Calcium peroxide nanoplatform-mediated cancer immunotherapy enhancement: current advances and perspective

Abstract

The efficacy of cancer immunotherapy is severely constrained by the immunosuppressive tumor microenvironment (ITME), with hypoxia, acidosis, and immune cell dysfunction being key factors contributing to treatment resistance. Calcium peroxide (CaO₂) nanomaterials leverage their unique hydrolysis behavior within the acidic tumor microenvironment (TME) to simultaneously release oxygen (O₂), hydrogen peroxide (H₂O₂), and calcium ions (Ca²⁺), while consuming hydrogen ions (H⁺). This process synergistically remodels the TME and enhances antitumor immunity through multiple mechanisms: O₂ alleviates hypoxia, thereby reversing immunosuppression and enhancing the efficacy of O₂-dependent therapies; H₂O₂ catalyzes the production of highly toxic reactive oxygen species (ROS) via Fenton or Fenton-like reactions, directly killing tumor cells; H⁺ consumption counteracts acidosis and improves immune cell function; and excessive Ca²⁺ influx induces calcium (Ca) overload, triggering mitochondrial and endoplasmic reticulum (ER) stress to further amplify apoptosis and immune activation. These effects form a multi-pathway, coordinated immunomodulatory network, offering a novel approach to overcome tumor immune resistance. This review summarizes the strategies and mechanisms of CaO₂ nanoplatforms in cancer immunotherapy, discusses their translational challenges and prospects, and provides insights to advance intelligent nanomedicine for overcoming immunotherapy resistance.

Introduction

Cancer remains one of the major threats to human life. While conventional treatments, including surgery, radiotherapy, and chemotherapy have achieved considerable success against primary cancers, however, failed in the control of metastasis and recurrence (Mellman, Coukos & Dranoff, 2011; Saxena et al., 2025). Over the past decades, immunotherapy has witnessed revolutionary breakthroughs (Song, Musetti & Huang, 2017), particularly, immune checkpoint inhibitors (ICIs) and chimeric antigen receptor T-cell (CAR-T) therapy have demonstrated outstanding and durable clinical efficacy across a spectrum of malignancies (Chen & Mellman, 2017). Cancer immunotherapy is a therapeutic strategy that utilizes and enhances the function of the immune system to identify, attack, and eliminate tumor cells (Eslami & Lu, 2024). However, its efficacy remains limited in immunologically “cold” tumors, posing a significant challenge in clinical application (Binnewies et al., 2018). Such “cold” tumors are characterized by a highly immunosuppressive tumor microenvironment (ITME), which creates multiple physiological barriers to effective immune activity. For instance, severe hypoxia not only inhibits the function of cytotoxic T lymphocytes (CTLs) and drives their exhaustion but also promotes the accumulation of immunosuppressive cells such as T-regulatory cells (Tregs) and M2-type tumor-associated macrophages (TAMs) (Noman et al., 2015). Concurrently, acidosis caused by abnormal glycolysis in tumor cells leading to excessive lactic acid (LA) production, directly impairs the activity and infiltration ability of immune cells (Vaupel & Multhoff, 2021). Furthermore, dense physical barrier and a lack of effective T-cell chemokines collectively result in insufficient immune cells infiltration (Binnewies et al., 2018). These interconnected mechanisms sustain a state of immune exclusion or suppression, hindering the effectiveness of even excellent immunotherapies (Bagchi, Yuan & Engleman, 2021). This underscores that the key to enhancing the efficacy of immunotherapy lies in overcoming the ITME.

Calcium peroxide (CaO₂), as a typical oxygen (O₂)-generating inorganic functional material, has shown prominent promise in cancer therapy (He et al., 2021). Its therapeutic potential stems primarily from its hydrolysis within the tumor microenvironment (TME). Specifically, CaO₂ reacts with H₂O and abundant hydrogen ions (H⁺) in the TME to continuously releases O₂ and hydrogen peroxide (H₂O₂) (Wu et al., 2020). The released O₂ effectively alleviates tumor tissue hypoxia, reverses the immunosuppression, and improves the efficacy of O₂-dependent cancer therapies, such as chemodynamic therapy (CDT) and photodynamic therapy (PDT) (Liu et al., 2017). H₂O₂, as a crucial substrate, catalyzes the generation of highly toxic reactive oxygen species (ROS) via Fenton or Fenton-like reactions, which directly induce tumor cell death and provoke immunogenic cell death (ICD) (Tang et al., 2019; Zhang et al., 2020). In addition, the excessive influx of calcium ions (Ca²⁺), a reaction by-product, induces calcium (Ca) overload within tumor cells, which trigger endoplasmic reticulum (ER) and mitochondrial stress, further exacerbating apoptosis and amplifying the ICD effect (Cheng et al., 2006; Bai et al., 2022). Thus, CaO₂ reshapes the ITME through a synergistic mechanism involving hypoxia alleviation, ROS substrates supply, and Ca overload induction, providing a compelling strategy to potentiate cancer immunotherapy.

Nanomaterials offer new possibilities for drug delivery and immunomodulation owing to their nanoscale size, huge specific surface area, enhanced reactivity, and tunable interfacial properties (Bayda et al., 2019). In recent years, a variety of nanomaterials have been widely employed to construct efficient delivery system for CaO₂ (Peer et al., 2007). Liposomes, benefiting from their excellent biocompatibility and modifiability, can effectively encapsulate and protect CaO₂ from premature degradation (Sercombe et al., 2015). Metal–organic frameworks (MOFs), featuring adjustable pore sizes and extremely high specific surface areas, enable high loading capacities and stimuli-responsive release of CaO₂ in response to TME stimulation (Furukawa et al., 2014). Moreover, mesoporous silica nanoparticles (MSNs), with their ordered pore structure, high loading capacity, and readily functionalized surface, also serve as excellent platforms for the targeted delivery and controlled release of CaO₂ (Li, Zhang & Feng, 2019). These nanocarriers target and aggregate in tumor tissues through enhanced penetration and retention (EPR) effect or via active targeting ligand modifications, subsequently releasing CaO₂ and its reactive products in response to TME-specific stimuli. This targeted approach maximizes therapeutic efficacy while minimizing systemic toxicity (Peer et al., 2007), thereby establishing a solid foundation for the efficient and safe application of CaO₂ in cancer immunotherapy. In this article, we comprehensively review recent advances in CaO₂ nanoparticle-mediated cancer immunotherapy, analyze and elucidate the underlying therapeutic mechanisms (Fig. 1), and provide insights into the current clinical translation challenges along with future prospects for this nanoplatform.

Figure 1. Schematic diagram of the underlying mechanism of CaO₂ nanoparticle-mediated cancer immunotherapy.

Nanoparticles such as liposomes, mesoporous silica nanoparticles, and metal–organic frameworks deliver CaO₂ to the tumor site. Within the acidic tumor microenvironment, CaO₂ hydrolyzes to release O₂, H₂O₂, and Ca²⁺, while consuming H⁺. Specifically, the released O₂ alleviates hypoxia, the generated H₂O₂ catalyzes the production of highly toxic ROS, the consumption of H⁺ counteracts acidosis, and the influx of Ca²⁺ induces calcium overload. These effects synergistically remodel the immunosuppressive tumor microenvironment.

Survey Methodology

Given that this review aims to synthesize the recent advancements and mechanistic insights into CaO₂ nanoplatforms for cancer immunotherapy, a systematic and iterative literature search strategy was employed. The primary objective was to capture a comprehensive collection of studies detailing the design, mechanisms, and antitumor immune responses of CaO₂-based nanotherapeutics.

The literature search was conducted across several major academic databases, including PubMed, Web of Science, Scopus, and the Chinese National Knowledge Infrastructure (CNKI). The search focused on articles published between 2018 and 2024 to ensure the inclusion of the most recent and relevant research, while seminal earlier publications were also considered. The initial search strategy utilized a core set of keywords and their combinations: “nanoparticle”, “CaO₂ nanoplatform”, “tumor immunotherapy”, “ICD”, “metal immunotherapy”, “ferroptosis”, and “cuproptosis”. As the research progressed and the scope of the literature became clearer, the search strategy was refined and expanded using additional specific keywords to capture the diversity of mechanisms and nanomaterial types. These included: “Ca overload”, “ROS”, “STING agonist”, “TME reprogramming”, “hypoxia alleviation”, “CDT”, “liposomes”, “MOFs”, and “MSNs”.

The initial search yielded over 3,000 publications, and were first filtered to retain studies within the fields of “pharmacology and pharmacy”, “oncology”, “immunology”, and “materials science”. The remaining studies were screened by their titles and abstracts against the following inclusion criteria: (1) Original research articles or reviews explicitly focusing on the synthesis and application of CaO₂-containing nanoparticles. (2) Studies where the core therapeutic mechanism involved CaO₂ hydrolysis (e.g., O₂/H₂O₂ production, Ca overload) for cancer treatment. (3) Research that investigated the subsequent immune responses, such as the induction of ICD, activation of dendritic cells (DCs)/T cells, or polarization of TAMs. Following the removal of duplicates and irrelevant articles, 22 key publications were selected as the primary literature for this in-depth review. To ensure comprehensiveness, the reference lists of these selected articles were also traced to identify any additional pertinent documents that may have been missed in the database search.

CaO₂ Produce O₂ to Enhance Immunotherapy

The aberrantly rapid proliferation of tumor tissues leads to a persistent hypoxic microenvironment, which not only promotes malignant progression but also severely suppresses the function of effector immune cells and facilitates the infiltration of immunosuppressive cells (DePeaux & Delgoffe, 2021). As an endogenous O₂ generator, the accumulation of CaO₂ at tumor sites directly alleviates hypoxia and reverses immunosuppression (Chen et al., 2019; Ruan et al., 2023). This section will focus on strategies that utilize CaO₂-mediated O₂ generation to ameliorate the TME, enhance therapeutic efficacy, and promote immune cell function.

Potentiating PDT through O₂ self-supply

The efficacy of numerous effective tumor ablation modalities such as PDT is strictly dependent on local O₂ concentration (Sun et al., 2025). The hydrolysis of CaO₂ enables continuous endogenous O₂ supply for these therapies, thereby elevating the O₂ partial pressure at the tumor site, significantly strengthening the cytotoxic efficacy of therapies like PDT, and further potentiating the ICD (Garg et al., 2017). For instance, Wei et al. (2025) designed a microneedle patch that utilizes a core CaO₂ nanoreactor to generate O₂ intratumorally, which significantly alleviated hypoxia, enhanced the PDT effect of the encapsulated photosensitizer, and intensified ICD through exacerbated ROS storm and mitochondrial damage. In combination with immunomodulatory molecules, this approach induces a down-regulation of M2-type TAMs infiltration, and nearly completely suppressed tumor growth in a melanoma model. However, such microneedle patches represent a local administration strategy, which may have limited applicability for deep-seated or metastasized tumors. Furthermore, the rate of O₂ generation and its diffusion distance require optimization in more complex models. Similarly, a multilayer core–shell nanoplatform employed an outer CaO₂ layer to ameliorates hypoxia and enhance the PDT of an internal photosensitizer. In a subcutaneous hepatocellular carcinoma xenograft mouse model, this combined therapeutic strategy achieved a tumor inhibition rate as high as 89.45%, with complete tumor ablation observed within 13 days post-treatment and no recurrence (An et al., 2024a; An et al., 2024b).

For tumors with deep physical or biochemical barriers, such as the mucus layer in colorectal cancer (CRC), passive O₂ diffusion may be insufficient. Innovatively, Wu et al. (2023) combined the O₂-generating capability of CaO₂ with the active motility of nanoparticles. Briefly, under near-infrared (NIR-II) radiation, the O₂ produced by CaO₂ acted synergistically with the photothermal effect to drive the CaO₂-loaded MSNs to penetrate the dense mucus barrier and accumulate effectively in the deep tumor tissue. This platform not only alleviated hypoxia but also significantly increased the proportions of CD4⁺ and CD8⁺ T cells in the spleen (by 1.9-fold and 2.4-fold respectively) and remodeled the gut microbiota. When combined with the immune checkpoint inhibitor αPD-L1, it demonstrated potent efficacy in eradicating primary tumors and inhibiting metastasis in an orthotopic CRC model (Wu et al., 2023). This O₂-driven penetration mode overcomes the limitation of passive diffusion inherent to traditional nanomedicines, providing a novel insight for the therapy of tumors with deep barriers. Nevertheless, this approach relies on external NIR-II laser irradiation, whose tissue penetration depth is finite and may not be suitable for tumors located too deeply.

Improving immune cell infiltration and function

Hypoxia within the TME directly impairs the cytotoxic function of CD8⁺ T cells, promotes their exhaustion by pathways such as hypoxia-inducible factor-1α (HIF-1α) activation, and recruits immunosuppressive cells like Tregs (Watson et al., 2021). Alleviating tumor hypoxia via CaO₂ can directly create a more favorable microenvironment for immune cells (Smith et al., 2023). For example, as self-triggered thermoelectric nanoheterojunction (BST/CaO₂) hydrolyzes in the TME to generate O₂ and heat, thereby driving the generation of ROS. Concurrently, the released Ca²⁺ was shown to promote DC maturation and tumor antigen presentation. In a CRC xenograft mouse model, this treatment increased the proportion of mature DCs by 4.1-fold compared to the control and significantly elevated serum levels of inflammatory cytokines interferon-γ (IFN-γ) and tumor necrosis factor-α (TNF-α), indicating systemic activation of anti-tumor immunity (Yuan et al., 2023). This study highlights the potential of CaO₂-induced O₂ generation to indirectly enhance antigen presentation and activate adaptive antitumor immunity. It is important to note that most current evidence originates from murine models, whether human immune cells respond identically to CaO₂-mediated microenvironmental alterations awaits validation in clinical studies.

CaO₂ Produce H₂O₂ to Enhance Immunotherapy

H₂O₂ serves as an essential reactive substrate for catalytic therapeutic strategies, especially CDT. However, the efficacy of these therapies is often constrained by the insufficient endogenous levels of H₂O₂ within tumors, limiting the initiation of a robust therapeutic response (Tang et al., 2019). Ingeniously, this critical challenge of substrate deficiency is effectively addressed by CaO₂, which undergoes hydrolysis in the acidic TME to provide a sustained, localized release of H₂O₂ (Shi et al., 2023). In this section, the therapeutic strategies that utilize CaO₂-mediated H₂O₂ generation as an energy source for catalytic reactions is focused. It details the role of CaO₂ as an in-situ H₂O₂ reservoir and how it drives a cascade of catalytic processes. The resultant generation of highly ROS induces intense oxidative stress, which not only directly damages tumor cells but also serves as a key danger signal to provoke and potentiate antitumor immune response (Zhang et al., 2019).

Amplifying CDT and ferroptosis

CDT operates on the principle of converting H₂O₂ into highly toxic hydroxyl radicals (⋅OH) via Fenton or Fenton-like reactions. The self-supplying H₂O₂ characteristic of CaO₂ significantly augments this process, making it one of the most widely adopted strategies to boost CDT efficacy (Meng et al., 2020; Liu et al., 2021). A typical design is the CCZC nanoplatform composed of curcumin (Cur)-coated CaO₂@ZIF-Cu nanoparticles. Upon disintegration within the TME, CCZC releases copper ions (Cu²⁺) and exposes CaO₂. The H₂O₂ generated from CaO₂ hydrolysis immediately reacts with Cu²⁺ in a Fenton-like reaction, markedly producing ⋅OH for potent CDT. In a melanoma model, this achieved a 78% tumor inhibition rate while significantly promoting DC maturation and CTLs proliferation (Mo et al., 2024). However, the Fenton reaction efficiency of Cu²⁺ in the weakly acidic TME is relatively lower compared to ferrous irons (Fe²⁺), and the long-term biosafety of Cu²⁺ requires further evaluation. Another design (Cu₂Se–CaO₂@LA) utilized NIR-II laser to control CaO₂ exposure, generating H₂O₂ in-situ for photothermally-enhanced CDT. This acted synergistically with Ca overload to induce mitochondria and ER stress via the ROS–PERK–eIF2α signaling pathway, triggering potent ICD, promoting DC maturation, increasing the infiltration of CD4⁺ and CD8⁺ T cells within tumors, elevating serum levels of inflammatory cytokines such as TNF-α, interleukin-6 (IL-6), and IFN-γ, and achieving an 83% inhibition rate in a breast cancer model (Feng et al., 2023). Liang et al. (2023) further integrated the functions of the hydrolysis products of CaO₂ within a MOF platform. They designed a hyaluronic acid (HA)-targeted, copper-doped ZIF-8 nanoparticle (denoted as HA/CaO₂-Ce6@Cu-ZIF) for the co-delivery of CaO₂ and the photosensitizer Ce6, which enhanced CDT via a Fenton-like reaction between the self-supplied H₂O₂ and Cu²⁺, significantly improved the PDT efficacy of Ce6 by using the simultaneously generated O₂ to alleviate hypoxia, and synergistically aggravated tumor cell death through induced Ca overload. In the Panc02 tumor-bearing mice model, this strategy achieved a tumor inhibition rate of 60.80% without inducing significant systemic toxicity, demonstrating its potential as a self-supplying nanoreactor for synergistic catalytic therapy.

Furthermore, H₂O₂ can be utilized to induce ferroptosis and synergize with immunomodulation. For example, an iron-based MOF nanoplatform employed CaO₂-generated H₂O₂ to engage in a Fenton reaction with reduced Fe²⁺, initiating ferroptosis. Concurrently, co-loaded oridonin (ORI) inhibited two key negative regulatory pathways, HSPB1/PCBP1 and FSP1/CoQ10, synergistically enhancing ferroptosis. In vivo experiments revealed its tumor suppression effect in melanoma that was 5.6 times higher than CDT alone, and it worked synergistically with fusion membrane (FM)-mediated immunotherapy (Cai et al., 2024). Similarly, a pH-responsive membrane-coated nanozyme system co-loaded with CaO₂ and ferriferrous oxide (Fe₃O₄) generated H₂O₂ from CaO₂ in the TME, which was subsequently catalyzed by Fe₃O₄ nanoparticles in a Fenton-like reaction to produce ⋅OH and induce ferroptosis. The accompanying pH change was also shown to induce the repolarization of TAMs, achieving a synergistic effect between ferroptosis and immunomodulation in a breast cancer model, significantly prolonging mouse survival with 100% survival at day 80 (Li & Rong, 2020). Feng et al. (2025) further complexed CaO₂ with ferric ions (Fe³⁺)-doped dendritic mesoporous organosilica (DMOS). In this system, the Fenton reaction initiated ferroptosis and ICD, elevated the maturation rate of splenic DCs to 38.10%, and enhanced local and systemic infiltration of both CD8⁺ and CD4⁺ T cells. When combined with anti-PD-1 therapy, the inhibition rate of primary breast cancer reached 89.10%, and the proportion of memory T cells in the spleen reached 43.60%, indicating that this therapy has stimulated long-term immune memory.

More sophisticated strategies aim to simultaneously induce multiple cell death modalities. For instance, a cascade nanoreactor utilized CaO₂-produced H₂O₂ to enhance Cu²⁺-based CDT, while Ca overload exacerbated oxidative stress. Excessive Cu²⁺ could both initiate cuproptosis and deplete GSH and accumulate lipid peroxide (LPO) to synergistically induce ferroptosis. This CaO₂-driven activation of multiple cell death modalities robustly stimulates ICD, effectively converting “cold” tumor into “hot” tumor in a breast cancer mouse model, achieving a 68.10% tumor inhibition rate, significantly promoting the maturation of DC, and increasing the proportion of intratumoral CD8⁺ T by 2.3-fold compared to the control (Tang et al., 2025). However, this cascade nanoreactor is overly complex, its dominant mechanism and the intersections among various pathways are difficult to precisely control in vivo, posing challenges for clinical translation. Moreover, the concurrent induction of cuproptosis and ferroptosis may lead to enhanced toxicity, necessitating more stringent safety evaluations regarding potential effects on normal tissues.

Synergizing with other catalytic modalities

Based on the foundation of Fenton reaction, the utility of H₂O₂ extends beyond CDT to potentiate other modalities such as sonodynamic therapy (SDT) (Du et al., 2023). Building on the concept of multi-modal enhancement, the CTFAP nanocomposite utilized H₂O₂ supplied by CaO₂, which acted both as a substrate for the sonosensitizer tetracarboxylic porphyrin under ultrasound to enhance SDT, and participated in the Fe³⁺-mediated Fenton-like reaction to synergistically initiate ferroptosis. Remarkably, this design established a self-reinforcing ferroptosis positive feedback loop driven by IFN-γ secreted by activated CTLs upregulation of ACSL4, which subsequently accelerated lipid peroxidation (Jiang et al., 2024). Despite the remarkable efficacy, controlling the intensity of such self-reinforcing loops remains challenging, and the potential risk of systemic inflammation requires attention in follow-up studies.

In exploring novel catalytic mechanisms, Zhang et al. (2024) introduced violet phosphorus quantum dots (VPQDs) as an exogenous-stimulus-free catalyst. They utilized the O₂ and H₂O₂ continuously supplied by CaO₂ decomposition as reaction substrates, overcoming the scarcity of substrate in tumors and effectively triggering oxidative stress-mediated apoptosis. Interestingly, the phosphate by-products generated in this process synergized with Ca²⁺ to promote tumor calcification in a 4T1 breast cancer model (Fig. 2), revealing a novel functional role for therapeutic metabolites. However, as a novel nanomaterial, the long-term biocompatibility of VPQDs and the clearance mechanisms of their degradation products in vivo require systematic investigation.

Figure 2. Schematic illustration of the preparation and antitumor mechanism of VPCaNPs.

The preparation of VPCaNPs contains the top-down synthesis of VPQDs and the one-pot fabrication of VPCaNPs. The antitumor properties are based on the fate of VPCaNPs, including the release of cargos, CaO₂ decomposition, VP-catalyzed ROS generation, O₂-mediated VP degradation, and calcification. Image source credit: https://www.nature.com/articles/s41467-024-50769-0/figures/1, CC BY-NC-ND 4.0.

CaO₂ consume H⁺ to enhance immunotherapy

The metabolic preference of tumor cells for glycolysis leads to substantial LA accumulation, resulting in an acidic TME that impairs immune function through multiple mechanisms (Watson et al., 2021). A low extracellular pH (typically pH 6.5−6.9) has been shown to inhibit T-cell receptor signaling and impair glycolytic metabolism essential for T cells (Calcinotto et al., 2012). Similarly, the cytolytic activity and IFN-γ production of natural killer (NK) cells are significantly dampened under acidic conditions (Harmon et al., 2019). By consuming H⁺, CaO₂ hydrolysis increases the local pH, thereby alleviating this direct inhibition and potentially restoring the metabolic fitness and cytotoxic potential of tumor-infiltrating lymphocytes (Wang et al., 2022).

The ability of CaO₂ to consume H⁺ and neutralize acidity can directly ameliorate the ITME. Qiu et al. (2024) developed a zinc-coordinated lipid nanoparticle co-delivering CaO₂ and the STING agonist diABZI-2. In the acidic TME, CaO₂ consumed H⁺ and release O₂, directly ameliorating acidosis and creating favorable conditions for the effective activation of the STING pathway. Simultaneously, zinc ion (Zn²⁺) and Ca²⁺ work in concert to induce robust ICD. The combination of a rectified TME, STING pathway activation, and ICD ultimately leads to a potent, systemic antitumor immune response. In CT26 CRC model, this treatment resulted in an increase in splenic CD8⁺ T cells to 11.30%, promoted DC maturation by more than 1.5-fold, and elicited long-term immune memory. However, the neutralization effect may be inconsistent due to the uneven acidity distribution of TME.

A more profound strategy aims to eliminate the root cause of acidity, Fang et al. (2025) constructed a sophisticated multi-channel immune nano-regulator. Specifically, ultrasound triggered O₂ generation from perfluorocarbon chains, accelerating H⁺ consumption. Crucially, this strategy not only directly elevated pH and relieved hypoxia but also inhibited glycolysis and LA production, thereby reversing LA-driven M2-type TAM polarization and the functional suppression of CTLs and NK cells. This led to comprehensive remodeling of the ITME, resulting in powerful antitumor immunity and significantly prolonged survival in both breast cancer cellular and animal models. While this strategy intervenes at the metabolic root, its complex nanostructure presents challenges for large-scale production and quality control.

CaO₂ produce Ca²⁺ to enhance immunotherapy

The high concentration of Ca²⁺ generated from the hydrolysis of CaO₂ induces lethal Ca overload within tumor cells. This serves not only as an effective direct cytotoxic mechanism but also as a potent inducer of ER and mitochondrial stress, efficiently triggering ICD (Liu et al., 2025a; Liu et al., 2025b). As a pivotal second messenger, the disruptive influx of Ca²⁺ disrupts cellular homeostasis, directly leading to ICD and concurrently modulating the function of various immune cells (Cheng et al., 2025; Wang et al., 2025). For instance, Ca signaling is integral to T cell receptor (TCR) activation and nuclear factor of activated T cells (NFAT) signaling, which governs T cell proliferation and effector functions (Feske, Wulff & Skolnik, 2015). Thus, the localized flux of Ca²⁺ from CaO₂ hydrolysis may potentially lower the activation threshold for adjacent T cells. The dual role of Ca²⁺, simultaneously killing tumor cells in an immunogenic manner and potentially enhancing the activity of adjacent immune effectors, highlights its unique value in designing combination immunotherapy strategies.

Inducing ICD via Ca dyshomeostasis

Ca overload rapidly induces severe ER stress, leading to the surface exposure of calreticulin (CRT) and the release of damage-associated molecular patterns (DAMPs) such as ATP and high-mobility group box 1 (HMGB1), making it an effective means to induce ICD (Krysko et al., 2012). Ingeniously, Li et al. (2025) combined the CaO₂ with irreversible electroporation (IRE). The introduction of Ca²⁺ from CaO₂ exacerbated the ER stress initiated by IRE, thereby intensifying ICD signaling. Furthermore, in CRC tumor-bearing mice, the vermiculite nanosheet carrier used in this platform adsorbed tumor antigens and DAMPs, forming an in-situ vaccine that dramatically promoted DC activation and antigen cross-presentation. Huang et al. (2022) employed CaO₂ to design a bidirectional enhancement ICD nanoplatform for breast cancer, in which CaO₂ hydrolysis-induced Ca overload synergized with copper sulphide (CuS)-based PDT, leading to exacerbated mitochondrial damage and stronger ICD response. Concurrently, the mitochondrial DNA released due to PDT-induced damage was shown to reprogram TAMs towards an anti-tumor M1 phenotype.

Ca overload can also be linked with other therapies to create complex metabolic interference and cell death. For example, a self-reinforcing bimetallic mitochondrial disrupter that intricately links Ca overload with chemotherapy and cuproptosis. In this system, Ca overload synergized with the chemotherapeutic agent doxorubicin (DOX) to exacerbate the ROS storm and inflict severe mitochondrial damage, leading to ATP depletion. The ensuing energy crisis directly impaired copper (Cu) transporter function, causing Cu²⁺ accumulate within mitochondria and thereby sensitizing the breast cancer cells to cuproptosis (Du et al., 2024).

Modulating immune cell activity through Ca signaling

Ca²⁺ serves not only as a death signal for tumor cells but also as a critical second messenger for immune cell activation. Fluctuations in extracellular Ca²⁺ concentration or the use of Ca²⁺ carriers can directly influence the maturation and antigen-presentation capacity of DCs (Saez et al., 2018). The NVscp nanovaccine leveraged CaO₂ to rapidly generate ROS and release Ca²⁺ within the endo/lysosomes of antigen-presenting cells (APCs), directly stimulating APC maturation and enhancing antigen cross-presentation. This induced a robust antigen-specific CD8⁺ T cell response and increased the ratio of CD8⁺ T/Treg in a melanoma model (Su et al., 2021). The immunomodulatory effect of Ca²⁺ can also be achieved indirectly by influencing tumor cell metabolism. For instance, EL4 cell membrane-coated nano-CaO₂, upon targeting tumors, induced Ca overload that inhibited glycolysis in breast cancer cells, thereby reducing the secretion of LA, which in turn contributed to reversing CTLs exhaustion (An et al., 2024a; An et al., 2024b), offering a unique metabolic perspective for Ca-based immunotherapy.

In addition, the immunomodulatory potential of Ca²⁺ extends to synergistic interactions with other metal ions. For example, the HMnO₂@CaO₂ nanoplatform utilized Ca overload to cause ER stress and mitochondrial damage in an osteosarcoma mouse model, while the released manganese ions (Mn²⁺) induced ferroptosis and promoted the repolarization of TAMs towards the anti-tumor M1 phenotype (Zhang et al., 2025). The (CaO₂/TA)-(Fe³⁺/BSA) self-enhancing nanoparticle synergized Ca overload with an intensified Fenton reaction based on Fe³⁺ self-reduction and H₂O₂ self-supply, synergistically inducing ferroptosis and ICD. This profoundly reshaped the immune microenvironment in a breast cancer model, as evidenced by increased proportions of mature DCs, M1-type macrophages, and intratumoral CD8⁺ T cells to 51.50%, 41.10%, and 45.60%, respectively, while significantly suppressing immunosuppressive cells like Tregs and myeloid-derived suppressor cells (MDSCs) (Zheng et al., 2024).

Intriguingly, Ca²⁺ signaling can be harnessed for temporal regulation of immune responses. The FePpy@CaO₂-modified bone implant material utilized Ca²⁺ to participate in activating pro-inflammatory M1 phenotype macrophages during the bone tumor treatment phase. Following tumor eradication, it adaptively promoted macrophage switch to the pro-repair M2 phenotype and enhanced osteogenesis, achieving spatiotemporally precise control of the immune response to integrate therapy with tissue regeneration (Liu et al., 2025a; Liu et al., 2025b).

Conclusion and Outlook

CaO₂ nanoplatforms have emerged as a highly promising sensitization strategy for cancer immunotherapy, with their unique TME responsive hydrolysis characteristics enable simultaneously generation of O₂, H₂O₂, and Ca²⁺ (Tang et al., 2019). The advantages and innovations of CaO₂ nanoplatform in cancer immunotherapy point to their outstanding multi-functional integration capabilities, including alleviating hypoxia, neutralizing acidosis, inducing Ca overload through a single nanoplatform. In addition, achieving synergistic amplification of immunotherapy effects by coordinating sonodynamic, photodynamic, or chemokinetic therapy and delivering immune agonists or chemotherapy drugs (Table 1) (Liu et al., 2019). More importantly, the CaO₂-based nanotherapeutic strategies have successfully promoted the exploration of metal immunotherapy. The H₂O₂ generated from CaO₂ hydrolysis involved into Fenton or Fenton-like reactions mediated by metal ions such as Cu²⁺ and Fe³⁺, leading to the production of ⋅ OH. This process amplifies intracellular ROS levels, induces mitochondrial damage, and directly modulates the functions of immune cells (Chen et al., 2022; Fan et al., 2025; Liu et al., 2025a; Liu et al., 2025b). Furthermore, CaO₂ effectively initiated novel regulatory cell death (RCD) like ferroptosis and cuproptosis (Jiang, Stockwell & Conrad, 2021; Tsvetkov et al., 2022), providing a new approach to overcome apoptotic resistance.

Table 1. The effects of CaO₂ combine with different therapeutic strategies on tumor cells.

Therapeutic strategy	Biological impact	Immunological impact	Representative literature
CaO2	1. Hydrolysis consumes H+, rapidly increasing extracellular pH; 2. Generates H2O2, leading to elevated intracellular ROS levels; 3. Ca overload causes endoplasmic reticulum and mitochondrial dysfunction; 4. Produces O2 to alleviate tissue hypoxia.	1. Reverses immunosuppression of immune cells caused by acidosis; 2. Induces baseline level of ICD.	/
Combined with SDT	CaO2 hydrolysis provides H2O2 as a substrate for sonosensitizers. Under ultrasound irradiation, it synergistically generates massive ROS, which cooperates with Ca overload to cause severe mitochondrial and ER damage.	Potent oxidative stress and organelle damage synergistically induce robust ICD, releasing tumor antigens and activating innate immunity.	Jiang et al. (2024) and Tang et al. (2025)
Combined with CDT	CaO2 acts as a self-supplying H2O2 reservoir, continuously providing substrate for Fe3+/Cu2+-mediated Fenton/Fenton-like reactions, leading to burst ROS accumulation and directly driving ferroptosis.	DAMPs released from ferroptosis effectively activate dendritic cells, remodel the immunosuppressive microenvironment, and synergize with immune checkpoint blockade.	Feng et al. (2023), Li & Rong (2020), Mo et al. (2024) and Feng et al. (2025)
Combined with PTT/PDT	1. O2 generated by CaO2 directly alleviates tumor hypoxia, overcoming the oxygen-dependent limitation of PDT; 2. Heat from PTT can trigger controlled release of CaO2 and synergize with Ca overload for killing.	Improved oxygenation combined with multiple stressors promotes potent ICD and enhances immune cell infiltration.	Wu et al. (2023), Huang et al. (2022), Wei et al. (2025) and Cai et al. (2024)
Combined with immune adjuvants	Remodels the TME such as neutralizing acidity, inhibiting lactate, and induces ICD, creating a foundation for immune modulation.	Immune adjuvants like TLR agonist R848 are used to reprogram macrophages, thereby directly modulating immune cells.	Fang et al. (2025)

Notes.

Ca

calcium

CaO₂

calcium peroxide

CDT

Chemodynamic therapy

Cu²⁺

copper ions

DAMPs

damage-associated molecular patterns

Fe³⁺

ferric ions

H⁺

hydrogen ions

H₂O₂

hydrogen peroxide

ICD

immunogenic cell death

O₂

oxygen

PDT

Photodynamic therapy

PTT

Photothermal therapy

ROS

reactive oxygen species

SDT

Sonodynamic therapy

TME

tumor microenvironment

However, the clinical translation of CaO₂ nanoplatforms remain faces severe challenges. (1) The chemical instability of CaO₂ imposes stringent requirements for its production and long-term storage (Mitragotri et al., 2015). (2) The long-term biological safety and metabolic clearance pathways of the excess reactive products like ROS generated by the hydrolysis of CaO₂ in vivo remain unclear (Nel et al., 2006). (3) Current studies remain at the preclinical stage, lacking large-scale animal experiments and clinical data to verify the efficacy and toxicity. (4) The individual differences in immune responses caused by tumor heterogeneity pose substantial difficulties in predicting therapeutic outcomes and designing personalized applications.

Therefore, in the future, it is necessary to develop more stable CaO₂ encapsulation technologies and intelligent stimulus–response release systems to enhance the delivery efficiency and safety. Secondly, elucidate the mechanisms by which CaO₂ nanoplatforms regulate the TME and activate immunity, potentially by integrating multi-omics techniques. Finally, explore combination strategies with pioneering immunotherapies such as CAR-T, mRNA vaccines, and bispecific antibodies to exert synergistic effects. And ultimately, advancing systematic safety evaluations of CaO₂ nanoplatform in large-scale animal models to facilitate early-phase clinical trials, thereby validating their clinical potential and achieving translational breakthroughs.

Abbreviations

APCs

antigen-presenting cells

Ca

calcium

Ca²⁺

calcium ions

CaO₂

calcium peroxide

CAR-T

chimeric antigen receptor T-cell

CDT

chemodynamic therapy

CNKI

Chinese National Knowledge Infrastructure

CRC

colorectal cancer

CRT

calreticulin

CTLs

cytotoxic T lymphocytes

Cu

copper

Cu²⁺

copper ions

Cur

curcumin

CuS

copper sulphide

DAMPs

damage-associated molecular patterns

DCs

dendritic cells

DMOS

dendritic mesoporous organosilica

DOX

doxorubicin

EPR

enhanced penetration and retention

ER

endoplasmic reticulum

Fe²⁺

ferrous irons

Fe³⁺

ferric ions

FM

fusion membrane

Fe₃O₄

ferriferrous oxide

GSH

glutathione

H⁺

hydrogen ions

HA

hyaluronic acid

HIF-1α

hypoxia-inducible factor-1α

HMGB1

high-mobility group box 1

H₂O₂

hydrogen peroxide

ICD

immunogenic cell death

ICIs

immune checkpoint inhibitors

IFN-γ

interferon-γ

IL-6

interleukin-6

IRE

irreversible electroporation

ITME

immunosuppressive tumor microenvironment

LA

lactic acid

LPO

lipid peroxide

MDSCs

myeloid-derived suppressor cells

Mn²⁺

manganese ions

MOFs

metal–organic frameworks

MSNs

mesoporous silica nanoparticles

NFAT

nuclear factor of activated T cells

NIR-II

near-infrared

NK

natural killer

O₂

oxygen

¹O₂

singlet oxygen

⋅OH

hydroxyl radicals

ORI

oridonin

PDT

photodynamic therapy

RCD

regulatory cell death

ROS

reactive oxygen species

SDT

sonodynamic therapy

TAMs

tumor-associated macrophages

TCR

T cell receptor

TME

tumor microenvironment

TNF-α

tumor necrosis factor-α

Tregs

T-regulatory cells

VMT

vermiculite nanosheets

VPQDs

violet phosphorus quantum dots

Zn²⁺

zinc ion

Funding Statement

This work was supported by Zhejiang Provincial Natural Science Foundation of China under Grant No. ZCLQ24H3001, Zhejiang Provincial Medical and health Science and Technology Program (2024KY1692, 2024KY1694), Jiaxing Science and Technology Program (2024AY40013). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.