Basis of pulmonary toxicity associated with cationic lipid-mediated gene transfer to the mammalian lung

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.

The replacement of helper lipids with charged alternatives in lipid nanoparticles facilities targeted mRNA delivery to the spleen and lungs

The broad clinical application of mRNA therapeutics has been hampered by a lack of delivery vehicles that induce protein expression in extrahepatic organs and tissues. Recently, it was shown that mRNA delivery to the spleen or lungs is possible upon the addition of a charged lipid to a standard four-component lipid nanoparticle formulation. This approach, while effective, further complicates an already complex drug formulation and has the potential to slow regulatory approval and adversely impact manufacturing processes. We were thus motivated to maintain a four-component nanoparticle system while achieving shifts in tropism. To that end, we replaced the standard helper lipid in lipidoid nanoparticles, DOPE, with one of eight alternatives. These lipids included the neutral lipids, DOPC, sphingomyelin, and ceramide; the anionic lipids, phosphatidylserine (PS), phosphatidylglycerol, and phosphatidic acid; and the cationic lipids, DOTAP and ethyl phosphatidylcholine. While neutral helper lipids maintained protein expression in the liver, anionic and cationic lipids shifted protein expression to the spleen and lungs, respectively. For example, replacing DOPE with DOTAP increased positive LNP surface charge at pH 7 by 5-fold and altered the ratio of liver to lung protein expression from 36:1 to 1:56. Similarly, replacing DOPE with PS reduced positive charge by half and altered the ratio of liver to spleen protein expression from 8:1 to 1:3. Effects were consistent across ionizable lipidoid chemistries. Regarding mechanism, nanoparticles formulated with neutral and anionic helper lipids best transfected epithelial and immune cells, respectively. Further, the lung-tropic effect of DOTAP was linked to reduced immune cell infiltration of the lungs compared to neutral or anionic lipids. Together, these data show that intravenous non-hepatocellular mRNA delivery is readily achievable while maintaining a four-component formulation with modified helper lipid chemistry.

Direct nose to the brain nanomedicine delivery presents a formidable challenge

This advanced review describes the anatomical and physiological barriers and mechanisms impacting nanomedicine translocation from the nasal cavity directly to the brain. There are significant physiological and anatomical differences in the nasal cavity, olfactory area, and airflow reaching the olfactory epithelium between humans and experimentally studied species that should be considered when extrapolating experimental results to humans. Mucus, transporters, and tight junction proteins present barriers to material translocation across the olfactory epithelium. Uptake of nanoparticles through the olfactory mucosa and translocation to the brain can be intracellular via cranial nerves (intraneuronal) or other cells of the olfactory epithelium, or extracellular along cranial nerve pathways (perineural) and surrounding blood vessels (perivascular, the glymphatic system). Transport rates vary greatly among the nose to brain pathways. Nanomedicine physicochemical properties (size, surface charge, surface coating, and particle stability) can affect uptake efficiency, which is usually less than 5%. Incorporation of therapeutic agents in nanoparticles has been shown to produce pharmacokinetic and pharmacodynamic benefits. Assessment of adverse effects has included olfactory mucosa toxicity, ciliotoxicity, and olfactory bulb and brain neurotoxicity. The results have generally suggested the investigated nanomedicines do not present significant toxicity. Research needs to advance the understanding of nanomedicine translocation and its drug cargo after intranasal administration is presented. This article is categorized under: Therapeutic Approaches and Drug Discovery > Nanomedicine for Neurological Disease Therapeutic Approaches and Drug Discovery > Emerging Technologies Toxicology and Regulatory Issues in Nanomedicine > Toxicology of Nanomaterials.

Lipids and Lipid Derivatives for RNA Delivery

RNA-based therapeutics have shown great promise in treating a broad spectrum of diseases through various mechanisms including knockdown of pathological genes, expression of therapeutic proteins, and programmed gene editing. Due to the inherent instability and negative-charges of RNA molecules, RNA-based therapeutics can make the most use of delivery systems to overcome biological barriers and to release the RNA payload into the cytosol. Among different types of delivery systems, lipid-based RNA delivery systems, particularly lipid nanoparticles (LNPs), have been extensively studied due to their unique properties, such as simple chemical synthesis of lipid components, scalable manufacturing processes of LNPs, and wide packaging capability. LNPs represent the most widely used delivery systems for RNA-based therapeutics, as evidenced by the clinical approvals of three LNP-RNA formulations, patisiran, BNT162b2, and mRNA-1273. This review covers recent advances of lipids, lipid derivatives, and lipid-derived macromolecules used in RNA delivery over the past several decades. We focus mainly on their chemical structures, synthetic routes, characterization, formulation methods, and structure-activity relationships. We also briefly describe the current status of representative preclinical studies and clinical trials and highlight future opportunities and challenges.

Formulation and clinical perspectives of inhalation-based nanocarrier delivery: a new archetype in lung cancer treatment

Despite tremendous research in targeted delivery and specific molecular inhibitors (gene delivery), cytotoxic drug delivery through inhalation has been seen as a core part in the treatment of the lung cancer. Inhalation delivery provides a high dose of the drug directly to the lungs without affecting other body organs, increasing the therapeutic ratio. This article reviews the research performed over the last several decades regarding inhalation delivery of various cancer therapeutics for the treatment of lung cancer. Nevertheless, pulmonary administration of nanocarrier-based cancer therapeutics for lung cancer therapy is still in its infancy and faces greater than expected challenges. This article focuses on the current inhalable nanocarrier-based drugs for lung cancer treatment.

Rationale and Application of PEGylated Lipid-Based System for Advanced Target Delivery of siRNA

RNA interference (RNAi) technology has become a powerful tool in application of unraveling the mechanism of disease and may hold the potential to be developed for clinical uses. Small interfering RNA (siRNA) can bind to target mRNA with high specificity and efficacy and thus inhibit the expression of related protein for the purpose of treatment of diseases. The major challenge for RNAi application is how to improve its stability and bioactivity and therefore deliver therapeutic agents to the target sites with high efficiency and accuracy. PEGylated lipid-based delivery system has been widely used for development of various medicines due to its long circulating half-life time, low toxicity, biocompatibility, and easiness to be scaled up. The PEGylated lipid-based delivery system may also provide platform for targeting delivery of nucleic acids, and some of the research works have moved to the phases for clinical trials. In this review, we introduced the mechanism, major challenges, and strategies to overcome technical barriers of PEGylated lipid-based delivery systems for advanced target delivery of siRNA in vivo. We also summarized recent advance of PEGylated lipid-based siRNA delivery systems and included some successful research works in this field.

Toxicological profile of lipid-based nanostructures: are they considered as completely safe nanocarriers?

Nanoparticles are ubiquitous in the environment and are widely used in medical science (e.g. bioimaging, diagnosis, and drug therapy delivery). Due to unique physicochemical properties, they are able to cross many barriers, which is not possible for traditional drugs. Nevertheless, exposure to NPs and their following interactions with organelles and macromolecules can result in negative effects on cells, especially, they can induce cytotoxicity, epigenicity, genotoxicity, and cell death. Lipid-based nanomaterials (LNPs) are one of the most important achievements in drug delivery mainly due to their superior physicochemical and biological characteristics, particularly its safety. Although they are considered as the completely safe nanocarriers in biomedicine, the lipid composition, the surfactant, emulsifier, and stabilizer used in the LNP preparation, and surface electrical charge are important factors that might influence the toxicity of LNPs. According to the author's opinion, their toxicity profile should be evaluated case-by-case regarding the intended applications. Since there is a lack of all-inclusive review on the various aspects of LNPs with an emphasis on toxicological profiles including cyto-genotoxiciy, this comprehensive and critical review is outlined.

siRNA Targeting and Treatment of Gastrointestinal Diseases

RNA interference via small interfering RNA (siRNA) offers opportunities to precisely target genes that contribute to gastrointestinal (GI) pathologies, such as inflammatory bowel disease, celiac, and esophageal scarring. Delivering the siRNA to the GI tract proves challenging as the harsh environment of the intestines degrades the siRNA before it can reach its target or blocks its entry into its site of action in the cytoplasm. Additionally, the GI tract is large and disease is often localized to a specific site. This review discusses polymer and lipid‐based delivery systems for protection and targeting of siRNA therapies to the GI tract to treat local disease.

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.

Nanoparticle uptake by circulating leukocytes: A major barrier to tumor delivery

Decades of research into improving drug delivery to tumors has documented uptake of particulate delivery systems by resident macrophages in the lung, liver, and spleen, and correlated short circulation times with reduced tumor accumulation. An implicit assumption in these studies is that nanoparticles present in the blood are available for distribution to the tumor. This study documents significant levels of lipoplex uptake by circulating leukocytes, and its effect on distribution to the tumor and other organs. In agreement with previous studies, PEGylation dramatically extends circulation times and enhances tumor delivery. However, our studies suggest that this relationship is not straightforward, and that particle sequestration by leukocytes can significantly alter biodistribution, especially with non-PEGylated nanoparticle formulations. We conclude that leukocyte uptake should be considered in biodistribution studies, and that delivery to these circulating cells may present opportunities for treating viral infections and leukemia.

CRISPR/Cas9-Based Genome Editing for Disease Modeling and Therapy: Challenges and Opportunities for Nonviral Delivery

Genome editing offers promising solutions to genetic disorders by editing DNA sequences or modulating gene expression. The clustered regularly interspaced short palindromic repeats (CRISPR)/associated protein 9 (CRISPR/Cas9) technology can be used to edit single or multiple genes in a wide variety of cell types and organisms in vitro and in vivo. Herein, we review the rapidly developing CRISPR/Cas9-based technologies for disease modeling and gene correction and recent progress toward Cas9/guide RNA (gRNA) delivery based on viral and nonviral vectors. We discuss the relative merits of delivering the genome editing elements in the form of DNA, mRNA, or protein, and the opportunities of combining viral delivery of a transgene encoding Cas9 with nonviral delivery of gRNA. We highlight the lessons learned from nonviral gene delivery in the past three decades and consider their applicability for CRISPR/Cas9 delivery. We also include a discussion of bioinformatics tools for gRNA design and chemical modifications of gRNA. Finally, we consider the extracellular and intracellular barriers to nonviral CRISPR/Cas9 delivery and propose strategies that may overcome these barriers to realize the clinical potential of CRISPR/Cas9-based genome editing.

Cyclic RGD peptide-modified liposomal drug delivery system for targeted oral apatinib administration: enhanced cellular uptake and improved therapeutic effects

Apatinib is an oral tyrosine kinase inhibitor, which selectively targets vascular endothelial growth factor receptor 2 and has the potential to treat many tumors therapeutically. Cyclic arginylglycylaspartic acid (cRGD)- and polyethylene glycol (PEG)-modified liposomes (cRGD-Lipo-PEG) were constructed to act as a targeted delivery system for the delivery of apatinib to the human colonic cancer cell line, HCT116. These cRGD-modified liposomes specifically recognized integrin α_vβ₃ and exhibited greater uptake efficiency with respect to delivering liposomes into HCT116 cells when compared to nontargeted liposomes (Lipo-PEG), as well as greater death of tumor cells and apoptosis. The mechanism by which cRGD-Lipo-PEG targets cells was elucidated further with competition assays. To determine the anticancer efficacy in vivo, nude mice were implanted with HCT116 xenografts and treated with apatinib-loaded liposomes or free apatinib intravenously or via intragastric administration. The active and passive targeting of cRGD-Lipo-PEG led to significant tumor treatment targeting ability, better inhibition of tumor growth, and less toxicity when compared with treatments using uncombined apatinib. The results presented strongly support the case for cRGD-Lipo-PEG representing a targeted delivery system for apatinib in the treatment of colonic cancer.

Physical properties and biological interactions of liposomes developed as a drug carrier in the field of regenerative medicine

Liposomes are used for encapsulation of the active compounds in different therapies, with the increasing frequency. The important areas of clinical applications of liposomes are cancer targeted treatment, antibiotic delivery or regenerative medicine. The liposomes can transfer both hydrophilic and hydrophobic compounds and have the lipid bilayer which imitates the cell membrane. Liposomes additionally may extend half-live period of drugs and protect them against the elimination in different ways, such as phagocytosis, enzymatic cleavage or exclusion by detoxification. The size and charge of liposomes play an important role in drug distribution and absorption into the cell. Limited data is available on the effects of liposomes on stem cells and progenitor cells. In this article, we examined the effect of charged conventional liposomes on growth of mesenchymal and blood stem cells isolated from umbilical cord. The data suggest a likelihood, that positively charged liposomes could impair stem cell growth and metabolism. Different methodological approaches allowed for the selection of negatively charged liposomes for further experiments, as the only type of liposomes which has the lowest cytotoxicity and does not affect hematopoietic cell proliferation.

Toll-like receptor 2 promiscuity is responsible for the immunostimulatory activity of nucleic acid nanocarriers

Lipopolyamines (LPAs) are cationic lipids; they interact spontaneously with nucleic acids to form lipoplexes used for gene delivery. The main hurdle to using lipoplexes in gene therapy lies in their immunostimulatory properties, so far attributed to the nucleic acid cargo, while cationic lipids were considered as inert to the immune system. Here we demonstrate for the first time that di-C18 LPAs trigger pro-inflammatory responses through Toll-like receptor 2 (TLR2) activation, and this whether they are bound to nucleic acids or not. Molecular docking experiments suggest potential TLR2 binding modes reminiscent of bacterial lipopeptide sensing. The di-C18 LPAs share the ability of burying their lipid chains in the hydrophobic cavity of TLR2 and, in some cases, TLR1, at the vicinity of the dimerization interface; the cationic headgroups form multiple hydrogen bonds, thus crosslinking TLRs into functional complexes. Unravelling the molecular basis of TLR1 and TLR6-driven heterodimerization upon LPA binding underlines the highly collaborative and promiscuous ligand binding mechanism. The prevalence of non-specific main chain-mediated interactions demonstrates that potentially any saturated LPA currently used or proposed as transfection agent is likely to activate TLR2 during transfection. Hence our study emphasizes the urgent need to test the inflammatory properties of transfection agents and proposes the use of docking analysis as a preliminary screening tool for the synthesis of new non-immunostimulatory nanocarriers.

Inhalation of Respirable Crystalline Rifapentine Particles Induces Pulmonary Inflammation

Rifapentine is an anti-tuberculosis (anti-TB) drug with a prolonged half-life, but oral delivery results in low concentrations in the lungs because of its high binding (98%) to plasma proteins. We have shown that inhalation of crystalline rifapentine overcomes the limitations of oral delivery by significantly enhancing and prolonging the drug concentration in the lungs. The delivery of crystalline particles to the lungs may promote inflammation. This in vivo study characterizes the inflammatory response caused by pulmonary deposition of the rifapentine particles. The rifapentine powder was delivered to BALB/c mice by intratracheal insufflation at a dose of 20 mg/kg. The inflammatory response in the lungs and bronchoalveolar lavage (BAL) was examined at 12 h, 24 h, and 7 days post-treatment by flow cytometry and histopathology. At 12 and 24 h post-treatment, there was a significant influx of neutrophils into the lungs, and this returned to normal by day 7. A significant recruitment of macrophages occurred in the BAL at 24 h. Consistent with these findings, histopathological analysis demonstrated pulmonary vascular congestion and significant macrophage recruitment at 12 and 24 h post-treatment. In conclusion, the pulmonary delivery of crystalline rifapentine caused a transient neutrophil-associated inflammatory response in the lungs that resolved over 7 days. This observation may limit pulmonary delivery of rifapentine to once a week at a dose of 20 mg/kg or less. The effectiveness of weekly dosing with inhalable rifapentine will be assessed in murine Mycobacterium tuberculosis infection.

Systemic delivery of siRNA by hyaluronan-functionalized calcium phosphate nanoparticles for tumor-targeted therapy

In this study, hyaluronan (HA)-functionalized calcium phosphate nanoparticles (CaP-AHA/siRNA NPs) were developed for an injectable and targetable delivery of siRNA, which were prepared by coating the alendronate-hyaluronan graft polymer (AHA) around the surface of calcium phosphate-siRNA co-precipitates. The prepared CaP-AHA/siRNA NPs had a uniform spherical core-shell morphology with an approximate size of 170 nm and zeta potential of -12 mV. The coating of hydrophilic HA improved the physical stability of nanoparticles over one month due to the strong interactions between phosphonate and calcium. In vitro experiments demonstrated that the negatively charged CaP-AHA/siRNA NPs could effectively deliver EGFR-targeted siRNA into A549 cells through CD44-mediated endocytosis and significantly down-regulate the level of EGFR expression. Also, the internalized CaP-AHA/siRNA NPs exhibited a pH-responsive release of siRNA, indicating that the acidification of lysosomes probably facilitated the disassembling of nanoparticles and the resultant ions sharply increased the inner osmotic pressure and thus expedited the release of siRNA from late lysosomes into the cytoplasm. Furthermore, in vivo tumor therapy demonstrated that high accumulation of CaP-AHA/siEGFR NPs in tumor led to a significant tumor growth inhibition with a specific EGFR gene silencing effect after intravenous administration in nude mice xenografted with A549 tumor, along with a negligible body weight loss. These results suggested that the CaP-AHA/siRNA NPs could be an effective and safe systemic siRNA delivery system for a RNAi-based tumor targeted therapy strategy.

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.

Minicircle DNA Provides Enhanced and Prolonged Transgene Expression Following Airway Gene Transfer

Gene therapy for cystic fibrosis using non-viral, plasmid-based formulations has been the subject of intensive research for over two decades but a clinically viable product has yet to materialise in large part due to inefficient transgene expression. Minicircle DNA give enhanced and more persistent transgene expression compared to plasmid DNA in a number of organ systems but has not been assessed in the lung. In this study we compared minicircle DNA with plasmid DNA in transfections of airway epithelial cells. In vitro, luciferase gene expression from minicircles was 5–10-fold higher than with plasmid DNA. In eGFP transfections in vitro both the mean fluorescence intensity and percentage of cells transfected was 2–4-fold higher with minicircle DNA. Administration of equimolar amounts of DNA to mouse lungs resulted in a reduced inflammatory response and more persistent transgene expression, with luciferase activity persisting for 2 weeks from minicircle DNA compared to plasmid formulations. Transfection of equal mass amounts of DNA in mouse lungs resulted in a 6-fold increase in transgene expression in addition to more persistent transgene expression. Our findings have clear implications for gene therapy of airway disorders where plasmid DNA transfections have so far proven inefficient in clinical trials.

Lipid nanoparticles for short interfering RNA delivery

The discovery of RNA interference (RNAi) in mammalian cells has created a new class of therapeutics based on the reversible silencing of specific disease-causing genes. This therapeutic potential depends on the ability to deliver inducers of RNAi, such as short-interfering RNA (siRNA) and micro-RNA (miRNA), to cells of target tissues. This chapter reviews various challenges and delivery strategies for siRNA, with a particular focus on the development of lipid nanoparticle (LNP) delivery technologies. Currently, LNP delivery systems are the most advanced technology for systemic delivery of siRNA, with numerous formulations under various stages of clinical trials. We also discuss methods to improve gene silencing potency of LNP-siRNA, as well as application of LNP technologies beyond siRNA to the encapsulation of other nucleic acids such as mRNA and clustered regularly interspaced short palindromic repeats (CRISPR).

Cationic nanocarriers induce cell necrosis through impairment of Na(+)/K(+)-ATPase and cause subsequent inflammatory response

Nanocarriers with positive surface charges are known for their toxicity which has limited their clinical applications. The mechanism underlying their toxicity, such as the induction of inflammatory response, remains largely unknown. In the present study we found that injection of cationic nanocarriers, including cationic liposomes, PEI, and chitosan, led to the rapid appearance of necrotic cells. Cell necrosis induced by cationic nanocarriers is dependent on their positive surface charges, but does not require RIP1 and Mlkl. Instead, intracellular Na⁺ overload was found to accompany the cell death. Depletion of Na⁺ in culture medium or pretreatment of cells with the Na⁺/K⁺-ATPase cation-binding site inhibitor ouabain, protected cells from cell necrosis. Moreover, treatment with cationic nanocarriers inhibited Na⁺/K⁺-ATPase activity both in vitro and in vivo. The computational simulation showed that cationic carriers could interact with cation-binding site of Na⁺/K⁺-ATPase. Mice pretreated with a small dose of ouabain showed improved survival after injection of a lethal dose of cationic nanocarriers. Further analyses suggest that cell necrosis induced by cationic nanocarriers and the resulting leakage of mitochondrial DNA could trigger severe inflammation in vivo, which is mediated by a pathway involving TLR9 and MyD88 signaling. Taken together, our results reveal a novel mechanism whereby cationic nanocarriers induce acute cell necrosis through the interaction with Na⁺/K⁺-ATPase, with the subsequent exposure of mitochondrial damage-associated molecular patterns as a key event that mediates the inflammatory responses. Our study has important implications for evaluating the biocompatibility of nanocarriers and designing better and safer ones for drug delivery.

Multifunctional, stimuli-sensitive nanoparticulate systems for drug delivery

The use of nanoparticulate pharmaceutical drug delivery systems (NDDSs) to enhance the in vivo effectiveness of drugs is now well established. The development of multifunctional and stimulus-sensitive NDDSs is an active area of current research. Such NDDSs can have long circulation times, target the site of the disease and enhance the intracellular delivery of a drug. This type of NDDS can also respond to local stimuli that are characteristic of the pathological site by, for example, releasing an entrapped drug or shedding a protective coating, thus facilitating the interaction between drug-loaded nanocarriers and target cells or tissues. In addition, imaging contrast moieties can be attached to these carriers to track their real-time biodistribution and accumulation in target cells or tissues. Here, I highlight recent developments with multifunctional and stimuli-sensitive NDDSs and their therapeutic potential for diseases including cancer, cardiovascular diseases and infectious diseases.

Inhaled gene therapy in lung cancer: proof-of-concept for nano-oncology and nanobiotechnology in the management of lung cancer

Lung cancer still remains one of the leading causes of death among cancer patients. Although novel targeted therapies have been established in everyday treatment practice, and conventional platinum-based doublets have demonstrated effective results regarding overall and progression-free survival, we have still failed to achieve long-term survival. Therefore, several strategies of applying locoregional therapy are under investigation. Aerosol chemotherapy is already under investigation and, taking this a step further, aerosol gene therapies with multiple delivery systems are being developed. Several efforts have demonstrated its efficiency and effectiveness, but there are still multiple factors that have to be considered and combined to achieve an overall more effective multifunctional treatment. In the current review, we present data regarding aerosol delivery systems, transporters, carriers, vectors, genes, toxicity, efficiency, specificity, lung microenvironment and delivery gene therapy systems. Finally, we present current studies and future perspectives.

PEG length and chemical linkage controls polyacridine peptide DNA polyplex pharmacokinetics, biodistribution, metabolic stability and in vivo gene expression

The pharmacokinetics (PK), biodistribution and metabolism of non-viral gene delivery systems administered systemically are directly related to in vivo efficacy. The magnitude of luciferase expression in the liver of mice following a tail vein dose of a polyplex, composed of 1 μg of pGL3 in complex with a polyethylene glycol (PEG) polyacridine peptide, followed by a delayed hydrodynamic (HD) stimulation (1-9 h), depends on the HD stimulation delay time and the structure of the polyacridine peptide. As demonstrated in the present study, the PEG length and the type of chemical linkage joining PEG to the polyacridine peptide dramatically influence the in vivo gene transfer efficiency. To understand how PEG length, linkage and location influence gene transfer efficiency, detailed PK, biodistribution and HD-stimulated gene expression experiments were performed on polyplexes prepared with an optimized polyacridine peptide modified through a single terminal Cys or Pen (penicillamine) with a PEG chain of average length of 2, 5, 10, 20, or 30 kDa. The chemical linkage was examined by attaching PEG(5 kDa) to the polyacridine peptide through a thiol-thiol (SS), thiol-maleimide (SM), thiol-vinylsulfone (SV), thiol-acetamide (SA), penicillamine-thiol-maleimide (PM) or penicillamine-thiol-thiol (PS). The influence of PEG location was analyzed by attaching PEG(5 kDa) to the polyacridine peptide through a C-terminal, N-terminal, or a middle Cys residue. The results established rapid metabolism of polyplexes containing SV and SA chemical linkages that leads to a decreased polyplex PK half-life and a complete loss of HD-stimulated gene expression at delay times of 5 h. Conversely, polyplexes containing PM, PS, and SM chemical linkages were metabolically stable, allowing robust HD-stimulated expression at delay times up to 5h post-polyplex administration. The location of PEG(₅ kDa) within the polyacridine peptide exerted only a minor influence on the gene transfer of polyplexes. However, varying the PEG length from 2, 5, 10, 20, or 30 kDa dramatically altered polyplex biodistribution, with a 30 kDa PEG maximally blocking liver uptake to 13% of dose, while maintaining the ability to mediate HD-stimulated gene expression. The combination of results establishes important relationships between PEGylated polyacridine peptide structure, physical properties, in vivo metabolism, PK and biodistribution resulting in an optimal PEG length and linkage that leads to a robust HD-stimulated gene expression in mice.

Cytokines as biomarkers of nanoparticle immunotoxicity

Nanoscale objects, whether of biologic origin or synthetically created, are being developed into devices for a variety of bionanotechnology diagnostic and pharmaceutical applications. However, the potential immunotoxicity of these nanomaterials and mechanisms by which they may induce adverse reactions have not received sufficient attention. Nanomaterials, depending on their characteristics and compositions, can interact with the immune system in several ways and either enhance or suppress immune system function. Cytokines perform pleiotropic functions to mediate and regulate the immune response and are generally recognized as biomarkers of immunotoxicity. While the specificity and validity of certain cytokines as markers of adverse immune response has been established for chemicals, small and macromolecular drugs, research on their applicability for predicting and monitoring the immunotoxicity of engineered nanomaterials is still ongoing. The goal of this review is to provide guidelines as to important cytokines that can be utilized for evaluating the immunotoxicity of nanomaterials and to highlight the role of those cytokines in mediating adverse reactions, which is of particular importance for the clinical development of nanopharmaceuticals and other nanotechnology-based products. Importantly, the rational design of nanomaterials of low immunotoxicity will be discussed, focusing on synthetic nanodevices, with emphasis on both the nanoparticle-forming materials and the embedded cargoes.

Factors affecting the pharmacokinetics and pharmacodynamics of liposomal drugs

Various attempts to increase the therapeutic index of the drug while minimizing side effects have been made in drug delivery systems. Among several promising strategies, liposomes represent an advanced technology to target active molecules to the site of action. Rapid clearance of circulating liposomal drugs administered intravenously has been a critical issue because circulation time in the blood affects drug exposure at the target site. The clinical use of liposomal drugs is complicated by large intra- and interindividual variability in their pharmacokinetics (PK) and pharmacodynamics (PD). Thus, it is important to understand the factors affecting the PK/PD of the liposomal formulation of drugs and to elucidate the mechanisms underlying the variability in the PK/PD of liposomal drugs. In this review article, we describe the characteristics of liposome formulations and discuss the effects of various factors, including liposome-associated factors, host-associated factors, and treatment on the PK/PD of liposomal agents.

Multiplexed nanoflares: mRNA detection in live cells

We report the development of the multiplexed nanoflare, a nanoparticle agent that is capable of simultaneously detecting two distinct mRNA targets inside a living cell. These probes are spherical nucleic acid (SNA) gold nanoparticle (Au NP) conjugates consisting of densely packed and highly oriented oligonucleotide sequences, many of which are hybridized to a reporter with a distinct fluorophore label and each complementary to its corresponding mRNA target. When multiplexed nanoflares are exposed to their targets, they provide a sequence specific signal in both extra- and intracellular environments. Importantly, one of the targets can be used as an internal control, improving detection by accounting for cell-to-cell variations in nanoparticle uptake and background. Compared to single-component nanoflares, these structures allow one to determine more precisely relative mRNA levels in individual cells, improving cell sorting and quantification.

Anionic liposomes enhance and prolong adenovirus-mediated gene expression in airway epithelia in vitro and in vivo

Adenoviral vector mediated gene therapy has received extensive attention in airway disease treatment. However, the lack of the requisite coxsackie-adenovirus receptor (CAR) on the apical surface of airway epithelium and the host immune response to adenoviruses limit their in vivo application. In our study, we developed for the first time a novel formulation composed of anionic liposomes and adenoviruses (AL-Ad5) using a calcium-induced phase change method. The obtained formulation was employed to enhance the transduction efficiency of airway gene delivery. Our results indicated that primary cultured airway epithelial cells infected by AL-Ad5 displayed higher LacZ gene expression compared to naked adenovirus. Importantly, AL-Ad5 significantly improved and prolonged LacZ gene expression in murine airway tissues when delivered in vivo by intratracheal instillation. Additionally, it was found that anionic liposomes provided immunoprotection to the adenovirus from neutralizing antibody, thus slowing down the elimination of Ad5 particles meanwhile reducing the inflammatory reaction caused by the Ad5 vector. These results suggested that the combination of anionic liposomes with adenovirus may be a useful strategy to deliver therapeutic genes into the airway epithelia and is promising in clinical application.

Lipid and polymeric carrier-mediated nucleic acid delivery

IMPORTANCE OF THE FIELD

Nucleic acids such as plasmid DNA, antisense oligonucleotide, and RNA interference (RNAi) molecules, have a great potential to be used as therapeutics for the treatment of various genetic and acquired diseases. To design a successful nucleic acid delivery system, the pharmacological effect of nucleic acids, the physiological condition of the subjects or sites, and the physicochemical properties of nucleic acid and carriers have to be thoroughly examined.

AREAS COVERED IN THIS REVIEW

The commonly used lipids, polymers and corresponding delivery systems are reviewed in terms of their characteristics, applications, advantages and limitations.

WHAT THE READER WILL GAIN

This article aims to provide an overview of biological barriers and strategies to overcome these barriers by properly designing effective synthetic carriers for nucleic acid delivery.

TAKE HOME MESSAGE

A thorough understanding of biological barriers and the structure-activity relationship of lipid and polymeric carriers is the key for effective nucleic acid therapy.

Application of PepFect peptides for the delivery of splice-correcting oligonucleotides

One oligonucleotide-based approach that appear very promising for the treatment of different genetic disorders are based on so-called splice-correcting oligonucleotides (SCOs) that are exploited to manipulate splicing patterns. In order to increase the bioavailability, cell-penetrating peptides (CPPs) have readily been covalently conjugated to SCOs to facilitate cellular internalization. While being a successful strategy for the delivery of uncharged oligonucleotides (ONs), it is extremely difficult to generate covalent conjugates between commonly used negatively charged ON analogs and cationic CPPs. Furthermore, high concentrations of ONs in the micromolar range are often needed to obtain biological responses, most likely as a result of endosomal entrapment of material. Therefore, exploring other vectorization methods using CPPs with endosomolytic properties are highly desired.A method of using stearyl modified CPP (i.e., TP10) analogs, named PepFect3 and PepFect4, are being described for the transfection of antisense SCOs using a simple one-step co-incubation procedure. These peptides form complexes with SCOs and efficiently promote cellular uptake by facilitating endosomal escape. This chapter describes the methods of how to form and characterize these nanoparticles and the cellular assay used to address the delivery.

Targeting liposomes toward novel pediatric anticancer therapeutics

Although modern multimodal treatment of pediatric cancer has resulted in long-term cure of many patients, clinical success has come with significant acute and chronic morbidity. Targeted therapy using anticancer agents encapsulated in nanoparticles holds considerable promise in further improving efficacy and reducing toxic side effects. This review highlights the current strategies toward developing such therapeutic tools with an emphasis on using liposomes as flexible delivery vehicles. Potential strengths and technical difficulties encountered in advancing this platform are summarized. Critical functional determinants of nanoparticle delivery systems and future strategies to improve efficacy and specificity are described.

TLR9 and IRF3 cooperate to induce a systemic inflammatory response in mice injected with liposome:DNA

Liposome:DNA is a promising gene therapy vector. However, this vector can elicit a systemic inflammatory response syndrome (SIRS). Prior reports indicate that liposome:DNA vectors activate Toll-like receptor (TLR)9. We hypothesized that liposome:DNA vectors also activate the cytosolic DNA-sensing pathway, which signals via interferon (IFN) regulatory factor (IRF)3. To test this, we treated dendritic cells (DCs) with liposome:DNA in vitro and found that IRF3 was phosphorylated independent of TLR9. To test the contribution of this pathway in vivo, we injected a liposome:DNA vector into wild-type (WT), TLR9-knockout (KO), IRF3-KO, and TLR9-IRF3-double-KO (DKO) mice. WT mice exhibited a systemic inflammatory response, evidenced by elevations in serum cytokines, serum enzyme changes indicating organ damage, hypothermia, and mortality. The cytokine response was reduced in TLR9-KO, IRF3-KO, and TLR9-IRF3-DKO mice and all three groups survived. We found that IFN-gamma-KO mice that receive liposome:DNA had a reduced cytokine response and 100% survival. CD11c(+) and NK1.1(+) cells produced IFN-gamma and depleting CD11c(+) cells reduced the cytokine response in mice injected with liposome:DNA. These findings may facilitate the development of immunologically inert gene therapy vectors and may provide general insight into the mechanisms of SIRS.

Lipid-based systemic delivery of siRNA

RNAi technology has brought a new category of treatments for various diseases including genetic diseases, viral diseases, and cancer. Despite the great versatility of RNAi that can down regulate almost any protein in the cells, the delicate and precise machinery used for silencing is the same. The major challenge indeed for RNAi-based therapy is the delivery system. In this review, we start with the uniqueness and mechanism of RNAi machinery and the utility of RNAi in therapeutics. Then we discuss the challenges in systemic siRNA delivery by dividing them into two categories-kinetic and physical barriers. At the end, we discuss different strategies to overcome these barriers, especially focusing on the step of endosome escape. Toxicity issues and current successful examples for lipid-based delivery are also included in the review.

Gene therapy for cystic fibrosis

Cystic Fibrosis (CF) is an autosomal recessive disorder due to mutations in the CF transmembrane conductance regulator (CFTR) gene that lead to defective ion transport in the conducting pulmonary airways and exocrine glands. Through a process that is not fully understood, CFTR defects predispose affected patients to chronic endobronchial infections with organisms such as Pseudomonas aeruginosa and Staphylococcus aureus. Following the discovery of the CFTR gene in 1989, CF became one of the primary targets for gene therapy research. Early enthusiasm surrounded the new field of gene therapy during most of the 1990s and it led academics and clinicians on a big effort to apply gene therapy for cystic fibrosis. Clinical studies have been pursued using recombinant adenovirus, recombinant adeno-associated virus, cationic liposomes, and cationic polymer vectors. Although to this date no dramatic therapeutic benefits have been observed, a lot of information has been gained from the pre-clinical and clinical studies that were performed. This learning curve has led to the optimization of vector technology and an appreciation of immune and mechanical barriers that have to be overcome for successful delivery.

Structural and formulation factors influencing pyridinium lipid-based gene transfer

A series of pyridinium lipids containing a heterocyclic ring and a nitrogen atom were synthesized to determine the structure-activity relationship for gene delivery. Pyrylium chloroaluminate was synthesized by monoacylation of mesityl oxide and converted into pyrylium hexafluorophosphate, which was used as the key intermediate for reaction with different primary amines, to yield hydroxyethylpyridinium hexafluorophosphate and aminoethylpyridinium hexafluorophosphate. Acylation of these pyridinium salts with different types of fatty acid chlorides afforded the final pyridinium lipids, which were mixed with a co-lipid, such as L-alpha-dioleoylphosphatidylethanolamine (DOPE) and cholesterol (Chol) to prepare cationic liposomes by sonication. These liposomes were mixed with plasmid DNA encoding enhanced green fluorescent protein (pCMS-EGFP) or luciferase (pcDNA3-Luc) and transfected into Chinese hamster ovary (CHO) cells. Several factors including hydrophobic anchor chain length, anchor chain type, configuration of double bond, linker type, co-lipid type, cationic lipid/co-lipid molar ratio, charge ratio (N/P), and cell type had significant influence on transfection efficiency and cytotoxicity. Pyridinium lipids with amide linker showed significantly higher transfection efficiency compared to their ester counterparts. Liposomes prepared at a 1:1 molar ratio of pyridinium lipid and co-lipid showed higher transfection efficiency when either DOPE or cholesterol was used as a co-lipid to prepare cationic liposomes for complex formation with plasmid DNA at 3:1(+/-) charge ratio. Pyridinium liposomes based on a hydrophobic anchor chain length of 16 showed higher transfection efficiency and lower cytotoxicity. The pyridinium lipid with a trans-configuration of the double bond in the fatty acid chain showed higher transfection efficiency than its counterpart with cis-configuration at the same fatty acid chain length. In the presence of serum, C16:0 and Lipofectamine significantly decreased their transfection efficiencies, which were completely lost at a serum concentration of 30% and higher, while C16:1 trans-isomer still had high transfection efficiency under these conditions. In conclusion, pyridinium lipids showed high transfection efficiency and have the potential to be used as transfection reagents in vitro and in vivo.

Multifunctional and stimuli-sensitive pharmaceutical nanocarriers

Currently used pharmaceutical nanocarriers, such as liposomes, micelles, and polymeric nanoparticles, demonstrate a broad variety of useful properties, such as longevity in the body; specific targeting to certain disease sites; enhanced intracellular penetration; contrast properties allowing for direct carrier visualization in vivo; stimuli-sensitivity, and others. Some of those pharmaceutical carriers have already made their way into clinic, while others are still under preclinical development. In certain cases, the pharmaceutical nanocarriers combine several of the listed properties. Long-circulating immunoliposomes capable of prolonged residence in the blood and specific target recognition represent one of the examples of this kind. The engineering of multifunctional pharmaceutical nanocarriers combining several useful properties in one particle can significantly enhance the efficacy of many therapeutic and diagnostic protocols. This paper considers the current status and possible future directions in the emerging area of multifunctional nanocarriers with primary attention on the combination of such properties as longevity, targetability, intracellular penetration, contrast loading, and stimuli-sensitivity.