Iontophoretic delivery of oligonucleotides across full thickness hairless mouse skin

Topical gene silencing by iontophoretic delivery of an antisense oligonucleotide-dendrimer nanocomplex: the proof of concept in a skin cancer mouse model

The study was aimed at investigating the feasibility of using a poly (amidoamine) (PAMAM) dendrimer as a carrier for topical iontophoretic delivery of an antisense oligonucleotide (ASO). Bcl-2, an anti-apoptotic protein implicated in skin cancer, was used as the model target protein to demonstrate the topical gene silencing approach. Confocal laser scanning microscopy studies demonstrated that the iontophoretically delivered ASO-dendrimer complex can reach the viable epidermis in porcine skin. In contrast, passively delivered free or dendrimer complexed ASO was mainly localized to the stratum corneum. The cell uptake of ASO was significantly enhanced by the dendrimer complex and the complex suppressed Bcl-2 levels in the cell. In the skin cancer mouse model, the iontophoretically delivered ASO-dendrimer complex reduced the tumor volume by 45% and was consistent with the reduction in Bcl-2 protein levels. The iontophoretically delivered ASO-dendrimer complex caused significant apoptosis in skin tumor. Overall, the findings from this study demonstrate that dendrimers are promising nanocarriers for developing topical gene silencing approaches for skin diseases.

Effect of iontophoresis on the in vitro trans-scleral transport of three single stranded oligonucleotides

Oligonucleotides represent a subject of clinical interest due to their potential ability to treat several diseases, including those affecting the posterior segment of the eye. Unfortunately, therapeutic oligonucleotides are currently administered by means of highly invasive approaches, such as intravitreal injections. The aim of the present work was to study in vitro, across isolated bovine sclera, the effect of iontophoresis on the transport of three single stranded oligonucleotides (ssDNA), 12-, 24- and 36-mer, selected as reference compounds in view of a non-invasive drug delivery to the back of the eye. All the three sequences were able to cross bovine sclera in vitro without iontophoresis. When anodal iontophoresis was applied, no change in flux was observed, while in the presence of cathodal iontophoresis the permeability coefficients increased four-fold compared to passive conditions. This behavior can be ascribed to the electrorepulsive mechanism, due to the negative charge of the nucleic acid backbone. It was also observed that the molecular weights of the three sequences did not affect trans-scleral transport, neither in passive, nor in current assisted permeation. Furthermore, increasing the current intensity from 1.75 mA to 3 mA, no effect on the trans-scleral transport of the 24-mer was noticed. Although preliminary, the results demonstrate that cathodal iontophoresis enhances trans-scleral transport of single stranded oligonucleotides and suggest its use as a novel non-invasive approach for the treatment of diseases affecting the posterior segment of the eye.

Noninvasive and efficient transdermal delivery of CpG-oligodeoxynucleotide for cancer immunotherapy

Oligodeoxynucleotides containing unmethylated cytosine-phosphate-guanosine motifs (CpG-ODN) possess immunostimulatory effects and potential antitumor activity. Since the skin is an easily available site of administration of CpG-ODN due to its accessibility and the presence of abundant antigen presenting cells, it is expected that the application of CpG-ODN to the skin would induce systemic immune response and antitumor activity. However, it is difficult to deliver hydrophilic macromolecules including CpG-ODN through the skin. We have previously demonstrated that small interfering RNA (siRNA) was efficiently delivered into rat epidermis by iontophoresis. In this report, we investigate the effect of transdermal iontophoretic delivery of CpG-ODN on the induction of immune responses and antitumor activity against B16F1 melanoma in mice. Iontophoresis promoted CpG-ODN delivery into the epidermis and dermis. Furthermore, iontophoretic delivery of CpG-ODN to the skin induced the expression of proinflammatory and Th1-type cytokines in the skin and draining lymph node. Finally, transdermal iontophoretic delivery of CpG-ODN led to antitumor activity against B16F1 melanoma. Interestingly, the CpG-ODN administration site is not restricted to the tumor area. In conclusion, CpG-ODN delivered transdermally induced potent antitumor activity, and our system is expected to serve as a simple and noninvasive approach for cancer immunotherapy.

Antisense targeting of cFLIP sensitizes activated T cells to undergo apoptosis and desensitizes responses to contact dermatitis

Contact dermatitis is the result of inflammatory responses mediated by hapten-specific activated CD8+ and CD4+ T cells. Activation-induced cell death (AICD) is a naturally occurring process regulating the resolution of T-cell responses through decreased expression of the antiapoptotic molecule cellular FLICE inhibitory protein (cFLIP). We show that targeting cFLIP expression in vitro and in vivo, with morpholino antisense applied systemically or topically in conjunction with antigen, sensitizes T cells to undergo "early" AICD resulting in tolerance. Analysis of antisense-treated CD8+ OT-1 splenocytes after co-culture with SIINFEKL-pulsed DCs showed apoptosis occurring in a dose-dependent manner with respect to cFLIP peptide-conjugated phosphorodiamidate morpholino oligomer (PPMO) concentration. A transplant acceptance model using male DO.11 donor cells and female BALB/c recipient mice showed that cFLIP antisense treatment could promote antigen tolerance. Hypersensitivity responses induced in mice by the epicutaneous application of the haptens FITC and oxazolone confirmed that topically applied cFLIP antisense could reduce inflammation. Treatment of the skin produced significant reduction in dermatitis and localized infiltration of lymphocytes. Moreover, the treatment was target- and antigen-specific, dose-dependent, and capable of inducing long-lived tolerance. These data suggest that the targeted expression of immune-regulating molecules is possible through the application of antisense to the skin.

State of the art and perspectives for the delivery of antisense oligonucleotides and siRNA by polymeric nanocarriers

Knocking down gene expression using either antisense oligonucleotides (AS-ODNs) or small interfering RNA (siRNAs) has raised a lot of interest in designing new pathways for therapeutics. Despite their potentialities, these negatively charged and hydrophilic molecules request chemical modifications or a carrier that allows cell recognition, cell internalization and moreover subcellular penetration. Although chemical modifications were brought to the basic AS-ODNs and siRNAs, their sensitivity to degradation and poor intracellular penetration is still hampering their clinical applications. We present here the potentialities of polymeric carriers or the use of alternative administration route such as oral, ocular and skin delivery to improve their delivery and to circumvent the hurdles for their clinical applications.

Transdermal drug delivery: Basic principles for the veterinarian

The use of topical pharmaceutical formulations is increasingly popular in veterinary medicine. A potential concern is that not all formulations are registered for the intended species, yet current knowledge strongly suggests that simple extrapolation of transdermal drug pharmacokinetics and pharmacodynamics between species, including humans, cannot be done. In this review, an overview is provided of the underlying basic principles determining the movement of topically applied molecules into and through the skin. Various factors that may affect transdermal drug penetration between species, between individuals of a particular species and regional differences in an individual are also discussed. A good understanding of the basic principles of transdermal drug delivery is critical to avoid adverse effects or lack of efficacy when applying topical formulations in veterinary medicine.

Transdermal delivery of phosphorodiamidate Morpholino oligomers across hairless mouse skin

The skin is the largest organ in the body and an obvious route for both local and systemic drug delivery. Antisense oligomers have tremendous potential as therapeutic agents for numerous diseases. The objective of this study was to investigate the influence of vehicle on the transdermal delivery of several phosphorodiamidate Morpholino oligomers (PMOs) with different sizes, lengths, base compositions, sequences, and lipophilicities. Eleven different PMOs were synthesized complementary to biologically relevant gene targets and delivered across hairless mouse skin in vitro using vehicles composed of 95% propylene glycol, 5% linoleic acid (PG/LA), water, 50% water:50% PG/LA, and 75% water:25% PG/LA. The data suggest that size, sequence and guanine composition all influence transdermal penetration. There was an inverse linear relationship between size and penetration for a given sequence when the PG/LA formulation was used (r2 = 0.94), but this trend was not evident when the vehicle contained water. An oligomer targeted to the gene p53 had lower than expected transdermal penetration based on its size, but was shown to localize within the skin, demonstrating that sequence and thus target will impact transdermal delivery. The presence of G-quartets correlated with better PMO penetration from a water vehicle. Overall, the data suggest that some oligomers and vehicles would be better for transdermal delivery and others for topical applications.

Antisense oligonucleotide treatments for psoriasis

Antisense oligonucleotides are emerging as an exciting therapeutic strategy for treating skin diseases such as psoriasis. Potential antisense targets are proteins upregulated in psoriatic skin, in particular those associated with inflammation (intercellular adhesion molecule [ICAM]-1, IL-2 and -8), proliferation (insulin-like growth factor type I receptor [IGF-IR], epidermal growth factor) and hyperangiogenesis (vascular endothelial growth factor [VEGF]). Whereas topical application and subsequent penetration of large oligonucleotides into normal skin is problematic, the impaired barrier function of psoriatic lesions permits the uptake of antisense drugs. Studies to date indicate that topically applied antisense molecules can be delivered to target cells in the epidermis and dermis of psoriatic skin. Antisense-mediated suppression of target mRNA and protein has been demonstrated in models of human skin grafted to immunosuppressed mice and in hairless mouse models of skin inflammation. In a xenograft model of human psoriasis, treatment with repeated intradermal injections of IGF-IR antisense caused a normalisation of the epidermal hyperproliferation. This class of drug, therefore, holds much potential for the successful treatment of psoriasis in the clinical setting.

Intradermal delivery of antisense oligonucleotides by the pulse depolarization iontophoretic system

The intradermal delivery of an antisense oligonucleotide was examined by iontophoresis. In this experiment, the antisense sequence of [(32)P]-labeled phosphodiester oligonucleotide ([(32)P]D-oligo, 18-mer) hybridizing to mouse interleukin 10 (IL-10) mRNA was used as a model D-oligo. In in vitro iontophoretic experiments, isolated hairless mouse skin was used with a horizontal diffusion cell. The enhancing effect of pulse depolarization (PDP) iontophoresis on the [(32)P]D-oligo permeation through the skin was better, and the skin irritation was less, than those of constant direct current (CDC) iontophoresis. The apparent fluxes of [(32)P]D-oligo were enhanced with the increasing current densities and [(32)P]D-oligo concentrations in the donor solution, whereas the enhanced flux decreased with the increasing NaCl concentrations in the donor solution. An optimum electric current was observed for the intradermal delivery of [(32)P]D-oligo, and intact [(32)P]D-oligo was detected within the skin after iontophoresis for 6 h. These results suggest that PDP iontophoresis may be useful for the intradermal delivery of antisense oligonucleotides.

Innovations in oligonucleotide drug delivery

Oligonucleotides (ONs) are a new class of therapeutic compounds under investigation for the treatment of a variety of disease states, such as cancer and HIV, and for FDA approval of an anti-CMV retinitis antisense molecule (Vitravene trade mark, Isis Pharmaceuticals). However, these molecules are limited not only by poor cellular uptake, but also by a general lack of understanding regarding the mechanism(s) of ON cellular uptake. As a result, various delivery vehicles have been developed that circumvent the proposed mechanism of uptake, endocytosis, while improving target specific delivery and/or drug stability. This review describes various traditional and novel delivery mechanisms that have been employed to improve ON cellular delivery, cost effectiveness, and therapeutic efficacy.

Iontophoresis-based transdermal delivery systems

Transdermal iontophoresis is the administration of ionic therapeutic agents through the skin by the application of a low-level electric current. This article presents an overview of transdermal iontophoretic delivery of drugs, including peptides and oligonucleotides. Recent advances in the area of iontophoretic delivery, including devices, hydrogel formulations, safety, clinical relevance and future prospects, are discussed. Electroporation, another method of electrically assisted drug delivery, is also briefly reviewed. Transdermal iontophoresis appears to be a promising technique for the delivery of a variety of compounds in a controlled and preprogrammed manner. Transdermal iontophoresis would be particularly useful in the delivery of hydrophilic drugs produced by biotechnology (peptides and oligonucleotides). However, because of the complex physicochemical properties of peptides, many factors must be carefully considered for the proper design of an iontophoretic drug delivery system for peptides. Iontophoresis has been successfully used in the delivery of small peptides, such as leuprolide and calcitonin analogues, in humans. However, it appears that transdermal iontophoresis may not be a suitable method for the systemic delivery of larger peptides (>7,000D). The combined use of iontophoresis and electroporation may be more effective in the delivery of peptides, proteins, genes and oligonucleotides. The long-term safety of iontophoresis, patient compliance with the technique and the commercial success of this technology are yet to be demonstrated. Iontophoretic delivery of drugs would be beneficial in the treatment of certain skin disorders such as skin cancer, psoriasis, dermatitis, venous ulcers, keloid and hypertrophic scars. Investigations on reverse iontophoresis may yield interesting results that would be useful in the noninvasive measurement of clinically important molecules in the body.

Distribution and quantification of polyethylenimine oligodeoxynucleotide complexes in human skin after iontophoretic delivery using confocal scanning laser microscopy

Iontophoresis may be a potentially useful technique for the delivery of oligonucleotides into the skin. To enhance intracellular uptake during iontophoresis, we investigated the dermal delivery of oligodeoxynucleotides (ODN) as a polyelectrolyte complex with polyethylenimine (PEI). Perpendicular cross-sectioning was performed to visualize and quantify the penetration properties of double labeled PEI/ODN complexes across full thickness human skin. Due to the net positive charge of the complexes, anodal iontophoresis was expected to enhance skin delivery by electrorepulsion compared to passive diffusion. Confocal laser scanning microscopy demonstrated that non-complexed ODN could penetrate the skin after 1 h of cathodal iontophoresis but not by passive diffusion or anodal iontophoresis. However, extensive degradation occurred as documented by a dramatic decrease of fluorescence intensity within viable skin tissue after 10 h. Anodal iontophoresis of the complexes led to a deep penetration of both the TAMRA-labeled ODN and the Oregon Green-labeled PEI. A constant increase in fluorescence indicated a protective effect of the polymer against nuclease degradation. Co-localization of red and green fluorescence was noted within numerous nuclei of epidermal keratinocytes. In contrast, passive diffusion of the complexes did not lead to successful uptake into keratinocytes and was limited to the stratum corneum. Complexation of ODN by PEI, therefore, seems to be a promising method to enhance both the transport of charged complexes into the skin and to facilitate intracellular uptake, which may potentially be useful for the local treatment of skin diseases using ODN.

C-5 propyne-modified oligonucleotides penetrate the epidermis in psoriatic and not normal human skin after topical application

We have previously shown that antisense oligonucleotides effectively reduced insulin-like growth factor I receptor expression in human psoriatic skin grafted on to nude mice when injected intradermally. We therefore investigated the penetration of C-5 propyne modified antisense oligonucleotides into human normal and psoriatic skin after topical administration. Oligonucleotide (37.5 microg; 250 microM) was applied in aqueous solution or 5% methylcellulose gel for 24 h, prior to live confocal microscopy and fluorescence microscopy of fixed sections. We found that oligonucleotide could penetrate through the stratum corneum of psoriatic but not normal human skin over large regions of the epidermis. The oligonucleotide was localized to the nucleus of large parakeratotic cells in the psoriatic skin as well as smaller basal and suprabasal keratinocytes. In normal human skin, oligonucleotide was confined to the stratum corneum, with little or no oligonucleotide apparent in the viable epidermis. Electrophoresis of oligonucleotide recovered from treated psoriatic and normal skin revealed that the oligonucleotide remained intact over the 24 h period. In summary, we found that C-5 propyne modified antisense oligonucleotides could reach the target cells (in this case basal keratinocytes) after topical administration to psoriatic but not normal skin.

Novel mechanisms and devices to enable successful transdermal drug delivery

Optimisation of drug delivery through human skin is important in modern therapy. This review considers drug-vehicle interactions (drug or prodrug selection, chemical potential control, ion pairs, coacervates and eutectic systems) and the role of vesicles and particles (liposomes, transfersomes, ethosomes, niosomes). We can modify the stratum corneum by hydration and chemical enhancers, or bypass or remove this tissue via microneedles, ablation and follicular delivery. Electrically assisted methods (ultrasound, iontophoresis, electroporation, magnetophoresis, photomechanical waves) show considerable promise. Of particular interest is the synergy between chemical enhancers, ultrasound, iontophoresis and electroporation.

Iontophoretic transport of oligonucleotides across human epidermal membrane: a study of the Nernst-Planck model

The objective of this study was to investigate the transport behavior of a series of oligonucleotides with human epidermal membrane (HEM) and to examine the applicability of the modified NERNST-PLANCK model to transdermal iontophoresis of these macromolecules. Iontophoretic transport experiments were first carried out in a synthetic model membrane system (Nuclepore membranes) with a four-electrode potentiostat to examine the baseline modified NERNST-PLANCK model. The modified NERNST-PLANCK model derived from the Einstein relation and the Stokes-Einstein equation taken from previous work did not hold for the oligonucleotides. Results obtained in the Nuclepore studies were, however, consistent with predictions of the modified NERNST-PLANCK model using the experimentally determined electromobilities and diffusion coefficients. The electromobilities of the oligonucleotides (determined by capillary electrophoresis) were found to be more than a factor of two smaller than expected from the Einstein relation between electromobilities and diffusion coefficients (the latter determined in diffusion cell experiments). A correlation between these electromobilities and the theoretical electromobilities estimated by considering the effects of counterion binding and the effects of mobility reduction according to colloid theory was also observed. These results suggest that the modified NERNST-PLANCK model predictions are satisfactory only when the electromobilities and the effective molecular size of the oligonucleotides are known and are used directly to predict the iontophoretically enhanced transport. Results with the HEM experiments generally agreed with model predictions based on the experimental electromobilities. The oligonucleotide HEM flux data also suggest the existence of pores with effective pore radii greater than the effective radii estimated in previous studies with small molecular weight model permeants.

Antisense oligonucleotides in cutaneous therapy

Antisense oligonucleotides have been the subject of intense interest as research tools to elucidate the functions of gene products and as therapeutic agents. Initially, their mode of action was poorly understood and the biological effects of oligonucleotides were often misinterpreted. However, research into these gene-based inhibitors of cellular action recently has succeeded in realising their exciting potential, particularly as novel therapeutic agents. An emerging application of this technology is in cutaneous therapy. The demand for more effective dermatological drugs will ensure further development of antisense strategies in skin, with key issues being drug delivery, therapeutic target selection, and clinical applicability.

Transdermal delivery of antisense compounds

Antisense technology holds tremendous promise for therapeutic applications and the study of gene function. A broadly applicable route of administration that would provide for non-invasive, simple, and convenient delivery is highly desirable. Application of oligonucleotides to the skin may represent a solution to the delivery question for both local treatment of skin disease and for systemic delivery. The iontophoretic mode of delivery for phosphorothioate oligonucleotides across hairless mouse skin reveals the potential limitation in the delivery of sufficient oligonucleotide to provide for efficacy. A potential solution to this problem is the use of significantly more potent C-5 propyne base modifications in a phosphorothioate oligonucleotide. The combination of the iontophoretic delivery mode with potent oligonucleotides resulted in selective inhibition of the CYP3A2 gene expression in the rat liver. Alternatively, oligomers with neutral charge combined with passive modes of transdermal delivery may also be feasible and represent an even more broadly applicable technology. Future studies will focus on specific applications of local and systemic therapy of antisense oligonucleotide in animal models for the design of treatment regimens.

Electroporation-mediated delivery of 3'-protected phosphodiester oligodeoxynucleotides to the skin

The feasibility of topical delivery in the skin of 3' end modified phosphodiester oligonucleotides using electroporation was investigated. Experiments were performed in vitro, using hairless rat skin. Five pulses of (200 V, 450 ms) were applied. The 3' end modifications of the 15 mer oligonucleotide were: (1) 3'-aminohexyl, (2) biotin, with a triethyleneglycol arm, (3) methylphosphonate links between nucleotides 13, 14 and 15, and (4) 2-O-methyl nucleotides at 13, 14 and 15 positions. All the modifications were efficient to protect the oligonucleotides against degradation in the skin. Electroporation increased the topical delivery of the 3' end-modified phosphodiesters by two orders of magnitude compared to passive diffusion, without significant differences between the derivatives. Oligonucleotide concentrations in the range of 1 microm could be achieved in the viable skin. The delivery of a phosphorothioate congener was lower than phosphodiester delivery due to the interaction of phosphorothioate with the stratum corneum. Consequently, 3' end-protected phosphodiesters could be an interesting alternative to phosphorothioate oligonucleotides for topical treatment of cutaneous diseases.

Delivery of nalbuphine and its prodrugs across skin by passive diffusion and iontophoresis

The in vitro transport of nalbuphine (NA) and its prodrugs across various skins was investigated in order to assess the effects of prodrug lipophilicity on passive as well as iontophoretic permeation. The passive diffusion of NA and its prodrugs increased with the drug lipophilicity. Iontophoresis significantly increased the transport of NA and its prodrugs; the enhancement ratio was highest for NA and decreased as the drug lipophilicity increased. Measurements using intact and stratum corneum (SC)-stripped skins showed that the SC was the major skin diffusion barrier for the passive permeation of NA and nalbuphine pivalate (NAP). The iontophoretic permeation of NA and NAP across intact and SC-stripped skins indicated that the SC layer was not rate-limiting for the permeation of NA, but remained the rate-limiting barrier for transdermal permeation of NAP. Permeation studies using SC-stripped and delipidized skins suggested that the intercellular pathway was the predominant route for the passive permeation of NA and NAP as well as the iontophoretic permeation of NAP across the SC. The relative rates of passive and iontophoretic permeation across Wistar rat skins demonstrated that a significant amount of NA may permeate skin via the appendageal routes, whereas NAP permeated predominantly through the lipid matrix.

Cutaneous vaccination: the skin as an immunologically active tissue and the challenge of antigen delivery

Vaccination is one of the major achievements of modern medicine. As a result of vaccination, diseases such as polio and measles have been controlled and small pox has been eradicated. However, despite these successes there are still many microbial diseases that cause tremendous suffering because there is no vaccine or the vaccines available are inadequate. In addition, even if vaccines were available for all infectious diseases there is no guarantee that people would use them routinely. One of the major impediments to ensuring vaccine efficacy and compliance is that of delivery. Presently most vaccines are given by intramuscular administration. Unfortunately this is often traumatic, especially in infants. Thus, if it was possible to replace intramuscular immunization by mucosal (oral/intranasal) or transdermal delivery it may be possible to both enhance mucosal immunity as well as improve overall compliance rates. The transdermal route has been used by the pharmaceutical industry for the delivery of various low molecular weight drugs. Some of the approaches used for smaller compounds may also have potential for delivery of either protein or polynucleotide vaccines. However, there is a greater challenge to delivering large molecular weight molecules through the skin due to size, charge and other physicochemical properties. This review will describe the recent advances that have been made in dermal and topical delivery as related to vaccines.

Visualization and analysis of electroosmotic flow in hairless mouse skin

PURPOSE

To identify the physiological structures in hairless mouse skin responsible for the generation of electroosmotic flow during iontophoresis. Also, to determine the effects of changing the pH of the contacting solution on the magnitude of electroosmotic flow in these structures.

METHODS

Localized diffusive and iontophoretic fluxes of a neutral molecule, hydroquinone (HQ), across hairless mouse skin were quantified using scanning electrochemical microscopy (SECM). The iontophoretic flux was determined as a function of the direction of the applied current and pH of the contacting solution.

RESULTS

SECM images of HQ transport recorded during iontophoresis at moderate current densities (+/-0.1 mA/cm2) demonstrate that electroosmotic flow is localized to hair follicles. The direction of flow is from anode to cathode at pH > 3.5 and from cathode to anode at pH <3.5.

CONCLUSIONS

Electroosmotic flow through hair follicles is an efficient and controllable means of transporting small, electrically neutral molecules across hairless mouse skin. Transport through the appendages is sensitive to the pH of the solution in contact with the skin. The isoelectric point of hair follicles, pI, is estimated to be 3.5 from the dependence of electroosmotic flow on the solution pH.

Absorption of antisense oligonucleotides in rat intestine: effect of chemistry and length

An in situ single-pass perfusion model was used to assess the effect of chemical modification and length on permeability and absorption of various oligonucleotides in rat intestine. Phosphorothioate oligodeoxynucleotides (PS-ODN) were compared with oligoribonucleotides with 2'-methoxyethyl (MOE) or 2'-O-methyl (OMe) modifications. A 25-mer PS-OMe-modified oligonucleotide showed relatively poor permeability in this model, as did unmodified 20-mer PS-ODN (permeability coefficient [P(eff)] = 2-8 X 10(-6)cm/sec). Modifying some or all of the oligonucleotides with 2'-MOE groups on deoxyribose and 5'-methylation of the cytosines substantially increased intestinal permeability of oligonucleotides. Both partially and fully modified PS-MOE oligonucleotides showed a (2-4)-fold increase in permeability as compared with unmodified PS-ODN. The presence of a phosphodiester backbone in MOE-modified compounds led to further increases in intestinal permeability. PS-MOE composed of 6, 8, 10, 12, 14, 16, 18, 20, and 22 nucleotides were also examined. It was found that the permeability of these oligonucleotides increased linearly with decreasing length.

Cell binding, uptake and cytosolic partition of HIV anti-gag phosphodiester oligonucleotides 3'-linked to cholesterol derivatives in macrophages

The purpose of this study is to evaluate the cell interactions of a new class of compounds composed of phosphodiester oligonucleotides linked to the cholesterol group at position 3, 7, or 22 of the steroid structure. The resulting conjugates were assessed for their capacity to bind, penetrate and partition in the cytoplasmic compartment of murine macrophages. The results showed that lipophilic conjugates bind to cells much faster (t(1/2) < or = 10 min) than do underivatized oligomers. Oligomers tethered to the cholesterol at positions 3 and 7 (PO-GEM-3-Chol and PO-GEM-7-Chol) interacted more efficiently with cell membranes and were better internalized than oligomers attached to the cholesterol moiety at position 22 (PO-GEM-22-Chol). The cytosolic fraction of internalized oligomers was studied by a digitonin-based membrane permeabilization method. The recovered fraction of oligomers that can freely diffuse from the cytosol was comparable for GEM-91, a phosphorothioate congener, and for PO-GEM-7-Chol (50-60% of the internalized oligomers), while that of PO-GEM-3-Chol was less (30% of the internalized oligomers) indicating a higher membrane affinity of the latter derivative as compared to the other investigated compounds. Membrane binding and cell internalization correlated well with the hydrophobicity of the conjugates as characterized by their partition coefficients in a water-octanol system. Due to their capacity of rapid binding and cytosolic partition in cells, cholesterol-derivatized oligonucleotides at position 3 or 7 of the steroid molecule appeared as good candidates for systemic delivery of anti-HIV antisense compounds.

An experimental model for interpreting percutaneous penetration of oligonucleotides that incorporates the role of keratinocytes

Oligonucleotides have been extensively studied for their potential as therapeutic agents. Phosphorothioate oligonucleotides have been demonstrated to be particularly useful due to their stability against nucleases, their ability to be internalized by many cell types, and the ease with which they hybridize with target mRNA. These compounds have previously been delivered across the skin with the aid of iontophoresis. During transdermal delivery, the first viable cells exposed to the oligonucleotides are the keratinocytes. The purpose of this study was to determine the relationship between internalization of these compounds by keratinocytes and their transport across the skin. The in vitro uptake of 15 different fluorescently labeled phosphorothioate oligonucleotides into human keratinocytes was quantitatively measured with a fluorometer. Photomicrographs of keratinocytes indicate diffuse cytoplasmic and nuclear localization. The ability of these molecules to enter cells was linearly related to size. Cellular uptake data were inversely correlated with previously reported steady-state transport levels of oligonucleotides that had been transdermally delivered by iontophoresis across hairless mouse skin. Oligonucleotides that readily entered keratinocytes had a decreased ability to penetrate skin under iontophoretic conditions. The results indicate that oligonucleotide sequences may be designed for treating skin diseases (high uptake, low transport) or systemic disorders (low uptake, high transport).

Localization of a FITC-labeled phosphorothioate oligodeoxynucleotide in the skin after topical delivery by iontophoresis and electroporation

PURPOSE

The aim of this study was to verify the hypothesis that the application of high voltage to the skin enhances both stratum corneum and keratinocyte permeability. Therefore, the transport of FITC labelled phosphorothioate oligonucleotides (FITC-PS) administered by passive diffusion, iontophoresis or electroporation was localized.

METHODS

Fluorescent microscopy and laser scanning confocal microscopy were used to visualize the FITC-PS transport at the tissue and cell level respectively in hairless rat skin after electroporation (5 x (200 V approximately 500 ms) or iontophoresis (same amount of charges transferred).

RESULTS

FITC-PS did not penetrate the viable skin by passive diffusion. Molecular transport in the skin upon electroporation or iontophoresis was localized and implied mainly hair follicles for iontophoresis. In the stratum corneum, the pathways for FITC-PS transport were more transcellular during electroporation and paracellular during iontophoresis. FITC-PS were detected in the nucleus of the keratinocytes a few minutes after pulsing. In contrast, iontophoresis did not lead to an uptake of the oligomer.

CONCLUSIONS

The internalization of FITC-PS in the keratinocytes after electroporation confirms the hypothesis and suggests that electroporation, which allows both efficient topical delivery and rapid cellular uptake of the oligonucleotides, might be useful for antisense therapy of epidermal diseases.

Parameters controlling topical delivery of oligonucleotides by electroporation

Electroporation, using high voltage electrical pulses has been recognized as a powerful method for delivering macromolecules such as DNA and proteins in cells, or smaller molecules through the skin. Transdermal electroporation could combine targeted delivery of drugs to the skin and permeabilization of skin cells, suggesting that electroporation could be an interesting alternative for topical delivery of oligonucleotides. This work is devoted to the determination of the electroporation parameters that allow optimal delivery of oligonucleotides to the viable tissues of hairless rat skin in vitro. Phosphorothioate derivatives were preferred to the phosphodiester congeners as the former were found to be much less degraded when extracted from the tissues. Long duration (100-500 ms)--medium voltage (100-200 V)--exponentially decaying pulses appeared to be the best conditions for delivering oligonucleotides to the skin. The oligonucleotide quantity permeating the viable tissues of the skin was controlled by the selection of the electrical parameters of the pulses (voltage, pulse time and number of pulses) or by the ON concentration in the donor compartment. After delivery by electroporation, therapeutic levels of oligonucleotides were reached in the viable tissues of the skin (above 1 microM or 10 microM in intact or stripped skin respectively). Taken together, our results show that electroporation could be an interesting method for the delivery of oligonucleotides to the skin.

Sequence dependency of the internalization and distribution of phosphorothioate oligonucleotides in vascular smooth muscle cells

Antisense studies imply the utilization of oligonucleotides (ODN) for sequence-specific down-regulation of genes. This usually consists in assessing antisense sequences versus control sequences (mismatched, inverted, scrambled, randomized or any sequence unrelated to the relevant target). Even though the investigated biological effect (knockdown of an unwanted protein) is observed only with the antisense sequence and weakly, if at all, with any of the control sequences, this is a necessary but not a sufficient condition to demonstrate an antisense effect. Indeed, biochemical parameters such as stability, uptake and subcellular compartmentalization of ODN in a given cellular system are most often sequence-dependent processes. In this work, a series of phosphorothioate ODN of different lengths and sequences were evaluated as to their binding, internalization and subcellular distribution properties in vascular smooth muscle cells. In addition to membrane binding and nuclear accumulation, the partition of ODN in the cytosol of cells was measured by a method based upon controlled permeabilization of the plasma membrane, permitting the recovery of the cytosolic content with minimal damage to the membranes of the endocytic vesicles and lysosomes. We found that the tested ODN showed striking differences in their uptake and distribution in smooth muscle cells. Our results gave rise to the problem of validating the observed biological effects when different sequences of ODN were compared. Cellular studies such as the one presented in this work could help in choosing the proper control sequences among ODN exhibiting similar cell interactions as compared to the antisense sequences. Moreover, this method could be useful for the selection of antisense sequences that can be efficiently internalized and preferentially distributed in the appropriate compartments in cells for in vitro antisense studies.

Effects of size and sequence on the iontophoretic delivery of oligonucleotides

Adequate cellular availability of synthetic oligonucleotides is crucial to their success as therapeutic agents. These compounds, however, are not expected to be orally active. This has led to interest in a variety of alternate drug delivery methods, including iontophoretically enhanced transdermal delivery. The purpose of this work is to begin characterizing the structure-activity relationship for iontophoresis of oligonucleotides through the skin. The in vitro permeation of 16 biologically relevant phosphorothioate oligonucleotides across hairless mouse skin was studied. Oligonucleotides with less than 20 bases (n = 10) had a wide range of steady-state flux levels (2.1-26.2 pmol/ cm2 h). A lower flux differential was observed for compounds ranging from 20 to 40 bases long (1.2-2.2 pmol/cm2 h). For the smaller compounds, transport, in general, decreased with increasing size; however, there were several oligonucleotides that did not follow this pattern. These data indicate that factors other than size influence transport and that the impact is greater at shorter lengths. Differential penetration between equal sized oligonucleotides synthesized with identical bases in reversed order indicates that sequences and not simply base composition affects steady-state flux across skin. Molecular structure, therefore, is a key contributor to iontophoretically assisted transport. Further studies are necessary to develop more precise predictions about the relationship between oligonucleotide structure and transdermal delivery.

Iontophoresis of poly-L-lysines: the role of molecular weight?

PURPOSE

(1) To determine the extent of iontophoretic transport as a function of molecular weight (MW) of the penetrant; and (2) to visually and quantitatively characterize the iontophoretic transport pathways (follicular (F) versus nonfollicular (NF) of the fluorescently-labeled poly-L-lysines employed.

METHODS

A series of fluorescently-labeled poly-L-lysines (FITC-PLLs) [4 KDa, 7 KDa and 26 KDa] were used to study the extent and distribution of iontophoretic skin penetration as a function of MW using laser scanning confocal microscopy (LSCM).

RESULTS

It was found that, relative to the passive controls, and under the electrical conditions considered, iontophoresis greatly enhanced the penetration of the 4 KDa analog, slightly elevated the delivery of the 7 KDa FITC-PLL, but had no effect on the transport of the larger 26 KDa FITC-PLL. Quantitative analyses of LSCM images revealed that iontophoresis increased transport via F pathways only slightly more than that through NF pathways for the 4 KDa and 7 KDa FITC-PLL molecules.

CONCLUSIONS

It is visually apparent that the iontophoretic transport pathways taken are importantly determined by the physicochemical properties (including size and charge) of the penetrant. The results presented here demonstrate an inverse dependence of iontophoretic delivery upon the MW of the penetrant.

[A simple method for the study of cytosolic content of oligonucleotides in cells]

Antisense oligonucleotides are currently used for the specific control of the expression of a selected gene. Their putative targets are located in the cytoplasm (messenger RNA) or the nucleus (pre-messenger RNA or DNA). This approach is conditioned by the presence of the antisense molecule inside the cell at sufficient concentrations and in the appropriate compartments. We propose in this paper a simple method for the study of the cytosolic content of internalized oligonucleotides. This method is based on the selective permeabilization of the plasmic membrane by the detergent digitonin. By complexing to membrane cholesterol, the detergent creates pores through which soluble and diffusible species can escape outside the cells. The selectivity of membrane permeabilization was controlled by using compartment markers: lactate dehydrogenase (LDH) for cytosol, dextrane-rhodamine (DEX) and hexosaminidase (HAM) for endocytic vesicles and lysosomes, respectively. Optimal digitonin concentrations and incubation times have been defined to reach the following pattern of membrane permeabilization: LDH > 80%; DEX and HAM < 15%. The method was applied to monitor the quantity of extractible oligonucleotides from cells after endocytosis. The results showed that phosphodiester and phosphorothioate oligomers are readily available in the cytosol (60-50% of the internalized species), whereas those bearing a hydrophobic moiety (fluorescein, cholesterol) are less diffusible probably owing to membrane binding. Internalization and cytosol partition were found to depend on the chemical nature of the oligonucleotide, and also on the sequence and the cell type. This method could be useful for the selection of antisense molecules that exhibit the best internalization and distribution in cells, and for a more appropriate choice of control sequences in antisense studies.

Iontophoretic delivery of a telomeric oligonucleotide

PURPOSE

To evaluate the feasibility of iontophoretically enhanced transdermal delivery of a phosphorothioate oligonucleotide across hairless mouse skin.

METHODS

The phosphorothioate sequence, 5'-d(TTAGGG)-3' (TAG-6) which mimics the repeat sequence of the telomere was used as a model compound. Iontophoresis was performed on hairless mouse skin using as in vitro flow-through diffusion system. Both 5'-FITC and uniformly 35S labeled oligonucleotide were used to monitor transdermal flux.

RESULTS

Cathodal delivery of TAG-6 resulted in substantial oligonucleotide flux. The molecular label did not alter transport properties. No flux was measured with either anodal or passive delivery. The oligonucleotide was not degraded as it crossed the skin. Molecular transport was donor condition dependent, with pH and salt concentration both having significant effects. Pre-treating the skin with ethanol reduced iontophoretic transport.

CONCLUSIONS

These data demonstrate that iontophoresis can enhance transdermal flux of an intact phosphorothioate oligonucleotide and that this penetration is donor condition dependent. Furthermore, iontophoretically enhanced transdermal delivery is a feasible approach to the administration of phosphorothioate oligonucleotides.

Iontophoresis of bases, nucleosides, and nucleotides

PURPOSE

To investigate whether transdermal iontophoresis may be potentially useful for delivery of oligonucleotide drugs, the electrotransport of representative bases (uracil and adenine), nucleosides (uridine and adenosine) and nucleotides (AMP, ATP, GTP and imido-GTP) across mammalian skin in vitro has been considered.

METHODS

While the passive permeability of all compounds investigated (from 1 mM solutions at pH 7.4) was very low, the application of constant current iontophoresis (0.55 mA/cm2) significantly enhanced the transport of both charged and uncharged species.

RESULTS

The efficiency of delivery depended only weakly upon lipophilicity, varied quite linearly with concentration (for AMP and ATP), was inversely sensitive to molecular weight, and was strongly influenced by charge. Neutral solutes were delivered better from the anode than the cathode, as expected; post-iontophoresis, passive permeabilities were greater than those of the untreated controls, suggesting that iontophoretically-induced changes in barrier function cannot be completely repaired in in vitro model systems. The triphosphate nucleotides, ATP and GTP, were essentially completely metabolized (presumably to their corresponding mono-phosphates) during their iontophoretic delivery, while imido-GTP was apparently resistant to enzymatic attack; however, comparison of the transport data from AMP and ATP suggested that ATP metabolism occurred primarily after the rate-limiting step of iontophoresis.

CONCLUSIONS

The results obtained are consistent with the general patterns of behavior previously observed in investigations of amino acid and peptide electrotransport. It remains to be seen whether extension of the research described here to larger oligonucleotide species is a feasible long-term objective.