Impact of Liposomal Spherical Nucleic Acid Structure on Immunotherapeutic Function

From Structure to Application: The Evolutionary Trajectory of Spherical Nucleic Acids

Since the proposal of the concept of spherical nucleic acids (SNAs) in 1996, numerous studies have focused on this topic and have achieved great advances. As a new delivery system for nucleic acids, SNAs have advantages over conventional deoxyribonucleic acid (DNA) nanostructures, including independence from transfection reagents, tolerance to nucleases, and lower immune reactions. The flexible structure of SNAs proves that various inorganic or organic materials can be used as the core, and different types of nucleic acids can be conjugated to realize diverse functions and achieve surprising and exciting outcomes. The special DNA nanostructures have been employed for immunomodulation, gene regulation, drug delivery, biosensing, and bioimaging. Despite the lack of rational design strategies, potential cytotoxicity, and structural defects of this technology, various successful examples demonstrate the bright and convincing future of SNAs in fields such as new materials, clinical practice, and pharmacy.

In Vivo Interactions of Nucleic Acid Nanostructures With Cells

Nucleic acid nanostructures, derived from the assembly of nucleic acid building blocks (e.g., plasmids and oligonucleotides), are important intracellular carriers of therapeutic cargoes widely utilized in preclinical nanomedicine applications, yet their clinical translation remains scarce. In the era of "translational nucleic acid nanotechnology", a deeper mechanistic understanding of the interactions of nucleic acid nanostructures with cells in vivo will guide the development of more efficacious nanomedicines. This review showcases the recent progress in dissecting the in vivo interactions of four key types of nucleic acid nanostructures (i.e., tile-based, origami, spherical nucleic acid, and nucleic acid nanogel) with cells in rodents over the past five years. Emphasis lies on the cellular-level distribution of nucleic acid nanostructures in various organs and tissues and the cellular responses induced by their cellular entry. Next, in the spirit of preclinical translation, this review features the latest interactions of nucleic acid nanostructures with cells in large animals and humans. Finally, the review offers directions for studying the interactions of nucleic acid nanostructures with cells from both materials and biology perspectives and concludes with some regulatory updates.

DNA Anchoring Strength Directly Correlates with Spherical Nucleic Acid-Based HPV E7 Cancer Vaccine Potency

Vaccination for cancers arising from human papillomavirus (HPV) infection holds immense potential, yet clinical success has been elusive. Herein, we describe vaccination studies involving spherical nucleic acids (SNAs) incorporating a CpG adjuvant and a peptide antigen (E711-19) from the HPV-E7 oncoprotein. Administering the vaccine to humanized mice induced immunity-dependent on the oligonucleotide anchor chemistry (cholesterol vs (C12)9). SNAs containing a (C12)9-anchor enhanced IFN-γ production >200-fold, doubled memory CD8+ T-cell formation, and delivered more than twice the amount of oligonucleotide to lymph nodes in vivo compared to a simple admixture. Importantly, the analogous construct with a weaker cholesterol anchor performed similar to admix. Moreover, (C12)9-SNAs activated 50% more dendritic cells and generated T-cells cytotoxic toward an HPV+ cancer cell line, UM-SCC-104, with near 2-fold greater efficiency. These observations highlight the pivotal role of structural design, and specifically oligonucleotide anchoring strength (which correlates with overall construct stability), in developing efficacious therapeutic vaccines.

Construction Strategy of Functionalized Liposomes and Multidimensional Application

Liposomes are widely used in the biological field due to their good biocompatibility and surface modification properties. With the development of biochemistry and material science, many liposome structures and their surface functional components have been modified and optimized one by one, pushing the liposome platform from traditional to functionalized and intelligent, which will better satisfy and expand the needs of scientific research. However, a main limiting factor effecting the efficiency of liposomes is the complicated environmental conditions in the living body. Currently, in order to overcome the above problem, functionalized liposomes have become a very promising strategy. In this paper, binding strategies of liposomes with four main functional elements, namely nucleic acids, antibodies, peptides, and stimuli-responsive motif have been summarized for the first time. In addition, based on the construction characteristics of functionalized liposomes, such as drug-carrying, targeting, long-circulating, and stimulus-responsive properties, a comprehensive overview of their features and respective research progress are presented. Finally, the paper critically presents the limitations of these functionalized liposomes in the current applications and also prospectively suggests the future development directions, aiming to accelerate realization of their industrialization.

Ultrasound-responsive spherical nucleic acid against c-Myc/PD-L1 to enhance anti-tumoral macrophages in triple-negative breast cancer progression

Triple-negative breast cancer (TNBC) is the most challenging breast cancer subtype because of its aggressive behavior and limited therapeutic targets. c-Myc is hyperactivated in the majority of TNBC tissues, however, it has been considered an "undruggable" target due to its disordered structure. Herein, we developed an ultrasound-responsive spherical nucleic acid (SNA) against c-Myc and PD-L1 in TNBC. It is a self-assembled and carrier-free system composed of a hydrophilic small-interfering RNA (siRNA) shell and a hydrophobic core made of a peptide nucleic acid (PNA)-based antisense oligonucleotide (ASO) and a sonosensitizer. We accomplished significant enrichment in the tumor by enhanced permeability and retention (EPR) effect, the controllable release of effective elements by ultrasound activation, and the combination of targeted therapy, immunotherapy and physiotherapy. Our study demonstrated significant anti-tumoral effects in vitro and in vivo. Mass cytometry showed an invigorated tumor microenvironment (TME) characterized by a significant alteration in the composition of tumor-associated macrophages (TAM) and decreased proportion of PD-1-positive (PD-1+) T effector cells after appropriate treatment of the ultrasound-responsive SNA (USNA). Further experiments verified that tumor-conditioned macrophages residing in the TME were transformed into the anti-tumoral population. Our finding offers a novel therapeutic strategy against the "undruggable" c-Myc, develops a new targeted therapy for c-Myc/PD-L1 and provides a treatment option for the TNBC.

Spherical nucleic acids: emerging amplifiers for therapeutic nanoplatforms

Gene therapy is a revolutionary treatment approach in the 21st century, offering significant potential for disease prevention and treatment. However, the efficacy of gene delivery is often compromised by the inherent challenges of gene properties and vector-related defects. It is crucial to explore ways to enhance the curative effect of gene drugs and achieve safer, more widespread, and more efficient utilization, which represents a significant challenge in amplification gene therapy advancements. Spherical nucleic acids (SNAs), with their unique physicochemical properties, are considered an innovative solution for scalable gene therapy. This review aims to comprehensively explore the amplifying contributions of SNAs in gene therapy and emphasize the contribution of SNAs to the amplification effect of gene therapy from the aspects of structure, application, and recent clinical translation - an aspect that has been rarely reported or explored thus far. We begin by elucidating the fundamental characteristics and scaling-up properties of SNAs that distinguish them from traditional linear nucleic acids, followed by an analysis of combined therapy treatment strategies, theranostics, and clinical translation amplified by SNAs. We conclude by discussing the challenges of SNAs and provide a prospect on the amplification characteristics. This review seeks to update the current understanding of the use of SNAs in gene therapy amplification and promote further research into their clinical translation and amplification of gene therapy.

Control of the Assembly and Disassembly of Spherical Nucleic Acids Is Critical for Enhanced Gene Silencing

Spherical nucleic acids─nanospheres with nucleic acids on their corona─have emerged as a promising class of nanocarriers, aiming to address the shortcomings of traditional nucleic therapeutics, namely, their poor stability, biodistribution, and cellular entry. By conjugating hydrophobic monomers to a growing nucleic acid strand in a sequence-defined manner, our group has developed self-assembled spherical nucleic acids (SaSNAs), for unaided, enhanced gene silencing. By virtue of their self-assembled nature, SaSNAs can disassemble under certain conditions in contrast to covalent or gold nanoparticle SNAs. Gene silencing involves multiple steps including cellular uptake, endosomal escape, and therapeutic cargo release. Whether assembly vs disassembly is advantageous to any of these steps has not been previously studied. In this work, we modify the DNA and hydrophobic portions of SaSNAs and examine their effects on stability, cellular uptake, and gene silencing. When the linkages between the hydrophobic units are changed from phosphate to phosphorothioate, we find that the SaSNAs disassemble better in endosomal conditions and exhibit more efficacious silencing, despite having cellular uptake similar to that of their phosphate counterparts. Thus, disassembly in the endolysosomal compartments is advantageous, facilitating the release of the nucleic acid cargo and the interactions between the hydrophobic units and endosomal lipids. We also find that SaSNAs partially disassemble in serum to bind albumin; the disassembled, albumin-bound strands are less efficient at cellular uptake and gene silencing than their assembled counterparts, which can engage scavenger receptors for internalization. When the DNA portion is cross-linked by G-quadruplex formation, disassembly decreases and cellular uptake significantly increases. However, this does not translate to greater gene silencing, again illustrating the need for disassembly of the SaSNAs when they are in the endosome. This work showcases the advantages of the dual nature of SaSNAs for gene silencing, requiring extracellular assembly and disassembly inside the cell compartments.

Impact of the Core Chemistry of Self-Assembled Spherical Nucleic Acids on their In Vitro Fate

Nucleic acid therapeutics (NATs), such as mRNA, small interfering RNA or antisense oligonucleotides are extremely efficient tools to modulate gene expression and tackle otherwise undruggable diseases. Spherical nucleic acids (SNAs) can efficiently deliver small NATs to cells while protecting their payload from nucleases, and have improved biodistribution and muted immune activation. Self-assembled SNAs have emerged as nanostructures made from a single DNA-polymer conjugate with similar favorable properties as well as small molecule encapsulation. However, because they maintain their structure by non-covalent interactions, they might suffer from disassembly in biologically relevant conditions, especially with regard to their interaction with serum proteins. Here, we report a systematic study of the factors that govern the fate of self-assembled SNAs. Varying the core chemistry and using stimuli-responsive disulfide crosslinking, we show that extracellular stability upon binding with serum proteins is important for recognition by membrane receptors, triggering cellular uptake. At the same time, intracellular dissociation is required for efficient therapeutic release. Disulfide-crosslinked SNAs combine these two properties and result in efficient and non-toxic unaided gene silencing therapeutics. We anticipate these investigations will help the translation of promising self-assembled structures towards in vivo gene silencing applications.

Advances in nanobased platforms for cardiovascular diseases: Early diagnosis, imaging, treatment, and tissue engineering

Cardiovascular diseases (CVDs) present a significant threat to health, with traditional therapeutics based treatment being hindered by inefficiencies, limited biological effects, and resistance to conventional drug. Addressing these challenges requires advanced approaches for early disease diagnosis and therapy. Nanotechnology and nanomedicine have emerged as promising avenues for personalized CVD diagnosis and treatment through theranostic agents. Nanoparticles serve as nanodevices or nanocarriers, efficiently transporting drugs to injury sites. These nanocarriers offer the potential for precise drug and gene delivery, overcoming issues like bioavailability and solubility. By attaching specific target molecules to nanoparticle surfaces, controlled drug release to targeted areas becomes feasible. In the field of cardiology, nanoplatforms have gained popularity due to their attributes, such as passive or active targeting of cardiac tissues, enhanced sensitivity and specificity, and easy penetration into heart and artery tissues due to their small size. However, concerns persist about the immunogenicity and cytotoxicity of nanomaterials, necessitating careful consideration. Nanoparticles also hold promise for CVD diagnosis and imaging, enabling straightforward diagnostic procedures and real-time tracking during therapy. Nanotechnology has revolutionized cardiovascular imaging, yielding multimodal and multifunctional vehicles that outperform traditional methods. The paper provides an overview of nanomaterial delivery routes, targeting techniques, and recent advances in treating, diagnosing, and engineering tissues for CVDs. It also discusses the future potential of nanomaterials in CVDs, including theranostics, aiming to enhance cardiovascular treatment in clinical practice. Ultimately, refining nanocarriers and delivery methods has the potential to enhance treatment effectiveness, minimize side effects, and improve patients' well-being and outcomes.

Harnessing biomaterial architecture to drive anticancer innate immunity

Immunomodulation is a powerful therapeutic approach that harnesses the body's own immune system and reprograms it to treat diseases, such as cancer. Innate immunity is key in mobilizing the rest of the immune system to respond to disease and is thus an attractive target for immunomodulation. Biomaterials have widely been employed as vehicles to deliver immunomodulatory therapeutic cargo to immune cells and raise robust antitumor immunity. However, it is key to consider the design of biomaterial chemical and physical structure, as it has direct impacts on innate immune activation and antigen presentation to stimulate downstream adaptive immunity. Herein, we highlight the widespread importance of structure-driven biomaterial design for the delivery of immunomodulatory cargo to innate immune cells. The incorporation of precise structural elements can be harnessed to improve delivery kinetics, uptake, and the targeting of biomaterials into innate immune cells, and enhance immune activation against cancer through temporal and spatial processing of cargo to overcome the immunosuppressive tumor microenvironment. Structural design of immunomodulatory biomaterials will profoundly improve the efficacy of current cancer immunotherapies by maximizing the impact of the innate immune system and thus has far-reaching translational potential against other diseases.

Cellular Export Fate of Liposomal Spherical Nucleic Acids

Liposomal spherical nucleic acids (LSNAs) are useful structures for oligonucleotide-based cell modulation because of their biocompatibility and ability to readily enter cells without transfection agents. Understanding LSNA trafficking is key to developing applications, but while much is understood about LSNA cell uptake, little is known about their export fate. Here, we study LSNA export through pulse-chase studies with fluorophore-labeled LSNAs. Our findings show that the components of LSNAs are differentially exported by cells, with the phospholipids showing 90-100% export and the oligonucleotides showing 30-45% export over 24 h in RAW264.7 macrophages. Despite the increase in the level of uptake of LSNAs, these percentages are not significantly influenced by whether the materials are taken up as LSNAs or as the individual components. The exported oligonucleotide material consists of a full-length oligonucleotide with the phospholipid anchor modified by loss of a fatty acid. The exported liposome-derived phospholipids also had a fatty acid removed. Moreover, the exported oligonucleotide-lysophospholipid conjugates retain immunostimulatory potential. These findings indicate that after cellular entry LSNAs are degraded into lysophospholipids, something to which they are susceptible due to the presence of hydrolyzable ester bonds. The export percentage of the resultant materials over 24 h is independent of the amount imported, such that greater initial import leads to a similar fold increase in exported material. This work therefore reveals an intracellular feature of LSNAs and shows that the enhanced uptake achieved with LSNAs can be exploited to maximize the amount of material subsequently exported, suggesting avenues for leveraging pharmacologic effects from exported LSNA components.

Spherical nucleic acids-based nanoplatforms for tumor precision medicine and immunotherapy

Precise diagnosis and treatment of tumors currently still face considerable challenges due to the development of highly degreed heterogeneity in the dynamic evolution of tumors. With the rapid development of genomics, personalized diagnosis and treatment using specific genes may be a robust strategy to break through the bottleneck of traditional tumor treatment. Nevertheless, efficient in vivo gene delivery has been frequently hampered by the inherent defects of vectors and various biological barriers. Encouragingly, spherical nucleic acids (SNAs) with good modularity and programmability are excellent candidates capable of addressing traditional gene transfer-associated issues, which enables SNAs a precision nanoplatform with great potential for diverse biomedical applications. In this regard, there have been detailed reviews of SNA in drug delivery, gene regulation, and dermatology treatment. Still, to the best of our knowledge, there is no published systematic review summarizing the use of SNAs in oncology precision medicine and immunotherapy, which are considered new guidelines for oncology treatment. To this end, we summarized the notable advances in SNAs-based precision therapy and immunotherapy for tumors following a classification standard of different types of precise spatiotemporal control on active species by SNAs. Specifically, we focus on the structural diversity and programmability of SNAs. Finally, the challenges and possible solutions were discussed in the concluding remarks. This review will promote the rational design and development of SNAs for tumor-precise medicine and immunotherapy.

Tuning DNA Dissociation from Spherical Nucleic Acids for Enhanced Immunostimulation

The stability of the core can significantly impact the therapeutic effectiveness of liposome-based drugs. While the spherical nucleic acid (SNA) architecture has elevated liposomal stability to increase therapeutic efficacy, the chemistry used to anchor the DNA to the liposome core is an underexplored design parameter with a potentially widespread biological impact. Herein, we explore the impact of SNA anchoring chemistry on immunotherapeutic function by systematically studying the importance of hydrophobic dodecane anchoring groups in attaching DNA strands to the liposome core. By deliberately modulating the size of the oligomer that defines the anchor, a library of structures has been established. These structures, combined with in vitro and in vivo immune stimulation analyses, elucidate the relationships between and importance of anchoring strength and dissociation of DNA from the SNA shell on its biological properties. Importantly, the most stable dodecane anchor, (C12)9, is superior to the n = 4-8 and 10 structures and quadruples immune stimulation compared to conventional cholesterol-anchored SNAs. When the OVA1 peptide antigen is encapsulated by the (C12)9 SNA and used as a therapeutic vaccine in an E.G7-OVA tumor model, 50% of the mice survived the initial tumor, and all of those survived tumor rechallenge. Importantly, the strong innate immune stimulation does not cause a cytokine storm compared to linear immunostimulatory DNA. Moreover, a (C12)9 SNA that encapsulates a peptide targeting SARS-CoV-2 generates a robust T cell response; T cells raised from SNA treatment kill >40% of target cells pulsed with the same peptide and ca. 45% of target cells expressing the entire spike protein. This work highlights the importance of using anchor chemistry to elevate SNA stability to achieve more potent and safer immunotherapeutics in the context of both cancer and infectious disease.

Transforming Hairpin-like siRNA-Based Spherical Nucleic Acids into Biocompatible Constructs

The design and synthesis of hairpin-like small interfering RNA spherical nucleic acids (siRNA-SNAs) based upon biocompatible liposome nanoparticle cores are described. The constructs were characterized by gel electrophoresis, dynamic light scattering, and OliGreen-based oligonucleotide quantification. These siRNA-SNA nanoconstructs enter cells 20-times more efficiently than linear siRNA in as little as 4 h, while exhibiting a 4-fold reduction in cytotoxicity compared with conventional siRNA-SNAs composed of gold nanoparticle cores. Importantly, these siRNA-SNA constructs effectively inhibit angiogenesis in vitro by silencing vascular endothelial growth factor, a key mediator of angiogenesis in a multitude of diseases, in human umbilical vein endothelial cells. This work shows how hairpin architectures can be chemically incorporated into biocompatible SNAs in a way that retains advantageous SNA properties and maximizes gene regulation capabilities.

Biomedical applications of nanomaterials in the advancement of nucleic acid therapy: Mechanistic challenges, delivery strategies, and therapeutic applications

In the past few decades, substantial advancement has been made in nucleic acid (NA)-based therapies. Promising treatments include mRNA, siRNA, miRNA, and anti-sense DNA for treating various clinical disorders by modifying the expression of DNA or RNA. However, their effectiveness is limited due to their concentrated negative charge, instability, large size, and host barriers, which make widespread application difficult. The effective delivery of these medicines requires safe vectors that are efficient & selective while having non-pathogenic qualities; thus, nanomaterials have become an attractive option with promising possibilities despite some potential setbacks. Nanomaterials possess ideal characteristics, allowing them to be tuned into functional bio-entity capable of targeted delivery. In this review, current breakthroughs in the non-viral strategy of delivering NAs are discussed with the goal of overcoming challenges that would otherwise be experienced by therapeutics. It offers insight into a wide variety of existing NA-based therapeutic modalities and techniques. In addition to this, it provides a rationale for the use of non-viral vectors and a variety of nanomaterials to accomplish efficient gene therapy. Further, it discusses the potential for biomedical application of nanomaterials-based gene therapy in various conditions, such as cancer therapy, tissue engineering, neurological disorders, and infections.

In Vivo Behavior of Ultrasmall Spherical Nucleic Acids

The biological properties of spherical nucleic acids (SNAs) are largely independent of nanoparticle core identity but significantly affected by oligonucleotide surface density. Additionally, the payload-to-carrier (i.e., DNA-to-nanoparticle) mass ratio of SNAs is inversely proportional to core size. While SNAs with many core types and sizes have been developed, all in vivo analyses of SNA behavior have been limited to cores >10 nm in diameter. However, "ultrasmall" nanoparticle constructs (<10 nm diameter) can exhibit increased payload-to-carrier ratios, reduced liver accumulation, renal clearance, and enhanced tumor infiltration. Therefore, we hypothesized that SNAs with ultrasmall cores exhibit SNA-like properties, but with in vivo behavior akin to traditional ultrasmall nanoparticles. To investigate, we compared the behavior of SNAs with 1.4-nm Au102 nanocluster cores (AuNC-SNAs) and SNAs with 10-nm gold nanoparticle cores (AuNP-SNAs). Significantly, AuNC-SNAs possess SNA-like properties (e.g., high cellular uptake, low cytotoxicity) but show distinct in vivo behavior. When intravenously injected in mice, AuNC-SNAs display prolonged blood circulation, lower liver accumulation, and higher tumor accumulation than AuNP-SNAs. Thus, SNA-like properties persist at the sub-10-nm length scale and oligonucleotide arrangement and surface density are responsible for the biological properties of SNAs. This work has implications for the design of new nanocarriers for therapeutic applications.

Preparation and Biological Properties of Oligonucleotide-Functionalized Virus-like Particles

Oligonucleotides are powerful molecules for programming function and assembly. When arrayed on nanoparticle scaffolds in high density, the resulting molecules, spherical nucleic acids (SNAs), become imbued with unique properties. We used the copper-catalyzed azide-alkyne cycloaddition to graft oligonucleotides on Qβ virus-like particles to see if such structures also gain SNA-like behavior. Copper-binding ligands were shown to promote the click reaction without degrading oligonucleotide substrates. Reactions were first optimized with a small-molecule fluorogenic reporter and were then applied to the more challenging synthesis of polyvalent protein nanoparticle-oligonucleotide conjugates. The resulting particles exhibited the enhanced cellular uptake and protection from nuclease-mediated oligonucleotide cleavage characteristic of SNAs, had similar residence time in the liver relative to unmodified particles, and were somewhat shielded from immune recognition, resulting in nearly 10-fold lower antibody titers relative to unmodified particles. Oligonucleotide-functionalized virus-like particles thus provide an interesting option for protein nanoparticle-mediated delivery of functional molecules.

Nucleotides Entrapped in Liposome Nanovesicles as Tools for Therapeutic and Diagnostic Use in Biomedical Applications

The use of nucleotides for biomedical applications is an old desire in the scientific community. As we will present here, there are references published over the past 40 years with this intended use. The main problem is that, as unstable molecules, nucleotides require some additional protection to extend their shelf life in the biological environment. Among the different nucleotide carriers, the nano-sized liposomes proved to be an effective strategic tool to overcome all these drawbacks related to the nucleotide high instability. Moreover, due to their low immunogenicity and easy preparation, the liposomes were selected as the main strategy for delivery of the mRNA developed for COVID-19 immunization. For sure this is the most important and relevant example of nucleotide application for human biomedical conditions. In addition, the use of mRNA vaccines for COVID-19 has increased interest in the application of this type of technology to other health conditions. For this review article, we will present some of these examples, especially focused on the use of liposomes to protect and deliver nucleotides for cancer therapy, immunostimulatory activities, enzymatic diagnostic applications, some examples for veterinarian use, and the treatment of neglected tropical disease.

Nanoarchitectonics of Spherical Nucleic Acids with Biodegradable Polymer Cores: Synthesis and Evaluation

Spherical nucleic acids (SNAs) have gained significant attention due to their unique properties allowing them to overcome the challenges that face current nanocarriers used for gene therapies. The aim of this study is to synthesize and characterize polymer-oligonucleotide conjugates of different architecture and to evaluate the possibility of forming SNAs with biodegradable cores. Initially, two types of azide (multi)functional polyester-based (co)polymers were successfully synthesized and characterized. In the next step, short oligonucleotide strands were attached to the polymer chains applying the highly efficient and metal-free "click" reaction, thus forming conjugates with block or graft architecture. Both conjugates spontaneously self-assembled in aqueous media forming nanosized SNAs with a biodegradable polyester core and a surface of oligonucleotide chains as evidenced from dynamic and electrophoretic light scattering measurements. The nano-assemblies were in vitro evaluated for potential cytotoxicity. Furthermore, the interactions of the newly synthesized SNAs with membrane lipids were studied. The preliminary results indicate that both types of polymer-based SNAs are good candidates for potential application in gene therapy and that it is worth to be further evaluated.

Locoregional Lymphatic Delivery Systems Using Nanoparticles and Hydrogels for Anticancer Immunotherapy

The lymphatic system has gained significant interest as a target tissue to control cancer progress, which highlights its central role in adaptive immune response. Numerous mechanistic studies have revealed the benefits of nano-sized materials in the transport of various cargos to lymph nodes, overcoming barriers associated with lymphatic physiology. The potential of sustained drug delivery systems in improving the therapeutic index of various immune modulating agents is also being actively discussed. Herein, we aim to discuss design rationales and principles of locoregional lymphatic drug delivery systems for invigorating adaptive immune response for efficient antitumor immunotherapy and provide examples of various advanced nanoparticle- and hydrogel-based formulations.

Original Synthesis of a Nucleolipid for Preparation of Vesicular Spherical Nucleic Acids

Spherical nucleic acids (SNAs)-nanostructures, consisting of a nanoparticle core densely functionalized with a shell of short oligonucleotide strands-are a rapidly emerging class of nanoparticle-based therapeutics with unique properties and specific applications as drug and nucleic acid delivery and gene regulation materials. In this contribution, we report on the preparation of hollow SNA nanoconstructs by co-assembly of an originally synthesized nucleolipid-a hybrid biomacromolecule, composed of a lipidic residue, covalently linked to a DNA oligonucleotide strand-with other lipids. The nucleolipid was synthesized via a click chemistry approach employing initiator-free, UV light-induced thiol-ene coupling of appropriately functionalized intermediates, performed in mild conditions using a custom-made UV light-emitting device. The SNA nanoconstructs were of a vesicular structure consisting of a self-closed bilayer membrane in which the nucleolipid was intercalated via its lipid-mimetic residue. They were in the lower nanometer size range, moderately negatively charged, and were found to carry thousands of oligonucleotide strands per particle, corresponding to a grafting density comparable to that of other SNA structures. The surface density of the strands on the bilayer implied that they adopted an unextended conformation. We demonstrated that preformed vesicular structures could be successfully loaded with either hydrophilic or hydrophobic dyes.

DNA-Liposome Hybrid Carriers for Triggered Cargo Release

The design of simple and versatile synthetic routes to accomplish triggered-release properties in carriers is of particular interest for drug delivery purposes. In this context, the programmability and adaptability of DNA nanoarchitectures in combination with liposomes have great potential to render biocompatible hybrid carriers for triggered cargo release. We present an approach to form a DNA mesh on large unilamellar liposomes incorporating a stimuli-responsive DNA building block. Upon incubation with a single-stranded DNA trigger sequence, a hairpin closes, and the DNA building block is allowed to self-contract. We demonstrate the actuation of this building block by single-molecule Förster resonance energy transfer (FRET), fluorescence recovery after photobleaching, and fluorescence quenching measurements. By triggering this process, we demonstrate the elevated release of the dye calcein from the DNA–liposome hybrid carriers. Interestingly, the incubation of the doxorubicin-laden active hybrid carrier with HEK293T cells suggests increased cytotoxicity relative to a control carrier without the triggered-release mechanism. In the future, the trigger could be provided by peritumoral nucleic acid sequences and lead to site-selective release of encapsulated chemotherapeutics.

Rational Vaccinology: Harnessing Nanoscale Chemical Design for Cancer Immunotherapy

Cancer immunotherapy is a powerful treatment strategy that mobilizes the immune system to fight disease. Cancer vaccination is one form of cancer immunotherapy, where spatiotemporal control of the delivery of tumor-specific antigens, adjuvants, and/or cytokines has been key to successfully activating the immune system. Nanoscale materials that take advantage of chemistry to control the nanoscale structural arrangement, composition, and release of immunostimulatory components have shown significant promise in this regard. In this Outlook, we examine how the nanoscale structure, chemistry, and composition of immunostimulatory compounds can be modulated to maximize immune response and mitigate off-target effects, focusing on spherical nucleic acids as a model system. Furthermore, we emphasize how chemistry and materials science are driving the rational design and development of next-generation cancer vaccines. Finally, we identify gaps in the field that should be addressed moving forward and outline future directions to galvanize researchers from multiple disciplines to help realize the full potential of this form of cancer immunotherapy through chemistry and rational vaccinology.

Glutathione-Sensitive Nanoglue Platform with Effective Nucleic Acids Gluing onto Liposomes for Photo-Gene Therapy

Liposomal spherical nucleic acids possess a high density of nucleic acids, e.g., DNA, on a liposomal core. There are two approaches to conjugate DNA onto the zwitterionic liposomes, i.e., covalent and noncovalent conjugation, otherwise using cationic liposomes. However, complex and expensive DNA chemical modification methods need to seek a novel and easy-operating approach to decorating DNA onto liposomes. Inspired by the nanoparticle solution as nanoglues for gels and biological tissues, we use MnO₂ nanosheets to "glue" DNA onto liposomes without DNA modification. In tumor cells with a high glutathione concentration, MnO₂-based nanoglues are degraded, generating water-soluble Mn²⁺ ions, further "unglue" DNA (i.e., DNAzyme), and liposomes. Using the intelligent liposomal nanoglue (DNAzyme/MnO₂/Lip) combining glutathione-sensitive MnO₂ nanosheets, gene silencing agent DNAzyme, and photosensitizer Chlorin e6 (Ce6) in liposomes, effective photo-gene therapy was demonstrated.

Spherical nucleic acids as an infectious disease vaccine platform

SignificanceUsing SARS-CoV-2 as a relevant case study for infectious disease, we investigate the structure-function relationships that dictate antiviral spherical nucleic acid (SNA) vaccine efficacy. We show that the SNA architecture can be rapidly employed to target COVID-19 through incorporation of the receptor-binding domain, and that the resulting vaccine potently activates human cells in vitro and mice in vivo. Furthermore, when challenged with a lethal viral infection, only mice treated with the SNA vaccine survived. Taken together, this work underscores the importance of rational vaccine design for infectious disease to yield vaccines that elicit more potent immune responses to effectively fight disease.

Spherical Nucleic Acids as Precision Therapeutics for the Treatment of Cancer-From Bench to Bedside

Spherical Nucleic Acids (SNAs) emerged as a new class of nanotherapeutics consisting of a nanoparticle core densely functionalized with a shell of radially oriented synthetic oligonucleotides. The unique three-dimensional architecture of SNAs protects the oligonucleotides from nuclease-mediated degradation, increases oligonucleotide bioavailability, and in the absence of auxiliary transfection agents, enables robust uptake into tumor and immune cells through polyvalent association with cell surface pattern recognition receptors. When composed of gene-regulatory small interfering (si)RNA or immunostimulatory DNA or RNA oligonucleotides, SNAs silence gene expression and induce immune responses superior to those raised by the oligonucleotides in their "free" form. Early phase clinical trials of gene-regulatory siRNA-based SNAs in glioblastoma (NCT03020017) and immunostimulatory Toll-like receptor 9 (TLR9)-agonistic SNAs carrying unmethylated CpG-rich oligonucleotides in solid tumors (NCT03086278) have shown that SNAs represent a safe, brain-penetrant therapy for inhibiting oncogene expression and stimulating immune responses against tumors. This review focuses on the application of SNAs as precision cancer therapeutics, summarizes the findings from first-in-human clinical trials of SNAs in solid tumors, describes the most recent preclinical efforts to rationally design next-generation multimodal SNA architectures, and provides an outlook on future efforts to maximize the anti-neoplastic activity of the SNA platform.

Spherical nucleic acids: Organized nucleotide aggregates as versatile nanomedicine

Spherical nucleic acids (SNAs) are composed of a nanoparticle core and a layer of densely arranged oligonucleotide shells. After the first report of SNA by Mirkin and coworkers in 1996, it has created a significant interest by offering new possibilities in the field of gene and drug delivery. The controlled aggregation of oligonucleotides on the surface of organic/inorganic nanoparticles improves the delivery of genes and nucleic acid-based drugs and alters and regulates the biological profiles of the nanoparticle core within living organisms. Here in this review, we present an overview of the recent progress of SNAs that has speeded up their biomedical application and their potential transition to clinical use. We start with introducing the concept and characteristics of SNAs as drug/gene delivery systems and highlight recent efforts of bioengineering SNA by imaging and treatmenting various diseases. Finally, we discuss potential challenges and opportunities of SNAs, their ongoing clinical trials, and future translation, and how they may affect the current landscape of clinical practices. We hope that this review will update our current understanding of SNA, organized oligonucleotide aggregates, for disease diagnosis and treatment.

A Biomimetic Approach for Spatially Controlled Cell Membrane Engineering Using Fusogenic Spherical Nucleic Acid

Engineering of the cell plasma membrane using functional DNA is important for studying and controlling cellular behaviors. However, most efforts to apply artificial DNA interactions on cells are limited to external membrane surface due to the lack of suitable synthetic tools to engineer the intracellular side, which impedes many applications in cell biology. Inspired by the natural extracellular vesicle-cell fusion process, we have developed a fusogenic spherical nucleic acid construct to realize robust DNA functionalization on both external and internal cell surfaces via liposome fusion-based transport (LiFT) strategy, which enables applications including the construction of heterotypic cell assembly for programmed signaling pathway and detection of intracellular metabolites. This approach can engineer cell membranes in a highly efficient and spatially controlled manner, allowing one to build anisotropic membrane structures with two orthogonal DNA functionalities.

Controlling the Biological Fate of Liposomal Spherical Nucleic Acids Using Tunable Polyethylene Glycol Shells

Liposomal spherical nucleic acids (LSNAs) modified with polyethylene glycol (PEG) units are studied in an attempt to understand how the circulation time and biodistribution of the constructs can be manipulated. Specifically, the effect of (1) PEG molecular weight, (2) PEG shell stability, and (3) PEG modification method (PEG in both the core and shell versus PEG in the shell only) on LSNA blood circulation, biodistribution, and in vivo cell internalization in a syngeneic, orthotopic triple-negative breast cancer mouse model is studied. Generally, high PEG molecular weight extends blood circulation lifetime, and a more lipophilic anchor stabilizes the PEG shell and improves circulation and tumor accumulation but at the cost of cell uptake efficiency. The PEGylation strategy has a minor effect on in vitro properties of LSNAs but significantly alters in vivo cell uptake. For example, surface-only PEG in one design contributed to higher in vivo cell internalization than its counterpart with PEG both in the shell and core. Taken together, this work provides guidelines for designing LSNAs that exhibit maximal in vivo cancer cell uptake characteristics in the context of a breast cancer model.