Evaluation of tissue-clearing techniques for intraorgan imaging of distribution of polymeric nanoparticles as drug carriers

Abstract

Objective The development of drug delivery systems using nanocarriers requires intraorgan imaging techniques for evaluating the distribution of nanocarriers. In this study, we evaluated the tissue-clearing techniques for the imaging of polymeric nanoparticles, a nanocarrier, in the liver used as a model of pigment-rich organ in mice. Significance The intraorgan imaging method of polymeric nanoparticles was examined without sectioning of organ samples for evaluating the delivery efficiency in preclinical studies. Methods DiI-loaded polymeric nanoparticles and fluorescence-tagged tomato lectin for fluorescence labeling of liver general structures were intravenously administered to mice. Tissue-clearing treatment of the mouse liver was performed using ClearT2, ScaleSQ(0), clearing agent comprising fructose, urea, and glycerol for imaging (FUnGI), clear unobstructed brain/body imaging cocktails and computational analysis (CUBIC), and modified CUBIC techniques. Intraorgan fluorescence imaging in the liver was performed by confocal laser microscopy. Results ClearT2 treatment exhibited insufficient clearing capability in the mouse liver. Although CUBIC treatment exhibited the best clearing capability, the CUBIC caused DiI leakage. ScaleSQ(0), FUnGI, and modified CUBIC treatments exhibited better clearing capability than ClearT2 technique while preserving the DiI. In the fluorescence imaging, the CUBIC and modified CUBIC exhibited deeper visualization than with the ScaleSQ(0) and FUnGI; however, the CUBIC led to a change in DiI distribution. The modified CUBIC enabled the deepest visualization while preserving the distribution of DiI. Conclusion The intraorgan imaging method was established using modified CUBIC technique by the intravenous administration of fluorescence-tagged tomato lectin for evaluating the distribution of polymeric nanoparticles in mouse pigment-rich organs.