Viral vectors for neurotrophic factor delivery: A gene therapy approach for neurodegenerative diseases of the CNS

The clinical manifestation of most diseases of the central nervous system results from neuronal dysfunction or loss. Diseases such as stroke, epilepsy and neurodegeneration (e.g. Alzheimer's disease and Parkinson's disease) share common cellular and molecular mechanisms (e.g. oxidative stress, endoplasmic reticulum stress, mitochondrial dysfunction) that contribute to the loss of neuronal function. Neurotrophic factors (NTFs) are secreted proteins that regulate multiple aspects of neuronal development including neuronal maintenance, survival, axonal growth and synaptic plasticity. These properties of NTFs make them likely candidates for preventing neurodegeneration and promoting neuroregeneration. One approach to delivering NTFs to diseased cells is through viral vector-mediated gene delivery. Viral vectors are now routinely used as tools for studying gene function as well as developing gene-based therapies for a variety of diseases. Currently, many clinical trials using viral vectors in the nervous system are underway or completed, and seven of these trials involve NTFs for neurodegeneration. In this review, we discuss viral vector-mediated gene transfer of NTFs to treat neurodegenerative diseases of the central nervous system.     

Viral vectors for use in the development of biodefense vaccines

The heightened concerns about bioterrorism and the use of biowarfare agents have prompted substantial increased efforts towards the development of vaccines against a wide range of organisms, toxins, and viruses. An increasing variety of platforms and strategies have been analyzed for their potential as vaccines against these agents. DNA vectors, live-attenuated viruses and bacteria, recombinant proteins combined with adjuvant, and viral- or bacterial-vectored vaccines have been developed as countermeasures against many potential agents of bioterrorism or biowarfare. The use of viruses, for example adenovirus, vaccinia virus, and Venezuelan equine encephalitis virus, as vaccine vectors has enabled researchers to develop effective means for countering the threat of bioterrorism and biowarfare. An overview of the different viral vectors and the threats they counter will be discussed.     

Viral vectors for gene delivery in tissue engineering

The goal of tissue engineering is the production of functional, biocompatible tissues by seeding cells within biological or synthetic scaffolds. One tissue engineering approach involves the genetic modification of cells that are seeded onto (or into) scaffolds prior to implantation. The genetic modification is achieved through gene delivery, with can utilize viral transduction or non-viral transfection systems. Although novel non-viral systems have continued to emerge as innovative vehicles for controlled gene delivery, viruses remain the most efficient means by which exogenous genes can be introduced into and expressed by mammalian cells. Retrovirus, adenovirus, adeno-associated virus and herpes virus are widely studied viral gene transfer systems and have attracted the most attention in the field of transduction. This review thoroughly discusses the genomic structures of each virus type, along with the advantages and disadvantages of their use in tissue engineering applications.     

Viral vectors for gene therapy: past, present and future

Gene delivery has been attempted in both experimental and clinical settings. These studies have shown that therapeutic gene transfer is possible, but it has not yet arrived as a practicable therapeutic intervention. This is due in large part to the inability of the vectors used to convey genetic material to a desired location in sufficient quantity and for long enough time to be effective. Current research on viral vectors for gene therapy has focused on reengineering viruses currently being tested as delivery agents, modifying the host to facilitate viral gene transfer and developing new viruses for use in gene transfer. It is too early to know which of these approaches will be effective; however, these ongoing studies are likely to make available in the future an array of gene delivery vehicles with different strengths and weaknesses. It is reasonable to expect that several of the vectors now being studied will prove useful for some therapeutic applications.     

Viral vectors and delivery strategies for CNS gene therapy

This review aims to provide a broad overview of the targets, challenges and potential for gene therapy in the CNS, citing specific examples. There are a broad range of therapeutic targets, with very different requirements for a suitable viral vector. By utilizing different vector tropisms, novel routes of administration and engineered promoter control, transgenes can be targeted to specific therapeutic applications. Viral vectors have proven efficacious in preclinical models for several disease applications, spurring several clinical trials. While the field has pushed the limits of existing adeno-associated virus-based vectors, a next generation of vectors based on rational engineering of viral capsids should expand the application of gene therapy to be more effective in specific therapeutic applications.     

Bupropion and naltrexone: a review of their use individually and in combination for the treatment of obesity

Background: Bupropion and naltrexone are centrally active drugs that have shown potential efficacy – alone and in combination – for the treatment of obesity. Objective: To explore the efficacy and safety of naltrexone and bupropion alone and in a novel combination drug that utilizes sustained-release (SR) formulations of both drugs and to evaluate their efficacy in promoting weight loss. The mechanisms of action of these centrally acting drugs are discussed. Preclinical and clinical studies of bupropion and naltrexone alone and in combination are reviewed. Results/conclusions: Both bupropion and naltrexone have been shown individually to induce weight loss. Bupropion has greater efficacy as monotherapy. Naltrexone SR potentiates the effects of bupropion SR; thus, this synergistic combination has the potential for additional weight loss compared to monotherapy. Current Phase III trials will yield further safety and efficacy information regarding these drugs in combination.     

Viral diseases of the skin: diagnosis and antiviral treatment

Viral diseases in children can present with characteristic mucocutaneous manifestations. This article focuses, from a practical clinical point of view, on the laboratory and clinical diagnoses, and treatment of pediatric dermatological diseases that have specific antiviral therapies: herpes virus infections (including varicella), papillomavirus infections and molluscum contagiosum. Special issues, such as viral infections in pregnancy, therapy of viral infections in immunosuppressed children, as well as special problems associated with the epidemiology of genital herpes and papillomavirus infections in adolescents are discussed. The antivirals discussed in detail include: aciclovir, valaciclovir, famciclovir, penciclovir, cidofovir, foscarnet and the immune response modulator, imiquimod. Since these antiviral drugs generally have not been evaluated in children, caution should be exercised with their usage.     

Emerging role of polyphenolic compounds in the treatment of neurodegenerative diseases: a review of their intracellular targets

Aging is the major risk factor for neurodegenerative diseases such as Alzheimer's and Parkinson's diseases. A large body of evidence indicates that oxidative stress is involved in the pathophysiology of these diseases. Oxidative stress can induce neuronal damages, modulate intracellular signaling, ultimately leading to neuronal death by apoptosis or necrosis. Thus antioxidants have been studied for their effectiveness in reducing these deleterious effects and neuronal death in many in vitro and in vivo studies. Increasing number of studies demonstrated the efficacy of polyphenolic antioxidants from fruits and vegetables to reduce or to block neuronal death occurring in the pathophysiology of these disorders. These studies revealed that other mechanisms than the antioxidant activities could be involved in the neuroprotective effect of these phenolic compounds. We will review some of these mechanisms and particular emphasis will be given to polyphenolic compounds from green tea, the Ginkgo biloba extract EGb 761, blueberries extracts, wine components and curcumin.     

SV40 pseudovirions as highly efficient vectors for gene transfer and their potential application in cancer therapy

Among viral and non-viral gene delivery systems, SV40-based vectors show great promise in the cancer gene therapy field. SV40 vectors very efficiently deliver genes such as anti-viral agents, DNA vaccine, genes for chemoprotection (such as ABC transporters genes), suicide genes and antiangiogenic genes. The recombinant SV40 vectors can infect a wide variety of cells-dividing cells as well as non-cycling ones. Most of the SV40-based vectors can incorporate larger transgenes than the capacity of the SV40 wild-type, which is 5.2 kb; Moreover, in vitro packaged vectors demonstrate efficient delivery of plasmids with a molecular weight of up to 17.7 kb. SV40-based vectors carry some SV40 viral sequences, but the SV40 in vitro-packaged vectors are free of any SV40 wild-type viral DNA sequences. These vectors are prepared with nuclear extracts of SF9 insect cells containing the main viral capsid protein of the SV40 wild-type virus, VP1. This review summarizes different strategies in which SV40 vectors are used to deliver genes in vitro, to living mice, and to tumors growing in nude mice.     

Novel lentiviral vectors for human gene therapy

This review summarises an emerging viral vector system for use in human gene therapy - lentiviral vectors. Lentiviral vectors have several advantages over existing viral vectors. They can stably express transgenes in non-dividing cells in vivo without provoking a significant immune response. They can be produced to a high titre and can be pseudotyped with heterologous envelope proteins to confer broad tropism. Although not without safety concerns, the properties of lentiviral vectors makes them an attractive choice for human gene therapy.     

Novel lentiviral vectors for human gene therapy

This review summarises an emerging viral vector system for use in human gene therapy - lentiviral vectors. Lentiviral vectors have several advantages over existing viral vectors. They can stably express transgenes in non-dividing cells in vivo without provoking a significant immune response. They can be produced to a high titre and can be pseudotyped with heterologous envelope proteins to confer broad tropism. Although not without safety concerns, the properties of lentiviral vectors makes them an attractive choice for human gene therapy.     

Antioxidant enzyme gene transfer for ischemic diseases

The balance of redox is pivotal for normal function and integrity of tissues. Ischemic insults occur as results of a variety of conditions, leading to an accumulation of reactive oxygen species (ROS) and an imbalanced redox status in the tissues. The oxidant stress may activate signaling mechanisms provoking more toxic events, and eventually cause tissue damage. Therefore, treatments with antioxidants, free radical scavengers and their mimetics, as well as gene transfer approaches to overexpress antioxidant genes represent potential therapeutic options to correct the redox imbalance. Among them, antioxidant gene transfer may enhance the production of antioxidant scavengers, and has been employed to experimentally prevent or treat ischemic injury in cardiovascular, pulmonary, hepatic, intestinal, central nervous or other systems in animal models. With improvements in vector systems and delivery approaches, innovative antioxidant gene therapy has conferred better outcomes for myocardial infarction, reduced restenosis after coronary angioplasty, improved the quality and function of liver grafts, as well as outcome of intestinal and cerebral ischemic attacks. However, it is crucial to be mindful that like other therapeutic armentarium, the efficacy of antioxidant gene transfer requires extensive preclinical investigation before it can be used in patients, and that it may have unanticipated short- or long-term adverse effects. Thus, it is critical to balance between the therapeutic benefits and potential risks, to develop disease-specific antioxidant gene transfer strategies, to deliver the therapy with an optimal time window and in a safe manner. This review attempts to provide the rationale, the most effective approaches and the potential hurdles of available antioxidant gene transfer approaches for ischemic injury in various organs, as well as the possible directions of future preclinical and clinical investigations of this highly promising therapeutic modality.     

Enhanced gene transfer activity of peptide-targeted gene-delivery vectors

We have evaluated the capacity of the cell-binding heptapeptide SIGYPLP to enhance transgene expression using non-viral and viral gene delivery vectors. Targeted polyplex based vectors showed good levels of DNA uptake in freshly isolated human umbilical vein endothelial cells (HUVECs) compared to untargeted controls, whilst displaying only modest increases in reporter gene activity. The targeted polyplexes showed reduced levels of DNA uptake in cells of a none endothelial origin although they mediated higher levels of transgene expression. The enhanced efficiency of transgene expression may relate to the more rapid rate of cell division. However, since in vivo application of polyplexes is compromised by instability to serum proteins, serum-resistant polyplexes (surface modified with multivalent reactive hydrophilic polymers based on poly[N-(2-hydroxypropyl)methacrylamide] (pHPMA)) were also evaluated for their ability to mediate transgene expression. Surface modification of polyplexes with pHPMA ablates non-specific cell entry, reducing levels of transgene expression, whilst the incorporation of the SIGYPLP peptide into the hydrophilic polymer resulted in restored transgene expression in all formulations tested. The technology of surface modification using pHPMA can also be applied in the context of viruses, masking receptor-binding epitopes and enabling the linkage of novel cell targeting ligands, enabling construction of a virus with receptor-specific infectivity. Retargeting of adenovirus based vectors using the same polymer-peptide construct enhanced levels of transgene expression in HUVECs to greater than 15 times that observed using parental (unmodified) virus, whilst restoring levels of transgene expression in non-endothelial cell lines tested. The use of constructs based on conjugates between hydrophilic polymers and small receptor-binding oligopeptides as agents for retargeting viral or non-viral vectors to cellular receptors represents a simple alternative to the use of antibodies as targeting ligands for cell specific gene delivery.     

Receptor-mediated gene transfer by phage-display vectors: applications in functional genomics and gene therapy

Recent studies have demonstrated targeted gene-delivery to mammalian cells using modified phage-display vectors. Specificity is determined by the choice of the genetically displayed targeting ligand. Without targeting, phage particles have virtually no tropism for mammalian cells. Thus, novel ligands can be selected from phage libraries by their ability to deliver a reporter gene to targeted cells. Together with advances in cDNA display technologies, these findings offer new opportunities for the use of phage-display technology in functional genomics. In addition, targeted phage particles have potential as alternative gene therapy vectors that can be further improved using directed evolution.     

Enhanced gene transfer activity of peptide-targeted gene-delivery vectors

We have evaluated the capacity of the cell-binding heptapeptide SIGYPLP to enhance transgene expression using non-viral and viral gene delivery vectors. Targeted polyplex based vectors showed good levels of DNA uptake in freshly isolated human umbilical vein endothelial cells (HUVECs) compared to untargeted controls, whilst displaying only modest increases in reporter gene activity. The targeted polyplexes showed reduced levels of DNA uptake in cells of a none endothelial origin although they mediated higher levels of transgene expression. The enhanced efficiency of transgene expression may relate to the more rapid rate of cell division. However, since in vivo application of polyplexes is compromised by instability to serum proteins, serum-resistant polyplexes (surface modified with multivalent reactive hydrophilic polymers based on poly[N-(2-hydroxypropyl)methacrylamide] (pHPMA)) were also evaluated for their ability to mediate transgene expression. Surface modification of polyplexes with pHPMA ablates non-specific cell entry, reducing levels of transgene expression, whilst the incorporation of the SIGYPLP peptide into the hydrophilic polymer resulted in restored transgene expression in all formulations tested. The technology of surface modification using pHPMA can also be applied in the context of viruses, masking receptor-binding epitopes and enabling the linkage of novel cell targeting ligands, enabling construction of a virus with receptor-specific infectivity. Retargeting of adenovirus based vectors using the same polymer-peptide construct enhanced levels of transgene expression in HUVECs to greater than 15 times that observed using parental (unmodified) virus, whilst restoring levels of transgene expression in non-endothelial cell lines tested. The use of constructs based on conjugates between hydrophilic polymers and small receptor-binding oligopeptides as agents for retargeting viral or non-viral vectors to cellular receptors represents a simple alternative to the use of antibodies as targeting ligands for cell specific gene delivery.     

Viral and non-viral methods for gene transfer into skeletal muscle

Skeletal muscle is an important target for genetic manipulation and its stable post-mitotic nature allows the use of both integrating and non-integrating viral and non-viral vectors. Adeno-associated viral vectors and naked plasmid DNA are currently the vectors of choice for gene transfer into muscle. The last couple of years have seen major breakthroughs in the field of vector delivery systems, particularly those using the vascular route, such that gene therapy of muscular dystrophies and the use of muscle as a platform for the production of secreted proteins has become a clinical possibility.     

Intra-articular drug delivery systems for the treatment of rheumatic diseases: A review of the factors influencing their performance

Osteoarthritis and rheumatoid arthritis are rheumatic diseases for which a curative treatment does not currently exist. Their management is directed towards pain relief achieved with different classes of drugs among which non-steroidal and steroidal anti-inflammatory substances are the most frequently used agents. Nevertheless, the oral or systemic administration of such drugs is hindered by numerous side effects, which could be overcome by their intra-articular (i-a.) administration as dosage forms capable of gradually releasing the active substance. The present review article summarises the research done in the field of drug delivery systems for i-a. injection vs. current management of osteoarthritis or rheumatoid arthritis. Aspects such as the influence of size, shape, polymer matrix or targeted drug on the i-a. retention time, phagocytosis and biological activity will be discussed. Finally, we will comment on the need for adapted delivery systems for the novel and very potent anti-inflammatory drugs, such as inhibitors of the p38 mitogen-activated protein kinase or the IL-1β conversion enzyme, which to date cannot be properly used due to the severe side effects associated with their systemic administration.