Pegaptanib, a targeted anti-VEGF aptamer for ocular vascular disease

Systemic Overexpression of Angiopoietin-2 Promotes Tumor Microvessel Regression and Inhibits Angiogenesis and Tumor Growth

Angiopoietin-2 (Ang-2) is a conditional antagonist and agonist for the endothelium-specific Tie-2 receptor. Although endogenous Ang-2 cooperates with vascular endothelial growth factor (VEGF) to protect tumor endothelial cells, the effect on tumor vasculature of high levels of exogenous Ang-2 with different levels of VEGF has not been studied in detail. Here, we report that systemic overexpression of Ang-2 leads to unexpected massive tumor vessel regression within 24 h, even without concomitant inhibition of VEGF. By impairing pericyte coverage of the tumor vasculature, Ang-2 destabilizes the tumor vascular bed while improving perfusion in surviving tumor vessels. Ang-2 overexpression transiently exacerbates tumor hypoxia without affecting ATP levels. Although sustained systemic Ang-2 overexpression does not affect tumor hypoxia and proliferation, it significantly inhibits tumor angiogenesis, promotes tumor apoptosis, and suppresses tumor growth. The similar antitumoral, antiangiogenic efficacy of systemic overexpression of Ang-2, soluble VEGF receptor-1, and the combination of both suggests that concomitant VEGF inhibition is not required for Ang-2-induced tumor vessel regression and growth delay. This study shows the important roles of Ang-2-induced pericyte dropout during tumor vessel regression. It also reveals that elevated Ang-2 levels have profound pleiotropic effects on tumor vessel structure, perfusion, oxygenation, and apoptosis.

Synthetic delivery systems for intravenous administration of nucleic acids

At present, there are no intravenously administered nucleic acid-based therapeutics that have been approved for human use. This reflects the difficulties in applying nucleic acid-based drugs: they are nuclease sensitive and have difficulties in reaching their site of action. Important challenges for intravenously administered nucleic acid formulations are the requirements that they can transport the nucleic acids efficiently in the circulation, have the ability to direct nucleic acids to the desired cell type and are able to steer their intracellular processing. Here, we evaluate nanotechnological strategies that improve the pharmacokinetics and colloidal stability of nucleic acids in the bloodstream, focus biodistribution towards the target tissue and facilitate interactions with and trafficking within the desired cell type.

Management of neovascular age-related macular degeneration

Neovascular age-related macular degeneration (AMD) is becoming an increasing socio-medical problem as the proportion of the aged population is continuously increasing. However, new insights in the pathogenesis of the disease offer the opportunity to develop targeted therapies that attack the disease process more successfully than ever. This review article will focus on summarizing the actual options in the management of neovascular AMD and provide a short overview about recent therapeutic options in clinical and preclinical evaluation. The recent development of anti-VEGF substances for use in clinical routine has markedly improved the prognosis of patients with neovascular AMD. Intravitreal treatment with substances targeting all isotypes of vascular endothelial growth factor (VEGF), for the first time in the history of AMD treatments, results in a significant increase in visual acuity in patients with neovascular AMD. Overall, anti-angiogenic approaches provide vision maintenance in over 90% and substantial improvement in 25-40% of patients. The combination with occlusive therapies like photodynamic therapy (PDT) potentially offers a reduction of re-treatment frequency and long-term maintenance of the treatment benefit. Further developments interacting with various steps in the angiogenic cascade are under clinical or preclinical evaluation and may soon become available. Nevertheless, the growing number of novel therapeutic options will have to provide proof of concept in randomized controlled clinical trials, a major challenge in view of the rapidly evolving field. For those therapies, which are already in clinical use, reasonable diagnostic tools for follow-up need to be developed, as the burden of continuous clinical monitoring of all patients and all indications is significant for patients and doctors. Ultimately, economic issues will be the limiting factor for the clinical availability of different treatment options.

Aptamers-based assays for diagnostics, environmental and food analysis

Aptamers are single stranded DNA or RNA ligands which can be selected for different targets starting from a huge library of molecules containing randomly created sequences. Aptamers have been selected to bind very different targets, from proteins to small organic dyes. In addition to the very important aspect of having an unlimited source of identical affinity recognition molecules available due to the selection process, aptamers can offer advantages over antibodies that make them very promising for analytical applications. The use of aptamers as therapeutic tools is nowadays well established. On the contrary, the analytical application of aptamers in diagnostic devices or in systems for environmental and food analysis, is still under investigation and the scientific community still need further research to demonstrate the advancements brought by this new kind of ligands. This review will focus on these latter applications with particular attention to the detection of food pathogens, terrorism threat agents, thrombin and cytokines.

Combination therapy for the treatment of ocular neovascularization

The growth of inappropriately regulated, leaky blood vessels is a prominent component of several debilitating eye diseases, such as age-related macular degeneration (AMD), proliferative diabetic retinopathy (PDR), and retinopathy of prematurity (ROP). New pharmacological therapies that target vascular endothelial growth factor-A (VEGF-A) have significantly enhanced the treatment of AMD by limiting the progression of the disease, and in some cases, by improving vision. Although anti-VEGF therapy will undoubtedly prove valuable in the treatment of other neovascular diseases of the eye, improvements with this type of therapy are still required. At present, anti-VEGF therapy requires intravitreal injection and a relatively frequent dosing regimen (4-6 weeks). Furthermore, in experimental models of neovascularization, anti-VEGF treatment becomes less effective at blocking vessel growth and at regressing vessels as the neovascularization develops over time. As such, the use of anti-VEGF therapy in late-stage AMD may be limited. An important strategy for improved treatment of neovascular diseases of the eye could be combination therapy. Combination therapy of anti-VEGF drugs with established treatments, such as photodynamic therapy with verteporfin (PDT-V), or with newly-developed drugs targeting specific kinases, presents opportunities for increased efficacy and improved therapeutic outcome. In this review, we evaluate the opportunities for combination therapy for the treatment of neovascular diseases of the eye.

Comparative antiproliferative and cytotoxic profile of bevacizumab (Avastin), pegaptanib (Macugen) and ranibizumab (Lucentis) on different ocular cells

AIM

To compare the antiproliferative and cytotoxic properties of bevacizumab (Avastin), pegaptanib (Macugen) and ranibizumab (Lucentis) on human retinal pigment epithelium (ARPE19) cells, rat retinal ganglion cells (RGC5) and pig choroidal endothelial cells (CEC).

METHODS

Monolayer cultures of ARPE19, RGC5 and CEC were used. Bevacizumab (0.1-0.3 mg/ml), pegaptanib (0.025-0.08 mg/ml) or ranibizumab (0.04-0.125 mg/ml) diluted in culture medium were added to the cells. Expression of VEGF-receptors (VEGFR1 and VEGFR2) and von Willebrand factor (a marker for endothelial cells) were analysed by immunohistochemistry. CEC cells were stimulated with VEGF. Cellular proliferative activity was monitored by BrdU-incorporation into cellular DNA. For cytotoxicity assays cells were grown to confluence and then cultured in a serum-depleted medium to ensure a static milieu. MTT-test was performed after one day.

RESULTS

CEC and ARPE19 cells stained positively for VEGFR1 and VEGFR2. More than 95% of the CEC cells were positive for von Willebrand factor. Ranibizumab reduced CEC cell proliferation by 44.1%, bevacizumab by 38.2% and pegaptanib by 35.1% when the drugs were used at their established clinical doses. The differences, however, between the three drugs in respect to cell growth inhibition were not statistically significant. Only a mild antiproliferative effect of bevacizumab or pegaptanib on ARPE19 cells could be observed. Ranibizumab did not alter ARPE19 cell proliferation. No cytotoxicity on RGC5, CEC and ARPE19 cells could be seen.

CONCLUSIONS

Bevacizumab, pegaptanib and ranibizumab significantly suppress choroidal endothelial cell proliferation. However, when used at the currently established doses none of the drugs was superior over the others in respect to endothelial cell growth inhibition. The biocompatibility of all three drugs--including the off-label bevacizumab--seems to be excellent when used at the currently recommended intravitreal dose.

Vascular Endothelial Growth Factor (VEGF) in Autoimmune Diseases

Vascular endothelial growth factor (VEGF) is a potent stimulating factor for angiogenesis and vascular permeability. There are eight isoforms with different and sometimes overlapping functions. The mechanisms of action are under investigation with emerging insights into overlapping pathways and cross-talk between other receptors such as the neuropilins, which were not previously associated to angiogenesis. VEGF has important physiological actions on embryonic development, healing, and menstrual cycle. It also has a great role in pathological conditions that are associated to autoimmune diseases. There is considerable evidence in various autoimmune diseases such as in systemic lupus erythematosus, rheumatoid arthritis, and multiple sclerosis of an interrelationship between the VEGF system and theses disorders. Serum levels of VEGF correlate with disease activity in a large number of autoimmune diseases and fall with the use of standard therapy. We raised the possible future therapeutic strategies in autoimmune diseases with the anti-VEGF or anti-VEGFR (receptor). So far, this therapy has been used in cancer and macular ocular degeneration in diabetes. This review outlines the evidence for VEGF participation in various autoimmune diseases and proposes lines for future research in this field.

RNA learns from antisense

RNA interference provides powerful tools for controlling gene expression in cultured cells. Whether RNAi will provide similarly powerful drugs is unknown. Lessons from development of antisense oligonucleotide drugs may provide some clues.

Mice expressing a humanized form of VEGF-A may provide insights into the safety and efficacy of anti-VEGF antibodies

VEGF-A is important in tumor angiogenesis, and a humanized anti-VEGF-A monoclonal antibody (bevacizumab) has been approved by the FDA as a treatment for metastatic colorectal and nonsquamous, non-small-cell lung cancer in combination with chemotherapy. However, contributions of both tumor- and stromal-cell derived VEGF-A to vascularization of human tumors grown in immunodeficient mice hindered direct comparison between the pharmacological effects of anti-VEGF antibodies with different abilities to block host VEGF. Therefore, by gene replacement technology, we engineered mice to express a humanized form of VEGF-A (hum-X VEGF) that is recognized by many anti-VEGF antibodies and has biochemical and biological properties comparable with WT mouse and human VEGF-A. The hum-X VEGF mouse model was then used to compare the activity and safety of a panel of VEGF Mabs with different affinities for VEGF-A. Although in vitro studies clearly showed a correlation between binding affinity and potency at blocking endothelial cell proliferation stimulated by VEGF, in vivo experiments failed to document any consistent correlation between antibody affinity and the ability to inhibit tumor growth and angiogenesis in most animal models. However, higher-affinity antibodies were more likely to result in glomerulosclerosis during long-term treatment.

Insulin-induced activation of hypoxia-inducible factor-1 requires generation of reactive oxygen species by NADPH oxidase

Hypoxia-inducible factor (HIF)-1 activation in response to hypoxia requires mitochondrial generation of reactive oxygen species (ROS). In contrast, the requirement of ROS for HIF-1 activation by growth factors like insulin remains unexplored. To explore that, insulin-sensitive hepatic cell HepG2 or cardiac muscle cell H9c2 cells were pretreated with NADPH oxidase inhibitor diphenyleneiodonium chloride (DPI) or apocynin and HIF-1 activation was tested by electrophoretic mobility shift and reporter gene assay. Antioxidants DPI or apocynin completely blocked insulin-stimulated HIF-1 activation. The restoration of HIF-1 activation by H2O2 in DPI-pretreated cells not only confirmed the role of ROS but also identified H2O2 as the responsible ROS. The role of NADPH oxidase was further confirmed by greater stimulation of HIF-1 during simultaneous treatment of suboptimal concentration of insulin along with NADPH but not by NADH. The role of oxidant generated by insulin is found to inhibit the protein tyrosine phosphatase as suggested by the following observations. First, tyrosine phosphatase-specific inhibitor sodium vanadate compensates DPI-inhibited HIF-1 activity. Second, sodium vanadate stimulates HIF-1 activation with suboptimal concentration of insulin. Third, DPI and pyrrolidene dithiocarbamate (PDTC) blocks insulin-receptor tyrosine kinase activation. The activity of phosphatidylinositol 3-kinase as evidenced by Akt phosphorylation, involved in HIF-1 activation, is also dependent on ROS generation by insulin. Finally, DPI pretreatment blocked insulin-stimulated expression of genes like VEGF, GLUT1, and ceruloplasmin. Overall, our data provide strong evidence for the essential role of NADPH oxidase-generated ROS in insulin-stimulated activation of HIF-1.

Combination angiostatic therapy completely inhibits ocular and tumor angiogenesis

Angiostatic therapies designed to inhibit neovascularization associated with multiple pathological conditions have only been partially successful; complete inhibition has not been achieved. We demonstrate synergistic effects of combining angiostatic molecules that target distinct aspects of the angiogenic process, resulting in the complete inhibition of neovascular growth associated with development, ischemic retinopathy, and tumor growth, with little or no effect on normal, mature tissue vasculature. Tumor vascular obliteration using combination angiostatic therapy was associated with reduced tumor mass and increased survival in a rat 9L gliosarcoma model, whereas individual monotherapies were ineffective. Significant compensatory up-regulation of several proangiogenic factors was observed after treatment with a single angiostatic agent. In contrast, treatment with combination angiostatic therapy significantly reduced compensatory up-regulation. Therapies that combine angiostatic molecules targeting multiple, distinct aspects of the angiogenic process may represent a previously uncharacterized paradigm for the treatment of many devastating diseases with associated pathological neovascularization.

R&D technology investments: misguided and expensive or a better way to discover medicines?

The pharmaceutical industry is in crisis owing to spiralling costs and a lack of new product launches. It is said that expensive investments in technology have not paid off. But is this really true? In this review, we explore some of the recent medicines that were, or are being, brought to market, and we discuss how they were discovered and what difference new technologies have made during the discovery of these medicines.

[Oligonucleotide therapeutics - an emerging novel class of compounds]

Oligonucleotide therapeutics are short, single- or double-stranded DNA or RNA molecules consisting of strands of 10-50 nucleotides. By targeted modulation of gene expression oligonucleotides provide the chance of targeting diseases at their molecular level. Within this novel emerging class of compounds oligonucleotide therapeutics are discriminated by their structure, function and mode of action. While antisense oligonucleotides, ribozymes and siRNAs suppress the expression of a protein by complementary hybridizing with their target mRNA, aptamers bind like antibodies to their target protein and thereby inhibit its function. Immunostimulatory oligonucleotides are due to sequence motifs within their nucleotide sequence able to trigger a therapeutic exploitable immune response. Currently, there are only two oligonucleotide therapeutics approved by the FDA, namely the antisense oligonucleotide Fomivirsen and the aptamer Macugen. In this review the mode of action of the diverse oligonucleotide therapeutics and their current status in clinical development will be discussed.

VEGF/VEGFR signalling as a target for inhibiting angiogenesis

VEGFs and a respective family of tyrosine kinases receptors (VEGFRs) are key proteins modulating angiogenesis, the formation of new vasculature from an existing vascular network. There has been considerable evidence in vivo, including clinical observations, that abnormal angiogenesis is implicated in a number of disease conditions, which include rheumatoid arthritis, inflammation, cancer, psoriasis, degenerative eye conditions and others. Antiangiogenic therapies based on inhibition of VEGF/VEGFR signalling were reported to be powerful clinical strategies in oncology and ophthalmology. Current efforts have yielded promising clinical data for several antiangiogenic therapeutics. In this review, the authors elucidate key aspects of VEGFR signalling, as well as clinically relevant strategies for the inhibition of VEGF-induced angiogenesis, with an emphasis on small-molecule VEGFR inhibitors.

Efficient non-viral ocular gene transfer with compacted DNA nanoparticles

Background

The eye is an excellent candidate for gene therapy as it is immune privileged and much of the disease-causing genetics are well understood. Towards this goal, we evaluated the efficiency of compacted DNA nanoparticles as a system for non-viral gene transfer to ocular tissues. The compacted DNA nanoparticles examined here have been shown to be safe and effective in a human clinical trial, have no theoretical limitation on plasmid size, do not provoke immune responses, and can be highly concentrated.

Methods and Findings

Here we show that these nanoparticles can be targeted to different tissues within the eye by varying the site of injection. Almost all cell types of the eye were capable of transfection by the nanoparticle and produced robust levels of gene expression that were dose-dependent. Most impressively, subretinal delivery of these nanoparticles transfected nearly all of the photoreceptor population and produced expression levels almost equal to that of rod opsin, the highest expressed gene in the retina.

Conclusions

As no deleterious effects on retinal function were observed, this treatment strategy appears to be clinically viable and provides a highly efficient non-viral technology to safely deliver and express nucleic acids in the retina and other ocular tissues.

Therapeutic potential of interfering with apelin signalling

The apelin receptor is a G protein-coupled receptor activated by several apelin fragments. Its tissue distribution suggests that apelin signalling is involved in a broad range of physiological functions. Endothelial cells, which express high levels of apelin receptors, respond to apelin through the phosphorylation of key intracellular effectors associated with cell proliferation and migration. In addition, apelin is a mitogen for endothelial cells and exhibits angiogenic properties in matrigel experiments. This review focuses on the therapeutic potential of apelin signalling, which is associated with pathologies that result from decreased vascularisation (ischemias) or neovascularisation (retinopathies and solid tumors).

Fabrication and characterization of RNA aptamer microarrays for the study of protein-aptamer interactions with SPR imaging

RNA microarrays were created on chemically modified gold surfaces using a novel surface ligation methodology and employed in a series of surface plasmon resonance imaging (SPRI) measurements of DNA-RNA hybridization and RNA aptamer-protein binding. Various unmodified single-stranded RNA (ssRNA) oligonucleotides were ligated onto identical 5'-phosphate-terminated ssDNA microarray elements with a T4 RNA ligase surface reaction. A combination of ex situ polarization modulation FTIR measurements of the RNA monolayer and in situ SPRI measurements of DNA hybridization adsorption onto the surface were used to determine an ssRNA surface density of 4.0 x 10(12) molecules/cm2 and a surface ligation efficiency of 85 +/- 10%. The surface ligation methodology was then used to create a five-component RNA microarray of potential aptamers for the protein factor IXa (fIXa). The relative surface coverages of the different aptamers were determined through a novel enzymatic method that employed SPRI measurements of a surface RNase H hydrolysis reaction. SPRI measurements were then used to correctly identify the best aptamer to fIXa, which was previously determined from SELEX measurements. A Langmuir adsorption coefficient of 1.6 x 10(7) M(-1) was determined for fIXa adsorption to this aptamer. Single-base variations from this sequence were shown to completely destroy the aptamer-fIXa binding interaction.

Targeting neuropilin-1 to inhibit VEGF signaling in cancer: Comparison of therapeutic approaches

Angiogenesis (neovascularization) plays a crucial role in a variety of physiological and pathological conditions including cancer, cardiovascular disease, and wound healing. Vascular endothelial growth factor (VEGF) is a critical regulator of angiogenesis. Multiple VEGF receptors are expressed on endothelial cells, including signaling receptor tyrosine kinases (VEGFR1 and VEGFR2) and the nonsignaling co-receptor Neuropilin-1. Neuropilin-1 binds only the isoform of VEGF responsible for pathological angiogenesis (VEGF₁₆₅), and is thus a potential target for inhibiting VEGF signaling. Using the first molecularly detailed computational model of VEGF and its receptors, we have shown previously that the VEGFR–Neuropilin interactions explain the observed differential effects of VEGF isoforms on VEGF signaling in vitro, and demonstrated potent VEGF inhibition by an antibody to Neuropilin-1 that does not block ligand binding but blocks subsequent receptor coupling. In the present study, we extend that computational model to simulation of in vivo VEGF transport and binding, and predict the in vivo efficacy of several Neuropilin-targeted therapies in inhibiting VEGF signaling: (a) blocking Neuropilin-1 expression; (b) blocking VEGF binding to Neuropilin-1; (c) blocking Neuropilin–VEGFR coupling. The model predicts that blockade of Neuropilin–VEGFR coupling is significantly more effective than other approaches in decreasing VEGF–VEGFR2 signaling. In addition, tumor types with different receptor expression levels respond differently to each of these treatments. In designing human therapeutics, the mechanism of attacking the target plays a significant role in the outcome: of the strategies tested here, drugs with similar properties to the Neuropilin-1 antibody are predicted to be most effective. The tumor type and the microenvironment of the target tissue are also significant in determining therapeutic efficacy of each of the treatments studied.

Neuropilin is a co-receptor for some of the isoforms of the vascular endothelial growth factor (VEGF) family. The presence of Neuropilin on endothelial or other cells increases binding of these isoforms to their signaling receptor VEGFR2, thus increasing pro-angiogenesis signaling and stimulating vascular growth. Neuropilin is thus a suitable target for anti-angiogenesis therapy, which holds promise for the treatment of vasculature-dependent diseases such as cancer and diabetic retinopathy. In this study, Mac Gabhann and Popel perform computational simulations of VEGF transport in breast cancer, using a previously validated model of VEGF–VEGF receptor interactions, as well as geometrical information on the tumor itself—tumor cells, vasculature, and extracellular matrix. Three different molecular therapies targeting Neuropilin are tested in silico, and the simulations predict that one of these therapies will be effective at reducing VEGFR2 signaling in certain types (or subtypes) of tumors, while the others will not. Thus, we demonstrate that identification of a target molecule is not sufficient; different therapeutic strategies targeting the same molecule may result in different outcomes.

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.

Development of ranibizumab, an anti-vascular endothelial growth factor antigen binding fragment, as therapy for neovascular age-related macular degeneration

BACKGROUND

Angiogenesis is a key aspect of the wet form of age-related neovascular (AMD), the leading cause of blindness in the elderly population. Substantial evidence indicated that vascular endothelial growth factor (VEGF)-A is a major mediator of angiogenesis and vascular leakage in wet AMD. VEGF-A is the prototype member of a gene family that includes also PlGF, VEGF-B, VEGF-C, VEGF-D and the orf virus-encoded VEGF-E. Several isoforms of VEGF-A can be generated due to alternative mRNA splicing. Various VEGF inhibitors have been clinically developed. Among these, ranibizumab is a high affinity recombinant Fab that neutralizes all isoforms of VEGF-A. The article briefly reviews the biology of VEGF and then focuses on the path that led to clinical development of ranibizumab.

RESULTS

The safety and efficacy of ranibizumab in the treatment of neovascular AMD have been evaluated in two large phase III, multicenter, randomized, double-masked, controlled pivotal trials in different neovascular AMD patient populations. Combined, the trial results indicate that ranibizumab results not only in a slowing down of vision loss but also in a significant proportion of patients experiencing a clinically meaningful vision gain. The visual acuity benefit over control was observed regardless of CNV lesion type. Furthermore, the benefit was associated with a low rate of serious adverse events.

CONCLUSIONS

Ranibizumab represents a novel therapy that, for the first time, appears to have the potential to enable many AMD patients to obtain a meaningful and sustained gain of vision. On June 30 2006, ranibizumab was approved by the US Food and Drug Administration for the treatment of wet AMD.

Selection and characterization of RNA aptamers to the RNA-dependent RNA polymerase from foot-and-mouth disease virus

Foot-and-mouth disease virus causes a highly contagious disease of agricultural livestock and is of enormous economic importance. Replication of the RNA genome of the virus, via negative strand intermediates, involves an RNA-dependent RNA polymerase (3Dpol). RNA aptamers specific to this enzyme have been selected and characterized. Some of these molecules inhibit enzymatic activity in vitro, with IC50 values of <20 nM and Ki values of 18-75 nM. Two of these show similarity, both with each other and with regions of the viral genome. Furthermore, truncated versions of one of the aptamers have been used to define the parts of the molecule responsible for its inhibitory activity.

Targeting VEGF-A to treat cancer and age-related macular degeneration

Inhibiting angiogenesis is a promising strategy to treat cancer and several other disorders, including intraocular neovascular syndromes. The identification of vascular endothelial growth factor (VEGF)-A as a major regulator of normal and pathological angiogenesis has enabled significant progress toward effective treatments for such disorders. Several VEGF inhibitors have been recently approved by the U.S. Food and Drug Administration for the treatment of cancer and the neovascular form of age-related macular degeneration. This review summarizes the basic biology of VEGF-A and illustrates the clinical progress in targeting this molecule.

An RNA aptamer that discriminates bovine factor IX from human factor IX

An RNA aptamer has been selected by SELEX against bovine factor IX using an RNA pool containing 74-nucleotides randomized region. Selected RNA aptamer (Clone 5) could discriminate bovine factor IX effectively from human factor IX. Interestingly, the nucleotide regions 73-78 and 80-83 of the selected aptamer were determined to be important for bovine factor IX-binding using phosphate interference. Based on phosphate interference and binding studies the minimal motif for aptamer with discriminating ability is found with the nucleotide regions from 65 to 106. The discriminating ability of this mini aptamer is calculated as more than 1,000 fold. The equilibrium dissociation constant (K(d)) for the above complex was 10 nM as determined by surface plasmon resonance. Based on the available structural informations, probable binding site of aptamer on the target was predicted.

Aptamers come of age - at last

Nucleic-acid aptamers have the molecular recognition properties of antibodies, and can be isolated robotically for high-throughput applications in diagnostics, research and therapeutics. Unlike antibodies, however, they can be chemically derivatized easily to extend their lifetimes in biological fluids and their bioavailability in animals. The first aptamer-based clinical drugs have recently entered service. Meanwhile, active research programmes have identified a wide range of anti-viral aptamers that could form the basis for future therapeutics.

Novel approach to analyzing RNA aptamer-protein interactions: toward further applications of aptamers

Surface plasmon-resonance analysis using a Biacore biosensor is a powerful tool for the detailed study of biomolecular interactions. The authors examined the methods of immobilizing proteins on the surface of NTA, SA, and CM5 sensor chips to study RNA aptamer-protein interactions. RNA aptamers and their deletion variants were loaded onto a protein-immobilized sensor chip, and their binding affinities were analyzed. Immobilizing the protein on a CM5 sensor chip via an anti-His-tag antibody was the only strategy that clearly detected the kinetic parameters of the interactions. DeltaNEO-III-14U, one of the deletion variants of the NS3 aptamer, had the highest binding affinity for the deltaNS3 protein in this study (KD = 4 x 10(-8)). Moreover, the 29-amino-acid spacer fragment was essential for protein immobilization using this strategy. This novel method will be useful in comparing the affinity of various RNA aptamers and selecting the most suitable candidates for a given target, as well as facilitating the in vitro selection procedure itself.