MnO2 Nanoflowers Induce Immunogenic Cell Death under Nutrient Deprivation: Enabling an Orchestrated Cancer Starvation-Immunotherapy

Embracing cancer immunotherapy with manganese particles

A substance integral to the sustenance and functionality of virtually all forms of life is manganese (Mn), classified as an essential trace metal. Its significance lies in its pivotal role in facilitating metabolic processes crucial for survival. Additionally, Mn exerts influence over various biological functions including bone formation and maintenance, as well as regulation within systems governing immunity, nervous signaling, and digestion. Manganese nanoparticles (Mn-NP) stand out as a beacon of promise within the realm of immunotherapy, their focus honed on intricate mechanisms such as triggering immune pathways, igniting inflammasomes, inducing immunogenic cell death (ICD), and sculpting the nuances of the tumor microenvironment. These minuscule marvels have dazzled researchers with their potential in reshaping the landscape of cancer immunotherapy - serving as potent vaccine enhancers, efficient drug couriers, and formidable allies when paired with immune checkpoint inhibitors (ICIs) or cutting-edge photodynamic/photothermal therapies. Herein, we aim to provide a comprehensive review of recent advances in the application of Mn and Mn-NP in the immunotherapy of cancer. We hope that this review will display an insightful view of Mn-NPs and provide guidance for design and application of them in immune-based cancer therapies.

Manganese-Based Nanotherapeutics for Targeted Treatment of Breast Cancer

Breast cancer (BC) is one of the most common cancers among women and is associated with high mortality. Traditional modalities, including surgery, radiotherapy, and chemotherapy, have achieved certain advancements but continue to combat challenges including harm to healthy tissues, resistance to treatment, and adverse drug reactions. The rapid advancements in nanotechnology recently facilitated the exploration of innovative strategies for breast cancer therapy. Manganese-based nanotherapeutics have attracted great attention because of their unique characteristics such as tunable structures/morphologies, versatility, magnetic/optical properties, strong catalytic activities, excellent biodegradability, and biocompatibility. In this review, we highlighted different types of Mn-based nanotherapeutics to modulate TME, including metal-immunotherapy, alleviating tumor hypoxia, and increasing reactive oxygen species production, and we emphasized its role in magnetic resonance imaging (MRI)-guided therapy, photoacoustic imaging, and theranostic-based therapy along with a therapeutic carrier, all of which were discussed in the context of breast cancer. Hopefully, the present review will provide insights into the current landscape and future directions of multifunctional applications of Mn-based nanotherapeutics in the field of breast cancer treatment.

Macrophage Membrane Coated Manganese Dioxide Nanoparticles Loaded with Rapamycin Alleviate Intestinal Ischemia-Reperfusion Injury by Reducing Oxidative Stress and Enhancing Autophagy

Background

Intestinal ischemia-reperfusion (I/R) injury is a common and severe clinical issue. With high morbidity and mortality, it burdens patients and the healthcare system. Despite the efforts in medical research, current treatment options are unsatisfactory, urging novel therapeutic strategies. Oxidative stress and dysregulated autophagy play pivotal roles in the pathogenesis of I/R injury, damaging intestinal tissues and disrupting normal functions. The aim of this study is to fabricate macrophage membrane-coated manganese dioxide nanospheres loaded with rapamycin [Ma@(MnO₂+RAPA)] for alleviating intestinal I/R injury.

Methods

We engineered honeycomb MnO2 nanospheres coated with a macrophage membrane to act as a drug delivery system, encapsulating RAPA. In vitro OGD/R model in IEC-6 cells and in vivo mouse I/R injury models were used. Targeting ability was evaluated through in-vivo imaging system. Effects on cell viability, reactive oxygen species (ROS) levels, oxygen generation, inflammatory factors, apoptosis, autophagy, and biocompatibility were detected by methods such as MTT assay, fluorescence microscopy, ELISA kit, TUNEL assay, Western blotting and histological analysis.

Results

In this study, Ma@(MnO₂+RAPA) efficiently deliver RAPA to damaged tissues and exhibited good ROS-responsive release. Our data showed that Ma@(MnO₂+RAPA) reduced ROS, increased O₂, inhibited inflammation, and promoted autophagy while reducing apoptosis in IEC-6 cells. In a mouse I/R model, Ma@(MnO₂+RAPA) significantly reduced Chiu's score, improved tight conjunction proteins, decreased apoptosis, reduced levels of inflammatory cytokines and oxidative stress. RAPA released from the Ma@(MnO₂+RAPA), enhanced the expression of autophagy-regulated proteins p62, Beclin-1, and LC3II. The biocompatibility and safety of Ma@(MnO₂+RAPA) were confirmed through histological analysis and biochemical detection in mice.

Conclusion

Our results demonstrated that Ma@(MnO₂+RAPA) alleviated intestinal I/R injury by reducing oxidative stress, promoting autophagy, and inhibiting inflammation. This study offers a potential therapeutic strategy for the treatment of intestinal ischemia-reperfusion injury.

Nanoplatform-based synergistic cancer Immuno-Chemodynamic therapy

Immunotherapy has made excellent breakthroughs in the field of cancer treatments, but faces challenges with low immunogenicity of tumor cells and an immunosuppressive tumor microenvironment (ITME). The emerging chemodynamic therapy (CDT) based on the Fenton/Fenton-like reaction can induce immunogenic cell death (ICD) to enhance tumor immunogenicity, facilitating the transition from immune-cold to immune-hot tumors. Synergistic CDT and immunotherapy based on advanced nanotechnology have shown immense promise for improving therapeutic efficacy while minimizing side effects in cancer treatment. This review summarizes and discusses recent advances in the field, with the goal of designing a high-quality nanoplatform to enhance synergistic CDT in combination with immunotherapy and lay the foundation for its future clinical translation.

Metal-based smart nanosystems in cancer immunotherapy

Metals are an emerging topic in cancer immunotherapy that have shown great potential in modulating cancer immunity cycle and promoting antitumor immunity by activating the intrinsic immunostimulatory mechanisms which have been identified in recent years. The main challenge of metal-assisted immunotherapy lies in the fact that the free metals as ion forms are easily cleared during circulation, and even cause systemic metal toxicity due to the off-target effects. With the rapid development of nanomedicine, metal-based smart nanosystems (MSNs) with unique controllable structure become one of the most promising delivery carriers to solve the issue, owing to their various endogenous/external stimuli-responsiveness to release free metal ions for metalloimmunotherapy. In this review, the state-of-the-art research progress in metal-related immunotherapy is comprehensively summarized. First, the mainstream mechanisms of MSNs-assisted immunotherapy will be delineated. The immunological effects of certain metals and categorization of MSNs with different characters and compositions are then provided, followed by the representative exemplar applications of MSNs in cancer treatment, and synergistic combination immunotherapy. Finally, we conclude this review with a summary of the remaining challenges associated with MSNs and provide the authors' perspective on their further advances.

Transition Metal (Molybdenum)-Doped Drug-like Conformational Nanoarchitectonics with Altered Valence States (Mn2+/Mn4+ and Mo5+/Mo6+) for Augmented Cancer Theranostics

Despite the advancements in cancer therapy, delivering active pharmaceutical ingredients (APIs) using nanoparticles remains challenging due to the failed conveyance of the required drug payload, poor targeting ability, and poor biodistribution, hampering their clinical translation. Recently, the appropriate design of materials with intrinsic therapeutic functionalities has garnered enormous interest in the development of various intelligent therapeutic nanoplatforms. In this study, we demonstrate the fabrication of transition metal (molybdenum, Mo)-doped manganese dioxide (MnO2) nanoarchitectures, exhibiting diagnostic (magnetic resonance imaging, MRI) and therapeutic (chemodynamic therapy, CDT) functionalities. The facile hydrothermal approach-assisted Mo-doped MnO2 flower-like nanostructures offered tailorable morphologies in altered dimensions, precise therapeutic effects, exceptional biocompatibility, and biodegradability in the tumor microenvironment. The resultant defects due to doped Mo species exhibited peroxidase and oxidase activities, improving glutathione (GSH) oxidation. The two sets of variable valence metal ion pairs (Mn2+/Mn4+ and Mo5+/Mo6+) and their interplay could substantially improve the Fenton-like reaction and generate toxic hydroxyl radicals (•OH), thus achieving CDT-assisted antitumor effects. As inherent T1-MRI agents, these MnO2 nanoparticles displayed excellent MRI efficacy in vitro. Together, we believe that these conformational Mo-doped MnO2 nanoarchitectures with two pairs of variable valence states could potentiate drugless therapy in pharmaceutics.

Advances in Nanomaterials for Immunotherapeutic Improvement of Cancer Chemotherapy

Immuno-stimulative effect of chemotherapy (ISECT) is recognized as a potential alternative to conventional immunotherapies, however, the clinical application is constrained by its inefficiency. Metronomic chemotherapy, though designed to overcome these limitations, offers inconsistent results, with effectiveness varying based on cancer types, stages, and patient-specific factors. In parallel, a wealth of preclinical nanomaterials holds considerable promise for ISECT improvement by modulating the cancer-immunity cycle. In the area of biomedical nanomaterials, current literature reviews mainly concentrate on a specific category of nanomaterials and nanotechnological perspectives, while two essential issues are still lacking, i.e., a comprehensive analysis addressing the causes for ISECT inefficiency and a thorough summary elaborating the nanomaterials for ISECT improvement. This review thus aims to fill these gaps and catalyze further development in this field. For the first time, this review comprehensively discusses the causes of ISECT inefficiency. It then meticulously categorizes six types of nanomaterials for improving ISECT. Subsequently, practical strategies are further proposed for addressing inefficient ISECT, along with a detailed discussion on exemplary nanomedicines. Finally, this review provides insights into the challenges and perspectives for improving chemo-immunotherapy by innovations in nanomaterials.

Progress of Nanomaterials Based on Manganese Dioxide in the Field of Tumor Diagnosis and Therapy

As a pivotal transition metal oxide, manganese dioxide (MnO2) has garnered significant attention owing to its abundant reserves, diverse crystal structures and exceptional performance. Nanosizing MnO2 results in smaller particle sizes, larger specific surface areas, optimized material characteristics, and expanded application possibilities. With the burgeoning research efforts in this field, MnO2 has emerged as a promising nanomaterial for tumor diagnosis and therapy. The distinctive properties of MnO2 in regulating the tumor microenvironment (TME) have attracted considerable interest, leading to a rapid growth in research on MnO2-based nanomaterials for tumor diagnosis and treatment. Additionally, MnO2 nanomaterials are also gradually showing up in the regulation of chronic inflammatory diseases. In this review, we mainly summarized the recent advancements in various MnO2 nanomaterials for tumor diagnosis and therapy. Furthermore, we discuss the current challenges and future directions in the development of MnO2 nanomaterials, while also envisaging their potential for clinical translation.

Nanomaterials: leading immunogenic cell death-based cancer therapies

The field of oncology has transformed in recent years, with treatments shifting from traditional surgical resection and radiation therapy to more diverse and customized approaches, one of which is immunotherapy. ICD (immunogenic cell death) belongs to a class of regulatory cell death modalities that reactivate the immune response by facilitating the interaction between apoptotic cells and immune cells and releasing specific signaling molecules, and DAMPs (damage-associated molecular patterns). The inducers of ICD can elevate the expression of specific proteins to optimize the TME (tumor microenvironment). The use of nanotechnology has shown its unique potential. Nanomaterials, due to their tunability, targeting, and biocompatibility, have become powerful tools for drug delivery, immunomodulators, etc., and have shown significant efficacy in clinical trials. In particular, these nanomaterials can effectively activate the ICD, trigger a potent anti-tumor immune response, and maintain long-term tumor suppression. Different types of nanomaterials, such as biological cell membrane-modified nanoparticles, self-assembled nanostructures, metallic nanoparticles, mesoporous materials, and hydrogels, play their respective roles in ICD induction due to their unique structures and mechanisms of action. Therefore, this review will explore the latest advances in the application of these common nanomaterials in tumor ICD induction and discuss how they can provide new strategies and tools for cancer therapy. By gaining a deeper understanding of the mechanism of action of these nanomaterials, researchers can develop more precise and effective therapeutic approaches to improve the prognosis and quality of life of cancer patients. Moreover, these strategies hold the promise to overcome resistance to conventional therapies, minimize side effects, and lead to more personalized treatment regimens, ultimately benefiting cancer treatment.

Turning harmful Mn2+ to treasure: In-situ formed ε-MnO2 for removing heavy metals from acid mine drainage

Acid mine drainage (AMD) contains high concentrations of heavy metals, causing serious environmental pollution. Current neutralization techniques fail to recover and utilize valuable heavy metals, and generate large quantities of hazardous sludge. Manganese (Mn) is generally present at high levels in AMD. Therefore, this paper proposed a technology to recover Mn from AMD, by adding KMnO4 to converting Mn into ε-MnO2. Ultra-Violet C (UVC) was used to photolyze the residual KMnO4. The study then evaluated the processes and mechanisms involved in the technology. The photolysis of KMnO4 in strong acidic conditions was determined, and new mechanisms were proposed. MnO2 produced by the photolysis process was formed through the reaction between Mn(III) and KMnO4. In the absence of KMnO4, Mn(III) underwent further photolysis and was reduced to Mn2+. The maximum adsorption capacities of in-situ formed ε-MnO2 for Pb2+, Cd2+, and Fe3+ were 449.80, 122.05, and 779.88 mg/g, respectively. Higher Mn-OH levels and MnO2 regeneration were crucial in improving adsorption performance. Proton exchange and inner-circle complexation were the main pathways for Pb2+ and Cd2+ adsorption by in-situ formed ε-MnO2. A phase transformation occurred when a substantial amount of Fe3+ was adsorbed, leading to the gradual transformation to MnFe binary oxides. When applying in-situ formed ε-MnO2 technology for actual AMD treatment, 98.62 % of Mn in AMD was recovered within 24 h in the presence of ε-MnO2 for possible further reuse in industries, with a final recovery of 0.76 kg/m3. Further, this technique removed other heavy metals and reduced the sludge volume by 20.99 % when used as a pre-treatment step for neutralization. These results demonstrated the broad potential of this treatment technology.

Mn(iii)-mediated carbon-centered radicals generate an enhanced immunotherapeutic effect

A strategy for designing cancer therapeutic nanovaccines based on immunogenic cell death (ICD)-inducing therapeutic modalities is particularly attractive for optimal therapeutic efficacy. In this work, a highly effective cancer therapeutic nanovaccine (denoted as MPL@ICC) based on immunogenic photodynamic therapy (PDT) was rationally designed and fabricated. MPL@ICC was composed of a nanovehicle of MnO2 modified with a host-guest complex using amino pillar[6]arene and lactose-pyridine, a prodrug of isoniazid (INH), and chlorine e6 (Ce6). The nanovaccine exhibited excellent biosafety, good targeting ability to hepatoma cells and enrichment at tumor sites. Most importantly, it could modulate the tumor microenvironment (TME) to facilitate the existence of Mn(iii) and Mn(iii)-mediated carbon-centered radical generation with INH released from the prodrug in situ to further strengthen ICD. This is the first report on Mn(iii)-mediated generation of carbon-centered radicals for successful anti-tumor immunotherapy using ICD, which provides a novel strategy for designing highly efficient cancer therapeutic nanovaccines.

MnO2 Decorated Metal-Organic Framework-Based Hydrogel Relieving Tumor Hypoxia for Enhanced Photodynamic Therapy

Photodynamic therapy (PDT) has emerged as a promising cancer treatment modality; however, its therapeutic efficacy is greatly limited by tumor hypoxia. In this study, a metal-organic framework (MOF)-based hydrogel (MOF Gel) system that synergistically combines PDT with the supply of oxygen is designed. Porphyrin-based Zr-MOF nanoparticles are synthesized as the photosensitizer. MnO2 is decorated onto the surface of the MOF, which can effectively convert H₂O₂ into oxygen. Simultaneously, the incorporation of MnO2 -decorated MOF (MnP NPs) into a chitosan hydrogel (MnP Gel) serves to enhance its stability and retention at the tumor site. The results show that this integrated approach significantly improves tumor inhibition efficiency by relieving tumor hypoxia and enhancing PDT. Overall, the findings underscore the potential for employing nano-MOF-based hydrogel systems as promising agents for cancer therapy, thus advancing the application of multifunctional MOFs in cancer treatment.

MnO2 Nanoflower Integrated Optoelectronic Biointerfaces for Photostimulation of Neurons

Optoelectronic biointerfaces have gained significant interest for wireless and electrical control of neurons. Three-dimentional (3D) pseudocapacitive nanomaterials with large surface areas and interconnected porous structures have great potential for optoelectronic biointerfaces that can fulfill the requirement of high electrode-electrolyte capacitance to effectively transduce light into stimulating ionic currents. In this study, the integration of 3D manganese dioxide (MnO2 ) nanoflowers into flexible optoelectronic biointerfaces for safe and efficient photostimulation of neurons is demonstrated. MnO2 nanoflowers are grown via chemical bath deposition on the return electrode, which has a MnO2 seed layer deposited via cyclic voltammetry. They facilitate a high interfacial capacitance (larger than 10 mF cm-2 ) and photogenerated charge density (over 20 µC cm-2 ) under low light intensity (1 mW mm-2 ). MnO2 nanoflowers induce safe capacitive currents with reversible Faradaic reactions and do not cause any toxicity on hippocampal neurons in vitro, making them a promising material for biointerfacing with electrogenic cells. Patch-clamp electrophysiology is recorded in the whole-cell configuration of hippocampal neurons, and the optoelectronic biointerfaces trigger repetitive and rapid firing of action potentials in response to light pulse trains. This study points out the potential of electrochemically-deposited 3D pseudocapacitive nanomaterials as a robust building block for optoelectronic control of neurons.

Biomedical applications of MnO2 nanomaterials as nanozyme-based theranostics

Manganese dioxide (MnO₂) nanoenzymes/nanozymes (MnO₂-NEs) are 1-100 nm nanomaterials that mimic catalytic, oxidative, peroxidase, and superoxide dismutase activities. The oxidative-like activity of MnO₂-NEs makes them suitable for developing effective and low-cost colorimetric detection assays of biomolecules. Interestingly, MnO₂-NEs also demonstrate scavenging properties against reactive oxygen species (ROS) in various pathological conditions. In addition, due to the decomposition of MnO₂-NEs in the tumor microenvironment (TME) and the production of Mn²⁺, they can act as a contrast agent for improving clinical imaging diagnostics. MnO₂-NEs also can use as an in situ oxygen production system in TME, thereby overcoming hypoxic conditions and their consequences in the progression of cancer. Furthermore, MnO₂-NEs as a shell and coating make the nanosystems smart and, therefore, in combination with other nanomaterials, the MnO₂-NEs can be used as an intelligent nanocarrier for delivering drugs, photosensitizers, and sonosensitizers in vivo. Moreover, these capabilities make MnO₂-NEs a promising candidate for the detection and treatment of different human diseases such as cancer, metabolic, infectious, and inflammatory pathological conditions. MnO₂-NEs also have ROS-scavenging and anti-bacterial properties against Gram-positive and Gram-negative bacterial strains, which make them suitable for wound healing applications. Given the importance of nanomaterials and their potential applications in biomedicine, this review aimed to discuss the biochemical properties and the theranostic roles of MnO₂-NEs and recent advances in their use in colorimetric detection assays of biomolecules, diagnostic imaging, drug delivery, and combinatorial therapy applications. Finally, the challenges of MnO₂-NEs applications in biomedicine will be discussed.

Manganese-Based Tumor Immunotherapy

As an essential micronutrient, manganese (Mn) participates in various physiological processes and plays important roles in host immune system, hematopoiesis, endocrine function, and oxidative stress regulation. Mn-based nanoparticles are considered to be biocompatible and show versatile applications in nanomedicine, in particular utilized in tumor immunotherapy in the following ways: 1) acting as a biocompatible nanocarrier to deliver immunotherapeutic agents for tumor immunotherapy; 2) serving as an adjuvant to regulate tumor immune microenvironment and enhance immunotherapy; 3) activating host's immune system through the cGAS-STING pathway to trigger tumor immunotherapy; 4) real-time monitoring tumor immunotherapy effect by magnetic resonance imaging (MRI) since Mn²⁺ ions are ideal MRI contrast agent which can significantly enhance the T₁ -weighted MRI signal after binding to proteins. This comprehensive review focuses on the most recent progress of Mn-based nanoplatforms in tumor immunotherapy. The characteristics of Mn are first discussed to guide the design of Mn-based multifunctional nanoplatforms. Then the biomedical applications of Mn-based nanoplatforms, including immunotherapy alone, immunotherapy-involved multimodal synergistic therapy, and imaging-guided immunotherapy are discussed in detail. Finally, the challenges and future developments of Mn-based tumor immunotherapy are highlighted.

Activating Nanomedicines with Electromagnetic Energy for Deep-Tissue Induction of Immunogenic Cell Death in Cancer Immunotherapy

Immunotherapy is an attractive approach for cancer therapy, while its antitumor efficacy is still limited, especially for non-immunogenic tumors. Nanomedicines can be utilized to convert the non-immunogenic "cold" tumors to immunogenic "hot" tumors via inducing immunogenic cell death (ICD), thereby promoting the antitumor immune response. Some nanomedicines that can produce local heat and reactive oxygen species upon the stimulation of electromagnetic energy are the main candidates for inducing the ICD effect. However, their applications are often restricted due to the poor tissue penetration depths of electromagnetic energy, such as light. By contrast, ultrasound, X-ray, alternating magnetic field, and microwave show excellent tissue penetration depths and thereby can be used for sonodynamic therapy, radiotherapy, magnetic hyperthermia therapy, and microwave ablation therapy, all of which can effectively induce ICD. Herein, the combination of deep-tissue electromagnetic energy with nanomedicines for inducing ICD and cancer immunotherapy are summarized. In particular, the designs of nanomedicines to amplify ICD effect in the presence of deep-tissue electromagnetic energy and sensitize tumors to various immunotherapies will be discussed. At the end of this review, a brief conclusion and discussion of current challenges and further perspectives in this subfield are provided.

Biomaterials That Induce Immunogenic Cell Death

The immune system takes part in most physiological and pathological processes of the body, including the occurrence and development of cancer. Immunotherapy provides a promising modality for inhibition and even the cure of cancer. During immunotherapy, the immunogenic cell death (ICD) of tumor cells induced by chemotherapy, radiotherapy, phototherapy, bioactive materials, and so forth, triggers a series of cellular responses by causing the release of tumor-associated antigens and damage-associated molecular patterns, which ultimately activate innate and adaptive immune responses. Among them, the ICD-induced biomaterials attract increasing conditions as a benefit of biosafety and multifunctional modifications. This Review summarizes the research progress in biomaterials for inducing ICD via triggering endoplasmic reticulum oxidative stress, mitochondrial dysfunction, and cell membrane rupture and discusses the application prospects of ICD-inducing biomaterials in clinical practice for cancer immunotherapy.

Rough Nanovaccines Boost Antitumor Immunity Through the Enhancement of Vaccination Cascade and Immunogenic Cell Death Induction

Nanovaccines have attracted intense interests for efficient antigen delivery and tumor-specific immunity. It is challenging to develop a more efficient and personalized nanovaccine to maximize all steps of the vaccination cascade by exploiting the intrinsic properties of nanoparticles. Here, biodegradable nanohybrids (MP) composed of manganese oxide nanoparticles and cationic polymers are synthesized to load a model antigen ovalbumin to form MPO nanovaccines. More interestingly, MPO could serve as autologous nanovaccines for personalized tumor treatment taking advantage of in situ released tumor-associated antigens induced by immunogenic cell death (ICD). The intrinsic properties of MP nanohybrids including morphology, size, surface charge, chemical, and immunoregulatory functions are fully exploited to enhance of all steps of the cascade and induce ICD. MP nanohybrids are designed to efficiently encapsulate antigens by cationic polymers, drain to lymph nodes by appropriate size, be internalized by dendritic cells (DCs) by rough morphology, induce DC maturation through cGAS-STING pathway, and enhance lysosomal escape and antigen cross-presentation through the "proton sponge effect". The MPO nanovaccines are found to efficiently accumulate in lymph nodes and elicit robust specific T-cell immune responses to inhibit the occurrence of ovalbumin-expressing B16-OVA melanoma. Furthermore, MPO demonstrate great potential to serve as personalized cancer vaccines through the generation of autologous antigen depot through ICD induction, activation of potent antitumor immunity, and reversal of immunosuppression. This work provides a facile strategy for the construction of personalized nanovaccines by exploiting the intrinsic properties of nanohybrids.

Nanomaterial-Based Antivascular Therapy in the Multimodal Treatment of Cancer

Abnormal tumor vasculature and a hypoxic tumor microenvironment (TME) limit the effectiveness of conventional cancer treatment. Recent studies have shown that antivascular strategies that focus on antagonizing the hypoxic TME and promoting vessel normalization effectively synergize to increase the antitumor efficacy of conventional therapeutic regimens. By integrating multiple therapeutic agents, well-designed nanomaterials exhibit great advantages in achieving higher drug delivery efficiency and can be used as multimodal therapy with reduced systemic toxicity. In this review, strategies for the nanomaterial-based administration of antivascular therapy combined with other common tumor treatments, including immunotherapy, chemotherapy, phototherapy, radiotherapy, and interventional therapy, are summarized. In particular, the administration of intravascular therapy and other therapies with the use of versatile nanodrugs is also described. This review provides a reference for the development of multifunctional nanotheranostic platforms for effective antivascular therapy in combined anticancer treatments.

Nanodrug constructed using dietary antioxidants for immunotherapy of metastatic tumors

Immunogenic cell death (ICD) induced by reactive oxygen species (ROS) represents a particular form of tumor cell death for approaching the problem of low immunogenicity of tumors in immunotherapy, while the oxidative damage to normal cells of current ICD inducers hinders their clinical application. Herein, a new ICD inducer VC@cLAV constructed solely by dietary antioxidants, lipoic acid (LA) and vitamin C (VC), is developed, which could promote heavy intracellular ROS production in cancer cells for ICD induction while acting as an anti-oxidant in non-cancer cells for cytoprotection, and thus hold high biosafety. In vitro studies show that VC@cLAV induced a release of antigens and a maturation rate of DCs up to 56.5%, approaching the positive control (58.4%). In vivo combined with αPD-1, VC@cLAV showed excellent antitumor activity against both primary and distant metastatic tumors with an inhibition rate of 84.8% and 79.0% compared to 14.2% and 10.0% in the αPD-1 alone group. Notably, VC@cLAV established a long-term antitumor immune memory effect against tumor rechallenging. This study not only presents a new kind of ICD inducer but also provides an impetus for the development of dietary antioxidant-based cancer drugs.

A New Sono-Chemo Sensitizer Overcoming Tumor Hypoxia for Augmented Sono/Chemo-Dynamic Therapy and Robust Immune-Activating Response

Novel sonosensitizers with intrinsic characteristics for tumor diagnosis, efficient therapy, and tumor microenvironment regulation are appealing in current sonodynamic therapy. Herein, a manganese (Mn)-layered double hydroxide-based defect-rich nanoplatform is presented as a new type of sono-chemo sensitizer, which allows ultrasound to efficiently trigger reactive oxygen species generation for enhanced sono/chemo-dynamic therapy. Moreover, such a nanoplatform is able to relieve tumor hypoxia and achieve augmented singlet oxygen production via catalyzing endogenous H2 O2 into O2 . On top of these actions, the released Mn2+ ions and immune-modulating agent significantly intensify immune activation and reverse the immunosuppressive tumor microenvironment to the immunocompetent one. Consequently, this nanoplatform exhibits excellent anti-tumor efficacy and effectively suppresses both primary and distant tumor growth, demonstrating a new strategy to functionalize nanoparticles as sono-chemo sensitizers for synergistic combination cancer therapy.

Immunomodulatory activity of manganese dioxide nanoparticles: Promising for novel vaccines and immunotherapeutics

Manganese (Mn), a nutrient inorganic trace element, is necessary for a variety of physiological processes of animal body due to their important roles in oxidative regulation effects and other aspects of activities. Moreover, manganese ion (Mn²⁺) has widely reported to be crucial for the regulations of different immunological responses, thus showing promising application as potential adjuvants and immunotherapeutics. Taking the advantages of Mn-based biological and immunological activities, Manganese dioxide nanoparticles (MnO₂ NPs) are a new type of inorganic nanomaterials with numerous advantages, including simple preparation, low cost, environmental friendliness, low toxicity, biodegradable metabolism and high bioavailability. MnO₂ NPs, as a kind of drug carrier, have also shown the ability to catalyze hydrogen peroxide (H₂O₂) to produce oxygen (O₂) under acidic conditions, which can enhance the efficacy of radiotherapy, chemotherapy and other therapeutics for tumor treatment by remodeling the tumor microenvironment. More importantly, MnO₂ NPs also play important roles in immune regulations both in innate and adaptive immunity. In this review, we summarize the biological activities of Manganese, followed by the introduction for the biological and medical functions and mechanisms of MnO₂ NPs. What's more, we emphatically discussed the immunological regulation effects and mechanisms of MnO₂ NPs, as well as their potentials to serve as adjuvants and immunomodulators, which might benefit the development of novel vaccines and immunotherapies for more effective disease control.

Reversing the immunosuppressive microenvironment with reduced redox level by microwave-chemo-immunostimulant Ce-Mn MOF for improved immunotherapy

BACKGROUNDS

Reversing the immunosuppressive tumor microenvironment (TME) in the tumor is widely deemed to be an effective strategy to improve immune therapy. In particular, the redox balance in TME needs to be well controlled due to its critical role in mediating the functions of various cells, including cancer cells and immune-suppressive cells.

RESULTS

Here, we propose an efficient strategy to reshape the redox homeostasis to reverse immunosuppressive TME. Specifically, we developed a microwave-chemo-immunostimulant CMMCP to promote the infiltration of the tumor-T cells by simultaneously reducing the reactive oxygen species (ROS) and glutathione (GSH) and improving the oxygen (O₂) levels in TME. The CMMCP was designed by loading chemotherapy drugs cisplatin into the bimetallic Ce-Mn MOF nanoparticles coated with polydopamine. The Ce-Mn MOF nanoparticles can effectively improve the catalytic decomposition of ROS into O₂ under microwave irradiation, resulting in overcoming hypoxia and limited ROS generation. Besides, the activity of intracellular GSH in TME was reduced by the redox reaction with Ce-Mn MOF nanoparticles. The reprogrammed TME not only boosts the immunogenic cell death (ICD) induced by cisplatin and microwave hyperthermia but also gives rise to the polarization of pro-tumor M2-type macrophages to the anti-tumor M1-type ones.

CONCLUSION

Our in vivo experimental results demonstrate that the microwave-chemo-immunostimulant CMMCP significantly enhances the T cell infiltration and thus improves the antitumor effect. This study presents an easy, safe, and effective strategy for a whole-body antitumor effect after local treatment.

Dual-Modal Imaging and Synergistic Spinal Tumor Therapy Enabled by Hierarchical-Structured Nanofibers with Cascade Release and Postoperative Anti-adhesion

Most treatments for spinal cancer are accompanied by serious side effects including subsequent tumor recurrence, spinal cord compression, and tissue adhesion, thus a highly effective treatment is crucial for preserving spinal and neurological functionalities. Herein, trilayered electrospun doxorubicin@bovine serum albumin/poly(ε-caprolactone)/manganese dioxide (DOX@BSA/PCL/MnO₂) nanofibers with excellent antiadhesion ability, dual glutathione/hydrogen peroxide (GSH/H₂O₂) responsiveness, and cascade release of Mn²⁺/DOX was fabricated for realizing an efficient spinal tumor therapy. In detail, Fenton-like reactions between MnO₂ in the fibers outermost layer and intra-/extracellular glutathione within tumors promoted the first-order release of Mn²⁺. Then, sustained release of DOX from the fibers' core layer occurred along with the infiltration of degradation fluid. Such release behavior avoided toxic side effects of drugs, regulated inflammatory tumor microenvironment, amplified tumor elimination efficiency through synergistic chemo-/chemodynamic therapies, and inhibited recurrence of spinal tumors. More interestingly, magnetic resonance and photoacoustic dual-modal imaging enabled visualizations of tumor therapy and material degradation in vivo, achieving rapid pathological analysis and diagnosis. On the whole, such versatile hierarchical-structured nanofibers provided a reference for rapid and potent theranostic of spinal cancer in future clinical translations.

Metal-Cyclic Dinucleotide Nanomodulator-Stimulated STING Signaling for Strengthened Radioimmunotherapy of Large Tumor

Combined treatment of immunotherapy and radiotherapy shows promising therapeutic effects for the regression of a variety of cancers. However, even multi-modality therapies often fail to antagonize the regression of large tumors due to the extremely immunosuppressive tumor microenvironment (TME). Here, a radioimmunotherapeutic paradigm based on stimulator of interferon genes (STING)-dependent signaling is applied to preclude large tumor progression by utilizing the metal-cyclic dinucleotide (CDN) nanoplatform, which integrates STING agonist c-di-AMP and immunomodulating microelement manganese (II) within the tannic acid nanostructure (TMA-NPs). As observed by magnetic resonance imaging, the localized administration of TMA-NPs effectively relieves hypoxia within TME and causes radical oxygen species overproduction and apoptosis in cancer cells after exposure to X-ray irradiation. The DNA fragments released from the apoptotic cells after the combined treatment augment the production of endogenous CDNs in cancer cells, hence significantly activating the STING-mediated pathway for stronger anti-tumor immunity. The localized therapy of TMA-NPs + X-ray not only inhibits the primary large tumor progression but also retards distant tumor growth by promoting dendritic cell maturation and activating cytotoxic immune cells whil suppressing immunosuppressive cells. Therefore, this work represents the combinatorial potency of TMA-NPs and X-rays on large tumor regression through strengthened STING-mediated radioimmunotherapeutics.

Oral Nanomotor-Enabled Mucus Traverse and Tumor Penetration for Targeted Chemo-Sono-Immunotherapy against Colon Cancer

The therapeutic outcomes of oral nanomedicines against colon cancer are heavily compromised by their lack of specific penetration into the internal tumor, favorable anti-tumor activity, and activation of anti-tumor immunity. Herein, hydrogen peroxide (H₂ O₂ )/ultrasound (US)-driven mesoporous manganese oxide (MnO_x )-based nanomotors are constructed by loading mitochondrial sonosensitizers into their mesoporous channels and orderly dual-functionalizing their surface with silk fibroin and chondroitin sulfate. The locomotory activities and tumor-targeting capacities of the resultant nanomotors (CS-ID@NMs) are greatly improved in the presence of H₂ O₂ and US irradiation, inducing efficient mucus-traversing and deep tumor penetration. The excess H₂ O₂ in the tumor microenvironment (TME) is decomposed into hydroxyl radicals and oxygen by an Mn²⁺ -mediated Fenton-like reaction, and the produced oxygen participates in sonodynamic therapy (SDT), yielding abundant singlet oxygen. The combined Mn²⁺ -mediated chemodynamic therapy and SDT cause effective ferropotosis of tumor cells and accelerate the release of tumor antigens. Importantly, animal experiments reveal that the treatment of combining oral hydrogel (chitosan/alginate)-embedding CS-ID@NMs and immune checkpoint inhibitors can simultaneously suppress the growth of primary and distal tumors through direct killing, reversion of immunosuppressive TME, and potentiation of systemic anti-tumor immunity, demonstrating that the CS-ID@NM-based platform is a robust oral system for synergistic treatment of colon cancer.

In-Situ Assembly of Janus Nanoprobe for Cancer Activated NIR-II Photoacoustic Imaging and Enhanced Photodynamic Therapy

Inorganic nanoprobes have attracted increasing attention in the biomedical field due to their versatile functionalities and excellent optical properties. However, conventional nanoprobes have a relatively low retention time in the tumor and are mostly applied in the first near-infrared window (NIR-I, 650-950 nm), limiting their applications in accurate and deep tissue imaging. Herein, we develop a Janus nanoprobe, which can undergo tumor microenvironment (TME)-induced aggregation, hence, promoting tumor retention time and providing photoacoustic (PA) imaging in the second NIR (NIR-II, 950-1700 nm) window, and enhancing photodynamic therapy (PDT) effect. Ternary Janus nanoprobe is composed of gold nanorod (AuNR) coated with manganese dioxide (MnO₂) and photosensitizer pyropheophorbide-a (Ppa) on two ends of AuNR, respectively, named as MnO₂-AuNR-Ppa. In the tumor, MnO₂ could be etched by glutathione (GSH) to release Mn²⁺, which is coordinated with multiple Ppa molecules to induce in situ aggregation of AuNRs. The aggregation of AuNR effectively improves the NIR-II photoacoustic signal in vivo. Moreover, the increased retention time of nanoprobes and GSH reduction in the tumor greatly improve the PDT effect. We believe that this work will inspire further research on specific in situ aggregation of inorganic nanoparticles.

Hybrid Mesoporous MnO2-Upconversion Nanoparticles for Image-Guided Lung Cancer Spinal Metastasis Therapy

Upconversion nanoparticles (UCNPs) and MnO₂ composite materials have broad prospects in biological applications due to their near-infrared (NIR) imaging capability and tumor microenvironment-responsive features. Nevertheless, the synthesis of such composite nanoplatforms still faces many hurdles such as redundant processing and uneven coatings. Here, we explored a simple, rapid, and universal method for precisely controlled coating of mesoporous MnO₂ (mMnO₂) using poly(ethylene imine) as a reducing agent and potassium permanganate as a manganese source. Using this strategy, a mMnO₂ shell was successfully coated on UCNPs. We further modified the mMnO₂-coated UCNPs (UCNP@mMnO₂) with a photosensitizer (Ce6), cisplatin drug (DSP), and tumor targeting pentapeptide (TFA) to obtain a nanoplatform UCNP/Ce6@mMnO₂/DSP-TFA for treating spinal metastasis of nonsmall cell lung cancer (NSCLC-SM). The utilization of both upconversion and downconversion luminescence of UCNPs with different NIR wavelengths can avoid the simultaneous initiation of NIR-II in vivo imaging and tumor photodynamic therapy, thus reducing damage to normal tissues. This platform achieved a high synergistic effect of photodynamic therapy and chemotherapy. This leads to beneficial antitumor effects on the therapy of NSCLC-SM.

A flowerlike FePt/MnO2/GOx-based cascade nanoreactor with sustainable O2 supply for synergistic starvation-chemodynamic anticancer therapy

The development of versatile nanotheranostic agents has received increasing interest in cancer treatment. Herein, in this study, we rationally designed and prepared a novel flowerlike multifunctional cascade nanoreactor, BSA-GOx@MnO2@FePt (BGMFP), by integrating glucose oxidase (GOx), manganese dioxide (MnO2) and FePt for synergetic cancer treatment with satisfying therapeutic efficiency. In an acidic environment, intratumoral H2O2 could be decomposed to O2 to accelerate the consumption of glucose catalyzed by GOx to induce cancer starvation. Moreover, the accumulation of gluconic acid and H2O2 generated along with the consumption of glucose would in turn promote the catalytic efficiency of MnO2 and boost O2 evolution, which could enhance the efficiency of starvation therapy. Moreover, FePt as an excellent Fenton agent could simultaneously convert H2O2 to the toxic hydroxyl radical (˙OH), subsequently resulting in amplified intracellular oxidative stress and cell apoptosis. Therefore, BGMFP could catalyze a cascade of intracellular biochemical reactions and optimize the unique properties of MnO2, GOx and FePt via mutual promotion of each other to realize O2 supply, chemodynamic therapy (CDT) and starvation therapy. The anticancer results in vitro and in vivo demonstrated that BGMFP possessed remarkable tumor inhibition capacity through enhancing the starvation therapy and CDT. It is appreciated that BGMFP could be a promising platform for synergetic cancer treatment.

Manganese oxide nanomaterials boost cancer immunotherapy

Immunotherapy, a strategy that leverages the host immune function to fight against cancer, plays an increasingly important role in clinical tumor therapy. In spite of the great success achieved in not only clinical treatment but also basic research, cancer immunotherapy still faces many huge challenges. Manganese oxide nanomaterials (MONs), as ideal tumor microenvironment (TME)-responsive biomaterials, are able to dramatically elicit anti-tumor immune responses in multiple ways, indicating great prospects for immunotherapy. In this review, on the basis of different mechanisms to boost immunotherapy, major highlighted topics are presented, covering adjusting an immunosuppressive TME by generating O2 (like O2-sensitized photodynamic therapy (PDT), programmed cell death ligand-1 (PD-L1) expression downregulation, reprogramming tumor-associated macrophages (TAMs), and restraining tumor angiogenesis and lactic acid exhaustion), inducing immunogenic cell death (ICD), photothermal therapy (PTT) induction, activating the stimulator of interferon gene (STING) pathway and immunoadjuvants for nanovaccines. We hope that this review will provide holistic understanding about MONs and their application in cancer immunotherapy, and thus pave the way to the translation from bench to bedside in the future.