During tumor growth and development, elevated level of hydrogen peroxide (H₂O₂) is often exhibited in solid tumors, which renders tumor cells more resistant to therapeutic treatment. It has been proposed that if the accumulated H₂O₂ can be converted instead for damaging tumor cells, there may be more effective tumor therapy with a mindset of ‘give tumor a taste of its own medicine’.

Natural enzymes with peroxidase activity were found to convert H₂O₂ into toxic reactive oxygen species (ROS) which effectively kills tumor cells. To improve natural enzymes' sensitivity and low stability in unfavorable environment, enzyme mimics or artificial enzymes have been developed using chemical synthesis. However, the catalytic efficiency of traditional enzyme mimics is often insufficient.

In a study published in Nature Communications, Prof. YAN Xiyun at Institute of Biophysics of Chinese Academy of Sciences and Prof. GAO Lizeng at School of Medicine, Yangzhou University, reported a novel tumor catalytic therapy using nanozymes which convert O₂ and H₂O₂ to toxic ROS for tumor destruction. 

Based on the intrinsic enzyme-like properties (nanozymes) of nanomaterials, scientists developed a novel nanozyme using nitrogen-doped porous carbon nanospheres (N-PCNSs), a nanomaterial which owns excellent biocompatibility, to mimic four enzyme-like activities (oxidase, peroxidase, catalase, superoxide dismutase) in this study.

As N-PCNSs were biodegradable under physiological conditions, they found that these nanozymes were able to regulate intracellular ROS and boosted ROS generation by oxidase and peroxidase activities under acidic microenvironment.

To utilize the enzymatic performance for tumor therapy, ferritin was introduced by scientists to target tumors and deliver N-PCNSs to lysosome for controlling ROS generation. In vivo tests demonstrated that ferritin-N-PCNSs specifically suppress tumors in animal model, indicating that the nanozymes activities are controllable to perform the desired purpose.

Meanwhile, ferritinylation ensured the nanozymes’ specificity and delivery to the tumor.

This work demonstrated the feasibility of using nanozymes for tumor catalytic therapy.

"If decorated with the right surface modifications, nanoparticles can function as Trojan horses, transporting cell death-facilitating compounds to tumour cells. Here, the authors prepare a particle with four enzyme-like activities and show that ferritin can direct nanoparticles to tumour cells," said the editor of Nature Communications.