplexes) and ultrasound (US) exposure. We investigated the effects of NF-κB decoy transfection on TAM phenotype in solid tumour-bearing mice. Post-transfection tumour growth and survival rates were also recorded. Th2 cytokine (IL-10) level in TAM was significantly lower by NF-κB decoy transfection using Man-PEG bubble lipoplexes and US exposure, while Th1 cytokine levels (IL-1β, TNF-α and IL-6) were significantly higher when compared with controls. In addition, mRNA levels of vascular endothelial growth factor, matrix metalloproteinase-9 and arginase were significantly lower in TAM post-NF-κB decoy transfection. Importantly, TAM-targeted NF-κB decoy transfection inhibited tumour growth and prolonged survival rates in mice. Therefore, TAM-targeted NF-κB decoy transfection using Man-PEG bubble lipoplexes and US exposure may be an effective approach for anti-cancer therapy based on TAM phenotypic conversion from M2 toward M1.

Crucial factors and emerging concepts in ultrasound-triggered drug delivery

Time and space controlled drug delivery still remains a huge challenge in medicine. A novel approach that could offer a solution is ultrasound guided drug delivery. “Ultrasonic drug delivery” is often based on the use of small gas bubbles (so-called microbubbles) that oscillate and cavitate upon exposure to ultrasound waves. Some microbubbles are FDA approved contrast agents for ultrasound imaging and are nowadays widely investigated as promising drug carriers. Indeed, it has been observed that upon exposure to ultrasound waves, microbubbles may (a) release the encapsulated drugs and (b) simultaneously change the structure of the cell membranes in contact with the microbubbles which may facilitate drug entrance into cells. This review aims to highlight (a) major factors known so far which affect ultrasonic drug delivery (like the structure of the microbubbles, acoustic settings, etc.) and (b) summarizes the recent preclinical progress in this field together with a number of promising new concepts and applications.

Co-transfection gene delivery of dendritic cells induced effective lymph node targeting and anti-tumor vaccination

PURPOSE

Successful genetically engineered Dendritic Cell (DC) can enhance DC's antigen presentation and lymph node migration. The present study aims to genetically engineer a DC using an efficient non-viral gene delivery vector to induce a highly efficient antigen presentation and lymph node targeting in vivo.

METHODS

Spermine-dextran (SD), a cationic polysaccharide vector, was used to prepare a gene delivery system for DC engineering. Transfection efficiency, nuclear trafficking, and safety of the SD/DNA complex were evaluated. A vaccine prepared by engineering DC with SD/gp100, a plasmid encoding melanoma-associated antigen, was injected subcutaneously into mice to evaluate the tumor suppression. The migration of the engineered DCs was also evaluated in vitro and in vivo.

RESULTS

SD/DNA complex has a better transfection behavior in vitro than commercially purchased reagents. The DC vaccine co-transfected with plasmid coding CCR7, a chemokine receptor essential for DC migration, and plasmid coding gp100 displayed superior tumor suppression than that with plasmid coding gp100 alone. Migration assay demonstrated that DC transfected with SD/CCR7 can promote DC migration capacity.

CONCLUSIONS

The study is the first to report the application of nonviral vector SD to co-transfect DC with gp100 and CCR7-coding plasmid to induce both the capacity of antigen presentation and lymph node targeting.

‘Smart’ non-viral delivery systems for targeted delivery of RNAi to the lungs

The emergence of RNAi offers a potentially exciting new therapeutic paradigm for respiratory diseases. However, effective delivery remains a key requirement for their translation into the clinic and has been a major factor in the limited clinical success seen to date. Inhalation offers tissue-specific targeting of the RNAi to treat respiratory diseases and a diminished risk of off-target effects. In order to deliver RNAi directly to the respiratory tract via inhalation, ‘smart’ non-viral carriers are required to protect the RNAi during delivery/aerosolization and enhance cell-specific uptake to target cells. Here, we review the state-of-the-art in therapeutic aerosol bioengineering, and specifically non-viral siRNA delivery platforms, for delivery via inhalation. This includes developments in inhaler device engineering and particle engineering, including manufacturing methods and excipients used in therapeutic aerosol bioengineering that underpin the development of smart, cell type-specific delivery systems to target siRNA to respiratory epithelial cells and/or alveolar macrophages.

Liposomal drug delivery systems: from concept to clinical applications

The first closed bilayer phospholipid systems, called liposomes, were described in 1965 and soon were proposed as drug delivery systems. The pioneering work of countless liposome researchers over almost 5 decades led to the development of important technical advances such as remote drug loading, extrusion for homogeneous size, long-circulating (PEGylated) liposomes, triggered release liposomes, liposomes containing nucleic acid polymers, ligand-targeted liposomes and liposomes containing combinations of drugs. These advances have led to numerous clinical trials in such diverse areas as the delivery of anti-cancer, anti-fungal and antibiotic drugs, the delivery of gene medicines, and the delivery of anesthetics and anti-inflammatory drugs. A number of liposomes (lipidic nanoparticles) are on the market, and many more are in the pipeline. Lipidic nanoparticles are the first nanomedicine delivery system to make the transition from concept to clinical application, and they are now an established technology platform with considerable clinical acceptance. We can look forward to many more clinical products in the future.

Liposome-based delivery system for vaccine candidates: constructing an effective formulation

The discovery of liposomes in 1965 by Bangham and coworkers changed the prospects of drug delivery systems. Since then, the application of liposomes as vaccine delivery systems has been studied extensively. Liposomal vaccine delivery systems are made up of nano- or micro-sized vesicles consisting of phospholipid bilayers, in which the bioactive molecule is encapsulated/entrapped, adsorbed or surface coupled. In general, liposomes are not immunogenic on their own; thus, liposomes combined with immunostimulating ligands (adjuvants) or various other formulations have been used as vaccine delivery systems. A thorough understanding of formulation parameters allows the design of effective liposomal vaccine delivery systems. This article provides an overview of various factors that influence liposomal immunogenicity. In particular, the effects of vesicle size, surface charge, bilayer composition, lamellarity, pegylation and targeting of liposomes are described.

Efficient microbubble- and ultrasound-mediated plasmid DNA delivery into a specific rat liver lobe via a targeted injection and acoustic exposure using a novel ultrasound system

To develop efficient gene delivery in larger animals, based on a previous mouse study, we explored the luciferase reporter gene transfer in rats by establishing a novel unfocused ultrasound system with simultaneous targeted injection of a plasmid and microbubble mixture into a specific liver lobe through a portal vein branch. Luciferase expression was significantly enhanced over 0-30 vol % of the Definity microbubbles, with a plateau between 0.5 and 30 vol %. The increase of gene delivery efficiency also depended on the acoustic peak negative pressure, achieving over 100-fold enhancement at 2.5 MPa compared with plasmid only controls. Transient, modest liver damage following treatment was assessed by transaminase assays and histology, both of which correlated with gene expression induced by acoustic cavitation. In addition, pulse-train ultrasound exposures (i.e., with relatively long quiescent periods between groups of pulses to allow tissue refill with microbubbles) produced gene expression levels comparable to the standard US exposure but reduced the extent of liver damage. These results indicated that unfocused high intensity therapeutic ultrasound exposure with microbubbles is highly promising for safe and efficient gene delivery into the liver of rats or larger animals.

In vivo site-specific transfection of naked plasmid DNA and siRNAs in mice by using a tissue suction device

We have developed an in vivo transfection method for naked plasmid DNA (pDNA) and siRNA in mice by using a tissue suction device. The target tissue was suctioned by a device made of polydimethylsiloxane (PDMS) following the intravenous injection of naked pDNA or siRNA. Transfection of pDNA encoding luciferase was achieved by the suction of the kidney, liver, spleen, and heart, but not the duodenum, skeletal muscle, or stomach. Luciferase expression was specifically observed at the suctioned region of the tissue, and the highest luciferase expression was detected at the surface of the tissue (0.12±0.03 ng/mg protein in mice liver). Luciferase expression levels in the whole liver increased linearly with an increase in the number of times the liver was suctioned. Transfection of siRNA targeting glyceraldehyde 3-phosphate dehydrogenase (GAPDH) gene significantly suppressed the expression of GAPDH mRNA in the liver. Histological analysis shows that severe damage was not observed in the suctioned livers. Since the suction device can be mounted onto the head of the endoscope, this method is a minimally invasive. These results indicate that the in vivo transfection method developed in this study will be a viable approach for biological research and therapies using nucleic acids.

Role of DNA topology in uptake of polyplex molecules by dendritic cells

Dendritic cells (DCs) are an attractive target for DNA vaccines as they are potent antigen presenting cells. This study demonstrated how non-viral gene delivery to DCs involving complexes of poly-l-lysine (PLL) and plasmid DNA (pDNA) (polyplexes) showed dependence on DNA vector topology. DNA topology is of importance from both production and regulatory viewpoints. In our previous study with CHO cells we demonstrated that polyplex uptake was dependent on DNA topology whereby complexes containing supercoiled (SC) pDNA were smaller, more resistant to nucleases and more effectively condensed by PLL than open circular (OC) and linear-pDNA complexes. In this study polyplex uptake in DCs was measured qualitatively and quantitatively by confocal microscopy along with gene expression studies and measurement of DC phenotype. PLL is known for its ability to condense DNA and serve as an effective gene delivery vehicle. Quantification studies revealed that by 1h following uptake 15% (±2.59% relative standard error [RSE]) of SC-pDNA polyplexes were identified to be associated (fluorescent co-localisation) with the nucleus, in comparison to no nuclear association identified for OC- and linear-pDNA complexes. By 48 h following uptake, 30% (±1.82% RSE) of SC-pDNA complexes associated with the nucleus in comparison to 16% (±4.40% RSE) and 12% (±6.97% RSE) of OC- and linear-pDNA polyplexes respectively. Confocal microscopy images showed how DNA and PLL remained associated following uptake by dual labelling. Polyplex (containing 20 μg pDNA) gene expression (plasmid encoded lacZ [β-galactosidase] reporter gene) in DCs was greatest for SC-pDNA polyplexes at 14.12% unlike that of OC- (9.59%) and linear-pDNA (7.43%). DCs express cell surface markers which contribute towards antigen presentation. Polyplex gene expression did not alter DC phenotype through surface marker expression. This may be due to the pDNA dose employed (20μg) as other studies have used doses as high as 200 μg pDNA to induce DC phenotypic changes. Although no change in DC phenotype occurred, this could be advantageous in terms of biocompatibility. Collectively these results indicate that DNA topology is an important parameter for DC vector design, particularly pDNA in the SC conformation in regards to DNA vaccination studies.

Transgene expression and local tissue distribution of naked and polymer-condensed plasmid DNA after intradermal administration in mice

DNA vaccination using cationic polymers as carriers has the potential to be a very powerful method of immunotherapy, but typical immune responses generated have been less than robust. To better understand the details of DNA vaccine delivery in vivo, we prepared polymer/DNA complexes using three structurally distinct cationic polymers and fluorescently labeled plasmid DNA and injected them intradermally into mice. We analyzed transgene expression (luciferase) and the local tissue distribution of the labeled plasmid at the injection site at various time points (from hours to days). Comparable numbers of luciferase expressing cells were observed in the skin of mice receiving naked plasmid or polyplexes one day after transfection. At day 4, however, the polyplexes appeared to result in more transfected skin cells than naked plasmid. Live animal imaging revealed that naked plasmid dispersed quickly in the skin of mice after injection and had a wider distribution than any of the three types of polyplexes. However, naked plasmid level dropped to below detection limit after 24h, whereas polyplexes persisted for up to 2 weeks. The PEGylated polyplexes had a significantly wider distribution in the tissue than the nonPEGylated polyplexes. PEGylated polyplexes also distributed more broadly among dermal fibroblasts and allowed greater interaction with antigen-presenting cells (APCs) (dendritic cells and macrophages) starting at around 24h post-injection. By day 4, co-localization of polyplexes with APCs was observed at the injection site regardless of polymer structure, whereas small amounts of polyplexes were found in the draining lymph nodes. These in vivo findings demonstrate the superior stability of PEGylated polyplexes in physiological milieu and provide important insight on how cationic polymers could be optimized for DNA vaccine delivery.

Polymer-mediated DNA vaccine delivery via bystander cells requires a proper balance between transfection efficiency and cytotoxicity

Direct targeting of dendritic cells is an ideal goal for DNA vaccine delivery in order to stimulate both arms of the immune system. However, dendritic cells are often difficult to transfect using nonviral polyplexes. Here we show that transfecting bystander cells such as fibroblasts with PEI/DNA complexes leads to efficient cross-presentation of a model antigen by dendritic cells and subsequent activation of antigen-specific CD8(+) T cells. Maturation of dendritic cells is also stimulated after co-culture with transfected fibroblasts. Such outcomes depend on a proper balance between transfection efficiency and polyplex-induced cytotoxicity in the fibroblasts. In fact, substantial cytotoxicity is desirable and even necessary for cross-presentation and cross-priming of T cells. This study illustrates a new pathway of polymer-based DNA vaccine delivery via bystander cells without direct targeting of antigen-presenting cells and highlights the importance of exploiting polymer-induced cytotoxicity for the benefit of immune activation.

Involvement of activated transcriptional process in efficient gene transfection using unmodified and mannose-modified bubble lipoplexes with ultrasound exposure

Recently, our group developed ultrasound (US)-responsive and mannose-modified gene carriers (Man-PEG(2000) bubble lipoplexes), and successfully obtained a high level of gene expression in mannose receptor-expressing cells following gene transfection using Man-PEG(2000) bubble lipoplexes and US exposure. We also reported that large amounts of plasmid DNA (pDNA) were transferred into the cytoplasm of the targeted cells in the gene transfection using this method. In the present study, we investigated the involvement of transcriptional processes on enhanced gene expression obtained by unmodified and Man-PEG(2000) bubble lipoplexes with US exposure. The transcriptional process related to activator protein-1 (AP-1) and nuclear factor-κB (NFκB) was activated by US exposure, and was founded to be involved in enhanced gene expression obtained by gene transfection using unmodified and Man-PEG(2000) bubble lipoplexes with US exposure. On the other hand, activation of AP-1 and NFκB pathways followed by US exposure was hardly involved in the inflammatory responses in the gene transfection using this method. These findings suggest that activation of AP-1 and NFκB followed by US exposure is involved in the enhanced gene expression using unmodified and Man-PEG(2000) bubble lipoplexes with US exposure, and the selection of pDNAs activated by US exposure is important in this gene transfection method.

The elucidation of gene transferring mechanism by ultrasound-responsive unmodified and mannose-modified lipoplexes

The development of gene transfection methods enhancing the level of gene expression under simple and low-toxic condition is required for gene therapy in clinical. Our group has developed the ultrasound (US)-mediated gene transfection method using Man-PEG(2000) bubble lipoplexes, which are US-responsive and mannose-modified gene carriers, and succeeded in obtaining the enhanced gene expression in mannose receptor-expressing cells selectively by the gene transfer using Man-PEG(2000) bubble lipoplexes with US exposure in vitro and in vivo. Here, we investigated pDNA transferring mechanism followed by US exposure to unmodified and Man-PEG(2000) bubble lipoplexes, in particular, focused on US exposure timing. Following investigation of intracellular transferring characteristics, a large amount of pDNA was transferred into the cytoplasm followed by US-mediated destruction of bubble lipoplexes in the gene transfer using both bubble lipoplexes with US exposure. Moreover, the effective gene expression was obtained without TNF-α production when US was exposed until 5 min after the addition of bubble lipoplexes. These findings suggest that the gene transfer using unmodified and Man-PEG(2000) bubble lipoplexes with US exposure enables to transfer pDNA into the cytoplasm, and optimized US exposure timing is important to achieve the high level of gene expression and the low level of pro-inflammatory cytokine production.

N-glycan targeted gene delivery to the dendritic cell SIGN receptor

A novel nonviral gene delivery vector composed of a high-mannose N-glycan conjugated to a polyacridine peptide was prepared. The glycopeptide was designed to bind to plasmid DNA by a combination of polyintercalation and ionic binding, and to the DC-SIGN (dendritic cell-specific intracellular adhesion molecule-3 grabbing nonintegrin) receptor expressed on CHO cells by recognition of the high-mannose N-glycan. The glycopeptide conjugate was prepared by purification of a high-mannose N-glycan from affinity fractionated soybean agglutinin (SBA). The SBA was proteolyzed to release the N-glycan which was then modified on its N-terminus with Tyr and a propionate maleimide. A DNA binding polyacridine peptide, Cys-(Acr-Lys)(4), was prepared by solid-phase peptide synthesis using Fmoc-Lys(Acr), then conjugated to the maleimide on the N-glycan to produce a glycopeptide. The glycopeptide bound to DNA with high affinity as determined by fluorophore displacement assay and DNA band shift on agarose gel. When bound to Cy5 labeled DNA, the glycopeptide mediated specific uptake in DC-SIGN CHO (+) cells as determined by FACS analysis. In vitro gene transfer studies established that the glycopeptide increased the specificity of gene transfer in DC-SIGN CHO (+) cells 100-fold relative to CHO (-) cells. These studies suggest that a high-mannose N-glycan conjugated to a polyacridine peptide may also facilitate receptor mediated gene delivery in dendritic cells and thereby find utility in the delivery of DNA vaccines.

Targeted liposomal drug delivery to monocytes and macrophages

As the role of monocytes and macrophages in a range of diseases is better understood, strategies to target these cell types are of growing importance both scientifically and therapeutically. As particulate carriers, liposomes naturally target cells of the mononuclear phagocytic system (MPS), particularly macrophages. Loading drugs into liposomes can therefore offer an efficient means of drug targeting to MPS cells. Physicochemical properties including size, charge and lipid composition can have a very significant effect on the efficiency with which liposomes target MPS cells. MPS cells express a range of receptors including scavenger receptors, integrins, mannose receptors and Fc-receptors that can be targeted by the addition of ligands to liposome surfaces. These ligands include peptides, antibodies and lectins and have the advantages of increasing target specificity and avoiding the need for cationic lipids to trigger intracellular delivery. The goal for targeting monocytes/macrophages using liposomes includes not only drug delivery but also potentially a role in cell ablation and cell activation for the treatment of conditions including cancer, atherosclerosis, HIV, and chronic inflammation.

Progress in the development of ultrasound-mediated gene delivery systems utilizing nano- and microbubbles

Recently, ultrasound-mediated gene delivery with nano- and microbubbles was developed as a novel non-viral vector system. In this gene delivery system, microstreams and microjets, which are induced by disruption of nano/microbubbles exposed to ultrasound, are used as the driving force to transfer genes into cells by opening transient pores in the cell membrane. This system can directly deliver plasmid DNA and siRNA into cytosol without endocytosis pathway. Therefore, these genes are able to escape from degradation in lysosome and result in enhancing the efficiency of gene expression. In addition, it is expected that ultrasound-mediated gene delivery using nano/microbubbles would be a system to establish non-invasive and tissue specific gene expression because ultrasound can transdermally expose to target tissues and organs. This review focuses on the current ultrasound-mediated gene delivery system using nano/microbubbles. We discuss about the feasibility of this gene delivery system as novel non-viral vector system.

Cancer gene therapy by IL-12 gene delivery using liposomal bubbles and tumoral ultrasound exposure

Interleukin-12 (IL-12) gene therapy is expected to be effective against cancers because it primes the immune system for cancer cells. In this therapy, it is important to induce IL-12 gene expression in the tumor tissue. Sonoporation is an attractive technique for developing non-invasive and non-viral gene delivery systems, but simple sonoporation using only ultrasound is not an effective cancer gene therapy because of the low efficiency of gene delivery. We addressed this problem by combining ultrasound and novel ultrasound-sensitive liposomes (Bubble liposomes) which contain the ultrasound imaging gas perfluoropropane. Our previous work showed that this is an effective gene delivery system, and that Bubble liposome collapse (cavitation) is induced by ultrasound exposure. In this study, we assessed the utility of this system in cancer gene therapy using IL-12 corded plasmid DNA. The combination of Bubble liposomes and ultrasound dramatically suppressed tumor growth. This therapeutic effect was T-cell dependent, requiring mainly CD8(+) T lymphocytes in the effector phase, as confirmed by a mouse in vivo depletion assay. In addition, migration of CD8(+) T cells was observed in the mice, indicating that the combination of Bubble liposomes and ultrasound is a good non-viral vector system in IL-12 cancer gene therapy.