Methods for Evaluating Cell-Specific, Cell-Internalizing RNA Aptamers

Immunomodulation with Nucleic Acid Nanodevices

The precise regulation of interactions of specific immunological components is crucial for controllable immunomodulation, yet it remains a great challenge. With the assistance of advanced computer design, programmable nucleic acid nanotechnology enables the customization of synthetic nucleic acid nanodevices with unprecedented geometrical and functional precision, which have shown promising potential for precise immunoengineering. Notably, the inherently immunologic functions of nucleic acids endow these nucleic acid-based assemblies with innate advantages in immunomodulatory engagement. In this review, the roles of nucleic acids in innate immunity are discussed, focusing on the definition, immunologic modularity, and enhanced bioavailability of structural nucleic acid nanodevices. In light of this, molecular programming and precise organization of functional modules with nucleic acid nanodevices for immunomodulation are emphatically reviewed. At last, the present challenges and future perspectives of nucleic acid nanodevices for immunomodulation are discussed.

Streptavidin-Saporin: Converting Biotinylated Materials into Targeted Toxins

Streptavidin-Saporin can be considered a type of ‘secondary’ targeted toxin. The scientific community has taken advantage of this conjugate in clever and fruitful ways using many kinds of biotinylated targeting agents to send saporin into a cell selected for elimination. Saporin is a ribosome-inactivating protein that causes inhibition of protein synthesis and cell death when delivered inside a cell. Streptavidin-Saporin, mixed with biotinylated molecules to cell surface markers, results in powerful conjugates that are used both in vitro and in vivo for behavior and disease research. Streptavidin-Saporin harnesses the ‘Molecular Surgery’ capability of saporin, creating a modular arsenal of targeted toxins used in applications ranging from the screening of potential therapeutics to behavioral studies and animal models. The reagent has become a well-published and validated resource in academia and industry. The ease of use and diverse functionality of Streptavidin-Saporin continues to have a significant impact on the life science industry.

Aptamers in Drug Design: An Emerging Weapon to Fight a Losing Battle

Implementation of novel and biocompatible polymers in drug design is an emerging and rapidly growing area of research. Even though we have a large number of polymer materials for various applications, the biocompatibility of these materials remains as a herculean task for researchers. Aptamers provide a vital and efficient solution to this problem. They are usually small (ranging from 20 to 60 nucleotides, single-stranded DNA or RNA oligonucleotides which are capable of binding to molecules possessing high affinity and other properties like specificity. This review focuses on different aspects of Aptamers in drug discovery, starting from its preparation methods and covering the recent scenario reported in the literature regarding their use in drug discovery. We address the limitations of Aptamers and provide valuable insights into their future potential in the areas regarding drug discovery research. Finally, we explained the major role of Aptamers like medical imaging techniques, application as synthetic antibodies, and the most recent application, which is in combination with nanomedicines.

Biotin oligonucleotide labeling reactions: A method to assess their effectiveness and reproducibility

The strong molecular interaction between biotin and streptavidin is widely used in the growing field of nucleic acid nanotechnology. Several biotin labeled oligonucleotide tools have been developed for the detection of biological molecules as well as for protein purification. For these reasons, biotinylation can be considered one of the main chemical reactions for nucleic acid labeling. However, despite its widespread application and the presence on the market of many reagents for the conjugation of biotin to oligonucleotides, it is not yet available a cheap, easy and sensitive system able to assess the effectiveness and reproducibility of this reaction. Here, we present an accurate and reliable method to achieve a qualitative and quantitative analysis of oligonucleotide biotinylation. The protocol employs basic laboratory instruments and standard software for molecular biology applications and does not require advanced expertise for its execution. Most importantly, our method is independent from complex kinetic equilibrium parameters and shows a limit of detection more than one order of magnitude lower than the current fluorometric gold standard assay. Therefore, this method could become a standard, inexpensive and routinely used quality test for post-synthesis evaluation of biotin conjugation reactions.

Cell-SELEX, an Effective Way to the Discovery of Biomarkers and Unexpected Molecular Events

Cell-SELEX can not only generate aptamers for specific cell isolation/detection, diagnosis, and therapy, but also lead to the discovery of biomarkers and unexpected molecular events. However, most cell-SELEX research is concentrated on aptamer generation and applications. In this progress report, recent research progress with cell-SELEX in terms of the discovery of biomarkers and unexpected molecular events is highlighted. In particular, the key technical challenges for cell-SELEX-based biomarker discovery, namely, the methods for identification and validation of target proteins of aptamers, are discussed in detail. Finally, the prospects of the applications of cell-SELEX in this field now and in the near future are described. It is expected that this report will attract attention to the benefit of cell-SELEX and provide a practical reference for biomedical researchers.

Aptamers as the chaperones (Aptachaperones) of drugs-from siRNAs to DNA nanorobots

Aptamers, nucleic acid ligands that are specific against their corresponding targets are increasingly employed in a variety of applications including diagnostics and therapeutics. The specificity of the aptamers against their targets is also used as the basis for the formulation of the aptamer-based drug delivery system. In this review, we aim to provide an overview on the chaperoning roles of aptamers in acting as the cargo or load carriers, delivering contents to the targeted sites via cell surface receptors. Internalization of the aptamer-biomolecule conjugates via receptor-mediated endocytosis and the strategies to augment the rate of endocytosis are underscored. The cargos chaperoned by aptamers, ranging from siRNAs to DNA origami are illuminated. Possible impediments to the aptamer-based drug deliveries such as susceptibility to nuclease resistance, potentiality for immunogenicity activation, tumor heterogeneity are speculated and the corresponding amendment strategies to address these shortcomings are discussed. We prophesy that the future of the aptamer-based drug delivery will take a trajectory towards DNA nanorobot-based assay.

An exploration of aptamer internalization mechanisms and their applications in drug delivery

INTRODUCTION

As 'chemical antibodies', aptamers have some advantages, such as lack of immunogenicity, rapid tissue penetration, cell internalization and so on. Consequently, more and more aptamers have been screened out by the systematic evolution of ligands through exponential enrichment for the desired cells or membrane receptors. On the basis of the result, researchers use aptamers to guide drug targeting to the desired cells and internalization in vivo.

AREAS COVERED

In this review, we explore the mechanisms of cargo- or aptamer-mediated internalization, and then briefly summarize five strategies for exploring the mechanism of aptamer internalization. Finally, we focus on four types of applications involving aptamer internalization: aptamers as drugs, aptamers as chemical drug-delivery systems, aptamer-based chimeras and aptamer-conjugated nanoparticles or block copolymer micelles.

EXPERT OPINION

Two aptamer-internalization mechanisms are known, namely receptor-mediated endocytosis and macropinocytosis. The latter mechanism, which is has only been verified in the internalization of nucleolin aptamer shuttles between the nucleus and cytoplasm, may be important for nuclear internalization and cargo molecule escape from the endosomal compartment. Thus, it is feasible to use some strategies to further explore the macropinocytosis internalization mechanism and then to screen for aptamers similar to the nucleolin aptamer for use with the desired cell types as a targeted delivery tool.

Three decades of nucleic acid aptamer technologies: Lessons learned, progress and opportunities on aptamer development

Aptamers are short single-stranded nucleic acid sequences capable of binding to target molecules in a way similar to antibodies. Due to various advantages such as prolonged shelf life, low batch to batch variation, low/no immunogenicity, freedom to incorporate chemical modification for enhanced stability and targeting capacity, aptamers quickly found their potential in diverse applications ranging from therapy, drug delivery, diagnosis, and functional genomics to bio-sensing. Aptamers are generated by a process called SELEX. However, the current overall success rate of SELEX is far from being satisfactory, and still presents a major obstacle for aptamer-based research and application. The need for an efficient selection strategy consisting of defined procedures to deal with a wide variety of targets is significantly important. In this work, by analyzing key aspects of SELEX including initial library design, target preparation, PCR optimization, and single strand DNA separation, we provide a comprehensive analysis of individual steps to facilitate researchers intending to develop personalized protocols to address many of the obstacles in SELEX. In addition, this review provides suggestions and opinions for future aptamer development procedures to address the concerns on key SELEX steps, and post-SELEX modifications.

Cell-SELEX-Based Identification of a Human and Mouse Cross-Reactive Endothelial Cell-Internalizing Aptamer

Increased interest and insights gained by researchers on the roles of endothelial cells in the pathophysiology of cancer, inflammatory, and cardiovascular diseases have led to the design of pharmacological interventions aimed at the endothelium lining in the diseased sites. Toward this end, we used established brain microvascular endothelial cell lines mouse (bEND3), human (hCMEC/D3), and Toggle Cell-SELEX to identify a species cross-reactive, endothelial cell-internalizing aptamer R11-3. This 2'F-modified RNA aptamer is specific for endothelial cells as no internalization was seen with cells of nonendothelial origin. R11-3 was truncated in size, and its potential in endothelial targeted therapeutics was established using VEGFR2 targeting long interfering RNA (liRNA) aptamer chimera. Due to its specificity for both mouse and human endothelial cells, we believe that this aptamer not only fits for development of endothelial targeted drug development for human diseases but is also suitable for preclinical evaluation in mice.

Using Genome Sequence to Enable the Design of Medicines and Chemical Probes

Rapid progress in genome sequencing technology has put us firmly into a postgenomic era. A key challenge in biomedical research is harnessing genome sequence to fulfill the promise of personalized medicine. This Review describes how genome sequencing has enabled the identification of disease-causing biomolecules and how these data have been converted into chemical probes of function, preclinical lead modalities, and ultimately U.S. Food and Drug Administration (FDA)-approved drugs. In particular, we focus on the use of oligonucleotide-based modalities to target disease-causing RNAs; small molecules that target DNA, RNA, or protein; the rational repurposing of known therapeutic modalities; and the advantages of pharmacogenetics. Lastly, we discuss the remaining challenges and opportunities in the direct utilization of genome sequence to enable design of medicines.

Selection and Identification of Skeletal-Muscle-Targeted RNA Aptamers

Oligonucleotide gene therapy has shown great promise for the treatment of muscular dystrophies. Nevertheless, the selective delivery to affected muscles has shown to be challenging because of their high representation in the body and the high complexity of their cell membranes. Current trials show loss of therapeutic molecules to non-target tissues leading to lower target efficacy. Therefore, strategies that increase uptake efficiency would be particularly compelling. To address this need, we applied a cell-internalization SELEX (Systematic Evolution of Ligands by Exponential Enrichment) approach and identified a skeletal muscle-specific RNA aptamer. A01B RNA aptamer preferentially internalizes in skeletal muscle cells and exhibits decreased affinity for off-target cells. Moreover, this in vitro selected aptamer retained its functionality in vivo, suggesting a potential new approach for targeting skeletal muscles. Ultimately, this will aid in the development of targeted oligonucleotide therapies against muscular dystrophies.

Challenging cancer targets for aptamer delivery

The extraordinary boost in the understanding of the genetic and epigenetic mechanisms underlying the development and progression of different types of cancer, is offering an unprecedented hope for the development of precise therapeutics able to interfere or replace the expression of target genes. In the last decade, the design of stable, safe and effective RNA-based therapeutics has been significantly improved increasing the number of molecules now in preclinical or in clinical trials for cancer gene therapy. However, with few exclusions as liver and hematological malignancies which are easy accessible to drugs, the development of effective systemic approaches for the delivery of RNA therapeutics to target cells is still unmet. To be effective, targeting carriers must be able to overcome both functional and physical barriers to safely carry and accumulate the therapeutic through the organism selectively to the tumor site, penetrate the target cancer mass, promote the uptake and localization in the appropriate intracellular compartment ultimately leading to the effective modulation of gene expression. Nucleic acid aptamers are folded single stranded oligonucleotides that bind at high affinity and high specificity their targets (proteins, lipids, small molecules etc), coupling the advantages of binding specificity proper of antibodies to the chemical nature of nucleic acids, sometimes also termed "nucleic acid antibodies". In several cases, aptamers targeting cell surface receptors are recycled into the cell together with the bound receptor enabling to drive conjugated therapeutics to cancer cells in a receptor-dependent manner. Therefore, besides other in vivo delivery strategies, the use of aptamers as precise and effective targeting moieties for anticancer RNA-based therapeutics has rapidly emerged and has been successfully addressed by several laboratories. In this Review, we will focus on the most recent and challenging progresses in the field that highlights the precision and flexibility of aptamer-based chimeras paving the way to the development of safe and effective carriers for cancer gene therapeutics.

Toward the Selection of Cell Targeting Aptamers with Extended Biological Functionalities to Facilitate Endosomal Escape of Cargoes

Over the past decades there have been exciting and rapid developments of highly specific molecules to bind cancer antigens that are overexpressed on the surfaces of malignant cells. Nanomedicine aims to exploit these ligands to generate nanoscale platforms for targeted cancer therapy, and to do so with negligible off-target effects. Aptamers are structured nucleic acids that bind to defined molecular targets ranging from small molecules and proteins to whole cells or viruses. They are selected through an iterative process of amplification and enrichment called SELEX (systematic evolution of ligands by exponential enrichment), in which a combinatorial oligonucleotide library is exposed to the target of interest for several repetitive rounds. Nucleic acid ligands able to bind and internalize into malignant cells have been extensively used as tools for targeted delivery of therapeutic payloads both in vitro and in vivo. However, current cell targeting aptamer platforms suffer from limitations that have slowed their translation to the clinic. This is especially true for applications in which the cargo must reach the cytosol to exert its biological activity, as only a small percentage of the endocytosed cargo is typically able to translocate into the cytosol. Innovative technologies and selection strategies are required to enhance cytoplasmic delivery. In this review, we describe current selection methods used to generate aptamers that target cancer cells, and we highlight some of the factors that affect productive endosomal escape of cargoes. We also give an overview of the most promising strategies utilized to improve and monitor endosomal escape of therapeutic cargoes. The methods we highlight exploit tools and technologies that can potentially be incorporated in the SELEX process. Innovative selection protocols may identify aptamers with extended biological functionalities that allow effective cytosolic translocation of therapeutics. This in turn may facilitate successful translation of these platforms into clinical applications.

Aptamers as targeted therapeutics: current potential and challenges

Nucleic acid aptamers, often termed 'chemical antibodies', are functionally comparable to traditional antibodies, but offer several advantages, including their relatively small physical size, flexible structure, quick chemical production, versatile chemical modification, high stability and lack of immunogenicity. In addition, many aptamers are internalized upon binding to cellular receptors, making them useful targeted delivery agents for small interfering RNAs (siRNAs), microRNAs and conventional drugs. However, several crucial factors have delayed the clinical translation of therapeutic aptamers, such as their inherent physicochemical characteristics and lack of safety data. This Review discusses these challenges, highlighting recent clinical developments and technological advances that have revived the impetus for this promising class of therapeutics.

Intracellular Expression of PAI-1 Specific Aptamers Alters Breast Cancer Cell Migration, Invasion and Angiogenesis

Plasminogen activator inhibitor-1 (PAI-1) is elevated in various cancers, where it has been shown to effect cell migration and invasion and angiogenesis. While, PAI-1 is a secreted protein, its intercellular levels are increased in cancer cells. Consequently, intracellular PAI-1 could contribute to cancer progression. While various small molecule inhibitors of PAI-1 are currently being investigated, none specifically target intracellular PAI-1. A class of inhibitors, termed aptamers, has been used effectively in several clinical applications. We previously generated RNA aptamers that target PAI-1 and demonstrated their ability to inhibit extracellular PAI-1. In the current study we explored the effect of these aptamers on intracellular PAI-1. We transiently transfected the PAI-1 specific aptamers into both MDA-MB-231 human breast cancer cells, and human umbilical vein endothelial cells (HUVECs) and studied their effects on cell migration, invasion and angiogenesis. Aptamer expressing MDA-MB-231 cells exhibited a decrease in cell migration and invasion. Additionally, intracellular PAI-1 and urokinase plasminogen activator (uPA) protein levels decreased, while the PAI-1/uPA complex increased. Moreover, a significant decrease in endothelial tube formation in HUVECs transfected with the aptamers was observed. In contrast, conditioned media from aptamer transfected MDA-MB-231 cells displayed a slight pro-angiogenic effect. Collectively, our study shows that expressing functional aptamers inside breast and endothelial cells is feasible and may exhibit therapeutic potential.

Nuclease activity as a specific biomarker for breast cancer

We report on the activity of nucleases derived from cancer cells as a means for specific targeting using nucleic acid probes (substrates). We hypothesize that cancer cells can be differentiated from healthy cells based on their nuclease activity profile, and thus, any method based on this property represents a novel alternative for diagnostic and therapeutic intervention.

AFBI assay - Aptamer Fluorescence Binding and Internalization assay for cultured adherent cells

The SELEX (Systematic Evolution of Ligands by Exponential Enrichment) process allows for the enrichment of DNA or RNA aptamers from a complex nucleic acid library that are specific for a target molecule. The SELEX process has been adapted from identifying aptamers in vitro using recombinant target protein to cell-based methodologies (Cell-SELEX), where the targets are expressed on the surface of cells. One major advantage of Cell-SELEX is that the target molecules are maintained in a native confirmation. Additionally, Cell-SELEX may be used to discover novel therapeutic biomarkers by performing selections on diseased versus healthy cells. However, a caveat to Cell-SELEX is that testing of single aptamers identified in the selection is laborious, time-consuming, and expensive. The most frequently used methods to screen for aptamer binding and internalization on cells are flow cytometry and quantitative PCR (qPCR). While flow cytometry can directly assess binding of a fluorescently-labeled aptamer to a target, it requires significant starting material and is not easily scalable. qPCR-based approaches are highly sensitive but have non-negligible experiment-to-experiment variability due to the number of sample processing steps. Herein we describe a cell-based aptamer fluorescence binding and internalization (AFBI) assay. This assay requires minimal reagents and has few experimental steps/manipulations, thereby allowing for rapid screening of many aptamers and conditions simultaneously and direct quantitation of aptamer binding and internalization.

Method for Confirming Cytoplasmic Delivery of RNA Aptamers

RNA aptamers are single-stranded RNA oligos that represent a powerful emerging technology with potential for treating numerous diseases. More recently, cell-targeted RNA aptamers have been developed for delivering RNA interference (RNAi) modulators (siRNAs and miRNAs) to specific diseased cells (e.g., cancer cells or HIV infected cells) in vitro and in vivo. However, despite initial promising reports, the broad application of this aptamer delivery technology awaits the development of methods that can verify and confirm delivery of aptamers to the cytoplasm of target cells where the RNAi machinery resides. We recently developed a functional assay (RIP assay) to confirm cellular uptake and subsequent cytoplasmic release of an RNA aptamer which binds to a cell surface receptor expressed on prostate cancer cells (PSMA). To assess cytoplasmic delivery, the aptamer was chemically conjugated to saporin, a ribosome inactivating protein toxin that is toxic to cells only when delivered to the cytoplasm (where it inhibits the ribosome) by a cell-targeting ligand (e.g., aptamer). Here, we describe the chemistry used to conjugate the aptamer to saporin and discuss a gel-based method to verify conjugation efficiency. We also detail an in vitro functional assay to confirm that the aptamer retains function following conjugation to saporin and describe a cellular assay to measure aptamer-mediated saporin-induced cytotoxicity.

How to measure the affinity of aptamers for membrane proteins expressed on the surface of living adherent cells

Recently, an increasing number of aptamers have been selected against biomarkers that are expressed at the surface of cells. This class of targets, mostly membrane proteins, is in close contact with the intra- and extra-cellular matrixes and their three-dimensional structures are inextricably linked to their inclusion in lipid bilayers. Therefore, although binding studies can be performed on the isolated form of these proteins, it remains crucial to measure the affinity of these aptamers in a more physiological environment, i.e., directly on living cells. Here, we describe a procedure for radioactive binding assays that can be adapted for measuring the affinity of aptamers against different cell lines. This method has been semi-automated using a liquid handling robot in order to reproducibly measure the apparent dissociation constant Kd and the apparent number of targets per cell. Relevant issues are discussed including the labeling of aptamers, the cells preparation, the incubation, the washings, the use of non-specific competitors, the data analysis and finally the reporting.

Manipulating the in vivo immune response by targeted gene knockdown

Aptamers, nucleic acids selected for high affinity binding to proteins, can be used to activate or antagonize immune mediators or receptors in a location and cell-type specific manner and to enhance antigen presentation. They can also be linked to other molecules (other aptamers, siRNAs or miRNAs, proteins, toxins) to produce multifunctional compounds for targeted immune modulation in vivo. Aptamer-siRNA chimeras (AsiCs) that induce efficient cell-specific knockdown in immune cells in vitro and in vivo can be used as an immunological research tool or potentially as an immunomodulating therapeutic.

A strain-promoted alkyne-azide cycloaddition (SPAAC) reaction of a novel EpCAM aptamer-fluorescent conjugate for imaging of cancer cells

For the first time, a novel EpCAM aptamer (SYL3C)-DIBO-AF594 fluorescent conjugate was synthesised by bioorthogonal chemistry utilizing a strain promoted alkyne-azide cycloaddition (copper free click) reaction (SPAAC). The ligation efficiency of SPAAC was improved by freeze-thaw cycles. The obtained conjugate showed target specific binding and aided in the imaging of various EpCAM positive cancer cell lines like MCF7, MDAMB453, Weri-RB1 and PC3.

Tumor targeting with a (99m)Tc-labeled AS1411 aptamer in prostate tumor cells

AS1411, a 26-base guanine-rich oligonucleotide aptamer, has high affinity to nucleolin, mainly on tumor cell surfaces. In this study, a modified AS1411 was labeled with (99m)Tc and evaluated as a potential tumor-targeting agent for imaging. The AS1411 aptamer was conjugated with HYNIC and labeled with (99m)Tc in the presence a co-ligand. Radiochemical purity and stability testing of the (99m)Tc-HYNIC-AS1411 aptamer were carried out with thin layer chromatography and a size-exclusion column in normal saline and human serum. Cellular nucleolin-specific binding, cellular internalization in DU-145 cells, as high levels of nucleolin expression, were performed. Additionally, biodistribution in normal mice and DU-145 tumour-bearing mice was assessed. Radiolabeling of the aptamer resulted in a reasonable yield and radiochemical purity after purification. The aptamer was stable in normal saline and human serum, and cellular experiments demonstrated specific binding of the AS1411 aptamer to the nucleolin protein. Based on biodistribution assessment of (99m)Tc-HYNIC-AS1411, rapid blood clearance was seen after injection and it appears that the excretion route was via the urinary system at 1 h post-injection. Tumours also showed a higher accumulation of radioactivity with this labeled aptamer. (99m)Tc-AS1411 can be a potential tool for the molecular imaging of nucleolin-overexpressing cancers.

Aptamers as drug delivery vehicles

The benefits of directed and selective therapy for systemic treatment are reasons for increased interest in exploiting aptamers for cell-specific drug delivery. Nucleic acid based pharmaceuticals represent an interesting and novel tool to counter human diseases. Combining inhibitory potential and cargo transfer upon internalization, nanocarriers as well as various therapeutics including siRNAs, chemotherapeutics, photosensitizers, or proteins can be imported via these synthetic nucleic acids. However, widespread clinical application is still hampered by obstacles that must be overcome. In this review, we give an overview of applications and recent advances in aptamer-mediated drug delivery. We also introduce prominent selection methods as well as useful approaches in choice of drug and conjugation method. We discuss the challenges that need to be considered and present strategies that have been applied to achieve intracellular delivery of effectors transported by readily internalized aptamers.

Binding of an RNA aptamer and a partial peptide of a prion protein: crucial importance of water entropy in molecular recognition

It is a central issue to elucidate the new type of molecular recognition accompanied by a global structural change of a molecule upon binding to its targets. Here we investigate the driving force for the binding of R12 (a ribonucleic acid aptamer) and P16 (a partial peptide of a prion protein) during which P16 exhibits the global structural change. We calculate changes in thermodynamic quantities upon the R12–P16 binding using a statistical-mechanical approach combined with molecular models for water which is currently best suited to studies on hydration of biomolecules. The binding is driven by a water-entropy gain originating primarily from an increase in the total volume available to the translational displacement of water molecules in the system. The energy decrease due to the gain of R12–P16 attractive (van der Waals and electrostatic) interactions is almost canceled out by the energy increase related to the loss of R12–water and P16–water attractive interactions. We can explain the general experimental result that stacking of flat moieties, hydrogen bonding and molecular-shape and electrostatic complementarities are frequently observed in the complexes. It is argued that the water-entropy gain is largely influenced by the geometric characteristics (overall shapes, sizes and detailed polyatomic structures) of the biomolecules.

Chlorin e6 Conjugated Interleukin-6 Receptor Aptamers Selectively Kill Target Cells Upon Irradiation

Photodynamic therapy (PDT) uses the therapeutic properties of light in combination with certain chemicals, called photosensitizers, to successfully treat brain, breast, prostate, and skin cancers. To improve PDT, current research focuses on the development of photosensitizers to specifically target cancer cells. In the past few years, aptamers have been developed to directly deliver cargo molecules into target cells. We conjugated the photosensitizer chlorin e6 (ce6) with a human interleukin-6 receptor (IL-6R) binding RNA aptamer, AIR-3A yielding AIR-3A-ce6 for application in high efficient PDT. AIR-3A-ce6 was rapidly and specifically internalized by IL-6R presenting (IL-6R(+)) cells. Upon light irradiation, targeted cells were selectively killed, while free ce6 did not show any toxic effect. Cells lacking the IL-6R were also not affected by AIR-3A-ce6. With this approach, we improved the target specificity of ce6-mediated PDT. In the future, other tumor-specific aptamers might be used to selectively localize photosensitizers into cells of interest and improve the efficacy and specificity of PDT in cancer and other diseases.Molecular Therapy-Nucleic Acids (2014) 3, e143; doi:10.1038/mtna.2013.70; published online 21 January 2014.

Aptamer-based therapeutics: new approaches to combat human viral diseases

Viruses replicate inside the cells of an organism and continuously evolve to contend with an ever-changing environment. Many life-threatening diseases, such as AIDS, SARS, hepatitis and some cancers, are caused by viruses. Because viruses have small genome sizes and high mutability, there is currently a lack of and an urgent need for effective treatment for many viral pathogens. One approach that has recently received much attention is aptamer-based therapeutics. Aptamer technology has high target specificity and versatility, i.e., any viral proteins could potentially be targeted. Consequently, new aptamer-based therapeutics have the potential to lead a revolution in the development of anti-infective drugs. Additionally, aptamers can potentially bind any targets and any pathogen that is theoretically amenable to rapid targeting, making aptamers invaluable tools for treating a wide range of diseases. This review will provide a broad, comprehensive overview of viral therapies that use aptamers. The aptamer selection process will be described, followed by an explanation of the potential for treating virus infection by aptamers. Recent progress and prospective use of aptamers against a large variety of human viruses, such as HIV-1, HCV, HBV, SCoV, Rabies virus, HPV, HSV and influenza virus, with particular focus on clinical development of aptamers will also be described. Finally, we will discuss the challenges of advancing antiviral aptamer therapeutics and prospects for future success.

Identification of RNA aptamers that internalize into HPV-16 E6/E7 transformed tonsillar epithelial cells

Human papillomavirus type 16 (HPV-16) associated oropharyngeal cancers are on a significant increase and better therapeutic strategies are needed. The HPV-16 oncogenes E6 and E7 are expressed in HPV-associated cancers and are able to transform human tonsillar epithelial cells (HTECs). We used cell-Systematic Evolution of Ligands by Exponential Enrichment (SELEX) to select for RNA aptamers that entered into HPV-16 E6/E7-HTECs. After 12 rounds of cell-SELEX, a pool of aptamers was obtained that had significantly greater internalization capacity (~5-fold) into E6/E7-HTECs as compared to primary HTECs or fibroblasts. Analysis of individual aptamers from the pool indicated variable internalization into E6/E7-HTECs (1-8-fold as compared to a negative control). Most of the individual aptamers internalized into E6/E7 and primary HTECs with similar efficiency, while one aptamer exhibited ~3-fold better internalization into E6/E7-HTECs. Aptamers that internalize into cells may be useful for delivering therapeutic agents to HPV-16 associated malignancies.