A Mitochondria-targeted Thiazoleorange-based Photothermal Agent For Enhanced Photothermal Therapy For Tumors

Photothermal therapy（PTT）is a method of employing photothermal agents（PA_S）to effectively convert light energy into heat energy,so as to ablate tumor cells to achieve the treatment of cancer.And PTT can reduce the adverse reactions caused by traditional radiotherapy and chemotherapy.Small organic molecules have broad application prospects in PTT because of their easy modification,high purity and good reproducibility.The fluorescence probes based on thiazole orange dye shows strong absorption,which represents a kind of contrast agent for imaging.However,whether it can be used as PA for PTT remains to be explored.In order to investigate if it has photothermal properties,and considering the thermal sensitivity of Mitochondria（Mito）,we designed and prepared a Mito-targeted organic small molecule photothermal therapeutic agent（Mito-BWQ）,it consists of three main parts:thiazole orange matrix unit,triphenylphosphine unit for mitochondrial localization and p-methylbenzoic acid group.The specific contents include:（1）The successful preparation of Mito-BWQ was confirmed by ¹HNMR,¹³C NMR and mass spectrum.The results of UV spectrum showed that the maximum UV absorption of Mito-BWQ was at 575 nm,and the maximum emission peak of 630 nm could be produced at this wavelength.（2）By studying the photothermal properties of Mito-BWQ,it was found that the photothermal conversion efficiency（PCE）of Mito-BWQ increased with the increase of laser power at a certain concentration,and increased with the increase of Mito-BWQ concentration at a certain laser power.The photothermal stability of Mito-BWQ is good.（3）In order to detect the biological properties of Mito-BWQ,we used two cell models,including breast cancer cell（MCF-7）and glioma cell（U87）.First of all,the CCK-8 toxicity test showed that Mito-BWQ could cause damage to cells only under external laser irradiation,while Mito-BWQ had no damage to cells under no external laser irradiation,and the photothermal toxicity was further confirmed by Calcein-AM and PI double staining experiments.Then we preliminarily determined that the location of Mito-BWQ staining was cytoplasm by cell imaging experiment,and further determined that the specific target site of Mito-BWQ staining was mitochondria by organelle co-localization experiment.Finally,the results of photothermal assay showed that Mito-BWQ had a good photothermal conversion in cells.（4）For the sake of evaluating the antitumor effect of Mito-BWQ in vivo,the subcutaneous breast cancer xenograft model was established.Photothermal imaging in vivo results showed that the temperature of Mito-BWQ in tumor tissue rose rapidly to about49.5℃under external laser irradiation,exhibiting superior photothermal conversion.Fluorescence imaging in vivo results showed that the fluorescence reaches the maximum at the 12th hour,we speculated that Mito-BWQ had the most sufficient binding with mitochondria at that time,which also revealed that Mito-BWQ could be used as a fluorescence contrast agent.Moreover,Mito-BWQ combined with laser therapy significantly inhibited the growth of tumor,indicating that it coud be employed as an effective photothermal therapeutic agent.By monitoring the weight of mice and H&E staining of heart,liver,spleen,lung and kidney,it reflected that this research strategy had good biological safety,and Mito-BWQ had no obvious toxic and side effects on other tissues.In this project,a Mito-BWQ based on the matrix unit of thiazole orange was developed to enhance PTT.It has high PCE,low cytotoxicity and good biological safety,and it can achieve good anti-tumor effect in vivo.This study offers an important starting point for the construction of PAs based on thiazole orange,and provides a basis for further promoting the in-depth development of PAs anticancer research and treatment.