Self-sufficing H2O2-responsive nanocarriers through tumor-specific H2O2 production for synergistic oxidation-chemotherapy

Zwitterionic-to-cationic charge conversion polyprodrug nanomedicine for enhanced drug delivery

Zwitterionic surface modification is a promising strategy for nanomedicines to achieve prolonged circulation time and thus effective tumor accumulation. However, zwitterion modified nanoparticles suffer from reduced cellular internalization efficiency.

Methods: A polyprodrug-based nanomedicine with zwitterionic-to-cationic charge conversion ability (denoted as ZTC-NMs) was developed for enhanced chemotherapeutic drug delivery. The polyprodrug consists of pH-responsive poly(carboxybetaine)-like zwitterionic segment and glutathione-responsive camptothecin prodrug segment.

Results: The ZTC-NMs combine the advantages of zwitterionic surface and polyprodrug. Compared with conventional zwitterionic surface, the ZTC-NMs can respond to tumor microenvironment and realize ZTC surface charge conversion, thus improve cellular internalization efficiency of the nanomedicines.

Conclusions: This ZTC method offers a strategy to promote the drug delivery efficiency and therapeutic efficacy, which is promising for the development of cancer nanomedicines.

Photo-triggered self-destructive ROS-responsive nanoparticles of high paclitaxel/chlorin e6 co-loading capacity for synergetic chemo-photodynamic therapy

To improve the anti-cancer therapeutic effect of nanosystems for chemo-photodynamic therapy, there remain several hurdles to be addressed, e.g., limited co-loading efficiency, insufficient stimulus-responsiveness and lack of synergetic effect. This work reported novel reactive‑oxygen-species (ROS)-responsive chlorin e6 (Ce6) and paclitaxel (PTX) co-encapsulated chondroitin sulfate-g-poly (propylene sulfide) nanoparticles (CP/ChS-g-PPS NPs), wherein the drug loading efficiencies of Ce6 and PTX were as high as 14.93% and 24.31%, respectively. To enlarge the ROS signal at tumor sites thus enhancing the ROS-responsiveness of ChS-g-PPS NPs, near-infrared (NIR) light was utilized to induce Ce6 to produce more ROS to destruct the NPs. Our data showed that the photo-triggered self-destructive property of NPs helped drugs to spread deeper in tumors upon laser irradiation, making the NPs promising to thoroughly remove tumor cells. CP/ChS-g-PPS NPs exhibited a synergetic chemo-photodynamic therapy effect in vitro, which was suggested by the combination indexes of PTX and Ce6 lower than 1 when 20-80% inhibition rates of MCF-7 cells were achieved. As for the in vivo antitumor activity, the tumor inhibition rates of CP/ChS-g-PPS NPs (with laser irradiation) were as high as 92.76% and 88.57% in 4T1 bearing BALB/c mice and MCF-7 bearing BALB/c nude mice, respectively, which were significantly higher than those of other treatment groups. This work provided a simple yet effective strategy to develop photo-triggered ROS-responsive NPs for synergetic chemo-photodynamic therapy with quick ROS-responsive self-destruction, spatiotemporally controllability, reduced off-target toxicity, and desirable therapeutic effect.

Stimuli-responsive nanocarriers for drug delivery, tumor imaging, therapy and theranostics

In recent years, much progress has been motivated in stimuli-responsive nanocarriers, which could response to the intrinsic physicochemical and pathological factors in diseased regions to increase the specificity of drug delivery. Currently, numerous nanocarriers have been engineered with physicochemical changes in responding to external stimuli, such as ultrasound, thermal, light and magnetic field, as well as internal stimuli, including pH, redox potential, hypoxia and enzyme, etc. Nanocarriers could respond to stimuli in tumor microenvironments or inside cancer cells for on-demanded drug delivery and accumulation, controlled drug release, activation of bioactive compounds, probes and targeting ligands, as well as size, charge and conformation conversion, etc., leading to sensing and signaling, overcoming multidrug resistance, accurate diagnosis and precision therapy. This review has summarized the general strategies of developing stimuli-responsive nanocarriers and recent advances, presented their applications in drug delivery, tumor imaging, therapy and theranostics, illustrated the progress of clinical translation and made prospects.

ROS-Sensitive Degradable PEG-PCL-PEG Micellar Thermogel

A reactive oxygen species (ROS)-sensitive degradable polymer would be a promising material in designing a disease-responsive system or accelerating degradation of polymers with slow hydrolysis kinetics. Here, a thermogelling poly(ethylene glycol)-polycaprolactone-poly(ethylene glycol) (PEG-PCL-PEG or EG₁₂ -CL₂₀ -EG₁₂ ) triblock copolymer with an oxalate group at the middle of the polymer is reported. The polymers form micelles with an average size of 100 nm in water. Thermogelation is observed in a concentration range of 8.0-37.0 wt%. In particular, the aqueous PEG-PCL-PEG triblock copolymer solutions are in a gel state at 37 °C in a concentration range of 25.0-37.0 wt%, whereas the aqueous PEG-PCL diblock copolymer solutions are in a sol state in the same concentration range at 37 °C. Thus, the gel depot could dissolve out once degradation of the triblock copolymers occurs at the oxalate group as confirmed by the in vitro experiment. In vivo gel formation is confirmed by injecting an aqueous PEG-PCL-PEG solution (36.0 wt%) into the subcutaneous layer of rats. The gel completely disappears in 21 d. A model polypeptide drug (cyclosporine A) is released over 21 d from the in situ formed gel. The micelle-based thermogel of PEG-PCL-PEG with ROS-triggering degradability is a promising injectable material for biomedical applications.

Glutathione and Reactive Oxygen Species Dual-Responsive Block Copolymer Prodrugs for Boosting Tumor Site-Specific Drug Release and Enhanced Antitumor Efficacy

A remarkable hallmark of cancer cells is the heterogeneous coexistence of overproduced intracellular glutathione (GSH) and a high level of reactive oxygen species (ROS) compared with those in normal cells, which have been frequently used as the stimuli to trigger drug release from the nanocarriers. Most of the stimuli-responsive delivery vehicles have been designed to respond to only one redox stimulus (e.g., GSH or ROS). Herein, we develop a GSH and ROS dual-responsive amphiphilic diblock copolymer prodrug (BCP) (GR-BCP) consisting of poly(ethylene glycol) (PEG)- and camptothecin (CPT)-conjugated poly(methacrylate) in the side chains via thioether bonds. In comparison, GSH or ROS single-responsive BCPs (G-BCPs or R-BCPs) were prepared, where CPT drugs were linked by disulfide or thioketal bonds, respectively. The three BCPs can form well-defined spherical micellar nanoparticles in an aqueous solution with a diameter of ∼50 nm. Compared with G-BCP and R-BCP, GR-BCP realized the highest cytotoxicity against HeLa cells with the half-inhibitory concentration (IC₅₀) of 6.3 μM, which is much lower than 17.8 μM for G-BCP and 28.9 μM for R-BCP. Moreover, for in vivo antitumor performance, G-BCP, R-BCP, and GR-BCP showed similar efficiencies in blood circulation and tumor accumulation after intravenous injection. However, GR-BCP realized the most efficient tumor suppression with few side effects. Our findings demonstrate that intracellular GSH and ROS dual-responsive BCPs show a more efficient responsive drug release inside tumor cells for boosting the antitumor efficacy as compared with GSH or ROS single-responsive BCPs, which provides novel strategies for designing redox-responsive BCPs.

A highly atom-economical bioactive nanocarrier for synergistically enhanced antitumor with reduced liver injury

The drug-cum-carrier-type delivery system makes up for conventional nanocarriers that have no therapeutic efficacy and health benefits.

Reactive oxygen species-responsive drug delivery systems for the treatment of neurodegenerative diseases

Neurodegenerative diseases and disorders seriously impact memory and cognition and can become life-threatening. Current medical techniques attempt to combat these detrimental effects mainly through the administration of neuromedicine. However, drug efficacy is limited by rapid dispersal of the drugs to off-target sites while the site of administration is prone to overdose. Many neuropathological conditions are accompanied by excessive reactive oxygen species (ROS) due to the inflammatory response. Accordingly, ROS-responsive drug delivery systems have emerged as a promising solution. To guide intelligent and comprehensive design of ROS-responsive drug delivery systems, this review article discusses the two following topics: (1) the biology of ROS in both healthy and diseased nervous systems and (2) recent developments in ROS-responsive, drug delivery system design. Overall, this review article would assist efforts to make better decisions about designing ROS-responsive, neural drug delivery systems, including the selection of ROS-responsive functional groups.

Enhanced Antitumor Efficacy by a Cascade of Reactive Oxygen Species Generation and Drug Release

Reactive oxygen species (ROS) can be used not only as a therapeutic agent for chemodynamic therapy (CDT), but also as a stimulus to activate release of antitumor drugs, achieving enhanced efficacy through the combination of CDT and chemotherapy. Here we report a pH/ROS dual-responsive nanomedicine consisting of β-lapachone (Lap), a pH-responsive polymer, and a ROS-responsive polyprodrug. In the intracellular acidic environment, the nanomedicine can realize pH-triggered disassembly. The released Lap can efficiently generate hydrogen peroxide, which will be further converted into highly toxic hydroxyl radicals via the Fenton reaction. Subsequently, through ROS-induced cleavage of thioketal linker, doxorubicin is released from the polyprodrug. In vivo results indicate that the cascade of ROS generation and antitumor-drug release can effectively inhibit tumor growth. This design of nanomedicine with cascade reactions offers a promising strategy to enhance antitumor efficacy.

Block copolymer prodrugs: Synthesis, self-assembly, and applications for cancer therapy

Block copolymer prodrugs (BCPs) have emerged as one of the most promising anticancer drug delivery strategies, which can self-assemble into nanoparticles with optimal physicochemical properties including sizes, morphologies, surface properties, and integration of multifunction for improved in vivo applications. Moreover, the utility of stimuli-responsive linkages to conjugate drugs onto the polymer backbones can achieve efficient and targeting drug release. Several BCP micellar delivery systems have been pushed ahead into the clinical trials, which showed great promising potentials for cancer therapy. In recent years, various novel and more efficient BCP systems have been developed for better in vivo performance. In this focus article, we focus on the recent advances of BCPs including the synthesis, self-assembly, and applications for cancer therapy. The synthetic methods are first introduced, and the self-assembly of BCPs for in vivo anticancer applications is discussed along the line of varying endogenous stimuli-responsive linkages including amide or ester bonds, pH, reduction, and oxidation-responsive linkages. Finally, conclusions along with the brief future perspectives are presented. This article is categorized under: Therapeutic Approaches and Drug Discovery > Nanomedicine for Oncologic Disease Nanotechnology Approaches to Biology > Nanoscale Systems in Biology.

A ROS-responsive polymeric prodrug nanosystem with self-amplified drug release for PSMA (-) prostate cancer specific therapy

BACKGROUND

The selectively accumulate in tumor site and completely release drug within cancer cells great limit the therapeutic effect of nano-drug delivery system. Moreover, absence of appropriate biomarker is one of the major challenges for prostate specific membrane antigen negative (PSMA (-)) prostate cancer therapy.

RESULTS

Herein, a PSMA (-) prostate cancer specific targeted and intracellular reactive oxygen species (ROS) amplification for ROS-responsive self-accelerating drug release nanoplatform (ATD-NPs) was developed. ATD-NPs was formed by three parts, including PSMA (-) prostate cancer specifically targeted part (DUP-PEG-DSPE), ROS-sensitive doxorubicin (DOX) polymeric prodrug (P(L-TK-DOX)), and the ROS generation agent (α-tocopheryl succinate, α-TOS); and this delivery system is expected to enhance PSMA (-) prostate cancer therapeutic effect, increase selective accumulation at tumor site and overcome intracellular incomplete drug release. After administration i.v injection, ATD-NPs could specifically accumulate in tumor site and markedly be internalized by cancer cells based on the DUP-1 (a PSMA (-) cancer cells specific target peptide). Subsequently, ATD-NPs could be dissociated under the high concentration reactive oxygen species (ROS) condition, resulting in DOX and α-TOS release. Then, the released α-TOS could be reacted with mitochondria to produce ROS, which in turn accelerating the release of drugs. Finally achieved the purpose of enhancing therapeutic efficacy and reducing side effect. Both in vitro and in vivo experiments demonstrated that the combination of tumor actively-targeted and self-amplifying ROS-responsive drug release showed more significant antitumor activity in the human PSMA (-) prostate cancer.

CONCLUSION

The described technology unifies the tumor actively targets, self-amplified drug release, and excellent biocompatibility into one formulation, are promising for cancer treatment.

Smart nanomedicine agents for cancer, triggered by pH, glutathione, H2O2, or H2S

Effective tumor diagnosis and therapy have always been a significant but challenging issue. Although nanomedicine has shown great potential for improving the outcomes of tumor diagnosis and therapy, the nonspecial targeted distribution of nanomedicine agents in the whole body causes a low diagnosis signal-to-noise ratio and a potential risk of systemic toxicity. Recently, the development of smart nanomedicine agents with diagnosis and therapy functions that can only be activated by the tumor microenvironment (TME) is regarded as an effective strategy to improve the theranostic sensitivity and selectivity, as well as reduce the potential side effects during treatment. This article will introduce and summarize the latest achievements in the design and fabrication of TME-responsive smart nanomedicine agents, and highlight their prospects for enhancing tumor diagnosis and therapy.

Tailored Design of an ROS-Responsive Drug Release Platform for Enhanced Tumor Therapy via "Sequential Induced Activation Processes"

The reactive oxygen species (ROS)-responsive intelligent drug delivery system has developed rapidly in recent years. However, because of the low concentration of ROS in most types of tumor cells, it is not possible to rapidly and effectively stimulate the drug delivery system to release the active drug. Here, we introduced "sequential induced activation processes" for efficient tumor therapy by designing a new ROS-responsive drug release platform. β-Lapachone, a positively charged nitrogen mustard (NM) prodrug, and two diblock molecules (mPEG-AcMH and PAsp-AcMH) are self-assembled to form prodrug primary micelles, which are further aggregated into nanoparticles that facilitate drug codelivery. When administered by intravenous injection, the nanoparticles reach the tumor site and enter the tumor cells by endocytosis. The β-lapachone released in the tumor cells induces a large amount of H₂O₂, and the ROS-responsive NM prodrug is activated to form activated NM, quinone methide, and boric acid under the induction of H₂O₂. The activated NM leads to tumor cell apoptosis.

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.

ROS-responsive targeting micelles for optical imaging-guided chemo-phototherapy of cancer

The combination of chemotherapy and phototherapy gives rise to a boom in cancer therapy methodology. An all-in-one nanoplatform is of particular interest for increased safety and efficacy geared toward personalized precision medicine. However, low drug loading efficiency, random dispersion and distribution without visualization are widespread concerns. Here, a reactive oxygen species (ROS) responsive drug delivery system for imaging-guided chemo-phototherapy was developed. Polymeric micelles were designed and synthesized using PTX (drug) and Cypate (fluorescence and photosensitizer) as hydrophobic segments and PEG as hydrophilic ones encapsulating PTX. Furthermore, folic acid, as a targeting moiety, was conjugated to PEG for directed drug delivery. We evaluated the ROS-responsive drug release profiles and chemo-phototherapy application in an anticancer therapy. The results suggest these biocompatible amphiphilic polymer conjugates would be promising for applications in imaging-guided chemo-phototherapy.

Tumor-Specific Drug Release and Reactive Oxygen Species Generation for Cancer Chemo/Chemodynamic Combination Therapy

The combination of chemotherapeutic drugs and reactive oxygen species (ROS) is a promising strategy to achieve improved anticancer effect. Herein, a nanomedicine (LaCIONPs) that can achieve tumor-specific chemotherapeutic drug release and ROS generation is developed for cancer chemo/chemodynamic combination therapy. The LaCIONPs are constructed by encapsulation of iron oxide nanoparticles (IONPs) and β-lapachone (La) in nanostructure assembled by hydrogen peroxide (H2O2)-responsive polyprodrug and pH-responsive polymer. Through the enhanced permeability and retention effect, the nanosized LaCIONPs can accumulate in tumor tissue. After the LaCIONPs are internalized by tumor cells, the structure of LaCIONPs is disintegrated in acidic intracellular environment, leading to rapid release of La and iron ions. Then the released La generates massive H2O2 through tumor specific catalysis. On the one hand, H2O2 further reacts with iron ions to produce highly toxic hydroxyl radicals for chemodynamic therapy. On the other hand, H2O2 also activates the release of camptothecin from the polyprodrug for chemotherapy. The potent antitumor effect of the LaCIONPs is demonstrated by both in vitro and in vivo results. Therefore, the LaCIONP is a promising nanomedicine for tumor-specific chemo/chemodynamic combination therapy.

A pH/ROS Cascade-Responsive Charge-Reversal Nanosystem with Self-Amplified Drug Release for Synergistic Oxidation-Chemotherapy

Poor cell uptake of drugs is one of the major challenges for anticancer therapy. Moreover, the inability to release adequate drug at tumor sites and inherent multidrug resistance (MDR) may further limit the therapeutic effect. Herein, a delivery nanosystem with a charge-reversal capability and self-amplifiable drug release pattern is constructed by encapsulating β-lapachone in pH/ROS cascade-responsive polymeric prodrug micelle. The surface charge of this micellar system would be converted from negative to positive for enhanced tumor cell uptake in response to the weakly acidic tumor microenvironment. Subsequently, the cascade-responsive micellar system could be dissociated in a reactive oxygen species (ROS)-rich intracellular environment, resulting in cytoplasmic release of β-lapachone and camptothecin (CPT). Furthermore, the released β-lapachone is capable of producing ROS under the catalysis of nicotinamide adenine dinucleotide (NAD)(P)H:quinone oxidoreductase-1 (NQO1), which induces the self-amplifiable disassembly of the micelles and drug release to consume adenosine triphosphate (ATP) and downregulate P-glycoprotein (P-gp), eventually overcoming MDR. Moreover, the excessive ROS produced from β-lapachone could synergize with CPT and further propagate tumor cell apoptosis. The studies in vitro and in vivo consistently demonstrate that the combination of the pH-responsive charge-reversal, upregulation of tumoral ROS level, and self-amplifying ROS-responsive drug release achieves potent antitumor efficacy via the synergistic oxidation-chemotherapy.

Logical design and application of prodrug platforms

This review summarizes the current state of prodrugs and elaborates the logical design and future development of the prodrug platform.

Integrated block copolymer prodrug nanoparticles for combination of tumor oxidative stress amplification and ROS-responsive drug release

In tumor tissues, reactive oxygen species (ROS) level is significantly higher than that in normal tissues, which has been frequently explored as the specific stimulus to trigger drug release. However, the low intrinsic ROS concentration and heterogeneous distribution in tumor tissues hinder the applications as the stimulus for drug delivery. Herein, we developed integrated nanoparticles to remold tumor microenvironment via specific amplification of the tumor oxidative stress and simultaneously realize ROS-responsive drug release. The amphiphilic block copolymer prodrugs composed of poly(ethylene glycol) and polymerized methacrylate monomer containing thioketal-linked camptothecin (CPT) were synthesized and self-assembled to form core-shell micelles for encapsulation of β-lapachone (Lapa@NPs). After tumor accumulation and internalization into tumor cells post systemic administration of Lapa@NPs, Lapa can selectively induce remarkable ROS level increase via the catalysis of NAD(P)H: quinone oxidoreductase-1 (NQO1) enzyme overexpressed in cancer cells. Subsequently, enhanced ROS concentration would trigger the cleavage of thioketal linkers to release drug. The released CPT together with high ROS level achieved a synergistic therapy to suppress tumor growth. Moreover, Lapa@NPs exhibited superior biosafety due to the tumor-specific activation of the cascade reaction. Accordingly, Lapa@NPs represent a novel polymer prodrug design and drug release strategy via tumor-specific oxidative stress amplification and subsequent ROS-responsive drug release.

An Adenosine Triphosphate-Responsive Autocatalytic Fenton Nanoparticle for Tumor Ablation with Self-Supplied H2O2 and Acceleration of Fe(III)/Fe(II) Conversion

Chemodynamic therapy (CDT) can efficiently destroy tumor cells via Fenton reaction in the presence of H₂O₂ and a robust catalyst. However, it has faced severe challenges including the limited amounts of H₂O₂ and inefficiency of catalysts. Here, an adenosine triphosphate (ATP)-responsive autocatalytic Fenton nanosystem (GOx@ZIF@MPN), incorporated with glucose oxidase (GOx) in zeolitic imidazolate framework (ZIF) and then coated with metal polyphenol network (MPN), was designed and synthesized for tumor ablation with self-supplied H₂O₂ and TA-mediated acceleration of Fe(III)/Fe(II) conversion. In the ATP-overexpressed tumor cells, the outer shell MPN of GOx@ZIF@MPN was degraded into Fe(III) and tannic acid (TA) and the internal GOx was exposed. Then, GOx reacted with the endogenous glucose to produce plenty of H₂O₂, and TA reduced Fe(III) to Fe(II), which is a much more vigorous catalyst for the Fenton reaction. Subsequently, self-produced H₂O₂ was catalyzed by Fe(II) to generate highly toxic hydroxyl radical (•OH) and Fe(III). The produced Fe(III) with low catalytic activity was quickly reduced to reactive Fe(II) mediated by TA, forming an accelerated Fe(III)/Fe(II) conversion to guarantee efficient Fenton reaction-mediated CDT. This autocatalytic Fenton nanosystem might provide a good paradigm for effective tumor treatment.

Hierarchical Tumor Microenvironment-Responsive Nanomedicine for Programmed Delivery of Chemotherapeutics

Nanomedicines have been demonstrated to have passive or active tumor targeting behaviors, which are promising for cancer chemotherapy. However, most nanomedicines still suffer from a suboptimal targeting effect and drug leakage, resulting in unsatisfactory treatment outcome. Herein, a hierarchical responsive nanomedicine (HRNM) is developed for programmed delivery of chemotherapeutics. The HRNMs are prepared via the self-assembly of cyclic Arg-Gly-Asp (RGD) peptide conjugated triblock copolymer, poly(2-(hexamethyleneimino)ethyl methacrylate)-poly(oligo-(ethylene glycol) monomethyl ether methacrylate)-poly[reduction-responsive camptothecin] (PC7A-POEG-PssCPT). In blood circulation, the RGD peptides are shielded by the POEG coating; therefore, the nanosized HRNMs can achieve effective tumor accumulation through passive targeting. Once the HRNMs reach a tumor site, due to the hydrophobic-tohydrophilic conversion of PC7A chains induced by the acidic tumor microenvironment, the RGD peptides will be exposed for enhanced tumor retention and cellular internalization. Moreover, in response to the glutathione inside cells, active CPT drugs will be released rapidly for chemotherapy. The in vitro and in vivo results confirm effective tumor targeting, potent antitumor effect, and reduced systemic toxicity of the HRNMs. This HRNM is promising for enhanced chemotherapeutic delivery.

Hypoxia-responsive block copolymer radiosensitizers as anticancer drug nanocarriers for enhanced chemoradiotherapy of bulky solid tumors

Radiosensitizers play an important role in the clinical radiotherapy of hypoxic solid tumors to improve therapeutic efficacy. However, the in vivo performance of clinically used small-molecule radiosensitizers is commonly compromised by low bioavailability in hypoxic tumor regions. Herein, amphiphilic block copolymer radiosensitizers are prepared from clinically approved poly(ethylene glycol)-block-poly(l-glutamic acid) (PEG-b-PLG) and metronidazole (MN) to obtain MN-grafted PEG-b-PLG (PEG-b-P(LG-g-MN)) via condensation reaction, which can self-assemble into core-shell micelles as nanoparticle-formulated radiosensitizers in aqueous solution. The radiosensitizers are demonstrated to possess significantly higher sensitization enhancement ratio (SER) of 2.18 and potent in vivo tumor ablation capability upon exposure to electron beam irradiation compared with clinically used sodium glycididazole (GS) with SER of 1.32. Moreover, after optimizing the ratios of carboxyl and MN groups, PEG-b-P(LG-g-MN) micelles can be used to encapsulate doxorubicin (DOX@HMs) efficiently. Hypoxia-responsive structural transformation of MN into hydrophilic aminoimidazole triggers fast DOX release from DOX@HMs. After intravenous injection of DOX@HMs, potent ablation capability against bulky solid tumors (∼500 mm³) is realized at a low radiation dose (4 Gy) via enhanced chemoradiotherapy. Therefore, the developed novel amphiphilic block copolymer radiosensitizers can be concurrently used as high-efficiency radiosensitizers and hypoxia-responsive DOX nanocarriers for enhanced chemoradiotherapy.

Glucose- and H2O2-Responsive Polymeric Vesicles Integrated with Microneedle Patches for Glucose-Sensitive Transcutaneous Delivery of Insulin in Diabetic Rats

Herein, a dual-responsive insulin delivery device by integrating glucose- and H₂O₂-responsive polymeric vesicles (PVs) with transcutaneous microneedles (MNs) has been designed. This novel microneedle delivery device achieves a goal of fast response, excellent biocompatibility, and painless administration. The PVs are self-assembled from a triblock copolymer including poly(ethylene glycol), poly(phenylboronic acid) (glucose-sensitive block), and poly(phenylboronic acid pinacol ester) (H₂O₂-sensitive block). After loading with insulin and glucose oxidase (GO _x), the drug-loaded PVs display a basal insulin release as well as a promoted insulin release in response to hyperglycemic states. The insulin release rate responds quickly to elevated glucose and can be further promoted by the incorporated GO _x, which will generate the H₂O₂ at high glucose levels and further break the chemical links of phenylboronic acid pinacol ester group. Finally, the transdermal delivery of insulin to the diabetic rats ((insulin + GO _x)-loaded MNs) presents an effective hypoglycemic effect compared to that of subcutaneous injection or only insulin-loaded MNs, which indicates the as-prepared MNs insulin delivery system could be of great importance for the applications in the therapy of diabetes.

Oxygen-independent combined photothermal/photodynamic therapy delivered by tumor acidity-responsive polymeric micelles

Tumor hypoxia strikingly restricts photodynamic therapy (PDT) efficacy and limits its clinical applications in cancer therapy. The ideal strategy to address this issue is to develop oxygen-independent PDT systems. Herein, the rationally designed tumor pH-responsive polymeric micelles are devised to realize oxygen-independent combined PDT and photothermal therapy (PTT) under near-infrared light (NIR) irradiation. The triblock copolymer, poly(ethylene glycol)-b-poly(ε-caprolactone)-b-poly(2-(piperidin-1-yl)ethyl methacrylate) (PEG-b-PCL-b- PPEMA), was prepared to co-encapsulate cypate and singlet oxygen donor (diphenylanthracene endoperoxide, DPAE) via self-assembly to obtain the micellar delivery system (C/O@N-Micelle). C/O@N-Micelle showed remarkable tumor accumulation and improved cellular internalization (2.1 times) as the pH value was changed from 7.4 during blood circulation to 6.8 in tumor tissues. The micelles could produce a potent hyperthermia for PTT of cypate under 808 nm NIR irradiation, which simultaneously induced thermal cycloreversion of DPAE generating abundant singlet oxygen for PDT without participation of tumor oxygen. Finally, the photothermally triggered PDT and PTT combination achieved efficient tumor ablation without remarkable systemic toxicity in an oxygen-independent manner. This work represents an efficient strategy for oxygen-independent combined PDT and PTT of cancers under NIR irradiation through co-encapsulation of cypate and DPAE into tumor pH-responsive polymeric micelles.

Fast Degradable Polycaprolactone for Drug Delivery

Polycaprolactone (PCL) was reported a long time ago; however, its biomedical applications has not been extensively investigated in comparison with poly(lactide- co-glycolide) (PLGA) due to its too slow degradation profile. Here, we are reporting an oxalate-connected oligocaprolactone multiblock copolymer (PCL-OX) as a fast degradable PCL while maintaining its crystalline properties and low melting point of PCL. The in vivo application of the paclitaxel-loaded PCL-OX microspheres provided a steady plasma drug concentration of 6-9 μg/mL over 28 days, similar to that of the PLGA microspheres. Both PCL and PLGA microspheres were completely cleared two months after in vivo implantation. The PCL-OX microspheres showed a similar tissue compatibility to that of PLGA microspheres in the subcutaneous layer of rats. These findings suggest that PCL-OX is a useful biomaterial that solves the slow degradation problems of PCL and, thus, may find uses in other biomedical applications as an alternative to PLGA.

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.

Novel Metal Polyphenol Framework for MR Imaging-Guided Photothermal Therapy

Phothermal therapy has received increasing attention in recent years as a potentially effective way to treat cancer. In pursuit of a more biocompatible photothermal agent, we utilize biosafe materials including ellagic acid (EA), polyvinylpyrrolidone (PVP), and iron element as building blocks, and we successfully fabricate a homogeneous nanosized Fe-EA framework for the first time by a facile method. As expected, the novel nanoagent exhibits no obvious cytotoxicity and good hemocompatibility in vitro and in vivo. The microenvironment responsiveness to both pH and hydrogen peroxide makes the NPs biodegradable in tumor tissues, and the framework should be easily cleared by the body. Photothermal potentials of the nanoparticles are demonstrated with relevant features of strong NIR light absorption, moderately effective photothermal conversion efficiency, and good photothermal stability. The in vivo photothermal therapy also achieved effective tumor ablation with no apparent toxicity. On the other hand, it also exhibits T2 MR imaging ability originated from ferric ions. Our work highlights the promise of the Fe-EA framework for imaging-guided photothermal therapy.

Oxidation-responsive micelles by a one-pot polymerization-induced self-assembly approach

Combining a sequential, one-pot RAFT polymerization with the polymerization-induced self-assembly process results in a versatile oxidation-responsive carrier system.

Polymer Prodrug-Based Nanoreactors Activated by Tumor Acidity for Orchestrated Oxidation/Chemotherapy

Therapeutic nanoreactors have been proposed to treat cancers through in situ transformation of low-toxicity prodrugs into toxic therapeutics in the body. However, the in vivo applications are limited by low tissue-specificity and different tissue distributions between sequentially injected nanoreactors and prodrugs. Herein, we construct a block copolymer prodrug-based polymersome nanoreactor that can achieve novel orchestrated oxidation/chemotherapy of cancer via specific activation at tumor sites. The block copolymers composed of poly(ethylene glycol) (PEG) and copolymerized monomers of camptothecin (CPT) and piperidine-modified methacrylate [P(CPTMA-co-PEMA)] were optimized to self-assemble into polymersomes in aqueous solution for encapsulation of glucose oxidase (GOD) to obtain GOD-loaded polymersome nanoreactors (GOD@PCPT-NR). GOD@PCPT-NR maintained inactive in normal tissues upon systemic administration. After deposition in tumor tissues, tumor acidity-triggered protonation of PPEMA segments resulted in high permeability of the polymersome membranes and oxidation reaction of diffused glucose and O₂ under the catalysis of GOD. The activation of the reaction generated H₂O₂, improving the oxidative stress in tumors. Simultaneously, a high level of H₂O₂ further activated PCPTMA prodrugs, releasing active CPT drugs. High tumor oxidative stress and released CPT drugs synergistically killed cancer cells and suppressed tumor growth via oxidation/chemotherapy. Our study provides a new strategy for engineering therapeutic nanoreactors in an orchestrated fashion for cancer therapy.

Integrated Nanoparticles To Synergistically Elevate Tumor Oxidative Stress and Suppress Antioxidative Capability for Amplified Oxidation Therapy

The improved antioxidant system of cancer cells renders them well-adaptive to the intrinsic oxidative stress in tumor tissues. On the other hand, cancer cells are more sensitive to elevated tumor oxidative stress as compared with normal cells due to their deficient reactive oxygen species-eliminating systems. Oxidation therapy of cancers refers to the strategy of killing cancer cells through selectively increasing the oxidative stress in tumor tissues. In this article, to amplify the oxidation therapy, we develop integrated nanoparticles with the properties to elevate tumor oxidative stress and concurrently suppress the antioxidative capability of cancer cells. The amphiphilic block copolymer micelles of poly(ethylene glycol)-b-poly[2-((((4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)benzyl)oxy)carbonyl)oxy)ethyl methacrylate] (PEG-b-PBEMA) are integrated with palmitoyl ascorbate (PA) to form hybrid micelles (PA-Micelle). PA molecules at pharmacologic concentrations serve as a prooxidant to upregulate the hydrogen peroxide (H₂O₂) level in tumor sites and the PBEMA segment exhibits H₂O₂-triggered release of quinone methide for glutathione depletion to suppress the antioxidative capability of cancer cells, which synergistically and selectively kill cancer cells for tumor growth suppression. Given the significantly low side toxicity against normal tissues, this novel integrated nanoparticle design represents a novel class of nanomedicine systems for high-efficiency oxidation therapy with the potentials to be translated to clinical applications.

ROS-Responsive Polyprodrug Nanoparticles for Triggered Drug Delivery and Effective Cancer Therapy

The application of nanoparticles (NPs) to drug delivery has led to the development of novel nanotherapeutics for the treatment of various diseases including cancer. However, clinical use of NP-mediated drug delivery has not always translated into improved survival of cancer patients, in part due to the suboptimal properties of NP platforms, such as premature drug leakage during preparation, storage, or blood circulation, lack of active targeting to tumor tissue and cells, and poor tissue penetration. Herein, an innovative reactive oxygen species (ROS)-responsive polyprodrug is reported that can self-assemble into stable NPs with high drug loading. This new NP platform is composed of the following key components: (i) polyprodrug inner core that can respond to ROS for triggered release of intact therapeutic molecules, (ii) polyethylene glycol (PEG) outer shell to prolong blood circulation; and (iii) surface-encoded internalizing RGD (iRGD) to enhance tumor targeting and tissue penetration. These targeted ROS-responsive polyprodrug NPs show significant inhibition of tumor cell growth both in vitro and in vivo.

Polymeric micelles with dual thermal and reactive oxygen species (ROS)-responsiveness for inflammatory cancer cell delivery

Background

The object of this study was to develop a thermally and reactive oxygen species-responsive nanocarrier system for cancer therapy.

Results

PPS-PNIPAm block copolymer was designed and synthesised using a combination of living anionic ring-opening polymerization and atom transfer radical polymerization. The synthesized polymer formed micellar aggregates in water and demonstrated dual responsiveness towards temperature and oxidants. Using doxorubicin (DOX) as a model drug, encapsulation and in vitro release of the drug molecules in PPS-PNIPAm nanocarriers confirmed the responsive release properties of such system. Cell uptake of the DOX loaded micelles was investigated with human breast cancer cell line (MCF-7). The results showed Dox-loaded micelles were able to be taken by the cells and mainly reside in the cytoplasma. In the stimulated cells with an elevated level of ROS, more released DOX was observed around the nuclei. In the cytotoxicity experiments, the Dox-loaded micelles demonstrated comparable efficacy to free DOX at higher concentrations, especially on ROS stimulated cells.

Conclusions

These results demonstrated that PPS-PNIPAm nanocarriers possess the capability to respond two typical stimuli in inflammatory cells: temperature and oxidants and can be used in anticancer drug delivery.

Electronic supplementary material

The online version of this article (doi:10.1186/s12951-017-0275-4) contains supplementary material, which is available to authorized users.

Synthesis of a phenylboronic ester-linked PEG-lipid conjugate for ROS-responsive drug delivery

A kind of phenylboronic ester-linked PEG-lipid conjugate was designed and synthesized for ROS-responsive drug delivery.