Long-term regulated expression of growth hormone in mice after intramuscular gene transfer

A peptide conjugate enables systemic injection of the morpholino inducer and more durable induction of T3H38 ribozyme-controlled AAV transgene in mice

Genetic switches that allow for precise control over transgene expression timing or levels may improve the safety and expand the use of adeno-associated viral (AAV) vector-based gene therapy technologies. We previously engineered an efficient RNA switch system that comprises a novel self-cleaving ribozyme (T3H38) and an octaguanidine dendrimer-conjugated morpholino oligonucleotide (v-M8) complementary to the ribozyme. This switch system can be used to efficiently regulate AAV-delivered transgenes with an up to 200-fold regulatory range in mice. However, this switch system has a relatively short induction half-life and only works well when v-M8 was locally but not systemically administered, representing two key limitations of the system. To address these issues, here, we tested replacing the octa-guanidine dendrimer in the v-M8 morpholino oligo with a cell-penetrating peptide (CPP). Two CPP-conjugated morpholino oligos (B-M8 and B-MSP-M8) were synthesized and compared with v-M8 for the induction of T3H38-regulated AAV-luciferase in mice. One of the CPP-conjugated oligos (B-MSP-M8) not only showed significantly improved induction half-life over that of v-M8, but also enabled efficient induction of AAV transgene expression when the oligo was systemically administered. This study improves in vivo performance and broadens the utility of the T3H38 ribozyme-based RNA switch system in gene therapy applications.

Advances in the Development and the Applications of Non-viral, Episomal Vectors for Gene Therapy

Nonviral and nonintegrating episomal vectors are reemerging as a valid, alternative technology to integrating viral vectors for gene therapy, due to their more favorable safety profile, significantly lower risk for insertional mutagenesis, and a lesser potential for innate immune reactions, in addition to their low production cost. Over the past few years, attempts have been made to generate highly functional nonviral vectors that display long-term maintenance within cells and promote more sustained gene expression relative to conventional plasmids. Extensive research into the parameters that stabilize the episomal DNA within dividing and nondividing cells has shed light into the genetic and epigenetic mechanisms that govern replication and transcription of episomal DNA within a mammalian nucleus in long-term cell culture. Episomal vectors based on scaffold/matrix attachment regions (S/MARs) do not integrate into the genomic DNA and address the serious problem of plasmid loss during mitosis by providing mitotic stability to established plasmids, which results in long-term transfection and transgene expression. The inclusion, in such vectors, of an origin of replication—initiation region—from the human genome has greatly enhanced their performance in primary cell culture. A number of vectors that function as episomes have arisen, which are either devoid or depleted of harmful CpG sequences and bacterial genes, and their effectiveness, as well as that of nonintegrating viral episomes, is enhanced when combined with S/MAR elements. As a result of these advances, an “S/MAR technology” has emerged for the production of efficient episomal vectors. Significant research continues in this field and innovations, in combination with promising systems based on nanoparticles and potentially combined with physical delivery methods, will enable the generation of optimized systems with scale-up and clinical application suitability utilizing episomal vectors.

Synthetic Biology: Emerging Concepts to Design and Advance Adeno-Associated Viral Vectors for Gene Therapy

Three recent approvals and over 100 ongoing clinical trials make adeno-associated virus (AAV)-based vectors the leading gene delivery vehicles in gene therapy. Pharmaceutical companies are investing in this small and nonpathogenic gene shuttle to increase the therapeutic portfolios within the coming years. This prospect of marking a new era in gene therapy has fostered both investigations of the fundamental AAV biology as well as engineering studies to enhance delivery vehicles. Driven by the high clinical potential, a new generation of synthetic-biologically engineered AAV vectors is on the rise. Concepts from synthetic biology enable the control and fine-tuning of vector function at different stages of cellular transduction and gene expression. It is anticipated that the emerging field of synthetic-biologically engineered AAV vectors can shape future gene therapeutic approaches and thus the design of tomorrow's gene delivery vectors. This review describes and discusses the recent trends in capsid and vector genome engineering, with particular emphasis on synthetic-biological approaches.

Introducing Genes into Mammalian Cells: Viral Vectors

Over the years, many different viral vector systems have been developed to take advantage of the specific biological properties and tropisms of a large number of mammalian viruses. As a result, researchers wanting to introduce and/or express genes in mammalian cells have many options, as discussed here.

A reversible RNA on-switch that controls gene expression of AAV-delivered therapeutics in vivo

Widespread use of gene therapy technologies is limited in part by the lack of small genetic switches with wide dynamic ranges that control transgene expression without the requirement of additional protein components^1-5. In this study, we engineered a class of type III hammerhead ribozymes to develop RNA switches that are highly efficient at cis-cleaving mammalian mRNAs and showed that they can be tightly regulated by a steric-blocking antisense oligonucleotide. Our variant ribozymes enabled in vivo regulation of adeno-associated virus (AAV)-delivered transgenes, allowing dose-dependent and up to 223-fold regulation of protein expression over at least 43 weeks. To test the potential of these reversible on-switches in gene therapy for anemia of chronic kidney disease⁶, we demonstrated regulated expression of physiological levels of erythropoietin with a well-tolerated dose of the inducer oligonucleotide. These small, modular and efficient RNA switches may improve the safety and efficacy of gene therapies and broaden their use.

Generation of Expression Plasmids for Angiostatin, Endostatin and Timp-2 for Cancer Gene Therapy

Antiangiogenic therapy may represent a promising approach to cancer treatment. Indeed, the efficacy of endogenous angiogenesis inhibitors, including angiostatin, endostatin and TIMPs, has been demonstrated in many types of solid tumors in animal models. In view of the possible problems associated with long-term administration of inhibitors as recombinant proteins, we propose their delivery as nucleic acids through a gene therapy approach. To this end, eukaryotic expression constructs for murine angiostatin and endostatin as well as human TIMP-2 were generated, and characterized in vitro. All constructs carry the relevant cDNAs under the control of the strong HCMV promoter/enhancer, and cleavable leader signals to allow protein secretion. Expression of the angiogenesis inhibitors was detected by in vitro transcription/translation experiments as well as transfection of 293T cells, followed by Western blotting (WB) or radioimmunoprecipitation analysis of both cell lysates and supernatants (SNs). These constructs might be used for in vivo intramuscular delivery of plasmid DNA and as a set of reagents for the development of retroviral as well as adeno-associated viral (AAV) vectors expressing angiogenesis inhibitors.

Preservation of Anticancer and Immunosuppressive Properties of Rapamycin Achieved Through Controlled Releasing Particles

Rapamycin is commonly used in chemotherapy and posttransplantation rejection suppression, where sustained release is preferred. Conventionally, rapamycin has to be administered in excess due to its poor solubility, and this often leads to cytotoxicity and undesirable side effects. In addition, rapamycin has been shown to be hydrolytically unstable, losing its bioactivity within a few hours. The use of drug delivery systems is hypothesized to preserve the bioactivity of rapamycin, while providing controlled release of this otherwise potent drug. This paper reports on the use of microparticles (MP) as a means to tune and sustain the delivery of bioactive rapamycin for up to 30 days. Rapamycin was encapsulated (100% efficiency) in poly(lactic-co-glycolic acid) (PLGA), polycaprolactone (PCL), or a mixture of both via an emulsion method. The use of different polymer types and mixture was shown to achieve a variety of release kinetics and profile. Released rapamycin was subsequently evaluated against breast cancer cell (MCF-7) and human lymphocyte cell (Jurkat). Inhibition of cell proliferation was in good agreement with in vitro release profiles, which confirmed the intact bioactivity of rapamycin. For Jurkat cells, the suppression of cell growth was proven to be effective up to 20 days, a duration significantly longer than free rapamycin. Taken together, these results demonstrate the ability to tune, sustain, and preserve the bioactivity of rapamycin using MP formulations. The sustained delivery of rapamycin could lead to better therapeutic effects than bolus dosage, at the same time improving patient compliance due to its long-acting duration.

Mouse species-specific control of hepatocarcinogenesis and metabolism by FGF19/FGF15

BACKGROUND & AIMS

Bile acid nuclear receptor farnesoid X receptor (FXR) is a key molecular mediator of many metabolic processes, including the regulation of bile acid, lipid and glucose homeostasis. A significant component of FXR-mediated events essential to its biological activity is attributed to induction of the enteric endocrine hormone fibroblast growth factor (FGF)19 or its rodent ortholog, FGF15. In this report, we compared the properties of human FGF19 and murine FGF15 in the regulation of hepatocarcinogenesis and metabolism in various mouse models of disease.

METHODS

Tumorigenicity was assessed in three mouse models (db/db, diet-induced obese, and multi-drug resistance 2 [Mdr2]-deficient) following continuous exposure to FGF19 or FGF15 via adeno-associated viral-mediated gene delivery. Glucose, hemoglobin A1c and β-cell mass were characterized in db/db mice. Oxygen consumption, energy expenditure, and body composition were evaluated in diet-induced obese mice. Serum levels of alkaline phosphatase, alanine aminotransferase, and aspartate aminotransferase were assessed in Mdr2-deficient mice. Expression profiles of genes encoding key proteins involved in bile acid synthesis and hepatocarcinogenesis were also determined.

RESULTS

Both FGF15 and FGF19 hormones repressed bile acid synthesis (p<0.001 for both). However, murine FGF15 lacked the protective effects characteristic of human FGF19 in db/db mice with overt diabetes, such as weight-independent HbA1c-lowering and β-cell-protection. Unlike FGF19, FGF15 did not induce hepatocellular carcinomas (HCC) in three mouse models of metabolic diseases (db/db, diet-induced obese, and multi-drug resistance 2 [Mdr2]-deficient mice), even at supra-pharmacological exposure levels.

CONCLUSIONS

Fundamental species-associated differences between FGF19 and FGF15 may restrict the relevance of mouse models for the study of the FXR/FGF19 pathway, and underscore the importance of clinical assessment of this pathway, with respect to both safety and efficacy in humans.

LAY SUMMARY

Activation of the nuclear receptor, FXR, leads to the production of a hormone called fibroblast growth factor 19 (FGF19) and subsequently regulation of multiple metabolic processes. Synthetic activators of FXR have been recently approved or are currently in clinical development for treatment of chronic liver diseases, including primary biliary cholangitis (PBC) and non-alcoholic steatohepatitis (NASH). The safety of these activators was partly assessed in mice exposed for prolonged periods of time. However, the results of this study show that mouse FGF15 and human FGF19 exhibit fundamentally different biological activities in mice. This could raise the concern of relying on rodent models for safety assessment of FXR activators. The potential risk of HCC development in patients treated with FXR agonists may need to be monitored.

Biological Approaches to Bone Regeneration by Gene Therapy

Safe, effective approaches for bone regeneration are needed to reverse bone loss caused by trauma, disease, and tumor resection. Unfortunately, the science of bone regeneration is still in its infancy, with all current or emerging therapies having serious limitations. Unlike current regenerative therapies that use single regenerative factors, the natural processes of bone formation and repair require the coordinated expression of many molecules, including growth factors, bone morphogenetic proteins, and specific transcription factors. As will be developed in this article, future advances in bone regeneration will likely incorporate therapies that mimic critical aspects of these natural biological processes, using the tools of gene therapy and tissue engineering. This review will summarize current knowledge related to normal bone development and fracture repair, and will describe how gene therapy, in combination with tissue engineering, may mimic critical aspects of these natural processes. Current gene therapy approaches for bone regeneration will then be summarized, including recent work where combinatorial gene therapy was used to express groups of molecules that synergistically interacted to stimulate bone regeneration. Last, proposed future directions for this field will be discussed, where regulated gene expression systems will be combined with cells seeded in precise three-dimensional configurations on synthetic scaffolds to control both temporal and spatial distribution of regenerative factors. It is the premise of this article that such approaches will eventually allow us to achieve the ultimate goal of bone tissue engineering: to reconstruct entire bones with associated joints, ligaments, or sutures. Abbreviations used: BMP, bone morphogenetic protein; FGF, fibroblast growth factor; AER, apical ectodermal ridge; ZPA, zone of polarizing activity; PZ, progress zone; SHH, sonic hedgehog; OSX, osterix transcription factor; FGFR, fibroblast growth factor receptor; PMN, polymorphonuclear neutrophil; PDGF, platelet-derived growth factor; IGF, insulin-like growth factor; TGF-β, tumor-derived growth factor β; CAR, coxsackievirus and adenovirus receptor; MLV, murine leukemia virus; HIV, human immunodeficiency virus; AAV, adeno-associated virus; CAT, computer-aided tomography; CMV, cytomegalovirus; GAM, gene-activated matrix; MSC, marrow stromal cell; MDSC, muscle-derived stem cell; VEGF, vascular endothelial growth factor.

The antidepressant-like effect of alarin is related to TrkB-mTOR signaling and synaptic plasticity

Alarin is a newly derived neuropeptide from a splice variant of the galanin-like peptide gene. We previously showed that alarin has an antidepressant-like effect by increasing the activity of the extracellular signal-regulated kinase (ERK) and protein kinase B (AKT) pathways, mediated by the tropomyosin-related kinase B receptor in the unpredictable chronic mild stress (UCMS) mouse model. Administration of rapamycin, a mammalian target of rapamycin (mTOR) inhibitor, prevents the rapid antidepressant-like effect induced by ketamine in animal models, indicating a vital role of mTOR in depression pathophysiology. mTOR is a target of the ERK and AKT pathways that regulates the initiation of protein translation via its downstream components: ribosomal protein S6 kinase (p70S6K) and eukaryotic initiation factor 4E binding protein 1 (4E-BP1). Therefore, we hypothesized that the antidepressant-like effects of alarin were achieved by activating ERK/AKT pathways, increasing the activity of mTOR and its downstream signaling components that contribute to protein synthesis required for synaptic plasticity. Our results suggest that intracerebroventricular administration of alarin significantly ameliorates depression-like behaviors in the UCMS mouse model. Furthermore, alarin restored UCMS-induced reductions of p70S6K and post-synaptic density 95 (PSD-95) mRNA levels, and of phospho-mTOR and phospho-4EBP1 in the prefrontal cortex, hippocampus, hypothalamus, and olfactory bulb. Additionally, alarin reversed the UCMS-induced downregulation of PSD-95 and synapsin I protein expression in these brain regions. Thus, the antidepressant-like effects of alarin may be mediated by restoring decreased activity of the mTOR signaling pathway and expression of synaptic proteins. Our findings help advance the understanding of depression pathophysiology.

Engineered fibroblast growth factor 19 reduces liver injury and resolves sclerosing cholangitis in Mdr2-deficient mice

Defects in multidrug resistance 3 gene (MDR3), which encodes the canalicular phospholipid flippase, cause a wide spectrum of cholangiopathy phenotypes in humans. Mice deficient in Mdr2 (murine ortholog of MDR3) develop liver diseases that closely reproduce the biochemical, histological, and clinical features of human cholangiopathies such as progressive familial intrahepatic cholestasis and primary sclerosing cholangitis. We hypothesized that modulating bile acid metabolism by the gut hormone fibroblast growth factor 19 (FGF19) may represent a novel approach for treating cholangiopathy and comorbidities. We introduced adeno-associated virus carrying the gene for either the endocrine hormone FGF19 or engineered FGF19 variant M70 to 12-week old Mdr2-deficient mice with fully established disease. Effects on serum levels of liver enzymes, liver histology, and bile acid homeostasis were evaluated. FGF19 and M70 rapidly and effectively reversed liver injury, decreased hepatic inflammation, attenuated biliary fibrosis, and reduced cholecystolithiasis in Mdr2-deficient mice. Mechanistically, FGF19 and M70 significantly inhibited hepatic expression of Cyp7a1 and Cyp27a1, which encode enzymes responsible for the rate-limiting steps in the classic and alternate bile acid synthetic pathways, thereby reducing the hepatic bile acid pool and blood levels of bile acids. Importantly, prolonged exposure to FGF19, but not M70, led to the formation of hepatocellular carcinomas in the Mdr2-deficient mice. Furthermore, M70 ameliorated the hepatosplenomegaly and ductular proliferation that are associated with cholangiopathy.

CONCLUSION

These results demonstrate the potential for treating cholangiopathy by safely harnessing FGF19 biology to suppress bile acid synthesis.

A nontumorigenic variant of FGF19 treats cholestatic liver diseases

Hepatic accumulation of bile acids is central to the pathogenesis of cholestatic liver diseases. Endocrine hormone fibroblast growth factor 19 (FGF19) may reduce hepatic bile acid levels through modulation of bile acid synthesis and prevent subsequent liver damage. However, FGF19 has also been implicated in hepatocellular carcinogenesis, and consequently, the potential risk from prolonged exposure to supraphysiological levels of the hormone represents a major hurdle for developing an FGF19-based therapy. We describe a nontumorigenic FGF19 variant, M70, which regulates bile acid metabolism and, through inhibition of bile acid synthesis and reduction of excess hepatic bile acid accumulation, protects mice from liver injury induced by either extrahepatic or intrahepatic cholestasis. Administration of M70 in healthy human volunteers potently reduces serum levels of 7α-hydroxy-4-cholesten-3-one, a surrogate marker for the hepatic activity of cholesterol 7α-hydroxylase (CYP7A1), the enzyme responsible for catalyzing the first and rate-limiting step in the classical bile acid synthetic pathway. This study provides direct evidence for the regulation of bile acid metabolism by FGF19 pathway in humans. On the basis of these results, the development of nontumorigenic FGF19 variants capable of modulating CYP7A1 expression represents an effective approach for the prevention and treatment of cholestatic liver diseases as well as potentially for other disorders associated with bile acid dysregulation.

Intravenous AAV8 Encoding Urocortin-2 Increases Function of the Failing Heart in Mice

Urocortin-2 (UCn2) peptide infusion increases cardiac function in patients with heart failure, but chronic peptide infusion is cumbersome, is costly, and provides only short-term benefits. Gene transfer would circumvent these shortcomings. We previously showed that a single intravenous (IV) injection of AAV8.UCn2 increases plasma UCn2 and left ventricular (LV) systolic and diastolic function for at least 7 months in normal mice. Here we test the hypothesis that IV delivery of AAV8.UCn2 increases function of the failing heart. Myocardial infarction (MI, by coronary ligation) was used to induce heart failure, which was assessed by echocardiography 3 weeks after MI. Mice with LV ejection fraction (EF) <25% received IV delivery of AAV8.UCn2 (5×10¹¹ gc) or saline, and 5 weeks later echocardiography showed increased LV EF in mice that received UCn2 gene transfer (p=0.01). In vivo physiological studies showed a 2-fold increase in peak rate of LV pressure development (LV +dP/dt; p<0.0001) and a 1.6-fold increase in peak rate of LV pressure decay (LV −dP/dt; p=0.0007), indicating increased LV systolic and diastolic function in treated mice. UCn2 gene transfer was associated with increased peak systolic Ca²⁺ transient amplitude and rate of Ca²⁺ decline and increased SERCA2a expression. In addition, UCn2 gene transfer reduced Thr286 phosphorylation of Cam kinase II, and increased expression of cardiac myosin light chain kinase, findings that would be anticipated to increase function of the failing heart. We conclude that a single IV injection of AAV8.UCn2 increases function of the failing heart. The simplicity of IV injection of a vector encoding a gene with beneficial paracrine effects to increase cardiac function is an attractive potential clinical strategy.

Transgene regulation using the tetracycline-inducible TetR-KRAB system after AAV-mediated gene transfer in rodents and nonhuman primates

Numerous studies have demonstrated the efficacy of the Adeno-Associated Virus (AAV)-based gene delivery platform in vivo. The control of transgene expression in many protocols is highly desirable for therapeutic applications and/or safety reasons. To date, the tetracycline and the rapamycin dependent regulatory systems have been the most widely evaluated. While the long-term regulation of the transgene has been obtained in rodent models, the translation of these studies to larger animals, especially to nonhuman primates (NHP), has often resulted in an immune response against the recombinant regulator protein involved in transgene expression regulation. These immune responses were dependent on the target tissue and vector delivery route. Here, using AAV vectors, we evaluated a doxycyclin-inducible system in rodents and macaques in which the TetR protein is fused to the human Krüppel associated box (KRAB) protein. We demonstrated long term gene regulation efficiency in rodents after subretinal and intramuscular administration of AAV5 and AAV1 vectors, respectively. However, as previously described for other chimeric transactivators, the TetR-KRAB-based system failed to achieve long term regulation in the macaque after intramuscular vector delivery because of the development of an immune response. Thus, immunity against the chimeric transactivator TetR-KRAB emerged as the primary limitation for the clinical translation of the system when targeting the skeletal muscle, as previously described for other regulatory proteins. New developments in the field of chimeric drug-sensitive transactivators with the potential to not trigger the host immune system are still needed.

Intravenous adeno-associated virus serotype 8 encoding urocortin-2 provides sustained augmentation of left ventricular function in mice

Urocortin-2 (UCn2) peptide infusion increases cardiac function in patients with heart failure, but chronic peptide infusion is cumbersome, costly, and provides only short-term benefits. Gene transfer would circumvent these shortcomings. Here we ask whether a single intravenous injection of adeno-associated virus type 8 encoding murine urocortin-2 (AAV8.UCn2) could provide long-term elevation in plasma UCn2 levels and increased left ventricular (LV) function. Normal mice received AAV8.UCn2 (5×10¹¹ genome copies, intravenous). Plasma UCn2 increased 15-fold 6 weeks and >11-fold 7 months after delivery. AAV8 DNA and UCn2 mRNA expression was persistent in LV and liver up to 7 months after a single intravenous injection of AAV8.UCn2. Physiological studies conducted both in situ and ex vivo showed increases in LV +dP/dt and in LV -dP/dt, findings that endured unchanged for 7 months. SERCA2a mRNA and protein expression was increased in LV samples and Ca²⁺ transient studies showed an increased rate of Ca²⁺ decline in cardiac myocytes from mice that had received UCn2 gene transfer. We conclude that a single intravenous injection of AAV8.UCn2 increases plasma UCn2 and increases LV systolic and diastolic function for at least 7 months. The simplicity of intravenous injection of a long-term expression vector encoding a gene with paracrine activity to increase cardiac function is a potentially attractive strategy in clinical settings. Future studies will determine the usefulness of this approach in the treatment of heart failure.

The potential of adeno-associated viral vectors for gene delivery to muscle tissue

INTRODUCTION

Muscle-directed gene therapy is rapidly gaining attention primarily because muscle is an easily accessible target tissue and is also associated with various severe genetic disorders. Localized and systemic delivery of recombinant adeno-associated virus (rAAV) vectors of several serotypes results in very efficient transduction of skeletal and cardiac muscles, which has been achieved in both small and large animals, as well as in humans. Muscle is the target tissue in gene therapy for many muscular dystrophy diseases, and may also be exploited as a biofactory to produce secretory factors for systemic disorders. Current limitations of using rAAVs for muscle gene transfer include vector size restriction, potential safety concerns such as off-target toxicity and the immunological barrier composing of pre-existing neutralizing antibodies and CD8(+) T-cell response against AAV capsid in humans.

AREAS COVERED

In this article, we will discuss basic AAV vector biology and its application in muscle-directed gene delivery, as well as potential strategies to overcome the aforementioned limitations of rAAV for further clinical application.

EXPERT OPINION

Delivering therapeutic genes to large muscle mass in humans is arguably the most urgent unmet demand in treating diseases affecting muscle tissues throughout the whole body. Muscle-directed, rAAV-mediated gene transfer for expressing antibodies is a promising strategy to combat deadly infectious diseases. Developing strategies to circumvent the immune response following rAAV administration in humans will facilitate clinical application.

Enhancing the utility of adeno-associated virus gene transfer through inducible tissue-specific expression

The ability to regulate both the timing and specificity of gene expression mediated by viral vectors will be important in maximizing its utility. We describe the development of an adeno-associated virus (AAV)-based vector with tissue-specific gene regulation, using the ARGENT dimerizer-inducible system. This two-vector system based on AAV serotype 9 consists of one vector encoding a combination of reporter genes from which expression is directed by a ubiquitous, inducible promoter and a second vector encoding transcription factor domains under the control of either a heart- or liver-specific promoter, which are activated with a small molecule. Administration of the vectors via either systemic or intrapericardial injection demonstrated that the vector system is capable of mediating gene expression that is tissue specific, regulatable, and reproducible over induction cycles. Somatic gene transfer in vivo is being considered in therapeutic applications, although its most substantial value will be in basic applications such as target validation and development of animal models.

Spatiotemporal control of vascular endothelial growth factor expression using a heat-shock-activated, rapamycin-dependent gene switch

A major challenge in regenerative medicine is to develop methods for delivering growth and differentiation factors in specific spatial and temporal patterns, thereby mimicking the natural processes of development and tissue repair. Heat shock (HS)-inducible gene expression systems can respond to spatial information provided by localized heating, but are by themselves incapable of sustained expression. Conversely, gene switches activated by small molecules provide tight temporal control and sustained expression, but lack mechanisms for spatial targeting. Here we combine the advantages of HS and ligand-activated systems by developing a novel rapamycin-regulated, HS-inducible gene switch that provides spatial and temporal control and sustained expression of transgenes such as firefly luciferase and vascular endothelial growth factor (VEGF). This gene circuit exhibits very low background in the uninduced state and can be repeatedly activated up to 1 month. Furthermore, dual regulation of VEGF induction in vivo is shown to stimulate localized vascularization, thereby providing a route for temporal and spatial control of angiogenesis.

Vector and helper genome rearrangements occur during production of helper-dependent adenoviral vectors

Helper-dependent adenoviral vectors (HD Ad) hold extreme promise for gene therapy of human diseases. All viral genes are deleted in HD Ad vectors, and therefore, the presence of a helper virus is required for their production. Current methods to minimize helper contamination in large-scale preparations rely on the use of the Cre/loxP system. The inclusion of loxP sites flanking the packaging signal results in its excision in the presence of Cre recombinase, preventing helper genome encapsidation. It is well established that the level of Cre recombinase activity is important in determining the degree of helper contamination. However, there is little information on other mechanisms that could also play an important role. We have generated several HD Ad vectors containing a rapalog-inducible system to regulate transgene expression, or LacZ under the control of the elongation factor 1 α promoter. Large-scale production of these vectors resulted in abundant helper contamination. Viral DNA analysis revealed the presence of rearrangements between vector and helper genomes. The rearrangements involved a helper DNA molecule with a fragment of the left arm of the HD Ad vector, including its ITR, packaging signal, and some stuffer sequence. Overall, our data suggest that helper DNA molecules that accumulate after Cre recombinase activity are prone to rearrangements, resulting in helper genomes that have incorporated a packaging signal from the vector. Helper particles with rearranged genomes have a growth advantage. This study identifies a novel mechanism leading to helper contamination during helper-dependent adenoviral vector production.

Long-term and stable correction of uremic anemia by intramuscular injection of plasmids containing hypoxia-regulated system of erythropoietin expression

Relative deficiency in production of glycoprotein hormone erythropoietin (Epo) is a major cause of renal anemia. This study planned to investigate whether the hypoxia-regulated system of Epo expression, constructed by fusing Epo gene to the chimeric phosphoglycerate kinase (PGK) hypoxia response elements (HRE) in combination with cytomegalovirus immediate-early (CMV IE) basal gene promoter and delivered by plasmid intramuscular injection, might provide a long-term physiologically regulated Epo secretion expression to correct the anemia in adenine-induced uremic rats. Plasmid vectors (pHRE-Epo) were synthesized by fusing human Epo cDNA to the HRE/CMV promoter. Hypoxia-inducible activity of this promoter was evaluated first in vitro and then in vivo in healthy and uremic rats (n = 30 per group). The vectors (pCMV-Epo) in which Epo expression was directed by a constitutive CMV gene promoter served as control. ANOVA and Student's t-test were used to analyze between-group differences. A high-level expression of Epo was induced by hypoxia in vitro and in vivo. Though both pHRE-Epo and pCMV-Epo corrected anemia, the hematocrit of the pCMV-Epo-treated rats exceeded the normal (P < 0.05), but that of the pHRE-Epo-treated rats didn't. Hypoxia-regulated system of Epo gene expression constructed by fusing Epo to the HRE/CMV promoter and delivered by plasmid intramuscular injection may provide a long-term and stable Epo expression and secretion in vivo to correct the anemia in adenine-induced uremic rats.

Dimerizer-mediated regulation of gene expression in vivo

Several systems have been developed that allow transcription of a target gene to be chemically controlled, usually by an allosteric modulator of transcription factor activity. An alternative is to use chemical inducers of dimerization, or "dimerizers," to reconstitute active transcription factors from inactive fusion proteins. The most widely used system employs the natural product rapamycin, or a biologically inert analog, as the dimerizing drug. A key feature of this system is the tightness of regulation, with basal expression usually undetectable and induced expression levels comparable to constitutive promoters. In our experiments, the use of the minimal interleukin-2 (IL-2) promoter is an important determinant of this; substitution of a minimal simian virus 40 (SV40) or cytomegalovirus (CMV) promoter results in significantly higher levels of basal expression. The key factor dictating the successful use of the system is achieving high expression levels of the activation domain fusion protein. In the context of clinical gene therapies, the system has the advantage of being built exclusively from human proteins, potentially minimizing immunogenicity in the clinical setting. The dimerizer system has been successfully incorporated into diverse vector backgrounds and has been used to achieve long-term regulated gene expression in vitro and in vivo. This protocol describes how to achieve rapamycin- or rapalog-inducible gene expression in vivo.

Allosteric activation of kinases: design and application of RapR kinases

Here we describe a method for the engineered regulation of protein kinases in living cells, the design and application of RapR (rapamycin regulated) kinases. The RapR kinase method enables activation of kinases with high specificity and precise temporal control. Insertion of an engineered allosteric switch, the iFKBP domain, at a structurally conserved position within the kinase catalytic domain makes the modified kinase inactive. Treatment with rapamycin or its non-immunosuppressive analogs triggers interaction with a small FKBP-rapamycin-binding domain (FRB), restoring the activity of the kinase. The reagents used in this method are genetically encoded or membrane permeable, enabling ready application in many systems. Based on the structural similarity of kinase catalytic domains, this method is likely applicable to a wide variety of kinases. Successful regulation has already been demonstrated for three kinases representing both tyrosine and serine/threonine kinase families (p38, FAK, Src). Procedures for designing and testing RapR kinases are discussed.

Improved function of the failing rat heart by regulated expression of insulin-like growth factor I via intramuscular gene transfer

Current methods of gene transfer for heart disease include injection into heart muscle or intracoronary coronary delivery, approaches that typically provide limited expression and are cumbersome to apply. To circumvent these problems, we selected a transgene, insulin-like growth factor-I (IGF-I), which may, in theory, have favorable effects on heart function when secreted from a remote site. We examined the feasibility and efficacy of skeletal muscle injection of adeno-associated virus 5 encoding IGF-I under Tet regulation (AAV5.IGFI-tet) to treat heart failure. Myocardial infarction (MI) was induced in rats by coronary occlusion; 1 week later, rats with impaired left ventricular (LV) function received 2×10(12) genome copies (GC) of AAV5.IGFI-tet in the anterior tibialis muscle, and 4 weeks later, were randomly assigned to receive doxycycline in drinking water to activate IGF-I expression (IGF-On; n=10), or not to receive doxycycline (IGF-Off; n=10). Ten weeks after MI (5 weeks after activation of IGF-I expression), LV size and function were assessed by echocardiography and physiological studies. IGF-On rats showed reduced LV end-systolic dimension (p=0.03) and increased LV ejection fraction (p=0.02). In addition, IGF-On rats showed, before and during dobutamine infusion, increases in cardiac output (p=0.02), stroke work (p=0.0001), LV + dP/dt (p<0.0001), LV relaxation (LV - dP/dt; p=0.03), and systolic arterial blood pressure (p=0.0003). Mean arterial pressure and systemic vascular resistance were unchanged. Activation of IGF-I expression reduced cardiac fibrosis (p=0.048), apoptosis (p<0.0001), and caspase-3/7 activity (p=0.04). Serum IGF-I was increased 5 weeks after transgene activation (p=0.008). These data indicate that skeletal muscle injection of AAV5.IGFI-tet enables tetracycline-activated expression, increases serum IGF-I levels, and improves function of the failing heart.

Assessment of the safety and biodistribution of a regulated AAV2 gene transfer vector after delivery to murine submandibular glands

Clinical gene transfer holds promise for the treatment of many inherited and acquired disorders. A key consideration for all clinical gene transfer applications is the tight control of transgene expression. We have examined the safety and biodistribution of a serotype 2, recombinant adeno-associated viral (AAV2) vector that encodes a rapamycin-responsive chimeric transcription factor, which regulates the expression of a therapeutic transgene (human erythropoietin [hEpo]). The vector, AAV2-TF2.3w-hEpo (2.5 × 10(7)-2.5 × 10(10) particles), was administered once to a single submandibular gland of male and female mice and mediated hEpo expression in vivo following a rapamycin injection but not in its absence. Control (saline treated) and vector-treated animals maintained their weight, and consumed food and water, similarly. Vector delivery led to no significant toxicological effects as judged by hematology, clinical chemistry, and gross and microscopic pathology evaluations. On day 3 after vector delivery, vector copies were not only abundant in the targeted right submandibular gland but also detected in multiple other tissues. Vector was cleared from the targeted gland much more rapidly in female mice than in male mice. Overall, our results are consistent with the notion that administration of the AAV2-TF2.3w-hEpo vector to salivary glands posed no significant risk in mice.

Vaccine protection against lethal homologous and heterologous challenge using recombinant AAV vectors expressing codon-optimized genes from pandemic swine origin influenza virus (SOIV)

The recent H1N1 influenza pandemic and the inevitable delay between identification of the virus and production of the specific vaccine have highlighted the urgent need for new generation influenza vaccines that can preemptively induce broad immunity to different strains of the virus. In this study we have produced AAV-based vectors expressing the A/Mexico/4603/2009 (H1N1) hemagglutinin (HA), nucleocapsid (NP) and the matrix protein M1 and have evaluated their ability to induce specific immune response and protect mice against homologous and heterologous challenge. Each of the vaccine vectors elicited potent cellular and humoral immune responses in mice. Although immunization with AAV-M1 did not improve survival after challenge with the homologous strain, immunization with the AAV-H1 and AAV-NP vectors resulted in survival of all mice, as did inoculation with a combination of all three vectors. Furthermore, trivalent vaccination also conferred partial protection against challenge with the highly heterologous and virulent A/PR/8/34 strain of H1N1 influenza.

Toward delivery of multiple growth factors in tissue engineering

Inspired by physiological events that accompany the "wound healing cascade", the concept of developing a tissue either in vitro or in vivo has led to the integration of a wide variety of growth factors (GFs) in tissue engineering strategies in an effort to mimic the natural microenvironments of tissue formation and repair. Localised delivery of exogenous GFs is believed to be therapeutically effective for replication of cellular components involved in tissue development and the healing process, thus making them important factors for tissue regeneration. However, any treatment aiming to mimic the critical aspects of the natural biological process should not be limited to the provision of a single GF, but rather should release multiple therapeutic agents at an optimised ratio, each at a physiological dose, in a specific spatiotemporal pattern. Despite several obstacles, delivery of more than one GF at rates mimicking an in vivo situation has promising potential for the clinical management of severely diseased tissues. This article summarises the concept of and early approaches toward the delivery of dual or multiple GFs, as well as current efforts to develop sophisticated delivery platforms for this ambitious purpose, with an emphasis on the application of biomaterials-based deployment technologies that allow for controlled spatial presentation and release kinetics of key biological cues. Additionally, the use of platelet-rich plasma or gene therapy is addressed as alternative, easy, cost-effective and controllable strategies for the release of high concentrations of multiple endogenous GFs, followed by an update of the current progress and future directions of research utilising release technologies in tissue engineering and regenerative medicine.

Characterization of the specific and sustained GH1 expression induced by rAAV2/1 in normal adult male rats

Our aim was to investigate the long-term effects of intramuscular injection of rAAV2/1-CMV-GH1 viral particles on GH1 expression in normal adult male rats. We found that specific and sustained GH1 expression did not improve muscle exercise performance despite inducing local muscle hypertrophy. Injection of rAAV2/1-CMV-GH1 had some systemic effects on the liver and heart and on lipid metabolism in the healthy rats. Serum levels of hGH (human growth hormone), insulin, glucose and leptin increased significantly, which might induce insulin resistance. The serum concentration of IGF-1 (insulin-like growth factor 1), IGF-BP3 (insulin-like growth factor binding protein 3) and PIIINP (N-terminal propeptide of type III procollagen) markedly increased at 24 weeks after injection of GH1. In conclusion, GH1 expression driven by AAV2/1 in normal animals did not improve muscle strength but did increase muscle mass and may have systemic effects in healthy animals.

A microarray gene analysis of peripheral whole blood in normal adult male rats after long-term GH gene therapy

The main aims of this study were to determine the effects of GH gene abuse/misuse in normal animals and to discover genes that could be used as candidate biomarkers for the detection of GH gene therapy abuse/misuse in humans. We determined the global gene expression profile of peripheral whole blood from normal adult male rats after long-term GH gene therapy using CapitalBio 27 K Rat Genome Oligo Arrays. Sixty one genes were found to be differentially expressed in GH gene-treated rats 24 weeks after receiving GH gene therapy, at a two-fold higher or lower level compared to the empty vector group (p < 0.05). These genes were mainly associated with angiogenesis, oncogenesis, apoptosis, immune networks, signaling pathways, general metabolism, type I diabetes mellitus, carbon fixation, cell adhesion molecules, and cytokine-cytokine receptor interaction. The results imply that exogenous GH gene expression in normal subjects is likely to induce cellular changes in the metabolism, signal pathways and immunity. A real-time qRT-PCR analysis of a selection of the genes confirmed the microarray data. Eight differently expressed genes were selected as candidate biomarkers from among these 61 genes. These 8 showed five-fold higher or lower expression levels after the GH gene transduction (p < 0.05). They were then validated in real-time PCR experiments using 15 single-treated blood samples and 10 control blood samples. In summary, we detected the gene expression profiles of rat peripheral whole blood after long-term GH gene therapy and screened eight genes as candidate biomarkers based on the microarray data. This will contribute to an increased mechanistic understanding of the effects of chronic GH gene therapy abuse/misuse in normal subjects.

PiggyBac transposon-based inducible gene expression in vivo after somatic cell gene transfer

Somatic cell gene transfer has permitted inducible gene expression in vivo through coinfection of multiple viruses. We hypothesized that the highly efficient plasmid-based piggyBac transposon system would enable long-term inducible gene expression in mice in vivo. We used a multiple-transposon delivery strategy to create a tetracycline-inducible expression system in vitro in human cells by delivering the two genes on separate transposons for inducible reporter gene expression along with a separate selectable transposon marker. Evaluation of stable cell lines revealed 100% of selected clones exhibited inducible expression via stable expression from three separate transposons simultaneously. We next tested and found that piggyBac-mediated gene transfer to liver or lung could achieve stable reporter gene expression in mice in vivo in either immunocompetent or immune deficient animals. A single injection of piggyBac transposons could achieve long-term inducible gene expression in the livers of mice in vivo, confirming our multiple-transposon strategy used in cultured cells. The plasmid-based piggyBac transposon system enables constitutive or inducible gene expression in vivo for potential therapeutic and biological applications without using viral vectors.

Drug-regulatable cancer cell death induced by BID under control of the tissue-specific, lung cancer-targeted TTS promoter system

Gene therapy and virotherapy are among the approaches currently being used to treat lung cancer. The success of cancer gene therapy depends on treatments where different types of tumors can be selectively targeted and destroyed without affecting normal cells and tissue. Previously, we described a promoter system (TTS) that we designed that is specifically targeted to lung cancer cells but which does not affect other types of cells including stem cells. In our study, we have enhanced the utility of the TTS system by inserting the pro-apoptotic gene BH3 domain interacting death agonist (Bid) into the TTS promoter system (TTS/Bid) to create a drug regulatable lung cancer-specific gene therapy. A recombinant adenoviral vector was used to introduce TTS/Bid (Ad-TTS/Bid) into lung cancer cells. BID expression and apoptosis occurred in A549 pulmonary adenocarcinoma cells but little Bid expression or apoptosis occurred in MCF7 breast cancer cells or in normal human lung fibroblasts. The use of cisplatin enhanced the processing of full length BID to t-BID which significantly increased lung cancer-specific cell death. In in vivo experiments, intraperitonal injection of cisplatin enhanced the antitumor effects of the vector in a lung cancer xeno-graft mouse model. Moreover, dexamethasone effectively suppressed exogenous BID expression and the antitumor effect of Ad-TTS/Bid both in vitro and in vivo. Here, we describe the efficacy of the use of cisplatin and dexamethasone with the anti lung cancer promoter system (Ad-TTS/Bid) for a safe and effective gene therapy against advanced lung cancer.

Partial rescue of growth failure in growth hormone (GH)-deficient mice by a single injection of a double-stranded adeno-associated viral vector expressing the GH gene driven by a muscle-specific regulatory cassette

Growth hormone (GH) deficiency (GHD) causes somatic growth impairment. GH has a short half-life and therefore it must be administered by daily subcutaneous injections. Adeno-associated viral (AAV) vectors have been used to deliver genes to animals, and double-stranded AAV (dsAAV) vectors provide widespread and stable transgene expression. In the present study we tested whether an intramuscular injection of dsAAV vector expressing GH under the control of a muscle creatine kinase regulatory cassette would ensure sufficient systemic GH delivery in conjunction with muscle-specific expression. Virus-injected GHD mice showed a significant (p < 0.05) increase in body length and body weight, without reaching full normalization, and significant (p < 0.05) reduction in absolute and relative visceral fat. Quantitative RT-PCR showed preferential GH expression in skeletal muscles that was confirmed by qualitative fluorescence analysis in mice injected with a similar virus expressing green fluorescent protein. The present study shows that systemic GH delivery to GHD animals is possible via a single intramuscular injection of dsAAV carrying a muscle-specific GH-expressing regulatory cassette.

Activated forms of VEGF-C and VEGF-D provide improved vascular function in skeletal muscle

The therapeutic potential of vascular endothelial growth factor (VEGF)-C and VEGF-D in skeletal muscle has been of considerable interest as these factors have both angiogenic and lymphangiogenic activities. Previous studies have mainly used adenoviral gene delivery for short-term expression of VEGF-C and VEGF-D in pig, rabbit, and mouse skeletal muscles. Here we have used the activated mature forms of VEGF-C and VEGF-D expressed via recombinant adeno-associated virus (rAAV), which provides stable, long-lasting transgene expression in various tissues including skeletal muscle. Mouse tibialis anterior muscle was transduced with rAAV encoding human or mouse VEGF-C or VEGF-D. Two weeks later, immunohistochemical analysis showed increased numbers of both blood and lymph vessels, and Doppler ultrasound analysis indicated increased blood vessel perfusion. The lymphatic vessels further increased at the 4-week time point were functional, as shown by FITC-lectin uptake and transport. Furthermore, receptor activation and arteriogenic activity were increased by an alanine substitution mutant of human VEGF-C (C137A) having an increased dimer stability and by a chimeric CAC growth factor that contained the VEGF receptor-binding domain flanked by VEGF-C propeptides, but only the latter promoted significantly more blood vessel perfusion when compared to the other growth factors studied. We conclude that long-term expression of VEGF-C and VEGF-D in skeletal muscle results in the generation of new functional blood and lymphatic vessels. The therapeutic value of intramuscular lymph vessels in draining tissue edema and lymphedema can now be evaluated using this model system.

Quorum-Sensing-Based Toolbox for Regulatable Transgene and siRNA Expression in Mammalian Cells

Technologies for regulated expression of multiple transgenes in mammalian cells have gathered momentum for bioengineering, gene therapy, drug discovery, and gene-function analyses. Capitalizing on recently developed mammalian transgene modalities (QuoRex) derived from Streptomyces coelicolor, we have designed a flexible and highly compatible expression vector set that enables desired transgene/siRNA control in response to the nontoxic butyrolactone SCB1. The construction-kit-like expression portfolio includes (i) multicistronic (pTRIDENT), (ii) autoregulated, (iii) bidirectional (pBiRex), (iv) oncoretro- and lentiviral transduction, and (v) RNA polymerase II-based siRNA transcription-fine-tuning vectors for straightforward implementation of QuoRex-controlled (trans)gene modulation in mammalian cells.

Adenovirus-mediated delivery of relaxin reverses cardiac fibrosis

We have evaluated the effectiveness of systemic adenovirally delivered mouse relaxin on reversing fibrosis in a transgenic murine model of fibrotic cardiomyopathy due to beta(2)-adrenergic receptor (beta(2)AR) overexpression. Recombinant adenoviruses expressing green fluorescent protein (Ad-GFP), rat relaxin (Ad-rRLN) and mouse relaxin (Ad-mRLN) were generated and Ad-rRLN and Ad-mRLN were demonstrated to direct the expression of bioactive relaxin peptides in vitro. A single systemic injection of Ad-mRLN resulted in transgene expression in the liver and bioactive relaxin peptide in the plasma. Ad-mRLN, but not Ad-GFP, treatment reversed the increased left ventricular collagen content in beta(2)AR mice to control levels without affecting collagen levels in other heart chambers or in the lung and kidney. Hence a single systemic injection of adenovirus producing mouse relaxin reverses cardiac fibrosis without adversely affecting normal collagen levels in other organs and establishes the potential for the use of relaxin gene therapy for the treatment of cardiac fibrosis.

Potential Use of Gene Transfer in Athletic Performance Enhancement

After only a short history of three decades from concept to practice, gene therapy has recently been shown to have potential to treat serious human diseases. Despite this success, gene therapy remains in the realm of experimental medicine, and much additional preclinical and clinical study will be necessary for proving the efficacy and safety of this approach in the treatment of diseases in humans. However, a potential complicating factor is that advances in gene transfer technology could be misused to enhance athletic performance in sports, in a practice termed "gene doping". Moreover, gene doping could be a precursor to a broader controversial agenda of human "genetic enhancement" with the potential for a significant long-term impact on society. This review addresses the possible ways in which knowledge and experience gained in gene therapy in animals and humans may be abused for enhancing sporting prowess. We provide an overview of recent progress in gene therapy, with potential application to gene doping and with the major focus on candidate performance-enhancement genes. We also discuss the current status of preclinical studies and of clinical trials that use these genes for therapeutic purposes. Current knowledge about the association between the natural "genetic make-up" of humans and their physical characteristics and performance potential is also presented. We address issues associated with the safety of gene transfer technologies in humans, especially when used outside a strictly controlled clinical setting, and the obstacles to translating gene transfer strategies from animal studies to humans. We also address the need for development and implementation of measures to prevent abuse of gene transfer technologies, and to pursue research on strategies for its detection in order to discourage this malpractice among athletes.

Vitamin H-regulated transgene expression in mammalian cells

Although adjustable transgene expression systems are considered essential for future therapeutic and biopharmaceutical manufacturing applications, the currently available transcription control modalities all require side-effect-prone inducers such as immunosupressants, hormones and antibiotics for fine-tuning. We have designed a novel mammalian transcription-control system, which is reversibly fine-tuned by non-toxic vitamin H (also referred to as biotin). Ligation of vitamin H, by engineered Escherichia coli biotin ligase (BirA), to a synthetic biotinylation signal fused to the tetracycline-dependent transactivator (tTA), enables heterodimerization of tTA to a streptavidin-linked transrepressor domain (KRAB), thereby abolishing tTA-mediated transactivation of specific target promoters. As heterodimerization of tTA to KRAB is ultimately conditional upon the presence of vitamin H, the system is vitamin H responsive. Transgenic Chinese hamster ovary cells, engineered for vitamin H-responsive gene expression, showed high-level, adjustable and reversible production of a human model glycoprotein in bench-scale culture systems, bioreactor-based biopharmaceutical manufacturing scenarios, and after implantation into mice. The vitamin H-responsive expression systems showed unique band pass filter-like regulation features characterized by high-level expression at low (0–2 nM biotin), maximum repression at intermediate (100–1000 nM biotin), and high-level expression at increased (>100 000 nM biotin) biotin concentrations. Sequential ON-to-OFF-to-ON, ON-to-OFF and OFF-to-ON expression profiles with graded expression transitions can all be achieved by simply increasing the level of a single inducer molecule without exchanging the culture medium. These novel expression characteristics mediated by an FDA-licensed inducer may foster advances in therapeutic cell engineering and manufacturing of difficult-to-produce protein therapeutics.

Long-term suppression of experimental arthritis following intramuscular administration of a pseudotyped AAV2/1-TNFR:Fc Vector

We previously reported that administration of an adeno-associated virus 2 (AAV2) vector encoding a rat tumor necrosis factor (TNF) receptor-immunoglobulin Fc (TNFR:Fc) fusion gene to rats with streptococcal cell wall-induced arthritis resulted in suppression of joint inflammation and cartilage and bone destruction, as well as expression of joint proinflammatory cytokines. In this study, we used an alternate rat model of arthritis to compare the serum levels and duration of TNFR:Fc protein expression following intramuscular administration of pseudotyped AAV-TNFR:Fc vectors based on serotypes 1, 2, and 5. All three pseudotyped AAV-TNFR:Fc vectors led to sustained expression of serum TNFR:Fc protein for at least one year. Serum TNFR:Fc protein levels in rats administered intramuscularly with AAV2/1-TNFR:Fc vector were up to 100- and 10-fold higher than in rats administered the AAV2-TNFR:Fc or AAV2/5-TNFR:Fc vectors, respectively. A single intramuscular administration of AAV2/1-TNFR:Fc vector at vector doses ranging from 10(10) to 10(12) DNase-resistant particles (DRP) per animal, resulted in complete and long-term suppression of recurrent joint inflammation for at least 150 days. Our results establish a proof of concept for administration of an AAV2/1-TNFR:Fc vector to the muscle to achieve long-term, sustained and therapeutically relevant levels of TNFR:Fc protein to treat chronic systemic inflammatory joint diseases.

An antibody delivery system for regulated expression of therapeutic levels of monoclonal antibodies in vivo

Monoclonal antibody (mAb) delivery by gene transfer in vivo may be an attractive alternative to current mAb therapies for applications that require long-term therapy. This article describes a transfer system that allows inducible high-level expression of unmodified mAbs in vivo. A recombinant adeno-associated viral (rAAV) vector is used that comprises an expression cassette consisting of a dimerizer-regulated promoter that drives expression of the antibody heavy and light chains linked by a 2A self-processing peptide and a furin cleavage site. Following intravenous injection of the rAAV vector, serum mAb levels >1 mg/ml were attained by administration of the inducer, rapamycin. Antibody expression could be rapidly shut off by discontinuing treatment with rapamycin. By optimizing the furin cleavage sequence, this system generated native antibody in vivo, decreasing the likelihood of a host immune response to foreign sequences. In summary, this optimized mAb expression system allows regulated high-level expression of native full-length mAbs in vivo and may offer a new opportunity for delivery of therapeutic mAbs in the clinic.

Viral vectors: a wide range of choices and high levels of service

Viruses are intracellular parasites with simple DNA or RNA genomes. Virus life revolves around three steps: infection of a host cell, replication of its genome within the host cell environment, and formation of new virions; this process is often but not always associated with pathogenic effects against the host organism. Since the mid-1980s, the main goal of viral vectorology has been to develop recombinant viral vectors for long-term gene delivery to mammalian cells, with minimal associated toxicity. Today, several viral vector systems are close to achieving this aim, providing stable transgenic expression in many different cell types and tissues. Here we review application characteristics of four vector systems, derived from adeno-associated viruses, adenoviruses, retroviruses and herpes simplex virus-1, for in vivo gene delivery. We discuss the transfer capacity of the expression vectors, the stability of their transgenic expression, the tropism of the recombinant viruses, the likelihood of induction of immunotoxicity, and the ease (or difficulty) of the virus production. In the end, we discuss applications of these vectors for delivery of three molecular systems for conditional mutagenesis, two for inducible transcriptional control of transgenic expression (the tet and the dimerizer systems), and the third one for inducible control of endogenous gene expression based on RNA interference.

Rapamycin-regulated control of antiangiogenic tumor therapy following rAAV-mediated gene transfer

Regulated gene expression may be required for the clinical development of certain gene therapies. Several approaches have been developed that allow pharmacologic control of transgene expression, including the dimerizer-regulated transcriptional system in which rapamycin or its analogs function as transcriptional inducers. These compounds can also act as direct antitumor agents via inhibition of mammalian target of rapamycin (mTOR). We describe the development of an optimized recombinant adeno-associated virus (AAV) expression cassette that allows dimerizer-regulated gene expression from a single vector in vitro and in vivo. After demonstrating multiple cycles of rapamycin-dependent transgene induction following a single administration of an AAV vector in vivo, application of this regulated AAV gene expression system to the pharmacologic control of antiangiogenic therapy was evaluated in preclinical tumor models. Dimerizer-regulated vectors were constructed encoding a soluble inhibitor of the vascular endothelial growth factor (VEGF) pathway. In two subcutaneous models of glioblastoma, regulated expression of the VEGF inhibitor via recombinant AAV-mediated gene transfer, in combination with rapamycin, was shown to decrease tumor growth rate significantly. The dual properties of rapamycin--as a transcriptional inducer and mTOR inhibitor--are exploited in combination with an AAV-encoded antiangiogenic agent to provide a novel approach for the treatment of malignant diseases.

A time- and dose-dependent STAT1 expression system

Background

The signal transducer and activator of transcription (STAT) family of transcription factors mediates a variety of cytokine dependent gene regulations. STAT1 has been mainly characterized by its role in interferon (IFN) type I and II signaling and STAT1 deficiency leads to high susceptibility to several pathogens. For fine-tuned analysis of STAT1 function we established a dimerizer-inducible system for STAT1 expression in vitro and in vivo.

Results

The functionality of the dimerizer-induced STAT1 system is demonstrated in vitro in mouse embryonic fibroblasts and embryonic stem cells. We show that this two-vector based system is highly inducible and does not show any STAT1 expression in the absence of the inducer. Reconstitution of STAT1 deficient cells with inducible STAT1 restores IFNγ-mediated gene induction, antiviral responses and STAT1 activation remains dependent on cytokine stimulation. STAT1 expression is induced rapidly upon addition of dimerizer and expression levels can be regulated in a dose-dependent manner. Furthermore we show that in transgenic mice STAT1 can be induced upon stimulation with the dimerizer, although only at low levels.

Conclusion

These results prove that the dimerizer-induced system is a powerful tool for STAT1 analysis in vitro and provide evidence that the system is suitable for the use in transgenic mice. To our knowledge this is the first report for inducible STAT1 expression in a time- and dose-dependent manner.

Bioluminescence imaging after HSV amplicon vector delivery into brain

BACKGROUND

Firefly luciferase (Fluc) has routinely been used to quantitate and analyze gene expression in vitro by measuring the photons emitted after the addition of ATP and luciferin to a test sample. It is now possible to replace luminometer-based analysis of luciferase activity and measure luciferase activity delivered by viral vectors directly in live animals over time using digital imaging techniques.

METHODS

An HSV amplicon vector expressing Fluc cDNA from an inducible promoter was delivered to cells in culture and into the mouse brain. In culture, expression of Fluc was measured after induction in a dose-dependent manner by a biochemical assay, and then confirmed by Western blot analysis and digital imaging. The vectors were then stereotactically injected into the mouse brain and Fluc expression measured non-invasively using bioluminescence imaging.

RESULTS

Rapamycin-mediated induction of Fluc from an HSV amplicon vector in culture resulted in dose-dependent expression of Fluc when measured using a luminometer and by digital analysis. In mouse cortex, a single injection of an HSV amplicon vector (2 microl, 1x10(8) transducing units (t.u.)/ml) expressing Fluc from a viral promoter (CMV) was sufficient to detect robust luciferase activity for at least 1 week. Similarly, an HSV amplicon vector expressing Fluc under an inducible promoter was also detectable in the mouse cortex after a single dose (2 microl, 1x10(8) t.u./ml) for up to 5 days, with no detectable signal in the uninduced state.

CONCLUSIONS

This HSV amplicon vector-based system allows for fast, non-invasive, semi-quantitative analysis of gene expression in the brain.

Intraperitoneal gene therapy by rAAV provides long-term survival against epithelial ovarian cancer independently of survivin pathway

Epithelial ovarian carcinoma is the leading cause of death from gynecological malignancies. Owing to the lack of an effective screening method, insidious onset, and non-specific symptoms, a majority of women present with advanced stage disease. Despite improvements from cytoreductive surgery and chemotherapy, recurrent disease remains a formidable challenge. In the present study, we demonstrate for the first time that stable intra-abdominal genetic transfer of endostatin and angiostatin (E+A) by recombinant adeno-associated virus (rAAV) provides sustained antitumor effects on the growth and dissemination of epithelial ovarian cancer in a mouse model. Further, when combined with paclitaxel (taxol), the effect of this therapy was dramatically increased and resulted in long-term tumor-free survival overcoming prior limitations of chemotherapy and gene therapy. The combined effects of angiosuppressive therapy and chemotherapy were found to be independently of survivin pathway. Evidence for the superior effects of the combination therapy was indicated by significantly lower ascites volume with less hemorrhage and tumor conglomerates, lower ascites vascular endothelial growth factor, higher tumor cell apoptosis and decreased blood vasculature, and long-term disease-free survival. Histopathology of visceral organs and liver enzyme assays indicated no toxicity or pathology.

Use of a stringent dimerizer-regulated gene expression system for controlled BMP2 delivery

Gene therapy using constitutively active viral promoters to drive expression of bone morphogenetic proteins (BMPs) has been extensively evaluated as a strategy for inducing bone regeneration. However, this approach offers little control over the concentration, timing, or duration of BMP synthesis. To gain greater control over BMP kinetics, we developed a new inducible system for the controlled expression of BMP2 using a two-component transcription factor that is dimerized with rapamycin (Rap). This approach provided stringent control over BMP2 synthesis with no BMP expression detected in the uninduced state. Rapamycin or the less immunosuppressive analogue, AP21967, rapidly and reversibly induced BMP2 in a dose-dependent manner (range 0.1-10 nM). Subcutaneous implants of fibroblasts containing the Rap-inducible system in syngeneic C57BL/6 mice were highly responsive to ip Rap injection (0.1-1 mg/kg). Peak BMP2 levels were detected within 24 h of a single Rap injection and declined to undetectable levels after 8-10 days. Alternate-day Rap injections (1 mg/kg) for 6 weeks induced subcutaneous ectopic bone formation. Rap-dependent healing of a critical-sized cranial defect was also achieved using this system. This regulated BMP2 expression system will be extremely useful for examining the role of timing and sequence of BMP delivery on bone regeneration.