Reduction of fibronectin expression by intravitreal administration of antisense oligonucleotides

Retinal capillary basement membrane thickening: Role in the pathogenesis of diabetic retinopathy

Vascular basement membrane (BM) thickening has been hailed over half a century as the most prominent histological lesion in diabetic microangiopathy, and represents an early ultrastructural change in diabetic retinopathy (DR). Although vascular complications of DR have been clinically well established, specific cellular and molecular mechanisms underlying dysfunction of small vessels are not well understood. In DR, small vessels develop insidiously as BM thickening occurs. Studies examining high resolution imaging data have established BM thickening as one of the foremost structural abnormalities of retinal capillaries. This fundamental structural change develops, at least in part, from excess accumulation of BM components. Although BM thickening is closely associated with the development of DR, its contributory role in the pathogenesis of DR is coming to light recently. DR develops over several years before clinical manifestations appear, and it is during this clinically silent period that hyperglycemia induces excess synthesis of BM components, contributes to vascular BM thickening, and promotes structural and functional lesions including cell death and vascular leakage in the diabetic retina. Studies using animal models show promising results in preventing BM thickening with subsequent beneficial effects. Several gene regulatory approaches are being developed to prevent excess synthesis of vascular BM components in an effort to reduce BM thickening. This review highlights current understanding of capillary BM thickening development, role of BM thickening in retinal vascular lesions, and strategies for preventing vascular BM thickening as a potential therapeutic strategy in alleviating characteristic lesions associated with DR.

Aptamer-based therapeutics of the past, present and future: from the perspective of eye-related diseases

Aptamers have emerged as a novel and powerful class of biomolecules with an immense untapped potential. The ability to synthesise highly specific aptamers against any molecular target make them a vital cog in the design of effective therapeutics for the future. However, only a minutia of the enormous potential of this dynamic class of molecule has been exploited. Several aptamers have been studied for the treatment of eye-related disorders, and one such strategy has been successful in therapy. This review gives an account of several eye diseases and their regulatory biomolecules where other nucleic acid therapeutics have been attempted with limited success and how aptamers, with their exceptional flexibility to chemical modifications, can overcome those inherent shortcomings.

Nanotechnology approaches for ocular drug delivery

Blindness is a major health concern worldwide that has a powerful impact on afflicted individuals and their families, and is associated with enormous socio-economical consequences. The Middle East is heavily impacted by blindness, and the problem there is augmented by an increasing incidence of diabetes in the population. An appropriate drug/gene delivery system that can sustain and deliver therapeutics to the target tissues and cells is a key need for ocular therapies. The application of nanotechnology in medicine is undergoing rapid progress, and the recent developments in nanomedicine-based therapeutic approaches may bring significant benefits to address the leading causes of blindness associated with cataract, glaucoma, diabetic retinopathy and retinal degeneration. In this brief review, we highlight some promising nanomedicine-based therapeutic approaches for drug and gene delivery to the anterior and posterior segments.

Nanoparticle diffusion in, and microrheology of, the bovine vitreous ex vivo

Intravitreal injection of biodegradable nanoparticles (NP) holds promise for gene therapy and drug delivery to the back of the eye. In some cases, including gene therapy, NP need to diffuse rapidly from the site of injection in order to reach targeted cell types in the back of the eye, whereas in other cases it may be preferred for the particles to remain at the injection site and slowly release drugs that may then diffuse to the site of action. We studied the movements of polystyrene (PS) NP of various sizes and surface chemistries in fresh bovine vitreous. PS NP as large as 510nm rapidly penetrated the vitreous gel when coated with polyethylene glycol (PEG), whereas the movements of NP 1190nm in diameter or larger were highly restricted regardless of surface chemistry owing to steric obstruction. PS NP coated with primary amine groups (NH2) possessed positively charged surfaces at the pH of bovine vitreous (pH=7.2), and were immobilized within the vitreous gel. In comparison, PS NP coated with COOH (possessing negatively charged surfaces) in the size range of 100-200nm and at particle concentrations below 0.0025% (w/v) readily diffused through the vitreous meshwork; at higher concentrations (~0.1% w/v), these nanoparticles aggregated within vitreous. Based on the mobility of different sized PEGylated PS NP (PS-PEG), we estimated the average mesh size of fresh bovine vitreous to be ~550±50nm. The bovine vitreous behaved as an impermeable elastic barrier to objects sized 1190nm and larger, but as a highly permeable viscoelastic liquid to non-adhesive objects smaller than 510nm in diameter. Guided by these studies, we next sought to examine the transport of drug- and DNA-loaded nanoparticles in bovine vitreous. Biodegradable NP with a diameter of 227nm, composed of a poly(lactic-co-glycolic acid) (PLGA)-based core coated with poly(vinyl alcohol) rapidly penetrated vitreous. Rod-shaped, highly-compacted CK30PEG10k/DNA with PEG coating (neutral surface charge; hydrodynamic diameter ~60nm) also diffused rapidly within vitreous. These findings will help guide the development of nanoparticle-based therapeutics for the treatment of vision-threatening ocular diseases.

Nano-vectors for the Ocular Delivery of Nucleic Acid-based Therapeutics

Nucleic acid-based therapeutics have gained a lot of interest for the treatment of diverse ophthalmic pathologies. The first to enter in clinic has been an oligonucleotide, Vitravene^® for the treatment of cytomegalovirus infection. More recently, research on aptamers for the treatment of age related macular degeneration has led to the development of Macugen^®. Despite intense potential, effective ocular delivery of nucleic acids is a major challenge since therapeutic targets for nucleic acid-based drugs are mainly located in the posterior eye segment, requiring repeated invasive administration. Of late, nanotechnology-based nano-vectors have been developed in order to overcome the drawbacks of viral and other non-viral vectors. The diversity of nano-vectors allows for ease of use, flexibility in application, low-cost of production, higher transfection efficiency and enhanced genomic safety. Using nano-vector strategies, nucleic acids can be delivered either encapsulated or complexed with cationic lipids, polymers or peptides forming sustained release systems, which can be tailored according to the ocular tissue being targeted. The present review focuses on developments and advances in various nano-vectors for the ocular delivery of nucleic acid-based therapeutics, the barriers that such delivery systems face and methods to overcome them.

Vascular basement membrane thickening in diabetic retinopathy

Vascular basement membrane (BM) thickening is a fundamental structural alteration of small blood vessels in diabetes. Over two decades of research has established hyperglycemia as the primary causal factor mediating this alteration. Various high glucose-induced mechanisms have been investigated and excess synthesis of BM components has been identified as a major contributing factor to BM thickening. Although BM thickening has been long hailed as the histological hallmark of diabetic microangiopathy, the consequences of BM thickening on the functionality of target organs of diabetes remain elusive even today. This review presents an overview of our current understanding of the BM structure and function, and focuses on how capillary BM thickening develops, its effect on retinal vascular function, and potential strategies for preventing the development of BM thickening in diabetic retinopathy.

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.

Arachidonic acid as a retrograde signal controlling growth and dynamics of retinotectal arbors

In the developing visual system, correlated presynaptic activity between neighboring retinal ganglion cells (RGC) stabilizes retinotopic synapses via a postsynaptic NMDAR (N-methyl-D-aspartate receptor)-dependent mechanism. Blocking NMDARs makes individual axonal arbors larger, which underlies an unsharpened map, and also increases branch turnover, as if a stabilizing factor from the postsynaptic partner is no longer released. Arachidonic acid (AA), a candidate retrograde stabilizing factor, is released by cytoplasmic phospholipase A2 (cPLA2) after Ca(2+) entry through activated NMDARs, and can activate presynaptic protein kinase C to phosphorylate various substrates such as GAP43 to regulate cytoskeletal dynamics. To test the role of cPLA2 in the retinotectal system of developing zebrafish, we first used PED6, a fluorescent reporter of cPLA2 activity, to show that 1-3 min of strobe flashes activated tectal cPLA2 by an NMDAR-dependent mechanism. Second, we imaged the dynamic growth of retinal arbors during both local inhibition of tectal cPLA2 by a pharmacological inhibitor, arachidonic tri-fluoromethylketone, and its suppression by antisense oligonucleotides (both injected intraventricularly). Both methods produced larger arbors and faster branch dynamics as occurs with blocking NMDARs. In contrast, intraocular suppression of retinal cPLA2 with large doses of antisense oligos produced none of the effects of tectal cPLA2 inhibition. Finally, if AA is the retrograde messenger, the application of exogenous AA to the tectum should reverse the increased branch turnover caused by blocking either NMDARs or cPLA2. In both cases, intraventricular injection of AA stabilized the overall branch dynamics, bringing rates down below the normal values. The results suggest that AA generated postsynaptically by cPLA2 downstream of Ca(2+) entry through NMDARs acts as a retrograde signal to regulate the dynamic growth of retinal arbors.

Novel nanomaterials for clinical neuroscience

Neurodegenerative disorders including Alzheimer's and Parkinson's diseases, amyotrophic lateral sclerosis, and stroke are rapidly increasing as population ages. The field of nanomedicine is rapidly expanding and promises revolutionary advances to the diagnosis and treatment of devastating human diseases. This paper provides an overview of novel nanomaterials that have potential to improve diagnosis and therapy of neurodegenerative disorders. Examples include liposomes, nanoparticles, polymeric micelles, block ionomer complexes, nanogels, and dendrimers that have been tested clinically or in experimental models for delivery of drugs, genes, and imaging agents. More recently discovered nanotubes and nanofibers are evaluated as promising scaffolds for neuroregeneration. Novel experimental neuroprotective strategies also include nanomaterials, such as fullerenes, which have antioxidant properties to eliminate reactive oxygen species in the brain to mitigate oxidative stress. Novel technologies to enable these materials to cross the blood brain barrier will allow efficient systemic delivery of therapeutic and diagnostic agents to the brain. Furthermore, by combining such nanomaterials with cell-based delivery strategies, the outcomes of neurodegenerative disorders can be greatly improved.

Nanomedicine in the diagnosis and therapy of neurodegenerative disorders

Neurodegenerative and infectious disorders including Alzheimer's and Parkinson's diseases, amyotrophic lateral sclerosis, and stroke are rapidly increasing as population's age. Alzheimer's disease alone currently affects 4.5 million Americans, and more than $100 billion is spent per year on medical and institutional care for affected people. Such numbers will double in the ensuing decades. Currently disease diagnosis for all disorders is made, in large measure, on clinical grounds as laboratory and neuroimaging tests confirm what is seen by more routine examination. Achieving early diagnosis would enable improved disease outcomes. Drugs, vaccines or regenerative proteins present "real" possibilities for positively affecting disease outcomes, but are limited in that their entry into the brain is commonly restricted across the blood-brain barrier. This review highlights how these obstacles can be overcome by polymer science and nanotechnology. Such approaches may improve diagnostic and therapeutic outcomes. New developments in polymer science coupled with cell-based delivery strategies support the notion that diseases that now have limited therapeutic options can show improved outcomes by advances in nanomedicine.

Polymer genomics: an insight into pharmacology and toxicology of nanomedicines

Synthetic polymers and nanomaterials display selective phenotypic effects in cells and in the body signal transduction mechanisms involved in inflammation, differentiation, proliferation, and apoptosis. When physically mixed or covalently conjugated with cytotoxic agents, bacterial DNA or antigens, polymers can drastically alter specific genetically controlled responses to these agents. These effects, in part, result from cooperative interactions of polymers and nanomaterials with plasma cell membranes and trafficking of polymers and nanomaterials to intracellular organelles. Cells and whole organism responses to these materials can be phenotype or genotype dependent. In selected cases, polymer agents can bypass limitations to biological responses imposed by the genotype, for example, phenotypic correction of immune response by polyelectrolytes. Overall, these effects are relatively benign as they do not result in cytotoxicity or major toxicities in the body. Collectively, however, these studies support the need for assessing pharmacogenomic effects of polymer materials to maximize clinical outcomes and understand the pharmacological and toxicological effects of polymer formulations of biological agents, i.e. polymer genomics.

Nanotools for megaproblems: probing protein misfolding diseases using nanomedicine modus operandi

Misfolding and self-assembly of proteins in nanoaggregates of different sizes and morphologies (nanoensembles, primary nanofilaments, nanorings, filaments, protofibrils, fibrils, etc.) is a common theme unifying a number of human pathologies termed protein misfolding diseases. Recent studies highlight increasing recognition of the public health importance of protein misfolding diseases, including various neurodegenerative disorders and amyloidoses. It is understood now that the first essential elements in the vast majority of neurodegenerative processes are misfolded and aggregated proteins. Altogether, the accumulation of abnormal protein nanoensembles exerts toxicity by disrupting intracellular transport, overwhelming protein degradation pathways, and/or disturbing vital cell functions. In addition, the formation of inclusion bodies is known to represent a major problem in the production of recombinant therapeutic proteins. Formulation of these therapeutic proteins into delivery systems and their in vivo delivery are often complicated by protein association. Thus, protein folding abnormalities and subsequent events underlie a multitude of human pathologies and difficulties with protein therapeutic applications. The field of medicine therefore can be greatly advanced by establishing a fundamental understanding of key factors leading to misfolding and self-assembly responsible for various protein folding pathologies. This article overviews protein misfolding diseases and outlines some novel and advanced nanotechnologies, including nanoimaging techniques, nanotoolboxes and nanocontainers, complemented by appropriate ensemble techniques, all focused on the ultimate goal to establish etiology and to diagnose, prevent, and cure these devastating 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.

Long-term safety of GDNF gene delivery in the retina

PURPOSE

To examine retinal function after the long-term, gene therapy-delivered expression of exogenous glial cell line-derived neurotrophic factor (GDNF).

METHODS

Forty Sprague-Dawley rats each received an intravitreal injection of recombinant adeno-associated virus expressing GDNF (rAAV-GDNF) in their right eye. The left eye was untreated. One year after viral transduction in ocular tissues, retinal morphology and function were compared between rAAV-GDNF-injected and normal naïve eyes. Synthesis and accumulation of GDNF within the retina were immunohistologically confirmed using enzyme-linked immunosorbent assay. Morphological analyses included light microscope examination of retinal sections and the counting of retinal ganglion cells. Inflammation by infiltration of leukocytes in retina was assessed immunohistochemically. Retinal function was assessed using electroretinography.

RESULTS

GDNF expression was confirmed. There was no obvious abnormality in retinal section or increased infiltration by leukocytes after retinal transduction of rAAV-GDNF for 1 year. Counts of retinal ganglion cells were not decreased in rAAV-GDNF-injected eyes. There were no statistical differences in amplitude as well as latency of the electroretinogram-determined a- and b-waves between transduced and untreated eyes.

CONCLUSIONS

Long-term expression of GDNF within the eyes can be achieved by intravitreal injection of rAAV vectors in the absence of morphological or functional deficits in the retina.

SiRNA strategy against overexpression of extracellular matrix in diabetic retinopathy

Increased synthesis of extracellular matrix (ECM) contributes to the development of vascular BM thickening, a prominent abnormality in diabetic retinopathy. RNA interference (RNAi) approach was used in this study to examine the effect of small interfering RNAs (siRNAs) for their ability to inhibit ECM-specific gene overexpression under high glucose condition in rat microvascular endothelial cells (RMECs). Four fibronectin (FN)-siRNAs, three collagen IV (Coll IV)-siRNAs, and four laminin (LM)-siRNAs, a total of 11 siRNAs were screened. RMECs were transfected with 10, 30, or 100 nm of each siRNAs in the presence of 8 microm lipofectin and subjected to analysis 72 hr after transfection. In long-term studies siRNA-transfected cells were examined after 12 days. Two FN siRNAs, two Coll IV siRNAs, and two LM siRNAs significantly reduced the respective target expressions. Findings from this study indicate that high glucose-induced abnormal expression of BM components may contribute to increased vascular permeability. SiRNA may be a useful tool in preventing excess vascular permeability, a characteristic feature of early diabetic retinopathy.

Stabilization of lysozyme-incorporated polyion complex micelles by the omega-end derivatization of poly(ethylene glycol)-poly(alpha,beta-aspartic acid) block copolymers with hydrophobic groups

To improve the stability of lysozyme-incorporated polyion complex (PIC) micelles in physiological condition, three types of hydrophobic groups, including phenyl (Phe), naphthyl (Nap), and pyrenyl (Py) terminal groups, were separately introduced to the omega-end of poly(ethylene glycol)-poly(alpha,beta-aspartic acid) block copolymers (PEG-P(Asp)). The goal was to enhance association forces between the enzyme, lysozyme, and PEG-P(Asp) carriers. Introduction of these hydrophobic groups significantly decreases micellar critical association concentration and increases the micellar tolerability against increasing NaCl concentrations. Particularly, PIC micelles formed from PEG-P(Asp) with Py groups was most stable against increasing NaCl concentrations up to 0.1 M. Significant deviation from a spherical shape for the micelles was also observed for the PEG-P(Asp)-Py system, consistent with an increased association number.

Pluronic Block Copolymers for Gene Delivery

Amphiphilic block copolymers of poly(ethylene oxide) and poly(propylene oxide) called Pluronic or poloxamer are commercially available pharmaceutical excipients. They recently attracted considerable attention in gene delivery applications. First, they were shown to increase the transfection with adenovirus and lentivirus vectors. Second, they were shown to increase expression of genes delivered into cells using non-viral vectors. Third, the conjugates of Pluronic with polycations, were used as DNA-condensing agents to form polyplexes. Finally, it was demonstrated that they can increase regional expression of the naked DNA after its injection in the skeletal and cardiac muscles or tumor. Therefore, there is substantial evidence that Pluronic block copolymers can improve gene expression with different delivery routes and different types of vectors, including naked DNA. These results and possible mechanisms of Pluronic effects are discussed. At least in some cases, Pluronic can act as biological adjuvants by activating selected signaling pathways, such as NF-kappaB, and upregulating the transcription of the genes.

Differential expression of connective tissue growth factor in microglia and pericytes in the human diabetic retina

BACKGROUND/AIM

Connective tissue growth factor (CTGF) stimulates extracellular matrix formation, fibrosis, and angiogenesis. It has a role in the pathogenesis of diabetic nephropathy and possibly in diabetic retinopathy (DR): in cultured retinal vascular cells CTGF is induced by VEGF-A. To further characterise this role the authors investigated CTGF expression in normal and diabetic human retina.

METHODS

CTGF expression patterns were studied by immunohistochemistry in the retina of eyes of 36 diabetic persons and 18 non-diabetic controls and compared with markers of endothelial cells (CD31, PAL-E), pericytes (NG2), astrocytes (GFAP), and microglia (CD45).

RESULTS

In the retina, distinct and specific staining of CTGF was observed in microglia, situated around or in close vicinity of retinal capillaries. In the control cases, sporadic staining of pericytes was also observed within the vascular wall. In contrast, in the retina of people with diabetes, CTGF staining in microglia was decreased and staining in pericytes was increased. This pattern of predominantly pericyte staining was observed in 20 out of 36 diabetic cases and in one out of 18 controls. The altered CTGF staining patterns in the diabetic cases did not correlate to staining of PAL-E, a marker of retinal vascular leakage associated with DR.

CONCLUSIONS

The study shows that CTGF is expressed in microglia in the normal retina whereas in a large subset of diabetic persons, CTGF expression shifts to microvascular pericytes. This altered CTGF expression pattern appears unrelated to manifest DR and may therefore represent a preclinical retinal change caused by diabetes. The results suggest a distinct, but as yet unidentified, role of CTGF in the pathogenesis of diabetic retinopathy.

Downregulation of fibronectin overexpression reduces basement membrane thickening and vascular lesions in retinas of galactose-fed rats

Overexpression of extracellular matrix (ECM) components is closely associated with the development of vascular basement membrane (BM) thickening, a histological hallmark of diabetic microangiopathy. To determine whether BM thickening of retinal capillaries could be prevented by down regulating synthesis of fibronectin, an ECM component, we used antisense oligos targeted against translation initiation site of the fibronectin transcript in galactose-fed rat, an animal model of diabetic retinopathy. After 2 months of galactose-feeding, intravitreal administration of 3 micro mol/l antisense fibronectin oligos was initiated at monthly intervals for 3 months. The antisense strategy significantly reduced fibronectin mRNA and protein level in the retinas of treated eyes compared with untreated eyes of galactose-fed rats (130 +/- 16 vs. 179 +/- 18% of control, P < 0.01, and 144 +/- 28 vs. 204 +/- 22% of control, respectively, r = 0.9) and resulted in partial reduction of retinal capillary BM width (123 +/- 16 vs. 201 +/- 12 nm, P < 0.03). In eyes treated with antisense fibronectin oligos, approximately 35% reduction in both pericyte loss and acellular retinal capillaries was observed (P < 0.04 and P < 0.03, respectively). Glycohemoglobin level was consistently elevated in the treated (6.9 +/- 0.6%) and untreated (6.5 +/- 0.7%) galactose-fed rats compared with control rats (4.5 +/- 0.8%). Overall, these results indicate that downregulation of fibronectin synthesis reduces BM thickening in retinal capillaries with beneficial effect to retinal lesions. The antisense fibronectin oligos may provide a useful approach for reducing vascular lesions in diabetic retinopathy. The thickened vascular BM may be a potential therapeutic target for preventing retinal lesions in diabetic retinopathy.

Vascular complications and gene therapy

For gene therapy, the last few years have been an exciting period. Encouraging results from several successful gene therapy trials were reported. Children born with a life-threatening immune system disorder, severe combined immune deficiency (SCID), were cured after receiving gene therapy for replacement of their defective adenosine deaminase (ADA) gene. Gene therapy successes related to vascular complications were also reported. The first human gene therapy trial for a blood-vessel disorder was performed successfully, in which copies of an angiogenic gene, the vascular endothelial growth factor (VEGF) gene, were directly delivered to the area surrounding the diseased artery of the leg of a patient with peripheral artery disease. Within a few days, this stimulated the growth of new blood vessels around the blockage in the ailing blood vessel and helped avoid amputation. In 1998, a patient with genetically small arteries became the first to receive VEGF gene therapy in the heart. Multiple copies of a plasmid with the VEGF gene were delivered into the damaged area of the heart, and a few days later angiogenesis ensued that helped bypass the blocked vessel, with markedly reduced chest pain in the patient. Gene therapy is becoming a reality and, more importantly, it appears to be safe and does not require supplementary immuno-suppressing drugs. Gene therapy seems to have begun delivering on its promises.

Glutathione-sensitive stabilization of block copolymer micelles composed of antisense DNA and thiolated poly(ethylene glycol)-block-poly(L-lysine): a potential carrier for systemic delivery of antisense DNA

Glutathione (GSH)-sensitive stabilization of polyion complex (PIC) micelles entrapping antisense oligonucleotide (ODN) was achieved by the reversible cross-linking of the core through disulfide bonds, aiming at the development of a novel DNA carrier system for antisense therapy following systemic administration. Thiolated poly(ethylene glycol)-block-poly(L-lysine) (PEG-thioPLL) and ODN spontaneously associated to form the PIC micelles with the core cross-linked through disulfide bonds. The diameters of the cross-linked micelles were similar to those of the non-cross-linked micelles and were determined to be about 40 nm by light scattering measurements. The micelles have sufficient colloidal stability due to the PEG shell surrounding the core of the polyion complex composed of PLL and ODN. The polyanion exchange studies suggested that the dissociation of the micelles was suppressed through the core cross-linking. The stability of the ODN in the core cross-linked micelles against nuclease was appreciably increased compared to that of free ODN and that in the micelles without cross-linking. On the other hand, the micelles dissociated to release ODN in the presence of GSH at a concentration comparable to the intracellular environment, featuring the potential ability of this system for intracellular ODN delivery.

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.

Influence of polymer architecture on the structure of complexes formed by PEG-tertiary amine methacrylate copolymers and phosphorothioate oligonucleotide

The influence of polymer structure on the characteristics of complexes of a phosphorothioate antisense oligonucleotide (ISIS 5132) was studied, using well-defined cationic copolymers based on 2-(dimethylamino) ethyl methacrylate (DMAEMA) and poly(ethylene glycol) (PEG). The three related copolymer structures were: DMAEMA-PEG (a diblock copolymer) DMAEMA-OEGMA 7 (a brush-type copolymer), DMAEMA-stat-PEGMA (a comb-type copolymer); each of these were examined together with DMAEMA homopolymer, which served as a control. The results revealed that all the polymers exhibited good binding ability with the oligonucleotide (ON). Interestingly, the comb-type polymer DMAEMA-stat-PEGMA demonstrated the highest binding ability and DMAEMA homopolymer the lowest, as judged by a dye displacement assay. DMAEMA homopolymer produced large agglomerates of smaller individual complexes as observed by optical density, photon correlation spectroscopy and transmission electron microscopy studies. In contrast, two PEG-block copolymers, DMAEMA-PEG and DMAEMA-OEGMA 7, formed compact complexes of 80-150 nm which had good long-term colloidal stability. This is attributed to the steric stabilisation effect of the PEG chains on the ON-copolymer complexes. These two copolymers are believed to form complexes with ON that have a micellar structure. Comb-type DMAEMA-stat-PEGMA copolymer formed highly soluble complexes with the ON that did not phase separate from the buffer solution. This study clearly demonstrates that varying the copolymer architecture allows access to a range of ON complexes. In vitro cytotoxicity experiments on HepG2 cells showed that all of the tertiary amine methacrylate copolymers displayed lower cytotoxicity than the control poly(L-lysine).

Block copolymer micelles for delivery of gene and related compounds

Block copolymers composed of a cationic segment and a hydrophilic segment spontaneously associate with polyanionic DNA to form block copolymer micelles. The distinct feature of the associate is that the core of the polyion complex between DNA and the polycation is coated by a layer of the hydrophilic polymer. The characteristic core-shell structure endows the associate with a high colloidal stability and reduced interaction with blood components. These desirable properties are the major advantages of the micellar DNA delivery system for in vivo application. In this article, the synthesis of block copolymers as well as graft copolymers utilized as DNA delivery systems are described. Particular emphasis is devoted to the association behavior and the physicochemical properties of polyion complex micelles entrapping DNA and related substances in relation to the biological aspects of the associates. Biodistribution and the factors that affect the intracellular fate of the micelles is also addressed based on recent studies in this field.

Pluronic block copolymers: novel functional molecules for gene therapy

Pluronic block copolymers are recognized pharmaceutical excipients listed in the US and British Pharmacopoeia. They have been used extensively in a variety of pharmaceutical formulations including delivery of low molecular mass drugs and polypeptides. This review describes novel applications of Pluronic block copolymers in gene therapy. In particular, these molecules can modify the biological response during gene therapy in the skeletal muscle, resulting in an enhancement of the transgene expression as well as an enhancement of the therapeutic effect of the transgene. Furthermore, Pluronic block copolymers are versatile molecules that can be used as structural elements of the polycation-based gene delivery systems (polyplexes). Based on these studies, the use of block copolymers in gene delivery is a promising area of research, in which new and important developments are expected.

The use of synthetic polymers for delivery of therapeutic antisense oligodeoxynucleotides

Developed over the past two decades, the antisense strategy has become a technology of recognised therapeutic potential, and many of the problems raised earlier in its application have been solved to varying extents. However, the adequate delivery of antisense oligodeoxynucleotides to individual cells remains an important and inordinately difficult challenge. Synthetic polymers appeared on this scene in the middle 1980s, and there is a surprisingly large variety used or proposed so far as agents for delivery of oligodeoxynucleotides. After discussing the principles of antisense strategy, certain aspects of the ingestion of macromolecules by cells, and the present situation of delivery procedures, this article analyses in detail the attempts to use synthetic polymers as carrier matrices and or cell membrane permeabilisation agents for delivery of antisense oligodeoxynucleotides. Structural aspects of various polymers, as well as the results, promises and limitations of their use are critically evaluated.

Antisense oligonucleotides modulate high glucose-induced laminin overexpression and cell proliferation: a potential for therapeutic application in diabetic microangiopathy

Vascular basement membrane (BM) thickening is a prominent and characteristic lesion of diabetic microangiopathy. Studies suggest that increased synthesis of laminin, a BM component, is associated with the development of thickened BM in diabetic vessels. In this study, we evaluated whether an interventive strategy using laminin antisense phosphorothioate oligonucleotides (Lam AS-oligos) could specifically inhibit high-glucose-induced laminin gene overexpression in vascular endothelial cells and normalize cell proliferation. Rat endothelial cells grown in high-glucose (30 mM) medium for 7 days showed increased laminin mRNA and protein level (195% +/- 28% of control, p < 0.05; 143% +/- 26% of control, p < 0.05, respectively) and reduced cell number (79% +/- 6% of control, p < 0.05) compared with cells grown in normal (5 mM) glucose medium. When cells grown in high-glucose medium were transfected with 0.4 microM Lam AS-oligos for 48 hours in the presence of 8 microM lipofectin, the laminin mRNA and protein level decreased (121% +/- 19% and 99% +/- 15% of control, respectively), and the cell number was restored to near normal level (93% +/- 7% of control). The results indicate that the antisense strategy is effective in selectively reducing laminin overexpression and improving endothelial cell proliferation under high-glucose conditions. Thus, the As-oligos may be potentially useful for preventing the development of thickened vascular BM in diabetic microangiopathy.

Potential therapeutic application of antisense oligonucleotides in the treatment of ocular diseases

Antisense oligonucleotides are a class of compounds being developed as therapeutic agents for many types of diseases. Although still relatively early in the clinical characterisation, the power of this technology lies in the ability to utilise genetic information and the known molecular mechanisms of disease to foster efficient and rational drug design. Consideration of novel approaches to treating ocular diseases is of interest because there are many ocular diseases with no satisfactory treatments. The recent availability of animal models of many ocular diseases provides the opportunity to use antisense oligonucleotides to understand the mechanisms of disease pathology and to potentially intervene therapeutically in ocular disease. There are already a number of examples where antisense oligonucleotides have been applied to the study of ocular physiology and disease and there is an antisense oligonucleotide approved for the treatment of cytomegalovirus (CMV) retinitis. We summarise current research in this area and highlight the properties of these compounds that are favourable for use as ocular therapeutics.

Block and graft copolymers and NanoGel copolymer networks for DNA delivery into cell

Self-assembling complexes from nucleic acids and synthetic polymers are evaluated for plasmid and oligonucleotide (oligo) delivery. Polycations having linear, branched, dendritic. block- or graft copolymer architectures are used in these studies. All these molecules bind to nucleic acids due to formation of cooperative systems of salt bonds between the cationic groups of the polycation and phosphate groups of the DNA. To improve solubility of the DNA/polycation complexes, cationic block and graft copolymers containing segments from polycations and non-ionic soluble polymers, for example, poly(ethylene oxide) (PEO) were developed. Binding of these copolymers with short DNA chains, such as oligos, results in formation of species containing hydrophobic sites from neutralized DNA polycation complex and hydrophilic sites from PEO. These species spontaneously associate into polyion complex micelles with a hydrophobic core from neutralized polyions and a hydrophilic shell from PEO. Such complexes are very small (10-40 nm) and stable in solution despite complete neutralization of charge. They reveal significant activity with oligos in vitro and in vivo. Binding of cationic copolymers to plasmid DNA forms larger (70-200 nm) complexes. which are practically inactive in cell transfection studies. It is likely that PEO prevents binding of these complexes with the cell membranes ("stealth effect"). However attaching specific ligands to the PEO-corona can produce complexes, which are both stable in solution and bind to target cells. The most efficient complexes were obtained when PEO in the cationic copolymer was replaced with membrane-active PEO-b-poly(propylene oxide)-b-PEO molecules (Pluronic 123). Such complexes exhibited elevated levels of transgene expression in liver following systemic administration in mice. To increase stability of the complexes, NanoGel carriers were developed that represent small hydrogel particles synthesized by cross-linking of PEI with double end activated PEO using an emulsification/solvent evaporation technique. Oligos are immobilized by mixing with NanoGel suspension, which results in the formation of small particles (80 nm). Oligos incorporated in NanoGel are able to reach targets within the cell and suppress gene expression in a sequence-specific fashion. Further. loaded NanoGel particles cross-polarized monolayers of intestinal cells (Caco-2) suggesting potential usefulness of these systems for oral administration of oligos. In conclusion the approaches using polycations for gene delivery for the design of gene transfer complexes that exhibit a very broad range of physicochemical and biological properties, which is essential for design of a new generation of more effective non-viral gene delivery systems.

Physicochemical and biological characterisation of an antisense oligonucleotide targeted against the bcl-2 mRNA complexed with cationic-hydrophilic copolymers

The aim of this study was to evaluate the use of cationic-hydrophilic copolymers for self-assembly with antisense oligonucleotides targeted to the bcl-2 mRNA in order to improve their biocompatibility and modulation of their pharmacokinetics for greater therapeutic usefulness. Examination of the ability of poly(trimethylammonioethyl methacrylate chloride)-poly[N-(2-hydroxypropyl)methacrylamide] (pHPMA-b-pTMAEM) block copolymers to condense the oligonucleotide by fluorescence and electrophoresis techniques showed that complexes were formed more efficiently than with copolymers containing poly(ethylene glycol) blocks grafted onto the backbone of poly(L-lysine) (pLL-g-pEG). In addition, the copolymer pTMAEM-b-pHPMA produced oligonucleotide complexes with the most favourable physicochemical properties appropriate for in vivo applications. The complexes were small (approximately 36 nm in diameter), with low surface charge as measured by zeta potential, relatively stable to physiological salt conditions and could be formed at a DNA concentration of 500 microg/ml. Complex formation with the copolymer pTMAEM-b-pHPMA or pLL-g-pEG reduced the urinary clearance of the oligonucleotide after intravenous injection into mice. However after 30 min, the oligonucleotide complexes were cleared from the bloodstream. These results indicate that for the systemic delivery of oligonucleotides the polymer-derived complexes are not stable enough for prolonged circulation. Instead, these complexes may be more suitable for localised in vivo applications.

Evaluation of polyether-polyethyleneimine graft copolymers as gene transfer agents

Cationic copolymers consisting of polycations linked to non-ionic polymers are evaluated as non-viral gene delivery systems. These copolymers are known to produce soluble complexes with DNA, but only a few studies have characterized the transfection activity of these complexes. This work reports the synthesis and characterization of a series of cationic copolymers obtained by grafting the polyethyleneimine (PEI) with non-ionic polyethers, poly (ethylene oxide) (PEO) or Pluronic 123 (P123). The PEO-PEI conjugates differ in the molecular mass of PEI (2 kDa and 25 kDa) and the degree of modification of PEI with PEO. All of these conjugates form complexes upon mixing with plasmids, which are stable in aqueous dispersion for several days. The sizes of the particles formed in these systems vary from 70 to 200 nm depending on the composition of the complex. However, transfection activity of these systems is much lower than that of PEI (25 kDa) or Superfect as assessed in in vitro transfection experiments utilizing a luciferase reporter expression in Cos-7 cells as a model system. In contrast, conjugate of P123 with PEI (2 kDa) mixed with free P123 (9:1(wt)) forms small and stable complexes with DNA (110 nm) that exhibit high transfection activity in vitro. Furthermore, gene expression is observed in spleen, heart, lungs and liver 24 h after i.v. injection of this complex in mice. Compared to 1,2-bis(oleoyloxy)-(trimethylammonio) propane:cholesterol (DOTAP:Chol) and PEI (25 kDa) transfection systems, the P123-PEI system reveals a more uniform distribution of gene expression between these organs, allowing a significant improvement of gene expression in liver.

Taking polycation gene delivery systems from in vitro to in vivo

It is widely believed that non-viral gene delivery systems may improve safety and overcome tissue-tropism limitations associated with viral-based gene therapies. Cationic liposome-based gene delivery currently accounts for 9-12% of ongoing gene therapy clinical trials in the United States and Europe. Polycation-based gene delivery is at an earlier development stage. However, both in vitro and in vivo studies have demonstrated that this is an area of much promise. Complexes of polycations with DNA result in major improvements in the control of size, charge, and the hydrophilic-lipophilic characteristics of the transfecting species, when compared with other non-viral systems. This review serves as an introduction to the current status of this field.