Gene expression from recombinant viral vectors in the central nervous system after blood-brain barrier disruption

Adenoviral gene transfer to spinal-cord neurons: intrathecal vs. intraparenchymal administration

The spinal cord is the site of many chronic, debilitating, neurological disorders that may be amenable to gene therapy. The present study, using quantitative and anatomical methods, examines the ability of replication deficient adenovirus to transfer a transcription cassette composed of the cytomegalovirus promoter driving the expression of the LacZ reporter gene (AdCMVbetagal) to spinal-cord neurons. Rats were microinjected with AdCMVbetagal into the spinal-cord parenchyma or subarachnoid space and sacrificed between 1 and 60 days post-infusion. The spinal cord was assayed for beta-galactosidase (beta-gal) activity fluorometrically (MUG). Intraparenchymal injection resulted in significant beta-gal activity at day 1, which peaked at day 7, and decreased at day 14 (21-, 57- and 9.8-fold of control respectively). The spatial distribution of beta-gal activity on day 7 was confined to the 1-cm section containing the injection site but was detected 2 cm caudal to this section by day 14. Histochemical staining and immunocytochemistry revealed a prominent reaction product in neurons, particularly motor neurons, and glia within the ventral grey matter bilaterally. Intrathecal viral injections showed comparatively modest, yet significant increases in beta-gal activity throughout the spinal cord with the greatest activity (170% control) closest to the catheter tip. This study demonstrates that AdCMVbetagal injected into the ventral spinal cord results in extensive in vivo neuronal gene transfer with beta-gal activity reaching a peak by day 7 and remaining detectable at 60 days. Intrathecal viral injections result in greater spatial distribution but a comparatively lower level of expression.

Outwitting the blood-brain barrier for therapeutic purposes: osmotic opening and other means

OBJECTIVE

This article reviews historical aspects of the blood-brain barrier (BBB) and recent advances in mechanisms to deliver therapeutic agents across the BBB for the treatment of intracerebral tumors and other neurological diseases.

METHODS

The development of the osmotic BBB disruption procedure as a clinically useful technique is described. Osmotic BBB disruption is contrasted with alternative methods for opening or bypassing the BBB, including pharmacological modification of the BBB with bradykinin and direct intracerebral infusion.

RESULTS

Laboratory studies have played a fundamental role in advancing our understanding of the BBB and delivery of agents to brain. Preclinical animal studies will continue to serve an integral function in our efforts to improve the diagnosis and treatment of a number of neurological disorders. Techniques involving the modification of the BBB and/or blood-tumor barrier to increase delivery of therapeutic agents have been advanced to clinical trials in patients with brain tumors with very favorable results.

CONCLUSION

Improving delivery of agents to the brain will play a major role in the therapeutic outcome of brain neoplasms. As techniques for gene therapy are advanced, manipulation of the BBB also may be important in the treatment of central nervous system genetic disorders.

The mechanism of reversible osmotic opening of the blood-brain barrier: role of intracellular calcium ion in capillary endothelial cells

Despite clinical and experimental interest in the osmotic opening of the blood-brain barrier (BBB), the mechanism underlying the phenomenon remain undetermined. The aim of this study is to investigate the mechanism of intracellular Ca2+ change in brain microvascular endothelial cells subjected to hyperosmotic stress. Cultured rat brain capillary endothelial cells were obtained by two-step enzymatic purification. Intracellular Ca2+ was measured by a confocal laser scanning microscope. After exposing the endothelial cells to 1.4 M mannitol for 30 seconds, the change of intracellular Ca2+ concentration was monitored. Intracellular Ca2+ concentration increased rapidly and reached its peak value within 10 seconds after the application of mannitol. The Ca2+ concentration returned to the basal level within 200 seconds. A calcium channel blocker nifedipine (100 microM, 10 microM) did not block the increase. A specific blocker (KB-R7943) of Na+/Ca2+ exchange did not affect the rapid elevation of intracellular Ca2+. However, it blocked the return phase almost completely. The results indicated that the Na+/Ca2+ exchanger pumped out the increased intracellular Ca2+ during the return phase. Reversible osmotic disruption and reconstruction of the BBB is not due to simple mechanical shrinkage of the endothelial cells but is due to the intracellular Ca(2+)-activated complex mechanism. The manipulation of the reconstruction phase, which depends on Na+/Ca2+ exchanger, may have clinical implications.

Adenovirus-mediated gene transfer to cultured nodose sensory neurons

Recent advances have enabled transfer of genes to various types of cells and tissues. The goals of the present study were to transfer genes to nodose sensory neurons using replication-deficient adenovirus vectors and to define the conditions needed to optimize the gene transfer. Neurons were dissociated from rat nodose ganglia and maintained in culture. Cultures were exposed for 30 min to vectors containing the beta-galactosidase gene lacZ driven by either the Rous sarcoma virus (RSV) or the cytomegalovirus (CMV) promoter. Cultures were fixed and treated with X-gal to evaluate lacZ expression 1-7 days after exposure to virus. Increasing concentrations of virus led to dose-related increases in the number of neurons expressing lacZ. LacZ was expressed in 8 +/- 2, 39 +/- 6, and 82 +/- 3% of neurons 1 day after exposure to 10(7), 10(8), and 10(9) pfu/ml of AdRSVlacZ, respectively (P < 0.05). The same doses of AdCMVlacZ led to expression in 41 +/- 9, 60 +/- 10, and 86 +/- 4% of neurons. Expression driven by the CMV promoter was essentially maximal within 1 day and remained stable for at least 7 days. In contrast, expression driven by the RSV promoter was less on day 1 but increased over time (1-7 days). There was no lacZ expression in vehicle-treated cultures and exposure to the adenovirus vectors did not adversely influence cell viability. Exposure of the neuronal cultures to an adenovirus vector containing the gene for green fluorescent protein (AdRSVgfp, 10(9) pfu/ml) enabled visualization of successful gene transfer in living neurons. The results indicate that gene transfer to cultured nodose neurons can be accomplished using adenovirus vectors. The expression of the transferred gene persists for at least 7 days, occurs more rapidly when expression is driven by the CMV compared with the RSV promoter, and occurs without adversely affecting cell viability.

Adenovirus vector-mediated gene transfer into human epileptogenic brain slices: prospects for gene therapy in epilepsy

As a first step in the development of a gene therapy approach to epilepsy, we evaluated the ability of adenovirus vectors to direct the transfer into and expression of a marker gene in human brain slices obtained from patients undergoing surgery for medically intractable epilepsy. Following injection of adenovirus vectors containing the Escherichia coli lacZ gene into hippocampal and cortical brain slices, lacZ mRNA, beta-galactosidase protein, and enzymatic activity were detected, confirming successful gene transfer, transcription, and translation into a functional protein. Transfected cells were predominantly glial, with some neurons expressing beta-galactosidase as well. These results support the potential of adenovirus vectors to transfer genetic information into human epileptogenic brain, resulting in expression of the gene into a functional protein. These findings also have implications for the development of gene therapy approaches to certain seizure disorders. A number of potential therapeutic approaches are discussed, including the elevation of inhibitory neurotransmitter or neuropeptide levels, expression or modulation of postsynaptic receptors, and manipulation of signal transduction systems.

Application of recombinant adenovirus for in vivo gene delivery to spinal cord

One strategy for treating spinal cord injury is to supply damaged neurons with the appropriate neurotrophins either by direct delivery or by transfer of the corresponding genes using viral vectors. Here we report the feasibility of using recombinant adenovirus for in vivo gene transfer in spinal cord. After injection of a recombinant adenovirus carrying a beta-galactosidase (beta-gal) reporter gene into the mid-thoracic spinal cord of adult rats, transgene expression occurred not only in several types of cells around the injection site but also in neurons whose axons project to this region from rostral or caudal to the injection site. Among labeled neurons were those of the red nucleus, the vestibular nuclei, reticular formation, locus coeruleus, and Clarke's nucleus. A non-specific immune reaction, which could be blocked by immunosuppression with Cyclosporin A, reduced the number of transduced cells surviving at the injection site by 1 month. In neurons away from the injection site, where the immune response was minimal, transgene expression lasted for at least 2 months. These results support the idea that recombinant adenovirus can be used in the spinal cord for in vivo delivery of therapeutic genes important for supporting neuron survival and axon regeneration.

Direct gene transfer into human epileptogenic hippocampal tissue with an adeno-associated virus vector: implications for a gene therapy approach to epilepsy

PURPOSE

Virus vectors capable of transferring genetic information into human cells provide hope for improved therapy in several neurological diseases, including epilepsy. We evaluated the ability of an adeno-associated virus (AAV) vector to transfer and cause expression of a lacZ marker gene in brain slices obtained from patients undergoing temporal lobectomy for control of medically intractable seizures.

METHODS

Human brain slices were injected with an AAV vector (AAVlacZ) encoding Escherichia coli beta-galactosidase and incubated for as long as 24 h. The presence of lacZ mRNA. beta-galactosidase protein and enzymatic activity were assayed by reverse transcriptase polymerase chain reaction (rtPCR), immunocytochemistry, and the X-Gal technique, respectively.

RESULTS

AAVlacZ directed the expression in human epileptogenic brain of E. coli beta-galactosidase that had functional activity. Expression was observed in < or =5 h and was sustained for as long as the slices were viable. Morphological analysis indicated that neurons were preferentially transfected, and there was no evidence of cytotoxicity.

CONCLUSIONS

Our results confirm the feasibility of using AAV vectors to transfer genes into the human CNS and in particular, into neurons. Replacement of the lacZ gene with a functional gene modulating hippocampal neuronal physiology, might allow a localized genetic intervention for focal seizures based on the stereotaxic or endovascular delivery of such a vector system into the appropriate brain region.

A flow cytometric method for the rapid detection of beta-galactosidase transfected cells: an in vitro and in vivo study

A flow cytometric method has been developed for the rapid analysis of lacZ transduced cells. The method described is based on an indirect immunofluorescence staining procedure using a monoclonal antibody which binds specifically to beta-galactosidase from E. coli and to beta-galactosidase fusion proteins. This technique was used for the quantification in vitro as well as in vivo of beta-galactosidase expression in B16 melanoma cells. The described method is appropriate for a variety of cell types (species, lineage), is simple, quantitative, reliable, rapid and applicable to all constructs containing the lacZ selectable markers. It should prove to be very helpful (1) for the quantification of cells expressing the lacZ reporter gene and (2) for studying gene regulation, including transfection modality, promoter efficacy, enhancer activity, and other regulatory factors.

Cellular and molecular neurosurgery: pathways from concept to reality--part II: vector systems and delivery methodologies for gene therapy of the central nervous system

Different vector systems that have been used and/or specifically developed for central nervous system (CNS) gene transfer studies are briefly discussed along with their advantages and disadvantages with respect to potential clinical application. These include retroviruses, recombinant herpes simplex virus, adenoviruses, adenoassociated viruses, encapsulation of plasmid deoxyribonucleic acid into cationic liposomes, and neural and oliogodendroglial stem cells. Particular attention has been paid to relate the modality of a specific CNS gene therapy to the strategy for adequate delivery of genetic material to the brain for either global or localized CNS neurodegenerative chronic disorder, as well as for CNS tumors and stroke. Techniques to circumvent the "impermeable" blood-brain barrier and how to breach the more versatile blood-brain-tumor barrier to deliver the genetic material to the target CNS cells are reviewed and include the following: 1) local stereotactic CNS injection/infusion of viral vectors, administration of vector producer cells, or cell replacement; 2) local administration of genetic material into the cerebrospinal fluid ventriculocisternal system; 3) osmotic opening of the blood-brain barrier; 4) local intra-arterial infusion; and 5) administration of blood-brain-tumor barrier permeabilizers, such as a bradykinin B2 agonist RMP-7. It is concluded that gene therapy for several brain disorders holds great potential, as suggested mainly by in vitro experiments and, to some extent, by a limited number of animal experiments. However, several drawbacks currently hamper the application of gene therapy under the clinical setting. The problems associated with gene therapy that still present major obstacles are as follows: 1) inefficient transfection of host cells by viral vectors; 2) restricted delivery of genetic material across vascular barriers of the CNS and brain tumors; 3) nonselective expression of the transgene; and 4) in situ CNS regulation of the transgene expression in a therapeutically controlled manner, as imposed by the course and phenotype of the CNS disease.

Recombinant adenovirus: a gene transfer vector for study and treatment of CNS diseases

Gene transfer to the CNS with recombinant adenoviral vectors is a relatively recent event. In initial reports it was clearly demonstrated that adenoviral vectors can transfer genetic material to multiple cell types within the CNS. The relative ease in generating recombinant adenovirus (Ad) led to feasibility studies in the CNS with application to animal models of inherited disease, neurodegenerative diseases (e.g., Parkinson's and amyotrophic lateral sclerosis), and cerebrovascular disease. In combination with Ad gene transfer to peripheral tissues, these experiments have identified specific limitations and directed further research to improve vector design, formulation, and delivery.

Adenovirus-mediated gene transfer and expression of human beta-glucuronidase gene in the liver, spleen, and central nervous system in mucopolysaccharidosis type VII mice

Mucopolysaccharidosis type VII (Sly syndrome) is a lysosomal storage disease caused by inherited deficiency of the lysosomal enzyme beta-glucuronidase. A murine model of this disorder has been well characterized and used to study a number of forms of experimental therapies, including gene therapy. We produced recombinant adenovirus that expresses human beta-glucuronidase and administered this recombinant adenovirus to beta-glucuronidase-deficient mice intravenously. The beta-glucuronidase activities in liver and spleen were elevated to 40% and 20%, respectively, of the heterozygote enzymatic level at day 16. Expression persisted for at least 35 days. Pathological abnormalities of these tissues were also improved, and the elevated levels of urinary glycosaminoglycans were reduced in treated mice. However, the beta-glucuronidase activity in kidney and brain was not significantly increased. After administration of the recombinant adenovirus directly into the lateral ventricles of mutant mice, the beta-glucuronidase activity in crude brain homogenates increased to 30% of heterozygote activity. Histochemical demonstration of beta-glucuronidase activity in brain revealed that the enzymatic activity was mainly in ependymal cells and choroid. However, in some regions, the adenovirus-mediated gene expression was also evident in brain parenchyma associated with vessels and in the meninges. These results suggest that adenovirus-mediated gene delivery might improve the central nervous system pathology of mucopolysaccharidosis in addition to correcting visceral pathology.

Adenovirus-mediated gene transfer to the brain: methodological assessment

The purpose of this short review is to analyse major advantages and limitations of the adenovirus (Ad), specifically with relevance to its use as a vector for gene transfer to the brain. The characteristics of Ad transduction include: the relative absence of cell type specificity; the limited spatial spread of the virus; and the long-term expression of the transgene. In the central nervous system, in contrast to that which occurs in other organs, Ad transduction in the adult does not systematically provoke cell death. Nevertheless, a proportion of the transduced cells do die, and this represents a conspicuous problem. Mechanisms leading to cell death in the brain may include immune rejection and inflammation-related toxicity, although this would not explain all of the results, and direct toxicity related to either inappropriate preparation or the transduction itself. Taking into account uncertainties concerning the innocuousness of Ad transduction, it may seem unwise to envisage Ad gene therapy for diseases that are not life-threatening and/or benefit from adequate drug or surgical treatments (e.g. Parkinson's disease or epilepsy). Ad vectors may not be easily used either in diseases displaying major immune dysfunction (e.g. multiple sclerosis). In contrast, malignant brain tumors and numerous neurodegenerative diseases (such as Huntington's, Alzheimer's diseases or amyotrophic lateral sclerosis) are directly life-threatening and deprived of any adequate treatment. They may be appropriate targets for Ad-mediated gene therapy, once both the vector and the gene of interest have been defined and optimized.

Adenovirus-mediated p53 gene transfer suppresses growth of human glioblastoma cells in vitro and in vivo

Alterations in the p53 tumor-suppressor gene occur in 35-60% of human glioblastomas, and re-introduction of p53 can suppress neoplastic growth. To evaluate the potential for p53 gene therapy of glioblastoma, we have analyzed the response of human glioblastoma cell lines in vitro and in vivo to experimental therapy with replication-deficient recombinant adenoviruses encoding wild-type p53 (rAd-p53). Western blot analyses showed high-level expression of p53 protein after treatment with rAd-p53, and transgene expression was dependent on promoter strength. A p53-specific dose-dependent inhibition of in vitro cellular proliferation was observed in 5 of 6 cell lines, and growth inhibition corresponded to adenovirus-mediated gene transfer and expression. p53-specific cell death was quantitated by release of the lactate dehydrogenase enzyme. Fragmentation of DNA into nucleosomal oligomers and the occurrence of a hypodiploid cell population detected by flow cytometry provided evidence for apoptosis. Studies in nude mice demonstrated that ex vivo infection with rAd-p53 suppressed the tumorigenic potential of human glioblastoma cells. Furthermore, direct injection of rAd-p53 into established s.c. xenografts inhibited tumor growth. Our observations suggest that re-introduction of wild-type p53 may have potential clinical utility for gene therapy of glioblastoma.

Prospects for gene therapy in Parkinson's disease

Numerous advances in in vivo and ex vivo gene-therapy approaches to Parkinson's disease offer promise for direct clinical trials in patients in the next several years. These systems are predicated on introducing gene that encode enzymes responsible for dopamine biosynthesis or neurotrophic factors that may delay nigrostriatal degeneration or facilitate regeneration. We review the current status of experimental approaches to gene therapy for Parkinson's disease. Comparative advantages and disadvantages of each system are enumerated, and preclinical trials of some of the systems are evaluated. Although the specific in vivo or ex vivo methods used for gene transfer into the brain are likely to be supplanted by newer technology over the next decade, the principles and approaches developed in current studies likely will remain the same.

Gene therapy for cerebral vascular disease

BACKGROUND

Gene transfer to peripheral arteries has been accomplished with catheter-based approaches. Recently, gene transfer to the carotid artery and intracranial vessels has been achieved both in vitro and in vivo. Although gene therapy for cerebral vascular disease may not be accomplished for years, currently available methods probably will allow novel approaches to the study of vascular biology.

PURPOSE

This mini-review summarizes current methodology and describes some potential goals of gene therapy. Transfection of vessels might be used to prevent vasospasm after subarachnoid hemorrhage, stimulate growth of collateral blood vessels, stabilize atherosclerotic plaques, and prevent restenosis after angioplasty. Gene transfer approaches also may be useful in treating ischemia by inhibition or overexpression of cytokines and by effects on neurons. Some formidable barriers to gene therapy are the current lack of safe and effective vectors for gene transfer, the difficulty in delivering vectors to intracranial vessels, and the transience of transfection.

CONCLUSIONS

At present, gene transfer is a promising tool for the study of vascular biology. Obstacles to gene therapy for cerebral vascular disease seem sufficiently large that new approaches, rather than refinement of current approaches, may be needed. Progress toward gene therapy probably will be made in steps rather than leaps.

Targeted DNA recombination in vivo using an adenovirus carrying the cre recombinase gene

Conditional gene expression and gene deletion are important experimental approaches for examining the functions of particular gene products in development and disease. The cre-loxP system from bacteriophage P1 has been used in transgenic animals to induce site-specific DNA recombination leading to gene activation or deletion. To regulate the recombination in a spatiotemporally controlled manner, we constructed a recombinant adenoviral vector, Adv/cre, that contained the cre recombinase gene under regulation of the herpes simplex virus thymidine kinase promoter. The efficacy and target specificity of this vector in mediating loxP-dependent recombination were analyzed in mice that had been genetically engineered to contain loxP sites in their genome. After intravenous injection of the Adv/cre vector into adult animals, the liver and spleen showed the highest infectivity of the adenovirus as well as the highest levels of recombination, whereas other tissues such as kidney, lung, and heart had lower levels of infection and recombination. Only trace levels of recombination were detected in the brain. However, when the Adv/cre vector was injected directly into specific regions of the adult brain, including the cerebral cortex, hippocampus, and cerebellum, recombination was detectable at the injection site. Furthermore, when the Adv/cre vector was injected into the forebrains of neonatal mice, the rearranged toxP locus from recombination could be detected in the injected regions for at least 8 weeks. Taken together, these results demonstrate that the Adv/cre vector expressing a functional cre protein is capable of mediating loxP-dependent recombination in various tissues and the recombined gene locus may in some cases be maintained for an extended period. The use of the adenovirus vector expressing cre combined with localized delivery to specific tissues may provide an efficient means to achieve conditional gene expression or knockout with precise spatiotemporal control.

Transporting therapeutics across the blood-brain barrier

In 1996, we are half-way through the Decade of the Brain, yet we still have few effective treatments for major disorders of the central nervous system. These include affective disorders, epilepsy, neurodegenerative disorders, brain tumours, infections and HIV encephalopathy; sufferers far outnumber the morbidity of cancer or heart disease. Increased understanding of the pharmacology of the brain and its blood supply, and methods for rational drug design, are leading to potential new drug therapies based on highly specific actions on particular target sites, such as neurotransmitter receptors and uptake systems. These methods are capable of reducing the side effects that are common with more general treatments. However, all these treatments and potential treatments meet a formidable obstacle--the blood-brain barrier. In this article, we review the properties of this barrier that complicate drug delivery to the brain, and some of the most hopeful strategies for overcoming or bypassing the barrier in humans.

The principles of gene therapy for the nervous system

Research pertaining to gene transfer into cells of the nervous system is one of the fastest growing fields in neuroscience. An important application of gene transfer is gene therapy, which is based on introducing therapeutic genes into cells of the nervous system by ex vivo or in vivo techniques. With the eventual development of efficient and safe vectors, therapeutic genes, under the control of a suitable promoter, can be targeted to the appropriate neurons or glial cells. Gene therapy is not only applicable to the treatment of genetic diseases of the nervous system and the control of malignant neoplasia, but it also has therapeutic potential for acquired degenerative encephalopathies (Alzheimer's disease, Parkinson's disease), as well as for promoting neuronal survival and regeneration in various pathological states.

Delivery of herpesvirus and adenovirus to nude rat intracerebral tumors after osmotic blood-brain barrier disruption

The delivery of viral vectors to the brain for treatment of intracerebral tumors is most commonly accomplished by stereotaxic inoculation directly into the tumor. However, the small volume of distribution by inoculation may limit the efficacy of viral therapy of large or disseminated tumors. We have investigated mechanisms to increase vector delivery to intracerebral xenografts of human LX-1 small-cell lung carcinoma tumors in the nude rat. The distribution of Escherichia coli lacZ transgene expression from primary viral infection was assessed after delivery of recombinant virus by intratumor inoculation or intracarotid infusion with or without osmotic disruption of the blood-brain barrier (BBB). These studies used replication-compromised herpes simplex virus type 1 (HSV; vector RH105) and replication-defective adenovirus (AdRSVlacZ), which represent two of the most commonly proposed viral vectors for tumor therapy. Transvascular delivery of both viruses to intracerebral tumor was demonstrated when administered intraarterially (i.a.) after osmotic BBB disruption (n = 9 for adenovirus; n = 7 for HSV), while no virus infection was apparent after i.a. administration without BBB modification (n = 8 for adenovirus; n = 4 for HSV). The thymidine kinase-negative HSV vector infected clumps of tumor cells as a result of its ability to replicate selectively in dividing cells. Osmotic BBB disruption in combination with i.a. administration of viral vectors may offer a method of global delivery to treat disseminated brain tumors.