Components of vectors for gene transfer and expression in mammalian cells

Cell-cycle arrest at the G1/S boundary enhances transient voltage-gated ion channel expression in human and insect cells

Heterologous expression of recombinant ion channel subunits in cell lines is often limited by the presence of a low number of channels at the cell surface level. Here, we introduce a combination of two techniques: viral expression using the baculovirus system plus cell-cycle arrest at the G1/S boundary using either thymidine or hydroxyurea. This method achieved a manifold increase in the peak current density of expressed ion channels compared with the classical liposome-mediated transfection methods. The enhanced ionic current was accompanied by an increase in the density of gating charges, confirming that the increased yield of protein and ionic current reflects the functional localization of channels in the plasma membrane. This modified method of viral expression coordinated with the cell cycle arrest will pave the way to better decipher the structure and function of ion channels and their association with ion channelopathies.

3'UTR enhances hCD47 cell surface expression, self-signal function, and reduces ER stress in porcine fibroblasts

INTRODUCTION

Macrophages contribute to xenograft rejection by direct cytotoxicity and by amplifying T cell-mediated immune responses. It has been shown that transgenic expression of hCD47 protects porcine cells from human macrophages by restoring the CD47-SIRPα self-recognition signal. It has also been reported that the long 3' untranslated region (3'UTR) of the hCD47 gene, which is missing from constructs previously used to make hCD47 transgenic pigs, is critical for efficient cell surface expression in human cells. The aim of this study was to investigate the impact of a modified form of the 3'UTR on the expression, localization, and function of hCD47 in transfected porcine cells.

METHODS

hCD47 constructs with and without the modified 3'UTR were knocked into the GGTA1 locus in porcine fetal fibroblasts using CRISPR. Flow cytometry of the transfected cells was used to analyze hCD47 localization. Endoplasmic reticulum (ER), mitochondrial, and oxidative stress were examined by gene expression analysis and confocal microscopy. Phagocytosis of transfected cells by human macrophages was measured by flow cytometry, and stimulation of human/non-human (NHP) primate lymphocytes by the cells was examined using a PBMCs proliferation assay.

RESULTS

Cells transfected with the construct lacking the 3'UTR (hCD47(3'UTR-)) exhibited predominantly intracellular expression of hCD47, and showed evidence of ER stress, dysregulated mitochondrial biogenesis, oxidative stress, and autophagy. Inclusion of the 3'UTR (hCD47(3'UTR+)) decreased intracellular expression of hCD47 by 36% and increased cell surface expression by 53%. This was associated with a significant reduction in cellular stress markers and a higher level of protection from phagocytosis by human macrophages. Furthermore, hCD47(3'UTR+) porcine cells stimulated significantly less proliferation of human/NHP T cells than hCD47(3'UTR-) cells.

CONCLUSION

Our results suggest the potential benefits of using hCD47 constructs containing the 3'UTR to generate genetically engineered hCD47-expressing donor pigs.

Rapid Generation of Attenuated Infectious Bursal Disease Virus from Dual-Promoter Plasmids by Reduction of Viral Ribonucleoprotein Activity

Infectious bursal disease virus (IBDV) of the Birnaviridae family leads to immunosuppression of young chickens by destroying B cells in the bursa of Fabricius (BFs). Given the increasing number of variant IBDV strains, we urgently require a method to produce attenuated virus for vaccine development. To accomplish this goal, the dual-promoter plasmids in which the RNA polymerase II and RNA polymerase I (Pol I) promoters were placed upstream of the IBDV genomic sequence, which was followed by mouse Pol I terminator and a synthetic polyadenylation signal, were developed for rapid generation of IBDV. This approach did not require trans-supplementation of plasmids for the expression of VP1 and VP3, the main components of IBDV ribonucleoprotein (RNP). Based on the finding in this study that the IBDV RNP activity was partially retained by VP1-FLAG, we successfully rescued the replication-competent IBDV/1FLAG expressing VP1-FLAG. Compared with its parental counterpart, IBDV/1FLAG formed smaller size plaques in cultured cells and induced the same 100% immune protection in vivo However, neither retarded development nor severe BFs lesion was observed in the IBDV/1FLAG-inoculated chickens. Collectively, this is the first report that viral RNP activity was affected by the addition of an epitope tag on the componential viral proteins. Furthermore, this work demonstrates the rapid generation of attenuated IBDV from dual-promoter plasmids via reducing viral RNP activity by a fused FLAG tag on the C terminus of VP1. This would be a convenient strategy to attenuate epidemic variant IBDV strains for rapid and efficient vaccine development.IMPORTANCE Immunosuppression in chickens as a result of infectious bursal disease virus (IBDV) infection leads to significant economic losses in the poultry industry worldwide every year. Currently, vaccination is still the best way to prevent the prevalence of IBDV. However, with the occurrence of increasing numbers of variant IBDV strains, it is challenging to develop antigen-matched live attenuated vaccine. Here, we first developed a dual-promoter reverse-genetic system for the rapid generation of IBDV. Using this system, the attenuated IBDV/1FLAG expressing VP1-FLAG, which displays the decreased viral RNP activity, was rescued. Moreover, IBDV/1FLAG inoculation induced a similar level of neutralizing antibodies to that of its parental counterpart, protecting chickens against lethal challenge. Our study, for the first time, describes a dual-promoter reverse-genetic approach for the rapid generation of attenuated IBDV while maintaining entire parental antigenicity, suggesting a potential new method to attenuate epidemic variant IBDV strains for vaccine development.

A critical comparison of lanthanide based upconversion nanoparticles to fluorescent proteins, semiconductor quantum dots, and carbon dots for use in optical sensing and imaging

The right choice of a fluorescent probe is essential for successful luminescence imaging and sensing and especially concerning in vivo and in vitro applications, the development of new classes have gained more and more attention in the last years. One of the most promising class are upconversion nanoparticles (UCNPs)-inorganic nanocrystals capable to convert near-infrared light in high energy radiation. In this review we will compare UCNPs with other fluorescent probes in terms of (a) the optical properties of the probes, such as their brightness, photostability and excitation wavelength; (b) their chemical properties such as the dispersibility, stability under experimental or physiological conditions, availability of chemical modification strategies for labelling; and (c) the potential toxicity and biocompatibility of the probe. Thereby we want to provide a better understanding of the advantages and drawbacks of UCNPs and address future challenges in the design of the nanocrystals.

Co-amplification of EBNA-1 and PyLT through dhfr-mediated gene amplification for improving foreign protein production in transient gene expression in CHO cells

Despite the relatively low transfection efficiency and low specific foreign protein productivity (q_p) of Chinese hamster ovary (CHO) cell-based transient gene expression (TGE) systems, TGE-based recombinant protein production technology predominantly employs CHO cells for pre-clinical research and development purposes. To improve TGE in CHO cells, Epstein-Barr virus nuclear antigen-1 (EBNA-1)/polyoma virus large T antigen (PyLT)-co-amplified recombinant CHO (rCHO) cells stably expressing EBNA-1 and PyLT were established using dihydrofolate reductase/methotrexate-mediated gene amplification. The level of transiently expressed Fc-fusion protein was significantly higher in the EBNA-1/PyLT-co-amplified pools compared to control cultures. Increased Fc-fusion protein production by EBNA-1/PyLT-co-amplification resulted from a higher q_p attributable to EBNA-1 but not PyLT expression. The q_p for TGE-based production with EBNA-1/PyLT-co-amplified rCHO cells (EP-amp-20) was approximately 22.9-fold that of the control culture with CHO-DG44 cells. Rather than improved transfection efficiency, this cell line demonstrated increased levels of mRNA expression and replicated DNA, contributing to an increased q_p. Furthermore, there was no significant difference in N-glycan profiles in Fc-fusion proteins produced in the TGE system. Taken together, these results showed that the use of rCHO cells with co-amplified expression of the viral elements EBNA-1 and PyLT improves TGE-based therapeutic protein production dramatically. Therefore, EBNA-1/PyLT-co-amplified rCHO cells will likely be useful as host cells in CHO cell-based TGE systems.

Effect of adenovirus infection on transgene expression under the adenoviral MLP/TPL and the CMVie promoter/enhancer in CHO cells

The adenovirus major late promoter (MLP) and its translational regulator - the tripartite leader (TPL) sequence - can actively drive efficient gene expression during adenoviral infection. However, both elements have not been widely tested in transgene expression outside of the adenovirus genome context. In this study, we tested whether the combination of MLP and TPL would enhance transgene expression beyond that of the most widely used promoter in transgene expression in mammalian cells, the cytomegalovirus immediate early (CMVie) promoter/enhancer. The activity of these two regulatory elements was compared in Chinese hamster ovary (CHO) cells. Although transient expression was significantly higher under the control of the CMVie promoter/enhance compared to the MLP/TPL, this difference was greater at the level of transcription (30 folds) than translation (11 folds). Even with adenovirus infection to provide additional elements (in trans), CMVie promoter/enhancer exhibited significantly higher activity relative to MLP/TPL. Interestingly, the CMVie promoter/enhancer was 1.9 folds more active in adenovirus-infected cells than in non-infected cells. Our study shows that the MLP-TPL drives lower transgene expression than the CMVie promoter/enhancer particularly at the transcription level. The data also highlight the utility of the TPL sequence at the translation level and/or possible overwhelming of the cellular translational machinery by the high transcription activity of the CMVie promoter/enhancer. In addition, here we present data that show stimulation of the CMVie promoter/enhancer by adenovirus infection, which may prove interesting in future work to test the combination of CMVie/TPL sequence, and additional adenovirus elements, for transgene expression.

Encapsulated cells for long-term secretion of soluble VEGF receptor 1: Material optimization and simulation of ocular drug response

Anti-angiogenic therapies with vascular endothelial growth factor (VEGF) inhibiting factors are effective treatment options for neovascular diseases of the retina, but these proteins can only be delivered as intravitreal (IVT) injections. To sustain a therapeutic drug level in the retina, VEGF inhibitors have to be delivered frequently, every 4-8weeks, causing inconvenience for the patients and expenses for the healthcare system. The aim of this study was to investigate cell encapsulation as a delivery system for prolonged anti-angiogenic treatment of retinal neovascularization. Genetically engineered ARPE-19 cells secreting soluble vascular endothelial growth factor receptor 1 (sVEGFR1) were encapsulated in a hydrogel of cross-linked collagen and interpenetrating hyaluronic acid (HA). The system was optimized in terms of matrix composition and cell density, and long-term cell viability and protein secretion measurements were performed. sVEGFR1 ARPE-19 cells in the optimized hydrogel remained viable and secreted sVEGFR1 at a constant rate for at least 50days. Based on pharmacokinetic/pharmacodynamic (PK/PD) modeling, delivery of sVEGFR1 from this cell encapsulation system is expected to lead only to modest VEGF inhibition, but improvements of the protein structure and/or secretion rate should result in strong and prolonged therapeutic effect. In conclusion, the hydrogel matrix herein supported the survival and protein secretion from the encapsulated cells. The PK/PD simulation is a convenient approach to predict the efficiency of the cell encapsulation system before in vivo experiments.

Molecular-genetic imaging of cancer

Molecular-genetic imaging of cancer using nonviral delivery systems has great potential for clinical application as a safe, efficient, noninvasive tool for visualization of various cellular processes including detection of cancer, and its attendant metastases. In recent years, significant effort has been expended in overcoming technical hurdles to enable clinical adoption of molecular-genetic imaging. This chapter will provide an introduction to the components of molecular-genetic imaging and recent advances on each component leading to safe, efficient clinical applications for detecting cancer. Combination with therapy, namely, generating molecular-genetic theranostic constructs, will provide further impetus for clinical translation of this promising technology.

Post-transcriptional regulatory elements for enhancing transient gene expression levels in mammalian cells

Low yield from transient gene expression in mammalian cells limits its application to areas where large amount of proteins are needed. One effective approach to enhance transient gene expression levels is to use post-transcriptional regulatory elements (PTREs). We have evaluated the effect of five PTREs on the transient gene expression of three proteins in two cell lines. Most of the elements increased expression but exhibited cell-specific and gene-specific effects. The tripartite leader sequence of human adenovirus mRNA linked with a major late promoter enhancer gave the most universal and highest enhancement of gene expression levels. It increased the expression of all three proteins in HEK293 cells and two proteins in CHO K1 cells by 3.6- to 7.6-fold. Combinations of multiple PTREs increased protein expression as much as 10.5-fold.

One-pot bio-synthesis: N-acetyl-D-neuraminic acid production by a powerful engineered whole-cell catalyst

Whole cell biocatalysis is an important tool for pharmaceutical intermediates synthesis, although it is hindered by some shortcomings, such as high cost and toxicity of inducer, mass transfer resistance caused by cell membrane and side reactions. Whole-cell catalysis using N-acetyl-d-glucosamine 2-epimerase (EC 5.1.3.8) and N-acetyl-d-neuraminic acid (Neu5Ac) aldolase (EC 4.1.3.3) is a promising approach for the production of Neu5Ac, a potential precursor of many anti-viral drugs. A powerful catalyst was developed by packaging the enzymes in an engineered bacterium and using a safe temperature-induced vector. Since the mass transfer resistance and the side reactions were substantially reduced, a high Neu5Ac amount (191 mM) was achieved. An efficient method was also presented, which allows one-pot synthesis of Neu5Ac with a safe and economic manner. The results highlight the promise of large-scale Neu5Ac synthesis and point at a potential of our approach as a general strategy to improve whole-cell biocatalysis.

EphA2 targeting peptide tethered bioreducible poly(cystamine bisacrylamide-diamino hexane) for the delivery of therapeutic pCMV-RAE-1γ to pancreatic islets

The pathogenesis of type-1 diabetes is complicated, and a clear, single mechanism has yet to be identified. Reports have indicated that the activating receptor NKG2D plays an important role in the development of disease. Exploiting a natural phenomenon observed in tumors, plasmid DNA encoding for a soluble ligand to NKG2D (sRAE-1γ) was isolated and engineered into a plasmid expression system. A polymeric gene delivery system was developed to deliver the soluble RAE-1 plasmid locally to the pancreatic islets for the prevention of type-1 diabetes. The bioreducible cationic polymer poly(cystamine bisacrylamide-diamino hexane) (p(CBA-DAH)) was modified with poly(ethylene glycol) (PEG) and the targeting peptide CHVLWSTRC, known to target the EphA2 and EphA4 receptors. The PEG serves to improve stability and tissue selectivity, while the peptide will target EphA2 and A4, overexpressed in the pancreatic microvasculature. The targeting polymer Eph-PEG-p(CBA-DAH) shows selective uptake by the target cell line, indicative of the targeting properties that will be seen in systemic administration. Using the delivery system, the therapeutic plasmid can be delivered to the pancreas, reduce interactions between the beta-cells and infiltrating NKG2D positive lymphocytes, and effectively protect beta-cells from autoimmune destruction and prevent type 1 diabetes.

Mutated polyadenylation signals for controlling expression levels of multiple genes in mammalian cells

A set of mutated SV40 early polyadenylation signals (SV40pA) with varying strengths is generated by mutating the AATAAA sequence in the wild-type SV40pA. They are shown to control the expression level of a gene over a 10-fold range using luciferase reporter genes in transient transfection assays. The relative strength of these SV40pA variants remains similar under three commonly used mammalian promoters and in five mammalian cell lines. Application of SV40pA variants for controlling expression level of multiple genes is demonstrated in a study of monoclonal antibody (mAb) synthesis in mammalian cells. By using SV40pA variants of different strengths, the expression of light chain (LC) and heavy chain (HC) genes encoded in a single vector is independently altered which results in different ratios of LC to HC expression spanning a range from 0.24 to 16.42. The changes in gene expression are determined by measuring mRNA levels and intracellular LC and HC polypeptides. It is found that a substantial decrease of HC expression, which increases the LC/HC mRNA ratio, only slightly reduces mAb production. However, reducing the LC expression by a similar magnitude, which decreases the LC/HC mRNA ratio results in a sharp decline of mAb production to trace amounts. This set of SV40pA variants offers a new tool for accurate control of the relative expression levels of multiple genes. It will have wide-ranging applications in fields related to the study of biosynthesis of multi-subunit proteins, proteomic research on protein interactions, and multi-gene metabolic engineering.

Heterologous and cell free protein expression systems

In recognition of the fact that a relatively small percentage of 'named' genes in databases have any experimental proof for their annotation, attention is shifting towards the more accurate assignment of functions to individual genes in a genome. The central objective will be to reduce our reliance on nucleotide or amino acid sequence similarities as a means to define the functions of genes and to annotate genome sequences. There are many unsolved technical difficulties associated with the purification of specific proteins from extracts of biological material, especially where the protein is present in low abundance, has multiple isoforms or is found in multiple post-translationally modified forms. The relative ease with which cDNAs can be cloned has led to the development of methods through which cDNAs from essentially any source can be expressed in a limited range of suitable host organisms, so that sufficient levels of the encoded proteins can be generated for functional analysis. Recently, these heterologous expression systems have been supplemented by more robust prokaryotic and eukaryotic cell-free protein synthesis systems. In this chapter, common host systems for heterologous expression are reviewed and the current status of cell-free expression systems will be presented. New approaches to overcoming the special problems encountered during the expression of membrane-associated proteins will also be addressed. Methodological considerations, including the characteristics of codon usage in the expressed DNA, peptide tags that facilitate subsequent purification of the expressed proteins and the role of post-translational modifications, are examined.

Recombinant protein production by transient gene transfer into Mammalian cells

The timely availability of recombinant proteins in sufficient quantity and of validated quality is of utmost importance in driving drug discovery and the development of low molecular weight compounds, as well as for biotherapeutics. Transient gene expression (TGE) in mammalian cells has emerged as a promising technology for protein generation over the past decade as TGE meets all the prerequisites with respect to quantity and quality of the product as well as cost-effectiveness and speed of the process. Optimized protocols have been developed for both HEK293 and CHO cell lines which allow protein production at any desired scale up to >100 l and in milligram to gram quantities. Along with an overview on current scientific and technological knowledge, detailed protocols for expression of recombinant proteins on small, medium, and large scale are discussed in the following chapter.

A set of vectors for introduction of antibiotic resistance genes by in vitro Cre-mediated recombination

Background

Introduction of new antibiotic resistance genes in the plasmids of interest is a frequent task in molecular cloning practice. Classical approaches involving digestion with restriction endonucleases and ligation are time-consuming.

Findings

We have created a set of insertion vectors (pINS) carrying genes that provide resistance to various antibiotics (puromycin, blasticidin and G418) and containing a loxP site. Each vector (pINS-Puro, pINS-Blast or pINS-Neo) contains either a chloramphenicol or a kanamycin resistance gene and is unable to replicate in most E. coli strains as it contains a conditional R6Kγ replication origin. Introduction of the antibiotic resistance genes into the vector of interest is achieved by Cre-mediated recombination between the replication-incompetent pINS and a replication-competent target vector. The recombination mix is then transformed into E. coli and selected by the resistance marker (kanamycin or chloramphenicol) present in pINS, which allows to recover the recombinant plasmids with 100% efficiency.

Conclusion

Here we propose a simple strategy that allows to introduce various antibiotic-resistance genes into any plasmid containing a replication origin, an ampicillin resistance gene and a loxP site.

Efficient Selection of Stable Chinese Hamster Ovary (CHO) Cell Lines for Expression of Recombinant Proteins by Using Human Interferon β SAR Element

We describe the development of an efficient expression system suitable for the stable expression of recombinant genes in Chinese hamster ovary (CHO) cells using the human interferon beta SAR element. The insertion of two copies of the human interferon beta SAR element at the 5' and 3' flanking regions of the beta-galactosidase reporter gene increased the frequency of beta-galactosidase positive colonies by up to 75% and enhanced beta-galactosidase expression by 15- to 20-fold after G418 selection or 30- to 40-fold at the initial stage of the MTX selection procedure. Deletion analysis showed that the whole DNA regions of the human interferon beta SAR element are required for beta-galactosidase expression enhancement. The developed expression system was also highly effective at enhancing the stable expression of two therapeutically important proteins, namely, erythropoietin (EPO) and hepatocyte growth factor (HGF). We isolated stable colonies with expression levels of 47 microg/10(6) cells/day for EPO and 13 microg/10(6) cells/day for HGF, suggesting that the developed expression system based on the human beta SAR element is suitable for expressing high levels of recombinant proteins in CHO cells.

Rational vector design for efficient non-viral gene delivery: challenges facing the use of plasmid DNA

Although non-viral gene delivery is a very straightforward technology, there are currently no FDA-approved gene medicinal products available. Therefore, improving potency, safety, and efficiency of current plasmid DNA vectors will be a major task for the near future. This article will provide an overview on factors influencing production yield and quality as well as safety issues that emerge from the vector design itself. Special focus will be on generating bacterial pDNA vectors by circumventing the use of antibiotic resistance genes, to generate safer gene medicinal products as well as smaller, more efficient DNA vectors.

A method for isolating prosurvival targets of NF-kappaB/Rel transcription factors

NF-KappaB/Rel transcription factors are critical regulators of immunity, inflammation, development, and cell survival. Activation of NF-KB inhibits programmed cell death (PCD) triggered by tumor necrosis factor alpha (TNFalpha) and several other stimuli. The prosurvival activity of NF-KB is also crucial to lymphopoiesis, neuroprotection, tumorigenesis, and cancer chemoresistance. The characterization of the downstream targets that mediate the prosurvival activity of NF-KB is therefore a topic of intense investigation. Early screens aimed at identifying these genes were mainly based on expression criteria and so were poised to only isolate genes already known to have protective effects. Here, we describe a new method for the identification of these genes, whereby expression libraries are screened for their ability to halt PCD in NF-KB-deficient cells. This complementation approach provides substantial advantages over other approaches, as it enables functional assessment of isolated genes without any preconceived notion about their sequence or presumed role. Expression libraries are generated from cells that are resistant to TNFalpha-induced cytotoxicity and are then enriched in prosurvival genes upon selection with TNFa in NF-kappaB/RelA-null cells, which are highly susceptible instead to this cytotoxicity. Upon enrichment, libraries are screened through a randomized two-step approach, whereby cDNAs are first tested for cytoprotective function and then for differential expression in NF-kappaB-proficient and NF-KappaB-deficient cells.

Efficiency of the elongation factor-1alpha promoter in mammalian embryonic stem cells using lentiviral gene delivery systems

The establishment of new technology for genetic modification in human embryonic stem (ES) cell lines has raised great hopes for achieving new ground in basic and clinical research. Recently, lentiviral vector technology has been shown to be highly effective and therefore could emerge as a popular tool for human ES cell genetic modification. The objectives of this study were to evaluate the efficiency of promoters in lentiviral gene delivery systems in mammalian ES cells, including mouse, monkey, and human, and to construct efficient and optimized conditions for lentivirus-mediated transfection systems. Mammalian ES cells were transfected with self-inactivating (SIN) human immunodeficiency virus type-1 (HIV-1)-based lentiviral vectors containing the human polypeptide chain elongation factor-1alpha (EF-1alpha) promoter or cytomegalovirus (CMV) promoter and analyzed by fluorescence-activated cell sorting (FACS) analysis for the expression of the enhanced green fluorescent protein (eGFP) reporter gene. The efficiency of the EF-1alpha promoter was higher than that of the CMV promoter in all ES cells tested. The EF-1alpha promoter efficiently drove gene expression (14.74%) compared with CMV promoter (3.69%) in human ES cells. We generated a stable eGFP+ human ES cell line (CHA3-EGFP human ES cells) that continuously expressed high levels of EGFP ( approximately 95%) from the EF-1alpha promoter and was maintained for up to 60 weeks with undifferentiated proliferation. The established CHA3-EGFP human ES cell lines were characterized as being negative for nondifferentiation markers and teratoma formation. These results imply that genetic modification by lentiviral vectors with specific promoters in ES cells constitute a powerful tool for guided differentiation as well as gene therapy.

Blood-brain barrier transport of non-viral gene and RNAi therapeutics

The development of gene- and RNA interference (RNAi)-based therapeutics represents a challenge for the drug delivery field. The global brain distribution of DNA genes, as well as the targeting of specific regions of the brain, is even more complicated because conventional delivery systems, i.e. viruses, have poor diffusion in brain when injected in situ and do not cross the blood-brain barrier (BBB), which is only permeable to lipophilic molecules of less than 400 Da. Recent advances in the "Trojan Horse Liposome" (THL) technology applied to the transvascular non-viral gene therapy of brain disorders presents a promising solution to the DNA/RNAi delivery obstacle. The THL is comprised of immunoliposomes carrying either a gene for protein replacement or small hairpin RNA (shRNA) expression plasmids for RNAi effect, respectively. The THL is engineered with known lipids containing polyethyleneglycol (PEG), which stabilizes its structure in vivo in circulation. The tissue target specificity of THL is given by conjugation of approximately 1% of the PEG residues to peptidomimetic monoclonal antibodies (MAb) that bind to specific endogenous receptors (i.e. insulin and transferrin receptors) located on both the BBB and the brain cellular membranes, respectively. These MAbs mediate (a) receptor-mediated transcytosis of the THL complex through the BBB, (b) endocytosis into brain cells and (c) transport to the brain cell nuclear compartment. The present review presents an overview of the THL technology and its current application to gene therapy and RNAi, including experimental models of Parkinson's disease and brain tumors.

The IE2 promoter/enhancer region from mouse CMV provides high levels of therapeutic protein expression in mammalian cells

Protein expression in mammalian cells is key for the production and manufacturing of bio-therapeutics with human-like properties and activities. As a molecular basis for reaching high protein expression levels, efficient promoter/enhancer systems are a prerequisite. Here we identify a novel enhancer from the mouse cytomegalovirus (CMV) immediate early 2 (IE2) region as a strong expression-promoting element. We further demonstrate its activity in bi-directional promoter architecture and apply it to generate production clones for IL-18BP, a protein with therapeutic indications in autoimmune diseases. These data show that the IE region from mouse CMV, and the IE2 enhancer/promoter in particular, have a broad potential for application in novel gene expression systems for research, development, and manufacturing of protein drugs.

Optimization of baculovirus transduction on FreeStyle293 cells for the generation of influenza B/Lee/40

Recombinant baculovirus expression vectors derived from the Autographa californica nuclear polyhedrosis virus can serve as efficient gene-transfer vehicles for transient expression of recombinant proteins in a wide range of mammalian cell types and are able to produce multisubunit particles such as viruses or virus like particles. In this study, we constructed eight recombinant baculoviruses each containing one of the influenza B/Lee/40 virus genes in a bidirectional expression cassette for simultaneous mRNA and viral RNA transcription. Baculoviruses were transduced into FreeStyle293 in combination with the specific histone deacetylase inhibitor trichostatin A (TSA). Cotransduction conditions were optimized with a set of five baculoviruses (influenza B/Lee/40 PB1, PB2, PA, and NP and the control construct NCR-NS-minus-sense orientated encoding green fluorescent protein [rGFP]), which led to GFP expression in each host cell transduced with all five constructs. Based on the optimization with five constructs, transduction with eight baculoviruses was performed at MOI 50 and 100 with high yield stocks and 1 microM TSA and led to successful rescue of infectious influenza B/Lee/40 viruses.

Recombinant protein production by large-scale transient gene expression in mammalian cells: state of the art and future perspectives

The expansion of the biologics pipeline depends on the identification of candidate proteins for clinical trials. Speed is one of the critical issues, and the rapid production of high quality, research-grade material for preclinical studies by transient gene expression (TGE) is addressing this factor in an impressive way: following DNA transfection, the production phase for TGE is usually 2-10 days. Recombinant proteins (r-proteins) produced by TGE can therefore enter the drug development and screening process in a very short time--weeks. With "classical" approaches to protein expression from mammalian cells, it takes months to establish a productive host cell line. This article summarizes efforts in industry and academia to use TGE to produce tens to hundreds of milligrams of r-proteins for either fundamental research or preclinical studies.

RNA interference and nonviral targeted gene therapy of experimental brain cancer

The human epidermal growth factor receptor (EGFR) plays an oncogenic role in solid cancer, including brain primary and metastatic cancers. Transvascular nonviral gene therapy in combination with EGFR-RNA interference (RNAi) represents a new therapeutic approach to silencing oncogenic genes in solid cancers. This is achieved with pegylated immunoliposomes (PIL) carrying short hairpin RNA expression plasmids driven by the U6 RNA polymerase promoter and directed to target EGFR expression by RNAi. The PIL is comprised of a mixture of known lipids containing polyethyleneglycol (PEG), which stabilizes the PIL structure in vivo in circulation. The tissue target specificity of PILs is given by conjugation of approximately 1% of the PEG residues to monoclonal antibodies (mAbs) that bind to specific endogenous receptors (i.e., insulin and transferrin receptors) located in the brain vascular endothelium, which forms the blood brain barrier (BBB), and brain cellular membranes, respectively. These mAbs are known to induce 1) receptor-mediated transcytosis of the PIL complex through the BBB and 2) transport to the brain cell nuclear compartment. Treatment of an experimental human brain tumor model in scid mice is possible with weekly intravenous RNAi gene therapy causing reduced tumor expression of EGFR and 88% increase in survival time of these mice with advanced intracranial brain cancer. The availability of additional RNAi tumor targets may improve the therapeutic efficacy of this new anticancer drug. The accessibility to chimeric and/or humanized mAbs directed to human BBB and brain cell specific-receptors may accelerate the application of this technology to the treatment of human tumors.

Influence of promoter choice and trichostatin A treatment on expression of baculovirus delivered genes in mammalian cells

The expression of recombinant proteins following transduction of CHO cells with recombinant baculoviruses containing a mammalian expression cassette with the CMV-promoter is enhanced by the addition of trichostatin A (TSA), a specific histone deacetylase inhibitor. To further investigate the effect of TSA treatment on protein production following BacMam transduction, viruses containing various viral promoters (SV40, CMV, and RSV) and one cellular promoter (human ubiquitin C) were compared with regard to expression level of a gfp-luciferase fusion protein following transduction of CHO, COS-1, and HEK293 cells. The overall effect on expression appears to be cell specific, indicating that different mechanisms are active within different cell lines. Further, COS cells transfected with naked viral DNA, plasmids, and baculovirus particles were compared in regard to TSA treatment. The increase in reporter gene expression observed following BacMam transduction and TSA treatment were greater than those for transfection of either naked viral DNA or plasmid DNA.

Glucagon-like peptide-1 plasmid construction and delivery for the treatment of type 2 diabetes

Glucagon-like peptide-1 (GLP-1) is a 30-amino-acid hormone produced by intestinal L cells. It has been proposed that GLP-1 can be used as a new treatment for type 2 diabetes mellitus because it acts to augment insulin secretion and its effectiveness is maintained in type 2 diabetic patients. Despite its many remarkable advantages as a therapeutic agent for diabetes, GLP-1 is not immediately clinically applicable because of its extremely short half-life. One way to overcome this drawback is GLP1 gene delivery, which enables GLP-1 production in the body. In this study, the effect of GLP1 gene delivery was evaluated both in vitro and in vivo using a new plasmid constructed with a GLP1 (7-37) cDNA. The expression of the GLP1 gene was driven by a SV40 promoter/enhancer. To increase the expression level of GLP-1, nuclear factor kappaB binding sites were introduced. The in vitro results showed expression of GLP-1 and in vitro activity of GLP-1, which is a glucose-dependent insulinotropic action. A single systemic administration of polyethyleneimine/pSIGLP1NFkappaB complex into DIO mice resulted in increasing insulin secretion and decreasing blood glucose levels for a duration longer than 2 weeks.

Production of recombinant protein therapeutics in cultivated mammalian cells

Cultivated mammalian cells have become the dominant system for the production of recombinant proteins for clinical applications because of their capacity for proper protein folding, assembly and post-translational modification. Thus, the quality and efficacy of a protein can be superior when expressed in mammalian cells versus other hosts such as bacteria, plants and yeast. Recently, the productivity of mammalian cells cultivated in bioreactors has reached the gram per liter range in a number of cases, a more than 100-fold yield improvement over titers seen for similar processes in the mid-1980s. This increase in volumetric productivity has resulted mainly from improvements in media composition and process control. Opportunities still exist for improving mammalian cell systems through further advancements in production systems as well as through vector and host cell engineering.

Improvement in nuclear entry and transgene expression of baculoviruses by disintegration of microtubules in human hepatocytes

Autographa californica multicapsid nucleopolyhedrovirus (AcMNPV), a potent virus for mammalian cell gene delivery, possesses an ability to transduce mammalian cells without viral replication. We examined the role of the cellular cytoskeleton in the cytoplasmic trafficking of viral particles toward the nucleus in human hepatic cells. Microscopic studies showed that capsids were found in the nucleus after either viral inoculation or cytoplasmic microinjection of nucleocapsids. The presence of microtubule (MT) depolymerizing agents caused the amount of nuclear capsids to increase. Overexpression of p50/dynamitin, an inhibitor of dynein-dependent endocytic trafficking from peripheral endosomes along MTs toward late endosomes, did not significantly affect the amount of nuclear accumulation of nucleocapsids in the inoculated cells, suggesting that viral nucleocapsids are released into the cytosol during the early stages of the endocytic pathway. Moreover, studies with recombinant viruses containing the nuclear-targeted expression beta-galactosidase gene (beta-gal) showed a markedly increased level in the cellular expression of beta-galactosidase in the presence of MT-disintegrating drugs. The maximal increase in expression at 10 h postinoculation was observed in the presence of 80 muM nocodazole or 10 muM vinblastine. Together, these data suggest that the intact MTs constitute a barrier to baculovirus transport toward the nucleus.

Intravenous RNA interference gene therapy targeting the human epidermal growth factor receptor prolongs survival in intracranial brain cancer

PURPOSE

The human epidermal growth factor receptor (EGFR) plays an oncogenic role in solid cancer, including brain cancer. The present study was designed to prolong survival in mice with intracranial human brain cancer with the weekly i.v. injection of nonviral gene therapy causing RNA interference (RNAi) of EGFR gene expression.

EXPERIMENTAL DESIGN

Human U87 gliomas were implanted in the brain of adult scid mice, and weekly i.v. gene therapy was started at day 5 after implantation of 500000 cells. An expression plasmid encoding a short hairpin RNA directed at nucleotides 2529-2557 within the human EGFR mRNA was encapsulated in pegylated immunoliposomes. The pegylated immunoliposome was targeted to brain cancer with 2 receptor-specific monoclonal antibodies (MAb), the murine 83-14 MAb to the human insulin receptor and the rat 8D3 MAb to the mouse transferrin receptor.

RESULTS

In cultured glioma cells, the delivery of the RNAi expression plasmid resulted in a 95% suppression of EGFR function, based on measurement of thymidine incorporation or intracellular calcium signaling. Weekly i.v. RNAi gene therapy caused reduced tumor expression of immunoreactive EGFR and an 88% increase in survival time of mice with advanced intracranial brain cancer.

CONCLUSIONS

Weekly i.v. nonviral RNAi gene therapy directed against the human EGFR is a new therapeutic approach to silencing oncogenic genes in solid cancers. This is enabled with a nonviral gene transfer technology that delivers liposome-encapsulated plasmid DNA across cellular barriers with receptor-specific targeting ligands.

Expression of human proteins at the Southeast Collaboratory for Structural Genomics

The human protein production group at the Southeast Collaboratory for Structural Genomics is charged with producing human proteins for both X-ray crystallography and NMR structural studies. Eukaryotic, and human proteins in particular, are notoriously difficult to express in bacterial systems. For various reasons, T7-based expression often results in protein expressed in an insoluble form. Overcoming this requires either introduction of a step to screen expression conditions or inclusion of a troublesome refolding step during purification. Our laboratory uses a trc-based expression vector that addresses many of the difficulties of the commonly used T7-based expression systems. Proteins expressed under the trc promoter, a weak promoter compared to the strong T7 promoter, are produced in a soluble form and include necessary cofactors. The details of this system will be discussed.

The successful long-term treatment of age related erectile dysfunction with hSlo cDNA in rats in vivo

PURPOSE

We have previously reported that 1 intracorporeal injection of 100 microg hSlo/pcDNA reversed the effect of aging on erectile function in a rat model in vivo for at least 2 months. We report our further investigations of the amplitude, duration and physiological relevance of this novel gene transfer approach.

MATERIALS AND METHODS

A total of 191 retired breeder Sprague-Dawley rats were given a single intracavernous injection of phosphate buffered saline, 1,000 microg pcDNA, or 10, 100 or 1,000 microg pcDNA/hSlo. The animals were studied 1 to 6 months after injection. The intracorporeal pressure (ICP) response to cavernous nerve stimulation and immunostaining as well as hematoxylin and eosin staining were done to evaluate effector nerve integrity and tissue histology, respectively.

RESULTS

Gene transfer prevented an age related decrease in resting ICP and a physiologically relevant, significant effect on normalizing erection in vivo, as determined by submaximal (0.5 mA) and maximal (4.0 mA) cavernous nerve stimulation. The effects were observed 1 month after transfection and sustained for 6 months at the 100 and 1,000 microg doses of pcDNA/hSlo (p <0.026).

CONCLUSIONS

The physiological manifestations of gene transfer were detected as an amelioration of the age related decrease in resting ICP, and parallel increase in the magnitude of the cavernous nerve stimulated an ICP response to a level at which visible erections were again observed in this rat model of aging in vivo.

Alphavirus cDNA-based expression vectors: effects of RNA transcription and nuclear export

The construction of layered DNA-RNA replicons has facilitated and expanded the use of alphavirus vectors to vaccine development, construction of packaging cell lines and long-term heterologous gene expression. In these vector systems, the alphavirus replicon is under the control of a strong RNA polymerase II promoter and replicon RNA is transcribed from DNA before transport to the cytoplasm. Efficient RNA amplification catalyzed by the viral replicase results in high levels of mRNA and the recombinant protein. Recently, we developed a temperature-regulated Sindbis replicon-based DNA expression system characterized by a linear increase of expression upon decrease of the temperature from 37 degrees C to 29 degrees C. Modifications known to affect transcription and nuclear export of RNA led to a 5-fold increase in expression in BHK cells and up to over 80-fold increase in CHO cells and BF fibroblasts in transient transfection experiments. Furthermore, reducing cell proliferation resulted in a further 2- to 3-fold higher expression. While increased expression per cell was responsible for some of the enhanced production, it was primarily the number of expressing cells that made the difference in most cell lines. Further experiments indicated that a threshold amount of replicon RNA had to reach the cytoplasm in order for replication to occur. Thus, alterations that improve transcription, nuclear export and stability of the RNA had a significant impact on protein production in the pCytTS expression system and probably in other layered DNA-based viral vectors. Furthermore the results indicate that RNA replication is differentially regulated in DNA layered RNA replicons versus viral infection.

Marked enhancement in gene expression by targeting the human insulin receptor

BACKGROUND

Exogenous genes can be delivered to cells without viral vectors using an "artificial virus" comprised of nonviral plasmid DNA encapsulated in the interior of 85 nm pegylated immunoliposomes (PIL). The liposomes are targeted to cells with receptor-specific targeting ligands such as receptor-specific peptidomimetic monoclonal antibodies.

METHODS

The levels of luciferase gene expression in human or rat glioma cells are measured after targeting the PIL-encapsulated plasmid DNA via the human insulin receptor, the human epidermal growth factor receptor, or the rat transferrin receptor. The luciferase expression plasmids were either derived from pCEP4, which contains the Epstein-Barr nuclear antigen-1/oriP replication system, or from pGL2, which lacks this system for episomal replication of plasmid DNA.

RESULTS

Depending on the plasmid construct used and the receptor targeted, the peak luciferase gene expression varied more than 200-fold from 1.8 +/- 0.1 to 419 +/- 31 pg luciferase per mg cell protein. With the same plasmid, the peak level of gene expression following delivery to the cell via the human insulin receptor was 100-200-fold higher than gene expression following delivery via either the epidermal growth factor receptor or the transferrin receptor. There was no gene expression if the targeting ligand on the PIL was replaced with a nonspecific isotype control antibody.

CONCLUSIONS

The extent to which an exogenous gene is expressed within a cell via a nonviral, receptor-mediated gene transfer technology is determined by the receptor specificity of the targeting ligand. The highest levels of gene expression are obtained after targeting the insulin receptor, and this may derive from the nuclear targeting properties of this receptor system.

Vectors for gene expression in mammalian cells

The achievement of robust and regulated protein production in mammalian cells is a complex process that requires careful consideration of many factors, including transcriptional and translational control elements, RNA processing, gene copy number, mRNA stability, the chromosomal site of gene integration, potential toxicity of recombinant proteins to the host cell, and the genetic properties of the host. Gene transfer into mammalian cells may be effected either by infection with virus that carries the recombinant gene of interest, or by direct transfer of plasmid DNA. This chapter discusses the molecular architecture of non-viral vectors for high-level protein production. Virus-based vectors for gene therapy, protein production, vaccine development and other applications are summarized in a table and described.

Enhanced expression of exogenous genes from retroviruses using HIV2/Tat

The capacity to produce large amounts of protein in mammalian cells is important in several contexts, including large-scale generation of biologically useful proteins, gene therapy, and transdominant genetics in cultured cells. For transdominant genetics, retroviral vectors are especially useful for delivery of expression libraries. However, even the potent CMV promoter is often unable to stimulate single-copy production of protein beyond the 1 microM level. We have adapted the HIV2/Tat expression system to retroviral vectors to boost expression above levels attainable with CMV promoters. We show that the system produces protein levels in four cell types tested which exceed levels attained by wild-type CMV or modified CMV promoters. In one cell line, the increase is 10-fold above CMV. Coupled with a stable expressed protein, levels of about 4 microM can be produced from presumptive single-copy retroviral transductants, and 30 microM from multicopy transductants.

Antisense gene therapy of brain cancer with an artificial virus gene delivery system

Therapeutic genes are delivered to the nuclear compartment of cancer cells following intravenous administration with a non-immunogenic "artificial virus" gene delivery system that uses receptor-specific monoclonal antibodies (MAb) to navigate the biological barriers between the blood and the nucleus of the cancer cell. Mice implanted with intracranial U87 human glial brain tumors are treated with a nonviral expression plasmid encoding antisense mRNA against the human epidermal growth factor receptor gene (EGFR). The plasmid DNA is packaged within the interior of polyethylene glycol-modified (PEGylated) immunoliposomes, and delivered to the brain tumor with MAbs that target the mouse transferrin receptor (TRFR) and the human insulin receptor (INSR). The mouse TRFR MAb enables transport across the tumor vasculature, which is of mouse brain origin, and the INSR MAb causes transport across the plasma membrane and the nuclear membrane of the human brain cancer cell. The lifespan of the mice treated weekly with an intravenous administration of the EGFR antisense gene therapy packaged within the artificial virus is increased 100% relative to mice treated either with a luciferase gene or with saline.

Intron-dependent stimulation of marker gene expression in cultured insect cells

We tested in a systematic fashion the effect of an intron on the level of luciferase expression in cultured C6/36 Aedes albopictus cells. The intron was inserted in both orientations, upstream and downstream of the luciferase coding region in two different luciferase expression vectors. The two parental luciferase expression vectors differed only in their promoters, one containing the Drosophila melanogaster actin5C promoter and the other the Autographa californica nuclear polyhedrosis virus hr5/ie1 enhancer/promoter. All resulting intron-containing constructs were tested for their ability to express luciferase in transient assays following electroporation into C6/36 cells. We found that the introns stimulate luciferase expression between twelve and sixtyfold, depending on the promoter. Enhanced expression was only seen when the intron was present in the correct orientation upstream of the luciferase ORF. When the 3' splice sites of the enhanced intron-containing constructs were mutated, the expression level dropped back to below the level of the intronless parental constructs, suggesting that the intron-dependent stimulation of luciferase expression is depending on splicing and is not due to other effects the intron may have on transcription or translation. The luciferase transcripts of all constructs were analysed by reverse transcription, PCR amplification and sequencing, and the results show a perfect correlation between efficient splicing of the intron and elevated levels of luciferase expression. Our findings have the potential to be very useful for boosting expression of foreign proteins in the widely used baculoviral or non-viral systems in insect cells.

Antiangiogenic potential of 10-hydroxycamptothecin

To investigate the antiangiogenic potential of 10-hydroxycamptothecin (HCPT), the proliferation of human microvascular endothelial cells (HMEC) and seven human tumor cell lines were detected by SRB assay, and the endothelial cell migration and tube formation were assessed using two in vitro model systems. Also, inhibition of angiogenesis was determined with a modification of the chick embryo chorioallantoic membrane (CAM) assay in vivo. Morphological assessment of apoptosis was performed by fluorescence microscope. HCPT 0.313-5 micromol x L(-1) treatment resulted in a dose-dependent inhibition of proliferation, migration and tube formation in HMEC cells, and HCPT 6.25-25 nmol x egg(-1) inhibited angiogenesis in CAM assay. HCPT 1.25-5 micromol x L(-1) elicited typical morphological changes of apoptosis including condensed chromatin, nuclear fragmentation, and reduction in volume in HMEC cells. HCPT significantly inhibited angiogenesis both in vitro and in vivo at relatively low concentrations, and this effect was related with induction of apoptosis in HMEC cells. These results taken collectively suggest that HCPT may be a potent antiangiogenetic and cytotoxic drug and further investigation is warranted.