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

Hyaluronic acid-functionalized ruthenium photothermal nanoenzyme for enhancing osteosarcoma chemotherapy: Cascade targeting and bidirectional modulation of drug resistance

Insufficient drug delivery efficiency in vivo and robust drug resistance are two major factors to induce suboptimal efficacy in chemotherapy of osteosarcoma (OS). To address these challenges, we developed polysaccharide hyaluronic acid (HA)-functionalized ruthenium nanoaggregates (Ru NAs) to enhance the chemotherapy of doxorubicin (DOX) for OS. These NAs, comprising Ru nanoparticles (NPs) and alendronate-modified HA (HA-ALN), effectively load DOX, resulting in DOX@Ru-HA-ALN NAs. The combination of HA and ALN in NAs ensures outstanding cascade targeting towards tumor-invaded bone tissues and CD44-overexpressing tumor cells, maximizing therapeutic efficacy while minimizing off-target effects. Concurrently, the Ru NPs in NAs function as "smart" photoenzymatic agent to not only in situ relieve hypoxia of OS via the catalysis of overexpressed H2O2 to produce O2, but also generate mild photothermal effect under 808-nm laser irradiation. They can bidirectionally overcome drug resistance of DOX via downregulation of resistance-related factors including multi-drug resistant associate protein, P-glycoprotein, heat shock factor 1, etc. The integration of cascade targeting with bidirectional modulation of drug resistance positions Ru-HA-ALN NAs to substantially enhance DOX chemotherapy for OS. Therefore, the present work highlights the potential of polysaccharide-functionalized nanomaterials in advancing tumor chemotherapy by addressing challenges of both delivery efficiency and drug resistance.

Metronidazole-modified Au@BSA nanocomposites for dual sensitization of radiotherapy in solid tumors

The hypoxic microenvironment of solid tumors can lead to reduced therapeutic DNA damage to the tumor cells, thus diminishing tumor sensitivity to radiotherapy. Although hypoxic radiosensitizers can improve radiotherapy efficacy by enhancing the role of oxygen, their effects are limited by the uneven distribution of oxygen within solid tumor tissues. In this study, a novel radiosensitizer via leveraging gold complexes and metronidazole (MN) was synthesized to improve radiotherapeutic efficacy. The gold atoms incorporated in the radiosensitizer enabled efficient deposition of high-energy radiation; the hydrophobic metronidazole was reduced to hydrophilic aminoimidazole under hypoxia conditions and further promoted radiotherapy sensitization. The results of CCK-8 assays, Live/Dead assays, γ-H2AX immunofluorescence indicated that metronidazole-modified Au@BSA nanocomposites (NCs) exhibited excellent antitumor effects. The in vivo antitumor tests further showed an inhibition rate of 100%. These results demonstrated that the NCs successfully enhanced radiotherapy efficacy by the dual sensitization strategy. Overall, we believe this multimodal radiosensitizing nanocomplex can significantly inhibit tumor growth and metastasis, with their hypoxia-oriented characteristics ensuring a higher efficacy and safety.

"Abraxane-Like" Radiosensitizer for In Situ Oral Cancer Therapy

Radiotherapy plays a vital role in cancer therapy. However, the hypoxic microenvironment of tumors greatly limits the effectiveness, thus it is crucial to develop a simple, efficient, and safe radiosensitizer to reverse hypoxia and ameliorate the efficacy of radiotherapy. Inspired by the structure of canonical nanodrug Abraxane, herein, a native HSA-modified CaO2 nanoparticle system (CaO2-HSA) prepared by biomineralization-induced self-assembly is developed. CaO2-HSA will accumulate in tumor tissue and decompose to produce oxygen, altering the hypoxic condition inside the tumor. Simultaneously, ROS and calcium ions will lead to calcium overload and further trigger immunogenic cell death. Notably, its sensitizing enhancement ratio (SER = 3.47) is much higher than that of sodium glycididazole used in the clinic. Furthermore, in animal models of in situ oral cancer, CaO2-HSA can effectively inhibit tumor growth. With its high efficacy, facile preparation, and heavy-metal free biosafety, the CaO2-HSA-based radiosensitizer holds enormous potential for oral cancer therapy.

Efficacy tumor therapeutic applications of stimuli-responsive block copolymer-based nano-assemblies

Block copolymers are composed of two or more blocks or segments with different chemical properties via various chemical bonds, which can assemble into nanoparticles with a "core-shell" structure. Due to the benefits of simple functionalization, superior drug-loading capacity, and good biocompatibility, various nano-assemblies based on block copolymers have become widely applied in the treatment of cancers in recent years. These nano-assemblies serve as carriers for anti-tumor bioactive, enhancing drug stability and prolonging their circulation time in vivo, which can reduce the toxic side effects of drugs and improve the therapeutic effect. However, the complex and heterogeneous tumor microenvironment poses challenges to the therapeutic efficacy of these nano-assemblies, having the result in the occurrence of drug resistance and the recurrence of tumors. Consequently, a diverse array of stimuli-responsive nano-assemblies has been devised in order to surmount these obstacles. This article provides a comprehensive overview of the utilization of stimuli-responsive nano-assemblies derived from block copolymers in the context of tumor treatment. The review summarizes block polymers responsive to internal stimuli (like ROS, redox, pH, and enzymes) and external stimuli (like light, and temperature), and discusses current challenges and prospects in this field, aiming to provide novel insights for clinical applications.

Hypoxia-Responsive Tetrameric Supramolecular Polypeptide Nanoprodrugs for Combination Therapy

Despite the intense progress of photodynamic and chemotherapy, however, they cannot prevent solid tumor invasion, metastasis, and relapse, along with inferior efficacy and severe side effects. The hypoxia-responsive nanoprodrugs integrating photodynamic functions are highly sought to address the above-mentioned problems and overcome the tumor hypoxia-reduced efficacy. Herein, a hypoxia-responsive tetrameric supramolecular polypeptide nanoprodrug (SPN-TAPP-PCB4) is constructed from the self-assembly of tetrameric porphyrin-central poly(l-lysine-azobenzene-chlorambucil) (TAPP-(PLL-Azo-CB)4) and an anionic water-soluble [2]biphenyl-extended-pillar[6]arene (AWBpP6) via the synergy of hydrophobic, π-π stacking, and host-guest interactions. Upon laser irradiation, the central TAPP can convert oxygen to generate single oxygen (1 O2 ) to kill tumor cells. Furthermore, under the acidic and PDT-aggravated hypoxia tumor cell microenvironment, SPN-TAPP-PCB4 is rapidly disassembled, and then efficiently releases activated CB through the hypoxic-responsive cleavage of azobenzene linkages. Both in vitro and in vivo biological studies showcase synergistic cancer-killing actions between photodynamic therapy (PDT) and chemotherapy (CT) with negligible toxicity. Consequently, this supramolecular polypeptide nanoprodrug offers an effective strategy to design a hypoxia-responsive nanoprodrug for a potential combo PDT-CT transition.

Key processes in tumor metastasis and therapeutic strategies with nanocarriers: a review

Cancer metastasis is the leading cause of cancer-related death. Metastasis occurs at all stages of tumor development, with unexplored changes occurring at the primary site and distant colonization sites. The growing understanding of the metastatic process of tumor cells has contributed to the emergence of better treatment options and strategies. This review summarizes a range of features related to tumor cell metastasis and nanobased drug delivery systems for inhibiting tumor metastasis. The mechanisms of tumor metastasis in the ideal order of metastatic progression were summarized. We focus on the prominent role of nanocarriers in the treatment of tumor metastasis, summarizing the latest applications of nanocarriers in combination with drugs to target important components and processes of tumor metastasis and providing ideas for more effective nanodrug delivery systems.

Synergistic cerium oxide nanozymes: targeting DNA damage and alleviating tumor hypoxia for improved NSCLC radiotherapy efficiency

Radiotherapy (RT) is one of the important treatment modalities for non-small cell lung cancer (NSCLC). However, the maximum radiation dose that NSCLC patient can receive varies little. Therefore, the exploitation of novel RT sensitization approaches is a critical need for the clinical treatment. RT resistance in NSCLC is linked to tumor microenvironment (TME) hypoxia, cell cycle arrest and associated genetic alterations. Here, we designed a novel method for targeted delivery of quercetin (QT) and CeO2 to enhance RT sensitivity. We loaded QT into CeO2@ZIF-8-HA nanoparticles to prevent its degradation in the circulatory system and successfully delivered QT and CeO2 targeted to NSCLC tumors. Under the protection and targeted delivery of Zeolitic Imidazolate Framework-8 (ZIF-8), the nanocomplexes exhibited excellent catalytic mimetic activity in decomposing H2O2 into O2, thus significantly reversing the hypoxia of TME, while the radiosensitizer QT caused DNA damage directly after RT. In a subcutaneous tumor model, CeO2@ZIF-8-HA overcame radiation resistance and enhanced therapeutic efficacy. This multiple sensitization strategy combining delivery of QT and CeO2@ZIF-8-HA nanozymes opens a promising approach for RT of NSCLC.

Stimuli-Responsive Nanoradiosensitizers for Enhanced Cancer Radiotherapy

Radiotherapy (RT) has been a classical therapeutic method of cancer for several decades. It attracts tremendous attention for the precise and efficient treatment of local tumors with stimuli-responsive nanomaterials, which enhance RT. However, there are few systematic reviews summarizing the newly emerging stimuli-responsive mechanisms and strategies used for tumor radio-sensitization. Hence, this review provides a comprehensive overview of recently reported studies on stimuli-responsive nanomaterials for radio-sensitization. It includes four different approaches for sensitized RT, namely endogenous response, exogenous response, dual stimuli-response, and multi stimuli-response. Endogenous response involves various stimuli such as pH, hypoxia, GSH, and reactive oxygen species (ROS), and enzymes. On the other hand, exogenous response encompasses X-ray, light, and ultrasound. Dual stimuli-response combines pH/enzyme, pH/ultrasound, and ROS/light. Lastly, multi stimuli-response involves the combination of pH/ROS/GSH and X-ray/ROS/GSH. By elaborating on these responsive mechanisms and applying them to clinical RT diagnosis and treatment, these methods can enhance radiosensitive efficiency and minimize damage to surrounding normal tissues. Finally, this review discusses the additional challenges and perspectives related to stimuli-responsive nanomaterials for tumor radio-sensitization.

Precision Dosing of Antibiotics and Potentiators by Hypoxia-Responsive Nanoparticles for Overcoming Antibiotic Resistance in Gram-Negative Bacteria

The stalling development of antibiotics, especially against intrinsically resistant Gram-negative pathogens associated with outer membranes, leads to an emerging antibiotic crisis across the globe. To breathe life into existing drugs, we herein report a hypoxia-responsive nanoparticle (NP) that encapsulates a hydrophobic antibiotic, rifampicin, and a cationic potentiator, polysulfonium. The simultaneous release of antibiotics and potentiators can be promoted and inhibited in response to the severity of bacterial-induced hypoxia, leading to antimicrobial dosing in a precision manner. Under the synergism of polysulfoniums with membrane-disruption capability, the NPs can intensively decrease the antibiotic dose by up to 66-95% in eliminating planktonic Gram-negative P. aeruginosa bacteria and achieve an 8-log reduction of bacteria in mature biofilms at rifampicin MIC. The NP formulation demonstrates that precision dosing of antibiotics and potentiators regulated by hypoxia provides a promising strategy to maximize efficacy and minimize toxicity in treating Gram-negative bacterial infection.

A multi-functional hypoxia/esterase dual stimulus responsive and hyaluronic acid-based nanomicelle for targeting delivery of chloroethylnitrosouea

Carmustine (BCNU), a vital type of chloroethylnitrosourea (CENU), inhibits tumor cells growth by inducing DNA damage at O6 position of guanine and eventually forming dG-dC interstrand cross-links (ICLs). However, the clinical application of BCNU is hindered to some extent by the absence of tumor selectivity, poor stability and O6-alkylguanine-DNA alkyltransferase (AGT) mediated drug resistance. In recent years, tumor microenvironment has been widely utilized for advanced drug delivery. In the light of the features of tumor microenvironment, we constructed a multifunctional hypoxia/esterase-degradable nanomicelle with AGT inhibitory activity named HACB NPs for tumor-targeting BCNU delivery and tumor sensitization. HACB NPs was self-assembled from hyaluronic acid azobenzene AGT inhibitor conjugates, in which O6-BG analog acted as an AGT inhibitor, azobenzene acted as a hypoxia-responsive linker and carboxylate ester bond acted as both an esterase-sensitive switch and a connector with hyaluronic acid (HA). The obtained HACB NPs possessed good stability, favorable biosafety and hypoxia/esterase-responsive drug-releasing ability. BCNU-loaded HACB/BCNU NPs exhibited superior cytotoxicity and apoptosis-inducing ability toward the human uterine cervix carcinoma HeLa cells compared with traditional combined medication of BCNU plus O6-BG. In vivo studies further demonstrated that after a selective accumulation in the tumor site, the micelles could respond to hypoxic tumor tissue for rapid drug release to an effective therapeutic dosage. Thus, this multifunctional stimulus-responsive nanocarrier could be a new promising strategy to enhance the anticancer efficacy and reduce the side effects of BCNU and other CENUs.

Hypoxia-Responsive Aggregation of Gold Nanoparticles for Near-Infrared-II Photoacoustic Imaging-Guided Enhanced Radiotherapy

By directly harming cancer cells, radiotherapy (RT) is a crucial therapeutic approach for the treatment of cancers. However, the efficacy of RT is reduced by the limited accumulation and short retention time of the radiosensitizer in the tumor. Herein, we developed hypoxia-triggered in situ aggregation of nanogapped gold nanospheres (AuNNP@PAA/NIC NPs) within the tumor, resulting in second near-infrared window (NIR-II) photoacoustic (PA) imaging and enhanced radiosensitization. AuNNP@PAA/NIC NPs demonstrated increased accumulation and retention in hypoxic tumors, mainly due to the hypoxia-triggered aggregation. After aggregation of AuNNP@PAA/NIC NPs, the absorption of the system extended from visible light to NIR-II light owing to the plasmon coupling effects between adjacent nanoparticles. Compared to the normoxic tumor, the PA intensity at 1200 nm in the hypoxic tumor increased from 0.42 to 1.88 at 24 h postintravenous injection of AuNNP@PAA/NIC NPs, leading to an increase of 4.5 times. This indicated that the hypoxic microenvironment in the tumor successfully triggered the in situ aggregation of AuNNP@PAA/NIC NPs. The in vivo radiotherapeutic effect demonstrated that this hypoxia-triggered in situ aggregation of radiosensitizers significantly enhanced radiosensitization and thus resulted in superior cancer radiotherapeutic outcomes.

Coordination-Driven Self-Assembly Strategy-Activated Cu Single-Atom Nanozymes for Catalytic Tumor-Specific Therapy

How to optimize the enzyme-like catalytic activity of nanozymes to improve their applicability has become a great challenge. Herein, we present an l-cysteine (l-Cys) coordination-driven self-assembly strategy to activate polyvinylpyrrolidone (PVP)-modified Cu single-atom nanozymes MoOx-Cu-Cys (denoted as MCCP SAzymes) aiming at catalytic tumor-specific therapy. The Cu single atom content of MCCP can be rationally modulated to 10.10 wt %, which activates the catalase (CAT)-like activity of MoOx nanoparticles to catalyze the decomposition of H2O2 in acidic microenvironments to increase O2 production. Excitingly, the maximized CAT-like catalytic efficiency of MCCP is 138-fold higher than that of typical MnO2 nanozymes and exhibits 14.3-fold higher affinity than natural catalase, as demonstrated by steady-state kinetics. We verify that the well-defined l-Cys-Cu···O active sites optimize CAT-like activity to match the active sites of natural catalase through an l-Cys bridge-accelerated electron transfer from Cys-Cu to MoOx disclosed by density functional theory calculations. Simultaneously, the high loading Cu single atoms in MCCP also enable generation of •OH via a Fenton-like reaction. Moreover, under X-ray irradiation, MCCP converts O2 to 1O2 for cascading radiodynamic therapy, thereby facilitating the multiple reactive oxygen species (ROS) for radiosensitization to achieve substantial antitumor.

NADPH Selective Depletion Nanomedicine-Mediated Radio-Immunometabolism Regulation for Strengthening Anti-PDL1 Therapy against TNBC

Anti-PD(L)1 immunotherapy recently arises as an effective treatment against triple-negative breast cancer (TNBC) but is only applicable to a small portion of TNBC patients due to the low PD-L1 expression and the immunosuppressive tumor microenvironment (TME). To address these challenges, a multifunctional "drug-like" copolymer that possesses the auto-changeable upper critical solution temperature and the capacity of scavenging reduced nicotinamide adenine dinucleotide phosphate (NADPH) inside tumor cells is synthesized and employed to develop a hypoxia-targeted and BMS202 (small molecule antagonist of PD-1/PD-L1 interactions)-loaded nanomedicine (BMS202@HZP NPs), combining the anti-PD-L1 therapy and the low-dose radiotherapy (LDRT) against TNBC. In addition to the controlled release of BMS202 in the hypoxic TNBC, BMS202@HZP NPs benefit the LDRT by upregulating the pentose phosphate pathway (PPP, the primary cellular source for NADPH) of TME whereas scavenging the NADPH inside tumor cells. As a result, the BMS202@HZP NPs-mediated LDRT upregulate the PD-L1 expression of tumor to promote anti-PD-L1 therapy response while reprogramming the immunometabolism of TME to alleviate its immunosuppression. This innovative nanomedicine-mediated radio-immunometabolism regulation provides a promising strategy to reinforce the anti-PD-L1 therapy against TNBC.

Prodrug Nanosensitizer Overcomes the Radiation Resistance of Hypoxic Tumor

Clinical radiation therapy (RT) is often hindered by the low radiation energy absorption coefficient and the hypoxic features of tumor tissues. Among the tremendous efforts devoted to overcoming the barriers to efficient RT, the application of hypoxic radiosensitizers and cell-cycle-specific chemotherapeutics has shown great potential. However, their effectiveness is often compromised by their limited bioavailability, especially in the hypoxic region, which plays a major role in radioresistance. Herein, to simultaneously improve the delivery efficacy of both hypoxic radiosensitizer and cell-cycle-specific drug, a gambogic acid (GA) metronidazole (MN) prodrug (GM) was designed and synthesized based on GA, a naturally occurring chemotherapeutic and multiple pathway inhibitor, and MN, a typical hypoxic radiosensitizer. In combination with MN-containing block copolymers, the prodrug nanosensitizer (NS) of GM was obtained. Owing to the bioreduction of MN, the as-designed prodrug could be efficiently delivered to hypoxic cells and act on mitochondria to cause the accumulation of reactive oxygen species. The strong G₂/M phase arrest caused by the prodrug NS could further sensitize treated cells to external radiation under hypoxic conditions by increasing DNA damage and delaying DNA repair. After coadministration of the NS with a well-established tissue-penetrating peptide, efficient tumor accumulation, deep tumor penetration, and highly potent chemoradiotherapy could be achieved.

Prognostic value of the cervical lymph node necrosis ratio in nasopharyngeal carcinoma

PURPOSE

Whether cervical lymph node necrosis (CNN) is an independent adverse prognostic factor in nasopharyngeal carcinoma (NPC) has not been determined. In this study, the CNN ratio was graded quantitatively to explore the prognostic value in NPC.

PARTICIPANTS AND METHODS

We retrospectively reviewed a total of 648 pathologically confirmed as NPC. We outlined metastatic lymph nodes and necrotic area of lymph nodes slice by slice on the magneticresonanceimages (MRI) cross section, and calculated the corresponding CNN ratio.

RESULTS

The median CNN ratio (17.37 %) was taken as the cut-off point, 256 (39.51 %) patients were divided into CNN1 group (<17.37 %, n = 128) and CNN2 group (≥17.37 %, n = 128), 392 (60.49 %) patients without lymph nodes necrosis were CNN0. Among the CNN0, CNN1 and CNN2 groups, five-year overall survival (OS) was 82.4 %, 76.6 % and 71.1 %, locoregional recurrence-free survival (LRRFS) was 91.3 %, 91.1 % and 90.5 %, distant metastasis-free survival (DMFS) was 83.7 %, 78.5 % and 68.7 %, progression-free survival (PFS) was 78.3 %, 71.7 % and 61.6 % respectively. By multivariate analysis, CNN was an independent prognostic factor for OS (P = 0.003), DMFS (P = 0.019) and PFS (P = 0.007). More than 3 cycles of chemotherapy significantly increased OS (P = 0.024) and DMFS (P = 0.015) in the CNN1 group.

CONCLUSIONS

This study indicated that CNN is one of the factors with the negative prognosis of NPC. The CNN ratio might be used as one of the reference factors in the formulation of individualized treatment plan.

Hypoxia-Activatable Nanovesicles as In Situ Bombers for Combined Hydrogen-Sulfide-Mediated Respiration Inhibition and Photothermal Therapy

Photothermal therapy (PTT) has emerged as a promising alternative or supplement to cancer treatments. While PTT induces the ablation of solid tumors, its efficiency is hampered by self-recovery within impaired cancer cells through glycolysis and respiration metabolism. Based on this, the introduction of hydrogen sulfide (H₂S)-mediated respiration inhibition is a good choice to make up for the PTT limitation. Herein, nanovesicles (NP1) are integrated by a hypoxia-responsive conjugated polymer (P1), polymetric H₂S donor (P2), and near-infrared (NIR) light-harvesting aza-BODIPY dye (B1) for the delivery of H₂S and synergistic H₂S gas therapy/PTT. The scaffold of NP1 undergoes disassembly in the hypoxic environments, thus triggering the hydrolysis of P2 to continuously long-term release H₂S. Dependent on the superior photothermal ability of B1, NP1 elicits high photothermal conversion efficiency (η = 19.9%) under NIR light irradiation for PTT. Moreover, NP1 serves as in situ H₂S bombers in the hypoxic tumor environment and suppresses the mitochondrial respiration through inhibiting expression of cytochrome c oxidase (COX IV) and cutting off the adenosine triphosphate (ATP) generation. Both in vitro and in vivo results demonstrate good antitumor efficacy of H₂S gas therapy/PTT, which will be recommended as an advanced strategy for cancer therapeutics.

Exploration of Site-Specific Drug Targeting-A Review on EPR-, Stimuli-, Chemical-, and Receptor-Based Approaches as Potential Drug Targeting Methods in Cancer Treatment

Cancer has been one of the most dominant causes of mortality globally over the last few decades. In cancer treatment, the selective targeting of tumor cells is indispensable, making it a better replacement for conventional chemotherapies by diminishing their adverse side effects. While designing a drug to be delivered selectively in the target organ, the drug development scientists should focus on various factors such as the type of cancer they are dealing with according to which drug, targeting moieties, and pharmaceutical carriers should be targeted. All published articles have been collected regarding cancer and drug-targeting approaches from well reputed databases including MEDLINE, Embase, Cochrane Library, CENTRAL and ClinicalTrials.gov, Science Direct, PubMed, Scopus, Wiley, and Springer. The articles published between January 2010 and December 2020 were considered. Due to the existence of various mechanisms, it is challenging to choose which one is appropriate for a specific case. Moreover, a combination of more than one approach is often utilized to achieve optimal drug effects. In this review, we have summarized and highlighted central mechanisms of how the targeted drug delivery system works in the specific diseased microenvironment, along with the strategies to make an approach more effective. We have also included some pictorial illustrations to have a precise idea about different types of drug targeting. The core contribution of this work includes providing a cancer drug development scientist with a broad preliminary idea to choose the appropriate approach among the various targeted drug delivery mechanisms. Also, the study will contribute to improving anticancer treatment approaches by providing a pathway for lesser side effects observed in conventional chemotherapeutic techniques.

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.

Hypoxia-responsive nanocarriers for chemotherapy sensitization via dual-mode inhibition of hypoxia-inducible factor-1 alpha

The overexpression of hypoxia-inducible factor-1 alpha (HIF-1α) in solid tumor compromises the potency of chemotherapy under hypoxia. The high level of HIF-1α arises from the stabilization effect of reduced nicotinamideadeninedinucleotide(phosphate) NAD(P)H: quinone oxidoreductase 1 (NQO1). It was postulated that the inhibition of NQO1 could degrade HIF-1α and sensitize hypoxic cancer cells to antineoplastic agents. In the current work, we report hypoxia-responsive polymer micelles, i.e. methoxyl poly(ethylene glycol)-co-poly(aspartate-nitroimidazole) orchestrate with a NQO1 inhibitor (dicoumarol) to sensitize the ovarian cancer cell line (SKOV3) to a model anticancer agent (sorafenib) at low oxygen conditions. Both cargos were physically encapsulated in the nanoscale micelles. The placebo micelles transiently induced the depletion of reduced nicotinamideadeninedinucleotidephosphate (NADPH) as well as glutathione and thioredoxin under hypoxia, which further inactivated NQO1 because NADPH was the cofactor of NQO1. As a consequence, the expression of HIF-1α was repressed due to the dual action of dicoumarol and polymer. The degradation of HIF-1α significantly increased the vulnerability of SKOV3 cells to sorafenib-induced apoptosis, as indicated by the enhancement of cytotoxicity, and increase of caspase 3 and cytochrome C. The current work opens new avenues of addressing hypoxia-induced drug resistance in chemotherapy.

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.

Nanomaterials Based on Functional Polymers for Sensitizing Cancer Radiotherapy

Despite being the mainstay treatment for many types of cancer in clinic, radiotherapy is undertaking great challenges in overcoming a series of limitations. Radiosensitizers are promising agents capable of depositing irradiation energy and generating free radicals to enhance the radiosensitivity of tumor cells. Combining radiosensitizers with functional polymer-based nanomaterials holds great potential to improve biodistribution, circulation time, and stability in vivo. The derived polymeric nano-radiosensitizers can significantly improve the efficiency of tumor targeting and radiotherapy, and reduce the side effect to healthy tissues. In this review, we provide an overview of functional polymer-based nanomaterials for radiosensitization in recent years. Particular emphases are given to the action mechanisms, drug loading methods, targeting efficiencies, the impact on therapeutic effects and biocompatibility of various radiosensitizing polymers, which are classified as polymeric micelles, dendrimers, polymeric nanospheres, nanoscale coordination polymers, polymersomes, and nanogels. The challenges and outlooks of polymeric nano-radiosensitizers are also discussed. This article is protected by copyright. All rights reserved.

A Three-In-One Assembled Nanoparticle Containing Peptide-Radio-Sensitizer Conjugate and TLR7/8 Agonist Can Initiate the Cancer-Immunity Cycle to Trigger Antitumor Immune Response

Radiotherapy (RT) has been shown to cause immunogenic cell death (ICD) of cancer cells, which promote the release of tumor-associated antigens, and trigger the cancer-immunity cycle (CIC). However, ICD induced by RT usually does not occur in hypoxic tumor cells due to their resistance to radiation. Moreover, RT also induces programmed death ligand 1 (PD-L1) upregulation on tumor cells, which has an inhibitory effect on T lymphocytes. Therefore, therapy based on CIC must selectively target the restricted steps of antitumor immunity. Herein, the authors design a versatile three-in-one assembling nanoparticle that can simultaneously execute these obstacles. The amphiphilic peptide drug conjugate NIA-D1, containing the hydrophobic radio-sensitizer 2-(2-nitroimidazol-1-yl) acetic acid (NIA), a peptide substrate of matrix metalloproteinase-2, and a hydrophilic PD-L1 antagonist ^D PPA-1, is constructed and co-assembled with hydrophobic Toll-like receptor (TLR) 7/8 agonist R848 to form nanoparticle NIA-D1@R848. The NIA-D1@R848 nanoparticles combined with RT can trigger the apoptosis of tumor cells and initiate the CIC. In the presence of R848, it promotes the maturation of dendritic cells, which together with protein programmed cell death protein 1 (PD-1) and its ligand PD-L1  blockade to relieve T cell suppression, and amplify the antitumor immune cycle. In conclusion, a functionalized three-in-one nanoparticle NIA-D1@R848 is successfully constructed, which can induce strong systemic antitumor immune response.

Transforming Nuclear Medicine with Nanoradiopharmaceuticals

Nuclear medicine is expected to make major advances in cancer diagnosis and therapy; tumor-targeted radiopharmaceuticals preferentially eradicate tumors while causing minimal damage to healthy tissues. The current scope of nuclear medicine can be significantly expanded by integration with nanomedicine, which utilizes nanoparticles for cancer diagnosis and therapy by capitalizing on the increased surface area-to-volume ratio, the passive/active targeting ability and high loading capacity, the greater interaction cross section with biological tissues, the rich surface properties of nanomaterials, the facile decoration of nanomaterials with a plethora of functionalities, and the potential for multiplexing several functionalities within one construct. This review provides a comprehensive discussion of nuclear nanomedicine using tumor-targeted nanoparticles for cancer radiation therapy with either pre-embedded radionuclides or nonradioactive materials which can be extrinsically triggered using various external nuclear particle sources to produce in situ radioactivity. In addition, it describes the prospect of combining nuclear nanomedicine with other modalities to enable synergistically enhanced combination therapies. The review also discusses advances in the fabrication of radionuclides as well as describes laser ablation technologies for producing nanoradiopharmaceuticals, which combine the ease of production with exceptional purity and rapid biodegradability, along with additional imaging or therapeutic functionalities. From a practical standpoint, these attributes of nanoradiopharmaceuticals may provide distinct advantages in diagnostic/therapeutic sensitivity and specificity, imaging resolution, and scalability of turnkey platforms. Coupling image-guided targeted radiation therapy with the possibility of in situ activation of nanomaterials as well as combining with other therapeutic modalities using a multifunctional nanoplatform could herald an era of exciting technological and therapeutic advances to radically transform the landscape of nuclear medicine. The review concludes with a discussion of current challenges and presents the authors' views on future opportunities to stimulate further research in this rewarding field of high societal impact.

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.

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.

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.

Recent advances in peptide-based nanomaterials for targeting hypoxia

Hypoxia is a prominent feature of many severe diseases such as malignant tumors, ischemic strokes, and rheumatoid arthritis. The lack of oxygen has a paramount impact on angiogenesis, invasion, metastasis, and chemotherapy resistance. The potential of hypoxia as a therapeutic target has been increasingly recognized over the last decade. In order to treat these disease states, peptides have been extensively investigated due to their advantages in safety, target specificity, and tumor penetrability. Peptides can overcome difficulties such as low drug/energy delivery efficiency, hypoxia-induced drug resistance, and tumor nonspecificity. There are three main strategies for targeting hypoxia through peptide-based nanomaterials: (i) using peptide ligands to target cellular environments unique to hypoxic conditions, such as cell surface receptors that are upregulated in cells under hypoxic conditions, (ii) utilizing peptide linkers sensitive to the hypoxic microenvironment that can be cleaved to release therapeutic or diagnostic payloads, and (iii) a combination of the above where targeting peptides will localize the system to a hypoxic environment for it to be selectively cleaved to release its payload, forming a dual-targeting system. This review focuses on recent developments in the design and construction of novel peptide-based hypoxia-targeting nanomaterials, followed by their mechanisms and potential applications in diagnosis and treatment of hypoxic diseases. In addition, we address challenges and prospects of how peptide-based hypoxia-targeting nanomaterials can achieve a wider range of clinical applications.

Ultrasound augments on-demand breast tumor radiosensitization and apoptosis through a tri-responsive combinatorial delivery theranostic platform

Advanced inoperable triple-negative breast cancer (TNBC) comprises aggressive tumors with a modest pathological response to neoadjuvant chemotherapy. The concomitant use of chemoradiotherapy improves the pathological response rates. However, the dose-dependent systemic toxicity of clinical radiosensitizers with poor circulation half-life and limited passive bioavailability limits their clinical utility. We address these challenges by rationally designing a stealth and tumor microenvironment responsive nano-conjugate platform for the ultrasound-mediated on-demand spatio-temporal delivery of plant flavonoid curcumin as a combinatorial regimen with clinically approved paclitaxel for the neoadjuvant chemoradiotherapy of locally advanced triple-negative breast cancer (TNBC). Interestingly, the focused application of ultrasound at the orthotopic TNBC xenograft of NOD-SCID mice facilitated the immediate infiltration of nano-conjugates at the tumor interstitium, and conferred in vivo safety over marketed paclitaxel formulation. In addition, curcumin significantly potentiated the in vivo chemoradiotherapeutic efficacy of paclitaxel upon loading into nano-conjugates. This gets further enhanced by the concurrent pulse of ultrasound, as confirmed by PET-CT imaging, along with a significant improvement in the mice survival. The quadrapeutic apoptotic effect by the combination of paclitaxel, curcumin, radiation, and ultrasound, along with a reduction in the tumor microvessel density and cell proliferation marker, confers the broad chemo-radiotherapeutic potential of this regimen for radio-responsive solid tumors, as well as metastatic niches.

Advances of Nanomedicine in Radiotherapy

Radiotherapy (RT) remains one of the current main treatment strategies for many types of cancer. However, how to improve RT efficiency while reducing its side effects is still a large challenge to be overcome. Advancements in nanomedicine have provided many effective approaches for radiosensitization. Metal nanoparticles (NPs) such as platinum-based or hafnium-based NPs are proved to be ideal radiosensitizers because of their unique physicochemical properties and high X-ray absorption efficiency. With nanoparticles, such as liposomes, bovine serum albumin, and polymers, the radiosensitizing drugs can be promoted to reach the tumor sites, thereby enhancing anti-tumor responses. Nowadays, the combination of some NPs and RT have been applied to clinical treatment for many types of cancer, including breast cancer. Here, as well as reviewing recent studies on radiotherapy combined with inorganic, organic, and biomimetic nanomaterials for oncology, we analyzed the underlying mechanisms of NPs radiosensitization, which may contribute to exploring new directions for the clinical translation of nanoparticle-based radiosensitizers.

Zwitterionic Block Copolymer Prodrug Micelles for pH Responsive Drug Delivery and Hypoxia-Specific Chemotherapy

Tirapazamine (TPZ) and its derivatives (TPZD) have shown their great potential for efficiently killing hypoxic cancer cells. However, unsatisfactory clinical outcomes resulting from the low bioavailability of the low-molecular TPZ and TPZD limited their further applications. Precise delivery and release of these prodrugs via functional nanocarriers can significantly improve the therapeutic effects due to the targeted drug delivery and enhanced permeability and retention (EPR) effect. Herein, zwitterionic block copolymer (BCP) micelles with aldehyde functional groups are prepared from the self-assembly of poly(2-methacryloyloxyethyl phosphorylcholine-b-poly(di(ethylene glycol) methyl ether methacrylate-co-4-formylphenyl methacrylate) [PMPC-b-P(DEGMA-co-FPMA)]. TPZD is then grafted onto PMPC-b-P(DEGMA-co-FPMA) to obtain a polymer-drug conjugate, PMPC-b-P(DEGMA-co-FPMA-g-TPZD) (BCP-TPZ), through the formation of a pH-responsive imine bond, exhibiting a pH-dependent drug release profile owing to the cleavage of the imine bond under acidic conditions. Outstandingly, BCP-TPZ shows around 13.7-fold higher cytotoxicity to hypoxic cancer cells in comparison to normoxic cancer cells evaluated through an in vitro cytotoxicity assay. The pH-responsiveness and hypoxia-specific cytotoxicity confer BCP-TPZ micelles a great potential to achieve precise delivery of TPZD and thus enhance the therapeutic effect toward tumor-hypoxia.

Photothermal photodynamic therapy and enhanced radiotherapy of targeting copolymer-coated liquid metal nanoparticles on liver cancer

The maximized therapeutic efficacy in tumor treatment can be achieved with combination therapy. Herein, a metronidazole (MN) and RGD peptides were linked with the copolymer chains of polyacrylic acid (PAA) and polyethylene glycol (PEG) by condensation and Michael addition reactions, respectively, named as RGD-PEG-PAA-MN. Subsequently, liquid-metal (LM) nanoparticles broken by ultrasonication were coated with modified copolymer, forming RGD-PEG-PAA-MN@LM nanoparticles. These nanoparticles with the degradation under an acidic condition could target to tumor cells, and LM of these composited nanoparticles could not only efficiently convert the photoenergy of near infrared (NIR) into thermal energy, but also produce more reactive oxygen species under NIR or X ray irradiation. Furthermore, MN in the composited nanoparticles could enhance their radiation sensitivity of tumor tissues with hypoxia condition. The synergic effect of these nanoparticles on cancer limitation after the sequential radiations of NIR and X ray was significantly higher than the single radiation. In the experiments of tumor bearing mice, the volume of the tumor in RGD-PEG-PAA-MN@LM group at 14th day after two radiations of NIR and X-ray were significantly smaller than LM group, and the tumor of RGD-PEG-PAA-MN@LM group at 14th day after two radiations almost disappeared, suggesting better synergistic effect of RGD-PEG-PAA-MN@LM nanoparticles on photothermal conversion, photodynamics under two irradiations and their enhanced sensitization of X-ray radiation. Our results indicated that the prepared nanoparticles would be applied in the combinational therapy of liver tumor by the photothermal, photodynamic and sensitized radiation.

Smart Nanoparticles for Chemo-Based Combinational Therapy

Cancer is a heterogeneous and complex disease. Traditional cancer therapy is associated with low therapeutic index, acquired resistance, and various adverse effects. With the increasing understanding of cancer biology and technology advancements, more strategies have been exploited to optimize the therapeutic outcomes. The rapid development and application of nanomedicine have motivated this progress. Combinational regimen, for instance, has become an indispensable approach for effective cancer treatment, including the combination of chemotherapeutic agents, chemo-energy, chemo-gene, chemo-small molecules, and chemo-immunology. Additionally, smart nanoplatforms that respond to external stimuli (such as light, temperature, ultrasound, and magnetic field), and/or to internal stimuli (such as changes in pH, enzymes, hypoxia, and redox) have been extensively investigated to improve precision therapy. Smart nanoplatforms for combinational therapy have demonstrated the potential to be the next generation cancer treatment regimen. This review aims to highlight the recent advances in smart combinational therapy.

Exploiting a New Approach to Destroy the Barrier of Tumor Microenvironment: Nano-Architecture Delivery Systems

Recent findings suggest that tumor microenvironment (TME) plays an important regulatory role in the occurrence, proliferation, and metastasis of tumors. Different from normal tissue, the condition around tumor significantly altered, including immune infiltration, compact extracellular matrix, new vasculatures, abundant enzyme, acidic pH value, and hypoxia. Increasingly, researchers focused on targeting TME to prevent tumor development and metastasis. With the development of nanotechnology and the deep research on the tumor environment, stimulation-responsive intelligent nanostructures designed based on TME have attracted much attention in the anti-tumor drug delivery system. TME-targeted nano therapeutics can regulate the distribution of drugs in the body, specifically increase the concentration of drugs in the tumor site, so as to enhance the efficacy and reduce adverse reactions, can utilize particular conditions of TME to improve the effect of tumor therapy. This paper summarizes the major components and characteristics of TME, discusses the principles and strategies of relevant nano-architectures targeting TME for the treatment and diagnosis systematically.

Designing Hypoxia-Responsive Nanotheranostic Agents for Tumor Imaging and Therapy

Hypoxia, a common feature of most solid tumors, plays an important role in tumor proliferation, metastasis, and invasion, leading to drug, radiation, and photodynamic therapy resistance, and resulting in a sharp reduction in the disease-free survival rate of tumor patients. The lack of sufficient blood supply to the interior regions of tumors hinders the delivery of traditional drugs and contrast agents, interfering with their accumulation in the hypoxic region, and preventing efficient theranostics. Thus, there is a need for the fabrication of novel tumor theranostic agents that overcome these obstacles. Reports, in recent years, of hypoxia-responsive nanomaterials may provide with such means. In this review, a comprehensive description of the physicochemical and biological characteristics of hypoxic tumor tissues is provided, the principles of designing the hypoxia-responsive tumor theranostic agents are discussed, and the recent research into hypoxia-triggered nanomaterials is examined. Additionally, other hypoxia-associated responsive strategies, the current limitations, and future prospects for hypoxia-responsive nanotheranostic agents in tumor treatment are discussed.

Selectively enhancing radiosensitivity of cancer cells via in situ enzyme-instructed peptide self-assembly

The radiotherapy modulators used in clinic have disadvantages of high toxicity and low selectivity. For the first time, we used the in situ enzyme-instructed self-assembly (EISA) of a peptide derivative (Nap-G^DF^DFpYSV) to selectively enhance the sensitivity of cancer cells with high alkaline phosphatase (ALP) expression to ionizing radiation (IR). Compared with the in vitro pre-assembled control formed by the same molecule, assemblies formed by in situ EISA in cells greatly sensitized the ALP-high-expressing cancer cells to γ-rays, with a remarkable sensitizer enhancement ratio. Our results indicated that the enhancement was a result of fixing DNA damage, arresting cell cycles and inducing cell apoptosis. Interestingly, in vitro pre-formed assemblies mainly localized in the lysosomes after incubating with cells, while the assemblies formed via in situ EISA scattered in the cell cytosol. The accumulation of these molecules in cells could not be inhibited by endocytosis inhibitors. We believed that this molecule entered cancer cells by diffusion and then in situ self-assembled to form nanofibers under the catalysis of endogenous ALP. This study provides a successful example to utilize intracellular in situ EISA of small molecules to develop selective tumor radiosensitizers.

•

The intracellular in situ enzyme-instructed self-assembly (in situ EISA) was firstly used for selective cancer radiosensitization.

•

Compared with the in vitro pre-assembled control formed by the same molecule, assemblies formed by in-situ EISA in cells greatly sensitized the ALP-high-expressing cancer cells to γ-rays.

•

This work provides a successful example to utilize intracellular in situ EISA of small molecules to develop selective tumor radiosensitizers.

Azo-inserted responsive hybrid liposomes for hypoxia-specific drug delivery

Stimuli-responsive drug delivery systems using endogenous stimuli from tumor microenvironments such as acidic pH, over-expressed enzyme, and high redox potential as triggers have shown tremendous promise in cancer therapy. However, their clinical application is severely limited because of tumor heterogeneity. Hypoxia, a physiological feature observed in almost all solid tumors and even in nodules with very small size, has currently emerged as a more general but efficient stimulus to trigger release. Herein, we developed hypoxia-responsive hybrid liposomes (HR-HLPs), composed of azo-inserted organokoxysilane-based lipid analogue as a responsive component and commercial phospholipid for reducing the rigidity of liposomal membrane caused by azo, for drug delivery targeting tumor hypoxia. HR-HLPs had the advantages of high structural stability to avoid premature drug leakage when circulating in the blood and high sensitivity in responding to hypoxia once reaching tumor sites. HR-HLPs exhibit deep tumor penetration capability, enabling effective delivery to hypoxic regions distant from tumor vessels. Moreover, HR-HLPs could selectively release their payload, co-localizing with over-expressed hypoxia inducible factor 1α (HIF-1α) in vitro and in vivo. As a result, HR-HLPs showed improved therapeutic outcome accompanied by reduced adverse effects. The results highlighted the potential application of azo-inserted responsive hybrid liposomes for hypoxia-targeted drug delivery. STATEMENT OF SIGNIFICANCE.

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.

Preparation of polyethylene glycol-polyacrylic acid block copolymer micelles with pH/hypoxic dual-responsive for tumor chemoradiotherapy

Block copolymers of poly(ethylene glycol)-poly(acrylic acid) linked with metronidazole (MN-PAA-PEG) were prepared via carbodiimide and esterification methods, and self-assembled into core-shell micelles as nano radiosensitizers and carriers of doxorubicin (DOX) delivery. These DOX/MN-PAA-PEG micelles exhibited good pH value and hypoxia dual-responsive properties via analyzing the change of micelle size and drug‒release behavior under hypoxia humor condition. The results of the cell test indicated that DOX was efficiently delivered by DOX/MN-PAA-PEG micelles into the cell nuclei. Compared to 22.4 % of their DOX release under pH 7.4, the rate of DOX release from DOX/MN-PAA-PEG micelles under reducing condition (pH 5.0) was up to 55.9 %. DOX-loaded micelles under 600 MU electron radiation and hypoxia induced the rapidest apoptosis of the tumor-cells, indicating the synergistic effect of their radiotherapy and chemotherapy from the prepared micelles. In vivo investigation and fluorescence imaging revealed that MN-PAA-PEG possessed no toxicity on main organs, and DOX/MN-PAA-PEG micelles were mainly accumulated in the tumor site at 10 h of post-injection, suggesting their good passive tumor-targeted effect. These results suggested that DOX/MN-PAA-PEG micelles were promising candidates for chemoradiotherapy on tumor.