Selection of fluorescent dye for tracking biodistribution of paclitaxel in live imaging

Fluorescence imaging is widely used to determine biodistribution of drugs in mice. However, the dye distribution may not be able to exactly reflect the true distribution of drug molecules. We synthesized PTX-Cy5.5 and mPEG-PLA-Cy5.5, and then prepared dye-loaded nanoparticles (NPs) (Cy5.5, DiR, PTX-Cy5.5, and mPEG-PLA-Cy5.5), dye and PTX co-loaded NPs, and PTX-loaded NPs, respectively. The particle sizes of resulting NPs were between 42.7 nm and 68.8 nm, and Zeta potential was between -0.86 mV and -8.49 mV. The biodistribution of fluorescent NPs (dye-loaded NPs and dye and PTX co-loaded NPs) on Bel-7402 tumor-bearing mice was studied via in vivo fluorescence imaging assays, results of which suggested that Cy5.5 loaded NPs and Cy5.5 conjugates (PTX-Cy5.5 and mPEG-PLA-Cy5.5) formulated NPs can reflect the tissue distribution of PTX whether it was incorporated or not. However, DiR failed to reflect true tissue distribution of PTX unless it was co-loaded with PTX. Based on these results, a guidance for the selection of dyes in drug distribution investigations and disease-targeted treatment was presented.