Use of Aptamers as Diagnostics Tools and Antiviral Agents for Human Viruses

Identification of In Vivo Internalizing Cardiac-Specific RNA Aptamers

Background

The pursuit of selective therapeutic delivery to target tissue types represents a key goal in the treatment of a range of adverse health issues, including diseases afflicting the heart. The development of new cardiac-specific ligands is a crucial step towards effectively targeting therapeutics to the heart.

Methods

Utilizing an ex vivo and in vivo SELEX approaches, we enriched a library of 2'-fluoro modified aptamers for ventricular cardiomyocyte specificity. Lead candidates were identified from this library, and their binding and internalization into cardiomyocytes was evaluated in both ex vivo and in vivo mouse studies.

Results

The ex vivo and in vivo SELEX processes generated an aptamer library with significant cardiac specificity over non-cardiac tissues such as liver and skeletal muscle. Our lead candidate aptamer from this library, CA1, demonstrates selective in vivo targeting and delivery of a fluorophore cargo to ventricular cardiomyocytes within the murine heart, while minimizing off-target localization to non-cardiac tissues, including the liver. By employing a novel RNase-based assay to evaluate aptamer interactions with cardiomyocytes, we discovered that CA1 predominantly internalizes into ventricular cardiomyocytes; conversely, another candidate CA41 primarily binds to the cardiomyocyte cell surface.

Conclusions

These findings suggest that CA1 and CA41 have the potential to be promising candidates for targeted drug delivery and imaging applications in cardiac diseases.

Development of Aptamers for RNase Inactivation in Xtract-Free™ Sample Collection and Transport Medium

There is a significant need to develop new environmentally friendly, extraction-free sample collection mediums that can effectively preserve and protect genetic material for point-of-care and/or self-collection, home-collection, and mail-back testing. Systematic evolution of ligands by exponential enrichment (SELEX) was used to create anti-ribonuclease (RNase) deoxyribonucleic acid (DNA) aptamers against purified RNase A conjugated to paramagnetic carboxylated beads. Following eight rounds of SELEX carried out under various stringency conditions, e.g., selection using Xtract-Free™ (XF) specimen collection medium and elevated ambient temperature of 28 °C, a panel of five aptamers was chosen following bioinformatic analysis using next-generation sequencing. The efficacy of aptamer inactivation of RNase was assessed by monitoring ribonucleic acid (RNA) integrity via fluorometric and real-time RT-PCR analysis. Inclusion of aptamers in reaction incubations resulted in an 8800- to 11,200-fold reduction in RNase activity, i.e., digestion of viral RNA compared to control. Thus, anti-RNase aptamers integrated into XF collection medium as well as other commercial reagents and kits have great potential for ensuring quality intact RNA for subsequent genomic analyses.

Inhibition of SARS-CoV-2 infection in human airway epithelium with a xeno-nucleic acid aptamer

BACKGROUND

SARS-CoV-2, the agent responsible for the COVID-19 pandemic, enters cells through viral spike glycoprotein binding to the cellular receptor, angiotensin-converting enzyme 2 (ACE2). Given the lack of effective antivirals targeting SARS-CoV-2, we previously utilized systematic evolution of ligands by exponential enrichment (SELEX) and selected fluoro-arabino nucleic acid (FANA) aptamer R8-9 that was able to block the interaction between the viral receptor-binding domain and ACE2.

METHODS

Here, we further assessed FANA-R8-9 as an entry inhibitor in contexts that recapitulate infection in vivo.

RESULTS

We demonstrate that FANA-R8-9 inhibits spike-bearing pseudovirus particle uptake in cell lines. Then, using an in-vitro model of human airway epithelium (HAE) and SARS-CoV-2 virus, we show that FANA-R8-9 significantly reduces viral infection when added either at the time of inoculation, or several hours later. These results were specific to the R8-9 sequence, not the xeno-nucleic acid utilized to make the aptamer. Importantly, we also show that FANA-R8-9 is stable in HAE culture secretions and has no overt cytotoxic effects.

CONCLUSIONS

Together, these results suggest that FANA-R8-9 effectively prevents infection by specific SARS-CoV-2 variants and indicate that aptamer technology could be utilized to target other clinically-relevant viruses in the respiratory mucosa.

Inhibition of SARS-CoV-2 Infection in Human Airway Epithelium with a Xeno-Nucleic Acid Aptamer

Background

SARS-CoV-2, the agent responsible for the COVID-19 pandemic, enters cells through viral spike glycoprotein binding to the cellular receptor, angiotensin-converting enzyme 2 (ACE2). Given the lack of effective antivirals targeting SARS-CoV-2, we previously utilized systematic evolution of ligands by exponential enrichment (SELEX) and selected fluoro-arabino nucleic acid (FANA) aptamer R8-9 that was able to block the interaction between the viral receptor-binding domain and ACE2.

Methods

Here, we further assessed FANA-R8-9 as an entry inhibitor in contexts that recapitulate infection in vivo.

Results

We demonstrate that FANA-R8-9 inhibits spike-bearing pseudovirus particle uptake in cell lines. Then, using an in-vitro model of human airway epithelium (HAE) and SARS-CoV-2 virus, we show that FANA-R8-9 significantly reduces viral infection when added either at the time of inoculation, or several hours later. These results were specific to the R8-9 sequence, not the xeno-nucleic acid utilized to make the aptamer. Importantly, we also show that FANA-R8-9 is stable in HAE culture secretions and has no overt cytotoxic effects.

Conclusions

Together, these results suggest that FANA-R8-9 effectively prevents infection by specific SARS-CoV-2 variants and indicate that aptamer technology could be utilized to target other clinically-relevant viruses in the respiratory mucosa.

Circular and Circulating DNA in Inflammatory Bowel Disease: From Pathogenesis to Potential Molecular Therapies

Inflammatory bowel diseases (IBD), including Crohn's Disease (CD) and Ulcerative Colitis (UC) are chronic multifactorial disorders which affect the gastrointestinal tract with variable extent. Despite extensive research, their etiology and exact pathogenesis are still unknown. Cell-free DNAs (cfDNAs) are defined as any DNA fragments which are free from the origin cell and able to circulate into the bloodstream with or without microvescicles. CfDNAs are now being increasingly studied in different human diseases, like cancer or inflammatory diseases. However, to date it is unclear how IBD etiology is linked to cfDNAs in plasma. Extrachromosomal circular DNA (eccDNA) are non-plasmidic, nuclear, circular and closed DNA molecules found in all eukaryotes tested. CfDNAs appear to play an important role in autoimmune diseases, inflammatory processes, and cancer; recently, interest has also grown in IBD, and their role in the pathogenesis of IBD has been suggested. We now suggest that eccDNAs also play a role in IBD. In this review, we have comprehensively collected available knowledge in literature regarding cfDNA, eccDNA, and structures involving them such as neutrophil extracellular traps and exosomes, and their role in IBD. Finally, we focused on old and novel potential molecular therapies and drug delivery systems, such as nanoparticles, for IBD treatment.

Novel Aptamers for the Reactivation of Latent HIV

INTRODUCTION

A "Shock and Kill" strategy has been proposed to eradicate the HIV latent viral reservoir. Effective Latency Reversal Agents (LRA) are a key requirement for this strategy. The search for LRAs with a novel mechanism of action is ongoing. This is the first study to propose aptamers for the reactivation of HIV.

OBJECTIVE

The purpose of this study was to identify an aptamer that potentially reactivates HIV via the NF-κβ pathway, specifically by binding to IkB and releasing NF-κβ.

METHODS

Aptamer selection was performed at Aptus Biotech (www.aptusbiotech.es), using ikB human recombinant protein with His tag bound to Ni-NTA agarose resin using the SELEX procedure. Activation of NF-κβ was measured by SEAP Assay. HIV reactivation was measured in JLat cells using a BD FACS-Canto™ II flow cytometer. All flow cytometry data were analyzed using Kaluza analyzing software.

RESULTS

Clones that had equivalent or greater activation than the positive control in the SEAP assay were regarded as potential reactivators of the NF-κβ pathway and were sequenced. The three ikb clones namely R6-1F, R6-2F, and R6-3F were found to potentially activate the NF-κβ pathway. Toxicity was determined by exposing lymphocytes to serial dilutions of the aptamers; the highest concentration of the aptamers that did not decrease viability by > 20% was used for the reactivation experiments. The three novel aptamers R6-1F, R6-2F, and R6-3F resulted in 4,07%, 6,72% and 3,42% HIV reactivation, respectively, while the untreated control showed minimal (<0.18%) fluorescence detection.

CONCLUSION

This study demonstrated the reactivation of latent HIV by aptamers that act via the NF-κβ pathway. Although the effect was modest and unlikely to be of clinical benefit, future studies are warranted to explore ways of enhancing reactivation.

Potential Therapeutic Use of Aptamers against HAT1 in Lung Cancer

Lung cancer is one of the leading causes of death worldwide and the most common of all cancer types. Histone acetyltransferase 1 (HAT1) has attracted increasing interest as a potential therapeutic target due to its involvement in multiple pathologies, including cancer. Aptamers are single-stranded RNA or DNA molecules whose three-dimensional structure allows them to bind to a target molecule with high specificity and affinity, thus making them exceptional candidates for use as diagnostic or therapeutic tools. In this work, aptamers against HAT1 were obtained, subsequently characterized, and optimized, showing high affinity and specificity for HAT1 and the ability to inhibit acetyltransferase activity in vitro. Of those tested, the apHAT610 aptamer reduced cell viability, induced apoptosis and cell cycle arrest, and inhibited colony formation in lung cancer cell lines. All these results indicate that the apHAT610 aptamer is a potential drug for the treatment of lung cancer.

Development of a Molecular Aptamer Beacon Applied to Magnetic-Assisted RNA Extraction for Detection of Dengue and Zika Viruses Using Clinical Samples

Limitations in the detection of cocirculating flaviviruses such as Dengue and Zika lead us to propose the use of aptameric capture of the viral RNA in combination with RT-PCR (APTA-RT-PCR). Aptamers were obtained via SELEX and next-generation sequencing, followed by colorimetric and fluorescent characterizations. An APTA-RT-PCR assay was developed, optimized, and tested against the viral RNAs in 108 serum samples. After selection, sequence APTAZC10 was designed as a bifunctional molecular beacon (APTAZC10-MB), exhibiting affinity for the viral targets. APTA-RT-PCR was able to detect Dengue and Zika RNA in 43% and 8% of samples, respectively. Our results indicate that APTAZC10-MB and APTA-RT-PCR will be useful to improve the detection of Dengue and Zika viruses in a fast molecular assay for the improvement of infectious disease surveillance.

Binding Affinity Measurements Between DNA Aptamers and their Virus Targets Using ELONA and MST

Aptamers have been selected with strong affinity and high selectivity for a wide range of targets, as recently highlighted by the development of aptamer-based sensors that can differentiate infectious from non-infectious viruses, including human adenovirus and SARS-CoV-2. Accurate determination of the binding affinity between the DNA aptamers and their viral targets is the first step to understanding the molecular recognition of viral particles and the potential uses of aptamers in various diagnostics and therapeutic applications. Here, we describe protocols to obtain the binding curve of the DNA aptamers to SARS-CoV-2 using Enzyme-Linked Oligonucleotide Assay (ELONA) and MicroScale Thermophoresis (MST). These methods allow for the determination of the binding affinity of the aptamer to the infectious SARS-CoV-2 and the selectivity of this aptamer against the same SARS-CoV-2 that has been rendered non-infectious by UV inactivation, and other viruses. Compared to other techniques like Electrophoretic Mobility Shift Assay (EMSA), Surface Plasmon Resonance (SPR), and Isothermal Titration Calorimetry (ITC), these methods have advantages for working with larger particles like viruses and with samples that require biosafety level 2 facilities.

Aptamers: A prospective tool for infectious diseases diagnosis

It is well known that people's health is seriously threatened by various pathogens (such as Mycobacterium tuberculosis, Treponema pallidum, Novel coronavirus, HIV, Mucor, etc.), which leads to heavy socioeconomic burdens. Therefore, early and accurate pathogen diagnosis is essential for timely and effective therapies. Up to now, diagnosing human contagious diseases at molecule and nano levels is remarkably difficult owing to insufficient valid probes when it comes to determining the biological markers of pathogens. Aptamers are a set of high‐specificity and high‐sensitivity plastic oligonucleotides screened in vitro via the selective expansion of ligands by exponential enrichment (SELEX). With the advent of aptamer‐based technologies, their merits have aroused mounting academic interest. In recent years, as new detection and treatment tools, nucleic acid aptamers have been extensively utilized in the field of biomedicine, such as pathogen detection, new drug development, clinical diagnosis, nanotechnology, etc. However, the traditional SELEX method is cumbersome and has a long screening cycle, and it takes several months to screen out aptamers with high specificity. With the persistent development of SELEX‐based aptamer screening technologies, the application scenarios of aptamers have become more and more extensive. The present research briefly reviews the research progress of nucleic acid aptamers in the field of biomedicine, especially in the diagnosis of contagious diseases.

Selection and Characterization of ssDNA Aptamers Targeting Largemouth Bass Virus Infected Cells With Antiviral Activities

Largemouth bass virus (LMBV) is one of the most devastating viral pathogens in farmed Largemouth bass. Aptamers are novel molecule probes and have been widely applied in the field of efficient therapeutic and diagnostic agents development. LMBV-infected fathead minnow cells (LMBV-FHM) served as target cells in this study, and three DNA aptamers (LBVA1, LBVA2, and LBVA3) were generated against target cells by SELEX technology. The selected aptamers could specifically bind to LMBV-FHM cells, with rather high calculated dissociation constants (Kd) of 890.09, 517.22, and 249.31 nM for aptamers LBVA1, LBVA2, and LBVA3, respectively. Three aptamers displayed efficient antiviral activities in vitro. It indicates that the selected aptamers have great potentials in developing efficient anti-viruses treatments. The targets of aptamers LBVA1, LBVA2, and LBVA3 could be membrane proteins on host cells. The targets of aptamers (LBVA1, LBVA2, and LBVA3) come out on the cells surface at 8, 10, 8 h post-infection. As novel molecular probes for accurate recognition, aptamer LBVA3 could detect LMBV infection in vitro and in vivo, it indicates that the selected aptamers could be applied in the development of rapid detective technologies, which are characterized by high sensitivity, accuracy, and easy operation.

Anti-HIV Aptamers: Challenges and Prospects

Human Immunodeficiency Virus (HIV) infection continues to be a significant health burden in many countries around the world. Current HIV treatment through a combination of different antiretroviral drugs (cART) effectively suppresses viral replication, but drug resistance and crossresistance are significant challenges. This has prompted the search for novel targets and agents, such as nucleic acid aptamers. Nucleic acid aptamers are oligonucleotides that attach to the target sites with high affinity and specificity. This review provides a target-by-target account of research into anti-HIV aptamers and summarises the challenges and prospects of this therapeutic strategy, specifically in the unique context of HIV infection.

Selection and Application of Aptamer Affinity for Protein Purification

Aptamers are affinity-based oligonucleotide ligands raised against a target molecule, which might be of proteic or other nature. Aptamers are developed by using a reiterative in vitro selection procedure, named SELEX, in which the target is exposed to a combinatorial oligonucleotide combinatorial library. Target bound oligonucleotides are eluted, and PCR amplified followed by the next SELEX round. The process is repeated until no further increase in target binding affinity and specificity is achieved. Selected aptamers are identified and immobilized for protein purification. In view of their stability against denaturation and capability of renaturation, low costs of production, easiness of modification and stabilization, oligonucleotide aptamers are excellent tools as high-affinity ligands for applications of protein purification.

Aptamers Against COVID-19: An Untested Opportunity

Given the lack of success in the development of effective drugs to treat COVID-19, which show "game-changing" potential, it is necessary to explore drugs with different modes of action. Single mode-of-action drugs have not been succeeded in curing COVID-19, which is a highly complex disease. This is the case for direct antivirals and anti-inflammatory drugs, both of which treat different phases of the disease. Aptamers are molecules that deliver different modes of action, allowing their effects to be bundled, which, when combined, support their therapeutic efficacy. In this minireview, we summarise the current activities in the development of aptamers for the treatment of COVID-19 and long-COVID. A special emphasis is placed on the capability of their multiple modes of action, which is a promising approach for treating complex diseases such as COVID-19.

A serum-stable RNA aptamer specific for SARS-CoV-2 neutralizes viral entry

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic has created an urgent need for new technologies to treat COVID-19. Here we report a 2'-fluoro protected RNA aptamer that binds with high affinity to the receptor binding domain (RBD) of SARS-CoV-2 spike protein, thereby preventing its interaction with the host receptor ACE2. A trimerized version of the RNA aptamer matching the three RBDs in each spike complex enhances binding affinity down to the low picomolar range. Binding mode and specificity for the aptamer-spike interaction is supported by biolayer interferometry, single-molecule fluorescence microscopy, and flow-induced dispersion analysis in vitro. Cell culture experiments using virus-like particles and live SARS-CoV-2 show that the aptamer and, to a larger extent, the trimeric aptamer can efficiently block viral infection at low concentration. Finally, the aptamer maintains its high binding affinity to spike from other circulating SARS-CoV-2 strains, suggesting that it could find widespread use for the detection and treatment of SARS-CoV-2 and emerging variants.

SARS-CoV-2 spike protein detection through a plasmonic D-shaped plastic optical fiber aptasensor

A specific aptameric sequence has been immobilized on short polyethyleneglycol (PEG) interface on gold nano-film deposited on a D-shaped plastic optical fiber (POFs) probe, and the protein binding has been monitored exploiting the very sensitive surface plasmon resonance (SPR) phenomenon. The receptor-binding domain (RBD) of the SARS-CoV-2 spike glycoprotein has been specifically used to develop an aptasensor. Surface analysis techniques coupled to fluorescence microscopy and plasmonic analysis have been utilized to characterize the biointerface. Spanning a wide protein range (25 ÷ 1000 nM), the SARS-Cov-2 spike protein was detected with a Limit of Detection (LoD) of about 37 nM. Different interferents (BSA, AH1N1 hemagglutinin protein and MERS spike protein) have been tested confirming the specificity of our aptasensor. Finally, a preliminary test in diluted human serum encouraged its application in a point-of-care device, since POF-based aptasensor represent a potentially low-cost compact biosensor, characterized by a rapid response, a small size and could be an ideal laboratory portable diagnostic tool.

Gold-Oligonucleotide Nanoconstructs Engineered to Detect Conserved Enteroviral Nucleic Acid Sequences

Enteroviruses are ubiquitous mammalian pathogens that can produce mild to life-threatening disease. We developed a multimodal, rapid, accurate and economical point-of-care biosensor that can detect nucleic acid sequences conserved amongst 96% of all known enteroviruses. The biosensor harnesses the physicochemical properties of gold nanoparticles and oligonucleotides to provide colourimetric, spectroscopic and lateral flow-based identification of an exclusive enteroviral nucleic acid sequence (23 bases), which was identified through in silico screening. Oligonucleotides were designed to demonstrate specific complementarity towards the target enteroviral nucleic acid to produce aggregated gold–oligonucleotide nanoconstructs. The conserved target enteroviral nucleic acid sequence (≥1 × 10⁻⁷ M, ≥1.4 × 10⁻¹⁴ g/mL) initiates gold–oligonucleotide nanoconstruct disaggregation and a signal transduction mechanism, producing a colourimetric and spectroscopic blueshift (544 nm (purple) > 524 nm (red)). Furthermore, lateral-flow assays that utilise gold–oligonucleotide nanoconstructs were unaffected by contaminating human genomic DNA, demonstrated rapid detection of conserved target enteroviral nucleic acid sequence (<60 s), and could be interpreted with a bespoke software and hardware electronic interface. We anticipate that our methodology will translate in silico screening of nucleic acid databases to a tangible enteroviral desktop detector, which could be readily translated to related organisms. This will pave the way forward in the clinical evaluation of disease and complement existing strategies to overcome antimicrobial resistance.

Rabies Prophylactic and Treatment Options: An In Vitro Study of siRNA- and Aptamer-Based Therapeutics

If the goal of eliminating dog-mediated human rabies by 2030 is to be achieved, effective mass dog vaccination needs to be complemented by effective prophylaxis for individuals exposed to rabies. Aptamers and short-interfering RNAs (siRNAs) have been successful in therapeutics, but few studies have investigated their potential as rabies therapeutics. In this study, siRNAs and aptamers-using a novel selection method-were developed and tested against rabies virus (RABV) in a post-infection (p.i.) scenario. Multiple means of delivery were tested for siRNAs, including the use of Lipofectamine and conjugation with the developed aptamers. One siRNA (N53) resulted in an 80.13% reduction in viral RNA, while aptamer UPRET 2.03 demonstrated a 61.3% reduction when used alone at 2 h p.i. At 24 h p.i., chimera UPRET 2.03-N8 (aptamer-siRNA) resulted in a 36.5% inhibition of viral replication. To our knowledge, this is the first study using siRNAs or aptamers that (1) demonstrated significant inhibition of RABV using an aptamer, (2) tested Lipofectamine RNAi-Max as a means for delivery, and (3) produced significant RABV inhibition at 24 h p.i. This study serves as a proof-of-concept to potentially use aptamers and siRNAs as rabies immunoglobulin (RIG) replacements or therapeutic options for RABV and provides strong evidence towards their further investigation.

Puerarin dry powder inhaler formulations for pulmonary delivery: Development and characterization

This study aims at developing and characterizing the puerarin dry powder inhaler (DPI) formulations for pulmonary delivery. The inhalable particles size (<2 μm) was accomplished by micronization and its morphology was examined by scanning electron microscopy (SEM). The puerarin-excipient interaction in powder mixtures was analyzed by using Fourier transform infrared spectroscopy (FTIR), Raman confocal microscopy, X-Ray powder Diffraction (XRD), and differential scanning calorimetry (DSC) methods. Using a Twin stage impinger (TSI), the in-vitro aerosolization of the powder formulations was carried out at a flow rate of 60 L/min and the drug was quantified by employing a validated HPLC method. No significant interactions between the drug and the excipients were observed in the powder formulations. The fine particle fraction (FPF) of the drug alone was 4.2% which has increased five to six-fold for the formulations with aerosolization enhancers. Formulation containing lactose as large carriers produced 32.7% FPF, which further increased with the addition of dispersibility enhancers, leucine and magnesium stearate (40.8% and 41.2%, respectively). The Raman and FTIR techniques are very useful tool for understanding structural integrity and stability of the puerarin in the powder formulations. The puerarin was found to be compatible with the excipients used and the developed DPI formulation may be considered as an efficient formulation for pulmonary delivery for the management of various diseases at a very low dose.

AptaNet as a deep learning approach for aptamer-protein interaction prediction

Aptamers are short oligonucleotides (DNA/RNA) or peptide molecules that can selectively bind to their specific targets with high specificity and affinity. As a powerful new class of amino acid ligands, aptamers have high potentials in biosensing, therapeutic, and diagnostic fields. Here, we present AptaNet-a new deep neural network-to predict the aptamer-protein interaction pairs by integrating features derived from both aptamers and the target proteins. Aptamers were encoded by using two different strategies, including k-mer and reverse complement k-mer frequency. Amino acid composition (AAC) and pseudo amino acid composition (PseAAC) were applied to represent target information using 24 physicochemical and conformational properties of the proteins. To handle the imbalance problem in the data, we applied a neighborhood cleaning algorithm. The predictor was constructed based on a deep neural network, and optimal features were selected using the random forest algorithm. As a result, 99.79% accuracy was achieved for the training dataset, and 91.38% accuracy was obtained for the testing dataset. AptaNet achieved high performance on our constructed aptamer-protein benchmark dataset. The results indicate that AptaNet can help identify novel aptamer-protein interacting pairs and build more-efficient insights into the relationship between aptamers and proteins. Our benchmark dataset and the source codes for AptaNet are available in: https://github.com/nedaemami/AptaNet .

Oligonucleotide-Based Approaches to Inhibit Dengue Virus Replication

Dengue fever is one of the most common viral infections affecting humans. It is an expanding public health problem, particularly in tropical and subtropical regions. No effective vaccine or antiviral therapies against Dengue virus (DENV) infection are available. Therefore, there is a strong need to develop safe and effective therapeutic strategies that can reduce the burden and duration of hospitalizations due to this life-threatening disease. Oligonucleotide-based strategies are considered as an attractive means of inhibiting viral replication since oligonucleotides can be designed to interact with any viral RNA, provided its sequence is known. The resultant targeted destruction of viral RNA interferes with viral replication without inducing any adverse effects on cellular processes. In this review, we elaborate the ribozymes, RNA interference, CRISPR, aptamer and morpholino strategies for the inhibition of DENV replication and discuss the challenges involved in utilizing such approaches.

G-quadruplexes in H1N1 influenza genomes

BACKGROUND

Influenza viruses are dangerous pathogens. Seventy-Seven genomes of recently emerged genotype 4 reassortant Eurasian avian-like H1N1 virus (G4-EA-H1N1) are currently available. We investigated the presence and variation of potential G-quadruplex forming sequences (PQS), which can serve as targets for antiviral treatment.

RESULTS

PQS were identified in all 77 genomes. The total number of PQS in G4-EA-H1N1 genomes was 571. Interestingly, the number of PQS per genome in individual close relative viruses varied from 4 to 12. PQS were not randomly distributed in the 8 segments of the G4-EA-H1N1 genome, the highest frequency of PQS being found in the NP segment (1.39 per 1000 nt), which is considered a potential target for antiviral therapy. In contrast, no PQS was found in the NS segment. Analyses of variability pointed the importance of some PQS; even if genome variation of influenza virus is extreme, the PQS with the highest G4Hunter score is the most conserved in all tested genomes. G-quadruplex formation in vitro was experimentally confirmed using spectroscopic methods.

CONCLUSIONS

The results presented here hint several G-quadruplex-forming sequences in G4-EA-H1N1 genomes, that could provide good therapeutic targets.

Application of Aptamer-Based Assays to the Diagnosis of Arboviruses Important for Public Health in Brazil

Arbovirus infections represent a global public health problem, and recent epidemics of yellow fever, dengue, and Zika have shown their critical importance in Brazil and worldwide. Whilst a major effort for vaccination programs has been in the spotlight, a number of aptamer approaches have been proposed in a complementary manner, offering the possibility of differential diagnosis between these arboviruses, which often present similar clinical symptoms, as well as the potential for a treatment option when no other alternative is available. In this review, we aim to provide a background on arbovirus, with a basic description of the main viral classes and the disease they cause, using the Brazilian context to build a comprehensive understanding of their role on a global scale. Subsequently, we offer an exhaustive revision of the diagnostic and therapeutic approaches offered by aptamers against arboviruses. We demonstrate how these promising reagents could help in the clinical diagnosis of this group of viruses, their use in a range of diagnostic formats, from biosensors to serological testing, and we give a short review on the potential approaches for novel aptamer-based antiviral treatment options against different arboviral diseases.

Advances in detection of infectious agents by aptamer-based technologies

Infectious diseases still remain one of the biggest challenges for human health. Accurate and early detection of infectious pathogens are crucial for transmission control, clinical diagnosis, and therapy. For a traditional reason, most immunological and microbiological laboratories are equipped with instruments designated for antibody-based assays in detection of infectious pathogens or clinical diagnosis. Emerging aptamer-based technologies have pushed a shift from antibody-based to aptamer-based assays due to equal specificity, even better sensitivity, lower manufacturing cost and more flexibility in amending for chemiluminescent, electrochemical or fluorescent detection in a multifaceted and high throughput fashion in comparison of aptamer-based to antibody-based assays. The nature of aptamer-based technologies is particularly suitable for point-of-care testing in remote areas at warm or hot atmosphere, and mass screening for potential infection in pandemic of emerging infectious agents, such as SARS-CoV or SARS-CoV-2 in an epicentre or other regions. This review intends to summarize currently available aptamer-based technologies in detection of bacterial, viral, and protozoan pathogens for research and clinical application. It is anticipated that potential technologies will be further optimized and validated for clinical translation in meeting increasing demands for prompt, precise, and reliable detection of specific pathogens in various atmospheric conditions.

Aptamer BC 007 - Efficient binder of spreading-crucial SARS-CoV-2 proteins

Corona virus disease 2019 (COVID-19) is a respiratory disease caused by a new coronavirus (SARS-CoV-2) which causes significant morbidity and mortality. The emergence of this novel and highly pathogenic SARS-CoV-2 and its rapid international spread poses a serious global public health emergency. To date 32,174,627 cases, of which 962,613 (2.99%) have died, have been reported (https://www.who.int/westernpacific/health-topics/coronavirus, accessed 23 Sep 2020). The outbreak was declared a Public Health Emergency of International Concern on 30 January 2020.

There are still not many SARS-CoV-2-specific and effective treatments or vaccines available. A second round of infection is obviously unavoidable.

Aptamers had already been at the centre of interest in the fight against viruses before now. The selection and development of a new aptamer is, however, a time-consuming process. We therefore checked whether a clinically developed aptamer, BC 007, which is currently in phase 2 of clinical testing for a different indication, would also be able to efficiently bind DNA-susceptible peptide structures from SARS-CoV-2-spreading crucial proteins, such as the receptor binding domain (RBD) of the spike protein and the RNA dependent RNA polymerase of SARS-CoV-2 (re-purposing). Indeed, several such sequence-sections have been identified. In particular for two of these sequences, BC 007 showed specific binding in a therapy-relevant concentration range, as shown in Nuclear magnetic resonance (NMR)- and Circular dicroism (CD)-spectroscopy and isothermal titration calorimetry (ITC). The excellent clinical toxicity and tolerability profile of this substance opens up an opportunity for rapid clinical testing of its COVID-19 effectiveness.

Novel monomolecular derivatives of the anti-HIV-1 G-quadruplex-forming Hotoda's aptamer containing inversion of polarity sites

Here we report on the design, preparation and investigation of four analogues of the anti-HIV G-quadruplex-forming Hotoda's aptamer, based on an unprecedented linear topology. In these derivatives, four TGGGAGT tracts have been joined together by exploiting 3'-3' and 5'-5' inversion of polarity sites formed by canonical phosphodiester bonds or a glycerol-based linker. Circular dichroism data suggest that all oligodeoxynucleotides fold in monomolecular G-quadruplex structures characterized by a parallel strand orientation and three side loops connecting 3'- or 5'-ends. The derivative bearing two lipophilic groups, namely HT353LGly, inhibited virus entry into the host cell, with anti-HIV-1 activity in the low nanomolar range; the other derivatives, albeit sharing the same base sequence and similar topology, were inactive. These results highlight that monomolecular Hotoda's aptamers with inversion of polarity sites represent a successful alternative strategy that merges the easiness of synthesis with the maintenance of remarkable activity. They also indicate that two lipophilic groups are necessary and sufficient for biological activity. Our data will inspire the design of further simplified derivatives with improved biophysical and antiviral properties.

SERS-Based Biosensors for Virus Determination with Oligonucleotides as Recognition Elements

Viral infections are among the main causes of morbidity and mortality of humans; sensitive and specific diagnostic methods for the rapid identification of viral pathogens are required. Surface-enhanced Raman spectroscopy (SERS) is one of the most promising techniques for routine analysis due to its excellent sensitivity, simple and low-cost instrumentation and minimal required sample preparation. The outstanding sensitivity of SERS is achieved due to tiny nanostructures which must be assembled before or during the analysis. As for specificity, it may be provided using recognition elements. Antibodies, complimentary nucleic acids and aptamers are the most usable recognition elements for virus identification. Here, SERS-based biosensors for virus identification with oligonucleotides as recognition elements are reviewed, and the potential of these biosensors is discussed.

DNA aptamers targeting Leishmania infantum H3 protein as potential diagnostic tools

Leishmaniasis is a disease caused by a parasite of the genus Leishmania that affects millions of people worldwide. These parasites are characterized by the presence of a DNA-containing granule, the kinetoplastid, located in the single mitochondrion at the base of the cell's flagellum. Interestingly, these flagellates do not condense chromatin during mitosis, possibly due to the specific molecular features of their histones. Although histones are extremely conserved proteins, kinetoplastid core histone sequences diverge significantly from those of higher eukaryotes. This divergence makes kinetoplastid core histones potential diagnostic and/or therapeutic targets. Aptamers are short single-stranded nucleic acids that are able to recognize target molecules with high affinity and specificity. Their binding capacity is a consequence of the particular three-dimensional structure acquired depending on their sequence. These molecules are currently used for detection, diagnosis and therapeutic purpose. Starting from a previously obtained ssDNA aptamer population against rLiH3 protein we have isolated two individual aptamers, AptLiH3#4 and AptLiH3#10. Next, we have performed ELONA, Western blot and slot blot assays to establish aptamer specificity and affinity for LiH3 histone. In addition, ELONA assays using peptides corresponding to overlapped sequences of LiH3 were made to map the aptamers:LiH3 interaction. Finally, different assays using aptamers were performed in order to evaluate the possibility of using these aptamers as sensing molecule to recognize the endogenous protein LiH3. Our results indicate that both aptamers have high affinity and specificity for the target and are able to detect the endogenous LiH3 histone protein in promastigotes lysates. In silico analysis reveals that these two aptamers have different potential secondary structure among them, however, both of them are able to recognize the same peptide sequences present in the protein. In conclusion, our findings indicate that these aptamers could be used for LiH3 histone detection and, in consequence, as potential biosensing molecules in a diagnostic tool for leishmaniasis.

Computational predictive approaches for interaction and structure of aptamers

Aptamers are short single-strand sequences that can bind to their specific targets with high affinity and specificity. Usually, aptamers are selected experimentally via systematic evolution of ligands by exponential enrichment (SELEX), an evolutionary process that consists of multiple cycles of selection and amplification. The SELEX process is expensive, time-consuming, and its success rates are relatively low. To overcome these difficulties, in recent years, several computational techniques have been developed in aptamer sciences that bring together different disciplines and branches of technologies. In this paper, a complementary review on computational predictive approaches of the aptamer has been organized. Generally, the computational prediction approaches of aptamer have been proposed to carry out in two main categories: interaction-based prediction and structure-based predictions. Furthermore, the available software packages and toolkits in this scope were reviewed. The aim of describing computational methods and tools in aptamer science is that aptamer scientists might take advantage of these computational techniques to develop more accurate and more sensitive aptamers.

Structural and Functional Aspects of G-Quadruplex Aptamers Which Bind a Broad Range of Influenza A Viruses

An aptamer is a synthetic oligonucleotide with a unique spatial structure that provides specific binding to a target. To date, several aptamers to hemagglutinin of the influenza A virus have been described, which vary in affinity and strain specificity. Among them, the DNA aptamer RHA0385 is able to recognize influenza hemagglutinins with highly variable sequences. In this paper, the structure of RHA0385 was studied by circular dichroism spectroscopy, nuclear magnetic resonance, and size-exclusion chromatography, demonstrating the formation of a parallel G-quadruplex structure. Three derivatives of RHA0385 were designed in order to determine the contribution of the major loop to affinity. Shortening of the major loop from seven to three nucleotides led to stabilization of the scaffold. The affinities of the derivatives were studied by surface plasmon resonance and an enzyme-linked aptamer assay on recombinant hemagglutinins and viral particles, respectively. The alterations in the loop affected the binding to influenza hemagglutinin, but did not abolish it. Contrary to aptamer RHA0385, two of the designed aptamers were shown to be conformationally homogeneous, retaining high affinities and broad binding abilities for both recombinant hemagglutinins and whole influenza A viruses.

Designer DNA architecture offers precise and multivalent spatial pattern-recognition for viral sensing and inhibition

DNA, when folded into nanostructures with a specific shape, is capable of spacing and arranging binding sites into a complex geometric pattern with nanometre precision. Here we demonstrate a designer DNA nanostructure that can act as a template to display multiple binding motifs with precise spatial pattern-recognition properties, and that this approach can confer exceptional sensing and potent viral inhibitory capabilities. A star-shaped DNA architecture, carrying five molecular beacon-like motifs, was constructed to display ten dengue envelope protein domain III (ED3)-targeting aptamers into a two-dimensional pattern precisely matching the spatial arrangement of ED3 clusters on the dengue (DENV) viral surface. The resulting multivalent interactions provide high DENV-binding avidity. We show that this structure is a potent viral inhibitor and that it can act as a sensor by including a fluorescent output to report binding. Our molecular-platform design strategy could be adapted to detect and combat other disease-causing pathogens by generating the requisite ligand patterns on customized DNA nanoarchitectures.

DNA is capable of self-assembling into a wide range of user-defined structures and so can be used as a scaffold to arrange binding motifs with nanometre precision. Now, DNA has been used to accurately display aptamers that fit the repeated epitope pattern of a dengue viral antigen to produce a nanostructure that can be a potent viral inhibitor or a fluorescent sensor.

Selection of 2'-Deoxy-2'-Fluoroarabino Nucleic Acid (FANA) Aptamers That Bind HIV-1 Integrase with Picomolar Affinity

Systematic Evolution of Ligands by Exponential Enrichment (SELEX) is the iterative process by which nucleic acids that can bind with high affinity and specificity (termed aptamers) to specific protein targets are selected. Using a SELEX protocol adapted for Xeno-Nucleic Acid (XNA) as a suitable substrate for aptamer generation, 2′-fluoroarabinonucleic acid (FANA) was used to select several related aptamers to HIV-1 integrase (IN). IN bound FANA aptamers with equilibrium dissociation constants (K_D,app) of ∼50–100 pM in a buffer with 200 mM NaCl and 6 mM MgCl₂. Comparisons to published HIV-1 IN RNA and DNA aptamers as well as IN genomic binding partners indicated that FANA aptamers bound more than 2 orders of magnitude more tightly to IN. Using a combination of RNA folding algorithms and covariation analysis, all strong binding aptamers demonstrated a common four-way junction structure, despite significant sequence variation. IN aptamers were selected from the same starting library as FA1, a FANA aptamer that binds with pM affinity to HIV-1 Reverse Transcriptase (RT). It contains a 20-nucleotide 5′ DNA sequence followed by 59 FANA nucleotides. IN-1.1 (one of the selected aptamers) potently inhibited IN activity and intasome formation in vitro. Replacing the FANA nucleotides of IN-1.1 with 2′-fluororibonucleic acid (F-RNA), which has the same chemical formula but with a ribose rather than arabinose sugar conformation, dramatically reduced binding, suggesting that FANA adopts unique structural conformations that promote binding to HIV-1 IN.

Application of Aptamers in Virus Detection and Antiviral Therapy

Viral infections can cause serious diseases for humans and animals. Accurate and early detection of viruses is often crucial for clinical diagnosis and therapy. Aptamers are mostly single-stranded nucleotide sequences that are artificially synthesized by an in vitro technology known as the Systematic Evolution of Ligands by Exponential Enrichment (SELEX). Similar to antibodies, aptamers bind specifically to their targets. However, compared with antibody, aptamers are easy to synthesize and modify and can bind to a broad range of targets. Thus, aptamers are promising for detecting viruses and treating viral infections. In this review, we briefly introduce aptamer-based biosensors (aptasensors) and describe their applications in rapid detection of viruses and as antiviral agents in treating infections. We summarize available data about the use of aptamers to detect and inhibit viruses. Furthermore, for the first time, we list aptamers specific to different viruses that have been screened out but have not yet been used for detecting viruses or treating viral infections. Finally, we analyze barriers and developing perspectives in the application of aptamer-based virus detection and therapeutics.

Relationship Between G-Quadruplex Sequence Composition in Viruses and Their Hosts

A subset of guanine-rich nucleic acid sequences has the potential to fold into G-quadruplex (G4) secondary structures, which are functionally important for several biological processes, including genome stability and regulation of gene expression. Putative quadruplex sequences (PQSs) G₃₊N_1-7G₃₊N_1-7G₃₊N_1-7G₃₊ are widely found in eukaryotic and prokaryotic genomes, but the base composition of the N_1-7 loops is biased across species. Since the viruses partially hijack their hosts' cellular machinery for proliferation, we examined the PQS motif size, loop length, and nucleotide compositions of 7370 viral genome assemblies and compared viral and host PQS motifs. We studied seven viral taxa infecting five distant eukaryotic hosts and created a resource providing a comprehensive view of the viral quadruplex motifs. Overall, short-looped PQSs are predominant and with a similar composition across viral taxonomic groups, albeit subtle trends emerge upon classification by hosts. Specifically, there is a higher frequency of pyrimidine loops in viruses infecting animals irrespective of the viruses' genome type. This observation is confirmed by an in-depth analysis of the Herpesviridae family of viruses, which showed a distinctive accumulation of thermally stable C-looped quadruplexes in viruses infecting high-order vertebrates. The occurrence of viral C-looped G4s, which carry binding sites for host transcription factors, as well as the high prevalence of viral TTA-looped G4s, which are identical to vertebrate telomeric motifs, provide concrete examples of how PQSs may help viruses impinge upon, and benefit from, host functions. More generally, these observations suggest a co-evolution of virus and host PQSs, thus underscoring the potential functional significance of G4s.

Specific detection of avian influenza H5N2 whole virus particles on lateral flow strips using a pair of sandwich-type aptamers

We report a selection of a cognate pair of aptamers for whole avian influenza virus particles of H5N2 by using graphene-oxide based systemic evolution of ligands by exponential enrichment (GO-SELEX), and the application of a pair of sandwich-type binding aptamers on the lateral flow strips. The aptamers were characterized by GO-FRET assay, and Kd values of the selected aptamers were estimated to be from 6.913 × 10⁵ to 1.27 × 10⁶ EID₅₀/ml (EID₅₀/ml: 50% egg infective dose). Based on the evidence from confocal laser scanning microscope (CLSM), surface plasmon resonance (SPR), and circular dichroism (CD) spectrum analysis, the aptamers, J₃APT and JH₄APT, were found to be working as a cognate pair that binds to the target virus at the different sites simultaneously. This cognate pair of aptamers then was successfully applied on the lateral flow strips, clearly showing sandwich-type binding images with the presence of the certain numbers of H5N2 virus particles. On the newly developed lateral flow strips, the target virus was detectable down to 6 × 10⁵ EID₅₀/ml in the buffer and 1.2 × 10⁶ EID₅₀/ml in the duck's feces, respectively, by the naked eye. By using the ImageJ software, the LOD was found to be 1.27 × 10⁵ EID₅₀/ml in the buffer and 2.09 × 10⁵ EID₅₀/ml in the duck's feces, respectively. Interestingly, on the lateral flow strips, enhanced specificity towards the target virus (H5N2) appeared over other subtypes of H5Nx. To the best of our knowledge, this is the first report about the application of the cognate pair of aptamers for the detection of influenza virus on the lateral flow strips. This study shows the promising perspective of a cognate pair of aptamers for the on-site detection system which could be useful for rapid detection of avian influenza viruses for preventing the pandemic influenza viruses from spreading.

G-Quadruplexes as An Alternative Recognition Element in Disease-Related Target Sensing

G-quadruplexes are made up of guanine-rich RNA and DNA sequences capable of forming noncanonical nucleic acid secondary structures. The base-specific sterical configuration of G-quadruplexes allows the stacked G-tetrads to bind certain planar molecules like hemin (iron (III)-protoporphyrin IX) to regulate enzymatic-like functions such as peroxidase-mimicking activity, hence the use of the term DNAzyme/RNAzyme. This ability has been widely touted as a suitable substitute to conventional enzymatic reporter systems in diagnostics. This review will provide a brief overview of the G-quadruplex architecture as well as the many forms of reporter systems ranging from absorbance to luminescence readouts in various platforms. Furthermore, some challenges and improvements that have been introduced to improve the application of G-quadruplex in diagnostics will be highlighted. As the field of diagnostics has evolved to apply different detection systems, the need for alternative reporter systems such as G-quadruplexes is also paramount.

Characterization of ssDNA aptamers specifically directed against Trachinotus ovatus NNV (GTONNV)-infected cells with antiviral activities

Nervous necrosis virus (NNV), is one of the most fatal viruses in marine fish aquaculture, and is capable of infecting over 50 different fish species. Trachinotus ovatus NNV (GTONNV) was isolated from diseased golden pompano. This T. ovatus strain was isolated from Guangxi, China. Single-stranded DNA (ssDNA) aptamers with high specificity for GTONNV-infected T. ovatus cerebellum cells (TOCC) were produced by Systematic Evolution of Ligands by Exponential Enrichment (SELEX). The characterization of these aptamers was performed using flow cytometry and laser scanning confocal microscopy. The selected aptamers showed significant specificity for GTONNV-infected cells. Based on MFOLD prediction, aptamers formed distinct stem-loop structures that could form the basis for the aptamers' specific binding to their cellular targets. Protease treatment results revealed that the target molecules for aptamers TNA1, TNA4 and TNA19 within GTONNV-infected cells may be membrane proteins that were trypsin-sensitive. Specific endocytosis of aptamer TNA1, TNA4 and TNA19 into GTONNV-infected cells was also shown. The selected aptamers demonstrated antiviral effects against GTONNV both in vitro and in vivo. This is the first time that aptamers targeting GTONNV-infected T. ovatus cells have been selected and characterized. These aptamers hold promise as rapid diagnostic reagents or targeted therapeutic drugs against GTONNV.

Oligonucleotide-Based Therapies for Inflammatory Bowel Disease

The growing understanding of the immunopathogenesis of inflammatory bowel diseases (IBDs) has contributed to the identification of new targets whose expression/activity can be modulated for therapeutic purposes. Several approaches have been employed to develop selective pharmaceutical compounds; among these, antisense oligonucleotides (ASOs) or synthetic oligonucleotides represent a valid option for inhibiting or enhancing, respectively, the expression/function of molecules that have been implicated in the control of IBD-related inflammation. In this context, data have been accumulated for the following compounds: alicaforsen, an ASO targeting intercellular adhesion molecule-1, a transmembrane glycoprotein that regulates rolling and adhesion of leukocytes to inflamed intestine; DIMS0150 and BL-7040, two oligonucleotides that enhance Toll-like receptor-9 activity; Mongersen, an ASO that inhibits Smad7, thereby restoring transforming growth factor-β1/Smad-associated signaling; STNM01, a double-stranded RNA oligonucleotide silencing carbohydrate sulfotransferase, an enzyme involved in fibrogenic processes, and hgd40, a specific DNAzyme inhibiting expression of the transcription factor GATA3. In this article, we review the rationale and the available data relative to the use of these agents in IBD. Although pre-clinical and phase II trials in IBD support the use of oligonucleotide-based therapies for treating the pathogenic process occurring in the gut of patients with these disorders, further work is needed to establish whether and which patients can benefit from specific ASOs and identify biomarkers that could help optimize treatment.

Molecular Application of Aptamers in the Diagnosis and Treatment of Cancer and Communicable Diseases

Cancer and infectious diseases such as Ebola, HIV, tuberculosis, Zika, hepatitis, measles and human schistosomiasis are serious global health hazards. The increasing annual morbidities and mortalities of these diseases have been blamed on drug resistance and the inefficacy of available diagnostic tools, particularly those which are immunologically-based. Antibody-based tools rely solely on antibody production for diagnosis and for this reason they are the major cause of diagnostic delays. Unfortunately, the control of these diseases depends on early detection and administration of effective treatment therefore any diagnostic delay is a huge challenge to curbing these diseases. Hence, there is a need for alternative diagnostic tools, discovery and development of novel therapeutic agents. Studies have demonstrated that aptamers could potentially offer one of the best solutions to these problems. Aptamers are short sequences of either DNA or RNA molecules, which are identified in vitro through a SELEX process. They are sensitive and bind specifically to target molecules. Their promising features suggest they may serve as better diagnostic agents and can be used as drug carriers for therapeutic purposes. In this article, we review the applications of aptamers in the theranostics of cancer and some infectious diseases.

Novel DNA Aptamers Against CCL21 Protein: Characterization and Biomedical Applications for Targeted Drug Delivery to T Cell-Rich Zones

The chemokine (C-C motif) ligand 21 (CCL21) is a cytokine that attracts CCR7-positive cells to the T cell (paracortical) zone of lymph nodes by directional migration of these cells along the CCL21 gradient. In this article, we sought to mimic this chemotactic mechanism, by identifying a novel aptamer that binds CCL21 with high affinity. In vitro selection of DNA aptamers was performed by the Systematic Evolution of Ligands by Exponential Enrichment. Quantitative polymerase chain reaction (qPCR) and enzyme-linked oligonucleotide assay were used to screen for high-affinity aptamers against human and mouse CCL21 protein, respectively. Three such aptamers were identified. Surface plasmon resonance showed equilibrium dissociation constant (K_d) for these three aptamers in the nano to picomolar range. Cytotoxicity assays showed <10% toxicity in HEK293 and HL-60 cells. Last, in vivo biodistribution was successfully performed and CCL21 chemokine-binding aptamers were quantified within the draining lymph nodes and spleen using qPCR. Fluorescence microscopy revealed that one of the aptamers showed significantly higher presence in the paracortex than the control aptamer. The use of anti-CCL21 aptamers to mimic the chemotaxis mechanism thus represents a promising approach to achieve targeted delivery of drugs to the T cell-rich zones of the lymph node. This may be important for the treatment of HIV infection and the eradication of HIV reservoirs.

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 affinity ligands in protein chromatography

The present review deals with the place of single chain oligonucleotide ligands (aptamers) in affinity chromatography applied to proteins. Aptamers are not the only affinity ligands available but they represent an emerging and highly promising route that advantageously competes with antibodies in immunopurification processes. A historical background of affinity chromatography from the beginning of the discipline to the most recent outcomes is first presented. Then the focus is centered on aptamers which represent the last step so far to the long quest for affinity ligands associating very high specificity, availability and strong stability against most harsh cleaning agents required in chromatography. Then technologies of ligand selection from large libraries followed by the most appropriate chemical grafting approaches are described and supported by a number of bibliographic references. Experimental results assembled from relevant published paper are reported; they are selected by their practical applicability and potential use at large scale. The review concludes with specific remarks and future developments that are expected in the near future to turn this technology into a large acceptance for preparative applications.

A DNA aptamer efficiently inhibits the infectivity of Bovine herpesvirus 1 by blocking viral entry

Bovine herpesvirus 1 (BoHV-1) is an important pathogen of domestic and wild cattle responsible for major economic losses in dairy and beef industries throughout the world. Inhibition of viral entry plays a crucial role in the control of BoHV-1 infection and aptamers have been reported to inhibit viral replication. In this study, nine DNA aptamers that target BoHV-1 were generated using systemic evolution of ligands by exponential enrichment. Of the nine candidates, aptamer IBRV-A4 exhibited the highest affinity and specificity for BoHV-1, which bound to BoHV-1 with a Kd value of 3.519 nM and demonstrated the greatest virus binding as shown by fluorescence imaging. The neutralizing ability of aptamer IBRV-A4 was determined using neutralization assays and real time PCR in BoHV-1 infected Madin-darby bovine kidney cells. Virus titration, immunofluorescence and confocal laser scanning microscopy showed virus replication significantly decreased when aptamer IBRV-A4 was added to BoHV-1 infected MDBK cells at 0 and 0.5 hours post-infection, whereas no change was seen when IBRV-A4 was added 2 hours post-infection. This concludes that aptamer IBRV-A4 efficiently inhibits viral entry of BoHV-1 in MDBK cells and is therefore a novel tool for diagnosis and treatment of BoHV-1 infection in cattle.

Development of Optimized Inhibitor RNAs Allowing Multisite-Targeting of the HCV Genome

Engineered multivalent drugs are promising candidates for fighting infection by highly variable viruses, such as HCV. The combination into a single molecule of more than one inhibitory domain, each with its own target specificity and even a different mechanism of action, results in drugs with potentially enhanced therapeutic properties. In the present work, the anti-HCV chimeric inhibitor RNA HH363-10, which has a hammerhead catalytic domain and an aptamer RNA domain, was subjected to an in vitro selection strategy to isolate ten different optimised chimeric inhibitor RNAs. The catalytic domain was preserved while the aptamer RNA domain was evolved to contain two binding sites, one mapping to the highly conserved IIIf domain of the HCV genome’s internal ribosome entry site (IRES), and the other either to IRES domain IV (which contains the translation start codon) or the essential linker region between domains I and II. These chimeric molecules efficiently and specifically interfered with HCV IRES-dependent translation in vitro (with IC₅₀ values in the low µM range). They also inhibited both viral translation and replication in cell culture. These findings highlight the feasibility of using in vitro selection strategies for obtaining improved RNA molecules with potential clinical applications.