ROS-induced biodegradable polythioketal nanoparticles for intracellular delivery of anti-cancer therapeutics

Reactive oxygen species driven prodrug-based nanoscale carriers for transformative therapies

Reactive oxygen species (ROS) drive processes in various pathological conditions serving as an attractive target for therapeutic strategies. This review highlights the development and use of ROS-dependent prodrug-based nanoscale carriers that has transformed many biomedical applications. Incorporating prodrugs into nanoscale carriers not only improves their stability and solubility but also enables site-specific drug delivery ultimately enhancing the therapeutic effectiveness of the nanoscale carriers. We critically examine recent advances in ROS-responsive nanoparticulate platforms, encompassing liposomes, polymeric nanoparticles, and inorganic nanocarriers. These platforms facilitate precise control over drug release upon encountering elevated ROS levels at disease sites, thereby minimizing off-target effects and maximizing therapeutic efficiency. Furthermore, we investigate the potential of combination therapies in which ROS-activated prodrugs are combined with other therapeutic agents and underscore their synergistic potential for treating multifaceted diseases. This comprehensive review highlights the immense potential of ROS-dependent prodrug-based nanoparticulate systems in revolutionizing biomedical applications; such nanoparticulate systems can facilitate selective and controlled drug delivery, reduce toxicity, and improve therapeutic outcomes for ROS-associated diseases.

Designed to Degrade: Tailoring Polyesters for Circularity

A powerful toolbox is needed to turn the linear plastic economy into circular. Development of materials designed for mechanical recycling, chemical recycling, and/or biodegradation in targeted end-of-life environment are all necessary puzzle pieces in this process. Polyesters, with reversible ester bonds, are already forerunners in plastic circularity: poly(ethylene terephthalate) (PET) is the most recycled plastic material suitable for mechanical and chemical recycling, while common aliphatic polyesters are biodegradable under favorable conditions, such as industrial compost. However, this circular design needs to be further tailored for different end-of-life options to enable chemical recycling under greener conditions and/or rapid enough biodegradation even under less favorable environmental conditions. Here, we discuss molecular design of the polyester chain targeting enhancement of circularity by incorporation of more easily hydrolyzable ester bonds, additional dynamic bonds, or degradation catalyzing functional groups as part of the polyester chain. The utilization of polyester circularity to design replacement materials for current volume plastics is also reviewed as well as embedment of green catalysts, such as enzymes in biodegradable polyester matrices to facilitate the degradation process.

Enhancing Precision in Photodynamic Therapy: Innovations in Light-Driven and Bioorthogonal Activation

Over the past few decades, photodynamic therapy (PDT) has evolved as a minimally invasive treatment modality offering precise control over cancer and various other diseases. To address inherent challenges associated with PDT, researchers have been exploring two promising avenues: the development of intelligent photosensitizers activated through light-induced energy transfers, charges, or electron transfers, and the disruption of photosensitive bonds. Moreover, there is a growing emphasis on the bioorthogonal delivery or activation of photosensitizers within tumors, enabling targeted deployment and activation of these intelligent photosensitive systems in specific tissues, thus achieving highly precise PDT. This concise review highlights advancements made over the last decade in the realm of light-activated or bioorthogonal photosensitizers, comparing their efficacy and shaping future directions in the advancement of photodynamic therapy.

Theranostic Fluorescent Probes

The ability to gain spatiotemporal information, and in some cases achieve spatiotemporal control, in the context of drug delivery makes theranostic fluorescent probes an attractive and intensely investigated research topic. This interest is reflected in the steep rise in publications on the topic that have appeared over the past decade. Theranostic fluorescent probes, in their various incarnations, generally comprise a fluorophore linked to a masked drug, in which the drug is released as the result of certain stimuli, with both intrinsic and extrinsic stimuli being reported. This release is then signaled by the emergence of a fluorescent signal. Importantly, the use of appropriate fluorophores has enabled not only this emerging fluorescence as a spatiotemporal marker for drug delivery but also has provided modalities useful in photodynamic, photothermal, and sonodynamic therapeutic applications. In this review we highlight recent work on theranostic fluorescent probes with a particular focus on probes that are activated in tumor microenvironments. We also summarize efforts to develop probes for other applications, such as neurodegenerative diseases and antibacterials. This review celebrates the diversity of designs reported to date, from discrete small-molecule systems to nanomaterials. Our aim is to provide insights into the potential clinical impact of this still-emerging research direction.

Structural Determinants of Stimuli-Responsiveness in Amphiphilic Macromolecular Nano-assemblies

Stimuli-responsive nano-assemblies from amphiphilic macromolecules could undergo controlled structural transformations and generate diverse macroscopic phenomenon under stimuli. Due to the controllable responsiveness, they have been applied for broad material and biomedical applications, such as biologics delivery, sensing, imaging, and catalysis. Understanding the mechanisms of the assembly-disassembly processes and structural determinants behind the responsive properties is fundamentally important for designing the next generation of nano-assemblies with programmable responsiveness. In this review, we focus on structural determinants of assemblies from amphiphilic macromolecules and their macromolecular level alterations under stimuli, such as the disruption of hydrophilic-lipophilic balance (HLB), depolymerization, decrosslinking, and changes of molecular packing in assemblies, which eventually lead to a series of macroscopic phenomenon for practical purposes. Applications of stimuli-responsive nano-assemblies in delivery, sensing and imaging were also summarized based on their structural features. We expect this review could provide readers an overview of the structural considerations in the design and applications of nanoassemblies and incentivize more explorations in stimuli-responsive soft matters.

Inflammation-responsive drug delivery nanosystems for treatment of bacterial-induced sepsis

Sepsis, a complication of dysregulated host immune systemic response to an infection, is life threatening and causes multiple organ injuries. Sepsis is recognized by WHO as a big contributor to global morbidity and mortality. The heterogeneity in sepsis pathophysiology, antimicrobial resistance threat, the slowdown in the development of antimicrobials, and limitations of conventional dosage forms jeopardize the treatment of sepsis. Drug delivery nanosystems are promising tools to overcome some of these challenges. Among the drug delivery nanosystems, inflammation-responsive nanosystems have attracted considerable interest in sepsis treatment due to their ability to respond to specific stimuli in the sepsis microenvironment to release their payload in a precise, targeted, controlled, and rapid manner compared to non-responsive nanosystems. These nanosystems posit superior therapeutic potential to enhance sepsis treatment. This review critically evaluates the recent advances in the design of drug delivery nanosystems that are inflammation responsive and their potential in enhancing sepsis treatment. The sepsis microenvironment's unique features, such as acidic pH, upregulated receptors, overexpressed enzymes, and enhanced oxidative stress, that form the basis for their design have been adequately discussed. These inflammation-responsive nanosystems have been organized into five classes namely: Receptor-targeted nanosystems, pH-responsive nanosystems, redox-responsive nanosystems, enzyme-responsive nanosystems, and multi-responsive nanosystems. Studies under each class have been thematically grouped and discussed with an emphasis on the polymers used in their design, nanocarriers, key characterization, loaded actives, and key findings on drug release and therapeutic efficacy. Further, this information is concisely summarized into tables and supplemented by inserted figures. Additionally, this review adeptly points out the strengths and limitations of the studies and identifies research avenues that need to be explored. Finally, the challenges and future perspectives on these nanosystems have been thoughtfully highlighted.

A road map on synthetic strategies and applications of biodegradable polymers

Biodegradable polymers have emerged as fascinating materials due to their non-toxicity, environmentally benign nature and good mechanical strength. The toxic effects of non-biodegradable plastics paved way for the development of sustainable and biodegradable polymers. The engineering of biodegradable polymers employing various strategies like radical ring opening polymerization, enzymatic ring opening polymerization, anionic ring opening polymerization, photo-initiated radical polymerization, chemoenzymatic method, enzymatic polymerization, ring opening polymerization and coordinative ring opening polymerization have been discussed in this review. The application of biodegradable polymeric nanoparticles in the biomedical field and cosmetic industry is considered to be an emerging field of interest. However, this review mainly highlights the applications of selected biodegradable polymers like polylactic acid, poly(ε-caprolactone), polyethylene glycol, polyhydroxyalkanoates, poly(lactide-co-glycolide) and polytrimethyl carbonate in various fields like agriculture, biomedical, biosensing, food packaging, automobiles, wastewater treatment, textile and hygiene, cosmetics and electronic devices.

Stimuli-responsive and biomimetic delivery systems for sepsis and related complications

Sepsis, a consequence of an imbalanced immune response to infection, is currently one of the leading causes of death globally. Despite advances in the discoveries of potential targets and nanotechnology, sepsis still lacks effective drug delivery systems for optimal treatment. Stimuli-responsive and biomimetic nano delivery systems, specifically, are emerging as advanced bio-inspired nanocarriers for enhancing the treatment of sepsis. Herein, we present a critical review of different stimuli-responsive systems, including pH-; enzyme-; ROS- and toxin-responsive nanocarriers, reported in the delivery of therapeutics for sepsis. Biomimetic nanocarriers, utilizing natural pathways in the inflammatory cascade to optimize sepsis therapy, are also reviewed, in addition to smart, multifunctional vehicles. The review highlights the nanomaterials designed for constructing these systems; their physicochemical properties; the mechanisms of drug release; and their potential for enhancing the therapeutic efficacy of their cargo. Current challenges are identified and future avenues for research into the optimization of bio-inspired nano delivery systems for sepsis are also proposed. This review confirms the potential of stimuli-responsive and biomimetic nanocarriers for enhanced therapy against sepsis and related complications.

Jensen L. Reactive Oxygen Species-Responsive Polymer Nanoparticles to Improve the Treatment of Inflammatory Skin Diseases

To improve the quality of life for people living with chronic inflammatory skin diseases, we propose a new treatment strategy by exploring a stimuli-responsive drug delivery system. Formulations designed by exploiting smart materials can be programmed to perform a specific action upon exposure to disease-related stimuli. For instance, increased levels of reactive oxygen species (ROS), especially the accumulation of hydrogen peroxide, can be utilized to differentiate between healthy and inflamed tissues. In this concept-proofing study, the polymer poly(1,4 phenyleneacetone dimethylene thioketal) (PPADT) was investigated for its ROS-responsive properties and potential to treat inflammatory skin diseases. PPADT nanoparticles were formulated by oil-in-water emulsification followed by solvent evaporation and characterized by size, zeta-potential, and release kinetic profiles. Release profiles revealed that the PPADT nanoparticles were sensitive toward elevated levels of ROS in an ROS-stimulus concentration (0.1-10 mM) and time-dependent manner (flare-up mimicked). The safety assessment proved that the PPADT polymer and the monomers generated by oxidation do not show any sign of being cytotoxic to fibroblasts and no mutagenic liabilities were observed. In conclusion, the PPADT polymer demonstrated to be a promising material for stimuli-responsive delivery of hydrophobic small molecules in the treatment of inflammatory skin diseases.

Promoting gene transfection by ROS responsive silicon nanowire arrays

The development of a fast and safe reactive oxygen species (ROS)-responsive vector is generally limited by the intracellular unstable ROS concentration, and a relatively long time is still needed for the complete intracellular release of drugs or genes induced by ROS. In this work, a gene transfection platform based on ROS-responsive silicon nanowire arrays (SN) is developed, to promote the gene transfection efficiency for several cell lines. Briefly, the surface of the ROS generating system, gold nanoparticle modified SN (SN-Au), is grafted with poly[(2-acryloyl)ethyl(p-boronic acid benzyl)diethylammonium bromide] (B-PDEAEA), an oxidation-responsive charge-reversal cationic polymer. Plasmid DNA (pDNA) bound on the surface through electrostatic interactions was directly delivered into the cells by the time the nanowires penetrate the cells. SN-Au can generate ROS under light treatment, which has an influence on the surface charge change of B-PDEAEA grafted on gold nanoparticles, realizing effective pDNA release in the cytosol for transfection. Nearly 80% of DNA released from the surface of the platform after treated with 1 mM ROS for 10 min. The transfection efficiency of the platform for several cell types was significantly enhanced after a short period of light exposure (3.2-fold for HeLa cells, 7.6-fold for L929 cells, 2.3-fold for BMSC cells and 6.2-fold for mESC cells). The platform also has good biocompatibility. Overall, our results suggest that ROS-responsive SN is a novel, efficient and safe platform for drug and gene transfection.

Applications of the ROS-Responsive Thioketal Linker for the Production of Smart Nanomedicines

Reactive oxygen species (ROS)-sensitive drug delivery systems (DDS) specifically responding to altered levels of ROS in the pathological microenvironment have emerged as an effective means to enhance the pharmaceutical efficacy of conventional nanomedicines, while simultaneously reducing side effects. In particular, the use of the biocompatible, biodegradable, and non-toxic ROS-responsive thioketal (TK) functional group in the design of smart DDS has grown exponentially in recent years. In the design of TK-based DDS, different technological uses of TK have been proposed to overcome the major limitations of conventional DDS counterparts including uncontrolled drug release and off-target effects. This review will focus on the different technological uses of TK-based biomaterials in smart nanomedicines by using it as a linker to connect a drug on the surface of nanoparticles, form prodrugs, as a core component of the DDS to directly control its structure, to control the opening of drug-releasing gates or to change the conformation of the nano-systems. A comprehensive view of the various uses of TK may allow researchers to exploit this reactive linker more consciously while designing nanomedicines to be more effective with improved disease-targeting ability, providing novel therapeutic opportunities in the treatment of many diseases.

Alleviating Oxidative Injury of Myocardial Infarction by a Fibrous Polyurethane Patch with Condensed ROS-Scavenging Backbone Units

Excessive reactive oxygen species (ROS) generated after myocardial infarction (MI) result in the oxidative injury in myocardium. Implantation of antioxidant biomaterials, without the use of any type of drugs, is very appealing for clinical translation, leading to the great demand of novel biomaterials with high efficiency of ROS elimination. In this study, a segmented polyurethane (PFTU) with a high density of ROS-scavenging backbone units is synthesized by the reaction of poly(thioketal) dithiol (PTK) and poly(propylene fumarate) diol (PPF) (soft segments), thioketal diamine (chain extender), and 1,6-hexamethylene diisocyanate (HDI). Its chemical structure is verified by gel permeation chromatography (GPC), ¹ H nuclear magnetic resonance (¹ H NMR) spectroscopy, and Fourier transform infrared (FTIR) spectroscopy. The electrospun composite PFTU/gelatin (PFTU/Gt) fibrous patches show good antioxidation capacity and ROS-responsive degradation in vitro. Implantation of the PFTU/gelatin patches on the heart tissue surface in MI rats consistently decreases the ROS level, membrane peroxidation, and cell apoptosis at the earlier stage, which are not observed in the non-ROS-responsive polyurethane patch. Inflammation and fibrosis are also reduced in the PFTU/gelatin-treated hearts, resulting in the reduced left ventricular remodeling and better cardiac functions postimplantation for 28 d.

Recent advances in the targeted delivery of paclitaxel nanomedicine for cancer therapy

Cancer cases have reached an all-time high in the current era.

Stimuli-Responsive Polymeric Nanomaterials for the Delivery of Immunotherapy Moieties: Antigens, Adjuvants and Agonists

Immunotherapy has been investigated for decades, and it has provided promising results in preclinical studies. The most important issue that hinders researchers from advancing to clinical studies is the delivery system for immunotherapy agents, such as antigens, adjuvants and agonists, and the activation of these agents at the tumour site. Polymers are among the most versatile materials for a variety of treatments and diagnostics, and some polymers are reactive to either endogenous or exogenous stimuli. Utilizing this advantage, researchers have been developing novel and effective polymeric nanomaterials that can deliver immunotherapeutic moieties. In this review, we summarized recent works on stimuli-responsive polymeric nanomaterials that deliver antigens, adjuvants and agonists to tumours for immunotherapy purposes.

Injectable thioketal-containing hydrogel dressing accelerates skin wound healing with the incorporation of reactive oxygen species scavenging and growth factor release

Wound healing is a complex dynamic process. During the occurrence of skin injury, the excessive reactive oxygen species (ROS) level is associated with sustained inflammatory response, which limits efficient wound repair. Although multifunctional hydrogels are considered ideal wound dressings due to their unique advantages, the development of hydrogel dressings with rapid gelling rates, shape adaptation, and antioxidant function is still a vital challenge. In this work, a ROS-responsive injectable polyethylene glycol hydrogel containing thioketal bonds (PEG-TK hydrogel) was synthesized and utilized to deliver epidermal growth factor (EGF). We adopted bio-orthogonal click chemistry for crosslinking the polymer chains to obtain the EGF@PEG-TK hydrogel with fast gelation time, injectability and shape-adaptability. More interestingly, the thioketal bonds in the PEG-TK hydrogel not only scavenged excessive ROS in the wound sites but also achieved responsive and controlled EGF release to facilitate regeneration. The EGF@PEG-TK hydrogel treatment offered the benefits of protecting cells from oxidative stress, accelerating wound closure, and reducing scar formation in the full-thickness skin defect model. This work provides a promising strategy for developing antioxidant hydrogel dressing for facilitating the repair of wounds.

Recent Advances in ROS-Sensitive Nano-Formulations for Atherosclerosis Applications

Over the past decade, ROS-sensitive formulations have been widely used in atherosclerosis applications such as ROS scavenging, drug delivery, gene delivery, and imaging. The intensified interest in ROS-sensitive formulations is attributed to their unique self-adaptive properties, involving the main molecular mechanisms of solubility switch and degradation under the pathological ROS differences in atherosclerosis. This review outlines the advances in the use of ROS-sensitive formulations in atherosclerosis applications during the past decade, especially highlighting the general design requirements in relation to biomedical functional performance.

Photo cleavable thioacetal block copolymers for controlled release

We present a new light cleavable polymer containing o-nitrobenzene thioacetal groups in the main chain. By conjugation to a PEG block, we synthesized block copolymers capable of forming nanoparticles in aqueous solution. We studied drug encapsulation and release using the model drug Nile Red. Irradiation with UV-A light (365 nm) leads to efficient degradation of the polymers and associated burst release of the payload. Unlike other thioacetal and thioketal polymers, these polymers are stable to reactive oxygen species (ROS), preventing non-triggered release. Moreover, the nanocarriers showed low cytotoxicity in cell viability experiments.

The o-nitrobenzene thioacetal group selectively cleaves upon UV-A irradiation. When incorporated in a block-copolymer, these photoactive groups can be used for controlled release of molecular cargo from polymer nanoparticles.

Bombesin-Tethered Reactive Oxygen Species (ROS)-Responsive Nanoparticles for Monomethyl Auristatin F (MMAF) Delivery

Dolastatin derivatives, represented by monomethylauristatin E (MMAE), have been translated in clinic with a form of antibody–drug conjugate; however, their potential in nanoparticle systems has not been well established due to the potential risk of immature release of extremely high cytotoxic dolastatin drugs during blood circulation. Herein, we rationally propose monomethylauristatin F (MMAF), a dolastatin-derived, loaded nanoparticle system composed of bombesin (BBN)-tethered ROS-responsive micelle system (BBN-PEG-PPADT) to achieve efficient anticancer therapy with targeted and efficient delivery of MMAF. The developed MMAF-loaded BBN-PEG-PPADT micelles (MMAF@BBN-PEG-PPADT) exhibited improved cellular uptake via interactions between BBN and gastrin-releasing peptide receptors on the cancer cells and the intracellular burst release of MMAF, owing to the ROS-responsive disruption, which allowed the efficient anticancer effects of MMAF in vitro. This study suggests the potential of nanoparticle systems in the delivery of dolastatin drugs.

Tumor microenvironment responsive drug delivery systems

Conventional tumor-targeted drug delivery systems (DDSs) face challenges, such as unsatisfied systemic circulation, low targeting efficiency, poor tumoral penetration, and uncontrolled drug release. Recently, tumor cellular molecules-triggered DDSs have aroused great interests in addressing such dilemmas. With the introduction of several additional functionalities, the properties of these smart DDSs including size, surface charge and ligand exposure can response to different tumor microenvironments for a more efficient tumor targeting, and eventually achieve desired drug release for an optimized therapeutic efficiency. This review highlights the recent research progresses on smart tumor environment responsive drug delivery systems for targeted drug delivery. Dynamic targeting strategies and functional moieties sensitive to a variety of tumor cellular stimuli, including pH, glutathione, adenosine-triphosphate, reactive oxygen species, enzyme and inflammatory factors are summarized. Special emphasis of this review is placed on their responsive mechanisms, drug loading models, drawbacks and merits. Several typical multi-stimuli responsive DDSs are listed. And the main challenges and potential future development are discussed.

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.

In-vitro photothermal therapy using plant extract polyphenols functionalized graphene sheets for treatment of lung cancer

Although the photothermal therapy (PTT) has achieved tremendous progress in the recent times, still it has to improve an extensive way to achieve the efficient targeted photothermal removal of the tumor cells. Owing to this requirement, we demonstrated a novel class of reduced graphene oxide based photothermal therapeutic agent for the ablation of lung cancer cells (A549). A single step bio facile fabrication of graphene nanosheets using Memecylon edule leaf extract intermediated reduction of Graphene Oxide (GO). This process does not include the utilization of any toxic or harmful reducing agents. The relative results of different characterizations of graphene oxide and Memecylon edule leaf extract RGO delivers a potential representation by excluding the groups containing oxygen from GO and consecutive stabilization of the developed RGO. The reduced GO functionalization with the oxidized polyphenols results in their stability by avoiding the aggregation. The poly phenol anchored Reduced Graphene Oxide (RGO) exhibited exceptional near-infrared (NIR) irradiation of the lung cancer cells directed in vitro to deliver cytotoxicity. In an area of restricted success in the treatment of cancer, the results of our translation can provide a path for designing targeted PTT agents and also responds to stimulus environment for the safe ablation of the devastating disease.

Recent Advances on Reactive Oxygen Species-Responsive Delivery and Diagnosis System

Reactive oxygen species (ROS) play crucial roles in biological metabolism and intercellular signaling. However, ROS level is dramatically elevated due to abnormal metabolism during multiple pathologies, including neurodegenerative diseases, diabetes, cancer, and premature aging. By taking advantage of the discrepancy of ROS levels between normal and diseased tissues, a variety of ROS-sensitive moieties or linkers have been developed to design ROS-responsive systems for the site-specific delivery of drugs and genes. In this review, we summarized the ROS-responsive chemical structures, mechanisms, and delivery systems, focusing on their current advances for precise drug/gene delivery. In particular, ROS-responsive nanocarriers, prodrugs, and supramolecular hydrogels are summarized in terms of their application for drug/gene delivery, and common strategies to elevate or diminish cellular ROS concentrations, as well as the recent development of ROS-related imaging probes were also discussed.

Controlling silicone networks using dithioacetal crosslinks

Rapid metal free cure of thiopropylsilicones occurs via facile thioacetal formation.

ROS-Responsive Biomaterial Design for Medical Applications

Stimuli-responsive biomaterials undergo significant alterations in material structure and property in response to changes of local environmental factors (e.g. pH, temperature, enzyme activation, and water absorption). In particular, reactive oxygen species (ROS) is considered as a major stimulus because over-production of ROS involves most types of major pathogenesis. The application of ROS-responsive biomaterials requires suitable material designs to program user-defined changes of their structure and property in response to a sudden change in the local ROS level. This chapter summarizes the progress in designing and applying major types of ROS-responsive biomaterials within the past 10 years.

Low-power and low-drug-dose photodynamic chemotherapy via the breakdown of tumor-targeted micelles by reactive oxygen species

Tumor-targeted delivery of anticancer agents using nanocarriers has been explored to increase the therapeutic index of cancer chemotherapy. However, only a few nanocarriers are clinically available because the physiological complexity often compromises their ability to target, penetrate, and control the release of drugs. Here, we report a method which dramatically increases in vivo therapeutic drug efficacy levels through the photodynamic degradation of tumor-targeted nanocarriers. Folate-decorated poly(ethylene glycol)-polythioketal micelles are prepared to encapsulate paclitaxel and porphyrins. Photo-excitation generates reactive oxygen species within the micelles to cleave the polythioketal backbone efficiently and facilitate drug release only at the illuminated tumor site. Intravenous injection of a murine xenograft model with a low dose of paclitaxel within the micelles, one-milligram drug per kg (mouse), corresponding to an amount less than that of Taxol by one order of magnitude, induces dramatic tumor regression without any acute systemic inflammation responses or organ toxicity under low-power irradiation (55 mW cm^-2) at 650 nm.

Redox-responsive Drug Delivery Systems

Disbalanced reactive oxygen species (ROS) and glutathione (GSH) are characteristic features of tumor cells. High intracellular GSH concentration in tumor cells is a well-documented fact that leads to a very high reducing intracellular bio-milieu. High accumulation of ROS is known to occur in almost all cancers and can act as a two-edged sword during tumor development, by either promoting or inhibiting growth. These two features present unique opportunities to design drug delivery systems that are responsive to reduction or/and oxidation stimuli and has attracted accrued interest from researchers. These nanocarriers change their structural integrity, either through disassembly or degradation, to deliver their payload in the presence of the trigger. The aim of this chapter is to summarize the key developments in the design of materials with redox-responsive behaviour and their subsequent application in the field of nanomedicine targeting cancer. Strategies into exploiting both stimuli in a single nano drug delivery system to enhance therapeutic efficacy are also addressed.

ROS-responsive drug delivery systems for biomedical applications

In the field of biomedicine, stimuli-responsive drug delivery systems (DDSs) have become increasingly popular due to their site-specific release ability in response to a certain physiological stimulus, which may result in both enhanced treatment outcome and reduced side effects. Reactive oxygen species (ROS) are the unavoidable consequence of cell oxidative metabolism. ROS play a crucial part in regulating biological and physiological processes, whereas excessive intracellular ROS usually lead to the oxidation stress which has implications in several typical diseases such as cancer, inflammation and atherosclerosis. Therefore, ROS-responsive DDSs have elicited widespread popularity for their promising applications in a series of biomedical research because the payload is only released in targeted cells or tissues that overproduce ROS. According to the design of ROS-responsive DDSs, the main release mechanisms of therapeutic agents can be ascribed to ROS-induced carrier solubility change, ROS-induced carrier cleavage or ROS-induced prodrug linker cleavage. This review summarized the latest development and novel design of ROS-responsive DDSs and discussed their design concepts and the applications in the biomedical field.

Cancer-targeted reactive oxygen species-degradable polymer nanoparticles for near infrared light-induced drug release

Nanocarriers can be translocated to the peripheral region of tumor tissues through the well-known enhanced permeability and retention effects.

Light-switchable systems for remotely controlled drug delivery

Light-switchable systems have recently received attention as a new mode of remotely controlled drug delivery. In the past, a multitude of nanomedicine studies have sought to enhance the specificity of drug delivery to target sites by focusing on receptors overexpressed on malignant cells or environmental features of diseases sites. Despite these immense efforts, however, there are few clinically available nanomedicines. We need a paradigm shift in drug delivery. One strategy that may overcome the limitations of pathophysiology-based drug delivery is the use of remotely controlled delivery technology. Unlike pathophysiology-based active drug targeting strategies, light-switchable systems are not affected by the heterogeneity of cells, tissue types, and/or microenvironments. Instead, they are triggered by remote light (i.e., near-infrared) stimuli, which are absorbed by photoresponsive molecules or three-dimensional nanostructures. The sequential conversion of light to heat or reactive oxygen species can activate drug release and allow it to be spatio-temporally controlled. Light-switchable systems have been used to activate endosomal drug escape, modulate the release of chemical and biological drugs, and alter nanoparticle structures to control the release rates of drugs. This review will address the limitations of pathophysiology-based drug delivery systems, the current status of light-based remote-switch systems, and future directions in the application of light-switchable systems for remotely controlled drug delivery.

Reactive-Oxygen-Species-Responsive Drug Delivery Systems: Promises and Challenges

Given the increasing evidence indicates that many pathological conditions are associated with elevated reactive oxygen species (ROS) levels, there have been growing research efforts focused on the development of ROS-responsive carrier systems because of their promising potential to realize more specific diagnosis and effective therapy. By judicious utilization of ROS-responsive functional moieties, a wide range of carrier systems has been designed for ROS-mediated drug delivery. In this review article, insights into design principle and recent advances on the development of ROS-responsive carrier systems for drug delivery applications are provided alongside discussion of their in vitro and in vivo evaluation. In particular, the discussions in this article will mainly focus on polymeric nanoparticles, hydrogels, inorganic nanoparticles, and activatable prodrugs that have been integrated with diverse ROS-responsive moieties for spatiotemporally controlled release of drugs for effective therapy.

In Vitro and In Vivo Tumor Targeted Photothermal Cancer Therapy Using Functionalized Graphene Nanoparticles

Despite the tremendous progress that photothermal therapy (PTT) has recently achieved, it still has a long way to go to gain the effective targeted photothermal ablation of tumor cells. Driven by this need, we describe a new class of targeted photothermal therapeutic agents for cancer cells with pH responsive bioimaging using near-infrared dye (NIR) IR825, conjugated poly(ethylene glycol)-g-poly(dimethylaminoethyl methacrylate) (PEG-g-PDMA, PgP), and hyaluronic acid (HA) anchored reduced graphene oxide (rGO) hybrid nanoparticles. The obtained rGO nanoparticles (PgP/HA-rGO) showed pH-dependent fluorescence emission and excellent near-infrared (NIR) irradiation of cancer cells targeted in vitro to provide cytotoxicity. Using intravenously administered PTT agents, the time-dependent in vivo tumor target accumulation was exactly defined, presenting eminent photothermal conversion at 4 and 8 h post-injection, which was demonstrated from the ex vivo biodistribution of tumors. These tumor environment responsive hybrid nanoparticles generated photothermal heat, which caused dominant suppression of tumor growth. The histopathological studies obtained by H&E staining demonstrated complete healing from malignant tumor. In an area of limited successes in cancer therapy, our translation will pave the road to design stimulus environment responsive targeted PTT agents for the safe eradication of devastating cancer.