Iron oxide core oil-in-water emulsions as a multifunctional nanoparticle platform for tumor targeting and imaging

Abstract

Nanoemulsions are increasingly investigated for the delivery of hydrophobic drugs to improve their bioavailability or make their administration possible. In the current study, oil-in-water emulsions with three different mean diameters (30, 60, and 95 nm) were developed as a new multimodality nanoparticle platform for tumor targeting and imaging. To that aim, hydrophobically coated iron oxide particles were included in the soybean oil core of the nanoemulsions to enable their detection with magnetic resonance imaging (MRI), while the conjugation of a near infrared fluorophore allowed optical imaging. The accumulation of this novel nanocomposite in subcutaneous human tumors in nude mice was demonstrated with MRI and fluorescence imaging in vivo, and with Perl's staining of histological tumor sections ex vivo.

Figure 1. Concept, size determinations and relaxometry

(A) Schematic depiction of the three different sized nanoemulsions used in this study. (B) Dynamic light scattering (DLS) size measurements and photographs of the nanoemulsion preparations. (C) Negative stain transmission electron microscopy (TEM) images of the corresponding formulations (smallest size left). (D) Corresponding values for the longitudinal (r₁) and the transverse (r₂) relaxivities (n=3, mean ± standard deviation). (E) Zeta potential values.

Figure 2. Pharmacokinetics

(A) Chart showing normalized pharmacokinetic curves of the three nanoemulsions after intravenous injection into nude mice. (B) In vivo NIR fluorescence imaging series showing the accumulation of the 30 nm nanoemulsion in a subcutaneous tumor after intravenous injection. (C) Region of interest (ROI) fluorescence analysis to determine the tumor to skin ratio, i.e. the quotient of the fluorescence photon count from the tumor and the skin determined in a ROI of the same size, for the three different nanoemulsions after intravenous administration.

Figure 3. MR images of nude mice bearing subcutaneous EW7 tumors, injected with the three different nanoemulsions

(A) T₂-weighted MR images of the pre-scans (TR 2500 ms, TE 53.3 ms), (B) corresponding T₂-weighted MR images 24 h after intravenous injection. The insets show the enlarged MR images of the tumors, respectively. White arrows indicate local hypointense regions within the tumor caused by iron oxide accumulations. (C) 3D images that show the proton density MR image (grey), the whole tumor in 3D (transparent green) and the areas of iron oxide deposition in red. The inset images show an oblique view of the tumor with contrast agent in order to illustrate its 3D structure.

Figure 4. Correlation between MRI and histology

(A) T₂-weighted MR image (TR 2500 ms, TE 53.3 ms) of a subcutaneous EW7 tumor in a nude mouse. (B) Corresponding T₂-weighted MR image 24 h after injection with the 30 nm nanoemulsion. The hypointense signal within the yellow outline indicates a local area of high iron content. (C) Image of a Perl’s stained histological section of the same tumor showing the iron deposits as blue stained areas. The inset depicts a higher magnification. The area of signal loss seen in the MR image from (B) matches the location of the iron staining (yellow outline) in the histology image from (C).