Pegaptanib for the treatment of age-related macular degeneration

Assembly of a multivalent aptamer for efficient inhibition of thermostable direct hemolysin toxicity induced by Vibrio parahaemolyticus

Thermostable direct hemolysin (TDH) is a key virulence factor of Vibrio parahaemolyticus, capable of causing seafood-mediated outbreaks of gastroenteritis, posing a threat to the aquatic environment and global public health. In the present study, we explored a multivalent aptamer-mediated inhibition strategy to mitigate TDH toxicity. Based on the characteristic structure of TDH, a stable multivalent aptamer, Ap3-5, was rationally designed by truncation, key fragment evolution, and end fixation. Ap3-5 exhibited strong affinity (Kd=39.24 nM), and thermal (Tm=57.6 °C) and enzymatic stability. In silico studies also revealed that Ap3-5 occupied more active sites of TDH and covered its central pore, indicating its potential as a blocking agent for inhibiting TDH toxicity. In the hemolysis assay, Ap3-5 significantly suppressed the hemolytic effect of TDH. A cellular study revealed a substantial (∼80 %) reduction in TDH cytotoxicity. Supporting these findings, in vivo trials confirmed the inhibitory action of Ap3-5 on both the acute and intestinal toxicity of TDH. Overall, benefiting from the strong binding affinity, high stability, and multisite occupation of the multivalent aptamer with TDH, Ap3-5 displayed robust potential against TDH toxicity by inhibiting membrane pore formation, providing a new approach for alleviating bacterial infections.

Recent advances of anti-angiogenic inhibitors targeting VEGF/VEGFR axis

Vascular endothelial growth factors (VEGF), Vascular endothelial growth factor receptors (VEGFR) and their downstream signaling pathways are promising targets in anti-angiogenic therapy. They constitute a crucial system to regulate physiological and pathological angiogenesis. In the last 20 years, many anti-angiogenic drugs have been developed based on VEGF/VEGFR system to treat diverse cancers and retinopathies, and new drugs with improved properties continue to emerge at a fast rate. They consist of different molecular structures and characteristics, which enable them to inhibit the interaction of VEGF/VEGFR, to inhibit the activity of VEGFR tyrosine kinase (TK), or to inhibit VEGFR downstream signaling. In this paper, we reviewed the development of marketed anti-angiogenic drugs involved in the VEGF/VEGFR axis, as well as some important drug candidates in clinical trials. We discuss their mode of action, their clinical benefits, and the current challenges that will need to be addressed by the next-generation of anti-angiogenic drugs. We focus on the molecular structures and characteristics of each drug, including those approved only in China.

Ocular Delivery of Therapeutic Proteins: A Review

Therapeutic proteins, including monoclonal antibodies, single chain variable fragment (ScFv), crystallizable fragment (Fc), and fragment antigen binding (Fab), have accounted for one-third of all drugs on the world market. In particular, these medicines have been widely used in ocular therapies in the treatment of various diseases, such as age-related macular degeneration, corneal neovascularization, diabetic retinopathy, and retinal vein occlusion. However, the formulation of these biomacromolecules is challenging due to their high molecular weight, complex structure, instability, short half-life, enzymatic degradation, and immunogenicity, which leads to the failure of therapies. Various efforts have been made to overcome the ocular barriers, providing effective delivery of therapeutic proteins, such as altering the protein structure or including it in new delivery systems. These strategies are not only cost-effective and beneficial to patients but have also been shown to allow for fewer drug side effects. In this review, we discuss several factors that affect the design of formulations and the delivery of therapeutic proteins to ocular tissues, such as the use of injectable micro/nanocarriers, hydrogels, implants, iontophoresis, cell-based therapy, and combination techniques. In addition, other approaches are briefly discussed, related to the structural modification of these proteins, improving their bioavailability in the posterior segments of the eye without affecting their stability. Future research should be conducted toward the development of more effective, stable, noninvasive, and cost-effective formulations for the ocular delivery of therapeutic proteins. In addition, more insights into preclinical to clinical translation are needed.

Aptamer-Based Probes for Cancer Diagnostics and Treatment

Aptamers are single-stranded DNA or RNA oligomers that have the ability to generate unique and diverse tertiary structures that bind to cognate molecules with high specificity. In recent years, aptamer researches have witnessed a huge surge, owing to its unique properties, such as high specificity and binding affinity, low immunogenicity and toxicity, and simplicity of synthesis with negligible batch-to-batch variation. Aptamers may bind to targets, such as various cancer biomarkers, making them applicable for a wide range of cancer diagnosis and treatment. In cancer diagnostic applications, aptamers are used as molecular probes instead of antibodies. They have the potential to detect various cancer-associated biomarkers. For cancer therapeutic purposes, aptamers can serve as therapeutic or delivery agents. The chemical stabilization and modification strategies for aptamers may expand their serum half-life and shelf life. However, aptamer-based probes for cancer diagnosis and therapy still face several challenges for successful clinical translation. A deeper understanding of nucleic acid chemistry, tissue distribution, and pharmacokinetics is required in the development of aptamer-based probes. This review summarizes their application in cancer diagnostics and treatments based on different localization of target biomarkers, as well as current challenges and future prospects.

Delivery strategies in treatments of leukemia

Leukemia is a hematological malignancy associated with the uncontrolled proliferation of mutant progenitors, suppressing the production of normal blood cells. Current treatments, including chemotherapy, radiotherapy, and immunotherapy, still lead to unsatisfactory results with a 5 year survival rate of only 30-50%. The poor prognosis is related to both disease relapse and treatment-associated toxicity. Delivery strategies can improve the in vivo pharmacokinetics of drugs, navigating the therapeutics to target cells or the tumor microenvironment and reversing drug resistance, which maximizes tumor elimination and alleviates systematic adverse effects. This review discusses available FDA-approved anti-leukemia drugs and therapies with a focus on the advances in the development of anti-leukemia drug delivery systems. Additionally, challenges in clinical translation of the delivery strategies and future research opportunities in leukemia treatment are also included.

Orally Administrable Therapeutic Nanoparticles for the Treatment of Colorectal Cancer

Colorectal cancer (CRC) is one of the most common and lethal human malignancies worldwide; however, the therapeutic outcomes in the clinic still are unsatisfactory due to the lack of effective and safe therapeutic regimens. Orally administrable and CRC-targetable drug delivery is an attractive approach for CRC therapy as it improves the efficacy by local drug delivery and reduces systemic toxicity. Currently, chemotherapy remains the mainstay modality for CRC therapy; however, most of chemo drugs have low water solubility and are unstable in the gastrointestinal tract (GIT), poor intestinal permeability, and are susceptible to P-glycoprotein (P-gp) efflux, resulting in limited therapeutic outcomes. Orally administrable nanoformulations hold the great potential for improving the bioavailability of poorly permeable and poorly soluble therapeutics, but there are still limitations associated with these regimes. This review focuses on the barriers for oral drug delivery and various oral therapeutic nanoparticles for the management of CRC.

Electrochemical aptasensor for NS1 detection: Towards a fast dengue biosensor

Dengue is one of the most commonly neglected tropical diseases transmitted by Aedes aegypti infected with Dengue virus. This virus belongs to the gender Flavivirus and produces a non-structural protein 1 (NS1), which is an important biomarker found at high levels in blood in early disease stage. Therefore, this study focused on the development of an electrochemical biosensor for NS1 detection using DNA aptamers. Gold electrodes were co-immobilized with specific aptamers and 6-mercapto-1-hexanol (MCH) to obtain a self-assembled monolayer. The molar ratio between aptamers and MCH was optimized and the platform characterized by electrochemical impedance spectroscopy and atomic force microscopy. Bovine serum albumin was added in NS1 solution to stabilize it and block the surface to avoid non-specific interactions. The biosensor performance was tested with NS1 protein serotype 4 (in phosphate saline buffer and human serum) and with a solution of serotype 1 in human serum. The results showed a sensitivity of 2.9%, 2.7% and 1.7% per decade, respectively, and low limit of detection (0.05, 0.022 and 0.025 ng/mL). The platform was also tested with Envelope protein as negative control. Furthermore, the aptamer sensor was able to detect NS1 in clinical range and it is a promising candidate for a new class for miniaturized point-of-care device for different Dengue serotypes.

ABL001, a Bispecific Antibody Targeting VEGF and DLL4, with Chemotherapy, Synergistically Inhibits Tumor Progression in Xenograft Models

Delta-like-ligand 4 (DLL4) is a promising target to augment the effects of VEGF inhibitors. A simultaneous blockade of VEGF/VEGFR and DLL4/Notch signaling pathways leads to more potent anti-cancer effects by synergistic anti-angiogenic mechanisms in xenograft models. A bispecific antibody targeting VEGF and DLL4 (ABL001/NOV1501/TR009) demonstrates more potent in vitro and in vivo biological activity compared to VEGF or DLL4 targeting monoclonal antibodies alone and is currently being evaluated in a phase 1 clinical study of heavy chemotherapy or targeted therapy pre-treated cancer patients (ClinicalTrials.gov Identifier: NCT03292783). However, the effects of a combination of ABL001 and chemotherapy on tumor vessels and tumors are not known. Hence, the effects of ABL001, with or without paclitaxel and irinotecan were evaluated in human gastric or colon cancer xenograft models. The combination treatment synergistically inhibited tumor progression compared to each monotherapy. More tumor vessel regression and apoptotic tumor cell induction were observed in tumors treated with the combination therapy, which might be due to tumor vessel normalization. Overall, these findings suggest that the combination therapy of ABL001 with paclitaxel or irinotecan would be a better clinical strategy for the treatment of cancer patients.

NEI-Supported Age-Related Macular Degeneration Research: Past, Present, and Future

Purpose

To review past and current National Eye Institute (NEI)–supported age-related macular degeneration (AMD) activities and initiatives and preview upcoming coordinated efforts for studying AMD.

Methods

We conducted and summarized a portfolio analysis and literature review of NEI intramural and extramural AMD activities.

Results

The NEI supports a broad range of AMD research, both by individual independent investigators as well as through networks and consortia. The International AMD Genomics Consortium, Age-Related Eye Disease Study, Age-Related Eye Disease Study 2 (AREDS2), and Comparison of AMD Treatments Trial legacy work probed the complex genetics, clinical presentation, and standards of patient care, respectively. The NEI AMD Pathobiology Working Group identified gaps and opportunities for future research efforts. The AMD Ryan Initiative Study and clinical trials testing the efficacies of minocycline to modulate retinal microglia activity and induced pluripotent stem cells–derived retinal pigmented epithelium (RPE) patch implants to rescue photoreceptor cell death are among the future directions for NEI-supported AMD research. Finally, NEI commissioned the creation of AREDS2 participant-derived induced pluripotent stem cell (iPSC) lines linked to their associated genomic and phenotypic datasets. These datasets will also be linked to the data obtained using their associated iPSC-derived cells (RPE, retina, choroid) and made publicly available.

Conclusions

Investments by NEI for AMD research will continue to provide invaluable resources to investigators committed to addressing this complex blinding disease and other retinal degenerative diseases.

Translational Relevance

NEI now stands poised to expand the resources available to clinical investigators to uncover disease mechanisms and move experimental therapies into clinical trials.

Aptamers: A Review of Their Chemical Properties and Modifications for Therapeutic Application

Aptamers are short, single-stranded oligonucleotides that bind to specific target molecules. The shape-forming feature of single-stranded oligonucleotides provides high affinity and excellent specificity toward targets. Hence, aptamers can be used as analogs of antibodies. In December 2004, the US Food and Drug Administration approved the first aptamer-based therapeutic, pegaptanib (Macugen), targeting vascular endothelial growth factor, for the treatment of age-related macular degeneration. Since then, however, no aptamer medication for public health has appeared. During these relatively silent years, many trials and improvements of aptamer therapeutics have been performed, opening multiple novel directions for the therapeutic application of aptamers. This review summarizes the basic characteristics of aptamers and the chemical modifications available for aptamer therapeutics.

Aptamedicine: a new treatment modality in personalized cancer therapy

Aptamers ( Aps ) are short single-strand nucleic acids exhibiting unique 3D structure which facilitate their targeting potential against various cancer molecular markers ( CMMs ). Such features of Aps not only make them as suitable homing agents in targeted drug delivery systems (DDSs) but also candidate them as macromolecules that inhibit the interaction of the target ligand with other proteins. On the other hand, the conjugation of Aps with another therapeutic molecule such as antisense oligonucleotides (ASOs), siRNAs/miRNAs, Aps , toxins, chemotherapeutic agents, DNAzymes/Ribozymes provides hopeful strategy to eradicate the malignancies and overcome the off-target unwanted side effects. Such prominent features of Aps make them a promising treatment modality to overcome the tumor complexity and heterogeneity, which can be consequently applied for personalized therapy of cancer by using bispecific Ap-based therapeutics.

ITC Measurement for High-Affinity Aptamers Binding to Their Target Proteins

Aptamers are nucleic acid molecules that bind to a target molecule with high affinity and specificity, which are generated by a process known as systematic evolution of ligands by exponential enrichment (SELEX). Because of their high affinity and specificity, aptamers were developed as therapeutic agents. Although aptamers are investigated as promising therapeutic agents, the mechanism of their high affinity and specificity is not clear. Therefore, structural and biophysical studies are important to know that. To date, ITC is increasingly being used to study the thermodynamic basis of aptamer-target protein interactions. Understanding the mechanism of aptamer binding would contribute to their development for therapeutic applications. In this chapter, we describe the protocol to study the thermodynamics of aptamer-protein interactions.

Bispecific therapeutic aptamers for targeted therapy of cancer: a review on cellular perspective

Aptamers (Aps), as short single-strand nucleic acids, can bind to their corresponding molecular targets with the high affinity and specificity. In comparison with the monoclonal antibodies (mAbs) and peptides, unique physicochemical and biological characteristics of Aps make them excellent targeting agents for different types of cancer molecular markers (CMMs). Much attention has been paid to the Ap-based multifunctional chimeric and therapeutic systems, which provide promising outcomes in the targeted therapy of various formidable diseases, including malignancies. In the Ap-based chimeric systems, a targeting Ap is conjugated to another therapeutic molecule (e.g., siRNA/miRNA, Ap, toxins, chemotherapeutic agents, DNAzyme/ribozymes) with a capability of binding to a specific cell surface receptor at the desired target site. Having been engineered as multifunctional nanosystems (NSs), Ap-based hybrid scaffolds can be used to concurrently target multiple markers/pathways in cancerous cells, causing drastic inhibitory effects on the growth and the progression of tumor cells. Multi/bispecific Aps composed of two/more Aps provide a versatile tool for the optimal and active targeting of cell surface receptor(s) with markedly high affinity and avidity. Targeting the optimum activity of key receptors and dominant signaling pathways in the activation of immunity, the multi/bispecific Ap-based therapeutics can also be used to enhance the antitumor activity of the immune system. Further, the bispecific systems can be designed to induce cytotoxicity in a heterogeneous population of cancer cells with different CMMs. In this review, we provide some important insights into the construction and applications of the Ap-based chimeric NSs and discuss the multifunctional Ap chimera and their effects on the signaling pathways in cancer.

Stem Cell Derived Retinal Pigment Epithelium: The Role of Pigmentation as Maturation Marker and Gene Expression Profile Comparison with Human Endogenous Retinal Pigment Epithelium

In age-related macular degeneration (AMD) the retinal pigment epithelium (RPE) deteriorates, leading to photoreceptor decay and severe vision loss. New therapeutic strategies aim at RPE replacement by transplantation of pluripotent stem cell (PSC)-derived RPE. Several protocols to generate RPE have been developed where appearance of pigmentation is commonly used as indicator of RPE differentiation and maturation. It is, however, unclear how different pigmentation stages reflect developmental stages and functionality of PSC-derived RPE cells. We generated human embryonic stem cell-derived RPE (hESC-RPE) cells and investigated their gene expression profiles at early pigmentation (EP) and late pigmentation (LP) stages. In addition, we compared the hESC-RPE samples with human endogenous RPE. We used a common reference design microarray (44 K). Our analysis showed that maturing hESC-RPE, upon acquiring pigmentation, expresses markers specific for human RPE. Interestingly, our analysis revealed that EP and LP hESC-RPE do not differ much in gene expression. Our data further showed that pigmented hESC-RPE has a significant lower expression than human endogenous RPE in the visual cycle and oxidative stress pathways. In contrast, we observed a significantly higher expression of pathways related to the process adhesion-to-polarity model that is typical of developing epithelial cells. We conclude that, in vitro, the first appearance of pigmentation hallmarks differentiated RPE. However, further increase in pigmentation does not result in much significant gene expression changes and does not add important RPE functionalities. Consequently, our results suggest that the time span for obtaining differentiated hESC-RPE cells, that are suitable for transplantation, may be greatly reduced.

Aptamers in HIV research diagnosis and therapy

Aptamers are high affinity single-stranded nucleic acid or protein ligands which exhibit specificity and avidity comparable to, or exceeding that of antibodies and can be generated against most targets. The functionality of aptamers is based on their unique tertiary structure, complexity and their ability to attain unique binding pockets by folding. Aptamers are selected in vitro by a process called Systematic Evolution of Ligands by Exponential enrichment (SELEX). The Kd values for the selected aptamer are often in the picomolar to low nanomolar range. Stable and nontoxic aptamers could be selected for a wide range of ligands including small molecules to large proteins. Aptamers have shown tremendous potential and have found multipurpose application in the field of therapeutic, diagnostic, biosensor and bio-imaging. While their mechanism of action can be similar to that of monoclonal antibodies, aptamers provide additional advantages in terms of production cost, simpler regulatory approval and lower immunogenicity as they are synthesized chemically. Human immunodeficiency virus (HIV) is the primary cause of acquired immune deficiency syndrome (AIDS), which causes significant morbidity and mortality with a significant consequent decrease in the quality of patient's lives. While cART has led to good viral control, people living with HIV now suffer from non-HIV comorbidities due to viral protein expression that cannot be controlled by cART. Hence pathophysiological mechanisms that govern these comorbidities with a focus on therapies that neutralize these HIV effects gained increased attention. Recent advances in HIV/AIDS research have identified several molecular targets and for the development of therapeutic and diagnostic using aptamers against HIV/AIDS. This review presents recent advances in aptamers technology for potential application in HIV diagnostics and therapeutics towards improving the quality of life of people living with HIV.

Aptamer: A potential oligonucleotide nanomedicine in the diagnosis and treatment of hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is one of the most common cancers with a high mortality rate. Late diagnosis and poor prognosis are still a major drawback since curative therapies such as liver resection and liver transplantation are effective only for an early stage HCC. Development of novel molecular targeting therapies against HCC may provide new options that will improve the efficiency of the diagnosis and the success of the therapy, thus ameliorating the life expectancy of the patients. The aptamer is an oligonucleotide nanomedicine that has high binding affinity and specificity to small and large target molecules in the intracellular and extracellular environment with agonist or antagonist function. Currently, several aptamers for diagnostic and therapeutic purposes are under development to recognize different molecules of HCC. In in vitro models, the aptamer has been shown to be able to reduce the growth of HCC cells and increase the sensitivity to conventional chemotherapies. In in vivo mouse models, aptamer could induce cell apoptosis with antitumor activity. Overall data had shown that aptamer has limited toxicity and might be safe in clinical application. This review summarizes recent information of aptamer as a potential oligonucleotide nanomedicine tool, in diagnostics, targeted therapy, and as drug delivery nano-vehicles.

Aptamers as therapeutic middle molecules

Therapeutic molecules can be classified as low-, middle- and high-molecular weight drugs depending on their molecular masses. Antibodies represent high-molecular weight drugs and their clinical applications have been developing rapidly. Aptamers, on the other hand, are middle-molecular weight molecules that are short, single-stranded nucleic acid sequences that are selected in vitro from large oligonucleotide libraries based on their high affinity to a target molecule. Hence, aptamers can be thought of as a nucleic acid analog to antibodies. However, several viewpoints hold that the potential of aptamers arises from interesting characteristics that are distinct from, or in some cases, superior to those of antibodies. Recently, therapeutic middle molecules gain considerable attention as protein-protein interaction (PPI) inhibitors. This review summarizes the recent achievements in aptamer development in our laboratory in terms of PPI and non-PPI inhibitors.

Advances in the development of aptamer drug conjugates for targeted drug delivery

A key goal of modern medicine is target-specific therapeutic intervention. However, most drugs lack selectivity, resulting in 'off-target' side effects. To address the requirements of 'targeted therapy,' aptamers, which are artificial oligonucleotides, have been used as novel targeting ligands to construct aptamer drug conjugates (ApDC) that can specifically bind to a broad spectrum of targets, including diseased cells. Accordingly, the application of aptamers in targeted drug delivery has attracted broad interest due to their impressive selectivity and affinity, low immunogenicity, easy synthesis with high reproducibility, facile modification, and relatively rapid tissue penetration with no toxicity. Functionally, aptamers themselves can be used as macromolecular drugs, and they are also commonly used in biomarker discovery and targeted drug delivery. In this review, we will highlight the most recent advances in the development of aptamers and aptamer conjugates, and discuss their potential in targeted therapy. WIREs Nanomed Nanobiotechnol 2017, 9:e1438. doi: 10.1002/wnan.1438 For further resources related to this article, please visit the WIREs website.

Aptamers Binding to c-Met Inhibiting Tumor Cell Migration

The human receptor tyrosine kinase c-Met plays an important role in the control of critical cellular processes. Since c-Met is frequently over expressed or deregulated in human malignancies, blocking its activation is of special interest for therapy. In normal conditions, the c-Met receptor is activated by its bivalent ligand hepatocyte growth factor (HGF). Also bivalent antibodies can activate the receptor by cross linking, limiting therapeutic applications. We report the generation of the RNA aptamer CLN64 containing 2'-fluoro pyrimidine modifications by systematic evolution of ligands by exponential enrichment (SELEX). CLN64 and a previously described single-stranded DNA (ssDNA) aptamer CLN3 exhibited high specificities and affinities to recombinant and cellular expressed c-Met. Both aptamers effectively inhibited HGF-dependent c-Met activation, signaling and cell migration. We showed that these aptamers did not induce c-Met activation, revealing an advantage over bivalent therapeutic molecules. Both aptamers were shown to bind overlapping epitopes but only CLN3 competed with HGF binding to cMet. In addition to their therapeutic and diagnostic potential, CLN3 and CLN64 aptamers exhibit valuable tools to further understand the structural and functional basis for c-Met activation or inhibition by synthetic ligands and their interplay with HGF binding.

EpCAM aptamer-functionalized mesoporous silica nanoparticles for efficient colon cancer cell-targeted drug delivery

Targeted delivery of anticancer agents by functional nanoparticles is an attractive strategy to increase their therapeutic efficacy while reducing toxicity. In this work, doxorubicin (DOX)-loaded mesoporous silica nanoparticles (MSNs) were modified with aptamer (Ap) against the epithelial cell adhesion molecule (EpCAM) for targeted delivery of DOX to colon cancer cells. These nanoparticles (Ap-MSN-DOX) were characterized by particle size, zeta potential, aptamer conjugation efficiency, drug encapsulation efficiency, and drug release properties. The in vitro cell recognition, cellular uptake, EpCAM protein inhibition efficiency, and cytotoxicity of Ap-MSN-DOX were also studied. Results demonstrated that EpCAM conjugation increased binding of Ap-MSN-DOX to EpCAM over-expressing SW620 colon cancer cells but not EpCAM-negative Ramos cells, resulting in enhanced cellular uptake and increased cytotoxicity of the DOX in SW620 cells when compared to non-Ap-modified nanoparticles (MSN-DOX). Additionally, Ap-MSN-DOX exhibited significant inhibition effects on the expression of EpCAM on SW620 cells. These results suggested that Ap-MSN-DOX has the potential for the targeted delivery of therapeutic agents into EpCAM positive colon cancer cells to improve therapeutic index while reducing side effects.

A Highlight of Recent Advances in Aptamer Technology and Its Application

Aptamers and SELEX (systematic evolution of ligands by exponential enrichment) technology have gained increasing attention over the past 25 years. Despite their functional similarity to protein antibodies, oligonucleotide aptamers have many unique properties that are suitable for clinical applications and industrialization. Aptamers may be superior to antibodies in fields such as biomarker discovery, in vitro and in vivo diagnosis, precisely controlled drug release, and targeted therapy. However, aptamer commercialization has not occurred as quickly as expected, and few aptamer-based products have yet successfully entered clinical and industrial use. Thus, it is important to critically review some technical barriers of aptamer and SELEX technology per se that may impede aptamer development and application. To date, how to rapidly obtain aptamers with superior bioavailability over antibodies remains the key issue. In this review, we discuss different chemical and structural modification strategies aimed to enhance aptamer bioavailability. We also discuss improvements to SELEX process steps to shorten the selection period and improve the SELEX process success rate. Applications in which aptamers are particularly suited and perform differently or superior to antibodies are briefly introduced.

One-Year Feasibility Study of Replenish MicroPump for Intravitreal Drug Delivery: A Pilot Study

PURPOSE

To determine the feasibility of the surgical procedure and to collect some safety data regarding the bioelectronics of a novel micro drug pump for intravitreal drug delivery in a Beagle dog model for up to 1 year.

METHODS

Thirteen Beagle dogs were assigned to two groups. The experimental group (n = 11) underwent pars plana implantation of MicroPump; the body of which was sutured episclerally, while its catheter was secured at a pars plana sclerotomy. The control group (n = 2) underwent sham surgeries in the form of a temporary suturing of the MicroPump, including placement of the pars plana tube. Baseline and follow-up exams included ophthalmic examination and imaging. The experimental animals were euthanized and explanted at predetermined time points after surgery (1, 3, and 12 months), while the control animals were euthanized at 3 months. All operated eyes were submitted for histopathology.

RESULTS

Eyes were scored according to a modified McDonald-Shadduck system and ophthalmic imaging. Neither the implanted eyes nor the control eyes showed clinically significant pathological changes beyond the expected surgical changes. The operated eyes showed neither significant inflammatory reaction nor tissue ingrowth through the sclerotomy site compared with the fellow eyes.

CONCLUSION

This study shows that the Replenish Posterior MicroPump could be successfully implanted with good safety profile in this animal model.

TRANSLATIONAL RELEVANCE

The results of this study in a Beagle dog model are supportive of the biocompatibility of Replenish MicroPump and pave the way to the use of these devices for ocular automated drug delivery after further testing in larger animal models.

Protective effect of a laser-induced sub-lethal temperature rise on RPE cells from oxidative stress

Recently introduced new technologies that enable temperature-controlled laser irradiation on the RPE allowed us to investigate temperature-resolved RPE cell responses. In this study we aimed primarily to establish an experimental setup that can realize laser irradiation on RPE cell culture with the similar temperature distribution as in the clinical application, with a precise time/temperature history. With this setup, we conducted investigations to elucidate the temperature-dependent RPE cell biochemical responses and the effect of transient hyperthermia on the responses of RPE cells to the secondary-exposed oxidative stress. Porcine RPE cells cultivated in a culture dish (inner diameter = 30 mm) with culture medium were used, on which laser radiation (λ = 1940 nm, spot diameter = 30 mm) over 10 s was applied as a heat source. The irradiation provides a radially decreasing temperature profile which is close to a Gaussian shape with the highest temperature in the center. Power setting for irradiation was determined such that the peak temperature (Tmax) in the center of the laser spot at the cells reaches from 40 °C to 58 °C (40, 43, 46, 50, 58 °C). Cell viability was investigated with ethidium homodimer III staining at the time points of 3 and 24 h following laser irradiation. Twenty four hours after laser irradiation the cells were exposed to hydrogen peroxide (H2O2) for 5 h, followed by the measurement of intracellular glutathione, intracellular 4-hydroxynonenal (HNE) protein adducts, and secreted vascular endothelial growth factor (VEGF). The mean temperature threshold for RPE cell death after 3 h was found to be around 52 °C, and for 24 h around 50 °C with the current irradiation setting. A sub-lethal preconditioning on Tmax = 43 °C significantly induced the reduced glutathione (GSH)/oxidized glutathione (GSSG) ratio, and decreased H2O2-induced increase of intracellular 4-HNE protein adducts. Although sub-lethal hyperthermia (Tmax = 40 °C, 43 °C, and 46 °C) caused a slight increase of VEGF secretion in 6 h directly following irradiation, secondary exposed H2O2-induced VEGF secretion was significantly reduced in the sub-lethally preheated groups, where the largest effect was seen following the irradiation with Tmax = 43 °C. In summary, the current results suggest that sub-lethal thermal laser irradiation on the RPE at Tmax = 43 °C for 10 s enhances cell defense system against oxidative stress, with increasing the GSH/GSSG ratio. Together with the results that the decreased amount of H2O2-induced 4-HNE in sub-lethally preheated RPE cells was accompanied by the lower secretion of VEGF, it is also strongly suggested that the sub-lethal hyperthermia may modify RPE cell functionality to protect RPE cells from oxidative stress and associated functional decrease, which are considered to play a significant role in the pathogenesis of age-related macular degeneration and other chorioretinal degenerative diseases.

Nucleic Acid aptamers: new methods for selection, stabilization, and application in biomedical science

The adoption of oligonucleotide aptamer is well on the rise, serving an ever increasing demand for versatility in biomedical field. Through the SELEX (Systematic Evolution of Ligands by EXponential enrichment), aptamer that can bind to specific target with high affinity and specificity can be obtained. Aptamers are single-stranded nucleic acid molecules that can fold into complex threedimensional structures, forming binding pockets and clefts for the specific recognition and tight binding of any given molecular target. Recently, aptamers have attracted much attention because they not only have all of the advantages of antibodies, but also have unique merits such as thermal stability, ease of synthesis, reversibility, and little immunogenicity. The advent of novel technologies is revolutionizing aptamer applications. Aptamers can be easily modified by various chemical reactions to introduce functional groups and/or nucleotide extensions. They can also be conjugated to therapeutic molecules such as drugs, drug containing carriers, toxins, or photosensitizers. Here, we discuss new SELEX strategies and stabilization methods as well as applications in drug delivery and molecular imaging.

RNA plasticity and selectivity applicable to therapeutics and novel biosensor development

Aptamers are short, single-stranded nucleic acid sequences that are selected in vitro from large oligonucleotide libraries based on their high affinity to a target molecule. Hence, aptamers can be thought of as a nucleic acid analog to antibodies. However, several viewpoints hold that the potential of aptamers arises from interesting characteristics that are distinct from, or in some cases, superior to those of antibodies. This review summarizes the recent achievements in aptamer programs developed in our laboratory against basic and therapeutic protein targets. Through these studies, we became aware of the remarkable conformational plasticity and selectivity of RNA, on which the published report has not shed much light even though this is evidently a crucial feature for the strong specificity and affinity of RNA aptamers.

Vascular endothelial growth factor as an anti-angiogenic target for cancer therapy

New blood vessel formation (angiogenesis) is fundamental to tumor growth, invasion, and metastatic dissemination. The vascular endothelial growth factor (VEGF) signaling pathway plays pivotal roles in regulating tumor angiogenesis. VEGF as a therapeutic target has been validated in various types of human cancers. Different agents including antibodies, aptamers, peptides, and small molecules have been extensively investigated to block VEGF and its pro-angiogenic functions. Some of these agents have been approved by FDA and some are currently in clinical trials. Combination therapies are also being pursued for better tumor control. By providing comprehensive real-time information, molecular imaging of VEGF pathway may accelerate the drug development process. Moreover, the imaging will be of great help for patient stratification and therapeutic effect monitoring, which will promote effective personalized molecular cancer therapy. This review summarizes the current status of tumor therapeutic agents targeting to VEGF and the applications of VEGF related molecular imaging.

Conformational plasticity of RNA for target recognition as revealed by the 2.15 A crystal structure of a human IgG-aptamer complex

Aptamers are short single-stranded nucleic acids with high affinity to target molecules and are applicable to therapeutics and diagnostics. Regardless of an increasing number of reported aptamers, the structural basis of the interaction of RNA aptamer with proteins is poorly understood. Here, we determined the 2.15 Å crystal structure of the Fc fragment of human IgG1 (hFc1) complexed with an anti-Fc RNA aptamer. The aptamer adopts a characteristic structure fit to hFc1 that is stabilized by a calcium ion, and the binding activity of the aptamer can be controlled many times by calcium chelation and addition. Importantly, the aptamer-hFc1 interaction involves mainly van der Waals contacts and hydrogen bonds rather than electrostatic forces, in contrast to other known aptamer-protein complexes. Moreover, the aptamer-hFc1 interaction involves human IgG-specific amino acids, rendering the aptamer specific to human IgGs, and not crossreactive to other species IgGs. Hence, the aptamer is a potent alternative for protein A affinity purification of Fc-fusion proteins and therapeutic antibodies. These results demonstrate, from a structural viewpoint, that conformational plasticity and selectivity of an RNA aptamer is achieved by multiple interactions other than electrostatic forces, which is applicable to many protein targets of low or no affinity to nucleic acids.

Modification of thiol functionalized aptamers by conjugation of synthetic polymers

Aptamers are known for their short in vivo circulating half-life and rapid renal clearance. Their conjugation to poly(ethylene glycol) (PEG) is a way to improve their residence in the body. Two aptamers (AptD and AptF), having a disulfide protected thiol modification on the 3' end, have been conjugated to maleimide activated PEGs of various molecular weights and structures (linear PEG20; branched PEG20 and 40; PolyPEG17, 40, and 60 kDa). The high yield coupling (70-80% in most of the cases) could be achieved using immobilized tris[2-carboxyethyl]phosphine hydrochloride (TCEP) as reducing agent at pH 4. The affinity of PEGylated AptD for its target was reduced by conjugation to linear PEG20 and branched PEG40, but not to branched PEG20 and PolyPEGs. This work demonstrates an alternative approach to PEGylation of aptamers, and that the effect of PEG on the affinity for the target varies according to the structure and conformation of the synthetic polymer.

A binary Cy3 aptamer probe composed of folded modules

Aptamers are short single-stranded DNA or RNA sequences that are selected in vitro based on their high affinity to a target molecule. Dye-binding aptamers are promising tools for real-time detection of not only DNA or RNA sequences but also proteins of interest both in vitro and in vivo. In this study, we aimed to isolate an RNA aptamer to Cy3, a widely used, membrane-permeant, and nontoxic fluorescent cyanine dye. Extensive selection of affinity RNA molecules to Cy3 yielded a unique sequence aptamer named Cy3_apt. The selected Cy3_apt was 83 nucleotides long and successfully shortened to 49 nucleotides long with increased affinity to Cy3 by multiple base changes. The shortest Cy3_apt is composed of two separate hairpin modules that are required for the affinity to Cy3 as monitored by the surface plasmon resonance (SPR) assay. Also, the fluorescence of Cy3 increased on binding to Cy3_apt. The two modules of Cy3_apt, when detached from each other, functioned as a binary aptamer probe. We demonstrate that the binary Cy3_apt probe is applicable to the detection of target oligonucleotides or RNA-RNA interaction by tagging with target sequences. This binary probe consists of two folded modules, referred to as a folded binary probe.

Aptamers as inhibitors of target proteins

BACKGROUND

Aptamers as inhibitors of proteins in therapeutic applications offer great advantages over their antibody counterparts and the promise to be developed into the next generation therapeutic agents. However, the control of aptamer intellectual property (IP) by two major players has made aptamers an area difficult to operate and often off-putting for academic and commercial organisations. Yet, their great potential is keeping aptamers at the research forefront, with one aptamer in the clinic and various at different stages of clinical trials.

OBJECTIVE

To provide a comprehensive review of the aptamer IP landscape and the issues associated with aptamer therapeutics against protein targets.

METHODS

Extensive review of the scientific and patent literature.

CONCLUSIONS

Following our experience in developing, patenting and commercialising our aptamers against MUC1 and an extensive review of the literature, we have identified a variety of issues pertaining to the development of aptamers against protein targets for therapeutic applications, their patenting and granting of patents, the original IP holders and their policy, as well as the current market and traits. Despite a slow start, aptamers have been developed against various therapeutic proteins and offer the promise of providing a novel generation of therapeutic entities with a variety of applications.

RNA aptamers to translational components

Potential applications for functional RNAs are rapidly expanding, not only to address functions based on primary nucleotide sequences, but also by RNA aptamers, which can suppress the activity of any target molecule. Aptamers are short DNA or RNA folded molecules that can be selected in vitro on the basis of their high affinity for a target molecule. Here, we summarize RNA aptamers selected against human translation initiation factors, and their superior potentials to recognize and inhibit their target proteins. Importantly, the high affinity of RNA aptamers to proteins without RNA recognition motifs or intrinsic, strong affinity to RNA is achieved through the capture of the protein's global conformation. In other words, RNA has a high potential to form a vast set of tertiary structures, which we would like to refer to as 'RNA plasticity'. This provides us with a solid and promising basis to take steps to create novel RNA molecules of therapeutic potential with distinct structures, which should be equivalent or superior to antibodies.

An aptamer-based biosensor for mammalian initiation factor eukaryotic initiation factor 4A

Aptamers are short single-stranded DNA or RNA sequences that are selected in vitro based on their high affinity to a target molecule. Here we demonstrate that an RNA aptamer selected against eukaryotic initiation factor 4A (eIF4A) serves as an efficient biosensor. The aptamer, when immobilized to resin, purifies eIF4A from crude cell extracts by affinity pull-down, and 32P-labeled aptamer can detect some 300 ng of eIF4A by dot-blot analysis. Moreover, by use of an aptamer-immobilized sensor chip, we developed a surface plasmon resonance assay to detect eIF4A at the nanogram level within whole cell lysates after optimizing sample preparation, thereby showing a real-time sensor for eIF4A in cell extract solution.

Iron behaving badly: inappropriate iron chelation as a major contributor to the aetiology of vascular and other progressive inflammatory and degenerative diseases

BACKGROUND

The production of peroxide and superoxide is an inevitable consequence of aerobic metabolism, and while these particular 'reactive oxygen species' (ROSs) can exhibit a number of biological effects, they are not of themselves excessively reactive and thus they are not especially damaging at physiological concentrations. However, their reactions with poorly liganded iron species can lead to the catalytic production of the very reactive and dangerous hydroxyl radical, which is exceptionally damaging, and a major cause of chronic inflammation.

REVIEW

We review the considerable and wide-ranging evidence for the involvement of this combination of (su)peroxide and poorly liganded iron in a large number of physiological and indeed pathological processes and inflammatory disorders, especially those involving the progressive degradation of cellular and organismal performance. These diseases share a great many similarities and thus might be considered to have a common cause (i.e. iron-catalysed free radical and especially hydroxyl radical generation).The studies reviewed include those focused on a series of cardiovascular, metabolic and neurological diseases, where iron can be found at the sites of plaques and lesions, as well as studies showing the significance of iron to aging and longevity. The effective chelation of iron by natural or synthetic ligands is thus of major physiological (and potentially therapeutic) importance. As systems properties, we need to recognise that physiological observables have multiple molecular causes, and studying them in isolation leads to inconsistent patterns of apparent causality when it is the simultaneous combination of multiple factors that is responsible.This explains, for instance, the decidedly mixed effects of antioxidants that have been observed, since in some circumstances (especially the presence of poorly liganded iron) molecules that are nominally antioxidants can actually act as pro-oxidants. The reduction of redox stress thus requires suitable levels of both antioxidants and effective iron chelators. Some polyphenolic antioxidants may serve both roles.Understanding the exact speciation and liganding of iron in all its states is thus crucial to separating its various pro- and anti-inflammatory activities. Redox stress, innate immunity and pro- (and some anti-)inflammatory cytokines are linked in particular via signalling pathways involving NF-kappaB and p38, with the oxidative roles of iron here seemingly involved upstream of the IkappaB kinase (IKK) reaction. In a number of cases it is possible to identify mechanisms by which ROSs and poorly liganded iron act synergistically and autocatalytically, leading to 'runaway' reactions that are hard to control unless one tackles multiple sites of action simultaneously. Some molecules such as statins and erythropoietin, not traditionally associated with anti-inflammatory activity, do indeed have 'pleiotropic' anti-inflammatory effects that may be of benefit here.

CONCLUSION

Overall we argue, by synthesising a widely dispersed literature, that the role of poorly liganded iron has been rather underappreciated in the past, and that in combination with peroxide and superoxide its activity underpins the behaviour of a great many physiological processes that degrade over time. Understanding these requires an integrative, systems-level approach that may lead to novel therapeutic targets.

Crystallization and preliminary X-ray diffraction studies of an RNA aptamer in complex with the human IgG Fc fragment

Aptamers, which are folded DNA or RNA molecules, bind to target molecules with high affinity and specificity. An RNA aptamer specific for the Fc fragment of human immunoglobulin G (IgG) has recently been identified and it has been demonstrated that an optimized 24-nucleotide RNA aptamer binds to the Fc fragment of human IgG and not to other species. In order to clarify the structural basis of the high specificity of the RNA aptamer, it was crystallized in complex with the Fc fragment of human IgG1. Preliminary X-ray diffraction studies revealed that the crystals belonged to the orthorhombic space group P2(1)2(1)2, with unit-cell parameters a = 83.7, b = 107.2, c = 79.0 A. A data set has been collected to 2.2 A resolution.

Smoking and the risk of age-related macular degeneration: a meta-analysis

PURPOSE

Some studies were undertaken to evaluate the association between cigarette smoking and age-related macular degeneration (AMD). This meta-analysis summarized the risk estimate of smoking and AMD and provided robust evidence for the association.

METHODS

Relevant studies were identified by searching PubMed and MEDLINE (from 1966 to June 2007) and reviewing the reference lists of key articles. The summary relative risk ratio (RR) or odds ratio (OR) and 95% confidence interval (CI) were calculated. Study-specific risk estimates were pooled using a random-effects model.

RESULTS

Five prospective cohort and eight case-control studies met our inclusion criteria. Ever smoking was statistically significant associated with increased risk of AMD among cohort studies (RR, 1.61; 95% CI, 1.01-2.57) or case-control studies (RR, 1.76; 95% CI, 1.56-1.99). Current smokers were at higher risk of AMD than past smokers. Both geographic atrophy (GA) and neovascular AMD (NV) are subtypes of AMD. A significant relationship was found between smoking and GA risk. Smoking increased the risk of NV, with marginal nonsignificance (RR, 1.47; 95% CI, 0.92-2.37) in cohort studies and significance in case-control studies (RR, 1.96; 95% CI, 1.69-2.27).

CONCLUSIONS

This meta-analysis indicated smoking, especially current smoking, was significantly associated with increased risks of AMD and its subtypes.

Structural and molecular basis for hyperspecificity of RNA aptamer to human immunoglobulin G

Potential applications for functional RNAs are rapidly expanding, not only to address functions based on primary nucleotide sequences, but also by RNA aptamer, which can suppress the activity of any target molecule. Aptamers are short DNA or RNA folded molecules that can be selected in vitro on the basis of their high affinity for a target molecule. Here, we demonstrate the ability of RNA aptamers to recognize--and bind to--human IgG with high specificity and affinity. An optimized 23-nucleotide aptamer, Apt8-2, was prepared, and was shown to bind to the Fc domain of human IgG, but not to other IgG's, with high affinity. Apt8-2 was observed to compete with protein A, but not with the Fcgamma receptor, for IgG binding. NMR chemical-shift analyses localized the aptamer-binding sites on the Fc subdomain, which partially overlaps the protein A binding site but not the Fcgamma receptor binding site. The tertiary structures of the predicted recognition sites on the Fc domain differ significantly between human IgG and other species of IgGs; this, in part, accounts for the high specificity of the selected aptamer. Apt8-2 can therefore be used as a protein A alternative for affinity purification of human IgG and therapeutic antibodies. Using Apt8-2 would have several potential advantages, raising the possibility of developing new applications based on aptamer design.

A mathematical analysis of SELEX

Systematic evolution of ligands by exponential enrichment (SELEX) is a procedure by which a mixture of nucleic acids that vary in sequence can be separated into pure components with the goal of isolating those with specific biochemical activities. The basic idea is to combine the mixture with a specific target molecule and then separate the target-NA complex from the resulting reaction. The target-NA complex is then separated by mechanical means (for example by filtration), the NA is then eluted from the complex, amplified by polymerase chain reaction (PCR) and the process repeated. After several rounds, one should be left with a pool of [NA] that consists mostly of the species in the original pool that best binds to the target. In Irvine et al. [Irvine, D., Tuerk, C., Gold, L., 1991. SELEXION, systematic evolution of nucleic acids by exponential enrichment with integrated optimization by non-linear analysis. J. Mol. Biol. 222, 739-761] a mathematical analysis of this process was given. In this paper we revisit Irvine et al. [Ibid]. By rewriting the equations for the SELEX process, we considerably reduce the labor of computing the round to round distribution of nucleic acid fractions. We also establish necessary and sufficient conditions for the SELEX process to converge to a pool consisting solely of the best binding nucleic acid to a fixed target in a manner that maximizes the percentage of bound target. The assumption is that there is a single nucleic acid binding site on the target that permits occupation by not more than one nucleic acid. We analyze the case for which there is no background loss (no support losses and no free [NA] left on the support). We then examine the case in which such there are such losses. The significance of the analysis is that it suggests an experimental approach for the SELEX process as defined in Irvine et al. [Ibid] to converge to a pool consisting of a single best binding nucleic acid without recourse to any a priori information about the nature of the binding constants or the distribution of the individual nucleic acid fragments.

Challenges and obstacles of ocular pharmacokinetics and drug delivery

Modern biological research has produced increasing number of promising therapeutic possibilities for medical treatment. These include for example growth factors, monoclonal antibodies, gene knockdown methods, gene therapy, surgical transplantations and tissue engineering. Ocular application of these possibilities involves drug delivery in many forms. Ocular drug delivery is hampered by the barriers protecting the eye. This review presents an overview of the essential factors in ocular pharmacokinetics and selected pharmacological future challenges in ophthalmology.