Genetic pharmacology: progresses in siRNA delivery and therapeutic applications.

In the RNA interference process, the catalytic degradation of an endogenous mRNA results from the Watson-Crick complementary recognition by either a small silencing synthetic double-stranded ribonucleotide (siRNA) or by a small hairpin RNA (shRNA) produced in the cell by transcription from a DNA template. This interference process ideally results in an exquisitely specific mRNA suppression. The present review is dedicated to siRNAs. It describes the mechanism of RNA silencing and the main siRNA delivery techniques, with a focus on siRNA self-complexing to cationic lipids to form nanoparticles, which are called lipoplexes. The addition to lipoplexes of an anionic polymer leads to the ternary formulation APIRL (Anionic-Polymer-Interfering-RNA-Lipoplexes) with increased in vivo stability and biological efficacy. In terms of clinical development, the review focuses on therapeutic applications by intravenous delivery to the liver and inflammatory joints, and to localized siRNA delivery to the ocular sphere.

Long-term efficacy of ciliary muscle gene transfer of three sFlt-1 variants in a rat model of laser-induced choroidal neovascularization.

Inhibition of vascular endothelial growth factor (VEGF) has become the standard of care for patients presenting with wet age-related macular degeneration. However, monthly intravitreal injections are required for optimal efficacy. We have previously shown that electroporation enabled ciliary muscle gene transfer results in sustained protein secretion into the vitreous for up to 9 months. Here, we evaluated the long-term efficacy of ciliary muscle gene transfer of three soluble VEGF receptor-1 (sFlt-1) variants in a rat model of laser-induced choroidal neovascularization (CNV). All three sFlt-1 variants significantly diminished vascular leakage and neovascularization as measured by fluorescein angiography (FA) and flatmount choroid at 3 weeks. FA and infracyanine angiography demonstrated that inhibition of CNV was maintained for up to 6 months after gene transfer of the two shortest sFlt-1 variants. Throughout, clinical efficacy was correlated with sustained VEGF neutralization in the ocular media. Interestingly, treatment with sFlt-1 induced a 50% downregulation of VEGF messenger RNA levels in the retinal pigment epithelium and the choroid. We demonstrate for the first time that non-viral gene transfer can achieve a long-term reduction of VEGF levels and efficacy in the treatment of CNV.

Non-viral gene therapy for GDNF production in RCS rat: the crucial role of the plasmid dose.

Glial cell line-derived neurotrophic factor (GDNF) is one of the candidate molecules among neurotrophic factors proposed for a potential treatment of retinitis pigmentosa (RP). It must be administered repeatedly or through sustained releasing systems to exert prolonged neuroprotective effects. In the dystrophic Royal College of Surgeon's (RCS) rat model of RP, we found that endogenous GDNF levels dropped during retinal degeneration time course, opening a therapeutic window for GDNF supplementation. We showed that after a single electrotransfer of 30 µg of GDNF-encoding plasmid in the rat ciliary muscle, GDNF was produced for at least 7 months. Morphometric, electroretinographic and optokinetic analyses highlighted that this continuous release of GDNF delayed photoreceptors (PRs) as well as retinal functions loss until at least 70 days of age in RCS rats. Unexpectedly, increasing the GDNF secretion level accelerated PR degeneration and the loss of electrophysiological responses. This is the first report: (i) demonstrating the efficacy of GDNF delivery through non-viral gene therapy in RP; (ii) establishing the efficacy of intravitreal administration of GDNF in RP associated with a mutation in the retinal pigment epithelium; and (iii) warning against potential toxic effects of GDNF within the eye/retina.

Soluble TNF-α receptor secretion from healthy or dystrophic mice after AAV6-mediated muscle gene transfer.

Muscle is an attractive target because it is easily accessible; it also offers a permissive environment for adeno-associated virus (AAV)-mediated gene transfer and has an abundant blood vascular supply providing an efficient transport system for the secretion of proteins. However, gene therapy of dystrophic muscle may be more difficult than that of healthy tissue because of degenerative-regenerative processes, and also because of the inflammatory context. In this study we followed the expression levels of secreted inhibitors of the proinflammatory tumor necrosis factor (TNF) cytokine after intramuscular (i.m.) injection of AAV6 into dystrophic mdx and healthy C57BL/10 mice. We used two chimeric proteins, namely, the human or murine TNF-soluble receptor I fused with the murine heavy immunoglobulin chain. We conducted an AAV6 dose-response study and determined the kinetics of transgene expression. In addition, we followed the antibody response against the transgenes and studied their expression pattern in the muscle. Our results show that transduction efficiency is reduced in dystrophic muscles as compared with healthy ones. Furthermore, we found that the immune response against the secreted protein is stronger in mdx mice. Together, our results underscore that the pathological state of the muscle has to be taken into consideration when designing gene therapy approaches.

Effects of ciliary muscle plasmid electrotransfer of TNF-alpha soluble receptor variants in experimental uveitis.

Intraocular inflammation has been recognized as a major factor leading to blindness. Because tumor necrosis factor-alpha (TNF-alpha) enhances intraocular cytotoxic events, systemic anti-TNF therapies have been introduced in the treatment of severe intraocular inflammation, but frequent re-injections are needed and are associated with severe side effects. We have devised a local intraocular nonviral gene therapy to deliver effective and sustained anti-TNF therapy in inflamed eyes. In this study, we show that transfection of the ciliary muscle by plasmids encoding for three different variants of the p55 TNF-alpha soluble receptor, using electrotransfer, resulted in sustained intraocular secretion of the encoded proteins, without any detection in the serum. In the eye, even the shorter monomeric variant resulted in efficient neutralization of TNF-alpha in a rat experimental model of endotoxin-induced uveitis, as long as 3 months after transfection. A subsequent downregulation of interleukin (IL)-6 and iNOS and upregulation of IL-10 expression was observed together with a decreased rolling of inflammatory cells in anterior segment vessels and reduced infiltration within the ocular tissues. Our results indicate that using a nonviral gene therapy strategy, the local self-production of monomeric TNF-alpha soluble receptors induces a local immunomodulation enabling the control of intraocular inflammation.

Generation of high-titer neutralizing antibodies against botulinum toxins A, B, and E by DNA electrotransfer.

Botulinum neurotoxins are known to be among the most toxic known substances. They produce severe paralysis by preventing the release of acetylcholine at the neuromuscular junction. Thus, new strategies for efficient production of safe and effective anti-botulinum neurotoxin antisera have been a high priority. Here we describe the use of DNA electrotransfer into the skeletal muscle to enhance antiserum titers against botulinum toxin serotypes A, B, and E in mice. We treated animals with codon-optimized plasmid DNA encoding the nontoxic but highly immunogenic C-terminal heavy chain fragment of the toxin. By employing both codon optimization and the electrotransfer procedure, the immune response and corresponding neutralizing antiserum titers were markedly increased. The cellular localization of the antigen and the immunization regimens were also shown to increase neutralizing titers to >100 IU/ml. This study demonstrates that DNA electrotransfer is an effective procedure for raising neutralizing antiserum titers to remarkably high levels.

Vascular endothelial growth factor reduced hypoxia-induced death of human myoblasts and improved their engraftment in mouse muscles.

Muscle precursor cell (myoblasts) transplantation is considered as a potential approach to restore dystrophin expression in Duchenne muscular dystrophy (DMD) patients. The study purpose was to verify the implication of hypoxia in the myoblast death observed after their transplantation and also to evaluate the potential beneficial effects of vascular endothelial growth factor (VEGF) overexpression on myoblast engraftment in a murine model. Pimonidazole hydrochloride (hypoxyprobe-1) was used to mark selectively myoblasts to evaluate their hypoxia in vivo. In vitro, hypoxia was induced by culturing human myoblasts in hypoxic environment. In vitro effects of VEGF(165) on survival of human cells was assessed by Hoescht-PI labeling. Tibialis anterior (TA) female mouse muscles were electroporated with a plasmid containing the VEGF(165) or with an empty vector. Circulating VEGF concentration was assessed by ELISA. After 2 weeks of electroporation, severe combined immunodeficient (SCID) mice were transplanted with 800 000 human male myoblasts labeled with radioactive thymidine. Mouse muscles were harvested 2 and 4 days later and myoblast survival and proliferation were evaluated by scintigraphy and Y chromosome quantitative PCR. The long-term graft success was evaluated using gamma-radiograph imaging and by counting the dystrophin positive muscle fibers. Hypoxyprobe labeling has shown that most of the transplanted myoblasts were hypoxic. The transplantation of radioactive male myoblasts in female mice electroporated with the VEGF(165) plasmid demonstrated that VEGF reduced their death by 10% but did not improve their proliferation. VEGF(165) enhanced human myoblast survival in vitro under hypoxic conditions. Electroporation of TA muscles of SCID mouse with the vector coding for VEGF(165) promoted angiogenesis and improved by 1.5-fold the success of myoblast transplantation in comparison with the control mice that were electroporated with the empty vector. These results indicate that hypoxia is partially responsible for the death of the transplanted myoblasts. VEGF can be used to improve myoblast survival and the graft success.

Intra-articular electrotransfer of plasmid encoding soluble TNF receptor variants in normal and arthritic mice.

BACKGROUND: Anti-inflammatory gene therapy is promising in inflammatory diseases such as rheumatoid arthritis (RA). We have previously demonstrated that intra-muscular (i.m.) electrotransfer (ET) of plasmids encoding three different human tumor necrosis factor-alpha-soluble receptor I variants (hTNFR-Is) exert protective effects in an experimental RA model. However, such a systemic approach could be responsible for side effects. The present study aimed at performing an intra-articular (i.a.) gene therapy by electrotransfer using the hTNFR-Is plasmids. METHODS AND RESULTS: We evaluated targeting of mice joints by CCD optical imaging after i.a. ET of a luciferase-encoding plasmid and we showed that ET led to strongly increased transgene expression in a plasmid dose-dependent manner. Moreover, articular and seric hTNFR-Is was detectable for 2 weeks. As expected, systemic hTNFR-Is rates were lower after i.a. ET than after i.m. ET. A longer protein secretion could be achieved with several i.a. ETs. Also, we observed that hTNFR-Is expression within arthritic joints was slightly higher than in normal joints. CONCLUSIONS: In collagen-induced arthritis (CIA), a mouse model for RA, we demonstrated that hTNFR-Is/mIgG1-encoding plasmid i.a. ET decreased joint destruction in the ankles. In conclusion, our results suggest that local TNFR-Is gene therapy may play a role in decreasing joint destruction in CIA.

Inflammation-inducible anti-TNF gene expression mediated by intra-articular injection of serotype 5 adeno-associated virus reduces arthritis.

BACKGROUND: The tumor necrosis factor (TNF)-alpha plays a central role in rheumatoid arthritis (RA) and current biotherapies targeting TNF-alpha have a major impact on RA treatment. The long-term safety concerns associated with the repetitive TNF blockade prompt optimization of therapeutic anti-TNF approaches. Since we recently demonstrated that intra-articular gene transfer using a recombinant adeno-associated virus serotype 5 (rAAV5) efficiently transduces arthritic joints, we evaluate its effect on collagen-induced arthritis (CIA) when encoding TNF antagonists. METHODS: Recombinant AAV5 vectors encoding the human TNFRp55 extracellular domain fused to the Fc region of mice IgG1 (TR1) or a small molecular weight dimeric human TNFRp75 extracellular domain (TR2), under two different promoters, the CMV or a chimeric NF-kappaB-based promoter inducible by inflammation, were injected into mouse CIA joints. RESULTS: Best protection against arthritis was obtained with the rAAV5 encoding the TR1, as reflected by delayed disease onset, decreased incidence and severity of joint damage. This effect was associated with a transient expression of the anti-TNF agent when expressed under a NF-kappaB-responsive promoter, only detectable during disease flare, while the antagonist expression was rapidly increased and stable when expressed from a CMV promoter. Importantly, using the intra-articular administration of the rAAV5-NF-kappaB-TR1 vector, we observed a striking correlation between local TR1 expression and inflammation. CONCLUSIONS: These findings strongly support the feasibility of improving the safety of anti-TNF approaches for the treatment of arthritis by local rAAV5-mediated gene expression under an inflammation-responsive promoter, able to provide a limited, transient and therapeutically relevant expression of anti-TNF compounds.

Reduction of arthritis following intra-articular administration of an adeno-associated virus serotype 5 expressing a disease-inducible TNF-blocking agent.

BACKGROUND: In the context of preclinical development, we studied the potential of intra-articular gene delivery using a recombinant adeno-associated virus 5 (rAAV5) encoding a chimeric human tumour necrosis factoralpha (TNFalpha) soluble receptor I linked to a mouse immunoglobulin heavy chain Fc portion (TNF receptor I; TNFRI-Ig). METHODS: Expression was under control of a nuclear factor kappa B (NFkappaB)-responsive promoter and compared with a cytomegalovirus (CMV) promoter (rAAV5.NFkappaB-TNFRI-Ig and rAAV5.CMV-TNFRI-Ig, respectively). RESULTS: Fibroblast-like synoviocytes transduced in vitro with rAAV5.NFkappaB-TNFRI-Ig were able to produce TNFRI-Ig protein in response to several stimuli, and this was inhibited upon treatment with a specific NFkappaB blocking agent. A bioassay revealed that the synthesised TNFRI-Ig was bioactive, showing a higher affinity for human than for rat TNFalpha. Transcription of the transgene and protein production were detectable in joints injected with both constructs. No dissemination of the vector was observed outside the joints. A significant reduction in paw swelling was seen in rats treated with rAAV5.NFkappaB-TNFRI-Ig. This clinical effect was accompanied by a decrease in pro-inflammatory cytokine levels and an increase in IL10 expression in the synovium. CONCLUSION: These results provide evidence that intra-articular gene therapy using rAAV5 encoding TNFRI-Ig may be a safe and feasible approach for the treatment of rheumatoid arthritis. The higher affinity for human TNFalpha suggests that in patients with rheumatoid arthritis the therapeutic effect might be even more pronounced than in rat adjuvant arthritis.

Electrotransfer into skeletal muscle for protein expression.

An efficient and safe method to deliver DNA in vivo is a requirement for several purposes, such as study of gene function and gene therapy applications. Among the different non-viral delivery methods currently under investigation, in vivo DNA electrotransfer has proven to be one of the most efficient and simple. This technique is a physical method of gene delivery consisting in local application of electric pulses after DNA injection. Although this technique can be applied to almost any tissue of a living animal, including tumors, skin, liver, kidney, artery, retina, cornea or even brain, this review will focus on electrotransfer of plasmid DNA into skeletal muscle and its possible uses in gene therapy, vaccination, or functional studies. Skeletal muscle is a good target for electrotransfer of DNA as it is: a large volume easily accessible, an endocrine organ capable of expressing several local and systemic factors, and muscle fibres as post-mitotic cells have a long lifespan that allows long-term gene expression. In this review, we describe the mechanism of DNA electrotransfer, we assess toxicity and safety considerations related to this technique, and we focus on important therapeutic applications of electrotransfer demonstrated in animal models in recent years.

A comparative study on intra-articular versus systemic gene electrotransfer in experimental arthritis.

BACKGROUND: Electric pulse mediated gene transfer has been applied successfully in vivo for increasing naked DNA administration in various tissues. To achieve non-viral gene transfer into arthritic joint tissue, we investigated the use of electrotransfer (ET). Because anti-inflammatory cytokine strategies have proven efficient in experimental models of arthritis, we compared the therapeutic efficiency of local versus systemic delivery of the interleukin-10 (IL-10) using in vivo ET. METHODS: A plasmid vector expressing IL-10 was transferred into DBA/1 mouse knee joints by ET with 12 pulses of variable duration and voltage. The kinetics of transgene expression were analyzed by specific enzyme-linked immunosorbent assay (ELISA) in sera and knees. Optimal conditions were then used to deliver increasing amounts of IL-10 plasmid intra-articularly (i.a.) in the collagen-induced arthritis (CIA) mouse model. The therapeutic efficiency was compared with the potency of intra-muscular (i.m.) ET. RESULTS: Following i.a. ET, local IL-10 secretion peaked on day 7 and dropped 2 weeks after. A second ET produced the same kinetics without enhancing gene transfer efficiency, while transgene was still detected in injected muscles 4 weeks after ET. Only the i.m. ET of 25 microg of IL-10 significantly inhibited all the clinical and biological features of arthritis. The i.a. ET only showed mild improvement of arthritis when 100 microg of IL-10 plasmid were electrotransfered weekly from day 18 following arthritis induction. CONCLUSIONS: The present results suggest that gene transfer into arthritic joints by ET is an effective means to deliver anti-inflammatory cytokines. However, short duration of transgene expression impedes a significant effect for the treatment of arthritis, making i.m. ET more potent than i.a. ET for clinical benefit in CIA.

Plasmid electrotransfer of eye ciliary muscle: principles and therapeutic efficacy using hTNF-alpha soluble receptor in uveitis.

Due to its small size and particular isolating barriers, the eye is an ideal target for local therapy. Recombinant protein ocular delivery requires invasive and painful repeated injections. Alternatively, a transfected tissue might be used as a local producer of transgene-encoded therapeutic protein. We have developed a nondamaging electrically mediated plasmid delivery technique (electrotransfer) targeted to the ciliary muscle, which is used as a reservoir tissue for the long-lasting expression and secretion of therapeutic proteins. High and long-lasting reporter gene expression was observed, which was restricted to the ciliary muscle. Chimeric TNF-alpha soluble receptor (hTNFR-Is) electrotransfer led to elevated protein secretion in aqueous humor and to drastic inhibition of clinical and histological inflammation scores in rats with endotoxin-induced uveitis. No hTNFR-Is was detected in the serum, demonstrating the local delivery of proteins using this method. Plasmid electrotransfer to the ciliary muscle, as performed in this study, did not induce any ocular pathology or structural damage. Local and sustained therapeutic protein production through ciliary muscle electrotransfer is a promising alternative to repeated intraocular protein administration for a large number of inflammatory, degenerative, or angiogenic diseases.

Improvement of porphyrin cellular delivery and activity by conjugation to a carrier peptide.

The chemical nuclease metalloporphyrin (manganese(III) porphyrin) can cleave DNA irreversibly and can thus constitute a potential antitumor drug. However, these molecules show low permeability to cell surface membranes. We report here the conjugation of an amphipathic carrier peptide to improve considerably its cellular delivery. The metalloporphyrin-peptide conjugate can be internalized by cells within only 5 min of incubation with a yield as high as 80%. Furthermore, the metalloporphyrin-peptide conjugate is able to cleave in vitro high or low molecular weight DNA to the same extend as metalloporphyrin alone without affecting the sequence-specific cleaving activity of the porphyrin. The conjugate is 100-fold more efficient at inducing tumor cells death than the free metalloporphyrin via a mechanism involving genomic DNA cleavage. The results are promising for further therapeutic applications with antitumor drugs such as metalloporphyrin, and also with other existing drugs by using a carrier peptide system in order to improve the cellular uptake of such molecules.

The DNMT1 target recognition domain resides in the N terminus.

DNA-cytosine-5-methyltransferase 1 (DNMT1) is the enzyme believed to be responsible for maintaining the epigenetic information encoded by DNA methylation patterns. The target recognition domain of DNMT1, the domain responsible for recognizing hemimethylated CGs, is unknown. However, based on homology with bacterial cytosine DNA methyltransferases it has been postulated that the entire catalytic domain, including the target recognition domain, is localized to 500 amino acids at the C terminus of the protein. The N-terminal domain has been postulated to have a regulatory role, and it has been suggested that the mammalian DNMT1 is a fusion of a prokaryotic methyltransferase and a mammalian DNA-binding protein. Using a combination of in vitro translation of different DNMT1 deletion mutant peptides and a solid-state hemimethylated substrate, we show that the target recognition domain of DNMT1 resides in the N terminus (amino acids 122-417) in proximity to the proliferating cell nuclear antigen binding site. Hemimethylated CGs were not recognized specifically by the postulated catalytic domain. We have previously shown that the hemimethylated substrates utilized here act as DNMT1 antagonists and inhibit DNA replication. Our results now indicate that the DNMT1-PCNA interaction can be disrupted by substrate binding to the DNMT1 N terminus. These results point toward new directions in our understanding of the structure-function of DNMT1.

Inhibition of DNA methyltransferase inhibits DNA replication.

Ectopic expression of DNA methyltransferase transforms vertebrate cells, and inhibition of DNA methyltransferase reverses the transformed phenotype by an unknown mechanism. We tested the hypothesis that the presence of an active DNA methyltransferase is required for DNA replication in human non-small cell lung carcinoma A549 cells. We show that the inhibition of DNA methyltransferase by two novel mechanisms negatively affects DNA synthesis and progression through the cell cycle. Competitive polymerase chain reaction of newly synthesized DNA shows decreased origin activity at three previously characterized origins of replication following DNA methyltransferase inhibition. We suggest that the requirement of an active DNA methyltransferase for the functioning of the replication machinery has evolved to coordinate DNA replication and inheritance of the DNA methylation pattern.

Transcriptional regulation of the human DNA Methyltransferase (dnmt1) gene.

DNA methylation is an important component of the epigenetic control of genome functions. Understanding the regulation of the DNA Methyltransferase (dnmt1) gene expression is critical for comprehending how DNA methylation is coordinated with other critical biological processes. In this paper, we investigate the transcriptional regulatory region of the human dnmt1 gene using a combination of RACE, RNase protection analysis and CAT assays. We identified one major and three minor transcription initiation sites in vivo (P1-P4), which are regulated by independent enhancers and promoter sequences. The minimal promoter elements of P1, P2 and P4 are mapped within 256 bp upstream of their respective transcription initiation sites. P1 is nested within a CG-rich area, similar to other housekeeping genes, whereas P2-P4 are found in CG-poor areas. Three c-Jun-dependent enhancers are located downstream to P1 and upstream to P2-P4, thus providing a molecular explanation for the responsiveness of dnmt1 to oncogenic signals that are mediated by the Ras-c-Jun oncogenic signaling pathway.

Identification of initiation sites for DNA replication in the human dnmt1 (DNA-methyltransferase) locus.

Vertebrates have developed multiple mechanisms to coordinate the replication of epigenetic and genetic information. Dnmt1 encodes the maintenance enzyme DNA-methyltransferase, which is responsible for propagating the DNA methylation pattern and the epigenetic information that it encodes during replication. Direct sequence analysis and bisulfite mapping of the 5' region of DNA-methyltransferase 1 (dnmt1) have indicated the presence of many sequence elements associated with previously characterized origins of DNA replication. This study tests the hypothesis that the dnmt1 region containing these elements is an origin of replication in human cells. First, we demonstrate that a vector containing this dnmt1 sequence is able to support autonomous replication when transfected into HeLa cells. Second, using a gel retardation assay, we show that it contains a site for binding of origin-rich sequences binding activity, a recently purified replication protein. Finally, using competitive polymerase chain reaction, we show that replication initiates in this region in vivo. Based on these lines of evidence, we propose that initiation sites for DNA replication are located between the first intron and exon 7 of the human dnmt1 locus.

Modified oligonucleotides as bona fide antagonists of proteins interacting with DNA. Hairpin antagonists of the human DNA methyltransferase.

The study of the biological role of DNA methyltransferase (DNA MeTase) has been impeded by the lack of direct and specific inhibitors. This report describes the design of potent DNA based antagonists of DNA MeTase and their utilization to define the interactions of DNA MeTase with its substrate and to study its biological role. We demonstrate that the size, secondary structure, hemimethylation, and phosphorothioate modification strongly affect the antagonists interaction with DNA MeTase whereas base substitutions do not have a significant effect. To study whether DNA MeTase is critical for cellular transformation, human lung non-small carcinoma cells were treated with the DNA MeTase antagonists. Ex vivo, hairpin inhibitors of DNA MeTase are localized to the cell nucleus in lung cancer cells. They inhibit DNA MeTase, cell growth, and anchorage independent growth (an indicator of tumorigenesis in cell culture) in a dose-dependent manner. The inhibitors developed in this study are the first documented example of direct inhibitors of DNA MeTase in living cells and of modified oligonucleotides as bona fide antagonists of critical cellular proteins.

Genomic structure of the human DNA methyltransferase gene.

We determined the genomic structure of the gene encoding human DNA methyltransferase (DNA MTase). Six overlapping human genomic DNA clones which include all of the known cDNA sequence were isolated. Analysis of these clones demonstrates that the human DNA MTase gene consists of at least 40 exons and 39 introns spanning a distance of 60 kilobases. Elucidation of the chromosomal organization of the human DNA MTase gene provides the template for future structure-function analysis of the properties of mammalian DNA MTase.