In vivo tailor-made protein corona of a prodrug-based nanoassembly fabricated by redox dual-sensitive paclitaxel prodrug for the superselective treatment of breast cancer

In situ customized apolipoprotein B48-enriched protein corona enhances oral gene delivery of chitosan-based nanoparticles

The formation of protein corona (PC) is important for promoting the in vivo delivery of nanoparticles (NPs). However, PC formed in the physiological environment of oral delivery is poorly understood. Here, we engineered seven types of trimethyl chitosan-cysteine (TC) NPs, with distinct molecular weights, quaternization degrees, and thiolation degrees, to deeply investigate the influence of various PC formed in the physiological environment of oral delivery on in vivo gene delivery of polymeric NPs, further constructing the relationship between the surface characteristics of NPs and the efficacy of oral gene delivery. Our findings reveal that TC7 NPs, with high molecular weight, moderate quaternization, and high sulfhydryl content, modulate PC formation in the gastrointestinal tract, thereby reducing particle size and promoting oral delivery of gene loaded TC7 NPs. Orally delivered TC7 NPs target macrophages by in situ adsorption of apolipoprotein (Apo) B48 in intestinal tissue, leading to the improved in vivo antihepatoma efficacy via the natural tumor homing ability of macrophages. Our results suggest that efficient oral delivery of genes can be achieved through an in situ customized ApoB48-enriched PC, offering a promising modality in treating macrophage-related diseases.

A paclitaxel prodrug nanoparticles with glutathion/reactive oxygen species dual-responsive and CD206 targeting to improve the anti-tumour effect

As a first-line anticancer drug, paclitaxel has shortcomings, such as poor solubility and lack of tumour cell selectivity, which limit its further applications in clinical practice. Therefore, the authors aimed to utilise the characteristics of prodrug and nanotechnology to prepare a reactive oxygen species (ROS) and GSH dual-responsive targeted tumour prodrug nanoparticle Man-PEG-SS-PLGA/ProPTX to improve the clinical application status of paclitaxel limitation. The characterisation of Man-PEG-SS-PLGA/ProPTX was carried out through preparation. The cytotoxicity of nanoparticles on tumour cells and the effect on apoptosis of tumour cells were investigated by cytotoxicity assay and flow cytometry analysis. The ROS responsiveness of nanoparticles was investigated by detecting the ROS level of tumour cells. The tumour cell selectivity of the nanoparticles was further investigated by receptor affinity assay and cell uptake assay. The particle size of Man-PEG-SS-PLGA/ProPTX was (132.90 ± 1.81) nm, the dispersion coefficient Polymer dispersity index was 0.13 ± 0.03, and the Zeta potential was (-8.65 ± 0.50) mV. The encapsulation rate was 95.46 ± 2.31% and the drug load was 13.65 ± 2.31%. The nanoparticles could significantly inhibit the proliferation and promote apoptosis of MCF-7, HepG2, and MDA-MB-231 tumour cells. It has good ROS response characteristics and targeting. The targeted uptake mechanism is energy-dependent and endocytosis is mediated by non-clathrin, non-caveolin, lipid raft/caveolin, and cyclooxygenase (COX)/caveolin with a certain concentration dependence and time dependence. Man-PEG-SS-PLGA/ProPTX is a tumour microenvironment-responsive nanoparticle that can actively target tumour cells. It restricts the release of PTX in normal tissues, enhances its selectivity to tumour cells, and has significant antitumour activity, which is expected to solve the current limitations of PTX use.

Transporter-Mediated Drug Delivery

Transmembrane transport of small organic and inorganic molecules is one of the cornerstones of cellular metabolism. Among transmembrane transporters, solute carrier (SLC) proteins form the largest, albeit very diverse, superfamily with over 400 members. It was recognized early on that xenobiotics can directly interact with SLCs and that this interaction can fundamentally determine their efficacy, including bioavailability and intertissue distribution. Apart from the well-established prodrug strategy, the chemical ligation of transporter substrates to nanoparticles of various chemical compositions has recently been used as a means to enhance their targeting and absorption. In this review, we summarize efforts in drug design exploiting interactions with specific SLC transporters to optimize their therapeutic effects. Furthermore, we describe current and future challenges as well as new directions for the advanced development of therapeutics that target SLC transporters.

Taxanes prodrug-based nanomedicines for cancer therapy

Malignant tumor remains a huge threat to human health and chemotherapy still occupies an important place in clinical tumor treatment. As a kind of potent antimitotic agent, taxanes act as the first-line broad-spectrum cancer drug in clinical use. However, disadvantages such as prominent hydrophobicity, severe off-target toxicity or multidrug resistance lead to unsatisfactory therapeutic effects, which restricts its wider usage. The efficient delivery of taxanes is still quite a challenge despite the rapid developments in biomaterials and nanotechnology. Great progress has been made in prodrug-based nanomedicines (PNS) for cancer therapy due to their outstanding advantages such as high drug loading efficiency, low carrier induced immunogenicity, tumor stimuli-responsive drug release, combinational therapy and so on. Based on the numerous developments in this filed, this review summarized latest updates of taxanes prodrugs-based nanomedicines (TPNS), focusing on polymer-drug conjugate-based nanoformulations, small molecular prodrug-based self-assembled nanoparticles and prodrug-encapsulated nanosystems. In addition, the new trends of tumor stimuli-responsive TPNS were also discussed. Moreover, the future challenges of TPNS for clinical translation were highlighted. We here expect this review will inspire researchers to explore more practical taxanes prodrug-based nano-delivery systems for clinical use.

HSA-Binding Prodrugs-Based Nanoparticles Endowed with Chemo and Photo-Toxicity against Breast Cancer

Exploiting the tumor environment features (EPR effect, elevated glutathione, reactive oxygen species levels) might allow attaining a selective and responsive carrier capable of improving the therapeutic outcome. To this purpose, the in situ covalent binding of drugs and nanoparticles to circulating human serum albumin (HSA) might represent a pioneering approach to achieve an effective strategy. This study describes the synthesis, in vitro and in vivo evaluation of bioresponsive HSA-binding nanoparticles (MAL-PTX₂S@Pba), co-delivering two different paclitaxel (PTX) prodrugs and the photosensitizer pheophorbide a (Pba), for the combined photo- and chemo-treatment of breast cancer. Stable and reproducible MAL-PTX₂S@Pba nanoparticles with an average diameter of 82 nm and a PTX/Pba molar ratio of 2.5 were obtained by nanoprecipitation. The in vitro 2D combination experiments revealed that MAL-PTX₂S@Pba treatment induces a strong inhibition of cell viability of MDA-MB-231, MCF7 and 4T1 cell lines, whereas 3D experiments displayed different trends: while MAL-PTX₂S@Pba effectiveness was confirmed against MDA-MB-231 spheroids, the 4T1 model exhibited marked resistance. Lastly, despite using a low PTX-PDT regimen (e.g., 8.16 mg/Kg PTX and 2.34 mg/Kg Pba), our formulation showed to foster primary tumor reduction and curb lung metastases growth in 4T1 tumor-bearing mice, thus setting the basis for further preclinical validations.

Delivery nanoplatforms based on dynamic covalent chemistry

As a paramount factor to restrict the potential action of drugs and biologics, nanoplatforms based on dynamic covalent chemistry have been demonstrated as promising candidates to fulfill the full requirements during the whole delivery process by the virtue of their remarkable features such as adaptiveness, stimuli-responsiveness, specificity, reversibility and feasibility. This contribution summarizes the latest progress in dynamic covalent bond-based nanoplatforms with improved delivery efficiency and therapeutic performance. In addition, major challenges and perspectives in this field are also discussed. We expect that this feature article will provide a valuable and systematic reference for the further development of dynamic covalent bond-based nanoplatforms.

Pure redox-sensitive paclitaxel-maleimide prodrug nanoparticles: Endogenous albumin-induced size switching and improved antitumor efficiency

A commercial albumin-bound paclitaxel nano-formulation has been considered a gold standard against breast cancer. However, its application still restricted unfavorable pharmacokinetics and the immunogenicity of exogenous albumin carrier. Herein, we report an albumin-bound tumor redox-responsive paclitaxel prodrugs nano-delivery strategy. Using diverse linkages (thioether bond and disulfide bond), paclitaxel (PTX) was conjugated with an albumin-binding maleimide (MAL) functional group. These pure PTX prodrugs could self-assemble to form uniform and spherical nanoparticles (NPs) in aqueous solution without any excipients. By immediately binding to blood circulating albumin after intravenous administration, NPs are rapidly disintegrated into small prodrug/albumin nanoaggregates in vivo, facilitating PTX prodrugs accumulation in the tumor region via albumin receptor-mediated active targeting. The tumor redox dual-responsive drug release property of prodrugs improves the selectivity of cytotoxicity between normal and cancer cells. Moreover, disulfide bond-containing prodrug/albumin nanoaggregates exhibit long circulation time and superior antitumor efficacy in vivo. This simple and facile strategy integrates the biomimetic characteristic of albumin, tumor redox-responsive on-demand drug release, and provides new opportunities for the development of the high-efficiency antitumor nanomedicines.

Drug Release from Disulfide-Linked Prodrugs: Role of Thiol Agents

The disulfide bond (SS) has been widely used in prodrugs for the redox-responsive drug release, but its drug release mechanism and rate were seldom compared in different thiol agents. Herein, self-assembling nanoaggregates (NAs) formed by camptothecin (CPT)-oleic acid (OA) prodrugs linked by two frequently used SS linkers (ETCSS and ACSS) were used for such comparative investigation. It is found that the cleavage of ETCSS was directly coupled with CPT release, whereas the breakage of ACSS resulted in the generation of CPT intermediates, the chemical stability of which determined CPT release. In both cases, the redox-responsive drug release was highly dependent on the reactivity between SS and thiol agents, with an order of dithiothreitol > cysteine ≈ glutathione. Moreover, the presence of SS significantly accelerated the extracellular CPT release, which was around 3-4 fold higher than intracellular CPT release. Therefore, the in vitro cytotoxicity of SS-linked CPT-OA NAs could not be ascribed to the glutathione-trigged intracellular drug release but rather to the SS-accelerated extracellular CPT release. The above results would effectively guide the rational design and evaluation of SS-linked prodrug NAs for efficient drug delivery.

An albumin-binding dimeric prodrug nanoparticle with long blood circulation and light-triggered drug release for chemo-photodynamic combination therapy against hypoxia-induced metastasis of lung cancer

Photodynamic therapy (PDT) has been widely used in cancer therapy, but its therapeutic effect is reduced by the aggravating hypoxic microenvironment via upregulating hypoxia-associated proteins and promoting tumor metastasis. To mitigate these issues, we designed an albumin-binding and light-triggered core-shell dimeric prodrug nanoparticle to inhibit hypoxia-induced tumor metastasis and enhance the PDT efficacy. The prodrug nanoparticles, Ce6&DHA-S-DHA@CMN NPs (CDC NPs), were prepared using a single thioether-linked dihydroartemisinin (DHA) dimer co-encapsulated with Chlorin e6 (Ce6) and stabilized by albumin-capturing maleimide- and hypoxia-sensitive 2-nitroimidazole-modified carboxymethyl chitosan (CMCTS-MAL&NI, CMN for short). Upon laser irradiation, Ce6 could generate reactive oxygen species (ROS), which not only exerted the effect of the PDT but also broke the ROS-sensitive single thioether bridge in the dimeric prodrug DHA-S-DHA, thus accelerating the disassembly of the nanoparticles. DHA-S-DHA served as both an ROS-responsive carrier for Ce6 and a chemotherapeutic drug, synergizing with PDT and inhibiting tumor metastasis by downregulating hypoxia-inducible factor-1α (HIF-1α)/vascular endothelial growth factor (VEGF). Polyethylene glycol (PEG) modification has been widely used to stabilize hydrophobic prodrug nanoparticles and prolong the circulation time, but the PEGylated nanoparticles always suffer from accelerated blood clearance (ABC), a phenomenon which restricts their application severely. In this study, PEG was replaced by an amphipathic micelle, CMN, which could specifically capture albumin in the blood, conferring the nanoparticles long circulation and no ABC phenomenon. Under the aggravating hypoxic condition during PDT, the conversion of 2-nitroimidazole groups to 2-aminoimidazole groups in CMN could destabilize the structure of the shell and accelerate drug release. Results showed that the novel CDC NPs exhibited unique advantages in chemo-photodynamic combination therapy, such as long systemic circulation, high tumor accumulation, light-triggered drug release, HIF-1α/VEGF downregulation, and anti-metastasis efficacy, which provided a new route to overcome the ABC phenomenon of the PEGylated prodrug nanoparticles and reverse the hypoxia-induced metastasis simultaneously.

Emerging nanotaxanes for cancer therapy

The clinical application of taxane (including paclitaxel, docetaxel, and cabazitaxel)-based formulations is significantly impeded by their off-target distribution, unsatisfactory release, and acquired resistance/metastasis. Recent decades have witnessed a dramatic progress in the development of high-efficiency, low-toxicity nanotaxanes via the use of novel biomaterials and nanoparticulate drug delivery systems (nano-DDSs). Thus, in this review, the achievements of nanotaxanes-targeted delivery and stimuli-responsive nano-DDSs-in preclinical or clinical trials have been outlined. Then, emerging nanotherapeutics against tumor resistance and metastasis have been overviewed, with a particular emphasis on synergistic therapy strategies (e.g., combination with surgery, chemotherapy, radiotherapy, biotherapy, immunotherapy, gas therapy, phototherapy, and multitherapy). Finally, the latest oral nanotaxanes have been briefly discussed.

Redox-responsive prodrug for improving oral bioavailability of paclitaxel through bile acid transporter-mediated pathway

Most anticancer drugs are not orally bioavailable due to their undesirable physicochemical properties and inherent physiological barriers. In this study, a polymeric prodrug strategy was presented to enhance the oral bioavailability of BCS class IV drugs using paclitaxel (PTX) as the model drug. PTX was covalently conjugated with cholic acid-functionalized PEG by a redox-sensitive disulfide bond. Cholic acid-functionalized PEGylated PTX (CPP) achieved remarkably improved PTX solubility (>30,000-fold), as well as favorable stability under the physiological environment and controlled drug release in the tumor. Meanwhile, CPP could self-assemble into nanoparticles with an average size of 56.18 ± 2.06 nm and drug loading up to 17.6% (w/w). Then, permeability study on Caco-2 cell monolayers demonstrated that CPP obtained an approximately 4-fold increase by apical sodium-dependent bile acid transporter (ASBT) mediated transport, compared with Taxol®. Pharmacokinetic studies carried out in rats confirmed that the oral bioavailability of CPP was 10-fold higher than that of Taxol®. Finally, significant improvement in the antitumor efficacy of CPP against breast cancer was confirmed on MDA-MB-231 cells. In summary, this prodrug-based cascade strategy offers new ways for chemotherapeutic drugs whose oral delivery is limited by solubility and permeability, also endows drugs with the capacity of tumor-specific release.

Nanoplatforms for Targeted Stimuli-Responsive Drug Delivery: A Review of Platform Materials and Stimuli-Responsive Release and Targeting Mechanisms

To achieve the promise of stimuli-responsive drug delivery systems for the treatment of cancer, they should (1) avoid premature clearance; (2) accumulate in tumors and undergo endocytosis by cancer cells; and (3) exhibit appropriate stimuli-responsive release of the payload. It is challenging to address all of these requirements simultaneously. However, the numerous proof-of-concept studies addressing one or more of these requirements reported every year have dramatically expanded the toolbox available for the design of drug delivery systems. This review highlights recent advances in the targeting and stimuli-responsiveness of drug delivery systems. It begins with a discussion of nanocarrier types and an overview of the factors influencing nanocarrier biodistribution. On-demand release strategies and their application to each type of nanocarrier are reviewed, including both endogenous and exogenous stimuli. Recent developments in stimuli-responsive targeting strategies are also discussed. The remaining challenges and prospective solutions in the field are discussed throughout the review, which is intended to assist researchers in overcoming interdisciplinary knowledge barriers and increase the speed of development. This review presents a nanocarrier-based drug delivery systems toolbox that enables the application of techniques across platforms and inspires researchers with interdisciplinary information to boost the development of multifunctional therapeutic nanoplatforms for cancer therapy.

Oxidation-strengthened disulfide-bridged prodrug nanoplatforms with cascade facilitated drug release for synergetic photochemotherapy

One of the major barriers in utilizing prodrug nanocarriers for cancer therapy is the slow release of parent drug in tumors. Tumor cells generally display the higher oxidative level than normal cells, and also displayed the heterogeneity in terms of redox homeostasis level. We previously found that the disulfide bond-linkage demonstrates surprising oxidation-sensitivity to form the hydrophilic sulfoxide and sulphone groups. Herein, we develop oxidation-strengthened prodrug nanosystem loaded with pyropheophorbide a (PPa) to achieve light-activatable cascade drug release and enhance therapeutic efficacy. The disulfide bond-driven prodrug nanosystems not only respond to the redox-heterogeneity in tumor, but also respond to the exogenous oxidant (singlet oxygen) elicited by photosensitizers. Once the prodrug nanoparticles (NPs) are activated under irradiation, they would undergo an oxidative self-strengthened process, resulting in a facilitated drug cascade release. The IC50 value of the PPa@PTX-S-S NPs without irradiation was 2-fold higher than those of NPs plus irradiation. In vivo, the PPa@PTX prodrug NPs display prolonged systemic circulation and increased accumulation in tumor site. The PPa@PTX-S-S NPs showed much higher efficiency than free PTX or the PPa@PTX-C-C NPs to suppress the growth of 4T1 tumors. Therefore, this novel oxidation-strengthened disulfide-bridged prodrug-nanosystem has a great potential in the enhanced efficacy of cancer synergetic photochemotherapy.

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.

Development of synthetic high-density lipoprotein-based ApoA-I mimetic peptide-loaded docetaxel as a drug delivery nanocarrier for breast cancer chemotherapy

In this study, a synthetic high-density lipoprotein (sHDL), peptide-based nanocarrier loaded with docetaxel (DTX) was constructed, against breast cancer. The thermodynamic and molecular dynamic analyses were conducted to examine the stability of nanoparticles synthesized from mimetic peptide 5 A and various types of phospholipids. Furthermore, the cellular uptake and in vivo fluorescence imaging analysis experiments, with scavenger receptor B-I (SR-BI) were carried out to examine the tumor-targeting ability of sHDL. The nanoparticles were investigated for their pharmacodynamic and cytotoxic effects to show their effectivity as anti-tumor agents. The results showed that the synthesized sHDL nanoparticles exhibited a high payload of DTX, sustained drug release properties, and excellent biocompatibility. Moreover, DTX-sHDL nanoparticles enhanced the uptake of DTX, increased the cytotoxicity against MCF-7 cells, and reduced the off-target side-effects to normal cells. Finally, experiments in 4T1 cell line-bearing mice indicate that inhibition of tumor growth by DTX-sHDL nanoparticles was superior to that of free DTX group. Thus, the sHDL nanoparticles are a promising drug delivery vehicle for improving the efficacy of anti-cancer drugs.

Emerging well-tailored nanoparticulate delivery system based on in situ regulation of the protein corona

The protein corona significantly changes the nanoparticle (NP) identity both physicochemically and biologically, and in situ regulation of specific plasma protein adsorption on NP surfaces has emerged as a promising strategy for disease-targeting therapy. In the past decade, great progress in protein corona regulation has been achieved via surface chemistry-based nanomedicine development. This review first outlines the latest advances in bio-nano interactions, with special attention to factors that influence the protein corona, including NP physicochemical properties, the biological environment and the duration time. Second, NP surface chemistry strategies designed to inhibit and regulate protein corona formation are highlighted, with special emphasis on albumin, transferrin, apolipoprotein (apo) E, vascular endothelial growth factor (VEGF) and retinol binding protein 4 (RBP4). Finally, the current techniques used to characterize the protein corona are briefly discussed.

Understanding the relevance of protein corona in nanoparticle-based therapeutics and diagnostics

Over the past few decades, nanoparticle-based therapeutic and diagnostic systems have gained immense recognition. A relative improvement in the status of the global cancer burden has been successful due to the advent of nanoparticle-based formulations. However, exposure of nanoparticles (NPs) to a real-time biological media alters its native identity due to the formation of the biomolecular corona. Such biological interactions hinder the efficiency of the NPs system. The parameters that govern such intricate interaction are generally overlooked while designing nano drugs and delivery systems (nano-DDS). Fabricating nano-DDS with prolonged circulation time, enhanced drug-loading, and release capacity along with efficient clearance, remain the primary concerns associated with cancer therapeutics. This present review firstly aims to summarize the critical aspects that influence protein coronation on therapeutic nanoparticles designed for anti-cancer therapy. The role of protein corona in modifying the overall pharmacodynamics of the nanoparticle-based DDS has been discussed. Further, the studies and patents that extend the concept of protein corona into diagnostics have been elaborated. An understanding of the pros and cons associated with protein coronation would not only help us gain better insights into the fabrication of effective anti-cancer drug-delivery systems but also improve the shortcomings related to the clinical translation of these nanotherapeutics.

Protein corona and its applications.

Manganese dioxide nanosheets: from preparation to biomedical applications

Advancements in nanotechnology and molecular biology have promoted the development of a diverse range of models to intervene in various disorders (from diagnosis to treatment and even theranostics). Manganese dioxide nanosheets (MnO₂ NSs), a typical two-dimensional (2D) transition metal oxide of nanomaterial that possesses unique structure and distinct properties have been employed in multiple disciplines in recent decades, especially in the field of biomedicine, including biocatalysis, fluorescence sensing, magnetic resonance imaging and cargo-loading functionality. A brief overview of the different synthetic methodologies for MnO₂ NSs and their state-of-the-art biomedical applications is presented below, as well as the challenges and future perspectives of MnO₂ NSs.

High Co-loading Capacity and Stimuli-Responsive Release Based on Cascade Reaction of Self-Destructive Polymer for Improved Chemo-Photodynamic Therapy

Photodynamic therapy (PDT) shows a promising synergy with chemotherapy in the therapeutic outcome of malignant cancers. The minimal invasiveness and nonsystemic toxicity are appealing advantages of PDT, but combination with chemotherapy brings in the nonselective toxicity. We designed a polymeric nanoparticle system that contains both a chemotherapeutic agent and a photosensitizer to seek improvement for chemo-photodynamic therapy. First, to address the challenge of efficient co-delivery, polymer-conjugated doxorubicin (PEG-PBC-TKDOX) was synthesized to load photosensitizer chlorin e6 (Ce6). Ce6 is retained with DOX by a π-π stacking interaction, with high loading (41.9 wt %) and the optimal nanoparticle size (50 nm). Second, light given in PDT treatment not only excites Ce6 to produce cytotoxic reactive oxygen species (ROS) but also spatiotemporally activates a cascade reaction to release the loaded drugs. Finally, we report a self-destructive polymeric carrier (PEG-PBC-TKDOX) that depolymerizes its backbone to facilitate drug release upon ROS stimulus. This is achieved by grafting the ROS-sensitive pendant thioketal to aliphatic polycarbonate. When DOX is covalently modified to this polymer via thioketal, target specificity is controlled by light, and off-target delivery toxicity is mostly avoided. An oral squamous cell carcinoma that is clinically relevant to PDT was used as the cancer model. We put forward a polymeric system with improved efficiency for chemo-photodynamic therapy and reduced off-target toxicity.

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.

Self-Strengthened Oxidation-Responsive Bioactivating Prodrug Nanosystem with Sequential and Synergistically Facilitated Drug Release for Treatment of Breast Cancer

Although environment-sensitive prodrug-based nanoparticles (NPs) have developed rapidly, lots of prodrug NPs still show poor selectivity and efficiency of parent drug bioactivation because of tumor heterogeneity. Herein, self-strengthened bioactivating prodrug-based NPs are fabricated via co-encapsulation of oxidation-responsive thioether-linked linoleic acid-paclitaxel conjugates (PTX-S-LA) and β-lapachone (LPC) into polymeric micelles (PMs). Following cellular uptake, PMs first release LPC to significantly elevate the reactive oxidative species (ROS) level through NAD(P)H: quinone oxidoreductase-1 (NQO1) catalysis. Then, NQO1-generated ROS in combination with endogenous high ROS levels in tumor cells could synergistically facilitate PTX-S-LA to release the active cytotoxic agent PTX. Such a novel prodrug nanosystem exhibits self-strengthened prodrug bioactivation, ultraselective release, and cytotoxicity between cancer and normal cells, prolonged circulation time, and enhanced tumor accumulation, leading to high antitumor efficiency and superior biosafety. Our findings pave the new way for the rational design of oxidation-responsive prodrug NPs for high-efficacy cancer chemotherapy.

Polydopamine-modified ROS-responsive prodrug nanoplatform with enhanced stability for precise treatment of breast cancer

Development of smart stimuli-responsive prodrug nanomaterials for fast drug release and efficient antitumor therapy has attracted great attention in recent years. However, the inherent instability of naked prodrugs in the blood is an important challenge limiting their biomedical applications. Although a number of strategies have been taken to prevent prodrugs from hydrolyzing due to blood composition, most of these strategies are unsatisfactory. Here, we designed an extraordinary ROS-triggered prodrug nanoplatform fabricated by using a single thioether linker to conjugate PTX with 6-maleimidocaproic acid (MAL), resulting in the PTX-S-MAL prodrug self-assembling into uniform size nanoparticles; then the prodrug nanoplatform was modified with a polydopamine coating and PEGylation to confer high solubility and stability. In in vitro experiments, the polydopamine-modified ROS-responsive prodrug nanosystem showed a high sensitivity in term of various H₂O₂ concentrations, and the PDA coating on the surface of the prodrug nanosystem didn't affect the drug release properties. Moreover, the excellent polydopamine-modified ROS-triggered prodrug nanoplatform selectively and rapidly releases PTX in response to the ROS overproduced in tumor cells, but showed less cytotoxicity against normal cells. In in vivo experiments, the prepared polydopamine-modified prodrug-nanosystem obviously enhances the stability and tumor accumulation of prodrug, producing a remarkably improved breast cancer treatment with minimal side effects. Our studies demonstrated that this modified nanoplatform could significantly improve chemotherapy efficiency, which will find great potential in cancer treatment.

Development of smart stimuli-responsive prodrug nanomaterials for fast drug release and efficient antitumor therapy has attracted great attention in recent years.