Intracellular route and transcriptional competence of polyethylenimine-DNA complexes

Tuning plasmid DNA amounts for cost-effective transfections of mammalian cells: when less is more

Transient gene expression (TGE) in mammalian cells is a well-known approach to the fast expression of recombinant proteins. The human cell line HEK (human embryonic kidney) 293F is widely used in this field, due to its adaptability to grow in suspension to high cell densities in serum-free media, amenability to transfection, and production of recombinant proteins in satisfactory quantities for functional and structural analysis. Amounts of plasmid DNA (pDNA) required in transfections for TGE remain high (usually 1 µg pDNA/mL, or even higher), representing a noticeable proportion of the overall cost. Thus, there is an economic need to reduce amounts of coding pDNA in TGE processes. In this work, amounts of both pDNA and transfecting agent used for TGE in HEK 293F cells have been explored in order to reduce them without compromising (or even improving) the productivity of the process in terms of protein yield. In our hands, minimal polyethyleneimine (PEI) cytotoxicity and optimum protein yields were obtained when transfecting at 0.5 µg pDNA/mL (equal to 0.5 µg pDNA/million cells) and a DNA-to-PEI ratio of 1:3, a trend confirmed for several unrelated recombinant proteins. Thus, carefully tuning pDNA and transfecting agent amounts not only reduces the economic costs but also results in higher recombinant protein yields. These results surely have a direct application and interest for the biopharmaceutical industry, always concerned in increasing productivity while decreasing economic costs. KEY POINTS: • Mammalian cells are widely used to produce recombinant proteins in short times. • Tuning DNA and transfecting agent are of great interest to optimize economic costs. • Reducing DNA and transfecting agent amounts result in higher protein yields.

Determining the Role of Surfactant on the Cytosolic Delivery of DNA Cross-Linked Micelles

Nucleic Acid Nanocapsules (NANs) are nucleic acid nanostructures that radially display oligonucleotides on the surface of cross-linked surfactant micelles. Their chemical makeup affords the stimuli-responsive release of therapeutically active DNA-surfactant conjugates into the cells. While NANs have so far demonstrated the effective cytosolic delivery of their nucleic acid cargo, as seen indirectly by their gene regulation capabilities, there remain gaps in the molecular understanding of how this process happens. Herein, we examine the enzymatic degradation of NANs and confirm the identity of the DNA-surfactant conjugates formed by using mass spectrometry (MS). With surface enhanced (resonance) Raman spectroscopy (SE(R)RS), we also provide evidence that the energy-independent translocation of such DNA-surfactant conjugates is contingent upon their release from the NAN structure, which, when intact, otherwise buries the hydrophobic surfactant tail in its interior. Such information suggests a critical role of the surfactant in the lipid disruption capability of the DNA surfactant conjugates generated from degradation of the NANs. Using NANs made with different tail lengths (C12 and C10), we show that this mechanism likely holds true despite significant differences in the physical properties (i.e., critical micelle concentration (CMC), surfactants per micelle, Nagg) of the resultant particles (C12 and C10 NANs). While the total cellular uptake efficiencies of C12 and C10 NANs are similar, there were differences observed in their cellular distribution and localized trafficking, even after ensuring that the total concentration of DNA was the same for both particles. Ultimately, C10 NANs appeared less diffuse within cells and colocalized less with lysosomes over time, achieving more significant knockdown of the target gene investigated, suggesting more effective endosomal escape. These differences indicate that the surfactant assembly and disassembly properties, including the number of surfactants per particle and the CMC can have important implications for the cellular delivery efficacy of DNA micelles and surfactant conjugates.

Endolysosomal trapping of therapeutics and endosomal escape strategies

Internalizing therapeutic molecules or genes into cells and safely delivering them to the target tissue where they can perform the intended tasks is one of the key characteristics of the smart gene/drug delivery vector. Despite much research in this field, endosomal escape continues to be a significant obstacle to the development of effective gene/drug delivery systems. In this review, we discuss in depth the several types of endocytic pathways involved in the endolysosomal trapping of therapeutic agents. In addition, we describe numerous mechanisms involved in nanoparticle endosomal escape. Furthermore, many other techniques are employed to increase endosomal escape to minimize entrapment of therapeutic compounds within endolysosomes, which have been reviewed at length in this study.

The intracellular visualization of exogenous DNA in fluorescence microscopy

In the development of non-viral gene delivery vectors, it is essential to reliably localize and quantify transfected DNA inside the cell. To track DNA, fluorescence microscopy methods are commonly applied. These mostly rely on fluorescently labeled DNA, DNA binding proteins fused to a fluorescent protein, or fluorescence in situ hybridization (FISH). In addition, co-stainings are often used to determine the colocalization of the DNA in specific cellular compartments, such as the endolysosomes or the nucleus. We provide an overview of these DNA tracking methods, advice on how they should be combined, and indicate which co-stainings or additional methods are required to draw precise conclusions from a DNA tracking experiment. Some emphasis is given to the localization of exogenous DNA inside the nucleus, which is the last step of DNA delivery. We argue that suitable tools which allow for the nuclear detection of faint signals are still missing, hampering the rational development of more efficient non-viral transfection systems.

Globoside Is an Essential Intracellular Factor Required for Parvovirus B19 Endosomal Escape

Human parvovirus B19 (B19V), like most parvoviruses, possesses phospholipase A2 (PLA2) activity, which is thought to mediate endosomal escape by membrane disruption. Here, we challenge this model and find evidence for a mechanism of B19V entry mediated by the glycosphingolipid globoside without endosome disruption and retrograde transport to the Golgi. We show that B19V PLA2 activity requires specific calcium levels and pH conditions that are not optimal in endosomes. Accordingly, endosomal membrane integrity was maintained during B19V entry. Furthermore, endosomes remained intact when loaded with MS2 bacteriophage particles pseudotyped with multiple B19V PLA2 subunits, providing superior enzymatic potential compared to native B19V. In globoside knockout cells, incoming viruses are arrested in the endosomal compartment and the infection is blocked. Infection can be rescued by promoting endosomal leakage with polyethyleneimine (PEI), demonstrating the essential role of globoside in facilitating endosomal escape. Incoming virus colocalizes with Golgi markers and interfering with Golgi function blocks infection, suggesting that globoside-mediated entry involves the Golgi compartment, which provides conditions favorable for the lipolytic PLA2. Our study challenges the current model of B19V entry and identifies globoside as an essential intracellular receptor required for endosomal escape.

Recent Progress in the Endosomal Escape Mechanism and Chemical Structures of Polycations for Nucleic Acid Delivery

Nucleic acid-based therapies are seeing a spiralling surge. Stimuli-responsive polymers, especially pH-responsive ones, are gaining widespread attention because of their ability to efficiently deliver nucleic acids. These polymers can be synthesized and modified according to target requirements, such as delivery sites and the nature of nucleic acids. In this regard, the endosomal escape mechanism of polymer-nucleic acid complexes (polyplexes) remains a topic of considerable interest owing to various plausible escape mechanisms. This review describes current progress in the endosomal escape mechanism of polyplexes and state-of-the-art chemical designs for pH-responsive polymers. The importance is also discussed of the acid dissociation constant (i.e., pKa) in designing the new generation of pH-responsive polymers, along with assays to monitor and quantify the endosomal escape behavior. Further, the use of machine learning is addressed in pKa prediction and polymer design to find novel chemical structures for pH responsiveness. This review will facilitate the design of new pH-responsive polymers for advanced and efficient nucleic acid delivery.

Effective delivery and selective insecticidal activity of double-stranded RNA via complexation with diblock copolymer varies with polymer block composition

BACKGROUND

Chemical insecticides are an important tool to control damaging pest infestations. However, lack of species specificity, the rise of resistance and the demand for biological alternatives with improved ecotoxicity profiles means that chemicals with new modes of action are required. RNA interference (RNAi)-based strategies using double-stranded RNA (dsRNA) as a species-specific bio-insecticide offer an exquisite solution that addresses these issues. Many species, such as the fruit pest Drosophila suzukii, do not exhibit RNAi when dsRNA is orally administered due to degradation by gut nucleases and slow cellular uptake pathways. Thus, delivery vehicles that protect and deliver dsRNA are highly desirable.

RESULTS

In this work, we demonstrate the complexation of D. suzukii-specific dsRNA for degradation of vha26 mRNA with bespoke diblock copolymers. We study the ex vivo protection of dsRNA against enzymatic degradation by gut enzymes, which demonstrates the efficiency of this system. Flow cytometry then investigates the cellular uptake of Cy3-labelled dsRNA, showing a 10-fold increase in the mean fluorescence intensity of cells treated with polyplexes. The polymer/dsRNA polyplexes induced a significant 87% decrease in the odds of survival of D. suzukii larvae following oral feeding only when formed with a diblock copolymer containing a long neutral block length (1:2 cationic block/neutral block). However, there was no toxicity when fed to the closely related Drosophila melanogaster.

CONCLUSION

We provide evidence that dsRNA complexation with diblock copolymers is a promising strategy for RNAi-based species-specific pest control, but optimisation of polymer composition is essential for RNAi success. © 2023 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Polyethylenimine (PEI) in gene therapy: Current status and clinical applications

Polyethlyenimine (PEI) was introduced 1995 as a cationic polymer for nucleic acid delivery. PEI and its derivatives are extensively used in basic research and as reference formulations in the field of polymer-based gene delivery. Despite its widespread use, the number of clinical applications to date is limited. Thus, this review aims to consolidate the past applications of PEI in DNA delivery, elucidate the obstacles that hinder its transition to clinical use, and highlight potential prospects for novel iterations of PEI derivatives. The present review article is divided into three sections. The first section examines the mechanism of action employed by PEI, examining fundamental aspects of cellular delivery including uptake mechanisms, release from endosomes, and transport into the cell nucleus, along with potential strategies for enhancing these delivery phases. Moreover, an in-depth analysis is conducted concerning the mechanism underlying cellular toxicity, accompanied with approaches to overcome this major challenge. The second part is devoted to the in vivo performance of PEI and its application in various therapeutic indications. While systemic administration has proven to be challenging, alternative localized delivery routes hold promise, such as treatment of solid tumors, application as a vaccine, or serving as a therapeutic agent for pulmonary delivery. In the last section, the outcome of completed and ongoing clinical trials is summarized. Finally, an expert opinion is provided on the potential of PEI and its future applications. PEI-based formulations for nucleic acid delivery have a promising potential, it will be an important task for the years to come to introduce innovations that address PEI-associated shortcomings by introducing well-designed PEI formulations in combination with an appropriate route of administration.

Characterization of polypropyleneimine as an alternative transfection reagent

Polypropyleneimine (PPI) was examined as a transfection reagent comparing with most widely used polymer, polyethyleneimine (PEI). PPI had better responsiveness to the endosomal pH and showed more condensation ability of plasmid DNA than PEI. Although the cytotoxicity of PPI was somewhat higher than PEI, the transfection efficacy of PPI was comparable with PEI or higher than PEI in some cell line. Thus, PPI would be an alternative transfection reagent.

Engineering poly- and micelleplexes for nucleic acid delivery - A reflection on their endosomal escape

For the longest time, the field of nucleic acid delivery has remained skeptical whether or not polycationic drug carrier systems would ever make it into clinical practice. Yet, with the disclosure of patents on polyethyleneimine-based RNA carriers through leading companies in the field of nucleic acid therapeutics such as BioNTech SE and the progress in clinical studies beyond phase I trials, this aloofness seems to regress. As one of the most striking characteristics of polymer-based vectors, the extraordinary tunability can be both a blessing and a curse. Yet, knowing about the adjustment screws and how they impact the performance of the drug carrier provides the formulation scientist committed to its development with a head start. Here, we equip the reader with a toolbox - a toolbox that should advise and support the developer to conceptualize a cutting-edge poly- or micelleplex system for the delivery of therapeutic nucleic acids; to be specific, to engineer the vector towards maximum endosomal escape performance at minimum toxicity. Therefore, after briefly sketching the boundary conditions of polymeric vector design, we will dive into the topic of endosomal trafficking. We will not only discuss the most recent knowledge of the endo-lysosomal compartment but further depict different hypotheses and mechanisms that facilitate the endosomal escape of polyplex systems. Finally, we will combine the different facets introduced in the previous chapters with the fundamental building blocks of polymer vector design and evaluate the advantages and drawbacks. Throughout the article, a particular focus will be placed on cellular peculiarities, not only as an additional barrier, but also to give inspiration to how such cell-specific traits might be capitalized on.

Liposome-mediated small RNA delivery to convert the macrophage polarity: A novel therapeutic approach to treat inflammatory uterine disease

Macrophages are present in all tissues for maintaining tissue homeostasis, and macrophage polarization plays a vital role in alleviating inflammation. Therefore, specific delivery of polarization modulators to macrophages in situ is critical for treating inflammatory diseases. We demonstrate that a size-controlled miRNA-encapsulated macrophage-targeting liposomes (miR/MT-Lip) specifically targets macrophages to promote M1-to-M2 polarization conversion, alleviating inflammation without cytotoxicity. miR/MT-Lip, approximately 1.2 μm, showed excellent internalization through phagocytosis and/or macropinocytosis in macrophages. miR-10a/MT-Lip, but not scramble miR-Fluorescein amidite (FAM)/MT-Lip as control, effectively converted the polarization of lipopolysaccharide (LPS)-induced M1 macrophages to M2 in vitro. When miR-10a/MT-Lip was intravenously delivered to mice insulted with LPS for inflammation, the proportion of M2 macrophages was significantly increased without disturbing the population of other immune cells. Furthermore, scramble miR-FAM/MT-Lip was mainly detected in macrophages, but not other immune cells. When our miR/MT-Lip was administered to mice with Asherman's syndrome that suffer from infertility because of sterile uterine inflammation, macrophage-specific targeting of miR-10a/MT-Lip facilitated M1-to-M2 conversion for angiogenesis in the impaired uterus, resulting in restoration of healthy uterine conditions. The results indicate that our MT-Lip encapsulating small RNAs has excellent potential to treat various inflammatory disorders by fine-tuning macrophage polarization in vivo without any side effects.

Microencapsulation of Lacticaseibacillus rhamnosus GG for Oral Delivery of Bovine Lactoferrin: Study of Encapsulation Stability, Cell Viability, and Drug Release

Probiotics are delivered orally for treating gastrointestinal tract (GIT) infections; thus, they should be protected from the harsh environment of the GIT, such as through microencapsulation. Here, we microencapsulated cells of the probiotic Lacticaseibacillus rhamnosus GG via the liquid-droplet-forming method and evaluated them for oral delivery of bovine lactoferrin (bLf). Briefly, sodium alginate capsules (G-capsules) were first prepared, crosslinked with calcium chloride (C-capsules), and then modified with disodium hydrogen phosphate (M-capsules). All capsules showed good swelling behavior in the order of G-capsules > C-capsules > M-capsules in simulated gastric fluid (SGF, pH 2) and simulated intestinal fluid (SIF, pH 7.2). FE-SEM observations showed the formation of porous surfaces and successful microencapsulation of L. rhamnosus GG cells. The microencapsulated probiotics showed 85% and 77% viability in SGF and SIF, respectively, after 300 min. Compared to the 65% and 70% viability of gelation-encapsulated and crosslinking-encapsulated L. rhamnosus GG cells, respectively, the mineralization-encapsulated cells showed up to 85% viability after 300 min in SIF. The entrapment of bLf in the mineralization-encapsulated L. rhamnosus GG cells did not show any toxicity to the cells. FTIR spectroscopy confirmed the successful surface modification of L. rhamnosus GG cells via gelation, crosslinking, and mineralization, along with the entrapment of bLf on the surface of microencapsulated cells. The findings of these studies show that the microencapsulated L. rhamnosus GG cells with natural polyelectrolytes could be used as stable carriers for the oral and sustainable delivery of beneficial biotherapeutics without compromising their viability and the activity of probiotics.

Tracking the Endosomal Escape: A Closer Look at Calcein and Related Reporters

Crossing the cellular membrane and delivering active pharmaceuticals or biologicals into the cytosol of cells is an essential step in the development of nanomedicines. One of the most important intracellular processes regarding the cellular uptake of biologicals is the endolysosomal pathway. Sophisticated nanocarriers have been developed overcoming a major hurdle, the endosomal entrapment, and delivering their cargo to the required site of action. In parallel, in vitro assays have been established analyzing the performance of these nanocarriers. Among them, the release of the membrane-impermeable dye calcein has become a popular and straightforward method. It is accessible for most researchers worldwide, allows for rapid conclusions about the release potential, and enables the study of release mechanisms. This review is intended to provide an overview and guidance for scientists applying the calcein release assay. It comprises a survey of several applications in the study of endosomal escape, considerations of potential pitfalls, challenges and limitations of the assay, and a brief summary of complementary methods. Based on this review, we hope to encourage further research groups to take advantage of the calcein release assay for their own purposes and help to create a database for more efficient cross-correlations between nanocarriers. This article is protected by copyright. All rights reserved.

Polyethylenimine-DNA Nanoparticles under Endosomal Acidification and Implication to Gene Delivery

Non-viral gene delivery using polyethylenimine (PEI) has shown tremendous promise as a therapeutic technique. Through the formation of nanoparticles (NPs), PEIs protect genetic material such as DNA from degradation. Escape of the NPs from endosomes and lysosomes is facilitated by PEI's buffering capacity over a wide range of pH. However, little is known about the effects of endosomal acidification on the morphology of the NPs. In this work, large-scale coarse-grained simulations performed to mimic endosomal acidification reveal that NPs undergo a resizing process that is highly dependent on the N/P ratio (ratio of PEI nitrogen to DNA phosphate) at which they are prepared. With a low N/P ratio, NPs further aggregate after endosomal acidification, whereas with a high N/P ratio they dissociate. The mechanisms behind such NP resizing and its consequences on endosomal escape and nuclear trafficking are discussed. Based on the findings, suggestions are made on the PEI architecture that may enhance NP dissociation driven by endosomal acidification.

Protection of Double-Stranded RNA via Complexation with Double Hydrophilic Block Copolymers: Influence of Neutral Block Length in Biologically Relevant Environments

Interaction between the anionic phosphodiester backbone of DNA/RNA and polycations can be exploited as a means of delivering genetic material for therapeutic and agrochemical applications. In this work, quaternized poly(2-(dimethylamino)ethyl methacrylate)-block-poly(N,N-dimethylacrylamide) (PQDMAEMA-b-PDMAm) double hydrophilic block copolymers (DHBCs) were synthesized via reversible addition-fragmentation chain-transfer (RAFT) polymerization as nonviral delivery vehicles for double-stranded RNA. The assembly of DHBCs and dsRNA forms distinct polyplexes that were thoroughly characterized to establish a relationship between the length of the uncharged poly(N,N-dimethylacrylamide) (PDMA) block and the polyplex size, complexation efficiency, and colloidal stability. Dynamic light scattering reveals the formation of smaller polyplexes with increasing PDMA lengths, while gel electrophoresis confirms that these polyplexes require higher N/P ratio for full complexation. DHBC polyplexes exhibit enhanced stability in low ionic strength environments in comparison to homopolymer-based polyplexes. In vitro enzymatic degradation assays demonstrate that both homopolymer and DHBC polymers efficiently protect dsRNA from degradation by RNase A enzyme.

Delivery Order of Nanoconstructs Affects Intracellular Trafficking by Endosomes

This paper reports how the endosomal pathways of nanoparticle (NP) constructs with different surface curvatures are affected by their order of delivery. Sequential incubation of cytosine-phosphate-guanine (CpG)-conjugated spiky and spherical gold NPs with macrophages resulted in different nanoconstruct ratios at the interior edges of endosomes. Application of spiky NPs after spherical NPs accelerated the formation of late-stage endosomes and resulted in larger endosomes, and the spherical NPs were enclosed by the spiky NPs. In contrast, the reverse incubation order produced an asymmetric distribution of the two nanoconstruct shapes in smaller endosomes. Macrophages with a higher proportion of the enclosed spherical NPs as well as a larger ratio of spiky to spherical NPs at the endosomal edge showed enhanced toll-like receptor 9 activation and secretion of proinflammatory cytokines and chemokines. Our results indicate that the subcellular trafficking of targeting nanoconstructs by vesicles is affected by both the delivery order and the endosomal distribution. Our study also establishes a new approach for nanoscale monitoring of intracellular therapeutics delivery with conventional electron microscopy.

Human macrophage polarization in the response to Mycobacterium leprae genomic DNA

Infection with Mycobacterium leprae, the causative organism of leprosy, is still endemic in numerous parts of the world including the southwestern United States. The broad variation of symptoms in the leprosy disease spectrum range from the milder tuberculoid leprosy (paucibacillary) to the more severe and disfiguring lepromatous leprosy (multibacillary). The established thinking in the health community is that host response, rather than M. leprae strain variation, is the reason for the range of disease severity. More recent discoveries suggest that macrophage polarization also plays a significant role in the spectrum of leprosy disease but to what degree it contributes is not fully established. In this study, we aimed to analyze if different strains of M. leprae elicit different transcription responses in human macrophages, and to examine the role of macrophage polarization in these responses. Genomic DNA from three different strains of M. leprae DNA (Strains NHDP, Br4923, and Thai-53) were used to stimulate human macrophages under three polarization conditions (M1, M1-activated, and M2). Transcriptome analysis revealed a large number of differentially expressed (DE) genes upon stimulation with DNA from M. leprae strain Thai-53 compared to strains NHDP and Br4923, independent of the macrophage polarization condition. We also found that macrophage polarization affects the responses to M. leprae DNA, with up-regulation of numerous interferon stimulated genes. These findings provide a deeper understanding of the role of macrophage polarization in the recognition of M. leprae DNA, with the potential to improve leprosy treatment strategies.

New insights on the mechanism of polyethylenimine transfection and their implications on gene therapy and DNA vaccines

Polyethylenimine (PEI) has been demonstrated as an efficient DNA delivery vehicle both in vitro and in vivo. There is a consensus that PEI-DNA complexes enter the cells by endocytosis and escape from endosomes by the so-called "proton sponge" effect. However, little is known on how and where the polyplexes are de-complexed for DNA transcription and replication to occur inside the cell nucleus. To better understand this issue, we (i) tracked the cell internalization of PEI upon transfection to human epithelial cells and (ii) studied the interaction of PEI with phospholipidic layers mimicking nuclear membranes. Both the biological and physicochemical experiments provided evidence of a strong binding affinity between PEI and the lipidic bilayer. Firstly, confocal microscopy revealed that PEI alone could not penetrate the cell nucleus; instead, it arranged throughout the cytoplasm and formed a sort of aureole surrounding the nuclei periphery. Secondly, surface tension measurements, fluorescence dye leakage assays, and differential scanning calorimetry demonstrated that a combination of hydrophobic and electrostatic interactions between PEI and the phospholipidic monolayers/bilayers led to the formation of stable defects along the model membranes, allowing the intercalation of PEI through the monolayer/bilayer structure. Results are also supported by molecular dynamics simulation of the pore formation in PEI-lipidic bilayers. As discussed throughout the text, these results might shed light on a the mechanism in which the interaction between PEI and the nucleus membrane might play an active role on the DNA release: on the one hand, the PEI-membrane interaction is anticipated to facilitate the DNA disassembly from the polyplex by establishing a competition with DNA for the PEI binding and on the other hand, the forming defects are expected to serve as channels for the entrance of de-complexed DNA into the cell nucleus. A better understanding of the mechanism of transfection of cationic polymers opens paths to development of more efficiency vectors to improve gene therapy treatment and the new generation of DNA vaccines.

Targeting the Inside of Cells with Biologicals: Chemicals as a Delivery Strategy

Delivering macromolecules into the cytosol or nucleus is possible in vitro for DNA, RNA and proteins, but translation for clinical use has been limited. Therapeutic delivery of macromolecules into cells requires overcoming substantially higher barriers compared to the use of small molecule drugs or proteins in the extracellular space. Breakthroughs like DNA delivery for approved gene therapies and RNA delivery for silencing of genes (patisiran, ONPATTRO^®, Alnylam Pharmaceuticals, Cambridge, MA, USA) or for vaccination such as the RNA-based coronavirus disease 2019 (COVID-19) vaccines demonstrated the feasibility of using macromolecules inside cells for therapy. Chemical carriers are part of the reason why these novel RNA-based therapeutics possess sufficient efficacy for their clinical application. A clear advantage of synthetic chemicals as carriers for macromolecule delivery is their favourable properties with respect to production and storage compared to more bioinspired vehicles like viral vectors or more complex drugs like cellular therapies. If biologicals can be applied to intracellular targets, the druggable space is substantially broadened by circumventing the limited utility of small molecules for blocking protein–protein interactions and the limitation of protein-based drugs to the extracellular space. An in depth understanding of the macromolecular cargo types, carrier types and the cell biology of delivery is crucial for optimal application and further development of biologicals inside cells. Basic mechanistic principles of the molecular and cell biological aspects of cytosolic/nuclear delivery of macromolecules, with particular consideration of protein delivery, are reviewed here. The efficiency of macromolecule delivery and applications in research and therapy are highlighted.

Liposomes with cyclodextrin channels and polyethyleneimine (PEI) improves cytoplasmic vaccine delivery and induces anti-cancer immune activity in mice

Cancer vaccines have been developed as an additional method of treatment in the fight against cancer. However, an important barrier to an effective vaccine is the inefficient presentation of exogenous antigen by dendritic cells to cytotoxic CD8 T cells. In this study, DPPC liposomes were modified with channels and loaded with polyethyleneimine (PEI) and 5,6-dimethylxanthenone-4-acetic acid (DMXAA) to produce a vaccine carrier. The liposomes were designed to be pH responsive to facilitate delivery of antigens directly to the cytoplasm of antigen presenting cells, bypassing the cross-presentation pathway and improving cellular immune responses. The lysis of liposomes in acidic cell-free conditions was measured using a validated dynamic light scattering assay in order to gain an insight into the mechanism of PEI-mediated lysis. Dendritic cell stimulation and T cell proliferation was investigated in vitro and the potential of this formulation to stimulate a therapeutic anti-cancer immune response was examined in a murine melanoma model. The modified formulation stimulated T cell activation in vitro and induced a small but significant increase in survival in immunized mice. Overall, liposomes modified with PEI and channels successfully delivered antigen to the cytoplasm of dendritic cells, which subsequently led to the development of an appropriate immune response.

Critical Evaluation of Different Lysosomal Labeling Methods Used to Analyze RNA Nanocarrier Trafficking in Cells

The use of nucleic acids to regulate gene expression is a rapidly developing field with immense clinical potential. Nanomaterials are frequently used to deliver nucleic acids into cells as they can overcome the poor cellular uptake and endo/lysosomal degradation of bare nucleic acids. For these nanocarriers to be effective, they must escape endo/lysosomal compartments to deliver their nucleic acid cargo into the cytosol (for ribonucleic acid (RNA)) or nucleus (for deoxyribonucleic acid (DNA)). This process is poorly understood and remains an area of active research toward the goal of developing effective delivery strategies. Fluorescent endo/lysosomal markers are among the most widely employed tools used to evaluate the endosomal escape of nucleic acid nanocarriers. However, the endo/lysosomal labeling method may alter the extent of and route of nanocarrier uptake by cells. The impact of these markers on cellular function and cell-nanocarrier interactions has not been probed in a systematic manner. To investigate this, we compared the effects of several common lysosomal labeling methods, namely, LysoTracker Red (LT Red), transient lysosomal-associated membrane protein 1-mutant green fluorescent protein (LAMP1-mGFP) transfection (Transient GFP), and stable lentiviral LAMP1-mGFP transfection (Stable GFP), on cellular metabolic activity, nanocarrier uptake, nanocarrier/lysosomal label colocalization, and gene silencing potency in U87 glioblastoma and MDA-MB-231 breast cancer cells using polyethyleneimine (PEI)/ribonucleic acid (RNA) polyplexes as a model nanocarrier. In both U87s and MDA-MB-231s, Transient GFP and LT Red labeling reduced metabolic activity relative to untransfected (Parental) cells, while Stable GFP labeling increased metabolic activity. Congruently, flow cytometry indicates Stable GFP cells have greater polyplex uptake than LT Red-labeled cells in both cell lines. Despite these similar trends in uptake, polyplex intracellular trafficking differs in the two cell lines, as confocal imaging revealed greater polyplex/lysosome colocalization in Stable GFP U87 cells than LT Red-labeled U87 cells, while the trend was reversed in MBA-MB-231s. The level of RNA-mediated gene silencing achieved in Parental versus Stable GFP U87 and MDA-MB-231 cells agreed with the observed levels of polyplex/lysosome colocalization, supporting the established concept that endosomal escape is the rate-limiting step for RNA interference. These findings indicate that lysosomal labels can profoundly alter cellular function and cell-nanocarrier interactions, presenting critical new considerations for researchers investigating nanoparticle trafficking.

Polycation-Mediated Transfection: Mechanisms of Internalization and Intracellular Trafficking

Polyplex-mediated gene transfection is now in its' fourth decade of serious research, but the promise of polyplex-mediated gene therapy has yet to fully materialize. Only approximately one in a million applied plasmids actually expresses. A large part of this is due to an incomplete understanding of the mechanism of polyplex transfection. There is an assumption that internalization must follow a canonical mechanism of receptor mediated endocytosis. Herein, we present arguments that untargeted (and most targeted) polyplexes do not utilize these routes. By incorporating knowledge of syndecan-polyplex interactions, we can show that syndecans are the "target" for polyplexes. Further, it is known that free polycations (which disrupt cell-membranes by acid-catalyzed hydrolysis of phospholipid esters) are necessary for (untargeted) endocytosis. This can be incorporated into the model to produce a novel mechanism of endocytosis, which fits the observed phenomenology. After membrane translocation, polyplex containing vesicles reach the endosome after diffusing through the actin mesh below the cell membrane. From there, they are acidified and trafficked toward the lysosome. Some polyplexes are capable of escaping the endosome and unpacking, while others are not. Herein, it is argued that for some polycations, as acidification proceeds the polyplexes excluding free polycations, which disrupt the endosomal membrane by acid-catalyzed hydrolysis, allowing the polyplex to escape. The polyplex's internal charge ratio is now insufficient for stability and it releases plasmids which diffuse to the nucleus. A small proportion of these plasmids diffuse through the nuclear pore complex (NPC), with aggregation being the major cause of loss. Those plasmids that have diffused through the NPC will also aggregate, and this appears to be the reason such a small proportion of nuclear plasmids express mRNA. Thus, the structural features which promote unpacking in the endosome and allow for endosomal escape can be determined, and better polycations can be designed.

A proton/macromolecule-sensing approach distinguishes changes in biological membrane permeability during polymer/lipid-based nucleic acid delivery

Endosomal escape is crucial for the delivery of nucleic acids. However, the understanding of the underlying mechanisms is still deficient. In this work, we explored the effects of lipid- and polymer-based transfection reagents on the permeability of cellular membranes through an innovative method combining a proton-sensing transistor and a cytosolic LDH leakage assay, which allows us to distinguish between modes of molecule permeation that may occur during endosomal escape. By testing the commercial reagents lipofectin and in vivo JetPEI under physiological and endosomal pH conditions, we found that both lipid- and polymer-based transfection reagents have pH-dependent pore-forming activity, with the former creating smaller pores than the latter. This versatile approach of assessing carrier-membrane interactions is expected to contribute to the development of next-generation nucleic acid delivery systems.

Novel enzymatic cross-linking-based hydrogel nanofilm caging system on pancreatic β cell spheroid for long-term blood glucose regulation

Pancreatic β cell therapy for type 1 diabetes is limited by low cell survival rate owing to physical stress and aggressive host immune response. In this study, we demonstrate a multilayer hydrogel nanofilm caging strategy capable of protecting cells from high shear stress and reducing immune response by interfering cell-cell interaction. Hydrogel nanofilm is fabricated by monophenol-modified glycol chitosan and hyaluronic acid that cross-link each other to form a nanothin hydrogel film on the cell surface via tyrosinase-mediated reactions. Furthermore, hydrogel nanofilm formation was conducted on mouse β cell spheroids for the islet transplantation application. The cytoprotective effect against physical stress and the immune protective effect were evaluated. Last, caged mouse β cell spheroids were transplanted into the type 1 diabetes mouse model and successfully regulated its blood glucose level. Overall, our enzymatic cross-linking-based hydrogel nanofilm caging method will provide a new platform for clinical applications of cell-based therapies.

Circumventing Drug Treatment? Intrinsic Lethal Effects of Polyethyleneimine (PEI)-Functionalized Nanoparticles on Glioblastoma Cells Cultured in Stem Cell Conditions

Simple Summary

Glioblastoma (GB) is the most frequent brain cancer that is highly difficult to treat. As with many cancer types, associated cancer stem cells can act as a reservoir of cancer-initiating cells, constituting a major hurdle for successful therapy. Herein, we report on a discovery of the intrinsic capability of polyethyleneimine-functionalized nanoparticles (PEI-NPs) to selectively eradicate glioblastoma stem cells (GSCs), contrary to current drug-based approaches to target and successfully eradicate GB. Already at negligible doses, PEI-NPs, without any anticancer therapeutic, very potently killed multiple GSC lines but not GB cells without stem cell characteristics. Moreover, PEI-NPs was observed in tumors in mice after both intravenous and intranasal administration, where the latter constitute a non-invasive administration route for drug delivery to the brain. These results, in turn, suggest that PEI-NPs can successfully cross the blood-brain barrier for the eradication of GSCs even without any anticancer drug, whereas the same NP platform can also be used for drug delivery thus opening up potential to reach synergistic therapeutic effects. This highly surprising intrinsic effect of the NP system on both the mechanistic action and specificity of GSC eradication puts forward a promising novel aspect of nanoparticles in medicine.

Abstract

Glioblastoma (GB) is the most frequent malignant tumor originating from the central nervous system. Despite breakthroughs in treatment modalities for other cancer types, GB remains largely irremediable due to the high degree of intratumoral heterogeneity, infiltrative growth, and intrinsic resistance towards multiple treatments. A sub-population of GB cells, glioblastoma stem cells (GSCs), act as a reservoir of cancer-initiating cells and consequently, constitute a significant challenge for successful therapy. In this study, we discovered that PEI surface-functionalized mesoporous silica nanoparticles (PEI-MSNs), without any anti-cancer drug, very potently kill multiple GSC lines cultured in stem cell conditions. Very importantly, PEI-MSNs did not affect the survival of established GB cells, nor other types of cancer cells cultured in serum-containing medium, even at 25 times higher doses. PEI-MSNs did not induce any signs of apoptosis or autophagy. Instead, as a potential explanation for their lethality under stem cell culture conditions, we demonstrate that the internalized PEI-MSNs accumulated inside lysosomes, subsequently causing a rupture of the lysosomal membranes. We also demonstrate blood–brain-barrier (BBB) permeability of the PEI-MSNs in vitro and in vivo. Taking together the recent indications for the vulnerability of GSCs for lysosomal targeting and the lethality of the PEI-MSNs on GSCs cultured under stem cell culture conditions, the results enforce in vivo testing of the therapeutic impact of PEI-functionalized nanoparticles in faithful preclinical GB models.

Shells of compacted DNA as nanocontainers transporting proteins in multiplexed delivery

Polyethyleneimine (PEI) polymers are known to compact DNA strands into spheroid, toroid, or rod structures. A formulation with mannose-grafted PEI (PEIm), however, was reported to compact DNA into ~100 nm spheroids that indented like thin-walled pressurized shells. The goal of the study is to understand why mannose bristles divert the traditional pathway of PEI-DNA compaction to produce shell-like structures, and to manipulate the process so that proteins can be packed into the core of the assembling shells for co-delivering DNA and proteins into cells. DLS, AFM, and TEM imaging provide a consistent picture that BSA proteins can be packed into the shells without altering the shell architecture, as long as the proteins were added during the time course of shell assembly. Force spectroscopy studies reveal that DNA shells that buckle also have a rich surface-coating of mannose, indicating that a micelle-like partitioning of hydrophobic and hydrophilic layers governs shell assembly. When HEK293T cells are spiked with BSA-laden DNA shells, co-transfection of DNA and BSA is observed at higher levels than control formulations. Distinct micron-sized features appear having both green fluorescence from BSA-FITC and blue fluorescence from NucBlue DNA stain, suggesting BSA release in nucleus and secretory granules. With DNA nanocontainers, proteins can take advantage of the efficiency of PEI-based DNA transfection for hitchhiking into cells while being shielded from the challenges of the intracellular route. DNA nanocontainers are rapid to assemble, not dependent on the DNA sequence, and can be adapted for different protein types; thereby having potential to serve as a high-throughput platform in scenarios where DNA and protein have to be released at the same site and time within cells (e.g., theranostics, multiplexed co-delivery, gene editing).

Cellular pathways of recombinant adeno-associated virus production for gene therapy

Recombinant adeno-associated viruses (rAAVs) are among the most important vectors for in vivo gene therapies. With the rapid development of gene therapy, current rAAV manufacturing capacity faces a challenge to meet the emerging demand for these therapies in the future. To examine the bottlenecks in rAAV production during cell culture, we focus here on an analysis of cellular pathways of rAAV production, based on an overview of assembly mechanisms first in the wild-type (wt) AAV replication and then in the common methods of rAAV production. The differences analyzed between the wild-type and recombinant systems provide insights into the mechanistic differences that may correlate with viral productivity. Based on these analyses, we identify potential barriers to high productivity of rAAV and discuss future directions for improvement to meet the emerging needs set by the growth of rAAV-based therapy and the needs of patients.

Polymeric Delivery of Therapeutic Nucleic Acids

The advent of genome editing has transformed the therapeutic landscape for several debilitating diseases, and the clinical outlook for gene therapeutics has never been more promising. The therapeutic potential of nucleic acids has been limited by a reliance on engineered viral vectors for delivery. Chemically defined polymers can remediate technological, regulatory, and clinical challenges associated with viral modes of gene delivery. Because of their scalability, versatility, and exquisite tunability, polymers are ideal biomaterial platforms for delivering nucleic acid payloads efficiently while minimizing immune response and cellular toxicity. While polymeric gene delivery has progressed significantly in the past four decades, clinical translation of polymeric vehicles faces several formidable challenges. The aim of our Account is to illustrate diverse concepts in designing polymeric vectors towards meeting therapeutic goals of in vivo and ex vivo gene therapy. Here, we highlight several classes of polymers employed in gene delivery and summarize the recent work on understanding the contributions of chemical and architectural design parameters. We touch upon characterization methods used to visualize and understand events transpiring at the interfaces between polymer, nucleic acids, and the physiological environment. We conclude that interdisciplinary approaches and methodologies motivated by fundamental questions are key to designing high-performing polymeric vehicles for gene therapy.

In vitro vascularization of tissue engineered constructs by non-viral delivery of pro-angiogenic genes

Vascularization is still one of the major challenges in tissue engineering. In the context of tissue regeneration, the formation of capillary-like structures is often triggered by the addition of growth factors which are associated with high cost, bolus release and short half-life. As an alternative to growth factors, we hypothesized that delivering genes-encoding angiogenic growth factors to cells in a scaffold microenvironment would lead to a controlled release of angiogenic proteins promoting vascularization, simultaneously offering structural support for new matrix deposition. Two non-viral vectors, chitosan (Ch) and polyethyleneimine (PEI), were tested to deliver plasmids encoding for vascular endothelial growth factor (pVEGF) and fibroblast growth factor-2 (pFGF2) to human dermal fibroblasts (hDFbs). hDFbs were successfully transfected with both Ch and PEI, without compromising the metabolic activity. Despite low transfection efficiency, superior VEGF and FGF-2 transgene expression was attained when pVEGF was delivered with PEI and when pFGF2 was delivered with Ch, impacting the formation of capillary-like structures by primary human dermal microvascular endothelial cells (hDMECs). Moreover, in a 3D microenvironment, when PEI-pVEGF and Ch-FGF2 were delivered to hDFbs, cells produced functional pro-angiogenic proteins which induced faster formation of capillary-like structures that were retained in vitro for longer time in a Matrigel assay. The dual combination of the plasmids resulted in a downregulation of the production of VEGF and an upregulation of FGF-2. The number of capillary-like segments obtained with this system was inferior to the delivery of plasmids individually but superior to what was observed with the non-transfected cells. This work confirmed that cell-laden scaffolds containing transfected cells offer a novel, selective and alternative approach to impact the vascularization during tissue regeneration. Moreover, this work provides a new platform for pathophysiology studies, models of disease, culture systems and drug screening.

Inorganic Nanomaterial-Mediated Gene Therapy in Combination with Other Antitumor Treatment Modalities

Cancer is a genetic disease originating from the accumulation of gene mutations in a cellular subpopulation. Although many therapeutic approaches have been developed to treat cancer, recent studies have revealed an irrefutable challenge that tumors evolve defenses against some therapies. Gene therapy may prove to be the ultimate panacea for cancer by correcting the fundamental genetic errors in tumors. The engineering of nanoscale inorganic carriers of cancer therapeutics has shown promising results in the efficacious and safe delivery of nucleic acids to treat oncological diseases in small-animal models. When these nanocarriers are used for co-delivery of gene therapeutics along with auxiliary treatments, the synergistic combination of therapies often leads to an amplified health benefit. In this review, an overview of the inorganic nanomaterials developed for combinatorial therapies of gene and other treatment modalities is presented. First, the main principles of using nucleic acids as therapeutics, inorganic nanocarriers for medical applications and delivery of gene/drug payloads are introduced. Next, the utility of recently developed inorganic nanomaterials in different combinations of gene therapy with each of chemo, immune, hyperthermal, and radio therapy is examined. Finally, current challenges in the clinical translation of inorganic nanomaterial-mediated therapies are presented and outlooks for the field are provided.

Highly Osmotic Oxidized Sucrose-Crosslinked Polyethylenimine for Gene Delivery Systems

In this work, highly osmotic oxidized sucrose-crosslinked polyethylenimine (SP2K) polymers were developed for gene delivery systems, and the transfection mechanism is examined. First, periodate-oxidized sucrose and polyethylenimine 2K (PEI2K) were crosslinked with various feed ratios via reductive amination. The synthesis was confirmed by ¹H NMR and FTIR. The synthesized SP2K polymers could form positively charged (~40 mV zeta-potential) and nano-sized (150–200 nm) spherical polyplexes with plasmid DNA (pDNA). They showed lower cytotoxicity than PEI25K but concentration-dependent cytotoxicity. Among them, SP2K7 and SP2K10 showed higher transfection efficiency than PEI25K in both serum and serum-free conditions, revealing the good serum stability. It was found that SP2K polymers possessed high osmolality and endosome buffering capacity. The transfection experiments with cellular uptake inhibitors suggest that the transfection of SP2K polymers would progress by multiple pathways, including caveolae-mediated endocytosis. It was also thought that caveolae-mediated endocytosis of SP2K polyplexes would be facilitated through cyclooxygenase-2 (COX-2) expression induced by high osmotic pressure of SP2K polymers. Confocal microscopy results also supported that SP2K polyplexes would be internalized into cells via multiple pathways and escape endosomes efficiently via high osmolality and endosome buffering capacity. These results demonstrate the potential of SP2K polymers for gene delivery systems.

Magnetic nanocomplexes for gene delivery applications

Gene delivery is an indispensable technique for various biomedical applications such as gene therapy, stem cell engineering and gene editing. Recently, magnetic nanoparticles (MNPs) have received increasing attention for their use in promoting gene delivery efficiency. Under magnetic attraction, gene delivery efficiency using viral or nonviral gene carriers could be universally enhanced. Besides, magnetic nanoparticles could be utilized in magnetic resonance imaging or magnetic hyperthermia therapy, providing extra theranostic opportunities. In this review, recent research integrating MNPs with a viral or nonviral gene vector is summarized from both technical and application perspectives. Applications of MNPs in cutting-edge research technologies, such as biomimetic cell membrane nano-gene carriers, exosome-based gene delivery, cell-based drug delivery systems or CRISPR/Cas9 gene editing, are also discussed.

Lysosomal Proton Buffering of Poly(ethylenimine) Measured In Situ by Fluorescent pH-Sensor Microcapsules

Poly(ethylenimine) (PEI) is frequently used as transfection agent for delivery of nucleic acids to the cytosol. After endocytosis of complexes of PEI and nucleic acids, a fraction of them can escape endosomes/lysosomes and reach the cytosol. One proposed mechanism is the so-called proton sponge effect, which involves buffering of the lysosomal pH by PEI. There are however also reports that report the absence of such buffering. In this work, the buffering capacity of PEI of the lysosomal pH was investigated in situ by combining PEI and pH-sensing ratiometric fluorophores in a single carrier particle. As carrier particles, hereby capsules were used, which were composed of polyelectrolyte walls based on layer-by-layer assembly, with the pH sensors located inside the capsule cavities. In this way, the local pH around individual particles could be monitored during the whole process of endocytosis. Results demonstrate the pH-buffering capability of PEI, which prevents the strong acidification of lysosomes containing PEI. This effect was related to the presence of PEI and was not related to the overall charge of the carrier particles. In case PEI was added in molecular form, no buffering of pH could be observed by endocytosed encapsulated pH-sensing ratiometric fluorophores. Co-localization experiments demonstrated that this was due to the fact that internalized free PEI and the encapsulated pH-sensing ratiometric fluorophores were not located in the same lysosomes. Missing co-localization might explain why also in other studies no pH buffering was found; in the case of co-delivery of PEI, the pH sensors could be clearly observed.

Nanoparticle Delivery Systems for DNA/RNA and their Potential Applications in Nanomedicine

The rapid development of nanotechnology has a great influence on the fields of biology, physiology, and medicine. Over recent years, nanoparticles have been widely presented as nanocarriers to help the delivery of gene, drugs, and other therapeutic agents with cellular targeting ability. Advances in the understanding of gene delivery and RNA interference (RNAi)-based therapy have brought increasing attention to understanding and tackling complex genetically related diseases, such as cancer, cardiovascular and pulmonary diseases, autoimmune diseases and infections. The combination of nanocarriers and DNA/RNA delivery may potentially improve their safety and therapeutic efficacy. However, there still exist many challenges before this approach can be practiced in the clinic. In this review, we provide a comprehensive summary on the types of nanoparticle systems used as nanocarriers, highlight the current use of nanocarriers in recombinant DNA and RNAi molecules delivery, and the current landscape of gene-based nanomedicine-ranging from diagnosis to therapeutics. Finally, we briefly discuss the biosafety concerns and limitations in the preclinical and clinical development of nanoparticle gene systems.

Rekindling RNAi Therapy: Materials Design Requirements for In Vivo siRNA Delivery

With the recent FDA approval of the first siRNA-derived therapeutic, RNA interference (RNAi)-mediated gene therapy is undergoing a transition from research to the clinical space. The primary obstacle to realization of RNAi therapy has been the delivery of oligonucleotide payloads. Therefore, the main aims is to identify and describe key design features needed for nanoscale vehicles to achieve effective delivery of siRNA-mediated gene silencing agents in vivo. The problem is broken into three elements: 1) protection of siRNA from degradation and clearance; 2) selective homing to target cell types; and 3) cytoplasmic release of the siRNA payload by escaping or bypassing endocytic uptake. The in vitro and in vivo gene silencing efficiency values that have been reported in publications over the past decade are quantitatively summarized by material type (lipid, polymer, metal, mesoporous silica, and porous silicon), and the overall trends in research publication and in clinical translation are discussed to reflect on the direction of the RNAi therapeutics field.

Improving Magnetofection of Magnetic Polyethylenimine Nanoparticles into MG-63 Osteoblasts Using a Novel Uniform Magnetic Field

This study aimed to improve the magnetofection of MG-63 osteoblasts by integrating the use of a novel uniform magnetic field with low molecular weight polyethylenimine modified superparamagnetic iron oxide nanoparticles (PEI-SPIO-NPs). The excellent characteristics of PEI-SPIO-NPs such as size, zeta potential, the pDNA binding and protective ability were determined to be suitable for gene delivery. The novel uniform magnetic field enabled polyethylenimine-modified superparamagnetic iron oxide nanoparticles/pDNA complexes (PEI-SPIO-NPs/pDNA complexes) to rapidly and uniformly distribute on the surface of MG-63 cells, averting local transfection and decreasing disruption of the membrane caused by the centralization of positively charged PEI-SPIO-NPs, thereby increasing the effective coverage of magnetic gene carriers during transfection, and improving magnetofection efficiency. This innovative uniform magnetic field can be used to determine the optimal amount between PEI-SPIO-NPs and pDNA, as well as screen for the optimal formulation design of magnetic gene carrier under the homogenous conditions. Most importantly, the novel uniform magnetic field facilitates the transfection of PEI-SPIO-NPs/pDNA into osteoblasts, thereby providing a novel approach for the targeted delivery of therapeutic genes to osteosarcoma tissues as well as a reference for the treatment of other tumors.

Single-domain antibody fusion proteins can target and shuttle functional proteins into macrophage mannose receptor expressing macrophages

The tumor microenvironment of numerous prevalent cancer types is abundantly infiltrated with tumor-associated macrophages (TAMs). Macrophage mannose receptor (MMR or CD206) expressing TAMs have been shown to be key promoters of tumor progression and major opponents of successful cancer therapy. Therefore, depleting MMR⁺ TAMs is an interesting approach to synergize with current antitumor therapies. We studied the potential of single-domain antibodies (sdAbs) specific for MMR to target proteins to MMR⁺ TAMs. Anti-MMR sdAbs were genetically coupled to a reporter protein, mWasabi (wasabi green, WG), generating sdAb "drug" fusion proteins (SFPs), referred to as WG-SFPs. The resulting WG-SFPs were highly efficient in targeting MMR⁺ macrophages both in vitro and in vivo. As we showed that second mitochondria-derived activator of caspase (SMAC) mimetics modulate MMR⁺ macrophages, we further coupled the anti-MMR sdAb to an active form of SMAC, referred to as tSMAC. The resulting tSMAC-SFPs were able to bind and upregulate caspase3/7 activity in MMR⁺ macrophages in vitro. In conclusion, we report the proof-of-concept of an elegant approach to conjugate anti-MMR sdAbs to proteins, which opens new avenues for targeted manipulation of MMR⁺ tumor-promoting TAMs.

Tri-mannose grafting of chitosan nanocarriers remodels the macrophage response to bacterial infection

Background

Infectious diseases are still a leading cause of death and, with the emergence of drug resistance, pose a great threat to human health. New drugs and strategies are thus urgently needed to improve treatment efficacy and limit drug-associated side effects. Nanotechnology-based drug delivery systems are promising approaches, offering hope in the fight against drug resistant bacteria. However, how nanocarriers influence the response of innate immune cells to bacterial infection is mostly unknown.

Results

Here, we used Mycobacterium tuberculosis as a model of bacterial infection to examine the impact of mannose functionalization of chitosan nanocarriers (CS-NCs) on the human macrophage response. Both ungrafted and grafted CS-NCs were similarly internalized by macrophages, via an actin cytoskeleton-dependent process. Although tri-mannose ligands did not modify the capacity of CS-NCs to escape lysosomal degradation, they profoundly remodeled the response of M. tuberculosis-infected macrophages. mRNA sequencing showed nearly 900 genes to be differentially expressed due to tri-mannose grafting. Unexpectedly, the set of modulated genes was enriched for pathways involved in cell metabolism, particularly oxidative phosphorylation and sugar metabolism.

Conclusions

The ability to modulate cell metabolism by grafting ligands at the surface of nanoparticles may thus be a promising strategy to reprogram immune cells and improve the efficacy of encapsulated drugs.

Electronic supplementary material

The online version of this article (10.1186/s12951-018-0439-x) contains supplementary material, which is available to authorized users.

Controlling endosomal escape using nanoparticle composition: current progress and future perspectives

Polymer nanoparticles offer significant benefits for improving delivery of biological therapeutics such as DNA and proteins, as they allow the cargo to be protected until it is delivered to a target cell. However, there are still challenges with achieving efficient delivery to the optimal cellular region. One significant roadblock is escape of nanoparticles from within the endosomal/lysosomal compartments into the cytosol. Here, we review the recent advances in understanding endosomal escape of polymer nanoparticles. We also discuss the current progress on investigating how nanoparticle structure can control endosomal escape. It is important to understand the fundamental biological processes that govern endosomal escape in order to design more effective therapeutic delivery systems.

Membrane reorganization after photochemical internalization to release transferrin-biofunctionalized polystyrene microparticles

Therapeutic drug carriers can drive their cargo to their target cells. However, an obstacle is usually the entrapment of the drug inside the endolysosomal compartment, which physically impedes its actuation by the impossibility of reaching its molecular site of action. To overcome this hurdle, photochemical internalization (PCI) has been proposed, but the extent of PCI-induced membrane disruption and its capability to allow the release of microparticles is unknown. The aim of the present study was to determine if PCI allows the release of microparticles from the endolysosomal compartment to the cytosol and to analyze at the ultrastructural level the effect of PCI on the membrane surrounding the particles. Confocal microscope allowed us to detect that endolysosomal membranes suffered some disruption after PCI, evidenced by the diffusion of soluble transferrin from the endolysosomes to the cytosol and by a decrease of LAMP1-microparticles co-localization. Transmission electron microscopy (TEM) showed a decrease in the number of well-defined membranes around microparticles after PCI, and scanning TEM combined with energy dispersive x-ray revealed an increase in the width of endolysosomal membranes after treatment. These results suggest that endolysosomal membranes suffered an ultrastructure alteration after PCI, enough to liberate soluble transferrin but not the entire microparticles.

Comparison between electroporation and polyfection in pig sperm: efficiency and cell viability implications

The aim of this study was to optimize protocols for electroporation (EP) and polyfection (PLF) using polyethyleneimine (PEI) for pig sperm transfection and to determine which method was the most efficient. For EP standardization, different voltages, amounts and times of electric pulses were tested using propidium iodide (PI) as reporter. For PLF standardization, different concentrations of fluorescein isothiocyanate (FITC)-labelled PEI (PEI/FITC) were incubated with sperm for different periods of time. Flow cytometry was performed to evaluate the best protocol in terms of cell viability, including cytoplasmic membrane, acrosome, chromatin integrities and mitochondrial potential using the FITC probe, PI, acridine orange (AO) and JC1. Transfections with the plasmid pmhyGENIE-5 were carried out under optimum conditions for each procedure (EP: 500 volts, 500 μs and two pulses; PLF: PEI 0.5 mg/ml and incubation time 10 min). Transfection efficacy was assessed by fluorescence in situ hybridization (FISH). A lower transfection rate was observed for sperm in the control group (17.8%) compared with EP (36.7%), with PLF (76.8%) being the most efficient. These results suggest that the EP and PEI could be an efficient and low cost transfection method for swine sperm. Notably, treated cells showed higher plasmatic the membrane damage (PMD) and/or acrosome damage (AD) indexes, therefore the combination of this procedure with biotechniques that facilitate fecundation (i.e. in vitro fertilization or intracytoplasmic sperm injection) or even inclusion of antioxidant or anti-apoptotic drugs to improve spermatozoa viability would be important.

Enhanced endosomal escape by photothermal activation for improved small interfering RNA delivery and antitumor effect

BACKGROUND

Effective endosomal escape is still a critical bottleneck for intracellular delivery of small interfering RNAs (siRNAs) to maximize their therapeutic efficacy. To overcome this obstacle, we have developed a photothermally triggered system by using the near-infrared (NIR) irradiation to achieve "on-demand" endosomal escape and subsequent siRNA release into cytoplasm.

MATERIALS AND METHODS

Herein, the poly-L-lysine (PLL) was successfully conjugated with melanin to obtain melanin-poly-L-lysine (M-PLL) polymer as a siRNA vehicle. The melanin was an efficient photothermal sensitizer, and the positive pendant amino groups of PLL could condense siRNAs to form stable complexes by electrostatic interactions.

RESULTS AND DISCUSSION

Inspired by its excellent photothermal conversion efficiency, the melanin was first involved in the siRNA delivery system. Confocal laser scanning microscopic observation revealed that after cellular uptake the photothermally induced endosomal escape could facilitate siRNAs to overcome endosomal barrier and be delivered into cytoplasm, which resulted in significant silence in the luciferase expression over the NIR- and melanin-free controls. Moreover, the anti-survivin siRNA-loaded M-PLL nanoparticles displayed great inhibitory effect on 4T1 tumor growth in vitro and in vivo.

CONCLUSION

These findings suggest that the M-PLL-mediated siRNA delivery is a promising candidate for therapeutic siRNA delivery and shows improved effect for cancer therapy via enhanced endosomal escape.

Fluorescence Correlation Spectroscopy to find the critical balance between extracellular association and intracellular dissociation of mRNA complexes

Fluorescence Correlation Spectroscopy (FCS) is a promising tool to study interactions on a single molecule level. The diffusion of fluorescent molecules in and out of the excitation volume of a confocal microscope leads to the fluorescence fluctuations that give information on the average number of fluorescent molecules present in the excitation volume and their diffusion coefficients. In this context, we complexed mRNA into lipoplexes and polyplexes and explored the association/dissociation degree of complexes by using gel electrophoresis and FCS. FCS enabled us to measure the association and dissociation degree of mRNA-based complexes both in buffer and protein-rich biological fluids such as human serum and ascitic fluid, which is a clear advantage over gel electrophoresis that was only applicable in protein-free buffer solutions. Furthermore, following the complex stability in buffer and biological fluids by FCS assisted to understand how complex characteristics, such as charge ratio and strength of mRNA binding, correlated to the transfection efficiency. We found that linear polyethyleneimine prevented efficient translation of mRNA, most likely due to a too strong mRNA binding, whereas the lipid based carrier Lipofectamine® messengerMAX did succeed in efficient release and subsequent translation of mRNA in the cytoplasm of the cells. Overall, FCS is a reliable tool for the in depth characterization of mRNA complexes and can help us to find the critical balance keeping mRNA bound in complexes in the extracellular environment and efficient intracellular mRNA release leading to protein production.

STATEMENT OF SIGNIFICANCE

The delivery of messenger RNA (mRNA) to cells is promising to treat a variety of diseases. Therefore, the mRNA is typically packed in small lipid particles or polymer particles that help the mRNA to reach the cytoplasm of the cells. These particles should bind and carry the mRNA in the extracellular environment (e.g. blood, peritoneal fluid, …), but should release the mRNA again in the intracellular environment. In this paper, we evaluated a method (Fluorescence Correlation Spectroscopy) that allows for the in depth characterization of mRNA complexes and can help us to find the critical balance keeping mRNA bound in complexes in the extracellular environment and efficient intracellular mRNA release leading to protein production.

Block Copolymer Micelles in Nanomedicine Applications

Polymeric micelles are demonstrating high potential as nanomedicines capable of controlling the distribution and function of loaded bioactive agents in the body, effectively overcoming biological barriers, and various formulations are engaged in intensive preclinical and clinical testing. This Review focuses on polymeric micelles assembled through multimolecular interactions between block copolymers and the loaded drugs, proteins, or nucleic acids as translationable nanomedicines. The aspects involved in the design of successful micellar carriers are described in detail on the basis of the type of polymer/payload interaction, as well as the interplay of micelles with the biological interface, emphasizing on the chemistry and engineering of the block copolymers. By shaping these features, polymeric micelles have been propitious for delivering a wide range of therapeutics through effective sensing of targets in the body and adjustment of their properties in response to particular stimuli, modulating the activity of the loaded drugs at the targeted sites, even at the subcellular level. Finally, the future perspectives and imminent challenges for polymeric micelles as nanomedicines are discussed, anticipating to spur further innovations.

Beyond Gene Transfection with Methacrylate-Based Polyplexes-The Influence of the Amino Substitution Pattern

Methacrylate-based polymers represent promising nonviral gene delivery vectors, since they offer a large variety of polymer architectures and functionalities, which are beneficial for specific demands in gene delivery. In combination with controlled radical polymerization techniques, such as the reversible addition-fragmentation chain transfer polymerization, the synthesis of well-defined polymers is possible. In this study we prepared a library of defined linear polymers based on (2-aminoethyl)-methacrylate (AEMA), N-methyl-(2-aminoethyl)-methacrylate (MAEMA), and N,N-dimethyl-(2-aminoethyl)-methacrylate (DMAEMA) monomers, bearing pendant primary, secondary, and tertiary amino groups, and investigated the influence of the substitution pattern on their gene delivery capability. The polymers and the corresponding plasmid DNA complexes were investigated regarding their physicochemical characteristics, cytocompatibility, and transfection performance. The nonviral transfection by methacrylate-based polyplexes differs significantly from poly(ethylene imine)-based polyplexes, as a successful transfection is not affected by the buffer capacity. We observed that polyplexes containing a high content of primary amino groups (AEMA) offered the highest transfection efficiency, whereas polyplexes bearing tertiary amino groups (DMAEMA) exhibited the lowest transfection efficiency. Further insights into the uptake and release mechanisms could be identified by fluorescence and transmission electron microscopy, emphasizing the theory of membrane-pore formation for the time-efficient endosomal release of methacrylate-based vectors.

Bioinspired Star-Shaped Poly(l-lysine) Polypeptides: Efficient Polymeric Nanocarriers for the Delivery of DNA to Mesenchymal Stem Cells

The field of tissue engineering is increasingly recognizing that gene therapy can be employed for modulating in vivo cellular response thereby guiding tissue regeneration. However, the field lacks a versatile and biocompatible gene delivery platform capable of efficiently delivering transgenes to mesenchymal stem cells (MSCs), a cell type often refractory to transfection. Herein, we describe the extensive and systematic exploration of three architectural variations of star-shaped poly(l-lysine) polypeptide (star-PLL) with varying number and length of poly(l-lysine) arms as potential nonviral gene delivery vectors for MSCs. We demonstrate that star-PLL vectors are capable of self-assembling with pDNA to form stable, cationic nanomedicines. Utilizing high content screening, live cell imaging, and mechanistic uptake studies we confirm the intracellular delivery of pDNA by star-PLLs to MSCs is a rapid process, which likely proceeds via a clathrin-independent mechanism. We identify a star-PLL composition with 64 poly(l-lysine) arms and five l-lysine subunits per arm as a particularly efficient vector that is capable of delivering both reporter genes and the therapeutic transgenes bone morphogenetic protein-2 and vascular endothelial growth factor to MSCs. This composition facilitated a 1000-fold increase in transgene expression in MSCs compared to its linear analogue, linear poly(l-lysine). Furthermore, it demonstrated comparable transgene expression to the widely used vector polyethylenimine using a lower pDNA dose with significantly less cytotoxicity. Overall, this study illustrates the ability of the star-PLL vectors to facilitate efficient, nontoxic nucleic acid delivery to MSCs thereby functioning as an innovative nanomedicine platform for tissue engineering applications.