CTb targeted non-viral cDNA delivery enhances transgene expression in neurons

Targeted delivery of oligonucleotides using multivalent protein-carbohydrate interactions

Cell surface protein-carbohydrate interactions are essential for tissue-specific recognition and endocytosis of viruses, some bacteria and their toxins, and many glycoproteins. Often protein-carbohydrate interactions are multivalent - multiple copies of glycans bind simultaneously to multimeric receptors. Multivalency enhances both affinity and binding specificity, and is of interest for targeted delivery of drugs to specific cell types. The first such example of carbohydrate-mediated drug delivery to reach the clinic is Givosiran, a small interfering ribonucleic acid (siRNA) that is conjugated to a trivalent N-acetylgalactosamine (GalNAc) ligand. This ligand enables efficient uptake of the nucleic acid by the asialoglycoprotein receptor (ASGP-R) on hepatocytes. Synthetic multivalent ligands for ASGP-R were among the first 'cluster glycosides' developed at the birth of multivalent glycoscience around 40 years ago. In this review we trace the history of 'GalNAc targeting' from early academic studies to current pharmaceuticals and consider what other opportunities could follow the success of this delivery technology.

Evaluation and Optimization of Poly-d-Lysine as a Non-Natural Cationic Polypeptide for Gene Transfer in Neuroblastoma Cells

Cationic polypeptides and cationic polymers have cell-penetrating capacities and have been used in gene transfer studies. In this study, we investigate the capability of a polymer of d-lysine (PDL), a chiral form of α–Poly-lysine, as a possible nonviral vector for releasing genetic materials to neuroblastoma cells and evaluate its stability against proteases. We tested and compared its transfection effectiveness in vitro as a vehicle for the EGFP plasmid DNA (pDNA) reporter in the SH-SY5Y human neuroblastoma, HeLa, and 3T3 cell lines. Using fluorescent microscopy and flow cytometry, we demonstrated high transfection efficiencies based on EGFP fluorescence in SH-SY5Y cells, compared with HeLa and 3T3. Our results reveal PDL as an efficient vector for gene delivery specifically in the SH-SY5Y cell line and suggest that PDL can be used as a synthetic cell-penetrating polypeptide for gene therapy in neuroblastoma cells.

Breaking Barriers: Bioinspired Strategies for Targeted Neuronal Delivery to the Central Nervous System

Central nervous system (CNS) disorders encompass a vast spectrum of pathological conditions and represent a growing concern worldwide. Despite the high social and clinical interest in trying to solve these pathologies, there are many challenges to bridge in order to achieve an effective therapy. One of the main obstacles to advancements in this field that has hampered many of the therapeutic strategies proposed to date is the presence of the CNS barriers that restrict the access to the brain. However, adequate brain biodistribution and neuronal cells specific accumulation in the targeted site also represent major hurdles to the attainment of a successful CNS treatment. Over the last few years, nanotechnology has taken a step forward towards the development of therapeutics in neurologic diseases and different approaches have been developed to surpass these obstacles. The versatility of the designed nanocarriers in terms of physical and chemical properties, and the possibility to functionalize them with specific moieties, have resulted in improved neurotargeted delivery profiles. With the concomitant progress in biology research, many of these strategies have been inspired by nature and have taken advantage of physiological processes to achieve brain delivery. Here, the different nanosystems and targeting moieties used to achieve a neuronal delivery reported in the open literature are comprehensively reviewed and critically discussed, with emphasis on the most recent bioinspired advances in the field. Finally, we express our view on the paramount challenges in targeted neuronal delivery that need to be overcome for these promising therapeutics to move from the bench to the bedside.

Directed Assembly of Homopentameric Cholera Toxin B-Subunit Proteins into Higher-Order Structures Using Coiled-Coil Appendages

The self-assembly of proteins into higher order structures is ubiquitous in living systems. It is also an essential process for the bottom-up creation of novel molecular architectures and devices for synthetic biology. However, the complexity of protein–protein interaction surfaces makes it challenging to mimic natural assembly processes in artificial systems. Indeed, many successful computationally designed protein assemblies are prescreened for “designability”, limiting the choice of components. Here, we report a simple and pragmatic strategy to assemble chosen multisubunit proteins into more complex structures. A coiled-coil domain appended to one face of the pentameric cholera toxin B-subunit (CTB) enabled the ordered assembly of tubular supra-molecular complexes. Analysis of a tubular structure determined by X-ray crystallography has revealed a hierarchical assembly process that displays features reminiscent of the polymorphic assembly of polyomavirus proteins. The approach provides a simple and straightforward method to direct the assembly of protein building blocks which present either termini on a single face of an oligomer. This scaffolding approach can be used to generate bespoke supramolecular assemblies of functional proteins. Additionally, structural resolution of the scaffolded assemblies highlight “native-state” forced protein–protein interfaces, which may prove useful as starting conformations for future computational design.

Disarmed anthrax toxin delivers antisense oligonucleotides and siRNA with high efficiency and low toxicity

Inefficient cytosolic delivery and vector toxicity contribute to the limited use of antisense oligonucleotides (ASOs) and siRNA as therapeutics. As anthrax toxin (Atx) accesses the cytosol, the purpose of this study was to evaluate the potential of disarmed Atx to deliver either ASOs or siRNA. We hypothesized that this delivery strategy would facilitate improved transfection efficiency while eliminating the toxicity seen for many vectors due to membrane destabilization. Atx complex formation with ASOs or siRNA was achieved via the in-frame fusion of either Saccharomyces cerevisiae GAL4 or Homo sapien sapien PKR (respectively) to a truncation of Atx lethal factor (LFn), which were used with Atx protective antigen (PA). Western immunoblotting confirmed the production of: LFN-GAL4, LFn-PKR and PA which were detected at ~45.9 kDa, ~37 kDa, and ~83 kDa respectively and small angle neutron scattering confirmed the ability of PA to form an annular structure with a radius of gyration of 7.0 ± 1.0 nm when placed in serum. In order to form a complex with LFn-GAL4, ASOs were engineered to contain a double-stranded region, and a cell free in vitro translation assay demonstrated that no loss of antisense activity above 30 pmol ASO was evident. The in vitro toxicity of both PA:LFn-GAL4:ASO and PA:LFn-PKR:siRNA complexes was low (IC50>100 μg/mL in HeLa and Vero cells) and subcellular fractionation in conjunction with microscopy confirmed the detection of LFn-GAL4 or LFn-PKR in the cytosol. Syntaxin5 (Synt5) was used as a model target gene to determine pharmacological activity. The PA:LFn-GAL4:ASO complexes had transfection efficiency approximately equivalent to Nucleofection® over a variety of ASO concentrations (24h post-transfection) and during a 72 h time course. In HeLa cells, at 200 pmol ASO (with PA:LFN-GAL4), 5.4 ± 2.0% Synt5 expression was evident relative to an untreated control after 24h. Using 200 pmol ASOs, Nucleofection® reduced Synt5 expression to 8.1 ± 2.1% after 24h. PA:LFn-GAL4:ASO transfection of non- or terminally-differentiated THP-1 cells and Vero cells resulted in 35.2 ± 19.1%, 36.4 ± 1.8% and 22.9 ± 6.9% (respectively) Synt5 expression after treatment with 200 pmol of ASO and demonstrated versatility. Nucleofection® with Stealth RNAi™ siRNA reduced HeLa Synt5 levels to 4.6 ± 6.1% whereas treatment with the PA:LFn-PKR:siRNA resulted in 8.5 ± 3.4% Synt5 expression after 24h (HeLa cells). These studies report for the first time an ASO and RNAi delivery system based upon protein toxin architecture that is devoid of polycations. This system may utilize regulated membrane back-fusion for the cytosolic delivery of ASOs and siRNA, which would account for the lack of toxicity observed. High delivery efficiency suggests further in vivo evaluation is warranted.

Endocytosis and intracellular trafficking as gateways for nanomedicine delivery: opportunities and challenges

More than 40 nanomedicines are already in routine clinical use with a growing number following in preclinical and clinical development. The therapeutic objectives are often enhanced disease-specific targeting (with simultaneously reduced access to sites of toxicity) and, especially in the case of macromolecular biotech drugs, improving access to intracellular pharmacological target receptors. Successful navigation of the endocytic pathways is usually a prerequisite to achieve these goals. Thus a comprehensive understanding of endocytosis and intracellular trafficking pathways in both the target and bystander normal cell type(s) is essential to enable optimal nanomedicine design. It is becoming evident that endocytic pathways can become disregulated in disease and this, together with the potential changes induced during exposure to the nanocarrier itself, has the potential to significantly impact nanomedicine performance in terms of safety and efficacy. Here we overview the endomembrane trafficking pathways, discuss the methods used to determine and quantitate the intracellular fate of nanomedicines, and review the current status of lysosomotropic and endosomotropic delivery. Based on the lessons learned during more than 3 decades of clinical development, the need to use endocytosis-relevant clinical biomarkers to better select those patients most likely to benefit from nanomedicine therapy is also discussed.

Progress toward liver-based gene therapy

The liver is involved in the synthesis of serum proteins, regulation of metabolism and maintenance of homeostasis and provides a variety of opportunities for gene therapy. The enriched vasculature and blood circulation, fenestrated endothelium, abundant receptors on the plasma membranes of the liver cells, and effective transcription and translation machineries in the hepatocytes are some unique features that have been explored for delivery, and functional analysis, of genetic sequences in the liver. Both viral and non-viral methods have been developed for effective gene delivery and liver-based gene therapy. This review describes the fundamentals of gene delivery, and the preclinical and clinical progress that has been made toward gene therapy using the liver as a target.

Neuron-specific delivery of nucleic acids mediated by Tet1-modified poly(ethylenimine)

BACKGROUND

The development of minimally invasive, non-viral gene delivery vehicles for the central nervous system (CNS) is an important technology goal in the advancement of molecular therapies for neurological diseases. One approach is to deliver materials peripherally that are recognized and retrogradely transported by motor neurons toward the CNS. Tet1 is a peptide identified by Boulis and coworkers to possess the binding characteristics of tetanus toxin, which interacts specifically with motor neurons and undergoes fast, retrograde delivery to cell soma. In this work, Tet1-poly(ethylenimine) (Tet1-PEI) was synthesized and evaluated as a neurontargeted delivery vehicle.

METHODS

Tet1-PEI and NT-PEI (neurotensin-PEI) were synthesized and complexed with plasmid DNA to form polyplexes. Polyplexes were assessed for binding and uptake in differentiated neuron-like PC-12 cells by flow cytometry and confocal microscopy. In order to determine gene delivery efficiency, polyplexes were exposed to PC-12 cells at various stages of differentiation. Targeted binding of polyplexes with primary neurons was studied using dorsal root ganglion cells.

RESULTS

Tet1-PEI and NT-PEI polyplexes bound specifically to differentiated PC-12 cells. The specificity of the interaction was confirmed by delivery to non-neuronal cells and by competition studies with free ligands. Tet1-PEI polyplexes preferentially transfected PC-12 cells undergoing NGF-induced differentiation. Finally, neuron-specific binding of Tet1-PEI polyplexes was confirmed in primary neurons.

CONCLUSIONS

These studies demonstrate the potential of Tet1-PEI as a neuron-targeted material for non-invasive CNS delivery. Tet1-PEI binds specifically and is internalized by neuron-like PC-12 cells and primary dorsal root ganglion. Future work will include evaluation of siRNA delivery with these vectors.

"Alternative" endocytic mechanisms exploited by pathogens: new avenues for therapeutic delivery?

Some pathogens utilize unique routes to enter cells that may evade the intracellular barriers encountered by the typical clathrin-mediated endocytic pathway. Retrograde transport and caveolar uptake are among the better characterized pathways, as alternatives to clathrin-mediated endocytosis, that are known to facilitate entry of pathogens and potential delivery agents. Recent characterization of the trafficking mechanisms of prion proteins and certain bacteria may present new paradigms for strategizing improvements in therapeutic spread and retention of therapy. This review will provide an overview of such endocytic pathways, and discuss current and future possibilities in using these routes as a means to improve therapeutic delivery.

Polymeric gene carrier for insulin secreting cells: poly(L-lysine)-g-sulfonylurea for receptor mediated transfection

Ex vivo transfer of therapeutic genes to cells is one of the potential strategies to prolong the life span of cell transplants. However, relatively safe non-viral carriers have not been extensively investigated due to their lower transfection efficiency. In this study, poly(L-lysine)-g-sulfonylurea varying SU content (PLL-SU) was synthesized to promote gene delivery efficacy to an insulin secreting cell line, RINm5F, which is known to express sulfonylurea receptor (SUR). The polymer formed complexes with a model reporter gene of pCMV-Luc (DNA) and the size of resulting particles was around 100 nm. The transfection efficiency of a polymer synthesized with 5 mol% of SU in the reaction feed (PLL-SU5%) to RINm5F cell was at least 5 times higher than that of PLL. The cytotoxicity of PLL-SU5%/DNA complex was equivalent to that of PLL/DNA complex. PLL-SU5% showed less transfection efficiency than PLL to NIH3T3 and HepG2 cells which are SUR negative. In RINm5F cells, the addition of free SU decreased the transfection efficiency of PLL-SU5%/DNA complex, suggesting that the complex shares the same receptors for SU. The PLL-SU5%/DNA complex seems to be internalized via SUR-mediated endocytosis pathway as suggested by vacuolar ATPases inhibition by Bafilomycin A1. It is noted that RINm5F cells treated with PLL-SU5%/DNA complex secreted more insulin than control, untreated cells, suggesting the insulinotropic effect of SU in PLL-SU5%. In conclusion, PLL-SU may be useful for transfer of therapeutic genes into insulin secreting cells.

Delivery into cells: lessons learned from plant and bacterial toxins

A number of protein toxins of bacterial and plant origin have cytosolic targets, and knowledge about these toxins have provided us with essential information about mechanisms that can be used to gain access to the cytosol as well as detailed knowledge about endocytosis and intracellular sorting. Such toxins include those that have two moieties, one (the B-moiety) that binds to cell surface receptors and another (the A-moiety) with enzymatic activity that enters the cytosol, as well as molecules that only have the enzymatically active moiety and therefore are inefficient in cell entry. The toxins discussed in the present article include bacterial toxins such as Shiga toxin and diphtheria toxin, as well as plant toxins such as ricin and ribosome-inactivating proteins without a binding moiety, such as gelonin. Toxins with a binding moiety can be used as vectors to translocate epitopes, intact proteins, and even nucleotides into the cytosol. The toxins fall into two main groups when it comes to cytosolic entry. Some toxins enter from endosomes in response to low endosomal pH, whereas others, including Shiga toxin and ricin, are transported all the way to the Golgi apparatus and the ER before they are translocated to the cytosol. Plant proteins such as gelonin that are without a binding moiety are taken up only by fluid-phase endocytosis, and normally they have a low toxicity. However, they can be used to test for disruption of endosomal membranes leading to cytosolic access of internalized molecules. Similarly to toxins with a binding moiety they are highly toxic when reaching the cytosol, thereby providing the investigator with an efficient tool to study endosomal disruption and induced transport to the cytosol. In conclusion, the protein toxins are useful tools to study transport and cytosolic translocation, and they can be used as vectors for transport to the interior of the cell.

Targeted polymers for gene delivery

Over the past decade, significant research has been done in the area of polymer-mediated gene delivery. Synthesis of new polymers and modifications to existing polymers has resulted in polyplexes with improved in vitro and in vivo transfection efficiencies. Targeting has been an important aspect of this research, and various strategies for obtaining selective and enhanced gene delivery to the target site have been evaluated. This review covers the different aspects involved in polyplex targeting. Development of targeted polyplexes involves a careful consideration of the target site, the targeting ligand and the physicochemical properties of the polyplex itself. The need to redirect the polyplexes by using the 'shield and target' approach by reducing nonspecific interactions with negatively charged components, while conferring specificity by incorporating targeting ligands, is discussed. Basic chemistry involved in modifying polymers is covered and examples of targeting strategies used for tissue-specific gene delivery are discussed. Targeting is also discussed in the broader context of developing safe and effective polymeric vectors for in vivo gene delivery. Maximum benefit of targeting can be obtained when it is used as part of a multi-functional complex containing elements designed to improve gene delivery and reduce overall toxicity of the polyplex.

Biomembrane-Active Molecular Switches as Tools for Intracellular Drug Delivery

Many therapeutic strategies, such as gene therapy and vaccine development require the delivery of polar macromolecules (e.g. DNA, RNA, and proteins) to intracellular sites at a therapeutic concentration. For such macromolecular therapeutics, cellular membranes constitute a major transport barrier that must be overcome before these drugs can exert their biological activity inside cells. A number of biological organisms, e.g. viruses and toxins, efficiently destabilize the cellular membranes upon a trigger, such as low pH, and facilitate the delivery of their biological cargo to the cytoplasm of host cell. pH-responsive synthetic peptides and polymers have been designed to mimic the function of membrane-destabilizing natural organisms and evaluated as a part of drug delivery systems. In this Review, pH-dependent membrane activity of natural and synthetic systems is reviewed, focussing on fundamental and practical aspects of pH-responsive, membrane-disruptive synthetic polymers in intracellular drug delivery.