DOT corrected fluorescence molecular tomography using targeted contrast agents for small animal tumor imaging

Abstract

Purpose: To demonstrate diffuse optical tomography (DOT) corrected fluorescence molecular tomography (FMT) for quantitatively imaging tumor-targeted contrast agents in a 4T1 mouse mammary tumor model.

Procedures: In the first set of experiments, we validated our DOT corrected FMT method using subcutaneously injected 4T1 cells pre-labeled with a near-infrared (NIR) Cy 5.5 dye labeled recombinant amino-terminal fragment (ATF) of the receptor binding domain of urokinase plasminogen activator (uPA), which binds to uPA receptor (uPAR) that is highly expressed in breast cancer tissues. Next, we apply the DOT corrected FMT method to quantitatively evaluate the ability of sensitive tumor imaging after systemic delivery of new uPAR-targeted optical imaging probes in the mice bearing 4T1 mammary tumors. These uPAR-targeted optical imaging probes are ATF peptides labeled with a newly developed NIR-830 dye being conjugated to magnetic iron oxide nanoparticles (IONPs).

Results: Our results have shown that DOT corrected FMT can accurately quantify and localize the injected imaging probe labeled 4T1 cells. Following systemic delivery of the targeted imaging nanoprobes into the mice bearing orthotopic mammary tumors, specific accumulation of the imaging probes in the orthotopic mammary tumors was detected in the mice that received uPAR targeted NIR-830-ATF-IONP probes but not in the mice injected with non-targeted NIR-830-mouse serum albumin (MSA)-IONPs. Additionally, DOT corrected FMT also enables the detection of both locally recurrent tumor and lung metastasis in the mammary tumor model 72 hrs after systemic administration of the uPAR-targeted NIR-830-labeled ATF peptide imaging probes.

Conclusions: DOT corrected FMT and uPAR-targeted optical imaging probes have great potential for detection of breast cancer, recurrent tumor and metastasis in small animals.

Fig. 1

A: NIR-830’s fluorescence spectrum in PBS solution and the insert is the chemical structure. B: molecular structure of NIR-830-ATF and NIR-830-ATF-IONP. (Colours are visible in the online version of the article; http://dx.doi.org/10.3233/XST-130365

Fig. 2

A. Photography of the experimental system, where the insert is the 3D finite element mesh of the region of interest from a mouse. B. The source node distribution of a typical sagittal projection. Blue stars are the voxels from the 3D mouse model and red circles are the projected source nodes from the finite element mesh. C. Scattering geometry for a diffusive object surrounded by air. The red rectangle indicates the focus plane of CCD camera and dΩ is a virtual detector on the focus plane of CCD to actually acquire signal from an arbitrarily shaped sample. (Colours are visible in the online version of the article; http://dx.doi.org/10.3233/XST-130365)

Fig. 3

Reconstructed 3D absorption and scattering images of a typical mouse under study (40 pmol of NIR-830 injections 4 days after administration: arrows indicate lungs and heart region, rectangle area indicates liver and spleen region). The adjacent organs are not separated due to the resolution limitation of diffuse optical tomography (DOT). A, B are the isosurface plot with 60% of the maximum value as threshold for absorption and scattering images. C, D are quantitative plot of absorption and scattering properties, units = mm⁻¹. (Colours are visible in the online version of the article; http://dx.doi.org/10.3233/XST-130365)

Fig. 4

Recovered 3D FMT images for a mouse displayed in sagittal A and coronal B projection. The exact tumor location (red mesh), and the isosurface plot of the fluorescent target recovered with (in golden) or without (in blue) DOT correction are shown for comparison. 2-D optical imaging using the Kodak FX in vivo imaging system immediately following injections shows location of injected tumor cells and intensity of NIR signal in each injected site (c). (Colours are visible in the online version of the article; http://dx.doi.org/10.3233/XST-130365)

Fig. 5

Comparison of reconstructed fluorescence images of the mice bearing the mammary tumors following systemic delivery of targeted or non-targeted optical imaging probes. The tumor bearing mice that received the tail vein delivery of 40 pmol of uPAR-targeted NIR-830-ATF-IONPs or non-targeted NIR-830-MSA-IONPs 6 days after administration of the probes. A. 3-D view of reconstructed whole body imaging by DOT corrected FMT method. Positive orthotopic mammary tumor is located on the upper right mammary gland of the mouse. B. Slice view of the mouse that received NIR-830-ATF-IONPs injection. Strong fluorescent signal is detected in the mammary tumor (green arrow, upper right) but not in most of normal tissue/organs. Weak fluorescent signals are also detected in the bladder, suggesting that the imaging probes can be eliminated through the kidney (Pink arrow, low left). C. Slice view of the mouse that received non-targeted NIR-830-MSA-IONP under the same color bar as B with the maximum value of 0.06. Fluorescent signal is low and not discernible in the mammary tumor located on the upper right mammary gland of the mouse (red arrow). D. Slice view of a mouse that received non-targeted NIR-830-MSA-IONP under a color bar with the maximum value of 0.006; non-targeted NIR 830 had biodistribution in many parts of body and was relatively more concentrated in liver region than targeted NIR 830. (Colours are visible in the online version of the article; http://dx.doi.org/10.3233/XST-130365)

Fig. 6

Detection of locally recurrent mammary tumor and lung metastasis using DOT-corrected FMT coupled with uPAR targeted NIR-optical imaging probes. The primary mammary tumor of the tumor-bearing mouse was surgically removed two weeks before the imaging procedure. A. Bioluminescence imaging revealed the presence of a locally recurrent tumor on the chest wall and two lung metastatic lesions. B. The mouse received the tail vein injection of 2.35 nmol of NIR-830-ATF peptides 72 hrs after administration of the probes. Reconstructed 3D image by DOT corrected FMT shows that the locally recurrent tumor and lung metastasis can be detected with depth information. C. A Coronal Slice indicate locally recurrent tumor (red arrow) and lung metastasis (pink arrow). (Colours are visible in the online version of the article; http://dx.doi.org/10.3233/XST-130365)