Vault nanoparticles engineered with the protein transduction domain, TAT48, enhances cellular uptake

Escherichia coli as a New Platform for the Fast Production of Vault-like Nanoparticles: An Optimized Protocol

Vaults are protein nanoparticles that are found in almost all eukaryotic cells but are absent in prokaryotic ones. Due to their properties (nanometric size, biodegradability, biocompatibility, and lack of immunogenicity), vaults show enormous potential as a bio-inspired, self-assembled drug-delivery system (DDS). Vault architecture is directed by self-assembly of the "major vault protein" (MVP), the main component of this nanoparticle. Recombinant expression (in different eukaryotic systems) of the MVP resulted in the formation of nanoparticles that were indistinguishable from native vaults. Nowadays, recombinant vaults for different applications are routinely produced in insect cells and purified by successive ultracentrifugations, which are both tedious and time-consuming strategies. To offer cost-efficient and faster protocols for nanoparticle production, we propose the production of vault-like nanoparticles in Escherichia coli cells, which are still one of the most widely used prokaryotic cell factories for recombinant protein production. The strategy proposed allowed for the spontaneous encapsulation of the engineered cargo protein within the self-assembled vault-like nanoparticles by simply mixing the clarified lysates of the producing cells. Combined with well-established affinity chromatography purification methods, our approach contains faster, cost-efficient procedures for biofabrication in a well-known microbial cell factory and the purification of "ready-to-use" loaded protein nanoparticles, thereby opening the way to faster and easier engineering and production of vault-based DDSs.

All-in-one biofabrication and loading of recombinant vaults in human cells

One of the most promising approaches in the drug delivery field is the use of naturally occurring self-assembling protein nanoparticles, such as virus-like particles, bacterial microcompartments or vault ribonucleoprotein particles as drug delivery systems (DDS). Among them, eukaryotic vaults show a promising future due to their structural features, in vitro stability and non-immunogenicity. Recombinant vaults are routinely produced in insect cells and purified through several ultracentrifugations, both tedious and time-consuming processes. As an alternative, this work proposes a new approach and protocols for the production of recombinant vaults in human cells by transient gene expression of a His-tagged version of the Major Vault Protein (MVP-H6), the development of new affinity-based purification processes for such recombinant vaults, and the all-in-one biofabrication and encapsulation of a cargo recombinant protein within such vaults by their co-expression in human cells. Protocols proposed here allow the easy and straightforward biofabrication and purification of engineered vaults loaded with virtually any INT-tagged cargo protein, in very short times, paving the way to faster and easier engineering and production of better and more efficient DDS.

The Vault Nanoparticle: A Gigantic Ribonucleoprotein Assembly Involved in Diverse Physiological and Pathological Phenomena and an Ideal Nanovector for Drug Delivery and Therapy

Simple Summary

In recent decades, a molecular complex referred to as vault nanoparticle has attracted much attention by the scientific community, due to its unique properties. At the molecular scale, it is a huge assembly consisting of 78 97-kDa polypeptide chains enclosing an internal cavity, wherein enzymes involved in DNA integrity maintenance and some small noncoding RNAs are accommodated. Basically, two reasons justify this interest. On the one hand, this complex represents an ideal tool for the targeted delivery of drugs, provided it is suitably engineered, either chemically or genetically; on the other hand, it has been shown to be involved in several cellular pathways and mechanisms that most often result in multidrug resistance. It is therefore expected that a better understanding of the physiological roles of this ribonucleoproteic complex may help develop new therapeutic strategies capable of coping with cancer progression. Here, we provide a comprehensive review of the current knowledge.

Abstract

The vault nanoparticle is a eukaryotic ribonucleoprotein complex consisting of 78 individual 97 kDa-“major vault protein” (MVP) molecules that form two symmetrical, cup-shaped, hollow halves. It has a huge size (72.5 × 41 × 41 nm) and an internal cavity, wherein the vault poly(ADP-ribose) polymerase (vPARP), telomerase-associated protein-1 (TEP1), and some small untranslated RNAs are accommodated. Plenty of literature reports on the biological role(s) of this nanocomplex, as well as its involvement in diseases, mostly oncological ones. Nevertheless, much has still to be understood as to how vault participates in normal and pathological mechanisms. In this comprehensive review, current understanding of its biological roles is discussed. By different mechanisms, vault’s individual components are involved in major cellular phenomena, which result in protection against cellular stresses, such as DNA-damaging agents, irradiation, hypoxia, hyperosmotic, and oxidative conditions. These diverse cellular functions are accomplished by different mechanisms, mainly gene expression reprogramming, activation of proliferative/prosurvival signaling pathways, export from the nucleus of DNA-damaging drugs, and import of specific proteins. The cellular functions of this nanocomplex may also result in the onset of pathological conditions, mainly (but not exclusively) tumor proliferation and multidrug resistance. The current understanding of its biological roles in physiological and pathological processes should also provide new hints to extend the scope of its exploitation as a nanocarrier for drug delivery.

Vault packaged enzyme mediated degradation of amino-aromatic energetic compounds

Amino-aromatic compounds, 2-amino-4-nitrotoluene (ANT), and 2,4-diaminotoluene (DAT) are carcinogens and environmentally persistent pollutants. In this study, we investigated their degradation by natural manganese peroxidase (nMnP) derived from Phanerochaete chrysosporium and recombinant manganese peroxidase packaged in vaults (vMnP). Encapsulation of manganese peroxidase (MnP) in ribonucleoprotein nanoparticle cages, called vaults, was achieved by creating recombinant vaults in yeast Pichia pastoris. Vault packaging increased the stability of MnP by locally sequestering multiple copies of the enzyme. Within 96  h, both vMnP and nMnP catalyzed over 72% removal of ANT in-vitro, which indicates that vault packaging did not limit substrate diffusion. It was observed that vMnP was more efficient than nMnP and P. chrysosporium for the catalysis of target contaminants. Only 57% of ANT was degraded by P. chrysosporium even when MnP activity reached about 480 U L^-1 in cultures. At 1.5 U L^-1 initial activity, vMnP achieved 38% of ANT and 51% of DAT degradation, whereas even 2.7 times higher activity of nMnP showed insignificant biodegradation of both compounds. These results imply that due to protection by vault cages, vMnP has lower inactivation rates. Thus, it works effectively at lower dosage for a longer duration compared to nMnP without requiring frequent replenishment. Collectively, these results indicate that fungal enzymes packaged in vault nanoparticles are more stable and active, and they would be effective in biodegradation of energetic compounds in industrial processes, waste treatment, and contaminated environments.

Latest Advances in the Development of Eukaryotic Vaults as Targeted Drug Delivery Systems

The use of smart drug delivery systems (DDSs) is one of the most promising approaches to overcome some of the drawbacks of drug-based therapies, such as improper biodistribution and lack of specific targeting. Some of the most attractive candidates as DDSs are naturally occurring, self-assembling protein nanoparticles, such as viruses, virus-like particles, ferritin cages, bacterial microcompartments, or eukaryotic vaults. Vaults are large ribonucleoprotein nanoparticles present in almost all eukaryotic cells. Expression in different cell factories of recombinant versions of the "major vault protein" (MVP) results in the production of recombinant vaults indistinguishable from native counterparts. Such recombinant vaults can encapsulate virtually any cargo protein, and they can be specifically targeted by engineering the C-terminus of MVP monomer. These properties, together with nanometric size, a lumen large enough to accommodate cargo molecules, biodegradability, biocompatibility and no immunogenicity, has raised the interest in vaults as smart DDSs. In this work we provide an overview of eukaryotic vaults as a new, self-assembling protein-based DDS, focusing in the latest advances in the production and purification of this platform, its application in nanomedicine, and the current preclinical and clinical assays going on based on this nanovehicle.

A fast and straightforward procedure for vault nanoparticle purification and the characterization of its endocytic uptake

BACKGROUND

Vaults are eukaryotic ribonucleoprotein particles composed of up 78 copies of the 97 kDa major vault protein that assembles into a barrel-like, "nanocapsule" enclosing poly(ADP-ribose) polymerase, telomerase-associated protein-1 and small untranslated RNAs. Overall, the molecular mass of vault particles amounts to about 13 MDa. Although it has been implicated in several cellular functions, its physiological roles remain poorly understood. Also, the possibility to exploit it as a nanovector for drug delivery is currently being explored in several laboratories.

METHODS

Using the baculovirus expression system, vaults were expressed and purified by a dialysis step using a 1 MDa molecular weight cutoff membrane and a subsequent size exclusion chromatography. Purity was assessed by SDS-PAGE, transmission electron microscopy and dynamic light scattering. Particle's endocytic uptake was monitored by flow cytometry and confocal microscopy.

RESULTS

The purification protocol here reported is far simpler and faster than those currently available and lead to the production of authentic vault. We then demonstrated its clathrin-mediated endocytic uptake by normal fibroblast and glioblastoma, but not carcinoma cell lines. In contrast, no significant caveolin-mediated endocytosis was detected.

CONCLUSIONS

These results provide the first evidence for an intrinsic propensity of the vault complex to undergo endocytic uptake cultured eukaryotic cells.

GENERAL SIGNIFICANCE

The newly developed purification procedure will greatly facilitate any investigation based on the use of the vault particle as a natural nanocarrier. Its clathrin-mediated endocytic uptake observed in normal and in some tumor cell lines sheds light on its physiological role.

Vault Nanoparticles: Chemical Modifications for Imaging and Enhanced Delivery

Vault nanoparticles represent promising vehicles for drug and probe delivery. Innately found within human cells, vaults are stable, biocompatible nanocapsules possessing an internal volume that can encapsulate hundreds to thousands of molecules. They can also be targeted. Unlike most nanoparticles, vaults are nonimmunogenic and monodispersed and can be rapidly produced in insect cells. Efforts to create vaults with modified properties have been, to date, almost entirely limited to recombinant bioengineering approaches. Here we report a systematic chemical study of covalent vault modifications, directed at tuning vault properties for research and clinical applications, such as imaging, targeted delivery, and enhanced cellular uptake. As supra-macromolecular structures, vaults contain thousands of derivatizable amino acid side chains. This study is focused on establishing the comparative selectivity and efficiency of chemically modifying vault lysine and cysteine residues, using Michael additions, nucleophilic substitutions, and disulfide exchange reactions. We also report a strategy that converts the more abundant vault lysine residues to readily functionalizable thiol terminated side chains through treatment with 2-iminothiolane (Traut's reagent). These studies provide a method to doubly modify vaults with cell penetrating peptides and imaging agents, allowing for in vitro studies on their enhanced uptake into cells.

Protein nanoparticles for therapeutic protein delivery

This review describes nanoparticles made from protein by self-assembly or desolvation as carriers for the delivery of therapeutic proteins.

Fifteen years of cell-penetrating, guanidinium-rich molecular transporters: basic science, research tools, and clinical applications

All living systems require biochemical barriers. As a consequence, all drugs, imaging agents, and probes have targets that are either on, in, or inside of these barriers. Fifteen years ago, we initiated research directed at more fully understanding these barriers and at developing tools and strategies for breaching them that could be of use in basic research, imaging, diagnostics, and medicine. At the outset of this research and now to a lesser extent, the "rules" for drug design biased the selection of drug candidates mainly to those with an intermediate and narrow log P. At the same time, it was becoming increasingly apparent that Nature had long ago developed clever strategies to circumvent these "rules." In 1988, for example, independent reports documented the otherwise uncommon passage of a protein (HIV-Tat) across a membrane. A subsequent study implicated a highly basic domain in this protein (Tat49-57) in its cellular entry. This conspicuously contradictory behavior of a polar, highly charged peptide passing through a nonpolar membrane set the stage for learning how Nature had gotten around the current "rules" of transport. As elaborated in our studies and discussed in this Account, the key strategy used in Nature rests in part on the ability of a molecule to change its properties as a function of microenvironment; such molecules need to be polarity chameleons, polar in a polar milieu and relatively nonpolar in a nonpolar environment. Because this research originated in part with the protein Tat and its basic peptide domain, Tat49-57, the field focused heavily on peptides, even limiting its nomenclature to names such as "cell-penetrating peptides," "cell-permeating peptides," "protein transduction domains," and "membrane translocating peptides." Starting in 1997, through a systematic reverse engineering approach, we established that the ability of Tat49-57 to enter cells is not a function of its peptide backbone, but rather a function of the number and spatial array of its guanidinium groups. These function-oriented studies enabled us and others to design more effective peptidic agents and to think beyond the confines of peptidic systems to new and even more effective nonpeptidic agents. Because the function of passage across a cell membrane is not limited to or even best achieved with the peptide backbone, we referred to these agents by their shared function, "cell-penetrating molecular transporters." The scope of this molecular approach to breaching biochemical barriers has expanded remarkably in the past 15 years: enabling or enhancing the delivery of a wide range of cargos into cells and across other biochemical barriers, creating new tools for research, imaging, and diagnostics, and introducing new therapies into clinical trials.

Development of the vault particle as a platform technology

Vaults are naturally occurring nanoparticles found widely in eukaryotes. The particles can be produced in large quantities and are assembled in situ from multiple copies of the single structural protein following expression. Using molecular engineering, recombinant vaults can be functionally modified and targeted, and their contents can be controlled by packaging. Here, we review the development of engineered vaults as a platform for a wide variety of therapeutic applications and we examine future directions for this unique nanoparticle system.