Nanozyme-Based Enhanced Cancer Immunotherapy

Abstract

Catalytic nanoparticles with natural enzyme-mimicking properties, known as nanozymes, have emerged as excellent candidate materials for cancer immunotherapy. Owing to their enzymatic activities, artificial nanozymes not only serve as responsive carriers to load drugs and therapeutic molecules for cancer treatment, but also act as enzymes for modulating the immunosuppression of the tumor microenvironment (TME) via the catalytic activities of catalase, peroxidase, superoxide dismutase, and oxidase. The immunosuppressive pro-tumor TME can be reversed to the immunoactive anti-tumor TME by utilizing both reactive oxygen species (ROS)-generating and ROS-scavenging nanozymes, which enhance the efficacy of cancer immunotherapy. In this review, we introduce representative ROS-generating and ROS-scavenging nanozymes and discuss how artificial nanozymes respond to the conditions of the TME. Based on the mutual interaction between nanozymes and TME, recent therapeutic pathways to provoke anti-cancer immune responses using nanozymes are discussed.

Keywords: Cancer immunotherapy; Immunogenic cell death; Nanozymes; Reactive oxygen species; Tumor microenvironment.

Fig. 1

Schematic of cancer immunity cycle with diverse cancer treatment paradigms. The cells involved in each step of the cancer immunity circle face various conditions including inhibition and stimulation. Tumor-associated antigens (TAAs) are released, followed by their uptake and presentation by professional antigen-presenting cells (e.g., dendritic cells (DCs)), boosting DCs maturation. These processes are inhibited by immunosuppressive cytokines (IL-4, IL-10, and IL-13). Mature DCs subsequently migrate to the lymphoid organs and activate naive T cells. The activated T cells are suppressed by physiological conditions in the tumor microenvironment (TME), indoleamine 2,3-dioxygenase (IDO)-expressing cells, myeloid-derived suppressor cells (MDSCs), Treg cells, tumor-associated macrophages (TAM), and immune checkpoint molecules (PD-1, PD-L1). Thus, CAR-T cells are trained and stimulated ex vivo to enhance the antigen-specific antitumor responses after infusion to patients. ICB therapy results in synergistic effects to enhance the tumor infiltration by cytotoxic T lymphocytes (CTLs) and tumor-killing effects

Fig. 2

Routes of mutual catalytic activity enzyme interaction (POD, SOD, OXD, CAT) through representative products such as H₂O₂, OH^., ^.O₂⁻, O₂, H₂O. By mimicking the catalytic activities of enzymes, nanozymes with diverse materials such as SOD- and CAT-mimicking cerium oxide, POD-mimicking iron oxide, or OXD-mimicking electron donors were discovered

Fig. 3

Physiological conditions and cellular interaction network of the protumor- and antitumor-microenvironment. Pro-tumor microenvironment is composed of immunosuppressive cells (MDSCs, Tregs, and M2-type macrophages), immunosuppressive cytokines (IL-10 and TGF-β), immunomodulatory enzymes (IDO-expressing cells). In addition, PD-L1, PD-1 and therapeutic barriers (high tumor hypoxia, acidic condition) can restrict the function of the effector T cells. In contrast, anti-tumor microenvironment is composed of a high number of innate immune cell (NK cells), effector T cells (CD8⁺ and CD4⁺ T cells), and M1-type macrophages for tumor-killing

Fig. 4

Therapeutic pathways of TME-responsive nanozymes for cancer immunotherapy. Red arrows indicate a strategy based on the catalytic activities of ROS-generating nanozymes (OXD- and POD-like activities) which induce high oxidative stress, resulting in the induction of immunogenic cell death (ICD). Death of tumor cells releases TAAs, subsequently be engulfed, and presented to the naïve T cells by DCs, leading to the activation of CD4⁺ and CD8⁺ T cells. Blue arrows indicate a strategy for the control of immune responses by modulating the TME. Treatment with ROS-scavenging nanozymes (SOD- and CAT-like activities) can relieve hypoxia and control ROS levels, leading to the modification of subsequent immunological cascades such as the reprogramming of M2 to M1 macrophages, decrease in hypoxia-adenosine signaling, suppression of Treg cells, and expression of effector T cells. In addition, other therapies are applied to synergistically enhance the adaptive immune responses such as TGF-β inhibitor, anti-PD-L1, anti-PD-1, and anti-CTLA-4 antibodies.

Fig. 5

Hyaluronic acid (HA) and polyethylene glycol-decorated copper-based nanozymes (Cu_2−xS) enhanced CAR-T cell therapy. Copper-based nanozymes with HA modification on the surface are targeted to tumor cells and react with endogenous H₂O₂ which can be transformed to OH^. through POD-like activity. High local ROS levels caused apoptosis, leading to the release of TAAs. CAR-T cells were engineered to recognize tumor-specific antigens; thus, the combination of nanozyme-based therapy and photothermal therapy (PTT) with CAR-T cells enhanced the tumor infiltration of and function of CAR-T cells. Reproduced from [51] with permission from Wiley–VCH. Copyright 2021

Fig. 6

Complex of glucose oxidase (GOx), hemin, and dihydroartemisinic acid (DHA) enveloped in ZIF-8 framework for cancer immunotherapy. Alkylating carbon-centered radical (R^.) and hydroxyl radical (OH^.) were generated by utilizing ROS-generating complexed framework through GOx and Fenton reaction. Elevated ROS levels caused tumor cell death and subsequent release of TAAs which are captured and presented on mature DCs. DCs travel to the lymph node for priming tumor-specific T cells, leading to their infiltration into tumor sites. The combination of the nanozyme platform and anti-PD-L1 therapy increased the efficacy of cancer treatment against primary and distant tumors. Reproduced from [52] with permission from Wiley–VCH. Copyright 2020

Fig. 7

Core–shell gold nanocage@manganese dioxide (AuNC@MnO₂) nanozymes for cancer immunotherapy. Under highly acidic condition in the TME, the complex structure was degraded. AuNC@MnO₂ nanozymes are ROS-scavenging nanozymes that produce elevated O₂ levels. Meanwhile, under near-infrared (NIR) irradiation, O₂ was converted into ^.O₂⁻, increasing ROS levels and leading to the induction of ICD. Subsequently, damage-associated molecular patterns (DAMPs; CRT, ATP, HMGB1) released due to ICD trigger DCs maturation and tumor antigen presentation for activating effector T cells against primary tumor and its metastasis. Reproduced from [53] with permission from Elsevier. Copyright 2018

Fig. 8

Phospholipid-coated Na₂S₂O₈ nanoparticles (PNSO NPs) are nanozymes merged with anti-CTLA-4 antibodies for treating cancer. Sulfate radicals (^.SO₄⁻) and OH^. were generated by activating the persulfate of PNSO NPs, resulting in high ROS levels, tumor cell death, and DAMPs release (ATP, CRT, and HMGB 1). Then, immature DCs capture and present TAAs and became mature DCs. The tumor antigen-exposed mature DCs migrate to the lymph node and prime tumor-specific T cells, leading to the attack of CTLs against cancer. Combination with anti-CTLA-4 antibodies suppresses the Treg activity and upregulates the expression of effector T cells, thus preventing the evasion of primary and distant tumors as well as lung metastasis. Reproduced from [55] with permission from the American Chemical Society (ACS). Copyright 2020

Fig. 9

Co-loading of Ce6 and DOX into hollow manganese dioxide (H-MnO₂) decorated by PEG enhanced antitumor responses when combined with anti-PD-L1 therapy. ROS-scavenging nanozymes based on H-MnO₂ could generate elevated O₂ levels, leading to the relieving tumor hypoxia. O₂ was converted into ^.O₂⁻ under light illumination, which induced the tumors to release TAAs. TAAs were then engulfed and presented to naïve T cells by DCs, resulting in CTL activation and tumor infiltration. The combination of photosensitizer (Ce6) and chemotherapeutic agents (DOX) accelerate the tumor-killing effects by triggering tumor cell death. Anti-PD-L1 antibody was employed to block the immune checkpoint PD-L1 on tumor cells, unleashing the cytotoxic function of the activated CTLs against tumors. Reproduced from [61] with permission from Nature. Copyright 2017

Fig. 10

Combination of oxygen-generating nanoparticles, chemotherapy, and anti-CTLA-4 therapy boosts cancer immunotherapy. O₂ is generated through the catalytic activity of CaO₂-based and MnO₂-based nanozymes, resulting in the relief of tumor hypoxia and suppression of Treg activity. The release of DOX from the nanoparticle core kills tumor cells and the resulting tumor cell death activates the surrounding immature DCs, which primes CTLs against the tumors. In combination with anti-CTLA-4 antibody, the Treg activity is suppressed and CTL response is upregulated. Reproduced from [63] with permission from Springer. Copyright 2019

Fig. 11

Iron-based (ROS-generating) and manganese-based (ROS-scavenging) components are encapsuled into mesoporous silica nanoparticles (MSN) loaded with TGF-β inhibitor. Systemic administration led to the accumulation of nanoparticles in the tumor site through the enhanced permeability and retention (EPR) effect. O₂ generation from the ROS-scavenging nanozymes relieve tumor hypoxia and regulate the TME through macrophage polarization. ROS-generating nanozymes increase local ROS levels through the Fenton-reaction, causing ferroptosis. Subsequently, tumor cell death releases TAAs which are captured, processed, and presented by DCs which activate effector T cells. TGF-β inhibitor was introduced to restrict the activation of Tregs. Reproduced from [62] with permission from Wiley–VCH. Copyright 2020