PVP-modified Multifunctional Bi₂WO₆ Nanosheets For Enhanced Cancer Radiotherapy

Objective:Malignant tumors are one of the main causes of human death.The clinical treatment methods for malignant tumors are usually surgery,chemotherapy,radiotherapy,high-intensity focused ultrasound therapy,etc.Radiotherapy,as a traditional and effective cancer treatment method,is widely used in clinical practice.During radiotherapy,ionizing radiation reacts with substances in tumor cells,and ionizing radiation can directly or indirectly react with biomolecules（such as proteins,lipids,etc.）in tissues,resulting in cell damage or apoptosis.However,in the course of clinical treatment,the indirect damage of ionizing radiation to normal tissues,the hypoxic environment inside tumor cells,and the radioresistance of tumor cells limit the further development of radiotherapy in clinical practice to a certain extent.With the in-depth study of nanomaterials,multifunctional inorganic high-atom nanomaterials are expected to be used as radiosensitizers to enhance the effect of tumor radiotherapy.Tungsten and bismuth contain high atomic coefficient elements,which have strong X-ray energy attenuation ability.In this study,we synthesized Bi₂WO₆nanosheets to study their radiosensitization effect and CT imaging ability on cancer.Methods:In our study,we first synthesized Bi₂WO₆nanosheets by a simple hydrothermal method,and modified polyvinylpyrrolidone（PVP）on their surface to make them more stable.The morphology,size and distribution of Bi₂WO₆were observed by transmission electron microscopy（TEM）,and whether the synthesized nanomaterials were Bi₂WO₆was verified by XRD spectrum.The cytotoxicity of PVP-Bi₂WO₆nanosheets on CAL27 cells was detected by CCK-8 assay.The apoptosis rate under different irradiation doses was analyzed by flow cytometry.The effect of PVP-Bi₂WO₆on the proliferation ability of tumor cells after X-ray irradiation was detected by clonogenic assay.ROS experiments were performed to verify that cells co-cultured with PVP-Bi₂WO₆nanosheets could significantly increase their intracellular ROS levels under x-ray irradiation.γ-H2AX immunofluorescence experiments were performed to detect that cells co-cultured with PVP-Bi₂WO₆nanosheets could increase the level of intracellular DNA double-strand breaks and promote cell apoptosis after X-ray irradiation.In animal experiments,BALB/c Nude mice were selected to construct a squamous cell carcinoma model,and 24 hours after the injection of PVP-Bi₂WO₆nanosheets through the tail vein,CT imaging was performed to evaluate the CT imaging ability of PVP-Bi₂WO₆.Tumor-bearing mice were X-rayed,and tumor volume and body weight of nude mice were continuously monitored for the next 18 days.After the animal experiment,the tumor was photographed to compare the therapeutic effect.The biosafety of the treatment was assessed by hematological testing and histopathological testing of major organs.Results:The TEM images showed that the size distribution of PVP-Bi₂WO₆nanosheets was relatively uniform without aggregation.In the XRD spectrum,the position of the diffraction peak corresponds to the height of the standard PDF card of bismuth tungstate,which proves that the nanomaterial is indeed PVP-Bi₂WO₆nanosheets.CCK-8 experiments demonstrated that PVP-Bi₂WO₆nanosheets was less cytotoxic.Flow cytometry experiments proved that cells co-cultured with PVP-Bi₂WO₆nanosheets could increase their apoptotic rate after X-ray irradiation.Analysis of colony formation experiments showed that PVP-Bi₂WO₆nanosheets could effectively reduce the proliferation ability of cells and reduce cell colony formation under X-ray irradiation.The results of the ROS experiment showed that the tumor cells incubated with PVP-Bi₂WO₆nanosheets could improve the ability of the cells to generate a large amount of ROS after being irradiated by X-rays.Theγ-H2AX experiment showed that PVP-Bi₂WO₆nanosheets can effectively enhance the ability of DNA double-strand breaks in cells under X-ray irradiation.These multifunctionalities endow the PVP-Bi₂WO₆nanosheets with enhanced radiotherapeutic effects in animal models.In addition,PVP-Bi₂WO₆nanosheets can also be used as a contrast agent for X-ray CT imaging,and the imaging effect is obvious.Conclusion:1.PVP-Bi₂WO₆nanosheets have a large surface area and a strong ability to absorb X-rays.After co-culture with cells,X-ray irradiation can increase the level of intracellular ROS,promote cell apoptosis,and reduce cell proliferation.2.PVP-Bi₂WO₆nanosheets are expected to be used as radiosensitizers and CT contrast agents to improve the effect of radiotherapy.