In vivo characterization of the biodistribution profile of amphipol A8-35

Full-length G glycoprotein directly extracted from rabies virus with detergent and then stabilized by amphipols in liquid and freeze-dried forms

Pathogen surface antigens are at the forefront of the viral strategy when invading host organisms. These antigens, including membrane proteins (MPs), are broadly targeted by the host immune response. Obtaining these MPs in a soluble and stable form constitutes a real challenge, regardless of the application purposes (e.g. quantification/characterization assays, diagnosis, and preventive and curative strategies). A rapid process to obtain a native-like antigen by solubilization of a full-length MP directly from a pathogen is reported herein. Rabies virus (RABV) was used as a model for this demonstration and its full-length G glycoprotein (RABV-G) was stabilized with amphipathic polymers, named amphipols (APols). The stability of RABV-G trapped in APol A8-35 (RABV-G/A8-35) was evaluated under different stress conditions (temperature, agitation, and light exposure). RABV-G/A8-35 in liquid form exhibited higher unfolding temperature (+6°C) than in detergent and was demonstrated to be antigenically stable over 1 month at 5°C and 25°C. Kinetic modeling of antigenicity data predicted antigenic stability of RABV-G/A8-35 in a solution of up to 1 year at 5°C. The RABV-G/A8-35 complex formulated in an optimized buffer composition and subsequently freeze-dried displayed long-term stability for 2-years at 5, 25, and 37°C. This study reports for the first time that a natural full-length MP extracted from a virus, complexed to APols and subsequently freeze-dried, displayed long-term antigenic stability, without requiring storage under refrigerated conditions.

Recombinant SARS-CoV-2 envelope protein traffics to the trans-Golgi network following amphipol-mediated delivery into human cells

The severe acute respiratory syndrome coronavirus 2 envelope protein (S2-E) is a conserved membrane protein that is important for coronavirus (CoV) assembly and budding. Here, we describe the recombinant expression and purification of S2-E in amphipol-class amphipathic polymer solutions, which solubilize and stabilize membrane proteins, but do not disrupt membranes. We found that amphipol delivery of S2-E to preformed planar bilayers results in spontaneous membrane integration and formation of viroporin cation channels. Amphipol delivery of the S2-E protein to human cells results in plasma membrane integration, followed by retrograde trafficking to the trans-Golgi network and accumulation in swollen perinuclear lysosomal-associated membrane protein 1-positive vesicles, likely lysosomes. CoV envelope proteins have previously been proposed to manipulate the luminal pH of the trans-Golgi network, which serves as an accumulation station for progeny CoV particles prior to cellular egress via lysosomes. Delivery of S2-E to cells will enable chemical biological approaches for future studies of severe acute respiratory syndrome coronavirus 2 pathogenesis and possibly even development of "Trojan horse" antiviral therapies. Finally, this work also establishes a paradigm for amphipol-mediated delivery of membrane proteins to cells.

Delivery of recombinant SARS-CoV-2 envelope protein into human cells

SARS-CoV-2 envelope protein (S2-E) is a conserved membrane protein that is essential to coronavirus assembly and budding. Here, we describe the recombinant expression and purification of S2-E into amphipol-class amphipathic polymer solutions. The physical properties of amphipols underpin their ability to solubilize and stabilize membrane proteins without disrupting membranes. Amphipol delivery of S2-E to pre-formed planar bilayers results in spontaneous membrane integration and formation of viroporin ion channels. Amphipol delivery of the S2-E protein to human cells results in membrane integration followed by retrograde trafficking to a location adjacent to the endoplasmic reticulum-to-Golgi intermediate compartment (ERGIC) and the Golgi, which are the sites of coronavirus replication. Delivery of S2-E to cells enables both chemical biological approaches for future studies of SARS-CoV-2 pathogenesis and development of "Trojan Horse" anti-viral therapies. This work also establishes a paradigm for amphipol-mediated delivery of membrane proteins to cells.

Covalently Labeled Fluorescent Exosomes for In Vitro and In Vivo Applications

The vertiginous increase in the use of extracellular vesicles and especially exosomes for therapeutic applications highlights the necessity of advanced techniques for gaining a deeper knowledge of their pharmacological properties. Herein, we report a novel chemical approach for the robust attachment of commercial fluorescent dyes to the exosome surface with covalent binding. The applicability of the methodology was tested on milk and cancer cell-derived exosomes (from U87 and B16F10 cancer cells). We demonstrated that fluorescent labeling did not modify the original physicochemical properties of exosomes. We tested this nanoprobe in cell cultures and healthy mice to validate its use for in vitro and in vivo applications. We confirmed that these fluorescently labeled exosomes could be successfully visualized with optical imaging.

Folding and stabilizing membrane proteins in amphipol A8-35

Membrane proteins (MPs) are important pharmacological targets because of their involvement in many essential cellular processes whose dysfunction can lead to a large variety of diseases. A detailed knowledge of the structure of MPs and the molecular mechanisms of their activity is essential to the design of new therapeutic agents. However, studying MPs in vitro is challenging, because it generally implies their overexpression under a functional form, followed by their extraction from membranes and purification. Targeting an overexpressed MP to a membrane is often toxic and expression yields tend to be limited. One alternative is the formation of inclusion bodies (IBs) in the cytosol of the cell, from which MPs need then to be folded to their native conformation before structural and functional analysis can be contemplated. Folding MPs targeted to IBs is a difficult task. Specially designed amphipathic polymers called 'amphipols' (APols), which have been initially developed with the view of improving the stability of MPs in aqueous solutions compared to detergents, can be used to fold both α-helical and β-barrel MPs. APols represent an interesting novel amphipathic medium, in which high folding yields can be achieved. In this review, the properties of APol A8-35 and of the complexes they form with MPs are summarized. An overview of the most important studies reported so far using A8-35 to fold MPs is presented. Finally, from a practical point of view, a detailed description of the folding and trapping methods is given.

In vivo studies investigating biodistribution of nanoparticle-encapsulated rhodamine B delivered via dissolving microneedles

Nanoparticles (NPs) have undergone extensive investigation as drug delivery and targeting vehicles. NP delivery is often via the parenteral route, reliant on administration using hypodermic needles, which can be associated with patient compliance issues and safety concerns. In the recent past, the intradermal delivery of NPs, via novel dissolving microneedle (MN) arrays has garnered interest in the pharmaceutical community. However, published studies using this combinatorial approach have been limited, in that they have focussed on the use of in vitro and ex vivo models only. The current study was designed to answer the fundamental question of how such NPs are distributed in an in vivo murine model, following MN-mediated delivery. Rhodamine B (RhB) was employed as a model tracer dye to facilitate study of biodistribution. Following MN application, RhB was detected in the livers, kidneys, spleens and superficial parotid lymph nodes of the mice. Uptake into the lymphatics was of particular note, as it points towards the potential for utilisation of a minimally-invasive MN delivery strategy in controlled targeting of active drug substances and vaccines to the lymphatics. The use of such a delivery system could, following further development, have far-reaching benefits in enhancement of immunomodulatory and anti-cancer therapies. As a consequence, further investigation of MN/NP combinatorial delivery strategies is warranted.

Labeling and functionalizing amphipols for biological applications

Amphipols (APols) are short amphipathic polymers developed as an alternative to detergents for handling membrane proteins (MPs) in aqueous solution. MPs are, as a rule, much more stable following trapping with APols than they are in detergent solutions. The best-characterized APol to date, called A8-35, is a mixture of short-chain sodium polyacrylates randomly derivatized with octylamine and isopropylamine. Its solution properties have been studied in detail, and it has been used extensively for biochemical and biophysical studies of MPs. One of the attractive characteristics of APols is that it is relatively easy to label them, isotopically or otherwise, without affecting their physical-chemical properties. Furthermore, several variously modified APols can be mixed, achieving multiple functionalization of MP/APol complexes in the easiest possible manner. Labeled or tagged APols are being used to study the solution properties of APols, their miscibility, their biodistribution upon injection into living organisms, their association with MPs and the composition, structure and dynamics of MP/APol complexes, examining the exchange of surfactants at the surface of MPs, labeling MPs to follow their distribution in fractionation experiments or to immobilize them, increasing the contrast between APols and solvent or MPs in biophysical experiments, improving NMR spectra, etc. Labeling or functionalization of APols can take various courses, each of which has its specific constraints and advantages regarding both synthesis and purification. The present review offers an overview of the various derivatives of A8-35 and its congeners that have been developed in our laboratory and discusses the pros and cons of various synthetic routes.

Amphipols for each season

Amphipols (APols) are short amphipathic polymers that can substitute for detergents at the transmembrane surface of membrane proteins (MPs) and, thereby, keep them soluble in detergent free aqueous solutions. APol-trapped MPs are, as a rule, more stable biochemically than their detergent-solubilized counterparts. APols have proven useful to produce MPs, most noticeably by assisting their folding from the denatured state obtained after solubilizing MP inclusion bodies in either SDS or urea. They facilitate the handling in aqueous solution of fragile MPs for the purpose of proteomics, structural and functional studies, and therapeutics. Because APols can be chemically labeled or functionalized, and they form very stable complexes with MPs, they can also be used to functionalize those indirectly, which opens onto many novel applications. Following a brief recall of the properties of APols and MP/APol complexes, an update is provided of recent progress in these various fields.

Synthesis of an oligonucleotide-derivatized amphipol and its use to trap and immobilize membrane proteins

Amphipols (APols) are specially designed amphipathic polymers that stabilize membrane proteins (MPs) in aqueous solutions in the absence of detergent. A8-35, a polyacrylate-based APol, has been grafted with an oligodeoxynucleotide (ODN). The synthesis, purification and properties of the resulting 'OligAPol' have been investigated. Grafting was performed by reacting an ODN carrying an amine-terminated arm with the carboxylates of A8-35. The use of OligAPol for trapping MPs and immobilizing them onto solid supports was tested using bacteriorhodopsin (BR) and the transmembrane domain of Escherichia coli outer membrane protein A (tOmpA) as model proteins. BR and OligAPol form water-soluble complexes in which BR remains in its native conformation. Hybridization of the ODN arm with a complementary ODN was not hindered by the assembly of OligAPol into particles, nor by its association with BR. BR/OligAPol and tOmpA/OligAPol complexes could be immobilized onto either magnetic beads or gold nanoparticles grafted with the complementary ODN, as shown by spectroscopic measurements, fluorescence microscopy and the binding of anti-BR and anti-tOmpA antibodies. OligAPols provide a novel, highly versatile approach to tagging MPs, without modifying them chemically nor genetically, for specific, reversible and targetable immobilization, e.g. for nanoscale applications.

Synthesis, characterization and applications of a perdeuterated amphipol

Amphipols are short amphipathic polymers that can substitute for detergents at the hydrophobic surface of membrane proteins (MPs), keeping them soluble in the absence of detergents while stabilizing them. The most widely used amphipol, known as A8-35, is comprised of a polyacrylic acid (PAA) main chain grafted with octylamine and isopropylamine. Among its many applications, A8-35 has proven particularly useful for solution-state NMR studies of MPs, for which it can be desirable to eliminate signals originating from the protons of the surfactant. In the present work, we describe the synthesis and properties of perdeuterated A8-35 (perDAPol). Perdeuterated PAA was obtained by radical polymerization of deuterated acrylic acid. It was subsequently grafted with deuterated amines, yielding perDAPol. The number-average molar mass of hydrogenated and perDAPol, ~4 and ~5 kDa, respectively, was deduced from that of their PAA precursors, determined by size exclusion chromatography in tetrahydrofuran following permethylation. Electrospray ionization-ion mobility spectrometry-mass spectrometry measurements show the molar mass and distribution of the two APols to be very similar. Upon neutron scattering, the contrast match point of perDAPol is found to be ~120% D2O. In (1)H-(1)H nuclear overhauser effect NMR spectra, its contribution is reduced to ~6% of that of hydrogenated A8-35, making it suitable for extended uses in NMR spectroscopy. PerDAPol ought to also be of use for inelastic neutron scattering studies of the dynamics of APol-trapped MPs, as well as small-angle neutron scattering and analytical ultracentrifugation.