Gadolinium chloride augments tumor-specific imaging of targeted quantum dots in vivo

Abstract

Nonspecific sequestration of nanoparticles by the reticulo-endothelial system (RES) results in the degradation of image quality of nanoparticle-based imaging. We demonstrate that gadolinium chloride (GdCl3) pretreatment inactivates RES macrophages, thereby increasing circulatory time and amplifying the tumor-specific signal of conjugated nanoparticles in vivo. The experimental results were validated using compartmental modeling, and the rate parameters for the observed kinetics pattern were estimated. This pretreatment strategy could have broad applicability across biomedical applications utilizing theranostic nanoparticles that are sequestered by the RES.

Figure 1

In vivo fluorescence images of animals at 0 h (“Background”), 3 min, 1 h, and 4 h after intravenous injection of QD, EGF-QD, or GdCl₃ pretreatment followed by EGF-QD.

Figure 2

Estimated mean tumor-to-background ratios (mean ± SE) from animals injected with (a) QD, (b) EGF-QD, or (c) GdCl₃ followed by EGF-QD. The three phases of influx, efflux, and accumulation are represented as I, II, and III, respectively. Based on the observed kinetic pattern, a two-compartment model was proposed to estimate the kinetic rate parameters (d) before and (e) after apparent dynamic equilibrium. The two-compartment model fit (blue dotted lines) to the tumor-to-background ratios before and after dynamic equilibrium is illustrated in (f) and (g), respectively, with the corresponding rate parameters represented in tables below the figures.

Figure 3

Ex vivo fluorescence images of organs harvested 4 h after (a) QD injection, (b) EGF-QD injection, and (c) GdCl₃ pretreatment followed by EGF-QD injection. (d) A cartoon representing the arrangement of organs where B, Lu, H, Li, S, K, N, and T represent the brain, lungs, heart, liver, spleen, kidney, lymph node, and tumor, respectively. The corresponding fluorescence levels (mean ± SE) from the extracts of tumor and liver tissues are represented in (e), where * represents the statistical significance (p < 0.001) based on an unpaired Student’s t test.

Figure 4

Fluorescence confocal images of frozen liver, tumor, and lymph node extracted 4 h after QD injection, EGF-QD injection, and GdCl₃ pretreatment followed by EGF-QD injection. Green represents autofluorescence, and red represents QD fluorescence. (Scale bar = 50 μm).

Figure 5

Activated Kupffer cell–specific anti-CD68 immunofluorescence staining of liver tissues extracted 4 h after (a) QD injection, (b) EGF-QD injection, and (c) GdCl₃ pretreatment followed by EGF-QD injection. Green represents CD68 staining, and red represents QD fluorescence. (Scale bar = 50 μm). (d) Quantified CD-68 stained activated Kupffer cells in the liver tissues from each group averaged over different field of views (n=7) shows statistically significant (p < 0.001) difference with and without GdCl₃ pretreatment.

Figure 6

Transmission electron microscopy image of liver tissue extracted 4 h after (a) EGF-QD injection and (b) GdCl₃ pretreatment followed by EGF-QD injection. The arrows in (a) represent the accumulation of QDs in the endocytotic vesicles within the Kupffer cells, and the insert represents the enlarged version of the vesicles containing the QDs. The labels V, KC, and RBC represent the vesicles, Kupffer cells, and red blood cells, respectively. (Scale bar = 5 μm).