Overcoming drug resistance with on-demand charged thermoresponsive dendritic nanogels

Nanogels: Smart tools to enlarge the therapeutic window of gene therapy

Gene therapy can potentially treat a great number of diseases, from cancer to rare genetic disorders. Very recently, the development and emergency approval of nucleic acid-based COVID-19 vaccines confirmed its strength and versatility. However, gene therapy encounters limitations due to the lack of suitable carriers to vectorize therapeutic genetic material inside target cells. Nanogels are highly hydrated nano-size crosslinked polymeric networks that have been used in many biomedical applications, from drug delivery to tissue engineering and diagnostics. Due to their easy production, tunability, and swelling properties they have called the attention as promising vectors for gene delivery. In this review, nanogels are discussed as vectors for nucleic acid delivery aiming to enlarge gene therapy's therapeutic window. Recent works highlighting the optimization of inherent transfection efficiency and biocompatibility are reviewed here. The importance of the monomer choice, along with the internal structure, surface decoration, and responsive features are outlined for the different transfection modalities. The possible sources of toxicological endpoints in nanogels are analyzed, and the strategies to limit them are compared. Finally, perspectives are discussed to identify the remining challenges for the nanogels before their translation to the market as transfection agents.

Evolution of Hybrid Hydrogels: Next-Generation Biomaterials for Drug Delivery and Tissue Engineering

Hydrogels, being hydrophilic polymer networks capable of absorbing and retaining aqueous fluids, hold significant promise in biomedical applications owing to their high water content, permeability, and structural similarity to the extracellular matrix. Recent chemical advancements have bolstered their versatility, facilitating the integration of the molecules guiding cellular activities and enabling their controlled activation under time constraints. However, conventional synthetic hydrogels suffer from inherent weaknesses such as heterogeneity and network imperfections, which adversely affect their mechanical properties, diffusion rates, and biological activity. In response to these challenges, hybrid hydrogels have emerged, aiming to enhance their strength, drug release efficiency, and therapeutic effectiveness. These hybrid hydrogels, featuring improved formulations, are tailored for controlled drug release and tissue regeneration across both soft and hard tissues. The scientific community has increasingly recognized the versatile characteristics of hybrid hydrogels, particularly in the biomedical sector. This comprehensive review delves into recent advancements in hybrid hydrogel systems, covering the diverse types, modification strategies, and the integration of nano/microstructures. The discussion includes innovative fabrication techniques such as click reactions, 3D printing, and photopatterning alongside the elucidation of the release mechanisms of bioactive molecules. By addressing challenges, the review underscores diverse biomedical applications and envisages a promising future for hybrid hydrogels across various domains in the biomedical field.

Weaving the next generation of (bio)materials: Semi-interpenetrated and interpenetrated polymeric networks for biomedical applications

Advances in polymer science have led to the development of semi-interpenetrated and interpenetrated networks (SIPN/IPN). The interpenetration procedure allows enhancing several important properties of a polymeric material, including mechanical properties, swelling capability, stimulus-sensitive response, and biological performance, among others. More interestingly, the interpenetration (or semi-interpenetration) can be achieved independent of the material size, that is at the macroscopic, microscopic, or nanometric scale. SIPN/IPN have been used for a wide range of applications, especially in the biomedical field, including tissue engineering, delivery of chemical compounds or biological macromolecules, and multifunctional systems as theragnostic platforms. In the last years, this fascinating field has gained a great interest in the area of polymers for therapeutics; therefore, a comprehensive revision of the topic is timely. In this review, we describe in detail the most relevant synthetic approaches to fabricate polymeric IPN and SIPN, ranging from nanoscale to macroscale. The advantages of typical synthetic methods are analyzed, as well as novel and promising trends in the field of advanced material fabrication. Furthermore, the characterization techniques employed for these materials are summarized from physicochemical, thermal, mechanical, and biological perspectives. The applications of novel (semi-)interpenetrated structures are discussed with a focus on drug delivery, tissue engineering, and regenerative medicine, as well as combinations thereof.

Physically stimulus-responsive nanoparticles for therapy and diagnosis

Nanoparticles offer numerous advantages in various fields of science, particularly in medicine. Over recent years, the use of nanoparticles in disease diagnosis and treatments has increased dramatically by the development of stimuli-responsive nano-systems, which can respond to internal or external stimuli. In the last 10 years, many preclinical studies were performed on physically triggered nano-systems to develop and optimize stable, precise, and selective therapeutic or diagnostic agents. In this regard, the systems must meet the requirements of efficacy, toxicity, pharmacokinetics, and safety before clinical investigation. Several undesired aspects need to be addressed to successfully translate these physical stimuli-responsive nano-systems, as biomaterials, into clinical practice. These have to be commonly taken into account when developing physically triggered systems; thus, also applicable for nano-systems based on nanomaterials. This review focuses on physically triggered nano-systems (PTNSs), with diagnostic or therapeutic and theranostic applications. Several types of physically triggered nano-systems based on polymeric micelles and hydrogels, mesoporous silica, and magnets are reviewed and discussed in various aspects.

PNIPAM/Hexakis as a thermosensitive drug delivery system for biomedical and pharmaceutical applications

Many technologies ranging from drug delivery approaches to tissue engineering purposes are beginning to benefit from the unique ability of "smart polymers." As a special case, thermo-sensitive hydrogels have great potential, e.g. in actuators, microfluidics, sensors, or drug delivery systems. Here, the loading of Doxorubicin (DOX) with novel thermo-sensitive polymer N-isopropyl acrylamide (PNIPAM) and its copolymers are investigated in order to increase the Doxorubicin's drug efficacy on the targeted tumor site. Therefore, a rational design accurate based on the use of classical molecular dynamics (MD) and well-tempered metadynamics simulations allows for predicting and understanding the behavior of thermo-responsive polymers in the loading of DOX on Hexakis nano-channel at 298 and 320 K. Furthermore, this work investigates the efficacy of this drug carrier for the release of DOX in response to stimuli like variations in temperature and changes in the physiological pH. The study concludes that the Hexakis-polymer composite is capable of adsorbing the DOX at neutral pH and by increasing the temperature of the simulated systems from 298 to 320 K, the strength of intermolecular attraction decreases. In addition, the obtained results of MD simulation revealed that the dominant interaction between DOX and Hexakis in the DOX/polymer/Hexakis systems is the Lennard-Jones (LJ) term due to the formation of strong π-π interaction between the adsorbate and substrate surface. Obtained results show that a higher aggregation of DMA chains around the Hexakis and the formation of stronger bonds with DOX. The results of the well-tempered metadynamics simulations revealed that the order of insertion of drug and polymer into the system is a determining factor on the fate of the adsorption/desorption process. Overall, our results explain the temperature-dependent behavior of the PNIPAM polymers and the suitability of the polymer-Hexakis carrier for Doxorubicin delivery.

Polyglycerols as Multi-Functional Platforms: Synthesis and Biomedical Applications

The remarkable and unique characteristics of polyglycerols (PG) have made them an attractive candidate for many applications in the biomedical and pharmaceutical fields. The presence of multiple hydroxy groups on the flexible polyether backbone not only enables the further modification of the PG structure but also makes the polymer highly water-soluble and results in excellent biocompatibility. In this review, the polymerization routes leading to PG with different architectures are discussed. Moreover, we discuss the role of these polymers in different biomedical applications such as drug delivery systems, protein conjugation, and surface modification.

Design and Testing of Efficient Mucus-Penetrating Nanogels-Pitfalls of Preclinical Testing and Lessons Learned

Mucosal surfaces pose a challenging environment for efficient drug delivery. Various delivery strategies such as nanoparticles have been employed so far; yet, still yielding limited success. To address the need of efficient transmucosal drug delivery, this report presents the synthesis of novel disulfide-containing dendritic polyglycerol (dPG)-based nanogels and their preclinical testing. A bifunctional disulfide-containing linker is coupled to dPG to act as a macromolecular crosslinker for poly-N-isopropylacrylamide (PNIPAM) and poly-N-isopropylmethacrylamide (PNIPMAM) in a precipitation polymerization process. A systematic analysis of the polymerization reveals the importance of a careful polymer choice to yield mucus-degradable nanogels with diameters between 100 and 200 nm, low polydispersity, and intact disulfide linkers. Absorption studies in porcine intestinal tissue and human bronchial epithelial models demonstrate that disulfide-containing nanogels are highly efficient in overcoming mucosal barriers. The nanogels efficiently degrade and deliver the anti-inflammatory biomacromolecule etanercept into epithelial tissues yielding local anti-inflammatory effects. Over the course of this work, several problems are encountered due to a limited availability of valid test systems for mucosal drug-delivery systems. Hence, this study also emphasizes how critical a combined and multifaceted approach is for the preclinical testing of mucosal drug-delivery systems, discusses potential pitfalls, and provides suggestions for solutions.

Protein corona formation and its influence on biomimetic magnetite nanoparticles

Biomimetic magnetite nanoparticles (BMNPs) synthesized in the presence of MamC, a magnetosome-associated protein from Magnetoccus marinus MC-1, have gained interest for biomedical applications because of their unique magnetic properties. However, their behavior in biological systems, like their interaction with proteins, still has to be evaluated prior to their use in clinics. In this study, doxorubicin (DOXO) as a model drug was adsorbed onto BMNPs to form nanoassemblies. These were incubated with human plasma to trigger protein corona (PC) formation. Proteins from the human plasma stably attached to either BMNPs or DOXO-BMNP nanoassemblies. In particular, fibrinogen was detected as the main component in the PC of DOXO-BMNPs that potentially provides advantages, e.g. protecting the particles from phagocytosis, thus prolonging their circulation time. Adsorption of PC to the BMNPs did not alter their magnetic properties but improved their colloidal stability, thus reducing their toxicity in human macrophages. In addition, PC formation enhanced cellular internalization and did not interfere with DOXO activity. Overall, our data indicate that the adsorption of PC onto DOXO-BMNPs in biological environment even increases their efficiency as drug carrier systems.

Revealing the NIR-triggered chemotherapy therapeutic window of magnetic and thermoresponsive nanogels

The combination of magnetic nanoparticles and thermoresponsive nanogels represents an appealing strategy for the development of theranostic probes. These hybrid nanocarriers present several advantages such as outstanding properties for guided therapy, magnetic resonance imaging, and triggered release of encapsulated cargoes. Most magnetic thermoresponsive nanogels are built with strategies that comprise a physical interaction of particles with the polymeric network or the covalent attachment of a single particle to the linear polymer. Herein, we report a facile synthetic approach for the synthesis of magnetic and thermoresponsive nanogels that allows the controlled incorporation of multiple superparamagnetic inorganic cores as covalent cross-linkers. An ultrasonication-assisted precipitation-polymerization afforded nanogels with sizes in the nanometric range and similar magnetization and light transduction properties compared to the discrete magnetic nanoparticles. The theranostic capability of these nanocarriers was further investigated both in vitro and in vivo. In vivo experiments demonstrated the capacity of these materials as nanocarriers for near-infrared (NIR) triggered chemotherapy and highlighted the relevance of the correct concentration/dose in this antitumoral modality to achieve a superior therapeutic efficacy.

Effect of conducting/thermoresponsive polymer ratio on multitasking nanogels

Semi-interpenetrated nanogels (NGs) able to release and sense diclofenac (DIC) have been designed to act as photothermal agents with the possibility to ablate cancer cells using mild-temperatures (<45 °C). Combining mild heat treatments with simultaneous chemotherapy appears as a very promising therapeutic strategy to avoid heat resistance or damaging the surrounding tissues. Particularly, NGs consisted on a poly(N-isopropylacrylamide) (PNIPAM) and dendritic polyglycerol (dPG) mesh containing a semi-interpenetrating network (SIPN) of poly(hydroxymethyl 3,4-ethylenedioxythiophene) (PHMeEDOT). The PHMeEDOT acted as photothermal and conducting agent, while PNIPAM-dPG NG provided thermoresponsivity and acted as stabilizer. We studied how semi-interpenetration modified the physicochemical characteristics of the thermoresponsive SIPN NGs and selected the best condition to generate a multifunctional photothermal agent. The thermoswitchable conductiveness of the multifunctional NGs and the redox activity of DIC could be utilized for its electrochemical detection. Besides, as proof of the therapeutic concept, we investigated the combinatorial effect of photothermal therapy (PTT) and DIC treatment using the HeLa cancer cell line in vitro. Within 15 min NIR irradiation without surpassing 45 °C we were able to kill 95% of the cells, demonstrating the potential of SIPN NGs as drug carriers, sensors and agents for mild PTT.

Amphiphilic nanogels: influence of surface hydrophobicity on protein corona, biocompatibility and cellular uptake

BACKGROUND AND PURPOSE

Nanogels (NGs) are promising drug delivery tools but are typically limited to hydrophilic drugs. Many potential new drugs are hydrophobic. Our study systematically investigates amphiphilic NGs with varying hydrophobicity, but similar colloidal features to ensure comparability. The amphiphilic NGs used in this experiment consist of a hydrophilic polymer network with randomly distributed hydrophobic groups. For the synthesis we used a new synthetic platform approach. Their amphiphilic character allows the encapsulation of hydrophobic drugs. Importantly, the hydrophilic/hydrophobic balance determines drug loading and biological interactions. In particular, protein adsorption to NG surfaces is dependent on hydrophobicity and critically determines circulation time. Our study investigates how network hydrophobicity influences protein binding, biocompatibility and cellular uptake.

METHODS

Biocompatibility of the NGs was examined by WST-1 assay in monocytic-like THP-1 cells. Serum protein corona formation was investigated using dynamic light scattering and two-dimensional gel electrophoresis. Proteins were identified by liquid chromatography-tandem mass spectrometry. In addition, cellular uptake was analyzed via flow cytometry.

RESULTS

All NGs were highly biocompatible. The protein binding patterns for the two most hydrophobic NGs were very similar to each other but clearly different from the hydrophilic ones. Overall, protein binding was increased with increasing hydrophobicity, resulting in increased cellular uptake.

CONCLUSION

Our study supports the establishment of structure-property relationships and contributes to the accurate balance between maximum loading capacity with low protein binding, optimal biological half-life and good biocompatibility. This is an important step to derive design principles of amphiphilic NGs to be applied as drug delivery vehicles.

Recent Advances in Degradable Hybrids of Biomolecules and NGs for Targeted Delivery

Recently, the fast development of hybrid nanogels dedicated to various applications has been seen. In this context, nanogels incorporating biomolecules into their nanonetworks are promising innovative carriers that gain great potential in biomedical applications. Hybrid nanogels containing various types of biomolecules are exclusively designed for: improved and controlled release of drugs, targeted delivery, improvement of biocompatibility, and overcoming of immunological response and cell self-defense. This review provides recent advances in this rapidly developing field and concentrates on: (1) the key physical consequences of using hybrid nanogels and introduction of biomolecules; (2) the construction and functionalization of degradable hybrid nanogels; (3) the advantages of hybrid nanogels in controlled and targeted delivery; and (4) the analysis of the specificity of drug release mechanisms in hybrid nanogels. The limitations and future directions of hybrid nanogels in targeted specific- and real-time delivery are also discussed.

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.

Thermoresponsive nanogels with film-forming ability

A one pot semibatch method was proposed for synthesizing poly(N-vinylcaprolactam)-based nanogels with particle coalescence ability.

Responsive Nanogels for Anti-cancer Therapy

Nanogels (or nano-sized hydrogels) have been extensively investigated as an effective drug delivery system due to their various advantageous properties. Among them, stimuli responsive ‘smart’ nanogels, which have the ability to respond to various external stimuli, such as pH, redox, temperature, enzymes, and light, are the most attractive in the area of controlled anti-cancer drug delivery. In this book chapter, we review and discuss recent progress in the synthesis and applications of polymer-based stimuli-responsive nanogels for anti-cancer therapy and their future prospects.

Rational design of dendritic thermoresponsive nanogels that undergo phase transition under endolysosomal conditions

In the last few decades, the synthesis of nanodevices has become a very active research field with many applications in biochemistry, biotechnology, and biomedicine. However, there is still a great need for smart nanomaterials that can sense and respond to environmental changes. Temperature- and pH-responsive nanogels (NGs), which are prepared in a one-pot synthesis from N-isopropylacrylamide (NiPAm) and a Newkome-type dendron (ABC) bearing carboxylic acid groups, are being investigated as multi-responsive drug carriers. As a result, NGs have been developed that are able to undergo a reversible volume phase transition triggered by acidic conditions, like the ones found in endolysosomal compartments of cancer cells. The NGs have been thoroughly characterized using dynamic light scattering and spectroscopies, such as infrared, nuclear magnetic resonance, UV-visible, and stimulated Raman. Strong hydrogen bonds have been detected when the ABC moieties are deprotonated, which has led to changes in the transition temperatures of the NGs and a reversible, pH-dependent aggregation. This pH-dependent phase change was exploited for the effective encapsulation and sustained release of the anticancer drug cisplatin and resulted in a faster release of the drug at endolysosomal pH values. The cisplatin-loaded NGs have exhibited high toxicities against A549 cells in vitro, while the unloaded NGs have been found to be not cytotoxic and hemocompatible.