PEG conjugation of a near-infrared fluorescent probe for noninvasive dual imaging of lung deposition and gene expression by pulmonary gene delivery

Abstract

Dual imaging of lung deposition and gene expression following the pulmonary delivery of a gene formulation is useful for a precise analysis of gene transfection efficiency in vivo. As a novel probe for evaluating lung deposition, in this study, a poly(ethylene glycol)-conjugated near-infrared fluorescent probe (PEG-NIRF) was newly synthesized, and compared with indocyanine green (ICG), for application to pDNA/polyethyleneimine (PEI) complex. PEG-NIRF had superior characteristics including a larger Stokes shift (absorption maximum, 662 nm; emission maximum, 772 nm) and relatively equivalent fluorescence intensity compared with ICG. ICG affected the physicochemical properties of pDNA/PEI complex with a loss of fluorescence intensity, while PEG-NIRF did not. Experiments in mice demonstrated that PEG-NIRF showed greater lung localization than ICG following pulmonary co-delivery with pDNA/PEI complex, indicating the possibility of accurately evaluating lung deposition. Moreover, it was clarified that the evaluation of lung deposition by PEG-NIRF even at 60 min could be significantly correlated with gene expression in each mouse following pulmonary co-delivery with pDNA/PEI complex. These results suggest that PEG-NIRF is widely applicable to the dual imaging of the lung deposition and gene expression of inhaled gene formulations.