Intracellular Trafficking Pathways for Nuclear Delivery of Plasmid DNA Complexed with Highly Efficient Endosome Escape Polymers

In situ transient transfection of 3D cell cultures and tissues, a promising tool for tissue engineering and gene therapy

Various research fields use the transfection of mammalian cells with genetic material to induce the expression of a target transgene or gene silencing. It is a tool widely used in biological research, bioproduction, and therapy. Current transfection protocols are usually performed on 2D adherent cells or suspension cultures. The important rise of new gene therapies and regenerative medicine in the last decade raises the need for new tools to empower the in situ transfection of tissues and 3D cell cultures. This review will present novel in situ transfection methods based on a chemical or physical non-viral transfection of cells in tissues and 3D cultures, discuss the advantages and remaining gaps, and propose future developments and applications.

Mediation of synergistic chemotherapy and gene therapy via nanoparticles based on chitosan and ionic polysaccharides

Nanoparticles (NPs)-based on various ionic polysaccharides, including chitosan, hyaluronic acid, and alginate have been frequently summarized for controlled release applications, however, most of the published reviews, to our knowledge, focused on the delivery of a single therapeutic agent. A comprehensive summarization of the co-delivery of multiple therapeutic agents by the ionic polysaccharides-based NPs, especially on the optimization of the polysaccharide structure for overcoming various extracellular and intracellular barriers toward maximized synergistic effects, to our knowledge, has been rarely explored so far. For this purpose, the strategies used for overcoming various extracellular and intracellular barriers in vivo were introduced first to provide guidance for the rational design of ionic polysaccharides-based NPs with desired features, including long-term circulation, enhanced cellular internalization, controllable drug/gene release, endosomal escape and improved nucleus localization. Next, four preparation strategies were summarized including three physical methods of polyelectrolyte complexation, ionic crosslinking, and self-assembly and a chemical conjugation approach. The challenges and future trends of this rapidly developing field were finally discussed in the concluding remarks. The important guidelines on the rational design of ionic polysaccharides-based NPs for maximized synergistic efficiency drawn in this review will promote the future generation and clinical translation of polysaccharides-based NPs for cancer therapy.

Viral Mimicry as a Design Template for Nucleic Acid Nanocarriers

Therapeutic nucleic acids hold immense potential in combating undruggable, gene-based diseases owing to their high programmability and relative ease of synthesis. While the delivery of this class of therapeutics has successfully entered the clinical setting, extrahepatic targeting, endosomal escape efficiency, and subcellular localization. On the other hand, viruses serve as natural carriers of nucleic acids and have acquired a plethora of structures and mechanisms that confer remarkable transfection efficiency. Thus, understanding the structure and mechanism of viruses can guide the design of synthetic nucleic acid vectors. This review revisits relevant structural and mechanistic features of viruses as design considerations for efficient nucleic acid delivery systems. This article explores how viral ligand display and a metastable structure are central to the molecular mechanisms of attachment, entry, and viral genome release. For comparison, accounted for are details on the design and intracellular fate of existing nucleic acid carriers and nanostructures that share similar and essential features to viruses. The review, thus, highlights unifying themes of viruses and nucleic acid delivery systems such as genome protection, target specificity, and controlled release. Sophisticated viral mechanisms that are yet to be exploited in oligonucleotide delivery are also identified as they could further the development of next-generation nonviral nucleic acid vectors.

A novel progress of drug delivery system for organelle targeting in tumour cells

At present, malignant tumours have become one of the most serious diseases that endanger human health. According to a survey on causes of death in Chinese population in early 1990s, the malignant tumours were the second leading cause of death. In the treatment of tumours, the ideal situation is that drugs should target and accumulate at tumour sites and destroy tumour cells specifically, without affecting normal cells and stem cells with regenerative capacity. This requires drugs to be specifically transported to the target organs, tissues, cells, and even specific organelles, like mitochondria, nuclei, lysosomes, endoplasmic reticulum (ER), and Golgi apparatus (GA). The nano drug delivery system can not only protect drugs from degradation but also facilitate functional modification and targeted drug delivery to the tumour site. This article mainly reviews the targeting of nano drug delivery systems to tumour cytoplasmic matrix, nucleus, mitochondria, ER, and lysosomes. Organelle-specific drug delivery system will be a major mean of targeting drug delivery with lower toxicity, less dosage and higher drug concentration in tumour cells.

pH-Driven Morphological Diversity in Poly[n-Butyl Acrylate-block-(2-(Dimethylamino)Ethyl Acrylate)] Amphiphilic Copolymer Solutions

Amphiphilic poly[n-butyl acrylate-block-(2-(dimethylamino)ethyl acrylate)] (PnBA-b-PDMAEA) block copolymers are synthesized by the reversible addition fragmentation chain transfer polymerization process. The pH-responsive self-assembly behavior in aqueous media is studied by dynamic, static, and electrophoretic light scattering and cryogenic transmission electron microscopy (Cryo-TEM) at different pHs. In particular, the PnBA₄₀ -b-PDMAEA₆₀ copolymer (where subscripts denote %wt composition of the components) shows remarkable morphological transitions in aqueous solutions of varying pH values forming, among others, an unusual and novel hierarchical vesicular morphology, as indicated by Cryo-TEM results. The observed transitions are attributed to synergistic effects involving alterations of the protonation degree of the PDMAEA block, in conjunction with the specific composition of the copolymer and the softness of PnBA blocks, with cumulative drive changes in the packing parameter of the copolymer system and result in the formation of various unexpected morphologies by simple pH changes.

Muscovy duck reovirus enters susceptible cells via a caveolae-mediated endocytosis-like pathway

Muscovy duck reovirus (MDRV) causes immunosuppression and results in high mortality among Muscovy ducklings. Cell entry is the first step of virus infection and represents a potential therapeutic target. However, very little is known about the mechanism by which MDRV penetrates the cells. The aim of this study was to explore the mechanism of MDRV cell entry and subsequent infection. DF-1 and Vero cells were pretreated with the inhibitors chlorpromazine (CPZ), cytochalasin D, methyl-beta-cyclodextrin (M-β-CD), genistein, dynasore, nocodazole, or NH₄Cl, and then infected with MDRV. The copy number of the MDRV p10.8 gene and the expression of viral sigma A protein were determined by RT-PCR and western blot, respectively. Both sigma A expression and p10.8 gene copy number were decreased by treatment with M-β-CD, genistein, dynasore, nocodazole, and NH₄Cl. In contrast, no effects on virus infection were detected when inhibitors of clathrin-mediated endocytosis or macropinocytosis were used. In addition, the colocalization between MDRV sigma A protein and caveolin-1 was evaluated by double-label immunofluorescence. Collectively, our data revealed that MDRV can enter susceptible cells through caveolin-dependent endocytosis involving dynamin and microtubules. Moreover, the acidic environment of the endosomes was found to be critical for efficient infection. Our findings provide new insights into the infection process of MDRV.

Kidney-targeted rhein-loaded liponanoparticles for diabetic nephropathy therapy via size control and enhancement of renal cellular uptake

The optimization of nanoparticle size for passing through glomerular filtration membrane, inefficient renal cellular uptake and rapid urinary excretion of nanoparticles are the major obstacles for renal disease treatment via a nanoparticle delivery system. Herein, we propose a concept of a two-step nanoparticular cascade of size control and enhancement of renal cellular uptake to overcome the renal delivery obstacles. Methods: We prepared kidney-targeted rhein (RH)-loaded liponanoparticles (KLPPR) with a yolk-shell structure composed by polycaprolactone-polyethyleneimine (PCL-PEI)-based cores and kidney targeting peptide (KTP)-modified lipid layers. The KLPPR size within the range of 30 ~ 80 nm allowed KLPPR distribute into kidney by passing through the glomerular filtration membrane and the KTP (sequence: CSAVPLC) decoration promoted the renal cellular uptake and endocytosis via a non-lysosomal pathway. Results: The KLPPR had an average size of 59.5±6.2 nm and exhibited high RH loading, sustained release, good stability and biocompatibility, rapid cellular uptake in HK-2 cells. In addition, intravenous administration of KLPPR resulted in excellent kidney-targeted distribution and low urinary excretion in mice with streptozocin-induced diabetic nephropathy (DN), lowered the parameters of urea nitrogen, serum creatinine and kidney index, as well as facilitated the recovery of renal physiological function in improving the levels of urinary creatinine and the creatinine clearance rate by suppressing secretion and accumulation of fibronectin and TGF-β1. Conclusion: Definitely, KLPPR were able to target the diseased kidney and improve the therapeutic effect of RH on DN by exploiting the two-step nanoparticular cascade of size control and enhancement of cellular uptake. This study offers a promising strategy for renal diseases treatment using liponanoparticle delivery system.

Quantitative colocalization analysis of DNA delivery by PEI-mediated cationic polymers in mammalian cells

Although cationic polymers are widely used for DNA delivery, the relationship between the properties of the formed complexes and their biological activity is not fully understood. Here, we propose a novel procedure consisting of superresolved images coupled with quantitative colocalization to analyse DNA release in living cells. This work compares the different workflows available in a quantitative colocalization study of DNA delivery using polyethylenimine as transfection reagent. A nimble workflow with deconvolution in three-dimensional images was developed. Among the different colocalization coefficients, Manders' colocalization coefficient was the best to track the complexes. Results showed that DNA/polyethylenimine complexes were tightly interacting at the time of transfection and their disassembly was observed between 2 and 10 h after their uptake. Heterogenicity was found in the intracellular fate of each complex. At 24 h, some complexes were still present underneath the nuclear envelope. Overall, this study opens the door for particle tracking assessment with three-dimensional imaging at intracellular level. LAY DESCRIPTION: DNA delivery technologies in living cells are of high relevance in the biotechnology field. The transient expression of a gene of interest enables the production of a wide range of new therapeutic candidates for clinical purposes. However, the introduction of an exogenous DNA construct into a cell culture requires the use of certain vehicles that protect the DNA from host cell DNases and deliver it into the cell nucleus. From the different systems available, polyethylenimine (PEI) has been extensively used in transient gene expression strategies for the last three decades. However, the intracellular fate of the formed DNA/PEI complexes and the DNA release from the complexes is still poorly understood. In this work, we propose the application of combined superresolved images through mathematical deconvolution to colocalization studies of DNA/PEI complexes evolution in living mammalian cell cultures. Both specimens were covalently labelled with Cy3 and Cy5 dye, respectively, and the kinetics of its disassembly process within the cells was tracked over the time. Because of the specific features of the formed-complexes, a comparative study of the different colocalization coefficients was performed towards optimizing the analysis of these particles with confocal microscopy. Besides, the 3D imaging of the process allowed the direct visualization of a partial DNA/PEI complexes disassembly and the location of those complexes underneath the nuclear envelope during the cell production phase (24 h after the uptake).

Comparison of Biological Responses of Polymers Based on Imine and Disulfide Backbones for siRNA Delivery

To achieve a successful delivery of siRNA by carriers in vivo, the degradation of polymers in response to tiny intracellular changes should be seriously considered. In addition, the balance between degradation and stability of polymers is another key point for high performance of carriers. In this study, imine and disulfide linkages, which are sensitive to pH changes and redox environment, respectively, were constructed as the main backbone of polymers to deliver siRNA at the intracellular and animal level. Comparisons were made between performances of these two different polymers. Both of the polymers synthesized here have good ability to condense siRNA. However, polyplexes formed by the imine backbone-based polymer (TPSP) showed a larger particle size and a higher zeta potential than that of the disulfide backbone-based polymer (DTDPS). Although both TPSP and DTDPS could deliver the target siRNA into 7721 cells, polyplexes formed by TPSP showed a higher silence efficiency in vitro and accomplished more accumulation in tumors. In conclusion, we believe TPSP is superior to be used for siRNA delivery and promises a potential for widespread use.

A Carbon Nanotube Optical Sensor Reports Nuclear Entry via a Noncanonical Pathway

Single-walled carbon nanotubes are of interest in biomedicine for imaging and molecular sensing applications and as shuttles for various cargos such as chemotherapeutic drugs, peptides, proteins, and oligonucleotides. Carbon nanotube surface chemistry can be modulated for subcellular targeting while preserving photoluminescence for label-free visualization in complex biological environments, making them attractive materials for such studies. The cell nucleus is a potential target for many pathologies including cancer and infectious diseases. Understanding mechanisms of nanomaterial delivery to the nucleus may facilitate diagnostics, drug development, and gene-editing tools. Currently, there are no systematic studies to understand how these nanomaterials gain access to the nucleus. Herein, we developed a carbon nanotube based hybrid material that elucidate a distinct mechanism of nuclear translocation of a nanomaterial in cultured cells. We developed a nuclear-targeted probe via cloaking photoluminescent single-walled carbon nanotubes in a guanidinium-functionalized helical polycarbodiimide. We found that the nuclear entry of the nanotubes was mediated by the import receptor importin β without the aid of importin α and not by the more common importin α/β pathway. Additionally, the nanotube photoluminescence exhibited distinct red-shifting upon entry to the nucleus, potentially functioning as a reporter of the importin β-mediated nuclear transport process. This work delineates a noncanonical mechanism for nanomaterial delivery to the nucleus and provides a reporter for the study of nucleus-related pathologies.

Recent Developments in the Synthesis of Biomacromolecules and their Conjugates by Single Electron Transfer-Living Radical Polymerization

Single electron transfer-living radical polymerization (SET-LRP) represents a robust and versatile tool for the synthesis of vinyl polymers with well-defined topology and chain end functionality. The crucial step in SET-LRP is the disproportionation of the Cu(I)X generated by activation with Cu(0) wire, powder, or nascent Cu(0) generated in situ into nascent, extremely reactive Cu(0) atoms and nanoparticles and Cu(II)X₂. Nascent Cu(0) activates the initiator and dormant chains via a homogeneous or heterogeneous outer-sphere single-electron transfer mechanism (SET-LRP). SET-LRP provides an ultrafast polymerization of a plethora of monomers (e.g., (meth)-acrylates, (meth)-acrylamides, styrene, and vinyl chloride) including hydrophobic and water insoluble to hydrophilic and water soluble. Some advantageous features of SET-LRP are (i) the use of Cu(0) wire or powder as readily available catalysts under mild reaction conditions, (ii) their excellent control over molecular weight evolution and distribution as well as polymer chain ends, (iii) their high functional group tolerance allowing the polymerization of commercial-grade monomers, and (iv) the limited purification required for the resulting polymers. In this Perspective, we highlight the recent advancements of SET-LRP in the synthesis of biomacromolecules and of their conjugates.

Maghemite-containing PLGA–PEG-based polymeric nanoparticles for siRNA delivery: toxicity and silencing evaluation

Gene therapy based on siRNA has emerged as an exciting new therapeutic approach. In this work, incorporation of PEI into PLGA-b-PEG and encapsulation of magnetic NPs as MRI contrast agent, resulted in unique theranostic nanoparticles.

Journey to the Center of the Cell: Current Nanocarrier Design Strategies Targeting Biopharmaceuticals to the Cytoplasm and Nucleus

New biopharmaceutical molecules, potentially able to provide more personalized and effective treatments, are being identified through the advent of advanced synthetic biology strategies, sophisticated chemical synthesis approaches, and new analytical methods to assess biological potency. However, translation of many of these structures has been significantly limited due to the need for more efficient strategies to deliver macromolecular therapeutics to desirable intracellular sites of action. Engineered nanocarriers that encapsulate peptides, proteins, or nucleic acids are generally internalized into target cells via one of several endocytic pathways. These nanostructures, entrapped within endosomes, must navigate the intracellular milieu to orchestrate delivery to the intended destination, typically the cytoplasm or nucleus. For therapeutics active in the cytoplasm, endosomal escape continues to represent a limiting step to effective treatment, since a majority of nanocarriers trapped within endosomes are ultimately marked for enzymatic degradation in lysosomes. Therapeutics active in the nucleus have the added challenges of reaching and penetrating the nuclear envelope, and nuclear delivery remains a preeminent challenge preventing clinical translation of gene therapy applications. Herein, we review cutting-edge peptide- and polymer-based design strategies with the potential to enable significant improvements in biopharmaceutical efficacy through improved intracellular targeting. These strategies often mimic the activities of pathogens, which have developed innate and highly effective mechanisms to penetrate plasma membranes and enter the nucleus of host cells. Understanding these mechanisms has enabled advances in synthetic peptide and polymer design that may ultimately improve intracellular trafficking and bioavailability, leading to increased access to new classes of biotherapeutics.

Recent progress in gene therapy to deliver nucleic acids with multivalent cationic vectors

Due to the potential use as transfecting agents of nucleic acids (DNA or RNA), multivalent cationic non-viral vectors have received special attention in the last decade. Much effort has been addressed to synthesize more efficient and biocompatible gene vectors able to transport nucleic acids into the cells without provoking an immune response. Among them, the mostly explored to compact and transfect nucleic acids are: (a) gemini and multivalent cationic lipids, mixed with a helper lipid, by forming lipoplexes; and (b) cationic polymers, polycations, and polyrotaxanes, by forming polyplexes. This review is focused on the progress and recent advances experimented in this area, mainly during the present decade, devoting special attention to the lipoplexes and polyplexes, as follows: (a) to its biophysical characterization (mainly electrostatics, structure, size and morphology) using a wide variety of experimental methods; and (b) to its biological activity (transfection efficacy and cytotoxicity) addressed to confirm the optimum formulations and viability of these complexes as very promising gene vectors of nucleic acids in nanomedicine.

The role of helper lipids in the intracellular disposition and transfection efficiency of niosome formulations for gene delivery to retinal pigment epithelial cells

In this work, we carried out a comparative study of four different niosome formulations based on the same cationic lipid and non-ionic tensoactive. The niosomes prepared by oil-in-water emulsion technique (o/w) only differed in the helper lipid composition: squalene, cholesterol, squalane or no helper lipid. Niosomes and nioplexes elaborated upon the addition of pCMS-EGFP reporter plasmid were characterized in terms of size, zeta potential and polydispersity index. The capacity of the niosomes to condense, release and protect the DNA against enzymatic degradation was evaluated by agarose gel electrophoresis. In vitro experiments were carried out to evaluate transfection efficiency and cell viability in retinal pigment epithelial cells. Moreover, uptake and intracellular trafficking studies were performed to further understand the role of the helper lipids in the transfection process. Interestingly, among all tested formulations, niosomes elaborated with squalene as helper lipid were the most efficient transfecting cells. Such transfection efficiency could be attributed to their higher cellular uptake and the particular entry pathways used, where macropinocytosis pathway and lysosomal release played an important role. Therefore, these results suggest that helper lipid composition is a crucial step to be considered in the design of niosome formulation for retinal gene delivery applications since clearly modulates the cellular uptake, internalization mechanism and consequently, the final transfection efficiency.

Cu(0)-mediated living radical polymerization: recent highlights and applications; a perspective

Cu(0)-mediated living radical polymerization or single electron transfer living radical polymerization (Cu(0)-mediated LRP or SET-LRP) is a versatile polymerization technique that has attracted considerable interest during the past few years for the facile preparation of advanced materials.

PHEA-g-PDMAEA well-defined graft copolymers: SET-LRP synthesis, self-catalyzed hydrolysis, and quaternization

This article reports the synthesis of well-defined graft copolymers containing a PHEA backbone and degradable PDMAEA side chains, by the combination of RAFT polymerization, SET-LRP, and the grafting-from strategy.

Endosomal-Escape Polymers Based on Multicomponent Reaction-Synthesized Monomers Integrating Alkyl and Imidazolyl Moieties for Efficient Gene Delivery

As one of the toughest tasks in the course of intracellular therapeutics delivery, endosomal escape must be effectively achieved, particularly for intracellular gene transport. In this report, novel endosomal-escape polymers were designed and synthesized from monomers by integrating alkyl and imidazolyl via Passerini reaction and reversible addition-fragmentation chain transfer polymerization (RAFT). After introducing the endosomal-escape polymers with proper degrees of polymerization (DPs) into poly(2-dimethylaminoethyl methacrylate) (PDMAEMA) as the gene delivery vectors, the block copolymers exhibited significantly enhanced hemolytic activity at endosomal pH, and the plasmid DNA (pDNA)-loaded polyplexes showed efficient endosomal escape compared with PDMAEMA, ultimately achieving dramatically increased gene transfection efficacy. These results suggest that the polymers that integrate alkyl and imidazolyl moieties for efficient endosomal escape have wide potential applications for intracellular gene delivery.

Enabling cytoplasmic delivery and organelle targeting by surface modification of nanocarriers

Nanocarriers are designed to specifically accumulate in diseased tissues. In this context, targeting of intracellular compartments was shown to enhance the efficacy of many drugs and to offer new and more effective therapeutic approaches. This is especially true for therapies based on biologicals that must be encapsulated to favor cell internalization, and to avoid intracellular endosomal sequestration and degradation of the payload. In this review, we discuss specific surface modifications designed to achieve cell cytoplasm delivery and to improve targeting of major organelles; we also discuss the therapeutic applications of these approaches. Last, we describe some integrated strategies designed to sequentially overcome the biological barriers that separate the site of administration from the cell cytoplasm, which is the drug's site of action.

The influence of polymer architecture on in vitro pDNA transfection

In the field of polymer-based gene delivery, the tuning potential of polymers by using different architectures like graft- and star-shaped polymers as well as self-assembled block copolymers is immense. In the last years numerous new polymer designs showed enhanced transfections properties in combination with a good biocompatibility.