Development of universal antidotes to control aptamer activity

Proteomics appending a complementary dimension to precision oncotherapy

Recent advances in high-throughput proteomic profiling technologies have facilitated the precise quantification of numerous proteins across multiple specimens concurrently. Researchers have the opportunity to comprehensively analyze the molecular signatures in plentiful medical specimens or disease pattern cell lines. Along with advances in data analysis and integration, proteomics data could be efficiently consolidated and employed to recognize precise elementary molecular mechanisms and decode individual biomarkers, guiding the precision treatment of tumors. Herein, we review a broad array of proteomics technologies and the progress and methods for the integration of proteomics data and further discuss how to better merge proteomics in precision medicine and clinical settings.

Targeted Delivery of AR-V7 siRNA with Bivalent PSMA Aptamers Effectively Suppresses the Growth of Enzalutamide-Resistant Prostate Cancer

Androgen deprivation therapy has been the primary treatment strategy for advanced prostate cancer (PCa). But most patients develop castration resistance over time. For FDA-approved second-generation androgen receptor (AR) antagonists, including enzalutamide (ENZ) and abiraterone (AA), patients who initially respond to them eventually develop resistance. The key mechanism for resistance to ENZ/AA involves AR splice variants (AR-Vs) and specifically AR-V7. Current AR antagonists cannot target AR-V7 due to its lack of the C-terminal ligand-binding domain (LBD) but keeping the AR N-terminal domain (NTD) which still can activate androgen-responsive genes. Therefore, targeting the AR NTD and AR-V7 is critically important to overcome ENZ resistance. Unfortunately, AR NTD has been considered an "undruggable" target due to the difficulty in defining its three-dimensional (3D) structure. In this context, siRNA is highly suitable to address this undruggable target. However, siRNA cannot freely diffuse into cells, and a carrier is needed. In this regard, nucleic acid-based aptamers are highly suitable for cell type-specific delivery of siRNA in vivo. In this study, we have developed a serum-stable bivalent prostate-specific membrane antigen (PSMA) aptamer-AR-V7 siRNA chimera (PAP). The results show that PAP can knock down both AR-full length and AR-V7 in PSMA-expressing castration-resistant cells. It can resensitize ENZ in cell lines and PCa xenografts. ENZ combined with PAP can significantly inhibit 22Rv1 xenograft growth in mice without experiencing castration. Owing to the low toxicity, PAP has potential to offer a new antiandrogen treatment for current ENZ-resistant PCa.

Computational aptamer design for spike glycoprotein (S) (SARS CoV-2) detection with an electrochemical aptasensor

A new bioinformatic platform (APTERION) was used to design in a short time and with high specificity an aptamer for the detection of the spike protein, a structural protein of SARS-CoV-2 virus, responsible for the COVID-19 pandemic. The aptamer concentration on the carbon electrode surface was optimized using static contact angle and fluorescence method, while specificity was tested using differential pulse voltammetry (DPV) associated to carbon screen-printed electrodes. The data obtained demonstrated the good features of the aptamer which could be used to create a rapid method for the detection of SARS-CoV-2 virus. In fact, it is specific for spike also when tested against bovine serum albumin and lysozyme, competitor proteins if saliva is used as sample to test for the virus presence. Spectrofluorometric characterization allowed to measure the amount of aptamer present on the carbon electrode surface, while DPV measurements proved the affinity of the aptamer towards the spike protein and gave quantitative results. The acquired data allowed to conclude that the APTERION bioinformatic platform is a good method for aptamer design for rapidity and specificity. KEY POINTS: • Spike protein detection using an electrochemical biosensor • Aptamer characterization by contact angle and fluorescent measurements on electrode surface • Computational design of specific aptamers to speed up the aptameric sequence time.

A neutralizable dimeric anti-thrombin aptamer with potent anticoagulant activity in mice

Heparin-induced thrombocytopenia (HIT) is a complication caused by administration of the anticoagulant heparin. Although the number of patients with HIT has drastically increased because of coronavirus disease 2019 (COVID-19), the currently used thrombin inhibitors for HIT therapy do not have antidotes to arrest the severe bleeding that occurs as a side effect; therefore, establishment of safer treatments for HIT patients is imperative. Here, we devised a potent thrombin inhibitor based on bivalent aptamers with a higher safety profile via combination with the antidote. Using an anti-thrombin DNA aptamer M08s-1 as a promising anticoagulant, its homodimer and heterodimer with TBA29 linked by a conformationally flexible linker or a rigid duplex linker were designed. The dimerized M08s-1-based aptamers had about 100-fold increased binding affinity to human and mouse thrombin compared with the monomer counterparts. Administration of these bivalent aptamers into mice revealed that the anticoagulant activity of the dimers significantly surpassed that of an approved drug for HIT treatment, argatroban. Moreover, adding protamine sulfate as an antidote against the most potent bivalent aptamer completely suppressed the anticoagulant activity of the dimer. Emerging potent and neutralizable anticoagulant aptamers will be promising candidates for HIT treatment with a higher safety profile.

A potent anticoagulant hybrid of snake venom derived FIX-binding protein and anti-factor IX RNA aptamer: Assessed by in-silico and electrochemical analyses

Anticoagulant therapies are crucial in the management of surgical complications as well as the prophylaxis of thrombosis. Many studies are being conducted on the Habu snake-venom anticoagulant, FIX-binding protein (FIX-Bp), for its greater potency and strong affinity to FIX clotting factor. On the other hand, the capacity to promptly reverse such acute anticoagulation is equally important. Combining a reversible anticoagulant with FIX-Bp may be advantageous in maintaining the balance between adequate anticoagulation and repealing when necessary. In this study, authors integrated FIX-Bp and RNA aptamer-based anticoagulants into a single target, FIX clotting factor, in order to achieve a robust anticoagulant effect. An in-silico and electrochemical approach were used to investigate the combination of FIX-Bp and RNA aptamers as a bivalent anticoagulant and to verify the competing or predominant binding sites of each anticoagulant. The in-silico analysis discovered that both the venom- and aptamer-anticoagulant had a strong affinity for the FIX protein at the Gla-domain and EGF-1 domain by holding 9 conventional hydrogen bonds with the binding energy of -34.859 kcal/mol. The electrochemical technique verified that both anticoagulants had different binding sites. The impedance load upon RNA aptamer binding to FIX protein was 14 %, whereas the addition of FIX-Bp caused a significant impedance rise of 37 %. This indicates that the addition of aptamers prior to FIX-Bp is a promising strategy for the conception of a hybrid anticoagulant.

In vitro selection of aptamers and their applications

The introduction of the in-vitro evolution method known as SELEX (Systematic Evolution of Ligands by Exponential enrichment) more than 30 years ago led to the conception of versatile synthetic receptors known as aptamers. Offering many benefits such as low cost, high stability and flexibility, aptamers have sparked innovation in molecular diagnostics, enabled advances in synthetic biology and have facilitated new therapeutic approaches. The SELEX method itself is inherently adaptable and offers near limitless possibilities in yielding functional nucleic acid ligands. This Primer serves to provide guidance on experimental design and highlight new growth areas for this impactful technology.

RNA aptamers with specific binding affinity to CD40 (CD40Apt) represents a promising antagonist of the CD40-CD40L signaling for thyroid-associated ophthalmopathy (TAO) treatment in mouse

Thyroid-associated ophthalmopathy (TAO) is the most common autoimmune inflammatory diseases of the orbit. The CD40-CD40L pathway has been regarded as a potential molecular mechanism contributing to the development and progression of TAO, and RNA aptamers with specific binding affinity to CD40 (CD40Apt) represents a promising inhibitor of the CD40-CD40L signaling in TAO treatment. In this study, CD40Apt was confirmed to specifically recognize mouse CD40-positive ortibtal fibroblast. Mouse orbital fibroblasts were isolated from TAO mice model orbital tissues and validated. In TGF-β-induced orbital fibroblast activation model in vitro, CD40Apt administration inhibited TGF-β-induced cell viability, decreased TGF-β-induced α-SMA, Collagen I, Timp-1, and vimentin levels, and suppressed TGF-β-induced phosphorylation of Erk, p38, JNK, and NF-κB. In TAO mice model in vivo, CD40Apt caused no significant differences to the body weight of mice; furthermore, CD40Apt improved the eyelid broadening, ameliorated inflammatory infiltration and the hyperplasia in orbital muscle and adipose tissues in model mice. Concerning orbital fibroblast activation, CD40Apt reduced the levels of CD40, collagen I, TGF-β, and α-SMA in orbital muscle and adipose tissues of model mice. Finally, CD40Apt administration significantly suppressed Erk, p38, JNK, and NF-κB phosphorylation. In conclusion, CD40Apt, specifically binds to CD40 proteins in their natural state on the cell surface with high affinity, could suppress mouse orbital fibroblast activation, therefore improving TAO in mice model through the CD40 and downstream signaling pathways. CD40Apt represents a promising antagonist of the CD40-CD40L signaling for TAO treatment.

Applications and future of aptamers that achieve rapid-onset anticoagulation

In this short Perspective, we discuss the history of, and recent progress toward, the development of aptamers that can serve as rapid onset anticoagulants during cardiopulmonary bypass (CPB), extracorporeal membrane oxygenation (ECMO), and catheter-based diagnostic and interventional procedures, several million of which are performed each year worldwide. Aptamer anticoagulants provide potent and antidote-controllable anticoagulation and have low immunogenicity. New methods of aptamer isolation and engineering have not only improved the quality of aptamers, but also accelerated their development. Unfortunately, no aptamer identified to date can produce an anticoagulant effect as potent as that produced by unfractionated heparin (UFH), the standard anticoagulant for CPB. We have suggested several possible strategies to amplify the anticoagulant potency of existing aptamer anticoagulants.

Aptamers in cancer therapy: problems and new breakthroughs

Aptamers, a class of oligonucleotides that can bind with molecular targets with high affinity and specificity, have been widely applied in research fields including biosensing, imaging, diagnosing, and therapy of diseases. However, compared with the rapid development in the research fields, the clinical application of aptamers is progressing at a much slower speed, especially in the therapy of cancer. Obstructions including nuclease degradation, renal clearance, a complex selection process, and potential side effects have inhibited the clinical transformation of aptamer-conjugated drugs. To overcome these problems, taking certain measures to improve the biocompatibility and stability of aptamer-conjugated drugs in vivo is necessary. In this review, the obstructions mentioned above are thoroughly discussed and the methods to overcome these problems are introduced in detail. Furthermore, landmark research works and the most recent studies on aptamer-conjugated drugs for cancer therapy are also listed as examples, and the future directions of research for aptamer clinical transformation are discussed.

Therapeutic Potential of Aptamer-Protein Interactions

Aptamers are single-stranded oligonucleotides (RNA or DNA) with a typical length between 25 and 100 nucleotides which fold into three-dimensional structures capable of binding to target molecules. Specific aptamers can be isolated against a large variety of targets through efficient and relatively cheap methods, and they demonstrate target-binding affinities that sometimes surpass those of antibodies. Consequently, interest in aptamers has surged over the past three decades, and their application has shown promise in advancing knowledge in target analysis, designing therapeutic interventions, and bioengineering. With emphasis on their therapeutic applications, aptamers are emerging as a new innovative class of therapeutic agents with promising biochemical and biological properties. Aptamers have the potential of providing a feasible alternative to antibody- and small-molecule-based therapeutics given their binding specificity, stability, low toxicity, and apparent non-immunogenicity. This Review examines the general properties of aptamers and aptamer-protein interactions that help to understand their binding characteristics and make them important therapeutic candidates.

Factor XI/XIa Inhibition: The Arsenal in Development for a New Therapeutic Target in Cardio- and Cerebrovascular Disease

Despite major advancements in the development of safer and more effective anticoagulant agents, bleeding complications remain a significant concern in the treatment of thromboembolic diseases. Improvements in our understanding of the coagulation pathways highlights the notion that the contact pathway-specifically factor XI (FXI)-has a greater role in the etiopathogenesis of thrombosis than in physiological hemostasis. As a result, a number of drugs targeting FXI are currently in different stages of testing and development. This article aims to review the different strategies directed towards FXI-inhibition with a brief summation of the agents in clinical development, and to comment on the therapeutic areas that could be explored for potential indications. Therapeutics targeting FXI/FXIa inhibition have the potential to usher in a new era of anticoagulation therapy.

Targeting DAMPs with nucleic acid scavengers to treat lupus

Systemic lupus erythematosus (SLE) is a chronic and often progressive autoimmune disorder marked clinically by a variable constellation of symptoms including fatigue, rash, joint pains, and kidney damage. The lungs, heart, gastrointestinal system, and brain can also be impacted, and individuals with lupus are at higher risk for atherosclerosis, thrombosis, thyroid disease, and other disorders associated with chronic inflammation . Autoimmune diseases are marked by erroneous immune responses in which the target of the immune response is a "self"-antigen, or autoantigen, driven by the development of antigen-specific B or T cells that have overcome the normal systems of self-tolerance built into the development of B and T cells. SLE is specifically characterized by the production of autoantibodies against nucleic acids and their binding proteins, including anti-double stranded DNA, anti-Smith (an RNA binding protein), and many others . These antibodies bind their nuclear-derived antigens to form immune complexes that cause injury and scarring through direct deposition in tissues and activation of innate immune cells . In over 50% of SLE patients, immune complex aggregation in the kidneys drives intrarenal inflammation and injury and leads to lupus nephritis, a progressive destruction of the glomeruli that is one of the most common causes of lupus-related death . To counter this pathology increasing attention has turned to developing approaches to reduce the development and continued generation of such autoantibodies. In particular, the molecular and cellular events that lead to long term, continuous activation of such autoimmune responses have become the focus of new therapeutic strategies to limit renal and other pathologies in lupus patients. The focus of this review is to consider how the innate immune system is involved in the development and progression of lupus nephritis and how a novel approach to inhibit innate immune activation by neutralizing the activators of this response, called Damage Associated Molecular Patterns, may represent a promising approach to treat this and other autoimmune disorders.

Combining Heparin and a FX/Xa Aptamer to Reduce Thrombin Generation in Cardiopulmonary Bypass and COVID-19

Known limitations of unfractionated heparin (UFH) have encouraged the evaluation of anticoagulant aptamers as alternatives to UFH in highly procoagulant settings such as cardiopulmonary bypass (CPB). Despite progress, these efforts have not been totally successful. We take a different approach and explore whether properties of an anticoagulant aptamer can complement UFH, rather than replace it, to address shortcomings with UFH use. Combining RNA aptamer 11F7t, which targets factor X/Xa, with UFH (or low molecular weight heparin) yields a significantly enhanced anticoagulant cocktail effective in normal and COVID-19 patient blood. This aptamer-UFH combination (1) supports continuous circulation of human blood through an ex vivo membrane oxygenation circuit, as is required for patients undergoing CPB and COVID-19 patients requiring extracorporeal membrane oxygenation, (2) allows for a reduced level of UFH to be employed, (3) more effectively limits thrombin generation compared to UFH alone, and (4) is rapidly reversed by the administration of protamine sulfate, the standard treatment for reversing UFH clinically following CPB. Thus, the combination of factor X/Xa aptamer and UFH has significantly improved anticoagulant properties compared to UFH alone and underscores the potential of RNA aptamers to improve medical management of acute care patients requiring potent yet rapidly reversible anticoagulation.

Aptamer-based factor IXa inhibition preserves hemostasis and prevents thrombosis in a piglet model of ECMO

Extracorporeal membrane oxygenation (ECMO) requires anticoagulation to prevent clotting when the patient’s blood contacts the circuit. Unfractionated heparin (UFH) usually prevents clotting but can cause life-threatening bleeding. An anticoagulant that selectively inhibits the contact activation (intrinsic) pathway while sparing the tissue factor (extrinsic) pathway of coagulation might prevent clotting triggered by the circuit while permitting physiologic coagulation at surgical sites. DTRI-178 is an RNA anticoagulant aptamer conjugated to polyethylene glycol that increases its half-life in circulation. This aptamer is based on a previously described molecule (9.3t) that inhibits intrinsic tenase activity by binding to factor IXa on an exosite. Using a piglet model of pediatric venoarterial (VA) ECMO, we compared thromboprevention and blood loss using a single dose of DTRI-178 versus UFH. In each of five experiments, we subjected two litter-matched piglets, one anticoagulated with DTRI-178 and the other with UFH, to simultaneous 12-h periods of VA ECMO. Both anticoagulants achieved satisfactory and comparable thromboprotection. However, UFH piglets had increased surgical site bleeding and required significantly greater blood transfusion volumes than piglets anticoagulated with DTRI-178. Our results indicate that DTRI-178, an aptamer against factor IXa, may be feasible, safer, and result in fewer transfusions and clinical bleeding events in ECMO.

Generation of an anticoagulant aptamer that targets factor V/Va and disrupts the FVa-membrane interaction in normal and COVID-19 patient samples

Coagulation cofactors profoundly regulate hemostasis and are appealing targets for anticoagulants. However, targeting such proteins has been challenging because they lack an active site. To address this, we isolate an RNA aptamer termed T18.3 that binds to both factor V (FV) and FVa with nanomolar affinity and demonstrates clinically relevant anticoagulant activity in both plasma and whole blood. The aptamer also shows synergy with low molecular weight heparin and delivers potent anticoagulation in plasma collected from patients with coronavirus disease 2019 (COVID-19). Moreover, the aptamer's anticoagulant activity can be rapidly and efficiently reversed using protamine sulfate, which potentially allows fine-tuning of aptamer's activity post-administration. We further show that the aptamer achieves its anticoagulant activity by abrogating FV/FVa interactions with phospholipid membranes. Our success in generating an anticoagulant aptamer targeting FV/Va demonstrates the feasibility of using cofactor-binding aptamers as therapeutic protein inhibitors and reveals an unconventional working mechanism of an aptamer by interrupting protein-membrane interactions.

Basic Principles and Recent Advances in Magnetic Cell Separation

Magnetic cell separation has become a key methodology for the isolation of target cell populations from biological suspensions, covering a wide spectrum of applications from diagnosis and therapy in biomedicine to environmental applications or fundamental research in biology. There now exists a great variety of commercially available separation instruments and reagents, which has permitted rapid dissemination of the technology. However, there is still an increasing demand for new tools and protocols which provide improved selectivity, yield and sensitivity of the separation process while reducing cost and providing a faster response. This review aims to introduce basic principles of magnetic cell separation for the neophyte, while giving an overview of recent research in the field, from the development of new cell labeling strategies to the design of integrated microfluidic cell sorters and of point-of-care platforms combining cell selection, capture, and downstream detection. Finally, we focus on clinical, industrial and environmental applications where magnetic cell separation strategies are amongst the most promising techniques to address the challenges of isolating rare cells.

Aptamer grafted nanoparticle as targeted therapeutic tool for the treatment of breast cancer

Breast carcinomas repeat their number and grow exponentially making it extremely frequent malignancy among women. Approximately, 70-80% of early diagnosed or non-metastatic conditions are treatable while the metastatic cases are considered ineffective to treat with current ample amount of therapy. Target based anti-cancer treatment has been in the limelight for decades and is perceived significant consideration of scientists. Aptamers are the 'coming of age' therapeutic approach, selected using an appropriate tool from the library of sequences. Aptamers are non-immunogenic, stable, and high-affinity ligand which are poised to reach the clinical benchmark. With the heed in nanoparticle application, the delivery of aptamer to the specific site could be enhanced which also protects them from nuclease degradation. Moreover, nanoparticles due to robust structure, high drug entrapment, and modifiable release of cargo could serve as a successful candidate in the treatment of breast carcinoma. This review would showcase the method and modified method of selection of aptamers, aptamers that were able to make its way towards clinical trial and their targetability and selectivity towards breast cancers. The appropriate usage of aptamer-based biosensor in breast cancer diagnosis have also been discussed.

The natural history of the concept of antidote

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For several centuries, the antidote paradigm was the same as the drug paradigm.

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However, when chemistry progressed, the concepts of a specific chemical antidote were assumed.

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In the face of the increasing number of acute poisoning, the ideas of a universal antidote play a more critical role.

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The development of toxicology prompts reflection on the price of civilization progress.

Over the centuries, the development of knowledge about poisons and antidotes depended on their conceptualization, however, a range of poisons and the concept of antidote evolved. With the passing of time, different substances of plant, animal, and mineral origin, moreover, man-made ones, were used deliberatively, accidentally, or unintentionally as poisons. The concept of antidote was changing in line with the progress of medicine and understanding of the mechanism of how poison works. From this perspective, the history of antidotes may be considered as the quintessence of changes within toxicology. Among the theories of antidote, the most interesting is the concept of a universal one, because it has never become obsolete. This review article focuses on the changing conceptualization of antidotes. It contains an analysis of historical toxicological treatises on antidotes and PubMed articles on the same topic.

Aptamers Against Live Targets: Is In Vivo SELEX Finally Coming to the Edge?

Targeted therapeutics underwent a revolution with the entry of monoclonal antibodies in the medical toolkit. Oligonucleotide aptamers form another family of target agents that have been lagging behind in reaching the clinical arena in spite of their potential clinical translation. Some of the reasons for this might be related to the challenge in identifying aptamers with optimal in vivo specificity, and the nature of their pharmacokinetics. Aptamers usually show exquisite specificity, but they are also molecules that display dynamic structures subject to changing environments. Temperature, ion atmosphere, pH, and other variables are factors that could determine the affinity and specificity of aptamers. Thus, it is important to tune the aptamer selection process to the conditions in which you want your final aptamer to function; ideally, for in vivo applications, aptamers should be selected in an in vivo-like system or, ultimately, in a whole in vivo organism. In this review we recapitulate the implementations in systematic evolution of ligands by exponential enrichment (SELEX) to obtain aptamers with the best in vivo activity.

An Appraisal of Antidotes' Effectiveness: Evidence of the Use of Phyto-Antidotes and Biotechnological Advancements

Poisoning is the greatest source of avoidable death in the world and can result from industrial exhausts, incessant bush burning, drug overdose, accidental toxication or snake envenomation. Since the advent of Albert Calmette’s cobra venom antidote, efforts have been geared towards antidotes development for various poisons to date. While there are resources and facilities to tackle poisoning in urban areas, rural areas and developing countries are challenged with poisoning management due to either the absence of or inadequate facilities and this has paved the way for phyto-antidotes, some of which have been scientifically validated. This review presents the scope of antidotes’ effectiveness in different experimental models and biotechnological advancements in antidote research for future applications. While pockets of evidence of the effectiveness of antidotes exist in vitro and in vivo with ample biotechnological developments, the utilization of analytic assays on existing and newly developed antidotes that have surpassed the proof of concept stage, as well as the inclusion of antidote’s short and long-term risk assessment report, will help in providing the required scientific evidence(s) prior to regulatory authorities’ approval.

Aptamers as Reversible Sorting Ligands for Preparation of Cells in Their Native State

Although antibodies are routinely used to label and isolate a desired cell type from a more complex mixture of cells, via either fluorescence-activated cell sorting (FACS) or magnetic-activated cell sorting (MACS), such antibody labeling is not easily reversible. We describe an FACS and MACS compatible method to reversibly label and purify cells using aptamers. Magnetic beads loaded with the epidermal growth factor receptor (EGFR)-binding antagonistic aptamer E07 specifically isolated EGFR-expressing cells, and pure, label-free cells were recovered via treatment with an "antidote" oligonucleotide complementary to the aptamer. Additionally, while FACS sorting cells with E07 or EGFR antibody yielded EGFR(+) cells with impeded EGFR signaling, stripping off the aptamer via antidote treatment restored receptor function, returning cells to their native state, which was not possible with the antibody. The ability to reversibly label or isolate cells without compromising their function is a valuable, versatile tool with important implications for both the laboratory and clinic.

G-Quadruplex-Forming Aptamers-Characteristics, Applications, and Perspectives

G-quadruplexes constitute a unique class of nucleic acid structures formed by G-rich oligonucleotides of DNA- or RNA-type. Depending on their chemical nature, loops length, and localization in the sequence or structure molecularity, G-quadruplexes are highly polymorphic structures showing various folding topologies. They may be formed in the human genome where they are believed to play a pivotal role in the regulation of multiple biological processes such as replication, transcription, and translation. Thus, natural G-quadruplex structures became prospective targets for disease treatment. The fast development of systematic evolution of ligands by exponential enrichment (SELEX) technologies provided a number of G-rich aptamers revealing the potential of G-quadruplex structures as a promising molecular tool targeted toward various biologically important ligands. Because of their high stability, increased cellular uptake, ease of chemical modification, minor production costs, and convenient storage, G-rich aptamers became interesting therapeutic and diagnostic alternatives to antibodies. In this review, we describe the recent advances in the development of G-quadruplex based aptamers by focusing on the therapeutic and diagnostic potential of this exceptional class of nucleic acid structures.

Duplexed aptamers: history, design, theory, and application to biosensing

Nucleic acid aptamers are single stranded DNA or RNA sequences that specifically bind a cognate ligand. In addition to their widespread use as stand-alone affinity binding reagents in analytical chemistry, aptamers have been engineered into a variety of ligand-specific biosensors, termed aptasensors. One of the most common aptasensor formats is the duplexed aptamer (DA). As defined herein, DAs are aptasensors containing two nucleic acid elements coupled via Watson-Crick base pairing: (i) an aptamer sequence, which serves as a ligand-specific receptor, and (ii) an aptamer-complementary element (ACE), such as a short DNA oligonucleotide, which is designed to hybridize to the aptamer. The ACE competes with ligand binding, such that DAs generate a signal upon ligand-dependent ACE-aptamer dehybridization. DAs possess intrinsic advantages over other aptasensor designs. For example, DA biosensing designs generalize across DNA and RNA aptamers, DAs are compatible with many readout methods, and DAs are inherently tunable on the basis of nucleic acid hybridization. However, despite their utility and popularity, DAs have not been well defined in the literature, leading to confusion over the differences between DAs and other aptasensor formats. In this review, we introduce a framework for DAs based on ACEs, and use this framework to distinguish DAs from other aptasensor formats and to categorize cis- and trans-DA designs. We then explore the ligand binding dynamics and chemical properties that underpin DA systems, which fall under conformational selection and induced fit models, and which mirror classical SN1 and SN2 models of nucleophilic substitution reactions. We further review a variety of in vitro and in vivo applications of DAs in the chemical and biological sciences, including riboswitches and riboregulators. Finally, we present future directions of DAs as ligand-responsive nucleic acids. Owing to their tractability, versatility and ease of engineering, DA biosensors bear a great potential for the development of new applications and technologies in fields ranging from analytical chemistry and mechanistic modeling to medicine and synthetic biology.

Comparison of Effects of Anti-thrombin Aptamers HD1 and HD22 on Aggregation of Human Platelets, Thrombin Generation, Fibrin Formation, and Thrombus Formation Under Flow Conditions

HD1 and HD22 are two of the most-studied aptamers binding to thrombin exosite I and exosite, respectively. To complete of their pharmacological profiles, the effects of HD1 and HD22 on thrombin-, ristocetin-, and collagen-induced human platelet aggregation, on thrombin generation and fibrin formation in human plasma, as well as on thrombus formation in human whole blood under flow conditions were assessed. The dissociation constants for HD1 and HD22 complexes with thrombin in simulated plasma ionic buffer were also evaluated. HD1 was more potent than HD22 in terms of inhibiting thrombin-induced platelet aggregation in platelet-rich plasma (PRP; 0.05-3 μM) and in washed platelets (WPs; 0.005-3 μM): approximately 8.31% (±6.99% SD) and 89.53% (±11.38% SD) for HD1 (0.5 μM) and HD22 (0.5 μM), respectively. Neither HD1 nor HD22 (3 μM) did influence platelets aggregation induced by collagen. Both of them inhibited ristocetin-induced aggregation in PRP. Surprisingly, HD1 and HD22 aptamers (3 μM) potentiated ristocetin-induced platelet aggregation in WP. HD1 reduced thrombin generation in a concentration-dependent manner [ETP at 3 μM: 1677.53 ± 55.77 (nM⋅min) vs. control 2271.71 ± 423.66 (nM⋅min)], inhibited fibrin formation (lag time at 3 μM: 33.70 min ± 8.01 min vs. control 7.91 min ± 0.91 min) and reduced thrombus formation under flow conditions [AUC30 at 3 μM: 758.30 ± 344.23 (kPa⋅min) vs. control 1553.84 ± 118.03 (kPa⋅min)]. HD22 (3 μM) also delayed thrombin generation but increased the thrombin peak. HD22 (3 μM) shortened the lag time of fibrin generation (5.40 min ± 0.26 min vs. control 7.58 min ± 1.14 min) but did not modify thrombus formation (3, 15 μM). K d values for the HD1 complex with thrombin was higher (257.8 ± 15.0 nM) than the K d for HD22 (97.6 ± 2.2 nM). In conclusion, HD1 but not HD22 represents a potent anti-thrombotic agent, confirming the major role of exosite I in the action of thrombin. HD22 aptamer blocking exosite II displays weaker anti-platelet and anti-coagulant activity, with surprising activating effects on thrombin and fibrin generation most likely induced by HD22-induced allosteric changes in thrombin dynamic structure.

Aptamer-iRNAs as Therapeutics for Cancer Treatment

Aptamers are single-stranded oligonucleotides (ssDNA or ssRNA) that bind and recognize their targets with high affinity and specificity due to their complex tertiary structure. Aptamers are selected by a method called SELEX (Systematic Evolution of Ligands by EXponential enrichment). This method has allowed the selection of aptamers to different types of molecules. Since then, many aptamers have been described for the potential treatment of several diseases including cancer. It has been described over the last few years that aptamers represent a very useful tool as therapeutics, especially for cancer therapy. Aptamers, thanks to their intrinsic oligonucleotide nature, present inherent advantages over other molecules, such as cell-based products. Owing to their higher tissue penetrability, safer profile, and targeting capacity, aptamers are likely to become a novel platform for the delivery of many different types of therapeutic cargos. Here we focus the review on interfering RNAs (iRNAs) as aptamer-based targeting delivered agents. We have gathered the most reliable information on aptamers as targeting and carrier agents for the specific delivery of siRNAs, shRNA, microRNAs, and antisense oligonucleotides (ASOs) published in the last few years in the context of cancer therapy.

Cationic nanoparticle as an inhibitor of cell-free DNA-induced inflammation

Cell-free DNA (cfDNA) released from damaged or dead cells can activate DNA sensors that exacerbate the pathogenesis of rheumatoid arthritis (RA). Here we show that ~40 nm cationic nanoparticles (cNP) can scavenge cfDNA derived from RA patients and inhibit the activation of primary synovial fluid monocytes and fibroblast-like synoviocytes. Using clinical scoring, micro-CT images, MRI, and histology, we show that intravenous injection of cNP into a CpG-induced mouse model or collagen-induced arthritis rat model can relieve RA symptoms including ankle and tissue swelling, and bone and cartilage damage. This culminates in the manifestation of partial mobility recovery of the treated rats in a rotational cage test. Mechanistic studies on intracellular trafficking and biodistribution of cNP, as well as measurement of cytokine expression in the joints and cfDNA levels in systemic circulation and inflamed joints also correlate with therapeutic outcomes. This work suggests a new direction of nanomedicine in treating inflammatory diseases.

Cell-free DNA (cfDNA) released from damaged or dead cells can activate DNA sensors that exacerbate the pathogenesis of rheumatoid arthritis (RA). Here the authors use ~40 nm cationic nanoparticles to scavenge cfDNA, and demonstrate the potential for nanomedicine to relieve debilitating RA symptoms.

Aptamer-based targeted therapy

Precision medicine holds great promise to harness genetic and epigenetic cues for targeted treatment of a variety of diseases, ranging from many types of cancers, neurodegenerative diseases, to cardiovascular diseases. The proteomic profiles resulting from the unique genetic and epigenetic signatures represent a class of relatively well accessible molecular targets for both interrogation (e.g., diagnosis, prognosis) and intervention (e.g., targeted therapy) of these diseases. Aptamers are promising for such applications by specific binding with cognate disease biomarkers. Nucleic acid aptamers are a class of DNA or RNA with unique three-dimensional conformations that allow them to specifically bind with target molecules. Aptamers can be relatively easily screened, reproducibly manufactured, programmably designed, and chemically modified for various biomedical applications, including targeted therapy. Aptamers can be chemically modified to resist enzymatic degradation or optimize their pharmacological behaviors, which ensured their chemical integrity and bioavailability under physiological conditions. In this review, we will focus on recent progress and discuss the challenges and opportunities in the research areas of aptamer-based targeted therapy in the forms of aptamer therapeutics and aptamer-drug conjugates (ApDCs).

Scavenging Circulating Mitochondrial DNA as a Potential Therapeutic Option for Multiple Organ Dysfunction in Trauma Hemorrhage

Trauma is a leading cause of death worldwide with 5.8 million deaths occurring yearly. Almost 40% of trauma deaths are due to bleeding and occur in the first few hours after injury. Of the remaining severely injured patients up to 25% develop a dysregulated immune response leading to multiple organ dysfunction syndrome (MODS). Despite improvements in trauma care, the morbidity and mortality of this condition remains very high. Massive traumatic injury can overwhelm endogenous homeostatic mechanisms even with prompt treatment. The underlying mechanisms driving MODS are also not fully elucidated. As a result, successful therapies for trauma-related MODS are lacking. Trauma causes tissue damage that releases a large number of endogenous damage-associated molecular patterns (DAMPs). Mitochondrial DAMPs released in trauma, such as mitochondrial DNA (mtDNA), could help to explain part of the immune response in trauma given the structural similarities between mitochondria and bacteria. MtDNA, like bacterial DNA, contains an abundance of highly stimulatory unmethylated CpG DNA motifs that signal through toll-like receptor-9 to produce inflammation. MtDNA has been shown to be highly damaging when injected into healthy animals causing acute organ injury to develop. Elevated circulating levels of mtDNA have been reported in trauma patients but an association with clinically meaningful outcomes has not been established in a large cohort. We aimed to determine whether mtDNA released after clinical trauma hemorrhage is sufficient for the development of MODS. Secondly, we aimed to determine the extent of mtDNA release with varying degrees of tissue injury and hemorrhagic shock in a clinically relevant rodent model. Our final aim was to determine whether neutralizing mtDNA with the nucleic acid scavenging polymer, hexadimethrine bromide (HDMBr), at a clinically relevant time point in vivo would reduce the severity of organ injury in this model.

CONCLUSIONS

We have shown that the release of mtDNA is sufficient for the development of multiple organ injury. MtDNA concentrations likely peak at different points in the early postinjury phase dependent on the degree of isolated trauma vs combined trauma and hemorrhagic shock. HDMBr scavenging of circulating mtDNA (and nuclear DNA, nDNA) is associated with rescue from severe multiple organ injury in the animal model. This suggests that HDMBr could have utility in rescue from human trauma-induced MODS.

Evaluation of activated charcoal and lipid emulsion treatment in model of acute rivaroxaban toxicity

AIM

Reducing or reversing the toxicity effects of new oral anticoagulants is an important question.The purpose of the present study is to evaluate the effect of lipid emulsion (LE) and Activated Charcoal (AC) therapy on the intoxication of rivaroxaban, on mice.

METHODS

Adult male Balb/c mice weighing approximately 30g were used in the study. Seven groups were assigned, with six mice in each group. Groups were defined; given only rivaroxaban, given only LE, given only AC, after the administration of rivaroxaban LE applied group in the 1st hour, after the administration of rivaroxaban LE applied group in the 3rd hour, after the administration of rivaroxaban AC applied group in the1st hour, after the administration of rivaroxaban AC applied group in the 1st hour and LE applied group in the 3rd hour. PT and Anti-Factor Xa activity were measured in all blood samples from subjects.

RESULTS

A statistically significant difference was found when all groups were compared in terms of mean PT values and Anti-FactorXa values. However, no statistically significant difference was found in the mean PT and Anti-FactorXa values when only rivaroxaban administrated group and after the administration of rivaroxaban LE and/or AC applied groups were compared one to one. No deaths occurred in groups during the observation.

CONCLUSION

Although the administration of either AC or LE alone or in combination resulted in a decrease in the mean values of PT and anti-Factor Xa, in case of rivaroxaban toxicity, but one-to-one comparison of the groups was not statistically significant.

Dynamic Control of Aptamer-Ligand Activity Using Strand Displacement Reactions

Nucleic acid aptamers are an expandable toolkit of sensors and regulators. To employ aptamer regulators within nonequilibrium molecular networks, the aptamer-ligand interactions should be tunable over time, so that functions within a given system can be activated or suppressed on demand. This is accomplished through complementary sequences to aptamers, which achieve programmable aptamer-ligand dissociation by displacing the aptamer from the ligand. We demonstrate the effectiveness of our simple approach on light-up aptamers as well as on aptamers inhibiting viral RNA polymerases, dynamically controlling the functionality of the aptamer-ligand complex. Mathematical models allow us to obtain estimates for the aptamer displacement kinetics. Our results suggest that aptamers, paired with their complement, could be used to build dynamic nucleic acid networks with direct control over a variety of aptamer-controllable enzymes and their downstream pathways.

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.

An in vivo strategy to counteract post-administration anticoagulant activity of azido-Warfarin

Drugs, usually long acting and metabolically stable molecules, might be the source of adverse effects triggered by complex drug interactions, anaphylaxis and drug-induced coagulopathy. To circumvent this growing drug safety issue, we herein investigate the opportunity offered by bio-orthogonal chemistry for in vivo drug neutralization. We design a small-molecule anticoagulant drug (Warfarin) containing an azide group that acts as a safety pin. It allows drug deactivation and restoration of physiological coagulation via in vivo click reaction with a suitable cyclooctyne-based neutralizing agent. In this strategy, the new molecule formed by reaction of the drug and the antidote is deprived of biological activity and prone to fast renal clearance. This 'Click &Clear' approach lays ground for new strategies in designing drugs with switchable biophysical properties.

Development of Cell-SELEX Technology and Its Application in Cancer Diagnosis and Therapy

SELEX (systematic evolution of ligands by exponential enrichment) is a process involving the progressive isolation of high selective ssDNA/RNA from a combinatorial single-stranded oligonucleotide library through repeated rounds of binding, partitioning and amplification. SELEX-derived single-stranded DNA/RNA molecules, called aptamers, are selected against a wide range of targets, including purified proteins, live cells, tissues, microorganisms, small molecules and so on. With the development of SELEX technology over the last two decades, various modified SELEX processes have been arisen. A majority of aptamers are selected against purified proteins through traditional SELEX. Unfortunately, more and more evidence showed aptamers selected against purified membrane proteins failed to recognize their targets in live cells. Cell-SELEX could develop aptamers against a particular target cell line to discriminate this cell line from others. Therefore, cell-SELEX has been widely used to select aptamers for the application of both diagnosis and therapy of various diseases, especially for cancer. In this review, the advantages and limitations of cell-SELEX and SELEX against purified protein will be compared. Various modified cell-SELEX techniques will be summarized, and application of cell-SELEX in cancer diagnosis and therapy will be discussed.

Identification of TIM3 2'-fluoro oligonucleotide aptamer by HT-SELEX for cancer immunotherapy

TIM3 belongs to a family of receptors that are involved in T-cell exhaustion and Treg functions. The development of new therapeutic agents to block this type of receptors is opening a new avenue in cancer immunotherapy. There are currently several clinical trials ongoing to combine different immune-checkpoint blockades to improve the outcome of cancer patients. Among these combinations we should underline PD1:PDL1 axis and TIM3 blockade, which have shown very promising results in preclinical settings. Most of these types of therapeutic agents are protein cell-derived products, which, although broadly used in clinical settings, are still subject to important limitations. In this work we identify by HT-SELEX TIM3 non-antigenic oligonucleotide aptamers (TIM3Apt) that bind with high affinity and specificity to the extracellular motives of TIM3 on the cell surface. The TIM3Apt1 in its monomeric form displays a potent antagonist capacity on TIM3-expressing lymphocytes, determining the increase of IFN-γ secretion. In colon carcinoma tumor-bearing mice, the combinatorial treatment of TIM3Apt1 and PDL1-antibody blockade is synergistic with a remarkable antitumor effect. Immunotherapeutic aptamers could represent an attractive alternative to monoclonal antibodies, as they exhibit important advantages; namely, lower antigenicity, being chemically synthesized agents with a lower price of manufacture, providing higher malleability, and antidote availability.

Aptamers: A New Technological Platform in Cancer Immunotherapy

The renaissance of cancer immunotherapy is, nowadays, a reality. In the near future, it will be very likely among the first-line treatments for cancer patients. There are several different approaches to modulate the immune system to fight against tumor maladies but, so far, monoclonal antibodies may currently be the most successful immuno-tools used to that end. The number of ongoing clinical trials with monoclonal antibodies has been increasing exponentially over the last few years upon the Food and Drug Administration (FDA) approval of the first immune-checkpoint blockade antibodies. In spite of the proved antitumor effect of these reagents, the unleashing of the immune system to fight cancer cells has a cost, namely auto-inflammatory toxicity. Additionally, only a small fraction of all patients treated with immune-checkpoint antibodies have a clinical benefit. Taking into account all this, it is urgent new therapeutic reagents are developed with a contained toxicity that could facilitate the combination of different immune-modulating pathways to broaden the antitumor effect in most cancer patients. Based on preclinical data, oligonucleotide aptamers could fulfill this need. Aptamers have not only been successfully used as antagonists of immune-checkpoint receptors, but also as agonists of immunostimulatory receptors in cancer immunotherapy. The simplicity of aptamers to be engineered for the specific delivery of different types of cargos to tumor cells and immune cells so as to harvest an efficient antitumor immune response gives aptamers a significant advantage over antibodies. In this review all of the recent applications of aptamers in cancer immunotherapy will be described.

In Vitro Evaluation of Aptamer-Based Reversible Inhibition of Anticoagulant Activated Protein C as a Novel Supportive Hemostatic Approach

Activated protein C (APC) is a critical regulator of thrombin formation and thereby protects against thrombosis. On the other hand, overwhelming formation of APC increases the risk of bleeding such as in trauma-induced coagulopathy. Thus, pharmacological inhibition of APC activity may improve blood clottability in certain clinical situations. In this study, we demonstrate that the DNA aptamer HS02-52G binds with fast onset (1.118 ± 0.013 × 10⁵ M^-1 s^-1) to APC and possesses a long residence time of 13.5 min within the aptamer-APC complex. Functional analysis revealed HS02-52G as a highly potent and specific inhibitor of APC in plasma and whole blood with IC₅₀ values ≤30 nM, whose activity can be readily neutralized by the short complementary DNA molecule AD22. These features qualify the novel aptamer-antidote pair as a candidate treatment option for acute APC-related bleedings.

Aptamers: A Feasible Technology in Cancer Immunotherapy

Aptamers are single-chained RNA or DNA oligonucleotides (ODNs) with three-dimensional folding structures which allow them to bind to their targets with high specificity. Aptamers normally show affinities comparable to or higher than that of antibodies. They are chemically synthesized and therefore less expensive to manufacture and produce. A variety of aptamers described to date have been shown to be reliable in modulating immune responses against cancer by either blocking or activating immune receptors. Some of them have been conjugated to other molecules to target the immune system and reduce off-target side effects. Despite the success of first-line treatments against cancer, the elevated number of relapsing cases and the tremendous side effects shown by the commonly used agents hinder conventional treatments against cancer. The advantages provided by aptamers could enhance the therapeutic index of a given strategy and therefore enhance the antitumor effect. Here we recapitulate the provided benefits of aptamers with immunomodulatory activity described to date in cancer therapy and the benefits that aptamer-based immunotherapy could provide either alone or combined with first-line treatments in cancer therapy.

Recent Progress in Aptamer-Based Functional Probes for Bioanalysis and Biomedicine

Nucleic acid aptamers are short synthetic DNA or RNA sequences that can bind to a wide range of targets with high affinity and specificity. In recent years, aptamers have attracted increasing research interest due to their unique features of high binding affinity and specificity, small size, excellent chemical stability, easy chemical synthesis, facile modification, and minimal immunogenicity. These properties make aptamers ideal recognition ligands for bioanalysis, disease diagnosis, and cancer therapy. This review highlights the recent progress in aptamer selection and the latest applications of aptamer-based functional probes in the fields of bioanalysis and biomedicine.

Status and Prospects of Aptamers as Drug Components

The unique properties of nucleic acid aptamers and their suitability to therapeutic applications have attracted the attention of researchers for more than 2 decades. Aptamers exhibit significant advantages relative to antibody-based therapeutics and can serve dual roles as either the therapeutic agent itself or a targeting modality. Despite this intense research interest, aptamers have been slow to reach the clinic, partly due to practical limitations that can be overcome by rational chemical modifications and ingenious aptamer selection approaches. This review highlights the latest efforts to use aptamers in therapeutic applications, the key properties of aptamers that can be exploited, the aptamers that are currently in clinical trials, as well as speculation on the future of aptamers in the field of nanomedicine.

Aptamers: A promising chemical antibody for cancer therapy

Aptamers, also known as chemical antibodies, are single-stranded nucleic acid oligonucleotides which bind to their targets with high specificity and affinity. They are typically selected by repetitive in vitro process termed systematic evolution of ligands by exponential enrichment (SELEX). Owing to their excellent properties compared to conventional antibodies, notably their smaller physical size and lower immunogenicity and toxicity, aptamers have recently emerged as a new class of agents to deliver therapeutic drugs to cancer cells by targeting specific cancer-associated hallmarks. Aptamers can also be structurally modified to make them more flexible in order to conjugate other agents such as nano-materials and therapeutic RNA agents, thus extending their applications for cancer therapy. This review presents the current knowledge on the practical applications of aptamers in the treatment of a variety of cancers.

Targeting inhibition of Foxp3 by a CD28 2'-Fluro oligonucleotide aptamer conjugated to P60-peptide enhances active cancer immunotherapy

The specific inhibition of Treg function has long been a major technical challenge in cancer immunotherapy. So far no single cell-surface marker has been identified that could be used to distinguish Treg cells from other lymphocytes. The only available specific marker mostly expressed in Treg is Foxp3, which is an intracellular transcription factor. A targeting molecule able to penetrate the membrane and inhibit Foxp3 within the cell is needed. P60-peptide is able to do that, but due to lack of target specificity, the doses are extremely high. In this study we have shown as a proof of concept that P60 Foxp3 inhibitor peptide can be conjugated with a CD28 targeting aptamer to deliver the peptide to CD28-expressing cells. The AptCD28-P60 construct is a clinically feasible reagent that improves the efficacy of the unconjugated P60 peptide very significantly. This approach was used to inhibit Treg function in a vaccination context, and it has shown a significant improvement in the induced immune response, entailing a lower tumor load in an antigen-specific cancer vaccine protocol.

Aptamers: current challenges and future prospects

INTRODUCTION

Aptamers are oligonucleotide molecules raised in vitro from large combinatorial libraries of nucleic acids and developed to bind to targets with high affinity and specificity. Whereas novel target molecules are proposed for therapeutic intervention and diagnostic, aptamer technology has a great potential to become a source of lead compounds.

AREAS COVERED

In this review, the authors address the current status of the technology and highlight the recent progress in aptamer-based technologies. They also discuss the current major technical limitations of aptamer technology and propose original solutions based on existing technologies that could result in a solid aptamer-discovery platform.

EXPERT OPINION

Whereas aptamers have shown to bind to targets with similar affinities and specificities to those of antibodies, aptamers have several advantages that could outweigh antibody technology and open new opportunities for better medical and diagnostic solutions. However, the current status of the aptamer technology suffers from several technical limitations that slowdown the progression of novel aptamers into the clinic and makes the business around aptamers challenging.

Targeting Two Coagulation Cascade Proteases with a Bivalent Aptamer Yields a Potent and Antidote-Controllable Anticoagulant

Potent and rapid-onset anticoagulation is required for several clinical settings, including cardiopulmonary bypass surgery. In addition, because anticoagulation is associated with increased bleeding following surgery, the ability to rapidly reverse such robust anticoagulation is also important. Previously, we observed that no single aptamer was as potent as heparin for anticoagulating blood. However, we discovered that combinations of two aptamers were as potent as heparin. Herein, we sought to combine two individual anticoagulant aptamers into a single bivalent RNA molecule in an effort to generate a single molecule that retained the potent anticoagulant activity of the combination of individual aptamers. We created four bivalent aptamers that can inhibit Factor X/Xa and prothrombin/thrombin and anticoagulate plasma, as well as the combination of individual aptamers. Detailed characterization of the shortest bivalent aptamer indicates that each aptamer retains full binding and functional activity when presented in the bivalent context. Finally, reversal of this bivalent aptamer with a single antidote was explored, and anticoagulant activity could be rapidly turned off in a dose-dependent manner. These studies demonstrate that bivalent anticoagulant aptamers represent a novel and potent approach to actively and reversibly control coagulation.

A Synthetic Aptamer-Drug Adduct for Targeted Liver Cancer Therapy

AS1411 (previously known as AGRO100) is a 26 nucleotide guanine-rich DNA aptamer which forms a guanine quadruplex structure. AS1411 has shown promising utility as a treatment for cancers in Phase I and Phase II clinical trials without causing major side-effects. AS1411 inhibits tumor cell growth by binding to nucleolin which is aberrantly expressed on the cell membrane of many tumors. In this study, we utilized a simple technique to conjugate a widely-used chemotherapeutic agent, doxorubicin (Dox), to AS1411 to form a synthetic Drug-DNA Adduct (DDA), termed as AS1411-Dox. We demonstrate the utility of AS1411-Dox in the treatment of hepatocellular carcinoma (HCC) by evaluating the targeted delivery of Dox to Huh7 cells in vitro and in a murine xenograft model of HCC.

Modulation of the Coagulation Cascade Using Aptamers

As a novel class of therapeutics, aptamers, or nucleic acid ligands, have garnered clinical interest because of the ease of isolating a highly specific aptamer against a wide range of targets, their chemical flexibility and synthesis, and their inherent ability to have their function reversed. The following review details the development and molecular mechanisms of aptamers targeting specific proteases in the coagulation cascade. The ability of these anticoagulant aptamers to bind to and inhibit exosite function rather than binding within the active site highlights the importance of exosites in blocking protein function. As both exosite inhibitors and reversible agents, the use of aptamers is a promising strategy for future therapeutics.