Turning mirror-image oligonucleotides into drugs: the evolution of Spiegelmer(®) therapeutics

An expanded substrate scope for cross-chiral ligation enables efficient synthesis of long l-RNAs

Despite the growing interest in mirror-image l-oligonucleotides, both as a robust nucleic acid analogue and as an artificial genetic polymer, their broader adoption in biochemical research and medicine remains hindered by challenges associated with the synthesis of long sequences, especially for l-RNA. Herein, we present a novel strategy for assembling long l-RNAs via the joining of two or more shorter fragments using cross-chiral ligase ribozymes together with new substrate activation chemistry. We show that 5'-monophosphorylated l-RNA, which is readily prepared by solid-phase synthesis, can be activated by chemical attachment of a 5'-adenosine monophosphate (AMP) or diphosphate (ADP), yielding 5'-adenosyl(di- or tri-)phosphate l-RNA. The activation reaction is performed in mild aqueous conditions, proceeds efficiently with short or large l-RNA, and, yielding few byproducts, requires little or no further purification after activation. Importantly, both groups, when added to l-RNA, are compatible with ribozyme-mediated ligation, with the 5'-adenosyltriphosphate permitting rapid and efficient joining of two long l-RNA strands. This is exemplified by the assembly of a 129-nt l-RNA molecule via a single cross-chiral ligation event. Overall, by relying on ribozymes that can be readily prepared by in vitro transcription and l-RNA substrates that can be activated through simple chemistry, these methods are expected to make long l-RNAs more accessible to a wider range of researchers and facilitate the expansion of l-ON-based technologies.

Progress in Aptamer Research and Future Applications

Aptamers are short, single-stranded DNA, RNA or synthetic XNA molecules that bind to target molecules with high specificity and affinity. These intrinsically structured RNA or DNA oligonucleotides are not only substitutes for antibodies, but also show great potential for applications in diagnostics, specific drug delivery, and treatment of certain diseases. While the process of aptamer identification and its core functional mechanism known as systematic evolution of exponentially enriched ligands (SELEX), SELEX involves a number of single processes, each contributing to the success or failure of aptamer generation. Today, aptamers are widely used to facilitate basic research discoveries and clinical diagnostics. In addition, aptamers play a promising role as clinical diagnostic and therapeutic agents. This review provides recent advances in this rapidly growing field of research, with special emphasis on aptamer generation and screening, small molecule aptamers, the development of aptamer applications, and applications in clinical medicine. And it also discusses the problems that still exist today with aptamers.

Recent advances in aptamer discovery, modification and improving performance

Aptamers are nucleic acid (Ribonucleic acid (RNA) and single strand deoxyribonucleic acid (ssDNA)) with a length of approximately 25-80 bases that can bind to particular target molecules, similar to monoclonal antibodies. Due to their many benefits, which include a long shelf life, minimal batch-to-batch variations, extremely low immunogenicity, the possibility of chemical modifications for improved stability, an extended serum half-life, and targeted delivery, they are receiving a lot of attention in a variety of clinical applications. The development of high-affinity modification approaches has attracted significant attention in aptamer applications. Stable three-dimensional aptamers that have undergone chemical modification can engage firmly with target proteins through improved non-covalent binding, potentially leading to hundreds of affinity improvements. This review demonstrates how cutting-edge methodologies for aptamer discovery are being developed to consistently and effectively construct high-performing aptamers that need less money and resources yet have a high chance of success. Also, High-affinity aptamer modification techniques were discussed.

The clinical potential of l-oligonucleotides: challenges and opportunities

Chemically modified nucleotides are central to the development of biostable research tools and oligonucleotide therapeutics. In this context, l-oligonucleotides, the synthetic enantiomer of native d-nucleic acids, hold great promise. As enantiomers, l-oligonucleotides share the same physical and chemical properties as their native counterparts, yet their inverted l-(deoxy)ribose sugars afford them orthogonality towards the stereospecific environment of biology. Notably, l-oligonucleotides are highly resistant to degradation by cellular nucleases, providing them with superior biostability. As a result, l-oligonucleotides are being increasingly utilized for the development of diverse biomedical technologies, including molecular imaging tools, diagnostic biosensors, and aptamer-based therapeutics. Herein, we present recent such examples that highlight the clinical potential of l-oligonucleotides. Additionally, we provide our perspective on the remaining challenges and practical considerations currently associated with the use of l-oligonucleotides and explore potential solutions that will lead to the broader adoption of l-oligonucleotides in clinical applications.

Specific Targeting and Imaging of RNA G-Quadruplex (rG4) Structure Using Non-G4-Containing l-RNA Aptamer and Fluorogenic l-Aptamer

RNA G-quadruplex structures (rG4s) play important roles in the regulation of biological processes. So far, all the l-RNA aptamers developed to target rG4 of interest contain G4 motif itself, raising the question of whether non-G4-containing l-RNA aptamer can be developed to target rG4. Furthermore, it is unclear whether an l-Aptamer-based tool can be generated for G4 detection in vitro and imaging in cells. Herein, a new strategy is designed using a low GC content template library to develop a novel non-G4-containing l-RNA aptamer with strong binding affinity and improved binding specificity to rG4 of interest. The first non-G4-containing l-Aptamer, l-Apt.1-1, is identified with nanomolar binding affinity to amyloid precursor protein (APP) D-rG4. l-Apt.1-1 is applied to control APP gene expression in cells via targeting APP D-rG4 structure. Moreover, the first l-RNA-based fluorogenic bi-functional aptamer (FLAP) system is developed, and l-Apt.1-1_Pepper is engineered for in vitro detection and cellular imaging of APP D-rG4. This work provides an original approach for developing non-G4-containing l-RNA aptamer for rG4 targeting, and the novel l-Apt.1-1 developed for APP gene regulation, as well as the l-Apt.1-1_Pepper generated for imaging of APP rG4 structure can be further used in other applications in vitro and in cells.

Nuclease-Resistant L-DNA Tension Probes Enable Long-Term Force Mapping of Single Cells and Cell Consortia

DNA-based tension probes with precisely programmable force responses provide important insights into cellular mechanosensing. However, their degradability in cell culture limits their use for long-term imaging, for instance, when cells migrate, divide, and differentiate. This is a critical limitation for providing insights into mechanobiology for these longer-term processes. Here, we present DNA-based tension probes that are entirely designed based on the stereoisomer of biological D-DNA, i.e., L-DNA. We demonstrate that L-DNA tension probes are essentially indestructible by nucleases and provide days-long imaging without significant loss in image quality. We also show their superiority already for short imaging times commonly used for classical D-DNA tension probes. We showcase the potential of these resilient probes to image minute movements, and for generating long term force maps of single cells and of collectively migrating cell populations.

A Visual Compendium of Principal Modifications within the Nucleic Acid Sugar Phosphate Backbone

Nucleic acid chemistry is a huge research area that has received new impetus due to the recent explosive success of oligonucleotide therapy. In order for an oligonucleotide to become clinically effective, its monomeric parts are subjected to modifications. Although a large number of redesigned natural nucleic acids have been proposed in recent years, the vast majority of them are combinations of simple modifications proposed over the past 50 years. This review is devoted to the main modifications of the sugar phosphate backbone of natural nucleic acids known to date. Here, we propose a systematization of existing knowledge about modifications of nucleic acid monomers and an acceptable classification from the point of view of chemical logic. The visual representation is intended to inspire researchers to create a new type of modification or an original combination of known modifications that will produce unique oligonucleotides with valuable characteristics.

Aptamers: Promising Reagents in Biomedicine Application

Nucleic acid aptamers, often termed "chemical antibodies," are short, single-stranded DNA or RNA molecules, which are selected by SELEX. In addition to their high specificity and affinity comparable to traditional antibodies, aptamers have numerous unique advantages such as wider identification of targets, none or low batch-to-batch variations, versatile chemical modifications, rapid mass production, and lack of immunogenicity. These characteristics make aptamers a promising recognition probe for scientific research or even clinical application. Aptamer-functionalized nanomaterials are now emerged as a promising drug delivery system for various diseases with decreased side-effects and improved efficacy. In this review, the technological strategies for generating high-affinity and biostable aptamers are introduced. Moreover, the development of aptamers for their application in biomedicine including aptamer-based biosensors, aptamer-drug conjugates and aptamer functionalized nanomaterials is comprehensively summarized.

Aptamer as a targeted approach towards treatment of breast cancer

Aptamers, a novel type of targeted ligand used in drug delivery, have quickly gained popularity due to their high target specificity and affinity. Different aptamer-mediated drug delivery systems, such as aptamer-drug conjugate (ApDC), aptamer-siRNA, and aptamer-functionalised nanoparticle systems, are currently being developed for the successful treatment of cancer based on the excellent properties of aptamers. These systems can decrease potential toxicity and enhance therapeutic efficacy by targeting the drug moiety. In this review, we provide an overview of recent developments in aptamer-mediated delivery systems for cancer therapy, specifically for breast cancer, and talk about the potential applications and current issues of novel aptamer-based techniques. This study in aptamer technology for breast cancer therapy highlights key aptamers targeting well-established biomarkers such as HER2, oestrogen receptor, and progesterone receptor. Additionally, we explore the potential of aptamers in overcoming various challenges such as drug resistance and improving the delivery of therapeutic agents. This review aims to provide a deeper understanding of the present aptamer-based targeted delivery applications through in-depth analysis to increase efficacy and create new therapeutic approaches that may ultimately lead to better treatment outcomes for cancer patients.

Probing the Conformational Restraints of DNA Damage Recognition with β-L-Nucleotides

The DNA building blocks 2'-deoxynucleotides are enantiomeric, with their natural β-D-configuration dictated by the sugar moiety. Their synthetic β-L-enantiomers (βLdNs) can be used to obtain L-DNA, which, when fully substituted, is resistant to nucleases and is finding use in many biosensing and nanotechnology applications. However, much less is known about the enzymatic recognition and processing of individual βLdNs embedded in D-DNA. Here, we address the template properties of βLdNs for several DNA polymerases and the ability of base excision repair enzymes to remove these modifications from DNA. The Klenow fragment was fully blocked by βLdNs, whereas DNA polymerase κ bypassed them in an error-free manner. Phage RB69 DNA polymerase and DNA polymerase β treated βLdNs as non-instructive but the latter enzyme shifted towards error-free incorporation on a gapped DNA substrate. DNA glycosylases and AP endonucleases did not process βLdNs. DNA glycosylases sensitive to the base opposite their cognate lesions also did not recognize βLdNs as a correct pairing partner. Nevertheless, when placed in a reporter plasmid, pyrimidine βLdNs were resistant to repair in human cells, whereas purine βLdNs appear to be partly repaired. Overall, βLdNs are unique modifications that are mostly non-instructive but have dual non-instructive/instructive properties in special cases.

Engineering a Low-Immunogenic Mirror-Image VHH against Vascular Endothelial Growth Factor

Immunogenicity is a major caveat of protein therapeutics. In particular, the long-term administration of protein therapeutic agents leads to the generation of antidrug antibodies (ADAs), which reduce drug efficacy while eliciting adverse events. One promising solution to this issue is the use of mirror-image proteins consisting of d-amino acids, which are resistant to proteolytic degradation in immune cells. We have recently reported the chemical synthesis of the enantiomeric form of the variable domain of the antibody heavy chain (d-VHH). However, identifying mirror-image antibodies capable of binding to natural ligands remains challenging. In this study, we developed a novel screening platform to identify a d-VHH specific for vascular endothelial growth factor A (VEGF-A). We performed mirror-image screening of two newly constructed synthetic VHH libraries displayed on T7 phage and identified VHH sequences that effectively bound to the mirror-image VEGF-A target (d-VEGF-A). We subsequently synthesized a d-VHH candidate that preferentially bound the native VEGF-A (l-VEGF-A) with submicromolar affinity. Furthermore, immunization studies in mice demonstrated that this d-VHH elicited no ADAs, unlike its corresponding l-VHH. Our findings highlight the utility of this novel d-VHH screening platform in the development of protein therapeutics exhibiting both reduced immunogenicity and improved efficacy.

The Application of Aptamer and Research Progress in Liver Disease

Aptamers, as a kind of small-molecule nucleic acid, have attracted much attention since their discovery. Compared with biological reagents such as antibodies, aptamers have the advantages of small molecular weight, low immunogenicity, low cost, and easy modification. At present, aptamers are mainly used in disease biomarker discovery, disease diagnosis, treatment, and targeted drug delivery vectors. In the process of screening and optimizing aptamers, it is found that there are still many problems need to be solved such as the design of the library, optimization of screening conditions, the truncation of screened aptamer, and the stability and toxicity of the aptamer. In recent years, the incidence of liver-related diseases is increasing year by year and the treatment measures are relatively lacking, which has attracted the people's attention in the application of aptamers in liver diseases. This article mainly summarizes the research status of aptamers in disease diagnosis and treatment, especially focusing on the application of aptamers in liver diseases, showing the crucial significance of aptamers in the diagnosis and treatment of liver diseases, and the use of Discovery Studio software to find the binding target and sequence of aptamers, and explore their possible interaction sites.

Development of Better Aptamers: Structured Library Approaches, Selection Methods, and Chemical Modifications

Systematic evolution of ligands by exponential enrichment (SELEX) has been used to discover thousands of aptamers since its development in 1990. Aptamers are short single-stranded oligonucleotides capable of binding to targets with high specificity and selectivity through structural recognition. While aptamers offer advantages over other molecular recognition elements such as their ease of production, smaller size, extended shelf-life, and lower immunogenicity, they have yet to show significant success in real-world applications. By analyzing the importance of structured library designs, reviewing different SELEX methodologies, and the effects of chemical modifications, we provide a comprehensive overview on the production of aptamers for applications in drug delivery systems, therapeutics, diagnostics, and molecular imaging.

Aptamers combined with immune checkpoints for cancer detection and targeted therapy: A review

In recent years, remarkable strides have been made in the field of immunotherapy, which has emerged as a standard treatment for many cancers. As a kind of immunotherapy drug, monoclonal antibodies employed in immune checkpoint therapy have proven beneficial for patients with diverse cancer types. However, owing to the extensive heterogeneity of clinical responses and the complexity and variability of the immune system and tumor microenvironment (TME), accurately predicting its efficacy remains a challenge. Recent advances in aptamers provide a promising approach for monitoring alterations within the immune system and TME, thereby facilitating targeted immunotherapy, particularly focused on immune checkpoint blockade, with enhanced antitumor efficiency. Aptamers have been widely used in tumor cell detection, biosensors, drug discovery, and biomarker screening due to their high specificity and high affinity with their targets. This review aims to comprehensively examine the research status and progress of aptamers in cancer diagnosis and immunotherapy, with a specific emphasis on those related to immune checkpoints. Additionally, we will discuss the future research directions and potential therapeutic targets for aptamer-based immune checkpoint therapy, aiming to provide a theoretical basis for targeting immunotherapy molecules and blocking tumor immune escape.

CCL2 chemokine inhibition primes the tumor vasculature for improved nanomedicine delivery and efficacy

Blood vessel functionality is crucial for efficient tumor-targeted drug delivery. Heterogeneous distribution and perfusion of angiogenic blood vessels contribute to suboptimal accumulation of (nano-) therapeutics in tumors and metastases. To attenuate pathological angiogenesis, an L-RNA aptamer inhibiting the CC motif chemokine ligand 2 (CCL2) was administered to mice bearing orthotopic 4T1 triple-negative breast cancer tumors. The effect of CCL2 inhibition on tumor blood vessel functionality and tumor-targeted drug delivery was evaluated via multimodal and multiscale optical imaging, employing fluorophore-labeled polymeric (10 nm) and liposomal (100 nm) nanocarriers. Anti-CCL2 treatment induced a dose-dependent anti-angiogenic effect, reflected by a decreased relative blood volume, increased blood vessel maturity and functionality, and reduced macrophage infiltration, accompanied by a shift in the polarization of tumor-associated macrophages (TAM) towards a less M2-like and more M1-like phenotype. In line with this, CCL2 inhibitor treatment improved the delivery of polymers and liposomes to tumors, and enhanced the antitumor efficacy of free and liposomal doxorubicin. Together, these findings demonstrate that blocking the CCL2-CCR2 axis modulates TAM infiltration and polarization, resulting in vascular normalization and improved tumor-targeted drug delivery.

Rapid qPCR-based quantitative immune cell phenotyping in mouse tissues

The immune microenvironment plays an important role in the regulation of diseases. The characterization of the cellular composition of immune cell infiltrates in diseases and respective models is a major task in pathogenesis research and diagnostics. For the assessment of immune cell populations in tissues, fluorescence-activated cell sorting (FACS) or immunohistochemistry (IHC) are the two most common techniques presently applied, but they are cost intensive, laborious, and sometimes limited by the availability of suitable antibodies. Complementary rapid qPCR-based approaches exist for the human situation but are lacking for experimental mouse models. Accordingly, we developed a robust, rapid RT-qPCR-based approach to determine and quantify the abundance of prominent immune cell populations such as T cells, helper T (Th) cells, cytotoxic T cells, Th1 cells, B cells, and macrophages in mouse tissues. The results were independently validated by the gold standards IHC and FACS in corresponding tissues and showed high concordance.

Advances in targeted therapy for pancreatic cancer

Pancreatic cancer (PC) represents a group of malignant tumours originating from pancreatic duct epithelial cells and acinar cells, and the 5-year survival rate of PC patients is only approximately 12%. Molecular targeted drugs are specific drugs designed to target and block oncogenes, and they have become promising strategies for the treatment of PC. Compared to traditional chemotherapy drugs, molecular targeted drugs have greater targeting precision, and they have significant therapeutic effects and minimal side effects. This article reviews several molecular targeted drugs that are currently in the experimental stage for the treatment of PC; these include antibody-drug conjugates (ADCs), aptamer-drug conjugates (ApDCs) and peptide-drug conjugates (PDCs). ADCs can specifically recognize cell surface antigens and reduce systemic exposure and toxicity of chemotherapy drugs. By delivering nucleic acid drugs to target cells, the targeting RNA of ApDCs can inhibit the expression or translation of mutated genes, thereby inhibiting tumour development. Moreover, PDCs can effectively penetrate tumour cells, and the peptide groups in PDCs preferentially target tumour cells with minimal side effects. In the targeted therapy of PC, molecular targeted drugs have very broad prospects, which provides new hope for the clinical treatment of PC patients and is worth further research.

Synthesis of 2'-O-Methyl/2'-O-MOE-L-Nucleoside Derivatives and Their Applications: Preparation of G-Quadruplexes, Their Characterization, and Stability Studies

Nucleosides and their analogues constitute an important family of molecules with potential antiviral and antiproliferative activity. The enantiomers of natural nucleosides, l-nucleoside derivatives, which have comparable biological activity but more favorable toxicological properties and greater metabolic stability than d-nucleosides, have emerged as a new class of therapeutic agents. Furthermore, l-nucleosides can be used as a building block to prepare l-oligonucleotides, which have identical physical properties in terms of solubility, hybridization kinetics, and duplex thermal stability as d-oligonucleotides but completely orthogonal in nature. Consequently, they are resistant to nuclease degradation, nontoxic, and immunologically passive, which are desirable properties for biomedical applications. Herein, we describe the synthesis of several 2'-O-methyl/2'-O-MOE-l-nucleoside pyrimidine derivatives and their incorporation into G-rich oligonucleotides. Finally, we evaluated the stability and resistance against nucleases of these new G-quadruplexes, demonstrating the potential of the l-nucleosides described in this work in providing enhanced nuclease resistance with a minimal impact in the nucleic acid structural properties.

Colorectal Liver Metastasis: Can Cytokines Make the Difference?

Colorectal cancer (CRC) is the third leading cause of cancer-related death worldwide. Metastasis is the prime driver of CRC-related mortality, and the liver is the organ most frequently involved. Despite the overall success of current treatments, colorectal liver metastasis (CRLM) is associated with poor prognoses and a survival rate of only 14%. Recent studies have highlighted the importance of the tumor microenvironment (TME) and the crosstalk within it in determining the invasion of distant organs by circulating cancer cells. In the TME, cellular communication is mediated via soluble molecules, among which cytokines have recently emerged as key regulators, involved in every aspect of tumor progression and the metastatic cascade. Indeed, in the serum of CRC patients elevated levels of several cytokines are associated with cancer development and progression. The current review evaluates the role of different cytokines during CRLM development. Additionally, considering the increasing amount of data concerning the importance of cytokine complex networks, we outline the potential of combination treatments using targeted cytokines together with other well-established therapies, such as immune checkpoint blockades, chemotherapy, or gene therapy, to improve therapeutic outcomes.

The role of C5a receptors in autoimmunity

The complement system is an essential component of the innate immune response and plays a vital role in host defense and inflammation. Dysregulation of the complement system, particularly involving the anaphylatoxin C5a and its receptors (C5aR1 and C5aR2), has been linked to several autoimmune diseases, indicating the potential for targeted therapies. C5aR1 and C5aR2 are seven-transmembrane receptors with distinct signaling mechanisms that play both partially overlapping and opposing roles in immunity. Both receptors are expressed on a broad spectrum of immune and non-immune cells and are involved in cellular functions and physiological processes during homeostasis and inflammation. Dysregulated C5a-mediated inflammation contributes to autoimmune diseases such as rheumatoid arthritis, systemic lupus erythematosus, multiple sclerosis, epidermolysis bullosa acquisita, antiphospholipid syndrome, and others. Therefore, targeting C5a or its receptors may yield therapeutic innovations in these autoimmune diseases by reducing the recruitment and activation of immune cells that lead to tissue inflammation and injury, thereby exacerbating the autoimmune response. Clinical trials focused on the inhibition of C5 cleavage or the C5a/C5aR1-axis using small molecules or monoclonal antibodies hold promise for bringing novel treatments for autoimmune diseases into practice. However, given the heterogeneous nature of (systemic) autoimmune diseases, there are still several challenges, such as patient selection, optimal dosing, and treatment duration, that require further investigation and development to realize the full therapeutic potential of C5a receptor inhibition, ideally in the context of a personalized medicine approach. Here, we aim to provide a brief overview of the current knowledge on the function of C5a receptors, the involvement of C5a receptors in autoimmune disorders, the molecular mechanisms underlying C5a receptor-mediated autoimmunity, and the potential for targeted therapies to modulate their activity.

Highly Parallelized Screening of Functionally Enhanced XNA Aptamers in Uniform Hydrogel Particles

Xeno-nucleic acid (XNA) aptamers based on evolvable non-natural genetic polymers hold enormous potential as future diagnostic and therapeutic agents. However, time-consuming and costly procedures requiring the purification of individual XNA sequences produced by large-scale polymerase-mediated primer extension reactions pose a major bottleneck to the discovery of highly active XNA motifs for biomedical applications. Here, we describe a straightforward approach for rapidly surveying the binding properties of XNA aptamers identified by in vitro selection. Our strategy involves preparing XNA aptamer particles in which many copies of the same aptamer sequence are distributed throughout the gel matrix of a polyacrylamide-encapsulated magnetic particle. Aptamer particles are then screened by flow cytometry to assess target binding affinity and deduce structure-activity relationships. This generalizable and highly parallel assay dramatically accelerates the pace of secondary screening by allowing a single researcher to evaluate 48-96 sequences per day.

RNA aptamer-mediated gene therapy of prostate cancer: lessons from the past and future directions

INTRODUCTION

Prostate cancer (PCa) is one of the most prevalent cancers in the world, and the fifth cause of death from cancer in men. Among the non-surgical treatments for PCa, gene therapy strategies are in the early stages of development and recent clinical trials have provided new insights suggesting promising future.

AREAS COVERED

Recently, the creation of targeted gene delivery systems, based on specific PCa cell surface markers, has been viewed as a viable therapeutic approach. Prostate-specific membrane antigen (PSMA) is vastly expressed in nearly all prostate malignancies, and the intensity of expression increases with tumor aggressiveness, androgen independence, and metastasis. RNA aptamers are short and single-stranded oligonucleotides, which selectively bind to a specific ligand on the surface of the cells, which makes them fascinating small molecules for target delivery of therapeutics. PSMA-selective RNA aptamers represent great potential for developing targeted-gene delivery tools for PCa.

EXPERT OPINION

This review provides a thorough horizon for the researchers interested in developing targeted gene delivery systems for PCa via PSMA RNA aptamers. In addition, we provided general information about different prospects of RNA aptamers including discovery approaches, stability, safety, and pharmacokinetics.

Involvement of CXCL12/CXCR4 axis in colorectal cancer: a mini-review

Migration of metastatic tumor cells is similar to the traffic of leukocytes and has been reported that can be guided by chemokines and their receptors, through the circulation to distant organs. The chemokine CXCL12 and its receptor CXCR4 play an essential role in hematopoietic stem cell homing and the activation of this axis supports malignant events. Binding of CXCL12 to CXCR4 activates signal transduction pathways, with broad effects on chemotaxis, cell proliferation, migration and gene expression. Thus, this axis serves as a bridge for tumor-stromal cell communication, creating a permissive microenvironment for tumor development, survival, angiogenesis and metastasis. Evidence suggests that this axis may be involved in the colorectal cancer (CRC) carcinogenesis. Therefore, we review emerging data and correlations between CXCL12/CXCR4 axis in CRC, the implications for cancer progression and possible therapeutic strategies that exploit this system.

Aptamer-Based Targeted Protein Degradation

The selective removal of misfolded, aggregated, or aberrantly overexpressed protein plays an essential role in maintaining protein-dominated biological processes. In parallel, the precise knockout of abnormal proteins is inseparable from the accurate identification of proteins within complex environments. Guided by these precepts, small molecules, or antibodies, are commonly used as protein recognition tools for developing targeted protein degradation (TPD) technology. Indeed, TPD has shown tremendous prospects in chronic diseases, rare diseases, cancer research, and other fields. Meanwhile, aptamers are short RNA or DNA oligonucleotides that can bind to target proteins with high specificity and strong affinity. Accordingly, aptamers are actively used in designing and constructing TPD technology. In this perspective, we provide a brief introduction to TPD technology in its current progress, and we summarize its application challenges. Recent advances in aptamer-based TPD technology are reviewed, together with corresponding challenges and outlooks.

DNA-Based Nanomaterials as Drug Delivery Platforms for Increasing the Effect of Drugs in Tumors

DNA nanotechnology has significantly advanced and might be used in biomedical applications, drug delivery, and cancer treatment during the past few decades. DNA nanomaterials are widely used in biomedical research involving biosensing, bioimaging, and drug delivery since they are remarkably addressable and biocompatible. Gradually, modified nucleic acids have begun to be employed to construct multifunctional DNA nanostructures with a variety of architectural designs. Aptamers are single-stranded nucleic acids (both DNAs and RNAs) capable of self-pairing to acquire secondary structure and of specifically binding with the target. Diagnosis and tumor therapy are prospective fields in which aptamers can be applied. Many DNA nanomaterials with three-dimensional structures have been studied as drug delivery systems for different anticancer medications or gene therapy agents. Different chemical alterations can be employed to construct a wide range of modified DNA nanostructures. Chemically altered DNA-based nanomaterials are useful for drug delivery because of their improved stability and inclusion of functional groups. In this work, the most common oligonucleotide nanomaterials were reviewed as modern drug delivery systems in tumor cells.

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.

The influence of chirality on the behavior of oligonucleotides inside cells: revealing the potent cytotoxicity of G-rich l-RNA

Due to their intrinsic nuclease resistance, mirror image l-oligonucleotides are being increasingly employed in the development of biomedical research tools and therapeutics. Yet, the influence of chirality on the behavior of oligonucleotides in living systems, and specifically, the extent to which l-oligonucleotides interact with endogenous biomacromolecules and the resulting consequences remain unknown. In this study, we characterized the intracellular behavior of l-oligonucleotides for the first time, revealing important chirality-dependent effects on oligonucleotide cytotoxicity. We show that exogenously delivered l-oligonucleotides have the potential to be highly cytotoxic, which is dependent on backbone chemistry, sequence, and structure. Notably, for the sequences tested, we found that single-stranded G-rich l-RNAs are more cytotoxic than their d-DNA/RNA counterparts, exhibiting low nanomolar EC₅₀ values. Importantly, RNA-seq analysis of differentially expressed genes suggests that G-rich l-RNAs stimulate an innate immune response and pro-inflammatory cytokine production. These data not only challenge the general perception that mirror image l-oligonucleotides are nontoxic and nonimmunogenic, but also reveal previously unrecognized therapeutic opportunities. Moreover, by establishing sequence/structure toxicity relationships, this work will guide how future l-oligonucleotide-based biotechnologies are designed and applied.

Chemically modified aptamers for improving binding affinity to the target proteins via enhanced non-covalent bonding

Nucleic acid aptamers are ssDNA or ssRNA fragments that specifically recognize targets. However, the pharmacodynamic properties of natural aptamers consisting of 4 naturally occurring nucleosides (A, G, C, T/U) are generally restricted for inferior binding affinity than the cognate antibodies. The development of high-affinity modification strategies has attracted extensive attention in aptamer applications. Chemically modified aptamers with stable three-dimensional shapes can tightly interact with the target proteins via enhanced non-covalent bonding, possibly resulting in hundreds of affinity enhancements. This review overviewed high-affinity modification strategies used in aptamers, including nucleobase modifications, fluorine modifications (2'-fluoro nucleic acid, 2'-fluoro arabino nucleic acid, 2',2'-difluoro nucleic acid), structural alteration modifications (locked nucleic acid, unlocked nucleic acid), phosphate modifications (phosphorothioates, phosphorodithioates), and extended alphabets. The review emphasized how these high-affinity modifications function in effect as the interactions with target proteins, thereby refining the pharmacodynamic properties of aptamers.

Aptamer-based Emerging Tools for Viral Biomarker Detection: A Focus on SARS-CoV-2

Viral infections can cause fatal illnesses to humans as well as animals. Early detection of viruses is therefore crucial to provide effective treatment to patients. Recently, the Covid-19 pandemic has undoubtedly given an alarming call to develop rapid and sensitive detection platforms. The viral diagnostic tools need to be fast, affordable, and easy to operate with high sensitivity and specificity equivalent or superior to the currently used diagnostic methods. The present detection methods include direct detection of viral antigens or measuring the response of antibodies to viral infections. However, the sensitivity and quantification of the virus are still a significant challenge. Detection tools employing synthetic binding molecules like aptamers may provide several advantages over the conventional methods that use antibodies in the assay format. Aptamers are highly stable and tailorable molecules and are therefore ideal for detection and chemical sensing applications. This review article discusses various advances made in aptamer-based viral detection platforms, including electrochemical, optical, and colorimetric methods to detect viruses, specifically SARS-Cov-2. Considering the several advantages, aptamers could be game-changing in designing high-throughput biosensors for viruses and other biomedical applications in the future.

Synthetic receptors in medicine

Cellular signaling is controlled by ligand receptor interaction and subsequent biochemical changes inside the cell. Manipulating receptors as per need that can be a strategy to alter the disease pathologies in various conditions. With recent advances in synthetic biology, now it is possible to engineer the artificial receptor "synthetic receptors." Synthetic receptors are the engineering receptors that have potential to alter the disease pathology by altering/manipulating the cellular signaling. Several synthetic receptors are being engineered that have shown positive regulation in several disease conditions. Thus, synthetic receptor-based strategy opens a new avenue in the medical field to cope up with various health issues. The current chapter summarizes updated information about the synthetic receptors and their applications in the medical field.

The role of CXCL12 axis in pancreatic cancer: New biomarkers and potential targets

Introduction

Chemokines are small, secreted peptides involved in the mediation of the immune cell recruitment. Chemokines have been implicated in several diseases including autoimmune diseases, viral infections and also played a critical role in the genesis and development of several malignant tumors. CXCL12 is a homeostatic CXC chemokine involved in the process of proliferation, and tumor spread. Pancreatic ductal adenocarcinoma (PDAC) is one of the most aggressive tumors, that is still lacking effective therapies and with a dramatically poor prognosis.

Method

We conducted a scientific literature search on Pubmed and Google Scholar including retrospective, prospective studies and reviews focused on the current research elucidating the emerging role of CXCL12 and its receptors CXCR4 - CXCR7 in the pathogenesis of pancreatic cancer.

Results

Considering the mechanism of immunomodulation of the CXCL12-CXCR4-CXCR7 axis, as well as the potential interaction with the microenvironment in the PDAC, several combined therapeutic approaches have been studied and developed, to overcome the "cold" immunological setting of PDAC, like combining CXCL12 axis inhibitors with anti PD-1/PDL1 drugs.

Conclusion

Understanding the role of this chemokine's axis in disease initiation and progression may provide the basis for developing new potential biomarkers as well as therapeutic targets for related pancreatic cancers.

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.

Aptamers, a New Therapeutic Opportunity for the Treatment of Multiple Myeloma

Multiple Myeloma (MM) remains an incurable disease due to high relapse rates and fast development of drug resistances. The introduction of monoclonal antibodies (mAb) has caused a paradigm shift in MM treatment, paving the way for targeted approaches with increased efficacy and reduced toxicities. Nevertheless, antibody-based therapies face several difficulties such as high immunogenicity, high production costs and limited conjugation capacity, which we believe could be overcome by the introduction of nucleic acid aptamers. Similar to antibodies, aptamers can bind to their targets with great affinity and specificity. However, their chemical nature reduces their immunogenicity and production costs, while it enables their conjugation to a wide variety of cargoes for their use as delivery agents. In this review, we summarize several aptamers that have been tested against MM specific targets with promising results, establishing the rationale for the further development of aptamer-based strategies against MM. In this direction, we believe that the study of novel plasma cell surface markers, the development of intracellular aptamers and further research on aptamers as building blocks for complex nanomedicines will lead to the generation of next-generation targeted approaches that will undoubtedly contribute to improve the management and life quality of MM patients.

A Long-Circulating Vector for Aptamers Based upon Polyphosphodiester-Backboned Molecular Brushes

Aptamers face challenges for use outside the ideal conditions in which they are developed. These difficulties are most palpable in vivo due to nuclease activities, rapid clearance, and off-target binding. Herein, we demonstrate that a polyphosphodiester-backboned molecular brush can suppress enzymatic digestion, reduce non-specific cell uptake, enable long blood circulation, and rescue the bioactivity of a conjugated aptamer in vivo. The backbone along with the aptamer is assembled via solid-phase synthesis, followed by installation of poly(ethylene glycol) (PEG) side chains using a two-step process with near-quantitative efficiency. The synthesis allows for precise control over polymer size and architecture. Consisting entirely of building blocks that are generally recognized as safe for therapeutics, this novel molecular brush is expected to provide a highly translatable route for aptamer-based therapeutics.

From a Carbohydrate Raw Material to an Important Building Block: Cost-Efficient Conversion of d-Fructose into 2-Deoxy-l-ribose

A straightforward method for the conversion of a low-cost carbohydrate (d-fructose) into an important carbohydrate building block (2-deoxy-l-ribose) is reported. This methodology involves a novel radical cyclization followed by a fragmentation reaction, selective enzymatic hydrolysis using a lipase, and oxidative cleavage of the vicinal diol. This method uses the cheapest starting material and employs the shortest synthetic route (7 steps) for converting a d-sugar into 2-deoxy-l-ribose.

The Medicinal Chemistry of Artificial Nucleic Acids and Therapeutic Oligonucleotides

Nucleic acids play a central role in human biology, making them suitable and attractive tools for therapeutic applications. While conventional drugs generally target proteins and induce transient therapeutic effects, nucleic acid medicines can achieve long-lasting or curative effects by targeting the genetic bases of diseases. However, native oligonucleotides are characterized by low in vivo stability due to nuclease sensitivity and unfavourable physicochemical properties due to their polyanionic nature, which are obstacles to their therapeutic use. A myriad of synthetic oligonucleotides have been prepared in the last few decades and it has been shown that proper chemical modifications to either the nucleobase, the ribofuranose unit or the phosphate backbone can protect the nucleic acids from degradation, enable efficient cellular uptake and target localization ensuring the efficiency of the oligonucleotide-based therapy. In this review, we present a summary of structure and properties of artificial nucleic acids containing nucleobase, sugar or backbone modifications, and provide an overview of the structure and mechanism of action of approved oligonucleotide drugs including gene silencing agents, aptamers and mRNA vaccines.

Analytical techniques for characterizing diastereomers of phosphorothioated oligonucleotides

Oligonucleotides have emerged as powerful therapeutics for treating diverse diseases. To fully unlock the therapeutic potential of oligonucleotides, there is still a great need to further improve their drug-like properties. Numerous chemical modifications have been explored to achieve this goal, with phosphorothioation being one of the most widely used strategies. However, phosphorothioate modification produces diastereomers that are reported to have different properties and performances, demanding detailed characterization of these diastereomers. Here we provide an overview of phosphorothioated oligonucleotide diastereomers, covering their origin and configurations, physicochemical and pharmacological properties, and stereo-selective chemical synthesis, followed by a summary of currently available analytical techniques for characterizing these diastereomers, with a focus on liquid chromatography-based approaches, including ion-pair reversed-phase liquid chromatography, anion exchange chromatography, mixed-mode chromatography, and hybrid approaches. Non-chromatographic techniques, such as capillary electrophoresis, spectroscopy and other methods, are also being reviewed.

Exploring the Utility of ssDNA Aptamers Directed against Snake Venom Toxins as New Therapeutics for Snakebite Envenoming

Snakebite is a neglected tropical disease that causes considerable death and disability in the tropical world. Although snakebite can cause a variety of pathologies in victims, haemotoxic effects are particularly common and are typically characterised by haemorrhage and/or venom-induced consumption coagulopathy. Antivenoms are the mainstay therapy for treating the toxic effects of snakebite, but despite saving thousands of lives annually, these therapies are associated with limited cross-snake species efficacy due to venom variation, which ultimately restricts their therapeutic utility to particular geographical regions. In this study, we sought to explore the potential of ssDNA aptamers as toxin-specific inhibitory alternatives to antibodies. As a proof of principle model, we selected snake venom serine protease toxins, which are responsible for contributing to venom-induced coagulopathy following snakebite envenoming, as our target. Using SELEX technology, we selected ssDNA aptamers against recombinantly expressed versions of the fibrinogenolytic SVSPs ancrod from the venom of C. rhodostoma and batroxobin from B. atrox. From the resulting pool of specific ssDNA aptamers directed against each target, we identified candidates that exhibited low nanomolar binding affinities to their targets. Downstream aptamer-linked immobilised sorbent assay, fibrinogenolysis, and coagulation profiling experiments demonstrated that the candidate aptamers were able to recognise native and recombinant SVSP toxins and inhibit the toxin- and venom-induced prolongation of plasma clotting times and the consumption of fibrinogen, with inhibitory potencies highly comparable to commercial polyvalent antivenoms. Our findings demonstrate that rationally selected toxin-specific aptamers can exhibit broad in vitro cross-reactivity against toxin isoforms found in different snake venoms and are capable of inhibiting toxins in pathologically relevant in vitro and ex vivo models of venom activity. These data highlight the potential utility of ssDNA aptamers as novel toxin-inhibiting therapeutics of value for tackling snakebite envenoming.

Racemic crystal structures of A-DNA duplexes

The ease with which racemic mixtures crystallize compared with the equivalent chiral systems is routinely taken advantage of to produce crystals of small molecules. However, biological macromolecules such as DNA and proteins are naturally chiral, and thus the limited range of chiral space groups available hampers the crystallization of such molecules. Inspiring work over the past 15 years has shown that racemic mixtures of proteins, which were made possible by impressive advances in protein chemical synthesis, can indeed improve the success rate of protein crystallization experiments. More recently, the racemic crystallization approach was extended to include nucleic acids as a possible aid in the determination of enantiopure DNA crystal structures. Here, findings are reported that suggest that the benefits may extend beyond this. Two racemic crystal structures of the DNA sequence d(CCCGGG) are described which were found to fold into A-form DNA. This form differs from the Z-form DNA conformation adopted by the chiral equivalent in the solid state, suggesting that the use of racemates may also favour the emergence of new conformations. Importantly, the racemic mixture forms interactions in the solid state that differ from the chiral equivalent (including the formation of racemic pseudo-helices), suggesting that the use of racemic DNA mixtures could provide new possibilities for the design of precise self-assembled nanomaterials and nanostructures.

Cell-specific aptamers as potential drugs in therapeutic applications: A review of current progress

Cell-specific aptamers are a promising emerging player in the field of disease therapy. This paper reviews the multidimensional research progress made in terms of their classification, modification, and application. Based on the target location of cell-specific aptamers, it is defined and classified cell-specific aptamers into three groups including aptamers for cell surface markers, aptamers for intracellular components, and aptamers for extracellular components. Moreover, the modification methods of aptamers to achieve improved stability and affinity are concluded. In addition, recent advances in the application of cell-specific aptamers are discussed, mainly focusing on the increasing research attraction of cell state improving helpers and cell recruitment mediators in the improvement of cellular microenvironments to achieve successful disease therapy. This review also highlights 11 types of clinical aptamer drugs. Finally, the challenges and future directions of potential clinical applications are presented. In summary, we believe that cell-specific aptamers are promising drugs in disease therapy.

Development of RNA G-quadruplex (rG4)-targeting L-RNA aptamers by rG4-SELEX

RNA G-quadruplex (rG4)-SELEX is a method that generates L-RNA aptamers to target an rG4 structure of interest, which can be applied to inhibit G-quadruplex-mediated interactions that have important roles in gene regulation and function. Here we present a Protocol Extension substantially modifying an existing SELEX protocol to describe in detail the procedures involved in performing rG4-SELEX to identify rG4-specific binders that can effectively suppress rG4-peptide and rG4-protein associations. This Protocol Extension improves the speed of aptamer discovery and identification, offering a suite of techniques to characterize the aptamer secondary structure and monitor binding affinity and specificity, and demonstrating the utility of the L-RNA aptamer. The previous protocol mainly describes the identification of RNA aptamers against proteins of interest, whereas in this Protocol Extension we present the development of an unnatural RNA aptamer against an RNA structure of interest, with the potential to be applicable to other nucleic acid motifs or biomolecules. rG4-SELEX starts with a random D-RNA library incubated with the L-rG4 target of interest, followed by binding, washing and elution of the library. Enriched D-aptamer candidates are sequenced and structurally characterized. Then, the L-aptamer is synthesized and used for different applications. rG4-SELEX can be carried out by an experienced molecular biologist with a basic understanding of nucleic acids. The development of rG4-targeting L-RNA aptamers expands the current rG4 toolkit to explore innovative rG4-related applications, and opens new doors to discovering novel rG4 biology in the near future. The duration of each selection cycle as outlined in the protocol is ~2 d.

Cancer immunomodulation using bispecific aptamers

Evasion of immune destruction is a major hallmark of cancer. Recent US Food and Drug Administration (FDA) approvals of various immunomodulating therapies underline the important role that reprogramming the immune system can play in combating this disease. However, a wide range of side effects still limit the therapeutic potential of immunomodulators, suggesting a need for more precise reagents with negligible off-target and on-target/off-tumor effects. Aptamers are single-chained oligonucleotides that bind their targets with high specificity and affinity owing to their three-dimensional (3D) structures, and they are one potential way to address this need. In particular, bispecific aptamers (bsApts) have been shown to induce artificial immune synapses that promote T cell activation and subsequent tumor cell lysis in various in vitro and in vivo pre-clinical models. We discuss these advances here, along with gaps in bsApt biology at both the cellular and resident tissue levels that should be addressed to accelerate their translation into the clinic. The broad application, minimal production cost, and relative lack of immunogenicity of bsApts give them some ideal qualities for manipulating the immune system. Building upon lessons from other novel therapies, bsApts could soon provide clinicians with an immunomodulating toolbox that is not only potent and efficacious but exercises a wide therapeutic index.

Functional Roles of Chemokine Receptor CCR2 and Its Ligands in Liver Disease

Chemokines are a family of cytokines that orchestrate the migration and positioning of immune cells within tissues and are critical for the function of the immune system. CCR2 participates in liver pathology, including acute liver injury, chronic hepatitis, fibrosis/cirrhosis, and tumor progression, by mediating the recruitment of immune cells to inflammation and tumor sites. Although a variety of chemokines have been well studied in various diseases, there is no comprehensive review presenting the roles of all known chemokine ligands of CCR2 (CCL2, CCL7, CCL8, CCL12, CCL13, CCL16, and PSMP) in liver disease, and this review aims to fill this gap. The introduction of each chemokine includes its discovery, its corresponding chemotactic receptors, physiological functions and roles in inflammation and tumors, and its impact on different immune cell subgroups.

Advances in Therapeutic L-Nucleosides and L-Nucleic Acids with Unusual Handedness

Nucleic-acid-based small molecule and oligonucleotide therapies are attractive topics due to their potential for effective target of disease-related modules and specific control of disease gene expression. As the non-naturally occurring biomolecules, modified DNA/RNA nucleoside and oligonucleotide analogues composed of L-(deoxy)riboses, have been designed and applied as innovative therapeutics with superior plasma stability, weakened cytotoxicity, and inexistent immunogenicity. Although all the chiral centers in the backbone are mirror converted from the natural D-nucleic acids, L-nucleic acids are equipped with the same nucleobases (A, G, C and U or T), which are critical to maintain the programmability and form adaptable tertiary structures for target binding. The types of L-nucleic acid drugs are increasingly varied, from chemically modified nucleoside analogues that interact with pathogenic polymerases to nanoparticles containing hundreds of repeating L-nucleotides that circulate durably in vivo. This article mainly reviews three different aspects of L-nucleic acid therapies, including pharmacological L-nucleosides, Spiegelmers as specific target-binding aptamers, and L-nanostructures as effective drug-delivery devices.

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.

Evolution of Functionally Enhanced α-l-Threofuranosyl Nucleic Acid Aptamers

Synthetic genetic polymers (xeno-nucleic acids, XNAs) have the potential to transition aptamers from laboratory tools to therapeutic agents, but additional functionality is needed to compete with antibodies. Here, we describe the evolution of a biologically stable artificial genetic system composed of α-l-threofuranosyl nucleic acid (TNA) that facilitates the production of backbone- and base-modified aptamers termed "threomers" that function as high quality protein capture reagents. Threomers were discovered against two prototypical protein targets implicated in human diseases through a combination of in vitro selection and next-generation sequencing using uracil nucleotides that are uniformly equipped with aromatic side chains commonly found in the paratope of antibody-antigen crystal structures. Kinetic measurements reveal that the side chain modifications are critical for generating threomers with slow off-rate binding kinetics. These findings expand the chemical space of evolvable non-natural genetic systems to include functional groups that enhance protein target binding by mimicking the structural properties of traditional antibodies.

Oligonucleotide aptamers: Recent advances in their screening, molecular conformation and therapeutic applications

Aptamers are single stranded oligonucleotides with specific recognition and binding ability to target molecules, which can be obtained by Systematic Evolution of Ligands by Exponential Enrichment (SELEX). Aptamers have the advantages of low molecular weight, low immunogenicity, easy modification and high stability. They play promising role in promoting food safety, monitoring the environment and basic research, especially in clinical diagnosis and therapeutic drugs. To date, great achievements regarding the selection, modifications and application of aptamers have been made. However, since it is still a challenge to obtain aptamers with high affinity in a more effective way, few aptamer-based products have already successfully entered into clinical use. This review aims to provide a thorough overview of the latest advances in this rapidly developing field, focusing on aptamer screening methods for different targets, the structure of the interaction between aptamers and target substances, and the challenges and potential of current therapeutic aptamers.

RNA Therapeutics - Research and Clinical Advancements

RNA therapeutics involve the use of coding RNA such as mRNA as well as non-coding RNAs such as small interfering RNAs (siRNA), antisense oligonucleotides (ASO) to target mRNA, aptamers, ribozymes, and clustered regularly interspaced short palindromic repeats-CRISPR-associated (CRISPR/Cas) endonuclease to target proteins and DNA. Due to their diverse targeting ability and research in RNA modification and delivery systems, RNA-based formulations have emerged as suitable treatment options for many diseases. Therefore, in this article, we have summarized different RNA therapeutics, their targeting strategies, and clinical progress for various diseases as well as limitations; so that it might help researchers formulate new and advanced RNA therapeutics for various diseases. Additionally, U.S. Food and Drug Administration (USFDA)-approved RNA-based therapeutics have also been discussed.