siRNA delivery to the lung: what's new?

Pulmonary siRNA Delivery with Sophisticated Amphiphilic Poly(Spermine Acrylamides) for the Treatment of Lung Fibrosis

RNA interference (RNAi) is an efficient strategy to post-transcriptionally silence gene expression. While all siRNA drugs on the market target the liver, the lung offers a variety of currently undruggable targets, which can potentially be treated with RNA therapeutics. To achieve this goal, the synthesis of poly(spermine acrylamides) (P(SpAA) is reported herein. Polymers are prepared via polymerization of N-acryloxysuccinimide (NAS) and afterward this active ester is converted into spermine-based pendant groups. Copolymerizations with decylacrylamide are employed to increase the hydrophobicity of the polymers. After deprotection, polymers show excellent siRNA encapsulation to obtain perfectly sized polyplexes at very low polymer/RNA ratios. In vitro 2D and 3D cell culture, ex vivo and in vivo experiments reveal superior properties of amphiphilic spermine-copolymers with respect to delivery of siRNA to lung cells in comparison to commonly used lipid-based transfection agents. In line with the in vitro results, siRNA delivery to human lung explants confirm more efficient gene silencing of protease-activated receptor 2 (PAR2), a G protein-coupled receptor involved in fibrosis. This study reveals the importance of the balance between efficient polyplex formation, cellular uptake, gene knockdown, and toxicity for efficient siRNA delivery in vitro, in vivo, and in fibrotic human lung tissue ex vivo.

A novel therapeutic outlook: Classification, applications and challenges of inhalable micron/nanoparticle drug delivery systems in lung cancer (Review)

Lung cancer represents a marked global public health concern. Despite existing treatment modalities, the average 5‑year survival rate for patients with patients with lung cancer is only ~20%. As there are numerous adverse effects of systemic administration routes, there is an urgent need to develop a novel therapeutic strategy tailored specifically for patients with lung cancer. Non‑invasive aerosol inhalation, as a route of drug administration, holds unique advantages in the context of respiratory diseases. Nanoscale materials have extensive applications in the field of biomedical research in recent years. The present study provides a comprehensive review of the classification, applications summarized according to existing clinical treatment modalities for lung cancer and challenges associated with inhalable micron/nanoparticle drug delivery systems (DDSs) in lung cancer. Achieving localized treatment of lung cancer preclinical models through inhalation is deemed feasible. However, further research is required to substantiate the efficacy and long‑term safety of inhalable micron/nanoparticle DDSs in the clinical management of lung cancer.

Nebulised delivery of RNA formulations to the lungs: From aerosol to cytosol

In the past decade RNA-based therapies such as small interfering RNA (siRNA) and messenger RNA (mRNA) have emerged as new and ground-breaking therapeutic agents for the treatment and prevention of many conditions from viral infection to cancer. Most clinically approved RNA therapies are parenterally administered which impacts patient compliance and adds to healthcare costs. Pulmonary administration via inhalation is a non-invasive means to deliver RNA and offers an attractive alternative to injection. Nebulisation is a particularly appealing method due to the capacity to deliver large RNA doses during tidal breathing. In this review, we discuss the unique physiological barriers presented by the lung to efficient nebulised RNA delivery and approaches adopted to circumvent this problem. Additionally, the different types of nebulisers are evaluated from the perspective of their suitability for RNA delivery. Furthermore, we discuss recent preclinical studies involving nebulisation of RNA and analysis in in vitro and in vivo settings. Several studies have also demonstrated the importance of an effective delivery vector in RNA nebulisation therefore we assess the variety of lipid, polymeric and hybrid-based delivery systems utilised to date. We also consider the outlook for nebulised RNA medicinal products and the hurdles which must be overcome for successful clinical translation. In summary, nebulised RNA delivery has demonstrated promising potential for the treatment of several lung-related conditions such as asthma, COPD and cystic fibrosis, to which the mode of delivery is of crucial importance for clinical success.

Impact of Peptide Sequence on Functional siRNA Delivery and Gene Knockdown with Cyclic Amphipathic Peptide Delivery Agents

Short-interfering RNA (siRNA) oligonucleotide therapeutics that modify gene expression by accessing RNA-interference (RNAi) pathways have great promise for the treatment of a range of disorders; however, their application in clinical settings has been limited by significant challenges in cellular delivery. Herein, we report a structure-function study using a series of modified cyclic amphipathic cell-penetrating peptides (CAPs) to determine the impact of peptide sequence on (1) siRNA-binding efficiency, (2) cellular delivery and knockdown efficiency, and (3) the endocytic uptake mechanism. Nine cyclic peptides of the general sequence Ac-C[XZ]4CG-NH2 in which X residues are hydrophobic/aromatic (Phe, Tyr, Trp, or Leu) and Z residues are charged/hydrophilic (Arg, Lys, Ser, or Glu) are assessed along with one acyclic peptide, Ac-(WR)4G-NH2. Cyclization is enforced by intramolecular disulfide bond formation between the flanking Cys residues. Binding analyses indicate that strong cationic character and the presence of aromatic residues that are competent to participate in CH-π interactions lead to CAP sequences that most effectively interact with siRNA. CAP-siRNA binding increases in the following order as a function of CAP hydrophobic/aromatic content: His < Phe < Tyr < Trp. Both cationic charge and disulfide-constrained cyclization of CAPs improve uptake of siRNA in vitro. Net neutral CAPs and an acyclic peptide demonstrate less-efficient siRNA translocation compared to the cyclic, cationic CAPs tested. All CAPs tested facilitated efficient siRNA target gene knockdown of at least 50% (as effective as a lipofectamine control), with the best CAPs enabling >80% knockdown. Significantly, gene knockdown efficiency does not strongly correlate with CAP-siRNA internalization efficiency but moderately correlates with CAP-siRNA-binding affinity. Finally, utilization of small-molecule inhibitors and targeted knockdown of essential endocytic pathway proteins indicate that most CAP-siRNA nanoparticles facilitate siRNA delivery through clathrin- and caveolin-mediated endocytosis. These results provide insight into the design principles for CAPs to facilitate siRNA delivery and the mechanisms by which these peptides translocate siRNA into cells. These studies also demonstrate the nature of the relationships between peptide-siRNA binding, cellular delivery of siRNA cargo, and functional gene knockdown. Strong correlations between these properties are not always observed, which illustrates the complexity in the design of optimal next-generation materials for oligonucleotide delivery.

RNAi therapies: Expanding applications for extrahepatic diseases and overcoming delivery challenges

The era of RNA medicine has become a reality with the success of messenger RNA (mRNA) vaccines against COVID-19 and the approval of several RNA interference (RNAi) agents in recent years. Particularly, therapeutics based on RNAi offer the promise of targeting intractable and previously undruggable disease genes. Recent advances have focused in developing delivery systems to enhance the poor cellular uptake and insufficient pharmacokinetic properties of RNAi therapeutics and thereby improve its efficacy and safety. However, such approach has been mainly achieved via lipid nanoparticles (LNPs) or chemical conjugation with N-Acetylgalactosamine (GalNAc), thus current RNAi therapy has been limited to liver diseases, most likely to encounter liver-targeting limitations. Hence, there is a huge unmet medical need for intense evolution of RNAi therapeutics delivery systems to target extrahepatic tissues and ultimately extend their indications for treating various intractable diseases. In this review, challenges of delivering RNAi therapeutics to tumors and major organs are discussed, as well as their transition to clinical trials. This review also highlights innovative and promising preclinical RNAi-based delivery platforms for the treatment of extrahepatic diseases.

Inhaled drug delivery for the targeted treatment of asthma

Asthma is a chronic lung disease affecting millions worldwide. While classically acknowledged to result from allergen-driven type 2 inflammatory responses leading to IgE and cytokine production and the influx of immune cells such as mast cells and eosinophils, the wide range in asthmatic pathobiological subtypes lead to highly variable responses to anti-inflammatory therapies. Thus, there is a need to develop patient-specific therapies capable of addressing the full spectrum of asthmatic lung disease. Moreover, delivery of targeted treatments for asthma directly to the lung may help to maximize therapeutic benefit, but challenges remain in design of effective formulations for the inhaled route. In this review, we discuss the current understanding of asthmatic disease progression as well as genetic and epigenetic disease modifiers associated with asthma severity and exacerbation of disease. We also overview the limitations of clinically available treatments for asthma and discuss pre-clinical models of asthma used to evaluate new therapies. Based on the shortcomings of existing treatments, we highlight recent advances and new approaches to treat asthma via inhalation for monoclonal antibody delivery, mucolytic therapy to target airway mucus hypersecretion and gene therapies to address underlying drivers of disease. Finally, we conclude with discussion on the prospects for an inhaled vaccine to prevent asthma.

RNA Therapeutics: A Healthcare Paradigm Shift

COVID-19 brought about the mRNA vaccine and a paradigm shift to a new mode of treating and preventing diseases. Synthetic RNA products are a low-cost solution based on a novel method of using nucleosides to act as an innate medicine factory with unlimited therapeutic possibilities. In addition to the common perception of vaccines preventing infections, the newer applications of RNA therapies include preventing autoimmune disorders, such as diabetes, Parkinson's disease, Alzheimer's disease, and Down syndrome; now, we can deliver monoclonal antibodies, hormones, cytokines, and other complex proteins, reducing the manufacturing hurdles associated with these products. Newer PCR technology removes the need for the bacterial expression of DNA, making mRNA a truly synthetic product. AI-driven product design expands the applications of mRNA technology to repurpose therapeutic proteins and test their safety and efficacy quickly. As the industry focuses on mRNA, many novel opportunities will arise, as hundreds of products under development will bring new perspectives based on this significant paradigm shift-finding newer solutions to existing challenges in healthcare.

Recent advances of metal-based nanoparticles in nucleic acid delivery for therapeutic applications

Recent efforts in designing nanomaterials to deliver potential therapeutics to the targeted site are overwhelming and palpable. Engineering nanomaterials to deliver biological molecules to exert desirable physiological changes, with minimized side effects and optimal dose, has revolutionized the next-generation therapy for several diseases. The rapid progress of nucleic acids as biopharmaceutics is going to alter the traditional pharmaceutics practices in modern medicine. However, enzymatic instability, large size, dense negative charge (hydrophilic for cell uptake), and unintentional adverse biological responses-such as prolongation of the blood coagulation and immune system activation-hamper the potential use of nucleic acids for therapeutic purposes. Moreover, the safe delivery of nucleic acids into the clinical setting is an uphill task, and several efforts are being put forward to deliver them to targeted cells. Advances in Metal-based NanoParticles (MNPs) are drawing attention due to the unique properties offered by them for drug delivery, such as large surface-area-to-volume ratio for surface modification, increased therapeutic index of drugs through site-specific delivery, increased stability, enhanced half-life of the drug in circulation, and efficient biodistribution to the desired targeted site. Here, the potential of nanoparticles delivery systems for the delivery of nucleic acids, specially MNPs, and their ability and advantages over other nano delivery systems are reviewed.

Unlocking the promise of mRNA therapeutics

The extraordinary success of mRNA vaccines against coronavirus disease 2019 (COVID-19) has renewed interest in mRNA as a means of delivering therapeutic proteins. Early clinical trials of mRNA therapeutics include studies of paracrine vascular endothelial growth factor (VEGF) mRNA for heart failure and of CRISPR-Cas9 mRNA for a congenital liver-specific storage disease. However, a series of challenges remains to be addressed before mRNA can be established as a general therapeutic modality with broad relevance to both rare and common diseases. An array of new technologies is being developed to surmount these challenges, including approaches to optimize mRNA cargos, lipid carriers with inherent tissue tropism and in vivo percutaneous delivery systems. The judicious integration of these advances may unlock the promise of biologically targeted mRNA therapeutics, beyond vaccines and other immunostimulatory agents, for the treatment of diverse clinical indications.

Spray drying siRNA-lipid nanoparticles for dry powder pulmonary delivery

While all the siRNA drugs on the market target the liver, the lungs offer a variety of currently undruggable targets which could potentially be treated with RNA therapeutics. Hence, local, pulmonary delivery of RNA nanoparticles could finally enable delivery beyond the liver. The administration of RNA drugs via dry powder inhalers offers many advantages related to physical, chemical and microbial stability of RNA and nanosuspensions. The present study was therefore designed to test the feasibility of engineering spray dried lipid nanoparticle (LNP) powders. Spray drying was performed using 5% lactose solution (m/V), and the targets were set to obtain nanoparticle sizes after redispersion of spray-dried powders around 150 nm, a residual moisture level below 5%, and RNA loss below 15% at maintained RNA bioactivity. The LNPs consisted of an ionizable cationic lipid which is a sulfur-containing analog of DLin-MC3-DMA, a helper lipid, cholesterol, and PEG-DMG encapsulating siRNA. Prior to the spray drying, the latter process was simulated with a novel dual emission fluorescence spectroscopy method to preselect the highest possible drying temperature and excipient solution maintaining LNP integrity and stability. Through characterization of physicochemical and aerodynamic properties of the spray dried powders, administration criteria for delivery to the lower respiratory tract were fulfilled. Spray dried LNPs penetrated the lung mucus layer and maintained bioactivity for >90% protein downregulation with a confirmed safety profile in a lung adenocarcinoma cell line. Additionally, the spray dried LNPs successfully achieved up to 50% gene silencing of the house keeping gene GAPDH in ex vivo human precision-cut lung slices at without increasing cytokine levels. This study verifies the successful spray drying procedure of LNP-siRNA systems maintaining their integrity and mediating strong gene silencing efficiency on mRNA and protein levels both in vitro and ex vivo. The successful spray drying procedure of LNP-siRNA formulations in 5% lactose solution creates a novel siRNA-based therapy option to target respiratory diseases such as lung cancer, asthma, COPD, cystic fibrosis and viral infections.

Nebulization of siRNA for inhalation therapy based on a microfluidic surface acoustic wave platform

The local delivery of therapeutic small interfering RNA or siRNA to the lungs has the potential to improve the prognosis for patients suffering debilitating lung diseases. Recent advances in materials science have been aimed at addressing delivery challenges including biodistribution, bioavailability and cell internalization, but an equally important challenge to overcome is the development of an inhalation device that can deliver the siRNA effectively to the lung, without degrading the therapeutic itself. Here, we report the nebulization of siRNA, either naked siRNA or complexed with polyethyleneimine (PEI) or a commercial transfection agent, using a miniaturizable acoustomicrofluidic nebulization device. The siRNA solution could be nebulised without significant degradation into an aerosol mist with tunable mean aerodynamic diameters of approximately 3 µm, which is appropriate for deep lung deposition via inhalation. The nebulized siRNA was tested for its stability, as well as its toxicity and gene silencing properties using the mammalian lung carcinoma cell line A549, which demonstrated that the gene silencing capability of siRNA is retained after nebulization. This highlights the potential application of the acoustomicrofluidic device for the delivery of efficacious siRNA via inhalation, either for systemic delivery via the alveolar epithelium or local therapeutic delivery to the lung.

Inhaled siRNA Formulations for Respiratory Diseases: From Basic Research to Clinical Application

The development of siRNA technology has provided new opportunities for gene-specific inhibition and knockdown, as well as new ideas for the treatment of disease. Four siRNA drugs have already been approved for marketing. However, the instability of siRNA in vivo makes systemic delivery ineffective. Inhaled siRNA formulations can deliver drugs directly to the lung, showing great potential for treating respiratory diseases. The clinical applications of inhaled siRNA formulations still face challenges because effective delivery of siRNA to the lung requires overcoming the pulmonary and cellular barriers. This paper reviews the research progress for siRNA inhalation formulations for the treatment of various respiratory diseases and summarizes the chemical structural modifications and the various delivery systems for siRNA. Finally, we conclude the latest clinical application research for inhaled siRNA formulations and discuss the potential difficulty in efficient clinical application.

Can pulmonary RNA delivery improve our pandemic preparedness?

The coronavirus pandemic has changed our perception of RNA medicines, and RNA vaccines have revolutionized our pandemic preparedness. But are we indeed prepared for the next variant or the next emerging virus? How can we prepare? And what does the role of inhaled antiviral RNA play in this regard? When the pandemic started, I rerouted much of the ongoing inhaled RNA delivery research in my group towards the inhibition and treatment of respiratory viral infections. Two years later, I have taken the literature, past and ongoing clinical trials into consideration and have gained new insights based on our collaborative research which I will discuss in this oration.

Inhibition of SARS-CoV-2 replication in the lung with siRNA/VIPER polyplexes

SARS-CoV-2 has been the cause of a global pandemic since 2019 and remains a medical urgency. siRNA-based therapies are a promising strategy to fight viral infections. By targeting a specific region of the viral genome, siRNAs can efficiently downregulate viral replication and suppress viral infection. However, to achieve the desired therapeutic activity, siRNA requires a suitable delivery system. The VIPER (virus-inspired polymer for endosomal release) block copolymer has been reported as promising delivery system for both plasmid DNA and siRNA in the past years. It is composed of a hydrophilic block for condensation of nucleic acids as well as a hydrophobic, pH-sensitive block that, at acidic pH, exposes the membrane lytic peptide melittin, which enhances endosomal escape. In this study, we aimed at developing a formulation for pulmonary administration of siRNA to suppress SARS-CoV-2 replication in lung epithelial cells. After characterizing siRNA/VIPER polyplexes, the activity and safety profile were confirmed in a lung epithelial cell line. To further investigate the activity of the polyplexes in a more sophisticated cell culture system, an air-liquid interface (ALI) culture was established. siRNA/VIPER polyplexes reached the cell monolayer and penetrated through the mucus layer secreted by the cells. Additionally, the activity against wild-type SARS-CoV-2 in the ALI model was confirmed by qRT-PCR. To investigate translatability of our findings, the activity against SARS-CoV-2 was tested ex vivo in human lung explants. Here, siRNA/VIPER polyplexes efficiently inhibited SARS-CoV-2 replication. Finally, we verified the delivery of siRNA/VIPER polyplexes to lung epithelial cells in vivo, which represent the main cellular target of viral infection in the lung. In conclusion, siRNA/VIPER polyplexes efficiently delivered siRNA to lung epithelial cells and mediated robust downregulation of viral replication both in vitro and ex vivo without toxic or immunogenic side effects in vivo, demonstrating the potential of local siRNA delivery as a promising antiviral therapy in the lung.

Treating Pulmonary Fibrosis with Non-Viral Gene Therapy: From Bench to Bedside

Idiopathic pulmonary fibrosis (IPF) is a chronic, progressive lung disease characterized by irreversible lung scarring, which achieves almost 80% five-year mortality rate. Undeniably, commercially available pharmaceuticals, such as pirfenidone and nintedanib, exhibit certain effects on improving the well-being of IPF patients, but the stubbornly high mortality still indicates a great urgency of developing superior therapeutics against this devastating disease. As an emerging strategy, gene therapy brings hope for the treatment of IPF by precisely regulating the expression of specific genes. However, traditional administration approaches based on viruses severely restrict the clinical application of gene therapy. Nowadays, non-viral vectors are raised as potential strategies for in vivo gene delivery, attributed to their low immunogenicity and excellent biocompatibility. Herein, we highlight a variety of non-viral vectors, such as liposomes, polymers, and proteins/peptides, which are employed in the treatment of IPF. By respectively clarifying the strengths and weaknesses of the above candidates, we would like to summarize the requisite features of vectors for PF gene therapy and provide novel perspectives on design-decisions of the subsequent vectors, hoping to accelerate the bench-to-bedside pace of non-viral gene therapy for IPF in clinical setting.

Perfluorocarbon Nanoemulsions Enhance Therapeutic siRNA Delivery in the Treatment of Pulmonary Fibrosis

Local pulmonary administration of therapeutic siRNA represents a promising approach to the treatment of lung fibrosis, which is currently hampered by inefficient delivery. Development of perfluorooctylbromide (PFOB) nanoemulsions as a way of improving the efficiency of pulmonary polycation-based delivery of siRNA is reported. The results show that the polycation/siRNA/PFOB nanoemulsions are capable of efficiently silencing the expression of STAT3 and inhibiting chemokine receptor CXCR4-two validated targets in pulmonary fibrosis. Both in vitro and in vivo results demonstrate that the nanoemulsions improve mucus penetration and facilitate effective cellular delivery of siRNA. Pulmonary treatment of mice with bleomycin-induced pulmonary fibrosis shows strong inhibition of the progression of the disease and significant prolongation of animal survival. Overall, the study points to a promising local treatment strategy of pulmonary fibrosis.

Synthesis and bioactivity of readily hydrolysable novel cationic lipids for potential lung delivery application of mRNAs

Lipid nanoparticles (LNPs) mediated mRNA delivery has gained prominence due to the success of mRNA vaccines against Covid-19, without which it would not have been possible. However, there is little clinical validation of this technology for other mRNA-based therapeutic approaches. Systemic administration of LNPs predominantly targets the liver, but delivery to other organs remains a challenge. Local approaches remain a viable option for some disease indications, such as Cystic Fibrosis, where aerosolized delivery to airway epithelium is the preferred route of administration. With this in mind, novel cationic lipids (L1-L4) have been designed, synthesized and co-formulated with a proprietary ionizable lipid. These LNPs were further nebulized, along with baseline control DOTAP-based LNP (DOTAP⁺), and tested in vitro for mRNA integrity and encapsulation efficiency, as well as transfection efficiency and cytotoxicity in cell cultures. Improved biodegradability and potentially superior elimination profiles of L1-L4, in part due to physicochemical characteristics of putative metabolites, are thought to be advantageous for prospective therapeutic lung delivery applications using these lipids.

Pulmonary delivery of siRNA against acute lung injury/acute respiratory distress syndrome

The use of small interfering RNAs (siRNAs) has been under investigation for the treatment of several unmet medical needs, including acute lung injury/acute respiratory distress syndrome (ALI/ARDS) wherein siRNA may be implemented to modify the expression of pro-inflammatory cytokines and chemokines at the mRNA level. The properties such as clear anatomy, accessibility, and relatively low enzyme activity make the lung a good target for local siRNA therapy. However, the translation of siRNA is restricted by the inefficient delivery of siRNA therapeutics to the target cells due to the properties of naked siRNA. Thus, this review will focus on the various delivery systems that can be used and the different barriers that need to be surmounted for the development of stable inhalable siRNA formulations for human use before siRNA therapeutics for ALI/ARDS become available in the clinic.

Targeting genomic SARS-CoV-2 RNA with siRNAs allows efficient inhibition of viral replication and spread

A promising approach to tackle the severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) could be small interfering (si)RNAs. So far it is unclear, which viral replication steps can be efficiently inhibited with siRNAs. Here, we report that siRNAs can target genomic RNA (gRNA) of SARS-CoV-2 after cell entry, and thereby terminate replication before start of transcription and prevent virus-induced cell death. Coronaviruses replicate via negative sense RNA intermediates using a unique discontinuous transcription process. As a result, each viral RNA contains identical sequences at the 5′ and 3′ end. Surprisingly, siRNAs were not active against intermediate negative sense transcripts. Targeting common sequences shared by all viral transcripts allowed simultaneous suppression of gRNA and subgenomic (sg)RNAs by a single siRNA. The most effective suppression of viral replication and spread, however, was achieved by siRNAs that targeted open reading frame 1 (ORF1) which only exists in gRNA. In contrast, siRNAs that targeted the common regions of transcripts were outcompeted by the highly abundant sgRNAs leading to an impaired antiviral efficacy. Verifying the translational relevance of these findings, we show that a chemically modified siRNA that targets a highly conserved region of ORF1, inhibited SARS-CoV-2 replication ex vivo in explants of the human lung. Our work encourages the development of siRNA-based therapies for COVID-19 and suggests that early therapy start, or prophylactic application, together with specifically targeting gRNA, might be key for high antiviral efficacy.

Recent Advances in the Noninvasive Delivery of mRNA

Over the past two decades, research on mRNA-based therapies has exploded, mainly because of the inherent advantages of mRNA, including a low integration probability, transient expression, and simple and rapid in vitro transcription production approaches. In addition, thanks to improved stability and reduced immunogenicity by advanced strategies, the application of mRNA has expanded from protein replacement therapy to vaccination, gene editing and other fields, showing great promise for clinical application. Recently, with the successive launch of two mRNA-based COVID-19 vaccines, mRNA technology has attracted an enormous amount of attention from scientific researchers as well as pharmaceutical companies. Because of the large molecular weight, hydrophilicity, and highly negative charge densities of mRNA, it is difficult to overcome the intracellular delivery barriers. Therefore, various delivery vehicles have been developed to achieve more effective mRNA delivery. In general, conventional mRNA administration methods are based on injection strategies, including intravenous, intramuscular, intradermal, and subcutaneous injections. Although these routes circumvent the absorption barriers to some extent, they bring about injection-related concerns such as safety issues, pain, low compliance, and difficulty in repeated dosing, increasing the need to explore alternative strategies for noninvasive delivery. The ideal noninvasive delivery systems are featured with easy to use, low risks of infection, and good patient compliance. At the same time, they allow patients to self-administer, reducing reliance on professional healthcare workers and interference with bodily functions and daily life. In particular, the noninvasive mucosal delivery of mRNA vaccines can induce mucosal immune responses, which are important for resisting pathogens infected through mucosal routes.Because of the potential clinical benefits mentioned above, we detailed the existing strategies for the noninvasive delivery of mRNA in this review, including delivery via the nasal, pulmonary, vaginal, and transdermal routes. First, we discussed the unique strengths and biological hindrances of each route on the basis of physiology. Next, we comprehensively summarized the research progress reported so far and analyzed the technologies and delivery vehicles used, hoping to provide some references for further explorations. Among these noninvasive routes, nasal and pulmonary delivery are the earliest and most intensively studied areas, mostly owing to their favorable physiological structures: the nasal or pulmonary mucosa is easily accessible, highly permeable and highly vascularized. In contrast, the development of vaginal mRNA delivery is relatively less reported, and the current research mainly focused on some local applications. In addition, microneedles have also been investigated to overcome skin barriers for mRNA delivery in recent years, making microneedle-based delivery an emerging alternative pathway. In summary, a variety of mRNA formulations and delivery strategies have been developed for noninvasive mRNA delivery, skillfully combining appropriate vehicles or physical technologies to enhance effectiveness. We surmise that continuous advances and technological innovations in the development of mRNA noninvasive delivery will accelerate the translation from experimental research to clinical application.

Delivery of synthetic mRNAs for tissue regeneration

In recent years, nucleic acid-based therapeutics have gained increasing importance as novel treatment options for disease prevention and treatment. Synthetic messenger RNAs (mRNAs) are promising nucleic acid-based drugs to transiently express desired proteins that are missing or defective. Recently, synthetic mRNA-based vaccines encoding viral proteins have been approved for emergency use against COVID-19. Various types of vehicles, such as lipid nanoparticles (LNPs) and liposomes, are being investigated to enable the efficient uptake of mRNA molecules into desired cells. In addition, the introduction of novel chemical modifications into mRNAs increased the stability, enabled the modulation of nucleic acid-based drugs, and increased the efficiency of mRNA-based therapeutic approaches. In this review, novel and innovative strategies for the delivery of synthetic mRNA-based therapeutics for tissue regeneration are discussed. Moreover, with this review, we aim to highlight the versatility of synthetic mRNA molecules for various applications in the field of regenerative medicine and also discuss translational challenges and required improvements for mRNA-based drugs.

Pulmonary surfactant as a versatile biomaterial to fight COVID-19

The COVID-19 pandemic has wielded an enormous pressure on global health care systems, economics and politics. Ongoing vaccination campaigns effectively attenuate viral spreading, leading to a reduction of infected individuals, hospitalizations and mortality. Nevertheless, the development of safe and effective vaccines as well as their global deployment is time-consuming and challenging. In addition, such preventive measures have no effect on already infected individuals and can show reduced efficacy against SARS-CoV-2 variants that escape vaccine-induced host immune responses. Therefore, it is crucial to continue the development of specific COVID-19 targeting therapeutics, including small molecular drugs, antibodies and nucleic acids. However, despite clear advantages of local drug delivery to the lung, inhalation therapy of such antivirals remains difficult. This review aims to highlight the potential of pulmonary surfactant (PS) in the treatment of COVID-19. Since SARS-CoV-2 infection can progress to COVID-19-related acute respiratory distress syndrome (CARDS), which is associated with PS deficiency and inflammation, replacement therapy with exogenous surfactant can be considered to counter lung dysfunction. In addition, due to its surface-active properties and membrane-interaction potential, PS can be repurposed to enhance drug spreading along the respiratory epithelium and to promote intracellular drug delivery. By merging these beneficial features, PS can be regarded as a versatile biomaterial to combat respiratory infections, in particular COVID-19.

Particle engineering principles and technologies for pharmaceutical biologics

The global market of pharmaceutical biologics has expanded significantly during the last few decades. Currently, pharmaceutical biologic products constitute an indispensable part of the modern medicines. Most pharmaceutical biologic products are injections either in the forms of solutions or lyophilized powders because of their low oral bioavailability. There are certain pharmaceutical biologic entities formulated into particulate delivery systems for the administration via non-invasive routes or to achieve prolonged pharmaceutical actions to reduce the frequency of injections. It has been well documented that the design of nano- and microparticles via various particle engineering technologies could render pharmaceutical biologics with certain benefits including improved stability, enhanced intracellular uptake, prolonged pharmacological effect, enhanced bioavailability, reduced side effects, and improved patient compliance. Herein, we review the principles of the particle engineering technologies based on bottom-up approach and present the important formulation and process parameters that influence the critical quality attributes with some mathematical models. Subsequently, various nano- and microparticle engineering technologies used to formulate or process pharmaceutical biologic entities are reviewed. Lastly, an array of commercialized products of pharmaceutical biologics accomplished based on various particle engineering technologies are presented and the challenges in the development of particulate delivery systems for pharmaceutical biologics are discussed.

Effects of sterol derivatives in cationic liposomes on biodistribution and gene-knockdown in the lungs of mice systemically injected with siRNA lipoplexes

Cationic liposomes can be intravenously injected to deliver short interfering (si)RNAs into the lungs. The present study investigated the effects of sterol derivatives in systemically injected siRNA/cationic liposome complexes (siRNA lipoplexes) on gene-knockdown in the lungs of mice. Cationic liposomes composed of 1,2-dioleoyl-3-trimethylammonium-propane or dimethyldioctadecylammonium bromide (DDAB) were prepared as a cationic lipid, with sterol derivatives such as cholesterol (Chol), β-sitosterol, ergosterol (Ergo) or stigmasterol as a neutral helper lipid. Transfected liposomal formulations composed of DDAB/Chol or DDAB/Ergo did not suppress the expression of the luciferase gene in LLC-Luc and Colon 26-Luc cells in vitro, whereas other formulations induced moderate gene-silencing. The systemic injection of siRNA lipoplexes formulated with Chol or Ergo into mice resulted in abundant siRNA accumulation in the lungs. In comparison, systemically injected DDAB/Chol or DDAB/Ergo lipoplexes of Tie2 siRNA effectively increased the suppression of the Tie2 mRNA expression in the lungs of mice. These findings indicated that DDAB/Chol and DDAB/Ergo liposomes could function as vectors for siRNA delivery to the lungs.

Engineering of Solid Dosage Forms of siRNA-Loaded Lipidoid-Polymer Hybrid Nanoparticles Using a Quality-by-Design Approach

Therapy based on RNA interference (RNAi), which can be mediated by exogenous small interfering RNA (siRNA), has potential for the management of diseases at the genetic level by silencing gene function(s). In all eukaryotic cells, RNAi is an endogenous regulatory mechanism, where messenger RNA (mRNA) is degraded, preventing its translation into protein. A significant advantage of RNAi therapy is that siRNA is very potent and gene silencing is highly specific, ensuring few off-target effects. However, the delivery of exogenous siRNA to the RNAi pathway in the cytosol is a challenge, and there is a need for development of advanced delivery systems to ensure safe and effective delivery of siRNA to the intracellular target site. Recently, we demonstrated the ability of lipid-polymer hybrid nanoparticles (LPNs) composed of cationic lipidoid 5 (L₅) and the biodegradable polymer poly(DL-lactic-co-glycolic acid) to effectively deliver siRNA directed against tumor necrosis factor alpha (TNF-α) intracellularly to macrophages. L₅ is a novel lipid-like material consisting of a tetraamine backbone linked to five C₁₂ alkyl chains. Here, we describe a systematic quality-by-design (QbD) approach including risk assessment and design of experiments to investigate the influence of critical formulation parameters (i.e., L₅ content and L₅:TNF-α siRNA ratio (w/w)) on the physicochemical properties and the TNF-α gene silencing ability of TNF-α siRNA-loaded LPNs, prepared by using a double emulsion solvent evaporation method. We then detail protocols for the manufacturing of more stable solid dosage forms of LPNs using freeze drying and spray drying processes, respectively. We also provide protocols for characterization of the physicochemical properties of the nanocomposite dry powders, including (1) process yield, (2) aerodynamic particle size, (3) surface morphology, (4) moisture content, and (5) solid state properties. General considerations are provided that emphasize the advantages and disadvantages of applying QbD approaches for optimizing nanoparticulate formulations.

Adverse immunological responses against non-viral nanoparticle (NP) delivery systems in the lung

There is a large, unmet medical need to treat chronic obstructive pulmonary disease, asthma, idiopathic pulmonary fibrosis and other respiratory diseases. New modalities are being developed, including gene therapy which treats the disease at the DNA/RNA level. Despite recent innovations in non-viral gene therapy delivery for chronic respiratory diseases, unwanted or adverse interactions with immune cells, particularly macrophages, can limit drug efficacy. This review will examine the relationship between the design and fabrication of non-viral nucleic acid nanoparticle (NP) delivery systems and their ability to trigger unwanted immunogenic responses in lung tissues. NP formulated with peptides, lipids, synthetic and natural polymers provide a robust means of delivering the genetic cargos to the desired cells. However NP, or their components, may trigger local responses such as cell damage, edema, inflammation, and complement activation. These effects may be acute short-term reactions or chronic long-term effects like fibrosis, increased susceptibility to diseases, autoimmune disorders, and even cancer. This review examines the relationship between physicochemical properties, i.e. shape, charge, hydrophobicity, composition and stiffness, and interactions of NP with pulmonary immune cells. Inhalation is the ideal route of administration for direct delivery but inhaled NP encounter innate immune cells, such as alveolar macrophages (AM) and dendritic cells (DC), that perceive them as harmful foreign material, interfere with gene delivery to target cells, and can induce undesirable side effects. Recommendations for fabrication and formulation of gene therapies to avoid adverse immunological responses are given. These include fine tuning physicochemical properties, functionalization of the surface of NP to actively target diseased pulmonary cells and employing biomimetics to increase immunotolerance.

siRNA Therapeutics against Respiratory Viral Infections-What Have We Learned for Potential COVID-19 Therapies?

Acute viral respiratory tract infections (AVRIs) are a major burden on human health and global economy and amongst the top five causes of death worldwide resulting in an estimated 3.9 million lives lost every year. In addition, new emerging respiratory viruses regularly cause outbreaks such as SARS-CoV-1 in 2003, the "Swine flu" in 2009, or most importantly the ongoing SARS-CoV-2 pandemic, which intensely impact global health, social life, and economy. Despite the prevalence of AVRIs and an urgent need, no vaccines-except for influenza-or effective treatments were available at the beginning of the COVID-19 pandemic. However, the innate RNAi pathway offers the ability to develop nucleic acid-based antiviral drugs. siRNA sequences against conserved, essential regions of the viral genome can prevent viral replication. In addition, viral infection can be averted prophylactically by silencing host genes essential for host-viral interactions. Unfortunately, delivering siRNAs to their target cells and intracellular site of action remains the principle hurdle toward their therapeutic use. Currently, siRNA formulations and chemical modifications are evaluated for their delivery. This progress report discusses the selection of antiviral siRNA sequences, delivery techniques to the infection sites, and provides an overview of antiviral siRNAs against respiratory viruses.

Self-assembled mRNA vaccines

mRNA vaccines have evolved from being a mere curiosity to emerging as COVID-19 vaccine front-runners. Recent advancements in the field of RNA technology, vaccinology, and nanotechnology have generated interest in delivering safe and effective mRNA therapeutics. In this review, we discuss design and self-assembly of mRNA vaccines. Self-assembly, a spontaneous organization of individual molecules, allows for design of nanoparticles with customizable properties. We highlight the materials commonly utilized to deliver mRNA, their physicochemical characteristics, and other relevant considerations, such as mRNA optimization, routes of administration, cellular fate, and immune activation, that are important for successful mRNA vaccination. We also examine the COVID-19 mRNA vaccines currently in clinical trials. mRNA vaccines are ready for the clinic, showing tremendous promise in the COVID-19 vaccine race, and have pushed the boundaries of gene therapy.

Pulmonary siRNA delivery for lung disease: Review of recent progress and challenges

Lung diseases are a leading cause of mortality worldwide and there exists urgent need for new therapies. Approval of the first siRNA treatments in humans has opened the door for further exploration of this therapeutic strategy for other disease states. Pulmonary delivery of siRNA-based biopharmaceuticals offers the potential to address multiple unmet medical needs in lung-related diseases because of the specific physiology of the lung and characteristic properties of siRNA. Inhalation-based siRNA delivery designed for efficient, targeted delivery to specific cells within the lung holds great promise. Efficient delivery of siRNA directly to the lung, however, is relatively complex. This review focuses on the barriers that impact pulmonary siRNA delivery and successful recent approaches to advance this field forward. We focus on the pulmonary barriers that affect siRNA delivery, the disease-dependent pathological changes and their role in pulmonary disease and impact on siRNA delivery, as well as the recent development on the pulmonary siRNA delivery systems.

Poly(lactide-co-glycolide) Nanoparticles Mediate Sustained Gene Silencing and Improved Biocompatibility of siRNA Delivery Systems in Mouse Lungs after Pulmonary Administration

Pulmonary delivery of small interfering RNA (siRNA)-based drugs is promising in treating severe lung disorders characterized by the upregulated expression of disease-causing genes. Previous studies have shown that the sustained siRNA release in vitro can be achieved from polymeric matrix nanoparticles based on poly(lactide-co-glycolide) (PLGA) loaded with lipoplexes (LPXs) composed of cationic lipid and anionic siRNA (lipid-polymer hybrid nanoparticles, LPNs). Yet, the in vivo efficacy, potential for prolonging the pharmacological effect, disposition, and safety of LPNs after pulmonary administration have not been investigated. In this study, siRNA against enhanced green fluorescent protein (EGFP-siRNA) was either assembled with 1,2-dioleoyl-3-trimethylammonium-propane (DOTAP) to form LPX or co-entrapped with DOTAP in PLGA nanoparticles to form LPNs. The disposition and clearance of LPXs and LPNs in mouse lungs were studied after intratracheal administration by using single-photon emission computed tomography/computed tomography (SPECT/CT) and gamma counting. Fluorescence spectroscopy, Western blot, and confocal laser scanning microscopy were used to evaluate the silencing of the EGFP expression mediated by the LPXs and LPNs after intratracheal administration to transgenic mice expressing the EGFP gene. The in vivo biocompatibility of LPXs and LPNs was investigated by measuring the cytokine level, total cell counts in bronchoalveolar lavage fluid, and observing the lung tissue histology section. The results showed that the silencing of the EGFP expression mediated by LPNs after pulmonary administration was both prolonged and enhanced as compared to LPXs. This may be attributed to the sustained release characteristics of PLGA, and the prolonged retention in the lung tissue of the colloidally more stable LPNs in comparison to LPXs, as indicated by SPECT/CT. The presence of PLGA effectively alleviated the acute inflammatory effect of cationic lipids to the lungs. This study suggests that PLGA-based LPNs may present an effective formulation strategy to mediate sustained gene silencing effects in the lung via pulmonary administration.

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.

Rational design of multistage drug delivery vehicles for pulmonary RNA interference therapy

Small interfering RNA (siRNA) therapy has significant potential for the treatment of myriad diseases, including cancer. While intravenous routes of delivery have been found to be effective for efficient targeting to the liver, achieving high accumulations selectively in other organs, including lung tissues, can be a challenge. We demonstrate the rational design and engineering of a layer-by-layer (LbL) nanoparticle-containing aerosol that is able to achieve efficient, multistage delivery of siRNA in vitro. For the purpose, LbL nanoparticles were, for the first time, encapsulated in composite porous micro scale particles using a supercritical CO2-assisted spray drying (SASD) apparatus using chitosan as an excipient. Such particles exhibited aerodynamic properties highly favorable for pulmonary administration, and effective silencing of mutant KRAS in lung cancer cells derived from tumors of a non-small cell lung cancer (NSCLC) autochthonous model. Furthermore, efficient alveolar accumulation following inhalation in healthy mice was also observed, corroborating in vitro aerodynamic results, and opening new perspectives for further studies of effective lung therapies These results show that multistage aerosols assembled by supercritical CO₂-assisted spray drying can enable efficient RNA interference therapy of pulmonary diseases including lung cancer.

A Method for Targeted Nonviral siRNA Delivery in Cancer and Inflammatory Diseases

Small interfering RNA (siRNA)-based therapy has been subject of intense research since the discovery of RNA interference (RNAi), providing a tool to potentially silence any chosen gene. Nevertheless, efficient delivery still presents a major hurdle to translating this promising technology into medical practice. Here, we describe a straightforward method to prepare and characterize an effective delivery system consisting of low-molecular-weight polyethylenimine (PEI) and transferrin (Tf). Tf-PEI polyplexes are not only able to successfully transport and protect the sensitive nucleic acid payload from degradation but also to selectively deliver the siRNA to transferrin receptor (TfR)-overexpressing cells, playing key roles in the pathology of numerous cancer types as well as inflammatory diseases.

RNAi therapeutics: an antiviral strategy for human infections

Gene silencing induced by RNAi represents a promising antiviral development strategy. This review will summarise the current state of RNAi therapeutics for treating acute and chronic human virus infections. The gene silencing pathways exploited by RNAi therapeutics will be described and include both classic RNAi, inducing cytoplasmic mRNA degradation post-transcription and novel RNAi, mediating epigenetic modifications at the transcription level in the nucleus. Finally, the challenge of delivering gene modifications via RNAi will be discussed, along with the unique characteristics of respiratory versus systemic administration routes to highlight recent advances and future potential of RNAi antiviral treatment strategies.

Treatment of acute lung inflammation by pulmonary delivery of anti-TNF-α siRNA with PAMAM dendrimers in a murine model

To improve the efficacy of nucleic acid-based therapeutics, e.g., small interfering RNA (siRNA), transfection agents are needed for efficient delivery into cells. Several classes of dendrimers have been found useful as transfection agents for the delivery of siRNA because their surface can readily be functionalized, and the size of the dendriplexes they form with siRNA is within the range of conventional nanomedicine. In this study, commercially available generation 3 poly(amidoamine) (PAMAM) dendrimer was investigated for pulmonary delivery of siRNA directed against tumor necrosis factor (TNF) α for the treatment of acute lung inflammation. Delivery efficiency was assessed in vitro in the RAW264.7 macrophage cell line activated with lipopolysaccharide (LPS), and efficacy was evaluated in vivo in a murine model of LPS-induced lung inflammation upon pre-treatment with TNF-α siRNA. The PAMAM dendrimer-siRNA complexes (dendriplexes) displayed strong siRNA condensation and high cellular uptake in macrophages compared with non-complexed siRNA. Q-PCR analyses showed that the dendriplexes mediated efficient and specific TNF-α silencing in vitro, as compared to non-complexed siRNA and dendriplexes with negative control siRNA. Also in vivo, the PAMAM dendriplexes induced efficacious TNF-α siRNA inhibition, as compared to non-complexed siRNA, upon pulmonary administration to mice with LPS-induced lung inflammation. Hence, these data suggest that PAMAM dendrimers are promising for the local delivery of TNF-α siRNA in the treatment of lung inflammation via pulmonary administration.

Polyprenol-Based Lipofecting Agents for In Vivo Delivery of Therapeutic DNA to Treat Hypertensive Rats

Development of efficient vectors for transfection is one of the major challenges in genetic engineering. Previous research demonstrated that cationic derivatives of polyisoprenoids (PTAI) may serve as carriers of nucleic acids. In the present study, the effectiveness of two PTAI-based formulations (PTAI-6–8 and 10–14) was investigated and compared to the commercial reagents. The purpose of applied gene therapy was to enhance the expression of vascular endothelial growth factor (VEGF-A) in the renal medulla of spontaneously hypertensive rats (SHR) and to test its potential as a novel antihypertensive intervention. In the first part of the study (in vitro), we confirmed that PTAI-based lipoplexes efficiently transfect XC rat sarcoma cells and are stable in 37 °C for 7 days. In the in vivo experiments, we administered selected lipoplexes directly to the kidneys of conscious SHR (via osmotic pumps). There were no blood pressure changes and VEGF-A level in renal medulla was significantly higher only for PTAI-10–14-based formulation. In conclusion, despite the promising results, we were not able to achieve VEGF-A expression level high enough to verify VEGF-A gene therapy usefulness in SHR. However, results of our study give important indications for the future development of PTAI-based DNA carriers and kidney-targeted gene delivery.

Nanocarriers in effective pulmonary delivery of siRNA: current approaches and challenges

Research on siRNA is increasing due to its wide applicability as a therapeutic agent in irreversible medical conditions. siRNA inhibits expression of the specific gene after its delivery from formulation to cytosol region of a cell. RNAi (RNA interference) is a mechanism by which siRNA is silencing gene expression for a particular disease. Numerous studies revealed that naked siRNA delivery is not preferred due to instability and poor pharmacokinetic performance. Nanocarriers based delivery of siRNA has the advantage to overcome physiological barriers and protect the integrity of siRNA from degradation by RNAase. Various diseases like lung cancer, cystic fibrosis, asthma, etc can be treated effectively by local lung delivery. The selective targeted therapeutic action in diseased organ and least off targeted cytotoxicity are the key benefits of pulmonary delivery. The current review highlights recent developments in pulmonary delivery of siRNA with novel nanosized formulation approach with the proven in vitro/in vivo applications.

Pulmonary delivery of siRNA as a novel treatment for lung diseases

Graphical abstract.

Quantitative comparison of three widely-used pulmonary administration methods in vivo with radiolabeled inhalable nanoparticles

Pulmonary formulations have been attracting much attention because of their direct effects on respiratory diseases, but also their non-invasive administration for the treatment of systemic diseases. When developing such formulations, they are typically first investigated in mice. As there are various pulmonary administration methods, the researcher has to decide on the best quantitative method for their preclinical investigations among candidate methods, both for total delivery and distribution within the lung lobes. In this study, we investigated the deposition and distribution of siRNA loaded PLGA nanoparticles (NPs) in the different lung lobes via three widely used pulmonary administration methods: intratracheal instillation, intratracheal spraying and intranasal instillation. The NPs were radiolabeled with ¹¹¹In, administered and a single photon emission computed tomography (SPECT/CT) whole body scan performed. Quantitative image volume of interest (VOI) analysis of all inhalation related organs was performed, plus sub-organ examinations using dissection and gamma counting. Intratracheal instillation and intratracheal spraying deposited >95% and >85% of radiolabeled NPs in the lung, respectively. However, the lung lobe distribution of the NPs was inhomogeneous. Intranasal instillation deposited only ~28% of the dose in the lungs, with even larger inhomogeneity and individual variation between animals. Furthermore, there was a high deposition of the NPs in the stomach. Intratracheal instillation and intratracheal spraying deposit a large number of NPs in the lungs, and are thus useful to test therapeutic effects in preclinical animal studies. However, the inhomogeneous distribution of formulation between lung lobes needs to be considered in the experimental design. Intranasal instillation should not be used as a means of pulmonary administration.

Pulmonary Administration: Strengthening the Value of Therapeutic Proximity

In recent years inhaled systems have shown momentum as patient-personalized therapies emerge. A significant improvement in terms of therapeutic efficacy and/or reduction adverse systemic effects is anticipated from their use owing these systems regional accumulation. Nevertheless, whatever safety and efficacy evidence required for inhaled formulations regulatory approval, it still poses an additional hurdle to gaining market access. In contrast with the formal intravenous medicines approval, the narrower adoption of pulmonary administration might rely on discrepancies in pre-clinical and clinical data provided by the marketing authorization holder to the regulatory authorities. Evidences of a diverse and inconsistent regulatory framework led to concerns over toxicity issues and respiratory safety. However, an overall trend to support general concepts of good practices exists. Current regulatory guidelines that supports PK/PD (pharmacokinetics/pharmacodynamic) assessment seeks attention threatening those inhaled formulations set to be approved in the coming years. A more complex scenario arises from the attempt of implementing nanomedicines for pulmonary administration. Cutting-edge image techniques could play a key role in supporting diverse stages of clinical development facilitating this pharmaceutics take off and speed to patients. The ongoing challenge in adapting conventional regulatory frameworks has proven to be tremendously difficult in an environment where market entry relies on multiple collections of evidence. This paper intention is to remind us that an acceptable pre-clinical toxicological program could emerge from, but not only, an accurate and robust data imaging collection. It is our conviction that if implemented, inhaled nanomedicines might have impact in multiple severe conditions, such as lung cancer, by fulfilling the opportunity for developing tailored treatments while solving dose-related toxicity issues; the most limiting threat in conventional lung cancer clinical management.

Cancer-targeted PEDF-DNA therapy for metastatic colorectal cancer

Colorectal cancer (CRC) is a major cause of cancer-related mortality worldwide. Moreover, metastasis is one of the main causes of death in CRC patients. Nanotechnology-based gene therapy has shown significant therapeutic benefits in recent clinical trials for cancer treatment. Recent studies have shown that pigment epithelium-derived factor (PEDF) protein can inhibit tumor growth and metastasis by anti-angiogenesis and pro-apoptosis. In this study, we prepared a PEDF-DNA-loaded liposome for cancer-targeted gene therapy for metastatic CRC using an iRGD peptide. Our results showed that cancer-targeted PEDF-DNA liposomes (R-LP/PEDF) exhibited enhanced inhibitory effects on invasion, migration, and pro-apoptosis of CRC cells in vitro. In addition, it reduced metastasis tumor nodules in lung and prolonged the survival time in a mouse model of metastatic CRC.

Increased Survival by Pulmonary Treatment of Established Lung Metastases with Dual STAT3/CXCR4 Inhibition by siRNA Nanoemulsions

Lung metastasis is a common and deadly occurrence in many types of solid tumors. Chemokine receptor CXCR4 and transcription factor signal transducer and activator of transcription 3 (STAT3) are among potential therapeutic targets in lung metastatic cancer. Both CXCR4 and STAT3 play important roles in the proliferation, angiogenesis, and metastasis of cancer cells. Here, we report on the development of a pulmonary delivery (p.d.) system based on perfluorocarbon (PFC) nanoemulsions for combined delivery of a partially fluorinated polymeric CXCR4 antagonist (FM) and anti-STAT3 small interfering RNA (siRNA). We have prepared FM-stabilized PFC (FM@PFC) as a delivery system of therapeutic siRNA adsorbed on the surface of the emulsion. These FM@PFC/siRNA nanoemulsions inhibited both CXCR4 and STAT3, as demonstrated by effective anti-invasive ability in vitro and related antimetastatic activity in vivo. The combined nanoemulsions provided a comprehensive anticancer effect in the model of established lung metastasis of breast carcinoma, which was dependent on induction of cancer cell apoptosis, anti-angiogenic effect, anti-invasive activity, and overcoming of the immunosuppressive tumor microenvironment. Direct comparison with intravenous (i.v.) injection showed superior activity of pulmonary administration as indicated by significantly increased animal survival. Overall, this work established the suitability of the PFC nanoemulsions for p.d. of combination anticancer treatments and as a promising method to treat lung metastasis.

RNAi therapeutic strategies for acute respiratory distress syndrome

Acute respiratory distress syndrome (ARDS), replacing the clinical term acute lung injury, involves serious pathophysiological lung changes that arise from a variety of pulmonary and nonpulmonary injuries and currently has no pharmacological therapeutics. RNA interference (RNAi) has the potential to generate therapeutic effects that would increase patient survival rates from this condition. It is the purpose of this review to discuss potential targets in treating ARDS with RNAi strategies, as well as to outline the challenges of oligonucleotide delivery to the lung and tactics to circumvent these delivery barriers.

Evaluating the Regulation of Cytokine Levels After siRNA Treatment in Antigen-Specific Target Cell Populations via Intracellular Staining

RNA interference (RNAi) offers a promising base for therapeutic knockdown of clinically relevant genes. Local delivery routes as well as targeted delivery to specific cell populations have been shown to circumvent several hurdles of successful siRNA delivery in vivo. To evaluate and quantify the treatment effect in a precise way, next to measuring the downregulation on gene and protein levels, it is equally essential to investigate the influence on downstream factors such as generated cytokines. Here, we describe an expressive method to specifically isolate the desired target cells and determine their levels of intracellular cytokines by flow cytometry using the example of murine lungs after pulmonary in vivo transfection with siRNA.Therefore, the lungs of treated mice are harvested and processed into single cell suspensions, in which CD4 positive T cells are marked by antibody-coupled magnetic beads and isolated via magnetic separation. These purified target cells are then fixed and permeabilized, making their intracellular interleukins accessible for staining with fluorescently labeled antibodies. Thus, the cytokine levels and hence the precise influence of the siRNA treatment on intracellular conditions can be measured.

Coming in and Finding Out: Blending Receptor-Targeted Delivery and Efficient Endosomal Escape in a Novel Bio-Responsive siRNA Delivery System for Gene Knockdown in Pulmonary T Cells

RNA interference (RNAi) offers the potential to selectively silence disease-related genes in defined cell subsets. Translation into the clinical routine is, however, still hampered by the lack of efficient carrier systems for therapeutic siRNA, endosomal entrapment presenting a major hurdle. A promising siRNA delivery system has previously been developed on the base of polyethylenimine (PEI) and the targeting ligand transferrin (Tf) to specifically reach activated T cells in the lung. In the present work, the focus is on optimizing Tf-PEI polyplexes for gene knockdown in primary activated T cells by improving their endosomal escape properties. Blending of the conjugate with membrane lytic melittin significantly enhanced endosomal release and thereby cytoplasmic delivery, while maintaining selective T cell targeting abilities and overall cell tolerability. The gathered data furthermore demonstrate that melittin addition also distinctly improves several other essential particle characteristics, such as siRNA encapsulation efficiency and stability in lung lining fluids. In conclusion, this results in a novel upgraded siRNA delivery system that is not only able to specifically deliver its payload to the desired target cells via receptor-mediated endocytosis, but also shows enhanced release from endosomal vesicles in order to initiate RNAi in the cytoplasm.