Bimetallic Nanozymes Regulate The Axial Conversion Of Reactive Oxygen Species(ROS) In Leukemia Cells

Acute myeloid leukemia（AML）is an aggressive malignant tumor of the hematopoietic system,accompanied by malignant proliferation of AML blasts and abnormal hematopoietic function.ROS derived from mitochondrial electron transport chain（ETC）or NOXs in AML cells mediates the continuous production of superoxide anion（O₂·-）in the cell,which is then quickly converted into stable H₂O₂ with the catalysis of superoxide dismutase（SOD）.There are two main conversion pathways for the generated H₂O₂,which can be further converted into the most cytotoxic·OH with the help of peroxidase（POD）or Fe²⁺to achieve a peroxidation conversion（O₂·-→H₂O₂→·OH）,or will be decomposed into H₂O and O₂ under the action of antioxidants such as CAT enzyme or GSH to achieve an antioxidant conversion（O₂·-→H₂O₂→H₂O/O₂）.Therefore,we used nanozymes assembly technology（SOD-like enzymes,POD-like enzymes,CAT-like enzymes）to assemble two kinds of dual-enzyme relay systems that can mimic intracellular SOD/POD or SOD/CAT to conduct a selective intervention to intracellular ROS peroxidation axial conversion or anti-oxidation axial transformation.The main research contents are as follows:（1）Cerium oxide nanoparticles（CeO₂ NPs）and ferric oxide nanoparticles（Fe₃O₄NPs）were assembled into the bimetallic nanozymes（Fe₃O₄@CeO₂）with a coronal shape.Fe₃O₄@CeO₂ has the relay catalytic function of SOD/POD,where CeO₂ NPs is to provide a SOD-like catalytic unit to realize the conversion of O₂·-→H₂O₂,Fe₃O₄NPs is to provide a POD-like catalytic unit to realize the conversion of H₂O₂→·OH.Compared to the physically mixed（Fe₃O₄+CeO₂）,proximity-assembled Fe₃O₄@CeO₂ obtains the enhanced POD-like activity and SOD-like activity.This assembly of Fe₃O₄@CeO₂ at sub-nanometer distance can in vitro effectively carry out the relay catalytic conversion to realize the peroxidation axial conversion of ROS（O₂·-→H₂O₂→·OH）.In AML cells,Fe₃O₄@CeO₂ also aggravates the axial transformation of endogenous ROS（O₂·-→H₂O₂→·OH）,which is manifested in the time-dependent decrease of endogenous O₂·-levels as well as the time-dependent increase of H₂O₂ and·OH levels after Fe₃O₄@CeO₂ treatment.Moreover,the treatment of Fe₃O₄@CeO₂ induces AML cells damage,showing the significant toxicity to AML cells.In the treatment experiment of AML mouse model,Fe₃O₄@CeO₂ shows the good therapeutic effect,not only reducing the spleen index,but also greatly prolonging the survival time of the mice.In short,Fe₃O₄@CeO₂drives the peroxidation axial conversion of endogenous ROS（O₂·-→H₂O₂→·OH）,which has a therapeutic effect on AML,indicating the value of this ROS directional relay conversion mechanism and providing an ideal tool for safe and effective intervention of ROS and adaptive ROS homeostasis in cancer cells.（2）Cerium oxide nanoparticles（CeO₂ NPs）and gold nanoparticles（Au NPs）were assembled into the bimetallic nanozymes（Au@Ce NPs）with a coronal shape.Au@Ce NPs has the relay catalytic function of SOD/CAT,where CeO₂ NPs is to provide a catalytic unit that mimics the SOD enzyme to realize the conversion of O₂·-→H₂O₂,Au NPs is to provide a CAT-like catalytic unit to realize the conversion of H₂O₂→H₂O/O₂ in the physiological p H condition.Upon the oxidation of H₂O₂,the assembled Au@Ce NPs can enhance the local plasmon resonance on the surface of Au NPs,and the active surface electrons can be captured by the CeO₂ NPs to resist the oxidation of H₂O₂ and maintain the stability of the Ce³⁺/Ce⁴⁺ratio.Therefore,Au@Ce NPs exhibits the high-performance SOD-mimicking enzyme activity even in the oxidative stress condition and successfully promotes the relay antioxidant axial transformation of ROS in AML cells（O₂·-→H₂O₂→H₂O/O₂）.This mechanism consistently and effectively reduced intracellular ROS levels,blocked the second messenger action of endogenous steady-state high levels of ROS,significantly blocked the AML cell cycle in G1 phase and inhibited AML cell proliferation.Furthermore,continuous tail vein treatment with Au@Ce NPs significantly suppressed sarcoma growth and prolonged the survival of mice in a therapeutic study of AML cell-transplanted nude mouse subcutaneous tumor model.Histological analysis also showed that Au@Ce NPs treatment reduced leukocyte infiltration in liver tissues and decreased cell proliferation indicators in the sarcoma tissues.In conclusion,Au@Ce NPs-driven antioxidative axial transformation of endogenous ROS from O₂·-→H₂O₂→H₂O/O₂ exhibits a proliferation-inhibitory effect on AML cells,further demonstrating the potential value of the nanoenzyme relay assembly technology in mediating ROS-directed relay catalytic transformation.（3）In the systemic AML mouse model of NOD-SCID mice,the therapeutic effects of Fe₃O₄@CeO₂ and Au@Ce NPs were compared.Compared with the survival period in the normal saline group,the survival period of the mice treated by Fe₃O₄@CeO₂ and Au@Ce NPs was both prolonged,but Fe₃O₄@CeO₂ showed a better effect on prolonging the survival time of mice.This indicates that when treating AML by interfering with endogenous ROS,the axial transformation of peroxidation（O₂·-→H₂O₂→·OH）mediated by Fe₃O₄@CeO₂ may be more advantageous than that of the axial transformation of antioxidation（O₂·-→H₂O₂→H₂O/O₂）by Au@Ce NPs.