The molecular weight of Artemia ribosomes, as determined from their refractive-index increment and light-scattering intensity

SEC coupled with in-line multiple detectors for the characterization of an oncolytic Coxsackievirus

V937 is an oncolytic virus immunotherapy clinical drug candidate consisting of a proprietary formulation of Coxsackievirus A21 (CVA21). V937 specifically binds to and lyses cells with over-expressed ICAM-1 receptors in a range of tumor cell types and is currently in phase I and II clinical trials. Infectious V937 particles consist of a ∼30 nm icosahedral capsid assembled from four structural viral proteins that encapsidate a viral RNA genome. Rapid and robust analytical methods to quantify and characterize CVA21 virus particles are important to support the process development, regulatory requirements, and validation of new manufacturing platforms. Herein, we describe a size-exclusion chromatography (SEC) method that was developed to characterize the V937 drug substance and process intermediates. Using a 4-in-1 combination of multi-detectors (UV, refractive index, dynamic and static light scattering), we demonstrate the use of SEC for the quantification of the virus particle count, the determination of virus size (molecular weight and hydrodynamic diameter), and the characterization of virus purity by assessing empty-to-full capsid ratios. Through a SEC analysis of stressed V937 samples, we propose CVA21 thermal degradation pathways that result in genome release and particle aggregation.

Supported Fluid Lipid Bilayer as a Scaffold to Direct Assembly of RNA Nanostructures

RNA architectonics offers the possibility to design and assemble RNA into specific shapes, such as nanoscale 3D solids or nanogrids. Combining the minute size of these programmable shapes with precise positioning on a surface further enhances their potential as building blocks in nanotechnology and nanomedicine. Here we describe a bottom-up approach to direct the arrangement of nucleic acid nanostructures by using a supported fluid lipid bilayer as a surface scaffold. The strong attractive electrostatic interactions between RNA polyanions and cationic lipids promote RNA adsorption and self-assembly. Protocol steps for the characterization of assembled RNA complexes via several complementary methods (QCM-D, ellipsometry, confocal fluorescence microscopy, AFM) are also provided. Due to their tunable nature, lipid bilayers can be used to organize RNA laterally on the micrometer scale and thus facilitate the building of more complex 3D structures. The bilayer-based approach can be extended to other programmable RNA or DNA objects to construct intricate structures, such as 2D grids or 3D cages, with high precision.

Methods for the physical characterization and quantification of extracellular vesicles in biological samples

BACKGROUND

Our body fluids contain a multitude of cell-derived vesicles, secreted by most cell types, commonly referred to as extracellular vesicles. They have attracted considerable attention for their function as intercellular communication vehicles in a broad range of physiological processes and pathological conditions. Extracellular vesicles and especially the smallest type, exosomes, have also generated a lot of excitement in view of their potential as disease biomarkers or as carriers for drug delivery. In this context, state-of-the-art techniques capable of comprehensively characterizing vesicles in biological fluids are urgently needed.

SCOPE OF REVIEW

This review presents the arsenal of techniques available for quantification and characterization of physical properties of extracellular vesicles, summarizes their working principles, discusses their advantages and limitations and further illustrates their implementation in extracellular vesicle research.

MAJOR CONCLUSIONS

The small size and physicochemical heterogeneity of extracellular vesicles make their physical characterization and quantification an extremely challenging task. Currently, structure, size, buoyant density, optical properties and zeta potential have most commonly been studied. The concentration of vesicles in suspension can be expressed in terms of biomolecular or particle content depending on the method at hand. In addition, common quantification methods may either provide a direct quantitative measurement of vesicle concentration or solely allow for relative comparison between samples.

GENERAL SIGNIFICANCE

The combination of complementary methods capable of detecting, characterizing and quantifying extracellular vesicles at a single particle level promises to provide new exciting insights into their modes of action and to reveal the existence of vesicle subpopulations fulfilling key biological tasks.

Assembly of RNA nanostructures on supported lipid bilayers

The assembly of nucleic acid nanostructures with controlled size and shape has large impact in the fields of nanotechnology, nanomedicine and synthetic biology. The directed arrangement of nano-structures at interfaces is important for many applications. In spite of this, the use of laterally mobile lipid bilayers to control RNA three-dimensional nanostructure formation on surfaces remains largely unexplored. Here, we direct the self-assembly of RNA building blocks into three-dimensional structures of RNA on fluid lipid bilayers composed of cationic 1,2-dioleoyl-3-trimethylammonium-propane (DOTAP) or mixtures of zwitterionic 1,2-dioleoyl-sn-glycero-3-phosphatidylcholine (DOPC) and cationic sphingosine. We demonstrate the stepwise supramolecular assembly of discrete building blocks through specific and selective RNA-RNA interactions, based on results from quartz crystal microbalance with dissipation (QCM-D), ellipsometry, fluorescence recovery after photobleaching (FRAP) and total internal reflection fluorescence microscopy (TIRF) experiments. The assembly can be controlled to give a densely packed single layer of RNA polyhedrons at the fluid lipid bilayer surface. We show that assembly of the 3D structure can be modulated by sequence specific interactions, surface charge and changes in the salt composition and concentration. In addition, the tertiary structure of the RNA polyhedron can be controllably switched from an extended structure to one that is dense and compact. The versatile approach to building up three-dimensional structures of RNA does not require modification of the surface or the RNA molecules, and can be used as a bottom-up means of nanofabrication of functionalized bio-mimicking surfaces.

Determination of exosome concentration in solution using surface plasmon resonance spectroscopy

Exosomes are cell-secreted nanometer-sized extracellular vesicles that have been reported to play an important role in intercellular communication. They are also considered potential diagnostic markers for various health disorders, and intense investigations are presently directed toward their use as carriers in drug-delivery and gene-therapy applications. This has generated a growing need for sensitive methods capable of accurately and specifically determining the concentration of exosomes in complex biological fluids. Here, we explore the use of label-free surface-based sensing with surface plasmon resonance (SPR) read-out to determine the concentration of exosomes in solution. Human mast cell secreted exosomes carrying the tetraspanin membrane protein CD63 were analyzed by measuring their diffusion-limited binding rate to an SPR sensor surface functionalized with anti-CD63 antibodies. The concentration of suspended exosomes was determined by first converting the SPR response into the surface-bound mass. The increase in mass uptake over time was then related to the exosome concentration in solution using a formalism describing diffusion-limited binding under controlled flow conditions. The proposed quantification method is based on a calibration and control measurements performed with proteins and synthetic lipid vesicles and takes into account (i) the influence of the broad size distribution of the exosomes on the surface coverage, (ii) the fact that their size is comparable to the ∼150 nm probing depth of SPR, and (iii) possible deformation of exosomes upon adsorption. Under those considerations, the accuracy of the concentration determination was estimated to be better than ±50% and significantly improve if the exosome deformation is negligible.