Surgical procedures for intravascular delivery of plasmid DNA to organs

Osteoinduction by repeat plasmid injection of human bone morphogenetic protein-2

BACKGROUND

Bone morphogenetic protein-2 (BMP-2) is an osteoinductive protein and is considered useful for the treatment of skeletal disorders. Previous studies using BMP-2 in clinical applications have encountered difficulties, including the lack of an efficient, safe, inexpensive and simple delivery system. The gene transfer approach is a promising option for utilizing BMP-2. Although viral vector-mediated gene transfer is efficient, safety concerns prevent its clinical application for common diseases. On the other hand, plasmid-based gene transfer is a safe method and can be harnessed for practical applications.

METHODS

A plasmid encoding human BMP-2 (pCAGGS-BMP-2) was used and injected repeatedly (one to eight times) into the skeletal muscle of mice at a divided dose. We compared the capability of osteoinduction in the skeletal muscle of mice after gene transfer by repeat injection. BMP-2 production was assessed via immunohistochemistry, and osteoinduction was evaluated using radiography, histology and biochemical assays.

RESULTS

The BMP-2 gene was transferred into the skeletal muscle of mice by repeat injection using pCAGGS-BMP-2. Mature bone was frequently observed in mice injected repeatedly with pCAGGS-BMP-2 at a divided dose. This confirms that, if the total dose is fixed, repeat injection with pCAGGS-BMP-2 at a divided dose causes osteoinduction more frequently in the skeletal muscle of mice.

CONCLUSIONS

These results suggest the possibility of the effective clinical use of human BMP-2 gene therapy by direct DNA injection, and facilitate the clinical application of BMP-2 gene therapy.

Systemic siRNA delivery via hydrodynamic intravascular injection

The main barrier to the use of RNAi in mammalian systems is the difficulty in delivering siRNA or shRNA to the appropriate tissues. Although progress has been made in this area, many of the technologies developed require specialized expertise and reagents that are beyond the reach of most investigators. In contrast, the hydrodynamic injection technique is simple to perform and enables highly efficient delivery of naked, unmodified siRNA to a number of tissues, especially the liver. This review describes the development of the technique and explores the possible mechanisms that enable uptake of siRNA to biological effect. Examples of the use of hydrodynamic injection in animal models of disease and for the study of gene function are presented and discussed.

Genetic immunization for antibody generation in research animals by intravenous delivery of plasmid DNA

Genetic immunization is an attractive approach to generate antibodies because native proteins are expressed in vivo with normal posttranscriptional modifications, avoiding time-consuming and costly antigen isolation or synthesis. Hydrodynamic tail or limb vein delivery of naked plasmid DNA expression vectors was used to induce antigen-specific antibodies in mice, rats, and rabbits. Both methods allowed the efficient generation of high-titer, antigen-specific antibodies with an overall success rate of Western detectable antibodies of 78% and 92%, respectively. High-titer antibodies were typically present after 3 hydrodynamic tail vein plasmid DNA deliveries, 5 weeks after the initial injection (i.e., prime). For hydrodynamic limb vein plasmid DNA delivery, two deliveries were sufficient to induce high-titer antibody levels. Tail vein delivery was less successful at generating antibodies directed against secreted proteins as compared with limb vein delivery. Material for screening was generated by transfection of the immunization vector into mammalian cell lines. The cell line (COS-7) that produced the highest level of antigen expression performed best in Western blot analysis screens. In summary, intravenous delivery of antigen-expressing plasmid DNA vectors is an effective genetic immunization method for the induction of antigen-specific antibodies in small and large research animals.

Delivery of siRNA and siRNA expression constructs to adult mammals by hydrodynamic intravascular injection

Extensive use of RNA interference in mammals has been hindered by the inability to effectively deliver small interfering RNAs (siRNAs) or DNA-based constructs designed to express siRNAs. In this chapter, we describe the high-pressure or hydrodynamic intravascular injection technique used to deliver these nucleic acids to mice and nonhuman primates. Emphasis is placed on the use of this technique for delivery to the liver.

The hydrodynamics-based procedure for controlling the pharmacokinetics of gene medicines at whole body, organ and cellular levels

Hydrodynamics-based gene delivery, involving a large-volume and high-speed intravenous injection of naked plasmid DNA (pDNA), gives a significantly high level of transgene expression in vivo. This has attracted a lot of attention and has been used very frequently as an efficient, simple and convenient transfection method for laboratory animals. Until recently, however, little information has been published on the pharmacokinetics of the injected DNA molecules and of the detailed mechanisms underlying the efficient gene transfer. We and other groups have very recently demonstrated that the mechanism for the hydrodynamics-based gene transfer would involve, in part, the direct cytosolic delivery of pDNA through the cell membrane due to transiently enhanced permeability. Along with the findings in our series of studies, this article reviews the cumulative reports and other intriguing information on the controlled pharmacokinetics of naked pDNA in the hydrodynamics-based gene delivery. In addition, we describe various applications reported so far, as well as the current attempts and proposals to develop novel gene medicines for future gene therapy using the concept of the hydrodynamics-based procedure. Furthermore, the issues associated with the clinical feasibility of its seemingly invasive nature, which is probably the most common concern about this hydrodynamics-based procedure, are discussed along with its future prospects and challenges.

Femoral intra-arterial injection: a tool to deliver and assess recombinant AAV constructs in rodents whole hind limb

With the aim of simplifying recombinant-adeno-associated virus (rAAV) delivery in muscle, a new femoral intra-arterial technique was designed and tested in rodents (rats and mice). Two serotypes, several promoters and transgenes (reporter or therapeutic) were tested using this administration route. The new route is both easy to perform and efficient. Its usefulness as a tool to assess gene delivery constructs in the muscle was established in the context of recombinant AAV serotypes 1 and 2, and with the ubiquitous CMV and two muscle-specific (C5-12 and CK6) promoters. Both serum monitoring of a secreted protein (murine alkaline phosphatase: muSEAP) and slide staining were used to compare the different constructs. Significantly different patterns of expression in kinetics of expression (muSEAP) and homogeneity of fiber transduction (staining) were evidenced with the different promoters tested, and compared with intra-muscular expression patterns. Detailed studies of differential transduction in leg and thigh muscles showed equivalent efficacy, except in rectus femoris, and to a lesser extent in soleus. In light of these results and prior data, intra-arterially mediated gene transfer mechanism is discussed.

Sleeping Beauty Transposon‐Mediated Gene Therapy for Prolonged Expression

The Sleeping Beauty (SB) transposon system represents a new vector for non-viral gene transfer that melds advantages of viruses and other forms of naked DNA transfer. The transposon itself is comprised of two inverted terminal repeats of about 340 base pairs each. The SB system directs precise transfer of specific constructs from a donor plasmid into a mammalian chromosome. The excision of the transposon from a donor plasmid and integration into a chromosomal site is mediated by Sleeping Beauty transposase, which can be delivered to cells vita its gene or its mRNA. As a result of its integration in chromosomes, and its lack of viral sequences that are often detected by poorly understood cellular defense mechanisms, a gene in a chromosomally integrated transposon can be expressed over the lifetime of a cell. SB transposons integrate nearly randomly into chromosomes at TA-dinucleotide base pairs although the sequences flanking the TAs can influence the probability of integration at a given site. Although random integration of vectors into human genomes is often thought to raise significant safety issues, evidence to date does not indicate that random insertions of SB transposons represent risks that are equal to those of viral vectors. Here we review the activities of the SB system in mice used as a model for human gene therapy, methods of delivery of the SB system, and its efficacy in ameliorating disorders that model human disease.

Systemic delivery of genes to striated muscles using adeno-associated viral vectors

A major obstacle limiting gene therapy for diseases of the heart and skeletal muscles is an inability to deliver genes systemically to muscles of an adult organism. Systemic gene transfer to striated muscles is hampered by the vascular endothelium, which represents a barrier to distribution of vectors via the circulation. Here we show the first evidence of widespread transduction of both cardiac and skeletal muscles in an adult mammal, after a single intravenous administration of recombinant adeno-associated virus pseudotype 6 vectors. The inclusion of vascular endothelium growth factor/vascular permeability factor, to achieve acute permeabilization of the peripheral microvasculature, enhanced tissue transduction at lower vector doses. This technique enabled widespread muscle-specific expression of a functional micro-dystrophin in the skeletal muscles of dystrophin-deficient mdx mice, which model Duchenne muscular dystrophy. We propose that these methods may be applicable for systemic delivery of a wide variety of genes to the striated muscles of adult mammals.

Progress and prospects: naked DNA gene transfer and therapy

Increases in efficiency have made naked DNA gene transfer a viable method for gene therapy. Intravascular delivery results in effective gene delivery to liver and muscle, and provides in vivo transfection methods for basic and applied gene therapy and antisense strategies with oligonucleotides and small interfering RNA (siRNA). Delivery via the tail vein in rodents provides an especially simple and effective means for in vivo gene transfer. Electroporation methods significantly enhance direct injection of naked DNA for genetic immunization. The availability of plasmid DNA expression vectors that enable sustained high level expression, allows for the development of gene therapies based on the delivery of naked plasmid DNA.