Ligand-dependent regulation of vascular endothelial growth factor and erythropoietin expression by a plasmid-based autoinducible GeneSwitch system

An Adapted GeneSwitch Toolkit for Comparable Cellular and Animal Models: A Proof of Concept in Modeling Charcot-Marie-Tooth Neuropathy

Investigating the impact of disease-causing mutations, their affected pathways, and/or potential therapeutic strategies using disease modeling often requires the generation of different in vivo and in cellulo models. To date, several approaches have been established to induce transgene expression in a controlled manner in different model systems. Several rounds of subcloning are, however, required, depending on the model organism used, thus bringing labor-intensive experiments into the technical approach and analysis comparison. The GeneSwitch™ technology is an adapted version of the classical UAS-GAL4 inducible system, allowing the spatial and temporal modulation of transgene expression. It consists of three components: a plasmid encoding for the chimeric regulatory pSwitch protein, Mifepristone as an inducer, and an inducible plasmid. While the pSwitch-containing first plasmid can be used both in vivo and in cellulo, the inducible second plasmid can only be used in cellulo. This requires a specific subcloning strategy of the inducible plasmid tailored to the model organism used. To avoid this step and unify gene expression in the transgenic models generated, we replaced the backbone vector with standard pUAS-attB plasmid for both plasmids containing either the chimeric GeneSwitch™ cDNA sequence or the transgene cDNA sequence. We optimized this adapted system to regulate transgene expression in several mammalian cell lines. Moreover, we took advantage of this new system to generate unified cellular and fruit fly models for YARS1-induced Charco-Marie-Tooth neuropathy (CMT). These new models displayed the expected CMT-like phenotypes. In the N2a neuroblastoma cells expressing YARS1 transgenes, we observed the typical "teardrop" distribution of the synthetase that was perturbed when expressing the YARS1CMT mutation. In flies, the ubiquitous expression of YARS1CMT induced dose-dependent developmental lethality and pan-neuronal expression caused locomotor deficit, while expression of the wild-type allele was harmless. Our proof-of-concept disease modeling studies support the efficacy of the adapted transgenesis system as a powerful tool allowing the design of studies with optimal data comparability.

Adaptation of vectors and drug-inducible systems for controlled expression of transgenes in the tumor microenvironment

Biological therapies based on recombinant proteins such as antibodies or cytokines are continuously improving the repertoire of treatments against cancer. However, safety and efficacy of this approach is often limited by inappropriate biodistribution and pharmacokinetics of the proteins when they are administered systemically. Local administration of gene therapy vectors encoding these proteins would be a feasible alternative if they could mediate long-term and controlled expression of the transgene after a single intratumoral administration. We describe a new vector platform specially designed for this purpose. Different combinations of transactivators and promoters were evaluated to obtain a fully humanized inducible system responsive to the well-characterized drug mifepristone. The optimal transactivator conformation was based on DNA binding domains from the chimeric protein ZFHD1 fused to the progesterone receptor ligand binding domain and the NFkb p65 activation domain. The expression of this hybrid transactivator under the control of the elongation factor 1α (EF1α) or the chimeric CAG promoters ensured functionality of the system in a variety of cancer types. Expression cassettes with luciferase as a reporter gene were incorporated into High-Capacity adenoviral vectors (HC-Ad) for in vivo evaluation. Systemic administration of the vectors into C57BL/6 mice revealed that the vector based on the EF1α promoter (HCA-EF-ZP) allows tight control of transgene expression and remains stable for at least two months, whereas the CAG promoter suffers a progressive inactivation. Using an orthotopic pancreatic cancer model in syngeneic C57BL/6 mice we show that the local administration of HCA-EF-ZP achieves better tumor/liver ratio of luciferase production than the intravenous route. However, regional spread of the vector led to substantial transgene expression in peritoneal organs. We reduced this leakage through genetic modification of the vector capsid to display RGD and poly-lysine motifs in the fiber knob. Safety and antitumor effect of this gene therapy platform was demonstrated using interleukin-12 as a therapeutic gene. In conclusion, we have developed a new tool that allows local, sustained and controlled production of therapeutic proteins in tumors.

A light-switchable bidirectional expression module allowing simultaneous regulation of multiple genes

Several light-regulated genetic circuits have been applied to spatiotemporally control transgene expression in mammalian cells. However, simultaneous regulation of multiple genes using one genetic device by light has not yet been reported. In this study, we engineered a bidirectional expression module based on LightOn system. Our data showed that both reporter genes could be regulated at defined and quantitative levels. Simultaneous regulation of four genes was further achieved in cultured cells and mice. Additionally, we successfully utilized the bidirectional expression module to monitor the expression of a suicide gene, showing potential for photodynamic gene therapy. Collectively, we provide a robust and useful tool to simultaneously control multiple genes expression by light, which will be widely used in biomedical research and biotechnology.

A novel approach for addressing diseases not yielding to effective vaccination? Immunization by replication-competent controlled virus

Vaccination involves inoculation of a subject with a disabled disease-causing microbe or parts thereof. While vaccination has been highly successful, we still lack sufficiently effective vaccines for important infectious diseases. We propose that a more complete immune response than that elicited from a vaccine may be obtained from immunization with a disease-causing virus modified to subject replication-essential genes to the control of a gene switch activated by non-lethal heat in the presence of a drug-like compound. Upon inoculation, strictly localized replication of the virus would be triggered by a heat dose administered to the inoculation site. Activated virus would transiently replicate with an efficiency approaching that of the disease-causing virus and express all viral antigens. It may also vector heterologous antigens or control co-infecting microbes.

Drug insight: selective agonists and antagonists of the glucocorticoid receptor

Glucocorticoid hormones exert a wide spectrum of metabolic and immunological effects. They function through the glucocorticoid receptor, a member of the nuclear receptor superfamily. Glucocorticoids are particularly effective as anti-inflammatory agents but often cause severe side effects. The structure of the ligand-binding domain of the glucocorticoid receptor has now been elucidated, and a series of studies have shown that even subtle changes to the ligand structure alter the final conformation of the ligand-receptor complex, with consequences for both protein recruitment and the function of the receptor. This has led to concerted efforts to find selective ligands for the glucocorticoid receptor that preserve the beneficial anti-inflammatory activity but reduce the side-effect profile. The direct health-care benefits of such a simple, safe, orally active agent targeting the underlying inflammatory process in, for example, rheumatoid arthritis would be considerable in terms of reduced patient suffering; furthermore, the indirect benefits in terms of reducing the costs of therapeutic delivery and preventing loss of productivity would be even greater.

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.

Development and Validation of a Robust and Versatile One-plasmid Regulated Gene Expression System

We have developed a one-plasmid regulated gene expression system, pBRES, based on a mifepristone (MFP)-inducible two-plasmid system. The various expression elements of the pBRES system (promoters, 5' and 3' untranslated regions (UTRs), introns, target gene, and polyA sequences) are bounded by restriction enzyme sites so that each module can be conveniently replaced by alternate DNA elements in order to tailor the system for particular tissues, organs, or conditions. There are four possible orientations of the two expression units relative to each other, and insertion of a variety of expression elements and target genes into the four different orientations revealed orientation- and gene-dependent effects on induced and uninduced levels of gene expression. Induced target gene expression from the pBRES system was shown to be comparable to the two-plasmid system and higher than the expression from the cytomegalovirus (CMV) promoter in vivo, while maintaining low uninduced levels of expression. Finally, a pBRES expression cassette was transferred to an adeno-associated virus (AAV) vector and shown to be capable of regulated gene expression in vivo for nearly 1 year.

A selective cellular screening assay for B-Raf and c-Raf kinases

The Ras/Raf signaling pathway has been recognized as an important process in cancer biology. Recently, activating mutations in the BRAF gene were reported to be present in approximately 66% of malignant melanomas as well as other malignancies such as colon cancer. Here, the authors report the development of a B-Raf-specific cellular assay to profile cell-active B-Raf inhibitors. Expression of the active B-Raf mutant (V600E) and the kinase-inactive form of its substrate, MEK1, was regulated by mifepristone, and the catalytic activity of B-Raf was monitored by following MEK1 phosphorylation. Target specificity was ensured because the phosphorylation of MEK1 was significantly inhibited when kinase-inactive B-Raf was used in place of the active kinase. A cellular c-Raf assay was similarly established to monitor the selectivity between B-Raf and c-Raf. Z' factor values were consistently above 0.50 with either kinase, indicating that assay performance was sufficiently robust for use as cellular profiling assays. The authors used this system to demonstrate that the selectivity profile of compounds targeted against B-Raf and c-Raf kinases could be quantitatively determined. This platform provides a quantitative cellular readout for a spectrum of specific inhibitors of B-Raf and c-Raf kinases that is particularly suitable for use in drug discovery.

Novel gene switches

Controlling gene activity in space and time represents a cornerstone technology in gene and cell therapeutic applications, bioengineering, drug discovery as well as fundamental and applied research. This chapter provides a comprehensive overview of the different approaches for regulating gene activity and product protein formation at different biosynthetic levels, from genomic rearrangements over transcription and translation control to strategies for engineering inducible secretion and protein activity with a focus on the development during the past 2 years. Recent advances in designing second-generation gene switches, based on novel inducer administration routes (gas phase) as well as on the combination of heterologous switches with endogenous signals, will be complemented by an overview of the emerging field of mammalian synthetic biology, which enables the design of complex synthetic and semisynthetic gene networks. This article will conclude with an overview of how the different gene switches have been applied in gene therapy studies, bioengineering and drug discovery.

Modelling the glucocorticoid receptor and producing therapeutic agents with anti-inflammatory effects but reduced side-effects

Glucocorticoid hormones exert a wide spectrum of metabolic and immunological effects. They are synthesized from a cholesterol precursor and are structurally related to the other steroid hormones, progesterone, aldosterone and oestrogen. They act through the glucocorticoid receptor (GR), a member of the nuclear receptor superfamily. The GR is an intracellular receptor; the hydrophobic ligand accesses its receptor by diffusion across the plasma membrane. The ligand-activated GR translocates to the nucleus to regulate expression of its target genes. The GR, in common with the rest of the receptor family, can be functionally divided into an N-terminal transcription activation domain, a central DNA binding domain and a C-terminal ligand binding domain, which also includes a second transactivation domain. Although synthetic glucocorticoids are the most potent anti-inflammatory agents known, their use is limited owing to the range and severity of their side-effects. The structure of the ligand binding domain of the glucocorticoid receptor has now been solved, and a series of studies has shown that even subtle changes to the ligand structure alter the final conformation of the ligand-receptor complex, with consequences for further protein recruitment and for the function of the receptor. This, coupled with the successful development of selective oestrogen receptor agonists, has led to concerted efforts to find selective GR ligands, with preserved beneficial anti-inflammatory activity, but reduced side-effect profile. Current efforts have identified several useful tool compounds, and further molecules are in development in several pharmaceutical companies.

Glucocorticoid sensitivity: pathology, mutations and clinical implications

Glucocorticoids exert diverse effects on virtually all cell types and tissues. Subtle changes in sensitivity may be generalized and congenital or acquired in a tissue-specific manner. Such changes may lead to altered susceptibility to metabolic diseases, such as ischemic heart disease, or to insensitivity to the therapeutic actions of synthetic glucocorticoids such as in inflammatory disease. This review will cover current theories of how glucocorticoids exert genetic and other congenital effects on glucocorticoid sensitivity, and acquired changes in glucocorticoid sensitivity seen principally in inflammatory and malignant disease. Recent important developments in the field include the impact of genetic variation within the glucocorticoid receptor gene, the effects of early life experience on long-term glucocorticoid sensitivity, studies identifying the role of nuclear factor κB in modulating glucocorticoid sensitivity in vitro and in vivo, and the action of macrophage migration inhibitory factor in modulating the anti-inflammatory effects of glucocorticoids. The role of chromatin organization in regulating glucocorticoid action on proinflammatory genes is discussed, as is the regulation of glucocorticoid sensitivity in human malignancy in the context of pathogenesis and treatment response.

Erythropoietin abuse and erythropoietin gene doping: detection strategies in the genomic era

The administration of recombinant human erythropoietin (rhEPO) increases the maximum oxygen consumption capacity, and is therefore abused as a doping method in endurance sports. The detection of erythropoietin (EPO) abuse is based on direct pharmacological and indirect haematological approaches, both of which have several limitations. In addition, current detection methods cannot cope with the emerging doping strategies of EPO mimicry, analogues and gene doping, and thus novel detection strategies are urgently needed. Direct detection methods for EPO misuse can be either pharmacological approaches that identify exogenous substances based on their physicochemical properties, or molecular methods that recognise EPO transgenes or gene transfer vectors. Since direct detection with molecular methods requires invasive procedures, it is not appropriate for routine screening of large numbers of athletes. In contrast, novel indirect methods based on haematological and/or molecular profiling could be better suited as screening tools, and athletes who are suspect of doping would then be submitted to direct pharmacological and molecular tests. This article reviews the current state of the EPO doping field, discusses available detection methods and their shortcomings, outlines emerging pharmaceutical and genetic technologies in EPO misuse, and proposes potential directions for the development of novel detection strategies.

Therapy of cancer by cytokines mediated by gene therapy approach

Gene therapy offers a new approach for treatment of cancer. Transfer of genes encoding immunostimulatory cytokines has been used with remarkable success to eliminate cancer in animals. However, clinical trials in patients with this strategy had limited efficacy. Therefore, improvement of gene transfer vector system is necessary. A hybrid viral vector, consisting of SFV replicon with either murine IL-12 or reporter LacZ gene, was constructed. This hybrid vector showed specificity and high level of expression in HCC both in vitro and in vivo. In a rat orthotropic liver tumor model, treatment of established tumors by the hybrid vector with mIL-12 gene resulted in a strong anti-tumor activity without accompanying toxicity. Subsequently, a helper-dependent adenovirus vectors containing a mifepristone (RU486) inducible system was constructed for controlled and liver-specific expression of human interleukin 12 (hIL-12) (HD-Ad/RUhIL-12) and mouse IL-12 (mIL-12) (HD-Ad/RUmIL-12). Data showed that high and sustained serum levels of hIL-12 could be attained by continuing administration of RU486 every 12 or 24 h. Repetitive induction of hIL-12 could be obtained over, at least, a period of 48 weeks after a single injection of HD-Ad/RUhIL-12. Treatment of liver metastases with of HD-Ad/RUmIL-12 plus RU846 resulted in complete tumor regression in all animals. Then, different cytokine genes were inserted into conditional replicative adenoviruses vectors (also called oncolytic adenovirus). Replication of adenovirus in tumor cells would kill tumor cells and release viruses, which infect surrounding tumor cells. The combination of cytopathic effect by oncolytic adenovirus and biological effect of transgene would exert strong antitumor activity. These new types of vectors may provide a potent and safe tool for cancer gene therapy.

Pharmacologic transgene control systems for gene therapy

Pharmacologic transgene-expression dosing is considered essential for future gene therapy scenarios. Genetic interventions require precise transcription or translation fine-tuning of therapeutic transgenes to enable their titration into the therapeutic window, to adapt them to daily changing dosing regimes of the patient, to integrate them seamlessly into the patient's transcriptome orchestra, and to terminate their expression after successful therapy. In recent years, decisive progress has been achieved in designing high-precision trigger-inducible mammalian transgene control modalities responsive to clinically licensed and inert heterologous molecules or to endogenous physiologic signals. Availability of a portfolio of compatible transcription control systems has enabled assembly of higher-order control circuitries providing simultaneous or independent control of several transgenes and the design of (semi-)synthetic gene networks, which emulate digital expression switches, regulatory transcription cascades, epigenetic expression imprinting, and cellular transcription memories. This review provides an overview of cutting-edge developments in transgene control systems, of the design of synthetic gene networks, and of the delivery of such systems for the prototype treatment of prominent human disease phenotypes.

Regulatable atrial natriuretic peptide gene therapy for hypertension

Hypertension (HTN) is a disease that begins with dysfunctional renal-sodium excretion and progresses to a syndrome of highly elevated systolic, diastolic, and mean arterial pressures. Inadequacies in the therapy of HTN have led to the investigation of the gene therapy of this disease by using systemic overproduction of vasodilatory peptides, such as atrial natriuretic peptide (ANP). However, gene-therapy approaches to HTN using ANP are limited by the need for long-term ANP gene expression and, most important, control of ANP gene expression. Here, we introduce a helper-dependent adenoviral vector carrying the mifepristone (Mfp)-inducible gene-regulatory system to control in vivo ANP expression. In the BPH/2 mouse model of HTN, Mfp-inducible ANP expression was seen for a period of >120 days after administration of vector. Physiological effects of ANP, including decreased systolic blood pressure, increased urinary cGMP output, and decreases in heart weight as a percentage of body weight were also under the control of Mfp. Given these capabilities, this vector represents a paradigm for the gene therapy of HTN.

Growth hormone releasing hormone plasmid supplementation, a potential treatment for cancer cachexia, does not increase tumor growth in nude mice

Growth hormone releasing hormone (GHRH) is known to have multiple anabolic effects and immune-stimulatory effects. Previous studies suggest that treatment with anabolic hormones also has the potential to mitigate the deleterious effects of cancer cachexia in animals. We studied the effects of plasmid-mediated GHRH supplementation on tumor growth and the role of antitumor immune cells with two different human tumor cell lines, NCI-H358 human bronchioalveolar carcinoma and MDA-MB-468 human breast adenocarcinoma, subcutaneously implanted in nude mice. GHRH supplementation by delivery of human GHRH from a muscle-specific GHRH expression plasmid did not increase tumor progression in tumor-bearing nude mice. Male animals implanted with the NCI-H358 tumor cell line and treated with the GHRH-expressing plasmid exhibited a 40% decrease in the size of the tumors (P<.02), a 48% increase in white blood cells (P<.025) and a 300% increase in monocyte count (P<.0001), as well as an increase in the frequency of activated CD3+ and CD4+ cells in the tumors, compared to tumors of control animals. No adverse effects were observed in animals that received the GHRH-plasmid treatment. The present study shows that physiological stimulation of the GHRH-GH-IGF-I axis in mice with cancer does not promote tumor growth and may provide a viable treatment for cancer cachexia in humans.

Stringent rosiglitazone-dependent gene switch in muscle cells without effect on myogenic differentiation

We have developed a gene switch based on the human transcription factor peroxisome proliferator-activated receptor gamma (PPARgamma) and its activation by rosiglitazone. However, ectopic expression of PPARgamma has been demonstrated to convert myogenic cells into adipocyte-like cells and, more generally, may interfere with the physiology of the target tissue. Consequently we modified the DNA-binding specificity of PPARgamma, resulting in a transcription factor that we named PPAR*. We demonstrated by histological and molecular assessment of cell phenotype that the overexpression of PPAR* did not alter the myogenic differentiation program of G8 myoblasts. We showed that PPAR* does not transactivate promoters containing PPARgamma-responsive elements but transactivates promoters containing PPAR*-responsive elements that are at least 80% identical to a 20-bp consensus. We improved the rosiglitazone-dependent gene switch by tuning PPAR* expression with a scaffold/matrix attachment region and by expressing both PPAR* and the reporter gene under the control of PPAR*-responsive elements. Treatment of cultured murine muscle cells (myotubes) with rosiglitazone induced reporter gene expression from assay background up to the level attained by a CMV I/E promoter-enhancer. These results indicate the potential of the PPAR* gene switch for use in gene therapy applications.

Gene therapy progress and prospects: transcription regulatory systems

The clinical efficacy and safety as well as the application range of gene therapy will be broadened by developing systems capable of finely modulating the expression of therapeutic genes. Transgene regulation will be crucial for maintaining appropriate levels of a gene product within the therapeutic range, thus preventing toxicity. Moreover, the possibility to modulate, stop or resume transgene expression in response to disease evolution would facilitate the combination of gene therapy with more conventional therapeutic modalities. The development of ligand-dependent transcription regulatory systems is thus of great importance. Here, we summarize the most recent progress in the field.

Regulating gene expression using self-inactivating lentiviral vectors containing the mifepristone-inducible system

Methods to regulate gene expression in vitro and in vivo are currently areas of intense research. The present study, therefore, was designed to determine the efficacy of transgene expression using the GeneSwitch mifepristone-regulatable system within the context of an integrating HIV-1 vector. Lentiviral transfer plasmids expressing the red (DsRed2) and green fluorescent protein (EGFP) markers were constructed for in vitro assessment on the basal and mifepristone-induced cell activation levels by FACS analyses. In our design, efficient cell activation and transgene expression were found using a binary lentivector system i.e., the trans-activator, Switch, and the inducible promoter-transgene expression cassette were cloned into separate vectors. Note that the Switch trans-activator performed optimally when cloned into the reverse-orientation, but the inducible promoter containing lentivector did not appear to be dependent upon the orientation within the lentivector backbone. This binary lentivector system resulted in tightly regulated transgene expression, with low basal cell activation in the absence of mifepristone (MFP). Upon induction, a 41- to 275-fold increase in the number of DsRed2- and EGFP-positive cells were detected (n=3). To determine the inducing ability of the GeneSwitch, we cloned the human alpha(1)-antitrypsin cDNA into the optimal lentiviral vector and transduced HeLa and Huh7 cells at increasing lentivector doses as determined by p24 Gag ELISA. We found that MFP could induce the expression of hAAT protein in HeLa cells from 310 to 15,000 ng hAAT/10(6) cells/24 h, which was a 48-fold induction. Similar results were observed in huH7 cells. In all, this study demonstrates that the GeneSwitch system can be designed within the context of a lentiviral vector for in vitro gene transfer, and this may also provide a viable method for temporally regulating gene expression for therapeutic applications in vivo or ex vivo.

Prolonged and inducible transgene expression in the liver using gutless adenovirus: a potential therapy for liver cancer

BACKGROUND AND AIMS

Gene therapy of liver diseases would benefit from systems allowing prolonged, regulable, and tissue-specific transgene expression. We attempted to produce a vector fulfilling these requirements.

METHODS

We generated gutless adenoviral vectors containing a mifepristone (RU486)-inducible system for controlled and liver-specific expression of human interleukin-12 (hIL-12) (GL-Ad/RUhIL-12) and mouse IL-12 (mIL-12) (GL-Ad/RUmIL-12). The properties of these vectors were tested both in vitro and in vivo.

RESULTS

Infection of cells with GL-Ad/RUhIL-12 resulted in high level of hIL-12 expression in the presence of RU486 only in hepatocytic cells. In animals injected with GL-Ad/RUhIL-12, the administration of RU486 induced a transient rise of serum hIL-12 that peaked at 10 hours and completely disappeared by 72 hours. The peak value of hIL-12 was dependent on the doses of the vector and the inducer. High and sustained serum levels of hIL-12 could be attained by continuing administration of RU486 every 12 or 24 hours. Repetitive induction of hIL-12 could be obtained over, at least, a period of 48 weeks after a single injection of GL-Ad/RUhIL-12. Although the vector was detected in many tissues after systemic injection, transcription of the transgene was only found in the liver. Treatment of liver metastases with 5 x 10(8) infectious units of GL-Ad/RUmIL-12 plus RU846 resulted in complete tumor regression in all animals.

CONCLUSION

Gutless adenoviral vectors allow liver-specific and regulable transgene expression for prolonged periods of time. These vectors are promising tools for gene therapy of liver cancer and could also be useful for other forms of hepatic disease.

Drugs for increasing oxygen and their potential use in doping: a review

Blood oxygenation is a fundamental factor in optimising muscular activity. Enhancement of oxygen delivery to tissues is associated with a substantial improvement in athletic performance, particularly in endurance sports. Progress in medical research has led to the identification of new chemicals for the treatment of severe anaemia. Effective and promising molecules have been created and sometimes used for doping purposes. The aim of this review is to present methods, and drugs, known to be (or that might be) used by athletes to increase oxygen transport in an attempt to improve endurance capacity. These methods and drugs include: (i) blood transfusion; (ii) endogenous stimulation of red blood cell production at altitude, or using hypoxic rooms, erythropoietins (EPOs), EPO gene therapy or EPO mimetics; (iii) allosteric effectors of haemoglobin; and (iv) blood substitutes such as modified haemoglobin solutions and perfluorochemicals. Often, new chemicals are used before safety tests have been completed and athletes are taking great health risks. Such new chemicals have also created the need for new instrumental strategies in doping control laboratories, but not all of these chemicals are detectable. Further progress in analytical research is necessary.

"Blue heart": characterization of a mifepristone-dependent system for conditional gene expression in genetically modified animals

A detailed characterization of a cardiac muscle-specific, ligand-regulated gene expression system was performed in transgenic mice using the inducing ligand mifepristone (MFP). Several lines of double transgenic mice were created that expressed a bacterial lacZ reporter gene in the heart, under the control of a MFP-activated transcription factor constitutively expressed in cardiac muscle. The transgenic mice, which were administered MFP at a dose of 1 micromol/l in the drinking water, responded to the ligand within 24 h. Induction of beta-galactosidase enzyme activity in the heart continued for up to 21 days and resulted in an average 17-fold increase in enzyme activity. The highest individual animal response measured was a 94-fold increase in enzyme activity. The EC(50) for MFP induction of beta-galactosidase activity in the heart was 0.7 micromol/l when MFP was administered in the drinking water. Pharmacokinetic analysis of MFP dosing in wild-type FVB/N mice showed that absorption was very rapid (T(max) 1-10 min), bioavailability was modest ( approximately 10%) and the t(1/2) of MFP in mouse plasma was determined to be approximately 5 h. Thus, the system functions effectively in transgenic mouse heart where induction of gene expression is sensitive and can be accomplished by a simple and broadly applicable drinking water protocol.

Regulated production of proteins from muscle using gene transfer: potential therapeutic applications

The ability to produce high-level transgene expression following the introduction of genetic material into a host cell has been well documented. Various vectors and methods for in vivo gene delivery have been shown to provide long-term expression from many different tissue types in rodents and large animals. However, many potential therapeutic targets for gene therapy involve the production of proteins that are toxic or lead to undesirable effects if overexpressed. Thus, the ability to achieve regulated gene expression following treatment will be required to ensure the safety of long-acting gene therapy products. Skeletal muscle, in particular, has been widely used as a target for gene therapy protocols, due to the ease of accessibility and ability to produce and secrete some proteins at very high levels. This review focuses on regulated gene therapy systems that are being evaluated for use in muscle, and discusses two classes of system: those dependent on exogenously administered drugs and those dependent on endogenously produced metabolites.

Construction of an rtTA2(s)-m2/tts(kid)-based transcription regulatory switch that displays no basal activity, good inducibility, and high responsiveness to doxycycline in mice and non-human primates

The tetracycline (Tc)-dependent system in its "on" version (rtTA system) displays a baseline activity in the uninduced state, severely limiting its potential applicability in human gene therapy. So far, two different strategies to circumvent this limitation have been described. On one side, co-expression of the tetracycline regulated repressor tTS(kid) has proved capable of substantially reducing the baseline activity of rtTA. On the other, novel versions of the activator, namely rtTA2(s)-S2 and rtTA2(s)-M2, with a lower basal activity have been engineered. We have combined these two approaches by co-expressing TS(kid) with the novel transactivators. Bicistronic vectors were constructed that co-express TS(kid) with rtTA, rtTA2(s)-S2, or rtTA2(s) M2, through an internal ribosome entry site (plasmids IRES-A, IRES-S2, and IRES-M2, respectively). IRES-M2 proved to be the most effective construct EX VIVO: it displayed a negligible basal activity, > 1000 fold inducibility, and high responsiveness to doxycycline (Dox). Upon delivery as plasmid DNA in mouse muscles, IRES-M2 facilitated 1000-fold induction of serum alkaline phosphatase (SEAP) gene expression and long-term, stringent, and strictly Dox-dose-dependent regulation of erythropoietin (Epo) gene expression. Tight regulation of the gene encoding SEAP was demonstrated also in non-human primates. Notably, the system was induced in animals by Dox-dosing regimens comparable to those used in humans.

Ligand-regulatable erythropoietin production by plasmid injection and in vivo electroporation

BACKGROUND

The development of an in vivo gene transfer approach to deliver physiologic levels of recombinant proteins to the systemic circulation would represent a significant advance in the treatment of protein deficiency disorders. However, the ability to regulate transgene expression is of paramount importance for safe and effective gene transfer therapy.

METHODS

We developed two plasmids, one encoder of chimeric GeneSwitch protein, and the other an inducible transgene for human erythropoietin (Epo). The level of secretion of Epo into the serum was modulated by intraperitoneal administration of mifepristone (MFP). Rats were divided into four groups: one group administered Epo plasmid with MFP for 50 days, a second group administered Epo plasmid with MFP for 15 days and then again from day 30 to day 50, a third group administered Epo plasmid without MFP, and a fourth group administered control plasmid. A pair of electrodes was inserted into the muscle of the right thigh, 100 mg of each plasmid was injected, and in vivo electroporation (8 pulses at 100 V for 50 msec) was performed.

RESULTS

The presence of vector-derived Epo mRNA was detected by RT-PCR only in the Epo plasmid and MFP(+) groups. The hematocrit levels increased continuously, from the pre-injection level of 41.2% to 55.0% on day 30 and 53.8% on day 50 in the Epo plasmid and MFP(+) groups. In the MFP re-challenged group, the hematocrit levels rose up to day 15, fell after 20 to 30 days, and then rose again after MFP re-administration. The serum Epo levels increased only in the Epo plasmid and MFP(+) groups. There were no significant changes in hematocrit levels and Epo levels in the Epo plasmid and MFP(-) group.

CONCLUSION

Epo gene transfer with the GeneSwitch system by in vivo electroporation is a useful procedure for efficient drug-regulated delivery of Epo.

Antiprogestin-controllable transgene regulation in vivo

Gene control systems that provide temporal and spatial regulation of transgene expression in response to orally delivered drugs are needed for advances in functional genomics, models of human disease and gene therapy. A regulation system based on the altered binding and activation properties of a truncated ligand-binding domain derived from the progesterone receptor has been shown to be effective in providing tissue-specific, antiprogestin-controllable gene expression in transgenic mice, transgenic fruit flies and animals that have been administered viral-based or plasmid-based gene therapy vectors.

Efficient gene regulation by PPAR gamma and thiazolidinediones in skeletal muscle and heart

We have developed a new gene regulation system for gene therapy. This system consists of two expression cassettes; one expresses the human peroxisome proliferator-activated receptor gamma(PPAR gamma), and the other expresses the therapeutic gene under the control of multiple peroxisome proliferator-activated receptor (PPAR) response elements (PPREs) linked to a basal promoter. Using direct injection of plasmid DNA into skeletal muscle or myocardium of rodents and oral administration of clinically approved PPAR gamma activators, we demonstrate that reporter gene expression can be induced more than 25-fold. We show that oral administration of PPAR gamma activator at intervals separated by several months results in repeated pulses of high-level reporter gene expression. We also document a PPAR gamma activator dose-response effect on reporter gene expression. This is the first report of a gene regulation system that makes use of a human transcription factor and that may be safer than chimeric transcription factors for human gene therapy.

Ligand-inducible transgene regulation for gene therapy

A synthetic ligand regulable system for gene transfer and expression has been developed in our laboratory based on mechanistic studies of steriod hormone receptor and transcriptional regulation. This gene switch system possesses most of the important features that are required for application of the system in biological research and clinical gene therapy in the future. As the primary ligand tested in this system, mifepristone can effectively turn on the regulatory circuit at doses much lower than those used in the clinic. By modification of the chimeric regulator and its feedback regulatory mode, this system has been optimized to produce very low basal activity with high inducibility in the presence of mifepristone. Also, improvements in regulator composition have been made to minimize immunogenicity and make the system more amenable to human gene therapy. Moreover, incorporation of this gene switch system into the HC-Ad vector system has further enhanced the efficiency of gene transfer and the long-term inducible expression of transgenes. However, for each application within a different biological system, the gene switch needs to be optimized to achieve appropriate inductions. In particular, the method used to deliver the transgenes and adjustment of ligand dosage are critical for in vivo gene expression.

The mifepristone-inducible gene regulatory system in mouse models of disease and gene therapy

The mifepristone (Mfp)-inducible gene regulatory system is designed to allow control of the spatiotemporal expression of transgenes in vivo in a ligand-dependent manner. This regulatory system is composed of two components: (1) a chimeric transactivator protein that activates transgene transcription only in the presence of the progesterone antagonist Mfp, and (2) a target transgene placed in the context of a promoter which is responsive only to the Mfp-bound chimeric transactivator. Incorporation of the components of the Mfp-inducible gene regulatory system into transgenic mice has resulted in the establishment of several novel, Mfp-dependent models of disease. Similarly, adaptation of the Mfp-inducible system for use in gene knockout models has resulted in the development of new gene ablation technology which is both tissue-specific and Mfp-dependent. Additionally, the Mfp-inducible gene regulatory system has been used in animal experiments involving somatic gene therapy, where it has shown considerable promise in the regulation of both reporter and therapeutic gene expression. This review focuses on recent application of the Mfp-inducible system to transgenic models, gene knockout models, and somatic gene therapy experiments. In so doing, it demonstrates the considerable promise that future use of this system holds for better understanding and treatment of human disease.

Enhanced animal growth via ligand-regulated GHRH myogenic-injectable vectors

Regulated animal growth occurred following a single electroporated injection of a mixture of two plasmids (10 microg of DNA), one expressing the GeneSwitch regulator protein, the other an inducible growth hormone releasing hormone (GHRH) gene, into the tibialis anterior muscles of adult SCID mice. Administration of the ligand mifepristone (MFP) up-regulated GHRH expression, as shown by elevations of IGF-I levels, and when MFP dosing was withdrawn, IGF-I returned to baseline levels. Five cycles of IGF-I induction were observed during a five-month period. Chronic MFP dosing for 25 days increased lean body mass, weight gain, and bone mineral density significantly compared with non-MFP treated controls. In summary, long-term drug-regulated GHRH expression was achieved following plasmid-based gene therapy, and chronic induction of GHRH expression in adult animals led to improvements in weight gain and body composition.

Stringent control of gene expression in vivo by using novel doxycycline-dependent trans-activators

The tetracycline (Tet)-dependent regulatory system has been widely used for controlling gene expression. The Tet-on version of the system, in which the reverse Tet-responsive transcriptional activator (rtTA) is positively regulated by Tet or its analogs, such as doxycycline (Dox), is of potential utility for gene therapy applications in humans. However, rtTA may display a high basal activity, especially when delivered in vivo by using episomal vectors such as plasmids. Two novel Dox-inducible activators, called rtTA2(S)-S2 and rtTA2(S)-M2, which have a significantly lower basal activity than rtTA in stably transfected cell lines, have been described. In this study we tested the capability of these trans-activators to control expression of mouse erythropoietin (mEpo) and to modulate hematocrit (Hct) increase in vivo on delivery of plasmids into quadriceps muscles of adult mice by DNA electroinjection. Both rtTA2(S)-M2 and rtTA2(S)-S2 displayed a considerably lower background activity and higher window of induction than rtTA in vivo. Moreover, a stringent control of mEpo gene expression and Hct levels in the absence of any background activity was maintained over a 10-month period by injecting as little as 1 microg of a single plasmid containing the rtTA2(S)-S2 expression cassette and the Tet-responsive mEpo cDNA. This constitutes the first report of a stringent ligand-dependent control of gene expression in vivo obtained by delivering a single plasmid encoding both the trans-activator and the regulated gene. Notably, the rtTA2(S)-S2-based system was induced by oral doses of doxycycline comparable to those normally used in clinical practice in humans.

Sustainable systemic delivery via a single injection of lentivirus into human skin tissue

The skin offers a tissue site accessible for delivery of gene-based therapeutics. To develop the capability for sustained systemic polypeptide delivery via cutaneous gene transfer, we generated and injected pseudotyped HIV-1 lentiviral vectors intradermally at a range of doses into human skin grafted on immune-deficient mice. Unlike Moloney murine leukemia virus (MLV)-based retrovectors, which failed to achieve detectable cutaneous gene transfer by this approach, lentivectors effectively targeted all major cell types within human skin tissue, including fibroblasts, endothelial cells, keratinocytes, and macrophages. After a single injection, lentivectors encoding human erythropoietin (EPO) produced dose-dependent increases in serum human EPO levels and hematocrit that increased rapidly within one month and remained stable subsequently. Delivered gene expression was confined locally at the injection site. Excision of engineered skin led to rapid and complete loss of human EPO in the bloodstream, confirming that systemic EPO delivery was entirely due to lentiviral targeting of cells within skin rather than via spread of the injected vector to visceral tissues. These findings indicate that the skin can sustain dosed systemic delivery of therapeutic polypeptides via direct lentivector injection and thus provide an accessible and reversible approach for gene-based delivery to the bloodstream.