Robust Polyion Complex Vesicles (PICsomes) under Physiological Conditions Reinforced by Multiple Hydrogen Bond Formation Derived by Guanidinium Groups

Effective design of PEGylated polyion complex (PIC) nanoparticles for enhancing PIC internalisation in cells utilising block copolymer combinations with mismatched ionic chain lengths

In nanomedicine, PEGylation of nanomaterials poses a dilemma since it inhibits their interaction with target cells and enables their retention in target tissues despite its biocompatibility and nonspecific internalisation suppression. PEGylated polypeptide-based polyion complexes (PICs) are fabricated via the self-assembly of PEGylated aniomers and homocatiomers based on electrostatic interactions. We propose that various parameters like block copolymer design and PIC domain characteristics can enhance the cell-PEGylated PIC interactions. Remarkably, the properties of the PIC domain were tuned by the matched/mismatched ionomer chain lengths, PIC domain crosslinking degree, chemical modification of cationic species after crosslinking, PIC morphologies (vesicles/micelles) and polyethylene glycol (PEG) chain lengths. Cellular internalisation of the prepared PICs was evaluated using HeLa cells. Consequently, mismatched ionomer chain lengths and vesicle morphology enhanced cell-PIC interactions, and the states of ion pairing, particularly cationic residues, affected the internalisation behaviours of PICs via acetylation or guanidinylation of amino groups on catiomers. This treatment attenuated the cell-PIC interactions, possibly because of reduced interaction of PICs with negatively charged species on the cell-surface, glycosaminoglycans. Moreover, morphology and PEG length were correlated with PIC internalisation, in which PICs with longer and denser PEG were internalised less effectively. Cell line dependency was tested using RAW 264.7 macrophage cells; PIC recognition could be maintained after capping amino groups on catiomers, indicating that the remaining anionic groups were still effectively recognised by the scavenger receptors of macrophages. Our strategy for tuning the physicochemical properties of the PEGylated PIC nanocarriers is promising for overcoming the PEG issue.

Bioinspired photocatalytic systems towards compartmentalized artificial photosynthesis

Artificial photosynthesis aims to produce fuels and chemicals from simple building blocks (i.e. water and carbon dioxide) using sunlight as energy source. Achieving effective photocatalytic systems necessitates a comprehensive understanding of the underlying mechanisms and factors that control the reactivity. This review underscores the growing interest in utilizing bioinspired artificial vesicles to develop compartmentalized photocatalytic systems. Herein, we summarize different scaffolds employed to develop artificial vesicles, and discuss recent examples where such systems are used to study pivotal processes of artificial photosynthesis, including light harvesting, charge transfer, and fuel production. These systems offer valuable lessons regarding the appropriate choice of membrane scaffolds, reaction partners and spatial arrangement to enhance photocatalytic activity, selectivity and efficiency. These studies highlight the pivotal role of the membrane to increase the stability of the immobilized reaction partners, generate a suitable local environment, and force proximity between electron donor and acceptor molecules (or catalysts and photosensitizers) to increase electron transfer rates. Overall, these findings pave the way for further development of bioinspired photocatalytic systems for compartmentalized artificial photosynthesis.

2D-3D-Convertible, pH-Responsive Lipid Nanosheets

2D nanosheets self-assembled with amphiphilic molecules are promising tools for biomedical applications; yet, there are challenges to form and stabilize these nanosheets under complex physiological conditions. Here, the development of lipid nanosheets with high structural stability that can be reversibly converted to cell-sized vesicles by changes in pH within the physiological range robustly, are described. The system is controlled by the membrane disruptive peptide E5 and a cationic copolymer anchored on lipid membranes. It is envisioned that nanosheets formed using the dual anchoring peptide/cationic copolymer system can be employed in dynamic lipidic nanodevices, such as the vesosomes described here, drug delivery systems, and artificial cells.

Dynamic frustrated charge hotspots created by charge density modulation sequester globular proteins into complex coacervates

This study presents a simple strategy for the sequestration of globular proteins as clients into synthetic polypeptide-based complex coacervates as a scaffold, thereby recapitulating the scaffold-client interaction found in biological condensates. Considering the low net charges of scaffold proteins participating in biological condensates, the linear charge density (σ) on the polyanion, polyethylene glycol-b-poly(aspartic acids), was reduced by introducing hydroxypropyl or butyl moieties as a charge-neutral pendant group. Complex coacervate prepared from the series of reduced-σ polyanions and the polycation, homo-poly-l-lysine, could act as a scaffold that sequestered various globular proteins with high encapsulation efficiency (>80%), which sometimes involved further agglomerations in the coacervates. The sequestration of proteins was basically driven by electrostatic interaction, and therefore depended on the ionic strength and charges of the proteins. However, based on the results of polymer partitioning in the coacervate in the presence or absence of proteins, charge ratios between cationic and anionic polymers were maintained at the charge ratio of unity. Therefore, the origin of the electrostatic interaction with proteins is considered to be dynamic frustrated charges in the complex coacervates created by non-neutralized charges on polymer chains. Furthermore, fluorescence recovery after photobleaching (FRAP) measurements showed that the interaction of side-chains and proteins changed the dynamic property of coacervates. It also suggested that the physical properties of the condensate are tunable before and after the sequestration of globular proteins. The present rational design approach of the scaffold-client interaction is helpful for basic life-science research and the applied frontier of artificial organelles.

Increased Enzyme Loading in PICsomes via Controlling Membrane Permeability Improves Enzyme Prodrug Cancer Therapy Outcome

Mesoscopic-sized polyion complex vesicles (PICsomes) with semi-permeable membranes are promising nanoreactors for enzyme prodrug therapy (EPT), mainly due to their ability to accommodate enzymes in their inner cavity. Increased loading efficacy and retained activity of enzymes in PICsomes are crucial for their practical application. Herein, a novel preparation method for enzyme-loaded PICsomes, the stepwise crosslinking (SWCL) method, was developed to achieve both high feed-to-loading enzyme efficiency and high enzymatic activity under in vivo conditions. Cytosine deaminase (CD), which catalyzes the conversion of the 5-fluorocytosine (5-FC) prodrug to cytotoxic 5-fluorouracil (5-FU), was loaded into PICsomes. The SWCL strategy enabled a substantial increase in CD encapsulation efficiency, up to ~44% of the feeding amount. CD-loaded PICsomes (CD@PICsomes) showed prolonged blood circulation to achieve appreciable tumor accumulation via enhanced permeability and retention effect. The combination of CD@PICsomes and 5-FC produced superior antitumor activity in a subcutaneous model of C26 murine colon adenocarcinoma, even at a lower dose than systemic 5-FU treatment, and showed significantly reduced adverse effects. These results reveal the feasibility of PICsome-based EPT as a novel, highly efficient, and safe cancer treatment modality.

Nanostructure Control of an Antibiotic-based Polyion Complex Using a Series of Polycations with Different Side-chain Modification Rates

Developing nanovehicles for delivering antibiotics is a promising approach to overcome the issue of antibiotic resistance. This study aims to utilize a polyion complex (PICs) system for developing novel nanovehicles for polymyxin-type antibiotics, which are known as last resort drugs. The formation of antibiotic-based PIC nanostructures was investigated using colistimethate sodium (CMS), an anionic cyclic short peptide, and a series of block catiomers bearing different amounts of guanidinium moieties on their side chains. In addition, only the modified catiomer, and not the unmodified catiomer, self-assembles with CMS, implying the importance of the guanidine moieties for enhancing the interaction between the catiomer and CMS via the formation of multivalent hydrogen bonding. Moreover, micellar and vesicular PIC nanostructures are selectively formed depending on the ratio of the guanidine residues. Size-exclusion chromatography revealed that the encapsulation efficiency of CMS is dependent on the guanidinium modification ratio. The antimicrobial activity of the PIC nanostructures is also confirmed, indicating that the complexation of CMS in the PICs and further release from the PICs successfully occurs. This article is protected by copyright. All rights reserved.

Current Perspectives on Synthetic Compartments for Biomedical Applications

Nano- and micrometer-sized compartments composed of synthetic polymers are designed to mimic spatial and temporal divisions found in nature. Self-assembly of polymers into compartments such as polymersomes, giant unilamellar vesicles (GUVs), layer-by-layer (LbL) capsules, capsosomes, or polyion complex vesicles (PICsomes) allows for the separation of defined environments from the exterior. These compartments can be further engineered through the incorporation of (bio)molecules within the lumen or into the membrane, while the membrane can be decorated with functional moieties to produce catalytic compartments with defined structures and functions. Nanometer-sized compartments are used for imaging, theranostic, and therapeutic applications as a more mechanically stable alternative to liposomes, and through the encapsulation of catalytic molecules, i.e., enzymes, catalytic compartments can localize and act in vivo. On the micrometer scale, such biohybrid systems are used to encapsulate model proteins and form multicompartmentalized structures through the combination of multiple compartments, reaching closer to the creation of artificial organelles and cells. Significant progress in therapeutic applications and modeling strategies has been achieved through both the creation of polymers with tailored properties and functionalizations and novel techniques for their assembly.

Interpolyelectrolyte Complexes as an Emerging Technology for Pharmaceutical Delivery of Polypeptides

Polyelectrolyte complexes and the derivatives thereof comprise some of the most promising vehicles for the encapsulation and delivery of macromolecular therapeutics. In particular, protein therapeutics, which present a host of special considerations, can often be effectively packaged and delivered using interpolyelectrolyte complexes. While the technologies are still in the developmental phase, there are numerous examples of complexes where control is exerted over spacial and temporal delivery of a model protein cargo or candidate protein therapeutic agent. Here we provide a historical and practical background to promote a deeper understanding of interpolyelectrolyte complexes and the derivative technologies. Additionally, we review the physical principles underlying the association of polyelectrolyte complexes and the application of those principles to novel strategies and technologies driving interpolyelectrolyte complexation. Then, the application of polyelectrolyte complex technology to protein therapeutics is discussed in detail including discussions of several types of protein cargo with a special emphasis on Brain-Derived Neurotrophic Factor. Finally, we focus on the use of stealth polymers in block ionomer complexes, specifically PEG; its benefits, flaws, and possible alternatives. Comprehensive understanding of the field may promote the continued development of derivative technologies for the delivery of particularly intransigent protein therapeutics, much as has been accomplished for small molecule drugs. We also aim to link current advances to the historical developments which inaugurated the field. With consideration to the field, industrial and academic researchers can utilize the discussed technologies and continue to elucidate novel modalities for a myriad of therapeutic and commercial applications.

Therapeutic nanoreactors for detoxification of xenobiotics: Concepts, challenges and biotechnological trends with special emphasis to organophosphate bioscavenging

The introduction of enzyme nanoreactors in medicine is relatively new. However, this technology has already been experimentally successful in cancer treatments, struggle against toxicity of reactive oxygen species in inflammatory processes, detoxification of drugs and xenobiotics, and correction of metabolic and genetic defects by using encapsulated enzymes, acting in single or cascade reactions. Biomolecules, e.g. enzymes, antibodies, reactive proteins capable of inactivating toxicants in the body are called bioscavengers. In this review, we focus on enzyme-containing nanoreactors for in vivo detoxification of organophosphorous compounds (OP) to be used for prophylaxis and post-exposure treatment of OP poisoning. A particular attention is devoted to bioscavenger-containing injectable nanoreactors operating in the bloodstream. The nanoreactor concept implements single or multiple enzymes and cofactors co-encapsulated in polymeric semi-permeable nanocontainers. Thus, the detoxification processes take place in a confined space containing highly concentrated bioscavengers. The article deals with historical and theoretical backgrounds about enzymatic detoxification of OPs in nanoreactors, nanoreactor polymeric enveloppes, realizations and advantages over other approaches using bioscavengers.

[Challenges to Creation of Artificial Organelle for Effective Editing of Cell Function]

In "cell-function editing", the combination of biological methods with artificial methods is a promising way to effectively implement functions that live cells do not originally possess. In the present symposium review, two approaches with methodology of building "artificial organelle" were implemented for editing cellular functions. One approach is the "membrane-bound artificial organelle", which is mainly created from polymeric nanocapsules that function in cells, and the other approach mimics the "membraneless organelle", which has recently gained immense interest in the field of cell biology. Furthermore, some examples of artificial cells are also described, which were constructed by utilizing artificial organelles. In this context, some recent progress has been observed in the author's research on the development of polyion complex (PIC) materials, in particular, PICsome-based nanoreactors, designer coacervates for protein sequestration, and yolk-shell PIC structures that are reminiscent of artificial cells. These technologies may contribute to effective "cell editing" or "cell renovation", which enables the edited cells to show higher performance at the target site in the human body, compared to the native cells.

Polymeric Nanoreactors as Emerging Nanoplatforms for Cancer Precise Nanomedicine

How to precisely detect and effectively cure cancer which is defined as precise nanomedicine has drawn great attention worldwide. Polymeric nanoreactors which can in situ catalyze inert species into activated ones, can greatly increase imaging quality and enhance therapeutic effects along with decreased background interference and reduced serious side effects. After a brief introduction, the design and preparation of polymeric nanoreactors are discussed from the following aspects, that is, solvent-switch, pH-tuning, film rehydration, hard template, electrostatic interaction, and polymerization-induced self-assembly (PISA). Subsequently, the biomedical applications of these nanoreactors in the fields of cancer imaging, cancer therapy, and cancer theranostics are highlighted. The last but not least, conclusions and future perspectives about polymeric nanoreactors are given. It is believed that polymeric nanoreactors can bring a great opportunity for future fabrication and clinical translation of precise nanomedicine.

α-Amino acid N-carboxyanhydride (NCA)-derived synthetic polypeptides for nucleic acids delivery

In recent years, gene therapy has come into the spotlight for the prevention and treatment of a wide range of diseases. Polypeptides have been widely used in mediating nucleic acid delivery, due to their versatilities in chemical structures, desired biodegradability, and low cytotoxicity. Chemistry plays an essential role in the development of innovative polypeptides to address the challenges of producing efficient and safe gene vectors. In this Review, we mainly focused on the latest chemical advances in the design and preparation of polypeptide-based nucleic acid delivery vehicles. We first discussed the synthetic approach of polypeptides via ring-opening polymerization (ROP) of N-carboxyanhydrides (NCAs), and introduced the various types of polypeptide-based gene delivery systems. The extracellular and intracellular barriers against nucleic acid delivery were then outlined, followed by detailed review on the recent advances in polypeptide-based delivery systems that can overcome these barriers to enable in vitro and in vivo gene transfection. Finally, we concluded this review with perspectives in this field.

Peptide-Based Polyion Complex Vesicles That Deliver Enzymes into Intact Plants To Provide Antibiotic Resistance without Genetic Modification

Direct delivery of enzymes into intact plants using cell-penetrating peptides (CPPs) is an attractive approach for modifying plant functions without genetic modification. However, by conventional methods, it is difficult to maintain the enzyme activity for a long time because of proteolysis of the enzymes under physiological conditions. Here, we developed a novel enzyme delivery system using polyion complex vesicles (PICsomes) to protect the enzyme from proteases. We created PICsome-bearing reactive groups at the surface by mixing an anionic block copolymer, alkyne-TEG-P(Lys-COOH), and a cationic peptide, P(Lys). The PICsome encapsulated neomycin phosphotransferase II (NPTII), a kanamycin resistance enzyme, and protected NPTII from proteases in vitro. A CPP-modified PICsome delivered NPTII into the root hair cells of Arabidopsis thaliana seedlings and provided kanamycin resistance in the seedlings that lasted for 7 days. Thus, the PICsome-mediated enzyme delivery system is a promising method for imparting long-term transient traits to plants without genetic modification.

Noncovalent Stabilization of Vesicular Polyion Complexes with Chemically Modified/Single-Stranded Oligonucleotides and PEG-b-guanidinylated Polypeptides for Intracavity Encapsulation of Effector Enzymes Aimed at Cooperative Gene Knockdown

For the simultaneous delivery of antisense oligonucleotides and their effector enzymes into cells, nanosized vesicular polyion complexes (PICs) were fabricated from oppositely charged polyion pairs of oligonucleotides and poly(ethylene glycol) (PEG)-b-polypeptides. First, the polyion component structures were carefully designed to facilitate a multimolecular (or secondary) association of unit PICs for noncovalent (or chemical cross-linking-free) stabilization of vesicular PICs. Chemically modified, single-stranded oligonucleotides (SSOs) dramatically stabilized the multimolecular associates under physiological conditions, compared to control SSOs without chemical modifications and duplex oligonucleotides. In addition, a high degree of guanidino groups in the polypeptide segment was also crucial for the high stability of multimolecular associates. Dynamic light scattering and transmission electron microscopy revealed the stabilized multimolecular associates to have a 100 nm sized vesicular architecture with a narrow size distribution. The loading number of SSOs per nanovesicle was determined to be ∼2500 using fluorescence correlation spectroscopic analyses with fluorescently labeled SSOs. Furthermore, the nanovesicle stably encapsulated ribonuclease H (RNase H) as an effector enzyme at ∼10 per nanovesicle through simple vortex-mixing with preformed nanovesicles. Ultimately, the RNase H-encapsulated nanovesicle efficiently delivered SSOs with RNase H into cultured cancer cells, thereby eliciting the significantly higher gene knockdown compared with empty nanovesicles (without RNase H) or a mixture of nanovesicles with RNase H without encapsulation. These results demonstrate the great potential of noncovalently stabilized nanovesicles for the codelivery of two varying bio-macromolecule payloads for ensuring their cooperative biological activity.

Dual-Sensitive Nanomicelles Enhancing Systemic Delivery of Therapeutically Active Antibodies Specifically into the Brain

Delivering therapeutic antibodies into the brain across the blood-brain barrier at a therapeutic level is a promising while challenging approach in the treatment of neurological disorders. Here, we present a polymeric nanomicelle (PM) system capable of delivering therapeutically effective levels of 3D6 antibody fragments (3D6-Fab) into the brain parenchyma for inhibiting Aβ aggregation. PM assembly was achieved by charge-converting 3D6-Fab through pH-sensitive citraconylation to allow complexation with reductive-sensitive cationic polymers. Brain targeting was achieved by functionalizing the PM surface with glucose molecules to allow interaction with recycling glucose transporter (Glut)-1 proteins. Consequently, 41-fold enhanced 3D6-Fab accumulation in the brain was achieved by using the PM system compared to free 3D6-Fab. Furthermore, therapeutic benefits were obtained by successfully inhibiting Aβ_1-42 aggregation in Alzheimer's disease mice systemically treated with 3D6-Fab-loaded glucosylated PM. Hence, this nanocarrier system represents a promising method for effectively delivering functional antibody agents into the brain and treating neurological diseases.

The rise of bio-inspired polymer compartments responding to pathology-related signals

Self-organized nano- and microscale polymer compartments such as polymersomes, giant unilamellar vesicles (GUVs), polyion complex vesicles (PICsomes) and layer-by-layer (LbL) capsules have increasing potential in many sensing applications. Besides modifying the physicochemical properties of the corresponding polymer building blocks, the versatility of these compartments can be markedly expanded by biomolecules that endow the nanomaterials with specific molecular and cellular functions. In this review, we focus on polymer-based compartments that preserve their structure, and highlight the key role they play in the field of medical diagnostics: first, the self-assembling abilities that result in preferred architectures are presented for a broad range of polymers. In the following, we describe different strategies for sensing disease-related signals (pH-change, reductive conditions, and presence of ions or biomolecules) by polymer compartments that exhibit stimuli-responsiveness. In particular, we distinguish between the stimulus-sensitivity contributed by the polymer itself or by additional compounds embedded in the compartments in different sensing systems. We then address necessary properties of sensing polymeric compartments, such as the enhancement of their stability and biocompatibility, or the targeting ability, that open up new perspectives for diagnostic applications.

Regulating vesicle bilayer permeability and selectivity via stimuli-triggered polymersome-to-PICsome transition

Compared to liposomes, polymersomes of block copolymers (BCPs) possess enhanced stability, along with compromised bilayer permeability. Though polyion complex vesicles (PICsomes) from oppositely charged block polyelectrolytes possess semipermeable bilayers, they are unstable towards physiologically relevant ionic strength and temperature; moreover, permselectivity tuning of PICsomes has remained a challenge. Starting from a single component diblock or triblock precursor, we solve this dilemma by stimuli-triggered chemical reactions within pre-organized BCP vesicles, actuating in situ polymersome-to-PICsome transition and achieving molecular size-selective cargo release at tunable rates. UV light and reductive milieu were utilized to trigger carboxyl decaging and generate ion pairs within hydrophobic polymersome bilayers containing tertiary amines. Contrary to conventional PICsomes, in situ generated ones are highly stable towards extreme pH range (pH 2-12), ionic strength (~3 M NaCl), and elevated temperature (70 °C) due to multivalent ion-pair interactions at high local concentration and cooperative hydrogen bonding interactions of pre-organized carbamate linkages.

ROS-Responsive Polymeric siRNA Nanomedicine Stabilized by Triple Interactions for the Robust Glioblastoma Combinational RNAi Therapy

Small interfering RNA (siRNA) holds inherent advantages and great potential for treating refractory diseases. However, lack of suitable siRNA delivery systems that demonstrate excellent circulation stability and effective at-site delivery ability is currently impeding siRNA therapeutic performance. Here, a polymeric siRNA nanomedicine (3I-NM@siRNA) stabilized by triple interactions (electrostatic, hydrogen bond, and hydrophobic) is constructed. Incorporating extra hydrogen and hydrophobic interactions significantly improves the physiological stability compared to an siRNA nanomedicine analog that solely relies on the electrostatic interaction for stability. The developed 3I-NM@siRNA nanomedicine demonstrates effective at-site siRNA release resulting from tumoral reactive oxygen species (ROS)-triggered sequential destabilization. Furthermore, the utility of 3I-NM@siRNA for treating glioblastoma (GBM) by functionalizing 3I-NM@siRNA nanomedicine with angiopep-2 peptide is enhanced. The targeted Ang-3I-NM@siRNA exhibits superb blood-brain barrier penetration and potent tumor accumulation. Moreover, by cotargeting polo-like kinase 1 and vascular endothelial growth factor receptor-2, Ang-3I-NM@siRNA shows effective suppression of tumor growth and significantly improved survival time of nude mice bearing orthotopic GBM brain tumors. New siRNA nanomedicines featuring triple-interaction stabilization together with inbuilt self-destruct delivery ability provide a robust and potent platform for targeted GBM siRNA therapy, which may have utility for RNA interference therapy of other tumors or brain diseases.

Macro- and Microphase Separated Protein-Polyelectrolyte Complexes: Design Parameters and Current Progress

Protein-containing polyelectrolyte complexes (PECs) are a diverse class of materials, composed of two or more oppositely charged polyelectrolytes that condense and phase separate near overall charge neutrality. Such phase-separation can take on a variety of morphologies from macrophase separated liquid condensates, to solid precipitates, to monodispersed spherical micelles. In this review, we present an overview of recent advances in protein-containing PECs, with an overall goal of defining relevant design parameters for macro- and microphase separated PECs. For both classes of PECs, the influence of protein characteristics, such as surface charge and patchiness, co-polyelectrolyte characteristics, such as charge density and structure, and overall solution characteristics, such as salt concentration and pH, are considered. After overall design features are established, potential applications in food processing, biosensing, drug delivery, and protein purification are discussed and recent characterization techniques for protein-containing PECs are highlighted.

Guanidinium Can Break and Form Strongly Associating Ion Complexes

Guanidinium is one of nature's strongest denaturants and is also a motif that appears in several interfacial contexts such as the RGD sequence involved in cell adhesion, cell penetrating peptides, and antimicrobial molecules. It is important to quantify the origin of guanidinium's ion-specific interactions so that its unique behavior may be exploited in synthetic applications. The present work demonstrates that guanidinium ions can both break and form strongly associating ion complexes in a context-dependent way. These insights into guanidinium's behavior are elucidated using polyelectrolyte complexes (PECs), where interpolymer ion pairs between oppositely charged polymers play an important role in determining material stability. Different polycation-polyanion combinations can span a large range of association affinities, where more strongly associating complexes can remain insoluble in concentrated salt solutions and in extreme pH conditions. This high stability is desirable in several application contexts for PECs, but also renders them challenging to process and, therefore, to study since they cannot be dissolved into polymer solutions. Here we demonstrate that guanidinium salts are very effective in dissolving the poly(styrenesulfonate)/poly(allylamine) (PSS:PAH) complex, which has one of the highest reported polycation-polyanion association affinities. We also demonstrate the importance of charge identity in complexation phenomena by functionalizing guanidinium directly into poly(allylamine), resulting in a complex that remains stable under highly denaturing conditions. The model system of PSS:PAH is used to glean insights into guanidinium's denaturing activity, as well as to broadly comment on the nature of ion-specific interactions in charged macromolecules.