Viral gene therapy strategies: from basic science to clinical application

Polyvalent nucleic acid nanostructures

Polyvalent oligonucleotide-nanoparticle conjugates possess several unique emergent properties, including enhanced cellular uptake, high antisense bioactivity, and nuclease resistance, which hypothetically originate from the dense packing and orientation of oligonucleotides on the surface of the nanoparticle. In this Communication, we describe a new class of polyvalent nucleic acid nanostructures (PNANs), which are comprised of only cross-linked and oriented nucleic acids. We demonstrate that these particles are capable of effecting high cellular uptake and gene regulation without the need of a cationic polymer co-carrier. The PNANs also exhibit cooperative binding behavior and nuclease resistance properties.

Bacterial spores as platforms for bioanalytical and biomedical applications

Genetically engineered bacteria-based sensing systems have been employed in a variety of analyses because of their selectivity, sensitivity, and ease of use. These systems, however, have found limited applications in the field because of the inability of bacteria to survive long term, especially under extreme environmental conditions. In nature, certain bacteria, such as those from Clostridium and Bacillus genera, when exposed to threatening environmental conditions are capable of cocooning themselves into a vegetative state known as spores. To overcome the aforementioned limitation of bacterial sensing systems, the use of microorganisms capable of sporulation has recently been proposed. The ability of spores to endow bacteria-based sensing systems with long lives, along with their ability to cycle between the vegetative spore state and the germinated living cell, contributes to their attractiveness as vehicles for cell-based biosensors. An additional application where spores have shown promise is in surface display systems. In that regard, spores expressing certain enzymes, proteins, or peptides on their surface have been presented as a stable, simple, and safe new tool for the biospecific recognition of target analytes, the biocatalytic production of chemicals, and the delivery of biomolecules of pharmaceutical relevance. This review focuses on the application of spores as a packaging method for whole-cell biosensors, surface display of recombinant proteins on spores for bioanalytical and biotechnological applications, and the use of spores as vehicles for vaccines and therapeutic agents.

The actin cytoskeleton has an active role in the electrotransfer of plasmid DNA in mammalian cells

Electrotransfer of molecules is a well established technique which finds extensive use for gene transfer and holds great promise for anticancer treatment. Despite its widespread application, the mechanisms governing the entry of DNA into the cell and its intracellular trafficking are not yet known. The aim of this study is to unravel the role of the actin cytoskeleton during gene electrotransfer in cells. We performed single-cell level approaches to observe the organization of the actin cytoskeleton in Chinese hamster ovary (CHO) cells. In addition, we performed experiments at the multiple-cell level to evaluate the efficiency of DNA transfer after alteration of the actin cytoskeleton using the drug latrunculin B. Actin patches colocalizing with the DNA at the plasma membrane were observed with additional characteristics similar to those of the DNA aggregates in terms of time, number, and size. The disruption of the microfilaments reduces the DNA accumulation at the plasma membrane and the gene expression. This is the first direct experimental evidence of the participation of the actin cytoskeleton in DNA electrotransfer.

Advances in Viral Vector-Based TRAIL Gene Therapy for Cancer

Numerous biologic approaches are being investigated as anti-cancer therapies in an attempt to induce tumor regression while circumventing the toxic side effects associated with standard chemo- or radiotherapies. Among these, tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) has shown particular promise in pre-clinical and early clinical trials, due to its preferential ability to induce apoptotic cell death in cancer cells and its minimal toxicity. One limitation of TRAIL use is the fact that many tumor types display an inherent resistance to TRAIL-induced apoptosis. To circumvent this problem, researchers have explored a number of strategies to optimize TRAIL delivery and to improve its efficacy via co-administration with other anti-cancer agents. In this review, we will focus on TRAIL-based gene therapy approaches for the treatment of malignancies. We will discuss the main viral vectors that are being used for TRAIL gene therapy and the strategies that are currently being attempted to improve the efficacy of TRAIL as an anti-cancer therapeutic.

EpCAM- and EGFR-targeted selective gene therapy for biliary cancers using Z33-fiber-modified adenovirus

A critical issue in adenovirus (Ad)-based cancer gene therapy is to improve the specificity of gene delivery to cancer cells for better efficacy and safety. We explored methods of retargeting Ad vectors for selective gene therapy of human biliary cancers using the Ad incorporating an IgG Fc-binding motif (Z33) from the Staphylococcus protein A (Ad-FZ33) combined with tumor-specific antibodies. Flow cytometry analysis revealed high-expression levels of epithelial cell adhesion molecule (EpCAM) and epidermal growth factor receptor (EGFR) on human biliary cancer cells. Ad-FZ33 expressing LacZ combined with antibodies against EpCAM or EGFR, followed by β-gal assay, demonstrated highly efficient gene transduction in these biliary cancer cells, compared to the treatment with control antibody or without antibody. Ad-FZ33 expressing uracil phosphoribosyl transferase (UPRT), an enzyme which greatly enhances the toxicity of 5-fluorouracil (FU), combined with antibodies against EpCAM or EGFR, remarkably enhanced the sensitivity of biliary cancer cells to 5-FU. By contrast, the treatment did not affect the 5-FU sensitivity of the cells not expressing EpCAM or EGFR including normal hepatocytes. Finally, treatments with the UPRT-expressing Ad-FZ33 with antibodies against EpCAM or EGFR, followed by 5-FU administration, significantly suppressed the growth of biliary cancer xenografts in nude mice. These results indicate that the gene therapy mediated by the Z33 fiber modified Ad with anti-EpCAM or anti-EGFR antibodies offers a potentially effective therapeutic modality against biliary cancers.

Tumor suppression by apoptotic and anti-angiogenic effects of mortalin-targeting adeno-oncolytic virus

BACKGROUND

Adeno-oncolytic (Adon) viruses offer an effective cancer therapeutic tool with several advantages, including wide host cell permeability, high transduction efficiency, safety, tumor selectivity, non-invasiveness, high genetic modifiability and high level of expression of the integrated transgenes. Armed Adon viruses in which the therapeutic efficacy of virus is enhanced by their coupling with cytotoxic, anti-angiogenic or anti-vascular gene products have gained importance because they engage additional mechanisms for tumor cell killing. In the present study, we selected mortalin, a stress chaperone that is tightly involved in human carcinogenesis, constructed a mortalin-targeting Adon (mot-Adon) virus and examined its therapeutic potential both in vitro and in vivo.

METHODS

Mortalin-targeting plasmid and viral vectors that harbored mortalin-specific small interfering RNA sequences were constructed. The therapeutic value of these vectors was investigated in vitro and in vivo by cell culture and nude mice tumor models.

RESULTS

We demonstrate that the mot-Adon virus has selective cytotoxicity for human cancer cells in vitro. Retrovirus-mediated overexpression of mortalin protected the cells against mot-Adon virus, confirming that mortalin silencing was the real cause of cancer cell death. Although mortalin overexpression enhanced malignant properties of cancer cells in breast xenograft models, mot-Adon virus elicited an enhanced anti-tumor effect. Immunohistochemical examination of the tumors showed that the mot-Adon virus caused enhanced apoptosis (mediated by reactivation of p53) and suppression of microvessel formation.

CONCLUSIONS

Mortalin is up-regulated in a large variety of tumors and hence mot-Adon virus is proposed as a candidate cancer therapeutic agent.

Indications for cell stress in response to adenoviral and baculoviral gene transfer observed by proteome profiling of human cancer cells

Gene transfer to cultured cells is an important tool for functional studies in many areas of biomedical research and vector systems derived from adenoviruses and baculoviruses are frequently used for this purpose. In order to characterize how viral gene transfer vectors affect the functional state of transduced cells, we applied 2-D PAGE allowing quantitative determination of protein amounts and synthesis rates of metabolically labeled cells and shotgun proteomics. Using HepG2 human hepatoma cells we show that both vector types can achieve efficient expression of green fluorescent protein, which accounted for about 0.1% of total cellular protein synthesis 72 h after transduction. No evidence in contrast was found for expression of proteins from the viral backbones. With respect to the host cell response, both vectors induced a general increase in protein synthesis of about 50%, which was independent of green fluorescent protein expression. 2-D PAGE autoradiographs identified a 3.6-fold increase of gamma-actin synthesis in adenovirus transduced cells. In addition shotgun proteomics of cytoplasmic and nuclear extract fractions identified a slight induction of several proteins related to inflammatory activation, cell survival and chromatin function by both virus types. These data demonstrate that commonly used gene transfer vectors induce a response reminiscent of stress activation in host cells, which needs to be taken into account when performing functional assays with transduced cells.

Pancreatic cancer: gene therapy approaches and gene delivery systems

IMPORTANCE OF THE FIELD

Due to the absence of early diagnosis, the highly invasive and metastatic features and the lack of effective therapeutic modalities, the prognosis of patients with pancreatic cancer is poor. Gene therapy is currently regarded as a potential and promising therapeutic modality for pancreatic cancer.

AREAS COVERED IN THIS REVIEW

This article summarizes an update of gene therapy approaches and reviews the latest progress in gene delivery systems that have been tested on pancreatic cancer.

WHAT THE READER WILL GAIN

The treatment effectiveness of gene combination therapy is better than that of the regulation of single-gene or single gene therapy approaches. Naked DNA is limited because of degradation by intracellular and extracellular nucleases. Virus vectors show high transfection efficiency but are limited due to immunogenicity, inflammatory response and potential carcinogenicity. Non-viral vectors, such as cationic polymers or inorganic nanoparticles, show an important feature that they can be easily modified, and the progress of materials science will provide more and better non-viral vectors, accordingly improving the efficiency and safety of gene therapy, which will make them the most promising vectors for pancreatic cancer.

Delivery of molecules into cells using carbon nanoparticles activated by femtosecond laser pulses

A major barrier to drug and gene delivery is crossing the cell's plasma membrane. Physical forces applied to cells via electroporation, ultrasound and laser irradiation generate nanoscale holes in the plasma membrane for direct delivery of drugs into the cytoplasm. Inspired by previous work showing that laser excitation of carbon nanoparticles can drive the carbon-steam reaction to generate highly controlled shock waves, we show that carbon black nanoparticles activated by femtosecond laser pulses can facilitate the delivery of small molecules, proteins and DNA into two types of cells. Our initial results suggest that interaction between the laser energy and carbon black nanoparticles may generate photoacoustic forces by chemical reaction to create transient holes in the membrane for intracellular delivery.

Stem cells are resistant to TRAIL receptor-mediated apoptosis

New therapeutic approaches aim to eradicate tumours by expression of tumouricidal proteins in the tumour stroma. One such anti-neoplastic protein is tumour necrosis factor-related apoptosis-inducing ligand (TRAIL) because it induces apoptosis in cancerous cells, but not in non-transformed cells. Stem cells can migrate to, survive and proliferate in tumours. We examined the suitability of bone marrow-derived adult mesenchymal stem cells (bmMSC), foetal-MSC and umbilical cord matrix stem cells (Wharton’s Jelly MSCs) as TRAIL-delivery vehicles. Although all MSC types expressed DR4 and/or DR5, none of them were sensitive to TRAIL-induced apoptosis. Selective activation of DR4 or DR5 with agonistic antibodies or DR5-selective TRAIL-mutant (D269H/E195R) revealed that the TRAIL receptors are inactive in MSCs. In fMSC DR5 was not fully inactivated, its activity however was minimal in comparison to the colon carcinoma cell, Colo205. The intracellular components of the TRAIL-apoptotic pathway, such as pro-caspase-8 and -9 were also expressed at very low; almost undetectable levels in all three MSC types. In conclusion, the MSC species examined are resistant to TRAIL and thus can be suitable tools for TRAIL delivery to tumours.

Transplantation of galectin-1-expressing human neural stem cells into the injured spinal cord of adult common marmosets

Delayed transplantation of neural stem/progenitor cells (NS/PCs) into the injured spinal cord can promote functional recovery in adult rats and monkeys. To enhance the functional recovery after NS/PC transplantation, we focused on galectin-1, a carbohydrate-binding protein with pleiotropic roles in cell growth, differentiation, apoptosis, and neurite outgrowth. Here, to determine the combined therapeutic effect of NS/PC transplantation and galectin-1 on spinal cord injury (SCI), human NS/PCs were transfected by lentivirus with galectin-1 and green fluorescent protein (GFP), (Gal-NS/PCs) or GFP alone (GFP-NS/PCs), expanded in vitro, and then transplanted into the spinal cord of adult common marmosets, 9 days after contusive cervical SCI. The animals' motor function was evaluated by their spontaneous motor activity, bar grip power, and performance on a treadmill test. Histological analyses revealed that the grafted human NS/PCs survived and differentiated into neurons, astrocytes, and oligodendrocytes. There were significant differences in the myelinated area, corticospinal fibers, and serotonergic fibers among the Gal-NS/PC, GFP-NS/PC, vehicle-control, and sham-operated groups. The Gal-NS/PC-grafted animals showed a better performance on all the behavioral tests compared with the other groups. These findings suggest that Gal-NS/PCs have better therapeutic potential than NS/PCs for SCI in nonhuman primates and that human Gal-NS/PC transplantation might be a feasible treatment for human SCI.

Gene therapy for bone healing

Clinical problems in bone healing include large segmental defects, spinal fusions, and the nonunion and delayed union of fractures. Gene-transfer technologies have the potential to aid healing by permitting the local delivery and sustained expression of osteogenic gene products within osseous lesions. Key questions for such an approach include the choice of transgene, vector and gene-transfer strategy. Most experimental data have been obtained using cDNAs encoding osteogenic growth factors such as bone morphogenetic protein-2 (BMP-2), BMP-4 and BMP-7, in conjunction with both nonviral and viral vectors using in vivo and ex vivo delivery strategies. Proof of principle has been convincingly demonstrated in small-animal models. Relatively few studies have used large animals, but the results so far are encouraging. Once a reliable method has been developed, it will be necessary to perform detailed pharmacological and toxicological studies, as well as satisfy other demands of the regulatory bodies, before human clinical trials can be initiated. Such studies are very expensive and often protracted. Thus, progress in developing a clinically useful gene therapy for bone healing is determined not only by scientific considerations, but also by financial constraints and the ambient regulatory environment.

Ultrasound-assisted non-viral gene transfer to the salivary glands

We report a non-viral gene transfer method using ultrasound induced microbubble destruction to allow the uptake of plasmid gene transfer vectors to the cells of the mouse salivary gland. The Luciferase (Luc) reporter gene, driven by a cytomegalovirus (CMV) promoter, was delivered unilaterally to the submandibular salivary gland via retroductal cannulation and Luc expression was monitored with in vivo imaging. The CMV-Luc plasmid was delivered to the salivary gland in a carrier solution containing microbubbles composed of lipid-encased perfluoropropane gas, with two different concentrations of microbubbles used (100 and 15% volume/volume). An Adenoviral (Ad) vector using an identical CMV-Luc expression cassette was used as a positive control at two different dosages. Whereas ultrasound-assisted gene transfer (UAGT) with 100% microbubbles was weak and rapidly extinguished, UAGT with the 15% microbubble solution was robust and stable for 28 days. UAGT seems to be a practicable and promising method for non-viral gene delivery to the salivary glands.

A probasin promoter, conditionally replicating adenovirus that expresses the sodium iodide symporter (NIS) for radiovirotherapy of prostate cancer

The sodium iodide symporter (NIS) directs the uptake and concentration of iodide in thyroid cells. We have extended the use of NIS-mediated radioiodine therapy to other types of cancer, we transferred and expressed the sodium-iodide symporter (NIS) gene into prostate, colon, and breast cancer cells using adenoviral vectors. To improve vector efficiency we have developed a conditionally replicating adenovirus (CRAd) in which the E1a gene is driven by the prostate specific promoter, Probasin and the cassette RSV promoter-human NIScDNA-bGH polyA replaces the E3 region (CRAd Ad5PB_RSV-NIS). In vitro infection of the prostate cancer cell line LnCaP resulted in virus replication, cytolysis, and release of infective viral particles. Conversely, the prostate cancer cell line PC-3 (androgen receptor negative) and the pancreatic cancer cell line Panc-1 were refractory to the viral cytopathic effect and did not support viral replication. Radioiodine uptake was readily measurable in LnCaP cells infected with Ad5PB_RSV-NIS 24 hours post-infection, confirming NIS expression. In vivo, LnCaP tumor xenografts in nude mice injected intratumorally with Ad5PB_RSV_NIS CRAd expressed NIS actively as evidenced by ⁹⁹Tc uptake and imaging. Administration of therapeutic ¹³¹I after virus injection significantly increased survival probability in mice carrying xenografted LnCaP tumors compared to virotherapy alone. The data indicate that Ad5PB_RSV_NIS replication is stringently restricted to androgen positive prostate cancer cells and results in effective NIS expression and uptake of radioiodine. This construct may allow multimodal therapy, combining cytolytic virotherapy with radioiodine treatment, to be developed as a novel treatment for prostate cancer.

Recent trends in non-viral vector-mediated gene delivery

Nucleic acids-based next generation biopharmaceuticals (i.e., pDNA, oligonucleotides, short interfering RNA) are potential pioneering materials to cope with various incurable diseases. However, several biological barriers present a challenge for efficient gene delivery. On the other hand, developments in nanotechnology now offer numerous non-viral vectors that have been fabricated and found capable of transmitting the biopharmaceuticals into the cell and even into specific subcellular compartments like mitochondria. This overview illustrates cellular barriers and current status of non-viral gene vectors, i.e., lipoplexes, liposomes, polyplexes, and nanoparticles, to relocate therapeutic DNA-based nanomedicine into the target cell. Despite the awesome impact of physical methods (i.e., ultrasound, electroporation), chemical methods have been shown to accomplish high-level and safe transgene expression. Further comprehension of barriers and the mechanism of cellular uptake will facilitate development of nucleic acids-based nanotherapy for alleviation of various disorders.

Gene therapy for mesothelioma and lung cancer

Both malignant pleural mesothelioma and advanced stage lung cancer are associated with a poor prognosis. Unfortunately, current treatment regimens have had only a modest effect on their progressive course. Gene therapy for thoracic malignancies represents a novel therapeutic approach and has been evaluated in a number of clinical trials over the last two decades. Using viral vectors or anti-sense RNA, strategies have included induction of apoptosis, tumor suppressor gene replacement, suicide gene expression, cytokine-based therapy, various vaccination approaches, and adoptive transfer of modified immune cells. This review will consider the clinical results, limitations, and future directions of gene therapy trials for thoracic malignancies.

A placental growth factor variant unable to recognize vascular endothelial growth factor (VEGF) receptor-1 inhibits VEGF-dependent tumor angiogenesis via heterodimerization

Angiogenesis is one of the crucial events for cancer development and growth. Two members of the vascular endothelial growth factor (VEGF) family, VEGF-A and placental growth factor (PlGF), which are able to heterodimerize if coexpressed in the same cell, are both required for pathologic angiogenesis. We have generated a PlGF1 variant, named PlGF1-DE in which the residues Asp72 and Glu73 were substituted with Ala, which is unable to bind and activate VEGF receptor-1 but is still able to heterodimerize with VEGF. Here, we show that overexpression in tumor cells by adenoviral delivery or stable transfection of PlGF1-DE variant significantly reduces the production of VEGF homodimer via heterodimerization, determining a strong inhibition of xenograft tumor growth and neoangiogenesis, as well as significant reduction of vessel lumen and stabilization, and monocyte-macrophage infiltration. Conversely, the overexpression of PlGF1wt, also reducing the VEGF homodimer production comparably with PlGF1-DE variant through the generation of VEGF/PlGF heterodimer, does not inhibit tumor growth and vessel density compared with controls but induces increase of vessel lumen, vessel stabilization, and monocyte-macrophage infiltration. The property of PlGF and VEGF-A to generate heterodimer represents a successful strategy to inhibit VEGF-dependent angiogenesis. The PlGF1-DE variant, and not PlGF1wt as previously reported, acts as a "dominant negative" of VEGF and is a new candidate for antiangiogenic gene therapy in cancer treatment.

Delivering the goods: viral and non-viral gene therapy systems and the inherent limits on cargo DNA and internal sequences

Viruses have long been considered to be the most promising tools for human gene therapy. However, the initial enthusiasm for the use of viruses has been tarnished in the light of potentially fatal side effects. Transposons have a long history of use with bacteria in the laboratory and are now routinely applied to eukaryotic model organisms. Transposons show promise for applications in human genetic modification and should prove a useful addition to the gene therapy tool kit. Here we review the use of viruses and the limitations of current approaches to gene therapy, followed by a more detailed analysis of transposon length and the physical properties of internal sequences, which both affect transposition efficiency. As transposon length increases, transposition decreases: this phenomenon is known as length-dependence, and has implications for vector cargo capacity. Disruption of internal sequences, either via deletion of native DNA or insertion of exogenous DNA, may reduce or enhance genetic mobility. These effects may be related to host factor binding, essential spacer requirements or other influences yet to be elucidated. Length-dependence is a complex phenomenon driven not simply by the distance between the transposon ends, but by host proteins, the transposase and the properties of the DNA sequences encoded within the transposon.

Strategies for the preparation of synthetic transfection vectors

In the late 1980s independent work by Felgner and Behr pioneered the use of cationic materials to complex and deliver nucleic acids into eukaryotic cells. Since this time, a vast number of synthetic transfection vectors, which are typically divided into two main "transfectors", have been developed namely: (1) cationic lipids and (2) polycationic polymers. In this chapter the main synthetic approaches used for the synthesis of these compounds will be reviewed with particular attention paid to: cationic lipids and dendrimers. This review is aimed primarily at the younger audience of doctoral students and non-specialist readers.

Amelioration of emphysema in mice through lentiviral transduction of long-lived pulmonary alveolar macrophages

Directed gene transfer into specific cell lineages in vivo is an attractive approach for both modulating gene expression and correcting inherited mutations such as emphysema caused by human alpha1 antitrypsin (hAAT) deficiency. However, somatic tissues are mainly comprised of heterogeneous, differentiated cell lineages that can be short lived and difficult to specifically transfect. Here, we describe an intratracheally instilled lentiviral system able to deliver genes selectively to as many as 70% of alveolar macrophages (AMs) in the mouse lung. Following a single in vivo lentiviral transduction, genetically tagged AMs persisted in lung alveoli and expressed transferred genes for the lifetime of the adult mouse. A prolonged macrophage lifespan, rather than precursor cell proliferation, accounted for the surprisingly sustained presence of transduced AMs. We utilized this long-lived population to achieve localized secretion of therapeutic levels of hAAT protein in lung epithelial lining fluid. In an established mouse model of emphysema, lentivirally delivered hAAT ameliorated the progression of emphysema, as evidenced by attenuation of increased lung compliance and alveolar size. After 24 weeks of sustained gene expression, no humoral or cellular immune responses to hAAT protein were detected. Our results challenge the dogma that AMs are short lived and suggest that these differentiated cells may be a possible target cell population for in vivo gene therapy applications, including the sustained correction of hAAT deficiency.

Recent advances in the manipulation of murine gene expression and its utility for the study of human neurological disease

Transgenic mouse models have vastly contributed to our knowledge of the genetic and molecular pathways underlying the pathogenesis of neurological disorders that affect millions of people worldwide. Not only have they allowed the generation of disease models mimicking the human pathological state but they have also permitted the exploration of the pathological role of specific genes through the generation of knock-out and knock-in models. Classical constitutive transgenic mice have several limitations however, due to behavioral adaptation process occurring and conditional mouse models are time-consuming and often lack extensive spatial or temporal control of gene manipulation. These limitations could be overcome by means of innovative methods that are now available such as RNAi, viral vectors and large cloning DNA vectors. These tools have been extensively used for the generation of mouse models and are characterized by the superior control of transgene expression that has been proven invaluable in the assessment of novel treatments for neurological diseases and to further investigate the molecular processes underlying the etiopathology of neurological disorders. Furthermore, in association with classical transgenic mouse models, they have allowed the validation of innovative therapeutic strategies for the treatment of human neurological disorders. This review describes how these tools have overcome the limitations of classical transgenic mouse models and how they have been of value for the study of human neurological diseases.

A comparative review of the potential role of adenovirus and Herpes Simplex Virus in the treatment of advanced squamous cell carcinoma of the head and neck

The unsatisfactory outcome of patients who receive intensive multimodality treatment for advanced squamous cell carcinoma of the head and neck (SCCHN) has motivated investigators to seek novel treatments to improve survival. Advances in molecular biology has led to the development of cancer gene therapy (CGT) and revived interest in viral vectors as a mechanism. SCCHN is an ideal model for CGT as disease remains locoregional and is amenable to injection of viruses. Adenovirus and Herpes Simplex Virus Type-1 (HSV) are the most studied Oncolytic Viruses (OVs). Both viruses have been shown to select and replicate in tumour cells and demonstrate anti-tumour effect in laboratory studies and clinical trials. Toxicity from OVs is minor and manageable. Different adenoviral mutants have been investigated with mixed responses. One vector, H101, has now been licensed after showing significant tumour regression in conjunction with chemotherapy. HSV has a larger capacity to carry genetic material and with the addition of the granulocyte–macrophage colony–stimulating factor, has the potential to stimulate an immune response systemically and at the site of disease. OVs are limited by the distribution of virus beyond injection site and by pre-existing or rapidly established immune response. Phase III studies are required.

Testing double mutants of the enzyme nitroreductase for enhanced cell sensitisation to prodrugs: effects of combining beneficial single mutations

Prodrug activation gene therapy for cancer involves expressing prodrug-activating enzymes in tumour cells, so they can be selectively killed by systemically administered prodrug. For example, Escherichia colinfsB nitroreductase (E.C. 1.6.99.7)(NTR), sensitises cells to the prodrug CB1954 (5-[aziridin-1-yl]-2,4-dinitrobenzamide), which it converts to a potent DNA-crosslinking agent. However, low catalytic efficiency with this non-natural substrate appears to limit the efficacy of this enzyme prodrug combination for eliminating the target cancer cells. To improve this, we aim to engineer NTR for improved prodrug activation. Previously, a number of single amino acid substitutions at six positions around the active site of the enzyme were found to increase activity, resulting in up to approximately 5-fold enhanced cell sensitisation to CB1954. In this study we have made pairwise combinations among some of the best mutants at each of these 6 sites. A total of 53 double mutants were initially screened in E. coli, then the 7 most promising were inserted into an adenovirus vector and compared in SKOV3 human ovarian carcinoma cells for sensitisation to CB1954 and two alternative prodrugs. The most effective mutants, T41L/N71S and T41L/F70A, were 14-17-fold more potent than WT NTR at sensitising the cancer cells to CB1954. The best mutant for activation of the dinitrobenzamide mustard prodrug SN23862 was T41L/F70A (4.8-fold improvement); and S40A/F124M showed 1.7-fold improvement over WT with the nitrobenzylphosphoramide mustard prodrug LH7. In two tumour xenograft models using SKOV3 or human prostate carcinoma PC3, T41L/N71S NTR demonstrated greater CB1954-dependent anti-tumour activity than WT NTR.

Gene therapy vectors: the prospects and potentials of the cut-and-paste transposons

Gene therapy applications require efficient tools for the stable delivery of genetic information into eukaryotic genomes. Most current gene delivery strategies are based on viral vectors. However, a number of drawbacks, such as the limited cargo capacity, host immune response and mutational risks, highlight the need for alternative gene delivery tools. A comprehensive gene therapy tool kit should contain a range of vectors and techniques that can be adapted to different targets and purposes. Transposons provide a potentially powerful approach. However, transposons encompass a large number of different molecular mechanisms, some of which are better suited to gene delivery applications than others. Here, we consider the range and potentials of the various mechanisms, focusing on the cut-and-paste transposons as one of the more promising avenues towards gene therapy applications. Several cut-and-paste transposition systems are currently under development. We will first consider the mechanisms of piggyBac and the hAT family elements Tol1 and Tol2, before focusing on the mariner family elements including Mos1, Himar1 and Hsmar1.

Construction of an MUC-1 promoter driven, conditionally replicating adenovirus that expresses the sodium iodide symporter for gene therapy of breast cancer

Introduction

The sodium iodide symporter (NIS) directs the uptake and concentration of iodide in thyroid cells. This in turn allows radioiodine imaging and therapy for thyroid cancer. To extend the use of NIS-mediated radioiodine therapy to other types of cancer, we successfully transferred and expressed the sodium-iodide symporter (NIS) gene in prostate, colon, and breast cancer cells both in vivo and in vitro by using non-replicating adenoviral vectors.

Methods

To improve virotherapy efficiency, we developed a conditionally replicating adenovirus (CRAd) in which the transcriptional cassette RSV promoter-human NIScDNA-bGH polyA was also inserted at the E3 region. The E1a gene is driven by the tumor-specific promoter MUC-1 in the CRAd Ad5AMUCH_RSV-NIS.

Results

In vitro infection of the MUC-1-positive breast cell line T47D resulted in virus replication, cytolysis, and release of infective viral particles. Conversely, the MUC-1-negative breast cancer cell line MDA-MB-231 was refractory to the viral cytopathic effect and did not support viral replication. The data indicate that Ad5AMUCH_RSV-NIS activity is stringently restricted to MUC-1-positive cancer cells. Radioiodine uptake was readily measurable in T47 cells infected with Ad5AMUCH_RSV-NIS 24 hours after infection, thus confirming NIS expression before viral-induced cell death.

Conclusions

This construct may allow multimodal therapy, combining virotherapy with radioiodine therapy to be developed as a novel treatment for breast and other MUC1-overexpressing cancers.

Systemic NK4 gene therapy inhibits tumor growth and metastasis of melanoma and lung carcinoma in syngeneic mouse tumor models

Hepatocyte growth factor (HGF) promotes malignant development of cancer cells by enhancing invasion and metastasis. NK4, a competitive antagonist for HGF, is a bifunctional molecule that acts as a HGF antagonist and angiogenesis inhibitor. Although successful tumor inhibition by NK4 gene expression in tumor models has been demonstrated, the effects of systemic NK4 gene introduction are yet to be addressed. Here we show that systemic administration of a replication-defective adenovirus expressing NK4 (Ad.NK4) inhibits tumor growth and lung metastasis of B16F10 melanoma and Lewis lung carcinoma in syngeneic mice. Single tail-vein injection of Ad.NK4 achieved therapeutic levels of NK4 in the circulation and in multiple organs. Despite NK4 expression that was highest in the liver, toxicity in the liver was minimal. Ad.NK4-mediated growth inhibition was associated with decreased blood vessel density and increased apoptosis in tumor tissues, which suggests that NK4 suppressed tumor growth as an angiogenesis inhibitor. Metastasis of B16F10 melanoma and Lewis lung carcinoma cells to the lung was potently inhibited by systemic Ad.NK4-administration. Our results demonstrated that the adenovirus-mediated induction of high levels of circulating NK4 significantly inhibited in vivo tumor growth and distant metastasis without obvious side effects. NK4 gene therapy is thus a safe and promising strategy for the treatment of cancer patients, and further validation in clinical trials is needed.

Gene- and viral-based therapies for brain tumors

Advances in understanding and controlling genes and their expression have set the stage to alter genetic material to fight or prevent disease with brain tumors being among one of the first human malignancies to be targeted by gene therapy. All proteins are coded for by DNA and most neoplastic diseases ultimately result from the expression or lack thereof with one or more proteins (e.g., coded by oncogenes or tumor suppressor genes, respectively). In theory, therefore, diseases could be treated by expression of the appropriate protein in the affected cells. Gene therapy is an experimental treatment that involves introducing genetic material (DNA or RNA) into cells, and it has made important advances in the past decade. Within this short time span, it has moved from the conceptual laboratory research stage to clinical translational trials for brain tumors. The most efficient approaches for gene delivery are based on viral vectors, which have been proven relatively safe in the CNS, despite occasional cases of morbidity and death in non-neurosurgical trials. However, the human response to various viral vectors can not be predicted in a reliable manner from animal experimentation, nor can size, consistency, and extent of experimental brain tumors in mouse models reflect the large, necrotic, infiltrative nature of malignant gliomas. Furthermore, the problem of delivering genetic vectors into solid brain tumors and the efficiency in situ gene transfer remains one of the most significant hurdles in gene therapy.

Technical note: a gene delivery system in the embryonic cells of avian species using a human adenoviral vector

Adenovirus (Ad) has been used in vivo and in vitro as a vector to carry a foreign gene for efficient gene delivery into various cell types and tissues of animals. The aim of the current study was to evaluate the Ad delivery system in primary avian cells. Primary cells isolated from the embryonic pectoralis major muscles of the chicken and quail were cultured and incubated with human recombinant Ad serotype 5 (Ad5) containing sequences encoding either the green fluorescence protein (GFP) gene alone, as a tracking marker, or both GFP and murine 3-hydroxyisobutyryl-CoA hydrolase (mHIBCH) as a target gene. The fluorescent GFP images showed the successful delivery of a target gene using Ad5 in the primary avian cultured cells. In addition, immunostaining of the myosin heavy chain (MyHC) in these cells indicated that a large population of the cells was myogenic. Colocalization of GFP-positive cells with MyHC staining was mostly found in MyHC-negative cells, indicating successful delivery of Ad5 into a large population of mononucleated cells. Furthermore, the current fluorescence study detected the dual expression of GFP and mHIBCH protein in GFP-positive cells. Finally, Western blot analysis confirmed that the Ad-mediated expression of mHIBCH protein was specific in primary cultures of avian myogenic cells and that the mHIBCH protein expression was continued for 15 d after infection in chicken primary cells. These data demonstrate that Ad5 is a feasible tool to express foreign genes in primary cultured cells of avian species, providing a new approach to study the function of genes of interest in muscle development and metabolism.

P-selectin dependent targeting to inflamed endothelium of recombinant P-selectin glycoprotein ligand-1 immunoglobulin chimera-coated poly[N-(2-hydroxypropyl) methacrylamide]-DNA polyplexes in vivo visualised by intravital microscopy

BACKGROUND

Developing vectors that target specifically to disease sites after systemic injection is an important goal in gene therapy research.

METHODS

We prepared fluorescent DNA polyplexes (< or =150 nm in diameter) comprising plasmid DNA condensed with poly(L-lysine) and coated with a multivalent reactive copolymer based on poly[N-(2-hydroxypropyl)methacrylamide] (pHPMA). These polyplexes were then surface modified with a recombinant P-selectin glycoprotein ligand-1 immunoglobulin chimera (rPSGL-Ig) previously investigated as a selectin antagonist in clinical studies.

RESULTS

Five minutes after jugular vein injection of these polyplexes, fluorescence accumulation in inflamed cremasteric venules of C57BL6 mice was more than eight-fold higher than that observed after injection of Fc-blocked control polyplexes. Fluorescence above background was not observed in P-selectin deficient mice, confirming the specificity for P-selectin in this model.

CONCLUSIONS

These data provide encouragement for the further development of rPSGL-Ig-coated polyplexes as potential nonviral vectors for targeted gene therapy in inflammatory conditions, such as ischaemia reperfusion injury, unstable atherosclerotic plaques and myocarditis. This approach may also be transferable to the use of other targeting ligands whose cognate partner is specifically upregulated on the vascular endothelium in individual pathological situations.

Abrogation of microsatellite-instable tumors using a highly selective suicide gene/prodrug combination

A substantial fraction of sporadic and inherited colorectal and endometrial cancers in humans is deficient in DNA mismatch repair (MMR). These cancers are characterized by length alterations in ubiquitous simple sequence repeats, a phenotype called microsatellite instability. Here we have exploited this phenotype by developing a novel approach for the highly selective gene therapy of MMR-deficient tumors. To achieve this selectivity, we mutated the VP22FCU1 suicide gene by inserting an out-of-frame microsatellite within its coding region. We show that in a significant fraction of microsatellite-instable (MSI) cells carrying the mutated suicide gene, full-length protein becomes expressed within a few cell doublings, presumably resulting from a reverting frameshift within the inserted microsatellite. Treatment of these cells with the innocuous prodrug 5-fluorocytosine (5-FC) induces strong cytotoxicity and we demonstrate that this owes to multiple bystander effects conferred by the suicide gene/prodrug combination. In a mouse model, MMR-deficient tumors that contained the out-of-frame VP22FCU1 gene displayed strong remission after treatment with 5-FC, without any obvious adverse systemic effects to the mouse. By virtue of its high selectivity and potency, this conditional enzyme/prodrug combination may hold promise for the treatment or prevention of MMR-deficient cancer in humans.

An shRNA silencing a non-toxic transgene reduces nutrient consumption and increases production of adenoviral vectors in a novel packaging cell

During production of an adenoviral vector in a packaging cell, transgene is expressed concomitantly with the adenoviral gene. Depending on the protein encoded by the transgene, the yield of an adenoviral vector can be reduced or blocked as a result of transgene expression in the packaging cell. We tested the effect of a short hairpin RNA (shRNA) inhibiting the expression of a transgene encoding hIcon, a therapeutic molecule that selectively destroys pathological angiogenic blood vessels, on the yield of an adenoviral vector containing the transgene. The results showed that the yield of infectious adenoviral vector particles was increased about 10-fold in a novel packaging cell with stable production of an shRNA that can silence the transgene, as compared to the yield in standard packaging line, and the consumption of nutrient in the novel packaging cell line is decreased due to silence of adenoviral transgene expression. The study indicates that shRNA can increase the production of adenoviral vectors by silencing transgene and reducing nutrient consumption of the novel packaging cell. The use of shRNA silencing expression of transgenes encoding therapeutic molecules can reduce the time and cost of producing adenoviral vectors for clinical use.

Tumor targeting using canine parvovirus nanoparticles

Advances in genetics, proteomics and cellular and molecular biology are being integrated and translated to develop effective methods for the prevention and control of cancer. One such combined effort is to create multifunctional nanodevices that will specifically recognize tumors and thus enable early diagnosis and provide targeted treatment of this disease. Viral particles are being considered for this purpose since they are inherently nanostructures with well-defined geometry and uniformity, ideal for displaying molecules in a precise spatial distribution at the nanoscale level and subject to greater structural control. Viruses are presumably the most efficient nanocontainer for cellular delivery as they have naturally evolved mechanisms for binding to and entering cells. Virus-based systems typically require genetic or chemical modification of their surfaces to achieve tumor-specific interactions. Interestingly, canine parvovirus (CPV) has a natural affinity for transferrin receptors (TfRs) (both of canine and human origin) and this property could be harnessed as TfRs are overexpressed by a variety of human tumor cells. Since TfR recognition relies on the CPV capsid protein, we envisioned the use of virus or its shells as tumor targeting agents. We observed that derivatization of CPV virus-like particles (VLPs) with dye molecules did not impair particle binding to TfRs or internalization into human tumor cells. Thus CPV-based VLPs with a natural tropism for TfRs hold great promise in the development of novel nanomaterial for delivery of a therapeutic and/or genetic cargo.

Immunotherapeutic polyoma and human papilloma virus-like particles

Polyomavirus and human papillomavirus (HPV) virus-like particles (VLPs) can be obtained by producing their major capsid protein VP1 (for polyomavirus) or L1 (for HPV) free from other viral genes in, for example, a baculovirus insect system, yeast, Escherichia coli or similar systems. Polyomavirus and HPV VLPs can immunize healthy individuals, and in some cases T-cell-deficient hosts, against primary infection with the corresponding virus. Chimeric VLPs from polyomaviruses or HPVs containing fusion proteins between the VP1/L1 or VP2/VP3/L2 minor capsid proteins and selected antigens can also be produced. These VLPs can then induce B- or T-cell immune responses and be used as preventive or therapeutic vaccines against cancers induced by the corresponding virus, or a cancer bearing the selected tumor antigen.

Surface immobilization of poly(ethyleneimine) and plasmid DNA on electrospun poly(L-lactic acid) fibrous mats using a layer-by-layer approach for gene delivery

The method of coating electrospun ultrafine poly(L-lactic acid) fibers with DNA, by building up polyelectrolyte layer(s) of poly(ethyleneimine) (PEI) and plasmid DNA using an electrostatic layer-by-layer deposition method, for gene delivery is presented. The pGL3 encoding luciferase was applied as plasmid DNA. The quantity of pGL3 immobilized on individual fibers increased with increasing pGL3 concentration in the immersion solution (0.017-0.870 mg/mL) and increasing bilayer number of PEI/pGL3 (single-triple). With the exception of one specimen prepared under the condition 0.870 mg/mL pGL3 solution and double PEI/pGL3 layers, the transfection efficiency of COS-7 cells, defined by the ratio of fluorescence intensity (resulting from the presence of luciferase) with respect to the quantity of cellular protein on the fibrous mat increased with increasing quantity of pGL3 on the fibers. In addition to the ease of controlling the quality of polyelectrolyte bilayer(s) by simply changing the concentrations of substances and number of immersing cycles, the features of the electrospun fibrous mat such as a very large surface-to-volume ratio and flexibility, could potentially be employed as a strategy for gene therapy combined with tissue engineering technology.

Oncolytic virus therapy for pancreatic cancer using the adenovirus library displaying random peptides on the fiber knob

A conditionally replicative adenovirus is a novel anticancer agent designed to replicate selectively in tumor cells. However, a leak of the virus into systemic circulation from the tumors often causes ectopic infection of various organs. Therefore, suppression of naive viral tropism and addition of tumor-targeting potential are necessary to secure patient safety and increase the therapeutic effect of an oncolytic adenovirus in the clinical setting. We have recently developed a direct selection method of targeted vector from a random peptide library displayed on an adenoviral fiber knob to overcome the limitation that many cell type-specific ligands for targeted adenovirus vectors are not known. Here we examined whether the addition of a tumor-targeting ligand to a replication-competent adenovirus ablated for naive tropism enhances its therapeutic index. First, a peptide-display adenovirus library was screened on a pancreatic cancer cell line (AsPC-1), and particular peptide sequences were selected. The replication-competent adenovirus displaying the selected ligand (AdDeltaCAR-SYE) showed higher oncolytic potency in several other pancreatic cancer cell lines as well as AsPC-1 compared with the untargeted adenovirus (AdDeltaCAR). An intratumoral injection of AdDeltaCAR-SYE significantly suppressed the growth of AsPC-1 subcutaneous tumors, and an analysis of adenovirus titer in the tumors revealed an effective replication of the virus in the tumors. Ectopic liver gene transduction following the intratumoral injection of AdDeltaCAR-SYE was not increased compared with the AdDeltaCAR. The results showed that a tumor-targeting strategy using an adenovirus library is promising for optimizing the safety and efficacy of oncolytic adenovirus therapy.

Heparin antagonism by polyvalent display of cationic motifs on virus-like particles

Particles to the rescue! The construction of cationic amino acid motifs on the surface of bacteriophage Qbeta by genetic engineering or chemical conjugation gives particles that are potent inhibitors of the anticoagulant action of heparin, which is a common anticlotting agent subject to clinical overdose.Polyvalent interactions allow biological structures to exploit low-affinity ligand-receptor binding events to affect physiological responses. We describe here the use of bacteriophage Qbeta as a multivalent platform for the display of polycationic motifs that act as heparin antagonists. Point mutations to the coat protein allowed us to generate capsids bearing the K16M, T18R, N10R, or D14R mutations; because 180 coat proteins form the capsid, the mutants provide a spectrum of particles differing in surface charge by as much as +540 units (K16M vs. D14R). Whereas larger poly-Arg insertions (for example, C-terminal Arg(8)) did not yield intact virions, it was possible to append chemically synthesized oligo-Arg peptides to stable wild-type (WT) and K16M platforms. Heparin antagonism by the particles was evaluated by using the activated partial thrombin time (aPTT) clotting assay; this revealed that T18R, D14R, and WT-(R(8)G(2))(95) were the most effective at disrupting heparin-mediated anticoagulation (>95 % inhibition). This activity agreed with measurements of zeta potential (ZP) and retention time on cation exchange chromatography for the genetic constructs, which distribute their added positive charge over the capsid surface (+180 and +360 for T18R and D14R relative to WT). The potent activity of WT-(R(8)G(2))(95), despite its relatively diminished overall surface charge is likely a consequence of the particle's presentation of locally concentrated regions with high positive charge density that interact with heparin's extensively sulfated domains. The engineered cationic capsids retained their ability to inhibit heparin at high concentrations and showed no anticlotting activity of the kind that limits the utility of antiheparin polycationic agents that are currently in clinical use.

An acute toxicology study with INGN 007, an oncolytic adenovirus vector, in mice and permissive Syrian hamsters; comparisons with wild-type Ad5 and a replication-defective adenovirus vector

Oncolytic (replication-competent) adenoviruses as anticancer agents provide new, promising tools to fight cancer. In support of a Phase I clinical trial, here we report safety data with INGN 007 (VRX-007), an oncolytic adenovirus with increased anti-tumor efficacy due to overexpression of the adenovirus-encoded ADP protein. Wild-type adenovirus type 5 (Ad5) and a replication-defective version of Ad5 were also studied as controls. A parallel study investigating the biodistribution of these viruses is described elsewhere in this issue. The toxicology experiments were conducted in two species, the Syrian hamster, which is permissive for INGN 007 and Ad5 replication and the poorly permissive mouse. The studies demonstrated that the safety profile of INGN 007 is similar to Ad5. Both viruses caused transient liver damage upon intravenous injection that resolved by 28 days post-infection. The No-Observable-Adverse-Effect-Level (NOAEL) for INGN 007 in hamsters was 3 x 10(10) viral particles per kg. In hamsters, the replication-defective vector caused less toxicity, indicating that replication of Ad vectors in the host is an important factor in pathogenesis. With mice, INGN 007 and Ad5 caused toxicity comparable to the replication-defective adenovirus vector. Partially based on these results, the FDA granted permission to enter into a Phase I clinical trial with INGN 007.

Gene delivery into hepatocytes with the preS/liposome/DNA system

Gene delivery into human hepatocytes remains a critical issue for the development of liver-directed gene therapy. Gene delivery based on non-viral vectors is an attractive approach relative to viral vectors. In this report, novel delivery system of preS/liposome/DNA virus-like particle (VLP) was developed for gene transfection into hepatocytes in vivo and in vitro. Plasmid pCMVbeta, expressing beta-galactosidase, was encapsulated with cationic liposome, and then the histidine-tagged preS domain of hepatitis B virus was coated on the surface of liposome/DNA to form preS/liposome/ DNA VLP. Transfection efficiencies of preS/liposome/DNA, liposome/DNA, naked DNA and preS were analyzed using several different human cell lines. The highest transfection efficiency was found using preS/liposome/DNA VLP as the transfection reagent in human hepatocyte (HH) cell line. Results show that preS domain of hepatitis B virus coated on liposome/DNA can be used for highly efficient gene transfection into human hepatocytes. Moreover, the target characteristic of preS/liposome/DNA was analyzed in vivo. After preS/liposome/DNA VLP was injected into immunocompromised (Nude) mice via the tail vein, most of beta-galactosidase was expressed in the liver; however, no significant target expression was found with the injection of liposome/ DNA or naked DNA. Our results show that preS/liposome/DNA VLP can be used as a novel liver-specific gene delivery system.