Pegylated GL67 lipoplexes retain their gene transfection activity after exposure to components of CF mucus

A new era of targeting cystic fibrosis with non-viral delivery of genomic medicines

Cystic fibrosis (CF) is a complex genetic respiratory disorder that necessitates innovative gene delivery strategies to address the mutations in the gene. This review delves into the promises and challenges of non-viral gene delivery for CF therapy and explores strategies to overcome these hurdles. Several emerging technologies and nucleic acid cargos for CF gene therapy are discussed. Novel formulation approaches including lipid and polymeric nanoparticles promise enhanced delivery through the CF mucus barrier, augmenting the potential of non-viral strategies. Additionally, safety considerations and regulatory perspectives play a crucial role in navigating the path toward clinical translation of gene therapy.

Biodegradable Cationic and Ionizable Cationic Lipids: A Roadmap for Safer Pharmaceutical Excipients

Cationic and ionizable cationic lipids are broadly applied as auxiliary agents, but their use is associated with adverse effects. If these excipients are rapidly degraded to endogenously occurring metabolites such as amino acids and fatty acids, their toxic potential can be minimized. So far, synthesized and evaluated biodegradable cationic and ionizable cationic lipids already showed promising results in terms of functionality and safety. Within this review, an overview about the different types of such biodegradable lipids, the available building blocks, their synthesis and cleavage by endogenous enzymes is provided. Moreover, the relationship between the structure of the lipids and their toxicity is described. Their application in drug delivery systems is critically discussed and placed in context with the lead compounds used in mRNA vaccines. Moreover, their use as preservatives is reviewed, guidance for their design is provided, and an outlook on future developments is given.

Current knowledge on the tissue distribution of mRNA nanocarriers for therapeutic protein expression

Exogenously delivered mRNA-based drugs are emerging as a new class of therapeutics with the potential to treat several diseases. Over the last decade, advancements in the design of non-viral delivery tools have enabled mRNA to be evaluated for several therapeutic purposes including protein replacement therapies, gene editing, and vaccines. However, in vivo delivery of mRNA to targeted organs and cells remains a critical challenge. Evaluation of the biodistribution of mRNA vehicles is of utmost importance for the development of effective pharmaceutical candidates. In this review, we discuss the recent advances in the design of nanoparticles loaded with mRNA and extrapolate the key factors influencing their biodistribution following administration. Finally, we highlight the latest developments in the preclinical and clinical translation of mRNA therapeutics for protein supplementation therapy.

Aerosol-Mediated Non-Viral Lung Gene Therapy: The Potential of Aminoglycoside-Based Cationic Liposomes

Aerosol lung gene therapy using non-viral delivery systems represents a credible therapeutic strategy for chronic respiratory diseases, such as cystic fibrosis (CF). Progress in CF clinical setting using the lipidic formulation GL67A has demonstrated the relevance of such a strategy while emphasizing the need for more potent gene transfer agents. In recent years, many novel non-viral gene delivery vehicles were proposed as potential alternatives to GL67 cationic lipid. However, they were usually evaluated using procedures difficult or even impossible to implement in clinical practice. In this study, a clinically-relevant administration protocol via aerosol in murine lungs was used to conduct a comparative study with GL67A. Diverse lipidic compounds were used to prepare a series of formulations inspired by the composition of GL67A. While some of these formulations were ineffective at transfecting murine lungs, others demonstrated modest-to-very-efficient activities and a series of structure-activity relationships were unveiled. Lipidic aminoglycoside derivative-based formulations were found to be at least as efficient as GL67A following aerosol delivery of a luciferase-encoding plasmid DNA. A single aerosol treatment with one such formulation was found to mediate long-term lung transgene expression, exceeding half the animal's lifetime. This study clearly supports the potential of aminoglycoside-based cationic lipids as potent GL67-alternative scaffolds for further enhanced aerosol non-viral lung gene therapy for diseases such as CF.

Inhalation delivery technology for genome-editing of respiratory diseases

The clustered regulatory interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein 9 (CRISPR/Cas9) system has significant therapeutic potentials for lung congenital diseases such as cystic fibrosis, as well as other pulmonary disorders like lung cancer and obstructive diseases. Local administration of CRISPR/Cas9 therapeutics through inhalation can achieve high drug concentration and minimise systemic exposure. While the field is advancing with better understanding on the biological functions achieved by CRISPR/Cas9 systems, the lack of progress in inhalation formulation and delivery of the molecule may impede their clinical translation efficiently. This forward-looking review discussed the current status of formulations and delivery for inhalation of relevant biologics such as genes (plasmids and mRNAs) and proteins, emphasising on their design strategies and preparation methods. By adapting and optimising formulation strategies used for genes and proteins, we envisage that development of inhalable CRISPR/Cas9 liquid or powder formulations for inhalation administration can potentially be fast-tracked in near future.

Delivery of genome-editing biomacromolecules for treatment of lung genetic disorders

Genome-editing systems based on clustered, regularly interspaced, short palindromic repeat (CRISPR)/associated protein (CRISPR/Cas), are emerging as a revolutionary technology for the treatment of various genetic diseases. To date, the delivery of genome-editing biomacromolecules by viral or non-viral vectors have been proposed as new therapeutic options for lung genetic disorders, such as cystic fibrosis (CF) and α-1 antitrypsin deficiency (AATD), and it has been accepted that these delivery vectors can introduce CRISPR/Cas9 machineries into target cells or tissues in vitro, ex vivo and in vivo. However, the efficient local or systemic delivery of CRISPR/Cas9 elements to the lung, enabled by either viral or by non-viral carriers, still remains elusive. Herein, we first introduce lung genetic disorders and their current treatment options, and then summarize CRISPR/Cas9-based strategies for the therapeutic genome editing of these disorders. We further summarize the pros and cons of different routes of administration for lung genetic disorders. In particular, the potentials of aerosol delivery for therapeutic CRISPR/Cas9 biomacromolecules for lung genome editing are discussed and highlighted. Finally, current challenges and future outlooks in this emerging area are briefly discussed.

Ex vivo dendritic cell generation-A critical comparison of current approaches

Dendritic cells (DCs) are professional antigen-presenting cells, required for the initiation of naïve and memory T cell responses and regulation of adaptive immunity. The discovery of DCs in 1973, which culminated in the Nobel Prize in Physiology or Medicine in 2011 for Ralph Steinman and colleagues, initially focused on the identification of adherent mononuclear cell fractions with uniquely stellate dendritic morphology, followed by key discoveries of their critical immunologic role in initiating and maintaining antigen-specific immunity and tolerance. The medical promise of marshaling these key capabilities of DCs for therapeutic modulation of antigen-specific immune responses has guided decades of research in hopes to achieve genuine physiologic partnership with the immune system. The potential uses of DCs in immunotherapeutic applications include cancer, infectious diseases, and autoimmune disorders; thus, methods for rapid and reliable large-scale production of DCs have been of great academic and clinical interest. However, difficulties in obtaining DCs from lymphoid and peripheral tissues, low numbers and poor survival in culture, have led to advancements in ex vivo production of DCs, both for probing molecular details of DC function as well as for experimenting with their clinical utility. Here, we review the development of a diverse array of DC production methodologies, ranging from cytokine-based strategies to genetic engineering tools devised for enhancing DC-specific immunologic functions. Further, we explore the current state of DC therapies in clinic, as well as emerging insights into physiologic production of DCs inspired by existing therapies.

Recent Developments in mRNA-Based Protein Supplementation Therapy to Target Lung Diseases

Protein supplementation therapy using in vitro-transcribed (IVT) mRNA for genetic diseases contains huge potential as a new class of therapy. From the early ages of synthetic mRNA discovery, a great number of studies showed the versatile use of IVT mRNA as a novel approach to supplement faulty or absent protein and also as a vaccine. Many modifications have been made to produce high expressions of mRNA causing less immunogenicity and more stability. Recent advancements in the in vivo lung delivery of mRNA complexed with various carriers encouraged the whole mRNA community to tackle various genetic lung diseases. This review gives a comprehensive overview of cells associated with various lung diseases and recent advancements in mRNA-based protein replacement therapy. This review also covers a brief summary of developments in mRNA modifications and nanocarriers toward clinical translation.

Self-emulsifying drug delivery system: Mucus permeation and innovative quantification technologies

Mucus is a dynamic barrier which covers and protects the underlying mucosal epithelial membrane against bacteria and foreign particles. This protection mechanism extends to include therapeutic macromolecules and nanoparticles (NPs) through trapping of these particles. Mucus is not only a physical barrier that limiting particles movements based on their sizes but it selectively binds with particles through both hydrophilic and lipophilic interactions. Therefore, nano-carriers for mucosal delivery should be designed to eliminate entrapment by the mucus barrier. For this reason, different strategies have been approached for both solid nano-carriers and liquid core nano-carriers to synthesise muco-diffusive nano-carrier. Among these nano-strategies, Self-Emulsifying Drug Delivery System (SEDDS) was recognised as very promising nano-carrier for mucus delivery. The system was introduced to enhance the dissolution and bioavailability of orally administered insoluble drugs. SEDDS has shown high stability against intestinal enzymatic activity and more importantly, relatively rapid permeation characteristics across mucus barrier. The high diffusivity of SEDDS has been tested using various in vitro measurement techniques including both bulk and individual measurement of droplets diffusion within mucus. The selection and processing of an optimum in vitro technique is of great importance to avoid misinterpretation of the diffusivity of SEDDS through mucus barrier. In conclusion, SEDDS is a system with high capacity to diffuse through intestinal mucus even though this system has not been studied to the same extent as solid nano-carriers.

Nanomedicine for Cystic Fibrosis

Cystic fibrosis is a genetic disease affecting more than 70,000 people worldwide. Caused by a mutation in the CFTR gene, cystic fibrosis can result in difficulty breathing, widespread bacterial infections, edema, malnutrition, pancreatitis, and death. Current drug-based treatments struggle to reach the site of action due to the thick mucus, and only manage symptoms such as blocked airways, lung infections, and limited ability to digest food. Nanotechnology opens up possibilities for improved treatment strategies by focusing on drug penetration through the mucus lining, eliminating resulting bacterial infections, and targeting the underlying genetic cause of the disease. In this review, we present recent nanoparticle developments for cystic fibrosis, challenges in nanomedicine therapeutics, and future research directions in gene editing and nonviral vectors for gene delivery.

"Click" hyaluronan based nanohydrogels as multifunctionalizable carriers for hydrophobic drugs

Highly hydrophilic and biocompatible nanocarriers based on polysaccharide hydrogels (nanohydrogels, NHs) were shown to be promising systems for drug delivery applications. Following the idea of these emerging drug carriers, the aim of the present work was to develop self-assembled hydrogel nanoparticles based on amphiphilic derivatives of hyaluronic acid (HA) and riboflavin (Rfv), synthesized by "click" Copper(I)-catalyzed Azide-Alkyne Cycloaddition (CuAAC) reaction. The obtained amphiphilic product (HA-c-Rfv) was able to form nanohydrogels in aqueous environments, in particular by applying an innovative autoclave-based method. HA of different molecular weights (M_w) and degrees of substitution (DS) were prepared and the effect of these parameters on the NHs formation was assessed. The derivative HA²²⁰-c-Rfv 40/40 was chosen as the most interesting system, capable to form NHs in the range of 150-200nm and with a negative ζ-potential. NHs were very stable in water solutions and, by adding dextrose as cryoprotectant, it was also possible to freeze-dry the NHs formulation. The developed system is proposed for the delivery of hydrophobic drugs; for this purpose, dexamethasone, piroxicam and paclitaxel were used as model drugs; these molecules were loaded into NHs with high efficiency by film-hydration technique. Furthermore, a HA-c-Rfv derivative bearing an excess of propargylic portions was capable to react with other N₃-derivatized molecules, opening the route to a wide spectrum of functionalization opportunities: in this direction, PEG-N₃ has been tested as a model molecule for the preparation of PEGylated NHs.

Barriers to inhaled gene therapy of obstructive lung diseases: A review

Knowledge of genetic origins of obstructive lung diseases has made inhaled gene therapy an attractive alternative to the current standards of care that are limited to managing disease symptoms. Initial lung gene therapy clinical trials occurred in the early 1990s following the discovery of the genetic defect responsible for cystic fibrosis (CF), a monogenic disorder. However, despite over two decades of intensive effort, gene therapy has yet to help patients with CF or any other obstructive lung disease. The slow progress is due in part to poor understanding of the biological barriers to inhaled gene therapy. Encouragingly, clinical trials have shown that inhaled gene therapy with various viral vectors and non-viral gene vectors is well tolerated by patients, and continued research has provided valuable lessons and resources that may lead to future success of this therapeutic strategy. In this review, we first introduce representative obstructive lung diseases and examine limitations of currently available therapeutic options. We then review key components for successful execution of inhaled gene therapy, including gene delivery systems, primary physiological barriers and strategies to overcome them, and advances in preclinical disease models with which the most promising systems may be identified for human clinical trials.

Nanoparticles for targeted delivery of therapeutics and small interfering RNAs in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is the 5^th most common malignancy which is responsible for more than half million annual mortalities; also, it is the third leading cause of cancer related death. Unfavorable systemic side-effects of chemotherapeutic agents and susceptibility to the degradation of small interfering RNAs (siRNAs), which can knock down a specific gene involved in the disease, have hampered their clinical application. So, it could be beneficial to develop an efficient carrier for the stabilization and specific delivery of drugs and siRNA to cells. Targeted nanoparticles have gained considerable attention as an efficient drug and gene delivery system, which is due to their capability in achieving the highest accumulation of cytotoxic agents in tumor tissue, modifiable drug pharmacokinetic- and bio-distribution, improved effectiveness of treatment, and limited side-effects. Recent studies have shed more light on the advantages of novel drug loaded carrier systems vs free drugs. Most of the animal studies have reported improvement in treatment efficacy and survival rate using novel carrier systems. Targeted delivery may be achieved passively or actively. In passive targeting, no ligand as homing device is used, while targeting is achieved by incorporating the therapeutic agent into a macromolecule or nanoparticle that passively reaches the target organ. However, in active targeting, the therapeutic agent or carrier system is conjugated to a tissue or cell-specific receptor which is over-expressed in a special malignancy using a ligand called a homing device. This review covers a broad spectrum of targeted nanoparticles as therapeutic and non-viral siRNA delivery systems, which are developed for enhanced cellular uptake and targeted gene silencing in vitro and in vivo and their characteristics and opportunities for the clinical applications of drugs and therapeutic siRNA are discussed in this article. Asialoglycoprotein receptors, low-density lipoprotein, ganglioside GM1 cell surface ligand, epidermal growth factor receptor receptors, monoclonal antibodies, retinoic acid receptors, integrin receptors targeted by Arg-Gly-Asp peptide, folate, and transferrin receptors are the most widely studied cell surface receptors which are used for the site specific delivery of drugs and siRNA-based therapeutics in HCC and discussed in detail in this article.

Nanocomplexes for gene therapy of respiratory diseases: Targeting and overcoming the mucus barrier

Gene therapy, i.e. the delivery and expression of therapeutic genes, holds great promise for congenital and acquired respiratory diseases. Non-viral vectors are less toxic and immunogenic than viral vectors, although they are characterized by lower efficiency. However, they have to overcome many barriers, including inflammatory and immune mediators and cells. The respiratory and airway epithelial cells, the main target of these vectors, are coated with a layer of mucus, which hampers the effective reaching of gene therapy vectors carrying either plasmid DNA or small interfering RNA. This barrier is thicker in many lung diseases, such as cystic fibrosis. This review summarizes the most important advancements in the field of non-viral vectors that have been achieved with the use of nanoparticulate (NP) systems, composed either of polymers or lipids, in the lung gene delivery. In particular, different strategies of targeting of respiratory and airway lung cells will be described. Then, we will focus on the two approaches that attempt to overcome the mucus barrier: coating of the nanoparticulate system with poly(ethylene glycol) and treatment with mucolytics. Our conclusions are: 1) Ligand and physical targeting can direct therapeutic gene expression in specific cell types in the respiratory tract; 2) Mucopenetrating NPs are endowed with promising features to be useful in treating respiratory diseases and should be now advanced in pre-clinical trials. Finally, we discuss the development of such polymer- and lipid-based NPs in the context of in vitro and in vivo disease models, such as lung cancer, as well as in clinical trials.

Effect of mucoadhesive polymers on the in vitro performance of insulin-loaded silica nanoparticles: Interactions with mucin and biomembrane models

The present paper focuses on the development and characterization of silica nanoparticles (SiNP) coated with hydrophilic polymers as mucoadhesive carriers for oral administration of insulin. SiNP were prepared by sol-gel technology under mild conditions and coated with different hydrophilic polymers, namely, chitosan, sodium alginate or poly(ethylene glycol) (PEG) with low and high molecular weight (PEG 6000 and PEG 20000) to increase the residence time at intestinal mucosa. The mean size and size distribution, association efficiency, insulin structure and insulin thermal denaturation have been determined. The mean nanoparticle diameter ranged from 289 nm to 625 nm with a PI between 0.251 and 0.580. The insulin association efficiency in SiNP was recorded above 70%. After coating, the association efficiency of insulin increased up to 90%, showing the high affinity of the protein to the hydrophilic polymer chains. Circular dichroism (CD) indicated that no conformation changes of insulin structure occurred after loading the peptide into SiNP. Nano-differential scanning calorimetry (nDSC) showed that SiNP shifted the insulin endothermic peak to higher temperatures. The influence of coating on the interaction of nanoparticles with dipalmitoylphosphatidylcholine (DPPC) biomembrane models was also evaluated by nDSC. The increase of ΔH values suggested a strong association of non-coated SiNP and those PEGylated nanoparticles coated with DPPC polar heads by forming hydrogen bonds and/or by electrostatic interaction. The mucoadhesive properties of nanoparticles were examined by studying the interaction with mucin in aqueous solution. SiNP coated with alginate or chitosan showed high contact with mucin. On the other hand, non-coated SiNP and PEGylated SiNP showed lower interaction with mucin, indicating that these nanoparticles can interdiffuse across mucus network. The results of the present work provide valuable data in assessing the in vitro performance of insulin-loaded SiNP coated with mucoadhesive polymers.

The importance of the vaginal delivery route for antiretrovirals in HIV prevention

The HIV/AIDS pandemic continues to be a global health priority, with high rates of new HIV-I infections persisting in young women. One HIV prevention strategy is topical pre-exposure prophylactics or microbicides, which are applied vaginally or rectally to protect the user from HIV and possibly other sexually transmitted infections. Vaginal microbicide delivery will be the focus of this review. Multiple nonspecific and specific antiretroviral microbicide products have been clinically evaluated, and many are in preclinical development, The events of HIV mucosal transmission and dynamics of the cervicovaginal environment should be considered for successful vaginal microbicide delivery. Beyond conventional vaginal formulations, intravaginal rings, tablets and films are employed as platforms in the hope to increase the likelihood of microbicide use. Furthermore, combining multiple antiretrovirals within a given formulation, combining a microbicide product with a vaginal device and integrating novel drug-delivery strategies within a microbicide product are approaches to successful vaginal-microbicide delivery.

Mucus penetrating nanoparticles: biophysical tool and method of drug and gene delivery

A method that could provide more uniform and longer-lasting drug and gene delivery to mucosal surfaces holds the potential to greatly improve the effectiveness of prophylactic and therapeutic approaches for numerous diseases and conditions, including sexually transmitted infections, cystic fibrosis, chronic rhinosinusitis, inflammatory bowel disease, and glaucoma to name a few. However, the body's natural defenses, including adhesive, rapidly cleared mucus linings coating nearly all entry points to the body not covered by skin, has limited the effectiveness of drug and gene delivery by nanoscale delivery systems. This article discusses the recent development of the “mucuspenetrating particle” or “MPP” nanotechnology, and how it has been used to both enhance understanding of the nanoscale barrier properties of human mucus secretions, and to achieve more uniform and longer-lasting drug delivery to mucosal tissues following topical administration. Drug loaded MPPs possess non-adhesive coatings that allow them to rapidly penetrate mucus layers through openings in the mucus mesh at rates nearly as fast as they would penetrate pure water. Critically, MPPs allow enhanced drug and gene delivery to mucosal tissues without diminishing the protective function of mucus. Recent progress in the development of MPPs as a biophysical tool to probe the length-scale dependent rheological properties of mucosal secretions and as a method for drug and gene delivery is highlighted.

Challenges and advances in the development of inhalable drug formulations for cystic fibrosis lung disease

INTRODUCTION

Cystic fibrosis (CF) is a multisystem genetic disorder, which usually results in significant respiratory dysfunction. At present there is no cure for CF, but advances in pharmacotherapy have gradually increased the life expectancy of CF patients. As many drugs used in the therapy of CF are delivered by inhalation, the demand for effective and convenient inhalational CF drug formulations will grow as CF patients live longer. Knowledge of the current limitations in inhalational CF drug delivery is critical in identifying new opportunities and designing rational delivery strategies.

AREAS COVERED

This review discusses current and emerging therapeutic agents for CF therapy, selected physiological challenges to effective inhalational medication delivery, and various approaches to overcoming these challenges. The reader will find an integrated view of the known inhalational drug delivery challenges and the rationales for recent investigational inhalational drug formulations.

EXPERT OPINION

An ideal drug/gene delivery system to CF airways should overcome the tenacious sputum, which presents physical, chemical and biological barriers to effective transport of therapeutic agents to the targets and various cellular challenges.

Intestinal delivery of non-viral gene therapeutics: physiological barriers and preclinical models

The future of nucleic acid-based therapeutics is dependent on achieving successful delivery. Recently, there has been an increasing interest in delivery via the gastrointestinal tract. Gene therapy via this route has many advantages, including non-invasive access and the versatility to treat local diseases, such as inflammatory bowel disease, as well as systemic diseases, such as haemophilia. However, the intestine presents several distinct barriers and, therefore, the design of robust non-viral delivery systems is key to future success. Several non-viral delivery strategies have provided evidence of activity in vivo. To facilitate the design of more efficient and safe gene medicines, more physiologically relevant models, at both the in vitro and in vivo levels, are essential.

Self assembly of amphiphilic (PEG)(3)-PLA copolymer as polymersomes: preparation, characterization, and their evaluation as drug carrier

(PEG)(3)-PLA copolymer has been explored for the formation of polymersomes. For this, three chains of methoxy-PEG(1100) were directly attached to citric acid by esterification. (Methoxy-PEG(1100))(3)-citrate was then reacted at its hydroxyl terminal with different moles of d,l-lactide by ring-opening polymerization to obtain polymers with five different PEG-to-PLA ratios ranging from 10:90 to 90:10. Polymers were characterized by GPC, FTIR, (1)H NMR, and DSC, films were characterized for hydrophilicity by contact angle, and surface topography was observed by SEM and AFM. All five polymers were evaluated for the formation of polymersomes. Among these, polymers with PEG content of 10-30% were able to self-assemble into polymersomes. To affirm their self-arrangement and drug carrier properties, hydrophilic and hydrophobic dyes were simultaneously encapsulated in these structures. SEM and TEM analysis of the blank polymersomes confirmed the vesicular nature of the polymersomes, whereas CLSM analysis of dye-loaded polymersomes demonstrated the presence of two separate regions viz. hydrophilic core and hydrophobic wall. Hydrophobic dye, fluorescein was released relatively faster from the wall of polymersomes, whereas hydrophilic dye, propidium iodide, was released in controlled fashion up to 18 days. It is expected that these systems may serve as a suitable carrier for simultaneous or separate delivery of drug molecules with varying physicochemical properties.

Impact of chronic pulmonary infection with Pseudomonas aeruginosa on transfection mediated by viral and nonviral vectors

Pseudomonas aeruginosa plays a crucial role in the lung pathology of cystic fibrosis (CF). We showed that acute infection with P. aeruginosa has a substantial impact on gene transfer into lung epithelial cells mediated by polyplexes. As an extension of those studies we report here on the effect of chronic pulmonary infection with P. aeruginosa on transfection of lung epithelial cells by viral and nonviral vectors. As an in vivo model of the persistent chronic infection in patients with CF we used C57BL/6 mice intratracheally infected with P. aeruginosa encapsulated in agar beads. Two weeks after infection the presence of viable bacteria in the lungs was confirmed, mostly in the bronchial lumen. In lung tissue sections stained with hematoxylin and eosin, extensive inflammatory infiltrations were found. At that time point the mice received an intratracheal dose of luciferase gene complexed with either Lipofectamine (Lf), a GL67 lipid mixture (GL67), or polyethylenimine (PEI) or with lentivirus (LV) as a carrier system. Luciferase activity was determined by a luminescence assay in supernatants of lung homogenates. The transfection level induced by PEI/DNA polyplexes complexed with serum albumin was decreased in infected mice. Lf-mediated transfection was almost completely blocked in infected mice. Transfection levels in mice treated with LV or plain PEI/DNA polyplexes were unchanged in infected animals as compared with control mice. The only carrier that displayed a clearly increased transfection level in infected mice was the GL67 lipid mixture, which is tentatively ascribed to the presence of polyethylene glycol in this carrier.

Vaccination of turkeys against Chlamydophila psittaci through optimised DNA formulation and administration

We have demonstrated that vaccination of turkeys with an unformulated DNA vaccine induces significant protection against Chlamydophila (Cp.) psittaci infections. Nevertheless, the immunogenicity of the DNA vaccine can still be improved by increasing translation and transfection efficiency. Therefore, the ompA codon was adapted to the codon usage in birds, resulting in pcDNA1/MOMP(opt). To increase gene transfer, polyplexes of pcDNA1/MOMP(opt)-EGFP with different cationic polymers, such as linear and branched polyethyleneimine (lPEI and brPEI) and starburst PAMAM dendrimers, and lipoplexes with cationic DOTAP/DOPE liposomes were created. Transfection of lPEI and brPEI polyplexes with an N/P ratio of 8 resulted in the highest transfection efficiencies, but lPEI polyplexes were completely destroyed following nebulisation. Secondly, we examined the capacity of nebulised or intramuscularly (IM) administered brPEI-pcDNA1/MOMP(opt) to induce a significant protective immune response in SPF turkeys experimentally infected with 10(8) TCID(50) of a virulent Cp. psittaci strain. Results were compared to IM administration of naked plasmid DNA and to results of non-vaccinated animals. Intramuscular administration of brPEI-pcDNA1/MOMP(opt) increased the immunogenicity of the Cp. psittaci DNA vaccine as compared to IM administration of pcDNA1/MOMP(opt) or aerosol delivery of brPEI-pcDNA1/MOMP(opt). Improved immunogenicity was correlated with increased protection. Vaccinated groups were significantly protected against Cp. psittaci challenge.

Materials engineering for immunomodulation

The engineering of materials that can modulate the immune system is an emerging field that is developing alongside immunology. For therapeutic ends such as vaccine development, materials are now being engineered to deliver antigens through specific intracellular pathways, allowing better control of the way in which antigens are presented to one of the key types of immune cell, T cells. Materials are also being designed as adjuvants, to mimic specific 'danger' signals in order to manipulate the resultant cytokine environment, which influences how antigens are interpreted by T cells. In addition to offering the potential for medical advances, immunomodulatory materials can form well-defined model systems, helping to provide new insight into basic immunobiology.

Extracellular barriers in respiratory gene therapy

Respiratory gene therapy has been considered for the treatment of a broad range of pulmonary disorders. However, respiratory secretions form an important barrier towards the pulmonary delivery of therapeutic nucleic acids. In this review we will start with a brief description of the biophysical properties of respiratory mucus and alveolar fluid. This must allow the reader to gain insights into the mechanisms by which respiratory secretions may impede the gene transfer efficiency of nucleic acid containing nanoparticles (NANs). Subsequently, we will summarize the efforts that have been done to understand the barrier properties of respiratory mucus and alveolar fluid towards the respiratory delivery of therapeutic nucleic acids. Finally, new and current strategies that can overcome the inhibitory effects of respiratory secretions are discussed.

Mucus-penetrating nanoparticles for drug and gene delivery to mucosal tissues

Mucus is a viscoelastic and adhesive gel that protects the lung airways, gastrointestinal (GI) tract, vagina, eye and other mucosal surfaces. Most foreign particulates, including conventional particle-based drug delivery systems, are efficiently trapped in human mucus layers by steric obstruction and/or adhesion. Trapped particles are typically removed from the mucosal tissue within seconds to a few hours depending on anatomical location, thereby strongly limiting the duration of sustained drug delivery locally. A number of debilitating diseases could be treated more effectively and with fewer side effects if drugs and genes could be more efficiently delivered to the underlying mucosal tissues in a controlled manner. This review first describes the tenacious mucus barrier properties that have precluded the efficient penetration of therapeutic particles. It then reviews the design and development of new mucus-penetrating particles that may avoid rapid mucus clearance mechanisms, and thereby provide targeted or sustained drug delivery for localized therapies in mucosal tissues.

Wanted and unwanted properties of surface PEGylated nucleic acid nanoparticles in ocular gene transfer

Ocular gene therapy may offer new hope for severe eye diseases. Many of these ocular diseases are due to a gene defect in the retina, a multi-layered sensory tissue that lines the back of the eye. However, it is well known that the blood-retina barrier and sclera prevent hydrophilic and high molecular weight drugs to reach the retina after systemic or topical application. Therefore, intravitreal injection of non-viral nucleic acid nanoparticles has been considered as a safe and promising approach in ocular gene transfer. However, after intravitreal injection the non-viral nucleic acid nanoparticles should be stable and mobile in the vitreous. In this overview we focus on the behavior of non-viral nucleic acid nanoparticles (lipoplexes) in vitreous and on PEGylation strategies that improve their behavior in vitreous, but that do not affect their transfection capacity.

Post-pegylated lipoplexes are promising vehicles for gene delivery in RPE cells

The retinal pigment epithelium (RPE) is a potential tissue for gene therapy. We recently demonstrated that pegylation of lipoplexes prevents their aggregation in the vitreous of the eye. However, pegylation of lipoplexes may affect their gene transfer capacity. Therefore we studied the effect of pegylation of lipoplexes on the transfection of RPE cells. "Pre-pegylated" lipoplexes were prepared by mixing pDNA with pegylated liposomes, while "post-pegylated" lipoplexes were obtained by pegylation of (non-pegylated) cationic liposome/DNA complexes with PEG-ceramides. Pre-pegylation of lipoplexes severely inhibited their transfection efficacy. The poor transfection was attributed to an inefficient and slower internalization of pre-pegylated lipoplexes by RPE cells, compared to non-pegylated lipoplexes. In addition, pre-pegylated lipoplexes also remained entrapped in the endosomes of the RPE cells. In contrast, post-pegylation of the lipoplexes with PEG-ceramides strongly improved their transfection efficiency. As PEG-ceramides are believed to leave the lipoplexes upon contact with the cell membranes, this "de-pegylation" results in non-pegylated lipoplexes which successfully escape from the endosomes. In conclusion, post-pegylation of lipoplexes with PEG-ceramides appears to be an attractive strategy to deliver therapeutic DNA to RPE cells as (a) it prevents the lipoplexes from aggregation in vitreous and (b) de-pegylation upon contact with RPE membranes results in successful DNA delivery.

Challenges in non-viral ocular gene transfer

Nowadays, there is no effective treatment for many retinal disorders. Knowledge of the genetic basis of many severe ocular diseases may allow for alternative treatments by gene therapy. Non-viral gene complexes, such as lipo- and poly-plexes, can be delivered to the posterior segment, most often the target tissue, by intravitreal or subretinal injection. Since subretinal injections are very invasive, intravitreal injection is a promising alternative route to deliver gene complexes into the eye. However, the drawback of this technique is the relative long distance the complexes have to travel through the vitreous gel before they reach the retina. This mini-review reports on how non-viral gene complexes behave in vitreous. It especially focuses on how the coating of lipoplexes with poly(ethylene glycol) influences their behaviour in vitreous and the transfection of retinal pigment epithelium.

Pegylation of liposomes favours the endosomal degradation of the delivered phosphodiester oligonucleotides

Liposomal vesicles have been widely investigated as carriers for the intracellular delivery of oligonucleotides (ONs). To avoid unspecific uptake by the reticulo endothelial system, 'pegylation' of the liposomes, by incorporating polyethyleneglycol (PEG) at the surface, has been an attractive strategy. While pegylation has a clear benefit on the systemic level, one could wonder if pegylation also benefits the delivery efficacy of liposomes at the intracellular level. We compared the intracellular distribution of non-pegylated and pegylated liposomes, with special attention to the integrity of the oligonucleotides they are carrying. After uptake in the cells, the non-pegylated liposomes efficiently escaped from the endosomes thereby releasing phosphodiester oligonucleotides (PO-ONs) in the cytoplasm of the cells. The PO-ONs were however rapidly degraded in the intracellular environment. In contrast to non-pegylated liposomes, pegylated liposomes failed in protecting the PO-ONs they were carrying, leading to rapid degradation of the PO-ONs in the endosomal compartment. Furthermore, the PEG chains inhibited the endosomal escape of the degraded ONs. These intracellular findings explain why pegylated liposomes failed in establishing an antisense effect.

The choice of a suitable oligosaccharide to prevent aggregation of PEGylated nanoparticles during freeze thawing and freeze drying

In a previous study we have shown that the oligosaccharide inulin can prevent aggregation of poly(ethylene glycol) (PEG) coated plasmid DNA/cationic liposome complexes ("PEGylated lipoplexes") during freeze thawing and freeze drying [Hinrichs et al., 2005. J. Control. Release 103, 465]. By contrast, dextran clearly failed as stabilizer. These results were ascribed to the fact that inulin and PEG are compatible while dextran and PEG are not. In this study the stabilizing capacities of inulin and dextran (of various molecular weights) during freeze thawing and freeze drying of four different types of nanoparticles, each type with different amounts of PEG at their surface, were investigated. Freeze drying and freeze thawing of 1,2-dioleoyl-3-trimethylammonium-propane (DOTAP)/dioleoyl-phosphatidyl-ethanolamine (DOPE) liposomes and egg phosphatidyl choline (EPC)/cholesterol (CHOL) liposomes showed that inulins are excellent stabilizers even for highly PEGylated liposomes while (especially higher molecular weight) dextrans dramatically lost their stabilizing capacity when increasing the degree of PEGylation of the liposomes. The same results were obtained for plasmid DNA/DOTAP/DOPE complexes. Finally, both inulin and dextran could prevent full aggregation of plasmid DNA/polyethylenimine (PEI) complexes independent whether PEI was PEGylated or not. It is concluded that inulins are preferred as stabilizers over dextrans for various types of PEGylated nanoparticles due to their compatibility with PEG.

Pegylated nanoparticles based on poly(methyl vinyl ether-co-maleic anhydride): preparation and evaluation of their bioadhesive properties

Pegylated nanoparticles based on poly(methyl vinyl ether-co-maleic anhydride) (PVM/MA) were prepared by simple solvent displacement method, in the absence of catalysts or specific chemical conditions. Pegylation efficiency increased with the increasing of molecular weight and bulk concentration of poly(ethylene glycols) (PEGs) investigated. In fact, the use of PEG with molecular weight less than 1000 Da did not lead to its attachment. 1H NMR spectroscopy was performed in order to estimate the conformation state of PEG-chains and to predict the nanoparticle structure. Pegylation with PEG 2000 gave surface modified nanoparticles ("brush" conformation), while the chains of PEG 1000 were distributed either in the core or physically adsorbed on the nanoparticle surface. The capacity of nanoparticles to adsorb mucin at pH 7.4 was significantly higher for PEG 1000-NP than for PEG 2000-NP. The "brush" layer seemed to decrease the interaction between PEG 2000-NP and mucin, which facilitated their penetration through the mucus gel. As a consequence, PEG 2000-NP displayed higher capacity to develop adhesive interactions with rat intestinal mucosa in vivo. Independent on the weaker bioadhesive potential of PEG 1000-NP, both types of pegylated nanoparticles demonstrated very high affinity to the intestinal mucosa rather than to the stomach wall, which could be established for drug targeting to the small intestine.

Serum albumin enhances polyethylenimine-mediated gene delivery to human respiratory epithelial cells

BACKGROUND

The interaction of polyethylenimine (PEI) polyplexes with proteins in cystic fibrosis (CF) airway secretions poses a significant hurdle to this nonviral delivery system. The aim of this study was to evaluate whether albumin may increase the efficiency of PEI complexes in mediating gene transfer into respiratory epithelial cells in the presence of CF mucus.

METHODS

PEI (25 kDa) was complexed to DNA in the presence of human serum albumin (HSA) and used to transfect confluent A549 and 9HTEo- cells. Alternatively, albumin was added to preformed PEI-DNA complexes. The cytotoxicity of complexes was analysed by the LDH (lactate dehydrogenase) assay. CF CFT1-C2 cells were allowed to polarise and were transfected either with luciferase- or CFTR-expressing plasmids. To evaluate the effect of CF respiratory secretions on transfection efficiency, confluent cells were transfected in the presence of sputum obtained from two CF patients.

RESULTS

The ternary PEI-HSA complexes increased luciferase expression in confluent cultures in a dose-dependent fashion up to 100 times as compared to PEI-DNA. The number of GFP-expressing cells, as evaluated by epifluorescence, was augmented several-fold. When HSA was added to preformed PEI-DNA complexes, a further 5-10-fold increase in gene expression was observed. No significant cytotoxicity was observed with either PEI or PEI-HSA polyplexes. The ternary complexes determined detectable CFTR gene transfer and expression at the apical membrane in polarised CFT1-C2 cells, as evaluated by confocal microscopy. CF sputum inhibited PEI-mediated gene transfer by 7-186-fold. Although luciferase expression mediated by PEI-HSA was still inhibited by CF sputum, these levels were 18-83.8-fold higher than with PEI.

CONCLUSIONS

Our results demonstrate that albumin increases PEI gene transfer efficiency in confluent and polarised respiratory epithelial cells and can allow CFTR gene expression in the appropriate cellular compartment. PEI-HSA complexes display a higher efficiency than PEI also in the presence of CF sputum, indicating that albumin-containing polyplexes may help overcome barriers imposed by CF airway secretions.

Three-dimensional fluorescence recovery after photobleaching with the confocal scanning laser microscope

Confocal scanning laser microscopes (CSLMs) are equipped with the feature to photobleach user-defined regions. This makes them a handy tool to perform fluorescence recovery after photobleaching (FRAP) measurements. To allow quantification of such FRAP experiments, a three-dimensional model has been developed that describes the fluorescence recovery process for a disk-shaped geometry that is photobleached by the scanning beam of a CSLM. First the general mathematical basis is outlined describing the bleaching process for an arbitrary geometry bleached by a scanning laser beam. Next, these general expressions are applied to the bleaching by a CSLM of a disk-shaped geometry and an analytical solution is derived that describes three-dimensional fluorescence recovery in the bleached area as observed by the CSLM. The FRAP model is validated through both the Stokes-Einstein relation and the comparison of the measured diffusion coefficients with their theoretical estimates. Finally, the FRAP model is used to characterize the transport of FITC-dextrans through bulk three-dimensional biological materials: vitreous body isolated from bovine eyes, and lung sputum expectorated by cystic fibrosis patients. The decrease in the diffusion coefficient relative to its value in solution was dependent on the size of the FITC-dextrans in vitreous, whereas it was size-independent in cystic fibrosis sputum.

Non-viral gene transfer therapy for cystic fibrosis

Non-viral methods of gene transfer are being investigated to treat cystic fibrosis (CF) and include naked DNA, lipid-DNA complexes and complexes of DNA with polycations such as poly-L-lysine (poly K) or polyethylenimine (PEI), all of which can carry the cystic fibrosis transmembrane conductance regulator (CFTR) gene. The most recent promising strategy is the use of polycation-DNA complexes, particularly those prepared with poly-K and substituted with polyethylene glycol. These complexes produced partial correction of the CF defect in a mouse model with minimal toxicity, and have advanced to clinical trial. Improvements in this and other non-viral methods are in process and include i). targeting the complexes to the desired cells using receptor ligands, ii). lessening toxicity by changing the mix of lipids or adding protective molecules to polycations, iii). modifying the plasmid DNA to reduce inflammatory CpG sequences and enhance intensity, duration and tissue specificity of expression, and iv). modification of the complexes to improve nuclear access.

Photo-control of the interaction between endothelial cells and photo-cation generatable water-soluble polymers

In this study photo-control of the non-biospecific interaction between endothelial cell membranes and photo-cation generatable water-soluble polymers were examined. The water-soluble polymers contained triphenylmethane leucohydroxide (malachite green) groups (contents: 0.4 and 1.6 mol%), which dissociate into triphenylmethyl cations and counter hydroxide ions upon ultraviolet light (UV) irradiation, and were prepared by free radical copolymerization of diphenyl(4-vinylphenyl)methane leucohydroxide and acrylamide. The nature and magnitude of the interaction was quantitatively assessed by direct luminescence measurement of the intracellular calcium ion concentration using a calcium-sensitive photoprotein, aequorin. When a PBS buffer of the photoreactive copolymers were added, prior to UV irradiation, to a PBS suspension of cultured bovine endothelial cells loaded with aequorin, no detectable elevation of Ca(2+) was measured. In contrast, cationic copolymers, derived from the photoreactive copolymers after UV irradiation at a wavelength of 290<lambda<410 nm, induced an immediate transient increase in the cytosolic free Ca(2+) concentration due to a Ca(2+) inflow from the extracellular space into the cells, which may be due to non-biospecific transmembrane stimulation. Longer UV irradiation exposures of the copolymers and higher concentrations of the polymers, with higher contents of the photodissociable group, resulted in more Ca(2+) inflow with little cellular damage. The photo-cation generatable copolymers developed here made possible to control the non-biospecific interaction with endothelial cell membranes by UV irradiation condition, and composition and amount of the copolymer.

Targeting of Synthetic Gene Delivery Systems

Safe, efficient, and specific delivery of therapeutic genes remains an important bottleneck for the development of gene therapy. Synthetic, nonviral systems have a unique pharmaceutical profile with potential advantages for certain applications. Targeting of the synthetic vector improves the specificity of gene medicines through a modulation of the carriers' biodistribution, thus creating a dose differential between healthy tissue and the target site. The biodistribution of current carrier systems is being influenced to a large extent by intrinsic physicochemical characteristics, such as charge and size. Consequently, such nonspecific interactions can interfere with specific targeting, for example, by ligands. Therefore, a carrier complex should ideally be inert, that is, free from intrinsic properties that would bias its distribution away from the target site. Strategies such as coating of DNA carrier complexes with hydrophilic polymers have been used to mask some of these intrinsic targeting effects and avoid nonspecific interactions. Preexisting endogenous ligand-receptor interactions have frequently been used for targeting to certain cell types or tumours. Recently exogenous ligands have been derived from microorganisms or, like antibodies or phage-derived peptides, developed de novo. In animal models, such synthetic vectors have targeted remote sites such as a tumour. Furthermore, the therapeutic proof of the concept has been demonstrated for fitting combinations of synthetic vectors and therapeutic gene.

Mobility and stability of gene complexes in biogels

The tenacious secretions lining the conductive airways of cystic fibrosis (CF) patients may pose a significant barrier to successful gene therapy to the lung. In this work, we evaluated the diffusion of nanospheres and cationic DOTAP lipoplexes through CF sputum and the influence of CF mucus components on the physicochemical properties and gene expression of cationic DOTAP lipoplexes and neutral, pegylated GL67 lipoplexes. The number of particles transported through the sputum was extremely low (<0.5%) and strongly depending on the size of the particles, with almost no transport for the largest nanospheres (560 nm). For small particles (<150 nm), the low transport was primarily due to the long distance they have to travel through the sputum, while for larger particles also sterical obstruction was responsible for the low transport. Upon exposure of the cationic DOTAP lipoplexes to albumin, linear DNA or mucin (at concentration ratios expected to occur in vivo) a significant decrease in gene transfection activity was observed. This was primarily due to aggregation of the lipoplexes. However, exposure of pegylated GL67 lipoplexes to the same components did not affect their gene transfection activity. Indeed, it was determined that CF mucus components did not interact significantly with these neutral, pegylated GL67 lipoplexes.

Barriers to nonviral gene delivery

The use of various synthetic lipids and polymers to deliver DNA for gene therapy applications has been the subject of intense examination for the last 15 years. Our understanding of the processes involved in the delivery of DNA, although still limited, can be described in terms of specific physical and chemical barriers encountered along the delivery pathway. Successful engagement of this pathway involves avoiding inactivation in the extracellular compartment and initial favorable interactions with the cell surface. Internalization of the delivery system by endocytosis results in a poorly defined endosomal trafficking process which, if not escaped, leads to degradation of the therapeutic DNA in lysosomes. For the small fraction of material that is able to escape this vesicular trafficking pathway, the cytosol provides additional physical and metabolic barriers to further trafficking to the nucleus. Finally, nuclear uptake has been demonstrated to be a significant barrier to gene delivery. In this review, we outline in greater detail the various processes involved in each step and describe various formulation variables that have been explored to overcome these delivery barriers to nonviral gene delivery.