Optimization of In Vivo Studies by Combining Planar Dynamic and Tomographic Imaging: Workflow Evaluation on a Superparamagnetic Nanoparticles System

Abstract

Molecular imaging holds great promise in the noninvasive monitoring of several diseases with nanoparticles (NPs) being considered an efficient imaging tool for cancer, central nervous system, and heart- or bone-related diseases and for disorders of the mononuclear phagocytic system (MPS). In the present study, we used an iron-based nanoformulation, already established as an MRI/SPECT probe, as well as to load different biomolecules, to investigate its potential for nuclear planar and tomographic imaging of several target tissues following its distribution via different administration routes. Iron-doped hydroxyapatite NPs (FeHA) were radiolabeled with the single photon γ-emitting imaging agent [^99mTc]TcMDP. Administration of the radioactive NPs was performed via the following four delivery methods: (1) standard intravenous (iv) tail vein, (2) iv retro-orbital injection, (3) intratracheal (it) instillation, and (4) intrarectal installation (pr). Real-time, live, fast dynamic screening studies were performed on a dedicated bench top, mouse-sized, planar SPECT system from t = 0 to 1 hour postinjection (p.i.), and consequently, tomographic SPECT/CT imaging was performed, for up to 24 hours p.i. The administration routes that have been studied provide a wide range of possible target tissues, for various diseases. Studies can be optimized following this workflow, as it is possible to quickly assess more parameters in a small number of animals (injection route, dosage, and fasting conditions). Thus, such an imaging protocol combines the strengths of both dynamic planar and tomographic imaging, and by using iron-based NPs of high biocompatibility along with the appropriate administration route, a potential diagnostic or therapeutic effect could be attained.

Figure 1

Radio TLC of [^99mTc]TcMDP-^FeCaPs on ITLC-SG chromatography paper with saline (0.9% v/v) as eluent.

Figure 2

FLASH-kidney-spleen prescan (a); FLASH-kidney-spleen 10 min p.i. (b). Annotation shows the liver (yellow arrows) and the spleen (green arrows).

Figure 3

RARE-liver prescan (a); RARE-liver 10 min p.i. (b).

Figure 4

FLASH-kidney prescan (a); FLASH-kidney 60 min p.i. (b). Annotation shows the liver (yellow arrows) and the spleen (green arrows).

Figure 5

RARE-liver prescan (a); RARE-liver 60 min p.i. (b).

Figure 6

SPECT/CT imaging (NanoSPECT/CT, Mediso) of a mouse at 10 min p.i. (a) and a mouse at 60 min p.i. (b), showing accumulation in the liver (yellow arrows) and in the spleen (green arrows). Both mice were injected iv (tail vein), euthanized at the specific time points, and imaged firstly on SPECT/CT and directly after on MRI (Figures 2–5).

Figure 7

In vivo molecular screening for all tested routes with γ-eye™, over the first hour p.i.: (a) standard IV tail vein injection, (b) retro-orbital IV injection, (c) intratracheal installation, and (d) per rectum administration. Time point postinjection is shown on each image. All images are decay-corrected. Indicative images are shown (n = 5 for each administration route).

Figure 8

In vivo molecular screening for all tested routes with γ-eye™, for the 4 hrs and 24 hrs p.i.: (a) standard IV tail vein injection, (b) retro-orbital IV injection, (c) intratracheal installation, and (d) per rectum administration. Time point postinjection is shown on each image. All images are decay-corrected. Indicative images are shown (n = 5 for each administration route).

Figure 9

Indicative images of all the administration routes (n = 5), for the selected times postadministration, taken with the Molecubes systems: (a) standard IV tail injection, (b) retro-orbital IV injection, (c) intratracheal installation, and (d) per rectum administration. Time point postinjection is shown on each image. All images are decay-corrected.