A Receptor-targeted Fluorescent Radiopharmaceutical for Multireporter Sentinel Lymph Node Imaging

Abstract

Purpose:To determine the imaging and receptor-binding properties of a multireporter probe designed for sentinel lymph node (SLN) mapping via nuclear and fluorescence detection. Materials and Methods:The animal experiments were approved by the institutional animal care and use committee. A multireporter probe was synthesized by covalently attaching cyanine 7 (Cy7), a near-infrared cyanine dye, to tilmanocept, a radiopharmaceutical that binds to a receptor specific to recticuloendothelial cells. In vitro binding assays of technetium 99m ( 99m Tc) -labeled Cy7 tilmanocept were conducted at 4°C by using receptor-bearing macrophages. Optical SLN imaging after foot pad administration was performed by using two molar doses of Cy7 tilmanocept. Six mice were injected with 0.11 nmol of 99m Tc-labeled Cy7 tilmanocept (low-dose group); an additional six mice were injected with 31 nmol of 99m Tc-labeled Cy7 tilmanocept (high-dose group) to saturate the receptor sites within the SLN. After 2.5 hours of imaging, the mice were euthanized, and the sentinel and distal lymph nodes were excised and assayed for radioactivity for calculation of SLN percentage of injected dose and extraction. Four mice were used as controls for autofluorescence. Standard optical imaging software was used to plot integrated fluorescence intensity against time for calculation of the SLN uptake rate constant and scaled peak intensity. Significance was calculated by using the Student t test. Results:In vitro binding assays showed subnanomolar affinity (mean dissociation constant, 0.25 nmol/L 6 0.10 [standard deviation]). Fluorescence imaging showed a detection sensitivity of 1.6 310 3 counts ⋅ sec 21 ⋅ mW 21 per picomole of Cy7. All four imaging metrics (percentage of injected dose, SLN extraction, SLN uptake rate constant, and expected peak fluorescence intensity) exhibited higher values (P = .005 to P = .042) in the low-dose group than in the high-dose group; this finding was consistent with receptor-mediated image formation. Conclusion:The multireporter probe

Sentinel Lymph Node Biopsy for Prostate Cancer: A Hybrid Approach

“…Other hybrid nanoparticles also have the potential to guide SLN biopsy (8). A recent preclinical example of a hybrid SLN tracer can be found in 99m Tc-tilmanocept labeled with the NIR dye Cy7 (9). Alternatively, Cerenkov imaging of positronemitting radionuclides has been proposed as a hybrid imaging technology; Thorek et al demonstrated that LNs could be detected after a subdermal injection of 18 F-FDG in the tail of a mouse (10).…”

Optimization via specific fluorescence brightness of a receptor-targeted probe for optical imaging and positron emission tomography of sentinel lymph nodes

“…The amount of IRDye 800CW within each SLN was calculated based on the amount of 800CW-tilmanocept and the IRDye 800CW density. The percent SLN extraction 23 was calculated as the difference between the SLN and distal lymph node counts divided by the sum of the SLN and distal lymph node counts.…”

“…After radiolabeling tilmanocept with 68 Ga, a generator-produced positron-emitting radionuclide, canine pelvic SLNs were imaged 1 h after a transrectal injection into the prostate gland. 21 Covalent attachment of Cy7, a cyanine fluorescent dye, to tilmanocept resulted in an NIR fluorescent-tagged tilmanocept, 22,23 which retained the properties exhibited by tilmanocept without the fluorescent tag. Fluorescent-labeled tilmanocept exhibited sub-nanomolar receptor affinity (K D < 1 nM) to a macrophage cell line that expresses the receptor (CD206), as well as in vivo behavior consistent with SLN receptor-mediated accumulation.…”

Prostate Cancer Imaging and Therapy: Potential Role of Nanoparticles

“…If the sentinel lymph node (the first node that drains the tumor) is free of malignant cells, then the remaining lymph nodes should also be free of metastatic disease (59). Conventional sentinel lymph node mapping is performed using 20-to 600-nm radiocolloids (Fig.…”

“…4) (60). A small study using the multireporter probe 99m Tc-labeled Cy7 tilmanocept demonstrated in vitro and in vivo receptor binding properties for successful receptor-targeted sentinel lymph node mapping with nuclear and optical imaging (59). 99m Tc-tilmanocept has a dextran frame linked with multiple diethylenetriaminepentaacetic acid and mannose residues.…”