Biodistribution of radioiodinated near infrared emitting quantum dot using Bolton-Hunter reagent

Objectives Quantum dots (QDs)have been employed for various applications in cancer biology, immunology, and cell therapeutics. However, biodistribution and quantification of QDs by in vivo fluorescence imaging is limited by tissue absorption of light. In this study, QDs were easily labeled with radioiodine using Bolton-Hunter reagent and biodistribution evaluated by fluorescence and radioactivity of radioiodinated QDs.

Methods The Bolton-Hunter reagent (N-succinimidyl-3-[4-hydroxyphenyl]propionate;SHPP) and water soluble SHPP (sulfo-SHPP) were used for radioiodination of near infrared emitting QDs (Qdot800 ITK Amino(PEG), 21 nm). Both reagents were compared in radiolabeling efficiency (%) and quantum yield for determining optimal radiolabeling condition. ¹²⁵I labeled QDs using sulfo-SHPP were intravenously injected into BALB/c mice (1.11 MBq/25 pmol). Biodistribution and fluorescence imaging of radiolabeled QDs were performed at 2 h and 24 h.

Results The radiolabeling efficiency of SHPP and sulfo-SHPP was 27.6 ± 6.1% and 33.4 ± 2.0%, respectively. The quantum yields of both reagents were decreased to 51.1 ± 1.2% and 75.4 ± 2.2%, respectively. In vivo fluorescence images, signals were mainly detected in the liver at all time point. However, ex vivo fluorescence images showed signals in liver, lung, spleen and femur at 2 and 24 h postinjection. The biodistribution by ex vivo gamma counting was similared with that by ex vivo fluorescence image.

Conclusions Radioiodination of QDs using sulfo-SHPP showed higher labeling efficiency and lower reduction of quantum yield than that using SHPP. QDs was predominantly accumulated in reticuloendothelial system such as liver and spleen. These results suggest that radiolabeling method using sulfo-SHPP could be easily used in the biodistribution and quantification of nanoparticles in vivo