Bismuth Sulfide Nanoparticles For Tumor Multimodal Imaging And Photothermal Therapy

Background:Cancer is still one of the biggest killers threatening human health,and there are many shortcomings in the traditional cancer treatment methods.With the rapid development of nanotechnology,nanomaterials have been widely used in the field of biomedicine,which also provides a new direction for the treatment of malignant tumors.Photothermal therapy（PTT）has been widely concerned because of its advantages of high efficiency,economy and minimally invasive.In the diagnosis of tumor,a single image often cannot provide complete disease information,and multiple imaging methods need to be combined.Through the design and construction of targeted nanomaterials,combining the two independent processes of diagnosis and treatment,the design of nanomaterials with the functions of multimodal imaging and photothermal therapy has become a research hotspot in recent years.Objective: In this study,rod-like Bi₂S₃ nanoparticles were designed and synthesized,and its applications in PA/CT bimodal imaging and photothermal therapy were explored.Methods: 1.Establish tumor-bearing mice model: the suspension of 200 μL containing 2×106 L-1 H22 cells was inoculated subcutaneously into the lower back of Kunming mice.After the tumor grew,the length and width of the tumor were measured with a vernier caliper every day,and then the volume was calculated.When the tumor reached 100 mm³,the target was reached.2.Sample characterization: physical properties such as sample morphology and hydrodynamic diameter were characterized by transmission electron microscope（TEM）and high resolution transmission electron microscope（HRTEM）.The pharmacokinetics and tissue distribution of the samples were evaluated in the Kunming mouse model.3.Photothermal conversion performance and stability test: a certain concentration of Bi₂S₃ nanorods PBS dispersion was placed in the centrifugal tube and an 808 nm laser with a power density of 1.0W /cm2 was used for continuous irradiation for 10 minutes.After the irradiation was stopped,the solution was naturally cooled to the ambient temperature,and an infrared thermal imaging device was used to measure the temperature change of the solution in real-time during the experiment.The above irradiation-cooling process is repeated for 3 times;4.Cell compatibility of samples and in vitro photothermal cytotoxicity tests: The survival rates of He La cells,MCF-7 cells and H22 cells before and after laser irradiation were analyzed by Methyl thiazolyl tetrazolium（MTT）method in vitro;5.In vitro PA/CT imaging experiment: plastic centrifuge tubes with different concentrations of samples were placed in PA and CT apparatus in order of concentration for imaging;6.In kunming mouse model evaluate pharmacokinetic and tissue distribution of sample: four without tumor-burdened kunming mice,the tail intravenous injection 100 mu L dose of 20 mg/kg of Bi₂S₃ nanorods material,after the injection of 0.5,1,2,5,8,14,24,40,50 h eyes take blood,blood samples treated with inductively coupled plasma emission spectrometer（ICP-and engage）determination of Bi ions content in blood samples,in order to evaluate pharmacokinetic sample.Eighteen tumor-bearing Kunming mice were randomly divided into 6 groups（n=3）.All mice were injected with 200 μL Bi₂S₃ nanorods containing 2.5 mg/m L Bi ion via tail vein.At 2,6,12,24,48 and 72 h after injection,the heart,liver,spleen,lung,kidney and tumor sites were sacrificed,respectively.After treatment,the content of Bi ion was determined by inductively coupled plasma emission spectrometer（ICP-OES）;7.In vivo PA/CT imaging experiment: Six tumor-bearing mice were selected for whole body imaging with PA/CT scanner（n=3）,and the samples were injected 12 hours later through the tail vein,and then PA/CT scanning was performed again.Finally,CT images were reconstructed by the reconstruction system;8.In vivo tumor photothermal therapy experiment:12 tumor-bearing mice were randomly divided into 4 groups（n=3）.Groups 1 to 4 were injected with normal saline,irradiated with 808 nm laser after injection of normal saline,injected with injection samples,irradiated with 808 nm laser,and the temperature changes in the tumor of mice were monitored by infrared thermal imager.Tumor length and width of the tumor-bearing mice were measured with a vernier caliper on the next day.Tumor volume was calculated according to the formula and the body weight of the mice was weighed on an electronic weight scale.After 7 days of recording,4 groups of mice were sacrificed and tumor tissues were taken for pathological section.Venous blood was collected for biochemical detection.Results :（1）Bi₂S₃ nanomaterials have uniform particle size and good crystallinity and dispersion.（2）After being irradiated by 808 nm laser for 10 minutes,the temperature of the sample can rise to 60℃.Under the same conditions,the temperature of PBS solution is only 23℃.After repeated irradiation-cooling process,the temperature rise and cooling of the sample were stable.（3）The survival rate of He La cells,MCF-7 cells and H22 cells without laser irradiation was nearly 100%;The survival rates of He La cells,MCF-7 cells and H22 cells were only 25%,23% and 21% after 10 minutes of 808 nm laser irradiation,respectively.（4）In the in vitro CT scan,the HU value of the sample increased with the increase of concentration.In the in vitro PA imaging,the photoacoustic signal value of the sample increases with the increase of the sample concentration,and it shows a good potential as a photoacoustic contrast agent when the excitation wavelength is 808 nm.（5）The pharmacokinetic curves of Bi₂S₃ nanorods showed that the metabolokinetics followed the classical second-order decay model,and the half-life of Bi₂S₃ nanorods was 0.365 h and 6.132 h,respectively.Bi₂S₃ nanoparticles mainly accumulate in the reticuloendothelial system,such as liver and spleen.（6）In vivo CT imaging results showed that compared with before injection,the HU value of the tumor site of mice was significantly increased after injection,and the image density was significantly enhanced.The same result also appeared in PA imaging.Compared with before the injection of the sample,the photoacoustic signal value of the tumor site of the mouse was significantly increased after the injection of the sample,forming a strong contrast.（7）Tumors in group 4 gradually shrank to unpalpable surface,while tumor growth in the other three groups was not inhibited.H&E staining of the exfoliated solid tumor revealed significant cell abnormalities and apoptosis.Blood biochemical results showed that the important indexes such as white blood cell count,red blood cell count,hemoglobin and mean red blood cell hemoglobin were normal.Conclusion :（1）This rod-like Bi₂S₃ nanomaterials have uniform particle size,good dispersion,low biological toxicity,long circulation time in vivo and can be highly enriched in tumor sites.（2）After 808 nm laser irradiation,Bi₂S₃ nanometer material can effectively convert 808 nm near-infrared photon energy into a large amount of heat,and then ablate tumor cells.（3）The photoacoustic signal intensity and HU value of PA/CT imaging of the novel Bi₂S₃ nanorods were positively correlated with the sample concentration.Under the appropriate sample concentration,the photoacoustic signal intensity and HU value of the tumor parts of mice after injection were much higher than before injection.（4）The rod-like Bi₂S₃ nanomaterial synthesized in this study can be used as photothermal therapeutic agent under the guidance of PA/CT bimodal imaging.