Enhanced in vitro oligonucleotide and plasmid DNA transport by VP1 virus-like particles

Production and biomedical applications of virus-like particles derived from polyomaviruses

Virus-like particles (VLPs), aggregates of capsid proteins devoid of viral genetic material, show great promise in the fields of vaccine development and gene therapy. These particles spontaneously self-assemble after heterologous expression of viral structural proteins. This review will focus on the use of virus-like particles derived from polyomavirus capsid proteins. Since their first recombinant production 27 years ago these particles have been investigated for a myriad of biomedical applications. These virus-like particles are safe, easy to produce, can be loaded with a broad range of diverse cargoes and can be tailored for specific delivery or epitope presentation. We will highlight the structural characteristics of polyomavirus-derived VLPs and give an overview of their applications in diagnostics, vaccine development and gene delivery.

Nanomedicines based on recombinant fusion proteins for targeting therapeutic siRNA oligonucleotides

The enormous promise of siRNA technology for rational and targeted therapy can only be realized if the inherent problems in terms of pharmaceutical development are overcome. Besides liposomal and polymeric nanoparticles, fusion proteins hold great potential for cell-type specific delivery of siRNA. Consisting of a protein binder and an oligonucleotide complexing domain, fusion proteins are designed for targeted delivery to a certain tissue or organ and subsequent release of the siRNA after cellular uptake. This article focuses on the possibilities and importance of targeting and complexing domains, including polymers and dendrimers. In vitro and in vivo evaluations are discussed with an in-depth view on pharmacokinetic properties. Remaining challenges concerning specificity on the tissue and molecular levels are highlighted.

Relevant uses of surface proteins--display on self-organized biological structures

Proteins are often found attached to surfaces of self‐assembling biological units such as whole microbial cells or subcellular structures, e.g. intracellular inclusions. In the last two decades surface proteins were identified that could serve as anchors for the display of foreign protein functions. Extensive protein engineering based on structure–function data enabled efficient display of technically and/or medically relevant protein functions. Small size, diversity of the anchor protein as well as support structure, genetic manipulability and controlled cultivation of phages, bacterial cells and yeasts contributed to the establishment of designed and specifically functionalized tools for applications as sensors, catalysis, biomedicine, vaccine development and library‐based screening technologies. Traditionally, phage display is employed for library screening but applications in biomedicine and vaccine development are also perceived. For some diagnostic purposes phages are even too small in size so other carrier materials where needed and gave way for cell and yeast display. Only recently, intracellular inclusions such as magnetosomes, polyhydroxyalkanoate granules and lipid bodies were conceived as stable subcellular structures enabling the display of foreign protein functions and showing potential as specific and tailor‐made devices for medical and biotechnological applications.

Virus-like particles templated by DNA micelles: a general method for loading virus nanocarriers

DNA amphiphile particles template formation of virus capsids and enable their loading.

Hamster polyomavirus-derived virus-like particles are able to transfer in vitro encapsidated plasmid DNA to mammalian cells

The authentic major capsid protein 1 (VP1) of hamster polyomavirus (HaPyV) consists of 384 amino acid (aa) residues (42 kDa). Expression from an additional in-frame initiation codon located upstream from the authentic VP1 open reading frame (at position -4) might result in the synthesis of a 388 aa-long, amino-terminally extended VP1 (aa -4 to aa 384; VP1(ext)). In a plasmid-mediated Drosophila Schneider (S2) cell expression system, both VP1 derivatives as well as a VP1(ext) variant with an amino acid exchange of the authentic Met1Gly (VP1(ext-M1)) were expressed to a similar high level. Although all three proteins were detected in nuclear as well as cytoplasmic fractions, formation of virus-like particles (VLPs) was observed exclusively in the nucleus as confirmed by negative staining electron microscopy. The use of a tryptophan promoter-driven Escherichia coli expression system resulted in the efficient synthesis of VP1 and VP1(ext) and formation of VLPs. In addition, establishment of an in vitro disassembly/reassembly system allowed the encapsidation of plasmid DNA into VLPs. Encapsidated DNA was found to be protected against the action of DNase I. Mammalian COS-7 and CHO cells were transfected with HaPyV-VP1-VLPs carrying a plasmid encoding enhanced green fluorescent protein (eGFP). In both cell lines eGFP expression was detected indicating successful transfer of the plasmid into the cells, though at a still low level. Cesium chloride gradient centrifugation allowed the separation of VLPs with encapsidated DNA from "empty" VLPs, which might be useful for further optimization of transfection. Therefore, heterologously expressed HaPyV-VP1 may represent a promising alternative carrier for foreign DNA in gene transfer applications.

DNA-loaded bacterial ghosts efficiently mediate reporter gene transfer and expression in macrophages

There is a demand for efficient and safe DNA delivery vehicles mediating gene transfer and expression. We present bacterial ghosts as a novel platform technology for DNA delivery and targeting of macrophages. Bacterial ghosts are cell envelopes of gram-negative bacteria that are devoid of the cytoplasmic content. Escherichia coli ghosts were loaded with plasmid DNA and linear double-stranded DNA. Confocal laser scanning microscopy and flow cytometry confirmed that the DNA localized to the inner lumen of bacterial ghosts and was not associated with the outer surface of the bacteria. Up to approximately 6000 plasmids could be loaded per single ghost and the amount of loaded DNA correlated with the DNA concentration used for loading. E. coli ghosts loaded with plasmids encoding the enhanced green fluorescent protein (EGFP) targeted efficiently murine macrophages (RAW264.7) and mediated effective gene transfer. The EGFP was expressed by more than 60% of the macrophages as measured by flow cytometry detecting the green fluorescence and immunocytochemical staining with antibodies specific for EGFP.

Comparison of antisense oligonucleotide drug delivery systems

Antisense oligonucleotides (AS-ONs) are specific drugs to inhibit gene expression at the transcriptional level. They possess a poor bioavailability and can be degraded by nucleases very rapidly. Therefore, a strong need for the development of oligonucleotide drug delivery systems exists. In the present study, two commercially available liposomes (DOTAP, lipofectin), one artificial virus capsoid (polyoma VP1), two cationic acrylate nanoparticles and two protamine-based nanoparticle preparations (proticles) were compared. Physical parameters of all carrier systems including z-average size, size distribution and surface charge regarding were determined. Cellular uptake was measured by a microplate fluorescence quantification method and, in addition, was visualized in mouse fibroblasts by confocal laser scan microscopy (CLSM). A comparison of cytotoxicity of the different drug delivery systems was performed in vitro using a MTT assay. Mouse fibroblasts which were stable transfected with the cDNA of a N-methyl-D-aspartate (NMDA) receptor also served as functional antisense oligonucleotide test system based on excitotoxicity (cell death). In addition, the efficiency of our oligonucleotide delivery systems was compared on the level of protein expression by Western blotting. Concluding the results, an increased uptake of the ON was found (2-18-fold) for all delivery systems compared to the free ON. Protamine-based nanoparticles showed a very low cytotoxicity in contradiction to all other carrier systems. Lipofectin could be identified as the most potent delivery system in terms of antisense effect, followed by protamine nanoparticles and DOTAP. Sequence-specific antisense effects up to 80% were observed in the functional cell death assay. The highest reduction of NMDA expression was obtained from liposomal preparations with approximately 60% analyzed by Western blot.

Virus-like particles as vaccines and vessels for the delivery of small molecules

Virus-like particles (VLPs) structurally mimic the viral capsid and have therefore been extensively, and quite successfully, used as vaccine and viral serology reagents. The ability of VLPs to include nucleic acids and small molecules has also made them novel vessels for gene and drug delivery. The regular, repetitive surface of VLPs has been exploited as a template for nanoscale synthesis. Recent progress has been made in the development of several virus models.

Efficient Intracellular Delivery of a Protein and a Low Molecular Weight Substance via Recombinant Polyomavirus-like Particles

Efficient encapsulation of foreign molecules like proteins and low molecular weight drugs into polyoma virus-like particles (capsoids) was achieved by the development of an anchoring technique based upon the specific interaction of the inner core protein VP2 with VP1 pentamers. A stretch of 49 amino acids of VP2 served as an anchor molecule, either expressed as a fusion protein with green fluorescent protein (GFP) or covalently linked to methotrexate (MTX). The loaded capsoids showed regular morphology and stability for several months. GFP and MTX were internalized into cells in vitro, as was demonstrated by the detection of GFP and VP1 fluorescence in mouse fibroblasts and the cytostatic effect of intracellularly released MTX on leukemia T cells.

Cell-type specific targeting and gene expression using a variant of polyoma VP1 virus-like particles

The variant VP1-Z of the polyomavirus coat protein VP1 has been recently described as an engineered fusion protein of VP1 and the antibody binding domain protein Z. This construct is able to specifically bind and functionally present antibodies on the surface of virus-like particles of VP1-Z. Here we demonstrate that with the binding of Herceptin, an antibody directed against the receptor tyrosine kinase ErbB2, a cell type-specific targeting was established. ErbB2-positive cell lines were transduced with different plasmids encoding eGFP or beta-galactosidase. With both reporter systems functional gene expression in transduced cells could be observed. The transduction was strictly dependent on the use of a ternary complex formed of VLPs of VP1-Z, Herceptin, and the reporter plasmid DNA. The use of single components or ErbB2-negative cell lines did not result in functional gene transfer. The transduction was also completely dependent on the use of chloroquine, a lysosomotropic reagent. This indicates that the complex is internalized by ErbB2-mediated endocytosis.

Assessment of cell type specific gene transfer of polyoma virus like particles presenting a tumor specific antibody Fv fragment

Application of delivery systems in cancer therapy is restricted as a result of the lack of cell specificity of the respective vectors. Recently, a vector system based on virus-like particles (VLPs) of modified polyoma-VP1 was described which were able to bind specifically a tumor-specific antibody fragment, thus directing the vector system towards tumor cells. The functional gene transfer using the VP1 variant VP1-E8C, coupled with the antibody fragment of the tumor-specific antibody B3 is described in this paper. The specific targeting of the antigen expressing cells was highly efficient as determined by fluorescence microscopy. However, only a low percentage of these cells showed a functional gene transfer. This discrepancy could be accounted for by a rather low capacity of the virus like particles to transport DNA and the mechanism of their internalization by the target cells, which led to a lysosomal degradation of the particles. These limitations could be surmounted partially in cell culture experiments, and the principles suitable for applying this vector system in vivo are discussed.