A differential efficiency of adenovirus-mediated in vivo gene transfer into skeletal muscle cells of different maturity

Magnetically-assisted viral transduction (magnetofection) medical applications: An update

Gene therapy involves replacing a faulty gene or adding a new gene inside the body's cells to cure disease or improve the body's ability to fight disease. Its popularity is evident from emerging concepts such as CRISPR-based genome editing and epigenetic studies and has been moved to a clinical setting. The strategy for therapeutic gene design includes; suppressing the expression of pathogenic genes, enhancing necessary protein production, and stimulating the immune system, which can be incorporated into both viral and non-viral gene vectors. Although non-viral gene delivery provides a safer platform, it suffers from an inefficient rate of gene transfection, which means a few genes could be successfully transfected and expressed within the cells. Incorporating nucleic acids into the viruses and using these viral vectors to infect cells increases gene transfection efficiency. Consequently, more cells will respond, more genes will be expressed, and sustained and successful gene therapy can be achieved. Combining nanoparticles (NPs) and nucleic acids protects genetic materials from enzymatic degradation. Furthermore, the vectors can be transferred faster, facilitating cell attachment and cellular uptake. Magnetically assisted viral transduction (magnetofection) enhances gene therapy efficiency by mixing magnetic nanoparticles (MNPs) with gene vectors and exerting a magnetic field to guide a significant number of vectors directly onto the cells. This research critically reviews the MNPs and the physiochemical properties needed to assemble an appropriate magnetic viral vector, discussing cellular hurdles and attitudes toward overcoming these barriers to reach clinical gene therapy perspectives. We focus on the studies conducted on the various applications of magnetic viral vectors in cancer therapies, regenerative medicine, tissue engineering, cell sorting, and virus isolation.

Protease-deleted adenovirus as an alternative for replication-competent adenovirus vector

For cancer therapy and vaccination an amplified expression of the therapeutic gene is desired. Previously, we have developed a single-cycle adenovirus vector (SC-AdV) by deleting the adenovirus protease (PS) gene. In order to keep the E1 region intact within the PS-deleted adenoviruses, we examined the insertion of two transgenes under the control of a constitutive or inducible promoters. These were inserted between E4 and the right inverted terminal repeat in a wide variety of backbones with various combinations of PS, E3 and E4 deletion. Our data showed that PS-deleted adenoviruses, expressed transgenes as strongly as replication-competent AdVs in HEK293A and a variant of HeLa cells. In a head-to-head comparison in four human cell lines, we demonstrated that SC-AdV, was comparable for transgene expression efficacy with its replication-competent counterpart. However, the SC-AdV expresses its transgene 10 to 16,000 times higher than its replication-defective counterpart.

Intramuscular Delivery of Gene Therapy for Targeting the Nervous System

Virus-mediated gene therapy has the potential to deliver exogenous genetic material into specific cell types to promote survival and counteract disease. This is particularly enticing for neuronal conditions, as the nervous system is renowned for its intransigence to therapeutic targeting. Administration of gene therapy viruses into skeletal muscle, where distal terminals of motor and sensory neurons reside, has been shown to result in extensive transduction of cells within the spinal cord, brainstem, and sensory ganglia. This route is minimally invasive and therefore clinically relevant for gene therapy targeting to peripheral nerve soma. For successful transgene expression, viruses administered into muscle must undergo a series of processes, including host cell interaction and internalization, intracellular sorting, long-range retrograde axonal transport, endosomal liberation, and nuclear import. In this review article, we outline key characteristics of major gene therapy viruses—adenovirus, adeno-associated virus (AAV), and lentivirus—and summarize the mechanisms regulating important steps in the virus journey from binding at peripheral nerve terminals to nuclear delivery. Additionally, we describe how neuropathology can negatively influence these pathways, and conclude by discussing opportunities to optimize the intramuscular administration route to maximize gene delivery and thus therapeutic potential.

The Subcellular Localization and Oligomerization Preferences of NME1/NME2 upon Radiation-Induced DNA Damage

Nucleoside diphosphate kinases (NDPK/NME/Nm23) are enzymes composed of subunits NME1/NDPK A and NME2/NDPK B, responsible for the maintenance of the cellular (d)NTP pool and involved in other cellular processes, such as metastasis suppression and DNA damage repair. Although eukaryotic NDPKs are active only as hexamers, it is unclear whether other NME functions require the hexameric form, and how the isoenzyme composition varies in different cellular compartments. To examine the effect of DNA damage on intracellular localization of NME1 and NME2 and the composition of NME oligomers in the nucleus and the cytoplasm, we used live-cell imaging and the FRET/FLIM technique. We showed that exogenous NME1 and NME2 proteins co-localize in the cytoplasm of non-irradiated cells, and move simultaneously to the nucleus after gamma irradiation. The FRET/FLIM experiments imply that, after DNA damage, there is a slight shift in the homomer/heteromer balance between the nucleus and the cytoplasm. Collectively, our results indicate that, after irradiation, NME1 and NME2 engage in mutual functions in the nucleus, possibly performing specific functions in their homomeric states. Finally, we demonstrated that fluorophores fused to the N-termini of NME polypeptides produce the largest FRET effect and thus recommend this orientation for use in similar studies.

Identification of Herpes Zoster-Associated Temporal Arteritis Among Cases of Giant Cell Arteritis

PURPOSE

To examine whether herpes zoster antigen (also called varicellazoster virus antigen) was detectable in temporal artery biopsies taken from individuals with giant cell arteritis (GCA).

DESIGN

Retrospective comparative case series.

METHODS

Sections of formalin-fixed paraffin-embedded temporal arteries were examined first by hematoxylin-eosin (H&E) staining to establish the diagnosis of GCA. Adjacent sections of the same biopsy were then examined by immunohistochemistry, using 2 different monoclonal antibodies against a major antigen of varicella-zoster virus called gE. Pathologic specimens were obtained from patients cared for at the University of Iowa and Washington University in St. Louis ophthalmology clinics.

RESULTS

The study included biopsies from 25 patients with symptoms of GCA as well as positive H&E pathology and 25 patients with symptoms compatible with GCA but negative H&E pathology. Among the GCA-positive group, 3 patients had positive staining for herpes zoster antigen. Among the GCA-negative group, herpes zoster antigen was not detected in any biopsy. In both groups of patients, false-positive staining for herpes zoster antigen was detected in the presence of calcifications in the arteries. False-positive staining was also detected on some extra-arterial skeletal muscle and erythrocytes.

CONCLUSION

Herpes zoster antigen was detected in 3 of 25 temporal arteries from patients with biopsy-proven GCA. One of the 3 positive cases was noteworthy because the patient had had herpes zoster ophthalmicus diagnosed 3 weeks before the onset of GCA symptoms. False-positive staining for herpes zoster antigen was detected on several temporal artery biopsies.

Retargeted and detargeted adenovirus for gene delivery to the muscle

We previously selected muscle binding peptides 12.51 and 12.52 from "context-specific" phage display libraries for introduction into adenovirus (Ad) vectors. In this work, these peptides were inserted into the hypervariable region (HVR) 5 loop of the Ad5 hexon protein to display 720 peptides per virions. HVR-12.51 and 12.52 increased transduction of C2C12 cells up to 20-fold when compared to unmodified Ad5. 12.51 increased in vivo muscle transduction 2 to 7-fold over unmodified Ad after intramuscular injection in mice and hamsters. 12.52 did not increase muscle transduction. Notably, insertion of 12.51 into the hexon reduced liver transduction 80-fold when compared to unmodified Ad5 after intravenous injection. Increased muscle transduction in mice translated into increased immune responses after gene-based vaccination. These data suggest there are merits to retargeting and detargeting benefits to modifying the hexons of Ads with peptide ligands.

Development of Approaches to Improve the Healing following Muscle Contusion

Muscle injuries are a challenging problem in traumatology, and the most frequent occurrence in sports medicine. Muscle contusions are among the most common muscle injuries. Although this injury is capable of healing, an incomplete functional recovery often occurs, depending on the severity of the blunt trauma. We have developed an animal model of muscle contusion in mice (high energy blunt trauma) and characterized the muscle's ability to heal following this injury using histology and immunohistochemistry to determine the level of muscle regeneration and the development of scar tissue. We have observed a massive muscle regeneration occurring in the first 2 wk postinjury that is subsequently followed by the development of muscle fibrosis. Based on these observations, we propose that the enhancement of muscle growth and regeneration, as well as the prevention of fibrotic development, could be used as approach(es) to improve the healing of muscle injuries. In fact, we have identified three growth factors (bFGF, IGF-1, and NGF) capable of enhancing myoblast proliferation and differentiation in vitro and improving the healing of the injured muscle in vivo. Furthermore, the ability of adenovirus to mediate direct and ex vivo gene transfer of β-galactosidase into the injured site opens possibilities of delivering an efficient and persistent expression of these growth factors in the injured muscle. These studies should help in the development of strategies to promote efficient muscle healing with complete functional recovery following muscle contusion. © 1998 Elsevier Science Inc.

Autotransplantation in mdx Mice of mdx Myoblasts Genetically Corrected by an HSV-1 Amplicon Vector

Duchenne muscular dystrophy (DMD) is an X-linked recessive disorder, characterized by a lack of dystrophin. To eliminate the need for immunosuppressive drugs, transplantation of genetically modified autologous myoblasts has been proposed as a possible therapy for this myopathy. An HSV-1 amplicon vector (HSVDGN), containing a 17.3-kb full-length MCK-driven mouse dystrophin cDNA, an eGFP gene, and a neomycin resistance gene driven by CMV or SV40 promoters, respectively, was constructed and used to transduce mdx primary myoblasts. The presence of the eGFP and neomycin resistance genes facilitated the evaluation of the initial transduction efficiency and the permanent transduction frequency. At low multiplicities of infection (MOI 1–5), the majority of myoblasts (60–90%) expressed GFP. The GFP-positive mdx myoblasts were sorted by FACS and selected with neomycin (300 μg/ml) for 2 weeks. Up to 2% of initially infected mdx myoblasts stably expressed the three transgenes without further selection at that time. These altered cells were grafted into the tibialis anterior muscles of 18 mdx mice. Some of the mice were immunosuppressed with FK506 due to the anticipation that eGFP and the product of neomycin resistance gene might be immunogenic. One month after transplantation, numerous muscle fibers expressing mouse dystrophin were detected by immunohistochemistry, in both immunosuppressed (10–50%) and nonimmunosuppressed (5–25%) mdx mice. Our results demonstrated the capability of permanently expressing a full-length dystrophin in dystrophic myoblasts with HSV-1 amplicon vector and raised the possibility of an eventual treatment of DMD based on the transplantation of genetically modified autologous myoblasts.

Targeting Motor End Plates for Delivery of Adenoviruses: An Approach to Maximize Uptake and Transduction of Spinal Cord Motor Neurons

Gene therapy can take advantage of the skeletal muscles/motor neurons anatomical relationship to restrict gene expression to the spinal cord ventral horn. Furthermore, recombinant adenoviruses are attractive viral-vectors as they permit spatial and temporal modulation of transgene expression. In the literature, however, several inconsistencies exist with regard to the intramuscular delivery parameters of adenoviruses. The present study is an evaluation of the optimal injection sites on skeletal muscle, time course of expression and mice’s age for maximum transgene expression in motor neurons. Targeting motor end plates yielded a 2.5-fold increase in the number of transduced motor neurons compared to injections performed away from this region. Peak adenoviral transgene expression in motor neurons was detected after seven days. Further, greater numbers of transduced motor neurons were found in juvenile (3–7 week old) mice as compared with adults (8+ weeks old). Adenoviral injections produced robust transgene expression in motor neurons and skeletal myofibres. In addition, dendrites of transduced motor neurons were shown to extend well into the white matter where the descending motor pathways are located. These results also provide evidence that intramuscular delivery of adenovirus can be a suitable gene therapy approach to treat spinal cord injury.

Magnetofection Enhances Adenoviral Vector-based Gene Delivery in Skeletal Muscle Cells

The goal of magnetic field-assisted gene transfer is to enhance internalization of exogenous nucleic acids by association with magnetic nanoparticles (MNPs). This technique named magnetofection is particularly useful in difficult-to-transfect cells. It is well known that human, mouse, and rat skeletal muscle cells suffer a maturation-dependent loss of susceptibility to Recombinant Adenoviral vector (RAd) uptake. In postnatal, fully differentiated myofibers, the expression of the primary Coxsackie and Adenoviral membrane receptor (CAR) is severely downregulated representing a main hurdle for the use of these vectors in gene transfer/therapy. Here we demonstrate that assembling of Recombinant Adenoviral vectors with suitable iron oxide MNPs into magneto-adenovectors (RAd-MNP) and further exposure to a gradient magnetic field enables to efficiently overcome transduction resistance in skeletal muscle cells. Expression of Green Fluorescent Protein and Insulin-like Growth Factor 1 was significantly enhanced after magnetofection with RAd-MNPs complexes in C2C12 myotubes in vitro and mouse skeletal muscle in vivo when compared to transduction with naked virus. These results provide evidence that magnetofection, mainly due to its membrane-receptor independent mechanism, constitutes a simple and effective alternative to current methods for gene transfer into traditionally hard-to-transfect biological models.

Repair or replace? Exploiting novel gene and cell therapy strategies for muscular dystrophies

Muscular dystrophies are genetic disorders characterized by skeletal muscle wasting and weakness. Although there is no effective therapy, a number of experimental strategies have been developed over recent years and some of them are undergoing clinical investigation. In this review, we highlight recent developments and key challenges for strategies based upon gene replacement and gene/expression repair, including exon-skipping, vector-mediated gene therapy and cell therapy. Therapeutic strategies for different forms of muscular dystrophy are discussed, with an emphasis on Duchenne muscular dystrophy, given the severity and the relatively advanced status of clinical studies for this disease.

Inhibition of the protein tyrosine phosphatase SHP-1 increases glucose uptake in skeletal muscle cells by augmenting insulin receptor signaling and GLUT4 expression

The protein tyrosine phosphatase (PTPase) Src-homology 2-domain-containing phosphatase (SHP)-1 was recently reported to be a novel regulator of insulin's metabolic action. In order to examine the role of this PTPase in skeletal muscle, we used adenovirus (AdV)-mediated gene transfer to express an interfering mutant of SHP-1 [dominant negative (DN)SHP-1; mutation C453S] in L6 myocytes. Expression of DNSHP-1 increased insulin-induced Akt serine-threonine kinase phosphorylation and augmented glucose uptake and glycogen synthesis. Pharmacological inhibition of glucose transporter type 4 (GLUT4) activity using indinavir and GLUT4 translocation assays revealed an important role for this transporter in the increased insulin-induced glucose uptake in DNSHP-1-expressing myocytes. Both GLUT4 mRNA and protein expression were also found to be increased by DNSHP-1 expression. Furthermore, AdV-mediated delivery of DNSHP-1 in skeletal muscle of transgenic mice overexpressing Coxsackie and AdV receptor also enhanced GLUT4 protein expression. Together, these findings confirm that SHP-1 regulates muscle insulin action in a cell-autonomous manner and further suggest that the PTPase negatively modulates insulin action through down-regulation of both insulin signaling to Akt and GLUT4 translocation, as well as GLUT4 expression.

BIOLOGICAL INTERVENTION BASED ON CELL AND GENE THERAPY TO IMPROVE MUSCLE HEALING AFTER LACERATION

Muscle laceration is a challenging problem in traumatology and is common in sports injuries, with functional recovery remaining slow and incomplete. Even though muscles retain their ability to regenerate after injury, muscles' healing process after such injuries has been found to be very slow and often leads to incomplete muscle recovery. Growth factors may have a role in enhancing recovery. Our previous study showed that IGF-1, β-FGF and NGF can improve myoblast proliferation and differentiation in vitro. We then investigated whether the delivery of IGF-1 would improve muscle healing after injuries. We observed that muscle regeneration was enhanced in lacerated muscles treated with IGF-1 protein, which consequently led to an improvement in muscle healing. However, the rapid clearance and short biological half-lives of these proteins may have limited the success of this approach. We then investigated the efficiency of gene therapy based on adenovirus to deliver a stable expression of the growth factor IGF-1. Although a slight improvement in the healing process occurred in the muscle injected with adenovirus (AIGF), the combination of myoblast transplantation and gene therapy with the ex vivo approach further improved the healing process. The injection of normal myoblasts into the injured muscle led to the best improvement of muscle healing at two weeks post-injection. Implantation of normal minced muscle into mdx mice was also capable of improving muscle healing at 2–4 weeks post-implantation. These studies will further our understanding of muscle healing post-injury and help in the development of strategies to promote efficient muscle healing and complete functional recovery after common muscle injuries.

Modulation of coxsackie and adenovirus receptor expression for gene transfer to normal and dystrophic skeletal muscle

BACKGROUND

Efficient adenovirus (AdV)-mediated gene transfer is possible only in immature muscle or regenerating muscle, suggesting that a developmentally regulated event plays a major role in limiting AdV uptake in mature skeletal muscle. Previously, we showed that the expression of the primary coxsackie and adenovirus receptor (CAR) is severely down-regulated during muscle maturation and that, in muscle-specific CAR transgenic mice, there is significant enhancement of AdV-mediated gene transfer to mature skeletal muscle.

METHODS

To evaluate whether increasing CAR expression can also augment gene transfer to dystrophic muscle that has many regenerating fibers, we crossed CAR transgenics with dystrophin-deficient mice (mdx/CAR). We also tested a two-step protocol in which CAR levels were increased in the target muscle, prior to administration of AdV, through the use of recombinant adeno-associated virus (AAV2) expressing CAR. Lastly, we assessed the effect of histone deacetylase inhibitors on CAR and AdV transduction efficiency in myoblasts and mdx muscle.

RESULTS

Although somewhat higher rates of transduction can be achieved in adult mdx mice than in normal mice as a result of ongoing muscle regeneration in these animals, CAR expression in the mdx background (mdx/CAR transgenics) still markedly improved the susceptibility of mature muscle to AdV-mediated gene transfer of dystrophin. Prior administration of AAV2-CAR to normal muscle led to significantly increased transduction by subsequent injection of AdV. The histone deacetylase inhibitor valproate increased CAR transcript and protein levels in myoblasts and mdx muscle, and also increased AdV-mediated gene transfer.

CONCLUSIONS

We have developed a method of increasing CAR levels in both normal and regenerating muscle.

Genomic integration of adenoviral gene transfer vectors following transduction of fertilized mouse oocytes

Adenoviral vectors (AdV) are popular tools to deliver foreign genes into a wide range of cells. They have also been used in clinical gene therapy trials. Studies on AdV-mediated gene transfer to mammalian oocytes and transmission through the germ line have been reported controversially. In the present study we investigated whether AdV sequences integrate into the mouse genome by microinjecting AdV into the perivitelline space of fertilized oocytes. We applied a newly developed PCR technique (HiLo-PCR) for identification of chromosomal junctions next to the integrated AdV. We demonstrate that mouse oocytes can be transduced by different recombinant adenoviral vectors (first generation and gutless). In one transgenic mouse line using the first generation adenoviral vector, the genome has integrated into a highly repetitive cluster located on the Y chromosome. While the transgene (GFP) was expressed in early embryos, no expression was detected in adult transgenic mice. The use of gutless AdV resulted in expression of the transgene, albeit the vector was not transmitted to progeny. These results indicate that under optimized conditions fertilized mouse oocytes are transduced by AdV and give rise to transgenic founder animals. Therefore, adequate precautions should be taken in gene therapy protocols of reproductive patients since transduction of oocytes or early embryos and subsequent chromosomal integration cannot be ruled out entirely.

Reduced expression of integrin alphavbeta8 is associated with brain arteriovenous malformation pathogenesis

Brain arteriovenous malformations (BAVMs) are a rare but potentially devastating hemorrhagic disease. Transforming growth factor-beta signaling is required for proper vessel development, and defective transforming growth factor-beta superfamily signaling has been implicated in BAVM pathogenesis. We hypothesized that expression of the transforming growth factor-beta activating integrin, alphavbeta8, is reduced in BAVMs and that decreased beta8 expression leads to defective neoangiogenesis. We determined that beta8 protein expression in perivascular astrocytes was reduced in human BAVM lesional tissue compared with controls and that the angiogenic response to focal vascular endothelial growth factor stimulation in adult mouse brains with local Cre-mediated deletion of itgb8 and smad4 led to vascular dysplasia in newly formed blood vessels. In addition, common genetic variants in ITGB8 were associated with BAVM susceptibility, and ITGB8 genotypes associated with increased risk of BAVMs correlated with decreased beta8 immunostaining in BAVM tissue. These three lines of evidence from human studies and a mouse model suggest that reduced expression of integrin beta8 may be involved in the pathogenesis of sporadic BAVMs.

Emerging strategies for cell and gene therapy of the muscular dystrophies

The muscular dystrophies are a heterogeneous group of over 40 disorders that are characterised by muscle weakness and wasting. The most common are Duchenne muscular dystrophy and Becker muscular dystrophy, which result from mutations within the gene encoding dystrophin; myotonic dystrophy type 1, which results from an expanded trinucleotide repeat in the myotonic dystrophy protein kinase gene; and facioscapulohumeral dystrophy, which is associated with contractions in the subtelomeric region of human chromosome 1. Currently the only treatments involve clinical management of symptoms, although several promising experimental strategies are emerging. These include gene therapy using adeno-associated viral, lentiviral and adenoviral vectors and nonviral vectors, such as plasmid DNA. Exon-skipping and cell-based therapies have also shown promise in the effective treatment and regeneration of dystrophic muscle. The availability of numerous animal models for Duchenne muscular dystrophy has enabled extensive testing of a wide range of therapeutic approaches for this type of disorder. Consequently, we focus here on the therapeutic developments for Duchenne muscular dystrophy as a model of the types of approaches being considered for various types of dystrophy. We discuss the advantages and limitations of each therapeutic strategy, as well as prospects and recent successes in the context of future clinical applications.

PEG-conjugated PAMAM dendrimers mediate efficient intramuscular gene expression

Generations 5 and 6 (G5 and G6) poly(amidoamine) (PAMAM) dendrimers have been shown to be highly efficient nonviral carriers in in vitro gene delivery. However, their high toxicity and unsatisfied in vivo efficacy limit their applications. In this study, to improve their characteristics as gene delivery carriers, polyethylene glycol (PEG, molecular weight 5,000) was conjugated to G5 and G6 PAMAM dendrimers (PEG-PAMAM) at three different molar ratios of 4%, 8%, and 15% (PEG to surface amine per PAMAM dendrimer molecular). Compared with unconjugated PAMAM dendrimers, PEG conjugation significantly decreased the in vitro and in vivo cytotoxicities and hemolysis of G5 and G6 dendrimers, especially at higher PEG molar ratios. Among all of the PEG-PAMAM dendrimers, 8% PEG-conjugated G5 and G6 dendrimers (G5-8% PEG, G6-8% PEG) resulted in the most efficient muscular gene expression when polyplexes were injected intramuscularly to the quadriceps of neonatal mice. Consistent with the in vivo results, these two 8% PEG-conjugated PAMAM dendrimers could also mediate the highest in vitro transfection in 293A cells. Therefore, G5-8% PEG and G6-8% PEG possess a great potential for gene delivery both in vivo and in vitro.

Alpha v beta 3 and alpha v beta 5 integrins and their role in muscle precursor cell adhesion

BACKGROUND INFORMATION

Functional adaptation of skeletal muscle is a requirement for different muscle groups (e.g. craniofacial, ocular and limb) to undergo site-specific changes. Such tissue remodelling depends on dynamic interactions between muscle cells and their extracellular matrix, via participation of multifunctional molecules such as integrins. In view of data suggesting a role in fundamental muscle biology and muscle development in other systems, the present study has focused on expression and function of alpha v integrins, in cultured adult human craniofacial muscle (masseter) precursor cells and myotubes, and the predominantly fibroblastic IC (interstitial cells) population.

RESULTS AND CONCLUSIONS

Flow-cytometric phenotyping and immunofluorescence phenotyping show that alpha v, alpha v beta 3 and alpha v beta 5 are expressed in all mononuclear cells (muscle precursors and IC) seeded on muscle extracellular molecules such as gelatin, VN (vitronectin) and FN (fibronectin). In this system, blockade of alpha v activity using a function-perturbing antibody abrogates cell migration on VN and FN. alpha v integrins act predominantly as VN receptors as cell-substrate attachment is diminished when alpha v neutralizing agents are introduced into cultures seeded on VN, and this inhibition is reversible; these integrins also appear to be minor FN receptors. These results demonstrate that the alpha v subset of integrins present on both myogenic precursors and IC is an essential cohort of VN and, to a lesser extent, FN receptors mediating cell adhesion and, either directly or indirectly, arbiters of cell motility.

Barriers for retinal gene therapy: separating fact from fiction

The majority of recent preclinical gene therapy studies targeting the retina have used adeno-associated virus (AAV) as the gene transfer vector. However, AAV has several limitations including the ability to generate innate inflammatory responses, the ability to cause insertional mutagenesis at a frequency of up to 56% in some tissues and a limited cloning capacity of 4.8Kb. Furthermore, AAV is known to generate limiting immune responses in humans despite the absence of similar immune responses in preclinical canine and murine studies. Three clinical trials to treat Leber's congenital amaurosis using AAV are under way. A clinical trial to treat Stargardt's using lentivirus vectors has also been recently announced. However, very limited evidence currently exists that lentivirus vectors can efficiently transduce photoreceptor cells. In contrast, very few preclinical ocular gene therapy studies have utilized adenovirus as the gene therapy vector. Nonetheless, the only two ocular gene therapy clinical trials performed to date have each used adenovirus as the vector and more significantly, in these published trials there has been no observed serious adverse event. These trials appear to be poised for Phase II/III status. Activation of cytotoxic T lymphocytes limits duration of transgene expression in the retina from first generation adenovirus vectors. However, an advanced class of adenovirus vectors referred to as Helper-dependent Adenovirus (Hd-Ad) have recently been shown to be capable of expressing transgenes in ocular tissues for more than one year. Hd-Ad vectors have many properties that potentially warrant their inclusion in the retinal gene therapy toolbox for the treatment of retinal degenerative diseases.

Survival motor neuron protein regulates apoptosis in an in vitro model of spinal muscular atrophy

Progressive spinal muscular atrophy (SMA), the most prevalent hereditary lower motor neuron disease, is caused by mutations in the telomeric copy of the survival of motor neuron (SMN1) gene. Unlike other cells, lower motor neurons cannot tolerate low levels of smn protein. However, it is unclear as to the nature of the cell death involved. There is evidence that lower motor neurons undergo apoptosis in SMA, leading to muscle weakness and wasting. This study investigated whether SMN1 regulation in a motor neuron model affected indices of apoptotic cell death. Decreased smn expression in neuroblastoma hybrid (NSC-34) cell lines by small interfering RNA (siRNA) was demonstrated at the mRNA and protein level. Smn-depleted cells showed elevated caspase-3 activity, decreased cell viability and increased percentage of TUNEL positive cells. Conversely, NSC-34 cell smn overexpression by adenoviral gene transfer decreased staurosporine-induced caspase-3 elevation and mitigated induced cell toxicity as assessed by 3-(4,5-dimethyl thiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay. However, increased smn expression by itself did not increase cell viability. These data suggest not only that decreased smn levels increase apoptosis in an in vitro model of SMA, but also that increased smn can protect against neural injury.

Adenovirus and adeno-associated virus-mediated delivery of human myophosphorylase cDNA and LacZ cDNA to muscle in the ovine model of McArdle's disease: expression and re-expression of glycogen phosphorylase

At present there is no satisfactory treatment for McArdle's disease, deficiency of myophosphorylase. Injection of modified adenovirus 5 (AdV5) and adeno-associated virus 2 (AAV2) vectors containing myophosphorylase expression cassettes, into semitendinosus muscle of sheep with McArdle's disease, produced expression of functional myophosphorylase and some re-expression of the non-muscle glycogen phosphorylase isoforms (both liver and brain) in regenerating fibres. Expression of both non-muscle isoforms was also seen after control injections of AdV5LacZ vectors. There was up to an order of magnitude greater expression of phosphorylase after myophosphorylase vector injection than after LacZ controls (62% of sections with over 1000 positive muscle fibres, versus 7%). The results presented here suggest that the use of viral vector-mediated phosphorylase gene transfer may be applicable to the treatment of McArdle's disease and that sustained re-expression of the brain and liver isoforms should also be investigated as a possible treatment.

Full-length dystrophin gene transfer to the mdx mouse in utero

In utero gene therapy for genetic diseases, such as muscular dystrophies, offers potential advantages over postnatal treatment including vector delivery at the earliest point in the disease and treatment prior to full maturation of the immune system. This study examines in utero gene delivery of full-length murine dystrophin to the murine mdx model for Duchenne muscular dystrophy using a high-capacity adenoviral vector. We examined dystrophin expression, spread of vector, morphology and specific force production of the tibialis anterior muscle 9 weeks after intramuscular in utero injection. Recombinant dystrophin was expressed in the hindlimb muscles, with the majority of animals having expression in two muscles of the injected hindlimb. The dystrophin-glycoprotein complex was restored in those muscle fibers expressing recombinant dystrophin. Analysis of the percentage of dystrophin-expressing muscle fibers with centrally placed nuclei revealed effective protection from cycles of degeneration and regeneration normally seen in muscle fibers lacking dystrophin. However, due to low levels of muscle gene transfer, further advances in the efficiency of adenoviral vector-mediated gene delivery would be required for clinical applications of in utero gene therapy for primary myopathies such as Duchenne muscular dystrophy.

The cumate gene-switch: a system for regulated expression in mammalian cells

Background

A number of expression systems have been developed where transgene expression can be regulated. They all have specific characteristics making them more suitable for certain applications than for others. Since some applications require the regulation of several genes, there is a need for a variety of independent yet compatible systems.

Results

We have used the regulatory mechanisms of bacterial operons (cmt and cym) to regulate gene expression in mammalian cells using three different strategies. In the repressor configuration, regulation is mediated by the binding of the repressor (CymR) to the operator site (CuO), placed downstream of a strong constitutive promoter. Addition of cumate, a small molecule, relieves the repression. In the transactivator configuration, a chimaeric transactivator (cTA) protein, formed by the fusion of CymR with the activation domain of VP16, is able to activate transcription when bound to multiple copies of CuO, placed upstream of the CMV minimal promoter. Cumate addition abrogates DNA binding and therefore transactivation by cTA. Finally, an adenoviral library of cTA mutants was screened to identify a reverse cumate activator (rcTA), which activates transcription in the presence rather than the absence of cumate.

Conclusion

We report the generation of a new versatile inducible expression system.

Increased Transduction of Skeletal Muscle Cells by Fibroblast Growth Factor-Modified Adenoviral Vectors

Gene therapy for Duchenne muscular dystrophy will likely require that the corrective dystrophin gene be delivered to a high fraction of muscle fibers in vivo. Because of the large size of the dystrophin cDNA, adenoviral (Ad) vectors have been developed for this application. However, Ad vectors transduce mature muscle inefficiently in part due to downregulation of Ad receptors on these cells. To circumvent this problem, we have tested fibroblast growth factor-2 (FGF) and insulin-like growth factor (IGF) as ligands for their ability to enhance Ad transduction of muscle cells. In this work, we demonstrate that covalent conjugation of FGF, but not IGF, to Ad5 vectors mediates substantial increases in transduction of skeletal muscle cells in vitro and dystrophic in vivo. Ad5 vectors expressing reporter genes were cross-linked to the ligands, using bifunctional polyethylene glycol (PEG) molecules. Ad-PEG-FGF mediated 1000- and 200-fold increases in transduction on C2C12 myoblasts and myotubes in vitro when compared with Ad5, Ad-PEG, or Ad-PEG-IGF. When tested in vivo in mdx mice, Ad-PEG-FGF mediated 6-fold higher transduction in skeletal muscle than unmodified Ad5. Similar results were seen when using lacZ as a reporter gene to observe transduction qualitatively. These data suggest that FGF may be a useful cell-binding ligand to enhance gene delivery by Ad and other vectors into skeletal muscle for the gene therapy of Duchenne muscular dystrophy and other muscle-related diseases.

Factors influencing the efficacy, longevity, and safety of electroporation-assisted plasmid-based gene transfer into mouse muscles

Intramuscular injection of plasmid is a potential alternative to viral vectors for the transfer of therapeutic genes into skeletal muscle fibers. The low efficiency of plasmid-based gene transfer can be enhanced by electroporation (EP) coupled with the intramuscular application of hyaluronidase. We have investigated several factors that can influence the efficiency of plasmid-based gene transfer. These factors include electrical parameters of EP, optimal use of hyaluronidase, age and strain of the host, and plasmid size. Muscles of very young and mature normal, mdx, and immunodeficient mice were injected with plasmids expressing beta-galactosidase, microdystrophin, full-length dystrophin, or full-length utrophin. Transfection efficiency, muscle fiber damage, and duration of transgene expression were analyzed. The best transfection level with the least collateral damage was attained at 175-200 V/cm. Pretreatment with hyaluronidase markedly increased transfection, which was also influenced by the plasmid size and the strain and the age of the mice. Even in immunodeficient mice, there was a significant late decline in transgene expression and plasmid DNA copies, although both still remained relatively high after 1 year. Thus, properly optimized EP-assisted plasmid-based gene transfer is a feasible, efficient, and safe method of gene replacement therapy for dystrophin deficiency of muscle but readministration may be necessary.

Selection of muscle-binding peptides from context-specific peptide-presenting phage libraries for adenoviral vector targeting

Production of cell-targeting vectors in part involves the addition of new targeting ligands to the vector to mediate binding to the cells of interest. For viral vectors, the ideal approach is to genetically engineer new ligands into the capsid proteins of the virus to generate a single agent to mediate therapy. Although this is ideal, this insertion of an exogenous ligand from one structural context into the differing structural context of a capsid protein can ablate the function of the ligand or disrupt viral assembly and function. To address this context problem for adenoviral vectors, we have engineered a "context-specific" peptide-presenting phage library. We have displayed a 12-amino-acid (12-mer) random peptide library between the H and I sheets of the fiber protein of adenovirus type 5 on the pIII protein of fd bacteriophage. This library was used for peptide selection against C2C12 mouse skeletal muscle cells. Five rounds of selection combined with four rounds of clearing on nontarget cells selected one primary peptide designated 12.51, which bound target C2C12 cells approximately 100-fold better than the positive control RGD peptide. Translation of 12.51 back into the fiber protein produced a ligand-modified adenoviral vector that mediated 14-fold-better transduction of target C2C12 cells. These data suggest context-specific peptide-presenting libraries may allow selection of compatible peptide ligands for functional translation into viral vectors for retargeting.

Stable transduction of myogenic cells with lentiviral vectors expressing a minidystrophin

Gene therapy for Duchenne muscular dystrophy (DMD) will require sustained expression of therapeutic dystrophins in striated muscles. Lentiviral vectors have a relatively large transgene carrying capacity and can integrate into nondividing cells. We therefore explored the use of lentiviral vectors for transferring genes into mouse skeletal muscle cells. These vectors successfully transferred a minidystrophin expression cassette into mdx muscles, and minidystrophin expression persisted and prevented subsequent muscle fiber degeneration for at least 6 months. However, only low to moderate levels of skeletal muscle transduction could be obtained by intramuscular injection of the highest currently available lentiviral doses. Using cultured cells, the lentiviral vectors effectively transduced proliferating and terminally differentiated muscle cells, indicating that cell cycling is not essential for transduction of myogenic cells. We further showed that lentiviral vectors efficiently transduced both primary myoblasts and multipotent adult progenitor cells (MAPCs) in vitro, and the cells persistently expressed transgenes without any obvious toxicity. When mdx primary myoblasts were genetically modified with minidystrophin vectors and transplanted into mdx skeletal muscles, significant numbers of dystrophin-expressing myofibers formed. Finally, we showed that a short, highly active CK6 regulatory cassette directed muscle-specific activity in the context of the lentiviral vectors. The ability of lentiviral vectors to transduce myogenic progenitors using a minidystrophin cassette regulated by a muscle-specific promoter suggests that this system could be useful for ex vivo gene therapy of muscular dystrophy.

Localization of coxsackie virus and adenovirus receptor (CAR) in normal and regenerating human muscle

The primary receptor for Adenovirus and Coxsackie virus (CAR) serves as main port of entry of the adenovirus vector mediating gene transfer into skeletal muscle. Information about CAR expression in normal and diseased human skeletal muscle is lacking. C'- or N'-terminally directed polyclonal antibodies against CAR were generated and immunohistochemical analysis of CAR on morphologically normal and regenerating human skeletal muscle of children and adults was performed. In morphologically normal human muscle fibers, CAR immunoreactivity was limited to the neuromuscular junction. In regenerating muscle fibers, CAR was abundantly co-expressed with markers of regeneration. The function of CAR at the neuromuscular junction is currently unknown. Co-expression of CAR with markers of regeneration suggests that CAR is developmentally regulated, and may serve as a marker of skeletal muscle fiber regeneration.

Parvalbumin gene delivery improves diastolic function in the aged myocardium in vivo

Abnormal relaxation of the heart, termed diastolic dysfunction, is a significant and growing problem that is a major cause of heart failure in the aged population. The potential of gene transfer of parvalbumin (Parv), a cytoplasmic calcium-binding protein, to improve diastolic function in the aged myocardium in vivo was evaluated. Despite evidence for an early developmental influence on the efficiency of Ad5 striated muscle transduction, results show that Ad5 gene transfer efficiency to adult cardiac myocytes in vitro is identical in young and old rats, suggesting that the basic processes of adenovirus binding and internalization are unaffected by aging. In contrast, Ad5-mediated Parv gene transfer to the myocardium in vivo is reduced in old rats compared to young rats. Nonetheless, Parv gene transfer and expression in vivo were sufficient to improve tau, a load-independent indicator of diastolic function, assessed using catheter-based micromanometry in the aged myocardium. These results suggest that expression of the calcium buffer Parv may represent an effective approach to functional correction of the failing heart in the aging.

Imaging of human sodium-iodide symporter gene expression mediated by recombinant adenovirus in skeletal muscle of living rats

PURPOSE

We evaluated the feasibility of non-invasive imaging of recombinant adenovirus-mediated human sodium-iodide symporter (hNIS) gene expression by (99m)TcO(4)(-) scintigraphy in skeletal muscle of rats.

METHODS

Replication-defective recombinant adenovirus encoding hNIS gene [Rad-CMV-hNIS 5x10(7), 2x10(8) or 1x10(9) plaque forming units (pfu)] or beta-galactosidase gene (Rad-CMV-LacZ 1x10(9) pfu) was injected into the right biceps femoris muscle of rats ( n=5-6 for each group). Three days after gene transfer, scintigraphy was performed using a gamma camera 30 min after injection of (99m)TcO(4)(-) (1.85 MBq). An additional two rats injected with 1x10(9) pfu of Rad-CMV-hNIS underwent (99m)TcO(4)(-) scintigraphy with sodium perchlorate. After the imaging studies, rats were sacrificed for assessment of the biodistribution of (99m)TcO(4)(-) and measurement of hNIS mRNA expression.

RESULTS

In all the rats injected with 1x10(9) pfu of Rad-CMV-hNIS, hNIS expression was successfully imaged by (99m)TcO(4)(-) scintigraphy, while rats injected with Rad-CMV-LacZ or lower doses of Rad-CMV-hNIS failed to show uptake. The biodistribution studies indicated that a significantly different amount of (99m)TcO(4)(-) was retained in the liver ( p<0.001) and the right muscle ( p<0.05), with the highest uptake in rats injected with 1x10(9) pfu of Rad-CMV-hNIS. The muscular hNIS mRNA level quantified by real-time reverse transcription-polymerase chain reaction was significantly higher in rats injected with 1x10(9) pfu of Rad-CMV-hNIS ( p<0.05), with a positive correlation with the imaging counts ( r=0.810, p<0.05) and the biodistribution ( r=0.847, p<0.001). Hot spots in rats injected with 1x10(9) pfu of Rad-CMV-hNIS were specifically inhibited by sodium perchlorate.

CONCLUSION

This study illustrated that (99m)TcO(4)(-) scintigraphy can monitor Rad-CMV-hNIS-mediated gene expression in skeletal muscle of rats, non-invasively and quantitatively.

Overexpression or ablation of JNK in skeletal muscle has no effect on glycogen synthase activity

c-Jun NH(2)-terminal kinase (JNK) is highly expressed in skeletal muscle and is robustly activated in response to muscle contraction. Little is known about the biological functions of JNK signaling in terminally differentiated muscle cells, although this protein has been proposed to regulate insulin-stimulated glycogen synthase activity in mouse skeletal muscle. To determine whether JNK signaling regulates contraction-stimulated glycogen synthase activation, we applied an electroporation technique to induce JNK overexpression (O/E) in mouse skeletal muscle. Ten days after electroporation, in situ muscle contraction increased JNK activity 2.6-fold in control muscles and 15-fold in the JNK O/E muscles. Despite the enormous activation of JNK activity in JNK O/E muscles, contraction resulted in similar increases in glycogen synthase activity in control and JNK O/E muscles. Consistent with these findings, basal and contraction-induced glycogen synthase activity was normal in muscles of both JNK1- and JNK2-deficient mice. JNK overexpression in muscle resulted in significant alterations in the basal phosphorylation state of several signaling proteins, such as extracellular signal-regulated kinase 1/2, p90 S6 kinase, glycogen synthase kinase 3, protein kinase B/Akt, and p70 S6 kinase, in the absence of changes in the expression of these proteins. These data suggest that JNK signaling regulates the phosphorylation state of several kinases in skeletal muscle. JNK activation is unlikely to be the major mechanism by which contractile activity increases glycogen synthase activity in skeletal muscle.

Helper-Dependent Adenoviral Vectors Containing Modified Fiber for Improved Transduction of Developing and Mature Muscle Cells

Adenoviruses (Ads) have shown great utility as vectors for the delivery of genes to mammalian cells, partly because of their ability to infect a wide range of different cell types independent of the replicative state of the cell. However, Ads do not transduce mature muscle efficiently because of low levels of the natural viral primary receptor, the coxsackie virus and adenovirus receptor, on the surface of adult muscle cells. In this study, we have addressed whether incorporation of polylysine [p(K)] or arginine-glycine-aspartic acid (RGD) placed in the H-I loop of the adenoviral fiber protein can improve helper-dependent Ad vector (hdAd) transduction of mature muscle cells. We show that incorporation of the p(K) motif into the fiber of early region 1 (E1)-deleted Ad results in enhanced transduction of undifferentiated and differentiated C2C12 cells relative to a virus, containing a wild-type fiber (12- and 21-fold enhancement, respectively). Incorporation of the RGD motif resulted in only a 60-70% increase in transduction efficiency in these cells. The two fiber modifications were then incorporated into helper viruses for use in the Cre-lox system for generating hdAd, and the resulting retargeted Ad vectors, which encoded the beta-galactosidase reporter gene (beta-Gal), demonstrated enhanced transduction of C2C12 cells in culture. Although hdAdpK also showed enhanced infection of mature mouse muscle in vivo, hdAdRGD did not. All hdAd vectors elicited only minor anti-Ad immune responses, compared with an E1-deleted control vector, but each vector elicited strong anti-beta-Gal immunoreactivity. Our results demonstrate that hdAd with modified cell tropism can be generated efficiently and, in the case of polylysine-modified hdAd, can lead to improved transduction of adult muscle cells in vivo.

Efficient delivery of Cre-recombinase to neurons in vivo and stable transduction of neurons using adeno-associated and lentiviral vectors

BACKGROUND

Inactivating genes in vivo is an important technique for establishing their function in the adult nervous system. Unfortunately, conventional knockout mice may suffer from several limitations including embryonic or perinatal lethality and the compensatory regulation of other genes. One approach to producing conditional activation or inactivation of genes involves the use of Cre recombinase to remove loxP-flanked segments of DNA. We have studied the effects of delivering Cre to the hippocampus and neocortex of adult mice by injecting replication-deficient adeno-associated virus (AAV) and lentiviral (LV) vectors into discrete regions of the forebrain.

RESULTS

Recombinant AAV-Cre, AAV-GFP (green fluorescent protein) and LV-Cre-EGFP (enhanced GFP) were made with the transgene controlled by the cytomegalovirus promoter. Infecting 293T cells in vitro with AAV-Cre and LV-Cre-EGFP resulted in transduction of most cells as shown by GFP fluorescence and Cre immunoreactivity. Injections of submicrolitre quantities of LV-Cre-EGFP and mixtures of AAV-Cre with AAV-GFP into the neocortex and hippocampus of adult Rosa26 reporter mice resulted in strong Cre and GFP expression in the dentate gyrus and moderate to strong labelling in specific regions of the hippocampus and in the neocortex, mainly in neurons. The pattern of expression of Cre and GFP obtained with AAV and LV vectors was very similar. X-gal staining showed that Cre-mediated recombination had occurred in neurons in the same regions of the brain, starting at 3 days post-injection. No obvious toxic effects of Cre expression were detected even after four weeks post-injection.

CONCLUSION

AAV and LV vectors are capable of delivering Cre to neurons in discrete regions of the adult mouse brain and producing recombination.

Fetal muscle gene transfer is not enhanced by an RGD capsid modification to high-capacity adenoviral vectors

High levels of alpha(v) integrin expression by fetal muscle suggested that vector re-targeting to integrins could enhance adenoviral vector-mediated transduction, thereby increasing safety and efficacy of muscle gene transfer in utero. High-capacity adenoviral (HC-Ad) vectors modified by an Arg-Gly-Asp (RGD) peptide motif in the HI loop of the adenoviral fiber (RGD-HC-Ad) have demonstrated efficient gene transfer through binding to alpha(v) integrins. To test integrin targeting of HC-Ad vectors for fetal muscle gene transfer, we compared unmodified and RGD-modified HC-Ad vectors. In vivo, unmodified HC-Ad vector transduced fetal mouse muscle with four-fold higher efficiency compared to RGD-HC-Ad vector. Confirming that the difference was due to muscle cell autonomous factors and not mechanical barriers, transduction of primary myogenic cells isolated from murine fetal muscle in vitro demonstrated a three-fold better transduction by HC-Ad vector than by RGD-HC-Ad vector. We hypothesized that the high expression level of coxsackievirus and adenovirus receptor (CAR), demonstrated in fetal muscle cells both in vitro and in vivo, was the crucial variable influencing the relative transduction efficiencies of HC-Ad and RGD-HC-Ad vectors. To explore this further, we studied transduction by HC-Ad and RGD-HC-Ad vectors in paired cell lines that expressed alpha(v) integrins and differed only by the presence or absence of CAR expression. The results increase our understanding of factors that will be important for retargeting HC-Ad vectors to enhance gene transfer to fetal muscle.

The alphavbeta5 integrin of hematopoietic and nonhematopoietic cells is a transduction receptor of RGD-4C fiber-modified adenoviruses

Epithelial and endothelial cells expressing the primary Coxsackie virus B adenovirus (Ad) receptor (CAR) and integrin coreceptors are natural targets of human Ad infections. The fiber knob of species A, C, D, E and F Ad serotypes binds CAR by mimicking the CAR-homodimer interface, and the penton base containing arginine-glycine-aspartate (RGD) motifs binds with low affinity to alphav integrins inducing cell activation. Here, we generated seven different genetically modified Ad vectors with RGD sequences inserted into the HI loop of fiber knob. All mutants bound and infected CAR and alphav integrin-positive epithelial cells with equal efficiencies. However, the Ads containing two additional cysteines, both N and C terminals of the RGD sequence (RGD-4C), were uniquely capable of transducing CAR-less hematopoietic and nonhematopoietic human tumor cell lines and primary melanoma cells. Both binding and transduction of RGD-4C Ad were blocked by soluble RGD peptides. Flow cytometry of cell surface integrins and virus binding to CAR-less cells in the presence of function-blocking anti-integrin antibodies indicated that the alphavbeta5 integrin, but not alphavbeta3, alphaIIbbeta3 or beta1,alpha5 or alpha6-containing integrins served as a functional transduction receptor of the RGD-4C Ads. However, in cells with low levels of alphavbeta5 integrin, the function-blocking anti-alphavbeta5 antibodies were not effective, unlike soluble RGD peptides. Collectively, our data demonstrate that the alphavbeta5 integrin is a functional transduction receptor of RGD-4C Ads in the absence of CAR, and that additional RGD receptors are targets of these viruses. The RGD-4C vectors further extend the tropism of Ads towards potential human therapies.

Binding of adenoviral fiber knob to the coxsackievirus-adenovirus receptor is crucial for transduction of fetal muscle

Adenoviral (Ad) infection involves attachment mediated by the Ad fiber protein binding to the coxsackievirus-adenovirus receptor (CAR) of a target cell and internalization facilitated by the interaction of the Ad penton base protein with alpha(v) integrins. To understand the relative importance of the Ad binding and internalization steps for the transduction of fetal skeletal muscle, we used a panel of genetically modified vectors that specifically ablate the fiber-CAR interaction (AdL.F*), the penton base-alpha(v) integrin interaction (AdL.PB*), or both (AdL.PB*F*) to transduce embryonic day 16 (E-16) mouse muscle in vivo and primary E-16 muscle cells in vitro. Quantification of transgene expression and vector genome copies revealed a striking absence of E-16 muscle transduction by AdL.F* and AdL.PB*F*. In contrast, fetal muscle transduction with AdL.PB* was not significantly different than with the unmodified vector. Similar results were observed with in vitro Ad infection studies in primary E-16 muscle cells. From these data we conclude that the fiber-CAR interaction is important for the transduction of fetal muscle by Ad vectors. The high dependence on fiber-CAR binding will impact the development of strategies for Ad vector retargeting to achieve muscle-specific transduction in utero.

Novel therapies for Duchenne muscular dystrophy

The development of therapeutic strategies that overcome the unique problems posed by Duchenne muscular dystrophy (DMD) has lead to the development of many contemporary approaches to human disease in general. Various treatment approaches have been explored--such as pharmacological therapies and cell-based, cytokine, and genetic therapies--that are all targeted to specific features of dystrophic DMD muscle pathology. In genetic therapies, the large size of the dystrophin gene has necessitated the development and use of novel functional minidystrophin and microdystrophin genes, muscle-specific promoter systems, and gutted adenoviral systems. In addition to these well defined viral strategies, plasmid vectors and the upregulation of utrophin (a dystrophin homologue) have potential. Various novel genetic approaches--such as antisense-mediated exon skipping, gene correction, and new cytokine approaches--are also being developed. Together these exciting developments bring an effective treatment for DMD closer than ever before.

Facilitated angiogenesis induced by heme oxygenase-1 gene transfer in a rat model of hindlimb ischemia

Heme oxygenase-1 (HO-1) is an inducible form of heme oxygenase that catabolizes heme to carbon monoxide, biliverdin, and ferrous iron. We have investigated whether HO-1 can induce angiogenic effects in vivo. Rats were subjected to a bolus injection of either wild type adenovirus (ad-wt) or adenovirus encoding HO-1 (ad-HO-1) through the right femoral artery, which was then removed immediately. HO-1 gene transfer resulted in about a sixfold increase in HO-1 protein levels as compared to the non-treated animals. The increase in both blood flow and capillary density was significantly greater in the ischemic hindlimbs that had been injected with ad-HO-1 than in those injected with ad-wt. These angiogenic effects of ad-HO-1 infection could be completely abolished by treating the animals with the HO inhibitor, zinc protoporphyrin, indicating that they were specifically due to the expression of HO-1. Thus, HO-1 gene transfer improves the blood flow in ischemic hindlimb, at least in part, via angiogenesis facilitated by the induction of this molecule.

Improved performance of a fully gutted adenovirus vector containing two full-length dystrophin cDNAs regulated by a strong promoter

Dystrophin gene transfer using gutted or helper-dependent adenoviruses (HDAd), which have most of their genes deleted, is a promising approach to treat Duchenne muscular dystrophy. In an attempt to boost the amount of dystrophin produced after gene transfer, we have constructed a fully deleted HDAd (HDCBDys2x) containing two human dystrophin cDNAs controlled by the powerful hybrid cytomegalovirus enhancer/beta-actin promoter. We demonstrated high dystrophin expression after infection of muscle cultures with HDCBDys2x. Similarly, high (mean=583) and moderate (mean=124) numbers of muscle fibers were transduced in anterior tibialis muscle after intramuscular injection of HDCBDys2x in neonate and adult dystrophindeficient (mdx) mice 10 days postinjection. In fact, in the neonatally injected mdx mice, the transferred dystrophin was five times more abundant than in normal human muscle. However, the high early transduction level was transient in both animal groups, and we observed a humoral response against the human dystrophin. In contrast, we demonstrated sustained dystrophin expression in immunodeficient mouse muscles. Dystrophin expression of HDCBDys2x could be further increased in the presence of an E1/E3-deleted (first-generation) adenovirus, thus demonstrating that the latter vector synthesizes trans-acting enhancing factors. We have achieved abundant dystrophin expression with our new, improved HDAd. It is anticipated that high longterm transgene expression will be possible by employing weaker immunogenic transgenes.

Gene transfer of glial cell-derived neurotrophic factor and cardiotrophin-1 protects PC12 cells from injury: involvement of the phosphatidylinositol 3-kinase and mitogen-activated protein kinase kinase pathways

Gene therapy for neurodegenerative diseases may utilize the expression of neurotrophic factors because of their potential to promote survival and regeneration of injured neuronal cells. Increasing numbers of these factors are being considered for gene transfer, but their specificity and efficacy in neuroprotection are greatly variable. The major aims of this study were to carry out gene transfer of various neurotrophic factors and investigate their mechanisms of action as well as their protective effects on the viability of rat pheochromocytoma (PC12) cells. We used glutamate, S-nitroso-N-acetyl-DL-penicillamine (SNAP), and staurosporine to induce excitatory damage, oxidative stress, and apoptosis, respectively, because these mechanisms are thought to participate in various disease processes leading to degeneration of cells. We utilized adenovirus vectors for efficient gene transfer of trophic factors (glial-cell derived neurotrophic factor [GDNF] and cardiotrophin-1 [CT-1]) or calbindin-D28k. We found that GDNF and CT-1 gene transfers were equally effective in saving PC12 cells from injury, but calbindin expression did not show any beneficial effects. GDNF gene transfer was much more efficient in protecting PC12 cells from damage than direct GDNF administration. The protection by GDNF expression against staurosporine was mediated through both phosphatidylinositol 3-kinase (PI3K) and mitogen-activated protein kinase kinase (MAPK kinase; MEK) pathways, but only the MEK pathway was involved in the protection against SNAP. In contrast, the protective effect of GDNF against glutamate toxicity was independent of these RET-dependent signal transduction pathways.

Adenovirus mediated gene transfer to skeletal muscle

Transfer of therapeutic genes into muscle tissue has promise for the treatment of a variety of muscular dystrophies. Various vectors have been used to deliver genes to skeletal muscle but their application has faced several major limitations including: (1) the lack of transgene persistence caused by the immune rejection of transduced myofibers and/or vector toxicity, and (2) the maturation dependence of viral transduction. While the immunorejection and/or cytotoxic problems are being overcome with the development of new vectors, maturation-dependent viral transduction is still a major hurdle in gene transfer to skeletal muscle. Poor adenoviral transduction in mature myofibers has been attributed to: (1) the extracellular matrix of mature myofibers may form a physical barrier and prevent the passage of large viral particles; (2) viral receptors are down-regulated with muscle maturation; and (3) loss of myoblasts with muscle maturation, which serve as intermediaries in the viral transduction. In this review, we will focus on recent developments in overcoming those hurdles of gene therapy in skeletal muscle, especially to adenovirus (Ad), including: (1) new mutant vectors lacking all viral genes to decrease immunogenicity, and hence, improve persistence of transgene expression in muscle in vivo; (2) using tissue specific promoters to evade immunorejection; (3) permeabilization of the extracellular matrix; (4) modifying the viral receptors in mature myofibers; and (5) myoblast or muscle stem cell mediated ex vivo gene transfer.

Increased survival and function of SOD1 mice after glial cell-derived neurotrophic factor gene therapy

Amyotrophic lateral sclerosis (ALS) is caused by a progressive degeneration of motor neurons. The cause of sporadic ALS is not known, but 1-2% of all cases are familial and caused by mutations in the copper-zinc superoxide dismutase (SOD1) gene. Transgenic SOD1 mice serve as a transgenic mouse model for these cases. Glial cell-derived neurotrophic factor (GDNF) has a potent trophic effect on motor neurons. Clinical trials in which growth factors have been systemically administered to ALS patients have not been effective, owing in part to the short half-life of these factors and their low concentrations at target sites. Gene transfer of therapeutic factors to motor neurons and/or their target cells, such as muscle, may overcome these problems. Previously, we and others have shown that intramuscularly administered adenovirus vector (AVR) results in foreign gene expression not only in muscle cells, but also in relevant motor neurons in the spinal cord, because of retrograde axonal transport. In this study we utilized an AVR to introduce GDNF into muscles of neonatal SOD1 mice. We showed that AVR-mediated GDNF expression delayed the onset of disease by 7 +/- 8 days (mean +/- SD), prolonged survival by 17 +/- 10 days, and delayed the decline in motor functions (as determined on a rotating rod) by 7-14 days. These results demonstrate that gene delivery to muscle and motor neurons has the potential to treat devastating neurodegenerative diseases such as ALS.

Age-dependent effects of repeated immunization with a first generation adenovirus vector on the immune response and transgene expression in young and old rats

We evaluated the kinetics of transgene expression and humoral and cellular immune responses against viral antigens and the product of the reporter gene LacZ in young (4 months) and old (20 months) Wistar rats. Animals received the intramuscular injection of a recombinant E1-deleted human type 5 adenovirus encoding beta-gal (Ad-LacZ) on days 0 and 30. The transgene expression evaluated on day 2 after infection revealed a significantly higher beta-gal activity in young than in old animals (1.9-fold increase, p<0.05). beta-gal expression decreased on day 6, and on day 15 transgene activity was undetectable in muscles from both groups. Ad-LacZ inoculation was repeated on day 30 in both animal groups. However, after the second adenovirus administration, no increase in beta-gal activity was observed. Humoral and cellular immune responses, evaluated after the first and second Ad-LacZ injection, developed with similar kinetics in young and old rats. In particular, the antigen specific antibodies were able to kill adenovirus-infected tumor cells in both complement-dependent cytotoxicity (CDC) and antibody-mediated cell-dependent cytotoxicity (ADCC) assays. Lymphocyte proliferation in response to the in vitro stimulation with specific antigens was significantly lower in old than in young animals whereas no difference was found in cytotoxic T lymphocyte activity against adenovirus-infected tumor cells. Our results demonstrate that repeated immunization with AdCMV.LacZ induces minor age-related differences in immune response which precludes gene expression both in young and old animals.

The short MCK1350 promoter/enhancer allows for sufficient dystrophin expression in skeletal muscles of mdx mice

First-generation adenovirus vectors (AdV) have been used successfully to transfer a human dystrophin minigene to skeletal muscle of mdx mice. In most studies, strong viral promoters such as the cytomegalovirus promoter/enhancer (CMV) were used to drive dystrophin expression. More recently, a short version of the muscle creatine kinase promoter (MCK1350) has been shown to provide muscle-specific reporter gene expression after AdV-mediated gene delivery. Therefore, we generated a recombinant AdV where dystrophin expression is controlled by MCK1350 (AdVMCKdys). AdVMCKdys was injected by the intramuscular route into anterior tibialis muscle of mdx mice shortly after birth. Dystrophin expression was assessed at 20, 30, and 60 days after AdV-injection. At 20 days, muscles of AdVMCKdys-injected mdx mice showed a high number of dystrophin-positive fibers (mean: 365). At 60 days, the number of dystrophin-positive fibers was not only maintained, but increased significantly (mean: 600). In conclusion, MCK1350 allows for sustained dystrophin expression after AdV-mediated gene transfer to skeletal muscle of newborn mdx mice. In contrast to previous studies, where strong viral promoters were used, dystrophin expression driven by MCK1350 peaks at later time points. This may have implications for the future use of muscle-specific promoters for gene therapy of Duchenne muscular dystrophy.