Thin multilayer films and microcapsules containing DNA quadruplex motifs

Template-Mediated Assembly of DNA into Microcapsules for Immunological Modulation

There is a need for effective vaccine delivery systems and vaccine adjuvants without extraneous excipients that can compromise or minimize their efficacy. Vaccine adjuvants cytosine-phosphate-guanosine oligodeoxynucleotides (CpG ODNs) can effectively activate immune responses to secrete cytokines. However, CpG ODNs are not stable in serum due to enzymatic cleavage and are difficult to transport through cell membranes. Herein, DNA microcapsules made of CpG ODNs arranged into 3D nanostructures are developed to improve the serum stability and immunostimulatory effect of CpG. The DNA microcapsules allow encapsulation and co-delivery of cargoes, including glycogen. The DNA capsules, with >4 million copies of CpG motifs per capsule, are internalized in cells and accumulate in endosomes, where the Toll-like receptor 9 is engaged by CpG. The capsules induce up to 10-fold and 20-fold increases in tumor necrosis factor (TNF)-α and interleukin (IL)-6 secretion, respectively, in RAW264.7 cells compared with CpG ODNs. Furthermore, the microcapsules stimulate TNF-α and IL-6 secretion in a concentration- and time-dependent manner. The immunostimulatory activity of the capsules correlates to their intracellular trafficking, endosomal confinement, and degradation, assessed by confocal and super-resolution microscopy. These DNA capsules can serve as both adjuvants to stimulate an immune reaction and vehicles to encapsulate vaccine peptides/genes to achieve synergistic immune effects.

Reversible reconfiguration of high-order DNA nanostructures by employing G-quartet toeholds as adhesive units

G-quadruplex structures are becoming useful alternative interaction modules for the assembly of DNA nanomaterials because of their unique inducibility by cations. In this study, we demonstrated a new strategy for the assembly of polymeric DNA nanoarchitectures in the presence of cations, such as K⁺ and Na⁺, by employing G-quartet toeholds at the edges of discrete mini-square DNA building blocks as adhesive units. In comparison with the Watson-Crick base-paired duplex linkers, G-quadruplex arrays embedded in the self-assembled DNA system exhibit higher thermal stability. The morphology of these doughnut-shaped or spherical-shaped DNA nanostructures is highly regulated by the orientation of the folded G-quadruplexes either in parallel or antiparallel orientation in response to different cations. Furthermore, this G-quadruplex-mediated assembly strategy is able to manipulate the cycling of DNA assemblies between discrete and polymeric states by means of introducing cations and chelating agents sequentially. This property enables the reversible manipulation of the DNA-based nanosystems for at least 4 cycles. The G-quadruplex array embedded in this self-assembled DNA system can become a scaffold for functional molecules, as a number of organic molecules and proteins exhibit specific binding to these G-quadruplex structures. Besides, embedded G-quadruplexes are also considered as functional components of nanoscale electronic materials due to their electron transport through the stacked orientation of the G-quartet. Therefore, this work is an important step towards obtaining reversible, responsive G-quadruplex-induced DNA-based nanomaterials with versatile functionalities which will be highly useful in further electronic, biomedical and drug-delivery applications.

Design of polyelectrolyte core-shells with DNA to control TMPyP binding

The interaction of DNA with 5,10,15,20-tetrakis(4-N-methylpyridiniumyl)porphyrin (TMPyP) in polyelectrolyte core-shells obtained via layer by layer adsorption of poly(sodium 4-styrenesulfonate), PSS, and poly(allylamine hydrochloride), PAH, polyelectrolytes was followed by steady state, time resolved fluorescence and by Fluorescence Lifetime Imaging Microscopy (FLIM). Our results show that DNA adsorption onto polyelectrolyte core-shell changes the TMPyP interaction within PSS/PAH core-shells structure and increase significantly the TMPyP uptake. Specific DNA/TMPyP interactions are also altered by DNA adsorption favouring porphyrin intercalation onto GC pair rich regions. Circular dichroism (CD) spectra reveal that DNA undergoes important conformational changes upon adsorption onto the core-shell surface, which are reverted upon TMPyP encapsulation.

DNA switches: from principles to applications

The base sequence of nucleic acid encodes structural and functional properties into the biopolymer. Structural information includes the formation of duplexes, G-quadruplexes, i-motif, and cooperatively stabilized assemblies. Functional information encoded in the base sequence involves the strand-displacement process, the recognition properties by aptamers, and the catalytic functions of DNAzymes. This Review addresses the implementation of the information encoded in nucleic acids to develop DNA switches. A DNA switch is a supramolecular nucleic acid assembly that undergoes cyclic, switchable, transitions between two distinct states in the presence of appropriate triggers and counter triggers, such as pH value, metal ions/ligands, photonic and electrical stimuli. Applications of switchable DNA systems to tailor switchable DNA hydrogels, for the controlled drug-release and for the activation of switchable enzyme cascades, are described, and future perspectives of the systems are addressed.

Formation of G-quadruplexes in poly-G sequences: structure of a propeller-type parallel-stranded G-quadruplex formed by a G₁₅ stretch

Poly-G sequences are found in different genomes including human and have the potential to form higher-order structures with various applications. Previously, long poly-G sequences were thought to lead to multiple possible ways of G-quadruplex folding, rendering their structural characterization challenging. Here we investigate the structure of G-quadruplexes formed by poly-G sequences d(TTG(n)T), where n = 12 to 19. Our data show the presence of multiple and/or higher-order G-quadruplex structures in most sequences. Strikingly, NMR spectra of the TTG₁₅T sequence containing a stretch of 15 continuous guanines are exceptionally well-resolved and indicate the formation of a well-defined G-quadruplex structure. The NMR solution structure of this sequence revealed a propeller-type parallel-stranded G-quadruplex containing three G-tetrad layers and three single-guanine propeller loops. The same structure can potentially form anywhere along a long G(n) stretch, making it unique for molecular recognition by other cellular molecules.

Emerging methods for the fabrication of polymer capsules

Hollow polymer capsules are attracting increasing research interest due to their potential application as drug delivery vectors, sensors, biomimetic nano- or multi-compartment reactors and catalysts. Thus, significant effort has been directed toward tuning their size, composition, morphology, and functionality to further their application. In this review, we provide an overview of emerging techniques for the fabrication of polymer capsules, encompassing: self-assembly, layer-by-layer assembly, single-step polymer adsorption, bio-inspired assembly, surface polymerization, and ultrasound assembly. These techniques can be applied to prepare polymer capsules with diverse functionality and physicochemical properties, which may fulfill specific requirements in various areas. In addition, we critically evaluate the challenges associated with the application of polymer capsules in drug delivery systems.