Sodium Iodide Symporter (Na/I Symporter) in Radionuclide Imaging and Radionuclide Therapy

Received 4/21/2003; revised 05/23/2003; accepted 5/30/2003. For correspondence or reprints contact: Wen-Sheng Huang, M.D., Department of Nuclear Medicine, Tri-Service General Hospital, 325, Section 2, Cheng-Kung Road, Taipei, Taiwan, R.O.C. Tel: (886)2-87927216, Fax: (886)2-87927217, E-mail: [email protected] The Na/I symporter (NIS) is the membrane protein mediating iodide translocation across cell membrane into cell using sodium gradient. NIS mediated iodine concentrating activity is the molecular basis for radioiodine imaging and therapy in patients with thyroid disorders. Prior to molecular cloning of NIS, the existence of alternative NIS substrate such as 99mTcO4 and the biodistribution of NIS have been suggested from the practice of nuclear medicine in thyroid and non-thyroid imaging. Now that our understanding of NIS has been expanded through the molecular characterization and regulation of NIS expression. To improve the therapeutic strategy of thyroid cancers by enhancing NIS expression/function has been on trial. Furthermore, a novel therapeutic approach by NIS gene delivery to facilitate radioiodine (or other radioactive NIS substrates) in non-thyroid malignancies has been proposed and studies in animal models. Additionally, the feasibility and usefulness of NIS gene expression as a reporter to monitor transgene activity is actively investigated in world-class research institutes. As a reporter gene, NIS is more attractive for the readiness of single photon emission tomography and the availability of 99mTcO4 in most nuclear medicine facilities. Thus, NIS has the potential to serve as a dual gene for radionuclide imaging and therapy.