Degradable Cationic Nanohydrogel Particles for Stimuli-Responsive Release of siRNA

Pulmonary siRNA Delivery with Sophisticated Amphiphilic Poly(Spermine Acrylamides) for the Treatment of Lung Fibrosis

RNA interference (RNAi) is an efficient strategy to post-transcriptionally silence gene expression. While all siRNA drugs on the market target the liver, the lung offers a variety of currently undruggable targets, which can potentially be treated with RNA therapeutics. To achieve this goal, the synthesis of poly(spermine acrylamides) (P(SpAA) is reported herein. Polymers are prepared via polymerization of N-acryloxysuccinimide (NAS) and afterward this active ester is converted into spermine-based pendant groups. Copolymerizations with decylacrylamide are employed to increase the hydrophobicity of the polymers. After deprotection, polymers show excellent siRNA encapsulation to obtain perfectly sized polyplexes at very low polymer/RNA ratios. In vitro 2D and 3D cell culture, ex vivo and in vivo experiments reveal superior properties of amphiphilic spermine-copolymers with respect to delivery of siRNA to lung cells in comparison to commonly used lipid-based transfection agents. In line with the in vitro results, siRNA delivery to human lung explants confirm more efficient gene silencing of protease-activated receptor 2 (PAR2), a G protein-coupled receptor involved in fibrosis. This study reveals the importance of the balance between efficient polyplex formation, cellular uptake, gene knockdown, and toxicity for efficient siRNA delivery in vitro, in vivo, and in fibrotic human lung tissue ex vivo.

Nanoparticular Carriers As Objects to Study Intentional and Unintentional Bioconjugation

Synthetic nanoparticles are interesting to use in the study of ligation with natural biorelevant structures. That is because they present an intermediate situation between reactions onto soluble polymers or onto solid surfaces. In addition, differently functionalized nanoparticles can be separated and studied independently thereafter. So what would be a "patchy functionalization" on a macroscopic surface results in differently functionalized nanoparticles, which can be separated after the interaction with body fluids. This paper will review bioconjugation of such nanoparticles with a special focus on recent results concerning the formation of a protein corona by unspecific adsorption (lower lines of TOC), which presents an unintentional bioconjugation, and on new aspects of intentionally performed bioconjugation by covalent chemistry (upper line). For this purpose, it is important that polymeric nanoparticles without a protein corona can be prepared. This opens, e.g., the possibility to look for special proteins adsorbed as a result of the natural compound ligated to the nanoparticle by covalent chemistry, like the Fc part of antibodies. At the same time, the use of highly reactive, bioorthogonal functional groups (inverse electron demand Diels-Alder cycloaddition) on the nanoparticles allows an efficient ligation after administration inside the body, i.e., in vivo.

Application of vinyl polymer-based materials as nucleic acids carriers in cancer therapy

Nucleic acid-based therapies have changed the paradigm of cancer treatment, where conventional treatment modalities still have several limitations in terms of efficacy and severe side effects. However, these biomolecules have a short half-life in vivo, requiring multiple administrations, resulting in severe suffering, discomfort, and poor patient compliance. In the early days of (nano)biotechnology, these problems caused concern in the medical community, but recently it has been recognized that these challenges can be overcome by developing innovative formulations. This review focuses on the use of vinyl polymer-based materials for the protection and delivery of nucleic acids in cancer. First, an overview of the properties of nucleic acids and their versatility as drugs is provided. Then, key information on the achievements to date, the most effective delivery methods, and the evaluation of functionalization approaches (stimulatory strategies) are critically discussed to highlight the importance of vinyl polymers in the new cancer treatment approaches. This article is categorized under: Nanotechnology Approaches to Biology > Nanoscale Systems in Biology Therapeutic Approaches and Drug Discovery > Nanomedicine for Oncologic Disease Biology-Inspired Nanomaterials > Nucleic Acid-Based Structures.

Shining Light on Polymeric Drug Nanocarriers with Fluorescence Correlation Spectroscopy

The use of nanoparticles as carriers is an extremely promising way for administration of therapeutic agents, such as drug molecules, proteins and nucleic acids. Such nanocarriers (NCs) can increase the solubility of hydrophobic compounds, protect their cargo from the environment, and if properly functionalized, deliver it to specific target cells and tissues. Polymer-based NCs are especially promising, because they offer high degree of versatility and tunability. However, in order to get a full advantage of this therapeutic approach and develop efficient delivery systems, a careful characterization of the NCs is needed. This Feature Article highlights the fluorescence correlation spectroscopy (FCS) technique as a powerful and versatile tool for NCs characterization at all stages of the drug delivery process. In particular, FCS can monitor and quantify the size of the NCs and the drug loading efficiency after preparation, the NCs stability and possible interactions with, e.g., plasma proteins in the blood stream and the kinetic of drug release in the cytoplasm of the target cells. This article is protected by copyright. All rights reserved.

Dual-responsive degradable core-shell nanogels with tuneable aggregation behaviour

We report the synthesis of core–shell nanogels by sequential addition of thermoresponsive monomers; N-isopropylacrylamide (NIPAM) and N-isopropylmethacrylamide (NIPMAM). The aggregation behaviour of aqueous dispersions of these particles in the presence of salt can be tuned by varying the monomer ratio. The inclusion of degradable cross-linker bis(acryloyl)cystamine (BAC) allows the nanogels to degrade in the presence of reducing agent, with nanogels composed of a copolymer of the two monomers not showing the same high levels of degradation as the comparable core–shell particles. These levels of degradation were also seen with physiologically relevant reducing agent concentration at pH 7. Therefore, it is hoped that the aggregation of these nanogels will have applications in nanomedicine and beyond.

Core–shell nanogels with a poly(N-isopropylmethacrylamide) core and poly(N-isopropylacrylamide) shell display tuneable thermoresponsive behaviour and high degradability.

Magnetic microgels and nanogels: Physical mechanisms and biomedical applications

Soft micro- and nanostructures have been extensively developed for biomedical applications. The main focus has been on multifunctional composite materials that combine the advantages of hydrogels and colloidal particles. Magnetic microgels and nanogels can be realized by hybridizing stimuli-sensitive gels and magnetic nanoparticles. They are of particular interest since they can be controlled in a wide range of biological environments by using magnetic fields. In this review, we elucidate physical principles underlying the design of magnetic microgels and nanogels for biomedical applications. Particularly, this article provides a comprehensive and conceptual overview on the correlative structural design and physical functionality of the magnetic gel systems under the concept of colloidal biodevices. To this end, we begin with an overview of physicochemical mechanisms related to stimuli-responsive hydrogels and transport phenomena and summarize the magnetic properties of inorganic nanoparticles. On the basis of the engineering principles, we categorize and summarize recent advances in magnetic hybrid microgels and nanogels, with emphasis on the biomedical applications of these materials. Potential applications of these hybrid microgels and nanogels in anticancer treatment, protein therapeutics, gene therapy, bioseparation, biocatalysis, and regenerative medicine are highlighted. Finally, current challenges and future opportunities in the design of smart colloidal biodevices are discussed.

Novel Opportunities for Cathepsin S Inhibitors in Cancer Immunotherapy by Nanocarrier-Mediated Delivery

Cathepsin S (CatS) is a secreted cysteine protease that cleaves certain extracellular matrix proteins, regulates antigen presentation in antigen-presenting cells (APC), and promotes M2-type macrophage and dendritic cell polarization. CatS is overexpressed in many solid cancers, and overall, it appears to promote an immune-suppressive and tumor-promoting microenvironment. While most data suggest that CatS inhibition or knockdown promotes anti-cancer immunity, cell-specific inhibition, especially in myeloid cells, appears to be important for therapeutic efficacy. This makes the design of CatS selective inhibitors and their targeting to tumor-associated M2-type macrophages (TAM) and DC an attractive therapeutic strategy compared to the use of non-selective immunosuppressive compounds or untargeted approaches. The selective inhibition of CatS can be achieved through optimized small molecule inhibitors that show good pharmacokinetic profiles and are orally bioavailable. The targeting of these inhibitors to TAM is now more feasible using nanocarriers that are functionalized for a directed delivery. This review discusses the role of CatS in the immunological tumor microenvironment and upcoming possibilities for a nanocarrier-mediated delivery of potent and selective CatS inhibitors to TAM and related APC to promote anti-tumor immunity.

Polymeric siRNA gene delivery - transfection efficiency versus cytotoxicity

Within the field of gene therapy, there is a considerable need for the development of non-viral vectors that are able to compete with the efficiency obtained by viral vectors, while maintaining a good toxicity profile and not inducing an immune response within the body. While there have been many reports of possible polymeric delivery systems, few of these systems have been successful in the clinical setting due to toxicity, systemic instability or gene regulation inefficiency, predominantly due to poor endosomal escape and cytoplasmic release. The objective of this review is to provide an overview of previously published polymeric non-coding RNA and, to a lesser degree, oligo-DNA delivery systems with emphasis on their positive and negative attributes, in order to provide insight in the numerous hurdles that still limit the success of gene therapy.

Monitoring drug nanocarriers in human blood by near-infrared fluorescence correlation spectroscopy

Nanocarrier-based drug delivery is a promising therapeutic approach that offers unique possibilities for the treatment of various diseases. However, inside the blood stream, nanocarriers' properties may change significantly due to interactions with proteins, aggregation, decomposition or premature loss of cargo. Thus, a method for precise, in situ characterization of drug nanocarriers in blood is needed. Here we show how the fluorescence correlation spectroscopy that is a well-established method for measuring the size, loading efficiency and stability of drug nanocarriers in aqueous solutions can be used to directly characterize drug nanocarriers in flowing blood. As the blood is not transparent for visible light and densely crowded with cells, we label the nanocarriers or their cargo with near-infrared fluorescent dyes and fit the experimental autocorrelation functions with an analytical model accounting for the presence of blood cells. The developed methodology contributes towards quantitative understanding of the in vivo behavior of nanocarrier-based therapeutics.

Bioresponsive functional nanogels as an emerging platform for cancer therapy

INTRODUCTION

Bioresponsive nanogels with a crosslinked three-dimensional structure and an aqueous environment that undergo physical or chemical changes including swelling and dissociation in response to biological signals such as mild acidity, hyperthermia, enzymes, reducing agents, reactive oxygen species (ROS), and adenosine-5'-triphosphate (ATP) present in tumor microenvironments or inside cancer cells have emerged as an appealing platform for targeted drug delivery and cancer therapy.

AREAS COVERED

This review highlights recent designs and development of bioresponsive nanogels for facile loading and triggered release of chemotherapeutics and biotherapeutics. The in vitro and in vivo antitumor performances of drug-loaded nanogels are discussed.

EXPERT OPINION

Bioresponsive nanogels with an excellent stability and safety profile as well as fast response to biological signals are unique systems that mediate efficient and site-specific delivery of anticancer drugs, in particular macromolecular drugs like proteins, siRNA and DNA, leading to significantly enhanced tumor therapy compared with the non-responsive counterparts. Future research has to be directed to the development of simple, tumor-targeted and bioresponsive multifunctional nanogels, which can be either constructed from natural polymers with intrinsic targeting ability or functionalized with targeting ligands. We anticipate that rationally designed nanotherapeutics based on bioresponsive nanogels will become available for future clinical cancer treatment.

ABBREVIATIONS

AIE, aggregation-induced emission; ATP, adenosine-5'-triphosphate; ATRP, atom transfer radical polymerization; BSA, bovine serum albumin; CBA, cystamine bisacrylamide; CC, Cytochrome C; CDDP, cisplatin; CT, computed tomography; DC, dendritic cell; DiI, 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate; DOX, doxorubicin; dPG, dendritic polyglycerol; DTT, dithiothreitol; EAMA, 2-(N,N-diethylamino)ethyl methacrylate; EPR, enhanced permeability and retention; GrB, granzyme B; GSH, glutathione tripeptide; HA, hyaluronic acid; HAase, hyaluronidases; HCPT, 10-Hydroxycamptothecin; HEP, heparin; HPMC, hydroxypropylmethylcellulose; LBL, layer-by-layer; MTX, methotrexate; NCA, N-carboxyanhydride; OVA, ovalbumin; PAH, poly(allyl amine hydrochloride); PBA, phenylboronic acid; PCL, polycaprolactone; PDEAEMA, poly(2-diethylaminoethyl methacrylate); PDGF, platelet derived growth factor; PDPA, poly(2-(diisopropylamino)ethyl methacrylate); PDS, pyridyldisulfide; PEG, poly(ethylene glycol); PEGMA, polyethyleneglycol methacrylate; PEI, polyethyleneimine; PHEA, poly(hydroxyethyl acrylate); PHEMA, poly(2-(hydroxyethyl) methacrylate; PNIPAM, poly(N-isopropylacrylamide); PMAA, poly(methacrylic acid); PPDSMA, poly(2-(pyridyldisulfide)ethyl methacrylate); PTX, paclitaxel; PVA, poly(vinyl alcohol); QD, quantum dot; RAFT, reversible addition-fragmentation chain transfer; RGD, Arg-Gly-Asp peptide; ROP, ring-opening polymerization; ROS, reactive oxygen species; TMZ, temozolomide; TRAIL, tumor necrosis factor-related apoptosis inducing ligand; VEGF, vascular endothelial growth factor.

Targeting Protumoral Tumor-Associated Macrophages with Nanobody-Functionalized Nanogels through Strain Promoted Azide Alkyne Cycloaddition Ligation

Tumor-associated macrophages (TAMs) with high expression levels of the Macrophage Mannose Receptor (MMR, CD206) exhibit a strong angiogenic and immune suppressive activity. Thus, they are a highly attractive target in cancer immunotherapy, with the aim to modulate their protumoral behavior. Here, we introduce polymer nanogels as potential drug nanocarriers which were site-specifically decorated with a Nanobody (Nb) specific for the MMR. Using azide-functionalized RAFT chain transfer agents, they provide access to amphiphilic reactive ester block copolymers that self-assemble into micelles and are afterwards core-cross-linked toward fully hydrophilic nanogels with terminal azide groups on their surface. MMR-targeting Nb can site-selectively be functionalized with one single cyclooctyne moiety by maleimide-cysteine chemistry under mildly reducing conditions which enables successful chemoorthogonal conjugation to the nanogels. The resulting Nb-functionalized nanogels were highly efficient in targeting MMR-expressing cells and TAMs both in vitro and in vivo. We believe that these findings pave the road for targeted eradication or modulation of pro-tumoral MMR^high TAMs.

Cationic Nanohydrogel Particles for Therapeutic Oligonucleotide Delivery

Short pharmaceutical active oligonucleotides such as small interfering RNA (siRNA) or cytidine-phosphate-guanosine (CpG) are considered as powerful therapeutic alternatives, especially to medicate hard-to-treat diseases (e.g., liver fibrosis or cancer). Unfortunately, these molecules are equipped with poor pharmacokinetic properties that prevent them from translation. Well-defined nanosized carriers can provide opportunities to optimize their delivery and guide them to their site of action. Among several concepts, this Feature Article focuses on cationic nanohydrogel particles as a universal delivery system for small anionic molecules including siRNA and CpG. Cationic nanohydrogels are derived from preaggregated precursor block copolymers, which are further cross-linked to obtain well-defined nanoparticles of tunable sizes and with (degradable) cationic cores. Novel opportunities for oligonucleotide delivery in vitro and in vivo with respect to liver fibrosis therapies will be highlighted as well as perspectives toward modulating the immune system. In general, the approach of covalently stabilized cationic carrier systems can contribute to find advanced oligonucleotide therapeutics.

Glutathione responsive polymers and their application in drug delivery systems

Materials which respond to biological cues are the subject of intense research interest due to their possible application in smart drug delivery vehicles.

Defined pH-sensitive nanogels as gene delivery platform for siRNA mediated in vitro gene silencing

An advanced cationic carrier system which combines high transfection efficiency with low cytotoxicity and a control over the release of the encapsulated genetic material by the reduction of the multivalent architecture upon pH triggered degradation was developed.

Design, synthesis and transfection efficiency of a novel redox-sensitive polycationic amphiphile

A novel redox-sensitive polycationic amphiphile (2S3) with disulphide linkers for nucleic acid delivery was developed. Cationic liposomes formed by 2S3 and the helper lipid DOPE demonstrated effective DNA delivery into HEK293 cells with a maximal transfection activity that is superior than both nonredox-sensitive cationic liposomes and Lipofectamine® 2000 at an N/P ratio of 6/1. Redox-sensitivity was tested by experiments with extracellular glutathione which shown the ability of disulphide linker degradation. Our results suggest that polycationic amphiphile 2S3 is a promising candidate for nucleic acid delivery.

Nanogels: An overview of properties, biomedical applications and obstacles to clinical translation

Nanogels have emerged as a versatile hydrophilic platform for encapsulation of guest molecules with a capability to respond to external stimuli that can be used for a multitude of applications. These are soft materials capable of holding small molecular therapeutics, biomacromolecules, and inorganic nanoparticles within their crosslinked networks, which allows them to find applications for therapy as well as imaging of a variety of disease conditions. Their stimuli-responsive behavior can be easily controlled by selection of constituent polymer and crosslinker components to achieve a desired response at the site of action, which imparts nanogels the ability to participate actively in the intended function of the carrier system rather than being passive carriers of their cargo. These properties not only enhance the functionality of the carrier system but also help in overcoming many of the challenges associated with the delivery of cargo molecules, and this review aims to highlight the distinct and unique capabilities of nanogels as carrier systems for the delivery of an array of cargo molecules over other nanomaterials. Despite their obvious usefulness, nanogels are still not a commonplace occurrence in clinical practice. We have also made an attempt to highlight some of the major challenges that need to be overcome to advance nanogels further in the field of biomedical applications.

In Vivo Gene-Silencing in Fibrotic Liver by siRNA-Loaded Cationic Nanohydrogel Particles

Cationic nanohydrogel particles loaded with anti-Col1α1 siRNA suppress collagen synthesis and deposition in fibrotic mice: Systemically administered 40 nm sized nanogel particles accumulate in collagen-expressing cells in the liver. Their siRNA payload induces a sequence specific in vivo gene knockdown affording an efficient antifibrotic effect in mice with liver fibrosis.

Templateless synthesis of polyacrylamide-based Nanogels via RAFT dispersion polymerization

This paper reports on the synthesis of well-defined polyacrylamide-based nanogels via reversible addition-fragmentation chain transfer (RAFT) dispersion polymerization, highlighting a templateless route for the efficient synthesis of nanogels based on water-soluble polymers. RAFT dispersion polymerization of acrylamide in co-nonsolvents of water-tert-butanol mixtures by chain extension from poly(dimethylacrylamide) shows well-controlled polymerization process, uniform nanogel size, and excellent colloidal stability. The versatility of this approach is further demonstrated by introducing a hydrophobic co-monomer (butyl acrylate) without disturbing the dispersion polymerization process.