Effects Of Iridium Oxide Nanozymes Mediated PTT/PDT For Combined Therapy Of Colorectal Cancer

Part 1.Synthesis,Characterization and Performance evaluation of IMPBcAims:Iridium oxide（Ir O₂）has photothermal properties and catalase-like（CAT）activity.We aimed to construct iridium-based nanozymes with CAT activity and loading photosensitizer Ce6,which can realize enhanced photodynamic therapy（PDT）by utilizing the abundant hydrogen peroxide（H₂O₂）in tumor microenvironment（TME）,and formed a synergistic enhancement of the therapeutic effect on colorectal cancer（CRC）with photothermal therapy（PTT）.In this part,IMPBc was synthesized,and its morphology was characterized,then evaluated its properties and stability.Methods:Ir Cl₃and PVP were dissolved in alkaline solutions by magnetic stirring for12 hours.A thin layer of MSN was coated on the nanoparticles,PDA was then coated on the surfaces of the Ir O₂@MSN particles under alkaline conditions,then a BSA modifier was grafted onto the Ir O₂@MSN@PDA.After adsorbing Ce6,we obtained IMPBc.The physical and chemical properties of IMPBc were observed by scanning electron microscope（SEM）and Fourier transform infrared spectrometer（FTIR）.Spectrometer,oxygen probe and infrared camera were used to evaluate the drug release performance,CAT activity,photodynamic performance,photothermal performance and stability.Results:Colloidal-stable IMPBc were prepared through facile hydrolysis method,with a diameter of about 84 nm.The experimental results showed that IMPBc had large drug loading ratio（8.6%）and stable drug release performance（<12%）.IMPBc had CAT-like activity and maintained good catalytic activity even in acidic environment with p H=6.0 or high temperature environment at 80℃.Under laser irradiation,photosensitizer Ce6 could produce cytotoxic singlet oxygen（¹O₂）.In H₂O₂environment,IMPBc could increase ¹O₂concentration and enhance photodynamic performance.Photothermal conversion efficiency of IMPBc was 29.8%and it maintained good stability in periodic photothermal experiments.Conclusions:The IMPBc was an versatile artificial nanzymes with CAT-like activity,who could maintain good catalytic activity even in the environment of low p H,high temperature and high H₂O₂,and exhibited excellent photodynamic performance and stable photothermal conversion performance.Thus providing a foundation for further synergistic PTT/PDT biomedicine studies.Part 2.Safety Evaluation of IMPBc and its Effects on CRCAims:In order to explore whether IMPBc could be transformed into clinical application,we evaluated its biosafety through the effects of IMPBc on L929 cells,mouse red blood cells（m RBC）,hemogram,biochemistry,histopathology and the biological distribution of silicon（Si）in mice.In further study,the effect of IMPBc mediated PTT/PDT on CRC cell HT29 and CRC tumor mice were discussed.Methods:The cytocompatibility was assessed by incubation of IMPBc with L929cells using CCK-8 kit and calcein AM/PI double staining.Hemolysis experiments were utilized to evaluate the effects of IMPBc on hemocompatibility.Hemogram,biochemistry and HE staining were used to observe the effects of IMPBc on the blood and vital organs of Kunming mice and evaluate its safety in vivo.ICP-OES was used to detect the biodistribution of silicon.HT29 cells co-cultured with IMPBc were irradiated by near infrared laser to achieve different modalities including PDT,PTT,enhanced PDT or combined PTT/PDT.Using CCK-8 kit and Calcein AM/PI double staining,we assessed the effect of IMPBc on HT29 proliferative activity;The tumor temperature changed in PTT of mice was recorded by a thermal camera;the effects of different modalities including PDT,PTT,PTT/PDT on CRC were evaluated by relative tumor volume.Results:IMPBc had no significant effect on L929 and m RBC within the experimental dose,showed excellent cyto-and hemocompatibility.Hemogram,biochemistry and HE staining were not differ among groups.The accumulation of Si in the liver and kidney was higher than that in other organs,but showed a decreasing trend with time.The results of calcein AM/PI double staining and CCK-8 kit both suggested that IMPBc could effectively kill CRC cells in vitro.Compared with the control group,the local temperature of the tumor increased significantly and the tumor volume decreased to various degrees in the mice,and no obvious CRC tissue growth was observed in the mice of the PTT/PDT combined treatment group.Conclusions:IMPBc,with good biosafety,could target tumor sites.Achieving PTT/PDT combined treatment of CRC with high efficiency and spatiotemporal controllability,IMPBc provided a new idea and basic support for the study of combination therapy of CRC.