Near-infrared fluorescent (NIRF) imaging of transferrin receptor in SNU-C5 tumor model

Abstract

1901

Objectives: To evaluate the feasibility of Transferrin-Cy5.5 as a near-infrared imaging agent for the detection of tumor

Methods: Apo-Transferrin in 0.1 M NaHCO3 at pH 9.0 was mixed with one equivalents of Cy5.5-NHS in DMSO anhydrous. After stirring at room temperature for 2 h, the reaction mixture was passed through a gel filtration PD-10 column. The iron incorporation was performed by addition of 1.25 ul 10 mM iron (III) citrate buffer per mg transferrin. Tumor uptake was studied in SNU-C5 (human colon cancer) xenografted Balb/c nude mice. Fluorescence images were then acquired with time after administration of Transferrin-Cy5.5 (0.5-0.8 mg transferrin/mouse). Tumor images were obtained every 15 min for 3 hours after intravenous injection of NIRF probe and every 1 h after injection for up to 6 hours, and then 24 h last images. Binding of Transferrin-Cy5.5 was blocked by free holo-transferrin.

Results: Transferrin protein has one or more lysine residues which is accessible to labeling Cy5.5-NHS. The molar ratio of Cy5.5 to transferrin was estimated to be 0.53:1. The yield of transferrin was typically 83-87%. Transferrin-Cy5.5 accumulated in SNU-C5 tumor model. Moreover, tumor uptake of Transferrin-Cy5.5 was inhibited 23% by free holo-transferrin at 24 h after injection.

Conclusions: SNU-C5 tumor was clearly visualized using Transferrin-Cy5.5. Our data suggest that Transferrin-Cy5.5 may be used to as a specific NIRF probe for transferrin receptor rich tumor cells.