Trafficking macrophage migration using reporter gene imaging with human sodium iodide symporter in animal models of inflammation

Abstract

The aim of this study was to investigate the feasibility of nuclear molecular imaging using the human sodium iodide symporter (hNIS) as a reporter gene to monitor macrophage migration toward the inflammatory foci. Methods: A stable macrophage cell line coexpressing hNIS and green fluorescent protein (GFP) genes (RAW264.7/hNIS-GFP and RNIS cell) was established from an immortalized macrophage cell line (RAW264.7 cells). 125I uptake was determined (for hNIS protein functional activity), and flow cytometry analysis (to examine GFP gene expression), a cell proliferation assay, a cytokine assay, and a phagocytic activity assay were performed. 99mTc-pertechnetate images were acquired at 1 d after sub-cutaneous inoculation of RNIS cells in nude mice. Chemical inflammation was induced for in vivo imaging in the thigh of nude mice by turpentine oil injection. Small-animal PET with 18F-FDG and 124I was performed with an intravenous administration of RAW264.7 or RNIS cells in inflammation-induced animals. Results: The expression of hNIS and GFP genes was confirmed in RNIS cells by flow cytometry and immuno-fluorescent staining. 125I uptake was about 67 times higher in RNIS cells than in RAW264.7 cells. No significant difference was observed in cell proliferation, cytokine production, and phagocytic activity between RAW264.7 and RNIS cells. 99mTc-pertechnetate imaging revealed increased tracer uptake at the inoculation site. PET with 124I demonstrated a donut-shaped uptake, correlating with uptake shown by the 18F-FDG PET images, at the inflammation site of mice administered RNIS cells. 124I uptake (percentage injected dose per gram) was about 2.12 times higher at the inflammation site in the RNIS mice than in RAW264.7 mice. By immunohistochemistry, the migration of macrophages was further confirmed by positive staining for GFP and hNIS at the inflammation site of RNIS mice. Conclusion: These data support the feasibility of hNIS reporter gene imaging to monitor the macrophage migration toward an inflammatory lesion. Macrophages expressing hNIS may provide a new strategy to investigate the cellular behavior seen with inflammatory response in a preclinical model. Copyright © 2010 by the Society of Nuclear Medicine, Inc.