Phosphorothioate oligonucleotides induction into experimental choroidal neovascularization by HVJ-liposome system

Recent perspectives in ocular drug delivery

Anatomy and physiology of the eye makes it a highly protected organ. Designing an effective therapy for ocular diseases, especially for the posterior segment, has been considered as a formidable task. Limitations of topical and intravitreal route of administration have challenged scientists to find alternative mode of administration like periocular routes. Transporter targeted drug delivery has generated a great deal of interest in the field because of its potential to overcome many barriers associated with current therapy. Application of nanotechnology has been very promising in the treatment of a gamut of diseases. In this review, we have briefly discussed several ocular drug delivery systems such as microemulsions, nanosuspensions, nanoparticles, liposomes, niosomes, dendrimers, implants, and hydrogels. Potential for ocular gene therapy has also been described in this article. In near future, a great deal of attention will be paid to develop non-invasive sustained drug release for both anterior and posterior segment eye disorders. A better understanding of nature of ocular diseases, barriers and factors affecting in vivo performance, would greatly drive the development of new delivery systems. Current momentum in the invention of new drug delivery systems hold a promise towards much improved therapies for the treatment of vision threatening disorders.

Non-viral ocular gene therapy: potential ocular therapeutic avenues

Non-viral vectors for potential gene replacement and therapy have been developed in order to overcome the drawbacks of viral vectors. The diversity of non-viral vectors allows for a wide range of various products, flexibility of application, ease of use, low-cost of production and enhanced "genomic" safety. Using non-viral strategies, oligonucleotides (ODNs) can be delivered naked (less efficient) or entrapped in cationic lipids, polymers or peptides forming slow release delivery systems, which can be adapted according to the organ targeted and the therapy purposes. Tissue and cell internalization can be further enhanced by changing by physical or chemical means. Moreover, a specific vector can be selected according to disease course and intensity of manifestations fulfilling specific requirements such as the duration of drug release and its level along with cells and tissues specific targeting. From accumulating knowledge and experience, it appears that combination of several non-viral techniques may increase the efficacy and ensure the safety of these evolving and interesting gene therapy strategies.

Ocular delivery of nucleic acids: antisense oligonucleotides, aptamers and siRNA

Nucleic acids have gained a lot of interest for the treatment of ocular diseases. The first to enter in clinic has been Vitravene an antisense oligonucleotide for the treatment of cytomegalovirus (CMV) infection and more recently, research on aptamers have led to the marketing of anti-vascular endothelial growth factor (VEGF) inhibitor (Macugen) for the treatment of age-related macular degeneration (AMD). The siRNAs appear very promising as they are very potent inhibitors of protein expression. Despite their potential, nucleic acids therapeutic targets of nucleic acid-based drugs are mainly located in the posterior segment of the eye requiring invasive administration which can be harmful if repeated. Their intracellular penetration in some cases needs to be enhanced. This is the reason why adequate delivery systems were designed either to insure cellular penetration, protection against degradation or to allow long-term delivery. A combination of both effects was also developed for an implantable system. In conclusion, the intraocular administration of nucleic acids offers interesting perspectives for the treatment of ocular diseases.

Scleral permeability of a small, single-stranded oligonucleotide

Developing more effective ocular drug delivery systems is essential to improving the treatment of posterior segment eye disease. The large target area provided by the sclera and potentially less vision threatening complications are advantages of transscleral administration compared to more traditional modalities of drug delivery to the posterior segment. We aimed to determine the permeability coefficient for the in vitro diffusion of a small, single-stranded, oligonucleotide across human sclera. Transscleral permeability was measured by placing 100 microL of 2.96 x 10(-4) mol single-stranded, fluorescein-labeled oligonucleotide (MW = 7998.3) on the episcleral surface of sclera mounted in a perfusion chamber. Fractions of choroidal perfusate were collected hourly for 24 hours. The permeability constant or K(trans) for the transscleral diffusion of the naked, single-stranded, fluorescein-labeled oligonucleotide was 7.67 +/- 1.8 x 10(-7) cm/s (mean +/- SEM, N = 7). The permeability constant or K(trans) after intrascleral injection of the same fluorescein-labeled oligonucleotide was 1.32 +/- 0.42 x 10(-7) (mean +/- SEM, N = 4). This analysis demonstrates that diffusion of a naked, 24-base, single-stranded, fluorescein-labeled oligonucleotide can be accomplished by both of the described methods. The ability to deliver single-stranded oligonucleotides across the sclera may prove to be advantageous given the development of several novel therapeutic strategies that use similar molecules.

Gene therapy for genetic and acquired retinal diseases

We present an overview of the current status of basic science and translational research being applied to gene therapy for eye disease, focusing on diseases of the retina. We discuss the viral and nonviral methods being used to transfer genes to the retina and retinal pigment epithelium, and the advantages and disadvantages of each approach. We review the various genetic and somatic treatment strategies that are being used for genetically determined and acquired diseases of the retina, including gene replacement, gene silencing by ribozymes and antisense oligonucleotides, suicide gene therapy, antiapoptosis, and growth factor therapies. The rationales for the specific therapeutic approaches to each disease are discussed. Schematics of gene transfer methods and therapeutic approaches are presented together with a glossary of gene transfer terminology.

Preclinical evaluation of a phosphorothioate oligonucleotide in the retina of rhesus monkey

Overexpression of vascular endothelial growth factor (VEGF) has been strongly implicated in the development of choroidal neovascularization (CNV) in patients with age-related macular degeneration. In this study, a phosphorothioate oligonucleotide (PS-oligo) targeting both human and rat VEGF(165) genes upstream of the translation initiation code, named DS135 in this study, was evaluated for its uptake dynamics and retinal tolerance after intravitreal (IV) and subretinal (SR) injections in the rhesus monkey. Intravitreal and SR injections of a fluorescent-labeled DS135 (FL-DS135) resulted in both dose- and time-dependent uptake and persistence, and FL-DS135 remained detectable in the retina for at least 3 weeks after injection. Ophthalmic examination showed transient vitreous haze after IV delivery of a high dose but not with a low dose of FL-DS135. Histologic examination showed no evidence of retinal degeneration with respect to IV delivery. After SR delivery, however, dose-related cellular infiltration, transient residual fluid, and slight distortion of the neuroretina were observed. The biologic efficacy of DS135 was further assessed in a laser-induced CNV model, and development of CNV was determined by fluorescein angiography and histologic examination. Incomplete inhibition of CNV formation was observed after IV and SR injection of DS135, but no statistically significant difference was achieved when compared with dose-matched control of PS-oligo. Analysis of fluorescein angiogram and histologic examination showed less than 30% incidence of CNV development in this monkey model. Our study demonstrated that PS-oligos can be successfully introduced into the retina, although with potential limitations, after SR delivery. DS135, a PS-oligo targeting the VEGF gene upstream of the translation initiation code, partially inhibited CNV formation. An improved CNV model is necessary for further confirmation of the full therapeutic potency of DS135 before clinical application.

Uptake dynamics and retinal tolerance of phosphorothioate oligonucleotide and its direct delivery into the site of choroidal neovascularization through subretinal administration in the rat

This study aimed to investigate uptake dynamics and retinal tolerance of phosphorothioate oligonucleotides (PS-oligos) following subretinal injection. A fluorescent-labeled PS-oligo (FL-oligo) with random sequence was administered into the subretinal space of rat by transsclera-choroid-retinal pigment epithelium (RPE) injection at doses of 0.129, 1.29, and 12.9 microg in 2.0 microl solution. The uptake dynamics were evaluated by fundus fluorescent photography in real time and by fluorescence microscopy using flat mounts and cryosections. Immunophenotyping for CD4+, CD8+ cytotoxic lymphocytes, and CD68+ macrophages was performed to assess cellular infiltration in the retina. In addition, the FL-oligo was injected subretinally in a rat model of choroidal neovascularization (CNV) for direct delivery into the site of CNV. Subretinal administration of FL-oligo resulted in both dose-dependent and time-dependent distribution in the retina, where it accessed the RPE and all layers of the neuroretina. CD4+, CD8+ cytotoxic lymphocytes, and CD68+ macrophages were observed at the site of needle penetration. However, in areas far from the injection site where the FL-oligo appeared strongly, cellular infiltration was absent, and the retinal morphology was preserved very well. The FL-oligo was successfully delivered into the site of intense laser photocoagulation. It was predominantly localized to the RPE, macrophages, and some choroid cells and remained detectable for at least 56 days after injection. Our results demonstrate for the first time that subretinal injection efficiently introduced PS-oligo into the RPE and neuroretina with an acceptable level of safety. Subretinal administration of antiangiogenic oligonucleotides may hold great potential for the treatment of CNV.

In vivo use of oligonucleotides to inhibit choroidal neovascularisation in the eye

BACKGROUND

We have previously demonstrated the in vivo uptake of oligonucleotides in the rat eye and have continued with experiments to look at the effectiveness of targeted oligonucleotide sequences. Vascular endothelial growth factor (VEGF) is correlated with new blood vessel formation and has been implicated in numerous eye diseases characterised by abnormal blood vessel proliferation. An oligonucleotide targeted to the VEGF sequence was examined for its effect on VEGF production in vitro and the development of choroidal neovascularisation in vivo in the eye.

METHODS

A series of sequences were assessed in an in vitro screening system using retinal pigment epithelial (RPE) cells to demonstrate a reduction in VEGF. A targeted sequence was further investigated using an animal model of choroidal neovascularisation where a krypton laser was used to produce a wound healing response in the choroid and retina. The oligonucleotide was injected into the vitreous and the development of choroidal neovascularisation assessed using fluorescein angiography.

RESULTS

The targeted sequence was shown in vitro to downregulate the VEGF produced by RPE cells grown under hypoxic conditions and when injected into laser treated eyes was shown to be preferentially taken up in the laser lesion. Fluorescein angiography demonstrated that the test oligonucleotide was successful in reducing laser-mediated choroidal neovascularisation.

CONCLUSIONS

A sequence corresponding to the 5'UTR of the VEGF gene has provided encouraging results for the treatment of neovascularisation.

Targeting tumor blood vessels: an adjuvant strategy for radiation therapy

BACKGROUND AND PURPOSE

The neovascularization of tumor cells is a prerequisite if a clinically relevant tumor size is to be reached. A continuously expanding vessel network supplying nutritional requirements and removing waste products is essential for continued tumor development, growth and survival.

RESULTS

In many tumors, the growing endothelium is unable to fully support the demands of the neoplastic cell population. As a consequence of the inadequacies of the resulting aberrant vasculature, microenvironmental conditions develop in tumors which are not only detrimental to the response of tumors to conventional anticancer treatments, but may lead to or predispose cells to genetic modifications resulting in more aggressive phenotypes and higher metastatic potential. Yet the utter dependence of the tumor on its induced vessel formation for growth, survival and spread has also created a great deal of enthusiasm for developing therapeutic approaches to specifically targeting the tumor microcirculation.

CONCLUSIONS

The application of such strategies as adjuvants to conventional radiation treatments offers unique opportunities to develop more effective cancer therapies.

Delivery systems for antisense oligonucleotides

In vitro, the efficacy of the antisense approach is strongly increased by systems delivering oligodeoxyribonucleotides (ODNs) to cells. Up to now, most of the developed vectors favor ODN entrance by a mechanism based on endocytosis. Such is the case for particulate systems, including liposomes (cationic or non-cationic), cationic polyelectrolytes, and delivery systems targeted to specific receptors. Under these conditions, endosomal compartments may represent a dead end for ODNs. Current research attempts to develop conditions for escaping from these compartments. A new class of vectors acts by passive permeabilization of the plasma membrane. It includes peptides, streptolysin O, and cationic derivatives of polyene antibiotics. In vivo, the interest of a delivery system, up to now, has appeared limited. Development of vectors insensitive to the presence of serum seems to be a prerequisite for future improvements.