ABSTRACT
Molecular radiotherapy (MRT) is a systemically administered targeted radionuclide therapy. The prototypical example of radionuclide therapy is radioidine treatment of thyroid cancer. Differentiated (papillary and follicular) thyroid carcinoma cells have the ability to concentrate iodine as part of the molecular machinery for making thyroid hormone. Medullary thyroid cancer treatment with radioiodine illustrates targeting of the radionuclide without the need for a carrier that recognizes tumor cells. The majority of targeted radionuclide therapy has been performed with radiolabeled antibodies. The Bexxar and Zevalin therapeutic regimens are based on intact antibodies. A lower molecular weight class of molecular radiotherapeutics, radiolabeled peptides has been the focus of European investigators. These peptides can achieve binding affinities in the low nanomolar range and have been found to be nonimmunogenic. Metaiodobenzylguanidine (MIBG) is an aralkylguanidine analog of catecholamine precursors, structurally similar to norepinephrine, which concentrates within secretory granules of catecholamine producing cells.
