Nuclear import of polypeptides, polynucleotides and supramolecular complexes

A novel nuclear localization region in SIPA1 determines protein nuclear distribution and epirubicin-sensitivity of breast cancer cells

Signal-induced proliferation-associated protein 1 (SIPA1) is highly expressed and mainly located in the nucleus in some breast cancer cell lines and clinical tumor tissues. Previous study revealed that nuclear localization of SIPA1 is functionally involved in breast cancer metastasis in the lymphatic gland. In the current study, we identified a non-typical region (140-179aa) of SIPA1 as a novel nuclear localization region (NLR) which is crucial for translocating the proteins into the nucleus in HEK293 cells and breast cancer cells. This region contained one basic amino acid, His160, and had no common features of typical nuclear localization signals. In addition, overexpressing SIPA1 without NLR could suppress breast cancer cell proliferation but could not promote cell migration in MCF7 cells. Furthermore, we found that a high expression of SIPA1 upregulated the expression of ABCB1, encoding multi-drug resistance protein MDR1, and promoted the resistance to epirubicin in breast cancer cells, while this effect was largely abolished in the cells with the expression of NLR-deleted SIPA1. This study overall, identified a nuclear localization-dependent region determining the nuclear distribution of SIPA1 and its regulation on epirubicin-sensitivity in breast cancer cells, which could be a potential drug target to facilitate the development of breast cancer chemotherapy.

The development of ruthenium(ii) polypyridyl complexes and conjugates for in vitro cellular and in vivo applications

Ruthenium(ii) [Ru(ii)] polypyridyl complexes have been the focus of intense investigations since work began exploring their supramolecular interactions with DNA. In recent years, there have been considerable efforts to translate this solution-based research into a biological environment with the intention of developing new classes of probes, luminescent imaging agents, therapeutics and theranostics. In only 10 years the field has expanded with diverse applications for these complexes as imaging agents and promising candidates for therapeutics. In light of these efforts this review exclusively focuses on the developments of these complexes in biological systems, both in cells and in vivo, and hopes to communicate to readers the diversity of applications within which these complexes have found use, as well as new insights gained along the way and challenges that researchers in this field still face.

Block copolymer micelles target Auger electron radiotherapy to the nucleus of HER2-positive breast cancer cells

Intracellular trafficking of Auger electron emitting radionuclides to perinuclear and nuclear regions of cells is critical to realizing their full therapeutic potential. In the present study, block copolymer micelles (BCMs) were labeled with the Auger electron emitter indium-111 ((111)In) and loaded with the radiosensitizer methotrexate. HER2 specific antibodies (trastuzumab fab) and nuclear localization signal (NLS; CGYGPKKKRKVGG) peptides were conjugated to the surface of the BCMs to direct uptake in HER2 expressing cells and subsequent localization in the cell nucleus. Cell uptake and intracellular distribution of the multifunctional BCMs were evaluated in a panel of breast cancer cell lines with different levels of HER2 expression. Indeed cell uptake was found to be HER2 density dependent, confirming receptor-mediated internalization of the BCMs. Importantly, conjugation of NLS peptides to the surface of BCMs was found to result in a significant increase in nuclear uptake of the radionuclide (111)In. Successful nuclear targeting was shown to improve the antipoliferative effect of the Auger electrons as measured by clonogenic assays. In addition, a significant radiation enhancement effect was observed by concurrent delivery of low-dose MTX and (111)In in all breast cancer cell lines evaluated.

Progress and outlook of inorganic nanoparticles for delivery of nucleic acid sequences related to orthopedic pathologies: a review

The anticipated growth in the aging population will drastically increase medical needs of society; of which, one of the largest components will undoubtedly be from orthopedic-related pathologies. There are several proposed solutions being investigated to cost-effectively prepare for the future--pharmaceuticals, implant devices, cell and gene therapies, or some combination thereof. Gene therapy is one of the more promising possibilities because it seeks to correct the root of the problem, thereby minimizing treatment duration and cost. Currently, viral vectors have shown the highest efficacies, but immunological concerns remain. Nonviral methods show reduced immune responses but are regarded as less efficient. The nonviral paradigms consist of mechanical and chemical approaches. While organic-based materials have been used more frequently in particle-based methods, inorganic materials capable of delivery have distinct advantages, especially advantageous in orthopedic applications. The inorganic gene therapy field is highly interdisciplinary in nature, and requires assimilation of knowledge across the broad fields of cell biology, biochemistry, molecular genetics, materials science, and clinical medicine. This review provides an overview of the role each area plays in orthopedic gene therapy as well as possible future directions for the field.

Delivery of plasmid DNA encoding bone morphogenetic protein-2 with a biodegradable branched polycationic polymer in a critical-size rat cranial defect model

This study investigated the delivery of plasmid DNA (pDNA) encoding bone morphogenetic protein-2 in the form of polyplexes with a biodegradable branched triacrylate/amine polycationic polymer (TAPP) that were complexed with gelatin microparticles (GMPs) loaded within a porous tissue engineering scaffold. More specifically, the study investigated the interplay between TAPP degradation, gelatin degradation, pDNA release, and bone formation in a critical-size rat cranial defect model. The pDNA release kinetics in vitro were not affected by the crosslinking density of the GMPs but depended, rather, on the degradation rates of the TAPPs. Besides the initial release of polyplexes not bound to the GMPs and the minimal release of polyplexes through diffusion or dissociation from the GMPs, the pDNA was likely released as naked pDNA or as part of an incomplete polyplex, after the degradation of fragments of the polycationic polymer. After 30 days, significantly higher amounts of pDNA were released (93%-98%) from composite scaffolds containing naked pDNA or pDNA complexed with P-AEPZ (synthesized with 1-[2-aminoethyl]piperazine, a faster degrading TAPP) compared with those containing pDNA complexed with P-DED (synthesized with N,N-dimethylethylenediamine, a slower degrading TAPP) (74%-82%). Composite scaffolds containing GMPs complexed with TAPP/pDNA polyplexes did not result in enhanced bone formation, as analyzed by microcomputed tomography and histology, in a critical-size rat cranial defect at 12 weeks postimplantation compared with those loaded with naked pDNA. The results demonstrate that polycationic polymers with a slow degradation rate can prolong the release of pDNA from the composite scaffolds and suggest that a gene delivery system comprising biodegradable polycationic polymers should be designed to release the pDNA in an intact polyplex form.

Targeting a ruthenium complex to the nucleus with short peptides

In an effort to develop octahedral metal complexes as chemotherapeutic and diagnostic agents targeted to DNA, it is critical to optimize the properties of their cellular uptake. Appending d-octaarginine has been found to improve both the uptake and nuclear localization efficiency of these complexes, but the increased positive charge interferes with selective DNA binding and hence activity. Herein, we evaluate the nuclear entry of a series of luminescent ruthenium peptide conjugates of shorter sequence and lower charge. As is the case for the d-octaarginine conjugate (Ru-D-R8), the tetrapeptide RrRK (where r=d-arginine) facilitates nuclear localization of the ruthenium complex above a threshold concentration, though the threshold is higher for this conjugate (Ru-RrRK) than for Ru-D-R8. Furthermore, appended fluorescein, which lowers the threshold concentration for Ru-D-R8, does not improve nuclear entry of Ru-RrRK, indicating that fluorescein conjugation is not a general strategy for modulating the distribution of cell-penetrating peptides. Similarly, the concentration required for nuclear entry of Ru-RrRK is much higher than has been reported for a thiazole orange RrRK conjugate, demonstrating the influence of payload on the efficiency of uptake and localization of cell-penetrating peptides.

Exploring the cellular accumulation of metal complexes

Transition metal complexes offer great potential as diagnostic and therapeutic agents, and a growing number of biological applications have been explored. To be effective, these complexes must reach their intended target inside the cell. Here we review the cellular accumulation of metal complexes, including their uptake, localization, and efflux. Metal complexes are taken up inside cells through various mechanisms, including passive diffusion and entry through organic and metal transporters. Emphasis is placed on the methods used to examine cellular accumulation, to identify the mechanism(s) of uptake, and to monitor possible efflux. Conjugation strategies that have been employed to improve the cellular uptake characteristics of metal complexes are also described.

The hsp90-FKBP52 complex links the mineralocorticoid receptor to motor proteins and persists bound to the receptor in early nuclear events

In this study, we demonstrate that the subcellular localization of the mineralocorticoid receptor (MR) is regulated by tetratricopeptide domain (TPR) proteins. The high-molecular-weight immunophilin (IMM) FKBP52 links the MR-hsp90 complex to dynein/dynactin motors favoring the cytoplasmic transport of MR to the nucleus. Replacement of this hsp90-binding IMM by FKBP51 or the TPR peptide favored the cytoplasmic localization of MR. The complete movement machinery, including dynein and tubulin, could be recovered from paclitaxel/GTP-stabilized cytosol and was fully reassembled on stripped MR immune pellets. The whole MR-hsp90-based heterocomplex was transiently recovered in the soluble fraction of the nucleus after 10 min of incubation with aldosterone. Moreover, cross-linked MR-hsp90 heterocomplexes accumulated in the nucleus in a hormone-dependent manner, demonstrating that the heterocomplex can pass undissociated through the nuclear pore. On the other hand, a peptide that comprises the DNA-binding domain of MR impaired the nuclear export of MR, suggesting the involvement of this domain in the process. This study represents the first report describing the entire molecular system that commands MR nucleocytoplasmic trafficking and proposes that the MR-hsp90-TPR protein heterocomplex is dissociated in the nucleus rather than in the cytoplasm.

Polyethylenimine-mediated gene delivery to the lung and therapeutic applications

Nonviral gene delivery is now considered a promising alternative to viral vectors. Among nonviral gene delivery agents, polyethylenimine (PEI) has emerged as a potent candidate for gene delivery to the lung. PEI has some advantages over other polycations in that it combines strong DNA compaction capacity with an intrinsic endosomolytic activity. However, intracellular (mainly the nuclear membrane) and extracellular obstacles still hamper its efficiency in vitro and in vivo, depending on the route of administration and the type of PEI. Nuclear delivery has been increased by adding nuclear localization signals. To overcome nonspecific interactions with biological fluids, extracellular matrix components and nontarget cells, strategies have been developed to protect polyplexes from these interactions and to increase target specificity and gene expression. When gene delivery into airway epithelial cells of the conducting airways is necessary, aerosolization of complexes seems to be better suited to guarantee higher transgene expression in the airway epithelial cells with lower toxicity than observed with either intratracheal or intravenous administration. Aerosolization, indeed, is useful to target the alveolar epithelium and pulmonary endothelium. Proof-of-principle that PEI-mediated gene delivery has therapeutic application to some genetic and acquired lung disease is presented, using as genetic material either plasmidic DNA or small-interfering RNA, although optimization of formulation and delivery protocols and limitation of toxicity need further studies.

Effect of peptides bearing nuclear localization signals on therapeutic ultrasound mediated gene delivery

BACKGROUND

One of the major limitations of nonviral gene delivery methods is nuclear transport of plasmid DNA (pDNA). Peptides bearing nuclear localization signal (NLS) were shown to mediate nuclear import of macromolecules. We have explored the use of cell-permeable peptides (CPP) bearing NLS sequences to enhance transfection mediated by a nonviral approach: therapeutic ultrasound (TUS).

METHODS

Two CPP-NLS peptides which differ in the location of the NLS relative to the CPP were used: S4 13-PV and PV-S4 13. The peptides were attached to pDNA using electrostatic interactions. Gel-electrophoresis and fluorescent assays were performed to evaluate pDNA-peptide interactions and condensation effects. Confocal microscopy was used to evaluate pDNA-peptide interaction inside cells. Transfection studies were conducted with the luciferase gene, using pDNA-peptides alone, or with the application of TUS.

RESULTS

Attachment of both peptides to pDNA condensed the pDNA, with higher affinity for the S4(13)-PV peptide. This interaction protected pDNA from endonucleases, but was also reversible. Both peptides mediated pDNA delivery to cell cytoplasm, but less significantly to the nucleus. Thus, both peptides produced transfection in cells, when added after incubation with DNA, with higher transfection-level for PV-S4 13. Application of TUS increased transfection mediated by these peptides, but was not higher compared to transfection using TUS and pDNA alone.

CONCLUSIONS

This study suggests that CPP-NLS peptides may be used for condensing pDNA and bringing it into the cell cytoplasm, but their ability to mediate nuclear import of pDNA is insignificant.

Improved cytotoxicity of doxorubicin by enhancing its nuclear delivery mediated via nanosized micelles

For antitumor drugs with an intracellular action site in the nucleus, effective internalization of the drugs into cancer cells and accumulation in the nucleus should be the determinant step for high antitumor activity. We synthesized a novel chitosan derivative by grafting stearic acid onto chitosan. The derivative can form self-aggregated micelles with about 50 nm size in the aqueous medium, and then can load a poorly soluble antitumor drug (doxorubicin, DOX) with high entrapment efficiency and drug loading. DOX release from the micelles was retarded significantly as a result of the encapsulation of the micelles. DOX concentration in nuclei was increased significantly via the transport of the micelles. Consequently, cytotoxicity of DOX loaded micelles was improved sharply due to the accumulation of the drug in its intracellular action site. The present micelles are a promising carrier candidate for effective therapy of antitumor drugs with the action site in the nucleus.

Nanoparticles as nonviral gene delivery vectors

Gene therapy, as therapeutic treatment to genetic or acquired diseases, is attracting much interest in the research community, leading to noteworthy developments over the past two decades. Although this field is still dominated by viral vectors, nonviral vectors have recently received an ever increasing attention in order to overcome the safety problems of their viral counterpart. This review presents the biological aspects involved in the gene delivery process and explores the recent developments and achievements of nonviral gene carriers.

A composite gene delivery system consisting of polyethylenimine and an amphipathic peptide KALA

BACKGROUND

Animal viruses such as enveloped virus carry multi-functional proteins in the virion that can mediate more than two distinct steps of a gene delivery process during the transfer of viral genome into host cells. We tested if the aspects of the viral gene delivery mechanism could be mimicked by forming composite formulae from multi-functional synthetic gene carriers having complementary action modes.

METHODS

Polyethylenimine (PEI) was chosen as the component responsible for endosome escape and DNA condensation and KALA for cellular entry and DNA condensation. Compact DNA-carrier particles consisting of the core part where DNA chains were tightly condensed by PEI and the outer layer lined with KALA were formulated, characterized and compared with monolithic cationic formulae in terms of gene delivery efficiency and mechanism.

RESULTS

High-level gene expression was observed when C2C12 cells were transfected with DNA that was first partially condensed with PEI and, then, fully with KALA. In these formulae KALA mediated enhanced cellular entry of DNA by facilitating endocytic vesicle formation, while PEI provided an effective endosomolytic capacity. An optimal PEI/KALA formula showed transfection efficiencies better than or comparable to the commercial cationic liposome in various cell types in culture and in vivo.

CONCLUSIONS

Gene delivery by combining the membrane-active property of KALA with the endosomolytic activity of PEI can be more efficient than that by either of the properties alone. It appears that, in these formulae, the predominant role of KALA is to facilitate cellular entry of DNA by providing a fusogenic capability, rather than an endosomolytic activity.

Undetectable levels of N6-methyl adenine in mouse DNA: Cloning and analysis of PRED28, a gene coding for a putative mammalian DNA adenine methyltransferase

Three methylated bases, 5-methylcytosine, N4-methylcytosine and N6-methyladenine (m6A), can be found in DNA. However, to date, only 5-methylcytosine has been detected in mammalian genomes. To reinvestigate the presence of m6A in mammalian DNA, we used a highly sensitive method capable of detecting one N6-methyldeoxyadenosine per million nucleosides. Our results suggest that the total mouse genome contains, if any, less than 10(3) m6A. Experiments were next performed on PRED28, a putative mammalian N6-DNA methyltransferase. The murine PRED28 encodes two alternatively spliced RNA. However, although recombinant PRED28 proteins are found in the nucleus, no evidence for an adenine-methyltransferase activity was detected.

Influence of serine O-glycosylation or O-phosphorylation close to the vJun nuclear localisation sequence on nuclear import

Nuclear import triggered by the nuclear-localisation sequence (NLS) of the viral Jun (vJun) protein is mediated by phosphorylation of a serine close to the NLS. Since phosphorylation and glycosylation of serine residues are often in a reciprocal "yin-yang" relationship, we investigated whether glycosylation of this serine with O-linked N-acetylglucosamine (O-GlcNAc) would also regulate nuclear import via the vJun NLS. Peptides containing the vJun NLS with an adjacent O-phosphorylated, O-GlcNAc-functionalised or unmodified serine, and equipped with an N-terminal biotin or a 7-nitrobenz-2-oxa-1,3-diazolyl (NBD) fluorescent label, were synthesised on the solid phase by means of an Fmoc/Boc strategy and a Pd0-sensitive HYCRON linker. Fluorescence-polarisation measurements on the NBD-labelled peptides indicated that modification with phosphate or O-GlcNAc leads to a decrease in affinity to the import-mediating adapter protein, importin alpha, of about one order of magnitude compared to the unmodified NLS. Microinjection of biotinylated NLS peptide conjugated with fluorescently labelled avidin into NIH/3T3 and MDCK cells, revealed that avidin-unmodified-NLS peptide was rapidly imported into the nucleus. However, either phosphate or O-GlcNAc next to the NLS caused almost complete exclusion of the protein conjugate from nuclear import. These findings indicate that nuclear import by the vJun NLS might not be regulated by a "yin-yang" modification of an adjacent serine with phosphate or O-GlcNAc. Rather, negative regulation of binding between the polybasic NLS and importin by a negatively charged or a bulky, uncharged residue appears likely.

Plasmid DNA and siRNA transfection of intestinal epithelial monolayers by electroporation

This study was conducted to evaluate the ability of electroporation to efficiently transfect differentiated intestinal epithelial monolayers with plasmid DNA and to determine whether electroporation can transfect these monolayers with short-interfering RNA (siRNA) to cause gene silencing. Confluent T84 monolayers were transfected with reporter plasmids expressing luciferase or green-fluorescent protein or with siRNA directed against the nuclear envelope proteins lamin A/C using electroporation. Optimized electroporation conditions resulted in luciferase and GFP expression. Both intracellular uptake of fluorescently labeled plasmid and expression of the reporter genes increased with increasing electroporation strength and DNA concentration. When monolayers were transfected by lipofection with the reporter plasmids, expression and DNA uptake were less than for electroporation. Electroporation was also found to transfect monolayers with siRNA, which resulted in up to 90% inhibition of targeted protein production. Silencing occurred within 24h of transfection and increased with increasing siRNA concentration. These results suggest that electroporation can provide a valuable research tool for transfection of intestinal epithelial monolayers and other differentiated cell systems, and may ultimately be useful for clinical gene therapy applications.

Novel molecular approaches to cystic fibrosis gene therapy

Gene therapy holds promise for the treatment of a range of inherited diseases, such as cystic fibrosis. However, efficient delivery and expression of the therapeutic transgene at levels sufficient to result in phenotypic correction of cystic fibrosis pulmonary disease has proved elusive. There are many reasons for this lack of progress, both macroscopically in terms of airway defence mechanisms and at the molecular level with regard to effective cDNA delivery. This review of approaches to cystic fibrosis gene therapy covers these areas in detail and highlights recent progress in the field. For gene therapy to be effective in patients with cystic fibrosis, the cDNA encoding the cystic fibrosis transmembrane conductance regulator protein must be delivered effectively to the nucleus of the epithelial cells lining the bronchial tree within the lungs. Expression of the transgene must be maintained at adequate levels for the lifetime of the patient, either by repeat dosage of the vector or by targeting airway stem cells. Clinical trials of gene therapy for cystic fibrosis have demonstrated proof of principle, but gene expression has been limited to 30 days at best. Results suggest that viral vectors such as adenovirus and adeno-associated virus are unsuited to repeat dosing, as the immune response reduces the effectiveness of each subsequent dose. Nonviral approaches, such as cationic liposomes, appear more suited to repeat dosing, but have been less effective. Current work regarding non-viral gene delivery is now focused on understanding the mechanisms involved in cell entry, endosomal escape and nuclear import of the transgene. There is now increasing evidence to suggest that additional ligands that facilitate endosomal escape or contain a nuclear localization signal may enhance liposome-mediated gene delivery. Much progress in this area has been informed by advances in our understanding of the mechanisms by which viruses deliver their genomes to the nuclei of host cells.

Carrier-based strategies for targeting protein and peptide drugs to the lungs

With greater interest in delivery of protein and peptide-based drugs to the lungs for topical and systemic activity, a range of new devices and formulations are being investigated. While a great deal of recent research has focused on the development of novel devices, attention must now be paid to the formulation of these macromolecular drugs. The emphasis in this review will be on targeting of protein/peptide drugs by inhalation using carriers and ligands.

Hoechst 33258 as a pH-Sensitive Probe to Study the Interaction of Amine Oxide Surfactants with DNA

The use of Hoechst 33258 (HO) as a fluorescent probe to characterize the interactions between DNA and pH-sensitive amphiphiles is discussed. In the case of amine oxide amphiphiles dodecyldimethylamine oxide (DDAO) and p-dodecyloxybenzyldimethylamine oxide (pDoAO), the decrease in fluorescence emission, which signals DNA-amphiphile association, is accompanied by a large hypsochromic shift in the emission maximum of the bound probe; this eventually reaches a value characteristic of HO in a neutral or slightly basic environment. These findings are compared to results obtained by using the more common ethidium bromide (EB) probe, which shows no such shift. Circular dichroism and fluorescence depolarization experiments indicate that fluorescence emission only occurs from the DNA-bound probe, and the observed shift in emission maximum when using HO as a fluorescent probe is due to a variation in the local pH in the vicinity of the probe.

Cyclodextrins and oligonucleotide delivery to solid tumours

Cyclodextrins (CyDs) have traditionally been used for dissolving hydrophobic chemicals into aqueous media, and more recently, for inducing cholesterol efflux from lipid-laden cells as a proposed mechanism for reversal of cardiovascular disease. This review discusses the potential of delivering therapeutic oligonucleotides to solid tumours using CyD molecules. The physicochemical properties of these oligosaccharide molecules, and the barriers posed by the solid tumour itself, factors that affect may affect the uptake of oligonucleotides by CyDs, are the major foci of this review.

Gene delivery in bone tissue engineering: progress and prospects using viral and nonviral strategies

Bone tissue loss as a consequence of the natural aging process or as a result of trauma and degenerative disease has led to the need for procedures to generate cartilage and bone for a variety of orthopedic applications. The ability to transfer genes into multipotential mesenchymal stem cells, while still in its infancy, offers considerable therapeutic hope in a variety of musculoskeletal disorders. However, the choice of gene delivery method is key. This review examines the various techniques and methods currently available to enable gene transfer into a target population from viral methods (transduction) to nonviral (transfection) methods and the limitations associated with each method. The potential applications and current understanding of each method are presented. Given the demographic challenge of an aging population, the ultimate goal remains the development of simple, safe, and reproducible strategies for gene delivery that will address the pressing orthopedic clinical imperatives of many.

Nanoparticles of compacted DNA transfect postmitotic cells

Charge-neutral DNA nanoparticles have been developed in which single molecules of DNA are compacted to their minimal possible size. We speculated that the small size of these DNA nanoparticles may facilitate gene transfer in postmitotic cells, permitting nuclear uptake across the 25-nm nuclear membrane pore. To determine whether DNA nanoparticles can transfect nondividing cells, growth-arrested neuroblastoma and hepatoma cells were transfected with DNA/liposome mixtures encoding luciferase. In both models, growth-arrested cells were robustly transfected by compacted DNA (6,900-360-fold more than naked DNA). To evaluate mechanisms responsible for enhanced transfection, HuH-7 cells were microinjected with naked or compacted plasmids encoding enhanced green fluorescent protein. Cytoplasmic microinjection of DNA nanoparticles generated a approximately 10-fold improvement in transgene expression as compared with naked DNA; this enhancement was reversed by the nuclear pore inhibitor, wheat germ agglutinin. To determine the upper size limit for gene transfer, DNA nanoparticles of various sizes were microinjected into the cytoplasm. A marked decrease in transgene expression was observed as the minor ellipsoidal diameter approached 25 nm. In summary, suitably sized DNA nanoparticles productively transfect growth arrested cells by traversing the nuclear membrane pore.

Design strategies to improve soluble macromolecular delivery constructs

Macromolecular therapeutics provide numerous benefits for the delivery of cytotoxic or poorly soluble drugs in vivo. However, these constructs often encounter barriers for drug delivery on both the systemic and subcellular level. Many soluble polymer carriers have been designed to surmount specific physiological barriers individually, but less work has been dedicated to designing an all-encompassing construct that addresses multiple therapeutic barriers at once. Incorporation of multiple agents already individually known to increase effectiveness into one carrier could further improve current drug delivery technology. Recent developments in subcellular delivery of therapeutic agents in soluble macromolecular carriers are discussed in the context of the future possibility for the design of an all-encompassing soluble multi-functional drug delivery vehicle.

Vehicles for oligonucleotide delivery to tumours

The vasculature of a tumour provides the most effective route by which neoplastic cells may be reached and eradicated by drugs. The fact that a tumour's vasculature is relatively more permeable than healthy host tissue should enable selective delivery of drugs to tumour tissue. Such delivery is relevant to carrier-mediated delivery of genetic medicine to tumours. This review discusses the potential of delivering therapeutic oligonucleotides (ONs) to tumours using cationic liposomes and cyclodextrins (CyDs), and the major hindrances posed by the tumour itself on such delivery. Cationic liposomes are generally 100-200 nm in diameter, whereas CyDs typically span 1.5 nm across. Cationic liposomes have been used for the introduction of nucleic acids into mammalian cells for more than a decade. CyD molecules are routinely used as agents that engender cholesterol efflux from lipid-laden cells, thus having an efficacious potential in the management of atherosclerosis. A recent trend is to employ these oligosaccharide molecules for delivering nucleic acids in cells both in-vitro and in-vivo. Comparisons are made with other ON delivery agents, such as porphyrin derivatives (< 1 nm), branched chain dendrimers (approximately 10 nm), polyethylenimine polymers (approximately 10 nm), nanoparticles (20-1,000 nm) and microspheres (> 1 microm), in the context of delivery to solid tumours. A discourse on how the chemical and physical properties of these carriers may affect the uptake of ONs into cells, particularly in-vivo, forms a major basis of this review.

Key issues in non-viral gene delivery

The future of non-viral gene therapy depends on a detailed understanding of the barriers to delivery of polynucleotides. These include physicomechanical barriers, which limit the design of delivery devices, physicochemical barriers that influence self-assembly of colloidal particulate formulations, and biological barriers that compromise delivery of the DNA to its target site. It is important that realistic delivery strategies are adopted for early clinical trials in non-viral gene therapy. In the longer term, it should be possible to improve the efficiency of gene delivery by learning from the attributes which viruses have evolved; attributes that enable translocation of viral components across biological membranes. Assembly of stable, organized virus-like particles will require a higher level of control than current practice. Here, we summarize present knowledge of the biodistribution and cellular interactions of gene delivery systems and consider how improvements in gene delivery will be accomplished in the future.

Gene medicine : a new field of molecular medicine

Gene therapy has emerged as a new concept of therapeutic strategies to treat diseases which do not respond to the conventional therapies. The principle of gene therapy is to introduce genetic materials into patient cells to produce therapeutic proteins in these cells. Gene therapy is now at the stage where a number of dinical trials have been carried out to patients with gene-deficiency disease or cancer. Genetic materials for gene therapy are generally composed of gene expression system and gene delivery system. For the dinical application of gene therapy in a way which conventional drugs are used, researches have been focused on the design of gene delivery system which can offer high transfection efficiency with minimal toxicity. Currently, viral delivery systems generally provide higher transfection efficiency compared with non-viral delivery systems while non-viral delivery systems are less toxic, less immunogenic and manufacturable in large scale compared with viral systems. Recently, novel strategies towards the design of new non-viral delivery system, combination of viral and non-viral delivery systems and targeted delivery system have been extensively studied. The continued effort in this area will lead us to develop gene medicine as 'gene as a drug' in the near future.

Development of biomaterials for gene therapy

Novel biocompatible polymeric gene carriers have been examined for their potential in treating various genetic and acquired diseases. The use of polymeric gene carriers may overcome the current problems associated with viral vectors in safety, immunogenicity, and mutagenesis. However, effective polymer-based gene therapy requires the control of cellular access and uptake, intracellular trafficking, and nuclear retention of plasmid DNA. Inefficient endosomal release, cytoplasmic transport, and nuclear entry of plasmids are currently limiting factors in the use of polymers for effective plasmid-based gene therapy. Therefore, several different polymeric gene carriers have been designed recently in an attempt to overcome these problems. This review explores the conceptual and experimental aspects of polymer-based gene delivery and presents an overview on the recent use of polymers to enhance the effectiveness of plasmid-based systems. Despite their current limitations, polymeric carriers have significant potential as commercially viable gene medicines.

The physical properties of biogels and their permeability for macromolecular drugs and colloidal drug carriers

Macromolecular drugs, either free or complexed with colloidal drug carriers, have created a great deal of interest during the last decade. If one wants to administer these new therapeutics via the oral, nasal, and cervical routes or through the conductive airways, one of the first barriers to overcome is the mucus layer that adheres to the related epithelia. In this review, the physicochemical properties of biogels, macromolecular drugs, and colloidal drug carriers that play a major role in transport through biogels are reviewed. Also, methods of studying the mobility of macromolecular drugs and colloidal drug carriers in and through biogels are addressed.

Pharmaceutical and biological properties of poly(amino acid)/DNA polyplexes

Physicochemical properties of polyplexes formed between pRSVlacZ and poly(amino acid)s were investigated as a paradigm of more complex, synthetic virus-like, DNA delivery systems, that are of interest to many gene delivery laboratories. We observed the interaction between polymer and DNA using ethidium exclusion, and determined the size distributions and the zeta potentials of polyplexes. We correlated these properties with their fundamental interactions with cultured B16 murine melanoma cells, and the resulting efficiency of transfection. A variety of poly(amino acid)s each condensed DNA to produce particles with mean hydrodynamic diameters of approximately 100 nm (a typical span of a population was 80-120nm). Poly(amino acid) polyplexes were unstable in electrolyte solutions such as cell culture media. The apparent particle size increased in electrolyte, depending on the charge ratio, to diameters up to 700 nm. This was thought to be due to aggregation, since neutral particles were most sensitive. When the charge ratio (+/-) exceeded unity polyplexes had positive zeta potentials (which peaked at approximately +30 mV), bound non-specifically to cells, were internalised and in the presence of an endosomolytic agent were able to transfect cells. Though all cationic poly(amino acid)s investigated formed polyplexes with similar physical properties, their biological properties were significantly different. Polyplexes prepared with poly-L-ornithine were the most effective transfection agents, but poly(lys-co-ala, 1: 1) systems appeared to be inactive. This may reflect the differences in uncoupling of DNA and polymer, which is expected to be necessary for passage through the nuclear pore. Uncoupling of polycation and DNA was investigated by exposing the complexes to dextran sulphate. Release of DNA was detected by increased fluorescence at 600 nm in the presence of ethidium. Release of DNA was incomplete from polyplexes formed with high molecular weight polylysine. This may explain the lower levels of transfection observed with high molecular weight polylysine. The significance of these observations for design of advanced non-viral gene delivery systems is discussed.

Key issues in non-viral gene delivery

The future of non-viral gene therapy depends on a detailed understanding of the barriers to delivery of polynucleotides. These include physicomechanical barriers, which limit the design of delivery devices, physicochemical barriers that influence self-assembly of colloidal particulate formulations, and biological barriers that compromise delivery of the DNA to its target site. It is important that realistic delivery strategies are adopted for early clinical trials in non-viral gene therapy. In the longer term, it should be possible to improve the efficiency of gene delivery by learning from the attributes which viruses have evolved; attributes that enable translocation of viral components across biological membranes. Assembly of stable, organized virus-like particles will require a higher level of control than current practice. Here, we summarize present knowledge of the biodistribution and cellular interactions of gene delivery systems and consider how improvements in gene delivery will be accomplished in the future.