Polymeric Nanoparticles Based on Tyrosine-Modified, Low Molecular Weight Polyethylenimines for siRNA Delivery

Hydrogels for Nucleic Acid Drugs Delivery

Nucleic acid drugs are one of the hot spots in the field of biomedicine in recent years, and play a crucial role in the treatment of many diseases. However, its low stability and difficulty in target drug delivery are the bottlenecks restricting its application. Hydrogels are proven to be promising for improving the stability of nucleic acid drugs, reducing the adverse effects of rapid degradation, sudden release, and unnecessary diffusion of nucleic acid drugs. In this review, the strategies of loading nucleic acid drugs in hydrogels are summarized for various biomedical research, and classify the mechanism principles of these strategies, including electrostatic binding, hydrogen bond based binding, hydrophobic binding, covalent bond based binding and indirect binding using various carriers. In addition, this review also describes the release strategies of nucleic acid drugs, including photostimulation-based release, enzyme-responsive release, pH-responsive release, and temperature-responsive release. Finally, the applications and future research directions of hydrogels for delivering nucleic acid drugs in the field of medicine are discussed.

Spray-drying of PEI-/PPI-based nanoparticles for DNA or siRNA delivery

Spray-drying of nucleic acid-based drugs designed for gene therapy or gene knockdown is associated with many advantages including storage stability and handling as well as the possibility of pulmonary application. The encapsulation of nucleic acids in nanoparticles prior to spray-drying is one strategy for obtaining efficient formulations. This, however, strongly relies on the definition of optimal nanoparticles, excipients and spray-drying conditions. Among polymeric nanoparticles, polyethylenimine (PEI)-based complexes with or without chemical modifications have been described previously as very efficient for gene or oligonucleotide delivery. The tyrosine-modification of linear or branched low molecular weight PEIs, or of polypropylenimine (PPI) dendrimers, has led to high complex stability, improved cell uptake and transfection efficacy as well as high biocompatibility. In this study, we identify optimal spray-drying conditions for PEI-based nanoparticles containing large plasmid DNA or small siRNAs, and further explore the spray-drying of nanoparticles containing chemically modified polymers. Poly(vinyl alcohol) (PVA), but not trehalose or lactose, is particularly well-suited as excipient, retaining or even enhancing transfection efficacies compared to fresh complexes. A big mesh size is critically important as well, while the variation of the spray-drying temperature plays a minor role. Upon spray-drying, microparticles in a ∼ 3.3 - 8.5 µm size range (laser granulometry) are obtained, dependent on the polymers. Upon their release from the spray-dried material, the nanoparticles show increased sizes and markedly altered zeta potentials as compared to their fresh counterparts. This may contribute to their high efficacy that is seen also after prolonged storage of the spray-dried material. We conclude that these spray-dried systems offer a great potential for the preparation of nucleic acid drug storage forms with facile reconstitution, as well as for their direct pulmonary application as dry powder.

Efficient polymeric nanoparticles for RNAi in macrophage reveal complex effects on polarization markers upon knockdown of STAT3/STAT6

Tumor associated macrophages (TAMs) are the most abundant immune cell type in the tissue microenvironment, affecting tumor progression, metastasis and therapeutic response. Different macrophage activation ("polarization") states can be distinguished: resting (M0; non-activated), pro-inflammatory/anti-tumorigenic (M1) and anti-inflammatory/pro-tumorigenic (M2). When exploring macrophages as targets in novel cancer immunotherapy approaches, TAM repolarization from the M2 into the M1 phenotype is an intriguing strategy to block their pro-tumoral and enhance their anti-tumoral properties. In the context of RNAi-based gene knockdown of M2 promoting genes, major bottlenecks include cellular siRNA delivery and correct intracellular processing. This is particularly true in case of macrophages as a cell type well-known to be notoriously hard-to-transfect. Among polymeric nanocarriers, the cationic polymer polyethylenimine (PEI) is widely explored for delivering nucleic acids. Further advanced nanocarriers are tyrosine-modified polymers based on PEI or polypropylenimine dendrimers (PPI) for highly efficient siRNA delivery in vitro and in vivo. In this paper, we explored a panel of PEI- or PPI-based nanoparticle systems for siRNA-mediated gene knockdown efficacy in macrophages and subsequent TAM repolarization. The tyrosine-modified linear 10 kDa PEI (LP10Y) or branched 5 kDa PEI (P5Y) as well as a tyrosine-modified PPI (PPI-Y) were found most efficient for gene knockdown in macrophage cell lines or primary macrophages, independent of their polarization. Knockdown of STAT6 or STAT3 led to repolarization of M2 macrophages, as indicated by alterations in various M2 and M1 marker levels. This highly specific approach also demonstrated non-redundant functions of STAT3 and STAT6. Importantly, macrophage re-polarization from M2 to M1 upon PPI-Y/siRNA-mediated STAT6 knockdown increased tumor cell phagocytosis in a co-culture model. In conclusion, we identify certain tyrosine-modified PEI- or PPI-based nanoparticles as particularly efficient for macrophage transfection, and the specific, siRNA-mediated STAT6 knockdown as a promising approach for macrophage repolarization and enhancement of their tumor cell suppressive role.

Novel aromatic moieties-modified poly(glycidyl amine)s with potent siRNA delivery and cancer treatment effect

The development of safe and effective delivery systems is critical for the clinical applications of siRNA-based therapeutics. Polymer-based vectors have garnered significant attention owing to their structural flexibility and functional tunability. Polyethyleneimine (PEI) has been extensively studied for nucleic acid delivery; nevertheless, its high cytotoxicity has posed challenges for clinical applications. In this study, we have reported poly(glycidyl amine) (PGAm), a linear PEI analogue, demonstrating remarkable siRNA delivery efficacy and improved biocompatibility. By introducing three aromatic moieties (tyrosine, p-hydroxybenzenepropanoic acid, and phenylalanine) at varying ratios to further modify PGAms, we successfully constructed a library comprising 36 PGAm-based carriers. In vitro evaluations revealed that PGAm-based carriers exhibited significantly enhanced biocompatibility and reduced non-specific protein absorption in comparison to PEI25k. Among them, 10 modified PGAms achieved a knockdown of target gene expressions exceeding 80%, and 26 modified PGAms maintained over 70% cell viability when utilized for the in vitro delivery of siRNA to HeLa cells. Explorations into the structure-activity relationship of PGAm-based polyplex nanoparticles (NPs) indicated that the siRNA delivery efficacy of NPs depended on factors such as the molecular weight of PGAm precursors, the type of modifying moieties, and the modification ratio. Furthermore, it was demonstrated that two top-performing NPs, namely 2T100/siLuc and 2A50/siLuc, exhibited potent silencing of target genes in tumors following i.v. injection into mice bearing HeLa-Luc xenografts. The in vivo efficacy of the selected NPs was further validated by a remarkable anti-cancer effect when employed for the delivery of siRNA targeting polo-like kinase 1 (siPLK1) to mice with PC-3 xenograft tumors. The intravenous administration of NPs resulted in a substantial inhibition of tumor growth without significant toxicity. These findings demonstrate the feasibility of employing PGAm in siRNA delivery and provide valuable insights for the development of efficient siRNA carriers based on PGAm.

Research progress of siVEGF complex and their application in antiangiogenic therapy

Vascular endothelial growth factor (VEGF) is an important factor in the development of some diseases such as tumors, ocular neovascular disease and endometriosis. Inhibition of abnormal VEGF expression is one of the most effective means of treating these diseases. The resistance and side effects of currently used VEGF drugs limit their application. Herein, small interfering RNA for VEGF (siVEGF) are developed to inhibit VEGF expression at the genetic level by means of RNA interference. However, as a foreign substance entering the organism, siVEGF is prone to induce an immune response or mismatch, which adversely affects the organism. It is also subjected to enzymatic degradation and cell membrane blockage, which greatly reduces its therapeutic effect. Targeted siVEGF complexes are constructed by nanocarriers to avoid their clearance by the body and precisely target cells, exerting anti-vascular effects for the treatment of relevant diseases. In addition, some multifunctional complexes allow for the combination of siVEGF with other therapeutic tools to improve the treat efficiency of the disease. Therefore, this review describes the construction of the siVEGF complex, its mechanism of action, application in anti-blood therapy, and provides an outlook on its current problems and prospects.

The effect of novel tyrosine-modified polyethyleneimines on human albumin structure - Thermodynamic and spectroscopic study

The interaction of proteins with nanoparticle components are crucial for the evaluation of nanoparticle function, toxicity and biodistribution. Polyethyleneimines (PEIs) with defined tyrosine modifications are a class of novel polymers designed for improved siRNA delivery. Their interactions with biomacromolecules are still poorly described. This paper analyzes the interaction of different tyrosine-modified PEIs with human serum albumin as the most abundant serum protein. The ability of tyrosine modified, linear or branched PEIs to bind human serum albumin (HSA) was analyzed and further characterized. The interaction with hydrophobic parts of protein were studied using 1- nilinonaphthalene-8-sulfonic acid (ANS) and changes in the HSA secondary structure were evaluated using circular dichroism (CD). Complex formation and sizes were studied by transmission electron microscopy (TEM) and dynamic light scattering methods (DLS). We demonstrate that tyrosine modified PEIs are able to bind human serum albumin. Based on thermodynamic studies, van der Waals interaction, H-bonding and hydrophobic interactions are determined as main molecular forces involved in complex formation. Analysis of secondary structures revealed that the polymers decreased α-helix content, while increasing levels of randomly folded structures. Complex formation was confirmed by TEM and DLS. These findings are crucial for understanding polymer-protein interactions and the properties of nanoparticles.

Non-Viral Carriers for Nucleic Acids Delivery: Fundamentals and Current Applications

Over the past decades, non-viral DNA and RNA delivery systems have been intensively studied as an alternative to viral vectors. Despite the most significant advantage over viruses, such as the lack of immunogenicity and cytotoxicity, the widespread use of non-viral carriers in clinical practice is still limited due to the insufficient efficacy associated with the difficulties of overcoming extracellular and intracellular barriers. Overcoming barriers by non-viral carriers is facilitated by their chemical structure, surface charge, as well as developed modifications. Currently, there are many different forms of non-viral carriers for various applications. This review aimed to summarize recent developments based on the essential requirements for non-viral carriers for gene therapy.

Synthesis and Application of Low Molecular Weight PEI-Based Copolymers for siRNA Delivery with Smart Polymer Blends

Polyethylenimine (PEI) is a commonly used cationic polymer for small-interfering RNA (siRNA) delivery due to its high transfection efficiency at low commercial cost. However, high molecular weight PEI is cytotoxic and thus, its practical application is limited. In this study, different formulations of low molecular weight PEI (LMW-PEI) based copolymers polyethylenimine-g-polycaprolactone (PEI-PCL) (800 Da-40 kDa) and PEI-PCL-PEI (5-5-5 kDa) blended with or without polyethylene glycol-b-polycaprolactone (PEG-PCL) (5 kDa-4 kDa) are investigated to prepare nanoparticles via nanoprecipitation using a solvent displacement method with sizes ≈100 nm. PEG-PCL can stabilize the nanoparticles, improve their biocompatibility, and extend their circulation time in vivo. The nanoparticles composed of PEI-PCL-PEI and PEG-PCL show higher siRNA encapsulation efficiency than PEI-PCL/PEG-PCL based nanoparticles at low N/P ratios, higher cellular uptake, and a gene silencing efficiency of ≈40% as a result of the higher molecular weight PEI blocks. These results suggest that the PEI-PCL-PEI/PEG-PCL nanoparticle system could be a promising vehicle for siRNA delivery at minimal synthetic effort.

Analysis of polymeric nanoparticle properties for siRNA/DNA delivery in a tumor xenograft tissue slice air-liquid interface model

BACKGROUND

Classical two-dimensional (2D) cell culture as a drug or nanoparticle test system only poorly recapitulates in vivo conditions. Animal studies are costly, ethically controversial, and preclude large-scale testing.

METHODS AND RESULTS

We established a three-dimensional (3D) tissue slice air-liquid interface (ALI) culture model for nanoparticle testing. We developed an optimized procedure for the reproducible generation of large sets of tissue slices from tumor xenografts that retain their tissue architecture. When used for the analysis of nanoparticles based on chemically modified polyethylenimines (PEIs) to deliver siRNA or DNA, differences in transfection efficacy and cytotoxicity between nanoparticles were observed more clearly than in 2D cell culture. While nanoparticle efficacies between cell culture and the tissue slice model overall correlated, the tissue slice model also identified particularly suitable candidates whose efficacy was underestimated in 2D cell culture and had already been shown in previous in vivo studies.

CONCLUSION

The ex vivo 3D tissue slice ALI culture model is a powerful system that allows the effective evaluation of biological nanoparticle efficacy and biocompatibility in an intact tissue environment. It is comparably inexpensive, time-saving, and follows the 3R principle, while allowing the identification of critical nanoparticle properties and optimal candidates for in vivo applications.

Comparison of tyrosine-modified low molecular weight branched and linear polyethylenimines for siRNA delivery

Polyethylenimines (PEIs) have been previously introduced for siRNA delivery. In particular, in the case of higher molecular weight PEIs, this is associated with toxicity, while low molecular weight PEIs are often insufficient for siRNA complexation. The tyrosine-modification of PEIs has been shown to enhance PEI efficacy and biocompatibility. This paper evaluates a set of tyrosine-modified low molecular weight linear or branched polyethylenimines as efficient carriers of siRNA. Complexation efficacies and biophysical complex properties were analyzed by zeta potential, dynamic light scattering and circular dichroism measurements as well as gel electrophoresis. Biological knockdown was studied in 2 D cell culture and 3 D ex vivo tissue slice air-liquid interface culture. The results demonstrate that siRNAs were able to form stable complexes with all tested polymers. Complexation was able to protect siRNA from degradation by RNase and to mediate target gene knockdown, as determined on the mRNA level and in PC3-Luc3/EGFP and HCT116-Luc3/EGFP expressing reporter cells on the protein level, using flow cytometry and confocal microscopy. The direct comparison of the studied polymers revealed differences in biological efficacies. Moreover, the tyrosine-modified PEIs showed high biocompatibility, as determined by LDH release and mitochondria integrity (J-aggregate assay) as well as caspase 3/7 (apoptosis) and H₂O₂ levels (ROS). In 3 D tissue slices, complexes based on LP10Y proved to be most efficient, by combining tissue penetration with efficient gene expression knockdown.

Current Advancements in Self-assembling Nanocarriers-Based siRNA Delivery for Cancer Therapy

Different therapeutic practices for treating cancers have significantly evolved to compensate and/or overcome the failures in conventional methodologies. The demonstrated potentiality in completely inhibiting the tumors and in preventing cancer relapse has made nucleic acids therapy (NAT)/gene therapy as an attractive practice. This has been made possible because NAT-based cancer treatments are highly focused on the fundamental mechanisms - i.e., silencing the expression of oncogenic genes responsible for producing abnormal proteins (via messenger RNAs (mRNAs)). However, the future clinical translation of NAT is majorly dependent upon the effective delivery of the exogenous nucleic acids (especially RNAs - e.g., short interfering RNAs (siRNAs) - herein called biological drugs). Moreover, nano-based vehicles (i.e., nanocarriers) are involved in delivering them to prevent degradation and undesired bioaccumulation while enhancing the stability of siRNAs. Herein, we have initially discussed about three major types of self-assembling nanocarriers (liposomes, polymeric nanoparticles and exosomes). Later, we have majorly reviewed recent developments in non-targeted/targeted nanocarriers for delivery of biological drugs (individual/dual) to silence the most important genes/mRNAs accountable for inducing protein abnormality. These proteins include polo-like kinase 1 (PLK1), survivin, vascular endothelial growth factor (VEGF), B-cell lymphoma/leukaemia-2 (Bcl-2) and multi-drug resistance (MDR). Besides, the consequent therapeutic effects on cancer growth, invasion and/or metastasis have also been discussed. Finally, we have comprehensively reviewed the improvements achieved in the cutting-edge cancer therapeutics while delivering siRNAs in combination with clinically approved chemotherapeutic drugs.

Advances in nanotechnology-based platforms for survivin-targeted drug discovery

INTRODUCTION

Due to its unique functional impact on multiple cancer cell circuits including proliferation, apoptosis, tumor dissemination, DNA damage repair and immune response, the inhibitor of apoptosis protein (IAP) survivin has gained high interest as a molecular target and a multitude of therapeutics were developed to interfere with survivin expression and functionality. First clinical evaluations of these therapeutics, however, were disappointing highlighting the need to develop advanced delivery systems of survivin-targeting molecules to increase stability, bioavailability as well as the selective guidance to tumor tissue.

AREAS COVERED

: This review focuses on advancements in nanocarriers to molecularly target survivin in human malignancies. A plethora of nanoparticle platforms, including liposomes, polymeric systems, dendrimers, inorganic nanocarriers, RNA/DNA nanotechnology and exosomes are discussed in the background of survivin-tailored RNA interference, small molecule inhibitors, dominant negative mutants or survivin vaccination or combined modality treatment with chemotherapeutic drugs and photo- dynamic/photothermal strategies.

EXPERT OPINION

Novel therapeutic approaches include the use of biocompatible nanoformulations carrying gene silencing or drug molecules to directly or indirectly target proteins, allow for a more precise and controlled delivery of survivin therapeutics. Moreover, surface modification of these nanocarriers may result in a tumor entity specific delivery. Therefore, nanomedicine exploiting survivin-tailored strategies in a multimodal background is considered the way forwaerd to enhance the development of future personalized medicine.

Advances in Nanoparticles for Effective Delivery of RNA Therapeutics

RNA therapeutics, including messenger RNA (mRNA) and small interfering RNA (siRNA), are genetic materials that mediate the translation of genetic direction from genes to induce or inhibit specific protein production. Although the interest in RNA therapeutics is rising globally, the absence of an effective delivery system is an obstacle to the clinical application of RNA therapeutics. Additionally, immunogenicity, short duration of protein expression, unwanted enzymatic degradation, and insufficient cellular uptake could limit the therapeutic efficacy of RNA therapeutics. In this regard, novel platforms based on nanoparticles are crucial for delivering RNAs to the targeted site to increase efficiency without toxicity. In this review, the most recent status of nanoparticles as RNA delivery vectors, with a focus on polymeric nanoparticles, peptide-derived nanoparticles, inorganic nanoparticles, and hybrid nanoparticles, is discussed. These nanoparticular platforms can be utilized for safe and effective RNA delivery to augment therapeutic effects. Ultimately, RNA therapeutics encapsulated in nanoparticle-based carriers will be used to treat many diseases and save lives.

Unmodified and tyrosine-modified polyethylenimines as potential carriers for siRNA: Biophysical characterization and toxicity

Polyethylenimines (PEIs) are being explored as efficient non-viral nanocarriers for nucleic acid delivery in vitro and in vivo. To address limitations regarding PEI efficacy and biocompatibility, modifications of the chemical structure of linear and branched PEIs have been introduced, including grafting with tyrosine. The aim has been to compare linear and branched polyethylenimines of a wider range of different molecular mass with their tyrosine-modified derivatives. To do so, physico-chemical and biological properties of the polymers were investigated. Even in the absence of a negatively charged nucleic acid counterpart, PEIs form particle structures with defined size and surface potential. Tyrosine modification of PEI led to significantly reduced toxicity, while simultaneously increasing interaction with cellular membranes. All the effects were also dependent on the PEI molecular weight and structure (i.e., linear vs. branched). Especially in the case of linear PEIs, the improved membrane interaction also translated into slightly enhanced hemolysis, whereas their genotoxic potential was essentially abolished. Due to the improvement of properties critical for nano-vector efficacy and biocompatibility, our data demonstrate that tyrosine-modified PEIs are very promising and safe nanocarriers for the delivery of small RNAs, like siRNAs and miRNAs.

Non-viral siRNA transfection of primary mesenchymal stromal cells (MSCs): Assessment of tyrosine-modified PEI and PPI efficacy and biocompatibility

Mesenchymal stromal cells (MSCs) are multipotent cells derived from different sources and able to differentiate into distinct cell lineages. For their possible biomedical application, the "tuning" of MSCs also involves the specific knockdown of defined target genes. A major limitation, however, is the notoriously low transfection efficacy especially of primary MSCs. In this paper, we systemically analyze a large set of tyrosine-modified linear or branched low molecular weight polyethylenimines (PEIs) of different sizes, as well as the tyrosine-modified polypropylenimine dendrimer PPI-G4, for their capacity of non-viral siRNA transfection into umbilical cord-derived MSCs from two different donors. Knockdown efficacies are determined on the molecular level and confirmed in functional assays. Beyond the determination of cell viabilities, acute cytotoxicity, induction of apoptosis/necrosis and mitochondrial membrane alterations are also studied. On the molecular level, caspase activation, ROS induction and genotoxic effects are analyzed. Major differences are observed between the various tyrosine-modified PEIs, with some candidates showing high knockdown efficacy and biocompatibility. PPI-G4-Y dendrimers, however, are identified as most efficient for siRNA transfection into MSCs. PPI-G4-Y/siRNA nanoparticles lead to particularly high gene knockdown, without cytotoxic and genotoxic effects on the cellular and molecular level, and are thus particularly well-suited for the tuning of MSCs.

Phenylboronic Acid-Modified Polyamidoamine Mediated the Transfection of Polo-Like Kinase-1 siRNA to Achieve an Anti-Tumor Efficacy

Background

The construction of tumor-targeting carriers with favorable transfection efficiency was of great significance to achieve the tumor gene therapy. The phenylboronic acid-modified polyamidoamine (namely PP) was employed as a carrier for the delivery of Polo-like kinase-1 siRNA (siPlk-1), inducing an obvious anti-tumor response.

Materials and Methods

The interaction between PP and siPlk-1 was evaluated by gel retardation assay. The transfection efficiency and tumor-targeting ability were analyzed by flow cytometry and confocal laser scanning microscopy, using hepatocarcinoma cell line HepG2 as a model. The anti-proliferation effect of PP/siPlk-1 and related mechanism were studied using the strategies of 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, cell apoptosis and cell cycle arrest. The anti-migration effect induced by PP/siPlk-1 delivery was assayed by wound healing and Transwell migration techniques. Finally, quantitative real-time PCR and Western blotting were performed to measure the expression level of Plk-1 and other key targets.

Results

The derivative PP could achieve the condensation of siPlk-1 into stable nanoparticles at nitrogen/phosphate groups ratio (N/P ratio) of >3.0, and it could facilitate the transfection of siPk-1 in a phenylboronic acid-dependent manner. The PP/siPlk-1 nanoparticles exhibited obvious anti-proliferation effect owing to the gene silence of Plk-1, which was identified to be associated with the cell apoptosis and cell cycle arrest at G2 phase. Meanwhile, PP/siPlk-1 transfection could efficiently suppress the migration and invasion of tumor cells.

Conclusion

The derivative PP has been demonstrated to be an ideal tumor-targeting carrier for the delivery of Plk-1 siRNA, exhibiting great potential in the gene therapy of malignant tumors.

Tyrosine-modified linear PEIs for highly efficacious and biocompatible siRNA delivery in vitro and in vivo

Therapeutic gene silencing by RNA interference relies on the safe and efficient in vivo delivery of small interfering RNAs (siRNAs). Polyethylenimines are among the most studied cationic polymers for gene delivery. For several reasons including superior tolerability, small linear PEIs would be preferable over branched PEIs, but they show poor siRNA complexation. Their chemical modification for siRNA formulation has not been extensively explored so far. We generated a set of small linear PEIs bearing tyrosine modifications (LPxY), leading to substantially enhanced siRNA delivery and knockdown efficacy in vitro in various cell lines, including hard-to-transfect cells. The tyrosine-modified linear 10 kDa PEI (LP10Y) is particularly powerful, associated with favorable physicochemical properties and very high biocompatibility. Systemically administered LP10Y/siRNA complexes reveal antitumor effects in mouse xenograft and patient-derived xenograft (PDX) models, and their direct application into the brain achieves therapeutic inhibition of orthotopic glioma xenografts. LP10Y is particularly interesting for therapeutic siRNA delivery.

The combined disulfide cross-linking and tyrosine-modification of very low molecular weight linear PEI synergistically enhances transfection efficacies and improves biocompatibility

Efficient and non-toxic DNA delivery is still a major limiting factor for non-viral gene therapy. Among the large diversity of non-viral vectors, the cationic polymer polyethylenimine (PEI) plays a prominent role in nucleic acid delivery. Since higher molecular weight of PEI is beneficial for transfection efficacy, but also leads to higher cytotoxicity, the biodegradable cross-linking of low-molecular PEIs, e.g. through disulfide-groups, has been introduced. Another promising strategy is the chemical modification of PEI, for example with amino acids like tyrosine. In the case of small RNA molecules, this PEI grafting has been found to enhance transfection efficacies and improve biocompatibility. In this paper, we report on the combination of these two strategies for improving DNA delivery: the (i) cross-linking of very small 2 kDa PEI ("P2") molecules through biodegradable disulfide-groups ("SS"), in combination with (ii) tyrosine-modification ("Y"). We demonstrate a surprisingly substantial, synergistic enhancement of transfection efficacies of these SSP2Y/DNA complexes over their non- or mono-modified polymer counterparts, accompanied by high biocompatibility as well as favorable physicochemical and biological properties. Beyond various cell lines, high biological activity of the SSP2Y-based complexes is also seen in an ex vivo tissue slice model, more closely mimicking in vivo conditions. The particularly high transfection efficacy SSP2Y/DNA complexes in 2D and 3D models, based on their optimized complex stability and DNA release, as well as their high biocompatibility thus provides the basis for their further exploration for therapeutic application.

The Role of Formamidine Groups in Dextran Based Nonviral Vectors for Gene Delivery on Their Physicochemical and Biological Characteristics

Dextran-formamidine esters (dextran-N-[(dimethylamino)methylene]-β-alanine ester) with different degrees of substitution (0.45-0.92) are synthesized in an one-pot reaction. Dextran (Mw 60 000 g mol^-1 ) is allowed to react with unprotected beta-alanine and iminium chloride and investigated regarding the potential as gene delivery system for the transfer of plasmid DNA. With degrees of substitution ≥ 0.63 improved DNA binding with formation of enzymatically stable complexes of about 130-160 nm with negative surface charges are obtained. These physicochemical characteristics correlated with increasing transfection rates in CHO-K1 cells determined by a luciferase reporter gene assay in dependency of the number of formamidine residues, N/P ratios and amount of DNA. The role of the number of formamidine groups is also highlighted by in vitro cyto- and hemotoxicity tests under the chosen conditions. These results indicate that dextran-formamidine esters are a very promising material for the safe and efficient gene delivery.

Tyrosine-Modification of Polypropylenimine (PPI) and Polyethylenimine (PEI) Strongly Improves Efficacy of siRNA-Mediated Gene Knockdown

The delivery of small interfering RNAs (siRNA) is an efficient method for gene silencing through the induction of RNA interference (RNAi). It critically relies, however, on efficient vehicles for siRNA formulation, for transfection in vitro as well as for their potential use in vivo. While polyethylenimines (PEIs) are among the most studied cationic polymers for nucleic acid delivery including small RNA molecules, polypropylenimines (PPIs) have been explored to a lesser extent. Previous studies have shown the benefit of the modification of small PEIs by tyrosine grafting which are featured in this paper. Additionally, we have now extended this approach towards PPIs, presenting tyrosine-modified PPIs (named PPI-Y) for the first time. In this study, we describe the marked improvement of PPI upon its tyrosine modification, leading to enhanced siRNA complexation, complex stability, siRNA delivery, knockdown efficacy and biocompatibility. Results of PPI-Y/siRNA complexes are also compared with data based on tyrosine-modified linear or branched PEIs (LPxY or PxY). Taken together, this establishes tyrosine-modified PPIs or PEIs as particularly promising polymeric systems for siRNA formulation and delivery.

Synthetic circular miR-21 RNA decoys enhance tumor suppressor expression and impair tumor growth in mice

Naturally occurring circular RNAs efficiently impair miRNA functions. Synthetic circular RNAs may thus serve as potent agents for miRNA inhibition. Their therapeutic effect critically relies on (i) the identification of optimal miRNA targets, (ii) the optimization of decoy structures and (iii) the development of efficient formulations for their use as drugs. In this study, we extensively explored the functional relevance of miR-21-5p in cancer cells. Analyses of cancer transcriptomes reveal that miR-21-5p is the by far most abundant miRNA in human cancers. Deletion of the MIR21 locus in cancer-derived cells identifies several direct and indirect miR-21-5p targets, including major tumor suppressors with prognostic value across cancers. To impair miR-21-5p activities, we evaluate synthetic, circular RNA decoys containing four repetitive binding elements. In cancer cells, these decoys efficiently elevate tumor suppressor expression and impair tumor cell vitality. For their in vivo delivery, we for the first time evaluate the formulation of decoys in polyethylenimine (PEI)-based nanoparticles. We demonstrate that PEI/decoy nanoparticles lead to a significant inhibition of tumor growth in a lung adenocarcinoma xenograft mouse model via the upregulation of tumor suppressor expression. These findings introduce nanoparticle-delivered circular miRNA decoys as a powerful potential therapeutic strategy in cancer treatment.