Gene therapy of Parkinson disease model rat by direct injection of plasmid DNA-lipofectin complex

Recent Advances in Messenger Ribonucleic Acid (mRNA) Vaccines and Their Delivery Systems: A Review

Messenger ribonucleic acid (mRNA) was found as the intermediary that transfers genetic information from DNA to ribosomes for protein synthesis in 1961. The emergency use authorization of the two covid-19 mRNA vaccines, BNT162b2 and mRNA-1273, is a significant achievement in the history of vaccine development. Because they are generated in a cell-free environment using the in vitro transcription (IVT) process, mRNA vaccines are risk-free. Moreover, chemical modifications to the mRNA molecule, such as cap structures and changed nucleosides, have proved critical in overcoming immunogenicity concerns, achieving sustained stability, and achieving effective, accurate protein production in vivo. Several vaccine delivery strategies (including protamine, lipid nanoparticles (LNPs), polymers, nanoemulsions, and cell-based administration) were also optimized to load and transport RNA into the cytosol. LNPs, which are composed of a cationic or a pH-dependent ionizable lipid layer, a polyethylene glycol (PEG) component, phospholipids, and cholesterol, are the most advanced systems for delivering mRNA vaccines. Moreover, modifications of the four components that make up the LNPs showed to increase vaccine effectiveness and reduce side effects. Furthermore, the introduction of biodegradable lipids improved LNP biocompatibility. Furthermore, mRNA-based therapies are expected to be effective treatments for a variety of refractory conditions, including infectious diseases, metabolic genetic diseases, cancer, cardiovascular and cerebrovascular diseases. Therefore, the present review aims to provide the scientific community with up-to-date information on mRNA vaccines and their delivery systems.

A brief review of mRNA therapeutics and delivery for bone tissue engineering

The therapeutics for bone tissue regeneration requires constant advancements owing to the steady increase in the number of patients suffering from bone-related disorders, and also to find efficient and cost-effective treatment modalities. One of the major advancements in the field of therapeutics is the development of mRNAs. mRNAs, which have been extensively tested for the vaccines, could be very well utilized as a potential inducer for bone regeneration. The ability of mRNAs to enter the cells and instruct the cellular machinery to produce the required native proteins such as BMP or VEGF is a great way to avoid the issues faced with growth factor deliveries such as the production cost, loss of biological function etc. However, there have been a few hurdles for using mRNAs as an effective therapeutic agent, such as proper dosing, tolerating the degradation by RNases, improving the half-life, controlling the spatio-temporal release and reducing the off-target effects. This brief review discusses the various developments in the field of mRNA therapeutics especially for bone tissue engineering, how nano-formulations are being developed to effectively deliver the mRNAs into the cells by evading the immune responses, how researchers have developed certain strategies to increase the half-life, to successfully deliver the mRNAs to specific bone defect area and bring about effective bone regeneration.

A single intrathecal injection of DNA and an asymmetric cationic lipid as lipoplexes ameliorates experimental autoimmune encephalomyelitis

Intrathecal delivery of gene therapeutics is a route of administration that overcomes several of the limitations that plague current immunosuppressive treatments for autoimmune diseases of the central nervous system (CNS). Here we report intrathecal delivery of small amounts (3 μg) of plasmid DNA that codes for an immunomodulatory fusion protein, OX40-TRAIL, composed of OX40, a tumor necrosis factor receptor, and tumor necrosis factor related apoptosis inducing ligand (TRAIL). This DNA was delivered in a formulated nucleic acid-lipid complex (lipoplexes) with an asymmetric two-chain cationic lipid myristoyl (14:0) and lauroyl (12:1) rosenthal inhibitor-substituted compound (MLRI) formed from the tetraalkylammonium glycerol-based compound N-(1-(2,3-dioleoyloxy)-propyl-N-1-(2-hydroxy)ethyl)-N,N-dimethyl ammonium iodide. Delivery and expression in the CNS of OX40-TRAIL in the mouse prior to onset of experimental autoimmune encephalomyelitis (EAE), an animal model for multiple sclerosis, decreased the severity of clinical disease. We believe this preclinical demonstration of rapid, widespread, and biologically therapeutic nonviral gene delivery to the CNS is important in further development of clinical lipid-based therapeutics for CNS disorders.

Relating chemical and biological diversity space: a tunable system for efficient gene transfection

Polyethyleneimine (PEI), a well-established nonviral transfection reagent, was combinatorially modified with varying proportions of methyl, benzyl, and n-dodecyl groups to create a library of 435 derivatized polymers. Screening of this library for transfection, DNA binding, and toxicity allows systematic correlation of the biological properties of our polymers to their derivatizations. Combinations of derivatizations bring about a 100-fold variation in transfection efficiency between library members. The best PEI derivatives exhibit increases in transfection efficiency of more than 80-fold over unmodified PEI (up to 28+/-7 % of cells transfected) and rival commercial reagents such as Lipofectamine 2000 (21+/-10 %) and JetPEI (32+/-5.0 %). In addition, we can identify compounds that are specifically tuned for efficient transfection in CHO-K1 over Ishikawa cells and vice versa, demonstrating that the approach can lead to cell-type selectivity of at least one order of magnitude. This work demonstrates that multivalent derivatization of a polymeric framework can create functional diversity substantially greater than the structural diversity of the derivatization building blocks and suggests an approach to a better understanding of the molecular underpinnings of transfection as well as their exploitation.

Compartmentalization of neuronal and peripheral serotonin synthesis in Drosophila melanogaster

In Drosophila, one enzyme (Drosophila tryptophan-phenylalanine hydroxylase, DTPHu) hydroxylates both tryptophan to yield 5-hydroxytryptophan, the first step in serotonin synthesis, and phenylalanine, to generate tyrosine. Analysis of the sequenced Drosophila genome identified an additional enzyme with extensive homology to mammalian tryptophan hydroxylase (TPH), which we have termed DTRHn. We have shown that DTRHn can hydroxylate tryptophan in vitro but displays differential activity relative to DTPHu when using tryptophan as a substrate. Recent studies in mice identified the presence of two TPH genes, Tph1 and Tph2, from distinct genetic loci. Tph1 represents the non-neuronal TPH gene, and Tph2 is expressed exclusively in the brain. In this article, we show that DTRHn is neuronal in expression and function and thus represents the Drosophila homologue of Tph2. Using a DTRHn-null mutation, we show that diminished neuronal serotonin affects locomotor, olfactory and feeding behaviors, as well as heart rate. We also show that DTPHu functions in vivo as a phenylalanine hydroxylase in addition to its role as the peripheral TPH in Drosophila, and is critical for non-neuronal developmental events.

Substrate regulation of serotonin and dopamine synthesis in Drosophila

In Drosophila melanogaster, serotonin (5-hydroxytryptamine, 5-HT) is required for both very early non-neuronal developmental events, and in the CNS as a neurotransmitter to modulate behavior. 5-HT is synthesized, at least in part, by the actions of Drosophila tryptophan-phenylalanine hydroxylase (DTPH), a dual function enzyme that hydroxylates both phenylalanine and tryptophan. DTPH is expressed in numerous tissues as well as dopaminergic and serotonergic neurons, but it does not necessarily function as both enzymes in these tissues. Deficiencies in DTPH could affect the production of dopamine and serotonin, and thus dopaminergic and serotonergic signaling pathways. In this paper, we show that DTPH exhibits differential hydroxylase activity based solely on substrate. When DTPH uses phenylalanine as a substrate, regulatory control (end product inhibition, decreased PAH activity following phosphorylation, catecholamine inhibition) is observed that is not seen when the enzyme uses tryptophan as a substrate. These studies suggest that regulation of DTPH enzymatic activity occurs, at least in part, through the actions of its substrate.

Gene therapy: a primer for neurosurgeons

Gene therapy involves the transfer of genes into cells with therapeutic intent. Although several methods can accomplish this, vectors based on viruses still provide the most efficient approach. For neurosurgical purposes, preclinical and clinical applications in the areas of glioma therapy, spinal neurosurgery, and neuroprotection for treatment of Parkinson's disease and cerebral ischemia are reviewed. In general, therapies applied in the neurosurgical realm have proven relatively safe, despite occasional, well-publicized cases of morbidity and death in non-neurosurgical trials. However, continued clinical and preclinical research in this area is critical, to fully elucidate potential toxicities and to generate truly effective treatments that can be applied in neurological diseases.

Invasive drug delivery

The central nervous system is a very attractive target for new therapeutic strategies since many genes involved in neurological diseases are known and often only local low level gene expression is required. However, as the blood brain barrier on one hand prevents some therapeutic agents given systematically from exerting their activity in the CNS, it also provides an immune privileged environment. Neurosurgical technology meanwhile allows the access of nearly every single centre of the CNS and provides the surgical tool for direct gene delivery via minimal invasive surgical approaches to the brain. Successful therapy of the central nervous system requires new tools for delivery of therapeutics in vitro and in vivo (Fig. 1). The application of therapeutic proteins via pumps into the CSF was shown to be only of limited value since the protein mostly is not sufficiently transported within the tissue and the half life of proteins limits the therapeutic success. Direct gene delivery into the host cell has been a main strategy for years, and in the beginning the direct DNA delivery or encapsulation in liposomes or other artificial encapsulation have been applied with different success. For several years the most promising tools have been vectors based on viruses. Viruses are able to use the host cell machinery for protein synthesis, and some of them are able to stably insert into the host cell genome and provide long term transgene expression as long as the cell is alive. The increasing knowledge of viruses and their live cycle promoted the development of viral vectors that function like a shuttle to the cell, with a single round of infection either integrating or transiently expressing the transgene. Viral vectors have proven to be one of the most efficient and stable transgene shuttle into the cell and have gained increasing importance. The limitations of some viral vectors like the adenoviral vector and adeno-associated viral vector have been improved by new constructs like HIV-1 based lentiviral vectors. The immune response caused by expression of viral proteins, or the inability of some viral vectors like the retroviral vector to infect only dividing cells have been overcome by these new constructs. Lentiviral vectors allow an efficient and stable transgene expression over years in vivo without effecting transgene expression or immune response. In this Chapter we will describe synthetic vectors, give an overview of the most common viral vectors and focus our attention on lentiviral vectors, since we consider them to be the most efficient tool for gene delivery in the CNS.

Gene therapy for Parkinson's disease: current status and future potential

Parkinson's disease appears to be a good candidate for gene therapy. The primary biochemical defect associated with the disease has been clearly determined as an absence of dopamine in the caudate-putamen, and the anatomical region where the neuropathologic hallmark of the disease, death of the nigral dopamine-producing neurons, occurs, remains circumscribed. Based on the biochemical and anatomical information gathered on Parkinson's disease, different gene therapy strategies have been devised to treat it. The first, and most explored strategy so far, consists in engineering cells to produce levodopa or dopamine so they will replace dopaminergic neurotransmission. Several types of cells have been employed in these experiments, and behavioral recovery has been reported in animal models of the disease. However, this approach cannot prevent neuronal death, nor reconstruct brain circuits. Another strategy is to protect cells by transferring genes that encode neurotrophic factors. Effort is now being concentrated into this research area, and promising results have recently been reported. Finally, an additional strategy aims at generating cells with a dopaminergic phenotype so they will be capable of replacing the missing dopaminergic neurons in biochemical, anatomical and functional terms. This has the potential to become an important constituent for an effective cure. Gene therapy holds significant promise for the treatment of neurodegenerative disorders, and Parkinson's disease treatment will benefit greatly from the knowledge and information arising from gene therapy research.

Therapeutic effects of astrocytes expressing both tyrosine hydroxylase and brain-derived neurotrophic factor on a rat model of Parkinson's disease

Tyrosine hydroxylase (TH) and brain-derived neurotrophic factor (BDNF), expressed in normal astrocytes, were used in combination for the treatment of Parkinson's disease (PD) symptoms in a rat model. Normal neonatal rat astrocytes were co-transfected with a vector expressing BDNF (AAVBDNF) and a retroviral vector expressing TH (termed TH-BDNF-DA(+) cells), and then implanted into the striatum of PD rats induced by 6-hydroxydopamine. TH-BDNF-DA(+) cells compensated for a severe insufficiency of endogenous dopaminergic neurons in the PD rats, resulting in a significant improvement of PD symptoms. The decrease in the rotational rate of PD rats implanted with TH-BDNF-DA(+) cells was more marked than that in PD rats implanted with normal astrocytes expressing either TH or BDNF alone (termed TH(+) and BDNF(+) cells, P<0.01 and 0.001, respectively), and suggested a synergistic effect between TH and BDNF. In contrast, the rotational rate was not altered from the baseline in PD rats without treatment or implanted with parental rat astrocytes alone (P>0.05). BDNF protected the dopaminergic neurons from apoptosis induced by 6-hydroxydopamine, and significantly increased the long-term survival of TH-positive cells in the striatum. Our data indicate that the combined use of TH and BDNF has a synergistic therapeutic effect, and is more efficient for the treatment of PD than a single gene therapy using either TH or BDNF alone.

In vivo gene transfer into the periventricular region by electroporation

Gene transfer by electroporation was attempted in the normal rat brain. The reporter gene pEGFP-C1 (25 micrograms/5 microliters) was injected into the striatum of young adult rats and various square electrical impulses were applied using a pair of electrodes implanted in the striatum. The brains were removed and sliced after 5 days. Histological examination revealed that the high energy impulses caused extensive tissue damage whereas lower energy impulses (200-400 mJ) resulted in the transfection of more than 300 cells per brain, which were widely distributed in the subependymal region of the lateral ventricle and extended long processes into the striatum.

Multi-lipofection efficiently transfected genes into astrocytes in primary culture

This study demonstrated that liposome-mediated transfection - lipofection - is suitable for delivering genes into astrocytes. By repeatedly lipofecting the same astrocyte cultures, a process we call multi-lipofection, the transfection efficiency of the beta-galactosidase (beta-gal) gene was improved from 2.6+/-0.6 to 17. 4+/-1.1%. This is the highest efficiency ever reported in gene-transfer with Lipofectin(R) in a primary culture of mouse cerebral cortical astrocytes. Furthermore, multi-lipofection did not cause observable disturbance to astrocytes as indicated by insignificant changes in the glial fibrillary acidic protein content in the cultures. In order to demonstrate that the transfected gene achieved a physiologically relevant expression level, a plasmid containing the pEF-hsp70 protein gene was lipofected into astrocytes. This produced colonies of astrocytes showing an increased resistance to heat-induced cell death. A similar experiment was performed with the glial-derived neurotrophic factor (GDNF) gene. Control astrocytes had no detectable GDNF. In the transfected astrocytes, the GDNF protein could be identified intracellularly by immunocytochemistry. Western blot analysis revealed, as compared to astrocytes with one lipofection, a 2.9-fold increase of GDNF with four lipofections. GDNF remained detectable in astrocytes 2 weeks after four lipofections. Thus, multi-lipofection provides a mild and efficient means of delivering foreign genes into astrocytes in a primary culture, making astrocytes good candidate vehicle cells for gene/cell therapy in the CNS.

Cytokine gene transfer in cancer therapy

New strategies based on gene transfer technology are employed in cancer therapy. Cytokines are polypeptides involved in immunity and inflammation, and essentially control the magnitude of the immune response. Genetically modified tumor cells releasing various cytokines have been shown to enhance tumor immunogenicity and to induce the regression of preexisting tumors. In some instances, immunological memory has been generated to resist the subsequent challenge with unmodified, parental tumor cells. Cytokine gene transfer into antitumor effector cells, as well as antigen presenting cells, is also being investigated to augment antitumor immune responses.

Nonviral glial cell-derived neurotrophic factor gene transfer enhances survival of cultured dopaminergic neurons and improves their function after transplantation in a rat model of Parkinson's disease

Transplantation of dopaminergic fetal mesencephalic tissue into the striatum is currently being developed for treatment of patients with advanced Parkinson's disease. Ethical concerns regarding the use of human fetal tissue, and the limited availability as well as poor survival and differentiation of dopaminergic neurons after transplantation have reduced the extent and outcome of this approach so far. With the purpose of finding means to increase the yield of dopaminergic neurons in transplants, and to reduce the amount of fetal tissue needed for each transplanted patient, we transfected rat fetal ventral mesencephalic (VM) tissue grown as organotypic free-floating roller tube (FFRT) cultures with a vector encoding human glial cell-derived neurotrophic factor (hGDNF). For transfer of an episomal expression vector (pRep7-GDNF8) a nonviral, nonliposomal cationic transfection technique was applied and optimized. Recombinant hGDNF expression resulted in a higher number of TH-positive neurons in the cultures as measured 6 days after transfection. Ventral mesencephalic cultures expressing hGDNF were then grafted into the striatum of unilaterally 6-hydroxydopamine (6-OHDA)-lesioned rats. Grafting of genetically modified VM cultures resulted in earlier functional recovery compared with grafting nontransfected cultures. We conclude that organotypic free-floating roller tube cultures can be successfully transfected to produce hGDNF with effects on TH-expressing neurons in vitro and functional effects after grafting in a rat Parkinson's disease model.

Introduction to gene therapy in neurological surgery

Gene therapy is an exciting new discipline in which neurosurgery and neurosurgeons can have a direct impact on both patient care and emerging scientific developments. Unlike other organs, the brain is unique in that it has a blood–brain barrier, often preventing efficient systemic gene delivery to the area of interest. Therefore, not only is gene delivery required, but it will often need to be accomplished in a local and specific manner. Although brain neoplasms have been the most commonly studied application of genetic therapeutics in neurological surgery, there are many other potential applications of this technology to neurosurgical disorders, including spinal instability, neurodegenerative disease, neurogenetic diseases, central nervous system (CNS) injury, aneurysms, trauma, stroke, and epilepsy. As the field of gene therapy for the CNS develops from the preclinical setting to clinical trials to mainstream therapy, the need for safe and specific gene delivery will be increasingly apparent. Neurosurgeons are in an enviable position as there is nobody more qualified to address the issue of how a gene can be delivered to the central nervous system. Not only do we have the training to operate on the nervous system and its coverings, but we have the ability to recognize and take care of complications that may arise from these procedures. However, the neurosurgeon's role in gene therapy for the brain and spine should not be confined to gene delivery only. Instead, we also need to understand and have a role in deciding what genes could have therapeutic utility in our patients. Herein lies our challenge in gene therapy: how can we as neurosurgeons interface with our basic science colleagues to address rapidly all of the problems that are blocking the advancement of nucleic acid therapeutics into the clinical setting.

Long-term phenotypic correction of rodent hemiparkinsonism by gene therapy using genetically modified myoblasts

Rat myoblasts were genetically modified to express tyrosine hydroxylase (TH) and produce dopamine in culture. Implanting TH gene-transfected myoblasts into the denervated striatum of 6-OHDA-lesioned rats significantly decreased rotational asymmetry by 50 to approximately 60%. Improvement persisted for up to 13 months. Genetically modified cells could survive and express transgene in the striatum as demonstrated by RT-PCR and immunohistochemical stain-ing. The dopamine content in the striatum tissue of the gene therapy group recovered to 49% of the normal level and was 25-fold higher than that of a control group receiving parental cells. Neither tumor formation nor immunorejection was observed in this study. These results show that myoblasts may be useful as gene carriers for ex vivo gene therapy in the CNS. Gene Therapy (2000) 7, 445-449.

Co-grafts of muscle cells and mesencephalic tissue into hemiparkinsonian rats: behavioral and histochemical effects

Extracts from skeletal muscle cell cultures have been shown to increase levels of the enzyme tyrosine hydroxylase (TH) and promote survival of different types of developing neurons in vitro. To determine the effect of muscle cell co-grafts on the survival of dopamine neurons in a rat model of Parkinson's disease, we transplanted an embryonic day (ED)-15 rat mesencephalic cell suspension alone or with neonatal muscle cells into 6-hydroxydopamine (6-OHDA) denervated rat striatum. In parallel experiments conducted in vitro, we cultured ED-15 rat mesencephalon or rat striatum in conditioned medium from neonatal rat muscle cultures (MC-CM). Our results showed that: (A) in vitro, MC-CM increased the number of TH-immunoreactive (TH-IR) neurons in embryonic mesencephalic cultures but did not induce expression of TH in embryonic striatal cultures; (B) in vivo, animals with co-grafts of muscle cells and ED-15 mesencephalon had more TH-IR in the grafted striatum compared to animals that received mesencephalic cells grafts alone, although the graft-induced reversal of circling behavior in response to methamphetamine was the same in both transplanted groups; and (C) grafts of muscle cells alone did not induce TH-IR in the denervated striatum and did not reduce methamphetamine-induced circling. These findings suggest that in vivo, neonatal muscle cells secrete factors that promote survival and/or outgrowth of fetal midbrain dopamine cells and improve the levels of TH-IR in grafted striatum.

Gene therapy in the CNS

Gene therapy for neurological disorder is currently an experimental concept. The goals for clinical utilization are the relief of symptoms, slowing of disease progression, and correction of genetic abnormalities. Experimental studies are realizing these goals in the development of gene therapies in animal models. Discoveries of the molecular basis of neurological disease and advances in gene transfer systems have allowed focal and global delivery of therapeutic genes for a wide variety of CNS disorders. Limitations are still apparent, such as stability and regulation of transgene expression, and safety of both vector and expressed transgene. In addition, the brain adds several challenges not seen in peripheral gene therapy paradigms, such as post-mitotic cells, heterogeneity of cell types and circuits, and limited access. Moreover, it is likely that several modes of gene delivery will be necessary for successful gene therapies of the CNS. Collaborative efforts between clinicians and basic researchers will likely yield effective gene therapy in the CNS.

Development of engineered cells for implantation in gene therapy

Human gene therapy is based on the technology of genetic engineering of cells, either through ex vivo or in vivo methods of gene transfer. Many autologous cell types have been successfully modified to deliver recombinant gene products. An alternate form of gene therapy based on genetic modification of non-autologous cells is described. Protection within immuno-isolating devices would allow implantation of well-established recombinant cell lines in different allogeneic hosts, potentially offering a more cost-effective approach to gene therapy. Implantation with microencapsulated fibroblasts and myoblasts has resulted in successful recombinant product delivery in vivo. Correction of disease phenotypes in animal models of human genetic diseases has also been achieved. Cell types such as myoblasts which can differentiate terminally within the implantation device are particularly promising for the future development of this method of gene therapy.

Cytokine Gene Therapy in Experimental Allergic Encephalomyelitis by Injection of Plasmid DNA-Cationic Liposome Complex into the Central Nervous System

Experimental allergic encephalomyelitis (EAE) is an autoimmune disease of the central nervous system with many similarities to multiple sclerosis. The main effector cells involved are CD4+ T cells, recognizing encephalitogenic epitopes within the central nervous system, and macrophages, both of which secrete proinflammatory cytokines, such as IFN-γ and TNF. Studies have shown that immunomodulation of this inflammatory response by anti-inflammatory cytokines (IL-4, IL-10, IFN-β, and TGF-β) can reduce clinical severity in EAE. The importance of TNF in EAE has been demonstrated by using soluble TNF-receptor molecules to inhibit EAE. However, the limitation of this type of therapy is the necessity for frequent administration of cytokine proteins due to their short biologic half-life. This study demonstrates that EAE can be inhibited by a single injection of therapeutic cytokine (IL-4, IFN-β, and TGF-β) DNA-cationic liposome complex directly into the central nervous system. DNA coding for a novel, dimeric form of human p75 TNF receptor also ameliorated clinical EAE. Local administration of DNA-cationic liposome complex has identified gene targets that may be more efficiently exploited using vectors producing more stable expression for effective treatment of neuroimmunologic disease.

Significant behavioral recovery in Parkinson's disease model by direct intracerebral gene transfer using continuous injection of a plasmid DNA-liposome complex

As an alternative to virus-mediated gene transfer, we previously demonstrated a simple, safe, and efficient transfer of foreign gene into the central nervous system using continuous injection of a plasmid DNA-cationic liposome complex. To explore whether this approach can be applied to the treatment of certain neurological disorders, we used an experimental model of Parkinson's disease (PD) in the present study. Following continuous injection for 7 days, tyrosine hydroxylase (TH) and aromatic L-amino acid decarboxylase (AADC) genes carried by a bovine papilloma virus-based plasmid vector were efficiently introduced into glial cells in the striatum of 6-hydroxydopamine-lesioned rats. Significant recovery in apomorphine-induced rotational behavior of PD models was obtained by transfection of TH gene and this effect continued for up to 5 weeks after injection. Moreover, cotransfection of TH with AADC genes was readily accomplished by this procedure and resulted in a greater and longer-lasting improvement of apomorphine-induced rotational behavior than was achieved by transfection of TH gene alone. We suggest that this approach is a controllable and manageable alternative to other methods of gene therapy for the treatment of PD.

Transgene expression of plasmid DNAs directed by viral or neural promoters in the rat brain

The use of circular plasmid DNA may be an alternative method for the transfer of genes into the brain and is presumably easier to use than other vectors, such as viruses or genetically engineered cells. The effectiveness and time course of the expression of a reporter gene (LacZ), directed by appropriate promoters, was studied after stereotaxic injection of naked plasmid DNAs into the rat thalamus, cortex or cerebellum. The efficiencies of three different promoters, the human cytomegalovirus (HCMV) promoter and the glial fibrillary acidic protein (GFAP) and neuron-specific enolase (NSE) promoters (specific for astrocytes and neurons, respectively) to drive reporter gene expression were compared. Efficient expression of beta-gal, detected by X-gal histochemistry or immunochemistry, required the use of 50 microg of DNA and was detectable as early as 48 h after injection. Expression increased until day 8, remained stable until day 15, then decreased over 2 months, probably as a result of non-specific degradation of the plasmids within the transfected cells rather than from specific down-regulation of promoters, as the same time course was seen with all three promoters tested. Depending on the promoter used (GFAP or NSE), LacZ was preferentially expressed within astrocytes or neurons, respectively. The GFAP promoter was found to be as efficient as the HCMV promoter, possibly due to the reactive gliosis induced by plasmid injection which is known to up-regulate GFAP expression.

In vitro and in vivo gene delivery mediated by a synthetic polycationic amino polymer

A synthetic polyamino polymer with a glucose backbone was used for gene transfer in vitro and in vivo. Gene transfer in vitro to various human carcinoma cell lines was achieved with an efficiency superior to a commercially available cationic liposome preparation. The polymer was resistant to inhibition by serum, which allowed for efficient gene transfer in vivo. Direct Intracranial tumor injection using this reagent resulted in reporter gene expression levels comparable to those achieved by a recombinant adenoviral vector. Thus, this compound represents a new class of agent that may have broad utility for gene transfer and gene therapy applications.

Gene therapy for central nervous system injury: the use of cationic liposomes: an invited review

This paper briefly reviews general principles of gene therapy with emphasis on the therapeutic potential of cationic liposome-mediated neurotrophin gene transfer to treat central nervous system (CNS) injury. Current developments in studies of gene therapy for CNS injury are both impressive and promising. Ex vivo gene transfer into the CNS is relatively mature in animal studies following more than a decade of experimental studies. In vivo gene transfer into the CNS has gained more attention recently. Although progress has been made using viral vectors, rapid advances in transfection technologies employing cationic liposomes, together with the relatively low toxicity of these nonviral vector systems, suggest that liposomes may have significant potential for clinical applications. Although many investigators have recognized that gene therapy may be useful for treatment of certain genetic defect diseases or cancer, gene therapy for CNS injury is relatively novel. In contrast to genetic defect disorders, temporary induction of transgenes may have therapeutic applications for CNS injuries such as stroke and trauma. Employing gene transfer techniques to achieve therapeutically useful levels of expression of neurotrophins in the CNS could provide a new strategy for treatment of the traumatically injured CNS.

Cellular and molecular neurosurgery: pathways from concept to reality--part I: target disorders and concept approaches to gene therapy of the central nervous system

Recent advances in cellular and molecular biology and better understanding of genetic and biochemical bases of different central nervous system (CNS) disorders have made gene therapy of the CNS a realistic goal. Concept approaches for gene therapy of CNS disorders are reviewed and include the following: 1) gene replacement with a single normal allele to correct the inherited global neurodegenerative disorders, such as enzyme deficiencies; 2) brain repair to restore the function of a particular subset of cells that were lost because of a neurodegenerative process; 3) gene therapy of brain tumors; and 4) gene therapy of stroke. Techniques of viral vector-mediated CNS transfer of a therapeutic gene, transplantation of genetically modified cells, fetal embryonic implantation and/or implantation of genetically engineered neural progenitor cells, and production of a specific enzyme, neurotransmitter, and/or growth factor are discussed with respect to the therapeutic potential for global and localized CNS neurodegenerative disorders and stroke. Transfection of the CNS tumor cells with the drug susceptibility ("suicide") gene and/or "toxic" gene and antisense strategies and a concept of adoptive immunotherapy of brain tumors are also discussed. Other approaches, such as transfer of drug-resistant genes and monoclonal antibody gene transfer, are briefly discussed. In addition to summarizing current principles of gene therapy for several groups of CNS disorders, the issues that remain to be resolved in clinical reality, such as delivery of the genetic material and regulation of the cellular expression of the transgene, and the negatives associated with the concepts of gene therapy, such as transient gene expression, toxicity of viral proteins, drawbacks of antisense therapy, and the problem of immune response to the transfected protein, have been also identified.

Gene therapy for Parkinson's disease: an approach to the prevention or palliation of levodopa-associated motor complications

Gene therapy holds considerable potential for the treatment of central nervous system disease. The introduction of functional genes into the brain of patients with Parkinson's disease may, for example, prove useful as a means to replace a defective gene, introduce a potentially neuroprotective or neurorestorative protein, or permit the physiological delivery of a deficient neurotransmitter. Recent observations suggest that the oral administration of currently available dopaminomimetics to relatively advanced parkinsonian patients leads to nonphysiologic intermittent stimulation of striatal neurons that express dopamine receptors. Resultant activation of signal transduction pathways from these dopaminergic receptors on medium-sized GABAergic neurons apparently induces long-term potentiation of adjacent glutamatergic receptors of the N-methyl-D-aspartate subtype. The effects of dopaminergic drugs thus become modified in ways that favor the clinical appearance of response fluctuations and peak-dose dyskinesias. In parkinsonian models was well as in patients with Parkinson's disease, continuous dopaminergic replacement tends to prevent or alleviate these adverse effects. By continuously maintaining appropriate cerebral dopamine concentrations, molecular techniques which stimulate an increase in the intrastriatal activity of tyrosine hydroxylase, the rate-limiting enzyme for dopamine synthesis, might be expected to palliate parkinsonian symptoms with less risk of the disabling consequences of current therapy. Clinical study of these approaches could also serve as initial, relatively simple, proof-of-principle evaluations of the safety and efficacy of genetic approaches to the treatment of basic disease processes in Parkinson's disease and related neurodegenerative disorders.