Uptake of exogenous DNA via the skin

Physical non-viral gene delivery methods for tissue engineering

The integration of gene therapy into tissue engineering to control differentiation and direct tissue formation is not a new concept; however, successful delivery of nucleic acids into primary cells, progenitor cells, and stem cells has proven exceptionally challenging. Viral vectors are generally highly effective at delivering nucleic acids to a variety of cell populations, both dividing and non-dividing, yet these viral vectors are marred by significant safety concerns. Non-viral vectors are preferred for gene therapy, despite lower transfection efficiencies, and possess many customizable attributes that are desirable for tissue engineering applications. However, there is no single non-viral gene delivery strategy that "fits-all" cell types and tissues. Thus, there is a compelling opportunity to examine different non-viral vectors, especially physical vectors, and compare their relative degrees of success. This review examines the advantages and disadvantages of physical non-viral methods (i.e., microinjection, ballistic gene delivery, electroporation, sonoporation, laser irradiation, magnetofection, and electric field-induced molecular vibration), with particular attention given to electroporation because of its versatility, with further special emphasis on Nucleofection™. In addition, attributes of cellular character that can be used to improve differentiation strategies are examined for tissue engineering applications. Ultimately, electroporation exhibits a high transfection efficiency in many cell types, which is highly desirable for tissue engineering applications, but electroporation and other physical non-viral gene delivery methods are still limited by poor cell viability. Overcoming the challenge of poor cell viability in highly efficient physical non-viral techniques is the key to using gene delivery to enhance tissue engineering applications.

Nanopolymeric micelle effect on the transdermal permeability, the bioavailability and gene expression of plasmid

This study attempts to investigate the transdermal permeability, the bioavailability and gene expression of plasmid formulated with nonionic poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) polymeric micelles (PM). Dynamic light scattering (DLS) and atomic force microscopy (AFM) were used to analyze the PM formulated pCMV-Lac Z (P/PM) containing the gene for β-galactosidase (β-Gal) driven by cytomegalovirus early promoter. Franz diffusion cell was used for in vitro transdermal permeability analysis. Real-time PCR was used to quantify the permeated plasmid in vitro and in vivo. β-Gal activity assay was performed to evaluate transgene expression in vivo. The size of P/PM was ~50 nm with round shape. PM significantly enhanced the in vitro transdermal permeability of plasmid in a direction- and temperature-dependent manner. Following transdermal application of P/PM, higher area under the curve (AUC(P/PM): 98.34 h·ng/mL) and longer half-life of plasmid were detected compared with that of plasmid alone (AUC(P): 10.12 h·ng/mL). Additionally, the β-Gal activity was significantly increased in skin, stomach, brain and spinal cord at both 48 and 72 h after P/PM application and in testis and spleen at 72 h postapplication. In conclusion, PM formulation enhanced the permeation of plasmid through skin into blood circulation, increasing its absorption and the transgene expression in various tissues.

The hairless mouse in skin research

The hairless (Hr) gene encodes a transcriptional co-repressor highly expressed in the mammalian skin. In the mouse, several null and hypomorphic Hr alleles have been identified resulting in hairlessness in homozygous animals, characterized by alopecia developing after a single cycle of relatively normal hair growth. Mutations in the human ortholog have also been associated with congenital alopecia. Although a variety of hairless strains have been developed, outbred SKH1 mice are the most widely used in dermatologic research. These unpigmented and immunocompetent mice allow for ready manipulation of the skin, application of topical agents, and exposure to UVR, as well as easy visualization of the cutaneous response. Wound healing, acute photobiologic responses, and skin carcinogenesis have been extensively studied in SKH1 mice and are well characterized. In addition, tumors induced in these mice resemble, both at the morphologic and molecular levels, UVR-induced skin malignancies in man. Two limitations of the SKH1 mouse in dermatologic research are the relatively uncharacterized genetic background and its outbred status, which precludes inter-individual transplantation studies.

Cutaneous gene expression of plasmid DNA in excised human skin following delivery via microchannels created by radio frequency ablation

The skin is a valuable organ for the development and exploitation of gene medicines. Delivering genes to skin is restricted however by the physico-chemical properties of DNA and the stratum corneum (SC) barrier. In this study, we demonstrate the utility of an innovative technology that creates transient microconduits in human skin, allowing DNA delivery and resultant gene expression within the epidermis and dermis layers. The radio frequency (RF)-generated microchannels were of sufficient morphology and depth to permit the epidermal delivery of 100 nm diameter nanoparticles. Model fluorescent nanoparticles were used to confirm the capacity of the channels for augmenting diffusion of macromolecules through the SC. An ex vivo human organ culture model was used to establish the gene expression efficiency of a beta-galactosidase reporter plasmid DNA applied to ViaDerm treated skin. Skin treated with ViaDerm using 50 microm electrode arrays promoted intense levels of gene expression in the viable epidermis. The intensity and extent of gene expression was superior when ViaDerm was used following a prior surface application of the DNA formulation. In conclusion, the RF-microchannel generator (ViaDerm) creates microchannels amenable for delivery of nanoparticles and gene therapy vectors to the viable region of skin.

DNA electrotransfer: its principles and an updated review of its therapeutic applications

The use of electric pulses to transfect all types of cells is well known and regularly used in vitro for bacteria and eukaryotic cells transformation. Electric pulses can also be delivered in vivo either transcutaneously or with electrodes in direct contact with the tissues. After injection of naked DNA in a tissue, appropriate local electric pulses can result in a very high expression of the transferred genes. This manuscript describes the evolution in the concepts and the various optimization steps that have led to the use of combinations of pulses that fit with the known roles of the electric pulses in DNA electrotransfer, namely cell electropermeabilization and DNA electrophoresis. A summary of the main applications published until now is also reported, restricted to the in vivo preclinical trials using therapeutic genes.

Uptake and trafficking of DNA in keratinocytes: evidence for DNA-binding proteins

The skin is an interesting organ for human gene therapy due to accessibility, immunologic potential and synthesis capabilities. In this study, we attempted to visualize and measure the uptake of naked FITC-labeled plasmid by FACS analysis detecting up to 15% internalization in a dose- and time-dependent manner. Cycloheximide treatment inhibited the uptake by >90%, suggesting a protein-mediated uptake. The inhibition of different internalization pathways demonstrated that blocking macropinocytosis (by amiloride and N,N-dimethylamylorid) reduced DNA uptake by >85%, while the inhibition of clathrin-coated pits (by chlorpromazine) and caveolae (by nystatin/filipin III) did not limit the uptake. Colocalization studies using confocal laser microscopy revealed a time-dependent accumulation of plasmid DNA in endosomes and lysosomes. When a green fluorescent protein (GFP) expression vector was used, specific GFP-RNA became detectable by reverse transcriptase-PCR, whereas measurable amounts of protein could not be identified in FACS experiments. To detect the potential DNA receptors on the keratinocyte surface, membrane proteins were extracted and subjected to South-Western blotting using digoxigenin-labeled calf thymus and lambda-phage DNA. Two DNA-binding proteins, ezrin and moesin, known as plasma membrane-actin linkers, were identified by one- and two-dimensional-South-Western blots and matrix-assisted laser desorption and ionization-mass spectrometry. Ezrin and moesin are functionally associated with a number of transmembrane receptors such as the EGF, CD44 or ICAM-1 receptor. Taken together, naked plasmid DNA seems to enter human keratinocytes through different pathways, mainly by macropinocytosis. Two DNA-binding proteins were identified that seemed to be involved in binding/trafficking of internalized DNA.

Skin permeation, biodistribution, and expression of topically applied plasmid DNA

BACKGROUND

Topical application is emerging as a new route of gene delivery. However, the extent of skin permeation and the in vivo fate of topically applied plasmid DNA are not fully understood.

METHODS

In vitro permeation of plasmid DNA across human skin and keratinocyte layers was tested using Franz diffusion cells. In vivo absorption and biodistribution of topically applied plasmid in mice were determined using quantitative polymerase chain reaction (PCR). The expression levels of plasmid DNA in various tissues were measured by semiquantitative reverse transcription PCR.

RESULTS

In vitro, topically applied DNA was capable of penetrating human skin and keratinocyte layers. Following topical application of plasmid DNA onto murine skin, the levels of plasmid DNA in the serum peaked at 4 hr. At 24 hr post-dose, topically applied DNA existed at higher levels than intravenously administered DNA in almost all tissues, and induced 11.4- and 22-fold higher mRNA expression in muscle and skin, respectively. Moreover, the topical route showed sustained expression of plasmid DNA in the regional lymph nodes over 5 days, whereas the intravenous route did not.

CONCLUSIONS

Taken together, our results show that topically applied plasmid DNA is capable of permeating the skin and being expressed for prolonged periods in various tissues including lymph nodes. This suggests that skin may provide an appealing, noninvasive route of delivery for DNA vaccines and other therapeutic genes.

Cell type-dependent divergence of transactivation by glucocorticoid receptor ligand

The glucocorticoid receptor regulates gene expression mainly by two mechanisms; transactivation and trans-repression. A ligand with strong transrepression and weak transactivation activity is predicted to be a beneficial agent with potent anti-inflammatory activity and minor adverse effects. Recently, the profile of a synthetic steroid, RU24858, has been reported to fulfill this condition in vitro, but others have reported no dissociation between the anti-inflammatory activity and side effects in vivo. To gain further information on the profile of this compound, we evaluated its transactivation ability using a reporter gene analysis both in vitro and in vivo. In the in vitro analysis, RU24858 demonstrated only a weak transactivation activity in HeLa cells, when compared with prednisolone. In CV-1 cells, however, these two glucocorticoids exhibited equivalent transactivation activities. This behavior is independent of whether the reporter gene is regulated by mouse mammary tumor virus promoter or multiple copies of glucocorticoid response element. When the reporter plasmid was inoculated into mouse abdominal skin using a gene gun, followed by orally administration of glucocorticoids, RU24858 induced significantly higher reporter enzyme activity than prednisolone. These results suggest that the profile of RU24858 is divergent and its transactivation ability is comparable to prednisolone depending on the cell-type both in vitro and in vivo.

Characterisation of LMD virus-like nanoparticles self-assembled from cationic liposomes, adenovirus core peptide mu and plasmid DNA

Liposome:mu:DNA (LMD) is a ternary nucleic acid delivery system built around the mu peptide associated with the condensed core complex of the adenovirus. LMD is prepared by precondensing plasmid DNA (D) with mu peptide (M) in a 1:0.6 (w/w) ratio and then combining these mu:DNA (MD) complexes with extruded cationic liposomes (L) resulting in a final lipid:mu:DNA ratio of 12:0.6:1 (w/w/w). Correct buffer conditions, reagent concentrations and rates of mixing are all crucial to success. However, once optimal conditions are established, homogeneous LMD particles (120 +/- 30 nm) will result that each appear to comprise an MD particle encapsulated within a cationic bilammellar liposome. LMD particles can be formulated reproducibly, they are amenable to long-term storage (>1 month) at -80 degrees C and are stable to aggregation at a plasmid DNA concentration up to 5 mg/ml (15 mM nucleotide concentration). Furthermore, LMD transfections are significantly more time and dose efficient in vitro than cationic liposome-plasmid DNA (LD) transfections. Transfection times as short as 10 min and plasmid DNA doses as low as 0.001 microg/well result in significant gene expression. LMD transfections will also take place in the presence of biological fluids (eg up to 100% serum) giving 15-25% the level of gene expression observed in the absence of serum. Results from confocal microscopy experiments using fluorescent-labelled LMD particles suggest that endocytosis is not a significant barrier to LMD transfection, although the nuclear membrane still is. We also confirm that topical lung transfection in vivo by LMD is at least equal in absolute terms with transfection mediated by GL-67:DOPE:DMPE-PEG(5000) (1:2:0.05 m/m/m), an accepted 'gold-standard' non-viral vector system for topical lung transfection, and is in fact at least six-fold more dose efficient. All these features make LMD an important new non-viral vector platform system from which to derive tailor-made non-viral delivery systems by a process of systematic modular upgrading.

Suppression of cutaneous inflammation by intradermal gene delivery

Biological effects of in vivo transfection of a potential anti-inflammatory gene, designated Sm16, cloned from the human parasite Schistosoma mansoni were analyzed in these studies. A single intradermal injection of a full-length cDNA of Sm16 resulted in the expression of Sm16 in the epidermis, dermis, skin migratory cells and skin-draining lymph nodes of mice for up to 7 days. Subsequently the anti-inflammatory effect of this gene expression was evaluated by inducing an inflammatory response in the skin of mice. These studies showed that Sm16 gene delivery resulted in a significant suppression of cutaneous inflammation as shown by a reduction in cutaneous edema, decrease in neutrophil infiltration, suppression of pro-inflammatory cytokine expression and down-regulation of ICAM-1 expression in the skin inflammatory site. Cells collected from the skin-draining lymph nodes showed reduced proliferation to mitogen. Multiple intradermal injection of Sm16 cDNA failed to induce any antibody response in mice for up to 8 weeks after initial injection. These findings suggest a potential for developing Sm16 gene delivery as a therapeutic agent for treating inflammatory skin disorders.

Enhanced cutaneous gene delivery following intradermal injection of naked DNA in a high ionic strength solution

Intradermal injection of naked DNA results in gene transfer to skin cells, but the efficiency of this gene transfer method is relatively low and variable. We have systematically optimized several parameters to obtain reproducible, high-level gene transfer to the mouse skin. Older mice (approximately 7 weeks) showed a significant decrease in gene expression compared with younger mice (4-5 weeks old). The composition of the solvent vehicle (electrolyte versus nonelectrolyte) strongly affected gene expression in the skin. A higher level of gene expression was achieved when naked DNA was dissolved in isotonic phosphate buffered saline solution compared with isotonic dextrose solution. Finally, transfection efficiency in older mice was greatly improved by increasing the ionic strength of the solvent vehicle. The improved transfection efficiency was due to an enhanced DNA uptake by the skin cells. Gene transfer was most evident in the subdermal smooth muscle cells and epidermal cells. With the optimized conditions, gene transfer mediated by intradermal injection of naked DNA was comparable in efficiency to electroporation. However, cellular distributions of the gene transfer of the two methods were different.

Safety and pharmacokinetics of naked plasmid DNA in the skin: studies on dissemination and ectopic expression

Gene therapy using naked DNA injected into muscle and skin is increasingly being used for vaccination and treatment purposes. Favorably, naked plasmid DNA does not exhibit the various limitations inherent to viral vectors, such as the elicitation of adverse immune responses and the risk of insertional mutagenesis. In order to assess the distribution and safety of naked plasmid DNA in a relevant animal model, we analyzed if intracutaneously injected plasmid DNA was transported to other organs and if ectopic expression occurred. When a "superdose" of a marker plasmid was injected intradermally, most organs were found transiently to contain the plasmid DNA for several days, whereas integration into the host genome was not detected. With the exception of ovary, however, mRNA expression only occurred in the skin, regional lymph nodes, and muscular tissues. From a safety standpoint, skin gene therapy with naked plasmid DNA can be considered safe due to the rapid biodegradation of plasmid DNA and the exclusive and transient expression of foreign genes in tissues known to take up DNA.

The use of PAMAM dendrimers in the efficient transfer of genetic material into cells

Polyamidoamine (PAMAM) dendrimers have steadily grown in popularity in the past decade in a variety of disciplines, ranging from materials science to biomedicine. This can be attributed in part to their use in applications that range from computer toners to medical diagnostics. PAMAM dendrimers are safe and nonimmunogenic, and can function as highly efficient cationic polymer vectors for delivering genetic material into cells. They have been shown to be as efficient or more efficient than either cationic liposomes or other cationic polymers (e.g. polyethylenimine, polylysine) for in vitro gene transfer. This article will focus on the application of PAMAM dendrimers as a nonviral gene delivery vector from the initial discovery of this capacity to the most recent experimental findings.