Evaluation of the effect of vector architecture on DNA condensation and gene transfer efficiency

Programming the Cellular Uptake of Protein-Based Viromimetic Nanoparticles for Enhanced Delivery

Viral mimetics is a noteworthy strategy to design efficient delivery systems without the safety drawbacks and engineering difficulties of modifying viral vectors. The triblock polypeptide CSB was previously designed de novo to self-assemble with DNA into nanocomplexes called artificial virus-like particles (AVLPs) due to their similarities to viral particles. Here, we show how we can incorporate new blocks into the CSB polypeptide to enhance its transfection without altering its self-assembly capabilities and the stability and morphology of the AVLPs. The addition of a short peptide (aurein) and/or a large protein (transferrin) to the AVLPs improved their internalization and specific targeting to cells by up to 11 times. Overall, these results show how we can further program the cellular uptake of the AVLPs with a wide range of bioactive blocks. This can pave the way to develop programmable and efficient gene delivery systems.

Re-examination of Peptide-Sequence-Dependent Gene Expression of Cysteine-Installed Pegylated Oligolysine/DNA Complexes

We previously synthesized cysteine-installed C-terminally PEGylated oligolysines with 20 amino acid residues to form cross-linked polymeric micelles (PMs) with luciferase-coding plasmid DNA as a candidate for artificial gene vectors. Luciferase gene expression in HeLa cells mediated by PEG-CK₁₈C, PEG-CK₉CK₉, and PEG-K₉CK₉C was reported to be 35-, 5.4-, and 1.3-fold higher than that mediated by cysteine-uninstalled PEGylated oligolysine PEG-K₂₀, respectively. However, after the publication, the survival rate of HeLa cells used in the previous study was found to be lower than usual when subcutaneously implanted into mice to create a xenograft model. In this study, to re-examine the peptide sequence-dependent gene expression, gene expression efficacy mediated by PEG-peptide PMs was compared with the PM cellular uptake results using newly obtained HeLa cell lines and the additional cell lines Huh-7, PANC-1, and BxPC3. As a result, PEG-K₉CK₉C PMs mediated the maximum gene expression in all cell lines, and the corresponding cellular uptake was also obtained. Therefore, we concluded that our previous results were erroneously obtained due to normality-depleted HeLa cells. A comparison of physicochemical characterizations, gene expression efficacy, and cellular uptake of PEG-peptide PMs is discussed in detail.

Self-assembly of an aptamer-decorated chimeric peptide nanocarrier for targeted cancer gene delivery

In this study, we developed a peptide-based non-viral carrier decorated with aptamer to overcome the specific gene delivery barriers. The carrier (KLN/Apt) was designed to contain multiple functional segments, including 1) two tandem repeating units of low molecular weight protamine (LMWP) to condense DNA into stable nanosize particles and protect it from enzymatic digestion, 2) AS1411 aptamer as targeting moiety to target nucleolin and promote carrier internalization, 3) a synthetic pH-sensitive fusogenic peptide (KALA) for disrupting endosomal membranes and enhancing cytosol escape of the nanoparticles, and 4) a nuclear localization signal (NLS) for active cytoplasmic trafficking and nuclear delivery of DNA. The obtained results revealed the developed carrier capacity in terms of specific cell targeting, overcoming cellular gene delivery barriers, and mediating efficient gene transfection. The KLN/pDNA/aptamer nanoparticles offer remarkable potential for the conceptual design and formation of promising multi-functionalized carriers towards the most demanding therapeutic applications.

A Global Review on Short Peptides: Frontiers and Perspectives

Peptides are fragments of proteins that carry out biological functions. They act as signaling entities via all domains of life and interfere with protein-protein interactions, which are indispensable in bio-processes. Short peptides include fundamental molecular information for a prelude to the symphony of life. They have aroused considerable interest due to their unique features and great promise in innovative bio-therapies. This work focusing on the current state-of-the-art short peptide-based therapeutical developments is the first global review written by researchers from all continents, as a celebration of 100 years of peptide therapeutics since the commencement of insulin therapy in the 1920s. Peptide "drugs" initially played only the role of hormone analogs to balance disorders. Nowadays, they achieve numerous biomedical tasks, can cross membranes, or reach intracellular targets. The role of peptides in bio-processes can hardly be mimicked by other chemical substances. The article is divided into independent sections, which are related to either the progress in short peptide-based theranostics or the problems posing challenge to bio-medicine. In particular, the SWOT analysis of short peptides, their relevance in therapies of diverse diseases, improvements in (bio)synthesis platforms, advanced nano-supramolecular technologies, aptamers, altered peptide ligands and in silico methodologies to overcome peptide limitations, modern smart bio-functional materials, vaccines, and drug/gene-targeted delivery systems are discussed.

The Multifaceted Histidine-Based Carriers for Nucleic Acid Delivery: Advances and Challenges

Histidines incorporated into carriers of nucleic acids may enhance the extracellular stability of the nanoparticle, yet aid in the intracellular disruption of the nanoparticle, enabling the release of the nucleic acid. Moreover, protonation of histidines in the endosomes may result in endosomal swelling with subsequent lysis. These properties of histidine are based on its five-member imidazole ring in which the two nitrogen atoms may form hydrogen bonds or act as a base in acidic environments. A wide variety of carriers have integrated histidines or histidine-rich domains, which include peptides, polyethylenimine, polysaccharides, platform delivery systems, viral phages, mesoporous silica particles, and liposomes. Histidine-rich carriers have played key roles in our understanding of the stability of nanocarriers and the escape of the nucleic acids from endosomes. These carriers show great promise and offer marked potential in delivering plasmids, siRNA, and mRNA to their intracellular targets.

Bio-inspired gene carriers with low cytotoxicity constructed via the assembly of dextran nanogels and nano-coacervates

Aim: To achieve safe and biocompatible gene carriers. Materials & methods: A core/shell-structured hierarchical carrier with an internal peptide/gene coacervate 'core' and a dextran nanogel 'shell' on the surface has been designed. Results: The dextran nanogels shield coacervate (DNSC) can effectively condense genes and release them in reducing environments. The dextran nanogel-based 'shell' can effectively shield the positive charge of the peptide/gene coacervate 'core', thus reducing the side effects of cationic gene carriers. In contrast with the common nonviral gene carriers that had high cytotoxicities, the DNSC showed a high transfection efficiency while maintaining a low cytotoxicity. Conclusion: The DNSC provides an effective environmentally responsive gene carrier with potential applications in the fields of gene therapy and gene carrier development.

Stepwise Development of Biomimetic Chimeric Peptides for Gene Delivery

Gene-based therapy largely relies on the vector type that allows a selective and efficient transfection into the target cells with maximum efficacy and minimal toxicity. Although, genes delivered utilizing modified viruses transfect efficiently and precisely, these vectors can cause severe immunological responses and are potentially carcinogenic. A promising method of overcoming this limitation is the use of non-viral vectors, including cationic lipids, polymers, dendrimers, and peptides, which offer potential routes for compacting DNA for targeted delivery. Although non-viral vectors exhibit reduced transfection efficiency compared to their viral counterpart, their superior biocompatibility, non-immunogenicity and potential for large-scale production make them increasingly attractive for modern therapy. There has been a great deal of interest in the development of biomimetic chimeric peptides. Biomimetic chimeric peptides contain different motifs for gene translocation into the nucleus of the desired cells. They have motifs for gene targeting into the desired cell, condense DNA into nanosize particles, translocate the gene into the nucleus and enhance the release of the particle into the cytoplasm. These carriers were developed in recent years. This review highlights the stepwise development of the biomimetic chimeric peptides currently being used in gene delivery.

Peptide Sequence-Dependent Gene Expression of PEGylated Peptide/DNA Complexes

Oligolysine-based PEG-peptides with 15 or 20 amino acid residues including two cysteines were synthesized to formulate cross-linked polyplex micelles (PMs) incorporating luciferase-coding plasmid DNA (pDNA). Two cysteine residues were separately allocated at the C-terminal, center, or N-terminal of peptide moieties. Although TEM observation showed that all PEG-peptides condensed pDNA into rod-like or toroidal morphologies, the rod length distribution of PMs was affected by both the amino acid sequence and the peptide length of PEG-peptides. In comparison to the cysteine-uninstalled PEG-peptides, the cysteine-installed PEG-peptides exhibited a reductive environment-responsive pDNA release, which was observed in a gel retardation assay. From physicochemical characterizations, a relationship between the amino acid sequence and the in vitro gene expression efficacy of PMs in a cell-free protein synthesis system has been clearly demonstrated. Finally, the cell-based assay using HeLa cells has been tested, and the differences between both results of cell-free and cell-based systems are discussed.

Stimulus-Responsive Peptide for Effective Delivery and Release of DNA in Plants

For efficient gene delivery in plant systems, nonviral vector and DNA complexes require extracellular stability, cell wall/membrane translocation capability, and the ability to mediate both endosomal escape and intracellular DNA release. Peptides make appealing gene delivery vectors due to their DNA-binding, cell-penetrating, and endosome escape properties. However, DNA release within cells has so far been inefficient, which results in poor and delayed gene expression, while the lack of understanding of both internalization and trafficking mechanisms is a further obstacle to the design of efficient peptide gene delivery vectors. Here, we report successful gene delivery into plants using a cellular environment-responsive vector, BPCH7, which is an efficient cell-penetrating peptide with a cyclic DNA-binding domain that is formed by a disulfide bond between two cysteines. The cyclic structure of BPCH7 confers high avidity attachment to DNA in vitro. Following endocytosis into cells, disulfide bond cleavage facilitated by intracellular glutathione induces structural changes within BPCH7 that enable the release of the associated DNA cargo. Comparative studies with BPKH, a cell-penetrating peptide with a linear DNA-binding domain, show that BPCH7 maximized and expedited gene transfer in cells and unveil for the first time the crucial role of plant stomata in the internalization of peptide-DNA complexes.

Development of a Recombinant Multifunctional Biomacromolecule for Targeted Gene Transfer to Prostate Cancer Cells

The objective of this study was to genetically engineer a fully functional single chain fusion peptide composed of motifs from diverse biological and synthetic origins that can perform multiple tasks including DNA condensation, cell targeting, cell transfection, particle shielding from immune system and effective gene transfer to prostate tumors. To achieve the objective, a single chain biomacromolecule (vector) consisted of four repeatative units of histone H2A peptide, fusogenic peptide GALA, short elastin-like peptide, and PC-3 cell targeting peptide was designed. To examine the functionality of each motif in the vector sequence, it was characterized in terms of size and zeta potential by Zetasizer, PC-3 cell targeting and transfection by flowcytometry, IgG induction by immunogenicity assay, and PC-3 tumor transfection by quantitative live animal imaging. Overall, the results of this study showed the possibility of using genetic engineering techniques to program various functionalities into one single chain vector and create a multifunctional nonimmunogenic biomacromolecule for targeted gene transfer to prostate cancer cells. This proof-of-concept study is a significant step forward toward creating a library of vectors for targeted gene transfer to any cancer cell type at both in vitro and in vivo levels.

Self-Assembly of a Multifunctional Lipid With Core-Shell Dendrimer DNA Nanoparticles Enhanced Efficient Gene Delivery at Low Charge Ratios into RPE Cells

Development of safe and effective gene delivery systems is essential in treating ocular genetic disorders. A hybrid nonviral system composed of a multifunctional lipid ECO and a G4 nanoglobule was designed for efficient gene delivery into RPE cells at low charge ratios. This system formed stable DNA nanoparticles at low N/P ratios, exhibited low cytotoxicity, and induced higher GFP expression in ARPE-19 cells at N/P = 6. The hybrid nanoparticles mediated significant reporter gene GFP expression ex-vivo in the retina from wild type C57 mice and in vivo in BALB/c mice. These hybrid nanoparticles are promising for in vitro and in vivo gene delivery at low charge ratios.

Peptide vectors for gene delivery: from single peptides to multifunctional peptide nanocarriers

The therapeutic use of nucleic acids relies on the availability of sophisticated delivery systems for targeted and intracellular delivery of these molecules. Such a gene delivery should possess essential characteristics to overcome several extracellular and intracellular barriers. Peptides offer an attractive platform for nonviral gene delivery, as several functional peptide classes exist capable of overcoming these barriers. However, none of these functional peptide classes contain all the essential characteristics required to overcome all of the barriers associated with successful gene delivery. Combining functional peptides into multifunctional peptide vectors will be pivotal for improving peptide-based gene delivery systems. By using combinatorial strategies and high-throughput screening, the identification of multifunctional peptide vectors will accelerate the optimization of peptide-based gene delivery systems.

From rationally designed polymeric and peptidic systems to sophisticated gene delivery nano-vectors

Lack of safe, efficient and controllable methods for delivering therapeutic genes appears to be the most important factor preventing human gene therapy. Safety issues encountered with viral vectors have prompted substantial attention to in vivo investigations with non-viral vectors throughout the past decade. However, developing non-viral vectors with effectiveness comparable to viral ones has been a challenge. The strategy of designing multifunctional synthetic carriers targeting several extracellular and intracellular barriers in the gene transfer pathway has emerged as a promising approach to improving the efficacy of gene delivery systems. This review will explain how sophisticated synthetic vectors can be created by combining conventional polycationic vectors such as polyethylenimine and basic amino acid peptides with additional polymers and peptides that are designed to overcome potential barriers to the gene delivery process.

Influence of histidine incorporation on buffer capacity and gene transfection efficiency of HPMA-co-oligolysine brush polymers

One of the major intracellular barriers to nonviral gene delivery is efficient endosomal escape. The incorporation of histidine residues into polymeric constructs has been found to increase endosomal escape via the proton sponge effect. Statistical and diblock copolymers of N-(2-hydroxypropyl)methacrylamide (HPMA), oligolysine, and oligohistidine were synthesized via reversible-addition fragmentation chain transfer (RAFT) polymerization and tested for in vitro transfection efficiency, buffering ability, and polyplex uptake mechanism via the use of chemical endocytic inhibitors. Interestingly, histidine-containing statistical and diblock polymers exhibited increased buffer capacity in different endosomal pH ranges. Statistical copolymers transfected better than block copolymers that contained similar amounts of histidine. In addition, only the polymer containing the highest incorporation of oligohistidine residues led to increases in transfection efficiency over the HPMA-oligolysine base polymer. Thus, for these polymer architectures, high histidine incorporation may be required for efficient endosomal escape. Furthermore, inhibitor studies indicate that nonacidified caveolae-mediated endocytosis may be the primary route of transfection for these copolymers, suggesting that alternative approaches for increasing endosomal escape may be beneficial for enhancing transfection efficiency with these HPMA-oligolysine copolymers.

Arginine-rich hydrophobic polyethylenimine: potent agent with simple components for nucleic acid delivery

Conjugation of various arginine-rich peptide sequences to vectors based on 10 kDa polyethylenimine (PEI) and its hydrophobic derivative (hexanoate-PEI) was investigated as a strategy for improving pDNA and siRNA transfection activities. Six different arginine-histidine (RH) sequences and two arginine-serine (RS) sequences with a range of R/H ratios were designed and coupled to PEI and hexanoate-PEI. All arginine-rich peptide derivatives of PEI significantly enhanced luciferase gene expression compared to PEI 10 kDa alone. Hexanoate-PEI derivatives exhibited higher transfection activity than underivatized PEI vectors. Improved transfection activity may have resulted at least in part from use of higher vector/DNA ratios made possible by reduced cytotoxicity of vectors, and to use of vectors with higher molecular weights. Vectors that were the most efficient in pDNA delivery and transfection were also the most effective in siRNA delivery and protein expression knock down.

Hyaluronic acid based self-assembling nanosystems for CD44 target mediated siRNA delivery to solid tumors

Anticancer therapeutics employing RNA interference mechanism holds promising potentials for sequence-specific silencing of target genes. However targeted delivery of siRNAs to tumor tissues and cells and more importantly, their intracellular release at sites of interest still remains a major challenge that needs to be addressed before this technique could become a clinically viable option. In the current study, we have engineered and screened a series of CD44 targeting hyaluronic acid (HA) based self-assembling nanosystems for targeted siRNA delivery. The HA polymer was functionalized with lipids of varying carbon chain lengths/nitrogen content, as well as polyamines for assessing siRNA encapsulation. From the screens, several HA-derivatives were identified that could stably encapsulate/complex siRNAs and form self-assembled nanosystems, as determined by gel retardation assays and dynamic light scattering. Many HA derivatives could transfect siRNAs into cancer cells overexpressing CD44 receptors. Interestingly, blocking the CD44 receptors on the cells using free excess soluble HA prior to incubation of cy3-labeled-siRNA loaded HA nano-assemblies resulted in >90% inhibition of the receptor mediated uptake, confirming target specificity. In addition, SSB/PLK1 siRNA encapsulated in HA-PEI/PEG nanosystems demonstrated dose dependent and target specific gene knockdown in both sensitive and resistant A549 lung cancer cells overexpressing CD44 receptors. More importantly, these siRNA encapsulated nanosystems demonstrated tumor selective uptake and target specific gene knock down in vivo in solid tumors as well as in metastatic tumors. The HA based nanosystems thus portend to be promising siRNA delivery vectors for systemic targeting of CD44 overexpressing cancers including tumor initiating (stem-) cells and metastatic lesions.

Coating of single DNA molecules by genetically engineered protein diblock copolymers

Coating DNA is an effective way to modulate its physical properties and interactions. Current chemosynthetic polymers form DNA aggregates with random size and shape. In this study, monodisperse protein diblock copolymers are produced at high yield in recombinant yeast. They carry a large hydrophilic colloidal block (≈400 amino acids) linked to a short binding block (≈12 basic amino acids). It is demonstrated that these protein polymers complex single DNA molecules as highly stable nanorods, reminiscent of cylindrical viruses. It is proposed that inter- and intramolecular bridging of DNA molecules are prevented completely by the small size of the binding block attached to the large colloidal stability block. These protein diblocks serve as a scaffold that can be tuned for application in DNA-based nanotechnology.

The role of protamine amount in the transfection performance of cationic SLN designed as a gene nanocarrier

Cationic solid lipid nanoparticles (SLN) have been recently proposed as non-viral vectors in systemic gene therapy. The aim of this study was to evaluate the effect of the protamine amount used as the transfection promoter in SLN-mediated gene delivery. Three protamine-SLN samples (Pro25, Pro100, and Pro200) prepared by adding increasing amounts of protamine were characterized for their size, zeta potential, and protamine loading level. The samples were evaluated for pDNA complexation ability by gel-electrophoresis analysis and for cytotoxicity and transfection efficiency by using different cell lines (COS-I, HepG2, and Na1300). The size of SLN was ~230 nm and only Pro200 showed few particle aggregates. Unlike the Pro25 sample with the lowest protamine loading level, the others SLN samples (Pro100 and Pro200) exhibited a good ability in complexing pDNA. A cell-line dependent cytotoxicity lower than that of the positive control PEI (polyethilenimmine) was observed for all the SLN. Among these, only Pro100, having an intermediate amount of protamine, appeared able to promote pDNA cell transfer, especially in a neuronal cell line (Na1300). In conclusion, the amount of protamine as the transfection promoter in SLN affects not only the gene delivery ability of SLN but also their capacity to transfer genes efficiently to specific cell types.

Development of recombinant cationic polymers for gene therapy research

Cationic polymers created through recombinant DNA technology have the potential to fill a void in the area of gene delivery. The recombinant cationic polymers to be discussed here are amino acid based polymers synthesized in E. coli with the purpose to not only address the major barriers to efficient gene delivery but offer safety, biodegradability, targetability and cost-effectiveness. This review helps the readers to get a better understanding about the evolution of recombinant cationic polymers; and the potential advantages that they could offer over viral and synthetic non-viral vectors for gene delivery. It also discusses some of the major challenges that must be addressed in future studies to turn recombinant polymers into clinically effective gene delivery systems. Recent advances with the biopolymer design suggest that this emerging new class of gene delivery systems has the potential to address some of the major barriers to efficient, safe and cost-effective gene therapy.

Modified polyethyleneimine with histidine-lysine short peptides as gene carrier

There are several strategies that can be utilized to improve transfection efficiency while reducing the cytotoxicity of polyethyleneimine (PEI) as a promising non-viral gene delivery vector. In this study, we evaluated the potential use of lysine-histidine (KH) peptides in modifying the PEI 10 kDa structure and enhancing its efficiency while maintaining low toxicity of PEI. PEI 10 kDa was modified with 6-bromohexanoic acid (alkyl) to increase its lipophilicity. Then, ethylenediamine (EDA) was attached to the carboxylic groups of PEI-hexanoate to restore the primary amines of PEI. Subsequently, six different KH short peptides were conjugated to PEIs and evaluated for the effect of the KH sequence on vector transfection efficiency and cytotoxicity. The transfection efficiency of PEI-peptides complexed with a luciferase reporter gene (pRLCMV) in Neuro-2A murine neuroblastoma cells showed that the PEI conjugated to KHHHKKHHHK peptide had a significantly higher rate of gene transfection efficiency in comparison with other KH peptides. This peptide was conjugated to PEI-alkyl and PEI-alkyl-EDA and significant improvement in efficiency with minimal cytotoxicity was observed. The results obtained suggest that the sequence and content of KH peptides will have a significant impact on the transfection efficiency of modified PEI 10 kDa.

Advances with the use of bio-inspired vectors towards creation of artificial viruses

IMPORTANCE OF THE FIELD

In recent years, there has been a great deal of interest in the development of recombinant vectors based on biological motifs with potential applications in gene therapy. Several such vectors have been genetically engineered, resulting in biomacromolecules with new properties that are not present in nature.

AREAS COVERED IN THIS REVIEW

This review briefly discusses the advantages and disadvantages of the current state-of-the-art gene delivery systems (viral and non-viral) and then provides an overview on the application of various biological motifs in vector development for gene delivery. Finally, it highlights some of the most advanced bio-inspired vectors that are designed to perform several self-guided functions.

WHAT THE READER WILL GAIN

This review helps the readers get a better understanding about the history and evolution of bio-inspired fusion vectors with the potential to merge the strengths of both viral and non-viral vectors in order to create efficient, safe and cost-effective gene delivery systems.

TAKE HOME MESSAGE

With the emergence of new technologies such as recombinant bio-inspired vectors, it may not take long before non-viral vectors are observed that are not just safe and tissue-specific, but even more efficient than viral vectors.

Development of a genetically engineered biomimetic vector for targeted gene transfer to breast cancer cells

A biomimetic vector was genetically engineered to contain at precise locations (a) an adenovirus mu peptide to condense pDNA into nanosize particles, (b) a synthetic cyclic peptide to target breast cancer cells and enhance internalization of nanoparticles, (c) a pH-responsive synthetic fusogenic peptide to disrupt endosome membranes and facilitate escape of the nanoparticles into the cytosol, and (d) a nuclear localization signal from human immunodeficiency virus for microtubule mediated transfer of genetic material to the nucleus. The vector was characterized using physicochemical and biological assays to demonstrate the functionality of each motif in the vector backbone. The results demonstrated that the vector is able to condense plasmid DNA into nanosize particles (<100 nm), protect pDNA from serum endonucleases, target ZR-75-1 breast cancer cells and internalize, efficiently disrupt endosome membranes, exploit microtubules to reach nucleus and mediate gene expression. The therapeutic potential of the vector was evaluated by complexing with plasmid DNA encoding TRAIL (pTRAIL) and transfecting ZR-75-1 cells. The results demonstrated that up to 62% of the ZR-75-1 breast cancer cells can be killed after administration of pTRAIL in complex with the vector.

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

DNA/cationic lipid (lipoplexes), DNA/cationic polymer (polyplexes) and DNA/cationic polymer/cationic lipid (lipopolyplexes) electrostatic complexes are proposed as non-viral nucleic acids delivery systems. These DNA-nanoparticles are taken up by the cells through endocytosis processes, but the low capacity of DNA to escape from endosomes is regarded as the major limitations of their transfection efficiency. Here, we present a current report on a particular class of carriers including the polymers, peptides and lipids, which is based on the exploitation of the imidazole ring as an endosome destabilization device to favour the nucleic acids delivery in the cytosol. The imidazole ring of histidine is a weak base that has the ability to acquire a cationic charge when the pH of the environment drops bellow 6. As it has been demonstrated for poly(histidine), this phenomena can induce membrane fusion and/or membrane permeation in an acidic medium. Moreover, the accumulation of histidine residues inside acidic vesicles can induce a proton sponge effect, which increases their osmolarity and their swelling. The proof of concept has been shown with polylysine partially substituted with histidine residues that has caused a dramatic increase by 3-4.5 orders of magnitude of the transfection efficiency of DNA/polylysine polyplexes. Then, several histidine-rich polymers and peptides as well as lipids with imidazole, imidazolinium or imidazolium polar head have been reported to be efficient carriers to deliver nucleic acids including genes, mRNA or SiRNA in vitro and in vivo. More remarkable, histidylated carriers are often weakly cytotoxic, making them promising chemical vectors for nucleic acids delivery.

Biosynthesis and characterization of a novel genetically engineered polymer for targeted gene transfer to cancer cells

A novel multi-domain biopolymer was designed and genetically engineered with the purpose to target and transfect cancer cells. The biopolymer contains at precise locations: 1) repeating units of arginine and histidine to condense pDNA and lyse endosome membranes, 2) a HER2 targeting affibody to target cancer cells, 3) a pH responsive fusogenic peptide to destabilize endosome membranes and enhance endosomolytic activity of histidine residues, and 4) a nuclear localization signal to enhance translocation of pDNA towards the cell nucleus. The results demonstrated that the biopolymer was able to condense pDNA into nanosize particles, protect pDNA from serum endonucleases, target HER2 positive cancer cells but not HER2 negative ones, efficiently disrupt endosomes, and effectively reach the cell nucleus of target cells to mediate gene expression. To reduce potential toxicity and enhance biodegradability, the biopolymer was designed to be susceptible to digestion by endogenous furin enzymes inside the cells. The results revealed no significant biopolymer related toxicity as determined by impact on cell viability.

A designer biomimetic vector with a chimeric architecture for targeted gene transfer

Designer biomimetic vectors are genetically engineered biomacromolecules that are designed to mimic viral characteristics in order to overcome the cellular barriers associated with the targeted gene transfer. The vector in this study was genetically engineered to contain at precise locations: a) four tandem repeating units of N-terminal domain of histone H2A to condense DNA into stable nanosize particles suitable for cellular uptake, b) a model targeting motif to target HER2 and enhance internalization of nanoparticles, and c) a pH-responsive synthetic fusogenic peptide to disrupt endosome membranes and promote escape of the nanoparticles into the cytosol. The results demonstrate that a fully functional, multi-domain, designer vector can be engineered to target cells with high specificity, overcome the biological barriers associated with targeted gene transfer, and mediate efficient gene transfer.

Perspectives in vector development for systemic cancer gene therapy

Gene therapy is perceived as a revolutionary technology with the promise to cure almost any disease, provided that we understand its genetic basis. However, enthusiasm has rapidly abated as multiple clinical trials have failed to show efficacy. The limiting factor seems to be the lack of a suitable delivery system to carry the therapeutic genes to the target tissue safely and efficiently. Therefore, advancements in cancer gene therapy in general depend on the development of novel vectors with maximum therapeutic efficacy at the target site and minimal toxicity to normal tissues. This mini-review highlights both the major fortes and the unique challenges associated with the state-of-the-art gene carriers currently being used in cancer gene therapy.