Engineering DNA scaffolds for delivery of anticancer therapeutics

Engineering Escherichia coli Nissle 1917 as a microbial chassis for therapeutic and industrial applications

Genetically engineered microbes, especially Escherichia coli, have been widely used in the biosynthesis of proteins and metabolites for medical and industrial applications. As a traditional probiotic with a well-established safety record, E. coli Nissle 1917 (EcN) has recently emerged as a microbial chassis for generating living therapeutics, drug delivery vehicles, and microbial platforms for industrial production. Despite the availability of genetic tools for engineering laboratory E. coli K-12 and B strains, new genetic engineering systems are still greatly needed to expand the application range of EcN. In this review, we have summarized the latest progress in the development of genetic engineering systems in EcN, as well as their applications in the biosynthesis and delivery of valuable small molecules and biomacromolecules of medical and/or industrial interest, followed by a glimpse of how this rapidly growing field will evolve in the future.

Re-endothelialization of Decellularized Scaffolds With Endothelial Progenitor Cell Capturing Aptamer: A New Strategy for Tissue-Engineered Heart Valve

Tissue-engineered heart valve (TEHV) is a promising alternative to current heart valve substitute. Decellularized porcine aortic heart valves (DAVs) are the most common scaffolds of TEHV. Hard to endothelialization is one of the disadvantages of DAVs. Therefore, we aimed to immobilize endothelial progenitor cell (EPC)-aptamer onto DAVs for accelerating endothelialization. In this study, three groups of scaffolds were constructed: DAVs, aptamer-immobilized DAVs (aptamer-DAVs), and glutaraldehyde crosslinked DAVs (GA-DAVs). The results of flow cytometry revealed that EPC-aptamer was specific to EPCs and was immobilized onto DAVs. Cells adhesion experiments demonstrated that EPCs adhered more tightly onto aptamer-DAVs group than other two groups of scaffolds. And cell proliferation assay indicated that EPCs seeded onto aptamer-DAVs group grew faster than DAVs group and GA-DAVs group. Moreover, dynamic capture experiment in flow conditions revealed that the number of EPCs captured by aptamer-DAVs group was more than other two groups. In conclusion, aptamer-DAVs could specifically promote adhesion and proliferation of EPCs and had ability to capture EPCs in simulated flow condition. This could promote re-endothelialization of scaffolds.

Targeted drug-loaded PLGA-PCL microspheres for specific and localized treatment of triple negative breast cancer

The paper presents the results of the experimental and analytical study of targeted drug-loaded polymer-based microspheres made from blend polymer of polylactic-co-glycolic acid and polycaprolactone (PLGA-PCL) for targeted and localized cancer drug delivery. In vitro sustained release with detailed thermodynamically driven drug release kinetics, over a period of three months using encapsulated targeted drugs (prodigiosin-EphA2 or paclitaxel-EphA2) and control drugs [Prodigiosin (PGS), and paclitaxel (PTX)] were studied. Results from in vitro study showed a sustained and localized drug release that is well-characterized by non-Fickian Korsmeyer-Peppas kinetics model over the range of temperatures of 37 °C (body temperature), 41 °C, and 44 °C (hyperthermic temperatures). The in vitro alamar blue, and flow cytometry assays in the presence of the different drug-loaded polymer formulations resulted to cell death and cytotoxicity that was evidence through cell inhibition and late apoptosis on triple negative breast cancer (TNBC) cells (MDA-MB 231). In vivo studies carried out on groups of 4-week-old athymic nude mice that were induced with subcutaneous TNBC, showed that the localized release of the EphA2-conjugated drugs was effective in complete elimination of residual tumor after local surgical resection. Finally, ex vivo histopathological analysis carried out on the euthanized mice revealed no cytotoxicity and absence of breast cancer metastases in the liver, kidney, and lungs 12 weeks after treatment. The implications of the results are then discussed for the development of encapsulated EphA2-conjugated drugs formulation in the specific targeting, localized, and sustain drug release for the elimination of local recurred TNBC tumors after surgical resection.

Engineered Extracellular Vesicles with Compound-Induced Cargo Delivery to Solid Tumors

Efficient delivery of functional factors into target cells remains challenging. Although extracellular vesicles (EVs) are considered to be potential therapeutic delivery vehicles, a variety of efficient therapeutic delivery tools are still needed for cancer cells. Herein, we demonstrated a promising method to deliver EVs to refractory cancer cells via a small molecule-induced trafficking system. We generated an inducible interaction system between the FKBP12-rapamycin-binding protein (FRB) domain and FK506 binding protein (FKBP) to deliver specific cargo to EVs. CD9, an abundant protein in EVs, was fused to the FRB domain, and the specific cargo to be delivered was linked to FKBP. Rapamycin recruited validated cargo to EVs through protein-protein interactions (PPIs), such as the FKBP-FRB interaction system. The released EVs were functionally delivered to refractory cancer cells, triple negative breast cancer cells, non-small cell lung cancer cells, and pancreatic cancer cells. Therefore, the functional delivery system driven by reversible PPIs may provide new possibilities for a therapeutic cure against refractory cancers.

Carbohydrates based stimulus responsive nanocarriers for cancer-targeted chemotherapy: A review of current practices

INTRODUCTION

Many nanocarriers have been developed to react physicochemically to exterior stimuli like ultrasonic, light, heat, and magnetic fields, along with various internal stimuli including pH, hypoxia, enzyme, and redox potential. Nanocarriers are capable to respond various stimuli within the cancer cells to enable on-demand drug delivery, activation of bioactive compounds, controlled drug release, and targeting ligands, as well as size, charge, and conformation conversion, enabling sensing and signaling, overcoming multidrug resistance, accurate diagnosis, and precision therapy.

AREAS COVERED

Carbohydrates are ubiquitous biomolecules with a high proclivity for supramolecular network formation. Numerous carbohydrate-based nanomaterials have been used in biological solicitations and stimuli-based responses. Particular emphasis has been placed on the utilization of carbohydrate-based NPs and nanogels in various fields including imaging, drug administration, and tissue engineering. Because the assembly process is irreversible, carbohydrate-based systems are excellent ingredients for the development of stimulus-responsive nanocarriers for cancer-targeted chemotherapy. This review aims to summarise current research on carbohydrate-based nanomaterials, with an emphasis on stimuli-sensitive nanocarriers for cancer-targeted chemotherapy.

EXPERT OPINION

Carbohydrates-based stimulus-responsive nanomaterials have been proved highly efficient for targeted delivery of anticancer drugs, thus leading to effective chemotherapy with minimum off-target effects.

Composite Materials Based on Gelatin and Iron Oxide Nanoparticles for MRI Accuracy

The majority of recent studies have focused on obtaining MRI materials for internal use. However, this study focuses on a straightforward method for preparing gelatin-based materials with iron oxide nanoparticles (G–Fe₂O₃ and G–Fe₃O₄) for external use. The newly obtained materials must be precisely tuned to match the requirements and usage situation because they will be in close touch with human/animal skin. The biocompatible structures formed by gelatin, tannic acid, and iron oxide nanoparticles were investigated by using FTIR spectroscopy, SEM-EDAX analysis, and contact angle methods. The physico-chemical properties were obtained by using mechanical investigations, dynamic vapor sorption analysis, and bulk magnetic determination. The size and shape of iron oxide nanoparticles dictates the magnetic behavior of the gelatin-based samples. The magnetization curves revealed a typical S-shaped superparamagnetic behavior which is evidence of improved MRI image accuracy. In addition, the MTT assay was used to demonstrate the non-toxicity of the samples, and the antibacterial test confirmed satisfactory findings for all G-based materials.

Exosome as a Delivery Vehicle for Cancer Therapy

Exosomes are small extracellular vesicles that are naturally produced and carry biomolecules such as proteins, microRNAs, and metabolites. Because of their small size and low level of biomolecule expression, the biological function of exosomes has only been identified recently. Despite the short history of investigation, exosomes seem to have remarkable potential as a delivery vehicle. With regards to cancer therapy, numerous antitumor agents demonstrate serious side effects (or toxicity), which has led to the unmet need for improving their selectivity and stability. Exosomes, either produced naturally or generated artificially, provide an attractive platform to load many types of molecules such as small molecules, biologics, and other therapeutic agents. Furthermore, the features of exosomes can be designed by selecting their source cells, or they can be engineered to incorporate affinity tags; thus, exosomes show promise as effective delivery vehicles for the complex tumor microenvironment. In this review, we focus on various exosomes produced from different cell types and their potential uses. Moreover, we summarize the current state of artificial exosomes as a drug carrier and provide an overview of the techniques used for their production.

Utilizing Edible Agar as a Carrier for Dual Functional Doxorubicin-Fe3O4 Nanotherapy Drugs

The purpose of this study was to use agar as a multifunctional encapsulating material to allow drug and ferromagnetism to be jointly delivered in one nanoparticle. We successfully encapsulated both Fe3O4 and doxorubicin (DOX) with agar as the drug carrier to obtain DOX-Fe3O4@agar. The iron oxide nanoparticles encapsulated in the carrier maintained good saturation of magnetization (41.9 emu/g) and had superparamagnetism. The heating capacity test showed that the specific absorption rate (SAR) value was 18.9 ± 0.5 W/g, indicating that the ferromagnetic nanoparticles encapsulated in the gel still maintained good heating capacity. Moreover, the magnetocaloric temperature could reach 43 °C in a short period of five minutes. In addition, DOX-Fe3O4@agar reached a maximum release rate of 85% ± 3% in 56 min under a neutral pH 7.0 to simulate the intestinal environment. We found using fluorescent microscopy that DOX entered HT-29 human colon cancer cells and reduced cell viability by 66%. When hyperthermia was induced with an auxiliary external magnetic field, cancer cells could be further killed, with a viability of only 15.4%. These results show that agar is an efficient multiple-drug carrier, and allows controlled drug release. Thus, this synergic treatment has potential application value for biopharmaceutical carrier materials.

Molecularly Imprinted Polymer-Based Smart Prodrug Delivery System for Specific Targeting, Prolonged Retention, and Tumor Microenvironment-Triggered Release

Prodrug and drug delivery systems are two effective strategies for improving the selectivity of chemotherapeutics. Molecularly imprinted polymers (MIPs) have emerged as promising carriers in targeted drug delivery for cancer treatment, but they have not yet been integrated with the prodrug strategy. Reported here is an MIP-based smart prodrug delivery system for specific targeting, prolonged retention time, and tumor microenvironment-triggered release. 5'-Deoxy-5-fluorocytidine (DFCR) and sialic acid (SA) were used as a prodrug and a marker for tumor targeting, respectively. Their co-imprinted nanoparticles were prepared as a smart carrier. Prodrug-loaded MIP specifically and sustainably accumulated at the tumor site and then gradually released. Unlike conventional prodrug designs, which often require in-liver bioconversion, this MIP-based prodrug delivery is liver-independent but tumor-dependent. Thus, this study opens new access to the development of smart prodrug delivery nanoplatforms.

In-vitro and in-vivo evaluation of polymeric microsphere formulation for colon targeted delivery of 5-fluorouracil using biocompatible natural gum katira

The aim was to develop oral site-specific rate-controlled anticancer drug delivery to pacify systemic side-effects and offer effective and safe therapy for colon cancer with compressed dose and duration of treatment. The double emulsion solvent evaporation method was employed. To check functionality, DAPI-staining and in-vivo anticancer study of Ehrlich Ascites Carcinoma bearing mice was tested. Histopathology of liver and kidney and Cell morphology of EAC cell was also performed. Formulated and optimized polymeric microsphere of 5-FU showed excellent physicochemical features. In-vitro, DAPI results pointed drug-treated groups displayed the prominent feature of apoptosis. The percentage of apoptotic of entrapped drug played in a dose-dependent manner. Significant decreases in EAC liquid tumors and increased life span of treated mice were observed. Rate of variation of cell morphology was more in 5-FU loaded microsphere than 5-FU injection. Hematological and biochemical parameter's and Histopathology of liver and kidney resulted that due to control released formulation have slow release rate, that gives less trace on liver and kidney function. Finally, we foresee that polymeric microsphere of 5-FU applying natural gum katira could be an assuring micro-carrier for active colon targeting delivery tool with augmented chemotherapeutic efficacy and lowering side effect against colon cancer.

Alginate-based hydrogels as drug delivery vehicles in cancer treatment and their applications in wound dressing and 3D bioprinting

Hydrogels are a three-dimensional and crosslinked network of hydrophilic polymers. They can absorb a large amount of water or biological fluids, which leads to their swelling while maintaining their 3D structure without dissolving (Zhu and Marchant, Expert Rev Med Devices 8:607-626, 2011). Among the numerous polymers which have been utilized for the preparation of the hydrogels, polysaccharides have gained more attention in the area of pharmaceutics; Sodium alginate is a non-toxic, biocompatible, and biodegradable polysaccharide with several unique physicochemical properties for which has used as delivery vehicles for drugs (Kumar Giri et al., Curr Drug Deliv 9:539-555, 2012). Owing to their high-water content and resembling the natural soft tissue, hydrogels were studied a lot as a scaffold. The formation of hydrogels can occur by interactions of the anionic alginates with multivalent inorganic cations through a typical ionotropic gelation method. However, those applications require the control of some properties such as mechanical stiffness, swelling, degradation, cell attachment, and binding or release of bioactive molecules by using the chemical or physical modifications of the alginate hydrogel. In the current review, an overview of alginate hydrogels and their properties will be presented as well as the methods of producing alginate hydrogels. In the next section of the present review paper, the application of the alginate hydrogels will be defined as drug delivery vehicles for chemotherapeutic agents. The recent advances in the application of the alginate-based hydrogels will be describe later as a wound dressing and bioink in 3D bioprinting.

Degradable porous drug-loaded polymer scaffolds for localized cancer drug delivery and breast cell/tissue growth

This paper presents the results of a combined experimental and analytical study of blended FDA-approved polymers [polylactic-co-glycolic acid (PLGA), polyethylene glycol (PEG) and polycaprolactone (PCL)] with the potential for sustained localized cancer drug release. Porous drug-loaded 3D degradable PLGA-PEG and PLGA-PCL scaffolds were fabricated using a multistage process that involved solvent casting and particulate leaching with lyophilization. The physicochemical properties including the mechanical, thermal and biostructural properties of the drug-loaded microporous scaffolds were characterized. The release of the encapsulated prodigiosin (PG) or paclitaxel (PTX) drug (from the drug-loaded polymer scaffolds) was also studied experimentally at human body temperature (37 °C) and hyperthermic temperatures (41 and 44 °C). These characteristic controlled and localized in vitro drug release from the properties of the microporous scaffold were analyzed using kinetics and thermodynamic models. Subsequently, normal breast cells (MCF-10A) were cultured for a 28-day period on the resulting 3D porous scaffolds in an effort to study the possible regrowth of normal breast tissue, following drug release. The effects of localized cancer drug release on breast cancer cells and normal breast cell proliferation are demonstrated for scenarios that are relevant to palliative breast tumor surgery for 16 weeks under in vivo conditions. Results from the in vitro drug release show a sustained anomalous (non-Fickian) drug release that best fits the Korsmeyer-Peppas (KP) kinetic model with a non-spontaneous thermodynamic process that leads to a massive decrease in breast cancer cell (MDA-MB-231) viability. Our findings from the animal suggest that localized drug release from drug-based 3D resorbable porous scaffolds can be used to eliminate/treat local recurred triple negative breast tumors and promote normal breast tissue regeneration after surgical resection.

Bifidobacterium spp: the promising Trojan Horse in the era of precision oncology

Selective delivery of therapeutic agents into solid tumors has been a major challenge impeding the achievement of long-term disease remission and cure. The need to develop alternative drug delivery routes to achieve higher drug concentration in tumor tissue, reduce unwanted off-target side effects and thus achieve greater therapeutic efficacy, has resulted in an explosive body of research. Bifidobacterium spp. are anaerobic, nonpathogenic, Gram-positive bacteria, commensal to the human gut that are a possible anticancer drug-delivery vehicle. In this review, we describe Bifidobacterium's microbiology, current clinical applications, overview of the preclinical work investigating Bifidobacterium's potential to deliver anticancer therapy, and review the different strategies used up to date. Finally, we discuss both current challenges and future prospects.

Targeted therapy in chronic diseases using nanomaterial-based drug delivery vehicles

The application of nanomedicines is increasing rapidly with the promise of targeted and efficient drug delivery. Nanomedicines address the shortcomings of conventional therapy, as evidenced by several preclinical and clinical investigations indicating site-specific drug delivery, reduced side effects, and better treatment outcome. The development of suitable and biocompatible drug delivery vehicles is a prerequisite that has been successfully achieved by using simple and functionalized liposomes, nanoparticles, hydrogels, micelles, dendrimers, and mesoporous particles. A variety of drug delivery vehicles have been established for the targeted and controlled delivery of therapeutic agents in a wide range of chronic diseases, such as diabetes, cancer, atherosclerosis, myocardial ischemia, asthma, pulmonary tuberculosis, Parkinson's disease, and Alzheimer's disease. After successful outcomes in preclinical and clinical trials, many of these drugs have been marketed for human use, such as Abraxane®, Caelyx®, Mepact®, Myocet®, Emend®, and Rapamune®. Apart from drugs/compounds, novel therapeutic agents, such as peptides, nucleic acids (DNA and RNA), and genes have also shown potential to be used as nanomedicines for the treatment of several chronic ailments. However, a large number of extensive clinical trials are still needed to ensure the short-term and long-term effects of nanomedicines in humans. This review discusses the advantages of various drug delivery vehicles for better understanding of their utility in terms of current medical needs. Furthermore, the application of a wide range of nanomedicines is also described in the context of major chronic diseases.

The Growing Development of DNA Nanostructures for Potential Healthcare-Related Applications

DNA self-assembly has proven to be a highly versatile tool for engineering complex and dynamic biocompatible nanostructures from the bottom up with a wide range of potential bioapplications currently being pursued. Primary among these is healthcare, with the goal of developing diagnostic, imaging, and drug delivery devices along with combinatorial theranostic devices. The path to understanding a role for DNA nanotechnology in biomedical sciences is being approached carefully and systematically, starting from analyzing the stability and immune-stimulatory properties of DNA nanostructures in physiological conditions, to estimating their accessibility and application inside cellular and model animal systems. Much remains to be uncovered but the field continues to show promising results toward developing useful biomedical devices. This review discusses some aspects of DNA nanotechnology that makes it a favorable ingredient for creating nanoscale research and biomedical devices and looks at experiments undertaken to determine its stability in vivo. This is presented in conjugation with examples of state-of-the-art developments in biomolecular sensing, imaging, and drug delivery. Finally, some of the major challenges that warrant the attention of the scientific community are highlighted, in order to advance the field into clinically relevant applications.

Minimalist Design of a Stimuli-Responsive Spherical Nucleic Acid for Conditional Delivery of Oligonucleotide Therapeutics

In this work, we report a component-minimal spherical nucleic acid (SNA) from monodisperse DNA-polymer conjugates that can load and release nucleic acid therapeutics in a stimuli-responsive manner. We show that this vehicle assembles from only four strands, and conditional release of its antisense therapeutic cargo can be induced upon recognition of specific oligonucleotide triggers via strand displacement. The latter (triggers) may be a microRNA that offers additional synergistic therapy, in addition to the previously shown ability of the SNA to load hydrophobic drugs. The SNA is easy to prepare, has dynamic character, releases its cargo only upon the presence of both triggers, and can survive biological conditions while protecting its cargo. The gene silencing potency of the cargo was tested in live cells and shown to be suppressed when loaded in the SNA, and its activity was restored only upon release with the two triggers. This vehicle has the essential characteristics of versatility, ease of synthesis, low cost, highly responsive behavior, and ability to support combination therapies, making it a promising candidate for cell-selective drug delivery and clinical transition.

Controlled drug delivery vehicles for cancer treatment and their performance

Although conventional chemotherapy has been successful to some extent, the main drawbacks of chemotherapy are its poor bioavailability, high-dose requirements, adverse side effects, low therapeutic indices, development of multiple drug resistance, and non-specific targeting. The main aim in the development of drug delivery vehicles is to successfully address these delivery-related problems and carry drugs to the desired sites of therapeutic action while reducing adverse side effects. In this review, we will discuss the different types of materials used as delivery vehicles for chemotherapeutic agents and their structural characteristics that improve the therapeutic efficacy of their drugs and will describe recent scientific advances in the area of chemotherapy, emphasizing challenges in cancer treatments.

Improving the delivery of cancer therapies to tumor sites is crucial to reduce unwanted side effects and patient mortality rates. Pralay Maiti and colleagues at the Indian Institute of Technology in Varanasi, India, review the latest developments in drug delivery vehicles and treatment approaches designed to enhance the effectiveness of current cancer therapies. New nanoparticle-based carriers, hydrogels and hybrid materials that offer controlled and sustained drug release are showing great promise in animal models. Furthermore, materials that respond to stimuli such as heat, light, magnetic or electric fields are also being tested to aid target-specific drug delivery and, thus, avoid damage to healthy tissues. Although there are some challenges in translating these findings to the clinic, there is no doubt that technological advances are shaping better and safer treatment options.

Intercalation-mediated nucleic acid nanoparticles for siRNA delivery

Tremendous effort has been made to improve stability and delivery efficacy of small RNA therapeutics. However, nearly all current nano-encapsulation carriers utilize the critical balance between only two interacting parameters: RNA-binding electrostatic interactions and nanoparticle-stabilizing hydrophobic interactions. We report the development of intercalation-meditated nucleic acid (IMNA) nanoparticles, which utilize intercalation as a third interaction to enhance small RNA delivery. This toolbox expansion of interaction parameters may inspire the use of additional forces in nanoparticle drug carriers to increase potency and stability.

Aptamer-integrated DNA nanostructures for biosensing, bioimaging and cancer therapy

The combination of nanostructures with biomolecules leading to the generation of functional nanosystems holds great promise for biotechnological and biomedical applications. As a naturally occurring biomacromolecule, DNA exhibits excellent biocompatibility and programmability. Also, scalable synthesis can be readily realized through automated instruments. Such unique properties, together with Watson-Crick base-pairing interactions, make DNA a particularly promising candidate to be used as a building block material for a wide variety of nanostructures. In the past few decades, various DNA nanostructures have been developed, including one-, two- and three-dimensional nanomaterials. Aptamers are single-stranded DNA or RNA molecules selected by Systematic Evolution of Ligands by Exponential Enrichment (SELEX), with specific recognition abilities to their targets. Therefore, integrating aptamers into DNA nanostructures results in powerful tools for biosensing and bioimaging applications. Furthermore, owing to their high loading capability, aptamer-modified DNA nanostructures have also been altered to play the role of drug nanocarriers for in vivo applications and targeted cancer therapy. In this review, we summarize recent progress in the design of aptamers and related DNA molecule-integrated DNA nanostructures as well as their applications in biosensing, bioimaging and cancer therapy. To begin with, we first introduce the SELEX technology. Subsequently, the methodologies for the preparation of aptamer-integrated DNA nanostructures are presented. Then, we highlight their applications in biosensing and bioimaging for various targets, as well as targeted cancer therapy applications. Finally, we discuss several challenges and further opportunities in this emerging field.

Advance of DNA and CCPs-based nanocarriers in drug delivery systems

Development of smart and functional polymeric carriers, which enable controlled or timed release of a bioactive material, thereby providing a better dosing pattern and minimizing side effects, becomes a new requirement in the field of drug delivery. In the recent few decades, a great many advancements of polymer synthetic methods have led to a new generation of bioactive polymers' applications as drug controlled release carriers. In this review, we focus on the use of bioactive polymers for drug delivery system, with a particular in the utility of DNA-based nanocarriers and cell-penetrating peptides (CCPs)-based nanocarriers to provide precision control for drug targeting or stimuli responsive systems.

Inflammation-Triggered Cancer Immunotherapy by Programmed Delivery of CpG and Anti-PD1 Antibody

Inflammation-triggered combination delivery of anti-PD-1 antibody and CpG oligodeoxynucleotides (CpG ODNs) has been demonstrated to prevent cancer relapse utilizing postsurgical inflammatory response. The controlled release of anti-PD1 and CpG ODN by CpG DNA-based "nano-cocoons" can induce considerable immune response, which in turn significantly prolongs the survival time of mice.

Local delivery of checkpoints antibodies

Immune checkpoint inhibitors (ICI) based cancer immunotherapy has recently attracted considerable interest in the field of cancer therapy. The relevant immunotherapeutic agents do not directly attack the tumor, but boost the body's immune system to recognize and kill cancer cells. In this commentary, recent efforts utilizing immunoengineering for local delivery of these immune checkpoint antibodies are introduced. Future opportunities and challenges in this research theme are also commented.

Crystal structure of a poly(rA) staggered zipper at acidic pH: evidence that adenine N1 protonation mediates parallel double helix formation

We have solved at 1.07 Å resolution the X-ray crystal structure of a polyriboadenylic acid (poly(rA)) parallel and continuous double helix. Fifty-nine years ago, double helices of poly(rA) were first proposed to form at acidic pH. Here, we show that 7-mer oligo(rA), i.e. rA₇, hybridizes and overlaps in all registers at pH 3.5 to form stacked double helices that span the crystal. Under these conditions, rA₇ forms well-ordered crystals, whereas rA₆ forms fragile crystalline-like structures, and rA₅, rA₈ and rA₁₁ fail to crystallize. Our findings support studies from ∼50 years ago: one showed using spectroscopic methods that duplex formation at pH 4.5 largely starts with rA₇ and begins to plateau with rA₈; another proposed a so-called ‘staggered zipper’ model in which oligo(rA) strands overlap in multiple registers to extend the helical duplex. While never shown, protonation of adenines at position N1 has been hypothesized to be critical for helix formation. Bond angles in our structure suggest that N1 is protonated on the adenines of every other rAMP−rAMP helix base pair. Our data offer new insights into poly(rA) duplex formation that may be useful in developing a pH sensor.

Transformable DNA nanocarriers for plasma membrane targeted delivery of cytokine

Direct delivery of cytokines using nanocarriers holds great promise for cancer therapy. However, the nanometric scale of the vehicles made them susceptible to size-dependent endocytosis, reducing the plasma membrane-associated apoptosis signaling. Herein, we report a tumor microenvironment-responsive and transformable nanocarrier for cell membrane targeted delivery of cytokine. This formulation is comprised of a phospholipase A2 (PLA2) degradable liposome as a shell, and complementary DNA nanostructures (designated as nanoclews) decorated with cytokines as the cores. Utilizing the tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) as a model cytokine, we demonstrate that the TRAIL loaded DNA nanoclews are capable of transforming into nanofibers after PLA2 activation. The nanofibers with micro-scaled lengths efficiently present the loaded TRAIL to death receptors on the cancer cell membrane and amplified the apoptotic signaling with reduced TRAIL internalization.

Recent advances of cocktail chemotherapy by combination drug delivery systems

Combination chemotherapy is widely exploited for enhanced cancer treatment in the clinic. However, the traditional cocktail administration of combination regimens often suffers from varying pharmacokinetics among different drugs. The emergence of nanotechnology offers an unparalleled opportunity for developing advanced combination drug delivery strategies with the ability to encapsulate various drugs simultaneously and unify the pharmacokinetics of each drug. This review surveys the most recent advances in combination delivery of multiple small molecule chemotherapeutics using nanocarriers. The mechanisms underlying combination chemotherapy, including the synergistic, additive and potentiation effects, are also discussed with typical examples. We further highlight the sequential and site-specific co-delivery strategies, which provide new guidelines for development of programmable combination drug delivery systems. Clinical outlook and challenges are also discussed in the end.

Advances in Functional Assemblies for Regenerative Medicine

The ability to synthesise bioresponsive systems and selectively active biochemistries using polymer-based materials with supramolecular features has led to a surge in research interest directed towards their development as next generation biomaterials for drug delivery, medical device design and tissue engineering.

Self-assembled DNA nanoclews for the efficient delivery of CRISPR-Cas9 for genome editing

CRISPR-Cas9 represents a promising platform for genome editing, yet means for its safe and efficient delivery remain to be fully realized. A novel vehicle that simultaneously delivers the Cas9 protein and single guide RNA (sgRNA) is based on DNA nanoclews, yarn-like DNA nanoparticles that are synthesized by rolling circle amplification. The biologically inspired vehicles were efficiently loaded with Cas9/sgRNA complexes and delivered the complexes to the nuclei of human cells, thus enabling targeted gene disruption while maintaining cell viability. Editing was most efficient when the DNA nanoclew sequence and the sgRNA guide sequence were partially complementary, offering a design rule for enhancing delivery. Overall, this strategy provides a versatile method that could be adapted for delivering other DNA-binding proteins or functional nucleic acids.