RNA-DNA fibers and polygons with controlled immunorecognition activate RNAi, FRET and transcriptional regulation of NF-κB in human cells

Cracking the Code: Enhancing Molecular Tools for Progress in Nanobiotechnology

Nature continually refines its processes for optimal efficiency, especially within biological systems. This article explores the collaborative efforts of researchers worldwide, aiming to mimic nature's efficiency by developing smarter and more effective nanoscale technologies and biomaterials. Recent advancements highlight progress and prospects in leveraging engineered nucleic acids and proteins for specific tasks, drawing inspiration from natural functions. The focus is developing improved methods for characterizing, understanding, and reprogramming these materials to perform user-defined functions, including personalized therapeutics, targeted drug delivery approaches, engineered scaffolds, and reconfigurable nanodevices. Contributions from academia, government agencies, biotech, and medical settings offer diverse perspectives, promising a comprehensive approach to broad nanobiotechnology objectives. Encompassing topics from mRNA vaccine design to programmable protein-based nanocomputing agents, this work provides insightful perspectives on the trajectory of nanobiotechnology toward a future of enhanced biomimicry and technological innovation.

cGAS Mediates the Inflammatory Responses of Human Microglial Cells to Genotoxic DNA Damage

Genomic instability is a key driving force for the development and progression of many age-related neurodegenerative diseases and central nervous system (CNS) cancers. Recently, the cytosolic DNA sensor, cyclic GMP-AMP synthase (cGAS), has been shown to detect and respond to self-DNA accumulation resulting from DNA damaging insults in peripheral cell types. cGAS has been shown to be important in the responses of microglia to DNA viruses and amyloid beta, and we have reported that it underlies the responses of human microglia to exogenous DNA. However, the role of this cytosolic sensor in the detection of self-DNA by glia is poorly understood and its ability to mediate the cellular responses of human microglia to genotoxic DNA damage has not been established. Here, we describe the ability of ionizing radiation and oxidative stress to elicit genomic DNA damage in human microglial cells and to stimulate the production of key inflammatory mediators by these cells in an NF-kB dependent manner. Importantly, we have utilized CRISPR/Cas9 and siRNA-mediated knockdown approaches and a pharmacological inhibitor of the cGAS adaptor protein stimulator of interferon genes (STING) to demonstrate that the cGAS-STING pathway plays a critical role in the generation of these microglial immune responses to such genotoxic insults. Together, these studies support the notion that cGAS mediates the detection of cytosolic self-DNA by microglia, providing a potential mechanism linking genomic instability to the development of CNS cancers and neurodegenerative disorders.

Design and Characterization of Compact, Programmable, Multistranded Nonimmunostimulatory Nucleic Acid Nanoparticles Suitable for Biomedical Applications

We report a thorough investigation of the role of single-stranded thymidine (ssT) linkers in the stability and flexibility of minimal, multistranded DNA nanostructures. We systematically explore the impact of varying the number of ssTs in three-way junction motifs (3WJs) on their formation and properties. Through various UV melting experiments and molecular dynamics simulations, we demonstrate that while the number of ssTs minimally affects thermodynamic stability, the increasing ssT regions significantly enhance the structural flexibility of 3WJs. Utilizing this knowledge, we design triangular DNA nanoparticles with varying ssTs, all showing exceptional assembly efficiency except for the 0T triangle. All triangles demonstrate enhanced stability in blood serum and are nonimmunostimulatory and nontoxic in mammalian cell lines. The 4T 3WJ is chosen as the building block for constructing other polygons due to its enhanced flexibility and favorable physicochemical characteristics, making it a versatile choice for creating cost-effective, stable, and functional DNA nanostructures that can be stored in the dehydrated forms while retaining their structures. Our study provides valuable insights into the design and application of nucleic acid nanostructures, emphasizing the importance of understanding stability and flexibility in the realm of nucleic acid nanotechnology. Our findings suggest the intricate connection between these ssTs and the structural adaptability of DNA 3WJs, paving the way for more precise design and engineering of nucleic acid nanosystems suitable for broad biomedical applications.

Change in Lipofectamine Carrier as a Tool to Fine-Tune Immunostimulation of Nucleic Acid Nanoparticles

Nucleic acid nanoparticles (NANPs) require a carrier to allow for their intracellular delivery to immune cells. Cytokine production, specifically type I and III interferons, allows for reliable monitoring of the carrier effect on NANP immunostimulation. Recent studies have shown that changes in the delivery platform (e.g., lipid-based carriers vs. dendrimers) can alter NANPs' immunorecognition and downstream cytokine production in various immune cell populations. Herein, we used flow cytometry and measured cytokine induction to show how compositional variations in commercially available lipofectamine carriers impact the immunostimulatory properties of NANPs with different architectural characteristics.

Toehold-Mediated Shape Transition of Nucleic Acid Nanoparticles

We introduce a toehold-mediated strand displacement strategy for regulated shape-switching of nucleic acid nanoparticles (NANPs) enabling their sequential transformation from triangular to hexagonal architectures at isothermal conditions. The successful shape transitions were confirmed by electrophoretic mobility shift assays, atomic force microscopy, and dynamic light scattering. Furthermore, implementation of split fluorogenic aptamers allowed for monitoring the individual transitions in real time. Three distinct RNA aptamers─malachite green (MG), broccoli, and mango─were embedded within NANPs as reporter domains to confirm shape transitions. While MG "lights up" within the square, pentagonal, and hexagonal constructs, the broccoli is activated only upon formation of pentagon and hexagon NANPs, and mango reports only the presence of hexagons. Moreover, the designed RNA fluorogenic platform can be employed to construct a logic gate that performs an AND operation with three single-stranded RNA inputs by implementing a non-sequential polygon transformation approach. Importantly, the polygonal scaffolds displayed promising potential as drug delivery agents and biosensors. All polygons exhibited effective cellular internalization followed by specific gene silencing when decorated with fluorophores and RNAi inducers. This work offers a new perspective for the design of toehold-mediated shape-switching nanodevices to activate different light-up aptamers for the development of biosensors, logic gates, and therapeutic devices in the nucleic acid nanotechnology.

3D RNA-scaffolded wireframe origami

Hybrid RNA:DNA origami, in which a long RNA scaffold strand folds into a target nanostructure via thermal annealing with complementary DNA oligos, has only been explored to a limited extent despite its unique potential for biomedical delivery of mRNA, tertiary structure characterization of long RNAs, and fabrication of artificial ribozymes. Here, we investigate design principles of three-dimensional wireframe RNA-scaffolded origami rendered as polyhedra composed of dual-duplex edges. We computationally design, fabricate, and characterize tetrahedra folded from an EGFP-encoding messenger RNA and de Bruijn sequences, an octahedron folded with M13 transcript RNA, and an octahedron and pentagonal bipyramids folded with 23S ribosomal RNA, demonstrating the ability to make diverse polyhedral shapes with distinct structural and functional RNA scaffolds. We characterize secondary and tertiary structures using dimethyl sulfate mutational profiling and cryo-electron microscopy, revealing insight into both global and local, base-level structures of origami. Our top-down sequence design strategy enables the use of long RNAs as functional scaffolds for complex wireframe origami.

Dynamic Nanostructures for Conditional Activation and Deactivation of Biological Pathways

Nucleic acid nanotechnology utilizes natural and synthetic structural motifs to build versatile nucleic acid nanoparticles (NANPs). These rationally designed assemblies can be further equipped with functional nucleic acids and other molecules such as peptides, fluorescent dyes, etc. In addition to nucleic acids that directly interact with the regulated target gene transcripts, NANPs can display decoys, wherein the oligonucleotide stretches with transcription factor binding sequences, preventing transcription initiation. The nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) is a group of five crucial transcription factors regulating the pathogenesis of inflammatory diseases and cancer; as such, they are relevant targets for therapy. One therapeutic approach involves interdependent self-recognizing hybridized DNA/RNA fibers designed to bind NF-κB and prevent its interaction with the promotor region of NF-κB-dependent genes involved in inflammatory responses. Decoying NF-κB results in the inability to initiate transcription of regulated genes, showing a promising approach to gene regulation and gene therapy. The protocol described herein provides detailed steps for the synthesis of NF-κB decoy fibers, as well as their characterization using polyacrylamide gel electrophoresis (to confirm desired physicochemical properties and purity) and functional bioassays (to confirm desired biological activity).

Therapeutic immunomodulation by rationally designed nucleic acids and nucleic acid nanoparticles

The immune system has evolved to defend organisms against exogenous threats such as viruses, bacteria, fungi, and parasites by distinguishing between "self" and "non-self". In addition, it guards us against other diseases, such as cancer, by detecting and responding to transformed and senescent cells. However, for survival and propagation, the altered cells and invading pathogens often employ a wide range of mechanisms to avoid, inhibit, or manipulate the immunorecognition. As such, the development of new modes of therapeutic intervention to augment protective and prevent harmful immune responses is desirable. Nucleic acids are biopolymers essential for all forms of life and, therefore, delineating the complex defensive mechanisms developed against non-self nucleic acids can offer an exciting avenue for future biomedicine. Nucleic acid technologies have already established numerous approaches in therapy and biotechnology; recently, rationally designed nucleic acids nanoparticles (NANPs) with regulated physiochemical properties and biological activities has expanded our repertoire of therapeutic options. When compared to conventional therapeutic nucleic acids (TNAs), NANP technologies can be rendered more beneficial for synchronized delivery of multiple TNAs with defined stabilities, immunological profiles, and therapeutic functions. This review highlights several recent advances and possible future directions of TNA and NANP technologies that are under development for controlled immunomodulation.

Metalated Nucleic Acid Nanostructures

Nucleic acid nanotechnology takes advantage of the self-assembling property of nucleic acids to form a variety of shapes and structures. The incorporation of metal ions into these structures introduces functionality for sensor and molecular electronic applications. Here, we describe a protocol for the incorporation of silver ions into polygonal nanoshapes that self-assemble from RNA and DNA modules.

Light-Assisted Drying for the Thermal Stabilization of Nucleic Acid Nanoparticles and Other Biologics

Cold-chain storage can be challenging and expensive for the transportation and storage of biologics, especially in low-resource settings. Nucleic acid nanoparticles (NANPs) are an example of new biological products that require refrigerated storage. Light-assisted drying (LAD) is a new processing technique to prepare biologics for anhydrous storage in a trehalose amorphous solid matrix at ambient temperatures. Small volume samples (10 μL) containing NANPs are irradiated with a 1064 nm laser to speed the evaporation of water and create an amorphous trehalose preservation matrix. In previous studies, samples were stored for 1 month at 4 °C or 20 °C without degradation. A FLIR SC655 mid-IR camera is used to record the temperature of samples during processing. The trehalose matrix was characterized using polarized light imaging to determine if crystallization occurred during processing or storage. Damage to LAD-processed NANPs was assessed after processing and storage using gel electrophoresis.

Anticoagulant Activity of Nucleic Acid Nanoparticles (NANPs) Assessed by Thrombin Generation Dynamics on a Fully Automated System

Rapidly reversible anticoagulant agents have great clinical potential. Oligonucleotide-based anticoagulant agents are uniquely positioned to fill this clinical niche, as they are able to be deactivated through the introduction of the reverse complement oligo. Once the therapeutic and the antidote oligos meet in solution, they are able to undergo isothermal reassociation to form short, inactive, duplexes that are rapidly secreted via filtration by the kidneys. The formation of the duplexes interrupts the structure of the anticoagulant oligo, allowing normal coagulation to be restored. To effectively assess these new anticoagulants, a variety of methods may be employed. The measurement of thrombin generation (TG) reflects the overall capacity of plasma to produce active thrombin and provides a strong contribution to identifying new anticoagulant drugs, including DNA/RNA thrombin binding aptamer carrying fibers which are used through this chapter as an example. Here we describe the TG assessed by Calibrated Automated Thrombogram (CAT) assay in a fully automated system. This method is based on the detection of TG in plasma samples by measuring fluorescent signals released from a quenched fluorogenic thrombin substrate and the subsequent conversion of these signals in TG curves.

Combining Experimental Restraints and RNA 3D Structure Prediction in RNA Nanotechnology

Precise RNA tertiary structure prediction can aid in the design of RNA nanoparticles. However, most existing RNA tertiary structure prediction methods are limited to small RNAs with relatively simple secondary structures. Large RNA molecules usually have complex secondary structures, including multibranched loops and pseudoknots, allowing for highly flexible RNA geometries and multiple stable states. Various experiments and bioinformatics analyses can often provide information about the distance between atoms (or residues) in RNA, which can be used to guide the prediction of RNA tertiary structure. In this chapter, we will introduce a platform, iFoldNMR, that can incorporate non-exchangeable imino protons resonance data from NMR as restraints for RNA 3D structure prediction. We also introduce an algorithm, DVASS, which optimizes distance restraints for better RNA 3D structure prediction.

Assessment of Intracellular Compartmentalization of RNA Nanostructures

Nucleic acid nanoparticles (NANPs) are extensively investigated as diagnostic and therapeutic tools. These innovative particles can be composed of RNA, DNA, and/or modified nucleic acids. Due to the regulatory role of nucleic acids in the cellular system, NANPs have the ability to identify target molecules and regulate expression of genes in disease pathways. However, translation of NANPs in clinical settings is hindered due to inefficient intracellular delivery, chemical instability, and off-target immunostimulatory effects following immune recognition. The composition of nucleic acids forming NANPs has been demonstrated to influence immunorecognition, subcellular compartmentalization, and physicochemical properties of NANPs. This chapter first outlines the methods used to generate a panel of NANPs with a uniform shape, size, charge, sequence, and connectivity. This includes the procedures for replacing the RNA strands with DNA or chemical analogs in the designated NANPs. Second, this chapter will also describe experiments to assess the effect of the chemical modification on enzymatic and thermodynamic stability, delivery efficiency, and subcellular compartmentalization of NANPs.

Dissecting Functional Biological Interactions Using Modular RNA Nanoparticles

Nucleic acid nanoparticles (NANPs) are an exciting and innovative technology in the context of both basic and biomedical research. Made of DNA, RNA, or their chemical analogs, NANPs are programmed for carrying out specific functions within human cells. NANPs are at the forefront of preventing, detecting, and treating disease. Their nucleic acid composition lends them biocompatibility that provides their cargo with enhanced opportunity for coordinated delivery. Of course, the NANP system of targeting specific cells and tissues is not without its disadvantages. Accumulation of NANPs outside of the target tissue and the potential for off-target effects of NANP-mediated cargo delivery present challenges to research and medical professionals and these challenges must be effectively addressed to provide safe treatment to patients. Importantly, development of NANPs with regulated biological activities and immunorecognition becomes a promising route for developing versatile nucleic acid therapeutics. In a basic research context, NANPs can assist investigators in fine-tuning the structure-function relationship of final formulations and in this review, we explore the practical applications of NANPs in laboratory and clinical settings and discuss how we can use established nucleic acid research techniques to design effective NANPs.

Biomotors, viral assembly, and RNA nanobiotechnology: Current achievements and future directions

The International Society of RNA Nanotechnology and Nanomedicine (ISRNN) serves to further the development of a wide variety of functional nucleic acids and other related nanotechnology platforms. To aid in the dissemination of the most recent advancements, a biennial discussion focused on biomotors, viral assembly, and RNA nanobiotechnology has been established where international experts in interdisciplinary fields such as structural biology, biophysical chemistry, nanotechnology, cell and cancer biology, and pharmacology share their latest accomplishments and future perspectives. The results summarized here highlight advancements in our understanding of viral biology and the structure-function relationship of frame-shifting elements in genomic viral RNA, improvements in the predictions of SHAPE analysis of 3D RNA structures, and the understanding of dynamic RNA structures through a variety of experimental and computational means. Additionally, recent advances in the drug delivery, vaccine design, nanopore technologies, biomotor and biomachine development, DNA packaging, RNA nanotechnology, and drug delivery are included in this critical review. We emphasize some of the novel accomplishments, major discussion topics, and present current challenges and perspectives of these emerging fields.

Artificial Immune Cell, AI-cell, a New Tool to Predict Interferon Production by Peripheral Blood Monocytes in Response to Nucleic Acid Nanoparticles

Nucleic acid nanoparticles, or NANPs, rationally designed to communicate with the human immune system, can offer innovative therapeutic strategies to overcome the limitations of traditional nucleic acid therapies. Each set of NANPs is unique in their architectural parameters and physicochemical properties, which together with the type of delivery vehicles determine the kind and the magnitude of their immune response. Currently, there are no predictive tools that would reliably guide the design of NANPs to the desired immunological outcome, a step crucial for the success of personalized therapies. Through a systematic approach investigating physicochemical and immunological profiles of a comprehensive panel of various NANPs, the research team developes and experimentally validates a computational model based on the transformer architecture able to predict the immune activities of NANPs. It is anticipated that the freely accessible computational tool that is called an "artificial immune cell," or AI-cell, will aid in addressing the current critical public health challenges related to safety criteria of nucleic acid therapies in a timely manner and promote the development of novel biomedical tools.

Expanding Structural Space for Immunomodulatory Nucleic Acid Nanoparticles (Nanps) via Spatial Arrangement of Their Therapeutic Moieties

Different therapeutic nucleic acids (TNAs) can be unified in a single structure by their elongation with short oligonucleotides designed to self-assemble into nucleic acid nanoparticles (NANPs). With this approach, therapeutic cocktails with precisely controlled composition and stoichiometry of active ingredients can be delivered to the same diseased cells for enhancing pharmaceutical action. In this work, an additional nanotechnology-based therapeutic option that enlists a biocompatible NANP-encoded platform for their controlled patient-specific immunorecognition is explored. For this, a set of representative functional NANPs is extensively characterized in vitro, ex vivo, and in vivo and then further analyzed for immunostimulation of human peripheral blood mononuclear cells freshly collected from healthy donor volunteers. The results of the study present the advancement of the current TNA approach toward personalized medicine and offer a new strategy to potentially address top public health challenges related to drug overdose and safety through the biodegradable nature of the functional platform with immunostimulatory regulation.

The Application of Light-Assisted Drying to the Thermal Stabilization of Nucleic Acid Nanoparticles

Background: Cold-chain storage can be challenging and expensive for the transportation and storage of biologics, especially in low-resource settings. Nucleic acid nanoparticles (NANPs) are an example of new biological products that require refrigerated storage. Light-assisted drying (LAD) is a new processing technique to prepare biologics for anhydrous storage in a trehalose amorphous solid matrix at ambient temperatures. In this study, LAD was used to thermally stabilize four types of NANPs with differing structures and melting temperatures. Methods: Small volume samples (10 μL) containing NANPs were irradiated with a 1064 nm laser to speed the evaporation of water and create an amorphous trehalose preservation matrix. Samples were then stored for 1 month at 4°C or 20°C. A FLIR C655 mid-IR camera was used to record the temperature of samples during processing. The trehalose matrix was characterized using polarized light imaging (PLI) to determine if crystallization occurred during processing or storage. Damage to LAD-processed NANPs was assessed after processing and storage using gel electrophoresis. Results: Based on the end moisture content (EMC) as a function time and the thermal histories of samples, a LAD processing time of 30 min is sufficient to achieve low EMCs for the 10 μL samples used in this study. PLI demonstrates that the trehalose matrix was resistant to crystallization during processing and after storage at 4°C and at room temperature. The native-polyacrylamide gel electrophoresis results for DNA cubes, RNA cubes, and RNA rings indicate that the main structures of these NANPs were not damaged significantly after LAD processing and being stored at 4°C or at room temperature for 1 month. Conclusions: These preliminary studies indicate that LAD processing can stabilize NANPs for dry-state storage at room temperature, providing an alternative to refrigerated storage for these nanomedicine products.

Locking and Unlocking Thrombin Function Using Immunoquiescent Nucleic Acid Nanoparticles with Regulated Retention In Vivo

The unbalanced coagulation of blood is a life-threatening event that requires accurate and timely treatment. We introduce a user-friendly biomolecular platform based on modular RNA-DNA anticoagulant fibers programmed for reversible extracellular communication with thrombin and subsequent control of anticoagulation via a "kill-switch" mechanism that restores hemostasis. To demonstrate the potential of this reconfigurable technology, we designed and tested a set of anticoagulant fibers that carry different thrombin-binding aptamers. All fibers are immunoquiescent, as confirmed in freshly collected human peripheral blood mononuclear cells. To assess interindividual variability, the anticoagulation is confirmed in the blood of human donors from the U.S. and Brazil. The anticoagulant fibers reveal superior anticoagulant activity and prolonged renal clearance in vivo in comparison to free aptamers. Finally, we confirm the efficacy of the "kill-switch" mechanism in vivo in murine and porcine models.

Anhydrous Nucleic Acid Nanoparticles for Storage and Handling at Broad Range of Temperatures

Recent advances in nanotechnology now allow for the methodical implementation of therapeutic nucleic acids (TNAs) into modular nucleic acid nanoparticles (NANPs) with tunable physicochemical properties which can match the desired biological effects, provide uniformity, and regulate the delivery of multiple TNAs for combinatorial therapy. Despite the potential of novel NANPs, the maintenance of their structural integrity during storage and shipping remains a vital issue that impedes their broader applications. Cold chain storage is required to maintain the potency of NANPs in the liquid phase, which greatly increases transportation costs. To promote long-term storage and retention of biological activities at higher temperatures (e.g., +50 °C), a panel of representative NANPs is first exposed to three different drying mechanisms-vacuum concentration (SpeedVac), lyophilization (Lyo), and light-assisted drying (LAD)-and then rehydrated and analyzed. While SpeedVac primarily operates using heat, Lyo avoids temperature increases by taking advantage of pressure reduction and LAD involves a near-infrared laser for uniform drying in the presence of trehalose. This work compares and defines refinements crucial in formulating an optimal strategy for producing stable, fully functional NANPs and presents a forward advancement in their development for clinical applications.

Redox signaling at the crossroads of human health and disease

Redox biology is at the core of life sciences, accompanied by the close correlation of redox processes with biological activities. Redox homeostasis is a prerequisite for human health, in which the physiological levels of nonradical reactive oxygen species (ROS) function as the primary second messengers to modulate physiological redox signaling by orchestrating multiple redox sensors. However, excessive ROS accumulation, termed oxidative stress (OS), leads to biomolecule damage and subsequent occurrence of various diseases such as type 2 diabetes, atherosclerosis, and cancer. Herein, starting with the evolution of redox biology, we reveal the roles of ROS as multifaceted physiological modulators to mediate redox signaling and sustain redox homeostasis. In addition, we also emphasize the detailed OS mechanisms involved in the initiation and development of several important diseases. ROS as a double‐edged sword in disease progression suggest two different therapeutic strategies to treat redox‐relevant diseases, in which targeting ROS sources and redox‐related effectors to manipulate redox homeostasis will largely promote precision medicine. Therefore, a comprehensive understanding of the redox signaling networks under physiological and pathological conditions will facilitate the development of redox medicine and benefit patients with redox‐relevant diseases.

Critical review of nucleic acid nanotechnology to identify gaps and inform a strategy for accelerated clinical translation

With numerous recent advances, the field of therapeutic nucleic acid nanotechnology is now poised for clinical translation supported by several examples of FDA-approved nucleic acid nanoformulations including two recent mRNA-based COVID-19 vaccines. Within this rapidly growing field, a new subclass of nucleic acid therapeutics called nucleic acid nanoparticles (NANPs) has emerged in recent years, which offers several unique properties distinguishing it from traditional therapeutic nucleic acids. Key unique aspects of NANPs include their well-defined 3D structure, their tunable multivalent architectures, and their ability to incorporate conditional activations of therapeutic targeting and release functions that enable diagnosis and therapy of cancer, regulation of blood coagulation disorders, as well as the development of novel vaccines, immunotherapies, and gene therapies. However, non-consolidated research developments of this highly interdisciplinary field create crucial barriers that must be overcome in order to impact a broader range of clinical indications. Forming a consortium framework for nucleic acid nanotechnology would prioritize and consolidate translational efforts, offer several unifying solutions to expedite their transition from bench-to-bedside, and potentially decrease the socio-economic burden on patients for a range of conditions. Herein, we review the unique properties of NANPs in the context of therapeutic applications and discuss their associated translational challenges.

Application of Nucleic Acid Frameworks in the Construction of Nanostructures and Cascade Biocatalysts: Recent Progress and Perspective

Nucleic acids underlie the storage and retrieval of genetic information literally in all living organisms, and also provide us excellent materials for making artificial nanostructures and scaffolds for constructing multi-enzyme systems with outstanding performance in catalyzing various cascade reactions, due to their highly diverse and yet controllable structures, which are well determined by their sequences. The introduction of unnatural moieties into nucleic acids dramatically increased the diversity of sequences, structures, and properties of the nucleic acids, which undoubtedly expanded the toolbox for making nanomaterials and scaffolds of multi-enzyme systems. In this article, we first introduce the molecular structures and properties of nucleic acids and their unnatural derivatives. Then we summarized representative artificial nanomaterials made of nucleic acids, as well as their properties, functions, and application. We next review recent progress on constructing multi-enzyme systems with nucleic acid structures as scaffolds for cascade biocatalyst. Finally, we discuss the future direction of applying nucleic acid frameworks in the construction of nanomaterials and multi-enzyme molecular machines, with the potential contribution that unnatural nucleic acids may make to this field highlighted.

RNA-DNA Hybrid Nanoshape Synthesis by Facile Module Exchange

The preparation of nucleic acid nanostructures has relied predominantly on procedures of additive fabrication in which complex architectures are assembled by concerted self-assembly and sequential addition of building blocks. We had previously established RNA-DNA hybrid nanoshapes with modular architectures that enable multistep synthetic approaches inspired by organic molecular synthesis where additive and transformative steps are used to prepare complex molecular architectures. We report the establishment of module replacement and strand exchange as synthetic transformations in nucleic acid hybrid nanoshapes, which are enabled by minimally destabilizing sequence elements such as a single unpaired overhang nucleotide or a mismatch base pair. Module exchange facilitated by thermodynamic lability triggers adds a powerful transformative approach to the repertoire of additive and transformative synthetic methods for the preparation of complex composite materials.

The International Society of RNA Nanotechnology and Nanomedicine (ISRNN): The Present and Future of the Burgeoning Field

The International Society of RNA Nanotechnology and Nanomedicine (ISRNN) hosts an annual meeting series focused on presenting the latest research achievements involving RNA-based therapeutics and strategies, aiming to expand their current biomedical applications while overcoming the remaining challenges of the burgeoning field of RNA nanotechnology. The most recent online meeting hosted a series of engaging talks and discussions from an international cohort of leading nanotechnologists that focused on RNA modifications and modulation, dynamic RNA structures, overcoming delivery limitations using a variety of innovative platforms and approaches, and addressing the newly explored potential for immunomodulation with programmable nucleic acid nanoparticles. In this Nano Focus, we summarize the main discussion points, conclusions, and future directions identified during this two-day webinar as well as more recent advances to highlight and to accelerate this exciting field.

Nano-sandwich composite by kinetic trapping assembly from protein and nucleic acid

Design and preparation of layered composite materials alternating between nucleic acids and proteins has been elusive due to limitations in occurrence and geometry of interaction sites in natural biomolecules. We report the design and kinetically controlled stepwise synthesis of a nano-sandwich composite by programmed noncovalent association of protein, DNA and RNA modules. A homo-tetramer protein core was introduced to control the self-assembly and precise positioning of two RNA–DNA hybrid nanotriangles in a co-parallel sandwich arrangement. Kinetically favored self-assembly of the circularly closed nanostructures at the protein was driven by the intrinsic fast folding ability of RNA corner modules which were added to precursor complex of DNA bound to the protein. The 3D architecture of this first synthetic protein–RNA–DNA complex was confirmed by fluorescence labeling and cryo-electron microscopy studies. The synthesis strategy for the nano-sandwich composite provides a general blueprint for controlled noncovalent assembly of complex supramolecular architectures from protein, DNA and RNA components, which expand the design repertoire for bottom-up preparation of layered biomaterials.

Exosomes as natural delivery carriers for programmable therapeutic nucleic acid nanoparticles (NANPs)

With recent advances in nanotechnology and therapeutic nucleic acids (TNAs), various nucleic acid nanoparticles (NANPs) have demonstrated great promise in diagnostics and therapeutics. However, the full realization of NANPs' potential necessitates the development of a safe, efficient, biocompatible, stable, tissue-specific, and non-immunogenic delivery system. Exosomes, the smallest extracellular vesicles and an endogenous source of nanocarriers, offer these advantages while avoiding complications associated with manufactured agents. The lipid membranes of exosomes surround a hydrophilic core, allowing for the simultaneous incorporation of hydrophobic and hydrophilic drugs, nucleic acids, and proteins. Additional capabilities for post-isolation exosome surface modifications with imaging agents, targeting ligands, and covalent linkages also pave the way for their diverse biomedical applications. This review focuses on exosomes: their biogenesis, intracellular trafficking, transportation capacities, and applications with emphasis on the delivery of TNAs and programmable NANPs. We also highlight some of the current challenges and discuss opportunities related to the development of therapeutic exosome-based formulations and their clinical translation.

Controlled Organization of Inorganic Materials Using Biological Molecules for Activating Therapeutic Functionalities

Precise control over the assembly of biocompatible three-dimensional (3D) nanostructures would allow for programmed interactions within the cellular environment. Nucleic acids can be used as programmable crosslinkers to direct the assembly of quantum dots (QDs) and tuned to demonstrate different interparticle binding strategies. Morphologies of self-assembled QDs are evaluated via gel electrophoresis, transmission electron microscopy, small-angle X-ray scattering, and dissipative particle dynamics simulations, with all results being in good agreement. The controlled assembly of 3D QD organizations is demonstrated in cells via the colocalized emission of multiple assembled QDs, and their immunorecognition is assessed via enzyme-linked immunosorbent assays. RNA interference inducers are also embedded into the interparticle binding strategy to be released in human cells only upon QD assembly, which is demonstrated by specific gene silencing. The programmability and intracellular activity of QD assemblies offer a strategy for nucleic acids to imbue the structure and therapeutic function into the formation of complex networks of nanostructures, while the photoluminescent properties of the material allow for optical tracking in cells in vitro.

Programmable DNA-augmented hydrogels for controlled activation of human lymphocytes

Contractile forces within the planar interface between T cell and antigen-presenting surface mechanically stimulate T cell receptors (TCR) in the mature immune synapses. However, the origin of mechanical stimulation during the initial, i.e., presynaptic, microvilli-based TCR activation in the course of immune surveillance remains unknown and new tools to help address this problem are needed. In this work, we develop nucleic acid nanoassembly (NAN)-based technology for functionalization of hydrogels using isothermal toehold-mediated reassociation of RNA/DNA heteroduplexes. Resulting platform allows for regulation with NAN linkers of 3D force momentum along the TCR mechanical axis, whereas hydrogels contribute to modulation of 2D shear modulus. By utilizing different lengths of NAN linkers conjugated to polyacrylamide gels of different shear moduli, we demonstrate an efficient capture of human T lymphocytes and tunable activation of TCR, as confirmed by T-cell spreading and pY foci.

Simultaneous silencing of lysophosphatidylcholine acyltransferases 1-4 by nucleic acid nanoparticles (NANPs) improves radiation response of melanoma cells

Radiation induces the generation of platelet-activating factor receptor (PAF-R) ligands, including PAF and oxidized phospholipids. Alternatively, PAF is also synthesized by the biosynthetic enzymes lysophosphatidylcholine acyltransferases (LPCATs) which are expressed by tumor cells including melanoma. The activation of PAF-R by PAF and oxidized lipids triggers a survival response protecting tumor cells from radiation-induced cell death, suggesting the involvement of the PAF/PAF-R axis in radioresistance. Here, we investigated the role of LPCATs in the melanoma cell radiotherapy response. LPCAT is a family of four enzymes, LPCAT1-4, and modular nucleic acid nanoparticles (NANPs) allowed for the simultaneous silencing of all four LPCATs. We found that the in vitro simultaneous silencing of all four LPCAT transcripts by NANPs enhanced the therapeutic effects of radiation in melanoma cells by increasing cell death, reducing long-term cell survival, and activating apoptosis. Thus, we propose that NANPs are an effective strategy for improving radiotherapy efficacy in melanomas.

Designed and biologically active protein lattices

Versatile methods to organize proteins in space are required to enable complex biomaterials, engineered biomolecular scaffolds, cell-free biology, and hybrid nanoscale systems. Here, we demonstrate how the tailored encapsulation of proteins in DNA-based voxels can be combined with programmable assembly that directs these voxels into biologically functional protein arrays with prescribed and ordered two-dimensional (2D) and three-dimensional (3D) organizations. We apply the presented concept to ferritin, an iron storage protein, and its iron-free analog, apoferritin, in order to form single-layers, double-layers, as well as several types of 3D protein lattices. Our study demonstrates that internal voxel design and inter-voxel encoding can be effectively employed to create protein lattices with designed organization, as confirmed by in situ X-ray scattering and cryo-electron microscopy 3D imaging. The assembled protein arrays maintain structural stability and biological activity in environments relevant for protein functionality. The framework design of the arrays then allows small molecules to access the ferritins and their iron cores and convert them into apoferritin arrays through the release of iron ions. The presented study introduces a platform approach for creating bio-active protein-containing ordered nanomaterials with desired 2D and 3D organizations.

Nucleic acid nanoparticles (NANPs) as molecular tools to direct desirable and avoid undesirable immunological effects

Nucleic acid nanoparticles (NANPs) represent a highly versatile molecular platform for the targeted delivery of various therapeutics. However, despite their promise, further clinical translation of this innovative technology can be hindered by immunological off-target effects. All human cells are equipped with an arsenal of receptors that recognize molecular patterns specific to foreign nucleic acids and understanding the rules that guide this recognition offer the key rationale for the development of therapeutic NANPs with tunable immune stimulation. Numerous recent studies have provided increasing evidence that in addition to NANPs' physicochemical properties and therapeutic effects, their interactions with cells of the immune system can be regulated through multiple independently programmable architectural parameters. The results further suggest that defined immunomodulation by NANPs can either support their immunoquiescent delivery or be used for conditional stimulation of beneficial immunological responses.

Non-Small-Cell Lung Cancer Regression by siRNA Delivered Through Exosomes That Display EGFR RNA Aptamer

Lung cancer is the second most common cancer in both men and women and is the leading cause of cancer death in the United States. The development of drug resistance to commonly used chemotherapeutics in non-small-cell lung cancer (NSCLC) poses significant health risks and there is a dire need to improve patient outcomes. In this study, we report the use of RNA nanotechnology to display ligand on exosome that was loaded with small interfering RNA (siRNA) for NSCLC regression in animal trials. Cholesterol was used to anchor the ligand targeting epidermal growth factor receptor on exosomes that were loaded with siRNA to silence the antiapoptotic factor survivin. The cytosolic delivery of siRNA overcame the problem of endosome trapping, leading to potent gene knockdown, chemotherapy sensitization, and tumor regression, thus achieving a favorable IC₅₀ of 20 nmol/kg siRNA encapsulated by exosome particles in the in vivo gene knockdown assessment.

In Vivo Production of RNA Aptamers and Nanoparticles: Problems and Prospects

RNA aptamers are becoming increasingly attractive due to their superior properties. This review discusses the early stages of aptamer research, the main developments in this area, and the latest technologies being developed. The review also highlights the advantages of RNA aptamers in comparison to antibodies, considering the great potential of RNA aptamers and their applications in the near future. In addition, it is shown how RNA aptamers can form endless 3-D structures, giving rise to various structural and functional possibilities. Special attention is paid to the Mango, Spinach and Broccoli fluorescent RNA aptamers, and the advantages of split RNA aptamers are discussed. The review focuses on the importance of creating a platform for the synthesis of RNA nanoparticles in vivo and examines yeast, namely Saccharomyces cerevisiae, as a potential model organism for the production of RNA nanoparticles on a large scale.

A simple screening strategy for complex RNA-DNA hybrid nanoshapes

The design of hybrid nucleic acid nanomaterials capitalizes on the partitioning of architectural and functional roles between structurally diverse RNA modules and chemically robust DNA components. Selecting optimal combinations of RNA and DNA building blocks is the key to preparing stable polygonal RNA-DNA hybrid nanoshapes. Here, we outline a simple screening strategy by gel electrophoresis under native folding conditions to identify combinations of RNA and DNA modules that self-assemble to robust polygonal hybrid nanoshapes. As a proof of concept, we outline the preparation of RNA-DNA hybrid nanoshapes containing a set of different RNA architectural joints, including internal loop motifs and three-way junction (3WJ) folds. For each hybrid nanoshape, we demonstrate the selection process used to identify optimal DNA modules from a library of DNA connectors. The simple screening strategy outlined here provides a general robust method to identify and prepare RNA-DNA hybrid nanoshapes from diverse libraries of discrete nucleic acid building blocks.

Induction of Cytokines by Nucleic Acid Nanoparticles (NANPs) Depends on the Type of Delivery Carrier

Recent insights into the immunostimulatory properties of nucleic acid nanoparticles (NANPs) have demonstrated that variations in the shape, size, and composition lead to distinct patterns in their immunostimulatory properties. While most of these studies have used a single lipid-based carrier to allow for NANPs' intracellular delivery, it is now apparent that the platform for delivery, which has historically been a hurdle for therapeutic nucleic acids, is an additional means to tailoring NANP immunorecognition. Here, the use of dendrimers for the delivery of NANPs is compared to the lipid-based platform and the differences in resulting cytokine induction are presented.

Multivalent rubber-like RNA nanoparticles for targeted co-delivery of paclitaxel and MiRNA to silence the drug efflux transporter and liver cancer drug resistance

Hepatocellular carcinoma (HCC) is the third leading cause of cancer-related death worldwide. Analogous to the border customs, liver mainly functions as a filter to detoxify chemicals and metabolite administered orally or intravenously. Besides, the liver cancer cells overexpress the drug exporters which cause high drug effluxion from liver cancer cells, leading to chemoresistance and a diminished chemotherapeutic effect on liver cancer. Recently, we found that RNA nanoparticles display rubber-like property that can rapidly deliver therapeutics to tumor site efficiently and the rest of the RNA nanoparticle were cleared by renal excretion within half hour after systemic injection. Therefore, we designed a new multivalent RNA nanoparticle harboring three copies of hepatocyte targeting-ligands, one copy of miR122, and 24 copies of Paclitaxel to overcome the drug effluxion and chemoresistance thus, synergistically treating HCC. The hepatocyte targeting ligands introduce tumor specificity to the RNA nanoparticles as they selectively bind and internalize into liver cancer cells. The rubber-like RNA nanoparticles allow for enhanced targeting ability to the HCC tumors. The RNA nanoparticles carrying miR122 and PTX were delivered to the liver cancer cells efficiently due to their rubber-like property to enhance their EPR as well as the receptor-mediated endocytosis by hepatocyte targeting-ligands. The miR122 efficiently silenced the drug exporters and the oncogenic proteins. The synergistic effect between miR122 and PTX was confirmed by HSA (Highest Single Agent) synergy model. IC₅₀ was determined to be 460 nM. In vivo studies on mice xenografts revealed that the RNA nanoparticle predominantly accumulated in HCC tumor sites and efficiently inhibited the tumor growth after multiple IV injection. This demonstrates the potential of the rubber-like multivalent RNA nanoparticles to conquest the liver cancer, a currently incurable lethal disease.

The immunorecognition, subcellular compartmentalization, and physicochemical properties of nucleic acid nanoparticles can be controlled by composition modification

Nucleic acid nanoparticles (NANPs) have become powerful new platforms as therapeutic and diagnostic tools due to the innate biological ability of nucleic acids to identify target molecules or silence genes involved in disease pathways. However, the clinical application of NANPs has been limited by factors such as chemical instability, inefficient intracellular delivery, and the triggering of detrimental inflammatory responses following innate immune recognition of nucleic acids. Here, we have studied the effects of altering the chemical composition of a circumscribed panel of NANPs that share the same connectivity, shape, size, charge and sequences. We show that replacing RNA strands with either DNA or chemical analogs increases the enzymatic and thermodynamic stability of NANPs. Furthermore, we have found that such composition changes affect delivery efficiency and determine subcellular localization, effects that could permit the targeted delivery of NANP-based therapeutics and diagnostics. Importantly, we have determined that altering NANP composition can dictate the degree and mechanisms by which cell immune responses are initiated. While RNA NANPs trigger both TLR7 and RIG-I mediated cytokine and interferon production, DNA NANPs stimulate minimal immune activation. Importantly, incorporation of 2'F modifications abrogates RNA NANP activation of TLR7 but permits RIG-I dependent immune responses. Furthermore, 2'F modifications of DNA NANPs significantly enhances RIG-I mediated production of both proinflammatory cytokines and interferons. Collectively this indicates that off-target effects may be reduced and/or desirable immune responses evoked based upon NANPs modifications. Together, our studies show that NANP composition provides a simple way of controlling the immunostimulatory potential, and physicochemical and delivery characteristics, of such platforms.

Exosome mediated delivery of functional nucleic acid nanoparticles (NANPs)

RNAi-based technologies have shown biomedical potential; however, safe and efficient delivery of RNA remains a barrier for their broader clinical applications. Nucleic acid nanoparticles (NANPs) programmed to self-assemble and organize multiple therapeutic nucleic acids (TNAs) also became attractive candidates for diverse therapeutic options. Various synthetic nanocarriers are used to deliver TNAs and NANPs, but their clinical translation is limited due to immunotoxicity. Exosomes are cell-derived nanovesicles involved in cellular communication. Due to their ability to deliver biomolecules, exosomes are a novel delivery choice. In this study, we explored the exosome-mediated delivery of NANPs designed to target GFP. We assessed the intracellular uptake, gene silencing efficiency, and immunostimulation of exosomes loaded with NANPs. We also confirmed that interdependent RNA/DNA fibers upon recognition of each other after delivery, can conditionally activate NF-kB decoys and prevent pro-inflammatory cytokines. Our study overcomes challenges in TNA delivery and demonstrates future studies in drug delivery systems.

Use of human peripheral blood mononuclear cells to define immunological properties of nucleic acid nanoparticles

This protocol assesses proinflammatory properties of nucleic acid nanoparticles (NANPs) using a validated preclinical model, peripheral blood mononuclear cells (PBMCs), that is highly predictive of cytokine responses. The experimental procedure details the preparation of pyrogen-free NANPs, isolation of PBMCs from freshly collected human blood, and analysis of characteristic biomarkers (type I and III interferons) produced by PBMCs transfected with NANPs. Although representative NANPs with high and low immunostimulatory potential are used as standards throughout the procedure, this protocol can be adapted to any NANPs or therapeutic nucleic acids, irrespective of whether they are carrier based or carrier free; additional cytokine biomarkers can also be included. We test several commercial platforms and controls broadly accessible to the research community to quantify all biomarkers in either single- or multiplex format. The continuous execution of this protocol takes <48 h; when immediate analysis is not feasible, single-use aliquots of the supernatants can be frozen and stored (-20 °C; 12 months).

Combination of Nucleic Acid and Mesoporous Silica Nanoparticles: Optimization and Therapeutic Performance In Vitro

Programmable nucleic acid nanoparticles (NANPs) with precisely controlled functional compositions can regulate the conditional activation of various biological pathways and responses in human cells. However, the intracellular delivery of NANPs alone is hindered by their susceptibility to nuclease activity and inefficient crossing of biological membranes. In this work, we optimized the internalization and therapeutic performance of several representative NANPs delivered with mesoporous silica nanoparticles (MSNPs) tailored for efficient electrostatic association with NANPs. We compared the immunostimulatory properties of different NA-MS-NP complexes formed with globular, planar, and fibrous NANPs and demonstrated the maximum immunostimulation for globular NANPs. As a proof of concept, we assessed the specific gene silencing by NA-MS-NP complexes functionalized with siRNA targeting green fluorescent protein expressed in triple-negative human breast cancer cells. We showed that the fibrous NANPs have the highest silencing efficiency when compared to globular or planar counterparts. Finally, we confirmed the multimodal ability of MSNPs to co-deliver a chemotherapy drug, doxorubicin, and NANPs targeting apoptosis regulator gene BCL2 in triple-negative breast cancer and melanoma cell lines. Overall, the combination of NANPs and MSNPs may become a new promising approach to efficiently treat cancer and other diseases via the simultaneous targeting of various pathways.

Opportunities, Barriers, and a Strategy for Overcoming Translational Challenges to Therapeutic Nucleic Acid Nanotechnology

Recent clinical successes using therapeutic nucleic acids (TNAs) have accelerated the transition of nucleic acid nanotechnology toward therapeutic applications. Significant progress in the development, production, and characterization of nucleic acid nanomaterials and nucleic acid nanoparticles (NANPs), as well as abundant proof-of-concept data, are paving the way toward biomedical applications of these materials. This recent progress has catalyzed the development of new strategies for biosensing, imaging, drug delivery, and immunotherapies with previously unrecognized opportunities and identified some barriers that may impede the broader clinical translation of NANP technologies. A recent workshop sponsored by the Kavli Foundation and the Materials Research Society discussed the future directions and current challenges for the development of therapeutic nucleic acid nanotechnology. Herein, we communicate discussions on the opportunities, barriers, and strategies for realizing the clinical grand challenge of TNA nanotechnology, with a focus on ways to overcome barriers to advance NANPs to the clinic.

Challenges to optimizing RNA nanostructures for large scale production and controlled therapeutic properties

Nucleic acids have been utilized to construct an expansive collection of nanoarchitectures varying in design, physicochemical properties, cellular processing and biomedical applications. However, the broader therapeutic adaptation of nucleic acid nanoassemblies in general, and RNA-based nanoparticles in particular, have faced several challenges in moving towards (pre)clinical settings. For one, the large-batch synthesis of nucleic acids is still under development, with multi-stranded and chemically modified assemblies requiring greater production capacity while maintaining consistent medical-grade outputs. Furthermore, the unknown immunostimulation by these nanomaterials poses additional challenges, necessary to be overcome for optimizing future development of clinically approved RNA nanoparticles.

Au nanoparticles deposited on ultrathin two-dimensional covalent organic framework nanosheets for in vitro and intracellular sensing

A novel composite nanomaterial is prepared by growing small Au nanoparticles on two-dimensional covalent organic framework nanosheets (Au NPs/COF NSs). The synthesized hybrid nanosheets are used as a new platform for multiplexed detection of hepatitis A virus DNA (HAV) and hepatitis B virus DNA (HBV). Additionally, this sensing platform based on Au NPs/COF NSs can be used as a candidate for monitoring the distribution of potassium ions (K⁺) and the intracellular K⁺ level in living cells. Accordingly, the sensing systems based on hybrid Au NPs/COF NSs have shown great potential for the investigation of biomolecules and related biological applications.

RNA-DNA hybrid nanoshapes that self-assemble dependent on ligand binding

Self-assembly of nucleic acid nanostructures is driven by selective association of oligonucleotide modules through base pairing between complementary sequences. Herein, we report the development of RNA-DNA hybrid nanoshapes that conditionally assemble under the control of an adenosine ligand. The design concept for the nanoshapes relies on ligand-dependent stabilization of DNA aptamers that serve as connectors between marginally stable RNA corner modules. Ligand-dependent RNA-DNA nanoshapes self-assemble in an all-or-nothing process by coupling adenosine binding to the formation of circularly closed structures which are stabilized through continuous base stacking in the resulting polygons. By screening combinations of various DNA aptamer constructs with RNA corner modules for the formation of stable complexes, we identified adenosine-dependent nanosquares whose shape was confirmed by atomic force microscopy. As a proof-of-concept for sensor applications, adenosine-responsive FRET-active nanosquares were obtained by dye conjugation of the DNA aptamer components.

Nucleic Acid Nanoparticles at a Crossroads of Vaccines and Immunotherapies

Vaccines and immunotherapies involve a variety of technologies and act through different mechanisms to achieve a common goal, which is to optimize the immune response against an antigen. The antigen could be a molecule expressed on a pathogen (e.g., a disease-causing bacterium, a virus or another microorganism), abnormal or damaged host cells (e.g., cancer cells), environmental agent (e.g., nicotine from a tobacco smoke), or an allergen (e.g., pollen or food protein). Immunogenic vaccines and therapies optimize the immune response to improve the eradication of the pathogen or damaged cells. In contrast, tolerogenic vaccines and therapies retrain or blunt the immune response to antigens, which are recognized by the immune system as harmful to the host. To optimize the immune response to either improve the immunogenicity or induce tolerance, researchers employ different routes of administration, antigen-delivery systems, and adjuvants. Nanocarriers and adjuvants are of particular interest to the fields of vaccines and immunotherapy as they allow for targeted delivery of the antigens and direct the immune response against these antigens in desirable direction (i.e., to either enhance immunogenicity or induce tolerance). Recently, nanoparticles gained particular attention as antigen carriers and adjuvants. This review focuses on a particular subclass of nanoparticles, which are made of nucleic acids, so-called nucleic acid nanoparticles or NANPs. Immunological properties of these novel materials and considerations for their clinical translation are discussed.

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.

Innate immune responses triggered by nucleic acids inspire the design of immunomodulatory nucleic acid nanoparticles (NANPs)

The unknown immune stimulation by nucleic acid nanoparticles (NANPs) has become one of the major impediments to a broad spectrum of clinical developments of this novel technology. Having evolved to defend against bacterial and viral nucleic acids, mammalian cells have established patterns of recognition that are also the pathways through which NANPs can be processed. Explorations into the immune stimulation brought about by a vast diversity of known NANPs have shown that variations in design correlate with variations in immune response. Therefore, as the mechanisms of stimulation are further elucidated, these trends are now being taken into account in the design phase to allow for development of NANPs that are tailored for controlled immune activation or quiescence.

Modulating Immune Response with Nucleic Acid Nanoparticles

Nano-objects made of nucleic acids are becoming promising materials in the biomedical field. This is, in part, due to DNA and RNA self-assembly properties that can be accurately computed to fabricate various complex nanoarchitectures of 2D and 3D shapes. The nanoparticles can be assembled from DNA, RNA, and chemically modified oligonucleotide mixtures which, in turn, influence their chemical and biophysical properties. Solid-phase synthesis allows large-scale production of individual oligonucleotide strands with batch-to-batch consistency and exceptional purity. All of these advantageous characteristics of nucleic-acid-based nanoparticles were known to be exceptionally useful as a nanoplatform for drug delivery purposes. Recently, several important discoveries have been achieved, demonstrating that nucleic acid nanoparticles (NANPs) can also be used to modulate the immune response of host cells. The purpose of this review is to briefly overview studies demonstrating architectural design principles of NANPs, as well as the ability of NANPs to control immune responses.