Poly(2-oxazoline)-based nanogels as biocompatible pseudopolypeptide nanoparticles

Esterase-Responsive Polyglycerol-Based Nanogels for Intracellular Drug Delivery in Rare Gastrointestinal Stromal Tumors

Rare gastrointestinal stromal tumors (GISTs) are caused by mutations in the KIT and PDGFRA genes. Avapritinib (BLU-285) is a targeted selective inhibitor for mutated KIT and PDGFRA receptors that can be used to treat these tumors. However, there are subtypes of GISTs that exhibit resistance against BLU-285 and thus require other treatment strategies. This can be addressed by employing a drug delivery system that transports a combination of drugs with distinct cell targets. In this work, we present the synthesis of esterase-responsive polyglycerol-based nanogels (NGs) to overcome drug resistance in rare GISTs. Using inverse nanoprecipitation mediated with inverse electron-demand Diels-Alder cyclizations (iEDDA) between dPG-methyl tetrazine and dPG-norbornene, multi-drug-loaded NGs were formed based on a surfactant-free encapsulation protocol. The obtained NGs displayed great stability in the presence of fetal bovine serum (FBS) and did not trigger hemolysis in red blood cells over a period of 24 h. Exposing the NGs to Candida Antarctica Lipase B (CALB) led to the degradation of the NG network, indicating the capability of targeted drug release. The bioactivity of the loaded NGs was tested in vitro on various cell lines of the GIST-T1 family, which exhibit different drug resistances. Cell internalization with comparable uptake kinetics of the NGs could be confirmed by confocal laser scanning microscopy (CLSM) and flow cytometry for all cell lines. Cell viability and live cell imaging studies revealed that the loaded NGs are capable of intracellular drug release by showing similar IC50 values to those of the free drugs. Furthermore, multi-drug-loaded NGs were capable of overcoming BLU-285 resistance in T1-α-D842V + G680R cells, demonstrating the utility of this carrier system.

Design and Synthesis of Hybrid Thermo-Responsive Hydrogels Based on Poly(2-oxazoline) and Gelatin Derivatives

The combination of natural and synthetic polymers to form hybrid hydrogels offers the potential of fabricating new materials that possess a combination of properties resulting from both types of polymer classes. Within this work, two alkene-functionalized poly(2-alkyl/aryl–2-oxazoline) (PAOx) copolymers and one gelatin derivative, thiolated gelatin (gel-SH), are synthesized as precursors for hybrid hydrogels through a photo-induced radical thiol-ene crosslinking process. In-situ photo-rheology revealed an increased mechanical stability for hydrogels that possess an excess amount of PAOx precursor. A final qualitative investigation of the thermo-responsive properties of a P(EtOx₂₇₀–norbornenOx₃₀):gel-SH (2:1) hydrogel film revealed a cloud point temperature (T_cp) in the same range as the T_cp of the P(EtOx₂₇₀–norbornenOx₃₀) polymer precursor, which is around 30 °C. This promising result demonstrates that thermo-responsive hybrid poly(2-oxazoline)-gelatin hydrogels could be prepared with predictable T_cps and that further investigation into this appealing feature might be of interest. Ultimately, this work shows a proof-of-concept of using PAOx as potential hybrid hydrogel precursor in combination with cell-interactive gelatin derivatives to potentially improve the mechanical stability of the final scaffolds and introduce additional features such as thermo-responsiveness for the purpose of drug delivery.

Understanding the Interaction of Polyelectrolyte Architectures with Proteins and Biosystems

The counterions neutralizing the charges on polyelectrolytes such as DNA or heparin may dissociate in water and greatly influence the interaction of such polyelectrolytes with biomolecules, particularly proteins. In this Review we give an overview of studies on the interaction of proteins with polyelectrolytes and how this knowledge can be used for medical applications. Counterion release was identified as the main driving force for the binding of proteins to polyelectrolytes: Patches of positive charge become multivalent counterions of the polyelectrolyte and lead to the release of counterions from the polyelectrolyte and a concomitant increase in entropy. This is shown from investigations on the interaction of proteins with natural and synthetic polyelectrolytes. Special emphasis is paid to sulfated dendritic polyglycerols (dPGS). The Review demonstrates that we are moving to a better understanding of charge-charge interactions in systems of biological relevance. Research along these lines will aid and promote the design of synthetic polyelectrolytes for medical applications.

Preparation and biological imaging of fluorescent hydroxyapatite nanoparticles with poly(2-ethyl-2-oxazoline) through surface-initiated cationic ring-opening polymerization

Fluorescent hydroxyapatite (HAp) nanoparticles have received significant attention in biomedical fields due to their outstanding advantages, such as low immunogenicity, excellent biocompatibility and biodegradability. However, fluorescent HAp nanoparticles with well controlled size and morphology are coated with hydrophobic molecules and their biomedical applications are largely restricted by their poor dispersibility in physiological solutions. Therefore, surface modification of these hydrophobic fluorescent HAp nanoparticles to render them water dispersibility is of utmost importance for biomedical applications. In this work, we reported for the first time for preparation of water-dispersible hydrophilic fluorescent Eu³⁺-doped HAp nanoparticles (named as HAp-PEOTx) through the cationic ring-opening polymerization using hydrophilic and biocompatible 2-ethyl-2-oxazoline (EOTx) as the monomer. The characterization techniques, such as nuclear magnetic resonance (NMR) spectroscopy, transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) have been used to characterize these samples. Results confirmed that we could successfully obtain the hydrophilic fluorescent HAp-PEOTx composites through the strategy described above. These fluorescent HAp-PEOTx composites display great water dispersibility, unique fluorescent properties and excellent biocompatibility, making them promising for in vitro bioimaging applications.

A facile surface modification strategy for fabrication of fluorescent silica nanoparticles with the aggregation-induced emission dye through surface-initiated cationic ring opening polymerization

Fluorescent silica nanoparticles (FSNPs) have attracted great interest for potential applications in biological and biomedical fields because they possess higher fluorescence quantum yield and better fluorescence stability as comparison with small organic fluorescent molecules. The encapsulation of covalent linkage with fluorescent organic dyes or fluorescent metal complexes has demonstrated to be the commonly adopted strategies for fabrication of FSNPs previously. However, it is still challengeable to obtain FSNPs based polymer composites with intensive fluorescence and good water dispersibility through a one-pot surface modification strategy. In this paper, we developed a facile method to fabricate novel FSNPs based polymer composites (PhE@MSNs-PEtOx) through introducing the aggregation-induced emission (AIE) dye (PhE-OH) and poly(2-ethyl-2-oxazoline) (PEtOx) onto mesoporous silica nanoparticles (MSNs) based on cationic ring opening polymerization (CROP). The resulting PhE@MSNs-PEtOx composites possess strong fluorescence emission, excellent hydrophilicity and biocompatibility. These features make the final FSNPs based polymer composites great potential for biomedical applications. Taken together, we have developed for the first time that FSNPs based polymer composites can be facilely prepared through the one-pot introduction of AIE dyes and hydrophilic PEtOx on MSNs. Moreover, the novel FSNPs based composites could also be utilized for other biomedical applications considered their properties.

Translatable High Drug Loading Drug Delivery Systems Based on Biocompatible Polymer Nanocarriers

Most nanocarriers possess low drug loading, resulting in frequently repeated administration and thereby high cost and increased side effects. Furthermore, the characteristics of nanocarrier materials, especially the drug loading capacity, plays a vital role in the drug delivery efficacy. In this review, we focus on the readily translatable polymeric drug delivery systems with high drug loading, which are comprised of biocompatible polymers such as poly(ethylene glycol), poly( N-vinylpyrrolidone), polyoxazoline, natural proteins like albumin and casein, non-natural proteins such as recombinant elastin-like polypeptides, as well as nucleic acids. At the end of this review, applications of these polymeric nanocarriers on the delivery of proteins and gene drugs are also briefly discussed.

Full and partial hydrolysis of poly(2-oxazoline)s and the subsequent post-polymerization modification of the resulting polyethylenimine (co)polymers

This review discusses the full and partial hydrolysis of poly(2-oxazoline)s as well as the synthetic methods that have been reported to modify the resulting secondary amine groups.

Biocompatible Soft Nanoparticles with Multiple Morphologies Obtained from Nanoprecipitation of Amphiphilic Graft Copolymers in a Backbone-Selective Solvent

Stealth nanocarriers are a promising technology for the treatment of diseases. However, the preparation and characterization of well-defined soft nanoparticulate systems remain challenging. Here we describe a platform of amphiphilic graft copolymers leading to nanoparticles with multiple morphologies and the role of the hydrophilic backbone in their interaction with a model protein. The amphiphilic graft copolymers platform was composed of hydrophilic backbone poly(2-methyl-2-oxazoline-co-2-pentyl-2-oxazoline) (P(MeOx-co-PentOx)), prepared via cationic ring-opening polymerization. Hydrophobic poly(d,l-lactide) (PLA) chains were grafted on the backbone via Huisgen 1,3-dipolar cycloaddition. The "click" copper-catalyzed cycloaddition reactions of azides with alkynes (CuAAC) were successfully carried out, and a series of amphiphilic copolymers were prepared containing a backbone with a number-average molecular weight of 14.2 × 10³ g mol^-1 and different hydrophobic PLA grafts with various molecular weights (2.8 × 10³-12.4 × 10³ g mol^-1). These original architectures of copolymers, when nanoprecipitated in water, the backbone-selective solvent, allowed us to obtain various structures of nanoparticles with a hydrodynamic diameter in the range of 65-99 nm. More interestingly, a plurality of morphologies going from unilamellar, multilamellar, and large compound vesicles to core-shell nanoparticles and depending on the PLA molecular weights were evidenced by combining cryo-transmission electron microscopy (cryo-TEM) and small-angle neutron scattering (SANS) studies. A first evaluation of their stealthiness by studying the stability and the interaction of these nano-objects with a model protein revealed the role played by the P(MeOx-co-PentOx) in these interactions, demonstrating the utility of this amphiphilic graft copolymers platform with well-defined architectures for the design of nanocarriers in drug delivery applications.

Well-defined hyperstar copolymers based on a thiol–yne hyperbranched core and a poly(2-oxazoline) shell for biomedical applications

Well defined ‘hyperstar’ copolymers were synthesized by combining hyperbranched polymers produced by thiol–yne chemistry with poly(oxazoline)s.

Tailored and biodegradable poly(2-oxazoline) microbeads as 3D matrices for stem cell culture in regenerative therapies

We present the synthesis of hydrogel microbeads based on telechelic poly(2-oxazoline) (POx) crosslinkers and the methacrylate monomers (HEMA, METAC, SPMA) by inverse emulsion polymerization. While in batch experiments only irregular and ill-defined beads were obtained, the preparation in a microfluidic (MF) device resulted in highly defined hydrogel microbeads. Variation of the MF parameters allowed to control the microbead diameter from 50 to 500 μm. Microbead elasticity could be tuned from 2 to 20 kPa by the POx:monomer composition, the POx chain length, net charge of the hydrogel introduced via the monomer as well as by the organic content of the aqueous phase. The proliferations of human mesenchymal stem cells (hMSCs) on the microbeads were studied. While neutral, hydrophilic POx-PHEMA beads were bioinert, excessive colonization of hMSCs on charged POx-PMETAC and POx-PSPMA was observed. The number of proliferated cells scaled roughly linear with the METAC or SPMA comonomer content. Additional collagen I coating further improved the stem cell proliferation. Finally, a first POx-based system for the preparation of biodegradable hydrogel microcarriers is described and evaluated for stem cell culturing.

Ionizing radiation-engineered nanogels as insulin nanocarriers for the development of a new strategy for the treatment of Alzheimer's disease

A growing body of evidence shows the protective role of insulin in Alzheimer's disease (AD). A nanogel system (NG) to deliver insulin to the brain, as a tool for the development of a new therapy for Alzheimer's Disease (AD), is designed and synthetized. A carboxyl-functionalized poly(N-vinyl pyrrolidone) nanogel system produced by ionizing radiation is chosen as substrate for the covalent attachment of insulin or fluorescent molecules relevant for its characterization. Biocompatibility and hemocompatibility of the naked carrier is demonstrated. The insulin conjugated to the NG (NG-In) is protected by protease degradation and able to bind to insulin receptor (IR), as demonstrated by immunofluorescence measurements showing colocalization of NG-In(FITC) with IR. Moreover, after binding to the receptor, NG-In is able to trigger insulin signaling via AKT activation. Neuroprotection of NG-In against dysfunction induced by amyloid β (Aβ), a peptide mainly involved in AD, is verified. Finally, the potential of NG-In to be efficiently transported across the Blood Brain Barrier (BBB) is demonstrated. All together these results indicate that the synthesized NG-In is a suitable vehicle system for insulin deliver in biomedicine and a very promising tool to develop new therapies for neurodegenerative diseases.

Core cross-linked nanogels based on the self-assembly of double hydrophilic poly(2-oxazoline) block copolymers

The synthesis of poly(2-oxazoline)-based block copolymers consisting of a cationic and a hydrophilic segment is described.