Radiotherapy (RT) remains a cornerstone of cancer treatment, but its therapeutic efficacy is often limited by tumour hypoxia, radiation resistance, and insufficient systemic antitumor immunity.

In particular, hypoxic tumour microenvironments can reduce radiation-induced DNA damage, while localised radiotherapy alone is generally insufficient to control distant metastases or prevent tumour recurrence.

Developing radiosensitising agents that can simultaneously enhance reactive oxygen species (ROS) generation, relieve tumour hypoxia, and activate systemic immune responses therefore represents an important challenge in cancer therapy.

In a recent study published in Nano-Micro Letters, Ruidan Li, Qinlong Wen and co-workers, led by Professor Chong Cheng and Professor Xingchen Peng, report the de novo design of an IrMn-cluster-based artificial metalloenzyme (IMM) that integrates enzyme-mimetic catalysis, radiosensitization, and immune modulation into a single therapeutic platform.

Inspired by natural manganese-containing peroxidase and catalase, the researchers constructed IrMn clusters coordinated with Mn-organic ligands to create electron-rich catalytic centres capable of simultaneously promoting ROS and O₂ generation.

Bioinspired Construction of Electron-Rich IrMn Catalytic Centres

The key concept of this work is the use of Mn-organic ligands to electronically regulate Ir clusters.

The resulting IMM adopts a spiky nanostructure, with ultrasmall Ir nanoclusters of approximately 1.5 nm uniformly distributed on the surface of the Mn-organic framework.

Spectroscopic and theoretical analyses reveal strong electronic interactions between the organic framework and Ir centres, with approximately 0.51 |e| electron transfer from the ligand to Ir.

This electron redistribution increases the electron density of the Ir catalytic centres and facilitates multielectron redox reactions involving oxygen-containing intermediates.

XANES and EXAFS analyses further confirm the local coordination environment of the Ir centres, revealing Ir–O, Ir–Ir, and Ir–Mn coordination structures.

Together with DFT calculations, these results establish a structure–electronic configuration relationship in which the Mn-organic ligands modulate the electronic state of Ir and thereby enhance its catalytic activity.

Dual Enzyme-Mimetic Activity for ROS and O₂ Generation

The engineered IMM exhibits two complementary catalytic functions: ROS generation and O₂ evolution.

Under tumour-microenvironment-mimicking conditions, IMM rapidly decomposes H₂O₂ and generates oxygen, reaching an O₂ concentration of 44.54 mg L^-1 within 100 s at 10 μg mL^-1 IMM.

Its peroxidase-like activity is also substantially enhanced compared with conventional Ir/C, with a maximum reaction velocity of 2.37 μM s^-1 and a turnover number of 134.7 × 10^-3 s^-1.

Importantly, X-ray irradiation further amplifies ROS production.

The generated ROS include •O₂⁻ and ¹O₂, while in situ FTIR measurements identify *OOH and *OH as key reaction intermediates.

DFT calculations indicate that ligand-induced electronic modulation weakens the adsorption of *OOH from −1.67 eV on Ir/C to −1.59 eV on IMM, facilitating intermediate desorption and accelerating catalytic turnover.

Thus, IMM functions as a catalytic platform that converts the H₂O₂-rich tumour microenvironment into both oxygen and highly reactive oxygen species, providing two complementary mechanisms for overcoming tumour hypoxia and enhancing radiation-induced oxidative damage.

Enhancing Radiotherapy by Relieving Hypoxia and Blocking DNA Repair

The biological consequences of this catalytic activity were subsequently investigated under hypoxic conditions.

In CT26 tumour cells, the combination of IMM and X-ray irradiation produced the highest apoptosis rate, reaching 43.17% ± 1.33%, while also strongly suppressing tumour-cell proliferation and migration.

The enhanced therapeutic effect originates from the synergistic generation of ROS and O₂.

IMM-generated O₂ alleviates tumour hypoxia, while ROS directly damage cellular components and amplify the oxidative stress induced by irradiation.

Consistently, IMM treatment substantially reduces HIF-1α expression under hypoxic conditions, indicating effective hypoxia reversal.

At the same time, RT+IMM treatment produces pronounced γ-H2AX signals and maintains elevated DNA double-strand breaks, demonstrating that IMM not only increases radiation-induced DNA damage but also suppresses DNA damage repair.

From Local Tumour Killing to Systemic Antitumor Immunity

Beyond direct tumour-cell killing, IMM-augmented RT induces immunogenic cell death (ICD).

The combined treatment promotes the release of damage-associated molecular patterns (DAMPs), including ATP and HMGB1, together with increased surface exposure of calreticulin.

These signals can facilitate antigen presentation and stimulate adaptive antitumor immunity.

In vivo studies further demonstrate that IMM-augmented RT remodels the tumour microenvironment.

The treatment promotes tumour-vessel normalisation, alleviates hypoxia, and enhances the recruitment and activation of immune cells.

In particular, increased CD8⁺ T-cell activation and dendritic-cell abundance suggest that IMM can help transform an immunosuppressive tumour microenvironment into one that is more favourable for antitumor immune responses.

Synergy with Anti-PD-1 Therapy Generates Antitumor Memory

A particularly important feature of this work is that the therapeutic effect of IMM extends beyond the irradiated tumour.

When IMM-augmented RT was combined with anti-PD-1 therapy, the treatment enhanced systemic antitumor responses and suppressed both primary and distant tumour lesions.

The treatment also increased CD8⁺ T-cell activation as well as populations of central memory T cells (TCMs) and effector memory T cells (TEMs), providing evidence for the establishment of sustained antitumor immune memory.

This combination therefore establishes a therapeutic cascade:

IMM → ROS/O₂ generation → hypoxia relief + DNA damage → immunogenic cell death → immune activation → anti-PD-1-enhanced systemic immunity → antitumor memory.

Such a strategy moves radiotherapy beyond localised tumour destruction toward a systemic therapeutic response capable of targeting distant lesions and reducing the risk of recurrence.

Suppressing Radioresistant Tumours and Lung Metastasis

The therapeutic potential of IMM was further validated in more clinically relevant models.

In a humanised patient-derived xenograft (PDX) model generated from recurrent head and neck tumours after radiotherapy, IMM-augmented RT significantly suppressed tumour growth, whereas RT alone showed limited therapeutic efficacy.

These findings indicate that IMM can enhance the radiosensitivity of radioresistant tumours.

In a spontaneous lung-metastasis breast cancer model, IMM-augmented RT produced sustained tumour suppression for 30 days after treatment.

Bioluminescence imaging showed complete tumour regression in the IMM-augmented RT group, while CT imaging and H&E staining revealed no detectable lung metastases in treated mice, in contrast to metastatic lesions observed in the control and RT groups.

Toward Systemic and Durable Cancer Therapy

Overall, this study presents an IrMn-cluster-based artificial metalloenzyme that integrates catalytic therapy, radiotherapy, and immunotherapy.

By transferring electron density from Mn-organic ligands to Ir clusters, IMM creates highly active catalytic centres capable of efficient ROS and O₂ generation.

This catalytic activity simultaneously alleviates tumour hypoxia, enhances radiation-induced DNA damage, and inhibits DNA repair, resulting in potent tumour-cell apoptosis.

More importantly, IMM-augmented RT promotes immunogenic cell death and remodels the tumour microenvironment, while its combination with anti-PD-1 therapy activates systemic antitumor immunity and establishes long-lasting immune memory.

The efficacy of this strategy has been demonstrated in radioresistant PDX and spontaneous lung-metastasis models, highlighting its potential for treating aggressive tumours and preventing metastatic progression and recurrence.

This work provides a promising bioinspired nanomedicine platform that transforms radiotherapy from a primarily local treatment into a coordinated strategy integrating radiosensitization, hypoxia modulation, tumour immune activation, and long-term antitumor memory, offering new opportunities for the treatment of malignant and radioresistant tumours.

Source: Shanghai Jiao Tong University Journal Center