Breast cancer continues to pose a formidable challenge in the field of oncology, especially with its propensity for metastasizing to distant organs such as bone, significantly worsening patient prognosis. Despite advances in treatment modalities that have enhanced survival rates for primary breast tumors, effective management of metastatic lesions remains elusive. Conventional therapeutic strategies primarily aim at controlling localized tumors but often fail to adequately address the dynamic and immunosuppressive microenvironment of metastatic sites. This critical therapeutic gap has catalyzed innovative research focusing on multifunctional treatment platforms capable of both eradicating tumor cells and reprogramming the tumor microenvironment to restore immune surveillance.
One particularly promising modality emerging in recent years is sonodynamic therapy (SDT), which exploits ultrasound waves to activate sonosensitizers preferentially accumulated within tumors. SDT offers superior deep tissue penetration and precise spatiotemporal control compared to traditional photodynamic therapy. However, existing sonosensitizers face substantial limitations. Inorganic-based systems often suffer from poor biodegradability and potential long-term toxicity. Meanwhile, purely organic small molecule sensitizers lack the versatility needed for multifunctional integration and efficient reactive oxygen species (ROS) generation. To surmount these obstacles, Ming Wu and colleagues at the Gongli Hospital of Pudong New Area have pioneered an innovative sonodynamic platform based on covalent organic frameworks (COFs), which are crystalline, porous polymers known for their tunable structures, biocompatibility, and abundant functionalization sites.
Their groundbreaking study reports the synthesis of ferrocene-modified nanoscale COFs (mCOFs) that marry the structural advantages of COFs with the catalytic properties of ferrocene moieties. By reacting microscale COFs with aminoferrocene, the researchers achieved effective nanosizing alongside the integration of Fenton-like catalytic centers. This dual functionality is pivotal: under ultrasonic irradiation, mCOFs generate singlet oxygen (^1O_2), a potent cytotoxic ROS, while the embedded ferrocene units catalyze the conversion of the naturally elevated hydrogen peroxide (H_2O_2) within the tumor microenvironment into highly reactive hydroxyl radicals (·OH). This tandem ROS amplification enables enhanced oxidative stress, resulting in robust tumor cell lethality.
Comprehensive physicochemical characterization confirmed that the mCOFs exhibit optimal particle size, dispersibility in biological media, and crystalline integrity—a foundation critical for reproducible biological activity. Additionally, in vitro assays demonstrated that mCOFs efficiently enter 4T1 breast cancer cells and induce markedly increased intracellular ROS upon ultrasound exposure. These ROS bursts trigger different cell death pathways, including apoptosis and ferroptosis, as evidenced by elevated lipid peroxidation and mitochondrial dysfunction markers. Unlike apoptosis, which is caspase-dependent programmed cell death, ferroptosis is characterized by iron-dependent lipid peroxidation, providing mechanistic synergy through complementary cytotoxic mechanisms.
Beyond direct tumoricidal effects, the mCOF + ultrasound combination stimulated immunogenic cell death (ICD)—a form of apoptosis that heightens anti-tumor immune responses. The hallmark features of ICD, such as the release of damage-associated molecular patterns (DAMPs) like ATP, were significantly upregulated. This, in turn, promoted the maturation and activation of dendritic cells (DCs), critical antigen-presenting cells in orchestrating adaptive immunity. Pro-inflammatory cytokines including interleukin-6 (IL-6) and tumor necrosis factor-alpha (TNF-α) were also elevated, fostering an inflamed microenvironment conducive to immune-mediated tumor clearance.
Moving from cell culture to animal models, the team employed orthotopic breast tumor-bearing mice to evaluate therapeutic efficacy and biodistribution. Intravenous administration of mCOFs achieved high tumor accumulation due to favorable nanoscale dimensions and surface properties, with sonodynamic activation significantly suppressing tumor growth without obvious systemic toxicity. Furthermore, in a clinically relevant bone metastasis model, mCOF treatment attenuated osteolytic lesions, preserving bone volume fraction and mineral density. These results underscore the ability of mCOFs not only to control primary tumors but also to mitigate metastatic spread and bone destruction, which are principal causes of morbidity and mortality.
Immunophenotyping of tumor-infiltrating leukocytes revealed striking increases in mature DCs, helper CD4+ T cells, cytotoxic CD8+ T cells, natural killer (NK) cells, and interferon-gamma (IFN-γ)-producing CD8+ T cells after mCOF + ultrasound treatment. This immune remodeling indicates that the sonodynamic platform effectively reverses tumor immunosuppression and mobilizes both innate and adaptive immune arms to mount a concerted attack against cancer. Such remodeling is critical for durable responses and prevention of metastatic recurrence.
The innovation in this study lies in the precise integration of sonodynamic therapy with Fenton reaction-based chemotherapy and immune modulation via a single nanoscale platform. The ferrocene modification imparts catalytic ROS amplification, overcoming the intrinsic oxidative resistance of tumors, while the COF scaffold ensures structural robustness and biocompatibility. By eliciting ICD alongside ferroptosis and apoptosis, the mCOFs stimulate systemic antitumor immunity—a distinct advantage over conventional therapies that often induce immunologically silent cell death facilitating tumor escape.
This research sets a precedent for the rational design of multifunctional sonosensitizers employing covalent organic frameworks as versatile carriers. The top-down approach to ferrocene incorporation opens avenues for tailoring nanoformulations with synergistic therapeutic mechanisms. Importantly, the successful suppression of both breast cancer progression and its devastating bone metastases highlights the clinical translational potential of mCOFs. Such innovations are urgently needed to address unmet needs in metastatic breast cancer treatment paradigms.
Ming Wu and collaborators emphasize that their findings also reinforce the concept that combining sonodynamic therapy with immunomodulation may overcome the historical limitations of therapies focused solely on primary tumor ablation. This multidimensional strategy disrupts the permissive tumor microenvironment favoring metastasis and immune evasion.
In conclusion, the ferrocene-modified nanoscale covalent organic framework platform represents a leap forward in cancer nanomedicine. It harnesses ultrasound-triggered ROS generation augmented by Fenton catalysis, induces dual apoptosis and ferroptosis pathways, and recalibrates the tumor immune milieu to achieve comprehensive tumor control. Future investigation into clinical translation, pharmacokinetics, and combinatorial regimens with immunotherapy could further enhance its therapeutic impact, potentially revolutionizing the management of metastatic breast cancer and other solid tumors.
Subject of Research: Ferrocene-Modified Nanoscale Covalent Organic Frameworks for Multifunctional Sonodynamic Therapy in Breast Cancer and Bone Metastasis
Article Title: Ferrocene-Modified Nanoscale Covalent Organic Frameworks for Ferroptosis-Based Sonodynamic Therapy Inhibit Breast Cancer and Its Bone Metastasis
News Publication Date: March 23, 2026
References: Published in Cyborg and Bionic Systems
Image Credits: Ming Wu, Gongli Hospital of Pudong New Area
Keywords: Breast cancer, bone metastasis, sonodynamic therapy, covalent organic frameworks, ferrocene, reactive oxygen species, ferroptosis, immunogenic cell death, tumor microenvironment, nanomedicine, oxidative stress, immune modulation
