Use of oligonucleotide aptamer ligands to modulate the function of immune receptors

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.

Aptamers as an approach to targeted cancer therapy

Conventional cancer treatments can cause serious side effects because they are not specific to cancer cells and can damage healthy cells. Aptamers often are single-stranded oligonucleotides arranged in a unique architecture, allowing them to bind specifically to target sites. This feature makes them an ideal choice for targeted therapeutics. They are typically produced through the systematic evolution of ligands by exponential enrichment (SELEX) and undergo extensive pharmacological revision to modify their affinity, specificity, and therapeutic half-life. Aptamers can act as drugs themselves, directly inhibiting tumor cells. Alternatively, they can be used in targeted drug delivery systems to transport drugs directly to tumor cells, minimizing toxicity to healthy cells. In this review, we will discuss the latest and most advanced approaches to using aptamers for cancer treatment, particularly targeted therapy overcoming resistance to conventional therapies.

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.

Construction and bioapplications of aptamer-based dual recognition strategy

Aptamer-based dual recognition strategy, using dual aptamers or the cooperation of aptamers with other recognition elements, can better utilize the advantages of each recognition molecule and increase the design flexibility to effectively overcome the limitations of a single molecule recognition strategy, thereby improving the sensitivity and selectivity and facilitating the regulation of biological process. Hence, this review systematically tracks the construction and application of dual aptamers recognition strategy in the versatile detection of protein biomarkers, pathogenic microorganisms, cancer cells, and the treatment of some diseases and, more importantly, in functional regulation and imaging of cell-surface protein receptors. Then, the cooperation of aptamers with other recognition elements are briefly introduced. Potential challenges facing this field have been highlighted, aiming to expand bioanalytical applications of aptamer-based dual or multiple recognition strategies and meet the growing demand for precision medicine.

Evolution of Peptide-Based Prostate-Specific Membrane Antigen (PSMA) Inhibitors: An Approach to Novel Prostate Cancer Therapeutics

BACKGROUND

Prostate cancer is one of the most common cancers worldwide, with approximately 1.1 million cases diagnosed annually. The rapid development of molecular imaging has facilitated greater structural understanding, which can help formulate novel combinations of therapeutic regimens and more accurate diagnosis, avoiding unnecessary prostate biopsies. This accumulated knowledge also provides a greater understanding of the aggressive stages of the disease and tumor recurrence. Recently, much progress has been made on developing peptidomimetic-based inhibitors as promising candidates to effectively bind to the prostate- specific membrane antigen (PSMA), which is expressed by prostate cancer cells.

OBJECTIVE

In this review, recent advances covering small-molecule and peptide-based PSMA inhibitors will be extensively reviewed, providing a base for the rational design of future PSMA inhibitors.

METHOD

Herein, the literature on selected PSMA inhibitors that have been developed from 1996 to 2020 were reviewed, emphasizing recent synthetic advances and chemical strategies whilst highlighting therapeutic potential and drawbacks of each inhibitor.

RESULTS

Synthesized inhibitors presented in this review demonstrate the clinical application of certain PSMA inhibitors, exhibited in vitro and in vivo.

CONCLUSION

This review highlights the clinical potential of PSMA inhibitors, analyzing the advantages and setbacks of the chemical synthetic methodologies utilized, setting precedence for the discovery of novel PSMA inhibitors for future clinical applications.

Recent Progress in Aptamer Discoveries and Modifications for Therapeutic Applications

Aptamers are oligonucleotide sequences with a length of about 25-80 bases which have abilities to bind to specific target molecules that rival those of monoclonal antibodies. They are attracting great attention in diverse clinical translations on account of their various advantages, including prolonged storage life, little batch-to-batch differences, very low immunogenicity, and feasibility of chemical modifications for enhancing stability, prolonging the half-life in serum, and targeted delivery. In this Review, we demonstrate the emerging aptamer discovery technologies in developing advanced techniques for producing aptamers with high performance consistently and efficiently as well as requiring less cost and resources but offering a great chance of success. Further, the diverse modifications of aptamers for therapeutic applications including therapeutic agents, aptamer-drug conjugates, and targeted delivery materials are comprehensively summarized.

Application and development of aptamer in cancer: from clinical diagnosis to cancer therapy

Traditional anticancer therapies can cause serious side effects in clinical treatment due to their nonspecific of tumor cells. Aptamers, also termed as 'chemical antibodies', are short DNA or RNA oligonucleotides selected from the synthetic large random single-strand oligonucleotide library by systematic evolution of ligands by exponential enrichment (SELEX) to bind to lots of different targets, such as proteins or nucleic acid structures. Aptamers have good affinities and high specificity with target molecules, thus may be able to act as drugs themselves to directly inhibit the proliferation of tumor cells, or own great potentialities in the targeted drug delivery systems which can be used in tumor diagnosis and target specific tumor cells, thereby minimizing the toxicity to normal cells. Here we review the unique properties of aptamer represents a great opportunity when applied to the rapidly developing fields of biotechnology and discuss the recent developments in the use of aptamers as powerful tools for analytic, diagnostic and therapeutic applications for cancer.

Current Perspectives on Aptamers as Diagnostic Tools and Therapeutic Agents

Aptamers are synthetic single-stranded DNA or RNA sequences selected from combinatorial oligonucleotide libraries through the well-known in vitro selection and iteration process, SELEX. The last three decades have witnessed a sudden boom in aptamer research, owing to their unique characteristics, like high specificity and binding affinity, low immunogenicity and toxicity, and ease in synthesis with negligible batch-to-batch variation. Aptamers can specifically bind to the targets ranging from small molecules to complex structures, making them suitable for a myriad of diagnostic and therapeutic applications. In analytical scenarios, aptamers are used as molecular probes instead of antibodies. They have the potential in the detection of biomarkers, microorganisms, viral agents, environmental pollutants, or pathogens. For therapeutic purposes, aptamers can be further engineered with chemical stabilization and modification techniques, thus expanding their serum half-life and shelf life. A vast number of antagonistic aptamers or aptamer-based conjugates have been discovered so far through the in vitro selection procedure. However, the aptamers face several challenges for its successful clinical translation, and only particular aptamers have reached the marketplace so far. Aptamer research is still in a growing stage, and a deeper understanding of nucleic acid chemistry, target interaction, tissue distribution, and pharmacokinetics is required. In this review, we discussed aptamers in the current diagnostics and theranostics applications, while addressing the challenges associated with them. The report also sheds light on the implementation of aptamer conjugates for diagnostic purposes and, finally, the therapeutic aptamers under clinical investigation, challenges therein, and their future directions.

Aptamers as Therapeutic Agents: Has the Initial Euphoria Subsided?

Aptamers are synthetic DNA or RNA oligonucleotide ligands with great potential for therapeutic applications. A vast number of disease-related targets have been used to identify agonistic, antagonistic, or inhibitory aptamers, or aptamer-based targeting ligands. However, only a few aptamers have reached late-stage clinical trials so far and the commercial infrastructure is still far behind that of other therapeutic agents such as monoclonal antibodies. The desirable properties of aptamers such as selectivity, chemical flexibility, or cost-efficiency are faced by challenges, including a short half-life in vivo, immunogenicity, and entrapment in cellular organelles. Aptamer research is still in an early stage, and a deeper understanding of their structure, target interactions, and pharmacokinetics is necessary to catch up to the clinical market. In this review, we will discuss the benefits and limitations in the development of therapeutic aptamers, as well as the advances and future directions of aptamer research. The progress towards effective therapies seems to be slow, but it has not stopped and the best is yet to come.

Aptamers, the Nucleic Acid Antibodies, in Cancer Therapy

The arrival of the monoclonal antibody (mAb) technology in the 1970s brought with it the hope of conquering cancers to the medical community. However, mAbs, on the whole, did not achieve the expected wonder in cancer therapy although they do have demonstrated successfulness in the treatment of a few types of cancers. In 1990, another technology of making biomolecules capable of specific binding appeared. This technique, systematic evolution of ligands by exponential enrichment (SELEX), can make aptamers, single-stranded DNAs or RNAs that bind targets with high specificity and affinity. Aptamers have some advantages over mAbs in therapeutic uses particularly because they have little or no immunogenicity, which means the feasibility of repeated use and fewer side effects. In this review, the general properties of the aptamer, the advantages and limitations of aptamers, the principle and procedure of aptamer production with SELEX, particularly the undergoing studies in aptamers for cancer therapy, and selected anticancer aptamers that have entered clinical trials or are under active investigations are summarized.

Discovery of tumoricidal DNA oligonucleotides by response-directed in vitro evolution

Drug discovery is challenged by ineffectiveness of drugs against variable and evolving diseases, and adverse effects due to poor selectivity. We describe a robust platform which potentially addresses these limitations. The platform enables rapid discovery of DNA oligonucleotides evolved in vitro for exerting specific and selective biological responses in target cells. The process operates without a priori target knowledge (mutations, biomarkers, etc). We report the discovery of oligonucleotides with direct, selective cytotoxicity towards cell lines, as well as patient-derived solid and hematological tumors. A specific oligonucleotide termed E8, induced selective apoptosis in triple-negative breast cancer (TNBC) cells. Polyethylene glycol-modified E8 exhibited favorable biodistribution in animals, persisting in tumors up to 48-hours after injection. E8 inhibited tumors by 50% within 10 days of treatment in patient-derived xenograft mice, and was effective in ex vivo organ cultures from chemotherapy-resistant TNBC patients. These findings highlight a drug discovery model which is target-tailored and on-demand.

Noam Mamet et al. describe a platform for rapid de novo discovery of DNA oligonucleotides that directly and selectively induce apoptosis in cancer cells. They report target-tailored discovery of tumoricidal oligonucleotides against tumor cell lines as well as patient-derived tumors.

CD200 mimetic aptamer PEG-M49 markedly increases the therapeutic effects of pegylated liposomal doxorubicin in a mouse model of metastatic breast carcinoma: an effect independent of CD200 receptor 1

We previously reported that CD200 overexpression in the host decreases progression and metastasis of the highly aggressive metastatic 4THM breast carcinoma. We have explored a possible synergistic interaction between the CD200 mimetic PEG-M49 and pegylated liposomal doxorubicin (Peg-Dox) in wild-type CD200 knockout (CD200^-/-) and CD200 Receptor 1 knockout (CD200R1^-/-) mice for the first time. A 4THM breast carcinoma model and three groups of BALB/c mice (wild type, CD200^-/- and CD200R1^-/-) were used. Five days after injection of tumor cells, mice were injected with Peg-Dox (ip, once a week) and PEG-M49 or a control aptamer (iv, every 3 days). Necropsies were performed either 12 (mid-point) or 24 (endpoint) days after injection and the extent of tumor growth, visceral metastasis and changes in the tumor-directed immune response were evaluated. PEG-M49 and Peg-Dox co-treatment induced complete tumor regression and loss of macroscopic lung metastasis in four out of seven WT mice. This synergistic anti-tumoral effect is thought to be due to Peg-M49-induced inhibition of Gr1 + CD11b + cells and Peg-Dox-induced increases in tumor-infiltrating CD8 + and CD8CD4 double-positive cells. Similar changes were observed in CD200R1^-/- mice indicating that the primary effects of Peg-M49 are mediated by non-CD200R1 receptors. We also demonstrated for the first time that tumor growth, metastasis, and tumor infiltrating GR1 + CD11b + cells were markedly increased in CD200R1^-/- mice, indicating an anti-inflammatory and protective role of CD200. CD200 mimetics might be a safe and effective immunomodulatory treatment in conjunction with classical chemotherapeutics for therapy of aggressive metastatic breast carcinoma.

Aptamers as Modular Components of Therapeutic Nucleic Acid Nanotechnology

Nucleic acids play a central role in all domains of life, either as genetic blueprints or as regulators of various biochemical pathways. The chemical makeup of ribonucleic acid (RNA) or deoxyribonucleic acid (DNA), generally represented by a sequence of four monomers, also provides precise instructions for folding and higher-order assembly of these biopolymers that, in turn, dictate biological functions. The sequence-based specific 3D structures of nucleic acids led to the development of the directed evolution of oligonucleotides, SELEX (systematic evolution of ligands by exponential enrichment), against a chosen target molecule. Among the variety of functions, selected oligonucleotides named aptamers also allow targeting of cell-specific receptors with antibody-like precision and can deliver functional RNAs without a transfection agent. The advancements in the field of customizable nucleic acid nanoparticles (NANPs) opened avenues for the design of nanoassemblies utilizing aptamers for triggering or blocking cell signaling pathways or using aptamer-receptor combinations to activate therapeutic functionalities. A recent selection of fluorescent aptamers enables real-time tracking of NANP formation and interactions. The aptamers are anticipated to contribute to the future development of technologies, enabling an efficient assembly of functional NANPs in mammalian cells or in vivo. These research topics are of top importance for the field of therapeutic nucleic acid nanotechnology with the promises to scale up mass production of NANPs suitable for biomedical applications, to control the intracellular organization of biological materials to enhance the efficiency of biochemical pathways, and to enhance the therapeutic potential of NANP-based therapeutics while minimizing undesired side effects and toxicities.

An in Vitro Selection Strategy Identifying Naked DNA That Localizes to Cell Nuclei

Combinatorial chemistry drives the biological generation of protein structural diversity in antibodies and T-cell receptors. When applied to nucleic acids, vast engineered random libraries of DNA and RNA strands allow selection of affinity reagents ("aptamers") against molecular targets. Selection involves cycles rewarding target binding affinity with amplification. Despite the success of this approach, delivery of selected aptamers across cell membranes and to specific subcellular compartments is an unmet need in chemical biology. Here, we address this challenge, demonstrating in vitro selection of DNA aptamers capable of homing to nuclei of cultured cells without transfection agents or viral transduction. Selection of such folded karyophilic DNA aptamers (∼100 nucleotides) is achieved by a biosensor strategy that rewards exposure to nuclear DNA ligase. Identified DNA molecules are preferentially delivered to cell nuclei within minutes. Related strategies can be envisioned to select aptamers that home to other subcellular compartments.

Bispecific Aptamer Induced Artificial Protein-Pairing: A Strategy for Selective Inhibition of Receptor Function

Cell surface receptors play a critical role in modulating intracellular signal transduction, making them important drug targets. However, it remains challenging to develop a selective and efficient strategy for regulating receptor function. Herein, we develop a strategy, called bispecific aptamer induced artificial protein-pairing, to selectively regulate receptor function. In this strategy, bispecific aptamer probes act as molecular mediators to bind to both a target receptor protein and a paired protein, which brings the two proteins into close proximity on the living cell membrane. Importantly, the paired proteins work not only as a cancer biomarker for enhancing cell selectivity but also as a blocking assistant to inhibit target receptor function via strong steric hindrance effect. Compared with single-aptamer-mediated regulation, the proposed bispecific aptamer probes afford substantial improvement in selective and efficient regulation of receptor function and downstream signaling pathways. This work offers a versatile methodology to design molecular mediators that can modulate receptor function, thereby providing a new way for developing novel therapeutic drugs.

Aptamedicine: a new treatment modality in personalized cancer therapy

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

Smart-Responsive Nucleic Acid Nanoparticles (NANPs) with the Potential to Modulate Immune Behavior

Nucleic acids are programmable and biocompatible polymers that have beneficial uses in nanotechnology with broad applications in biosensing and therapeutics. In some cases, however, the development of the latter has been impeded by the unknown immunostimulatory properties of nucleic acid-based materials, as well as a lack of functional dynamicity due to stagnant structural design. Recent research advancements have explored these obstacles in tandem via the assembly of three-dimensional, planar, and fibrous cognate nucleic acid-based nanoparticles, called NANPs, for the conditional activation of embedded and otherwise quiescent functions. Furthermore, a library of the most representative NANPs was extensively analyzed in human peripheral blood mononuclear cells (PBMCs), and the links between the programmable architectural and physicochemical parameters of NANPs and their immunomodulatory properties have been established. This overview will cover the recent development of design principles that allow for fine-tuning of both the physicochemical and immunostimulatory properties of dynamic NANPs and discuss the potential impacts of these novel strategies.

Functional-DNA-Driven Dynamic Nanoconstructs for Biomolecule Capture and Drug Delivery

The discovery of sequence-specific hybridization has allowed the development of DNA nanotechnology, which is divided into two categories: 1) structural DNA nanotechnology, which utilizes DNA as a biopolymer; and 2) dynamic DNA nanotechnology, which focuses on the catalytic reactions or displacement of DNA structures. Recently, numerous attempts have been made to combine DNA nanotechnologies with functional DNAs such as aptamers, DNAzymes, amplified DNA, polymer-conjugated DNA, and DNA loaded on functional nanoparticles for various applications; thus, the new interdisciplinary research field of "functional DNA nanotechnology" is initiated. In particular, a fine-tuned nanostructure composed of functional DNAs has shown immense potential as a programmable nanomachine by controlling DNA dynamics triggered by specific environments. Moreover, the programmability and predictability of functional DNA have enabled the use of DNA nanostructures as nanomedicines for various biomedical applications, such as cargo delivery and molecular drugs via stimuli-mediated dynamic structural changes of functional DNAs. Here, the concepts and recent case studies of functional DNA nanotechnology and nanostructures in nanomedicine are reviewed, and future prospects of functional DNA for nanomedicine are indicated.

Aptamer Chimeras for Therapeutic Delivery: The Challenging Perspectives

Nucleic acid-based aptamers have emerged as efficient delivery carriers of therapeutics. Thanks to their unique features, they can be, to date, considered one of the best targeting moieties, allowing the specific recognition of diseased cells and avoiding unwanted off-target effects on healthy tissues. In this review, we revise the most recent contributes on bispecific and multifunctional aptamer therapeutic chimeras. We will discuss key examples of aptamer-mediated delivery of nucleic acid and peptide-based therapeutics underlying their great potentiality and versatility. Achieved objectives and challenges will be highlighted as well.

Nucleic acids delivering nucleic acids

Nucleic acid therapeutics, including siRNAs, miRNAs/antimiRs, gRNAs and ASO, represent innovative and highly promising molecules for the safe treatment of a wide range of pathologies. The efficiency of systemic treatments is impeded by 1) the need to overcome physical and functional barriers in the organism, and 2) to accumulate in the intracellular active site at therapeutic concentrations. Although oligonucleotides either as modified naked molecules or complexed with delivery carriers have revealed to be effectively delivered to the affected target cells, this is restricted to topic treatments or to a few highly vascularized tissues. Therefore, the development of effective strategies for therapeutic nucleic acid selective delivery to target tissues is of primary importance in order to reduce the occurrence of undesired effects on non-target healthy tissues and to permit their translation to clinic. Due to their high affinity for specific ligands, high tissue penetration and chemical flexibility, short single-stranded nucleic acid aptamers are emerging as very attractive carriers for various therapeutic oligonucleotides. Yet, different aptamer-based bioconjugates, able to provide accumulation into target tissues, as well as efficient processing of therapeutic oligonucleotides, have been developed. In this respect, nucleic acid aptamer-mediated delivery strategies represent a powerful approach able to increase the therapeutic efficacy also highly reducing the overall toxicity. In this review, we will summarize recent progress in the field and discuss achieved objectives and optimization of aptamers as delivery carriers of short oligonucleotides.

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

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

A Synthetic Cross-Species CD200R1 Agonist Suppresses Inflammatory Immune Responses In Vivo

Functional aptamers displaying agonistic or antagonistic properties are showing great promise as modulators of immune responses. Here, we report the development of a polyethylene glycol-modified (PEGylated) DNA aptamer as a cross-species (murine and human) CD200R1 agonist that modulates inflammatory responses in vivo. Specifically, DNA aptamers were discovered by performing independent SELEX searches on recombinant murine and human CD200R1. Aptamer motifs identified by next generation sequencing (NGS) were subsequently compared, leading to the discovery of motifs common to both targets. The CD200R1 DNA aptamer CCS13 displayed the highest agonistic activity toward CD200R1 in terms of suppressing the induction of cytotoxic T-lymphocytes (CTLs) in both human and murine allogeneic-mixed lymphocyte cultures (allo-MLCs). A 20-kDa polyethylene glycol (PEG) chain was covalently attached to the 5′ end of this aptamer, and the resulting conjugate was shown to block inflammatory responses in murine models of skin graft rejection and house-dust-mite-induced allergic airway inflammation. Importantly, this agonistic aptamer does not suppress CTL induction in 5-day allo-MLCs with responder cells derived from CD200R1^−/− mice, indicating that its mode of action is directly linked to CD200R1 activation. This study suggests that one can derive agonistic DNA aptamers that can be verified as immuno-modulators in murine models with outcomes potentially translatable to the treatment of human conditions.

Current Advances in Aptamers for Cancer Diagnosis and Therapy

Nucleic acid aptamers are single-stranded oligonucleotides that interact with target molecules with high affinity and specificity in unique three-dimensional structures. Aptamers are generally isolated by a simple selection process called systematic evolution of ligands by exponential enrichment (SELEX) and then can be chemically synthesized and modified. Because of their high affinity and specificity, aptamers are promising agents for biomarker discovery, as well as cancer diagnosis and therapy. In this review, we present recent progress and challenges in aptamer and SELEX technology and highlight some representative applications of aptamers in cancer therapy.

Size, Shape, and Sequence-Dependent Immunogenicity of RNA Nanoparticles

RNA molecules have emerged as promising therapeutics. Like all other drugs, the safety profile and immune response are important criteria for drug evaluation. However, the literature on RNA immunogenicity has been controversial. Here, we used the approach of RNA nanotechnology to demonstrate that the immune response of RNA nanoparticles is size, shape, and sequence dependent. RNA triangle, square, pentagon, and tetrahedron with same shape but different sizes, or same size but different shapes were used as models to investigate the immune response. The levels of pro-inflammatory cytokines induced by these RNA nanoarchitectures were assessed in macrophage-like cells and animals. It was found that RNA polygons without extension at the vertexes were immune inert. However, when single-stranded RNA with a specific sequence was extended from the vertexes of RNA polygons, strong immune responses were detected. These immunostimulations are sequence specific, because some other extended sequences induced little or no immune response. Additionally, larger-size RNA square induced stronger cytokine secretion. 3D RNA tetrahedron showed stronger immunostimulation than planar RNA triangle. These results suggest that the immunogenicity of RNA nanoparticles is tunable to produce either a minimal immune response that can serve as safe therapeutic vectors, or a strong immune response for cancer immunotherapy or vaccine adjuvants.

Selection and Application of Aptamers and Intramers

Aptamers are auspicious nucleic acid ligands for targeting different molecules, such as small molecules, peptides, proteins, or even whole living cells. They are short single-stranded DNA or RNA oligonucleotides, which can fold into complex three-dimensional structures and bind selectively their targets. Using the combinatorial chemistry process SELEX (Systematic Evolution of Ligands by EXponential Enrichment), target specific aptamers can be selected. These aptamers have a variety of application possibilities and can be used as sensors, diagnostic, imaging or therapeutic agents, and in the field of regenerative medicine for tissue engineering.

Identification of LAG3 high affinity aptamers by HT-SELEX and Conserved Motif Accumulation (CMA)

LAG3 receptor belongs to a family of immune-checkpoints expressed in T lymphocytes and other cells of the immune system. It plays an important role as a rheostat of the immune response. Focus on this receptor as a potential therapeutic target in cancer immunotherapy has been underscored after the success of other immune-checkpoint blockade strategies in clinical trials. LAG3 showcases the interest in the field of autoimmunity as several studies show that LAG3-targeting antibodies can also be used for the treatment of autoimmune diseases. In this work we describe the identification of a high-affinity LAG3 aptamer by High Throughput Sequencing SELEX in combination with a study of potential conserved binding modes according to sequence conservation by using 2D-structure prediction and 3D-RNA modeling using Rosetta. The aptamer with the highest accumulation of these conserved sequence motifs displays the highest affinity to LAG3 recombinant soluble proteins and binds to LAG3-expressing lymphocytes. The aptamer described herein has the potential to be used as a therapeutic agent, as it enhances the threshold of T-cell activation. Nonetheless, in future applications, it could also be engineered for treatment of autoimmune diseases by target depletion of LAG3-effector T lymphocytes.

Potential Diagnostic and Therapeutic Applications of Oligonucleotide Aptamers in Breast Cancer

Breast cancer is one of the most common causes of cancer related deaths in women. Currently, with the development of early detection, increased social awareness and kinds of treatment options, survival rate has improved in nearly every type of breast cancer patients. However, about one third patients still have increased chances of recurrence within five years and the five-year relative survival rate in patients with metastasis is less than 30%. Breast cancer contains multiple subtypes. Each subtype could cause distinct clinical outcomes and systemic interventions. Thereby, new targeted therapies are of particular importance to solve this major clinical problem. Aptamers, often termed “chemical antibodies”, are functionally similar to antibodies and have demonstrated their superiority of recognizing target with high selectivity, affinity and stability. With these intrinsic properties, aptamers have been widely studied in cancer biology and some are in clinical trials. In this review, we will firstly discuss about the global impacts and mechanisms of breast cancer, then briefly highlight applications of aptamers that have been developed for breast cancer and finally summarize various challenges in clinical translation of aptamers.

Generation and Applications of a DNA Aptamer against Gremlin-1

Gremlin-1, a highly conserved glycosylated and phosphorylated secretory protein, plays important roles in diverse biological processes including early embryonic development, fibrosis, tumorigenesis, and renal pathophysiology. Aptamers, which are RNA or DNA single-stranded oligonucleotides capable of binding specifically to different targets ranging from small organics to whole cells, have potential applications in targeted imaging, diagnosis and therapy. In this study, we obtained a DNA aptamer against Gremlin-1 (G-ap49) using in vitro Systematic Evolution of Ligands by Exponential Enrichment (SELEX). Binding assay and dot-blot showed that G-ap49 had high affinity for Gremlin-1. Further experiments indicated that G-ap49 was quite stable in a cell culture system and could be used in South-Western blot analysis, enzyme-linked aptamer sorbent assay (ELASA), and aptamer-based cytochemistry and histochemistry staining to detect Gremlin-1. Moreover, our study demonstrated that G-ap49 is capable of revealing the subcellular localization of Gremlin-1. These data indicate that G-ap49 can be used as an alternative to antibodies in detecting Gremlin-1.

Recent Advances in Aptamers Targeting Immune System

The immune system plays important role in protecting the organism by recognizing non-self molecules from pathogen such as bacteria, parasitic worms, and viruses. When the balance of the host defense system is disturbed, immunodeficiency, autoimmunity, and inflammation occur. Nucleic acid aptamers are short single-stranded DNA (ssDNA) or RNA ligands that interact with complementary molecules with high specificity and affinity. Aptamers that target the molecules involved in immune system to modulate their function have great potential to be explored as new diagnostic and therapeutic agents for immune disorders. This review summarizes recent advances in the development of aptamers targeting immune system. The selection of aptamers with superior chemical and biological characteristics will facilitate their application in the diagnosis and treatment of immune disorders.

INTEGRATED MICROFLUIDIC SELEX USING FREE SOLUTION ELECTROKINETICS

Systematic evolution of ligands by exponential enrichment (SELEX) offers a powerful method to isolate affinity oligonucleotides known as aptamers, which can then be used in a wide range of applications from drug delivery to biosensing. However, conventional SELEX methods rely on labor intensive and time consuming benchtop operations. A simplified microfluidic approach is presented which allows integration of the affinity selection and amplification stages of SELEX for the isolation of target-binding oligonucleotides by combining bead-based biochemical reactions with free solution electrokinetic oligonucleotide transfer. Free solution electrokinetics allows coupling of affinity selection and amplification for closed loop oligonucleotide enrichment without the need for offline processes, flow handling components or gel components, while bead based selection and amplification allow efficient manipulation of reagents and reaction products thereby realizing on-chip loop closure and integration of the entire SELEX process. Thus the approach is capable of multi-round enrichment of oligonucleotides using simple transfer processes while maintaining a high level of device integration, as demonstrated by the isolation of an aptamer pool against a protein target (IgA) with significantly higher binding affinity than the starting library in approximately 4 hours of processing time.

Aptamers as targeted therapeutics: current potential and challenges

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

Local Delivery of the Toll-Like Receptor 9 Ligand CpG Downregulates Host Immune and Inflammatory Responses, Ameliorating Established Leishmania (Viannia) panamensis Chronic Infection

Infection by Leishmania (Viannia) panamensis, the predominant etiologic agent for cutaneous leishmaniasis in Colombia, is characterized by a chronic mixed inflammatory response. Current treatment options are plagued by toxicity, lengthy treatment regimens, and growing evidence of drug resistance. Immunotherapy, modulating the immune system to mount a protective response, may provide an alternate therapeutic approach. We investigated the ability of the Toll-like receptor 9 (TLR9) ligand CpG to modulate established disease in the L (V) panamensis mouse model. Treatment of established infection with a high dose (50 μg) of CpG ameliorated disease and lowered parasite burden. Interestingly, immediately after treatment there was a significant increase in transforming growth factor β (TGF-β) and concomitantly an increase in T regulatory cell (Treg) function. Although a general reduction in cell-mediated immune cytokine and chemokine (gamma interferon [IFN-γ], interleukin 10 [IL-10], IL-13, IL-6, granulocyte-macrophage colony-stimulating factor [GM-CSF], IL-4, and MIP-1α) responses of the treated mice was observed, certain chemokines (RANTES, monocyte chemoattractant protein 1[MCP-1], and IP-10) were increased. Further, in peripheral blood mononuclear cells (PBMCs) from patients with cutaneous leishmaniasis, CpG treatment similarly exhibited a dose-response effect on the production of IFN-γ, IL-17, IL-10, and IL-13, with reductions observed at higher doses. To further understand the underlying mechanisms and cell populations driving the CpG mediated response, we examined the ex vivo dose effects mediated by the TLR9⁺ cell populations (dendritic cells, macrophages, and B cells) found to accumulate labeled CpG in vivo Notably, B cells altered the production of IL-17, IL-13, and IFN-γ, supporting a role for B cells functioning as antigen-presenting cells (APCs) and/or regulatory cells during infection. Interestingly, B cells have been previously demonstrated as a primary type of APC in patients infected with L (V) panamensis and thus may be useful targets of immunotherapy. Collectively, our results show that CpG-induced immune regulation leads to a dampening of the host immune response and healing in the mouse model, and it may provide an alternate approach to treatment of cutaneous leishmaniasis caused by L (V) panamensis.

An Integrated Microfluidic SELEX Approach Using Combined Electrokinetic and Hydrodynamic Manipulation

This article presents a microfluidic approach for the integration of the process of aptamer selection via systematic evolution of ligands by exponential enrichment (SELEX). The approach employs bead-based biochemical reactions in which affinity-selected target-binding oligonucleotides are electrokinetically transferred for amplification, while the amplification product is transferred back for affinity selection via pressure-driven fluid flow. The hybrid approach simplifies the device design and operation procedures by reduced pressure-driven flow control requirements and avoids the potentially deleterious exposure of targets to electric fields prior to and during affinity selection. In addition, bead-based reactions are used to achieve the on-chip coupling of affinity selection and amplification of target-binding oligonucleotides, thereby realizing on-chip loop closure and integration of the entire SELEX process without requiring offline procedures. The microfluidic approach is thus capable of closed-loop, multiround aptamer enrichment as demonstrated by selection of DNA aptamers against the protein immunoglobulin E with high affinity ( KD = 12 nM) in a rapid manner (4 rounds in approximately 10 h).

A Novel PD-L1-targeting Antagonistic DNA Aptamer With Antitumor Effects

The PD-1/PD-L1 axis is a major pathway involved in tumor immune evasion. Here, we report the novel PD-L1 antagonizing DNA aptamer (aptPD-L1) and demonstrate an integrated pipeline that expedites therapeutic aptamer development. Aptamer can exert antibody-mimic functions and is advantageous over antibody for its chemically synthetic nature, low immunogenicity, and efficient tissue penetration. Our results showed that aptPD-L1 blocked the binding between human PD-1 and PD-L1. Experiments using murine models showed that aptPD-L1 promoted in vitro lymphocyte proliferation and suppressed in vivo tumor growth without the induction of observable liver or renal toxicity. Analyses on the aptPD-L1-treated tumors further revealed elevated levels of infiltrating CD4⁺ and CD8⁺ T cells, intratumoral IL-2, TNF-α, interferon (IFN)-γ and the C-X-C motif chemokines, CXCL9 and CXCL10. The CD8⁺ T cells in the aptPD-L1-treated tumors had higher CXCR3 expression level compared to the random-sequence oligonucleotides-treated ones. Besides, the length and density of CD31⁺ intratumoral microvessels were significantly decreased in the aptPD-L1 treatment group. Collectively, our data suggested that aptPD-L1 helps T cell function restoration and modifies tumor microenvironment. These chemokines might orchestrate together to attract more T cells into the tumor tissues to form the positive amplification loop against tumor growth, indicating the translational potential of aptPD-L1 in cancer immunotherapy.

Multivalent Aptamers: Versatile Tools for Diagnostic and Therapeutic Applications

Nucleic acid aptamers generated through an in vitro selection are currently extensively applied as very valuable biomolecular tools thanks to their prominent advantages. Diversity of spatial structures, ease of production through chemical synthesis and a large variety of chemical modifications make aptamers convenient building blocks for the generation of multifunctional constructs. An opportunity to combine different aptamer functionalities with other molecules of interest such as reporter groups, nanoparticles, chemotherapeutic agents, siRNA or antisense oligonucleotides provides a widest range of applications of multivalent aptamers. The present review summarizes approaches to the design of multivalent aptamers, various examples of multifunctional constructs and the prospects of employing them as components of biosensors, probes for affinity capture, tools for cell research and potential therapeutic candidates.

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 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.

Integrated Microfluidic Isolation of Aptamers Using Electrophoretic Oligonucleotide Manipulation

We present a microfluidic approach to integrated isolation of DNA aptamers via systematic evolution of ligands by exponential enrichment (SELEX). The approach employs a microbead-based protocol for the processes of affinity selection and amplification of target-binding oligonucleotides, and an electrophoretic DNA manipulation scheme for the coupling of these processes, which are required to occur in different buffers. This achieves the full microfluidic integration of SELEX, thereby enabling highly efficient isolation of aptamers in drastically reduced times and with minimized consumption of biological material. The approach as such also offers broad target applicability by allowing selection of aptamers with respect to targets that are either surface-immobilized or solution-borne, potentially allowing aptamers to be developed as readily available affinity reagents for a wide range of targets. We demonstrate the utility of this approach on two different procedures, respectively for isolating aptamers against a surface-immobilized protein (immunoglobulin E) and a solution-phase small molecule (bisboronic acid in the presence of glucose). In both cases aptamer candidates were isolated in three rounds of SELEX within a total process time of approximately 10 hours.

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.

Aptamers Against Immunologic Targets: Diagnostic and Therapeutic Prospects

The concept of in vitro selection of nucleic acid aptamers emerged 25 years ago, and since then tremendous progress has been achieved in the development of different aptamers and their applications for various bioanalytical and therapeutic purposes. Among other protein targets of aptamers, immune system proteins are of particular interest both as diagnostic markers and therapeutic targets. The present review summarizes up-to-date articles concerning the selection and design of DNA and RNA aptamers against immunologic targets such as antibodies, cytokines, and T-cell and B-cell receptors. We also discuss the prospects of employing aptamers as recognizing modules of diagnostic aptasensors, potential therapeutic candidates for the treatment of autoimmune diseases and cancer, and specific tools for functional studies of immune system proteins.

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.

2-fluoro-RNA oligonucleotide CD40 targeted aptamers for the control of B lymphoma and bone-marrow aplasia

Recent studies have underscored the importance of immunomodulatory antibodies in the treatment of solid and hematological tumors. ODN-Aptamers are rising as a novel class of drugs that can rival therapeutic antibodies. The success of some of the current cancer immunotherapy approaches in oncological patients depends on the intrinsic antigenicity of each tumor as has recently been disclosed, and it is hampered in those patients that are treated with myeloablative chemotherapy or radiotherapy, which induce profound immunosuppression. CD40 agonist and antagonist molecules offer a new therapeutic alternative which has the potential to generate anticancer effects by different mechanisms. HS-SELEX was performed to identify high-affinity aptamers against CD40, and three therapeutic CD40 constructs were engineered as: CD40 agonist aptamer, CD40 antagonist aptamer and CD40 agonistic aptamer-shRNA chimera. It is shown that CD40 agonist aptamers can be used to promote bone-marrow aplasia recovery. CD40 antagonist aptamers are revealed to have a direct antitumor effect on CD40-expressing B-cell lymphoma in vitro and in vivo. Further, in order to identify a therapeutic reagent that will generate the optimal conditions for cancer immunotherapy (antigen-presenting cell activation, tumor antigenicity enhancement and bone-marrow aplasia recovery), CD40 agonist aptamer-shRNA chimera was generated to target the inhibition of the Nonsense mRNA Mediated Decay (NMD) to tumor cells.

Agonists of Co-stimulation in Cancer Immunotherapy Directed Against CD137, OX40, GITR, CD27, CD28, and ICOS

T and natural killer (NK) lymphocytes are considered the main effector players in the immune response against tumors. Full activation of T and NK lymphocytes requires the coordinated participation of several surface receptors that meet their cognate ligands through structured transient cell-to-cell interactions known as immune synapses. In the case of T cells, the main route of stimulation is driven by antigens as recognized in the form of short polypeptides associated with major histocompatibility complex (MHC) antigen-presenting molecules. However, the functional outcome of T-cell stimulation towards clonal expansion and effector function acquisition is contingent on the contact of additional surface receptor-ligand pairs and on the actions of cytokines in the milieu. While some of those interactions are inhibitory, others are activating and are collectively termed co-stimulatory receptors. The best studied belong to either the immunoglobulin superfamily or the tumor necrosis factor-receptor (TNFR) family. Co-stimulatory receptors include surface moieties that are constitutively expressed on resting lymphocytes such as CD28 or CD27 and others whose expression is induced upon recent previous antigen priming, ie, CD137, GITR, OX40, and ICOS. Ligation of these glycoproteins with agonist antibodies actively conveys activating signals to the lymphocyte. Those signals, acting through a potentiation of the cellular immune response, give rise to anti-tumor effects in mouse models. Anti-CD137 antibodies are undergoing clinical trials with evidence of clinical activity and anti-OX40 monoclonal antibodies (mAbs) induce interesting immunomodulation effects in humans. Antibodies anti-CD27 and GITR have recently entered clinical trials. The inherent dangers of these immunomodulation strategies are the precipitation of excessive systemic inflammation or/and invigorating silent autoimmunity. Agonist antibodies, recombinant forms of the natural ligands, and polynucleotide-based aptamers constitute the pharmacologic tools to manipulate such receptors. Preclinical data suggest that the greatest potential of these agents is achieved in combined treatment strategies.

4-1BB Agonists: Multi-Potent Potentiators of Tumor Immunity

Immunotherapy is a rapidly expanding field of oncology aimed at targeting, not the tumor itself, but the immune system combating the cancerous lesion. Of the many approaches currently under study to boost anti-tumor immune responses; modulation of immune co-receptors on lymphocytes in the tumor microenvironment has thus far proven to be the most effective. Antibody blockade of the T cell co-inhibitory receptor cytotoxic T lymphocyte antigen-4 (CTLA-4) has become the first FDA approved immune checkpoint blockade; however, tumor infiltrating lymphocytes express a diverse array of additional stimulatory and inhibitory co-receptors, which can be targeted to boost tumor immunity. Among these, the co-stimulatory receptor 4-1BB (CD137/TNFSF9) possesses an unequaled capacity for both activation and pro-inflammatory polarization of anti-tumor lymphocytes. While functional studies of 4-1BB have focused on its prominent role in augmenting cytotoxic CD8 T cells, 4-1BB can also modulate the activity of CD4 T cells, B cells, natural killer cells, monocytes, macrophages, and dendritic cells. 4-1BB’s expression on both T cells and antigen presenting cells, coupled with its capacity to promote survival, expansion, and enhanced effector function of activated T cells, has made it an alluring target for tumor immunotherapy. In contrast to immune checkpoint blocking antibodies, 4-1BB agonists can both potentiate anti-tumor and anti-viral immunity, while at the same time ameliorating autoimmune disease. Despite this, 4-1BB agonists can trigger high grade liver inflammation which has slowed their clinical development. In this review, we discuss how the underlying immunobiology of 4-1BB activation suggests the potential for therapeutically synergistic combination strategies in which immune adverse events can be minimized.

Immunological and hematological toxicities challenging clinical translation of nucleic acid-based therapeutics

INTRODUCTION

Nucleic acid-based therapeutics (NATs) are proven agents in correcting disorders caused by gene mutations, as treatments against cancer, microbes and viruses, and as vaccine adjuvants. Although many traditional small molecule NATs have been approved for clinical use, commercialization of macromolecular NATs has been considerably slower, and only a few have successfully reached the market. Preclinical and clinical evaluation of macromolecular NATs has revealed many assorted challenges in immunotoxicity, hematotoxicity, pharmacokinetics (PKs), toxicology and formulation. Extensive review has been given to the PK and toxicological concerns of NATs including approaches designed to overcome these issues. Immunological and hematological issues are a commonly reported side effect of NAT treatment; however, literature exploring the mechanistic background of these effects is sparse.

AREAS COVERED

This review focuses on the immunomodulatory properties of various types of therapeutic nucleic acid concepts. The most commonly observed immunological and hematological toxicities are described for various NAT classes, with citations of how to circumvent these toxicities.

EXPERT OPINION

Although some success with overcoming immunological and hematological toxicities of NATs has been achieved in recent years, immunostimulation remains the main dose-limiting factor challenging clinical translation of these promising therapies. Novel delivery vehicles should be considered to overcome this challenge.

Aptamers in immunological research

In recent years aptamers, synthetic DNA or RNA single-chain oligonucleotides, have been used in various immunological studies to bind specific ligands. Detailed data on the interactions of an RNA aptamer with a human Fc fragment were obtained by X-ray crystallography. The complex formation involves multiple weak interactions that resemble protein-protein interactions. Aptamers specific to cell surface receptors may serve as antagonists or agonists blocking or stimulating cell activities. As aptamers can modify T-cell reactions, they could be useful in the treatment of chronic diseases such as autoimmune and oncological pathologies. In chimeras constructed for the delivery of active substances to defined targets, aptamers specific to surface proteins may be used to transport constructs directed to targets such as tumor cells. Aptamers are also employed as highly specific reagents in immunological assays after being labeled with reporter groups such as fluorescent dyes or following immobilization on insoluble carriers such as membranes or microspheres.