Efficient gene delivery using reconstituted chromatin enhanced for nuclear targeting

CRISPR-dCas9-Guided and Telomerase-Responsive Nanosystem for Precise Anti-Cancer Drug Delivery

Nanodrug delivery systems are very promising for highly efficient anticancer drug delivery. However, the present nanosystems are commonly located in the cytoplasm and mediate uncontrolled release of drugs into cytosol, while a large number of anticancer drugs function more efficiently inside the nucleus. Here, we constructed a CRISPR-dCas9-guided and telomerase-responsive nanosystem for nuclear targeting and smart release of anticancer drugs. CRISPR-dCas9 technology has been employed to achieve conjugation of mesoporous silica nanoparticles (MSNs) with a high payload of the active anticancer drug, doxorubicin (DOX). A specifically designed wrapping DNA was used as a telomerase-responsive biogate to encapsulate DOX within MSNs. The wrapping DNA is extended in the presence of telomerase, which is highly activated in tumor cells, but not in normal cells. The extended DNA sequence forms a rigid hairpin-like structure and diffuses away from the MSN surface. CRISPR-dCas9 specifically targets telomere-repetitive sequences at the tips of chromosomes, facilitating the precise delivery of the nanosystem to the nucleus, and effective drug release triggered by telomerase that was enriched around telomeric repeats. This study provides a strategy and nanosystem for nuclear-targeted delivery and tumor-specific release of anticancer drugs that will maximize the efficiency of cancer cell destruction.

A New Perspective on the Origin of DNA Double-Strand Breaks and Its Implications for Ageing

It is estimated that 10-50 DNA double-strand breaks (DSBs) occur in a nucleated human cell per cell cycle. We reviewed the present state of knowledge and hypothesized that the currently accepted mechanisms cannot explain such high frequency of DSBs occurring daily under normal physiological conditions. We propose an alternative model that implicates illegitimate genomic integration into healthy cells of cell-free chromatin (cfCh) particles released from the billions of cells that die in the body every day. Repeated genomic integration of cfCh may have catastrophic consequences for the cell, such as DSBs, their faulty repair by nonhomologous end joining (NHEJ) followed by apoptosis with release of more cfCh which would integrate into genomes of surrounding cells. This can creates a vicious cycle of cfCh integration, DSBs, NHEJ, and more apoptosis, thereby providing a potential explanation as to why so many billions of cells die in the body on a daily basis. We also recount the recent observation that cfCh integration and the resulting DSBs activate inflammatory cytokines. This leads us to propose that concurrent DSBs and induction of inflammation occurring throughout life may be the underlying cause of ageing, degenerative disorders, and cancer. Finally, we discuss the prospect that agents that can inactivate/degrade cfCh may hold the key to making healthy ageing a realizable goal.

Cellular uptake of extracellular nucleosomes induces innate immune responses by binding and activating cGMP-AMP synthase (cGAS)

The nucleosome is the basic structural repeating unit of chromatin. DNA damage and cell apoptosis release nucleosomes into the blood circulatory system, and increased levels of circulating nucleosomes have been observed to be related to inflammation and autoimmune diseases. However, how circulating nucleosomes trigger immune responses has not been fully elucidated. cGAS (cGMP-AMP synthase) is a recently discovered pattern recognition receptor that senses cytoplasmic double-stranded DNA (dsDNA). In this study, we employed in vitro reconstituted nucleosomes to examine whether extracellular nucleosomes can gain access to the cytoplasm of mammalian cells to induce immune responses by activating cGAS. We showed that nucleosomes can be taken up by various mammalian cells. Additionally, we found that in vitro reconstituted mononucleosomes and oligonucleosomes can be recognized by cGAS. Compared to dsDNA, nucleosomes exhibit higher binding affinities to cGAS but considerably lower potency in cGAS activation. Incubation of monocytic cells with reconstituted nucleosomes leads to limited production of type I interferons and proinflammatory cytokines via a cGAS-dependent mechanism. This proof-of-concept study reveals the cGAS-dependent immunogenicity of nucleosomes and highlights the potential roles of circulating nucleosomes in autoimmune diseases, inflammation, and antitumour immunity.

Antibody-targeted chromatin enables effective intracellular delivery and functionality of CRISPR/Cas9 expression plasmids

We report a novel system for efficient and specific targeted delivery of large nucleic acids to and into cells. Plasmid DNA and core histones were assembled to chromatin by salt gradient dialysis and subsequently connected to bispecific antibody derivatives (bsAbs) via a nucleic acid binding peptide bridge. The resulting reconstituted vehicles termed ‘plasmid-chromatin’ deliver packaged nucleic acids to and into cells expressing antigens that are recognized by the bsAb, enabling intracellular functionality without detectable cytotoxicity. High efficiency of intracellular nucleic acid delivery is revealed by intracellular expression of plasmid encoded genes in most (∼90%) target cells to which the vehicles were applied under normal growth/medium conditions in nanomolar concentrations. Specific targeting, uptake and transgene expression depends on antibody-mediated cell surface binding: plasmid chromatin of identical composition but with non-targeting bsAbs or without bsAbs is ineffective. Examples that demonstrate applicability, specificity and efficacy of antibody-targeted plasmid chromatin include reporter gene constructs as well as plasmids that enable CRISPR/Cas9 mediated genome editing of target cells.

Illegitimate and Repeated Genomic Integration of Cell-Free Chromatin in the Aetiology of Somatic Mosaicism, Ageing, Chronic Diseases and Cancer

Emerging evidence suggests that an individual is a complex mosaic of genetically divergent cells. Post-zygotic genomes of the same individual can differ from one another in the form of single nucleotide variations, copy number variations, insertions, deletions, inversions, translocations, other structural and chromosomal variations and footprints of transposable elements. High-throughput sequencing has led to increasing detection of mosaicism in healthy individuals which is related to ageing, neuro-degenerative disorders, diabetes mellitus, cardiovascular diseases and cancer. These age-related disorders are also known to be associated with significant increase in DNA damage and inflammation. Herein, we discuss a newly described phenomenon wherein the genome is under constant assault by illegitimate integration of cell-free chromatin (cfCh) particles that are released from the billions of cells that die in the body every day. We propose that such repeated genomic integration of cfCh followed by dsDNA breaks and repair by non-homologous-end-joining as well as physical damage to chromosomes occurring throughout life may lead to somatic/chromosomal mosaicism which would increase with age. We also discuss the recent finding that genomic integration of cfCh and the accompanying DNA damage is associated with marked activation of inflammatory cytokines. Thus, the triple pathologies of somatic mosaicism, DNA/chromosomal damage and inflammation brought about by a common mechanism of genomic integration of cfCh may help to provide an unifying model for the understanding of aetiologies of the inter-related conditions of ageing, degenerative disorders and cancer.

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.

Histone-targeted gene transfer of bone morphogenetic protein-2 enhances mesenchymal stem cell chondrogenic differentiation

Skeletal tissue regeneration following traumatic injury involves a complex cascade of growth factor signals that direct the differentiation of mesenchymal stem cells (MSCs) within the fracture. The necessity for controlled and localized expression of these factors has highlighted the role gene therapy may play as a promising treatment option for bone repair. However, the design of nanocarrier systems that negotiate efficient intracellular trafficking and nuclear delivery represents a significant challenge. Recent investigations have highlighted the roles histone tail sequences play in directing nuclear delivery and activating DNA transcription. We previously established the ability to recapitulate these natural histone tail activities within non-viral nanocarriers, improving gene transfer and expression by enabling effective navigation to the nucleus via retrograde vesicular trafficking. Herein, we demonstrate that histone-targeting leads to ∼4-fold enhancements in osteogenic bone morphogenetic protein-2 (BMP-2) expression by MSCs over 6 days, as compared with standard polymeric transfection reagents. This improved expression augmented chondrogenesis, an essential first step in fracture healing. Importantly, significant enhancements of cartilage-specific protein expression were triggered by histone-targeted gene transfer, as compared with the response to treatment with equivalent amounts of recombinant BMP-2 protein. In fact, an ∼100-fold increase in recombinant BMP-2 was required to achieve similar levels of chondrogenic gene and protein expression. The enhancements in differentiation achieved using histone-targeting were in part enabled by an increase in transcription factor expression, which functioned to drive MSC chondrogenesis. These novel findings demonstrate the utility of histone-targeted gene transfer strategies to enable substantial reductions in BMP-2 dosing for bone regenerative applications.

STATEMENT OF SIGNIFICANCE

This contribution addresses significant limitations in non-viral gene transfer for bone regenerative applications by exploiting a novel histone-targeting approach for cell-triggered delivery that induces osteogenic BMP-2 expression coincident with the initiation of bone repair. During repair, proliferating MSCs respond to a complex series of growth factor signals that direct their differentiation along cellular lineages essential to mature bone formation. Although these MSCs are ideal targets for enhanced transfection during cellular mitosis, few non-viral delivery approaches exist to enable maximization of this effect. Accordingly, this contribution seeks to utilize our histone-targeted nanocarrier design strategy to stimulate BMP-2 gene transfer in dividing MSCs. This gene-based approach leads to significantly augmented MSC chondrogenesis, an essential first step in bone tissue repair.

Physical shearing imparts biological activity to DNA and ability to transmit itself horizontally across species and kingdom boundaries

Background

We have recently reported that cell-free DNA (cfDNA) fragments derived from dying cells that circulate in blood are biologically active molecules and can readily enter into healthy cells to activate DNA damage and apoptotic responses in the recipients. However, DNA is not conventionally known to spontaneously enter into cells or to have any intrinsic biological activity. We hypothesized that cellular entry and acquisition of biological properties are functions of the size of DNA.

Results

To test this hypothesis, we generated small DNA fragments by sonicating high molecular weight DNA (HMW DNA) to mimic circulating cfDNA. Sonication of HMW DNA isolated from cancerous and non-cancerous human cells, bacteria and plant generated fragments 300–3000 bp in size which are similar to that reported for circulating cfDNA. We show here that while HMW DNAs were incapable of entering into cells, sonicated DNA (sDNA) from different sources could do so indiscriminately without heed to species or kingdom boundaries. Thus, sDNA from human cells and those from bacteria and plant could enter into nuclei of mouse cells and sDNA from human, bacterial and plant sources could spontaneously enter into bacteria. The intracellular sDNA associated themselves with host cell chromosomes and integrated into their genomes. Furthermore, sDNA, but not HMW DNA, from all four sources could phosphorylate H2AX and activate the pro-inflammatory transcription factor NFκB in mouse cells, indicating that sDNAs had acquired biological activities.

Conclusions

Our results show that small fragments of DNA from different sources can indiscriminately enter into other cells across species and kingdom boundaries to integrate into their genomes and activate biological processes. This raises the possibility that fragmented DNA that are generated following organismal cell-death may have evolutionary implications by acting as mobile genetic elements that are involved in horizontal gene transfer.

Electronic supplementary material

The online version of this article (doi:10.1186/s12867-017-0098-8) contains supplementary material, which is available to authorized users.

Evidence for cell-free nucleic acids as continuously arising endogenous DNA mutagens

There is extensive literature to show that nucleic acids can be taken up by cells under experimental conditions and that foetal DNA can be detected in maternal tissues. The uptaken DNA can integrate into host cell genomes and can be transcribed and translated into proteins. They can also cause chromosomal damage and karyotype alterations. Cell-free nucleic acids (cfNAs)-based non-invasive DNA diagnostic techniques are being extensively researched in the field of cancer with the potential to advance new prognostic parameters and direct treatment decisions. However, whether extracellular cfNAs that are released into circulation from dying cells as a consequence of normal physiology have any functional significance has not been explored. A recent study has demonstrated that circulating cfNAs have the ability to cause DNA damage and mutagenesis by illegitimately integrating into healthy cells of the body, thereby acting as mobile genetic elements. Fluorescently-labeled cfNAs isolated from sera of cancer patients and healthy volunteers were shown to be readily taken up by host cells followed by activation of a DNA-damage-repair-response which led their large scale integration into the host cell genomes. The latter caused dsDNA breaks and apoptosis in cells in vitro and in those of vital organs when injected intravenously into mice. Cell-free chromatin was consistently more active than cell-free DNA, while cfNAs derived from cancer patients were significantly more active than those from healthy volunteers. This study suggests that circulating extracellular cfNAs act as physiological continuously arising DNA mutagens with implications for ageing, cancer and a host of other degenerative human pathologies.

The dark side of circulating nucleic acids

Free circulating or cell‐free DNA (cfDNA), possibly from dying cells that release their contents into the blood as they break down, have become of major interest as a source for noninvasive diagnostics. Recent work demonstrated the uptake of human cfDNA in mouse cells in vitro and in vivo, accompanied by the activation of a cellular DNA damage response (DDR) and the appearance of apoptotic proteins in the host cells. By acting as a source of mobile genetic elements, cfDNA could be a continuous source of DNA mutagenesis of healthy cells in the body throughout life, promoting progressive cellular aging in vivo. As such, cfDNA may causally contribute to multiple aging‐related diseases, such as cancer, diabetes, and Alzheimer's disease.

Importin-4 Regulates Gene Delivery by Enhancing Nuclear Retention and Chromatin Deposition by Polyplexes

For successful gene delivery, plasmid DNA must be able to access the nucleus in order to be transcribed. Numerous studies have shown that gene delivery occurs more readily in dividing cells, which is attributed to increased nuclear access when the nuclear envelope disassembles during mitosis; however, nonviral carriers continue to have low transfection efficiencies and require large quantities of DNA per cell to achieve reasonable gene transfer, even in dividing cells. Therefore, we hypothesized that using histone-derived nuclear localization sequences (NLS)s to target polyplexes might enhance nuclear delivery by facilitating interactions with histone effectors that mediate nuclear partitioning and retention during mitosis. We discovered a novel interaction between polyplexes linked to histone 3 (H3) N-terminal tail peptides and the histone nuclear import protein importin-4, as evidenced by strong spatial colocalization as well as significantly decreased transfection when importin-4 expression was reduced. A fraction of the histone-targeted polyplexes was also found to colocalize with the retrotranslocon of the endoplasmic reticulum, Sec61. Super resolution microscopy demonstrated a high level of polyplex binding to chromatin postmitosis, and there also was a significant decrease in the amount of chromatin binding following importin-4 knockdown. These results provide evidence that natural histone effectors mediate both nuclear entry and deposition on chromatin by histone-targeted polyplexes, and a translocation event from the endoplasmic reticulum into the cytosol may occur before mitosis to enable the polyplexes to interact with these essential cytoplasmic proteins.

Novel delivery approaches for cancer therapeutics

Currently, a majority of cancer treatment strategies are based on the removal of tumor mass mainly by surgery. Chemical and physical treatments such as chemo- and radiotherapies have also made a major contribution in inhibiting rapid growth of malignant cells. Furthermore, these approaches are often combined to enhance therapeutic indices. It is widely known that surgery, chemo- and radiotherapy also inhibit normal cells growth. In addition, these treatment modalities are associated with severe side effects and high toxicity which in turn lead to low quality of life. This review encompasses novel strategies for more effective chemotherapeutic delivery aiming to generate better prognosis. Currently, cancer treatment is a highly dynamic field and significant advances are being made in the development of novel cancer treatment strategies. In contrast to conventional cancer therapeutics, novel approaches such as ligand or receptor based targeting, triggered release, intracellular drug targeting, gene delivery, cancer stem cell therapy, magnetic drug targeting and ultrasound-mediated drug delivery, have added new modalities for cancer treatment. These approaches have led to selective detection of malignant cells leading to their eradication with minimal side effects. Lowering multi-drug resistance and involving influx transportation in targeted drug delivery to cancer cells can also contribute significantly in the therapeutic interventions in cancer.

Circulating nucleic acids damage DNA of healthy cells by integrating into their genomes

Whether nucleic acids that circulate in blood have any patho-physiological functions in the host have not been explored.We report here that far from being inert molecules, circulating nucleic acids have significant biological activities of their own that are deleterious to healthy cells of the body. Fragmented DNA and chromatin (DNAfs and Cfs) isolated from blood of cancer patients and healthy volunteers are readily taken up by a variety of cells in culture to be localized in their nuclei within a few minutes. The intra-nuclear DNAfs and Cfs associate themselves with host cell chromosomes to evoke a cellular DNA-damage-repair-response (DDR) followed by their incorporation into the host cell genomes. Whole genome sequencing detected the presence of tens of thousands of human sequence reads in the recipient mouse cells. Genomic incorporation of DNAfs and Cfs leads to dsDNA breaks and activation of apoptotic pathways in the treated cells. When injected intravenously into Balb/C mice, DNAfs and Cfs undergo genomic integration into cells of their vital organs resulting in activation of DDR and apoptotic proteins in the recipient cells. Cfs have significantly greater activity than DNAfs with respect to all parameters examined, while both DNAfs and Cfs isolated from cancer patients are more active than those from normal volunteers. All the above pathological actions of DNAfs and Cfs described above can be abrogated by concurrent treatment with DNase I and/or anti-histone antibody complexed nanoparticles both in vitro and in vivo. Taken together, our results suggest that circulating DNAfs and Cfs are physiological, continuously arising, endogenous DNA damaging agents with implications to ageing and a multitude of human pathologies including initiation of cancer.

Enhanced tumour cell nuclear targeting in a tumour progression model

BACKGROUND

There is an urgent need for new approaches to deliver bioactive molecules to cancer cells efficiently and specifically.

METHODS

Here we fuse the cancer cell nuclear targeting module of the Chicken Anaemia Virus Apoptin protein to the core histones H2B and H3 and utilise them in transfection, protein transduction and DNA binding assays.

RESULTS

We found subsequent nuclear accumulation of these proteins to be 2-3 fold higher in tumour compared to normal cells in transfected isogenic human osteosarcoma and breast tumour progression models. This represents the first demonstration of enhanced nuclear targeting by Apoptin in a tumour progression model, and its functionality in a heterologous protein context. Excitingly, we found that the innate transduction ability of histones could be exploited in combination with the Apoptin nuclear targeting module to effect an overall 13-fold higher delivery of protein to osteosarcoma cancer cell nuclei compared to their isogenic normal counterparts.

CONCLUSIONS

This is the first report of cancer-cell specificity by a cell penetrating protein, with important implications for the use of protein transduction as a vehicle for gene/drug delivery in the future, and in particular in the development of highly specific and effective anti-cancer agents.

Principles of electrostatic interactions and self-assembly in lipid/peptide/DNA systems: applications to gene delivery

Recently, great progress has been achieved in development of a wide variety of formulations for gene delivery in vitro and in vivo, which include lipids, peptides and DNA (LPD). Additionally, application of natural histone-DNA complexes (chromatin) in combination with transfection lipids has been suggested as a potential route for gene delivery (chromofection). However, the thermodynamic mechanisms responsible for formation of the ternary lipid-peptide-DNA supramolecular structures have rarely been analyzed. Using recent experimental studies on LPD complexes (including mixtures of chromatin with cationic lipids) and general polyelectrolyte theory, we review and analyze the major determinants defining the internal structure, particle composition and size, surface charge and ultimately, transfection properties of the LPD formulations.

Pullulan-histone antibody nanoconjugates for the removal of chromatin fragments from systemic circulation

The billions of cells that die in the adult human body daily release considerable amounts of fragmented chromatin in the form of mono- and oligonucleosomes into the circulation in normal individuals, and in higher quantities in many disease conditions. Recent results suggest that circulating chromatin fragments (Cfs) especially from abnormal cells can spontaneously enter into healthy cells to damage their DNA and induce genomic instability. Furthermore, Cfs isolated from cancer patients may induce oncogenic transformation in the recipients' cells. Thus, it follows that if such Cfs emanating from apoptotic cells could be prevented from reaching other cells, it could potentially inhibit pathological conditions, including cancer. Here we have developed pullulan based histone antibody nanoconjugates for the removal of Cfs. Nanoconjugates were developed and various physico-chemical characterizations were carried out. The efficacy of these nanoconjugates on removing Cfs was evaluated both in vitro and in vivo. Our results indicate that nanoconjugates may have therapeutic value in the efficient removal of Cfs, reducing inflammation and fatality in a mouse model of sepsis, and in preventing neutropenia following treatment with Adriamycin.

Enhanced transgene expression from chromatinized plasmid DNA in mouse liver

Plasmid DNA was chromatinized with core histones (H2A, H2B, H3, and H4) in vitro and was delivered into mouse liver by hydrodynamics-based administration. Transgene expression from the chromatinized plasmid DNA was more efficient than that from plasmid DNA delivered in the naked form. The use of acetylation-enriched histones isolated from cells treated with a histone deacetylase inhibitor (trichostatin A) seemed to be more effective. These results indicated that chromatinized plasmid DNA is useful for efficient transgene expression in vivo.

Nucleic acids in circulation: are they harmful to the host?

It has been estimated that 10(11) -10(12) cells, primarily of haematogenous origin, die in the adult human body daily, and a similar number is regenerated to maintain homeostasis. Despite the presence of an efficient scavenging system for dead cells, considerable amounts of fragmented genetic material enter the circulation in healthy individuals. Elevated blood levels of extracellular nucleic acids have been reported in various disease conditions; such as ageing and age-related degenerative disorders, cancer; acute and chronic inflammatory conditions, severe trauma and autoimmune disorders. In addition to genomic DNA and nucleosomes, mitochondrial DNA is also found in circulation, as are RNA and microRNA. There is extensive literature that suggests that extraneously added nucleic acids have biological actions. They can enter into cells in vitro and in vivo and induce genetic transformation and cellular and chromosomal damage; and experimentally added nucleic acids are capable of activating both innate and adaptive immune systems and inducing a sterile inflammatory response. The possibility as to whether circulating nucleic acids may, likewise, have biological activities has not been explored. In this review we raise the question as to whether circulating nucleic acids may have damaging effects on the host and be implicated in ageing and diverse acute and chronic human pathologies.

Ivermectin is a specific inhibitor of importin α/β-mediated nuclear import able to inhibit replication of HIV-1 and dengue virus

The movement of proteins between the cytoplasm and nucleus mediated by the importin superfamily of proteins is essential to many cellular processes, including differentiation and development, and is critical to disease states such as viral disease and oncogenesis. We recently developed a high-throughput screen to identify specific and general inhibitors of protein nuclear import, from which ivermectin was identified as a potential inhibitor of importin α/β-mediated transport. In the present study, we characterized in detail the nuclear transport inhibitory properties of ivermectin, demonstrating that it is a broad-spectrum inhibitor of importin α/β nuclear import, with no effect on a range of other nuclear import pathways, including that mediated by importin β1 alone. Importantly, we establish for the first time that ivermectin has potent antiviral activity towards both HIV-1 and dengue virus, both of which are strongly reliant on importin α/β nuclear import, with respect to the HIV-1 integrase and NS5 (non-structural protein 5) polymerase proteins respectively. Ivermectin would appear to be an invaluable tool for the study of protein nuclear import, as well as the basis for future development of antiviral agents.

Apoptin gene transfer via modified wheat histone H4 facilitates apoptosis of human ovarian cancer cells

Nonviral approaches have been used extensively for intracellular gene transfer and gene therapy. A modified wheat histone H4 protein, H4TL (H4-TAT-LHRH), as a protein-based gene delivery vector that was able to form stable complexes with plasmid DNA and increase gene delivery efficiency has been described previously. In this study, H4TL has been used to deliver apoptin gene into a human ovarian carcinoma cell line HO8910. After transfection, increased expression of apoptin at both mRNA and protein levels was detected in HO8910 cells, accompanied by reduced rate of growth of HO8910 cells in vitro and the loss of mitochondrial membrane potential in these cells. These data demonstrate that H4TL-mediated transfer of apoptin initiates mitochondrial death pathway in ovarian cancer cells and suggest a novel therapeutic strategy for cancer.

An AlphaScreen®-based assay for high-throughput screening for specific inhibitors of nuclear import

Specific viral proteins enter the nucleus of infected cells to perform essential functions, as part of the viral life cycle. The integrase (IN) molecule of human immunodeficiency virus (HIV)-1 is of particular interest in this context due to its integral role in integrating the HIV genome into that of the infected host cell. Most IN-based antiviral compounds target the IN/DNA interaction, but since IN must first enter the nucleus before it can perform these critical functions, nuclear transport of IN is also an attractive target for therapeutic intervention. Here the authors describe a novel high-throughput screening assay for identifying inhibitors of nuclear import, particularly IN, based on amplified luminescent proximity homogeneous assay (AlphaScreen(®)) technology, which is high throughput, requires low amounts of material, and is efficient and cost-effective. The authors use the assay to screen for specific inhibitors of the interaction between IN and its nuclear transport receptor importin α/β, successfully identifying several inhibitors of the IN/importin α/β interaction. Importantly, they demonstrate that one of the identified compounds, mifepristone, is effective in preventing active nuclear transport of IN in transfected cells and hence may represent a useful anti-HIV therapeutic. The screen also identified broad-spectrum importin α/β inhibitors such as ivermectin, which may represent useful tools for nuclear transport research in the future. The authors validate the activity and specificity of mifepristone and ivermectin in inhibiting nuclear protein import in living cells, underlining the utility of the screening approach.

Intracellular organelle-targeted non-viral gene delivery systems

Gene therapy is a rapidly growing approach for the treatment of various diseases. To achieve successful gene therapy, a gene delivery system is necessary to overcome several barriers in the extracellular and intracellular spaces. Polymers, peptides, liposomes and nanoparticles developed as gene carriers have achieved efficient cellular uptake of genes. Among these carriers, cationic polymers and peptides have been further developed as intracellular organelle-targeted delivery systems. The cytoplasm, nucleus and mitochondria have been considered primary targets for gene delivery using targeting moieties or environment-responsive materials. In this review, we explore recently developed non-viral gene carriers based on reducible systems specialized to target the cytoplasm, nucleus and mitochondria.

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.

Gene therapy and bone marrow stem-cell transfer to treat autoimmune disease

Current treatment of human autoimmune disease by autologous bone marrow stem-cell transfer is hampered by frequent disease relapses. This is most probably owing to re-emergent self-reactive lymphocytes. Gene therapy combined with bone marrow stem cells has successfully introduced genes lacking in immunodeficiences. Because the bone marrow compartment has a key role in establishing immune tolerance, this combination strategy should offer a rational approach to prevent re-emergent self-reactive lymphocytes by establishing solid, life-long immune tolerance to causative self-antigen. Indeed, we have recently demonstrated the success of this combination approach to prevent and cure an experimental autoimmune disease. We suggest that this combination strategy has the potential for translation to treat human autoimmune diseases in which causative self-antigens are known.

Tissue-specific and transcription factor-mediated nuclear entry of DNA

Low levels of gene transfer and a lack of tissue-specific targeting of vectors have limited the therapeutic potential of non-viral gene therapy. This is due to the numerous cellular barriers that hinder nuclear delivery of vectors and the paucity of methods that restrict expression to specific cells types. In non-dividing cells, the nuclear envelope is an especially problematic hurdle to gene transfer. Given that the majority of target tissues are non-dividing in vivo, the nuclear membrane is a major obstacle to therapeutic gene transfer. In this review, the various barriers to gene transfer are discussed. In particular, the role of the nuclear pore complex (NPC) in regulating passage of plasmid vectors during interphase is reviewed. Several methods of modifying plasmid (pDNA) vectors to enhance nuclear import through the NPC are also discussed, including the use of tissue-specific transcription factors to mediate nuclear entry of pDNA in a cell-specific manner.