Integrity of lipid nanocarriers in bloodstream and tumor quantified by near-infrared ratiometric FRET imaging in living mice

Abstract

Lipid nanocarriers are considered as promising candidates for drug delivery and cancer targeting because of their low toxicity, biodegradability and capacity to encapsulate drugs and/or contrasting agents. However, their biomedical applications are currently limited because of a poor understanding of their integrity in vivo. To address this problem, we report on fluorescent nano-emulsion droplets of 100 nm size encapsulating lipophilic near-infrared cyanine 5.5 and 7.5 dyes with a help of bulky hydrophobic counterion tetraphenylborate. Excellent brightness and efficient Förster Resonance Energy Transfer (FRET) inside lipid NCs enabled for the first time quantitative fluorescence ratiometric imaging of NCs integrity directly in the blood circulation, liver and tumor xenografts of living mice using a whole-animal imaging set-up. This unique methodology revealed that the integrity of our FRET NCs in the blood circulation of healthy mice is preserved at 93% at 6 h of post-administration, while it drops to 66% in the liver (half-life is 8.2 h). Moreover, these NCs show fast and efficient accumulation in tumors, where they enter in nearly intact form (77% integrity at 2 h) before losing their integrity to 40% at 6 h (half-life is 4.4 h). Thus, we propose a simple and robust methodology based on ratiometric FRET imaging in vivo to evaluate quantitatively nanocarrier integrity in small animals. We also demonstrate that nano-emulsion droplets are remarkably stable nano-objects that remain nearly intact in the blood circulation and release their content mainly after entering tumors.

Functionalizing Nanoemulsions with Carboxylates: Impact on the Biodistribution and Pharmacokinetics in Mice

“…Using nanocarriers is a realistic solution for performing an efficient drug targeting, and thus an accumulation of the drug specifically on the desired location and not in the healthy tissues. Drug targeting is particularly crucial in antitumor therapies, taking benefit of the particular physico‐chemical and physiological properties of the tumor microenvironment for enhancing the nanocarrier accumulation . Associating the drug with a nanocarrier will, after in vivo administration, modify its biodistribution, pharmacokinetics, and elimination pathway in comparison with administrating the drug alone.…”

Efficient co-delivery of immiscible hydrophilic/hydrophobic chemotherapeutics by lipid emulsions for improved treatment of cancer

“…NIRF imaging is now widely accepted as one of the convenient methods to mimic the drug biodistribution in vivo. 48,49 NIRF imaging was applied to trace the biodistribution of LEs. As shown in Figure 8, most of the free DiR were distributed in the liver and spleen, while scarcely in the tumor at all time intervals.…”

Real‐Time Monitoring of Nanoparticle Formation by FRET Imaging

“…Upon nanoemulsion formation, the FRET pair was spontaneously incorporated into the oil core, triggering energy transfer due to the close proximity of the dye molecules. [14] As a result, the donor (DiO) peak’s intensity decreased while that of the FRET peak (DiO excited, DiI emission observed) increased (Figure 1b). The FRET/DiO intensity ratio is linearly related with the DiI/DiO concentration ratio (Figure 1c) and thus can be used as a measure of nanoemulsion formation progress.…”