Molecular nuclear medicine using sodium/iodide symporter

Abstract

Iodide uptake occurs across the membrane of thyroid cells via an active transporter, sodium/iodide symporter (NIS). Decreased NIS expression levels account for the reduced iodide uptake in thyroid carcinomas. We found that thyroid cancer patients with positive immunostaining for NIS responded to I-131 therapy better than did the patients with negative immunostaining. Thus, NIS gene can be used for radionuclide gene therapy. Targeted expression of functional NIS in cancer cells would enable these cells to concentrate iodide from plasma and would, therefore, offer the possibility of radioiodine therapy. We and others have shown that gene transfer of NIS into a variety of cell types confers increased radioiodine uptake up to several hundred-fold that of controls. Imaging reporter gene is useful in noninvasively determining the location, duration and magnitude of transgene expression in living animal. We could monitor not only exogenous gene expression, but also endogenous gene expression such as p53 and nuclear receptor activity such as retinoic acid receptor using cis-NIS reporter imaging gene system. This reporter gene imaging can also be used for monitoring cancer cells, stem cells and immune cells. In conclusion, the NIS has the potential to expand molecular nuclear medicine in the near future.