Radioiodine Labelled Melanin Nanoparticles And Its Biomedical Applications

Purpose:Radioiodine is widely used in nuclear medicine,mainly serving as tracer and therapeutic agent,benefit from its various radioactive isotopes of iodine.Implantation of ¹²⁵I particles in neoplasms has been widely used for brachytherapy.However,drawbacks still exit such as metal toxicity,easy to fall off and poor tolerance.This study attempt to utlize melanin,a kind of natural materials,to prepare the melanin nanoparticles?MNPs?,with the diameter of 4-5 nm.Two methods,chloramine T method and silver iodide precipitation method,will be used to label MNPs.Then the labeling yield and stability will be investigated.Methods:Chloramine T method and silver ions precipitation method were used to label MNPs.The non-radioactive MNP-Ag-I,MNP-I were prepared and characteristized first.Subsequently,the labeling rates and stabilities in PBS and serum of MNP-Ag-¹³¹I,MNP-¹³¹I were investigated by dialysis and TLC,respectively.The toxicity of MNP-Ag-I on PC-3 and L929 cells was detected by MTT and acridine orange?AO?/propidium iodide?PI?double-staining experiment.Meanwhile,MTT assay was used to detect the cytotoxicity of MNP-Ag-¹³¹I.Cherenkov imaging was performed by intratumoral injection of MNP-Ag-¹³¹I and the intratumoral retention time was measured.Tumor volume was measured to observe the curative effect.After treatment,HE staining was used to identify whether the normal tissues were injuryed.Immunohistochemistry?IHC?staining was used to detect the expression of Ki67 after treatment.Results:MNPs can be successfully labeled both by chloramine T method and silver iodide method.The labeling time of chloramine T method was 30 minutes,and the labeling rate was 66.27±1.87%.The 48-hour stabilities of MNP-I in serum and PBS were 46.69±9.92%and 60.43±10.57%respectively.Silver ions precipitation method costed only 2 minutes,with the labeling rate of 99.69±0.43%.48 hours latter,the stabilities in serum and PBS were 96.80±1.46%and 96.63±0.13%respectively.In vitro cell viability assays showed that L929 and PC-3 cells didn't be injuryed after treated by MNP-Ag and MNP-Ag-I even the concentration reached 0.4 mg/mL.At the same time,MNP-Ag-¹³¹I can kill PC-3 cells effectively,whose IC50 value was determined to be 75?Ci/mL.The in vivo cherenkov imaging showed that the retention time of MNP-Ag-¹³¹I was about 8 hours.7 days after administeration,the tumour volume of the MNP-Ag-¹³¹I group was similar to the initial volume,while the other two group were nearly 1.5times comparing with the initial volume.Meanwhile,during the therapeutic period,the body weight of these mice didn't change significantly.After the whole therapy,there was no pathological change in the main organs?liver,kidney,spleen,lung and heart?of mice from all groups detected by hematoxylin and eosin?H&E?staining,suggesting no systematic toxicity induced by MNP-Ag-131I and 131I.The radio-MNPs prepared by this way could be used in the brachytherapy,whose further research is undergoing.Conclusion:Silver ions precipitation method can successfully label the natural material melanin with high labeling rate and good stability.The significant toxicity in vivo or in vitro didn't be observed obviously.Considering this,it can be utlized in SPECT imaging,Cherenkov imaging and brachytherapy.With remarkable curative effect,the MNP-Ag-¹³¹I needs to be further explored.