Hypoxia-responsive nanoparticle based drug delivery systems in cancer therapy: An up-to-date review

Enhancing the therapeutic efficacy of nanoparticles for cancer treatment using versatile targeted strategies

Poor targeting of therapeutics leading to severe adverse effects on normal tissues is considered one of the obstacles in cancer therapy. To help overcome this, nanoscale drug delivery systems have provided an alternative avenue for improving the therapeutic potential of various agents and bioactive molecules through the enhanced permeability and retention (EPR) effect. Nanosystems with cancer-targeted ligands can achieve effective delivery to the tumor cells utilizing cell surface-specific receptors, the tumor vasculature and antigens with high accuracy and affinity. Additionally, stimuli-responsive nanoplatforms have also been considered as a promising and effective targeting strategy against tumors, as these nanoplatforms maintain their stealth feature under normal conditions, but upon homing in on cancerous lesions or their microenvironment, are responsive and release their cargoes. In this review, we comprehensively summarize the field of active targeting drug delivery systems and a number of stimuli-responsive release studies in the context of emerging nanoplatform development, and also discuss how this knowledge can contribute to further improvements in clinical practice.

Photoacoustic-triggered nanomedicine delivery to internal organs using a dual-wavelength laparoscope

Precise drug delivery for internal organs is always an important clinical issue. In this study, we developed a dual-wavelength optical resolution photoacoustic laparoscope, and achieved precise and efficient delivery of nanomedicine to multiple abdominal organs. The laparoscope integrated 532 and 820 nm light to map the vascular network, and visually deliver the nanoparticles to the targeted area using photoacoustic radiation force, respectively. To achieve endoscopic use, we employed a micro-electro-mechanical-system (MEMS) scanner to realize internal two-dimensional raster scanning of the optical beams. Using phantom experiments, the lateral resolutions were measured as 3.75 μm for 532 nm, and 5.25 μm for 820 nm, respectively. Besides, we demonstrated the feasibility of targeted drug delivery using mouse-ear tumor model, normal organs, and colon tumor model. All the experimental results suggested that this strategy can serve as a promising precise drug delivery method for the effective treatment of internal organ diseases.

A self-activating nanoized vascular disrupting agent for selective anti-tumor therapy

Vascular disrupting agents (VDAs) have great potential in antitumor therapy, while the efficiency is limited by cardiovascular toxicity. In this study, a self-activating nanoized plinabulin (poly (_l-glutamic acid) grafted Azo-Plinabulin, AzoP-NP) was constructed. The AzoP-NPs can selectively be activated to an amino derivative of plinabulin (AmP) by intrinsic tumor hypoxia, disrupting tumor vessels and amplifying hypoxia, whilst be activated by self-amplified tumor hypoxia, then selectively inhibit tumor growth. In 4T1 tumor model, the AzoP-NPs had a selective biodistribution in tumor, as the free AmP in tumors at 24 h after AzoP-NPs treatment was 18.6 fold of that after AmP treatment and significantly higher than that in other tissues. Accordingly, AzoP-NPs resulted in no obvious acute cardiovascular toxicity (plasma von Willebrand factor in PBS, AzoP-NPs and AmP group: 143.1, 184.0 and 477.6 ng/mL) and a significantly stronger tumor inhibition than AmP. And the sustained release of drug in AzoP-NPs led to a higher maximum tolerated dose (MTD) (MTD of AzoP-NPs and AmP: > 80 vs 20 mg/kg). In addition, AzoP-NPs amplified tumor hypoxic, and synergized the anti-tumor effect of Tirapazamine (TPZ), a hypoxia-activated drug in clinical trials, with an inhibition rate of 97.7% and Q value of 1.89. Therefore, our findings provide new insights into next generation VDAs and their application in tumor therapy.

Ferroptosis-based nano delivery systems targeted therapy for colorectal cancer: Insights and future perspectives

There are limited options for patients who develop liver metastasis from colorectal cancer (CRC), the leading cause of cancer-related mortality worldwide. Emerging evidence has provided insights into iron deficiency and excess in CRC. Ferroptosis is an iron-dependent form of programmed cell death characterized by aberrant iron and lipid metabolism, which play crucial roles in tumorigenesis, tumor progression, and treatment options. A better understanding of the underlying molecular mechanism of ferroptosis has shed light on the current findings of ferroptosis-based nanodrug targeting strategies, such as driving ferroptosis in tumor cells and the tumor microenvironment, emerging combination therapy and against multidrug resistance. Furthermore, this review highlights the challenge and perspective of a ferroptosis-driven nanodrug delivery system for CRC-targeted therapy.

Drug Delivery Systems with a “Tumor-Triggered” Targeting or Intracellular Drug Release Property Based on DePEGylation

Coating nanosized anticancer drug delivery systems (DDSs) with poly(ethylene glycol) (PEG), the so-called PEGylation, has been proven an effective method to enhance hydrophilicity, aqueous dispersivity, and stability of DDSs. What is more, as PEG has the lowest level of protein absorption of any known polymer, PEGylation can reduce the clearance of DDSs by the mononuclear phagocyte system (MPS) and prolong their blood circulation time in vivo. However, the “stealthy” characteristic of PEG also diminishes the uptake of DDSs by cancer cells, which may reduce drug utilization. Therefore, dynamic protection strategies have been widely researched in the past years. Coating DDSs with PEG through dynamic covalent or noncovalent bonds that are stable in blood and normal tissues, but can be broken in the tumor microenvironment (TME), can achieve a DePEGylation-based “tumor-triggered” targeting or intracellular drug release, which can effectively improve the utilization of drugs and reduce their side effects. In this review, the stimuli and methods of “tumor-triggered” targeting or intracellular drug release, based on DePEGylation, are summarized. Additionally, the targeting and intracellular controlled release behaviors of the DDSs are briefly introduced.

Copper-based metal-organic frameworks for biomedical applications

Metal-organic frameworks (MOFs) are a class of important porous, crystalline materials composed of metal ions (clusters) and organic ligands. Owing to the unique redox chemistry, photochemical and electrical property, and catalytic activity of Cu^2+/+, copper-based MOFs (Cu-MOFs) have been recently and extensively explored in various biomedical fields. In this review, we first make a brief introduction to the synthesis of Cu-MOFs and their composites, and highlight the recent synthetic strategies of two most studied representatives, three-dimensional HKUST-1 and two-dimensional Cu-TCPP. The recent advances of Cu-MOFs in the applications of cancer treatment, bacterial inhibition, biosensing, biocatalysis, and wound healing are summarized and discussed. Furthermore, we propose a prospect of the future development of Cu-MOFs in biomedical fields and beyond.

Hypoxia responsive and tumor-targeted mixed micelles for enhanced cancer therapy and real-time imaging

Most chemotherapy agents have serious side effects due to lack of tumor targeting, which affects their clinical application. In addition, as an essential characteristic of malignant tumor, hypoxia is attracting exclusive research focus regarding its non-invasive real-time tracing in novel targeting delivery system. Herein, we designed a mixed micelle with tumor targeting and hypoxia responsiveness for tumor therapy and imaging. In particular, the dual-modified mix micelles were self-assembled by folic acid (FA) and 2-(2-nitroimidazole) ethylamine (NI) conjugated polymers, in which paclitaxel (PTX) and quantum dots (QDs) were co-loaded into the hydrophobic core. The drug loaded micelles showed satisfactory drug encapsulation, good storage stability, and sustained release properties. In vitro cell experiments showed that the mixed micelles exhibited enhanced cytotoxic effect and improved the cellular uptake, especially under hypoxic conditions, which was due to the FA mediated active targeting effect and NI induced hypoxic responsive release. In vivo experiments further proved that the mixed micelles possessed outstanding tumor targeting and hypoxia responsive properties. Furthermore, the drug loaded micelles showed excellent anti-tumor effect and can realize real-time in vivo imaging. This work demonstrates that the dual-modified mixed micelles co-loading with PTX and QDs might provide a novel approach for tumor therapy and imaging.

Recent Progress in Bio-Responsive Drug Delivery Systems for Tumor Therapy

Spatially- and/or temporally-controlled drug release has always been the pursuit of drug delivery systems (DDSs) to achieve the ideal therapeutic effect. The abnormal pathophysiological characteristics of the tumor microenvironment, including acidosis, overexpression of special enzymes, hypoxia, and high levels of ROS, GSH, and ATP, offer the possibility for the design of stimulus-responsive DDSs for controlled drug release to realize more efficient drug delivery and anti-tumor activity. With the help of these stimulus signals, responsive DDSs can realize controlled drug release more precisely within the local tumor site and decrease the injected dose and systemic toxicity. This review first describes the major pathophysiological characteristics of the tumor microenvironment, and highlights the recent cutting-edge advances in DDSs responding to the tumor pathophysiological environment for cancer therapy. Finally, the challenges and future directions of bio-responsive DDSs are discussed.

A Hypoxia-Sensitive Drug Delivery System Constructed by Nitroimidazole and its Application in the Treatment of Hepatocellular Carcinoma

Hypoxia is an important pathological phenomenon, and it can induce many tumor microenvironment changes, such as accumulations of intracellular lactic acid, decrease of tumor microenvironment pH value, and regulate a series of physiological and pathological processes such as adhesion, metastasis, and immune escape. Hypoxic tumor cells act as a key target for treating tumor. In this research, we designed and prepared PEG-nitroimidazole grafts, PEG-NI, and FA-PEG-NI. We first explored their physical and chemical properties to serve as a drug carrier. Then, the hypoxia-sensitive properties such as particle size changes and drug release were investigated. Finally, the tumor targeting ability was studied in vitro and in vivo, and anti-tumor capacity was determined. Both grafts showed excellent property as a nanodrug carrier and showed favorable drug encapsulation ability of sorafenib with the help of the hydrophobic chain of 6-(BOC-amino) hexyl bromide. The micelles responded to the hypoxic tumor environment with chemical and spatial structure changes leading to sensitive and fast drug release. With the modification of folic acid, FA-PEG-NI gained tumor targeting ability in vivo. FA-PEG-NI graft proved a potential targeting drug delivery system in the treatment of hypoxic hepatocellular carcinoma.

Hypoxia-Reinforced Antitumor RNA Interference Mediated by Micelleplexes with Programmed Disintegration

The performance of polycation-mediated siRNA delivery is often hurdled by the multiple systemic and cellular barriers that pose conflicting requirements for materials properties. Herein, micelleplexes (MPs) capable of programmed disintegration were developed to mediate efficient delivery of siRNA against XIAP (siXIAP) in a hypoxia-reinforced manner. MPs were assembled from azobenzene-crosslinked oligoethylenimine (AO), acid-transformable diblock copolymer PPDHP with conjugated photosensitizer, and siXIAP. AO efficiently condensed siXIAP via electrostatic interaction, and PPDHP rendered additional hydrophobic interaction with AO to stabilize the MPs against salt. The hydrophilic PEG corona enhanced the serum stability of MPs to prolong blood circulation and promote tumor accumulation. After internalization into cancer cells, the endolysosomal acidity triggered shedding of PPDHP, exposing AO to induce endolysosomal escape. Then, light irradiation generated lethal amount of ROS, and concurrently aggravated intracellular hypoxia level to degrade AO into low-molecular weight segments, release siXIAP, and potentiate the XIAP silencing efficiency. Thus, siXIAP-mediated pro-apoptosis cooperated with generated ROS to provoke pronounced anti-cancer efficacy against Skov-3 tumors in vitro and in vivo. This study provides a hypoxia-instructed strategy to overcome the multiple barriers against anti-cancer siRNA delivery in a programmed manner. STATEMENT OF SIGNIFICANCE: : The success of RNA interference (RNAi) heavily depends on delivery systems that can enable spatiotemporal control over siRNA delivery. Herein, we developed micelleplexes (MPs) constructed from hypoxia-degradable, azobenzene-crosslinked oligoethylenimine (AO) and acid-responsive, photosensitizer-conjugated diblock copolymer PPDHP, to mediate efficient anti-tumor siRNA (siXIAP) delivery via programmed disintegration. MPs possessed high salt/serum stability and underwent acid-triggered PPDHP detachment to promote endolysosomal escape. Then, light irradiation aggravated hypoxia to trigger AO degradation and intracellular siXIAP release, which cooperated with photodynamic therapy to eradicate tumor cells. This study presents a new example of hypoxia-degradable polycation to mediate hypoxia-reinforced RNAi, and it also renders an effective strategy to overcome the complicated extracellular/intracellular barriers against systemic siRNA delivery.

Hypoxia responsive phytonanotheranostics: A novel paradigm towards fighting cancer

Hypoxia enhances tumor aggressiveness, thereby reducing the efficacy of anticancer therapies. Phytomedicine, which is nowadays considered as the new panacea owing to its dynamic physiological properties, is often plagued by shortcomings. Incorporating these wonder drugs in nanoparticles (phytonanomedicine) for hypoxia therapy is a new prospect in the direction of cancer management. Similarly, the concept of phytonanotheranostics for the precise tumor lesion detection and treatment monitoring in the hypoxic scenario is going on a rampant speed. In the same line, smart nanoparticles which step in for "on-demand" drug release based on internal or external stimuli are also being explored as a new tool for cancer management. However, studies regarding these smart and tailor-made nanotheranostics in the hypoxic tumor microenvironment are very limited. The present review is an attempt to collate these smart stimuli-responsive phytonanotherapeutics in one place for initiating future research in this upcoming field for better cancer treatment.

Smart nanomaterials for cancer diagnosis and treatment

Innovations in nanomedicine has guided the improved outcomes for cancer diagnosis and therapy. However, frequent use of nanomaterials remains challenging due to specific limitations like non-targeted distribution causing low signal-to-noise ratio for diagnostics, complex fabrication, reduced-biocompatibility, decreased photostability, and systemic toxicity of nanomaterials within the body. Thus, better nanomaterial-systems with controlled physicochemical and biological properties, form the need of the hour. In this context, smart nanomaterials serve as promising solution, as they can be activated under specific exogenous or endogenous stimuli such as pH, temperature, enzymes, or a particular biological molecule. The properties of smart nanomaterials make them ideal candidates for various applications like biosensors, controlled drug release, and treatment of various diseases. Recently, smart nanomaterial-based cancer theranostic approaches have been developed, and they are displaying better selectivity and sensitivity with reduced side-effects in comparison to conventional methods. In cancer therapy, the smart nanomaterials-system only activates in response to tumor microenvironment (TME) and remains in deactivated state in normal cells, which further reduces the side-effects and systemic toxicities. Thus, the present review aims to describe the stimulus-based classification of smart nanomaterials, tumor microenvironment-responsive behaviour, and their up-to-date applications in cancer theranostics. Besides, present review addresses the development of various smart nanomaterials and their advantages for diagnosing and treating cancer. Here, we also discuss about the drug targeting and sustained drug release from nanocarriers, and different types of nanomaterials which have been engineered for this intent. Additionally, the present challenges and prospects of nanomaterials in effective cancer diagnosis and therapeutics have been discussed.

Hypoxia-Responsive Stereocomplex Polymeric Micelles with Improved Drug Loading Inhibit Breast Cancer Metastasis in an Orthotopic Murine Model

Tumor metastasis is a leading cause of breast cancer-related death. Taxane-loaded polymeric formulations, such as Genexol PM and Nanoxel M using poly(ethylene glycol)-poly(d,l-lactide) (PEG-PLA) micelles as drug carriers, have been approved for the treatment of metastatic breast cancer. Unfortunately, the physical instability of PEG-PLA micelles, leading to poor drug loading, premature drug leakage, and consequently limited drug delivery to tumors, largely hinders their therapeutic outcome. Inspired by the enantiomeric nature of PLA, this work developed stereocomplex PEG-PLA micelles through stereoselective interactions of enantiomeric PLA, which are further incorporated with a hypoxia-responsive moiety used as a hypoxia-cleavable linker of PEG and PLA, to maximize therapeutic outcomes. The results showed that the obtained micelles had high structural stability, showing improved drug loading for effective drug delivery to tumors as well as other tissues. Especially, they were capable of sensitively responding to the hypoxic tumor environment for drug release, reversing hypoxia-induced drug resistance and hypoxia-promoted cell migration for enhanced bioavailability under hypoxia. In vivo results further showed that the micelles, especially at a high dose, inhibited the growth of the primary tumor and improved tumor pathological conditions, consequently remarkably inhibiting its metastasis to the lungs and liver, while not causing any systemic toxicity. Hypoxia-responsive stereocomplex micelles thus emerge as a reliable drug delivery system to treat breast cancer metastasis.

Chemical Modification of Chitosan for Developing Cancer Nanotheranostics

Cancer is a worldwide public health issue that has not been conquered. Theranostics, the combination of a therapeutic drug and imaging agent in one formulation using nanomaterials, has been developed to better cure cancer in recent years. Although diverse biomaterials have been applied in cancer theranostics, chitosan (CS), a natural polysaccharide bearing easy modification sites with excellent biocompatibility and biodegradability, shows great potential for developing cancer nanotheranostics. In this review, we seek to describe the chemical functionalities of CS used in cancer theranostics and their synthesis methods. We also present recent discoveries and research progresses on how the CS functionalization could improve the delivery efficiency of CS-based nanotheranostics. Finally, we report several case studies about the application of CS-based nanotheranostics. This paper focuses on the strategies to construct CS-based theranostics systems via chemical routes and highlights their applications in cancer treatment, which can provide useful references for further studies.

Chitosan derivatives functionalized dual ROS-responsive nanocarriers to enhance synergistic oxidation-chemotherapy

The efficient triggering of prodrug release has become a challengeable task for stimuli-responsive nanomedicine utilized in cancer therapy due to the subtle differences between normal and tumor tissues and heterogeneity. In this work, a dual ROS-responsive nanocarriers with the ability to self-regulate the ROS level was constructed, which could gradually respond to the endogenous ROS to achieve effective, hierarchical and specific drug release in cancer cells. In brief, DOX was conjugated with MSNs via thioketal bonds and loaded with β-Lapachone. TPP modified chitosan was then coated to fabricate nanocarriers for mitochondria-specific delivery. The resultant nanocarriers respond to the endogenous ROS and release Lap specifically in cancer cells. Subsequently, the released Lap self-regulated the ROS level, resulting in the specific DOX release and mitochondrial damage in situ, enhancing synergistic oxidation-chemotherapy. The tumor inhibition Ratio was achieved to 78.49%. The multi-functional platform provides a novel remote drug delivery system in vivo.

Stimulus-responsive self-assembled prodrugs in cancer therapy

Small-molecule prodrugs have become the main toolbox to improve the unfavorable physicochemical properties of potential therapeutic compounds in contemporary anti-cancer drug development. Many approved small-molecule prodrugs, however, still face key challenges in their pharmacokinetic (PK) and pharmacodynamic (PD) properties, thus severely restricting their further clinical applications. Self-assembled prodrugs thus emerged as they could take advantage of key benefits in both prodrug design and nanomedicine, so as to maximize drug loading, reduce premature leakage, and improve PK/PD parameters and targeting ability. Notably, temporally and spatially controlled release of drugs at cancerous sites could be achieved by encoding various activable linkers that are sensitive to chemical or biological stimuli in the tumor microenvironment (TME). In this review, we have comprehensively summarized the recent progress made in the development of single/multiple-stimulus-responsive self-assembled prodrugs for mono- and combinatorial therapy. A special focus was placed on various prodrug conjugation strategies (polymer-drug conjugates, drug-drug conjugates, etc.) that facilitated the engineering of self-assembled prodrugs, and various linker chemistries that enabled selective controlled release of active drugs at tumor sites. Furthermore, some polymeric nano-prodrugs that entered clinical trials have also been elaborated here. Finally, we have discussed the bottlenecks in the field of prodrug nanoassembly and offered potential solutions to overcome them. We believe that this review will provide a comprehensive reference for the rational design of effective prodrug nanoassemblies that have clinic translation potential.

Acid-Degradable Hydrogen-Generating Metal-Organic Framework for Overcoming Cancer Resistance/Metastasis and Off-Target Side Effects

The development of stimuli-responsively degradable porous carriers for both controlled drug release and high biosafety is vitally important to their clinical translation, but still challenging at present. A new type of porphyrin-iron metal organic framework (Fe-MOF) nanocrystals is engineered here as acid-degradable drug carrier and hydrogen donor by the coordination between porphyrin and zero-valence Fe atom. Fe-MOF nanocrystals exhibit excellent acid-responsive degradation for H₂ generation and simultaneous release of the loaded drug for combined hydrogen-chemotherapy of cancer multidrug resistance (MDR) and metastasis and for local hydrogen eradication of the off-target induced toxic side effects of the drug to normal cells/tissues. Mechanistically, released H₂ assists chemotherapeutic drug to efficiently inhibit cancer metastasis by immunoactivating intratumoral M1-phenotype macrophages and consequently downregulating the expression of metastasis-related matrix metalloproteinase-2 (MMP-2) and can also downregulate the expressions of both P-glycoprotein (P-gp) protein and adenosine triphosphate (ATP) in MDR cancer cells to sensitize chemotherapeutic drug for enhanced damage to mitochondria and DNA. High anti-MDR/antimetastasis efficacies and high biocompatibility endow Fe-MOF nanocrystals and the Fe-MOF-based nanomedicine with high potential for clinical translation.

Anticancer nanomedicines harnessing tumor microenvironmental components

INTRODUCTION

Small-molecular drugs are extensively used in cancer therapy, while they have issues of nonspecific distribution and consequent side effects. Nanomedicines that incorporate chemotherapeutic drugs have been developed to enhance the therapeutic efficacy of these drugs and reduce their side effects. One of the promising strategies is to prepare nanomedicines by harnessing the unique tumor microenvironment (TME).

AREAS COVERED

The TME contains numerous cell types that specifically express specific antibodies on the surface including tumor vascular endothelial cells, tumor-associated adipocytes, tumor-associated fibroblasts, tumor-associated immune cells and cancer stem cells. The physicochemical environment is characterized with a low pH, hypoxia, and a high redox potential resulting from tumor-specific metabolism. The intelligent nanomedicines can be categorized into two groups: the first group which is rapidly responsive to extracellular chemical/biological factors in the TME and the second one which actively and/or specifically targets cellular components in the TME.

EXPERT OPINION

In this paper, we review recent progress of nanomedicines by harnessing the TME and illustrate the principles and advantages of different strategies for designing nanomedicines, which are of great significance for exploring novel nanomedicines or translating current nanomedicines into clinical practice. We will discuss the challenges and prospects of preparing nanomedicines to utilize or alter the TME for achieving effective, safe anticancer treatment.

Self-Rectifiable and Hypoxia-Assisted Chemo-Photodynamic Nanoinhibitor for Synergistic Cancer Therapy

Photodynamic therapy (PDT) can eradicate cancer cells under light irradiation, mainly because of reactive singlet oxygen (¹O₂) being transformed from intratumoral oxygen. Nonetheless, the consumption of oxygen during PDT results in serious hypoxic conditions and an elevated hypoxia-inducing factor-1α (HIF-1α) level that hamper further photodynamic efficacy and induce tumor metastasis. To address this problem, we developed hypoxia-assisted NP-co-encapsulating Ce6 (photosensitizer) and YC-1 (HIF-1α inhibitor) as a self-rectifiable nanoinhibitor for synergistic antitumor treatment. PDT-aggravated intracellular hypoxic stress facilitated NP dissociation to release the drug (YC-1), which achieved tumor killing and HIF-1α inhibition to further enhance the therapeutic effect of PDT and prevent tumor metastasis. Besides, in vivo studies revealed that the HC/PI@YC-1 NPs afforded synergistic anticancer efficacy with minimal toxicity. Therefore, this study provides a prospective approach against PDT drawbacks and combination cancer therapy.

Facile Synthesis of a Redox-Responsive Hyperbranched Polymer Prodrug as a Unimolecular Micelle for the Tumor-Selective Drug Delivery

Demicellization of the self-assembled multimolecular micelles upon dilution restricts their application as drug delivery systems (DDSs) for tumor treatment. Here, a redox-responsive hyperbranched polymer prodrug (HBPP) was designed with a high drug content of 62.0% as a unimolecular micelle for the tumor-selective drug delivery, via the facile self-condensing vinyl polymerization (SCVP) of redox-responsive doxorubicin-based prodrug monomer MA-SS-DOX and poly(ethylene glycol) methacrylate (PEGMA) with p-chloromethylstyrene (CMS) as an inimer. The unimolecular micelle could be easily obtained with a hydrodynamic diameter of 122 nm, showing excellent GSH-triggered drug release performance with a cumulative release of 60.9% within 85 h but a low premature drug leakage of 3.2%. The unimolecular micelle exhibited selective tumor growth inhibition on HepG2 cells but no obvious cytotoxicity on L02 cells.

Nature-inspired dynamic gene-loaded nanoassemblies for the treatment of brain diseases

Gene therapy has great potential to treat brain diseases. However, genetic drugs need to overcome a cascade of barriers for their full potential. The conventional delivery systems often struggle to meet expectations. Natural biological particles that are highly optimized for specific functions in body, can inspire optimization of dynamic gene-loaded nanoassemblies (DGN). The DGN refer to gene loaded nanoassemblies whose functions and structures are changeable in response to the biological microenvironments or can dynamically interact with tissues or cells. The nature-inspired DGN can meet the needs in brain diseases treatment, including i) Non-elimination in blood (N), ii) Across the blood-brain barrier (A), iii) Targeting cells (T), iv) Efficient uptake (U), v) Controllable release (R), vi) Eyeable (E)-abbreviated as the "NATURE". In this Review, from nature to "NATURE", we mainly summarize the specific application of nature-inspired DGN in the "NATURE" cascade process. Furthermore, the Review provides an outlook for this field.

Biomimic Binding Affinity Gradients Triggered GSH-Response of Core-Shell Nanoparticles for Cascade Chemo/Chemodynamic Therapy

In eukaryotes and prokaryotes, some copper transportations driven by gradient copper-binding affinities exhibit typical glutathione (GSH)-responsive features. Inspired by these delicate endogenous processes, a biomimic copper-ion mediated GSH-responsive nanomedicine is designed based on the gradient copper-binding strengths between polydopamine (PDA) species and GSH. The nanomedicine is constructed as core-shell nanoparticles with copper-polydopamine (Cu-PDA) coordinated shell and micellar core encapsulating chemotherapeutic drug of β-lapachone (β-lapa). In tumor cells, the excess intracellular GSH will reduce and extract the Cu(II) from the Cu-PDA network, triggered by the binding affinity gradients between Cu-PDA and Cu-GSH, resulting in the breaking of the shell and the releasing of β-lapa and Fenton agent copper. The additional Fenton reaction of copper ions induces excess oxidative damage of tumor cells assisted by the abundant H₂ O₂ amplified by β-lapa, achieving cascade anticancer effects combining chemodynamic therapy with chemotherapy. This multilevel anticancer system exhibits an efficient tumor inhibitory rate and a negligible systematic toxicity for normal organs in vivo, presenting a new bioinspired GSH-responsive strategie to develop stimuli-responsive structures.

Tumor-Microenvironment-Responsive Nanomedicine for Enhanced Cancer Immunotherapy

The past decades have witnessed great progress in cancer immunotherapy, which has profoundly revolutionized oncology, whereas low patient response rates and potential immune-related adverse events remain major clinical challenges. With the advantages of controlled delivery and modular flexibility, cancer nanomedicine has offered opportunities to strengthen antitumor immune responses and to sensitize tumor to immunotherapy. Furthermore, tumor-microenvironment (TME)-responsive nanomedicine has been demonstrated to achieve specific and localized amplification of the immune response in tumor tissue in a safe and effective manner, increasing patient response rates to immunotherapy and reducing the immune-related side effects simultaneously. Here, the recent progress of TME-responsive nanomedicine for cancer immunotherapy is summarized, which responds to the signals in the TME, such as weak acidity, reductive environment, high-level reactive oxygen species, hypoxia, overexpressed enzymes, and high-level adenosine triphosphate. Moreover, the potential to combine nanomedicine-based therapy and immunotherapeutic strategies to overcome each step of the cancer-immunity cycle and to enhance antitumor effects is discussed. Finally, existing challenges and further perspectives in this rising field with the hope for improved development of clinical applications are discussed.

Current understandings and clinical translation of nanomedicines for breast cancer therapy

Breast cancer is one of the most frequently diagnosed cancers that is threatening women's life. Current clinical treatment regimens for breast cancer often involve neoadjuvant and adjuvant systemic therapies, which somewhat are associated with unfavorable features. Also, the heterogeneous nature of breast cancers requires precision medicine that cannot be fulfilled by a single type of systemically administered drug. Taking advantage of the nanocarriers, nanomedicines emerge as promising therapeutic agents for breast cancer that could resolve the defects of drugs and achieve precise drug delivery to almost all sites of primary and metastatic breast tumors (e.g. tumor vasculature, tumor stroma components, breast cancer cells, and some immune cells). Seven nanomedicines as represented by Doxil® have been approved for breast cancer clinical treatment so far. More nanomedicines including both non-targeting and active targeting nanomedicines are being evaluated in the clinical trials. However, we have to realize that the translation of nanomedicines, particularly the active targeting nanomedicines is not as successful as people have expected. This review provides a comprehensive landscape of the nanomedicines for breast cancer treatment, from laboratory investigations to clinical applications. We also highlight the key advances in the understanding of the biological fate and the targeting strategies of breast cancer nanomedicine and the implications to clinical translation.

pH-responsive hollow Fe-gallic acid coordination polymer for multimodal synergistic-therapy and MRI of cancer

Tumor-microenvironment (TME) responsive nanostructures are attractive for drug delivery in clinical cancer treatment. The coordination polymer Fe-gallic acid (Fe-GA) is one of the promising drug carriers due to its pH-response, good biocompatibility, and minimal side effects. However, the hollow nanostructures of Fe-GA have not been reported until now, which seriously limits the quantity of drug delivery. Herein, hollow Fe-GA nanospheres were prepared for the first time with bovine serum albumin (BSA) combination (denoted as Fe-GA/BSA) under mild reaction conditions. Then, the antitumor drug doxorubicin (DOX) was loaded in the hollow Fe-GA/BSA to obtain Fe-GA/BSA@DOX. A series of experiments in vitro and in vivo indicated that the Fe-GA/BSA@DOX could efficiently respond to TME and release DOX and Fe(iii) ions. Furthermore, the Fe(iii) could consume overexpressed glutathione (GSH) in cancer cells and generate Fe(ii) to trigger the Fenton reaction, producing ·OH for chemodynamic treatment (CDT) of cancer. In addition, the Fe-GA/BSA@DOX could effectively convert near-infrared (NIR) light into heat by acting as a photothermal therapy (PTT) agent. Besides that, magnetic resonance imaging (MRI) data also showed that the Fe-GA/BSA had beneficial T₁ and T₂ imaging effects, demonstrating that the hollow Fe-GA/BSA has potential for multimodal synergistic cancer MRI diagnosis and therapies of drugs, CDT, and PTT.

Recent advances in in situ oxygen-generating and oxygen-replenishing strategies for hypoxic-enhanced photodynamic therapy

Cancer is a leading cause of death worldwide, accounting for an estimated 10 million deaths by 2020. Over the decades, various strategies for tumor therapy have been developed and evaluated. Photodynamic therapy (PDT) has attracted increasing attention due to its unique characteristics, including low systemic toxicity and minimally invasive nature. Despite the excellent clinical promise of PDT, hypoxia is still the Achilles' heel associated with its oxygen-dependent nature related to increased tumor proliferation, angiogenesis, and distant metastases. Moreover, PDT-mediated oxygen consumption further exacerbates the hypoxia condition, which will eventually lead to the poor effect of drug treatment and resistance and irreversible tumor metastasis, even limiting its effective application in the treatment of hypoxic tumors. Hypoxia, with increased oxygen consumption, may occur in acute and chronic hypoxia conditions in developing tumors. Tumor cells farther away from the capillaries have much lower oxygen levels than cells in adjacent areas. However, it is difficult to change the tumor's deep hypoxia state through different ways to reduce the tumor tissue's oxygen consumption. Therefore, it will become more difficult to cure malignant tumors completely. In recent years, numerous investigations have focused on improving PDT therapy's efficacy by providing molecular oxygen directly or indirectly to tumor tissues. In this review, different molecular oxygen supplementation methods are summarized to alleviate tumor hypoxia from the innovative perspective of using supplemental oxygen. Besides, the existing problems, future prospects and potential challenges of this strategy are also discussed.

Hyaluronic Acid Derived Hypoxia-Sensitive Nanocarrier for Tumor Targeted Drug Delivery

Hyaluronic acid (HA) is conjugated with BHQ3 moiety with azo bonds to prepare hypoxia-responsive polymer conjugate. Because of the amphiphilic nature, the polymer conjugate self-assembles to HA-BHQ3 nanoparticles (NPs). The anticancer drug doxorubicin (DOX) is loaded into the NPs. In the physiological environment, DOX is released slowly. In contrast, under hypoxic conditions, the azo bond in BHQ3 is cleaved, thus significantly enhancing the DOX release rate. For instance, after 24 h, 25% of DOX is released under normal conditions, while 74% of DOX is released under hypoxic conditions. In vitro cytotoxicity demonstrates higher toxicity in the hypoxic conditions. DOX@HA-BHQ3 NPs exhibit greater toxicity levels against 4T1 cells in hypoxic conditions. The fluorescent microscope images confirm the oxygen-dependent intracellular DOX release from the NPs. The in vivo biodistribution results suggest the tumor targetability of HA-BHQ3 NPs in 4T1 tumor-bearing mice.

Novel strategies to improve tumour therapy by targeting the proteins MCT1, MCT4 and LAT1

Poor selectivity, potential systemic toxicity and drug resistance are the main challenges associated with chemotherapeutic drugs. MCT1 and MCT4 and LAT1 play vital roles in tumour metabolism and growth by taking up nutrients and are thus potential targets for tumour therapy. An increasing number of studies have shown the feasibility of including these transporters as components of tumour-targeting therapy. Here, we summarize the recent progress in MCT1-, MCT4-and LAT1-based therapeutic strategies. First, protein structures, expression, relationships with cancer, and substrate characteristics are introduced. Then, different drug targeting and delivery strategies using these proteins have been reviewed, including designing protein inhibitors, prodrugs and nanoparticles. Finally, a dual targeted strategy is discussed because these proteins exert a synergistic effect on tumour proliferation. This article concentrates on tumour treatments targeting MCT1, MCT4 and LAT1 and delivery techniques for improving the antitumour effect. These innovative tactics represent current state-of-the-art developments in transporter-based antitumour drugs.

Conquering the Hypoxia Limitation for Photodynamic Therapy

Photodynamic therapy (PDT) has aroused great research interest in recent years owing to its high spatiotemporal selectivity, minimal invasiveness, and low systemic toxicity. However, due to the hypoxic nature characteristic of many solid tumors, PDT is frequently limited in therapeutic effect. Moreover, the consumption of O₂ during PDT may further aggravate the tumor hypoxic condition, which promotes tumor proliferation, metastasis, and invasion resulting in poor prognosis of treatment. Therefore, numerous efforts have been made to increase the O₂ content in tumor with the goal of enhancing PDT efficacy. Herein, these strategies developed in past decade are comprehensively reviewed to alleviate tumor hypoxia, including 1) delivering exogenous O₂ to tumor directly, 2) generating O₂ in situ, 3) reducing tumor cellular O₂ consumption by inhibiting respiration, 4) regulating the TME, (e.g., normalizing tumor vasculature or disrupting tumor extracellular matrix), and 5) inhibiting the hypoxia-inducible factor 1 (HIF-1) signaling pathway to relieve tumor hypoxia. Additionally, the O₂ -independent Type-I PDT is also discussed as an alternative strategy. By reviewing recent progress, it is hoped that this review will provide innovative perspectives in new nanomaterials designed to combat hypoxia and avoid the associated limitation of PDT.

Hypoxia-responsive pullulan-based nanoparticles as erlotinib carriers

A hypoxia-responsive pullulan-based co-polymer was developed to assess its efficacy to deliver erlotinib (ERL) to the cervical cancer cells. Upon exposure to hypoxic condition, the synthesized and structurally characterized co-polymer i.e. succinyl pullulan-g-6-(2-nitroimidazole) hexylamine (Pull-SA-HA-NI) exhibited a hypochromic shift in the UV spectra and alteration in its self-assembled structures as compared to the control co-polymer, succinyl pullulan-g-hexylamine (Pull-SA-HA). Its corresponding ERL-loaded nanoparticles (NPs) displayed an attenuated crystallinity of pure ERL with excellent drug-trapping capacity (DEE, 94.23 ± 1.36%) and acceptable zeta potential (+39.21 ± 1.09 mV) and diameter (84.10 ± 2.10 nm) values. These also evidenced a faster drug release profile under hypoxic condition relative to the normoxic condition. The cellular internalization of the NPs was mediated through the energy-dependent endocytic process, which could utilize its multiple pathways (i.e., macropinocytosis, clathrin- and caveolae-mediated endocytosis). The ERL-loaded NPs suppressed HeLa cell proliferation and induced apoptosis more efficiently than the pristine drug.

Self-Remedied Nanomedicine for Surmounting the Achilles' Heel of Photodynamic Tumor Therapy

Oxygen-dependent photodynamic therapy (PDT) could exacerbate tumor hypoxia to induce the upregulation of hypoxia-inducible factor-1α (HIF-1α), which would promote tumor growth and metastasis. In this paper, a self-remedied nanomedicine is developed based on a photosensitizer and a HIF-1α inhibitor to surmount the Achilles' heel of PDT for enhanced antitumor efficacy. Specifically, the nanomedicine (designated as CYC-1) is prepared by the self-assembly of chlorine e6 (Ce6) and 3-(5'-hydroxy-methyl-2'-furyl)-1-benzylindazole (YC-1) through π-π stacking and hydrophobic interactions. Of special note, carrier-free CYC-1 holds an extremely high drug loading rate and avoids excipient-triggered adverse reactions. Intravenously administered CYC-1 prefers to accumulate in the tumor tissue for effective cellular uptake. More importantly, it is verified that CYC-1 is capable of inhibiting the HIF-1α activity, thereby improving its PDT efficacy on tumor suppression. Besides, CYC-1 has the overwhelming superiority in restraining tumor proliferation over the combined administration of Ce6 and YC-1, which highlights the advantage of this self-remedied strategy in drug delivery and tumor therapy. This study sheds light on the development of self-delivery nanomedicine for efficient PDT against malignancies.

Hypoxia-responsive block copolymer polyprodrugs for complementary photodynamic-chemotherapy

The inherent hypoxic microenvironment of solid tumors has an important influence on tumor growth, distant metastasis, and invasiveness. The heterogeneous distribution of hypoxic regions inside tumors limits the therapeutic efficacy of O₂-assisted therapeutic strategy (e.g. photodynamic therapy (PDT)). On the other hand, the hypoxia-activable prodrugs cannot work effectively in the regions with enough O₂ concentration. To address the issues, we prepare a block copolymer polyprodrug consisting of polyethylene glycol (PEG) and copolymerized segments of nitroimidazole-linked camptothecin (CPT) methacrylate and 5,10,15,20-tetraphenylporphyrin (TPP)-containing methacrylate monomers for complementary photodynamic-chemotherapy. The polyprodrug can self-assemble into polymeric micelles in aqueous solution with suitable size and high stability. After intravenous injection, the polyprodrug micelles show tumor accumulation. Followed by light irradiation (650 nm) at tumor sites, TPP moieties induce singlet oxygen (¹O₂) production in the oxygen-rich area to exert PDT and cause transformation of the oxygen-rich areas into hypoxia. Simultaneously, in the hypoxic areas, the hypoxia-responsive polyprodrugs can be activated to release free CPT due to the cleavage of nitroimidazole linkages. The polyprodrug micelles with the segments for PDT and hypoxia-activable CPT efficiently suppress the growth of HeLa tumors. The well-defined polyprodrug amphiphiles offer an effective strategy to overcome the disadvantages of single treatment of PDT or hypoxia-responsive prodrugs for complementary photodynamic-chemotherapy of cancers.

Innovations in Disease State Responsive Soft Materials for Targeting Extracellular Stimuli Associated with Cancer, Cardiovascular Disease, Diabetes, and Beyond

Recent advances in polymer chemistry, materials sciences, and biotechnology have allowed the preclinical development of sophisticated programmable nanomedicines and materials that are able to precisely respond to specific disease-associated triggers and microenvironments. These stimuli, endogenous to the targeted diseases, include pH, redox-state, small molecules, and protein upregulation. Herein, recent advances and innovative approaches in programmable soft materials capable of sensing the aforementioned disease-associated stimuli and responding via a range of dynamic processes including morphological and size transitions, changes in mobility and retention, as well as disassembly are described. In this field generally, the majority of ongoing and past research effort has focused on oncology. Given this interest, examples of the latest innovative approaches to chemo- and immunotherapy treatment strategies for cancer are presented. Moreover, as the field broadens its attention, applications of programmable materials in other diseases are highlighted, with a special focus on cardiovascular disease and diabetes mellitus, where limited attention is paid by the field, but where many promising avenues exist with high potential impact.

Magnetic nanoparticles and clusters for magnetic hyperthermia: optimizing their heat performance and developing combinatorial therapies to tackle cancer

Magnetic hyperthermia (MHT) is a therapeutic modality for the treatment of solid tumors that has now accumulated more than 30 years of experience. In the ongoing MHT clinical trials for the treatment of brain and prostate tumors, iron oxide nanoparticles are employed as intra-tumoral MHT agents under a patient-safe 100 kHz alternating magnetic field (AMF) applicator. Although iron oxide nanoparticles are currently approved by FDA for imaging purposes and for the treatment of anemia, magnetic nanoparticles (MNPs) designed for the efficient treatment of MHT must respond to specific physical-chemical properties in terms of magneto-energy conversion, heat dose production, surface chemistry and aggregation state. Accordingly, in the past few decades, these requirements have boosted the development of a new generation of MNPs specifically aimed for MHT. In this review, we present an overview on MNPs and their assemblies produced via different synthetic routes, focusing on which MNP features have allowed unprecedented heating efficiency levels to be achieved in MHT and highlighting nanoplatforms that prevent magnetic heat loss in the intracellular environment. Moreover, we review the advances on MNP-based nanoplatforms that embrace the concept of multimodal therapy, which aims to combine MHT with chemotherapy, radiotherapy, immunotherapy, photodynamic or phototherapy. Next, for a better control of the therapeutic temperature at the tumor, we focus on the studies that have optimized MNPs to maintain gold-standard MHT performance and are also tackling MNP imaging with the aim to quantitatively assess the amount of nanoparticles accumulated at the tumor site and regulate the MHT field conditions. To conclude, future perspectives with guidance on how to advance MHT therapy will be provided.

Carrier Free Photodynamic Synergists for Oxidative Damage Amplified Tumor Therapy

Tumor cells adapt to excessive oxidative stress by actuating reactive oxygen species (ROS)-defensing system, leading to a resistance to oxidation therapy. In this work, self-delivery photodynamic synergists (designated as PhotoSyn) are developed for oxidative damage amplified tumor therapy. Specifically, PhotoSyn are fabricated by the self-assembly of chlorine e6 (Ce6) and TH588 through π-π stacking and hydrophobic interactions. Without additional carriers, nanoscale PhotoSyn possess an extremely high drug loading rate (up to 100%) and they are found to be fairly stable in aqueous phase with a uniform size distribution. Intravenously injected PhotoSyn prefer to accumulate at tumor sites for effective cellular uptake. More importantly, TH588-mediated MTH1 inhibition could destroy the ROS-defensing system of tumor cells by preventing the elimination of 8-oxo-2'-deoxyguanosine triphosphate (8-oxo-dG), thereby exacerbating the oxidative DNA damage induced by the photodynamic therapy (PDT) of Ce6 under light irradiation. As a consequence, PhotoSyn exhibit enhanced photo toxicity and a significant antitumor effect. This amplified oxidative damage strategy improves the PDT efficiency with a reduced side effect by increasing the lethality of ROS without generating superabundant ROS, which would provide a new insight for developing self-delivery nanoplatforms in photodynamic tumor therapy in clinic.

One-pot synthesis chlorin e6 nano-precipitation for colorectal cancer treatment Ce6 NPs for colorectal cancer treatment

The drug nanoparticles free of additional carriers hold great promise in drug delivery and are suitable for the therapy of cancers. Herein, we developed a one-pot method to prepare chlorin e6 (Ce6) nano-precipitations (Ce6 NPs) for effective photodynamic therapy of colorectal cancer. The drug loading of Ce6 NPs was around 81% and showed acceptable stability, high biocompatibility as well as effective reactive oxygen species (ROS) generation capability. As a result, the Ce6 NPs can produce significantly elevated ROS upon laser irradiations and achieved better anticancer benefits than free Ce6.

Effects of hypoxia and nanocarrier size on pH-responsive nano-delivery system to solid tumors

One of the special features of solid tumors is the acidity of the tumor microenvironment, which is mainly due to the presence of hypoxic regions. Therefore, pH-responsive drug delivery systems have recently been highly welcomed. In the present study, a comprehensive mathematical model is presented based on extravascular drug release paradigm. Accordingly, drug delivery system using pH-responsive nanocarriers is taken into account to examine the impacts of hypoxic regions as well as the size of nanocarriers for cancerous cell-death. The extent of hypoxic regions is controlled by vascular density. This means that regions with very low vascular density represent regions of hypoxia. Using this mathematical model, it is possible to simulate the extracellular and intracellular concentrations of drug by considering the association/disassociation of the free drug to the cell-surface receptors and cellular uptake. Results show that nanocarriers with smaller sizes are more effective due to higher accumulation in the tumor tissue interstitium. The small size of the nanocarriers also allows them to penetrate deeper, so they can expose a larger portion of the tumor to the drug. Additionally, the presence of hypoxic regions in tumor reduces the fraction of killed cancer cells due to reduced penetration depth. The proposed model can be considered for optimizing and developing pH-sensitive delivery systems to reduce both cost and time of the process.

H2O2 Self-Supplying and GSH-Depleting Nanoplatform for Chemodynamic Therapy Synergetic Photothermal/Chemotherapy

Chemodynamic therapy (CDT) that utilizes Fenton-type reactions to convert endogenous hydrogen peroxide (H₂O₂) into hydroxyl radicals (^•OH) is a promising strategy in anticancer treatment, but the overexpression of glutathione (GSH) and limited endogenous H₂O₂ make the efficiency of CDT unsatisfactory. Here, an intelligent nanoplatform CuO₂@mPDA/DOX-HA (CPPDH), which induced the depletion of GSH and the self-supply of H₂O₂, was proposed. When CPPDH entered tumor cells through the targeting effect of hyaluronic acid (HA), a release of Cu²⁺ and produced H₂O₂ were triggered by the acidic environment of lysosomes. Then, the Cu²⁺ was reduced by GSH to Cu⁺, and the Cu⁺ catalyzed H₂O₂ to produce ^•OH. The generation of ^•OH could be distinctly enhanced by the GSH depletion and H₂O₂ self-sufficiency. Besides, an outstanding photothermal therapy (PTT) effect could be stimulated by NIR irradiation on mesoporous polydopamine (mPDA). Meanwhile, mPDA was an excellent photoacoustic reagent, which could monitor the delivery of nanocomposite materials through photoacoustic (PA) imaging. Moreover, the successful delivery of doxorubicin (DOX) realized the integration of chemotherapy, PTT, and CDT. This strategy could solve the problem of insufficient CDT efficacy caused by the limited H₂O₂ and overexpression of GSH. This multifunctional nanoplatform may open a broad path for self-boosting CDT and synergistic therapy.

A Nitronaphthalimide Probe for Fluorescence Imaging of Hypoxia in Cancer Cells

The bioreductive enzymes typically upregulated in hypoxic tumor cells can be targeted for developing diagnostic and drug delivery applications. In this study, a new fluorescent probe 4-(6-nitro-1,3-dioxo-1H-benzo[de]isoquinolin-2(3H)-yl)benzaldehyde (NIB) based on a nitronaphthalimide skeleton that could respond to nitroreductase (NTR) overexpressed in hypoxic tumors is designed and its application in imaging tumor hypoxia is demonstrated. The docking studies revealed favourable interactions of NIB with the binding pocket of NTR-Escherichia coli. NIB, which is synthesized through a simple and single step imidation of 4-nitro-1,8-naphthalic anhydride displayed excellent reducible capacity under hypoxic conditions as evidenced from cyclic voltammetry investigations. The fluorescence measurements confirmed the formation of identical products (NIB-red) during chemical as well as NTR-aided enzymatic reduction in the presence of NADH. The potential fluorescence imaging of hypoxia based on NTR-mediated reduction of NIB is confirmed using in-vitro cell culture experiments using human breast cancer (MCF-7) cells, which displayed a significant change in the fluorescence colour and intensity at low NIB concentration within a short incubation period in hypoxic conditions.

Recent progress in sono-photodynamic cancer therapy: From developed new sensitizers to nanotechnology-based efficacy-enhancing strategies

Many sensitizers have not only photodynamic effects, but also sonodynamic effects. Therefore, the combination of sonodynamic therapy (SDT) and photodynamic therapy (PDT) using sensitizers for sono-photodynamic therapy (SPDT) provides alternative opportunities for clinical cancer therapy. Although significant advances have been made in synthesizing new sensitizers for SPDT, few of them are successfully applied in clinical settings. The anti-tumor effects of the sensitizers are restricted by the lack of tumor-targeting specificity, incapability in deep intratumoral delivery, and the deteriorating tumor microenvironment. The application of nanotechnology-based drug delivery systems (NDDSs) can solve the above shortcomings, thereby improving the SPDT efficacy. This review summarizes various sensitizers as sono/photosensitizers that can be further used in SPDT, and describes different strategies for enhancing tumor treatment by NDDSs, such as overcoming biological barriers, improving tumor-targeted delivery and intratumoral delivery, providing stimuli-responsive controlled-release characteristics, stimulating anti-tumor immunity, increasing oxygen supply, employing different therapeutic modalities, and combining diagnosis and treatment. The challenges and prospects for further development of intelligent sensitizers and translational NDDSs for SPDT are also discussed.

Reactive oxygen species-sensitive polymeric nanocarriers for synergistic cancer therapy

Reactive oxygen species (ROS)-responsive nanocarriers have aroused widespread interest in recent years. On the one hand, a high ROS level has been detected in many types of tumor cells. On the other hand, ROS generation is also induced during photodynamic, sonodynamic, or chemodynamic therapy. In addition, multiple types of polymers are sensitive to ROS. Therefore, numerous ROS-responsive polymeric nanocarriers with unique ROS-responsive characteristics have been developed. This review discusses ROS-sensitive polymeric nanocarriers to improve drug delivery efficacy. In particular, ROS-responsive nanocarriers for synergistic cancer therapy are highlighted. The development of novel ROS-sensitive nanocarriers holds great potential for combining ROS-mediated therapy, such as photodynamic therapy, and other therapies to achieve synergistic anticancer efficacy. STATEMENT OF SIGNIFICANCE: Reactive oxygen species (ROS)-responsive nanocarriers aroused widespread interest in recent years. On the one hand, a high level of ROS has been found in many types of tumor cells. On the other hand, the ROS generation can also be induced during the photodynamic, sonodynamic, or chemodynamic therapy. Besides, multiple types of polymers were sensitive to the ROS. Therefore, numerous ROS-responsive polymeric nanocarriers with unique ROS responsive characteristics have been developed. This review focuses on the ROS-sensitive polymeric nanocarriers to improve drug delivery efficacy for synergistic cancer therapy.

Self-delivery nanomedicine for chemotherapy sensitized photodynamic therapy

A chlorine e6 (Ce6) and curcumin (Cur) based self-delivery nanomedicine (CeCu) is prepared for chemotherapy sensitized photodynamic therapy (PDT). The chemotherapeutic agent of Cur could inhibit the TrxR activity to destroy the cellular ROS-defence system for enhanced PDT, which provides synergistic effects for tumor precision therapy in consideration of the unfavorable tumor microenvironments.