Histone H1-mediated transfection: serum inhibition can be overcome by Ca2+ ions

Performance of nanoparticles for biomedical applications: The in vitro/in vivo discrepancy

Nanomedicine has a great potential to revolutionize the therapeutic landscape. However, up-to-date results obtained from in vitro experiments predict the in vivo performance of nanoparticles weakly or not at all. There is a need for in vitro experiments that better resemble the in vivo reality. As a result, animal experiments can be reduced, and potent in vivo candidates will not be missed. It is important to gain a deeper knowledge about nanoparticle characteristics in physiological environment. In this context, the protein corona plays a crucial role. Its formation process including driving forces, kinetics, and influencing factors has to be explored in more detail. There exist different methods for the investigation of the protein corona and its impact on physico-chemical and biological properties of nanoparticles, which are compiled and critically reflected in this review article. The obtained information about the protein corona can be exploited to optimize nanoparticles for in vivo application. Still the translation from in vitro to in vivo remains challenging. Functional in vitro screening under physiological conditions such as in full serum, in 3D multicellular spheroids/organoids, or under flow conditions is recommended. Innovative in vivo screening using barcoded nanoparticles can simultaneously test more than hundred samples regarding biodistribution and functional delivery within a single mouse.

A comprehensive review on histone-mediated transfection for gene therapy

Histone has been considered to be an effective carrier in non-viral gene delivery due to its unique properties such as efficient DNA binding ability, direct translocation to cytoplasm and favorable nuclear localization ability. Meanwhile, the rapid development of genetic engineering techniques could facilitate the construction of multifunctional fusion proteins based on histone molecules to further improve the transfection efficiency. Remarkably, histone has been demonstrated to achieve gene transfection in a synergistic manner with cationic polymers, affording to a significant improvement of transfection efficiency. In the review, we highlighted the recent developments and future trends in gene delivery mediated by histones or histone-based fusion proteins/peptides. This review also discussed the mechanism of histone-mediated gene transfection and provided an outlook for future therapeutic opportunities in the viewpoint of transfection efficacy and biosafety.

Serum-resistant complex nanoparticles functionalized with imidazole-rich polypeptide for gene delivery to pulmonary metastatic melanoma

To enhance serum-resistance and overcome the lysosomal barrier are effective and feasible strategies to increase the transfection efficiency of non-viral gene delivery system. For the systemic delivery of therapeutic gene, we previously developed self-assemble carboxymethyl poly(l-histidine) (CM-PLH)/poly(β-amino ester) (PbAE)/pDNA ternary complex nanoparticles based on electrostatic coating as an effective pDNA carrier. Recharging cationic PbAE/pDNA polyplexes with CM-PLH was a promising method to reduce the cytotoxicity and enhance the stability in vivo of positive charged polyplexes. In the present study, the transfection activities of ternary complex nanoparticles were further evaluated in vitro and in vivo. The transfection efficiency of ternary complex nanoparticles showed significant serum-resistance (CM-PLH-containing (51.9±4.35)% in 50% FBS>CM-PLH-free (14.7±5.66)% in 50% FBS), cell line dependent (HEK293>MCF-7>COS7>B16F10>A549>Hela>SPC-A1>CHO>SKOV3) and incubation period dependent (24 h, 20 h, 16 h>12 h>8 h>4 h>2 h>1 h>0.5 h). After transfected with ternary complex nanoparticles loading pGV240-MDA-7/IL-24, the B16F10 cells exhibited significant apoptosis and proliferation inhibition due to the expression of IL-24. Moreover, in the pulmonary metastatic melanoma model, ternary complex nanoparticles loading pGV240-MDA-7/IL-24 showed significant antitumor therapeutic efficacy in vivo. These results suggested that CM-PLH/PbAE/pDNA ternary complex nanoparticles were promising and challenging gene vector for practical application.

Incorporation of histone derived recombinant protein for enhanced disassembly of core-membrane structured liposomal nanoparticles for efficient siRNA delivery

A novel recombinant protein tetra-H2A (TH) derived from histone H2A has been developed to replace protamine as a conditionally reversible, nucleic acid condensing agent. The novel protein will address the insufficient release of nucleic acid therapeutics, which is captured by protamine for siRNA delivery. TH is composed of 4 tandem repeats of the histone H2A N-terminal sequence, intervened by the cathepsin D cleavage site. The repeating H2A sequence enhances the binding affinity to anionic nucleic acids, forming more stable condensates, as demonstrated by the binding affinity assay. The TH/siRNA condensates are formulated into a core-membrane structured liposomal nanoparticle (NP). The endosomes of cancer cells are rich in cathepsin D, allowing on-site degradation of TH and facilitating the intracellular release of siRNA. The NPs assembled with TH produced a higher silencing efficiency of target genes in vitro and in vivo than the NPs assembled with protamine as the nucleic acid condensing agent. The exploitation of TH in the NP formulation exhibited a biocompatibility profile similar to that of protamine, with minimal immunostimulating and systemic toxicity observed after repeated administration.

Salt-induced stability and serum-resistance of polyglutamate polyelectrolyte brushes/nuclear factor-κB p65 siRNA Polyplex enhance the apoptosis and efficacy of doxorubicin

Short interfering RNAs (siRNAs) as chemotherapeutic RNAi agents hold great promise for a significant improvement in cancer therapy. Despite the promise, effective transport of siRNA with minimal side effects remains a challenge. The common problem associated with the low delivery efficiencies of current polycation-based gene delivery systems is their low stability in the presence of salt and serum. In the present study we developed the polyglutamate derivatives (PGS) polyelectrolyte brushes for NF-κB p65 siRNA delivery. The PGS polyelectrolyte brushes/siRNA polyplex was colloidally stable (150 nm diameter) in physiological saline (150 mM NaCl), likely due to the osmotic brushes of PGS. The size-controlled siRNA/PGS polyplex also showed the serum resistance resulting in their efficient cellular uptake was not negatively influenced by the presence of serum. The endothermic profile of ITC, their low values of Gibbs free energy and binding constants Kb under salt conditions provided the direct evidence that PGS polyelectrolyte brushes had a much lower binding affinity for serum proteins, compared with PEI 25KDa. PGS polyelectrolyte brushes delivering NF-κB p65 siRNA achieved efficient down-regulation of NF-κB p65 protein in HeLa cells. The NF-κB p65 down-regulation mediated by PGS polyelectrolyte brushes was more significant than PEI 25KDa and comparable to Lipofectamine 2000. Furthermore, the combination treatment with PGS polyelectrolyte brushes/NF-κB p65 siRNA polyplex and doxorubicin demonstrated synergistic apoptotic and cytotoxic effects on HeLa cancer cells. The high stability in physiological saline and salt-induced serum resistance of PGS polyelectrolyte brushes/siRNA polyplex has potential applications together with standard chemotherapies such as doxorubicin to be a viable method to improve the clinical outcomes in cancer therapies.

Synergistic effects between natural histone mixtures and polyethylenimine in non-viral gene delivery in vitro

Nanoparticles made of plasmid DNA (pDNA) and cationic polymers are promising strategies for non-viral gene delivery. However, many cationic polymers are toxic to cells when used in higher concentrations. Positively charged proteins, such as histones, are biodegradable and a good alternative, especially for potential in vivo applications. It has previously been shown that histones are able to complex DNA and mediate transfection of cells. To investigate possible synergistic effects between the different histone types and to avoid the use of recombinant proteins, we analysed whether natural histone mixtures would be functional as gene carriers. Core and linker histones from calf thymus and from chicken erythrocytes were used to transfect different cell lines. The protein mixtures efficiently complexed the pDNA, and the resulting particles entered the cells. However, only marginal expression of the gene encoded by the pDNA was observed. Transfection rates increased drastically when minimal amounts of the basic polymer polyethylenimine (PEI) were added to the particles. Neither PEI nor histones alone mediated any transfection under the conditions where a combination of both worked efficiently, and the combined particles were well tolerated by the cells. These results demonstrate that histone mixtures from natural sources in combination with minimal amounts of PEI can be used as gene carriers. This might have consequences for the development of novel gene delivery strategies, such as DNA vaccines, with minimal side-effects.

Poly(α-glutamic acid) combined with polycation as serum-resistant carriers for gene delivery

The transfection efficiency of cationic polymers decreases dramatically in the presence of serum, which hampers the in vivo application of these polymers for gene delivery. Due to its shielding effect of poly(alpha-glutamic acid) (PGA) from negatively charged serum proteins, it was introduced into DNA polyplexes to overcome the serum inhibitory effect. In the present studies, the transfection efficiency of DNA/PEI/PGA terplex system was compared to PEI 25 kDa and Lipofectamine 2000 in the presence of serum. The successful formation of DNA/PEI/PGA terplexes was confirmed by their near-neutral surface charge. Interaction between components in the terplex system demonstrated that PGA was competing with DNA to combine with PEI. PEI/PGA combined carriers were not cytotoxic at a C/N ratio higher than 0.3. The in vitro transfection efficiency of DNA/PEI/PGA terplexes was not significantly different from those of DNA/PEI25kDa in serum-free medium. Importantly, in serum-containing medium, the DNA terplexes at their optimal C/N ratios maintained the same level of transfection efficiency as that of serum-free medium, even though the transfection efficiency of PEI 25 kDa and Lipofectamine 2000 was significantly decreased under serum-containing conditions. CLSM results confirmed that the cellular import of pDNA delivered by PEI/PGA combined carriers was more efficient than PEI 25 kDa alone under serum-containing conditions. Therefore, PGA could be used as a versatile serum-resistant reagent to overcome the serum inhibitory effect of polycations for gene delivery.

Reducible poly(oligo-D-arginine) for enhanced gene expression in mouse lung by intratracheal injection

Nonarginine (D-R9) has been reported to be one of the most efficacious protein transduction domains (PTDs) for the intracellular cargo delivery such as DNA, RNA, proteins, and particles. Although oligoarginines are capable of forming polyplex with DNA by electrostatic interaction, the length of oligoarginine can affect the toxicity and gene expression. The reducible poly(oligo-D-arginine) (rPOA) composed of the Cys-(D-R9)-Cys repeating unit forming disulfide bonds between terminal cysteinyl-thiol groups of short peptides was hypothesized to show efficient gene transfection without toxicity. The reducible high molecular weight poly(oligo-D-arginine) may fragment into the Cys-(D-R9)-Cys in cellular environments such as cytosol, cell surface, endosomes, and lysosomes, and enhance DNA transfection efficiency. In the present study, in vitro stability, cytotoxicity, and transfection efficiency of DNA/poly(oligo-D-arginine) polyplex were evaluated. In addition, in vivo delivery of DNA into the lung was performed by intratracheal injection of DNA/poly(oligo-D-arginine) polyplex. The in vivo study with rPOA showed higher level of gene expression than PEI, sustaining for 1 week without toxicity. Reducible high molecular weight poly(oligo-D-arginine) based on R9 PTD is a very promising nonviral gene carrier for lung diseases by efficiently condensing, stabilizing, and transfecting DNA.

"Soft" calcium crosslinks enable highly efficient gene transfection using TAT peptide

PURPOSE

Typically, low molecular weight cationic peptides or polymers exhibit poor transfection efficiency due to an inability to condense plasmid DNA into small nanoparticles. Here, efficient gene delivery was attained using TAT/pDNA complexes containing calcium crosslinks.

METHODS

Electrostatic complexes of pDNA with TAT or PEI were studied with increasing calcium concentration. Gel electrophoresis was used to determine DNA condensation. The morphology of the complexes was probed by transmission electron microscopy. Transfection efficiency was assessed using a luciferase reporter plasmid. The accessibility of phosphate and amine groups within complexes was evaluated to determine the effect of calcium on structure.

RESULTS

TAT/pDNA complexes were condensed into small, 50-100 nm particles by optimizing the concentration of calcium. Complexes optimized for small size also exhibited higher transfection efficiency than PEI polyplexes in A549 cells. TAT and TAT complexes displayed negligible cytotoxicity up to 5 mg/mL, while PEI exhibited high cytotoxicity, as expected. Probing the TAT-Ca/pDNA structure suggested that calcium interacted with both phosphate and amine groups to compact the complexes; however, these "soft" crosslinks could be competitively disrupted to facilitate DNA release.

CONCLUSION

Small and stable TAT-Ca/pDNA complexes were obtained via "soft" calcium crosslinks leading to sustained gene expression levels higher than observed for control PEI gene vectors. TAT-Ca/pDNA complexes were stable, maintaining particle size and transfection efficiency even in the presence of 10% of FBS. TAT-Ca complexes offer an effective vehicle offering potential for translatable gene delivery.

The importance of particle size and DNA condensation salt for calcium phosphate nanoparticle transfection

Calcium phosphate has been used for over 30 years to deliver genetic material to mammalian cells. This vector has proven advantages over other transfection species such as viruses and dendrimers in terms of superior biocompatibility and reduced immune response. However, clinical application of calcium phosphate based transfection techniques is hampered by poor understanding of the key factors underlying its action. Despite widespread in vitro use, little attention has been given to the physico-chemical characteristics of the calcium phosphate particles mediating transfection. In this study parameters were optimised to produce calcium phosphate nanoparticles onto which plasmid DNA (pDNA) was adsorbed that were more effective than a commercial dendrimer vector in delivering pDNA to an osteoblastic cell line and compared favourably in a fibroblastic cell line without the need for special culture conditions such as cell cycle synchronization or glycerol shock treatment. Addition of the pDNA after nanoparticle synthesis allowed for characterisation of particle morphology, size, surface charge and composition. We found that the key parameters for effective calcium phosphate nanoparticle transfection were an optimal concentration of calcium and chloride ions and a nanosized non-agglomerated precipitate.

An archaeal histone-like protein mediates efficient p53 gene transfer and facilitates its anti-cancer effect in vitro and in vivo

The improvement of the transfection efficiency of the non-viral-based gene delivery systems is a key issue for the application in gene therapy. We have previously described an archaeal histone-like protein-based (HPhA) gene delivery system and showed that HPhA formed stable non-covalent complexes with nucleic acids and improved their delivery by using beta-galactosidase as a reporter gene. In this study, the wild-type p53 gene was transfected into the cancer cells using the HPhA as a vector, and the expression level and the activity of p53 gene were evaluated both in vitro and in vivo. Gene expression was determined by real-time reverse transcriptase-PCR and western blotting analysis. The cellular growth inhibition and apoptosis of HPhA-mediated p53 transfection were assessed by XTT (sodium 3'-[1-(phenylaminocarbonyl)-3,4-tetrazolium]-bis(4-methoxy-6-nitro)benzene sulfonic acid hydrate) assay and annexin V-FITC (fluorescein isothiocyanate) staining, respectively. Further more, transfection of HPhA/p53 into CNE (nasopharyngeal carcinoma cell line)-xenografted nude mice was performed and tumor growth was measured. The present study demonstrates that HPhA enhances the efficiency of p53 gene transfer and antitumor activity compared with the widely used Lipofectamine. These results demonstrate that HPhA enhances the in vitro and in vivo efficiency of p53 gene transfer and suggest that it may be served as a promising tool for gene delivery and gene therapy.

Nucleocytoplasmic transport of DNA: enhancing non-viral gene transfer

Gene therapy, the correction of dysfunctional or deleted genes by supplying the lacking component, has long been awaited as a means to permanently treat or reverse many genetic disorders. To achieve this, therapeutic DNA must be delivered to the nucleus of cells using a safe and efficient delivery vector. Although viral-based vectors have been utilized extensively due to their innate ability to deliver DNA to intact cells, safety considerations, such as pathogenicity, oncogenicity and the stimulation of an immunological response in the host, remain problematical. There has, however, been much progress in the development of safe non-viral gene-delivery vectors, although they remain less efficient than the viral counterparts. The major limitations of non-viral gene transfer reside in the fact that it must be tailored to overcome the intracellular barriers to DNA delivery that viruses already master, including the cellular and nuclear membranes. In particular, nuclear transport of the therapeutic DNA is known to be the rate-limiting step in the gene-delivery process. Despite this, much progress had been made in recent years in developing novel means to overcome these barriers and efficiently deliver DNA to the nuclei of intact cells. This review focuses on the nucleocytoplasmic delivery of DNA and mechanisms to enhance to non-viral-mediated gene transfer.

Histonefection: Novel and potent non-viral gene delivery

Protein/peptide-mediated gene delivery has recently emerged as a powerful approach in non-viral gene transfer. In previous studies, we and other groups found that histones efficiently mediate gene transfer (histonefection). Histonefection has been demonstrated to be effective with various members of the histone family. The DNA binding domains and natural nuclear localisation signal sequences make histones excellent candidates for effective gene transfer. In addition, their positive charge promotes binding to anionic molecules and helps them to overcome the negative charge of cells that is an important barrier to cellular penetration. Histonefection appears to have particular promise in cancer gene transfer and therapy.

Role of calcium in gene delivery

The treatment of genetic diseases using therapeutic gene transfer is considered to be a significant development. This development has brought with it certain limitations, and the process of overcoming these barriers has seen a drastic change in gene delivery. Many metal ions such as Mg2+, Mn2+, Ba2+ and, most importantly, Ca2+ have been demonstrated to have significant roles in gene delivery. Recently, calcium phosphate alone, or in combination with viral and nonviral vectors, was found to exert a positive effect on gene transfer when incorporated in the colloidal particulate system, which is an advancing approach to gene delivery. This review elaborates on various successful methods of using calcium in gene delivery.

Calcium enhances the transfection potency of stabilized plasmid–lipid particles

Previous work from this laboratory has shown that plasmid DNA can be encapsulated in small (70-nm-diameter) stabilized plasmid-lipid particles (SPLP) that consist of a single plasmid encapsulated within a bilayer lipid vesicle. SPLP preferentially transfect tumor tissue following intravenous administration. Although the levels of transgene expression in vivo are greater for SPLP than can be achieved with naked DNA or complexes, they are lower than may be required for therapeutic benefit. In the present work we examine whether Ca2+ can enhance the transfection potency of SPLP. It is shown that Ca2+ can enhance SPLP transfection potency in bovine hamster kidney cells by 60- to 100-fold when treated in serum containing medium and an additional 60-fold when serum is absent for the initial 10 min of the transfection period. When cells are treated with SPLP in the presence of Ca2+, there is a fivefold increase in intact plasmid in the cell. It is also shown that this Ca2+ effect involves the formation of calcium phosphate precipitates; however, these precipitates are not directly associated with the SPLP plasmid DNA. The ability of calcium phosphate to facilitate delivery of other macromolecules without direct association is also demonstrated by the release of large-molecular-weight dextrans from endosomal/lysosomal compartments in the presence of calcium phosphate. Finally, it is shown that, unlike naked DNA, SPLP transfection potency in the presence of calcium phosphate is not affected by nuclease activity.

pDNA loaded calcium phosphate nanoparticles: highly efficient non-viral vector for gene delivery

Nanoparticles of calcium phosphate encapsulating plasmid DNA (pDNA) of size 100-120 nm in diameter were prepared. XRD studies of these nanoparticles showed them to be crystalline in nature having hydroxyapatite structure. The maximum loading of pDNA and its release from nanoparticles were studied using gel electrophoresis. The time dependent size measurement of these particles demonstrated that these particles show strong aggregational behaviour in aqueous dispersion. Calcium phosphate nanoparticles were found to be dissolved even in low acidic buffer (pH 5.0) releasing the pDNA, which suggested that DNA release from these particles in the endosomal compartment was possible. In vitro transfection efficiency of these calcium phosphate nanoparticles was found to be higher than that of the commercial transfecting reagent Polyfect.

A recombinant H1 histone-based system for efficient delivery of nucleic acids

We describe here a unique transfer system based on a truncated form of the human linker histone H1F4 for the delivery of nucleic acids to a variety of cells. The efficiency of truncated histone H1.4F was assessed using both primary mammalian and immortalised insect and mammalian cell lines. Our results indicated that recombinant histone H1.4F was able to deliver DNA, dsRNA and siRNA in all cells tested. Quantitative analysis based on reporter gene expression or silencing of target genes revealed that the transfection efficiency of histone H1.4F was comparable to, or better than, liposome-based systems. Notably, the efficiency of histone H1.4F was associated with very low toxicity for transfected cells. The human H1.4F recombinant protein is easily purified in large-scale from bacterial lysates using inexpensive simplified processing. This versatile transfection system represents an important advance in the field of gene delivery and an improvement over earlier nucleic acid delivery methods.

Structure and function correlation in histone H2A peptide-mediated gene transfer

Histone H2A has been found to be efficient in DNA delivery into a number of cell lines. We have reasoned that this DNA-delivery activity is mediated by two mechanisms: (i) electrostatically driven DNA binding and condensation by histone and (ii) nuclear import of these histone H2A.DNA polyplexes via nuclear localization signals in the protein. We have identified a 37-aa N-terminal peptide of histone H2A that is active in in vitro gene transfer. This peptide can function as a nuclear localization signal and can bind DNA. Amino acid substitutions that replace positively charged residues and/or DNA-binding residues of this peptide obliterate transfection activity. The introduction of a proline in the first turn of an alpha-helix of this 37-mer obliterates transfection activity, suggesting that the integrity of the alpha-helical structure of the N-terminal region of histone H2A is related to its transfection activity.

Improvement of DNA transfection with cationic liposomes

The increasing use of cationic liposomes as vectors for DNA transfection of eukaryotic cells is due to its high efficiency and reproducibility. After the interaction of the DNA cationic-liposome complexes (DNA-CLC) with the plasma membrane, the entry into the cells delivers the DNA-CLC to the endosome-lysosome pathway where some of the DNA-CLC are degraded. The non-degraded DNA that escapes to the cytoplasm, still has to transverse the nuclear membrane to be transcribed and then translated. To improve the efficiency of the whole process, we can manipulate the DNA (sequences, promoters, enhancers, nuclear localisation signals, etc), the DNA-CLC (lipids) or the plasmatic, endosomal and/or nuclear cellular membranes (ultrasound, electroporation, Ca++, pH of the endosomes, mitosis, fusogenic peptides, nuclear localisation signals, etc). Most of these methods have been generally used individually but in combination, may greatly improve the efficiency and reproducibility of in vitro transfection. While much of this work remains yet to be done and present results further explored, the application of these efforts is essential to the future development of new gene therapy strategies.