Poly(PS-b-DMA) micelles for reactive oxygen species triggered drug release

Precise modulation and use of reactive oxygen species for immunotherapy

Reactive oxygen species (ROS) play an important role in regulating the immune system by affecting pathogens, cancer cells, and immune cells. Recent advances in biomaterials have leveraged this mechanism to precisely modulate ROS levels in target tissues for improving the effectiveness of immunotherapies in infectious diseases, cancer, and autoimmune diseases. Moreover, ROS-responsive biomaterials can trigger the release of immunotherapeutics and provide tunable release kinetics, which can further boost their efficacy. This review will discuss the latest biomaterial-based approaches for both precise modulation of ROS levels and using ROS as a stimulus to control the release kinetics of immunotherapeutics. Finally, we will discuss the existing challenges and potential solutions for clinical translation of ROS-modulating and ROS-responsive approaches for immunotherapy, and provide an outlook for future research.

Cleavage and Noncleavage Chemistry in Reactive Oxygen Species (ROS)-Responsive Materials for Smart Drug Delivery

The design and development of advanced drug delivery systems targeting reactive oxygen species (ROS) have gained significant interest in recent years for treating various diseases, including cancer, psychiatric diseases, cardiovascular diseases, neurological diseases, metabolic diseases, and chronic inflammations. Integrating specific chemical bonds capable of effectively responding to ROS and triggering drug release into the delivery system is crucial. In this Review, we discuss commonly used conjugation linkers (chemical bonds) and categorize them into two groups: cleavable linkers and noncleavable linkers. Our goal is to clarify their unique drug release mechanisms from a chemical perspective and provide practical organic synthesis approaches for their efficient production. We showcase numerous significant examples to demonstrate their synthesis routes and diverse applications. Ultimately, we strive to present a comprehensive overview of cleavage and noncleavage chemistry, offering insights into the development of smart drug delivery systems that respond to ROS.

Self-Report Amphiphilic Polymer-Based Drug Delivery System with ROS-Triggered Drug Release for Osteoarthritis Therapy

The development of drug delivery systems with real-time cargo release monitoring capabilities is imperative for optimizing nanomedicine performance. Herein, we report an innovative self-reporting drug delivery platform based on a ROS-responsive random copolymer (P1) capable of visualizing cargo release kinetics via the activation of an integrated fluorophore. P1 was synthesized by copolymerization of pinacol boronate, PEG, and naphthalimide monomers to impart ROS-sensitivity, hydrophilicity, and fluorescence signaling, respectively. Detailed characterization verified that P1 self-assembles into 11 nm micelles with 10 μg mL-1 CMC and can encapsulate hydrophobic curcumin with 79% efficiency. Fluorescence assays demonstrated H2O2-triggered disassembly and curcumin release with concurrent polymer fluorescence turn-on. Both in vitro and in vivo studies validated the real-time visualization of drug release and ROS scavenging, as well as the therapeutic effect on osteoarthritis (OA). Overall, this nanotheranostic polymeric micelle system enables quantitative monitoring of drug release kinetics for enhanced treatment optimization across oxidative stress-related diseases.

A guide to modern methods for poly(thio)ether synthesis using Earth-abundant metals

Polyethers and polythioethers have a long and storied history dating back to the start of polymer science as a distinct field. As such, these materials have been utilized in a wide range of commercial applications and fundamental studies. The breadth of their material properties and the contexts in which they are applied is ultimately owed to their diverse monomer pre-cursors, epoxides and thiiranes, respectively. The facile polymerization of these monomers, both historically and contemporaneously, across academia and industry, has occurred through the use of Earth-abundant metals as catalysts and/or initiators. Despite this, polymerization methods for these monomers are underutilized compared to other monomer classes like cyclic olefins, vinyls, and (meth)acrylates. We feel a focused review that clearly outlines the benefits and shortcomings of extant synthetic methods for poly(thio)ethers along with their proposed mechanisms and quirks will help facilitate the utilization of these methods and by extension the unique polymer materials they create. Therefore, this Feature Article briefly describes the applications of poly(thio)ethers before discussing the feature-set of each poly(thio)ether synthetic method and qualitatively scoring them on relevant metrics (e.g., ease-of-use, molecular weight control, etc.) to help would-be poly(thio)ether-makers find an appropriate synthetic approach. The article is concluded with a look ahead at the future of poly(thio)ether synthesis with Earth-abundant metals.

Dual Thermal- and Oxidation-Responsive Polymers Synthesized by a Sequential ROP-to-RAFT Procedure Inherently Temper Neuroinflammation

This study is about multiple responsiveness in biomedical materials. This typically implies "orthogonality" (i.e., one response does not affect the other) or synergy (i.e., one increases efficacy or selectivity of the other), but an antagonist effect between responses may also occur. Here, we describe a family of very well-defined amphiphilic and micelle-forming block copolymers, which show both oxidative and temperature responses. They are produced via successive anionic ring-opening polymerization of episulfides and RAFT polymerization of dialkylacrylamides and differ only in the ratio between inert (N,N-dimethylacrylamide, DMA) and temperature-sensitive (N,N-diethylacrylamide, DEA) units. By scavenging Reactive Oxygen Species (ROS), these polymers are anti-inflammatory; through temperature responsiveness, they can macroscopically aggregate, which may allow them to form depots upon injection. The localization of the anti-inflammatory action is an example of synergy. An extensive evaluation of toxicity and anti-inflammatory effects on in vitro models, including BV2 microglia, C8D30 astrocytes and primary neurons, shows a link between capacity of aggregation and detrimental effects on viability which, albeit mild, can hinder the anti-inflammatory potential (antagonist action). Although limited in breadth (e.g., only in vitro models and only DEA as a temperature-responsive unit), this study suggests that single-responsive controls should be used to allow for a precise assessment of the (synergic or antagonist) potential of double-responsive systems.

Hybrid Shear-thinning Hydrogel Integrating Hyaluronic Acid with ROS-Responsive Nanoparticles

Nanoparticle (NP) supra-assembly offers unique opportunities to tune macroscopic hydrogels' mechanical strength, material degradation, and drug delivery properties. Here, synthetic, reactive oxygen species (ROS)-responsive NPs are physically crosslinked with hyaluronic acid (HA) through guest-host chemistry to create shear-thinning NP/HA hydrogels. A library of triblock copolymers composed of poly(propylene sulfide)-bl-poly(N,N-dimethylacrylamide)-bl-poly(N,N-dimethylacrylamide-co-N-(1-adamantyl)acrylamide) are synthesized with varied triblock architectures and adamantane grafting densities and then self-assembled into NPs displaying adamantane on their corona. Self-assembled NPs are mixed with β-cyclodextrin grafted HA to yield eighteen NP/HA hydrogel formulations. The NP/HA hydrogel platform demonstrates superior mechanical strength to HA-only hydrogels, susceptibility to oxidative/enzymatic degradation, and inherent cell-protective, antioxidant function. The performance of NP/HA hydrogels is shown to be affected by triblock architecture, guest/host grafting densities, and HA composition. In particular, the length of the hydrophilic second block and adamantane grafting density of self-assembled NPs significantly impacts hydrogel mechanical properties and shear-thinning behavior, while ROS-reactivity of poly(propylene sulfide) protects cells from cytotoxic ROS and reduces oxidative degradation of HA compared to HA-only hydrogels. This work provides insight into polymer structure-function considerations for designing hybrid NP/HA hydrogels and identifies antioxidant, shear-thinning hydrogels as promising injectable delivery platforms for small molecule drugs and therapeutic cells.

Hydrazone-Based Amphiphilic Brush Polymer for Fast Endocytosis and ROS-Active Drug Release

Due to the high reactivity of reactive oxygen species (ROS), it is essential to sweep them away in time. In this study, ClO^--responsible amphiphilic brush polymers were prepared by free radical polymerization using two monomers consisting of polyethylene glycol as the hydrophilic part, and an alkyl chain connected by hydrazone as the hydrophobic part. The macromolecules assemble into particles with nanoscaled dimensions in a neutral buffer, which ensures quick cellular internalization. The polymer has a low critical micellization concentration and can encapsulate hydrophobic drug molecules up to 19% wt. The micelles formed by the polymer disassemble in a ClO^--rich environment and release 80% of their cargo within 2 h, which possesses a faster release rate compared to the previous systems. The relatively small size and the quick response of hydrazone toward ClO^- ensure a quick uptake and elimination of ROS in vitro and in vivo.

ROS-Responsive Glycopolymeric Nanoparticles for Enhanced Drug Delivery to Macrophages

Macrophages play a diverse, key role in many pathologies, including inflammatory diseases, cardiovascular diseases, and cancer. However, many therapeutic strategies targeting macrophages suffer from systemic off-target toxicity resulting in notoriously narrow therapeutic windows. To address this shortcoming, the development of poly(propylene sulfide)-b-poly(methacrylamidoglucopyranose) [PPS-b-PMAG] diblock copolymer-based nanoparticles (PMAG NPs) capable of targeting macrophages and releasing drug in the presence of reactive oxygen species (ROS) is reported. PMAG NPs have desirable physicochemical properties for systemic drug delivery, including slightly negative surface charge, ≈100 nm diameter, and hemo-compatibility. Additionally, due to the presence of PPS in the NP core, PMAG NPs release drug cargo preferentially in the presence of ROS. Importantly, PMAG NPs display high cytocompatibility and are taken up by macrophages in cell culture at a rate ≈18-fold higher than PEGMA NPs-NPs composed of PPS-b-poly(oligoethylene glycol methacrylate). Computational studies indicate that PMAG NPs likely bind with glucose transporters such as GLUT 1/3 on the macrophage cell surface to facilitate high levels of internalization. Collectively, this study introduces glycopolymeric NPs that are uniquely capable of both receptor-ligand targeting to macrophages and ROS-dependent drug release and that can be useful in many immunotherapeutic settings.

Temporally programmed polymer - solvent interactions using a chemical reaction network

Out of equilibrium operation of chemical reaction networks (CRNs) enables artificial materials to autonomously respond to their environment by activation and deactivation of intermolecular interactions. Generally, their activation can be driven by various chemical conversions, yet their deactivation to non-interacting building blocks remains largely limited to hydrolysis and internal pH change. To achieve control over deactivation, we present a new, modular CRN that enables reversible formation of positive charges on a tertiary amine substrate, which are removed using nucleophilic signals that control the deactivation kinetics. The modular nature of the CRN enables incorporation in diverse polymer materials, leading to a temporally programmed transition from collapsed and hydrophobic to solvated, hydrophilic polymer chains by controlling polymer-solvent interactions. Depending on the layout of the CRN, we can create stimuli-responsive or autonomously responding materials. This concept will not only offer new opportunities in molecular cargo delivery but also pave the way for next-generation interactive materials.

The potential of oxygen and nitrogen species-regulating drug delivery systems in medicine

The focus of this review is to present most significant advances in biomaterials used for control of reactive oxygen/nitrogen species (ROS/RNS, RONS) in medicine. A summary of the main pathways of ROS production and the main pathways of RNS production are shown herein. Although the physiological and pathological roles of RONS have been known for at least 2decades, the potential of their control in management of disease went unappreciated. Recently, advances in the field of biochemical engineering and materials science have allowed for development of RONS-responsive biomaterials for biomedical applications, which aim to control and change levels of reactive species in tissue microenvironments. These materials utilize polymers, inorganic nanoparticles (NPs), or organic-inorganic hybrids. Thus, biomaterials like hydrogels have been developed to promote tissue regeneration by actively scavenging and reducing RONS levels. Their promising utility comes from thermo- and RONS-sensitivity, stability as a delivery-medium, ease for incorporation into other materials and facility for injection. Their particular attractiveness is attributed to drug release realized in targeted tissues and cells with elevated RONS levels, which leads to enhanced treatment outcomes and reduced adverse effects. The mechanism of their action depends on the functional groups employed and their response to oxidation, and may be based on solubility changes or cleavage of chemical bonds. When talking about antioxidants, one should also mention oxidative stress, which we call the imbalance between antioxidants and reactive oxygen species, which occurs due to a deficiency of endogenous antioxidants and a low supply of exogenous antioxidants. This study is a review of articles in English from the databases PubMed and Web of Science retrieved by applying the search terms “Oxygen Species, Nitrogen Species and biomaterials” from 1996 to 2021.

ROS-responsive copolymer micelles for inflammation triggered delivery of ibuprofen

Non-steroidal anti-inflammatory drugs (NSAIDs) are commonly used for the treatment of pain, inflammation and fever. However, most NSAIDs are poorly water soluble, making it difficult to be administered thus high doses are required to reach the intended therapeutic effect, resulting in associated side effects. In this study, ROS-responsive micellar systems based on a block copolymer consisting of methylpropyl thioether (MTPA) and N'N-dimethylacrylamide was developed and loaded with ibuprofen (IBU). Using lipopolysaccharide activated RAW 264.7 macrophage like cells, we demonstrated that IBU was released from the copolymer, specifically in the presence of ROS. Interestingly, IBU encapsulated in ROS-responsive nanoparticles exhibited greater anti-inflammatory potency compared to its free form. The work highlights the potential of the ROS-responsive micellar system developed in this work to be used as carrier of NSAIDs for the treatment of relevant inflammatory conditions.

Intranasal Administration of Self-Oriented Nanocarriers Based on Therapeutic Exosomes for Synergistic Treatment of Parkinson's Disease

The treatment of Parkinson's disease (PD) has been hindered by the complex pathologies and multiple membrane barriers during drug delivery. Although exosomes derived from mesenchymal stem cells (MSCs) have great potential for PD, MSC-derived exosomes alone could not fully meet the therapeutic requirements due to their limitation in therapy and delivery. Here, we develop a self-oriented nanocarrier called PR-EXO/PP@Cur that combines therapeutic MSC-derived exosomes with curcumin. PR-EXO/PP@Cur can be self-oriented across the multiple membrane barriers and directly release drugs into the cytoplasm of target cells after intranasal administration. With enhanced accumulation of drugs in the action site, PR-EXO/PP@Cur achieves three-pronged synergistic treatment to deal with the complex pathologies of PD by reducing α-synuclein aggregates, promoting neuron function recovery, and alleviating the neuroinflammation. After treatment with PR-EXO/PP@Cur, the movement and coordination ability of PD model mice are significantly improved. These results show that PR-EXO/PP@Cur has great prospects in treatment of PD or other neurodegenerative diseases.

ROS-Sensitive Polymer Micelles for Selective Degradation in Primary Human Monocytes from Patients with Active IBD

Inflammatory bowel disease (IBD) is characterized by increased levels of reactive oxygen species (ROS) in inflamed areas of the gastrointestinal tract and in circulating immune cells, providing novel opportunities for targeted drug delivery. In recent experiments, oxidation-responsive polymeric nanostructures selectively degrade in the presence of H₂ O₂ . Based on these results, hypothesize that such degradation process can be triggered in a similar way by the incubation with stimulated monocytes isolated from patients with IBD. A first indication is given by a significant correlation between excessive ROS and degradation of micelles in monocytes isolated from healthy individuals after phorbol 12-myristate 13-acetate (PMA) stimulation. But even if the ROS-sensitive micelles are incubated with non-stimulated monocytes from patients with active IBD, a spontaneous degradation is observed in contrast to micelles incubated with monocytes from healthy donors. The findings indicate that the thioether-based micelles are indeed promising for selective drug release in the presence of activated immune cells.

Thioanisole ester based logic gate cascade to control ROS-triggered micellar degradation

Thioanisole ester polymer side chains hydrolyze exclusively upon thioether oxidation, showing logic gate response. ROS-induced ester hydrolysis on the hydrophobic domain leads to nanocarrier disassembly with potential for targeted drug release.

Size-Adjustable Nano-Drug Delivery Systems for Enhanced Tumor Retention and Penetration

Over the past decades, nano-drug delivery systems have shown great potential in improving tumor treatment. And the controllability and design flexibility of nanoparticles endow them a broad development space. The particle size is one of the most important factors affecting the potency of nano-drug delivery systems. Large-size (100–200 nm) nanoparticles are more conducive to long circulation and tumor retention, but have poor tumor penetration; small-size (<50 nm) nanoparticles can deeply penetrate tumor but are easily cleared. Most of the current fixed-size nanoparticles are difficult to balance the retention and penetration, while the proposal of size-adjustable nano-drug delivery systems offers a solution to this paradox. Many endogenous and exogenous stimuli, such as acidic pH, upregulated enzymes, temperature, light, catalysts, redox conditions, and reactive oxygen species, can trigger the in situ transformation of nanoparticles based on protonation, hydrolysis, click reaction, phase transition, photoisomerization, redox reaction, etc. In this review, we summarize the principles and applications of stimuli-responsive size-adjustable strategies, including size-enlargement strategies and size-shrinkage strategies. We also propose the challenges faced by size-adjustable nano-drug delivery systems, hoping to promote the development of this strategy.

Thioether-Based Polymeric Micelles with Fine-Tuned Oxidation Sensitivities for Chemotherapeutic Drug Delivery

Oxidation-sensitive drug delivery systems (DDSs) have attracted attention due to the potential to improve efficacy and safety of chemotherapeutics. These systems are designed to release the payload in response to oxidative stress conditions, which are associated with many types of cancer. Despite extensive research on the development of oxidation-sensitive DDS, the lack of selectivity toward cancer cells over healthy cells remains a challenge. Here, we report the design and characterization of polymeric micelles containing thioether groups with varying oxidation sensitivities within the micellar core, which become hydrophilic upon thioether oxidation, leading to destabilization of the micellar structure. We first used the thioether model compounds, 3-methylthiopropylamide (TPAM), thiomorpholine amide (TMAM), and 4-(methylthio)benzylamide (TPhAM) to investigate the effect of the chemical structures of the thioethers on the oxidation by hydrogen peroxide (H₂O₂). TPAM shows the fastest oxidation, followed by TMAM and TPhAM, showing that the oxidation reaction of thioethers can be modulated by changing the substituent groups bound to the sulfur atom. We next prepared micelles containing these different thioether groups within the core (TP, TM, and TPh micelles). The micelles containing the thioether groups with a higher oxidation sensitivity were destabilized by H₂O₂ at a lower concentration. Micelle destabilization was also tested in human liver cancer (HepG2) cells and human umbilical vein endothelial cells (HUVECs). The TP micelles having the highest oxidation sensitivity were destabilized in both HepG2 cells and HUVECs, while the TPh micelles, which showed the lowest reactivity toward H₂O₂, were stable in these cell lines. The TM micelles possessing a moderate oxidation sensitivity were destabilized in HepG2 cells but were stable in HUVECs. Furthermore, the micelles were loaded with doxorubicin (Dox) to evaluate their potential in drug delivery applications. Among the micelles, the TM micelles loaded with Dox showed the enhanced relative toxicity in HepG2 cells over HUVECs. Therefore, our approach to fine-tune the oxidation sensitivity of the micelles has potential for improving therapeutic efficacy and safety of drugs in cancer treatment.

Oxidation-Responsive, Tunable Growth Factor Delivery from Polyelectrolyte-Coated Implants

Polyelectrolyte multilayer (PEM) coatings, constructed on the surfaces of tissue engineering scaffolds using layer-by-layer assembly (LbL), promote sustained release of therapeutic molecules and have enabled regeneration of large-scale, pre-clinical bone defects. However, these systems primarily rely on non-specific hydrolysis of PEM components to foster drug release, and their pre-determined drug delivery schedules potentially limit future translation into innately heterogeneous patient populations. To trigger therapeutic delivery directly in response to local environmental stimuli, an LbL-compatible polycation solely degraded by cell-generated reactive oxygen species (ROS) was synthesized. These thioketal-based polymers were selectively cleaved by physiologic doses of ROS, stably incorporated into PEM films alongside growth factors, and facilitated tunable release of therapeutic bone morphogenetic protein-2 (BMP-2) upon oxidation. These coatings' sensitivity to oxidation was also dependent on the polyanions used in film construction, providing a simple method for enhancing ROS-mediated protein delivery in vitro. Correspondingly, when implanted in critically-sized rat calvarial defects, the most sensitive ROS-responsive coatings generated a 50% increase in bone regeneration compared with less sensitive formulations and demonstrated a nearly threefold extension in BMP-2 delivery half-life over conventional hydrolytically-sensitive coatings. These combined results highlight the potential of environmentally-responsive PEM coatings as tunable drug delivery systems for regenerative medicine.

Oxidation-Sensitive Core-Multishell Nanocarriers for the Controlled Delivery of Hydrophobic Drugs

A synthetic route for oxidation-sensitive core-multishell (osCMS) nanocarriers was established, and their drug loading and release properties were analyzed based on their structural variations. The nanocarriers showed a drug loading of 0.3-3 wt % for the anti-inflammatory drugs rapamycin and dexamethasone and the photosensitizer meso-tetra-hydroxyphenyl-porphyrin (mTHPP). Oxidative processes of the nanocarriers were probed in vitro by hydrogen peroxide, and the degradation products were identified by infrared spectroscopy supported by ab initio calculations, yielding mechanistic details on the chemical changes occurring in redox-sensitive nanocarriers. Oxidation-triggered drug release of the model drug Nile Red measured and assessed by time-dependent fluorescence spectroscopy showed a release of up to 80% within 24 h. The drug delivery capacity of the new osCMS nanocarriers was tested in ex vivo human skin with and without pretreatments to induce local oxidative stress. It was found that the delivery of mTHPP was selectively enhanced in skin under oxidative stress. The number and position of the thioether groups influenced the physicochemical as well as drug delivery properties of the carriers.

Inflammation-responsive delivery systems for the treatment of chronic inflammatory diseases

Inflammation is the biological response of immune system to protect living organisms from injurious factors. However, excessive and uncontrolled inflammation is implicated in a variety of devastating chronic diseases including atherosclerosis, inflammatory bowel disease (IBD), and rheumatoid arthritis (RA). Improved understanding of inflammatory response has unveiled a rich assortment of anti-inflammatory therapeutics for the treatment and management of relevant chronic diseases. Notwithstanding these successes, clinical outcomes are variable among patients and serious adverse effects are often observed. Moreover, there exist some limitations for clinical anti-inflammatory therapeutics such as aqueous insolubility, low bioavailability, off-target effects, and poor accessibility to subcellular compartments. To address these challenges, the rational design of inflammation-specific drug delivery systems (DDSs) holds significant promise. Moreover, as compared to normal tissues, inflamed tissue-associated pathological milieu (e.g., oxidative stress, acidic pH, and overexpressed enzymes) provides vital biochemical stimuli for triggered delivery of anti-inflammatory agents in a spatiotemporally controlled manner. In this review, we summarize recent advances in the development of anti-inflammatory DDSs with built-in pathological inflammation-specific responsiveness for the treatment of chronic inflammatory diseases.

Synaptic vesicle-inspired nanoparticles with spatiotemporally controlled release ability as a "nanoguard" for synergistic treatment of synucleinopathies

Synaptic vesicle-inspired nanoparticles (RT-PPB NPs) as a "nanoguard" were designed for clearing the toxic α-synuclein aggregates in diseased neurons and preventing the culprits from escaping to affect other normal cells. The NPs could overcome a series of tissue and cellular barriers and controllably release drugs in the diseased neurons, which ensured the optimization of synergistic treatment. This study indicates that the synaptic vesicle-inspired NPs may have the potential to open up a new avenue for the treatment of synucleinopathies, as well as other neurodegenerative diseases.

Antibody conjugated lipid nanoparticles as a targeted drug delivery system for hydrophobic pharmaceuticals

Cancer remains a significant health issue worldwide. The most common group of chemotherapeutic agents are small-molecule drugs, which often are associated with toxic side-effects and non-specific delivery, leading to limited therapeutic effect. This paper describes the development of a targeted drug delivery system based on lipid nanoparticles for cancer therapy. The lipid nanoparticles consist of a lipid core conjugated to an albumin stealth coating and targeting antibodies through thiol chemistry synthesized utilizing a one-step method. Applying the developed method, lipid nanoparticles with diameters down to 87 nm, capable of encapsulating small molecule compounds were synthesized. Cellular uptake studies of the lipid nanoparticles loaded with the model drug Nile red demonstrated that stealth-coating reduced non-specific cell uptake by up to a 1000-fold compared to free drug. Moreover, antibody-conjugation led to a significant cellular retargeting. Finally, it was shown that the lipid nanoparticles undergo cellular uptake through the endocytic pathway. The lipid nanoparticles are simple to synthesize, stabile in serum and have the potential to be versatile targeted towards receptors selectively expressed by diseased cells using antibodies. Thus, the system may reduce the toxic side-effects of cancer drugs while improving their delivery to cancer cells, increasing the therapeutic effect.

Polymeric micelles in drug delivery: An insight of the techniques for their characterization and assessment in biorelevant conditions

Polymeric micelles, i.e. aggregation colloids formed in solution by self-assembling of amphiphilic polymers, represent an innovative tool to overcome several issues related to drug administration, from the low water-solubility to the poor drug permeability across biological barriers. With respect to other nanocarriers, polymeric micelles generally display smaller size, easier preparation and sterilization processes, and good solubilization properties, unfortunately associated with a lower stability in biological fluids and a more complicated characterization. Particularly challenging is the study of their interaction with the biological environment, essential to predict the real in vivo behavior after administration. In this review, after a general presentation on micelles features and properties, different characterization techniques are discussed, from the ones used for the determination of micelles basic characteristics (critical micellar concentration, size, surface charge, morphology) to the more complex approaches used to figure out micelles kinetic stability, drug release and behavior in the presence of biological substrates (fluids, cells and tissues). The techniques presented (such as dynamic light scattering, AFM, cryo-TEM, X-ray scattering, FRET, symmetrical flow field-flow fractionation (AF4) and density ultracentrifugation), each one with their own advantages and limitations, can be combined to achieve a deeper comprehension of polymeric micelles in vivo behavior. The set-up and validation of adequate methods for micelles description represent the essential starting point for their development and clinical success.

Diflunisal-loaded poly(propylene sulfide) nanoparticles decrease S. aureus-mediated bone destruction during osteomyelitis

Osteomyelitis is a debilitating infection of bone that results in substantial morbidity. Staphylococcus aureus is the most commonly isolated pathogen causing bone infections and features an arsenal of virulence factors that contribute to bone destruction and counteract immune responses. We previously demonstrated that diflunisal, a nonsteroidal anti-inflammatory drug, decreases S. aureus-induced bone destruction during osteomyelitis when delivered locally from a resorbable drug delivery depot. However, local diflunisal therapy was complicated by bacterial colonization of the depot's surface, highlighting a common pitfall of devices for local drug delivery to infected tissue. It is, therefore, critical to develop an alternative drug delivery method for diflunisal to successfully repurpose this drug as an antivirulence therapy for osteomyelitis. We hypothesized that a nanoparticle-based parenteral delivery strategy would provide a method for delivering diflunisal to infected tissue while circumventing the complications associated with local delivery. In this study, we demonstrate that poly(propylene sulfide) (PPS) nanoparticles accumulate at the infectious focus in a murine model of staphylococcal osteomyelitis and are capable of efficaciously delivering diflunisal to infected bone. Moreover, diflunisal-loaded PPS nanoparticles effectively decrease S. aureus-mediated bone destruction, establishing the feasibility of systemic delivery of an antivirulence compound to mitigate bone pathology during osteomyelitis.

Living polymerizations of propylene sulfide initiated with potassium xanthates characterized by unprecedentedly high propagation rates

In this paper we describe the original thiol-free approach towards the polymerization of propylene sulfide (PS) under various conditions (bulk, solution, and emulsion) initiated with potassium xanthates.

Modifying Cell Membranes with Anionic Polymer Amphiphiles Potentiates Intracellular Delivery of Cationic Peptides

Rapid, facile, and noncovalent cell membrane modification with alkyl-grafted anionic polymers was sought as an approach to enhance intracellular delivery and bioactivity of cationic peptides. We synthesized a library of acrylic acid-based copolymers containing varying amounts of an amine-reactive pentafluorophenyl acrylate monomer followed by postpolymerization modification with a series of alkyl amines to afford precise control over the length and density of aliphatic alkyl side chains. This synthetic strategy enabled systematic investigation of the effect of the polymer structure on membrane binding, potentiation of peptide cell uptake, pH-dependent disruption of lipid bilayers for endosome escape, and intracellular bioavailability. A subset of these polymers exhibited pK_a of ∼6.8, which facilitated stable membrane association at physiological pH and rapid, pH-dependent endosomal disruption upon endocytosis as quantified in Galectin-8-YFP reporter cells. Cationic cell penetrating peptide (CPP) uptake was enhanced up to 15-fold in vascular smooth muscle cells in vitro when peptide treatment was preceded by a 30-min pretreatment with lead candidate polymers. We also designed and implemented a new and highly sensitive assay for measuring the intracellular bioavailability of CPPs based on the NanoLuciferase (NanoLuc) technology previously developed for measuring intracellular protein-protein interactions. Using this split luciferase class of assay, polymer pretreatment enhanced intracellular delivery of the CPP-modified HiBiT peptide up to 30-fold relative to CPP-HiBiT without polymer pretreatment (p < 0.05). The overall structural analyses show that polymers containing 50:50 or 70:30 molar ratios of carboxyl groups to alkyl side chains of 6-8 carbons maximized peptide uptake, pH-dependent membrane disruption, and intracellular bioavailability and that this potentiation effect was maximized by pairing with CPPs with high cationic charge density. These results demonstrate a rapid, mild method for polymer modification of cell surfaces to potentiate intracellular delivery, endosome escape, and bioactivity of cationic peptides.

Bioresponsive drug delivery systems for the treatment of inflammatory diseases

Inflammation is intimately related to the pathogenesis of numerous acute and chronic diseases like cardiovascular disease, inflammatory bowel disease, rheumatoid arthritis, and neurodegenerative diseases. Therefore anti-inflammatory therapy is a very promising strategy for the prevention and treatment of these inflammatory diseases. To overcome the shortcomings of existing anti-inflammatory agents and their traditional formulations, such as nonspecific tissue distribution and uncontrolled drug release, bioresponsive drug delivery systems have received much attention in recent years. In this review, we first provide a brief introduction of the pathogenesis of inflammation, with an emphasis on representative inflammatory cells and mediators in inflammatory microenvironments that serve as pathological fundamentals for rational design of bioresponsive carriers. Then we discuss different materials and delivery systems responsive to inflammation-associated biochemical signals, such as pH, reactive oxygen species, and specific enzymes. Also, applications of various bioresponsive drug delivery systems in the treatment of typical acute and chronic inflammatory diseases are described. Finally, crucial challenges in the future development and clinical translation of bioresponsive anti-inflammatory drug delivery systems are highlighted.

Redox-Responsive Nanobiomaterials-Based Therapeutics for Neurodegenerative Diseases

Redox regulation has recently been proposed as a critical intracellular mechanism affecting cell survival, proliferation, and differentiation. Redox homeostasis has also been implicated in a variety of degenerative neurological disorders such as Parkinson's and Alzheimer's disease. In fact, it is hypothesized that markers of oxidative stress precede pathologic lesions in Alzheimer's disease and other neurodegenerative diseases. Several therapeutic approaches have been suggested so far to improve the endogenous defense against oxidative stress and its harmful effects. Among such approaches, the use of artificial antioxidant systems has gained increased popularity as an effective strategy. Nanoscale drug delivery systems loaded with enzymes, bioinspired catalytic nanoparticles and other nanomaterials have emerged as promising candidates. The development of degradable hydrogels scaffolds with antioxidant effects could also enable scientists to positively influence cell fate. This current review summarizes nanobiomaterial-based approaches for redox regulation and their potential applications as central nervous system neurodegenerative disease treatments.

3D Bone Morphology Alters Gene Expression, Motility, and Drug Responses in Bone Metastatic Tumor Cells

Patients with advanced skeletal metastases arising from primary cancers including breast, lung, and prostate suffer from extreme pain, bone loss, and frequent fractures. While the importance of interactions between bone and tumors is well-established, our understanding of complex cell–cell and cell–microenvironment interactions remains limited in part due to a lack of appropriate 3D bone models. To improve our understanding of the influence of bone morphometric properties on the regulation of tumor-induced bone disease (TIBD), we utilized bone-like 3D scaffolds in vitro and in vivo. Scaffolds were seeded with tumor cells, and changes in cell motility, proliferation, and gene expression were measured. Genes associated with TIBD significantly increased with increasing scaffold rigidity. Drug response differed when tumors were cultured in 3D compared to 2D. Inhibitors for Integrin β3 and TGF-β Receptor II significantly reduced bone-metastatic gene expression in 2D but not 3D, while treatment with the Gli antagonist GANT58 significantly reduced gene expression in both 2D and 3D. When tumor-seeded 3D scaffolds were implanted into mice, infiltration of myeloid progenitors changed in response to pore size and rigidity. This study demonstrates a versatile 3D model of bone used to study the influence of mechanical and morphometric properties of bone on TIBD.

Enhanced stem cell retention and antioxidative protection with injectable, ROS-degradable PEG hydrogels

Poly(ethylene glycol) (PEG) hydrogels crosslinked with enzyme-cleavable peptides are promising biodegradable vehicles for therapeutic cell delivery. However, peptide synthesis at the level required for bulk biomaterial manufacturing is costly, and fabrication of hydrogels from scalable, low-cost synthetic precursors while supporting cell-specific degradation remains a challenge. Reactive oxygen species (ROS) are cell-generated signaling molecules that can also be used as a trigger to mediate specific in vivo degradation of biomaterials. Here, PEG-based hydrogels crosslinked with ROS-degradable poly(thioketal) (PTK) polymers were successfully synthesized via thiol-maleimide chemistry and employed as a cell-degradable, antioxidative stem cell delivery platform. PTK hydrogels were mechanically robust and underwent ROS-mediated, dose-dependent degradation in vitro, while promoting robust cellular infiltration, tissue regeneration, and bioresorption in vivo. Moreover, these ROS-sensitive materials successfully encapsulated mesenchymal stem cells (MSCs) and maintained over 40% more viable cells than gold-standard hydrogels crosslinked with enzymatically-degradable peptides. The higher cellular survival in PTK-based gels was associated with the antioxidative function of the ROS-sensitive crosslinker, which scavenged free radicals and protected encapsulated MSCs from cytotoxic doses of ROS. Improved MSC viability was also observed in vivo as MSCs delivered within injectable PTK hydrogels maintained significantly more viability over 11 days compared against cells delivered within gels crosslinked with either a PEG-only control polymer or a gold-standard enzymatically-degradable peptide. Together, this study establishes a new paradigm for scalable creation and application of cell-degradable hydrogels, particularly for cell delivery applications.

Assessing the range of enzymatic and oxidative tunability for biosensor design

Development of multi-functional materials and biosensors that can achieve an in situ response designed by the user is a current need in the biomaterials field, especially in complex biological environments, such as inflammation, where multiple enzymatic and oxidative signals are present. In the past decade, there has been extensive research and development of materials chemistries for detecting and monitoring enzymatic activity, as well as for releasing therapeutic and diagnostic agents in regions undergoing oxidative stress. However, there has been limited development of materials in the context of enzymatic and oxidative triggers together, despite their closely tied and overlapping mechanisms. With research focusing on enzymatically and oxidatively triggered materials separately, these systems may be inadequate in monitoring the complexity of inflammatory environments, thus limiting in vivo translatability and diagnostic accuracy. The intention of this review is to highlight a variety of enzymatically and oxidatively triggered materials chemistries to draw attention to the range of synthetic tunability available for the construction of novel biosensors with a spectrum of programmed responses. We focus our discussion on several types of macromolecular sensors, generally classified by the causative material response driving ultimate signal detection. This includes sensing based on degradative processes, conformational changes, supramolecular assembly/disassembly, and nanomaterial interactions, among others. We see each of these classes providing valuable tools toward coalescing current gaps in the biosensing field regarding specificity, selectivity, sensitivity, and flexibility in application. Additionally, by considering the materials chemistry of enzymatically and oxidatively triggered biomaterials in tandem, we hope to encourage synthesis of new biosensors that capitalize on their synergistic roles and overlapping mechanisms in inflammatory environments for applications in disease diagnosis and monitoring.

Influence of Core Cross-Linking and Shell Composition of Polymeric Micelles on Immune Response and Their Interaction with Human Monocytes

Block copolymer micelles have received increasing attention in the last decades, in particular for their appealing properties in nanomedicine. However, systematic investigations of the interaction between polymeric micelles and immune cells are still rare. Therefore, broader studies comparing the structural effects remain inevitable for a comprehensive understanding of the immune response and for the design of efficient, nonimmunogenic delivery systems. Here, we present novel block copolymer micelles with the same hydrophobic core, based on a copolymer of BA and VDM, and various hydrophilic shells ranging from common PEG derivatives to morpholine-based materials. The influence of these shells on innate immune responses was studied in detail. In addition, we investigated the impact of micelle stability by varying the cross-linking density in the micellar core. Surprisingly, whereas different shells had only a minor impact on immune response, micelles with reduced cross-linking density considerably enhanced the release of cytokines from isolated human monocytes. Moreover, the uptake of non-cross-linked micelles by monocytes was significantly higher as compared to cross-linked materials. Our study emphasizes the importance of the micellar stability on the interaction with the immune system, which is the key for any stealth properties in vivo. Polymers based on morpholines result in a similar low response as the PEG derivative and may represent an interesting alternative to the common PEGylation.

ROS and GSH-responsive S-nitrosoglutathione functionalized polymeric nanoparticles to overcome multidrug resistance in cancer

Multidrug resistance of cancer cells is one of the major obstacle for chemotherapeutic efficiency. Nitric oxide (NO) has raised the potential to overcome multidrug resistance (MDR) with low side effects. Herein, we report a reactive oxygen species (ROS) and glutathione (GSH) responsive nanoparticle for the delivery of NO prodrug such as S-nitrosoglutathione (GSNO), which was chemically conjugated to an amphiphilic block copolymer. The GSNO functionalized nanoparticles show high NO loading capacity, good stability and sustained NO release with specific GSH activated NO-releasing kinetics. Such GSNO functionalized nanoparticles delivered doxorubicin (DOX) in a ROS triggered manner and increased the intracellular accumulation of DOX. However, in normal healthy cells, showing physiological concentrations of ROS, these nanoparticles presented good biocompatibility. The present work indicated that these multifunctional nanoparticles can serve as effective co-delivery platforms of NO and DOX to selectively kill chemo-resistant cancer cells through increasing chemo-sensitivity. STATEMENT OF SIGNIFICANCE: In this work, we constructed nitric oxide donor (S-nitrosoglutathione, GSNO) functionalized amphiphilic copolymer (PEG-PPS-GSNO) to deliver doxorubicin (DOX). The developed PEG-PPS-GSNO@DOX nanoparticles presented high NO capacity, ROS triggered DOX release and GSH triggered NO release. Thus NO reversed the chemo-resistance in HepG2/ADR cells increasing intrcellular accumulation of DOX. Furthermore, these PEG-PPS-GSNO@DOX nanoparticles exhibited biocompatibility to healthy cells and toxicity to cancer cells, due to elevated ROS.

Tuning Ligand Density To Optimize Pharmacokinetics of Targeted Nanoparticles for Dual Protection against Tumor-Induced Bone Destruction

Breast cancer patients are at high risk for bone metastasis. Metastatic bone disease is a major clinical problem that leads to a reduction in mobility, increased risk of pathologic fracture, severe bone pain, and other skeletal-related events. The transcription factor Gli2 drives expression of parathyroid hormone-related protein (PTHrP), which activates osteoclast-mediated bone destruction, and previous studies showed that Gli2 genetic repression in bone-metastatic tumor cells significantly reduces tumor-induced bone destruction. Small molecule inhibitors of Gli2 have been identified; however, the lipophilicity and poor pharmacokinetic profile of these compounds have precluded their success in vivo. In this study, we designed a bone-targeted nanoparticle (BTNP) comprising an amphiphilic diblock copolymer of poly[(propylene sulfide)-block-(alendronate acrylamide-co-N,N-dimethylacrylamide)] [PPS-b-P(Aln-co-DMA)] to encapsulate and preferentially deliver a small molecule Gli2 inhibitor, GANT58, to bone-associated tumors. The mol % of the bisphosphonate Aln in the hydrophilic polymer block was varied in order to optimize BTNP targeting to tumor-associated bone by a combination of nonspecific tumor accumulation (presumably through the enhanced permeation and retention effect) and active bone binding. Although 100% functionalization with Aln created BTNPs with strong bone binding, these BTNPs had highly negative zeta-potential, resulting in shorter circulation time, greater liver uptake, and less distribution to metastatic tumors in bone. However, 10 mol % of Aln in the hydrophilic block generated a formulation with a favorable balance of systemic pharmacokinetics and bone binding, providing the highest bone/liver biodistribution ratio among formulations tested. In an intracardiac tumor cell injection model of breast cancer bone metastasis, treatment with the lead candidate GANT58-BTNP formulation decreased tumor-associated bone lesion area 3-fold and increased bone volume fraction in the tibiae of the mice 2.5-fold. Aln conferred bone targeting to the GANT58-BTNPs, which increased GANT58 concentration in the tumor-associated bone relative to untargeted NPs, and also provided benefit through the direct antiresorptive therapeutic function of Aln. The dual benefit of the Aln in the BTNPs was supported by the observations that drug-free Aln-containing BTNPs improved bone volume fraction in bone-tumor-bearing mice, while GANT58-BTNPs created better therapeutic outcomes than both unloaded BTNPs and GANT58-loaded untargeted NPs. These findings suggest GANT58-BTNPs have potential to potently inhibit tumor-driven osteoclast activation and resultant bone destruction in patients with bone-associated tumor metastases.

Reactive oxygen species (ROS)-responsive ferrocene-polymer-based nanoparticles for controlled release of drugs

Ferrocene-containing nanoparticles show reversible redox activity that could trigger drug release mediated by reactive oxygen species (ROS).

The influence of directed hydrogen bonds on the self-assembly of amphiphilic polymers in water

HYPOTHESIS

Molecules forming directed intermolecular hydrogen bonds, such as the well-known benzene-1,3,5-tricarboxamides (BTA) motif, are known to self-assemble into long fibrous structures. However, only a few of these systems have so far demonstrated the ability to form such anisotropic nanostructures, if they are combined with hydrophilic polymers to create an amphiphilic material. Here, we designed BTA-polymer conjugates to investigate whether the directionality of the hydrogen bonds or the ratio of hydrophobic to hydrophilic parts of the molecule, and thus the packing parameter, is decisive for obtaining anisotropic supramolecular structures in water.

EXPERIMENTS

Poly(ethylene glycol) was conjugated to BTA moieties with varying lengths of hydrophobic alkyl spacers ranging from two to twelve methylene units. The resulting amphiphilic materials were characterized in aqueous solution by light and small-angle neutron scattering, analytical ultracentrifugation, and cryo-transmission electron microscopy.

FINDINGS

While spherical micelles were observed for C₆ and C₁₀ alkyl spacers, anisotropic structures were only present in case of the C₁₂ spacer. The comparison to an analogous material, which lacks the directed hydrogen bonds, revealed that the BTA motif cannot provide a sufficient driving force to induce anisotropic structures, but increases the packing density in the hydrophobic part. Therefore, the packing parameter governs the appearance of anisotropic aggregates.

Manganese dioxide nanoparticles protect cartilage from inflammation-induced oxidative stress

Oxidative stress has been implicated in the pathogenesis of osteoarthritis and has become an important therapeutic target. Investigations of various antioxidant supplements, reactive oxidative species (ROS) pathway mediators, and free radical scavengers for treating osteoarthritis have demonstrated common disadvantages including poor bioavailability and stability, as well as rapid joint clearance or release profiles from delivery vehicles. Moreover, these therapies do not target cartilage, which irreversibly degenerates in the presence of oxidative stress. The goal of this study was to engineer a nanoparticle system capable of sustained retention in the joint space, localization to cartilage, and mitigation of oxidative stress. Towards this goal, ROS scavenging manganese dioxide nanoparticles with physicochemical properties (less than 20 nm and cationic) that facilitate their uptake into cartilage were developed and characterized. These particles penetrated through the depth of cartilage explants and were found both in the extracellular matrix as well as intracellularly within the resident chondrocytes. Furthermore, the particles demonstrated chondroprotection of cytokine-challenged cartilage explants by reducing the loss of glycosaminoglycans and release of nitric oxide. Quantitative PCR analysis revealed that the particles mitigated impacts of oxidative stress related genes in cytokine-challenged chondrocytes. When injected intra-articularly into rats, the particles persisted in the joint space over one week, with 75% of the initial signal remaining in the joint. Biodistribution and histological analysis revealed accumulation of particles at the chondral surfaces and colocalization of the particles with the lacunae of chondrocytes. The results suggest that the manganese dioxide nanoparticles could be a promising approach for the chondroprotection of osteoarthritic cartilage.

Evaluation of Charge-Regulated Supramolecular Copolymerization to Tune the Time Scale for Oxidative Disassembly of β-Sheet Comonomers

A multistimuli-responsive supramolecular copolymerization is reported. The copolymerization is driven by hydrogen bond encoded β-sheet-based charge co-assembly into 1D nanorods in water, using glutamic acid or lysine residues in either of the peptide comonomers. The incorporation of methionine as hydrophobic amino acid supports β-sheet formation, but oxidation of the thioether side-chain to a sulfoxide functional group destabilizes the β-sheet ordered domains and induces disassembly of the supramolecular polymers. Using H₂ O₂ as reactive oxygen species, the time scale and kinetics of the oxidative disassembly are probed. Compared to the charge neutral homopolymers, it is found that the oxidative disassembly of the charged ampholytic copolymers is up to two times faster and is operative at neutral pH. The strategy is therefore an important addition to the growing field of amphiphilic polythioether containing (macro)molecular building blocks, particularly in view of tuning their oxidation induced disassembly which tends to be notoriously slow and requires high concentrations of reactive oxygen species or acidic reaction media.

Thioether Phosphatidylcholine Liposomes: A Novel ROS-Responsive Platform for Drug Delivery

Liposomes are the most valuable nanocarriers in clinical use because of their biocompatibility, biodegradation, and effective encapsulation of hydrophilic or hydrophobic drugs. However, their applications are limited by the structure and functions of the most common phospholipids used as the main component of the liposomes. In this work, novel series of thioether phosphatidylcholines (S-PCs) and S-PC-based liposomes (S-LPs) were developed for reactive oxygen species (ROS)-responsive drug release. First of all, S-PCs with different chain lengths were synthesized by a combination of click reaction and heterogeneous esterification. Differential scanning calorimetry studies indicated that S-PCs had different phase transition temperatures depending on their chain lengths. Their critical aggregation concentrations were measured by the fluorescence probe technique indicating the self-assembly ability. After that, S-PC-based stealth liposomes (S-LPs) containing DSPE-PEG₂₀₀₀ and cholesterol were prepared via a classic thin-film method. Doxorubicin (DOX) as a model drug was loaded in the stealth liposomes (DOX/S-LPs) by using the ammonium sulfate gradient method with high encapsulation efficiency. DOX/S-LPs were characterized by dynamic light scattering (DLS), transmission electron microscope (TEM), and cryogenic TEM, confirming their spherical structure with the bilayer thickness of about 4 nm. The ROS sensitivity of S-PCs and S-LPs was carefully evaluated in the presence of H₂O₂ by means of mass spectrometry, DLS, TEM, and ultraviolet spectroscopy and release study. The results indicated the significant structural change of S-LPs after H₂O₂ treatment, which demonstrated that S-LPs possessed an efficient ROS-triggered disintegration because of thioether oxidation of S-PCs. Finally, in vitro and in vivo anticancer efficiency assays revealed the improved drug potency of DOX/S-LPs, which can be attributed to ROS-triggered destruction of S-LPs after the uptake by tumor cells followed by rapid release of DOX. All together, as alternatives of traditional phosphatidylcholines, S-PC-based stealth liposomes are promising ROS-responsive carriers for the controlled delivery of drugs.

Oxidation- and Temperature-Responsive Poly(hydroxyethyl acrylate-co-phenyl vinyl sulfide) Micelle as a Potential Anticancer Drug Carrier

Poly(hydroxyethyl acrylate-co-phenyl vinyl sulfide) (P(HEA-co-PVS)), as an oxidizable amphiphilic polymer, was prepared for the fabrication of an oxidation- and temperature-responsive micelle for the delivery of doxorubicin (DOX). The interfacial activity of H2O2-treated P(HEA-co-PVS) was significantly lower than that of the untreated variety, possibly because of the oxidization of PVS. P(HEA-co-PVS) exhibited a lower critical solution temperature (LCST) behavior and the LCST increased upon H2O2 treatment. The copolymer micelles, prepared by the dialysis method, were found to be round particles (less than 100 nm) on TEM micrograph. The release degree of Nile red loaded in the micelles was higher when the H2O2 concentration was higher, possibly because the micelles could be solubilized more readily at a higher H2O2 concentration. The release degree was more strongly dependent on the oxidizing agent concentration when the temperature was higher. DOX loaded in the micelles suppressed the in vitro growth of KB cells (a human cancer cell type originating from the cervix) much more effectively than DOX loaded in an unoxidizable control micelle and free DOX, possibly because the copolymer would undergo an increase in its LCST, lose its amphiphilic property, and the micelles would be disassembled. The DOX-loaded micelles were readily internalized into KB cells, as evidenced by flow cytometry (FACS) and confocal laser scanning microscopy (CLSM).