Artificial viral envelopes containing recombinant Human Immunodeficiency Virus (HIV) gp160

A review of RGD-functionalized nonviral gene delivery vectors for cancer therapy

The development of effective treatments that enable many patients suffering from cancer to be successfully cured is highly demanded. Angiogenesis, which is a process for the formation of new capillary blood vessels, has a crucial role in solid tumor progression and the development of metastasis. Antiangiogenic therapy designed to prevent tumor angiogenesis, thereby arresting the growth or spread of tumors, has emerged as a non-invasive and safe option for cancer treatment. Due to the fact that integrin receptors are overexpressed on the surface of angiogenic endothelial cells, various strategies have been made to develop targeted delivery systems for cancer gene therapy utilizing integrin-targeting peptides with an exposed arginine-glycine-aspartate (RGD) sequence. The aim of this review is to summarize the progress and prospect of RGD-functionalized nonviral vectors toward targeted delivery of genetic materials in order to achieve an efficient therapeutic outcome for cancer gene therapy, including antiangiogenic therapy.

HVJ liposomes and HVJ envelope vectors

This protocol describes techniques for construction of fusion-mediated vectors based on inactivated HVJ (hemagglutinating virus of Japan; Sendai virus). HVJ liposomes are constructed by fusing liposomes containing DNA with inactivated HVJ. The HVJ envelope vector, a more simplified vector, incorporates DNA into inactivated HVJ particles without liposomes. Both vectors have many advantages. They can be used to introduce proteins, peptides, oligonucleotides (including antisense oligonucleotides, decoy oligonucleotides, and ribozymes), and short interfering RNA (siRNA), as well as plasmid DNA, into cultured cells in vitro and into organs in vivo. Fusion-mediated delivery avoids the degradation of therapeutic molecules before reaching the cytoplasm. Finally, repeated injection of the vector in vivo is not inhibited and even enhances the effects of the delivered molecules. These vectors have been used in many gene therapy experiments in animal models to address problems such as liver cirrhosis, hearing impairment, ischemic brain damage, peripheral arterial diseases, and cancers. This protocol describes methods for the preparation of HVJ liposomes and of HVJ envelope vectors and their use in delivery of plasmid DNA into various cells and tissues.

Cell-specific targeting of lipid-based carriers for ODN and DNA

It is well recognized that there is an urgent need for non-toxic systemically applicable vectors for biologically active nucleotides to fully exploit the current potential of molecular medicine in gene therapy. Cell-specific targeting of non-viral lipid-based carriers for ODN and DNA is a prerequisite to attain the concentration of nucleic acids required for therapeutic efficacy in the target tissue. In this review we will address the most promising approaches to selective targeting of liposomal nucleic acid carriers in vivo. In addition, the routes of entry and intracellular processing of these carrier systems are discussed as well as physiological factors potentially interfering with the biological and/or therapeutic activity of their nucleotide pay-load.

Efficient gene delivery with serum into human cancer cells using targeted anionic liposomes

Success of human gene therapy depends upon the development of delivery vehicles or vectors, which can selectively deliver therapeutic genes to target cells with efficiency and safety. Previous studies have shown an efficient, systemic trans-gene expression in many cell lines (in vitro) by using an anionic liposomal vector, based on the composition of retroviral envelopes (artificial viral envelopes, AVEs). The AVE-liposomes and their complexes with plasmid (DNA) were characterized according to zeta potential measurements and transmission electron microscopy (TEM). We successfully demonstrated that AVE liposomes, dispersed in 10% serum-containing growth medium, efficiently delivered plasmid DNA to HuH-7 (human hepatoma cell line) cells. We assessed the utility of liver-targeted vesicles as a drug/gene delivery system for the treatment of liver diseases. We found that small unilamellar AVE vesicles containing 15 mol% digalactosyl diglyceride (DGDG) are efficiently targeted to the liver via the hepatic asialoglycoprotein receptor.

Encapsulation of gadobutrol in AVE-based liposomal carriers for MR detectability

Artificial virus-like envelopes (AVEs) are liposomal carriers that may be useful for target-site-specific delivery of contrast agents. We speculated that T(1) relaxation times of a suspension of Gadolinium-filled AVEs might be shortened after internalization and lysosomal breakdown. To test this hypothesis we evaluated the T(1) relaxation times of Gadobutrol-containing AVEs before and after degradation in vitro and after receptor-mediated cellular uptake. AVEs were filled with 1 M Gadobutrol (Gadovist; Schering AG, Berlin, Germany) yielding Gd-chelate-AVEs. T(1)-relaxation times were calculated using an inversion recovery technique for different concentrations of the liposomal suspension. AVEs were degraded in vitro to mimic the release of the encapsulated Gadolinium in cells and to determine a putative increase of the T(1)-effect. Finally, Gd-chelate-AVEs where equipped with integrin-binding RGD ligands and the T1 relaxation times of these Gd-chelate-RDG-AVEs were determined after cellular uptake into endothelial or melanoma cells. Gadobutrol could be encapsulated into AVEs at a high concentration of 1 M (Gd-chelate-AVEs). The Gd-chelate-AVEs could be visualized by MRI. Concentrations down to 1:4 x 10(3) showed a significant T(1)-shortening effect. The degradation of the liposomes with Triton X-100 resulted in a further reduction down to concentrations of 1:10 x 10(3). In addition, cellular uptakes of Gd-chelate-RGD-AVEs also lead to a significant T(1)-shortening. Our study shows that Gadolinium can be efficiently encapsulated into AVEs and that Gd-chelate-AVEs can be detected by MRI T(1)-weighted measurements. The MRI detectability is enhanced by degradation. Gd-chelate-RGD-AVEs can be used to enhance the Gd uptake in cells expressing the alpha(v)beta(3) receptor.

Aerosolization of lipoplexes using AERx Pulmonary Delivery System

The lung represents an attractive target for delivering gene therapy to achieve local and potentially systemic delivery of gene products. The objective of this study was to evaluate the feasibility of the AERx Pulmonary Delivery System for delivering nonviral gene therapy formulations to the lung. We found that "naked" DNA undergoes degradation following aerosolization through the AERx nozzle system. However, DNA formulated with a molar excess of cationic lipids (lipoplexes) showed no loss of integrity. In addition, the lipoplexes showed no significant change in particle size, zeta (zeta) potential, or degree of complexation following extrusion. The data suggest that complexation with cationic lipids had a protective effect on the formulation following extrusion. In addition, there was no significant change in the potency of the formulation as determined by a transfection study in A-549 cells in culture. We also found that DNA formulations prepared in lactose were aerosolized poorly. Significant improvements in aerosolization efficiency were seen when electrolytes such as NaCl were added to the formulation. In conclusion, the data suggest that delivery of lipoplexes using the AERx Pulmonary Delivery System may be a viable approach for pulmonary gene therapy.

A new colloidal lipidic system for gene therapy

A novel type of liposomal vector for gene therapy is described (Artificial Virus Particles; AVPs). This vector is based on the composition of retroviral envelopes, serum-resistant and non-toxic and smaller than 200 nm in size. The DNA is condensed using low molecular weight branched PEI. Equipment of these particles with a cyclic RGD peptide ligand as targeting device renders them selective for tumor endothelial and melanoma cells expressing high levels of alphavbeta3-integrins, and allows for an efficient delivery of the enclosed genetic material. The specificity of the vector system for melanoma cells could be further improved by using a melanocyte-specific tyrosinase promoter to drive transgene expression.

Combined transductional and transcriptional targeting of melanoma cells by artificial virus-like particles

BACKGROUND

Artificial virus-like particles (AVPs) represent a novel type of liposomal vector resembling retroviral envelopes. AVPs are serum-resistant and non-toxic and can be endowed with a peptide ligand as a targeting device. The vitronectin receptor, alphavbeta3-integrin, is commonly upregulated on malignant melanoma cells. In the present study we investigated whether AVPs carrying cyclic peptides with an RGD integrin binding motif (RGD-AVPs) are suitable for the specific and efficient transduction of human melanoma cells.

METHODS

Plasmid DNA was complexed with low molecular weight non-linear polyethyleneimine and packaged into anionic liposomes. Transduction efficiencies were determined after transient transfection of different cell lines in serum-free medium using green fluorescent protein or luciferase reporter genes.

RESULTS

We demonstrated that RGD-AVPs transduced human melanoma cells with high efficiencies of > 60%. Efficient transduction was clearly dependent on the presence of the cyclic RGD ligand and was selective for melanoma cells. The specificity of the vector system could be further enhanced by using the melanocyte-specific tyrosinase promoter to drive transgene expression.

CONCLUSION

Our findings suggest that the AVP technology is a useful approach for generating highly efficient and specific non-viral vectors for melanoma targeting, in particular in a setting of combined transductional and transcriptional targeting.

Nuclear transport of oligonucleotides in HepG2-cells mediated by protamine sulfate and negatively charged liposomes

PURPOSE

The aim of this study was to characterize the intracellular fate and nuclear uptake kinetics of oligonucleotides (ON) that were complexed with protamine sulfate (PS) and negatively charged liposomes at different ratios of ON to PS.

METHODS

Double-fluorescence labelling of ON and liposomal lipid was applied to simultaneously monitor the interaction as well as the individual fate of active agent and carrier upon intracellular delivery using confocal laser scanning microscopy (CLSM). A DNA-analogue of a 68-mer intramolecular double-stranded RNA:DNA-hybridoligonucleotide (chimeraplasts) with unmodified phosphate backbone was employed. This construct was condensed with PS and coated with a liposomal formulation (AVE-3 = artificial viral envelope).

RESULTS

PS-ON complexes and AVE -3-coated complexes with a defined composition were very effective in nuclear transport of ON for a ON:PS charge ratio of 1:3. Nucleus:cytosol fluorescence ratios peaked at about 10 hrs and started to decrease again at 21 hrs.

CONCLUSIONS

AVE associates with PS-condensed ON, and this complex is able to be taken up by cells and to deliver ON to the nucleus. PS-ON complexes are released from the liposomal formulation, mainly as an extranuclear enzymatic degradation of the liposomal phospholipids. The results of the kinetic analysis can be used to optimize transfection protocols with ON in HepG2 cells.

Virosomes: evolution of the liposome as a targeted drug delivery system

The drug delivery system (DDS) is attractive as a therapeutic method. Liposomes are of particular interest as a DDS because they can reduce drug toxicity, and offer promise as gene carriers. An evolution has occurred in the construction of liposomes in the effort to develop efficient vectors for in vivo use. To avoid uptake by the reticuloendothelial system (RES); Lipid components have been optimized. To enhance tissue targeting, liposome surface has been modified with antibodies or ligands recognized by specific cell types. To enhance the efficiency of gene delivery by the introduction of molecules directly into cells, virosomes have been developed by combining liposomes with fusiogenic viral envelope proteins. Liposomes are now being used in the treatment of intractable human diseases such as cancer and monogenic disorders. In the future, many medical procedures will be performed using liposomes.

Nuclear gene targeting using negatively charged liposomes

Oligonucleotides are a very useful tool to control gene activity. Oligos work by complementary base-pairing with target sequences either in the nucleus or in the cytosol (Zelphati, O., Szoka, F.C., Jr., 1996. Liposomes as a carrier for intracellular delivery of antisense oligonucleotides: a real or magic bullet? J. Contr. Rel. 41, 99-119). In a new approach using chimeric oligonucleotides (Yoon, K., Cole Strauss, A., Kmiec, E.B., 1996. Targeted gene correction of episomal DNA in mammalian cells mediated by a chimeric RNA-DNA oligonucleotide. Proc. Natl. Acad. Sci. USA 93, 2071-2076) conversion of single base mutations with help of intranuclear repair mechanisms maybe an advantageous method to cure genetic diseases which are based on single point mutations. These chimeric oligonucleotides are constructed in a way that they form an intramolecular double strand of DNA and modified RNA-bases. We used a fluorescent labelled pure 68-mer DNA-analogue of a chimeric oligonucleotides to follow the intracellular fate of these kind of genetic material. The oligos were complexed with protamine sulfate and coated with three different liposomal formulations. The AVE-3 formulation shows enhanced properties compared to a classical neutral and negatively charged formulation. Nuclear localisation of oligos could only be observed with the AVE-3 formulation. Furthermore only the negatively charged liposome formulations interact with the protamine-complexed oligonucleotides.

Gene therapy using HVJ-liposomes: the best of both worlds?

A new concept for the development of novel vectors is to overcome the limitations of individual vectors by combining them. The HVJ-liposome was developed by combining liposomes with fusion proteins derived from the hemagglutinating virus of Japan (HVJ), also known as Sendai virus. Gene transfer in vivo using this delivery system can be repeated because it is much less immunogenic and cytotoxic than other viral-vector systems. By coupling the Epstein-Barr virus (EBV) replicon apparatus with HVJ-liposomes, transgene expression can be sustained in vitro and in vivo. In animal models, this system has shown promise for several diseases, including cancer and cardiovascular disease.

Malaria circumsporozoite protein inhibits protein synthesis in mammalian cells

Native Plasmodium circumsporozoite (CS) protein, translocated by sporozoites into the cytosol of host cells, as well as recombinant CS constructs introduced into the cytoplasm by liposome fusion or transient transfection, all lead to inhibition of protein synthesis in mammalian cells. The following findings suggest that this inhibition of translation is caused by a binding of the CS protein to ribosomes. (i) The distribution of native CS protein translocated by sporozoites into the cytoplasm as well as microinjected recombinant CS protein suggests association with ribosomes. (ii) Recombinant CS protein binds to RNase-sensitive sites on rough microsomes. (iii) Synthetic peptides representing the conserved regions I and II-plus of the P.falciparum CS protein displace recombinant CS protein from rough microsomes with dissociation constants in the nanomolar range. (iv) Synthetic peptides representing region I from the P.falciparum CS protein and region II-plus from the P.falciparum, P.berghei or P.vivax CS protein inhibit in vitro translation. We propose that Plasmodium manipulates hepatocyte protein synthesis to meet the requirements of a rapidly developing schizont. Since macrophages appear to be particularly sensitive to the presence of CS protein in the cytosol, inhibition of translation may represent a novel immune evasion mechanism of Plasmodium.

Development and characterization of cationic liposomes conjugated with HVJ (Sendai virus): reciprocal effect of cationic lipid for in vitro and in vivo gene transfer

Today, nonviral gene transfer vectors attract more attention as a therapeutic strategy for human diseases, because viral vectors such as adenoviral and herpes viral vectors have been proven to have problems, especially in immunogenicity and cytotoxicity. However, the main limitation of nonviral vectors has been low efficiency of gene expression. To overcome this defect, we have developed a new class of transfection vehicles, HVJ-cationic liposomes. The use of the cationic lipid DC-cholesterol facilitates efficient entrapment of negatively charged macromolecules (plasmid DNA, oligodeoxynucleotides, and proteins) and efficient interaction with negatively charged plasma membranes of cultured cells in vitro. Moreover, the fusogenic envelope proteins of hemagglutinating virus of Japan (HVJ) enhance delivery of the enclosed materials into cells. Using firefly luciferase as a marker, we optimized the liposome formula. As a result, we have succeeded in obtaining 100-800 times higher gene expression in vitro than with the conventional HVJ-anionic liposomes. However, in vivo gene transfer experiments have revealed that the use of cationic lipid instead of anionic lipid reduced the transgene expression dramatically in organs such as muscle and liver. We further discovered that the use of anionic liposomes with a viral-mimic king lipid composition increased transfection efficiency by several times in vivo. We conclude that the alternative usage of transfer vectors, for example, HVJ-anionic liposomes for in vivo delivery to extended areas of organs and HVJ-cationic liposomes for in vitro delivery (and possibly for in vivo delivery to a restricted area of organs), is of significance.

(Patho)physiologic pathways to drug targeting: artificial viral envelopes

The goal of this study was to exploit molecular recognition of cell surface receptors by viral surface glycoproteins as a means for the selective intracellular delivery of macromolecules. To accomplish this, artificial viral envelopes (AVE) resembling the human immunodeficiency virus-1 (HIV-1) were designed as a model system. Recombinant HIV-1 surface glycoprotein gp160 (HIV-1 rgp160) was inserted in the artificial envelope by a two-step detergent dialysis process. The artificial HIV-1 envelope recognized the CD4 cell surface receptor. FITC-dextran and ricin A were employed as model macromolecules as they cannot passively diffuse across cell membranes. Selective transfer of FITC-dextran encapsulated in HIV-1 rgp160 AVE into a CD4-positive cell line (REX-1B) versus a CD4-negative cell line (KG-1) was demonstrated. Ricin A at concentrations as low as 2 ng/ml arrested cell growth of CD4-positive MOLT-4 cells, whereas 8 ng/ml ricin A in solution had no effect on cell growth. The arrest of cell growth was reverted in the presence of excess anti-gp120 monoclonal antibody. Naked envelopes (without HIV-1 rgp160 inserted) were also found to interact with cells and transfer material, although less efficiently and in a non-specific manner. Viral mimicry using AVE may be a means for targeted intracellular delivery of peptides, proteins, enzymes, toxins, oligodeoxynucleotides, gene constructs, and other non-diffusive, labile or toxic macromolecules.

The new frontier: gene and oligonucleotide therapy

Gene and oligonucleotide therapy are emerging as clinically viable therapeutic regimens for genetic, neoplastic, and infectious diseases. Approaches include insertion of human genes in viral vectors including recombinant retrovirus, adenovirus, adeno-associated virus, and herpes simplex virus-1, or recombinant bacterial plasmids. Viral vectors transfect cells directly; plasmid DNA is delivered with the help of cationic liposomes (lipofection), polylysine conjugates, gramicidin S, artificial viral envelopes or other such intracellular carriers. Major areas of interest include replacement of the cystic fibrosis transmembrane regulator gene and the alpha 1-antitrypsin gene; arrest of human immunodeficiency virus infection; and reversal of tumorigenicity and cancer immunization, among others. Oligonucleotide therapy is principally focusing on the same areas, although the approach is to halt DNA transcription or messenger RNA translation with code-blocking triple-helix-forming or "antisense" oligomers. Contributions from the pharmaceutical sciences are expected in pharmaceutical chemistry, drug delivery systems design, analytical chemistry, and biopharmaceutics.