Nucleic Acid Nanocapsules for Enzyme-Triggered Drug Release

Nucleic Acid Nanocapsules as a New Platform to Deliver Therapeutic Nucleic Acids for Gene Regulation

ConspectusTherapeutic nucleic acids have shown enormous potential to treat a vast number of diseases, ranging from cancers to inflammatory diseases. siRNA formulated within lipid nanoparticles (LNPs) achieved FDA approval for a rare liver disorder in 2018, followed shortly after by successful application of mRNA formulated in LNPs in 2020 to stave off a worldwide pandemic. Thus, in only a few short years, interest in nucleic acid drugs has skyrocketed, both within the academic world and the pharmaceutical industry. Despite the excitement surrounding these genetically encodable medicines, there remains much work to do to enable them to be as far reaching of a drug class as they have the potential to be. The major roadblock limiting their clinical potential is the inability of formulations to efficiently deliver nucleic acid cargo to the cytosol of cells, largely due to endosomal entrapment. Additionally, there are challenges associated with the ability of formulations to target nucleic acids to specific cells and subcellular locations. Here, we describe how our lab has been working to address many of these challenges using a new chemical formulation that is distinctly different from traditional liposomes and LNPs, built from the bottom up to specifically enable endosomal escape of its nucleic acid cargo. We took direct inspiration from viruses with the goal of imitating their dynamic design that changes in response to binding and internalization into cells, enabling them to release their genetic cargo into the cytosol by locally disrupting membranes all while maintaining the cells overall integrity.Herein, we will detail the design considerations and applications of our formulation, which we refer to as a Nucleic Acid Nanocapsule (NAN), a versatile, programmable DNA nanomaterial that can be broken down by enzymes to release DNA surfactant conjugates (DSCs) with lipid membrane disrupting capabilities. We will describe how viral structure, cellular entry, and genome release mechanisms are being used in our lab as roadmaps for designing next generation nanocarriers and how such bioinspired synthetic approaches have led to our advancements in the areas of therapeutic efficacy and cytosolic delivery of nucleic acids. We will explain how our nanoscale NANs can be functionalized with therapeutically active RNA, catalytically functional DNA, and cell targeting aptamers by straightforward enzymatic ligation procedures. We will then discuss how structural tuning of the nanocapsule's chemical building blocks results in changes to its uptake mechanism and endosomal escape efficiency and how this modularity has enabled us to enhance oligonucleotide delivery. We will also describe details regarding how oligonucleotide cargo can be stabilized by our nanocarrier and the importance of the particle design as it relates to membrane disruption capabilities necessary for cytosolic delivery. Lastly, we will discuss the vast therapeutic potential of NANs based on the bioactivity of delivered nucleic acids in terms of gene silencing, protein expression, and subcellular targeting, highlighting both in vitro and in vivo studies. We will end with a vision for what still remains in order to achieve the ideal nonviral nucleic acid carrier formulation that could accelerate nucleic acids to clinical application.

Tumor-Selective Gene Therapy: Using Hairpin DNA Oligonucleotides to Trigger Cleavage of Target RNA by Endogenous flap endonuclease 1 (FEN 1) Highly Expressed in Tumor Cells

Nucleic acid drugs, which trigger gene silencing by hybridizing with target genes, have shown great potential in targeting those undruggable targets. However, most of the existing nucleic acid drugs are only sequence specific for target genes and lack cellular or tissue selectivity, which challenges their therapeutic safety. Here, the study proposes a tumor cell-specific gene silencing strategy by using hairpin DNA oligonucleotides to trigger target RNA degrading by highly expressed endogenous flap endonuclease 1 (FEN1) in tumor cells, for selective tumor therapy. Using Kirsten rat sarcoma viral oncogene homolog (KRASG12S) and B-cell lymphoma 2 (Bcl-2) genes as targets, it is verified that the hairpin DNA oligonucleotides show cytotoxicity only to tumor cells but very low effects on normal cells. In addition, hairpin DNA oligonucleotides designed for KRAS inhibition, which are encapsulated in lipid nanoparticles, inhibit tumor growth in mice and demonstrate excellent antitumor efficacy in combination with gefitinib, but has little effect on normal tissues, suggesting that the proposed strategy enables highly selective tumor therapy and has the potential to give rise to a new class of nucleic acid drugs.

Advanced disease therapeutics using engineered living drug delivery systems

Biological barriers significantly impede the delivery of nanotherapeutics to diseased tissues, diminishing therapeutic efficacy across pathologies such as cancer and inflammatory disorders. Although conventional strategies integrate multifunctional designs and molecular components into nanomaterials (NMs), many approaches remain insufficient to overcome these barriers. Key challenges, including inadequate drug accumulation at target sites and nonspecific biodistribution, persist in nanotherapeutic development. NMs, which harness the ability to precisely modulate drug delivery spatiotemporally and control release kinetics, represent a transformative platform for targeted cancer therapy. In this review, we highlight the biological obstacles limiting effective cancer treatment and evaluate how stimuli-responsive NMs address these constraints. By leveraging exogenous and endogenous stimuli, such NMs improve therapeutic specificity, reduce off-target effects, and amplify drug activity within pathological microenvironments. We systematically analyze the rational design and synthesis of stimuli-responsive NMs, driven by advances in oncology, biomaterials science, and nanoscale engineering. Furthermore, we highlight advances across NM classes-including polymeric, lipid-based, inorganic, and hybrid systems and explore functionalization approaches using targeting ligands, antibodies, and biomimetic coatings. Diverse delivery strategies are evaluated, such as small-molecule prodrug activation, peptide- and protein-based targeting, nucleic acid payloads, and engineered cell-mediated transport. Despite the promise of stimuli-responsive NMs, challenges such as biocompatibility, scalable fabrication, and clinical translation barriers must be addressed. By elucidating structure-function relationships and refining stimulus-triggered mechanisms, these NMs pave the way for transformative precision oncology strategies, enabling patient-specific therapies with enhanced efficacy and safety. This synthesis of interdisciplinary insights aims to catalyze innovation in next-generation nanomedicine for cancer treatment.

Enzymatic interlocking aptamer-micelles for enhanced cellular internalization and nucleus-targeted cancer phototherapy

Multifunctional micelles that permit both diagnosis and treatment present enormous advantage and potential for precision medicine. However, the inherent complexities and structural instability of these systems often cause unsatisfactory targeting and therapeutic performances. Herein, by ingenious design of a 2,5-bis(2-thienyl)pyrrole (SNS) modifier to covalently link with AS1411 aptamer and lipid segment, a simple strategy is proposed for one-step enzymatic preparation of interlocked aptamer-micelle (IApM) under bio-friendly conditions. The interlocked poly(SNS) skeleton in IApM can not only stabilize the micelle structure but also enhance near-infrared (NIR) absorption ability, thus further enhancing cellular internalization and photothermal therapy. In addition, the multivalent AS1411 aptamers tethered in the hydrophilic shell can simultaneously increase the specific binding affinity of DNA micelles and induce nucleus-targeted accumulation for DNA damage-triggered apoptosis. This DNA micelle achieves "best of both worlds" with enhanced biostability for cellular internalization and improved NIR photothermal conversion efficiency for nucleus-targeted therapy, which provides a promising formulation strategy for precision cancer treatment.

Enzymatically Ligated Nucleic Acid Nanocapsules for the Delivery of Therapeutic Nucleic Acids and Small Molecule Drugs

Spherical nucleic acids (SNAs) offer intriguing properties for cellular uptake and stability. A novel SNA-like structure known as the nucleic acid nanocapsule (NAN) combines the benefits of SNAs with the added properties of nucleic acid functionalization and drug cargo release. Herein, we will discuss various ways NANs can be adapted to allow for gene targeting via the delivery of nucleic acids, as well as the delivery of small molecule drugs for combination therapies.

Determining the Role of Surfactant on the Cytosolic Delivery of DNA Cross-Linked Micelles

Nucleic Acid Nanocapsules (NANs) are nucleic acid nanostructures that radially display oligonucleotides on the surface of cross-linked surfactant micelles. Their chemical makeup affords the stimuli-responsive release of therapeutically active DNA-surfactant conjugates into the cells. While NANs have so far demonstrated the effective cytosolic delivery of their nucleic acid cargo, as seen indirectly by their gene regulation capabilities, there remain gaps in the molecular understanding of how this process happens. Herein, we examine the enzymatic degradation of NANs and confirm the identity of the DNA-surfactant conjugates formed by using mass spectrometry (MS). With surface enhanced (resonance) Raman spectroscopy (SE(R)RS), we also provide evidence that the energy-independent translocation of such DNA-surfactant conjugates is contingent upon their release from the NAN structure, which, when intact, otherwise buries the hydrophobic surfactant tail in its interior. Such information suggests a critical role of the surfactant in the lipid disruption capability of the DNA surfactant conjugates generated from degradation of the NANs. Using NANs made with different tail lengths (C12 and C10), we show that this mechanism likely holds true despite significant differences in the physical properties (i.e., critical micelle concentration (CMC), surfactants per micelle, Nagg) of the resultant particles (C12 and C10 NANs). While the total cellular uptake efficiencies of C12 and C10 NANs are similar, there were differences observed in their cellular distribution and localized trafficking, even after ensuring that the total concentration of DNA was the same for both particles. Ultimately, C10 NANs appeared less diffuse within cells and colocalized less with lysosomes over time, achieving more significant knockdown of the target gene investigated, suggesting more effective endosomal escape. These differences indicate that the surfactant assembly and disassembly properties, including the number of surfactants per particle and the CMC can have important implications for the cellular delivery efficacy of DNA micelles and surfactant conjugates.

Enzyme-Responsive Supramolecular Self-Assembly in Small Amphiphiles

Enzyme-responsive molecular assemblies have recently made remarkable progress, owing to their widespread applications. As a class of catalysts with high specificity and efficiency, enzymes play a critical role in producing new molecules and maintaining metabolic stability in living organisms. Therefore, the study of enzyme-responsive assembly aids in understanding the origin of life and the physiological processes occurring within living bodies, contributing to further advancements across various disciplines. In this Review, we summarize three kinds of enzyme-responsive assembly systems in amphiphiles: enzyme-triggered assembly, disassembly, and structural transformation. Furthermore, motivated by the fact that biological macromolecules and complex structures all originated with small molecules, our focus lies on the small amphiphiles (e.g., peptides, surfactants, fluorescent molecules, and drug molecules). We also provide an outlook on the potential of enzyme-responsive assembly systems for biomimetic development and hope this Review will attract more attention to this emerging research branch at the intersection of assembly chemistry and biological science.

Recent advances in photodynamic therapy combined with chemotherapy for cervical cancer: a systematic review

INTRODUCTION

Despite the evidence that photodynamic therapy (PDT) associated with chemotherapy presents great potential to overcome the limitations of monotherapy, little is known about the current status of this combination against cervical cancer. This systematic review aimed to address the currently available advances in combining PDT and chemotherapy in different research models and clinical trials of cervical cancer.

METHODS

We conducted a systematic review based on PRISMA Statement and Open Science Framework review protocol using PubMed, Web of Science, Embase, Scopus, LILACS, and Cochrane databases. We selected original articles focusing on 'Uterine Cervical Neoplasms' and 'Photochemotherapy and Chemotherapy' published in the last 10 years. The risk of bias in the studies was assessed using the CONSORT and SYRCLE tools.

RESULTS

Twenty-three original articles were included, focusing on HeLa cells, derived from endocervical adenocarcinoma and on combinations of several chemotherapeutics. Most of the combinations used modern drug delivery systems for improved simultaneous delivery and presented promising results with increased cytotoxicity compared to monotherapy.

CONCLUSION

Despite the scarcity of animal studies and the absence of clinical studies, the combination of chemotherapy with PDT presents a potential option for cervical cancer therapy requiring additional studies.

OSF REGISTRATION

https://doi.org/10.17605/OSF.IO/WPHN5 [Figure: see text].

Cellular Uptake Mechanism of Nucleic Acid Nanocapsules and Their DNA-Surfactant Building Blocks

Nucleic acid nanocapsules (NANs) are enzyme-responsive DNA-functionalized micelles built for the controlled release of DNA-surfactant conjugates (DSCs) that present sequences with demonstrated therapeutic potential. Here, we investigate the mechanisms by which DSCs gain access to intracellular space in vitro and determine the effects of serum on the overall uptake and internalization mechanism of NANs. Using pharmacological inhibitors to selectively block certain pathways, we show, through confocal visualization of cellular distribution and flow cytometry quantification of total cellular association, that scavenger receptor-mediated, caveolae-dependent endocytosis is the major cellular uptake pathway of NANs in the presence and absence of serum. Furthermore, as NANs can be triggered to release DSCs by external stimuli such as enzymes, we sought to examine the uptake profile of particles degraded by enzymes prior to cell-based assays. We found that while scavenger receptor-mediated, caveolae-dependent endocytosis is still at play, energy-independent pathways as well as clathrin-mediated endocytosis are also involved. Overall, this study has helped to elucidate early steps in the cytosolic delivery and therapeutic activity of DSCs packaged into a micellular NAN platform while shedding light on the way in which DNA functionalized nanomaterials in general can be trafficked into cells both as nanostructures and as molecular entities. Importantly, our study also shows that the NAN design in particular is able to stabilize nucleic acids when delivered in the presence of serum, a critical step for effective therapeutic nucleic acid delivery.

Recent advancements in design of nucleic acid nanocarriers for controlled drug delivery

Research of nanoscale nucleic acid carriers has garnered attention in recent years due to their distinctive and controllable properties. However, current knowledge is limited in how we can efficiently utilize these systems for clinical applications. Several researchers have pioneered new and innovative nanocarrier drug delivery systems, but understanding physiochemical properties and behavior in vivo is vital to implementing them as clinical drug delivery platforms. In this review, we outline the most significant innovations in the synthesis, physical properties, and utilization of nucleic acid nanocarriers in the past 5 years, addressing the crucial properties which improve nanocarrier characteristics, delivery, and drug release. The challenges of controlling the transport of nucleic acid nanocarriers and therapeutic release for biological applications are outlined. Barriers which inhibit effective transport into tissue are discussed with emphasis on the modifications needed to overcome such obstacles. The novel strategies discussed in this work summarize the pivotal features of modern nucleic nanocarriers and postulate where future developments could revolutionize the translation of these tools into a clinical setting.

Gold Complexes in Anticancer Therapy: From New Design Principles to Particle-Based Delivery Systems

The discovery of the medicinal properties of gold complexes has fuelled the design and synthesis of new anticancer metallodrugs, which have received special attention due to their unique modes of action. Current research in the development of gold compounds with therapeutic properties is predominantly focused on the molecular design of drug leads with superior pharmacological activities, e.g., by introducing targeting features. Moreover, intensive research aims at improving the physicochemical properties of gold compounds, such as chemical stability and solubility in the physiological environment. In this regard, the encapsulation of gold compounds in nanocarriers or their chemical grafting onto targeted delivery vectors could lead to new nanomedicines that eventually reach clinical applications. Herein, we provide an overview of the state-of-the-art progress of gold anticancer compounds, andmore importantly we thoroughly revise the development of nanoparticle-based delivery systems for gold chemotherapeutics.

Opportunities and Challenges of Switchable Materials for Pharmaceutical Use

Switchable polymeric materials, which can respond to triggering signals through changes in their properties, have become a major research focus for parenteral controlled delivery systems. They may enable externally induced drug release or delivery that is adaptive to in vivo stimuli. Despite the promise of new functionalities using switchable materials, several of these concepts may need to face challenges associated with clinical use. Accordingly, this review provides an overview of various types of switchable polymers responsive to different types of stimuli and addresses opportunities and challenges that may arise from their application in biomedicine.

Multi-layered stimuli responsive DNA micelles for the stepwise controlled release of small molecules

DNA functionalized Multi layered Surface Crosslinked Micelles (mlSCMs) can compartmentalize two small molecule cargo in distinct layers. In response to the appropriate trigger, mlSCMs can release cargo for chemical and biochemical applications.

From vesicles to materials: bioinspired strategies for fabricating hierarchically structured soft matter

Certain organisms including species of mollusks, polychaetes, onychophorans and arthropods produce exceptional polymeric materials outside their bodies under ambient conditions using concentrated fluid protein precursors. While much is understood about the structure-function relationships that define the properties of such materials, comparatively less is understood about how such materials are fabricated and specifically, how their defining hierarchical structures are achieved via bottom-up assembly. Yet this information holds great potential for inspiring sustainable manufacture of advanced polymeric materials with controlled multi-scale structure. In the present perspective, we first examine recent work elucidating the formation of the tough adhesive fibres of the mussel byssus via secretion of vesicles filled with condensed liquid protein phases (coacervates and liquid crystals)-highlighting which design principles are relevant for bio-inspiration. In the second part of the perspective, we examine the potential of recent advances in drops and additive manufacturing as a bioinspired platform for mimicking such processes to produce hierarchically structured materials. This article is part of the theme issue 'Bio-derived and bioinspired sustainable advanced materials for emerging technologies (part 1)'.

Live-Cell Imaging of Survivin mRNA by Using a Dual-Color Surface-Cross-Linked Nanoquencher

Precise detection of cancer-related mRNAs can significantly benefit the early diagnosis and potential therapy of cancers. Herein, we report organic dark quencher-encapsulated surface-cross-linked micelles (qSCMs) as a new sort of nanoquencher for construction of potential multiple-color fluorescence imaging nanosensors. Such nanoquenchers featured simple preparation (one-pot), broad-spectrum quenching (450-800 nm), high quenching efficiency (>94%), good stability, negligible cargo leakage, facile covalent surface modification, and finally excellent modularity. As a proof-of-concept demonstration, a mRNA-detecting qSCM nanosensor was generated, capable of simultaneous live-cell imaging of endogenous actin mRNA (a house-keeping gene) and cancer-related survivin mRNA. This nanosensor was found to be GSH- and DNase I-resistant, and with actin mRNA as an intrinsic reference, it was used to image the precise survivin mRNA expression across different mammalian cells through convenient normalization of the signal readouts. Moreover, the nanosensor was further used to quantitatively image the downregulation of endogenous survivin mRNA in HeLa cells upon treatment of YM155 (an imidazolium bioactive compound known to suppresses endogenous survivin mRNA expression). These results clearly demonstrated the promising application of these qSCMs as new nanoquenchers in potential multicolor imaging of various endogenous biomarkers.

A GATA3 Targeting Nucleic Acid Nanocapsule for In Vivo Gene Regulation in Asthma

Allergic asthma is one of the leading chronic lung diseases of both children and adults worldwide, resulting in significant morbidity and mortality in affected individuals. Many patients have severe asthma, which is refractory to treatment, illustrating the need for the development of new therapeutics for this disease. Herein, we describe the use of a peptide cross-linked nucleic acid nanocapsule (NAN) for the delivery of a GATA3-specific DNAzyme to immune cells, with demonstration of modulated transcriptional activity and behavior of those cells. The NAN, built from peptide cross-linked surfactants, is chemically designed to degrade under inflammation conditions releasing individual DNAzyme-surfactant conjugates in response to proteolytic enzymes. Using the NAN, GATA3 DNAzymes were delivered efficiently to human peripheral blood mononuclear cells, with clear evidence of uptake by CD4+ helper T cells without the need for harsh transfection agents. Knockdown of GATA3 was achieved in vitro using human Jurkat T cells, which express GATA3 under homeostatic conditions. Additionally, mice treated with DNAzyme-NANs during house dust mite (HDM)-induced asthma developed less severe allergic lung inflammation than HDM-only control mice, as measured by pulmonary eosinophilia. This study suggests that peptide cross-linked GATA3 DNAzyme-NANs may have the potential to decrease the severity of asthma symptoms in human patients, and development of this technology for human use warrants further investigation.

Surface ligand rigidity modulates lipid raft affinity of ultra-small hydrophobic nanoparticles: insights from molecular dynamics simulations

Differential preferences between lipids and proteins drive the formation of dynamical nanoscale membrane domains (lipid rafts), which play key roles in the proper functioning of cells. On the other hand, due to the potent physicochemical properties of nanoparticles (NPs), they have been widely used in drug delivery, bio-imaging and regulating various essential biological processes of the cells. Hence, in this work, we aim to design ultra-small hydrophobic NPs with tunable raft affinity, which is supposed to partition into the hydrophobic region of lipid membranes and be able to regulate the dynamics of the lipid raft domains. A series of μs-scale coarse-grained molecular dynamics simulations and umbrella sampling free energy calculations were performed to investigate the role of surface ligand rigidity of ultra-small hydrophobicNPs in their raft affinity. Our results indicated that the preferred localization of NPs can be tuned by adjusting their surface ligand rigidity. Generally, rigid NPs tended to target the raft domain, while soft NPs preferred the interface of the raft and non-raft domains. The free energy analysis further indicated that the surface ligand rigidity of NPs can enhance their targeting to lipid raft domains. Besides, we found that these ultra-small NPs had no significant effects on the phase separation of the lipid membrane although they might cause some local interference to surrounding lipids. These results indicate that the targeting to the lipid raft domain can be achieved by the surface ligand rigidity of NPs, which provides helpful insights for further regulations of lipid raft-mediated biological processes.

Programmably tiling rigidified DNA brick on gold nanoparticle as multi-functional shell for cancer-targeted delivery of siRNAs

Small interfering RNA (siRNA) is an effective therapeutic to regulate the expression of target genes in vitro and in vivo. Constructing a siRNA delivery system with high serum stability, especially responsive to endogenous stimuli, remains technically challenging. Herein we develop anti-degradation Y-shaped backbone-rigidified triangular DNA bricks with sticky ends (sticky-YTDBs) and tile them onto a siRNA-packaged gold nanoparticle in a programmed fashion, forming a multi-functional three-dimensional (3D) DNA shell. After aptamers are arranged on the exterior surface, a biocompatible siRNA-encapsulated core/shell nanoparticle, siRNA/Ap-CS, is achieved. SiRNAs are internally encapsulated in a 3D DNA shell and are thus protected from enzymatic degradation by the outermost layer of YTDB. The siRNAs can be released by endogenous miRNA and execute gene silencing within tumor cells, causing cell apoptosis higher than Lipo3000/siRNA formulation. In vivo treatment shows that tumor growth is completely (100%) inhibited, demonstrating unique opportunities for next-generation anticancer-drug carriers for targeted cancer therapies.

DNA Transformations for Diagnosis and Therapy

Due to its unique physical and chemical characteristics, DNA, which is known only as genetic information, has been identified and utilized as a new material at an astonishing rate. The role of DNA has increased dramatically with the advent of various DNA derivatives such as DNA-RNA, DNA-metal hybrids, and PNA, which can be organized into 2D or 3D structures by exploiting their complementary recognition. Due to its intrinsic biocompatibility, self-assembly, tunable immunogenicity, structural programmability, long stability, and electron-rich nature, DNA has generated major interest in electronic and catalytic applications. Based on its advantages, DNA and its derivatives are utilized in several fields where the traditional methodologies are ineffective. Here, the present challenges and opportunities of DNA transformations are demonstrated, especially in biomedical applications that include diagnosis and therapy. Natural DNAs previously utilized and transformed into patterns are not found in nature due to lack of multiplexing, resulting in low sensitivity and high error frequency in multi-targeted therapeutics. More recently, new platforms have advanced the diagnostic ability and therapeutic efficacy of DNA in biomedicine. There is confidence that DNA will play a strong role in next-generation clinical technology and can be used in multifaceted applications.

Viral Mimicry as a Design Template for Nucleic Acid Nanocarriers

Therapeutic nucleic acids hold immense potential in combating undruggable, gene-based diseases owing to their high programmability and relative ease of synthesis. While the delivery of this class of therapeutics has successfully entered the clinical setting, extrahepatic targeting, endosomal escape efficiency, and subcellular localization. On the other hand, viruses serve as natural carriers of nucleic acids and have acquired a plethora of structures and mechanisms that confer remarkable transfection efficiency. Thus, understanding the structure and mechanism of viruses can guide the design of synthetic nucleic acid vectors. This review revisits relevant structural and mechanistic features of viruses as design considerations for efficient nucleic acid delivery systems. This article explores how viral ligand display and a metastable structure are central to the molecular mechanisms of attachment, entry, and viral genome release. For comparison, accounted for are details on the design and intracellular fate of existing nucleic acid carriers and nanostructures that share similar and essential features to viruses. The review, thus, highlights unifying themes of viruses and nucleic acid delivery systems such as genome protection, target specificity, and controlled release. Sophisticated viral mechanisms that are yet to be exploited in oligonucleotide delivery are also identified as they could further the development of next-generation nonviral nucleic acid vectors.

Harnessing Endogenous Stimuli for Responsive Materials in Theranostics

Materials that respond to endogenous stimuli are being leveraged to enhance spatiotemporal control in a range of biomedical applications from drug delivery to diagnostic tools. The design of materials that undergo morphological or chemical changes in response to specific biological cues or pathologies will be an important area of research for improving efficacies of existing therapies and imaging agents, while also being promising for developing personalized theranostic systems. Internal stimuli-responsive systems can be engineered across length scales from nanometers to macroscopic and can respond to endogenous signals such as enzymes, pH, glucose, ATP, hypoxia, redox signals, and nucleic acids by incorporating synthetic bio-inspired moieties or natural building blocks. This Review will summarize response mechanisms and fabrication strategies used in internal stimuli-responsive materials with a focus on drug delivery and imaging for a broad range of pathologies, including cancer, diabetes, vascular disorders, inflammation, and microbial infections. We will also discuss observed challenges, future research directions, and clinical translation aspects of these responsive materials.

Novel Lipid-Oligonucleotide Conjugates Containing Long-Chain Sulfonyl Phosphoramidate Groups: Synthesis and Biological Properties

New lipid conjugates of DNA and RNA incorporating one to four [(4-dodecylphenyl)sulfonyl]phosphoramidate or (hexadecylsulfonyl)phosphoramidate groups at internucleotidic positions near the 3′ or 5′-end were synthesized and characterized. Low cytotoxicity of the conjugates and their ability to be taken up into cells without transfection agents were demonstrated. Lipid-conjugated siRNAs targeting repulsive guidance molecules a (RGMa) have shown a comparable gene silencing activity in PK-59 cells to unmodified control siRNA when delivered into the cells via Lipofectamine mediated transfection.

Redox-Responsive Nanocapsules for the Spatiotemporal Release of Miltefosine in Lysosome: Protection against Leishmania

Leishmaniasis, a vector-borne disease, is caused by intracellular parasite Leishmania donovani. Unlike most intracellular pathogens, Leishmania donovani are lodged in parasitophorous vacuoles and replicate within the phagolysosomes in macrophages. Effective vaccines against this disease are still under development, while the efficacy of the available drugs is being questioned owing to the toxicity for nonspecific distribution in human physiology and the reported drug-resistance developed by Leishmania donovani. Thus, a stimuli-responsive nanocarrier that allows specific localization and release of the drug in the lysosome has been highly sought after for addressing two crucial issues, lower drug toxicity and a higher drug efficacy. We report here a unique lysosome targeting polymeric nanocapsules, formed via inverse mini-emulsion technique, for stimuli-responsive release of the drug miltefosine in the lysosome of macrophage RAW 264.7 cell line. A benign polymeric backbone, with a disulfide bonding susceptible to an oxidative cleavage, is utilized for the organelle-specific release of miltefosine. Oxidative rupture of the disulfide bond is induced by intracellular glutathione (GSH) as an endogenous stimulus. Such a stimuli-responsive release of the drug miltefosine in the lysosome of macrophage RAW 264.7 cell line over a few hours helped in achieving an improved drug efficacy by 200 times as compared to pure miltefosine. Such a drug formulation could contribute to a new line of treatment for leishmaniasis.

DNA hydrogel-based gene editing and drug delivery systems

Deoxyribonucleic acid (DNA) is a promising synthesizer for precisely constructing almost arbitrary geometry in two and three dimensions. Among various DNA-based soft materials, DNA hydrogels are comprised of hydrophilic polymeric networks of crosslinked DNA chains. For their properties of biocompatibility, porosity, sequence programmability and tunable multifunctionality, DNA hydrogels have been widely studied in bioanalysis and biomedicine. In this review, recent developments in DNA hydrogels and their applications in drug delivery systems are highlighted. First, physical and chemical crosslinking methods for constructing DNA hydrogels are introduced. Subsequently, responses of DNA hydrogels to nonbiological and biological stimuli are described. Finally, DNA hydrogel-based delivery platforms for different types of drugs are detailed. With the emergence of gene therapy, this review also gives future prospects for combining DNA hydrogels with the gene editing toolbox.

Lipid-oligonucleotide conjugates for bioapplications

Lipid-oligonucleotide conjugates (LONs) are powerful molecular-engineering materials for various applications ranging from biosensors to biomedicine. Their unique amphiphilic structures enable the self-assembly and the conveyance of information with high fidelity. In particular, LONs present remarkable potential in measuring cellular mechanical forces and monitoring cell behaviors. LONs are also essential sensing tools for intracellular imaging and have been employed in developing cell-surface-anchored DNA nanostructures for biomimetic-engineering studies. When incorporating therapeutic oligonucleotides or small-molecule drugs, LONs hold promise for targeted therapy. Moreover, LONs mediate the controllable assembly and fusion of vesicles based on DNA-strand displacements, contributing to nanoreactor construction and macromolecule delivery. In this review, we will summarize the general synthesis strategies of LONs, provide some characterization analysis and emphasize recent advances in bioanalytical and biomedical applications. We will also consider the relevant challenges and suggest future directions for building better functional LONs in nanotechnology and materials-science applications.

Tracking nucleic acid nanocapsule assembly, cellular uptake and disassembly using a novel fluorescently labeled surfactant

Intracellular trafficking and delivery of nucleic acids is an area of growing interest, particularly as it relates to therapeutic applications. Spectroscopic methods have been used to observe and quantitatively measure the delivery of oligonucleotides both in vitro and in vivo. Herein we demonstrate the use of a new fluorophore labeled surfactant presenting a solvatochromatic chromophore for tracking the assembly and degradation of a hybrid biomaterial we refer to as a nucleic acid nanocapsule (NAN). We show that the surfactant enables critical micelle concentration determination, monitoring of NAN disassembly in vitro, and the ability to track the cellular movement and activity of surfactant-oligonucleotide conjugates in cells when coupled with quantitative PCR analysis.

Preparation of ROS-responsive core crosslinked polycarbonate micelles with thioketal linkage

Herein, we prepared novel reactive oxygen species (ROS) responsive core crosslinked (CCL/TK) polycarbonate micelles conveniently by click reaction between amphiphilic diblock copolymer poly(ethylene glycol)-poly(5-methyl-5-propargylxycar-bonyl-1,3-dioxane-2-one) (PEG-PMPC) with pendant alkynyl group and thioketal containing azide derivative bis (2-azidoethyl) 3, 3'- (propane-2, 2-diylbis (sulfanediyl)) dipropanoate (TK-N₃). The CCL/TK micelles were obtained with small size of 146.4 nm, showing excellent stability against dilution and high doxorubicin (DOX) loading. In vitro toxicity tests demonstrated that the obtained CCL/TK micelles have good biocompatibility and low toxicity with cell viability above 95 %. Furthermore, DOX-loaded CCL/TK micelles showed significantly superior toxicity with IC₅₀ values for HeLa and MCF-7 cells about 3.74 μg/mL and 3.91 μg/mL, respectively. Confocal laser scanning microscope (CLSM) and flow cytometry showed excellent internalization efficiency and intracellular drug release of DOX-loaded CCL/TK micelles. The obtained ROS-responsive CCL/TK micelles showed great potential for anticancer drug delivery.

Crosslinked polymer nanocapsules for therapeutic, diagnostic, and theranostic applications

Crosslinked polymer nanocapsules (CPNCs) are hollowed nanoparticles with network-like polymeric shells stabilized by primary bonds. CPNCs have drawn broad and significant interests as nanocarriers for biomedical applications in recent years. As compared with conventional polymeric nanoparticles systems without cavity and/or crosslinking architectures, CPNCs possess significant biomedical relevant advantages, including (a) superior structural stability against environmental conditions, (b) high loading capacity and ability for region-specific loading of multiple cargos, (c) tuneable cargo release rate via crosslinking density, and (d) high specific surface area to facilitate surface adsorption, modification, and interactions. With appropriate base polymers and crosslinkages, CPNCs can be biocompatible and biodegradable. While CPNC-based biomedical nanoplatforms can possess relatively stable physicochemical properties owing to their crosslinked architectures, various biomedically relevant stimuli-responsivities can be incorporated with them through specific structural designs. CPNCs have been studied for the delivery of small molecule drugs, genes, proteins, and other therapeutic agents. They have also been investigated as diagnostic platforms for magnetic resonance imaging, ultrasound imaging, and optical imaging. Moreover, CPNCs have been utilized to carry both therapeutics and bioimaging agents for theranostic applications. This article reviews the therapeutic, diagnostic and theranostic applications of CPNCs, as well as the preparation of these CPNCs, reported in the past decade. This article is categorized under: Therapeutic Approaches and Drug Discovery > Nanomedicine for Oncologic Disease Implantable Materials and Surgical Technologies > Nanomaterials and Implants Diagnostic Tools > in vivo Nanodiagnostics and Imaging.

Tumor microenvironment responsive drug delivery systems

Conventional tumor-targeted drug delivery systems (DDSs) face challenges, such as unsatisfied systemic circulation, low targeting efficiency, poor tumoral penetration, and uncontrolled drug release. Recently, tumor cellular molecules-triggered DDSs have aroused great interests in addressing such dilemmas. With the introduction of several additional functionalities, the properties of these smart DDSs including size, surface charge and ligand exposure can response to different tumor microenvironments for a more efficient tumor targeting, and eventually achieve desired drug release for an optimized therapeutic efficiency. This review highlights the recent research progresses on smart tumor environment responsive drug delivery systems for targeted drug delivery. Dynamic targeting strategies and functional moieties sensitive to a variety of tumor cellular stimuli, including pH, glutathione, adenosine-triphosphate, reactive oxygen species, enzyme and inflammatory factors are summarized. Special emphasis of this review is placed on their responsive mechanisms, drug loading models, drawbacks and merits. Several typical multi-stimuli responsive DDSs are listed. And the main challenges and potential future development are discussed.

Controlled release of small molecules and proteins from DNA-surfactant stabilized metal organic frameworks

This work highlights a multifunctional nanoscale material which can effectively compartmentalize small molecules and biomolecules into a single, micellar structure with programmable degradation properties resulting in highly controllable release properties. The nanomaterial consists of a ZIF-8 metal organic framework (MOF) encapsulated within a DNA surfactant micelle assembly, referred to as a nucleic acid nanocapsule (NAN). NANs have been demonstrated to enter cells through endocytosis and result in intracellular cargo release upon enzyme-triggered degradation. By combining the favorable properties of MOFs (large storage capacity) with those of NANs (triggerable release), we show diverse molecular cargo can be integrated into a single, highly programmable nanomaterial with controllable release profiles. The hybrid MOF-NANs exhibit double-gated regulation capabilities as evidenced by kinetic studies of encapsulated enzymes that indicate individual layers of the particle influence the overall enzymatic rate of turnover. The degradation of MOF-NANs can be controlled under multiple combined stimuli (i.e. varying pH, enzymes), enabling selective release profiles in solutions representative of more complex biological systems. Lastly, the enhanced control over the release of small molecules, proteins and plasmids, is evaluated through a combination of cell culture and in vitro fluorescence assays, indicating the potential of MOF-NANs for both therapeutic and diagnostic applications.

Cross-linked small-molecule capsules with excitation wavelength-dependent photoluminescence and high loading capacity: design, synthesis and application in imaging-guided drug delivery

The cross-linked small-molecule micelles (cSMs) have found applications in many fields but their low loading capacity and non-fluorescence property hindered their further development. Herein, water-soluble organic nanoparticles were applied as templates to "stretch" the hydrophobic core of cSMs and photo-cross-linking was employed to supply photoluminescence. The resulting cross-linked small-molecule capsules (cSCs) not only reserve the superior properties of cSMs of accurate monomer, easy functionalization and robust stability, but also achieve high drug loading capacity and excitation wavelength-dependent fluorescence, where the drug loading contents (DLCs) for various hydrophobic drugs were more than 30-fold higher than that of cSMs, and the maximum quantum yield could be as high as 12.0%. Featuring these superiorities, the cSCs hold promising potential in many fields and an example of doxorubicin-loaded cSCs (DOX@cSCs) for multichannel imaging-guided drug delivery is shown in this work.

Peptide-Driven Shape Control of Low-Dimensional DNA Nanostructures

We report the rational design and fabrication of unusual low-dimensional DNA nanostructures through programmable and sequence-specific peptide interactions. Dual-bioactive block copolymers composed of DNA and amino acid-based polymers (DNA-b-poly(amino acid)) were synthesized by coupling oligonucleotides to phenylalanine (Phe)-based polymers. Unlike prototypical DNA block copolymers, which typically form simple spherical micelles, DNA-b-poly(amino acid) assemble into various low-dimensional structures such as nanofibers, ribbons, and sheets through controllable amino acid interactions. Moreover, DNA-b-poly(amino acid) assemblies can undergo protease-induced fiber-to-sheet shape transformations, where the morphology change is dictated by the type of enzymes and amino acid sequences. The peptide-based self-assembly reported here provides a programmable approach to fabricate dynamic DNA assemblies with diverse and unusual low-dimensional structures.

DNAzyme-powered nucleic acid release from solid supports

Here, we demonstrate use of a Mg²⁺-dependent, site-specific DNA enzyme (DNAzyme) to cleave oligos from polyacrylamide gel beads, which is suitable for use in drop-based assays. We show that cleavage efficiency is improved by use of a tandem-repeat cleavage site. We further demonstrate that DNAzyme-released oligos function as primers in reverse transcription of cell-released mRNA.

Capping Silica Nanoparticles with Tryptophan-Mediated Cucurbit[8]uril Complex for Targeted Intracellular Drug Delivery Triggered by Tumor-Overexpressed IDO1 Enzyme

Nanosystems responsive to tumor-specific enzymes are considered as a highly attractive approach to intracellular drug release for targeted cancer therapy. Mesoporous silica nanoparticles are capped with tryptophan-mediated cucurbit[8]uril complex with Fe₃ O₄ to minimize the premature drug leakage while being able to deliver the payload on demand at the target tissue. The supramolecular interaction between tryptophan and cucurbit[8]uril is disrupted in the presence of indoleamine 2,3-dioxygenase 1 (IDO1) enzyme (abundant in the tumor intracellular microenvironment), which catalyzes the metabolism of tryptophan into N-formylkynurenine, resulting in the disassembly of the "gate-keeper" of the nanocarriers and intracellular release of therapeutics exclusively in tumor cells. The drug release from the nanocarrier with high selectivity to overexpressed IDO1 enzyme induces significant cytotoxicity against HepG2 cells in vitro, as well as the superior antitumor effects in vivo. This robust supramolecular nanosystem with sophisticated structure and property provides a promising platform for intracellular drug release targeting the intrinsic microenvironmental enzyme inside the tumor cells.

A smart fluorescent biosensor for the highly sensitive detection of BRCA1 based on a 3D DNA walker and ESDR cascade amplification

Nucleic acid analysis plays an important role in the diagnosis of diseases. There is a continuous demand to develop rapid and sensitive methods for the specific detection of nucleic acids. Herein, we constructed a highly sensitive and rapid fluorescent biosensor for the detection of BRCA1 by coupling a 3D DNA walker machine with spontaneous entropy-driven strand displacement reactions (ESDRs). In this study, the 3D DNA walker machine was well activated by the target DNA; this resulted in the cyclic utilization of the target DNA and the release of intermediate DNAs. Subsequently, the free intermediate DNAs triggered the circulation process of ESDRs with the help of the assistant probe A, leading to a significant enhancement of the fluorescence intensity. Due to the robust execution of the 3D DNA walker machine and highly efficient amplification capability of ESDRs, the developed biosensing method shows a wide linear range from 0.1 pM to 10 nM with the detection limit as low as 41.44 fM (S/N = 3). Moreover, the constructed biosensor displays superior specificity and has been applied to monitor BRCA1 in complex matrices. Thus, this elaborated cascade amplification biosensing strategy provides a potential platform for the bioassays of nucleic acids and the clinical diagnosis of diseases.

Dynamic Nanostructures from DNA-Coupled Molecules, Polymers, and Nanoparticles

Dynamic and reconfigurable systems that can sense and react to physical and chemical signals are ubiquitous in nature and are of great interest in diverse areas of science and technology. DNA is a powerful tool for fabricating such smart materials and devices due to its programmable and responsive molecular recognition properties. For the past couple of decades, DNA-based self-assembly is actively explored to fabricate various DNA-organic and DNA-inorganic hybrid nanostructures with high-precision structural control. Building upon past development, researchers have recently begun to design and assemble dynamic nanostructures that can undergo an on-demand transformation in the structure, properties, and motion in response to various external stimuli. In this Review, recent advances in dynamic DNA nanostructures, focusing on hybrid structures fabricated from DNA-conjugated molecules, polymers, and nanoparticles, are introduced, and their potential applications and future perspectives are discussed.

Pro-Nifuroxazide Self-Assembly Leads to Triggerable Nanomedicine for Anti-cancer Therapy

Transcription factor STAT3 has been shown to regulate genes that are involved in stem cell self-renewal and thus represents a novel therapeutic target of great biological significance. However, many small-molecule agents with potential effects through STAT3 modulation in cancer therapy lack aqueous solubility and high off-target toxicity, hence impeding efficient bioavailability and activity. This work, for the first time, reports a prodrug-based strategy for selective and safer delivery of STAT3 inhibitors designed toward metastatic and drug-resistant breast cancer. We have synthesized a novel lipase-labile SN-2 phospholipid prodrug from a clinically investigated STAT3 inhibitor, nifuroxazide (Pro-nifuroxazide), which can be regioselectively cleaved by the membrane-abundant enzymes in cancer cells. Pro-nifuroxazide self-assembled to sub 20 nm nanoparticles (NPs), and the cytotoxic ability was screened in ER(+)-MCF-7 and ER(-)-MD-MB231 cells at 48-72 h using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetra-zolium bromide proliferation assay. Results indicated that Pro-nifuroxazide NPs are multifold more effective toward inhibiting cancer cells in a time-dependent manner compared to parent nifuroxazide. A remarkable improvement in the local concentration of drugs to as high as ∼240 fold when assembled into NPs is presumably the reason for this functional improvement. We also introduced molecular dynamics simulations to generate Pro-nifuroxazide nano-assembly, as a model assembly from triggerable anti-cancer drugs, to provide molecular insights correlating physicochemical and anti-cancer properties. In silico properties of Pro-nifuroxazide including size, chemistry of NPs and membrane interactions with individual molecules could be validated by in vitro functional activities in cells of breast cancer origin. The in vivo anti-cancer efficiencies of Pro-nifuroxazide NPs in nude mice xenografts with MCF-7 revealed remarkable growth inhibition of as high as 400%. Histopathological analysis corroborated these findings to show significantly high nuclear fragmentation and retracted cytoplasm. Immunostaining on tumor section demonstrated a significantly lower level of pSTAT-3 by Pro-nifuroxazide NP treatment, establishing the inhibition of STAT-3 phosphorylation. Our strategy for the first time proposes a translatable prodrug agent self-assembled into NPs and demonstrates remarkable enhancement in IC50, induced apoptosis, and reduced cancer cell population through STAT-3 inhibition via reduced phosphorylation.

Expanding the materials space of DNA via organic-phase ring-opening metathesis polymerization

Herein, we develop a facile route to bring DNA to the organic phase, which greatly expands the types of structures accessible using DNA macromonomers. Phosphotriester- and exocyclic amine-protected DNA was synthesized and further modified with a norbornene moiety, which enables homopolymerization via ring-opening metathesis to produce brush-type DNA graft polymers in high yields. Subsequent deprotection cleanly reveals the natural phosphodiester DNA. The method not only achieves high molecular weight DNA graft polymers but when carried out at low monomer:catalyst ratios, yields oligomers that can be further fractionated to molecularly pure, monodisperse entities with one through ten DNA strands per molecule. In addition, we demonstrate substantial simplification in the preparation of traditionally difficult DNA-containing structures, such as DNA/poly(ethylene glycol) diblock graft copolymers and DNA amphiphiles. We envision that the marriage of oligonucleotides with the vast range of organic-phase polymerizations will result in many new classes of materials with yet unknown properties.

Recent Developments in the Area of Click-Crosslinked Nanocarriers for Drug Delivery

Click-crosslinking has been widely used for the fabrication of nanocarriers in recent years. Crosslinking can enhance the stability of nanocarriers that have served as an emerging platform for drug delivery to achieve cancer diagnosis and therapy. In crosslinking methods, click reactions have attracted increasing attention owing to their high reaction specificity and physiologically stable products. These reports on click-crosslinked nanocarriers are divided into four sections (nanogels, nanoparticles, micelles, and capsules) according to the types of nanocarriers. Click-crosslinked nanocarriers enhance the solubility of hydrophobic drugs and improve the efficacy of drug delivery owing to their good stability. Stimuli-responsive and targeted strategies can be introduced into click-crosslinked nanocarriers to enhance drug accumulation in tumors.

Magnetic thermosensitive micelles with upper critical solution temperature for NIR triggered drug release

Smart micelles which undergo dramatic property changes in response to temperature have aroused extensive interest in specific cancer therapy.

RNA-Cleaving DNAzymes: Old Catalysts with New Tricks for Intracellular and In Vivo Applications

DNAzymes are catalytically active DNA molecules that are normally isolated through in vitro selection methods, among which RNA-cleaving DNAzymes that catalyze the cleavage of a single RNA linkage embedded within a DNA strand are the most studied group of this DNA enzyme family. Recent advances in DNA nanotechnology and engineering have generated many RNA-cleaving DNAzymes with unique recognition and catalytic properties. Over the past decade, numerous RNA-cleaving, DNAzymes-based functional probes have been introduced into many research areas, such as in vitro diagnostics, intracellular imaging, and in vivo therapeutics. This review focus on the fundamental insight into RNA-Cleaving DNAzymes and technical tricks for their intracellular and in vivo applications, highlighting the recent progress in the clinical trial of RNA-Cleaving DNAzymes with selected examples. The challenges and opportunities for the future translation of RNA-cleaving DNAzymes for biomedicine are also discussed.

DNA Polymer Nanoparticles Programmed via Supersandwich Hybridization for Imaging and Therapy of Cancer Cells

Spherical nucleic acid (SNA) constructs are promising new single entity materials, which possess significant advantages in biological applications. Current SNA-based drug delivery system typically employed single-layered ss- or ds-DNA as the drug carriers, resulting in limited drug payload capacity and disease treatment. To advance corresponding applications, we developed a novel DNA-programmed polymeric SNA, a long concatamer DNA polymer that is uniformly distributed on gold nanoparticles (AuNPs), by self-assembling from two short alternating DNA building blocks upon initiation of immobilized capture probes on AuNPs, through a supersandwich hybridization reaction. The long DNA concatamer of polymeric SNA enables to allow high-capacity loading of bioimaging and therapeutics agents. We demonstrated that both of the fluorescence signals and therapeutic efficacy were effectively inhibited in resultant polymeric SNA. By further modifying with the nucleolin-targeting aptamer AS1411, this polymeric SNA could be specifically internalized into the tumor cells through nucleolin-mediated endocytosis and then interact with endogenous ATP to cause the release of therapeutics agents from long DNA concatamer via a structure switching, leading to the activation of the fluorescence and selective synergistic chemotherapy and photodynamic therapy. This nanostructure can afford a promising targeted drug transport platform for activatable cancer theranostics.