Chemical vectors for gene delivery: a current review on polymers, peptides and lipids containing histidine or imidazole as nucleic acids carriers

Lipophosphoramidate-based bipolar amphiphiles: their syntheses and transfection properties

A series of cationic bipolar amphiphiles were readily prepared by thiol–ene click reaction. These compounds were formulated in liposomal solutions and assessed as vector for gene delivery.

Nanoparticles as transfection agents: a comprehensive study with ten different cell lines

The performance of transfection agents to deliver nucleic acids into cells strongly depends on the cell type.

Synthesis, characterization and evaluation of diglycidyl-1,2-cyclohexanedicarboxylate crosslinked polyethylenimine nanoparticles as efficient carriers of DNA

Crosslinked PEI nanoparticles were synthesized, which efficiently transported DNA inside the cells with minimal cytotoxicity.

Evaluation of the transfection efficacies of quaternary ammonium salts prepared from sophorolipids

Two quaternary ammonium sophorolipids proved to be suitable as transfection vectors for gene delivery.

Evaluation of New Fluorescent Lipophosphoramidates for Gene Transfer and Biodistribution Studies after Systemic Administration

The objective of lung gene therapy is to reach the respiratory epithelial cells in order to deliver a functional nucleic acid sequence. To improve the synthetic carrier's efficacy, knowledge of their biodistribution and elimination pathways, as well as cellular barriers faced, depending on the administration route, is necessary. Indeed, the in vivo fate guides the adaptation of their chemical structure and formulation to increase their transfection capacity while maintaining their tolerance. With this goal, lipidic fluorescent probes were synthesized and formulated with cationic lipophosphoramidate KLN47 (KLN: Karine Le Ny). We found that such formulations present constant compaction properties and similar transfection results without inducing additional cytotoxicity. Next, biodistribution profiles of pegylated and unpegylated lipoplexes were compared after systemic injection in mice. Pegylation of complexes led to a prolonged circulation in the bloodstream, whereas their in vivo bioluminescent expression profiles were similar. Moreover, systemic administration of pegylated lipoplexes resulted in a transient liver toxicity. These results indicate that these new fluorescent compounds could be added into lipoplexes in small amounts without perturbing the transfection capacities of the formulations. Such additional properties allow exploration of the in vivo biodistribution profiles of synthetic carriers as well as the expression intensity of the reporter gene.

Polymeric oncolytic adenovirus for cancer gene therapy

Oncolytic adenovirus (Ad) vectors present a promising modality to treat cancer. Many clinical trials have been done with either naked oncolytic Ad or combination with chemotherapies. However, the systemic injection of oncolytic Ad in clinical applications is restricted due to significant liver toxicity and immunogenicity. To overcome these issues, Ad has been engineered physically or chemically with numerous polymers for shielding the Ad surface, accomplishing extended blood circulation time and reduced immunogenicity as well as hepatotoxicity. In this review, we describe and classify the characteristics of polymer modified oncolytic Ad following each strategy for cancer treatment. Furthermore, this review concludes with the highlights of various polymer-coated Ads and their prospects, and directions for future research.

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.

Cyclodextrin- and calixarene-based polycationic amphiphiles as gene delivery systems: a structure-activity relationship study

Multi-head/multi-tail facial amphiphiles built on cyclodextrin (CD) and calixarene (CA) scaffolds are paradigmatic examples of monodisperse gene delivery systems. The possibility to precisely control the architectural features at the molecular level offers unprecedented opportunities for conducting structure-activity relationship studies. A major requirement for those channels is the design of a sufficiently diverse ensemble of compounds for parallel evaluation of their capabilities to condense DNA into transfection nanoparticles where the gene material is protected from the environment. Here we have undertaken the preparation of an oriented library of β-cyclodextrin (βCD) and calix[4]arene (CA4) vectors with facial amphiphilic character designed to ascertain the effect of the cationic head nature (aminothiourea-, arginine- or guanidine-type groups) and the macrocyclic platform on the abilities to complex plasmid DNA (pDNA) and in the efficiency of the resulting nanocomplexes to transfect cells in vitro. The hydrophobic domain, formed by hexanoyl or hexyl chains, remains constant in each series, matching the overall structure found to be optimal in previous studies. DLS, TEM and AFM data support that all the compounds self-assemble in the presence of pDNA through a process that involves initially electrostatic interactions followed by formation of βCD or CA4 bilayers between the oligonucleotide filaments. Spherical transfectious nanoparticles that are monomolecular in DNA are thus obtained. Evaluation in epithelial COS-7 and human rhabdomyosarcoma RD-4 cells evidenced the importance of having primary amino groups in the vector to warrant high levels of transfection, probably because of their buffering capacity. The results indicate that the optimal cationic head depends on the macrocyclic core, aminothiourea groups being preferred in the βCD series and arginine groups in the CA4 series. Whereas the transfection efficiency relationships remain essentially unchanged within each series, irrespective of the cell type, the optimal platform (βD or CA4) strongly depends on the cell type. The results illustrate the potential of monodisperse vector prototypes and diversity-oriented strategies on identifying the optimal candidates for gene therapy applications.

Screening for Methylated Poly(l-histidine) with Various Dimethylimidazolium/Methylimidazole/Imidazole Contents as DNA Carrier

Methylated poly(l-histidine) (PLH-Me), our original polypeptide, has controlled the contents of dimethylimidazolium, τ/π-methylimidazole and imidazole groups for efficient gene delivery. The screening for the PLH-Me as DNA carrier has been carried out by use of the PLH with 25 mol% (τ-methyl, 16 mol%; π-methyl, 17 mol%; deprotonated imidazole, 41 mol%), 68 mol% (τ-methyl, 16 mol%; π-methyl, 8 mol%; deprotonated imidazole, 8 mol%) and 87 mol% (τ-methyl, 7 mol%; π-methyl, 4 mol%; deprotonated imidazole, 2 mol%) dimethylimidazolium groups, that is, PLH-Me(25), PLH-Me(68) and PLH-Me(87), respectively. The screening of the chemical structure of PLH-Me has been carried out for DNA carrier properties, which are the stability of its DNA polyion complexes and gene expression. The DNA complexes with the 25 mol% and 68 mol% dimethylated PLH-Me possessed almost same ability to retain DNA, as compared with the 87 mol% dimethylated PLH-Me, which was examined by competitive exchange with dextran sulfate. From the gene transfection experiment against HepG2 cells, human hepatoma cell line, the PLH-Me(25)/DNA complex was revealed to mediate highest gene expression. These results suggest that the dimethyl-imidazolium/methylimidazole/imidazole balance of the PLH-Me is important for DNA carrier design.

Synthesis of oligodiaminomannoses and analysis of their RNA duplex binding properties and their potential application as siRNA-based drugs

The synthesis of artificial cationic oligodiaminosaccharides, α-(1 → 4)-linked-2,6-diamino-2,6-dideoxy-d-mannopyranose oligomers (ODAMans), and their interactions with RNA duplexes are described. The monomer through the pentamer, all of which bear unnatural 2,6-diaminomannose moieties, were successfully prepared. UV melting and fluorescence anisotropy analyses revealed that the ODAMans bound and thermodynamically stabilized both 12mer RNA duplexes and an siRNA. Furthermore, it was clearly shown that the siRNA acquired substantial RNase A resistance due to its binding to the ODAMan 4mer.

A cell-penetrating foldamer with a bioreducible linkage for intracellular delivery of DNA

Despite significant advances in foldamer chemistry, tailored delivery systems based on foldamer architectures, which provide a high level of control over secondary structure, are curiously rare among non-viral technologies for transporting nucleic acids into cells. A potent pH-responsive, bioreducible cell-penetrating foldamer (CPF) was developed through covalent dimerization of a short (8-mer) amphipathic oligourea sequence bearing histidine-type units. This CPF exhibits a high capacity to assemble with pDNA and mediates efficient delivery of nucleic acids into the cell. Furthermore, it does not adversely affect cellular viability and was shown to compare favorably with a cognate peptide transfection agent based on His-rich sequences.

Heterocyclic amine-modified polyethylenimine as gene carriers for transfection of mammalian cells

Branched polyethylenimine (PEI) is extensively used as a polycationic non-viral vector for gene delivery. Polyplexes formed with PEI are believed to be released from endocytotic vesicles by the osmotic burst mechanism in the rate-limiting step in transfection. Increasing the buffering capacity of PEI derivatives in the endosomal pH range of 4.5-7.5 should enhance transfection efficiency. In this study, PEI was derivatized by covalently attaching heterocyclic amine moieties (piperazine, pyridine and imidazole rings with pKa values from 5.23 to 6.04) through amide bonds. PEI derivatives with 50% of the primary amines on PEI exhibited increased buffering capacity, increased transfection activity and decreased cytotoxicity in murine neuroblastoma (Neuro-2a) cells. The relative effectiveness in enhancing transfection efficiency was piperazine>pyridine>histidine, but each type of amine was the most effective under a particular set of conditions. Modified vectors could significantly improve transfection efficiency in murine mesenchymal stem cells. PEI25 derivatized at 50% with histidine administered as polyplexes in the tail veins of mice resulted in remarkably enhanced luciferase gene expression in the expected organ distribution and much lower toxicity than underivatized PEI25.

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.

Delivery of therapeutic oligonucleotides with cell penetrating peptides

Oligonucleotide-based drugs have received considerable attention for their capacity to modulate gene expression very specifically and as a consequence they have found applications in the treatment of many human acquired or genetic diseases. Clinical translation has been often hampered by poor biodistribution, however. Cell-penetrating peptides (CPPs) appear as a possibility to increase the cellular delivery of non-permeant biomolecules such as nucleic acids. This review focuses on CPP-delivery of several classes of oligonucleotides (ONs), namely antisense oligonucleotides, splice switching oligonucleotides (SSOs) and siRNAs. Two main strategies have been used to transport ONs with CPPs: covalent conjugation (which is more appropriate for charge-neutral ON analogues) and non-covalent complexation (which has been used for siRNA delivery essentially). Chemical synthesis, mechanisms of cellular internalization and various applications will be reviewed. A comprehensive coverage of the enormous amount of published data was not possible. Instead, emphasis has been put on strategies that have proven to be effective in animal models of important human diseases and on examples taken from the authors' own expertise.

Multivalent dendritic polyglycerolamine with arginine and histidine end groups for efficient siRNA transfection

The success of siRNA-based therapeutics highly depends on a safe and efficient delivery of siRNA into the cytosol. In this study, we post-modified the primary amines on dendritic polyglycerolamine (dPG-NH2) with different ratios of two relevant amino acids, namely, arginine (Arg) and histidine (His). To investigate the effects from introducing Arg and His to dPG, the resulting polyplexes of amino acid functionalized dPG-NH2s (AAdPGs)/siRNA were evaluated regarding cytotoxicity, transfection efficiency, and cellular uptake. Among AAdPGs, an optimal vector with (1:3) Arg to His ratio, showed efficient siRNA transfection with minimal cytotoxicity (cell viability ≥ 90%) in NIH 3T3 cells line. We also demonstrated that the cytotoxicity of dPG-NH2 decreased as a result of amino acid functionalization. While the incorporation of both cationic (Arg) and pH-responsive residues (His) are important for safe and efficient siRNA transfection, this study indicates that AAdPGs containing higher degrees of His display lower cytotoxicity and more efficient endosomal escape.

Histidine-rich stabilized polyplexes for cMet-directed tumor-targeted gene transfer

Overexpression of the hepatocyte growth factor receptor/c-Met proto oncogene on the surface of a variety of tumor cells gives an opportunity to specifically target cancerous tissues. Herein, we report the first use of c-Met as receptor for non-viral tumor-targeted gene delivery. Sequence-defined oligomers comprising the c-Met binding peptide ligand cMBP2 for targeting, a monodisperse polyethylene glycol (PEG) for polyplex surface shielding, and various cationic (oligoethanamino) amide cores containing terminal cysteines for redox-sensitive polyplex stabilization, were assembled by solid-phase supported syntheses. The resulting oligomers exhibited a greatly enhanced cellular uptake and gene transfer over non-targeted control sequences, confirming the efficacy and target-specificity of the formed polyplexes. Implementation of endosomal escape-promoting histidines in the cationic core was required for gene expression without additional endosomolytic agent. The histidine-enriched polyplexes demonstrated stability in serum as well as receptor-specific gene transfer in vivo upon intratumoral injection. The co-formulation with an analogous PEG-free cationic oligomer led to a further compaction of pDNA polyplexes with an obvious change of shape as demonstrated by transmission electron microscopy. Such compaction was critically required for efficient intravenous gene delivery which resulted in greatly enhanced, cMBP2 ligand-dependent gene expression in the distant tumor.

High-throughput screening identifies small molecules that enhance the pharmacological effects of oligonucleotides

The therapeutic use of antisense and siRNA oligonucleotides has been constrained by the limited ability of these membrane-impermeable molecules to reach their intracellular sites of action. We sought to address this problem using small organic molecules to enhance the effects of oligonucleotides by modulating their intracellular trafficking and release from endosomes. A high-throughput screen of multiple small molecule libraries yielded several hits that markedly potentiated the actions of splice switching oligonucleotides in cell culture. These compounds also enhanced the effects of antisense and siRNA oligonucleotides. The hit compounds preferentially caused release of fluorescent oligonucleotides from late endosomes rather than other intracellular compartments. Studies in a transgenic mouse model indicated that these compounds could enhance the in vivo effects of a splice-switching oligonucleotide without causing significant toxicity. These observations suggest that selected small molecule enhancers may eventually be of value in oligonucleotide-based therapeutics.

Miniaturization of gene transfection assays in 384- and 1536-well microplates

The miniaturization of gene transfer assays to either 384- or 1536-well plates greatly economizes the expense and allows much higher throughput when transfecting immortalized and primary cells compared with more conventional 96-well assays. To validate the approach, luciferase and green fluorescent protein (GFP) reporter gene transfer assays were developed to determine the influence of cell seeding number, transfection reagent to DNA ratios, transfection time, DNA dose, and luciferin dose on linearity and sensitivity. HepG2, CHO, and NIH 3T3 cells were transfected with polyethylenimine (PEI)-DNA in both 384- and 1536-well plates. The results established optimal transfection parameters in 384-well plates in a total assay volume of 35μl and in 1536-well plates in a total assay volume of 8μl. A luciferase assay performed in 384-well plates produced a Z' score of 0.53, making it acceptable for high-throughput screening. Primary hepatocytes were harvested from mouse liver and transfected with PEI DNA and calcium phosphate DNA nanoparticles in 384-well plates. Optimal transfection of primary hepatocytes was achieved on as few as 250cellsperwell in 384-well plates, with CaPO4 proving to be 10-fold more potent than PEI.

Efficient single-cell poration by microsecond laser pulses

Payloads including FITC-Dextran dye and plasmids were delivered into NIH/3T3 fibroblasts using microbubbles produced by microsecond laser pulses to induce pores in the cell membranes. Two different operational modes were used to achieve molecular delivery. Smaller molecules, such as the FITC-Dextran dye, were delivered via a scanning-laser mode. The poration efficiency and the cell viability were both 95.1 ± 3.0%. Relatively larger GFP plasmids can be delivered efficiently via a fixed-laser mode, which is a more vigorous method that can create larger transient pores in the cell membrane. The transfection efficiency of 5.7 kb GFP plasmid DNA can reach to 86.7 ± 3.3%. Using this cell poration system, targeted single cells can be porated with high resolution, and cells can be porated in arbitrary patterns.

Bioreducible polyethylenimine nanoparticles for the efficient delivery of nucleic acids

Electrostatically crosslinked bioreducible nanoparticles of polyethylenimine (DP NPs) have been prepared and evaluated for their cytotoxicity and capability to transport nucleic acids inside the cells.

Cationic lipid-mediated delivery of proteins enables efficient protein-based genome editing in vitro and in vivo

Efficient intracellular delivery of proteins is needed to fully realize the potential of protein therapeutics. Current methods of protein delivery commonly suffer from low tolerance for serum, poor endosomal escape and limited in vivo efficacy. Here we report that common cationic lipid nucleic acid transfection reagents can potently deliver proteins that are fused to negatively supercharged proteins, that contain natural anionic domains or that natively bind to anionic nucleic acids. This approach mediates the potent delivery of nM concentrations of Cre recombinase, TALE- and Cas9-based transcription activators, and Cas9:sgRNA nuclease complexes into cultured human cells in media containing 10% serum. Delivery of unmodified Cas9:sgRNA complexes resulted in up to 80% genome modification with substantially higher specificity compared to DNA transfection. This approach also mediated efficient delivery of Cre recombinase and Cas9:sgRNA complexes into the mouse inner ear in vivo, achieving 90% Cre-mediated recombination and 20% Cas9-mediated genome modification in hair cells.

I2-catalyzed synthesis of substituted imidazoles from vinyl azides and benzylamines

A novel and efficient I₂-catalyzed oxidative tandem cyclization of simple vinyl azides and benzylamines has been developed for the synthesis of substituted imidazoles.

Non viral vectors in gene therapy- an overview

Non-viral vectors are simple in theory but complex in practice. Apart from intra cellular and extracellular barriers, number of other challenges also needs to be overcome in order to increase the effectiveness of non-viral gene transfer. These barriers are categorized as production, formulation and storage. No one-size-fits-all solution to gene delivery, which is why in spite of various developments in liposome, polymer formulation and optimization, new compounds are constantly being proposed and investigated. In this review, we will see in detail about various types of non-viral vectors highlighting promising development and recent advances that had improved the non-viral gene transfer efficiency of translating from "Bench to bedside".

In vitro and in vivo gene transfection using biodegradable and low cytotoxic nanomicelles based on dendritic block copolymers

Dendritic PCL-b-PDMAEMA copolymers have been used as non-viral vectors for gene transfection and exhibited high transfection efficiencies and low cytotoxicity.

A novel collagen-nanohydroxyapatite microRNA-activated scaffold for tissue engineering applications capable of efficient delivery of both miR-mimics and antagomiRs to human mesenchymal stem cells

Manipulation of gene expression through the use of microRNAs (miRNAs) offers tremendous potential for the field of tissue engineering. However, the lack of sufficient site-specific and bioactive delivery systems has severely hampered the clinical translation of miRNA-based therapies. In this study, we developed a novel non-viral bioactive delivery platform for miRNA mimics and antagomiRs to allow for a vast range of therapeutic applications. By combining nanohydroxyapatite (nHA) particles with reporter miRNAs (nanomiRs) and collagen-nanohydroxyapatite scaffolds, this work introduces the first non-viral, non-lipid platform to date, capable of efficient delivery of mature miRNA molecules to human mesenchymal stem cells (hMSCs), a particularly difficult cell type to transfect effectively, with minimal treatment-associated cytotoxicity. Firstly, miRNAs were successfully delivered to hMSCs in monolayer, with internalisation efficiencies of 17.4 and 39.6% for nanomiR-mimics and nanoantagomiRs respectively, and both nanomiR-mimics and nanoantagomiRs yielded sustained interfering activity of greater than 90% in monolayer over 7 days. When applied to 3D scaffolds, significant RNA interference of 20% for nanomiR-mimics and 88.4% for nanoantagomiRs was achieved with no cytotoxicity issues over a 7 day period. In summary, in-house synthesised non-viral nHA particles efficiently delivered reporter miRNAs both in monolayer and on scaffolds demonstrating the immense potential of this innovative miRNA-activated scaffold system for tissue engineering applications.

Lipid-based mRNA vaccine delivery systems

Synthetic mRNAs can become biopharmaceutics allowing vaccination against cancer, bacterial and virus infections. Clinical trials with direct administration of synthetic mRNAs encoding tumor antigens demonstrated safety and induction of tumor-specific immune responses. Although immune responses are generated by naked mRNAs, their formulations with chemical carriers are expected to provide more specificity and internalization in dendritic cells (DCs) for better immune responses and dose reduction. This review reports lipid-based formulations (LBFs) that have proved preclinical efficacy. The selective delivery of mRNA LBFs to favor intracellular accumulation in DCs and reduction of the effective doses is discussed, notably to decorate LBFs with carbohydrates or glycomimetics allowing endocytosis in DCs. We also report how smart intracellular delivery is achieved using pH-sensitive lipids or polymers for an efficient mRNA escape from endosomes and limitations regarding cytosolic mRNA location for translation.

Exploring advantages/disadvantages and improvements in overcoming gene delivery barriers of amino acid modified trimethylated chitosan

PURPOSE

Present study aimed at exploring advantages/disadvantages of amino acid modified trimethylated chitosan in conquering multiple gene delivery obstacles and thus providing comprehensive understandings for improved transfection efficiency.

METHODS

Arginine, cysteine, and histidine modified trimethyl chitosan were synthesized and employed to self-assemble with plasmid DNA (pDNA) to form nanocomplexes, namely TRNC, TCNC, and THNC, respectively. They were assessed by structural stability, cellular uptake, endosomal escape, release behavior, nuclear localization, and in vitro and in vivo transfection efficiencies. Besides, sodium tripolyphosphate (TPP) was added into TRNC to compromise certain disadvantageous attributes for pDNA delivery.

RESULTS

Optimal endosomal escape ability failed to bring in satisfactory transfection efficiency of THNC due to drawbacks in structural stability, cellular uptake, pDNA liberation, and nuclear distribution. TCNC evoked the most potent gene expression owing to multiple advantages including sufficient stability, preferable uptake, efficient pDNA release, and high nucleic accumulation. Undesirable stability and insufficient pDNA release adversely affected TRNC-mediated gene transfer. However, incorporation of TPP could improve such disadvantages and consequently resulted in enhanced transfection efficiencies.

CONCLUSIONS

Coordination of multiple contributing effects to conquer all delivery obstacles was necessitated for improved transfection efficiency, which would provide insights into rational design of gene delivery vehicles.

[Development of artificial nucleic acids functionalized for damaged gene diagnosis, gene inhibition and delivery system]

Artificial nucleic acids have recently been widely used with their properties optimized for various technologies such as the inhibition of gene expression (antisense/antigene strategies, RNA interference) and genetic diagnosis (single nucleotide polymorphism (SNP), damaged nucleobase). For practical application of nucleic acid therapeutics, establishment of an effective delivery system for oligonucleotides is also required because of their poor permeability into cells. Various useful delivery technologies including lipoplexes formed using cationic lipids and polyplexes made with cationic polymers have been developed; however, there is no crucial tool for oligonucleotide therapeutics at present. If technologies of functional nucleic acids and adequate delivery systems are cooperatively developed, the realization of nucleic acid therapeutics might be effectively accelerated. Based on this concept, we have been cooperatively developing these technologies based on organic synthetic chemistry during the past decade. This paper summarizes our recent results: 1) development of a specific fluorescent probe for 8-oxoguanine; 2) synthesis and evaluation of a prodrug-type small interfering RNA (siRNA) molecule; and 3) targeted intracellular delivery of oligonucleotides via conjugation with receptor-targeted ligands.

Gene delivery efficiency and intracellular trafficking of novel poly(allylamine) derivatives

Non-viral gene carriers for safe and efficient gene transfection have become of particular interest among researchers of different disciplines ranging from physical chemistry to biotechnology. Recently polymeric vectors have been extensively studied as potentially new gene transfer agents. Until now most of the research efforts were made to optimize the gene-to-polymer weight ratio of polyplexes for safe and efficient gene transfection. In this work, we report on the development of novel poly(allylamine) derivatives with different balance of the primary, secondary, tertiary, and quaternary amino groups. All derivatives were able to complex pDNA into polyplexes at low gene-to-polymer weight ratios i.e., 1:1 or 1:2. Moreover, the examined polyplexes were less cytotoxic and showed better transfection efficiency when compared to linear poly(ethyleneimine). These results indicate that the presence of quaternary ammonium groups is important in the formation of stable polyplexes. Polymers with all types of amino groups showed large potential for gene delivery. Furthermore, polyplexes with such derivatives were well internalized by cells and ended up into acidic late endosomes.

Fine tuning of mixed ionic and hydrogen bond interactions for plasmid delivery using lipoplexes

Non viral gene transfection has been mostly reached via cationic polymer and lipid, required for DNA complexation and cell internalisation. However, cationic charges often induce cytotoxicity and limit the efficacy of the lipoplexes in vivo due to their fast elimination from the blood stream. Few years ago, we had developed noncationic lipid interacting with DNA via hydrogen bond interactions. To take advantage of both the internalisation efficacy of cationic complexes and the higher DNA release efficacy of non cationic lipids, we chose to mix both ionic and hydrogen bond interactions within one lipoplex. The idea behind this strategy would be to reduce the overall charge while maintaining a high level of transfection. Four mixed formulations of cationic lipid and thiourea lipid were prepared. We found that decreasing ionic interactions and increasing hydrogen bond interactions improved cationic lipoplexes properties. Indeed, we showed that replacement of net positive charges by hydrogen bond interactions with DNA phosphates led to efficient lipoplexes for in vitro DNA transfection at lower cationic charge content, which consequently reduced lipoplex cytotoxicity.

Parallel synthesis of cell-penetrating peptide conjugates of PMO toward exon skipping enhancement in Duchenne muscular dystrophy

We describe two new methods of parallel chemical synthesis of libraries of peptide conjugates of phosphorodiamidate morpholino oligonucleotide (PMO) cargoes on a scale suitable for cell screening prior to in vivo analysis for therapeutic development. The methods represent an extension of the SELection of PEPtide CONjugates (SELPEPCON) approach previously developed for parallel peptide-peptide nucleic acid (PNA) synthesis. However, these new methods allow for the utilization of commercial PMO as cargo with both C- and N-termini unfunctionalized. The synthetic methods involve conjugation in solution phase, followed by rapid purification via biotin-streptavidin immobilization and subsequent reductive release into solution, avoiding the need for painstaking high-performance liquid chromatography purifications. The synthesis methods were applied for screening of PMO conjugates of a 16-member library of variants of a 10-residue ApoE peptide, which was suggested for blood-brain barrier crossing. In this work the conjugate library was tested in an exon skipping assay using skeletal mouse mdx cells, a model of Duchene's muscular dystrophy where higher activity peptide-PMO conjugates were identified compared with the starting peptide-PMO. The results demonstrate the power of the parallel synthesis methods for increasing the speed of optimization of peptide sequences in conjugates of PMO for therapeutic screening.

Design and evaluation of endosomolytic biocompatible peptides as carriers for siRNA delivery

Gene therapy using RNA interference (RNAi) technology has been explored to treat cancers, by regulating the expression of oncogene. However, even though small interfering RNA (siRNA), which triggers RNAi, may have great therapeutic potential, efforts at using them in vivo have been hampered by the difficulty of effective and safe delivery into cells of interest. In this study, to develop a safe and efficient carrier for in vitro and in vivo siRNA delivery, we designed a peptide library. These peptides are improved variants of a known peptide based siRNA carrier C6. All the modifications improved the transfection efficiency of C6 to some degree. After completing prescreening for activity, several promising candidates were used for further evaluation. Selected peptides C6M3 and C6M6 could form stable complexes with siRNA. These complexes could be greatly uptaken by cells and showed a punctate perinuclear distribution. Moreover, peptide/siRNA complexes achieved high transfection efficiency in vitro without inducing substantial cytotoxicity. We have validated the therapeutic potential of this strategy for cancer treatment by targeting Bcl-2 gene in mouse tumor models, and demonstrated that tumor growth was inhibited. In order to address possible immune side effects of these peptide carriers, biocompatibility study in terms of complement activation and cytokine activation assay were carried out, whereas none of the peptides induced such effects. In conclusion, these results support the potential of these peptides as therapeutic siRNA carrier.