Nanomedicine for combination of chemodynamic therapy and immunotherapy of cancers

Waqas Ahmad ^ab, Wasim Sajjad ^ab, Qinghao Zhou *^a and Zhishen Ge *^a
aSchool of Chemistry, Xi'an Jiaotong University, Xi'an 710049, Shaanxi, China. E-mail: gezs@ustc.edu.cn; zhouqh@xjtu.edu.cn
^bCAS Key Laboratory of Soft Matter Chemistry, Department of Polymer Science and Engineering, University of Science and Technology of China, Hefei 230026, Anhui, China

First published on 4th March 2024

---

---

1. Introduction

The Fenton reaction is a classical reaction that uses the ferrous ion (Fe²⁺) to catalyze the production of powerful oxidative hydroxyl radicals (˙OH).^1,2 This reaction has been widely utilized to break down organic debris in sewage.^3,4 With the aid of nanotechnology and nanomaterials, this type of reaction has expanded into other fields, especially tumor treatment or antibiosis in recent years.^5–7 Notably, the emergence and growth of malignant tumors can produce a distinct microenvironment, such as low catalase activity, overexpression of H₂O₂, weak acidity, etc.^8–10 In addition to offering tumors ideal growth circumstances, the unique microenvironment of tumor tissues also offers the chance for effective and targeted tumor treatment.^10–13 On the basis of the high level of H₂O₂ and weakly acidic microenvironments, it is possible to introduce particular catalysts (e.g. Fe²⁺) to activate the Fenton/Fenton-like reaction and effectively create ˙OH radicals to kill tumor cells.

In 2016, the Bu group applied the Fenton reaction to tumor treatment and named it chemodynamic therapy (CDT).^14,15 This method was defined as taking the mild acidity of the microenvironment in the tumor lesion as the reaction condition, overexpressed H₂O₂ as the reaction raw material, and transition metal nanomaterials as the catalyst, to initiate an in situ Fenton-like reaction inside tumor tissues. The reaction can produce substantial oxidative reactive oxygen species (ROS) and ˙OH, to induce tumor cell apoptosis. The produced ˙OH from the Fenton reaction can effectively oxidize the tumor cell membrane, protein molecules, or DNA to trigger cell apoptosis. Notably, in the normal tissues without H₂O₂, relatively low side toxicity can be observed. Therefore, as compared with traditional clinical strategies including radiotherapy, chemotherapy, and phototherapy, CDT has the advantages of tumor specificity, low systemic toxicity and side effects, no need for external excitation in the treatment process, and relatively low treatment costs.^5,16,17 In fact, CDT has been applied in the field of anti-cancer, such as bleomycin, anthracycline and other DNA-targeting drugs, the process of action requires the combination of iron ions, which catalyze the Fenton reaction to produce free radicals to destroy DNA. The emergence of functional nanomaterials can improve the efficiency of the Fenton/Fenton-like reactions, thus significantly improving the efficacy of CDT. However, the concentration of H₂O₂ in tumor tissues is not sufficient for efficient CDT and ablation of tumors completely. In recent years, a lot of studies mainly focused on the optimization of nanomaterials and regulation of the tumor microenvironment, such as increasing the H₂O₂ amount inside tumors, and reducing glutathione (GSH).^16,18–21 Further improvement of the therapeutic efficiency of CDT against cancers is still needed.

Cancer immunotherapy refers to the treatment modality that inhibits tumor growth or metastasis by modulating the patient's own immune responses.^22,23 A number of clinical applications and trials have shown the great potential of immunotherapy in tumor treatment, which is playing an increasingly important role in oncology.^24–26 In general, the function of the immune response is performed by both innate and adaptive aspects of the immune system. Innate immunity is a kind of natural defense system formed in human evolution, which plays the role of the first line of defense in the complex immune system of the human body. Innate immunity is mainly composed of dendritic cells and macrophages. The adaptive immune system is the immune system that develops when the body is exposed to microorganisms that eliminate pathogens, and it is mainly composed of T lymphocytes and B lymphocytes.²⁷ The production of cancer immunity consists of several key steps, including the release of tumor cell-associated antigens, presentation of tumor cell-associated antigens by antigen-presenting cells, activation of T cells, migration of effector T cells, and tumor invasion, where effector T cells can recognize and kill tumor cells. Various immunotherapy methods have been developed.²⁸ However, most of the immunotherapy approaches frequently face significant problems, such as varying response rates and unpredictable therapeutic effects, lack of specific biomarkers, presence of a tumor immunosuppressive tumor environment, treatment-related toxicity and tumor recurrence, which greatly limit their ability to treat cancer cancers and the translation into clinical practice.^29–31 Thus, it is highly desired to further improve the therapeutic efficacy of cancer immunotherapy.

Combination therapy is gradually proposed as a powerful antitumor strategy. Combination therapy is defined as a treatment regimen that uses at least two standard forms of treatment. Due to the rapid development of nanotechnology, various nanocarriers have been developed to provide more effective methods for combination therapy.^32–34 To improve the therapeutic efficacies of a single treatment modality of CDT and immunotherapy and overcome their shortcomings, the combination of CDT and immunotherapy was widely explored by using the nanocarriers.^35–39 In this review paper, we summarize the progress of nanomedicine for the combination of CDT and immunotherapy. We discuss various immunotherapy strategies that have been used to combine with CDT including immunogenic death of tumor cells, immune checkpoint inhibitors, and STING activation (Scheme 1).

2. CDT and immunogenic cell death

When tumor cells undergo apoptosis due to some treatment modalities, this process can often induce the transformation from non-immunogenic to immunogenic and facilitate the body's immune response against tumors, which is known as immunogenic cell death (ICD).^40–44 When tumor cells develop ICDs, they generate a sequence of signaling molecules known as damage-associated molecular patterns (DAMPs), including calreticulin (CRT), high mobility group protein-1 (HMGB-1) secreted by tumor cells, adenosine triphosphate (ATP) molecules secreted by cells, and heat shock proteins (HSP70, HSP90). DAMPs produced during ICD attach to PRRs, a pattern recognition receptor on the surface of dendritic cells, initiating a series of cytological responses that ultimately trigger both adaptive and innate immune responses. CDT can promote the production of in situ cytotoxicity ˙OH through the Fenton reaction. This process can result in the extensive demise of tumor cells and has been confirmed to possess the feature of ICD.^45,46 Therefore, CDT can induce ICD to further stimulate the maturation of DCs, and ultimately increase the invasion of T cells to the tumor site to achieve efficient immune activation (Table 1).

---

---

---

In one example, a nanometallic organic framework (nMOF) (expressed as mFe(SS)/DG) was coated with cancer cell membranes to load glucose oxidase (GOx) and adriamycin (DOX).⁴⁷ The cancer cell membrane's tumor homologous targeting allows the drug delivery nanosystem to efficiently accumulate at the tumor site. Fe³⁺ in the mFe(SS)/DG composition and organic ligands with disulfide bonds efficaciously cleared glutathione (GSH) within the tumor and down-regulated glutathione peroxide-4 (GPX4). GOx catalyzes glucose to generate a large amount of H₂O₂ and thus enhance the Fenton reaction, resulting in massive ROS production in the tumor, which concurrently induces iron death and suppresses glycolysis. The combination of DOX and iron death can stimulate ICD and release tumor antigens, augment tumor immunogenicity, and trigger anti-tumor immunity. By preventing glycolysis, the drug delivery method lowers the amount of lactic acid at the tumor location, and then weakens the immunosuppression caused by excess lactic acid at the tumor site, and reshapes the immune microenvironment to enhance anti-tumor immunity. This intelligent bionic nanodrug delivery system regulates tumor metabolism based on ROS, and induces the combination of CDT and immunotherapy.

Similarly, a multifunctional therapeutic nanoplatform (DOX-TAF@FN) was prepared using the DOX-loaded tannic acid (TA)–iron (Fe) network and coated fibronectin (FN) for the combination of chemotherapy/chemodynamic/immunotherapy.⁴⁸ The DOX-TAF@FN nanocomplexes that were formed by the local coordination of TA, and Fe(III) and the physical coating of FN had a uniform particle size and particle stability. DOX and Fe³⁺ can be released due to the weak acidity of the tumor microenvironment. Due to the coexistence of the TAF network and DOX, through the synergistic effect of iron-based CDT and DOX-based chemotherapy, significant ICD can be induced by enhancing the iron apoptosis of cancer cells. It can further enhance the therapeutic efficacy of the related immune responses.

Yang et al.⁴⁹ fabricated artesunate (ART) loaded polydopamine (PDA)/iron (Fe) nanocomplexes (FDRF NCs) coated with FN for targeted MR imaging-guided combined chemo/CDT/immune therapy. The three major innovation points are as follows: (1) the fibronectin-mediated co-delivery of ART and Fe²⁺ can be accomplished to boost CDT premium FDRF NCs synthesized via a microfluidic synthesis procedure, (2) an enhanced ICD mediated immune stimulation can be achieved via the amalgamation of ART-mediated CT and augmented CDT via the Fenton reaction of Fe²⁺ and Fe³⁺ facilitated GSH oxidation to prolong TME regulation; and (3) the FDRF NCs can attain effective T1 MR imaging-assisted cancer therapy by the integration of αPD-L1-assisted ICB and elevated ICD triggered immune activation.

Moreover, a ROS cascade nanoplatform that combines a Fe-based CDT scaffold with an upconversion nanoparticle (UCNP)-based photodynamic therapy (PDT) system demonstrated a potent synergistic anticancer impact.^50,51 Because the constructed UCNPs can convert near-infrared excitation into visible/ultraviolet emission, they were used to enable PDT under near-infrared light irradiation. Moreover, the complexes of Fe–tannic acid (FeTA) were used to achieve cascade CDT. The pH of the FeTA complex varies. In neutral circumstances, it exhibits tight complexity. The complexes dissociate in an acidic tumor environment. TA as a highly active reductant effectively transforms Fe³⁺ into Fe²⁺ for the Fenton reaction and causes excess H₂O₂ in tumor cells to induce the CDT effect. The Fe³⁺/Fe²⁺ conversion byproduct O₂ improves PDT by reducing the hypoxic microenvironment. Hypoxia is an immunosuppressive factor to immunotherapy, thus, developing stimuli-responsive nanocarriers, especially hypoxia-sensitive immunotherapeutic nanocarriers, not only could potentiate anticancer immunity, but also could sensitize responses of tumors to immunotherapy.^52–54 The combination therapy of CDT and PDT increases tumor immunogenicity and activates the anticancer immune response by inducing a ROS cascade that further evokes ICD of tumor cells with greater immune cell infiltration. When used in conjunction with the programmed death ligand-1 (PD-L1) antibody, this nanosystem uses the systemic immunotherapy response to block the growth of both distant and primary tumors. Additionally, the nanosystem enables the integration of tumor diagnosis and treatment through multimodal tumor imaging by using both computed tomography (CT) and magnetic resonance imaging (MRI).

Recently, Zhao et al.⁵⁵ developed a DNA adjuvant hydrogel which contains CpG oligodeoxynucleotides (ODNs) to integrate the GOx-ferrocene (Fc) cascade for combined CDT and immunotherapy. CpG ODNs form a Y-shaped scaffold, and a linker within DNA hydrogels. Fc and GOx were incorporated into DNA adjuvant hydrogels via connecting with DNA strands and forming a linear linker. The length between GOx and Fc can be controlled by adjusting the lengths of DNA strands which are connected to the catalysts, and hence enhances the enzyme cascade reaction efficiency. It was determined that if the GOx and Fc distance is 6.28 nm, it would convert glucose into ˙OH efficiently, which can boost ICD. Moreover, the DNA adjuvant hydrogel has the ability to generate ˙OH for continuous four days for tumor eradication. By injecting the DNA adjuvant hydrogel intratumorally, it integrates enzyme cascades, and thus inhibits tumor growth and eliminates the development of localized tumors. Furthermore, this CDT immunotherapy substantially restrains tumor recurrence and metastasis.

Notably, Liu et al.⁵⁶ described a novel nanoparticle on the basis of micro-ecology differentiation in both oncogenic and normal tissue, as well as microbiome-triggered reversion of cold tumors gives a new perception of the accurate and effective immune-therapy of triple negative breast cancer (TNBC) (Fig. 1).⁵⁶ An outer membrane vesicle derived from bacteria was used to coat the antibiotic metronidazole (MTD) encapsulated MOF, that contained Fe³⁺, imprecisely specific tumor tissue for the eradication of both F. nucleatum and cancer cells, thus transforming the intratumoral bacteria into immune enhancers in immunotherapy of triple negative breast cancer. By using homologous interaction and Fap2 lectin-Gal-GalNAc recognition ability of outer membrane vesicles, the nanocomposite binds and recongnises F. nucleatum and cancer cells.^57–59 Inside the tumor microenvironment, the nanoplatform releases Fe³⁺ and MTD to eradicate F. nucleatum and tumor cells via CDT.⁶⁰ The antigen associated molecular patterns and DAMPs secreted by dead tumor cells substantially improve immunogenicity. Non-cellular outer membrane vesicles that contain a range of immune activating constituents from their parent cells act as effective immune modulators. More importantly, dead F. nucleatum transformed into an enhancer, which uses the secreted PAMPs to augment the development of dendritic cells and resultant T-cell infiltration, inhibiting the proliferation and metastasis of the cancer.

A multifaceted drug delivery nanosystem comprising folic acid-adapted metal phenolic networks (MPNs) was developed to load with GOx and chlorogenic acid (CHA) (F-MGC) (Fig. 2).⁶¹ F-MGC is readily and rapidly synthesized by using the auto-assembly of folic acid-adapted polyethylene glycol (FA-PEG) polyphenol, CHA, and Fe³⁺, in which GOx was concurrently encapsulated. In this system, PEG, the primary nanoparticle skeleton, extends the blood circulation half-life, and presumably adapted folic acid can target tumors by enhancing the concentration of nanoparticles. To release GOx, CHA, and Fe³⁺, F-MGC easily breaks down in the slightly acidic TME or in the lysosomes of tumor cells. Tumor cells that produce H₂O₂ and gluconic acid can be starved by the released GOx, which can speed up glucose intake. The minted gluconic acid has the ability to lower the pH in the tumor microenvironment even more, which speeds up the breakdown of F-MGC and encourages the Fenton reaction, which is catalyzed by Fe³⁺. Then, as a component of CDT, ˙OH produced by H₂O₂ might cause cancer cell ferroptosis. By repolarizing tumor associated macrophages (TAMs) from the M2 to the M1 phenotype, CHA transforms the immunosuppressive status of the TME into immunological activation. Moreover, to eradicate tumor cells directly, enhanced tumor-specific cellular immunity resulting from the ICD effect also reduces the spread and recurrence of cancer. The overall combined therapeutic efficacy indicates that it is helpful in the treatment of cancers.

A cascade, catalytic nanoplatform, IONP-GOD@ART, was prepared, which contained GOD-tailored iron oxide (IONP) and impregnated with artemisinin (ART) (Fig. 3).⁶² IONP-GOD@ART would initiate a severe cascade catalysis inside the tumor tissue. In addition to realizing tumor starvation therapy, GOD was able to efficiently catalyze the oxidation of glucose into gluconic acid, which produced H₂O₂ for the IONP-mediated Fenton reaction. In an acidic tumor microenvironment, mesoporous IONP would simultaneously liberate Fe²⁺ and Fe³⁺ ions. In an acidic TME, iron ions conducted the Fenton reaction, which produced ˙OH for CDT. On the other hand, in order to accomplish the therapeutic goal, the endoperoxide bridge in ART was disrupted in the presence of Fe and further produced ROS. ROS from the Fenton reaction and ART would then lead to the production of ICD to provide antitumor immunity. Furthermore, ROS caused the repolarization of the M2 phenotype, which reprogrammed the immunosuppressive tumor microenvironment for improved immunotherapy. The cascade catalytic nanoplatform (IONPGOD@ART) achieved completely effective cancer immunotherapy for tumor regression and metastasis via precise design that gave rise to “the butterfly effect”.

In addition to the Fe^2+/3+ ion as a catalyst to catalyze the Fenton reaction to achieve CDT, there are also related studies that use other metal ions such as Mn²⁺ and Cu⁺ to catalyze the generation of the CDT effect and induce ICD to improve the anti-tumor immune effect.

Lin et al.⁶³ developed a type of manganese (Mn) oxide nanomaterial. In the tumor microenvironment, Mn oxide nanoparticles can achieve biodegradation, activate antigen delivery, and regulate the immunosuppressive microenvironment. Mn²⁺ ions can induce ICD of a large number of cells through CDT, thus, significantly enhancing the efficacy of the treatment of primary and remote/metastatic tumors. Similarly, Li et al.⁶⁴ implanted manganese zinc sulfide NPs (ZMS) and IR780 dye into a thermo-sensitive amphiphilic polyethylene glycol poly(2-hexoxy-2-oxy-1,3,2-dioxophosphorane) copolymer by ultrasonic encapsulation. The thermally responsive copolymer micelle PPIR780-ZMS was prepared. At the tumor site, non-invasive near-infrared irradiation triggers photothermal conversion of IR780 in the tumor, thus releasing ZMS nanoparticles from the polymer micelles, which can further generate a large number of toxic ˙OH via a Fenton-like reaction for CDT, and further activate effective ICD-related DAMPs exposure for immunotherapy.

Despite the various applications of MnO nanomaterials, the fundamental immunogenesity of Mn-based nanomaterials is unclear. To overcome the challenges in nanomedicine, Ding et al.⁶⁵ synthesized manganese oxide nanoparticles as nanospikes (MnO_x NSs) which works as tumor microenvironment-responsive nanoadjuvants and ICD (Fig. 4). The NSs have high loading efficiency of OVA and tumor cell fragment. The combined CDT for ICD and immunotherapy has shown better tumor ablation. Mn²⁺ not only acts as the catalyst for the Fenton reaction-based CDT, but also as the adjuvant to improve the therapeutic efficacy of immunotherapy.

Moreover, a kind of yolk–shell nanohybrid (Fe₃O₄@C/MnO₂-PGEA, FCMP) has been developed (Fig. 5).⁶⁶ This well-designed multilayer structure enables macrophage M1 polarization, dendritic cell maturation, and ICD, reversing the tumor immunosuppressive microenvironment, promoting antigen presentation, and ultimately enhancing the body's immune response. In the nanoparticles, the iron ions released from Fe₃O₄ can catalyze tumor-enriched H₂O₂ to produce ROS for CDT and induce immunogenic death of tumor cells. Fe₃O₄ can polarize immunosuppressive M2 macrophages into immune-promoting M1 macrophages. Mn²⁺ can not only activate dendritic cells, but also promote the invasion of killer T cells into the tumor and the activation of natural killer cells.

In addition, Cu-containing nanoparticles have been used to catalyze Fenton reactions to achieve CDT-induced immunotherapy effects. Chen et al.⁶⁷ used monomolecular albumin as a template to prepare copper(II) carbonate hydroxide nanocrystals within single albumin nanocages (CuCH-NCs) as preenzymes by regulating the crystallization and precipitation of Cu²⁺ and CO₃²⁻ in alkaline solution (Fig. 6).⁶⁷ CuCH-NCs can release Cu²⁺ ions in response to pH, and reduce Cu²⁺ under the action of GSH, and then catalyze intracellular H₂O₂ to form highly cytotoxic ˙OH, showing enzymatic catalytic activity similar to the natural enzyme horse radish peroxidase (HRP), and finally produce chemical kinetics-based tumor inhibition. Meanwhile, CuCH-NCs/disulfiram (DSF) combination can effectively induce ICD in 4T1 tumors and up-regulate the expression of PD-L1 inside tumor cells. The experimental results of the combined treatment of CuCH-NCs/DSF and αPD-L1 antibody showed that chemodynamic therapy, chemotherapy and immunotherapy substantially suppressed the growth of tumors in situ and reduced lung metastatic nodules of breast cancer, indicating good tumor synergistic treatment and anti-metastasis effects.

Moreover, the photothermal effect has also been explored to be incorporated into the combination of CDT and ICD. Li et al.⁶⁸ have artificially designed an ICD nanohybrid amplifier (FeOOH@STA/Cu-LDH) that regulates nucleation and growth with sodium lactate (Fig. 7). It consists of three functional elements that interact with each other: a special Fenton agent as FeOOH nanodots which act as a ROS inducer, a high-efficiency photothermal convertor Cu-containing layered double hydroxide (Cu-LDH) functioned as the ROS generation booster,^69,70 and an integrated Hsp90 inhibitor called STA-9090 as heat shock protein inhibitor. Synergistically, the three-functional nanoparticle showed remarkable 4T1 cancer-ICD multiplication in terms of promoting systemic anti-tumor immunogenicity by stimulating cytotoxic T lymphocytes (CTLs), triggering cell death, and increasing CRT membrane translocation. After the second near-infrared boosting treatment, this high-performance nanohybrid thus totally destroyed the primary tumor and greatly controlled the distant tumor. By presenting a novel treatment method that increases the therapeutic regimen to include invisible or unreachable tumors under fever-like conditions, the nanoparticle-type ICD amplifier in these findings redefines tumor-specific immunotherapy and offers insights into tumor immunotherapy.

Xu et al.⁷¹ reported a copper chelated polydopamine nanosystem (Cu-PDA) with surface pegylation and folic acid targeted modification (Cu-PDA-FA), which can generate a large amount of heat under light and lead to thermal death of tumor cells (Fig. 8). At the same time, the occurrence of a Fenton-like reaction catalyzed by Cu-PDA promotes the production of toxic ˙OH, thus killing tumor cells specifically. Most importantly, synergistic photothermal therapy (PTT)/CDT can effectively induce tumor ICD, which can activate a systemic anti-tumor immune response to prevent tumor regrowth and metastasis.

Although the combination of CDT with ICD has shown excellent results against different types of tumors, but some of the tumors cannot be completely removed only by CDT and ICD. Reasonably, the CDT-induced ICD effect can cause immune responses which can be limited by the immune escape capability of the tumor cells, especially the metastatic tumor cells. More efficient combination approaches have been further explored.

3. Combination of CDT and immune checkpoint therapy

Immune checkpoints, as the regulator of the immune system, are essential for preserving autoimmune tolerance and controlling the scope and duration of immune reactions in peripheral tissues.^72–74 However, “tumors can hijack” these pathways and are continuously activated by inhibiting the antitumor immunity to promote tumor occurrence. There are usually two kinds of widely studied checkpoint molecules that are related to immune regulation, the stimulant checkpoint molecules and the inhibitory checkpoint molecules.^73,75,76 Inhibitory checkpoint molecules are targets for cancer immunotherapy and have the potential to be used in several types of cancers, including FDA-approved checkpoint inhibitors block CTLA-4 and programmed cell death protein 1 (PD-1). CDT has been demonstrated to reverse the tumor immunosuppressive microenvironment by inducing tumor immunogenic death, thus combining CDT with immune checkpoint inhibitors will be an excellent tumor treatment strategy (Table 1).

In our group, we developed a strategy of the αPDL1/GOx-encapsulated ROS-responsive nanocomplex (P/G@EF-TKNPs) system to combine CDT and immune checkpoint inhibitors to treat tumor growth (Fig. 9).⁷⁷ CDT is achieved in part by the Fenton reaction, specifically, in this protocol, H₂O₂ produced by GOx interacts with Fe³⁺ to generate hydroxyl radicals, while the inhibitor of the immune checkpoint uses αPDL1. Oligomerized-epigallocatechin-3-O-gallate (OEGCG) was used as a protein delivery carrier to deliver both GOx and αPDL1 as the core, and a ROS responsive diblock compound poly(oligo-(ethylene glycol)-methacrylate) and the block with thio-ketal bond-linked dopamine moieties (POEGMA-b-PTKDOPA) were used as a shell to wrap the core. The core and shell formed nanocomplexes by chelating polyphenol groups with Fe³⁺. After reaching the tumor site through an enhanced permeation and retention (EPR) effect, GOx oxidizes glucose at the tumor site and reacts with Fe³⁺ to produce hydroxyl free radicals. On the one hand, GOX can induce ICD; on the other hand, it can also promote the release of αPDL1 by breaking the ROS responsive shell, thus reducing damage to healthy and normal tissues.

For multifaceted imaging-guided CDT/PDT-improved immunotherapy, a cascade-amplified nanoimmunomodulator (CMZM) with multi-enzyme-like activities has been developed (Fig. 10).⁷⁸ It incorporates superoxide dismutase (SOD), CAT, peroxidase (POD), and glutathione oxidase (GSHOx), which dissociates in the low pH and GSH-rich tumor microenvironment.⁷⁹ In addition to generating ROS (˙OH and ¹O₂) and depleting GSH to reveal necrotic cell fragments and overcome the immunosuppressive microenvironment by eliciting the development of dendritic cells and penetration of CTLs in tumors, robust multi-enzyme-like activities can also produce O₂ to enhance hypoxia and develop the polarization of M2 to M1 macrophages. Thus, in combination with the αPD-L1 blocking antibody, hampering effects on both primary and distant cancers are attained. By modifying immunosuppressive microenvironment. This cascade multi-enzyme-based nanoplatform offers a clever approach for extremely effective ICB immunotherapy against “cold” cancers.

In another study, Zhang et al.⁸⁰ declared the use of inhibitory checkpoints with CDT for breast cancer inhibition. They demonstrated that a liposomal nano-formulation simultaneously co-delivers the hypoxia inducible factor 1 (HIF-1) inhibitor acriflavine (ACF) and the Fenton catalyst copper oleate for the inhibition of breast cancer (Fig. 11). It has been presented through in vitro and in vivo tests that ACF reinforces copper-oleate initiated CDT by inhibiting the HIF-1-GSH pathway, hence increasing ICD for improved immunotherapeutic results. Meanwhile, ACF also worked as an immunoadjuvant to drastically lower the lactate and adenosine levels as well as to downregulate the expression of PD-L1, which in turn promoted the antitumor immune response without the need for CDT. As a result, the “one stone” ACF was completely utilized to improve immunotherapy and CDT (two birds), both of which improved the therapeutic result.

TNBC corresponds to formidability challenges owing to the lack of human epidermal growth factor receptor-2 (HER-2), progesterone receptors (PR) and estrogen receptors (ER) and renders it unresponsive to conventional and hormonal therapies. To overcome the challenges, Chen and colleagues prepared one type of mesoporous polydopamine (mPDA) nanoreactors (NRs), mPDA@CuO₂ NRs, which are composed of mPDA and CuO₂ (Fig. 12).⁸¹ The mPDA@CuO₂ NRs is capable of self-supplying H₂O₂ for CDT and enhanced immunotherapy. mPDA@CuO₂ NRs were modified with immune checkpoint antagonists nanoreactors (dAbPD-L1/CD24) resulting in the synthesis of dual antibody-aided mesoporous (dAbPD-L1/CD24-mPDA@CuO₂) NRs. The combined chemodynamic and immune checkpoint blockade effect of dAbPD-L1/CD24-mPDA@CuO₂ NRs efficiently target and block the PD-L1 and CD24 proteins found on breast cancer cells, dAbPD-L1/CD24-mPDA@CuO₂ NRs exhibit tumor-targeted CDT by activation of the Fenton reaction, which activates macrophages and T cells. The potential for checkpoint blockade immunotherapy considerably boost antitumor efficacy, presenting a viable therapeutic method for the treatment of breast cancer, especially TNBC.⁸²

By using post synthetic metalation, Ni et al.⁸³ produced Hf-DBP-Fe (DBP, 5,15-di(p-benzoato) porphyrin) and nMOF to implant biomimetic porphyrin-FeCl centers, which functioned as a structural imitation of the CAT active site. They showed that porphyrin-FeCl decomposition raised the levels of H₂O₂ in hypoxic tumors to produce both O₂ and ˙OH, which not only causes direct damage to tumors but also relieves tumor hypoxia. The generated O₂ attenuated hypoxia to enable radiation therapy upon X-ray irradiation while ˙OH damage the tumor cells via CDT which results in significantly better local tumor therapy with ionizing radiation. Importantly, in combination with αPD-L1, an immune checkpoint inhibitor, Hf-DBP-Fe-mediated RT-RDT and CDT not only eliminate primary tumors but also reject distant tumors by immunotherapy on a hypoxic bilateral MC38 colorectal tumor model of immunocompetent C57BL/6 mice.

Interestingly, in another study, Liu et al.⁸⁴ developed a multifunctional therapeutic covalent organic framework (COF) by using TAPB-2,5-dimethoxyterephthaldehyde (DMTP)-COF that exhibits immunotherapy, CDT, PDT, and synergistic PTT for both the main tumor and tumor metastases. Under 650 nm laser irradiation, the produced materials exhibit the photodynamic effect. The Fe³⁺/Fe²⁺ redox pair may also catalyze excess H₂O₂ in the acidic tumor microenvironment through Fenton reactions. For PTT, poly(p-phenylenediamine) might be utilized. Interestingly, after PDT, PTT and CDT were used in synergy, a higher temperature may also increase the effects of CDT. The generated tumor fragments may trigger an antitumor immune response, and the presence of αPD-L1 can effectively suppress primary tumor and tumor metastasis.

Biologically influenced by the composition and role of metalloproteins, endogenous enzymes as protein scaffolds integrating artificial metal nanozymes as novel cofactors could provide significant potential for creating a new category of highly effective catalysts for addressing real world biological challenges. In this connection, Sun et al.⁸⁵ designed FeS@GOx, a hybrid nanozyme to accomplish an elevated ROS cascade for augmenting tumor CDT immunotherapy. As FeS@GOx is internalized within breast cancer cells, GOx can catalyze the conversion of excessive glucose to H₂O₂ and gluconic acid, which decreases the pH and results in the elevation of H₂O₂ in the TME. Consequently GOx-arbitrated biocatalysis significantly enhanced the POD like activation of the synthesized FeS nanozymes, which speeds up the sequential production of ˙OH. Interestingly, the reduced intracellular pH might stimulate the breakdown of FeS nanozymes, leading to the liberation of H₂S, which inhibits the activity of CAT and thioredoxin reductase (TrxR), resulting in reduced ROS eradication. The elevated ROS aggregation could enhance ICD in combination with immune checkpoint blockade and additionally trigger the comprehensive anti-tumor immune response. Overall, the bioinspired hybrid nanozyme substantially promotes a feasible H₂S amplified ROS cascade, a technique for multi-enzyme-mediated TME modulation to obtain precise and effective CDT immunotherapy.

Wang and colleagues additionally created a ferrocene (Fc)-based MOF vitamin k3 (Vk3)-loaded cascade catalytic nanoplatform (Vk3@Co-Fc) (Fig. 13).⁸⁶ The advantage of this nanoplatform is its degradability in the tumor microenvironment. Nicotinamide adenine dinucleotide hydrogen phosphate (NAD(P)H) quinone oxidoreductase-1 (NQO1), which is prominently detected in cancer cells, processed Vk3 after it was released. This resulted in a significant amount of H₂O₂, which then reacted with Fe^2+/3+via the Fenton reaction to enable in situ generation of cytotoxic ˙OH. Tumor ICD is the result of this process, which also stimulates DC maturation and, in turn, boosts T cell infiltration into the tumor site. The nano-platform was adequate for improving tumor-associated immune responses in breast cancer, as demonstrated by raising the frequencies of CD45+ leukocytes and CD8+ cytotoxic T lymphocytes. This prevented tumor metastasis to the lungs and improved murine survival results when combined with PD-1 checkpoint blockade approaches. The Vk3@Co-Fc cascading catalytic nanoplatform offers effective cancer immunotherapy for the prevention and decline of breast cancer metastases.

In addition to the combination with αPD-L1, the combination of CDT with the CTLA4 checkpoint blockade was also widely explored. For example, Chang et al.⁸⁷ has manufactured a multi-functional cascade bioreactor on the basis of a void mesoporous Cu₂MoS₄ (CMS) infused with GOx (Fig. 14). It is used to achieve the synergistic effect of CDT/starvation therapy/PT/immunotherapy for tumors. CMS containing polyvalent metals (Cu^+/2+, Mo^4+/6+) shows Fenton-like reaction as well as GSH POD-like and CAT-like activity. When CMS is taken up by the tumor cells, it can generate ˙OH through the Fenton reaction and exhaust the elevated GSH inside tumor cells. Additionally, in the hypoxic microenvironment, the CAT-like component can react with endogenous H₂O₂ to produce O₂, which then activates the catalytic oxidation of glucose by GOx for starvation therapy, this coexistence with the regeneration of H₂O₂ can be used to achieve GO_X-enhanced CDT. At the same time, CMS can also kill tumor cells through its exceptional photothermal conversion ability and superoxide anion (˙O₂) producing properties. After combination with anti-CTLA-4, pegylated CMS@GOx can effectively ablate the primary tumor, hinder tumor metastasis, and produce a strong immune response.

Moreover, Gong et al.⁸⁸ prepared FeWO_X nanosheets as cascade bioreactors to regulate the microenvironment and further enhance tumor radiotherapy and immunotherapy to improve the modulation of the tumor microenvironment and to enhance multimodal cancer therapeutic strategies. FeWO_X-PEG containing polyvalent metallic elements (Fe³⁺, W⁶⁺) show high catalytic efficiency to generate ˙OH for CDT via the Fenton reaction. GSH reduces Fe³⁺ and W⁶⁺ to Fe²⁺ and W⁵⁺, respectively, and enhances oxidative stress in the tumor. Upon interaction with X-ray-based radiotherapy and combination with CTLA-4 checkpoint blockade, ROS induced by FeWO_X-PEG trigger the immune system and boost tumor invasion of multiple types of immune cells. It can stimulate dendritic cell maturation, increase T cells, reduce regulatory T (T_reg) cells, and change tumor associated macrophages polarization and other powerful immune responses, effectively defeating tumors and prolonging the survival time.

Further studies revealed the synthesis of multifunctional nanoplatforms to maximize the synergistic effect on tumor suppression. For example, Yao et al.⁸⁹ prepared multifunctional nanomaterials by loading the ferroptosis agent FePt NPs into polyethylenimine (PEI)-modified black phosphorus nanosheets (BPNs), the FePt/black phosphorus-folic acid (FA) based nano-clusters (FePt/BP-PEI-FA NCs) that exhibit outstanding photothermal and photodynamic effects (Fig. 15). The FePt-based Fenton reaction has the potential to convert endogenous H₂O₂ into ˙OH in an acidic tumor microenvironment, which in turn can initiate ferroptosis. The combined effects of PTT, PDT, and CDT notably inhibited the growth of the primary tumor. Furthermore, the combination with CTLA-4 checkpoint blockade FePt/BP-PEI-FA NCs can improve immunotherapy and inhibit the growth of residual and metastatic tumors.

The combination of CDT and immune checkpoint inhibitors showed impressive success due to the following advantages. CDT can reverse the tumor immunosuppressive microenvironment via the production of cytotoxic ˙OH and induce the apoptosis of cancer cells. Conversely, the immune checkpoint inhibitors can further activate the tumor cells to avoid immune escape. Thus, the primary tumors usually with a relatively bulky size can be ablated and the metastatic tumor cells or tumors can be treated by the activated immune system.

4. Combination of CDT and STING activation

An essential part of human immunity, interferon stimulating factor (STING) is a protein located in the endoplasmic reticulum consisting of 379 primary amino acids. This protein is expressed in a range of endothelial cells, immunological cells, and hematopoietic stem cells and functions as an activation and triggering agent of immune responses.⁹⁰ The generation of anti-tumor innate immunity, primarily through activation of the cGAS-STING signaling pathway targeting STING, has emerged as a significant therapeutic strategy.^91–93 Normal conditions will prevent STING from being triggered while pathogens that break DNA or infiltrate cells cause the STING pathway to become activated and produce immunity in the body. The emergence of several extremely potent STING agonists and the well-defined activation route of the STING protein has led to numerous scientific achievements in STING-activated tumor immunotherapy.^94–96 CDT in conjunction with STING immunotherapy has been gaining attention over the past few years (Table 1).⁹²

In order to accomplish chemodynamically driven immunoenhancement therapy for STING, our research group initially designed a pH-responsive nanoreactor D/G@PFc co-loaded with non-nucleoside small molecule STING agonist and GOx (Fig. 16).⁹⁷ By reacting with ferrocene groups in the vesicle, the Fenton reaction produces more hydroxyl radicals (˙OH). ˙OH is a very poisonous material that can efficiently kill cancer cells in order to carry out CDT. In addition to inducing cell death, CDT can reverse the immune-inhibiting tumor microenvironment and liberate DNA fragments and tumor-associated antigens. Simultaneously, the pH-responsive release of symmetry-linked amidobenzimidazole (DiABZI) triggers the STING pathway and generates the antitumor immune response. Therefore, through chemodynamic immunotherapy, DiABZI and CDT work in combination to improve anti-tumor immunity. The treatment was successful in stopping the growth of the distant tumor that had developed after the tumor was entirely reduced.

A synergistic approach of a nanozyme was combined with an agonist of the cGAS-STING pathway by preparing carbon dots doped with CoN that exhibited peroxidase-like activity.⁹⁸ This carbon dot material could catalyze H₂O₂, incite the production of ROS in the tumor tissues, and induce intracellular DNA damage. The damaged DNA may cause cGAS to produce 2′3′-cyclic guanosine-monophosphate-adenosine-monophosphate (cGAMP) for STING activation. In addition, cGAMP can boost associated cytokine secretion and augment autoimmune function simultaneously, strengthening the antitumor action. As the first report on combinatorial nanozymes and cGAS-STING pathway activation, this system can be used for immunomodulation of the tumor microenvironment to enhance cancer immunotherapy. Regulation of the STING pathway using the cGAS-STING agonist can promote antitumor inhibition for cancer therapy, but the quick clearance of plasma, inadequate cytosolic transportation of STING agonists and limited membrane permeability greatly compromise their therapeutic efficacy.

Gao et al.⁹⁹ report the use of a MnO₂ entrapping dendrimer nanocarrier to co-deliver GOx and cGAMP, a STING agonist for improved tumor CDT/starvation/immune therapy. Methoxy polyethylene glycol (mPEG) and phenylboronic acid (PBA)-modified generation 5 (G5) poly(amidoamine) dendrimers were entrapped with MnO₂ NPs generating MnO₂@G5-mPEG-PBA (MGPP) NPs, having a core diameter of 2.8 nm with high GSH reduction, and Mn²⁺ release catalyzing a Fenton-like reaction under TME conditions and T1-weighted MR imaging. MGPP-facilitated GOx delivery aids the enhancement CDT/starvation therapy of tumor cells in vitro, and co-delivery of cGAMP can efficiently initiate ICD for dendritic cell maturation. In a colorectal tumor model, the dendrimer delivery nanosystem exhibits a robust and highly effective antitumor execution exhibiting a robust abscopal effect, greatly enhancing the comprehensive mouse survival rate. Significantly, the dendrimer-mediated coadministration not only enables the coordination of Mn²⁺ with GOx and cGAMP for respective CDT/starvation-activated ICD and enhanced STING activation that amplify the systemic antitumor immune responses, but also facilitate T1-weighted tumor MR imaging, potentially acting as a viable nanoplatform for augmented antitumor therapy.

In addition to cGAS-STING agonist activation, a series of other methods have been reported for the activation of the STING agonist, like nanoparticles, metal ions, and some external stimuli activation. Some studies reported STING activation by metal ions for example Mn²⁺, Zn²⁺ and Fe²⁺. He et al.¹⁰⁰ also synthesized a dual-responsive Mn-based zinc protoporphyrin nanoplatform coated with polydopamine and embedded with NH₄HCO₃ (MPCZ NPs) for cancer innate immunotherapy. They accumulate in tumor sites through the ERP effect, and then undergo photothermal degradation under high-level GSH in tumor cells. The release of Mn²⁺ can activate the STING pathway, CDT, and photothermal therapy in tumor cells. The collapse of hMnO₂ promotes ZPP release, and hemeoxygenase (HO-1) inhibits antioxidant activity. The exogenous laser irradiation and high-level GSH can turn on MPCZ NPs, generating ROS and Mn²⁺ in tumor cells, and efficiently activating the cGAS-STING signaling pathway and enhancing innate immunotherapy.

Zhan et al.¹⁰¹ activated the intracellular STING agonist by degrading the extracellular matrix (ECM) for tumor therapy. They synthesized an extracellular matrix-degrading nanoagonist (dNAc) with NIR-II and has the ability to activate the intracellular STING pathway which can be used for mild photothermal enhancement chemodynamic immunotherapy for breast cancer. dNAc consists of a heat-responsive liposome loaded with ferrous sulfide (FeS₂) nanoparticles as an IR-II photothermal converter and Fenton catalyst. cGAMP as the STING agonist and ECM-degrading enzyme such as bromelain were covered on the surface of the liposome. The heat generated by dNAc under the irradiation of near IR-II light can improve the ability of the Fenton reaction to kill tumor cells via ICD. The thermo-responsive liposome can achieve controlled release of the STING agonist under light. The combination of photothermal activation of the STING pathway with ICD can promote antitumor immune response and improve tumor invasion ability of T cells. Thus, both primary and distant tumors were suppressed and liver and lung metastases can be effectively suppressed after dNAc treatment in a mouse model activated by NIR-II light.

Mn²⁺ was used as the combination therapy of CDT and STING immunotherapy by Chen et al.¹⁰² who formulated a nanocomposites (MnCpGPNCs) based on Mn²⁺/cytosine-phosphate-guanine oligonucleotides (CpG oligonucleotides), in which Mn²⁺ ions released under weak acid conditions produce ˙OH through a Fenton-like reaction, triggering cell apoptosis while the CpG oligonucleotides induce immunotherapy. At the same time, Mn²⁺ induced CDT can jointly trigger the activation of the STING pathway. The subsequent development of DC and the release of pro-inflammatory cytokines produced a powerful anti-tumor immunity. In CT26 tumor mouse models, cytosine-phosphate-guanine oligonucleotides (CpG ODNs) (MnCpGPNCs) can effectively inhibit primary/distant tumor development and inhibit tumorigenesis.

Moreover, Sun et al.¹⁰³ designed and synthesized immunomodulatory manganese oxide based nanoparticles (MnO@mSiO₂-iRGD NPs), demonstrating their potential application in magnetic resonance image-mediated tumor immunotherapy and CDT (Fig. 17). The therapeutic mechanism of the synthesized nanomaterials involves the release of Mn²⁺ from MnO@mSiO₂-iRGD NPs in tumor tissues, and Mn²⁺ serves as cGAS-STING agonists to boost the interferon secretion, followed by the stimulation of effector T cells for tumor immunotherapy. At the same time, Mn²⁺ can catalyze endogenous conversion of H₂O₂ into ˙OH for CDT. Additionally, MnO NPs have been described for their capability to serve as brain MRI T1 contrast agents.

Pang et al.¹⁰⁴ designed a nanoplatform with Mn²⁺ and a tannic acid phenolic network platform (TMPD) for the co-delivery of Mn²⁺ and DOX via a metal–phenol network. In the nanoparticle, Mn²⁺ can produce ˙OH to kill cancer cells through a Fenton-like reaction and induce an ICD effect of tumor cells together with DOX-mediated chemotherapy, thus causing adaptive immune response. In addition, Mn²⁺ can amplify cGAS-STING pathway activation and induce a powerful innate immune response. The proportion of CD3⁺ and CD8⁺ T cells and CD80⁺ and CD86⁺ DC in the tumor and lymph nodes were significantly increased, and the proportion of T_reg cells and the myeloid-derived suppressor cells (MDSCs) were inhibited. TMPD has a significant immune response. After systemic injection therapy, TMPD obviously has a good tumor inhibition effect. In another example, He et al.¹⁰⁵ constructed a nano-synergistic combination by conjugating manganese dioxide (MnO₂) with adenosine deaminase (ADA) and dihydroporphyria e6 (Ce6). Under ultrasound, NP-MCA can simultaneously mediate CDT and SDT to produce abundant ROS in deep tumors. In addition, ROS and Mn²⁺ produced by NP-MCA can trigger ICD and up-regulate STING in tumor cells, thus activating the immune response against tumors.¹⁰⁵

Interestingly, MRI contrast agents with the capability to release metal ions have been explored as a STING stimuli-responsive contrast agent (CA) for MRI-guided tumor immunoferroptosis combined therapy, which resolved the issues with ferroptosis therapy and immunotherapy (Fig. 18).¹⁰⁶ Fe₃O₄/Gd₂O₃ hybrid nanoparticles (FeGd-HN) are generally used for covering tannic acid (TA) and complexing of Fe²⁺ and SN38, generating FeGd-HN@TA-Fe²⁺-SN38. FeGd-HN is a superior T1-weighted MRI, CA possessing elevated longitudinal relaxivity r1, small particle size (∼5.5 nm), having excellent water dispersibility and stability. The enhanced permeability and retention (EPR) effect of FeGd-HN@TA-Fe²⁺-SN38 causes it to concentrate at solid tumors following intravenous administration. Under acidic conditions, FeGd-HN@TA-Fe²⁺-SN38 can release TA, Fe²⁺, and SN38. Tumor high contrast MRI can be performed by using the produced FeGd-HN. By means of the Fenton reaction with intracellular H₂O₂, the liberated Fe²⁺ can trigger ferroptosis,¹⁰¹ producing Fe³⁺ and ˙OH. Because of the electron transfer from the ortho-phenolic OH group of TA to Fe³⁺, the liberated TA helps with ferroptosis through the Fenton reaction and contributes to the transfer of Fe³⁺ to Fe²⁺. Strong ROS generation causes lipid peroxides (LPO) buildup, cell membrane rupture, GSH/GPX4 downregulation, and cell ferroptosis. The liberated SN38 can promote IFN-β production, trigger NK and CD8⁺ T cells for immunotherapy, and stimulate the STING pathway through DNA-containing exosomes. The release of exosomes containing DNA is facilitated by the breakdown of the cell membrane, which further activates the STING pathway. Strong IFN-γ secreted in the stimulated STING pathway can promote LPO accumulation for ferroptosis therapy by inhibiting the glutamate-cystine antiporter system (Xc⁻) and activating the GPX4 pathway. Therefore, immunoferroptosis synergistic therapy of tumors can be applied with MRI-CA, FeGd-HN@TA-Fe²⁺-SN38.

From these advances, CDT has shown an obvious synergistic effect on tumor ablation and immune activation after combination with STING agonists, which has tremendous promise to improve the therapeutic efficacy against refractory or metastatic tumors.

5. Conclusion and perspectives

CDT is a treatment strategy that destroys tumor cells through tumoral endogenous H₂O₂ in the tumor microenvironment, which endows CDT with the advantage of high specificity. However, the therapeutic efficacy of CDT is limited due to relatively low H₂O₂. Therefore, a series of studies were performed to improve the therapeutic efficacy by improving the tumor H₂O₂ level using nanomaterials. The CDT effect is hindered by the delivery efficiency of metal catalysts and H₂O₂ improvement. On the other hand, cancer immunotherapy refers to a type of treatment that inhibits tumor growth or metastasis by modulating the patient's own immune response. Immunotherapy has less severe side effects than commonly used chemotherapy or radiotherapy. Although research on cancer immunotherapy has made great progress in many aspects, immunotherapy still faces many challenges in terms of clinical efficacy and biosafety. The off-target effect and tumor immunosuppressive microenvironments limit the therapeutic efficacy and response rates of patients. To combine the advantages of CDT and immunotherapy and overcome their disadvantages, their combination was anticipated to show some significant features to improve the therapeutic efficacy. The development of nanomedicine paved the way for their efficient combination.

In recent years, great progress has been made in the field of nanomedicine for the combination of CDT and immunotherapy. In this review paper, we have summarized the advances in this field. Firstly, CDT can induce ICD and improve immune activation. Secondly, CDT can be combined with immune checkpoint inhibitors to alleviate and reverse the tumor immunosuppressive microenvironment, achieving a highly effective therapeutic effect. In addition, STING immunotherapy, as a simple and efficient immunotherapy, has been explored to combine with CDT.

However, the combination of CDT and immunotherapy still faces some key challenges for further clinical translation. Firstly, although remarkable results have been achieved, the detection of relevant biosafety is not perfect, and especially the long-term side toxicity has never been studied systemically. The utility of metal ions for CDT may induce some severe side toxicity. Thus, the side toxicity and metabolism of metal-containing nanosystems should be studied thoroughly for the possibility of clinical translation. Secondly, more efficient CDT methods are still needed to be explored through improvement of the tumoral H₂O₂ level and high-efficiency catalysis. Thirdly, in recent years, immunotherapy methods developed quickly and various immunotherapy strategies have been invented. The combination of CDT and other immunotherapy strategies is needed to be explored, such as indoleamine 2,3-dioxygenase (IDO) inhibition,^109,110 tumor vaccine,^111,112etc. Finally, future work can focus more on the advantages of nanocarriers as delivery vehicles. Through accurate targeted delivery, precise activation of immunity can ensure both the safety of the treatment and the long-term effectiveness of the combination treatment of CDT and immunotherapy.

Conflicts of interest

The authors declare no competing financial interest.

Acknowledgements

The authors gratefully acknowledge the financial support from the National Natural Science Foundation of China (NNSFC) Project (22275144 and 21875234).

References

1. W. Zhang, S. Hu, J.-J. Yin, W. He, W. Lu, M. Ma, N. Gu and Y. Zhang, J. Am. Chem. Soc., 2016, 138, 5860–5865 CrossRef CAS PubMed .
2. J. He, X. Yang, B. Men and D. Wang, J. Environ. Sci., 2016, 39, 97–109 CrossRef CAS PubMed .
3. M. Gagol, A. Przyjazny and G. Boczkaj, Chem. Eng. J., 2018, 338, 599–627 CrossRef CAS .
4. J. Hu, S. Wang, J. Yu, W. Nie, J. Sun and S. Wang, Environ. Sci. Technol., 2021, 55, 1260–1269 CrossRef CAS PubMed .
5. Z. Tang, Y. Liu, M. He and W. Bu, Angew. Chem., Int. Ed., 2019, 58, 946–956 CrossRef CAS PubMed .
6. D. Wang, H. Wu, C. Wang, L. Gu, H. Chen, D. Jana, L. Feng, J. Liu, X. Wang, P. Xu, Z. Guo, Q. Chen and Y. Zhao, Angew. Chem., Int. Ed., 2021, 60, 3001–3007 CrossRef CAS PubMed .
7. L. Z. Gao, J. Zhuang, L. Nie, J. B. Zhang, Y. Zhang, N. Gu, T. H. Wang, J. Feng, D. L. Yang, S. Perrett and X. Yan, Nat. Nanotechnol., 2007, 2, 577–583 CrossRef CAS PubMed .
8. T. Wu and Y. Dai, Cancer Lett., 2017, 387, 61–68 CrossRef CAS PubMed .
9. Y. Xiao and D. Yu, Pharmacol. Ther., 2021, 221, 107753 CrossRef CAS PubMed .
10. Z. S. Ge and S. Y. Liu, Chem. Soc. Rev., 2013, 42, 7289–7325 RSC .
11. Y. L. Dai, C. Xu, X. L. Sun and X. Y. Chen, Chem. Soc. Rev., 2017, 46, 3830–3852 RSC .
12. F. Gong, N. L. Yang, X. W. Wang, Q. Zhao, Q. Chen, Z. Liu and L. Cheng, Nano Today, 2020, 32, 100851 CrossRef CAS .
13. S. J. Peng, F. F. Xiao, M. W. Chen and H. L. Gao, Adv. Sci., 2022, 9, 2103836 CrossRef CAS PubMed .
14. C. Zhang, W. Bu, D. Ni, S. Zhang, Q. Li, Z. Yao, J. Zhang, H. Yao, Z. Wang and J. Shi, Angew. Chem., Int. Ed., 2016, 55, 2101–2106 CrossRef CAS PubMed .
15. Z. M. Tang, P. R. Zhao, H. Wang, Y. Y. Liu and W. B. Bu, Chem. Rev., 2021, 121, 1981–2019 CrossRef CAS PubMed .
16. S.-L. Li, P. Jiang, F.-L. Jiang and Y. Liu, Adv. Funct. Mater., 2021, 31, 2100243 CrossRef CAS .
17. K. Yang, G. Yu, Z. Yang, L. Yue, X. Zhang, C. Sun, J. Wei, L. Rao, X. Chen and R. Wang, Angew. Chem., Int. Ed., 2021, 60, 17570–17578 CrossRef CAS PubMed .
18. C. Jia, Y. Guo and F.-G. Wu, Small, 2022, 18, 2103868 CrossRef CAS PubMed .
19. P. Manivasagan, A. Joe, H.-W. Han, T. Thambi, M. Selvaraj, K. Chidambaram, J. Kim and E.-S. Jang, Mater. Today Bio, 2022, 13, 100197 CrossRef CAS PubMed .
20. B. Y. Niu, K. X. Liao, Y. X. Zhou, T. Wen, G. L. Quan, X. Pan and C. B. Wu, Biomaterials, 2021, 277, 121110 CrossRef CAS PubMed .
21. P. Yu, X. D. Li, G. H. Cheng, X. Zhang, D. Wu, J. Chang and S. Wang, Chin. Chem. Lett., 2021, 32, 2127–2138 CrossRef CAS .
22. I. Mellman, G. Coukos and G. Dranoff, Nature, 2011, 480, 480–489 CrossRef CAS PubMed .
23. A. Ribas and J. D. Wolchok, Science, 2018, 359, 1350–1355 CrossRef CAS PubMed .
24. C. L. Liu, M. X. Yang, D. Z. Zhang, M. Chen and D. Zhu, Front. Immunol., 2022, 13, 961805 CrossRef CAS PubMed .
25. E. Esin, BioMed. Res. Int., 2017, 2017, 1623679 Search PubMed .
26. G. Wakabayashi, Y. C. Lee, F. Luh, C. N. Kuo, W. C. Chang and Y. Yen, J. Biomed. Sci., 2019, 26, 96 CrossRef CAS PubMed .
27. N. P. Restifo, M. E. Dudley and S. A. Rosenberg, Nat. Rev. Immunol., 2012, 12, 269–281 CrossRef CAS PubMed .
28. A. D. Waldman, J. M. Fritz and M. J. Lenardo, Nat. Rev. Immunol., 2020, 20, 651–668 CrossRef CAS PubMed .
29. M. A. Postow, R. Sidlow and M. D. Hellmann, N. Engl. J. Med., 2018, 378, 158–168 CrossRef CAS PubMed .
30. J. M. Michot, C. Bigenwald, S. Champiat, M. Collins, F. Carbonnel, S. Postel-Vinay, A. Berdelou, A. Varga, R. Bahleda, A. Hollebecque, C. Massard, A. Fuerea, V. Ribrag, A. Gazzah, J. P. Armand, N. Amellal, E. Angevin, N. Noel, C. Boutros, C. Mateus, C. Robert, J. C. Soria, A. Marabelle and O. Lambotte, Eur. J. Cancer, 2016, 54, 139–148 CrossRef CAS PubMed .
31. F. Martins, L. Sofiya, G. P. Sykiotis, F. Lamine, M. Maillard, M. Fraga, K. Shabafrouz, C. Ribi, A. Cairoli, Y. Guex-Crosier, T. Kuntzer, O. Michielin, S. Peters, G. Coukos, F. Spertini, J. A. Thompson and M. Obeid, Nat. Rev. Clin. Oncol., 2019, 16, 563–580 CrossRef CAS PubMed .
32. C. L. He, Z. H. Tang, H. Y. Tian and X. S. Chen, Adv. Drug Delivery Rev., 2016, 98, 64–76 CrossRef CAS PubMed .
33. S. Rawal and M. M. Patel, J. Controlled Release, 2019, 301, 76–109 CrossRef CAS PubMed .
34. R. X. Zhang, H. L. Wong, H. Y. Xue, J. Y. Eoh and X. Y. Wu, J. Controlled Release, 2016, 240, 489–503 CrossRef CAS PubMed .
35. X. W. Wang, X. Y. Zhong, Z. Liu and L. Cheng, Nano Today, 2020, 35, 100946 CrossRef CAS .
36. Y. F. Zhou, S. Y. Fan, L. L. Feng, X. L. Huang and X. Y. Chen, Adv. Mater., 2021, 33, 2104223 CrossRef CAS PubMed .
37. L. Zhang, C. X. Li, S. S. Wan and X. Z. Zhang, Adv. Healthcare Mater., 2022, 11, e2101971 CrossRef PubMed .
38. W. Q. Wang, Y. L. Jin, Z. A. Xu, X. Liu, S. Z. Bajwa, W. S. Khan and H. J. Yu, Wires Nanomed. Nanobiotechnol., 2020, 12, e1614 CrossRef PubMed .
39. Q. Chen, M. C. Chen and Z. Liu, Chem. Soc. Rev., 2019, 48, 5506–5526 RSC .
40. M. C. Rodrigues, J. A. V. Morais, R. Ganassin, G. R. T. Oliveira, F. C. Costa, A. A. C. Morais, A. P. Silveira, V. C. M. Silva, J. P. F. Longo and L. A. Muehlmann, Pharmaceutics, 2022, 14, 1564 CrossRef CAS PubMed .
41. J. Y. Zhou, G. Y. Wang, Y. Z. Chen, H. X. Wang, Y. Q. Hua and Z. D. Cai, J. Cell. Mol. Med., 2019, 23, 4854–4865 CrossRef PubMed .
42. G. Kroemer, L. Galluzzi, O. Kepp and L. Zitvogel, Annu. Rev. Immunol., 2013, 31, 51–72 CrossRef CAS PubMed .
43. D. V. Krysko, A. D. Garg, A. Kaczmarek, O. Krysko, P. Agostinis and P. Vandenabeele, Nat. Rev. Cancer, 2012, 12, 860–875 CrossRef CAS PubMed .
44. J. Gao, W. Q. Wang, Q. Pei, M. S. Lord and H. J. Yu, Acta Pharmacol. Sin., 2020, 41, 986–994 CrossRef CAS PubMed .
45. Q. Chen, C. Y. Li and Q. B. Wang, Small Methods, 2023, 7, 2201457 CrossRef CAS PubMed .
46. Y. Sun, T. Lian, Q. C. Huang, Y. W. Chang, Y. Li, X. Y. Guo, W. R. Kong, Y. F. Yang, K. Zhang, P. Wang and X. B. Wang, J. Controlled Release, 2023, 364, 174–194 CrossRef CAS PubMed .
47. J. Yang, S. Ma, R. Xu, Y. Wei, J. Zhang, T. Zuo, Z. Wang, H. Deng, N. Yang and Q. Shen, J. Controlled Release, 2021, 334, 21–33 CrossRef CAS PubMed .
48. Y. Xu, Y. Guo, C. Zhang, M. Zhan, L. Jia, S. Song, C. Jiang, M. Shen and X. Shi, ACS Nano, 2022, 16, 984–996 CrossRef CAS PubMed .
49. R. Yang, M. Zhan, Z. Ouyang, H. Guo, J. Qu, J. Xia, M. Shen and X. Shi, Mater. Today Bio, 2023, 20, 100670 CrossRef CAS PubMed .
50. D. Cen, Q. Zheng, B. Zheng, R. Zhou, X. Xiao, T. Zhang, Z. Huang, T. Yan, J. Yu, X. Li, R. Deng and X. Cai, Adv. Funct. Mater., 2023, 33, 2211402 CrossRef CAS .
51. H. Lin, Y. Chen and J. Shi, Chem. Soc. Rev., 2018, 47, 1938–1958 RSC .
52. J. Liu, X. X. Ai, H. Cabral, J. L. Liu, Y. Huang and P. Mi, Biomaterials, 2021, 273, 120847 CrossRef CAS PubMed .
53. J. Liu, H. Cabral, B. Song, I. Aoki, Z. Y. Chen, N. Nishiyama, Y. Huang, K. Kataoka and P. Mi, ACS Nano, 2021, 15, 13526–13538 CrossRef CAS PubMed .
54. P. Mi, Theranostics, 2020, 10, 4557–4588 CrossRef CAS PubMed .
55. Y. Zhao, J. N. Du, Z. H. Xu, L. H. Wang, L. Ma and L. L. Sun, Adv. Sci., 2024, 2308229 CrossRef CAS PubMed .
56. X. Liu, M. Sun, F. Pu, J. Ren and X. Qu, J. Am. Chem. Soc., 2023, 145, 26296–26307 CrossRef CAS PubMed .
57. S. Wu, Y. Huang, J. Yan, Y. Li, J. Wang, Y. Y. Yang, P. Yuan and X. Ding, Adv. Funct. Mater., 2021, 31, 2103442 CrossRef CAS .
58. C. Schwechheimer and M. J. Kuehn, Nat. Rev. Microbiol., 2015, 13, 605–619 CrossRef CAS PubMed .
59. L. Parhi, T. Alon-Maimon, A. Sol, D. Nejman, A. Shhadeh, T. Fainsod-Levi, O. Yajuk, B. Isaacson, J. Abed, N. Maalouf, A. Nissan, J. Sandbank, E. Yehuda-Shnaidman, F. Ponath, J. Vogel, O. Mandelboim, Z. Granot, R. Straussman and G. Bachrach, Nat. Commun., 2020, 11, 3259 CrossRef CAS PubMed .
60. S. A. Dingsdag and N. Hunter, J. Antimicrob. Chemother., 2018, 73, 265–279 CrossRef CAS PubMed .
61. Z. Fu, Y. Zhang, X. Chen, N. Wang, R. Ma, X. Luo, X. Pan, Y. Yang and W. Xue, Adv. Funct. Mater., 2023, 33, 2211869 CrossRef CAS .
62. Y. Shao, Z. Wang, Y. Hao, X. Zhang, N. Wang, K. Chen, J. Chang, Q. Feng and Z. Zhang, Adv. Healthcare Mater., 2021, 10, 2002171 CrossRef CAS PubMed .
63. B. Ding, P. Zheng, F. Jiang, Y. Zhao, M. Wang, M. Chang, P. a. Ma and J. Lin, Angew. Chem., Int. Ed., 2020, 59, 16381–16384 CrossRef CAS PubMed .
64. Z. Li, Z. Chu, J. Yang, H. Qian, J. Xu, B. Chen, T. Tian, H. Chen, Y. Xu and F. Wang, ACS Nano, 2022, 16, 15471–15483 CrossRef CAS PubMed .
65. B. Ding, P. Zheng, F. Jiang, Y. Zhao, M. Wang, M. Chang, P. a. Ma and J. Lin, Angew. Chem., Int. Ed., 2020, 59, 16381–16384 CrossRef CAS PubMed .
66. X. Zhao, K. Guo, K. Zhang, S. Duan, M. Chen, N. Zhao and F.-J. Xu, Adv. Mater., 2022, 34, 2108263 CrossRef CAS PubMed .
67. T. Li, Y. Zhang, J. Zhu, F. Zhang, A. a. Xu, T. Zhou, Y. Li, M. Liu, H. Ke, T. Yang, Y. a. Tang, J. Tao, L. Miao, Y. Deng and H. Chen, Adv. Mater., 2023, 35, 2210201 CrossRef CAS PubMed .
68. B. Li, G. Hao, B. Sun, Z. Gu and Z. P. Xu, Adv. Funct. Mater., 2020, 30, 1909745 CrossRef CAS .
69. Z. Cao, L. Zhang, K. Liang, S. Cheong, C. Boyer, J. J. Gooding, Y. Chen and Z. Gu, Adv. Sci., 2018, 5, 1801155 CrossRef PubMed .
70. L. Liu, S. Luo, Y. Qing, N. Yan, Y. Wu, X. Xie and F. Hu, Macromol. Rapid Commun., 2018, 39, 1700836 CrossRef PubMed .
71. N. Xu, A. Hu, X. Pu, J. Wang, X. Liao, Z. Huang and G. Yin, J. Mater. Chem. B, 2022, 10, 3104–3118 RSC .
72. P. Darvin, S. M. Toor, V. S. Nair and E. Elkord, Exp. Mol. Med., 2018, 50, 1–11 CrossRef PubMed .
73. J. A. Marin-Acevedo, B. Dholaria, A. E. Soyano, K. L. Knutson, S. Chumsri and Y. Lou, J. Hematol. Oncol., 2018, 11, 39 CrossRef PubMed .
74. Y. Shiravand, F. Khodadadi, S. M. A. Kashani, S. R. Hosseini-Fard, S. Hosseini, H. Sadeghirad, R. Ladwa, K. O'Byrne and A. Kulasinghe, Curr. Oncol., 2022, 29, 3044–3060 CrossRef PubMed .
75. D. M. Pardoll, Nat. Rev. Cancer, 2012, 12, 252–264 CrossRef CAS PubMed .
76. J. A. Marin-Acevedo, E. O. Kimbrough and Y. Lou, J. Hematol. Oncol., 2021, 14, 45 CrossRef CAS PubMed .
77. X. Li, Q. Zhou, A. A. W. M. M. Japir, D. Dutta, N. Lu and Z. Ge, ACS Nano, 2022, 16, 14982–14999 CrossRef CAS PubMed .
78. R. Wang, M. Qiu, L. Zhang, M. Sui, L. Xiao, Q. Yu, C. Ye, S. Chen and X. Zhou, Adv. Mater., 2023, 35, 2306748 CrossRef CAS PubMed .
79. F. Gong, L. Cheng, N. Yang, O. Betzer, L. Feng, Q. Zhou, Y. Li, R. Chen, R. Popovtzer and Z. Liu, Adv. Mater., 2019, 31, 1900730 CrossRef PubMed .
80. X. Zhang, C. He, X. He, S. Fan, B. Ding, Y. Lu and G. Xiang, J. Controlled Release, 2023, 356, 649–662 CrossRef CAS PubMed .
81. W. Cheng, X. Zeng, H. Chen, Z. Li, W. Zeng, L. Mei and Y. Zhao, ACS Nano, 2019, 13, 8537–8565 CrossRef CAS PubMed .
82. Y.-T. Chen, Y.-X. Luo, S.-H. Chan, W.-Y. Chiu and H.-W. W. Yang, J. Nanobiotechnol., 2023, 21, 385 CrossRef CAS PubMed .
83. K. Ni, G. Lan, Y. Song, Z. Hao and W. Lin, Chem. Sci., 2020, 11, 7641–7653 RSC .
84. T. Li, Y. Wang, S. Li, X. Liu and J. Sun, Adv. Mater., 2020, 32, 2002706 CrossRef PubMed .
85. W. Y. Sun, C. Y. Zhu, J. Song, S. C. Ji, B. P. Jiang, H. Liang and X. C. Shen, Adv. Healthcare Mater., 2023, 12, 2300385 CrossRef CAS PubMed .
86. X. Wang, J. Luo, J. Wang, J. Cao, Y. Hong, Q. Wen, Y. Zeng, Z. Shi, G. Ma, T. Zhang and P. Huang, ACS Appl. Mater. Interfaces, 2023, 15, 6442–6455 CrossRef CAS PubMed .
87. M. Chang, M. Wang, M. Wang, M. Shu, B. Ding, C. Li, M. Pang, S. Cui, Z. Hou and J. Lin, Adv. Mater., 2019, 31, 1905271 CrossRef CAS PubMed .
88. F. Gong, M. Chen, N. Yang, Z. Dong, L. Tian, Y. Hao, M. Zhuo, Z. Liu, Q. Chen and L. Cheng, Adv. Funct. Mater., 2020, 30, 2002753 CrossRef CAS .
89. X. Yao, B. Yang, S. Wang, Z. Dai, D. Zhang, X. Zheng and Q. Liu, J. Mater. Chem. B, 2020, 8, 8010–8021 RSC .
90. Y. Zhu, X. An, X. Zhang, Y. Qiao, T. Zheng and X. Li, Mol. Cancer, 2019, 18, 152 CrossRef PubMed .
91. D. Shae, K. W. Becker, P. Christov, D. S. Yun, A. K. R. Lytton-Jean, S. Sevimli, M. Ascano, M. Kelley, D. B. Johnson, J. M. Balko and J. T. Wilson, Nat. Nanotechnol., 2019, 14, 269–278 CrossRef CAS PubMed .
92. M. Jiang, P. Chen, L. Wang, W. Li, B. Chen, Y. Liu, H. Wang, S. Zhao, L. Ye, Y. He and C. Zhou, J. Hematol. Oncol., 2020, 13, 81 CrossRef CAS PubMed .
93. A. Amouzegar, M. Chelvanambi, J. N. Filderman, W. J. Storkus and J. J. Luke, Cancers, 2021, 13, 2695 CrossRef CAS PubMed .
94. Q. H. Zhou, Y. Zhou, T. Y. Li and Z. S. Ge, Macromol. Biosci., 2021, 21, 2100133 CrossRef CAS PubMed .
95. J. M. Ramanjulu, G. S. Pesiridis, J. S. Yang, N. Concha, R. Singhaus, S. Y. Zhang, J. L. Tran, P. Moore, S. Lehmann, H. C. Eberl, M. Muelbaier, J. L. Schneck, J. Clemens, M. Adam, J. Mehlmann, J. Romano, A. Morales, J. Kang, L. Leister, T. L. Graybill, A. K. Charnley, G. S. Ye, N. Nevins, K. Behnia, A. I. Wolf, V. Kasparcova, K. Nurse, L. P. Wang, Y. Li, M. Klein, C. B. Hopson, J. Guss, M. Bantscheff, G. Bergamini, M. A. Reilly, Y. Q. Lian, K. J. Duffy, J. Adams, K. P. Foley, P. J. Gough, R. W. Marquis, J. Smothers, A. Hoos and J. Bertin, Nature, 2018, 564, 439–443 CrossRef CAS PubMed .
96. B. S. Pan, S. A. Perera, J. A. Piesvaux, J. P. Presland, G. K. Schroeder, J. N. Cumming, B. W. Trotter, M. D. Altman, A. V. Buevich, B. Cash, S. Cemerski, W. Chang, Y. P. Chen, P. J. Dandliker, G. Feng, A. Haidle, T. Henderson, J. Jewell, I. Kariv, I. Knemeyer, J. Kopinja, B. M. Lacey, J. Laskey, C. A. Lesburg, R. Liang, B. J. Long, M. Lu, Y. H. Ma, E. C. Minnihan, G. O'Donnell, R. Otte, L. Price, L. Rakhilina, B. Sauvagnat, S. Sharma, S. Tyagarajan, H. Woo, D. F. Wyss, S. Xu, D. J. Bennett and G. H. Addona, Science, 2020, 369, 935–945 CrossRef PubMed .
97. Q. Zhou, Y. Wang, X. Li, N. Lu and Z. Ge, Adv. Ther., 2021, 4, 2100130 CrossRef CAS .
98. B. M. Johnson, T. Uchimura, M. D. Gallovic, M. Thamilarasan, W.-C. Chou, S. A. Gibson, M. Deng, J. W. Tam, C. J. Batty, J. Williams, G. K. Matsushima, E. M. Bachelder, K. M. Ainslie, S. Markovic-Plese and J. P. Y. Ting, J. Immunol., 2021, 206, 2015–2028 CrossRef CAS PubMed .
99. Y. Gao, Z. Ouyang, S. Shen, H. Yu, B. Jia, H. Wang, M. Shen and X. Shi, ACS Nano, 2023, 17, 23889–23902 CrossRef CAS PubMed .
100. Q. He, R. Zheng, J. Ma, L. Zhao, Y. Shi and J. Qiu, Biomater. Res., 2023, 27, 29 CrossRef CAS PubMed .
101. M. Zhan, X. Yu, W. Zhao, Y. Peng, S. Peng, J. Li and L. Lu, J. Nanobiotechnol., 2022, 20, 23 CrossRef CAS PubMed .
102. J. Chen, J. Lu, Y. Shan, Y. Wang, Z. Xu, J. Xi, L. Fan and L. Gao, Adv. Ther., 2023, 6, 2200175 CrossRef CAS .
103. Z. Sun, Z. Wang, T. Wang, J. Wang, H. Zhang, Z. Li, S. Wang, F. Sheng, J. Yu and Y. Hou, ACS Nano, 2022, 16, 11862–11875 CrossRef CAS PubMed .
104. X. Pang, C. Fu, J. Chen, M. Su, R. Wei, Y. Wang, W. Lin, X. Wei, X. Jiang, X. Yang, H. Yang, J. Wang and R. Yang, Biomater. Sci., 2023, 11, 3840–3850 RSC .
105. M. Zhan, F. Wang, Y. Liu, J. Zhou, W. Zhao, L. Lu, J. Li and X. He, Adv. Sci., 2023, 10, e2207200 CrossRef PubMed .
106. S. Guo, W. Xiong, J. Zhu, J. Feng, R. Zhou, Q. Fan, Q. Zhang, Z. Li, J. Yang, H. Zhou, P. Yi, Y. Feng, S. Yang, X. Qiu, Y. Xu and Z. Shen, Biomaterials, 2023, 302, 122300 CrossRef CAS PubMed .
107. B. Li, J. Tang, W. Chen, G. Hao, N. Kurniawan, Z. Gu and Z. P. Xu, Biomaterials, 2018, 177, 40–51 CrossRef CAS PubMed .
108. Y. Gao, Z. J. Ouyang, S. Y. Shen, H. W. Yu, B. Y. Jia, H. Wang, M. W. Shen and X. Y. Shi, ACS Nano, 2023, 17, 23889–23902 CrossRef CAS PubMed .
109. J. Godin-Ethier, L. A. Hanafi, C. A. Piccirillo and R. Lapointe, Clin. Cancer Res., 2011, 17, 6985–6991 CrossRef CAS PubMed .
110. L. Brochez, I. Chevolet and V. Kruse, Eur. J. Cancer, 2017, 76, 167–182 CrossRef CAS PubMed .
111. H. Wu, X. L. Fu, Y. J. Zhai, S. Gao, X. Y. Yang and G. X. Zhai, Adv. Healthcare Mater., 2021, 10, 2100299 CrossRef CAS PubMed .
112. S. Kreiter, M. Diken, A. Selmi, Ö. Türeci and U. Sahin, Curr. Opin. Immunol., 2011, 23, 399–406 CrossRef CAS PubMed .

This journal is © The Royal Society of Chemistry 2024